MEMCAL 
 
 Gift of the 
 
 Panama-Pac if ic Internat 
 exposition Company 
 
MANUAL 
 
 OF 
 
 CHEMISTRY. 
 
 A GUIDE TO LECTURES AND LABORATORY WORK FOR BEGINNERS 
 
 IN CHEMISTRY. A TEXT-BOOK SPECIALLY ADAFfED FOR 
 
 STUDENTS OF MEDICINE, PHARMACY, AND 
 
 DENTISTRY. 
 
 BY 
 
 W. J>IMON, PH.D., M.D., 
 
 PROFESSOR OF CHEMISTRY IN THE COLLEGE OF PHYSICIANS AND SURGEONS OF BALTIMORE, AND IN 
 
 THE BALTIMORE COLLEGE OF DENTAL SURGERY; EMERITUS PROFESSOR IN THE MARYLAND 
 
 COLLEGE OF PHARMACY, DEPARTMENT OF THE UNIVERSITY OF MARYLAND. 
 
 AND 
 
 DANIEL BASE, PH.D., 
 
 PROFESSOR OF CHEMISTRY IN THE MARYLAND COLLEGE OF PHARMACY, DEPARTMENT OF THE 
 UNIVERSITY OF MARYLAND, AND OF ANALYTICAL CHEMISTRY IN THE DEPART- 
 MENT OF MEDICINE, UNIVERSITY OF MARYLAND, BALTIMORE. 
 
 TENTH EDITION, THOROUGHLY REVISED. 
 
 WITH EIGHTY-TWO ILLUSTRATIONS, ONE COLORED SPECTRA PLATE, 
 
 AND 
 
 EIGHT COLORED PLATES REPRESENTING SIXTY-FOUR CHEMICAL 
 
 REACTIONS. 
 
 LEA & FEBIGEK, 
 PHILADELPHIA AND NEW YORK. 
 1912. 
 
Copyright, 1912, by 
 LEA & FEBIGER. 
 
 Authority to use for comment the Pharmacopoeia of the United States 
 of America (Eighth Decennial Revision), in this volume, has been granted 
 by the Board of Trustees of the United States Pharmacopceial Convention ; 
 which Board of Trustees is in no way responsible for the accuracy of any 
 translations of the Official Weights and Measures, or for any statement as 
 to strength of Official Preparations. 
 
555 
 
 PREFACE TO THE TENTH EDITION. 
 
 IN this new edition the Manual preserves the plan and characteristics 
 that have won for it the degree of approval shown in the exhaustion of 
 the nine previous issues, each in several large printings. Numerous 
 additions have been made, most of which are of fundamental importance, 
 and again bring the Manual abreast of modern thought in chemistry to 
 its date of issue. They embrace articles on the following subjects: 
 Exothermic and endothermic reactions ; reversible reactions and chemical 
 equilibrium ; mass action ; extension of the articles on acids and bases ; 
 thermochemistry;* a new chapter on solution, in which, among other 
 matters, the solution of gases and Henry's law, freezing-points, boiling- 
 points and osmotic pressure, Raoult's law and the laws of osmotic pres- 
 sure are discussed, and the existence of ions foreshadowed ; a new chapter 
 on the theory of electrolytic dissociation, in which are considered the 
 origin of the theory, ionic equilibrium, ionization of acids, bases, and 
 salts, reactions on the ionic basis, activity of acids and bases, hydrolysis 
 of salts, neutralization, electrolysis and Faraday's laws, etc. ; electrolytic 
 solution tension of metals ; principle of the storage-battery ; and ionic 
 explanation of the action of indicators. Ionic relations are discussed in 
 practically every chapter on acids and the metals, and a number of 
 compounds have been added to the sections on inorganic and organic 
 chemistry. Many of these are of medical interest, for example, sodium 
 cacodylate, atoxyl and salvarsan, phenolphthalein, fluorescein, phenol- 
 sulphonephthalein. 
 
 The section on physiological chemistry has been rewritten and brought 
 in line with present-day knowledge and theories. A table of inter- 
 national atomic weights on the 'oxygen = 16 basis has been added to 
 the U. S. P. table of weights on the hydrogen = 1 basis. 
 
 It is hoped that with these alterations and additions the Manual will 
 fully accomplish its object, viz., to furnish to the student in concise form a 
 clear presentation of the science, an intelligent discussion of those substances 
 which are of interest to him, and a trustworthy guide to his work in the 
 laboratory. 
 
 As heretofore, the subject has been divided into seven parts, each one 
 of which contains so much of the matter under consideration as is believed 
 to be necessary for a fair understanding of the subject. At the same time 
 care has been taken to place in the foreground all facts and data which 
 are of direct interest to, the physician, pharmacist, and dentist. 
 
 iii 
 
 865 
 
 '/ 
 
iv PREFACE TO THE TENTH EDITION. 
 
 In the first part, treating of chemical physics, the student finds a brief 
 discussion of those physical conditions of matter which have a close rela- 
 tionship to chemical phenomena, and also of the principles which lead to 
 an understanding of many of the instruments, such as the spectroscope, 
 polariscope, etc., which he uses in his chemical operations. 
 
 The second part treats of those principles of chemistry which are the 
 foundation of the science, and enters briefly into a discussion of theoretical 
 views regarding the constitution of matter. Though the authors prefer 
 to present these theories to their classes at the proper times during the 
 course of lectures, they do not deem it desirable to have them scattered 
 throughout the work, believing it better to assemble them compactly in 
 print, so that the student may be able to study them after having acquired 
 some knowledge of chemical phenomena. 
 
 The third and fourth parts are devoted to the consideration of the non- 
 metallic and metallic elements and their compounds. While the periodic 
 law furnishes a most admirable basis for a scientific classification of ele- 
 ments, yet their consideration according to a strict adherence to periodicity 
 does not seem advisable in this book. For this reason the old classifica- 
 tion of metals and non-metals, organic and inorganic compounds has been 
 retained, since experience has shown it to be well adapted for the instruc- 
 tion of beginners in chemistry. 
 
 The fifth part is devoted to analytical chemistry and will serve the 
 student as a guide in his laboratory work. Qualitative methods are 
 chiefly considered, but a chapter is added giving official methods for 
 volumetric determinations. 
 
 The sixth part treats of organic chemistry. Though it is impossible to 
 include within the limits of this text-book an extended consideration of a 
 branch of chemical science so highly developed, yet it is believed that an 
 intelligent study of this part will familiarize the student with carbon 
 compounds sufficiently to give him a clear understanding of their general 
 character, and a knowledge of the bodies which are most important in 
 medical science. 
 
 The seventh and last part gives the principal facts of physiological 
 chemistry. Special care has been taken also to introduce here the most 
 modern methods for chemical examination in clinical diagnosis. 
 
 The authors will be grateful for any suggestions looking to the im- 
 provement of the book. 
 
 The authors wish to express here their obligations to G. Howard 
 White, Jr., M. D., by whom the section on physiological chemistry was 
 rewritten. 
 
 W. S. 
 
 D. B. 
 
 BALTIMORE, 1912. 
 
CONTENTS. 
 
 i. 
 
 CHEMICAL PHYSICS. 
 
 PAGE 
 
 1. Fundamental properties of matter. 
 
 Matter Extension Solid state Force Energy Crystal- 
 lization Liquid and gaseous state Divisibility Molecular 
 theory Gravitation Weight Specific weight Weight of 
 gases Barometer Surface-action Adhesion Capillary at- 
 traction Absorption Diffusion Osmose Indestructibility 17-42 
 
 2. Heat. 
 
 Motion of molecules Latent heat Sources of heat Heat 
 effects Thermometers Absolute zero and absolute tempera- 
 ture Mechanical equivalent of heat Specific heat Conduc- 
 tion, Convection, and radiation Melting, boiling, and evapo- 
 ration 43-55 
 
 3. Light. 
 
 Light a form of energy Reflection Refraction Prisms 
 Dispersion The spectroscope Bright line spectra Absorp- 
 tion spectra Double refraction Polarization The polari- 
 scope Chemical effects of light 56-68 
 
 4. Electricity. 
 
 Electricity generated by friction Conductors and non- 
 conductors Duality of Electricity Induction Electrical 
 machines Static electricity Magnetism Electricity gener- 
 ated by chemical action Galvanic cells Current electricity 
 Electromotive force Electric units Electromagnets 
 Electricity generated by magnetism Voltaic induction In- 
 duction coil Conversion of electric energy into heat, light, 
 and chemical action Electric furnace Electric spark 
 Cathode ray Rontgen rays Radio-activity 69-86 
 
 II. 
 PRINCIPLES OF CHEMISTRY. 
 
 5. Element, compound, chemical affinity, modes of effecting 
 
 chemical change. 
 
 Decomposition by heat Elements Compound substances 
 Decomposition by electricity, by light, and by mutual action 
 of substances upon each other Physical phenomena accom- 
 panying chemical action Chemical or internal energy Ex- 
 othermic and endothermic actions Chemical affinity .... 87-93 
 
 6. Laws and theories of chemistry. 
 
 Law of the constancy of composition Law of multiple 
 
 (v) 
 
vi CONTENTS. 
 
 PAGE 
 
 proportions Combining weights of elements Atomic theory 
 Atomic weight Atoms and molecules Chemical symbols 
 Formulas of compounds Law of chemical combinations by 
 volume Law of equivalents Valence or quantivalence . . . 93-104 
 
 7. Determination of atomic and molecular weights. 
 
 Determination of atomic weights by chemical decomposition, 
 by means of specific weights of gases or vapors, by means of spe- 
 cific heat Determination of molecular weights Raoult's law 105-110 
 
 8. Chemical equations. Types of chemical change. Reversible 
 
 actions and chemical equilibrium. Mass action. 
 Acids, bases, neutralization, salts. Radical. Consti- 
 tutional formulas ..." 110-124 
 
 9. General remarks regarding elements. 
 
 Relative importance of different elements Classification of 
 elements Metals and non-metals Natural groups of elements 
 MendelejefF's periodic law Physical properties of elements 
 Allotropic modifications Relationship between elements 
 and the compounds formed by their union Nomenclature 
 How to study chemistry 124-133 
 
 III. 
 NON-METALS AND THEIR COMBINATIONS. 
 
 Symbols, atomic weights, and derivation of names Occur- 
 rence in nature Time of discovery Valence 135-136 
 
 10. Oxygen. 
 
 History Occurrence in nature Preparation Physical and 
 chemical properties Combustion Ozone Thermo-chemistry 137-144 
 
 11. Hydrogen. Water. Hydrogen dioxide. 
 
 History Occurrence in nature Preparation Properties 
 Nascent state Water Mineral waters Drinking-water Dis- 
 tilled water Analysis and synthesis Explanation of efflor- 
 escence and deliquescence Hydrogen dioxide 144-156 
 
 12. Solution. 
 
 General remarks Terms employed Heat of solution So- 
 lution of gases Henry's law Freezing-points, boiling-points, 
 and osmotic pressure of solutions Raoult's law Laws of os- 
 motic pressure 157-164 
 
 13. Nitrogen. 
 
 Occurrence in nature Preparation Properties Atmo- 
 spheric air Argon Helium Ammonia Hydrazine Hy- 
 droxylamine Triazoic acid Compounds of nitrogen and 
 oxygen Nitrogen monoxide Nitric acid ; tests for it ... 164-177 
 
 14. Carbon. Silicon. Boron. 
 
 Occurrence in nature Properties Diamond Graphite 
 Tests for carbon Carbon dioxide Carbonic acid Tests for 
 carbonic acid Carbon monoxide Carbonyl chloride Com- 
 pounds of carbon and hydrogen Flame Silicon Silicic acid 
 
CONTENTS. vii 
 
 PAGE 
 
 Carborundum Boron, boric acid; tests for it Sodium per- 
 borate 178-189 
 
 15. Theory of electrolytic dissociation, or ionization, etc. 
 
 Theory of electrolytic dissociation Composition of ions 
 Ions and atoms not the same Symbols representing ions 
 Ionic equilibrium. Ionization constant Effects of ionic equi- 
 librium in chemical reactions Precipitation Electrolysis 
 Secondary changes in electrolysis Faraday's laws Conduc- 
 tivity Electromotive force required in electrolysis Electro- 
 chemical series of the metals Acids Independence of ions 
 Analytical reactions or tests Kinds of ions formed by acids 
 Activity or " strength " of acids Bases Salts Acid and basic 
 salts Hydrolysis of salts Neutralization Heat of neutrali- 
 zation Degree of dissociation of common substances .... 189-203 
 
 16. Sulphur. Selenium. Tellurium. 
 
 Occurrence in nature Properties Crude, sublimed, washed, 
 and precipitated sulphur Sulphur dioxide Sulphurous acid ; 
 tests for it Sulphur trioxide Sulphuric acid : its manufac- 
 ture, properties, and ions Tests for sulphates Sulphur acids 
 Pyrosulphuric acid Thiosulphuric acid Hydrogen sul- 
 phide ; tests for it Ions of hydrogen sulphide and its salts 
 Use of it in analysis Carbon disulphide Selenium Tellu- 
 rium Ionic mechanism of the solution by acids of salts that 
 are insoluble in water 204-219 
 
 17. Phosphorus. 
 
 Occurrence in nature Manufacture, properties, and modi- 
 fications Poisonous properties and detection in cases of pois- 
 oning Oxides of phosphorus Hypophosphorous acid ; tests 
 for it Phosphorous acid ; tests for it Metaphosphoric, pyro- 
 phosphoric, orthophosphoric acids; tests for them Ions of 
 phosphoric acid and its salts Hydrogen phosphide Phos- 
 phorus tri- and pentachloride 219-229 
 
 18. Chlorine. 
 
 Halogens Occurrence in nature, preparation, and proper- 
 ties of chlorine Chlorine water Hydrochloric acid ; tests for 
 it Nitrohydrochloric acid Compounds of chlorine with oxy- 
 gen Hypochlorous acid Hypochlorites Solution of chlor- 
 inated soda Chloric acid ; tests for it Perchloric acid . . . 230-238 
 
 19. Bromine. Iodine. Fluorine. 
 
 Bromine Hydrobromic acid Tests for bromides Hypo- 
 bromous and bromic acid Iodine Hydriodic acid Tests for 
 iodine and iodides lodic acid Sulphur iodide Compounds 
 of iodine with bromine and chlorine Compounds of nitrogen 
 with halogens Fluorine Hydrofluoric acid 239-245 
 
viii CONTENTS. 
 
 IV. 
 
 METALS AND THEIR COMBINATIONS. 
 
 PAGE 
 
 20. General remarks regarding metals. 
 
 Derivation of names, symbols, and atomic weights Melting- 
 points, specific gravities, time of discovery, valence, occur- 
 rence in nature, classification, and general properties of metals 
 Alloys, their manufacture and properties 217-255 
 
 21. Potassium. 
 
 General remarks regarding the alkali metals Occurrence in 
 nature Potassium hydroxide, oxide, carbonate, bicarbonate, 
 percarbonate, nitrate, chlorate, sulphate, sulphite, hypophos- 
 phite, iodide, bromide Analytical reactions 255-262 
 
 22. Sodium. Lithium. Caesium. Rubidium. 
 
 Occurrence in nature Sodium chloride, hydroxide, perox- 
 ide, carbonate, bicarbonate, sulphate, sulphite, thiosulphate, 
 phosphate, nitrate, borate Analytical reactions Lithium 
 Caesium Rubidium 262-268 
 
 23. Ammonium. 
 
 General remarks Ammonium ion Ammonium chloride, 
 carbonate, sulphate, nitrate, phosphate, iodide, bromide, and 
 sulphide Analytical reactions Summary of analytical char- 
 acters of the alkali-metals 268-272 
 
 24. Magnesium. 
 
 General remarks Occurrence in nature Metallic magne- 
 sium Magnesium carbonate, oxide, sulphate, nitride Re- 
 marks on tests for metals Analytical reactions 272-276 
 
 25. Calcium. Strontium. Barium. Radium. 
 
 General remarks regarding alkaline earths Occurrence in 
 nature Calcium oxide, hydroxide, carbonate, sulphate, phos- 
 phate, acid phosphate, and hypophosphite Bone-black and 
 bone-ash Chlorinated lime, calcium chloride and bromide 
 Sulphurated lime Calcium carbide Analytical reactions and 
 ionic equations for calcium Barium and strontium ; their salts 
 and analytical reactions Radium Summary of analytical 
 characters of the alkaline-earth metals 277-285 
 
 26. Aluminum. Cerium. 
 
 Occurrence in nature Metallic aluminum Alum Alumi- 
 num hydroxide, oxide, sulphate, and chloride Ionic equations 
 Clay Glass Cement Ultramarine Analytical reactions 
 Cerium Summary of Analytical characters of the earth- 
 metals and chromium 285-292 
 
 27. Iron. 
 
 General remarks regarding the metals of the iron group 
 Occurrence in nature Manufacture of Iron Properties 
 Reduced iron Ferrous and ferric oxides, hydroxides, and 
 chlorides Dialyzed iron Ferrous iodide, bromide, sulphide, 
 
CONTENTS. ix 
 
 PAGE 
 
 and sulphate Ferric sulphate and nitrate Ferrous carbonate, 
 phosphate, and hypophosphite Analytical reactions Ions of 
 iron 292-302 
 
 28. Manganese. Chromium. Cobalt. Nickel. 
 
 [Manganese ; its oxides, sulphate, and hypophosphite Po- 
 tassium permanganate Manganese reactions Ions of man- 
 ganese compounds Chromium Potassium dichromate 
 Chromium trioxide Ions of chromates and dichromates 
 Chromic oxide and hydroxide Perchromic Acid Reactions 
 for chromium compounds Cobalt and nickel 303-312 
 
 29. Zinc. Cadmium. 
 
 Occurrence in nature Metallic zinc Zinc oxide, chloride, 
 oxychloride, oxyphosphate, bromide, iodide, carbonate, sul- 
 phate Analytical reactions Ions of zinc Antidotes Cad- 
 mium Summary of analytical characters of metals of the iron 
 group 312-318 
 
 30. Lead. Copper. Bismuth. 
 
 General remarks regarding the metals of the lead group 
 Lead Electrolytic solution tension Lead oxides Storage 
 battery Lead nitrate, carbonate, iodide Poisonous proper- 
 ties of lead Antidotes Lead reactions Copper Cupric and 
 ' cuprous oxide Cupric sulphate and carbonate Ammonio- 
 copper compounds Poisonous properties and antidotes 
 Copper reactions Bismuth Bismuth subnitrate and subcar- 
 bonate Bismuth reactions . . . 318-330 
 
 31. Silver. Mercury. 
 
 Silver Silver nitrate Photography Silver oxide Anti- 
 dotes Complex silver compounds Silver reactions Ions of 
 silver Mercury Amalgams Mercurous and mercuric ox- 
 ides, chlorides, iodides, sulphates, nitrates, sulphides Am- 
 moniated mercury Antidotes Mercury reactions Ions of 
 mercury compounds Summary of analytical characters of 
 metals of the lead group 330-346 
 
 32. Arsenic. 
 
 General remarks regarding the metals of the arsenic group 
 Arsenic Arsenous and arsenic oxides and acids Sodium 
 arsenate Lead arsenate Hydrogen arsenide Sulphides of 
 arsenic Arsenous iodide Analytical reactions Ions of ar- 
 senous and arsenic acids Preparatory treatment of organic 
 matter for arsenic analysis Antidotes , 346-358 
 
 33. Antimony. Tin. Gold. Platinum. Iridium. Molybdenum. 
 
 Antimony Trisulphide and pentasulphide of antimony 
 Antimonous chloride and oxide Antidotes Antimony reac- 
 tions Tin Stannous and stannic hydroxide and chloride 
 Metastannic acid Tin reactions Gold Refining gold Gold 
 chloride Platinum Iridium Molybdenum Summary of 
 analytical characters of metals of the arsenic group 358-369 
 
X CONTENTS. 
 
 V. 
 
 ANALYTICAL CHEMISTRY. 
 
 PAGE 
 
 34. Introductory remarks and preliminary examination. 
 
 General remarks Apparatus needed for qualitative analysis 
 Reagents needed General mode of proceeding in qualitative 
 analysis Use of reagents Preliminary examination Physi- 
 cal properties Action on litmus Heating on platinum foil 
 Heating on charcoal alone and mixed with sodium carbonate 
 Flame-tests Colored borax-beads Liquefaction of solid 
 substances Table I.: Preliminary examination 371-381 
 
 35. Separation of metals into different groups. 
 
 General remarks Group reagents Acidifying the solution 
 Addition of hydrogen sulphide Separation of the metals of 
 the arsenic group from those of the lead group Addition of 
 ammonium sulphide and ammonium carbonate Table II. : 
 Separation of metals into different groups 382-387 
 
 36. Separation of the metals of each group. 
 
 Table III. : Treatment of the precipitate formed by hydro- 
 chloric acid Treatment of the precipitate formed by hydrogen 
 sulphide Table IV. : Treatment of that portion of the hydro- 
 gen sulphide precipitate which is insoluble in ammonium sul- 
 phide Table V. : Treatment of that portion of hydrogen 
 sulphide precipitate which is soluble in ammonium sulphide 
 Table VI. : Treatment of the precipitate formed by ammo- 
 nium hydroxide and sulphide Table VII. : Treatment of the 
 precipitate formed by ammonium carbonate Table VIII. : 
 Detection of the alkalies and of magnesium 387-390 
 
 37. Detection of acids. 
 
 General remarks Detection of acids by means of the action 
 of strong sulphuric acid Table IX. : Preliminary examina- 
 tion for acids Detection of acids by means of reagents added 
 to their neutral or acid solution Table X. : Detection of the 
 more important acids by means of reagents added to the solu- 
 tion Table XI. : Systematically arranged table, showing the 
 solubility and insolubility of inorganic salts and oxides 
 Table XII. : Table of solubility Special remarks 391-401 
 
 38. Methods for quantitative determinations. 
 
 General remarks Gravimetric methods Volumetric 
 methods Standard solutions Normal solutions Different 
 methods of volumetric determination Indicators and ionic 
 explanation of their action Titration Acidimetry and alka- 
 limetry Normal acid and alkali solution Oxidimetry Po- 
 tassium permanganate and dichromate lodimetry Solutions 
 of iodine, sodium thiosulphate, bromine, silver nitrate, sodium 
 chloride, and potassium sulphocyanate Gas analysis Water 
 analysis 402-432 
 
CONTENTS. xi 
 
 PAGE 
 
 39. Detection of impurities in official inorganic chemical prep- 
 
 arations. 
 
 General remarks Official chemicals and their purity Tests 
 as to identity Qualitative tests for impurities Quantitative 
 tests for the limit of impurities 433-437 
 
 VI. 
 
 CONSIDERATION OF CARBON COMPOUNDS, OR ORGANIC 
 
 CHEMISTRY. 
 
 40. Introductory remarks. Elementary analysis, 
 
 Definition of organic chemistry Elements entering into or- 
 ganic compounds General properties of organic compounds 
 Difference in the analysis of organic and inorganic substances 
 Qualitative analysis of organic substances Ultimate or 
 elementary analysis Determination of carbon, hydrogen, 
 oxygen, nitrogen, sulphur, and phosphorus Determination of 
 atomic composition from results obtained by elementary 
 analysis Empirical and molecular formulas Rational, con- 
 stitutional, structural, or graphic formulas 439-448 
 
 41. Constitution, decomposition, and classification of organic 
 
 compounds. 
 
 Radicals or residues Chains Homologous series Sub- 
 stitution Derivatives Isomerism Metamerism Polymer- 
 ism Stereo-isomerism Various modes of decomposition 
 Action of heat upon organic substances Dry or destructive 
 distillation Action of oxygen upon organic substances 
 Combustion Decay Fermentation and putrefaction Anti- 
 septics, disinfectants, and deodorizers Action of chlorine, bro- 
 mine, nitric acid, alkalies, dehydrating and reducing agents 
 upon organic substances Classification of organic compounds 448-462 
 
 42. Hydrocarbons. Haloid derivatives. 
 
 Occurrence in nature Formation of hydrocarbons Prop- 
 erties Paraffin or methane series Methane Ethane Coal 
 Natural gas Coal-oil, petroleum Illuminating gas Coal- 
 tar Unsaturated hydrocarbons Olefines Ethylene Amyl- 
 ene Acetylene Halogen derivatives of hydrocarbons 
 Methyl chloride Dichlor- and Tetrachlor-methane Chloro- 
 form Bromoform lodoform Ethyl chloride, bromide, and 
 iodide Compounds of alkyl radicals with other elements 
 Sodium cacodylate 462-478 
 
 43. Alcohols. 
 
 Constitution of alcohols Occurrence in nature Formation 
 and properties of alcohols Monatomic normal alcohols 
 Methyl alcohol Ethyl alcohol Denatured alcohol Alcoholic 
 liquors Wines, beer, spirits Amyl alcohol Allyl alcohol 
 Glycerin Glycerin trinitrate Dynamite Glycerin-phos- 
 phoric acid 479-489 
 
xii CONTEXTS. 
 
 PAGE 
 
 44. Aldehydes. Ketones. 
 
 Aldehydes Formic aldehyde Formalin Acetic aldehyde 
 Paraldehyde Trichloraldehyde Hydrated chloral Acrylic 
 aldehyde Ketones Acetone Sulphur derivatives Sulpho- 
 nal Trional Tetronal 489-496 
 
 45. Monobasic fatty acids. 
 
 General constitution of organic acids Occurrence in nature 
 Formation of acids Properties Fatty acids Formic acid 
 Acetic acid Vinegar Reactions for acetates Acetate of 
 potassium, sodium, zinc, iron, lead, and copper Trichlor- 
 acetic acid Acetyl chloride Acetic anhydride Butyric acid 
 Valeric acid and its salts Stearic acid Oleic acid Disso- 
 ciation of formic acid and its homologues 496-507 
 
 46. Polybasic and hydroxy-acids. 
 
 Oxalic acid, oxalates, and analytical reactions Glycolic 
 acid Lactic acid Malic acid Tartaric acid ; analytical re- 
 actions Potassium tartrate Potassium-sodium tartrate An- 
 timony-potassium tartrate Action of certain organic acids 
 upon certain metallic oxides Scale compounds Citric acid ; 
 analytical reactions Citrates 508-518 
 
 47. Ethers and esters. 
 
 Constitution Formation of ethers Occurrence in nature 
 General properties Ethyl ether Acetic ether Ethyl nitrite 
 Amyl nitrite Fats and fat oils Soap Lanolin 518-527 
 
 48. Carbohydrates. 
 
 Constitution Properties Occurrence in nature Classifica- 
 tion Monosaccharides Dextrose ; tests for it Levulose 
 Galactose Inosite Disaccharides Cane-sugar Maltose 
 Lactose Polysaccharides Starch Dextrin Gums Cellu- 
 losePyroxylin Collodion Glycogen Glucosides 528-539 
 
 49. Compounds containing nitrogen. 
 
 Derivatives of nitric acid Nitro, nitroso, and isonitroso 
 compounds Ammonia derivatives Amines Poly-amines 
 Amino-acids Amino-acetic and amino-formic acid Ure- 
 thanes Ethyl carbamate Sarcosine Cystine Leucine 
 Taurine Aspartic acid, asparagine Guanidine Creatine 
 Urea Ureids Veronal Cyanogen compounds Hydrocyanic 
 acid Dissociation of cyanogen compounds Cyanides of po- 
 tassium, silver, and mercury Cyanogen derivatives obtained 
 from atmospheric nitrogen Cyanic acid Metallocyanides 
 Potassium ferrocyanide and ferri cyanide Sodium nitroferri- 
 cyanide Nitriles and isocyanides Iso-sulpho-cyanides 
 Myronic acid Allyl mustard oil 539-557 
 
 50. Benzene series. Aromatic compounds. 
 
 General remarks Constitution Benzene series of hydro- 
 carbons Benzene Toluene Xylenes Cymene Amino com- 
 pounds of benzene Aniline Acetanilide Sulphanilic acid 
 Diphenyl-amine Meta-phenylene-diamine Methylene-blue 
 
CONTENTS. xiii 
 
 PAGE 
 
 Diazo compounds Phenyl hydrazine Atoxyl Salvarsan 
 Hydroxyl derivatives Phenols Carbolic acid Acetphene- 
 tidin Trinitro-phenol Phenolsulphonicacid Cresols Creo- 
 sote Guaiacol and its compounds Veratrol Eugenol Safrol 
 Thymol and the iodide Resorcinol Quinol Pyrogallol 
 Phloroglucinol Aromatic alcohols Aromatic aldehydes 
 Benzaldehyde Oil of bitter almond Cinnamic aldehyde 
 Vanillin Cumarin Acids of the benzene series Benzoic acid 
 Benzoyl chloride Benzosulphinide Phthalic acids Phe- 
 nolphthalein Fluorescein, Eosin Phenolsulphonphthalein 
 Salicylic acid Aspirin Salicin Methyl salicylate Phenyl 
 salicylate Gallic and tannic acid Naphthalene Naphthol 
 Santonin Pyrrol Antipyrine Pyridine Quinoline Kai- 
 rine Thalline 557-594 
 
 51. Terpenes and their derivatives. 
 
 Volatile or essential oils Terpenes Terebene Sesquiter- 
 penes Rubber Gutta-percha Stearoptenes Camphor 
 Cineol Menthol Resins Balsams Turpentine 594-599 
 
 52. Alkaloids. 
 
 General remarks Properties Assay methods Antidotes- 
 Detection Classification The pyridine group Pi perin 
 Coniine Pilocarpine Nicotine Sparteine The tropine 
 group Atropine Homatropine Hyoscyarnine Hyoscine 
 Cocaine and its substitutes The quinoline group Cinchona 
 alkaloids Quinine and quinidine Cinchonine and cinchoni- 
 dine Strychnine Brucine Veratrine The isoquinoline 
 group Morphine, apomorphine Codeine Narcotine, narce- 
 ine Meconic acid Hydrastine, hydrastinine Berberine 
 The xanthine alkaloids Caffeine Theobromine Unclassified 
 alkaloids Physostigmine Aconitine Colchicine Pto- 
 maines ; their formation and properties Leucomaines . . . 600-621 
 
 VII. 
 
 PHYSIOLOGICAL CHEMISTRY. 
 
 53. Proteins. 
 
 Occurrence in nature General properties Classification 
 Simple proteins Albumins Globulins Glutelins Prola- 
 mines or alcohol-soluble proteins Albuminoids Histones 
 Protamines Conjugated proteins Nucleoproteins Glycopro- 
 teins Phosphoproteins Haemoglobins Lecithoproteins 
 Derived proteins Proteans Metaproteins Coagulated pro- 
 teins Proteoses Peptones Peptides Products of proteo- 
 lysis Tyrosine Leucine Hydrolysis Enzymes Pepsin 
 Pancreatin 623-639 
 
 54. Chemical changes in plants and animals. 
 
 Difference between vegetable and animal life Formation of 
 organic substances by the plant Animal food Digestibility 
 
xiv CONTENTS. 
 
 PAGE 
 
 Nutrition Digestion Absorption Respiration AVaste- 
 products of animal life Chemical changes after death . . . 639-649 
 
 55. Animal fluids and tissues. 
 
 Constituents of the animal body Blood ; its properties and 
 composition Blood-plasma and blood-serum Blood-pigments 
 Fibrin Hemoglobin Haematin Hrematoporphyrin 
 Spectroscopic examination Examination of blood-stains 
 Immune bodies of the blood-serum Lymph Bone Teeth 
 Hair, nails, etc. Muscle Muscle extractives Creatine and 
 Creatinine Xanthine bases Purine bases Xanthine and 
 hypoxanthine Meat-extracts The thyroid gland Brain 
 Lecithins Cholesterin 649-671 
 
 56. Digestion. , 
 
 General remarks Salivary digestion Saliva, tests for it 
 Gastric digestion Gastric juice, its clinical examination 
 Intestinal digestion Pancreatic secretions Bile Biliary pig- 
 ments, acids, and calculi Fermentative and putrefactive 
 changes Absorption, assimilation Feces ; their chemical ex- 
 amination The liver Glycogen Indole Skatole 672-694 
 
 57. Milk. 
 
 Properties and composition Milk-proteins Casein Milk- 
 fat Butter Lactose ; tests for it Changes in milk on stand- 
 ing Milk preservatives Analysis of milk Human milk 
 Modified milk 695-703 
 
 58. Urine and its constituents. 
 
 Excretion of urine General properties Points to be con- 
 sidered in the analysis of urine Color Odor Volume Re- 
 action Specific gravity Composition Normal and patho- 
 logical constituents Determination of total solids and inor- 
 ganic constituents Nitrogen in the urine Urea, its reactions 
 and determination Ammonia in urine and its determination 
 Creatine and creatinine Uric acid, its tests and determination 
 Xanthine bodies Allan torn Hippuric acid Chlorides and 
 their determination Phosphoric acid Sulphur compounds in 
 urine Indican Phenol Pyrocatechin Proteins in urine and 
 tests Blood and its tests Carbohydrates and tests Deter- 
 mination of dextrose in urine Laevulose, maltose, lactose, and 
 pentoses Glycuronic acid Acetone, diacetic, and beta-oxy- 
 butyric acids Bile Alkaptonic acids Diazo-reaction Func- 
 tional tests of the kidney Urinary sediments Urinary cal- 
 culi 703-746 
 
 APPENDIX. 
 
 Table of weights and measures 747 
 
 Table of elements 749 
 
 Index .... 751 
 
LIST OF ILLUSTRATIONS. 
 
 FIG. PAGE 
 
 1. The cube 22 
 
 2. Regular octahedron 22 
 
 3. Quadratic octahedron 23 
 
 4. Right-square or quadratic prism 23 
 
 5. Rhombic octahedron 23 
 
 6. Double six-sided pyramid 23 
 
 7. Rhombohedron ." 24 
 
 8. Six-sided prism ... 24 
 
 9. Monoclinic double pyramid 24 
 
 10. Monoclinic prism 24 
 
 11. Triclinic prism 25 
 
 12. Triclinic octahedron 25 
 
 13. 14. Structure of matter 29 
 
 15. Dialyzer . . . . 41 
 
 16. Thermometric scales 47 
 
 17. Reflection 57 
 
 18. Refraction by a parallel plate 58 
 
 19. Refraction through a prism ^ 58 
 
 20. Prismatic spectrum 59 
 
 21. Spectroscope - 60 
 
 22. Direct-vision spectroscope 61 
 
 23. Double refraction 63 
 
 24. Tourmaline plates 64 
 
 25. Undulation in a cord 64 
 
 26. Explanatory diagrams of the action of tourmaline plates 65 
 
 27. Nicol's prism 66 
 
 28. Lippich's polariscope 68 
 
 29. Daniell's cell 75 
 
 30. Induction coil - . . 79 
 
 31. Electric furnace '. 80 
 
 32. Longitudinal section of carborundum furnace 81 
 
 33. Exterior view of carborundum furnace 81 
 
 34. Electrolysis of water 82 
 
 35. Apparatus for the decomposition of mercuric oxide 87 
 
 36. Diagram of periodic system in spiral form 130 
 
 37. Apparatus for generating oxygen 140 
 
 38. Apparatus for generating hydrogen 146 
 
 39. Apparatus for generating ammonia 168 
 
 40. Distillation of nitric acid 175 
 
 41. Structure of flame i85 
 
 42. Apparatus for making sulphurous acid 207 
 
 (xv) 
 
xvi LIST OF ILLUSTRATIONS. 
 
 FIG- PAGE 
 
 43. Apparatus for detection of phosphorus 223 
 
 44-47. Detection of arsenic 353-357 
 
 48-52. Apparatus for analytical operations 372, 373 
 
 53. Heating of solids in bent glass tube 377 
 
 54. Heating on charcoal by means of blowpipe 377 
 
 55. Washing and decanting in agate mortar 378 
 
 56. Platinum wire for blowpipe experiments v 379 
 
 57. 58. Apparatus for generating hydrogen sulphide 384 
 
 59. Drying-oven 403 
 
 60. Desiccator 404 
 
 61. Watch-glass for weighing filters 404 
 
 62. Liter flask 405 
 
 63. Pipettes 405 
 
 64. Mohr's burette and clamp 406 
 
 (}"). Mohr's burette and holder 406 
 
 66. Gay Lussac's burette 407 
 
 67. Flask for dissolving iron . 419 
 
 68. Gas-furnace for organic analysis 444 
 
 69. Flasks for fractional distillation 463 
 
 70. Liebig's condenser, with flask 484 
 
 71. Isomeric salts of tartaric acid 513 
 
 72. Absorption-spectra of blood constituents 658 
 
 73. Uriuometer 707 
 
 74. Doremus' ureometer 714 
 
 75. Esbach's albuminometer 727 
 
 76. Various forms of uric acid crystals 741 
 
 77. Calcium oxalate crystals 742 
 
 78. Crystalline phosphates 742 
 
 79. Ammonium urate crystals ....... 743 
 
 80. Crystals of leucine ^ 743 
 
 81. Tyrosine crystals 744 
 
 82. Crystals of cystine 744 
 
COLORED PLATES. 
 
 PLATE Of Spectra 
 
 " I. Compounds of iron, cobalt, and nickel 
 
 II. Compounds of manganese and chromium 
 
 III. Compounds of copper, lead, and bismuth 
 
 IV. Compounds of silver and mercury 
 
 V. Compounds of arsenic, antimony, and tin 
 
 VI. Reactions of alkaloids .... 
 
 VII. Indicators for alkalies and acids . 
 
 t VIII. Physiological reactions .... 
 
 . Frontispiece. 
 
 facing page 302 
 
 " 312 
 
 " 326 
 
 " " 344 
 
 " " 352 
 
 " " 602 
 
 " 680 
 738 
 
 ABBREVIATIONS. 
 
 c.c. = Cubic centimeter. 
 
 B. P. = Boiling-point. 
 
 F. P. = Fusing-pointc 
 
 Sp. gr. = Specific gravity. 
 
 U. S. P. = United States Pharmacopeia. 
 
 (xvii) 
 
PRACTICAL CHEMISTRY, 
 MEDICAL AND PHARMACEUTICAL, 
 
 I. 
 
 CHEMICAL PHYSICS. 
 
 BOTH sciences, chemistry and physics, have for their object the 
 study of all substances, or of all varieties of matter, and the changes 
 which they undergo. When these alterations affect the composition 
 of matter we have chemical changes, which are considered by chem- 
 istry ; when the composition is not affected Ve have physical changes, 
 considered by physics. But whenever chemical changes take place 
 they are accompanied by physical changes. Indeed, there exists such 
 a close relation, such a mutual dependency, between these two series 
 of phenomena that they cannot be studied altogether independently 
 of one another. Moreover, the chemist uses constantly in his opera- 
 tions instruments or appliances the construction of which is based on 
 physical principles. A knowledge of certain parts of physics is 
 therefore essential for the proper understanding of chemistry. It is 
 for this reason that a few chapters dealing with certain physical con- 
 ditions of matter precede the parts on chemistry. 
 
 Physics is defined above as the study of those changes in matter which do 
 not involve an alteration of the composition or constitution of the matter. 
 The phenomena of light, heat, electricity, magnetism, sound, motion, attrac- 
 tion, etc., fall within its province. A few examples of physical changes may 
 help to make the subject clearer. A piece of iron heated sufficiently becomes 
 luminous, radiates heat, and increases in size. All these are physical changes, 
 because if the iron be cooled it will be found to be the same in character as 
 before it was heated. There has been no change in the substance iron. A 
 body in rapid motion is quite different from the same body at rest, as is evident 
 if the body hit an individual, yet the nature or composition of the body is not 
 altered. A wire through which an electric current is passing is different from 
 2 17 
 
18 CHEMICAL PHYSICS. 
 
 one in which there is no current, although the substance of both wires is the 
 same. Many other examples of physical change might be cited. 
 
 Chemistry is the study of those changes in bodies which affect their compo- 
 sition, and in this respect chemical changes differ from all other kinds of 
 changes. Another good and broad definition given by the great Russian chem- 
 ist, Mendelejeff, is the following: Chemistry is concerned with the study of the 
 homogeneous substances or materials of which all objects of the universe are 
 made up, with the transformations of these substances into one another, and 
 with the phenomena which accompany such transformations. When a piece 
 of paper burns, an ash is left, which is altogether different from the original 
 paper. Moreover, if proper care be taken to catch the products escaping dur- 
 ing the burning, water vapor and gases will be found, which are also unlike 
 the paper. These are new substances and the change is, therefore, a chemical 
 one. But at the same time several physical changes will be observed, namely, 
 heat and light. 
 
 When a piece of the metal magnesium is ignited, it burns and leaves an ash 
 entirely different from the metal, being white and brittle. This is a chemical 
 change, but heat and intense light are observed at the same time, which are 
 physical changes. 
 
 When a piece of marble is heated to redness for some time, a substance 
 remains on cooling which, although having the same form as the piece o> 
 marble, is nevertheless entirely different in its composition and properties, anr* 
 is known as quick-lime. When water is poured upon the latter, great heat is 
 produced .and the solid lump falls down to a white powder, known as slaked- 
 lime, whereas marble is not affected by water. By a suitably arranged appa- 
 ratus it could also be shown tfiat an invisible gas is given off when the marble 
 is heated. 
 
 These illustrations will be sufficient to point out the nature of physical and 
 chemical changes, and we may proceed now to the discussion of some element- 
 ary subjects of physics. 
 
 1. FUNDAMENTAL PROPERTIES OF MATTER. 
 
 Matter is anything that occupies space and may be apprehended 
 by the aid of our senses. While there are many thousands of various 
 kinds of matter, possessing widely different properties, yet there are 
 properties in common which belong to 'every kind of matter, and 
 these are known as essential or fundamental properties. The funda- 
 mental properties of matter having a special interest for those study- 
 ing chemistry are : Extension, Divisibility, Gravitation, Porosity, and 
 Indestructibility. 
 
 Extension. The common property of matter to occupy space is 
 known as extension. All bodies, without exception, fill a certain 
 quantity of space ; they all have length, breadth, and thickness. 
 That portion of matter lying within the surrounding surface of a 
 body is called its mass; or we may define mass as the quantity of 
 
FUNDAMENTAL PROPERTIES OF MATTER. 19 
 
 matter which a body possesses. A body is a definite portion of 
 matter, such as a knife, a piece of chalk, or a lump of coal. The 
 term substance is used to designate some particular kind of matter, 
 possessed of definite qualities, such as gold, water, glass, etc. We 
 distinguish three different conditions of matter, namely : Solids, 
 Liquids, and Gases. 1 These conditions of matter are known as the 
 three states of aggregation, and we will now consider the peculiarities 
 of matter when existing in either of these states. 
 
 Solid state. Solids are distinguished by a self-subsistent figure 
 i. e., they have a definite size and shape. A solid substance forms 
 for itself, as it were, a casing in which its smallest particles 1 are en- 
 closed. The questions arise, By what means are these particles con- 
 nected? How are they kept together? No answer can be given 
 other than that the particles themselves attract each other to such an 
 extent that force is necessary to make them alter their relative posi- 
 tions. We see, consequently, that some form of attraction or at- 
 tractive power is acting between the particles of a solid mass, and 
 we call this kind of attraction cohesion, to distinguish it from other 
 forms of attraction. 
 
 Force may be defined as the action of one body upon another 
 body, or as the action of particles of matter upon other particles 
 either of the same or of another body. Strictly speaking, we may 
 say that force is the cause tending to produce, change, or arrest 
 motion ; or it is any action upon matter changing or tending to change 
 its form or position. Force is a manifestation of energy, and may 
 be originated in a variety of ways. 
 
 Energy is a universal property of matter ; it is its capacity for 
 doing work, and is measured by the work it can do. Doing work con- 
 sists in a transfer of motion, or energy, from the body doing work to 
 the body on which work is done. Wherever we find matter in motion 
 we have a certain quantity of energy which may be made to do work. 
 
 As examples of different forms of energy we have motion of masses, heat, 
 light, electricity, chemical changes, etc. Under the influence of the different 
 forms of energy matter is constantly undergoing change. There are changes 
 in position, in temperature, in appearance, in the composition of substances, 
 and in many other directions. 
 
 1 It has been shown lately that matter may exist in a fourth state as radiant matter. This 
 condition will be considered later. 
 
 2 It will be shown later that all matter is supposed to consist of smallest particles, which we 
 call molecules. 
 
20 CHEMICAL PHYSICS. 
 
 Energy may be potential (i. e., stored up) or kinetic (i. e., actual). For 
 instance, potential energy is the energy which we have in a mass held by 
 the hand, or by a support ; as soon as the support is withdrawn the mass falls, 
 and in this instance we witness kinetic or actual energy. 
 
 Other instances of potential energy are a drawn bow, a wound-up watch- 
 spring, an elevated tank of water, etc. This potential energy may manifest 
 itself as kinetic energy by sending an arrow through space, by keeping the 
 watch in motion, or by rotating a water-wheel. During the conversion of 
 potential into kinetic energy there is neither gain nor loss ; both are absolutely 
 alike in quantity. 
 
 Crystallization. The external appearance or the figure of solid 
 bodies is various. It may be an irregular or a natural regular figure. 
 Of these two forms, only the latter is here of interest, as it includes 
 all the different crystallized substances. 
 
 Crystals are solid substances bounded by plane surfaces symmetri- 
 cally arranged according to fixed laws. In explaining the formation 
 of crystals we have to assume that the particles are endowed with the 
 power of attracting one another in certain directions, thereby building 
 themselves up into geometrical forms. 
 
 The external form of a crystal is only an outward expression of a regular 
 internal structure. This is shown by the fact that in non-crystalline homo- 
 geneous bodies such properties as elasticity, hardness, cohesion, transmission 
 of light, etc., are the same in all directions, while crystallized bodies show dif- 
 ferences along different directions. A model of glass would not be a crystal, 
 since the necessary internal structure is absent. 
 
 The first condition essential to the formation of crystals is the possi- 
 bility of free motion of the smallest particles of the matter to be crys- 
 tallized ; in that case only will they be able to attract each other in 
 such a way as to assume a regular shape, or form crystals. Particles 
 of a solid mass can move freely only after they have been transferred 
 to the liquid or gaseous state. There are two different methods of 
 liquefaction, viz., by means of heat (melting), or solution in some 
 suitable agent (dissolving). In the liquid condition thus produced, 
 the smallest particles can follow their own attraction, and unite to 
 form crystals on removal of the cause of liquefaction (heat or solvent). 
 
 In the great majority of cases the method employed for obtaining crystals 
 is to dissolve the substance in a liquid, usually water, taking advantage of the 
 fact that, with very few exceptions, substances are more soluble in hot than in 
 cold liquids. When such a concentrated hot solution, filtered if necessary to 
 remove solid matter, is allowed to cool, the particles of the excess of the sub- 
 stance, beyond what is soluble at the lower temperature, gradually arrange 
 
FUNDAMENTAL PROPERTIES OF MATTER. 21 
 
 themselves around certain points as nuclei according to the directions of great- 
 est cohesion, and thus crystals with regular faces and angles and definite 
 internal arrangement are built up. The size of the crystals obtained will 
 depend on several factors, but whatever the size may be, the angles between 
 the faces and the position of the faces will be the same for every individual 
 substance. Hence the shape of crystals is a valuable means of identifying 
 substances. If a concentrated hot solution of a substance be cooled quickly, 
 and especially if the liquid be disturbed, as by stirring, the crystals will be 
 small, sometimes almost microscopic in size. But this is often an advantage, 
 because large crystals are apt to enclose some of the liquid containing the 
 impurities between the layers. On the large scale, as in industries, enormous 
 crystals are obtained by the slow cooling of a great volume of solution, for 
 example, in the case of alum, potassium dichromate, etc. When a substance 
 is not much more soluble in a hot than in a cold liquid, for example, common 
 salt in water, the liquid must be removed by allowing it to evaporate, either at 
 ordinary or at elevated temperature, to obtain a good yield of the substance 
 in crystal form. 
 
 Sometimes sticks, strings, wires, strips of lead, etc., are suspended in the 
 solutions, to offer starting-points for the formation of crystals and a ready 
 means for removing the crystals from the liquor. A familiar example is the 
 string in the center of a stick of rock-candy. 
 
 A relatively few substances when heated pass from the solid to the gaseous 
 state, without undergoing intermediate liquefaction. When the vapor of such 
 substances comes in contact with cool surfaces, it is deposited in crystals which 
 sometimes attain to remarkable size and beauty. This process is known as 
 sublimation and is used in the case of several medicinal agents on the market, 
 for example, iodine, benzoic acid, ammonium chloride, etc. The words iodine 
 resublimed, found on labels, and the popular name for mercuric chloride, namely, 
 corrosive sublimate, refer to the process of sublimation employed in obtaining 
 these substances. 
 
 If two or more (non-isomorphous) substances for instance, common salt 
 and Glauber's salt be dissolved together in water, and the solution be allowed 
 to crystallize, the attraction of like particles for one another will be readily 
 noticed by the formation of distinct crystals of common salt alongside of 
 crystals of Glauber's salt ; neither do the particles of common salt help to 
 build up a crystal of Glauber's salt, nor the particles of the latter a crystal of 
 common salt. Advantage is taken of this property in separating (by crystal- 
 lization) solids from each other, when they are contained in the same solution. 
 
 Not all matter can form crystals ; some substances never have been 
 obtained in a crystallized state, such as starch, gum, glue, etc. A 
 solid substance showing no crystalline structure whatever is called 
 amorphous. 
 
 Some substances capable of crystallization may be obtained also in 
 an amorphous state (carbon, sulphur). Other substances are capable 
 of assuming different crystalline shapes under different conditions. 
 Thus sulphur, when liquefied by heat, assumes, on cooling, a shape 
 different from the sulphur crystallized from a solution. One and the 
 
22 
 
 CHEMICAL PHYSICS. 
 
 same substance under the same conditions always assumes the same 
 shape. Substances capable of assuming in solidifying two or more 
 different shapes or conditions, are said to be dimorphous and poly- 
 morphous, respectively. When substances of different kinds crystallize 
 in exactly the same form we call them isomorphous (magnesium sul- 
 phate and zinc sulphate). Also, a crystal of one kind of matter must 
 have the power of growing in the solution of another kind before 
 the two kinds of matter are considered isomorphous. If two iso- 
 morphous substances be contained in one solution, they will crystallize 
 together, and the crystals be made up of particles of both substances, 
 
 Crystal Systems. The study of crystals forms an extensive field, known 
 as crystallography. The limited scope of this book forbids any detailed study 
 of crystals, and the reader must be referred to the large works on chemistry or 
 works on crystallography for such information. But a brief description of the 
 classification of crystals may not be out of place here. 
 
 All crystals are referred to axes or imaginary lines drawn through the cen- 
 ter. The great variety of forms of crystals depends upon the number and 
 length of these axes and their relative inclination that is, the angles at which 
 they intersect. All crystal forms have been divided into two large groups, the 
 orthometric and the clinometric, and these have been further subdivided into six 
 systems. Orthometric refers to the fact that the axes intersect at right angles, 
 while clinometric means that the axes intersect at oblique angles. 
 
 FIG. 1. 
 
 FIG. 2. 
 
 The cube. Regular octahedron. 
 
 The orthometric group includes the following systems : 
 
 (1) Kegular system, also known as the monometric, cubic, octahedral, or 
 tessular system. 
 
 The crystals have three axes of equal length and intersecting at right angles. 
 The fundamental forms of this system are the cube and the octahedron (Figs. 
 1 and 2). Some substances crystallizing in this system are alum, phosphorus, 
 arsenic trioxide, diamonds, alkali iodides, chlorides, fluorides, and cyanides, 
 and many metals and their sulphides. 
 
 (2) Quadratic system, also known as the dimetric, square prismatic, or tet- 
 ragonal system. 
 
FUNDAMENTAL PROPERTIES OF MATTER. 
 
 The crystals have three axes intersecting at right angles, two of which are 
 of equal length and one either longer or shorter than the other two. The fun- 
 damental forms of this system are the quadratic octahedron (also known as 
 square-based double pyramid) and the right square prism (Figs. 3 and 4). 
 
 FIG. 3. FIG. 4. 
 
 Quadratic octahedron. Right-square or quadratic prism. 
 
 Some substances crystallizing in this system are potassium ferrocyanide, calo- 
 mel, nickel sulphate, tin, tin oxide, magnesium sulphate, zinc sulphate. 
 
 (3) Rhombic system, also known as the trimetric or right prismatic system. 
 
 FIG. 5. FIG. 6. 
 
 Rhombic octahedron. Double six-sided pyramid. 
 
 The crystals have three unequal axes intersecting at right angles. The fun- 
 damental form of this system is the rhombic octahedron or right rhombic 
 double pyramid (Fig. 5). Some substances crystallizing in this system are 
 
24 
 
 CHEMICAL PHYSICS. 
 
 potassium sulphate and nitrate, resorcin, zinc sulphate, citric acid, iodine, 
 Rochelle salt, mercuric chloride, barium chloride, tartar emetic, codeine, sali- 
 cylic acid, piperin, Epsom salt, silver nitrate, ammonium sulphate, cream of 
 tartar. 
 
 (4) Hexagonal or rhombohedral system. 
 
 The crystals have four axes, three of which are of equal length, while the 
 fourth is either longer or shorter than the other three. The three equal axes 
 are in the same plane and intersect at an angle of 60, while the fourth axis 
 intersects these at right angles. The fundamental form is the double six-sided 
 pyramid. The rhombohedron and regular six-sided prism are modifications 
 of this system (Figs. 6, 7, and 8). Some substances crystallizing in this system 
 
 FIG. 7. 
 
 FIG. 8. 
 
 i i i 
 
 i 
 
 
 j 
 j 
 
 
 L 
 
 <L.., 
 
 Rhombohedron. 
 
 Six-sided prism. 
 
 are sodium nitrate, camphor, graphite, ammonium chloride, ice, calcspar, thy- 
 mol, metallic bismuth and antimony, arsenic, silicic acid. 
 
 The clinometric group includes the following systems : 
 
 (5) Monociinic system, also known as the monosymmetric, clinorhombic, or 
 oblique prismatic system. 
 
 The crystals have three unequal axes, two intersecting at oblique angles and 
 both intersecting the third at right angles. The fundamental forms of this 
 system are the monoclinic double pyramid or octahedron and the monoclinic 
 prism (Figs. 9 and 10). Some substances crystallizing in this system are 
 
 FIG. 9. FIG. 10. 
 
 Monoclinic double pyramid. Monoclinic prism. 
 
 ferrous sulphate, borax, lead acetate, cupric acetate, tartaric acid, potassium 
 chlorate, and sodium acetate, sulphate, thiosulphate, phosphate, and carbonate. 
 (6) Triclinic system, also known as the asymmetric, clinorhombohedral, or 
 doubly oblique prismatic system. 
 
FUNDAMENTAL PROPERTIES OF MATTER. 25 
 
 The crystals are the most unregular of all, having three unequal axes, all 
 intersecting at oblique angles. The fundamental forms of this system are the 
 triclinic prism and the triclinic octahedron or double pyramid (Figs. 11 and 
 12). Some substances crystallizing in this system are copper sulphate, potas- 
 sium dichromate, gypsum, boric acid, manganous sulphate. 
 
 The pyramidal form is found in all the systems, while the cube is confined 
 to the regular system, and prisms occur in all but the regular system. 
 
 FIG. 11. FIG. 12. 
 
 Triclinic prism. Triclinic octahedron. 
 
 For some reason or other crystals sometimes grow mainly in one or two 
 directions and then show forms that are distorted and have little or no resem- 
 blance to the normal forms of the system to which they belong. Examples of 
 such forms are the following : 
 
 Tabular crystals or flat plates, as potassium chlorate, iodine, etc. 
 
 Laminar crystals, thin plates or leaflets, as acetanilid, naphthol, calcium 
 hypophosphite, etc. 
 
 Acicular crystals or needles, as aloin, cinchonidine sulphate, quinine 
 salts, etc. 
 
 Prismatic crystals or prisms, extended chiefly in the direction of the longest 
 axis, as salicylic acid, santonin, cinchonine sulphate, etc. 
 
 The shapes of gems must not be confused with crystal forms. They are the 
 result of cutting and polishing for the purpose of causing the gem to reflect 
 more light. 
 
 Characteristic properties of solids. Solid substances show a 
 great variety of properties caused by the differences in the cohesion 
 of the particles (molecules) composing the substances, and accordingly 
 we distinguish between hard and soft, brittle, tenacious, malleable, 
 and ductile substances. 
 
 Hardness is that property in virtue of which some bodies resist attempts to 
 force passage between their particles, or which enables solids to resist the dis- 
 placement of their particles. Diamond and quartz are extremely hard, while 
 wax and lead are comparatively soft. 
 
26 CHEMICAL PHYSICS. 
 
 Brittleness is that property of solids which causes them to be broken easily 
 when external force is applied to them. Glass, sulphur, coal, etc., are brittle. 
 
 Tenacity is that property in virtue of which solids resist attempts to pull 
 their particles asunder. Steel is one of the most tenacious substances. 
 
 Malleability, possessed by some solids, is the property in virtue of which they 
 may be hammered or rolled into sheets. Gold is so malleable that it may be 
 beaten into sheets so thin that it would require about 300,000 laid upon one 
 another to measure one inch. 
 
 Ductility is the property in virtue of which some solids may be drawn into 
 wire or thin sheets as, for instance, copper, iron, and platinum. 
 
 Liquid state. The characteristic features of liquids are, that they 
 have no self-subsistent figure; that they consequently require some 
 vessel to hold them ; and that they present a horizontal surface. While 
 in a solid substance the smallest particles are held together by cohe- 
 sion to such an extent that they cannot change their relative position 
 without force, in a liquid this cohesion acts with much less energy 
 and permits of a comparatively free motion of the particles; the 
 repellant and attractive forces nearly balance each other in a liquid. 
 That cohesion is not altogether suspended in a liquid is shown by the 
 formation of drops or round globules, which, of course, consist of a 
 large number of smallest particles. If there were no cohesion at all 
 between these particles of a liquid, drops could not be formed. 
 
 The terms semi-solid and semi-liquid substances are used for bodies occupy- 
 ing a position intermediate between true solids and fluids; butter, asphalt, 
 amorphous sulphur, are instances of this kind. 
 
 Gaseous state. Matter in the gaseous state has absolutely no 
 self-subsistent figure. Any quantity of gas in a closed vessel will 
 fill it completely ; the smallest particles show the highest degree of 
 mobility and move freely in every direction. Cohesion is entirely sus- 
 pended in gases ; indeed, there is no attraction between the particles, 
 but they are in rapid motion and tend to spread out in all directions ; 
 hence must be retained in a closed vessel. The motion of the par- 
 ticles causes bombardment on the sides of the vessel, and thus pro- 
 duces pressure. This characteristic property, possessed by all gases, 
 is known as elasticity, or, better, as tension, and is so unvarying that 
 a law 1 has been established in relation to it. This law is known 
 as the Law of Boyle, who discovered it in 1661 ; sometimes it is 
 referred to as the Law of Mariotte. It may be expressed thus : The 
 volume of a gas is inversely as the pressure ; the density and elastic 
 force are directly as the pressure and inversely as the volume. 
 
 1 In science, a law or generalization is a brief statement which describes some constant mode 
 of behavior, or sums up the constant features of a set of phenomena of a like kind. 
 
FUNDAMENTAL PROPERTIES OF MATTER 27 
 
 The subject will be clearer from the following considerations : A 
 gas behaves much like a spring. If we put weights (force) on the 
 spring it will be compressed that is, its volume will become less, and 
 if the weights be gradually removed, the spring will expand. Sim- 
 ilarly, if we take a metallic tube closed at one end, and fitted with a 
 piston and handle and containing a certain volume of air, for 
 example, a bicycle pump, and then press down upon the handle, the 
 volume of air will become smaller and smaller as the pressure on the 
 handle is increased. It will be observed also that as the volume 
 becomes smaller it oifers more and more resistance to compression, 
 that is, its tension or elastic force becomes greater. Also, since the 
 amount of material in the original volume of air remains the same 
 during the experiment, it is plain that when the air is compressed to 
 a small volume, the amount of material in a unit volume, say 1 cubic 
 inch, is very much increased ; in other words, the density of the gas is 
 increased as the pressure is increased. If accurate measurements be 
 made of the different pressures applied and the corresponding vol- 
 umes assumed by the air, a constant relationship will be discovered, 
 such as is expressed in Boyle's Law, stated above. The meaning of 
 the phrase in the law, the volume of a gas is inversely as the pressure, 
 is that as the one quantity is increased the other is decreased in just 
 the same proportion. To illustrate, if a volume of a gas measure 1 
 cubic foot under a pressure of 10 pounds, and the pressure be 
 increased to 15 pounds, in other words, || or f times, then the vol- 
 ume will change from 1 cubic foot to 1 -s- f = f cubic foot. If the 
 pressure be decreased to say 6 pounds, or -f^ - f of its original value, 
 then the volume will become 1 -*- f = f cubic foot, that is, it will 
 expand. 
 
 Such a relation as is expressed in Boyle's Law is known in algebra 
 as inverse proportion. Since one of the quantities is always decreased 
 in the same ratio as the other is increased, it follows that the product 
 of the two quantities thus related must always be the same, that is, a 
 constant. Hence, another way of expressing Boyle's Law is to say 
 that the product of the pressure and the corresponding volume of a 
 definite quantity of a gas is always the same. If V and V 1 repre- 
 sent the volumes of a certain amount of gas, at the corresponding 
 pressures, P and F, then V X P = V 1 X P. In the example 
 given above, Y == 1 cubic foot, P = 10 pounds, and P 1 = 15 pounds, 
 hence, 1 X 10 = V 1 X 15, or V 1 == |g- = f cubic foot. 
 
 As will be seen later, this law is of great value in all experiments 
 where results are calculated from measurements of gas volumes. 
 
28 CHEMICAL PHYSICS. 
 
 Vapors from liquids and solids at sufficient temperatures above their 
 points of condensation behave just like gases. 
 
 Divisibility. All matter admits of being subdivided into smaller 
 particles, and this property is called divisibility. The processes by 
 which we accomplish the comminution of a solid substance may 
 be of a mechanical nature, such as cutting, crushing, grinding ; but 
 beside these modes of subdivision we have other agents or causes 
 by which matter may be divided into smaller particles, and one of 
 these agents is heat. 
 
 Action of heat on matter. Let us take a piece of ice and 
 convert it, by means of mortar and pestle, into a very fine powder. 
 When the smallest particle of this finely powdered ice is placed 
 under the microscope and heat applied, we shall observe that it 
 becomes liquid, thus proving that it was capable of further sub- 
 division, that it consisted of smaller particles, which have now by 
 the action of heat become movable. By further applying heat to the 
 liquid particle of water we may convert it into a gas or vapor, which 
 will escape into the air, or which we may collect in an empty flask. 
 The flask will be filled completely by this water-gas (or steam) 
 obtained by vaporizing that minute particle of ice-dust. This fact 
 demonstrates that mechanical comminution does not carry us beyond 
 a certain degree of subdivision of matter. That is to say, the smallest 
 fragment of the finest powder still consists of a very large number of 
 much smaller particles. To the smallest particles which compose 
 matter the name molecules has been given. 
 
 Molecular theory. The expression molecule is derived from the 
 Latin word molecula a little mass, and means the smallest particle 
 of matter that can exist by itself, or into which matter is capable of 
 being subdivided by physical actions. To explain more fully what is 
 meant by the expression molecule, we will return to the conversion of 
 water into steam. 
 
 When water boils at the ordinary atmospheric pressure it expands 
 about 1800 times, or one cubic inch of water yields about 1800 cubic 
 inches, equal to about one cubic foot of steam. In explaining this 
 fact we have either to assume that the water, as well as the steam, is 
 continuous matter (Fig. 13), or that the water consisted of small par- 
 ticles of a given size, which now exist in the steam again as such, 
 
FUNDAMENTAL PROPERTIES OF MATTER. 29 
 
 FIG. 13. 
 
 with the only difference that they are more widely separated from 
 each other (Fig. 14). 
 
 FIG. 14. 
 
 Of the many proofs which we have of the fact that the latter 
 assumption is correct, one may be sufficient, viz., that the quantities 
 of vapor formed by volatile liquids at any certain temperature above 
 the boiling-point, in close vessels of the same size, are the same, no 
 matter whether the vessel was entirely empty or contains the vapors 
 of one, two, or more other substances. For instance : If we place 
 one cubic inch of water in a flask holding one cubic foot, from which 
 flask the air has been previously removed, and then heat the flask to 
 the boiling-point, the cubic inch of water will evaporate, filling the 
 vessel with steam. Upon now introducing into the flask a second and 
 
30 CHEMICAL PHYSICS. 
 
 a third liquid for instance, alcohol and ether we find that of each 
 of these liquids exactly the same quantity will evaporate which would 
 have evaporated if these liquids had been introduced into the empty 
 flask. 1 This fact is evidence that there must be small particles of 
 steam which are not in close contact, that there are spaces between 
 these particles which may be occupied by the particles of a second, 
 third, or more substances. To these particles of matter we give the 
 name molecules, and the spaces between them we call intermolecular 
 
 We have thus demonstrated the correctness, or, at least, the likeli- 
 hood, of the so-called molecular theory, but the proof given is but one 
 of many. Other facts which lead us to accept the theory of the 
 molecular condition cf matter are : The passage of gases through 
 solids : for example, of carbon dioxide gas through red-hot iron ; of 
 water under pressure through gold ; the decrease in a volume of water 
 when a salt is dissolved in it ; the extreme divisibility of matter as 
 shown by solution, etc. 
 
 Our conception of molecules (though individually by far too small to make 
 any impression whatever upon our senses) is so perfect that we have formed an 
 idea of the actual size of these minute particles of matter. Very good reasons 
 lead us to believe that the diameter of a molecule is equal to about CTnn&rnnnj 
 of one inch, and that one cubic inch of a gas under ordinary conditions con- 
 tains about one hundred thousand million million milions of molecules. 
 
 These figures at first glance appear to be beyond the limit of human con- 
 ception, but in order to give some idea of the size of these molecules it may be 
 mentioned that if a mass of water as large as a pea were to be magnified to the 
 size of our earth, each molecule being magnified in the same proportion, these 
 molecules would represent balls of about two inches in diameter. 
 
 While molecules consequently are exceedingly small particles, yet they are 
 not entirely immeasurable ; they are, as Sir W. Thomson says, pieces of matter 
 of measurable dimensions, with shape, motion, and laws of action, intelligible 
 subjects of scientific investigation. 
 
 Intimately connected with the molecular theory is the Law (more 
 correctly, the hypothesis) of Avogadro, which may be stated as follows : 
 All gases or vapors, without exception, contain, in the same volume, the 
 same number of molecules, provided temperature and pressure are the 
 same. Or, in other words : Equal volumes of different gases contain, 
 under equal circumstances, the same number of molecules. The correct- 
 ness of this law has good mathematical support deduced from the law 
 of Boyle, many other facts and considerations leading to the same 
 
 1 As each gas, in consequence of its tension, exerts a certain pressure, the pressure in the 
 flask rises with the introduction of every additional gas. 
 
FUNDAMENTAL PROPERTIES OF MATTER. 31 
 
 assumption. We shall learn, hereafter, that the law of Avogadro is 
 one of the greatest importance to the science of chemistry. 
 
 Gravitation. Every particle of matter in the universe attracts 
 every other particle ; consequently, all masses attract each other, and 
 this attraction is known as gravitation. The action of gravitation 
 between the thousands of heavenly bodies moving in the universe is 
 to be considered by astronomy, but some of the phenomena caused 
 by the mutual attraction of the substances composing the earth are 
 of importance for our present consideration. 
 
 Such phenomena caused by gravitation are the falling of substances, 
 the flowing of rivers, the resistance which a substance offers on being 
 lifted or carried. A body thrown up into the air or deprived of its 
 support will fall back upon the earth. In this case the mutual attrac- 
 tion between the earth and the substance has caused its fall. It 
 might appear that in this case the attraction was not mutual, but ex- 
 erted by the earth only; it has been proved, however, by most exact 
 experiments, that there is also an attraction of the falling substance 
 for the earth, but the amount of the force of this attraction is directly 
 proportional to th.e mass of the bodies, and consequently too insig- 
 nificant in the above case to be noticed. 
 
 The law of gravitation, known as Newton's law, may thus be stated : 
 All bodies attract each other with a force directly proportional to 
 their masses and inversely proportional to the squares of their distance 
 apart. With regard to the earth and bodies upon it at a given place, 
 the mass of the earth and the distance between the earth and the 
 bodies remain the same, so that the only thing that varies is the mass 
 of the bodies. Hence, according to Newton's Law, the force with 
 which such bodies are attracted to the earth varies directly as their 
 masses. In other words, if a body A has twice the mass or quan- 
 tity of matter as a body B, it will be attracted with twice as much 
 force to the earth as the body B. 
 
 Weight is an expression used to denote the quantity of mutual 
 attraction between the earth and the body weighed. When we weigh 
 bodies on a balance, we primarily compare two forces, namely, the 
 pull of the earth on each of the bodies on the pans of the balance, 
 nevertheless, we can use the balance to measure mass or quantity of 
 matter. For if two bodies are exactly balanced, that is, " weigh " 
 the same, we know that the pull of the earth is the same on each, and 
 since this attraction, as was shown above, is directly proportional to 
 
32 CHEMICAL PHYSICS. 
 
 the masses or quantity of matter in the two bodies, the masses must 
 be equal. That weight and mass are different ideas is evident from 
 the fact that the force with which a given body is attracted by the 
 earth varies according to latitude and elevation above the earth, while 
 the quantity of matter remains the same. But if two bodies weigh 
 the same in one place, they will do so in any other place. All our 
 weighing is a comparison with, or measurement by, some standard 
 weight, such as pound, ounce, gramme, etc. 
 
 For scientific purposes the weight of bodies is sometimes deter- 
 mined invacuo, because it eliminates an error due to the buoyant effect 
 of atmospheric air. Weight thus determined is called absolute weighty 
 while by ordinary methods we obtain apparent weight. 
 
 "Weights and measures. For scientific purposes the metric or decimal 
 system of weights and measures is used the world over. This system is used also 
 for general purposes by practically all except the English-speaking nations. 
 While metric weights and measures were legalized in the United States and 
 Great Britain in 1866, unfortunately neither country has as yet enforced their 
 general adoption. The U. S. Pharmacopoeia, however, uses the metric system 
 exclusively, and it finds application in all departments of the U. S. govern- 
 ment, as also for many other purposes. The basis of the metric system is a 
 quadrant (one-fourth) of the earth's circumference. This divided into ten mil- 
 lion parts gives a measure of length termed meter (39.37 inches), and this 
 unit of linear measure is the basis for the measures of extension and of weight. 
 
 Subdivisions of all units of metric measure are denoted by prefixes of Latin 
 numerals i. e., ^ by deci, ^Q by centi, -^Q by milli ; while multiples are 
 denoted by prefixes of the Greek numerals L e., 10 by deka, 100 by hecto, 1000 
 by kilo. 
 
 The unit of measure of capacity is the cubic decimeter called liter (1.0567 
 U. S. quart), and the unit of weight is the weight of one cubic centimeter of 
 water at the temperature of its greatest density, 4 C. (39.2 F.), and this unit 
 is called gramme (15.43-)- grains). One liter of water, equal to 1000 cubic centi- 
 meters, at its greatest density weighs 1000 grammes or one kilogram. While 
 gramme is the unit for weights up to a kilogram, the latter is the unit for all 
 larger weights, and is generally abbreviated to kilo (2.2046 pounds, avoirdupois). 
 
 While in our country for commercial purposes the avoirdupois weight is 
 chiefly used, the apothecaries' weight is employed in this country and Great 
 Britain in prescription-writing by all who do not use the metric system. The 
 common link connecting avoirdupois, troy, apothecaries', and Imperial weights 
 is the grain, which is the same in the four systems. (For table of weights and 
 measures, see Appendix.) 
 
 Specific weight or specific gravity denotes the weight of a body, 
 as compared with the weight of an equal bulk or equal volume of 
 another substance, which is taken as a standard or unit. This standard 
 adopted for all solids and liquids, if not otherwise stated, is water at 
 
FUNDAMENTAL PROPERTIES OF MATTER. 33 
 
 a temperature of 25 C. (77 F.) ; that for gases is either atmospheric 
 air or, more generally, hydrogen at a temperature of C, (32 F.). 
 
 Specific weight is generally expressed in numbers which denote how 
 many times the weight of an equal bulk of water is contained in the 
 weight of the substance in question. If we say that mercury has a 
 specific gravity or density of 13.6, or that alcohol has a specific gravity 
 of 0.79, we mean that equal volumes of water, mercury, and alcohol 
 represent weights in the proportion of 1, 13.6, and 0.79, or 100, 1360, 
 and 79. 
 
 Since all liquids and solids expand or contract with change of tem- 
 perature, it is very important to note the temperature in taking the 
 specific gravity of substances. For example, the specific gravity of 
 alcohol is less at 25 C. than that at 15 C., because alcohol expands 
 with rise of temperature. Likewise, at a given temperature, say 25 C. 
 it is greater when compared with water at 25 C. than when com- 
 pared with water at 4 C. or 15 C., because a volume of water 
 weighs less at 25 C. than it does at 15 C. or 4 C. Since the 
 change in volume of solids with change in temperature is much less 
 than in the case of liquids, the difference in specific gravity at differ- 
 ent temperatures is much less noticeable for solids than for liquids. 
 
 Density. Density, in physics, is defined as the mass or quantity 
 of matter in a unit volume of the substance. In the^metric system 
 the mass of a unit volume of water at 4 C. (39.2 F.) is 1 gramme, 
 that is, the density of water at 4 C. is unity. At any other temper- 
 ature the density of water is less than one. It can be seen that when 
 the specific gravity of a substance is determined by comparison with 
 water at 4 C., the number expressing this specific gravity is identical 
 with the number expressing the density of the substance. 
 
 When the comparison is made with water at any other temperature 
 than 4 C., the figures for the specific gravity and the density of a 
 substance are not identical, although the difference between them is 
 usually very small. 
 
 The specific gravity of solids heavier than water is generally determined by 
 first weighing the substance in air and then while suspended in water. The 
 body will be found to weigh less in water because it displaces a volume of water 
 equal to its own, and loses a weight equal to that of the water displaced. Con- 
 sequently the relation between the loss in weight and the weight in air is also 
 the relation between the weights of equal volumes of water and the substance 
 examined. If, for instance, a body is found to weigh 6 grammes in air and 2 
 grammes in water, the loss being 4 grammes, then the relation between the 
 weights of equal volumes of water and the substance is as 4 to 6, or 1 to 1.5; 
 the latter being the specific gravity of the substance examined. 
 
 The specific gravity of a solid soluble in water is determined by weighing it 
 3 
 
34 CHEMICAL PHYSICS. 
 
 first in air, then in a liquid of known specific gravity, but having no solvent 
 action on the substance. The weight of the solid in air divided by the weight 
 of the liquid displaced and the quotient then multiplied by the specific gravity 
 of the liquid employed, gives the specific weight of the substance examined. 
 
 The specific gravity of a solid lighter than water is determined by weighing 
 it first in air, then in water attached to some heavy substance, the weight of 
 which in water has been ascertained. The two substances combined will weigh 
 less in water than the heavy solid alone. The difference in weight between the 
 two weighings in water added to the weight of the light substance in air gives 
 the weight of water displaced, and this sum, divided into the weight of the 
 solid in air, gives its specific gravity. 
 
 The method of finding the specific gravity of a solid by weighing in a liquid 
 depends on the Principle of Archimedes, which says : A body immersed in a liquid 
 loses a part of its weight equal to the weight of the displaced liquid. 
 
 The specific gravity of liquids or gases is determined by weighing in suitable 
 glass flasks equal volumes of the standard substance and the body to be examined. 
 The weight of the latter divided by the weight of the standard substance gives 
 the specific gravity. 
 
 Small glass flasks suitably arranged for taking the specific gravity of liquids 
 are known as pycnometers. 
 
 A second method by which the specific gravity of liquids may be determined 
 is by means of the instruments known as hydrometers, or, if made for some 
 special purposes, as alcoholometers, urinometers, alkalimeters, lactometers, etc. 
 
 Hydrometers are instruments generally made of glass tubes, 
 having a weight at the lower end to maintain them in an upright 
 position in the fluid to be tested as to specific gravity, and a stem 
 above, bearing a scale. The principle upon which their construction 
 depends is the fact that a solid substance when placed in a liquid 
 heavier than itself displaces a volume of this liquid equal to the 
 whole weight of the displacing substance. The hydrometer will 
 consequently sink lower in liquids of lower specific gravity than in 
 heavier ones, as the instrument has to displace a larger bulk of liquid 
 in the lighter than in the heavier liquid in order to displace its own 
 weight. 
 
 "Weight of gases. We have so far considered the gravity of solids 
 and liquids only, and the next question will be : Do gases also possess 
 weight are they also attracted by the earth ? The fact that a gas, 
 when generated or liberated, expands in every direction, might indi- 
 cate that the molecules of a gas have no weight, are not attracted by 
 the earth. A few simple experiments will, however, show that gases, 
 Jike all other substances, have weight. Thus a flask from which the 
 atmospheric air has been removed will weigh less than the same flask 
 when filled with atmospheric air or any other gas. 
 
FUNDAMENTAL PROPERTIES OF MATTER. 35 
 
 Barometer. A second method by which may be demonstrated 
 the fact that atmospheric air possesses weight, is by means of the 
 barometer. The atmosphere is that ocean of gas which encircles the 
 earth with a layer some 50 or 100 miles in thickness, exerting a con- 
 siderable pressure upon all substances by its weight. The instru- 
 ments used for measuring that pressure are known as barometers, and 
 the most common form of these is the mercury barometer. It may 
 be constructed by filling with mercury a glass tube closed at one end 
 (and about three feet long) and then inverting it in a vessel contain- 
 ing mercury, when it will be found that the mercury no longer fills 
 the tube to the top,' but only to a height of about 30 inches, leaving 
 a vacuum above. The column of mercury is maintained at this 
 height by the pressure of the, atmosphere upon the surface of the 
 mercury in the vessel ; a column of mercury about 30 inches high 
 must consequently exert a pressure equal to the pressure of a column 
 of the atmosphere of the same diameter as that of the mercury 
 column. 
 
 As the weight of a column of mercury, having a base of one square 
 inch and a height of about 30 inches, is equal to about 15 pounds, a 
 column of atmosphere having also a base of one square inch must also 
 weigh 15 pounds. In other words, the atmospheric pressure is equal 
 to about 15 pounds to the square inch, or about one ton to the square 
 foot. This enormous pressure is borne without inconvenience by the 
 animal frame in consequence of the perfect uniformity of the pressure 
 in every direction. 
 
 A barometer may be constructed of other liquids than mercury, but as the 
 height of the column must always bear an inverse proportion to the density of 
 the liquid used, the length of the tube required must be greater for lighter 
 liquids. As water is 13.6 times lighter than mercury, the height of a water 
 column to balance the atmospheric pressure is 13.6 times 30 inches, or about 34 
 feet, which would, therefore, be the height of the column of water required. 
 
 It is evident that the pressure of the atmosphere is equal to the weight of a 
 column of mercury, and also that this weight is directly proportional to the 
 length of the mercury column. Hence, different atmospheric pressures can be 
 compared in terms of the length of the mercury column of the barometer, 
 instead of in terms of pounds per square inch. For example, at a pressure of 
 15 pounds per square inch, the mercury column is about 30 inches, while at a 
 pressure of 10 pounds per square inch, it is 20 inches. ^ The ratio of the pres- 
 sures in pounds is 10 : 15 or 2 : 3, and the ratio of the mercury columns is 20 : 30 
 or 2 : 3, which is the same. This fact is of interest in experiments in which 
 gas volumes are dealt with, because calculations have to be made involving a 
 ratio of pressure*, and since this ratio is the same as that of the lengths of the 
 mercury column corresponding to the pressures, it simplifies matters greatly to 
 express pressures in terms of the length of a column of mercury. 
 
36 CHEMICAL PHYSICS. 
 
 Changes in the atmospheric pressure. The height of the mer- 
 cury column in a barometer is not the same at all times, but varies 
 within certain limits. These variations are due to a number of causes 
 disturbing the density of the atmosphere, and are chiefly atmospheric 
 currents, temperature, and the amount of moisture contained in the 
 atmosphere. 
 
 As the height and with it the density of the atmosphere diminishes 
 gradually from the level of the sea upward, the height of the mercury 
 column will be lower in localities situated at an elevation. This 
 diminution of pressure is so constant that the barometer is used for 
 estimating elevations. 
 
 Porosity. We have seen that the molecules of any substance are 
 not in absolute contact, but that there are spaces between them which 
 we call intermolecular spaces ; the property of matter to have spaces 
 between the particles composing it is known as porosity. 
 
 In the case of solids, these spaces or pores are scmetimes of con- 
 siderable size, visible even to the naked eye, as, for instance, in 
 charcoal, while in most cases they cannot be discovered, even by the 
 microscope. That even apparently very dense substances are porous, 
 can be demonstrated by the fact that liquids may be pressed through 
 metallic disks of considerable thickness, that gases may be caused to 
 pass through plates of metal or stone, that solids dissolve in liquids 
 without showing a corresponding increase in volume of the solution 
 thus obtained, and, finally, also by the fact that substances suffer ex- 
 pansion or contraction in consequence of increased or diminished 
 heat, or in consequence of mechanical pressure. 
 
 Surface. In every-day life the expression "surface" refers to that 
 part of a substance which is open to our senses, visible and measur- 
 able ; but from a more scientific point of view, we have also to take 
 into consideration those surfaces which, in consequence of porosity, 
 extend to the interior of matter and are invisible to our eyes and 
 absolutely immeasurable by instruments. 
 
 Surface-action. Attraction acts differently under different condi- 
 tions, and, accordingly, we assign different names to it. We call it 
 cohesion when it acts between molecules, gravitation when acting 
 between masses, and surface-action or surface-attraction when the 
 attraction is exerted either by the visible surface or by that surface 
 which pervades the whole interior of matter. The phenomena caused 
 
FUNDAMENTAL PROPERTIES OF MATTER. 37 
 
 by this surface-action are extremely manifold, and some are of suffi- 
 cient interest to be taken into consideration. 
 
 Adhesion. Most solid substances, when immersed in water, 
 alcohol, or many other liquids, become moist ; immersed in mercury, 
 they remain dry. We explain this fact by saying that the surfaces 
 of most solid substances exert an attraction for the particles of such 
 liquids as water and alcohol to such an extent that these particles 
 adhere to the surface of the solids. Such an attraction, however, 
 does not manifest itself for the particles of mercury. This form of 
 surface-attraction by which liquids are caused to adhere to solids is 
 called adhesion. 
 
 This adhesion may be noticed also between two plates having plane 
 surfaces. A drop of water pressed between these plates will cause 
 them to adhere to each other. The application and use of glue and 
 mucilage, our methods of writing and painting, the welding together 
 of pieces of metal, etc., depend on this kind of surface action. 
 
 Capillary attraction. While it is the general rule that liquids 
 in vessels present a horizontal surface, this rule does not hold good 
 near the sides of the vessel. When the liquids wet the vessel, as in 
 the case of water in a glass vessel, the surface is somewhat concave 
 in consequence of the attraction of the glass surface for the particles 
 of water ; on the contrary, when the liquids do not wet the vessel, as 
 in the case of mercury in a glass vessel, the surface is somewhat 
 convex. The smaller the diameter of the vessel holding the liquids, 
 the more concave or convex will the surface be. If a narrow tube is 
 placed in a liquid, this surface-action will be more striking, and it 
 will be found that a liquid wetting the tube will not only have a 
 completely concave surface, but the level of the liquid stands per- 
 ceptibly higher in the tube than the level of the liquid outside. 
 Substances not wetting the tube will show the reverse action, namely, 
 the surface inside of the tube will be convex, and will be below the 
 level of the liquid outside. 
 
 The attraction of the surface of tubes for liquids, manifesting 
 itself in the concave shape of the surface and in the elevation of the 
 liquid near the tube, is known as capillary attraction. Capillary 
 elevations and depressions depend upon the diameter of the tube, 
 temperature, and the nature of the liquid. The narrower the tube, 
 the higher the elevation or the lower the depression ; both are 
 diminished by increased temperature. Capillary elevations and 
 
38 CHEMICAL PHYSICS. 
 
 depressions, all other circumstances being equal, are inversely pro- 
 portional to the diameters of the tubes. 
 
 Defining the phenomena of capillary attraction more scientifically, 
 we may say that the adhesive force of glass, wood, etc., for water and 
 most other liquids exceeds the cohesive force acting between the 
 molecules of these liquids, while in mercury the cohesive force pre- 
 dominates over the adhesive. 
 
 The rise or fall of liquids in capillary tubes is explained thus : There is an 
 attraction between the particles in the surface of a liquid which causes the 
 surface to act like a stretched membrane. It requires force to separate the 
 particles in the surface and this force is spoken of as the surface tension of the 
 liquid. Proof of this tension is seen in the fact that insects can stand on water 
 without breaking through, and that an oily needle can float on water although 
 it is heavier than it. Another principle in physics is that a stretched surface 
 of a spherical form exerts a force toward the center of curvature of the surface, 
 and tends to contract toward the center. Illustrations of this are seen in the 
 fact that drops of liquids assume a spherical form, and that soap bubbles con- 
 tract when the air in the interior of them is allowed to escape. Now, when a 
 fine tube is dipped into a liquid that wets it, particles of the liquid are drawn 
 up by adhesion of the glass, thus causing a curved surface, which, acting like a 
 membrane, draws up the particles below it by cohesion. The liquid rises until 
 the weight of the column counterbalances the cohesion between the particles 
 in the curved surface, that is, the surface tension. Thus we see also why liquids 
 rise higher in fine tubes than wider ones, since it requires a shorter column 
 of liquid of greater diameter to equal in weight a longer column of smaller 
 diameter. Moreover, since surface tension of liquids diminishes as tempera- 
 ture rises, we see why capillary elevation diminishes as temperature increases. 
 The same kind of argument will explain why liquids which do not wet a tube, 
 for example, mercury, will sink in. the tube below the level of the liquid 
 outside. 
 
 Familiar examples of capillary phenomena are the action of lamp-wicks, 
 the rise of water in wood, sponges, bibulous paper, sand, sugar, and the rise of 
 sap in the vessels of plants. 
 
 Surface-attraction of solids for gases. Any dry solid sub- 
 stance, carefully weighed, will, after having been exposed to a higher 
 temperature, show a decrease in weight while yet warm. Upon 
 cooling, the original weight will be restored. This fact cannot be 
 explained otherwise than that some substance or substances must 
 have been expelled by heat, and that this substance or these sub- 
 stances are reabsorbed on cooling. 
 
 This is actually the case, and the substances expelled and reab- 
 sorbed are the gaseous constituents of the atmospheric air, chiefly the 
 aqueous vapor. 
 
 Every solid substance upon our earth condenses upon its surface 
 
FUNDAMENTAL PROPERTIES OF MATTER. 39 
 
 more or less of the gaseous constituents of the atmosphere. This 
 condensation takes place upon the outer as well as upon the inner 
 surface. The amount of gas absorbed depends upon the nature of 
 the gas as well as upon the nature of the absorbing solid. Some of 
 the so-called porous substances, such as charcoal, generally condense 
 or absorb larger quantities than solids of a more dense and compact 
 structure. Heat, as stated above, counteracts this absorbing power. 
 
 The absorptive power of charcoal for gases varies with the nature of the 
 charcoal and the gas absorbed, as will be seen from the following table: 
 
 Unit volume of charcoal absorbs 
 
 Boxwood. Cocoanut. 
 
 Ammonia gas 90 vols. 172 vols. 
 
 Hydrochloric acid gas 85 " 
 
 Sulphur dioxide 65 ' 
 
 Hydrogen sulphide 55 ' 
 
 Nitrogen monoxide 40 ' 86 vols. 
 
 Carbon dioxide 35 ' 68 " 
 
 Ethylene gas 35 ' 75 " 
 
 Carbon monoxide . 9.42 ' 21 " 
 
 Oxygen 9.25 ' 18 " 
 
 Nitrogen 7.5 ' 15 " 
 
 Hydrogen 1.75 ' 4 " 
 
 Pine charcoal has about one-half the absorptive power of boxwood char- 
 coal. Platinum sponge absorbs about 250 times its volume of oxygen. Other 
 porous substances, as meerschaum, gypsum, silk, etc., are also very absorbent. 
 
 Surface-attraction of solids for liquids or for solids held in 
 solution. When a mixture of different liquids, or a mixture of 
 different solids dissolved in a liquid, is brought in contact with or 
 filtered through a porous solid substance, such as charcoal or bone- 
 black, it will be found that the surface of the solid substance retains 
 a certain amount of the liquids or of the solids held in solution, and 
 that it retains more of one kind than of another. 
 
 It is this peculiarity of surface-attraction which is made use of in 
 purifying drinking-water by allowing it to pass through charcoal. 
 Bone-black is similarly used for decolorizing sugar-syrup and other 
 liquids. 
 
 Absorbing- power of liquids. In a similar manner as in the 
 case of solids, liquids also exert an attraction for gases. When a 
 gas is condensed within the pores or upon the surface of a solid, or 
 when it is taken up and condensed by a liquid, we call the process 
 absorption. This absorbing power of different liquids for different 
 gases varies greatly ; it is facilitated by low temperature and high 
 
40 CHEMICAL PHYSICS. 
 
 pressure, and counteracted by high temperature and removal of 
 pressure. Thus : One volume of water absorbs at ordinary tempera- 
 ture and pressure about 0.03 volume of oxygen, 1 volume of carbon 
 dioxide, 30 volumes of sulphur dioxide, and 800 volumes of ammonia. 
 
 Diffusion. When a cylindrical glass vessel has been partially 
 filled with water, and alcohol, which is specifically lighter than 
 water, is poured upon it, care being taken to prevent a mixing of the 
 two liquids, so as to form two distinct layers, it will be found that 
 after a certain lapse of time the two liquids have mixed with each 
 other, particles of water having entered the alcohol and particles of 
 alcohol the water, until a uniform mixture of the two liquids has 
 taken place. Upon repeating the experiment with a layer of water 
 over a column of solution of common salt, it will again be found that 
 the two liquids gradually enter one into the other until a uniform 
 salt solution has been formed. 
 
 In a similar manner, two or more gases introduced into a vessel or 
 a room will readily mix with each other. This gradual passage of 
 one liquid into another, of a dissolved substance into another liquid, 
 or of one gas into another gas, is called diffusion. 
 
 The rate of diffusion is different for different substances. Saline substances 
 may be divided into a number of equidiffusive groups. The quantity of a sub- 
 stance diffused varies also with the temperature. Thus, the rate of diffusion 
 of hydrochloric acid at 49 C. is 2.18 times that at 15 C. The following table 
 gives the approximate times of equal diffusion for the substances named : 
 
 Hydrochloric acid 1.0 Magnesium sulphate .... 7.0 
 
 Sodium chloride 2.3 Albumin 49.0 
 
 Sugar 7.0 Caramel 98.0 
 
 Magnesium sulphate is one of the least diffusible saline substances, yet it 
 diffuses 7 times faster than albumin and 14 times faster than caramel. 
 
 Diffusion is exhibited also by solids, even at ordinary temperature. Sir "\V. 
 Roberts- Austen placed gold and lead in contact four years at 18 C., and 
 found the surfaces united. Gold had penetrated the lead to more than o milli- 
 meters from the surface, while within 0.75 millimeter from the surface gold 
 was found at the rate of 1 oz. 6 pwt. per ton, which would be profitable to 
 extract. 
 
 The phenomena of diffusion can be explained only on the theory that matter 
 is made up of particles or molecules in motion. They are one of the strong 
 links in the chain of evidence upon which the molecular theory of matter is 
 founded. 
 
 Osmose. Dialysis. This diffusion takes place also when two 
 liquids are separated by a porous diaphragm, sucb as bladder or 
 parchment paper, and it is then called osmose, endosmosis, or dialysis. 
 
FUNDAMENTAL PROPERTIES OF MATTER. 41 
 
 The apparatus used for dialysis is called a dialyzer (Fig. 1 5), and 
 consists usually of a glass cylinder, open at one end and closed at the 
 other by the membrane to be used as the separating medium. This 
 vessel is placed into another, and 
 the two liquids are introduced into 
 the two vessels. If the inner 
 vessel be filled with a salt solution 
 and the outer one with pure water, 
 it will be found that part of the 
 salt solution passes through the 
 membrane into the water, whilst 
 at the same time water passes 
 over to the salt solution 
 
 On subjecting different sub- 
 stances to this process of dialysis, it has been found that some sub- 
 stances pass through the membrane with much greater facility or in 
 larger quantities than others, and that some do not pass through at 
 all. As a general rule, crystallizable substances pass through more 
 freely than amorphous substances. Those substances which do not 
 pass through membranes in the process of dialysis are known as col- 
 loids, those which diffuse rapidly crystalloids. 
 
 Capillary attraction, or, more generally speaking, surface-attrac- 
 tion, is undoubtedly to some extent the cause of the phenomena of 
 osmose, the surface of the diaphragm exercising an attraction upon 
 the liquids. 
 
 Diffusion through the membrane will not take place unless the 
 membrane is in contact with water, and, moreover, its limit will be 
 reached when the concentration outside is the same as that inside the 
 dialyzer. Hence, a large quantity of water should be on the outside 
 and often renewed. Generally, water flows through the membrane 
 toward the denser liquid, which increases in volume, but alcohol and 
 ether are exceptions. They act like liquids which are denser than 
 water. In the case of acids, water flows either into the acids or from 
 the acids, according as they are more or less dilute. When a dilute 
 alcohol is kept for a time in a bladder the volume diminishes, but 
 the alcoholic strength increases. The reason of this is, no doubt, 
 that the bladder permits the water to pass rather than the alcohol. 
 
 An interesting effect of osmosis is seen in the purgative action of 
 magnesium sulphate. A solution of this salt is not readily absorbed 
 and causes a flow of water from the intestinal bloodvessels by 
 osmosis, which, together with the direct stimulating action of the 
 salt to peristalsis, causes purging action. All strong saline solutions, 
 
42 CHEMICAL PHYSICS. 
 
 above 0.7 per cent., abstract liquids from animal tissues when in con- 
 tact with them. 
 
 Diffusion of gases. A diffusion similar to that of liquids takes 
 place also when two different gases are separated from each other by 
 some porous substance, such as burned clay, gypsum, and others. 
 
 It has been found that specifically lighter gases diffuse with greater rapidity 
 than the heavier ones. The quantities of two different gases which diffuse 
 into one another in a given time are, as a general rule, inversely as the square 
 roots of their specific gravities. Oxygen is sixteen times as heavy as hydrogen ; 
 when the two gases diffuse, it will be found that four times as much hydrogen 
 has penetrated into the oxygen as of the latter gas into the hydrogen. This 
 regularity in the diffusion of gases is expressed in the Law of Graham, thus: 
 The velocity of the diffusion of any gas is inversely proportional to the square 
 root of its density. 
 
 Indestructibility. All matter is indestructible i. e., cannot pos- 
 sibly be destroyed by any means whatever, and this property is known 
 as indestructibility. Form, shape, appearance, properties, etc., of 
 matter may be changed in many different ways, but the matter itself 
 can never be annihilated. Apparently, matter often disappears, as, 
 for instance, when water evaporates or oil burns; but these apparent 
 destructions indicate simply a change in the form of matter; in both 
 cases gases are formed, which become invisible constituents of the 
 atmospheric air, and can, therefore, not be seen for the time being, 
 but may be recoudensed or rendered visible in various ways. 
 
 Not only is matter indestructible, energy also partakes of this 
 property. This is expressed in the Law of the conservation of energy, 
 which says that in a limited system of bodies no gain or loss of 
 energy is ever observed. But energy may be converted from one 
 form into some other form. Motion may be converted into heat, and 
 heat into motion, or this motion into electrical energy and chemical 
 energy. In fact, all the different forms of energy are convertible one 
 into the other, theoretically, without loss. This fact is spoken of as 
 the Law of the correlation of energies. 
 
 QUESTIONS. Define matter, force, and energy. Describe the character- 
 istic properties of matter in the solid, liquid, and gaseous states. State the dif- 
 ference between amorphous, crystalline, polymorphous, and isomorphous sub- 
 stances. State the laws of Boyle and Avogadro. Explain the terms mass and 
 molecule. What are cohesion, adhesion, and gravitation? Mention instances 
 of their action. Give a definition of weight and of specific weight. Explain 
 construction and use of the mercury barometer. Define capillary attraction, 
 absorption, diffusion, and osmose ; give instances illustrating their action. 
 What is meant by saying that matter and energy are indestructible? 
 
HEAT. 43 
 
 2. HEAT. 
 
 Motion of molecules. If we place over a gas-flame a vessel con- 
 taining a lump of ice of the temperature of C., or 32 F., the ice 
 melts and becomes converted into water ; but if we measure with a 
 thermometer the temperature of the water at the moment when the 
 last particle of ice is melted, we still find it at the freezing-point, 
 C. or 32 F. From the position of the vessel over the flame, as 
 well as from .the fact that the ice has been liquefied, we know that 
 the vessel and its contents have absorbed heat. Yet vessel and water 
 show the same temperature as before. If the heat of the flame is 
 allowed to continue its action on the ice-cold water, the thermometer 
 will soon indicate a rapid absorption of heat until the temperature 
 reaches 100 C. or 212 F. Then the water begins to boil and 
 escapes in the form of steam, but the temperature remains stationary 
 until the last particle of water has disappeared. 
 
 There must be, consequently, some relation between the state of 
 aggregation of a substance and that agent which we call heat. It was 
 the heat which liquefied the ice, it was the heat which converted the 
 liquid water into steam or gaseous water. Yet the water, having 
 absorbed considerable heat during the process of melting, shows a 
 temperature of C. (32 F.), and the steam also having absorbed 
 large quantities of heat, shows 100 C. (212 F.), the temperature of 
 boiling water. A certain amount of heat has consequently been lost 
 or at least hidden. What has become of it? 
 
 To answer this we must first examine a little further into the 
 nature of heat. It is a well-known fact that when two solid bodies 
 are rubbed together heat is produced. Ice may be melted and water 
 boiled by friction ; wood may be made to ignite by rubbing it suita- 
 bly. It is found by accurate experiments that there is an intimate 
 relation between the amount of heat generated and the amount of 
 work done to generate it. The amount of heat is always equivalent 
 to the amount of work expended. This fact is one of the manifesta- 
 tions of the law known as the law of the correlation of energy. 
 
 Many other illustrations of production of heat by the expenditure 
 of work could be given, and all would point to the conclusion that 
 heat is associated in some way with the condition of the small parti- 
 cles of which substances are made up i. e., the molecules. 
 
 It is believed that the molecules of all bodies are in motion. 
 Those of gases are perfectly free to move in any direction, while in 
 liquids and solids they are restricted in their motion. In solids the 
 
44 CHEMICAL PHYSICS. 
 
 molecules are held rigidly in a fixed position and can vibrate only 
 back and forth. The molecules thus have a certain energy of motion 
 which is called kinetic energy, and in liquids and solids an energy of 
 position also, known as potential energy. This potential energy is 
 due to the position or molecular arrangement of the particles, and to 
 make a change in this necessitates the overcoming of the forces 
 which hold the molecules in place by an expenditure of energy from 
 some outside source. 
 
 Thus it is believed that whenever heat energy is added to a body 
 it either goes to increasing the motion of molecules i. e., the kinetic 
 energy, or to making a change in the relative positions of the mole- 
 cules i. e., in their potential energy, or to both. 
 
 When the motion of the molecules is increased i. e, when the 
 kinetic energy is increased there is a rise in temperature, which we 
 can measure by a thermometer. What we call temperature is the 
 degree or intensity of the sensible heat of a body. 
 
 On the other, hand, heat is absorbed whenever solids pass into the 
 liquid state ; or liquids into the gaseous state. This fact is often 
 made use of in producing artificial cold. Thus, liquefied ammonia is 
 employed in the manufacture of ice, the required low temperature 
 being produced by evaporation of the ammonia. Similarly, the heat 
 absorbed during the liquefaction of snow or powdered ice by an 
 admixture of common salt and the liquefaction of the latter through 
 solution serve for generating a low temperature. The action of the 
 various freezing-mixtures depends on this principle. 
 
 Latent heat. Sometimes heat may be added to a body without 
 any change of temperature, as above in the case of the melting of ice 
 and the boiling of water. In such cases it is believed that the heat 
 added is absorbed in changing the relative arrangement of the mole- 
 cules, which change must evidently take place in passing from solid 
 to liquid water and from liquid to gaseous water. This will account 
 for the apparent loss of heat in melting ice or in boiling water. It 
 is lost only to our senses, and exists in another form as potential 
 energy of the molecules ; hence it is called latent heat. 
 
 This latent heat is given out again when the molecules return to 
 their former arrangement. Hence steam in condensing to water, and 
 water in assuming the solid state, give off large quantities of heat. 
 
 Sources of heat. Our principal source of heat is the sun. Other 
 sources are : The interior of the earth, the high temperature of which 
 is made manifest by the existence of volcanoes and by the increase of 
 
SEAT. 45 
 
 temperature noted in boreholes sunk into the earth's crust ; mechan- 
 ical actions, as friction and compression ; electric currents ; and, finally, 
 chemical action, as witnessed in the ordinary processes of combustion 
 and of animal life. 
 
 Up to within a few years ago the principal method for generating heat de- 
 pended on combustion. Heat generated by electricity is now at our command. 
 The introduction of the electric furnace has provided means for obtaining much 
 higher temperatures than formerly. It is through these modern means that 
 temperatures are produced sufficiently high for the liquefaction or volatilization 
 of all substances. 
 
 On the other hand, during the last few years methods have been invented 
 for producing very much lower temperatures than formerly. Several gases 
 which were believed to be permanent can now be liquefied, and even solidified. 
 
 Heat Effects. The most familiar changes resulting from the 
 application of heat, that is, from the absorption of heat energy, are 
 those affecting the volume, the temperature, and the molecular arrange- 
 ment or physical state of matter. These changes do not take place 
 independently, but accompany one another. Chemical changes are 
 also often produced by application of heat, but these are considered 
 in chemistry. 
 
 Increase of volume by heat. As a general rule^ the volume of 
 any mass increases with increase in its temperature, but this increase is 
 not alike for all matter. Gases expand more than liquids, liquids 
 more than solids, and of the latter the metals more than most other 
 solid substances. While the expansion of any two or more different 
 solids or liquids is not alike, gases show a fixed regularity in this 
 respect, namely, all gases without exception expand or contract 
 alike when the temperature is raised or lowered an equal number of 
 degrees. 
 
 This expansion or contraction of gases is 0.3665 per cent., or ^ of their 
 volume at C. for every degree centigrade ; thus 100 volumes of air become 
 100.3665 volumes when heated from to 1 C., or 136.65 when heated from 
 to 100 C. This regularity in the expansion and contraction of gases is 
 expressed in the Law of Charles, which says : If the pressure remain constant, the 
 volume of a gas increases regularly as the temperature increases, and decreases as 
 the temperature decreases. If heat be applied to a gas confined in a closed ves- 
 sel and be thus prevented from expanding, the increase of heat will manifest 
 itself as pressure, which rises with the same regularity as shown for expansion, 
 viz., 0.3665 per cent, for every degree centigrade. 
 
 It often becomes necessary to reduce the volume of a gas measured at any 
 temperature and at any pressure to the volume it would occupy at C. and 
 760 mm. pressure, which have been adopted as normal temperature and press- 
 
46 CHEMICAL PHYSICS. 
 
 ure. The method for making this calculation is given in the paragraph on 
 gas-analysis, for which see Index. 
 
 In expansion of solids and liquids the heat energy applied is utilized partly 
 in forcing the molecules farther apart or overcoming cohesion, partly in raising 
 the temperature or giving the molecules greater motion, and partly in doing 
 external work, that is, work that the expanding body does in raising a load that 
 may be resting upon it, or overcoming any force exerted against it. In the 
 expansion of gases, there being no cohesion between the molecules, the heat 
 energy is utilized in raising the temperature and in doing work by the gas against 
 external force. 
 
 Expansion is a very important thing which must be taken into account by 
 constructors, for example, of bridges, railroad beds, etc. Also in very careful 
 physical measurements, expansion of glass apparatus, solutions, barometers, 
 etc., must be carefully noted. 
 
 Increase in temperature by heat. As was said above, the present 
 molecular theory of matter regards the molecules as in motion, and 
 the result of this energy of motion is what we call temperature, or 
 intensity or degree of heat. Anything that increases this motion of 
 the molecules, causes a rise of temperature. Our skin is possessed of 
 nerve structures by which we can judge whether a body is hot or 
 cold or whether one body is hotter than another, but these are not 
 delicate enough to make quantitative distinctions between tempera- 
 tures. For this purpose we make use of instruments called 
 
 Thermometers. In these, use is made of the fact that bodies expand 
 while the temperature rises, and that the expansion is proportional to 
 rise of temperature. Thermometers, therefore, measure directly only 
 expansion, and indirectly degrees of heat, but the expansion is used 
 as a measure of the degree of heat. The most common thermometer 
 is the mercury thermometer. This instrument may be easily con- 
 structed by filling a glass tube, having a bulb at the lower end, with 
 mercury, and heating the tube until the mercury boils and all air has 
 been expelled, when the tube is sealed. It is then placed in steam 
 arising from water boiling actively under normal barometric pressure 
 of 760 millimeters of mercury, and the point to which the mercury 
 rises is marked B. P. (boiling-point) ; after which it is placed in melting 
 ice, and the point to which the mercury sinks is marked F. P. (freezing- 
 point). The distance between the boiling- and freezing-points is then 
 divided into 100 degrees in the so-called centigrade or Celsius 
 thermometer, into 80 degrees in the Reaumur thermometer, and into 
 180 degrees in the Fahrenheit thermometer. The inventor of the 
 latter instrument, Fahrenheit, commenced counting not from the 
 freezing-point, but 32 degrees below it, which causes the freezing- 
 
HEAT. 
 
 47 
 
 point to be at 32, and the boiling-point at 180 degrees above it, or at 
 212. (Fig. 16.) Degrees of temperature below the zero point of 
 either instrument are designated by , i. e. y minus. 
 
 100 
 
 
 
 FIG. 16. 
 
 ....BE 
 
 212 
 
 As 100 degrees centigrade are equivalent to 180 degrees Fahrenheit, it follows 
 that 1 degree C. = 1.8 degree F., or 1 degree F. = 
 \% degree C. In converting the degrees from one 
 scale to the other it must be remembered that the 
 zero point of Fahrenheit is 32 degrees below the 
 zero on the centigrade scale. Consequently, in 
 converting the reading on a Fahrenheit scale into 
 centigrade degrees, 82 degrees must be deducted, 
 or, vice versa, be added, before the calculation can 
 be made. In other words, to convert Fahrenheit 
 into centigrade : Subtract 32 and divide by 1.8 ; to 
 convert centigrade into Fahrenheit : Multiply by 
 1.8 and add 32. 
 
 Recording or self-registering thermome- 
 ters. One kind of these instruments is so con- 
 structed as to show the highest, the other the 
 lowest temperature to which the thermometer had 
 been exposed from the time it was last adjusted. 
 The physician's fever thermometer is a maximum 
 recording thermometer with a scale ranging usu- 
 ally from 94 to 112 F. These thermometers 
 have near the bulb a constriction in the tube 
 which breaks the column of mercury when it con- 
 tracts. Consequently the thin column of mercury 
 retains its position on cooling, but may be forced 
 back through the constriction into the bulb by 
 shaking the instrument. 
 
 p-p. 
 
 32 
 
 Centigrade. Fahrenheit. 
 Thermometric scales. 
 
 Absolute temperature. If differences 
 
 of temperature are due to faster or slower motion of molecules, we 
 can well imagine that there is a limit in both directions. Where the 
 limit is to be found for rapidity of motion is unknown, but good rea- 
 sons lead us to believe that we know the point at which molecular 
 motion ceases. 
 
 One of the reasons which lead us to believe in the correctness of 
 this statement is the Law of Charles, above mentioned. In accord- 
 ance with this law, it follows that if a mass of air at C. is heated, 
 its volume is increased -3-7-3- of the original volume for every degree 
 its temperature is raised. At 273 C. its volume is consequently 
 
48 CHEMICAL PHYSICS. 
 
 doubled, and at 546 C. tripled. If a mass of air is cooled below 
 C., its volume is diminished ^^ of its volume for every degree 
 its temperature is lowered. Consequently, if its volume were to 
 continue to decrease at that rate until it reached 273 C., mathe- 
 matically speaking its volume would become nothing. In fact, 
 the air long before this low temperature had been reached would 
 cease to be a gas would first liquefy, then solidify, and at the tem- 
 perature of 273 C. would become a compact mass in which the 
 molecules were at absolute rest. This point of no heat is called the 
 absolute zero, and temperature reckoned from this point is called 
 absolute temperature. 
 
 The fraction -^7-3- is called the coefficient of expansion for centigrade 
 degrees, while ^y is the coefficient of expansion for degrees of 
 Fahrenheit. The absolute temperature may be found by adding 273 
 to the reading on a centigrade thermometer, or 459 to the reading on 
 a Fahrenheit thermometer. 
 
 While the temperature of absolute zero may never be obtainable by man, 
 so much successful work in the field of low temperatures has been done lately 
 that temperatures within 9 degrees of absolute zero have been observed. 
 
 In chemistry and other fields, temperature is often indicated by such phrases 
 as red heat, white heat, etc. The following table gives approximately the 
 degrees corresponding to such expressions : 
 
 Incipient red heat 525 C. (977 F.). 
 
 Dark red heat 700 C. (1292 F.). 
 
 Bright red heat 950 C. (1742 F.). 
 
 Yellow heat 1100 C. (2012 F.). 
 
 Incipient white heat . , 1300 C. (2372 P.). 
 
 White heat 1500 C. (2732 F.). 
 
 Mechanical equivalent of heat. While thermometers indicate 
 the intensity of heat, it is often desirable to measure heat quantities. 
 These determinations are based on the intimate relationship existing 
 between heat and mechanical or molecular motion, which are capable 
 of being converted one into the other. Thus, friction produces heat 
 and heat produces motion in the steam engine. Heat, through its 
 power to produce motion, can do work, and the amount of work it 
 can do depends on the quantity of heat. 
 
 The unit of heat quantity now universally used in chemical and physiological 
 work is the calorie. It is the amount of heat consumed in raising 1 kilogram 
 of water from C. to 1 C. (or, approximately, 1 pound of water 4 degrees of 
 Fahrenheit). If this amount of heat could all be made to do mechanical work. 
 
HEAT. 49 
 
 it would be sufficient to raise. 420 kilograms 1 meter high, or 3000 pounds 1 foot 
 high L e., the calorie is equivalent to 420 kilogram-meters, or 3000 foot pounds. 
 The heat generated by combustion is determined in the laboratory by means of 
 an apparatus known as the calorimeter. This is generally so constructed that 
 a definite weight of substance may be burned in a chamber surrounded by cold 
 water. The rise in temperature of this known quantity of water serves as the 
 basis for calculation. 
 
 Specific heat. Equal weights of different substances require dif- 
 ferent quantities of heat to raise them to the same temperature. For 
 instance : The same quantity of heat which is sufficient to raise 1 
 pound of water from 60 to 70 will raise the temperature of 1 
 pound of olive oil from 60 to 80, or that of 2 pounds of olive oil from 
 60 to 70. Olive oil consequently requires only one-half of the heat 
 necessary to raise an equal weight of water the same number of degrees. 
 As water has been selected as the standard for comparison, we may 
 say that specific heat is the heat required to raise a certain weight of 
 a substance a certain number of degrees, compared with the heat 
 required to raise an equal weight of water the same number of 
 degrees. 
 
 The heat required to raise 1 gramme of water 1 degree centigrade 
 is usually taken as the unit of comparison. On thus comparing 
 olive oil, we find its specific heat to be J. If we say the specific 
 heat of mercury is ^-, we indicate that equal quantities of heat will 
 be required to raise 1 pound of water or 32 pounds of mercury 1 
 degree, or that the heat which raises 1 pound of water 1 degree will 
 raise 1 pound of mercury 32 degrees. 
 
 Conduction of heat. When the end of a metallic bar is heated, 
 a rise in its temperature is soon noticed at a distance from the heated 
 part. This transfer of heat from some source, for instance from a 
 flame to a cold substance, is practically a transfer of motion from 
 more rapidly moving molecules to those moving more slowly. It 
 may be compared to the motion imparted to a billiard ball at rest or 
 moving slowly by another ball propelled with greater velocity. The 
 more rapidly moving ball will lose part of its velocity in imparting 
 motion to the other ball. Similarly the rapidly moving molecules of 
 the hot body in transferring motion to molecules moving slowly in 
 the cold body lose some of their velocity i. e., the hot body itself 
 becomes cooler. The expression " cooling off" must never be under- 
 stood to imply a transfer of cold, but always a removal of heat. In 
 taking a cold bath, or in applying an ice-bag to a fever patient, we 
 
50 CHEMICAL PHYSICS. 
 
 bring about a slower molecular motion in the tissues exposed to the 
 cold material. 
 
 The direct transfer of molecular motion is called conduction of heat, 
 but in examining various materials we find that they show a great 
 difference in their power to conduct heat. For instance, if we hold in 
 a flame the end of a glass rod, it may be made red-hot, while but little 
 increase of heat will be perceived at the other end. We accordingly 
 distinguish between good and bad conductors of heat. Gases and 
 liquids (mercury excepted) are bad conductors, and of the solids 
 the metals are the best. The following table gives the comparative 
 heat-conducting power of a number of substances, that of silver being 
 taken as the standard, and represented by 1 : 
 
 Copper . . . .0.96 
 
 Iron . . . - . 0.20 
 
 Stone .... 0.006 
 Water 0.002 
 
 Glass .... 0.0005 
 
 Wool .... 0.00012 
 
 Paper .... 0.000094 
 
 Air . 0.000049 
 
 Convection. On fastening a piece of ice to the bottom of a test- 
 tube, and filling this with water and holding it over a flame in such 
 a manner that only the upper portion of the tube is heated, the water 
 may be made to boil before the ice has been melted. The reason is 
 that water is a bad conductor of heat. If the flame be applied to the 
 lower part of the test-tube, the whole mass of water will remain 
 cold until the ice has melted, and the temperature will then rise 
 evenly through the mass of water, because the heated lighter par- 
 ticles will move upward while the colder ones move downward. 
 Thus ascending and descending currents are produced, equalizing the 
 temperature. The term convection is applied to this method of con- 
 veying and distributing heat. Air or gases behave similarly, and 
 this fact is of practical interest in the construction of chimneys and 
 in heating and ventilating buildings. 
 
 Radiation of heat. A heated body, for instance a ball of red-hot 
 iron, suspended in the air or in a vacuum will heat objects near by. 
 If a screen is placed between these objects and the heated body, no 
 rise in temperature is noticed. Heat is here propagated through 
 space in straight lines, commonly spoken of as heat rays. 
 
 In order to explain these phenomena, as also others closely related 
 to them, such as those of light and electricity, it has been necessary 
 to assume the existence of some agent that serves as a means for this 
 propagation. This hypothetical agent, called ether, is a medium of 
 
HEAT. 51 
 
 extreme tenuity and elasticity supposed to be diffused throughout 
 the universe, and indeed permeating all matter. 
 
 Similarly as waves of water are generated by dropping a stone into 
 it, and as sound waves are produced in air by causing it to vibrate, 
 so heat waves are produced in the ether whenever it is disturbed by 
 the rapid molecular motion of a heated body. 
 
 While our views regarding the nature of ether are of a hypothetical 
 character, there can be no doubt of the existence of these heat waves. 
 Indeed, their length, their velocity, and many other features have 
 been fully determined ; they obey largely the same laws which have 
 been established for light waves i. e., when striking against a body 
 they are generally reflected, transmitted, diffused, or absorbed. It 
 is this absorption of heat, as we call it, which causes the heating- 
 effects through space. It may be compared to the motion that can 
 be imparted to an object floating on still water. By disturbing the 
 water, as by dropping a stone into it at a distance from the floating 
 object, concentric ripples or waves pass from the point where the 
 water was disturbed, and in striking the floating object cause it to 
 move. Similarly waves of heat pass from a heated body through 
 the ether in every direction, and in striking against a body cause its 
 molecules to move faster i. e., render it warmer. It is by this 
 process that heat is transmitted from the sun to the earth. 
 
 Change in molecular state. As was pointed out above in the discus- 
 sion of the nature of heat, it requires energy to bring about a change 
 in the relative position of the molecules of a substance, which is 
 called internal work. This is true for solids and liquids, but not for 
 gases, since there is practically no cohesion between the particles of a 
 gas, and so no work is required to change the position of the particles. 
 Several familiar phenomena involve change in the molecular state. 
 
 Fusion or melting-. This name is applied to the process by which 
 a solid passes into the liquid state. When a liquid passes into the solid 
 state, the process is known as solidification. As a rule, when solids 
 are heated, they begin to melt at a definite temperature, which is known 
 as the fusion-point or melting-point. Conversely, when liquids are 
 cooled, they begin to solidify at a definite temperature, which is iden- 
 tical with the melting-point of the solid. Moreover, the temperature 
 remains constant as long as fusion or solidification continues. 
 
 Solids that are individuals (not mixtures) and are perfectly pure as 
 far as they melt without decomposition, have definite or sharp melting- 
 
52 CHEMICAL PHYSICS. 
 
 points, which fact is utilized in chemistry extensively for determining 
 the identity of substances and their purity. A small amount of 
 impurity in a substance often causes a notable change in its melting- 
 point and the temperature rises between the beginning and the end of 
 melting, instead of remaining constant. 
 
 Some solids, like wax and paraffin, which are mixtures, do not remain 
 at the same temperature during fusion, and in such cases the melting- 
 point is taken as the average of the temperatures at which fusion and 
 solidification begin. 
 
 The determination of the melting-point is carried out by introducing 
 a column about J inch long of the finely powdered substance into a 
 capillary glass tube sealed at one end, and attaching this to the bulb 
 of a thermometer. The latter is then dipped into a liquid of high 
 boiling-point and the temperature is slowly raised. The instant the 
 substance melts, the temperature is noted, which is the melting-point, 
 often abbreviated m.-p. 
 
 Latent heat of fusion. This is the number of heat units (calories) 
 required to make 1 gramme of a substance fuse. Different substances 
 have different latent heats of fusion, but water (ice) has the greatest. 
 To melt 1 gramme of ice at C. to water at C. requires 80 calories, 
 or as. much heat becomes latent as will raise 1 gramme of water from 
 C. to 80 C. 
 
 Change of volume by fusion. When any solid fuses, a change in 
 volume always occurs. Some substances expand during fusion, for 
 example, bismuth, wax ; others contract, for example, brass, cast-iron, 
 ice. When a solid floats in its own liquid, this is evidence that it con- 
 tracts on fusion, because the density of the solid is less than that of its 
 liquid. When a solid sinks in its own liquid, there is expansion on 
 fusion. 
 
 Evaporation and boiling-. Many liquids, even some solids, 
 evaporate or assume the gaseous state at nearly all temperatures. 
 Water and ice, mercury, camphor, and many other substances vapor- 
 ize at temperatures which are far below their regular boiling-points. 
 This fact is to be explained by the assumption that during the rapid 
 vibratory motion of the particles of these masses, some particles are 
 driven from the surface beyond the sphere to which the surrounding 
 molecules exert an attraction, and thus intermingle with the mole- 
 cules of the surrounding air. 
 
HEAT. 53 
 
 This evaporation, which takes place at various temperatures and at 
 the surface only, is not to be confounded with boiling, which is the 
 rapid conversion of a liquid into a gas at a fixed temperature with 
 the phenomena of ebullition, due to the formation of gas in the mass 
 of liquid. Boiling-point may, therefore, be defined as the highest 
 point to which any liquid can be heated under the normal pressure of 
 one atmosphere. 
 
 A liquid in a closed space evaporates until a definite pressure is 
 attained by the vapor at a fixed temperature, when the liquid and 
 vapor remain in equilibrium. When this limit is reached the vapor 
 is said to be " saturated." If the temperature is increased, more 
 liquid evaporates and the pressure increases. If the temperature of 
 a saturated vapor falls, some vapor is condensed to liquid, or if the 
 pressure is increased, some vapor will also condense to liquid. At a 
 given temperature a saturated vapor exerts a definite pressure, 
 which is different for different vapors. Thus, in terms of a column 
 of mercury, at 20 C. (68 F.), water vapor exerts a pressure of 17 
 mm., alcohol vapor, 60 mm., and ether vapor, 450 mm. 
 
 As a rule, in experiments where gas volumes are measured, the gas is satu- 
 rated with aqueous vapor, which has to be taken into account in making calcu- 
 lations. If a volume of gas saturated with water-vapor is measured at atmo- 
 spheric pressure, the tension of the gas alone is the difference between the 
 barometric pressure and the tension of the saturated water-vapor at the given 
 temperature. 
 
 Tension of Saturated Water-vapor (Regnault). 
 
 Temperature, 
 
 Tension 
 
 Temperature, 
 
 Tensic 
 
 Centigrade. 
 
 in mm. 
 
 Centigrade. 
 
 in nan 
 
 
 
 4.6 
 
 16 
 
 13.5 
 
 1 
 
 4.9 
 
 17 
 
 14.4 
 
 2 
 
 5.3 
 
 18 
 
 15.4 
 
 3 
 
 5.7 
 
 19 
 
 16.3 
 
 4 
 
 61 
 
 20 
 
 17.4 
 
 5 
 
 6.5 
 
 21 
 
 , 18.5 
 
 6 
 
 7.0 
 
 22 
 
 19.7 
 
 7 
 
 7.5 
 
 23 
 
 20.9 
 
 8 
 
 8.0 
 
 24 
 
 22.2 
 
 9 
 
 8.5 
 
 25 
 
 23.6 
 
 ]0 
 
 9.1 
 
 26 
 
 , S . . . . 25.0 
 
 11 
 
 9.8 
 
 27 
 
 26.5 
 
 12 
 
 10.4 
 
 28 
 
 28.1 
 
 13 
 
 11.1 
 
 29 
 
 29.8 
 
 14 
 
 . . . . 11.9 
 
 30 
 
 31.6 
 
 15 ... 
 
 12.7 
 
 
 
 Distillation is the conversion of a liquid into a gas, and the con- 
 
54 CHEMICAL PHYSICS. 
 
 densation of the gas into a liquid, by causing the gas to pass through 
 a cooling device or condenser, whereby the heat that was made latent 
 and is necessary for maintaining the gaseous state, is extracted. Dis- 
 tillation is usually carried on by boiling the liquid under atmospheric 
 pressure, but sometimes it is done under reduced pressure by exhaust- 
 ing the air from the apparatus, and then the liquid boils at a much 
 lower temperature. Distillation is a very useful process for purify- 
 ing liquids, as, thereby, non- volatile impurities may be easily removed 
 from liquids. Moreover, mixtures of liquids having different boiling- 
 points may be separated approximately into the constituents by dis- 
 tillation (see Fractional Distillation in Index). 
 
 The process of vaporization, known as sublimation, has been men- 
 tioned under Crystals, page 21. 
 
 The determination of the boiling-point is best done in a flask, as 
 shown in Fig. 69, If inflammable or noxious vapors are likely to 
 be evolved, they may be condensed to the liquid state by connecting 
 the exit tube of the flask with a condenser. It is important that the 
 thermometer should not be immersed in the liquid, but should be 
 surrounded only by the vapor of the liquid. Heat is applied to the 
 flask until the liquid assumes a state of active ebullition, and when 
 vapor is escaping freely and the temperature ceases to rise, the latter 
 is noted. This is the boiling-point of the liquid at the atmospheric 
 pressure prevailing at the time. 
 
 Pure liquids, under the same pressure, always have the same boil- 
 ing-points, and this property is very important in chemistry in 
 judging of the purity of liquids. Impure liquids not only have dif- 
 ferent boiling-points from the pure substances, but also the tempera- 
 ture rises during boiling instead of remaining constant. 
 
 The boiling-points of different liquids vary widely. Thus, mer- 
 cury boils at 357 C., water at 100 C., alcohol at 78 C., chloroform 
 at 61 C., ether at 35 C., oxygen at -182.5 C., hydrogen at 
 252.5 C., under standard atmospheric pressure. 
 
 Latent heat of vaporization. When a liquid passes to the gas- 
 eous state, heat energy is absorbed or becomes latent^ and, conversely, 
 when a vapor is condensed to a liquid, the same heat energy is given 
 out. If the heat is not added to the liquid from the outside, the heat 
 is absorbed from the liquid itself during vaporization and its tem- 
 perature falls. The sensation of cold produced by the evaporation 
 of water, alcohol, ether, chloroform, etc., from the skin is familiar to 
 every one. It is by evaporation of moisture from the skin that the 
 
HEAT. 55 
 
 temperature of our body is kept normal in heated weather. A thin 
 glass beaker, containing ether and resting on some water on a glass 
 plate, may quickly be frozen to the plate by passing a rapid current 
 of air through the ether. 
 
 The number of calories of heat required to vaporize 1 gramme of 
 any liquid at a given temperature is called its latent heat of vaporiza- 
 tion. The latent heat of steam at 100 C. is 535.9 calories, that is, 
 it requires as much heat to convert 1 gramme of water at 100 C. 
 into steam at 100 C., as would raise 535.9 grammes of water 1 C. 
 in temperature. Steam has the largest latent heat of all known sub- 
 stances, hence, its value in warming houses, etc., by the steam-heat- 
 ing process. 
 
 Influence of pressure on state of aggregation. We have seen 
 that the volume of a substance, and, more especially, of a gas, depends 
 upon pressure and temperature, an increase of pressure or decrease of 
 temperature causing the volume to become smaller. We learned also 
 that liquids may be converted into gases, and that this conversion 
 takes place at a certain fixed temperature, called the boiling-point. 
 This point, however, changes with the pressure. An increased pres- 
 sure will raise, a decreased pressure will lower, the boiling-point. 
 
 Thus, water boils at the normal pressure of one atmosphere at 100 C. (212 
 F.), but it will boil at a lower temperature on mountains in consequence of the 
 diminished atmospheric pressure. If the pressure be increased, as, for instance, 
 in steam-boilers, the boiling-point will be raised. Thus, the boiling-point of 
 water under a pressure of two atmospheres is at 122 C. (251 F.), of five atmo- 
 spheres at 153 C. (307 F.), of ten atmospheres at 180 C. (356 F.). A differ- 
 ence of pressure of 10 millimeters from the normal atmospheric pressure (760 
 mm.) produces a difference of 0.36 C. in the boiling-point of water, 100 C. 
 
 QUESTIONS. What is the view in regard to the nature of heat? What is 
 meant by sensible heat and latent heat? What is the law in regard to expan- 
 sion of gases when heated? Explain the construction of a thermometer and 
 the principle on which it depends. What Fahrenheit temperature corresponds 
 to 50 C., to 130 C., to 40 C.? What Centigrade temperature corresponds 
 to 167 F., to 311 F., to 14 F. ? What is meant by absolute temperature? 
 Give a definition of the following : Calorie, specific heat, conduction, convec- 
 tion, and radiation of heat. Define melting and state how the melting-point is 
 determined ; define latent heat of fusion. State the difference between evapo- 
 ration and boiling. What is distillation and sublimation? What is meant by 
 latent heat of vaporization ? What is the influence of pressure on the boiling- 
 point of liquids ? 
 
56 CHEMICAL PHYSICS. 
 
 3. LIGHT. 
 
 Light a form of energy. It has been shown in the preceding 
 chapter that a heated body sends forth waves through the ether, 
 which in striking a cooler body cause its molecules to vibrate more 
 quickly i. e., heat it to a higher temperature. But an increased 
 molecular motion may produce other effects than heat, as we may 
 observe by heating an iron bar, which, when sufficiently hot, will 
 emit light. That light is different in effect from heat, though both 
 come from the same hot body, may be observed in the action of 
 luminously hot bodies on certain chemicals ; for example, the silver 
 salts, which undergo a change in their chemical composition. The 
 action of sunlight on photographic plates is an excellent illustration. 
 
 The explanation of these phenomena is that ether waves of diverse 
 characters produce different effects. Thus, the waves coming to us 
 from the sun may affect the sense of touch, and we call the effect 
 heat ; they may affect the sense of sight, and we term it light ; or 
 they may affect the composition of matter, when we speak of it as 
 chemical action. But in all these results we have simply different 
 manifestations of some form of radiant energy. Light is that form 
 of energy which may be appreciated by the organ of vision. 
 
 Color. Both heat- and light-producing waves or oscillations are 
 propagated through ether with the same velocity, viz., at the rate of 
 300,000 kilometers, or 186,000 miles, per second ; but the waves 
 differ in regard to length and in the amplitude of vibration. Waves 
 of a particular limited range of frequency (477,000,000 millions to 
 699,000,000 millions per second) when falling upon the eye produce 
 a sensation of light. Of these, the slowest i. e., the waves with 
 the least frequency and the greatest wave-length produce a sensa- 
 tion of red light ; as the frequency increases, the sensation produced 
 by them is successively that which is termed orange, yellow, green, 
 blue, indigo, and violet light. 
 
 Ether waves of frequency too limited to be visible are called infra- 
 red waves ; they have, however, great heating power when falling 
 upon a substance. On the other hand, there are waves of greater 
 frequency than those which produce a sensation of violet ; they are 
 also invisible, but have the power of producing chemical action ; they 
 are called ultra-violet or actinic waves. There is no inherent difference 
 between any of the different kinds of waves here mentioned ; indeed, 
 they all may be produced at the same time by the same body. 
 
 In what is called daylight there is a mixture of waves of different 
 frequencies, affecting our eye simultaneously in such a manner 
 
LIGHT. 
 
 57 
 
 that none of the specific colors predominates. The reason that even 
 under the influence of this white light most objects show a distinct 
 color is not, as might be supposed, an inherent color possession of 
 these objects, but an effect of the light. Without light all objects 
 are black i. <?., without light there is no color. There is a great 
 diversity in the behavior of different substances toward white light. 
 It may either be absorbed or reflected, or partly absorbed and partly 
 reflected. If all be absorbed, black is the result ; if all rays except 
 the red ones be absorbed, the body appears red, etc. 
 
 Not only has the number of wave oscillations per second been 
 determined, but also their length. The longest waves are those pro- 
 ducing heat ; the shortest ones are the actinic waves. Between them 
 are the light waves ranging from 650 millionths of a millimeter in 
 length for red light, to 442 millionths of a millimeter in length for 
 violet light. 
 
 Light rays. Light travels through homogeneous media, as air, 
 water, and glass, in straight lines, and a very narrow cylinder of light 
 is called a ray, beam, or pencil of light. Those bodies which readily 
 transmit luminous rays are said to be transparent, those not trans- 
 mitting light are called opaque, while translucent bodies are those 
 permitting light to pass through them to a limited extent. 
 
 A body may be self-luminous, like the sun or a flame ; or it may 
 be luminous by reflected light, like the moon or any object that is 
 illuminated by daylight or by any luminous body. 
 
 Light of itself is invisible, as can be shown by admitting a sun- 
 beam through a small hole into a dark room. If the air be free 
 from dust, the beam is invisible ; but if the eye, or any object upon 
 
 which it mav strike, is placed in its path, 
 
 ~ V. 
 we are made aware of its presence, not 
 
 by seeing the light, but by seeing the ob- 
 ject which emits it or intercepts it. 
 
 Reflection. When a ray of light strikes 
 a mirror or a polished surface obliquely 
 we notice that a ray of light is thrown off 
 
 or reflected from the mirror. On measuring 
 ,1 , . ,_.. . , , . 
 
 the angle ^ (Fig. 17) made by the entering 
 or incident ray CB and a perpendicular NB, and the angle r made 
 by the reflected ray AB and the perpendicular, they will be found 
 equal. In other words, in plane mirrors the angle of incidence is 
 always equal to the angle of reflection. 
 
 FIG. 17. 
 
 Reflection. 
 
58 
 
 CHEMICAL PHYSICS. 
 
 Upon this reflection depends the formation of the image seen in mirrors. 
 If a reflecting surface were an absolutely smooth plane, it would be invisible, 
 and we would see in it simply the images of other subjects. Most objects are 
 not bounded by absolutely smooth surfaces, and, consequently, the light which 
 falls upon them is scattered or diffused, thus rendering them visible in all 
 directions. 
 
 Refraction. While a light ray travels in a straight line through 
 homogeneous media, the ray is bent when passing from a medium 
 of one density to that of another density, as from air to glass or to 
 water. Under these conditions, unless the ray enter perpendicularly, 
 
 it is bent out of its course, still moving, 
 however, in a straight path in the 
 second medium, but in a different 
 direction from that in the first. This 
 bending of rays is known as refrac- 
 tion. It is refraction which causes a 
 straight stick, when held obliquely 
 in clear water, to appear bent at the 
 point of entering the water. 
 
 In Fig. 18, SI represents a ray of 
 light entering a denser medium say 
 a plate of glass with parallel sides. 
 Here the ray is bent toward the per- 
 pendicular N'R ; on leaving the denser medium and re-entering the 
 air it is again bent, but away from the perpendicular to such an 
 extent that the rays SI and US' (or rather their extensions) are 
 parallel to one another. 
 
 Refraction through prisms. A prism, in optics, is any trans- 
 parent medium comprised between two plane surfaces inclined to 
 
 Refraction by a parallel plate. 
 
 Refraction through a prism. 
 
 each other. The intersection of the two planes is called the edge, and 
 
LIGHT. 
 
 59 
 
 the angle between them is called the refracting angle. Triangular 
 glass prisms are generally used. 
 
 In Fig. 19, ABC is a section of a prism. A is called the summit or 
 apex, and BC the base. A ray of light, SI, falling upon the prism 
 will not pass through it in a straight line, SIS', but is bent out of its 
 course twice, in accordance with the law of refraction, first from 
 I to I', and then to K. The amount of bending depends on the 
 angle of the prism, its material, and the angle of incidence of the 
 ray, shown in i, while r is the angle of refraction. The angle D 
 represents the angle of deviation. 
 
 Dispersion. In Fig. 19, the ray is represented by a single line 
 throughout. In reality, matters are more complicated, as white 
 light is made up of rays of different colors, each of which has a dif- 
 ferent angle of refraction. The result is that when a beam of white 
 light falls on a prism it does not come through as white light, but 
 the constituent colors are refracted at different angles, giving rise to a 
 band of light containing all the colors of the rainbow, viz., red, 
 orange, yellow, green, blue, indigo, violet ; red being less refracted, 
 violet most. Such a band of colors is known as the prismatic 
 spectrum. 
 
 In Fig. 20, A represents a ray of light which if unbent would strike 
 a screen at X, but the prism P intervening the ray is refracted and 
 at the same time resolved into its constituents, which form the spec- 
 trum, the colors of which are indicated by the initial letters. This 
 
 FIG. 20. 
 
 Prismatic spectrum. 
 
 spreading out of light, and its separation into different colors, are 
 called dispersion. 
 
 The spectroscope is an instrument that serves for conveniently 
 observing the spectrum. Differently constructed instruments are 
 
60 
 
 CHEMICAL PHYSICS. 
 
 employed, of which Fig. 21 represents the single-prism spectroscope, 
 which is most largely used. It consists of the prism P and of 
 three telescopes directed toward it. The light is permitted to enter 
 the tube A through a narrow slit at its distal end, while at the 
 other end a convex lens, called the collimator, serves to collect the 
 light into nearly parallel beams. These beams pass through the 
 prism where the dispersion is brought about, and the spectrum thus 
 formed is observed at d through the telescope B. Through the third 
 
 FIG. 21. 
 
 Spectroscope. 
 
 tube, C, a fine scale for measurement of the relative position of lines 
 or colors is reflected to the eye of the observer. This scale is usually 
 photographed on glass, and when illuminated by a candle or some 
 other stronger light the image of the scale is directed upon the face 
 of the prism in such a manner that it is reflected down the axis of 
 the observing telescope, and is seen above or below the spectrum, 
 according to the direction given to the axis of the scale tube. The 
 glass vessel a serves as a container for a liquid to be examined spec- 
 troscopically. 
 
 A second form of spectroscope, known as the direct-vision spec- 
 troscope, is shown in Fig. 22. It consists of a cylindrical tube 
 provided with ocular and containing from three to seven prisms, 
 
LIGHT. 61 
 
 a draw-tube with adjustable slit, and a collimator lens placed 
 between them to render the rays parallel. The prisms placed 
 opposite to one another are made of crown glass and flint glass, re- 
 spectively. The dispersive power of the latter is nearly double that 
 of crown glass, while the deviating powers of the two glasses do not 
 differ much. The result 
 
 is that a beam of light Fl - 22 - 
 
 entering through the slit 
 undergoes but little de- 
 viation from its original 
 
 COlirse, while there is Direct-vision spectroscope. 
 
 sufficient dispersion be- 
 tween its colors to produce a spectrum available for spectroscopic 
 uses. When the luminous flame of a candle, oil, or gas is examined 
 spectroscopically, it shows a continuous spectrum i. e., this white 
 light has been decomposed into its constituents. 
 
 Bright line spectra. If into a non-luminous flame of a Bunsen 
 burner a platinum wire which has been previously dipped into 
 common salt (sodium chloride) be held, the flame will be colored 
 yellow, and if it be examined by the spectroscope there will be seen 
 a bright-yellow line in the yellow part of the spectrum, w r hile no 
 other colors are visible. In thus examining salts of other metals, 
 such as potassium, lithium, calcium, etc., by holding in the flame by 
 means of platinum wire, it will be seen that each one gives a number 
 of characteristic bands or lines in different parts of the spectrum, the 
 remaining portion being quite dark. So characteristic are these 
 spectra of different elements that they furnish a distinctive means 
 of recognition ; and indeed some elements have been discovered by 
 this method. These spectra can be seen only when the substance is 
 heated to a point where volatilization takes place, because gases alone 
 show the property of giving discontinuous, or bright line, spectra, 
 and no two gases give the same spectrum. 
 
 The reason that luminous flames give a continuous spectrum is 
 that the luminosity is due to light emitted by particles of solid carbon 
 floating in the burning gas. This shows that the spectroscope fur- 
 nishes a reliable means of determining whether light proceeds from 
 a luminous solid or a luminous gas, as all luminous solids and liquids 
 give continuous spectra. 
 
 Absorption spectra. If the spectroscope is so arranged that a 
 continuous spectrum is obtained from a strongly luminous flame, or 
 
62 CHEMICAL PHYSICS. 
 
 from an electric light, and if then a little sodium chloride be evapo- 
 rated in the flame of a Bunsen burner that has been placed between 
 the slit and the luminous flame, it will be seen that the spectrum is 
 no longer continuous, but that a black line intercepts it, a line hold- 
 ing precisely the position occupied by the yellow sodium line seen 
 on a dark background when the luminous flame is removed. In 
 repeating the experiment with the salts of various metals, we find 
 like conditions, viz., the discontinuous bright color spectra of indi- 
 vidual metals are converted into spectra showing black lines in the 
 continuous spectrum obtained from the luminous flame. (See spectra 
 on plate facing title page. 
 
 From these facts we- may draw the conclusion that the vapors of 
 different substances absorb precisely the same rays that they are 
 capable of emitting. Such spectra are called absorption spectra, or 
 reversed spectra. 
 
 Absorption spectra are also of interest because, if white sunlight 
 be examined with a spectroscope of sufficiently high power, it is found 
 not to be continuous, but to contain many hundreds of black lines, 
 called after their discoverer Frauenhofer lines. The more prominent 
 lines are designated by letters or numbers, as shown in the solar spec- 
 trum represented on the accompanying plate. On comparing these 
 lines in the sun spectrum with the positions of lines obtained by known 
 elements, such as iron, sodium, calcium, etc., it is found that they 
 correspond exactly to one another. The explanation given is this : 
 The main body of the sun consists of a highly luminous mass sur- 
 rounded by an atmosphere of cooler vapor. The luminous body 
 would give a continuous spectrum, but the rays passing through the 
 vapors of the sun's atmosphere are partly absorbed, and thus a large 
 number of black lines are produced. Absorption-spectra are, further- 
 more, of great interest, because when light passes through certain 
 liquids, such as blood or a solution of quinine sulphate, dark line 
 spectra are obtained, sufficiently characteristic to assist in the recog- 
 nition of these substances. 
 
 From what has been said, we learn that we have three kinds of 
 spectra, viz., continuous spectra, produced by luminous solids or 
 liquids, and possibly by luminous gases tinder high pressure ; bright 
 line spectra, produced by luminous vapors ; and absorption spectra, 
 produced by light that has passed through certain media. 
 
 The value of the spectroscope depends on the use made of it in 
 spectroscopic analysis, as both the bright line spectra and absorption 
 spectra enable us to determine the nature of many substances, and 
 
LIGHT. 63 
 
 to differentiate between elements present not only on our globe, but 
 in other celestial bodies likewise. 
 
 Double refraction. A plate of glass will not interfere with read- 
 ing printed matter over which the plate is laid. But in trying to 
 read through several varieties of transparent crystalline substances a 
 
 FIG. 23. 
 
 Double refraction. 
 
 peculiar phenomenon is noticed ; as then each letter will be dupli- 
 cated, as shown in Fig. 23, where a piece of Iceland spar (crystallized 
 calcium carbonate) is placed over reading matter. 
 
 If a pinhole be made through a card, and the card be placed over a 
 crystal of Iceland spar and held before the eye toward the light, there 
 will appear to be two holes, with light shining through each. If 
 the crystal be made to rotate in a plane parallel with the card, then 
 one of the holes will appear to remain nearly at rest, while the 
 other rotates about it. These facts show that a ray of light on enter- 
 ing the crystal is divided into two parts, one of which obeys the 
 law of regular refraction, and is called the ordinary ray, while the 
 other, which does not, is termed the extraordinary ray. This power 
 of certain substances to refract light rays in two directions is known 
 as double refraction. . 
 
 In all crystals which produce double refraction there is one direc- 
 tion (in some even two directions) in which an object, looked at 
 through the crystal, does not appear double. The line through 
 which double refraction is suspended is called the optic qxis, and is a 
 line around which the molecules appear to be arranged symmetrically. 
 
 Polarization. The semitransparent mineral tourmaline is another 
 substance refracting double. Two rays, the ordinary and the ex- 
 traordinary, are formed when a ray of light is passed through a plate 
 
64 
 
 CHEMICAL PHYSICS. 
 
 of this substance, just as in the case of Iceland spar; but tourmaline 
 possesses the peculiar property of absorbing the ordinary ray, while 
 the extraordinary one passes through. 
 
 If two plates, cut parallel to the axis of the crystal, are laid upon 
 each other in a crossed position, as AB in Fig. 24, it is found that 
 
 FIG. 24. 
 
 Tourmaline plates. 
 
 light from the first plate is cut off by the second one, and darkness 
 results. If one plate be turned round upon the other, it will be 
 found that the combination is most transparent in two positions dif- 
 fering by 180 degrees, one of them, ab, being the natural position 
 which the plates originally occupied in the crystal. The combina- 
 tion is most opaque in the two positions at right angles with these, 
 while intermediate positions, such as a'b', show intermediate be- 
 havior. These facts show that light which has passed through one 
 such plate is in a peculiar condition. It is said to be plane-polarized. 
 In order to understand polarization of light, we should bear in 
 mind that the particles of ether undulate in a variety of planes per- 
 pendicular to the line of propagation. We assume that in polarized 
 light the undulations of the ether particles take place in a single 
 plane. These ether undulations may be compared to those taking 
 place in a cord fastened at one end and shaken by the hand at the 
 
 FIG. 25. 
 
 Undulation in a cord. 
 
 other end, as in Fig. 25. According to whether we move the hand 
 horizontally, obliquely, or vertically, the undulations will lie in a 
 horizontal, oblique, or vertical plane, as represented at A. 
 
LIGHT. 65 
 
 If a cardboard, with a long slit in it, be held over the string, 
 the string will vibrate in one plane only, viz., in that of the slit. 
 Instead of one cardboard, two or more may be used, and as long as 
 the slits are in one plane the vibrations will proceed in that plane. 
 If, however, the slit of one card be set at a right angle to that of 
 another card placed over the string, then vibrations will no longer 
 be propagated. 
 
 To make the action of the tourmaline plates still more intelligible, 
 we may compare it to that of a grating, A, Fig. 26, formed of parallel 
 vertical rods which permit the passage of all vertical planes, as 
 aa, but intercept that of horizontal planes, cc. As long as the rods 
 
 FIG. 26. 
 A 
 
 GH 
 
 a 
 
 .,,11111 
 
 Explanatory diagram of the action of tourmaline plates. 
 
 of the gratings A and B are in the same plane, a string may be 
 made to vibrate through these gratings parallel to the rods, but when 
 set at a right angle this becomes impossible. 
 
 When a ray of light strikes a plate of tourmaline it permits the 
 passage of those undulations which are parallel with its axis, but it 
 absorbs those undulations which are in planes at right angles to its 
 axis. The rays which pass through the plate produce the polarized 
 light. 
 
 Polariscope. As the unaided eye cannot differentiate between 
 common and polarized light, instruments are constructed by which 
 the phenomena of polarization can be studied, and these instruments 
 are known as polariscopes, polarimeters, or, in a special case, sac- 
 clmrimeters. They all contain some substance, known as a polarizer, 
 such as tourmaline, Iceland spar, etc., serving as a polarizer of light ; 
 and a second substance, called an analyzer, for the detection of that 
 light. In the above experiment with tourmaline plates the first 
 plate serves as a polarizer and the second as an analyzer. 
 
 The material used generally for polarization is Iceland spar, as it 
 is more transparent than tourmaline. Instead of using plates of 
 this material, prisms, known as NicoVs prisms, are made by sawing 
 
 5 
 
66 CHEMICAL PHYSICS. 
 
 through a crystal from one obtuse angle to the other. The two 
 
 parts, after their surfaces have 
 been well polished, are joined 
 by a transparent cement of 
 Canada balsam. Fig. 27 rep- 
 resents a section of this prism. 
 DB indicates the line where the 
 crystal has been cut and ce- 
 mented. A ray of light passing 
 
 Nicol's prism. fr m the b J ect tO th f side AD 
 
 is doubly refracted in such a 
 
 manner that the ordinary ray on striking the balsam is totally re- 
 flected to the side AB, and there refracted out of the crystal, while 
 the extraordinary ray passes on and emerges at the side BC as a 
 polarized ray. If this ray is now passed into a second NicoPs prism 
 parallel to the first, as if it were a continuation of the latter, it will 
 pass through unchanged. If the second prism be turned through an 
 angle of 90 degrees that is, if the two prisms be crossed the ray of 
 light will be cut off entirely. The ray in the second prism becomes 
 an ordinary one, and is totally reflected at the layer of balsam 
 through the side of the prism and is lost, as in the case of the first 
 prism. In intermediate positions between the crossed and the parallel 
 ones the extraordinary ray from the first prism is decomposed in the 
 second one partly into an ordinary and partly into an extraordinary 
 ray. The former is reflected out of the prism, while the latter goes 
 through, so that more and more light will pass through as the second 
 prism is turned so as to approach parallelism to the first. Thus it is 
 easily seen that a Nicol prism may serve not only to produce polar- 
 ized light, but also to detect such light. 
 
 Polarized light is extensively used in the examination of minerals 
 and salts, as thin slices of crystals belonging to different crystallo- 
 graphic systems when brought between two NicoPs prisms show 
 rings or bands of colors characteristic of the respective systems. 
 
 Many organic liquids and solids in solution have a peculiar action 
 on polarized light. Such substances, for example, are sugars, tar- 
 taric acid, alkaloids, essential oils, etc. If two NicoPs prisms are 
 crossed so that no light is emitted, and a solution of sugar, for ex- 
 ample, is placed in a glass tube between the prisms, light will pass. 
 The sugar turns the direction of vibrations of the light as it comes 
 from the first prism, and the effect is the same as if the second prism 
 had been turned with respect to the first one as described above, 
 
LIGHT. 67 
 
 where nothing intervened between the prisms. Substances which 
 have such an effect on polarized light are said to turn the plane of 
 polarization, and are called optically active. The amount of this 
 turning or rotation of the plane of polarization can be measured by 
 noting to what extent the second prism must be turned to the right 
 or left to produce the original condition, namely, darkness. 
 
 Substances which act in such a manner that the analyzer must be 
 turned to the right to produce darkness are called dextrorotatory, or 
 right-handed; while those substances acting in the opposite manner 
 are called levorotatory , or left-handed. Substances acting in neither 
 way are called optically inactive. 
 
 The degree of rotation varies with the quantity of substance in 
 solution for a definite length of a column of the latter, and hence is 
 used to determine the percentage strength, for example, that of sugar 
 in urine and other liquids. Polariscopes are therefore valuable quan- 
 titative analytical instruments. 
 
 All polariscopes consist essentially of a polarizer and an analyzer, 
 with a tube between them for containing the substance to be exam- 
 ined, and a scale for reading the amount of rotation produced, all 
 carried on a suitable metallic support. In addition to these essential 
 parts, the polariscopes of different makers are provided with numer- 
 ous contrivances rendering the instruments more perfect and the 
 analytical results obtained more accurate. 
 
 Plates of crystalline substances, as quartz, have a noteworthy 
 effect when placed in the path of polarized light between a polarizer 
 and an analyzer. Not only do they prevent the light from being 
 entirely shut off when the Nicol prisms are crossed, but they produce 
 sharply defined appearances, as color tints, alternate lines of light 
 and darkness, equal or unequal illumination of the two halves of 
 the field of view, etc. The appearances depend on the particular 
 arrangement and direction of cutting of the crystalline plates. A 
 full explanation of the cause of these effects is beyond the scope of 
 this work. 
 
 Fig. 28 shows Lippich's polariscope, used chiefly for sugar solu- 
 tions. The optical arrangement is shown above the drawing of the 
 instrument, and consists of a telescope, a-a, the analyzer 6, a station- 
 ary polarizer, c, a movable polarizer, d, and the condensing lens e ; 
 /represents a number of diaphragms. The liquid to be examined is 
 placed in the tube, and the rotatory power of the substance is deter- 
 mined by turning the polarizer to the right or left, as the case may 
 require. The amount of turning necessary to establish the same con- 
 
68 
 
 CHEMICAL PHYSICS. 
 
 ditions existing before the optically active substance was brought 
 between the prisms is read off on the movable disk, which is pro- 
 
 FIG. 28. 
 
 a b f 
 
 fe dfe 
 
 Lippich's polariscope. 
 
 vided with a scale. A lamp supplies the illumination by means of 
 a flame colored yellow by sodium. 
 
 Chemical effects of light. The well-known bleaching effect that 
 sunlight has on many dye-stuffs shows that light has the power to 
 bring about chemical changes. The art of photography is one of 
 the practical applications of this principle. Plant-life is dependent 
 on the light that reaches us from the sun. The storage of many 
 chemicals in the dark, or in colored glass bottles, is often necessary to 
 protect them from the decomposing influence of light. 
 
 QUESTIONS. What are our views regarding the nature and propagation of 
 light? Explain reflection, refraction, and dispersion of light. What is the 
 prismatic spectrum, and how is it obtained ? Give a full explanation of the 
 spectroscope and of its use in chemical analysis. Define continuous, bright- 
 line, and absorption-spectra, and state the conditions under which they are 
 formed. What is meant by double refraction and by polarization of light? 
 Mention the essential parts of the polariscope, and the use made of it in chem- 
 ical analysis. How are the different colors produced under the influence of 
 white light? What is revealed to us by the Frauenhofer lines in the solar 
 spectrum? Explain the terms dextrorotatory, levorotatory, and optically 
 inactive substances. 
 
ELECTRICITY. 69 
 
 4. ELECTRICITY. 
 
 Electricity generated by friction. When a glass tube is rubbed 
 with a piece of silk, it will be found to have acquired the property 
 of attracting light bodies, such as scraps of paper, sawdust, etc. 
 Moreover, if the tube be brought close to the face, a sensation similar 
 to that produced by the contact of a cobweb will be experienced. 
 If a knuckle be held near the tube, a peculiar noise is heard, and 
 a spark may be seen to pass between the tube and the knuckle. 
 
 These phenomena show that the tube has acquired peculiar 
 properties by friction. It is said to be electrified, and the name 
 electricity is given to the cause producing these phenomena. The 
 term electricity is derived from the Greek electron, amber, in which 
 substance the property of attracting light objects after the applica- 
 tion of friction was first noticed about twenty-five hundred years ago. 
 
 Conductors and non-conductors. Besides glass and amber, 
 there are many substances, such as sulphur, sealing-wax, hard 
 rubber, etc., which can be readily electrified by friction. On the 
 other hand, a bar of metal cannot be electrified unless it be fitted to 
 a glass rod, a piece of rubber, or to certain other substances, and 
 held by this handle while being rubbed with flannel. . Moreover, it 
 can be shown that a piece of glass or sulphur will attract particles 
 i. c., becomes electrified at that spot only where it has been rubbed, 
 while a tube of metal, fastened to a suitable handle, becomes elec- 
 trified over the whole surface of the tube. These facts show that 
 electricity when generated in such bodies as glass, sulphur, and 
 rubber, remains where it has been produced, while in metals it 
 immediately spreads over the whole mass. 
 
 Bodies of the first kind, such as glass, etc., are said to be non-con- 
 ductors, while materials such as metals are said to be conductors. A 
 non 7 conductor is often called an insulator, and a conductor supported 
 by a non-conductor is said to be insulated. 
 
 The reason that conductors, such as metals, cannot be electrified 
 by friction unless held by a non-conductor, is that the human body is 
 a good conductor, and therefore carries off the electricity as quickly 
 as it is generated. 
 
 No substance is absolutely non-conducting, but the difference in 
 this power possessed by what are termed good conductors and non- 
 conductors is very great. Of conductors, may be mentioned : All 
 metals, charcoal, acids, saline solutions, living animals and vege- 
 
70 CHEMICAL PHYSICS. 
 
 tables, water, moist earth and stones. Non-conductors are : Shellac, 
 rubber, resins, sulphur, wax, glass, silk, wool, porcelain, dry paper 
 and dry air. 
 
 Duality of electricity. For a further study of electrical phe- 
 nomena the simple instrument known as the electric pendulum or 
 pith -ball electroscope may be used. It consists of a pith-ball sus- 
 pended by a silk fibre from an insulated support. When an electri- 
 fied glass rod is brought near the ball, the latter is attracted ; but 
 as soon as it touches the rod the attraction is changed to repulsion, 
 which lasts as long as the ball retains the electricity it has acquired 
 by contact. The same phenomena may be shown by employing any 
 other electrified body, for example a piece of sealing-wax, sulphur, 
 etc., in place of the glass rod. If while the pith-ball exhibits re- 
 pulsion for the glass electrified resin is brought near the ball, it is 
 attracted by the resin ; and when it is repelled by the resin it is 
 attracted by the glass. These phenomena clearly show that the 
 electricity developed on the resin is not of the same kind as that 
 developed on the glass. They exhibit opposite forces toward any 
 third electrified body, each attracting what the other repels. They 
 have accordingly received names which indicate opposition. The 
 electricity which glass acquires when rubbed with silk is called vitre- 
 ous or positive, and that which resin acquires by friction with flannel, 
 resinous or negative electricity. 
 
 On repeating the experiment with other substances, it is found 
 that all electrified bodies behave like either glass or resin. An elec- 
 trified body is spoken of as being charged with electricity ; the 
 charge may be either positive or negative. Experiments show 
 that, whenever electricity of one kind is developed, whether by 
 friction or other means, an equal quantity of the opposite kind is 
 simultaneously developed. Thus, in rubbing glass and silk the glass 
 is charged with positive, the silk with negative electricity. If a 
 conductor receives two charges of electricity of equal quantity but 
 opposite kind, it exhibits no trace of electricity, the two charges 
 having neutralized one another. 
 
 The kind of electricity which a body obtains by friction with 
 another body evidently depends on the nature of the bodies. For 
 instance, if glass be rubbed with cat's skin the glass becomes charged 
 with negative, but if rubbed with silk it becomes charged with posi- 
 tive electricity. In the following " potential series " any one of the 
 bodies named becomes positively electrified when rubbed with one 
 
ELECTRICITY. 71 
 
 of the bodies following, but negatively electrified when rubbed with 
 one of those which precede it : 
 
 1. Cat's skin. 5. Silk. 9. Sealing-wax. 
 
 2. Flannel. 6. Human body. 10. Resin. 
 
 3. Ivory. 7. Wool. 11. Sulphur. 
 
 4. Glass. 8. Metals. 12. Gutta-percha. 
 
 When an electrified body is brought to its normal condition it is 
 said to be discharged. The discharge may take place slowly through 
 the air, or rapidly by bringing the charged body in contact with the 
 earth directly or by means of a conductor, such as the human body 
 or a piece of wire. The discharge may be accompanied by a flash of 
 light, called a spark. 
 
 Induction. A body charged with electricity will exert an influ- 
 ence upon surrounding unelectrified bodies and destroy the neutral 
 condition existing in them, attracting to the surface next to the elec- 
 trified body a charge the opposite to that which it contains. But 
 while one kind of electricity is drawn toward the original electrified 
 body, an equal quantity of the opposite kind of electricity is driven 
 toward the farther extremity of the bodies which are under the influ- 
 ence of the electrified body. This action exerted by an electrified 
 body on another body is called induction. 
 
 Induction of bodies connected with the earth can last only so long 
 as they are under the influence of the electrified body, because as 
 soon as this is removed the induced electricity is immediately carried 
 off by the earth. But if an insulated body be brought near one that 
 is electrified, and while under its influence be touched at the end 
 opposite to the electrified body so as to carry off the electricity there 
 gathered, then on removing the electrified body the previously neu- 
 tral body will be found to be electrified with a charge opposite in 
 character to that of the originally electrified body. This method of 
 imparting electricity is called charging by induction. Induction 
 furnishes us the explanation of the attraction and repulsion of light 
 materials by electrified bodies. A positively excited body decdm- 
 poses the normal charge present in other bodies, and if sufficiently 
 light they move toward the excited body, discharging their negative 
 electricity and becoming charged positively through contact; they 
 are now repelled, as both bodies are electrified alike. 
 
 Electrical machines. Electricity produced by friction or by 
 induction is called static electricity, or electricity at rest, to differ- 
 
72 CHEMICAL PHYSTCS. 
 
 cntiate it from current electricity, or electricity in motion, which will 
 be considered later. Various machines have been constructed to 
 generate static electricity. In the older forms of such machines 
 friction between glass plates or glass cylinders and pads of silk served 
 as the generating source. In the newer and more powerful forms 
 of static machines, such as the Toepler-Holtz machines, induction 
 chiefly is used to generate the electricity. 
 
 Nature of Electricity. The most modern theory of the nature of elec- 
 tricity teaches that it is a manifestation of some manner of strain set up in the 
 hypothetical ether. But this theory cannot be discussed to advantage in this 
 volume. However, the following lines may assist the student in getting an 
 idea of what electricity is, and how it acts. 
 
 It has been stated that energy is a universal property of matter, and that 
 energy, like matter, can neither be created nor destroyed. But energy, like 
 matter, can be changed from one form .to another, or from one place to 
 another. According to whether energy manifests itself in masses, in mole- 
 cules, or in atoms, we speak of mass energy, molecular energy, and atomic 
 energy. Mass energy becomes manifest in the attractions due to gravitation, 
 such as the fall of bodies; in magnetic attractions, as when a magnet attracts 
 iron ; in electric attractions, as when an electrified body attracts light particles 
 of matter. Molecular energy manifests itself in heat, in light, in magnetism, 
 and in electricity. Just what the difference is between the different kinds of 
 molecular motion that produce in one case heat, in others light or electricity, 
 has never been discovered. It is supposed to be in the form of undulations 
 or vibrations, the heat undulations having one form, the electric undulations 
 another form, so that while both kinds of motion are found in the same body 
 at the same time, they do not interfere with each other. 
 
 Exactly as in the case of heat and light, we have to assume that the propa- 
 gation of electricity through space takes place in the ether. There is, more- 
 over, a mutual reaction between the vibratory motion of the molecules and the 
 undulatory motion of the ether, the vibrations producing the undulations, and 
 the undulations, in turn, producing the vibrations; just as the vibratory strokes 
 of an oar produce waves, which in turn may produce vibrations in other oars 
 resting in the water. 
 
 The conclusion, therefore, to which we come in regard to the nature of elec- 
 tricity is this : Electricity is a manifestation of energy believed to consist in 
 undulations of the ether and vibrations of the grosser molecules of matter. 
 
 We see, then, that electricity is neither energy nor matter, but, like heat, 
 light, and sound, it is an effect produced by energy on matter. But as the 
 effect cannot be separated from its cause, it is convenient to speak of it as 
 electric energy, in the same sense as we speak of mechanical enegy, vital energy, 
 heat energy, or energy in any other form in which it becomes manifest as asso- 
 ciated with matter. 
 
 To obtain electricity, energy in some other form must be expended, whether 
 it be the energy of our body expended in rubbing together pieces of glass and 
 silk, or the energy of chemical action, as in a battery cell, or the potential 
 
ELECTRICITY. 73 
 
 energy of coal used in the mechanical working of a dynamo. All methods of 
 generating electricity bring about a disturbance of the electrical equilibrium 
 existing under normal conditions in ail matter. Whenever this equilibrium is 
 disturbed there is a tendency to re-establish it, and it is during the process of 
 re-establishing the equilibrium that work is done electrically. 
 
 One of the principal reasons that electrical phenomena offered great diffi- 
 culties to the investigator is that the electric undulations taking place in the 
 ether produce no effect whatever on our senses. Waves of air in striking certain 
 nerves in the ear produce the sensation of sound ; waves of ether affect certain 
 other nerves in such a manner as to produce the sensations of heat and light, 
 but man has no nerves that are affected by electric or magnetic waves i. e., 
 he is magnetically and electrically blind and deaf. The slow development of the 
 science of electricity was due to this fact. 
 
 Magnetism. The native iron ore known as lodestone or mag- 
 netite (ferrous ferric oxide) has the power of attracting bits of steel 
 or iron, and also possesses the property of pointing north and south 
 when suspended by a thread. Pieces of iron may be caused to 
 acquire the same properties, and all bodies possessing them are called 
 magnets, while magnetism is the term used to designate the magnetic 
 condition of matter. 
 
 Any bar of steel or iron may be magnetized by drawing over it 
 lengthwise a magnet ; but while a piece of hard steel will remain 
 a magnet almost indefinitely, soft iron loses its magnetism very 
 readily. A pivoted or suspended magnet always places itself in the 
 direction of the " magnetic meridian' 7 of the earth i.e., nearly 
 north and south. The end of the magnet pointing north is called 
 its north pole, the other its south pole. On bringing one pole of a 
 magnet near a suspended magnet it is found that with magnetism, as 
 with electricity, like poles repel and unlike poles attract each other. 
 There exists also magnetic induction, corresponding to induction by 
 electricity. This can be shown by placing a bar of iron near a 
 magnet, when it is found that the end of the bar nearest the north 
 pole is converted into a south pole, and vice versa. 
 
 
 When a magnetized bar is dipped into iron filings, masses of the filings adhere 
 to the two extremities i. e., to the two poles while none are found at the 
 centre. When a magnetic bar is cut in halves at the non-magnetic centre, 
 two magnets are produced ; and this cutting into smaller lengths may be con- 
 tinned indefinitely, with the result that each length, and finally each particle, 
 possesses two poles and an intermediate neutral zone. This fact, as well as 
 other considerations, has led to the assumption that each molecule of iron is 
 a magnet in itself. In ordinary iron these little magnets are not arranged 
 systematically, while in magnetized iron all the north poles point in one direc- 
 tion, all the south poles in the opposite direction. Moreover, it is supposed 
 
74 CHEMICAL PHYSICS. 
 
 that each magnetic molecule is traversed by a closed electric circuit, which 
 currents become parallel upon magnetization of ordinary iron. According to 
 this theory, magnetism is a manifestation of electrical energy. 
 
 The shape given to magnets is usually that of a bar or of a horse- 
 shoe. A bar of soft iron laid over the poles of a horseshoe magnet 
 is called an armature; it serves to retain the full power of the 
 magnet. 
 
 When fine iron filings are sprinkled on a piece of glass or card- 
 board which has been placed over a magnet, the filings arrange 
 themselves in lines radiating from either pole, forming graceful 
 curves from pole to pole. These lines, called lines of magnetic force, 
 represent the resultant of the combined action of the two poles, the 
 space surrounding a magnet as far as its influence extends being 
 termed its magnetic field. A magnetic needle placed anywhere in 
 this field follows the lines of magnetic force, always assuming a 
 position tangent to the magnetic curve. 
 
 The explanation given for the fact that the magnetic needle points 
 north and south is that the earth itself is an immense magnet, pos- 
 sessing two magnetic poles which are close to the geographical poles. 
 
 Electricity generated by chemical action. On placing a strip 
 of ordinary zinc in diluted sulphuric acid, bubbles of hydrogen gas 
 are evolved on its surface and the zinc gradually dissolves ; a piece 
 of platinum placed in the acid is not affected at all. If, however, 
 strips of zinc and platinum are placed in a vessel containing diluted 
 acid, on connecting the plates above the liquid by a conductor, 
 for instance by a piece of copper wire, characteristic changes take 
 place. First, the evolution of gas stops on the zinc, while bubbles 
 of hydrogen escape from the surface of the platinum. Next, on 
 placing the connecting wire near a magnetic needle, this is turned 
 from its course i. e., deflected. And again, on cutting the wire and 
 placing the tongue between the two ends, a metallic taste and a 
 tingling sensation are perceived. All these phenomena cease as soon 
 as the connection between the plates is broken, and reappear when 
 connection is again established. 
 
 Undoubtedly something takes place in the wire while the plates 
 are in the diluted acid. Further investigation shows that during 
 the action of the acid on the metals electricity is generated, which 
 travels through the wire, imparting to it characteristic properties. 
 
 Galvanic or voltaic cells. In place of zinc, platinum, and sul- 
 
ELECTRICITY. 75 
 
 phuric acid, many other materials may be used to bring about the 
 
 conditions described in the preceding paragraph ; indeed, electricity 
 
 is generated whenever two solids (plates or cylinders are generally 
 
 used), conductors themselves and connected by a conductor, are 
 
 placed in a liquid that has the power to act chemically on one of the 
 
 solids. Any such arrangement is termed 
 
 a galvanic or voltaic cell. Here chemical FIG. 29. 
 
 action causes the generation of electricity, 
 
 resulting in the zinc-platinum cell in the 
 
 splitting up of sulphuric acid, H 2 SO 4 , 
 
 the hydrogen, H 2 , escaping from the 
 
 platinum plate, while the group SO 4 
 
 combines with the zinc, forming zinc 
 
 sulphate, ZnSO 4 , which dissolves in the 
 
 water. 
 
 Many combinations are employed in 
 the different cells for generating elec- 
 tricity. Fig. 29 represents the Daniell Danieii's ceil. 
 cell. It consists of the glass jar S, con- 
 taining a saturated solution of cupric sulphate, in which stands the 
 copper cylinder C. Inside of this cylinder fits a porous cell, A, con- 
 taining sulphuric acid, and into this dips the zinc plate. Z. 
 
 Chemically pure zinc is scarcely acted on by diluted sulphuric acid ; ordi- 
 nary zinc contains metallic impurities, and as these are in contact with zinc, 
 they set up a galvanic action, and thus bring about the chemical changes above 
 described. 
 
 What is believed to take place in any galvanic cell is that the 
 electrolytic fluid i. e., the active agent in the liquid state is split 
 up into two component parts, called ions, and that these ions, charged 
 with positive and negative electricity, respectively, unload these 
 charges on the two plates, while an equalizing effect is brought about 
 through the connecting wire. In other words, there is a constant 
 disturbance of the electrical equilibrium through chemical action, 
 and a tendency to re-establish the equilibrium, which tendency pro- 
 duces the current. 
 
 One of the plates (platinum, in the case cited above) is known 
 as the positive electrode or anode, while the other one (zinc) is the 
 negative electrode or cathode of the cell. The same terms are used 
 also to designate the terminals of the wires leading from the two 
 plates, which terminals are called also + and poles. 
 
76 CHEMICAL PHYSICS. 
 
 Whenever the plates are connected by the conducting wire elec- 
 tricity passes from the anode through the wire to the cathode, and 
 through the liquid back to its point of origin. This continuous 
 motion is called the electric current, and the different parts through 
 which the current passes are known as the circuit. Whenever the 
 connection is broken at any point the circuit is said to be open ; 
 otherwise it is closed. If the circuit be open, both plates become 
 charged with positive and negative electricity, respectively ; but as 
 there is no conductor to carry off these charges, further accumulation 
 stops, and chemical action ceases until the circuit is again closed. 
 
 Whenever two or more galvanic cells are connected so as to use in 
 one circuit the electricity generated by all the cells, the arrangement 
 is spoken of as a galvanic battery; at present this term is likewise 
 applied to a single cell. 
 
 Electromotive force. The fact that electricity flows continuously 
 in a closed circuit containing a galvanic cell shows that the cell has 
 the power of setting electricity in motion, and this power is desig- 
 nated as electromotive force (E. M. F.), electrical tension, or potential. 
 It is the result of the tendency to re-establish equilibrium, and 
 depends upon the difference in the electrical condition of the two 
 plates ; the greater this difference the greater the E. M. F. 
 
 The action of an electric battery may be compared to a pump sending water 
 from a reservoir through a pipe to a higher elevation ; the water will return to 
 its former level with a certain force, depending on the height to which it has 
 been lifted, and the water while descending can be made to do mechanical 
 work turn a wheel or set in motion other machinery. Similarly the cur- 
 rent of electricity on its return trip can be made to do work, and the quantity 
 of it depends on the E. M. F. generated by the battery. 
 
 Electric units. For obvious reasons, it is desirable to measure the 
 intensity and quantity of electric currents similarly as heat or other 
 forms of energy are measured. The three chief units adopted for 
 such measurements are named, in honor of three great pioneers in 
 electricity, the ohm, the ampere, and the volt. 
 
 It has been stated that we differentiate between conductors and 
 non-conductors, but even the best conductors offer resistance to the 
 passage of an electric current. The unit of this resistance is called 
 the ohm, and represents the resistance to a current in a column of 
 mercury having a section of 1 square millimeter and a length of 
 106.28 centimeters, at a temperature of C. For practical pur- 
 
ELECTRICITY. 77 
 
 poses, sets of coils, known as resistance coils, having a known resist- 
 ance, are used for measuring electrical resistance. 
 
 An ampere is the unit of quantity of current, which may be deter- 
 mined by measuring the amount of oxygen and hydrogen liberated 
 by the current from water within a given time. 
 
 The weight of copper deposited electrolytically by the current is used also 
 as a means of determining its amperage. One ampere of current deposits 1.177 
 grammes of copper per hour. For practical purposes, instruments known as 
 amperemeters, or ammeters, are used for measuring amperage; use is made in 
 these instruments of the fact that a current deflects a magnetic needle, which 
 is made to move over a dial-face graduated in amperes. 
 
 In using electric currents for medical purposes, 1 ampere is often too strong 
 for the tissues of the body. For this reason the unit is divided into 1000 parts, 
 each part being designated as a milliampere. 
 
 The volt is the unit for electromotive force, and is the pressure 
 required to maintain a current of 1 ampere through a resistance of 
 1 ohm. 
 
 The relation existing between these three units is expressed in 
 Ohm's law : The strength of the current is equal to the E. M. F. 
 divided by the resistance of the current. 
 
 The chief diiference between frictional and galvanic electricity is 
 that the first is of high tension but small in amount, while current 
 electricity is of low tension but greater in amount. 
 
 Electromagnets. When a piece of insulated wire is wound in 
 spiral form around a bar of soft iron, and an electric current is made 
 to pass through the wire, the iron becomes a magnet for the time 
 being, and is then called an electromagnet. If a piece of steel is 
 treated in the same way, it remains a magnet even after the current 
 is broken, or after it has been taken from the spiral. 
 
 As the strength of an electromagnet is proportional to the strength 
 of the current and the length of wire wound around it, electromagnets 
 of very much greater power than ordinary magnets can be made 
 The position of the north and south poles of the magnet depends on 
 the direction of the current, a reversion of the latter producing a 
 reversion of the polarity in the electromagnet. Practical use is made 
 of the electromagnet in telegraph instruments, in the telephone, the 
 electric bell, and in many other contrivances. 
 
 Electricity generated by magnetism. Not only can magnets be 
 made by subjecting iron to the influence of electric currents, butj 
 
78 CHEMICAL PHYSICS. 
 
 vice versa, electric currents, termed magneto-electric currents, can be 
 generated by the action of magnets on metallic wires. Indeed, when- 
 ever a magnet is brought near to, or taken away from, a wire, or is 
 moved about in its neighborhood ; or if, vice versa, a mass of wire is 
 moved around a magnet i. e., whenever metallic wires are made to 
 pass through a magnetic field temporary electric currents are always 
 set up in the wire. These induced currents are the result of the 
 conversion of mechanical energy i. e.. the energy required to move 
 a wire or a magnet into electrical energy. 
 
 Use is made of these facts for the generation of electric currents 
 by suitably constructed machines, known as magneto-electric machines. 
 In the smaller ones a permanent horseshoe magnet is used. Between 
 or in front of its poles revolve two coils of insulated wire with soft 
 iron cores, known as armatures. During rapid revoluting the soft 
 iron cores are magnetized while opposite one of the poles of the per- 
 manent magnet, demagnetized while equidistant from the two poles, 
 and reversed while passing to the opposite pole. The magnetization 
 and demagnetization of the iron cores have the same effect on the 
 coils of wire as if a magnet were suddenly introduced into the coil 
 and as quickly withdrawn. Thus currents will be induced in the 
 wire, and they will run in opposite directions as the polarity of the 
 cores changes with each half revolution. Such currents are known 
 as alternating currents. 
 
 The same principle is made use of in the dynamo-electrical machines 
 for generating the currents employed for motive power, electric 
 lighting, etc. Instead of permanent magnets, powerful electro- 
 magnets are here used, and in place of an armature with two coils 
 of wire, armatures with many coils are employed. Moreover, an 
 arrangement known as the commutator is often used to change the 
 alternating to a direct or continuous current i. e., the generated 
 electricity is collected in such a manner that it moves in one direction 
 continuously. 
 
 Electric motors are essentially dynamos in which the action is re- 
 versed i. e., electric currents convert iron into electromagnets, which 
 by successive attraction and repulsion of the iron in the armature 
 cause its rapid rotation, which motion may be communicated to other 
 machinery. 
 
 Voltaic induction. It has been mentioned that a body charged 
 with static electricity causes, by induction, an electric disturbance in 
 all bodies near by. Similarly an electric current passing through 
 
ELECTRICITY. 
 
 79 
 
 one wire sets up induced currents in neighboring wires. One of the 
 principal applications made of these induced currents is in the induc- 
 tion coil, or Ruhmkorf coil, shown diagrammatically in Fig. 30. It 
 consists of a hollow cylinder covered with a coil of insulated and 
 relatively coarse wire, P, connected with a battery, B. Over this 
 first or primary coil is wound another, the secondary coil, S, com- 
 posed of much longer and finer wire. 
 
 FIG. 30. 
 
 Induction coil. 
 
 While a current passes through the primary wire nothing is noticed 
 in the secondary wire, but the instant the current is closed an instan- 
 taneous induced current is set up in the secondary wire in one direc- 
 tion, and on opening the circuit in the opposite direction. It follows 
 that it requires a rapid closure and opening of the circuit to generate 
 electricity in the secondary coil. The opening and closing of the 
 current are accomplished by the following self-acting arrangement. 
 In the hollow portion of the primary coil are placed bars of soft iron, 
 which are magnetized whenever a current passes through the coil. 
 Near one terminal of the iron bars is a movable metallic hammer, H, 
 held by a spring in such a position that the current is closed by it. 
 When the bars are magnetized, they raise the hammer, thereby open- 
 ing the circuit ; the cessation of the current causes the iron to be de- 
 magnetized and the hammer falls to its original position, closing the 
 circuit, and this action continues as long as the current is allowed 
 to flow. This arrangement, known as a " make and break " con- 
 trivance, generates, through the very rapid opening and closing of 
 the primary circuit, in the secondary coil that current which is known 
 as secondary, induced, interrupted, or/aradic current. 
 
 The object of the induction coil is to generate from a battery current of low 
 E. M. F. induced currents of very high E. M. F. The effectiveness of the 
 
80 
 
 CHEMICAL PHYSICS. 
 
 induction coil increases with the length of its wire, which in large instruments 
 is fifty miles and more. While such machines are in operation sparks several 
 feet in length will pass between the terminals of the secondary coil at A. 
 
 Conversion of electrical energy into heat and light. "When- 
 ever a current passes through a wire (or through any other mass) it 
 offers more or less resistance, the amount of which depends on the 
 nature of the material and the thickness of the wire. This resistance 
 gives rise to the conversion of electrical energy into heat. Practical 
 use is now extensively made of these heating effects by passing strong 
 currents through poor conductors, as is done in the heaters used for 
 heating cars or buildings, in stoves for cooking purposes, in the 
 vulcanizers used in dental operations, and in electric furnaces. In 
 
 M 
 
 Electric furnace. 
 
 the latter, powerful currents are employed to produce temperatures 
 unattainable by processes of combustion or by any other means at 
 our disposal. These furnaces have not only revolutionized many 
 processes of manufacture, but have led to the discovery of a number 
 of substances. 
 
 The construction of electric furnaces differs widely according to 
 the use made of them. Fig. 31 represents the vertical section of a 
 furnace used for the manufacture of aluminum-bronze. The material 
 to be acted on is contained in a graphite crucible, A, resting on the 
 
ELECTRICITY. 
 
 81 
 
 metallic plate P, and surrounded by a mass of carbon, C, the whole 
 being enclosed by the furnace wall M. D is a carbon rod, and acts 
 as the anode, while connection through the metallic plate is made 
 with the cathode from below. 
 
 Fig. 32 gives a sectional, and Fig. 33 an exterior, view of an elec- 
 tric furnace used in the manufacture of carborundum. The current 
 
 FIG. 32. 
 
 Longitudinal section of carborundum furnace. 
 
 enters and leaves through the cables which terminate in carbon elec- 
 trodes fastened in the wall. Between the electrodes is a mass of 
 
 FIG. 33. 
 
 Exterior view of carborundum furnace. 
 
 coke, which, while conducting the current, offers sufficient resistance 
 to be heated to an extremely high temperature. (For details of the 
 chemical action see the article on Carborundum.) 
 
 The electric arc lamp and the incandescent lamp are well-known examples 
 of the conversion of electrical energy into light. In the former lamp electricity 
 6 
 
82 
 
 CHEMICAL PHYSICS. 
 
 FIG. 34. 
 
 of very high electromotive force (1000-3000 volts) passes between terminals of 
 pencils of hard carbon, which, while infusible, burn away gradually, requiring 
 an automatically acting contrivance to keep the two pencils at a constant dis- 
 tance. In the incandescent lamp a filament of carbon, fastened in an exhausted 
 glass globe, is heated to a white heat by a current of about 50 to 120 volts. 
 
 Conversion of electrical energy into chemical action. A highly 
 important effect of electric currents is their power to cause chemical 
 decomposition i. e., the splitting- up of matter into two of its com- 
 ponent parts. Thus, if the terminals of a battery are placed in a 
 vessel with acidified water, gas-bubbles rise from 
 both terminals, and on examination the gases 
 are found to be hydrogen and oxygen, which 
 are the constituents of water. In order to col- 
 lect the gases and measure their volume, the 
 apparatus shown in Fig. 34 may be used. It 
 consists of three connected glass tubes, which 
 are filled with water acidified with sulphuric 
 acid. The electric current is made to pass 
 through the liquid from the poles, in this case 
 preferably pieces of platinum foil fastened to 
 platinum wire fused in the glass tubes. On 
 passing a current through the liquid, oxygen 
 rises from the positive, and hydrogen from the 
 negative pole. The process of splitting up a 
 compound body by electricity is called elec- 
 trolysis ; the bodies undergoing decomposition 
 are termed electrolytes. The metallic conductors 
 by which the current enters and leaves a liquid 
 or gaseous electrolyte are called poles or elec- 
 trodes, and are designated by the same names 
 given to the plates in the generating cell i. e., 
 they are called positive ( + ) pole or anode, and negative ( ) pole 
 or cathode. The decomposition product appearing at the positive 
 pole is said to be electronegative, the one appearing at the nega- 
 tive pole is electropositive. 
 
 Electrolysis of water. 
 
 Electropositive are : 
 Hydrogen, 
 Metals, 
 Bases and basic radicals. 
 
 Electronegative are : 
 Oxygen, 
 
 Halogens (chlorine, etc.), 
 Acids and acid radicals. 
 
 When an electric current passes through a solution of any salt, 
 this is split up into the base and the acid composing the salt. If 
 
ELECTRICITY. 83 
 
 the base be a metal, such as copper, it will be deposited on the elec- 
 tronegative pole. Use is made of this property in the different 
 processes of electroplating and electrotyping. Among the metals 
 requiring the weakest current for their electrolytic precipitation are 
 copper, silver, gold, and nickel, and these are often precipitated upon 
 other metals which form the negative pole. 
 
 Electrolysis is used also on a large scale for separating metals from 
 ores, or from one another, and on a small scale for analytical opera- 
 tions ; it also plays an important part in the work done by the elec- 
 tric furnace, in which often both the required high temperature and 
 the decomposing influence are furnished by the electric current. 
 
 Discharge through gases. When an electric current of suffi- 
 ciently high E. M. F. is discharged through a gas, for instance, 
 through air, the gas is rendered luminous by its passage i. e., we 
 have what is called an electric spark, in appearance like that of a flash 
 of lightning. This spark in many cases exerts chemical action, as, 
 for instance, when oxygen is converted into ozone, which change will 
 be considered later. 
 
 If the discharge take place in a gas inclosed in a glass globe from 
 which the gas may be removed by means of an air-pump, it is found 
 that at a sufficiently reduced pressure the spark ceases and the inte- 
 rior of the globe assumes a beautiful luminosity, the nature of which 
 depends on the kind of gas operated on. 
 
 By exhausting the air from suitably constructed bulbs or tubes 
 still further until an almost perfect vacuum is obtained, the electric 
 discharges passing through this vacuum again show decided changes. 
 If the cathode of such a vacuum tube be formed of a metallic disk, 
 while the anode be a straight wire, then on passing the current 
 through the vacuum tube a pale purplish beam of light radiates from 
 the face of the disk. This beam is known as the cathode ray ; it has 
 been shown to consist of streams of portions of matter negatively 
 charged, and moving with great velocity. 
 
 Rontgen rays. During the generation of the cathode rays in the 
 vacuum tube another kind of rays of a very peculiar character are formed. 
 They have been called Rontgen rays, after their discoverer, who him- 
 self named them x-rays. These rays differ from other rays in many 
 respects ; thus they can pass readily through many kinds of matter 
 which are opaque to ordinary light ; they cause many substances tg 
 emit light when they fall upon them ; they affect photographic plates, 
 
84 CHEMICAL PHYSICS. 
 
 and have a decided physiological action on various parts of the 
 human body. 
 
 Radio-activity. In 1896 the French scientist Becquerel dis- 
 covered that the metal uranium and its compounds exert sponta- 
 neously and continuously a certain influence upon their surroundings. 
 This influence was found to be due to rays (now called Becquerel 
 rays) of a peculiar kind. They act upon the photographic plate ; they 
 pass through black paper and metals ; they render the gases through 
 which they pass conductors of electricity ; they cannot be reflected or 
 refracted. Any substance exhibiting the power of sending out such 
 rays is said to be radio-active. Besides uranium and its compounds 
 those of thorium were found to possess the same properties. 
 
 The subject of radio-activity was next studied by Madam Curie, 
 who showed that certain minerals (such as pitch-blende) contain- 
 ing uranium are more radio-active than uranium itself, and in the 
 course of her investigation demonstrated that in uranium ores are 
 several substances which show radio-activity to a remarkable extent. 
 
 The work, carried yet farther by a number of scientists, has 
 brought out the following results : Three substances, named polonium, 
 actinium, and radium, have been obtained from pitch-blende and 
 show a radio-activity a million times greater than that of uranium 
 or thorium. 
 
 Of these three substances at least one the radium has been posi- 
 tively proven to be an elementary substance of metallic nature form- 
 ing well-defined salts, such as radium chloride and bromide. Radium 
 salts show all the previously mentioned properties of Becquerel rays, 
 but in addition they exhibit some other features. 
 
 Thus, radium salts are permanently luminous and render luminous 
 (or phosphorescent) for a shorter or longer period a great number of 
 other substances. The most sensitive are barium platinocyanide, zinc 
 sulphide, diamond, etc. Not only do radium salts impart luminosity 
 to other substances, but these salts communicate little by little their 
 radio-active properties to substances in their neighborhood, and these 
 in turn emit Becquerel rays for some time. 
 
 Another startling discovery was made when it was shown that 
 radium salts develop heat continuously, and consequently are in 
 themselves warmer than their surroundings. A small flask containing 
 0.7 gramme of radium bromide shows a temperature of 3 C. higher 
 than the surrounding air. Calorimetric measurements have shown 
 that radium bromide evolves enough heat to convert per hour its own 
 
ELECTRICITY. 85 
 
 weight of ice into water, or that one gramme of radium bromide will 
 raise the temperature of 80 grammes of water one degree C. per 
 hour. 
 
 Just as sun rays are made up of heat rays, light rays, and rays of 
 actinic power, so it has been found that there is a difference in the 
 rays of a radio-active body. There are at least three kinds, of which 
 the first group, called alpha rays, possesses remarkable penetrating 
 power and great photographic energy ; they are not deviated from 
 their path under the influence of a magnetic field, and resemble the 
 Rontgen rays in their action. The beta rays produce heat, are devi- 
 able under the influence of a magnetic field, and resemble cathode 
 rays. The third group gamma rays is easily absorbed. 
 
 Of great interest is the physiological action of radium compounds 
 on the animal system. Radium bromide, even when enclosed in a 
 wooden or metallic box, brought near the closed eye causes the sensa- 
 tion of light. While nothing is felt when radium salts are brought 
 close to our body, yet a strong influence, similar to that of Rontgen 
 rays, is exerted upon the tissues. This is shown by the fact that days 
 or weeks after the body had been exposed to radium rays the skin 
 reddens and, if the exposure was of sufficient duration, sores and 
 ulcerations will form which require a long time for healing. A sealed 
 glass tube, containing a little radium bromide, when placed in a bowl 
 of water with small fishes will cause their death in a few hours. 
 Attempts are now being made to use radium rays like Rontgen rays 
 in the treatment of skin diseases, lupus, etc. 
 
 When the apparently never-diminishing power of radium to give 
 out continuously light and heat was discovered, it appeared as if our 
 views regarding matter and energy were completely upset. A closer 
 investigation, however, has shown that this apparently unlimited 
 source of energy may be explained in a way conforming to our pre- 
 vious views. 
 
 What is supposed to take place is this : All radio-active substances 
 send out with enormous velocity particles, called corpuscles, which are 
 a thousand times smaller than a hydrogen atom. This substance 
 which is thrown off, and which Crookes designates the fourth state of 
 matter, or radiant matte)*, is called emanation. The phenomena of 
 radio-activity, previously described, are due to these emanations 
 which cause a bombardment of everything lying in their paths. 
 
 The discovery of radiant matter has modified our views regarding 
 atoms. It is now believed that the atom, as revealed in chemistry, is 
 a mass of a great number of small corpuscles which have come to a 
 
86 CHEMICAL PHYSICS. 
 
 state of stability or equilibrium, in which state they cannot be sepa- 
 rated by our ordinary chemical operations, and thus appear as single 
 units or atoms. In radium and in other radio-active bodies these 
 complexes of corpuscles are in unstable equilibrium and possess 
 potential energy which has a tendency to diminish in quantity, thus 
 causing the state of unrest exhibited by radio-active bodies. The 
 potential energy becomes kinetic in the form of heat, light, etc., and 
 meantime the complexes are transformed to stable forms which do not 
 possess radio-activity and which act like the chemical atoms. 
 
 This would involve the transformation of one element into a new 
 element. And that is exactly what has been found to take place in 
 the case of radium, namely, that the emanation from radium contains 
 helium. (For the manufacture of radium compounds, see the article 
 on Radium.) 
 
 QUESTIONS. Name some conductors and non-conductors of electricity, and 
 explain their behavior in connection with electrical phenomena. What is 
 meant by positive and negative, and by static and current electricity ? Describe 
 three methods for generating electricity. Name the three principal units used 
 in the measurement of electrical currents, and explain the methods employed. 
 Explain the construction and action of a galvanic cell. What is a permanent 
 magnet, and what is an electromagnet ? How are they made, and what are their 
 characteristic properties? Define the following terms: Anode, cathode, circuit, 
 electric current, induction, and electromotive force. Describe construction of 
 the electric furnace, and explain its action. How may electricity be used in 
 the generation of heat, light, mechanical motion, and chemical action? 
 
II. 
 
 PRINCIPLES OF CHEMISTRY. 
 
 5. ELEMENT, COMPOUND, CHEMICAL AFFINITY, MODES OF 
 EFFECTING CHEMICAL CHANGE. 
 
 HAVING considered some of the subjects of physics, we may now 
 pass to the field of chemistry. The nature of a chemical change and 
 the scope of chemistry have already been discussed on page 18. One 
 of the simplest means of bringing about a change in the composition 
 of matter is by applying heat. Let us see what may be learned 
 from the following experiment. 
 
 Decomposition by heat. The results of the action- of heat upon 
 matter have been stated to be : Increased velocity of the motion of 
 molecules, increase in volume of the substance heated, and in many 
 cases a conversion of solids into liquids and of these into gases. Be- 
 sides these results there frequently may be noticed another. 
 
 FIG. 35. 
 
 Decomposition of mercuric oxide in A ; collection of mercury in B, and of oxygen in C. 
 
 To illustrate this action of heat, we will select the red oxide of 
 mercury, a solid substance which is insoluble in water, almost taste- 
 , and of a brick-red color. When this oxide of mercury is placed 
 
 87 
 
88 PRINCIPLES OF CHEMISTRY. 
 
 in a glass tube and heated, it will be found to disappear gradually, 
 and we might assume that it has been converted into a gas from 
 which, upon cooling, the red oxide of mercury would be re-obtained. 
 If the apparatus for heating the oxide of mercury be so constructed 
 that the escaping gases may be collected and cooled, we shall not find 
 the red oxide in our receiver, but in its place a colorless gas, while at 
 the same time globules of metallic mercury will be found deposited 
 in the cooler parts of the apparatus (Fig. 35). 
 
 The action of heat consequently has in this case produced an effect 
 entirely different from the effects spoken of heretofore. There is no 
 doubt that the first action of the heat upon the oxide of mercury is 
 an increased velocity of the motion of its molecules and simulta- 
 neously an increase of its volume, but afterward a decomposition of 
 the oxide takes place, and two substances are liberated, each different 
 from the oxide. 
 
 One of these substances is a silvery-w T hite, heavy, liquid metal, the 
 mercury ; the other substance is a colorless, odorless gas, which sup- 
 ports combustion much more freely than does atmospheric air, and is 
 known as oxygen. 
 
 Elements. We have thus succeeded in proving that red oxide of 
 mercury may be converted or decomposed by the mere action of heat 
 into mercury and oxygen. It is but natural to inquire whether it 
 would be possible further to subdivide the mercury or the oxygen 
 into two or more new substances of different properties. To this 
 question, which has been experimentally propounded to Nature over 
 and over again, we have but one answer, viz. : Oxygen and mercury 
 are substances incapable of decomposition by any method or means 
 as yet known to us. They resist the powerful influences of electricity 
 and heat, even when raised to the highest attainable degrees of in- 
 tensity, and they issue unchanged from every variety of reaction 
 hitherto devised with the view of resolving them into simpler forms 
 of matter. 
 
 Therefore we are justified in regarding oxygen and mercury as non- 
 decomposable or simple substances, in contradistinction to compound 
 or decomposable substances, such as the red oxide of mercury. 
 
 All substances which cannot by any known means be resolved into 
 simpler forms of matter, are called elements; all substances which 
 may, by one process or another, be subdivided or decomposed in such 
 a manner that new substances with new properties are formed, are 
 called compound substances or compounds. 
 
ELEMENT, COMPOUND, CHEMICAL AFFINITY, ETC. 89 
 
 While the number of known compounds exceeds many thousands, 
 the number of elements is comparatively small, about seventy-six of 
 these simple substances being known to exist on our earth. And yet 
 this small number of elements, by combining with each' other in many 
 different proportions, form all that boundless variety of matter which 
 we see in nature. 
 
 In the case of oxide of mercury heat has evidently caused a weak- 
 ening of the attractive force which held the two elements, mercury 
 and oxygen, together, thus permitting them to part company. Such 
 a change is known as decomposition. But, in other cases, heat 
 increases the attraction between elements, so that they unite to form 
 more complex bodies, which would not occur at ordinary tempera- 
 ture. Such a change is known as combinatioyi . For example, mag- 
 nesium metal does not unite with the oxygen of the air at ordinary 
 temperature, but when heated sufficiently, it unites with oxygen 
 with great vigor. In fact, mercury unites with oxygen when heated 
 to a temperature a little below its boiling-point, and forms the red 
 oxide, but if the latter is heated to a higher temperature it is decom- 
 posed. 
 
 The student must not think that elements are obtained in* all cases 
 of decomposition by heat. In some instances the new products ob- 
 tained are themselves compounds, while in others an element and a 
 new compound result. For example, when calcium carbonate is 
 heated (see page 18), calcium oxide, a solid compound, and carbon 
 dioxide, a gaseous compound, are obtained. When potassium chlor- 
 ate, a compound of potassium, chlorine, and oxygen, is heated, the 
 element oxygen is evolved, while a new compound composed, of po- 
 tassium and chlorine, and known as potassium chloride, remains as a 
 solid in the vessel. 
 
 The quantity of heat required for decomposition differs widely 
 according to the nature of the substance. Some substances can be 
 produced only at a temperature below the freezing-point of water, 
 a higher temperature causing their decomposition ; other substances 
 may be decomposed at temperatures between the freezing- and 
 boiling-points; others again, and to these belong the majority of 
 inorganic compounds, may be raised to red or white heat before decom- 
 position sets in; and still another number of compounds have never 
 yet been decomposed by heat. Theoretically, however, we assume 
 that all compounds may be decomposed by heat, should it be possible 
 to raise it to a sufficiently high degree. 
 
90 PRINCIPLES OF CHEMISTRY. 
 
 Decomposition by electricity. It has been shown in Chapter 4 
 that electricity exerts under certain conditions a strong decomposing 
 influence on many compounds. It was also stated that this process 
 of decomposition is called electrolysis, while the term electrolyte is 
 given to the material acted upon. This material must be a conductor 
 of electricity, and either in the liquid or gaseous state. The electro- 
 lyte is brought into the liquid state either by melting it if solid or 
 dissolving it in some other molten medium, or, as is most frequently 
 the case, by dissolving it in water, which in some cases is rendered 
 acid or alkaline, before electrolysis is carried out. 
 
 Electricity is widely used at the present day in chemical industries 
 and in quantitative chemical analysis. Some examples of chemicals 
 obtained thus are metallic sodium and potassium, caustic potash, 
 chlorine which is converted into bleaching powder, potassium chlor- 
 ate, aluminum by electrolysis of a solution of aluminum oxide in 
 molten cryolite, pure copper from the impure product, pure iron, 
 nitric acid by a powerful electric discharge through air. 
 
 Decomposition by light. Another cause of decomposition is, in 
 many cases, the action of light. The art of photography is based 
 upon this kind of decomposition. Many substances, easily affected 
 by light, have to be kept in the dark to prevent them from being 
 decomposed. 
 
 The phenomena of heat, light, and electricity resemble each other in so far 
 as they are phenomena of motion. Heat is the consequence of the motion of 
 material particles (molecules) ; light is the consequence of the vibratory motion 
 of the hypothetical medium ether ; probably the same is true of electricity. 
 
 These motions, in being transferred, have, as shown above, frequently the 
 tendency of splitting up the molecules of compound substances. 
 
 Mutual action of substances upon each other. As a general 
 rule, it may be said that no chemical action takes place between two 
 substances both of which are in the solid state, because the molecules 
 do not come in sufficiently close proximity to exchange their parts. 
 The free motion of the molecules in liquid or gaseous substances 
 facilitates such a proximity, and consequently chemical action. It is 
 often sufficient to have but one of the acting substances in the gaseous 
 or liquid state, while the second one is a solid. By converting two 
 solids into extremely fine powder and mixing them together thor- 
 oughly, chemical combination may follow, provided the affinity 
 between them be sufficiently strong. 
 
ELEMENT, COMPOUND, CHEMICAL AFFINITY, ETC. 91 
 
 Physical phenomena accompanying- chemical action. By a 
 careful observation of all the details in a great variety of chemical 
 actions, an intimate connection between physics and chemistry be- 
 comes apparent. A noteworthy fact that stands out prominently is 
 that in every change in composition, energy in some form is produced 
 or consumed. In the decomposition of red oxide of mercury, heat 
 energy is constantly being absorbed and rendered latent as the oxide 
 separates into the free elements, oxygen and mercury. As soon as 
 the heat-supply is withdrawn the decomposition ceases. When mag- 
 nesium burns, that is, unites with oxygen, a great quantity of heat 
 and intense light is produced, and the action after starting is self-sus- 
 taining. "We have seen that electric energy is consumed in bringing 
 about chemical change. On the other hand, chemical action under 
 proper control can be made to produce electric energy, that is, an 
 electric current. In some cases the energy of light rays is consumed 
 in producing chemical change, for example, in photography. De- 
 composition can be accomplished in certain instances by mechanical 
 energy, as violent trituration, while, on the other hand, the production 
 of mechanical energy by chemical action is illustrated by the explo- 
 sion of gunpowder and movement of muscles. 
 
 Chemical or internal energy. Exothermic and endothermic 
 actions. From the previous discussion, we learn that there must be 
 another kind of energy stored up in latent form in matter which 
 under proper conditions is converted into forms of energy with which 
 we have already become familiar in Section I. on Physics ; namely, 
 heat, electricity, light, mechanical energy. This form of energy, 
 which is made manifest during chemical change, is called chemical 
 or internal energy. Every element and compound should be looked 
 upon not merely as consisting of certain kinds of matter, but also as 
 a storehouse of chemical energy. In many chemical changes part of 
 the internal energy is liberated in forms which can be measured, such 
 as heat, electricity, etc. This portion is known as free or available 
 internal energy, and is different in amount according to the nature of 
 the substances concerned in the chemical change. For example, the 
 same weight of various articles of food, when undergoing combustion 
 in the animal body, produces very different amounts of heat, and 
 therefore these foods have different values as fuels for keeping up the 
 temperature of the animal body. 
 
 Sometimes it is necessary to augment the internal energy of sub- 
 stances from a supply of energy such as heat, electricity, etc., in order 
 
92 PRINCIPLES OF CHEMISTRY. 
 
 to bring about chemical change. Indeed, it has been found that all 
 chemical changes maybe divided into two classes: (1) those which 
 take place spontaneously and in which a certain amount of the chem- 
 ical energy of the substances acting is liberated and converted into 
 some other forms of energy, which thus become available for use ; (2) 
 those which do not take place spontaneous! v, but which must be sus- 
 tained by the addition of energy from without to the substances act- 
 ing. The energy set free in spontaneous chemical actions usually 
 appears as heat, and all actions proceeding with liberation of heat 
 are called exothermic, while those actions which absorb heat are called 
 endothermic. The study of the energy changes in chemical actions is 
 very important for a full understanding of such actions. The study 
 of the heat produced or absorbed in chemical changes constitutes a 
 subdivision known as Thermochemistry. 
 
 Chemical reaction, in its broadest sense, refers to any chemical 
 change, but is used more especially when the intention is to study 
 the nature of the substances decomposed or formed. The expression 
 reagent is applied to those substances used for bringing about such 
 changes. 
 
 Chemical affinity. There must be some cause which enables or 
 even forces the different elements to unite with each other so as to 
 form compound bodies. There must be, for instance, a cause which 
 enables oxygen and mercury to combine and form a red powder. 
 
 This cause is to be found in the existence of another form of 
 attraction which causes the smallest particles of different elements 
 to unite to form new substances with new properties. This kind of 
 attractive power is called chemical force or chemical affinity, and 
 bodies possessing this capacity of uniting with each other are said 
 to have an affinity for each other. 
 
 There is a great difference between chemical attraction and the 
 various forms of attraction spoken of heretofore. Cohesion simply 
 holds together the molecules of the same substance, adhesion acts 
 chiefly between the molecules of solid and liquid substances, gravita- 
 tion acts between masses. But all these forces do not change the 
 nature, the external and internal properties of matter ; this is done 
 when chemical force or affinity is operating, when a chemical change 
 takes place. 
 
 For instance : In a piece of yellow sulphur the molecules are held 
 together by cohesion, and we can counteract this cohesion by mechan- 
 ical subdivision, reducing the sulphur to a fine powder ; or by the 
 
LAWS AND THEORIF:S OF CHEMISTRY. 93 
 
 application of heat we can further subdivide the sulphur, melt, and 
 finally volatilize it ; or we can throw a piece of sulphur into the air, 
 when it will fall back upon the earth in consequence of gravitation ; 
 or we can dip it into water, when it becomes moist in consequence of 
 surface-action. Yet in all these cases sulphur remains sulphur. 
 
 It is entirely different when sulphur enters into chemical combina- 
 tion exerting chemical attraction, for instance, when it burns; this 
 means when it combines with the oxygen of the atmospheric air. In 
 this case a new substance, a disagreeably smelling gas, a compound of 
 oxygen and sulphur, is formed. 
 
 It is^ consequently a complete change in the properties of matter 
 which follows the action of true chemical attraction ; we might define 
 affinity to be a force by which elements unite and new substances are 
 generated. 
 
 It should be noted that affinity does not really explain why chem- 
 ical union takes place, why an attraction between elements exists. 
 It is merely a term that has come into use to express a fact that can 
 be observed ; namely, that elements do unite, but why they do so no 
 one knows. Likewise no one knows why fhe earth attracts bodies, 
 although we say it is due to gravitation. This is simply equivalent 
 to saving that an attractive force exists between the earth and bodies 
 upon it, a fact which anyone can observe. But no one knows why 
 this force exists or its nature. 
 
 6. LAWS AND THEORIES OF CHEMISTRY. 1 
 
 Law of the constancy of composition. This law, also known 
 as the law of definite proportions, was the first ever recognized in 
 chemical science ; it was discovered toward the close of the 18th 
 century, and may be stated thus : A definite compound always contains 
 the same elements in the same proportion; or, in other words, All chemi- 
 cal compounds are definite in their nature and in their composition. 
 
 To make this law perfectly understood, the difference between a 
 mechanical mixture and a chemical compound must be pointed out. 
 Two powders, for instance sugar and starch, may be mixed together 
 very intimately in a mortar, so that it seems impossible for the eye to 
 discover more than one body. But in looking at this powder with 
 the aid of a microscope, the particles of sugar as well as those of 
 
 1 The subject matters of chapters 6, 7, 8, and 9 are grouped together for convenience. It is 
 not intended that they should be taken up in lectures or class work at once after chapter 5, 
 nor in the exact order given here, but each instructor will introduce them in what, to him, 
 seems the most logical sequence. 
 
94 PRINCIPLES OF CHEMISTRY. 
 
 starch may be easily distinguished. The mixture thus produced is n 
 mechanical mixture of. molecule clusters. 
 
 It is somewhat different when two substances, for instance two 
 metals, are fused together, or when two gases or two liquids (oxygen 
 and nitrogen, water and alcohol) are mixed together, or when finally 
 a solid is dissolved in a liquid (sugar in water). In these instances 
 no separate particles can be discovered even by the microscope. The 
 mixtures thus produced are mixtures of molecules. Such mixtures 
 always exhibit properties intermediate between those of their constitu- 
 ents and in regular gradation according to the quantity of each one 
 present. The proportions in which substances may be mixed are 
 variable. 
 
 In a true chemical compound the proportions of the constituent 
 elements admit of no variation whatever ; it is not formed by the 
 mixing of molecules, but by the combination of molecules; the prop- 1 
 erties of a compound thus formed usually differ very widely from 
 those of the combining elements. 
 
 Powdered iron and powdered sulphur may be mixed together in many 
 different proportions. If such a mixture be heated until the sulphur becomes 
 liquid, the two elements, iron and sulphur, combine chemically, but they do so 
 in one proportion only, 56 parts by weight of iron combining with 32 parts by 
 weight of sulphur, to form 88 parts of sulphide of iron. If the two substances 
 are mixed together in any other proportion than the one mentioned, the excess 
 of one will be left uncornbined. 
 
 Law of multiple proportions. While two or more elements 
 may unite in certain definite proportions to give one definite com- 
 pound, it does not follow that, under other conditions, they may not 
 unite in other proportions to give another entirely different com- 
 pound, but still perfectly definite in its composition. Many such ex- 
 amples are known in chemistry. Copper unites with oxygen in two 
 proportions, forming two distinct oxides. Tin does the same. There 
 are four different compounds of the elements potassium, chlorine, and 
 oxygen, and nitrogen and oxygen unite in five different ways. In 
 1804 John Dalton, of England, by a study of such multiple com- 
 pounds, proposed the law of multiple proportions. He had studied 
 the composition of two gaseous compounds of carbon and hydrogen, 
 and found one (olefiant gas) to contain 6 parts of carbon to 1 part of 
 hydrogen, while the other (marsh gas) contained 6 parts of carbon 
 to 2 parts of hydrogen. Upon what seems now to be a slight basis, 
 Dalton put forth his law, which, however, has been verified by every 
 
LAWS AND THEORIES OF CHEMISTRY. 95 
 
 exact analysis since his time, and which is one of the most important 
 foundation-stones upon which the structure of chemical science is 
 reared. The law of multiple proportions maybe stated thus: If 
 tiro dements, A and B, are capable of uniting in several proportions, 
 the quantities of B which combine with a fixed quantity of A bear a 
 xitnple ratio to each other. 
 
 Besides the above illustrations of the law, several other examples 
 may be mentioned. Sulphur and oxygen unite in two proportions to 
 form two distinct compounds, one a gas known as sulphur dioxide, 
 the other a solid known as sulphur trioxide. In these the quantities 
 of oxygen, united with a fixed weight of sulphur, are in the ratio of 
 
 1 : 1 J or 2 : 3. There are two sulphides of iron, known respectively 
 as ferrous sulphide and pyrite ; in these the weights of sulphur 
 united with a fixed weight of iron are in the ratio of 1 : 2. The 
 phrase simple ratio, in the law, means in the ratio of small whole 
 numbers. This feature of the law is strikingly illustrated in the 
 case of the four compounds containing potassium, chlorine, and 
 oxygen, in which the variable weights of oxygen united with fixed 
 weights of potassium and chlorine are in the ratio of 1:2:3:4; 
 also in the case of the five compounds of nitrogen and oxygen, in 
 which the weights of oxygen united with a fixed weight of nitrogen 
 bear the ratio of 1 : 2 : 3 : 4 : 5. 
 
 Combining- weights of elements. The proportions in which any 
 two elements unite may be expressed by any two figures which stand 
 in the proper ratio. Thus we may say that water is made up of 
 hydrogen and oxygen in the proportions by weight of 1 to 8, or 
 
 2 to 16, or 5 to 40. Similarly we may state the composition of 
 ferrous sulphide as 7 parts of iron to 4 parts of sulphur, or 56 parts 
 of iron to 32 parts of sulphur. Expressing the composition of com- 
 pounds thus in a random manner, there seems to be no relationship 
 between the relative quantities with which the different elements 
 unite with one another. But upon closer inspection of the propor- 
 tions by weight in which the elements unite, it is found chat they can 
 be reduced to a system of figures which show a remarkable relation- 
 ship. It is found, purely from the results of analysis and inde- 
 pendently of any theory, that a certain figure can be assigned to each 
 element, which has the remarkable property that it or a simple mul- 
 tiple of it expresses the relative proportion by weight in which that 
 element unites with the other elements. Chemists soon became 
 aware of the fact that hydrogen is the lightest of all known matter 
 
96 PRINCIPLES OF CHEMISTRY. 
 
 and also that it enters into union with other elements in the smallest 
 proportions. Hence in establishing the above-mentioned system of 
 numbers, one part by weight of hydrogen is taken as the standard of 
 reference, which offers the advantage that none of the figures is less 
 than unity. Let us illustrate by a few examples: One part of 
 hydrogen unites with 35.18 parts of chlorine, 35.18 parts of chlorine 
 unite with 38.82 parts of potassium, 2 X 38.82 parts of potassium 
 unite with 15.88 parts of oxygen. But 2x1 parts of hydrogen also 
 unite with 15.88 parts of oxygen. Also 15.88 parts of oxygen unite 
 with 64.91 parts of zinc, and 64.91 parts of zinc unite with 2 X 35.18 
 parts of chlorine. Thus we see that the figures in these instances are 
 reciprocally related, and the same is true for the figures assigned to 
 all the other elements. This system of figures is called combining 
 weights, and has a deep significance, which will appear clearer when 
 the atomic theory is discussed. 
 
 Atomic theory. One of the objects of men of science, besides 
 experimenting and observing facts and laws, is to determine causes^ 
 that is, to furnish an answer to the question, Why do things take 
 place as they do? If the senses, even when fortified with delicate 
 instruments, are not sufficiently refined to perceive the causes, 
 the philosopher, with the aid of his reasoning faculties, tries to 
 imagine a cause which will account in the most satisfactory manner 
 for what he observes. Such an imagined cause is called an hypothe- 
 sis or theory. For example, to account for the uniform behavior of 
 all gases as summed up in the Laws of Boyle, Charles, and Avogadro, 
 it was imagined that the nature of gases is that they are made up of 
 exceedingly minute particles in motion, acting as elastic bits of 
 matter and with practically no cohesion between them. This is 
 known as the kinetic-molecular theory of gases, and from it all the 
 behaviors of gases can be deduced mathematically. We may never 
 be able to actually see a gas particle, nevertheless we are willing to 
 accept that it exists as long as the hypothesis accounts satisfactorily 
 for what is observed. 
 
 There must be some reason for the chemical behavior of the 
 elements as set forth in the Laws of Definite and Multiple Propor- 
 tions and the fact that the elements unite in proportions represented 
 in the system of figures called combining weights. This cause must 
 lie in the constitution or physical make-up of matter. Reflection 
 upon the constitution of matter is not peculiar to modern science, for 
 the ancients had their conceptions, and some (Democritus, Lucretius) 
 
LAWS AND THEORIES OF CHEMISTRY. 97 
 
 advocated a theory of atoms. But the views of the ancients were 
 speculative and had no physical basis resting upon experiments, and 
 therefore were of no service to science. It was not until 1804 that a 
 theory or conception of matter was proposed by John Dalton, of 
 England, that had the merits of being capable of being put to tests 
 and from which deductions could be made that lent themselves to ex- 
 perimental verification. Dalton's atomic theory holds that (1) elements 
 arc made up of inconceivably small particles which are indivisible in 
 chemical actions and called atoms (from the Greek dro//oc, uncut, or 
 not yet divided) ; (2) the atoms not only have definite weights, but 
 the atoms of any one element have the same weight, which is differ- 
 ent from the weight of the atoms of some other element ; (3) when 
 the elements unite chemically, the action takes place between the 
 atoms. If we assume this theory to be correct and argue from it as 
 a basis, w can deduce the laws of definite proportions and multiple 
 proportions. Let us suppose that two certain elements, A and B, 
 unite, and the union is of the simplest kind possible, that is, in each 
 instance an atom of A is united with an atom of B. No matter what 
 the mass of the resulting product may be, whether an ounce, pound, 
 or ton, the whole chemical action is simply a repetition throughout 
 the mass of what might be called the unit action, that is, the union 
 of one atom of A with one atom of B. Hence the ratio between 
 the weights of the elements in the resulting compound, that is, its 
 composition, must be the same as the ratio between the weights of 
 the aton? of A and the atom of B. But the weights of these atoms 
 arc definite and constant, hence the composition of the compound 
 must be constant, or, in other words, the compound is an illustration 
 of the law of definite proportions. By a simple extension of the 
 above argument, the law of multiple proportions may be deduced. 
 The theory also accounts for the fact that if two elements are brought 
 together in other than certain proportions, say 56 parts of iron to 32 
 parts of sulphur, after union has taken place, part of the one or the 
 other element is found uncombined. It is easy to see, too, that, if 
 the theory is correct, the elements ought to combine according to a 
 system of figures such as were discussed above as combining weights, 
 for these weights are bound to be proportional to the weight of atoms, 
 which are definite. The atomic theory has been found in accord with 
 the facts of chemistry for a century or more, and we are justified in 
 accepting it, although we cannot prove absolutely the existence of 
 atoms. 
 
 7 
 
'98 PRINCIPLES OF CHEMISTRY. 
 
 Atomic weight. If atoms exist, they must have weight, since 
 they are concrete masses of matter, and all matter is attracted by the 
 earth. But, of course, it is impossible to weigh single atoms, and we 
 have no knowledge of the absolute weight of an atom. It is possi- 
 ble, however, to determine the relative weights of the atoms, that is, 
 how many times heavier one atom is than another. How this is done 
 will be briefly indicated in the next chapter. In any process of 
 weighing, we adopt a unit with which to make a comparison. For 
 example, in commerce we have a mass of iron which is called a 
 pound, and we say a body weighs so many times the mass of iron, or 
 so many pounds. We proceed similarly in the case of atomic 
 weights. We use the weight of an atom of one element as the unit, 
 and compare the weight of the atoms of the other elements with it. 
 The thing to decide is, Which atom shall be chosen as the unit 
 weight ? As was said in discussing combining weights, hydrogen is 
 the lightest known substance, and it unites with other elements in the 
 smallest proportions, hence its atom is chosen as the unit weight. 
 The figures assigned to the other elements as atomic weights simply 
 signify how many times heavier those atoms are than the atom of 
 hydrogen. In other words, the atomic weights are nothing more 
 than ratios. On the page preceding the Index is a table of the ele- 
 ments, with symbols and atomic weights. 
 
 Atoms and molecules. In Section I, on Physics, we learned that 
 all matter is made up of exceedingly minute particles, called mole- 
 cules, and, from a chemical study of matter, we are led to believe 
 that there is another kind of small particle, the atom. The atoms 
 unite in chemical action and form the larger masses called molecules. 
 The molecules of compounds consist of atoms of different kinds. 
 The elements also, like any kind of matter, consist of molecules, 
 which evidently must be made up of atoms of the same kind. There 
 are a few exceptional elements of which the molecule consists of only 
 one atom, that is, the molecule and atom of these are identical. The 
 atoms of an element have the power of uniting not only with atoms 
 of a different kind, but also with themselves, to form molecules of 
 the element. The present conception as to atoms may be summed 
 up in the following definition : "Atoms are the indivisible constitu- 
 ents of molecules. They are the smallest particles of the elements 
 that take part in chemical reactions, and are, for the greater part, in- 
 capable of existence in the free state, being generally found in com- 
 bination with other atoms, either of the same kind 'or of different 
 kinds" (Remsen). 
 
LAWS AND THEORIES OF CHEMISTRY. 99 
 
 We may define molecules as the smallest particles of matter that 
 can exist in the free state and still retain all the properties of the 
 substance to which they belong. If we divide the molecule, we 
 destroy the properties of the substance as we know it in the free state. 
 
 Chemical symbols. For reasons to be better understood hereafter, 
 chemists designate each element by a symbol, and the first or first two 
 letters of the Latin name of the element have generally been selected. 
 Thus, the symbol of hydrogen is H, of oxygen O, of mercury Hg 
 (from hydrargyrum), of sulphur S, etc. These symbols designate, 
 moreover, not only the elements, but one atom of these elements. 
 For instance : O not only signifies oxygen, but one atom or 15.88 parts 
 by weight of oxygen ; and Hg, one atom or 198.5 parts by weight of 
 mercury. 
 
 Symbols or formulas of compounds. By suitable experiments 
 it is possible for the chemist to determine not only the kinds of ele- 
 ments in a compound and their proportions, but also how many atoms 
 are in a molecule of the substance. For the sake of economy of 
 time and space and to give a better insight into their nature, sub- 
 stances are represented by formulas, which is a shorthand way of 
 telling what would require many words. A formula primarily rep- 
 resents the composition of a molecule, but as any quantity of a sub- 
 stance is simply the sum of a great multitude of molecules all. alike, 
 the formula, in a broader sense, stands for the substance itself. Thus 
 we say HgO is mercuric oxide, although it shows the composition of 
 a molecule of the oxide, namely, that it consists of one atom of mer- 
 cury and one atom of oxygen. 
 
 The formulas are formed by writing the symbols of the constituent 
 elements side by side, and the number of atoms of each element, 
 when more than one atom is present, is represented by a figure below 
 and to the right of the symbol of the element ; thus H 2 O means that 
 a molecule of water consists of two atoms of hydrogen and one atom 
 of oxygen ; CO 2 means that the carbon dioxide molecule consists of 
 one atom of carbon and two atoms of oxygen. A number placed before 
 a formula signifies so many molecules, thus 2H 2 O means two mole- 
 cules of water. As the formulas represent the size of the molecules, 
 they are called molecular formulas, and the sum of the atomic weights 
 of all the atoms composing the molecules is called the molecular 
 weight, which shows how many times heavier the molecule is than an 
 atom of hydrogen. 
 
100 PRINCIPLES OF CHEMISTRY. 
 
 To establish a molecular formula requires a careful quantitative determina- 
 tion of the proportions of the constituents of a compound; conversely, if we 
 know the molecular formula of a compound, we can calculate from it the rela- 
 tive quantities of the elements, or the percentage composition of the com- 
 pound. Also, if we know the formula, and the weight of one constituent, we 
 can calculate the weight of the other constituents, and the total weight of the 
 compound. Let us consider the red oxide of mercury, which has the molec- 
 ular formula, HgO. In the molecule there is an atom of mercury weighing 
 198.5 times as much as an atom of hydrogen, and an atom of oxygen weighing 
 15.88 times as much as an atom of hydrogen. It is evident that the weights 
 of the mercury and oxygen in a molecule are to each other as 198.5 : 15.88. 
 What is true of one molecule must be true of any number of molecules, that 
 is, of any quantity of oxide of mercury; hence we can conclude that in the 
 oxide there are 198.5 parts of mercury to every 15.88 parts of oxygen, making 
 198.5 + 15.88 = 214.38 parts of oxide. To calculate the percentage composi- 
 tion, or parts per hundred, we use the proportions, 
 
 214.38 HgO : 198.5 Hg : : 100 HgO : x Hg and 
 214.38 HgO : 15.88 O : : 100 HgO : x O. 
 
 Of course, in all cases where there are only two constituents, and we find the 
 per cent, of one, the other need not be calculated. 
 
 If we had a quantity of oxide of mercury that we knew contained, say, 30 
 parts of mercury, and we wanted to know the weight of the oxygen present or 
 the total weight of oxide, the following proportions would give us the answers: 
 
 198.5 Hg : 15.88 O : : 30 Hg : x O. 
 198.5 Hg : 214.38 HgO : : 30 Hg : x HgO. 
 
 We learn from the discussion above that the elements enter into combina- 
 tion in quantities represented by their atomic weights, or multiples of these, 
 to produce a quantity of compound represented by the molecular weight. 
 
 The law of chemical combination by volume, or the Law of 
 Gay-Lussac, may be stated as follows : When two or more gaseous 
 constituents combine chemically to form a gaseous compound, the volumes 
 of the individual constituents bear a simple relation to the volume of the 
 product. The law may be divided into two laws, thus : 1. Gases 
 combine by volume in a simple ratio. 2. The resulting volume of 
 the compound, when in the form of a gas, bears a simple ratio to the 
 volumes of the constituents. For instance : 1 volume of hydrogen 
 combines with 1 volume of chlorine, forming 2 volumes of hydro- 
 chloric acid gas ; 2 volumes of hydrogen combine with 1 volume of 
 oxygen, forming 2 volumes of water-vapor ; 3 volumes of hydrogen 
 combine with 1 volume of nitrogen, forming 2 volumes of ammonia. 
 
 If the different combining volumes of the gases mentioned are 
 
LAWS AND THEORIES OF CHPIMISTRY. 
 
 101 
 
 weighed, it will be found that there exists a simple relation between 
 these weights and the atomic or molecular weights of the elements. 
 
 For instance : Equal volumes of hydrogen and chlorine combine, 
 and the weights of these volumes are as 1:35.18, which numbers 
 represent also the atomic weights of the two elements. Two volumes 
 of hydrogen combine with one volume of oxygen, and the weights of 
 the volumes are as 1 : 7.94 or 2 : 15.88, the latter being the atomic 
 weight of oxygen. 
 
 2 Vol umes 
 
 Hydrochl j oric Acid gas. 
 W = ! 36.18 
 
 2 Vol ; umes 
 
 j 
 Water i -vapor 
 
 W = j 17.88 
 
 2 Vol j umes 
 Anna ; onia gas. 
 W = I 16.93 
 
 2 Vol umes 
 Sulphur ic acid gas. 
 Weight !=B 97.36 
 
 The above diagram shows the simple relation which exists between 
 combining volumes and atomic and molecular weights. It was, 
 besides other factors, the discovery of this relation that led to the 
 adoption of Avogadro's Law, which has been stated. (See Chapter 
 I., page 30.) 
 
 Taking the law of combination by volume and Avogadro's Law as a basis of 
 argument, we can prove directly in the case of some of the elementary gases 
 that their molecules consist of more than one atom. One volume of hydrogen 
 combines with one volume of chlorine to give two volumes of hydrochloric acid 
 gas. According to Avogadro's Law the volume of hydrogen and chlorine con- 
 tain the same number of molecules, and the two volumes of product formed 
 must contain twice as many molecules as does the volume of hydrogen or chlo- 
 
102 PRINCIPLES OF CHEMISTRY. 
 
 rine. Hence the molecules of hydrogen and chlorine must be divided to form 
 part of a product consisting of twice as many molecules, since each molecule of 
 hydrochloric acid contains some hydrogen and some chlorine. But if the mole- 
 cules of hydrogen and chlorine can be divided, they must consist of more than 
 one atom. Everything that is known about hydrochloric acid justifies the 
 assumption that its molecule contains one atom each of hydrogen and chlorine. 
 If this is true, it follows then that the molecule of hydrogen and of chlorine 
 contains two atoms. The same kind of argument in the case of the union of 
 hydrogen and oxygen to form water-vapor, leads to the conclusion that the 
 molecule of oxygen contains at least two atoms. In fact, from various experi- 
 ments and processes of reasoning, it has been established that the molecule of 
 nearly all the elements, in the gaseous state, consists of two atoms. 
 
 Theory (Law) of equivalents. Valence, or Quantivalence. 
 When one element replaces another element in a compound, the 
 quantities of the two elements are said to be equivalent to each other, 
 and according to the law of equivalents the replacement of elements 
 one by another takes place always in definite proportions. Formerly 
 it was believed that the atoms of all elements were equivalent one 
 with another ; accordingly, atomic weights were frequently designated 
 as equivalent weights. 
 
 This view, however, is not correct, as it ir> found that one atom of 
 one element frequently displaces two or more atoms of another 
 element. This fact, as well as other considerations, has led to the 
 assumption of the quantivalence of atoms. This property will be 
 understood best by selecting for consideration a few compounds of 
 different elements with hydrogen. 
 
 i. ii. m. iv. 
 
 HCl H 2 H 3 N H,C 
 
 HBr H 2 S H 3 As H 4 Si 
 
 HI H 2 Se H 3 P 
 
 We see here that Cl, Br, and I combine with H in the proportion 
 of atom for atom ; O, S, Se combine with H in the proportion of 2 
 atoms of hydrogen for 1 atom of the other element ; N, As, P com- 
 bine with 3; C and Si with 4 atoms of hydrogen. 
 
 Moreover, it has been found that the compounds mentioned in 
 column I. are the only ones which can be formed by the union of 
 the elements Cl, Br, and I with H. They invariably combine in this 
 proportion only. Other elements show a similar behavior. For 
 instance, the metal sodium combines with chlorine or bromine in one 
 proportion only, forming the compound Nad or NaBr. 
 
 Looking at columns II., III., and IV., we see that the elements 
 mentioned there combine with 2, 3, and 4 atoms of hydrogen, 
 respectively. It is evident, therefore, that there must be some pecu- 
 
LAWS AND THEORIES OF CHEMISTRY. 103 
 
 liarity in the power of attraction of different elements toward other 
 elements, and to this property of the atoms of elements of holding 
 in combination one, two, three, four, or more atoms of other ele- 
 ments the name atomicity, quantivalence, or simply valence, has been 
 given. 
 
 According to this theory of the valence of atoms, we distinguish 
 univalent, bivalent, trivalent, quadrivalent, quinquivalent, sexivalent, 
 and septivalent elements. All elements which combine with hydro- 
 gen in the proportion of one atom to one atom are univalent, as, for 
 instance, Cl, Br, I, F, and all elements which combine with these in 
 but one proportion, that is, atom with atom, bear the same valence, 
 or are also univalent, as, for instance, Na, K, Ag, etc. 
 
 Those elements which combine with hydrogen or other univalent 
 elements in the proportion of one atom to two atoms are bivalent, 
 such as O, S, Se. 
 
 Trivalent and quadrivalent elements are those the atoms of which 
 combine with 3 or 4 atoms of hydrogen, respectively. Figuratively 
 speaking, we may say that the atoms of univalent elements have but 
 one, those of bivalent elements two, of trivalent elements three, of 
 quadrivalent elements four bonds or points of attraction, by means of 
 which they may attach themselves to other atoms. 
 
 Elementary atoms are often named according to their valence : 
 monads, diads, triads, tetrads, pentads, hexads, and heptads. 
 
 To indicate the valence of the elements frequently dots or numbers 
 are placed above the chemical symbols, thus H 1 , O u , N m , C mi or C iv . 
 
 The bonds are often graphically represented by lines, thus : 
 
 H-, -0-, -N-, -0- 
 
 It is needless to say that such representations are merely symbolical, 
 and express the view that atoms have a definite power to combine 
 with others. 
 
 When atoms combine with one another the bonds are said to be 
 satisfied, and it is graphically expressed thus : 
 
 I / 
 
 -N- 
 
 H Cl, H O H or O , H-N-H or N-H 
 
 XH \ H 
 
 While the valence of some elements is invariably the same under 
 all circumstances, other elements show a different valence (this means 
 a different combining power for other atoms) under different condi- 
 
104 PRINCIPLES OF CHEMISTRY. 
 
 tions. For instance : Phosphorus combines both with 3 and 5 atoms 
 of chlorine, forming the compounds PC1 3 and PC1 5 . As chlorine is 
 a univalent element, we have to assume that phosphorus has in one 
 case 3, in another case 5 points of attraction. Many similar instances 
 are known, and will be spoken of later. 
 
 An explanation which is sometimes given in regard to the variability of 
 the valence of atoms is the assumption that sometimes one or more of the 
 bonds of an atom unite with other bonds of the same atom. If, for instance, 
 in the quinquivalent phosphorus atom two bonds unite with one another a 
 trivalent atom will remain. 
 
 It is noticed that the valence of atoms in nearly all cases increases or di- 
 minishes by two, which could not be otherwise, if the explanation given be 
 correct. Thus chlorine, the valence of which generally is I., may also have a 
 valence equal to III., V., or VII., while sulphur shows a valence either of II., 
 IV., or VI. Atoms whose valence is even, as in the case of sulphur, are called 
 artiadu ; those whose valence is expressed in uneven numbers, as chlorine and 
 phosphorus, are called perissads. 
 
 While it is now being assumed that most of the elements possess more than 
 one valence, in consequence of the assumed power of bonds in the same atom 
 to saturate one another, in this book will be mentioned chiefly that valence 
 which the element seems to possess predominantly. 
 
 The doctrine of the valence of atoms has modified our views of the 
 equivalence of atoms. We now say that all atoms of a like valence 
 are equivalent to each other. The atoms of each univalent element 
 are equivalent to each other, and so of the atoms of any other valence, 
 but two atoms of a univalent element are equivalent to one atom of 
 a bivalent element, or two atoms of a bivalent element to one atom 
 of a quadrivalent element, etc. 
 
 QUESTIONS. Define a chemical change and state the various modes of 
 effecting it, with examples. Define element, compound, combination, and 
 decomposition. About how many elements exist? What is chemical energy? 
 Define exothermic and endothermic actions. What is chemical affinity and 
 how does it differ from other forces? State the law of constancy of composi- 
 tion. What is the distinction between a mixture and a chemical compound? 
 Give examples of each. State the law of multiple proportions. Give in full 
 Dalton's atomic theory and show how it accounts for the laws of combination. 
 What is the relation of atoms to molecules? Define atomic and molecular 
 weight. What atom is chosen as the unit of atomic weights, and why? What 
 are chemical symbols and what do they signify? Calculate the per cent, of 
 oxygen and hydrogen in water, H 2 O. What weight of carbon dioxide, CO,, 
 would result from 25 grammes of carbon? What regularity regarding volume 
 is noticed when gases combine? Define valence. What were considered for- 
 merly as equivalent quantities, and what are such at present? Mention some 
 univalent, bivalent, trivalent, and quadrivalent elements. What explanation 
 is offered for variable valence ? 
 
DETERMINATION OF ATOMIC WEIGHTS. 105 
 
 7. DETERMINATION OF ATOMIC AND MOLECULAR WEIGHTS. 1 
 
 Determination of atomic weights by chemical decomposition. 
 The great difficulties originally encountered in the determination of 
 atomic weights cannot well be described here. Consideration will be 
 given alone to the three principal methods at present in use. These 
 methods depend either on chemical action or on physical properties. 
 
 One of the chemical methods used for the determination of atomic 
 weights depends upon the determination of the proportions by weight in 
 which the element, the atomic weight of which is unknown, combines 
 with an element the atomic weight of which is known. For instance : 
 If in decomposing a substance we find it to contain in 72 parts by 
 weight, 16 parts by weight of oxygen 2 and 56 parts by weight of 
 another element, we have a right to assume the atomic weight of this 
 second element to be 56, provided, however, that the compound is 
 actually formed by the union of one atom of oxygen and one atom of 
 the other element. These 56 parts by weight might, however, repre- 
 sent 2, 3, or more atoms. If 56 represented 2 atoms, the atomic 
 weight would be but 28 ; if 4 atoms, 14. 
 
 As this mode of determination gives no clue to the number of 
 atoms present in the molecule, the results obtained are liable to be 
 incorrect. In fact, the atomic weights of a number of elements had 
 originally been determined incorrectly by using the above or similar 
 methods, and many of these old atomic weights had to be changed 
 (generally doubled) in order to obtain the correct numbers. 
 
 Thus, in examining water, it was found that it contained 8 parts 
 by weight of oxygen to 1 part of hydrogen, and the conclusion was 
 drawn that the atomic weight of oxygen was 8, and that the molecule 
 of water was formed by the union of one atom of hydrogen and one 
 atom of oxygen. It will be demonstrated below why we assume to- 
 day that the atomic weight of oxygen is 16, and that the molecule of 
 water is composed of 2 atoms of hydrogen and 1 of oxygen. 
 
 Another chemical method of determining atomic weights is the 
 replacement of hydrogen atoms in a known substance by the element 
 the atomic weight of which is to be determined. For instance : Hy- 
 drochloric acid is composed of one atom of chlorine weighing 35.2, 
 and one atom of hydrogen weighing 1, the molecular weight of hy- 
 drochloric acid being 36.2. If in this acid the hydrogen be replaced 
 by some other element, for instance by sodium, we are enabled to 
 determine the atomic weight of sodium by weighing its quantity and 
 
 1 The consideration of Chapter 7 should be postponed until the student has become famil- 
 iar with chemical phenomena generally. 
 
 2 For purposes of discussion, whole numbers are often used in place of exact atomic weights 
 when these contain decimals. 
 
106 PRINCIPLES OF CHEMISTRY. 
 
 that of the liberated hydrogen. Suppose that by the action of 36.2 
 grammes of hydrochloric acid on sodium, 1 gramme of hydrogen 
 was replaced by 23 grammes of sodium. In that case we would say 
 that the atomic weight of sodium is equal to 23. 
 
 The difficulty which was alluded to above exists also in this mode 
 of determination of atomic weights, viz., not knowing whether it 
 was actually one atom of sodium that replaced the one part of hy- 
 drogen, a doubt is left as to whether or not the determination is correct. 
 
 Determination of atomic weights by means of specific weights 
 of gases or vapors. It has been stated before that equal volumes of 
 gases contain, under like conditions, the same number of molecules 
 (no matter how few or many the atoms within the molecules may be), 
 and that the molecules of elements contain (in most cases) two atoms. 
 These facts give in themselves the necessary data for the determina- 
 tion of atomic weights. 
 
 For instance: If a certain volume of hydrogen is found to weigh 
 2 grammes, and an equal volume of some other gaseous element is 
 found to weigh 71 grammes, then the atomic weight of the latter 
 element must be 35.5, because 2 and 71 represent the relative weights 
 of the molecules of the two elements. Each molecule being com- 
 posed of 2 atoms, these molecular weights have to be divided by 2 in 
 order to find the atomic weights, which are, consequently, 1 and 35.5 
 respectively. 
 
 In comparing by this method oxygen with hydrogen, it is found 
 that equal volumes of these gases weigh 32 and 2 respectively, that 
 the atomic weight of oxygen is consequently 16, and not 8, as deter- 
 mined by chemical methods. 
 
 This mode of determining atomic weights may be applied to all 
 elements which are gases or which may without decomposition be 
 converted into gas. There are, however, elements which cannot be 
 volatilized, and in this case it becomes necessary to determine the 
 specific gravity of some gaseous compound of the element. The 
 element carbon itself has never been volatilized, but we know many 
 of its volatile compounds, and these may be used in the determina- 
 tion of its atomic weight. 
 
 Determination of atomic weights by specific heat. Specific 
 heat has been stated to be the quantity of heat required to raise the 
 temperature of a given weight of any substance a given number of 
 degrees, as compared with the quantity of heat required to raise the 
 temperature of the same weight of water the same number of degrees. 
 
DETERMINATION OF ATOMIC WEIGHTS. 107 
 
 In comparing atomic weights with the numbers expressing the spe- 
 cific heats, it is found that the higher the atomic weight the lower tHe 
 specific heat, and the lower the atomic weight the higher the specific 
 heat. This simple relation may be thus expressed : Atomic weights 
 are inversely proportional to the specific heats ; or the product of the 
 atomic weight multiplied by the specific heat is a constant quantity 
 for the elements examined. 
 
 Elements. Specific heat*. Atomic weights. Product of specific heal 
 
 (Water = 1 .) X atomic weight. 
 
 Lithium, 09408 7 6.59 
 
 Sodium, 0.2934 23 6.75 
 
 Sulphur, 2026 32 6 48 
 
 Zinc, 00956 65 6.22 
 
 Bromine (solid), 0.0843 79 6.66 
 
 Silver, 0.0570 107 6.10 
 
 Bismuth, 0.0308 209 644 
 
 An examination of this table will show this relation between 
 atomic weight and specific heat, and also that the product of atomic 
 weight multiplied by specific heat is equal to about 6.5. The varia- 
 tions noticed in this constant quantity of about 6.5 may be due to 
 errors made in the determinations of the specific heats, and subse- 
 quent determinations may cause a more absolute agreement. 
 
 However, the agreement is sufficiently close to justify the deduction 
 of a law which says : The atoms of all elements have exactly the same 
 capacity for heat. This law was first recognized by Dulong and Petit 
 in 1819, and is simply a generalization of the facts stated. 
 
 To show more clearly what is meant by saying that all atoms have 
 the same capacity for heat, we will select three elements to illustrate 
 this law. 
 
 If we take of lithium 7 grammes, of sulphur 32 grammes, of silver 
 107 grammes, we have of course in these quantities equal numbers of 
 atoms, because 7, 32, and 107 represent the atomic weights of these 
 elements. If we expose these stated quantities of the three elements to 
 the same action of heat, we shall find that the temperature increases 
 equally for all three substances that is to say, the same heat will be 
 required to raise 7 grammes of lithium 1, which is necessary to raise 
 either 32 grammes of sulphur or 107 grammes of silver 1. 
 
 The quantity of heat necessary to raise the atom of any element a 
 certain number of degrees is, consequently, the same. As heat is the 
 consequence of motion, the result of the facts stated may also be ex- 
 pressed by saying : It requires the same energy to cause different 
 atoms to vibrate with such a velocity as to acquire the same tempera- 
 ture, no matter whether these atoms be light or heavy. 
 
108 PRINCIPLES OF CHEMISTRY. 
 
 It is evident that these facts give us another means of determining 
 atomic weights, by simply dividing 6.5 by the specific heat of the ele- 
 ment. The specific heat of sulphur, for instance, has been found to be 
 0.2026. 6.5 divided by this number is 31.6, or nearly 32. Originally 
 the atomic weight of sulphur had been determined by chemical methods 
 to be 16, but its specific heat, as well as other properties, has shown 
 this number to be but one-half of the weight, 32, now adopted. 
 
 Tt may be mentioned that elements possess essentially the same 
 specific heat whether they exist in a free state or are in combination ; 
 this fact will, in many cases, be of use in the determination of atomic 
 weights. 
 
 Determination of molecular weights. From the statements 
 made regarding the determination of atomic weights, it is evident 
 that we may use a number of methods for determining molecular 
 weights, these methods being to some extent analogous to the former. 
 
 Thus we have methods which are based entirely on chemical analysis 
 or on chemical changes generally. If, for instance, the analysis of a 
 substance shows of calcium 40 per cent., of carbon 12 per cent., and 
 of oxygen 48 per cent., we have a right to assume that the molecule is 
 made up of 1 atom of calcium, 1 atom of carbon, and 3 atoms of 
 oxygen, as the atomic weights of these elements are 40, 12, and 16 
 approximately. The molecular weight in this case is 100, and the com- 
 position is expressed by the formula CaCO 3 , but the molecular weight 
 might be 200 and the correct formula Ca 2 C 2 O 6 . There are actually 
 substances which contain such multiples of atoms, as, for instance, the 
 compounds C 2 H 2 and C 6 H 6 , and as their percentage composition is 
 identical, analytical methods are insufficient to indicate the number 
 of atoms contained in these molecules. 
 
 The second method, based on Avogadro's law, is applicable to all 
 substances which are or can be converted into gases or vapors without 
 decomposition. Since equal volumes of all gases at the same temper- 
 ature and pressure contain the same number of molecules, the weights 
 of equal volumes of gases must bear the same ratio to one another as 
 the weights of the individual molecules. But the weights of mole- 
 cules are in the same ratio as the molecular weights. Hence we 
 deduce the following rule from Avogadro's Law : Densities of gases at 
 the same temperature and pressure are to each other as their molecular 
 weights. If we know the molecular weight of any gas and its 
 density, by comparing any other gas with it we can determine its molec- 
 ular weight. As we have seen, the molecule of hydrogen is known 
 to contain two atoms, that is, its molecular weight is 2, if we call the 
 
DETERMINATION OF ATOMIC WEIGHTS. 109 
 
 weight of its atom 1. Hydrogen is usually chosen for comparison 
 with other gases. Suppose it is desired to find the molecular weight 
 of oxygen. One liter of oxygen at C. and 760 mm. of pressure 
 weighs 1.429 grammes, one liter of hydrogen under the same conditions 
 weighs 0.08987 gramme. Hence by the proportion, 
 
 0.08987:1.429 : : 2:x, 
 
 x = 1 .429 X 2 -5- 0.08987 = 31.8, 
 
 that is, the molecular weight of oxygen is 31.8, or the molecule is 15.9 
 times heavier than the molecule of hydrogen. 
 
 If we call the density of hydrogen 1, and refer the densities of 
 other gases to this standard, then the figures indicate how many times 
 heavier the gases are than hydrogen under like conditions, or, what 
 comes to the same thing, how many times heavier the molecules of the 
 gases are than the molecule of hydrogen. Hence, a simple rule for 
 finding molecular weight is to multiply the density of a gas on the 
 hydrogen basis by 2. 
 
 Conversely, if we know the molecular weights of two gases, and 
 the density of one of them, we can calculate the density of the other 
 gas. The density of any gas is equal to the density of hydrogen 
 multiplied by half the molecular weight of the gas. 
 
 A third method, that of Raoult, is based upok the fact that the 
 freezing-point of a liquid is lowered to the same extent by dissolving 
 in it compounds in quantities proportional to their molecular weights. 
 For example : Water begins to solidify at 32 F. (0 C.), but by dis- 
 solving in it say 4 per cent, of its weight of a salt (the molecular weight 
 of which is known) the freezing-point is lowered, say 1 C. If, then, 
 another salt (the molecular weight of which is not known) be dissolved 
 in water, and it be found that to reduce the freezing-point 1 C. there 
 must be dissolved a quantity equal to 7 per cent, of the weight of the 
 
 QUESTIONS. What are the three principal methods used for the determina- 
 tion of atomic weights ? Why are chemical means not always sufficient to 
 determine atomic weights ? How can the specific gravity of elements in the 
 gaseous state be used for the determination of atomic weight? Describe a 
 method of the determination of atomic weight by chemical means. State one 
 of the reasons why the atomic weight of oxygen has been changed from 8 to 16. 
 What relation exists between atomic weight and specific heat? State the law 
 of Dulong and Petit. Suppose the specific heat of an element to be 0.1138, 
 what will its atomic weight be? Suppose the specific gravity of an elementary 
 gas to be 14, what will its atomic weight be? Suppose 214.24 grammes of an 
 element replace 2 grammes of hydrogen in 72.36 grammes of HC1, what will 
 the atomic weight of the element be? 
 
110 PRINCIPLES OF CHEMISTRY. 
 
 water used then are the molecular weights of the two salts to each 
 other as is 4 to 7. 
 
 In regard to this method of Raoult it should be stated that it is 
 applicable only to such substances as do not act chemically upon the 
 solvent used, and that the ratio of the lowering of the freezing-point 
 is not the same for all substances, but only for members of the same 
 class of substances. 
 
 8. CHEMICAL EQUATIONS. TYPES OF CHEMICAL CHANGE. 
 REVERSIBLE ACTIONS AND CHEMICAL EQUILIBRIUM. 
 MASS ACTION. ACIDS, BASES, SALTS. RADICAL. CONSTI- 
 TUTIONAL FORMULAS. 
 
 Chemical equations. We have seen that the composition of sub- 
 stances can be expressed by symbols or formulas, which show at a 
 glance the kind of elements and their proportions present in the sub- 
 stances. Similarly, a method of representing what takes place in a 
 chemical change concisely and in a way that can be quickly grasped 
 has been devised. This is done by means of chemical equations. 
 Such an equation is formed by writing the formulas of the substances 
 that react on the left of the sign of equality, and connecting them by 
 the sign +, and the formulas of the products of the reaction on the 
 right of the sign of equality, also connected by the -f sign. For 
 example, hydrochloric acid and silver nitrate mutually decompose 
 each other and give an insoluble white substance, silver chloride and 
 nitric acid. This may be represented thus, HC1 -f AgNO 3 = AgCl 
 -f HNO 3 . The + sign should be read and, and the = sign should be 
 read gives. A chemical equation has nothing in common with an 
 algebraic one, except its form. It cannot be factored, or in any way 
 be handled as an algebraic equation. It is simply a statement of facts 
 learned by experiment. Until we have learned beforehand the com- 
 position of the substances entering into chemical reaction and also of 
 the products formed, and the proportions involved, we have no basis 
 upon which we can legitimately write an equation. The unit of 
 chemical action is the molecule, and the chemical equations are intended 
 to show the action taking place between the molecules. Thus, in the 
 reaction above, one molecule of hydrochloric acid decomposes one 
 molecule of silver nitrate. We often, however, read an equation in a 
 broader and less definite manner, thus, in the above case, we say 
 hydrochloric acid decomposes silver nitrate and gives silver chloride 
 and nitric acid. When more than one molecule is represented, a 
 numeral is placed before the symbol. The symbols 2NaCl and Na 2 Cl 2 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. Ill 
 
 represent the same number of atoms and the same proportions by 
 wciuht of the elements, but they are quite different, for NaCl is the 
 actual size of the molecule, and 2NaCl stands for two molecules, while 
 Xa.,CU represents a molecule double the size of that of sodium chloride, 
 Na( -1, as actually known. Often in writing equations, for convenience 
 we represent elements in the atomic state, while in reality they exist 
 in the molecular state. The equations are true, however, as far as 
 proportions are concerned. For example, we represent the union of 
 hydrogen and oxygen to form water thus, H 2 + O = H 2 O, but to be 
 in keeping with the fact that molecules of hydrogen and oxygen are 
 really involved, we should write 2H 2 -|- O 2 = 2H 2 O. 
 
 Every correct chemical equation is correct mathematically also 
 i. e.y the sum of the atoms as well as that of the molecular weights of 
 the factors equals the sum of the atoms and that of the molecular 
 weights of the products respectively. For instance : Sodium car- 
 bonate and calcium chloride form calcium carbonate and sodium 
 chloride. Expressed in chemical equation we say : 
 
 NaaCOs + CaCl 2 = CaCO 3 + 2NaCl. 
 
 Sodium carbonate and calcium chloride are the factors, calcium car- 
 bonate and sodium chloride the products. Adding together the 
 molecular weights of the factors and those of the products we find 
 equal quantities, as follows : 
 
 2Na = 45.76 
 O=11.91 
 
 3O = 47.64 
 105.31 
 
 Ca = 39.80 
 2C1 = 70.36 
 
 -f "lioTe 
 
 Ca = 39.80 
 C = 11.91 
 3O = 47.64 
 
 2Na = 45.76 
 2C1 = 70.36 
 
 99.35 
 
 + 316.12 
 
 Chemical equations not only are used for representing chemical 
 changes, but also are the starting-point in all the chemical calcula- 
 tions in which the quantities of substances entering into chemical 
 actions, or the quantities of the product formed, are concerned. 
 
 The above calculation teaches, for instance, that 105.31 parts by 
 weight of sodium carbonate are acted upon by 110.16 parts by weight 
 of calcium chloride, and that 99.35 parts by weight of calcium car- 
 bonate and 116.12 parts by weight of sodium chloride are formed by 
 tins action. These data may, of course, be utilized to find how much 
 calcium chloride may be needed for the decomposition of one pound 
 or of any other definite weight of sodium carbonate ; or how much 
 of these two substances may be required to produce one hundred 
 pounds, or any other definite weight, of calcium carbonate. 
 
 While in many cases of chemical decomposition the change which is 
 
112 PRINCIPLES OF CHEMISTRY. 
 
 to take place cannot be foretold, but has to be studied experimentally, 
 there are other chemical changes which can be predicted with certainty. 
 This is more especially true in the case of the action of acids on 
 bases and the action of one salt on another salt. This will be easily 
 seen when the relationship between acids, bases, and salts is under- 
 stood. Among these classes of compounds the results can usually be 
 foretold, and there is little difficulty in representing the change by 
 the proper equation. In doing this it must be borne in mind that 
 equivalent quantities replace one another; that, for instance, two atoms of a 
 univalent element are required to replace one atom of a bivalent element, 
 as, for instance, in the case of the decomposition taking place between 
 potassium iodide and mercuric chloride, when two molecules of the 
 first are required to decompose one molecule of the second compound : 
 
 K I rr /Cl TJ- /I K Cl 
 
 K-I + Hg \Cl : Hg \I K-C1 
 or 
 
 2KI + HgCl 2 = HgI 2 + 2KC1. 
 
 Whenever the exchange of atoms takes place between univalent 
 and trivalent elements, three of the first are required for one of the 
 second, as in the case of the action of sodium hydroxide on bismuth 
 chloride : 
 
 Na OH /Cl /OH Na Cl 
 
 Na OH + Bi Cl == Bi OH + Na Cl 
 Na OH \C1 \OH Na Cl 
 
 or 
 
 3NaOH + BiCl 3 = Bi(OH) 3 + 3NaCl. 
 
 In the following examples of double decomposition an exchange 
 takes place between the atoms of metallic elements, or between the 
 metallic elements and the hydrogen. The student, in completing the 
 equations, has also to select the correct quantity, i. e., the correct 
 number of molecules of the factors required for the change. The 
 interrogation marks indicate that more than one atom or one molecule 
 of the substance is needed for the reaction. 
 
 Na' + H'Cl Cu"SO 4 + H/S = 
 
 H/S0 4 -f K'(?) Ba"Cl 2 + Na/SO 4 
 
 Ca" + H'Cl (?) = Na/C0 3 + H/SO 4 
 
 Fe" + H/S0 4 = Bi"'(N0 3 ) 3 + K'OH (?) = 
 
 H'Cl -f Ag'NOg = Al a /// (S0 4 ) 8 + K'OH (?) =r 
 
 Ca"Cl 2 +Ag'N0 3 (?)= A1/"(S0 4 ) S + Ca"(OH) 2 (?) = 
 
 Bi'^CL, + Ag'NOat?) = Fe 2 "'Cl 6 + Ag'NO 3 (?) = 
 
 Types of chemical change. There are four principal ways in 
 which chemical actions take place. These may be represented by the 
 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 113 
 
 following equations, in which the letters stand for elements or groups 
 of elements : 
 
 1. A -|- B = AB direct combination or addition. 
 
 2. (a) AB = A + B i 
 
 (6) ABC = AB -|- C > simple decomposition. 
 (c) ABC = AC f BCJ 
 
 3. AB + C =-- CB + A displacement, 
 
 4. AB -f- CD AD + CB double decomposition or metathesis. 
 
 The following concrete examples will serve to illustrate the above 
 types of change : 
 
 1. Mg -f O = MgO. 
 
 When magnesium metal is heated to the ignition point it unites 
 with oxygen of the air, and gives a white ash known as magnesium 
 oxide. 
 
 2. (a) HgO = Hg + O. 
 
 Mercuric oxide, when heated to a sufficient temperature, decom- 
 poses into its elements mercury and oxygen. 
 
 (6) KC1O 3 = KC1 + 30. 
 
 When potassium chlorate is heated sufficiently high and long it de- 
 composes into the compound potassium chloride and the element 
 oxygen. 
 
 (c) CaCO 3 = CaO + CO 2 . 
 
 When calcium carbonate is heated to redness it is decomposed into 
 two new compounds namely, calcium oxide and carbon dioxide. 
 
 3. Fe + 2HC1 = FeCl 2 + 2H. 
 
 When a solution of hydrochloric acid is poured upon some iron, a 
 brisk evolution of hydrogen gas takes place ; and a new compound, 
 ferrous chloride, remains in the solution. 
 
 Although in a sense there is a displacement of one element by 
 another in every chemical action between two substances in which 
 two new substances result, by custom the term displacement is used 
 in those cases where the element displaced is left in the free or uncom- 
 bined state. 
 
 4. HC1 + AgNO 3 == AgCl + HNO 3 . 
 
 When a solution of hydrochloric acid is added to a solution of 
 silver nitrate, silver chloride is obtained as a white precipitate, and 
 nitric acid is left in solution. This type of change, known as double 
 decomposition or metathesis, is one of the most frequently occurring 
 kinds of chemical change in analysis and chemical industry. 
 
 8 
 
114 PRINCIPLES OF CHEMISTRY. 
 
 Reversible actions and chemical equilibrium. Experimental study 
 has shown that in many instances a chemical action, when once started, runs 
 to completion, that is, continues until the substance, or one of two substances, 
 undergoing change is used up. For example, when a piece of magnesium is 
 ignited the action continues until all the metal is used up, or the oxygen in 
 the supply of air is exhausted. Moreover, this action cannot be reversed, that 
 is, made to proceed in the opposite manner, no matter how much heat, or what 
 degree of heat, available in the laboratory, we apply to the magnesium oxide. 
 In other words, we cannot decompose the latter into magnesium element and. 
 oxygen by heat alone. 
 
 On the other hand, there are many instances in which chemical action, 
 under a given set of conditions, is not complete, but proceeds to a certain point 
 beyond which the products formed tend to act in a reverse manner, and repro- 
 duce the original substance or substances. Such changes are known as revers- 
 ible actions, and evidently, while the conditions are maintained, the whole 
 chemical process comes apparently to a standstill. But in the light of the 
 kinetic-molecular theory of matter it is believed that action is constantly going 
 on, although there is no progress made in either direction. The forward action 
 of the system is counterbalanced by the reverse action which proceeds at the 
 same speed, and thus is produced a condition of seeming rest, or chemical equi- 
 librium. An example of equilibrium as a result of two equal and opposite 
 actions is the case of a liquid in a closed container. At a definite temperature, 
 the space above the liquid is saturated with its vapor which exerts a constant 
 pressure. Although there is apparent rest, molecules of the liquid are passing 
 off into the space above it, while vapor molecules are flying back into the 
 liquid. These opposite actions finally balance each other, and then the system 
 is in equilibrium. If the conditions are changed, for example, by a rise in 
 temperature, the equilibrium is disturbed, a readjustment and new equilibrium 
 follow, in which more vapor molecules exist in the space above the liquid, 
 and a higher vapor pressure is produced. 
 
 Reversible chemical actions are represented by equations which differ from 
 the ordinary chemical equations, in that the equality sign is replaced by two 
 oppositely directed arrows, thus : 
 * AB + CD 7=1 AD -f CB. 
 
 Such an equation indicates that the action takes place in two directions, for- 
 ward and backward, and when equilibrium has been reached as much material 
 continues to be transformed in one direction as in the reverse direction. 
 
 While in many cases the action is reversible, yet it runs far toward comple- 
 tion in one direction. This condition may be represented by making one of 
 the arrows heavier than the other, thus : 
 
 MN -f PR ;i MR + PN. 
 
 The following is a good example of a reversible chemical change. If finely 
 divided iron and water vapor be heated in a sealed glass tube so that none of 
 the products can escape, a state of equilibrium will result, in which four prod- 
 ucts exist in the tube namely, iron, iron oxide, water vapor, and hydrogen. 
 
 3Fe + 4H 2 O 7 Fe 3 O 4 -f 8H. 
 This means that at the equilibrium stage the hydrogen reduces the iron 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 115 
 
 oxide reversely as fast as the iron reduces the water vapor ill the forward 
 direction. 
 
 When the experiment is performed in the same manner as above, with iron 
 oxide and hydrogen sealed in the tube at the equilibrium point, the same kinds 
 of products exist as in the first case, thus : 
 
 Fe 3 O 4 + 8H Til 3Fe + 4H 2 O. 
 
 Evidently a necessary condition for maintaining a chemical equilibrium in 
 any reversible action is the keeping intact of all the factors taking part. If 
 one of the products of an action be removed from the field of action as fast as 
 it is formed, we might reasonably predict that the action would proceed to 
 completion in the direction made easiest by the removal of such product. This 
 is exactly what happens, as may be shown in the above instances. When steam 
 is passed over highly heated iron through an open tube, the action takes place 
 to completion, thus : 
 
 Fe 3 + 4H 2 = Fe 3 4 + H. 
 
 The hydrogen is swept out of the tube and away from contact with the iron 
 oxide by the current of steam. The action continues until all the iron is 
 exhausted. 
 
 Conversely, when hydrogen gas is passed over heated iron oxide in an open 
 tube, the action runs to completion reversely thus : 
 
 Fe 3 O 4 + 8H = 3Fe + 4H 2 O. 
 
 The current of hydrogen sweeps the water vapor (steam) out of the tube as fast 
 as it is produced. The action continues until all the iron oxide is exhausted 
 by conversion to elementary iron. 
 
 If one considered only the first action he would conclude that iron has a 
 greater affinity for oxygen than hydrogen has, whereas if he considered only 
 the second action, he would say that hydrogen has a greater affinity for oxygen 
 than iron has, which apparently is a contradiction. But both conclusions are 
 correct, depending on circumstances. In fact, in reversible actions affinity 
 plays a minor part in determining which direction a chemical change will 
 take, this being controlled in largest measure by the physical conditions of the 
 experiment, which have nothing to do with affinity. This is admirably shown 
 by the following example : When common salt (sodium chloride, NaCl) is dis- 
 solved in 20 per cent, aqueous solution of sulphuric acid (H 2 SO 4 ), nothing 
 apparently happens except solution of the salt. Yet a reversible action takes 
 place, thus : 
 
 2NaCl + H 2 SO 4 7=1 Na 2 SO 4 -f 2HC1. 
 
 Four products are present in solution in equilibrium. When, however, con- 
 centrated sulphuric acid, which is about 95 per cent., is -poured upon salt, a 
 brisk evolution of hydrochloric acid gas takes place, because of the fact that it 
 is nearly insoluble in concentrated sulphuric acid. One of the factors in the 
 equilibrium equation above is thus removed from the field of action, which 
 thus allows the action to go forward nearly to completion and leaves the'im- 
 pression that the sulphuric acid has a greater affinity for the metal sodium than 
 has the hydrochloric acid, or, as it is put sometimes in text-books, that sul- 
 phuric acid is a " stronger " acid than hydrochloric, which, in fact, is not true. 
 
116 PRINCIPLES OF CHEMISTRY. 
 
 On the other hand, when hydrochloric acid gas is passed into a saturated 
 aqueous solution of sodium sulphate until no more is absorbed, nearly all of 
 the sodium is precipitated as sodium chloride, because the latter is almost 
 insoluble in concentrated hydrochloric acid solution, and sulphuric acid is 
 liberated and remains in the solution. In this case one of the factors in the 
 above equilibrium equation is practically removed from the field of action by 
 precipitation, thus allowing the reverse action to proceed nearly to completion, 
 and leaving the impression that hydrochloric acid is a "stronger" acid than 
 sulphuric. 
 
 Mass action. The vigor and extent of a chemical action depends upon 
 the freedom with which the molecules can clash as well as upon the affinity 
 between substances. Hence it is found that chemical action is aided far better 
 in homogeneous mixtures, as when the substances are present in the gaseous 
 state or in solution. Such physical systems as gas arid solid, gas and liquid, 
 liquid and solid, solid and solid, offer only limited contact between molecules, 
 and, therefore, more or less impede chemical change. In homogeneous mix- 
 tures, in the case of reversible actions, the proportion of the substances changed 
 chemically is different in different cases. The range extends all the way from 
 slight change to nearly complete change. But in each individual case the 
 amount of transformation is found to depend upon the concentration of each 
 substance as well as upon the affinity between the substances. This is often 
 called the Law of Mass Action, which may be stated thus : The amount of a 
 chemical change taking place in a given lime will be dependent upon the molecular 
 concentration of each substance. 
 
 In chemical operations it is usually desirable to obtain one or other of the 
 products of a chemical change in as large a yield as possible. If the action 
 employed is a non-reversible one, little difficulty will be experienced in obtain- 
 ing a full yield. In reversible actions, according to the law of mass action, 
 the amount of the new product formed can be increased in two ways, either 
 (1) by increasing the concentration of one or the other of the reacting sub- 
 stances, or (2) by removing one or the other of the products formed. The 
 second method namely, the removal of one of the products of the action, thus 
 affecting the equilibrium of the system in such a way that the action tends 
 toward completion is the more effective way of increasing the yield. This is 
 most conveniently done by selecting such actions that automatically remove 
 one of the products of the system in the form of an escaping gas or an insol- 
 uble body (precipitate 1 ). 
 
 As instances of the removal of one of the products, and, therefore, more or 
 less complete action, may be mentioned the formation of all the hundreds of 
 insoluble metallic salts which are produced by the action of one salt solution 
 upon another salt solution, the first solution containing a metal which, with the 
 acid of the second solution, may form an insoluble compound, which is then 
 invariably produced as a precipitate. For instance: Calcium carbonate, 
 CaCO 3 , is insoluble ; if we bring together two solutions containing a soluble 
 calcium salt and a soluble carbonate, such as calcium chloride, CaCl 2 , and 
 sodium carbonate, Na 2 CO 3 , calcium carbonate is precipitated. 
 
 1 The term precipitate is used to designate an insoluble substance which separates by chem- 
 ical action in a liquid, while sediment is applied to the collection of insoluble matter that may 
 be floating in a liquid, and does not imply chemical action. 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 117 
 
 Examples of complete action because of the removal of one of the products 
 as a gas are: Action of any acid on any carbonate, whereby carbon dioxide 
 gas is liberated ; action of caustic alkalies, lime or magnesia, on ammonium 
 salts, whereby ammonia gas is liberated. 
 
 Acids. The many compounds formed by the union of elements 
 are so various in their nature, that no system of classification pro- 
 posed up to the present time can be called perfect. There are, how- 
 ever, a few groups or classes of compounds, the properties of which 
 are so well marked, that a substance belonging to either of them may 
 be easily recognized. These groups are the acids, bases, and neutral 
 substances. 
 
 The term acid is applied to those compounds of hydrogen with an 
 electro-negative element or group of elements which are character- 
 ized by the following properties : 
 
 1. The hydrogen present is replaceable by metals, the compound 
 thus formed being a salt. 
 
 2. They change the color of many organic substances. Thus, 
 litmus, a coloring-matter obtained from certain lichens, is changed 
 from blue to red. 
 
 3. They have (when soluble in water) usually an acid or sour taste. 
 
 The great majority of acids are the result of union between water and the 
 oxides of those elements which are devoid of characteristic metallic properties. 
 We might, therefore, classify non-metallic elements as acid-forming elements. 
 There are a few exceptional metals which form a series of oxides, some of 
 which, when united with water, give acids; for example, chromic acid, H 2 CrO 4 , 
 permanganic acid, HMnO 4 . The formation of acids from oxides is shown by 
 the following equations : 
 
 SO 3 -f H 2 = H 2 SO 4 . 
 
 Sulphur Sulphuric 
 
 trioxide. acid. 
 
 P 2 5 -f 3H 2 O : 2H 3 P0 4 . 
 
 Phosphorus Phosphoric 
 
 pentoxide. acid. 
 
 C0 2 + H 2 O = H 2 C0 3 . 
 
 Carbon Carbonic 
 
 dioxide. acid. 
 
 Evidently in the acids containing oxygen, often called oxyacids, the hydrogen 
 is derived from the water molecules with which the acidic oxides unite. Those 
 oxides which unite with water to give acids are called acidic oxides or acid 
 anhydrides. As was said before, the great majority of acidic oxides are derived 
 from the non-metals, but there are some oxides of the non-metals which do not 
 form acids, for example, carbon monoxide, CO, and nitrogen monoxide, N 7 O. 
 
 A few acids contain no oxygen, and these are sometimes called hydracids. 
 They have no corresponding oxides and are combinations of hydrogen with 
 non-metallic elements, or groups of elements called radicals. The principal 
 ones are hvdrochloric acid, HC1, hydrobromic acid, HBr, hydriodic acid, HI, 
 
118 PRINCIPLES OF CHEMISTRY. 
 
 hydrofluoric acid, HF, or H 2 F 2 , hydrogen sulphide, H 2 S, hydrocyanic acid, 
 H(CN>. 
 
 However much the acids may differ in certain properties, such as consist- 
 ency, that is, whether solid, liquid, or gas, solubility in water, degree of acid 
 taste and action on litmus paper, corrosiveness to organic matter, such as skin, 
 wood, cloth, etc., they are all alike in one respect, namely, in containing hy- 
 drogen which is separable from the rest of the molecule, and replaceable by 
 metals, either by direct action of a metal on the acid, as when zinc acts on a 
 solution of sulphuric or hydrochloric acid, or in a round-about way. There 
 seems to be a strong tendency to separation between the hydrogen and the rest 
 of the molecule of an acid which remains intact as a unit. 
 
 According to the number of hydrogen atoms replaceable by metals, we dis- 
 tinguish monobasic, dibasic, and tribasic acids. Hydrochloric acid, HC1, is a 
 monobasic ; sulphuric acid, H 2 SO 4 , is a dibasic ; phosphoric acid, H 3 PO 4 , is a 
 tribasic acid. 
 
 Many of the acids sold in trade, as well as the reagents used in the labora- 
 tory, are solutions of acids in water. It is customary to call these solutions 
 by the names given to the acids themselves. 
 
 Bases or basic substances show properties which are chemically 
 opposite to those of acids. As a general rule bases are compounds 
 of electro-positive elements (metals) with oxygen (oxides) or more 
 generally with oxygen and hydrogen (hydroxides). Thus, silver 
 oxide, Ag 2 O, and sodium hydroxide, NaOH, are basic substances. 
 Other properties characteristic of bases are : 
 
 1. When acted upon by acids, they form salts ; for instance, 
 when sodium hydroxide and nitric acid are brought together water 
 and the salt sodium nitrate are formed : 
 
 NaOH + HN0 3 = H 2 O + NaNO 3 . 
 
 2. They have (when soluble in water) an alkaline reaction, i. e., 
 they restore the color of organic substances when previously changed 
 by acids : for instance, that of litmus, from red to blue. 
 
 3. They have (when soluble in water) the taste of lye, or an alka- 
 line taste. 
 
 The term base was originally applied to the metallic oxides, because when 
 salts of the metals were highly heated they were decomposed, leaving a non- 
 volatile calx or ash, the oxide of the metal, while the acid radical of the salt 
 was driven off. Thus the metallic oxides were regarded as the base or stable 
 groundwork of the salts. In the present-day classification, metallic hydroxides 
 are called bases, but as the oxides bear such a close relationship to the hy- 
 droxides, in fact, many of them being converted into hydroxides in contact 
 with water, many authors also include metallic oxides in the class of bases. 
 The relationship between metallic oxides and hydroxides is well shown in the 
 case of quick-lime, calcium oxide. Nearly everyone is familiar with the 
 process of slaking lime by adding water to quick-lime. The action takes 
 place thus, CaO + H a O = Ca(OH) 2 . The slaked lime, Ca(OH) 2 , is a 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC 119 
 
 hydroxide of calcium. The relation might be made more striking by writing 
 the formula thus, CaO H 2 O. 
 
 Some oxides do not unite with water to form hydroxides, but, as far as they 
 are acted upon by acids, they give the same end product (a salt) as the hy- 
 droxides do, as may be illustrated in the following reactions : 
 
 ZnO '+ H 2 S0 4 == ZnSO 4 + H 2 O. 
 Zn(OH) 2 + H 2 SO 4 = ZnSO 4 + 2H 2 O. 
 
 It should be noted that one of the products that is always formed when an 
 acid acts on a metallic hydroxide, or oxide, is water. This is shown in the 
 above reactions. 
 
 The hydroxides evidently are compounds derived from water by the re- 
 placement of part of the hydrogen in the water molecule by metal, thus 
 leaving the radical, (OH), which is known as hydroxyl, in combination with 
 metal. Hence, these compounds are called hydroxides. In a few cases hy- 
 droxides can be obtained by the direct action of the metals on water, the dis- 
 placed hydrogen escaping as a gas. This seems to be good evidence of the 
 relationship between the hydroxides and water. Most metals, however, do not 
 act on water, and their hydroxides are obtained in an indirect way. (See 
 Remarks on Tests for Metals, in the chapter on Magnesium.) 
 
 There are some hydroxides of radicals which can unite with acids just as 
 the metallic hydroxides do, and these are also classed as basic substances. In 
 them the radical plays the part of a metal. 
 
 Most of the metallic oxides and hydroxides are practically insoluble in 
 water, and therefore have no appreciable action on litmus paper and no taste. 
 Hence, alkaline action and taste are not a sure criterion of a basic substance. 
 But the hydroxides insoluble in water can act on acids and replace their hy- 
 drogen by metal, just as the soluble hydroxides do. 
 
 The hydroxides differ very much in regard to specific properties, such as 
 solubility in water, color, taste, etc., but there is one feature common to all of 
 them, namely, the presence of the hydroxyl group, which is responsible for 
 the class properties upon which such compounds are classified as basic sub- 
 stances. 
 
 It should be noted that there appears to be a tendency to easy separation 
 between the metal and the hydroxyl radical in the bases, just as there is be- 
 tween the hydrogen and the acid radical in the case of acids. The significance 
 of these facts will appear when the Ionic Theory is discussed. 
 
 Neutralization is the term applied to the interaction between 
 acids and bases with the result that both acid and basic properties, 
 disappear i. e., are neutralized. 
 
 All substances which are acid in character contain hydrogen as 
 one of their constituents. This hydrogen can readily be replaced by 
 metals, for instance by magnesium, when hydrogen is liberated. 
 Not all substances containing hydrogen behave in this manner ; for 
 example, magnesium does not liberate hydrogen from petroleum, 
 olive oil, sugar, etc., which all contain hydrogen. Hence the hydro- 
 gen of acids must be in a peculiar condition. That it is this hydro- 
 
120 PRINCIPLES OF CHEMISTRY. 
 
 gen, and the peculiar condition in which it is present, which impart 
 to acids their peculiar properties, are demonstrated by the fact that the 
 acid properties disappear as soon as the hydrogen is replaced by a 
 metal. Thus, the acid characteristics of hydrochloric acid, HC1, 
 vanish when it is acted on by sodium, or by the basic substance 
 caustic soda (sodium hydroxide, NaOH), both of which cause a re- 
 placement of the acid hydrogen by sodium. These actions can be 
 represented by the equations : 
 
 HC1 -f Na NaCl + H. 
 
 HC1 + NaOH NaCl -f H 2 O. 
 
 In both cases sodium chloride, NaCl (common salt), is formed, which 
 possesses neither acid nor basic properties. 
 
 Neutral substances. All substances having neither acid nor basic 
 properties are neutral. Water, for instance, is a neutral substance, 
 having no acid or alkaline taste, and no action on red or blue litmus. 
 Many neutral substances, to some extent even water, appear to possess 
 the characteristic properties of both classes, acids and bases ; of neither 
 class, however, to a very great extent. 
 
 Salts. Salts are acids in which hydrogen has been replaced by 
 metals or by basic radicals. There are several general methods by 
 which salts may be obtained : 
 
 1. By the action of an acid on a metal. This is illustrated in the 
 preparation of hydrogen from sulphuric or hydrochloric acid and 
 
 zinc or iron. 
 
 Zn + H 2 S0 4 = ZnS0 4 + H 2 . 
 Fe + 2HC1 = FeCl 2 + H 2 . 
 
 2. By the action of an acid on an oxide or hydroxide of a metal. 
 This is of wider application than the previous method. 
 
 ZnO + H 2 SO 4 = ZnSO 4 + H 2 0. 
 MgO + 2HC1 = MgCl 2 -f H 2 O. 
 NaOH + HC1 = NaCl + H 2 O. 
 
 3. By the action of an acid on a salt of a volatile acid. This finds 
 most extensive and useful application in the case of carbonates, which 
 are decomposed by nearly all other acids, and are found ready-formed 
 in nature or can be easily made. 
 
 MgCO s + H. 2 S0 4 = MgS0 4 + H 2 + C0 2 . 
 CaC0 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 . 
 
 Other volatile acids whose salts are decomposed by acids are sulphur- 
 ous, nitrous, hydrogen sulphide, hydrocyanic, etc. The manufacture 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 121 
 
 of hydrochloric and nitric acids by the aid of concentrated sulphuric 
 acid is an example of the method, and large quantities of sodium 
 sulphate are obtained as a by-product for the market. 
 
 4. By the action of one salt upon another salt. This method is 
 chiefly used when one of the products is insoluble or very nearly so, 
 and is known as precipitation. Usually the insoluble product is the 
 desired one, but the soluble one may also be isolated. A great many 
 of the analytical reactions, called tests, fall under this method. 
 Nearly all carbonates and phosphates are obtained by precipitation. 
 
 CaCl 2 + Na 2 CO 3 = CaC0 3 + 2NaCl. 
 CaCl 2 + Na 2 HPO, = CaHP0 4 + 2NaCl. 
 
 Calcium carbonate and phosphate are precipitated and may be re- 
 moved. 
 
 An example of the use of the method to get the soluble product is 
 shown by the equation : 
 
 CuS0 4 + BaCl 2 = BaS0 4 + CuCl,. 
 
 A solution of copper chloride is obtained by filtering off the barium 
 sulphate. 
 
 In the case of certain salts it is simpler or more economic to 
 follow special methods, which may be seen under the respective salts. 
 Some of these salts are ferrous iodide, ammonium iodide, sodium 
 hypochlorite, iodide, and thiosulphate, potassium permanganate, 
 dichromate and chlorate, sodium carbonate, mercurous and mercuric 
 chloride, etc. 
 
 According to the number of hydrogen atoms replaced in an acid, 
 we distinguish normal and acid salts. A normal salt is one formed by 
 the replacement of all the replaceable hydrogen atoms of an acid. 
 For instance : Potassium chloride, KC1, potassium sulphate, K 2 SO 4 , 
 potassium phosphate, K 3 PO 4 . (As monobasic acids have but one atom 
 of hydrogen which can be replaced, they form normal salts only.) 
 
 Normal salts often have a neutral reaction to litmus, but they may 
 have an acid or even an alkaline reaction. 
 
 It is found that soluble normal salts derived from a weakly ioniz- 
 ing acid, as carbonic, boric, phosphoric, sulphurous, hypochlorous, 
 silicic, hydrogen sulphide, and a strongly ionizing base, as sodium 
 and potassium hydroxide, and some others, have an alkaline reaction, 
 while those derived from a strongly ionizing acid and a weakly ioniz- 
 ing base, as the hydroxide of many of the heavy metals, such as 
 Fe(OH) 2 , A1(OH) 3 , Cu(OH) 2 , etc., have an acid reaction. The reason 
 
122 PRINCIPLES OF CHEMISTRY. 
 
 for this is that such salts are partially decomposed or hydrolyzed by 
 water. Thus, in the case of ferrous sulphate, 
 
 FeS0 4 -f 2H 2 = Fe(OH) 2 + H 2 SO 4 , 
 
 the small quantity of free acid formed affects litmus-paper, Fe(OH) 2 
 being neutral. Sodium carbonate is acted on thus : 
 
 Na 2 C0 3 + H 2 = NaHC0 3 + NaOH, 
 
 the free alkali causes litmus to turn blue, while NaHCO 3 is neutral. 
 
 Acid salts are acids in which there has been replaced only a portion 
 of their replaceable hydrogen atoms. For instance : KHSO 4 , K 2 H PO 4 , 
 KH 2 PO 4 . While acid salts have generally an acid reaction to litmus, 
 there are many exceptions to this rule. Indeed, the reaction may be 
 neutral or even alkaline, as, for instance, in the case of the ordinary 
 sodium phosphate, Na 2 HPO 4 , which is slightly alkaline to litmus. 
 
 Basic salts are salts containing a higher proportion of a base than 
 is necessary for the formation of a normal salt. Instances are basic 
 mercuric sulphate, HgSO 4 .(HgO) 2 , basic lead nitrate, Pb(NO 3 ) 2 . 
 Pb(OH) 2 . According to modern views basic salts are looked upon 
 as derived from bases by replacement of part of their hydrogen by acid 
 radicals. In the base lead hydroxide, Pb(OH) 2 , one of the hydrogen 
 atoms may be replaced by the radical of nitric acid, when basic lead 
 
 nitrate, Pb<TT 3 ' is formed. 
 
 In bismuth hydroxide, Bi(OH) 3 , one, two, or three hydrogen atoms 
 may be replaced by nitric acid, when the salts Bi(^ /QTT\ 
 
 and Bi(NO 3 ) 3 are formed. The first two compounds are basic salts, 
 while the third one is the normal salt. 
 
 Double salts are salts formed by replacement of hydrogen in an 
 acid by more than one metal. For instance : Potassium-sodium sul- 
 phate, KNaSO 4 . 
 
 Residue, radical, or compound radical, are expressions for un- 
 saturated groups of atoms known to enter as a whole into different 
 compounds, but having no separate existence. For instance: The 
 bivalent oxygen combines with two atoms of the univalent hydrogen, 
 forming the saturated compound H 2 O, water. If we take from this 
 H 2 O one atom of H, there is left the group of atoms HO (generally 
 written OH), consisting of an atom of oxygen in which but one point 
 of attraction is actually saturated, the second one not being pro- 
 vided for. 
 
 This group, OH, is a residue or radical, and is known to enter into 
 
CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 123 
 
 many compounds ; it is, for instance, a constituent of all the different 
 hydroxides (formerly called hydrates), such as potassium hydroxide, 
 KOH, calcium hydroxide, Ca(OH) 2 , etc. 
 
 According to the number of points of attraction left unprovided 
 for in a radical, we distinguish univalent, bivalent, trivalent, and 
 quadrivalent radicals. 
 
 Carbon is a quadrivalent element forming with the univalent hy- 
 drogen the saturated compound CH 4 . By removal of one, two, or 
 three hydrogen atoms the radicals CH 3 ', CH/', CH'", are formed. 
 
 Constitutional or graphic formulas. Though it is impossible 
 to examine the structure of a molecule by means of a microscope, yet 
 we may obtain some information of the atomic arrangement within 
 the molecules by a study of the formation and decomposition which 
 they undergo under different conditions. 
 
 Such investigations lead to the conclusion that molecules are not 
 merely clusters of atoms held together irregularly, but that the 
 atoms are arranged systematically and occupy a definite position 
 within the molecules of each individual substance. 
 
 In order to represent figuratively our views regarding the atomic 
 arrangement the so-called constitutional or graphic formulas are often 
 used. Thus, while sulphuric acid is represented by the molecular 
 formula H 2 SO 4 , we may assign to it the graphic formula SO/'. (OH) 2 , 
 which indicates that sulphuric acid is made up of the bivalent radi- 
 cal SO 2 and of two univalent radicals OH. In order to give a yet 
 fuller expression of our views regarding the linkage of the atoms, sul- 
 phuric acid may be graphically represented thus : 
 
 O H 
 
 01 vv, 
 
 -H 
 
 QUESTIONS. What are chemical equations and how do they serve as a basis 
 for calculations? Mention the principal types of chemical change, with exam- 
 ples. Define reversible actions and chemical equilibrium. How may a revers- 
 ible action be made to run to completion in one direction? Give an example. 
 What is the law of mass action? Define an acid, and state the general proper? 
 ties of basic and neutral substances. By what means can they be recognized? 
 Distinguish between mono-, di-, and tri-basic acids. What are salts and how 
 are they formed? Define neutral, acid, and double salts. Explain the term 
 radical or residue. 
 
124 PRINCIPLES OF CHEMISTRY. 
 
 In these formulas we show that sulphur exerts the valence of six, 
 that four of its affinities are saturated by oxygen, while the two re- 
 maining are attached to two oxygen atoms, the unsaturated affinities 
 of which are satisfied by hydrogen. 
 
 9. GENERAL REMARKS REGARDING ELEMENTS. 
 
 Relative importance of different elements. Of the total 
 number of about seventy-six elements, comparatively few (about 
 one-fourth) are of great and general importance for the earth, and the 
 phenomena taking place upon it. These important elements form 
 the greater part of the mass of the solid portion of the earth, and of 
 the water and atmosphere, and of all animal and vegetable matter. 
 
 Another number of elements are of less importance, because either 
 they are not found in any large quantity, or do not take any active 
 or essential part in the formation of organic matter ; yet they are of 
 interest and importance on account of being used, in their elementary 
 state or in the form of different compounds, in every-day life for 
 various purposes. 
 
 A third number of elements are found in such minute quantities 
 in nature that they are almost exclusively of scientific interest. Even 
 the existence of some elements, the discovery of which has been 
 claimed, is doubtful. 
 
 The elements enumerated in column I. are those of great and gen- 
 eral interest ; in II. those claiming interest on account of the special 
 use made of them ; in III. those having scientific interest chiefly. 
 
 I. II. 
 
 Aluminum Antimony Iridiuin 
 
 Calcium Arsenic Lead 
 
 Carbon Barium Lithium 
 
 Chlorine Bismuth Manganese 
 
 Hydrogen Boron Mercury 
 
 Iron Bromine Molybdenum 
 
 Magnesium Cadmium Nickel 
 
 Nitrogen Cerium Platinum 
 
 Oxygen Chromium Radium 
 
 Phosphorus Cobalt Silver 
 
 Potassium Copper Strontium 
 
 Silicon Fluorine Tin 
 
 Sodium Gold Uranium 
 
 Sulphur Iodine Zinc 
 
GENERAL REMARKS REGARDING ELEMENTS. 125 
 III. 
 
 Argon 
 
 Neon 
 
 Thallium 
 
 Beryllium (Glucinum) 
 
 Osmium 
 
 Thorium 
 
 Caesium 
 
 Palladium 
 
 Thulium 
 
 Columbium (Niobium) 
 
 Praseodymium 
 
 Titanium 
 
 Erbium 
 
 Rhodium 
 
 Tungsten 
 
 Gadolinium 
 
 Rubidium 
 
 Vanadium 
 
 Gallium 
 
 Ruthenium 
 
 Xenon 
 
 Germanium 
 
 Samarium 
 
 Ytterbium 
 
 Helium 
 
 Scandium 
 
 Yttrium 
 
 Indium 
 
 Selenium 
 
 Zirconium 
 
 Krypton 
 
 Tantalum 
 
 
 Lanthanum 
 
 Tellurium 
 
 
 Neodymium 
 
 Terbium 
 
 
 Classification of elements may be based upon either physical or 
 chemical properties, or upon a consideration of both. A natural 
 classification of all elements is the one dividing them into two groups 
 of metals and non-rnetals. 
 
 Metals are all elements which have that peculiar lustre known as 
 metallic lustre ; which are good conductors of heat and electricity ; 
 which, in combination with oxygen, form compounds generally 
 showing basic properties ; and which are capable of replacing hy- 
 drogen in acids, thus forming salts. 
 
 Non-metals or metalloids are all elements not having the above- 
 mentioned properties. Their oxides in combination with water gen- 
 erally have acid properties. In all other respects the chemical and 
 physical properties of non-metals differ widely. Their number 
 amounts to 18, the other 58 elements being metals. 
 
 Natural groups of elements. Besides classifying all elements 
 into metals and non-metals, certain members of both classes exhibit 
 so much resemblance in their properties, that many of them have 
 been arranged into natural groups. The members of such a natural 
 group frequently show some connection between atomic weights and 
 properties. 
 
 Chlorine, 35.2 Sulphur, 31.8 Lithium, 7.0 Calcium, 39.8 
 Bromine, 79.3 Selenium, 78.6 Sodium, 22.9 Strontium, 86.9 
 Iodine, 125.9 Tellurium, 126.6 Potassium, 38.8 Barium, 136.4 
 
 Each three elements mentioned in the above four columns resemble 
 each other in many respects, forming a natural group. The relation 
 
126 PRINCIPLES OF CHEMISTRY. 
 
 between the atomic weights will hardly be suspected by looking at 
 the figures, but will be noticed at once by adding together the atomic 
 weights of the first and last elements and dividing this sum by 2, 
 when the atomic weights (very nearly, at least) of the middle mem- 
 bers of the series are obtained. Thus : 
 8S.2 + 125.9 _ go 55 . 31.8 + 126.6 __ 79 _ 2 . 7.0 + 38.8 = 22>g . 39.8 + 136.4 = g8 _ L 
 
 Mendelejeff's periodic law. 1 The relationship between atomic 
 weights and properties has been used for arranging all elements sys- 
 tematically in such a manner that the existing relation is clearly 
 pointed out. Of the various schemes proposed, the one arranged by 
 Mendelejeff may be selected as most suitable to show this relation. 
 
 Looking at Mendelejeff's table on page 128 it will be seen that all 
 the elements are arranged in the order of their atomic weights, and 
 that the latter increase gradually by only a unit or a few units. 
 Moreover, the arrangement is such that nine groups and twelve 
 series are formed. The remarkable features of this classification 
 may thus be stated : Elements which are more or less closely allied 
 in their physical and chemical properties are made to stand together 
 in a group, as may be seen by pointing out a few of the more gen- 
 erally known instances as found in the groups I., II., and VII., the 
 first one containing the alkali metals, the second, the metals of the 
 alkaline earths, the last the halogens. 
 
 There is, moreover, to be noticed a periodic repetition in the prop- 
 erties of the elements arranged in the horizontal lines from left to 
 right. Leaving out groups and VIII. for the present, we find 
 that the power of the elements to combine with oxygen atoms 
 increases regularly from the left to the right, while the power of the 
 elements to combine with hydrogen atoms increases from the right to 
 the left, as may be shown by the following instances : 
 
 I. II. III. IV. V. VI. VII. 
 
 N^O MgO A1 2 3 SiO 2 P 2 O 5 SO 3 Cl a O 7 
 
 Hydrogen compounds unknown SiH 4 PHs SH 2 C1H 
 
 The oxides on the left show strongly basic properties, as illustrated 
 by sodium oxide ; these basic properties become weaker in the second, 
 and still weaker in the third group ; the oxides of the fourth group 
 show either indifferent, or but slightly acid properties, which latter 
 increase gradually in the fifth, sixth, and seventh groups. 
 
 i The consideration of this law should be postponed until the student has become acquainted 
 with the larger number of important elements. 
 
GENERAL REMARKS REGARDING ELEMENTS. 127 
 
 While some elements show an exception, it may be stated that 
 most of the elements of group I. are univalent, of II. bivalent, of 
 III. trivalent, of IV. quadrivalent, of V. quinquivalent, of VI. 
 sexivalent, and of VII. septivalent. 
 
 Properties other than those above mentioned might be enumerated 
 in order to show the regular gradation which exists between the 
 members of the various series, but what has been pointed out will 
 suffice to prove that there exists a regular gradation in. the properties 
 of the elements belonging to the same series, and that the same change 
 is repeated in the other series, or that the changes in the properties of 
 elements are periodic. It is for this reason that a series of elements 
 is called a period (in reality a small period, in order to distinguish it 
 from a large period, an explanation of which term will be given 
 directly). 
 
 The 12 series or periods given in the following table show another 
 highly characteristic feature, which consists in the iact that the corre- 
 sponding members of the even (2, 4, 6, etc.) periods and of the uneven 
 (3, 5, 7, etc.) periods resemble each other more closely than the mem- 
 bers of the even periods resemble those of the uneven periods. Thus 
 the metals calcium, strontium, and barium, of the even periods, 4, 6, 
 and 8, resemble each other more closely than they resemble the metals 
 magnesium, zinc, and cadmium, of the uneven periods, 3, 5, and 7, the 
 latter metals again resembling each other greatly in many respects. 
 
 It is for this reason that in the table the elements belonging to one 
 group are not placed exactly underneath each other, but are divided 
 into two lines containing the members of even and uneven periods 
 separately, whereby the elements resembling each other most are 
 made to stand together. 
 
 In arranging the elements by the method indicated, it was found 
 that the elements mentioned in group VIII. could not be placed in 
 any of the 12 small periods, but that they had to be kept separately 
 in a group by themselves, three of these metals always forming aL 
 intermediate series following the even periods 4, 6, and 10. 
 
 An uneven and even series, together with an intermediate series, 
 form a large period, the number of elements contained in a complete 
 large period being, therefore, 8 + 8 + 3 = 19. 
 
 An apparently objectionable feature is the incompleteness of the 
 table, many places being left blank ; but it is this very point which 
 renders the table so highly interesting and valuable. 
 
 Mendelejeff, in arranging his scheme, claimed that the places left 
 blank belonged to elements not yet discovered, and he predicted not 
 only the existence of these as yet missing elements, but also described 
 
128 
 
 PRINCIPLES OF CHEMISTRY. 
 
 
 
 
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GENERAL REMARKS REGARDING ELEMENTS. 129 
 
 their properties. Fortunately his predictions have, in several cases, 
 been verified, a number of the missing elements having since been 
 discovered. Among them may be mentioned scandium, gallium, and 
 ycntianium. These elements not only fitted in the previously blank 
 spaces by virtue of their atomic weights, but their general properties 
 also assigned to them the places which they now occupy. 
 
 When the table was first arranged it did not show group 0. The 
 elements forming this group have all been discovered since the year 
 1894, and their discovery necessitated the addition of an extra group. 
 In order to avoid renumbering the previously known groups the new 
 group was designated by zero. 
 
 Another graphic representation of the periodic law is obtained by 
 arranging the elements according to the increase in their atomic 
 weights on a spiral line, as shown on the diagram (Fig. 36). 
 From the centre of the spiral extend 20 radii, and in placing the 
 elements on the intersections of the spiral and a radius three im- 
 portant facts are noticed, viz. : 1. The distances of the elements 
 from the centre of the spiral are proportionate (or nearly so) to 
 their atomic weights. 2. From left to right the elements, arranged 
 on the diametric lines, follow one another according to the periodic 
 grouping. 3. The elements belonging to the even series of one of 
 the groups are on one radius, while the elements belonging to the 
 uneven series of the same group find their position on the radius 
 opposite. For example, calcium, strontium, and barium, of the 
 even series 4, 6, and 8 of group II., are on a radius opposite the 
 one on which we find magnesium, zinc, and cadmium, of the uneven 
 series 3, 5, and 7 of group II. 
 
 Physical properties of elements. Most elements are, at the 
 ordinary temperature, solid substances, two are liquids (bromine and 
 mercury), and of the more important elements five are gases (oxy- 
 gen, hydrogen, nitrogen, chlorine, and fluorine). 
 
 Most, if not all, of the solid elements may be obtained in the crys- 
 tallized state; a few are amorphous and crystallized, or polymorphous. 
 The physical properties of many elements in these different states 
 differ widely. For instance : Carbon is known crystallized as diamond 
 and graphite, or amorphous as charcoal. The property of elements to 
 assume such different conditions is called allotropy, and the different 
 forms of an element are termed allotropic modifications. 
 
 Some of the gaseous elements are also capable of existing in allo- 
 tropic modifications For instance: Oxygen is known as such and as 
 ozone, the latter differing from the common oxygen both in its physi- 
 cal and chemical properties. The explanation given for this surprising 
 
130 
 
 PRINCIPLES OF CHEMISTRY. 
 
 fact, that one and the same element has different properties in certain 
 modifications, is, that either the molecules or the atoms within the 
 molecules are arranged differently. Ozone, for instance, has three 
 atoms of oxygen in the molecule, while the common oxygen molecule 
 contains but two atoms. 
 
 Most of the elements are tasteless and odorless ; a few, however, 
 have a distinct odor and taste, as, for instance, iodine and bromine. 
 
 FIG. 36. 
 
 fu~ 
 
 Diagram of periodic system in spiral form. 
 
 Relationship between elements and the compounds formed 
 by their union. The properties of the compounds formed by the 
 combination of elements are so various that it is next to impossible 
 to give any general rule by which they may be indicated. It may 
 
GENERAL REMARKS REGARDING ELEMENTS. 131 
 
 be said, however, that nearly all of the gaseous compounds contain 
 at least one gaseous element, and that solid elements, when combining 
 with each other, generally form solid substances, rarely liquids, and 
 never compounds showing the gaseous state at the ordinary tem- 
 perature. 
 
 Nomenclature. The chemical nomenclature of compound sub- 
 stances has undergone considerable changes within the last twenty- 
 five years. These changes were made in conformity with our present 
 views of the constitution of the compounds. 
 
 Whenever the syllable ide is used to replace the ending of a non- 
 metallic element it designates that this element has entered into com- 
 bination with another element or with a radical. Thus, we speak of 
 <>x/Vcs, sulphicfos, carbides, chlorides, etc., when referring to compounds 
 formed by the union of oxygen, sulphur, carbon, or chlorine with 
 another element or with a radical. 
 
 When two elements combine in one proportion only, little difficulty 
 is experienced in the formation of a name, as, for instance, in iodide 
 of potassium or potassium iodide, KI, chloride of sodium or sodium 
 chloride, NaCl. 
 
 When two elements combine in more than one proportion, the 
 syllables, mono, di, tri, tetra, and penta are frequently used to designate 
 the relative quantity of the elements. For instance : Carbon mon- 
 oxide, CO, carbon dioxide, CO 2 , phosphorus tfn'chloride, PC1 3 , nitrogen 
 t< '//-oxide, N 2 O 4 , phosphorus >entachloride, PC1 5 . 
 
 In many cases the syllables ous and ie are used to distinguish the 
 proportions in which two elements combine ; the syllable ous being 
 used for the simpler or lower, the syllable ic for the more complex or 
 higher form of combination. For instance : Phosphorous chloride, 
 PC1 3 , and phosphoric chloride, PC1 5 ; ferrous oxide, FeO, ferric 
 oxide, Fe 2 O 3 . 
 
 The syllable sesqui is used occasionally to indicate that a compound 
 contains one-half more of an element than another compound formed 
 from the same elements. Thus, ferric chloride, FeCl 3 , is sometimes 
 called sesgiiichloride of iron, as it contains one-half more of chlorine 
 than does ferrous chloride, FeCl 2 . 
 
 The syllables proto or sub and per have also been used as prefixes 
 to differentiate between compounds formed by the same elements. 
 For instance, mercurous chloride, HgCl, is called protochloMe or 
 sw6chloride, while mercuric chloride, HgCl 2 , is often designated as 
 jwchloride of mercury. 
 
 When two oxides of the same element ending in ous and ic form 
 
132 PRINCIPLES OF CHEMISTRY, 
 
 acids (by entering in combination with water), the same syllables are 
 used to distinguish these acids. Phosphor<n*s oxide, P 2 O 3 , forms 
 phosphoroits acid ; phosphoric oxide, P 2 O 5 , forms phosphoric acid. 
 
 The salts formed by these acids are distinguished by using the syl- 
 lables lie and ate. Phosphite of sodium is derived from phosphorous 
 acid, phosphate of sodium from phosphoric acid. Sulphites and sul- 
 phates are derived from sulphurous and sulphuric acid, respectively. 
 
 When an element forms more than two acids the syllables hypo and 
 per are often used to designate the nature of these acids, as also that 
 of their respective salts. Hypo is prefixed to the compound contain- 
 ing less oxygen than the ous acid ; and per is prefixed to the com- 
 pound containing more oxygen than the ic acid. For instance, hypo- 
 chlorous acid, HC1O ; chlorous acid, HC1O 2 ; chloric acid, HC1O< ; 
 perchloric acid, HC1O 4 . The salts formed from these acids are called 
 hypochlorites, chlorites, chlorates, and perchlorates. 
 
 According to the new nomenclature, the name of the metal precedes 
 that of the acid or acid radical in an acid. For instance, sodium 
 phosphite, instead of phosphite of sodium ; potassium sulphate, instead 
 of sulphate of potassium. The acids themselves are looked upon as 
 hydrogen salts, and are sometimes named accordingly : hydrogen 
 nitrate for nitric acid, hydrogen chloride for hydrochloric acid, etc. 
 
 When the number of elements and the number of atoms increase in 
 the molecule, the names become in most cases more complicated. The 
 rules applied to the formation of such complicated names will be 
 spoken of later. 
 
 How to study chemistry. In studying chemistry, the student 
 is advised to impress upon his memory five points regarding every 
 important element or compound. These points are : 
 
 1. Occurrence in nature. Whether in free or combined state; 
 whether in the air, water, or solid part of the earth. 
 
 2. Mode of preparation by artificial means. 
 
 3. Physical properties. State of aggregation and influence of heat 
 upon it ; color, odor, taste, solubility, etc. 
 
 4. Chemical properties. Atomic and molecular weight ; valence ; 
 amount of attraction toward other elements or compounds ; acid, 
 alkaline, or neutral reaction ; reactions by which it may be recog- 
 nized and distinguished from other substances. 
 
 5. Application and use made of it in e very-day life, in the arts, 
 manufactures, or medicine. 
 
 Of the most important elements and compounds, the history 
 
GENERAL REMARKS REGARDING ELEMENTS. 133 
 
 their discovery, and, occasionally, some special points of interest, 
 should be noticed also. 
 
 " All students having the facility for working in a chemical labora- 
 tory are strongly advised to make all those experiments and reactions 
 which will be mentioned in connection with the different substances 
 to be considered in this book. 
 
 By adopting this mode of studying chemistry the student will soon 
 acquire a fair knowledge of chemical facts, yet he might know little 
 of the science of chemistry. In order to acquire this latter knowl- 
 edge he should study not only facts, but also the relationship existing 
 between them and between the laws governing the phenomena con- 
 nected with these facts. It is by this method only that the science 
 of chemistry can be successfully mastered. 
 
 QUESTIONS. Why are not all the elements of equal importance? State the 
 physical and chemical properties of metals. How are metals distinguished 
 from non-metals ? What relation often exists between the atomic weights of 
 elements belonging to the same group? Explain the term allotropic modifica- 
 tion. Mention some elements capable of existing in allotropic modifications. 
 What relation exists between the properties of elements and the properties of 
 the compounds formed by their union ? In which cases are the syllables mono-, 
 di-, tri-, tetra-, and penta- used in chemical nomenclature? What use is made 
 of the syllables ous and ic, ite and ate, in distinguishing compounds from each 
 other? What are the principal features of the periodic law? 
 
III. 
 
 NON-METALS AND THEIR COMBINATIONS. 
 
 THE total number of the non-metals is about eighteen ; some of 
 them, such as selenium, tellurium, argon, helium, and a few others, 
 are of so little importance that they will be but briefly considered 
 in this book. 
 
 Symbols, atomic weights, and derivation of names. 
 
 Boron, B = 10.9. From borax, the substance from which boron was first 
 
 obtained. 
 
 Bromine, Br = 79.36. From the Greek fip&jios (bromos), stench, in allusion to 
 the intolerable odor. 
 
 Carbon, C = 11.91. From the Latin carbo, coal, which is chiefly carbon. 
 
 Chlorine, Cl = 35.18. From the Greek ^Awpdf (chloros), green, in allusion to its 
 green color. 
 
 Fluorine, F = 18.9. From fluorspar, the mineral calcium fluoride, used as flux 
 (fluo, to flow.) 
 
 Hydrogen, H = 1. From the Greek v6up (hudor), water, and -yewdu (gennao), 
 to generate. 
 
 Iodine, I = 125.9. From the Greek lav (ion), violet, referring to the color of 
 
 its vapors. 
 
 Nitrogen, N = 13.93. From the Greek virpov (nitron), nitre, and -yewdo (gen- 
 
 nao), to generate. 
 Oxygen, O =; 15.88. From the Greek ofvf (oxus), acid, and yevvdu (gennao), . 
 
 to generate. 
 Phosphorus, P = 30.77. From the Greek 0f (phos), light, and tfpetv (pherein), to 
 
 bear. 
 Silicon, Si = 28.2. From the Latin silex, flint, or silica, the oxide of silicon 
 
 Sulphur, S = 31.83. From sal, salt, and nvp (pur), fire, referring to the com- 
 bustible properties of sulphur. 
 
 135 
 
136 NON-METALS AND THEIR COMBINATIONS. 
 
 State of aggregation. 
 Under ordinary conditions the non-metals show the following states: 
 
 Gases. Liquids. Solids. 
 
 B. P. B. P. F. P. B. P. 
 
 Hydrogen, 253 C. Bromine, 64 C. Phosphorus, 44 C. 280 0. 
 
 Oxygen, 183 Iodine, 11 175 
 
 Nitrogen, 194 Sulphur, 114 400 
 
 Chlorine, - 33 Carbon, | Slightly volatile 
 
 Fluorine, 190 Boron, > in electric 
 
 Silicon, ) furnace. 
 
 Occurrence in nature. 
 
 a. In a free or combined state. 
 
 Carbon in coal, organic matter, carbon dioxide, carbonates. 
 Nitrogen in air, ammonia, nitrates, organic matter. 
 Oxygen in air, water, organic matter, most minerals. 
 Sulphur chiefly as sulphates and sulphides. 
 
 b. In combination only. 
 Boron in boric acid and borax. 
 
 Bromine in salt wells and sea-water as magnesium bromide, etc. 
 Chlorine as sodium chloride in sea-water, etc. 
 Fluorine as calcium fluoride, fluorspar. 
 Hydrogen in water and organic matter. 
 Iodine as iodides in sea-water. 
 
 Phosphorus as phosphate of calcium, iron, etc., in bones and rocks. 
 Silicon as silicic acid or silica, and in silicates. 
 
 Time of discovery. 
 
 Sulphur, ) Long known in the elementary state ; recognized as elements in the 
 
 Carbon, / latter part of the eighteenth century. 
 
 Phosphorus, 1669, by Brandt, of Germany. 
 
 Chlorine, 1774, by Scheele, of Sweden. 
 
 Nitrogen, 1772, by Kutherford, of England. 
 
 Oxygen, 1773, by Scheele, of Sweden ; 1774, by Priestley, of England. 
 
 Hydrogen, 1766, by Cavendish, of England. 
 
 Boron, 1808, by Gay-Lussac, of France. 
 
 Fluorine, 1810, by Ampere, of France 
 
 Iodine, 1812, by Courtois, of France. 
 
 Silicon, 1823, by Berzelius, of Sweden. 
 
 Valence. 1 
 
 Univalent. Bivalent. Trivalent or quinquivalent. Quadrivalent. 
 
 Hydrogen, Oxygen, Nitrogen, Carbon, 
 
 Chlorine, Sulphur. Boron, Silicon. 
 
 Bromine, Phosphorus. 
 
 Iodine, 
 Fluorine. 
 
 1 The valences here given are the ones generally exerted by the elements, but it will be 
 shown later that most of the elements may exhibit a valence differing from the ones here 
 mentioned. 
 
OXYGEN. 137 
 
 10. OXYGEN. 1 
 
 O" = 15.88. 
 
 History. Oxygen was discovered in the year 1773 by Scheele, in 
 Sweden, and one year later by Priestley, in England, independently 
 of each other ; its true nature was soon afterward recognized by La- 
 voisier, of France, who gave it the name oxygen, from the two Greek 
 words, oc^c (oxtis), acid, and ysvvda) (gennao), to produce or generate. 
 Oxygen means, consequently, generator of acids. 
 
 Occurrence in nature. There is no other element on our earth 
 present in so large a quantity as oxygen. It has been calculated that 
 not less than about one-third, possibly as much as 45 per cent., of the 
 total weight of our earth is made up of oxygen ; it is found in a free 
 or uncombined state in the atmosphere, of which it forms about one- 
 fifth of the weight. Water contains eight-ninths of its weight of 
 oxygen, and most of the rocks and different mineral constituents of 
 our earth contain oxygen in quantities varying from 30 to 50 per 
 cent. ; finally, it is found as one of the common constituents of most 
 animal and vegetable matters. 
 
 If the unknown interior of our earth should be similar in composition to the 
 solid crust of mineral constituents which have been analyzed, then the sub- 
 joined table will give approximately the proportions of those elements present 
 in the largest quantity. 
 
 Oxygen . . .45 parts. Calcium . . .4 parts. 
 
 Silicon . . . 28 " Magnesium . . 2 " 
 
 Aluminum . 8 " Sodium . . . 2 " 
 
 Iron . . . 6 " Potassium . . 2 " 
 
 Preparation. The oxides of the so-called noble metals (gold, 
 silver, mercury, platinum) are by heat easily decomposed into the 
 metal and oxygen : 
 
 HgO= Hg + O; 
 Ag,0=2Ag + O. 
 
 A more economical method of obtaining oxygen is the decomposi- 
 tion of potassium chlorate, KC1O 3 , into potassium chloride, KC1, 
 and oxygen by application of heat : 
 
 KC1O 3 = KC1 + 3O. 
 
 While the above formula represents the final result of the decomposition, it 
 1 Many instructors prefer to postpone the discussion of the laws of combination, atomic 
 theory, symbols, and chemical equations until after a few elements and compounds have been 
 studied as an introduction and foundation. If such a procedure is followed by those who use 
 this book, the equations in the chapters that may be taken up before the theoretical matters 
 are presented which make the equations intelligible, should, of course, be omitted. They 
 are given in each chapter for the sake of completeness and reference. 
 
138 NON-METALS AND THEIR COMBINATIONS. 
 
 takes place actually in two stages. At first potassium chlorate gives up but 
 one-fifth of its total oxygen, forming potassium chloride and perchlorate, 
 KC10 4 , thus : 
 
 5KC1O 3 = 3KC1O, + 2KC1 + 3O. 
 
 This part of the decomposition takes place at a comparatively low temper- 
 ature ; after it is complete, the temperature rises considerably and the decom- 
 position of the perchlorate begins : 
 
 KC1O 4 = KC1 + 4O. 
 
 If the potassium chlorate be mixed with 30-50 per cent, of man- 
 ganese dioxide, and this mixture be heated, the liberation of oxygen 
 takes place with greater facility and at a lower temperature than by 
 heating potassium chlorate alone. Apparently, the manganese dioxide 
 takes no active part in the decomposition, as its total amount is found 
 in an unaltered condition after all potassium chlorate has been decom- 
 posed by heat. A satisfactory explanation regarding this action of 
 manganese dioxide is yet wanting. 
 
 A third method is to heat to redness, in an iron vessel, manganese 
 dioxide (MnO 2 ), which suffers then a partial decomposition : 
 3MnO 2 = Mn g O 4 -f 2O. 
 
 In this case there is liberated but one-third of the total amount of 
 oxygen present, while two-thirds remain in combination with the 
 manganese. 
 
 Other methods of obtaining oxygen are : Decomposition of water by elec- 
 tricity, heating of dichromates, nitrates, barium dioxide, and other substances, 
 which evolve a portion of the oxygen contained in the molecules. 
 
 Heating a concentrated solution of bleaching powder with a small quantity 
 of a cobalt salt (cobaltous chloride) furnishes a liberal supply of oxygen, the 
 calcium hypochlorite of the bleaching powder being decomposed into calcium 
 chloride and oxygen : 
 
 Ca(ClO) 2 = CaCl 2 + 2O. 
 
 Oxygen may be obtained at the ordinary temperature by adding water to a 
 mixture of powdered potassium ferricyanide and barium dioxide, and also by 
 the decomposition of potassium permanganate and hydrogen dioxide in the 
 presence of dilute sulphuric acid. 
 
 A commercial method operated largely in England is Erin's process, which 
 consists in pumping purified air under pressure over barium oxide contained 
 in a tube and heated to about 700 C., whereby barium dioxide is formed. The 
 accumulated nitrogen of the air escapes by a valve from the end of the tube. 
 When formation of barium dioxide is complete, the air-supply is cut off and 
 the pump is reversed, thus producing a partial vacuum in the tube. Under 
 this condition, although the same temperature is maintained as before, the 
 
OXYGEN. 139 
 
 barium dioxide decomposes into barium oxide and oxygen, which latter is 
 pumped away and stored in tanks. Oxygen of about 96 per cent, is obtained. 
 The changes taking place in the two stages are represented thus : 
 
 BaO + O = BaO 2 ; 
 
 This process is a good example of the kind of change known as Reversible 
 Action (see page 114). When the dioxide is exhausted, the process is re- 
 peated. One kilogram of barium oxide yields about ten liters of oxygen at a 
 single operation. 
 
 The quantity of oxygen liberated from a given quantity of a substance may 
 be easily calculated from the atomic and molecular weights of the substance 
 or substances suffering decomposition. For instance : 100 pounds of oxygen 
 may be obtained from how many pounds of potassium chlorate, or from how 
 many pounds of manganese dioxide? (See page 100.) 
 
 The molecular weight of potassium chlorate is found by adding together 
 the weights of 1 atom of potassium = 38.86 + 1 atom of chlorine 35.18 + 3 
 atoms of oxygen = 47.64; total = 121.68. Every 121.68 parts by weight of 
 potassium chlorate liberate the weight of 3 atoms, or 47.64 parts by weight, of 
 oxygen. If 47.64 are obtained from 121.68, 100 are obtained from 255.4. 
 
 47.64 : 121.68 : : 100 : x 
 
 x = 255.4. 
 
 In a similar manner, it will be found that 815.7 pounds of manganese dioxide 
 are necessary to produce 100 pounds of oxygen. Mn0 2 = 54.6 -4- 31.76 = 86.36. 
 3Mn0 2 = 3 X 86.36 = 259.08. Every 259.08 parts furnish 2 x 15.88 = 31.76 
 parts of oxygen. 
 
 31.76 : 259.08 : : 100 : x 
 
 * = 815.7, 
 
 The density of a gas is the weight of 1 liter. To find what volume corre- 
 sponds to a given weight of a gas, divide the weight by the density. The den- 
 sity of oxygen is 1.429 grammes in 1 liter at C. and 760 mm. pressure. 
 Hence, under these conditions, 100 grammes of oxygen would measure 100 -*- 
 1.429 = 69.979 liters. (For method of calculating gas volumes under other than 
 standard conditions of temperature and pressure, see article on Gas Analysis.) 
 
 The densities of gases are generally given in books, but they can be calcu- 
 lated, if the molecular weights of the gases are known. The relation between 
 densities and molecular weights of gases is discussed on page 108. The density 
 of any gas is equal to the density of hydrogen multiplied by one-half the 
 molecular weight of the gas ; 1 liter of hydrogen at C. and 760 mm. pressure 
 weighs 0.08987 gramme, the molecular weight of oxygen is 31.76; hence 1 liter 
 of oxygen weighs 0.08987 X 15.88 = 1.427 grammes. 
 
 Experiment 1. Generate oxygen by heating a small quantity (about 
 grammes) of potassium chlorate in a dry flask of about 100 c.c. capacity, to 
 which, by means of a perforated cork, a bent glass tube has been attached, 
 which leads under the surface of water contained in a dish (Fig. 37). Collect 
 the gas by placing over the delivery-tube large test-tubes (or other suitable ves- 
 
140 
 
 NON-METALS AND THEIR COMBINATIONS. 
 
 sels) filled with water. Notice that a strip of wood, a wax candle, or any other 
 substance which burns in air. burns with greater energy in oxygen, and that 
 an extinguished taper, on which a spark yet remains, is rekindled when placed 
 in oxygen gas. Notice, also, the physical properties of the gas. If the decompo- 
 sition has been too rapid by using too large a flame, the gas will appear cloudy, 
 due to the dragging over of some of the contents of the flask by it. The cloud 
 will disappear upon standing. 
 
 CAUTION. In all experiments of this kind, where a vessel is filled wiih a hot gas, 
 the exit tube should be removed from water before removing the flame, to prevent water 
 from being drawn back into the vessel as the gas cools and contracts. 
 
 Experiment 2. In a porcelain crucible held in a pipe-stem triangle, place a 
 layer of potassium chlorate about J inch deep. Heat moderately at first until 
 
 Apparatus for generating oxygen. 
 
 frothing ceases, and then gradually to low red heat. Cool and dissolve the 
 residue in a little water in the crucible, warming to hasten solution. Taste the 
 solution. Does it taste like common salt (sodium chloride)? Compare with 
 the taste of potassium chlorate. Pour some of the solution into a test-tube and 
 add a few drops of a solution of silver nitrate. Do the same with a solution of 
 common salt. The white clotted substance, known as a precipitate, is silver 
 chloride, and is given by all soluble chlorides. Also add some silver nitrate 
 solution to a solution of a little potassium chlorate. Is any precipitate formed? 
 All chlorates are soluble. 
 
 Physical properties. Oxygen is a colorless, inodorous, tasteless 
 gas, slightly heavier than air. Under a pressure of 50 atmospheres, 
 and at a temperature of -118 C. (-180.4 F.) it condenses to a 
 transparent, pale-bluish liquid, which under ordinary atmospheric 
 pressure boils at -183 C. (-297.4 F.). Its absolute boiling-point, 
 above which it cannot be condensed to a liquid by any pressure, no 
 matter how high, is -118 C. (-180.4 F.). 
 
OXYGEN. 141 
 
 For practical, including medical, purposes oxygen is sold stored in 
 strong steel cylinders, the gas being condensed by a pressure, gen- 
 erally, of 225 pounds to about -fa of its volume. 
 
 The temperature above which a gas cannot be liquified by pressure is 
 known as its critical temperature. The failure of former attempts to liquefy 
 oxygen and a few other gases was due to the fact that, though an enormous 
 pressure was used, the gas was not brought to the critical temperature. 
 
 Oxygen is but sparingly soluble in water (about 3 volumes in 100 
 at common temperature). A liter of oxygen under 760 mm. pressure, 
 and at the temperature of C. (32 F.), weighs 1.429 grammes. 
 
 Chemical properties. The principal feature of oxygen is its great 
 affinity for almost all other elements, both metals and non-metals; 
 with nearly all of which it combines in a direct manner. The more 
 important elements with which oxygen does not combine directly are : 
 Cl, Br, I, F, Au, Ag, and Pt; but even with these it combines in- 
 directly, excepting F. 
 
 The act of combination between other substances and oxygen is 
 called oxidation, and the products formed, oxides. The large number 
 of oxides are divided usually into three groups, and distinguished as 
 basic oxides (sodium oxide, Na 2 O, calcium oxide, CaO), neutral oxides 
 (water, H 2 O, manganese dioxide, MnO 2 , lead dioxide, PbO 2 ), and 
 acid-forming or acidic oxides, also called anhydrides (carbon dioxide, 
 CO 2 , sulphur trioxide, SO 3 ). Whenever the heat generated by oxida- 
 tion (or by any other chemical action) is sufficient to cause the emis- 
 sion of light, the process is called combustion. Oxygen is the chief 
 supporter of all the ordinary phenomena of combustion. Substances 
 which burn in atmospheric air burn with greater facility in pure 
 oxygen. This property is taken advantage of to recognize and dis- 
 tinguish oxygen from most other gases. Processes of oxidation evolv- 
 ing no light are called slow combustion. An instance of slow combus- 
 tion is the combustion of the different organic substances in the living 
 animal, the oxygen being supplied by respiration. 
 
 In some cases the heat generated by the slow combustion of a sub- 
 stance may raise its temperature sufficiently high to cause ignition, 
 which is then called spontaneous combustion. Thus, greasy rags or wet 
 hay, when piled in heaps, may ignite spontaneously, because some oils 
 and damp hay undergo slow oxidation, which raises the temperature. 
 
 For a process of oxidation it is not absolutely necessary that free 
 oxygen be present. Many substances contain oxygen in such a form 
 of combination that they part with it easily when brought in contact 
 with substances having a greater affinity for it. Such substances are 
 
142 NON-METALS AND THEIR COMBINATIONS. 
 
 called oxidizing agents, as, for instance, nitric acid, potassium chlorate, 
 potassium permanganate, etc. 
 
 In all combustions we have at least two substances acting chemically upon 
 one another, which substances are generally spoken of as combustible bodies 
 and supporters of combustion. Illuminating gas is a combustible substance, 
 and oxygen a supporter of combustion ; but these terms are only relatively 
 correct, since oxygen may be caused to burn in illuminating gas, whereby it is 
 made to assume the position of a combustible substance, while illuminating gas 
 is the supporter of combustion. 
 
 While some substances, such as iron and phosphorus, undergo slow combus- 
 tion at the ordinary temperature, there is a certain degree of temperature, 
 characteristic of each substance, at which it inflames. This point is known as 
 kindling temperature, and varies widely in different substances. Zinc ethyl 
 ignites at the ordinary temperature, phosphorus at 50 C. (122 F.), sulphur at 
 about 450 C. (842 F.}, carbon at a red heat, and iron at a white heat. The 
 heat produced by the combustion is generally higher than the kindling tem- 
 perature, and it is for this reason that a substance continues to burn until it is 
 consumed, provided the supply of oxygen be not cut off, and the temperature 
 be not through some cause lowered below the kindling temperature. 
 
 The total amount of heat evolved during the combustion of a substance is 
 the same as that generated by the same substance when undergoing slow com- 
 bustion, but the intensity depends upon the time required for the oxidation. 
 A piece of iron may require years to combine with oxygen, and it may be 
 burned up in a few minutes ; yet the total heat generated in both cases is the 
 same, though we can notice and measure it in the first instance by most deli- 
 cate instruments only, while in the second it is very intense. 
 
 While heat is evolved when two or more elements combine chemically, heat 
 is absorbed when decomposition takes place. In fact, the quantities of heat 
 evolved and absorbed by combining and decomposing identical quantities of 
 matter are absolutely alike. Thus, heat is evolved when mercury and oxygen 
 combine, but the same quantity of heat .is absorbed when the mercuric oxide 
 thus formed is decomposed into its elements by the action of heat. 
 
 Whenever a substance has the power to unite with others, it can do chemical 
 work ; it possesses chemical energy. Consequently, all combustible substances 
 can do work ; i. e., by combining with oxygen they evolve heat, which in turn 
 may be transformed into motion or into some other form of energy. 
 
 The chief supply of chemical energy at our disposal is derived from plant- 
 life. All kinds of wood, and its decomposition-product, coal, possess chemical 
 energy. This energy is stored up in vegetable matter, because the sun's heat 
 caused a decomposition of water and carbon dioxide, which substances are the 
 two chief compounds used in the construction of plant tissue. In burning 
 vegetable matter the oxygen removed from the water and carbon dioxide by 
 the action of the sun's rays is taken up again, and heat is evolved. 
 
 Ozone is an allotropic modification of oxygen, which is formed 
 when non-luminous electric discharges pass through atmospheric air 
 or through oxygen ; when phosphorus, partially covered with water, 
 
OXYGEN. 143 
 
 is exposed to air, and also during a number of chemical decomposi- 
 tions. Ozone differs from ordinary oxygen by possessing a peculiar 
 odor, by being an even stronger oxidizing agent than common oxygen, 
 by liberating iodine from potassium iodide, etc. This latter action 
 may be used for demonstrating the presence of ozone by suspending 
 in the gas a paper moistened with a solution of potassium iodide and 
 starch. The iodine, liberated by the ozone, forms with starch a dark- 
 blue compound. Theoretically, we assume that ozone contains three, 
 common oxygen but two, atoms in the molecule, which is substan- 
 tiated by the fact that three volumes suffer a condensation to two 
 volumes when converted into ozone, which would indicate that three 
 molecules of oxygen furnish two molecules of ozone, thus : 
 
 30 2 = 20 3 ; or 3 [O = O] =2 
 
 [A] 
 
 Ozone is obtained in a pure condition by passing the impure gas through a 
 tube cooled by liquid oxygen. It is then a blue liquid which boils at 110 C. 
 ( 166 F.), forming a blue gas. Atmospheric air, in which part of the oxygen 
 has been converted into ozone by the electrical method, is used for bleaching 
 purposes, purification of starch, resinifying oils, purifying water of germs and 
 organic matter, etc. 
 
 Ozone occurs in small quantities in country air, but is rarely noticed in 
 cities, where it is decomposed too quickly by the impurities of the atmospheric 
 air. It has been assumed that ozone acts advantageously, as it has a tendency 
 to destroy matters which are unwholesome. Too little, however, is known of 
 the subject to justify a positive opinion in regard to it. 
 
 Thermo-chemistry. It is stated in Chapter 5 that the free or available 
 chemical energy in a chemical change usually appears as heat. This heat can 
 be measured in calories in an apparatus called a calorimeter (see page 48). 
 The equations ordinarily used to represent chemical changes do not express 
 energy changes, but simply what kinds of substances are concerned in the 
 change, and what new substances are formed. For example, the expression, 
 2H -}- O = H 2 O, when translated means that when hydrogen and oxygen unite 
 water is formed, but it says nothing about the fact that a great amount of chem- 
 ical energy is liberated as heat. Likewise the expression, HgO = Hg + O, 
 which means that when mercuric oxide undergoes decomposition (by heat) 
 mercury and oxygen are formed, says nothing about the fact that during the 
 change, heat energy is "absorbed and transformed into chemical energy. For 
 the purpose of showing the energy change involved, use is made of thermal 
 equations. The amount of heat energy in calories represented in thermal equa- 
 tions as liberated or absorbed refers to certain weights of the substances in- 
 volved in the chemical change. These weights are the number of grammes cor- 
 responding to the chemical symbols of the substances. For instance, the thermal 
 equation for the formation of water is written, 2H + O = H 2 O + 67,883 cal., 
 which means that when 2 grammes of hydrogen unite with 15.88 grammes of 
 oxygen to form 17.88 grammes of water (corresponding to the symbol H 2 O), 
 
144 NON-METALS AND THEIR COMBINATIONS. 
 
 67,883 calories of heat are liberated, or enough to raise nearly 68 kilogrammes 
 of water one degree in temperature. The thermal equation, 
 
 HgO = Hg -t O 30,370.5 cal., 
 
 means that when 214.38 grammes of oxide of mercury (corresponding to HgO) 
 are decomposed by heat into mercury and oxygen, 30,370.5 calories of heat 
 are absorbed and converted into chemical energy which is associated with the 
 elements mercury and oxygen. The plus sign is used when heat is liberated in 
 the formation of a compound, and the latter is termed exothermic; while the 
 minus sign indicates absorption of heat, and the compound is termed endother- 
 mic. Exothermic compounds are relatively stable, while endothermic ones are 
 unstable and often explosive. They decompose easily with liberation of heat. 
 
 Ozone is endothermic, as heat is absorbed during its formation from oxygen. 
 When it decomposes heat is liberated. The thermal equation, 2O 3 3O 2 + 
 64,314 cal., states that when 95.28 grammes of ozone (corresponding to 2O 3 ) 
 decomposes into ordinary oxygen, 64,314 calories of heat are liberated. The 
 greater chemical energy of ozone over that of oxygen accounts for its greater 
 chemical activity as compared with oxygen. 
 
 Thermo-chemical measurements are of great importance in several practical 
 directions; for example, for determining the fuel values of samples of coal, 
 coke, wood, fuel values of articles of food in the field of physiology, etc. 
 
 11. HYDROGEN. WATER. HYDROGEN DIOXIDE. 
 H = 1. H 2 O = 17.88. H 2 O 2 = 33.76. 
 
 History. Hydrogen was obtained by Paracelsus in the 16th cen- 
 tury ; its elementary nature was recognized by Cavendish, in 1766. 
 The name is derived from Mvp (hudor), water, and yewfo (gennao), to 
 generate, in allusion to the formation of water by the combustion of 
 hydrogen. 
 
 Occurrence in nature. Hydrogen is found chiefly as a component 
 element of water ; it enters into the composition of most animal and 
 vegetable substances, and is a constituent of all acids. Small quanti- 
 ties of free hydrogen are found in the gases produced by the decom- 
 position of organic matters (as, for instance, in the intestinal gases), 
 and also in the natural gas escaping from the interior of the earth. 
 
 QUESTIONS. By whom and at what time was oxyge'n discovered? How is 
 oxygen found in nature? Mention three processes by which oxygen may be 
 obtained. How much oxygen may be obtained from 490 grammes of potas- 
 sium chlorate? State the physical and chemical properties of oxygen. Ex- 
 plain the terms combustion, slow combustion, combustible substance, and sup- 
 porter of combustion. Mention some oxidizing agents. What is ozone, and 
 how does it differ from common oxygen? Under what circumstances is ozone 
 formed? What is thermo-chemistry ? What is a thermal reaction? 
 
HYDROGEN. 145 
 
 Preparation. Hydrogen may be obtained by passing an electric 
 current through water previously acidified with sulphuric acid, by 
 which it is decomposed into its elements : 
 
 H 2 O = 2H + O. 
 
 A second process is the decomposition of water by metals. Some 
 metals, such as potassium and sodium, decompose water at the ordi- 
 nary temperature ; while others, iron, for instance, decompose it at a 
 
 red heat : 
 
 K + H,0 == KOH + H ; 
 3Fe + 4H 2 = Fe s O 4 + 8H. 
 
 A very convenient way of liberating hydrogen is the decomposition 
 of dilute hydrochloric or sulphuric acid by zinc or iron : 
 
 Zn + 2HC1 = ZnCl 2 + 2H; 
 
 Zinc 
 chloride. 
 
 Fe + H 2 S0 4 = FeSO, + 2H. 
 Ferrous 
 sulphate. 
 
 Hydrogen may also be obtained by heating granulated zinc or 
 aluminum with strong solutions of potassium or sodium hydroxide, 
 in which case the decomposition is explained thus : 
 
 Zn -f 2KOH == K 2 ZnO 2 -f 2H; 
 
 Potassium 
 zincate. 
 
 Al + 3NaOH = Na 3 AlO 3 + 3H. 
 
 Sodium 
 aluminate. 
 
 Whenever hydrogen is generated, care should be taken to expel all 
 atmospheric air from the vessel in which the generation takes place, 
 before the hydrogen is ignited, as otherwise an explosion may result. 
 
 Experiment 3. Place a few pieces of granulated zinc (about 10 grammes) in 
 a flask of about 200 c.c. capacity, which is arranged as shown in Fig. 38. Cover 
 the zinc with water, and pour upon it through the funnel tube a little sulphuric 
 acid, adding more when gas ceases to be evolved. Notice the effervescence 
 around the zinc. Collect the gas in test-tubes over water and ignite it by taking 
 the test-tube (with mouth downward) to a flame near by. Notice that the first 
 portions of gas collected, which are a mixture of hydrogen and atmospheric 
 air, explode when ignited in the test-tube, while the subsequent portions burn 
 quietly. Pour the contents of one test-tube into another one by allowing the 
 light hydrogen gas to rise into and replace the air in a test-tube held over the 
 one filled with hydrogen. Take two test-tubes completely filled with the gas; 
 hold one mouth upward, the other one mouth downward : notice that from the 
 first one the gas escapes after a few seconds, while it remains in the second 
 tube a few minutes, as may be shown by holding the tubes near a flame to 
 cause ignition. 
 10 
 
146 
 
 NON-METALS AND THEIR COMBINATIONS. 
 
 After having ascertained that all atmospheric air has been expelled from the 
 flask, the gas may be ignited directly at the mouth of the delivery tube, after 
 moving it out of the water. 
 
 Continue to add acid until the zinc is nearly all dissolved, remembering that 
 the action is not instantaneous and some time should be allowed before the 
 next addition of acid. Warming the flask will hasten the action, and as long 
 as small gas-bubbles arise from the zinc, action is not over. Avoid adding too 
 much acid, but if there is an excess, it may be removed by adding more zinc. 
 Note the dark particles floating in the liquid and the bad odor of the hydrogen, 
 which are due to the impurities in the zinc. Finally, filter the solution (by 
 folding a circle of filter-paper twice at right angles through the center, open- 
 ing it into a cone, placing in a funnel, wetting with water, and pouring the 
 solution into it), and evaporate it to about one-third its volume at a tempera- 
 ture a little below boiling. Set aside a day to cool and crystallize. If no 
 crystals appear, evaporate further, The crystals are zinc sulphate, the same 
 
 FIG. 38. 
 
 Apparatus for generating hydrogen. 
 
 as is used in medicine. They are an illustration of the formation of a salt by 
 the action of an add on a metal. Filter the crystals and examine them care- 
 fully. Expose some to the air for several days. Does any change take place ? 
 Save the crystals for Experiment 37. 
 
 Experiment 4. Pour into a test-tube of not less than 50 c.c. capacity, 5 c.c. of 
 hydrochloric acid, fill up with water, close the tube with the thumb and set it 
 inverted into a porcelain dish partly filled with water. Weigh of metallic 
 zinc 0.04 gramme, and bring it quickly under the mouth of the test-tube, so 
 that the generated hydrogen rises in the tube. Prepare a second tube in the 
 same manner, and introduce 0.04 gramme of metallic magnesium. In case the 
 decomposition of the acids by the metals should proceed too slowly, a little 
 more acid may be poured into the dishes. 
 
 When the metals are completely dissolved it will be seen that the volumes 
 of hydrogen in the two tubes bear a relation to each other of about 10 to 27. 
 
 In order to measure the gas volumes as correctly as the simple apparatus 
 permits, the tubes should be transferred to a large beaker filled with cold water, 
 
HYDROGEN. 147 
 
 bringing the surfaces of the liquids in the test-tube and beaker on a level, and 
 marking on the outside of the test-tubes (with a file or paper strip) the exact 
 height of the gas. 
 
 After having emptied the test-tubes, they may be filled with water from a 
 pipette or from a burette to the point which has been marked, and thus the 
 exact volume of gas generated is ascertained. 
 
 Kepeat the operation, using 0.065 gramme of zinc and 0.024 gramme of mag- 
 nesium. Notice that in this case equal volumes of hydrogen are obtained. 
 Calculate the weight of hydrogen from the cubic centimetres liberated, and 
 compare this weight with the weights of zinc and magnesium used. What 
 relation is there between the weights of the liberated hydrogen and the metala 
 used, and the atomic weights of these three elements ? 
 
 Properties. Hydrogen is a colorless, inodorous, tasteless gas ; it 
 is the lightest of all known substances, having a specific gravity of 
 0.0695 as compared with atmospheric air ( = 1). One liter of hydro- 
 gen at C. (32 F.), and a barometric pressure of 760 mm., weighs 
 0.08987 gramme, or one gramme occupies a space of 11.127 liters; 
 100 cubic inches weigh about 2.265 grains. 
 
 Hydrogen and helium resist liquefaction more than other gases. Hydro- 
 gen has been liquefied by causing the gas, cooled to a temperature of 
 205 C. ( 337 F.), to escape under certain conditions from a vessel in 
 which it was stored at a pressure of 180 atmospheres. Liquid hydrogen is 
 clear and colorless ; it has a sp. gr. of 0.07, and boils at 253 C. (- 423 F.), 
 under normal atmospheric pressure ; it also has been solidified lately, and the 
 temperature reached is thought to be about 256 C. (428 F.). 
 
 In its chemical properties, hydrogen resembles the metals more than 
 the non-metals ; it burns easily in atmospheric air, or in pure oxygen, 
 with a non-luminous, colorless, or slightly bluish flame producing 
 during this process of combustion a higher temperature than can be 
 obtained by the combustion of an equal weight of any other substance. 
 
 Two volumes of hydrogen combine with one volume of oxygen, 
 forming two volumes of gaseous water, and the formation of water 
 by the combustion of hydrogen distinguishes it from other gases. 
 
 The chemical affinity which hydrogen possesses for oxygen is so 
 great that it abstracts the oxygen from many oxides. Thus, if 
 hydrogen at a red heat be passed over the oxides of copper or iron 
 the metals are set free, while water is formed : 
 CuO + 2H = H 2 + Cu. 
 
 This process of abstracting oxygen from an oxide is called reduc- 
 tion or deoxidation, and substances having the power of accomplish- 
 ing this result are called reducing or deoxidizing agents. Hydrogen, 
 consequently, is a reducing agent. . 
 
148 NON-METALS AND THEIR COMBINATIONS. 
 
 We thus see that, while in physical properties O and H resemble 
 one another closely, their chemical properties are practically the re- 
 verse of each other. Elements which, like the metals, combine readily 
 with oxygen, do not combine with hydrogen ; and, vice versa, ele- 
 ments which, like chlorine, combine most readily with hydrogen, will 
 scarcely combine with oxygen. It will be shown later that, as a 
 general rule, elements which resemble one another in chemical prop- 
 erties are not apt to combine with one another, while those differing 
 widely have great affinity for one another. 
 
 Nascent hydrogen. It was stated above that hydrogen is a good reduc- 
 ing agent, but as far as hydrogen in the free state is concerned reduction takes 
 place, as a rule, only when heat is employed. There is a condition of hydrogen, 
 however, in which it is able to reduce many compounds at ordinary tempera- 
 ture, while free hydrogen has no measurable action on the same. For exam- 
 ple, the hydrogen liberated during electrolysis of a dilute acid is able to reduce 
 many compounds present in solution immediately around the pole (cathode) at 
 which the hydrogen is produced. It also shows different degrees of activity 
 according to the material of which the pole is made. Similarly, hydrogen 
 generated by the action of dilute acids on metals has reducing power on sub- 
 stances immediately surrounding the metals during action, whereas free 
 hydrogen gas passed through a solution of the same substances or in contact 
 with them in the dry state has no action. To illustrate : hydrogen gas passed 
 through a solution of arsenous oxide, As 2 3 , has no effect, but if the oxide is 
 present in a mixture of dilute hydrochloric acid and zinc the hydrogen formed 
 quickly reduces it to arsine gas, AsH 3 . This is one of the most delicate tests 
 for arsenic. The more active condition of hydrogen at the time of its libera- 
 tion is spoken of as the nascent state. It seems that this increased activity of 
 hydrogen in contact with the substances that liberate it is an example of con- 
 tact or catalytic action (see page 154). Good support to this view is the fact 
 that the efficiency of the nascent hydrogen varies according to the nature of 
 the material in association with which the hydrogen is produced. 
 
 Water, H 2 O = 17.88. Hydrogen monoxide. Water exists on 
 our globe in the three states of aggregation. Air at all temperatures 
 contains water in the gaseous form. Liquid water occurs plentifully 
 in the oceans, rivers, etc., and also in plants and animals. Seven- 
 tenths of the human body is water; potatoes contain of it 75 per 
 cent, and watermelons as much as 94 per cent. Solid water exists 
 not only as ice and snow, but it also enters into the composition of 
 many rocks, and is a constituent of many crystals containing water 
 of crystallization. 
 
 Absolutely pure water is not found in nature. The purest natural 
 water is rain-water collected after the air has been purified from 
 dust, etc., by previous rain. Comparatively pure water may be 
 
WATER. 149 
 
 obtained by melting ice, since, when water containing impurities is 
 frozen partially, these are mostly left in the uncongeaieu water. 
 
 The waters of springs, wells, rivers, etc., differ widely from each 
 other ; they all contain more or less of substances dissolved by the 
 water in its course through the atmosphere or through the soil and 
 rocks. The constituents thus absorbed by the water are either solids 
 or gases. 
 
 Solids generally found in natural waters are common salt (sodium 
 chloride), gypsum (calcium sulphate), and carbonate of lime (calcium 
 carbonate) ; frequently found are chlorides and sulphates of potassium 
 and magnesium, traces of silica and salts of iron. Gases absorbed 
 by water are constituents of the atmospheric air, chiefly oxygen, 
 nitrogen, and carbon dioxide. One hundred volumes of water con- 
 tain about two volumes of nitrogen, one volume of oxygen, and one 
 volume of carbon dioxide. 
 
 Water is said to be hard when it contains so much of salts of cal- 
 cium and magnesium that the formation of lather by soap is delayed 
 because these salts form insoluble compounds with the soap. Water 
 containing but little of inorganic matter is said to be soft. 
 
 When the hardness is caused by metallic sulphates or chlorides the 
 water is called permanently hard, while it is termed temporarily hard 
 when the metals are present as carbonates, dissolved by carbonic acid. 
 On boiling such water carbon dioxide escapes, the carbonates of the 
 metals are precipitated, and the water is rendered soft. 
 
 Mineral waters are spring waters containing one or more sub- 
 stances in such quantities that they impart to the water a peculiar 
 taste and generally a decided medicinal action. According to the 
 predominating constituents we distinguish bitter waters, containing 
 larger quantities of magnesium salts ; iron or chalybeate waters, 
 containing carbonate or sulphate of iron ; sulphur or hepatic waters, 
 containing hydrogen sulphide ; effervescent waters, strongly charged 
 with carbonic acid ; cathartic waters, generally containing sodium or 
 magnesium sulphate, etc. 
 
 Drinking-water. A good drinking-water should be free from 
 color, odor, and taste ; it should neither be an absolutely pure water, 
 nor a water containing too much of foreign matter. Water containing 
 from 2 to 4 parts of total inorganic solids (chiefly carbonate of lime 
 and common salt) in 10,000 parts of water and about 1 volume of 
 carbon dioxide in 100 volumes of water, may be said to be a good 
 
150 NON-METALS AND THEIR COMBINATIONS. 
 
 drinking-water. There are, however, good drinking-waters which 
 contain more of total solids than the amount mentioned above. 
 
 Most objectionable in drinking-water are organic substances, espe- 
 cially when derived from animal matter, and more especially when 
 in a state of decomposition, because such decomposing organic matter 
 is frequently accompanied by living organisms (germs) which may 
 cause disease. Boiling of water destroys these germs, and by subse- 
 quent filtering of the boiled water through sand, charcoal, spongy 
 iron, etc., an otherwise unwholesome water may be rendered fit for 
 drinking. 
 
 In nature water is rendered free from organic impurities by the 
 oxidizing power of atmospheric oxygen, which is taken up by the 
 water and is readily transferred upon organic matter present. 
 
 It should be remembered that no filter can remain efficient for any length 
 of time, as the impurities of the water are retained by the materials used as a 
 filter, and this may become, therefore, a source of pollution instead of a puri- 
 fier. By heating to a low red heat the materials used for filtering, these are 
 cleaned and may be used again. The methods applied to the analysis of 
 drinking-water will be mentioned later. (See Index.) 
 
 Distilled water, Aqua destillata. The process for obtaining 
 pure water is distillation in a suitable apparatus. From 1000 parts 
 of water used for distillation, the first 100 parts distilled over should 
 not be used, as they contain the gaseous constituents. The solids 
 contained in the water are left in the undistilled portion, which should 
 not be less than 100 parts. 
 
 Composition of water. Until the discovery of oxygen, water 
 was thought to be a simple substance. In 1781 Cavendish, of Eng- 
 land, discovered the qualitative composition of water when he 
 obtained it by causing hydrogen and oxygen to unite. Water was 
 thus produced synthetically. 
 
 The proportion of hydrogen and oxygen in water has been determined 
 accurately by weighing the oxygen and the water formed by union with hydro- 
 gen, also by weighing both constituents and the water after union. The results 
 of the most accurate experiments showed that water contains 11.185 per cent. 
 of hydrogen and 88.815 per cent, of oxygen, or 2 parts by weight of hydrogen 
 to 15.88 parts, by weight, of oxygen. It has been ascertained that the mole- 
 cule of water is made up of two atoms of hydrogen and one atom of oxygen, 
 H 2 O. Hence, it follows that the atomic weight of oxygen is 15.88. By vol- 
 ume, hydrogen and oxygen unite in the proportion of 2 : 1 to form water. 
 
WATER. 151 
 
 Analysis and synthesis. These terms refer to two methods of 
 research in chemistry, accomplished by two kinds of reaction, ana- 
 lytical and synthetical. 
 
 Analysis is that mode of research by which compound substances 
 are broken up into their elements or into simpler forms of combina- 
 tion, and analytical reactions are all chemical processes by which the 
 nature of an element, or of a group of elements, may be recognized. 
 
 Synthesis is that method of research by which bodies are made to 
 unite to produce substances more complex. 
 
 Analytical and synthetical methods, or reactions, frequently blend 
 into one another. This means : A reaction made with the intention 
 of recognizing a substance, may at the same time produce some com- 
 pound of interest from a synthetical point of view. 
 
 Properties of water. Water is an inodorous, tasteless, and, in 
 small quantities, colorless liquid. Thick layers of water show a blue 
 color. On cooling, water contracts until it reaches the temperature 
 of 4 C. (39.2 F.), at which point it has its greatest density. If 
 cooled below this temperature it expands and the specific gravity of 
 ice is somewhat less than that of water. Water is perfectly neutral, 
 yet it has a tendency to combine with both acid and basic substances. 
 These compounds are usually called hydroxides (formerly hydrates), 
 such as NaOH, Ca(OH) 2 , etc. These compounds are often formed by 
 direct union of an oxide with water, thus : 
 
 CaO + H 2 = Ca(OH) 2 . 
 SO 3 + H 2 O = SO 2 (OH) 2 . 
 
 Water is the most common solvent, both in nature and in artificial 
 processes. As a general rule, solids are dissolved more quickly and 
 in larger quantities by hot water than by cold, but to this there are 
 many exceptions. For instance : Common salt is nearly as soluble 
 in cold as in hot water ; sodium sulphate is most soluble in water of 
 33 C. (91 F.), and some calcium salts are less soluble in hot than 
 in cold water. 
 
 The term solution is applied to any clear and homogeneous liquid 
 obtained by causing the transformation of matter from a solid or 
 gaseous state to the liquid state by means of a liquid called a solvent 
 or menstruum ; solutions may also be obtained from two liquids, as 
 when we dissolve oil in ether. A solution is said to be saturated when 
 the solvent will not take up any more of the substance being dissolved. 
 
 Two kinds of solutions are distinguished viz., simple solutions and complex 
 or chemical solutions. In the former we have a mere physical change, the mole- 
 
152 , NON-METALS AND THEIR COMBINATIONS. 
 
 cules of the dissolved body being present with all their characteristic proper- 
 ties, and on evaporation the dissolved solid will be re-obtained unchanged. 
 Instances of this kind are solutions of sugar or table salt and water. (The 
 breaking down of molecules into ions during simple solution will be considered 
 later.) 
 
 In chemical solutions there takes place a rearrangement of the atoms within 
 the molecules, both of the solvent and of the substance dissolved. Moreover, 
 on evaporation of the solution a substance is obtained entirely different from 
 the one which has been dissolved. Instances of this kind are the dissolving of 
 sodium in water, when sodium hydroxide is formed ; or the dissolving of zinc 
 in sulphuric acid, when zinc sulphate is formed. The term emulsion is used 
 to designate a more or less homogeneous liquid rendered opaque or rnilky by 
 the suspension in it of finely divided particles of fat, oil, or resin. The milk 
 of mammalia and the milk-like juice of certain plants are instances of true 
 emulsions. 
 
 Many salts combine with water in crystallizing ; crystallized sodium 
 sulphate, for instance, contains more than half its weight of water. 
 This water is called ivater of crystallization, and is expelled generally 
 at a temperature of 100 C. (212F.). Some crystallized substances 
 lose water of crystallization when exposed to the air ; this property is 
 known as efflorescence. Crystals of sodium carbonate, ferrous sulphate, 
 etc., effloresce, as is shown by the formation of powder upon the crys- 
 talline surface. Substances are said to be anhydrous when they are 
 destitute of water, for instance, when crystals have lost their water 
 of crystallization or when ether or alcohol have been freed from dis- 
 solved water. The term anhydride is sometimes used for oxyacids 
 which have been deprived of all water, so that they are no longer 
 acids, but oxides. Thus, by removing water from sulphuric acid, 
 H 2 SO 4 , there is left sulphur trioxide, or sulphuric acid anhydride, 
 SO 3 . The term deliquescence is applied to the power of certain solid 
 substances to absorb moisture from the air, thereby becoming damp 
 or even liquid, as, for instance, potassium hydroxide, calcium chloride, 
 etc. Such substances are spoken of also as being hygroscopic, and 
 are used for drying gases. 
 
 The term effervescence refers to the escape of a gas from water or 
 from any other liquid in which the gas was held under pressure or in 
 which it may be generated ; as, for instance, when an acid is added 
 to a carbonate, whereupon carbon dioxide escapes with energetic 
 bubbling. 
 
 The explanation of effervescence and deliquescence is found in a well-known 
 principle of physics. It is well known that liquids will evaporate in a closed 
 space until the pressure of the vapor is equal to the vapor tension of the liquid, 
 
HYDROGEN DIOXIDE. 153 
 
 when equilibrium is established and evaporation of the liquid apparently 
 ceases. This means that vapor particles fly back into the liquid at the same 
 rate that liquid particles leave the surface of the liquid to become vapor. If 
 the vapor pressure in any way becomes greater than the vapor tension of the 
 liquid, some vapor will be condensed to liquid. On the other hand, if the 
 vapor pressure is constantly lower than the vapor tension of the liquid, evapo- 
 ration will go on until no more liquid is left. One way of accomplishing this 
 is by free exposure of liquids to the atmosphere. Of course the amount of the 
 vapor pressure varies with the temperature. Now it is found that substances 
 containing water of crystallization have a vapor tension just as water has. 
 For example, when a crystal of sodium sulphate (Na 2 SO 4 .10H 2 0) is allowed 
 to rise to the top of a barometer tube at 9 C., it exerts a vapor tension of 5.5 
 mm. that is, the pressure of the water vapor given off by the crystal is enough 
 to depress the mercury column 5.5 mm. Those substances crystallizing with 
 water which at ordinary temperature exert a vapor tension greater than the 
 pressure of the water vapor in the atmosphere, are efflorescent and must be 
 kept in closed containers, just as water must be to prevent loss of water. 
 When the vapor tension of the substances is about the same or less than the 
 atmospheric vapor pressure, the substances are stable and need not be carefully 
 bottled, except to keep them clean. The average pressure of the water vapor 
 in the atmosphere at 9 C. is about 5 mm. At this temperature crystals of 
 sodium sulphate have a vapor tension of 5.5 mm. and are efflorescent, while 
 those of copper sulphate have a vapor tension of 2 mm. and are stable in the 
 air. 
 
 Deliquescent substances are always very soluble in water. A layer of 
 moisture condenses on these just as it does on all bodies exposed to the atmo- 
 sphere. In the case of extremely soluble substances, the condensed moisture 
 forms a thin layer of very concentrated solution upon their surfaces. Concen- 
 trated solutions have a vapor tension less than that of water, and much less 
 than the atmospheric vapor pressure. The result is that water vapor continues 
 to condense from the atmosphere upon the substances until they dissolve and 
 form solutions so dilute that their correspondingly increased vapor tension bal- 
 ances the vapor pressure of the moisture in the atmosphere. 
 
 0-H 
 Hydrogen dioxide, Hydrogen peroxide, H 2 O 2 , or I This 
 
 O H 
 
 compound may be obtained in aqueous solution from several metallic 
 dioxides which, when treated with an acid, yield a portion of their 
 oxygen to water. 
 
 Sodium dioxide and barium dioxide are the compounds chiefly 
 employed in its manufacture, the acid used being either carbonic, 
 hydrochloric, hydrofluoric, sulphuric, or phosphoric acid. The de- 
 composition, when sulphuric acid and barium dioxide are used, is 
 this : 
 
 BaO 2 + H 2 SO 4 = BaSO 4 + H 2 O 2 . 
 
154 NON-METALS AND THEIR COMBINATIONS. 
 
 In no case is it possible to obtain, as might appear from the 
 above equation, pure hydrogen dioxide directly, as a considerable 
 quantity of water has to be present in order to effect the de- 
 composition. The aqueous solution, if quite pure, can be concen- 
 trated by evaporation at a temperature not exceeding 60 C. (140 
 F.) until it has a strength of 50 per cent. If this be further heated 
 in vacuo at a gradually increased temperature, a nearly pure hydro- 
 gen dioxide distils over at a temperature of 85 C. (185 F.). 
 
 Pure hydrogen dioxide is a colorless, oily liquid, of a specific 
 gravity 1.45. It is soluble in water, alcohol, and ether, which latter 
 extracts it from its aqueous solutions. 
 
 Hydrogen dioxide decomposes slowly at ordinary temperature, 
 more rapidly on exposure to light and at higher temperatures ; at 
 100 C. the decomposition is often explosively rapid. Many inert 
 subtances, in powder, cause its decomposition, and it is for this 
 reason that even dust particles from the air act decomposingly, 
 especially during evaporation. The presence of very small quanti- 
 ties of certain substances retards the decomposition. Traces of free 
 acids, as also boro-glycerin, have been used for this purpose. It has 
 been found that a very small quantity of acetanilide is an excellent 
 preservative and it is now added to commercial hydrogen dioxide 
 solution. 
 
 Catalytic action. There are a number of instances in chemistry 
 where a substance, which apparently undergoes no change itself, 
 causes by its presence an increase in chemical change in other sub- 
 stances, or induces a change where, without it, there would be no 
 chemical action. This is known as catalytic or contact action and 
 the process is called catalysis. Examples of this action are seen in 
 the decomposition of hydrogen dioxide by dust particles, or finely 
 divided platinum, the influence of manganese dioxide on potassium 
 chlorate in the preparation of oxygen, and the explosion of a mixture 
 of hydrogen and oxygen when platinum black is introduced into it. 
 
 Hydrogen dioxide possesses bleaching, caustic, and antiseptic 
 properties. It is used as a bleaching agent for hair, wool, teeth, and 
 other articles, and as an antiseptic in surgical and in dental opera- 
 tions. It effervesces with pus, as also with saliva, in consequence of 
 the liberation of oxygen. 
 
 Solution of hydrogen dioxide, Aqua hydrogenii dioxidi, should 
 contain about 3 per cent, by weight, of pure dioxide, corresponding 
 to about 10 volumes of available oxygen in 1 volume of the solution. 
 
HYDROGEN DIOXIDE. 155 
 
 The solution is colorless and without odor, and has a slightly acidu- 
 lous taste, producing a peculiar sensation and soapy froth in the 
 mouth. It is liable to deteriorate by age, especially on exposure to 
 heat and light. 
 
 Pyrozone is the trade name under which a 50 per cent, hydrogen peroxide 
 is sold, but diluted pyrozone also is found in the market. 
 
 Glycozone is hydrogen dioxide dissolved in glycerin instead of in water. 
 
 Hydrogen dioxide, owing to its instability and tendency to decom- 
 pose into water and oxygen, is an excellent oxidizing agent. It is 
 frequently used in preference to other such agen-ts, because by its use 
 no other products are introduced into solutions than water and oxy- 
 gen. Toward a few substances, which themselves are unstable and 
 easily give up oxygen, it also acts as a reducing agent. For example, 
 silver oxide is reduced to metallic silver thus : 
 
 Ag 2 + H 2 2 = 2Ag -f 2 + H 2 0. 
 
 When hydrogen dioxide decomposes into water and oxygen, heat is liberated. 
 The thermal equation is 
 
 H 2 O 2 = H 2 O + O -f 22,926 cal. 
 
 that is, when 33.76 grammes of hydrogen dioxide corresponding to the formula, 
 H 2 2 , decomposes, 22,926 calories of heat energy are liberated. This is in 
 addition to the heat that is produced when the liberated oxygen unites with 
 other substances. In this way the great activity of hydrogen dioxide as an 
 oxidizer is accounted for. 
 
 Tests 1 for solution of hydrogen dioxide. 
 
 (Use the commercial solution after diluting about five times with water.) 
 
 1. To a beaker half full of water, add 1 or 2 c.c. of solution of 
 
 potassium iodide (see Reagents) and about 2 c.c. of the hydrogen 
 
 dioxide solution. Is any yellow color produced ? Then add a few 
 
 drops of starch solution (for which, see Index). A deep blue color 
 
 is produced by the action of the starch on the iodine liberated from 
 
 potassium iodide by the oxidizing action of the hydrogen dioxide : 
 
 2KI -f H 2 2 = 2KOH + 21. 
 The action is more intense if the water is first acidified with 5 or 10 
 
 1 Tests are reactions to which a substance may be subjected for the purpose of recognition. 
 Acids turn blue litmus red, and we call that a test for acids. Carbon dioxide gas gives a 
 milky appearance to lime-water, which is a test for the gas. Some tests are much more strik- 
 ing than others, indeed, they are so characteristic that they tell at once the nature of the sub- 
 stance tested. Such tests might be called decisive, in distinction to others which are only cor- 
 roborative, and to which several substances may respond. 
 
156 NON-METALS AND THEIR COMBINATIONS. 
 
 drops of a dilute acid. This is not a decisive test, since other sub- 
 stances besides hydrogen dioxide give the same test. 
 
 2. To a test-tube half full of water, add in succession, 1 c.c. of the 
 hydrogen dioxide solution, a few drops of dilute sulphuric acid, and 
 2 drops of solution of potassium dichromate, and mix. A blue com- 
 pound, known as perchromic acid, HCrO 4 , is produced, which fades 
 after a short time. The color may be made more permanent by 
 shaking the mixture with ether, which dissolves the compound and 
 collects on the surface on standing. This is a very delicate and 
 decisive test. 
 
 3. Acidify a few c.c. of the hydrogen dioxide solution with about 
 2 c.c. of dilute sulphuric acid, and add solution of potassium per- 
 manganate, a little at a time. The purple color vanishes quickly and 
 a gas is given off (oxygen). The permanganate is an unstable oxi- 
 dizing agent, which gives up its oxygen. This unites with oxygen 
 from the dioxide, and escapes as a gas. The reaction will be under- 
 stood when the chemistry of manganese is studied. Other substances 
 also decolorize permanganate. 
 
 If a solution is colorless, odorless, practically neutral to litmus- 
 paper, volatilizes completely upon heating, and responds to the above 
 tests, especially number 2, it is, without doubt, hydrogen dioxide. 
 
 QUESTIONS. Mention two processes by which hydrogen may be obtained. 
 Show by symbols the decomposition of water by potassium, and of sulphuric 
 acid by iron. State the chemical and physical properties of hydrogen. Define 
 the nascent state. What explanation is offered to account for it? State the 
 composition of water in parts by weight and by volume. Mention the most 
 common solid and gaseous constituents of natural waters. How does a mineral 
 water differ from other waters? Mention some different kinds of mineral 
 waters and their chief constituents. What are the characteristics of a good 
 drinking-water ? What are the purest natural waters, and by what process 
 may chemically pure water be obtained? State composition, mode of manu- 
 facture, and properties of hydrogen dioxide. What is the explanation of efflo- 
 rescence and deliquescence ? 
 
SOLUTION. 157 
 
 12. SOLUTION. 
 
 As stated under Water, the term solution is applied to any homo- 
 geneous liquid mixture that results when solids, liquids, or gases 
 an; brought in contact with a liquid and disappear in the liquid. 
 (There are a few instances of solution of a gas in a solid, and of a 
 solid in a solid.) Solutions are transparent, and the dissolved mate- 
 rial is so thoroughly disseminated that its particles cannot be dis- 
 tinguished by the eye from those of the solvent. Moreover, there is 
 perfect distribution of the dissolved matter and no tendency for it to 
 settle. An opalescent or opaque appearance of a liquid is evidence 
 that there is matter held in suspension, and this matter will settle in 
 time, or may be filtered out. Dissolved substances cannot be re- 
 moved by filtration, as they pass through the pores of the paper as 
 readily as the liquid does. 
 
 For the majority of substances there is a limit to the amount that 
 can be dissolved in a given amount of liquid. This limit ranges 
 from an almost infinitesimal amount in some cases to a fairly large 
 quantity in others. Thus, at ordinary temperature, the amount of 
 ferric oxide that is dissolved by 100 c.c. of pure water is extremely 
 small, while about 90 grammes of crystallized magnesium sulphate are 
 dissolved. No substance is absolutely insoluble, but many are so 
 sparingly soluble that for practical purposes they are considered in- 
 soluble. In some cases two substances may be mixed in any pro- 
 portions, for example, water and alcohol. But usually the solubility 
 of one liquid in another is limited, and when two such liquids are 
 shaken together they separate after a time into two layers, the liquid 
 in each layer being saturated with the other liquid. Thus, when ether 
 and water are shaken together at ordinary temperature they separate 
 on standing with the lighter (ether) layer on top, and 100 grammes 
 of water dissolve 2.1 grammes of ether, while 100 grammes of ether 
 dissolve 11 grammes of water. Pairs of liquids which are only slightly 
 soluble in each other are known as immiscible solvents, and are often 
 employed in certain kinds of chemical work for transferring a sub- 
 stance from one liquid to another. This operation is known as ex- 
 traction, and depends for its success upon a great difference of solu- 
 bility of the given substance in the two solvents. The division of a 
 substance between two immiscible solvents, after thorough shaking 
 and separation of the liquids, is proportional to its solubility in each 
 solvent. If a substance is 100 times more soluble in chloroform 
 than in water, and its aqueous solution is shaken thoroughly with 
 chloroform, the concentration of the substance in the chloroform 
 
158 NON-METALS AND THEIR COMBINATIONS. 
 
 layer will be found 100 times that in the water layer. The process 
 of extraction must be repeated several times for the complete removal 
 of a substance from a liquid. 
 
 Terms employed. The liquid in which a substance is dissolved 
 is called the solvent, while the substance, to avoid circumlocution, is 
 often called the solute. The word strength is frequently used to refer 
 to the amount of substance in solution, but a more exact term to 
 employ is concentration. A solution that contains a small quantity, 
 say 5 grammes of a substance in 100 c.c., is said to have a small con- 
 centration, or to be dilute. Concentrated solutions contain a relatively 
 large amount of dissolved substance ; they are often spoken of as very 
 strong solutions. Concentrating a solution is the removal of part of 
 the solvent by evaporation. A saturated solution is one that contains 
 the maximum amount of dissolved substance. This condition may 
 be attained by long agitation of the liquid with an excess of the sub- 
 stance. If the latter is a solid, it should be finely divided. The 
 solubility of a substance is its concentration in saturated solution, and 
 is expressed in terms of the number of grammes of the substance in 100 
 grammes of the solvent, or in 100 c.c. of the solution, or of the grammes 
 of solvent required to dissolve 1 gramme of the substance. The solu- 
 bility of substances varies with the temperature, being, as a rule, in 
 the case of solids, much greater at boiling than at ordinary temper- 
 ature. In most cases, when a hot concentrated solution is allowed 
 to cool, the excess of material over what corresponds to the solubility 
 at lower temperature, separates as crystals from the solution (see 
 Crystals, Chapter 1). But in some instances the excess of material 
 does not separate from the solution as it cools ; such a solution is 
 then said to be supersaturated. Crystallization can be induced by 
 placing in the cool solution a fragment of the same substance as that 
 in solution. A solution in contact with the solid substance cannot 
 be more than saturated with respect to that substance. There is an 
 equilibrium between the solid and the saturated solution. Sulphate, 
 thiosulphate, and chlorate of sodium have a marked tendency to give 
 supersaturated solutions, especially if the solutions are freed from all 
 floating particles by careful filtration. 
 
 The solution of certain substances in water takes place with libera- 
 tion of heat and rise in temperature of the solution, while in other 
 cases there is an absorption of heat and a fall in temperature. Heat 
 of solution is the number of calories liberated or absorbed when the 
 weight of a substance in grammes corresponding to its chemical form- 
 ula (molecular weight) is dissolved in an unlimited amount of water. 
 
SOLUTION. 159 
 
 AVhen 95.35 grammes of sulphuric acid (corresponding to H 2 SOj are 
 thus dissolved, 38,880 calories of heat are liberated, or enough heat 
 to raise over 38 liters of water 1 C. in temperature. When 284.11 
 grammes of crystallized sodium carbonate (Na 2 CO 3 .10H 2 O) are dis- 
 solved, 16,038 calories are absorbed, but solution of an equivalent 
 weight of anhydrous sodium carbonate (Na 2 CO 3 ), or 105.31 grammes, 
 liberates 5,598 calories of heat. If a substance absorbs heat during 
 solution, it develops the same amount of heat when it comes out of 
 solution as by crystallization. For example, a supersaturated solu- 
 tion of sodium sulphate, when crystallizing suddenly, produces quite 
 an appreciable rise in temperature. 
 
 Solution of gases. Henry's Law. Gases dissolve in liquids to a vari- 
 able degree. The range of solubility is quite wide, as may be seen from the 
 following examples: At C. and 760 mm. pressure, 1 volume of water dissolves 
 0.02 volume of hydrogen, or nitrogen, 0.04 volume of oxygen, 1.8 volumes of 
 carbon dioxide, 80 volumes of sulphur dioxide, 550 volumes of hydrochloric 
 acid gas, and 1050 volumes of ammonia gas. 
 
 The solubility of a gas varies with the nature of the solvent; thus, at C., 
 a volume of alcohol dissolves twice as much carbon dioxide as the same volume 
 of water does. It also varies with the temperature, decreasing, as a rule, as the 
 temperature increases. Thus, 100 volumes of water dissolve about 4 volumes 
 of oxygen at C., 3 at 20 C., 1.8 at 50 C., and none at 100 C. In many 
 instances a gas is completely removed from its solution by boiling, but this is 
 not possible in the case of certain very soluble gases, like hydrochloric acid. 
 There is in such cases a chemical action, in part at least, between the gas and 
 the solvent. A 20.2 per cent, aqueous solution of hydrochloric acid distills 
 unchanged under normal atmospheric pressure. 
 
 The solubility of a gas increases with increased pressure on the gas. Com- 
 mercial aerated water is a good illustration. The water is charged with carbon 
 dioxide under considerable pressure. When drawn from the container and 
 exposed to the atmosphere the excess of gas, which cannot remain dissolved 
 under the diminished pressure, escapes, causing effervescence. Such a solution 
 is often called soda water. Solutions of gases in liquids fall into two classes : 
 (1) those from which the gas is completely removed by heat or by decrease of 
 pressure ; (2) those from which the gas is not thus completely removed. Very 
 soluble gases give rise to the second class of solutions, in which a complete 
 chemical and physical independence of the molecules of solvent and gas is 
 lacking. In solutions of the first class there is a fixed relationship between the 
 solubility of a gas and pressure, which is known as Henry's Law. It may be 
 stated thus : The quantity of a gas dissolved by a given quantify of a liquid is pro- 
 portional to the pressure of the gas. Since the volume of a gas is inversely 
 proportional to the pressure, another form in which the law may be stated is : 
 A given quantity of a liquid dissolves the same volume of a gas at all pressures. 
 
 In the case of a mixture of gases in contact with a liquid, each gas dissolves 
 as if it were present alone, and in proportion to its own partial pressure in the 
 mixture, 
 
160 NON-METALS AND THEIR COMBINATIONS. 
 
 Henry's law holds in the case of absorption of gases by saline solutions, if 
 the gas has no chemical action on the salt in solution, for example, in the 
 absorption of carbon dioxide, oxygen, or nitrogen, by a solution of sodium 
 chloride (common salt). When the gas acts chemically on the dissolved salt, 
 as carbon dioxide does on ordinary sodium phosphate or sodium carbonate, 
 one portion of the gas is absorbed in accordance with Henry's law, and an 
 additional portion is absorbed as a result of chemical action and is independent 
 of pressure. 
 
 Freezing-points of solutions. The freezing-point of a solution is always 
 lower than that of the pure solvent. It is also easily observed, by introducing 
 small quantities of solutions and pure solvents over the mercury in barometer 
 tubes, that the vapor tension of the solutions is always less than that of the 
 pure solvents, no matter what the temperature is. This difference in vapor 
 tension accounts for the fact that the freezing-point of solutions is depressed. 
 Theoretical considerations show that freezing (separation of some of the solvent 
 in the solid state) can take place only at such a temperature at which the solu- 
 tion and the solid state of the solvent have the same vapor tension, whereby 
 they are in physical equilibrium and can co-exist permanently (see discussion 
 under Efflorescence and Deliquescence, p. 152). Since the vapor tension of a 
 solution is always less than that of the pure solvent, it follows that the freezing- 
 point of a solution must be lower than that of the pure solvent, in order that 
 the vapor tension of the solution and of the ice that separates may balance 
 each other. (On this principle the low temperature of freezing mixtures, such 
 as snow (or ice) and salt, is explained). 
 
 For a description of apparatus and details of method in making determina- 
 tions of the freezing-points of solutions, the student must be referred to books 
 on physical chemistry. 
 
 For solutions not too concentrated and in which there is no chemical action 
 between the solvent and the substance dissolved, the following law has been 
 found to hold : The depression of the freezing-point is directly proportional to the 
 iveight of dissolved substance in a given amount of the solvent. By calculations 
 made on the results obtained with dilute solutions, the following law has been 
 found to hold theoretically for molecular quantities of substances : The molec- 
 ular weights in grammes of different substances dissolved in 1000 grammes of the 
 same solvent produce the same depression of the freeezing -point. The depression 
 thus produced is called the molecular depression constant, and has a different 
 numerical value for each solvent. For water it is 1.89 C.; for benzene, 4.9 C., 
 and for phenol, 7.5 C. 
 
 The above law gives a basis for a method of determining molecular weights, 
 which was first applied extensively by Raoult, and is sometimes called the 
 cryoscopic method. It is valuable in the case of substances which cannot be 
 volatilized without decomposition. The molecular weight is calculated from 
 the equation 
 
 D = d X Vv-' 
 
 M X g 
 
 in which D is the amount of depression in any actual experiment, d the molec- 
 ular depression constant, W the weight of the substance, M its molecular 
 weight, and g the weight of the solvent in grammes. 
 
SOLUTION. 161 
 
 The above law, often called the law of Eaoult, does not hold in some cases, 
 especially in those of solutions of acids, bases, and salts in water. For ex- 
 ample, one molecular weight of sodium chloride, 58.06 grammes, dissolved in 
 1000 grammes of water, depresses the freezing-point about 3.5 C., or nearly 
 twice the amount produced by a cane-sugar solution of equivalent concentra- 
 tion, 1.89 C., which is taken as the molecular depression of normally acting 
 substances. It is also a noteworthy fact that aqueous solutions of substances 
 that have abnormal freezing-point depressions are just such as conduct an 
 electric current, while solutions of substances that give normal depressions do 
 not conduct a current. The same number of molecules of different substances 
 in a given amount of solvent produces the same lowering of the freezing-point, 
 and the molecular weights in grammes contain the same number of molecules. 
 The fact that the depression of the freezing-point of a solution of the molecular 
 weight in grammes of sodium chloride in 1000 grammes of water is much 
 greater than that of a similar solution of cane-sugar, can be accounted for on 
 the assumption that the number of particles in the sodium chloride solution 
 must be increased somehow over the number of particles in the sugar solution. 
 This increase can only take place by a decomposition of the molecule of sodium 
 chloride, thus, 
 
 NaCl = Na + Cl. 
 
 The particles Na and Cl must be different in condition from sodium and chlo- 
 rine as we know them in the free state, but as far as their effect upon the 
 freezing-point is concerned they act the same as undecomposed dissolved mole- 
 cules. This assumption of the decomposition of molecules is applied in the 
 case of all abnormally acting solutions where the freezing-point depressions 
 are greater than normal, and will be referred to again farther on under 
 lonization. 
 
 In the field of medicine the determination of the freezing-point of certain 
 fluids is sometimes carried out in order to learn something of the manner in 
 which the organs are functioning. Normal blood has a lower freezing-point 
 than water, the difference is 0.56 C. A greater difference than this indicates 
 that the kidneys are not properly eliminating the solid waste products from 
 the blood. The freezing-point depression of normal urine is 1.2-2.3 C. Of 
 cows' milk it is 0.55-0.56 C. A lower depression indicates that the milk has 
 been tampered with. 
 
 Boiling-points of solutions. These are always higher than the boiling- 
 points of the pure solvents. The boiling-point of any solution is that temper- 
 ature at which the vapor tension of the solution is equal to the atmospheric 
 pressure. Since the vapor tension of solutions is less than that of the pure 
 solvent, it follows that a solution must be heated to a higher temperature than 
 that at which the pure solvent boils, in order to make its vapor tension equal 
 to the atmospheric pressure ; in other words, to make it boil. The elevations in 
 the boiling-points are proportional to the concentrations of the different solutions of 
 any one substance. The molecular weight in grammes of normally acting sub- 
 stances, dissolved in 1000 grammes of water, elevates the boiling-point from 
 100 to 100.52 C. The difference, 0.52, is called the molecular boiling-point 
 constant for water. Just as in the case of freezing-points, so here a method 
 11 
 
162 NON-METALS AND THEIR COMBINATIONS. 
 
 of determining molecular weights has been devised, but for a description 
 of the apparatus and details of working, reference must be made to special 
 books. 
 
 The substances which show abnormalities in the depression of the freezing- 
 point are also those which give abnormal elevations in the boiling-points of 
 their solutions. The abnormal behavior is also accounted for by the same ex- 
 planation, namely, a decomposition of some of the molecules of the dissolved 
 substance. The deviations from normal behavior are particularly observed in 
 aqueous solutions. 
 
 Osmotic pressure. Soluble substances in contact with a liquid dissolve 
 and diffuse throughout the liquid until the concentration is uniform in every 
 part of the solution (see Diffusion, p. 40). In the liquid the substance behaves 
 somewhat like a gas, in that its molecules tend to spread out and fill the whole 
 space occupied by the liquid. The cohesion between the molecules of the sub- 
 stance is overcome and there is freedom of motion, somewhat as in a gas. 
 Just as a gas exerts a pressure on any partition or membrane that resists the 
 motion of its molecules, so likewise do the molecules of a substance in solution 
 exert pressure upon a membrane that prevents their diffusion into a less con- 
 centrated region of the solution, or into the pure solvent. This pressure is 
 called osmotic pressure. In the article on Dialysis it is shown that a substance 
 in aqueous solution on one side of certain kinds of membranes, as bladder or 
 parchment, will diffuse into pure water on the other side. Osmotic pressure is 
 exhibited here, but such membranes are not suitable for its study, because the 
 motion (diffusion) of the molecules of the dissolved substance is not stopped, 
 but only hindered. It is possible, however, to prepare membranes which are 
 permeable to the solvent, but impermeable to the dissolved substance. These 
 are known as semi-permeable membranes, and by their means the phenomena 
 of osmotic pressure can be studied qualitatively and quantitatively. W. 
 Pfeffer, a botanist, was the first to successfully construct (1877) an artificial 
 semi-permeable membrane by causing a precipitate of copper ferrocyanide to 
 be formed within the walls of a porous unglazed porcelain cup. 1 Such cups 
 are known as osmotic cells. When a solution of any substance, say, cane-sugar, 
 is placed in the cell and the latter is placed in water, it is observed that water 
 passes through the cell into the solution, but no sugar passes out into the 
 water. If the flow of water is unobstructed, it will continue until the solution 
 is so much diluted that it is practically the same as water. If the accumulation 
 of water in the cell is obstructed by using a closed cell filled with the solution 
 and fitted with a manometer, pressure is seen to develop in the cell, due to the 
 tendency of the water to pass into it, and corresponding to the amount that 
 would have passed into it had the water not been obstructed. It requires some 
 hours for this pressure to reach a maximum, and the amount in atmospheres 
 can be read on the manometer. At the maximum the pressure on the water 
 within the cell causes it to tend to flow out as fast as the water outside tends 
 to flow in, thus producing a system in equilibrium. The pressure read on the 
 manometer is equal to the osmotic pressure of the molecules of the dissolved 
 substance against the membrane of the cell. 
 
 1 It was rather difficult to prepare such membranes until a method was devised by Prof. 
 H. N. Morse, by which practically flawless osmotic cups can be readily made. See Amer- 
 Chem. Jour., July, 1905, and later. 
 
 
SOLUTION. 163 
 
 In osmotic cells the pure solvent always passes into the solution, or the sol- 
 vent passes from a solution of less concentration into one of greater concentra- 
 tion. This flow can be accounted for on the physical principle of equilibrium, 
 namely, that in any system capable of movement or adjustment a strain in one 
 part will cause a movement tending to remove or equalize the strain. A 
 system of a membrane and a liquid on each side of it can be in equilibrium 
 only when the osmotic pressure on the two sides of the membrane is the same. 
 In the case of a semi-permeable membrane, the molecules of the dissolved sub- 
 stance cannot pass, so the only other way of equalizing osmotic pressure is by 
 the solvent passing from the exterior of the cell into the solution, until the 
 osmotic pressure is the same on each side of the membrane. If this passage is 
 obstructed the tendency still exists, which manifests itself as pressure. 
 
 In 1887 van't Hoff deduced from theoretical considerations the laws of 
 osmotic pressure, which are verified by experiments. These laws are analogous 
 to the gas laws, and are as follows : 
 
 The osmotic pressures of solutions of the same substance are proportional to their 
 concentrations. This is analogous to Boyle's law for gas pressures, and in gen- 
 eral is independent of the nature of the solvent. It is illustrated by the 
 following results : 
 
 Grammes of cane-sugar in 1000 grammes of water.. . . 
 
 68.4 
 
 136.8 
 
 171 
 
 342 
 
 
 483 
 
 972 
 
 1215 
 
 2446 
 
 
 
 
 
 
 Osmotic pressure increases in proportion to the absolute temperature. This is 
 analogous to the law of Charles for gases. 
 
 Solutions which at the same temperature have equal osmotic pressure contain 
 equal numbers of molecules of the dissolved substance in equal volumes. This is 
 analogous to Avogadro's law for gases. 
 
 The osmotic pressure of a substance in solution is the same in value as the gas- 
 eous pressure which it would exhibit if the same weight of it were contained as a 
 gas in the same volume at the same temperature. The osmotic pressure of a solution 
 of the molecular weight in grammes of a substance in one liter of water at 
 G. is 22 to 23 atmospheres, and the same weight of the substance in gas form 
 at C., and occupying a liter volume, would have a gas pressure of 22 to 23 
 atmospheres. 
 
 Solutions of different substances having the same osmotic pressure are said 
 to be is-osmotic or isofonic. It is not an easy matter to carry out measurements 
 of osmotic pressure except in specially equipped laboratories, but isotonic 
 solutions can be prepared, nevertheless, by taking advantage of the fact that 
 such solutions have the same freezing-points, and determination of freezing- 
 points is a routine task in laboratories. Blood-serum freezes at 0.56 C., 
 which corresponds to an osmotic pressure of about 6.6 atmospheres. A 0.95 
 per cent, aqueous solution of sodium chloride freezes at 0.56 C., and, there- 
 fore, exerts the same osmotic pressure as blood-serum. It is isotonic with 
 blood-serum. A solution of higher osmotic pressure than that of blood-serum 
 is called hypertonic, and one of lower pressure is called hypotonic. 
 
164 NON-METALS AND THEIR COMBINATIONS. 
 
 In regard to the laws of osmotic pressure, deviations from them are observed 
 in the case of aqueous solutions of the same substances for which the freezing- 
 point and boiling-point laws do not hold, namely, acids, bases, and salts. 
 These always show greater osmotic pressures than those calculated, and than 
 that shown by cane-sugar, which is a type of normally acting substance. The 
 deviations are explained by the same assumption that is made to explain devi- 
 ations from the freezing-point law (see above), namely, decomposition of mole- 
 cules into a greater number of particles, that is, ions. 
 
 13. NITROGEN. 
 Niii = 14 (13.93). 
 
 Occurrence in nature. By far the larger quantity of nitrogen is 
 found in the atmosphere in a free state. Compounds containing 
 nitrogen are chiefly the nitrates, ammonia, and many organic sub- 
 stances. 
 
 Preparation. Nitrogen is obtained usually from atmospheric air 
 by the removal of its oxygen. This may be accomplished by burn- 
 ing a piece of phosphorus in a confined portion of air, when phos- 
 phoric oxide, a white solid substance, is formed, while nitrogen is left 
 in an almost pure state. 
 
 Other methods for obtaining nitrogen are by heating a mixture of 
 potassium nitrite and ammonium chloride dissolved in water : 
 
 KNO 2 -f NH 4 C1 = KC1 -f 2H 2 O + 2N; 
 or by heating ammonium nitrite in a glass retort : 
 NH 4 NO 2 = 2H 2 + 2N. 
 
 Experiment 5. Use an apparatus as shown in Fig. 37, page 140. Place in the 
 flask about 10 grammes of potassium nitrite and nearly the same amount of 
 ammonium chloride; add enough water to dissolve the salts, and apply heat, 
 which is to be carefully regulated from the time the decomposition begins, as 
 
 QUESTIONS. Give a definition of solution and its general characteristics. 
 What are immiscible solvents and how are they employed? Define dilute, 
 concentrated, and saturated solutions. What is meant by the solubility of a 
 substance, and by heat of solution ? What is Henry's law regarding the solu- 
 tion of gases in liquids? What is the relation between the freezing-points of 
 solutions and the weights of dissolved substances? What use is made of the 
 cryoscopic method ? What is osmotic pressure? What is a semi-permeable 
 membrane? How do the laws of osmotic pressure compare with the gas laws? 
 What are isotonic, hypertonic, and hypotonic solutions ? What is the expla- 
 nation of the abnormal behavior shown by solutions of acids, bases, and salts 
 in their freezing-points, boiling-points, and osmotic pressures? 
 
NITROGEN. 165 
 
 the evolution of gas may otherwise become too rapid. Collect the gas, and 
 notice its properties mentioned below. 
 
 Properties. Nitrogen is a colorless, inodorous, tasteless gas; 
 which, at a temperature of 130 C. (202 F.) and a pressure of 
 280 atmospheres, may be condensed to a colorless liquid. It is neither, 
 like oxygen, a supporter of combustion, nor, like hydrogen, a com- 
 bustible substance ; in fact, nitrogen is distinguished by having very 
 little affinity for any other element, and it scarcely enters directly into 
 combination with any substance. Nitrogen is not poisonous, yet not 
 being a supporter of combustion it cannot sustain animal life. 
 Nitrogen is trivalent in some compounds, quinquivalent in others. 
 
 Atmospheric air is a mixture of about four-fifths of nitrogen and 
 one-fifth of oxygen, with small quantities of aqueous vapor, argon, 
 carbon dioxide, and ammonia, containing frequently also traces of 
 nitrous or nitric acid, and occasionally hydrogen sulphide, sulphur 
 dioxide, and hydrocarbons. Besides these gases there are always 
 suspended in the air solid particles of dust and very minute cells of 
 either animal or vegetable origin. 
 
 100 volumes of atmospheric air contain of 
 
 Oxygen 20.60 volumes. 
 
 Nitrogen 77.16 " 
 
 Argon 0.80 volume. 
 
 Carbon dioxide . . . . 0.03-0.04 " 
 Aqueous vapor .... 0.5 -1.40 " 
 
 Ammonia } . traces. 
 
 Nitric acid -* 
 
 Omitting all minor constituents, the composition of air by volume 
 is about 79 per cent, of nitrogen and 21 per cent, of oxygen, corre- 
 sponding in weight to 77 per cent, of nitrogen and 23 per cent, of 
 oxygen. 
 
 That atmospheric air is a mixture and not a compound of oxygen and 
 nitrogen is shown by the facts that the composition is not absolutely constant, 
 that the two elements may be mixed in the proper quantities without showing 
 the least evidence that chemical change has taken place, and that pure water 
 absorbs from air the two elements in quantities different from those in which 
 they occur in air. 
 
 Humidity, specifically called relative humidity, designates the amount 
 of aqueous vapor in the atmosphere, compared with that which is 
 required to saturate it at the respective temperature. When the air 
 is completely saturated the humidity is expressed at 100; if perfectly 
 
166 NON-METALS AND THEIR COMBINATIONS. 
 
 dry, as 0. The instruments used to determine humidity are called 
 hygrometers. 
 
 An analysis of air maybe made by the following method : A graduated glass 
 tube, containing a measured volume of air, is placed with the open end down- 
 ward into a dish containing mercury. A small piece of phosphorus is then 
 introduced and allowed to remain in contact with the air for several hours, 
 when it gradually combines with the oxygen. The remaining volume of air is 
 chiefly nitrogen, the loss in volume represents oxygen. 
 
 For the determination of carbon dioxide and water, a measured volume of 
 .air is passed through two U-shaped glass tubes. One of these tubes has previ- 
 ously been filled with pieces of calcium chloride, the other tube with pieces of 
 potassium hydroxide, and both tubes have been weighed separately. In pass- 
 ing the measured air through these tubes the first one will retain all the 
 moisture, the second one all the carbon dioxide ; the increase in weight of the 
 tubes at the end of the operation will give the amounts of the two constituents. 
 
 That oxygen is found in the atmosphere in a free state is explained 
 by the fact that all elements having affinity for oxygen have entered 
 into combination with it, while the excess is left uncombined. Mtro- 
 gen is found uncombined, because it has so little affinity for other 
 elements. 
 
 Liquefaction of air on a large scale has been made possible by a process 
 which depends on first subjecting air to a pressure of 2000 pounds to the square 
 inch and then permitting the compressed gases to escape from a needle-point 
 orifice. During the expansion of the gas heat is absorbed, i. e., the air as well 
 as the tubes in which it is contained are cooled off'. The cold thus produced 
 is used to cool another portion of compressed air, which, on expanding, becomes 
 colder than the first portion. By repeating the operation a third time the 
 temperature is brought down to 191 C. and below, and at this temperature 
 liquefaction takes place. 
 
 Liquefied air is a mobile, slightly bluish liquid which can be kept for some 
 little time in open vessels i. e., so long as the temperature of nearly 200 C. 
 below freezing is maintained by the evaporation of the liquid. 
 
 As nitrogen is somewhat more volatile than oxygen, the liquefied air, when 
 permitted to stand in open vessels, becomes gradually richer in oxygen, so that 
 finally a liquid is left containing over 80 per cent, of oxygen. Notwithstand- 
 ing the low temperature of this liquid it acts most energetically as a supporter 
 of combustion. 
 
 Of interest are the changes which are brought about in the physical proper- 
 ties of different bodies when cooled down to nearly 200 by immersion in 
 liquid air. Many malleable metals, many soft or elastic bodies, such as rubber 
 and paraffin, when subjected to this low temperature, become as brittle as badly 
 cooled glass ; changes in color, as well as in other properties, take place also. 
 
 Argon, mentioned above as a normal constituent of air, is a gaseous element, 
 discovered in 1894. It may appear strange that a normal constituent of air, 
 present to the extent of nearly 1 per cent., should have been overlooked for so 
 many years, although air had been carefully analyzed many hundred times. 
 
NITROGEN. 167 
 
 The only explanation that can be offered is the fact that argon has scarcely 
 any chemical affinity for other elements, and consequently its presence was not 
 revealed by any of the ordinary reactions used in air analysis. In fact, the 
 total of argon present had invariably been reported as nitrogen up to the time 
 of the discovery of the new element. 
 
 Helium is another gaseous element discovered in 1895. It occurs absorbed 
 in a number of rare minerals from which it is expelled by heating. It is also 
 a constituent of the gases which are disengaged from certain spring waters, 
 and, in very small quantities, is a constituent of atmospheric air. Both argon 
 and helium are very inert. Helium has an atomic weight of about 4, while 
 that of argon is 40. One volume of helium is contained in 245,000 volumes of 
 air. 
 
 Compounds of nitrogen. Nitrogen has very little tendency to 
 combine directly with other elements, bat it is an easy matter to 
 obtain compounds of nitrogen. These, however, are all obtained in 
 indirect ways, being either furnished ready made by processes of nature 
 or obtained as by-products in manufacturing industries. Conversely, 
 as a result of the inactivity of nitrogen, most of its compounds are 
 more or less unstable, either at ordinary or elevated temperatures, or 
 when brought together with other substances. We have already seen 
 how easily ammonium nitrite is radically decomposed by heat, and 
 ammonium nitrate acts in the same way, as will be seen below. 
 
 The two principal compounds of nitrogen are ammonia and nitric 
 acid, and nearly all the others with which we have to do in inorganic 
 chemistry are derived from these. The valence of nitrogen is 3 in 
 ammonia, which represents the limit of reduction, while it is 5 in 
 nitric acid, which is the limit of oxidation of nitrogen. 
 
 Ammonia, NH 3 16.93. This compound is constantly forming 
 in nature by the decomposition of organic (chiefly animal) matter, such 
 as meat, urine, blood, etc. It is also obtained during the process of 
 destructive distillation, which is the heating of non-volatile organic 
 substances in suitable vessels to such an extent that decomposition 
 takes place, the generated volatile products being collected in re- 
 ceivers. The manufacture of illuminating gas is such a process of 
 destructive distillation ; coal is heated in retorts, and most of the 
 nitrogen contained in the coal is converted into and liberated as 
 ammonia gas, which is absorbed in water, through which the gas is 
 made to pass. This is the source of nearly all the ammonium salts 
 on the market. 
 
 Another method of obtaining ammonia is through decomposition 
 of ammonium salts by the hydroxides of sodium, potassium, or cal- 
 
168 
 
 NON-METALS AND THEIR COMBINATIONS. 
 
 cium. Usually ammonium chloride is mixed with calcium hydroxide 
 
 and heated, when calcium chloride, water, and ammonia are formed : 
 
 2(NH 4 C1) + Ca(OH) 2 = CaCl 2 + 2H 2 O + 21s T H 3 . 
 
 Experiment 6. Mix about equal weights (10 grammes of each) of ammonium 
 chloride and calcium hydroxide (slaked lime) in a flask of about 200 c.c. capac- 
 ity, and arranged as in Fig. 39; cover the mixture with water and apply heat. 
 
 FIG. 39. 
 
 
 Apparatus for generating amuioiiia. 
 
 As long as any atmospheric air remains in the apparatus, bubbles of it will 
 pass through the water contained in the cylinder; afterward all gas will be 
 readily and completely absorbed by the water. Notice the odor and alkaline 
 reaction on litmus of the ammonia water thus obtained. When the gas is 
 being freely liberated, move the tube upward, as shown in B, and collect the 
 gas by upward displacement in a cylinder or tube, which when filled with gas 
 is held mouth downward into water, which will rapidly rise in the tube by 
 absorption of the gas. Notice that ammonia is not readily combustible, by 
 applying a flame to the gas escaping from the delivery tube. 
 
 Ammonia is a colorless gas, of a very pungent odor, an alkaline 
 taste, and a strong alkaline reaction. In pure oxygen it burns, form- 
 ing water and free nitrogen. 
 
 By the mere application of a pressure of seven atmospheres or by 
 intense cold (40 C., 40 F.), ammonia may be converted into a 
 liquid, which at 80 C. (112 F.) forms a solid crystalline mass. 
 Water, at its freezing-point, dissolves as much as 1050 volumes of 
 ammonia gas, and at 15 C. (59 F.) still retains 727 volumes of the 
 gas in solution. This solution contains ammonium hydroxide : 
 NH 3 + H 2 = NH 4 OH. 
 
 Certain experimental evidence indicates that only a small propor- 
 tion of the gas is combined with water to form hydroxide, most of it 
 
NITROGEN. 169 
 
 being simply dissolved. By boiling, all the ammonia is finally driven 
 out of solution. 
 
 It has a strong alkaline action on litmus and has basic properties 
 like those of sodium and potassium hydroxide. It neutralizes acids 
 forming salts, thus : 
 
 NH 4 OH + HC1 = NH 4 C1 + H 2 O. 
 
 Ammonia gas also unites with acids directly without elimination of 
 water. For example, with hydrochloric acid gas, a dense white cloud 
 of ammonium chloride is formed : 
 
 NH 3 + HC1 = NH 4 C1. 
 
 The union of water or hydrochloric acid directly with ammonia is 
 explained by the increase of valence of the nitrogen atom from 3 to 
 5. In the hydroxide and all the salts, there is a group of atoms, 
 (NH 4 ) , which acts exactly like an atom of metal. It has, therefore, 
 been called ammonium. This radical and its analytical reactions will 
 be discussed under Ammonium compounds. 
 
 Experiment 7. To about 20 c.c. of dilute ammonia water, add concentrated 
 hydrochloric acid until litmus-paper is just turned from blue to red by the 
 liquid. Evaporate to dryness in a porcelain dish over a small flame. Note 
 appearance of residue and compare its taste with that of the ammonia water, 
 and dilute hydrochloric acid and also that of ammonium chloride. What is 
 the residue? This is an example of the formation of a salt by neutralization 
 of an acid by an alkali. 
 
 Ammonia "water, Aqua ammoniae (Spirit of hartshorn). This is 
 a solution of ammonia gas in water or ammonium hydroxide in water. 
 The common ammonia water contains 10 per cent, by weight, equal 
 to 125 volumes of ammonia, and has a specific gravity of 0.958 at 
 25 C. ; the stronger ammonia water, aqua ammonias fortior, contains 
 28 per cent., and has a specific gravity of 0.897 at 25 C. Ammonia 
 water has the odor, taste, and reaction which characterize the gas. 
 
 Hydrazine, N 2 H 4 (Diamine], is a compound obtainable from organic com- 
 pounds by processes which cannot be considered here. It is a colorless gas at 
 summer heat, readily liquefying at a somewhat lower temperature, and solidi- 
 fying at the freezing-point of water. 
 
 Exposed to the air it takes up oxygen, forming water and nitrogen. In its 
 chemical properties hydrazine resembles ammonia, forming a hydrate of 
 the composition N 2 H 4 .H 2 O, and salts with acids, such as N 2 H 4 .H 2 SO 4 and 
 N 2 H 4 (HC1) 2 . The constitution of hydrazine may be represented by the 
 
 H \ / H 
 
 formula >N NC 
 
 H/ \H 
 
 Hydroxylamine, NH 2 OH. The term amine is used to designate com- 
 
170 NON-METALS AND THEIR COMBINATIONS. 
 
 pounds derived from ammonia by replacement of one or more hydrogen atoms 
 by basic atoms or radicals, and it is in keeping with this terminology that the 
 compound under consideration is known as hydroxyl-amine, while hydrazine 
 is termed di-amine. 
 
 Hydroxylamine is prepared by the action of nascent hydrogen on nitric acid : 
 
 HN0 3 + 6H = NH 2 OH -f 2H 2 O. 
 
 The compound is known only in solution ; with acids it forms well-defined 
 salts, which appear to be ammonium salts in which a hydrogen atom has been 
 replaced by hydroxyl. The formation of salts may be represented thus : 
 
 NH 2 OH +HN0 3 - NH 3 OHNO S 
 NH 2 OH + HC1 == NH 3 OHC1 
 
 Triazoic acid, N 3 H (Hydrazoic add). This remarkable substance was first 
 isolated in 1890 from organic compounds. It is now obtained also from inor- 
 ganic material by the action of sodium on ammonia, when a compound of 
 the composition NH 2 Na is formed, which by treatment with nitrogen monoxide 
 produces water and sodium triazoate. The latter, by the action of an acid, is 
 converted into a sodium salt and free triazoic acid. The three steps of the 
 process may be represented thus : 
 
 NH 3 + Na = NH 2 Na + H 
 
 NH 2 Na + N 2 = Na N/ || + H 2 O 
 
 /N /N 
 
 2Na-N/ || + H 2 SO 4 = N a2 SO 4 + 2HN/ |^ 
 
 Triazoic acid is a colorless gas, possessing a disagreeable odor. It is soluble 
 in water, and this solution can be distilled, but the operation is dangerous, as 
 the compound is apt to decompose with explosive violence. When inhaled it 
 acts as a poison, producing violent headache. 
 
 While the three compounds of hydrogen with nitrogen considered above are 
 of a basic nature, triazoic acid has decidedly acid properties. In fact, it is a 
 stronger acid than acetic acid, and resembles hydrochloric acid in precipitating 
 soluble silver and rnercurous salts. 
 
 Compounds of nitrogen and oxygen. Five distinct compounds 
 of nitrogen and oxygen are known. They are named and constituted 
 as follows : 
 
 Composition. 
 
 By weight. By volume. 
 
 NO NO 
 
 Nitrogen monoxide, N 2 O ... 28 16 2 1 
 
 Nitric oxide, NO 28 32 2 2 
 
 Nitrogen trioxide, N 2 O 3 ... 28 48 2 3 
 
 Nitrogen tetroxide, N 2 O 4 = 2(NO 2 ) . 28 64 24 
 
 Nitrogen pentoxide, N 2 O 5 ... 28 80 2 5 
 
 The trioxide and pentoxide are called also acid anhydrides, or ni- 
 trous and nitric anhydride respectively, because they combine with 
 
NITROGEN. 171 
 
 water to give nitrous and nitric acid. Conversely, when the acids are 
 deprived of the elements of water, the respective oxides of nitrogen 
 are obtained. The monoxide corresponds to hyponitrous acid, 
 H 2 N 2 O 2 , but does not yield the acid with water. It is, hence, not an 
 anhydride. All of the oxides are obtained from nitric acid, directly 
 or indirectly. The last one is formed by abstraction of water from 
 nitric acid, the others involve reduction of nitric acid or, in reality, 
 of nitrogen pentoxide. 
 
 While our knowledge of the structure of the oxides of nitrogen is unsatis- 
 factory, the following graphic formulas, in which the valence of nitrogen is 
 assumed to be either 1, 3, or 5, have been proposed to show the manner in which 
 the atoms may be linked together : 
 
 Nitrogen monoxide, N O N or N N 
 
 Nitric oxide, N = O 
 
 Nitrogen trioxide, O = N O N=Oor 
 
 Nitrogen tetroxide, 
 
 Nitrogen pentoxide, 
 
 Nitrogen tetroxide, at high temperature, has the composition N0 2 , and it is 
 possible that in NO 2 , and nitric oxide, NO, the valence of nitrogen is 4 and 2 
 respectively. The truth is that we have not sufficient knowledge of the struc- 
 ture of the oxides of nitrogen to make any positive statement as to the valence 
 of nitrogen in them. 
 
 The structure of the nitrogen acids may be represented thus : 
 
 N OH 
 Hyponitrous acid, N OH, or possibly II ^ 
 
 Nitrous acid, O = N - OH, or N \OH 
 
 //O 
 Nitric acid, ^N OH, or 
 
 Nitrogen tetroxide, at low temperature, has the formula N 2 O 4 , but at 
 elevated temperatures this splits up into 2NO 2 , to form again N 2 O 4 , when 
 the temperature is decreased. There are many other cases like 
 chemistry. 
 
172 N OX-METALS AND THEIR COMBINATIONS. 
 
 Such a decomposition which proceeds at high temperatures, while at lower ones 
 the constituents can recombine, is called dissociation. 
 
 When electric sparks pass through atmospheric air some ozone is generated 
 which oxidizes nitrogen, forming first the lower and then also the higher 
 oxides; these combine with water to form nitrous and nitric acid, which acids 
 are taken up by the ammonia present in the air, forming the respective 
 ammonium salts. 
 
 Nitrogen monoxide, N 2 O (sometimes called nitrous oxide ; 
 also laughing gas). This compound was discovered by Priestley in 
 1776; its anaesthetic properties were first noticed in 1800 by Sir 
 Humphry Davy, and it was first used in dentistry by Dr. Horace 
 Wells, a dentist of Hartford, Conn., in 1844. It may be easily 
 obtained by heating ammonium nitrate in a flask at a temperature 
 not exceeding 250 C. (482 F.), when the salt is decomposed into 
 nitrogen monoxide and water : 
 
 NH<NO 3 = 2H,O + N 3 O. 
 
 When nitrous oxide is prepared for use as an anesthetic it should 
 be passed through two wash-bottles containing caustic soda and ferrous 
 sulphate respectively ; these agents will retain any impurities that may 
 be formed during the decomposition, especially from an impure salt 
 
 Ammonium nitrate to be used for generating pure nitrous oxide should be 
 completely volatilized when heated on platinum foil ; its solution in water 
 should not be rendered turbid by silver nitrate, as this would indicate the 
 presence of chlorides. These latter are objectionable because gaseous com- 
 pounds of chlorine with the oxides of nitrogen may be formed. If the gas is 
 prepared as directed above, it can be used with safety. 
 
 Impurities found in the gas when not properly made are air, nitric oxide, 
 chlorine, chloronitrous and chloronitric oxides. 
 
 If the gas is stored over water, considerable loss is experienced on account 
 of the solubility of nitrous oxide in cold water. This loss can be diminished 
 by using hot water or a concentrated solution of common salt in water, both of 
 which liquids dissolve less of the gas. 
 
 Experiment 8. Use apparatus as represented in Fig. 37, page 140. Place in the 
 dry flask about 10 grammes of ammonium nitrate, apply heat, collect the gas 
 in cylinders over water, and verify by experiments and observations the correct- 
 ness of the statements below regarding the physical and chemical properties 
 of nitrogen monoxide. 
 
 Nitrogen monoxide is a colorless, almost inodorous gas, of dis- 
 tinctly sweet taste. It supports combustion almost as energetically 
 as oxygen, but differs from this element by its solubility in cold water, 
 which absorbs nearly its own volume. Under a pressure of about 
 50 atmospheres it condenses to a colorless liquid, the boiling-point of 
 which is at about -90 C. (-130 F.) and the freezing-point at 
 -102 C. (-151.6 F.). 
 
NITROGEN. 173 
 
 When inhaled it causes exhilaration, intoxication, anaesthesia, and, 
 finally, asphyxia. The gas is used in dentistry as an anesthetic, the 
 liquefied compound being sold for this purpose in wrought-iron 
 cylinders. There are two sizes of these cylinders : the smaller con- 
 tain about one and a half pounds of the liquid, equal to 100 gallons 
 of gas; the larger size contains about five times that quantity. 
 
 Nitric oxide, NO. This is a colorless gas which is formed gener- 
 ally when nitric acid acts upon metals or upon substances which 
 deoxidize it. It is capable of combining directly with one or more 
 atoms of oxygen, thereby forming nitrogen tetroxide, called nitrogen 
 peroxide, NO 2 or N 2 O 4 , which is a gas of deep red color and poison- 
 ous properties. Nitrogen trioxide, N 2 O 3 , exists as an indigo-blue 
 liquid at temperatures below 21 C. (-6 F.); above this tem- 
 perature it decomposes into NO and NO 2 . 
 
 Experiment 9. Use apparatus as shown in Fig. 38. Put about 20 grammes 
 of copper or brass turnings into the flask and pour through the funnel tube a 
 mixture of 30 c.c. concentrated nitric acid and 50 c.c. water. Apply gentle 
 heat and collect several bottles of gas. ^Note that the gas. in the flask is at 
 first colored. Why? Remove the cover from a bottle of the gas, and explain 
 the result. Insert a stick with a flame into another bottle of the gas, and com- 
 pare with the action of nitrous oxide. If copper is used, filter the solution 
 after all copper is dissolved, and evaporate to get blue crystals of copper 
 nitrate. For explanation of the reaction, see below, under Nitric Acid. 
 
 Hyponitrous acid, HNO, or possibly H 2 N 2 2 , is a very unstable white, 
 flaky solid. Neither the acid, nor its salts, the hyponitrifces, are of practical 
 interest. 
 
 Nitrous acid, HNO 2 , has not been obtained in a pure state, but 
 exists in solution. Several of its salts, the nitrites, are well known 
 and are used analytically and otherwise. Nitrous acid very readily 
 breaks down into water and its anhydride, N 2 O 3 , which escapes as 
 brown fumes from the solution. Hence, the salts of the acid are 
 decomposed by nearly all other acids. Nitrous acid acts as an oxid- 
 izing agent toward some substances, being itself reduced to lower 
 oxides, and as a reducing agent toward others, being then oxidized to 
 nitric acid. A solution of nitrous acid in water or other acids has a 
 pale blue color. 
 
 Tests for nitrous acid and nitrites. 
 (Use about a 5 per cent, solution of sodium or potassium nitrite.) 
 1. To 5 c.c. of the solution, add a little strong sulphuric acid. Note 
 the colored fumes and effervescence and the bluish color of the liquid. 
 
174 NON-METALS AND THEIR COMBINATIONS. 
 
 2. To the same amount of the solution, add some acidified solution 
 of potassium permanganate, which is decolorized at once. What 
 becomes of the nitrite ? 
 
 3. Carry out the directions of Test 1, under Hydrogen Dioxide, 
 using a few drops of the nitrite solution in place of the hydrogen 
 dioxide. Note that the blue color is not developed until an acid is 
 added. Only free nitrous acid acts on potassium iodide : 
 
 HN0 2 + HI == H 2 + NO + I. 
 This is a very delicate test, but not decisive alone. 
 
 4. Dilute 1 drop of the nitrite solution in half a beakerful of 
 water, add 1 c.c. of meta-phenylene-diamine reagent (see Nitrous Acid, 
 under Water Analysis, at end of chapter 38). A yellow to dark 
 brown color is produced, according to the proportion of nitrite. The 
 test is used only for very small amounts of nitrite. 
 
 Test 1 is usually sufficient to recognize a nitrite. 
 
 Nitric acid, Acidum nitricum, HNO 3 ; NO 2 OH, = 62.57 (Aqua 
 fortis). Nitrogen pentoxide, N 2 O 5 , a white, solid, unstable compound, 
 is of scientific interest only. Whjsn brought in contact with water it 
 readily combines with it, forming nitric acid : 
 
 N 2 O 5 + H 2 = 2HNO 3 . 
 
 The usual method for obtaining nitric acid is the decomposition of 
 sodium nitrate by sulphuric acid : 
 
 NaNO 3 + H 2 SO 4 == HNO 3 + HNaSO 4 ; 
 
 Sodium 
 bisulphate. 
 
 or 
 
 2NaNO 3 + H 2 SO. = 2HNO 3 + Na^SO,. 
 
 Sodium 
 sulphate. 
 
 At the present time nitric acid is produced also from the atmosphere by 
 causing the nitrogen and oxygen to unite under the influence of electric dis- 
 charges. The nitrogen tetroxide formed, when dissolved in water, gives nitric 
 acid and nitric oxide : 
 
 3N0 2 + H 2 == 2HN0 3 + NO. 
 
 The NO unites with oxygen to give N0 2 , which is again dissolved. The com- 
 mercial success of this method depends upon the cost of electric power. It is 
 interesting as offering a source of nitrates when the native supply shall have 
 been exhausted. 
 
 Experiment 10. Prepare an apparatus as shown in Fig. 40. Heat in a retort of 
 about 250-c.c. capacity a mixture of about 50 grammes of potassium nitrate 
 
NITROGEN. 175 
 
 and nearly the same weight of sulphuric acid. Nitric acid is evolved and distils 
 over into the receiver, which is to be kept cool during the operation by pouring 
 cold water upon it or by surrounding it with pieces of ice. Examine the 
 properties of nitric acid thus made, and use it for the tests mentioned below. 
 How much pure nitric acid can be obtained from 50 grammes of potassium 
 nitrate? Weigh the acid which you obtain in the experiment and compare 
 this weight with the theoretical quantity. 
 
 Nitric acid is an almost colorless, fuming, corrosive liquid, of 
 a peculiar, somewhat suffocating odor, and a strongly acid reaction. 
 When exposed to sunlight it assumes a yellow or yellowish-red 
 color in consequence of its decomposition into nitrogen tetroxide, 
 water, and oxygen. 
 
 Common nitric acid, of a specific gravity 1.403 at 25 C., is com- 
 posed of 68 per cent, of HNO 3 and 32 per cent, of water. The diluted 
 nitric acid of the U. S. P. is made by mixing ten parts by weight of 
 the common acid with fifty-eight parts of water, and contains 10 per 
 cent, of absolute nitric acid ; it has a specific gravity of 1.054 at 
 25 C. 
 
 Fuming nitric add has a brown-red color, due to nitrogen tetroxide, 
 and emits vapors of the same color. Specific gravity 1.45 to 1 50. 
 
 FIG. 40. 
 
 Distillation of nitric acid. 
 
 Nitric acid is completely volatilized by heat ; it stains animal matter 
 distinctly yellow and destroys the tissue ; it is a monobasic acid, form- 
 ing salts called nitrates. These salts are all soluble in water, for 
 which reason nitric acid cannot be precipitated by any reagent. 
 
176 NON-METALS AND THEIR COMBINATIONS. 
 
 Nitric acid is a strong oxidizing agent ; this means that it is capable 
 of giving off part of its oxygen to substances having affinity for it. 
 
 Nitric acid of 68 per cent, has a constant boiling-point and distils un- 
 changed. A more concentrated acid decomposes in part when distilled, 
 2HNO 3 = 2NO 2 4- H 2 + O, while a more dilute acid gives off water at first. 
 In either case, repeated distillation gives a 68 per cent. acid. 
 
 The action of nitric acid upon such metals as copper, silver, and many others 
 involves two changes, viz. : displacement of the hydrogen of the acid by the 
 
 metal : 
 
 Cu + 2HNO 3 = Cu(NO 3 ) 2 + 2H; 
 
 and the deoxidation of another portion of nitric acid by the liberated hydrogen 
 while yet in the nascent state. Thus : 
 
 HNO 3 + 3H = 2H 2 O + NO. 
 
 The liberated nitrogen dioxide, which is colorless, readily absorbs oxygen 
 from the air, forming red vapors of nitrogen tetroxide. 
 
 Another explanation of the chemical action of nitric acid on metals is based 
 on our knowledge of the fact that nitric acid readily gives up part of its oxygen 
 to any substance having affinity for it. Therefore, it majjfce assumed that the 
 first action of the acid on metals 'is their conversion into oxides, which are 
 immediately changed into nitrates, thus: 
 
 2HN0 3 + 3Cu = 3CuO + H 2 O + 2NO. 
 CuO + 2HNO,= Cu(NO 3 ) 2 + H 2 O. 
 
 Tests for nitric acid or nitrates. 
 (Potassium nitrate, KNO 3 , may be used as a nitrate ) 
 
 1. Fairly strong nitric acid with copper turnings gives copious red 
 fumes. Rather dilute acid, however, has not a very marked action, 
 even when heated, but the action is increased by the addition of some 
 concentrated sulphuric acid. A nitrate, dry or in solution, has no 
 action on copper, but addition of concentrated sulphuric acid (to set 
 free the nitric acid) causes evolution of red fumes. 
 
 2. The solution of a nitrate, to which a few small pieces of ferrous 
 sulphate have been added, will show a reddish-purple or black color- 
 ation upon pouring a few drops of strong sulphuric acid down the 
 side of the test-tube, so that it may form a layer at the bottom of the 
 tube. The black color is due to the formation of an unstable com- 
 pound of the composition 2FeSO 4 .NO. Free nitric acid also re- 
 sponds to this test, which is delicate and very often used. 
 
 3. Nitrates deflagrate when heated on charcoal by means of the 
 blow-pipe flame. The high temperature causes the nitrate to decom- 
 pose and liberate oxygen, which unites with the charcoal energetically. 
 
NITROGEN. 177 
 
 Such action is called dcf (if/ration. Other oxidizing substances act 
 like nitrates. 
 
 4. When a few drops of a solution of 0.1 gramme of diphenylamine 
 in ;")() c.c. of 10 per cent, sulphuric acid are added to a very dilute 
 solution of a nitrate, and then some concentrated sulphuric acid is 
 carefully poured down the side of the test-tube, a deep blue color is 
 produced at the line of contact. 
 
 A similar reaction is also produced by hypochlorites, chlorates, 
 chromium trioxide, ferric salts, and similar oxidizing agents. 
 
 When the test is made with a similar solution of pyrogallic acid 
 instead of the diphenylamine solution, a deep brown color is 
 produced. 
 
 The tests with diphenylamine and pyrogallic acid show 1 part of nitric 
 acid in three and ten million parts of water respectively, and are used chiefly 
 to detect traces of nitric acid in drinking-water. As sulphuric acid may con- 
 tain nitric acid, the tests should also be made with the sulphuric acid alone in 
 order to prove its purity. 
 
 Tests 1 and 2 are sufficient to identify nitric acid or its salts. Nitrites also 
 respond to these tests, but they give red fumes by merely adding a dilute acid, 
 thus differing from nitrates. 
 
 Poisonous properties; antidotes. Strong nitric acid is a corrosive, 
 violent poison. It first stains the tissues with which it comes in contact a 
 bright-yellow color, and then corrodes them. 
 
 As an antidote in cases of poisoning by nitric acid a solution of sodium car- 
 bonate, or a mixture of magnesia and water, milk of lime, or other alkalies 
 well diluted may be administered with the view of neutralizing the acid. 
 
 QUESTIONS. State the physical and chemical properties of nitrogen. Men- 
 tion the principal constituents of atmospheric air and the quantity in which 
 they are present. By what processes can the four chief constituents of atmo- 
 spheric air be determined? Mention some decompositions by which ammonia 
 is generated. Explain the process of making ammonia water. State the 
 physical and chemical properties of ammonia gas and ammonia water. How 
 is nitrogen monoxide obtained, and what are its properties? Describe the 
 process for making nitric acid, and give symbols for decomposition. How 
 does nitric acid act on animal matter, and what are its properties generally? 
 Give tests and antidote for nitric acid. 
 12 
 
178 NON-METALS AND THEIR COMBINATIONS. 
 
 14. CARBON. SILICON. BORON. 
 O = 12 (11.91). Si* = 28.3. B' = 10.9. 
 
 Occurrence in nature. Carbon is a constituent of all organic 
 matter. In a pure state it is found crystallized as diamond and 
 graphite, amorphous in a more or less pure condition in the various 
 kinds of coal, charcoal, boneblack, lampblack, etc. As carbon 
 dioxide, carbon is found in the air; as carbonic acid, in water; as 
 carbonates (marble, limestone, etc.), in the solid portion of our earth. 
 
 Properties. The three different allotropic modifications of carbon 
 differ widely from each other in their physical properties. 
 
 Diamond is the purest form of carbon, in which it is crystallized in 
 regular octahedrons, cubes, or in some figure geometrically connected 
 with these. Diamond is the hardest substance known ; when heated 
 intensely in the presence of oxygen it burns, forming carbon dioxide. 
 
 Graphite, plumbago, or black-lead, is carbon crystallized in short 
 six-sided prisms ; it is a somewhat rare, dark-gray mineral, having 
 an almost metallic lustre. It feels soft and greasy between the fingers 
 and leaves a black mark when drawn over a white surface. It is 
 used to make lead pencils, and also as a lubricator, in stove polish, 
 as an admixture with clay used for crucibles, etc. 
 
 Amorphous carbon is always a black solid, but the hardness and 
 specific gravity of the different kinds of amorphous coal differ widely. 
 Amorphous carbon in the various kinds of coal is the chief agent for 
 generating heat by combustion. In the form of lamp-black it is used 
 in printer's ink ; in bone-black it serves for decolorizing sugar syrups 
 and other liquids. 
 
 Neither form of carbon is soluble in any of the common solvents, 
 but it dissolves to some extent in melted iron. On cooling, under 
 ordinary conditions, most of the dissolved carbon separates in the 
 form of graphite ; when cooling takes place under high pressure 
 small diamond-like crystals may be obtained. By the intense heat 
 produced by electricity carbon becomes softened and in small quan- 
 tities also volatilized. 
 
 Carbon is a quadrivalent element ; it has little affinity for metals, 
 though at high temperatures it combines with many, forming com- 
 pounds, termed carbides. It does not enter into combination with 
 oxygen at ordinary temperature, but at red heat it combines eagerly 
 with free or combined oxygen, serving in many cases as a deoxidizing 
 agent. Compounds of carbon with other non-metallic elements are 
 mostly formed by indirect processes. 
 
CARBON, SILICON, BORON. 179 
 
 Carbon compounds. The chemistry of the carbon compounds is 
 very extensive and intricate. There are more compounds containing 
 carbon than the total of all other compounds, and for good reasons 
 they are ptudied in a subdivision of chemistry, called Organic Chem- 
 istry. A few simple compounds are taken up in Inorganic Chem- 
 istry because of their similarity in properties to the other inorganic 
 compounds. These are the two oxides of carbon, the carbonates, 
 carbon disulphide, and sometimes the cyanides and sulphocyanates. 
 
 Nearly all animal and vegetable substances contain carbon, and 
 when heated they usually undergo decomposition and char, that is, 
 leave a residue of black carbon. This is because the other elements 
 go off first in various combinations, while carbon remains last. But 
 some of the carbon also passes off as volatile products. If the heat 
 is high enough and air has access, the carbon finally disappears or, as 
 is said, the substance burns up. Carbon compounds that are volatile 
 when heated do not char. For example, alcohol, ether, chloroform, 
 and many others simply vaporize when heated, although they contain 
 carbon. Carbon may be shown to be present in such compounds by 
 burning them in the air (when combustible) under a funnel and draw- 
 ing the products through lime-water, or by causing the vapors to come 
 in contact with copper oxide heated to redness in a tube and passing 
 the products through lime-water. When carbon compounds are 
 burned up, either in air or by oxidizing agents, as copper oxide, the 
 carbon passes off as gaseous carbon dioxide, CO 2 , which unites with 
 lime-water to form insoluble white calcium carbonate. In fact, this 
 is the only common gas which acts in this way with lime-water. 
 
 When carbon compounds containing non-volatile metals are 
 charred, the metals remain as carbonates or oxides mixed with the 
 residue of carbon. Many carbon compounds char when heated with 
 concentrated sulphuric acid because the acid extracts hydrogen and 
 oxygen in the proportions to form water, for which it has a powerful 
 affinity, thus leaving a residue of carbon. 
 
 Experiment 11. a. Heat a little starch on charcoal with the blow-pipe 
 flame. Note that it blackens and burns up completely. 
 
 6. Heat a small knifepointful of sugar in a dry test-tube, gradually increas- 
 ing the temperature. Note the melting, browning condensation of water on 
 the walls of the tube, odor, and final charring. 
 
 c. Heat gradually a little Eochelle salt (K.Na.C 4 H 4 O 6 ) in a porcelain cru- 
 cible held in a triangle. The salt melts, effervesces, evolves inflammable 
 vapors, and chars. Heat finally to redness, cool, and add some dilute acid. 
 Any effervescence ? Explain. Make the same experiment with tartaric acid. 
 Note any difference in results. Note also the odor while heating. 
 
180 NON-METALS AND THEIR COMBINATIONS. 
 
 d. Insert a burning stick of wood into a pint bottle or flask, mouth down, 
 until flame is extinguished ; then remove the stick (is it charred?), pour into 
 the bottle about 50 c.c. of lime-water and shake it. Explain results. 
 
 e. Heat slowly about 2 c.c. concentrated sulphuric acid in a dry test-tube with 
 a bit of starch, sugar, Rochelle salt, and wood respectively. Describe and 
 explain the results. 
 
 Carbon dioxide, CO 2 . (Formerly named carbonic acid, or anhy- 
 drous carbonic acid.) This compound is always formed during the 
 combustion of carbon or of organic matter ; also during the decay 
 (slow combustion), fermentation, and putrefaction (process of decom- 
 position) of organic matter; it is constantly produced in the animal 
 system, exhaled from the lungs, and given off through the skin. 
 
 Many spring waters contain considerable quantities of the gas, a 
 part of which escapes from the water as it rises to the surface. 
 
 By heating, many carbonates are decomposed into oxides of the 
 metals and carbon dioxide. 
 
 Lime-burning is such a process of decomposition : 
 
 CaCO 3 = CaO -f CO 2 . 
 Calcium Calcium 
 carbonate, oxide. 
 
 Another method for the generation of carbon dioxide is the decom- 
 position of any carbonate by an acid : 
 
 CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 . 
 Calcium Hydrochloric Calcium 
 carbonate. acid. chloride. 
 
 The reason the action takes place readily and proceeds to completion 
 is because carbonic acid is only slightly soluble in water and easily 
 breaks up into water and carbon dioxide gas, which escapes and is 
 removed from the field of action, thus permitting the decomposition 
 to be constantly renewed. Almost any acid will liberate carbon di- 
 oxide from a carbonate. The same principle is involved here as in 
 the case of the liberation of nitrous acid from nitrites, nitric acid 
 from nitrates, sulphurous acid from sulphites, or hydrochloric acid 
 from chlorides. (See Reversible Actions, p. 114.) 
 
 Experiment 12. Use apparatus represented in Fig. 38, page 146. Place about 
 20 grammes of marble, CaCO 3 , in small pieces (sodium carbonate or any other 
 carbonate may be used) in the flask, cover it with water, and add hydrochloric 
 acid through the funnel-tube. The escaping gas may be collected over water, 
 as in the case of hydrogen, or by downward displacement, i. e., by passing the 
 delivery-tube to the bottom of a tube or other suitable vessel, when the carbon 
 dioxide, on account of its being heavier than atmospheric air, gradually dis- 
 places the latter. This will be shown by examining the contents of the vessel 
 with a burning taper, which is extinguished as soon as most of the air has 
 been expelled. 
 
CARBON, SILICON, BO RON. 181 
 
 Examine the gas for its high specific gravity by pouring it from one vessel 
 into another ; for its power of extinguishing flames, by mixing it with an equal 
 volume of air, which mixture will be found not to support the combustion of 
 a taper notwithstanding that oxygen is contained in it. Add to one portion of 
 the collected gas some lime-water, shake it, and notice that it becomes turbid. 
 Blow air exhaled from the lungs through a glass tube into lime-water, and 
 notice that it also turns turbid. 
 
 Continue to pass the gas through the turbid liquid, and notice that it becomes 
 clear in consequence of the dissolving action of carbonic acid water on calcium 
 carbonate. On heating the solution carbon dioxide is expelled and calcium 
 carbonate is reprecipitated. (So-called " hard " waters often contain calcium 
 carbonate dissolved by carbonic acid. On heating these hard waters they 
 become "soft," because the dissolved carbonate is precipitated.) 
 
 If marble has been used for the experiment, neutralize the liquid in the flask, 
 if acid, by adding more marble until action ceases, filter, and evaporate it in a 
 dish to dry ness. The solid residue is a salt, calcium chloride. Expose some 
 of it to the air for a long time and note that it absorbs moisture or deliquesces. 
 What method of salt formation is illustrated by this experiment? 
 
 If sodium carbonate has been used, neutralize the liquid by adding acid 
 or carbonate, as may be required, filter, and evaporate it to dryness. Taste 
 the residue. What is it ? Taste also sodium carbonate and the acid. 
 
 Carbon dioxide is a colorless, odorless gas, having a faintly acid 
 taste. By a pressure of 38 atmospheres, at a temperature of C. 
 (32 F.), carbon dioxide is converted into a colorless liquid, which by 
 intense cold ( 79 C., 110 F.) may be converted into a white, 
 solid, crystalline, snow-like substance. The specific gravity of carbon 
 dioxide is 1.529 ; it is consequently about one-half heavier than 
 atmospheric air. One liter at C. and 760 mm. pressure weighs 
 1.977 grammes. 
 
 Cold water absorbs at the ordinary pressure about its own volume 
 of carbon dioxide, but the solubility is increased one volume for every 
 increase of one atmosphere in pressure (soda water). 
 
 Carbon dioxide is not combustible, and not a supporter of combus- 
 tion ; on the contrary, it has a decided tendency to extinguish flames, 
 air containing one-tenth of its volume of carbon dioxide being unable 
 to support the combustion of a candle. While not poisonous when 
 taken into the stomach, carbon dioxide acts indirectly as a poison 
 when inhaled, because it cannot support respiration, and prevents, 
 moreover, the proper exchange between the carbon dioxide of the 
 blood and the oxygen of the atmospheric air. 
 
 Common atmospheric air contains about 4 volumes of carbon 
 dioxide in 10,000 of air, or 0.04 per cent. In the process of respira- 
 tion this air is inhaled, and a portion of the oxygen is absorbed in 
 the lungs by the blood, which conveys it to the different portions of the 
 
182 NON-METALS AND THEIR COMBINATIONS. 
 
 animal body, and receives in exchange for the oxygen a quantity of 
 carbon dioxide, produced by the union of a former supply of oxygen 
 with the carbon of the different organs to which the blood is supplied. 
 The air issuing from the lungs contains this carbon dioxide, in 
 quantity about 4 volumes in 100 of exhaled air, which is 100 times 
 more than contained in fresh air. 
 
 Exhaled air is, moreover, contaminated by other substances than carbon 
 dioxide, such as ammonia, hydrocarbons, and most likely traces of other or- 
 ganic bodies, the true nature of which has not been fully recognized, but which 
 seem to be directly poisonous. The bad effects experienced in breathing air 
 which has become contaminated by the exhalations from the lungs, are most 
 likely due to these unknown bodies. As we have as yet no methods of ascer- 
 taining the quantity of these poisonous substances present in exhaled air, the 
 determination of the amount of exhaled carbon dioxide present must serve as 
 an indicator of the fitness of an air for breathing purposes. As a general rule, 
 it may be stated that it is not advisable to breathe, for any length of time, air 
 containing more than 0.1 per cent, of exhaled carbon dioxide; in air contain- 
 ing 0.5 per cent, most persons are attacked by headache, still larger quantities 
 produce insensibility, and air containing 8 per cent, of carbon dioxide causes 
 death in a few minutes. 
 
 As exhaled air contains from 3.5 to 4 per cent, of carbon dioxide, it is unfit 
 to be breathed again.. The total amount of carbon dioxide evolved by the 
 lungs and skin of a grown person amounts to about 0.7 cubic foot per hour. 
 Hence the necessity for a constant supply of fresh air by ventilation. This 
 becomes the more necessary where an additional quantity of carbon dioxide is 
 supplied by illuminating flames. 
 
 Mentioned above are many processes by which carbon dioxide is 
 constantly produced in nature, and we might assume that the amount 
 of 0.04 per cent, of carbon dioxide contained in atmospheric air 
 would gradually increase. This, however, is not the case, because 
 plants, and more especially all their green parts, are capable of ab- 
 sorbing carbon dioxide from the air, while at the same time they 
 liberate oxygen. 
 
 This process of vegetable respiration (if we may so call it), which 
 takes place under the influence of sunlight, is, consequently, the 
 reverse of that of animal respiration. The animal uses oxygen and 
 liberates carbon dioxide ; the plant consumes this carbon dioxide and 
 liberates oxygen. 
 
 Carbon dioxide is an acid oxide, which combines with water, form- 
 ing carbonic acid : 
 
 CO 2 + H 2 O = H 2 CO 3 . 
 
 Carbonic acid, H 2 CO 3 , CO(OH) 2> is not known in a pure state, but 
 always diluted with much water, as in all the different natural waters. 
 
CARBON, SILICON, BORON. 183 
 
 Carbonic acid is a dibasic, extremely weak acid, the salts of which are 
 known as carbonates. Many of these carbonates (calcium carbonate, 
 for instance) are abundantly found in nature. Only the alkali car- 
 bonates and bicarbonates are soluble in water. Acid carbonates of 
 some other metals, such as magnesium, calcium, zinc, iron, are also 
 slightly soluble in water, but these do not exist in the dry state. The 
 bicarbonates when heated to about 100 C. give up carbon dioxide 
 and form carbonates : 
 
 2NaHCO 3 = Na 2 CO 3 -f H 2 O -f CO^ 
 At high temperatures only alkali carbonates are not decomposed. 
 
 Tests. Since nearly all carbonates are insoluble in water, these 
 are formed as precipitates whenever a solution of an alkali carbonate 
 (those of potassium, sodium, or ammonium) is added to a solution of 
 a salt of any other metal. This is a corroborative test for a soluble 
 carbonate, but the best and decisive test for all carbonates and car- 
 bonic acid is found in Experiment 12, namely, the liberation of 
 carbon dioxide and its action on lime-water. 
 
 Carbon monoxide, carbonic oxide, CO. While carbon, as a 
 general rule, is quadrivalent, in this compound it exerts a valence of 
 2. Carbon monoxide is a colorless, odorless, tasteless, neutral gas, 
 almost insoluble in water ; it burns with a pale-blue flame, forming 
 carbon dioxide ; it is very poisonous when inhaled, forming with the 
 coloring matter of the blood a compound which prevents the absorp- 
 tion of oxygen. Carbon monoxide is formed when carbon dioxide is 
 passed over red-hot coal : 
 
 C0 2 + C = 2CO. 
 
 The conditions necessary for the formation of carbon monoxide are, 
 consequently, present in any stove or furnace where coal burns with 
 an insufficient supply of air. The carbon dioxide formed in the lower 
 parts of the furnace is decomposed by the coal above. The blue 
 flames frequently playing over a coal fire are burning carbon mon- 
 oxide. This gas is formed also by the decomposition of oxalic acid 
 (and many other organic substances) by sulphuric acid : 
 H 2 C 2 O 4 + H 2 SO 4 = H 2 SO,.H 2 O + CO 2 + CO. 
 
 Oxalic Sulphuric 
 
 acid. acid. 
 
 Carbon monoxide is now manufactured on a large scale by causing the de- 
 composition of steam by coal heated to red heat. The decomposition takes 
 
 place thus: 
 
 H 2 + C == 2H + CO. 
 
184 NON-METALS AND THEIR COMBINATIONS. 
 
 The gas mixture thus obtained, known as water-gas, may be used for heating 
 purposes directly, but has to be mixed with hydrocarbons when used as an 
 illuminating agent, for reasons which will be pointed out below when consider- 
 ing the nature of flames. 
 
 Carbonyl chloride, COC1 2 . This is formed when a mixture of carbon 
 monoxide and chlorine is exposed to sunlight, and, hence, is also known as 
 phosgene. Commercially it is made by passing a mixture of the two gases over 
 animal charcoal, which acts as a catalytic agent. Carbonyl chloride is gas- 
 eous above 8 C., has a suffocating odor, and dissolves readily in benzene. 
 Water decomposes it at once into carbonic and hydrochloric acids, COC1 2 + 
 2H 2 O = H 2 C0 3 H- 2HC1. It is used in making certain synthetic organic 
 compounds.. 
 
 Compounds of carbon and hydrogen. There are no other two 
 elements which are capable of forming so large a number of different 
 combinations as are carbon and hydrogen. Several hundred of these 
 hydrocarbons are known, and their consideration belongs to the 
 domain of organic chemistry. 
 
 Two of these hydrocarbons, however, may be briefly mentioned, 
 as they are of importance in the consideration of common flames. 
 These compounds are: methane (marsh-gas, fire-damp), CH 4 ; and 
 efhene (olefiant gas), C 2 H 4 . 
 
 Both compounds are colorless, almost odorless gases, and both are 
 products of the destructive distillation of organic substances. De- 
 structive distillation is the heating of non-volatile organic substances 
 in such a manner that the oxygen of the atmospheric air has no access, 
 and to such an extent that the molecules of the organic matter are 
 split up into simpler compounds. Among the gaseous products 
 formed by this operation, more or less of the two hydrocarbons 
 mentioned above is found. 
 
 Marsh-gas is formed frequently by the decomposition of organic 
 matter in the presence of moisture (leaves, etc., in swamps) ; and dur- 
 ing the formation of coal in the interior of the earth the gas often 
 gives rise to explosion in coal mines. During these explosions of the 
 methane (mixed with air and other gases), called fire-damp by the 
 miners, carbon is converted into carbon dioxide, which the miners 
 speak of as choke-damp, or after-damp. 
 
 Flame is gas in the act of combustion. Of combustible gases, 
 have been mentioned : hydrogen, carbon monoxide, marsh-gas, and 
 olefiant gas. These four gases are actually those which are found 
 chiefly in any of the common flames produced by the combustion o? 
 organic matter, such as paper, wood, oil, wax, or illuminating gas itself 
 
 These gases are generated by destructive distillation, the heat being 
 
CARBON, SILICON, BORON. 
 
 185 
 
 supplied either by a separate process (manufacture of illuminating 
 gas by heating wood or coal in retorts), or generated during the 
 combustion itself. 
 
 In burning a candle, for instance, fat is constantly decomposed by 
 the heat of the flame itself, the generated gases burning continuously 
 until all fat has been decomposed, and the products of decomposition 
 have been burned up, i. e., have been converted into carbon dioxide 
 and water. 
 
 An ordinary flame (Fig. 41) consists of three parts or cones. The 
 inner portion is chiefly unburnt gas ; the second is formed of partially 
 burnt and burning gas ; the outer cone, showing scarcely any light, is 
 that part of the flame where complete combustion takes place. The 
 highest temperature is found between the second and third cone. 
 
 The light of a flame is caused by solid particles of carbon heated 
 to a white heat. The changes that take place in a flame are difficult 
 to study, but sufficient has been done experimentally to permit the 
 conclusion to be drawn that the separation of carbon in a flame is due 
 to dissociation of some of the hydrocarbons, of which ethylene 
 (ethene) is the most important. It is well known that when ethylene 
 (C 2 H 4 ) is heated it yields acetylene (C 2 H 2 ), which in turn gives carbon 
 and hydrogen. Evidence that acetylene is present in a gas flame is 
 furnished by the fact that when a Bunsen flame " strikes 
 back," that is, burns at the base of the tube so that 
 incomplete combustion of the gases takes place, a large 
 quantity of acetylene is formed. 
 
 If a sufficient amount of air be previously mixed with 
 the illuminating gas, as is done in the Bunsen burner, no 
 separation of carbon takes place, and, therefore, no light 
 is produced, but a more intense heat is generated. A 
 similar effect is produced by the aid of the blow-pipe or 
 by means of the blast lamp, which serve to direct a cur- 
 rent of air directly into the cone of the flame. The 
 luminous and non-luminous Bunsen flame, using the 
 same flow of gas, must produce the same amount of heat 
 for a definite amount of gas burned, since the end- 
 products of combustion are the same in both cases. 
 But the non-luminous flame is much shorter than the 
 luminous one, and thus the heat is concentrated within a smaller 
 space, and, therefore, the temperature is much higher than in the 
 luminous flame. 
 * The cause of non-luminosity of a flame when air or oxygen is 
 
 FIG. 41. 
 
 Structure of 
 flame. 
 
186 NON-METALS AND THEIR COMBINATIONS. 
 
 admitted into the interior, as in a Bunsen burner, is difficult to explain. 
 That it is due to other causes than the presence of the oxygen is shown 
 bv the fact that nitrogen or carbon dioxide will also destroy luminosity. 
 The introduction of cold gases into a flame lowers the temperature of 
 the inner cone, where the dissociation of ethylene takes place. It 
 seems probable that this lowering of temperature and dilution of the 
 gases diminish the decomposition of ethylene to such an extent that 
 not enough carbon is separated to give luminosity. 
 
 Silicon or Silicium, Si = 28.3, is found in nature very abundantly as 
 silicon dioxide, or silica, SiO 2 (rock-crystal, quartz, agate, sand), and in the 
 form of silicates, which are silicic acid in which the hydrogen has been replaced 
 by metals. Most of our common rocks, such as granite, porphyry, basalt, 
 feldspar, mica, etc., are such silicates or a mixture of them. Small quantities 
 of silica are found in spring- waters, as well as in vegetable and animal matters. 
 
 Silicon resembles carbon both in its physical and chemical properties. Like 
 carbon, it is known in the amorphous state, and forms two kinds of crystals, 
 which resemble graphite and diamond. Like carbon, silicon is quadrivalent, 
 forming silicon dioxide, Si0 2 , silicic acid, H. 2 SiO 3 , silicon hydride, SiH 4 , silicon 
 chloride, SiCl 4 , which compounds are analogous to the corresponding carbon 
 compounds, C0 2 , H 2 CO 3 , CH 4 , and CC1 4 . 
 
 The compounds formed by the union of silicon with hydrogen, chlorine, and 
 fluorine are gases. The latter compound, silicon fluoride, SiF 4 , is obtained by 
 the action of hydrofluoric acid on silica or silicates, thus : 
 
 Si0 3 -f 4HF = SiF 4 -f 2H 2 O. 
 
 This reaction is used in the analysis of silicates, which are decomposed and 
 rendered soluble by the action of hydrofluoric acid. 
 
 Silicon fluoride is decomposed by water into silicic acid and hydrofluosilicic 
 acid, H 2 SiF 6 , thus : 
 
 3SiF 4 + 3H 2 O = H 2 Si0 3 + 2H 2 SiF 6 . 
 
 Several varieties of silicic acid are known, of which may be mentioned the 
 normal silicic acid, H 4 SiO 4 , and the ordinary silicic acid, H 2 SiO 3 , from the latter 
 of which, by heating, water may be expelled, when silicon dioxide, SiO 2 , is left. 
 
 Tests for silicic acid and silicates. 
 
 (Soluble glass or flint may be used.) 
 
 1. Silicic acid and most silicates are insoluble in water and acids. By fusing 
 silicates with about 5 parts of a mixture of the carbonates of sodium and potas- 
 sium the silicates of these metals (known as soluble glass) are formed. By 
 dissolving this salt in water and acidifying the solution with hydrochloric acid 
 a portion of the silica separates as the gelatinous hydroxide. 
 
 Complete separation of the silica is accomplished by evaporating the mixt- 
 ure to complete dryness over a water-bath, and re-dissolving the chlorides of 
 the metals in water acidulated with hydrochloric acid ; silica remains undis- 
 solved as a white amorphous powder. 
 
 2. Silica or silicates when added to a bead of microcosmic salt (see index) 
 form on heating before the blowpipe the so-called silica-skeleton. 
 
 Silicon carbide, SiO. (Carborundum, Carbon silicide). This compound 
 
CARBON, SILICON, BORON. 187 
 
 furnishes a typical illustration of the possibilities of the electric furnace for 
 manufacturing purposes. Figs. 32 and 33, page 81, give a sectional and an 
 exterior view of the furnace used. The current enters and leaves the furnace 
 through cables terminating in carbon electrodes fastened in the wall. Between 
 them is placed a core of coke, surrounded by a mixture of carbon, sand, and 
 salt. The current heats the mass to about 3500 C. (6332 F.), when the 
 carbon combines with both elements of the sand, thus: 
 
 Si0 2 + 3C = 2CO + SiC. 
 
 Carborundum forms beautiful, dark-green, iridescent crystals of extreme hard- 
 ness, in the latter quality being exceeded only by the diamond. It is extensively 
 used as a polishing agent, gradually replacing emery, to which it is far superior. 
 
 Boron, B'" = 10.9, is found in but few localities, either as boric 
 (boracic) acid or sodium borate (borax). Formerly the total supply 
 of boron was derived from Italy : large quantities of borax are now 
 obtained from Nevada and California. 
 
 Boron exists as a greenish -brown amorphous powder and also in the form 
 of hard and often highly lustrous crystals. Boron combines with many of the 
 non-metals, forming such compounds as boron trichloride, BC1 3 , trifluoride, 
 BF 3 , and hydride, BH 3 . It is one of the few elements which at a high tempera- 
 ture combine directly with nitrogen, forming nitrogen boride, BN. 
 
 Boric acid, Acidum boricum, H 3 BO 3 , B(OH) 3 = 61.54 (Boracic 
 acid), is a white, crystalline substance, which is sparingly soluble in 
 cold water or alcohol, but more soluble in glycerin ; it has but weak 
 acid properties. When heated to 100 C. (212 F.) it loses water, 
 and is converted into mdaboric acid, HBO 2 , which when heated to 
 160 C. is converted into tetraboric acid, H 2 B 4 O 7 , from which borax, 
 Na 2 B 4 O 7 -f 10H 2 O, is derived. At a white heat boric acid loses all 
 water, and is converted into boron trioxide, B 2 O 3 . From a boiling 
 solution boric acid readily volatilizes with the steam. 
 
 Boric acid is obtained by adding hydrochloric acid to a hot satur- 
 ated solution of borax, when boric acid separates on cooling. The 
 chemical change is this : 
 
 7 + 2HC1 + 5H 2 O = 4H 3 B0 3 + 2NaCl. 
 
 It is rather odd that while the usual form of boric acid in the uncombined 
 state is the orthoboric acid, H 3 BO 3 , salts of this form are hardly known. Salts 
 of metaboric acid occur, but the best-known salts are derived from tetraboric 
 acid, and the best representative is the sodium salt, borax. On the other hand, 
 when the acid is liberated from the salts, it assumes the ortho form. From the 
 formula of tetraboric acid, it appears that four molecules of the ortho acid com- 
 bine with elimination of water to form a more complex molecule : 
 
 4H 3 B0 3 H 2 B 4 7 + 5H 2 0. 
 
 There are other cases of this kind, as will be seen later. 
 
188 NON-METALS AND THEIR COMBINATIONS. 
 
 Borax may be looked upon as containing sodium metaborate and boric 
 oxide, 2NaBO 2 + B,O 3 . When it is heated with basic oxides, these unite with 
 the excess of B 2 O 3 > forming a fused mixed metaborate. This action explains 
 the use of borax on hot metal surfaces which are to be welded. Some of these 
 metaborates have distinctive colors. For this reason borax beads are used as 
 tests for certain metals (see under Sodium Borate). 
 
 Boric acid is such a weak acid that its solution has only a slight action on 
 litmus-paper, and it is displaced from its salts by nearly every other acid. The 
 borates of the alkali metals only are easily soluble in water, the others being 
 either insoluble or nearly so. Hence, when a solution of an alkali borate (but 
 not of free boric acid) is added to a solution of a saltof other metals, a precipitate 
 is obtained. Alkali borates show a strong alkaline reaction to litmus because 
 they are partly hydrolyzed in solution to free alkali and boric acid. It will be 
 ?een that boric acid is very much like carbonic acid in behavior. 
 
 Boric acid and borax are practically the only compounds of boron that are 
 used. Both are used in medicine and as preservatives. When powdered they 
 look much alike, but can be distinguished by the fact that the acid is soluble 
 in alcohol while borax is not, and that borax has a marked alkaline reaction to 
 litmus, and when held in a Bunsen flame on platinum wire gives a yellow color, 
 while free boric acid gives a green color. 
 
 Tests for boric acid and borates. 
 
 1. When borax is heated on the loop of a platinum wire in a Bunsen 
 flame it first puffs up very much, and then gradually melts into a 
 transparent, colorless bead. If the bead is moistened with concen- 
 trated sulphuric acid and heated again, a green color is produced. 
 Boric acid also melts into a colorless bead. Note any difference in 
 color of the flame. 
 
 2. Mix in a porcelain dish some borax with 2 c.c. of concentrated 
 sulphuric acid, add about 10 c.c. of alcohol, and ignite. The flame 
 has a mantle of green color, which is best seen by alternately extin- 
 guishing and relighting the alcohol. Eepeat the experiment, omitting 
 the acid ; no green color is seen. Free boric acid is volatilized with 
 alcohol, but not its salts. 
 
 QUESTIONS. How is carbon found in nature? State the physical and 
 chemical properties of carbon in its three allotropic modifications. Mention 
 three different processes by which carbon dioxide is generated in nature, and 
 some processes by which it is generated by artificial means. State the physical 
 and chemical properties of carbon dioxide. Explain the process of respiration 
 from a chemical point of view. What is the percentage of carbon dioxide in 
 atmospheric air, and why does its amount not increase ? State the composition 
 of carbonic acid and of a carbonate. How can they be recognized by analyt- 
 ical methods? Under what circumstances will carbon monoxide form, and 
 how does it act when inhaled? What is destructive distillation, and what 
 gases are generally formed during that process? Explain the structure and 
 luminosity of flames. 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 189 
 
 3. A solution of boric acid, or of a boratc acidulated with dilute 
 hydrochloric acid, colors a strip of t turmeric paper dark red, which 
 becomes more intense on drying. The color is changed to bluish black 
 by dilute ammonia water. 
 
 Sodium perborate, NaBO. 5 .4H. 2 O. When a mixture of 248 grammes of 
 boric acid and 78 grammes of sodium peroxide is gradually added to 2 liters of 
 cold water a crystallized compound is obtained. When the latter in solution is 
 treated with the proper proportion of an acid, sodium perborate separates. It 
 is very stable when dry, but in solution it has all the properties of a solution of 
 hydrogen dioxide. It is a good antiseptic and deodorant, and may be applied 
 as a dusting-powder or in solution. 
 
 15. THEORY OF ELECTROLYTIC DISSOCIATION, OR IONIZATION. 
 ELECTROLYSIS. DISSOCIATION THEORY APPLIED TO ACIDS, 
 BASES, SALTS, AND NEUTRALIZATION. 
 
 Theory of Electrolytic Dissociation. 
 
 It was observed long ago tbat aqueous solutions of certain kinds 
 of substances, of which cane-sugar is a good type, do not conduct an 
 electric current, while aqueous solutions of other substances, of which 
 common salt or hydrochloric acid is a good example, are excellent 
 conductors of electricity. Moreover, it was also observed that sub- 
 stances which conduct electricity in aqueous solution do not conduct 
 when they are dissolved in certain solvents, like benzene, ether, chlo- 
 roform, etc. This fact evidently points to the conclusion that water 
 has some peculiar action on some substances whereby they become 
 possessed of the power to conduct a current. The same kind of 
 effect is also noticed in regard to chemical behavior. For example, 
 dry hydrochloric acid gas dissolved in dry benzene neither conducts 
 electricity nor has an acid reaction on litmus, nor appreciably acts 
 on zinc, whereas an aqueous solution of the gas conducts well, has a 
 marked acid reaction on litmus, and attacks zinc vigorously. It appears, 
 therefore, that hydrochloric acid molecules in aqueous solution must 
 be in a state different from that when they are dissolved in benzene. 
 It should be noted that pure water itself is not a conductor, nor are 
 the other substances when dry, but their solutions in water conduct. 
 There are a few other liquids which show this property, but to a far 
 less extent than water does, to which this discussion will be confined. 
 
 Substances whose aqueous solutions conduct electricity are known 
 as electrolytes, those whose solutions do not are called non-electrolytes. 
 It is found experimentally that acids, bases, and salts are electrolytes, 
 and it is precisely these substances whose aqueous solutions show 
 
190 NON-METALS AND THEIR COMBINATIONS. 
 
 abnormally large values of freezing-point depressions, boiling-point 
 elevations, and osmotic pressures. In the discussion of the latter 
 subjects (which see) it is pointed out that the abnormally acting sub- 
 stances behave as if there are more particles in solution than the 
 number of molecules corresponding to the weights of the substances 
 dissolved, which fact can be accounted for only on the supposition 
 that some molecules are decomposed by the solvent into smaller par- 
 ticles. Further, since molecules which, like those of sugar, act nor- 
 mally in regard to freezing-point, boiling-point, and osmotic pressure 
 phenomena, and thus show no indication of decomposition by the 
 solvent, do not conduct electricity, it follows that the fragments of 
 decomposed molecules must be responsible for the ability to conduct 
 in the case of solutions of electrolytes. In electrolysis (see page 82) 
 these fragments are the particles that are attracted to the charged 
 poles, hence the further assumption is made that the fragments (or 
 ions as they are called) are themselves charged with electricity, be- 
 cause it is known that electricity attracts only bodies that possess a 
 charge of electricity. Briefly summed up, then, the THEORY OF 
 ELECTROLYTIC DISSOCIATION assumes that molecules of electrolytes 
 when dissolved in water break up to a varying degree into independent 
 particles charged with electricity, and that the nature and number of 
 these charged particles determine to a large degree certain physical and 
 chemical properties of solutions. 
 
 This theory was proposed by the Swedish physicist Arrhenius in 
 lSS7 its general adoption has been hastened by the work of van't 
 Hoff, Ostwald, and Nernst. 
 
 The dissociation of molecules in solution is also called IONIZATION, 
 and the electrically charged particles are called ions. These are al- 
 ways of two kinds, namely, electro-positive ions, or cations, because 
 they are attracted to the negative pole or cathode during electrolysis, 
 and electro-negative ions, or anions, because they are attracted to the 
 positive pole or anode. Since solutions are themselves electrically 
 neutral, that is, show no charge of electricity as a whole, it follows 
 that the sum of the electric charges of the positive ions equals the 
 sum of the charges of the negative ions. The two kinds of ions are 
 in electrical balance. 
 
 Composition of ions. This is learned from a study of the pro- 
 ducts that are attracted to the anode and cathode, respectively, in 
 electrolysis, and from the manner in which molecules of electrolytes 
 exchange their parts or radicals in chemical actions. In molecules 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 191 
 
 of acids hydrogen is readily separated in chemical actions from the 
 rest of the molecule, which is a radical, consisting of a non-metallic 
 element, or a group of atoms acting as a unit and remaining intact. 
 In electrolysis, division occurs in the same manner, hydrogen sepa- 
 rating at the cathode, and acid radical being attracted to the anode. 
 Salts behave in the same manner as acids in regard to the division 
 of the molecules, which is only what we should expect, since they 
 are so closely related to acids. Indeed, some chemists put both in 
 the same class, regarding acids as salts of hydrogen. Bases in chemical 
 action and in electrolysis show a division between the metal and 
 the hydroxyl (OH) radical, the metal going to the cathode, and the 
 hydroxyl radical to the anode. It appears, then, from the side of 
 chemical action as well as that of electrolysis that an aqueous solution 
 of an acid contains positive hydrogen ions and negative acid radical 
 ions; a solution of a salt contains positive ions of a metal and negative 
 acid radical ions; and a solution of a base contains positive ions of a 
 metal and negative hydroxyl ions. 
 
 Ions and atoms not the same. The student should note partic- 
 ularly that a substance in the ionic state is quite different from the 
 substance in the free state. Simple ions are atoms plus a charge of 
 electricity, while atoms of free elements are not charged, and this 
 difference is sufficient to account for the difference of behavior. 
 Thus, when sodium chloride (NaCl) is dissolved in water, many of 
 the molecules break up into Na-ions and Cl-ions, but there is tio 
 chemical action between the water and Na-ions or Cl-ions, whereas 
 sodium in the free state acts violently on water, and chlorine dissolves 
 in water with some chemical action and imparts its odor and bleach- 
 ing properties to the water. A solution of sodium chloride has no 
 odor or bleaching action. 
 
 Symbols representing- ions. Ions are represented by the usual 
 chemical symbols, with the addition of marks to indicate positive and 
 negative charges. Thus, Na + , or Na', stands for a positively charged 
 sodium ion, and Cl~, or Cl', stands for a negatively charged ion of 
 chlorine. Quantitative experiments in electrolysis show that the 
 amounts of electricity possessed by ions is proportional to the valence 
 of the atoms or radicals constituting the ions. If the charge on a 
 sodium or on a chlorine ion is taken as the unit charge, then the 
 charge on an ion of a bivalent atom or radical is two units, and is 
 represented thus, Ca ++ , or Ca", and SO7~, or SO/'. The ion of 
 trivalent aluminum is written Al +++ , or Al" ', etc. 
 
192 NON-METALS AND THEIR COMBINATIONS. 
 
 Ionic equilibrium. The dissociation of molecules into ions must 
 be considered as a species of chemical change, and, like many others, 
 it is a reversible action (see page 114). In ordinary dilute solutions 
 there is always a certain proportion of undissociated molecules which 
 are in equilibrium with the ions. The degree of dissociation varies 
 with the concentration of the solution, and of course with the nature 
 of the dissolved substance, since for the same concentration different 
 substances vary widely in the amount of dissociation. If the solution 
 is made more concentrated, as by evaporation, more and more of the 
 ions unite to form molecules, until finally, when all the solvent is 
 removed, the dry substance is left entirely in the molecular state. On 
 the other hand, diluting a solution results in more molecules being 
 dissociated. Many substances in highly diluted solutions are almost 
 completely dissociated. The reversible character of dissociation is 
 represented by reversible ionic equations thus : 
 
 HC1 ^ H- -f Cl' ; NaCl ; Na' + Cl' ; NaOH ; Na' -f (OH)'. 
 
 The first equation means that in any given solution of hydrochloric 
 acid there is a certain proportion of molecules and a certain propor- 
 tion of ions. The molecules tend to form ions, but only as fast as 
 the ions tend to revert to the molecular state, so that an equilibrium 
 is maintained. By changing the conditions, ions may be forced to 
 unite to form molecules, or vice versa. In other words, the equilib- 
 rium may be displaced forward or backward. Likewise for the other 
 two equations dealing with sodium chloride and sodium hydroxide 
 respectively. 
 
 Theoretical deductions, as well as experimental results, show that 
 in varying solutions of the same substance there is a constant rela- 
 tionship, which is expressed thus : The product of the concentration of 
 the ions divided by the concentration of the undissociated molecules is a 
 constant quantity (or nearly so in some cases), expressed by a numeral, 
 and called the IONIZATION CONSTANT. The concentration is ex- 
 pressed in terms of the number of molecular weights or ion weights 
 in grammes in a liter of solution. A solution containing one molec- 
 ular weight or ion weight per liter is taken as unit concentration. 
 
 Effect of ionic equilibrium in chemical reactions. Some fa- 
 miliar results. If in any manner, as by precipitation, one kind of 
 the ions of a substance is removed from solution, some molecules of 
 the substance are dissociated to replace the kind of ions removed, 
 until the balance between ions and molecules, as indicated in the 
 lonization constant, is restored. This process may go on until all the 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 193 
 
 molecules are dissociated. Conversely, if the concentration of one 
 kind of ion is increased, as by the addition of a substance giving the 
 same kind of ion for example, addition of hydrochloric acid to a 
 
 solution of sodium chloride (both having a common ion, Cl') the 
 
 result is a reunion of some of the ions of the original substance to 
 form molecules, until the balance between its molecules and all of the 
 ions of the kinds that it gives satisfies the demands of the ionization 
 constant. If the solution is saturated in the beginning, and there- 
 fore contains all the undissociated molecules that it can hold, the for- 
 mation of an additional number of molecules by union of ions gives 
 rise to supersaturation and precipitation of some of the substance. 
 Thus, the addition of hydrochloric acid gas to a saturated solution of 
 common salt causes a copious precipitate of the salt. Likewise, addi- 
 tion of some saturated solution of the very soluble sodium chlorate 
 to one of the less soluble potassium chlorate causes precipitation of 
 some of the latter salt. The reason the sodium chlorate is not also 
 reciprocally precipitated is that the additional molecules formed by 
 union of its ions, Na" and CIO/, are not sufficient to supersaturate the 
 volume of liquid through which the sodium chlorate is distributed. 
 The principle just discussed furnishes an explanation of the fact that 
 is often observed in practical work ; namely, that many substances 
 are much less soluble in solutions of other substances of similar com- 
 position than in pure water. 
 
 In the case of a solution of a slightly dissociating substance, the 
 addition of another substance having a common ion with the first 
 may so far cause a reversal of dissociation of the first substance that 
 practically only its undissociated molecules exist in the solution, with 
 an accompanying loss of some of its properties. Thus, in a solution 
 containing per liter the molecular weight of sodium acetate and the 
 molecular weight of acetic acid, the latter no longer is able to affect 
 the indicator methyl-orange, because there are too few hydrogen ions 
 of the acid left in solution. 
 
 Precipitation. When molecules of a substance are dissolved, some 
 dissociate until a balance is established between ions and molecules, as 
 represented by the ionization constant. Conversely, when there are 
 present in a solution two substances which between them produce ions 
 corresponding to a third substance, some molecules of the third sub- 
 stance are formed up to the point that corresponds to its ionization 
 constant. The following ionic equations for a mixture of potassium 
 chloride and sodium nitrate in solution will illustrate : 
 
 13 
 
194 NON-METALS AND THEIR COMBINATIONS. 
 
 KC1 ^K- +Cl'j Xaa 
 NaN0 3 ^ N0' 3 + Na- J 
 
 It 
 KN0 3 
 
 Evidently molecules of four products will be present in this mixture, 
 and likewise in all similar ones. If all the products are readily solu- 
 ble and of large dissociating power, and the solution is rather dilute, 
 there are few undissociated molecules present. The mixture then is 
 practically a mixture of ions, and nothing can be observed by the 
 eye to have taken place. But if one of the new products is " insolu- 
 ble" in water, there are more of its ions present than can be main- 
 tained in a saturated solution of the same, the excess of ions unite to 
 form molecules, and the excess of molecules are removed by precipi- 
 tation. In this way one factor in the equilibrium is removed and the 
 action runs to completion. This principle is at the basis of all cases 
 of precipitation in chemical reactions. The precipitation of silver 
 chloride is a good example, and is represented thus : 
 
 It 
 
 NaN0 3 soluble. 
 
 A simple equation, in which only the ions are represented, may be 
 used : 
 
 Ag- + NO S ' + Na- + Cl' = AgCl 4- Na' 4- NO 3 '. 
 
 The simplest equation of all is one which shows only those ions that 
 are actually involved in the precipitation, thus : 
 
 Ag- 4- Cl' = AgCl. 
 
 Reasoning parallel to the above may be applied when one of the 
 new products formed is a gas with slight solubility in water at ordi- 
 nary or higher temperatures, or a liquid which is volatile at elevated 
 temperature. In either case, the new product is removed as fast as 
 it is formed and the action runs to completion. In the liberation of 
 ammonia, the ionic equations are : 
 
 2XH 4 C1 ^ 2C1' 4- 2NH 4 - 1 _ 
 
 Ca(OH) 2 ; Ca- 4- 2(OHV / *~ 2 ^^*^H = 2H 2 O 4- 2NH 3 (gas) undissociated. 
 
 It. 
 CaCl 2 soluble. 
 
 Or, more simply, 
 
 Ca- 4- 2(OH)' 4- 2NH 4 - 4- 2C1' == Ca' +2C1' 4- 2NH 4 OH. 
 
 Ammonium hydroxide is only slightly ionized, and by heating is 
 easily broken up and driven out of solution as ammonia*gas. 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 195 
 
 For the liberation of carbon-dioxide gas the representation is this : 
 
 Na 2 C0 3 ^ 2Na' + CO/ ' ) ^ rn 
 
 H 2 S0 4 ^S0 4 " + 2H- /- H 2 C 3= H 2 + C0 2 (gas). 
 
 I t 
 Na 2 SO 4 soluble. 
 
 Or simply 
 
 2Na- + CO/ ' + 2H- + SO/ ' = 2Na' + SO/ ' + H 2 CO 3 . 
 
 Carbonic acid is only slightly ionized and very little soluble. Hence 
 it escapes as fast as it is liberated. This description will serve also 
 for the liberation of nitrous acid from nitrites. 
 The formation of nitric acid is represented thus : 
 
 it 
 
 K 2 SO 4 non-volatile. 
 
 Or simply 
 
 2K- + 2NO 3 ' + 2H- + SO/' = 2K- + SO/' + 2HNO 3 . 
 
 As concentrated sulphuric acid and dry potassium nitrate are used in 
 this process, only a relatively small number of ions are present at one 
 time, but as fast as ions are removed as nitric acid, new ions are 
 formed to replace them until the operation is completed. 
 
 The above discussions on the formation of precipitates, gases, and 
 volatile liquids, and consequent completion of chemical reactions, is a 
 presentation in terms of the ionic theory of the same subjects dis- 
 cussed in a simpler form on p. 114, under Reversible Actions and 
 Chemical Equilibrium, and furnish an explanation of what is there 
 stated. 
 
 Chemical actions in aqueous solutions are nearly always actions 
 between ions. Indeed, there are some who claim that chemical action 
 does not take place except between ions, and the fact that action does 
 occur is itself evidence of the presence of ions. This is an extreme 
 view and is not well taken, as there are undoubted examples of action 
 in solution in which ions do not exist. In the case of acids, bases, 
 and salts in solution, action is practically always ionic. 
 
 Electrolysis. 
 
 This name is given to the series of changes that take place when an electric 
 current is passed through a solution of an electrolyte, and the subject is briefly 
 discussed on page 82. The process is carried out in an electrolytic cell, which 
 consists of a suitable vessel holding a solution into which are immersed the 
 electrodes of the circuit. Fig. 34 illustrates one form of such a cell, which 
 
]96 NON-METALS AND THEIR COMBINATIONS. 
 
 is designed to collect gases. The electrodes are made of materials which are 
 not affected by the products that collect on them. Platinum plates are often 
 used. 
 
 The result of passing a current through a solution of an electrolyte is a 
 chemical decomposition. The products that appear at the electrodes are always 
 different. For illustration, one of the simplest cases of electrolysis may be 
 considered, namely, the decomposition of hydrochloric acid. When the appa- 
 ratus (Fig. 34) is filled with the concentrated acid and a current is turned on, 
 hydrogen gas is found to collect and rise into the tube from the cathode or 
 ( ) electrode, and chlorine gas collects in the other tube from the anode or 
 (+) electrode. The mechanism of the process is conceived to be as follows : 
 The solution of the acid contains some ions of hydrogen (H') and of chlorine 
 (Cl'), the presence of which is entirely independent of the electric current. 
 These ions, before the current is turned on, are attracted no more in one direc- 
 tion than in any other. When the current is turned on, one electrode receives 
 from the battery or dynamo, or whatever the source of electricity, a positive 
 charge, and the other receives a negative charge, and a constant difference of 
 voltage or electromotive force is maintained between the electrodes. If the 
 latter should be connected by a continuous conductor, as a piece of copper wire, 
 a current would flow from the positive to the negative electrode by their dis- 
 charge through the wire. But the source of electricity would constantly renew 
 the charges on the electrodes, and thus a continuous current would be kept up. 
 When the connecting wire is replaced by hydrochloric acid, the positive elec- 
 trode attracts the negatively charged chlorine ions and repels the positive 
 hydrogen ions, while the negative electrode attracts the positive hydrogen ions 
 and repels the negative chlorine ions. In this way there is a general move- 
 ment of all positive ions to one electrode, and of all negative ions to the other. 
 When the ions come in contact with the electrodes, they lose their charges by 
 neutralizing the charges of opposite kind on the electrodes. The discharged 
 ions then unite and pass off as molecules of hydrogen and chlorine respect- 
 ively. The discharged electrodes receive new charges as before, and the pro- 
 cess is repeated until all of the electrolyte is removed from the solution. The 
 effect as far as the conduction of the current is concerned is the same as if a 
 wire connected the electrodes, and the current flowed through a circuit entirely 
 metallic. In the light of this ionic explanation of electrolysis, we can under- 
 stand why solutions of substances which do not dissociate into ions like sujrar 
 do not conduct electricity, and why substances which conduct in aqueous solu- 
 tion do not conduct in solvents in which they are not dissociated. 
 
 Secondary changes in electrolysis. In the electrolysis of hydrochloric 
 
 id the products liberated consist of the same elements of which the ions are 
 
 constituted, but the majority of cases are not so simple as this one. Many ions 
 
 are atomic groups which are not known in the free state, but exist only as ions 
 
 solution. When these lose their charges, secondary chemical changes occur 
 
 the resulting products accumulate around the electrodes. Thus in the 
 
 case^of sulphuric acid, the H' ions become molecules of hydrogen gas, but the 
 
 >0 4 ion when discharged becomes a group not known in the free state It 
 
 reacts with water thus : H 2 O + SO 4 = H 2 SO 4 + O. Sulphuric acid accumu- 
 
 ound the positive electrode, but is gradually disseminated again through 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 197 
 
 the solvent by diffusion. The oxygen escapes and can be collected. The 
 amount of hydrogen and oxygen liberated are in the same proportion as in 
 water, and thus we have an explanation of the " decomposition of water by 
 electrolysis." 
 
 When copper sulphate is electrolyzed metallic copper is deposited on the 
 negative electrode, and sulphuric acid and oxygen collect at the other. In the 
 case of sodium sulphate the sodium ion when discharged acts on water, result- 
 ing in the accumulation of sodium hydroxide and hydrogen around the nega- 
 tive electrode, and as before sulphuric acid and oxygen collect at the positive 
 electrode. 
 
 Faraday's laws of electrolysis, Michael Faraday, of England, was the 
 first to make a careful quantitative study of electrolysis, and announced the 
 following two laws: 
 
 I. The amount of a substance liberated in an electrolytic cell is proportional to 
 the quantity of electricity that has passed through it. 
 
 II. Chemically equivalent quantities of ions are liberated by the passage of equal 
 quantities of electricity. Chemically equivalent quantities are determined by 
 valence. Thus for every divalent ion liberated, two univalent ions are liber- 
 ated, etc., by the same amount of electricity. 
 
 The liberation of 1 gramme of hydrogen requires the passage of 96,540 units 
 (coulombs) of electricity. A current strength of 1 ampere is such that 1 cou- 
 lomb of electricity flows through a circuit in 1 second. Hence a current of 
 1 ampere will require 96,540 seconds (26 hours and 49 minutes) to liberate 
 1 gramme of hydrogen (nearly 11 liters). A current of 5 amperes would do the 
 same work in one-fifth of the time. 
 
 One coulomb (a current of 1 ampere flowing 1 second) will liberate 0.0000104 
 gramme of hydrogen, 0.0000828 gramme of oxygen, 0.0003294 gramme of 
 copper, 0.001118 gramme of silver, etc. These quantities are proportional to 
 the chemical equivalents, and are called in electrical science, electro-chemical 
 equivalents. 
 
 An instrument constructed for determining the amount of a substance as 
 silver or copper liberated by a current in a given time, and from this the cur- 
 rent strength, is called a voltameter (see page 77). Suppose a current flowing 
 for 1 hour through a voltameter liberates 0.59292 gramme of copper upon the 
 cathode, the current strength is 
 
 0.59292 gm. copper = i ^ 
 
 3600 seconds X 0.0003294 elect, chem. equiv. of copper 
 
 Conductivity. Every solution of an electrolyte offers a certain resistance 
 to the flow of the current, which can be measured in ohms (see page 76). If 
 the resistance is small, the solution offers an easy passage for the current, hence 
 it is said to have a high conductivity. A solution of great resistance is said to 
 have a low conductivity. The numerical value for conductivity is the recip- 
 rocal of the resistance, thus: 
 
 Conductivity = 
 
 resistance 
 
 In order that results may be compared, conductivity measurements are made 
 with electrodes 1 cm. apart. The algebraic character used to represent con- 
 
198 NON-METALS AND THEIR COMBINATIONS. 
 
 ductivity is A v , which means the conductivity shown by the molecular weight 
 of the substance in v liters of solution. 
 
 The conductivity increases with dilution. This is what we should expect, 
 since conductivity is proportional to the number of ions, which also increases 
 with dilution. By measuring the conductivity in a given dilution and also in 
 very large dilution, it is a simple matter to calculate the degree of ionization 
 of the substance in the given dilution. This method of study is called the 
 conductivity method. 
 
 Electromotive force required in electrolysis. The amount of work 
 that can be done by any form of energy depends not merely on the quantity, 
 but also on the intensity of the energy. Thus, the quantity of steam in a loco- 
 motive boiler, however large, will not cause the driving-wheels to turn if the 
 pressure (intensity factor) is not sufficiently large. Likewise, in electrolysis, 
 different substances require for decomposition currents of different electro- 
 motive force. If the latter is less than the required minimum, there is no 
 liberation of ions at the electrodes, that is, no electrolysis. The quantity of 
 current only controls the amount of material liberated, but the electromotive 
 force decides whether there will be any decomposition at all. The reason for 
 the latter fact is that as soon as the electrodes are coated with the products of 
 electrolysis, a reverse electromotive force and current tend to develop which 
 oppose the original current. The electrodes are then said to be polarized. To 
 overcome this polarization current requires a certain minimum electromotive 
 force in the electrolyzing current. The electromotive force required for a few 
 common electrolytes are as follows : 
 
 Hydriodic acid 0.53 volts. 
 
 Silver nitrate 0.7(5 " 
 
 Hydrochloric acid 1.41 " 
 
 Sulphuric acid 1.92 " 
 
 Zinc sulphate . . 2.70 " 
 
 Electrochemical series of the metals. If the metals are arranged in 
 the order of the electromotive force required to liberate them in electrolysis, 
 we have the following electropositive series : 
 
 Electrochemical series of metals. 
 
 Potassium Gold 
 
 Sodium Platinum 
 
 Lithium Palladium 
 
 Calcium Silver 
 
 Strontium Mercury 
 
 Barium Bismuth 
 
 Magnesium Antimony 
 
 Aluminum Copper 
 
 Manganese Arsenic 
 
 Zinc Hydrogen 
 Chromium Lead 
 Cadmium Tin 
 Iron Nickel 
 Cobalt 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 199 
 
 The electromotive force required decreases from the potassium end of the 
 series to the gold end. If the metals are arranged in a series according to the 
 decreasing intensity of their chemical activity in the free state toward other 
 substances, the same order is observed as that in the above series. Metals 
 higher up in the series will displace others following from solutions of their 
 salts, but not vice versa. All the metals, from potassium to hydrogen, will 
 displace hydrogen from dilute acids, but those following hydrogen will not. 
 The metals, down to copper inclusive, will rust in the air. The oxides of the 
 metals, down to manganese inclusive, cannot be reduced to the metal by heat- 
 ing in hydrogen, but oxides of cadmium and the metals following can. The 
 metals down to hydrogen do not occur in the free state in nature. 
 
 The non-metals and negative radicals into which they enter (acid radicals) 
 can also be arranged into a similar electronegative series. 
 
 Discociation theory applied to acids, bases, salts, and neutral- 
 ization. 
 
 Acids. A general discussion of acids, bases, and salts is given in Chapter 
 8. In terms of the ionic theory, acids are substances which give positive hy- 
 drogen ions in solution, associated with negative ions tbat may be either 
 simple, as OF, or complex, as SO/', or CO 3 // . The properties common to all 
 acids are due to the hydrogen ions ; for example, sour taste, action on litmus, 
 action on metals with displacement of the hydrogen. The latter action is rep- 
 resented in the case of zinc by the ionic equation, Zn + 2ET -|- SO/' = Zn** 4- 
 SO 4 " + H 2 . This stands as a type for all acids, and it will be observed that 
 the action is essentially between the metal and hydrogen ions, and is independ- 
 ent of the negative ion. The charges on the hydrogen ions are transferred to 
 the zinc atoms, which then become ionic, and the discharged hydrogen ions 
 escape as molecules. 
 
 The specific properties of the acids in solution are due to the different com- 
 position of the negative radicals. These radicals are the same whether acids 
 or their salts are used. When a solution of silver nitrate is added to one of 
 potassium chloride, a white precipitate of silver chloride is obtained, but when 
 added to potassium chlorate in solution, no visible change takes place. Both 
 of these salts contain chlorine, but the first gives the ion CK, and the second 
 the ion CIO/. In other words, the composition of the negative radicals is 
 different, which results in a different behavior toward the positive silver ion. 
 Silver chloride is an insoluble substance and is formed in solutions only when 
 silver ions and chlorine ions are brought together. Chlorine ions are formed 
 only from hydrochloric acid or the chlorides. Silver chlorate is a soluble 
 body, and, therefore, nothing that we can see happens when silver ions and 
 chlorate ions are brought together in solution. 
 
 Independence of ions. The above discussion leads to the conclusion 
 that the ions of acids are distinct substances with individual physical and 
 chemical properties. Each kind of ion behaves as if it were alone present in 
 the solution. This is true of all ions. To illustrate, two instances may be 
 given that have to do with a physical property, namely, color of salts or acids. 
 All copper salts of colorless acids have a blue color in dilute solutions. The 
 blue color is due to the copper ion, and all copper salts that are soluble give 
 
200 NON-METALS AND THEIR COMBINATIONS. 
 
 the copper ion. The molecules of copper salts in solution are not blue, as can 
 be shown by the following experiment: If to a solution of copper chloride 
 concentrated hydrochloric acid be added, there will be a point at which the 
 blue changes to a yellowish-green color. The effect of the acid is to reverse 
 the ionization of the copper chloride so far that the color of the remaining 
 ions of copper is overbalanced by the color of the molecules of the salt. 
 
 Again, permanganic acid in dilute solution is deeply colored, due to th e 
 MnO/ ion (hydrogen ion is colorless). Likewise all its salts in dilute solu- 
 tions are deeply colored, because they all form the common ion, MnO/. For 
 equivalent concentrations, the tint of the color is the same in all the solutions. 
 
 Analytical reactions or tests. Since acids, bases, and salts ionize, and 
 chemical actions concern primarily the ions, it is not difficult to see that the 
 tests made in solutions (wet way) for identifying substances are tests for ions. 
 Thus, when we test for carbonic acid by lime-water we are testing, not for the 
 acid H 2 CO 3 , but for the ion CO/'. Nevertheless we infer the nature of the 
 molecules from a study of the reactions of the ions. Since the tests apply to 
 ions, we have an explanation of the fact that tests for a given ion can be used 
 in the case of all substances which give that ion in solution, irrespective of the 
 nature of the other ions. Thus, the silver nitrate test for " chlorine " succeeds 
 for all chlorides that are soluble. Likewise, the barium chloride test for all 
 soluble sulphates. It is evident also that two kinds of tests must be made in 
 the case of each substance, namely, one kind for the positive ion and the other 
 kind for the negative ion. 
 
 Kinds of ions formed by acids. Monobasic acids, as HC1, HNO 3 , etc., 
 can form only one hydrogen ion from each molecule. Dibasic acids, like 
 H 2 SO 4 , form one or two hydrogen ions, according to concentration. In rather 
 concentrated solution of sulphuric acid the ionization is principally thus: 
 H 2 SO 4 : H- + HSO/. The ion HSO/ is an acid, but much less active than 
 sulphuric. When the acid is highly diluted, further ionization takes place to 
 a great degree, thus, HSO/ ^ H* -f SO/'. All dibasic acids dissociate in 
 two stages, like sulphuric. Tribasic acids show a similar behavior. 
 
 Activity or "strength" of acids. A proper comparison of acids can 
 only be made under like conditions of temperature, concentration, etc. For 
 this purpose like concentration means solutions containing in a given volume 
 chemically equivalent weights of the respective acids. These are such weights 
 in grammes as contain the same weight of replaceable hydrogen. For ex- 
 ample, two molecular weights of HC1 are equivalent to one moleculer weight 
 of H 2 SO 4 . All conditions being equal, the activity of acids is proportional to 
 the degree of dissociation ; that is, to the concentration of the hydrogen ions. 
 Those acids that ionize most are the "strongest," and vice versa. 
 
 Bases. Bases are substances which give negative hydroxyl (OH) ions in 
 solution, associated with a positive ion, which is usually metallic, but may be 
 a group of atoms not containing a metal, as NH 4 . The properties common to 
 bases in general when dissolved are due to the hydroxyl ion, for example, 
 action on litmus, soapy taste, neutralization of acids. Most of the bases are 
 so sparingly soluble that not enough (OH) ions are present to affect litmus. 
 Zinc and iron hydroxides are examples of such. In other cases, just enough 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC, 201 
 
 (OH) ions dissolve to give a faint action on litmus, for example, magnesium 
 hydroxide. Just as in the case of acids, the activity of bases is proportional 
 to the degree of ionization. The most active common bases are potassium 
 and sodium hydroxides, called alkalies, and sometimes caustic alkalies. Their 
 solutions are called lyes. The hydroxides of barium, strontium, and calcium 
 are next in activity. Ammonium hydroxide is a rather weak base. The rest 
 are either sparingly soluble or insoluble. 
 
 Salts. The relationship between salts and acids has already been discussed. 
 As a rule, salts ionize to a considerable degree, and do not show as wide a range in 
 the degree as do the acids. Non-metals are never found in the positive ion of salts, 
 except they occur in a composite radical, as NH 4 . Hence we have no such salts 
 as nitrogen carbonate, carbon sulphate, or sulphur phosphate. The ions of salts 
 do not affect litmus, it is only H' and (OH) 7 ions that have an effect. 
 
 Acid salts. These may be acid, neutral, or alkaline to litmus, depending 
 on the mode of ionization. An acid salt of a highly ionizing acid shows an 
 acid reaction in solution, because of the presence of hydrogen ions. For ex- 
 ample, sodium bisulphate acts thus in solution : 
 
 NaHSO 4 ? Na' + HSO/ 
 HSO/ ?H- 4- SO/ 
 
 Acid salts of weak acids, like carbonic, phosphoric, boric, etc., may be neutral 
 or even alkaline, because the remaining hydrogen of the acid does not become 
 ionic. Sodium bicarbonate is neutral to litmus, because it ionizes thus : 
 
 NaHCO 3 ^ Na- + HCO 3 '. 
 
 The ion HCO/ does not furnish sufficient H' ions by further dissociation to 
 affect litmus. 
 
 Basic salts, These are the reverse of acid salts. They are derived from 
 bases containing more than one (OH) group in the molecule, and the union 
 with acids is such that not all of the (OH) groups are replaced by acid radical. 
 
 /Cl 
 
 Thus Mg (OH) 2 can form Mg<f QTT which shows the plan of structure of all 
 
 basic salts. They are, in nearly all cases, insoluble in water and show slight or 
 no action on litmus. 
 
 Hydrolysis of salts. Some salts, which we would expect from their for- 
 mulas, such as normal salts, to have a neutral reaction in solution, show a 
 noticeable acid reaction, while others show an alkaline one. Such salts are 
 related to an acid or to a base of slight dissociating power, and the cause is 
 found in the slight ionization of water, which, though extremely minute, 
 makes itself felt in some cases. The acid reaction of copper sulphate is ex- 
 plained by the following ionic reaction : 
 
 2H 2 :2H' + 2(OH)' 
 Copper hydroxide dissociates very slightly, being in this respect on a par 
 with water. As a consequence, some Cu" and (OH)' ions unite to form 
 molecules of Cu(OH) 2 . The removal of (OH)' ions of water allows more to 
 be formed, and more Cu(OH) 2 results. This process soon comes to a stop, but 
 not before enough H' ions have been produced to give the solution an acid re- 
 action. The molecules of Cu(OH) 2 are not precipitated, but remain in solu- 
 tion. The quantity is too small. 
 
202 NON-METALS AND THEIR COMBINATIONS. 
 
 The ionic equation for sodium carbonate which shows marked alkaline reac- 
 
 Na 2 C0 3 ; 2Na' + CO/ 1 _^ HCQ , 
 H 2 ; (OH)' + H ; . /."* 
 
 Here a small quantity of (OH) 7 ions are produced, which give the solution an 
 alkaline reaction. This action of water on salts is called hydrolysis. The 
 changes are usually represented by the simpler reactions : 
 
 CuS0 4 + 2H 2 = Cu(OH), + H 2 S0 4 
 Na 2 C0 3 + H 2 = NaOH + NaHCO. 
 
 Soap always shows an alkaline reaction, which is due to hydrolysis. Salts 
 containing bivalent or trivalent radicals, metallic or acid, are more prone to 
 undergo hydrolysis than those containing univalent radicals only. 
 
 Neutralization. Broadly speaking, the replacement of hydrogen of an acid 
 by metal is neutralization, but, as shown in the preceding paragraph, certain 
 salts have an acid or alkaline reaction in solution, and consequently it is 
 impossible in such instances to produce an exactly neutral solution by bring- 
 ing the acid and base together in the proportions to form the salt. A great 
 many salts, however, are neutral, and in these cases it is possible to bring 
 together the corresponding acids and bases, and have complete reactions and 
 neutral solutions. In the more restricted sense neutralization refers to such 
 complete reactions. They can be employed for quantitative determinations 
 of the acids or bases in solutions. This subject is treated under Acidimetry 
 and Alkalimetry in the section on Volumetric Analysis. 
 
 Neutralization is an example of double decomposition and of a complete 
 reaction. The interpretation of this is found in the ionic theory. In the 
 beginning before mixing, there are H* ions which have an acid reaction, and 
 (OH)' ions which are alkaline. When they are brought together by mixing 
 the acid and base and the neutral point is established, both H* and (OH)' ions 
 disappear, as is proved experimentally by conductivity tests. This disappear- 
 ance results from the fact that water is practically undissociated. and, there- 
 fore, these ions cannot exist in the same solution, but unite to form molecules 
 of water. Of course, the metal ions and acid radical ions also unite to some 
 extent to form molecules, but if the solutions are quite dilute the proportion 
 of undissociated molecules is negligible. 
 
 The ionic equation for the neutralization of sodium hydroxide and nitric 
 acid serves as a type for all instances : 
 
 NaOH ^ Na' + (OH)') 
 HN0 3 ; NO./ + H- / " 
 
 It' 
 NaNO 3 
 
 As fast as H' and (OH)' unite more. NaOH and HNO 3 dissociate, until finally 
 all is dissociated, and only ions of sodium nitrate and some undissociated mole- 
 cules of the same are left in the solution at the point of neutrality. 
 The essential reaction may be shown in the simplified equation : 
 
 Na- + (OH)' + H- + N0 3 ' = Na' + NO 3 ' -f H 2 O, 
 
 or by the following still simpler equation, which expresses the fact that neu- 
 tralization is a reaction between H- and (OH)' ions : 
 
THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 203 
 
 Heat of neutralization. Heat is produced when an acid and a base neu- 
 tralize each other. If what is stated above is true, then the heat is due to the 
 formation of water molecules, and should be the same for all active acids and 
 bases in dilute solutions. This is exactly what is found by experiment to be 
 true. The heat of neutralization refers to such weights of acids and bases that 
 will furnish enough H* and (OH) X ions to form one molecular weight (17.88 
 gin.) of water, and is nearly 13,600 calories. 
 
 Degree of dissociation. The degree of dissociation of electrolytes varies 
 with the nature of the substance and the concentration of the solution. Usu- 
 ally it is small in concentrated solutions, and increases rapidly with dilution. 
 In 62 per cent, nitric acid only about 9 per cent, of the molecules are ionized, 
 while in the 6.3 per cent, acid about 80 per cent, are ionized. Comparisons 
 for degree of dissociation must be made with solutions of the same relative con- 
 centrations. Usually normal solutions at 18 C. are used, except when the 
 substance is not sufficiently soluble. The following table gives the per cent. 
 of dissociation in normal solutions 1 at 18 C., except when otherwise specified, 
 of some acids, bases, and salts. 
 
 PerCent ' 
 
 Electrolyte. .. Electrolyte. / , 
 
 dissociation. dissociation. 
 
 Nitric acid ........... 82 Sodium phosphate, very dilute . . 83 
 
 Hydrochloric acid ....... 78.4 Ammonium chloride ...... 74 
 
 Sulphuric acid ......... 51 Sodium chloride ........ 67.5 
 
 Hydrofluoric acid ...... .7 Potassium nitrate ........ 64 
 
 Acetic acid ...... ..... 0.4 Potassium acetate ........ 64 
 
 Carbonic acid (^) ....... 0.17 Silver nitrate . . . 
 
 , n ^ Potassium sulphate ....... 53 
 
 Hydrogen sulphide (jg) ..... 0.07 godium acetate ......... 53 
 
 Boric acid (^\ ......... 0.01 Sodium bicarbonate ....... 52 
 
 . , / n \ A A1 Potassium carbonate , ...... 49 
 
 Hydrocyanic acid ( 1?) ) ..... 0.01 
 
 Sodium sulphate ........ 44.5 
 
 Phosphoric acid (~ at 25 C.) . . .17 Zinc sulphate .......... 24 
 
 Potassium hydroxide ...... 77 Zinc chloride .......... 48 
 
 Sodium hydroxide ....... 73 Copper sulphate ........ 22 
 
 Calcium hydroxide, sat. sol. at 25 C. 90 Mercuric chloride, less than ... 1 
 
 Ammonium hydroxide ...... 0.4 Mercuric cyanide ....... minute 
 
 Mathematical formulas have been constructed for calculating the degree 
 of dissociation from the results obtained by four methods of work, namely, 
 freezing-point, boiling-point, osmotic pressure, and conductivity methods. 
 The results of calculation all agree. The simplest method in execution is the 
 conductivity method. 
 
 QUESTIONS. State the theory of electrolytic dissociation or ionization. 
 Upon what experimental facts does it rest? What is an electrolyte? What 
 substances are found to be electrolytes ? What is a cation ; an anion ? Write 
 the ionic equation for the dissociation of sodium chloride in solution. Write 
 the ionic equation for the precipitation of silver chloride from solution. What 
 is electrolysis, and how is it explained? How are acids, bases, and salts defined 
 in terms of the ionic theory ? How is the activity or " strength " of acids and bases 
 related to dissociation ? How is the fact that some acid salts have an acid action 
 on litmus, while others are neutral, accounted for.? What is hydrolysis? 
 1 The concentration of normal solutions is denned in the section on Volumetric Analysis. 
 
204 NON-METALS AND THEIR COMBINATIONS. 
 
 16. SULPHUR. 
 S" = 32 (31.83). 
 
 Occurrence in nature. Sulphur is found in the uncombined 
 state, mixed with earthy matter, in volcanic districts, the chief sup- 
 ply having been derived until lately from Sicily. Considerable 
 quantities are now also mined in the United States, chiefly in Louis- 
 iana, Utah, California, and Nevada. In combination sulphur is widely 
 diffused in the form of sulphates (gypsum, CaSO 4 .2H 2 O), and fre- 
 quently occurs as sulphides (iron pyrites, FeS 2 , galena, PbS, cinnabar, 
 HgS, etc.). Sulphur enters also into organic compounds, being a 
 normal constituent of all proteids, during the decomposition of which 
 sulphur is often evolved as hydrogen sulphide, which gas is also a 
 constituent of some waters. 
 
 Properties. Sulphur is a, yellow, brittle, solid substance, having 
 neither taste nor odor. It is insoluble in water and nearly so in 
 alcohol ; soluble in benzene, benzin, ether, chloroform, carbon di- 
 sulphide, oil of turpentine, and fat oils. Sulphur is polymorphous ; 
 it crystallizes, from a solution in disnlphide of carbon, in octahedrons 
 with a rhombic base ; when, however, liquefied by heat it crystallizes 
 in six-sided prisms, and is obtained as a brown, amorphous plastic 
 substance by pouring melted sulphur into cold water. 
 
 Sulphur melts at 115 C. (239 F.) to an amber-colored liquid, 
 which is fluid as water ; increasing the heat gradually, it becomes 
 brown and thick, and at about 200 C. (392 F.) it is so tenacious 
 that it scarcely flows ; when heated still further it again becomes 
 thin and liquid, and, finally, boils at a temperature of about 440 C. 
 (824 F.). 
 
 In its chemical properties sulphur resembles oxygen, being like 
 this element generally bivalent, and supporting, when in the form 
 of vapor, the combustion of many substances, especially the metals. 
 Many compounds of oxygen and sulphur show an analogous compo- 
 sition, as, for instance, H 2 O and H 2 S, CO 2 and CS 2 , CuO and CuS. 
 While the valence of sulphur as a general rule is 2, in some com- 
 pounds it shows a valence of 4 or 6, as in SO 2 and SO 3 . 
 
 Crude sulphur is obtained by heating the rock containing sul- 
 phur sufficiently high to cause the sulphur to melt, and thus to 
 separate from the earthy matters. As peculiar conditions (great depth 
 and quicksand) prevented successful working of the sulphur deposits 
 m Louisiana by the ordinary methods, sulphur is now mined there by 
 the following ingenious process : Superheated water, forced through 
 iron pipes to the deposits of sulphur, causes the latter to melt, and this 
 
SULPHUR. 205 
 
 liquefied sulphur is raised through other pipes to the surface by means 
 of compressed air. Crude sulphur generally contains from 2 to 4 per 
 cent, of earthy impurities. 
 
 Sublimed sulphur, Sulphur sublimatum (Flowers of sulphur). 
 Obtained by heating sulphur to the boiling-point in suitable vessels, 
 and passing the vapor into large chambers, where it deposits in the 
 form of a powder, composed of small crystals. Sublimed sulphur, 
 when melted and poured into round moulds, is known as roll-sulphur 
 or brimstone. 
 
 "Washed sulphur, Sulphur lotum, is sublimed sulphur washed 
 with a very dilute ammonia water, and then with pure water ; the 
 object of this treatment being to free the sulphur from all adhering 
 sulphurous and sulphuric acid, as also from arsenic compounds which 
 are sometimes present. 
 
 Precipitated sulphur, Sulphur prsecipitatum (Milk of sulphur). 
 Made by boiling one part of calcium hydroxide with two parts of 
 sulphur and thirty parts of water, filtering the solution, adding to it 
 dilute hydrochloric acid until nearly neutral, washing and drying the 
 precipitated sulphur. 
 
 By the action of sulphur on calcium hydroxide are formed calcium polysul- 
 phide, calcium thiosulphate, and water: 
 
 3Ca(OH) 2 + 12S : : 2CaS 5 + CaS 2 O 3 + 3H 2 O. 
 
 On adding hydrochloric acid to the solution, both substances are decom- 
 posed and sulphur is liberated : 
 
 2CaS 5 + CaS 2 O 3 + 6HC1 = 3CaCl 2 -f- 3H 2 O + 12S. 
 
 While the above equation gives the final result, the decomposition takes 
 place in stages, thus : 
 
 CaS 5 -f 2HC1 = CaCl 2 + H 2 S + 4S 
 CaS 2 O 3 + 2HC1 = CaCl 2 + H 2 S 2 O 8 
 2H 2 S + H 2 S 2 8 = 3H 2 O + 4S. 
 
 Precipitated sulphur differs from sublimed sulphur by being in a more finely 
 divided state, and by having a much paler yellow, almost white color. 
 
 Experiment 13. Mix in a beaker about 10 grammes of powdered sulphur, 20 
 grammes of slaked lime, and 200 c.c. of water, and boil until the liquid has a 
 deep brown color. Renew the water that is lost by evaporation occasionally. 
 Note that the color deepens as boiling is continued. This is due to the poly- 
 sulphide of calcium, which is colored. Finally, filter into a large flask or 
 beaker, wash the filter, dilute to about half a liter, and add dilute hydrochloric 
 acid until the solution is nearly neutral. Note the milk-like appearance of the 
 liquid. Let the sulphur settle fully, decant the liquid, filter and wash the sulphur, 
 and let it dry in the air. Compare its appearance with that of lump sulphur. 
 
206 NON-METALS AND THEIR COMBINATIONS. 
 
 The following four oxides are known : Sulphur sesquioxide, S 2 O 3 ; 
 sulphur dioxide, SO 2 ; sulphur trioxide, SO 3 ; sulphur heptoxide, S 2 O 7 . 
 The three last named are acid oxides, which, on combining with one 
 molecule of water, form sulphurous, sulphuric, and persulphuric acid 
 respectively. 
 
 Sulphur dioxide, SO 2 = 63.59 (Sulphurous anhydride, improperly 
 also called sulphurous acid), is formed when sulphur or substances con- 
 taining it in a combustible form (H 2 S, CS 2 , etc.) burn in air. It is 
 generated also by the action of strong sulphuric acid on many metals 
 (Cu, Hg, Ag, etc.), or on charcoal : 
 
 2H 2 SO 4 + Cu = CuSO 4 +-2H 2 O + SO 2 . 
 2H 2 SO 4 + C = CO 2 + 2H 2 O + 2SO 2 . 
 
 Sulphur dioxide is a colorless gas, having a suffocating, disagreeable 
 odor; it liquefies at a temperature of 10 C. (14 F.), and solidifies 
 at 75 C. ( 103 F.) ; it is very soluble in water, forming sulphur- 
 ous acid ; it is a strong, deoxidizing, bleaching, and disinfecting 
 agent ; when inhaled in a pure state it is poisonous ; when diluted 
 with air it produces coughing and irritation of the air-passages. 
 
 Sulphurous acid, Acidum sulphurosum, H 2 SO 3 , SO 2 .H.OH. This 
 acid, similar to carbonic acid, is not known in a pure state, but is 
 believed to exist in aqueous solution, which decomposes into water 
 and sulphur dioxide when attempts are made to concentrate it. One 
 volume of cold water absorbs about 40 volumes of sulphur dioxide, 
 equal to about 11 per cent, by weight. The official acid must contain 
 not less than 6 per cent, by weight, equal to about 2000 volumes of 
 gas dissolved in 100 of water. According to the U. S. P. the acid 
 is made by generating sulphur dioxide from charcoal and sulphuric 
 acid in a flask, and passing the gas through a wash-bottle containing 
 water, inta distilled water for absorption. 
 
 Experiment 14. Use an apparatus as shown in Fig. 42. Place in the flask 
 about 20 grammes of charcoal in small pieces, cover it with sulphuric acid, 
 apply heat, and pass the generated gas first through a small quantity of water 
 contained in the wash-bottle, and then into pure water, contained in the 
 cylinder. 
 
 The solution, sulphurous acid, may be used for the tests mentioned below ; 
 when the neutral solution of a sulphite is required, make this by adding solu- 
 tion of sodium carbonate to a portion of the sulphurous acid until litmus-paper 
 shows neutral reaction. Examine also the contents of the wash-bottle by 
 means of the tests given below for sulphuric acid ; most likely some of the 
 latter will be found. How much carbon and how much H 2 S0 4 are required to 
 make 100 grammes of a 6.4 per cent, sulphurous acid? 
 
SULPHUR. 
 
 207 
 
 Sulphurous acid is a colorless acid liquid, which has the odor as well as the 
 disinfecting and bleaching properties of sulphur dioxide; it is completely 
 volatilized by heat. Sulphurous acid is a dibasic acid, the salts of which are 
 termed sulphites. Both the acid and its salts are easily oxidized by the air, 
 and hence almost always give the tests for sulphuric acid. In its chemical be- 
 havior sulphurous acid is very much like carbonic acid. It is a weak acid, 
 being displaced from its salts by all acids except carbonic and boric. The sul- 
 phites of the alkali metals are freely soluble in water, but the normal sulphites of 
 all other metals are insoluble or nearly so ; hence addition of a solution of an 
 alkali sulphite to a solution of salts of the other metals causes precipitates. A 
 
 FIG. 42. 
 
 Apparatus for making sulphurous acid. 
 
 few sulphites are soluble in a solution of sulphurous acid, like carbonates, but 
 are precipitated on boiling. Acid sulphites of the alkali metals can be obtained in 
 the solid state. These show an acid reaction to litmus, but the normal sul- 
 phites of these metals have an alkaline reaction, due to hydrolysis by water 
 into bisulphite and free alkali. All the common sulphites are white. 
 
 The ionic equations for the liberation of sulphurous acid from a sulphite, 
 and the ionization of normal and bisulphites in solution, are ir all respects like 
 those pertaining to the liberation of carbonic acid and the ionization of normal 
 and bicarbonate of sodium, which are given on pages 195 and 201. The reason 
 that bisulphites are slightly acid in solution, and not neutral as bicarbonates 
 are, is that an appreciable amount of hydrogen ions are formed, thus : 
 
 NaHSO 3 ^ 
 
 HS0 3 ' 
 SO 3 ". 
 
 The second reaction takes place only to a small degree. 
 
208 NON-METALS AND THEIR COMBINATIONS. 
 
 Tests for sulphurous acid and sulphites. 
 (Sodium sulphite, Na,SO 3 .7H 2 O, may be used.) 
 
 1. Add sulphur dioxide gas, or a solution of it in water, or a solu- 
 tion of a sulphite to an acidified solution of potassium permanganate. 
 The latter is decolorized, due to its giving up oxygen, which oxidizes 
 the sulphurous acid, thus : 
 
 H,S0 3 + O H 2 S0 4 . 
 
 Make the same experiment with acidified solution of potassium 
 dichromate. The same kind of change takes place, but the decom- 
 position products of the dichromate are green. The reaction will be 
 understood when chromium is studied. 
 
 2. Add a few drops of a solution of sulphurous acid or of a sul- 
 phite to a tube containing some zinc and dilute sulphuric acid 
 (nascent hydrogen). Hydrogen sulphide is liberated, which can be 
 detected by the odor, or a piece of filter-paper, wet with solution of 
 lead acetate, which blackens when held in the mouth of the tube : 
 
 H 2 S0 3 + 6H H 2 S + 3H 2 O. 
 
 3. Add to a few drops of the sulphite solution about 2 c.c. of silver 
 nitrate solution. A white precipitate of silver sulphite is formed, 
 which darkens on heating, due to reduction to metallic silver : 
 
 Ag 2 S0 3 + H 2 2Ag + H 2 S0 4 . 
 
 Silver sulphite is soluble in an excess of the sulphite solution. 
 
 4. A strip of filter-paper, moistened with mercurous nitrate solu- 
 tion, turns black when suspended in sulphur dioxide, due to reduction 
 to metallic mercury : 
 
 2HgN0 3 + 2H 2 + S0 2 = 2Hg + H 2 SO 4 + 2HNO 3 . 
 
 Tests 1 and 4, along with the odor of sulphur dioxide, are usually suf- 
 ficient to recognize sulphurous acid or sulphites. 
 
 Sulphur trioxide, SO 3 (Sulphuric acid anhydride). This is 
 a white, silk-like solid substance, having a powerful affinity for 
 water; it may be obtained by the action of phosphoric oxide on 
 strong sulphuric acid, or by passing sulphur dioxide and oxygen 
 together over heated platinum-sponge. It is now made on the large 
 scale by the latter method for producing fuming sulphuric acid. 
 
 Sulphuric acid, Acidum sulphuricum, H 2 SO 4 , SO 2 (OH) 2 ^ 97.35 
 
 (0 if of vitriol). There is no other acid, and perhaps no other sub- 
 
SULPHUR. 209 
 
 stance, manufactured by chemical action which is so largely used in 
 chemical operations and in the manufacture of so many of the most 
 important articles, as is sulphuric acid. 
 
 Impure sulphuric acid was known in the eighth century ; in the 
 fifteenth a purer acid was obtained by heating ferrous sulphate (green 
 vitriol) in a retort. To the liquid distilling over the name of oil of 
 vitriol was given, in allusion to its tl.ick or oily appearance and the 
 green vitriol from which it was obtained. The change is shown in 
 the following reaction : 
 
 4FeSO 4 + H 2 O = 2Fe 2 O 3 + 2SO., + H 2 SO 4 .S0 3 . 
 
 Sulphuric acid is found in nature in combination with metals as 
 sulphates. Thus calcium sulphate (gypsum), barium sulphate (heavy- 
 spar), magnesium sulphate (Epsom salt), and others occur in nature. 
 
 Manufacture of sulphuric acid. Sulphuric acid is manufactured 
 on a very large scale by passing into large leaden chambers simul- 
 taneously, the vapors of sulphur dioxide (obtained by burning sulphur 
 or pyrites in furnaces), nitric acid, and steam, a supply of atmospheric 
 air also being provided for. The most simple explanation that can 
 be given for the manufacture of sulphuric acid is the fact that sul- 
 phur dioxide when treated with an oxidizing agent, in the presence 
 of water, is converted into sulphuric acid : 
 
 S0 2 + O + H 2 O = H 2 SO 4 . 
 
 Only a portion of the oxygen necessary for oxidation is derived 
 from the nitric acid directly ; the larger quantity is obtained from 
 the atmospheric air, the oxides of nitrogen serving as agents for the 
 transfer of the atmospheric oxygen. 
 
 By the action of nitric acid on sulphur dioxide and steam are formed sul- 
 phuric acid and nitrogen trioxide : 
 
 2SO 2 + H 2 O + 2HNO 3 = 2H 2 SO 4 + N 2 O 3 . 
 
 Nitrogen trioxide next takes up sulphur dioxide, water, and oxygen, forming 
 a compound called nitrosyl-sulphuric acid : 
 
 2SO 2 + N 2 O 3 + 2O + H 2 O = 2(SO 2 .OH.NO 2 ). 
 
 This complex compound is readily decomposed by steam into sulphuric acid 
 and nitrogen trioxide : 
 
 2(SO 2 .OH.NO 2 ) + H 2 O = 2H 2 S0 4 + N 2 O 3 
 
 The nitrogen trioxide again forms nitrosyl-sulphuric acid, which again suffers 
 
 decomposition, and so on indefinitely, as long as the constituents necessary for 
 
 the changes are supplied. These facts show that a given quantity of nitric acid 
 
 will convert an unlimited amount of sulphurous acid into sulphuric acid. 
 
 14 
 
210 NON-METALS AND THP:iR COMBINATIONS. 
 
 There is, however, an unavoidable loss of small portions of nitric acid, or 
 oxides of nitrogen, for which reason some nitric acid has to be supplied daily. 
 It is likely that other chemical changes than the ones mentioned take place 
 in the acid chamber, but according to modern investigations these are the 
 principal ones. 
 
 The liquid sulphuric acid formed in the lead-chamber collects at 
 the bottom of the chamber, whence it is drawn oif. In this state it 
 is known as chamber acid (specific gravity 1.50), and is not pure, but 
 contains about 36 per cent, of water, and frequently either sulphurous 
 or nitric acid. By evaporation in shallow leaden pans it is further 
 concentrated, until it shows a specific gravity of 1.72. When this 
 point is reached the acid acts upon the lead, wherefore the further 
 concentration is conducted in vessels of glass or platinum, until a 
 specific gravity of 1.84 is obtained. This acid contains about 95 
 per cent, of sulphuric acid ; the remaining 5 per cent, of water can- 
 not be expelled by heat. 
 
 Properties of sulphuric acid. Pure acid has a specific gravity of 
 1.848 ; it is a colorless liquid, of oily consistence, boiling at 330 C. 
 (626 F.). When cooled it forms crystals, which melt at 10 C. 
 (50 F.). When heated to about 160 C. (320 F.), the acid begins 
 to fume and gives off sulphur trioxide. The 100 per cent, acid 
 gives off sulphur trioxide, and diluted acid gives off water when 
 heated, until an acid of 98.33 per cent, is reached, which boils 
 at the constant temperature of 330 C. It has a great tend- 
 ency to combine with water, absorbing it readily from atmo- 
 spheric air. Upon mixing sulphuric acid and water, heat is gen- 
 erated in consequence of the combination taking place between the 
 two substances. To the same tendency of sulphuric acid to com- 
 bine with water must be ascribed its property of destroying 
 and blackening organic matter. It is due to this decomposing 
 action of sulphuric acid upon organic matter that traces of the latter 
 color sulphuric acid dark yellow, brown, and, when present in larger 
 quantities, almost black. The poisonous caustic properties are due 
 to the same action. (See Experiments, page 179.) 
 
 Sulphuric acid is a very strong dibasic acid, which expels or dis- 
 places most other acids ; its salts are known- as sulphates. 
 
 The sulphuric acid of the U. S. P. should contain not less than 
 92.5 per cent, of H 2 SO 4 , corresponding to a specific gravity of not 
 V>ss than 1.826 at 25 C. 
 
 The diluted sulphuric acid, Acidum mlphuricum dilutum, is a mix- 
 ture of 100 parts by weight of acid and 825 parts of water, or of 
 
SULPHUR. 211 
 
 about 60 c.c. of acid and 900 c.c. of water. This corresponds to 10 
 per cent, of H 2 SO 4 , and a specific gravity of 1.067 at 25 C. 
 
 Great care should be taken in diluting concentrated sulphuric acid. 
 The acid should always be poured slowly into water with constant stir- 
 ring. It is dangerous to pour the hot acid into water and foolhardy 
 to pour water into the hot acid. Ignorance or disregard of these rules 
 may lead to sad consequences. 
 
 When diluted sulphuric acid acts on metals, hydrogen is liberated and 
 escapes as a gas ; but if these same metals are acted on by concentrated sul- 
 phuric acid, which usually requires heating, other products are formed, such 
 as sulphur dioxide, hydrogen sulphide, or sulphur. This is due to the fact 
 that the concentrated acid acts as an oxidizing agent toward the hydrogen that 
 would otherwise be evolved, and itself is reduced. Certain metals do not act 
 on dilute sulphuric acid at all, but only on the hot concentrated acid, and 
 under these conditions hydrogen is never evolved. This is illustrated in the 
 preparation of sulphur dioxide by heating the concentrated acid with copper. 
 Other substances, as charcoal, sulphur, etc., that can be oxidized, act in the 
 same way on the hot, strong acid. 
 
 Most sulphates are soluble in water. There are practically only three which 
 are insoluble in water or dilute acids, namely, barium, strontium, and lead. 
 Calcium sulphate is slightly soluble in water, and more so in hydrochloric 
 acid. A solution of it is used as a reagent. 
 
 Most sulphates are more or less easily decomposed when heated, but those of 
 potassium, sodium, lithium, calcium, strontium, and barium can stand red 
 heat. 
 
 Sulphuric acid, like all dibasic acids, has two modes of ionizing according 
 to concentration (see page 200). In more concentrated solutions, the ions H* 
 and HSO/ predominate; in dilute solutions, 2H* and SO/ X predominate. 
 Upon diluting a more concentrated solution, HSO/ ions dissociate further, 
 thus: 
 
 H- + SO/'. 
 
 The same thing takes place when SO/ 7 ions are removed by precipitation, 
 which has an effect equivalent to diluting the acid. 
 
 Tests 1 and 2 below are examples of reversible reactions that run practically 
 to completion, because of the removal of one of the factors by precipitation, 
 due to its insolubility (page 114). These tests, like all similar ones that fol- 
 low, are explained in terms of the ionic theory on pages 193 and 200. 
 
 Tests for sulphuric acid and sulphates. 
 
 1. When a solution of barium chloride is added to dilute sulphuric 
 acid, or a solution of any sulphate, a white precipitate of barium 
 sulphate is obtained, which is insoluble in all dilute acids : 
 
 Na 2 S0 4 + BaCl 2 == BaSO 4 + 2NaCl 
 2Na- + SO/' + Ba" + 2C1' = BaSO 4 + 2Na + 2C1'. 
 
212 NON-METALS AND THEIR COMBINATIONS. 
 
 Usually this test alone is sufficient for recognition, as all other 
 ordinary barium salts are soluble in hydrochloric or nitric acid. It 
 is very delicate. 
 
 2. When a solution of lead nitrate or acetate is employed, a 
 white precipitate of lead sulphate, PbSO 4 is obtained. This is solu- 
 ble in a solution of ammonium acetate. 
 
 3. Grind together in a mortar a knife-pointful of a sulphate, sul- 
 phur, or any compound containing it, with 5 to 10 times its bulk of 
 sodium carbonate and about 3 times its bulk of potassium cyanide. 
 Place the mixture in a hole in a piece of charcoal and heat with the 
 blow-pipe flame until it is thoroughly fused. The mass now contains 
 yellowish-brown alkali sulphide (hepar), due to reduction of the sul- 
 phate by the hot charcoal and potassium cyanide. The sodium car- 
 bonate serves as &flux, or fusing material. 
 
 Remove the mass, place it upon a silver coin, and moisten it with 
 dilute hydrochloric acid. A black stain of silver sulphide will be 
 formed. This test is of value in the case of insoluble sulphates and 
 sulphides. 
 
 The above procedure is known as the charcoal reduction test, and is 
 one of the steps taken in systematic qualitative analysis. 
 
 Antidotes. Magnesia, sodium carbonate, chalk, and soap, to neutralize 
 the acid. 
 
 Acids of sulphur. While but four oxides of sulphur exist in the 
 separate state, there are a large number of acids containing sulphur, 
 some of which, however, are known only as constituents of the 
 respective salts. The acids are : 
 
 Hyposulphurous acid, H 2 S 2 O 4 . Thiosulphuric acid, H 2 S a O s . 
 
 Sulphurous acid, H 2 SO 3 . Dithiouic acid, H 2 S 2 O 6 . 
 
 Sulphuric acid, H 2 SO 4 . Trithionic acid, H 2 S 3 O 6 . 
 
 Pyre-sulphuric acid, H 2 S 2 O 7 . Tetrathionic acid, H 2 S 4 O 6 . 
 
 Persulphuric acid, H 2 S 2 O 8 . Pentathionic acid, H 2 S 5 O 6 . 
 
 Hydrogen sulphide, H 2 S. 
 
 Pyrosulphuric acid, H 2 S 2 O 7 (Disulphuric acid, fuming sulphuric 
 acid, Nordhausen oil of vitriol). This acid is made by passing sulphur 
 trioxide (obtained by heating ferrous sulphate) into sulphuric acid, 
 when direct combination takes place : 
 
 H 2 S0 4 + S0 3 = H 2 S 2 7 . 
 
 It is a thick, highly corrosive liquid, which gives off dense fumes 
 when exposed to the air, and decomposes readily into sulphur trioxide 
 and sulphuric acid when heated. 
 
SULPHUR. 213 
 
 Thiosulphuric acid, formerly Hyposulphurous acid, H. 2 S 2 O 3 , 
 SO 2 .SH.OH, is of interest because some of its salts are used, as, for 
 instance, sodium thiosulphate, Na 2 S 2 O 3 , the sodium hyposulphite of 
 commerce. The acid itself is not known in the separate state, since 
 it decomposes into sulphur and sulphurous acid when attempts are 
 made to liberate it from its salts. 
 
 Sulphuric is the most stable acid of sulphur, and all the others have a tend- 
 ency to pass to this acid. It is for this reason that both sulphites and thiosul- 
 phates are good reducing agents. A solution of a thiosulphate, when added 
 to an acidified solution of potassium permanganate or dichromate, acts in the 
 same way as a sulphite does. The essential reaction is : 
 
 Na 2 S 2 O 3 + 4O + H 2 O = Na 2 S0 4 + H 2 S0 4 . 
 
 Thiosulphates also react with the halogen elements in the manner shown by 
 this reaction : 
 
 2Na 2 S 2 O 3 + 21 = Na 2 S 4 6 + 2NaI, 
 
 forming sodium tetrathionate and sodium iodide. This reaction is used for the 
 quantitative estimation of free iodine and in the preparation of so-called de- 
 colorized tincture of iodine. It may also be used for removing iodine stains 
 from the skin or fabrics. 
 
 Most of the thiosulphates are soluble in water, those of barium, lead, and 
 silver being only very sparingly soluble. Alkali thiosulphates have a marked 
 solvent action on many salts that are insoluble in water, forming double thio- 
 sulphates. All thiosulphates are decomposed by acids. 
 
 Tests for thiosulphates. 
 (Use about a 5 per cent, solution of sodium thiosulphate. ) 
 
 1. The solution, upon addition of dilute sulphuric or hydrochloric 
 acid, liberates sulphur dioxide, while sulphur is precipitated more or 
 less rapidly, according to the concentration and temperature. The 
 formation of these two products is characteristic and the test is suffi- 
 cient for recognition of a thiosulphate. The precipitate of sulphur 
 distinguishes it from a sulphite. 
 
 2. Addition of silver nitrate gives a white precipitate of silver 
 thiosulphate, Ag 2 S 2 O 3 , which is immediately dissolved if the sodium 
 thiosulphate is in excess. The precipitate is rather unstable, and 
 decomposes on standing, and more rapidly on heating, giving black 
 silver sulphide and sulphuric acid, 
 
 Ag 2 S 2 3 + H 2 Ag 2 S + H 2 S0 4 . 
 
 Addition of solution of lead nitrate or acetate to thiosulphate solution 
 gives similar results. Most thiosulphates are unstable, like those of 
 silver and lead. 
 
214 NON-METALS AND THEIR COMBINATIONS. 
 
 3. Barium chloride solution gives a white precipitate of barium 
 thiosulphate, BaS 2 O 3 - Calcium chloride, however, gives no precipi- 
 tate, whereas with a sulphite a precipitate is formed. 
 
 Persulplmric acid, H 2 S 2 8 , is obtained by passing an electric current 
 through sulphuric acid of a specific gravity 1.3 to 1.5. The reaction is 
 2H 2 S0 4 = 2H + H 2 S 2 8 . 
 
 The ammonium or potassium salts of this acid are obtained by the electrol- 
 ysis of saturated solutions of the bisulphates of the metals, thus : 
 2KHS0 4 = K 2 S 2 8 + H 2 . 
 
 Persulphuric acid and its salts act as strong oxidizing agents, liberating, 
 for instance, chlorine from hydrochloric acid or from chlorides. 
 
 Hydrogen sulphide, H 2 S (Sulphuretted hydrogen). This compound 
 has been mentioned as being liberated by the decomposition of organic 
 matter (putrefaction) and as a constituent of some spring waters. It 
 is formed also during the destructive distillation of organic matter 
 containing sulphur. The best mode of obtaining it is the decomposi- 
 tion of metallic sulphides by diluted sulphuric or hydrochloric acid. 
 Ferrous sulphide is usually selected for decomposition : 
 FeS + H 2 SO, = FeS0 4 + HJ3. 
 
 Experiment 15. Use apparatus shown in Fig. 42, page 207. Place about 20 
 grammes of ferrous sulphide in the flask, cover the pieces with water, and add 
 sulphuric or hydrochloric acid. Pass a portion of the washed gas into water, 
 another portion into ammonia water. Use the solutions for the tests mentioned 
 below. Ignite the gas at the delivery tube and notice that sulphur is deposited 
 upon the surface of a cold plate held in the flame. Place the apparatus in the 
 fume chamber during the operation. How much ferrous sulphide is required 
 to liberate a quantity of hydrogen sulphide sufficient to convert 1000 grammes 
 of 10 per cent, ammonia water into ammonium sulphide solution? The reac- 
 tion taking place is this : 
 
 2NH 3 + H 2 S = (NHJ 2 S. 
 
 Hydrogen sulphide is a colorless gas, having an exceedingly offen- 
 sive odor and a disgusting taste. Water absorbs about three volumes 
 of the gas, and this solution is feebly acid. It is highly combustible 
 in air, burning with a blue flame, and forming sulphur dioxide and 
 water. It is directly poisonous when inhaled, its action depending 
 chiefly on its power of reducing, and combining with, the blood- 
 coloring matter. Plenty of fresh air, or air containing a very little 
 chlorine, should be used as an antidote. 
 
 Hydrogen sulphide can be driven completely from its aqueous solu- 
 tion by heating. It is a rather unstable compound, being easily 
 broken up into its constituents. For this reason it is a good reduc- 
 
SULPHUR. 215 
 
 ing agent. For example, sulphur dioxide is reduced by it to sulphur, 
 but is not affected by free hydrogen gas : 
 
 2H 2 S + SO 2 = 2H 2 O + 38. 
 
 It is probable that native sulphur found in volcanic regions is produced 
 in this way. Because of the instability of the gas, its sulphur often 
 acts like sulphur in the free state. Thus, the metals from potassium 
 to silver inclusive in the electrochemical series (see page 198) soon 
 become tarnished with a layer of sulphide when exposed to the gas : 
 
 2Ag + H 2 S = Ag 2 S + 2H. 
 
 The solution of hydrogen sulphide is slowly affected by oxygen of the 
 air with precipitation of sulphur, H 2 S -f O H 2 O -f S. Hence, 
 it does not keep except in full bottles. In solution it is a dibasic 
 acid of extremely weak character, only 0.07 per cent, of the molecules 
 being dissociated, mainly according to this equation : 
 
 H 2 S 7 H- + HS'. 
 
 The ion HS' also dissociates, but to a less degree even than water : 
 
 HS'^H- + S". 
 
 Hydrogen sulphide, like any dibasic acid, can give two kinds of salts, 
 acid and normal ; for example, sodium hydrosulphide, NaHS, and 
 sodium sulphide, Na 2 S. The acid salt is obtained in solution, when 
 hydrogen sulphide is passed into a solution of sodium hydroxide to 
 saturation. It has a neutral reaction : 
 
 NaOH + H 2 S = NaHS + H 2 O. 
 In solution it dissociates, thus : 
 
 NaHS 7 Na- + HS'. 
 
 The normal salt, Na 2 S, does not exist in solution, but can be obtained 
 in the dry state by adding to the acid salt an amount of alkali equal 
 to that used in making the same, and evaporating to dry ness : 
 
 NaHS 4- NaOH = Na 2 S -f H 2 O. 
 
 When the dry salt is dissolved in water, it is completely hydrolyzed 
 into the acid salt and free alkali, and, therefore, has a strong alkaline 
 
 reaction : 
 
 Na 2 S + H 2 = NaHS + NaOH. 
 
 Hydrogen sulphide gas and its solution in water are frequently 
 used as reagents in analytical chemistry for precipitating and recog- 
 nizing metals. This use depends on the property of the sulphur to 
 
216 NON-METALS AND THEIR COMBINATIONS. 
 
 combine with many metals to form insoluble compounds, the color 
 of which frequently is very characteristic : 
 
 CuS0 4 + H 2 S = CuS + H 2 S0 4 . 
 
 The sulphides that are insoluble in water fall approximately into three 
 groups: 
 
 1. Those that are almost completely insoluble in water, such as the sul- 
 phides of lead, copper, bismuth, silver, mercury, arsenic, antimony, tin, and a 
 few others. These, moreover, are not dissolved by dilute acids, and hence are 
 precipitated from solutions of salts of the metals bypassing hydrogen sulphide 
 into them even when a little free acid is present : 
 
 Pb(N0 3 ) 2 + H 2 S = PbS + 2HN0 3 , 
 Lead sulphide. 
 
 or Pb" + 2(N0 3 )' + 2H- + S" = PbS + 2H- + 2(NO 3 )'. 
 
 2. Those that are practically insoluble in water, yet more soluble than the 
 sulphides of group 1, and are dissolved by even very dilute active acids. The 
 metals iron, cobalt, nickel, manganese, zinc, and a few others form such sul- 
 phides. Some of these sulphides are so readily soluble in dilute acids that they 
 are prevented from being precipitated by hydrogen sulphide by the acid that 
 would be liberated in the reaction (see equation above). In the case of zinc 
 salts partial precipitation takes place until equilibrium is reached, but if some 
 free acid is present, no precipitation takes place. To form the sulphides of 
 this group, a salt of hydrogen sulphide, such as ammonium or sodium sul- 
 phide, is applied to neutral solutions of the salts of the metals, thus : 
 
 FeS0 4 + (NH 4 ) 2 S = FeS + (NH 4 ) 2 SO 4 , 
 Iron sulphide. 
 
 or Fe" + S0 4 " + 2(NH 4 ) + S" = FeS + 2(NH 4 )- -f SO 4 ". 
 
 3. Those that are known only in the dry state, and although they are insol- 
 uble as such in water, yet they dissolve because they are hydrolyzed into solu- 
 ble products, thus : 
 
 2CaS -f 2H 2 = Ca(OH) 2 + Ca(SH) 2 . 
 
 The sulphides of barium, strontium, and calcium belong to this class. They 
 cannot be precipitated, either by hydrogen sulphide or ammonium sulphide. 
 They are generally made from the sulphate by heating with carbon (reduction 
 to sulphide). 
 
 Solutions of normal sulphides, as Na 2 S, and acid sulphides, as NaHS, or 
 NH 4 HS, when used as reagents in precipitation of insoluble sulphides, give 
 the same results because of the presence of S /x ions, which unite with the ions 
 of the other metals. 
 
 Tests for hydrogen sulphide or sulphides. 
 1. Hydrogen sulphide or soluble sulphides (ammonium sulphide 
 may be used) when added to soluble salts of lead, copper, mercury, 
 etc., give black precipitates of the sulphides of those metals. 
 ^ 2. From insoluble sulphides (ferrous sulphide, FeS, may be used) 
 liberate the gas by dilute sulphuric or hydrochloric acid, and test as 
 
SULPHUR. 217 
 
 above, or suspend a piece of filter-paper, moistened with solution of 
 lead acetate, in the liberated gas, when the paper turns dark. Some 
 sulphides, for instance, those of mercury, gold, platinum, as also FeS 2 , 
 and a few others, are not decomposed by the acids mentioned, unless 
 zinc be added. 
 
 Carbon disulphide, Carbonei disulphidum, CS 2 75.57. This 
 com pound is obtained by passing vapors of sulphur over heated 
 charcoal. It is a colorless, highly refractive, very volatile, and 
 inflammable neutral liquid, having a characteristic odor and a sharp, 
 aromatic taste. It boils at 46 C. (115 F.) ; it is almost insoluble 
 in water, soluble in alcohol, ether, chloroform, fixed and volatile oils ; 
 for the latter two it is an excellent solvent, but dissolves, also, many 
 other substances, such as sulphur, phosphorus, iodine, many alka- 
 loids, etc. 
 
 Selenium, Se, and Tellurium, Te, are but rarely met with. Both elements 
 show much resemblance to sulphur; both are polymorphous; both combine 
 with hydrogen, forming H. 2 Se and H 2 Te, gaseous compounds having an odor 
 more disagreeable even than that of H 2 S. Like sulphur, they form dioxides. 
 Se0 2 and TeO 2 , which combine with water, forming the acids H 2 SeO 3 and 
 H 2 Te0 3 , analogous to H 2 SO 3 . The acids H 2 Se0 4 and H 9 TeO 4 , corresponding 
 to H 2 SO 4 , also are known. 
 
 Ionic mechanism of the solution by acids of salts that are insol- 
 uble in water. The operation of dissolving by the aid of an acid, salts that 
 are insoluble in water is resorted to frequently in general chemical work, and 
 particularly in chemical analysis. It is a matter of observation, too, that a 
 salt will dissolve in some acids, but not in others; also that of salts of the same 
 acid with different metals, some will dissolve in a given acid, while others will 
 not. Thus zinc sulphide is soluble in dilute hydrochloric acid, but not in 
 acetic, and the same is true of calcium oxalate and calcium phosphate. Iron 
 sulphide is soluble in most any dilute acid, but copper sulphide is not appre- 
 ciably dissolved by the same acids. The student often wonders what the ex- 
 planation is of such facts as these. The ionic theory gives a physical basis for 
 accounting for them. 
 
 Solution is the converse of precipitation. In the discussion of the latter 
 subject (see page 193) it is stated that whenever there are more ions of a sub- 
 stance than a saturated solution of that substance can maintain, the excess of 
 ions unite to molecules, which separate from solution as a precipitate. The 
 more insoluble the substance is the smaller is the concentration of molecules 
 and ions that can be maintained in its saturated solution, and the more com- 
 plete is the precipitation. Every "insoluble" substance is soluble to some 
 extent in water, even if only minutely. But many of the so-called insoluble 
 salts are slightly soluble in water, which is an important factor in accounting 
 for the solution of salts by acids. Now, water in contact with such a salt be- 
 
218 NON-METALS AND THEIR COMBINATIONS. 
 
 comes saturated, that is, it takes up the maximum number of molecules and 
 ions that it can hold (which, of course, is not large), and these are in equi- 
 librium. If in any way the concentration of the negative (acid radical) ion is 
 diminished, more molecules dissociate to keep up the concentration of that 
 ion, which results in the dissolving of more molecules of the solid salt to keep 
 up saturation and equilibrium. If the negative ions of the salt are of an acid 
 that has a slight dissociating power, their concentration will be diminished 
 when an active (highly dissociating) acid is added to the mixture, thereby 
 furnishing an abundance of H' ions, with which the negative ions of the salt 
 unite to form undissociated molecules of the acid. If the concentration of the 
 negative ions of the salt is greater than that which can be maintained by the 
 corresponding acid, the salt will dissolve by the addition of an active acid, in 
 keeping with the principle of equilibrium as involved in the dissociation con- 
 stant (see page 192). Even an acid of a moderate degree of dissociation may 
 have its dissociation reversed to such an extent in the presence of an excess 
 of a highly dissociating acid, like hydrochloric, that it becomes equivalent to 
 a slightly dissociating acid, and does not maintain as great a concentration of 
 its negative ion as is maintained by its slightly soluble salts in water. This is 
 illustrated by the solution of calcium oxalate in excess of hydrochloric acid. 
 In the case of highly insoluble salts, like barium sulphate, the amount dis- 
 solved, and consequently the concentration of its ions, is so extremely small 
 that addition of active acids has very little effect in reducing the concentration 
 of the negative ion. Hence, extremely little of such a salt is dissolved by 
 acids. Such salts evidently can be precipitated in an acid medium, whereas 
 the salts that are dissolved by a given acid cannot be precipitated in the 
 presence of that acid. 
 
 The points just discussed may be given a more concrete form by the consid- 
 eration of the sulphide of iron and of copper. When dilute hydrochloric acid 
 is added to iron sulphide, hydrogen sulphide is evolved. The ionic repre- 
 sentation of the act of solution is the following : 
 
 FeS (slightly soluble) ^ Fe' + S" \ R s 
 2HC1 ^ 2Cr + 2H' / " 
 
 The negative ion S" coming from the slight amount of FeS dissolved in water 
 is also the ion of H 2 S. Hydrogen sulphide dissociates to a less degree than 
 does FeS ; that is, the concentration of S x/ that can be maintained by H 2 S in 
 solution is less than that which can be maintained by FeS in solution. The 
 result is that some S x/ ions unite with H' ions of the hydrochloric acid to 
 form undissociated molecules of H a S, thus reducing the concentration of S /x 
 ion. More FeS dissolves to keep up the equilibrium. This is kept up until 
 all the FeS is dissolved, or until (if FeS is in excess) the HC1 is so much ex- 
 hausted that the little which remains is in equilibrium with the other products. 
 As the H,S accumulates, the solution becomes saturated and the excess escapes 
 as gas. 
 
 In the case of copper sulphide, dilute hydrochloric acid has no action. The 
 ionic reactions would be : 
 
 CuS (very slightly soluble) \ ; Cu' + S" \ _^ R ~ 
 2HC1 / i 2C1' + 2H' / *~ 2 
 
PHOSPHORUS. 219 
 
 But the concentration of S /x ions maintained by CuS in solution is less than 
 that maintained by H 2 S in solution, even in the presence of the excess of H- 
 ions of the dilute hydrochloric acid, which repress to some extent the disso- 
 ciation of H 2 S. Hence, not only is there no solution of the copper sulphide, 
 but if H 2 S is passed into an acidified solution of a copper salt, CuS is precipi- 
 tated. Only a rather concentrated solution of hydrochloric acid will so far 
 reduce the concentration of S x/ ions as to allow the copper sulphide to 
 dissolve. 
 
 The subject may be summed up in a general statement, thus : The difficultly 
 soluble salts of weaker (less ionized) acids are, as a rule, dissolved by solutions 
 of the stronger (more ionized) acids. Exceptions are salts of extreme insolubility 
 of stronger acids, and, in a few cases, even of weaker acids. 
 
 17. PHOSPHORUS. 
 
 pi = 31 (30.77). 
 
 Occurrence in nature. Phosphorus is found in nature chiefly ID 
 the form of phosphates of calcium (apatite, phosphorite), iron, and 
 aluminum, which minerals form deposits in some localities, but- occur 
 also diffused in small quantities through all soils upon which plants 
 will grow, phosphorus being an essential constituent of the food of 
 most plants. Through the plants it enters the animal system, where 
 it is found either in organic compounds, or and this in by far the 
 greater quantity as tricalcium phosphate principally in the bones, 
 which contain about 60 per cent, of it. From the animal system it 
 is eliminated chiefly in the urine. 
 
 Manufacture of phosphorus. Phosphorus was discovered and 
 made first in 1669 by Brandt, of Hamburg, Germany, who obtained 
 it in small quantities by distilling urine previously evaporated and 
 mixed with sand. 
 
 QUESTIONS. How is sulphur found in nature? Mention of sulphur: 
 atomic weight, valence, color, odor, taste, solubility, behavior when heated, 
 and allotropic modifications. State the processes for obtaining sublimed, 
 washed, and precipitated sulphur. State composition and mode of preparing 
 sulphur dioxide and sulphurous acid ; what are they used for, and what are 
 their properties ? Explain the process for the manufacture of sulphuric acid 
 on a large scale. Mention of sulphuric acid : color, specific gravity, its action 
 on water and organic substances. Give tests for sulphates and sulphites, sul- 
 phuric and sulphurous acids. What is the difference between sulphates, sul- 
 phites, and sulphides? How is hydrogen sulphide formed in nature, and by 
 what process is it obtained artificially ? What are its properties, and what is 
 it used for? Mention antidotes in case of poisoning by sulphuric acid and 
 hydrogen sulphide. 
 
220 NON-METALS AND THEIR COMBINATIONS. 
 
 The manufacture of phosphorus to-day depends on the deoxida- 
 tion of metaphosphoric acid by carbon at a high temperature in 
 retorts. 
 
 The acid is obtained by adding to any suitable tricalcium phophate sulphuric 
 acid in a quantity sufficient to combine with the total amount of calcium 
 present. The first action of sulphuric acid upon the phosphate consists in a 
 removal of only two-thirds of the calcium present, and the formation of an 
 acid phosphate : 
 
 CagCPOJa + 3HaSO 4 = CaH 4 (PO 4 ) 2 -f 2CaSO 4 + H 2 SO 4 . 
 
 The nearly insoluble calcium sulphate is separated by filtration, and the 
 solution of acid phosphate containing free sulphuric acid is evaporated to the 
 consistency of a syrup, when more calcium sulphate separates and a solution 
 of nearly pure phosphorig acid is left : 
 
 CaH 4 (PO 4 ) 2 + H 2 SO 4 = CaS0 4 -f 2(H 3 POJ. 
 
 This syrupy phosphoric acid is mixed with coal and heated to a temperature 
 sufficiently high to expel water and convert the ortho- into meta-phosphoric 
 acid: 
 
 2(H 3 POJ = 2HPO 3 + 2H 2 O. 
 
 The dry solid mixture of this acid and charcoal is now introduced into 
 retorts and heated to a strong red heat, when the following decomposition 
 takes place : 
 
 2(HP0 3 ) + 50 = H 2 + SCO + 2P. 
 
 The three products formed escape in the form of gases from the retort, and by 
 passing them through cold water phosphorus is converted into a solid. The 
 reaction in the retorts is somewhat more complicated than above stated in the 
 equation, as some gaseous hydrogen phosphide and. a few other products are 
 formed in small quantities. 
 
 Also phosphorus is now made by subjecting to the action of a strong electric 
 current a mixture of tricalcium phosphate and carbon, when phosphorus is set 
 free, while calcium carbide and carbonic oxide are formed : 
 
 Ca,(PO 4 ) 2 + 140 = 2P + 3CaC 2 -4- SCO. 
 
 Properties of phosphorus. When recently prepared, phos- 
 phorus is a colorless, translucent, solid substance, which has some- 
 what the appearance and consistency of bleached wax. In the 
 course of time, and especially on exposure to light, it becomes by 
 degrees less translucent, opaque, white, yellow, and finally yellowish- 
 red. At the freezing-point phosphorus is brittle ; as the temperature 
 increases it gradually becomes softer, until it fuses at 44 C. (111F.), 
 forming a yellowish fluid, which at 290 C. (554 F.) (in the absence 
 of oxygen) is converted into a colorless vapor. Specific gravity 1.83 
 at 10 C. (50 F.) 
 
 The most characteristic features of phosphorus are its great affinity 
 for oxygen, and its luminosity, visible in the dark, from which 
 
PHOSPHORUS. 221 
 
 latter property its name, signifying " carrier of light," has been 
 derived. In consequence of its affinity for oxygen, phosphorus has 
 to be kept under water, as it invariably takes fire when exposed to 
 the air, the slow oxidation taking place upon the surface of the 
 phosphorus soon raising it to 50 C. (122 F.) at which temperature 
 it ignites, burning with a bright white flame, and giving off dense, 
 white fumes of phosphoric oxide. The luminosity of phosphorus, 
 due to this slow oxidation, is seen when a piece of it is exposed to 
 the air, and whitish vapors are emitted which are luminous in the 
 dark ; at the same time an odor resembling that of garlic is noticed. 
 
 Phosphorus is insoluble in water, sparingly soluble in alcohol, 
 ether, fatty and essential oils, very soluble in chloroform and in 
 disulphide of carbon, from which solution it separates in the form of 
 crystals. 
 
 Although nitrogen has very weak chemical affinities, while those 
 of phosphorus are extremely strong, yet there is a close resemblance 
 in the chemical properties of these two elements. Both are chiefly 
 either trivalent or quinquivalent; both form compounds corresponding 
 to one another in composition, as also in properties. Thus we know 
 the two gaseous compounds NH 3 and PH 3 ; the oxides N 2 O 3 , N 2 O 5 , 
 and P 2 O 3 , P 2 O 5 . There is also metaphosphoric acid, HPO 3 , corre- 
 sponding to nitric acid, HNO 3 . The chlorides NC1 3 and PC1 3 are 
 known, and many other corresponding features may be pointed out 
 It will be shown later that nitrogen and phosphorus have a great 
 resemblance to the metallic elements arsenic and antimony. 
 
 Phosphorus not only combines directly with oxygen, but also with 
 chlorine, bromine, iodine, sulphur, and with many metals, the latter 
 compounds being known as phosphides. 
 
 Phosphorus is trivalent in some compounds, as in PC1 3 , P 2 O 3 ; 
 quinquivalent in others, as in PC1 5 , P 2 O 6 . 
 
 The molecules of most elements contain two atoms ; phosphorus is 
 an exception to this rule, its molecule containing four atoms. The 
 molecular weight of phosphorus is consequently 4 X 30.77 = 123.08. 
 
 Allotropic modifications. Several allotropic modifications of 
 phosphorus are known, of which the red phosphorus (frequently 
 called amorphous phosphorus) is the most important. This variety is 
 obtained by exposing common phosphorus for some time to a tem- 
 perature of 260 C (500 F.), in an atmosphere of carbon dioxide. 
 The change takes place rapidly when a higher temperature is used 
 and pressure is applied. This modified phosphorus is a red powder, 
 which differs widely from common phosphorus. It is not poisonous. 
 
222 NON-METALS AND THEIR COMBINATIONS. 
 
 not luminous, not soluble in the solvents above mentioned, not com- 
 bustible until it has been heated to about 280 C (536 F.), when it 
 is reconverted into common phosphorus. 
 
 Use of phosphorus. By far the largest quantity of all phos- 
 phorus (both common and red) is used for matches, which are made 
 by dipping wooden splints into some combustible substance, as 
 melted sulphur or paraffin, and then into a paste made by thoroughly 
 mixing phosphorus with glue in which some oxidizing agent (potas- 
 sium nitrate or chlorate) has been dissolved. 
 
 The so-called " safety matches" contain a mixture of antimony trisulphide, 
 red lead, and the chlorate and dichromate of potassium. This mixture will not 
 ignite by simple friction, but does so when drawn across a surface upon which 
 is a mixture of red phosphorus and antimony pentasulphide. 
 
 Pharmaceutical preparations containing phosphorus in the elementary state 
 are phosphorated oil, pills of phosphorus, and spirit of phosphorus. The second 
 is official. 
 
 Phosphorus is also used for making phosphoric acid and other compounds. 
 
 Poisonous properties of phosphorus ; antidotes. Common phosphorus is 
 extremely poisonous, two kinds of phosphorus-poisoning being distinguished. 
 They are the acute form, consequent upon the ingestion of a poisonous dose, 
 and the chronic form affecting the workmen employed in the manufacture of 
 phosphorus or of lucifer matches. 
 
 In cases of poisoning by phosphorus, efforts should be made to eliminate the 
 poison as rapidly as possible by means of stomach-pump, emetics, or cathartics. 
 As antidote a one-tenth per cent, solution of potassium permanganate has been 
 used successfully; it acts by oxidizing the phosphorus, converting it into 
 ortho-phosphoric acid. Oil of turpentine has also been used as an antidote, 
 though its action has not been sufficiently explained. Oil or fatty matter 
 (milk) must not be given, as they act as solvents of the phosphorus, causing its 
 more ready assimilation. 
 
 Detection of phosphorus in cases of poisoning. Use is made of its luminous 
 properties in detecting phosphorus, when in the elementary state. Organic 
 matter (contents of stomach, food, etc.) containing phosphorus will often show 
 this luminosity when agitated in the dark. If this process fails, in consequence 
 of too small a quantity of the poison, a portion of the matter to be examined 
 is rendered fluid by the addition of water, slightly acidulated with sulphuric 
 acid, and placed in a flask, which is connected with a bent glass tube leading 
 to a Liebig's condenser. The apparatus (Fig. 43) is placed in the dark, and 
 the flask is heated. If phosphorus be present, a luminous ring will be seen 
 where the glass tube, leading from the flask, enters the condenser. The heat 
 should be raised gradually to the boiling-point, the liquid kept boiling for 
 some time, and the products of distillation collected in a glass vessel. Phos- 
 phorus volatilizes with the steam, and small globules of it may be found in the 
 collected fluid. If, however, the quantity of phosphorus in the examined 
 matter was very small, it may all have become oxidized during the distillation, 
 and the fluid will then contain phosphorous acid, the tests for which will be 
 stated below. 
 
PHOSPHORUS. 223 
 
 It should be mentioned that the luminosity of phosphorus vapors is dimin- 
 ished, or even prevented, by vapors of essential oils (oil of turpentine, for 
 instance), ether, olefiant gas, and a few other substances. 
 
 Oxides of phosphorus. Four oxides of phosphorus are known. 
 They are phosphorus monoxide, P 4 O, phosphorus trioxidc, P 2 O 3 , phos- 
 phorus tetroxide, P 2 O 4 , and phosphorus pentoxide, P 2 O 5 . The three 
 lower oxides are obtained by slow oxidation, or by the burning of 
 phosphorus in a limited supply of air ; while the pentoxide is formed 
 
 FIG. 43. 
 
 Apparatus for detection of phosphorus in cases of poisoning. 
 
 whenever phosphorus burns under ordinary conditions. The pent- 
 oxide is a white powder possessing an intense affinity for water, 
 with which it combines to form phosphoric acid, while the trioxide 
 with water produces phosphorous acid. 
 
 Hypophosphorous acid, Acidum hypophosphorosum, H 3 PO 2 , 
 PO.H 2 .OH = 65.53. When phosphorus is heated with solution of 
 potassium, sodium,, or calcium hydroxide, the hypophosphite of these 
 
224 NON-METALS AND THEIR COMBINATIONS. 
 
 metals is formed, while gaseous hydrogen phosphide, PH 3 , is lib- 
 erated and ignites spontaneously. The action may be represented 
 thus : 
 
 3KOH + 4P + 3H 2 = 3KPH 2 O 2 + PH 3 . 
 or 
 
 3Ca(OH) 2 + 8P + 6H 2 O = 3Ca(PH 2 O 2 ) 2 + 2PH 3 . 
 
 From calcium hypophosphite the acid may be obtained by decom- 
 posing the salt with oxalic acid, which forms insoluble calcium 
 oxalate, while hypophosphorous acid remains in solution : 
 
 Ca(PH 2 2 ) 2 + H 2 C 2 4 = CaC 2 4 + 2HPH 2 O 2 . 
 
 From potassium hypophosphite the acid may be liberated by the 
 addition of tartaric acid and alcohol, when potassium acid tartrate 
 forms, which is nearly insoluble in dilute alcohol and may be sepa- 
 rated by filtration. 
 
 Pure hypophosphorous acid is a white crystalline substance, acting 
 energetically as a deoxidizing agent. Although containing three 
 atoms of hydrogen, it is a monobasic acid, only one of the hydrogen 
 atoms being replaceable by metals. 
 
 Hypophosphorous acid of the U. S. P. contains 30 per cent, and 
 the diluted acid 10 per cent, of the pure acid dissolved in water. 
 Both preparations are colorless acid liquids, which, upon heating, lose 
 water and are afterward decomposed into phosphoric acid and hydrogen 
 phosphide, which ignites : 
 
 2H 3 P0 2 H 3 P0 4 + PH 3 . 
 
 Similar to the case of sulphur, the most stable acid of phosphorus is phos- 
 phoric acid, and the others show a tendency to pass to it. These are, therefore, 
 easily oxidized and also easily reduced. Thus, hypophosphorous acid is not 
 only quickly oxidized by the usual oxidizing agents, but even precipitates many 
 metals from their salts. Hypophosphites, when brought into the presence of 
 nascent hydrogen, are reduced to phosphine gas, PH 3 (compare with sulphites). 
 All hypophosphites are soluble in water and nearly all are colorless. About 
 six are used in medicine. 
 
 Tests for hypophosphites. 
 
 (Use about a 5 per cent, solution of the sodium salt, NaPH 2 O 2 .) 
 1. Heat a small quantity of the dry sodium salt in a porcelain dish 
 until it ignites. The salt is decomposed into a phosphate and phos- 
 phine, which burns with a characteristic brilliant light, emitting a 
 white cloud of oxide of phosphorus. Some red phosphorus is also 
 formed. 
 
 2NaPH 2 2 = Na 2 HPO, + PH 3 . 
 2PH 3 + 80 = P 2 5 + 3H 2 0. 2PH 3 + 30 = 2P + 3H,O. 
 
PHOSPHORUS. 225 
 
 2. Acidify about 5 c.c. of the solution with dilute hydrochloric 
 acid, and add some mercuric chloride solution. A white precipitate 
 of mercurous chloride is formed. Above 60 C. and with excess of the 
 hypophosphite, further reduction to dark metallic mercury takes place. 
 
 4HgCl 2 + Na.PHA + 2H 2 O = 4HgCl + H,PO 4 + NaCl + 3HC1. 
 4HgCl + NaPHA + 2H 2 O == 4Hg + H S PO 4 + NaCl + 3HC1. 
 
 3. Addition of silver nitrate solution causes a dark precipitate of 
 metallic silver. In the first instant, a white precipitate of silver hypo- 
 phosphite is seen, but this is very unstable. 
 
 NaPH 2 Q 2 + 4AgN0 3 + 2H 2 O == 4Ag + NaH 2 PO 4 + 4HN0 3 . 
 
 4. When the solution is added to acidified potassium permanganate 
 solution, the latter is decolorized. The essential reaction is this, 
 
 NaPH 2 2 + 2 = NaH 2 P0 4 . 
 
 Tests 1 and 2 are very distinctive and usually sufficient to recognize 
 the acid or its salts. 
 
 Phosphorous acid, H 3 PO 3 , PO.H.(OH) 2 . This is a dibasic acid 
 obtained by dissolving phosphorous oxide in water: 
 
 PA + 3H 2 = 2H 3 P0 3 . 
 
 or still better by the action of water on phosphorus trichloride : 
 PC1 3 + 3H 2 O == H 3 P0 3 + 3HC1. 
 
 It is a colorless acid liquid, which forms salts known as phos- 
 phites ; it is a strong deoxidizing agent, easily absorbing oxygen, 
 forming phosphoric acid. 
 
 Tests. Phosphorous acid and its salts give practically the same 
 reactions as the hypophosphites. The following are the chief dis- 
 tinctions : Phosphites when added to solutions of calcium, barium, and 
 strontium salts give precipitates of phosphites of these metals, whereas 
 hypophosphites do not give a precipitate. Acidified permanganate 
 solution is decolorized only after some time by phosphites, but imme- 
 diately by hypophosphites. 
 
 Phosphites are of very little importance. 
 
 Phosphoric acids. Phosphoric oxide is capable of combining 
 chemically with one, two, or three molecules of water, forming 
 thereby three different acids. 
 
 P 2 O 5 + H 2 O = H 2 P 2 O 6 = 2HPO 3 Metaphosphoric acid. 
 P 2 O 5 -f 2H/) = H 4 P 2 O 7 Pyrophosphoric acid. 
 
 P 2 O 5 + 3H 2 O = H 6 P 2 O 8 = 2H 3 PO 4 Orthophosphoric acid. 
 15 
 
226 NON-METALS AND THEIR COMBINATIONS. 
 
 These three acids show different reactions, act differently upon the 
 animal system, and form different salts. 
 
 Metaphosphoric acid, HPO 3 , PO 2 OH (Glacial phosphoric, acid). 
 This acid is always formed when phosphoric oxide is dissolved in 
 water ; gradually, and more rapidly on heating with water, it absorbs 
 the latter, forming orthophosphoric acid; by heating the latter to 
 near a red heat metaphosphoric acid is re-formed. 
 
 Metaphosphoric acid is a monobasic acid which forms colorless, 
 transparent, amorphous masses, readily soluble in water. It coagu- 
 lates albumin (pyro- and orthophosphoric acids do not) and gives a 
 white precipitate with ammonio-silver nitrate ; it is not precipitated 
 by magnesium sulphate in the presence of ammonia and ammonium 
 chloride. It acts as a poison, while common phosphoric acid is 
 comparatively harmless. 
 
 Pyrophosphoric acid, H 4 P 2 O 7 , P 2 O 3 (OH) 4 . This is a tetra-basic acid 
 which gives a white precipitate with ammonio-silver nitrate, while orthophos- 
 phoric acid gives a yellowish precipitate ; it is not precipitated by ammonium 
 molybdate, and does not coagulate albumin. 
 
 Phosphoric acid, Orthophosphoric acid, Acidum phosphoricum, 
 H 3 PO 4 , PO(OH) 3 = 97.29 (Common or tribasic phosphoric acid). 
 Nearly all phosphates found in nature are orthophosphates. 
 
 Phosphoric acid may be made by burning phosphorus, dissolving 
 the phosphoric oxide in water, and boiling for a sufficient length of 
 time to convert the meta- into orthophosphoric acid. 
 
 Experiment 16. Place a piece of phosphorus (about 0.5 gramme), after having 
 dried it quickly between filter paper, in a small porcelain dish, standing upon 
 a glass plate ; ignite the phosphorus by touching it with a heated wire, and 
 place over the dish an inverted large beaker. The white vapors of phosphoric 
 oxide soon condense into flakes, which fall on the glass plate. Collect the 
 white mass with a glass rod, 'and dissolve in a few c.c. of water. Use a portion 
 of the solution for tests of metaphosphoric acid; evaporate the remaining 
 quantity in a porcelain dish until it becomes syrupy, dilute with water and use 
 it for making tests for orthophosphoric acid, either as such or after having 
 neutralized with sodium carbonate. How much phosphorus is needed to make 
 490 grammes of the U.S. P. 10 per cent, phosphoric acid? 
 
 Phosphoric acid is also made by gently heating pieces of phos- 
 phorus with diluted nitric acid, when the phosphorus is oxidized, 
 red fumes of nitrogen tetroxide escaping : 
 
 3P + 5HNO 3 + 2H 2 O = 3H 3 PO 4 + 5NO. 
 
 The liquid is evaporated until the excess of nitric acid has been 
 
PHOSPHORUS. 227 
 
 expelled, and enough of water added to obtain an acid which contains 
 85 per cent, of the pure H 3 PO 4 . Specific gravity 1.707 at 25 C. 
 
 Diluted phosphoric acid, U. S. P., is made by mixing 100 Gm. of 
 the 85 per cent, acid with 750 Gm. of water. It contains 10 per cent, 
 of absolute orthophosphoric acid. 
 
 Phosphoric acid, U. S. P., is a colorless, odorless, strongly acid 
 liquid, which, on evaporation, forms a thick syrupy liquid. This, on 
 cooling, slowly solidifies in the form of large crystals, which are 
 highly deliquescent. Heated to a sufficiently high temperature the 
 acid loses water, being converted successively into pyrophosphoric 
 and metaphosphoric acid, which is finally volatilized at a low red 
 heat. It is a tribasic acid, forming three series of salts, namely : 
 
 Na 3 PO 4 = Trisodium phosphate. 
 
 Na 2 HPO 4 = Disodium hydrogen phosphate. 
 NaH 2 PO 4 = Sodium dihydrogen phosphate. 
 
 If the metal be bivalent, the formulas are thus : 
 
 Ca 3 (PO 4 ) 2 = Tricalcium phosphate. 
 Ca2H 2 (PO 4 ) 2 = Dicalcium orthophosphate. 
 CaH 4 (PO 4 ) 2 = Monocalcium orthophosphate. 
 
 According to the number of hydrogen atoms replaced in the acid, 
 the salts formed are also termed primary, secondary, and tertiary 
 phosphates ; KH 2 PO 4 being, for instance, primary potassium phos- 
 phate ; Na 2 HPO 4 secondary sodium phosphate ; Ag 3 PO 4 tertiary sil- 
 ver phosphate. All the alkali phosphates, but only primary phos- 
 phates of the other metals, are soluble in water. 
 
 All phosphates insoluble in water are dissolved by nitric, hydrochloric, or 
 sulphuric acid ; also by acetic acid, except those of lead, aluminum, and ferric 
 iron. All are soluble in phosphoric acid (forming acid phosphates), except those 
 of lead, tin, mercury, and bismuth. Primary alkali phosphates are acid to 
 litmus, but secondary alkali phosphates, although they are acid salts, are alka- 
 line to litmus because of partial hydrolysis by water into primary phosphate and 
 free alkali. Tertiary alkali phosphates are decomposed by water into the second- 
 ary salt and free alkali. 
 
 Phosphoric acid belongs to the class of weak acids, and the three hydrogen 
 atoms in the molecule show very different degrees of dissociation. It dissoci- 
 ates chiefly according to this equation, H 3 PO 4 ~. H* + H 2 PO/. The dihy- 
 drophosphate ion, H 2 PO/, dissociates to a small degree into H* and HPO/' 
 ions, as is shown by the fact that monosodium phosphate has a slightly acid 
 reaction to litmus, thus : 
 
 NaH 2 PO 4 ^ Na* + H 2 PO/ 
 H 2 PO 4 ' ^1 H' + HP0 4 /X . 
 
 The ion HPO/' is practically not dissociated into H' and PO/' ions, as is 
 
228 NON-METALS AND THEIR COMBINATIONS. 
 
 evidenced by the slightly alkaline reaction of disodium phosphate, which dis- 
 sociates thus, 
 
 Na 2 HP0 4 i 2Na- + HPO 4 ". 
 
 The alkaline reaction is due to the formation of a slight quantity of free alkali 
 by the ions of water (hydrolysis) thus, 
 
 2Na + HPO/'l^ Hjpo, 
 (OH)' + H- / 
 
 Na 2 HPO 4 + H 2 = NaOH + NaH 2 PO 4 , 
 
 Trisodium phosphate is completely hydrolyzed in solution into disodium phos- 
 phate and sodium hydroxide, Na 3 PO 4 + H 2 O = Na 2 HPO 4 + NaOH. 
 
 Tests for phosphoric acid and phosphates. 
 (Sodium phosphate, Na^HPO^ may be used.) 
 
 1. Add to phosphoric acid, or to an aqueous solution of a phos- 
 phate, a mixture of magnesium sulphate, ammonium chloride, and 
 ammonia water ; a white crystalline precipitate falls, which is mag- 
 nesium ammonium phosphate : 
 
 H 3 P0 4 + MgS0 4 + 3NH 4 OH = MgNH 4 PO 4 + (NH 4 ) 2 SO 4 + 3H 2 O; 
 Na-jHPO, -f MgS0 4 + NH 4 OH = MgNH 4 PO 4 + NaO 4 + H 2 O. 
 
 2. Add to a solution of disodium phosphate, silver nitrate ; a yellow 
 precipitate of silver phosphate is produced, which is soluble both in 
 ammonia and nitric acid : 
 
 Na,HP0 4 + 3AgN0 3 = Ag 3 PO 4 + 2NaNO 3 + HN0 3 . 
 
 3. Add to phosphoric acid, or to a phosphate dissolved in water 
 or in nitric acid, an excess of a solution of ammonium molybdate in 
 dilute nitric acid, and heat gently ; a yellow precipitate of phospho- 
 molybdate of ammonium, (NH 4 ) 3 PO 4 .10MoO 3 .2H 2 O, is produced ; 
 the precipitate is readily soluble in ammonia water. This test is by 
 far the most delicate, and even traces of phosphoric acid may be 
 recognized by it ; moreover, it can be used in an acid solution, while 
 the first two tests cannot. Only a few drops of the solution to be 
 tested should be used. 
 
 4. Add to a solution of a phosphate, calcium or barium chloride ; 
 a white precipitate of calcium or barium phosphate is produced, which 
 is soluble in acids. 
 
 5. Ferric chloride produces a yellowish-white precipitate of ferric 
 phosphate, Fe 2 (PO 4 ) 2 , thus : 
 
 2Na,HP0 4 + Fe.Cle = Fe 2 (PO 4 ) 2 + 4NaCl + 2HC1. 
 The liberated hydrochloric acid dissolves some of the precipitate, 
 which may be avoided by adding previously some sodium acetate ; 
 
PHOSPHORUS. 229 
 
 the hydrochloric acid combines with the sodium of the acetate, and 
 the acetic acid which is set free has no dissolving action upon the 
 ferric phosphate. 
 
 Hydrogen phosphide, PH 3 (Phosphoretted hydrogen, phosphine). The forma- 
 tion of this compound has been mentioned in the paragraph on Hypophos- 
 phorous acid. It is a colorless, badly smelling, poisonous gas, which, when 
 generated as directed above, is .spontaneously inflammable. This last-named 
 property is due to the presence of small quantities of another compound of 
 phosphorus and hydrogen which has the composition P 2 H 4 , and is spontaneously 
 inflammable, while the compound PH 3 is not. 
 
 Hydrogen phosphide corresponds to the analogous composition of ammonia, 
 NH 3 . While the latter is readily soluble in water and has strong basic prop- 
 erties, hydrogen phosphide is but sparingly soluble in water and its basic prop- 
 erties are very weak. However, a few salts, such as the phosphonium chloride, 
 PH 4 C1, analogous to ammonium chloride, NH 4 C1, are known. 
 
 There is no scientific evidence whatever for the correctness of the statement, 
 found in some text-books, that hydrogen phosphide is a product of the putre- 
 faction of certain organic compounds. 
 
 Phosphorus trichloride, PC1 3 . This is a colorless liquid, heavier than 
 water, boiling at 76 C. Its vapors are very pungent. Water decomposes it 
 very rapidly into phosphorous and hydrochloric acids, thus, PC1 3 -f- 3H 2 O = 
 HsP0 3 + 3HC1. For this reason the liquid gives white fumes in moist air. 
 It can only be obtained by direct union of the elements. This is done by 
 leading chlorine gas over phosphorus in a retort, when the elements unite with 
 combustion, and the trichloride distils over into a cold receiver. It is purified 
 by redistillation in contact with some phosphorus, which removes any penta- 
 chloride present. 
 
 Phosphorus pentachloride, PC1 5 . This consists of pale yellow crystals, 
 and is obtained by passing chlorine into phosphorus trichloride. It decom- 
 poses at once in water into phosphoric and hydrochloric acids, PC1 5 + 4H 2 O 
 H 3 PO 4 -f 5HC1. It fumes strongly in moist air. At 300 C. it is completely 
 dissociated into trichloride and chlorine. With a small proportion of water it 
 forms phosphorus oxychloride thus, PC1 5 + H 2 O = POC1 3 + 2HC1. The oxy- 
 chloride is a colorless liquid that boils at 107.2 C. The pentachloride is often 
 used in organic chemistry to substitute chlorine for hydroxyl (OH) in compounds. 
 
 The bromine compounds of phosphorus, PBr 3 and PBr 5 , are very similar to 
 the chlorine compounds, and are made in the same way. 
 
 QUESTIONS. In what forms of combination is phosphorus found in na- 
 ture? Give an outline of the process for manufacturing phosphorus. What 
 are the symbol, valence, atomic, and molecular weights of phosphorus. State 
 the chemical and physical properties both of common and red phosphorus. 
 By what methods may phosphorus be detected in cases of poisoning? What 
 two oxides of phosphorus are known ; what is their composition, and what 
 four acids do they form by combining with water? State the official process 
 for making phosphoric acid, and what are its properties? By what tests may 
 the three phosphoric acids be recognized and distinguished from phosphorous 
 acid? What is a phosphide, phosphite, phosphate, and hypophosphite ? 
 What is glacial phosphoric acid, and in what respect does its action upon the 
 animal system differ from the action of common phosphoric acid? 
 
230 NON-METALS AND THEIR COMBINATIONS. 
 
 18. CHLOEINE. 
 
 Cl' = 35 (35.18). 
 
 Halogens. The four elements, fluorine, chlorine, bromine, and 
 iodine, which form a natural group of elements, are known as halogens, 
 the term meaning producers of salt. The relation shown by the atomic 
 weights of these four elements has been mentioned in connection with 
 the consideration of natural groups of elements generally (see page 
 125). In many other respects a resemblance or relation can be dis- 
 covered. For instance- : While the haloids as a general rule act as 
 univalent elements, they all form compounds into which they enter 
 with a valence of either 3, 5, or 7 ; they combine with hydrogen, 
 forming the acids HF, HC1, HBr, HI, all of which are colorless 
 gases, soluble in water ; they combine directly with most metals, 
 forming fluorides, chlorides, bromides, and iodides. The relative 
 combining energy lessens as the atomic weight increases ; fluorine 
 with the lowest atomic weight having the greatest, iodine with the 
 highest atomic weight the smallest, affinity for other elements. The 
 first two members of the group are gases, the third (bromine) is a 
 liquid, the last (iodine) a solid, at ordinary temperature. They all 
 show a distinct color in the gaseous state, have a disagreeable odor, 
 and possess disinfecting properties. 
 
 Occurrence in nature. Chlorine is found chiefly as sodium 
 chloride or common salt, NaCI, either dissolved in water (small 
 quantities in almost every spring water, larger quantities in some 
 mineral waters, and the principal amount in sea-water), or as solid 
 deposits in the interior of the earth as rock salt. 
 
 Other chlorides, such as those of potassium, magnesium, calcium, 
 also are found in nature. As common salt, chlorine enters the animal 
 system, taking there an active part in many of the physiological and 
 chemical changes. 
 
 Preparation of chlorine. Most methods of liberating chlorine 
 depend on an oxidation of the hydrogen of hydrochloric acid by 
 suitable oxidizing agents, the hydrogen being converted into water, 
 while chlorine is set free. 
 
 As oxidizing agents, may be used potassium chlorate, potassium 
 dichromate, potassium permanganate, chromic acid, nitric acid, and 
 many other substances. 
 
 The most common and cheapest mode of obtaining chlorine is to 
 heat manganese dioxide, usually called black oxide of manganese, 
 
CHLORINE. 231 
 
 with hydrochloric acid, or a mixture of manganese dioxide and 
 sodium chloride with sulphuric acid : 
 
 Mn0 2 + 4HC1 = MnCl 2 -f 2H 2 O + 2C1. 
 
 MnO 2 + 2NaCl -f 2H 2 SO 4 = MnSO 4 -f Na 2 SO 4 -f 2H 2 O + 2C1. 
 Chlorine is liberated also by the action of sulphuric or hydrochloric acid on 
 bleaching-powder, which is a mixture of calcium chloride and calcium hypo- 
 chlorite : 
 
 CaCl 2 .Ca(ClO) 2 -f 2H 2 SO 4 = 2CaSO 4 + 2H 2 O + 401. 
 
 Chlorine is now also produced by electrolysis of sodium chloride solution in 
 suitably constructed apparatus. 
 
 Experiment 17. Use apparatus as in Fig. 39, page 168. Conduct operation 
 in a fume-chamber. Place about 50 grammes of manganese dioxide in coarse 
 powder in the flask, cover it with hydrochloric acid, shake up well to insure 
 that no dry powder be left at the bottom of the flask, apply heat, and collect 
 the gas in dry bottles by downward displacement. Keep the bottles loosely 
 covered with pieces of stiff paper while filling them. Use the gas for the 
 following experiments : 
 
 a. Fill a test-tube with chlorine, a second test-tube of same size with hydro- 
 gen ; place them over one another so that the gases mix by diffusion, then 
 hold them near a flame ; a rapid combustion or explosion ensues. 
 
 b. Hold in one of the bottles filled with chlorine a lighted wax candle, and 
 notice that it continues to burn with liberation of carbon. The hydrogen con- 
 tained in the wax is in this case the only constituent of the wax which burns, 
 i. e., combines with chlorine. 
 
 c. Moisten a paper with oil of turpentine, C 10 H 16 , and drop it into another 
 bottle filled with the gas ; combustion ensues spontaneously, a black smoke of 
 carbon being liberated. 
 
 d. Drop some finely powdered antimony into another bottle, and notice that 
 each particle of the metal burns while passing through the gas, forming white 
 antimonous chloride, SbCl s . 
 
 e. Pass some chlorine gas into water, and suspend in the chlorine water thus 
 formed colored flowers or pieces of dyed cotton, and notice that the color fades 
 and in many cases disappears completely in a few hours. 
 
 Properties. Chlorine is a yellowish-green gas, having a disagree- 
 able taste and an extremely penetrating, suffocating odor, acting 
 energetically upon the air-passages, producing violent coughing and 
 inflammation. It is about two and a half times heavier than air, 
 soluble in water, and convertible into a greenish-yellow liquid by a 
 pressure of about six atmospheres. 
 
 Chemically, the properties of chlorine are well marked, and there 
 are but few elements which have as strong an affinity for other ele- 
 ments as chlorine ; it unites with all of them directly, except with 
 oxygen, nitrogen, and carbon, but even with these it may be made to 
 combine indirectly. The act of combination between chlorine and 
 other elements is frequently attended by the evolution of so much 
 
232 NON-METALS AND THEIR COMBINATIONS. 
 
 heat that light is produced, or, in other words, combustion takes place. 
 Thus, hydrogen, phosphorus, and many metals burn easily in chlorine. 
 The affinity between chlorine and hydrogen is intense, a mixture of 
 the two gases being highly explosive. Such a mixture, kept in the 
 dark, will not undergo chemical change, but when ignited, or when 
 exposed to direct sunlight, combination between the two elements 
 occurs instantly with an explosion. The affinity of chlorine for 
 hydrogen is also demonstrated by its property of decomposing water, 
 ammonia, and many hydrocarbons (compounds of carbon with hydro- 
 gen), such as oil of turpentine, C 10 H 16 , and others : 
 
 H 2 + 2C1 = 2HC1 -f O. 
 
 NH 3 + 3C1 = 3HC1 + N. 
 
 C 10 H 16 + 16C1 = 16HC1 + IOC. 
 
 As shown by these formulas, hydrochloric acid is formed, while 
 the other elements are set free. 
 
 Chlorine is a strong disinfecting, deodorizing, and bleaching agent ; 
 it acts as such either directly by combining with certain elements of 
 the coloring or odoriferous matter, or, indirectly, by decomposing 
 water with liberation of oxygen, which in the nascent state that is, 
 at the moment of liberation has a strong tendency to oxidize other 
 substances. 
 
 It should be noted that perfectly dry chlorine has practically no action on 
 other substances when also dried. In the absence of all moisture it has no 
 bleaching action. This inactivity of dry chlorine is exemplified by the fact that 
 it is now sold in steel cylinders. As ordinarily used, however, it acts readily, 
 because of the moisture in the atmosphere, and on objects, even if water is not 
 supplied directly. 
 
 Compound solution of chlorine, Liquor chlori compositus (Chlorine 
 water). Cold water absorbs about two volumes of chlorine, which is equal to 
 0.4 per cent, by weight. This solution is unstable because the chlorine grad- 
 ually combines with hydrogen of water, while oxygen is set free. It is for this 
 reason that the U. S. P. has substituted for ordinary chlorine water the com- 
 pound solution of chlorine, which is to be freshly made when wanted. It is 
 prepared by digesting in a large flask potassium chlorate with hydrochloric 
 acid and then adding water to dissolve the liberated chlorine, as also some 
 chlorinated products and the potassium chloride which are formed. The 
 reaction, when complete, is this : 
 
 KC10 3 + 6HC1 == KC1 + 3H 2 O + 6C1. 
 Chlorine water is a greenish-yellow liquid, having the odor of chlorine. 
 
 Hydrochloric acid, Acidum hydrochloricum, ifCl = 36.18 
 (Muriatic acid). This acid occurs in the gastric juice of mammalia, 
 
CHLORINE. 233 
 
 and has been found in some volcanic gases. One volume of hydrogen 
 combines with one volume of chlorine to form two volumes of hydro- 
 chloric acid. 
 
 For all practical purposes the acid is obtained by the decomposition 
 of a chloride by sulphuric acid : 
 
 NaCl + H 2 S0 4 = HC1 + NaHSO 4 ; 
 or 
 
 2NaCl + H 2 S0 4 = 2HC1 
 
 Experiment 18. Use apparatus as in Fig. 39, p. 168. Place about 20 grammes 
 of sodium chloride into the flask (which should be provided with a funnel-tube) 
 and add about 30 c.c. of concentrated sulphuric acid ; mix well, apply heat, and 
 pass the gas into water for absorption. If a pure acid be desired, the gas has 
 to be passed through water contained in a wash-bottle ; apparatus shown in 
 Fig. 42, page 207, may then be used. Use the acid made for tests mentioned 
 below. How much of the U. S. P. 31.9 per cent, hydrochloric acid can be 
 made from 117 pounds of sodium chloride? 
 
 The liberation of hydrochloric acid from a chloride by sulphuric acid is an 
 example of reversible reactions that run to completion because of the removal 
 of one of the factors that is necessary to maintain an equilibrium (see page 
 114). The character of the reaction is like that in the case of the liberation 
 of nitric acid, the ionic features of which are discussed in Chapter 15. The 
 ionic reaction is this : 
 
 NaCl ^ Na* + C1M ^ HC1 HC1. 
 H 2 SO 4 ^ HSO/ + H- / dissolved gas. 
 
 Hydrochloric acid is a colorless gas, has a sharp, penetrating odor, 
 and is very irritating when inhaled. It is neither combustible nor 
 a supporter of combustion, and has great affinity for water, which 
 property is the cause of the formation of white clouds whenever the gas 
 comes in contact with the vapors of water, or with moist air ; the white 
 clouds being formed of minute particles of liquid hydrochloric acid. 
 
 While hydrochloric acid is a gas, this name is used also for its 
 solution in water, one volume of which at ordinary temperature takes 
 up over 400 volumes of the gas. 
 
 The hydrochloric acid of the U. S. P. is an acid containing 31.9 
 per cent, of HC1. It is a colorless, fuming liquid, having the odor 
 of the gas, strong acid properties, and a specific gravity of 1.158. 
 The official diluted hydrochloric acid is made by mixing 100 parts 
 by weight of the above acid with 219 parts of water. It contains 10 
 per cent, of HCL 
 
 The same antidotes may be used as for nitric acid. 
 
 A 20.2 per cent, solution of hydrochloric acid distils unchanged at 110 C. 
 (230 F.) under 760 mm. pressure. When a more concentrated solution is 
 heated,, it first loses mainly the gas, and a more dilute solution mainly water 
 
234 NON-METALS AND THEIR COMBINATIONS. 
 
 vapor, until 20.2 per cent, is reached, when the residue in the flask passes over 
 unchanged. Other acids for example, sulphuric, nitric, hydriodic, hydro- 
 brornic show a similar property. 
 
 Neither the dry gas (HC1) nor the liquefied gas has any marked acid char- 
 acter. They do not conduct electricity and have no action on dry litmus- 
 paper or on zinc, but the presence of water causes strong acid properties to be 
 developed. This is explained on the Dissociation Theory, which holds that 
 only hydrogen ions have acid properties. Water is required for the ionization 
 of HC1, and without it the gas lacks acid character. A solution of the gas in 
 liquids like benzene and toluene, which have scarcely any ionizing power, has 
 practically no effect on zinc, which is freely attacked by an aqueous solution 
 of the gas. The same is true of hydrobromic and hydriodic acids (Chapter 
 15). 
 
 Nearly all chlorides are soluble in water. Of those ordinarily met with 
 only two are insoluble in water, namely, silver and mercurous chlorides, and 
 one is difficultly soluble in cold water, but more readily in hot water, namely, 
 lead chloride. 
 
 Tests for hydrochloric acid and chlorides. 
 (Sodium chloride, NaCl, may be used.) 
 
 1. To hydrochloric acid, or to solution of chlorides, add silver 
 nitrate : a white, curdy precipitate is produced, which is soluble in 
 ammonia water, even when very dilute, but insoluble in nitric acid : 
 
 AgN0 3 + Nad = AgCl. -f NaNO 3 . 
 Ag' + NO/ + Na' + Cl' AgCl '+ Na' + NO/. 
 
 2. Add solution of mercurous salt (mercurous nitrate) : a white 
 precipitate of mercurous chloride (calomel) is produced, which black- 
 ens on the addition of ammonia : 
 
 HgN0 3 + NaCl = HgCl + NaNO 3 . 
 Hg' + N0 3 ' + Na- + Cl' HgCl + JNV + NO/. 
 
 3. Add solution of lead acetate : a white precipitate of lead chloride 
 is formed, which is soluble in hot, or in much cold water, and is, there- 
 fore, not formed in dilute solutions. Its composition is PbCl 2 . 
 
 Pb(C 2 H 3 2 ) 2 + 2NaCl PbCl 2 + 2Na(C 2 H 3 O 2 ). 
 
 Pb" + 2(C,H 3 2 )' + 2Na- + 201' - PbCl 2 + 2Na' + 2(C 2 H 3 O 2 )'. 
 
 4. To a dry chloride add strong sulphuric acid and heat : hydro- 
 chloric acid gas is evolved, which may be recognized by the odor, or 
 by its action on silver nitrate, when a drop of the solution on the end 
 of a glass rod is held in the gas. (The insoluble chlorides of silver, 
 lead, and mercury do not give this reaction.) 
 
 5. Chlorides treated with sulphuric acid and manganese dioxide 
 evolve chlorine. 
 
 Test 1, combined with test 5, is the most decisive proof of hydro- 
 
CHLORINE. 235 
 
 chloric acid or chlorides. The others are more corroborative than 
 decisive. 
 
 Nitro-hydrochloric acid, Acidum nitro-hydrochloricum, Aqua 
 regla (Nitro-muriatic acid). Obtained by mixing 18 c.c. of nitric 
 acid with 82 c.c. of hydrochloric acid. The two acids act chemically 
 upon each other, forming chloronitrous gas, chlorine, and water : 
 
 HN0 3 + 3HC1 = NOC1 + 2H 2 O + 2C1. 
 
 The dissolving power of this acid upon gold and platinum depends 
 on the action of the free chlorine. The action on platinum is repre- 
 sented by this equation : 
 
 2HNO 3 + 8HC1 + Pt = H 2 Pt.Cl 6 f 2NOC1 -f 4H 2 O. 
 
 Chloroplatinic acid, H 2 PtCl 6 , is in solution. This is used as a test- 
 solution. 
 
 The official diluted nitrohydrochloric acid is made by mixing 182 c.c. of hydro- 
 chloric acid with 40 c.c. of nitric acid and adding, when effervescence has 
 ceased, 782 c.c. of water. 
 
 Compounds of chlorine -with oxygen. There is no method known 
 by which to combine chlorine and oxygen directly, all the compounds formed 
 by the union of these ele%ients being obtained by indirect processes. The 
 oxides of chlorine are the following: 
 
 Chlorine monoxide or hypochlorous oxide, C1 2 O. 
 Chlorine dioxide, C1Q 2 . 
 
 Chlorine heptoxide, C1 2 O 7 . 
 
 The first two oxides are yellow or brownish-yellow gases ; the third one is a 
 colorless liquid ; all combine with water, forming hypochlorous, chlorous and 
 chloric, and perchloric acid, thus : 
 
 C1 2 O + H 2 O = 2HC1O. 
 
 2C10 2 + H 2 HC10 2 + HC10 3 . 
 
 C1 2 O 7 + H 2 O 2HC10 4 . 
 
 The oxide, C1 2 O 5 , from which chloric acid, HC1O 3 , might be formed, is not 
 known. The chlorine oxides, the acids, and many of their salts are distin- 
 guished by the great facility with which they decompose, frequently with vio- 
 lent explosion, for which reason care must be taken in the preparation and 
 handling of these compounds. 
 
 Chlorine acids. 
 
 Hypochlorous acid, HC1O. Chloric acid, HC1O 8 . 
 
 Chlorous acid, HC1O 2 . Perchloric acid, HC1O 4 . 
 
 Hydrochloric acid, HC1. 
 
236 NON-METALS AND THEIR COMBINATIONS. 
 
 With the exception of hydrochloric acid, which has been considered, 
 none of the five acids is of practical interest as such, but many of 
 the salts of hypochlorous and chloric acids, known as hypochlorites 
 and chlorates respectively, are of great and general importance. 
 
 The constitution of the chlorine acids may be represented by the following 
 graphic formulas. It is here assumed that chlorine is univalent in hypochlo- 
 rous, trivalent in chlorous, quinquivalent in chloric, and septivalent in per- 
 chloric acid : 
 
 II II 
 
 H O Cl, H O Cl = 0, H O Cl, H O Cl = O 
 
 O O 
 
 Chlorine monoxide, C1 2 O, and Hypochlorous acid, HC1O. When 
 chlorine is passed over yellow mercuric oxide in a tube, chlorine mon- 
 oxide is formed, thus, 
 
 2HgO + 2C1 2 = HgO.HgCL, + C1 2 O. 
 
 It is a brownish-yellow gas which decomposes with explosion when 
 heated. One volume of water dissolves 200 volumes of the gas, 
 giving a yellow solution of hypochlorous acid which has the strong 
 odor of the chlorine monoxide, 
 
 C1 2 O + H 2 O = 2HC1O. 
 
 Hypochlorous acid is also obtained in solution when chlorine gas is 
 passed into a suspension of mercuric oxide in water, thus, 
 
 2HgO + 2C1 2 + H 2 = HgO.HgCl, -f 2HC1O. 
 
 The compound known as mercury oxychloride is formed and may be 
 removed, being insoluble. 
 
 Properties. Hypochlorous acid is a feeble (slightly ionizing) mono- 
 basic acid, which unites with active bases, forming hypochlorites. It 
 can be obtained only in solution, and keeps only when dilute and 
 cold. When concentrated it changes gradually to a considerable ex- 
 tent into chloric and hydrochloric acids, thus, 
 3HC10 = HC10 3 + 2HC1. 
 
 Warming a solution of the acid, or exposing it to sunlight, causes a 
 rapid evolution of oxygen, 
 
 2HC10 = 2HC1 + 2O. 
 
 As a result of this action, the acid is a strong oxidizer. This decom- 
 position is interesting, as it explains the oxidizing action of chlorine 
 in the presence of water, and the fact that chlorine water exposed to 
 bright light does not keep, but gives off oxygen and leaves a solution 
 of nothing but hydrochloric acid. When chlorine is dissolved, a re- 
 versible reaction takes place, thus, 
 
 C1 2 + H 2 ^ HC1 + HC10. 
 
CHLORINE. 237 
 
 Only a slight quantity of hypochlorous acid is formed at one time, 
 but its decomposition and constant removal in this way allows the 
 action to go forward to completion. The final result makes it appear 
 that chlorine decomposes water with direct liberation of oxygen, 
 which is usually represented by the equation, 
 
 C1 2 + H 2 O = 2HC1 + O. 
 
 Hypochlorites. For practical purposes solutions of free hypochlorous 
 acid are not made, but the acid is liberated from its salts when wanted. The 
 hypochlorites are formed by the action of chlorine on the hydroxide of potas- 
 sium, sodium, calcium, etc., at the ordinary temperature. As stated above, 
 chlorine with water forms HC1 and HC1O, but the action does not go far, 
 because these two acids tend to decompose each other in the reverse direction 
 to produce chlorine. But if they are removed, as by neutralization, action 
 will be complete, thus, 
 
 2C1 -f H 2 O = HC1 + HC1O 
 
 HC1 + NaOH = NaCl + H 2 O 
 
 HC10 + NaOH = NaCIO + H 2 O. 
 
 It will be seen that when hypochlorite is made in this manner there is always 
 an equivalent amount of a chloride in the mixture. The reaction is generally 
 written, 
 
 2C1 + 2NaOH = NaCl + NaCIO + H 2 O. 
 
 When a hypochlorite is acidified with an active acid, the reverse of the above 
 reactions takes place, hydrochloric and hypochlorous acids being liberated, 
 which between them evolve chlorine (see bleaching powder). When a hypo- 
 chlorite is heated, it decomposes into chlorate and chloride, thus, 
 
 SNaCIO = NaClO s + 2NaCl. 
 
 Under some conditions a hypochlorite slowly gives off oxygen, leaving a chlo- 
 ride, but the action may be enormously increased by adding a catalytic agent, 
 for example, a cobalt salt (see under Oxygen). 
 
 Solution of chlorinated soda, Liquor sodae chlorinatse (Solution of 
 sodium hypochlorite, Labarraque 's solution). This is a solution that yields 2.4 
 per cent, of available chlorine. It contains chloride and hypochlorite of sodium, 
 and is made by adding sodium carbonate to a solution of bleaching powder 
 (calcium hypochlorite), thus precipitating calcium carbonate : 
 
 CaCl 2 -f Ca(ClO) 2 -f 2Na 2 CO 3 = 2CaCO 3 -f 2NaCl + 2NaClO. 
 
 It is a clear pale greenish liquid, having a faint chlorine-like odor and strong 
 bleaching properties. 
 
 Chloric acid, HC1O 3 , may be obtained from potassium chlorate b}* 
 the action of hydrofluosilicic acid ; it is, however, an unstable sub- 
 stance which will decompose, frequently with a violent explosion. 
 Chlorates are generally obtained by the action of chlorine on alkali 
 hydroxides at a temperature of about 100 C. (212 F.). 
 6KOH + 6C1 as 5KC1 + KC10 3 + 3H 2 O. 
 
238 NON-METALS AND THEIR COMBINATIONS. 
 
 The explanation of this action is that chlorine first forms a hypo- 
 chlorite, which, as stated above, decomposes by heating into chlorate 
 and chloride. The change will be clearer if written in two steps : 
 6KOH + 6C1 = 3KC1 -f 3KC1O + 3H 2 O. 
 
 3KC10 = 2KC1 + KC10 3 . 
 
 In recent years large quantities of chlorates, especially potassium 
 chlorate, are made by passing an electric current, under proper con- 
 ditions, through an alkaline solution of potassium chloride. 
 
 Perchloric acid, HC1O 4 . This is a colorless liquid, which, in the pure 
 state, decomposes, and often explodes spontaneously when kept. A 70 
 per cent, aqueous solution is stable. Although it contains more oxygen than 
 the other acids of chlorine, it is the most stable one of all. It can be prepared 
 by distilling a mixture of potassium perchlorate and concentrated sulphuric 
 acid in a vacuum. It was seen in the chapter on oxygen that potassium chlor- 
 ate, when heated, gives the perchlorate, chloride, and oxygen. The perchlor- 
 ate, being difficultly soluble in water, can be separated easily from the far more 
 soluble chloride. 
 
 Tests for chlorates and hypochlorites. 
 (Potass, chlorate, KC1O 3 , and bleaching powder, Ca(ClO) 2 .CaCl 2 , may be used.) 
 
 1. Chlorates liberate oxygen when heated by themselves. 
 
 2. Chlorates liberate chlorine dioxide, C1O 2 , a deep-yellow explo- 
 sive gas, on the addition of strong sulphuric acid. 
 
 2KC10 3 + H 2 S0 4 = K 2 S0 4 + 2HC1O 3 . 
 3HC10 3 = HC10 4 + H 2 + 2C10 2 . 
 
 This test should be made only on a quantity about the size of a pea. 
 
 3. Chlorates deflagrate when sprinkled on red-hot charcoal. 
 
 4. Hypochlorites are strong bleaching agents, and evolve a pecu- 
 liarly smelling gas (chlorine) on the addition of acid (see page 236). 
 
 QUESTIONS. State the names and general physical and chemical properties 
 of the four halogens. How is chlorine found in nature, and why does it not 
 occur in a free state? State the general principle for liberating chlorine from 
 hydrochloric acid, and explain the action of the latter on manganese dioxide. 
 Mention of chlorine : its atomic weight, molecular weight, valence, color, odor, 
 action when inhaled, and solubility in water. How does chlorine act chemi- 
 cally upon metals, hydrogen, phosphorus, water, ammonia, hydrocarbons, and 
 coloring matters? Mention two processes for making hydrochloric acid; state 
 its composition, properties, and tests by which it may be recognized. What is 
 aqua regia? State the composition of hypochlorous and chloric acids. What 
 is the difference in the action of chlorine upon a solution of potassium hydrox- 
 ide at ordinary temperature and at the boiling-point ? How many pounds of 
 manganese dioxide, and how many of hydrochloric acid gas are required to 
 liberate 142 pounds of chlorine ? 
 
BROMINE IODINE- FL UORINE. 239 
 
 19. BROMINE IODINE FLUORINE. 
 
 Bromine, Bro'mum, Br = 79.36. This element is found in sea- 
 water and many mineral waters, chiefly as magnesium, calcium, and 
 sodium bromides, which compounds, however, represent in all these 
 waters a comparatively small percentage of the total quantity of the 
 different salts present. Most of these salts are separated from the 
 water by evaporation and crystallization, and the remaining mother- 
 liquor, containing the bromides, is treated with chlorine, which liber- 
 ates bromine, the vapors of which are condensed in cooled receivers : 
 
 MgBr 2 -f 2C1 = MgCl 2 + 2Br. 
 
 Bromine is at common temperature a heavy, dark reddish-brown 
 liquid, giving off yellowish-red fumes of an exceedingly suffocating 
 and irritating odor; it is very volatile, freezes at about 24 C. 
 ( 11 F.), and has a specific gravity of 2.99; it is soluble in 33 
 parts of water, more freely in alcohol, abundantly in ether and bisul- 
 phide of carbon ; it is a strong disinfectant, and its aqueous solution 
 is also a bleaching agent ; it acts as a corrosive poison. 
 
 Hydrobromic acid, Acldum hydrobromicum, HBr = 8O.36. 
 This acid cannot well be obtained by the action of concentrated sul- 
 phuric acid upon bromides, since the hydrobromic acid first formed 
 becomes readily decomposed with formation of sulphur dioxide and 
 free bromine. Thus : 
 
 2NaBr + H 2 SO 4 = 2HBr + Na 2 SO 4 ; 
 2HBr + H 2 SO 4 = 2Br + SO 2 + 2H 2 O. 
 
 If, however, dilute sulphuric acid is added to a warm solution of 
 potassium bromide, potassium sulphate is formed, a portion of which 
 crystallizes on cooling. From the remaining portion of the salt, the 
 hydrobromic acid may be separated by distillation. 
 
 Hydrobromic acid may also be obtained by the formation of bromide of 
 phosphorus, PBr 5 (the two elements combine directly), and its decomposition 
 
 by water : 
 
 PBr 5 + 4H 2 = 5HBr + H 3 PO 4 . 
 
 In the form of solution this acid may be prepared also by treating bromine 
 under water with hydrogen sulphide until the brown color of bromine has 
 entirely disappeared. The reaction is as follows : 
 
 lOBr + 2H 2 S + 4H 2 = lOHBr + H 2 SO, + S. 
 
 The liquid is filtered from the sulphur and separated from the sulphuric acid 
 by distillation, 
 
240 NON-METALS AND THEIR COMBINATIONS. 
 
 Hydrobromic acid is, like hydrochloric acid, a colorless gas, of 
 strong acid properties, easily soluble in water. 
 
 Diluted hydrobromic avid, Acidum hydrobromicum dilutum, is a solu- 
 tion of 10 per cent, of hydrobromic acid in water. It is a colorless, 
 odorless, acid liquid of the specific gravity 1.076. 
 
 Hydrobromic acid acts in nearly all respects like hydrochloric. It is less 
 stable, and less powerful oxidizing agents will liberate the bromine than are 
 required to liberate chlorine. Nearly all bromides are soluble in water, the 
 insoluble ones being those of silver, mercury (ous), and lead. Bromides are 
 mostly white. 
 
 The ionic reactions for bromine compounds are analogous to those for chlo- 
 rine compounds. 
 
 Hypobromous acid, HBrO ; Bromic acid, HBrO 3 , and their 
 salts, the hypobromites and bromates, are analogous to the corre- 
 sponding chlorine compounds, and may be obtained by analogous 
 processes. Oxides of bromine are not known. 
 
 Tests for Bromides. 
 (Potassium bromide, KBr, may be used.) 
 
 1. Silver nitrate produces in solutions of bromides a slightly yel- 
 lowish-white precipitate of silver bromide, insoluble in nitric acid, 
 sparingly soluble in ammonia water. 
 
 2. Addition of chlorine water, or heating with nitric acid, liberates 
 bromine, which may be dissolved by shaking with carbon disulphide. 
 Excess of chlorine oxidizes bromine to colorless bromic acid. Hence, 
 it must be added cautiously, else a small quantity of bromine will 
 escape detection. The test is a delicate one. 
 
 3. Mucilage of starch added to the liberated bromine is colored 
 yellow. The starch may be held in the vapor on the end of a rod. 
 
 4. A solution of mercurous nitrate, or of lead acetate produces 
 a white precipitate of mercurous bromide, or lead bromide, both of 
 which are insoluble in water and dilute acids. 
 
 5. Strong sulphuric acid added to a dry bromide liberates hydro- 
 bromic acid, HBr, a portion of which decomposes with liberation of 
 yellowish-red vapors of bromine. See explanation above. 
 
 Tests 2 and 5 combined with test 1 are decisive and sufficient to 
 recognize hydrobromic acid and its salts, and to distinguish them 
 from chlorides. 
 
 Iodine, lodum, I = 125.90. Iodine is found in nature in com- 
 bination with sodium and potassium, in some spring waters and in 
 
BE OMINE- IODINE FL UOIilNE. 241 
 
 sea-water, from which latter it is taken up by sea-plants and many 
 aquatic animals. Iodine is derived chiefly from the ashes of sea- 
 weeds known as kelp. By washing these ashes with water, the soluble 
 constituents are dissolved, the larger quantities of sodium chloride, 
 sodium and potassium carbonates are removed by evaporation and 
 crystallization, and from the remaining mother-liquor iodine is ob- 
 tained by treating the liquor with manganese dioxide and hydro- 
 chloric (or sulphuric) acid : 
 
 2KI -f MnO 2 + 2H 2 SO 4 = K^SO^ + MnSO 4 + 2H 2 O -f 21. 
 
 The liberated iodine distils, and is collected in cooled receivers. 
 Sodium nitrate found in Chili contains a small quantity of sodium 
 iodate, and the mother-liquors, from which the nitrate has been crystal- 
 lized, contain enough iodate to be employed for the preparation of iodine. 
 
 lodins is a bluish-black, crystalline substance of a somewhat 
 metallic lustre, a distinctive odor, a sharp and acrid taste, and a neu- 
 tral reaction. Specific gravity 4.948 at 17 C. (62.6 F.). It fuses 
 at 114 C. (237 F.), and boils at 180 C.(356 F.), being converted 
 into beautiful purple-violet vapors ; also, it volatilizes in small quanti- 
 ties at ordinary temperature. It is soluble in about 5000 parts of 
 water, more soluble in water containing salts, for instance, potassium 
 iodide ; the official Liquor iodi compositus (LugoPs solution) is a 
 preparation based on this property. It contains 5 parts of iodine and 
 10 parts of potassium iodide in 100 parts of aqueous solution. Iodine 
 is soluble in 10 parts of alcohol, very soluble in ether, disulphide of 
 carbon, and chloroform. The solution of iodine in alcohol or ether 
 has a brown, the solution in disulphide of carbon or in chloroform a 
 violet, color. Iodine stains the skin brown, and when taken inter- 
 nally acts as an irritant poison. 
 
 Tincture of iodine, Tinctura iodi, is a dark reddish-brown solution 
 of 70 grammes of iodine and 50 grammes of potassium iodide in 
 enough alcohol to make 1000 c.c. of solution. 
 
 The increased solubility of iodine in solutions of iodides, or of 
 hydriodic acid, is due to the formation of definite compounds by a re- 
 versible action, thus, 
 
 KI + 21 ^ KI 3 . 
 
 The brown color of solutions of iodine in certain solvents, as alcohol, 
 ether, etc., has been shown to be due to a feeble combination between 
 one molecule of iodine and one molecule of the solvent. In violet- 
 colored solutions there is no combination. 
 
 Iodine in very small quantity is a constituent of the human body and that 
 of animals. The greatest portion is found in the thyroid gland, as a complex 
 16 
 
242 NON-METALS AND THEIR COMBINATIONS. 
 
 substance known as tbyro-iodine, which is of great value in certain diseases, 
 especially cretinism, resulting from deficient development of the thyroid gland. 
 Bauman discovered (1895) iodine in this gland. The thyroid of sheep, which 
 in the dried form is official, contains 0.17 per cent, of iodine. 
 
 Hydriodic acid, Acidum hydriodicum, HI = 126.9. This is a 
 colorless gas readily soluble in water ; the solution is unstable, being 
 easily decomposed with liberation of iodine. It may be obtained by 
 processes analogous to those mentioned for the preparation of hydro- 
 bromic acid. The action of hydrogen sulphide upon iodine in the 
 presence of water is as follows : 
 
 H 2 S + 21 2HI + S. 
 
 The official method for making diluted hydriodic acid depends on the decom- 
 position of an aqueous solution of potassium iodide by an alcoholic solution of 
 tartaric acid in the presence of a small quantity of potassium hypophosphite, 
 which acts as a preservative. Upon cooling the mixture to the freezing-point, 
 acid potassium tartrate separates, while hydriodic acid remains in solution, 
 which is further diluted until a 10 per cent, acid is obtained. The decomposi- 
 tion taking place is this : 
 
 KI + H 2 C 4 H 4 O 6 : KHC 4 II 4 O 6 -j- HI. 
 
 While hydriodic acid itself is not of much importance, many of 
 its salts, the iodides, are of great interest. 
 
 At C. an aqueous solution can be obtained containing as much as 90 per 
 cent. HI. Nearly all iodides are soluble in water. The insoluble ones are of 
 silver, mercury, copper (ous). Lead iodide is sparingly soluble. 
 
 The ionic reactions for iodine compounds are analogous to those for chlorine 
 compounds. 
 
 Tests for iodine and iodides. 
 
 (Any soluble iodide may be used.) 
 
 1. Add to solution of an iodide, solution of silver nitrate: a pale- 
 yellow precipitate of silver iodide, Agl, falls, which is insoluble in 
 nitric acid, very sparingly soluble in ammonia water, but soluble in 
 solution of sodium thiosulphate or potassium cyanide. (See Photog- 
 raphy in Chapter 31, under Silver.) 
 
 2. Add lead acetate to a solution of an iodide : a yellow precipi- 
 tate of lead iodide, PbI 2 , is produced. When the precipitate is dis- 
 solved in a large volume (200 c.c.) of boiling water, and the solution 
 is cooled slowly, beautiful golden spangles are formed. 
 
 3. Add mercuric chloride solution to a solution of an iodide : a red 
 precipitate of mercuric iodide, HgI 2 , is produced, which is soluble in 
 solutions of mercuric chloride and potassium iodide. Note that the 
 corresponding chloride and bromide of mercury are soluble and white. 
 
BR OM1NE IODINE FL UORINE. 243 
 
 Also make the test with solution of mercurous nitrate. A green- 
 ish-yellow precipitate of mercurous iodide, Hgl, is obtained. The 
 corresponding chloride and bromide are white and also insoluble. 
 
 4. To the solution of an iodide add some chlorine water, or a few 
 drops of concentrated nitric acid ; iodine is liberated, which, with 
 strongly diluted starch solution, gives a blue color. Iodine in com- 
 bination has no action on starch. Excess of chlorine oxidizes iodine 
 to colorless iodic acid ; hen.ce, the same precaution must be used as 
 given in test 2 for bromides. 
 
 Traces of iodine may be detected readily by the fine violet color 
 given to chloroform or carbon disulphide when the liquid is shaken 
 with them. 
 
 5. Add a little concentrated sulphuric acid to a few granules of an 
 iodide and warm gently. Colorless hydriodic acid gas is liberated, 
 which causes white fumes with the moisture of the air; also free 
 iodine, which may be recognized by its violet vapor. 
 
 Tests 3 and 4 are usually sufficient to identify iodides or hydriodic 
 acid. 
 
 Iodic acid, HI0 3 . When iodine is dissolved in strong nitric acid, this solu- 
 tion being then evaporated to dryness and heated to about 200 C. (392 F.) 
 a white residue remains, which is iodine pentoxide : 
 
 61 -f 10HNO 3 == 5N 2 O 2 + 5H 2 O + 3I 2 O 6 . 
 By dissolving this oxide in water, iodic acid is obtained : 
 IA + H 2 = 2HI0 3 . 
 
 Iodic acid is a white crystalline substance, very soluble in water. From 
 iodic acid or from iodates, sulphurous acid and many other reducing agents 
 liberate iodine. 
 
 Hypoiodous acid and its salts are not known. Periodic acid and its salts 
 can be obtained. These oxygen compounds, in marked contrast to those of 
 chlorine, are stable. Iodine pentoxide is the only oxide of the element 
 known. 
 
 Sulphur iodide, Sulphuris iodidum, S 2 I 2 . When the two elements, 
 sulphur and iodine, are mixed together in the proportion of their atomic 
 weights, and this mixture is heated, direct combination takes place. The 
 fused mass is grayish-black, brittle, has a 'crystalline fracture and a metallic 
 lustre. It is almost insoluble in water, but soluble in glycerin and in carbon 
 disulphide. 
 
 Compounds of iodine with bromine and chlorine. While the affinity 
 between the halogens is feeble, yet a few compounds formed by their union are 
 known ; all of them are unstable, decomposing readily on heating and some 
 also in contact with water. Of some interest is iodine trichloride, IC1 3 , obtain- 
 able as an orange, crystalline substance by passing dry chlorine gas over iodine, 
 
244 NON-METALS AND THEIR COMBINATIONS. 
 
 when at first iodine monochloride, IC1, and then the trichloride is formed. The 
 latter has been used as a disinfectant. 
 
 Compounds of nitrogen with the halogens. When chlorine or iodine 
 acts on ammonia the hydrogen of the latter combines with the halogens, while 
 nitrogen is either set free or also enters into combination with the halogens, 
 thus: 
 
 NH 3 + 3C1 = 3HC1 + N, 
 
 NH 3 + 6C1 == 3HC1 -f NC1 3 . 
 
 The compounds NH 2 C1 and NHC1 2 , as also the corresponding iodine com- 
 pounds, are known. All these bodies are very unstable ; nitrogen trichloride, 
 an oily liquid, is one of the most explosive substances known ; nitrogen iodide, 
 a black powder, also explodes readily. 
 
 Fluorine, F = 18.9. This element is found in nature, chiefly as 
 fluorspar, calcium fluoride, CaF 2 ; traces of fluorine occur in many 
 minerals, in some waters, and also in the enamel of teeth, and in the 
 bones of mammals. Fluorine was, until 1887, scarcely known in the 
 elementary state, because all attempts to isolate it were frustrated by 
 the powerful affinities which this element possesses, and which render 
 it difficult to obtain any material (from which a vessel may be made) 
 which is not chemically acted upon, and, therefore, destroyed, by 
 fluorine. 'The method used now for liberating fluorine depends upon 
 the decomposition of hydrofluoric acid by a strong current of electricity 
 in an apparatus constructed of platinum with stoppers of fluorspar. 
 To prevent too rapid corrosion of the platinum vessels, the decom- 
 position is accomplished at a temperature below the freezing-point. 
 Fluorine is a gas of yellowish color, having a highly irritating and 
 suffocating odor, and possessing affinities stronger than those of any 
 other element. As a supporter of combustion, fluorine leaves oxygen 
 far behind ; it combines spontaneously even in the dark and at low 
 temperature with hydrogen; sulphur, phosphorus, lampblack, and 
 also many metals ignite readily in fluorine ; even the noble metals, 
 gold, platinum, and mercury, are converted into fluorides; from 
 sodium chloride the chlorine is liberated with the formation of 
 sodium fluoride ; organic substances, such as oil of turpentine, alco- 
 hol, ether, and even cork ignite spontaneously when brought in 
 contact with this remarkable element. 
 
 Hydrofluoric acid, HF. A colorless gas, very irritating, soluble 
 in water. It is obtained by the action of sulphuric acid on fluorspar : 
 
 CaF 2 + H 2 SO< = 2HF + CaSO 4 . 
 
 Hydrofluoric acid, either in the gaseous state or its, solution in 
 
BROMINE-IODINE-FL UOttINK 245 
 
 water, is used for etching on glass. This effect is due to the action of 
 the acid upon the silica of the glass, which is converted into either 
 silicon fluoride, SiF 4 ; or into hydrofl uosilicic acid, H 2 SiF 6 . 
 
 Hydrofluoric acid, or strong solutions of it, are powerful antiseptics. In 
 small quantities the acid is used as an admixture to fermenting liquids, as it 
 has been found that it does not act upon the principal ferment of yeast, which 
 causes the decomposition of sugar into alcohol and carbon dioxide, while it 
 readily destroys a number of objectionable ferments. The yield of alcohol is 
 thus considerably increased. 
 
 Experiment 19, Prepare a glass plate by heating it slightly and covering its 
 surface with a thin layer of wax or paraffin ; after cooling, scratch some letters 
 or figures through the wax, thus exposing the glass. Set the plate over a dish 
 (one made of lead or platinum answers best), in which a few grammes of pow- 
 dered fluorspar have been mixed with about an equal weight of sulphuric acid, 
 and set in the open air for a few hours (heating slightly facilitates the action); 
 upon removing the wax or paraffin, the glass will be found to be etched where 
 its surface was exposed to the vapors of the acid. This experiment serves also 
 as the best test for fluorides. (See under Silicon, p. 186.) 
 
 QUESTIONS. How is bromine found in nature? State the physical and 
 chemical properties of bromine. What is hydrobromic acid, and how can it be 
 made ? By what tests may bromine and bromides be recognized ? What is the 
 chief source of iodine? What are the chemical and physical properties of 
 iodine? What is tincture of iodine, what is its color, and how does it stain 
 the skin ? Mention reactions by which iodine and iodides may be recognized. 
 By what element may bromine and iodine be liberated from their compounds? 
 How is hydrofluoric acid made, and what is it used for? 
 
IV. 
 METALS AND THEIR COMBINATIONS. 
 
 Cobalt, 
 Copper, 
 
 20. GENERAL REMARKS REGARDING METALS. 
 
 OF the total number of sixty metallic elements only about one-half 
 are of sufficient general interest and importance to deserve considera- 
 tion in this book. 
 
 Derivation of names, symbols, and atomic weights. 
 
 Aluminum, Al = 26.9. From alum, a salt containing it. 
 Antimony, Sb = 119.3. From the Greek avrl (anti), against, and raotne, a 
 (Stibium.) French word for monk, from the fact that some 
 
 monks were poisoned by compounds of antimony. 
 Stibium, from the Greek, orijSi (stibi), the name 
 for the native sulphide of antimony. 
 Arsenic, As = 74.4. From the Greek aposvucbv (arsenicon), the name for 
 
 the native sulphide of arsenic. 
 
 Barium, Ba = 136.4 From the Greek fiapvs (barys), heavy, in allusion to 
 
 the high specific gravity of barium sulphate, or 
 heavy-spar. 
 
 From the German wixmuth, an expression used long 
 ago by the miners in allusion to the variegated 
 tints of the metal when freshly broken. 
 From the Greek nadfida (kadmeia) the old name for 
 calamine (zinc carbonate), with which cadmium 
 is frequently associated. 
 
 Calcium, Ca = 39.8. From the Latin calx, lime, the oxide of calcium. 
 
 Chromium, Cr = 51.7. From the Greek XP"/^ a (chroma), color, in allusion 
 
 to the beautiful colors of all its compounds. 
 Co = 58.56, From the German Kobold, which means a demon 
 
 . inhabiting the mines. 
 
 Cu = 63.1. ' From the Latin cuprum, copper, and this from the 
 Island of Cyprus, where copper was first obtained 
 by the ancients. 
 Gold, Au = 195.7. Gold means bright yellow in several old languages. 
 
 (Aurum.) The Latin aurum signifies the color of fire. 
 
 Iridium, Ir = 191.5. From iris, rainbow, in allusion to the varying tints 
 
 of its salt solutions. 
 
 Fe = 55.5. Iron probably means metal; the derivation of the 
 Latin ferrum is not definitely known. 
 
 247 
 
 Bismuth, Bi = 206.9. 
 
 Cadmium, Cd =111.6. 
 
 Iron, 
 
248 
 
 METALS AND THEIR COMBINATIONS. 
 
 Lead, Pb 
 
 (Plumbum.) 
 
 Lithium, Li 
 
 Magnesium, Mg 
 
 = 205.35. Both words signify something heavy. 
 
 6.98. 
 24.18. 
 
 Manganese, Mn = 54.6. 
 
 198.5. 
 
 Mercury, Hg 
 
 (Hydrargyrum ) 
 
 Molybdenum, Mo 
 
 Nickel, Ni 
 
 95.3. 
 
 58.3. 
 
 Platinum, Pt = 193.3. 
 
 Potassium, K 38.86. 
 (Kalium.) 
 
 Silver, Ag 
 
 (Argentum.) 
 
 Sodium, Na 
 
 (Natrium.) 
 
 107.12. 
 
 22.88. 
 
 Strontium, Sr = 86.94. 
 118.1. 
 64.9. 
 
 Tin, Sn 
 
 (Stannum.) 
 Zinc, Zn 
 
 From the Greek Weiog (litheios), stony. 
 From Magnesia, a town in Asia Minor, where mag- 
 nesium carbonate was found as a mineral. 
 Probably from magnesium, with the compounds of 
 
 which it was long confounded. 
 From Mercury, the messenger of the Greek gods. 
 
 Hydrargyrum means liquid silver. 
 From the Greek n6"kvfi6og (molybdos), lead. 
 From the old German word nickel, which means 
 
 worthless. 
 Platina is the diminutive of the Spanish word plata, 
 
 silver. 
 From pot-ash ; potassium carbonate being the chief 
 
 constituent of the lye of wood-ashes. Kali is the 
 
 Arabic word for ashes. 
 Both words signify white. 
 
 From soda-ash, or sod-ash, the ashes of marine plants 
 which are rich in sodium carbonate Natron is an 
 old name for natural deposits of sodium carbonate. 
 
 From Strontian, a village in Scotland, where stron- 
 tium carbonate is found. 
 
 Both words most likely signify stone. 
 
 Most likely from the German zinn or tin, the metals 
 having been confounded with each other. 
 
 Melting-points of metals. 
 
 c. F. 
 
 Fusible below the f Mercury 40 40 
 
 boiling-point of -[ Potassium . . . -f 62 -f-144 
 
 water, ^ Sodium 97 207 
 
 f Lithium ..... 180 356 
 
 I Tin 228 443 
 
 Cadmium ...... 310 590 
 
 Bismuth 260 500 
 
 Lead 325 617 
 
 Zinc 412 773 
 
 Magnesium . . . .700 1292 
 
 Antimony .... 425 797 
 
 Aluminum . 700 1292 
 
 Barium. 
 
 Calcium. 
 
 Strontium. 
 
 Fusible below red 
 heat, 
 
 Fusible 
 heat, 
 
 at red 
 
TIME OF DISCOVERY OF THE METALS. 
 
 249 
 
 
 r Silver 
 
 
 Copper 
 
 
 Gold 
 
 
 Cast- iron . 
 
 
 Pure iron, 
 
 Infusible below a 
 
 Nickel, 
 
 red heat. 
 
 Cobalt, 
 
 
 Manganese, 
 
 
 Molybdenum, ^ 
 
 
 Chromium, J 
 
 
 Platinum, 1 
 
 
 Iridi.um, 
 
 1020 
 1100 
 1200 
 1150 
 
 1868 
 2012 
 2192 
 2102 
 
 Highest heat of forge. 
 
 | Agglomerate, but do not melt in forge. 
 Fusible in the oxyhydrogen blowpipe 
 
 flame. 
 
 Arsenic does not fuse, but volatilizes at a low red heat. 
 
 Specific gravities of metals at 15.5 C, 
 
 ^lithium 
 
 Potassium 
 
 Sodium 
 
 Calcium 
 
 Magnesium . 
 
 Strontium 
 
 Aluminum . 
 
 Barium 
 
 Arsenic 
 
 Antimony 
 
 Zinc 
 
 Tin 
 
 Iron 
 
 0.593 
 
 0.865 
 
 0.972 
 
 1.57 
 
 1.75 
 
 2.54 
 
 2.67 
 
 4.00 
 
 5.88 
 
 6.72 
 
 6.90 
 
 7.29 
 
 7.79 
 
 Manganese 
 Molybdenum 
 Cadmium 
 Nickel . 
 Cobalt . 
 Copper . 
 Bismuth . 
 Silver 
 Lead 
 
 Mercury . 
 Gold 
 
 Platinum . 
 Iridium 
 
 800 
 
 863 
 
 870 
 
 870 
 
 8.95 
 
 896 
 
 990 
 
 10.50 
 
 11.36 
 
 1359 
 
 19.36 
 
 21.50 
 
 22.42 
 
 Time of discovery of the metals. 
 
 Gold, 
 
 Silver, 
 
 Mercury, 
 
 Copper, 
 
 Zinc, 
 
 Tin, 
 
 Iron, 
 
 Lead, 
 
 Antimony, 
 
 Bismuth, 
 
 Arsenic, 
 
 Cobalt, 
 
 Platinum, 
 
 Nickel, 
 
 Manganese, 
 
 Molybdenum, 
 
 Chromium, 
 
 Iridium, 
 
 These metals were known to the ancients, because 
 either they are found in a metallic state, or can be 
 obtained by comparatively simple processes from 
 the oxides. 
 
 J 
 
 | Latter part of the fifteenth century. 
 
 1694, by Schroder. 
 
 1733, by Brandt. 
 
 1741, by Wood. 
 
 1751, by Cronstedt. 
 
 1774, by Galm. 
 
 1782, by Hjelm. 
 
 1797, by Vauquelin. 
 
 1804, by Smithson Tennant. 
 
250 
 
 METALS AND THEIR COMBINATIONS. 
 
 Potassium, 
 
 
 Sodium, 
 
 ( H 
 
 Barium, 
 
 . 1807-1808 ] 
 
 Calcium, 
 
 I 
 
 Strontium, 
 
 
 Magnesium, J 
 
 Cadmium, 1817, by Stromeyer. 
 
 Lithium, 1817, by Arfvedson. 
 
 Aluminum, 1828, by Wohler. 
 
 Davy discovered methods for the 
 separation of these metals from 
 their oxides. 
 
 Valence of metals. 1 
 
 Univalent. 
 
 Lithium, 
 
 Potassium, 
 
 Sodium, 
 
 Silver. 
 
 Bivalent. 
 
 Barium, 
 
 Calcium, 
 
 Strontium, 
 
 Magnesium, 
 
 Cadmium, 
 
 Zinc, 
 
 Copper, 
 
 Mercury. 
 
 Trivalent. 
 Aluminum, 
 
 Bi, tri, or sexivalent. 
 Chromium, 
 Cobalt, 
 Iron, 
 
 Manganese, 
 Nickel, 
 Molybdenum. 
 
 Bi- and quadrivalent. 
 Iridium, 
 Platinum, 
 Tin. 
 
 Tri- and quinquivalent. 
 
 Antimony, 
 
 Arsenic, 
 , Bismuth. 
 
 Uni- or trivalent. 
 Gold. 
 
 Occurrence in nature. 
 
 a. In a free or combined state. 
 
 Almost exclusively in the metallic state. 
 
 Gold, 
 
 Iridium, 
 
 Platinum, 
 
 Silver, 
 
 Mercury, 
 
 Bismuth, generally metallic, also as oxide and sulphide. 
 
 Copper, rarely metallic ; chiefly as sulphide, oxide, and carbonate 
 
 I As metals or sulphides. 
 
 Potassium, 
 
 Sodium, 
 
 Lithium, 
 
 6. In combination only. 
 Chiefly as chlorides or silicates. 
 
 1 The valence here given is the one chiefly exerted by the elements, but several compounds 
 are known in which some of the metals exhibit a yet different valence ; thus copper and mer- 
 cury seem to be univalent in certain compounds, while some metals exhibiting a valence of 
 six (iron, chromium, etc.) are also bi- and trivalent. 
 
CLASSIFICATION OF METALS. 251 
 
 Barium, as sulphate. 
 
 Calcium, \ 
 
 Strontium, > As carbonates, sulphates, silicates. 
 
 Magnesium, J 
 
 Aluminum, in silicates. 
 
 Iron, ^ 
 
 Zinc, [ As oxides, carbonates, sulphide. 
 
 Cadmium, J 
 
 Arsenic, 
 
 Antimony, 
 
 Cotit, Chiefly as sulphides. 
 
 Nickel, 
 
 Molybdenum, J 
 
 Chromium, ^ 
 
 Manganese, > Chiefly as oxides. 
 
 Tin, 
 
 Classification of metals. 
 
 For the purpose of study, metals may be differently arranged into 
 groups according to the selection of those properties which are made 
 the basis for comparison. Thus, the valence alone may serve for 
 classification, and in that case the arrangement will also largely cor- 
 respond to the periodic system. The scheme adopted below is based 
 more especially on the analytical behavior of the metals. While 
 this classification brings together in many cases those metals belong- 
 ing to one group of the periodic system, in a few cases the elements 
 of one periodic group are separated, as for instance in the case of 
 magnesium, zinc, and cadmium. These elements resemble one 
 another closely in many respects, and are found together in group 
 II. of the periodic system, while in a classification based chiefly on 
 analytical properties these metals are found in different groups. 
 
 Light metals. Heavy metals. 
 
 Sp. gr. from 6 to 4. Sp gr. from 6 to 22.4. 
 
 Sulphides soluble in water. Sulphides insoluble in water. 
 
 Light metals. 
 
 Earth metals. Alkaline earth metals. Alkali-metal. 
 
 Al, and many rare metals. Ba, Ca, Sr, (Mg). K, Na, Li, (NH 4 ). 
 
 Oxides insoluble. Oxides soluble ; Oxides, carbonates, and 
 
 Carbonates insoluble. most salts soluble. 
 
 Heavy metals. 
 
 Arsenic group. Lead group. Iron group. 
 
 As, Sb, Sn, Au, Pt, Mo. Pb, Cu, Bi, Ag, Hg, Cd. Fe, Co, Ni, Mn, Zn, Cr. 
 
 -v Sulphides soluble in 
 
 Sulphides insoluble in dilute acids. dilute acids. 
 
 Sulphides soluble in am- Sulphides insoluble in 
 monium sulphide. ammonium sulphide. 
 
252 METALS AND THEIR COMBINATIONS. 
 
 Properties of metals. All metals have a peculiar lustre krrown 
 as metallic lustre, and all are more or less good conductors of heat 
 and electricity. The color of most metals is white, grayish, or 
 bluish-white, or dark gray ; a few metals show a distinct color, as, 
 for instance, gold (yellow) and copper (red). 
 
 At ordinary temperatures metals are solids with the exception of 
 mercury, all are fusible, and some are so volatile that they may be 
 distilled. Most, probably all, metals may be obtained in a crystal- 
 lized condition. 
 
 Metals show a wide difference in the properties of malleability, ductility, and 
 tenacity. Gold is both the most malleable and most ductile metal, while lead 
 possesses comparatively little of these qualities. In many cases heat increases 
 or develops malleability and ductility, but diminishes tenacity ; however, the 
 tenacity of iron, which surpasses that of any other metal, is not lessened by 
 heating. 
 
 The term annealing denotes the process of restoring the malleability and 
 ductility of some metals after these properties have been diminished, by caus- 
 ing a change in the molecular structure of the metals through hammering, 
 rolling, or sudden cooling. Annealing consists in heating the metal and per- 
 mitting it to cool slowly (in a few cases quickly) in order to allow the cohesive 
 force to produce the most stable arrangement of the molecules. 
 
 Tempering, which term at times is used analogously with annealing, consists 
 in heating the metal and chilling it suddenly. The result of annealing is the 
 highest development of softness and in case of some metals the restoration of 
 cohesiveness ; the object of tempering is the attainment of a certain degree of 
 hardness and elasticity. 
 
 Elasticity, i. e., the power of recovering original form when twisted or bent, 
 and sonorousness, i. e., the property of yielding a musical sound when struck, 
 are possessed only by the harder metals, and to a high degree by certain 
 mixtures of metals. 
 
 All metals expand when heated, but the rate, of expansion of the different 
 metals differs. Within certain limits of temperature the expansion of a metal 
 occurs uniformly in direct ratio to the increase in temperature. The great 
 expansibility of zinc is an important property of the metal when used as a die 
 in dental prosthesis. 
 
 Metals do not combine chemically with one another. Their mix- 
 tures (alloys) still exhibit the* metallic nature in their general physical 
 characters. It is different, however, when metals combine with non- 
 metals ; in this case the metallic characters are lost almost invariably. 
 All metals combine with chlorine, fluorine, and oxygen ; most metals 
 also with sulphur, bromine, and iodine ; many also with carbon and 
 phosphorus, forming the respective chlorides, fluorides, oxides, sul- 
 phides, bromides, iodides, carbides, and phosphides. Metals replace 
 hydrogen in acids, forming salts. 
 
PROPERTIES OF METALS. 253 
 
 The intensity with which metals combine with non-metals or with acids 
 differs widely. Selecting the combinations with oxygen as a typical instance 
 we find that the affinity between the alkali metals and the alkaline earth 
 metals is so intense that these metals cannot be exposed to the atmosphere for 
 even a few hours without undergoing complete oxidation. It is for this reason 
 that these metals cannot be used in the metallic state for purposes requiring 
 constant exposure to air. Other metals, such as iron, will oxidize (rust) slowly 
 at ordinary temperature or will burn when heated sufficiently high. Yet other 
 metals retain their metallic lustre in dry or moist air at low or high tempera- 
 ture. Indeed, the oxides of these metals are decomposed into oxygen and the 
 respective metal by the mere application of heat. The metals showing this 
 behavior are often called noble mefals, while all others are designated as base 
 metals. The noble metals are gold, silver, mercury, platinum, iridium, and a 
 few other metals related to platinum. (See also page 198.) 
 
 Manufacture of metals. Most metals may be obtained from their 
 oxides by heating the latter with charcoal, the carbon combining with 
 the oxygen of the oxide, while the metal is liberated : 
 
 MO + C = CO + M; 
 or 
 
 2MO + C = CO 2 + 2M. 
 
 Also hydrogen may be used in some cases as the deoxidizing agent : 
 
 MO + 2H = H 2 -f M. 
 
 Some metals are found in nature chiefly as sulphides, which usually 
 are converted into oxides (before the metal can be obtained) by roast- 
 ing. The term roasting, when used in metallurgy, means heating 
 strongly in an oxidizing atmosphere, when the sulphides are con- 
 verted into sulphates or oxides, thus : 
 
 MS + 4O = MS0 4 ; or MS + 3O = MO + SO 2 . 
 
 A few metals are obtained by heating the chloride with metallic 
 sodium, when sodium chloride is formed, while the other metal is 
 set free. Electrolysis is also one of the means for obtaining metals 
 from their compounds. 
 
 Recently a generally applicable method of obtaining metals has been devised, 
 which consists in the action of aluminum powder on the oxides of the metals, 
 especially of those that have a high fusing-point and form difficultly reducible 
 oxides. So much heat is developed in these reductions that the method may be 
 used for welding, for example, the joints between rails. 
 
 Alloys are combinations or, more correctly speaking, mixtures of 
 two or more metals. Whenever mercury is a constituent of an alloy 
 it is called amalgam. All alloys exhibit metallic nature in their 
 physical properties i. e., they have metallic lustre and are more or 
 less good conductors of heat and electricity. 
 
254 METALS AND THEIR COMBINATIONS. 
 
 While alloys are generally looked upon as molecular mixtures, and 
 not as definite chemical compounds, yet there are many alloys the 
 properties of which are not intermediate between those of the elements 
 entering into these alloys, as we should expect if they were mechanical 
 mixtures. For this reason it is assumed that, in at least some cases, 
 compounds are formed which, however, are generally dissolved in, or 
 mixed with, an excess of one of the constituent metals. 
 
 On the other hand, there are cases where there is an utter lack of 
 affinity between the component parts of an alloy. Thus, alloys of 
 copper and lead, usually termed pot-metal alloys, show particles of the 
 two metals side by side, when the fractured surface is examined with 
 the microscope. 
 
 Manufacture of alloys. Alloys are generally obtained by fusing the 
 metals together ; but in order to do it successfully such properties of the com- 
 ponents as fusibility, specific gravity, proneness to oxidize, etc., should be con- 
 sidered. As a general rule the metal having the highest fusing-point is melted 
 first, and to it are added the other metals in the diminishing order of their 
 fusing- points. Loss or deterioration by oxidation should be guarded against 
 by covering the surface of the liquid mass with charcoal or with such fluxes as 
 borax, sodium chloride, or ammonium chloride. The heat should at no time 
 be higher than is necessary for the liquefaction. 
 
 Properties of alloys. Alloys generally are harder and more brittle, but 
 less ductile and malleable than the constituent metals possessing these qualities 
 in the highest degree. The union even of two ductile metals may destroy that 
 property more or less completely, as is shown by the absence of ductility in an 
 alloy of gold and a small portion of lead. The combination of a brittle and a 
 ductile metal always yields a brittle alloy. 
 
 Tenacity is generally increased. Thus, copper alloyed with 12 per cent, of 
 tin has its tenacity trippled ; gold, when alloyed with copper, silver, or plat- 
 inum, has its tensile resistance nearly doubled ; aluminum bronze, an alloy of 
 copper and aluminum, has a greater tenacity than that of either of the con- 
 stituent metals. 
 
 Certain metals impart to alloys specific properties. Thus, bismuth and 
 cadmium increase fusibility; tin and lead, both of which are soft metals, 
 impart hardness and tenacity ; arsenic and antimony produce brittle alloys. 
 
 QUESTIONS. How many metals are known, and about how many are of gen- 
 eral interest? Mention some metals having very low and some having very 
 high fusing-points. What range of specific gravities do we find among the 
 metals ? Mention some univalent and some bivalent metals ; also some which 
 show a different valence under different conditions. Mention some metals which 
 are found in nature in an uncombined state; some which are found as oxides, 
 sulphides, chlorides, and carbonates, respectively. Into what two groups are 
 the metals divided? State the three groups of light metals. What is a metal ? 
 What is an alloy, and what is an amalgam ? By what process can most metals 
 be obtained from their oxides? 
 
POTASSIUM. 255 
 
 The fusibility of an alloy is invariably greater than that of its least fusible 
 constituent, and may be greater than that of its most fusible constituent. Thus 
 an alloy of 2 parts of tin, 3 of lead, and 5 of bismuth fuses at 91 C., while 
 tin alone melts at 228, lead at 325, and bismuth at 260 C. 
 
 The conductivity of alloys for heat and . electricity is less than that of the 
 pure metals. The color of alloys is generally a modification of the predom- 
 inating ingredient, but instances are known where the color of alloys has no 
 relation to its constituents. For instance, German silver is perfectly white 
 although it contains a considerable portion of red copper. 
 
 21. POTASSIUM (KALIUM). 
 
 K' = 39 (38.86). 
 
 General remarks regarding- alkali-metals. The metals potas- 
 sium, sodium, lithium (rubidium and caesium) form the group of the 
 alkali-metals, which, in many respects, show a great resemblance to 
 each other in chemical and physical properties. For reasons to be 
 explained hereafter, the compound radical ammonium is usually 
 classed among the alkali-metals. 
 
 The alkali-metals are all univalent; they decompose water at the 
 ordinary temperature, with liberation of hydrogen; they combine 
 spontaneously with oxygen and chlorine ; their hydroxides, sulphates, 
 nitrates, phosphates, carbonates, sulphides, chlorides, iodides, and 
 nearly all other of their salts are soluble in water ; all these com- 
 pounds are white, solid substances, most of which are fusible at a 
 red heat. Of all metals, those of the alkalies are the only ones form- 
 ing hydroxides and carbonates which are not decomposed by heat. 
 
 The metals themselves are of a silver-white color, and extremely 
 soft; on account of their tendency to combine with oxygen they 
 must be kept in a liquid, such as coal-oil, which is not acted on by 
 them, or in an atmosphere of hydrogen. 
 
 The metals may be obtained by heating their carbonates with 
 carbon in iron retorts, the escaping vapors being passed under coal- 
 oil for condensation of the metal : 
 
 K 2 C0 3 + 20 = 3CO + 2K. 
 
 At present most of the alkali metals are obtained by the electrol- 
 ysis of the fused hydroxides, the metal and hydrogen being liberated 
 at the negative, oxygen at the positive pole : 
 KOH == K 4- H + O. 
 
 Occurrence in nature. Potassium is found in nature chiefly as a 
 double silicate of potassium and aluminum (granite rocks, feldspar, 
 and other minerals), or as chloride and nitrate. By the gradual dis- 
 integration of the different granite rocks containing potassium silicate, 
 
256 METALS AND THEIR COMBINATIONS. 
 
 this has entered into the soil, whence it is taken up by plants as one 
 of the necessary constituents of their food. 
 
 In the plant potassium enters largely into the combination of 
 organic compounds, and when the plant is burned ashes are left 
 containing the potassium, now in the form of carbonate. By ex- 
 tractincr such ashes with water, the potassium carbonate, along with 
 small quantities of chlorides and sulphates of potassium and sodium, 
 is obtained in solution, by the evaporation of which to dryness an 
 impure article is obtained, known as crude potash. Formerly this 
 was the chief source of potassium compounds, but about the year 
 1850 the inexhaustible salt mines of Stassfurt, Germany, were discov- 
 ered. The salt there mined contains, besides the chlorides and sul- 
 phates of sodium, magnesium, calcium, and other salts, considerable 
 quantities of potassium chloride, and the Stassfurt mines at present 
 are practically the source of all potassium compounds. 
 
 Potassium hydroxide, Potassii hydroxidum, KOH == 55.74 
 (Caustic potash), may be obtained by the action of the metal on water : 
 
 K -h H,O = H + KOH 
 
 The usual process for making potassium hydroxide is to boil together 
 a dilute solution of potassium carbonate or bicarbonate and calcium 
 
 hydroxide : 
 
 K 2 C0 3 + Ca(OH) 2 = CaC0 3 + 2KOH. 
 
 Large quantities of high-grade potassium hydroxide are now 
 manufactured directly from the chloride by electrolysis. 
 
 Experiment 20. Add gradually 5 grammes of calcium hydroxide (slaked 
 lime) to a boiling solution of about 5 grammes of potassium carbonate in 50 
 c.c. of water, and continue to boil until the conversion of potassium carbonate 
 into hydroxide is complete. This can be shown by filtering off a few drops of 
 the liquid, and supersaturating with dilute hydrochloric acid, which should not 
 cause effervescence. Set aside to cool, and when all solids have subsided, pour 
 off the clear solution of potassium hydroxide, which may be used for Experi- 
 ment 21 . What quantities of K 2 CO 3 and Ca(OH) 2 are required to make one liter 
 of a 5 per cent, solution of potassium hydroxide ? 
 
 Potassium hydroxide is a white, hard, highly deliquescent sub- 
 stance, soluble in 0.5 part of water and 2 parts of alcohol ; it fuses 
 at a low red heat, forming an oily liquid, which may be poured into 
 suitable moulds to form pencils; at a strong red heat it is slowly 
 volatilized without decomposition; it is strongly alkaline and a 
 powerful base, readily combining with all acids ; it rapidly destroys 
 organic tissues, and when taken internally acts as a powerful corrosive, 
 and most likely otherwise as a poison- 
 
POTASSIUM. 257 
 
 Antidotes : dilute acids, vinegar, to form salts ; or fat, oil, or milk, to form soap. 
 Liquor potassii hydroxidi is a 5 per cent, solution of potassium hydroxide in 
 water. 
 
 Potassium oxide, K 2 O. This compound can be obtained either 
 by burning potassium in air and subsequent heating of the product 
 to a high temperature, or by fusing together potassium hydroxide 
 and metallic potassium : 
 
 2KOH -f 2K = 2K 2 O + 2H. 
 
 Besides this potassium monoxide, corresponding to water in its composition, 
 two other oxides of the composition K 2 O 2 (corresponding to hydrogen perox- 
 ide, H 2 O 2 ) and K 2 O 4 are known. The latter oxide is obtained by the com- 
 bustion of potassium in oxygen. It is a strong oxidizing agent, and at a high 
 temperature is decomposed into oxide and oxygen. 
 
 Potassium carbonate, Potassii carbonas, K 2 CO 3 = 137.27, is 
 obtained from wood-ashes in an impure state as described above, or 
 from the native chloride by the so-called Leblanc process, which will 
 be described in connection with sodium carbonate. It is also made 
 by passing carbon dioxide into solution of potassium hydroxide, 
 obtained by the electrolytic process. 
 
 Pure potassium carbonate is obtained by heating the bicarbonate, 
 which is decomposed as follows : 
 
 2KHCO 3 = K 2 CO 3 + H 2 O + CO 2 . 
 
 Potassium carbonate is deliquescent, is soluble in about an equal 
 weight of water, insoluble in alcohol, and has strong basic and alka- 
 line properties. 
 
 The strong alkaline reaction of potassium and sodium carbonate in solution 
 is due to hydrolysis of the salts into bicarbonate, which is neutral to litmus and 
 free alkali. (See pages 122 and 201.) 
 
 K 2 C0 3 + H 2 = KHCO 3 + KOH. 
 
 Potassium bicarbonate, Potassii bicarbonas, KHCO 3 = 99.41. 
 Obtained by passing carbon dioxide through a strong solution of 
 potassium carbonate, when the less soluble bicarbonate forms and 
 separates into crystals : 
 
 K 2 CO 3 + H 2 O + CO 2 2KHC0 3 . 
 
 Potassium percarbonate, K 2 C 2 O 6 , also exists as a bluish-white powder, 
 which liberates oxygen when heated, and in dilute acid solution gives off hydro- 
 gen dioxide. It is obtained by electrolysis of a concentrated solution of potas- 
 sium carbonate at about 10 C. (14 F.). It is a good oxidizer. 
 17 
 
258 METALS AND THEIR COMBINATIONS. 
 
 Potassium nitrate, Potassii nitras, KNO 3 = 100.43 (Niter, Salt- 
 peter). Potassium and sodium nitrate are found as an incrustation upon 
 and throughout the soil of certain localities in dry and hot countries, 
 as, for instance, in Peru, Chile, and India. The formation of these 
 nitrates is to be explained by the absorption of ammonia by the soil, 
 where it gradually is oxidized and converted into nitric acid. This 
 nitrification, i.4. 9 the conversion of ammonia into nitric acid, seems to 
 be due largely to the action of micro-organisms, termed the nitrifying 
 ferment. The acid after being formed combines with the strongest 
 base present in the soil. If this base be potash, potassium nitrate 
 will be formed ; if soda, sodium nitrate ; if lime, calcium nitrate. 
 
 Upon the same principle is based the manufacture of niter on a large scale, 
 which is accomplished by mixing animal refuse matter with earth and lime, 
 and placing the mixture in heaps under a roof to prevent lixiviation by rain. 
 By decomposition (putrefaction) of the animal matter ammonia is formed, 
 Which, by oxidation, is converted into nitric acid, which then combines with 
 the calcium of the lime, forming calcium nitrate. This is dissolved in water, 
 and to the solution potassium carbonate (or chloride) is added, when calcium 
 carbonate (or chloride) and potassium nitrate are formed : 
 
 Ca(N0 3 ) 2 + K 2 CO 3 == 2KN0 3 + CaCO,. 
 
 Large quantities of potassium nitrate are made also by mixing hot concen- 
 trated solutions of sodium nitrate and potassium chloride, when, on cooling, 
 potassium nitrate separates in crystals, because it is much less soluble in cold 
 water than sodium nitrate is. (See page 193.) 
 
 NaNO 3 + KC1 = KNO 3 + NaCl. 
 
 Potassium nitrate crystallizes in six-sided prisms ; it is soluble in 
 about 3.8 parts of cold, and 0.4 part of boiling water. It has a cool- 
 ing, saline, and pungent taste, and a neutral reaction. When heated 
 with deoxidizing agents or combustible substances, these are readily 
 oxidized. 
 
 It is this oxidizing power which is made use of in the manufacture 
 of gunpowder an intimate mixture of potassium nitrate, sulphur, 
 and carbon. Upon heating or igniting the gunpowder, the sulphur 
 and carbon are oxidized, a considerable quantity of various gases 
 (CO, CO 2 , N, SO 2 , etc.) being formed, the sudden generation and 
 expansion of which cause the explosion. 
 
 Potassium chlorate, Potassii chloras, KC1O 3 =121.68 (Chlorate 
 of potash). This salt may be obtained by the action of chlorine on a 
 boiling solution of potassium hydroxidej as explained on page 237. 
 
 A cheaper process for its manufacture is the action of chlorine 
 
POTASSIUM. 259 
 
 upon a boiling solution of potassium carbonate, to which calcium 
 hydroxide has been added : 
 
 K 2 C0 3 + 6Ca(OH) 2 + 12C1 == 2KC1O 3 + OaCO 3 + 5CaCl 2 + 6H 2 O. 
 
 Practically all potassium chlorate is manufactured now by electrol- 
 ysis of solutions of potassium chloride under proper conditions. 
 
 Potassium chlorate crystallizes in white plates of a pearly lustre ; 
 it is soluble in 16.7 parts of cold, and 1.7 parts of boiling water. It 
 is even a stronger oxidizing agent than potassium nitrate, for which 
 reason care must be taken in mixing it with organic matter or other 
 deoxidizing agents, or with strong acids, which will liberate chloric 
 acid. When heated by itself, it is decomposed into potassium chloride 
 and oxygen. 
 
 Potassium sulphate, Potassii sulphas, K 2 SO 4 = 173. 04. Ob- 
 tained by the decomposition of potassium chloride, nitrate, or carbo- 
 nate, by sulphuric acid : 
 
 2KC1 + H 2 SO 4 = 2HC1 + K 2 SO 4 ; 
 K 2 C0 3 + H 2 S0 4 = H 2 + C0 3 + K 2 S0 4 . 
 
 Potassium sulphate exists in small quantities in plants, and in 
 nearly all animal tissues and fluids, more abundantly in urine. 
 
 Potassium hydrogen sulphate, bisulphafe, or potassium acid sulphate, may be 
 obtained by the action of one molecule of potassium chloride upon one mole- 
 cule of sulphuric acid : 
 
 KC1 + H 2 SO 4 = HC1 -f KHSO 4 . 
 
 Potassium sulphite. Obtained by the decomposition of potassium carbonate 
 by sulphurous acid : 
 
 K 3 CO 3 + H 2 SO S = H 2 O + CO 2 + K 2 SO S . 
 
 Potassium hypophosphite, Potassii hypophosphis, KPH 2 O 2 = 
 103.39, may be obtained by decomposing a solution of calcium hypo- 
 phosphite by potassium carbonate : 
 
 Ca(PH 2 O 2 ) 2 + K 2 CO 3 = 2KPH 2 O 2 + CaCO 3 . 
 
 The filtered solution is evaporated at a very gentle heat, stirring 
 constantly from the time it begins to thicken until a dry, granular 
 salt is obtained, which is soluble in 0.5 part of cold and 0.3 part of 
 boiling water. 
 
 Potassium iodide, Potassii iodidum, KI = 164.76, is made by 
 the addition of iodine to a solution of potassium hydroxide until the 
 dark-brown color no longer disappears : 
 
 6KOH + 61 = 5KI + KI0 3 + 3H 2 O. 
 
260 METALS AND THEIR COMBINATIONS. 
 
 Iodide and iodate of potassium are formed, and may be separated 
 by crystallization. A better method, however, is to boil to dryness 
 the liquid containing both salts, and to heat the mass after having 
 mixed it with some charcoal, in a crucible, when the iodate is con- 
 verted into iodide : 
 
 KIO 3 + 30 = KI + SCO. 
 
 Experiment 21. Add to a solution of about 3 grammes of potassium hydroxide 
 in about 25 c.c. of water (or to the solution obtained by making Experiment 
 20) iodine until the brown color no longer disappears. (How much iodine will 
 be needed for 3 grammes of KOH?) Evaporate the resulting solution (What 
 does this solution contain now ?) to dryness, mix the powdered mass with about 
 10 per cent, of powdered charcoal and heat the mixture in a crucible until 
 slight deflagration has taken place. Dissolve the cold mass in hot water, filter 
 and set aside for crystallization ; if too much water has been used for dissolving, 
 the liquid must be concentrated by evaporation. 
 
 Potassium iodide forms colorless, cubical crystals, which are soluble 
 in 0.5 part of boiling and 0.8 part of cold water, also soluble in 12 
 parts of alcohol, and 2.5 parts of glycerin. When heated it fuses, 
 and at a bright-red heat is volatilized without decomposition. 
 
 Potassium bromide, Potassii bromidum, KBr = 118.22, may be 
 obtained in a manner analogous to that given for potassium iodide, 
 by the action of bromine upon potassium hydroxide, etc. 
 
 Or it may be made by the decomposition of a solution of ferrous 
 bromide by potassium carbonate : 
 
 Ferrous carbonate is precipitated, while potassium bromide remains 
 in solution, from which it is obtained by crystallization. 
 
 Potassium salts of interest, which have not yet been mentioned, will be con- 
 sidered under the head of their respective acids. Some of these salts are 
 potassium chromate and permanganate, and the salts formed from organic 
 acids, such as potassium tartrate, acetate, etc. 
 
 Tests for potassium. 
 
 (Potassium chloride, KC1, or nitrate, KNO 3 , may be used.) 
 1. To a solution of any potassium salt add some solution of chloro- 
 platinic acid. A yellow crystalline precipitate of potassium chloro- 
 platinate is obtained : 
 
 2KN0 3 + H 2 PtCl 6 = K 2 PtCl 6 + 2HN0 3 ; 
 
 or 2K- + 2NQ,' + 2H + PtCl 6 " = K 2 PtCl 6 + 2H' + 2NQ/ . 
 This test is not very delicate, as 1 part of the precipitate is soluble in 
 about 100 parts of water. It is much less soluble in alcohol, which 
 is usually added to facilitate precipitation. 
 
POTASSIUM. 261 
 
 2. To a neutral or slightly acid solution of a potassium salt add solu- 
 tion of sodium cobaltic nitrite: a yellow precipitate of potassium cobaltic 
 nitrite, (KNO 2 ) 6 .Co 2 (NO 2 ) 6 + H 2 O, is produced. (The reaction is 
 not influenced by the presence of alkaline earths, earths, or metals of 
 the iron group, but is not suitable in case of potassium iodide, since 
 iodine is liberated by the nitrous acid of the cobalt solution, and 
 interferes with the test.) 
 
 3. Add to a concentrated solution of a neutral potassium salt a 
 freshly prepared strong solution of tartaric acid : a white precipitate 
 of potassium acid tartrate, KHC 4 H 4 O 6 , is slowly formed. Addition 
 of alcohol facilitates precipitation. 
 
 Tartaric acid, H 2 .C 4 H 4 O 6 , is dibasic and dissociates chiefly into H* 
 and HC 4 H 4 O/ ions. Potassium ions, K', and HC 4 H 4 O 6 ' ions unite 
 to form the difficultly soluble acid tartrate ; 
 
 K- + NO./ -f H- + HC 4 H 4 O 6 ' = KHC 4 H 4 6 + H' + NO,'. 
 
 One part of the salt is soluble in about 200 parts of water, but prac- 
 tically insoluble in alcohol, even when diluted. 
 
 4. Potassium compounds color violet the flame of a Bunsen burner 
 or of alcohol. The presence of sodium, which colors the flame in- 
 tensely yellow, interferes with this test, as it masks the violet caused 
 by potassium. The difficulty may be overcome by observing the 
 flame through a blue glass or through a thin vessel filled with a solu- 
 tion of indigo. The yellow light is absorbed by the blue medium, 
 while the violet light passes through and can be recognized. 1 
 
 With few exceptions, potassium compounds are white, soluble in 
 water, and not volatile at a low red heat. Of the above tests, the 
 
 1 The flame reaction for metals is one of the steps taken in qualitative analysis. For this 
 purpose the platinum wire should be kept immersed in hydrochloric acid in a test-tube. 
 When needed, it is cleaned by alternately holding it in the flame and dipping it in the acid, 
 until no color is given to the flame. The salt best adapted for flame tests is a chloride ; hence 
 the substance to be tested should be moistened in a dish with hydrochloric acid before intro- 
 ducing it into the flame on the loop of the wire. Chlorides are readily volatilized. Unless the 
 substance is volatile, there will be 110 flame reaction. 
 
 QUESTIONS. How is potassium found in nature, and from what sources is 
 the chief supply of potassium salts obtained ? What color have the salts of the 
 alkali metals, and which are insoluble ? Mention two processes for making potas- 
 sium hydroxide, and what are its properties? Show by symbols the conversion 
 of carbonate into bicarbonate of potassium. Explain the principle of the man- 
 ufacture of potassium nitrate, and what is the office of the latter in gunpowder? 
 How is potassium chlorate made, and what are its properties ? Give the proc- 
 esses for manufacturing iodide and bromide of potassium, both in words and 
 symbols. State the composition of potassium sulphate and sulphite. How can 
 they be obtained? Mention tests for potassium compounds. How much iodine 
 is contained in 33 grammes of potassium iodide? 
 
262 METALS AND THEIR COMBINATIONS. 
 
 second is the most delicate. Some other difficultly soluble salts of 
 potassium arc the picrate, perchlorate and fluosilicate. With the 
 exception of the acid tartrate (cream of tartar) and the picrate, the 
 other difficultly soluble salts of potassium are of a kind not usually met 
 with. 
 
 22. SODIUM (NATRIUM). 
 
 Na i -=23 (22.88). 
 
 Occurrence in nature. Sodium is found very widely diffused in 
 small quantities through all soils. It occurs in large quantities in 
 combination with chlorine, as rock-salt, or common salt, which forms 
 considerable deposits in some regions, or is dissolved in spring waters, 
 and is by them carried to the rivers, and finally to the ocean, which 
 contains immense quantities of sodium chloride. It is found, also, 
 as nitrate, and in double silicates. 
 
 Sodium chloride, Sodii chloridum, NaCl 58.06 (Common salt}. 
 This is the most important of all sodium compounds, and also is the 
 material from which the other compounds are directly or indirectly 
 obtained. Common table-salt frequently contains small quantities 
 of calcium and magnesium chlorides, the presence of which causes 
 absorption of moisture, as these compounds are hygroscopic, while 
 pure sodium chloride is not. 
 
 In the animal system, sodium chloride is found in all parts, it 
 being of great importance in aiding the absorption of albuminoid 
 substances and the phenomena of osmose; also by furnishing, 
 through decomposition, the hydrochloric acid of the gastric juice. 
 
 Sodium chloride is soluble in 2.8 parts of cold water, and in 2.5 
 parts of boiling water ; almost insoluble in alcohol ; it crystallizes in 
 cubes and has a neutral reaction. 
 
 Sodium hydroxide, Sodii hydroxidum, NaOH 39.76 (Caustic 
 soda), may be obtained by the processes mentioned for potassium 
 hydroxide, which compound it closely resembles in its chemical and 
 most of its physical properties. 
 
 Experiment 22. Examine the consistency and lustre of sodium metal by 
 cutting a piece the size of a pea. (Do not get water on it while handling it. 
 Why ?) Throw small chips of the metal into a little water in a porcelain dish. 
 When all the metal has disappeared, taste the solution and test its action on 
 red litmus. Add dilute hydrochloric acid to slight acid reaction and evaporate 
 to dryness. Taste the residue. What is it ? Explain all that took place and 
 write reactions. 
 
SODIUM. 263 
 
 Sodium peroxide, Na 2 2 . is now extensively used as a bleaching and ox- 
 idi/ing agent. It is a white or yellowish-white powder, readily decomposed by 
 water into sodium hydroxide and oxygen; when dissolved in a dilute acid, 
 hydrogen peroxide is formed. It is made by heating sodium in a current of 
 oxygen. When it is brought in contact with water or dilute acids, great care 
 must be taken to have a low temperature, else violent action will take place, 
 with evolution of oxygen. 
 
 Sodium carbonate, Na 2 CO 3 .10H 2 O (Washing soda, Sal sodce). 
 This compound is, of all alkaline substances, the one manufactured in 
 the largest quantities, being used in the manufacture of many highly 
 important articles, as, for instance, soap, glass, etc. 
 
 Sodium carbonate is made, according to Leblanc's process, from 
 the chloride by first converting it into sulphate (salt-cake) by the 
 action of sulphuric acid : 
 
 2NaCl + H 2 S0 4 == 2HC1 + Na 2 SO 4 
 
 The escaping vapors of hydrochloric acid are absorbed in water, 
 and this liquid acid is used largely in the manufacture of bleaching- 
 powder. The sodium sulphate is mixed with coal and limestone 
 (calcium carbonate) and the mixture heated in reverberatory furnaces, 
 when decomposition takes place, calcium sulphide, sodium carbonate, 
 and carbonic oxide being formed : 
 
 Na 2 SO 4 + 40 + CaCO 3 = CaS + Na,CO 8 + 4CO 
 
 The resulting mass, known as black-ash, is washed with water, 
 which dissolves the sodium carbonate, while calcium sulphide enters 
 into combination with calcium oxide, thus forming an insoluble 
 double compound of oxy-sulphide of calcium. 
 
 The liquid obtained by washing the black-ash, when evaporated 
 to dryness, yields crude sodium carbonate, or " soda ash" ; when this 
 is dissolved and crystallized it takes up ten molecules of water, 
 forming the ordinary washing soda. 
 
 Sodium carbonate is manufactured also by the so-called ammonia 
 process, or the Solvay process. This depends on the decomposition 
 of sodium chloride by ammonium bicarbonate under pressure, when 
 sodium bicarbonate and ammonium chloride are formed, thus : 
 
 NaCl + NH 4 HCO 3 = NH 4 C1 + NaHCO 3 . 
 
 
 
 The sodium acid carbonate thus obtained is converted into carbo- 
 nate by heating : 
 
 2NaHCO, == Na 2 CO 3 + H 2 O + CO 2 . 
 
 The carbon dioxide obtained by this action is caused to act upon 
 ammonia, liberated from the ammonium chloride, obtained as one of 
 
264 METALS AND THEIR COMBINATIONS. 
 
 the products in the first reaction. Ammonium bicarbonate is thus 
 regenerated and used in a subsequent operation for the decomposition 
 of common salt. 
 
 Sodium carbonate has strong alkaline properties ; it is soluble in 
 1.6 parts of cold water, and in much less water at higher temper- 
 atures ; the crystals lose water on exposure to the air, falling into a 
 white powder; heat facilitates the expulsion of the water of crys- 
 tallization, and is applied in making the monohydrated sodium car- 
 bonate, Sodii carbonas monohydras, Na 2 CO 3 .H 2 O = 123.19, which 
 should contain about 85 per cent, of anhydrous sodium carbonate. 
 
 Sodium bicarbonate, Sodii bicarbonas, NaHCO 3 = 83.43 (Bak- 
 ing-soda). Obtained, as stated in the previous paragraph, by the 
 ammonia-soda process. It can also be made by passing carbon 
 dioxide over monohydrated sodium carbonate. 
 
 Na,CO 3 .H 2 O + CO 2 = = 2NaHCO 3 . 
 
 It is a white powder, having a cooling, mildly saline taste, and a 
 slightly alkaline reaction. Soluble in 12 parts of cold water and 
 insoluble in alcohol. It is decomposed by heat or by hot water into 
 sodium carbonate, water, and carbon dioxide. 
 
 Sodium bicarbonate is a constituent of the various baking-powders, the action 
 of which depends on the gradual liberation of carbon dioxide in the dough. 
 This is brought about through a second constituent, generally an acid salt such 
 as potassium bitartrate or calcium acid phosphate, which decomposes the 
 bicarbonate. 
 
 Sodium sulphate, Sodii sulphas, Na 2 SO 4 lOH 2 O = 319.91 (Glau- 
 ber's salt). Made, as mentioned above, by the action of sulphuric acid 
 on sodium chloride, dissolving the salt thus obtained in water, and crys- 
 tallizing. Large, colorless, transparent crystals, rapidly efflorescing 
 on exposure to air. Soluble in 2.8 parts of water at 15 C. (59 F.). 
 in 0.25 part at 34 C. (93 F.), and in 0.47 part of boiling water. 
 
 Experiment 23. Dissolve about 10 grammes of crystallized sodium carbonate 
 in 10 c.c. of hot water, add to this solution dilute sulphuric acid until all effer- 
 vescence ceases and the reaction on litmus-paper is exactly neutral. Evaporate 
 to about 20 c.c., and set aside for crystallization. Explain the action taking 
 place, and state how much H 2 S0 4 , and how much of the diluted sulphuric 
 acid, U. S. P., are needed for the decomposition of 10 grammes of crystallized 
 sodium carbonate. 
 
 Sodium sulphite, Sodii sulphis, Na 2 SO 3 .7H 2 O -- = 25O.39. 
 Sodium bisulphite, Sodii bisulphis, NaHSO 3 = 1O3.35. By 
 
SODIUM. 265 
 
 saturating a cold solution of sodium carbonate with sulphur dioxide, 
 sodium bisulphite is formed, and separates in opaque crystals : 
 
 Na-jCOg -f 2SO 2 + H 2 O = 2NaHSO 3 -f CO 2 . 
 
 If to the sodium bisulphite thus obtained a quantity of sodium car- 
 bonate be added, equal to that first employed, the normal salt is formed : 
 2NaHSO 3 -(- Na. 2 CO 3 = 2NaaSO s + H 2 O + CO 2 . 
 
 Sodium thiosulphate, Sodium hyposulphite, Sodii thiosul- 
 phas, Na 2 S 2 O 3 .5H 2 O = 246.46. Made by digesting a solution of 
 sodium sulphite with powdered sulphur, when combination slowly 
 takes place : 
 
 Na 2 S0 3 + S : Na 2 SA- 
 
 It is used under the name of " h^po " in photography to dissolve 
 chloride, bromide, or iodide of silver. 
 
 Sodium phosphate, Sodii phosphas, Na 2 HPO 4 .12H 2 O 355.61, 
 is made from calcium phosphate by the action of sulphuric acid, which 
 removes two-thirds of the calcium, forming calcium sulphate, while 
 acid phosphate of calcium is formed and remains in solution : 
 
 Ca 3 (PO 4 ) 2 + 2H 2 S0 4 = 2CaSO 4 -f CaH 4 (PO 4 ) 2 . 
 
 The solution is filtered and sodium carbonate added, when calcium 
 phosphate is precipitated, phosphate of sodium, carbon dioxide, and 
 water being formed : 
 
 CaH 4 (P0 4 ) 2 + Na 2 CO 8 = CaHPO 4 -f H 2 O + CO 2 -f N^HPO,. 
 
 The filtered and evaporated solution yields crystals of sodium 
 phosphate, which have a slightly alkaline reaction to litmus, but not 
 to phenol-phthalein. 
 
 By exposure of the crystallized sodium phosphate to warm air its water of 
 crystallization is expelled and the dry salt is Exsiccated sodium phosphate, 
 Sodii phosphas exsiccatus. This salt, when mixed with the proper quantities 
 of sodium bicarbonate and tartaric and citric acids, is official under the name 
 of Effervescent sodium phosphate, Sodii phosphas effervescens. 
 
 Experiment 24. Mix thoroughly 30 grammes of bone-ash with 10 c.c. of 
 sulphuric acid, let stand for some hours, add 20 c.c. of water, and again set 
 aside for some hours. Mix with 40 c.c. of water, heat to the boiling-point, and 
 filter. The residue on the filter is chiefly calcium sulphate. To the hot filtrate 
 of calcium acid phosphate add concentrated solution of sodium carbonate until 
 a precipitate ceases to form and the liquid is faintly alkaline, filter, evaporate, 
 and let crystallize. 
 
 Sodium pyrophosphate, Sodii pyrophosphas, Na 4 P 2 O 7 .lOH 2 O = 
 443.O2. When exsiccated sodium phosphate is heated to a low red 
 
266 METALS AND THEIR COMBINATIONS. 
 
 heat it loses water, and is converted into pyrophosphate, which, dis- 
 solved in hot water and crystallized, forms the official salt. The 
 chemical change taking place is this : 
 
 2(Na 2 HP0 4 ) Na 4 P 2 7 + H 2 O. 
 
 The normal sodium phosphate, Na 3 PO 4 , is known also, but it is not a very 
 stable compound, being acted upon even by the moisture and carbon dioxide 
 of the air, with the formation of sodium carbonate and disodium hydrogen 
 phosphate, thus : 
 
 H 2 + C0 2 = 
 
 Sodium nitrate, Sodii nitras, NaNO 3 = 84.45 (Chile saltpeter, 
 Cubic niter). Found in nature, and is purified by crystallization. 
 The crystals are transparent, deliquescent, and readily soluble. 
 
 Sodium nitrite, Sodii nitris, NaNO 2 = 68.57, is formed by heating the nitrate 
 to a sufficiently high temperature to expel one-third of the oxygen ; or, better, 
 by treating the fused nitrate with metallic lead, which latter is converted into 
 oxide. The sodium nitrite which is formed is dissolved and purified by crystal- 
 lization. 
 
 Sodium borate, Sodii boras, Na 2 B 4 O 7 .lOH 2 O = 379.32 (Borax). 
 This salt occurs in Clear Lake, Nevada, and in several lakes in Asia. 
 It is manufactured by adding sodium carbonate to the boric acid 
 found in Tuscany, Italy. It forms colorless, transparent crystals, 
 but is sold mostly in the form of a white powder. It is slightly 
 efflorescent, is soluble in 16 parts of cold, and in 0.5 part of boiling 
 water ; insoluble in alcohol, but soluble in one part of glycerin at 
 80 C. (176 F.). When heated, borax puffs up, loses water of 
 crystallization, and at red heat it melts, forming a colorless liquid 
 which, on cooling, solidifies to a transparent mass, known as fused 
 borax, or borax glass. Molten borax has the power to combine with 
 metallic oxides, forming double borates, some of which have a char- 
 acteristic color, for which reason borax is used in blow-pipe analysis. 
 Borax has antiseptic properties, preventing the decomposition of some 
 organic substances. 
 
 A solution of borax is alkaline and has no action on carbonates or bicarbon- 
 ates, but if an equal volume of glycerin is added to the solution, it becomes 
 strongly acid and decomposes carbonates and bicarbonates with effervescence. 
 This behavior has an important bearing in prescription writing. On diluting 
 the glycerin mixture strongly with water, the alkaline reaction returns. 
 
 Other sodium salts which are official are sodium hypophosphite, 
 NaPH 2 O 2 + H 2 O; bromide, NaBr; iodide, Nal ; chlorate, NaClO 3 . 
 
SODIUM. 267 
 
 These salts may be obtained by processes analogous to those given 
 for the corresponding potassium compounds. 
 
 Sodium compounds are nearly all white and are not volatile at or 
 below a red heat. 
 
 Tests for sodium. 
 
 (Sodium chloride, NaCl, may be used.) 
 
 1. As all salts of sodium are soluble in water, we cannot precipi- 
 tate this metal in the form of a compound by any of the common 
 reagents. (Potassium antimoniate precipitates neutral solution of 
 sodium salts, but this test is not reliable.) 
 
 2. The chief reaction for sodium is the flame-test, compounds of 
 sodium imparting to a colorless flame a yellow color, which is very 
 intense. A crystal of potassium dichromate appears colorless, and a 
 paper coated with red mercuric iodide appears white when illuminated 
 by the yellow sodium flame. (The spectroscope shows a characteristic 
 yellow line.) 
 
 As practically all substances contain a trace of some sodium com- 
 pound, and give a momentary sodium flame, the yellow flame can only 
 be used to judge the presence of an actual sodium compound when 
 it persists for a long time. 
 
 Lithium, Li = 6.98. Found in nature in combination with silicic acid in 
 a few rare minerals or as a chloride in some spring waters. Of inorganic 
 salts, lithium bromide and carbonate are official. Hydroxide, carbonate, and 
 phosphate of lithium are much less soluble than the corresponding com- 
 pounds of potassium and sodium. Sodium phosphate added to a strong solu- 
 tion of a lithium salt produces, on boiling, a white precipitate of lithium 
 phosphate, Li 3 PO 4 . Lithium compounds color the flame a beautiful crimson 
 or carmine-red. 
 
 LiOH is soluble in 14.5 parts of water at 20 C., Li 2 CO 3 in 75 parts at 20 C., 
 and 140 parts of boiling water, Li 3 PO 4 in 2540 parts of plain water and 3920 
 parts of ammoniacal water. 
 
 Caesium, Cs, and Rubidium, Rb, occur widely distributed, but only in 
 small quantities, and generally in company with potassium, which they resem- 
 
 QUESTIONS. What is the composition of common salt ; how is it found in 
 nature, and what is it used for? Describe Leblanc's and the Solvay process 
 for manufacturing sodium carbonate on a large scale. How much water is in 
 100 pounds of the crystallized sodium carbonate ? What is Glauber salt, and 
 how is it made ? State the composition of disodium hydrogen phosphate, and 
 how is it prepared from calcium phosphate? What difference exists between 
 sodium carbonate and bicarbonate both in regard to physical and chemical 
 properties? Give the composition of sodium thiosulphate; what is it used for? 
 Which sodium salts are. soluble, and which are insoluble? How does sodium 
 and how does lithium color the flame? Which lithium salts are official? 
 
268 METALS AND THEIR COMBINATIONS. 
 
 ble closely. Kubidium occurs in carnallite of the Stassfurt beds, and is obtained 
 as rubidium alum, from the mother-liquors after the potassium chloride is 
 crystallized out. Csesium takes fire in air at the ordinary temperature, and it 
 is the most electropositive of all metals. Kubidium takes fire in air and decom- 
 poses water with greater energy than does potassium, the hydroxide formed, 
 Rb(OH), having even stronger basic properties than potassium hydroxide. 
 Both rubidium and caesium have a marked power of forming double salts. All 
 the salts are white and soluble in water. Probably the one most often used 
 medicinally is ccesium-rubidium-ammonium bromide, (CsEb)Br 2 .3NH 4 Br. Rubid- 
 ium bromide, RbBr, and iodide, Rbl, have been recommended as substitutes for 
 the corresponding potassium salts. Cesium bromide, CsBr, has also been used. 
 
 23. AMMONIUM. 
 NH^IS (17.93). 
 
 General remarks. The salts of ammonium show so much resem- 
 blance, both in their physical and chemical properties, to those of the 
 alkali-metals, that they may be studied most conveniently at this 
 place. 
 
 The compound radical NH 4 acts in these ammonium salts very 
 much like one atom of an alkali-metal, and, therefore, frequently has 
 been looked upon as a compound metal. The physical metallic prop- 
 erties (lustre, etc.) of ammonium cannot be fully demonstrated, as it 
 is not capable of existing in a separate or free state. There is known, 
 however, an alloy of ammonium and mercury, which may be obtained 
 by dissolving potassium in mercury, and adding to the potassium- 
 amalgam thus formed, a strong solution of ammonium chloride, when 
 potassium chloride and ammonium-amalgam are formed. The latter 
 is a soft, spongy, metallic-looking substance, which readily decomposes 
 into mercury, ammonia, and hydrogen : 
 
 HgK + NH 4 C1 = KC1 + NH 4 Hg; 
 NH 4 Hg = NH 3 + H + Hg. 
 
 The source of all ammonium compounds is ammonia NH 3 , or am- 
 monium hydroxide, NH 4 OH, both of which have been considered 
 heretofore. 
 
 A solution of ammonia has much weaker basic properties than a solution 
 of sodium or potassium hydroxide has. In a normal solution (about 1.7 per 
 cent.) only about 0.4 per cent, of the ammonia molecules are dissociated into 
 NH 4 - and (OH) / ions. There is much free NH 3 , besides the NH 4 OH which 
 results from union of NH 3 with water. It is only the ionized portion of the 
 NH 4 OH which shows basic properties. 
 
 The ionic equation for the neutralization of ammonia water with an acid is 
 this: 
 
 NH 4 -,-f OH' + H- + d' -> NH 4 - + Cl' + H 2 O. 
 As fast as (OH) 7 and H' ions unite to form water, more NH 4 OH dissociates 
 
AMMONIUM. 269 
 
 and more NH 3 unites with water to form NH 4 OH until the reaction is com- 
 plete. All ammonium salts are highly dissociated in dilute solutions. 
 
 The reverse of the above action, namely, the liberation of ammonia from its 
 salts by an alkali, is discussed from the ionic point of view on page 194. 
 
 Ammonium chloride, Ammonii chloridum, NH 4 C1~ 53.11 (Sal- 
 ammoniac). Obtained by saturating the "ammoniacal liquor" of the 
 gas-works with hydrochloric acid, evaporating to dryness, and puri- 
 fying the crude article by sublimation. 
 
 Pure ammonium chloride either is a white, crystalline powder, or 
 occurs in the form of long, fibrous crystals, which are tough and 
 flexible ; it has a cooling, saline taste ; is soluble in 2 parts of cold, 
 and in 1 part of boiling water; and, like all ammonium compounds, 
 is completely volatilized by heat. 
 
 Carbamic acid, CO.NH 2 .OH. This acid may be looked upon as carbonic 
 acid, CO.(OH) 2 , in which one of the hydroxyl groups is replaced by NH^ The 
 ammonium salt of this acid, CO.NH. 2 .ONH 4 , is formed when dry ammonia gas 
 and dry carbon dioxide are brought together, direct combination taking place, 
 
 thus: 
 
 NH 2 
 CO 2 + 2NH 3 = CO( 
 
 \ONH 4 
 
 Ammonium carbonate, Ammonii carbonas, NH 4 HCO 3 .NH 4 
 NH 2 CO 2 = 156. Ol (Ammonium sesquicarbonate, sal volatile, Preston 
 salt). Commercial ammonium carbonate is not the normal salt, but, 
 as shown by the above formula, a combination of acid ammonium 
 carbonate with ammonium carbamate. It is obtained by sublimation 
 of a mixture of ammonium chloride and calcium carbonate, when 
 calcium chloride is formed, ammonia gas and water escape, and am- 
 monium carbonate condenses in the cooler part of the apparatus : 
 
 2CaC0 3 + 4NH 4 C1 = NH 4 HCO 3 NH 4 NH 2 CO 2 + 2CaCl 2 + H 2 O + NH 3 . 
 
 Ammonium carbonate thus obtained forms white, translucent masses, losing 
 both ammonia and carbon dioxide on exposure to the air, becoming opaque, 
 and finally converted into a white powder of acid ammonium carbonate. 
 
 NH 4 HCO 3 NH 4 NH 2 CO 2 = NH 4 HCO 3 + 2NH 3 -f CO 2 . 
 
 When commercial ammonium carbonate is dissolved in water the carbamate 
 unites with one molecule of water, forming normal ammonium carbonate. 
 
 NH 4 NH 2 CO 2 + H 2 O = (NH 4 ) 2 C0 8 . 
 
 A solution of the common ammonium carbonate in water is, consequently, a 
 liquid containing both acid and normal carbonate of ammonium ; by the addi- 
 tion of some ammonia water the acid carbonate is converted into the normal 
 salt. The solution thus obtained is used frequently as a reagent. 
 
 The Aromatic spirit of ammonia is a solution of normal ammonium carbonate 
 in diluted alcohol to which some essential oils have been added. 
 
270 METALS AND THEIR COMBINATIONS. 
 
 Ammonium sulphate, (NH 4 ) 2 SO 4 , Ammonium nitrate, NH 4 NO 3 , 
 and Ammonium phosphate, (NH 4 ) 2 HPO 4 , may be obtained by the 
 addition of the respective acids to ammonia water or ammonium 
 carbonate : 
 
 H 2 S0 4 + 2NH 4 OH = (NH 4 ) 2 S0 4 -f 2H 2 O. 
 HNO 3 + NH 4 OH = NH 4 NO 3 -f H 2 O. 
 H 3 P0 4 + 2NH 4 OH = (NH 4 ) 2 HP0 4 + 2H 2 O. 
 H 2 S0 4 -f (NH 4 ) 2 C0 3 = (NH 4 ) 2 S0 4 + H 2 O + CO a . 
 
 Ammonium iodide, Ammonii iodidum, NH 4 I, and Ammonium 
 bromide, Ammonii bromidum, NH 4 Br, may be obtained by mixing 
 together strong solutions of potassium iodide (or bromide) and am- 
 monium sulphate, and adding alcohol, which precipitates the potas- 
 sium sulphate formed ; by evaporation of the solution the ammonium 
 iodide (or bromide) is obtained : 
 
 2KI + (NH 4 ) 2 SO 4 = 2NH 4 I -f K 2 SO 4 ; 
 2KBr + (NH 4 ) 2 S0 4 = 2NH 4 Br 
 
 Another mode of preparing these compounds is by the decomposi- 
 tion of ferrous bromide (or iodide) by ammonium hydroxide : 
 FeBr 2 + 2NH 4 OH = 2NH 4 Br + Fe(OH) 2 . 
 
 Ammonium iodide is the principal constituent of the Decolorized 
 tincture of iodine. 
 
 Ammonium hydrogen sulphide, NH 4 SH (Ammonium hydro- 
 sulphide, Ammonium sulphydrate). Obtained by passing hydrogen 
 sulphide through ammonia water until this is saturated : 
 
 H 2 S + NH 4 OH = NH 4 SH 4- H 2 O. 
 
 The solution thus obtained is, when recently prepared, a colorless 
 liquid, having the odor of both ammonia and of hydrogen sulphide ; 
 when exposed to the air it soon assumes a yellow color. This behavior 
 is characteristic of the soluble hydrosulphides in general, and is due 
 to the liberation of sulphur by oxidation, thus : 
 
 NH 4 SH + O = NH 4 OH + S. 
 
 The sulphur combines with undecomposed hydrosulphide, forming 
 polysulphides, which are yellow. The normal sulphide, (NH 4 ) 2 S, can 
 be obtained in the solid state, but it quickly loses half of its ammonia 
 and forms hydrosulphide. In solution it is almost completely hydro- 
 lyzed, thus : 
 
 (NH 4 ) 2 S + H 2 ^ NH 4 OH + NH 4 SH. 
 A mixture corresponding to the normal sulphide is obtained by add- 
 
AMMONIUM. 271 
 
 ing to a solution of the hydrosulphide, prepared as above, an equiva- 
 lent amount of ammonia water. 
 
 These solutions can easily be freed from the sulphide by boiling. Both sub- 
 stances, the ammonium hydrogen sulphide and ammonium sulphide, are valu- 
 able reagents, frequently used for precipitation of certain heavy metals, or for 
 dissolving certain metallic sulphides. (See under Hydrogen Sulphide.). 
 
 Tests for ammonium compounds. 
 
 (Ammonium chloride, NH 4 C1, may be used.) 
 
 1. Ammonium salts give the same form of precipitates as potas- 
 sium with solution of platinic chloride, sodium cobaltic nitrite, and 
 tartaric acid (see tests for potassium). 
 
 2. All compounds of ammonium are volatilized below or at a low 
 red heat, either with or without decomposition (see preparation of 
 nitrogen and nitrogen monoxide in chapter on Nitrogen). If the 
 acid constituent of the salt is volatile and not decomposed by heat, 
 the salt volatilizes without decomposition. 
 
 Heat with a small flame a little ammonium chloride in a covered 
 porcelain crucible. The salt sublimes upon the sides and cover of 
 the crucible. 
 
 3. The best test and one which is sufficient for recognition of any 
 ammonium compound is to heat a mixture of it and slaked lime or 
 strong alkali in a tube. Ammonia gas is liberated, which may be 
 recognized by its odor and action on red litmus-paper, and by causing 
 dense white fumes when a rod, moistened with strong hydrochloric 
 acid, is held in the mouth of the tube. 
 
 All commonly occurring ammonium salts are colorless, soluble in 
 water, and odorless, with the exception of the carbonate and sulphide. 
 Traces of ammonium compounds are detected by Nessler's 
 
 QUESTIONS. What is ammonium, and why is it classed with the alkali- 
 metals? Is ammonium known in a separate state? What is ammonium- 
 amalgam, how is it obtained, and what are its properties? What is the source 
 of ammonium compounds? State the composition, mode of preparation, and 
 properties of sal ammoniac. How is ammonium carbonate manufactured, and 
 what difference exists between the solid article and its solution ? State the 
 composition of ammonium sulphide and of ammonium hydrogen sulphide ; 
 how are they made, and what are they used for? By what process may ammo- 
 nium sulphate, nitrate, and phosphate be obtained from ammonium hydroxide 
 or ammonium carbonate, and what chemical change takes place ? How does 
 heat act upon ammonium compounds? Give analytical reactions for ammo- 
 nium salts. 
 
272 
 
 METALS 'AND THEIR COMBINATIONS. 
 
 solution (see Index), which causes a reddish-brown precipitate or 
 coloration. (See under Water Analysis, end of chapter 38.) 
 
 Summary of analytical characters of the alkali-metals. 
 
 
 Potassium. 
 
 /Sodium. 
 
 Lithium. 
 
 Ammonium. 
 
 Sodium cobaltic nitrite . . 
 Platinic chloride .... 
 Sodium bitartrate . . . 
 Sodium phosphate . . . 
 
 Sodium hydroxide . . . 
 Action of heat .... 
 
 Yellow pre- 
 cipitate. 
 Yellow pre- 
 cipitate. 
 White preci- 
 pitate. 
 
 
 
 Yellow pre- 
 cipitate. 
 Yellow pre- 
 cipitate. 
 White preci- 
 pitate. 
 
 
 
 
 
 
 White preci- 
 pitate in cone, 
 solution on 
 boiling. 
 
 
 
 Ammonia 
 gas. 
 Volatile. 
 
 Fusible. 
 Violet. 
 
 Fusible. 
 Yellow. 
 
 Fusible. 
 Crimson. 
 
 
 
 24. MAGNESIUM. 
 Mg 11 = 24.18. 
 
 General remarks. Magnesium occupies a position intermediate 
 between the alkali metals and the alkaline earths. To some extent 
 it resembles also the heavy metal zinc, with which it has in common 
 the volatility of the chloride, the solubility of the sulphate, and the 
 isomorphism of several of its compounds with the analogously con- 
 stituted compounds of zinc. 
 
 Occurrence in nature. Magnesium is widely diffused in nature, 
 and several of its compounds are found in large quantities. It occurs 
 as chloride and sulphate in many spring waters and in the salt-mines 
 at Stassfurt; as carbonate in the mineral magnesite; as double car- 
 bonate of magnesium and calcium in the mineral dolomite (magnesian 
 limestone), which forms entire mountains ; as silicate of magnesium 
 in the minerals serpentine, meerschaum, tale, asbestos, soapstone, etc. 
 
 Metallic magnesium may be obtained by the decomposition of 
 magnesium chloride by sodium ; but is now made in large quantities 
 by electrolysis of the molten double chloride of magnesium and 
 potassium, MgCl 2 .KCl. The furnace used for the operation is shown 
 in Fig. 31, page 80. 
 
 Magnesium is an almost silver-white metal, losing its lustre rap- 
 idly in moist air by oxidation of the surface. It decomposes hot 
 
MAGNESIUM. 273 
 
 water with liberation of hydrogen ; and when heated to a red 
 heat burns with a brilliant bluish-white light, which is extensively 
 used for photographic purposes. 
 
 Magnesium carbonate, Magnesii carbonas. Approximately : 
 (MgC0 3 ) 4 .Mg(OH) 2 .5H,0 == 482.26 (Magnesia alba). The normal 
 magnesium carbonate, MgCO 3 , is found in nature, but the official 
 preparation contains carbonate, hydroxide, and water. It is ob- 
 tained by boiling a solution of magnesium sulphate with solution 
 of sodium carbonate, when the carbonate is precipitated, some carbon 
 dioxide evolved, and sodium sulphate remains in solution: 
 
 5MgSO 4 + SN^COg + 6H 2 O == (MgCO 3 ) 4 Mg(OH) 2 5H 2 O + 5Na 2 SO 4 + CO 3 . 
 
 By filtering, washing, and drying the precipitate, it is obtained in 
 the form of a white, light powder. 
 
 Experiment 25. Dissolve 10 grammes of magnesium sulphate in hot water 
 and add a concentrated solution of sodium carbonate until no more precipitate 
 is formed. Collect the precipitated magnesium carbonate on a filter and dry it 
 at a low temperature. (How much crystallized sodium carbonate is needed 
 for the decomposition of 10 grammes of crystallized magnesium sulphate?) 
 Notice that the dried precipitate evolves carbon dioxide when heated with 
 acids. 
 
 Magnesium oxide, Mag-nesii oxidum, MgO 40.O6 (Calcined 
 magnesia), is obtained by heating light magnesium carbonate in a 
 crucible to a full red heat, when all carbon dioxide and water are 
 expelled : 
 
 (MgC0 3 ) 4 .Mg(OH) 2 .5H 2 O = 5MgO -f 4CO 2 + 6H 2 O. 
 
 It is a very light, amorphous, white, almost tasteless powder, which 
 absorbs moisture and carbon dioxide gradually from the air; in con- 
 tact with water it forms the hydroxide Mg(OH) 2 , which is almost 
 insoluble in water, requiring of the latter over 50,000 parts for solu- 
 tion. Milk of magnesia is the hydroxide suspended in water (1 part 
 in about 15). 
 
 Heavy magnesium oxide, magnesii oxidum ponderosum, differs from the com- 
 mon or light magnesia, not in its chemical composition, but merely in its 
 physical condition, being denser and heavier. 
 
 Experiment 26. Place 1 gramme of magnesium carbonate, obtained in per- 
 forming Experiment 25, into a weighed crucible and heat to redness, or until 
 by further heating no more loss in weight ensues. Treat the residue with 
 dilute hydrochloric acid and notice that no evolution of carbon dioxide takes 
 place. What is the calculated loss in weight of magnesium carbonate when 
 converted into oxide, and how does this correspond with the actual loss deter- 
 mined by the experiment? 
 18 
 
274 NON-METALS AND THEIR COMBINATIONS. 
 
 Magnesium sulphate, Magnesii sulphas, MgSO 4 .7H 2 O = 244.69 
 (Epsom salt), is obtained from spring waters, from the mineral 
 Kieserite, MgSO r H 2 O, and by decomposition of the native carbonate 
 by sulphuric acid : 
 
 MgC0 3 + H 2 SO 4 = MgS0 4 + C0 2 + H 2 O. 
 
 It forms colorless crystals, which have a cooling, saline, and bitter 
 taste, a neutral reaction, and are easily soluble in water. 
 
 Effervescent magnesium sulphate, Magnesii sulphas efferves- 
 cens, is a granular mixture of magnesium sulphate, sodium bicarbonate, tar- 
 taric and citric acids, in proper proportions. It contains what is equal to 50 
 per cent, of crystallized magnesium sulphate, and, like all effervescent salts, 
 gives off carbonic acid when dissolved, which makes it more palatable. 
 
 Magnesium nitride, Mg 3 N 2 , is obtained as a yellow, porous mass by 
 heating magnesium to red heat in nitrogen. With water it forms magnesium 
 hydroxide and ammonia, thus : 
 
 Mg 3 N 2 + 6H 2 = 3Mg(OH) 2 + 2NH 3 , 
 
 Remarks on tests for metals. Many of the tests for magnesium 
 and the metals to follow have already been before us when discuss- 
 ing the acids. They involve reactions of double decomposition, re- 
 sulting in the formation of an insoluble product. The solubilities of 
 the different classes of salts, such as chlorides, carbonates, sulphates, 
 etc., have been stated under the various acids, and the student, by 
 keeping these facts in mind, will be able to anticipate many of the 
 tests enumerated under the metals. Some of these are not distinctive 
 at all, but simply corroborative, because two or more metals may re- 
 spond to the same test. For example, to obtain a white precipitate 
 on adding a solution of sodium carbonate or phosphate to a solution 
 of a substance is no more a test for magnesium than for calcium, 
 strontium, barium, or any other metal whose carbonate or phosphate is 
 white and insoluble in water. In cases where distinctive tests are 
 lacking, a systematic procedure of elimination is followed. This is 
 known as qualitative analysis. 
 
 The solubilities of the classes of salts and the different methods 
 of producing salts have been mentioned, and something has been 
 said in this respect about the two classes of compounds of metals 
 known as oxides and hydroxides. In regard to solubility in water, 
 the oxides and hydroxides are very much alike : that is, if a hydrox- 
 ide is soluble, the corresponding oxide is also soluble, and vice versa. 
 The hydroxides of the common metals that are soluble in water are 
 those of potassium, sodium, lithium, barium, strontium, and the hypo- 
 
M AGNES fUM. 275 
 
 thetical metal, ammonium. Calcium hydroxide is slightly soluble, 
 less than calcium sulphate, but sufficiently soluble to be employed as 
 a reagent. Hydroxides of the other metals are either insoluble or so 
 little soluble as to be classed insoluble. These are obtained as pre- 
 cipitates by adding a soluble hydroxide (usually of sodium, potas- 
 sium, or ammonium) to a salt of the metals whose hydroxides are in- 
 soluble. The principle involved here is the same as in the case of 
 precipitation of insoluble carbonates, namely, bringing together in 
 solution constituents which by their union can form insoluble prod- 
 ucts and thus be eliminated from the solution, thereby allowing the 
 reaction to go on to completion. This reaction is given as a test under 
 many of the metals. 
 
 Ammonium hydroxide acts, in general, like the alkalies, but 
 toward certain metals it shows a marked difference. For example, 
 calcium hydroxide is precipitated from fairly concentrated solutions 
 of calcium salts by the alkalies, but not by ammonia water. This is 
 explained by the ionic or dissociation theory by the fact that ammo- 
 nium hydroxide is only slightly dissociated. According to this 
 theory, practically all reactions in aqueous solutions take place be- 
 tween ions (see page 195). The alkalies are largely dissociated into 
 metal ions and (OH) ions, which latter unite with the metal ions of 
 the other metals to form the slightly ionized and insoluble hydrox- 
 ides. Now ammonium hydroxide is only slightly ionized in fact, 
 to a less extent than calcium hydroxide so that only a small amount 
 of calcium hydroxide is formed, which remains in solution, because 
 somewhat soluble. The presence of this calcium hydroxide in solu- 
 tion prevents further ionization of the ammonium hydroxide to such 
 an extent that it ceases to act as an alkali or soluble hydroxide. In 
 fact, the slight ionization of ammonium hydroxide accounts for the 
 reverse action, namely, the liberation of ammonia from its salts by 
 the action of calcium hydroxide. 
 
 In the presence of ammonium salts, ammonium hydroxide ionizes 
 only to a very slight extent, so that it loses almost all the character 
 of a hydroxide as far as precipitating other metallic hydroxides is 
 concerned, only the extremely insoluble ones being precipitated. 
 This accounts for the fact that magnesium hydroxide is not precipi- 
 tated by ammonia water when ammonium salts are present. The 
 magnesium hydroxide, although being nearly insoluble, is sufficiently 
 soluble and ionizable not to be precipitated by ammonia water under 
 these conditions. Alkalies, on the other hand, precipitate magnesium 
 hydroxide copiously, because they are almost completely ionized in 
 
276 METALS AND THEIR COMBINATIONS. 
 
 dilute solutions, and thus act as strong bases, as we say. Ammonium 
 carbonate behaves very much like ammonia water toward magnesium 
 and some other metals. 
 
 Hydroxides of nearly all metals, when heated sufficiently, lose 
 water and give the oxide. Many oxides are prepared in this way. 
 Only a few oxides unite with water to form a hydroxide. One of the 
 best examples of this is the process of slaking lime. Oxides may 
 also be obtained by heating carbonates or nitrates, or directly from 
 the metals. The method followed in any particular case is deter- 
 mined by the properties of the metal, the question of economy, etc. 
 
 Tests for magnesium. 
 (Use the reagent solution of magnesium sulphate. ) 
 
 1. The addition of an alkali carbonate solution causes a white pre- 
 cipitate of basic magnesium carbonate (see Experiment 25). 
 
 2. Add to the solution some caustic alkali : a white precipitate of 
 magnesium hydroxide, Mg(OH) 2 , is formed, insoluble in excess of alkali. 
 
 Mg" + SO/' + 2Na' + 2(OH)' = Mg(OH), + 2Na' + SO/'. 
 
 3. Add to the solution ammonia water or ammonium carbonate : 
 part of the magnesium is precipitated as hydroxide or carbonate. 
 The latter is increased on heating. If an equal volume of ammo- 
 nium chloride solution is previously added, no precipitate is obtained 
 (for explanation, see Remarks on Tests above). 
 
 4. To the solution add an equal volume of solution of ammonium 
 chloride and some ammonia water. The mixture should be clear. 
 Then add sodium phosphate solution : a white, finely crystalline pre- 
 cipitate of the double salt, ammonium magnesium phosphate, is pro- 
 duced, which increases by shaking (see reactions under test 1 for 
 phosphoric acid). This is a delicate and decisive test for magnesium, 
 when other metals which resemble it are eliminated. This is easily 
 done by adding to a solution some chloride, sulphide, and carbonate 
 of ammonium, which will remove by precipitation all metals except 
 magnesium and alkali metals. 
 
 QUESTIONS. How is magnesium found in nature? By what process is 
 metallic magnesium obtained? Give the physical and chemical properties of 
 magnesium. State two methods by which magnesium oxide can be obtained. 
 What is calcined magnesia? State the composition and properties of the 
 official magnesium carbonate, and how it is made. What is Epsom salt, and 
 how is it obtained? Which compounds of magnesium are insoluble? Give 
 tests for magnesium compounds. How can the presence of magnesium be 
 demonstrated in a mixture of magnesium sulphate and sodium sulphate ? 
 
CALCIUM. 277 
 
 25. CALCIUM. STRONTIUM. BARIUM. 
 Ca" = 40 (39.81 ). Sr" = 86.94. Ba" = 136.4. 
 
 General remarks regarding the metals of the alkaline earths. 
 
 The three metals, calcium, barium, and strontium, form the second 
 group of light metals. Similar to the alkali-metals, they decompose 
 water at the ordinary temperature with liberation of hydrogen; their 
 separation in the elementary state is even more difficult than that of 
 the alkali-metals. 
 
 They differ from the latter by forming insoluble carbonates and 
 phosphates (those of the alkalies are soluble), from the earths by 
 their soluble hydroxides (those of the earths are insoluble), and from 
 all heavy metals by the solubility of their sulphides (those of heavy 
 metals are insoluble). ' The sulphates are either insoluble (barium) 
 or sparingly soluble (strontium and calcium). The hydroxides and 
 carbonates are decomposed by heat, water or carbon dioxide being 
 expelled and the oxides formed. In case of calcium carbonate this 
 decomposition takes place easily, while the carbonates of barium 
 and strontium require a much higher temperature. They are bivalent 
 elements. 
 
 Occurrence in nature. Calcium is one of the most abundantly 
 occurring elements. As carbonate (CaCO 3 ) it is found in the form 
 of calc-spar, limestone, chalk, marble, shells of eggs and mollusca, 
 etc., or, as acid carbonate, dissolved in water. The sulphate is found 
 as gypsum or alabaster, CaSO 4 2H 2 O; the phosphate, Ca 3 (PO 4 ) 2 , in 
 the different phosphatic rocks (apatite, etc.) ; the fluoride, CaF 2 , as 
 fluor-spar; the chloride, CaCl 2 , in some waters, and the silicate in 
 many rocks. It enters the vegetable and animal system in various 
 forms of combination, chiefly, however, as phosphate and sulphate. 
 
 Calcium oxide, Lime, Calx, CaO = 55.68 (Quick-lime, Burned 
 lime), is obtained on a large scale by the common process of lime- 
 burning, which is the heating of limestone or any other calcium car- 
 bonate to about 800 C. (1472 F.), in furnaces termed lime-kilns. 
 On a small scale decomposition may be accomplished in a suitable 
 crucible over a blowpipe flame : 
 
 CaCO 3 = CaO + CO 2 . 
 
 The pieces of oxide thus formed retain the shape and size of the 
 carbonate used for decomposition. 
 
 Lime is a white, odorless, amorphous, infusible substance, of alka- 
 
278 METALS AND THEIR COMBINATIONS. 
 
 line taste and reaction; exposed to the air it gradually absorbs 
 acid among acids, and is used directly or indirectly in many branches 
 of chemical manufacture. 
 
 Calcium hydroxide, Calcium hydrate, Ca(OH) 2 (Slaked lime). 
 When water is sprinkled upon pieces of calcium oxide, the two sub- 
 stances combine chemically, liberating much heat; the pieces swell 
 up, and are converted gradually into a dry, white powder, which is 
 the slaked lime. When this is mixed with water, the so-called milk 
 of lime is formed. 
 
 Freshly slacked lime, made into a thin paste with water and mixed with 3 
 to 4 times as much sand as lime used, forms the ordinary mortar, employed for 
 building purposes. The hardening of mortar is due first to loss of water, fol- 
 lowed by a gradual conversion of calcium hydroxide into carbonate. In the 
 course of years calcium silicate is also formed. 
 
 Lime-water, Liquor calcis (Solution of lime). This is a sat- 
 urated solution of calcium hydroxide in water : 10,000 parts of the 
 latter dissolving about 15 to 17 parts of hydroxide. In making 
 lime-water, 1 part of calcium oxide is slaked and agitated occasionally 
 during half an hour with 30 parts of water. The mixture is then 
 allowed to settle, and the liquid, containing besides calcium hydroxide 
 the salts of the alkali-metals which may have been present in the 
 lime, is decanted and thrown away. To the calcium hydroxide left, 
 and thus purified, 300 parts of water are added and occasionally 
 shaken in a well -stoppered bottle, from which the clear liquid may 
 be poured off for use. 
 
 Lime-water is a colorless, odorless liquid, having a feebly caustic 
 taste and an alkaline reaction. When heated to boiling it becomes 
 turbid by precipitation of calcium hydroxide (or perhaps oxide) which 
 re-dissolves when the liquid is cooled. Carbon dioxide causes a pre- 
 cipitation of calcium carbonate, soluble in an excess of carbonic acid. 
 
 Experiment 27. Make lime-water according to directions given above. 
 
 Calcium carbonate, Calcii carbonas praecipitatus, CaCO 3 = 
 99.35. Precipitated calcium carbonate is obtained as a white, taste- 
 less, neutral, impalpable powder by mixing solutions of calcium 
 chloride and sodium carbonate: 
 
 CaCl 2 + Na^CO, = 2NaCl + CaCO 3 . 
 
CALCIUM. 279 
 
 Experiment 28. Add to about 10 grammes of marble (calcium carbonate), in 
 small pieces, hydrochloric acid as long as effervescence takes place ; filter the 
 solution of calcium chloride thus obtained and add to it solution of sodium 
 carbonate as long as a precipitate is formed, collect the precipitate on a filter, 
 wash and dry it. 
 
 Dried calcium sulphate, Calcii sulphas exsiccatus, CaSO 4 =; 
 135.15 (Dried gypsum, Plaster-of-Paris, Calcined plaster). It has 
 been mentioned above that the mineral gypsum is native calcium 
 sulphate in combination with 2 molecules of water of crystallization, 
 By heating to about 115 C. (239 F.) about three-fourths of this 
 water is expelled, and a nearly anhydrous sulphate formed. This 
 article readily recombines with water, becoming a hard mass, for 
 which reason it is used for making moulds and casts, and in surgery. 
 If the gypsum is heated to a higher temperature than the one men- 
 tioned, all water is expelled, and the product thus obtained combines 
 with water but very slowly. 
 
 Precipitated calcium phosphate, Calcii phosphas preecipitatus, 
 Ca s( p 04)2 = 307.98 (Phosphate of lime). By dissolving bone-ash 
 (bone from which all organic matter has been expelled hy heat) in 
 hydrochloric acid, and precipitating the solution with ammonia water 
 there is obtained calcium phosphate, which contains traces of calcium 
 fluoride and magnesium phosphate. 
 
 A pure article is made by precipitating a solution of calcium 
 chloride by sodium phosphate and ammonia : 
 
 2Na 2 HPO 4 + 3CaCl 2 + 2NH 4 OH = Ca 3 (PO 4 ) 2 + 4NaCl + 2NH 4 C1 + 2H 2 O. 
 
 It is a white, tasteless, amorphous powder, insoluble in cold water, 
 soluble in hydrochloric or nitric acids. 
 
 Superphosphate, or acid phosphate of lime. Among the inorganic sub- 
 stances which serve as plant-food, calcium phosphate is a highly important 
 one. As this compound is found usually in very small quantities as a con- 
 stituent of the soil, and as this small quantity is soon removed by the various 
 crops taken from a cultivated soil, it becomes necessary to replace it in order 
 to enable the plant to grow and to form seeds. 
 
 For this purpose the various phosphatic rocks (chiefly calcium phosphate) 
 are converted into commercial fertilizers, which is accomplished by the addi- 
 tion of sulphuric acid to the ground rock. The sulphuric acid removes from 
 the tricalcium phosphate one or two atoms of calcium, forming mono- or 
 dicalcium phosphate and calcium sulphate. The mixture of these substances, 
 containing also the impurities originally present in the phosphatic rocks, is 
 sold as acid phosphate or superphosphate. 
 
 Bone-black and bone-ash. Phosphates enter the animal system 
 in the various kinds of food, and are to be found in every tissue and 
 
280 METALS AND THEIR COMBINATIONS. 
 
 fluid, but most abundantly in the bones and teeth. Bones contain 
 about 30 per cent, of organic and 70 per cent, of inorganic matter, 
 most of which is tricalcium phosphate. When bones are burned until 
 all the organic matter has been destroyed and volatilized, the result- 
 ing product is known as bone-ash. If, however, the bones are sub- 
 jected to the process of destructive distillation (heating with exclusion 
 of air), the organic matter suffers decomposition, many volatile 
 products escape, and most of the non-volatile carbon remains mixed 
 with the inorganic portion of the bones, which substance is known 
 as bone-black or animal charcoal, carbo animalis. It contains about 
 85 per cent, of inorganic matter, the balance being chiefly carbon. 
 
 Calcium hypophosphite, Calcii hypophosphis, Ca(PH 2 O 2 ) 2 = 
 168.86. Obtained by heating pieces of phosphorus with milk of lime 
 until hydrogen phosphide ceases to escape. From the filtered liquid 
 the excess of lime is removed by carbon dioxide, and the clear liquid 
 evaporated to dryness. (Great care must be taken during the whole 
 of the operation, which is somewhat dangerous on account of the 
 inflammable and explosive nature of the compounds.) 
 
 8P + 6H 2 O + 3[Ca(OH) 2 ] = 3[Ca(PH 2 O 2 ) 2 ] + 2PH 3 . 
 
 Calcium hypophosphite is generally met with as a white, crystal- 
 line powder with a pearly lustre ; it is soluble in 6 parts of water 
 and has a neutral reaction to litmus. 
 
 Calcium chloride, Calcii chloridum, CaCl 2 = 11O.16, and 
 Calcium bromide, Calcii bromidum, CaBr 2 = 198.52, may both 
 be obtained by dissolving calcium carbonate in hydrochloric acid or 
 hydrobromic acid, until the acids are neutralized. Both salts are 
 highly deliquescent. 
 
 Chlorinated lime, Calx chlorinata (Bleaching -powder, incorrectly 
 called Chloride of lime\ This is chiefly a mixture (according to some, 
 a compound) of calcium chloride with calcium hypochlorite, and is 
 manufactured on a very large scale by the action of chlorine upon 
 calcium hydroxide : 
 
 2Ca(OH) 2 + 4C1 = 2H 2 + Ca(ClO) 2 + CaCl 2 . 
 Calcium hydroxide. Chlorinated lime. 
 
 Bleaching-powder is a white powder, having a feeble chlorine-like 
 odor ; exposed to the air it becomes damp from absorption of moist- 
 ure, undergoing decomposition at the same time; with dilute acids it 
 
CALCIUM. 281 
 
 evolves chlorine, of which it should contain not less than 30 per cent, 
 in available form. The action of hydrochloric acid takes place thus: 
 
 Ca(ClO), -f 2HC1 = CaCl 2 + 2HC1O; 
 2HC10 -f 2HC1 = 2H 2 O + 4C1. 
 
 Bleaching-powder is a powerful disinfecting and bleaching agent. 
 
 Sulphurated lime, Calx sulphurata, is a mixture of calcium sulphide and 
 sulphate, obtained by heating to redness in a crucible a mixture of dried cal- 
 cium sulphate, starch, and charcoal until the contents have lost their black 
 color. By the deoxidizing action of the coal and starch the larger portion of 
 the calcium sulphate is converted into sulphide. 
 
 Calcium carbide, C. 2 Ca, is manufactured on a large scale by heating in 
 an electric furnace a mixture of lime and coal, or coal-tar. The combined 
 action of the high temperature and of the electric current causes this decompo* 
 sition to take place : 
 
 CaO + 30 = CaC 2 + CO. 
 
 Calcium carbide thus made is not pure; it forms gray or brown masses of 
 extreme hardness ; it is used extensively for generating acetylene gas, C 2 H 8 , which 
 is evolved when calcium carbide acts on water : 
 
 C 2 Ca + H 2 O = C 2 H 2 -f- CaO. 
 
 Tests for calcium. 
 (The reagent solution of calcium chloride, CaCl^ may be used.) 
 
 1. Add to solution of a calcium salt, the carbonate of either potas- 
 sium, sodium, or ammonium : a white precipitate of calcium carbon- 
 ate, CaCO 3 , is produced. Try the test also on solution of calcium 
 sulphate and lime-water. 
 
 2. Add sodium phosphate to neutral solution of a calcium salt : a 
 white precipitate of calcium phosphate, CaHPO 4 , is produced. 
 
 3. Add ammonium (or potassium) oxalate to solution of a calcium 
 salt : a white precipitate of calcium oxalate, CaC 2 O 4 , is produced, 
 which is insoluble in acetic, soluble in hydrochloric acid. Try the test 
 also on solution of calcium sulphate and lime-water. 
 
 4. Sulphuric acid or soluble sulphates produce a white precipitate 
 of calcium sulphate, CaSO 4 , in concentrated, but not in dilute solu- 
 tions of a calcium salt. Try the test also on lime-water. 
 
 5. Add potassium or sodium hydroxide : a white precipitate of 
 calcium hydroxide, Ca(OH) 2 , is produced in concentrated, but not in 
 diluted solutions. Ammonia water gives no precipitate. (See Remarks 
 on Tests, page 274.) 
 
 6. Volatile compounds of calcium impart a reddish-yellow color to 
 the Bunsen flame. Non-volatile compounds, as the oxide, carbonate, 
 phosphate, etc., have scarcely any effect on the flame. (Try it.) These 
 
282 METALS AND THEIR COMBINATIONS. 
 
 should first be moistened with strong hydrochloric acid to convert 
 them to the volatile chloride before introducing into the flame. (See 
 note to test 4 for potassium.) 
 
 Test 3, done in dilute solution, combined with tests 4 and 6, is 
 decisive for recognizing calcium compounds. The oxide, carbonate, 
 and phosphate may be dissolved by dilute hydrochloric acid for tests. 
 The phosphate solution cannot be neutralized without precipitation, 
 but if left weakly acid and considerably diluted test 3 can be applied. 
 
 The above tests are examples of more or less complete reactions, due to the 
 formation of insoluble or sparingly soluble substances, and their removal from 
 the field of action by precipitation (see pages 116 and 193). The ionic equa- 
 tions in the tests are as follows : 
 
 Test 1. Ca" -f 2C1' + 2Na' + CO 3 " = CaCO 3 + 2Na" + 2C1'; 
 Ca" + SO/' + 2Na' + CO 3 " = CaCO 3 + 2Na' + SO/'; 
 Ca" + 2(OH)' + 2Na- + CO 3 " - CaCO 3 + 2Na' + 2(OH)'. 
 
 Test 2. Ca" + 2C1' + 2Na' + HPO 4 " = CaHPO 4 + 2Na- + 2C1'; 
 Test 3. Ca" + 2C1' + 2NH 4 '+ C,O 4 " = CaC 2 O 4 + 2NH 4 - -f- 2C1'. 
 The equations for sulphate and hydroxide of calcium are similar (see test 1). 
 Test 4. Ca" + 2C1' + 2H- + SO/' = CaSO 4 + 2H- 4- 2C1'; 
 Test 5. Ca" + 2C1' + 2Na + 2(OH) 7 = Ca(OH) 2 + 2Na -f- 2C1'. 
 
 The ionic equations in the tests for strontium and barium are like those for 
 calcium. 
 
 Strontium, Sr" = 86.94. Found in a few localities in the minerals 
 strontianite, SrCO 3 , and celestite, SrSO 4 . Its compounds resemble 
 those of calcium and barium. The oxide, SrO, cannot be obtained 
 easily by heating the carbonate, as this is much more stable than 
 calcium carbonate. It may, however, be readily prepared by heating 
 the nitrate. The hydroxide, Sr(OH) 2 , is formed when the oxide is 
 brought in contact with water; it is more soluble than calcium 
 hydroxide. 
 
 Strontium nitrate, Sr(NO 3 ) 2 , Strontium chloride, SrCl 2 , Strontium 
 bromide, SrBr 2 , and Strontium iodide, SrI 2 , may be obtained by dis- 
 solving the carbonate in the respective acids. The nitrate is used 
 extensively for pyrotechnic purposes, as strontium imparts a beau- 
 tiful red color to flames ; the bromide and iodide are official. 
 
 Tests for strontium. 
 
 (Use about a 5 per cent, solution of strontium nitrate.) 
 
 1 . The reactions of strontium with soluble carbonates, oxalates, and 
 phosphates are analogous to those of calcium. 
 
STRONTIUM. 283 
 
 2. Add calcium sulphate solution : a white precipitate of strontium 
 sulphate, SrSO 4 , is formed after a few minutes. This test shows that 
 the sulphate is less soluble than calcium sulphate. 
 
 3. Add dilute sulphuric acid or a solution of a sulphate : a white 
 precipitate forms at once in concentrated, after a while in dilute, 
 solutions. 
 
 4. Add potassium chromate solution : a pale-yellow precipitate of 
 strontium chromate, SrCrO 4 , is formed, which is soluble in acetic acid 
 and in hydrochloric acid. (Potassium dichromate causes no precipi- 
 tation.) 
 
 5. Volatile strontium compounds color the Bunsen flame crimson 
 (see remarks in test 6 for calcium.) The color appears at the moment 
 when the substance is first introduced into the flame, whereby the color 
 can be seen, even in the presence of barium. Lithium is the only 
 other metal which gives a similar flame, but strontium may be dis- 
 tinguished from it by test 3 applied in somewhat dilute solution. 
 
 Tests 2 and 3 combined with 5 give conclusive proof of strontium 
 compounds. Insoluble compounds are treated as directed under tests 
 for calcium. 
 
 Barium, Ba 11 = 136.4. Occurs in nature chiefly as sulphate in 
 barite or heavy spar, BaSO 4 , but also as carbonate in witherite, BaCO 3 . 
 Barium and its compounds resemble closely those of calcium and 
 strontium. 
 
 Barium chloride, BaCl 2 + 2H 2 O, is prepared by dissolving the 
 carbonate in hydrochloric acid. It crystallizes in prismatic plates, 
 and is used as a valuable reagent. 
 
 Barium dioxide or peroxide, BaO 2 , is made by heating the oxide to 
 a dark -red heat in the air or in oxygen. When heated above the tem- 
 perature at which it is formed, decomposition into oxide and oxygen 
 takes place. This power to absorb oxygen from air and to give it up 
 again at a higher temperature has been used as a method of preparing 
 oxygen on the large scale. Unfortunately, the barium oxide cannot 
 be used for an unlimited number of operations, as it loses the power 
 to absorb oxygen after it has been heated several times. The use 
 made of barium dioxide in preparing hydrogen dioxide has been 
 mentioned before. 
 
 Barium dioxide is a heavy, grayish-white, amorphous powder, 
 almost insoluble in water, with which, however, it forms a hydroxide, 
 and to which it imparts an alkaline reaction. 
 
284 METALS AND THEIR COMBINATIONS. 
 
 Barium oxide, BaO, is made by heating barium nitrate, Ba(N0 3 ) 2 , which 
 itself is made by dissolving barium carbonate in nitric acid. 
 
 Barium salts are poisonous ; antidotes are sodium and magnesium sulphates. 
 
 Tests for barium. 
 (Use the reagent solution of barium chloride.) 
 
 1. The reactions of barium salts with soluble carbonates, oxalates, 
 and phosphates are analogous to those of solutions of calcium salts. 
 
 2. Add dilute sulphuric acid or solution of a sulphate : a white 
 precipitate of barium sulphate, BaSO 4 , is produced immediately, even 
 in dilute solutions. The precipitate is insoluble in all diluted acids. 
 
 3. Add calcium sulphate solution : a white precipitate, insoluble in 
 all diluted acids, is formed immediately (compare with test 2 under 
 Strontium). 
 
 4. Add potassium chromate or dichromate solution : a pale-yellow 
 precipitate of barium chromate, BaCrO 4 , is formed, insoluble in acetic 
 acid, but soluble in hydrochloric or nitric acid. 
 
 5. Volatile barium compounds color a Buusen flame yellowish 
 green (see remarks under test 6 for calcium). 
 
 Tests 3, 4, and 5 give conclusive proof of barium. Insoluble com- 
 pounds are treated as directed under tests for calcium. 
 
 Radium, Ha = 223.3, This element, discovered in 1899, has been men- 
 tioned in the article on radio-activity, page 85. While radium is closely 
 related to barium it has not been found in the native barium compounds, except 
 when they occur associated with uranium as in pitch-blende, an ore from which 
 uranium compounds are extracted. This ore contains, however, but 0.1 gramme 
 of radium in 1000 kilograms, which is equal to 0.00001 per cent. The residue 
 left, after the uranium has been eliminated, contains from 2 to 3 times as much 
 radium as the original ore. From 1000 kilograms of this residue 10 to 15 kilo- 
 grams of radiferous barium salt (chloride or bromide) are extracted, and from 
 
 QUESTIONS. Which metals form the group of the alkaline earths, and in 
 what respect do their compounds differ from those of the alkali-metals? How 
 is calcium found in nature? What is burned lime; from what, and by what 
 process is it made, and how does water act on it? What is lime-water; how 
 is it made, and what are its properties? Mention some varieties of calcium 
 carbonate as found in nature, and how is it obtained by an artificial process 
 from the chloride ? What is Plaster-of-Paris, and what is gypsum ; what are 
 they used for? State composition and mode of manufacturing bleaching- 
 powder ; what are its properties, and how do acids act upon it ? What is bone- 
 black, bone-ash, acid phosphate, and precipitated tricalcium phosphate ? How 
 are they made? Give tests for barium, calcium, and strontium ; how can they 
 be distinguished from each other ? Which compounds of barium and stron- 
 tium are of interest, and what are they used for? 
 
ALUMINUM. 
 
 285 
 
 this the radium salt is prepared by repeated fractional crystallization. The 
 small yield of radium obtained after long and tedious operations make it the 
 most costly material of the day. 
 
 Both the chloride and bromide of radium are white, crystalline substances 
 turning grayish in the course of time. Lack of a liberal supply of radium has 
 so far prevented a closer study of its chemical behavior. 
 
 Summary of analytical characters of the alkaline earth-metals. 
 
 
 Magnesium. 
 
 Calcium. 
 
 Strontium. 
 
 Barium. 
 
 
 
 
 
 Yellow pre- 
 
 
 
 
 Yellow pre- 
 
 cipitate. 
 Yellow pre- 
 
 
 
 
 cipitate. 
 White pre- 
 
 cipitate. 
 White pre- 
 
 Ammonium carbonate . . 
 
 White preci- 
 pitate soluble 
 in NH 4 C1. 
 \Vhite pre- 
 
 White pre- 
 cipitate. 
 
 cipitate form- 
 ing slowly 
 White pre- 
 cipitate. 
 
 cipitate form- 
 ing at once. 
 White pre- 
 cipitate. 
 
 Ammonium oxalate . . . 
 Sodium phosphate . . . 
 
 cipitate 
 No precipi 
 tate unless 
 very con- 
 centrated 
 White pre- 
 cipitate. 
 
 White pre- 
 cipitate in 
 dilute 
 solution 
 White pre- 
 cipitate. 
 Yello wish- 
 
 White pre- 
 cipitate in 
 strong 
 solution. 
 White pre- 
 cipitate. 
 Eed 
 
 White pre- 
 cipitate in 
 strong 
 solution. 
 White pre- 
 cipitate 
 Yellowish- 
 
 One part of hydroxide is 
 soluble in 
 
 One part of sulphate is 
 soluble in 
 
 50,000 parts 
 of water. 
 
 1.5 parts of 
 
 red. 
 
 666 parts of 
 water. 
 
 400 parts of 
 
 50 parts of 
 water. 
 
 8000 parts of 
 
 green. 
 
 28.6 parts of 
 water. 
 
 400,000 parts 
 
 
 water. 
 
 water. 
 
 water. 
 
 of water. 
 
 26. ALUMINUM. 
 
 Al iu 27 (26.9). 
 
 Aluminum is the representative of the metals of the earths proper ; 
 all other members of this class are found in nature in very small 
 quantities, and are chiefly of scientific interest, with the exception of 
 cerium, which furnishes an official preparation. 
 
 Occurrence in nature. Aluminum is found almost exclusively 
 in the solid mineral portion of the earth ; rarely more than traces of 
 aluminum compounds are found dissolved in water, and the occur- 
 rence of aluminum in the animal organism seems to be purely 
 accidental. 
 
 By far the largest quantity of aluminum is found in combination 
 
286 METALS AND THEIR COMBINATIONS. 
 
 with silicic acid in the various silicated rocks forming the greater 
 mass of our earth, such as feldspar, slate, basalt, granite, mica, horn- 
 blende, etc., or in the various modifications of clay formed by their 
 decomposition. 
 
 The minerals known as corundum, ruby, sapphire, and emery, are 
 aluminum oxide in a crystallized state, and more or less colored by 
 traces of other substances. 
 
 Metallic aluminum may be obtained by the decomposition of 
 aluminum chloride by metallic sodium : 
 
 A1C1 3 + 3Na SNaCl -f Al. 
 
 It is now manufactured by the electrolysis of aluminum and sodium 
 fluoride, or of other aluminum compounds. 
 
 Aluminum is an almost silver- white metal of a very low specific 
 gravity (2.67) ; it is capable of assuming a high polish, and for this 
 reason is used for ornamental articles ; it is very ductile and malleable 
 and ranks with silver in hardness, as also in its power of conducting 
 heat and electricity. 
 
 Aluminum is not oxidized to any great extent in dry or moist air 
 nor is it affected by hydrogen sulphide. It is not readily acted on by 
 nitric or sulphuric acid, but easily dissolves in hydrochloric acid and 
 in solutions of the alkali hydroxides. 
 
 Aluminum forms alloys with nearly all metals, lead being an exception. 
 The hardness and elasticity of tin is increased by addition of aluminum ; 
 readily obtainable alloys with zinc are used as solders for aluminum. A small 
 quantity of aluminum added to wrought iron so increases its fusibility that it 
 may be poured as easily as cast iron. Largely used is aluminum-bronze, an alloy 
 resembling gold and composed of 10 parts of aluminum with 90 of copper. 
 
 Aluminum would be an ideal base for artificial dentures, were it not that 
 the corrosive action of alkaline fluids upon it limits its use. 
 
 Aluminum is trivalent, and the composition of the chloride and 
 hydroxide is therefore given as A1C1 3 and Al(OH), respectively. 
 
 Alum is the general name for a group of isomorphous double sul- 
 phates containing an atom each of a univaletit and a trivalent metal, 
 combined in crystallizing with 12 molecules of water. The general 
 formula of an alum is consequently M i M iii (SO 4 ) 2 .12H 2 O. M i repre- 
 sents in this case a univalent, M iu a trivalent metal. 
 
 Alums known are, for instance : 
 
 Ammonium-aluminum sulphate, NH 4 A1(SO 4 ) 2 .12H 2 O. 
 Potassium-chromium sulphate, KCr(SO 4 ) 2 .12H 2 O. 
 Ammonium-ferric sulphate, NH 4 Fe(SO 4 ) 8 .12H 8 O. 
 
ALUMINUM. 287 
 
 The official alum, (i/iimen, is the potassium alum, KA1(SO 4 ) 2 .12H 2 O 
 = 471.02, a white salt crystallizing in large octahedrons, soluble in 
 10 parts of cold and 0.3 part of boiling water; this solution has an 
 acid reaction and a sweetish astringent taste. 
 
 Alum is manufactured on a large scale by decomposing certain 
 kinds of clay (aluminum silicates) by sulphuric acid, when aluminum 
 sulphate is formed, to the solution of which potassium or ammonium 
 sulphate is added, when, on evaporation, potassium or ammonium 
 alum crystallizes. 
 
 Dried alum ; Alumen exsiccatum, KA1(SO 4 ) 2 = 256.46 (Burnt 
 alum). This is common alum, from which the water of crystallization 
 has been expelled by heat. It is a white powder, dissolving very 
 slowly in cold, but quickly in boiling water. 
 
 Aluminum hydroxide, Alumini hydroxidum, A1(OH) 3 = 77.54. 
 Obtained by adding ammonia water or solution of sodium carbonate 
 to solution of alum, when aluminum hydroxide is precipitated in the 
 form of a highly gelatinous substance, which, after being well washed, 
 is dried at a temperature not exceeding 40 C. (104 F.). 
 
 2KA1(SO 4 ) 2 + 6NH 4 OH = K 2 SO 4 + 3(NH 4 ) 2 SO 4 + 2A1(OH) 3 ; 
 2KA1(SO 4 ) 2 + 3Na 2 CO 3 + 3H 2 O = K 2 SO 4 + 3Na 2 SO 4 + 3CO 2 + 2A1(OH) S . 
 
 When aluminum hydroxide is heated, water is expelled and the 
 oxide is left, which is often termed alumina. 
 
 The usual decomposition between a soluble carbonate and any soluble salt 
 (provided decomposition takes place at all) is the formation of an insoluble 
 carbonate ; according to this rule, the addition of a soluble carbonate to alum 
 should produce aluminum carbonate. The basic properties of aluminum 
 oxide, however, are so weak that it is not capable of uniting with so weak an 
 acid as carbonic acid, and it is for this reason that the decomposition takes 
 place as shown by the above formula, with liberation of carbon dioxide, 
 while the hydroxide is formed. (Other metals, the oxides of which have weak 
 basic properties, show similar reactions, as, for instance, chromium, and iron in 
 the ferric salts.) 
 
 The weak basic properties of aluminum are shown also by the fact that alu- 
 minum sulphate, chloride, and nitrate, and even alum itself, have an acid 
 reaction, while the corresponding salts of the alkalies or alkaline earths are 
 neutral. 
 
 Aluminum salts in solution give the ion Al*'% which forms insoluble 
 compounds with hydroxyl ion (OH) 7 , carbonate ion COg", phosphate ion 
 PO/ X/ , sulphide ion S /x , etc. The carbonate and sulphide are hydrolyzed 
 with elimination of CO 2 and H 2 S respectively. Aluminum hydroxide has 
 such weak basic properties that it actually shows an acid character toward the 
 
288 METALS AND THEIR COMBINATIONS. 
 
 active bases, and is dissolved by them to form compounds called aluminates. 
 This means that A1(OH) 3 has two modes of ionization, namely, 
 A1(OH) 3 ^ Al f 3(OH)'; 
 Al(OH), ; A10/" + 3H-. 
 
 The first mode takes place mainly, and in the presence of acids, salts are 
 formed thus : 
 
 Al- -f- 3(OH)' -f 3H- + 3C1' = Al- + 3C1' + 3H 2 O. 
 
 The second mode of ionization takes place to a less extent, but in the presence 
 of excess of alkalies action results thus : 
 
 A10 S "' -f 3H- + SNa- + 3(OH)' = A1O 3 ' " -f 3Na' + 3H,O. 
 These reactions are generally written thus : 
 
 A1(OH) 3 + 3HC1 = A1C1 3 + 3H 2 O; 
 A1(OH) 3 -f 3NaOH = Na 3 AlO 3 + 3H 2 O. 
 
 The compounds of the form Na 3 AlO 3 , called aluminates, are largely hydrolyzed 
 by water into NaOH and A1(OH) 3 . Hence, an excess of alkali is required to 
 dissolve the aluminum hydroxide. Ammonium hydroxide is too weak a base 
 to unite with it. 
 
 Aluminum hydroxide, in common with many other substances, as hydroxide 
 of iron, chromium, tin, tannic acid, etc., has the power of uniting with dyes and 
 forming colored compounds which adhere firmly to cotton and linen fabrics. 
 Such substances are called mordants (meaning biting), and without their use it 
 is impossible to dye cotton and linen permanently with most dyes. The insoluble 
 compounds of dyes with mordants are called lakes. When aluminum hy- 
 droxide is to be the mordant, the fabric is immersed in a hot solution of alum, 
 aluminum sulphate or acetate, or sodium aluminate, by which some aluminum 
 hydroxide, formed by hydrolysis of the compounds, is taken up by the fibres 
 of the fabric. The latter is then boiled in water containing the dye, which 
 unites with the mordant in the fibres, to form an insoluble permanent color. 
 
 Experiment 29. Dissolve 10 grammes of sodium carbonate in 100 c.c. of 
 water, heat it to boiling, and add to it, with constant stirring, a hot solution, 
 made by dissolving 10 grammes of alum in 100 c.c. of water. Wash the pre- 
 cipitate first by decantation, and then upon a filter, until the washings are not 
 rendered turbid by barium chloride. Dry a portion of the precipitate at a low 
 temperature, and use as aluminum hydroxide. Mix a small quantity of the 
 wet precipitate with a decoction of logwood (made by boiling about 0.2 
 grammes of logwood with 50 c.c. of water), agitate for a few minutes, and 
 filter. Notice that the red color of the solution has entirely disappeared, or 
 nearly so, in consequence of the combination of the aluminum hydroxide 
 and coloring matter. 
 
 Aluminum sulphate, Alumini sulphas, A1 2 (SO 4 ) 3 .16H 2 O = 
 625.93. A white crystalline powder, soluble in about its weight 
 _of water, obtained by dissolving the oxide or hydroxide in sulphuric 
 acid and evaporating the solution to dryness over a water-bath. 
 
 2A1(OH) 3 + 3H 2 S0 4 == A1. 2 (S0 4 ), + 6H 2 O. 
 
ALUMINUM. 289 
 
 Aluminum chloride, A1C1 3 . This compound is of interest on account of 
 being the salt from which the metal was formerly obtained. Most chlorides 
 may be formed by dissolving the metal, its oxide, hydroxide, or carbonate in 
 hydrochloric acid. Accordingly aluminum chloride may be obtained in 
 solution : 
 
 A1(OH) 3 + 3HC1 = A1C1 3 + 3H 2 O. 
 
 On evaporating the solution to dryness, however, and heating the dry mass 
 further with the view of expelling all water, decomposition takes place, hydro- 
 chloric acid escapes, and aluminum oxide is left: 
 
 2A1CL, + 3H 2 O = A1 2 3 -f 6HC1. 
 
 Aluminum chloride, consequently, cannot be obtained in a pure state (free 
 from water) by this process, but it may be made by exposing to the action of 
 chlorine a heated mixture of aluminum oxide and carbon. Neither carbon 
 nor chlorine alone causes decomposition of the aluminum oxide, but by the 
 united efforts of these two substances decomposition is accomplished : 
 
 A1 2 O 3 f 3C + GC1 = 3CO + 2A1CL,. 
 
 Clay is the name applied to a large class of mineral substances, 
 differing considerably in composition, but possessing in common the 
 two characteristic features of plasticity and the predominance of 
 aluminum silicate in combination with water. A white clay, known as 
 kaolin, consists chiefly of a silicate of the composition 
 
 The various kinds of clay have been formed in the course of time from such 
 double silicates as feldspar and others, by a process which is partly of a 
 mechanical, partly of a chemical nature, and consists chiefly in the disintegra- 
 tion of rocks and a removal of potassium and sodium by the chemical action of 
 carbonic acid, water, and other agents. 
 
 The various kinds of clay are used in the manufacture of bricks, earthenware, 
 stoneware, porcelain, etc. The process of burning these substances accom- 
 plishes the hardening by expelling water which is present in the clay. Pure 
 clay is white ; the red color of the common varieties is due to the presence of 
 ferric oxide. For china or porcelain, clay is used containing silicates of the 
 alkalies which, in burning, melt, causing the production of a more homoge- 
 neous mass, while in common earthenware the pores, produced by expelling 
 the moisture, remain unfilled. 
 
 Glass is similar in composition to the better varieties of porcelain. 
 All varieties of glass are mixtures of fusible, insoluble silicates, made 
 by fusing silicic acid (white sand) with different metallic oxides or 
 carbonates, the silicic acid combining chemically with the metals. 
 Sodium and calcium are the chief metals in common glass, though 
 potassium, lead, and others also are frequently used. Color is im- 
 parted to the glass by the addition of certain metallic oxides, which 
 
 19 
 
290 METALS AND THEIR COMBINATIONS. 
 
 have a coloring effect, as. for instance, manganese violet, cobalt blue, 
 chromium green, etc. 
 
 Cement or hydraulic mortar is the name given to a finely powdered 
 mineral, consisting chiefly of basic silicates of lime and alumina, and having 
 the power of forming an insoluble solid mass when mixed with water. Some 
 native limestones, containing also magnesium carbonate and aluminum silicate, 
 furnish cement after being heated to expel water and carbon dioxide. Other 
 cements are made by burning mixtures of limestone and clay of a suitable com- 
 position. The slag of iron furnaces also furnishes the material for cement. 
 
 Ultramarine is a beautiful blue substance, found in nature as the mineral 
 " lapis lazuli" which was highly valued by artists as a color before the dis- 
 covery of the artificial process for manufacturing it. 
 
 Ultramarine is now manufactured on a very large scale by heating a mix- 
 ture of clay, sodium sulphate and carbonate, sulphur, and charcoal in large 
 crucibles, when decomposition takes place and the beautiful blue compound 
 is obtained. As neither of the substances used in the manufacture has a ten- 
 dency to form colored compounds, the formation of this blue ultramarine is 
 rather surprising, and the true chemical constitution of it is yet unknown. 
 
 Ultramarine is insoluble in water and is decomposed by acids with libera- 
 tion of hydrogen sulphide, which shows the presence of sodium sulphide. A 
 green ultramarine is now also manufactured. The approximate formula of the 
 blue compound is Na 2 S 2 .4NaAlSiO 4 . 
 
 Tests for aluminum. 
 (Use about a 5 percent, solution of alum or aluminum sulphate.) 
 
 1. To the solution add solution of potassium or sodium hydroxide : 
 a faintly bluish-white gelatinous precipitate of aluminum hydroxide, 
 A1(OH) 3 , is produced. The physical appearance of the precipitate is 
 characteristic. It is soluble in excess of the alkali, forming an 
 al-uminate, thus : 
 
 A1(OH) 3 + 3NaOH = Al(ONa) 3 + 3H 2 O. 
 
 This shows that A1(OH) 3 has weak acid character toward strong alka- 
 lies. It is reprecipitated on adding ammonium chloride and heating. 
 Aluminum hydroxide is soluble in acids, even acetic acid. 
 
 2. To the solution add ammonia water : the same precipitate as 
 above is obtained, but it is insoluble in an excess of the reagent (dif- 
 ference from zinc) and also in ammonium chloride solution (difference 
 from magnesium). 
 
 3. A solution of a carbonate produces the same precipitate as 
 above, with liberation of carbon dioxide, not very noticeable in dilute 
 solutions (see explanation in text). 
 
ALUMINUM. 291 
 
 4. Solution of ammonium sulphide produces the same precipitate, 
 with generation of hydrogen sulphide : 
 
 A1 2 (S0 4 ) 3 + 3(NH 4 ) 2 S + 6H 2 = 2A1(OH), + 3(NH 4 ) 2 SO 4 + 3H 2 S. 
 
 5. Solution of sodium phosphate produces a white precipitate of 
 aluminum phosphate, A1PO 4 .4H 2 O, soluble in mineral acids, but not 
 acetic, and in fixed alkalies (difference from iron). 
 
 6. Heat a dry aluminum salt on charcoal strongly with the blow- 
 pipe flame. The residue is aluminum oxide, which, when moistened 
 with solution of cobalt nitrate and again heated, gives a blue com- 
 pound, cobalt aluminate. 
 
 Test 1 combined with Tests 5 and 6 are conclusive. evidence of the 
 presence of aluminum. The salts are white, have a sweetish, astringent 
 taste, are acid to litmus, and decomposed by heat, leaving a residue 
 of oxide. 
 
 Cerium, Ce = 141. This element occurs in nature sparingly in a few rare 
 minerals, chiefly as silicate in cerite. In its general deportment cerium resem- 
 bles aluminum. Cerous solutions give with either ammonium sulphide or 
 ammonium and sodium hydroxide, a white precipitate of cerous hydroxide, 
 Ce 2 (OH) 6 . Ammonium oxalate forms a white precipitate of cerium oxalate, 
 ceriioxalas, Ce 2 (C 2 4 ) 3 10H 2 O, which is the only official cerium preparation. 
 Cerium oxalate is a white, granular powder, insoluble in water and alcohol, 
 but soluble in hydrochloric acid. Exposed to a red heat it is decomposed and 
 converted into reddish-yellow eerie oxide. If this oxide, or the residue obtained 
 by heating any cerium salt to red heat, is dissolved in concentrated sulphuric 
 acid, and a crystal of strychnine added, a deep blue color appears, which 
 changes first to purple and then to red. The official cerium oxalate contains 
 also a small quantity of the oxalates of didymiuin, lanthanum, and other rare 
 earths. 
 
 Monazite sand, found in North Carolina and elsewhere, contains, besides 
 cerite. the silicates or oxides or phosphates of other earth metals, especially 
 of zirconium, erbium, and thorium. It is chiefly the oxide of thorium which is 
 used in the mantle of the Welsbach incandescent burner, on account of the 
 bright white light which this oxide emits at a comparatively low temperature. 
 
 QUESTIONS. Mention some varieties of crystallized aluminum oxide found 
 in nature and some silicates containing it. Give the general formula of an 
 alum, and mention some alums. Which alum is official, how is it made, what 
 are its properties, and what is it used for? What is dried alum, and how does 
 it differ from common alum? How is aluminum chloride made, and how ia 
 the metal obtained from it? State the properties of aluminum. What change 
 takes place when ammonium hydroxide, and what change when sodium car- 
 bonate is added to a solution of alum ? What is the composition of earthen- 
 ware, porcelain, and glass ; how and from what materials are they manufac- 
 tured? What is ultramarine ? Give tests for aluminum compounds. 
 
292 
 
 METALS AND THEIR COMBINATIONS. 
 
 Summary of analytical characters of the earth-metals and 
 
 chromium. 
 
 
 Aluminum, 
 
 Cerium. 
 
 Chromium. 
 
 Ammonium sulphide . 
 
 White precipitate. 
 
 White precipitate. 
 
 Green precipitate. 
 
 Potassium hydroxide . 
 Ammonia water . . . 
 
 White precipitate. 
 Soluble in KOH. 
 Not re-precipitated 
 by boiling. 
 White precipitate. 
 
 W T hite precipitate. 
 Insoluble in KOH 
 
 White precipitate. 
 
 Green precipitate. 
 Soluble in KOH. 
 Re-precipitated 
 by boiling. 
 Green precipitate. 
 
 Ammonium carbonate 
 
 White precipitate. 
 
 White precipitate. 
 
 Green precipitate. 
 
 27. IRON. (Ferrum.) 
 Fe = 55.5. 
 
 General remarks regarding- the metals of the iron group. The 
 six metals (Fe, Co, Ni, Mn, Cr, Zn) belonging to this group are distin- 
 guished by forming sulphides (chromium excepted) which are insolu- 
 ble in water, but soluble in dilute mineral acids; they are, conse- 
 quently, not precipitated from their neutral or acid solutions by 
 hydrogen sulphide, but by ammonium sulphide as sulphides 
 (chromium as hydroxide); their oxides, hydroxides, carbonates, 
 phosphates, and sulphides are insoluble; their chlorides, iodides, 
 bromides, sulphates, and nitrates are soluble in water. 
 
 With the exception of zinc, these metals are magnetic ; they de- 
 compose water at a red heat, the oxide being formed and hydrogen 
 liberated; in dilute hydrochloric or sulphuric acid they dissolve 
 with formation of chlorides or sulphates respectively, and liberation 
 of hydrogen. 
 
 Zinc is constantly bivalent, nickel is usually bivalent, but trivalent 
 in a few compounds, cobalt is bi- and trivalent, iron and chromium 
 are bi-, tri-, and sexivalent, manganese is bi-, tri-, sexi-, and septiva- 
 lenf. All the metals, except zinc, form several oxides, the higher 
 ones of which have acid character, as iron trioxide, chromium tri- 
 oxide, manganese trioxide and heptoxide. 
 
 Occurrence in nature. Among all the heavy metals, iron is both 
 the most useful and the most widely and abundantly diffused in 
 nature. It is found, though usually in but small quantities, in nearly 
 all forms of rock, clay, sand, and earth ; its presence in these being 
 
IRON. 293 
 
 indicated generally by their color (red, reddish-brown, or yellowish- 
 red), as iron is the most common of all natural, inorganic coloring 
 agents. It is found also, though in small quantities, in plants, and 
 in somewhat larger proportions in the animal system, chiefly in the 
 blood. In the metallic state iron is scarcely ever found, except in 
 the meteorites or metallic masses which fall occasionally upon our 
 earth out of space. 
 
 The chief compounds of iron found in nature are : 
 
 Hematite, ferric oxide, Fe 2 O 3 . 
 
 Magnetic iron ore, ferrous-ferric oxide, FeO.Fe 2 O 9 . 
 
 Spathic iron ore, ferrous carbonate, FeCO s . 
 
 Iron pyrites, bisulphide of iron, FeS 2 . 
 
 The carbonate and sulphate are found sometimes in spring waters, 
 which, when containing considerable quantities of iron, are called 
 chalybeate waters. Finally, iron is a constituent of some organic 
 substances which are of importance in the animal system. 
 
 Manufacture of iron. There is no other metal manufactured in 
 such immense quantities as iron, the use of which in thousands of 
 different tools, machines, and appliances is highly characteristic of 
 our present age. Iron is manufactured from the above-named oxides 
 or the carbonate by heating them with coke and limestone in large 
 blast furnaces, which have a somewhat cylindrical shape, and are 
 constantly fed from above with a mixture of the substances named, 
 while hot air is forced into the furnace through suitable apertures 
 near its hearth. The chemical change which takes place in the upper 
 and less heated part of the furnace is a deoxidation of the iron oxide 
 
 by the carbon : 
 
 Fe 2 O 3 + 30 == SCO -f 2Fe 
 
 The heat necessary for this decomposition and fusion of the re- 
 duced iron is produced by the combustion of the fuel, maintained by 
 the oxygen of the air blown into the furnace. At the same time the 
 lime and other bases combine with the silica contained in the ore, 
 forming a fusible glass, called cinder or slag. The iron and slag 
 collect at the bottom of the furnace, where they separate by gravity, 
 and are run off every few hours. 
 
 Iron thus obtained is known as cast-iron, or pig-iron, and is not 
 pure, but always contains, besides silicon (also sulphur, phosphorus, 
 and various metals), a quantity of carbon varying from 2 to 5 per 
 cent. It is the quantity of this carbon and its condition which im- 
 parts to the different kinds of iron different properties. Steel contains 
 
294 METALS AND THEIR COMBINATIONS. 
 
 from 0.16 to 2 per cent,, wrought- or bar-iron but very small quanti- 
 ties, of carbon. Wrought-iron is made from cast-iron by the process 
 known as puddling, which is a burning-out of the carbon by oxida- 
 tion, accomplished by agitating the molten mass in the presence of 
 an oxidizing flame. Steel is made either from cast-iron by partially 
 removing the carbon, or from wrought-iron by recombining it with 
 carbon i. e., by agitating together molten wrought- and cast-iron in 
 proper proportions. 
 
 Properties. The high position which iron occupies among the useful metals 
 is due to a combination of valuable properties not found in any other metal. 
 Although possessing nearly twice as great a tenacity or strength as any of the 
 other metals commonly used in the metallic state, it is yet one of the lightest, 
 its specific gravity being about 7.7. Though being when cold the least yield- 
 ing or malleable of the metals in common use, its ductility when heated is such 
 that it admits of being rolled into the thinnest sheets and drawn into the finest 
 wire, the strength of which is so great that a wire of one-tenth of an inch in 
 diameter is capable of sustaining TOO pounds. Finally, iron is, with the ex- 
 ception of platinum, the least fusible of all the useful metals. 
 
 For certain articles, such as armor plate, rock breakers, lathe tools, etc., steel 
 is hardened by alloying it with small quantities of certain other metals, chiefly 
 with chromium, nickel, or manganese. 
 
 Iron is little affected by dry air, but is readily acted upon by moist air, when 
 ferric oxide and ferric hydroxide (rust) are formed. 
 
 Hardening and tempering steel. Steel contains carbon both in the ele- 
 mentary state as graphite, and chemically combined as iron carbide. Within 
 certain limits the tenacity of the metal, and its hardness after having been 
 heated and suddenly cooled, bear a direct ratio to the amount of combined 
 carbon. The more of the latter is present the harder is the steel and vice versd. 
 
 If steel be heated to redness and suddenly chilled it has attained its maxi- 
 mum hardness; if, however, it be permitted to cool slowly after heating, it 
 becomes soft. Any degree of hardness between these extremes can be obtained 
 by the process known as tempering or " letting down." It consists in carefully 
 reheating the previously hardened metal to a certain temperature and then 
 plunging it into cold water. To the experienced worker the required temper- 
 ature is indicated by a series of colors appearing successively on the surface of 
 the steel. These colors are due to a gradually thickening film of iron oxides 
 while the iron softens. The colors pass successively from pale yellow through 
 several shades of darker yellow to brown, purple, blue, and bluish black. The 
 highest temperature gives the least hardness and vice versd. 
 
 In hardening steel, prior to tempering, care should be taken not to injure 
 the metal by overheating, which causes oxidation of the carbon and blisters the 
 metallic surface, rendering a fine temper impossible. In tempering small 
 instruments a coating of some material, such as soap, is necessary to prevent 
 oxidation as far as possible. 
 
 Elasticity and tenacity desired for specific purposes, as in the case of springs, 
 is imparted to steel by hammering. This causes a condensation of the particles 
 
IRON. 295 
 
 and the conversion of the crystalline structure to a fibrous condition, in which 
 state steel is more elastic, tougher, and of greater tensile strength. 
 
 Iron forms two series of compounds, distinguished as ferrous and 
 ferric compounds ; in the former, iron is bivalent, in the latter, 
 apparently trivalent. Almost all ferrous compounds show a tendency 
 to pass into ferric compounds when exposed to the air, or more readily 
 when treated with oxidizing agents, such as nitric acid, chlorine, etc. 
 As the reaction of iron in ferrous and ferric compounds diifers con- 
 siderably, they must be studied separately. Ferrous oxide and 
 hydroxide are more strongly basic than ferric oxide and hy- 
 droxide. 
 
 Reduced iron, Ferrum reductum. This is metallic iron, obtained 
 as a very fine, grayish-black, lustreless powder by passing hydrogen 
 gas (purified and dried by passing it through sulphuric acid) over 
 ferric oxide, heated in a glass tube : 
 
 FeA + 6H = 3H 2 + 2Fe. 
 
 The official article should have at least 90 per cent, of metallic 
 iron. 
 
 Ferrous oxide, FeO (Monoxide or suboxide of iron). This com- 
 pound is little known in the separate state, as it has (like most ferrous 
 compounds) a great tendency to absorb oxygen from the air. The 
 ferrous hydroxide, Fe(OH) 2 , may be obtained by the addition of any 
 alkaline hydroxide to the solution of any ferrous salt, when a white 
 precipitate is produced which rapidly turns bluish -green, dark-gray, 
 black, and finally brown, in consequence of absorption of oxygen 
 (see Plate I., 2) : 
 
 FeSO 4 + 2NH.OH = (NH 4 ) 2 SO 4 + Fe(OH) 2 ; 
 2Fe(OH) 2 + O + H 2 = Fe 2 (OH) 6 . 
 
 The precipitation of ferrous hydroxide is not complete, some iron 
 always remaining in solution. 
 
 Ferrous oxide is a strong base, uniting with acids to form salts, 
 which have usually a palo-groen color. 
 
 Ferric oxide, Fe 2 O 3 . A reddish-brown powder, which may be 
 obtained by heating ferric hydroxide to expel water : 
 
 2Fe(OH) 3 = Fe 2 O 3 + 3K.O. 
 It is a feeble base ; its salts show usually a brown color. 
 
296 METALS AND THEIR COMBINATIONS. 
 
 In the preparation of fuming sulphuric acid (which see) by heating ferrous 
 sulphate there is left a residue of ferric oxide, known as rouge, which is used 
 as a red pigment and as a polishing powder. 
 
 4FeS0 4 + H 2 = 2Fe,O, + H 2 S0 4 .SO 3 4- 2SO 2 . 
 
 A specially fine variety of rouge for polishing is manufactured by heating 
 ferrous oxalate, FeC 2 O 4 , in contact with the air. 
 
 Ferric hydroxide, Ferri hydroxidum, Fe(OH) 3 = 106.14, Is 
 obtained by precipitation of ferric sulphate or ferric chloride by am- 
 monium or sodium hydroxide (see Plate I., 3) : 
 
 Fe 2 (S0 4 ) 3 + 6NH 4 OH = 3[(NH 4 ) 2 SOJ -f 2Fe(OH) 3 . 
 
 Precipitation is complete, no iron remaining in solution as in the 
 case of ferrous salts. 
 
 Ferric hydroxide is a reddish-brown powder, sometimes used as 
 an antidote in arsenic poisoning ; for this purpose it is not used in 
 the dry state, but after having been freshly precipitated and washed, 
 it is mixed with water, and this mixture used. 
 
 Ferric hydroxide with magnesium oxide, U. S. P., is a mixture freshly made, 
 when called for, by adding magnesia to a solution of ferric sulphate, when 
 magnesium sulphate and ferric hydroxide are formed; the two substances are 
 not separated from each other, the mixture being intended for immediate 
 administration as an antidote in cases of arsenic poisoning. 
 
 Ferrous-ferric oxide, FeO.Fe 2 O 3 (Magnetic oxide). This com- 
 pound, which shows strong magnetic properties, has been mentioned 
 above as one of the iron ores, and is known as loadstone. It has a 
 metallic lustre and iron-black color, and is produced artificially by 
 the combustion of iron in oxygen, or in the hydrated state by the 
 addition of ammonium hydroxide to a mixture of solutions of ferrous 
 and ferric salts. 
 
 Iron trioxide, FeO 3 . Not known in a separate state, but in com- 
 bination with alkalies. In these compounds, called ferrates, FeO 3 
 acts as an acid oxide, analogous to chromium trioxide, CrO 3 , in chro- 
 mates. The composition of potassium ferrate is K 2 FeO 4 . 
 
 Ferrous Chloride, FeCl 2 (Protochloride of iron), is obtained as a 
 pale-green solution by dissolving iron in hydrochloric acid : 
 Fe + 2HC1 = FeCl 2 + 2H. 
 
 The anhydrous salt cannot be obtained by evaporation of the solu- 
 tion, as it decomposes ; but it may be made by heating iron in a cur- 
 
IKON. 297 
 
 rent of dry hydrochloric acid gas. The solution and salt absorb 
 oxygen very readily : 
 
 3FeCl 2 -f O = FeO + 2FeCl 3 . 
 
 Ferric chloride, Perri chloridum, FeCl r 6H 2 O =268.32 (Chlo- 
 ride, sesqui-chloride, or perchloride of iron), is obtained by adding to 
 the solution of ferrous chloride (obtained as mentioned above) hydro- 
 chloric and nitric acids in sufficient quantities, and applying heat 
 until complete oxidation has taken place. The nitric acid oxidizes 
 the hydrogen of the hydrochloric acid to water, while the chlorine 
 combines with the ferrous chloride, nitrogen dioxide being formed 
 also : 
 
 3FeCl 2 + HNO 8 + 3HC1 = 3FeCl s + 2H 2 O + NO. 
 
 By sufficient evaporation of the solution, ferric chloride is obtained 
 as a crystalline mass of an orange-yellow color; it is very deli- 
 quescent, has an acid reaction, and a strongly styptic taste. The 
 water of crystallization cannot be expelled by heat, because heat 
 decomposes the salt, free hydrochloric acid and ferric oxide being 
 formed. 
 
 Experiment 30. Dissolve by the aid of heat 1 gramme of fine iron wire in 
 about 4 c.c. of hydrochloric acid, previously diluted with 2 c.c. of water. 
 Filter the warm solution of ferrous chloride, mix it with 2 c.c. of hydrochloric 
 acid, and add to it slowly and gradually about 0.6 c.c. of nitric acid. Evap- 
 orate in a fume chamber as long as red vapors escape ; then test a few drops 
 with potassium ferricyanide, which should not give a blue precipitate ; if it 
 does, the solution has to be heated with a little more nitric acid until the con- 
 version into ferric chloride is complete and the potassium ferricyanide pro- 
 duces no precipitate. Ferric chloride thus obtained may be mixed with 4 c.c. 
 of hot water and set aside, when it forms a solid mass of FeCl 3 .6H 2 O. How 
 much FeCl 2 , how much FeCl 3 , and how much FeCl 3 .6H 2 O can be obtained 
 from 1 gramme of iron? 
 
 Solution of ferric chloride, Liquor ferri chloridi. This is a 
 solution in water, containing 29 per cent, of the anhydrous ferric 
 chloride. It is a reddish-brown liquid of specific gravity 1.315, hav- 
 ing the taste and reaction of the dry salt. This solution, mixed with 
 alcohol in the proportion of 35 to 65 parts by volume, and left stand- 
 ing in a closed vessel for at least three months, forms the tincture of 
 ferric chloride, Tinctura ferri chloridi. By the action of the alcohol 
 on ferric chloride this is reduced to the ferrous state, while at the 
 same time a number of other compounds are formed, imparting to the 
 liquid an ethereal odor. 
 
 Solutions of ferric salts usually have a brown color and show an acid reac- 
 tion. This is due to the partial hydrolysis of the salts, forming ferric hydroxide 
 
298 METALS AND THEIR COMBINATIONS. 
 
 and free acid. Addition of acid, by preventing hydrolysis, renders the solu- 
 tions colorless or nearly so. Hydrolysis is increased by heating the solutions, 
 hence hot ferric solutions have a deeper color than cold ones. 
 
 Ferrous salts are much less hydrolyzed than ferric salts, as ferrous iron is a 
 stronger base than ferric iron. They also are not as acid to litmus as the 
 ferric salts. 
 
 Dialyzed iron is an aqueous solution of about 5 per cent, of ferric hydrox- 
 ide with some ferric chloride. It is made by slowly adding ammonium hy- 
 droxide to a solution of ferric chloride as long as the precipitate of ferric 
 hydroxide formed is redissolved in the ferric chloride solution, on shaking 
 violently. The clear solution thus obtained is placed in a dialyzer floating in 
 water which latter is renewed every day until it shows no reaction with silver 
 nitrate. The ammonium chloride passes through the membrane of the dialyzer 
 into the water, while all iroir as hydroxide with some chloride, is left in 
 solution. 
 
 The combination of an oxide or hydroxide with a normal salt is called 
 usually a basic salt or oxy-salt ; dialyzed iron is a highly basic oxychloride 
 of iron. 
 
 Ferrous iodide, Fel^ and Ferrous bromide, FeBr 2 , may both be 
 obtained by the action of iodine and bromine, respectively, on iron filings, 
 when combination takes place. Both salts are unstable, absorbing oxygen 
 from the air very readily. 
 
 Experiment 31. Cover some fine iron wire with water, heat gently, and add 
 iodine in fragments as long as the red color of iodine disappears. Notice that 
 the iron is dissolved gradually, the result of the reaction being the formation 
 of a pale-green solution of ferrous iodide. 
 
 Ferrous sulphide, FeS. Easily obtained as a black, brittle mass, 
 by heating iron filings with sulphur, when the elements combine. It 
 is used chiefly for liberating hydrogen sulphide, by the addition of 
 sulphuric acid. Iron combines with sulphur in several proportions; 
 some of these iron sulphides are found in nature. 
 
 Ferrous sulphate, Ferri sulphas, FeSO 4 .7H 2 O = 276.O1 (Sul- 
 phate of iron, Green vitriol, Copperas). Obtained by dissolving iron 
 in dilute sulphuric acid, evaporating, and crystallizing : 
 Fe + H 2 S0 4 = 2H + FeSO 4 . 
 
 Also obtained as a by-product in some branches of chemical indus- 
 try, and by heap-roasting of the native iron sulphide : 
 
 FeS 2 + 60 = FeS0 4 + SO 2 . 
 
 Ferrous sulphate crystallizes in large, bluish-green prisms ; it is 
 soluble in water, insoluble in alcohol. Exposed to the air, it loses 
 water of crystallization and absorbs oxygen. 
 
IKON. 299 
 
 The exsiccated ferrous sulphate, U. S. P., is made by expelling 
 nearly all the water of crystallization by heating to 100 C. (212 F.) ; 
 the granulated (precipitated) ferrous sulphate is made by quickly 
 cooling a hot saturated solution of ferrous sulphate, slightly acidu- 
 lated with sulphuric acid, while stirring, when ferrous sulphate sepa- 
 rates as a crystalline powder, which is filtered, washed with alcohol, 
 and dried. 
 
 Experiment 32. In a flask put 10 c.c. of concentrated sulphuric acid diluted 
 with 40 c.c. of water, add iron wire, card teeth, or nails, in portions, until the 
 acid is exhausted, as seen by the cessation of effervescence. Gently heating 
 facilitates the action at the end. Note the bad odor of the hydrogen, due to 
 impurities, and the dark flakes of carbon in the solution. Finally, filter the 
 hot solution and set it aside to crystallize. If crystals do not form, evaporate 
 further. 
 
 Ferrous sulphate readily forms double salts with alkali sulphates, which are 
 not efflorescent, and in the dry state are less readily oxidized than ferrous sul- 
 phate. When a hot, strong solution of 1 part of ammonium sulphate is added 
 to a similar solution of 2 parts of crystals of ferrous sulphate, on cooling, a 
 salt with the composition, (NHJ 2 SO 4 .FeSO 4 .6H. 2 0, separates (Mohr's salt). 
 This is often used when a stable ferrous salt is wanted. 
 
 Ferric sulphate, Fe 2 (SO 4 ) 3 . The solution of this salt, Liquor ferri 
 tersulphatis, is made by adding sulphuric and nitric acids to a solution 
 of ferrous sulphate and heating : 
 
 6FeS0 4 + 3H 2 S0 4 + 2HNO 3 = 3[Fe 2 (SO 4 ) 3 ] + 2NO + 4H 2 O. 
 
 The action of nitric acid is similar to that described above under 
 ferric chloride. The hydrogen of the sulphuric acid is oxidized, and 
 the radical SO 4 unites with the ferrous sulphate, nitrogen dioxide 
 being liberated. 
 
 Experiment 33. Dissolve several crystals of ferrous sulphate in about 20 c.c. 
 of water, add about 5 c.c. of dilute sulphuric acid. Warm the solution and 
 add concentrated nitric acid, in drops, until the dark color first produced sud- 
 denly turns to reddish-brown. Note the red fumes of oxide of nitrogen 
 escaping. The dark color is due to the union of nitric oxide, NO (see reaction 
 above), with unoxidized ferrous sulphate (see test 2 for nitric acid). Heat the 
 solution to expel oxide of nitrogen and excess of nitric acid. Dilute a few 
 drops and test with ferricyanide, as in Experiment 30. 
 
 Solution of ferric sulphate is used in the preparation of Ferric 
 ammonium sulphate, Ferri et ammonii sulphas, FeNH 4 (SO 4 ) 2 .12H 2 O 
 (iron alum, or ammonio-ferric alum), which is made by mixing a solu- 
 tion of ferric sulphate with ammonium sulphate and crystallizing. 
 The salt has a pale violet color and is readily soluble in water. 
 
300 METALS AND THEIR COMBINATIONS. 
 
 Solution of ferric subsulphate, Liquor ferri subsulphatis 
 (Mouses solution). This is a solution similar to the preceding, but 
 contains less sulphuric acid, and is, therefore, looked upon as a basic 
 ferric sulphate, of the doubtful composition 5[Fe 2 (SO 4 ) 3 ].Fe 2 (OH) 6 . 
 
 Ferrous carbonate, PeCO 3 . Occurs in nature; maybe obtained 
 by mixing solutions of ferrous sulphate and sodium carbonate or 
 bicarbonate : 
 
 FeS0 4 + 2NaHC0 3 = NaJSO, -f FeCO 3 + CO 2 + H 2 O. 
 
 The precipitate is first nearly white, but soon assumes a gray color 
 from oxidation. The saccharated ferrous carbonate, U. S. P., is made 
 by mixing the washed precipitate with sugar, and drying. The 
 sugar prevents, to some extent, rapid oxidation. The preparation 
 contains 15 per cent, of ferrous carbonate. 
 
 Ferric carbonate does not exist, the affinity between the feeble ferric 
 oxide and the weak carbonic acid not being sufficient to unite them 
 chemically. 
 
 Ferrous phosphate, Fe 3 (PO 4 ) 2 . When sodium phosphate is 
 added to solution of ferrous sulphate, a precipitate of the composi- 
 tion FeHPO 4 is formed : 
 
 NajHPO^ + FeSO 4 = FeHPO 4 + Na.jSO 4 . 
 
 If, however, sodium acetate is added, a precipitate of the composi- 
 tion Fe 3 (PO 4 ) 2 is formed : 
 
 3FeSO 4 + 2N02HPO4 = Fe 3 (PO 4 ) 2 + 2Na 2 SO 4 -f H 2 SO 4 . 
 
 The sulphuric acid liberated, as shown in this formula, decomposes 
 the sodium acetate, forming sodium sulphate and free acetic acid. 
 Ferrous phosphate is a slate-colored powder, absorbing oxygen 
 readily, becoming darker in color. 
 
 Ferric phosphate, FePO 4 , may be obtained from ferric chloride 
 solution by precipitation with an alkali phosphate. The Soluble ferric 
 phosphate and the Soluble ferric pyrophosphate of the U. S. P., are 
 scale compounds. (See index.) 
 
 Ferric hypophosphite, Ferri hypophosphis, Fe(H 2 PO 2 ) 3 = 
 249.09 (Hypophosphite of iron). It is obtained by adding a solution 
 of sodium hypophosphite to a solution of ferric chloride or sulphate, 
 free from excess of acid. The precipitate is filtered, washed, and dried. 
 It is a grayish-white powder, slightly soluble in water, soluble in 
 hydrochloric acid, in hypophosphorous acid, and in a warm, concen- 
 trated solution of an alkali citrate. 
 
IRON. 
 
 301 
 
 Tests for iron. 
 
 1. Ammonium sul- 
 phide. 
 
 2. Hydrogen sul- 
 phide. 
 
 3. Ammonium, so- 
 dium, or potas- 
 sium hydroxide 
 
 4. Ammonium, so- 
 dium, or potas- 
 sium carbonate. 
 
 5. Alkali phosphates 
 
 or arsenates 
 
 6. Potassium ferro- 
 
 cyanide. 
 
 K 4 Fe(CN) 6 . 
 
 7. Potassium ferri- 
 
 cyanide. 
 
 K 6 Fe 2 (CN) 12 . 
 
 8. Tannic acid. 
 
 9 Potassium sul- 
 phocyanate. 
 KCNS. 
 
 Ferrous salts. 
 
 (Use FeSO 4 .) 
 
 Black precipitate of ferrous 
 sulphide (Plate I., 1). 
 FeSO 4 + (NH 4 ) 2 S = 
 (NH 4 ) 2 SO 4 + FeS. 
 
 No change, except sometimes 
 a slight black discoloration, 
 due to the formation of a 
 trace of FeS. . 
 
 White precipitate of ferrous 
 hydroxide soon turning 
 green, black, and brown. 
 Precipitation not complete 
 (Plate I., 2). 
 
 2NaCl+ Fe(OH) 2 . 
 
 White precipitate of ferrous 
 carbonate, soon turning 
 darker. 
 
 FeCl 2 + Na 2 CO 8 = 
 2NaCl 4- FeCO 3 . 
 
 Almost white precipitate, soon 
 turning darker. 
 
 Almost white precipitate, 
 K 2 Fe[Fe(CN) 6 ], soon turning 
 blue by absorption of oxygen 
 (Plate I., 4). 
 
 Blue precipitate of ferrous ferri- 
 
 cyanide, or Turnbull's blue. 
 
 3FeCl 2 + K 6 Fe 2 (CN) 12 = 
 
 6KC1 + Fe 8 Fe a (CN) lr 
 
 No change, provided oxidation 
 of the ferrous salt has not 
 taken place. 
 
 As above. 
 
 Ferric taltt. 
 
 (UseFeCl,.) 
 
 Black precipitate of ferrous sul- 
 phide mixed with sulphur. 
 2FeCl 3 + 3[(NH 4 ) 2 S]= 
 6NH 4 C1 + 2FeS + S. 
 
 Ferric salts are converted into 
 ferrous salts with precipita- 
 tion of sulphur. 
 
 2FeCl. 2 + 2HCl-f S.. 
 
 Keddish-brown precipitate of 
 ferric hydroxide. Precipita- 
 tion is complete (Plate I., 3). 
 3(NH 4 OH) = 
 Fe(OH) 3 : 
 
 Reddish-brown precipitate of 
 ferric hydroxide, with libera- 
 tion of carbon dioxide (Plate 
 I., 3). 
 
 2FeCl 3 -f 3Na 2 CO 3 + 3H,O - 
 GNaCl + 2Fe(OH) 8 + 3CO 2 . 
 
 A yellowish-white precipitate 
 is produced. 
 
 Dark-blue precipitate of ferric 
 ferrocyanide, or Prussian blue. 
 Decomposed by alkalies ; in- 
 soluble in acids (Plate I., 5). 
 3[K 4 Fe(CN) 6 ] = 
 Fe 4 3[Fe(CN) fl ]. 
 
 No precipitate is produced, but 
 the liquid is darkened to a 
 greenish-brown hue. 
 
 A dark greenish-black precipi- 
 tate of ferric tannate is pro- 
 duced. 
 
 Deep blood-red solution of fer- 
 ric sulphocyanate, Fe(CNS) 3 
 (Plate I., 6). 
 
302 METALS AND THEIR COMBINATIONS. 
 
 Remarks to tests. In test 1 iron in the ferric state is too weakly 
 basic to form ferric sulphide, but in the ferrous state it is a stronger 
 base, so that the ferric sulphide breaks down at the moment of forma- 
 tion to ferrous sulphide and sulphur. If ferrous iron were as weakly 
 basic as aluminum and chromium, no precipitate of sulphide would 
 be obtained. 
 
 In test 2 no precipitate is formed, because of the acid that would 
 be set free by the reaction. Ferric salts are easily reduced to ferrous 
 salts, and vice versa. H 2 S is a good reducing agent, and, when acting 
 as such, always gives a precipitate of milk of sulphur, which easily 
 passes through filter-paper and causes annoyance in the course of 
 qualitative analysis. 
 
 In test 4 the weak basic character of ferric iron and the resem- 
 blance to aluminum and chromium is again shown. 
 
 Tests 6, 7, 8, and 9 are not only delicate and decisive, but permit 
 iron in either state to be detected in the presence of the other. 
 
 Ferrous compounds form the divalent ion Fe", which is pale-green, and 
 ferric compounds form the trivalent ion Fe*", which is nearly colorless. The 
 ionic reactions for the tests for iron are of the same form as those given under 
 the tests for calcium. In test 2, the reduction of ferric to ferrous salt by H 2 S 
 is expressed by the ionic equation : 
 
 2Fe'" + 6C1' + 2H- + S" = 2Fe" + 2H* + 6C1' + S. 
 Each of the iron ions loses a charge of electricity and the sulphur ion loses 
 its two charges, which mutually neutralize each other, and elementary sulphur 
 is precipitated. The reduction with ammonium sulphide is represented by a 
 similar equation. 
 
 The formation of ferric from ferrous chloride is expressed thus : 
 
 Fe" + 2CP + Cl = Fe- + 3C1'. 
 
 The iron ion assumes another positive charge, becoming trivalent ion, and the 
 chlorine atom assumes a negative charge, becoming chlorine ion. A similar 
 equation holds in the case of the sulphate. 
 
 QUESTIONS Which metals belong to the " iron group," and what are their 
 general properties? How is iron found in nature, and what compounds are 
 used in its manufacture ? Describe the process for manufacturing iron on a 
 large scale, and state the difference between cast-iron, wrought-iron, steel, and 
 reduced iron. State the composition and mode of preparation of ferrous and 
 ferric hydroxides. What are their properties? Describe in words and chem- 
 ical symbols the process for making ferric chloride. What is tincture of chlo- 
 ride of iron? How are ferrous iodide and bromide made? State the proper- 
 ties of ferrous sulphate. Under what other names is it known, and how is it 
 made? What change takes place when soluble carbonates are added to soluble 
 ferrous and ferric salts? Mention agents by which ferrous compounds may be 
 converted into ferric compounds, and these into ferrous compounds. Explain 
 the chemical changes taking place. Mention tests for ferrous and ferric com- 
 pounds. 
 
IRON. COBALT. NICKEL, 
 
 PLATE I. 
 
 Ferrous sulphide, precipitated from 
 ferrous solutions by ammonium sulphide. 
 
 Ferrous hydroxide, passing into 
 ferric hydroxide. Ferrous solutions precipi- 
 tated by alkali hydroxides. 
 
 Ferric hydroxide, precipitated from 
 ferric solutions by alkali hydroxides. 
 
 Ferrous solutions, precipitated by 
 potassium ferrocyanide. 
 
 Ferric solutions, precipitated by 
 
 potassium ferrocyanide, or, Ferrous 
 
 solutions precipitated by potassium 
 ferricyanide. 
 
 Ferric solutions, treated with alkali 
 sulphocyanates. 
 
 Cobaltous carbonate, precipitated 
 from cobaltous solutions by sodium 
 carbonate. 
 
 8 
 
 Nickelous carbonate, precipitated 
 from nickelous solutions by sodium 
 carbonate. 
 
 A ftoen &Co LM Babuiion. . ltd 
 
MANGANESE-CHROMIUM COBALT-NICKEL. 303 
 
 28. MANGANESE CHROMIUM COBALT MCKEL. 
 
 Manganese, Mn = 54.6. The principal ore is the dioxide (black 
 oxide of manganese, pyrolusite), MnOj, which is always accompanied 
 by iron compounds. Other forms occurring in nature are braunite, 
 Mn f O 3 , hausmannite, Mn^O^, and manganese spar, MnCO 3 . In small 
 quantities it is a constituent of many minerals. 
 
 Metallic manganese resembles iron in its physical and chemical 
 properties, and may be obtained by reducing the carbonate with 
 charcoal. Manganese is darker in color than iron, considerably 
 harder, and somewhat more easily oxidized. Alloys of iron and 
 manganese (20 to 80 per cent.), known as ferro-manganese, are used 
 in the arts. 
 
 Oxides of manganese. Six oxides are known. MnO 3 and 
 Mn 2 O 7 have been obtained in the free state, but they are very unsta- 
 ble, and are known best through their compounds : 
 
 Manganoos oxide (monoxide or protoxide), MnO. 
 
 Manganous manganic oxide, MnOMn,0^ = Mn^O^ 
 
 Manganic oxide (sesquioxide), MiijQj. 
 
 Manganese dioxide (binoxide, peroxide, black oxide), MnO r 
 
 Manganese trioxide, MnQ,. 
 
 Manganese heptoxide, Mn,Oj. 
 
 The chemical behavior of these oxides varies with the degree of oxidation, 
 or, in other words, with the valence of the manganese. MnO is strongly basic ; 
 Mn,Oj is weakly basic; MnOj has feebly acidic character; MnO s is more 
 strongly acidic, being the anhydride of manganic acid, HjMnO 4 , which is 
 known only in its salts ; Mn s O T is the anhydride of permanganic acid, which 
 is known in aqueous solution, and has strong acid character. 
 
 The only stable salts of manganese are the manganou.* salts, derived from 
 manganons oxide, MnO, in which the valence of manganese is 2. When any 
 oxide of manganese (or compounds of those oxides which are unstable in the 
 free state) is heated with an acid, a manganous salt is obtained. In this action 
 the oxides higher than MnO give off oxygen, or oxidize the excess of acid (see 
 action of hydrochloric acid on MnOj). The decomposition of potassium per- 
 manganate, which has been used hitherto as an oxidizer, may now be explained. 
 In dilute sulphuric acid solution permanganic acid is liberated thus : 
 
 2KMn0 4 + H,SO 4 = K,SO 4 + 2HMnO 4 . 
 
 The acid is stable enough when nothing else is present that can be oxidized, 
 but if such a substance is added the permanganic acid breaks down to mangan- 
 ous oxide and oxygen : 
 
 2HMnO 4 = H S O + MnA, 
 Mn,O, = 5O + 2MnO, 
 
 2MnO + 2HjSO 4 = 2MnSO 4 + 2H,O. 
 
 The manganous oxide is dissolved by the acid to form the colorless manganous 
 
304 METALS AND THEIR COMBINATIONS. 
 
 sulphate, MnSO 4 . The oxygen does not escape, but goes to the reducing com- 
 pound. Conversely, when oxygen is forcibly added to any of the lower oxides 
 in the presence of alkalies, the MnO 3 state of oxidation is attained, that is, 
 salts of manganic acid, or manganates, are produced, as K 2 MnO 4 , from which 
 the more stable permanganates are readily obtained (see below). 
 
 While manganous salts are stable and do not absorb oxygen like ferrous 
 salts, manganous hydroxide and carbonate readily absorb oxygen and turn 
 dark, resembling in this respect iron. 
 
 Manganous oxide is a greenish-gray powder obtainable by heating 
 the carbonate ; or as a nearly white hydroxide by precipitating a 
 manganous salt by sodium hydroxide. It is a strong base, saturating 
 acids completely, and forming salts which have generally a rose 
 color or a pale reddish tint. 
 
 Manganese dioxide, MnO 2 , is by far the most important com- 
 pound of manganese found in nature, as it is largely used for gener- 
 ating chlorine and oxygen, as described in former chapters. 
 
 Precipitated manganese dioxide, Mangani dioxidum praecipitatum, 
 MnO.j 86.36, is obtained by pouring a mixture of ammonia water and 
 hydrogen peroxide into a solution of manganese sulphate, when manganese 
 dioxide mixed with some oxide is precipitated as a heavy, black powder : 
 
 MnS0 4 + 2NH 4 OH + H 2 O 2 = (NH 4 ) a SO 4 + 2H 2 O -f MnO 2 . 
 
 Experiment 34. Mix 10 c.c. of 5 per cent, ammonia water with 10 c.c. of 
 1.5 per cent, hydrogen dioxide solution, and pour slowly while stirring into 
 20 c.c. of a 5 per cent, solution of manganous sulphate. Let the mixture 
 stand for one hour, stirring frequently. Then filter and wash thoroughly with 
 hot water, let drain, and dry. Heat some of the precipitate with hydrochloric 
 acid in a test-tube and explain the result. 
 
 Manganese sulphate, Mangani sulphas, MnSO 4 .4H 2 O = 221.47, 
 maybe obtained by dissolving the oxide or dioxide in sulphuric acid ; 
 in the latter case oxygen is evolved : 
 
 MnO 2 + H,SO 4 = MnSO 4 -f H 2 O -f O. 
 
 As manganese dioxide generally contains iron oxide, the solution contains 
 sulphates of both metals. By evaporating to dryness and strongly igniting, 
 the iron salt is decomposed. The ignited mass is now lixiviated with water, 
 and the filtered solution evaporated for Crystallization. 
 
 It is an almost colorless, or pale rose-colored substance, isomorphous with 
 the sulphates of magnesium and zinc ; it is easily soluble in water. 
 
 Manganese hypophosphite, Mangani hypophosphis, Mn(PH 2 2 ) 2 .H,0 
 
 = 201.54, may be made by mixing a solution of 1 part of calcium hypo- 
 phosphite with a solution of 1.31 parts of manganous sulphate, allowing 
 
MANGANESE CHROMIUM-COBALT-NICKEL. 305 
 
 the precipitate of calcium sulphate to settle, and evaporating the filtrate to 
 dryness. It is a pink crystalline powder, permanent in the air, and soluble in 
 6.6 parts of water. Its chief use is as a constituent of compound syrup of 
 
 hypophosphites. 
 
 Potassium permanganate, Potassii permanganas, KMnO 4 = 
 156.98. Whenever a compound (any oxide or salt) of manganese is 
 fused with alkali carbonates (or hydroxides) and alkali nitrates (or 
 chlorates) the manganese is converted into manganic acid, which 
 combines with the alkali, forming potassium (or sodium) manganate: 
 3MnO a -f 3K 8 CO 8 + KC1O 3 = 3K 2 MnO 4 + 3CO ? + KC1. 
 
 The fused mass has a dark-green color, and when dissolved in 
 water* gives a dark emerald-green solution, from which, by evapora- 
 tion, green crystals of potassium manganate may be obtained. 
 
 The green solution is decomposed easily by any acid (or even by 
 water in large quantity) into a red solution of potassium perman- 
 ganate and a precipitate of manganese dioxide. 
 
 3K 2 Mn0 4 + 2H 2 SO 4 = MnO 2 + 2K 2 SO 4 + 2KMnO 4 + 2H 2 O. 
 
 By evaporation and crystallization potassium permanganate is ob- 
 tained in slender, prismatic crystals, of a dark- purple color, and a 
 somewhat metallic lustre. The solution in water has a deep purple, 
 or, when highly diluted, a pink color (Plate II., 1). It is a power- 
 ful oxidizing agent, and an excellent disinfectant, both properties 
 being due to the facility with which a portion of the oxygen is given 
 off to any substance which has affinity for it. If the oxidation 
 takes place in the absence of an acid, a lower oxide of manganese is 
 formed, which separates as an insoluble substance. If an acid is 
 present, both the potassium and manganese combine with it, forming 
 salts, thus : 
 
 2(KMnO 4 ) 4- 6HC1 + x = 2KC1 + 2MnCl 2 + 3H 2 O -f xO 5 . 
 
 x represents here any substance capable of combining with oxygen 
 while in solution. 
 
 Experiment 35. Heat in an iron crucible a mixture of 2 grammes man- 
 ganese dioxide, 2 grammes potassium hydroxide, and 1 gramme potassium 
 chlorate, until the fused mass has turned dark-green. Dissolve the cooled 
 mass with water, filter the green solution of potassium manganate, and pass 
 carbon dioxide through it until it has assumed a purple color, showing that 
 the conversion into permanganate is complete. Notice that the acidified solu- 
 tion is readily decolorized by ferrous salts and other deoxidizing agents. 
 
 Permanganic acid, HMn0 4 , can now be obtained in solution by electrol- 
 20 
 
306 METALS AND THEIR COMBINATIONS. 
 
 ysis of potassium permanganate. It has the color of the potassium salt, is 
 stable, and from it the permanganates of other metals may be made. 
 
 Tests for manganese. 
 (A 5 per cent, solution of manganous sulphate may be used.) 
 
 1. Ammonium sulphide produces a yellowish-pink or flesh-colored 
 precipitate of hydrated inanganous sulphide, MnS.H 2 O, soluble in 
 acetic and in mineral acids (Plate II., 2). 
 
 2. Ammonium (or sodium) hydroxide produces a white precipi- 
 tate of manganous hydroxide, which soon darkens by absorption 
 of oxygen (Plate II., 3) and dissolves in oxalic acid with a rose-red 
 color. The presence of ammonium salts prevents the precipitation of 
 manganous hydroxide by ammonia-water (see test 2 for magnesium). 
 
 3. Sodium (or potassium) carbonate produces a nearly white pre- 
 cipitate of manganous carbonate, which oxidizes to brown manganic 
 hydroxide. 
 
 4. Any compound of manganese heated on platinum foil with a 
 mixture of sodium carbonate and nitrate forms a bluish-green mass, 
 giving a green solution in water, which turns red on addition of an 
 acid. (See explanation above.) 
 
 5. Manganese compounds fused with borax on a platinum wire 
 give a violet color to the borax bead. Only a very small quantity of 
 the manganese compound should be used. 
 
 6. Heat a trace of manganese compound (not the dioxide) with about 
 5 c.c. of dilute nitric acid and a small knife-pointful of red oxide of 
 lead (minium) to boiling, dilute with water, and let stand to settle. 
 A reddish-purple color of permanganic acid will be seen. This is a 
 very delicate test. 
 
 Tests 4, 5, and 6 are the most decisive for manganese compounds. 
 Test 2 is also characteristic. Permanganate is usually recognized by 
 its color and action on reducing agents. Manganese salts are neu- 
 tral and colorless, or light red to pink. 
 
 The most common ions of manganese are the divalent Mn' ions of the man- 
 ganous salts, and the univalent permanganate ions MnO/, which are purple 
 (see page 200). The divalent manganate ions MnO/ x , which are green, exist 
 only in neutral or alkaline solutions. In acid solutions they pass into MnO/ 
 ions. The ionic equations in the tests above for manganous ions, Mn' * are 
 similar to those given under the tests for calcium. 
 
 Chromium, Cr = 51.7. Found in nature almost exclusively as 
 chromite, or chrome-iron ore, FeO.Cr 2 O 3 , a mineral analogous in 
 composition to magnetic iron ore, FeO.Fe ? O ? . The name chromium. 
 
MA NGANESE CHROMIUM-COB A LT- NICKEL. 307 
 
 from the Greek %po>/jLa (chroma), color, was given to this metal on 
 account of the beautiful colors of its different compounds, none of 
 which is colorless. Chromium forms two basic oxides, Chromous 
 oxide, CrO, the salts of which are, however, very unstable, and chromic 
 oxide or chromium sesquiozide, Cr 2 O 8 , and an acid oxide, chromium 
 trioxide, CrO 8 , the combinations and reactions of which have to be 
 studied separately. While chromium is closely allied to aluminum 
 and iron on one side, it also shows a resemblance to sulphur, as indi- 
 cated by the trioxide, CrO 3 , and the acid, H 2 CrO 4 , which are analogous 
 to SO 3 and H 2 SO 4 . Moreover, the barium and lead salts of chromic 
 and sulphuric acids are both insoluble in water. 
 
 Metallic chromium is used in small proportion as an admixture to steel to 
 which it imparts great hardness. 
 
 Potassium dichromate, Potassii dichromas, K 2 Cr 2 O 7 = 292.28 
 (Bichromate or red chr ornate of potash). This salt is by far the most 
 important of all chromium compounds, and is the source from which 
 they are obtained. 
 
 Potassium dichromate is manufactured on a large scale by expos- 
 ing a mixture of the finely ground chrome-iron ore with potassium 
 carbonate and calcium hydroxide to the heat of an oxidizing flame 
 in a reverberatory furnace, when both constituents of the ore become 
 oxidized, ferric oxide and chromic acid being formed, the latter 
 combining with the potassium, forming normal potassium chromate, 
 K 2 Cr0 4 . 
 
 2(FeOCr 2 3 ) + 4K 2 CO 3 + 7O = Fe 2 O 3 + 4CO 2 + 4(K 2 CrOJ. 
 
 By treating the furnaced mass with water a yellow solution of 
 potassium chromate is obtained, which, upon the addition of sul- 
 phuric acid, is decomposed into potassium dichromate and potassium 
 
 sulphate : 
 
 2(K 2 CrO 4 ) + H 2 SO 4 = K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O. 
 
 The two salts may be separated by crystallization. Potassium 
 dichromate forms large, orange-red, transparent crystals, which are 
 easily soluble in water; heated by itself oxygen is evolved, heated 
 with hydrochloric acid chlorine is liberated, heated with organic 
 matter or reducing agents these are oxidized. 
 
 Sodium dichromate, Na 2 Cr 2 O 7 .2H 2 O (Bichromate of soda), is manufac- 
 tured by a process analogous to that used for potassium dichromate. The 
 crystallized compound resembles the potassium salt, but dissolves in less than 
 its own weight of water. The crystals being deliquescent, a granulated anhy- 
 drous salt which is but slightly hygroscopic, is also manufactured, and has 
 largely replaced the use of potassium dichromate. 
 
308 METALS AND THEIR COMBINATIONS. 
 
 Chromium trioxide, Chromii trioxidum, CrO 3 = 99.34 (Chromic 
 acid, Chromic anhydride), is prepared by adding sulphuric acid to a 
 saturated solution of potassium dichromate, when chromium trioxide 
 separates in crystals : 
 
 K 2 2 7 -f H 2 S0 4 = K 2 S0 4 + H 2 + 2CrO 3 . 
 
 Thus prepared, it forms deep purplish-red, needle-shaped crystals, 
 which are deliquescent, and very soluble in water; it is destructive 
 to animal and vegetable matter, and one of the strongest oxidizing 
 agents ; the solution in water has strong acid properties, but neither 
 chromic nor dichromic acid are known in a pure state as an aqueous 
 solution of chromium trioxide, on concentration breaks up into the 
 oxide and water. 
 
 Experiment 36. Dissolve a few grammes of potassium dichromate in water 
 and add to 4 volumes of the cold saturated solution 5 volumes of strong sul- 
 phuric acid ; chromium trioxide separates on cooling. Collect the crystals on 
 asbestos, wash them with a little nitric acid, and dry them by passing warm 
 dry air through a tube in which they have been placed for this purpose. 
 
 Chromates and dichromates, When chromium trioxide is dissolved in 
 water, dichromic acid is mainly formed thus : 
 
 200. + H 2 = H 2 Cr 2 7 , 
 
 which gives the ions 2H* and Cr 2 O 7 ". The Cr 2 O 7 x/ ion is yellowish red in 
 color. There is, however, a slight amount of chromic acid formed, thus : 
 
 Ci0 3 + H 2 = H 2 CrO 4 , 
 
 which gives the ions 2H' and CrO 4 ". The ion CrO 4 " is yellow. Chromic acid 
 is known through its salts, the chromates, which give the ion, CrO/'. 
 
 Potassium and sodium chromate in solution show a basic reaction which is 
 not due to any weak acid character of chromic acid, but to the fact that chro- 
 mates have a great tendency to pass to salts of dichromic acid. They are de- 
 composed to some extent by water, thus : 
 
 2K 2 CrO 4 + H 2 == K 2 Cr 2 O 7 + 2KOH. 
 
 If an acid, even a weak one, is added to the solution, the decomposition be- 
 comes practically complete by the removal of the KOH by union with the 
 acid. The color changes from yellow to red, and, upon concentration, the 
 rather moderately soluble dichromate crystallizes out in the case of the potas- 
 sium salt. Potassium dichromate is almost neutral in reaction ; it is, therefore, 
 not an acid chromate. In fact acid chromates are not known in which respect 
 chromic acid diners from sulphuric acid. The acid salt of the composition, 
 KHCr0 4 , which we would expect to be formed by acidifying a solution of the 
 chromate, changes at once into the salt of dichromic acid, thus : 
 2KHCr0 4 = K 2 Cr 2 7 -f H 2 O. 
 
 Although potassium dichromate contains no acid hydrogen, it acts essen- 
 tially like an acid salt toward alkalies. When potassium hydroxide is added 
 
MANGANESE-CHROMIUMCOBALT-NICKEL. 309 
 
 to the dichromate the solution turns yellow, and upon evaporation a salt of 
 the composition, K 2 CrO 4 , is obtained. The reason for this is the fact that, 
 although the dichromate dissociates in the main into 2K' and Cr.,0/' ions, it 
 also dissociates to a slight extent, thus : 
 
 K 2 Cr 2 7 + H 2 O ^ 2K- + 2H- + 2CrO 4 ". 
 As alkali is added, the hydrogen ions are neutralized, thus : 
 2K- + 2(OH)' + 2H- = 2K- + 2H 2 O. 
 
 To keep up the equilibrium, more H* ions and CrO/' ions are formed from the 
 dichromate, the H* ions react with more alkali, etc., until by this process the 
 dichromate is practically all converted into chromate. This change is usually 
 represented by the simple equation : 
 
 K. 2 Cr 2 7 -f- 2KOH =r 21^010, + H 2 O. 
 
 Many chromates, for example, those of barium, lead, silver, mercury, etc., are 
 insoluble in water and are obtained by precipitation. The ionic reaction in 
 the case of barium will serve to illustrate the other cases : 
 
 2K- -f Cr0 4 " + Ba- * + 2C1' = BaCiO 4 + 2K> + 2C1'. 
 
 The same precipitates result when a solution of a dichromate is used, because 
 it contains some CrO/' ions, and as fast as these are removed by precipitation, 
 others are produced to take their place in the system. But the precipitation 
 of the metal as chromate is not complete, as so.me dichromate of the metal re- 
 mains in solution, because of the acid that is liberated in the reaction. The 
 essential change is represented by the simple equation : 
 
 K 2 Cr 2 O 7 -f 2BaCl 2 + H 2 O = 2BaCrO 4 + 2KC1 + 2HC1. 
 
 This reaction is analogous to that between barium chloride and potassium 
 bisulphate : 
 
 KHS0 4 + BaCl 2 = BaSO 4 + KC1 + HC1, 
 
 with the difference that barium sulphate is so difficultly soluble, even in acids, 
 that precipitation is practically complete, whereas the chromates are more 
 easily soluble in acids, and precipitation therefore is only partial. 
 
 Chromic oxide, Cr 2 O 3 (Sesquioxide of chromium), is obtained by 
 heating potassium dichromate with sulphur, when potassium sulphate 
 and chromic oxide are formed : 
 
 K 3 Cr 2 O 7 -1- S = K 2 S0 4 + Cr 2 O 3 . 
 
 By washing the heated mass with water, the chromic oxide is left 
 as a green powder, which is used as a green color, especially in the manu- 
 facture of painted glass and porcelain. Prepared by this method at 
 high temperature the oxide is insoluble in acids, but when obtained 
 in the form of its hydroxide by precipitation it is soluble in acids 
 forming the chromic salts. It is, therefore, a basic oxide. 
 
310 METALS AND THEIR COMBINATIONS. 
 
 Chromic hydroxide, Cr(OH) 3 . A solution of potassium dichro- 
 rnate may be deoxidized by the action of hydrogen sulphide, sul- 
 phurous acid, alcohol, or any other deoxidizing agent, in the presence 
 of sulphuric or hydrochloric acid : 
 
 K 2 Cr 2 7 + 4H 2 S0 4 + 3H 2 S = K 2 SO 4 -f 7H 2 O + 3S + Cr 2 (SO 4 ) 3 . 
 
 As shown by this formula, the sulphates of potassium and chro- 
 mium are formed and remain in solution, while sulphur is precipi- 
 tated, the hydrogen of the hydrogen sulphide having been oxidized 
 and converted into water. 
 
 By adding ammonium hydroxide to the solution thus obtained, 
 chromic hydroxide is precipitated as a bluish-green gelatinous sub- 
 stance : 
 
 Cr a (S(Vs + 6NH 4 OH = 3(NH 4 ) 2 SO 4 -f 2Cr(OH) 3 . 
 
 By dissolving this hydroxide in the different acids, the various 
 salts, such as chloride, CrCl 3 , sulphate, etc., are obtained. Chromic 
 sulphate, similar to aluminum sulphate, combines with potassium or 
 ammonium sulphate and water, forming chrome alum, KCr(SO 4 ) 2 . 
 12H 2 O; it is a purple salt, and is isomorphous with other alums. 
 
 Perchromic acid, H 2 Cr 2 O 8 . This acid is of interest because it is analogous 
 to persulphuric acid, H 2 S 2 O 8 , and is formed in the test for hydrogen dioxide. 
 The ethereal solution is obtained when an acidified saturated aqueous solution 
 of potassium dichromate is shaken with ether and just sufficient hydrogen 
 dioxide solution to give an intense blue color. Excess of hydrogen dioxide 
 must be avoided. The ethereal solution is much more permanent than an 
 aqueous solution of the acid. When it is cooled to 20 C. (4 F.) and 
 treated with metallic potassium, a purplish-black precipitate of potassium per- 
 chromate, K 2 Cr,,O 8 , is formed. This is stable only at low temperature, decom- 
 posing at ordinary temperature into oxygen and potassium chromate. Several 
 other salts have been prepared ; they are all very unstable. 
 
 The chemical conduct of chromium, according to the degree of oxidation or 
 the valence of the metal, is like that of manganese. Chromous salts, corres- 
 ponding to the oxide CrO, are known, but, like ferrous salts, they are very 
 readily oxidized and pass to the stable chromic salts, corresponding to the oxide 
 Cr 2 O 3 . The chromates and the acid, derived from the oxide CrO 3 , although 
 stable when alone in solution, readily give up oxygen in acid solutions to 
 reducing agents, just like permanganates, and the chromium gives salts of the 
 lower oxide, Cr 2 O 8 , which are green : 
 
 K 2 Cr 2 7 + H 2 S0 4 = K 2 S0 4 + H 2 Cr 2 7 , 
 
 H 2 Cr 2 O 7 ^ H 2 O + 2CrO 3 ; 2Cr0 3 = Cr 2 O 3 + 3O, 
 Cr 2 3 + 3H 2 S0 4 = 2 (S0 4 ) 3 + 3H 2 O. 
 
MANGA NESE- CJIR OMIUM- COB A LT- NICK EL . 311 
 
 Tests for chromium. 
 
 a. Of chromates. 
 
 (Use the reagent solution of potassium chromate, K 2 CrO 4 .) 
 .1. Hydrogen sulphide added to an acidified warm solution of a 
 chromate changes the red color into green with precipitation of sulphur. 
 The solution now contains chromium in the basic form. (See explana- 
 tion above.) (Plate II., 4.) The conversion of a chromate to a 
 chromium salt is more readily accomplished by heating the chromic 
 solution with alcohol and hydrochloric acid; the alcohol is partly 
 oxidized, being converted into aldehyde, which has a peculiar but 
 pleasant odor. 
 
 2. Soluble lead salts produce a yellow precipitate of lead chromate 
 (chrome yellow), PbCrO 4 , insoluble in acetic, soluble in hydrochloric 
 acid and in sodium hydroxide (Plate II., 6) : 
 
 K 2 CrO 4 + Pb(NO 3 ) 2 = PbCrO 4 + 2KNO 3 . 
 
 3. Barium chloride produces a pale yellow precipitate of barium 
 chromate, BaCrO 4 ; insoluble in sodium hydroxide. 
 
 4. Silver nitrate produces a dark-red precipitate of silver chromate, 
 Ag 2 Cr0 4 (Plate II., 7). ' 
 
 5. Mercurous nitrate produces a red precipitate of mercurous chro- 
 mate, Hg 2 CrO 4 (Plate II., 8). 
 
 6. On pouring a layer of ether upon a solution of hydrogen 
 dioxide, adding a few drops of potassium dichromate solution, a 
 little sulphuric acid, and shaking, the ether assumes a blue color, due 
 to the formation of unstable perchromic acid. A very delicate test. 
 
 b. Of salts of chromium. 
 (Use a 5 per cent, solution of chrome-alum, or chromic chloride, CrCl 3 .) 
 
 7. To the solution add ammonium hydroxide or ammonium sul- 
 phide : in both cases the green hydroxide of chromium, Cr(OH) 3 , is 
 precipitated (Plate II., 5). Compare with aluminum. 
 
 2CrCl 3 + 3(NH 4 ) 2 S + 6H,O = 6NH 4 C1 + 3H 2 S + 2Cr(OH) 3 . 
 
 8. Potassium or sodium hydroxide causes a similar green precipi- 
 tate of chromic hydroxide, which is soluble in an excess of the 
 reagent, but is re-precipitated on boiling for a few minutes. 
 
 Ammonia water causes precipitation of chromic hydroxide, but 
 the precipitate is nearly insoluble in excess of the reagent. 
 
312 METALS AND THEIR COMBINATIONS. 
 
 c. Of chromium in any form. 
 
 9. Compounds of chromium, when mixed with sodium (or potas- 
 sium) carbonate and nitrate, give, when heated upon platinum foil or 
 in a crucible, a yellow mass of the alkali chromate. 
 
 10. Compounds of chromium impart a green color to the borax 
 bead. Use only a very small quantity of the chromium compound. 
 
 Chromium salts have a green or violet to purple color. Solutions 
 of the violet salts turn green when heated. They are acid to litmus, 
 due to hydrolysis in solution. Chromates are all red or yellow, and 
 mostly insoluble in water. The color of a chromate is noticeable in 
 very dilute solution (made with the aid of an acid in the case of in- 
 soluble salts). 
 
 Cobalt and Nickel, Co =58.56, Ni = 58.3. These two metals show much 
 resemblance to each other in their chemical and physical properties, and occur 
 in nature often associated with each other as sulphides or arsenides. 
 
 Both metals are nearly silver-white ; the salts of cobalt show generally a red, 
 those of nickel a green color. The solutions of both metals give a black pre- 
 cipitate of the respective sulphides on the addition of ammonium sulphide. 
 Ammonium hydroxide produces in solutions of cobalt a blue, in solutions of 
 nickel a green precipitate of the hydroxides, both of which are soluble in an 
 excess of the reagent ; potassium or sodium hydroxide produces similar pre- 
 cipitates, which are insoluble in an excess. Sodium carbonate produces in 
 solutions of cobalt a violet, and in solutions of nickel a green precipitate of the 
 respective carbonates. (Plate I., 7 and 8.) 
 
 Cobalt is used chiefly when in a state of combination (for coloring glass blue) ; 
 nickel when in the metallic state. (German silver is an alloy of nickel, copper, 
 and zinc.) 
 
 29. ZINC. 
 Zn == 64.9. 
 
 Occurrence in nature. Zinc is found chiefly either as sulphide 
 (zinc-blende), ZnS, or as carbonate (calamine), ZnCO 3 ; it occurs also 
 as silicate, H 2 Zn 2 SiO 5 , and as oxide in combination with the oxides 
 of iron or manganese. 
 
 QUESTIONS. How is manganese found in nature? Mention the different 
 oxides of manganese. What is the dioxide used for ? What is the color of 
 manganese salts, of manganates, and of permanganates? How is potassium 
 permanganate made; what are its properties, and what is it used for? Give 
 tests for manganese. State composition and properties of potassium dichro- 
 mate. How is chromium trioxide made ; what are its properties ; what is it 
 used for ; and under what other name is it known ? By what process may 
 chromium sesquioxide be converted into chromates ? What is the composition 
 of the oxide and hydroxide of chromium, and how are they made? Mention 
 tests for chromates and chromium salts. 
 
MANGANESE. CHROMIUM. 
 
 PLATE II. 
 
 Potassium permanganate solution, 
 more or less saturated. Boraxbead colored 
 by manganese. 
 
 Manganous sulphide, precipitated 
 from manganous solutions by ammonium 
 sulphide. 
 
 Manganous hydroxide, passing into 
 the higher oxides. Manganous solution* 
 precipitated by alkali hydroxides. 
 
 Potassium dichromate solution de- 
 oxidized by reducing agents. 
 
 Chromic hydroxide, precipitated 
 from chromic solutions by alkali hydrox- 
 ides. 
 
 Lead chromate, precipitated from 
 soluble cbromates by lead acetate. 
 
 Silver chromate, precipitated from 
 neutral chromates by silver nitrate. 
 
 Mercurous chromate, precipitated 
 from neutral chromates by mercurous bolu- 
 tious. 
 
 , I.,rli tiolniuorf, . IM 
 
ZINC. 313 
 
 Metallic Zinc is obtained by heating in retorts the oxide or 
 carbonate mixed with charcoal, when decomposition takes place. 
 The liberated metal is vaporized, and distils into suitable receivers, 
 where it solidifies. 
 
 Zinc is a bluish-white metal, which slowly tarnishes in the air, 
 becoming coated with a film of oxide and carbonate ; it has a crys- 
 talline structure and is, under ordinary circumstances, brittle ; when 
 heated to about 130-150C. (260-302 F.) 'it is malleable, and 
 may be rolled or hammered without fracture. Zinc thus treated 
 retains this malleability when cold ; the sheet-zinc of commerce is 
 thus made. When zinc is further heated to about 300 C. (572 F.), 
 it loses its malleability and becomes so brittle that it may be pow- 
 dered ; at 410 C. (760 F.) it fuses, and at a bright- red heat it 
 boils, volatilizes, and, if air be not excluded, burns with a splendid 
 greenish -white light, generating the oxide. 
 
 Zinc is used by itself in the metallic state or fused together with 
 other metals (German silver and brass contain it) ; galvanized iron 
 is iron coated with metallic zinc. 
 
 Zinc combines- with mercury forming a crystalline amalgam of the compo- 
 sition Zn 2 Hg. As a constituent of dental amalgam alloys zinc hastens the 
 setting, aids in controlling shrinkage and to some extent prevents discoloration. 
 While zinc unites with tin in all proportions forming excellent alloys for dental 
 dies, it is not suitable for alloying with lead. 
 
 Zinc is a bivalent metal, forming but one oxide and one series of 
 salts, most of which have a white color, 
 
 As has been pointed out in Chapter 24, zinc bears a close chemical relation- 
 ship to magnesium, and both these metals resemble cadmium in their chemical 
 properties. In fact,, the three elements magnesium, zinc, and cadmium form a 
 natural group similar to that of the alkali metals or the alkaline earth metals. 
 
 Zinc oxide, Zinci oxiduni, ZnO = 80.78 (Flores zinci, Zinc-white), 
 may be obtained by burning the metal, but if made for medicinal 
 purposes, by heating the carbonate, when carbon dioxide and water 
 escape and the oxide is left : 
 
 3[Zn(OH) 2 J.2ZnCO 3 = 5ZnO -f 2CO 2 + 3H 2 O. 
 
 It is an amorphous, white, tasteless powder, insoluble in water, 
 soluble in acids; when strongly heated it turns yellow, but on 
 cooling resumes the white color. 
 
 Zinc hydroxide, Zn(OH) 2 , is obtained by precipitating zinc salts 
 with the hydroxide of sodium or ammonium ; the precipitate, how- 
 ever, is soluble in an excess of either of the alkali hydroxides. 
 
314 METALS AND THEIR COMBINATIONS. 
 
 Zinc chloride, Zinci chloridum, ZnCl 2 = 135.26. Made by dis- 
 solving zinc or zinc carbonate in hydrochloric acid and evaporating 
 the solution to dryness : 
 
 Zn + 2HC1 = ZnCl 2 + 2H. 
 
 It is met with either as a white crystalline powder, or in white 
 opaque pieces ; it is very deliquescent and easily soluble in water 
 and alcohol; it combines readily with albuminoid substances; it 
 fuses at about 115C. (239 F.), and is volatilized, with partial 
 decomposition, at a higher temperature. 
 
 Liquor zinci chloridi, U. S. P., is an aqueous solution of zinc chloride, con- 
 taining 50 per cent, of the salt. 
 
 Zinc oxychloride is used extensively for dental purposes, and is made by 
 mixing zinc oxide with a strong solution of zinc chloride. At first a plastic 
 mass forms, which rapidly hardens. The proportions in which the two sub- 
 stances are mixed differ widely, the weights corresponding all the way from 3 
 to 9 molecules of zinc oxide for each molecule of zinc chloride. Whether or 
 to what extent the oxychloride of zinc is a true chemical compound is not 
 known. 
 
 Zinc oxyphosphate is a preparation used similarly to the oxychloride. It 
 is made by mixing zinc oxide with phosphoric acid. The acid used is either 
 ortho- or metaphosphoric acid, or a mixture of both. In all cases a zinc phos- 
 phate is formed, but as the quantity of zinc oxide used is larger than needed 
 for saturating the acid completely, the mass as used by dentists is generally a 
 mixture of zinc phosphate with zinc oxide. 
 
 Zinc bromide, Zinci bromidum, ZnBr 2 = 223.62. Obtained 
 analogously to the chloride by dissolving zinc in hydrobromic acid ; 
 it is a white powder, resembling the chloride in its properties. 
 
 Zinc iodide, Zinci iodidum, ZnI 2 = 316.7. The two elements 
 zinc and iodine combine readily when heated with water ; the color- 
 less solution when evaporated to dryness yields a powder whose 
 physical properties resemble those of the chloride. 
 
 Zinc carbonate, Zinci carbonas prsecipitatus, 2ZnCO 3 .3Zn(OH) 2 
 (Precipitated carbonate of zinc). Solutions of equal quantities of zinc 
 sulphate and sodium carbonate are mixed and boiled, when a white pre- 
 cipitate is formed, which is a mixture of the carbonate and hydroxide 
 of zinc, corresponding more or less to the formula given above. 
 5ZnSO 4 + 5Na 2 CO 3 + 3H 2 O = 3CO 2 + 5Na 2 SO 4 -f 2(ZnCO 3 ).3Zn(OH) 2 . 
 
 Precipitated zinc carbonate is a white, impalpable powder, odorless 
 and tasteless, insoluble in water, soluble in acids and in ammonia water. 
 
 Experiment 37. Dissolve 10 grammes of the zinc sulphate obtained in Experi- 
 
ZINC. 315 
 
 ment 3, in about 200 c.c. of water, heat to boiling, and add slowly, while stir- 
 ring, concentrated solution of sodium carbonate until precipitation is complete. 
 After the precipitate has settled, pour off the liquid, and wash the former sev- 
 eral times with hot water by decantation. Then filter and wash the precipitate 
 again several times with hot water, drain, and dry. 
 
 Heat some of the dried zinc carbonate gradually to redness in a porcelain 
 crucible with the cover on. What is formed? What color has it while hot? 
 When the crucible is cold, place the residue in a tube and add dilute acid. 
 Does any effervescence take place. Write reaction. Compare with experi- 
 ments 25 and 26. 
 
 Zinc sulphate, Zinci sulphas, ZnSO 4 .7H 2 O = 285.4 ( White vit- 
 riol), is obtained by dissolving zinc in dilute sulphuric acid : 
 H 2 SO 4 + a:H 2 O + Zn = ZnSO 4 + xH 2 O -f 2H. 
 
 If zinc be added to strong cold sulphuric acid, no decomposition 
 takes place, because there are no ions present, and an acid does not 
 exhibit acid properties unless ions *are formed, as explained in 
 Chapter 15. 
 
 Dilute sulphuric acid scarcely acts on pure zinc, but addition of a few c.c. of 
 solution of cupric sulphate or platinic chloride causes brisk action. This is 
 due to the deposition of the copper or platinum on the zinc, thus forming an 
 electric couple, whereby solution of zinc is facilitated. 
 
 Zinc sulphate forms small, colorless crystals, which are isomor- 
 phous with magnesium sulphate ; it is easily soluble in water. It is 
 so much like magnesium sulphate in appearance that it is sometimes 
 taken in mistake for the latter salt. The tests given below will dis- 
 tinguish between the two salts. 
 
 Antidotes. Soluble zinc salts (sulphate, chloride) have a poisonous effect. 
 If the poison have not produced vomiting, this should be induced. Milk, 
 white of egg, or, still better, some substance containing tannic acid (with which 
 zinc forms an insoluble compound) should be given. 
 
 Tests for zinc. 
 (Use a 5 per cent, solution of zinc sulphate.) 
 
 1. Add to the solution some ammonium sulphide. A white precipi- 
 tate of zinc sulphide, ZnS, is produced, which is soluble in mineral 
 acids, but not in acetic acid. (Of the familiar metals, zinc is the only 
 one whose sulphide is white.) 
 
 If the zinc salt is not pure, the sulphide may appear more or less 
 gray instead of white : 
 
 ZnS0 4 + (NH 4 ) 2 S = (NH 4 ) 2 S0 4 + ZnS. 
 
316 
 
 
 
 1 
 
 METALS AND THEIR COMBINATIONS. 
 3 4 * & g 
 
 .2* 
 ft 
 
 O 
 
 2 3 
 
 a> ft 3 
 
 o 
 
 S 
 
 1 
 
 - 
 
 * 
 
 s.s 
 
 8 S PQ 
 
 1 
 
 S o> 
 
 as 
 
 3 -sis- 
 
 | & E 
 
 I 5* 4> a 
 
 N 
 
 1:1 
 
 ftg 
 
 oT S 
 
 ?T3 
 
 al 
 
 ^'3 
 
 s 
 
 - - . 
 
 43-33 a 
 
 o>^-> ot 
 
 
 
 T3 . a 
 
 25 '3 
 
 .d S -^ 
 
 '3 
 
 <U 
 
 
 . 
 
 
 8 o 
 
 g'e 
 
 ^ ftp 
 
 ,0 
 
 "3 S 
 
 1 
 
 a g a 
 
 . S 
 
 r 
 
 a 
 
 15 
 
 1 
 
 'O 
 
 fl 
 
 o 
 
ZINC. 317 
 
 2. Hydrogen sulphide passed into the solution gives a partial pre- 
 cipitate of zinc sulphide because of the solvent action of the acid 
 liberated. In the presence of sodium acetate, however, the precipi- 
 tate is complete because of the liberation of acetic acid, in which the 
 sulphide is insoluble : 
 
 ZnS0 4 -I- 2Na(C 2 H 3 2 ) + H 2 S = ZnS + Na 2 SO 4 + 2H.C 2 H 3 2 . 
 
 3. Addition of caustic alkali or ammonia water gives a white pre- 
 cipitate of zinc hydroxide, Zn(OH) 2 . It is soluble in excess of the 
 alkali, forming zincates : 
 
 Zn(OH) 2 + 2NaOH = Zn(ONa) 2 + 2H 2 0. 
 
 The hydroxide is also soluble in excess of ammonia water, forming 
 a complex compound, Zn(NH 3 ) 4 .(OH) 2 . In this respect zinc differs 
 from magnesium. The ions of this compound are Zn(NH 3 ) 4 " and 
 2(OH)'. 
 
 4. Addition of a solution of acarbftnate or phosphate, gives a white 
 precipitate of zinc carbonate or phosphate : 
 
 ZnSO 4 -f Na 2 HPO 4 = ZnHPO 4 + Na 2 S0 4 . 
 
 Zinc carbonate is soluble in excess of ammonium carbonate. 
 
 5. Solution of potassium ferrocyanide gives a white precipitate of zinc 
 ferrocyanide. (Distinction from magnesium and aluminum, which give 
 no precipitate.) The precipitate is Zn 2 Fe(CN) 6 , and is difficultly 
 soluble in hydrochloric acid. 
 
 Tests 1, 3, and 5 together are conclusive for zinc salts. Practically 
 all the compounds of zinc are colorless. The oxide, carbonate, phos- 
 phate, ferrocyanide, and sulphide are insoluble in water; the chloride, 
 bromide, iodide, nitrate, sulphate, and acetate are soluble in water. 
 These are the common salts. The soluble zinc salts are hydrolyzed 
 somewhat in water, and therefore show an acid reaction. This explains 
 the solvent action of a zinc chloride solution when used on metal sur- 
 faces in soldering. The coat of metallic oxide is thus removed. 
 
 Zinc forms the divalent ion Zn", which unites with acid radicals to form 
 the zinc salts. The ionic equations for the above tests are of the same form as 
 those given under the tests for calcium. Zn(OH) 2 has weak basic properties, 
 and still weaker acid properties. Like aluminum and chromium hydroxides, 
 it is slightly soluble and ionizes in two ways, thus : 
 
 Zn(OH) 2 ^ Zn" 4 2(OH)'. 
 With acids, zinc salts are formed by the union of (OH) 7 and H* ions to form water. 
 
 Also, Zn(OH) 2 ; Zn0 2 " 4- 2H', 
 
 and with considerable excess of alkali the hydroxide dissolves to form zincates 
 
318 METALS AND THEIR COMBINATIONS. 
 
 by the union of H* ions with (OH)' ions of the alkali. The equation in sim- 
 ple form is written, 9 
 Zn(OH) 2 + 2XaOH = Na. 2 ZnO 2 -f 2H 2 O. 
 
 Cadmium, Cd = 111.6. Found in nature associated (though in very small 
 quantities) with the various ores of zinc, with which metal it has in common a 
 number of physical and chemical properties. Cadmium differs from zinc by 
 forming a yellow sulphide (with hydrogen sulphide), insoluble in diluted acids. 
 Cadmium and its compounds are of little interest here; the yellow sulphide is 
 used as a pigment, the sulphate and iodide sometimes for medicinal purposes. 
 
 Cadmium is a constituent of many alloys distinguished by very low fusing 
 points. 
 
 30. LEAD -COPPER -BISMUTH. 
 
 General remarks regarding the metals of the lead group. The 
 six metals belonging to this group (Pb, Cu, Bi, Ag, Hg, and Cd) are 
 distinguished by forming sulphides which are insoluble in water, 
 insoluble in dilute mineral acids, insoluble in ammonium sulphide ; 
 consequently they are precipitated from neutral, alkaline, or acid 
 solutions by hydrogen sulphide or ammonium sulphide. 
 
 The metals themselves do not decompose water at any temperature, 
 and are not acted upon by dilute sulphuric acid ; heated with strong 
 sulphuric acid, most of these metals are converted into sulphates with 
 liberation of sulphur dioxide ; nitric acid converts all of them into 
 nitrates with liberation of nitric oxide. 
 
 The oxides, iodides, sulphides, carbonates, phosphates, and a few of 
 the chlorides and sulphates of these metals are insoluble ; all the 
 nitrates, and most of the chlorides and sulphates are soluble. 
 
 In regard to valence, they show no uniformity whatever, silver 
 being univalent, copper, cadmium, and mercury bivalent, bismuth 
 trivalent, and lead either bivalent or quadrivalent. 
 
 Lead, Pb 11 = 2O5.35 (Plumbum). This metal is obtained chiefly 
 from the native lead sulphide (galena), PbS, by first roasting it, 
 whereby part is converted into oxide and sulphate. By heating this 
 
 QUESTIONS. How is zinc found in nature, and by what process is it ob- 
 tained? Mention the properties of metallic zinc, and what is it used for? 
 Mention two processes for making zinc oxide. How does heat act on zinc 
 oxide? Show by chemical symbols the action of hydrochloric and sulphuric 
 acids on zinc. State the properties of chloride and of sulphate of zinc. AVhat 
 is white vitriol? Explain the formation of precipitated zinc carbonate, and 
 state its composition. Mention tests for zinc compounds. How many pounds 
 of crystallized zinc sulphate may be obtained from 21.7 pounds of metallic 
 zinc? i 
 
LEAD-COPPER-BISMUTH. 319 
 
 mixture with undecomposed sulphide to a higher temperature lead is 
 formed, thus : 
 
 PbS + 2PbO == 3Pb + S0 2 and PbS + PbSO 4 == 2Pb + 2SO 2 . 
 Lead owes its usefulness in the metallic state chiefly to its softness, 
 fusibility, and resistance to acids, which properties are of advantage 
 in using it for tubes or pipes, or in constructing vessels to hold or 
 manufacture sulphuric acid. 
 
 Lead is exceedingly malleable and somewhat ductile, but not very tenacious. 
 It is a constituent of many alloys, as for instance of type metal, britannia metal, 
 shot, etc. Common solder is an alloy of equal weights of lead and tin. The 
 noble metals are rendered brittle and unworkable when alloyed with even a 
 small quantity of lead. 
 
 Experiment 38. Dissolve 1 gramme of lead acetate or lead nitrate in about 
 200 c.c. of water, suspend in the centre of the solution a piece of metallic zinc, 
 and set aside. Notice that metallic lead is deposited slowly upon the zinc in a 
 crystalline condition, while zinc passes into solution, which may be verified by 
 analytical methods. The chemical change taking place is this : 
 
 Pb(N0 3 ) 2 + Zn Zn(N0 3 ) 2 + Pb. 
 
 Electrolytic solution tension. The precipitation of lead from solution 
 by zinc in the experiment above is represented by the ionic equation : 
 
 Zn + Pb" + 2NO 3 ' = Zn" + 2NO 3 ' + Pb. 
 
 The lead ions lose their charges to zinc which becomes ionic, while metallic 
 lead is precipitated. This action is pretty much like the liberation of hydrogen 
 from acids by some metals : 
 
 Zn + 2H* + SO 4 " = Zn" + SO 4 " -f H 2 . 
 
 The explanation of this type of chemical change is found in the theory of elec- 
 trolytic solution tension proposed by Nernst. According to this, a metal when 
 immersed in water or a solution sends some positive ions into the solution, and 
 itself assumes negative charges of electricity. This proceeds to a point where 
 the metal is sufficiently charged negatively that it attracts its positive ions at 
 the same rate at which they tend to be given off from the metal. An equilib- 
 rium between the two tendencies is reached. The tension or pressure that 
 drives the ions into the solution differs for different metals, the order of decrease 
 being the same as the order in the electrochemical series of the metals (page 
 198). Any metal in the series has a higher tension than those following, and 
 will displace them from solutions of their salts, but not vice versa. Zinc has 
 a much greater solution tension than lead. When it is placed in the lead solu- 
 tion, it acquires a greater negative charge of electricity than does a piece of 
 lead when it is placed in a solution. The result is that the lead ions are 
 attracted to the zinc and discharged, and metallic lead is deposited. This 
 process continues until all the lead has been deposited from the solution, which 
 then contains an equivalent amount of zinc salt. 
 
 Lead oxide, Plumbi oxidum, PbO = 221.23 (Litharge). Obtained 
 by exposing melted lead to a current of air, when the metal is 
 
320 METALS AND THEIR COMBINATIONS. 
 
 gradually oxidized with the formation of a yellow powder, known 
 as massicot; at a high temperature this fuses, forming reddish-yellow 
 crystalline scales, known as litharge ; by heating still further in con- 
 tact with air, a portion of the oxide is converted into dioxide (or 
 peroxide), PbO 2 , and a red powder is formed, known as red lead (or 
 minium), which probably is a mixture (or combination) of oxide and 
 dioxide of lead, PbO 2 (PbO) 2 . 
 
 Lead oxide is used in the manufacture of lead salts, lead plaster, 
 glass, paints, etc. 
 
 Nitric acid when heated with red lead combines with the oxide, 
 while lead dioxide, PbO 2 , is left as a dark-brown powder, which, on 
 heating with hydrochloric acid, evolves chlorine (similar to man- 
 ganese 'dioxide). Lead dioxide is a conductor of electricity, differ- 
 ing thus from most oxides. 
 
 Accumulator or storage battery. This consists of two sets of lead 
 plates made in the form of gratings. One set, which are all connected, have 
 the spaces in the gratings filled up with spongy lead ; the other set, likewise 
 connected, are filled up with lead dioxide. When the plates are dipped into 
 dilute sulphuric acid they show a difference of potential, and when connected 
 a current flows. When in action or discharging, the SO/' ions of the sul- 
 phuric acid are attracted to the plates filled with spongy lead, give up their 
 negative charges to the plate, and form lead sulphate. The H* ions of the acid 
 pass to the plates filled with PbO 2 , give up their positive charges, and reduce 
 PbO 2 to PbO, which combines with sulphuric acid and forms lead sulphate. 
 The current flows in the outside circuit from the plates filled with PbO 2 to the 
 plates filled with spongy lead, and has a voltage of about 2. Both plates ulti- 
 mately become filled with PbSO 4 , and the battery then is exhausted. Sul- 
 phuric acid is removed from the solution, and the specific gravity of the latter 
 falls. By this means one can tell when the battery is approaching exhaustion. 
 
 Charging the battery consists in restoring the plates to their original state, 
 and is accomplished bypassing a current from a dynamo through it in a direc- 
 tion opposite to that of the current produced by the battery. By this action 
 electrical energy is stored up in the battery as chemical energy, which is given 
 back again as electrical energy when the battery is discharged. When the 
 dynamo current passes, H* ions of the acid solution pass to the plates originally 
 filled with lead, and form sulphuric acid with SO/ X ions of the lead sulphate, 
 leaving the plate finally filled with reduced spongy lead. At the same time, 
 SO 4 X/ ions of the acid solution pass to the other plates, where they are dis- 
 charged and enter into reaction with the lead sulphate in the plates, thus : 
 
 PbS0 4 + SO, -f 2H 2 = PbO 2 + 2H 2 S0 4 . 
 
 All the lead sulphate is ultimately converted into lead dioxide, and this set of 
 plates are restored to the original state. All the sulphuric acid is restored to 
 the liquid, and the battery is ready for use. The changes involved in the com- 
 plete cycle may be written in one equation, thus: 
 
 discharging. 
 
 2PbS0 4 -(- 2H 2 ^ Pb + 2H 2 S0 4 -f PbO 2 . 
 charging * 
 
LEAD COPPER BISMUTH. 321 
 
 Lead nitrate, Plumbi nitras, Pb(NO 3 ) 2 328.49. Obtained by 
 dissolving the oxide in nitric acid : 
 
 PbO + 2HN0 3 = H 2 + Pb(N0 3 ) 2 . 
 
 Lead nitrate is the only salt of lead (with a mineral acid) which is 
 easily soluble in water ; it has a white color, and a sweetish, astrin- 
 gent, and afterward metallic taste. It is insoluble in strong nitric 
 acid ; hence lead is insoluble in this acid. 
 
 Experiment 39. Heat 30 c.c. of dilute nitric acid, but not to the boiling- 
 point, and dissolve in it, with stirring, small portions of lead oxide, until no 
 more is taken up. Filter the solution if necessary, and let it cool to crystallize. 
 If no crystals form, concentrate further. The crystals are octahedra. Examine 
 their appearance and form. Which one of the methods of forming salts does 
 this experiment illustrate ? 
 
 Heat some of the dried and powdered crystals in a porcelain crucible mod- 
 erately. Note the brown fumes of nitrogen tetroxide and residue of brown lead 
 oxide, which becomes yellow on cooling. This experiment illustrates the 
 instability of most nitrates when heated, and the method by which some oxides 
 are obtained : 
 
 Pb(N0 3 ) 2 = PbO + N 2 4 + O. 
 
 Lead carbonate, PbCO 3 , occurs in nature as the mineral cerussite, 
 and may be obtained by precipitation of a lead acetate solution with 
 sodium bicarbonate. While this normal salt is scarcely used, the basic 
 lead carbonate or white lead of the approximate composition 2PbCO 3 . 
 Pb(OH) 2 is used very largely as a constituent of paints. It is man- 
 ufactured on a large scale directly from lead, by exposing it to the 
 simultaneous action of air, carbon dioxide, and vapors of acetic acid. 
 The latter combines with the lead, forming a basic acetate, which is 
 converted into the carbonate (almost as soon as produced) by the 
 carbon dioxide present. 
 
 The action of acetic acid on lead or lead oxide will be considered 
 in connection with acetic acid. 
 
 Lead carbonate is a heavy, white, insoluble, tasteless powder ; the 
 white-lead of commerce frequently is found adulterated with barium 
 sulphate, gypsum or lead sulphate. 
 
 Lead iodide, Plumbi iodidum, PbI 2 = 457.15. Made by adding 
 solution of potassium iodide to lead nitrate (Plate III., 6) : 
 Pb(NO 3 ) 2 + 2KI = 2KNO S + PbI 2 . 
 
 It is a heavy, bright yellow, almost insoluble powder, which ma/ 
 be distinguished from lead chromate by its solubility in ammonium 
 chloride solution on boiling, lead chromate being insoluble in this 
 solution. 
 
 21 
 
322 .METALS AND THEIR COMBINATIONS. 
 
 Poisonous properties and antidotes. Compounds of lead are directly 
 poisonous, and it happens, not infrequently, that water passing through leaden 
 pipes or collected in leaden tanks becomes contaminated with lead. Water 
 free from air and salts scarcely acts on lead ; but if it contain air, oxide of lead 
 is formed, which is either dissolved by the water or is decomposed by the 
 nitrates or chlorides present in the water, the soluble nitrate or chloride of lead 
 being formed. 
 
 If the water contains carbonates and sulphates, however, these will form 
 insoluble compounds, producing a film or coating over the lead, preventing 
 further contact with the water. Rain water, in consequence of its containing 
 atmospheric constituents, and no sulphates, acts as a solvent on lead pipe ; 
 spring and river waters generally do not. 
 
 Water containing lead will show a dark color on passing hydrogen sulphide 
 through it ; if the quantity present be very small, the water should be evapo- 
 rated to ^ or even -^ of its original volume before applying the test. 
 
 The constant handling of lead compounds is one of the causes of lead 
 poisoning (painters' colic). As an antidote, mangesium sulphate should be 
 used, which forms with lead an insoluble sulphate ; the purgative action of 
 magnesia is also useful. (In lead works workmen often drink water containing 
 a little sulphuric acid.) 
 
 Tests for lead. 
 (Use a 5 per cent, solution of lead acetate or lead nitrate.) 
 
 1. Hydrogen sulphide or ammonium sulphide added to the solution 
 produces a black precipitate of lead sulphide (Plate III.,, 1), insol- 
 uble in dilute acids or alkalies. A very delicate reaction : 
 
 Pb(N0 3 ) 2 + H 2 S PbS + 2HN0 3 . 
 
 2. Dilute sulphuric acid or a solution of a sulphate gives a white 
 precipitate of lead sulphate, PbSO 4 . This is one of the four insoluble 
 sulphates. (See test 2 for sulphates.) 
 
 3. Other reagents which give precipitates with solutions of lead 
 salts are : 
 
 Hydrochloric acid or solution of a chloride, producing white lead 
 chloride, PbCl 2 . (See test 3 for hydrochloric acid.) 
 
 Potassium iodide, producing yellow lead iodide, PbI 2 (Plate III., 
 6). (See test 2 for iodides.) 
 
 Potassium chromate, producing yellow lead chromate (chrome-yel- 
 low), PbCr0 4 (Plate II., 6). (See test 2 for chromates.) 
 
 Alkali carbonates, producing white basic lead carbonate. 
 
 Alkali phosphates, producing white lead phosphate, PbHPO 4 . 
 
 Solution of sodium hydroxide, producing white lead hydroxide, 
 Pb(OH) 2 , which dissolves in excess of the alkali, forming sodium 
 plumbite, Pb(ONa) 2 . (See comments on tests for zinc, page 317.) 
 
LEAD COPPER BISMUTH. 323 
 
 C When a charcoal reduction test (for which see directions in test 
 3 for sulphates) is made on any dry lead compound, a globule of 
 metallic lead is obtained, which is recognized by its softness and 
 malleability. Try its solubility in dilute hydrochloric, sulphuric, and 
 nitric acids. 
 
 Tests 1, 2, and 4 are sufficient for recognition of a lead compound. 
 Lead salts are mostly colorless. Lead nitrate has an acid reaction, 
 due to hydrolysis in water. 
 
 Copper, Cu u = 63.1 (Cuprum). Found in nature sometimes in the 
 metallic state generally, however, combined with sulphur or oxygen. 
 The commonest copper-ore is Copper pyrites, a double sulphide of 
 copper and iron, CuFeS 2 or Cu 2 S.Fe 2 S 3 , having the color and lustre 
 of brass or gold. Other ores are : Copper glance, cuprous sulphide, 
 having a dark-gray color and the composition Cu 2 S ; malachite, a 
 beautiful green mineral, being a carbonate and hydroxide of copper, 
 CuCO 3 .Cu(OH) 2 . Cuprous and cupric oxide also are found occasion- 
 ally. Copper is obtained from the oxide by reducing it with coke ; 
 sulphides previously are converted into oxide by roasting. 
 
 Copper is the only metal showing a distinct red color ; it is so 
 malleable that, of the metals in common use, only gold and silver 
 surpass it in that respect ; it is one of the best conductors of heat and 
 electricity, it does not change in dry air, but becomes covered with a 
 film of green subcarbonate when exposed to moist air. 
 
 Copper frequently is used in the manufacture of alloys, of which 
 the more important are : 
 
 Copper. Zinc. Tin. Nickel. Antimony. 
 
 Brass .... 64 36 
 
 German silver ... 51 31 ... 18 
 
 Bell-metal ... 78 ... 22 
 
 Bronze .... 80 16 4 
 
 Gun-metal ... 90 ... 10 
 
 Babbit-metal ... 43 ... 43 ... 14 
 
 Copper frequently is alloyed with gold and silver. 
 
 Copper forms two oxides, and corresponding to these are two series 
 of salts, known as cuprous and cupr/c compounds. Cuprous salts of 
 oxygen acids do not exist. The principal cuprous compounds are 
 Cu 2 O, CuCl, CuBr, Cul, Cu(CN), Cu 2 S. All these, except Cu 2 Oand 
 Cu 2 S, are white and insoluble in water. Cupric iodide, (CuI 2 ), and 
 cyanide, (Cu(CN) 2 ), cannot be obtained, as they decompose into the 
 cuprous salt and free iodine or cyanogen, CuI 2 = Cul + I. These are 
 obtained when potassium iodide or cyanide solution is added to solu- 
 tion of cupric sulphate : 
 
 CuS0 4 -f 2KI = Cul + I + K 2 SO 4 , 
 
324 METALS AND THEIR COMBINATIONS. 
 
 Cupric compounds are more numerous, as they embrace the salts of 
 oxygen acids as well as salts of some of the halogen acids. The 
 anhydrous salts are usually white or yellow, but the solutions as well as 
 the hydrated crystals are usually blue or greenish blue. The cupric 
 compounds are more important and familiar than the cuprous salts, 
 and those most frequently employed are the sulphate, acetate, and 
 oxide. The valence of copper in cupric compounds is 2. Some facts 
 indicate that in the cuprous compounds the valence of copper is 1, 
 while others indicate that it is 2. Some writers assign the valence of 
 2 to copper in all its compounds, and use double formulas for the 
 cuprous salts to account for the apparent univalence of copper, thus, 
 Cu 2 Cl 2 or Cl-Cu Cu-Cl, assuming that two atoms of copper are 
 united by one bond. The behavior of the cuprous salts can very 
 readily be represented by the simple formulas and univalence of copper, 
 and there is no need for using double formulas. 
 
 Cupric oxide, CuO (Black oxide or monoxide of copper). Heated 
 to redness, copper becomes covered with a black scale, which is cupric 
 oxide ; it is obtained also by heating cupric nitrate or carbonate, both 
 compounds being decomposed with formation of the oxide ; finally, 
 it may be made by adding sodium or potassium hydroxide to the 
 solution of a cupric salt, when a bulky, pale-blue precipitate of cupric 
 hydroxide, Cu(OH) 2 , is formed, which, upon boiling, is decomposed into 
 water and cupric oxide, a heavy dark-brown powder (Plate III., 2) : 
 
 CuS0 4 + 2KOH = K 2 SO 4 + Cu(OH) 2 ; 
 Cu(OH) 2 = H 2 O + CuO. 
 
 Cuprous oxide, Cu 2 O ( Red oxide or suboxide of copper). When 
 cupric oxide is heated with metallic copper, charcoal, or organic 
 matter, the cupric oxide is decomposed, and cuprous oxide is formed. 
 (Excess of carbon or organic matter reduces the oxide to metallic 
 copper.) 
 
 CuO -f Cu = Cu 2 O; 
 2CuO + C = Cu 2 O + CO. 
 
 Some organic substances, especially grape-sugar, decomposes alkaline 
 solutions of cupric sulphate with precipitation of cuprous oxide, which 
 is a red, insoluble powder. 
 
 Experiment 40. To 5 c.c. of a 5 per cent, solution of copper sulphate add 
 about 20 c.c. of the reagent solution of sodium hydroxide. Note the blue pre- 
 cipitate of copper hydroxide, Cu(OH) 2 . Add to the mixture about 2 grammes 
 of Rochelle salt (sodium potassium tartrate) and shake. The precipitate dis- 
 
LEA D COPPERBISMUTH. 325 
 
 solves to a deep blue solution, which is essentially Fehling's solution (see Index). 
 The copper enters the negative tartaric acid radical or ion, and while in the 
 cupric state is not precipitated by alkali. If the copper is reduced to the 
 cuprous state, it can no longer remain in solution and is precipitated as the 
 reddish cuprous oxide, Cu 2 O. 
 
 Heat the blue solution to boiling and add a little dilute glucose solution and 
 heat again a few minutes. A precipitate of cuprous oxide is produced, due to 
 the reducing action of the glucose. This is usually employed as a test for 
 glucose in urine. 
 
 Cupric sulphate, Cupri sulphas, CuSO 4 .5HO 2 = 247.85 (Sul- 
 phate of copper, Slue vitriol, Blue-stone). This is the most important 
 compound of copper. It is manufactured on a large scale, either 
 from copper pyrites, or by dissolving cupric oxide in sulphuric acid, 
 evaporating and crystallizing the solution. 
 
 Cupric sulphate forms large, transparent, deep-blue crystals, which 
 are easily soluble in water, and have a nauseous, metallic taste. By 
 heating it to about 200 C. (392 F.) all water of crystallization is 
 expelled, and the anhydrous cupric sulphate formed, which is a white 
 powder. By further heating this is decomposed, sulphuric and 
 sulphurous oxides are evolved, and cupric oxide is left. 
 
 Experiment 41. Boil about 5 grammes of fine copper wire with 15 c.c. of 
 concentrated sulphuric acid until the action ceases and most of the copper 
 is dissolved. Dilute with about 15 c.c. of hot water, filter, and set aside for 
 crystallization State the exact quantities of copper and H 2 S0 4 required to 
 make 100 pounds of crystallized cupric sulphate. 
 
 Cupric carbonate is obtained by the addition of sodium carbonate 
 to solution of cupric sulphate, when a bluish-green precipitate is 
 formed, which is cupric carbonate with hydroxide (Plate III., 4); by 
 dissolving this in the various acids, the different cupric salts are 
 obtained. 
 
 Ammoniocopper compounds. A number of compounds are 
 known which are either double salts of ammonia and copper, or are 
 derived from ammonium salts and contain copper. Thus, cupric 
 chloride forms with ammonia the compounds : CuCl 2 (NH 3 ) 2 , CuCl 2 
 (NH 3 ) 4 , and CuCl 2 (NH 3 ) 6 . Cupric sulphate forms in like manner, 
 cupric- diammonium sulphate, CuSO 4 (NH 3 ) 2 , and cupric tetrammo- 
 nium sulphate, CuSO 4 (NH 3 ) 4 , which is a deep azure-blue compound 
 taking up one molecule of water during crystallization. 
 
 It is this formation of soluble ammonio-copper compounds which 
 causes the deep blue color in solutions of cupric salts on the addition 
 of ammonia water. 
 
326 METALS AND THEIR COMBINATIONS. 
 
 All copper salts, except the sulphide, are soluble in ammonia water. Hence, 
 copper cannot be precipitated from ammoniacal solution by any reagent except 
 hydrogen sulphide or alkali sulphides. Copper hydroxide with excess of am- 
 monia water forms the deep-blue soluble compound, Cu(NH 3 ) 4 .(OH) 2 , in which 
 the copper is held in the complex radical or ion, Cu(NH 3 ) 4 ". The ammonio- 
 copper salts are derived from the hydroxide above, and also contain the radical 
 Cu(NH 3 ) 4 ", which is the cause of the blue color. The sulphate has the for- 
 mula Cu(NH 3 ) 4 .SO 4 .H 2 O. 
 
 With excess of alkali cyanides, copper also forms complex double cyanides, 
 from which copper cannot be precipitated by any reagent, not even hydrogen 
 sulphide. 
 
 Poisonous properties and antidotes. The use of copper for culinary vessels 
 Is frequently the cause of poisoning by this metal. A perfectly clean surface of 
 metallic copper is not affected by any of the substances used in the preparation 
 of food, but as the metal is very apt to become covered with a film of oxide 
 when exposed to the air, and as the oxide is easily dissolved by the combined 
 action of water, carbonic or other .acids, such as are found in .vinegar, the juice 
 of fruits, or rancid fats, the use of copper for culinary vessels is always 
 dangerous. Actual adulterations of food with compounds of copper have been 
 detected. 
 
 In cases of poisoning by copper the stomach-pump should be used, vomiting 
 induced, and albumen (white of egg) administered, which forms an insoluble 
 compound with copper. Reduced iron, or a very dilute solution of potassium 
 ferrocyanide, may be of use as antidotes. 
 
 Tests for copper. 
 (Use a 5 per cent, solution of copper sulphate.) 
 
 1. Add to the solution hydrogen sulphide or ammonium sulphide : 
 q, black precipitate of cupric sulphide is formed. (Plate III., 1) : 
 
 CuS0 4 + H 2 S == H 2 SO 4 -f CuS. 
 
 2. Add solution of sodium or potassium hydroxide : a bluish pre- 
 cipitate of cupric hydroxide, Cu(OH) 2 , is formed, which is converted 
 into dark-brown cupric oxide, CuO, by boiling. (See equation 
 above.) (Plate III., 2.) 
 
 3. Add ammonia water : a bluish precipitate of cupric hydroxide 
 is formed which readily dissolves in an excess of the reagent, forming 
 a deep azure-blue solution containing an ammonio-copper compound. 
 (See explanation above.) (Plate III., 3.) 
 
 The delicacy of this test is shown by diluting the solution of the 
 copper salt until its color is no longer visible, and then adding 
 ammonia. 
 
COPPER. LEAD. BISMUTH. 
 
 PLATE 
 
 Cupric sulphide or lead .sulphide, 
 
 precipiiateil from Milutioiih of nipper or 
 lead by liydi ouen sulphide. 
 
 Cupric hydroxide passing into cupric 
 oxide. Cupric solutions precipitated by 
 potassium hydroxide and boiling. 
 
 Cupric solutions treated with am- 
 monia water. 
 
 Cupric carbonate, precipitated from 
 
 cupric solutions by sodium carbonate. 
 
 Cupric ferrocyanide, precipitated 
 from cupric solutions by potassium, ferro- 
 cyanide. 
 
 Lead iodide, precipitated from lead 
 solutions by soluble iodides. 
 
 Lead solutions with soluble chlorides, 
 sulphates or carbonates. Bismuth solu- 
 tions with alkali hydroxides or carbonates. 
 
 Bismuth sulphide, precipitated from 
 bismuth solutions by hydrogen sulphide. 
 
 , Litti Balliinocr. . Ifd 
 
LEA D COPPER BISM mi. 327 
 
 4. Add solution of potassium ferrocyanide : a reddish-brown pre- 
 cipitate of cupric ferrocyanide, Cu 2 Fe(CN) 6 , is obtained. (Plate III., 5.) 
 
 This is a very delicate test, and should also be made on a highly 
 diluted solution made as directed in test 3. 
 
 5. Add solution of sodium or potassium carbonate : green cupric 
 carbonate with hydroxide is precipitated. (Plate III., 4.) 
 
 6. Immerse a piece of iron or zinc, showing a bright surface, in an 
 acidified solution of copper : the latter is precipitated upon the iron, an 
 equivalent amount of iron passing into solution. (See page 319.) 
 
 CuS0 4 + Fe FeS0 4 + Cu. 
 
 7. Most compounds of copper color the flame green, cupric chloride, 
 blue. The cupric chloride flame can be made very striking by dis- 
 solving the copper salt in a little concentrated hydrochloric acid, 
 pouring this solution on the corner of a piece of iron wire gauze, and 
 holding it in the Bunsen flame. 
 
 8. Cupric compounds give a blue, cuprous compounds a red, borax 
 bead. 
 
 Tests 3, 4, 6, and 8 are sufficient to identify copper compounds. The 
 insoluble ones are made soluble by treating with mineral acids. The 
 sulphate, nitrate, chloride, acetate, and ammonio-salts of copper are 
 soluble in water, most of the other compounds are insoluble. The 
 soluble normal salts redden litmus, due to hydrolysis. 
 
 The ionic equations for the tests are of the same form as those given under 
 the tests for calcium. 
 
 Bismuth, Bi iu = 206.9. Found in nature chiefly in the metallic 
 state, disseminated, in veins, through various rocks. The extraction 
 of the metal is a mere mechanical process, the earthy matter contain- 
 ing it being heated in iron cylinders, and the melted bismuth collected 
 in suitable receivers. 
 
 Bismuth is grayish-white, with a pinkish tinge, very brittle, gen- 
 erally showing a distinct crystalline structure. Occasionally it is 
 used in alloys and in the manufacture of a few medicinal prepara- 
 tions. 
 
 Bismuth has the property of expanding while passing from the liquid to the 
 solid state, and of greatly lowering the fusing point of other metals. These 
 properties make it a useful constituent of many alloys. The presence of bis- 
 muth in dental amalgams renders them sticky and adhesive and causes them 
 to require a larger proportion of mercury. 
 
 Bismuth is trivalent, as a rule, as shown in the chloride, BiCl 3 , or 
 oxide, Bi 2 O 3 , but it is also quinquivalent, as shown by the oxide, 
 
328 METALS AND THEIR COMBINATIONS. 
 
 Bi 2 O 5 , corresponding to P 2 O 5 , Sb 2 O 5 , I 2 O 5 , or N 2 O 5 . In fact, bismuth 
 forms, besides the two oxides mentioned, two others of the composition 
 Bi 2 O 2 and Bi 2 O 4 , corresponding to the respective nitrogen oxides. 
 A characteristic property of this metal is decomposition of the con- 
 centrated solution of any of its normal salts by the addition of much 
 water, with the formation and precipitation of so-called oxysalts or 
 subsalts of bismuth, while some bismuth with a large quantity of 
 acid remains in solution. This is due to the very weak basic charac- 
 ter of Bi(OH) 3 . 
 
 The true constitution of these subsalts is as yet doubtful, but a 
 comparison of them has led to the assumption of a radical Bismuthyl, 
 BiO, which behaves like an atom of a univalent metal. 
 
 The relation between the normal or bismuth salts, and the subsalts 
 or bismuthyl salts, will be shown by the composition of the following 
 compounds : 
 
 Bismuth chloride, BiCl 3 . Bismuth yl chloride, (BiO)CL 
 
 " bromide, BiBr 3 . " bromide, (BiO)Br. 
 
 iodide, BiI 3 . ' iodide, (BiO)I. 
 
 " nitrate, Bi(NO 3 ) 3 . " nitrate, (BiO)NO 3 . 
 
 sulphate, Bi 2 (S0 4 ) 3 . " sulphate, (BiO) 2 SO 4 . 
 
 carbonate, Bi 2 (CO 3 ) 3 j carbonate, (BiO) 2 CO 3 . 
 
 not known. ) 
 
 The nature of normal bismuth salts and bismuthyl salts may be 
 explained by saying that the first are derived from the triacid base 
 Bi(OH) 3 , the latter from the monacid base BiO.OH. These two 
 hydroxides are related to one another thus : 
 
 Bi(OH) 3 = Bi/ H + H 2 0. 
 
 Bismuth subnitrate, Bismuthi subnitras, BiONO 3 .H 2 O ? (Oxy- 
 nitrate of bismuth}. By dissolving metallic bismuth in nitric acid, a 
 solution of bismuth nitrate is obtained, nitrogen dioxide escaping : 
 Bi + 4HNO 3 = Bi(NO 3 ) 3 + NO + 2H 2 O. 
 
 Upon evaporation of the solution, colorless crystals of bismuth 
 nitrate, Bi(NO 3 ) 3 5H 2 O, are obtained. 
 
 If, however, the solution (or the dissolved crystals) be poured into 
 a large quantity of water, the salt is decomposed with the formation 
 of bismuthyl nitrate and nitric acid, which latter keeps in solution 
 some bismuth : 
 
 Bi(N(V 3 + 2H 2 = BiON0 3 .H 2 O + 2HNO 3 
 
 Subnitrate of bismuth is a heavy, white, tasteless powder, of a 
 
LEAD- COPPER BISMUTH. 329 
 
 somewhat varying chemical composition ; it is almost insoluble in 
 water, soluble in most acids. 
 
 Experiment 42. Dissolve by the aid of heat about 1 gramme of metallic bis- 
 muth in a mixture of 2 c.c. of nitric acid and 1 c.c. of water. Evaporate the 
 clear solution to about one-half its volume, in order to remove excess of acid, 
 and pour this solution of normal bismuth nitrate into 100 c.c. of water. Col- 
 lect the precipitate of bismuthyl nitrate on a filter, wash and dry it. Prove 
 the presence of bismuth in the filtrate by tests mentioned below. 
 
 Bismuth subcarbonate, Bismuth! subcarbonas (BiO) 2 CO 3 . 
 H 2 O (?) (Oxy carbonate of bismuth, Pearl-white). Made by adding 
 sodium carbonate to solution of bismuth nitrate, when the subcarbo- 
 nate is precipitated, some carbon dioxide escaping : 
 
 2Bi(N0 3 ) s + 3Na 2 CO 3 + H 2 O = 6NaNO 3 -f 2CO 2 + (BiO) 2 CO 3 .H 2 O. 
 A white, or pale yellowish-white powder, resembling the subnitrate. 
 It readily loses water and carbon dioxide on heating, when the yellow 
 oxide, Bi 2 O 3 , is left. 
 
 A mixture of bismuth subnitrate, sodium bicarbonate, and water is often 
 prescribed, but, as such a mixture gives off carbon dioxide, it is better to sub- 
 stitute the subcarbonate for the subnitrate. 
 
 Tests for Bismuth. 
 
 Use a solution made by dissolving bismuth subnitrate or subcar- 
 bonate in the least possible quantity of dilute nitric acid, with gentle 
 heat. Dilute cautiously with water, adding a few drops more of the 
 acid if there is any tendency to precipitation. 
 
 1. Add to the solution hydrogen sulphide or ammonium sulphide : 
 a dark-brown (almost black) precipitate of bismuth sulphide, Bi 2 S 3 , 
 is produced (Plate III., 8) : 
 
 2BiCl 3 + 3H 2 S = 6HC1 + Bi 2 S 3 . 
 
 2. Add solution of ammonium or sodium hydroxide, or carbonate : 
 a white precipitate of bismuth hydroxide, Bi(OH) 3 , or of bismuthyl 
 carbonate is produced. (See explanation above.) 
 
 3. Solution of potassium iodide precipitates brown bismuth iodide, 
 B5I 3 , soluble in excess of the reagent. 
 
 4. Solution of potassium dichromate precipitates yellow bismuthyl 
 dichromate, (BiO) 2 Cr 2 O 7 . 
 
 5. A small quantity of bismuth or of any bismuth compound, 
 mixed with equal quantities of sulphur and potassium iodide, and 
 
330 METALS AND THEIR COMBINATIONS. 
 
 heated moderately upon charcoal before the blowpipe, forms a scar- 
 let-red incrustation of bismuthyl iodide, BiOI. 
 
 6. Apply the reduction test on charcoal (see directions in test 3 
 for sulphuric acid) to any dry bismuth compound. A hard, brittle bead 
 of metallic bismuth is produced, which, if dissolved in a little con-, 
 centrated hydrochloric acid, aided by a few drops of nitric acid, and 
 the solution then be strongly diluted with water, gives a dense white 
 precipitate of bismuth subchloride, 
 
 BiCL, + H 2 = BiOCl + 2HC1. 
 
 Tests 1, 5, and 6 together are sufficient to identify a bismuth com- 
 pound. The insoluble or sub-salts are the most stable, and can be dis- 
 solved by acids, forming the normal salts. The latter cannot exist 
 in aqueous solution, except in the presence of an acid. The decomposi- 
 tion of normal salts of bismuth by water into insoluble sub-salts is the 
 most characteristic property of bismuth. One other metal resembles 
 it in this respect, namely, antimony, but its sulphide has an orange 
 color. 
 
 The most readily obtained sub-salt of bismuth is the subchloride, 
 BiOCl . If no precipitate occurs when diluting the nitrate solution 
 (because of too much acidity), addition of solution of ammonium or 
 sodium chloride produces a precipitate of the subchloride imme- 
 diately. 
 
 31. SILVER MERCURY. 
 
 Silver, Ag = 107.12 (Argentum). This metal is found sometimes 
 in the metallic state, but generally as a sulphide, which is nearly 
 always in combination with large quantities of lead sulphide, such 
 ore being known as argentiferous galena. The lead manufactured 
 from this ore contains the silver, and is separated from it by roasting 
 the alloy in a current of air, whereby lead is oxidized and converted 
 into litharge, while pure silver is left. 
 
 QUESTIONS. What are the properties of lead, and from what ore is it ob- 
 tained? What is litharge, and how does it differ from red lead? Give the 
 composition of nitrate, carbonate, and iodide of lead; how are they made? 
 State the analytical reactions for lead. How is copper found in nature ? How 
 many oxides of copper are known ; what is their composition, and under what 
 conditions are they formed? What is "blue vitriol"; how is it made, and 
 what are its properties? How does ammonium hydroxide act on cupric solu- 
 tions? Mention tests for copper. What is the composition of subnitrate and 
 subcarbonate of bismuth ; how are they made from metallic bismuth, and what 
 explanation is given in regard to their constitution ? 
 
SILVER MERCURY. 331 
 
 Silver is 'the whitest of all metals, and takes the highest polish ; 
 it is the best conductor of heat and electricity, and melts at about 
 1000 C. (1832 F.); it is univalent, and forms but one series of salts; 
 it is not affected by the oxygen of the air at any temperature, but is 
 readily acted upon by traces of hydrogen sulphide, which forms a 
 black film of sulphide upon the surface of metallic silver. Hydro- 
 chloric acid scarcely acts on silver, nitric and sulphuric acids dis- 
 solve it. 
 
 While many of the non-metallic elements have long been known to exist in 
 allotropic forms, none of the metals had been obtained in such a condition 
 until quite recently, when it was shown that silver is capable of assuming a 
 number of allotropic modifications. These are obtained chiefly by precipi- 
 tating silver from solutions by different reducing agents. While normal silver 
 is white, the allotropic forms have distinct colors blue, bluish-green, red, pur- 
 ple, yellow and differ also in many other respects. Thus they are converted 
 into silver chloride by highly diluted hydrochloric acid, which does not act 
 on common silver; they are soluble in ammonia water, and act as reducing 
 agents upon a number of substances, such as permanganates, ferricyanides, 
 etc. Allotropic silver can be converted into the common form by dift 
 ferent forms of energy for instance, by heat, electricity, and the action of 
 strong acids. 
 
 This allotropic form of silver is known as colloidal silver, and its solution in 
 water is not a true, but a colloidal solution. Such a solution has the same freez- 
 ing- and boiling-point as water itself, and it has been shown that the colloid is 
 simply suspended in the liquid, although it is in too fine a state of division to 
 be retained by a filter-paper. Colloidal solutions of silver, gold, or platinum 
 result when electric discharges pass between wires of these metals held under 
 water. 
 
 Collargol (Argentum Crede) is a preparation of colloidal (soluble) 
 silver, said to contain 85.87 per cent, of silver and a small amount of albumin. 
 It is bluish-black, scale-like, soluble in 20 parts of water. Albumin is added 
 to prevent precipitation of silver from its solution by acids and salts, or by 
 heating. It is incompatible with the usual silver reagents. 
 
 Collargol Ointment (Unguentum Crede") is an ointment containing 15 per 
 cent, of collargol, of a dark, bluish-gray color. 
 
 Silver is too soft for use as coin or silverware, and, therefore, is 
 alloyed with from 5 to 25 per cent, of copper, which causes it to be- 
 come harder, and consequently gives it more resistance to the wear 
 and tear by friction. 
 
 Pure silver may be obtained by dissolving silver coin in nitric acid, 
 when a blue solution, containing the nitrates of copper and silver, is 
 formed. By the addition of sodium chloride to the solution a white 
 curdy precipitate of silver chloride, AgCl, forms, while cupric nitrate 
 
332 METALS AND THETR COMBINATIONS. 
 
 remains in solution. The silver chloride is washed, dried, mixed 
 with sodium carbonate, and heated in a crucible, when sodium chlo- 
 ride is formed, carbon dioxide escapes, and a button of silver is found 
 at the bottom of the crucible : 
 
 2AgCl + Na 2 C0 3 = 2NaCl + CO 2 + 2Ag + O. 
 
 Experiment 43. Dissolve a small silver coin in nitric acid, dilute with water, 
 and precipitate the clear liquid with an excess of solution of sodium chloride. 
 The washed precipitate of silver chloride may be treated with sodium carbon- 
 ate, as stated above, or may be converted into metallic silver by the following 
 method : Place the dry chloride in a small porcelain crucible and apply a 
 gentle heat until the chloride has fused ; when cold, place a piece of sheet 
 zinc upon the chloride, cover with water, to which a few drops of sulphuric 
 acid have been added, and set aside for a day, when the silver chloride will be 
 found to have been decomposed with liberation of metallic silver and forma- 
 tion of zinc chloride. 
 
 A simpler method is to heat the silver chloride with a solution of formal- 
 dehyde and a few drops of alkali, or with glucose and alkali. Metallic silver 
 in a finely divided state is obtained, which, after washing, may be fused into 
 a lump. 
 
 Silver nitrate, Arg-enti nitras, AgNO 3 = 168.69. Pure silver is 
 dissolved in nitric acid : 
 
 3Ag + 4HN0 3 = NO + 2H 2 O + 3AgNO 3 . 
 
 The solution is evaporated to dryness with the view of expelling all 
 free acid, the dry mass dissolved in hot water and crystallized. 
 
 If the silver used should contain copper, the latter may be elimin- 
 ated from the mixture of silver and cupric nitrate by evaporating to 
 dryness and fusing, when the latter salt is decomposed, insoluble 
 cupric oxide being formed. The fused mass is dissolved in water, 
 filtered, and again evaporated for crystallization. 
 
 When silver nitrate, after the addition of 4 per cent, of hydro- 
 chloric acid, is fused and poured into suitable moulds it yields the 
 white cylindrical sticks which are known as moulded silver nitrate, 
 caustic, lunar caustic, or lapis infernalis. 
 
 When fused with twice its weight of potassium nitrate and formed 
 into similar rods, it forms the mitigated or diluted silver nitrate (mit- 
 igated caustic) of the U. S. P. 
 
 Silver nitrate forms colorless, transparent, tabular, rhombic crys- 
 tals, or, when fused, a white, hard substance; it is soluble in less 
 than its own weight of water, the solution having a neutral reaction. 
 Exposed to the light, especially in the presence of organic matter, 
 silver nitrate blackens in consequence of decomposition ; when 
 
8IL VERMERCUR Y. 333 
 
 brought in contact with animal matter, it is readily decomposed into 
 free nitric acid and metallic silver, which produces the characteristic 
 black stain ; it is this decomposition, and the action of the free nitric 
 acid, to which the strongly caustic properties of silver nitrate are 
 due. 
 
 Silver nitrate is used for various kinds of indelible inks and hair- 
 dyes, and very largely in the manufacture of those silver compounds 
 employed for photographic purposes. 
 
 Photography is the art of obtaining images of objects by means 
 of chemical changes produced in certain substances (chiefly com- 
 pounds of silver or platinum) by the action of light. Three separate 
 operations are required to obtain the image ; they are exposure, devel- 
 oping and fixation. 
 
 The exposure of a light-sensitive surface to a projected image of the object to 
 be photographed is made in the camera, which is so arranged that the image 
 can be thrown upon the surface by means of a lens. The surface used is gen- 
 erally that of a glass plate or a gelatine film, sensitized with the bromide or 
 iodide of silver. 
 
 On the exposed plate a chemical change has taken place in the silver salt 
 wherever light has acted on it. The exact nature of this change is not under- 
 stood, and nothing can be detected on the plate with the eye after exposure. 
 But when the exposed plate is treated with certain solutions, called developers, 
 that portion of the silver salt which has been acted upon by light is decomposed 
 with the formation of a deposit of metallic silver, forming the visible image. 
 The acting constituent of developers are deoxidizing agents, such as pyrogallol, 
 hydroquinone, ferrous sulphate, etc. 
 
 After the silver image has appeared there yet remains on the plate that por- 
 tion of the silver salt which has not been acted on by light, and consequently 
 not by the developer. This portion of the undecomposed silver salt must be 
 removed before the plate can be taken to the light, and this removal, called 
 fixation, is accomplished by immersion of the plate in a fixing solution of 
 sodium thiosulphate, Na 2 S 2 3 (hyposulphite), which dissolves the salt in con- 
 sequence of the formation of a double salt of the composition Ag 2 S 2 3 . 2Na 2 S 2 3 ; 
 this is eliminated by washing in water. 
 
 The image thus obtained is called a negative, because it shows dark what 
 ought to be light, and vice versa. By placing this negative upon sensitized 
 material (generally paper) and permitting light to pass through the negative 
 to the underlying paper the light-sensitive material is chemically affected most 
 where the silver deposit in the negative is the thinnest, and vice versa. By 
 developing and fixing the exposed paper the positive picture is obtained. 
 
 Silver oxide, Arg-enti oxidum, Ag 2 O = 23O.12. Made by the 
 addition of an alkali hydroxide to silver nitrate : 
 
 2AgN0 3 + 2KOH = 2KNO 3 + H 2 O + Ag 2 O 
 
334 METALS AND THEIR COMBINATIONS. 
 
 A dark-brown, almost, black powder, but very sparingly soluble 
 in water, imparting to the solution a weak alkaline reaction. It is a 
 strong base, and easily decomposed into silver and oxygen. 
 
 Antidotes. Sodium chloride, white of egg, or milk, followed by an emetic. 
 
 Complex silver compounds. A great many combinations of silver 
 with organic substances have been introduced and a few are extensively em- 
 ployed in medicine. These compounds usually differ in properties from the 
 inorganic salts of silver. They are antiseptic and less irritating than silver 
 nitrate. 
 
 Argonin, silver-casein, is a soluble casein compound containing 4.28 per cent. 
 of silver. It is a nearly white powder, soluble in water, from which the silver 
 is not precipitated by sodium chloride or hydrogen sulphide. It is also soluble 
 in alkalies, egg-albumin, blood-serum, etc. 
 
 Argyrol, silver vitellin, is a compound of a derived proteid and silver oxide, 
 containing from 20 to 25 per cent, of silver. It occurs as black, glistening 
 hygroscopic scales, freely soluble in water and glycerin, insoluble in oils and 
 alcohol. It is said to be incompatible with acids and most of the neutral and 
 acid salts in strong solution. 
 
 Protargol is a compound of albumin and silver, containing 8.3 per cent, of 
 silver. It is a yellow powder, soluble in 2 parts of cold water. The silver is 
 not precipitated by the usual reagents, such as alkalies, sulphides, chlorides, 
 bromides, iodides, nor by heat. It is compatible with picric acid and its salts 
 and with most metallic salts, but is precipitated by cocaine hydrochloride, 
 which, however, may be prevented by addition of boric acid. It is a non-irri- 
 tant bactericide and antiseptic, extensively used as a substitute for silver 
 nitrate. 
 
 Tests for Silver. 
 (Use a 1 per cent, solution of silver nitrate in distilled water.) 
 
 1. Add to the solution hydrogen sulphide or ammonium sulphide : 
 a dark-brown precipitate of silver sulphide is produced : 
 
 2AgNO, + HaS = 2HNO 3 + Ag 2 S. 
 
 2. Add hydrochloric acid, or solution of any soluble chloride : a 
 white, curdy precipitate of silver chloride is produced, which is in- 
 soluble in dilute acids, but soluble in ammonium hydroxide and in 
 potassium cyanide : 
 
 AgN0 3 + NaCl = NaN0 3 + AgCl. 
 
 3. Add potassium chromate or dichromate solution : a red precipi- 
 tate of silver chromate, Ag 2 CrO 4 , is formed (Plate II., 7). 
 
 4. Add sodium phosphate solution : a pale-yellow precipitate of 
 silver phosphate, Ag 3 PO 4 , is formed, which is soluble in ammonia 
 and in nitric acid. Free phosphoric acid does not give a precipitate. 
 
SILVER MERCURY. 335 
 
 5. Solution of alkali hydroxides precipitates dark-brown silver 
 oxide, soluble in ammonia water, forming a complex hydroxide 
 Ag(NH 3 ) 2 .OH. 
 
 6. Solution of potassium iodide or bromide gives a pale-yellow 
 precipitate. 
 
 7. Metallic copper or zinc precipitates metallic silver from solu- 
 tions of silver in any form of combination. (See page 319.) 
 
 Test 2 is sufficient to identify silver in ordinary solutions, for, 
 although mercurous and lead chloride are insoluble in water and 
 dilute acids, silver chloride alone of these three insoluble chlorides 
 is soluble in ammonia water. Silver forms a number of complex 
 combinations with organic compounds from which it is not easily pre- 
 cipitated, but by reduction of the silver to the metallic state, and 
 solution of the metal in nitric acid, the tests may be applied. The 
 same procedure applies also to inorganic insoluble silver compounds, 
 as AgCl, AgBr, Agl, Ag 2 S. 
 
 All silver salts are soluble in ammonia water, except the iodide and sul- 
 phide ; hence the latter alone can be precipitated from an ammoniacal solution. 
 In these solutions complex combinations, as Ag(NH 3 ) 2 .NO 3 , Ag(NH,) t Cl, are 
 formed, which are salts of the hydroxide, Ag(NH 3 ) 2 .OH. In this respect silver 
 acts very much like copper. These compounds dissociate thus: 
 
 Ag(NH 3 ) 2 N0 3 5 Ag(NH 3 ) 2 - + NO/. 
 
 The Ag(NH 3 )./ ions yield a slight amount of Ag* ions, but not enough to be 
 precipitated by any of the reagents except iodide and sulphide. The concen- 
 tration of Ag' ions given by the latter precipitates is less than that given by 
 the Ag(NH 3 ) 2 * ions, hence precipitation takes place. (See page 193.) 
 
 Solutions of alkali cyanides and thiosulphates dissolve all silver compounds, 
 giving complex substances of the form KAg(CN) 2 and Na 3 Ag(S 2 O 3 ) 2 . The ions 
 of these are K* + Ag(CN)/, and 3Na* -f Ag(S 2 O 3 )/ // . Such a slight amount 
 of Ag* ions are formed from these compounds that no reagent will give a pre- 
 cipitate. That there are some Ag* ions, however, is shown by the fact that 
 active metals, like zinc, separates the silver from the solutions. Also that in 
 electroplating silver is deposited from cyanide solution. 
 
 Soluble silver salts are not hydrolyzed, and are, therefore, neutral. 
 
 Mercury, Hydrargyrum, Hg = 198.5 (Quicksilver). Mercury is 
 found sometimes in small globules in the metallic state, but generally 
 as mercuric sulphide or cinnabar, a dark-red mineral. The chief 
 supply was formerly obtained from Spain and Austria ; now, how- 
 ever, large quantities are obtained from California ; it is also 
 imported from Peru and Japan. 
 
 Mercury is obtained from cinnabar either by roasting it, whereby 
 the sulphur is converted into sulphur dioxide, or by heating it with 
 lime, which combines with the sulphur, while the metal volatilizes, 
 and is condensed by passing the vapors through suitable coolers. 
 
336 METALS AND THEIR COMBINATIONS. 
 
 Mercury is the only metal showing the liquid state at the ordinary 
 temperature ; it solidifies at -40 C. (-40 F.), and boils at 357 C. 
 (675 F.) ; but is slightly volatile at all temperatures ; it is almost 
 silver-white, and has a bright metallic lustre ; its specific gravity is 
 13.56 at 15 C. (59 F.). 
 
 Pure mercury should present a bright surface even after agitation with air; 
 when dropped on paper it should form globules which roll about freely, retain 
 their globular form and leave no streaks. Commercial mercury is often con- 
 taminated with tin, lead, bismuth and zinc. Such impurities cause a trail of 
 dross when globules are made to roll over paper. 
 
 Mercury can be purified by repeated distillation, or by covering the metal 
 with nitric acid and agitating the mass frequently during two days. The total 
 of the base metals, with some mercury, pass in solution, which is washed out with 
 water, after which the mercury is dried by setting it in a warm place. 
 
 Mercury is peculiar in that its molecule contains but one atom, at 
 least when in the state of a gas ; in the liquid and solid states it may 
 contain two atoms, like most other elements, but we have as yet no 
 means of proving this fact. 
 
 Mercury forms, like copper, two series of compounds, distinguished 
 as mercuric and mercurous compounds. In the former, mercury is 
 bivalent, while in mercurous compounds the atom exerts a valence of 
 one. It was long supposed that this was due to the fact that two 
 mercury atoms were joined together, each atom thereby losing one 
 of its points of affinity, leaving but one point for combining Avith 
 another atom or radicle. This view necessitated the existence of two 
 mercury atoms in the molecule of every mercurous compound, the 
 composition, for instance, of mercurous chloride being CIHg-HgCl or 
 Hg 2 Cl 2 . There are, however, good reasons to believe that mercury is 
 univalent in mercurous compounds, the composition of mercurous 
 chloride being, consequently, HgCL Similarly, copper is assumed to 
 be univalent in cuprous compounds. 
 
 Mercury is not affected by the oxygen of the air, nor by hydro- 
 chloric acid, while chlorine, bromine, and iodine combine with it 
 directly, and warm sulphuric and nitric acids dissolve it. 
 
 Mercury is used in the metallic state for many scientific instruments 
 (thermometer, barometer, etc.); for making amalgams; for extracting 
 gold from the ore ; for manufacturing from it all of the various mer- 
 cury compounds, and those official preparations in which mercury 
 exists in the metallic state. 
 
 These latter preparations are : Mercury with chalky mass of mercury, 
 or blue pill, mercurial ointment, and mercurial plaster. Mercury exists 
 in a metallic, but highly subdivided, state in these preparations, which 
 are made by intimately mixing (triturating) metallic mercury with 
 
SILVER MERCURY. 337 
 
 the different substances used (viz., chalk, pill-mass, fat, lead -pi aster). 
 It is most probable that the action of these agents upon the animal 
 system is chiefly due to the conversion of small quantities of mercury 
 into mercurous oxide, which, in contact with the acids of the gastric 
 juice or with perspiration, are converted into soluble compounds 
 capable of being absorbed. 
 
 Amalgams. Alloys containing mercury are termed amalgams. Mercury 
 unites with most metals, and with some of them it forms definite compounds. 
 Dental alloys used for amalgamation are composed chiefly of silver and tin with 
 one or more of the following metals : gold, platinum, copper, zinc. Dental 
 amalgams are made by reducing the alloy ingot to fine shavings or filings, 
 which are triturated with the necessary quantity of mercury to form a plastic 
 mass, which becomes hard or sets. 
 
 The properties most essential for a good amalgam are strength, immutability 
 as to volume, freedom from discoloration, and resistance to the action of the 
 oral secretions. Many formulas have been suggested to obtain these results. 
 
 The addition of either gold, platinum, copper or zinc to a silver-tin alloy 
 facilitates setting, while this is retarded by an excess of mercury or by the em- 
 ployment of an alloy that has been long exposed to the air or has been annealed. 
 The change in form i. e., expansion or contraction which an amalgam under- 
 goes in hardening is very objectionable and difficult to completely overcome. 
 
 The discoloration of amalgams is in great measure due to the formation of 
 sul phides, particularly upon those amalgams in which there is not complete chem- 
 ical union of the metallic constituents. A proper proportion of zinc in an alloy 
 prevents discoloration considerably, making, however, the alloy difficult to amal- 
 gamate, while the presence of copper greatly increases the tendency to discolor. 
 
 Mercurous oxide, Hg^O (Black oxide or suboxide of mercury). An 
 almost black, insoluble powder, made by adding an alkaline hydroxide 
 to a solution of mercurous nitrate : 
 
 2HgN0 3 + 2KOH == 2KNO 3 + H 2 O -f Hg. 2 O. 
 
 A similar decomposition takes place when alkaline hydroxides are 
 added to insoluble mercurous chloride. A mixture of lime-water and 
 mercurous chloride (calomel) is known as black-wash ; when the two 
 substances are mixed, calomel is converted into mercurous oxide, while 
 calcium chloride is formed : 
 
 2HgCl + Ca(OH) 2 = CaCl 2 -f H 2 O + Hg 2 O. 
 
 Mercuric oxide, HgO = 214.38. There are two mercuric oxides 
 which are official ; they do not differ in their chemical composition, 
 but in their molecular structure. 
 
 The yellow mercuric oxide, Hydrargyrioxidumflavum, is made by pour- 
 ing a solution of mercuric chloride into a solution of sodium hydroxide, 
 when an orange-yellow, heavy precipitate is produced, which is washed 
 and dried at a temperature not exceeding 30 C. (86 F.) (Plate IV., 3) : 
 HgCl 2 + 2NaOH = HgO + SNaCl + H 2 O. 
 
 The red mercuric oxide, Hydrargyri oxidum rubrum, is made by 
 
 22 
 
338 METALS AND THEIR COMBINATIONS. 
 
 heating mercuric nitrate, either by itself or after it has been intimately 
 mixed with an amount of metallic mercury equal to the mercury in 
 the nitrate used (Plate IV., 4). In the first case, nitrous fumes and 
 oxygen are given off, mercuric oxide remaining : 
 
 Hg(N0 3 ) 2 = HgO + 2N0 2 -f O. 
 In the other case, no oxygen is evolved : 
 
 Hg(N0 8 ), + Hg = 2HgO + 2N0 2 . 
 
 The red oxide of mercury differs from the yellow oxide in being 
 more compact, and of a crystalline structure; while the yellow oxide 
 is in a more finely divided state, and consequently acts more energeti- 
 cally when used in medicine. Yellow oxide, when digested on a 
 water-bath with a strong solution of oxalic acid, is converted into 
 white mercuric oxalate within fifteen minutes, while red oxide is not 
 acted upon by oxalic acid under the same conditions. 
 
 When mercuric chloride is added to lime-water, a mixture is 
 formed holding in suspension yellow mercuric oxide; this mixture 
 is known as yellow-wash. 
 
 Experiment 44. Shake a small knifepointful of mercurous chloride (calomel) 
 with 50 c.c. of lime-water. Note that the chloride instantly turns dark, due to 
 formation of mercurous oxide (see reaction in text). The lime-water must be 
 in excess. 
 
 Add about 1 c.c. of reagent solution of mercuric chloride to 50 c.c. of lime- 
 water and stir. Yellow mercuric oxide is formed at once (see reaction in text). 
 If the lime-water is not in excess, the precipitate will not be pure yellow, but 
 whitish, due to formation of an oxychloride, Hg 2 OCl 2 . 
 
 Caustic alkalies produce the same results as above, but any excess of these 
 stronger alkalies is objectionable for the purposes for which these " washes " are 
 used. 
 
 Experiment 45. Heat some mercuric nitrate in a porcelain dish, placed in a 
 ftime chamber, until red fumes no longer escape. The remaining red powder 
 is mercuric oxide, which, by further heating, may be decomposed into its ele- 
 ments. 
 
 Mercurous chloride, Hydrargyrum chloridum mite, HgCl = 
 233.68 (Calomel , Mild chloride of mercury, Subchloride or proto- 
 chloride of mercury). Mercurous chloride, like mercurous oxide, 
 may be made by different processes, but the article used medicinally 
 is the one obtained (except it be otherwise stated) by sublimation 
 and the rapid condensation of the vapor in the form of powder. 
 
 It is made either by subliming a mixture of mercuric chloride 
 and mercury: 
 
 HgCl, + Hg = 2HgCl. 
 
SILVER MERCURY. 339 
 
 or by thoroughly mixing with mercuric sulphate a quantity of mer- 
 cury equal to that contained in the sulphate ; by this operation mer- 
 curous sulphate is obtained, which is mixed with sodium chloride, 
 and sublimed from a suitable apparatus into a large chamber, so that 
 the sublimate may fall in powder to the floor : 
 
 HgS0 4 -f Hg + 2NaCl = Na 2 SO 4 + 2HgCl. 
 
 Precipitated calomel, being in a finer state of subdivision, acts 
 more energetically when used medicinally. It is obtained by pre- 
 cipitation of a soluble mercurous salt by any soluble chloride: 
 
 HgNO 3 + NaCl = NaNO 8 + HgCl. 
 
 Mercurous chloride, made by either process, generally contains 
 traces of mercuric chloride, and should, therefore, be washed with 
 hot water until the washings are no longer acted upon by ammonium 
 sulphide or silver nitrate. 
 
 Mercurous chloride is a white, impalpable, tasteless powder, in- 
 soluble in water and alcohol ; it volatilizes without fusing previously ; 
 when given internally, it should not be mixed with either mineral 
 acids, alkali bromides, iodides, hydroxides, or carbonates, except the 
 action of the decomposition products be desired. 
 
 Mercuric chloride, Hydrargyri chloridum corrosivum, Hg-CL, 
 268.86 (Corrosive chloride of mercury, Corrosive sublimate, Perchlo- 
 ride or bichloride of mercury). Made by thoroughly mixing mercuric 
 sulphate with sodium chloride, and subliming the mixture, when 
 mercuric chloride is formed, and passes off in white fumes which are 
 condensed in the cooler part of the apparatus, while sodium sulphate 
 
 is left : 
 
 HgSO, + 2NaCl = Na 2 SO 4 + HgCl 2 . 
 
 Mercuric chloride is a heavy, white powder, or occurs in heavy, 
 colorless, rhombic crystals or crystalline masses; it is soluble in 16 
 parts of cold and 2 parts of boiling water, and in about 3 parts of 
 alcohol, in 4 parts of ether, and in about 14 parts of glycerin; when 
 heated, it fuses and is volatilized ; it has an acrid, metallic taste, an 
 acid reaction, and strongly poisonous and antiseptic properties. 
 
 The halogen salts of mercury are very little ionized in solution. On this 
 account, mercuric chloride is much less hydrolyzed than mercuric nitrate, that 
 is, there is not so much tendency to precipitate a basic salt. Mercuric chloride 
 also has the tendency to form complex salts. Thus sodium chloride increases its 
 solubility in water and causes the solution to become neutral, because of the 
 formation of the salt, HgCl 2 .NaCl or NaHgCl 3 . Mercuric chloride tablets are 
 
340 METALS AND THEIR COMBINATIONS. 
 
 made up witih sodium chloride, because the latter prevents the formation of in- 
 soluble chlorides and facilitates solution, although the activity of the mercury 
 compound is somewhat lessened. Mercuric chloride is sometimes used as a 
 preservative of specimens. It forms insoluble compounds with albumin and 
 prevents its decay. On this principle, albumin is given as an antidote in mer- 
 curic chloride poisoning. 
 
 Mercurous iodide, Hydrargyri iodidum flavum, Hgl = 324.4 
 ( Yellow iodide, green iodide, or protiodide of mercury). Both iodides 
 of mercury may be obtained either by rubbing together mercury and 
 iodine in the proportions represented by the respective atomic weights, 
 or by precipitation of soluble mercurous or mercuric salts by potas- 
 sium iodide. 
 
 According to the U. S. P., mercurous iodide is made by the pre- 
 cipitation of a solution of mercurous nitrate, to which some nitric acid 
 has been added, by a solution of potassium iodide : 
 
 HgNO 3 + KI = KNO 3 H- Hgl. 
 
 The precipitate is collected on a filter, well washed with water and 
 alcohol, and dried between paper at a temperature not exceeding 
 40 C. (104 F.). During the whole operation light should be ex- 
 cluded as much as possible, as it decomposes the compound. 
 
 Mercurous iodide is a yellow, tasteless powder, almost insoluble in 
 water. It is easily decomposed into mercuric iodide and mercury, 
 becoming darker and assuming a greenish -yellow to green tint, due 
 to the admixture of metallic mercury, which, in a finely divided 
 state is blue, and consequently causes a greenish mixture with the 
 yellow iodide. (Plate IV., 5.) 
 
 Mercuric iodide, Hydrargyri iodidum rubrum, Hg-I 2 45O.3 
 (Red iodide or biniodide of mercury). Made by mixing solutions of 
 potassium iodide and mercuric chloride, when a pale-yellow precipi- 
 tate is formed, turning red immediately (Plate IV., 6) : 
 
 HgCl 2 + 2KI = 2KC1 + HgI 2 . 
 
 Mercuric iodide is soluble both in solution of potassium iodide and 
 mercuric chloride, for which reason an excess of either substance will 
 cause a loss of the salt when prepared. It is a scarlet-red, tasteless 
 powder, almost insoluble in water and but slightly soluble in alcohol ; 
 on heating or subliming it turns yellow in consequence of a molecular 
 change which takes place ; on cooling, and, more quickly, on pressing 
 or rubbing the yellow powder, it reassumes the original condition 
 and the red color. 
 
SILVER MERCUHY. 341 
 
 When mercuric iodide is dissolved in potassium iodide solution, a complex 
 salt is formed, HgI 2 .2KI, or K 2 HgI 4 , from which many of the usual reagents fail 
 to precipitate the mercury. For example, caustic potash has no effect on the 
 compound, and such an alkaline solution is known as Nessler's reagent. This 
 reagent gives a yellow color with traces of ammonia, and a brown precipitate 
 with larger amounts : 
 
 2HgI 2 + 4NH 3 Hg 2 NI + 3NHJ. 
 
 Nessler's reagent is used in water analysis for detecting traces of ammonia. 
 The compound, Hg 2 NI, is called dimercur-ammonium iodide. 
 
 Mercuric sulphate, Hg-SO 4 . When mercury is heated with strong 
 sulphuric acid (the presence of nitric acid facilitates the formation) 
 chemical action takes place between the two substances, sulphur 
 dioxide being liberated and mercuric sulphate formed, which upon 
 evaporation of the solution is obtained as a heavy, white, crystalline 
 powder : 
 
 Hg + 2H 2 S0 4 = HgS0 4 + 2H 2 + SO 2 . 
 
 Yellow mercuric subsulphate, Hg-SO 4 .(Hg-O) 2 (Basic mercuric 
 sulphate, Turpeth mineral, Mercuric oxy-sulphate). When mercuric 
 sulphate, prepared as directed above, is thrown into boiling water, it 
 is decomposed into an acid salt which remains in solution, and a basic 
 salt which is precipitated. As shown by its composition, it may be 
 looked upon as mercuric sulphate in combination with mercuric oxide. 
 It is a heavy, lemon-yellow, tasteless powder, almost insoluble in 
 water. 
 
 Mercurous sulphate, Hg 2 SO 4 . When mercuric sulphate is triturated 
 with a sufficient quantity of mercury, direct combination takes place, 
 and the mercurous salt is formed : 
 
 H g S0 4 + Hg = Hg 2 S0 4 . 
 
 Nitrates of mercury. Mercurous nitrate, HgNO 3 , and Mer- 
 curic nitrate, Hg(NO 3 ) 2 , may both be obtained as white salts by dis- 
 solving mercury in nitric acid. The relative quantities of the two 
 substances present determine whether mercurous or mercuric nitrate 
 be formed. If mercury is present in excess the mercurous salt, if nitric 
 acid is present in excess the mercuric salt, is formed, the latter espe^ 
 cially on heating. Both salts are white and soluble in water contain- 
 ing free acid. Water alone causes decomposition of the nitrates, 
 similar to that of the sulphates, resulting in the formation of insoluble 
 basic salts, the composition of which depends on the relative propor- 
 tions of the mercury salt and water used. 
 
 Experiment 46. Heat gently a small globule (about 1 gramme) of mercury 
 with 2 c.c. of nitric acid until red fumes cease to escape. If some of the mer- 
 
342 METALS AND THEIR COMBINATIONS. 
 
 cury remains undissolved, the solution will deposit crystals of mercurous 
 nitrate on cooling. Use some of the solution, after being diluted with much 
 water, for mercurous tests. Use another portion as follows : Heat the solution, 
 or some of the crystals, with about an equal weight of nitric acid until no more 
 red fumes escape. Add to a few drops of the diluted liquid a little hydro- 
 chloric acid, which, if the conversion of the mercurous into mercuric salt has 
 been complete, will give no precipitate. If, however, one should be formed, the 
 solution is heated with more nitric acid until no precipitate is formed by hydro- 
 chloric acid, when the solution is evaporated and set aside for crystallization. 
 The respective changes may be represented by the following equations : 
 
 3H g + 4HN0 3 == 3HgNO 3 + 2H 2 O + NO ; 
 3HgNO 3 + 4HN0 3 = 3Hg(NO 3 ) 2 -f 2H 2 O + NO. 
 
 Mercuric sulphide, HgS. This compound has been mentioned as 
 the chief ore of mercury, occurring crystallized as cinnabar, which 
 has a red color (Plate IV., 2). The same compound may, however, 
 be obtained by passing hydrogen sulphide through mercuric solutions, 
 when at first a white precipitate is formed (a double compound of the 
 sulphide of mercury in combination with the mercuric salt), which 
 soon turns black (Plate IV., 1) : 
 
 HgCl 2 + H-jS = 2HC1 + HgS. 
 
 The black, amorphous, mercuric sulphide may be converted into the 
 red, crystallized variety by sublimation, and is then the preparation 
 known as red sulphide of mercury, cinnabar, or vermilion. It forms 
 brilliant dark-red crystalline masses, or a fine bright scarlet powder, 
 which is insoluble in water, hydrochloric or nitric acid, but soluble 
 in nitro-hydrochloric acid. 
 
 Mercuric and mercurous sulphides may be made also by triturating 
 the elements mercury and sulphur in the proper proportions, when 
 they combine directly. 
 
 Ammoniated mercury, Hydrargyrum ammoniatum, NH^HgCl 
 = 249.61 ( White, precipitate, Mercuric-ammonium chloride). This com- 
 pound is made by pouring solution of mercuric chloride into ammonia 
 water, when a white precipitate falls, which is washed with highly 
 diluted ammonia water and dried at a low temperature : 
 
 HgCl 2 + 2NH 4 OH == NH 2 HgCl + NH 4 C1 + 2H 2 O. 
 
 As shown by the composition of this compound, it may be re- 
 garded as ammonium chloride, NH 4 C1, in which two atoms of hydro- 
 gen have been replaced by one atom of the bivalent mercury. The 
 mercuric-ammonium salts are of a different type from those combina- 
 
SIL VERMERCUR Y. 
 
 343 
 
 tions formed when copper, silver, zinc, etc., salts are dissolved in am- 
 monia water. The former are all insoluble in water. 
 
 Ammoniated mercury is a white, tasteless, insoluble powder. 
 
 Mercurous salts with ammonia water give black insoluble precipi- 
 tates consisting of a mixture of mercuric-ammonium salts and mercury, 
 which causes the black appearance. For mercurous chloride and 
 nitrate the reactions are : 
 
 2HgCl + 2NH 3 = HgNH 2 .Cl -f Hg -f NH 4 C1. 
 2HgN0 3 -f 2NH 3 = HgNH 2 .N0 3 + Hg + NH 4 NO 3 . 
 
 It should be noted that in the case of mercury salts, ammonia water 
 does not precipitate hydroxides, as it does in other cases. 
 
 Tests for mercury. 
 
 Mercurous salts. 
 
 (Mercurous nitrate, HgNO 3 may 
 be used. ) 
 
 1. Hydrogen sul- 
 phide, or ammo- 
 nium sulphide. 
 
 2. Potassium iodide. 
 
 3. Potassium or so- 
 dium hydroxide. 
 
 4. Ammonium hy- 
 droxide. 
 
 5. Potassium or so- 
 dium carbonate. 
 
 6. Hydrochloric 
 acid or soluble 
 chlorides. 
 
 Black precipitate of mercuric 
 sulphide, with mercury. 
 2HgN0 3 -f H a S = 
 2HN0 3 + HgS + Hg. 
 
 Green precipitate of mercurous 
 iodide (Plate IV., 7): 
 
 KN0 3 + Hgl. 
 
 Dark-brown precipitate of mer 
 curous oxide, Hg 2 O (Plate 
 IV., 5). 
 
 Black precipitate of a mixture 
 of mercury and mercuric-am- 
 monium chloride (see expla- 
 nation above). 
 
 Yellowish precipitate of mer- 
 curous carbonate, which is 
 unstable. 
 
 White precipitate of mercurous 
 chloride is produced : 
 HgN0 3 + HC1 = 
 HN0 3 -f- HgCl. 
 
 Mercuric salts. 
 
 (Mercuric chloride, HgCl 2 , may 
 be used.) 
 
 Black precipitate of mercuric 
 sulphide. (Precipitate may be 
 white or gray, with an insuffi- 
 cient quantity of the reagent.) 
 (See above) (Plate IV., 1.) 
 
 Red precipitate of mercuric 
 iodide (See above.) (Plate 
 IV, 6.) 
 
 Yellow precipitate of mercuric 
 
 oxide HgO. (See above.) 
 
 (Plate IV., 3.) 
 White precipitate of a mercuric 
 
 ammonium salt is formed. 
 
 ( See explanation above.) 
 
 Brownish-red precipitate of 
 basic mercuric carb., mixed 
 with mercuric oxychloride. 
 
 No change. 
 
 7. Stannous- chloride produces, in solutions of mercury, a white 
 precipitate, which turns dark-gray on heating with an excess of the 
 reagent. The reaction is due to the strong reducing or deoxidizing 
 property of the stannous chloride, which itself is converted into stannic 
 chloride, while the mercury salt is first converted into a mercurous 
 salt and afterward into metallic mercury : 
 
 2HgCl 2 + SnCl 2 = 2HgCl -f SnCl 4 ; 
 2HgCl + SnCl 2 = 2Hg + SnCl,. 
 
344 
 
 METALS AND THEIR COMBINATIONS. 
 
 
 
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MERCURY. SILVER. 
 
 PLATE IV. 
 
 Mercuric sulphide, precipitated fro 
 mercuric solutions by hydrogen sulphid 
 
 Mercuric sulphide, Cinnabar. 
 
 Yellow mercuric oxide, precipitat* 
 from mercuric solutions by potassium h 
 droxide. 
 
 Red mercuric oxide, obtained 1 
 heating mercuric nitrate. 
 
 Mercurous oxide, precipitated fro 
 mercurous solutions by potassium hydro: 
 ide. 
 
 Silver sulphide, precipitated fro 
 silver solutions by hydrogen sulphide. 
 
 flercuric iodide, precipitated froi 
 mercuric solutions by alkali iodides. 
 
 Mercurous iodide, precipitated froi 
 mercurous solutions by alkali iodides. 
 
 8 
 
 Mercuric solutions with ammoniui 
 hydroxide, flercurous solutions wit 
 soluble chlorides. Silver solutions wit 
 soluble chlorides. 
 
 A.Hoen&CftLith 
 
ARSENIC. 345 
 
 8. Dry mercury compounds, when mixed with sodium carbonate 
 and potassium cyanide, and heated in a narrow test-tube, are decom- 
 posed with liberation of metallic mercury, which condenses in small 
 globules in the cooler part of the tube. 
 
 9. A piece of bright metallic copper when placed in a slightly acid 
 mercury solution becomes coated with a dark film of metallic mer- 
 cury, which by rubbing becomes bright and shining, and may be 
 volatilized by heat. (See Solution tension, page 319.) 
 
 10. All compounds of mercury are completely volatilized by heat, 
 either with or without decomposition. 
 
 Tests 2, 4, 7, 8, and 9 will show the presence of mercury in any of 
 its compounds. Those that are insoluble in water may be dissolved 
 by a little concentrated hydrochloric with a few drops of nitric acid, 
 forming mercuric chloride. Excess of acid is removed by evaporation . 
 
 Antidotes. Albumen (white of egg), of which, however, not too much should 
 be given at one time, lest the precipitate formed by the mercuric salt and 
 albumin be redissolved. The antidote should be followed by an emetic to 
 remove the albuminous mercury compound. 
 
 Ionic conditions. The simple mercury compounds give mercurous ions, Hg", 
 and mercuric ions, Hg", which show different behaviors toward reagents, as 
 seen in the tests above. The mercury ions are colorless, and are not formed 
 extensively from any compound. The disinfecting and poisonous properties of 
 mercury compounds depend upon the presence of the ions. Mercuric chloride 
 in the dry state is inactive, and its solution in alcohol or ether is almost inert 
 as a disinfectant, because there are practically no mercury ions formed. 
 
 Salts in general have a high degree of ionization, but salts of mercury and 
 cadmium are remarkable exceptions. For this reason mercury salts show some 
 peculiar behaviors. For example, the halogen salts of mercury dissociate so 
 little (the bromide and iodide less than the chloride) that they are scarcely 
 affected by sulphuric or nitric acid. Sodium chloride with sulphuric acid gives 
 hydrochloric acid, and with nitric acid it gives chlorine. Mercuric cyanide, 
 Hg(CN) 2 , is so minutely dissociated, that the presence of either Hg" ions or 
 (CN)' ions cannot be shown by precipitation with many reagents. Thus, silver 
 nitrate does not precipitate the (ON) 7 ions, as AgCN, nor do alkalies precipitate 
 Hg* * ions, as HgO. But hydrogen sulphide precipitates mercury from any of 
 its soluble compounds, because mercuric sulphide is practically completely in- 
 soluble and unionized. It is for this reason that the sulphide is not dissolved 
 by any acid, even when concentrated and heated, except nitrohydrochloric. 
 
 Mercury is deposited from all its compounds, whether soluble in water or 
 not, by the metals higher up in the electrochemical series. Hence, it is not 
 advisable to use vermilion in paint to be applied to metallic surfaces. Eed lead 
 is better for this purpose. 
 
 The complex salts which mercuric chloride forms with alkali chlorides dis- 
 sociate in part so that mercury is contained in the complex negative ion, and 
 to this extent loses its disinfectant property. The ionization equation for this 
 
346 METALS AND THEIR COMBINATIONS. 
 
 type of compound is illustrated in the case of the sodium compounds, NaCl.- 
 HgCl 2 or NaHgCl 3 , and 2NaCl.HgCl 2 or Na 2 HgCl 4 : 
 
 NaHgCl 3 Z Na* -f HgCL,'; 
 Na 2 HgCl 4 ^ 2Na* + HgCl/'. 
 
 But there is considerable dissociation also into Hg* ions and Cl' ions. Hence 
 with not too much sodium chloride present and in very dilute solution, the 
 mercuric chloride tablets containing sodium or ammonium chloride do not 
 lose materially in germicidal power, since a relatively large proportion of the 
 ions are the active Hg* ions. 
 
 The complex potassium mercuric iodide, K 2 HgI 4 , gives K* ions and Hgl/ 7 
 ions, but very few Hg* * ions. Hence the failure of some reagents, as alkalies 
 and carbonates, to give a precipitate in a solution of the compound. 
 
 32. ARSENIC. 
 As = 74.4. 
 
 General remarks regarding 1 the metals of the arsenic group. 
 The metals belonging to either of the five groups, considered hereto- 
 fore, show much resemblance -to each other in their chemical prop- 
 erties, and consequently in their combinations. This is much less 
 the case among the six metals (As, Sb, Sn, Au, Pt, Mo) which are 
 classed together in this group. In fact, the chief resemblance which 
 unites these metals is the insolubility of their sulphides in dilute 
 acids and the solubility of these sulphides in ammonium sulphide 
 (or alkali hydroxides), with which they form soluble double com- 
 pounds ; the oxides have also a tendency to form acids. In most 
 other respects no general resemblance exists between these metals. 
 On the other hand, arsenic and antimony have many properties in 
 common, and resemble in many respects the non-metallic elements 
 phosphorus and nitrogen, as may be shown by a comparison of their 
 hydrides, oxides, acids, and chlorides. 
 
 QUESTIONS. How is silver obtained from the native ores, and how may it 
 be prepared from silver coin? State of silver nitrate: its composition, mode 
 of preparation, properties, and names by which it is known. Give analytical 
 reactions for silver. How is mercury found in nature ; how is it obtained from 
 the native ore ; what are its physical and chemical properties? Mention the 
 three oxides of mercury; how are they made, what is their composition, what 
 is their color and solubility ? State of the two chlorides of mercury : their 
 names, composition, mode of preparation, solubility, color, and other proper- 
 ties. Mention the same of the two iodides, as above, for the chlorides. State 
 the difference between mercuric sulphate, basic mercuric sulphate, and mer- 
 curous sulphate. What is formed when ammonium hydroxide, calcium hydrox- 
 ide, potassium or sodium hydroxide is added to either mercurous or mercuric 
 chloride ? Give tests answering for any mercury compound, and tests by which 
 mercuric compounds may be distinguished from mercurous compounds. 
 
ARSENIC. 347 
 
 NH 3 N 2 3 NA NC1 3 . 
 
 PH 3 P 2 S PA H 3 P0 4 PC1 3 . 
 
 AsH 3 As 2 O 3 As 2 O 5 H 3 AsO 4 AsCl 3 . 
 
 SbH. SbA Sb 2 5 SbCl 3 . 
 
 Arsenic. Found in nature sometimes in the native state, but 
 generally as sulphide or arsenide. One of the most common arsenic 
 ores is the arsenio-sulphide of iron, or mispiekel, FeSAs. Realgar is 
 the native red sulphide, As 2 S 2 , and orpiment or aurijrigment, the native 
 yellow sulphide, As 2 S 3 . Arsenides of cobalt, nickel, and other metals 
 are not infrequently met with in nature. Certain mineral waters 
 contain traces of arsenic compounds. 
 
 Arsenic may be obtained easily by heating arsenous oxide with 
 charcoal, or by allowing vapors of arsenous oxide to pass over char- 
 coal heated to redness : 
 
 AsA + 3C = SCO + 2As. 
 
 In both cases the arsenic, when liberated by the reducing action of 
 the charcoal, exists in the form of vapor, which condenses in the 
 cooler part of the apparatus as a steel-gray metallic mass, which 
 when exposed to the amospheric air, loses the metallic lustre in conse- 
 quence of the formation of a film of oxide. 
 
 Experiment 47. Eub together in a mortar a small quantity of arsenous oxide 
 and about ten times as much charcoal. Heat the mixture in a covered porce- 
 lain crucible with a small flame. After a time examine the cover for a dark 
 deposit of arsenic. 
 
 When pure, arsenic is odorless and tasteless ; it is very brittle, and 
 volatilizes unchanged and without melting when heated to 180 C. 
 (356 F.), without access of air. Heated in air, it burns with a 
 bluish-white light, forming arsenous oxide. Although insoluble in 
 water, yet water digested with arsenic soon contains some arsenous 
 acid in solution, the oxide of arsenic being formed by oxidation of 
 the metal by the oxygen absorbed in the water. 
 
 Arsenic is used in the metallic state as fly-poison, and in some 
 alloys, chiefly in shot, an alloy of lead and arsenic. 
 
 The molecule of arsenic contains four atoms, and not two, like 
 most elements. It is trivalent in some compounds, quinquivalent in 
 others. 
 
 Although arsenic is grouped with the metals in the analytical system of 
 classification, in nearly all respects it behaves like a non-metal and should prop- 
 erly be classed as such. The oxides have only acidic character, and do not form 
 salts with acids, as nitrates, sulphates, etc. The chloride, AsCl 3 , can be obtained, 
 
348 METALS AND THEIR COMBINATIONS. 
 
 but it decomposes at once in water, giving arsenous acid. It exists in solution 
 only in the presence of excess of hydrochloric acid. When the solution is 
 evaporated to dryness, arsenous oxide remains. 
 
 Arsenic trioxide, Arseni trioxidum, As 2 O 3 = 196.44 (Arsenous 
 oxide. White arsenic, Arsenous anhydride, improperly Arsenous acid). 
 This compound is frequently obtained as a by-product in metallurgical 
 operations during the manufacture of metals from ores containing 
 arsenic Such ores are roasted (heated in a current of air), when 
 arsenic is converted into arsenous oxide, which, at that temperature. 
 is volatilized and afterward condensed in chambers or long flues. 
 
 Arsenous oxide is a heavy, white solid, occurring either as an 
 opaque, slightly crystalline powder, or in transparent or semi-trans- 
 parent masses which frequently show a stratified appearance; 
 recently sublimed arsenous oxide exists as the amorphous semi- 
 transparent glassy mass known as vitreous arsenous oxide, which 
 gradually becomes opaque and ultimately resembles porcelain. This 
 change is due to a rearrangement of the molecules into crystals which 
 can be seen under the microscope. 
 
 The two modifications of arsenous oxide differ in their solubility 
 in water, the amorphous or glassy variety dissolving more freely than 
 the crystallized. One part of arsenous oxide dissolves in from 30 to 
 80 parts of cold and in 15 parts of boiling water, the solution having 
 at first a faint acrid and metallic, and afterward a sweetish taste. 
 This solution contains the arsenous oxide not as such, but as arsenous 
 add, H 3 AsO 3 , which compound, however, cannot be obtained in an 
 isolated condition, but is known in solution only : 
 
 3H 2 = 2H 3 As0 3 . 
 
 A second arsenous acid, termed met-arsenous acid or meta-arsenous acid, 
 s0 2 , is known in some salts, as, for instance, in sodium metarsenite, NaAsO* 
 which salt may be obtained by the action of arsenous oxide on the carbonate, 
 bicarbonate, or hydroxide of sodium : 
 
 As 2 3 + 2NaOH = 2NaAsO 2 + H 2 O. 
 
 When heated to about 218 C. (424 F.) arsenous oxide is volatil- 
 ized without melting; the vapors, when condensed, form small, 
 shining^ eight-sided crystals; when heated on charcoal, it is deoxi- 
 dized, giving off, at the same time, an odor resembling that of garlic. 
 
 Arsenous oxide is frequently used in the arts and for manufacturing 
 purposes, as, for instance, in the manufacture of green colors, of 
 opaque white glass, in calico-printing, as a powerful antiseptic for 
 the preservation of organic objects of natural history, and, finally, as 
 the substance from which all arsenic compounds are obtained. 
 
ARSENIC. 349 
 
 The official Solution of arsenous acid, Liquor acidi arxcnosi, is a 
 
 1 per cent, solution of arsenous oxide in water to which 5 per cent, 
 of diluted hydrochloric acid has been added. 
 
 The official Solution of potassium arsenite, Liquor potassii arsenitis, or 
 Fowler's solution, is made by dissolving 1 part of arsenous oxide and 
 
 2 parts of potassium bicarbonate in 94 parts of water and adding 
 
 3 parts of compound tincture of lavender ; the solution contains the 
 arsenic as potassium met-arsenite. 
 
 Arsenic oxide, As 2 O 5 (Arsenic pentoxide, Arsenic acid anhydride). 
 When arsenous oxide is heated with nitric acid, it becomes oxidized 
 and is converted into arsenic acid, H 3 AsO 4 , from which the water 
 may be expelled by further heating, when arsenic oxide is left : 
 2H 3 AsO 4 = As 2 O 5 + 3H 2 O. 
 
 Arsenic oxide is a heavy, white, solid substance which, in contact 
 with water, is converted into arsenic acid. This acid resembles phos- 
 phoric acid in composition, but diifers from it in not forming pyro- 
 and metarsenic acids. Arsenic acid when moderately heated loses all 
 its water and leaves the pentoxide, which at higher heat is decom- 
 posed into the trioxide and oxygen. Phosphoric acid, however, when 
 heated is converted into metaphosphoric which can be volatilized, 
 and phosphorus pentoxide does not decompose by heating. Sodium 
 pyroarsenate, perhaps, is formed when sodium arsenate is heated, 
 but when the mass is dissolved in water arsenate is formed at once, 
 whereas the pyrophosphate can be crystallized from water. 
 
 Arsenic oxide and arsenic acid are used largely as oxidizing agents 
 in the manufacture of aniline colors. 
 
 Disodium hydrogen arsenate, Sodii arsenas, Na 2 HAsO 4 .7H 2 O 
 = 3O9.84 (Sodium arsenate). This salt is made by fusing arsenous 
 oxide with carbonate and nitrate of sodium. 
 
 As 2 O 3 -f 2NaNO 3 + Na 2 CO 3 = Na 4 As 2 O 7 + N 2 O 3 + CO,. 
 
 Sodium pyroarsenate is formed, nitrogen trioxide and carbon dioxide 
 escaping. By dissolving in water and crystallizing, the official salt is 
 obtained in colorless, transparent crystals : 
 
 Na 4 As 2 7 -f 15H 2 O = 2(Na 2 HAsO 4 .7H 2 O). 
 
 Exsiccated sodium arsenate, Sodii arsenas exsiceatus, Na 2 HAsO 4 , is 
 the product obtained by driving off all the water of crystallization at 
 150 C. (302 F.). Liquor sodii arsenatis is a 1 per cent, solution of 
 
350 METALS AND THEIR COMBINATIONS. 
 
 exsiccated sodium arsenate in water, corresponding to 1.68 per cent, 
 of the crystallized salt. 
 
 Lead arsenate, Pb 3 (AsO 4 ) 2 , is used for spraying plants to exterminate 
 moths. It is a white, fusible powder, insoluble in water, ammonia, and ammo- 
 nium salts. It is obtained by precipitation of basic lead acetate (subacetate) 
 with sodium arsenate, or lead nitrate with excess of sodium arsenate : 
 
 3Pb(NO 3 ) 2 + 4Na 2 HAsO 4 = Pb 3 (AsO 4 ) 2 -f 6NaNO 3 + 2NaH 2 AsO 4 . 
 
 Hydrogen arsenide, AsH 3 .(Arsine, Arsenetted or arseniuretted 
 hydrogen). This compound is formed always when either arsenous 
 or arsenic oxides or acids, or any of their salts, are brought in con- 
 tact with nascent hydrogen, for instance, with zinc and diluted 
 sulphuric acid, which evolve hydrogen : 
 
 As 2 O 3 + 12H = 2AsH 3 + 3H 2 O. 
 As-A + 16H = 2AsH 3 + 5H 2 O. 
 AsCl 3 + 6H = AsH 3 + 3HC1. 
 
 Hydrogen arsenide is a colorless, highly poisonous gas, having a 
 strong garlic odor. Ignited, it burns with a bluish flame, giving off 
 white clouds of arsenous oxide : 
 
 2AsH 3 + 6O = As 2 O 3 + 3H 2 O. 
 
 When a cold plate (porcelain answers best) is held in the flame of 
 arsenetted hydrogen, a dark deposit of metallic arsenic (arsenic spots) 
 is produced upon the plate (in a similar manner as a deposit of 
 carbon is produced by a common luminous flame). The formation of 
 this metallic deposit may be explained by the fact that the heat of the 
 flame decomposes the gas, and that, furthermore, of the two liberated 
 elements, arsenic and hydrogen, the latter has the greater affinity for 
 oxygen. In the centre of the flame, to which but a limited amount 
 of oxygen penetrates, the latter is taken up by the hydrogen, arsenic 
 being present in the metallic state until it burns in the outer cone of 
 the flame. It is this liberated arsenic which is deposited upon a cold 
 substance held in the flame. 
 
 Arsenetted hydrogen, when heated to redness, is decomposed into 
 its elements ; by passing the gas through a glass tube heated to red- 
 ness, the liberated arsenic is deposited in the cooler part of the tube, 
 forming a bright metallic ring. 
 
 Sulphides of arsenic. Three sulphides of arsenic are known. Two 
 have been mentioned above as the native disulphide or realgar, As 2 S 2 , 
 
ARSENIC. 351 
 
 and the bisulphide or orpiment, As 2 S 3 . Bisulphide of arsenic is an 
 orange-red, fusible, and volatile substance, used as a pigment; it 
 may be made by fusing together the elements in the proper propor- 
 tions. Trisulphide is a golden-yellow, fusible, and volatile substance, 
 which also may be obtained by fusing the elements, or by precipitating 
 an arsenic solution by hydrogen sulphide (Plate V., 1). 
 
 The pentasulphide, As 2 S 5 , has the same color as the trisulphide, and 
 is most readily obtained by acidifying a solution of a sulph-arsenate : 
 
 2(NH 4 ) 3 AsS 4 4- 6HC1 2H 3 AsS 4 + 6NH 4 C1. 
 
 2H 3 AsS 4 = 3H 2 S + As 2 S 5 . 
 
 The tri- and pentasulphide of arsenic have acid properties, similar to 
 the corresponding oxides. They unite with alkali sulphides to form 
 soluble meta-sulph-arsenites and sulph-arsenates : 
 
 As. 2 S 3 + (NH 4 ) 2 S = 2NH 4 AsS 2 . 
 As 2 S 5 + 3(NH 4 ) 2 S = 2(NH 4 ) 3 AsS 4 . 
 
 When the trisulphide is dissolved in a solution of a polysulphide 
 (yellow ammonium sulphide), a sulph-arsenate is formed, 
 
 As 2 S 3 4- 3(NH 4 ) 2 S 4- S, = 2(NH 4 ) 3 AsS 4 , 
 
 from which acids precipitate the pentasulphide. Both sulphides are 
 also soluble in solutions of alkali hydroxides or carbonates, forming a 
 mixture of met-arsenite and meta-sulph-arsenite, and arsenate and 
 sulph-arsenate respectively. 
 
 Arsenous iodide, Arseni iodidum, AsI 3 = 454.5 (Iodide of arsenic), may 
 be obtained by direct combination of the elements, and forms orange-red crys- 
 talline masses, soluble in water and alcohol, but decomposed by boiling with 
 either of these liquids. It is used in the official preparation, Solution of arsenous 
 and mercuric iodides, Donovan's solution, which is made by dissolving one part 
 each of arsenous iodide and mercuric iodide in 98 parts of water. 
 
 Tests for arsenic. 
 
 (For arsenous compound, use a solution of arsenous oxide made by dissolving 0.5 
 gramme in 100 c.c. of hot water and allowing to cool ; for arsenic compound, use a 5 
 per cent, solution of sodium arsenate.) 
 
 1. Hydrogen sulphide produces in the solution of arsenous acid a 
 yellowish coloration, but no precipitate. This is due to the fact that 
 the arsenic trisulphide remains in solution in the colloidal state and is 
 precipitated only after a long time. Addition of some hydrochloric 
 acid causes precipitation immediately of the yellow trisulphide (Plate 
 
 V, 1): 
 
 2H 3 AsO 3 4- 3H 8 S ~ 6H.p 4- As 2 S 3 . 
 
352 METALS AND THEIR COMBINATIONS. 
 
 When a rapid stream of hydrogen sulphide is passed into a hot acid-. 
 ified solution of an arsenate, a yellow precipitate of arsenic pentasul- 
 phide is gradually formed : 
 
 2H 3 AsO 4 + 5H 2 S 8H 2 O + As 2 S 5 . 
 
 Solution of ammonium sulphide or caustic alkali readily dissolves 
 both sulphides of arsenic. Addition of acid reprecipitates the 
 sulphides. 
 
 2. Add 1 or 2 c.c. of silver nitrate solution to about 5 c.c. of the 
 arsenousacid solution ; no precipitate results. Now pour carefully upon 
 the surface of the mixture a little very dilute ammonia water ; a yellow 
 precipitate of silver arsenite (Plate V., 3) is formed at the line of con- 
 tact of the two liquids, which may be increased by cautiously mixing 
 the liquids. The precipitate is soluble in excess of ammonia or in 
 nitric acid. When solution of an arsenite instead of free arsenous 
 acid is used, silver nitrate gives a precipitate at once, without addition 
 of ammonia water : 
 
 H 3 As0 3 + 3AgN0 3 + 3NH 4 OH == Ag 3 AsO 3 + 3NH 4 NO 8 + 3H 2 O. 
 
 Na 3 AsO 3 + 3AgNO 3 == Ag 3 AsO 3 + 3NaNO 3 . 
 
 Dissolve the precipitate in a slight excess of ammonia water, add a 
 few drops of caustic soda, and apply heat ; a mirror of metallic silver 
 is formed, due to the reducing action of the arsenite, which becomes 
 arsenate. 
 
 When silver nitrate is added to the sodium arsenate solution (about 
 3 c.c.), a reddish-brown precipitate of silver arsenate is formed, which 
 is soluble in ammonia water or nitric acid (Plate V., 4) : 
 
 Na 2 HAsO 4 4- 3AgNO 3 = Ag 3 AsO 4 + 2NaNO 3 + HNO 3 . 
 
 3. Add 2 or 3 drops (avoid excess) of copper sulphate solution to 
 about 5 c.c. of the arsenous acid, and overlay the mixture with very 
 dilute ammonia water as in test 2 (if an arsenite is used, ammonia 
 water is unnecessary) ; a green precipitate of copper arsenite, Scheele's 
 green, CuHAsO 3 , is produced (Plate V., 2). Add some caustic alkali 
 solution to the precipitate and boil ; red cuprous oxide is formed, due to 
 reduction by the arsenite, which becomes arsenate. (Schweinfurt green, 
 copper aceto-arsenite, 3Cu(AsO 2 ) 2 .Cu(C 2 H 3 O 2 ) 2 , is obtained by adding 
 solution of copper acetate to a boiling solution of an arsenite. This 
 and Scheele's green are often called Paris green.) 
 
 When copper sulphate solution is added to the sodium arsenate solu- 
 tion, a greenish-blue precipitate of copper arsenate, CuHAsO 4 , is 
 
ARSENIC ANTIMONY, TIN. 
 
 PLATE V 
 
 Arscnous sulphide, precipitated fr< 
 arsenous solutions by hydrogen sulphii 
 
 Cupric arsenite, precipitated fr< 
 arsenous solutions by cupric-ammonh 
 sulphate. 
 
 Silver arsenite, precipitated frc 
 arsenous solutions by silver nitrate. 
 
 Silver arsenate, precipitated fro 
 arsenic solutions by silver nitrate. 
 
 Antimonous sulphide, precipital 
 from solutions of antimony by hydrog 
 sulphide. 
 
 Native or crystallized antimono 
 sulphide. 
 
 Stannous sulphide, precipitated frc 
 stannous solutions by hydrogen sulphic 
 
 Stannic sulphide, precipitated fn 
 stannic solutions by hydrogen sulphide. 
 
 Affoen & Co LiUi. Baltimore, . 
 
ARSENIC. 353 
 
 formed. All these precipitates are soluble in ammonia water and in 
 acids. 
 
 4. Add to a little of the arsenate solution, a clear mixture of mag- 
 nesium sulphate, ammonium chloride and ammonia water, and shake ; 
 a white precipitate of ammonium magnesium arsenate is formed, 
 NH 4 MgAsO 4 (see test 1 under phosphoric acid). 
 
 Magnesium arsenite is insoluble in water, but soluble in ammonia 
 water and in ammonium chloride solution. 
 
 5. Add to a few drops of the arsenate solution, excess of ammonium 
 molybdate solution (about 5 c.c.) and warm gently ; a* yellow precipi- 
 tate of ammonium arseno-molybdate is formed, similar in all respects 
 to the corresponding phosphorus compound. (Arsenic is the only 
 other element which behaves like phosphorus toward the molybdate 
 reagent.) Arsenites give no precipitate with the reagent. 
 
 6. Heat any dry arsenic compound, after being mixed with some 
 charcoal and dry potassium carbonate in a very narrow test-tube (or, 
 better, in a drawn-out glass tube having a small bulb on the end) : the 
 arsenic compound is decomposed and the element arsenic deposited 
 as a metallic ring in the upper part of the contraction. (Fig. 44.) 
 
 FIG. 44. 
 
 7. Heat arsenous or arsenic oxide upon a piece of charcoal by 
 means of a blow-pipe : a characteristic odor of garlic is percep- 
 tible. 
 
 8. Reimch's test. A thin piece of copper, having a bright metallic 
 surface, placed in a solution of arsenic, strongly acidified with con- 
 centrated hydrochloric acid, becomes, upon heating the solution, coated 
 
 23 
 
354 METALS AND THEIR COMBINATIONS. 
 
 with a dark steel-gray deposit of arsenic, which can be vaporized by 
 application of heat. Antimony also responds to this test. 
 
 9. Bettendorf's test, U. S. P. Add to any arsenic compound, dis- 
 FIG 45 solved in concentrated hydrochloric acid, an equal vol- 
 ume of freshly prepared saturated solution of stannous 
 chloride in concentrated hydrochloric acid, and heat in 
 boiling water for 15 minutes ; a brown color or precipi- 
 tate is formed, due to separation of the arsenic. Anti- 
 mony does not respond to this test. 
 
 10. Gutzeit's test. Place a small piece (about 1 
 gramme) of pure zinc in a test-tube, add about 5 c.c. 
 of dilute (5 per cent.) sulphuric acid and a few drops 
 of any arsenic solution, which should not be alkaline. 
 Fasten over the mouth of the test-tube a cap made of 
 three thicknesses of pure filter-paper, and moisten the 
 upper paper with a drop of a saturated solution of 
 silver nitrate in water acidulated with about 1 per 
 cent, of nitric acid. (Fig. 45.) Place the tube in a 
 box so as to exclude all light, and examine the paper 
 cap after awhile. Upon it will appear a bright-yellow 
 stain, rapidly if the quantity of arsenic be considerable, 
 slowly if it be small. Upon moistening the yellow 
 stain with water the color changes to brown or black. 
 The action of hydrogen arsenide upon silver nitrate in 
 the absence of water takes place with the formation of a yellow com- 
 pound, thus : 
 
 AsH 3 + 6AgNO 3 = 3HNO, -f Ag 3 As.(AgNO 3 ) 3 . 
 
 In the presence of water metallic silver is separated, showing a 
 black or brown color : 
 
 AsH 3 + 6AgN0 3 + 3H 2 =-- 6HNO, + H 3 AsO 3 + 6Ag. 
 
 Compounds of antimony treated in the above manner produce a 
 dark spot upon the paper, but cause no previous yellow color. 
 
 Modified Gutzeit's test, U. S. P. This is employed in nearly all 
 instances in the U. S. P. where traces of arsenic are tested for in official 
 products. It cannot be used in the case of bismuth or antimony 
 compounds, for which Bettendorf's test is employed. The test is 
 carried out as follows : 
 
 All the tests for arsenic bearing proper names are intended to be 
 applied for the detection of minute quantities of arsenic. If arsenic 
 
ARSENIC. 355 
 
 compounds themselves are used, only very dilute solutions should be 
 tested, in order to appreciate the delicacy of the tests. The arsenic 
 should be in the form of an arsenows compound for the above test, as 
 in this condition it is more readily reduced to arsine. This is insured 
 by adding to 5 c.c. of a 10 per cent, aqueous solution of the chemical 
 to be tested (in some instances special previous treatment is neces- 
 sary, which may be seen in the U. S. P.) 1 c.c. of a mixture of equal 
 volumes of concentrated sulphuric acid and water, and 10 c.c. of 
 fresh saturated solution of sulphur dioxide. The liquid is evaporated 
 over boiling water until it is free from sulphur dioxide and has been 
 reduced to 5 c.c. in volume. It is then introduced into a 75 c.c. flask 
 containing 2 or 3 grammes of granular zinc and 20 c.c. of 8 per cent, 
 hydrochloric acid, a small wad of clean dry gauze is inserted into the 
 lower end of the neck of the flask, followed by a wad moistened with 
 lead acetate solution. The mouth of the flask is then covered by 
 folding over it a filter-paper, the center of which has previously been 
 three times successively wet with a saturated alcoholic solution of 
 mercuric chloride and dried. After one-half to one hour, the paper cap 
 is examined for a yellow stain, which indicates arsenic. The presence 
 of arsenic much in excess of the permissible limit of the U. S. P. 
 (1 in 100,000) is shown by a distinct yellow to orange spot. All the 
 reagents used must be free from arsenic, which is determined by 
 making a blank test, omitting the chemical to be tested. The stu- 
 dent should carry out the test on 2 or 3 c.c. of a -\-$ per cent, solu- 
 tion of arsenic trioxide, which need not be submitted to the reduc- 
 tion with sulphur dioxide. Antimony gives a dark coloration. 
 
 11. Fleitmann's test. This is similar to the Gutzeit's test, the 
 chief difference being that hydrogen is evolved in alkaline solution, 
 which has the advantage that the presence of antimony does not 
 interfere, because this metal does not form antimonetted hydrogen in 
 alkaline solutions. 
 
 Place about 1 gramme of pure zinc in a test-tube, add about 5 c.c. 
 of potassium hydroxide solution and a few drops of the arsenic solu- 
 tion, which should not be acid. Provide paper cap as described in 
 Gutzeit's test, and set the test-tube in a box containing sand heated 
 to about 90 C. (194 F.). A brown or black stain of metallic silver 
 will appear upon the paper. 
 
 12. Marsh's test. While this test is not used now for qualitative 
 determinations as much as formerly, it is of great value because it 
 may serve for collecting the total amount of arsenic present in a 
 specimen, thus permitting quantitative estimation. The apparatus 
 
356 METALS AND THEIR COMBINATIONS. 
 
 (Fig. 46) used for performing this test consists of a glass vessel (flask 
 or WoulPs bottle) provided with a funnel-tube and delivery-tube 
 (bent at right angles), which is connected with a wider tube, filled 
 with pieces of calcium chloride or plugs of asbestos; this drying-tube 
 is again connected with a piece of hard glass tube, about one foot 
 long, having a diameter of J inch, drawn out at intervals of about 
 3 inches, so as to reduce its diameter to J inch. Hydrogen is gener- 
 ated in the flask by the action of sulphuric acid on zinc, and ex- 
 amined for its purity by heating the glass tube to redness at one of 
 its wide parts for at least 30 minutes ; if no trace of a metallic mirror 
 is formed at the constriction beyond the heated point, the gas and the 
 substances used for its generation may be pronounced free from 
 arsenic. (Both zinc and sulphuric acid often contain arsenic.) 
 
 FIG. 46. 
 
 lllillllillllllllMIMII1!linil1lll1tl)l1limnilinnitiiMiiiiitiiiiimni 
 
 uliliililiilllillllillliilllllllllM 
 
 Marsh's apparatus for detection of arsenic. 
 
 After having thus demonstrated the purity of the hydrogen, the 
 
 uspected liquid, which must contain the arsenic either as oxide or 
 
 chlonde (not as sulphide), is poured into the flask through the funnel- 
 
 If arsenic is present in not too small quantities, the gas ignited 
 
 the end of the glass tube shows a flame decidedly different from 
 
 tiiut ot Durnino* hvdroo'pn TM fl K i 
 
 appt^whichfs'ml^ " f P f ^^^it a wSdteud 
 
 ovpr tli fl r SS se > a c ld test-tube held inverted 
 
 lame will be covered upon its walls with a white deposit of 
 ctahedral crystals of n, senous oxide . a piece rf coId P porce . 
 
 coated with a brown stain (arsenic 
 above in connection with 
 
ARSENIC. 
 
 357 
 
 > 
 
 The glass tube heated, as above mentioned, at one of its wide parts, 
 will show a bluish-black metallic mirror at the constriction beyond. 
 
 If quantitative determination is desired, the glass tube is heated in two 
 places so as to cause all hydrogen arsenide to be decomposed. To collect, 
 however, the arsenic from any gas that might escape, the end of the tube 
 is inverted and placed into solution of nitrate of silver, which is decomposed 
 by the hydrogen arsenide, silver and arsenous acid being formed. The arsenic 
 solution should be introduced into the hydrogen generator in small portions, 
 so as not to produce more hydrogen arsenide at a time than can be decom- 
 posed by the method given. 
 
 The only element which, under the same conditions, forms spots and mirrors 
 similar to arsenic, is antimony ; there are, however, sufficiently reliable tests 
 to distinguish arsenic spots from those of antimony. 
 
 Arsenic spots treated with solution of hypochlorites (solution of bleaching- 
 powder) dissolve readily ; antimony spots are not affected. When nitric acid 
 is added to an arsenic spot and evaporated to dryness and the spot moistened 
 with a drop of silver nitrate, it turns brick-red ; antimony spots treated in like 
 manner remain white. Arsenic spots dissolved in ammonium sulphide and 
 evaporated to dryness show a bright-yellow, antimony spots an orange-red, 
 residue. Fig. 47 represents a simpler form of Marsh's appara- 
 tus, which generally will answer for students' tests. 
 
 Preparatory treatment of organic matter for arsenic 
 analysis. If organic matter is to be examined for arsenic 
 (or for any other metallic poison), it ought to be treated as 
 follows : The substance, if not liquid, is cut into pieces, well 
 mashed and mixed with water; the liquid or semi-liquid sub- 
 stance is heated in a porcelain dish over a steam bath with 
 hydrochloric acid and potassium chlorate until the mass has a 
 uniform light yellow color and has no longer the odor of 
 chlorine. By this operation all poisonous metals (lead and 
 silver excepted, because insoluble silver chloride and possibly 
 insoluble lead sulphate are formed) are rendered soluble evgn 
 when present as sulphides, and may now be separated by filtra- 
 tion from the remaining solid matter The clear solution is 
 heated and treated with hydrogen sulphide gas for several 
 hours, when arsenic and all metals of the arsenic and lead 
 groups are precipitated as sulphides, a little organic matter 
 also being precipitated generally. 
 
 The precipitate is collected upon a small filter and treated with warm ammo- 
 nium sulphide, which dissolves the sulphides of arsenic and antimony, leaving 
 behind the sulphides of the lead group, which may be dissolved in nitric, or, if 
 mercury be present, in nitro-hydrochloric acid, and the solution tested by the 
 methods mentioned for the respective metals. The ammonium sulphide solu- 
 tion is evaporated to dryness, this residue mixed with nitrate and carbonate of 
 sodium, and the mixture fused in a small porcelain crucible. By the oxidizing 
 action of the nitrate, both sulphides are converted into the higher oxides, 
 arsenic forming sodium arsenate, antimony forming antimonic oxide. By 
 treating the mass with warm water, sodium arsenate is dissolved and may be 
 
358 METALS AND THEIR COMBINATIONS, 
 
 filtered off, while antimonic oxide remains undissolved, and may be dissolved in 
 hydrochloric acid. Both solutions may now be used for making the respective 
 tests for arsenic or antimony. 
 
 Comments. Tests 1, 6, and 3 are sufficient to identify arsenic compounds. 
 Test 3 will detect an arsenite in presence of an arsenate, and tests 4 and 5 an 
 arsenate in presence of an arsenite. Test 10, especially in the modified form, 
 and Test 12 are most often used to detect traces of arsenic. 
 
 Alkali arsenites are soluble in water; all others are either insoluble or diffi- 
 cultly soluble in water. Alkali arsenates and acid arsenates of the alkaline 
 earths are soluble in water. All the salts are soluble in mineral acids. 
 
 Arsenous acid dissociates very slightly, and is therefore a weak acid. Its 
 soluble salts are hydrolyzed to a considerable extent, and show an alkaline 
 reaction. Boiling a solution of arsenous acid or its salts in hydrochloric acid 
 results in a loss of arsenic by volatilization as arsenous chloride. Solutions 
 of arsenic acid or its salts suffer no loss of arsenic in this manner. 
 
 Arsenic acid dissociates very much like phosphoric acid, but to a little less 
 extent than the latter in solutions of equal concentration. Even in high dilu- 
 tion the dissociation is mainly thus : 
 
 H 3 AsO 4 ^ H- -f H 2 AsO 4 '. 
 Further dissociation into HAsO/' and AsO/" ions is very slight. 
 
 Antidotes. Moist, recently prepared ferric hydroxide or dialyzed iron are 
 the best antidotes. Vomiting should be induced by tickling the fauces or by 
 administering zinc sulphate, but not tarter emetic. 
 
 33. ANTIMONY TIN-GOLD PLATINUM MOLYBDENUM. 
 
 Antimony, Sb : = 119.3 (Stibium). This metal is found in nature 
 chiefly as the trisulphide, Sb 2 S 3 , an ore which is known as black anti- 
 mony, crude antimony, or stibnite. 
 
 The metal is obtained from the sulphide by roasting, when it is 
 converted into oxide, which is reduced by charcoal. Antimony is a 
 brittle, bluish-white metal, having a crystalline structure ; it fuses at 
 
 QUESTIONS. Which metals belong to the arsenic group ; what are their 
 characteristics? Which non-metallic elements does arsenic resemble? Men- 
 tion some of the compounds showing this analogy. How is arsenic obtained 
 in the free state; what are its physical and chemical properties; how does 
 leat act upon it? What is white arsenic? State its composition, mode of 
 manufacture, appearance, solubility, and other properties. Which three solu- 
 ns, containing arsenic, are official, and what is their composition ? How is 
 3 acid obtained from arsenous oxide, and which arsenate is official? 
 composition and properties of arsenetted hydrogen, and explain its for- 
 mation. What use is made of it in testing for arsenic ? State the composition 
 realgar, orpiment, Scheele's green, and Schweinfurth green. Give a detailed 
 tion of the process by which arsenic can be detected in organic matter. 
 Describe in detail the principal tests for arsenic. 
 
ANTIMONY. 359 
 
 450 C. (842 F.), and may at a higher temperature be distilled without 
 change, provided air is excluded ; heated in air it burns brilliantly. 
 
 Antimony is used in a number of important alloys, for instance, in 
 type-metal, an alloy of lead, tin, and antimony. 
 
 The best solvent for antimony is hydrochloric acid, containing a 
 little nitric acid, whereby antimonous or antimonic chloride is 
 formed. Nitric acid converts it into antimonous or antimonic oxide, 
 which are almost insoluble in the liquid. 
 
 Three oxides of antimony are known, namely, trioxide, Sb 2 O 3 , 
 pentoxide, Sb 2 O 5 , and tetroxide, Sb 2 O 4 . Antimony differs from 
 arsenic in that the trioxide is more basic than acidic, forming salts 
 with mineral and organic acids. The salts with mineral acids, how- 
 ever, are decomposed by water, and require the presence of free acid 
 for solution. Antimony pentoxide is exclusively acidic in character, 
 forming met-antimonates and pyro-antimonates with caustic alkalies. 
 The tetroxide is neither basic nor acidic. It is formed when either 
 of the other oxides is heated in air to a dull redness for a long time. 
 
 The compounds of antimony commonly met with are the chloride, 
 sulphide, and double tartrate (tartar emetic). 
 
 Antimony trisulphide, Sb 2 S 3 (Antimonous sulphide). The above- 
 mentioned native sulphide, the black antimony, is found generally 
 associated with other ores or minerals, from which it is freed by heat- 
 ing the masses, when the antimony sulphide fuses and is made to run 
 off into suitable vessels for cooling. Thus obtained it forms steel- 
 gray masses of a metallic lustre, and a striated, crystalline fracture, 
 forming a grayish-black, lustreless powder, which is insoluble in 
 water, but soluble in hydrochloric acid with liberation of hydrogen 
 sulphide. 
 
 Antimonous sulphide found in nature is crystallized and steel-gray 
 (Plate V., 6), but it may be obtained also in an amorphous condition 
 as an orange-red (Plate V., 5) powder by passing hydrogen sulphide 
 through an antimouous solution. By heating the orange-red sul- 
 phide, it is converted into the black variety. 
 
 The sulphides and oxides of antimony, like those of arsenic, combine with 
 many metallic sulphides or oxides to form sulpho-salts or oxy-salts. Thus the 
 sodium sulph-antimonite, Na 3 SbS 3 , and the sodium antimonite, NaSb0 2 , are 
 formed when antimonous sulphide is boiled with sodium hydroxide. 
 
 Sb 2 S 3 + 4NaOII = Na 3 SbS 3 + NaSbO, + 2H 2 O. 
 
 By the addition of sulphuric acid, both salts are decomposed, sodium sulphate 
 is formed, and antimonous sulphide is precipitated : 
 
 Na 3 SbS 3 + NaSbO 2 + 2H 2 SO 4 = Sb 2 S 3 + 2Na 2 SO 4 + 2H 2 O. 
 

 360 METALS AND THEIR COMBINATIONS. 
 
 While the above is the principal reaction, there is formed also some anti- 
 mony oxide. 
 
 Experiment 48. Intimately mix about 0.5 gramme of finely powdered black 
 antimony sulphide with some sodium carbonate and potassium cyanide. 
 Heat this mixture with a blowpipe flame on charcoal till it fuses thoroughly 
 and a bead of metallic antimony is obtained. Drop the molten antimony 
 from the height of about a foot upon a sheet of paper and notice that 
 characteristic grayish-white streaks are formed, radiating in all directions. 
 Test the crust (left on the charcoal) on a silver coin for sulphur. Examine 
 another bead of antimony for cplor, hardness, malleability, etc. ; then try its 
 solubility in acids in the order of hydrochloric, dilute sulphuric, nitric, and 
 nitre-hydrochloric acids. 
 
 Antimony pentasulphide, Sb 2 S 5 (Golden sulphur et of antimony). 
 A red powder, which, like antimonotis sulphide, forms sulpho-salts. 
 It may be obtained by precipitation of acid solutions of antimonic 
 acid by hydrogen sulphide. 
 
 Antimonous chloride, SbCl 3 (Antimony terchloride, Butter of anti- 
 mony). Obtained by boiling the native sulphide with hydrochloric 
 acid: 
 
 Sb 2 S 3 4- 6HC1 = 3H 2 S 4- 2SbCl 3 . 
 
 The clear solution is evaporated and the remaining chloride dis- 
 tilled, when it is obtained as a white, crystalline, semi-transparent 
 mass. 
 
 By passing chlorine over antimonous chloride it is converted into 
 antimonic chloride, SbCl 5 , which is a fuming liquid. 
 
 Experiment 49. Boil about 2 grammes of black antimony with 10 c. c. of 
 hydrochloric acid until most of the sulphide is dissolved. Set aside for sub- 
 sidence, pour off the clear solution of antimonous chloride, evaporate to about 
 half its volume and use solution for next experiment. 
 
 Antimonous oxide (Antimony trioxide). When antimonous chlo- 
 ride is added to water decomposition takes place similar to the one 
 which normal bismuth salts undergo by the action of water, viz., a 
 white precipitate of oxy-chloride of antimony (antimonyl chloride), 
 BbOCl, is formed, which, however, is mixed with antimonous oxide, 
 as the following two reactions take place : 
 
 SbCl 3 + H 2 O = SbOCl 4- 2HC1. 
 2SbCl 3 4- 3H 2 = Sb 2 3 4- 6HC1. 
 
 The relative proportions of the two constituents depend on the 
 mode of manipulating and on the quantity of water used. 
 
 The white precipitate was formerly known as powder of Algaroth. 
 
ANTIMONY. 361 
 
 It is completely converted into oxide by treating it with sodium car- 
 bonate : 
 
 2SbOCl + Na 2 CO 3 = Sb,O 3 -f 2NaCl + CO 2 . 
 
 The precipitate when washed and dried is a heavy, grayish-white, 
 tasteless powder, insoluble in water, soluble in hydrochloric acid, and 
 also in a warm solution of tartaric acid. Antimonous oxide, while 
 yet moist, dissolves readily in potassium acid tartrate, forming the 
 double tartrate of potassium and antimony, or tartar emetic, which salt 
 will be more fully considered hereafter. 
 
 Experiment 50. Pour the antimonous chloride solution (obtained by Ex- 
 periment 49), which should have been boiled sufficiently to expel all hydrogen 
 sulphide, into 100 c.c. of water, wash by decantation the white precipitate of 
 oxychloride thus obtained, and add to it an aqueous solution of about 1 gramme 
 of sodium carbonate. After effervescence ceases, collect the precipitate on a 
 filter, wash well and treat some of the precipitate, while yet moist, with a solu- 
 tion of potassium acid tartrate, which dissolves it readily, forming tartar emetic. 
 (For the latter compound see index.) 
 
 Antidotes. Poisonous doses of any preparation of antimony are generally 
 quickly followed by vomiting : if this, however, have not occurred, the stomach- 
 pump must be applied. Tannic acid in any form, or recently precipitated ferric 
 hydroxide, should be administered. 
 
 Tests for antimony. 
 
 (Use a solution of antimony chloride prepared as in Experiment 49, and diluted to 
 about 30 c.c. by adding, first, 2 or 3 c.c. of dilute hydrochloric acid, and then water 
 cautiously. Also a 5 percent, solution of tartar emetic, K(SbO)C 4 H 4 O 6 , in water. 
 Note that the latter dissolves easily and without decomposition.) 
 
 1. Add hydrogen sulphide to some of the solution of antimony 
 chloride : an orange-red precipitate of antimonons sulphide (Sb 2 S 3 ) is 
 produced (Plate V., 5). 
 
 Hydrogen sulphide produces the same precipitate in the solution of 
 tartar emetic. 
 
 2. Add yellow ammonium sulphide to the precipitated sulphide of 
 antimony : this is dissolved and may be reprecipitated by neutralizing 
 with an acid. The same results are obtained with caustic alkalies. 
 
 3. Produce a concentrated solution of antimonous chloride by 
 evaporation or by dissolving the sulphide in hydrochloric acid, and 
 pour it into water : a white precipitate of oxychloride is formed. (See 
 explanation above.) 
 
 Add a few drops of dilute hydrochloric acid to some of the solution 
 of tartar emetic : a white precipitate of oxychloride is also formed. In 
 analysis, this might be mistaken for a chloride of silver, lead, or mer- 
 cury, but it differs from the latter by being soluble in excess of the acid. 
 
362 METALS AND THEIR COMBINATIONS. 
 
 4. Add sodium hydroxide, ammonium hydroxide, or sodium car- 
 bonate to the antimony chloride solution : in either case white anti- 
 moDOus hydroxide, Sb(OH) 3 , is produced, which is soluble in excess 
 of sodium hydroxide. 
 
 The same reagents added to the solution of tartar emetic produce 
 scarcely any precipitate, due to the solvent effect of the organic (tartaric) 
 acid. 
 
 5. Boil a piece of bright metallic copper in the solution of anti- 
 monous chloride : a black deposit of antimony is formed upon the cop- 
 per. By heating the latter in a narrow test-tube, the antimony is volatil- 
 ized and deposited as a white incrustation of antimonous oxide upon 
 the glass. 
 
 6. Use Gutzeit's or Marsh's test as described under tests for arsenic. 
 
 Tin, Sn = 118.8 (8tannum). This metal is found in nature chiefly 
 as stannic oxide or tin-stone, SnO 2 , from which the metal is easily 
 obtained by heating with coal : 
 
 Sn0 2 + 20 = Sn + 2CO. 
 
 Tin is an almost silver-white, very malleable metal, fusing at the 
 comparatively low temperature of 228 C. (440 F.). It is used in 
 many alloys, and chiefly in the manufacture of tin-plate, which is 
 sheet-iron covered with a thin layer of tin. 
 
 Tin is bivalent in some compounds, quadrivalent in others. These 
 combinations are distinguished as stanuous and stannic compounds. 
 
 Stannous hydroxide, Sn(OH) 2 , is not known. When a solution of 
 sodium hydroxide or carbonate is added to a solution of stannous 
 chloride, a precipitate, H 2 Sn 2 O 3 , is formed, which is derived from 
 Sn(OH) 2 . When it is heated in an atmosphere of carbon dioxide, 
 black stannous oxide, SnO, is formed, which ignites when heated in 
 air, giving stannic oxide. 
 
 Stannic hydroxide (Stannic acid), H 2 SnO 3 , is formed when a solu- 
 tion of stannic chloride is boiled : 
 
 SnCl 4 + 3H 2 = H 2 Sn0 3 + 4HC1. 
 
 It is also formed when sodium hydroxide or carbonate is added to a 
 solution of stannic chloride, or when just enough of an acid is added 
 to a solution of a stannate to effect decomposition : 
 
 Na 2 Sn0 3 + 2HC1 = 2NaCl + H 2 Sn0 3 . 
 
 It is a white substance insoluble in water, but easily soluble in 
 hydrochloric, nitric, or sulphuric acid, forming the corresponding salt, 
 and in caustic alkalies, forming stannates. 
 
TIN. 363 
 
 Metastannic acid is formed when tin is treated with concentrated 
 nitric acid. It is a white powder insoluble in water and acids, hut 
 seems to have the same composition as stannic acid. It forms salts 
 with alkalies which are entirely different in properties and composition 
 from the stannates, and are known as meta stannates. Two sodium salts 
 are known, Na.^Sn^Oj! and Na 2 Sn 9 O 19 . When the acid is heated, 
 stannic oxide, SnO 2 , is formed. 
 
 Stannous chloride, SnCl 2 (Protochloride of tin). Obtained by 
 dissolving tin in hydrochloric acid by the aid of heat : 
 Sn + 2HC1 = SnCl 2 + 2H. 
 
 Sufficiently evaporated, the solution yields crystals of the composi- 
 tion SnCl 2 .2H 2 O. Stannous chloride is a strong deoxidizing agent, 
 frequently used as a reagent for arsenic, mercury, and gold, which 
 metals are precipitated from their solutions in the metallic state. It 
 is used also in calico printing. 
 
 Stannic chloride, SnCl 4 (Perchloride of tin). Stannous chloride 
 may be converted into stannic chloride either by passing chlorine 
 through its solution or by heating with hydrochloric and nitric acids. 
 
 Tests for tin. 
 (Stannous chloride, SnCl. 2 , and stannic chloride, SnCl 4 , may be used.) 
 
 1 . Add hydrogen sulphide to solution of a stannous salt : brown 
 stannous sulphide is precipitated (Plate V., 7) : 
 
 SnCl 2 + -H 2 S 2HC1 + SnS. 
 
 The precipitate is soluble in yellow ammonium sulphide. 
 
 2. Add hydrogen sulphide to a solution of a stannic salt : yellow 
 stannic sulphide is precipitated (Plate V., 8) : 
 
 SnCl 4 + 4H 2 S = 4HC1 -f SnS 2 . 
 
 The precipitate is soluble in ammonium sulphide. 
 
 3. Sodium or potassium hydroxide added to a stannous salt pro- 
 duces a white precipitate of stannous hydroxide, Sn(OH) 2 . The same 
 reagents added to a stannic salt produce white stannic acid, H 2 SnO 3 . 
 Both precipitates are soluble in excess of the alkali, forming stannite, 
 Na 2 SnO 2 , and stannate, Na 2 SnO 3 . 
 
 Gold, Au = 195.7 (Aurum). Gold occurs in nature chiefly in the 
 free state, generally associated with silver, copper, and possibly with 
 
364 METALS AND THP:1R COMBINATIONS. 
 
 other metals, sometimes also in combination with selenium and tellu- 
 rium. This impure gold is separated from most of the adhering 
 sand and rock by a mechanical process of washing, in which advan- 
 tage is taken of the high specific gravity of the metallic masses. The 
 remaining mixture of heavy material is treated with mercury, which 
 dissolves gold and silver, leaving behind most other impurities. The 
 gold amalgam is placed in a retort and heated, when the mercury 
 distils over, while the gold is left behind. 
 
 From ores containing but little gold the metal is now extracted 
 largely by treating the finely powdered material with a solution of 
 potassium cyanide, which forms a soluble double cyanide of gold and 
 potassium, AuK(CN) 2 . From the solution gold is precipitated elec- 
 trolytically or by adding metallic zinc. 
 
 Refining gold. Gold obtained by either of the above processes is not pure, 
 but has to be purified or refined by methods which differ according to the nature 
 or quantity of the impurities present, or according to the use to be made of the 
 gold. The methods employed may be divided into two classes, viz., dry and 
 wet processes. In the dry or crucible methods the operation is conducted at a 
 temperature sufficiently high to melt the gold, while in the wet processes the 
 dissolving action of acids is made use of. 
 
 Of dry methods may be mentioned the following : The gold is fused in a 
 clay or graphite crucible which has been glazed on the inside with borax, and 
 a stream of chlorine is passed through the molten mass. The chlorides of zinc, 
 bismuth, arsenic, and antimony, when present, are volatilized, while the chlo- 
 rides of silver and copper rise to the top, forming, with some of the borax, a 
 layer over the purified gold. Another method consists in melting the gold in 
 a crucible, prepared as before mentioned, and adding gradually a mixture of 
 potassium nitrate and carbonate with borax. All base metals are converted 
 into oxides which become dissolved in the borax; but silver is not eliminated 
 by this method. It may, however, be gotten rid of by heating to a temperature 
 just below fusion, the granulated gold with about one-sixth of its weight of 
 sulphur. The mixture should be protected with a layer of fine charcoal. 
 Silver sulphide is formed during the operation and the gold, after being fused, 
 may be cast into an ingot mold. 
 
 Another dry method, used, however, more for assaying gold ores or gold alloys 
 than for purifying gold on a large scale, is the cupellation process. It depends 
 on the solubility of gold in molten lead and the readiness with which lead takes 
 up oxygen when heated in an oxidizing flame. In carrying out the process the 
 material to be operated on is fused with a quantity of lead amply sufficient to 
 dissolve the metals present. The resulting alloy, called the lead button, is then 
 submitted to fusion on a very porous support, made of bone-ash, and called a 
 cupel. All metals except gold and silver are oxidized ; the lead oxide, which is 
 fusible, takes up all other oxides, and the whole of this mass is absorbed by the 
 porous bone-ash, on the surf ace of which is finally left a button of gold and silver. 
 
 Of wet processes for the separation of gold and silver is to be mentioned the 
 method known as parting. It depends on the extraction of the silver (and cop- 
 
GOLD. 365 
 
 per, if present) by treating the granulated alloy with nitric acid of a specific 
 gravity of 1.32. This dissolves silver and copper, but does not act on the gold. 
 The process, however, is not applicable to an alloy containing more than 33 
 per cent, of gold, and it was believed that it should not exceed 25 per cent. 
 In order to subject to this process an alloy which is richer in gold, the alloy is 
 first fused with silver, and as it was customary to use 3 parts of silver for 1 part 
 of impure gold the process became known as quartation or inquartation. In 
 place of nitric acid, sulphuric acid of a specific gravity of 1.84 may be used. Gold 
 which has been freed from base metals and silver by any of the above-described 
 methods is known as refined gold, but it is rarely absolutely pure. It retains 
 traces of base metals or silver and all of the platinum if originally present. 
 
 Chemically pure gold, or as it is termed by the mints gold 1000 fine, may be 
 obtained by the following process. Nitro-hydrochloric acid, consisting of one 
 part of nitric acid and two parts of hydrochloric acid, is added in small por- 
 tions to the granulated gold, refined by one of the ordinary processes, until its 
 solution, with the aid of heat, has been effected. This solution of gold chloride 
 is evaporated nearly to dryness at a moderate heat. If platinum be suspected 
 the remaining mass is dissolved in very little water, and to the solution is added 
 an equal volume of alcohol and some ammonium chloride. If platinum be 
 present it is precipitated as ammonium platinic chloride and separated by fil- 
 tration. The filtrate is diluted with four parts of water and permitted to stand 
 for several days in order to cause complete precipitation of any silver chloride 
 present. To the filtrate a clear solution of ferrous sulphate is added which 
 causes the precipitation of gold. After decanting the supernatant liquid and 
 thoroughly washing the precipitate with distilled water it is treated with hot 
 concentrated acid, to eliminate traces of iron or copper. The purified gold is 
 again washed, dried, fused in a borax-lined crucible and poured into an ingot 
 mold. The chemical reaction which occurs in the precipitation of gold with 
 ferrous sulphate is this : 
 
 AuCl 3 + 3FeS0 4 = FeCl 3 + Fe 2 (SO 4 ) 3 + Au. 
 
 Many other reducing agents may be used in place of ferrous sulphate for 
 the precipitation of gold. Thus it is precipitated in a spongy or crystalline 
 condition by gently heating the gold solution with oxalic acid: 
 2AuCl 3 + 3H 2 C 2 O 4 = 6HC1 + 6CO 2 + 2Au. 
 
 Sulphurous acid precipitates gold in scales: 
 
 2AuCl 3 -f- 3H,SO 3 + 3H 2 = 6HC1 + 3H 2 SO 4 + 2Au. 
 Zinc and many other base metals precipitate gold as a brown powder: 
 2AuCl 3 -f 3Zn = 3ZnCl 2 + 2Au. 
 
 Elementary phosphorus, and many other organic and inorganic reducing 
 agents, may be used similarly for the precipitation of gold from its solutions, 
 or this precipitation may be effected electrolytically. 
 
 Cohesive gold, used in dentistry, may be obtained by heating gold foil to 
 redness, by which is restored its cohesiveness, which is greatly diminished 
 during the conversion of pieces of gold into foil by beating. 
 
 Gold is orange-yellow by reflected light, and green by transmitted 
 light ; it fuses at 1200 C. (2192 F.), has a specific gravity of 19.36, 
 
366 METALS AND THEIR COMBINATIONS. 
 
 and is a good conductor of heat and electricity. It is so malleable and 
 ductile that 1 grain can be hammered into a film covering 54 square 
 inches, and can be drawn into a wire, if protected by some more tena- 
 cious metal such as silver, so fine that 1 grain will measure 550 feet. 
 Tin, lead, antimony, arsenic, and bismuth destroy the ductility and malle- 
 ability of gold, making it very brittle. A small proportion of platinum con- 
 fers upon gold elasticity and increases its hardness. 
 
 Pure gold is too soft for general use, and therefore is alloyed with 
 various proportions of silver and copper. It is customary to express 
 the purity or fineness of gold in carats, an old term meaning a 
 twenty-fourth part. Pure gold is 24 carats, while an alloy contain- 
 ing 75 per cent, of gold is said to be of 18 carats fineness. Ameri- 
 can coin is an alloy of 90 parts of gold and 10 parts of copper ; 
 jeweller's gold contains generally 75 per cent, or more of gold, the 
 other metals being copper and silver ; the varying proportions are 
 well indicated by the color. 
 
 Gold is not affected by either hydrochloric, nitric, or sulphuric 
 acid, but is dissolved by nitro-hydrochloric acid, by free chlorine and 
 bromine, and by mercury, with which it forms an amalgam. 
 
 Gold is trivalent generally, as in auric chloride, AuCl 3 , but also 
 univalent in some compounds, as in aurous chloride, AuCl. 
 
 Gold chloride, Au01 3 (Auric chloride). Obtained by dissolving 
 pure gold in nitro-hydrochloric acid and evaporating the solution to 
 dryness. A mixture of equal parts by weight of gold chloride and 
 sodium chloride is official under the name of gold and sodium chloride. 
 It is an orange-yellow, very soluble powder, containing about 30 per 
 cent, of metallic gold. 
 
 Tests for gold. 
 (Solution of auric chloride, AuCl 3 , may be used.) 
 
 1. Add hydrogen sulphide to the solution : brown auric sulphide, 
 Au 2 S 3 , is precipitated, which is soluble in yellow ammonium sulphide. 
 
 2. Add ferrous sulphate to the solution and set aside for a few 
 hours metallic gold is precipitated as a dark powder : 
 
 AuCl 3 + 3FeS0 4 = Fe,(S0 4 ) s -f FeCl 3 + AU. 
 
 3. Many other reagents cause the separation of metallic gold from 
 its solution, as, for instance, oxalic acid, sulphurous and arsenous 
 acids, potassium nitrite, etc. 
 
PLATINUM. 367 
 
 Platinum, Pt =193.3. Platinum, like gold, is found in nature in 
 the free state, the chief supply being derived from the Ural mountains, 
 where it is associated with a number of metals (iridium, ruthenium, 
 osmium, palladium, rhodium) resembling platinum in their properties. 
 
 While the solubility of platinum in molten lead is sometimes used for its 
 separation by the cupellation process (see refining of gold) the abstraction of 
 platinum is usually accomplished by the wet process. The material contain- 
 ing it is treated with nitre-hydrochloric acid under slight pressure, when pla- 
 tinic chloride is formed. The solution is evaporated to dryness and the mass 
 heated to a temperature of 125 C. in order to decompose the higher chlorides 
 of iridium and palladium, which metals, if present, would otherwise accompany 
 the platinum. After dissolving the residue in water, ammonium chloride is 
 added, which precipitates platinum as ammonium platinic chloride, PtCl 4 . 
 2NH 4 C1. The washed precipitate when heated to redness is completely decom- 
 posed, metallic platinum being left as a gray, spongy mass, which may be fused 
 by means of the oxy-hydrogen flame or in an electric furnace. 
 
 Platinum is of great importance and value on account of its high 
 fusing-point and its resistance to the action of most chemical agents, 
 for which reason it is used in the manufacture of vessels serving in 
 chemical operations. While sulphuric, nitric, hydrochloric, and hydro- 
 fluoric acids have no action on platinum it is readily attacked by 
 chlorine, and at a red heat by caustic alkalies, sulphur, and phosphorus. 
 
 Platinum is of a silver-white color with a tinge of blue ; it is very malleable 
 and ductile ; its rate of expansion by heat is low, about that of glass. This 
 property is of value in the use of the metal for the pins of artificial teeth, and 
 as a base for continuous gum work. Addition of iridium renders platinum 
 harder, more rigid and more elastic, all of which properties platinum confers 
 upon silver and gold. 
 
 The property of platinum to condense oxygen upon its surface and to dis- 
 solve hydrogen is made very conspicuous in platinum sponge and platinum black. 
 The former is made by heating precipitated ammonium chloroplatinate, by 
 which a gray mass of finely divided platinum is left; the latter is obtained as 
 a black powder by adding zinc to chloroplatinic acid. Either of these forms 
 or platinum, when thrown into a mixture of oxygen and hydrogen, causes 
 instant explosion. This is an example of catalytic action, in which the speed 
 of a chemical change is enormously increased. The gases condensed in the 
 pores of the finely divided metal unite rapidly with production of sufficient 
 heat to cause the rest of the gases to unite with explosion. 
 
 Chloroplatinic acid, H 2 PtCl 6 .6H 2 O (often called Platinic chloride), 
 is obtained as reddish-brown deliquescent crystals when platinum is 
 dissolved in aqua regia and the solution evaporated. It serves as a 
 valuable reagent for potassium and ammonium, as explained in con- 
 nection with the analytical reactions of these bodies. In the acid and 
 
368 METALS AND THEIR COMBINATIONS. 
 
 its salts platinum is in the anion, as PtCl,/'. The chloride, PtCl 4 , is 
 obtained by heating the chloroplatinic acid in a current of chlorine 
 at 360 C. Its solution in water gives red, non-deliquescent crystals 
 of the composition, H 2 PtCl 4 O.4H 2 O. 
 
 Chloroplatinous acid, H 2 PtCl 4 , results when platinous chloride, 
 PtCl 2 , is dissolved in hydrochloric acid. The potassium salt, 
 K 2 PtCl 4 , is used in making platinum prints in photography. The 
 corresponding barium platinocyanide, BaPt(CN) 4 .4H 2 O, forms light 
 yellow crystals. Screens coated with this salt become luminous when 
 Rontgen rays (#-rays) fall upon them. Such fluorescent screens are 
 used for observing x-ray pictures. Ultra-violet and radium rays also 
 affect the screens. 
 
 Iridium, Ir = 191.5. This element has been mentioned as one of the metals 
 which accompany platinum in nature. It is obtained from the material left 
 in the working of platinum ores. 
 
 Iridium has a grayish- white color and resembles polished steel ; it is harder, 
 more brittle, specifically heavier and less fusible than platinum. The increased 
 hardness, rigidity and elasticity which iridium imparts to platinum makes the 
 alloy a valuable dental material. Gold pens are often tipped with iridium 
 which renders them more durable. 
 
 Compact pieces of iridium are insoluble in all acids; when finely divided it 
 dissolves in nitro-hydrochloric acid. It is for these reasons that most of the 
 iridium is left in the residue of the material from which platinum has been 
 extracted. Several oxides, hydroxides and chlorides of iridium are known. 
 
 Molybdenum, Mo = 95.3. This metal is found in nature chiefly as sul- 
 phide, MoS. 2 , from which, by roasting, molybdic oxide. MoO 3 , is obtained. The 
 oxide, when dissolved in water, forms an acid which combines with metals, 
 forming a series of salts termed molybdates. Of interest is ammonium molyb- 
 date, a solution of which in nitric acid is an excellent reagent for phosphoric- 
 acid, with which it forms a yellow precipitate, insoluble in acids, soluble in 
 ammonium hydroxide. 
 
 QUESTIONS. How is antimony found in nature, and what are the proper- 
 ties of this metal ? State the composition of antimonous sulphide, and its 
 color when crystallized and amorphous. How do hydrochloric acid and alkali 
 hydroxides act upon antimonous sulphide? Mention the two chlorides of 
 antimony and state their properties. How is antimonous oxide made, and for 
 what is it used? Give tests for antimony. State the use made of tin in the 
 metallic state; mention the two chlorides of tin, and the use of stannous chlo- 
 ride. Describe processes for refining gold by the dry and wet methods. How 
 are gold and platinum found in nature ; by what acid may they be dissolved, 
 and what is the composition of the compounds formed? Which is the most 
 important compound of molybdenum, and what is its use? 
 
THE ARSENIC GROUP. 
 
 369 
 
 Summary of analytical characters of metals of the arsenic 
 
 group. 
 
 
 Arsenic. 
 
 Antimony. 
 
 Tin. 
 
 Gold. 
 
 Platinum. 
 
 Hydrogen sulphide . 
 
 Precipitate heated ^j 
 in strong hydro- y 
 chloric acid . . J 
 
 Potassium hydroxide 
 
 Yellow pre- 
 cipitate. 
 
 Insoluble. 
 
 Orange 
 precipitate 
 
 Soluble. 
 White 
 
 Yellow 
 or brown 
 precipitate. 
 
 Soluble. 
 White 
 
 Black 
 precipitate 
 
 Insoluble. 
 Brownish 
 
 Dark- 
 brown 
 precipitate. 
 
 Insoluble. 
 1 With ex- 
 
 Ammonia water 
 
 
 precipitate, 
 soluble 
 in excess. 
 
 White 
 
 precipitate, 
 soluble 
 in excess. 
 
 White 
 
 precipitate, 
 soluble 
 in excess. 
 
 Brownish 
 
 cess of 
 hydro- 
 chloric 
 f acid a 
 yellow 
 
 Gutzeit's test 
 
 Yellow stain 
 
 precipitate. 
 Dark stain 
 
 precipitate. 
 
 yellow 
 precipitate 
 
 precipi- 
 J tate. 
 
 Fleitmann's test 
 
 turning dark 
 with water. 
 
 Dark stain 
 
 
 
 
 
 
 
 
 
 
 
 24 
 
V. 
 
 ANALYTICAL CHEMISTRY. 
 
 34. INTRODUCTORY REMARKS AND PRELIMINARY 
 EXAMINATION. 
 
 General remarks. Analytical chemistry is that part of chemistry 
 which treats of the different analytical methods by which substances 
 are recognized and their chemical composition determined. This 
 determination may be either qualitative or quantitative, and, accord- 
 ingly, a distinction is made between a qualitative analysis, by which 
 simply the nature of the elements (or groups of elements) present in 
 the substance under examination is determined, and a quantitative 
 analysis, by which also the exact amount of these elements is ascer- 
 tained. 
 
 In this book qualitative analysis will be considered chiefly, as the 
 methods for quantitative determinations of the different elements are 
 so numerous and so varied that a detailed description of them would 
 occupy more space than can be devoted to analytical chemistry in this 
 work. Some brief directions concerning quantitative determinations, 
 especially by volumetric methods, are given in Chapter 38. Every- 
 one studying analytical chemistry should do it practically, that is, 
 should perform for himself in a laboratory all those reactions which 
 have been mentioned heretofore as characteristic of the different ele- 
 ments and their compounds, and, furthermore, should make himself 
 acquainted with the methods by which substances are recognized 
 when mixed with others, by analyzing various complex substances. 
 
 Such a course of practical work in a suitable laboratory is of the 
 greatest advantage to all studying chemistry, and students cannot be 
 too strongly advised to avail themselves of any facilities offered in 
 performing chemical experiments, analytically or otherwise. 
 
 Apparatus needed for qualitative analysis. 
 
 1. Iron stand. (Fig. 48.) 
 
 2. Bunsen lamp with flexible tube (Fig. 48) or (where without gas-supply) 
 
 spirit-lamp and alcohol. 
 
 371 
 
372 
 
 ANALYTICAL CHEMISTRY. 
 
 3. Test-tube stand and one dozen assorted test-tubes. (Fig. 49.) 
 
 4. Three beakers from 100 to 150 c.c. capacity. (Fig. 50, A.) 
 
 5. Two flasks of 100 to 150 c.c. capacity. (Fig. 50, B.) 
 
 FIG. 48. 
 
 FIG. 49. 
 
 FIG. 50. 
 
 6. Wash-bottle of about 400 c.c. capacity. (Fig. 51, A.) 
 
 7. Three small glass funnels, about one and a half to two inches in diameter. 
 
 (Fig. 51, B.) 
 
INTRODUCTORY REMARKS. 
 
 373 
 
 8. A few pieces of glass tubing about ten inches long, and some India-rubber 
 
 tubing to fit the glass tubing. 
 
 9. Three glass rods. 
 
 FIG. 51. 
 
 10. Three small porcelain evaporating dishes, about two inches in diameter. 
 
 (Fig. 52, A.) 
 
 11. Blowpipe. (Fig. 52, B.) 
 
 12. Crucible tongs. (Fig. 52, C.) 
 
 FIG. 52. 
 
 13. Round and triangular file 
 
 14. Wire gauze, about six inches square, or sand tray. 
 
 15. One square inch of platinum foil (not too light), and six inches of 
 
 platinum wire. 
 
 16. Filter-paper. 
 
 17. Pair of scissors. 
 
 18. One or two dozen assorted corks. 
 
 19. Sponge and towel. 
 
 20. Two watch-glasses. 
 
 21. Small pestle and mortar. (Fig. 52, D.) 
 
 22. Small porcelain crucible. 
 
 23. Small platinum crucible. (Fig. 52, E.) 
 
 24. Wire triangle to support the crucible. (Fig. 52, F.) 
 
374 ANALYTICAL CHEMISTRY. 
 
 Reagents needed in qualitative analysis. 
 a. Liquids. 
 
 1. Sulphuric acid, sp. gr. 1.84, H 2 SO 4 . 
 
 2. Sulphuric acid diluted, sp gr 1.068 (1 part sulphuric acid, 9 parts water). 
 
 3. Hydrochloric acid, sp. gr. 1.16, HC1. 
 
 4- Hydrochloric acid diluted, sp. gr. 1.049 (6 parts hydrochloric acid, 13 parts 
 water). 
 
 5. Nitric acid, sp. gr. 1.42, HNO 3 . 
 
 6. Acetic acid, sp. gr. 1.048, C 2 H 4 O 2 . 
 
 7. Hydrogen sulphide, either the gas or its solution in water, H 2 S. 
 
 8. Ammonium sulphide, (NH 4 ) 2 S. 
 
 9. Ammonium hydroxide (ammonia water), NH 4 OH. 
 
 10. Ammonium carbonate, (NH 4 ) 2 CO 3 . A solution of one part of the commercial 
 
 salt in a mixture of four parts of water and one part of ammonia water. 
 
 11. Ammonium chloride, NH 4 C1 ; ten per cent solution. 
 
 12 Ammonium oxalate, (NH 4 ) 2 C 2 O 4 ; five per cent, solution. 
 
 13. Ammonium molybdate, (NH 4 ) 2 MoO 4 - A five per cent solution of the salt in a 
 
 mixture of equal parts of water and nitric acid. 
 
 14. Sodium hydroxide, NaOH. ~| 
 
 15. Sodium carbonate, 
 
 16. Sodium phosphate, NaHPO A . m i .- 
 
 ,_ c, ,. }- Ten per cent, solutions. 
 
 17. Sodium acetate, NaC 2 H 3 O 2 . 
 
 18 Potassium chromate, K 2 CrO 4 . 
 
 19 Potassium dichromate, K 2 Cr 2 O r 
 20. Potassium iodide, KI 
 
 21 Potassium ferrocyanide, K 4 Fe(CN) 8 . ,-,. 
 
 oo T> * f -j T ^ /nxTx r Five per cent, solutions. 
 
 22. Potassium ferricyanide, K 6 Fe 2 (CN) 12 . 
 
 23 Potassium sulphocyanate, KCNS. 
 
 24. Magnesium sulphate, MgSO 4 . ^ 
 
 25. Barium chloride, BaCl 2 . L Ten per cent, solutions. 
 
 26. Calcium chloride. CaCl 2 . ) 
 
 27. Calcium hydroxide, CaiOH) 2 (lime-water). 1 
 
 28 Calcium sulphate, CaSO, I Crated solutions. 
 
 29 Ferric chloride, FeCl 3 . n 
 
 30 Lead acetate, Pb.(C 2 H 3 2 ) 2 . 
 
 31. Silver nitrate, AgNO 3 . [ Five per cent, solutions. 
 
 32. Mercuric chloride, HgCl 2 . 
 
 33. Platinic chloride, H 2 PtCl e . 
 
 34. Stannous chldride, SnCl 2 .2H 2 O; ten per cent, solution. 
 
 35. Solution of indigo 
 
 36. Alcohol, C 2 H 5 OH. 
 
 37. Sodium cobaltic nitrite solution, Co 2 (NO 2 ) 6 .6NaNO 2 + H 2 O. Four grammes of 
 
 cobaltous nitrate, Co(NO 3 ) 2 .6H 2 O, and 10 grammes of sodium nitrite, NaNO.., 
 are dissolved in about 50 c.c. of water, 2 c.c. of acetic acid are added, and then 
 water to make 100 c.c. 
 
 38. Alkaline mercuric-potassium iodide solution (Nessler's solution). Five grammes 
 
 of potassium iodide are dissolved in hot water, and to this is added a hot 
 olution, made by dissolving 2.5 grammes of mercuric chloride in 10 c.c. of 
 water. To the turbid red mixture is added a solution made by dissolving 16 
 
INTRODUCTORY REMARKS. 375 
 
 grammes of potassium hydroxide in 40 c.c. of water, and the whole diluted to 
 100 c.c. Some mercuric iodide deposits on cooling, and may be left in the 
 bottle, the clear solution being decanted as needed. 
 
 b. Solids. 
 
 1. Litmus or blue and red litmus paper. 
 2 Turmeric paper. 
 
 3. Sodium carbonate, dried, Na 2 CO 3 . 
 
 4. Sodium biborate, borax, Na 2 B 4 O 7 .10H 2 O. 
 
 5. Sodium-ammonium-hydrogen phosphate (microcoamic salt), 
 
 Na(NH 4 )HPO 4 .4H 2 O. 
 
 6. Potassium carbonate, K 2 CO 3 . 
 
 7. Potassium nitrate, KNO 3 . 
 
 8. Potassium chlorate, KC1O 3 . 
 
 9. Potassium permanganate, KMnO 4 . 
 10- Potassium cyanide, KCN. 
 
 11. Calcium hydroxide, Ca(OH) 2 . 
 
 12. Ferrous sulphide, FeS. 
 
 13. Ferrous sulphate, FeSO 4 .7H 2 O. 
 
 14. Manganese dioxide, MnO 2 . 
 
 15. Zinc, granulated, Zn. 
 
 16. Copper, Cu. 
 
 17. Cupric oxide, CuO. 
 
 18. Cupric sulphate, CuSO 4 5H,O. 
 
 19. Tartaric acid, H 2 C 4 H 4 O 6 . 
 
 20. Tannic acid, H C U H 9 O 9 
 
 21. Pyrogallic acid, C 6 H 3 (OH) 3 . 
 
 22. Diphenylamine, (C 6 H 5 ) 2 NH. 
 
 23. Starch, C 6 H 10 O 5 . 
 
 While the apparatus and reagents here enumerated are the more 
 important ones, the analyst will occasionally require others not men- 
 tioned in the above list. 
 
 General mode of proceeding- in qualitative analysis. Every 
 step taken in analysis should be properly written down in a note- 
 book, and these remarks should be made directly after a reaction has 
 been performed, and not after the nature of the substance has been 
 revealed by perhaps numerous reactions. 
 
 Not only the reactions by which positive results have been obtained 
 should be noted, but also those tests and reagents mentioned which 
 have been applied with negative results that is, which have been 
 applied without revealing the presence of any substance, or any group 
 of substances. Such negative results are, however, positive in so far 
 as they prove the absence of a certain substance, or certain substances, 
 for which reason they are of direct value, and should be noted. 
 
 In comparing, finally, the result obtained by the analysis with the 
 
376 ANALYTICAL CHEMISTRY. 
 
 notes taken during the examination, none of them should be contra- 
 dictory to the conclusions drawn. If, for instance, the preliminary 
 examination showed the substance to have been volatilized by heating 
 upon platinum foil with the exception of a very slight residue, and if, 
 afterward, other tests show the presence of ammonia and hydro- 
 chloric acid and the absence of everything else, and if, then, the con- 
 clusion be drawn that the substance is pure ammonium chloride, this 
 conclusion must be incorrect, because pure ammonium chloride is 
 wholly volatile, and does not leave a residue. It will then be the task 
 of the operator to find where the mistake occurred, and to correct it. 
 
 Use of reagents. A mistake made by most beginners in analyz- 
 ing is the use of too large quantities both of the substance applied 
 for testing and of the reagents added. This excessive use of material 
 is not only a waste of money, but, what is of greater importance, a 
 waste of time. Some experience in analyzing will soon convince the 
 student of the truth contained in this remark, and will also enable 
 him to select the correct quantities of materials to be used, which 
 rarely exceed 0.2-1.0 gramme. A smaller amount in fact, as little 
 as a few milligrams frequently may answer, and a much larger 
 quantity may occasionally be needed, as, for instance, in cases where 
 highly diluted reagents, such as calcium sulphate solution, lime- 
 water, hydrogen sulphide water, etc., are applied. 
 
 Preliminary examination. This examination includes the fol- 
 lowing points : 
 
 1. Physical properties. Solid or liquid; crystallized or amor- 
 phous; color, odor, hardness, gravity, etc. (On account of possible 
 poisonous properties, the greatest care should be exercised in tasting 
 a substance.) 
 
 2. Action on litmus. Examined by holding litmus-paper in the 
 liquid, or by placing the powdered solid upon red and blue litmus- 
 paper, moistened with water. (It should be remembered that many 
 normal salts, as, for instance, aluminum sulphate, ferrous sulphate, 
 etc., have an acid reaction to litmus-paper, and that such a reaction 
 consequently is not conclusive of the presence of a free acid, nor even 
 of an acid salt.) 
 
 3. Heating on platinum foil or in a dry glass tube, open at 
 both ends. (If the substance to be examined be a liquid, it should 
 
INTRODUCTORY REMARKS. 377 
 
 be evaporated in a small porcelain dish to see whether a solid residue 
 be left or not. If a residue be left, it should be treated like a solid.) 
 The heating of a small quantity of a solid substance upon platinum 
 foil, or upon a piece of mica, held over the flame of a Bunsen burner, 
 is a test which should never be omitted, as it discloses in most cases 
 the fact whether the substance is of an organic or inorganic nature. 
 
 Most organic (non-volatile) substances when thus heated will burn with a 
 luminous flame, leaving in many cases a black residue of carbon, which upon 
 further heating disappears. In cases where the organic nature of a compound 
 is not clearly demonstrated by heating on platinum foil, the substance is heated 
 with an excess of cupric oxide in a test-tube or other glass tube, provided with 
 a delivery-tube which passes into lime-water. Upon heating the mixture the 
 carbon of the organic matter is converted into carbon dioxide, which renders 
 lime-water turbid. 
 
 The analytical processes by which the nature of an organic substance is 
 determined are not considered in this part of the book, but will be mentioned 
 when considering the carbon compounds. Some substances ruin platinum when 
 heated on it. Thus, salts of easily reducible metals, as lead, bismuth, antimony, 
 tin, especially their organic salts, are apt to do so, because these metals form 
 fusible alloys with the platinum. Thiosulphates corrode and hypophosphites 
 destroy platinum. Should the presence of any of the substances be suspected, 
 heating on platinum should be omitted. Indeed, tests 4 and 5 can be applied 
 first, as they may show the presence of these objectionable substances. 
 
 An inorganic substance heated on platinum foil may either be volatilized, 
 change color, become oxidized, suffer decomposition, or remain unchanged. 
 (See Table I., page 381.) 
 
 FIG. 53. FIG. 54. 
 
 Heating of solids in bent glass tube. Heating on charcoal by means of blowpipe. 
 
 Some substances, containing small quantities of water enclosed 
 between the crystals (common salt, for instance), decrepitate when 
 heated, the small fragments being thrown from the foil; such sub- 
 
378 ANALYTICAL CHEMISTRY. 
 
 stances should be heated in a dry test-tube to expel the water and 
 then be examined on platinum foil. 
 
 In many cases it is preferable to heat the substance in a bent glass 
 tube, as shown in Fig. 53, instead of on platinum foil, because vola- 
 tile products evolved during the process of heating may become re- 
 condensed in the cooler part of the tube, and thus saved for further 
 examination. 
 
 The presence of water, sulphur, mercury, arsenic, etc., may often 
 be readily demonstrated by this mode of operating. 
 
 4. Heating 1 on charcoal by means of the blowpipe. This test 
 reveals the presence of chlorates and nitrates by the vivid combus- 
 tion of the charcoal (known as deflagration), which takes place in 
 consequence of the oxidizing action of these substances. 
 
 Arsenic is indicated by a characteristic odor of garlic. 
 
 5. Heating- on charcoal with sodium carbonate and potas- 
 sium cyanide. A small quantity of the finely powdered substance 
 is mixed with twice its weight of potassium cyanide and dry sodium 
 carbonate. This mixture is placed in a small hole made in a piece 
 of charcoal, and heat applied by means of the blowpipe (see Fig. 54). 
 Many metallic compounds may be recognized by this test, the metals 
 being liberated and found as metallic globules or shining particles in 
 the fused mass after this has been removed from the charcoal and 
 washed with water in a small mortar. (See Fig. 55.) 
 
 FIG. 55. 
 
 A characteristic incrustation is formed by some metals, due to the 
 precipitation of a metallic oxide around the heated spot on the char- 
 coal. 
 
 If sulphur as such, or in any form of combination, be present in 
 the substance examined by this test, the fused mass contains a sulphide 
 of the alkali (hepar), which may be recognized by placing it en a 
 piece of bright silver (coin) moistened with a drop of water, when the 
 
INTRODUCTORY REMARKS. 879 
 
 silver will be stained black in consequence of the formation of silver 
 sulphide. The presence of the alkali sulphide may also be demon- 
 strated by the addition of a few drops of hydrochloric acid to the 
 fused mass, when hydrogen sulphide is evolved and may be recog- 
 nized by its odor. 
 
 6. Flame tests. Many substances impart a characteristic color 
 to a non-luminous flame. The best mode of performing this test is 
 as follows : A platinum wire is cleaned by washing in hydrochloric 
 acid and water, and heating it in the flame until the latter is no 
 longer colored. One end of the wire is fused in a short piece of 
 glass tubing (see Fig. 56), the other end is bent so as to form a small 
 
 FIG. 56. 
 
 loop, which is heated, dipped into the substance to be examined, and 
 again held in the lower part of the flame, which then becomes colored. 
 
 Some substances show the color-test after being moistened with 
 hydrochloric or sulphuric acid. 
 
 A second method of showing flame reactions is to mix the substance 
 with alcohol in a small dish ; the alcohol, upon being ignited, shows 
 a colored flame, especially in the dark. 
 
 7. Colored borax beads. The compounds of some metals when 
 fused with glass, impart to it characteristic colors. For analytical 
 purposes not the silica-glass, but borax-glass is generally used. This 
 latter is made by dipping the loop, of a platinum wire in powdered 
 borax and heating it in the flame (directly, or by means of the blow- 
 pipe) until all water has been expelled and a colorless, transparent 
 bead has been formed. To this colorless bead a little of the finely 
 powdered substance is added and the bead strongly heated. The 
 metallic compound is chemically acted upon by the boric acid, a bo rate 
 being formed which colors the bead more or less intensely, according 
 to the quantity of the metallic compound used. 
 
 Some metals (copper, for instance) forming two series of compounds give 
 different colors to the bead when present in either the higher or the lower state 
 of oxidation. 
 
 By modifying the blowpipe flame so as either to oxidize (by supplying an 
 excess of atmospheric oxygen), or deoxidize (by allowing some unburnt carbon 
 in the flame), the metallic compound in the bead may be made to assume the 
 
380 ANALYTICAL CHEMISTRY. 
 
 higher or lower state of oxidation. A copper bead may thus be changed from 
 blue to red, or red to blue, the blue bead containing the copper in the cupric, 
 the red bead in the cuprous form. In some cases microcosmic salt, NaNH 4 HPO 4 , 
 is used for making the bead. 
 
 8. Liquefaction of solid substances. Most solid substances 
 have to be dissolved for analysis. The solution obtained may be 
 either a simple or chemical solution. In a simple solution the dis- 
 solved body retains all of its original properties, with the exception 
 of its shape, and may be re-obtained by evaporation. Sodium 
 chloride and sugar dissolved in water form simple solutions. A 
 chemical solution is one in which the chemical composition of the sub- 
 stance has been changed during the process of dissolving, as, for 
 instance when calcium carbonate is dissolved in hydrochloric acid ; 
 this solution now contains and leaves on evaporation calcium 
 chloride. The solvents used are water, or the mineral acids for 
 substances insoluble in water, especially dilute, or, if necessary, strong 
 hydrochloric acid. The dissolving action of the acid should be facil- 
 itated by the aid of heat. Nitric or even nitro-hydrochloric acid 
 may have to be used in some cases. 
 
 Three mistakes ore frequently made by beginners in dissolving sub- 
 stances in acids , viz. : The substance is not powdered as finely as it 
 should be ; sufficient time is not given for the acid to act ; too large an 
 excess of the acid is used. 
 
 If a substance is partly dissolved by water and partly by one or 
 more other solvents, it may be well to examine the different solutions 
 separately. 
 
 Substances insoluble in water and in acids have to be rendered 
 soluble by fusion with a mixture of potassium and sodium carbonate, 
 or with potassium acid sulphate, or by the action of hydrofluoric 
 acid. 
 
 The insoluble sulphates of the alkaline earths, when fused with the 
 alkaline carbonates, are con verted into carbonates, while the sulphates 
 of the alkalies are formed. The latter compounds may be eliminated 
 by washing the fused mass with water and filtering : the solid residue 
 upon the filter contains the carbonates of the alkaline earths, which 
 may be dissolved in hydrochloric acid. 
 
 Insoluble silicates may be decomposed by the methods mentioned 
 on page 186. 
 
I y TROD UCTOR Y REMA RKS. 
 
 381 
 
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 ! ,lo|||| 
 
 s? 
 
 g 
 
382 ANALYTICAL CHEMISTRY. 
 
 35. SEPARATION OF METALS INTO DIFFERENT GROUPS. 
 
 General remarks. The preliminary examination will, in most 
 cases, decide whether or not a metal or metals are present in the sub- 
 stance to be examined. If there be metals, the solution should be 
 treated according to Table II., page 344, in order to find the group 
 or groups to which these metals belong, and also to separate them 
 into these groups, the individual nature of the metals themselves 
 being afterward demonstrated by special methods. 
 
 The simplest method of separating from each other the 57 metals 
 known, if all were in one solution, would be to add successively 57 
 different reagents, each of which should form an insoluble compound 
 with but one of the metals. By separating this insoluble compound 
 from the metals remaining in solution (by filtration), and by thus pre- 
 cipitating one metal after the other, they all could be easily separated. 
 We have, however, no such 57 reagents, and are, consequently, com- 
 pelled to precipitate a number of metals together, and the reagents 
 used for this purpose are known as group-reagents. 
 
 They are : 
 
 1. Hydrogen sulphide, added to the solution previously acidified by 
 hydrochloric acid. Precipitated are : the metals of the arsenic and 
 lead groups as sulphides. 
 
 2. Ammonium sulphide, added after supersaturating with ammonium 
 hydroxide. Precipitated are : the metals of the iron group and of 
 the earths as sulphides or hydroxides. 
 
 3. Ammonium carbonate. Precipitated are : the metals of the 
 alkaline earths as carbonates. 
 
 4. In solution are left : the metals of the alkalies and magnesium. 
 The order in which these group-reagents are added cannot be 
 
 QUESTIONS. What is analytical chemistry, and what is the object of quali- 
 tative and of quantitative analysis? What properties of a substance should 
 be noticed first in- making a qualitative analysis? By what tests may organic 
 compounds be distinguished from inorganic compounds? Explain the terms 
 decrepitation and deflagration. Mention some substances which are completely 
 volatilized by heat, some which are fusible, and some which are not changed 
 by heating them. What is meant by " hepar," and which element is indicated 
 by the formation of hepar? Mention some metals which may be liberated 
 from their compounds by heating on charcoal with potassium cyanide and car- 
 bonate. Which metallic compounds and which acids are capable of coloring a 
 non-luminous flame? Name the colors imparted. State the metals which im- 
 part characteristic colors to a borax bead. Which solvents are used for lique- 
 fying solids, and what precautions should be observed in this operation? 
 
SEPARATION OF METALS INTO DIFFERENT GROUPS. 383 
 
 reversed or changed, because ammonium sulphide added first would 
 precipitate not only the metals of the iron group and the earths, but 
 also the metals of the lead group ; .ammonium carbonate would pre- 
 cipitate also most of the heavy metals. 
 
 For the same reasons, in separating metals of the different groups, the group- 
 reagents must be added in excess, that is, enough of them must be added to 
 precipitate the total quantity of the metals of one group, before it is possible 
 to test for metals of the next group. Suppose, for instance, a solution to con- 
 tain a salt of bismuth only. Upon the addition of hydrogen sulphide to the 
 acidified solution, a dark-brown precipitate (of bismuth sulphide) is produced, 
 indicating the presence of a metal of the lead group. Suppose, further, that 
 hydrogen sulphide has not been added in sufficient quantity to precipitate the 
 whole of the bismuth, then ammonium sulphide, as the next group-reagent, 
 would produce a further precipitation in the filtrate, which fact would lead to 
 the assumption that a metal of the iron group was present, which, however, 
 would not be the case. 
 
 If the solution contain but one metal, the group-reagents are added 
 successively in small quantities to the same solution, until tJ*e reagent 
 is found which causes a precipitation, which reagent is then added in 
 somewhat larger quantity in order to produce a sufficient amount of 
 the precipitate for further examination. 
 
 Acidifying- the solution. Hydrogen sulphide has to be added 
 to the acidified solution for two reasons, viz. : In a neutral or alkaline 
 solution some metals of the arsenic group (which are to be pre- 
 cipitated) would not be precipitated by hydrogen sulphide ; some of 
 the metals of the iron group (which are not to be precipitated) would 
 be thrown down. 
 
 The best acid to be used in acidifying is dilute hydrochloric acid ; 
 but this acid forms insoluble compounds with a few of the metals of 
 the lead group, causing them to be precipitated. Completely pre- 
 cipitated by hydrochloric acid are mercurous and silver compounds ; 
 partially precipitated are compounds of lead, chloride of lead being 
 somewhat soluble in water. The precipitate formed by hydrochloric 
 acid may be examined by Table III., page 387. 
 
 Hydrochloric acid added to a solution may, in a few cases (other 
 than those just mentioned), cause a precipitate, as, for instance, when 
 added to solutions containing certain compounds of antimony or bis- 
 muth (the precipitated oxychlorides of these metals are soluble in 
 excess of the acid), to metallic oxides or hydroxides which have been 
 dissolved by alkali hydroxides (for instance, hydroxide of zinc dis- 
 solved in potassium or ammonium hydroxide), to solutions of alkali 
 silicates, when silica separates, etc. 
 
ANALYTICAL CHEMISTRY. 
 
 Addition of hydrogen sulphide. This reagent is employed 
 either in the gaseous state (by passing it through the heated solution) 
 or as hydrogen sulphide water. The latter reagent answers in those 
 cases where but one metal is present; if, however, metals of the 
 arsenic and lead groups are to be separated from metals of other 
 groups, the gas must be used. 
 
 FIG. 57 F '- 58 - 
 
 Apparatus for generating hydro- 
 gen sulphide. 
 
 Apparatus for generating hydro- 
 gen sulphide. 
 
 For generating hydrogen sulphide the directions given on page 214 may,, 
 be followed. In place of the apparatus there mentioned for generating the 
 gas, others may be used which have the advantage to the analyst that the 
 supply of gas may be better regulated. Fig. 57 shows such an apparatus for 
 the continuous preparation of the gas. It consists of three glass bulbs ; the 
 upper bulb, prolonged by a tube reaching to the bottom of the lowest one, is 
 ground air-tight into the neck of the second. Ferrous sulphide is introduced 
 into the middle bulb through the tubulure, which is then closed by a perforated 
 cork through which connection is made with the wash-bottle. Acid poured in 
 through the safety tube, runs into the bottom globe and rises to the ferrous 
 sulphide in the second bulb. Upon closing the delivery tube, the pressure of 
 the generated gas forces the liquid from the second bulb through the lower to 
 the upper, thus preventing contact of acid and ferrous sulphide until the gas is 
 used again. 
 
 A convenient and cheaper apparatus is shown in Fig. 58. A glass tube, 
 drawn at its lower end to a small point and partly filled with pieces of ferrous 
 sulphide, is suspended through a cork (not air-tight) in a cylinder containing 
 the acid. The gas supply is regulated by closing or opening the stop-cock, and 
 also by raising or lowering the tube in the acid. 
 
SEPARATION OF METALS INTO DIFFERENT GROUPS. 385 
 
 White. 
 
 Black. 
 
 3^^., 2 
 
 l> 
 
 S ^&1 
 %?** 
 
 - 
 
 C CTQ 
 
 3 
 
 8 S- 
 
 IS 
 
 g-l 
 
 p, 
 
 ^ 
 
 pi 
 
 *.' o 
 
 1 1 
 
 2. as O 
 "2. B & 
 
 .o S' 
 
 *B* 
 
386 ANALYTICAL CHEMISTRY. 
 
 In some cases sulphur is precipitated on the addition of hydrogen 
 sulphide, while a change in color may take place. This change is 
 due to the deoxidizing action of hydrogen sulphide, the hydrogen of 
 this reagent becoming oxidized and converted into water, while sul- 
 phur is liberated. Thus, brown ferric compounds are converted into 
 pale-green ferrous compounds; red solutions of acid chromates 
 become green; and red permanganates or green manganates are 
 decolorized. 
 
 The same deoxidizing action of hydrogen sulphide is the reason 
 why this reagent cannot be employed in a solution containing free 
 nitric acid, which latter compound oxidizes the hydrogen sulphide. 
 
 Separation of the metals of the arsenic from those of the lead 
 group. The precipitate produced by hydrogen sulphide in acid solu- 
 tion contains the metals of the arsenic and lead groups. They are 
 separated by means of ammonium sulphide, which dissolves the sul- 
 phides of the arsenic group, but does not act on those of the lead 
 group. 
 
 Addition of ammonium sulphide. This reagent should never 
 be added to the acid solution, but the solution should be previously 
 supersaturated by ammonium hydroxide, as. otherwise, a precipitate 
 of sulphur may be formed. The yellow ammonium sulphide is 
 almost invariably a polysulphide of ammonium, that is, ammonium 
 sulphide which has combined with one or more atoms of sulphur. If 
 an acid be added to this compound, an ammonium salt is formed, 
 hydrogen sulphide is liberated, and sulphur precipitated : 
 
 (NH 4 ) 2 S 2 + 2HC1 == 2NH 4 C1 -f H 2 S + S. 
 
 Ammonium sulphide precipitates the metals of the iron group as 
 sulphides, with the exception of chromium, which is precipitated as 
 hydroxide ; aluminum is precipitated in the same form of combina- 
 tion. 
 
 Ammonium sulphide (or ammonium hydroxide) causes also the 
 precipitation of metallic salts which have been dissolved in acids, as, 
 for instance, of the phosphates, borates, silicates, or oxalates of the 
 alkaline earths, magnesium, and others. The processes by which the 
 nature of some of these precipitates is to be recognized are found in 
 Table VI., page 389. 
 
 Addition of ammonium carbonate. The reagent used is the 
 commercial salt, dissolved in water, to which some ammonia water 
 
SEPARATION OF THE METALS OF EACH GROUP. 387 
 
 has been added. Heating facilitates complete precipitation of the 
 carbonates of the alkaline earths. 
 
 36. SEPARATION OF THE METALS OF EACH GROUP. 
 TABLE III. Treatment of the precipitate formed by hydrochloric acid. 
 
 The precipitate may contain silver, mercurous, and lead chlorides. Boil 
 the washed precipitate with much water, and filter while hot. 
 
 Filtrate may contain lead 
 chloride. Add dilute 
 sulphuric acid ; a white 
 precipitate of lead sul- 
 phate is produced. 
 
 Residue may consist of mercurous and silver chlor- 
 ides. Digest residue with ammonia water. 
 
 Solution may contain sil- 
 ver. Neutralize with 
 nitric acid, when silver 
 chloride is re-precipi- 
 tated. 
 
 A dark gray residue indi- 
 cates mercury, the white 
 mercurous chloride having 
 been converted into mer- 
 curic-ammonium chloride 
 and mercury. 
 
 Treatment of the precipitate formed by hydrogen sulphide in 
 warm acid solution. The precipitate is collected upon a small 
 filter, well washed with water, and then examined for its solubility 
 in ammonium sulphide. This is done by placing a portion of the 
 washed precipitate in a test-tube, adding ammonium sulphide, and 
 warming gently. It is either wholly insoluble (metals of the lead 
 group), and treated according to Table IV., or fully soluble (metals 
 of the arsenic group), and treated according to Table V., or it is 
 partly soluble and partly insoluble (metals of both groups). In the 
 latter case, the total quantity of the washed precipitate is to be 
 treated with warm ammonium sulphide; upon filtering, an insoluble 
 residue is left, which is treated according to Table IV. ; to the fil- 
 
 QUESTIONS. State the three groups of heavy, and the three groups of light 
 metals. By which two reagents may all heavy metals be precipitated? Why 
 is a solution acidified before the addition of hydrogen sulphide, when testing 
 for metals? Which metals are precipitated by hydrochloric acid? Which two 
 groups of metals are precipitated by hydrogen sulphide in acid solution ? How 
 are the sulphides of the arsenic group separated' from those of the lead group? 
 Why is an acid solution neutralized or supersaturated by ammonium hydroxide, 
 before adding ammonium sulphide? Which two groups of metals are precipi- 
 tated by ammonium sulphide, and in what forms of combination? Name the 
 group-reagent for the alkaline earths. Which metals may be left in solution 
 after hydrogen sulphide, ammonium sulphide, and ammonium carbonate have 
 been added ? 
 
388 
 
 ANALYTICAL CHEMISTRY. 
 
 trate, diluted sulphuric acid is added as long as a precipitate is 
 formed, which precipitate contains the metals of the arsenic group as 
 sulphides, generally with some sulphur from the ammonium sulphide. 
 
 TABLE IV. Treatment of that portion of the hydrogen sulphide 
 precipitate which is insoluble in ammonium sulphide. 
 
 The precipitate may contain the sulphides of lead, copper, mercury, 
 bismuth, and cadmium. Heat the well-washed precipitate with nitric acid in 
 a test-tube, and filter. 
 
 Residue may con- 
 consist of: 
 Mercuric sulph- 
 ide, which is 
 black and easily 
 dissolves in nitro- 
 hydrochloric acid, 
 which solution, 
 after sufficient 
 evaporation, is 
 tested by potas- 
 sium iodide, etc. 
 Lead sulphate is 
 white, pulveru- 
 lent, and soluble 
 in ammonium 
 tartrate. 
 Sulphur is yellow 
 and combustible. 
 
 Filtrate may contain the nitrates of lead, copper, bis- 
 muth, and cadmium. Add to the solution a few drops 
 of dilute sulphuric acid. 
 
 Precipitated is 
 lead, as white 
 lead sulphate 
 which is solu- 
 ble in ammo- 
 nium tartrate 
 with excess of 
 ammonium 
 hydroxide. 
 
 Solution may contain copper, bismuth, 
 and cadmium. Supersaturate with am- 
 monium hydroxide. 
 
 Precipitated is 
 white bis- 
 muth hy- 
 droxide. 
 Dissolve in 
 hydrochloric 
 acid and ap- 
 ply tests for 
 bismuth. 
 
 Solution may contain copper 
 and cadmium 
 Divide solution in two parts, 
 and test for copper by potas- 
 sium ferrocyanide in the 
 acidified solution; a red pre- 
 cipitate indicates copper. 
 To second part add potas- 
 sium cyanide and hydro- 
 gen sulphide. A yellow 
 precipitate indicates cad- 
 mium. 
 
 TABLE V. Treatment of the hydrogen sulphide precipitate which is 
 soluble in ammonium sulphide. 
 
 The precipitate may contain the sulphides of arsenic, antimony, tin, 
 and a few of those metals which are but rarely met with in qualitative analysis, 
 such as gold, platinum, molybdenum, and others, which latter metals, if 
 suspected, may be detected by special tests. 
 
 Boil the washed precipitate with strong hydrochloric acid. 
 
 An insoluble yellow residue consists 
 of arsenous sulphide 
 
 The residue is dissolved by boiling 
 with hydrochloric acid and a little 
 potassium chlorate, and the solu- 
 tion examined by Fleitmann's 
 test. 
 
 A dark-colored residue may indi- 
 cate gold or platinum, for which 
 use special tests. 
 
 The solution may contain the chlorides of 
 antimony and tin. 
 
 The solution is introduced into Marsh's appara- 
 tus when all antimony is gradually evolved 
 as antimoniuretted hydrogen, while tin re 
 mains with the undissolved zinc as a black 
 metallic powder, which may be collected, 
 washed, dissolved in hydrochloric acid, and 
 the solution tested by the special tests for 
 tin. 
 
SEPARATION OF THE METALS OF EACH GROUP. 
 
 389 
 
 I f| mm* 
 
 Ml*isff *ii 
 
 4I%!I1F 
 
 O W ~ OB fTl *-** ? U Jk. f 
 
 2 S 
 
 I fill 1.1= B 
 
 f >irf fil 
 
 
 -ilHiliMl 
 
 :WkNi:i 
 
 Ml. 
 
 
 &i^ ^ g ^p,& 
 
 Is 
 
 1 
 
 tbTJ S ^ B 
 
 8 BtS'^ g 
 
 I-^c|l 
 
 B.1 
 
390 ANALYTICAL CHEMISTRY. . 
 
 The precipitation of sulphur, in the absence of metals of the arsenic group, 
 frequently leads beginners to the assumption that metals of this group are 
 present. The precipitate consisting only of sulphur is white and milky, but 
 flocculent, and more or less colored in the presence of the metals of the 
 arsenic group. 
 
 TABLE VII. Treatment of the precipitate formed by ammonium 
 
 carbonate. 
 
 The precipitate may contain the carbonates of barium, caloium, and 
 Strontium. 1 Dissolve the precipitate in acetic acid, and add potassium dichromate. 
 
 Precipitated is 
 barium, as 
 pale yellow 
 barium 
 
 chromate. 
 
 Solution may contain calcium and strontium Neutralize 
 solution with ammonia water and add potassium chromate. 
 
 Precipitated is stron- 
 tium, as pale yellow 
 strontium chromate. 
 
 Solution may contain calcium Add 
 ammonium oxalate: a white precipi- 
 tate indicates calcium. 
 
 TABLE VIII. Detection of the alkalies and of magnesium. 
 
 The fluid which has been treated with hydrochloric acid, hydrogen sulphide, am- 
 monium hydroxide, sulphide, and carbonate, may contain magnesium and the 
 alkalies. 
 
 Divide solution into two portions. 
 
 To the first portion add sodium phosphate. A white crystalline precipitate indi- 
 cates magnesium. 2 
 
 The second portion is evaporated to dryness, further heated (or ignited) until all 
 ammonium compounds are expelled, and white fumes are no longer given off. The 
 residue is dissolved in water, and sodium cobaltic nitrite added. A yellow precipitate 
 indicates potassium. The residue is also examined by flame test : a yellow color 
 indicating sodium, a red color lithium. 
 
 Ammonium compounds have to be tested for in the original fluid by treating 
 it with calcium hydroxide, when ammonia gas is liberated 
 
 1 If an insufficient quantity of ammonium chloride should have been present, some magnesia 
 may also be contained in this precipitate, and may be redissolved by treating it with ammonium 
 chloride solution. 
 
 2 If an insufficient quantity of ammonium chloride has been produced in the original solution 
 by the addition of hydrochloric acid and ammonium hydroxide, a portion of the magnesia may 
 have been precipitated by the ammonium hydroxide or carbonate. 
 
 QUESTIONS. By what tests can mercurous chloride be distinguished from 
 the chloride of silver or lead ? How can it be proved that a precipitate pro- 
 duced by hydrogen sulphide in an acid solution contains a metal or metals of 
 
DETECTION OF ACIDS. 391 
 
 37. DETECTION OF ACIDS. 
 
 General remarks. There are no general methods (similar to those 
 for the separation of metals) by which all acids can be separated, first 
 into different groups, and afterward into the individual acids. It is, 
 moreover, impossible to render all acids soluble (when in combination 
 with certain metals) without decomposition, as, for instance, in the 
 case of carbonic acid when in combination with calcium ; calcium 
 carbonate is insoluble in water, and when the solution is attempted 
 by means of acids, decomposition takes place with liberation of carbon 
 dioxide. Many other acids suffer decomposition in a similar manner, 
 when attempts are made to render soluble the substances in which 
 they occur. 
 
 It is due to these facts that a complete separation of all acids is 
 not so easily accomplished as the separation of metals. There is, 
 however, for each acid a sufficient number of characteristic tests by 
 which it may be recognized ; moreover, the preliminary examination, 
 as well as the solubility of the substance, and the nature of the metal 
 or metals present, will aid in pointing out the acid or acids which 
 are present. 
 
 If, for instance, a solid substance be completely soluble in water, 
 and if the only metal found were iron, it would be unnecessary to 
 test for carbonic and phosphoric acids and hydrogen sulphide, because 
 the combinations of these with iron are insoluble in water ; there might, 
 however, be present sulphuric, hydrochloric, nitric, and many other 
 acids, which form soluble salts with iron. 
 
 Detection of acids by means of the action of strong sulphuric 
 acid upon the dry substance. The action of sulphuric acid upon 
 a dry powdered substance often furnishes such characteristic indica- 
 
 either the arsenic or lead group? How can mercuric sulphide be separated 
 from the sulphides of copper and bismuth? How does ammonium hydroxide 
 act on a solution containing bismuth and copper ? State the action of strong, 
 hot hydrochloric acid on the sulphides of arsenic and antimony. Suppose a 
 solution to contain salts of iron, aluminum, zinc, and manganese, by what 
 process could these four metals be separated and recognized ? How can barium, 
 calcium, and strontium be recognized when dissolved together ? By what tests 
 is magnesium recognized? State a method of separating potassium when mixed 
 with other metallic compounds. How are ammonium compounds recognized 
 when in solution with other metals ? 
 
392 ANALYTICAL CHEMISTRY. 
 
 tions of the presence or absence of certain acids, that this treatment 
 should never be omitted when a search for acids is made. 
 
 When the substance under examination is liquid, a portion should 
 be evaporated to dryness, and, if a solid residue remains, it should 
 be treated in the same manner as a solid. 
 
 Most non-volatile, organic substances (including most organic 
 acids) color sulphuric acid dark when heated with it. 
 
 Dry inorganic salts when heated with sulphuric acid either are 
 decomposed, with liberation of the acid (which may escape in the 
 gaseous state), or with liberation of volatile products (produced by 
 the decomposition of the acid itself), or no apparent action takes 
 place. See Table IX. 
 
 Detection of acids by means of reagents added to their 
 neutral or acid solution. Whenever a substance is soluble in 
 water, there is little difficulty of finding the acid by means of Table 
 X. ; but if the substance is insoluble in water, and has to be rendered 
 soluble by the action of acids, this table may, in some cases, be of no 
 use, because the acid originally present in the substance may have 
 been liberated, and escaped in a gaseous state (as, for instance, when 
 dissolving insoluble carbonates in acids), or the tests mentioned in 
 the table may refer to neutral solutions, while it is impossible to 
 render the solution neutral without re-precipitating the dissolved 
 acid. If calcium phosphate, for instance, be dissolved by hydro- 
 chloric acid, the magnesium test for phosphoric acid cannot be used, 
 because this test can be applied to a neutral or an alkaline solution 
 only ; in attempting, however, to neutralize the hydrochloric acid 
 solution, calcium phosphate itself is re-precipitated. 
 
 Table XI., showing the solubility or insolubility (in water) of over 
 300 of the most important inorganic salts, oxides, and hydroxides, 
 will greatly aid the student in studying this important feature. It 
 will also guide him in the analysis of inorganic substances, as it gives 
 directions for over 300 (positive or negative) tests for metals, and an 
 equal number for acids. 
 
 To understand this, it must be remembered that any salt (or oxide 
 or hydroxide) which is insoluble in water may be produced and pre- 
 cipitated by mixing two solutions, one containing the metal, the other 
 containing the acid of the insoluble salt to be formed. For instance : 
 Table XI. states that the carbonates of most metals are insoluble in 
 water. To produce, therefore, the carbonate of any of these metals 
 (zinc, for instance) it becomes necessary to add to any solution of 
 
DETECTION OF ACIDS. 393 
 
 zinc (sulphate, chloride, or nitrate of zinc) any soluble carbonate 
 (sodium or potassium carbonate), when the insoluble zinc carbonate 
 is produced. 
 
 Soluble carbonates consequently are reagents for soluble zinc salts, 
 while at the same time soluble zinc salts are reagents for soluble 
 carbonates. 
 
 For similar reasons soluble zinc salts are, according to Table XI., 
 reagents for soluble phosphates, arsenates, arsenites, hydroxides, and 
 sulphides, but not for iodides, chlorides, sulphates, nitrates, or 
 chlorates. 
 
 The insolubility of a compound in water is not an absolute guide 
 for preparing this compound according to the general rule given 
 above for the precipitation of insoluble compounds, there being some 
 exceptions. 
 
 For instance : Cupric hydroxide is insoluble in water ; therefore, 
 by adding solution of cupric sulphate to any soluble hydroxide, the 
 insoluble cupric hydroxide should be precipitated, and is precipitated 
 by the soluble hydroxides of potassium and sodium, but not perma- 
 nently by the soluble hydroxide of ammonium, on account of the 
 formation of the soluble ammonium cupric sulphate. 
 
 There are not many such exceptions, and to mention them in the 
 table would have greatly interfered with its simplicity, for which 
 reason they have been omitted. 
 
 For the same reason some compounds, which are not known at all, 
 have not been specially mentioned. For instance, according to Table 
 XI., aluminum carbonate and chromium carbonate are insoluble salts : 
 actually, however, these compounds can scarcely be formed, the 
 affinity between the weak carbonic acid and the feeble bases not 
 being sufficient to unite them. Also, bismuth nitrate and a lew 
 other salts are reported as soluble, while actually they suffer a 
 decomposition by water. 
 
 Finally, it may be stated that no well-defined line can be drawn 
 between soluble and insoluble substances. There is scarcely any 
 substance which is not slightly soluble in water, and many of the 
 so-called soluble substances are but very sparingly soluble, as, for 
 instance, the hydroxide and sulphate of calcium. 
 
 Table XII. shows the solubility of a large number of compounds 
 more accurately than Table XL ; it may be used for reference. 
 
394 
 
 ANALYTICAL CHEMISTRY. 
 
 i 
 
 
 
 o 
 
 1 
 
 
 =3 
 
 
 H 
 
 abo 
 
 th 
 phuric 
 
 w 
 
 ance is treated 
 g-point of sul 
 
 l 
 
 g 
 
 ta 
 
 M 
 
 -< 3 
 
 | 
 1 
 
 5 
 
 E 
 
 1 
 
 o 
 
 8 
 
 A 
 
 | ^ 
 
 &B 
 
 .2 -a 
 
 ^1 
 i 
 
 52 
 
 
 
 M.l 
 
 d 2^"^^ 
 
 s s a 1 1 
 
 Co o3 S I-M CD 
 
 ffi pq O }zi 
 
 I 
 1 
 
 .^ "S 
 !S * 
 
 |1 
 
 P 
 25 
 
 ^ 
 .!41 1 
 
 ! 
 
 lillllll 
 
 .fa > 
 
 by the above 
 ion of the acid 
 
 are indi 
 he cons 
 
 B. 
 
 o5 o> 
 53 
 
 I* 
 
 o 
 
 X 
 
DETECTION OF ACIDS. 
 
 395 
 
 11: 1 1 1 
 
 s 
 
 llfj I f t 
 
 Chrom 
 
 low. 
 
 i> W O .hj 
 
 2 S B Ig" 
 
 go g* ?5 
 
 ? S & ? 
 
 2. I 
 
 n. M. r" 
 
 5! S- 
 ^ 
 
 B 
 
 o S-*- 1 
 
 c^B 
 
 o 
 
 i! 
 
 0^ 
 
 |> bd 
 
 2 S 
 
 g o" 
 
 S' g 
 
 g pi 
 
 d tJ 
 o o 
 o K - 
 
 02 02 
 
 tT 5' 
 
 P 1 P' 
 
 P P 
 
 O 
 
 2 P- 
 
 P 1 P 1 "sj 
 
 
 s, 
 s- 
 
 1 
 
 o 
 
 3- 
 
 Btflfa. 
 
 & OIE! 
 
 ill! s 
 
 l-^s- & g^?ir *. s.. 
 
 g K go H o i 
 
 ^ * rt fe 
 
 rri 
 ted 
 
 g E. 2. f 
 
 g f - ft I 
 II If 
 
 a I 
 
 hydrox 
 and ca 
 
 si 
 
 ? 
 
 v 
 
 o tr g p 
 flfll 
 
 s: S ^ E a 
 
 S-' g M 
 111 
 
 1 
 
 P 
 
 pi 2. s 
 
 a o ^.^^^ cp 
 8 I lol? & 
 
 s i an 
 1 1 
 
 S & s- g 
 
 U 
 
 
 
 if I II 
 
 I 'I 
 
 & 2 
 
 
 5 1 W 
 & 2, 
 
 o 
 
 I 
 
 o 
 
 I!' I 
 
 ill - 5 
 
 5 & * 
 
 f 
 
 5! 2. 5' 
 
 *& *3 
 
 p^ sr*^ 
 
 ** =1 
 
 o 
 
 
 I P 1 
 
 I 
 
 I 
 
396 
 
 ANALYTICAL CHEMISTRY. 
 
 Table XI. 
 
 Systematically arranged table showing the solubility and 
 insolubility of inorganic salts and oxides in water. 
 
 The dark squares represent insoluble, the white soluble compounds. 
 
 Ca 
 
 
 Potassium 
 
 Sodium 
 
 Ammonium 
 
 M 
 
 Calcium 
 
 Barium 
 
 Strontium 
 
 Magnesium 
 
 Aluminum 
 
 Ferric 
 
 Ferrous 
 
 Zinc 
 
 Chromium 
 
 Nickel 
 
 Cobalt 
 
 Manganese 
 
 Stannic 
 
 Stannous 
 
 Arsenic 
 
 Arsenous 
 
 Antimony 
 
 Gold 
 
 Platinum 
 
 Copper 
 
 Bismuth 
 
 Cadmium 
 
 Mercuric 
 
 Mercurous 
 
 Silver. 
 
 Lead, 
 
 O 
 
DETECTION OF ACIDS. 
 
 397 
 
 
 333: 3: 333333333333333333 
 
 P ^ P 
 
 P P p 3 P 
 
 4 s 
 
 
 P P 3 c* : ^ 
 
 ^ P rt- P P P ^ 
 
 333333333333333333333333 
 
 ALUMINUM. 
 
 AMMONIUM. 
 
 ANTIMONY. 
 
 BARIUM. 
 
 BISMUTH. 
 
 CADMIUM. 
 
 CALCIUM. 
 
 CHROMIUM. 
 
 COBALT. 
 
 COPPKR. 
 
 FERROUS. 
 
 FERRIC. 
 
 LEAD. 
 
 MAGNESIUM. 
 
 MANGANESE. 
 
 MERCUROUS. 
 
 MERCURIC. 
 
 NICKEL. 
 
 POTASSIUM. 
 
 STRONTIUM 
 
 ZINC. 
 
 II 
 8 
 
 II * 
 15 
 II 
 
 S 
 
 W I 
 
 P ? 
 
 W I 
 
 t^ o 
 
 s, 
 
 ~ 
 
 i g- 
 
 CT* . 
 
 " 
 
 5- 
 
 . 
 
 S 
 
 If 
 
398 ANALYTICAL CHEMISTRY. 
 
 Special remarks. Often a solution is presented for analysis instead of a 
 solid substance, in which case some of it is evaporated to dryness. If a dry 
 residue is left, this is tested for acids, as already described. But no residue may 
 remain, and if the solution has a strongly acid reaction, the presence of the 
 volatile acids is indicated, and the student, guided by the odor and change of 
 color upon evaporation, should make tests for the following acids: hydro- 
 chloric, hydrobromic, hydriodic, nitric, sulphurous (hydrocyanic, acetic, 
 formic). 
 
 If a strongly acid, fuming, oily residue is left, sulphuric acid is indicated. 
 
 A strongly acid, pasty, non-fuming residue indicates phosphoric acid. 
 
 If the solution is strongly acid and leaves a solid residue, the substance may 
 be either an acid salt, or a salt held in solution by an acid, such as hydrochloric, 
 nitric, sulphuric, etc., in which case several acids would have to be looked for. 
 The presence of the volatile acids would be indicated by holding wet blue 
 litmus-paper in the vapor as the liquid approached high concentration. If the 
 residue upon evaporation is decidedly alkaline, this maybe due to a salt having 
 an alkaline reaction, or to a hydroxide, or both. The presence of a hydroxide 
 is shown by adding some solution of silver nitrate to the diluted solution, when 
 a dark precipitate of silver oxide is formed at once. In the absence of carbon- 
 ate, the presence of hydroxide is also shown by adding some dry ammonium 
 chloride to the solution and warming, when ammonia is liberated. A solution 
 containing a hydroxide must, of course, be neutralized before applying the tests 
 for acids. The acid usually employed for this is dilute nitric, but if tests are 
 also to be made for the latter acid, another portion of the solution is neutralized 
 with hydrochloric or acetic acid. 
 
 A solution may be colorless, odorless, practically neutral, leave no residue 
 upon evaporation, and still not be plain water. In such a case, the student may 
 suspect hydrogen dioxide. He would have reason to suspect this compound if 
 he proceeded to search for metals before evaporating and found none, but got a 
 precipitate of sulphur when using hydrogen sulphide, showing an oxidizing 
 action. 
 
 The presence of some metals interferes with certain tests for acids, and these 
 should be removed. After determining the kind of metal or metals in a sub- 
 stance or a mixture, and it is seen that there will be interference with the tests 
 for acids, boil some of the substance with a slight excess of sodium or potassium 
 carbonate for some time and filter. Non-alkali metals, except arsenic and 
 antimony, remain behind, while the acids pass into the filtrate as alkali salts 
 (with few exceptions). The filtrate is then exactly neutralized with nitric acid 
 and boiled to expel all carbonic acid, and used for the various tests for acids. 
 Arsenic and antimony may be removed by passing hydrogen sulphide into the 
 warm acidified solution and filtering. 
 
 Substances insoluble in water. When a single substance, or that part of a 
 mixture which is insoluble in water, is treated with hydrochloric acid in order 
 to prepare a solution for the analysis of metals, something can be learned as to 
 the nature of the acids in combination. Carbonates, sulphites, phosphates, 
 arsenates, and arsenites behave the same as when treated with concentrated 
 sulphuric acid in Table IX. Sulphides give the odor of hydrogen sulphide. If 
 chlorine gas is given oif, the presence of a higher oxide, like MnO 2 , PbO 2 , BaO 2 , 
 etc., or a chromate is indicated. If effervescence takes place and an inflamma- 
 
DETECTION OF ACIDS. 399 
 
 ble gas is given off, the presence of a free metal is indicated. If the substance 
 simply dissolves and no acids are subsequently found, the presence of an oxide 
 or hydroxide is indicated, which can also be judged from a knowledge of the 
 known compounds of the metals present. 
 
 The tests distinguishing between an arsenite and an arsenate (see Chapter on 
 Arsenic) cannot be applied when the substance is insoluble in water (except the 
 inolybdate test, which can be used in an acid solution), but the treatment with 
 hydrogen sulphide can be used to differentiate, because an arsenite gives a pre- 
 cipitate instantly even in cold solution, while an arsenate precipitates only after 
 a long time. 
 
 If bismuth is present, remove it before testing for the acids by boiling with 
 sodium carbonate, filtering, etc., as described above. 
 
 Substances insoluble in water and hydrochloric acid are next treated with 
 nitric acid. Ordinarily very few such substances are presented. If brown 
 vapors are evolved and sulphur separates, a sulphide is indicated, which the 
 appearance of the substance will also suggest. If brown vapors alone are 
 evolved, a free metal is indicated. 
 
 If the preliminary tests for metals show the presence of mercury, and the 
 substance dissolves slowly on boiling with nitric acid, it is one of the halogen 
 salts. The mercury should be removed by boiling the substance with an excess 
 of caustic alkali, filtering, neutralizing the filtrate with nitric acid, and testing 
 it for chloride, bromide, or iodide. 
 
 Before examining for metals, nitric acid solutions must be evaporated to dry- 
 ness to expel excess of the acid. The residue is dissolved in water. 
 
 A few substances require nitro-hydrochloric acid for solution. The one most 
 likely to occur ordinarily is mercuric sulphide, which is indicated by the pres- 
 ence of mercury, its black or vermilion color, and volatility on heating. 
 
 Of substances insoluble in all acids, the sulphates of barium, strontium, and 
 lead are the most likely to be presented ordinarily. The treatment of these by 
 fusion with sodium carbonate has already been mentioned. The presence of 
 silver (as shown by the preliminary tests for metals) would indicate a chloride, 
 bromide, iodide, or cyanide of this metal. The metal should be removed by 
 boiling with caustic alkali and the filtrate tested. Silver iodide does not yield 
 to this treatment, but its color and insolubility in strong ammonia is sufficient 
 evidence of iodide. Silver cyanide with hydrochloric acid forms silver chloride 
 and hydrocyanic acid, which is in solution and recognized by its odor. 
 
 The insoluble halogen salts of silver, lead, and mercury, also mercuric chloride 
 and bromide, scarcely react when treated with concentrated sulphuric acid 
 (Table IX). 
 
 Most of the points in the discussion above are shown in more convenient 
 form in the following Tables, XIII and XIV, which are more detailed than Table 
 IX, and will perhaps be of greater help to the student. Table XIV deals with 
 difficultly soluble or insoluble substances, which may be subnitrate ; subchlor- 
 ide; chloride (Pb, Hg(ous),Ag) ; bromide (Pb, Hg(ous),Ag) ; iodide; sulphate 
 (Ca, Sr, Ba, Pb, Hg(ous) ; sulphite (except of alkalies) ; sulphide (except of 
 alkalies and alkaline earths) ; carbonate, borate, phosphate, arsenate, arsenite 
 (except of alkalies in each case); chromate (high color) ; fluoride; cyanide; 
 oxide or hydroxide (except of alkali and alkaline earth metals) ; and a few 
 others. 
 
 In the case of mixtures,, the tables may be used to determine as far as 
 
400 
 
 ANALYTICAL CHEMISTRY. 
 
 possible the nature of the acids, after which such other acids must be 
 looked for as are not clearly indicated by the tables, but may be suggested 
 as probably present by the preliminary examinations and the nature of the 
 metals found. 
 
 TABLE XIII. Substances soluble in water. 
 
 A. When the substance is 
 already in solution, test with 
 litmus paper and evaporate 
 20 c.c. to dryness : 
 
 B. When the substance is ir 
 to litmus paper and 
 
 I. Warm a little with di- 
 lute sulphuric acid : 
 
 \, the dry state, test its reaction 
 
 II. If I gives no indication, 
 heat moderately a small quan- 
 
 
 
 tny with concentrated sul- 
 phuric acid. 
 
 strongly acid and 
 
 
 
 HC1, HBr, HI, HNO 3 , 
 HCN* or H 2 SO 3 . Note 
 odor of vapors and test for 
 the acid indicated by odor, 
 etc. 
 
 a. Copious effervescence, 
 no color or odor test for 
 carbonate (strongly alka- 
 line) or bicarbonate (weakly 
 alkaline). 
 
 a. White fumes test for 
 HC1, HF or HN0 3 . Note 
 odor. The salt is neutral 
 or slightly acid. 
 
 
 
 
 
 
 L (-1 -i j f 
 
 6. A strongly acid, fum- 
 ing residue test for free 
 H 2 S0 4 . 
 
 b. Moderate efferves- 
 cence. TIO color, but with an 
 1. Odor of SO 2 test for 
 
 1. Brownish test for 
 bromide. 
 2. V i o 1 e t test for 
 iodide. 
 
 c. A strongly acid, soft, 
 non-fuminq mass test for 
 free H 3 PO 4 . 
 
 sulphite (alkaline). 
 Odor of SO 2 -j- precipi- 
 tate of sulphur test for 
 thiosulphate (neutral). 
 
 3. Greenish -yellow test 
 for chlorate. 
 (Bromates and iodates, 
 like chlorates, also give 
 
 d. A strongly acid, com- 
 bustible mass test for free 
 
 A. \JQOT ot i 2 o test lor 
 a sulphide (alkaline). 
 3. Odor of HCN* test 
 
 colored fumes and defla- 
 grate on charcoal.) 
 
 H 3 PO 2 : a neutral combus- 
 tible mass, indicates a salt 
 of H 3 PO 2 (hypophosphor- 
 ous acid). 
 
 for cyanide (alkaline). 
 4. Odor of HCN and a 
 cryst. deposit, often bluish 
 test for ferro- or ferri- 
 cyanide. 
 
 c. Chromates and dichro- 
 mates are recognized by 
 their color and give green 
 solutions in hot concen- 
 
 e. Strongly acid, leaving 
 
 5. Odor of HCN -f ppt. 
 of sulphur test for a sul- 
 
 trated H 2 SO 4 . 
 
 a solid residue it may be 
 an acid salt or a salt held 
 in solution by an acid, as 
 
 phocyanate. 
 
 d. No change takes place. 
 It may be sulphate (neu- 
 
 HC1, HN0 3 , H 2 S0 4 , etc. 
 Refer to B. 
 
 c. Colored fumes. 
 
 tral or slightly acid), phos- 
 phate (alkaline), arsenate 
 or arsenite (alkaline), bo- 
 
 f. A slightly acid white 
 residue which melts at high 
 heat test for free boric 
 acid. 
 
 trite (alkaline). 
 2. Greenish, with odor 
 of Cl test for hypochlorite 
 (alkaline). 
 
 rate (alkaline), boric acid, 
 or a free base. All these 
 acids would be indicated in 
 the preliminary examina- 
 tions and the analysis for 
 the metals. If the sub- 
 
 g. A weakly acid, neu- 
 tral, or alkaline residue 
 it may be a salt or a free 
 base, or both. Refer to B. 
 
 * Caution. Take care in 
 smelling vapors of HCN, 
 as they are poisonous. 
 
 stance is alkaline and gives 
 a precipitate (dark) with 
 solution of AgNO 3 , a free 
 base is present. Test also 
 on NH 4 C1. 
 
DETECTION OF 'ACIDS. 401 
 
 TABLE XIV. Substances insoluble or very difficultly soluble in water. 
 
 A. When the substance is 
 soluble in cold or hot, dilute 
 or strong hydrochloric acid: 
 
 Note. It Pb, Hg(ous), 
 Ag, are indicated by the 
 preliminary examination, 
 omit treatment with HC1, 
 but use HNO 3 . 
 
 . Note whether the 
 effects are the same as in 
 Table XIII, B, 7, a and b. 
 Make tests for the acids 
 indicated there. 
 
 b. If chlorine is given 
 off, a peroxide is present, 
 as MnO 2 , PbO ? , BaO 2 , etc., 
 or chromate (high color) . 
 
 c. If no change takes 
 place except solution 
 
 1. Subnitrate (or sub- 
 chloride) is suspected if Bi 
 or Sb is found as metal. 
 Boil substance in slight ex- 
 cess Na 2 CO s , filter, neutral- 
 ize filtrate and test for the 
 acid. 
 
 2. Test for phosphate by 
 molybdate solution. 
 
 3. Test for borate by al- 
 cohol flame. 
 
 4. Arsenate and arsenite 
 are detected in analysis for 
 metals: make further tests 
 to distinguish the two. 
 
 5. If no acid is found 
 and the substance is alka- 
 line, it is CaO or Ca(OH) 2 ; 
 if neutral, it is an oxide, as 
 ZnO, MgO, PbO, etc., or 
 their hydroxides. 
 
 d. Effervescence and in- 
 flammable gas indicate a 
 free metal, as Zn, Fe, Sn, 
 etc. 
 
 7>. When the substance is 
 insoluble or difficultly soluble 
 in hydrochloric, but soluble in 
 cold or hot, dilute or strong 
 nitric acid : 
 
 a. Brown vapors and a 
 precipitate of sulphur indi- 
 cate a sulphide. 
 
 6. Brown vapors alone 
 indicate free metal, as Ag, 
 Pb, Hg, Bi, Cu, etc. 
 
 c. If the substance is 
 white, volatile on foil by 
 heat, turns black with 
 XII 4 OH, and soluble in 
 HNO 3 on long boiling, it 
 is likely HgCl or HgBr. 
 Test for the acid by boiling 
 some with dilute NaOH, 
 filter, acidify filtrate with 
 HNO S and add AgNO 3 . 
 
 (Likewise for Hgl and 
 HgI 2 , which are yellow and 
 red respectively.) 
 
 d. If no change except 
 solution, the substance is 
 likely an oxide or hydrox- 
 ide. This will also be indi- 
 cated by the metal present 
 and the appearance of the 
 compound. 
 
 C. When the substance is 
 insoluble in either hydro- 
 chloric or nitric, but is solu- 
 ble in a mixture of the acids : 
 
 It may be 
 
 a. Mercuric sulphide, 
 HgS, black or red, and 
 volatile on foil by heat. 
 
 b. Gold. 
 
 c. Mercurous chloride, 
 HgCl. (Slowly soluble in 
 HNO 3 . See E, c.} 
 
 d. A few sulphides and 
 oxides. 
 
 D. When the substance is 
 insoluble in all acids : 
 
 It may be 
 
 a. Sulphate of Ba, Sr, 
 Pb. These must be fused 
 with Na 2 CO 3 . 
 
 6. Lead chloride, PbCl 2 
 (PbBr 2 , PbI 2 ) (if not re- 
 moved by much hot water.) 
 
 c. Chloride, bromide, 
 iodide, or cyanide of silver, 
 AgCl, AgBr, Agl, AgCN. 
 Test solubility in XH 4 OH 
 and Na 2 S 2 O 3 . 
 
 (AgCN with HC1 forms 
 insoluble AgCl and leaves 
 HCN in solution recognized 
 by odor.) 
 
 d. Silicic acid and most 
 silicates, native A1 2 O H , 
 Cr 2 O 3 , SnO 2 , CaF 2 . 
 
402 ANALYTICAL CHEMISTRY. 
 
 38. METHODS FOR QUANTITATIVE DETERMINATIONS. 
 
 General remarks. Quantitative determination of the different 
 elements or groups of elements may be accomplished by various 
 methods, which differ generally with the nature of the substance to 
 be examined. But even one and the same substance may often be 
 analyzed quantitatively by entirely different methods, of which the 
 two principal ones are the gravimetric and volumetric methods. 
 
 In the gravimetric method, the quantities of the constituents of a 
 substance are determined by separating and weighing them either as 
 such, or in the form of some compound the exact composition of 
 which is known. For instance : From cupric sulphate, the copper 
 may be precipitated as such by electrolysis and weighed as metallic 
 copper, or it may be precipitated by sodium hydroxide as cupric oxide, 
 CuO, and weighed as such. Knowing that every 79.6 parts by weight 
 of cupric oxide contain of oxygen 16 parts and of copper 63.6 parts, 
 the weight of copper contained in the cupric oxide found may be 
 readily calculated. 
 
 In the volumetric method, the determination is accomplished by add- 
 ing to a weighed quantity of the substance to be examined, a solution 
 of a reagent of a known strength until the reaction is just completed, 
 no excess being allowed. For instance : We know that every 80.12 
 parts by weight of sodium hydroxide precipitate 79.6 parts by weight 
 of cupric oxide, containing 63.6 parts by weight of copper. There- 
 fore, if we add a solution of sodium hydroxide of known strength to a 
 weighed portion of cupric sulphate until all the copper is precipitated, 
 
 QUESTIONS. Why is sulphuric acid added to a solid substance when it is to 
 be examined for acids ? Mention some acids which cause the liberation of 
 colorless, and some which cause the liberation of colored gases when the salts 
 of these acids are heated with sulphuric acid. Mention an acid which is pre- 
 cipitated by barium chloride in acid solution, and some acids which are pre- 
 cipitated by the same reagent in neutral solution. Which acids may be pre- 
 cipitated by silver nitrate from neutral solutions, and which from either neutral 
 or acid solutions? Mention some acids which form soluble salts only. Mention 
 three soluble, and three insoluble carbonates, phosphates, arsenates, sulphates, 
 and sulphides respectively. Which oxides or hydroxides are soluble, and 
 which are insoluble in water? Mention some metals the solutions of which 
 are precipitated by soluble chlorides, iodides, and sulphides. State a general 
 rule according to which most insoluble salts may be formed from two other 
 compounds. Why is it sometimes impossible to render a substance soluble in 
 order to test for the acid in the solution obtained ? 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 403 
 
 we may calculate from the volume of soda solution used the weight of 
 sodium hydroxide, and from this the weight of copper which has been 
 precipitated. The operation of volumetric analysis is termed titration. 
 
 Gravimetric methods. While the quantitative determinations by 
 these methods differ widely in some cases, there are a number of oper- 
 ations so often and so generally employed that a few remarks may be 
 of advantage to the beginner. A small quantity (generally from 0.5 
 to 1 gramme) of the substance to be analyzed is very exactly weighed 
 on a delicate balance, transferred to a beaker, and dissolved in a suit- 
 able agent (\vater or acid). From this solution the constituent to be 
 
 FIG. 59. 
 
 Drying-oven. 
 
 determined is precipitated completely, which is ascertained by allow- 
 ing the precipitate to subside and adding to the clear liquid a few 
 drops more of the agent used for precipitation. The, precipitate is 
 next collected upon a small filter of good filter paper containing as 
 little of inorganic constituents (ash) as possible ; the particles of pre- 
 cipitate which may adhere to the beaker are carefully washed off by 
 means of a camelVhair brush. The precipitate is well washed (gen- 
 erally with pure water) until free from adhering solution, and dried 
 by placing funnel and contents in a drying- oven, Fig. 59, in which a 
 constant temperature of about 100 C. (212 F.) is maintained. The 
 dried filter is then taken from the funnel and its contents are trans- 
 ferred to a platinum (or porcelain) crucible, which has been previously 
 
404 
 
 ANALYTICAL CHEMISTRY. 
 
 weighed and stands on a piece of glazed, colored paper in order to 
 collect any particle of the dried precipitate which may happen to fall 
 beside the crucible. The filter, from which the precipitate has been 
 removed as completely as possible, by slightly rubbing it, is now 
 folded, placed upon the lid of the crucible, which rests on a triangle 
 over a gas burner, and completely incinerated. The remaining filter- 
 ash, with particles of the precipitate mixed with it, is transferred to 
 the crucible, which is now placed over the burner and heated until 
 all water (or possibly other substances) is completely expelled. After 
 cooling, the crucible is weighed, the weight of the empty crucible and 
 that of the filter-ash (the latter having been previously determined 
 by burning a few filters of the same kind) deducted, and thus the 
 quantity of the precipitate determined. 
 
 As platinum crucibles and many precipitates, after ignition, absorb 
 moisture from the air, it is well to allow the heated crucible to cool 
 in a desiccator. This is a closed vessel in which the contained air is 
 kept dry by means of concentrated sulphuric acid. Fig. 60 shows a 
 convenient form of desiccator. 
 
 The empty crucibles should be weighed under the same conditions 
 i. e., after having been heated and cooled in a desiccator. 
 
 FIG. 60. 
 
 FIG. 61. 
 
 Desiccator. 
 
 Watch-glasses for weighing filters. 
 
 Some precipitates (as, for instance, potassium platinic chloride), 
 cannot be ignited without suffering partial or complete decomposition. 
 It is for this reason that some precipitates are collected upon filters 
 which have been previously dried at 100 C. (212 F.) and weighed 
 carefully. The precipitate is then collected upon the weighed filter, 
 well washed, dried at 100 C. (212 F.) and weighed. 
 
 The weighing of dried filters is best accomplished by placing them 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 405 
 
 between two watch-glasses held together by means of a brass or nickel 
 clamp, as shown in Fig. 61. 
 
 The above-described methods may be employed for the determina- 
 tion of those substances which can be precipitated from their solu- 
 tions in the form of some stable compound. Aluminum, zinc, iron, 
 bismuth, copper, etc., may, for instance, be precipitated as hydroxides 
 and weighed as oxides, into which the precipitated compound is con- 
 verted by ignition. Sulphuric acid may be precipitated and weighed 
 as barium sulphate, phosphoric acid may be precipitated by magnesia 
 mixture and weighed as magnesium pyrophosphate, etc. Some sub- 
 stances, like nitric acid, chloric acid, etc., cannot be precipitated from 
 their solutions, for which reason other methods have to be employed 
 
 for their determination. 
 
 FIG. 63. 
 
 FIG. 62. 
 
 10 CO 
 
 Liter flask. 
 
 Pipettes. 
 
406 ANALYTICAL CHEMISTRY. 
 
 Volumetric methods. The great advantage of volumetric over 
 gravimetric analysis consists chiefly in the rapidity with which these 
 determinations are performed. Unfortunately, volumetric methods 
 cannot be employed to advantage for the estimation of all substances. 
 
 The special apparatus required for volumetric analysis consists of 
 a few flasks, some pipettes, burettes, and a burette-holder. The flasks 
 should have a mark on the neck, indicating a capacity of 100, 250, 
 500, and 1000 c.c. respectively. (See Fig. 62.) 
 
 FIG. 64. FIG. 65. 
 
 Mohr'8 burette and clamp. Mohr , g burette and hoMer 
 
 Of pipettes (Fig. 63) are mostly used those having a capacity of 
 5, 10, 25, and 50 cubic centimeters. 
 
 Of burettes many different forms are used; in most cases Mohr's 
 burette (Pigs. 64 and 65) answers all requirements, but its applica- 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 407 
 
 tion is excluded whenever the test solution is chemically affected by 
 rubber, as in the case of solutions of silver, permanganate, and a few 
 other substances. For such solutions p IQ 66 
 
 Mohr*s burette with glass stopcock, or 
 Gay Lussac's burette (Fig. 66) is generally 
 used. 
 
 Standard solutions are solutions con- 
 taining a known and definite quantity of 
 some reagent employed in volumetric 
 analysis. A standard solution may be 
 normal, or it may be an empirical solu- 
 tion. In the latter case it contains in 
 a liter some arbitrarily chosen weight of 
 reagent. As an instance may be men- 
 tioned Fehling's solution, used for the 
 determination of sugar. This solution 
 is so adjusted that 1 c.c. decomposes or 
 indicates 0.005 gm. of grape-sugar. 
 
 Normal solutions. The solutions gen- 
 erally used in volumetric analysis are 
 known as normal solutions, and are 
 chemically equivalent to each other be- 
 cause of the standard adopted in their 
 preparation. This standard is one gm. 
 of hydrogen, or the weight of one atom 
 of hydrogen expressed in grammes, or 
 the chemical equivalent of one gm, of 
 hydrogen, contained in one liter of solu- 
 tion. For the sake of convenience the terms 
 gram-atom and gram-molecule are often 
 used in connection with volumetric work, Gay Lussac's burette. 
 and refer, of course, to the atomic or molecular weight of the substance 
 considered, expressed in grammes. 
 
 A consideration of the application of these principles to practical work is 
 volumetric analysis may assist the student in understanding them fully. 
 
 Thus, a normal add solution may be defined as one containing in a liter 
 as much acid as contains one gram-atom of replaceable hydrogen. In such 
 acids as HC1, HBr, HN0 3 , a liter solution containing the gram-molecule would 
 be normal, since each solution would contain one gram-atom of replaceable 
 hydrogen. In order to make a normal solution of such acids as H 2 SO 4 , H 2 C 2 O 4 , 
 
408 ANALYTICAL CHEMISTRY. 
 
 one-half the gram-molecule must be taken, since this quantity contains one 
 atom of hydrogen, and so on. 
 
 A normal alkali solution may be defined as one containing that quantity of 
 alkali in a liter which is chemically equivalent to i. e., neutralizes^ one gram- 
 atom of acid hydrogen. For such compounds as KOH, NaOH, NH 4 OH, the 
 whole gram-molecule must be taken to make a liter of normal solution. In 
 case of Ba(OH) 2 or Ca(OH) 2 , one half the gram-molecule is taken. 
 
 It will easily be seen that all the acid solutions made as described are of 
 equivalent strength and are exactly equivalent to the solutions of alkali i. e., one 
 liter normal HC1 will exactly neutralize one liter of normal KOH, or NaOH, 
 or Ba(OH) 2 . That this is so will appear at once on writing the equations 
 which express the reactions between these alkalies and acids, thus: 
 
 HC1 + KOH = KC1 + H 2 O. 
 36.18 55.74 
 
 2HC1 + Ba(OH) 2 = BaCl 2 + 2H 2 O. 
 
 36.18 
 
 L 
 
 KOH + H 2 SO * = KO*- + H 2 O. 
 55,4 ^ 
 
 The above equations show that 36.18 gramme of HC1 are equivalent to 
 55.74 gramme of KOH, but these are the quantities taken for a liter of normal 
 solution respectively, hence these normal solutions must be equivalent. Simi- 
 larly for HC1 and Ba(OH) 2 , for KOH and H 2 SO 4 , etc. 
 
 Conversely, if a solution of unknown strength be compared by titration with 
 a second solution known to be normal, and then be properly diluted so that the 
 two are equivalent, volume for volume, the first solution will also be normal, 
 and from the definition of normal solutions the quantity of reagent in a liter 
 of the solution becomes at once known. For example, if a solution of sul- 
 phuric acid be made equivalent to a normal solution of caustic alkali it will 
 then contain 48.675 grammes of absolute sulphuric acid per liter. It is thus 
 an easy matter to prepare normal solutions, although it may be impossible to 
 weigh exactly the amount of reagent necessary for a liter of such solutions. 
 All that is required is one normal solution as a starting-point. 
 
 Sodium carbonate, Na 2 C0 3 , may be used as an alkali, just as KOH or NaOH, 
 because it neutralizes acids in precisely the same manner, for the carbonic acid 
 has no effect, being volatile and escaping into the air. The decomposition 
 taking place thus: 
 
 Na 2 CO 3 + 2HC1 = 2NaCl + H 2 O + CO 2 , 
 
 shows that one molecule of sodium carbonate neutralizes two molecules of 
 hydrochloric acid, consequently one-half gram-molecule of sodium carbonate 
 must be taken to make a liter of normal solution. A similar consideration 
 will show that of sodium bicarbonate the whole gram-molecule should be 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 409 
 
 taken for a liter of normal solution, because this salt contains but one atom of 
 aodium in the molecule. 
 
 A normal salt solution may be defined as one containing in a liter the quan- 
 tity of salt resulting from the neutralization, or replacement of the hydrogen 
 
 in a normal acid solution by metal. Thus, ^^^ Na (j^ AgNO 3 , BaC1 2 ? e x- 
 
 L 2 
 
 pressed in grammes, would be contained in a liter of normal solution of the 
 respective salts. 
 
 Often normal solutions are too strong, and are diluted ten or a hundred 
 times. They are then called deci- or centi-normal solutions, respectively. 
 
 Normal solutions are generally designated by *, deci-normal solu- 
 tions by ~ y centi-riorraal solutions by ^ ; solutions containing twice 
 the amount are designated as double normal, | ; half the amount 
 semi-normal, *. 
 
 Different methods of volumetric determination. Of these we 
 have at least three, which may be called the direct, the indirect, and 
 the method of rest or residue. 
 
 The direct methods are used in all cases in which the quantities of 
 volumetric solutions can be added until the reaction is complete : for 
 instance, until an alkaline substance has been neutralized by an acid, 
 or a ferrous salt has been converted into a ferric salt by potassium 
 permanganate, etc. 
 
 In the indirect methods one substance, which cannot well be deter- 
 mined volumetrically, is made to act upon a second substance, with 
 the result that, by this action, an equivalent quantity of a substance 
 Is generated or liberated, which may be titrated. For instance : Per- 
 oxides, chromic and chloric acids when boiled with strong hydro- 
 chloric acid, liberate chlorine, which is not determined directly, but 
 is caused to act upon potassium iodide, from which it liberates the 
 iodine, which may be titrated with sodium thiosulphate. 
 
 The methods of residue are based upon the fact that while it is im- 
 possible or extremely difficult to obtain complete decomposition 
 between certain substances and reagents, when equivalent quantities 
 are added to one another, such a complete decomposition is accom- 
 plished by adding an excess of the reagent, which excess is afterward 
 determined by a second volumetric solution. For instance: Car- 
 bonate of calcium, magnesium, zinc, etc., cannot well be determined 
 directly, for which reason an excess of normal acid is used for their 
 decomposition, this excess being titrated afterward by means of an 
 alkali. 
 
 Indicators. In all cases of volumetric determination it is of the 
 greatest importance to observe accurately the completion of the reac- 
 
41 () ANALYTICAL CHEMISTRY. 
 
 tion. In some cases the final point is indicated by a change in color, 
 as, for instance, in the case of potassium permanganate, which changes 
 from a red to a colorless solution, or chromic acid, which changes 
 from orange to green under the influence of deoxidizing agents. In 
 other cases the determination is indicated by the formation or cessa- 
 tion of a precipitate, and in yet others the final point could not be 
 noticed with precision unless rendered visible by a third substance 
 added for that purpose. 
 
 Such substances are termed indicators. Litmus, phenolphthalein, 
 methyl-orange, etc., are used as indicators in acidimetry and alka- 
 limetry. Starch paste is an indicator for iodine, potassium chromate 
 for silver, etc. Of indicators, a few drops are in most cases sufficient 
 for the purpose. (See colored Plate VII.) 
 
 Litmus solution. This is made by exhausting coarsely powdered litmus with 
 boiling alcohol, which removes a red coloring matter, erythrolitmin. The 
 residue is treated with about an equal weight of cold water, so as to dissolve 
 the excess of alkali present in litmus. The remaining mass is extracted with 
 about five times its weight of boiling water, and filtered. The solution should 
 be kept in wide-mouthed bottles, stoppered with loose plugs of cotton to ex- 
 clude dust but to admit air. Blue and red litmus paper is made by impregnat- 
 ing strips of unsized white paper with the blue solution obtained by the above 
 process, or with this solution after just enough hydrochloric acid has been 
 added to impart to it a distinct red tint. 
 
 Phenolphthalein solution. 1 gramme of phenolphthalein is dissolved in 50 c.c. 
 of alcohol and water added to make 100 c.c. The colorless solution is colored 
 deep purplish-red by alkali hydrates or carbonates, but not by bicarbonates ; 
 acids render the red solution colorless. The solution is not suitable as an indi- 
 cator for ammonia. Carbonates must be titrated in boiling solution to drive 
 off carbon dioxide. 
 
 Methyl-orange solution. 1 gramme of methyl-orange (also known as helian- 
 thin, tropseolin D, or Poirier's orange 3 P), the sodium or ammonium salt of 
 dimethylamido-azobenzol-sulphonic acid (CH 3 ) 2 N.C 6 H 4 .N.NC 6 H 4 .SO 3 H, is dis- 
 solved in 1000 c.c. of water. To the solution is carefully added, with constant 
 stirring, jj sulphuric acid, in drops, until the liquid turns red and just ceases 
 to be transparent; it is then filtered. The solution is yellow when in contact 
 with alkaline hydrates, carbonates, or .bicarbonates. Carbonic acid does not 
 affect it, but mineral acids change its color to crimson. It should be used in 
 cold solutions. 
 
 Hcematoxylin solution. 0.2 gramme of hsematoxylin ( ( a vegetable coloring- 
 matter derived from hsematoxylon) is dissolved in 100 c.c. of alcohol. The alka- 
 line solution has a purple color which is changed to yellow or orange by acids. 
 
 Rosolic acid solution. 1 gramme of commercial rosolic acid (chiefly C 20 H ]6 O 3 ) 
 is dissolved in 10 c.c. of alcohol, and water added to make 100 c.c. The solu- 
 tion turns violet red with alkalies, yellow with acids. 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 411 
 
 Other indicators used at times in acidimetry are solutions of bra- 
 zil-wood, cochineal, methyl-violet, alizarin, iodeosin, Congo red, turmeric, 
 etc. 
 
 Ionic explanation of the action of indicators. The substances used to indicate 
 the neutralization point are themselves very weak acids or bases, capable of 
 forming salts with the bases or acids that are brought together in solution for 
 the purpose of neutralization. The undissociated molecules of the indicator 
 have a different color from its ions, and it must have feeble dissociating power 
 in the uncombined state. The latter is a characteristic of feeble acids in gen- 
 eral. The salts of the indicators are easily dissociated into ions. Substances 
 that are strong acids or bases cannot be used as indicators, because they disso- 
 ciate in the free state, and thus give no different color when they are neutral- 
 ized. The indicators that dissociate least in the free state are the most sensitive 
 in color changes when combined with traces of acids or bases. The neutral 
 point in neutralization experiments is really overstepped by the amount 
 of acid or alkali required to produce change of color with the indicator, 
 but in the case of sensitive indicators this amount is a mere trace and is 
 negligible. 
 
 Litmus is an acid with slight dissociating power, which in pure water gives 
 a violet color. Addition of acids represses the slight dissociation and the color 
 changes to red, which is the color of the undissociated molecules of litmus. 
 Alkalies form salts with litmus, which dissociate easily, the negative ions show- 
 ing a blue color. 
 
 Phenolphthalein is an acid of less dissociating power than litmus. In 
 pure water or acids it is colorless, in alkaline solutions it is red, which is 
 the color of the negative ions of the dissociated molecules of the salt of the 
 indicator. 
 
 Methyl-orange is an acid of greater dissociating power than litmus. It dis- 
 sociates slightly when greatly diluted in water, giving a yellow color, which is 
 the color of the negative ions. With less water the color is orange, which is 
 the resultant of the yellow color of the ions and the red color of the un- 
 dissociated molecules. In acid solutions the dissociation of the indi- 
 cator is repressed, and the color is pure red. In alkaline solutions, salts 
 of the indicator are formed which dissociate freely and give an intense 
 yellow color. 
 
 Because different indicators, as well as different acids and bases, show great 
 differences in their degrees of dissociation, marked variations in the sensitive- 
 ness of indicators to acids and bases are observed. Hence, indicators must be 
 chosen to suit the particular case of neutralization in hand for accurate work. 
 For example, if an active acid is titrated with ammonia and phenolphthalein 
 as indicator, color is not produced sharply at the neutral point, because am- 
 monium hydroxide is so little dissociated that it requires an appreciable excess 
 beyond the neutral point to produce the dissociated salt with the indicator. In 
 this case litmus or methyl-orange is suitable to use. 
 
 Titration. This term is used for the process of adding the 
 volumetric solution from the burette to the solution of the 
 
412 ANALYTICAL CHEMISTRY. 
 
 weighed substance until the reaction is completed. We also 
 speak of the standard or titer of a volumetric test-solution, when 
 we refer to its strength per volume (per liter or per cubic centi- 
 meter). 
 
 Of the principal processes of titration, or of volumetric meth- 
 ods used, may be mentioned those based upon neutralization (acid- 
 imetrv and alkalimetry), oxidation and reduction (permanganates 
 and chromates as oxidizing, oxalic acid and ferrous salts as 
 reducing agents) precipitation (silver nitrate by sodium chloride), 
 and finally those which depend on the action of iodine and thio- 
 sulphate (iodimetry). 
 
 The substance to be titrated should be diluted with pure water to a 
 volume of about 75 c.c. The relationship between any two volumetric 
 solutions, for example, acid and alkali, should also be determined in 
 the same volume. Any convenient quantity, as 10 or 20 c.c., of one 
 solution is drawn from a burette into a beaker and diluted to about 
 75 c.c. before titrating with the other solution. If the comparison is 
 made in a much smaller or much greater volume, a somewhat different 
 relationship will be found. In general, the titer of a volumetric solu- 
 tion should be determined in a volume corresponding approximately to 
 that in which the titration of a substance is to be carried out. This 
 is usually the volume stated above, but sometimes, for certain reasons, 
 it may be much greater. 
 
 Acidimetry and alkalimetry. Preparing the volumetric test- 
 solutions is often more difficult than to make a volumetric deter- 
 mination. Whenever the reagents employed can be obtained in a 
 chemically pure condition it is an easy task to prepare the solution, 
 because a definite weight of the reagent is dissolved in a definite 
 volume of water. In many instances, however, the reagent cannot 
 be obtained absolutely pure, and in such cases a solution is made and 
 its standard adjusted afterward by methods which will be spoken of 
 later. 
 
 Neither the common mineral acids, such as sulphuric, hydro- 
 chloric, and nitric acids, nor the alkaline substances, such as sodium 
 hydroxide or ammonium hydroxide, are sufficiently pure to permit of 
 being used directly for volumetric solutions, because these substances 
 contain water, and an absolutely correct determination of the amount 
 of this water is an operation which involves a knowledge of gravi- 
 metric methods. 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 413 
 
 It is for this reason that the basis in preparing a volumetric normal 
 acid solution is oxalic acid, a substance which can be readily obtained 
 in a pure crystallized condition. 
 
 Normal acid solution. Crystallized oxalic acid has the com- 
 position H 2 C 2 O 4 .2H 2 O and a molecular weight of 125.1. Being 
 dibasic, only half of its weight is taken for the normal solution, 
 which is made by placing 62.55 grammes of pure crystallized oxalic 
 acid in a liter flask, dissolving it in pure water, filling up to the 
 mark at the temperature of 25 C. (77 F.) and mixing thoroughly. 
 
 Normal solutions of sulphuric or hydrochloric acid are, for various 
 reasons, often preferred to oxalic acid. These solutions are best 
 made by diluting approximately the acids named, titrating the solu- 
 tion with normal sodium hydroxide, using phenolphthalein as an 
 indicator, and adding water until equal volumes saturate one another. 
 For instance, if it should be found that 10 c.c. normal alkali solution 
 neutralize 7.6 c.c. of the acid, then 24 c.c. of water have to be added 
 to every 76 c.c. of the acid in order to obtain a normal solution. 
 Normal sulphuric acid contains 48.675 grammes of H 2 SO 4 , and normal 
 hydrochloric acid 36.18 grammes of HC1 per liter. 
 
 These normal solutions can be made conveniently by diluting either 30 c.c. 
 of pure, concentrated sulphuric acid of sp. gr. 1.84, or 130 c.c. of hydrochloric 
 acid of sp. gr. 1.16 to 1000 c.c. The solutions thus obtained are yet too con- 
 centrated and are adjusted as described above. 
 
 Other methods of determining the exact standard of normal acids depend 
 upon the precipitation of 10 c.c. of the sulphuric acid solution by barium 
 chloride, or of 10 c.c. of the hydrochloric acid solution by silver nitrate, and 
 weighing the precipitated barium sulphate or silver chloride. Ten c.c. of 
 normal sulphuric acid give 1.1587 grammes of barium sulphate, and 10 c.c. of 
 normal hydrochloric acid 1.423 grammes of silver chloride. 
 
 A third method depends on the formation of, and the weighing as, an 
 ammonium salt. Ten c.c. of either acid are neutralized (or slightly super- 
 saturated) with ammonia water. The solution is evaporated in a previously 
 weighed platinum dish over a water-bath, the dry salt is repeatedly moistened 
 with alcohol, and finally dried in an air-bath at a temperature of 105 C. 
 (221 F.) for about half an hour. Ten c.c. of normal sulphuric acid give of 
 ammonium sulphate 0.65605 gramme, and 10 c.c. of normal hydrochloric acid 
 of ammonium chloride 0.5311 gramme. 
 
 Normal alkali solution. A normal solution of sodium carbonate 
 may be made by dissolving 52.655 grammes (one-half the molecular 
 weight) of pure sodium carbonate (obtainable by heating pure sodium 
 bicarbonate to a low red-heat) in water, and diluting to one liter. 
 This solution, however, is not often used, but may serve for standard- 
 
414 ANALYTICAL CHEMISTRY. 
 
 izing acid solutions, as it has the advantage of being prepared from a 
 substance that can be easily obtained in a pure condition, which is 
 not the case in preparing the otherwise more useful normal solutions 
 of potassium or sodium hydroxide, both of which substances contain 
 and absorb water. 
 
 The solutions are made by dissolving about 70 grammes of potas- 
 sium hydroxide or 60 grammes of sodium hydroxide in about 1000 
 c.c. of water, titrating this solution with normal acid, and' diluting it 
 with water, until equal volumes of both solutions neutralize each 
 other exactly. 
 
 The indicators used in alkalimetry are chiefly solution of litmus 
 or phenolphthalein, only a few drops of either solution being needed 
 for a determination. 
 
 The method adopted by the U. S. P. for standardizing the caustic 
 alkali solution, prepared as above mentioned, depends on the use of 
 chemically pure potassium bitartrate which acts on the alkali thus : 
 
 KHC 4 H 4 O 6 + KOH = K 2 C 4 H 4 O 6 + H 2 O. 
 
 As the molecular weight of potassium bitartrate is 186.78 it follows 
 that this weight in grammes will neutralize one liter of normal alkali 
 solution. The Pharmacopoeia directs to dissolve 9.339 grammes of 
 potassium bitartrate in boiling water and titrating with a portion of the 
 caustic alkali solution, the remainder of which is then diluted until 50 c.c. 
 are required for neutralization. Phenolphthalein is used as indicator. 
 Whenever carbonates are titrated with acids, or vice versa, the 
 solution has to be boiled towaid the end of the reaction in order to 
 drive off the carbon dioxide, as neither of the two indicators men- 
 tioned gives reliable results in the presence of carbonic acid or an 
 acid carbonate. This boiling is unnecessary when methyl orange is 
 used, because it is not influenced by carbonic acid. 
 
 When salts of organic acids with alkali metals are to be titrated with normal 
 acids, these salts are first converted into carbonates. This is accomplished by 
 igniting the weighed quantity of the salt in a crucible of porcelain or platinum. 
 The chemical action which takes place during the ignition of potassium acetate 
 may be shown thus : 
 
 2KC 2 H 3 2 -f 80 = K 2 CO 3 + 3H 2 O + 3CO 2 . 
 
 In a similar manner the alkali salts of all organic acids are converted into 
 carbonates. Frequently some carbon is left unburned ; this, however, does not 
 interfere with the result of the titration. The titration is made with the liquid 
 obtained by dissolving in water the residue left after ignition. 
 
 Method for calculating results. Before one can calculate how 
 much, say, of an acid is in a solution which he is titrating with a 
 
. METHODS FOR QUANTITATIVE DETERMINATIONS. 415 
 
 normal alkali, it is necessary to know how much of the acid in 
 question is equivalent to i. e., is required to neutralize one c.c. of 
 the alkali. Knowing this, it is easy to find how much acid is equiva- 
 lent to a certain number of c.c. of normal alkali used in titration. 
 These alkali equivalents of normal acid, or acid equivalents of a 
 normal alkali, are easily found by the student from the equation 
 of reaction. 
 
 Thus, to find how much HC1 is equivalent to one c.c. of normal alkali, we 
 use the equation : 
 
 HC1 + KOH == KC1 + H 2 O, 
 36.18 55.74 
 from which we see that 
 
 36.18 gm. HC1 = 55.74 gm. KOH == 1000 c.c. normal KOH, 
 or, 0.03618 gm. HC1 1 " 
 
 2KOH + H 2 S0 4 = K 2 S0 4 + 2H 2 O. 
 2 X 55.74 97.35 
 
 97.35 gm. H 2 SO 4 = 2 X 55.74 gm. KOH = 2000 c.c. normal KOH. 
 48.675 " " 55.74 " " = 1000 " 
 
 0.048675 " 1 " 
 
 Phosphoric acid presents a peculiar case. When tropaeolin is used as an 
 indicator the change in color takes place when this reaction is completed : 
 
 H 3 P0 4 + KOH = KH 2 P0 4 + H 2 0. 
 97.29 55.74 
 Hence, 
 
 97.29 gm. H 3 PO 4 =r 55.74 gm. KOH == 1000 c.c. normal KOH. 
 
 0.09729 " " = 1 " 
 
 With phenolphthalein, the indicator changes color when the subjoined reac- 
 tion is completed : 
 
 H 3 P0 4 + 2KOH = K 2 HPO 4 + 2H 2 O. 
 Hence, 
 
 97.29 gm. H 3 P0 4 = 2 X 55.74 gr. KOH ~ 2000 c.c. normal KOH. 
 or 0.04864 " " 1 " 
 
 The calculation for the amount of acid or alkali is made in this way. Sup- 
 pose we weigh off 10 grammes of dilute sulphuric acid. On titrating with 
 normal KOH it is found that 20 c.c. are required to cause the change in the 
 indicator (litmus) i. e., to completely neutralize the acid. We know from the 
 above that 1 c.c. normal KOH requires 0.04867 gramme H 2 SO 4 for neutraliza- 
 tion, hence 20 c.c. normal KOH require 0.04867 X 20 = 0.9735 gramme H 2 SO 4 , 
 That is, in the 10 grammes dilute acid weighed off there are 0.9735 gramme 
 H 2 SO 4 , or in 100 grammes there are 9.735 grammes, or 9.73 per cent. This 
 instance will serve as a type for all calculations of percentages. 
 
 Use of empirical solutions. The primary advantage in using normal, deci- 
 normal, etc., solutions is the fact that the calculations of results is very much 
 simplified in a system which involves molecular and atomic weights, or simple 
 fractions thereof. But any solution of definite strength can be employed. All 
 
416 ANALYTICAL CHEMISTRY. 
 
 normal, decinormal, etc., solutions deteriorate in time, some very slowly, others 
 rapidly, especially when not properly preserved. To restore the titer of such 
 solutions each time they are to be used involves an unnecessary outlay of time. 
 All that is necessary to know is the exact ratio between the solutions and a normal 
 or decinormal solution, to determine which an accurately standardized solution 
 should be always available. To illustrate, suppose 12.5 c.c. of a hydrochloric 
 acid solution exactly neutralize 10 c.c. of normal potassium hydroxide solution, 
 then 1 c.c. of the hydrochloric acid is equivalent to 0.8 c.c. of normal acid, and 
 the volume of acid used in any titration is readily converted into the equivalent 
 volume of normal acid by multiplying by the factor 0.8. 
 
 Neutralization equivalents. The normal solutions of acid and 
 alkali may be used for the determination of a large number of sub- 
 stances, either directly (as in the case of free acids, caustic and alka- 
 line carbonates and bicarbonates) or indirectly (as in the case of salts 
 of most of the organic acids, with alkalies, which are first converted 
 into carbonates by ignition). 
 
 One c.c. of normal acid is the equivalent of: 
 
 Gramme. 
 
 Ammonia, NH 3 0.01693 
 
 Ammonium carbonate, (NHJ 2 CO 3 0.04770 
 
 Ammonium carbonate (U. S. P.), NH 4 HCO 3 .NH 4 NH 2 CO 2 . . 0.05200 
 
 Lead acetate, crystalHzed Pb(C 2 H 3 O 2 ) 2 .3H 2 6 1 .... 0.18807 
 
 Lead subacetate, Pb 2 O(C 2 H 3 O 2 ) 2 1 0.13593 
 
 Lithium benzoate, LiC 7 H 5 O 2 2 0.12711 
 
 Lithium carbonate, Li 2 CO 3 0.03675 
 
 Lithium citrate, Li 3 C 6 H 5 O 7 2 0.06952 
 
 Lithium salicylate, LiC 7 H 5 O 3 2 0.14299 
 
 Potassium acetate, KC 2 H 3 O 2 2 0.09744 
 
 Potassium bicarbonate, KHCO 3 ....... 0.09941 
 
 Potassium bitartrate, KHC 4 H 4 O 6 * 0.18678 
 
 Potassium carbonate, K 2 CO 3 0.06863 
 
 Potassium citrate, crystallized, K 3 C 6 H 5 O 7 H 2 O 2 . . . .. 0.10736 
 
 Potassium hydroxide, KOH 0.05574 
 
 Potassium permanganate, KMnO 4 3 0.03139 
 
 Potassium sodium tartrate, KNaC 4 H 4 O 6 .4H 2 O 2 . . . ' . 0.14009 
 
 Potassium tartrate, 2K 2 C 4 H 4 O 6 .H 2 O 2 0^11679 
 
 Sodium acetate, NaC 2 H 3 O 2 .3H 2 O 2 0.13510 
 
 Sodium benzoate, NaC 7 H 5 O 2 2 ....... 0.14301 
 
 Sodium bicarbonate, NaHCO 3 0.08343 
 
 Sodium borate, crystallized, Na^CVlOH.O ....'. Q.18966 
 
 Sodium carbonate, monohydrate, Na,CO 3 .H 2 O .... 0.06159 
 
 Sodium carbonate, Na 2 CO 3 0.05265 
 
 Sodium hydroxide, NaOH .... 03976 
 
 Sodium salicylale, Na(C 7 H 5 3 ) 2 ..!!.'.' .' O.'l5889 
 
 One c.c. of normal sodium carbonate, potassium hydroxide, or 
 sodium hydroxide, is the equivalent of: 
 
 i With sulphuric acid and methyl-orange. 2 After ignition. 3 With OX alic acid only. 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 417 
 
 Acetic acid, HC 2 H 3 O 2 ........ 0.05958 
 
 Boric acid, H 3 IK), .......... 0.06154 
 
 Citric acid, crystallized, H.,C 6 H 5 O 7 .H 2 O ...... 0.06950 
 
 Hydrobromic acid, HBr ......... 0.08036 
 
 Hydrochloric acid, HC1 ......... 0.03618 
 
 Hydriodic acid, HI .......... 0.12690 
 
 Hypophosphorous acid, HPH 2 O 2 . ...... 0.06553 
 
 Lactic acid. HC 3 H 5 O 3 ......... 0.08937 
 
 Nitric acid,' HNO 3 .......... 0.06257 
 
 Oxalic acid, crystallized, H 2 C 2 O 4 .2H 2 O ...... 0.06255 
 
 Phosphoric acid, H 3 PO 4 (to form K 2 HPO 4 ; with phenol-phthalein) 0.04864 
 Phosphoric acid, H 3 PO 4 (to form KH 2 PO 4 ; with methyl-orange) . 0.09729 
 Potassium dichromate, K 2 Cr 2 O 7 (with phenol-phthalein) . . 0.14614 
 Sulphuric acid, H 2 SO 4 ......... 0.04867 
 
 Tartaric acid, H 2 C 4 H 4 O 6 . . ..... . . . 0.07446 
 
 Oxidimetry. A normal oxidizing solution is one which will 
 liberate from a liter as much oxygen as is chemically equivalent to 
 one gram-atom of hydrogen. This is one-half gram-atom, or 8 
 grammes of oxygen, for 
 
 H 2 + O = H 2 0, or H + = 
 
 The substances generally used in oxidimetry are potassium per- 
 manganate and potassium dichromate. 
 
 Potassium permanganate, KMnO 4 , 156.98, is chiefly used for 
 normal or decinormal oxidizing solution, and the titration is always 
 carried out in solution acidified with sulphuric acid. When the salt 
 breaks up to give off oxygen, it does so in this manner : 
 
 2KMn0 4 + 3H 2 SO 4 = K 2 SO 4 + 2MnSO 4 + 5O + 3H 2 O. 
 
 The oxygen is used in oxidizing the substance which is titrated. 
 The object of adding the acid is to facilitate the decomposition of 
 the KMnO 4 and to take up the potassium and manganese to form 
 salts, which being colorless form a colorless solution. 
 
 As 2 molecules of permanganate give up 5 atoms of oxygen, the 
 
 quantity to be taken to liberate \ atom or 8 gm. is - ^~* = -f^> 
 
 or l O i. e., J the molecular weight in grammes, or 31.396 gm. It 
 is this quantity which is contained in one liter of normal solution. 
 
 When oxalic acid is oxidized with permanganate solution this reaction 
 takes place: 
 
 H 2 C 2 4 .2H 2 + O = 2C0 2 + 3H 2 O, 
 
 or more fully, 
 
 5H 8 C 2 4 .2H 2 + 2KMn0 4 + 3H,SO 4 = 10CO 2 + 1^H 2 O + K 2 SO 4 -f 2MnSO 4 . 
 
418 ANALYTICAL CHEMISTRY. 
 
 This shows that one molecule of oxalic acid requires one atom of oxygen 
 for oxidation, or one-half molecule of acid requires one-half atom of oxygen. 
 As one-half gram-molecule of oxalic acid is the quantity in one liter of normal 
 solution, it follows that the liter of normal oxalic acid is exactly oxidized by a 
 liter of normal permanganate solution i. e., the two solutions are equivalent, 
 since a liter of normal permanganate solution gives off one-half gram-atom of 
 oxygen. Hence, it is convenient to use normal or deci-normal oxalic acid for 
 standardizing the permanganate solution. 
 
 Permanganate solution, when recently made, without observing certain pre- 
 cautions, will deteriorate for a certain length of time i. e., until all traces of 
 organic and other deoxidizing matters have become oxidized by the per- 
 manganate. 
 
 To prepare a permanent ^ solution of potassium permanganate, dissolve 
 about 3.3 grammes of the pure crystals (Potassii Permanganas, U. S. P.) in 1000 
 c.c. of distilled water in a flask, and boil for 5 minutes. Close the flask with 
 absorbent cotton, and set aside for at least two days, so that suspended matters 
 may deposit. Then decant the clear liquid without stirring up the sediment, 
 or for greater precaution filter it through a layer of purified shredded asbestos 
 (paper or cotton should not be used). The water to be employed for di- 
 luting this solution should be distilled from about 1 gramme of potassium per- 
 manganate. 
 
 To determine the strength of the solution draw off 10 c.c. of deci-normal 
 oxalic acid solution into a beaker, add 1 c.c. of pure concentrated sulphuric 
 acid, heat the mixture to about 80 C. (176 F.), then add gradually from a 
 glass-cock burette the permanganate, while stirring constantly, until a faint 
 pink color is produced, which remains permanent for one-half minute. Note 
 the number of cubic centimetres consumed and dilute the solution so that it is 
 exactly equivalent to the deci-norrnal oxalic acid. Verify the accuracy of the 
 dilution by a new titration. When properly prepared and preserved in glass- 
 stoppered bottles, permanganate solution will keep for at least six months with- 
 out changing its strength. 
 
 A second method for preparing a deci-normal solution of permanganate through 
 the medium of a deci-normal thiosulphate solution is described in the U. S. P. 
 as follows : 
 
 To a solution of about 1 gramme of potassium iodide in 10 c.c. of dilute sul- 
 phuric acid, 20 c.c. of the permanganate solution to be standardized are added. 
 This reaction takes place : 
 
 2HI + O = H 2 -j- 21. 
 
 The mixture is at once diluted with about 200 c.c. of pure water, and deci-normal 
 thiosulphate solution slowly added from a burette with constant stirring until 
 the color of the iodine is just discharged. The number of c.c. of the thiosul- 
 phate solution is noted, and the permanganate solution is diluted so that equal 
 volumes of the two solutions correspond to each other. 
 
 Instead of using oxalic acid for standardizing permanganate solution, 
 metallic iron may be used, and the operation should be conducted as follows : 
 0.2 gramme of pure, thin iron wire is dissolved in about 20 c.c. of dilute sul- 
 phuric acid (1 acid, 5 water) by the aid of heat, and in a flask arranged as 
 in Fig. 67. The flask is provided, by means of a perforated cork, with a 
 
METHODS FOE QUANTITATIVE DETERMINATIONS. 419 
 
 piece of glass tubing, to which is attached a piece of rubber tubing in which 
 is cut a vertical slit about one inch long and which is closed at the upper 
 end by a piece of glass rod ; gas or steam generated in the flask may escape, 
 while atmospheric air cannot enter, the ferrous solution being thus protected 
 from oxidation. 
 
 The iron solution, obtained from the 0.2 gramme of iron, is cooled and 
 diluted with about 300 c.c. of water, and then deci-normal potassium perman- 
 ganate solution is added with constant stirring until the solution is tinged 
 pinkish. 
 
 As 1 c.c. of deci-normal permanganate solution corresponds to 0.00555 
 
 FIG. 67. 
 
 Flu.sk for dissolving iron for volumetric determination. 
 
 gramme of metallic iron, the 0.2 gramme of iron wire used will consume 36.03 
 c.c. of the solution. 
 
 Permanganate is often used in determinations of iron and iron compounds. 
 Many of the latter contain iron in the ferric state, which must be converted 
 into ferrous compounds before titration. This conversion is accomplished by 
 heating the solution of a weighed quantity of the ferric compound with nascent 
 hydrogen i. e., with metallic zinc and dilute sulphuric acid in a flask 
 arranged as the one spoken of above, and shown in Fig. 67. 
 
 A very much quicker reduction of the ferric into a ferrous compound may be 
 accomplished by adding very slowly with constant stirring a saturated solution 
 of sodium sulphite to the boiling, acidified iron solution contained in the flask 
 until the liquid becomes colorless. All excess of sulphur dioxide is expelled 
 before titrating, by boiling the solution (which should contain a sufficient 
 quantity of sulphuric acid to decompose all sodium sulphite) for about ten 
 minutes in a flask, arranged as the one mentioned above. 
 
 Equivalents. The equivalent of 1 c.c. normal KMnO 4 for the 
 various substances which can be oxidized by it must be deduced 
 from the equations of reaction, just as in the case of acids and 
 alkalies. 
 
420 ANALYTICAL CHEMISTRY. 
 
 All nitrites react thus : 
 
 MNO 2 + O = MNO 3 , where M = metal. 
 MNO 2 = 1 atom O = quantity liberated by 2 liters KMnO 4 , 
 
 MNQ 2 = i = l liter *. KMn0 4 , 
 2 1 
 
 MNO, = 1 liter ^ " 
 
 2 X 10 10 
 
 MNO, 
 
 = ! c c . 
 
 2 X 10 X 1000 10 
 
 In this manner all other equivalents are found. The reactions 
 between permanganate and ferrous salts, and hydrogen dioxide respect- 
 ively, are expressed in these equations : 
 
 2FeS0 4 -f H 2 S0 4 + O = Fe 2 (SO 4 ) 3 + H 2 O. 
 H 2 2 + O = H 2 + 20. 
 
 One c.c. of deci-normal potassium permanganate, containing of this 
 salt 0.0031396 gramme, is the equivalent of: 
 
 Gramme. 
 
 Ferrous ammonium sulphate, Fe(NH 4 ) 2 (SO 4 ) 2 6H.,O . . . 0.038934 
 
 Ferrous carbonate, FeCO 3 0.011505 
 
 Ferrous oxide, FeO 0.007138 
 
 Ferrous sulphate, FeSO 4 ........ 0.015085 
 
 Ferrous sulphate, crystallized, FeSO 4 .7H 2 O 0.027601 
 
 Ferrous sulphate, dried, 2FeSO 4 + 3H 2 O 0.017767 
 
 Hydrogen dioxide, H 2 O 2 0.001688 
 
 Iron, in ferrous compounds, Fe - 0.005550 
 
 Oxalic acid, crystallized, H 2 C 2 O 4 .2H 2 O 0.006255 
 
 Oxygen, O 0.000794 
 
 Potassium nitrite, KNO 2 . . . . . . . . 0.004227 
 
 Sodium nitrite, NaNO 2 0.003428 
 
 Potassium dichromate, K 2 Cr 2 O 7 = 292.28. Whenever this salt 
 oxidizes other substances in acid solution it breaks up according to 
 this equation : 
 
 K a CrA + 4H 2 S0 4 = K 2 SO 4 + Cr 2 (SO 4 ) 3 -f 3O + 4H 2 O. 
 
 That is, one molecule of K 2 Cr 2 O 7 gives up three atoms of oxygen. 
 Hence to make a normal solution one-sixth the molecular weight of 
 K 2 Cr 2 O 7 (48.7133 grammes) is taken in the liter, and one-tenth this 
 quantity, equal to 4.8713 grammes of the pure salt, for deci-normal 
 solution. 
 
 The disadvantage of this solution is that the final point of titration cannot 
 be well seen, for which reason in the determination of iron, for which it is 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 421 
 
 chiefly used, the end of the reaction is determined by the method of spotting, 
 i. e., by taking out a drop of the solution and testing it on a white porcelain 
 plate with a drop of freshly prepared potassium ferricyanide solution ; when this 
 no longer gives a blue color the reaction is at an end. 
 
 In all determinations by this solution dilute sulphuric acid has to be added, 
 because both the potassium and the chromium require an acid to combine with, 
 as shown in the above equation. 
 
 The titration equivalents of this solution for ferrous salts are the same as 
 those of deci-normal potassium permanganate solution. 
 
 lodimetry. Solutions of iodine and of sodium thiosulphate (hypo- 
 sulphite) act upon each other with the formation of sodium iodide 
 and sodium tetrathionate : 
 
 21 + 2Na 2 S 2 O 3 = 2NaI + Na 2 S 4 O 6 . 
 
 A normal solution of one can be standardized by a normal solution 
 of the other. As indicator, is used starch solution, which is colored 
 blue by minute portions of free iodine. 
 
 Starch solution is made by mixing 1 gramme of starch with 10 c.c. of cold 
 water, and then adding enough boiling water, with constant stirring, to make 
 about 200 c.c. of a transparent jelly. If the solution is to be preserved for any 
 length of time, 10 grammes of zinc chloride should be added. 
 
 Many other substances, such as sulphurous acid^ hydrogen sulphide, 
 arsenous oxide, act upon iodine with the formation of colorless com- 
 pounds, and may, therefore, be estimated by normal solution of iodine, 
 while the iodine may be standardized by the thiosulphate solution. 
 In many cases the latter solution is also used for the determination of 
 chlorine, which is caused to act upon potassium iodide, the liberated 
 iodine being titrated. 
 
 Deci-normal iodine solution. Iodine being a univalent element, 
 the weight of its atom, 125.90, in grammes, is used to make one 
 liter of normal solution. Deci-normal solution is generally employed, 
 and is made by dissolving 12.590 grammes of pure iodine in a solu- 
 tion of 18 grammes of potassium iodide in about 300 c.c of water, 
 and diluting the solution to 1000 c.c. 
 
 To the article to be estimated by this solution is added a little starch 
 solution, and then the iodine solution until, on stirring, the blue color 
 ceases to be discharged. 
 
 Iodine of sufficient purity to permit of weighing an exact amount for a stand- 
 ard solution does not occur in the market. It can be purified, but as this is 
 somewhat tedious, a simpler plan of making a solution, which is given in the 
 U. S. P., is generally followed. It consists in making a liter of solution, some- 
 what stronger than decinormal, by dissolving about 14 grammes of iodine 
 
422 
 
 ANALYTICAL CHEMISTRY. 
 
 instead of 12.59 grammes as described above. 10 c.c. of this solution are titrated, 
 while stirring constantly, with deci-normalthiosulphate solution until the yellow 
 color of iodine just vanishes. The iodine solution is then properly diluted so 
 that it is exactly equivalent to the thiosulphate solution. 
 
 Many substances, such as sulphurous acid and its salts, hydrogen sulphide, 
 arsenous oxide, etc., are acted upon by iodine in such a manner that this 
 element enters into combination with constituents of the compounds named, or 
 iodine acts as an oxidizing agent through the medium of water. The quantity 
 of iodine thus taken up forms the basis for calculating the quantity of the sub- 
 stance acted upon. 
 
 In the case of arsenous oxide the titration is made in alkaline solution. 
 Arsenous oxide and sodium bicarbonate are dissolved in water, and this solu- 
 tion, containing sodium met-arsenite, is titrated with iodine solution, when 
 sodium met-arsenate and sodium iodide are formed : 
 
 NaAs0 2 + 21 + 2NaHC0 3 = NaAsO 3 + 2NaI + H 2 O + 2CO 2 . 
 
 The essential change in the above reaction may be shown thus : 
 As 2 3 + 41 + 2H 2 O = As 2 O 5 + 4HL 
 
 That is, the arsenous oxide which may be considered present in the metarsenite 
 is oxidized to arsenic oxide in the metarsenates. Hence it is seen that 1 liter 
 
 As 2 O 3 
 of one-tenth normal solution is equivalent to 4 y in in grammes. 
 
 When hydrogen sulphide, sulphurous acid, sulphites, or acid sulphites are titrated 
 with iodine the addition of an alkali is unnecessary ; but in titrating these sub- 
 stances they must be added to a measured excess of iodine solution, and the 
 excess after the reaction is complete determined by back -titration with thio- 
 sulphate solution ; the action is this : 
 
 H 2 S -f- 21 = 2HI + S. 
 H 2 SO 3 + 21 + H 2 O = H 2 SO 4 -f 2HI. 
 Na^SOg + 21 + H 2 O = Na. 2 SO 4 + 2HI. 
 
 In the titration of antimony and potassium tartrate by iodine an alkaline solu- 
 tion is required, and for this reason sodium bicarbonate is added to the solution. 
 The reaction which takes place is somewhat doubtful, but the following equa- 
 tion, even if not absolutely correct, corresponds to the quantities of the substances 
 acting upon one another : 
 
 2KSbOC 4 H 4 6 + H 2 O + 41 + 4NaHCO 3 = 
 2HSbO 3 + 2KHC 4 H 4 6 + 4NaI + 4CO 2 + H 2 O. 
 
 One c.c. of deci-normal iodine solution, containing of iodine 
 0.01259 gramme, is the equivalent of: 
 
 Gramme. 
 
 Antimony and potassium tartrate, 2KSbOC 4 H 4 O 6 .H a O . . 0.016495 
 
 Arsenous oxide, As 2 O 3 . 0.004911 
 
 Hydrogen sulphide, H 2 S . 0.001691 
 
 Potassium sulphite, crystallized, K 2 SO 3 .2H 2 O . . 0.009648 
 
 Sodium bisulphite, NaHS0 3 ... . 0.005168 
 
 Sodium hyposulphite (thiosulphate), Na2S 2 O 3 .5H 2 O . . . 0.024646 
 
 Sodium sulphite, crystallized, Na. 2 SO 3 .7H 2 O 0.012520 
 
 Sulphur dioxide, SO 2 . 0.003180 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 
 Sodium thiosulphate (Hyposulphite). From the equation : 
 
 2Na. 2 S 2 O 3 .5H 2 O + 21 Na 2 S 4 O 6 + 10II 2 O + 2NaI. 
 
 2X246.46 2X125.9 
 
 we see that 246.46 grammes of crystallized sodium thiosulphate are 
 equivalent to e., will exactly decolorize 125.90 grammes of iodine ; 
 hence, to make a f solution of this compound, 246.46 grammes must 
 be taken in a liter, and for a ^ solution 24.646 grammes are used. 
 If the salt should not be absolutely pure, a somewhat larger quan- 
 tity (30 grammes) should be dissolved in 1000 c.c. of water, and 
 this solution titrated with deci-normal solution of iodine and diluted 
 with a sufficient quantity of water to obtain the deci-normal solu- 
 tion. 
 
 If a decinormal iodine solution is not at hand, and perfectly pure sodium 
 thiosulphate cannot be obtained, the method adopted by the U. S. P. may be 
 followed. 30 grammes of the ordinary thiosulphate are dissolved and made up 
 to 1000 c.c. To a solution of about 1 gramme of potassium iodide in 10 c.c. of 
 dilute sulphuric acid in a flask, 20 c.c. of decinormal potassium dichromate 
 solution are slowly added from a burette, and the solution shaken after each 
 addition. The flask is then covered with a watch-glass and allowed to stand 5 
 minutes, after which about 250 c.c. of pure water are added, and the thiosul- 
 phate solution dropped in from a burette slowly, with constant shaking, until 
 most of the iodine is decolorized. Finally, a little starch solution is added and, 
 cautiously, more thiosulphate until the blue color changes to a light green. 
 After noting the volume used, the thiosulphate is diluted so that it is exactly 
 equivalent to the deci-normal dichromate solution. 
 
 Potassium dichromate can be obtained pure, and the decinormal solution 
 easily made by weighing the exact quantity needed. The solution, moreover, 
 is perfectly stable. 
 
 The article to be tested, containing free iodine, either in itself or 
 after the addition of potassium iodide, is treated with this solution 
 until the color of iodine is nearly discharged, when a little starch 
 liquor is added, and the addition of the solution continued until the 
 blue color has just disappeared. 
 
 The titration of iron in ferric salts by thiosulphate is based on 
 the liberation of iodine from potassium iodide by all ferric salts : 
 
 2FeCl 3 + 2KI = 2FeCl 2 + 2KC1 + 21. 
 
 The reaction shown in the above equation requires a temperature 
 of 40 to 50 C. (104 to 122 F.), and at least half an hour's time 
 to make sure of its completion. The digestion should be performed 
 
424 ANALYTICAL CHEMISTRY. 
 
 in a closed flask. If iron be present in combination with organic 
 acids, the addition of some hydrochloric acid becomes necessary. 
 Before titration the solution is allowed to cool, and the titration 
 should be promptly finished, as otherwise errors by re-oxidation of 
 the ferrous salt may be made. 
 
 One c.c. of deci-normal solution of sodium thiosulphate, containing 
 of the crystallized salt 0.024646 gramme, is the equivalent of : 
 
 Gramme. , 
 
 Bromine, Br 0.007936 
 
 Chlorine, Cl 0.003518 
 
 Chromium trioxide, CrO 3 0.003311 
 
 Iodine, I 0.012590 
 
 Iron, Fe, in ferric salts 0.005550 
 
 Deci-normal bromine solution (Koppeschaar's solution). The 
 great volatility of bromine, even from aqueous solutions, interferes 
 very much with the stability of volumetric solutions. For this 
 reason a solution is prepared which does not contain free bromine, 
 but an alkali bromide and bromate, from which, by addition of an 
 acid, a definite quantity of bromine (7.936 grammes per liter) may 
 be liberated when required. The chemical change is this : 
 SNaBr -f NaBrO 3 -f 6HC1 = 6NaCl -f 3H 2 O -f 6Br. 
 
 As the bromine salts are rarely chemically pure, a solution is made 
 which is stronger than necessary and is then adjusted to the titer of 
 thiosulphate solution. 
 
 The solution is prepared as follows : Dissolve 3.2 grammes of potassium 
 bromate and 50 grammes of potassium bromide in 900 c.c. of water. Of this 
 solution, which is too concentrated, transfer 20 c.c. into a bottle of about 250 c.c., 
 provided with a glass stopper. Next add 75 c.c. of water and 5 c.c. of pure 
 hydrochloric acid, and immediately insert the stopper. Shake the bottle a few 
 times to cause liberation of the bromine, then quickly introduce 1 gramme of 
 potassium iodide, taking care that no bromine vapor escapes. Gradually an 
 equivalent quantity of iodine is liberated from the potassium iodide by the 
 bromine. When this has taken place add, from a burette, deci-normal thiosul- 
 phate solution until the iodine tint is discharged, using toward the end a few 
 drops of starch solution as indicator! Note the number of c.c. of sodium thio- 
 sulphate solution thus consumed, and then dilute the bromine solution so that 
 equal volumes of it and of g sodium thiosulphate solution will exactly corre- 
 spond to each other^ 
 
 The use of bromine solution is directed by the U.S. P. in one case only, viz., 
 for the volumetric determination of phenol (carbolic acid). This substance 
 forms with bromine tribromphenol and hydrobromic acid : 
 C 6 H 5 OH + 6Br = C 6 H 2 Br 3 OH 4- SHBr. 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 425 
 
 The molecular weight of phenol is 93.36, and as ii reacts with 6 atoms of 
 bromine, one-sixth of 93.36, or 15.56 grammes of phenol correspond to 1 liter 
 of normal, and 1.556 grammes to deci-normal bromine solution i. e., I c.c. of 
 deci-normal bromine solution corresponds to 0.001556 gramme of phenol. The 
 U. S. P. directs the assay to be made as follows : Dissolve 1.556 grammes of the 
 specimen in water to make 1 liter. Transfer 25 c.c. of this solution (0.0389 
 phenol) to a glass-stoppered bottle of about 200 c.c. capacity, and add 30 c.c. of 
 deci-normal bromine solution and 5 c.c. of hydrochloric acid. Shake the con- 
 tents of the bottle repeatedly, during half an hour, then quickly introduce 1 
 gramme of potassium iodide, allow the reaction to take place and titrate the 
 solution with deci-normal thiosulphate, as described above. Deduct the num- 
 ber of c.c. of thiosulphate used from the 30 c.c. of bromine solution. The 
 remainder multiplied by 4 indicates the percentage of phenol in the carbolic 
 acid examined. 
 
 Deci-normal solution of silver. The pure, dry crystallized 
 silver nitrate, AgNO 3 = 168.69, is used for this solution, which is 
 made by dissolving 16.869 grammes of the salt in water to make 
 1000 c.c. The standard of this solution may be found by means of 
 a deci-uormal solution of sodium chloride containing of this salt 
 5.806 grammes in one liter. 
 
 Volumetric silver solution is used directly for the estimation of 
 most chlorides, iodides, bromides, and cyanides, including the free 
 acids of these salts. Insoluble chlorides must first be converted into 
 a soluble form by fusing them with sodium hydroxide, dissolving the 
 fused mass (containing sodium chloride) in water, filtering and neu- 
 tralizing with nitric acid. 
 
 The hydroxides and carbonates of alkali metals and of alkaline 
 earths may be converted into chlorides by evaporation to dryness 
 with pure hydrochloric acid, and heating to about 120 C. (248 F.). 
 The chlorides thus obtained may be titrated with silver solution. 
 
 In the case of chlorides, iodides, and bromides, normal potassium 
 chromate is used as an indicator. This salt forms wi*th silver nitrate 
 a red precipitate of silver chromate, but not before the silver chloride 
 (bromide or iodide) has been precipitated entirely. In case free acids 
 are determined by silver, these are neutralized with sodium hydroxide 
 before titration. 
 
 The operation is conducted as follows : The weighed quantity of 
 the chloride is dissolved in 50-100 c.c. of water, neutralized if neces- 
 sary, mixed with a little potassium chromate, and silver solution 
 added from the burette until a red coloration is just produced, which 
 does not disappear on shaking. 
 
 In estimating cyanides, the operation can be conducted as above 
 described, or it can be modified, use being made of the formation of 
 
4-26 ANALYTICAL CHEMISTRY. 
 
 
 
 soluble double cyanides of silver and an alkali metal. The reaction 
 takes place thus : 
 
 2KCN + AgN0 3 = AgK(CN), + KNO 3 . 
 
 In the process adopted by the U. S. P., a suitable quantity of hydrocyanic 
 acid, or of a cyanide, is diluted with water, and 5 c.c. of ammonia water and 
 a few drops of potassium iodide solution are added. Silver solution is then 
 added until a slight permanent cloudiness is produced, at which point half of 
 the cyanide is converted into silver cyanide, which is held in solution by the 
 other half of the cyanide as a double salt. The least excess of silver solution 
 after this stage is indicated by the insoluble silver iodide formed. As but one- 
 half of the silver solution has been added which is needed for the complete 
 conversion of the cyanogen present into silver cyanide, the number of c.c. of 
 the standard silver solution employed will indicate exactly one-half of the 
 equivalent amount of cyanide present in the solution. 
 
 One c.c. of deci-normal silver nitrate solution, containing 0.016869 
 gramme of AgNO 3 , is the equivalent of: 
 
 Gramme. 
 
 Ammonium bromide, NH 4 Br . 0.009729 
 
 Ammonium chloride, NH 4 C1 . 0.005311 
 
 Ammonium iodide, NH 4 I . . 0.014383 
 
 Calcium bromide, CaBr 2 ..,.,. . 0.009926 
 
 Ferrous bromide, FeBr 2 0.010711 
 
 Ferrous iodide, FeI 2 0.015365 
 
 Hydriodic acid, HI 0.012690 
 
 Hydrobromic acid, HBr . 0.008036 
 
 Hydrochloric acid, HC1 . . . . . . . . 0.003618 
 
 Hydrocyanic acid, HCN, to first formation of precipitate . . 0.005368 
 
 Hydrocyanic acid, HCN, with indicator 0.002684 
 
 Lithium bromide, LiBr 0.008634 
 
 Potassium bromide, KBr ........ 0.011822 
 
 Potassium chloride, KC1 0.007404 
 
 Potassium cyanide, KCN, to first formation of precipitate . . 0.012940 
 
 Potassium cyanide, ECN, with indicator 0.006470 
 
 Potassium iodide, KI 0.016476 
 
 Potassium sulphocyanate, KCNS 0.009653 
 
 Sodium bromide, NaBr 0.010224 
 
 Sodium chloride, NaCl 0.005806 
 
 Sodium iodide, Nal . 0.014878 
 
 Strontium bromide, SrBr 2 .6H 2 O . 0.017647 
 
 Strontium iodide, SrI 2 .6H 2 O 0.022301 
 
 Zinc bromide, ZnBr 2 0.011181 
 
 Zinc chloride, ZnCl 2 0.006763 
 
 Zinc iodide, ZnI 2 0.015835 
 
 Deci-normal solution of sodium chloride is made by dissolving 
 5.806 grammes of pure sodium chloride in enough water to make 
 1000 c.c. The titration is made in neutral solution, normal potas^ 
 sium chromate being used as an indicator. (See explanation in 
 previous paragraph on silver solution.) 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 427 
 
 One c.c. of deci-normal sodium chloride solution, containing 
 0.005806 gramme of Nad, is the equivalent of: 
 
 Gramme 
 
 Silver, Ag 0.010712 
 
 Silver nitrate, AgNO 3 0.016869 
 
 Silver oxide, Ag 2 O 0.011506 
 
 Deci-normal solution of potassium sulphocyanate ( Volhard's 
 solution). This solution, like the sodium chloride solution, is used 
 as a companion to silver nitrate ; it has the advantage that it can be 
 used in acid solutions, with ferric ammonium sulphate (ferric alum) 
 as indicator. Silver nitrate forms in the potassium sulphocyanate a 
 white precipitate of silver sulphocyanate : 
 
 KCNS + AgNO 3 = AgCNS + KNO 3 . 
 
 As indicator is used ferric alum, which produces with sulpho- 
 cyanate a deep brownish-red color, which, however, does not appear 
 permanently until all silver has been precipitated. 
 
 As potassium sulphocyanate is rarely pure, 10 grammes, which is 
 about 3 per cent, more than the quantity required, are dissolved in 
 1000 c.c. of water. This solution has to be adjusted by standardizing 
 with deci-normal silver solution until equal volumes decompose one 
 another exactly. 
 
 The sulphocyanate solution is used in the determination of the 
 amount of ferrous iodide in the saccharated salt and in the syrup. 
 
 The operation is performed thus : To the solution of the ferrous 
 iodide are added nitric acid, ferric alum, and of deci-normal silver 
 nitrate solution a quantity more than sufficient to convert all iodine 
 into silver iodide. . The excess of silver nitrate present in the mix- 
 ture is determined by sulphocyanate solution. The ferric alum and 
 nitric acid must not be added until the silver nitrate has precipitated 
 all iodine, otherwise iodine will be liberated. This holds in all cases 
 where iodides are titrated. 
 
 Gas-analysis. The analysis of gases is generally accomplished by measur- 
 ing gas volumes in graduated glass tubes (eudiometers) over mercury (in some 
 cases over water), noting carefully the pressure and temperature at which the 
 volume is determined. 
 
 From gas mixtures, the various constituents present may often be eliminated 
 by causing them to be absorbed one after another by suitable agents. For 
 instance : From a measured volume of a mixture of nitrogen, oxygen, and 
 carbon dioxide, the latter compound may be removed by allowing the gas to 
 
428 ANALYTICAL CHEMISTRY. 
 
 remain in contact for a few hours with potassium hydroxide, which will absorb 
 all carbon dioxide, the diminution in volume indicating the quantity of carbon 
 dioxide originally present. The volume of oxygen may next be determined by 
 introducing a piece of phosphorus, which will gradually absorb the oxygen, 
 the remaining volume being pure nitrogen. 
 
 In some cases gaseous constituents of liquids or solids are eliminated and 
 measured as gases. Thus, the carbon dioxide of carbonates, the nitrogen 
 dioxide evolved from nitrates, the nitrogen of urea and other nitrogenous 
 bodies, are instances of substances which are eliminated from solids in the 
 gaseous state and determined by direct measurement. 
 
 The gas volume thus found is, in most cases, converted into parts by weight. 
 The basis of this calculation is the weight of 1 c.c. of hydrogen, which, at the 
 temperature of C. (32 F.) and a pressure of 760 mm. of mercury is 0.0000898 
 gramme. 1 c.c. of any other gas weighs as many times the weight of 1 c.c. 
 hydrogen as the molecule of this substance is heavier than that of hydrogen. 
 Thus the molecular weight of carbon dioxide is 21.835 times greater than that 
 of hydrogen, consequently 1 c.c. of carbon dioxide weighs 21. 835 times heavier 
 than 1 c.c. of hydrogen, or 0.0019608 gramme. 
 
 It has been shown on pages 26 and 45 that heat and pressure cause a regular 
 increase or decrease in volume. The data there given are used in calculating 
 the volume of the measured gas at the temperature of C. (32 F.) and a 
 pressure of 760 m.m. 
 
 The reason for reducing volumes of gases to C. and 760 m.m. pressure, 
 known as normal temperature and pressure, is that the densities of gases are 
 given for these conditions. Therefore, to find the weight of any volume of 
 gas it must be reduced to normal temperature and pressure. 
 
 A simple rule for reducing volumes of gases to C. is this : The volume of 
 a gas is proportional to its absolute temperature. The absolute temperature is 
 obtained by adding 273 to the reading of the centigrade scale. Thus, if a gas 
 measures 66 c.c. at 54.6 C., its volume at C. is found from the proportion : 
 
 66 c.c. : [54.6 + 273] : : x : [0 + 273], 
 or, 
 
 66 : 327.6 : : x : 273, 
 and 
 
 In this reduction the pressure is supposed to remain constant. That is, the 
 volume of 55 c.c. at C. is still at the same pressure as the volume 66 c.c. was. 
 
 To reduce a gas volume under any pressure to the volume it would occupy 
 if the pressure were changed to the normal i. e., to 760 m.m. use is made of 
 Boyle's law, viz., the product of the pressure times the corresponding volume 
 of a gas is always constant when the temperature is the same. This law is 
 expressed in the equation, PV=pv, where PV and pv are corresponding 
 pressures and volumes. 
 
 If we assume that in the above case the volume of 55 c.c. is under a pressure 
 of 750 m.m., its volume at normal, or 760 m.m. pressure, is found by using the 
 equation : 
 
 55 X 750 = x X 760, 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 429 
 
 This shows that the gas-volume of 66 c.c. at 54.6 C. and 750 m.m. pressure 
 becomes 54.28 c.c. at C. and 760 m.m. pressure. Knowing the volume at 
 C. and 760 m.m. pressure, and the weight of 1 c.c. of the gas under these 
 conditions, the weight of the total volume is easily found. 
 
 The reduction for temperature and pressure can be made in one operation 
 by using the formula : 
 
 V = v X P X 273 
 
 760 X (273 -f t) ' 
 
 V= volume at C. and 760 m.m. pressure, which is to be found. 
 
 v = volume read at some pressure, p, other than the normal. 
 
 t = temperature in centigrade degrees at which volume v is read. 
 
 Thus, in above case : 
 
 V = 66 X 750 X 273 = ,, 2g 
 
 760 X (273 -f- 54.6) 
 
 Methods of gas-analysis have been adopted by the U. S. P. in the quantita- 
 tive determination of amyl nitrite and ethyl nitrite. The operation is per- 
 formed in an apparatus known as a nitrometer, consisting of two glass tubes held 
 in upright position and connected at the lower ends by a piece of rubber 
 tubing. One of the tubes is open, the other one is graduated and provided 
 with a glass stopcock near the upper end. In using the nitrometer for the 
 analysis of ethyl nitrite the graduated tube is filled with saturated solution of 
 sodium chloride, in which nitrogen dioxide is almost insoluble. Next are 
 introduced through the stopcock the measured (or weighed) quantity of ethyl 
 nitrite with a sufficient amount of solution of potassium iodide and sulphuric 
 acid. By the action of these agents nitrogen dioxide is liberated, and from the 
 volume obtained the quantity of nitrite present is calculated. The decom- 
 position is shown by the equation : 
 
 C 2 H 5 N0 2 -f KI + H 2 S0 4 = C 2 H 5 OH + I + KHSO 4 + NO. 
 
 Water analysis. The objects of water analysis are various. Thus, the 
 analysis may serve to decide the fitness of a water for manufacturing, medici- 
 nal, or household purposes. Accordingly, more or less stress is laid on the 
 exact determination of certain constituents. While the student is referred to 
 special books treating on the different methods of water analysis, a brief outline 
 of the chemical examination of drinking-water is here given. 
 
 It should be remembered that the results obtained by chemical examination 
 only are sometimes insufficient to furnish positive proof of the fitness of a 
 water for drinking-purposes. The reason is that micro-organisms may be 
 present which cannot be detected by chemical means. It is the microscope, 
 aided by appropriate bacteriological methods, which has to be used in such 
 cases, and these methods cannot, of course, be considered in this book. 
 
 Standard of purity. A fixed standard has not as yet been generally 
 adopted for judging the purity of wholesome drinking-water, but most authori- 
 ties agree that the following maxima of admixtures should not be exceeded. 
 They are expressed in milligrams per liter i. e., parts by weight in one million. 
 The following data refer to one liter of water used : 
 
430 ANALYTICAL CHEMISTRY. 
 
 Total residue left on evaporation : 500 mg. 
 
 Potassium permanganate decomposed by organic matter: 10 mg. 
 
 (=31.71 c.c. ^KMn0 4 ). 
 
 Ammonia, present as such or as an ammonium salt : 0.05 mg. 
 Albuminoid ammonia i. e., ammonia formed from nitrogenous organic 
 
 matter by distillation with KMnO 4 : 0.1 mg. 
 Mtrates : 10 mg. of N 2 O 5 . 
 
 Nitrites : a mere trace, not to exceed Q.05 mg. of N 2 O 3 . 
 Sulphates : 60 to 100 mg. of H 2 S0 4 . 
 Chlorine : 15 mg. 
 Phosphates : a mere trace. 
 The water should be clear, colorless, odorless and practically tasteless. 
 
 Total solids. If the water be turbid, a liter of it is passed through a small 
 filter, previously dried and weighed. After drying at 110 C., filter and con- 
 tents are weighed together and the difference is quantity of suspended solids. 
 The evaporation to dryness of one liter of the clear water in a platinum or 
 nickel dish at a moderate temperature, with subsequent heating to 110 C., 
 gives the total inorganic and organic solids in solution. 
 
 The subsequent heating of the dried residue to redness causes the expul- 
 sion of all organic matter ; but as also inorganic matters, such as carbon dioxide 
 from acid carbonate, oxygen from nitrates, etc., may escape, the determination 
 is of relatively little value. 
 
 Organic matters. While we have no good method by which the quantity 
 of organic matter in water can be readily determined, the oxidizing power of 
 permanganate for organic matters is used for an approximate determination. 
 This is made by acidifying 100 c.c. of water with 5 c.c. of sulphuric acid, and 
 adding 10 c.c. of -~- potassium permanganate, or enough to impart a distinct 
 
 red color. The liquid is boiled for ten minutes. Should the red color disap- 
 pear, more permanganate must be added. When color remains permanent, 
 10 c.c. of ~ oxalic acid are added and the mixture is again heated. To this 
 
 solution permanganate is added until it shows a red tint. From the total 
 number of c.c. of permanganate used, 10 c.c. are deducted for the oxalic acid 
 added. 
 
 As the organic constituents in water at different times and places have no 
 uniform composition, the quantity of organic matter present cannot be calculated 
 from the quantity of permanganate used. It is therefore customary to speak 
 simply of the oxygen- consuming power of water. It should, however, be re- 
 membered that water may contain deoxidizing agents, other than organic 
 matters, such as hydrogen sulphide, nitrites, ferrous salts, etc. 
 
 Ammonia. Nitrogenous organic matters, when undergoing decomposition 
 by the agency of bacteria, generate ammonia, which is gradually converted 
 into nitrites and nitrates. It is for this reason that the presence of these three 
 compounds is looked upon as indicative of nitrogenous matters, though small 
 quantities of ammonia and nitrites may also be present in the water by ab? 
 sorption from the air. 
 
METHODS FOR QUANTITATIVE DETERMINATIONS. 431 
 
 It is customary to speak in water analysis of free ammonia and albuminoid 
 ammonia. By free ammonia is meant the ammonia present as ammonium 
 hydroxide, or more generally as an ammonium salt, chiefly carbonate. Albu- 
 minoid ammonia refers to the ammonia obtainable from nitrogenous matter 
 by oxidation with alkaline permanganate solution. 
 
 The process for the determination of both kinds of ammonia is carried out 
 as follows: 500 c.c. of the water are placed in a flask of about one liter 
 capacity and 5 c.c. of a saturated solution of sodium carbonate are added. The 
 flask is connected with a suitable condenser whose outlet is so connected with a 
 receiver that no loss of ammonia can occur. Heat is then applied to the flask 
 until 300 c.c. have distilled over. To this distillate, containing all the " free 
 ammonia," is added enough pure water to restore the original volume of 500 
 c.c., and the distillate is s^t aside for Nesslerizing. 
 
 To the liquid remaining in the distilling flask are now added 50 c.c. of an 
 alkaline permanganate solution (made by dissolving 8 gm. of KMnO 4 and 200 
 gm. KOH in water to make 1 liter), and distillation is resumed until 200 c.c. 
 have passed over, which distillate is also diluted to the original volume of 
 water used i. e., to 500 c.c. 
 
 Both distillates, containing the free and the albuminoid ammonia respect- 
 ively, are now ready to be tested for ammonia by a method depending on 
 the intensity of color imparted to them by Nessler's reagent. This reagent 
 gives with highly diluted ammonia a color varying from pale straw-yellow to 
 brown. In order to have a standard for comparison of the colors, an empirical 
 solution of ammonium chloride is made, containing of this salt 3.137 gm. in 1 
 liter, corresponding to 1 mg. of NH 3 in each c.c. Just before use, 5 c.c. of this 
 solution are diluted with pure water to 100 c.c., of which 1 c.c. now contains 
 0.05 mg. NH 3 . 
 
 To make the test there are required five small cylinders of colorless glass, 
 of about 30 m.m. diameter and about 100 m.m high, each having a mark at 50 
 c.c., and being numbered from 1 to 5. Into four of these cylinders are measured 
 0.5, 1, 1.5, and 2 c.c., respectively, of the standard ammonium chloride solu- 
 tion, and all are then filled with water up to the 50 c.c. mark. This makes the 
 contents of the four cylinders correspond to water containing 0.5, 1, 1.5, and 2 
 mg. of NH 3 per liter. 
 
 Cylinder No. 5 is next filled with 50 c.c. of the water specimen prepared for 
 the ammonia determination, and to each of the five cylinders, standing on white 
 paper, is added 1 c.c. of ^essler's reagent (see index), which is well mixed with 
 the water. A comparison of the yellow color produced in the sample with that 
 of the cylinders 1 to 4, containing known quantities, will afford an estimate of 
 the quantity of ammonia in the water examined. 
 
 Should the color of the specimen be deeper than that of cylinder No. 4, or 
 lighter than that of No. 1, then the experiment has to be repeated, the water 
 or the standard solution being diluted in definite proportions until similarity 
 of color is reached. The calculation is based on the dilution made. 
 
 Of course, both distillates have to be treated in this manner. Great care 
 must be taken to make sure that the water, reagents, and apparatus used in 
 the operation are absolutely free from ammonia. When only free ammonia is 
 to be determined the distillation can be dispensed with. If the water should 
 contain any considerable quantity of calcium salts, these must be precipitated 
 
432 ANALYTICAL CHEMISTRY. 
 
 by digesting the water with a little sodium carbonate and sodium hydroxide 
 before Nesslerizing. 
 
 Nitric acid. While there are methods by which nitric acid can be deter- 
 mined more accurately, it often suffices to make the tests with brucine, 
 diphenylamine, and pyrogallic acid, as described under the analytical reactions 
 of nitric acid on page 177. 
 
 Nitrous acid. A solution made by dissolving 1 gm. of metaphenylene- 
 diamine in 200 c.c. water, containing 5 gm. H 2 SO 4 , is used for the determina- 
 tion of nitrites in the same manner as Nessler's solution is used for ammonia. 
 The required standard nitrite solution is prepared by dissolving 0.406 gm. silver 
 nitrite and 0.225 gm. potassium chloride in hot water, mixing and, after cool- 
 ing, filling up to 1 liter. After filtering off the precipitated silver chloride, 
 lOo'c.c. of the nitrate are diluted to 1000 c.c. This solution contains nitrous 
 acid equivalent to 10 mg. of N 2 O 3 per liter. 
 
 Metaphenylene-diamine solution, prepared as above, gives with nitrites a 
 yellow color, the intensity of which serves for the quantitative estimation of the 
 nitrites present. The test is made by using definite dilutions of the above 
 standard nitrite solution in the four test-cylinders, adding 1 c.c. of the meta- 
 phenylene-diamine to each 50 c.c., and comparing the colors produced with that 
 obtained in the water specimen, treated in like manner. Immersion of the 
 cylinders in warm water accelerates the reaction. 
 
 Sulphates. While there are volumetric methods for the determination of 
 sulphates, this can be conveniently made by the gravimetric method i. e. t by 
 precipitating the sulphate with barium chloride and weighing the precipitated 
 BaS0 4 . From 100 to 250 c.c. of water should be used. 
 
 Chlorine. If the water under examination has had an opportunity to 
 become charged with sodium chloride from its proximity to the sea coast, to 
 salt lakes, or by flowing through strata containing salt deposits, then a con- 
 siderable quantity of chlorides may be present and yet the water may be used 
 without detriment to health. But in other cases the chlorides are derived 
 from cesspools, sewage, etc., and their presence is then indicative of dangerous 
 pollution. 
 
 The determination of chlorine is made by titrating 100 c.c. of water with 
 ^ AgN0 3 , using potassium ~,hromate as an indicator. For water containing 
 much organic matter the gravimetric method should, be used. 
 
 Phosphates. The ammonium molybdate test (see analytical reactions of 
 phosphoric acid, page 228) should give no indication of phosphoric acid, as the 
 presence of soluble phosphates in water is almost positive proof that pollution 
 with urine has taken place. 
 
 QUESTIONS. Explain the principles which are made use of in gravimetric 
 and volumetric determinations. Give an outline of the operations to be per- 
 formed in the gravimetric determination of copper in cupric sulphate. What 
 are normal and deci-normal solutions, and how are they made? What is the 
 use of indicators in volumetric analysis ? Mention some indicators and explain 
 
DETECTION OF IMPURITIES. 433 
 
 39. DETECTION OF IMPURITIES IN OFFICIAL INOKGANIC 
 CHEMICAL PREPARATIONS. 
 
 General remarks. Very little has been said, heretofore, about 
 impurities which may be present in the various chemical prepara- 
 tions, and this omission has been intentional, because it would have 
 increased the bulk of this book beyond the limits considered neces- 
 sary for the beginner. 
 
 Impurities present in chemical preparations are either derived from 
 the materials used in their manufacture, or they have been intention- 
 ally added as adulterations. In regard to the last, no general rule 
 for detecting them can be given, the nature of the adulterating article 
 varying with the nature of the substance adulterated ; the general 
 properties of the substance to be examined for purity will, in most 
 cases, suggest the nature of those substances which possibly may have 
 been added, and for them a search has to be made, or, if necessary, a 
 complete analysis, by which is proved the absence of everything else 
 but the constituents of the pure substance. 
 
 Impurities derived from the materials used in the manufacture of 
 a substance (generally through an imperfect or incorrect process of 
 manufacture), or from the vessels used in the manufacture, are usually 
 but few in number (in any one substance), and their nature can, in 
 most cases, be anticipated by one familiar with the process of manu- 
 facture. For one not acquainted with the mode of preparation it 
 would be a rather difficult task to study the nature of the impurities 
 which might possibly be present. 
 
 their action. Why is oxalic acid preferred in preparing normal acid solution? 
 What quantity of oxalic acid is contained in a liter, and why is this quantity 
 used? Suppose 2 grammes of crystallized sodium carbonate require 14 c.c. 
 of normal acid for neutralization : What are the percentages of crystallized 
 sodium carbonate and of pure sodium carbonate contained in the specimens 
 examined. Ten grammes of dilute hydrochloric acid require 35.5 c.c. of nor- 
 mal sodium hydroxide solution for neutralization ; what is the strength of 
 this acid? Explain the action of potassium permanganate and of potassium 
 dichromate when used for volumetric purposes. Which substances may be 
 determined volumetrically by solutions of iodine and sodium thiosulphate? 
 Explain the mode in which the determinations by these agents are accom- 
 plished. Suppose 1 gramme of potassium iodide requires for titration 60 c.c. 
 of deci-normal solution of silver nitrate: What quantity of pure potassium 
 iodide is indicated by this determination? Describe in detail the volumetric 
 determination of carbolic acid. For what purposes is potassium sulphocya- 
 nate used volumetrically, and what is its action ? Explain the method used 
 for the analysis of ethyl nitrite. 
 28 
 
434 ANALYTICAL CHEMISTRY. 
 
 The same remarks apply to the methods by which the impurities 
 can be detected. One familiar with analytical chemistry can easily 
 find, in most cases, a good method by which the presence or absence 
 of an impurity can be demonstrated ; but to one unacquainted with 
 chemistry it might be an impossibility to detect impurities, even if 
 a method were given. 
 
 For these reasons little stress has been laid upon the occurrence of 
 impurities in the various chemical preparations heretofore considered. 
 Moreover, the U. S. P. gives, in most cases, directions for the detec- 
 tion of impurities, so explicit that anyone acquainted with analytical 
 operations will find no difficulty in performing these tests satisfac- 
 torily. 
 
 However, while the Pharmacopeia gives exact instructions how to 
 manipulate, it furnishes no explanations why certain methods have 
 been adopted, or why certain operations are to be performed. It is 
 for this reason, and for the special benefit of the beginner, that a few 
 paragraphs are devoted to the consideration of official methods for 
 testing the chemical preparations of the U. S. P. 
 
 Official chemicals and their purity. Absolute purity of chemi- 
 cals is essential in some cases, as, for instance, when they are intended 
 as reagents ; such chemicals are commercially designated as C. P. 
 (chemically pure). For the majority of medicinal chemicals, how- 
 ever, such absolute purity is unnecessary, as the small proportion of 
 harmless impurities present in nowise interferes* with the therapeutic 
 action of the substance, and a demand for absolute purity, which 
 greatly enhances the cost of chemicals, is therefore unreasonable and 
 not required by the Pharmacopeia. 
 
 The presence of a small fraction of one per cent, of sodium chloride 
 in many official chemicals cannot be looked upon as objectionable, 
 while the same amount of arsenic would render the preparation unfit 
 for medicinal use. 
 
 The methods used by the Pharmacopoeia to determine the qualit/ 
 of a chemical preparation may be divided into four classes, as follows : 
 1. Tests as to identity ; 2. Qualitative tests for impurities ; 3. Quan- 
 titative tests for the limit of impurities ; 4. Quantitative determina- 
 tion of the chief constituent. 
 
 Tests as to identity. These tests are partly of a physical, partly 
 of a chemical character. They include, in the physical part, the 
 examination of the appearance, color, crystalline structure, specific 
 gravity, fusing-point, boiling-point, etc. 
 
DETECTION OF IMPURITIES. 435 
 
 The chemical tests given are sufficiently characteristic to leave no 
 doubt as to the true nature or identity of the substance. In order to 
 accomplish this object it is not necessary to apply all the analytical 
 reagents characteristic of the substance or its component parts, but 
 the U. S. P. selects from the often large number of known tests one, 
 or possibly a few, which answer best in the special case. 
 
 For instance, while we have a number of tests, both for potassium 
 and iodine, the U. S. P., in the article on potassium iodide, gives but 
 one reaction for each of these elements. Yet these tests have been 
 selected with sufficient judgment to admit of no doubt regarding the 
 nature of the substance. 
 
 Qualitative tests for impurities. These tests are in many cases 
 described minutely, i. e., the quantity to be taken of both the sub- 
 stance to be examined and the reagent to be added is stated. More- 
 over the amount of solvent (water, acid, etc.) to be used is mentioned, 
 and other details are given. The object of this exactness in describ- 
 ing the tests is not only to render the work easy for one not fully 
 familiar with analytical methods, but also, in some cases, to fix a 
 limit for the admissible quantity of an impurity. A certain reagent 
 may, in a concentrated solution, indicate the presence of a trace of 
 an impurity, while in a more dilute solution this reagent will fail to 
 detect it. The selection of the reagents used in certain tests is also 
 made with the view of establishing a sufficient purity for pharmaco- 
 poeial purposes of the article examined without demanding an absolute 
 purity. 
 
 A few instances may help to illustrate these remarks : Potassium 
 can be precipitated from a solution of its salts by a number of re- 
 agents, which, however, differ widely in sensitiveness. Thus, tartaric 
 acid will cause the formation of a precipitate of potassium bitartrate 
 in a solution containing at least 0.1 per cent, of potassium ; in solu- 
 tions containing a less amount no precipitate is formed. Platinic 
 chloride is somewhat more sensitive than tartaric acid, and sodium 
 cobaltic nitrite, which is still more delicate, causes a precipitate in 
 solutions containing even as little as 0.04 per cent, of potassium. It 
 is evident that by using either one or the other of the three reagents 
 mentioned for the detection of potassium, this metal may or may not 
 be found, according to the quantity present in a solution. The 
 Pharmacopoeia, in directing the use of one of these reagents, limits 
 the amount of a permissible quantity of potassium according to the 
 sensitiveness of the reagent. 
 
ANALYTICAL CHEMISTRY. 
 
 Again, in testing for arsenic, the chemist has his choice between a 
 number of more or less delicate tests. Gutzeit's test is so sensitive 
 that by means of it arsenic can be detected in a solution containing 
 only 0.000001 gramme of arsenous oxide in a cubic centimeter. This 
 test would be, therefore, by far too severe when applied to a number 
 of pharmaceutical preparations, for which reason the Pharmacopoeia 
 directs in many cases the less sensitive hydrogen sulphide test. 
 
 Quantitative tests for the limit of impurities. While, as above 
 stated, even the qualitative tests are often so made as to be to some 
 extent of a quantitative character, the U. S. P. recommends in many 
 cases methods by which a stated limit of an impurity can be detected 
 without the necessity of determining by quantitative analysis the 
 actual amount of the impurity present. 
 
 Formerly it was, and to some extent it is now, customary to limit 
 the amount of a permissible quantity of an impurity by referring to 
 the intensity of the reaction. In case the impurity was to be detected 
 by precipitation (as, for instance, sulphates or chlorides in potassium 
 nitrate) it was stated that the respective reagents used for the detec- 
 tion (in the case named, barium chloride or silver nitrate) should not 
 produce more than a very slight precipitate, or turbidity, or cloudi- 
 ness, etc. These descriptions are, of course, very indefinite, and the 
 conclusion arrived at depends largely upon the individuality of the 
 observer. 
 
 In order to obviate this uncertainty the U. S. P. has introduced a 
 number of more exact methods. These depend upon the addition of 
 a definite quantity of a reagent capable of eliminating a certain quan- 
 tity of the impurity from a given quantity of the substance to be 
 examined. In thus examining a preparation the impurity may or 
 may not be present ; if present, the permissible quantity will be re- 
 moved by the operation, and if originally not present in larger quan- 
 tity, the substance will now be found free from the impurity, while 
 if present in larger proportions than can be removed by the quantity 
 of reagent added, the excess can be detected by appropriate tests. 
 
 If an excess of impurity is thus discovered, regardless of the fact 
 whether the excess be large or small, the substance examined does 
 not come up to the pharmacopoeial requirements. 
 
 Thus, in potassium bromide, the pharmacopoeial limit of potassium carbon- 
 ate is 0.068 per cent. In order to determine whether or not this limit is ex- 
 ceeded, the Pharmacopeia directs the addition of 0.1 c.c. of sulphuric acid 
 
DETECTION OF IMPURITIES. 437 
 
 to a solution of 1 gramme of the salt in 10 c.c. of water. Since 0.1 c.c. of 5 
 sulphuric acid is capable of neutralizing 0.000686 gramme of potassium carbon- 
 ate, the whole quantity allowed would be neutralized by the addition of the 
 prescribed quantity of acid, and no red tint should be imparted to the heated 
 liquid by adding a few drops of phenolphthalein solution ; a red color would 
 indicate that more alkali carbonate was present in the weighed sample than 
 could be neutralized by the quantity of acid added. 
 
 Quantitative determination of the principal constituent. 
 These determinations are made in the majority of cases volumetric- 
 ally, and require no special explanation here, as the methods have 
 been fully considered in the previous chapter. Gravimetric methods 
 are used in the determination of several alkaloids and also in a few 
 other cases. 
 
 QUESTIONS. What are the sources of the impurities found in chemical 
 preparations ? Why is it not obligatory to use chemically pure chemicals for 
 medicinal purposes ? Which are the leading features adopted by the U. S. P. 
 in the identification of chemical preparations? State the reasons why the 
 U. S. P. describes the tests for impurities so minutely. Why can we not use 
 indiscriminately either one of a number of reagents or tests by which the pres- 
 ence of the same impurity may be indicated ? What is the principle applied 
 in the methods of the Pharmacopeia for the determination of a permitted 
 quantity of an impurity ? How can we decide the question whether a sample 
 of potassium acetate contains more than 1 per cent, of potassium chloride with- 
 out making a quantitative estimation of chlorine? 
 
VI. 
 
 CONSIDERATION OF CARBON COMPOUNDS, 
 OR ORGANIC CHEMISTRY. 
 
 40. INTRODUCTORY REMARKS. ELEMENTARY ANALYSIS. 
 
 Definition of organic chemistry. The term organic chemistry 
 was originally applied to the consideration of compounds formed in 
 plants and in the bodies of animals, and these compounds were 
 believed to be created by a mysterious power, called " vital force/' 
 supposed to reside in the living organism. 
 
 This assumption was partly justified by the failure of the earlier 
 attempts to produce these compounds by artificial means, and also by 
 the fact that the peculiar character of the compounds, and the 
 numerous changes which they constantly undergo in nature, could 
 not be sufficiently explained by the experimental methods then 
 known, and the laws then established. 
 
 It was in accordance with these views that a strict distinction was 
 made between inorganic and organic compounds, and accordingly 
 between inorganic and organic chemistry, the latter branch of the 
 science considering the substances formed in the living organism 
 and those compounds which were produced by their decomposition. 
 
 Since that time it has been shown that many substances which 
 formerly were believed to be produced exclusively in the living 
 organism, under the influence of the so-called vital force, can be 
 formed artificially from inorganic matter, or by direct combination 
 of the elements. It was in consequence of this fact that the theory 
 of the supposed " vital force," by which organic substances could be 
 formed exclusively, had to be abandoned. 
 
 The first instance of the preparation of an organic compound from inorganic 
 material occurred in 1828, when Wohler discovered that an aqueous solution 
 of ammonium cyanate, on evaporation, yields crystals of urea. The latter up 
 
 439 
 
440 CONSIDERATION OF CARBON COMPOUNDS. 
 
 to that time had been believed to be formed in the animal system exclusively. 
 As potassium cyanate may be obtained by oxidation of the cyanide, and as the 
 latter can be made by passing nitrogen over a heated mixture of potassium 
 carbonate and carbon, it follows that urea can be made from the elements. 
 
 The conversion of ammonium cyanate into urea is due to a rearrangement 
 of the atoms within the molecule, thus: 
 
 Ammonium cyanate. Urea. 
 
 An organic compound, according to modern views, is simply a 
 compound of carbon generally containing hydrogen, frequently also 
 oxygen and nitrogen, and sometimes other elements. As this defini- 
 tion would include carbonic acid and its salts, such as marble, CaCO 3 , 
 spathic iron ore, FeCO 3 , and others i.e. 9 substances which we are 
 accustomed to look upon as belonging to the mineral kingdom it is 
 better to omit carbon dioxide, carbonic acid, and carbonates, and 
 define organic compounds as compounds containing carbon in a com- 
 bustible form. 
 
 The definition usually given is : Organic chemistry is the chemistry 
 of the hydrocarbons and their derivatives. Hydrocarbons, as the name 
 implies, are compounds of carbon and hydrogen, which are to organic 
 chemistry what the elements are to inorganic chemistry. 
 
 In a strictly systematically arranged text-book of chemistry organic com- 
 pounds should be considered in connection with the element carbon itself, 
 but as these carbon compounds are so numerous, their composition often so 
 complicated, and the decompositions which they suffer under the influence of 
 heat or other agents so varied, it has been found best for purposes of instruc- 
 tion to defer the consideration of these compounds until the other elements and 
 their combinations have been studied. 
 
 Elements entering- into organic compounds. Organic com- 
 pounds contain generally but a small number of elements. These 
 are, besides carbon, chiefly hydrogen, oxygen, and nitrogen, and 
 sometimes sulphur and phosphorus. Other elements, however, enter 
 occasionally into organic compounds, and by artificial means all 
 metallic and non-metallic elements may be made to enter into organic 
 combinations. 
 
 Here the question presents itself: Why is it that the four elements 
 carbon, hydrogen, oxygen, and nitrogen are capable of producing 
 such an immense number (in fact, millions) of different combinations? 
 To this question but one answer can be given, which is that these 
 four elements differ more widely from each other, in their chemical 
 and physical properties, than perhaps any other four elements. 
 
 Carbon is a black, solid substance, which can scarcely be fused 
 
INTRODUCTORY REMARKS. 441 
 
 or volatilized, while hydrogen, oxygen, and nitrogen are colorless 
 gases which can only be converted into liquids with difficulty. More- 
 over, hydrogen is very combustible, oxygen is a supporter of combus- 
 tion, while nitrogen is perfectly indifferent. Finally, hydrogen is 
 univalent, oxygen bivalent, nitrogen trivalent, and carbon quadri- 
 valent. These elements are, therefore, capable of forming a greater 
 number and a greater variety of compounds than would be the case 
 if they were elements of equal valence and of similar properties. 
 
 It will be shown later that carbon atoms have, to a higher degree 
 than the atoms of any other element, the power of combining with one 
 another by means of a portion of the affinities possessed by each atom, 
 thus increasing the possibilities of the formation of complex compounds. 
 
 The number of thoroughly investigated organic compounds is estimated at 
 150,000, and each year is increased by 8000 to 9000. 
 
 General properties of organic compounds. The substances 
 formed by the union of the four elements just mentioned have prop- 
 erties in some respects intermediate to those of their components. 
 Thus, no organic substance is as permanently solid l as carbon, nor 
 as permanently gaseous as hydrogen, oxygen, and nitrogen. 
 
 Some organic substances are solids, others liquids, others gases ; 
 generally they are solids when the carbon atoms predominate ; they 
 are liquids or gases when the gaseous elements, and especially hydro- 
 gen, predominate ; likewise, it may also be said that compounds con- 
 taining a small number of atoms in the molecule are gases or liquids 
 which are easily volatilized ; they are liquids of high boiling- 
 points, or solids, when the number of atoms forming the molecules 
 is large. 
 
 The combustible property of carbon and hydrogen is transferred 
 to all organic substances, every one of which will burn when suffi- 
 ciently heated in atmospheric air. (If carbon dioxide, carbonic acid 
 and its salts be considered organic compounds, we have an exception 
 to the rule, as they are not combustible.) 
 
 The properties possessed by organic compounds are many and 
 widely different. There are organic acids, organic bases, and organic 
 neutral substances; there are some organic compounds which are 
 perfectly colorless, tasteless, and odorless, while others show every 
 possible variety of color, taste, and odor ; many serve as food, while 
 others are most poisonous ; in short, organic substances show a greater 
 variety of properties than the combinations formed by any other 
 four elements. 
 
 1 Non-volatile organic substances are decomposed by heat with generation of volatile 
 products. 
 
442 CONSIDERATION OF CARBON COMPOUNDS. 
 
 And yet, the cause of all the boundless variety of organic matter 
 is that peculiar attraction called chemical affinity, acting between the 
 atoms of a comparatively small number of elements and uniting them 
 in many thousand different proportions. 
 
 It would, of course, be entirely inconsistent with the object of 
 this book, if all the many organic substances already known (the 
 number of which is continually being increased by new discoveries) 
 were to be considered, or even mentioned. It must be sufficient to 
 state the general properties of the various groups of organic sub- 
 stances, to show by what processes they are produced artificially or 
 how they are found in nature, how they may be recognized and 
 separated, and, finally, to point out those members of each group 
 which claim a special attention for one reason or another. 
 
 Difference in the analysis of organic and inorganic sub- 
 stances. The analysis of organic substances differs from that of 
 inorganic substances, in so far as the qualitative examination of an 
 organic substance furnishes in many cases but little proof of the true 
 nature of the substance (except that it is organic), while the quali- 
 tative analysis of an inorganic substance discloses in most cases the 
 true nature of the substance at once. 
 
 For instance : If a white, solid substance, upon examination, be 
 found to contain potassium and iodine, and nothing else, the conclu- 
 sion may at once be drawn that the compound is potassium iodide, 
 containing 38.86 parts by weight of potassium, and 125.9 parts by 
 weight of iodine. Or, if another substance be examined, and found 
 to be composed of mercury and chlorine, the conclusion may be drawn 
 that the compound is either mercurous or mercuric chloride, as no 
 other compounds containing these two elements are known, and 
 whether the examined substance be the lower or higher chloride of 
 mercury, or a mixture of both, can easily be determined by a few 
 simple tests. 
 
 While thus the qualitative examination discloses the nature of the 
 substance, it is different with organic compounds. Many thousand 
 times the analysis might show carbon, hydrogen, and oxygen to be 
 present, and yet every one of the compounds examined might be 
 entirely different ; it is consequently not only the quality of the ele- 
 ments, but chiefly the quantity present which determines the nature 
 of an organic substance, and in order to identify an organic substance 
 with certainty, it frequently becomes necessary to make a quantitative 
 determination of the various elements present, and this quantitative 
 analysis is generally called ultimate or elementary analysis. 
 
INTRODUCTORY REMARKS. 443 
 
 There are, however, for many organic substances such character- 
 istic tests that these substances may be recognized by them ; these 
 reactions will be mentioned in the proper places. 
 
 An analysis by which different organic substances, when mixed 
 together, are separated from each other is frequently termed proximate 
 analysis. Such an analysis includes the separation and determination 
 of essential oils, fats, alcohols, sugars, resins, organic acids, albuminous 
 substances, etc., and is one of the most difficult branches of analytical 
 chemistry. 
 
 Qualitative analysis of organic substances. The presence of 
 carbon in a combustible form is decisive in regard to the organic 
 nature of a compound. If, consequently, a substance burns with 
 generation of carbon dioxide (which may be identified by passing the 
 gas through lime-water), the organic nature of this substance is 
 established. (See Chapter on Carbon.) 
 
 The presence of hydrogen can be proven by allowing the gaseous 
 products of the combustion to pass through a cool glass tube, when 
 drops of water will be deposited. 
 
 It is difficult to show by qualitative analysis the presence or 
 absence of oxygen in an organic compound, and its determination is 
 therefore generally omitted. 
 
 The presence of nitrogen is determined by heating the substance 
 with dry soda-lime (a mixture of two parts of calcium hydroxide and 
 one part of sodium hydroxide), when the nitrogen is converted into 
 ammonia gas, which may be recognized by its odor or by its action 
 on paper moistened with solution of cupric sulphate, a dark-blue 
 color indicating ammonia. 
 
 Ultimate or elementary analysis. While the student must be 
 referred to books on analytical chemistry for a detailed description of 
 the apparatus required and the methods employed for elementary 
 analysis, it may here be stated that the quantitative determination of 
 carbon and hydrogen is generally accomplished by the following pro- 
 cess : A weighed quantity of the pure and dry substance is mixed 
 with a large excess of dry cupric oxide, and this mixture is introduced 
 into a glass tube, the open end of which is connected by means of a 
 perforated cork and tubing with two glass vessels, the first one of 
 which (generally a U-shaped tube) is filled with pieces of calcium 
 chloride, the other (usually a tube provided with several bulbs) with 
 solution of potassium hydroxide. The two glass vessels, containing 
 the absorbents named, are weighed separately after having been 
 
444 CONSIDERATION OF CARBON COMPOUNDS. 
 
 filled. Upon heating the combustion-tube in a suitable furnace, the 
 organic matter is burned by the oxygen of the cupric oxide, the 
 hydrogen is converted into water (steam), which is absorbed by the 
 calcium chloride, and the carbon is converted into carbon dioxide, 
 which is absorbed by the potassium hydroxide. The apparatus repre- 
 sented in Fig. 68 shows the gas-furnace in which rests the coinbustion- 
 
 FIG. 68. 
 
 Gas-furnace for organic analysis. 
 
 tube with calcium chloride tube and potash bulb attached. Upon 
 re-weighing the two absorbing vessels at the end of the operation, the 
 increase in weight will indicate the quantity of water and carbon 
 dioxide formed during the combustion, and from these figures the 
 amount of carbon and hydrogen present in the organic matter may 
 easily be calculated. 
 
 For instance : 0.81 gramme of a substance having been analyzed, 
 furnishes, of carbon dioxide 1.32 gramme, and of water 0.45 gramme. 
 As every 44 parts by weight of carbon dioxide contain 12 parts by 
 weight of carbon, the above 1.32 gramme contains of carbon 0.36 
 gramme, or 44.444 per cent. As every 17.88 parts of water contain 
 2 parts of hydrogen, the above 0.45 gramme consequently contains 
 0.0503 gramme, or 6.213 per cent. 
 
 Oxygen is scarcely ever determined directly, but generally indi- 
 rectly, by determining the quantity of all other elements and deduct- 
 ing their weight, calculated to percentages from 100. The difference 
 is oxygen. 
 
 If, in the above instance, 44.444 per cent, of carbon and 6.213 per 
 cent, of hydrogen were found to be present, and all other elements, 
 
INTRODUCTORY REMARKS. 445 
 
 except oxygen, to be absent, the quantity of oxygen is, then, equal 
 to 49.384 per cent, and the composition of the substance is as 
 follows : 
 
 Carbon . 44.444 per cent. 
 
 Hydrogen 6.213 " 
 
 Oxygen 49.343 
 
 100.000 
 
 Determination of nitrogen. Nitrogen is generally determined 
 by the Kjeldahl method, which consists in boiling in a suitable flask a 
 weighed quantity of the organic compound with 30 to 40 times its 
 weight of sulphuric acid and a little potassium permanganate or mer- 
 curic oxide. By this treatment all nitrogen present is converted into 
 ammonium sulphate, from which by the addition of an excess of 
 sodium hydroxide ammonia is liberated. This ammonia is distilled 
 over into a known volume of normal acid. By titration with normal 
 alkali the unsaturated portion of acid is determined and from the 
 result the percentage of nitrogen is calculated. 
 
 Nitrogen may also be determined by the Will- Varr entrap method, which is 
 based on the formation of ammonia whenever nitrogenous matter is heated 
 with soda-lime (a mixture of sodium hydroxide and calcium oxide). The 
 method is not applicable to all compounds, because the nitrogen of some is not 
 all converted into ammonia by the process. 
 
 A third method, known as the Dumas or absolute method, consists in oxidiz- 
 ing, at a red heat, the nitrogenous substance by means of cupric oxide and 
 then decomposing, by means of highly-heated metallic copper, any oxide of 
 nitrogen which may have been formed. By this operation all nitrogen is 
 obtained in the elementary state ; it is collected, measured, and from the volume 
 the weight is calculated. 
 
 For the details of manipulation in the above method, which are simply out- 
 lined, large works on quantitative analysis must be consulted. 
 
 Determination of sulphur and phosphorus. These elements are 
 determined by mixing the organic substance with sodium carbonate 
 and nitrate, and heating the mixture in a crucible. The oxidizing 
 action of the nitrate converts all carbon into carbon dioxide, hydrogen 
 into water, sulphur into sulphuric acid, phosphorus into phosphoric 
 acid. The latter two acids combine with the sodium of the sodium 
 carbonate, forming sulphate and phosphate of sodium. The fused 
 mass is dissolved in water, and sulphuric acid precipitated by barium 
 chloride in the acidified solution, phosphoric acid by magnesium 
 sulphate and ammonium hydroxide and chloride. From the weight 
 of barium sulphate and magnesium pyrophosphate (obtained by heat- 
 ing the magnesium ammonium phosphate) the weight of sulphur and 
 phosphorus is calculated. 
 
446 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Determination of atomic composition from results obtained 
 by elementary analysis. The elementary analysis gives the quan- 
 tity of the various elements present in percentages, and from these 
 figures the relative number of atoms may be found by dividing the 
 figures by the respective atomic weights. For instance : The analysis 
 above mentioned gave the composition of a compound, as carbon 
 44.444 per cent,, hydrogen 6.213 per cent., and oxygen 49.343 per 
 cent. By dividing each quantity by the atomic weight of the respec- 
 tive element, the following results are obtained : 
 
 11.91 
 
 = 3.731 
 
 La 
 
 15.88 
 
 49 ' 34; =3.107 
 
 The figures 3.731, 6.213, and 3.107 represent the relative number 
 of atoms present in a molecule of the compound examined. In order 
 to obtain the most simple proportion expressing this relation, the 
 greatest divisor common to the whole has to be found, a task which 
 is sometimes rather difficult on account of slight errors made in the 
 quantitative determination itself. In the above case, 0.6213 is the 
 greatest divisor, which gives the following results : 
 
 3.731 6.213 _ . 3.107 
 
 0.6213 ' 0.6213 ' 0.6213 
 
 The simplest numbers of atoms are, accordingly, carbon 6, hydrogen 
 10, oxygen 5, or the composition is C 6 H 10 O 5 . 
 
 Empirical and molecular formulas. A chemical formula is 
 termed empirical when it merely gives the simplest possible expression 
 of the composition of a substance. In the above case, the formula 
 C 6 H 10 O 5 would be the empirical formula. It might, however, be 
 possible that this formula did not represent the actual number of 
 atoms in the molecule, which might contain, for instance, twice or 
 three times the number of atoms given, in which case the true com- 
 position would be expressed by the formula C 12 H 20 O 10 or C 18 H 30 O 15 . 
 
 If it could be proven that one of the latter formulas is the correct 
 one, it would be termed the molecular formula, because it expresses 
 not only the numerical relations existing between the atoms, but also 
 the absolute number of atoms of each element contained in the 
 molecule. 
 
ELEMENTARY ANALYSIS. 447 
 
 The best method for determining the actual number of atoms con- 
 tained in the molecule is the determination of the specific weight of 
 the gaseous compound, taking hydrogen as the unit. For instance : 
 Assume the analysis of a liquid substance gave the following result : 
 
 Carbon 92.308 per cent. 
 
 Hydrogen 7-692 " 
 
 100.000 
 
 From this result the empirical formula, CH, is deduced by apply- 
 ing the method stated above. If this formula were the molecular 
 formula, the density of the vapors of the substance would, when com- 
 pared with hydrogen (according to the law of Avogadro), be equal to 
 6.455, because a molecule of hydrogen weighs 2 and a molecule of the 
 compound CH weighs 12.91. 
 
 Suppose, however, the density of the gaseous substance is found to 
 be 38.73, then the molecular formula would be expressed by C 6 H 6 , 
 because its molecular weight (6 X 11.91 -f 6 X 1) is equal to 77.46, 
 which weight, when compared with the molecular weight of hydrogen 
 = 2, gives the proportions 77.46 : 2, or 38.73 : 1. 
 
 Not all organic compounds can be converted into gases or vapors 
 without undergoing decomposition, and the determination of the 
 molecular formulas of such compounds has to be accomplished by 
 other methods. If the substance, for instance, is an acid or a base, 
 the molecular formula may be determined by the analysis of a salt 
 formed by these substances. For instance : The empirical formula of 
 acetic acid is CH 2 O ; the analysis of the potassium acetate, however, 
 shows the composition KC 2 H 3 O 2 , from which the molecular formula 
 HC 2 H 3 O 2 is deduced for acetic acid. 
 
 In many cases, however, it is as yet absolutely impossible to give 
 with certainty the molecular formula of some compounds. 
 
 Rational, constitutional, structural, or graphic formulas. 
 These formulas are intended to represent the theories which have 
 been formed in regard to the arrangement of the atoms within the 
 molecule, or to represent the modes of the formation and decom- 
 position of a compound, or the relation which allied compounds bear 
 to one another. 
 
 The molecular formula of acetic acid, for instance, is C 2 H 4 O 2 , but 
 different constitutional formulas have been used to represent the 
 structure of the acetic acid molecule. 
 
 Thus, H.C 2 H 3 O 2 is a formula analogous to H.NO 3 , indicating that 
 acetic acid (analogous to nitric acid), is a monobasic acid, containing 
 one atom of hydrogen, which can be replaced by metallic atoms. 
 
448 CONSIDERATION OF CARBON COMPOUNDS. 
 
 C H O.OH 1 is a formula indicating that acetic acid is composed of 
 two univalent radicals which may be taken out of the molecule and 
 replaced by other atoms or groups of atoms. This formula indicates 
 also that acetic acid is analogous to hydroxides, the radical C 2 H 3 O 
 having replaced one atom of hydrogen in H 2 O. 
 
 CH .CO 2 H l is a formula indicating that acetic acid is composed of 
 the two compound radicals, methyl and carboxyl. 
 
 It may be said finally, that quite a number of other rational 
 formulas have been applied, or, at least, have been proposed by 
 different chemists and at different times, to represent the structure of 
 acetic acid, but it should be remembered that these formulas are not 
 intended to represent the actual arrangement of the atoms in space, 
 but only, as it were, their relative mode of combination, showing 
 which atoms are combined directly and which only indirectly, that 
 is, through the medium of others. 
 
 41. CONSTITUTION, DECOMPOSITION, AND CLASSIFICATION 
 OF ORGANIC COMPOUNDS. 
 
 Radicals or residues. The nature of a radical or residue has 
 been stated already in Chapter 8, but the important part played by 
 radicals in organic compounds renders it necessary to consider them 
 more fully. 
 
 In most compounds there is one or several groups of atoms which re- 
 main unchanged in the various reactions to which the compounds may 
 be submitted. The group behaves like a unit or an element, although 
 it cannot exist in the free state. Such groups are called radicals. 
 
 QUESTIONS. What is organic chemistry, according to modern views ? Men- 
 tion the four chief elements entering into organic compounds, and name the 
 elements which may be made to enter into organic compounds by artificial 
 processes. State the reason why the four elements, carbon, hydrogen, oxy- 
 gen, and nitrogen, are better adapted to form a larger number of compounds 
 than most other elements. State the general properties of organic compounds. 
 Why does a qualitative analysis of an organic*com pound, in most cases, 'not 
 disclose its true nature? By what test may the organic nature of a compound 
 be established? By what tests may the^ presence of carbon, hydrogen, and 
 nitrogen be demonstrated in organic compounds? State the methods by which 
 the elements carbon, hydrogen, oxygen, sulphur, and phosphorus are deter- 
 mined quantitatively. By what general method may a formula be deduced 
 from the results of a quantitative analysis ? What is meant by an empirical, 
 molecular, and constitutional formula ; how are they determined, and what is 
 the difference between them ? 
 
CONSTITUTION OF ORGANIC COMPOUNDS. 449 
 
 Kadicals exist in organic and inorganic compounds ; an inorganic 
 radical spoken of heretofore is the water residue or hydroxyl, OH, 
 obtained by removal of one atom of hydrogen from one molecule of 
 water. Hydroxyl does not exist in the separate state, but it exists in 
 hydrogen dioxide, H 2 O 2 , or HO OH, and is also a constituent of the 
 various hydroxides, as, for instance, of KOH, Ca(OH) 2 , Fe(OH) 3 , etc. 
 
 If one atom of hydrogen be removed from the saturated hydro- 
 carbon methane, CH 4 , the univalent residue methyl, CH 3 , is left, 
 which is capable of combining with univalent elements, as in methyl 
 chloride, CH 3 C1, or, with univalent residues, as in methyl hydroxide, 
 CH 3 OH. 
 
 If two atoms of hydrogen be removed from CH 4 , the bivalent resi- 
 due methylene, CH 2 , is left, capable of forming the compounds 
 CH 2 C1 2 , CH 2 (OH) 2 , etc. 
 
 If three atoms of hydrogen be removed from CH 4 , the trivalent 
 residue CH is left, capable of combining with three atoms of univa- 
 lent elements, as in CHC1 3 , or with another trivalent radical, etc. 
 
 Chains. The expression, chain, designates a series of multivalent 
 atoms (generally, but not necessarily, of the same element), held 
 together by one or more affinities. While such linkage of atoms into 
 chains occurs with a number of elements, it appears that silicon and 
 carbon have a greater tendency to form chains than other elements. 
 
 The linkage of carbon atoms may be represented thus : 
 
 II III I I I I 
 
 _C C , C C C , C C C C , etc. 
 
 II III till 
 
 The above carbon chains have 6, 8, and 10 available affinities, 
 respectively, which may be saturated by the greatest variety of atoms 
 or radicals. The chain combination of carbon, above indicated by the 
 first three members of a series, may, as far as is known, be continued 
 indefinitely. This fact, in connection with the possibility of saturating 
 the other affinities with various atoms or radicals, indicates the almost 
 unlimited number of possible combinations to be formed in this way. 
 In fact, the existence of such an enormous number of carbon com- 
 pounds is greatly due to the property of carbon to form these chains. 
 
 It is not always the case that the atoms when forming a chain are 
 united by one affinity only, as above, but they may be united by two 
 or three affinities, as indicated by the compounds C 2 H 4 and C 2 H 2 , the 
 graphic formulas of which may be represented by 
 
 H \ / H 
 
450 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Finally, it is assumed that the carbon atoms are united partially 
 by double and partially by single union, as, for instance, in the so- 
 called closed chain of C 6 , capable of forming the hydrocarbon benzene, 
 C 6 H 6 : 
 
 H 
 
 \ C A C / H \c/ 
 
 A C A H A C A H 
 
 ' i 
 
 A chain has also been termed a skeleton, because it is that part of an organic 
 compound around which the other elements or radicals arrange themselves, 
 filling up, as it were, the unsaturated affinities. 
 
 Homologous series. This term is applied to any series of organic 
 compounds the terms or members of which, preceding or following 
 each other, differ by CH 2 , Moreover, the general character, the con- 
 stitution, and the general properties of the members of an homologous 
 series are similar. 
 
 The explanation regarding the formation of an homologous series 
 is to be found in the above-described property of carbon to form 
 chains. By saturating, for instance, the affinities in the open carbon 
 chains mentioned above, we obtain the compounds CH 4 , C 2 H 6 , C 3 H 8 , 
 C 4 H 10 , etc. 
 
 H HH HHH HHHH 
 
 H-C-H, H-C-C-H, H-C-C-C-H, H-C-C-C-C-H, 
 
 H HH HHH HHHH 
 
 Many homologous series of various organic compounds are known, 
 as, for instance : 
 
 C H 3 Cl, C H 4 O, C H 2 2 . 
 
 C 2 H 5 Cl, C 2 H 6 O, C 2 H 4 2 . 
 
 QA Cl, C 3 H 8 O, C 3 H 6 2 . 
 
 C 4 H 9 C1, C 4 H 10 0, C 4 H 8 2 . 
 
 c 5 H n ci, cjr.A cjw 
 
 etc. etc. etc- 
 
 Substitution is a term used for those reactions or chemical changes 
 which depend on the replacement of an atom or a group of atoms by 
 other atoms or groups of atoms. Substitution takes place in organic 
 or inorganic substances, and its nature may be illustrated by the fol- 
 lowing instances : 
 
 etc. 
 
CONSTITUTION OF ORGANIC COMPOUNDS. 451 
 
 K + H 2 O = KOH + H. 
 Potassium. Water. Potassium Hydrogen. 
 hydroxide. 
 
 C 2 H 4 2 + 2C1 : C 2 H 3 C10 2 + HC1. 
 Acetic acid. Chlorine. Monochloracetic Hydrochloric 
 acid. " acid. 
 
 C 6 H 6 + HN0 3 = C 6 H 5 N0 2 + H 2 O. 
 Benzene. Nitric acid. Nitro-benzene. Water. 
 
 Derivatives. This term is applied to bodies derived from others 
 by some kind of decomposition, generally by substitution. Thus, 
 nitro-benzene is a derivative of benzene; chloroform, CHC1 3 , is a 
 derivative of methane, CH 4 , obtained from the latter by replacement 
 of three atoms of hydrogen by the same number of atoms of chlorine. 
 
 Isomerism. Two or more substances may have the same elements 
 in the same proportion by weight (or the same centesimal composi- 
 tion), and yet be different bodies, showing different properties. Such 
 substances are called isomeric bodies. Three kinds of isomerism are 
 distinguished, viz., metamerism, polyinerism, and stereo-isomerism. 
 
 Metamerism. Substances are metameric when their molecules con- 
 tain equal numbers of atoms of the same elements. Thus, cane- 
 sugar and milk-sugar have both the composition C 12 H 22 O n , and yet 
 they have different physical properties, and may be distinguished by 
 their solubility and by a number of characteristic tests. 
 
 The explanation given regarding this difference of properties is, 
 that the atoms are arranged differently within the molecule. In 
 some cases this arrangement is as yet unknown, in other cases struc- 
 tural or graphic formulas showing this atomic arrangement may be 
 given. 
 
 For instance : Acetic acid and methyl formate both have the com- 
 position C 2 H 4 O 2 , but the arrangement of the atoms (or the structure) 
 is very different, as shown by the formulas : 
 
 Acetic acid. Methyl formate. 
 
 C 2 H S 0\ CHO\ 
 
 a 0< 
 
 CH 3 X 
 
 As another instance may be mentioned the compound CN 2 H 4 O, 
 which represents either ammonium cyanate or urea : 
 
 Ammonium cyanate. Urea. 
 
 NH 4 \ NH A CO 
 
 CN/ U NH 2 / OU ' 
 
 Polymerism. Substances are said to be polymeric when they have 
 the same centesimal composition, but a different molecular weight, or. 
 
452 CONSIDERATION OF CARBON COMPOUNDS. 
 
 in other words, when one substance contains some multiple of 
 the number of each of the atoms contained in the molecule of the 
 
 other. 
 
 For instance, some volatile oils have the composition C 20 H 32 , which 
 is double the number of atoms contained in oil of turpentine, C 10 H 16 ; 
 acetylene, C 2 H 2 , is polymeric with benzene, C 6 H 6 , and styrene, C 8 H 8 ; 
 formaldehyde, CH 2 O, acetic acid, C 2 H 4 O 2 > lactic acid, C 3 H 6 O 3 > and 
 glucose, C 6 H 12 O 6 , are polymeric compounds. 
 
 Stereo-isomerism. There has long been known a number of 
 bodies having the same molecular and constitutional formulas (i. e., 
 behaving alike chemically), but which exhibit differences in prop- 
 erties, as, -for instance, in their behavior toward polarized light 
 and in the form of their crystals. The explanation at present 
 given of these differences is based on this assumption : that the dif- 
 ferent atoms or radicals in combination with a carbon atom may 
 occupy toward it different relative positions, and that actually 
 they do. 
 
 In order to understand what is meant by this statement we should 
 bear in mind that we represent the grouping of our atoms on the 
 flat surface of paper, while actually the formation of molecules takes 
 place in space i. e. y in three directions. If we assume, for instance, 
 that four different radicals are in combination with a carbon atom, 
 we can well imagine that the relative positions in which these radicals 
 are grouped around the carbon atom have an influence on the nature 
 of the compound. There are bodies which contain the same elements 
 in the same quantities but in which the molecular structures seem to 
 be reversed, precisely as they would be if seen directly and then 
 observed after reflection from a mirror. In fact, there are known 
 isomeric bodies the crystals of which seem to exhibit exactly that 
 relation to each other. 
 
 The term stereo-isomerism is, therefore, used for that kind of 
 isomerism found in substances which contain apparently the same 
 radicals, show practically the same chemical behavior toward other 
 agents, but differ in certain physical properties. Of stereo-isomeric 
 substances may be mentioned 2 malic acids, 3 lactic acids, 4 tartaric 
 acids, etc. (For details of stereo-isomerism the student is referred 
 to works treating more fully on this subject.) 
 
 Various modes of decomposition. The principal changes which 
 a molecule may suffer are as follows : 
 
DECOMPOSITION OF ORGANIC COMPOUNDS. 453 
 
 a. The atoms may arrange themselves differently within the mole- 
 cule. Ammonium cyanate, NH 4 CNO, is easily converted into urea, 
 CO(NH 2 ) 2 . This is called molecular rearrangement. 
 
 b. A molecule may split up into two or more molecules. For 
 instance : 
 
 C 6 H 12 6 : : 2C 2 H 6 O + 2CO 2 . 
 Grape-sugar. Alcohol. Carbon dioxide. 
 
 This decomposition is spoken of as cleavage. When cleavage is 
 accompanied by the taking up of the constituents of water the change 
 is called hydrolytic cleavage or hydrolysis. The following reaction 
 belongs to this class : 
 
 C 9 H 9 NO 3 + H 2 O = C 7 H60 2 + C 2 H 3 NH 2 O 2 . 
 
 Hippur'ic acid. Benzoic acid. Glycocoll. 
 
 c. Two molecules, either of the same kind, or of different sub- 
 stances, may unite directly : 
 
 C 2 H 4 -f 2Br = C 2 H 4 Br 2 . 
 Ethylene. Bromine. Ethylene bromide. 
 
 d. Atoms may be removed from a compound without replacing 
 them by other atoms : 
 
 C 2 H 6 + O = C 2 H 4 O + H 2 O. 
 Alcohol. Oxygen. Aldehyde. Water. 
 
 e. Atoms may be removed and replaced by others at the same 
 time (substitution) : 
 
 C 2 H 4 O 2 + 2C1 = C 2 H 3 C1O 2 + HC1. 
 
 Acetic acid. Chlorine. Monochloracetic Hydrochloric 
 acid. acid. 
 
 Action of heat upon organic substances. As a general rule, 
 organic bodies are distinguished by the facility with which they 
 decompose under the influence of heat or chemical agents ; the more 
 complex the body is, the more easily does it undergo decomposition 
 or transformation. 
 
 Heat acts differently upon organic substances, some of which may 
 be volatilized without decomposition, while others are decomposed 
 by heat with generation of volatile products. This process of heating 
 non-volatile organic substances in such a manner that the oxygen of 
 the atmospheric air has no access, and to such an extent that decom- 
 position takes place, is called dry or destructive distillation. 
 
 The nature of the products formed during this process varies not 
 only with the nature of the substance heated, but also with the tem- 
 perature applied during the operation. The products formed by 
 destructive distillation are invariably less complex in composition, 
 
454 CONSIDERATION OF CAftSON COMPOUNDS. 
 
 that is, have a smaller number of atoms in the molecule, than the 
 substance which suffered decomposition ; in other words, a complex 
 molecule is split up into two or more molecules less complex in 
 composition. 
 
 Otherwise, the products formed show a great variety of properties ; 
 some are gases, others volatile liquids or solids, some are neutral, 
 others basic or acid substances. In most cases of destructive distilla- 
 tion a non-volatile residue is left, which is nearly pure carbon. 
 
 Action of oxygen upon organic substances. Combustion. 
 Decay. All organic substances are capable of oxidation, which 
 takes place either rapidly with the evolution of heat and light and is 
 called combustion, or it takes place slowly without the emission of 
 light, and is called slow combustion or decay. The heat generated 
 during the decay of a substance is the same as that generated by 
 burning the substance ; but as this heat is liberated in the first 
 instance during weeks, months, or perhaps years, its generation is so 
 slow that it can scarcely be noticed. 
 
 No organic substance found or formed in nature contains a suffi- 
 cient quantity of oxygen to cause the complete combustion of the 
 combustible elements (carbon and hydrogen) present; by artificial 
 processes such substances may, however, be produced, and are then 
 either highly combustible or even explosive. 
 
 During common combustion, provided an excess of atmospheric oxygen be 
 present, the total quantity of carbon is converted into carbon dioxide, hydrogen 
 into water, sulphur and phosphorus into sulphuric and phosphoric acids, while 
 nitrogen is generally liberated in the elementary state. 
 
 During the process of decay the compounds mentioned above are produced 
 finally, although many intermediate products are generated. For instance : If 
 a piece of wood be burnt, complete oxidation takes place ; intermediate pro- 
 ducts also are formed chiefly in consequence of the destructive distillation of 
 a portion of the wood, but they are consumed almost as fast as they are pro- 
 duced, as was mentioned in connection with the consideration of flame. Again, 
 when a piece of wood is exposed to the action of the atmosphere, it slowly 
 burns or decays. The intermediate products formed in this case are entirely 
 different from those produced during common combustion. 
 
 Common alcohol has the composition C 2 H 6 O ; in burning, it requires 
 six atoms of oxygen, when it is converted into carbon dioxide and water : 
 C a HO + 60 = 2C0 3 + 3H 2 O. 
 
 But alcohol may also undergo slow oxidation, in which case oxygen 
 first removes hydrogen, with which it combines to form water, while 
 at the same time a compound known as acetic aldehyde, C 2 H 4 O, is 
 formed : 
 
DECOMPOSITION OF ORGANIC COMPOUNDS. 455 
 
 C 2 H 6 -f O C 2 H 4 -f H a O. 
 
 This aldehyde, when further acted upon by oxygen, takes up an 
 atom of this element, thereby forming acetic acid : 
 
 C 2 H 4 + O = : C 2 H 4 2 
 
 The three instances given above illustrate the action of oxygen 
 upon organic substances, which action may consist in a mere removal 
 of hydrogen, in a replacement of hydrogen by oxygen, or in an 
 oxidation of both the carbon and hydrogen, and also of sulphur and 
 phosphorus, if they be present. 
 
 An organic substance, when perfectly dry and exposed to dry air 
 only, may not suffer decay for a long time (not even for centuries), 
 but in the presence of moisture and air this oxidizing action takes 
 place almost invariably. 
 
 Besides the slow oxidation or decay which all dead organic matter 
 undergoes in the presence of moisture, there is another kind of slow 
 oxidation, called respiration, which takes place in the living animal ; 
 this process will be more fully considered in the physiological part of 
 this book. 
 
 Fermentation and putrefaction. These terms are applied to 
 peculiar kinds of decomposition, by which the molecules of certain 
 organic substances are split up into two or more molecules of a less 
 complicated composition. These decompositions take place when 
 three factors are simultaneously acting upon the organic substance. 
 These factors are : presence of moisture, favorable temperature, and 
 presence of a substance generally termed ferment. 
 
 The most favorable temperature for these decompositions lies 
 between 25 and 40 C. (77 and 104 F.), but they may take place 
 at lower or higher temperatures. No substance, however, will either 
 ferment or putrefy at or below the freezing-point, or at or above the 
 boiling-point of water. 
 
 The nature of the various ferments differs widely, and their true 
 action cannot, in many cases, be explained; what we do know is, 
 that the presence of comparatively small (often minute) quantities of 
 one substance (the ferment) is sufficient to cause the decomposition of 
 large quantities of certain organic substances, the ferment itself suf- 
 fering often no apparent change during this decomposition. 
 
 Ferments have been divided into two classes : 1. Organized fer- 
 ments (sometimes called true ferments), being unicellular living micro- 
 organisms chiefly of vegetable origin. 2. Soluble ferments, unorganized 
 
456 CONSIDERATION OF CARBON COMPOUNDS. 
 
 ferments, or enzymes (false ferments) which are in most cases nitro- 
 genous substances closely related to the proteins. 
 
 This classification was based on the belief that the living cell itself 
 was the acting agent. It has, however, been shown that this view is 
 incorrect and that the decomposing influence exerted by these fer- 
 ments is due to some substance produced by the living cell, from 
 which it may be separated or extracted in a more or less pure condi- 
 tion. It is consequently more in conformity with our present views 
 to apply the term enzyme to that agent which causes the decomposi- 
 tion. Enzymes are always products of the cell action of a living 
 organism, but this organism may be a micro-organism, such as the 
 yeast cell ; or it may be a highly developed plant, such as the almond 
 tree which produces emulsine, an enzyme which decomposes amyg- 
 dalin ; or it may be an animal or man, generating such enzymes 
 as ptyalin, pepsin, etc. (Enzymes will be more fully considered 
 later on.) 
 
 The nature of the ferment generally determines the nature of the 
 decomposition which a substance suffers, or, in other words, one and 
 the same substance will under the influence of one ferment decom- 
 pose with liberation of certain products, while a second ferment 
 causes other products to be evolved. Sugar, for instance, under the 
 influence of yeast, is converted into alcohol and carbon dioxide, 
 while under the influence of certain other ferments it is converted 
 into lactic acid. 
 
 The difference between fermentation and putrefaction is that the 
 first term is used in those cases where the decomposing substance 
 belongs to the group of carbohydrates, all of which contain the 
 elements carbon, hydrogen, and oxygen only, while substances be- 
 longing to the proteins, which contain, in addition to these three 
 elements, also nitrogen and sulphur, undergo putrefaction. The two 
 last-named elements are generally evolved as ammonia or derivatives 
 of ammonia and hydrogen sulphide, which gases give rise to an 
 offensive odor, the putrefying mass being generally designated as 
 fetid matter. 
 
 As a general rule the oxygen of the air takes no part in either fer- 
 mentation or putrefaction, but the presence or absence of atmospheric 
 air may cause or prevent decomposition, inasmuch as the atmosphere 
 is filled with millions of bacteria, which may act as ferments when in 
 contact with organic matter under favorable conditions. 
 
DECOMPOSITION OP OttOANlC COMPOUNDS. 457 
 
 One of the fermentations in which oxygen takes part is acetic acid fermen- 
 tation, resulting in the conversion of alcohol into acetic acid by oxidation. 
 This conversion may be brought about by suitable oxidizing agents, or even by 
 atmospheric oxygen, and is then practically a slow combustion or decay. But 
 the transfer of oxygen may be brought about by micro-organisms and the pro- 
 cess is then defined as fermentation. 
 
 Whenever organic bodies (a dead animal, for instance) undergo de- 
 composition in nature, the processes of fermentation and putrefaction 
 are generally accompanied by oxidation or decay. 
 
 The conditions under which a substance will ferment or putrefy 
 have been stated above, and the non-fulfilment of these conditions 
 enables us to prevent decomposition artificially. 
 
 Thus, we make use of a low temperature in our refrigerators or by 
 cold storage. We expel water by drying or by dehydrating agents 
 such as absolute alcohol. We prevent the action of the ferments 
 either by antiseptic agents (salt, carbolic or salicylic acid, etc.) which 
 are incompatible with organic life, or by excluding the air, and with 
 it the ferments, by enclosing the substances in air-tight vessels (glass 
 jars, tin cans, etc.), which, when filled, are heated sufficiently to destroy 
 any bacteria which may have been present. 
 
 Antiseptics and disinfectants. While the term antiseptics is 
 applied to those substances which retard or prevent fermentation and 
 putrefaction, the term disinfectants refers to those agents actually 
 destroying the organisms which are the causes of these decomposi- 
 tions. If we assume that all infectious diseases are due to micro- 
 organisms, or germs of various kinds, disinfectants may be considered 
 as equivalent to germicides. Disinfectants are generally antiseptics 
 also, but the latter are not in all cases disinfectants. The solution 
 of a substance of certain strength may act as a disinfectant and 
 antiseptic, while the same solution diluted further may act as an 
 antiseptic only, but not as a disinfectant. 
 
 Deodorizers are those substances which convert the strongly smell- 
 ing products of decomposition into inodorous compounds. Strong 
 oxidizing agents are generally good deodorizers, as, for instance, 
 chlorine, potassium permanganate, hydrogen dioxide, etc. Among 
 the best antiseptics and disinfectants are mercuric chloride (a solution 
 of 1 : 500 or 1 : 1000) ; carbolic acid (5 per cent, solution) ; potassium 
 permanganate (5 per cent, solution) ; chlorine (generally used in the 
 form of a 4 per cent, solution of calcium hypochlorite) ; formaldehyde, 
 
458 CONSIDERATION OF CARBON COMPOUNDS. 
 
 used in solution or as a gas ; hydrogen peroxide, salicylic acid, boric 
 acid, sulphur dioxide, ferrous or cupric sulphate, alcohol, chloroform, 
 thymol, etc. 
 
 The selection of a disinfectant depends on the respective conditions. While 
 the relatively harmless salicylic acid is often used as a preservative for articles 
 of food it is the powerful but strongly poisonous mercuric chloride which is 
 used externally in the operating room. The surgeon disinfects his hands by 
 first scrubbing with soap and water, immersing in a saturated solution of potas- 
 sium permanganate and washing finally in solution of oxalic acid. The latter 
 removes through its deoxidizing and dissolving power that portion of the per- 
 manganate which adheres to the hands. For the disinfection of rooms gases^ 
 such as formaldehyde, sulphur dioxide or chlorine, are indicated. Instruments 
 may be disinfected by heat or by immersion in suitable solutions. 
 
 The term asepsis refers to the absence of living germs of fermentation, putre- 
 faction or disease, while the term sterilization is used for the process of destroy- 
 ing all living micro-organisms in the object or material operated on. Aseptic 
 conditions by means of sterilizing may be brought about either by the use of 
 antiseptic agents or by application of heat. 
 
 Action of chlorine and bromine. These two elements act upon 
 organic substances (similarly to oxygen) in three different ways, viz., 
 they either (rarely, however) combine directly with the organic sub- 
 stance, or remove hydrogen, or replace hydrogen. The following 
 equations illustrate this action : 
 
 C 2 H 4 + 2Br = C 2 H 4 Br 2 . 
 Ethylene. Bromine. Ethylene bromide. 
 
 C 2 H 6 + 2C1 : : G 2 H 4 + 2HC1. 
 Ethyl alcohol. Chlorine. Aldehyde. Hydrochloric acid. 
 
 C 2 H 4 2 + 2C1 C 2 H 3 C10 2 + HC1. 
 
 Acetic acid. Chlorine. Monochloracetic Hydrochloric 
 acid. acid. 
 
 In the presence of water, chlorine and bromine often act as oxidiz- 
 ing agents by combining with the hydrogen of the water and liber- 
 ating oxygen ; iodine may act in a similar manner as an oxidizing 
 agent, but it rarely acts directly by substitution. 
 
 Action of nitric acid. This substance acts either by direct com- 
 bination with organic bases forming salts, or as an oxidizing agent, 
 or by substitution of nitryl, NO 2 , for hydrogen. As instances of the 
 latter action may be mentioned the formation of nitro-benzene and 
 cellulose nitrate: 
 
DECOMPOSITION OF ORGANIC COMPOUNDS. 459 
 
 C 6 H 6 + HN0 3 = C 6 H 5 N0 2 + H 2 O. 
 Benzene. Nitric acid. Nitro-benzene. Water. 
 
 C 6 H ]0 5 + 3HN0 3 : C 6 H 7 N(V,0 5 + 3H 2 O. 
 Cellulose. Nitric acid. Cellulose trinitrate. Water. 
 
 The additional quantity of oxygen thus introduced into the mole- 
 cules renders them highly combustible, or even explosive. 
 
 Action of dehydrating- agents. Substances having a great 
 affinity for water, such as strong sulphuric acid, phosphoric oxide, 
 and others, act upon many organic substances by removing from them 
 the elements of hydrogen and oxygen, and combining with the water 
 formed, while, at the same time, frequently dark or even black com- 
 pounds are formed, which consist largely of carbon. The black 
 color imparted to sulphuric acid by organic matter depends on this 
 action. 
 
 Action of alkalies. The hydroxides of potassium and sodium 
 act in various ways on organic substances. 
 
 In some cases substitution products are decomposed : 
 
 C 2 H 5 C1 -f KOH KC1 -f C 2 H 5 OH. 
 
 Ethyl chloride. Potassium Potassium Ethyl alcohol, 
 
 hydroxide. chloride. 
 
 Salts are formed : 
 
 C 2 H 4 2 -f NaOH -= NaC 2 H 3 O 2 + H 2 O. 
 Acetic Sodium Sodium Water, 
 
 acid. hydroxide. acetate. 
 
 Fats are decomposed with the formation of soap : 
 
 C 3 H 5 (C 18 H 3 A) 3 + 3NaOH = C 3 H 5 (OH) 3 -f 3NaC 18 H 33 O 2 . 
 Oleate of glyceryl. Sodium hydroxide. Glycerin. Sodium oleate. 
 
 Oxidation takes place, while hydrogen is liberated : 
 
 C,H 6 O -f KOH = KC 2 H 3 O 2 -f 4H. 
 
 Ethyl Potassium Potassium Hydrogen, 
 
 alcohol. hydroxide. acetate. 
 
 From compounds containing nitrogen, ammonia is evolved : 
 
 NH 2 C 2 H 3 -f KOH KC 2 H 3 2 + NH 3 . 
 
 Acetamide. Potassium Potassium Ammonia, 
 
 hydroxide. acetate. 
 
 Action of reducing- agents. Deoxidizing or reducing agents, 
 especially hydrogen in the nascent state, act upon organic substances 
 either by direct combination : 
 
 C 2 H 4 O + 2H = C 2 H 6 0. 
 Acetic aldehyde. Ethyl alcohol. 
 
 or by removing oxygen (and also chlorine or bromine) : 
 
460 CONSIDERATION OF CARBON COMPOUNDS. 
 
 C 7 H 6 2 + 2H = C 7 H 6 + H 2 0. 
 Benzoic acid. Benzole aldehyde. 
 
 C 7 H 6 O + 2H = C 7 H 8 O. 
 Benzoic aldehyde. Benzylic alcohol. 
 
 In some cases hydrogen replaces oxygen : 
 
 C 6 H 5 N0 2 + 6H = C 6 H 5 NH 2 + 2H 2 O. 
 Nitro-benzene. Aniline. 
 
 Classification of organic compounds. There are great diffi- 
 culties in arranging the immense number of organic substances 
 properly, and in such a manner that natural groups are formed the 
 members of which are similar in composition and possess like 
 k properties. 
 
 Various modes of classification have been proposed, some of which, 
 however, are so complicated that the beginner will find it difficult to 
 make use of them. The grouping of organic substances here adopted, 
 while far from being perfect, has the advantages of being simple, 
 easily understood, and remembered. 
 
 1. Hydrocarbons. All compounds containing the two elements 
 carbon and hydrogen only. For instance, CH 4 , C 6 H 6 , C 10 H 16 , etc. 
 
 2. Alcohols. These are hydrocarbon radicals in combination 
 with hydroxyl, OH. For instance, ethyl alcohol, CjH^OH, glycerin, 
 C 3 H iii 5 (OH) 3 , etc. 
 
 3. Aldehydes. Hydrocarbon radicals in combination with the 
 radical COH ; they are compounds intermediate between alcohols 
 and acids, or alcohols from which hydrogen has been removed. 
 For instance : 
 
 C 2 H 6 0, CH 3 .COH, C 2 H 4 2 , 
 
 Ethyl alcohol. Aldehyde. Acetic acid. 
 
 4. Organic acids. Hydrocarbon radicals in combination with 
 carboxyl, a radical having the composition CO 2 H, or compounds 
 formed by replacement of hydrogen in hydrocarbons by carboxyl. 
 Instances : Acetic acid, CH 3 CO 2 H ; pyrotartaric acid, C 3 H 6 (CO 2 H) 2 . 
 
 5. Ethers. Compounds formed from alcohols by replacement of 
 the hydrogen of the hydroxyl by other hydrocarbon radicals, or, 
 what is the same, by other alcohol radicals. For instance : 
 
 Ethyl alcohol. Ethyl ether. Ethyl-methyl ether. 
 
 6. Compound ethers or esters. Formed from alcohols by replace- 
 ment of the hydrogen of the hydroxyl by acid radicals, or from acids 
 
DECOMPOSITION OF ORGANIC COMPOUNDS. 461 
 
 by replacement of the hydrogen of carboxyl by alcoholic radicals. 
 For instance : 
 
 Q . CH 3 CO\ C 2 H 5 \ H\ 
 
 C C ~ h 
 
 H/ ~ CH 3 CO/ 
 Ethyl alcohol. Acetic acid. Acetic ether. Water. 
 
 The various fats belong to this group of compound ethers. 
 
 7. Carbohydrates. (Sugars, starch, cellulose, etc.) These are 
 compounds of carbon, hydrogen, and oxygen, in which the number 
 of carbon and oxygen atoms is the same, while the number of 
 hydrogen atoms is double that of the oxygen atoms. As the hydro- 
 gen and oxygen are present in the proportion to form water, they are 
 hence called carbohydrates. There are only a few exceptions to the 
 above statement. Most carbohydrates are capable of fermentation, 
 or of being easily converted into fermentable bodies. Instances : 
 C 6 H 12 6 , C 6 H I0 5 , etc. 
 
 Glucosides are substances the molecules of which may be split up 
 in such a manner that several new bodies are formed, one of which 
 is sugar. 
 
 8. Amines and amides. Substances formed by replacement of 
 hydrogen in ammonia by alcohol or acid radicals. For instance : 
 ethyl amine, NH 2 .C 2 H 5 , urea, N 2 H 4 .CO, etc. The alkaloids belong 
 to this group. 
 
 9. Cyanogen and its compounds. Substances containing the radical 
 cyanogen, CN. For instance : potassium cyanide, KCN. 
 
 10. Proteins or albuminous substances. These, besides carbon, 
 hydrogen, and oxygen, always contain nitrogen and sulphur, some- 
 times also other elements. Instances : albumin, casein, fibrin, etc. 
 
 In connection with each of these groups have to be considered the 
 derivatives obtained from them directly or indirectly. 
 
 As all those organic compounds the constitution of which has 
 been explained may be looked upon as derivatives of either methane, 
 CH 4 , or benzene, C 6 H 6 , a separation of organic compounds is made 
 
 QUESTIONS. Explain the term residue or radical. What is understood by 
 the expression chain, when used in chemistry? What are the characteristics 
 of an homologous series ? Give an explanation of the terms isomerism, meta- 
 merism, and polymerism. How does heat act upon organic compounds? 
 What is destructive distillation? State the difference between combustion, 
 decay, fermentation, and putrefaction ; what is the nature of these processes, 
 and under what conditions do they take place? How do chlorine, nitric acid, 
 and alkalies act upon organic substances ? What is the action of hydrogen 
 and of dehydrating agents upon organic substances ? Mention the chief 
 groups of organic compounds. 
 
462 CONSIDERATION OF CARBON COMPOUNDS. 
 
 into two large classes, each one embodying all the derivatives of one 
 of the two hydrocarbons named. The derivatives of methane are 
 often termed fatty compounds, those of benzene aromatic compounds. 
 Methane derivatives have representatives in each one of the above 
 ten groups : benzene derivatives are missing in a few. As far as 
 practicable, the two classes will be considered separately, because 
 the properties of fatty and aromatic compounds diifer so widely, in 
 some respects, that this method of studying the nature of carbon 
 compounds is to be preferred. 
 
 42. HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 
 
 Occurrence in nature. Hydrocarbons are seldom derived from 
 animal sources, being more frequently products of vegetable life; 
 thus, the various essential oils (oil of turpentine and others) of the 
 composition C 10 H 16 or C 20 H 32 are frequently found in plants. 
 
 Other hydrocarbons are found in nature as products of the decom- 
 position of organic matter. Thus methane, CH 4 , is generally formed 
 during the decay of organic matter in the presence of moisture ; the 
 higher members of the methane series are found in crude coal-oil. 
 
 Formation of hydrocarbons. It is difficult to combine the two 
 elements carbon and hydrogen directly; as an instance of such direct 
 combination may be mentioned acetylene, C 2 H 2 , which is formed 
 when electric sparks pass between electrodes of carbon in an atmos- 
 phere of hydrogen. 
 
 Many hydrocarbons are obtained by destructive distillation of 
 organic matter, and their nature depends on the composition of the 
 material used and upon the degree of heat applied for the decompo- 
 sition. Hydrocarbons may also be obtained by the decomposition 
 (other than destructive distillation) of numerous organic bodies, such 
 as alcohols, acids, amines, etc., and from derivatives of these sub- 
 stances. 
 
 The hydrocarbons found in nature are generally separated from 
 other matter, as well as from each other, by the process known as 
 fractional distillation. As the boiling-points of the various compounds 
 differ more or less, they may be separated by carefully distilling off 
 the compounds of lower boiling-points, while noting the temperature 
 of the vapors above the boiling liquid by means of an inserted ther- 
 mometer, and changing the receiver every time an increase of the 
 boiling-point is noticed. This separation of volatile liquids, known 
 as fractional distillation, is, however, not absolutely complete, because 
 
HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 463 
 
 traces of substances having a higher boiling-point are simultaneously 
 volatilized with the distilling substance. 
 
 FIG. 
 
 Flasks arranged for fractional distillation. 
 
 For fractional distillation of small quantities of liquids as well as 
 for the determination of boiling-points, flasks arranged like those 
 shown in Fig. 69 may be used. 
 
 Properties of hydrocarbons. There are no other two elements 
 which combine together in so many proportions as carbon and hydro- 
 gen. Several hundred hydrocarbons are known, many of which 
 form either homologous series or are metameric or polymeric. 
 
 Hydrocarbons occur either as gases, liquids, or solids. If the mole- 
 cule contains not over 4 atoms of carbon, the compound is generally 
 a gas at the ordinary temperature ; if it contains from 4 to 10 or 12 
 atoms of carbon, it is a liquid ; and if it contains a yet higher number 
 of carbon atoms, it is generally a solid. 
 
 All hydrocarbons may be volatilized without decomposition, all 
 are colorless substances, and many have a peculiar and often charac- 
 teristic odor ; they are generally insoluble in water but soluble in 
 alcohol, ether, disulphide of carbon, etc. 
 
464 
 
 CONSIDERATION OF CARBON COMPOUNDS. 
 
 First member. 
 CH 4 
 C 2 H 4 
 C 2 H 2 
 
 In regard to chemical properties, it may be said that hydrocarbons 
 are neutral substances, behaving rather indifferently toward most 
 other chemical agents. Many of them are, however, oxidized by the 
 oxygen of the air, by which process liquid hydrocarbons are often 
 converted into solids. The action of halogens on hydrocarbons will 
 be considered later on. 
 
 A number of homologous series of hydrocarbons are known, of 
 which the following are the most important : 
 
 General formula. 
 
 Methane series or paraffins, C n H2 U + 2 
 
 Ethene series or olefins, C n H 2n 
 
 Eihine series or acetylenes, C n H 2n _ 2 
 
 Terpenes, C n H 2n _ 4 C 10 H 16 
 
 Benzene series, C n H 2n - e C 6 He 
 
 Of the acetylene series and of the terpenes only a few homologues 
 are known. 
 
 The univalent radicals of the members of the methane series are designated 
 by changing the termination ane to yl (methane, methyl, CH 3 ! ) ; the bivalent 
 radicals by changing ane to ene (rnethene, CH 2 ]i ) ; and the trivalent radicals 
 by changing the final e of ene to yl (methenyl, CH U1 ). The derivatives of the 
 bivalent radicals are indicated by the termination ylene, as methylene iodide, 
 CH 2 I 2 . 
 
 i 
 
 Hydrocarbons of the paraffin or methane series. The hydro- 
 carbons having the general composition C n H 2n + 2 are known as 
 paraffins, the name being derived from the higher members of the 
 series which form the paraffin of commerce. The following table 
 gives the composition, boiling-points, etc., of the first sixteen mem- 
 bers of this series : 
 
 Methane or methyl hydride, 
 Ethane or ethyl hydride, 
 Propane or propyl hydride, 
 Butane or butyl hydride, 
 Pentane or amyl hydride, 
 Hexane or hexyl hydride, 
 Heptane or heptyl hydride, 
 Octane or octyl hydride, 
 Nonane or nonyl hydride, 
 Decane or decyl hydride, 
 Undecane or undecyl hydride, 
 Dodecane or dodecyl hydride, 
 Tridecane or tridecyl hydride, 
 Tetradecane or tetradecyl hydride, 
 Pentadecane or pentadecyl hydride, 
 Hexadecane or hexadecyl hydride, 
 etc. 
 
 B. P. 
 
 Sp. gr. 
 
 H 
 
 H 
 
 H 
 
 1C. 
 
 
 38 
 
 0.628 
 
 70 
 
 0.669 
 
 99 
 
 0.690 
 
 125 
 
 0.726 
 
 148 
 
 0.741 
 
 166 
 
 0.757 
 
 184 
 
 0.766 
 
 202 
 
 0.778 
 
 218 
 
 0.796 
 
 236 
 
 0.809 
 
 258 
 
 0.825 
 
 280 
 
 
HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 465 
 
 The above table shows that the paraffins form an homologous 
 series; the first four members are gases, most of the others liquids, 
 regularly increasing in specific gravity, boiling-point, viscidity, and 
 vapor density, as their molecular weight becomes greater. 
 
 The paraffins are saturated hydrocarbons, the constitution of which 
 has been already explained; they are incapable of uniting directly 
 with monatomic elements or residues, but they easily yield sub- 
 stitution-derivatives when subjected to the action of chlorine or bro- 
 mine, hydrogen in all cases being given up from the hydrocarbon. 
 
 Most of the paraffins are known in two (or even more) modifications ; there 
 are, therefore, other homologous series of hydrocarbons of the same composition 
 as the above normal paraffins, which show some difference from the normal 
 paraffins in boiling-points and other properties. In these isomeric paraffins the 
 atoms are arranged differently from those in the normal hydrocarbons, which 
 fact may be proven by the difference in decomposition which these substances 
 suffer when acted upon by chemical agents. 
 
 No isomeric hydrocarbons of the first three members of the paraffin series are 
 known, which fact is in accordance with our present theories. Assuming that 
 the quadrivalent carbon atoms exert their full valence, and that they are held 
 together by one bond only, we can arrange the atoms in the compounds, 
 CH 4 , C 2 H 6 , and C 3 H 8 , not otherwise than thus: 
 
 / H 
 ^H 
 
 In the next compound, butane, C 4 H 10 , we have two possibilities explaining 
 the structure of the molecule, namely, these : 
 
 CEBH 3 
 
 C=:H 2 C=H 3 
 
 (j=tiy O^=Ii 3 OH G^^-tl 3 . 
 
 LH 
 
 L/ r 3 
 
 Both these compounds are known, and termed normal butane and isobutane, 
 respectively. 
 
 The next member, pentane, C 5 H 12 , shows three possibilities of constitution, 
 thus: 
 
 C=H 3 
 
 C=H a CEEH 3 
 
 | C=H 3 -C-H. | 
 
 C=H 2 | C=H 3 C C^H, 
 
 C=H 2 | _ O=H 3 . 
 
 C^5iHj| 
 
 C=H 3 
 
 These compounds also are known. With the higher members of the paraffins 
 the number of possible isomers rises rapidly according to the law of permuta- 
 30 
 
466 CONSIDERATION OF CARBON COMPOUNDS. 
 
 tion, so that we have of the seventh member 9, of the tenth 75, and of the 
 thirteenth member 80<>, possible isomeric hydrocarbons. 
 
 Methane, CH 4 (Marsh-gas, Fire-damp). This hydrocarbon has 
 been spoken of in Chapter 14, where it was stated that it is a color- 
 less, combustible gas, which is formed by the decay of organic matter 
 in the presence of moisture, during the formation of coal in the 
 interior of the earth, and by the destructive distillation of various 
 organic matters. Methane is of special interest, because it is the 
 compound from which thousands of other substances are derived. It 
 may be made by the action of inorganic substances upon one another; 
 for instance, by the action of water on aluminum carbide, a compound 
 of the metal aluminum, and carbon, A1 4 C 3 , the following change tak- 
 ing place : 
 
 A1 4 C 3 + 12H 2 = = 3CH 4 + 4A1(OH) 3 . 
 
 Bearing in mind that aluminum carbide, as well as water, may be 
 obtained by direct union of the elements, it is evident that methane 
 may be formed indirectly, by means of the above method, from the 
 elements carbon and hydrogen. 
 
 Experiment 51. Use apparatus shown in Fig. 35, page 87, omitting the bent 
 tube B. Mix in a mortar 20 grammes of sodium acetate with 20 grammes of 
 potassium (or sodium) hydroxide and 30 grammes of calcium hydroxide ; fill 
 with this mixture the tube A, which should be made of glass fusing with 
 difficulty, or of so-called "combustion tubing;" apply heat and collect the gas 
 over water. The decomposition takes place thus : 
 
 NaC 2 H 3 O 2 + NaOH = NajCOg + CH 4 . 
 
 Ignite the gas, and notice that its flame is but slightly luminous. Mix some 
 of the gas in a wide-mouth cylinder, of not more than about 200 c.c. capacity, 
 with an equal volume of air and ignite. Eepeat this experiment with mixtures 
 of one volume of methane with 2, 4, 6, 8, and 10 volumes of atmospheric air. 
 Which mixture is most explosive, and why ? How many volumes of oxygen 
 and how many volumes of atmospheric air are needed for the complete com- 
 bustion of one volume of methane ? 
 
 Ethane, C-^Hg, is a constituent of natural gas and of crude petroleum. It 
 can be obtained from methane by first replacing in it a hydrogen atom by 
 iodine, when iodo-methane, or methyl-iodide, CH 3 I, is formed, which, when 
 acted on by sodium, is decomposed thus: 
 
 CH 3 I + CH 3 I + 2Na = 2NaI + C 2 H fi . 
 
 This formation of ethane illustrates one of the methods for producing by 
 synthesis i. e., for building up more complex from simpler hydrocarbons. 
 Another method, accomplishing the same result, depends on the action of a 
 
HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 467 
 
 zinc compound of the radicals on the iodides of the radicals. The radicals 
 may be the same or different ones; for instance: 
 
 Zn(CH 3 ) 2 + 2CH 3 T = ZnI 2 + 2C 2 He, 
 Zinc methyl. Methyl iodide. Zinc iodide. Ethane. 
 
 Zn(CH s ) 2 + 2C 2 H 5 I = ZnI 2 -f- 2C 3 H 8 . 
 Ethyl iodide. Propane. 
 
 Coal. As methane is one of the products generated during the 
 formation of coal, it may be well to consider this process here briefly. 
 
 The various substances classed togther under the name of coal con- 
 sist principally of carbon, associated with smaller quantities of hydro- 
 gen, oxygen, nitrogen, sulphur, and certain inorganic mineral matters 
 which compose the ash. Coal is formed from buried vegetable 
 matter by a process of decomposition which is partly a fermentation, 
 partly a decay, and chiefly a slow destructive distillation, the heat 
 for this latter process being derived from the interior of the earth, or 
 by the decomposition itself. 
 
 The principal constituent of the organic matter furnishing coal is 
 wood (or woody fibre, cellulose), and a comparison of the composition 
 of this substance with the various kinds of coal gradually formed 
 will help to illustrate the chemical change taking place : 
 
 Carbon. Hydrogen. Oxygen. 
 
 Wood 100 12.18 83.07 
 
 Peat 100 9.85 55.67 
 
 Lignite 200 8.37 42.42 
 
 Bituminous coal . . . .100 6.12 21.23 
 
 Anthracite coal 100 2.84 1.74 
 
 This table shows a progressive diminution in the proportions of 
 hydrogen and oxygen during the passage from wood to anthracite. 
 These two elements must, therefore, be eliminated in some form of 
 combination which allows them to move, viz., as gases or liquids. 
 The gases formed are chiefly carbon dioxide (which finds its way 
 through the rocks and soils to the surface either in the gaseous state 
 or after having been absorbed by water in the form of carbonic acid 
 springs) and methane, known to coal-miners as fire-damp, frequently 
 causing the formation of explosive gas mixtures in the coal mines, or 
 escaping, like carbon dioxide, through fissures to the surface of the 
 earth, where it may be ignited. 
 
 Natural gas. While methane and other combustible gases are 
 undoubtedly formed during the formation of coal, the gas mixture 
 now generally termed natural gas (a mixture of methane, ethane, 
 propane, hydrogen, and a few other gases), and used largely for 
 
f Liquids 
 Coal-tar -! 
 
 470 CONSIDERATION OF CARBON COMPOUNDS. 
 
 B. P. 
 
 f Benzene .... C 6 H 6 80 
 
 Toluene . . C 7 H 8 
 
 Aniline C 6 H 5 NH 2 182 
 
 Acetic acid . C 2 H 4 O 2 117 
 
 Water H 2 O 100 
 
 Carbolic acid . . . C 6 H 6 O 188 
 
 Kresylic acid . . . C 7 H 8 O 
 
 Naphthalene .... C 10 H 8 220 
 
 Anthracene .... C U H 10 360 
 
 Paraffin C 16 H 34 280 
 
 Solid residue : Coke, chiefly carbon and inorganic matter. 
 
 The gases are purified by condensing ammonia (and some other 
 gases) in water, carbon dioxide and hydrogen sulphide in calcium 
 hydroxide. The following is the composition of a purified illumi- 
 nating gas obtained from cannel-coal : 
 
 Hydrogen 46 volumes. 
 
 Methane 41 " 
 
 Ethene 6 
 
 Carbon monoxide .... 4 " 
 
 Carbon dioxide 2 " 
 
 Nitrogen 1 volume. 
 
 The poisonous properties of illuminating gas are due chiefly to car- 
 bon monoxide, all other constituents being more or less harmless. 
 
 Experiment 53. Use apparatus shown in Fig. 35, page 87. Fill the combus- 
 tion-tube A with sawdust (almost any other non-volatile organic matter may be 
 used), apply heat and continue it as long as gases are evolved. Notice that by 
 this process of destructive distillation are formed a gas (or gas mixture), which 
 may be ignited, a dark, almost black liquid (tar), which condenses in the tube 
 B, and that a residue is left which is chiefly carbon. The tarry liquid shows an 
 acid reaction, due to acetic and other acids present. 
 
 Coal-tar, obtained as a by-product in the manufacture of illumi- 
 nating gas, contains, as shown by the above table, many valuable sub- 
 stances, such as benzene, aniline, carbolic acid, paraffin, etc., which 
 are separated from each other by making use of the diiference in their 
 boiling-points and specific gravities, or of their solubility or insolu- 
 bility in various liquids, or, finally, of their basic, acid, or neutral 
 properties. 
 
 Unsaturated hydrocarbons. The terms saturated and un- 
 saturated compounds are used for inorganic and organic substances. 
 A compound is said to be unsaturated when it has the power to enter 
 directly into combination with elements or compounds. Thus, car- 
 
HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 471 
 
 bon monoxide and phosphorus trichloride are un saturated, as they 
 combine directly with a number of substances ; for instance, with 
 
 chlorine, thus : 
 
 CO + 2C1 = COC1 2 , 
 
 PC1 3 + 2C1 = PC1 5 . 
 
 The hydrocarbons of the methane series are saturated ; they can- 
 not be made to enter directly into combination with other substances, 
 because there are no bonds left unprovided for. 
 
 On the other hand, we have several homologous series of hydro- 
 carbons which are unsaturated. The olefins belong to this kind, 
 and the reason is found in the structure of the molecules. 
 
 Looking at the graphic formulas of the normal hydrocarbons of the methane 
 series on page 465, we find all affinities completely saturated. The structure 
 of ethylene, C 2 H 4 , the first member of the olefines, may be represented by either 
 of the following formulas : 
 
 H H H H 
 
 H C C H 
 
 Each of these representations shows that two bonds are left unsaturated, and 
 as certain considerations lead us to assume that two hydrogen atoms are in 
 combination with one carbon atom the second representation is the one agree- 
 ing with our views. Instead of leaving the affinities unsaturated in our for- 
 mulas as above, we use double linkage, and give to ethylene the formula 
 
 H H 
 H C=C H or H 3 C=CH 2 . 
 
 Whenever direct combination between ethylene and another substance 
 occurs the double linkage is broken and the bonds are utilized for holding 
 
 the respective atoms, or radicals, thus : 
 
 Br Br 
 
 H 2 C=CH 2 + 2Br = H 2 C CH 2 . 
 
 As the higher members of the ethylene series are obtained by replacement 
 of hydrogen atoms by hydrocarbon radicals in ethylene, which replacement 
 does not alter the double linkage of its carbon atoms, all members behave like 
 unsaturated compounds. 
 
 In a similar manner we represent the unsaturated hydrocarbon acetylene 
 C 2 H 2 , by the formula HC=CH, showing triple linkage between the carbon 
 atoms. That this view is in keeping with the facts is shown by the action of 
 bromine or of hydrobromic acid on acetylene, thus : 
 
 HC=CH + 4Br = Br 2 HC CHBr^ 
 HfeCH + 2HBr = BrH 2 C CH 3 Br. 
 
Coal-tar - 
 
 Solids 
 
 470 CONSIDERATION OF CARBON COMPOUNDS. 
 
 B. P. 
 
 f Benzene .... C 6 H 6 80 
 
 I Toluene . . . C 7 H 8 110 
 
 Liquids -j Aniline C 6 H 5 NH 2 182 
 
 ' Acetic acid .... C 2 H 4 O 2 117 
 
 Water H 2 O 100 
 
 Carbolic acid . . . C 6 H 6 O 188 
 
 Kresylicacid . . . C 7 H 8 O 201 
 
 Naphthalene .... C IO H 8 220 
 
 Anthracene .... C U H 10 360 
 
 I Paraffin C 16 H 34 280 
 
 Solid residue : Coke, chiefly carbon and inorganic matter. 
 
 The gases are purified by condensing ammonia (and some other 
 gases) in water, carbon dioxide and hydrogen sulphide in calcium 
 hydroxide. The following is the composition of a purified illumi- 
 nating gas obtained from cannel-coal : 
 
 Hydrogen 46 volumes. 
 
 Methane 41 " 
 
 Ethene 6 " 
 
 Carbon monoxide .... 4 " 
 
 Carbon dioxide 2 " 
 
 Nitrogen 1 volume. 
 
 The poisonous properties of illuminating gas are due chiefly to car- 
 bon monoxide, all other constituents being more or less harmless. 
 
 Experiment 53. Use apparatus shown in Fig. 35, page 87. Fill the combus- 
 tion-tube A with sawdust (almost any other non-volatile organic matter may be 
 used), apply heat and continue it as long as gases are evolved. Notice that by 
 this process of destructive distillation are formed a gas (or gas mixture), which 
 may be ignited, a dark, almost black liquid (tar), which condenses in the tube 
 B, and that a residue is left which is chiefly carbon. The tarry liquid shows an 
 acid reaction, due to acetic and other acids present. 
 
 Coal-tar, obtained as a by-product in the manufacture of illumi- 
 nating gas, contains, as shown by the above table, many valuable sub- 
 stances, such as benzene, aniline, carbolic acid, paraffin, etc., which 
 are separated from each other by making use of the difference in their 
 boiling-points and specific gravities, or of their solubility or insolu- 
 bility in various liquids, or, finally, of their basic, acid, or neutral 
 properties. 
 
 Unsaturated hydrocarbons. The terms saturated and un- 
 saturated compounds are used for inorganic and organic substances. 
 A compound is said to be unsaturated when it has the power to enter 
 directly into combination with elements or compounds. Thus, car- 
 
HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 471 
 
 bon monoxide and phosphorus trichloride are unsaturated, as they 
 combine directly with a number of substances ; for instance, with 
 chlorine, thus : 
 
 CO -f 2C1 = COC1 2 , 
 
 PC1 3 + 2C1 = PC1 5 . 
 
 The hydrocarbons of the methane series are saturated ; they can- 
 not be made to enter directly into combination with other substances, 
 because there are no bonds left unprovided for. 
 
 On the other hand, we have several homologous series of hydro- 
 carbons which are unsaturated. The olefins belong to this kind, 
 and the reason is found in the structure of the molecules. 
 
 Looking at the graphic formulas of the normal hydrocarbons of the methane 
 series on page 465, we find all affinities completely saturated. The structure 
 of ethylene, C 2 H 4 , the first member of the olefines, may be represented by either 
 of the following formulas : 
 
 H H H H 
 
 H C C H C C H 
 
 A 1 ' ' 
 
 Each of these representations shows that two bonds are left unsaturated, and 
 as certain considerations lead us to assume that two hydrogen atoms are in 
 combination with one carbon atom the second representation is the one agree- 
 ing with our views. Instead of leaving the affinities unsaturated in our for- 
 mulas as above, we use double linkage, and give to ethylene the formula 
 
 H H 
 H C=C H or H a C=CH r 
 
 Whenever direct combination between ethylene and another substance 
 occurs the double linkage is broken and the bonds are utilized for holding 
 
 the respective atoms, or radicals, thus : 
 
 Br Br 
 
 H 2 C=CH 2 -f 2Br = H 2 C CH 3 . 
 
 As the higher members of the ethylene series are obtained by replacement 
 of hydrogen atoms by hydrocarbon radicals in ethylene, which replacement 
 does not alter the double linkage of its carbon atoms, all members behave like 
 unsaturated compounds. 
 
 In a similar manner we represent the unsaturated hydrocarbon acetylene 
 C 2 H 2 , by the formula HfeCH, showing triple linkage between the carbon 
 atoms. That this view is in keeping with the facts is shown by the action of 
 bromine or of hydrobromic acid on acetylene, thus : 
 
 HfeCH + 4Br = Br 2 HC CHBry 
 2HBr = BrH 2 C CH 8 Br. 
 
472 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Olefins. The hydrocarbons of the general formula C n H 2n are 
 termed olefins. To this series belong : 
 
 Ethylene or ethene C 2 H 4 . 
 
 Propylene or propene .... C 3 H 6 . 
 
 Butylene or butene C 4 H 8 . 
 
 Amylene or pentene .... C 5 H 10 . 
 
 Hexylene or hexene .... C 6 H 12 . 
 
 Methene, CH 2 , the lowest term of this series, is not known. The 
 hydrocarbons of this series are not only homologous, but also poly- 
 meric with one another. 
 
 Ethylene, C 2 H 4 (Ethene, olefiant gas), the first member of the 
 olefins, is of special interest on account of its normal occurrence in 
 illuminating gas made from coal, as also in most common flames, the 
 luminosity of which depends largely on the quantity of this compound 
 present in the burning gas. 
 
 Besides destructive distillation there are several reactions by which ethylene 
 can be obtained. Of these two are of interest. The first one depends on the 
 action of an alcoholic solution of potassium hydroxide on ethyl chloride, bro- 
 mide, or iodide : 
 
 C 2 H 5 Br + KOH = C 2 H 4 + KBr + H 2 O. 
 
 This reaction shows the possibility of preparing an unsaturated compound 
 of the ethylene series from a saturated hydrocarbon ; and as the method is 
 applicable to compounds of other classes it furnishes the means to pass from 
 any saturated compound to the corresponding unsaturated compound of the 
 ethylene series. 
 
 The second method for preparing ethylene depends on the dehydrating action 
 of sulphuric acid on ethyl alcohol : 
 
 C 2 H 5 OH H 2 = C 2 H 4 . 
 
 Ethylene combines directly with an equal volume of chlorine forming ethy- 
 lene dichloride, C 2 H 4 C1 2 , an oily liquid, whence the name olefiant gas. 
 
 Amylene, C 5 H 10 . Of the three isomeric hydrocarbons of the composition 
 C 5 H 10 , two have been used medicinally. It is especially the amylene of the 
 
 CH CH 
 
 composition Qjj 3 ^>C = C<JT 3 i. e., trimethyl-ethylene which has been in- 
 troduced as an anaesthetic under the name of pental. It is formed from tertiary 
 amyl alcohol (amylene hydrate) by the action of dehydrating agents. It is a 
 colorless, very volatile liquid, insoluble in water, but miscible in all proportions 
 with chloroform, ether, and alcohol. It has a penetrating odor, reminding of 
 mustard oil. 
 
HALOGEN DERIVATIVES OF HYDROCARBONS. 473 
 
 Acetylene, C 2 H 2 , is the first member of a hydrocarbon series of 
 the general composition C n H 2n _ 2 . It has been stated before that 
 acetylene is formed by direct union of the elements when an electric 
 current passes between two carbon poles in an atmosphere of hydro- 
 gen. It is also formed during the incomplete combustion of coal- 
 gas, such as takes place when the flame of a Btinsen burner " strikes 
 back " i. e., burns at the base of the burner. 
 
 The method now extensively used in the manufacture of acetylene 
 for illuminating purposes depends on the decomposition of calcium 
 carbide by water : 
 
 C 2 Ca + H 2 O = CaO + C 2 H 2 . 
 
 Pure acetylene is a gas of agreeable ethereal odor, while the gas as ordi- 
 narily prepared possesses an unpleasant odor, due to impurities. With an 
 ordinary burner acetylene burns with a luminous but sooty flame, while by 
 the use of specially constructed burners flames may be obtained giving a very 
 pure, intensely luminous white light. Like ethene, it combines directly with 
 halogens, and when heated to a sufficiently high temperature it is converted 
 into the polymeric compounds, benzene, C 6 H 6 , and styrene, C 8 H 8 . 
 
 A characteristic property of acetylene is the readiness with which its 
 hydrogen may be replaced by metals ; thus, by treating acetylene with sodium, 
 either monosodium acetylid, C 2 HNa, or disodium acetylid, C 2 Na,, may be ob- 
 tained. Silver acetylid, C 2 Ag 2 , a white crystalline compound, and cuprous 
 acetylid, C 2 Cu 2 , a red powder, may be obtained by passing the gas through 
 ammoniacal solutions of silver and cuprous salts, respectively. When dry, 
 both compounds explode violently when heated, the silver compound even 
 when rubbed with a glass rod. 
 
 Halogen derivatives of hydrocarbons. 
 
 Substitution products. When a mixture of methane and chlorine 
 is exposed to diffused daylight chemical action takes place gradually, 
 resulting in the successive substitution of hydrogen by chlorine, thus : 
 
 CH 4 + 2C1 = CH 3 C1 + HC1. 
 CH 3 C1 + 2C1 = CH 2 C1 2 + HC1. 
 CH 2 C1 2 + 2C1 == CHC1 3 + HC1. 
 CHC1 3 + 2C1 = CC1 4 + HC1. 
 
 These reactions between methane and chlorine are more or less 
 characteristic of the general interaction between the halogens and 
 hydrocarbons, most of the latter being very susceptible to the action 
 of halogens. The 4 substitution products formed are designated 
 respectively as monochlor-methane or chlor-methane, dichlor-methane, 
 trichlor-methane, and tetracUor-methane or carbon tetmcMoride. These 
 compounds may also be looked upon as chlorides of the radicals CH 3 ', 
 
474 CONSIDERATION OF CARBON COMPOUNDS. 
 
 methyl ; CH 2 H , methylene ; CH m , meihenyl ; and of carbon C Uii . The 
 univalent radicals such as methyl, ethyl, propyl are called alkyl or 
 alcohol radicals, while the term alkylene designates bivalent radicals 
 such as methylene, ethylene, propylene, etc. 
 
 A characteristic feature of these halogen derivatives is the behavior of the 
 halogens towards such reagents as silver nitrate. Chlorine and iodine when in 
 combination with hydrogen or metals readily form with a soluble silver salt 
 insoluble chloride or iodide. The halogens which have replaced hydrogen in 
 organic compounds are, as a general rule, not affected by silver salts in solu- 
 tion. This behavior shows that the substitution products are not dissociable 
 i. e., there are no halogen ions present. While above a general method has 
 been given by which the halogen compounds can be made, there are usually 
 employed other processes for their manufacture. Also the names given above 
 are not always those in general use. Thus, trichlor-methane or methenyl 
 chloride is generally called chloroform and the corresponding bromine and 
 iodine compounds bromoform and iodoform. 
 
 Methyl chloride, CH 3 C1 (Monochlor-methane), is readily obtainable by the 
 action of hydrochloric acid on methyl alcohol : 
 
 CH 3 OH + HC1 = CH 3 C1 + H 2 O. 
 
 It is a colorless, inflammable gas which can be liquefied by pressure. This 
 liquid which produces an intense cold by its evaporation has been used locally 
 for neuralgia. 
 
 Dichlor-methane, CH 2 C1 2 (Methylene chloride), is obtained by the action of 
 nascent hydrogen on chloroform : 
 
 CHC1 3 + 2H = CH 8 Cl a + HC1. 
 
 It is a colorless, oily liquid, boiling at 40 C. (104 F.) ; sp. gr. 1.344. It has 
 an odor similar to that of chloroform, and has been employed as an anaesthetic. 
 
 Tetrachlor-methane, CC1 4 (Carbon tefrachloride), is obtained by the action 
 of chlorine on carbon disulphide, or by treating chloroform with iodine chloride : 
 
 CH.CL, -f IC1 = CC1 4 + HI. 
 
 It is a colorless liquid possessing anaesthetic properties, but, like the previous 
 compound, is dangerous. 
 
 By far the most important halogen derivatives of methane are the 
 trisubstitution products : chloroform, bromoform and iodoform. The 
 gaseous chlorine and the liquid bromine convert through their sub- 
 stitution the gaseous methane into colorless, heavy, volatile liquids, 
 while the solid iodine confers the solid state upon the compound. 
 
 Chloroform, Chloroformum, CHOI, = 118.45 (Trichlor-methane), 
 is obtained by the action of bleaching-powder and calcium hydroxide 
 
HALOGEN DERIVATIVES OF HYDROCARBONS. 475 
 
 on alcohol. The three substances named, after being mixed with a 
 considerable quantity of water, are heated in a retort until distilla 
 tion commences ; the crude product of distillation is an impure chloro- 
 form, which is purified by mixing it with strong sulphuric acid and 
 allowing the mixture to stand ; the upper layer of chloroform is 
 removed and treated with sodium carbonate (to remove any acids) 
 and distilled over calcium chloride (to remove water). 
 
 A full explanation of the formation of chloroform by the above process will 
 be given later on in connection with the consideration of chloral, where it will 
 be shown that alcohol is converted by the action of chlorine first into aldehyde 
 and subsequently into chloral, which, upon being treated with alkalies, is 
 decomposed into an alkali formate and chloroform. 
 
 The action of the chlorine of the calcium hypochlorite (which is the active 
 principle in bleaching-powder) upon the alcohol is similar to that of free 
 chlorine upon alcohol; in both cases aldehyde, and afterward chloral, are 
 formed, which latter, in the manufacture of chloroform, is decomposed by the 
 calcium hydroxide into chloroform and calcium formate. The last-named salt 
 is, however, not found in the residue of the distillation, because it is decomposed 
 by bleaching-powder and calcium hydroxide into calcium carbonate, chloride, 
 and water : 
 
 Ca(CHO 2 ) 2 + Ca(ClO) 2 + Ca(OH) 3 = 2CaCO 3 + CaCl 2 + 2H 2 O. 
 
 If the various intermediate steps of the decomposition are not considered, the 
 process may be represented by the following equation : 
 
 4C 2 H 6 + 8Ca(C10) 2 = 2CHC1 3 -f 3[Ca(CHO 2 ) 2 ] + 5CaCl 2 + 8H 2 O. 
 Alcohol. Calcium Chloroform. Calcium Calcium Water, 
 
 hypochlorite. formate. chloride. 
 
 Chloroform is now made extensively by the action of bleaching-powder upon 
 acetone ; the reaction takes place thus : 
 
 2CO(CH 3 ) 2 -f 3Ca(C10) 2 = 2CHC1 3 + 2Ca(OH) 2 + Ca(C 2 H 3 <V 2 
 Acetone. Calcium Chloroform. Calcium Calcium 
 
 hypochlorite. hydroxide. acetate. 
 
 Pure chloroform is a heavy, colorless liquid, of a characteristic 
 ethereal odor, a burning, sweet taste, and a neutral reaction ; it is but 
 very sparingly soluble in water, but miscible with alcohol and ether 
 in all proportions ; the specific gravity of pure chloroform is 1.50, 
 but a small quantity of alcohol (from one-half to one per cent.), 
 allowed to be present by the U. S. P., causes the specific gravity to 
 be about 1.48; boiling-point 61 C. (141.8 F.), but rapid evapora- 
 tion takes place at all temperatures. 
 
 Chloroform or its vapors do not ignite readily, but at a high tem- 
 perature chloroform burns with a green flame. When kept in a 
 partially filled bottle exposed to daylight it decomposes with the for- 
 mation of the highly irritating carbonyl chloride : 
 
476 CONSIDERATION OF CARBON COMPOUNDS. 
 
 CHC1 3 + O = COC1 2 -f- HC1. 
 
 Chloroform containing some alcohol is less apt to undergo this oxida- 
 tion, but the latter also takes place when chloroform is used for inha- 
 lation near an exposed flame. 
 
 Analytical reactions for chloroform. 
 
 1. Dip a strip of paper into chloroform and ignite. The flame has 
 a green mantle and emits vapors of hydrochloric acid, rendered more 
 visible upon the approach of a glass rod moistened with ammonia water. 
 
 2. Add a drop of chloroform and a drop of aniline to some alco- 
 holic solution of potassium hydroxide and heat gently : a peculiar, 
 penetrating, offensive odor of benzo-isonitrile, C 6 H 5 NC, is noticed. 
 (Chloral shows the same reaction.) 
 
 CHClg -f 3KOH + C 6 H 5 .NH 2 = C 6 H 5 NC + 3KC1 + 3H 2 O. 
 
 3. Add some chloroform to Fehling's solution and heat : red 
 cuprous oxide is precipitated. 
 
 4. Vapors of chloroform, when passed through a glass tube heated 
 to redness, are decomposed into carbon, chlorine, and hydrochloric 
 acid. The two latter should be passed into water, and may be recog- 
 nized by their action on silver nitrate (white precipitate of silver 
 chloride) and on mucilage of starch, to which potassium iodide has 
 been added (blue iodized starch is formed). 
 
 5. Heat some chloroform with solution of potassium hydroxide and 
 a little alcohol. Chloroform is decomposed into potassium chloride 
 and formate : 
 
 CHC1 3 -f 4KOH == 3KC1 + KCH0 2 + 2H 2 O. 
 
 Divide solution into two portions. Acidulate one portion with 
 nitric acid, boil, and add silver nitrate : white precipitate of silver 
 chloride. To second portion add a little ammonia water and a crystal 
 of silver nitrate : a mirror of metallic silver will be formed after 
 heating slightly. 
 
 6. Add to 1 c.c. of chloroform about 0.3 gramme of resorcin in 
 solution, and 3 drops of solution of sodium hydroxide ; boil strongly : 
 a yellowish-red color is produced, and the liquid shows a beautiful 
 yellow-green fluorescence. (Chloral shows the same reaction.) 
 
 In cases of poisoning chloroform is generally to be sought for in the lungs 
 and blood, which are placed in a flask connected with a tube of difficultly 
 fusible glass. By heating the flask the chloroform is expelled and decomposed 
 in the heated glass tube, as stated above in reaction 4. Another portion of 
 chloroform should be distilled without decomposing it, and the distillate tested 
 as above stated. 
 
 There is no chemical antidote which may be used in cases of poisoning by 
 
HALOGEN DERIVATIVES OF HYDROCARBONS. 477 
 
 chloroform, and the treatment is, therefore, confined to the use of the stomach- 
 pump, to the maintenance of respiration with oxygen inhalation, and to the 
 use of strychnine hypodermically. 
 
 Bromoform, Bromoformum, CHBr 3 (Tribrom-methane), is an 
 extremely heavy, colorless mobile liquid, with an ethereal odor, and 
 a penetrating, sweet taste, resembling chloroform, specific gravity 
 2.884 ; B. P. 148 C. It is sparingly soluble in water, soluble in 
 alcohol and ether. Its physiological action is similar to that of 
 chloroform. 
 
 Bromoform may be obtained by gradually adding bromine to a cold solution 
 of potassium hydroxide in ethyl alcohol until the color is no longer discharged, 
 and rectifying over calcium chloride. It is also made by the action of an alkali 
 hypobromite on acetone. 
 
 lodoform, lodoformum, CHI 3 = 390.61 (Triiodo-methane). This 
 compound is analogous in its constitution to chloroform and bromo- 
 form. It is made by heating together an aqueous solution of an alkali 
 carbonate, iodine, and alcohol until the brown color of iodine has 
 disappeared ; on cooling, iodoform is deposited in yellow scales, which 
 are well washed with water and dried between filtering paper. (For 
 an explanation of the chemical changes taking place see chloral and 
 chloroform.) 
 
 lodoform occcurs in small, lemon-yellow, lustrous crystals, having 
 a peculiar, penetrating odor, and an unpleasant, sweetish taste ; it is 
 nearly insoluble in water and acids, soluble in alcohol, ether, fatty 
 and essential oils. It contains 96.7 per cent, of iodine. 
 
 lodoform digested with an alcoholic solution of potassium hy- 
 droxide imparts, after acidulation with nitric acid, a blue color to 
 starch solution. (See reaction in Test 5 under Chloroform.) 
 
 Experiment 54. Dissolve 4 grammes of crystallized sodium carbonate in 6 
 c.c. of water : add to this solution 1 c.c. of alcohol ; heat to about 70 C. (158 
 F.), and add gradually 1 gramme of iodine. A yellow crystalline deposit of 
 iodoform separates. 
 
 Ethyl chloride, ^Jthylis chloridum, C 2 H 5 C1 = 64 (Chlor-cthane), 
 is prepared analogously to methyl chloride by the action of hydro- 
 chloric acid gas upon absolute ethyl alcohol : 
 
 C 2 H 5 OH + HC1 = C 2 H 5 C1 + H 2 0. 
 In place of hydrochloric acid phosphorus pentachloride may be used : 
 
 C 2 H 6 OH + PC1 5 = C 2 H 5 C1 + POC1, + HCL 
 
 Ethyl chloride is a gas at ordinary temperature, but by pressure it 
 is converted into a colorless, mobile, very volatile liquid which boils at 
 
478 CONSIDERATION OF CARBON COMPOUNDS. 
 
 12.5 C. The compressed liquid is sold in tubes, from which it is permit- 
 ted to escape through a small opening when used as a local anaesthetic. 
 It is highly inflammable. It is known also as kelene or chelene. 
 
 Ethyl bromide, C 2 H 5 Br (Brom-ethane, Hydrobromlc ether], is obtained by 
 the same reactions as ethyl chloride, substituting bromine for chlorine. It is 
 a colorless, heavy, volatile liquid. Specific gravity 1.473; B. P. 40 C. When 
 inhaled it rapidly produces anaesthesia, followed by quick recovery. 
 
 Somnoform is said to be a mixture of 60 parts of ethyl chloride, 35 parts of 
 methyl chloride, and 5 parts of ethyl bromide. It is used to some extent in 
 dentistry as an anaesthetic. 
 
 Ethyl iodide, C 2 H 5 I, may be obtained similarly to the chlorine or bromine 
 compound. It is a colorless liquid with the boiling-point of 72 C. 
 
 Compounds of hydrocarbon (alkyl) radicals with other elements. Some 
 metals, as zinc, magnesium, cadmium, aluminum, etc., can form compounds 
 with alkyl radicals; for example, Zn(CH 3 ) 2 , Sn(C 2 H 5 ) 4 . Likewise, alkyl rad- 
 icals can be substituted for one or more atoms of hydrogen in ammonia (NH 3 ), 
 arsine (AsH 3 ), and phosphine (PH 3 ) ; for example, NH. 2 .CH 3 , AsH(CH 3 ) 2 , 
 P(CH 3 ) 3 . The alkyl derivatives of ammonia are treated in chapter 49. One 
 of the arsenic compounds possesses some interest because of its use in med- 
 icine, although its employment is limited. When arsenous oxide and potas- 
 sium acetate are distilled together, a heavy, horribly-smelling, poisonous, 
 fuming oil is formed, the principal constituent of which has the composition, 
 [(CH 3 ) 2 As] 2 O. The reaction is, As 2 O 3 + 4CH 3 COQK = K 2 C0 3 + 2CO 2 + 
 [(CH 3 ) 2 As] 2 O. Dimethyl arsine oxide is known best as cacodyl oxide, the 
 word cacodyl having been adopted in allusion to the disgusting odor of the 
 compound. It contains the univalent radical, (CH 3 ) 2 As , which acts like an 
 atom of a univalent metal. Cacodyl itself, (CH 3 ) 2 As As(CH 3 ) 2 , also exists. 
 The oxide has a strong affinity for oxygen, and inflames in oxygen gas, but not 
 in air. By oxidizing cacodyl oxide with mercuric oxide, cacodylic acid is formed, 
 (CH 3 ) 2 AsO.OH, which yields odorless prisms, easily soluble in water. Sodium 
 cacodylate, (CH 3 ) 2 AsO.ONa -f 3H 2 O, also called sodium dimethyl arsenate, is 
 evidently closely related to mono-sodium arsenate. It is a white odorless 
 powder, very soluble in water, forming needle-shaped crystals, which are hygro- 
 scopic, but otherwise very stable. The aqueous solution is alkaline to litmus, 
 but nearly neutral to phenolphthalein. Its action is similar to that of other 
 arsenic compounds, but it is said to be much less toxic, and also less apt to 
 cause undesirable side-effects. 
 
 QUESTIONS. How do hydrocarbons occur in nature, and by what processes 
 are they formed in nature or artificially? State the general physical and 
 chemical properties of hydrocarbons. State the composition and properties 
 of methane, and also the conditions under which it is formed in nature. What 
 is coal, what are its constituents, from what is it derived, and by what process 
 has it been formed ? What is crude coal-oil, what is petroleurn-benzin, and wh at 
 is petrolatum? How is illuminating gas manufactured, and what are its chief 
 constituents? Mention some of the important substances found in coal-tar. 
 State of chloroform : composition, properties, two processes for its manufacture, 
 and method of detection. Explain the action of chlorine on methane and 
 name the products. How is iodoform made and what are its properties ? 
 
ALCOHOLS. 479 
 
 43. ALCOHOLS. 
 
 Constitution of alcohols. The old term "alcohol" originally 
 indicated but one substance (ethyl alcohol), but it is now applied to a 
 large group of substances which may be looked upon as being derived 
 from hydrocarbons by replacement of one, two, or more hydrogen 
 atoms by hydroxyl, OH. In other words, alcohols are hydrocar- 
 bon radicals in combination with hydroxyl. 
 
 If hydroxyl replaces but one atom of hydrogen in a hydrocarbon, 
 the alcohol is termed monatomic ; diatomic and triatomic alcohols are 
 formed by replacement of two or three hydrogen atoms respectively. 
 (Diatomic alcohols are also termed glycols.) As an instance of a 
 diatomic alcohol may be mentioned ethylene alcohol, C 2 H 4 (OH) 2 , 
 while glycerin, C 3 H 5 (OH) 3 , is a triatomic alcohol. Tetratomic, 
 pentatomic, and hexatomic alcohols are also known. 
 
 It has been shown before that the higher members of the paraffin series are 
 capable of forming a number of isomeric compounds. Running parallel to the 
 various series of hydrocarbons (and their isomers) we have homologous series 
 of alcohols. The isomeric alcohols also show properties different from one 
 another, and yield different decomposition products. 
 
 Normal alcohols are those with a straight carbon chain derived from normal 
 hydrocarbons. Alcohols are also divided, according to the linkage between tho 
 hydroxyl groups and a carbon atom, into primary, secondary, and tertiary 
 alcohols. 
 
 A primary alcohol is one in which the hydroxyl group is linked to a carbon 
 atom which is united to but one other carbon atom, or, in other words, it is one 
 containing the univalent group, CH 2 OH. For instance, ethyl alcohol, 
 CH 3 CH 2 OH, represents a primary alcohol. Primary alcohols yield by 
 oxidation aldehydes and acids. 
 
 A secondary alcohol is one in which the hydroxyl group is linked to a car- 
 bon atom which is joined to two other carbon atoms-*. ., the hydroxyl forms 
 a side chain and the bivalent group characteristic of secondary alc( 
 is>CH-OH. For instance, iso-propyl alcohol, ggpCH-OH. Secondary 
 
 alcohols yield ketones by oxidation. 
 
 A tertiary alcohol is one in which the hydroxyl group is linked to a carbon 
 atom which is joined to three other carbon atoms, or one containing the tnva- 
 
 CH 3 \ 
 lent group ^C-OH. For instance, tertiary butyl alcohol, CHpC 
 
 tiary alcohols by oxidation yield decomposition products. 
 
 By saturating with hydrogen the three bonds in the above tnatomic radical 
 methyl alcohof, H.O-OH, is obtained. Methyl alcohol ato known as 
 carbinol, and the term carbinoh is used for the hydrocarbon derivative*, 
 
480 CONSIDERATION OF CARBON COMPOUNDS. 
 
 methyl alcohol ; for instance, ethyl alcohol may be called methyl-carbinol. 
 
 Alcohols correspond in their composition to the hydroxides of 
 inorganic substances ; both classes of compounds containing hydroxyl, 
 OH, which, in the case of alcohols, is in combination with radicals 
 containing carbon and hydrogen, in the case of inorganic hydroxides 
 with metals, as, for instance, in potassium hydroxide, KOH. 
 
 If we represent any hydrocarbon radical by E, the general formula 
 of the alcohols will be : 
 
 Monatomic alcohol. Diatomic alcohol. Triatomic alcohol. 
 
 /OTT /OH 
 
 Ki OH RJi<^ Riii OH 
 
 ^ OH ~ \OH 
 
 or 
 
 Kii(OH) 2 
 
 corresponding to 
 
 KOH CaW(OH) 2 Bim(OH) 3 . 
 
 Of the many reactions which justify our views regarding the 
 structure of alcohols, a few may be mentioned. We believe that 
 hydroxyl exists in metallic hydroxides, because they can be made by 
 the action of metals on water, and similarly, by acting with potassium 
 on an alcohol, we obtain a potassium compound and free hydrogen : 
 
 Also, when we act on a metallic hydroxide with an acid a salt is 
 formed and water produced ; the corresponding reaction takes place 
 between alcohols and acids : 
 
 K.OH + HC1 = KC1 + H 2 0, 
 CH 3 .OH + HC1 = CH 3 C1 + H 2 O. 
 
 Many other reactions might be mentioned which furnish proof 
 that each oxygen atom contained in an alcohol molecule is in com- 
 bination with an atom of hydrogen i. e., that alcohols are hydroxides 
 of hydrocarbon radicals. 
 
 Occurrence in nature. Alcohols are not found in nature in a free 
 or uucombined state, but generally in combination with acids as com- 
 pound ethers, Some plants,, for instance, contain compound ethers 
 
ALCOHOLS. 481 
 
 mixed with volatile oils. The triatomic alcohol glycerin is a normal 
 constituent of all fats or fatty oils, and is therefore found in many 
 plants and in most animals. 
 
 Formation of alcohols. Alcohols are often produced by fermen- 
 tation (ethyl alcohol from sugar), sometimes by destructive distillation 
 (methyl alcohol from wood) : they are obtained from compound ethers 
 (which are compounds of acids and alcohols) by treating them with the 
 alkali hydroxides, when the acid enters into combination with the alkali, 
 while the alcohols are liberated according to the general formula : 
 
 RTO> + KOH = 
 
 Alcohols may be obtained artificially by various processes, as, for 
 instance, by treating hydrocarbons with chlorine, when the chloride 
 of a hydrocarbon residue is formed, which may be decomposed by 
 alkali hydroxides in order to replace the chlorine by hydroxyl, when 
 an alcohol is formed. For instance : 
 
 C 2 H 6 + 2C1 == C 2 H 5 C1 + HC1. 
 
 Ethane. Ethyl chloride. 
 
 C 2 H 5 C1 + KOH KC1 -f C 2 H 5 OH. 
 
 Ethyl Potassium Potassium Ethyl 
 
 chloride. hydroxide. chloride. alcohol. 
 
 Another method by which alcohols can be obtained depends on 
 the action of nitrous acid on amines containing radicals of the 
 methane series. For instance : 
 
 C 2 H 5 NH 2 + NOOH = C 2 H 5 OH + 2N + H,O. 
 
 Ethyl amine. Nitrous Ethyl 
 
 acid. alcohol. 
 
 Properties of alcohols. Alcohols are generally colorless, neutral 
 liquids ; some of the higher members are solids, none is gaseous at 
 the ordinary temperature. Most alcohols are specifically lighter than 
 water; the lower members are soluble in or mix with water in 
 all proportions ; the higher members are less soluble, and, finally, 
 insoluble. Most alcohols are volatile without decomposition; 
 some of the highest members, however, decompose before being 
 volatilized. 
 
 Although alcohols are neutral substances, it is possible to replace 
 the hydrogen of the hydroxyl by metals, as has been shown above. 
 The oxygen of alcohols may be replaced by sulphur, when com- 
 pounds are formed known as hydrosulphides or mercaptans; these 
 bodies may be obtained by treating the chlorides of hydrocarbon 
 radicals with potassium sulphydrate. 
 
 C 2 H 5 C1 -f KSH = KC1 + 
 31 
 
482 CONSIDERATION OF CARBON COMPOUNDS. 
 
 By replacement of the hydrogen of the hydroxyl in alcohols by 
 alcohol radicals ethers are formed ; by replacing the same hydrogen 
 with acid radicals compound ethers are produced. Suitable oxidizing 
 agents convert alcohols first into aldehydes then into acids. 
 
 Monatomic normal alcohols of the general composition 
 
 or C n H 2n + 2 O. 
 
 Methyl a 
 Ethyl 
 
 Icohol 
 u 
 
 . C H 3 OH 
 C H 5 OH 
 
 B. P. 
 
 67 C. 
 78 
 
 Propyl 
 
 
 
 C H OH 
 
 07 
 
 Butyl 
 
 M 
 
 C 4 H 9 OH 
 
 115 
 
 Amyl 
 Hexyl 
 
 
 H 
 
 . C 5 H U OH 
 
 r H OH 
 
 132 
 150 
 
 Heptyl 
 Octyl 
 Nonyl 
 Cetyl 
 Ceryl 
 
 t( 
 U 
 it 
 
 It 
 
 . . C 7 H 15 OH 
 . C 8 H 17 OH 
 . C 9 H 19 OH 
 . . . C K H 33 OH 
 C 97 H~OH 
 
 168 
 186 
 204 
 
 50 i 
 yg 1 Fusing- 
 
 Melissyl 
 
 u 
 
 
 85 J P int ' 
 
 Methyl alcohol, CH 3 OH (Methyl hydroxide, Carbinol, Wood-spirit, 
 Wood-naphtha). Methyl alcohol is one of the many products obtained 
 by the destructive distillation of wood. When pure it is a thin color- 
 less liquid, similar in odor and taste to ethyl alcohol, and is often sub- 
 stituted for the latter for various purposes in the arts and manu- 
 factures. 
 
 Crude wood-spirit, which contains many impurities, has an offensive odor, 
 a burning taste, and is strongly poisonous. A more or less impure article is 
 sold under the name of Columbian spirit, while methylated spirit is ordinary 
 alcohol containing 10 per cent, of methyl alcohol. 
 
 The physiological intoxicating and poisonous properties of methyl alcohol 
 are similar to those of ordinary alcohol, but more pronounced. Cases of 
 poisoning, if recovery takes place, may be followed by more or less blindness, 
 due to atrophy of the optic nerve. 
 
 Ethyl alcohol, C 2 H 5 OH =45.7 (Common alcohol, Ethyl hydroxide, 
 Spirit), may be obtained from ethene, C 2 H 4 , by addition of the 
 elements of water, which may be accomplished by agitating ethene 
 with strong sulphuric acid, when direct combination takes place and 
 ethyl sulphuric acid is formed : 
 
 C 2 H 4 + H,S0 4 = C 2 H 3 HS0 4 . 
 Ethene. Sulphuric acid. Ethyl sulphuric acid. 
 
 Ethyl sulphuric acid mixed with water and distilled yields sul- 
 phuric acid and ethyl alcohol : 
 
 C 2 H 6 HS0 4 + H 2 = H 2 SO 4 + C 2 H 5 OH. 
 
ALCOHOLS. 483 
 
 Ethyl alcohol may also be obtained, as already mentioned, by treat- 
 ing ethyl chloride with potassium hydroxide : 
 
 C 2 H 5 C1 + KOH KC1 + C 2 H 6 OH. 
 
 While the above methods for obtaining alcohol are of scientific 
 interest, there is but one mode of manufacturing it on a large scale, 
 namely, by the fermentation of certain kinds of sugar, especially 
 grape-sugar or glucose, C 6 H 12 O 6 . A diluted solution of grape-sugar 
 under the influence of certain ferments (yeast) suffers decomposition, 
 yielding carbon dioxide and alcohol : 
 
 C 6 H 12 6 = 2CO 2 + 2C 2 H 5 OH. 
 Glucose. Carbon Ethyl 
 
 dioxide. alcohol. 
 
 From 94 to 96 per cent, of the sugar is decomposed, according to 
 the above reaction, the rest forming glycerin (3 per cent.), succinic 
 acid (0.6 per cent.), and higher alcohols designated " fusel oil." 
 
 Experiment 55. To a solution of 25 grammes of commercial glucose (grape- 
 sugar) in 1000 c.c. of water, add a little brewer's yeast and introduce this mix- 
 ture into a flask. Attach to the flask, by means of a perforated cork, a bent 
 glass tube leading into clear lime-water, contained in a small flask. After 
 standing (a warm place should be selected in winter for this operation) a few 
 hours fermentation will commence, which can be noticed by the evolution of 
 carbon dioxide, which, in passing through the lime-water, causes the precipi- 
 tation of calcium carbonate. 
 
 After fermentation ceases connect the flask with a condenser and distil over 
 50 to 100 c.c. of the liquid. Verify in the distilled portion the presence of 
 alcohol by applying the tests mentioned below. For condensation of the dis- 
 tilling vapors a Liebig's condenser, represented in Fig. 70, may be used. 
 
 The alcoholic strength of fermented sugar solutions is never over 
 14 per cent., since above this point the yeast ceases to act. On the 
 large scale this liquid is distilled in apparatus so arranged that the 
 vapors are repeatedly condensed and vaporized, thus yielding by a 
 single distillation an alcohol of about 90 per cent. This is further 
 purified by treatment with charcoal and rectifying in so-called column 
 stills, when alcohol containing as much as 94 to 95 per cent, is ob- 
 tained. To remove the last portions of water the liquid is distilled 
 over calcium oxide, which forms calcium hydroxide. 
 
 The alcohol thus obtained, and containing not more than 1 per 
 cent, of water, is known as pure, absolute, or real alcohol (alcohol 
 absolutum). The alcohol of the U. 8. P. contains 92.3 per cent, by 
 weight or 94.9 per cent, by volume of real alcohol, and has a specific 
 gravity of 0.816 at 15.6 C. (60 F.). The diluted alcohol, is made 
 by mixing equal volumes of water and alcohol, and has a specific 
 
484 
 
 CONSIDERATION OF CARBON COMPOUNDS. 
 
 gravity of 0.936 ; it is identical with the proof-spirit of the U. 8. 
 Custom-house and Internal Revenue service. 
 
 Pure alcohol is a transparent, colorless, mobile, and volatile liquid, 
 of a characteristic rather agreeable odor, and a burning taste; it boils 
 at 78 C. (172 F.), has a specific gravity of 0.797, is of a neutral 
 reaction, becomes syrupy at 110 C. (166 F.), and solidifies at 
 130 C. ( 202 F.); it burns with a non-luminous flame; when 
 mixed with water a contraction of volume occurs, and heat is liber- 
 ated ; the attraction of alcohol for water is so great that strong 
 alcohol absorbs moisture from the air or abstracts it from membranes, 
 
 FIG. 70. 
 
 Liebig's condenser with distilling-flask. 
 
 tissues, and other similar substances immersed in it; to this property 
 are due its coagulating action on albumin and its preservative action 
 on animal substances. The solvent powers of alcohol are very exten- 
 sive, both for inorganic and organic substances ; of the latter it readily 
 dissolves essential oils, resins, alkaloids, and many other bodies, for 
 which reason it is used in the manufacture of the numerous official 
 tinctures, extracts, and fluid extracts. 
 
 Alcohol taken internally in a dilute form has intoxicating proper- 
 ties ; pure alcohol acts poisonously ; it lowers the temperature of the 
 body from 0.5 to 2 C. (0.9 to 3.6 F.), although the sensation of 
 warmth is experienced. Alcohol is not a food in the ordinary sense 
 of the word. Small quantities of diluted alcohol are oxidized jn the 
 
ALCOHOLS. 485 
 
 system to carbon dioxide and water ; larger amounts are eliminated, 
 for the most part unchanged, by the lungs and kidneys. 
 
 The treatment of acute alcohol poisoning is chiefly restricted to the evacua- 
 tion of the stomach, warm applications to the extremities, and possibly hypo- 
 dermic injections of strychnine to sustain the heart. 
 
 Denatured alcohol. Alcohol may be withdrawn from bond without the 
 payment of internal revenue tax for use in the arts and industries, and for 
 fuel, light, and power, provided said alcohol shall have been mixed, under 
 certain prescribed regulations, with specified denaturing material, whereby it is 
 rendered unfit for beverage or medicinal purposes. 
 
 Completely denatured alcohol must contain either methyl alcohol and ben- 
 zin, or methyl alcohol and pyridine bases. Tax-free alcohol may also be used 
 for manufacturing chemicals, where the alcohol is changed into some other 
 chemical substance and does not appear in the finished product as alcohol, 
 Inasmuch as the agents present in completely denatured alcohol render it 
 unfit for use in many chemical industries, special denaturants have been 
 authorized by the Commissioner of Internal Revenue where absolutely neces- 
 sary. About fifteen special denaturing formulas are in use at the present time. 
 
 Hospitals are allowed to denature alcohol with substances which render it 
 unfit as a beverage, but not for external use. For this purpose such substances 
 as camphor, thymol, boric acid, etc., may be used. . 
 
 For a full account of the subject of denatured alcohol, and the various for- 
 mulas for this purpose, see the article on Alcohol in the National Standard 
 Dispensatory. 
 
 Analytical reactions for ethyl alcohol. 
 
 1. Dissolve a small crystal of iodine in about 2 c c. of alcohol ; 
 add to the cold solution potassium hydroxide until the brown color 
 of the solution disappears ; a yellow precipitate of iodoform, CHI 3 , 
 forms. Many other alcohols, aldehyde, acetone, etc., show the same 
 reaction. 
 
 2. Add to about 1 c.c. of alcohol the same volume of sulphuric 
 acid ; heat to boiling and add gradually a little more alcohol : the 
 odor of ethyl ether will be noticed distinctly on further heating. 
 
 3. Add to a mixture of equal volumes of alcohol and sulphuric, 
 acid, a crystal (or strong solution) of sodium acetate: acetic ether is 
 formed and recognized by its odor. 
 
 4. To about 2 c.c. of potassium dichromate solution add 0.5 c.c. of 
 sulphuric acid and 1 cc. of alcohol: upon heating gently the liquid 
 becomes green from the formation of chromic sulphate, while alde- 
 hyde is formed and may be recognized by its odor. 
 
 Alcoholic liquors. Numerous substances containing sugar or starch (which 
 may be converted into sugar) are used in the manufacture of the various alco- 
 
486 CONSIDERATION OF CARBON COMPOUNDS. 
 
 holic liquors, all of which contain more or less of ethyl alcohol, besides color- 
 ing matter, ethers, compound ethers, and many other substances. 
 
 White and red wines are obtained by the fermentation of the grape-juice ; the 
 so-called light wines contain from 10 to 12, the strong wines, such as port and 
 sherry, from 19 to 25 per cent, of alcohol ; if the grapes contain much sugar, 
 only a portion of it is converted into alcohol, while another portion is left 
 undecomposed ; such wines are known as sweet wines. Effervescent wines, as 
 champagne, are bottled before the fermentation is complete ; the carbonic acid 
 is disengaged under pressure and retained in solution in the liquid. 
 
 Beer is prepared by fermentation of germinated grain (generally barley) to 
 which much water and some hops have been added; the active principle of 
 hops is lupulin, which confers on the beer a pleasant, bitter flavor, and the 
 property of keeping without injury. Light beers have from 2 to 4, strong beers, 
 as porter or stout, from 4 to 6 per cent, of alcohol. 
 
 /Spirits differ from either wines or beers in so far as the latter are not dis- 
 tilled, and therefore contain also non-volatile organic and inorganic substances, 
 such as salts, etc., not found in the spirits, which are distilled liquids contain- 
 ing volatile compounds only. Moreover, the quantity of alcohol in spirits is 
 very much larger, and varies from 45 to 55 per cent. Of distilled spirits may 
 be mentioned : American whiskey, made from fermented rye or Indian corn ; 
 Irish whiskey, from potatoes ; Scotch whiskey, from barley ; brandy or cognac, by 
 distilling French wines ; rum, by fermenting and distilling molasses ; gin, from 
 various grains flavored with juniper berries. 
 
 Amyl alcohol, C 5 H n OH. Theoretically eight amyl alcohols are possible, 
 and all are known. The common amyl alcohol is iso-butyl-carbinol, (CH 3 ) 2 .- 
 CH.CH 2 .CH 2 OH. It is frequently formed in small quantities during the fer- 
 mentation of corn, potatoes, and other substances. When the alcoholic liquors 
 are distilled, amyl alcohol passes over toward the end of the distillation, gener- 
 ally accompanied by propyl, butyl, and other alcohols, and by certain ethers 
 and compound ethers. A mixture of these substances is known as fusel oil, 
 and from this liquid amyl alcohol may be obtained in a pure state. It is an 
 oily, colorless liquid, having a peculiar odor and a burning, acrid taste ; it is 
 soluble in alcohol, but not in water. By oxidation of amyl alcohol valerianic 
 acid is obtained. 
 
 Amylene hydrate, Ethyl-dimethyl-carbinol, (CH 3 } 2 .COff.C 2 H 5 , is an alcohol 
 isomeric with the above amyl alcohol, but yielding only acetic acid on oxida- 
 tion. It is a colorless liquid, having a pungent, ethereal odor, and a, boiling- 
 point of 100 C. (212 F.). It has been used as an hypnotic. 
 
 Allyl alcohol, C 3 H 5 OH, is an unsaturated monatomic alcohol which can be 
 obtained from glycerin by several reactions. It is most readily obtained by 
 distilling a mixture of glycerin and oxalic acid between 220 and 230 C., 
 when allyl alcohol, CH 2 = CH CH 2 OH, passes over. When glycerin is 
 treated with iodide of phosphorus, allyl iodide, CH 2 = CH.CH 2 I, is obtained. 
 This reacts with silver hydroxide, forming silver iodide and allyl alcohol. 
 Allyl iodide is employed in the artificial preparation of oil of mustard, or allyl 
 iso-sulpho-cyanate, and oil of garlic, or allyl sulphide. These products are 
 found in nature and are salts of allyl alcohol. 
 
 By oxidation with potassium permanganate allyl alcohol is reconverted into 
 glycerin. 
 
ALCOHOLS. 487 
 
 Allyl alcohol is a colorless liquid possessing a disagreeable penetrating odor. 
 It is soluble in water in all proportions ; B. P. 96.5 C. 
 
 Glycerin, Glycerinum, C 3 H 5 (OH) 3 = 91.37 (Glycerol). This is 
 a triatomic alcohol, in which three OH groups have replaced three 
 hydrogen atoms in propane, CH 3 .CH 2 .CH 3 . Synthetic methods have 
 shown the glycerin to be CH 2 OH.CHOH.CH 2 OH. 
 
 Glycerin is a normal constituent of all fats, which are glycerin in which the 
 three atoms of hydrogen of the hydroxyl have been replaced by radicals of 
 fat acids. It is obtained as a by-product in the manufacture of soap, but it is 
 also largely manufactured by passing steam under 120 to 150 pounds pressure 
 into fats contained in large copper digesters. By this treatment the fats are 
 decomposed into glycerin, which remains dissolved in the water; non-volatile 
 fatty acids, floating on the surface of the solution ; and volatile fatty acids, 
 which escape with the steam. The aqueous solution of glycerin is first con- 
 centrated by evaporation, and then treated with superheated steam, with which 
 glycerin volatilizes and is condensed in suitably constructed vessels. 
 
 Pure glycerin is a clear, colorless, odorless liquid of a syrupy con- 
 sistence, smooth to the touch, hygroscopic, very sweet, and neutral in 
 reaction, soluble in water and alcohol in all proportions, but insoluble 
 in ether, chloroform, benzol, and fixed oils ; its specific gravity is 
 1.246 at 25 C. ; it cannot be distilled by itself without decomposition, 
 but is volatilized in the presence of water or when steam is passed 
 through it. 
 
 Glycerin is a good solvent for a large number of organic and inorganic sub- 
 stances ; the solutions thereby obtained are often termed glycerites ; official are 
 the glycerites of starch, carbolic acid, tannic acid, and a few others. 
 
 Boroglycerin is made by heating a mixture of boric acid and gly- 
 cerin, when an ether of the composition C 3 H 5 BO 3 is obtained. It is 
 used as a mild antiseptic agent. 
 
 Analytical reactions. 
 
 1. A borax bead immersed for a few minutes in a solution of 
 glycerin (made slightly alkaline with potassium hydroxide) imparts 
 a green color to a non-luminous flame, owing to the liberation of 
 boric acid. 
 
 2. Glycerin slightly warmed with an equal volume of sulphuric 
 acid should not turn dark, but, on further heating, the characteristic, 
 irritating odor of acrolein is noticed. 
 
 Glycerin trinitrate, C 3 H 5 (NO 3 ) 3 (Nitro-glycerin, Glonoin). When 
 glycerin is treated with nitric acid, or, better, with a mixture of con- 
 centrated sulphuric and nitric acids, chemical action takes place 
 
488 CONSIDERATION OF CARBON COMPOUNDS. 
 
 resulting in the formation of glyceryl mono-nitrate, or tri-nitrate, 
 substances belonging to the group of compound ethers, the constitu- 
 tion of which will be explained later. 
 
 C 3 H 5 (OH) 3 + 3HN0 3 = C 3 H 5 (N0 3 ) 3 + 3H 2 O. 
 
 The tri-nitro-glycerin is the common nitro-glyceriu, a pale-yellow 
 oily liquid, which is nearly insoluble in water, soluble in alcohol, 
 crystallizes at 20 C. ( 4 F.) in long needles, and explodes very 
 violently by concussion ; it may be burned in an open vessel, but 
 explodes when heated over 250 C. (482 F.). 
 
 Spirit of g-lyceryl trinitrate, Spiritus g-lycerylis nitratis (Spirit 
 of glonoiri) is an alcoholic solution of nitro-glycerin, containing of this 
 substance 1 per cent. 
 
 Dynamite. One kilogram of nitro-glycerin yields after explosion 713 liters 
 of gas, measured at normal temperature and pressure. As the gas temperature 
 is raised by explosion to about 7000 C. (13,000 F.), the volume is comparatively 
 larger, and the explosive power of nitro-glycerin compared with that of gun- 
 powder is about 13 to 1. Indeed, the explosions of pure nitro-glycerin are so 
 violent that it is generally mixed with inert substances, such as clay, sawdust, 
 infusorial (diatomaceous) earth, etc. When mixed with the latter it forms the 
 extensively used dynamite, which is more useful and less dangerous to handle 
 than pure nitro-glycerin. While it is not readily exploded by pressure or jar, 
 it is by percussion ; for instance,, by fulminating mercury explosion. 
 
 Mixtures of nitro-glycerin and gun-cotton form explosive gelatine, or gelatine- 
 dynamite. 
 
 Glycerin-phosphoric acid, C 3 H 5 (OH) 2 O.PO(OH) 2 . Compounds 
 of this acid are met with in blood, flesh, the brain, and the nerves. 
 It also occurs together with cholin, as a result of the splitting up of 
 lecithin (see Index). 
 
 The absolute acid is very unstable, decomposing easily into glycerin 
 and phosphoric acid. The commercial article is a 20 per cent, aqueous 
 solution. It is obtained by dissolving gradually glacial phosphoric 
 acid in an equal weight of 95 per cent, glycerin with moderate heat, and 
 subsequently heating the mixture for several hours at 110 C. Union 
 takes place thus : 
 
 C 3 H 5 (OH) 3 -f HPO 3 = C 3 H 5 (OH) 2 O.PO(OH) 2 . 
 
 The tenacious mass is dissolved in water, neutralized with milk of 
 lime, and filtered. The excess of lime is precipitated by a current 
 of carbon dioxide and filtered off. The filtrate is concentrated in a 
 vacuum and precipitated with alcohol or evaporated to dryness. The 
 calcium salt is washed with alcohol to remove glycerin, dissolved in 
 water, and decomposed with a calculated amount of diluted sulphuric 
 acid. (The filtrate is evaporated to the proper concentration.) 
 
ALDEHYDES. KETOXES. 489 
 
 Glycerin-phosphoric acid is a clear colorless liquid which gradually 
 turns yellow, and decomposes slowly in the cold, more rapidly when 
 heated. It is a dibasic acid of decidedly acid taste and reaction. 
 The normal salts are soluble in water, but insoluble in alcohol, and 
 generally have an alkaline reaction. The usual reagents for phos- 
 phoric acid do not affect the solution of glycerin-phosphoric acid in 
 the cold. The calcium, potassium, sodium, lithium, iron, and quinine 
 salts of the acid have been introduced into medicine. 
 
 Calcium glycerin -phosphate, C 3 H 5 (OH). 2 CaPO 4 + H,O, is a white 
 crystalline powder, soluble in 20 parts of water, but less soluble in hot water. 
 It is neutral to litmus, but the commercial product is sometimes acid. It loses 
 its water of crystallization at or above 130 C. 
 
 Sodium glycerin-phosphate, C 3 H 5 (OH) 2 .Na 2 PO 4 + H 2 O, is obtained 
 by neutralizing glycerin-phosphoric acid. It occurs in the market as a 50 per 
 cent, solution of a clear, light yellow color. 
 
 44. ALDEHYDES. KETONES. 
 
 Aldehydes. The name aldehyde is derived from alcohol dehydro- 
 genatum, referring to its method of formation, viz., by the removal 
 of hydrogen from alcohols, as, for instance : 
 
 C 2 H 6 O 2H = C 2 H 4 O. 
 Ethyl alcohol. Acetic aldehyde. 
 
 This removal of hydrogen may be accomplished by various methods, 
 as, for instance, by oxidation of alcohols, when one atom of oxygen 
 combines with two atoms of hydrogen, forming water, while an alde- 
 hyde is formed at the same time. Aldehydes, when further oxidized, 
 are converted into acids ; aldehydes are, consequently, the interme- 
 diate products between alcohols and acids, and are frequently looked 
 upon as the hydrides of the acid radicals. The constitution of acetic 
 
 QUESTIONS. What is the general constitution of alcohols, and what is the 
 difference between monatomic, diatomic, and triatomic alcohols? How do 
 alcohols occur in nature ? By what processes may alcohols be formed arti- 
 ficially, and how may they be separated from their combinations ? State the 
 general properties of alcohols. Mention names and composition of the first 
 five members of alcohols of the general composition C n H2n+iOH. By what 
 process is methyl alcohol obtained, under what other names is it known, and 
 what are its properties? Describe the manufacture of pure alcohol from 
 sugar. Give the alcoholic strength of the alcohol and diluted alcohol of the 
 U. S. P., and also of spirit of wine, proof-spirit, light wines, heavy wines, beers, 
 and spirits. What are the general properties of common alcohol ? How is 
 alcohol denatured ? What is glycerin, how is it found in nature, how is it 
 obtained, and what are its properties ? 
 
490 CONSIDERATION OF CARBON COMPOUNDS. 
 
 acid may be represented by the formula CH 3 .CO.OH ; the radical of 
 acetic acid or acetyl is the group CH 3 .CO, and the hydride of acetyl 
 
 /TT /FT 
 
 is acetic aldehyde, CH 3 .C^Q. It is the group C\o which is char- 
 acteristic of, and found in, all aldehydes. Only a few aldehydes are 
 of practical interest, as, for instance, formaldehyde, acetic aldehyde, 
 paraldehyde, and benzoic aldehyde. 
 
 xTT 
 
 Formic aldehyde, CH 2 O or H.C/Q (Formaldehyde, methyl alde- 
 hyde). This is obtained by the dry distillation of calcium formate, 
 or by gentle oxidation of methyl alcohol. The latter process is 
 carried out by passing vapors of methyl alcohol with air over a 
 heated spiral of platinum or copper. The condensed vapors are 
 formaldehyde dissolved in undecomposed methyl alcohol. Another 
 process is by heating paraformaldehyde, which yields formaldehyde 
 in a pure condition. 
 
 Formaldehyde is a colorless gas, possessing a strong, penetrating 
 odor; it may be condensed to a liquid which boils at 20 C. 
 (-4 F.). 
 
 Solution of formaldehyde, Liquor formaldehydi. Forma-lde- 
 hyde is readily soluble in water, and a solution containing 37 per cent, 
 by weight is official. It is a colorless liquid which has a pungent 
 odor and caustic taste ; its vapors act as an irritant upon the mucous 
 membrane. Sometimes on standing, always on slow evaporation, white, 
 solid paraformaldehyde separates. With ammonio-silver nitrate the 
 solution gives a precipitate of metallic silver. The solution is a 
 strong antiseptic, and when diluted to 4 or 5 per cent, it is one of the 
 best hardening and preserving agents for tissues. 
 
 Formic aldehyde may be recognized by Schijf's reaction: A solution of 
 fuchsin (rosanilin chloride) decolorized or nearly so with sulphurous acid turns 
 pink or violet when brought in contact with any aldehyde solution. For the 
 examination of air, suspended filter-paper, moistened with the decolorized 
 fuchsin solution, may be used. 
 
 Paraformaldehyde, C 3 H 6 O 3 or (CH 2 O) 3 (Formalin). On slow 
 evaporation of a solution of formaldehyde in methyl alcohol poly- 
 merization takes place, and paraformaldehyde separates in colorless 
 crystals which are insoluble in water. On heating the compound, 
 which is now found in the market in the form of tablets, it splits 
 up into three molecules of formaldehyde, which, escaping as a 
 gas, is used for disinfecting purposes. It acts powerfully on all 
 germs, and has the advantage over chlorine and sulphur dioxide that 
 it does not act injuriously on the fabric or color of household goods. 
 
ALDEHYDES. KETONES. 491 
 
 Formaldehyde gas is now very generally used for disinfecting rooms, etc., 
 and has practically displaced the method of burning sulphur to obtain sulphur 
 dioxide. The simplest method of filling a closed space with the gas is to pour 
 the commercial solution of formaldehyde upon small crystals of potassium per- 
 manganate, contained in a spacious metallic vessel. A vigorous reaction takes 
 place, with destruction of a portion of the formaldehyde, approximately 
 according to this reaction : 
 
 4KMn0 4 + 3HCOH + H 2 = 4MnO(OH) 2 + 2K 2 C0 3 + CO 2 . 
 
 The great heat produced causes nearly all the remaining solution to vaporize 
 and fill the space with formaldehyde gas and water vapor, which latter is an 
 essential factor in the disinfection. The temperature of the room should be 
 not less than 10 C. (50 F.), but a higher temperature is better. The propor- 
 tions adopted by some Boards of Health are 500 c.c. of formaldehyde solution 
 and 237 grammes of potassium permanganate per 1000 cubic feet of space. It 
 is well known that formaldehyde is mainly a surface disinfectant, having very 
 little power to penetrate objects, as clothing, etc. 
 
 The formaldehyde odor clinging for days to rooms which have been disin- 
 fected by it may be quickly removed by evaporation of some ammonia water, 
 hexamethylene tetramin, (CH 2 ) 6 N 4 , being formed. 
 
 Acetic aldehyde, C 2 H 4 O or CH 3 .C (Ethyl aldehyde). Alcohol 
 
 may be converted into aldehyde by the action of various oxidizing 
 agents ; the one generally used is potassium dichromate in the pres- 
 ence of sulphuric acid, which oxidizes two hydrogen atoms of the 
 alcohol molecule, converting it into aldehyde : 
 
 C 2 H 6 + O = C 2 H 4 + H 2 0. 
 
 Experiment 56. Place in a 500 c.c. flask, provided with a funnel-tube and 
 connected with a Liebig's condenser, 6 grammes of potassium dichromate. 
 Pour upon this salt through the funnel-tube, very slowly, a previously pre- 
 pared and cooled mixture of 5 c.c. of sulphuric acid, 24 c.c. of water and 6 c.c. 
 of alcohol. Chemical action begins generally without application of heat, and 
 often becomes so violent that the liquid boils up, for which reason a large flask 
 is used. The escaping vapors, which are a mixture of aldehyde, alcohol, and 
 water, are collected in a receiver kept cold by ice. From this mixture pure 
 aldehyde may be obtained by repeated distillation. Use the distillate for 
 silvering a test-tube by adding some ammoniated silver nitrate. How much 
 potassium dichromate is needed for the conversion of 5 grammes of pure 
 alcohol into aldehyde? 
 
 Aldehyde is a neutral, colorless liquid, having a strong and charac- 
 teristic odor ; it mixes with water and alcohol in all proportions and 
 boils at 21 C. (69.8 F.). The most characteristic chemical property 
 of aldehyde is its tendency to combine directly with a great number 
 of substances; thus it combines with hydrogen to form alcohol, with 
 oxygen to form acetic acid, with ammonia to form aldehyde-ammonia, 
 
492 CONSIDERATION OF CARBON COMPOUNDS. 
 
 C 2 H 4 O.NH S , a beautifully crystallizing substance, with hydrocyanic 
 acid to form aldehyde hydrocyanide, C 2 H 4 O.HCN, with acid sulphites 
 and with many other substances. In the absence of such other sub- 
 stance it unites often with itself, forming polymeric modifications, 
 such as paraldehyde and metaldehyde. 
 
 Aldehyde is a strong reducing agent, which property is used in the 
 silvering of glass, which is done by adding aldehyde to an ammoniacal 
 solution of silver nitrate, when metallic silver is deposited on the walls 
 of the vessel or upon substances immersed in the solution. 
 
 Paraldehyde, C 6 H 12 O 3 . When a few drops of concentrated sul- 
 phuric acid are added to aldehyde, this becomes hot and solidifies on 
 cooling to C. (32 F.). This solid crystalline mass of paralde- 
 hyde, which liquefies at 10.5 C. (51 F.), has been formed by the 
 direct union of three molecules of common aldehyde. Paraldehyde 
 is soluble in 8.5 parts of water, boils at 124 C. (253 F.), and is 
 reconverted into common aldehyde by boiling it with dilute sulphuric 
 or hydrochloric acid. It is official as Paraldehydum and a hypnotic. 
 
 Metaldehyde, (C 2 H 4 0) 3 , is stereo-isomeric with paraldehyde ; it is obtained by a 
 process similar to the one mentioned for paraldehyde, but at a lower tempera- 
 ture. It is a solid crystalline substance, insoluble in water, but slightly soluble 
 in alcohol, ether, and chloroform. 
 
 Trichloraldehyde, Chloral, C^CLjO or CC1 3 .C^Q (Trichlorace- 
 tyl hydride). This substance may be looked upon as acetic aldehyde, 
 C 2 H 4 O, in which three atoms of hydrogen have been replaced by 
 chlorine. It is made by passing a rapid stream of dry chlorine into 
 pure alcohol to saturation, keeping the alcohol cool during the first 
 few hours, and warming it gradually until the boiling-point is 
 reached. According to the quantity of alcohol operated on, the con- 
 version requires several hours or even days. The crude liquid pro- 
 duct separates into two layers ; the lower is removed and shaken with 
 three times its volume of strong sulphuric acid and distilled, the dis- 
 tillate is mixed with calcium oxide and again distilled ; the portion 
 passing over between 94 and 99 C. (201 and 210 F.) is collected. 
 
 The decomposition taking place between alcohol and chlorine may 
 be explained by the formation of aldehyde : 
 
 C 2 H 6 O + 2C1 = C 2 H 4 O + 2HC1, 
 
 and by the subsequent replacement of hydrogen by chlorine : 
 C 2 H 4 O + 6C1 = C 2 HC1 3 + 3HC1 
 
ALDEHYDES. KETONES. 493 
 
 The actual decomposition is, however, somewhat more complicated, 
 numerous intermediate bodies and other decomposition products 
 being formed at the same time. 
 
 Chloral is a colorless, oily liquid, having a penetrating odor and an 
 acrid, caustic taste; its specific gravity is 1.5, and its B. P. 95 C. 
 (202 F.). 
 
 Hydrated chloral, Chloralum hydratum, CC1 3 .CH(OH) 2 =164.12. 
 When water is added to chloral the two substances combine, heat is dis- 
 engaged, and the hydrate of chloral is formed, which is a crystalline, 
 colorless substance, having an aromatic, penetrating odor, a bitter, 
 caustic taste, and a neutral reaction ; it is freely soluble in water. 
 alcohol, and ether, also soluble in chloroform, carbon disulphide, 
 benzene, fatty and essential oils, etc. ; it liquefies when mixed with 
 carbolic acid or with camphor; it melts at 58 C.(136 F.),and boils 
 at 95 C. (203 F.), and also volatilizes slowly at ordinary temperature. 
 
 Chloral, and its hydrate, are decomposed by weak alkalies into 
 chloroform and a formate of the alkali metal : 
 
 C 2 HC1 3 + KHO : KCHO 2 + CHC1 3 . 
 Chloral. Potassium Potassium Chloroform. 
 
 hydroxide. formate. 
 
 This decomposition was believed to take place in the animal body, and 
 especially in the blood, whenever chloral was given internally, but recent in- 
 vestigations seem to contradict this assumption. There is no chemical antidote 
 which may be used in cases of poisoning by chloral, and the treatment is, 
 therefore, confined to the use of the stomach-pump and to the maintenance of 
 respiration. 
 
 Analytical reactions for chloral. 
 
 1. Chloral or hydrated chloral heated with potassium hydroxide is 
 converted into potassium formate and chloroform, which latter may 
 be recognized by its odor. (See explanation above.) 
 
 2. Heated with silver nitrate and ammonium hydroxide a silver- 
 mirror is formed on the glass. 
 
 3. Heated with Fehling's solution a red precipitate is formed. 
 See also reactions 2 and 6 for chloroform. 
 
 Acrylic aldehyde, CH 2 = CH.C (Acrolein), may be obtained by 
 the careful oxidation of allyl alcohol, or by the dehydrating action 
 of potassium acid sulphate on glycerin : 
 
 C 3 H 8 3 - 2H,0 = C 3 H 4 0. 
 
 It is also formed by the destructive distillation of glycerin, which is a 
 constituent of fats. Hence, acrolein is formed when fats are heated 
 
494 CONSIDERATION OF CARBON COMPOUNDS. 
 
 to a point of decomposition, and its presence is noticed by the pecu- 
 liar penetrating odor. 
 
 Acrolein is a highly volatile liquid, boiling at 52.4 C. It has a 
 characteristic, penetrating odor and its vapors act on the eyes, causing 
 the secretion of tears. Acrolein shows in its chemical behavior its 
 aldehydic nature. It takes up oxygen forming acrylic acid; com- 
 bines with hydrogen forming allyl alcohol ; combines directly with 
 hydrochloric acid, ammonia, etc. 
 
 Ketones or acetones. These are compounds containing the 
 bivalent radical carbonyl, CO <, to which two hydrocarbon radicals 
 are attached. The relation existing between carbonic acid, organic 
 acids, aldehydes, and ketones is best shown by the following formulas, 
 in which R stands for any hydrocarbon radical : 
 
 Carbonic acid. Organic acid. Aldehyde. Ketone. 
 
 While aldehydes are obtained by the oxidation of primary alcohols, ketones 
 are the first product of the oxidation of secondary alcohols. For instance : 
 
 C 2 H 5 .CH 2 .OH + O = C 2 H 5 .COH + H 2 O. 
 
 Primary propyl Propionic 
 
 alcohol. aldehyde. 
 
 . O = , CO + H 2 0. 
 
 Secondary propyl Dimethyl 
 
 alcohol. ketone. 
 
 Ketones are neutral substances which resemble aldehyde in so far as they 
 have the power to unite directly with many substances with which aldehydes 
 combine ; as, for instance, with the acid sulphites. On the other hand, while 
 aldehydes readily take up oxygen directly and form acids, ketones are decom- 
 posed by oxidizing agents. 
 
 Acetone, Acetonum, CH 3 .CO.CH 3 = 57.61 (Dimethyl-ketone). 
 This compound is obtained by the destructive distillation of acetates 
 (and of a number of other substances). The decomposition which 
 calcium acetate suffers may be shown by the equation : 
 
 CH 3 COO\p __ CHgXpp, | p_p/-i 
 CH 3 COO/ Ca - CH 3 X C( CaC0 *- 
 Calcium acetate. Acetone. 
 
 Acetone is a colorless liquid, boiling at 56.5 C. (133.7 1?.), rnis- 
 eible with water, alcohol, and ether in all proportions ; it has a pecu- 
 liar ethereal, somewhat mint-like odor, and burns with a luminous 
 non-sooty flame. 
 
ALDEHYDES. KETONES. 495 
 
 Sulphur derivatives. A comparison of such inorganic compounds 
 as H 2 S, CS 2 , NH 4 SH, with H 2 O, CO 2 , NH 4 OH, shows that sulphur 
 often replaces oxygen. Correspondingly, sulphur frequently replaces 
 oxygen in organic compounds. When this replacement takes place 
 in alcohols compounds are formed, called mercaptans, mlpho-alcohols, 
 or thio-alcohoh; when it takes place in aldehydes sulph-aldehydes are 
 formed. These bodies, as a general rule, are ill-smelling compounds, 
 some of which are the result of putrefaction in proteids. 
 
 When mercaptans are treated with oxidizing agents three atoms of oxygen 
 e taken up and compounds are formed which are called sulphonic acids, 
 
 na 
 
 are 
 thus: 
 
 C 2 H 5 SH -f 30 = C 2 H 5 .S0 2 OH. 
 
 Ethyl Ethyl sulphonic 
 
 mercaptan. acid. 
 
 Sulphonic acids correspond to sulphurous acid in which a hydrogen atom 
 has been replaced by a hydrocarbon radical. 
 
 Ketones form condensation products with both alcohols and mercaptans 
 thus: 
 
 CH 3 \ m HO.C 2 H 5 CH 3 \ p /OC 2 H 
 CH 3 X CO + HO.C 2 H 5 5 " 
 
 Acetone. Ethyl Ketol. 
 
 alcohol. 
 
 Acetone. Ethyl Mercaptol. 
 
 mercaptan. 
 
 By oxidizing mercaptol with potassium permanganate it takes up oxygen 
 (similar to mercaptans), with the result that a compound is formed containing 
 sulphonic acid : 
 
 CH 3 \ r /SC 2 H 5 CH 3 \ r /S0 2 C 2 H 5 
 
 C + ' = CH 3 / C \S0 2 C 2 H 6 ' 
 
 Mercaptol. Diethylsulphon- 
 
 dimethyl-methane. 
 
 This compound is used medicinally under the name of sulphonal. 
 
 The relations between methane and some of its derivatives, which have been 
 considered in this chapter, may be shown graphically thus : 
 
 H\ p /Cl H\ n /I H\ C /COH 
 
 H/\H C1X C \C1 I/ C \I H/\H 
 
 Methane. Chloroform. lodoform. Aldehyde. 
 
 Cl\ r /COH ^p/CH,, CH 3 \ r /S0 2 C 2 H 6 
 
 Cl/Sd / C \CH 3 CH 3 X\S0 2 C 2 H 6 
 
 Chloral. Acetone. Hul phonal. 
 
 Sulphonmethane, Sulphonmethanum, Sulphonal, (CH 3 ) 2 C- 
 (C 2 H 5 SO 2 ) 2 = 226.55 (Diethylsulphon-dimethyl-methane). Sulphonal 
 is a white crystalline substance, having neither odor nor taste ; it is 
 
496 CONSIDERATION OF CARBON COMPOUNDS. 
 
 soluble in 15 parts of boiling and 360 parts of cold water, soluble 
 with difficulty in alcohol; it fuses at 125.5 C. (258 F.), and vola- 
 tilizes at about 300 C. (572 F.), with partial decomposition. A 
 mixture of sul phonal with either wood charcoal or with potassium 
 cyanide evolves, on heating, the characteristic odor of mercaptan. It 
 is used as an hypnotic and soporific. 
 
 Sulphonethylmethane, Trional, (?H'>C<c 2 2 H?S0 2 2 (Diethylsulphon- 
 
 methyl-ethyl-methane), and Tetronal, c'EP^C^H-o^ (Diethylsulphon- 
 diethyl-methane), are both colorless solids, forming lustrous crystals, soluble in 
 hot water and in alcohol and ether. The therapeutic action of these bodies 
 is similar to that of sulphonal. 
 
 45. MONOBASIC FATTY ACIDS. 
 
 General constitution of organic acids. When hydroxyl, OH, 
 replaces hydrogen in hydrocarbons, alcohols are formed ; when the 
 univalent group, CO 2 H, known as carboxyl, replaces hydrogen in 
 hydrocarbons, acids are formed ; and all acids containing this radical 
 are termed carboxylic acids. Monatomic, diatomic, and triatomic 
 alcohols are formed by introducing hydroxyl once, twice, or three 
 times respectively into hydrocarbon molecules; monobasic, dibasic, 
 and tribasic acids are formed by substituting one, two, or three 
 hydrogen atoms by carboxyl. For instance : 
 
 Hydrocarbons. Monobasic acids. Dibasic acids. 
 
 CH 4 CH 3 C0 2 H CH 2 \C%H- 
 
 Methane. Acetic acid. Malonic acid. 
 
 C 2 H 6 C 2 H 5 CO 2 H ^ 2 ^*\CO 2 H* 
 
 Ethane. Propionic acid. Succinic acid. 
 
 As stated before, organic acids may also be considered as carbonic 
 
 QUESTIONS. What is an aldehyde, and what are its relations to alcohols 
 and acids ? Give composition, mode of manufacture, and properties of form- 
 aldehyde. Explain the action of chlorine upon alcohol. Give the compo- 
 sition and properties of chloral and hydrated chloral. What decomposition 
 takes place when alkalies act upon chloral ? Under what conditions is acro- 
 lein formed and what are its properties ? Give the general composition of 
 ketones and a general method of obtaining them. How is acetone prepared? 
 Which compounds are called mercaptans, and how are they converted into 
 sulphonic acids ? Give method for preparing sulphonal, and state its prop- 
 erties. 
 
MONOBASIC FATTY ACIDS. 497 
 
 acid in which one of the hydroxyl groups has been replaced by a 
 hydrocarbon radical, thus: 
 
 Carbonic acid. Acetic acid. f^ 
 
 D \OH 
 Malonic acid. 
 
 This shows that carboxyl, CO 2 H, is made up of hydroxyl, OH, 
 and the bivalent radical, CO, termed carbonyl. By replacement of 
 the hydrogen of the hydroxyl (or of the carboxyl, which is the same) 
 by metals the various salts are formed. 
 
 What is termed the acid radical is the group of the total number 
 of atoms present in the molecule, with the exception of the hydroxyl. 
 In acetic acid, C 2 H 4 O 2 , for instance, the radical is CH 3 CO, or C 2 H 3 O, 
 which group of atoms, known as acetyl, is characteristic of acetic 
 acid, and of all acetates, and may often be transferred from one com- 
 pound into another without decomposition. 
 
 The difference between alcohol radicals and acid radicals may also 
 be stated, by saying that the first contain carbon and hydrogen only, 
 while acid radicals contain carbon, hydrogen, and oxygen. 
 
 In a similar manner, as there are homologous series of alcohols 
 corresponding to the various series of hydrocarbons, there are also 
 homologous series of organic acids running parallel with the corre- 
 sponding series of hydrocarbons or alcohols. 
 
 Occurrence in nature. Organic acids are found and formed both 
 in vegetables and animals, and are present either in the free state, or 
 (and more generally) in combination with bases as salts, or with 
 alcohols as compound ethers. Uncombined or as salts are found, for 
 instance, citric, tartaric, and oxalic acids in plants, formic acid in 
 some insects, uric acid in urine, etc. ; as compound ethers are found 
 many of the fatty acids in the various fats. 
 
 Some organic acids are also found as products of the decomposition 
 of organic matters in nature. 
 
 Formation of acids. Many acids are produced by oxidation of 
 alcohols. As intermediate products are formed aldehydes, which 
 may be looked upon (as stated in the last chapter) as alcohols from 
 which two atoms of hydrogen have been removed. 
 
 The change of a primary alcohol into an aldehyde, and of this 
 into an acid, takes place according to the general formulas : 
 
 32 
 
498 CONSIDERATION OF CARBON COMPOUNDS. 
 
 R.CH 2 OH + O == O=C^ + H 2 0. 
 Alcohol. Aldehyde. 
 
 =<H + O = =<OH- 
 Aldehyde. Acid. 
 
 Acids are obtained from compound ethers by boiling them with 
 alkalies, Avhen salts are formed, which may be decomposed by sul- 
 phuric or other acids. For instance : 
 
 + KOH = 
 
 Ethyl acetate. 
 
 2C 2 H 3 KO 2 
 
 Potassium 
 acetate. 
 
 Potassium 
 hydroxide. 
 
 + H 2 SO 4 = 
 
 Sulphuric 
 acid. 
 
 Potassium 
 acetate. 
 
 = 2C 2 H 4 O 2 - 
 Acetic acid. 
 
 Ethyl alcohol. 
 
 f K 2 S0 4 . 
 
 Potassium 
 sulphate. 
 
 Acids are formed also by destructive distillation (acetic acid) ; by 
 fermentation (lactic acid) ; by putrefaction (butyric acid) ; by oxida- 
 tion of many organic substances (oxalic acid by oxidation of 
 starch), etc. 
 
 Properties. Organic acids show the characteristics mentioned of 
 inorganic acids, viz., when soluble, have an acid or sour taste, redden 
 litmus, and contain hydrogen replaceable by metals, with the forma- 
 tion of salts. 
 
 Most organic acids, and especially the higher members, show these 
 acid properties in a less marked degree than inorganic acids ; in fact, 
 they become so weak that the acid properties can often scarcely be 
 recognized. As stated above, mono-, di-, and tri-basic organic acids 
 are known, the latter two being capable of forming normal,, acid, or 
 double salts. 
 
 Most organic acids are colorless, some of the lower and volatile 
 acids have a characteristic odor, but most of them are odorless ; most 
 organic acids are solids, some liquids, scarcely any gaseous at the ordi- 
 nary temperature. Any salt formed by the union of an organic acid 
 and a non-volatile metal (especially alkali metal) leaves the carbonate 
 of this metal after the salt has suffered combustion. It is for this 
 reason that ashes contain metals largely in the form of carbonates. 
 
 While the hydrogen of the hydroxyl may be replaced by metals 
 or by other residues, the hydrogen of the acid radical may often be 
 replaced by chlorine, and the oxygen of the hydroxyl by sulphur. 
 The acids formed by this last reaction are known as thio acids, for 
 instance, thio-acetic acid, C 2 H 4 OS. 
 
 When the hydrogen of the hydroxyl is replaced by a second acid 
 
MONOBASIC FATTY ACIDS, 
 
 499 
 
 radical (of the same kind as the one forming the acid) the so-called 
 anhydrides are produced, which correspond to the inorganic anhy- 
 drides. For instance : 
 
 Nitric acid. 
 
 N0 2 \o 
 N0 2 / 
 
 Nitric anhydride. 
 
 C 2 H 4 O 2 or C 2 H 3 O.OH. 
 Acetic acid. 
 
 C 2 H 3 0\ 
 C 2 H 3 0/ a 
 
 Acetic andydride. 
 
 It is evident from the above that, while acids are hydroxides of 
 acid radicals, the anhydrides are oxides. They are often formed by 
 abstracting water from two molecules of an acid, thus : 
 
 C 2 H 3 O.Oin _ C 2 H 3 0\ , H0 
 C 2 H 3 O.OH/ - C 2 H30/ + H2 ' 
 
 Amino-acids are compounds obtained from acids by replacement of 
 a hydrogen atom of the acid radical by NH 2 ; these compounds will 
 be spoken of later in connection with amides. 
 
 Patty acids of the general composition, 
 C n H 2n 2 or C n H 2n + 1 C0 2 H. 
 
 Occurs in : 
 
 Fusing- Boiling- 
 point, point. 
 
 Formic acid, 
 
 H CO 2 H 
 
 -f 4C. 
 
 100' 
 
 Acetic acid, 
 
 C H 3 C0 2 H 
 
 +17 
 
 118 
 
 Propionic acid, 
 
 C 2 H 5 C0 2 H 
 
 21 
 
 140 
 
 Butyric acid, 
 
 C 3 H 7 CO 2 H 
 
 20 
 
 162 
 
 Valeric acid, 
 
 C 4 H 9 CO 2 H 
 
 16 
 
 185 
 
 Caproic acid, 
 
 C 5 H U C0 2 H 
 
 2 
 
 205 
 
 (Enanthylic acid, 
 
 C 6 H 13 C0 2 H 
 
 10 
 
 224 
 
 Caprylic acid, 
 
 C 7 H 15 C0 2 H 
 
 +14 
 
 236 
 
 Pelargonic acid, 
 
 C 8 H 17 C0 2 H 
 
 18 
 
 254 
 
 Capric acid, 
 
 C 9 H 19 C0 2 H 
 
 30 
 
 270 
 
 Laurie acid, 
 
 C U H 23 C0 2 H 
 
 43 
 
 
 
 Myristic acid, 
 
 C 13 H 27 C0 2 H 
 
 54 
 
 
 
 Palmitic acid, 
 
 C 15 H 31 CO 2 H 
 
 62 
 
 
 
 Margaric acid, 
 
 CieHssCOjjH 
 
 60 
 
 
 
 Otearic acid, 
 
 C 17 H 35 C0 2 H 
 
 70 
 
 
 
 Arachidic acid, 
 
 /""I TT f~^r\ TT 
 L^igilggVAyg " 
 
 75 
 
 
 
 Behenic acid, 
 
 C 21 H 43 CO 2 H 
 
 76 
 
 
 
 Hysenic acid, 
 
 C 24 H 49 C0 2 H 
 
 77 
 
 
 Cerotic acid, 
 
 C 26 H 53 C0 2 H 
 
 80 
 
 
 
 Melissic acid, 
 
 C^ TT C*f} TT 
 
 90 
 
 
 
 Vegetable and animal fluids. 
 
 Sweat, fluids of the stomach, etc. 
 
 Butter. 
 
 Valerian root. 
 
 Butter. 
 
 Castor oil. 
 
 Butter ; cocoanut oil. 
 
 Leaves of geranium. 
 
 Butter. 
 
 Cocoanut oil. 
 
 Palm oil, butter. 
 (Obtained artificially.) 
 Most solid animal fats. 
 
 Oils of certain plants. 
 Beeswax. 
 
 The name fatty acids has been given to these acids on account of 
 their frequent occurrence in fats, and also in allusion to the some- 
 what fatty appearance of the higher members of the series. 
 
 The gradual change of properties which the members of an homol- 
 ogous series show, is well marked in the series of fatty acids, thus : 
 
500 CONSIDERATION OF CARBON COMPOUNDS. 
 
 First member. Last member. 
 
 Is liquid. Is solid. 
 
 Volatilized at 100 C. Not volatilized without decomposition. 
 
 Strongly acid . Scarcely acid. 
 
 Strongly odoriferous. Odorless. 
 
 Easily soluble in water. Insoluble in water. 
 
 Produces no grease spot. Produces a grease spot. 
 Forms salts easily soluble without Forms salts which are insoluble or de- 
 decomposition, composed by water. 
 
 The intermediate members of the series show intermediate proper- 
 ties, and this change in properties is in proportion to the gradual 
 change in molecular weight. 
 
 Formic acid, H.CO 2 H or CHO.OH. This acid is found in the 
 red ant and in other insects, which eject it when irritated. It is also 
 contained in some plants, as, for instance, in the leaves of the sting- 
 ing-nettle. 
 
 It is formed by the oxidation of methyl alcohol : 
 
 CH 4 4- 2 = CH. 2 2 4- H 2 O, 
 Methyl alcohol. Formic acid. 
 
 by the action of carbonic oxide on potassium hydroxide: 
 
 KOH 4- CO ; KCHO 2 , 
 
 Potassium formate. 
 
 by the action of potassium hydroxide on chloroform : 
 CHCl a 4- 4KOH = 3KC1 4- 2H 2 O 4 KCHO 2 , 
 
 by the action of potassium on moist carbon dioxide : 
 2CO 2 4- ttjO 4- 2K = KHCO 3 + KCHO 2 , 
 
 by heating equal parts of glycerin and oxalic acid, when the latter is 
 split up into carbon dioxide and formic acid, which may be separated 
 from the glycerin by distillation : 
 
 C 2 H 2 O 4 = CO 2 4- CH 2 O 2 . 
 Oxalic acid. Formic acid. 
 
 It is also a product of the decomposition of sugar, starch, etc. 
 Formic acid is a colorless liquid having a penetrating odor, and a 
 strongly acid taste ; it produces blisters on the skin ; it is a powerful 
 deoxidizer, being, when thus acting, converted into carbon dioxide 
 
 and water : 
 
 CH 2 O 2 + O = C0 2 4- H 2 0. 
 
 Acetic acid, H.C 2 H 3 O 2 , or C 2 H 3 O.OH, or CH 3 .CO 2 H = 59.58. 
 The most important alcohol is ethyl alcohol, and the most largely 
 used organic acid is acetic acid, obtained from ethyl alcohol by oxi- 
 
MONOBASIC FATTY ACIDS. 501 
 
 dation. Acetic acid is found in combination with alkali metals in 
 the juices of many plants, also in the secretions of some glands, etc. 
 
 There are many reactions by which acetic acid can be obtained 
 similar to formic acid. For all practical purposes, however, it is 
 made either by the oxidation of alcohol (and aldehyde) or by the 
 destructive distillation of wood. It is produced commercially on a 
 large scale as follows : A diluted alcohol (8 to 10 per cent.) is allowed 
 to trickle down slowly through wood shavings contained in high 
 casks having perforated sides in order to allow a free circulation of 
 the air ; the temperature is kept at about 24 to 30 C. (75 to 86 
 F.), and the liquid having passed through the shavings is repeatedly 
 poured back in order to cause complete oxidation. When the latter 
 object has been accomplished the liquid is a diluted acetic acid. 
 
 It appears that the conversion of alcohol into acetic acid is greatly 
 facilitated by the presence of a microscopic organism (mycoderma 
 aceti) commonly termed " mother of vinegar." This serves in some 
 unexplained way to convey the atmospheric oxygen to the alcohol. 
 The term " acetic fermentation " is often applied to this conversion, 
 although it is not a true fermentation, since no splitting up of the 
 alcohol molecule into other less complex compounds, but a process of 
 slow oxidation, takes place. 
 
 The second process for manufacturing acetic acid is the heating of 
 wood to a red heat in iron retorts, when numerous products (gases, 
 aqueous and tarry substances) are formed. The aqueous products 
 contain, besides other substances, methyl alcohol and acetic acid. 
 The liquid is neutralized with calcium hydroxide and distilled, when 
 methyl alcohol, water, etc., evaporate and a solid residue is left, which 
 is an impure calcium acetate. From this latter, acetic acid is obtained 
 by distilling with sulphuric (or hydrochloric) acid, calcium sulphate 
 (or chloride) being formed and left in the retort, while acetic acid 
 distils over. 
 
 Experiment 57. Add to 54 grammes of sodium acetate contained in a small 
 flask which is connected with a Liebig's condenser, 40 grammes of sulphuric 
 acid. Apply heat and distil over about 35 c.c. ' Determine volumetrically the 
 amount of pure acetic acid in this liquid. 
 
 Pure acetic acid, or glacial acetic acid, is solid at or below 15 C. 
 (59 F.); at higher temperatures it is a colorless liquid having a 
 characteristic, penetrating odor, boiling at 118 C. (244.4 F.), and 
 causing blisters on the skin ; its specific gravity is 1.049 at 25 C. ; 
 it is miscible with water, alcohol, and ether, is strongly acid, forming 
 salts known as acetates, which are all soluble in water. 
 
502 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Vinegar is dilute acetic acid (about 6 per cent.), containing often 
 other substances, such as coloring matter, compound ethers, etc. 
 Vinegar was formerly obtained exclusively by the oxidation of fer- 
 mented fruit-juices (wine, cider, etc.), the various substances present 
 in them imparting a pleasant taste and odor to the vinegar ; to-day 
 vinegar is often made artificially by adding various coloring and 
 odoriferous substances to dilute acetic acid. Vinegar should be tested 
 for sulphuric and hydrochloric acids, which are sometimes fraudu- 
 lently added. 
 
 Acidum aceticum, Acidum aceticum dilutum, and Acidum aceticum 
 glaciale are the three official forms of acetic acid. The first-named 
 acid contains 36 per cent., the second 6 per cent., the third at least 99 
 per cent, of pure acetic acid. 
 
 Acetic acid shows an exceptional behavior in regard to the specific 
 gravity of its aqueous solutions. The highest specific gravity of 
 1.0748 belongs to an acid of 78 per cent., which is equal to an acid 
 containing one molecule of water and one of acetic acid, or C 2 H 4 O 2 .H 2 O. 
 When the acid and water are mixed in this proportion, a maximum 
 rise in temperature and contraction in volume take place, which fact 
 indicates the existence of ortho-acetic acid, CH 3 C(OH) 3 , some ethereal 
 salts of which are known. The addition of either acetic acid or of 
 water causes the liquid to become lighter. For instance, the specific 
 gravity of an acid containing 95 per cent, is equal to that containing 
 56 per cent, of pure acid, both solutions having a specific gravity of 
 1.066. 
 
 The specific gravity of dilute acetic acid cannot, therefore, be 
 used as a means of determining the amount of pure acid ; this is 
 done by exactly neutralizing a weighed portion of the acid with 
 an alkali ; from the quantity of the latter used, the quantity of 
 actual acid present may be easily calculated. (See also volumetric 
 methods in Chapter 39.) 
 
 The vapor density of absolute acetic acid at just a little above its boiling- 
 point is twice as great as that corresponding to the formula, C 2 H 4 O 2 . At 
 200 C. or above, the vapor density is normal. This kind of behavior has 
 been observed in the case of other substances. 
 
 While vinegar is used in our diet, it should be remembered that acetic acid 
 acts as an irritant and corrosive, having caused in some instances perforation 
 of the stomach, and death in 6 to 15 hours. Milk of magnesia should be given 
 as an antidote with a view of neutralizing the acid. 
 
MONOBASIC FATTY ACIDS. 503 
 
 Analytical reactions. 
 (Sodium acetate, NaC 2 H 3 O 2 , may be used.) 
 
 1. Any acetate heated with sulphuric acid evolves acetic acid, 
 which may be recognized by its odor. 
 
 2. Acetic acid or acetates heated with sulphuric acid and alcohol 
 give a characteristic odor of acetic ether. 
 
 3. A solution containing acetic acid, or an acetate carefully neutral- 
 ized, turns deep red on the addition of solution of ferric chloride, 
 and forms, on boiling, a reddish-brown precipitate of an oxyacetate 
 of iroa 
 
 Potassium acetate, Potassii acetas, KC 2 H 3 O 2 = 97.44. Sodium 
 acetate, Sodii acetas, NaC 2 H 3 O 2 .3H 2 O === 135.1. Zinc acetate, 
 Zinci acetas, Zn (C 2 H 3 O 2 ) 2 .2H 2 O = 217.82. These three salts may 
 be obtained by neutralizing the respective carbonates with acetic acid 
 and evaporating the solution ; they are white salts, easily soluble in 
 water. 
 
 Ammonium acetate, NH 4 C 2 H 3 O 2 , is official in the form of a 7 
 per cent, solution, which is known as Spirit of Mindererus. 
 
 Iron acetates. Both the ferrous acetate, Fe(C 2 H 3 O 2 ) 2 .4H 2 0, and the ferric 
 acetate, Fe(C 2 H 3 O 2 ) 3 , are known. The latter is formed by adding sodium ace- 
 tate to the solution of a ferric salt, as is indicated by the deep-red color which 
 the solution assumes. As stated above in reaction 3, on boiling, decomposition 
 of the salt takes place. The separation of manganese and some other metals 
 from iron depends on this reaction. 
 
 Lead acetate, Plumbi acetas, Pb(C 2 H 3 O 2 ) 2 3H 2 O = 376.15 (Sugar 
 of lead), is made by dissolving lead oxide in diluted acetic acid. It 
 forms colorless, shining, transparent crystals, easily soluble in water; 
 on heating, it melts and then loses water of crystallization ; at yet 
 higher temperatures it is decomposed ; it has a sweetish, astringent, 
 afterward metallic taste. Commercial sugar of lead contains often an 
 excess of lead oxide in the form of basic salts ; such an article when 
 dissolved in spring water gives generally a turbid solution, in conse- 
 quence of the formation of lead carbonate ; the addition of a few 
 drops of acetic acid renders the liquid clear by dissolving the pre- 
 cipitate. 
 
 When a mixture of lead acetate and lead oxide is digested or boiled 
 frith water, the acetate combines with the oxide, forming a basic lead 
 
504 CONSIDERATION OF CARBON COMPOUNDS. 
 
 acetate, approximately Pb(C 2 H 3 O 2 ) 2 .PbO, a 25 per cent, solution of 
 which is the Liquor plumbi subacetatis, or Goulard's extract, while a 
 solution containing about 1 per cent, is the Liquor plumbi subacetatis 
 dilutus, or lead-water. Other more basic compounds are known. So- 
 called tribasic lead acetate has the formula Pb(C 2 H 3 O 2 ) 2 .2PbO. 
 
 Cupric acetate, Cu(C 2 H 3 O 2 ) 2 H 2 O. The commercial verdigris is a 
 basic acetate of copper, Cu(C 2 H 3 O 2 ) 2 CuO 7 made by the action of 
 dilute acetic acid and atmospheric air on metallic copper. By adding 
 to this basic acetate more acetic acid, the neutral acetate is obtained, 
 but this may be made directly also by dissolving cupric hydroxide 
 or carbonate in acetic acid. It forms deep green, prismatic crystals, 
 which are soluble in water. 
 
 By boiling verdigris with arsenous oxide, cupric aceto-arsenite, 
 3CuAs 2 O 4 -f- Cu(C 2 H 3 O 2 ) 2 , is formed, which is the chief constituent 
 of emerald green or Schweinfurt green, a substance often used as a 
 coloring matter. Paris green is of a similar composition, but less 
 pure. 
 
 Chlorine substitution products of acetic acid. The action of chlor- 
 ine gas and of phosphorus trichloride on acetic acid furnishes an additional 
 proof of the correctness of our views regarding its constitution and, conse- 
 quently, of the constitution of organic acids in general. It has been shown 
 that chlorine in acting on a hydrocarbon (methane) will successively replace all 
 hydrogen present. Similarly we can, by treatment with chlorine, replace that 
 hydrogen in acetic acid which is derived from the hydrocarbon, with the result 
 that monochlor, dichlor, and trichlor acetic acids are formed : 
 
 CH 3 .COOH + 2C1 : : CH 2 C1.COOH + HC1, 
 CH 2 C1.COOH + 2C1 = CHC1 2 .COOH + HC1, 
 CHC1 2 .COOH + 2C1 CC1 3 .COOH -f HC1. 
 
 The fourth atom of hydrogen cannot be directly replaced by chlorine. As it is 
 this carboxyl hydrogen atom to which the acid properties are due the above 
 three compounds have acid properties. 
 
 The action of phosphorus trichloride on water, on methyl alcohol, and on 
 acetic acid takes place thus : 
 
 3**>0 + PC1 3 3HC1 + P(OH) 3 , 
 
 + PC1 3 = 3CH 3 C1 + P(OH) 3 , 
 3 C 2 H 3 >0 + pcla = 3C 2 H 3 OC1 + P(OH) 3 . 
 
 In all three cases the hydro*xyl group is replaced by chlorine, with the result 
 that hydrogen chloride (hydrochloric acid), methyl chloride, and acetyl chloride 
 are formed. 
 
MONOBASIC FATTY ACIDS. 505 
 
 'Trichlor-acetic acid, Acidum trichloraceticum, CC1 3 .CO 2 H 
 162.12. As shown in the previous paragraph, this acid may be ob- 
 tained by the direct action of chlorine on acetic acid, but it is usually 
 made by the oxidation with nitric acid of chloral (tricolor-aldehyde), 
 which requires but one atom of oxygen for its conversion into tri- 
 chlor-acetic acid. 
 
 Trichlor-acetic acid is a white, deliquescent, crystalline substance. 
 It has a slight, characteristic odor, is readily soluble in water, alcohol, 
 and ether. The aqueous solution, on boiling, is decomposed into 
 chloroform and carbon dioxide. It is used as a local caustic and as 
 a reagent for albumin. 
 
 Acetyl chloride, CH 3 .COC1, is obtained by distilling a mixture of 9 parts 
 of glacial acetic acid and 6 parts of phosphorus trichloride on a water-bath at 
 a slightly elevated temperature. It is a colorless liquid, having a suffocating 
 odor, boiling-point of 55 C., and specific gravity 1.13 at C. It fumes in 
 the air, and acts on water energetically, thus : 
 
 CH 3 COC1 + H 2 O = CH 3 COOH + HC1. 
 
 It is a valuable reagent for testing for alcoholic hydroxyl groups in organic 
 compounds, which may be illustrated by its action on ordinary alcohol, thus: 
 
 CH 3 COC1 + C 2 H 5 OH = CH 3 COOC 2 H 5 + HC1. 
 
 Acetates are thus formed by the replacement of hydrogen of hydroxyl by the 
 acetyl radical. 
 
 Acetic anhydride or acetyl oxide, (CH 3 CO) 2 0, is formed by distilling a 
 mixture of anhydrous sodium acetate and acetyl chloride : 
 
 CH 3 COONa + CH 3 COC1 = (CH 3 CO) 2 O + NaCl. 
 
 It is a colorless liquid with a disagreeable odor, boiling at 137 C., and having 
 a specific gravity of 1.073 at 20 C. It is soluble in about 10 parts of water, 
 the solution decomposing slowly with formation of acetic acid. Like acetyl 
 chloride, it unites with hydroxyl groups in organic compounds, forming ace- 
 tates. This process of making acetates from alcoholic compounds is called 
 acetylization, and is often used in analysis of substances. 
 
 Butyric acid, HC 4 H 7 2 . Among the glycerides of butter those of butyric 
 acid are found ; they exist also in cod-liver oil, croton oil, and a few other fatty 
 oils ; some volatile oils contain compound ethers of butyric acid ; free butyric 
 acid occurs in sweat and in cheese. It may be obtained by a peculiar fermen- 
 tation of lactic acid (which itself is a product of fermentation), and is also 
 generated during the putrefaction of albuminous substances. Butyric acid is 
 a colorless liquid, having a characteristic, unpleasant odor; it mixes with 
 water in all proportions. 
 
 Valeric acid, HC 5 H 9 O 2 (Valerianic avid). This acid occurs in 
 valerian root and angelica root, from which it may be separated ; it 
 
506 CONSIDERATION OF CARBON COMPOUNDS. 
 
 is, however, generally obtained by oxidation of amyl alcohol by 
 potassium dichromate and sulphuric acid. After oxidation has taken 
 place the mixture is distilled, when valeric acid with some valerate 
 of amyl distils over. The change of amyl alcohol into valeric acid is 
 analogous to the conversion of ethyl alcohol into acetic acid : 
 
 C 5 H n OH + 2O = HC 5 H 9 2 + H 2 O. 
 Amyl alcohol. Valeric acid. 
 
 Pure valeric acid is an oily, colorless liquid, having a penetrating, 
 highly characteristic odor ; it is slightly soluble in water, but soluble 
 in alcohol ; it boils at 185 C. (365 F.). 
 
 Ammonium valerate and zinc valerate are official. Both are white solids hav- 
 ing the odor of valeric acid. The ammonium salt is readily, the zinc salt spar- 
 ingly soluble in water. 
 
 Stearic acid, Acidum stearicum, HC^H^C^ = 282.14. The 
 official stearic acid is the commercial, more or less impure article 
 made from solid fats, chiefly tallow. It is a hard, white, somewhat 
 glossy solid without odor or taste. It is insoluble in water, but solu- 
 ble in alcohol, ether and alkalies. Both stearic acid and palmitic 
 acid, HC 16 H 31 O 2 , occur largely in solid fats. The general properties 
 of palmitic acid are nearly identical with those of stearic acid. (See 
 analytical reactions of fats.) 
 
 Oleic acid, Acidum oleicum, HC 18 H 33 O 2 = 280.14. As shown by 
 its formula, oleic acid does not belong to the above-described series of 
 fatty acids of the composition C n H 2n O 2 , but to a series having the 
 general composition C n H 2n -2O 2 . 
 
 These acids belong to the ethylene series i. e., they contain two 
 carbon atoms held together by a double bond, in virtue of which 
 they are oxidized more readily than the corresponding saturated 
 acids. They also form addition products ; oleic acid, for instance, 
 combines directly with 2 atoms of hydrogen, forming stearic acid, 
 and with bromine to form dibrom-stearic acid. 
 
 Oleic acid is a constituent of most fats, especially of fat oils. 
 Thus, olive oil is mainly oleate of glyceryl. By boiling olive oil with 
 potassium hydroxide, potassium oleate is formed, which may be 
 decomposed by tartaric acid, when oleic acid is liberated. 
 
 Oleic acid is a nearly colorless, yellowish, or brownish-yellow, 
 neutral oily liquid, having a peculiar, lard-like odor and taste. It is 
 insoluble in water, soluble in alcohol, chloroform, oil of turpentine, 
 and fat oils, crystallizing near the freezing-point of water ; exposed 
 
MONOBASIC FATTY ACIDS. 507 
 
 to the air it decomposes and shows then an acid reaction. Lead 
 oleate is soluble in ether, lead palmitate and lead stearate are 
 not. 
 
 The official oleates of mercury, quinine, veratrine, atropine, and 
 cocaine are obtained by dissolving the yellow mercuric oxide, quinine, 
 veratrine, atropine, or cocaine in oleic acid. 
 
 Dissociation of formic acid and its homologues. In Chapter 15 it is 
 stated that the " strength " or relative activity of acids and'bases is propor- 
 tional to their degree of dissociation in solution. Organic acids in solution are 
 dissociated only to a small degree and are much " weaker " than such mineral 
 acids as hydrochloric, nitric, and sulphuric, which are almost completely disso- 
 ciated in very dilute solutions. The following table shows the percentage of 
 molecules dissociated in aqueous solutions containing the molecular weight in 
 grams of the respective acids diluted to 8 liters : 
 
 Formic acid. 
 
 Acetic acid. 
 
 Propionic acid. 
 
 Normal butyric acid. 
 
 4.05 
 
 1.193 
 
 1.016 
 
 1.068 
 
 Further dilution does not increase the percentage of dissociation very much. 
 For example, the molecular weight of acetic acid in 16 liters of solution disso- 
 ciates only to the extent of 1.673 per cent., whereas in a similar solution of 
 hydrochloric acid the dissociation is 95.5 per cent. Formic acid dissociates 
 more than the others of the series, and is, therefore, the strongest acid of the 
 series. The salts of organic acids are dissociated much more than the acids 
 are. Thus, in a normal solution of acetic acid only 0.4 per cent, of the molecules 
 are dissociated, while in normal solutions of sodium and potassium acetate 
 53 per cent, and 64 per cent, respectively, of the molecules are dissociated. 
 
 QUESTIONS. What is the constitution of organic acids, what group of 
 atoms is found in all of them, and how does an alcohol radical differ from an 
 acid radical? Give some processes by which organic acids are formed in nature 
 or artificially. Mention the general properties of organic acids. Which series 
 of acids is known as fatty acids, and why has this name been given to them ? 
 Mention names, composition, and occurrence in nature of the first five mem- 
 bers of the series of fatty acids. By what processes may formic acid be ob- 
 tained, and what are its properties? Describe the processes of manufacturing 
 acetic acid from alcohol and from wood. What is vinegar, and what is glacial 
 acetic acid ? Give tests for acetic acid and for acetates. Describe the pro- 
 cesses for making the acetates of potassium, zinc, iron, lead, and copper, and 
 also of Goulard's extract and lead-water ; state their composition and proper- 
 ties. Where and in what form of combination is oleic acid found in nature, 
 and what are its properties ? 
 
510 CONSIDERATION OF CARBON COMPOUNDS. 
 
 tion. This fact indicates that the iron is held in a complex ion, 
 
 since the color of simple ferrous salts in solution is usually pale green. 
 
 The salt has strong reducing properties and is used as a developer in 
 
 photography. 
 
 Potassium ferric oxalate, K 3 Fe(C 2 O 4 ) 3 , gives a green solution, and the iron is 
 ^robably held in a complex ion, Fe(C 2 O 4 ) 3 /// . It is rapidly reduced by sun- 
 light, thus, 
 
 2K 3 Fe(CA) 3 = 2K 2 Fe(C 2 4 ) 2 + K 2 C 2 O 4 + 2CO 2 , 
 and, therefore, is useful in making platinotypes in photography. 
 
 Hydroxy-acids. 
 
 In the acids heretofore considered, the hydrogen is derived either 
 from the hydrocarbon radical or from carboxyl. There are, however, 
 compounds containing as a third radical hydroxyl i. e., that radical 
 characteristic of alcohols. Consequently Ave may look upon these 
 compounds as acids into which alcoholic hydroxyl has been intro- 
 duced, or as alcohols into which carboxyl has been introduced. The 
 acid properties of these compounds are so predominating that the 
 compounds are spoken of as acids, and according to the number of 
 carboxyl groups present we have monobasic, dibasic, etc., acids. The 
 hydrogen of the carboxyl is, of course, replaceable by metals, while 
 the hydrogen of the alcoholic hydroxyl can be replaced by hydrocar- 
 bon radicals. In order to indicate this diiference in the function of 
 the hydrogen the number of the respective groups present is given in 
 the name. Thus, tartaric acid, which contains 2 hydroxyl and 2 car- 
 boxyl groups, is designated as a dibasic hydroxy-acid, or as dihy- 
 droxy-dicarboxylic acid, while citric acid, which contains 1 hydroxyl 
 and 3 carboxyl groups, is a monohydroxy-tribasic acid or hydroxy- 
 tricarboxylic acid. 
 
 Of the several methods known for obtaining hydroxy-acids only one shall be 
 mentioned. It corresponds to one of the methods used for the introduction of 
 hydroxyl into hydrocarbons ; in one case the halogen of a hydrocarbon, in the 
 other case the halogen of an acid is replaced by hydroxyl : 
 
 CH 3 Br + H 2 : CH 3 OH + HBr, 
 
 Brom-acetic acid. Hydroxy-acetic acid. 
 
 It is evident from what has been said that we have running parallel to every 
 series of acids another series of hydroxy-acids. For instance thus : 
 
POLYBASIC AND HYDROXY-ACIDS. 511 
 
 Fatty acids. Hydroxy-acids. 
 
 Formic acid, ILCO 2 H. Hydroxy-formic acid, OH.CO 2 H. 
 
 Acetic acid, CH 3 .CO 2 .H. Hydroxy-acetic acid, CH 2 .OH.CO 2 H. 
 
 Propionic acid, C 2 H 6 .CO 2 H. Hydroxy-propionic acid, C 2 H 4 .OH.CO;,H. 
 
 etc. etc. 
 
 The first member of these hydroxy-acids designated as hydroxy-formic acid 
 
 is simply carbonic acid and does not partake of the general character of 
 hydroxy-acids. 
 
 Monohydroxy-monobasic acids. 
 
 Gly colic acid, CH 2 .OH.CO 2 H (Hydroxy-acetic acid), is found in 
 unripe grapes and in the leaves of the wild grape. It can be obtained 
 synthetically, as shown in the previous paragraph. It may also be 
 made by the oxidation of ethylene alcohol or ylycol, C 2 H 4 (OH) 2 thus : 
 
 C 2 H 4 (OH) 2 -f 20 = CH 2 .OH.C0 2 H + H 2 O. 
 
 Glycolic acid is a white deliquescent, crystalline substance, easily 
 soluble in water, alcohol, and ether. 
 
 Lactic acid, Acidum lacticum, C 2 H 4 .OH.CO 2 H 89.37 (Hy- 
 droxy-propionic acid), occurs in many plant-juices; it is formed from 
 sugar by a peculiar fermentation known as "lactic fermentation," 
 which causes the presence of this acid in sour milk and in many sour, 
 fermented substances, as in ensilage, sauer-kraut, etc. The formation 
 of lactic acid from sugar may be expressed by the equation : 
 
 C 6 H 12 6 = 2(HC 3 H 5 3 ). 
 
 Sugar. Lactic acid. 
 
 For practical purposes lactic acid is made by mixing a solution of 
 sugar with milk, putrid cheese, and chalk, and digesting this mixture 
 for several weeks at a temperature of about 30 C. (86 F.). The 
 bacteria in the cheese act as a ferment, and the chalk neutralizes the 
 acid generated during the fermentation. The calcium lactate thus 
 obtained is purified by crystallization and decomposed by oxalic acid, 
 which forms insoluble calcium oxalate. 
 
 Lactic acid is a colorless, syrupy liquid, of strongly acid properties ; 
 it mixes in all proportions with water and alcohol. The official 
 lactic acid contains 75 per cent, of absolute acid. 
 
 Three isomeric lactic acids are known : 
 
 a. Fermentation lactic acid, obtained as described above from milk, is opti- 
 cally inactive. 
 
 b. Sarcolactic or paralactic acid is dextrorotatory and occurs in muscle and 
 other parts of the body. It forms a constituent of meat-juice, and, therefore, 
 of meat extract. 
 
 c. Lcevolactic acid is laevorotatory, and is obtained from cane sugar by fer- 
 mentation by a special micro-organism. 
 
510 CONSIDERATION OF CARBON COMPOUNDS. 
 
 tion. This fact indicates that the iron is held in a complex ion, Fe(C 2 O 4 ) 2 // , 
 since the color of simple ferrous salts in solution is usually pale green. 
 The salt has strong reducing properties and is used as a developer in 
 photography. 
 
 Potassium ferric oxalate, K 3 Fe(C 2 O 4 ) 3 , gives a green solution, and the iron is 
 ,robably held in a complex ion, Fe(C 2 O 4 ) 3 /// . It is rapidly reduced by sun- 
 light, thus, 
 
 2K 3 Fe(CA) 3 = 2K 2 Fe(C 2 4 ) 2 + K 2 C 2 O 4 + 2CO 2 , 
 and, therefore, is useful in making platinotypes in photography. 
 
 Hydroxy-acids. 
 
 In the acids heretofore considered, the hydrogen is derived either 
 from the hydrocarbon radical or from carboxyl. There are, however, 
 compounds containing as a third radical hydroxyl i. e., that radical 
 characteristic of alcohols. Consequently we may look upon these 
 compounds as acids into which alcoholic hydroxyl has been intro- 
 duced, or as alcohols into which carboxyl has been introduced. The 
 acid properties of these compounds are so predominating that the 
 compounds are spoken of as acids, and according to the number of 
 carboxyl groups present we have monobasic, dibasic, etc., acids. The 
 hydrogen of the carboxyl is, of course, replaceable by metals, while 
 the hydrogen of the alcoholic hydroxyl can be replaced by hydrocar- 
 bon radicals. In order to indicate this difference in the function of 
 the hydrogen the number of the respective groups present is given in 
 the name. Thus, tartaric acid, which contains 2 hydroxyl and 2 car- 
 boxyl groups, is designated as a dibasic hydroxy-acid, or as dihy- 
 droxy-dicarboxylic acid, while citric acid, which contains 1 hydroxyl 
 and 3 carboxyl groups, is a monohydroxy-tribasic acid or hydroxy- 
 tricarboxylic acid. 
 
 Of the several methods known for obtaining hydroxy-acids only one shall be 
 mentioned. It corresponds to one of the methods used for the introduction of 
 hydroxyl into hydrocarbons ; in one case the halogen of a hydrocarbon, in the 
 other case the halogen of an acid is replaced by hydroxyl : 
 
 CH 3 Br + H 2 : CH 3 OH + HBr, 
 
 Brom-acetic acid. Hydroxy-acetic acid. 
 
 It is evident from what has been said that we have running parallel to every 
 series of acids another series of hydroxy-acids. For instance thus : 
 
POLYBASIC AND HYDROXY-ACIDS. 511 
 
 Fatty acids. Hydroxy-acids. 
 
 Formic acid, H.CO 2 H. Hydroxy-formic acid, OH.CO 2 H. 
 
 Acetic acid, CH 3 .CO 2 .H. Hydroxy-acetic acid, CH 2 .OH.CO 2 H. 
 
 Propionic acid, C 2 PI 6 .CO 2 H. Hydroxy-propionic acid, C 2 H 4 .OH.CO.,H. 
 
 etc. etc. 
 
 The first member of these hydroxy-acids designated as hydroxy-formic acid 
 is simply carbonic acid and does not partake of the general character of 
 hydroxy-acids. 
 
 Monohydroxy-monobasic acids. 
 
 Gly colic acid, CH 2 .OH.CO 2 H (Hydroxy-acetic acid), is found in 
 unripe grapes and in the leaves of the wild grape. It can be obtained 
 synthetically, as shown in the previous paragraph. It may also be 
 made by the oxidation of ethylene alcohol or ylycol, C 2 H 4 (OH) 2 thus : 
 
 C 2 H 4 (OH) 2 -f 2O = CH 2 .OH.CO 2 H + H 2 O. 
 
 Glycolic acid is a white deliquescent, crystalline substance, easily 
 soluble in water, alcohol, and ether. 
 
 Lactic acid, Acidum lacticum, C 2 H 4 .OH.CO 2 H = 89.37 (Hy- 
 droxy-propionic acid), occurs in many plant-juices; it is formed from 
 sugar by a peculiar fermentation known as " lactic fermentation," 
 which causes the presence of this acid in sour milk and in many sour, 
 fermented substances, as in ensilage, sauer-kraut, etc. The formation 
 of lactic acid from sugar may be expressed by the equation : 
 
 C 6 H 12 6 = 2(HC 3 H 5 3 ). 
 
 Sugar. Lactic acid. 
 
 For practical purposes lactic acid is made by mixing a solution of 
 sugar with milk, putrid cheese, and chalk, and digesting this mixture 
 for several weeks at a temperature of about 30 C. (86 F.). The 
 bacteria in the cheese act as a ferment, and the chalk neutralizes the 
 acid generated during the fermentation. The calcium lactate thus 
 obtained is purified by crystallization and decomposed by oxalic acid, 
 which forms insoluble calcium oxalate. 
 
 Lactic acid is a colorless, syrupy liquid, of strongly acid properties ; 
 it mixes in all proportions with water and alcohol. The official 
 lactic acid contains 75 per cent, of absolute acid. 
 
 Three isomeric lactic acids are known : 
 
 a. Fermentation lactic acid, obtained as described above from milk, is opti- 
 cally inactive. 
 
 b. Sarcolactic or paralactic acid is dextrorotatory and occurs in muscle and 
 other parts of the body. It forms a constituent of meat-juice, and, therefore, 
 of meat extract. 
 
 c. Lcevolactic acid is laevorotatory, and is obtained from cane sugar by fer- 
 mentation by a special micro-organism. 
 
512 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Dibasic and tribasic hydroxy-acids. 
 
 Mono-hydroxy-succinic acid, or malic acid = 
 
 /OH CH.OH.COJH 
 
 C 4 H 6 5 or C 2 H 3 ^C0 2 H or j 
 
 X CO 2 H CH 2 .CO 2 H 
 
 Di-hydroxy-succinic acid, or tartaric acid = 
 
 /OH 
 
 //OH CH.OH.CO 2 H 
 
 C 4 H 6 O 6 or C 2 H 2 or | 
 
 \>C0 2 H CH.OH.C0 2 H 
 
 \CO 2 H 
 
 Malic acid, H 2 C 4 H 4 O 5 , occurs in the juices of many fruits, as 
 apples, currants, cherries, etc. It may be extracted from these fruits 
 or prepared synthetically. 
 
 Tartaric acid, Acidum tartaricum, H 2 C 4 H 4 O 6 - 148.92. Fre- 
 quently found in vegetables, and especially in fruits, sometimes free, 
 generally as the potassium or calcium salt ; grapes contain it chiefly 
 as potassium acid tartrate, which is obtained in an impure state as a 
 by-product in the manufacture of wine. During the fermentation of 
 grape-juice, its sugar is converted into alcohol ; potassium acid tar- 
 trate is less soluble in alcoholic fluids than in water, and therefore is 
 deposited gradually, forming the crude tartar, or argol, of commerce, 
 a substance containing chiefly potassium acid tartrate, but also cal- 
 cium tartrate, some coloring matter, and traces of other substances. 
 Crude tartar is the source of tartaric acid and its salts. 
 
 Tartaric acid is obtained from potassium acid tartrate by neutral- 
 izing with calcium carbonate, and decomposing the remaining neutral 
 potassium tartrate by calcium chloride : 
 
 2(KHC 4 H 4 O 6 ) + CaCO 3 == CaC 4 H 4 O 6 + K 2 C 4 H 4 O 6 + H 2 O + CO 2 . 
 Potassium acid Calcium Calcium Potassium Water. Carbon 
 
 tartrate. carbonate. tartrate. tartrate. dioxide. 
 
 K 2 C 4 H 4 6 + CaCl 2 = CaC 4 H 4 6 + 2KC1. 
 Potassium Calcium Calcium Potassium 
 
 tartrate. chloride. tartrate. chloride. 
 
 The whole of the tartaric acid is thus converted into calcium tar- 
 trate, which is precipitated as an insoluble powder ; this is collected, 
 well washed, and decomposed by boiling with sulphuric acid, when 
 calcium sulphate is formed as an almost insoluble residue, while tar- 
 taric acid is left in solution, from which it is obtained by evaporation 
 and crystallization : 
 
 CaC 4 H 4 O 6 + H 2 SO 4 = H,C 4 H 4 O 6 -f CaSO 4 . 
 
 Calcium Sulphuric Tartaric Calcium 
 
 tartrate. acid. acid. sulphate. 
 
POLYBASIC AND HYDROXY-ACIDS. 
 
 513 
 
 Tartaric acid crystallizes in colorless, translucent prisms ; it has a 
 strongly acid, but not disagreeable taste ; it is readily soluble in water 
 and alcohol, and fuses at 135 C. (275 F.). 
 
 FIG 71. 
 
 Isomerism of tartaric acid. Four tartaric acids are known. They are : 
 dextrotartaric or common tartaric acid; favot ar tar ic acid ; mesotartaric or inact- 
 ive tartaric acid; and racemic add. These four acids have the same composi- 
 tion and show the same chemical reactions, proving that they are built up from 
 the same radicals ; but in some respects they possess different physical proper- 
 ties. Thus, mesotartaric and racemic acids are optically inactive ; the others, 
 as indicated by their names, are active, one turning polarized light to the right, 
 the other to the left. 
 
 Pasteur first observed that the spontaneous evaporation of a solution of 
 ammonium sodium racemate yields two 
 kinds of stereo-isomeric crystals. These 
 crystals (Fig. 71) are rectangular prisms P, 
 M, T, having the lateral edges replaced by 
 the faces b' , and the intersection of these 
 faces with the face T replaced by a face h. 
 The crystals are hemihedral, having four of 
 these h faces placed alternately. In the two 
 kinds of crystals these hemihedral faces oc- 
 cupy opposite positions, so that if one kind 
 of crystal be placed before a mirror its re- 
 flection will represent the arrangement of 
 the hemihedral faces of the other kind of crystal. The crystals are called 
 right-handed and left-handed respectively. 
 
 From these two kinds of crystals two tartaric acids can be separated ; one is 
 dextrotartaric acid, the other laevotartaric acid. When the two acids are brought 
 together in solution they unite forming racemic acid. These observations, sup- 
 ported by chemical data, have led to assume in tartaric acids the existence of 
 two asymmetric carbon atoms, about which the hydrogen atoms and the radi- 
 cals are arranged differently. Three of these forms may be represented by the 
 formulas : 
 
 Isomeric salts of tartaric acid. 
 
 C0 2 H 
 
 H C OH 
 OH C II 
 
 C0 2 H 
 
 Dextrotartaric acid. 
 
 CO 2 H 
 OH C H 
 
 H 
 
 -OH 
 
 II- 
 
 -C-OH 
 
 C0 2 H 
 Laevotartaric acid. 
 
 H O-OH 
 
 ! 
 CO,H 
 
 Mesotartaric acid 
 
 Racemic acid results from the combination of dextrotartaric and laevotartaric 
 acids. 
 
 In a tenth-normal solution of tartaric acid at 25 C., 8.2 per cent, of the acid 
 is dissociated into H g and H.C^O/ ions. 
 33 
 
514 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Analytical reactions. 
 (Potassium sodium tartrate, KNaC 4 H 4 O 6 , may be used.) 
 
 1. A neutral solution of a tartrate gives with calcium chloride a 
 white precipitate of calcium tartrate, which, after being quickly col- 
 lected on a filter and washed, is soluble in potassium hydroxide ; from 
 this solution calcium tartrate is precipitated on boiling. (Calcium 
 citrate is insoluble in potassium hydroxide.) 
 
 Calcium tartrate is soluble in a solution of an alkali tartrate; 
 hence, unless a sufficient amount of calcium chloride is added, a pre- 
 cipitate will not be obtained. 
 
 2. A strong solution of a tartrate, acidulated with acetic acid, gives 
 a white precipitate of potassium acid tartrate on the addition of potas- 
 sium acetate. The precipitate, which forms slowly, is soluble in alka- 
 lies and in mineral acids. 
 
 In the case of potassium sodium tartrate, or potassium tartrate, 
 addition of acetic acid alone precipitates potassium acid tartrate. 
 
 3. A neutral solution of a tartrate gives with silver nitrate a white 
 precipitate of silver tartrate, Ag 2 C 4 H 4 O 6 , which blackens on boiling, 
 in consequence of the decomposition of the salt, with separation of 
 silver. If, before boiling, a drop of ammonia water be added, a 
 mirror of metallic silver will form upon the glass. 
 
 Silver tartrate is soluble in a solution of alkali tartrate ; hence the 
 silver nitrate solution must be added in sufficient quantity to obtain 
 a permanent precipitate. 
 
 4. Sulphuric acid heated with tartrates chars them readily. 
 
 5. Tartrates, when heated, are decomposed (blacken), and evolve a 
 somewhat characteristic odor, resembling that of burnt sugar. 
 
 The above reaction, 3, can be used to advantage for silvering glass by operat- 
 ing as follows : Dissolve 1 gramme of silver nitrate in 20 c.c. of water, add 
 ammonia water until the precipitate which forms is nearly redissolved, and 
 dilute with water to 100 c.c. Make a second solution by dissolving 0.2 gramme 
 of silver nitrate in 100 c.c. of boiling water, add 0.166 gramme of potassium 
 sodium tartrate, boil until the precipitate becomes gray, and filter. Mix the 
 two solutions cold and set aside for one hour, when a mirror of metallic silver 
 will be found. 
 
 Potassium acid tartrate, Potassii bitartras. KHC^O,, = 186.78 
 (Potassium bitartrate, Cream of Tartar). The formation of this salt in 
 
POLYBASIC AND HYDROXY-ACIDS. 515 
 
 the crude state (argol) has been explained above. It is purified by 
 dissolving in hot water and crystallizing, when it is obtained in color- 
 less crystals, or as a white, somewhat gritty powder of a pleasant, 
 acidulous taste ; it is soluble in about 200 parts of cold, easily sol- 
 uble in hot water, but insoluble in alcohol. 
 
 The name cream of tartar was given to the salt for the reason that 
 small crystals, which float on the liquid, separate on rapidly cooling 
 a hot solution of potassium bitartrate. 
 
 Potassium tartrate, 2(K 2 C 4 H 4 6 ).H,0. Obtained by saturating a solution 
 of potassium acid tartrate with potassium carbonate : 
 
 2KHC 4 H 4 O e + K 2 C0 3 = 2K 2 C 4 H 4 O 6 + H 2 O + CO,. 
 Potassium acid Potassium Potassium 
 tartrate. carbonate. tartrate. 
 
 Small transparent or white crystals, or a white neutral powder, soluble in 
 less than its own weight of water. 
 
 Potassium sodium tartrate, Potassii et sodii tartras, 
 KNaC 4 H 4 O 6 .4H 2 O = 280.18 (Rochelle salt). If in the above-described 
 process for making neutral potassium tartrate, sodium carbonate is 
 substituted for potassium carbonate, the double tartrate of potassium 
 and sodium is formed. It is a white powder, or occurs in colorless, 
 transparent crystals which are easily soluble in water. 
 
 Experiment 59. Add gradually 24 grammes of potassium acid tartrate to a 
 hot solution of 20 grammes of crystallized sodium carbonate in 100 c.c. of 
 water. Heat until complete solution has taken place, filter, evaporate to about 
 one-half the volume, and set aside for the potassium sodium tartrate to crys- 
 tallize. How much crystallized sodium carbonate is required for the conversion 
 of 25 grammes of potassium acid tartrate into Eochelle salt? 
 
 Seidlitz powders (Compound effervescing powders) consist of a mixture 
 of 7.75 grammes (120 grains) of Rochelle salt with 2.58 grammes 
 (40 grains) of sodium bicarbonate (wrapped in blue paper), and 2.25 
 grammes (35 grains) of tartaric acid (wrapped in white paper). 
 When dissolved in water the tartaric acid acts upon the sodium 
 bicarbonate, causing the formation of sodium tartrate, while the 
 escaping carbon dioxide causes effervescence. 
 
 Antimony and potassium tartrate, Antimonii et potassii 
 tartras, 2(KSbO.C 4 H 4 O 6 ).H,O=659.8 (Potassium antimonyl tartrate, 
 Tartar emetic). This salt is made by dissolving freshly prepared 
 antimonous oxide (while yet moist) in a solution of potassium acid 
 
516 CONSIDERATION OF CARBON COMPOUNDS. 
 
 tartrate. From the solution somewhat evaporated, tartar emetic 
 separates in colorless, transparent rhombic crystals : 
 
 2KHC 4 H 4 O 6 + Sb 2 O 3 = = 2KSbO.C 4 H 4 O 6 + H,O. 
 
 Potassinm acid Antimonous Tartar emetic, 
 
 tartrate. oxide. 
 
 The fact that not antimony itself, but the group SbO, replaces the 
 hydrogen, has led to the assumption of the hypothetical radical SbO, 
 termed antimonyl. 
 
 Tartar emetic is soluble in water, insoluble in alcohol ; it has a 
 sweet, afterward disagreeable metallic taste. 
 
 Action of certain organic acids upon certain metallic oxides. The solu- 
 tion of a ferric salt (or certain other metallic salts) is precipitated by alkali 
 hydroxides, a salt of the alkali and ferric hydroxide being formed. When a 
 sufficient quantity of either tartaric, citric, oxalic, or various other organic 
 acids has been added previously to the iron solution (or to certain other metallic 
 solutions) no such precipitate is produced by the alkali hydroxides, because 
 organic salts or double salts are formed which are soluble, and from which the 
 metallic hydroxides are not precipitated by alkali hydroxides. Upon evapora- 
 tion no crystals (of the organic salt) form, and in order to obtain the com- 
 pounds in a dry state, the liquid, after being evaporated to the consistence of 
 a syrup, is spread on glass plates which are exposed to a temperature not 
 exceeding 60 C. (140 F.), when brown, green, yellowish-green, amorphous, 
 shining, transparent scales are formed, which are the scale compounds of the 
 U. S. P. 
 
 Instead of obtaining these compounds, 'as stated above, by adding the 
 organic acids (or their salts) to the inorganic salts, they are more generally 
 obtained by dissolving the freshly precipitated metallic hydroxide in the 
 organic acid. 
 
 The true chemical constitution of many of these scale compounds has not 
 as yet been determined with certainty. 
 
 Of official scale compounds containing tartaric acid may be mentioned the 
 iron and ammonium tartrate, and the iron and potassium tartrate. The first com- 
 pound is obtained by dissolving freshly precipitated ferric hydroxide in a solu- 
 tion of ammonium acid tartrate ; the second, by dissolving ferric hydroxide in 
 potassium acid tartrate. The clear solutions, after having been sufficiently 
 evaporated, are dried, as mentioned above, on glass plates. 
 
 Citric acid, Acidum citricum, H 3 C 6 H 5 O 7 .H 2 O = 2O8.5. Citric 
 acid is a tribasic acid containing three atoms of hydrogen replaceable 
 by metals ; its constitution may be expressed by the graphic formulas : 
 
 /OH CH 2 .C0 2 H 
 
 />C0 2 H | 
 
 C 3 H 4 or COH.CO 2 H 
 
 \\C0 2 H | 
 
 \C0 2 H CH 2 .C0 2 H 
 
 Citric acid is found in the juices of many fruits (strawberry, rasp- 
 berry, currant, cherry, etc.), and in other parts of plants. It is 
 obtained from the juice of lemons by saturating it with calcium car- 
 
POLYBASIC AND HYDEOXY- ACIDS. 517 
 
 bonate and decomposing by sulphuric acid the calcium citrate thus 
 formed. (100 parts of lemons yield about 5 parts of the acid.) It 
 forms colorless crystals, easily soluble in water. 
 
 Analytical reactions. 
 (Potassium citrate, K 3 C 6 H 5 O 7 , may be used.) 
 
 1. Neutral solutions of citrates yield with calcium chloride on 
 boiling (not in the cold) a white precipitate of calcium citrate, which 
 is insoluble in potassium hydroxide, but soluble in cupric chloride. 
 
 2. Neutral solutions of citrates are precipitated white by silver 
 nitrate. The precipitate does not blacken on boiling, as in the case 
 of tartrates. Silver citrate is soluble in a solution of an alkali ci- 
 trate ; hence, sufficient silver nitrate solution must be added to obtain 
 a permanent precipitate. 
 
 3. A solution of citrate made alkaline with a little sodium hydrox- 
 ide solution, to which a few drops of potassium permanganate solu- 
 tion are added, turns green slowly, whereas, atartrate under the same 
 conditions decolorizes permanganate quickly, with precipitation of 
 brown manganese dioxide. 
 
 4. When ignited, it is decomposed without emitting an odor resem- 
 bling burning sugar. (Difference from tartaric acid.) 
 
 5. Tartaric acid in citric acid may be detected by adding about 1 
 c.c. of an aqueous solution of ammonium molybdate to about 1 
 gramme of the citric acid, then 2 or 3 drops of sulphuric acid, 
 and warming on the water-bath. The presence of 0.1 per cent, or 
 more of tartaric acid gives a blue color to the solution. 
 
 Citrates. Potassium citrate, K 3 C 6 H 5 O 7 .H 2 O, and Lithium citrate, 
 Li 3 C 6 H 5 O 7 .4H 2 O, are official. Both are white deliquescent salts, easily 
 soluble in water, and obtained by dissolving the carbonates in citric 
 acid. Sodium citrate, 2Na 3 C 6 H 5 O 7 .llH 2 O, is also official. 
 
 The effervescent potassium citrate, lithium citrate, and magnesium sulphate are 
 granulated mixtures, all containing citric acid, tartaric acid, and sodium bicar- 
 bonate, mixed respectively with potassium citrate, lithium citrate, and mag- 
 nesium sulphate. 
 
 The official solution of magnesium citrate is made by dissolving magnesium 
 carbonate in an excess of citric acid solution to which some syrup is added, 
 and dropping into this mixture, which should be contained in a strong bottle, 
 potassium bicarbonate. The bottle is immediately closed with a cork in order 
 to retain the liberated carbon dioxide. 
 
 Bismuth citrate, BiC 6 H 5 O 7 , is obtained by boiling a solution of citric acid 
 with bismuth nitrate, when the latter is gradually converted into citrate, while 
 
518 CONSIDERATION OF CARBON COMPOUNDS. 
 
 nitric acid is set free; the insoluble bismuth citrate is collected, washed, and 
 dried; it forms a white, amorphous powder, which is insoluble in water, but 
 soluble in ammonia water. 
 
 Bismuth ammonium citrate is a scale compound obtained by dissolving bismuth 
 citrate in ammonia water and evaporating the solution at a low temperature. 
 
 Ferric citrate, Ferri citras. Obtained in transparent, red scales, by dissolving 
 ferric hydroxide in citric acid and evaporating the solution as mentioned here- 
 tofore. By mixing solution of ferric citrate with either ammonia water or 
 quinine, strychnine, sodium phosphate, or sodium pyrophosphate, evaporating 
 to the consistence of syrup and drying on glass plates, the following scale com- 
 pounds are obtained respectively : Iron and ammonium citrate, iron and quinine 
 citrate, iron and strychnine citrate, soluble ferric phosphate, and soluble ferric pyro- 
 phosphate. 
 
 47. ETHERS AND ESTERS. 
 
 Constitution. It has been shown that alcohols are hydrocarbon 
 residues in combination with hydroxyl, OH, and that acids are hydro- 
 carbon residues in combination with carboxyl, CO.OH ; it has further 
 been shown that carboxyl may be considered as being composed of 
 CO, and hydroxyl, OH, and that the term acid radical is applied to 
 that group of atoms in acids which embraces the hydrocarbon residue 
 -f- CO. If we represent a hydrocarbon radical by R, and an acid 
 radical by R.CO, the general formula of an alcohol is R.OH, or 
 
 ^>O, and of an acid, R.CO.OH, or R ' C >O. 
 
 Ethers are formed by replacement of the hydrogen of the hydroxyl 
 in alcohols by hydrocarbon residues, and esters, also called compound 
 ethers, or ethereal salts are formed by replacement of the hydrogen of 
 the hydroxyl (or carboxyl) in acids by hydrocarbon residues. While 
 alcohols correspond in their constitution to hydroxides, ethers corre- 
 spond to oxides, and esters to salts. For instance : 
 
 QUESTIONS. Name the more common organic acids found in vegetables 
 and especially in sour fruits. What is the composition of oxalic acid, how is 
 it manufactured, and what are its properties? Explain the formation of crude 
 tartar during the fermentation of grape-juice, and how is tartaric acid obtained 
 from it? Give properties of and tests for tartaric acid. State the composition 
 and formation of cream of tartar, Rochelle salt, and tartar emetic. What are 
 Seidlitz powders, and what changes take place when they are dissolved ? Give 
 the general composition of hydroxy-acids, and state a method for preparing 
 them synthetically. From what and by what process is citric acid obtained ? 
 Mention tests by which citric acid may be distinguished from tartaric acid. 
 From what and by what process is lactic acid obtained ; what are its prop- 
 erties ? 
 
ETHERS AND ESTERS. 519 
 
 Hydroxides. Oxides. Acids. 
 
 KOH = g\0 K 2 = \0 HN0 3 = N ^)0 KNO 3 - N( j>O 
 Potassium hydroxide. Potassium oxide. Nitric acid. Potassium nitrate. 
 
 Ethyl alcohol. Ethyl ether. Acetic acid. Ethyl acetate, or 
 
 acetic ether. 
 
 ET R H R* 
 
 Alcohol. Ether. Acid. Ester. 
 
 It is not necessary that the two hydrocarbon residues in au ether 
 should be alike, as in the above ethyl ether, but they may be different, 
 in which case the ethers are termed mixed ethers. For instance : 
 
 CH 3 .C 2 H 5 = g H\o q,H,AH u .O = 
 
 Methyl-ethyl ether. Propyl-amyl ether. 
 
 In diatomic or triatomic alcohols, or in dibasic or tribasic acids, 
 containing more than one atom of hydrogen derived from hydroxyl 
 or carboxyl, these hydrogen atoms may be replaced by various other 
 univalent, bivalent, or trivalent residues. This fact shows that the 
 number of ethers or esters which are capable of being formed is very 
 large. 
 
 Formation of ethers. Ethers may be formed by the action of 
 the chloride or iodide of a hydrocarbon residue upon an alcohol, in 
 which the hydroxyl hydrogen has been replaced by a metal. For 
 instance : 
 
 C <> + QftI = %!;> + Nal. 
 Sodium ethylate. Ethyl iodide. Ethyl ether. Sodium iodide. 
 
 Sodium Methyl Ethyl-methyl Sodium 
 
 ethylate. iodide. ether. iodide. 
 
 Ethers are also formed by the action of sulphuric acid upon alco- 
 hols ; the sulphuric acid removing water in this case, thus : 
 
 2(C 2 H 5 OH) : 2 H 5 + 
 
 Ethyl alcohol. Ethyl ether. Water. 
 
 Esters are formed by the combination of acids with alcohols and 
 elimination of water. (Presence of sulphuric acid facilitates this 
 action.) 
 
 + C 2 H S 0\ = 
 
 Ethyl alcohol. Acetic acid. Ethyl acetate. Water. 
 
520 CONSIDERATION OF CARBON COMPOUNDS. 
 
 They are also formed by the action of hydrocarbon chlorides (or 
 iodides) on salts. For instance : 
 
 C 5 H U C1 + CH )0 : ^g)o + KC1 
 
 Amyl Potassium Amyl Potassium 
 
 chloride. formate. formate. chloride. 
 
 Occurrence in nature. Many ethers are products of vegetable 
 life and occur in some essential oils ; wax contains the compound 
 ether melissyl palmitate, C 3(J H 61 .C 16 H 31 O.O, and spermaceti, a solid 
 substance found in the head of the whale, is cetyl palmitate, C^H^. 
 C 16 H 31 O.O. The most important group of esters are the fats and 
 fatty oils, which are distributed widely in the vegetable, but even 
 more so in the animal kingdom. 
 
 General properties. The ethers and esters of the lower members 
 of the monatomic alcohols and fatty acids have generally a character- 
 istic and pleasant odor. Fruit essences consist mainly of such esters, 
 and what is generally known as the " bouquet " or " flavor " of wine 
 and other alcoholic liquors is due chiefly to ethers or compound ethers, 
 which are formed during (and after) the fermentation by the action 
 of the acids present upon the alcohol or the alcohols formed. The 
 improvement which such alcoholic liquids undergo " by age " is caused 
 by a continued chemical action between the substances named. 
 
 All esters are neutral substances ; those formed by the lower alco- 
 hols and acids are generally volatile liquids, those of the higher 
 members are non-volatile solids. When esters are heated with alka- 
 lies, the acid combines with the latter, while the alcohol is liberated. 
 (The properties of the esters, termed fats, will be considered further 
 on.) 
 
 One of the chief points of distinction between ethers and esters is 
 that ethers are not acted on by alkalies, while esters are decomposed, 
 an alcohol and a salt of the alkali metal being formed. 
 
 Ethyl ether, Either, (C 2 H 5 ) 2 O = 73.52 (Ether, sulphuric ether, Ethyl 
 oxide). The name of the whole group of ethers is derived from this 
 (ethyl-) ether, in the same way that common (ethyl-) alcohol has 
 given its name to the group of alcohols. The name sulphuric ether 
 was given at a time when its true composition was yet unknown, and 
 for the reason that sulphuric acid was used in its manufacture. 
 
 Ether is manufactured by heating to about 140 C. (284 F.) a 
 mixture of 1 part of alcohol and 1.8 parts of concentrated sulphuric 
 acid in a retort, which is so arranged that additional quantities of 
 alcohol may be allowed to flow into it, while the open end is connected 
 
ETHERS AND ESTERS. 521 
 
 with a tube, leading through a suitable cooler, in order to condense 
 the highly volatile product of the distillation. 
 
 Experiment 60. Mix 100 grammes of alcohol with 180 grammes of ordinary 
 sulphuric acid, allow to stand and pour the cooled mixture into a flask which 
 is provided with a perforated cork through which pass a thermometer and a 
 bent glass tube leading to a Liebig's condenser. Apply heat and notice that 
 the liquid commences to boil at about 140 C. (284 F.). Distil about 50 c.c., 
 pour this liquid into a stoppered bottle and add an equal volume of water. 
 Ethyl ether will separate into a distinct layer over the water, and may be 
 removed by means of a pipette. Eepeat the washing with water, add to the 
 ether thus freed from alcohol a little calcium chloride and distil it from a dry 
 flask, standing in a water-bath. The greatest care should be exercised and the 
 neighborhood of flames avoided in working with ether, on account of its 
 volatility and the inflammability of its vapors. 
 
 The apparatus described above for etherification can be constructed so as to 
 make the process continuous. This may be done by using with the boiling- 
 flask a cork with a third aperture through which a glass tube passes into the 
 liquid. The other end of the tube is connected by means of rubber tubing 
 with a vessel filled with alcohol and standing somewhat above the flask. As 
 soon as distillation commences alcohol is allowed to flow into the flask at a 
 rate equal to that of the distillation, keeping the temperature at about 140 C. 
 (284 F.). The flow of alcohol is regulated by a stop-cock. 
 
 The action of sulphuric acid upon alcohol is not quite so simple as 
 described above in connection with the general methods for obtaining 
 ethers, where the final result only was given An intermediate pro- 
 duct, known as ethyl sulphuric acid or sulpho-vinic acid, is formed, 
 which, by acting upon another molecule of alcohol, forms sulphuric 
 acid and ether, which latter is volatilized as soon as formed. The 
 decomposition is shown by the equations : 
 
 C 2 H 5 OH 
 
 Su 
 acid. 
 
 C 2 H 5 OH = (C 2 H 5 ) 2 
 
 Alcohol. Sulphuric Ethyl-sulphuric 
 
 acid. 
 
 Ethyl-sulphuric Alcohol. Ether. Sulphuric 
 
 acid. acid. 
 
 The liberated sulphuric acid at once attacks another molecule of alcohol, 
 again forming ethyl-sulphuric acid, which is again decomposed, etc. Theo- 
 retically, a given quantity of sulphuric acid should be capable, therefore, of 
 converting any quantity of alcohol into ether ; practically, however, this is not 
 the case, because secondary reactions take place simultaneously, and because the 
 water which is constantly formed does not all distil with the ether, and there- 
 fore dilutes the acid to such an extent that it no longer acts upon the alcohol. 
 
 Ether thus obtained is not pure, but contains water, alcohol, sulphurous and 
 sulphuric acids, etc. ; it is purified by mixing it with chloride and oxide of 
 calcium, pouring off the clear liquid and distilling it. 
 
522 CONSIDERATION OF CARBON COMPOUNDS. 
 
 The official ether contains of ethyl-ether 96 per cent, and of 
 alcohol 4 per cent. It is a very mobile, colorless, highly volatile 
 liquid, of a refreshing, characteristic odor, a burning and sweetish 
 taste, and a neutral reaction ; it is soluble in alcohol, chloroform, 
 liquid hydrocarbons, fixed and volatile oils, and dissolves in ten 
 volumes of water. Specific gravity is 0.716 at 25 C. (77 F.); 
 boiling-point 35 C. (95 F.). It is easily combustible and burns 
 with a luminous flame. When inhaled, it causes intoxication and 
 then loss of consciousness and sensation. The great volatility and 
 combustibility of ether necessitate special care in the handling of this 
 substance near fire or light. 
 
 Spiritus cetheris and Spiritus cetheris compositus are mixtures of about one 
 part of ether and two parts of alcohol, 3 per cent, of certain ethereal oils being 
 added to the second preparation. 
 
 Methyl ether, (CH 3 ) 2 0, is made from methyl alcohol and sulphuric acid. It 
 is a gas at ordinary temperature, but readily convertible by pressure or cold 
 into a mobile liquid. 
 
 Methyl-ethyl ether, CH 3 .C 2 H5.0, is a mixed ether which can be prepared 
 by the action of ethyl iodide upon sodium methylate : 
 
 C 2 H 6 I -f NaOCH 3 = Nal + C 2 H 5 .O.CH 3 . 
 
 Methyl-ethyl ether is a colorless, highly volatile, and inflammable liquid of 
 peculiar odor; it boils at 11 C. (52 F.). It has been used as an anesthetic, 
 and for that purpose is sold in cylinders. 
 
 Acetic ether, ^3ther aceticus, C 2 H 5 C 2 H.p 2 = 87.4 (Ethyl acetate). 
 Made by mixing dried sodium acetate with alcohol and sulphuric 
 acid, distilling and purifying the crude product by shaking with 
 calcium chloride and rectifying : 
 
 C 2 H 5 OH + NaC 2 H 3 2 + H 2 SO 4 = C 2 H 5 C 2 H 3 O 2 + NaHSO 4 + H 2 O. 
 Ethyl Sodium Acetic ether. Sodium acid 
 
 alcohol. acetate. sulphate. 
 
 Experiment 61. Add to a mixture of 40 grammes of pure alcohol and 100 
 grammes of concentrated sulphuric acid 60 grammes of sodium acetate. In- 
 troduce this mixture into a boiling-flask, connect it with a Liebig's condenser 
 and distil about 50 c. c. Eedistil the liquid from a flask, as represented in Fig. 
 69, page 463. and collect the portion which passes over at a temperature of 
 IT C. (170 F.) ; it is nearly pure ethyl acetate. 
 
 Acetic ether is a colorless, neutral, and mobile liquid, of a strong 
 ethereal and somewhat acetous odor, soluble in alcohol, ether, chloro- 
 form, etc., in all proportions, and in 7 parts of water. Specific 
 gravity 0.894. Boiling-point about 72 C. (161 F.). 
 
ETHERS AND ESTERS. 523 
 
 Ethyl nitrite, C 2 H,NO 2 = 74.51 (Nitrous ether). Can be made by 
 distilling a mixture of alcohol, sulphuric acid, and sodium nitrite : 
 C 2 H 5 OH + NaNOj + H 2 SO 4 = C 2 H 6 NO, + NaHSO< + H 2 O 
 
 The distillate, which contains, besides ethyl nitrite, some alcohol 
 and often some decomposition products, is washed with ice-cold water, 
 in which ethyl nitrite is nearly insoluble, and with sodium carbonate 
 to remove traces of acid ; finally, it is freed from water by treatment 
 with anhydrous potassium carbonate. It boils at 17 C. (62.6 F.). 
 
 The process adopted by the Pharmacopoeia differs from the former by 
 dispensing with the distillation and using the insolubility of the ether 
 in ice-cold salt solution for its separation. The process is carried out by 
 pouring a cold solution of sodium nitrite very slowly into an ice-cold 
 mixture of sulphuric acid, alcohol, and water. Decomposition takes 
 place as in the reaction given above. Some sodium-acid sulphate is 
 precipitated and has to be separated from the liquid, which is poured 
 into a separating funnel where two layers form. The lower aqueous 
 solution is drawn off and the remaining nitrous ether is purified like 
 the distillate obtained in the first process. (For assay-method of ethyl 
 nitrite, see paragraph on gas-analysis.) 
 
 Spirit of nitrous ether, Spiritus cetheris nitrosi, Sweet spirit of niter. 
 This is a mixture of about 4 parts of ethyl nitrite with 96 parts 
 of alcohol. It is a clear, mobile, volatile, and inflammable liquid, of 
 a pale straw color inclining slightly to green, a fragrant, ethereal 
 odor, and a sharp, burning taste. It is neutral, or but very slightly 
 acid to litmus paper but evolves no carbon dioxide with potassium 
 bicarbonate. 
 
 Amyl nitrite, Amylis nitris, C 5 H U NO 2 = 116.24. Made by a 
 process analogous to the first one mentioned above for ethyl nitrite, 
 substituting amyl alcohol for ethyl alcohol. 
 
 The official amyl nitrite contains of this ether about 80 per cent., 
 together with variable quantities of undetermined compounds ; it is 
 a clear, pale-yellowish liquid, of an ethereal, fruity odor, an aromatic 
 taste, and a neutral or slightly acid reaction. Specific gravity 0.865. 
 Boiling-point 96 C. (205 F.). The low boiling-point necessitates 
 special precautions in storing the article. It is best kept in sealed 
 vials and dispensed in sealed glass bulbs, each containing only a few 
 drops of the liquid. 
 
 Fats and fat oils. All true fats are esters of the triatomic alcohol 
 glycerin, in which the three replaceable hydrogen atoms of the hy- 
 
524 CONSIDERATION OF CARBON COMPOUNDS. 
 
 droxyl are replaced by three univalent radicals of the higher members 
 of the fatty acids. For instance : 
 
 /OH 
 
 Glycerin = C 3 H 5 .(OH> 3 or C 3 H /OH 
 
 \OH 
 
 Stearicacid = C 18 H 35 O.OH or C 18 H 35 O\ O 
 
 H/ 
 
 /(C 18 H 35 0).0 
 
 Stearin or tristearin = C 3 H 5 .(C 18 H35O) 3 .O 3 or C 3 H 5 ^_(C ]8 H3 5 O).O 
 
 \(C 18 H 35 0).0 
 
 While all natural fats are glycerin in which the three hydrogen 
 atoms are replaced, we may by artificial means introduce but one or 
 two acid radicals, thus forming : 
 
 /(C 18 H 35 O)O /(C 18 H, 5 0)O 
 
 Monostearin = C 3 H 5 ^OH Distearin = C 3 H 5 /(C 18 H 35 O)O 
 
 \OH 
 
 Fats are often termed glycerides ; stearin being, for instance, the 
 glyceride of stearic acid. 
 
 The principal fats consist of mixtures of palmitin, C 3 H 5 .(C 16 H 31 O) 3 . 
 3 , stearin, C 3 H 5 .(C 18 H 35 O) 3 .O 3 , and olein, C^C^O^O,,. 
 Stearin and palmitin are solids, olein is a liquid at ordinary tem- 
 perature ; the relative quantity of the three fats mentioned determines 
 its solid or liquid condition. The liquid fats, containing generally 
 olein as their chief constituent, are called fatty oils or fixed oils in 
 contradistinction to volatile or essential oils. 
 
 All fats, when in a pure state, are colorless, odorless, and tasteless 
 substances, which stain paper permanently ; they are insoluble in 
 water, difficultly soluble in cold alcohol, easily soluble in ether, disul- 
 phide of carbon, benzene, etc. The taste and color of fats are due to 
 foreign substances, often produced by a slight decomposition which 
 has taken place in some of the fat. All fats are lighter than water, 
 and all solid fats fuse below 100 C. (212 F.) ; fats can be distilled 
 without change at about 300 C. (572 F.), but are decomposed at a 
 higher temperature with the formation of numerous products, some 
 of which have an extremely disagreeable odor, as, for instance, 
 acrolem, which has been mentioned before. 
 
 Fats being lighter than, and insoluble in, water will float on it, but mechani- 
 cal mixtures of both substances exist in emulsions. These contain finely di- 
 vided fat globules, suspended in the water, or better in water containing some 
 gum-arabic or a similar substance. Milk and certain plant juices are examples 
 of natural emulsions. 
 
 Some fats keep without change when pure ; since, however, they gen- 
 erally contain impurities, such as albuminous matter, etc., they suffer 
 
ETHERS AND ESTERS. 525 
 
 decomposition (a kind of fermentation aided by oxidation), which re- 
 sults in a liberation of the fatty acids, which impart their odor and taste 
 to the fats, causing them to become what is generally termed rancid. 
 
 Some fats, especially some oils, suffer oxidation, which renders 
 them hard. These drying oils differ from other oils in being mixtures 
 of olein with another class of glycerides, containing unsaturated acids 
 with less hydrogen in relation to carbon than oleic acid. Drying oils 
 are prevented from drying by albuminous impurities, which may be 
 removed by treating the oil with 4 per cent of concentrated sulphuric 
 acid ; the acid does not act on the fat, but quickly destroys the albu- 
 minous matters, which, with the sulphuric acid, sink to the bottom, 
 while the " refined " oil may be removed by decantation. 
 
 Fats are largely distributed in the animal and vegetable kingdoms. 
 They exist in plants chiefly in the seeds, while in animals they are found 
 generally under the skin, around the intestines, and on the muscles. 
 
 Human fat, beef tallow, mutton tallow, and lard are mixtures of 
 palmitin and stearin with some olein. Butter consists of the glycer- 
 ides of butyric acid, capro'ic acid, caprylic acid, and capric acid, 
 which are volatile with water vapors, and of myristic, palmitic, oleic, 
 and stearic acids, which are not volatile. 
 
 The principal non-drying vegetable oils (consisting chiefly of olein) 
 are olive oil, cottonseed oil, cocoanut oil, palm oil, almond oil. 
 
 Among the drying oils are of importance : linseed oil, castor oil, 
 croton oil, hemp oil, cod-liver oil. 
 
 Whenever fats are treated with alkaline hydroxides, or with a 
 number of other metallic oxides, decomposition takes place, the fatty 
 acids combining with the metals, while glycerin is set free. Some 
 of the substances thus formed are of great importance, as, for instance, 
 the various kinds of soap. 
 
 The term saponification, as used by physiologists, is applied to the 
 decomposition which occurs when neutral fat is split into its constitu- 
 ents, glycerin and fatty acid. This decomposition is a hydrolytic 
 cleavage, and can be produced by the action of boiling alkalies, super- 
 heated steam, various enzymes, etc. In other words, the formation 
 of a soap is not an essential part of the process. 
 
 Soap. Any fat boiled with sodium or potassium hydroxide will 
 form soap. Soft soap is potassium soap, hard soap is sodium soap. 
 The better kinds of hard soap are made by boiling olive oil with 
 sodium hydroxide : 
 
 C 3 H 5 (C ]8 H 33 2 ) 3 + SNaOH = SNaC^O, + C 3 H 5 (OH) 3 . 
 Oleateof erlvceryl Sodium Sodium oleate Glycerin, 
 
 (olive oil). hydroxide. (hard soap). 
 
526 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Soaps are soluble in water and alcohol ; they contain rarely less 
 than 30 per cent., but sometimes as much as 70-80 per cent, of water. 
 
 Potassium or soft soap is usually yellowish, but it is sometimes tinted green 
 artificially, and is then called "green soap." It contains, besides the potas- 
 sium salts of the fatty acids, the glycerin liberated in the saponification and 
 relatively much water. Hard or sodium soap is separated from the solution 
 after saponification by adding common salt to the boiling mixture to satura- 
 tion. The soap, being insoluble in the salt solution, separates as a molten 
 layer, which can be removed after cooling and solidifying. This method of 
 separating the soap is known as the "salting out" process. The soap is free 
 from glycerin, but contains some water. 
 
 Ammonia liniment, Linimentum ammonice, and lime liniment, Lini- 
 mentum calcis, are obtained by mixing cottonseed oil with ammonia- 
 water and lime-water respectively. The oleate of ammonium or 
 calcium is formed, and remains mixed with the liberated glycerin. 
 
 Lead plaster. Chiefly lead oleate, Pb(C 18 H 3 3O 2 ) 2 . Obtained by boiling lead 
 oxide with olive oil and water for several hours, until a homogeneous, pliable, 
 and tenacious mass is formed. Lead oleate differs from the oleate of the alkalies 
 by its complete insolubility in water. 
 
 Experiment 62. Dissolve in a 500 c.c. flask 15 grammes of potassium hy- 
 droxide in 100 c.c. of alcohol. Melt 50 grammes of lard in an evaporating dish 
 and pour the liquefied fat into the flask. Heat over a water bath, and shake 
 cautiously when the alcohol begins to boil. Saponification takes place very 
 rapidly, and its completion is determined by pouring a few drops of the liquid 
 into a test-tube of water, when any unsaponified fat will float on the surface. 
 When saponification is complete the solution contains soap, glycerin, and any 
 excess of caustic potash. 
 
 Pour the contents of the flask into 250 c.c. of hot 5 per cent, sulphuric acid ; 
 the fatty acids separate as an oily layer which solidifies on cooling. The solu- 
 tion contains potassium acid sulphate, sulphuric acid, and glycerin. When the 
 solution is neutralized, evaporated to crystallization, and extracted with alco- 
 hol, glycerin can be obtained by evaporation of the alcoholic extract. 
 
 Reactions of fats and fatty acids. 
 
 1. Boil 5 grammes of suet with 25 c.c. of alcohol and filter while 
 hot. Wash the residue with a little ether, squeeze as dry as possible 
 and then dry in the air. The resulting fibrous mass is the connective 
 tissue network of the adipose tissue and a little fat. Show the pres- 
 ence of protein in connective tissue by the xanthoproteic and Millon's 
 reactions. On evaporation of the alcoholic filtrate, fat is left. 
 
 2. Rub a little fat on glazed white paper. Notice that this " grease- 
 spot" appears dark on a white background in reflected light, but 
 light (transparent) in transmitted light. The stain does not disappear 
 on heating. 
 
ETHERS AND ESTERS. 527 
 
 3. Heat in a dry test-tube a small quantity of fat with an equal 
 portion of potassium bisulphate. Acrolein is formed and recognized 
 by its odor. 
 
 4. Heat about 2 grammes of fatty acids with 100 c.c. of water and 
 enough sodium carbonate to dissolve the fatty acids. A solution of 
 sodium soap is formed, of which use a few c.c. for each of the follow- 
 ing reactions : 
 
 a. Heat with an excess of hydrochloric acid ; fatty acids are lib- 
 erated. 
 
 6. Add calcium chloride solution ; insoluble calcium soap is formed, 
 and the solution does not foam on shaking. 
 
 c. Add lead acetate solution ; a white precipitate of an insoluble 
 lead salt (lead plaster) is formed, becoming sticky on heating. 
 
 d. Add some olive oil and shake well ; a homogeneous milk-like 
 mixture i. e., emulsion is formed. 
 
 Wool-fat, Lanolin, Adeps lanse. This is the fat, or a mixture of fats, 
 found in sheep's wool and obtained by treating the wool with soap-water, and 
 acidifying the wash liquor, when the fats separate unchanged. These fats 
 differ from the fats spoken of above in so far as the alcohol present is not 
 glycerin, but an alcohol, or rather two isomeric alcohols of the composition 
 C 26 H 4:! OH and known as cholesterin and isocholesterin. These alcohols, which 
 are white, crystalline, fusible substances, when in combination with fatty acids 
 form the compound ethers known as lanolin. 
 
 Lanolin is a yellowish-white (or, when not sufficiently purified, a more or 
 less brownish), fat-like substance, having the peculiar odor of sheep's wool and 
 fusing at about 40 C. (104 F.), forming an oily liquid. Unlike true fats, 
 lanolin is capable of mixing with twice its weight of water or aqueous solutions 
 and yet retaining its fatty consistency ; it is, moreover, much less liable to de- 
 compose than fats, and it is this property and its power to mix with aqueous 
 solutions which have rendered lanolin a valuable agent in certain pharma- 
 ceutical preparations. Official is also hydrous wool-fat, the purified fat mixed 
 with not more than 30 per cent, of water. 
 
 QUESTIONS. Explain the constitution of simple and mixed ethers ancfr 
 esters. To what inorganic compounds are they analogous? State the general 
 processes for the formation of ethers and esters. What is the composition of 
 ethyl ether ? Explain the process of its manufacture in words and symbols, 
 and state its properties. How is acetic ether made, and what are its proper- 
 ties? What is sweet spirit of niter, and how is it made? State the general 
 composition of fats and the chief constituents of tallow, butter, and olive oil. 
 What is the solubility of fats in water, alcohol, and ether; how do heat and 
 oxygen act upon them ; what is the cause of their becoming rancid? Explain 
 the composition and manufacture of soap, and state the difference between hard 
 and soft soap. How are ammonia liniment, lime liniment, and lead plaster 
 made, and what is their composition ? What is the source of lanolin ; what 
 are its constituents and properties ? 
 
528 CONSIDERATION OF CARBON COMPOUNDS. 
 
 48. CARBOHYDRATES. 
 
 General remarks. The name carbohydrates was originally given 
 to a class of compounds found chiefly in plants, and containing in 
 the molecule 6 atoms of carbon (or a multiple of 6) in combination 
 with hydrogen and oxygen in the proportion to form water, as shown 
 in the formula for grape-sugar, C 6 H 12 O 6 , cane-sugar, C 12 H 22 O U , etc. 
 While even formerly the name was not well chosen, because it 
 implies that these subfetances are carbon in combination with water, 
 to-day it is still less suitable, because members of the group have been 
 found which do not contain oxygen and hydrogen in the proportion 
 mentioned ; as, for instance, a sugar, termed rhamnose, having the 
 composition C 6 H 12 O 5 . We also know now carbohydrates containing 
 carbon atoms in numbers which have no relation to 6. While, there- 
 fore, the term carbohydrate no longer implies what it formerly 
 did, and no longer refers to the restricted number of compounds 
 which it formerly included, yet it is retained for the whole group of 
 compounds now to be considered. 
 
 The group includes now, as heretofore, the different sugars, starches, 
 gums, etc., and also a number of compounds obtained by artificial or 
 synthetical processes. In order to show in its name that a substance 
 belongs to the carbohydrates, the ending ose is used to distinguish 
 these bodies from the members of other groups. 
 
 Constitution. While the true atomic structure of many carbo- 
 hydrates is as yet not fully understood, the structure of others is 
 well known. It appears that some carbohydrates are true aldehydes, 
 while others are closely related to ketones, and yet others are the 
 anhydrides, or condensation products of the former. 
 
 Thus, a sugar of the composition C 3 H 6 O 3 , termed glycerose, is obtained by the 
 action of mild oxidizing agents on glycerin, thus : 
 
 C 3 H 8 3 + O = C 3 H 6 3 + H 2 0. 
 
 If we bear in mind the fact that glycerin, C 3 H 5 (OH) 3 , is a triatomic alcohol, 
 and that alcohols by oxidation yield aldehydes, we realize the analogy existing 
 between the above reaction and that leading to the formation of the aldehydes, 
 previously considered. 
 
 In a manner similar to the one producing glycerose from glycerin, a sugar 
 of the composition C 4 H 8 O 4 , and called erythrose, is obtained from the tetratomic 
 alcohol erythrite, C 4 H 6 (OH) 4 , while a sugar of the composition C 6 H 12 O 6 is ob- 
 tainable from the hexatomic alcohol mannite, C 6 H 8 (OH) 6 . In both cases two 
 atoms of hydrogen are split off from the alcohol molecules. 
 
 The relationship existing between the sugars of the composition C 6 H ]2 O 6 
 
CA RBOH YDEA TES. 529 
 
 and other carbohydrates having the composition C 6 PTi O 5 or C 12 H 22 O n can he 
 readily shown by the equations : 
 
 *(C 6 H 12 6 - H 2 0) (C 6 H 10 5 )z 
 
 2(C 6 H 12 6 )- H 2 : C 12 H 22 O n , 
 
 which show that abstraction of water leads to the formation of compounds 
 having the composition of starch, C 6 H 10 O 5 , and cane-sugar, C 12 H 22 O n , respec- 
 tively. While this abstraction of water is difficult, it is an easy matter to 
 cause starch or cane-sugar to take up water, with the result that sugars of the 
 composition C 6 H 12 O 6 are formed. 
 
 Properties. Carbohydrates are either fermentable, or can, in most 
 cases, be converted into substances which are capable of fermentation. 
 They are not volatile, but suffer decomposition when sufficiently 
 heated ; they have neither acid nor basic properties, but are of a neu- 
 tral reaction. Oxidizing agents convert them into saccharic and 
 mucic acids and finally into oxalic acid. (Soluble carbohydrates 
 have generally the property of turning the plane of polarized light.) 
 
 Most carbohydrates are white, solid substances, and, with the ex- 
 ception of a few, soluble in water. Those carbohydrates belonging 
 to the sugars have a more or less sweet taste. Many of them, 
 especially glucose, are good reducing agents, as is shown by the 
 fact that they deoxidize in alkaline solution salts (or oxides) of 
 copper, bismuth, mercury, gold, etc., either to a lower state of 
 oxidation or to the metallic state. 
 
 Occurrence in nature. No other organic substances are found in 
 such immense quantities in the vegetable kingdom as the members 
 of this group, cellulose being a chief constituent of all, starch and 
 various kinds of sugar of most plants. Carbohydrates are also found 
 as products of animal life, as, for instance, the sugar in milk, in bees' 
 honey, etc. 
 
 Classification. The carbohydrates are conveniently divided into 
 the following three groups : 
 
 1. Monosaccharides, or simple sugars. To this group belong the 
 sugars which cannot be broken down into two or more simple sugars. 
 They contain from 3 to 9 atoms of carbon, in most cases the same 
 number of oxygen atoms, and double the number of hydrogen atoms. 
 (Dextrose, levulose, galactose, etc.) 
 
 2. Disaccharides, or complex sugars. These are sugars which, on 
 taking up 1 molecule of water, split up into two simple sugars. 
 (Cane-sugar, maltose, lactose, etc.) 
 
 3. Polysaccharides. These do not resemble sugars, have no sweet 
 taste, and form simple sugars only after repeated cleavages. (Starches, 
 gums, cellulose, etc.) 
 
 34 
 
530 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Monosaccharides. 
 
 The monosaocharides are white, odorless, sweet, crystallizable, neu- 
 tral substances, readily soluble in water, sparingly soluble in alcohol, 
 insoluble in ether. Like all aldehydes and ketones they are easily 
 oxidized, acting as strong reducing agents. Trommer's, Fehling's, 
 and Boettger's " reduction tests " depend on this property. Solutions 
 of monosaccharides, acidified with acetic acid, give with phenyl-hy- 
 drazine crystalline precipitates of substances called osazones. The tri- 
 oses, hexoses, and nonoses are capable of alcoholic fermentation, the 
 others are not. Most of the monosaccharides are optically active. 
 
 According to the number of carbon atoms present, the monosaccharides are 
 again subdivided into classes called trioses, tetroses, pentoses, hexoses, heptoses, 
 octoses, and nonoses, having the composition C 3 H 6 O 3 , C 4 H 8 O 4 , C 5 H 10 O 5 , C 6 H 12 CX., 
 C 7 H U O 7 , C 8 H 16 8 , and C 9 H 18 O 9 , respectively. The hexoses are the best-known 
 group, which is again subdivided into two groups, viz., the aldoses, containing 
 the alcohol group, CH. 2 OH, and the aldehyde group, COH ; and the ketoses, 
 containing the alcohol group and the ketone group, CO. The constitution of 
 these compounds is shown thus : 
 
 Aldoses 
 
 Ketoses 
 
 Glucose is an aldose-hexose, while fructose is a ketose-hexose. 
 
 Dextrose, Glucose, Grape-sugar, C 6 H 12 O 6 . This substance is 
 very abundantly diffused throughout the vegetable kingdom, and is 
 generally accompanied by fruit-sugar. It is contained in large quan- 
 tities in the juice of many fruits; the percentage of grape-sugar in 
 the dried fig is about 65, in grape 10-20, in cherry 11, in mulberry 9, 
 in strawberry 6, etc. 
 
 Dextrose is found also in honey and in minute quantities in the 
 normal blood (0.1 per cent, or less), and traces occur, perhaps, in 
 normal urine, the quantity in both liquids rising, however, during 
 certain diseases, as high as 5 per cent, or higher. 
 
 Grape-sugar is produced in the plant from starch by the action of 
 the vegetable acids present; it may be obtained artificially from 
 starch (and from many other carbohydrates) by heating with dilute 
 mineral (sulphuric) acids, which convert starch first into dextrin and 
 
 Trioses. 
 
 Tetroses. 
 
 Pentoses. 
 
 Hexoses. 
 
 f COH 
 
 COH 
 
 COH 
 
 COH 
 
 I 
 CHOH 
 
 (CHOH), 
 
 (CHOH) 3 
 
 (CHOH) 4 
 
 1 
 
 
 | 
 
 1 
 
 [ CH 2 OH 
 
 CH,OH 
 
 CH. 2 OH 
 
 CH.OH. 
 
 f CH 2 OH 
 
 CH,OH 
 
 CH 2 OH 
 
 CH 2 OH 
 
 1 
 
 1 
 
 1 
 
 I 
 
 CO 
 
 CO 
 
 CO 
 
 CO 
 
 1 
 
 1 
 
 1 
 
 1 
 
 CH 2 OH 
 
 CHOH 
 
 (CHOH) 2 
 
 (CHOH) 3 
 
 
 ! 
 CH,OH 
 
 Cff,OH 
 
 CH 2 OH. 
 
CARBOHYDRATES. 531 
 
 then into grape-sugar. Corn-starch is now largely used for that pur- 
 pose, the excess of sulphuric aoid being removed by treating the solu- 
 tion with chalk ; the filtered solution is either evaporated to a syrup 
 and sold as "glucose," or evaporated to dryness, when the com- 
 mercial " grape-sugar " is obtained. 
 
 Experiment 63. Heat to boiling 100 c.c. of a 1 per cent, sulphuric acid and 
 add to it very gradually and with constant stirring a mixture made by rub- 
 bing together 25 grammes of starch and 25 grammes of water. Continue to boil 
 until iodine no longer causes a blue color (which shows complete conversion of 
 starch into either dextrin or glucose), and until 1 c.c. of the solution is no longer 
 precipitated on the addition of 6 c.c. of alcohol (which shows the conversion of 
 dextrin into sugar, dextrin being precipitated by alcohol). Apply to a portion 
 of the glucose solution thus obtained, and neutralized by sodium carbonate, the 
 tests mentioned below. To the remaining solution add a quantity of precipitated 
 calcium carbonate sufficient to convert all sulphuric acid into calcium sulphate. 
 Filter, evaporate the solution to a syrup and notice its sweet taste. 
 
 Glucose is met with generally as a thick syrup which crystallizes 
 with difficulty, combining during crystallization with one molecule of 
 water; but anhydrous crystals, closely resembling those of cane- 
 sugar, are also known. Glucose is soluble in its own weight of 
 water and is less sweet than cane-sugar, the sweetness of glucose com- 
 pared to that of cane-sugar being about 3 to 5 ; when heated to 170 
 C. (338 F.) it loses water, and is converted into glucosan, C 6 H 10 O 5 ; 
 by stronger heating it loses more water and forms caramel, a mixture 
 of various substances ; it turns the plane of polarized light to the 
 right. 
 
 By gentle oxidation dextrose is first converted into monobasic glu- 
 conic acid, C 6 H 12 O 7 = C 5 H 6 .(OH) 5 .CO 2 H, and then into dibasic sac- 
 charic acid, C 6 H 10 O 8 = C 4 H 4 .(OH) 4 .(CO 2 H) 2 . Further oxidation 
 results in the formation of acids of lower molecular weight, due to 
 splitting up of the molecules. (Saccharic acid is soluble in less than 
 its own weight of water.) 
 
 Dextrose combines with various metallic oxides (alkalies, alkaline 
 earths, etc.), and also with a number of other substances, forming a 
 series of compounds known as glucosides. 
 
 Dextrose may be recognized analytically : 
 
 1. By causing a bright-red precipitate of cuprous oxide, when 
 boiled with a solution of cupric sulphate in sodium hydroxide, to 
 which tartaric acid has been added. (A solution containing these 
 three substances in definite proportions is known as Fehling's solu- 
 tion. See index.) 
 
 2. By precipitating metallic silver, bismuth, and mercury, when 
 
532 CONSIDERATION OF CARBON COMPOUNDS. 
 
 compounds of these metals are heated with it in the presence of 
 caustic alkalies. 
 
 3. By easily fermenting when yeast is added to the solution, alco- 
 hol and carbon dioxide being formed : 
 
 C 6 H 12 6 = 2C 2 H 5 OH + 2C0 2 . 
 
 4. By forming with an excess of phenyl-hydrazine, in a solution 
 acidified with acetic acid, a yellow crystalline precipitate of phenyl- 
 dextrosazone. 
 
 Levulose, Fructose, C 6 H 12 O 6 (Fruit-sugar), occurs with glucose in 
 sweet fruits and honey ; it resembles glucose in most chemical and 
 physical properties, but does not crystallize from an aqueous solution ; 
 it may, however, be obtained in white silky needles from an alcoholic 
 solution ; it is met with generally as a thick syrup, is about as sweet 
 as cane-sugar, and turns the plane of polarized light to the left ; it is 
 formed by the action of dilute mineral acids or ferments on cane- 
 sugar, which latter takes up water and breaks up thus : 
 
 C ]2 H 22 O n + H 2 = C 6 H I2 6 + C 6 H 12 6 . 
 Cane-sugar. Dextrose. Fructose. 
 
 Levulose has been made by the polymerization of formic aldehyde, 
 CH 2 O, and also by several other reactions. 
 
 Mannose, C 6 H 12 O 6 . Obtained by the oxidation of mannite ; it does 
 not crystallize and resembles grape-sugar. 
 
 Galactose, C 6 H 12 O 6 , is formed together with dextrose when either 
 milk-sugar or gum-arabic is boiled with dilute sulphuric acid. Galac- 
 tose crystallizes, reduces an alkaline copper solution, but does not fer- 
 ment with yeast. 
 
 When oxidized by heating with nitric acid, galactose forms galactonic add 
 and mucic acids, which are isomeric with the above-mentioned gluconic and 
 saccharic acids. Mucic acid is easily distinguished from saccharic acid by 
 being almost insoluble in water. 
 
 Inosite, C 6 H 12 O 6 (Muscle-sugar). This compound was classed with 
 the carbohydrates on account of its sweet taste; its readiness to 
 undergo lactic and butyric fermentation; and the identity of its 
 molecular formula with that of the hexoses. It has, however, been 
 shown that inosite has an entirely different constitution, being a benzol 
 derivative, viz., hexahydroxy-benzol, C 6 H 6 (OH) 6 . 
 
 Inosite occurs somewhat abundantly in unripe beans and peas, and 
 sparingly in the liquid of muscular tissue ; traces are found in urine, 
 the quantity increasing in certain diseases. It does not ferment with 
 yeast, does not reduce alkaline copper solution, and is optically in-- 
 active. 
 
CARBOHYDRATES. 533 
 
 Disaccharides. 
 
 The general physical properties and the solubility of disaccharides 
 are identical with those of the monosaccharides. They differ from them 
 by not fermenting directly and by not forming osazones. The empiri- 
 cal formula is C 12 H 22 O U . By treatment with dilute mineral acids or 
 by the action of certain enzymes they undergo hydrolysis i. e., take 
 up a molecule of water and are resolved into two hexose molecules. 
 Thus, cane-sugar splits up into dextrose and levulose ; lactose into 
 dextrose and galactose ; maltose into two molecules of dextrose. 
 
 Cane-sugar is dextrorotatory, but the mixture obtained by the hy- 
 drolysis of cane-sugar is laevorotatory, because levulose turns the 
 plane of polarization more to the left than dextrose does to the right. 
 For this reason the mixture is called inverted sugar and the hydrol- 
 ysis inversion. The term inversion is therefore used to designate the 
 splitting of disaccharides into simpler sugars. The building up of 
 complex sugars from simple sugars is called reversion. 
 
 Lactose and maltose reduce alkaline copper solution ; cane-sugar 
 does not. 
 
 Cane-sugar, Saccharum, C 12 H 22 O U = 339.6 (Saccharose, Com- 
 mon sugar, Beet-sugar}. Cane-sugar is found in the juices of 
 many plants, especially in that of the different grasses (sugar-cane), 
 and also in the sap of several forest trees (maple), in the roots, stems, 
 and other parts of various plants (sugar-beet), etc. Plants contain- 
 ing cane-sugar do not contain free organic acids, which latter would 
 convert it into grape-sugar. 
 
 Cane-sugar is manufactured from various plants containing it by 
 crushing them between rollers, expressing the juice, heating and 
 adding to it milk of lime, which precipitates vegetable albuminous 
 matter. The clear liquid is evaporated to the consistency of a syrup, 
 which is further purified (refined) by filtering it through bone-black 
 and evaporating the solution in " vacuum pans" to the crystallizing- 
 point; the mother-liquors are further evaporated, and yield lower 
 grades of sugar; finally a syrup is left which is known as molasses. 
 
 Cane-sugar forms white, hard, distinctly crystalline granules, but 
 may be obtained also in well-formed, large, monocliuic prisms. It 
 dissolves in 0.2 part of boiling, in 0.5 part of cold water, and in 175 
 parts of alcohol ; when heated to 160 C. (320 F.) it fuses, and the 
 liquid, on cooling, forms an amorphous, transparent mass, known as 
 barley sugar; at a higher temperature cane-sugar is decomposed, 
 water is evolved, and a brown, almost tasteless substance is formed, 
 which is known as caramel or burnt sugar. Oxidizing agents act 
 
534 CONSIDERATION OF CARBON COMPOUNDS. 
 
 energetically upon cane-sugar, which is a strong reducing agent. A 
 mixture of cane-sugar and potassium chlorate will deflagrate when 
 moistened with sulphuric acid ; potassium permanganate is readily 
 deoxidized in acid solution ; cane-sugar, however, does not affect an 
 alkaline copper solution, and does not itself ferment ; but when heated 
 with dilute acids or left in contact with yeast in the presence of vari- 
 ous bacteria it is decomposed into dextrose and levulose, both of which 
 are fermentable. Like dextrose, cane-sugar forms compounds with met- 
 als, metallic oxides, and salts, which compounds are known as sucrates. 
 
 Experiment 64 Make a one per cent, cane-sugar solution ; test it with 
 Fehling's solution and notice that no cuprous oxide is precipitated. Add to 
 50 c c. of the cane-sugar solution 5 drops of hydrochloric acid and heat on a 
 water-bath for half an hour. Again examine the liquid with Fehling's solu- 
 tion ; a precipitate of cuprous oxide is now formed, proving the conversion of 
 cane-sugar into dextrose (grape-sugar) and levulose. 
 
 Maltose, C 12 H 22 O n , is obtained by the action of diastase on starch. 
 Diastase is a substance formed during the germination of various 
 seeds (rye, wheat, barley, etc.), and it is for this reason that grain 
 used for alcoholic liquors is converted into malt i. e., is allowed to 
 germinate, during which process diastase is formed, which, acting 
 upon the starch present, converts it into maltose and dextrin : 
 
 3(C 6 H 10 5 ) + H 2 = C 12 H 22 U + C 6 H 10 6 . 
 Starch. Maltose. Dextrin. 
 
 Maltose is also formed by the action of dilute sulphuric acid upon 
 starch, and is hence often present in commercial glucose ; by further 
 treatment with sulphuric acid it is converted into dextrose. Maltose 
 crystallizes, reduces alkaline copper solutions, and ferments with 
 yeast. 
 
 Melitose, C 12 H 22 O n , is the chief constituent of Australian manna. 
 
 Sugar of milk, Saccharum lactis, C 12 H 22 O n + H 2 O = 357.48 
 (Lactose). Found almost exclusively in the milk of the mammalia. 
 Obtained by freeing milk from casein and fat and evaporating the 
 remaining liquid (whey) to a small bulk, when the milk-sugar crys- 
 tallizes on cooling. 
 
 It forms white, hard, crystalline masses ; it is soluble in about 6 
 parts of water (at 15 C., 59 F.) and in 1 part of boiling water, 
 insoluble in alcohol and ether; it is much harder than cane-sugar, 
 and but faintly sweet; it is not easily brought into alcoholic fermen- 
 tation by the action of yeast, but easily undergoes " lactic fermenta- 
 tion" when cheese is added. During this process milk-sugar is 
 
CARBOHYDRATES. 535 
 
 converted into lactic acid. By hydrolysis, lactose is split into dextrose 
 and galactose. 
 
 Milk-sugar resembles dextrose in its action on alkaline solution of 
 copper, from which it precipitates cuprous oxide ; it differs from it by 
 not fermenting with yeast, and in forming mucic acid when heated with 
 nitric acid. 
 
 Polysaccharid.es. 
 
 To the poly saccha rides belong the starches, gums, cellulose, glyco- 
 gen, etc. They differ from the two previous groups by being insoluble 
 in water or soluble with difficulty ; by not crystallizing and not being 
 diffusible. These latter properties are generally characteristic of sub- 
 stances of high molecular weight. By hydrolysis polysaccharides split, 
 forming dextrins, disaccharides, and monosaccharides ; their general 
 composition is indicated by (C 6 H 10 O 5 ) X , which means that the mole- 
 cules are made up of an unknown multiple of C 6 H 10 O 5 . The consti- 
 tution is unknown. 
 
 Starch, Amylum, (C 6 H 10 O 5 ) X . Starch is very widely distributed 
 in the vegetable kingdom, and is found chiefly in the seeds of cereals 
 and leguminosa?, but also in the roots, stems, and seeds of nearly all 
 plants. 
 
 It is prepared from wheat, potatoes, rice, beans, sago, arrow-root, 
 etc., by a mechanical operation. The vegetable matter containing 
 the starch is comminuted by rasping or grinding, in order to open 
 the cells in which it is deposited, and then steeped in water; the 
 softened mass is then rubbed on a sieve under a current of water 
 which washes out the starch, while cellular fibrous matter remains on 
 the sieve; the starch deposits slowly from the washings, and is 
 further purified by treating it with water. 
 
 Starch forms white, amorphous, tasteless masses, which are pecu- 
 liarly slippery to the touch, and easily converted into a powder; it 
 is insoluble in cold water, alcohol, and ether; when boiled with water, 
 it yields a white jelly (mucilage of starch, starch-paste) which cannot 
 be looked upon as a true solution, but is a suspension of the swollen 
 starch particles in water ; by continued boiling with much water some 
 starch passes into solution. 
 
 Starch, when examined under the microscope, is seen to consist of 
 granules differing in size, shape, and appearance, according to the 
 plant from which the starch was obtained. Concentric layers, which 
 are more or less characteristic of starch-granules, show that they are 
 formed in the plant by a gradual deposition of starch matter. 
 
 The most characteristic test for starch is the dark-blue color which 
 
536 CONSIDERATION OF CARBON COMPOUNDS. 
 
 iodine imparts to it (or better to the mucilage). This color is due to 
 the formation of iodized starch, an unstable dark-blue compound of 
 the doubtful composition C 6 H 9 IO 5 L 
 
 Starch is an important article of food, especially when associated, as in 
 ordinary flour, with albuminous substances. In the body starch, as well as 
 other carbohydrates, must be converted into monosaccharides before being 
 absorbed. This hydrolysis of starch may be made outside the body acting on 
 starch paste with some diastatic enzyme, or by prolonged boiling with very 
 dilute (1 per cent.) mineral acid. The intermediate products of the hydrolysis 
 are the same in either case. Starch is first converted into soluble starch or 
 amylo-dextrin, which gives a blue color with iodine ; the soluble starch next 
 passes into malto-dextrin and ery thro- dextrin, giving a red color with iodine ; 
 erythro-dextrin passes into malto-dextrin and achroo-dexfrin, giving no color 
 with iodine, but forming a white precipitate with alcohol. Achroo-dextrin 
 passes into maltose, and maltose into dextrose. The hydrolysis is a progressive 
 reaction, all these compounds being present in the solution at one time. 
 
 Dextrin, C 6 H 10 O 5 (British gum). This name is given to a mixture 
 of the dextrins just mentioned, and formed by hydrolysis of starch 
 by means of diluted acids, or by subjecting starch to a dry heat of 
 175 C. (347 F.), or by the action of diastase (infusion of malt) upon 
 starch. Malt is made by steeping barley in water until it germinates, 
 and then drying it. 
 
 Dextrin is a colorless or slightly yellowish, amorphous powder, re^ 
 sembling gum-arabic in some respects ; it is soluble in water, does not 
 reduce alkaline copper solution, and is colored light wine-red by iodine. 
 It is extensively used in mucilage as a substitute for gum-arabic. 
 
 Gums. These are amorphous substances of vegetable origin, 
 soluble in water or swelling up in it, forming thick, sticky masses; 
 they are insoluble in alcohol, and are converted into glucose by boil- 
 ing with dilute sulphuric acid. Some gums belong to the saccharoses, 
 others to the amy loses. 
 
 Acacia, Gum-arabic is a gummy exudation from Acacia Senegal ; 
 it consists chiefly of the calcium salt of arable acid, C 12 H 22 O U . Other 
 gums occur in the cherry tree, in linseed or flaxseed, in Irish moss, 
 in marsh-mallow root, etc. 
 
 Gum-arabic dissolves slowly in 2 parts of water ; this solution 
 shows an acid reaction with litmus, and yields precipitates with lead 
 acetate or ferric chloride. 
 
 Cellulose (C 6 H 10 O 5 ) X , perhaps C 18 H 30 O 15 (Plant fibre, Lignin). 
 Cellulose constitutes the fundamental material of which the cellular 
 membrane of vegetables is built up, and forms, therefore, the largest 
 portion of the solid parts of every plant ; it is well adapted to this 
 purpose on account of its insolubility in water and most other sol- 
 
CARBOIIYDRA TES. 537 
 
 vents, its resistance to either alkaline or acid liquids, and its tough 
 and flexible nature. Some parts of vegetables (cotton, hemp, and 
 flax, for instance) are nearly pure cellulose. 
 
 Pure cellulose is a white, translucent mass, insoluble in all the 
 common solvents. It is not colored blue by iodine. 
 
 The best solvent for cellulose is an ammoniacal solution of copper hydrox- 
 ide, known as Schweizer's reagent, a very efficient preparation of which is 
 obtained as follows : 2 grammes of pure crystallized copper sulphate are dis- 
 solved in 100 c.c. of water to which a few drops of a concentrated solution of 
 ammonium chloride have been added. 1 gramme of potassium hydroxide is 
 dissolved in 100 c.c. of water and a little of a solution of barium hydroxide 
 added to precipitate any carbonate in the alkali. The two solutions are mixed 
 and the precipitate thoroughly washed by decantation and on the filter-paper. 
 The moist copper hydroxide is finally covered in a beaker with just enough 
 concentrated ammonia water to dissolve it. The clear solution is decanted or 
 filtered through glass wool. It must be preserved in a dark place. 
 
 Cellulose is precipitated from its solution in Schweizer's reagent by acids as 
 a gelatinous mass which forms a grayish powder when dried. 
 
 Treated with concentrated sulphuric acid it swells up and gradu- 
 ally dissolves ; water precipitates from such solutions a substance 
 known as amyloid, which is an altered cellulose giving a blue color 
 with iodine. Upon diluting the sulphuric acid solution with water 
 and boiling it, the cellulose is gradually converted into dextrin and 
 dextrose. 
 
 Unsized paper (which is chiefly cellulose), dipped into a mixture 
 of two volumes of sulphuric acid and one volume of water, forms, 
 after being washed and dried, the so-called " parchment paper," 
 which possesses all the valuable properties of parchment. 
 
 Official purified cotton, known commercially as absorbent cotton, is prepared 
 from raw cotton by boiling it in a weak solution of alkali to remove fatty 
 matter, then treating it with a weak solution of chlorinated lime to bleach it, 
 It is then washed and dried. 
 
 Medicated cotton is usually prepared by impregnating absorbent cotton with 
 a solution of the medicinal agent in alcohol and glycerin, and drying. The 
 glycerin is not volatilized and serves as an adhesive agent for retaining the 
 active ingredient on the fiber of the cotton. Benzoated, borated, carbolated, 
 iodized, salicylated, and other medicated cotton is prepared in this or a simi- 
 lar manner. The percentage of medicinal agent present must be calculated on 
 the basis of finished product ; thus, 25 grammes of 10 per cent, borated cotton 
 should contain 2.5 grammes of boric acid, or 10 grammes of 5 per cent, carbo- 
 lated cotton should contain 0.5 gramme of pure carbolic acid. 
 
 Pyroxylin, Pyroxylinum, chiefly cellulose tetm-nitrate, C 12 H 16 O 6 - 
 (NO 3 ) 4 . (Soluble gun-cotton, Nitro-cellulose.) Cellulose has the 
 
538 CONSIDERATION OF CARBON COMPOUNDS. 
 
 power to unite with acids to form ethereal salts (esters), thus exhibit- 
 ing alcoholic character. When immersed in varying mixtures of con- 
 centrated nitric and sulphuric acids, and for different lengths of time, 
 di-, tri-, tetra-, penta-, and hexa-nitrate are formed, thus : 
 
 C 12 H 20 10 + 2HNO, - 2H 2 + C u H 18 O 8 (NO,) a . 
 C 12 H 20 10 + 4HN0 8 - 4H 2 + C U H 16 O 6 (NO S ) 4 . 
 C 12 H 20 10 + 6HN0 3 = 6H 2 + C U H M O 4 (N0 8 ) 6 . 
 
 The sulphuric acid used takes no part in the reaction, but facilitates 
 the same by absorbing the water which is eliminated. 
 
 The di-, tri-, and tetrad-nitrate are soluble in a mixture of alcohol 
 and ether, which solution is known as collodion. These lower soluble 
 nitrates, better known as collodion cotton, are official in the U. S. 
 and British Pharmacopoeias as pyroxylin ; -colloxylin is also used as a 
 synonym in this country. In Europe, pyroxylin is applied to the 
 higher (penta- and hexa-) nitrates, which are insoluble in a mixture 
 of alcohol and ether, while colloxylin is applied to the soluble collo- 
 dion cotton. The penta- and hexa-nitrates form the highly explosive 
 gun-cotton. A solution of collodion cotton in molten camphor hard- 
 ens upon cooling and is then known as celluloid. When warmed it 
 becomes plastic and can be molded into various shapes. 
 
 Flexible collodion is a mixture of collodion, castor oil, and Canada 
 balsam, which is much less constringent than official collodion. Can- 
 tharidal (blistering) collodion contains extract of cantharides and has 
 blistering properties. Styptic collodion contains tannin. For medi- 
 cation, any substance, soluble in ether, may be added to collodion, 
 such as iodine, iodoform, salicylic acid, croton oil, extract of Indian 
 cannabis, mercuric chloride, resorcin, pyrogallol, atropine, etc. 
 
 Smokeless gunpowder is gun-cotton, first made gelatinous by 
 acetone, acetic ether, or like substances, then dried and granulated. 
 Smokeless powder occupies less space and burns more slowly than 
 gun-cotton. 
 
 Experiment 65. Immerse 2 grammes of dry cotton for ten hours in a pre- 
 viously cooled mixture of 28 c.c. of nitric acid and 44 c.c. of sulphuric acid. 
 Wash the pyroxylin thus obtained with cold water until the washings have no 
 longer an acid reaction. Dissolve 1 gramme of the dry pyroxylin in a mixture 
 of 25 c.c. of ether and 8 c.c. of alcohol. The solution obtained is collodion. 
 
 Pyroxylin in well-closed bottles exposed to light decomposes with 
 evolution of nitrous vapors and a carbonaceous mass is left. It 
 should be kept dry and in a carton. The compound ether nature of 
 all cellulose nitrates is shown by the fact that the nitric acid is elimi- 
 
CARBOHYDRATES. 539 
 
 nated and cellulose reformed by the action of alkalies, of concentrated 
 sulphuric acid, and by reducing agents. Treated with a solution of 
 a ferrous salt in hydrochloric acid, they decompose just as any 
 nitrate, liberating nitric oxide gas. 
 
 Glycog-en (C 6 H 10 O 5 ) X . Found exclusively in animals ; it occurs in 
 the liver, the white blood-corpuscles, in many embryonic tissues, and 
 in muscular tissue. Pure glycogen is a white, starch-like, amorphous 
 substance, insoluble in alcohol. It forms an opalescent solution with 
 water, gives a red color with iodine, and by hydrolysis is converted 
 into glucose. 
 
 Glucosides. This term is applied to a group of substances (chiefly 
 of vegetable origin) which, by the action of dilute acids or enzymes, 
 are decomposed with the production of a sugar, and one or two other 
 substances not carbohydrates. To this class of bodies belong amyg- 
 dalin, digitalin, indican, myronic acid, salicin, etc. Some of these 
 compounds will be considered later on. 
 
 49. COMPOUNDS CONTAINING NITROGEN. 
 Organic compounds may contain nitrogen in three forms, viz., as 
 nitric (or nitrous) acid, ammonia, cyanogen, or derivatives of these 
 compounds. 
 
 Derivatives of nitric acid. 
 
 Organic compounds containing nitrogen in the nitric acid form do 
 not occur in nature, but are obtained exclusively by artificial means, 
 often by treatment of the organic substance with concentrated nitric 
 acid. Many of these compounds are highly combustible or more or 
 less explosive, as, for instance, cellulose trinitrate, mercuric fulminate, 
 and others. 
 
 QUESTIONS. To which group of substances is the term " carbohydrates " 
 applied ? State the general properties of carbohydrates. Mention the three 
 groups of carbohydrates, and the composition and characteristics of the mem- 
 bers of each group. Mention some fruits in which grape-sugar, and some 
 plants in which cane-sugar is found. What is the difference between grape- 
 sugar and cane-sugar, and by what tests can they be distinguished ? From 
 what source, and by what process, is milk-sugar obtained ? What is starch, 
 what are its properties, by what tests can it be recognized, and what substance 
 is formed when diastase or dilute acids act upon it ? Where is cellulose found 
 in nature, and what are its properties? What compounds may be obtained by 
 the action of nitric acid upon cellulose, and what are they used for? What 
 substances are termed glucosides ? Mention some of the more important glu- 
 cosides. 
 
540 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Nitric or nitrous acid may combine with organic bases, forming 
 salts, such as strychnine nitrate, urea nitrate, etc. ; or with alcohols 
 when esters result, such as glyceryl nitrate, ethyl nitrite, etc. Some 
 of these compounds have been considered before. 
 
 Nitro compounds. These consist of radicals in combination with the 
 nitric acid residue N0 2 ; thus, R.NO 2 . They are isomeric with the esters of 
 nitrous acid, but behave quite differently from these; for instance, they yield 
 no alkali nitrite when treated with alkalies, as is the case when esters are thus 
 treated. The difference in structure is represented thus : 
 
 K O NO, R NO 2 , 
 
 Nitrite. Nitro compound. 
 
 The highly important nitro compounds of the benzene series can be 
 obtained by treating the hydrocarbons directly with nitric acid; thus: 
 
 C 6 H 6 + HON0 2 = C 6 H 5 N0 2 + H 2 O. 
 
 Nitric acid does not react with fatty hydrocarbons, but their nitro deriva- 
 tives can be obtained by indirect processes, for instance, by treating the halo- 
 gen derivatives with silver nitrite: 
 
 CH 3 C1 + AgNO 2 r= CH 3 N0 2 - + AgCl 
 Methyl chloride. Nitro-me thane. 
 
 This reaction is anomalous, since we would expect to obtain a true ester of 
 nitrous acid, corresponding to silver nitrite, whereas the resulting product is 
 not an ester, but a uitro compound. A rearrangement takes place during the 
 reaction of the two substances on each other. Other cases of this kind are 
 known, for example, the formation of organic isocyanides (which see) from 
 silver cyanide. 
 
 Nitroso and isonitroso compounds. While compounds containing the 
 group NO 2 are called nitro compounds, those containing the group NO are 
 termed nitroso derivatives, and those containing = N OH are known as iso- 
 nitroso derivatives. 
 
 When a compound containing the group = CH is treated with nitrous acid 
 a reaction takes place which results in the formation of a nitroso compound, 
 thus : 
 
 E 3 .CH + HNO 2 R 3 .C.NO + H 2 O. 
 
 Nitroso compound. 
 
 Isonitroso compounds are formed by the action of hydroxylamine on alde- 
 hydes or ketones : 
 
 H 2 NOH + >CO = ^>C = N OH + H 2 O. 
 
 Hydroxylamine. Ketone. Isonitroso compound. 
 
 Isonitroso compounds are isomeric with nitroso compounds; the different 
 linkage of carbon and nitrogen in the two classes of compounds is indicated in 
 the two equations given above. 
 
 Both nitro and nitroso compounds, when treated with nascent hydrogen, 
 yield ammonia derivatives, as will be shown later. Isonitroso compounds are 
 
COMPOUNDS CONTAINING NITROGEN. 541 
 
 also termed oximes ; those obtained from aldehydes are designated as aldoxiine* ; 
 those derived from ketones as acetoximes, or ketoximes. 
 
 C=N OH 
 Fulminio acid, C 2 N 2 O 2 H 2 , || , seems to be an isonitroso com- 
 
 C=N OH 
 
 pound. The free acid is extremely unstable, but some of its metallic salts are 
 well known, especially mercuric fulminate, which is used as an explosive in per- 
 cussion caps, etc. It is made by adding alcohol to a solution of mercury in 
 nitric acid. Silver fulminate can be obtained by a similar process. 
 
 Ammonia derivatives. 
 
 Several groups of organic compounds are known, which are formed 
 by replacement of hydrogen in ammonia by different radicals. Ac- 
 cording to the nature of the latter the compounds are known as 
 (tin hies, amides, or amino acids, respectively. There are, however, 
 other compounds, such as the proteins, containing nitrogen in the am- 
 monia form, which do not belong to either one of these three groups. 
 
 Formation of amines and amides. These substances are found 
 as products of animal life (urea), of vegetable life (alkaloids), of 
 destructive distillation (aniline, pyridine), of putrefaction (ptomaines), 
 and may also be produced synthetically for instance, by the action 
 of ammonia upon the chloride or iodide of an alcohol or acid radical: 
 C 2 H 3 .I + NH 3 = HI + NH 2 C 2 H 5 . 
 
 Ethyl iodide. Ammonia. Hydriodic Ethylamine. 
 acid. 
 
 C 2 H 3 O.C1 -f 2NH 3 = NH 4 C1 -f NH 2 .C 2 H S O. 
 
 Acetyl Ammonia. Ammonium Acetamide. 
 
 chloride. chloride. 
 
 By using in the above reaction two or three molecules of ethyl 
 iodide for one molecule of ammonia, diethyl or triethyl amine is 
 formed. 
 
 Amines may also be formed by the action of nascent hydrogen 
 upon the cyanides of the alcohol radicals : 
 
 CH 3 CN + 4H = NH 2 .C 2 H 5 . 
 Methyl cyanide. Ethyl amine. 
 
 They are also formed by the action of nascent hydrogen upon 
 nitro-compounds ; the manufacture of aniline depends on this de- 
 composition : 
 
 C 6 H 5 N0 2 + 6H = 2H 2 + NH 2 C 6 H 5 . 
 Nitro-benzene. Hydrogen. Water. Phenylamine, 
 
 or aniline. 
 
 Occurrence of organic bases in nature. The various organic 
 basic substances found in nature are either amines or amides. But 
 
542 CONSIDERATION OF CARBON COMPOUNDS. 
 
 a small number of organic bases is found in the animal system, 
 urea being the most important one. In plants organic bases are 
 frequently met with, and are grouped together under the name of 
 alkaloids. While the constitution of many alkaloids has not yet 
 been sufficiently explained, we know that many of them are deriv- 
 atives of aromatic compounds, for which reason the consideration of 
 the whole group will be deferred until benzene and its derivatives 
 are spoken of. The large number of basic substances found in putre- 
 fying matter and termed ptomaines will also be considered later on. 
 
 ^xll /G%H / xC 2 H 5 / /C 2 H 5 /C H 3 
 
 \ TT \ rT \ TT \O TT \/^ TT 
 
 U2-tL 5 ^4*19 
 
 Or 
 
 NH 3 , N(C 2 H 5 )FT 2) N(C 2 H 5 ) 2 H, N(C 2 H 5 V NCH 3 .C 2 H 5 C 4 H 9 . 
 
 Ammonia. Ethylamine. Diethylamine. Triethylamine. Methyl-ethyl-butylamine. 
 
 The above formulas show that by replacement of either 1, 2, or 3 
 hydrogen atoms, mono-, di-, or tri-amines are obtained. These are 
 also sometimes designated as primary, secondary, and tertiary amines, 
 respectively. Primary ajnines may also be considered as hydrocar- 
 bons, with one hydrogen atom replaced by the radical NH 2 , which is 
 called the amine- or amino-group, and compounds containing it are 
 designated as amino compounds. Thus, CH 3 NH 2 is amino-methane, 
 or methyl-amine. The radical NH is known as the imine- or imino- 
 group, and as this group occurs in secondary amines, these are also 
 termed imino compounds. 
 
 Amines resemble ammonia in their chemical properties ; they are, 
 like ammonia, basic substances; they combine with acids, directly 
 and without elimination of water, thus : 
 
 NH 3 + HC1 = NH 4 C1; 
 
 N(C 2 H 5 ) 3 + HC1 = N(C 2 H 5 ) 3 HC1. 
 Triethylamine. Triethylamine 
 
 chloride. 
 
 The methyl amines are gases at ordinary temperature; the ethyl amines are 
 liquids. Many of them are inflammable ; they have a strong ammoniacal, 
 fishy odor, are readily soluble in water, have strong basic properties (some of 
 them more so than ammonia), and precipitate metallic salts like ammonia. 
 
 The most important reaction of primary amines is that taking place with 
 nitrous acid, thus : 
 
 CH 3 NH 2 + HONO = CH 3 NH 3 ONO = CH 3 OH + H 2 O + 2N. 
 
 Methyl Nitrous Methyl 
 
 amine. acid. alcohol. 
 
 The reaction shows the possibility of replacing the amino group, NH 2 , by 
 hydroxyl, which in this way may be introduced into various compounds. The 
 
COMPOUNDS CONTAINING NITROGEN. 543 
 
 reaction is analogous to the decomposition of ammonium nitrite by heat, thus : 
 NH 4 ONO == HOH + H 2 + 2N. 
 
 Aromatic amines behave differently toward nitrous acid, as will be shown 
 later. 
 
 Another characteristic reaction which, as in the previous case, distinguishes 
 primary from the other amines, is that with chloroform and alkalies, giving rise 
 to the formation of iso-nitriles, substances having a most disagreeable odor. 
 (See tests for chloroform.) The reaction is this : 
 
 C 2 H 5 NH 2 + CHC1.3 = C 2 H 5 NC + 3HC1. 
 Ethyl amine. Chloroform. Ethyl isonitrile. 
 
 Poly-amines. Whenever two or more ammonia molecules are 
 linked together by hydrocarbon radicals, this is indicated by desig- 
 nating them as diamines, triamines, etc. 
 
 Diethylene diamine (O 2 H 4 ) 2 (NH) 2 , (Piper azine), is a white, crystalline 
 substance, used medicinally on account of its solvent action on uric acid. 
 
 Hexamethylenamine, Hexamethylenamina, (CH 2 ) 6 N 4 = 139.18 
 (Hexamdhylene tetramine, Urotropin). This compound results from 
 the action of ammonia on formaldehyde : 
 
 6CH 2 + 4NH 3 = (CH 2 ) 6 N A -f- 6H 2 O. 
 
 It is due to this reaction that ammonia is used to remove the 
 odor of formaldehyde after its use as a disinfectant. The compound 
 forms colorless, odorless crystals, which are soluble in 1.5 parts of 
 water; this solution has an alkaline reaction on red litmus. On 
 heating it sublimes with partial decomposition. When heated with 
 diluted sulphuric acid, it is decomposed into formaldehyde and 
 ammonia. 
 
 This substance is sold under various trade names, such as cystogen, amino- 
 form, formin, uritone, urotropin. These are all identical with the official 
 hexamethylenamine. 
 
 Some derivatives of hexamethylenamine have been introduced under 
 special names, such as salicylate (saliform), bromethylate (bromalin, bromo- 
 formin), tannate (tannopin or tannon), iodoform (iodoformin). 
 
 Amides are substances derived from ammonia by replacement of 
 hydrogen atoms by acid radicals. Thus : 
 
 Ammonia. Acetamide. Diacetamide. Carbamide or urea. 
 
 Amides also resemble ammonia in their chemical properties ; to a 
 
544 CONSIDERATION OF C A EBON COMPOUNDS. 
 
 less extent, however, than amines, because the acid radicals have a 
 tendency to neutralize the basic properties of ammonia. 
 
 The introduction of an acid radicle into ammonia may be accomplished by 
 one of three generally applicable methods: 
 
 1. By heating the ammonium salt of organic acids, 
 
 CH 3 .COONH 4 = CH 3 .CONH 2 + H 2 O. 
 
 Acetamicle. 
 
 2. By the action of ammonia on ethereal salts, 
 
 CH 3 ,COOC 2 H 5 -f NH 3 CII 3 .CONH 2 + G 2 H 5 OH. 
 
 Ethyl acetate. 
 
 3. By the action of ammonia on acid chlorides. This reaction is most fre- 
 quently used : 
 
 CH 3 .COC1 + NH 3 = CH 3 .CONH 2 + HC1. . 
 Acetyl chloride. 
 
 Formamide, H.CONH 2 , is a colorless liquid, obtained by heating ethyl for- 
 mate with an alcoholic solution of ammonia. This compound is of interest 
 because it combines with chloral, forming Chloralformamide, Chloralformami- 
 dum (CMoralami.de}, H.CONH 2 .CC1 3 CHO, a substance used as a hypnotic. It 
 is a colorless, odorless, crystalline substance, having a faintly bitter taste. It 
 is soluble in about 20 parts of cold water and in 1.5 parts of alcohol. By heat- 
 ing the aqueous solution to 60 C. (140 F.) it is decomposed into chloral and 
 formamide. 
 
 Amino-acids are acids in which hydrogen has been replaced by 
 the amino-group, NH 2 . Consequently, amino-acids bear the same 
 relation to acids that amines bear to hydrocarbons. Amino-acids 
 have both acid and basic properties i. e., they unite with bases to 
 form salts by replacement of the carboxyl hydrogen ; and they com- 
 bine with acids to form weak salts ; they also combine with other salts 
 to form double salts. 
 
 Amino-acids may be obtained by the action of ammonia on a halo- 
 gen derivative of an acid : 
 
 CH 2 C1.CO 2 H -f 2NH 3 = CH 2 .NH 2 .CO 2 H -f NH 4 C1. 
 Monochloracetic acid. Ammo-acetic acid. 
 
 Amino -acetic acid, obtained as above, is also known as glycocoll 
 or glycine. It is a product of the decomposition of either glycocholic 
 or hippuric acid by hydrochloric acid. By oxidation amino-acetic 
 acid splits up thus : 
 
 CH 2 NH 2 C0 2 H -f 30 : 2CO 2 -f NH 3 + H 2 O. 
 Amino-acids occur in the animal system, and by oxidation suffer 
 
COMPOUNDS CONTAINING NITROGEN. 545 
 
 the change indicated above. Ammonia and carbon dioxide unite to 
 form ammonium carbamate: 
 
 2NH 3 + C0 2 = NH 4 .NH 2 .CO 2 . 
 By removal f water this salt is converted into urea : 
 NH 4 .NH 2 .CO a = (NH 2 ) 2 CO + H a O. 
 
 Amino-formic acid or carbamic acid, NH 2 .COOH, is the acid 
 which, in the form of the ammonium salt, is a constituent of the com- 
 mercial ammonium carbonate. It is formed by the direct action of 
 carbon dioxide upon ammonia, as shown above. 
 
 Urethanes are ethereal salts of carbamic acid, a class of comr 
 pounds having hypnotic properties. The class name is derived from 
 one member, which is official and generally known as " Urethane." 
 It is ethyl urethane, or 
 
 Ethyl carbamate, ^Jthylis carbamas, CO.OC 2 H 5 .NH 2 = 88.42. 
 Obtained by the action of alcohol on urea or on one of its salts : 
 
 It is a white crystalline powder, readily soluble in water, alcohol, or ether. 
 Heated with solution of potassium hydroxide, ammonia is liberated, while the 
 addition of sodium carbonate and iodine causes, on warming, the precipitation 
 of iodoform. 
 
 Several similar compounds have been introduced under specific names, 
 thus: Euphorin, or phenyl-urethane, C 6 H 5 NH.COOC 2 H 5 , a crystalline powder, 
 sparingly soluble in cold water; neurodin, or acetyloxyphenyl-urethane, 
 
 pr > colorless, sparingly soluble crystals ; thermodm, or phe- 
 
 nacetin-urethane, C 6 H 4 C^ * <COOC 2 H ' colorless > verv sparingly sol- 
 
 O FT 
 
 uble needles ; hedonal, ormethylpropylcarbinol-urethane, NH 2 .COOCH<Q jj 
 
 a difficultly soluble white powder. 
 
 The amino-acids and acid-amides are of considerable interest because many 
 products of animal and plant life belong to these classes of compounds. Some 
 of these are considered in the subsequent chapters on Physiological Chemistry, 
 but may be briefly mentioned here. 
 
 Sarcosine, Methyl-glycocoll, CI^NH.CI^CC^H, a product of the 
 decomposition of creatine, which is found in flesh, and of caffeine, and may be 
 obtained by boiling these compounds with a solution of barium hydroxide. It 
 is much like glycocoll in properties. 
 
 Cystine, (SC(CH 3 )NH 2 CO 2 H.) 2 , a derivative of a-araino-propionic acid, 
 sometimes found in the sediment of urine (see Index). 
 35 
 
546 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Leucine, a-amino-caproic acid, CH 3 .(CH 2 ) 3 .OH(NH 2 ).CO 2 H, is widely 
 distributed in small quantity in glands of animals and in the sprouts of plants. 
 It is one of the products of the decomposition of albumins and gelatin (see 
 Index). 
 
 Taurine, Amino-ethyl-sulprionic acid, NH 2 .CH 2 .CH 2 .SO 3 H, is com- 
 bined with cholic acid to form taurocholic acid, which is one of the constitu- 
 ents of bile. It forms very stable monoclinic prisms (see Index). 
 
 Aspartic acid, Amino-succinic acid, C 2 H 3 (NH 2 ).(CO 2 H) 2 , occurs in 
 pumpkin seeds, and is often formed when natural compounds are boiled with 
 dilute acids. In this manner it may be obtained from casein and albumin. It 
 forms prisms difficultly soluble in water. When treated with nitrous acid, it 
 yields malic acid. 
 
 CH 2 .CONH 2 
 
 Asparagine, Amino-succinamic acid, | occurs in 
 
 CH(NH 2 ).CO 2 H, 
 
 asparagus, liquorice, vetches, beans, beets, peas, and in wheat. It forms large 
 crystals, difficultly soluble in cold water. Boiling with acids or alkalies con- 
 verts it into aspartic acid and ammonia. 
 
 Guanidine, (NH)C(NH 2 ) 2 , is obtained by the oxidation of guanine which 
 occurs in guano. Guanine, C 5 H 3 (NH 2 )N 4 O, is the amirio derivative of xan- 
 thine (see Index), which is closely related to uric acid, and which is found in 
 all the tissues of the body and in the urine. Guanidine is an imide of urea, 
 OC(NH 2 ) 2 , is strongly alkaline, and when boiled with dilute sulphuric acid or 
 barium hydroxide solution yields urea and ammonia. 
 
 Creatine, Methyl-guanidine-acetic acid, (HN)C< NG |j Q-^ Q O ,H 
 
 is found in the muscles of all vertebrates, and is closely related to guanidine 
 and to sarcosine. It forms colorless, transparent prisms, soluble in 75 parts 
 of cold water. When evaporated in dilute acid solution, it loses water to 
 form the anhydride, 
 
 NH-CO 
 
 Creatinine, (HN)C\ which forms prisms, readily soluble in 
 
 \NCH 3 -CH 2 , 
 
 water. It is a strong base. It is a constant constituent of urine. Creatine and 
 creatinine are discussed at greater length further on (see Index). 
 
 Urea, Carbamide, CO(NH 2 ) 2 , is the amide of carbonic acid. It occurs 
 in the urine and blood of all mammals, particularly of carnivorous animals. 
 It has been made by various synthetic methods, but is most easily obtained 
 from urine (see Index). It crystallizes in rhombic prisms, melting at 132 C., 
 easily soluble in water and alcohol. When boiled with dilute acids or alka- 
 lies, it yields carbon dioxide and ammonia, thus : 
 
 CO(NH 2 ) 2 + H 2 : C0 2 + 2NH S . 
 
 Urea unites with acids, thus : urea hydrochloride, CO(NH 2 ) 2 .HC1 ; urea ni- 
 trate, CO(NH 2 ) 2 .HNO 3 , which is difficultly soluble in nitric acid; urea phos- 
 
COMPOUNDS CONTAINING NITROGEN. 547 
 
 phate, CO(NH,) 2 .H 3 PO 4 . It also unites with metallic oxides, thus : CO(NH 3 ) a .- 
 HgO, and also with salts, of which HgCl 2 .CO(NH 2 ) 2 and HgO.CO(NH 2 ) 2 .HNO, 
 are examples. 
 
 Ureids. Urea contains ammonia residues and, therefore, acts in many 
 respects like ammonia. Thus, one or more hydrogen atoms of the NH 3 groups 
 can be replaced by acid radicals, forming compounds analogous to the acid 
 amides. These are known as ureids. The following ureids are of interest. 
 
 CO NH, 
 
 Oxalyl urea, Parabanic acid, | \CO, is formed when uric 
 
 CO NH X 
 
 acid is boiled with concentrated nitric acid, and also when a mixture of urea 
 and oxalic acid is treated with phosphorus oxychloride,POC! 3 , which abstracts 
 the elements of water. It acts as an acid, since the hydrogen of the NH group 
 can be replaced by metals. 
 
 Malonyl urea, Barbituric acid, CH 2 <JQ~*J|*>CO, like the previous 
 
 compound, can also be obtained from uric acid, and synthetically by treating 
 a mixture of urea and malonic acid with phosphorus oxychloride. It breaks 
 up into urea and malonic acid when treated with an alkali. Closely related 
 to it is 
 
 Veronal, Diethyl-malonyl urea, c 2 H 5>C< CO NH >CO ' which oc ~ 
 curs as a white, faintly bitter, crystalline powder, melting at 191 C., and sub- 
 lirnable without residue. It is soluble in about 145 parts of water at 20 C., in 
 about 12 parts of boiling water, and readily in warm alcohol. Veronal is one 
 of the most valuable hypnotics, being prompt and relatively innocuous in small 
 doses (8 grains), and dangerous only in large doses. 
 
 Uric acid, C 5 H 4 N 4 O 3 , xanthine, C 5 H 4 N 4 O 2 , theobromine (dimethyl-xanthine), 
 C 5 H 3 (CH 3 ) 2 N 4 O 2 , and caffeine (theine, trimethyl-xanthine), C 5 H(CH 3 ) 3 N 4 O 2 + 
 H 2 O, are all interesting and important compounds, but rather complex, for a 
 discussion of which see Index. 
 
 Cyanogen compounds. 
 
 Cyanogen itself does not occur in nature, but compounds contain- 
 ing it are found in a few plants (amygdalin), and also in some animal 
 fluids (saliva contains sodium sulphocyanate). Gases issuing from 
 volcanoes (or from iron furnaces) sometimes contain cyanogen com- 
 pounds. Their formation from inorganic matter can be shown by the 
 action of ammonia on red-hot charcoal, when ammonium cyanide and 
 methane are generated : 
 
 4NJEL, -f 3C = 2(NH 4 CN) -j- CH 4 . 
 
 The univalent radical cyanogen, C = N, or CN, was the first 
 compound radical distinctly proved to exist by Gay-Lussac in 1814. 
 
548 CONSIDERATION OF CARSON COMPOUNDS. 
 
 The name cyanogen signifies " generating blue/' in allusion to the 
 various blue colors (Prussian and TurnbulPs blue) containing it. 
 
 Cyanogen and its compounds show much resemblance to the halo- 
 gens and their compounds, as indicated by the composition of the 
 following substances : 
 
 C1C1, 
 Chlorine, 
 
 na, 
 
 Hydrochloric 
 acid. 
 
 KI, 
 
 Potassium 
 iodide. 
 
 HC10, 
 
 Hypochlorous 
 acid. 
 
 CNCN, 
 
 Cyanogen. 
 
 HBr, 
 
 Hydrobromic 
 acid. 
 
 KCN, 
 
 Potassium 
 cyanide. 
 
 HCNO, 
 
 Cyanic acid. 
 
 CNC1, 
 
 Cyanogen 
 chloride. 
 
 HCN, 
 
 Hydrocyanic 
 acid. 
 
 AgCN, 
 
 Silver 
 cyanide. 
 
 HCNS, 
 
 Sulphocyanic 
 acid. 
 
 Dicyanogen, (CN) 2 . The unsaturated radical CN does not exist 
 as such in a free state, but combines whenever liberated with another 
 CN, forming dicyanogen. It may be obtained by heating mercuric 
 
 cyanide : 
 
 Hg(CN) 2 = Hg + 2CN. 
 
 It is a colorless gas, having an odor of bitter almonds, and burn- 
 ing with a purple flame, forming carbon dioxide and nitrogen; it is 
 soluble in water, and may be converted into a colorless liquid by 
 pressure ; it acts as a poison, both to animal and vegetable life, even 
 when present in but small proportions in the air. 
 
 Hydrocyanic acid, HCN = 26.84 (Prussic acid). This compound 
 is found in the water distilled from the disintegrated seeds or leaves 
 of amygdalus, prunus, laurus, etc. It is also found among the prod- 
 ucts of the destructive distillation of coal, and is formed by a great 
 number of chemical decompositions. For instance : 
 
 By the action of ammonia on chloroform : 
 
 CHC1 3 + NH 3 : HCN + 3HC1. 
 Chloroform. Hydrocyanic Hydrochloric 
 
 acid. acid. 
 
 By heating ammonium formate to 200 C. (392 F.) : 
 
 NH 4 CH0 2 : HCN + 2H 2 0. 
 Ammonium Hydrocyanic Water, 
 formate. acid. 
 
 By the action of hydrogen sulphide upon mercuric cyanide : 
 
 Hg(CN), + H 2 S = : HgS + 2HCN. 
 
COMPOUNDS CONTAINING NITROGEN. 549 
 
 By the decomposition of alkali cyanides by diluted acids : 
 
 KCN 4- HC1 = KC1 + HCN. 
 By the action of hydrochloric acid upon silver cyanide : 
 
 AgCN + HC1 = AgCl -f HCN. 
 By distilling potassium ferrocyanide with diluted sulphuric acid : 
 
 2K 4 Fe(CN) 6 + 6(H 2 SO 4 ) K 2 Fe 2 (CN) 6 + 6KHSO 4 + 6HCN. 
 
 Potassium Sulphuric Potassium ferrous Potassium acid Hydrocyanic 
 
 ferrocyanide. acid. ferrocyanide. sulphate. acid. 
 
 Experiment 66. Place 20 grammes of potassium ferrocyanide and 40 c.c. of 
 water into a boiling-flask of about 200 c.c. capacity ; provide the flask with a 
 funnel-tube and connect it with a suitable condenser, the exit of which should 
 dip into 60 c.c. of diluted alcohol, contained in a receiver, which latter should 
 be kept cold by ice during the operation. After having ascertained that all 
 the joints are tight, add through the funnel-tube a previously prepared mixture 
 of 15 grammes of sulphuric acid and 20 c.c. of water. Apply heat and slowly 
 distil until there is little liquid left with the salts remaining in the flask. 
 
 Determine the strength of the alcoholic solution of hydrocyanic acid thus 
 prepared volumetrically and dilute it with water until it contains exactly two 
 per cent, of HCN. 
 
 Pure hydrocyanic acid is, at a temperature below 26 C. (78.8 F.), 
 a colorless, mobile liquid, of a penetrating, characteristic odor resem- 
 bling that of bitter almonds ; it boils at 26.5 C. (80 F.) and crystal- 
 lizes at 15 C. (5 F.). It is readily soluble in water, and a 2 per 
 cent, solution is the diluted hydrocyanic acid, Acidum hydrocyanicum 
 dilutam. 
 
 According to the U. S. P., this diluted acid is made by the decom- 
 position of 6 grammes of silver cyanide by 15.54 c.c. of diluted hy- 
 drochloric acid, mixed with 44.10 c.c. of water, allowing the silver 
 chloride to subside and pouring off the clear liquid. 
 
 The diluted acid has the characteristic odor of bitter almonds, a 
 slightly acid reaction, and is completely volatilized by heating. Pure 
 absolute hydrocyanic acid may be kept unchanged, but when water 
 or ammonia is present, the acid decomposes comparatively rapidly, 
 giving ammonia, formic acid, oxalic acid, and other products. The 
 official 2 per cent, acid deteriorates appreciably within several weeks, 
 and, therefore, should not be kept in stock for a long time, but should 
 be prepared as it is needed. 
 
 The salts of hydrocyanic acid are called cyanides, and are nearly 
 all insoluble in water. The cyanides of the alkali metals, the alka- 
 line-earth metals, and of mercury are soluble. 
 
 Dissociation of cyanogen compounds. Hydrocyanic acid is an extremely 
 weak acid, and its aqueous solution conducts electricity very badly, that is, it 
 
550 CONSIDERATION OF CARBON COMPOUNDS. 
 
 has a very low conductivity, due to its extremely small degree of dissociation. 
 In a tenth-normal solution at 18 C., only 0.01 per cent, of the acid molecules 
 are dissociated, thus : 
 
 HCN ^ H- f CN'. 
 
 As in the case of the mercury salts, the poisonous character of hydrocyanic 
 acid and its salts depends upon the degree of dissociation into CN X ions. A 
 number of complex cyanides are known, in which the cyanogen groups are 
 combined with metals to form complex radicals, in which both the cyanogen 
 and the metals are masked, and do not respond to the usual analytical reagents. 
 The best examples of such compounds are the ferrocyanide and ferricyanide of 
 potassium, K 4 FeCN 6 and K 3 Fe(CN) 6 , respectively. These compounds are not 
 poisonous because they do not form CN X ions, being dissociated in solution 
 according to the following equations : 
 
 K 4 Fe(CN) 6 ^ 4K- + Fe(CN) 6 "" 
 
 Ferrocyanogen ion. 
 
 K 3 Fe(CN) 6 ^ 3K- + Fe(CN) 6 '" 
 
 Ferricyanogen ion. 
 
 The alkali cyanides are decomposed by such a weak acid as carbonic acid, 
 hence they have the odor of hydrocyanic acid, due to the action of the carbonic 
 acid of the atmosphere. In aqueous solution they have a strong alkaline re- 
 action, due to hydrolysis : 
 
 KCN ; K- + CN'\ _ TT PV 
 HOH ^ (OH)/ + H- / ' 
 
 The action is due to the extremely weak dissociating power of hydrocyanic 
 acid (see Chapter 15). 
 
 For peculiarities of mercury cyanide see chapter on Mercury. 
 
 Potassium cyanide, Potassii cyanidum, KCN 64.7. The pure 
 salt may be obtained by passing hydrocyanic acid into an alcoholic 
 solution of potassium hydroxide. The commercial article, however, 
 Is a mixture of potassium cyanide with potassium cyanate. It is 
 obtained by fusing potassium ferrocyanide with potassium carbonate 
 in a crucible, when potassium cyanide and cyanate are formed, while 
 carbon dioxide escapes, and metallic iron is set free and collects on 
 the bottom of the crucible. The decomposition is as follows : 
 
 K 4 Fe(CN) 6 -f K 2 CO 3 = 5KCN + KCNO + Fe + CO 2 . 
 Potassium Potassium Potassium Potassium Iron. Carbon 
 
 ferrocyanide. carbonate. cyanide. cyanate. dioxide. 
 
 A mixture of pure potassium and sodium cyanides, free from cyanate, 
 is now manufactured on a large scale by heating together anhydrous 
 potassium ferrocyanide and metallic sodium : 
 
 K 4 Fe(CN) 6 -f 2Na = 2NaCN + 4KCN + Fe. 
 
 Potassium cyanide, U. S. P., should contain at least 95 per cent, of 
 potassium cyanide ; it is a white^ deliquescent substance, odorless when 
 
COMPOUNDS CONTAINING NITROGEN. 551 
 
 perfectly dry, but emitting the odor of hydrocyanic acid when moist ; 
 it is soluble in about 2 parts of water ; this solution has an alkaline 
 reaction but is unstable, decomposition soon taking place with the 
 formation of potassium formate and ammonia, along with other 
 
 products : 
 
 KCN + 2H 2 O = CHK0 2 + NH 3 . 
 
 A solution of potassium cyanate decomposes slowly in the cold, 
 but rapidly on heating, with the formation of potassium and ammo- 
 nium carbonates : 
 
 2KCNO + 4H 2 O = K 2 CO 3 + (NH 4 ) 2 CO 8 . 
 
 Potassium cyanides and other alkali cyanides show a tendency to 
 combine with the cyanides of heavy metals, forming a number of 
 double cyanides, such as the cyanide of sodium and silver, NaCN. 
 AgCN, etc., which are soluble in water. Hence, precipitates formed by 
 addition of alkali cyanides to solutions of metallic salts, are dissolved 
 in excess of the reagent. Double cyanides of silver and gold are used 
 in commercial electroplating. A large proportion of the alkali cyanides 
 manufactured is used in extracting gold from its ores, especially in 
 Transvaal. In 1889 not more than 50 tons of cyanide per annum 
 were consumed, while in 1905 the consumption was about 10,000 tons, 
 one-third of which was used in Transvaal. 
 
 Silver cyanide, Argenti cyanidum, AgCN = 132.96. A white 
 powder, obtained by precipitating a solution of potassium cyanide 
 with silver nitrate. It is insoluble in water, slowly soluble in ammonia 
 water, sodium thiosulphate, and potassium cyanide when heated it 
 evolves cyanogen, metallic silver being left. 
 
 Mercuric cyanide, Hg(CN) 2 . A white crystalline salt, obtained by 
 dissolving mercurous oxide in hydrocyanic acid ; it is soluble in water 
 and alcohol and evolves cyanogen when heated. 
 
 Mercuric oxycyanide, Hg(ON) 2 .HgO. (Basic mercuric cyanide.) This is 
 obtained by triturating mercuric oxide, dilute sodium hydroxide solution, and 
 mercuric cyanide until the mixture becomes colorless. The salt is purified by 
 washing with cold water, or recrystallizing from hot water. It occurs as a 
 white, crystalline powder, soluble in 17 parts of water, and turns red litmus 
 blue. It is recommended as a substitute for mercuric chloride, as it is claimed 
 to have greater antiseptic power, to be less irritating, and to have no corroding 
 action on steel instruments. 
 
 Analytical reactions for hydrocyanic acid. 
 
 (Potassium cyanide, KCN, may be used.) 
 
 1. Hydrocyanic acid, or soluble cyanides, give with silver nitrate 
 a white precipitate of silver cyanide, which is sparingly soluble in 
 
552 CONSIDERATION OF CARBON COMPOUNDS. 
 
 ammonia, soluble in alkali cyanides or thiosulphates, but insoluble 
 in diluted nitric acid. 
 
 HCN + AgNO 3 = AgCN -f HNO 3 . 
 
 2. Hydrocyanic acid, mixed with yellow ammonium sulphide and 
 evaporated to dry ness, forms sulphocyanic acid, which, upon being 
 slightly acidulated with hydrochloric*acid, gives with ferric chloride 
 a blood-red color of ferric sulphocyanate. (Excess of ammonium 
 sulphide must be avoided.) 
 
 3. Hydrocyanic acid, or soluble cyanides, give, when mixed with 
 ferrous and ferric salts and potassium hydroxide, a greenish precipi- 
 tate, which, upon being dissolved in hydrochloric acid, forms a pre- 
 cipitate of Prussian blue, Fe 4 (FeC 6 ]S" 6 ) 3 . This reaction depends on 
 the formation of potassium ferrocyanide by the action of the cyanogen 
 upon both the potassium of the potassium hydroxide and the iron of 
 the ferrous salt. In alkaline solutions, the blue precipitate does not 
 form, for which reason hydrochloric acid is added. 
 
 4. Hydrocyanic acid heated with dilute solution of picric acid gives 
 a deep-red color on cooling. 
 
 In cases of poisoning, the matter under examination is distilled (if neces- 
 sary after the addition of water) from a retort connected with a cooler. To 
 the distilled liquid the above tests are applied. If the substance under ex- 
 amination should have an alkaline or neutral reaction, the addition of some 
 sulphuric acid may be necessary in order to liberate the hydrocyanic acid. 
 The objectionable feature to this acidifying is the fact that non-poisonous 
 potassium ferrocyanide might be present, which upon the addition of sulphuric 
 acid would liberate hydrocyanic acid. In cases where the addition of an acid 
 becomes necessary, a preliminary examination should, therefore, decide 
 whether or not ferro- or ferricyanides are present. 
 
 Antidotes. Hydrocyanic acid is a powerful poison both when inhaled or 
 swallowed in the form of the acid or of soluble cyanides. As an antidote is 
 recommended a mixture of ferrous sulphate and ferric chloride with either 
 sodium carbonate or magnesia. The action of this mixture is explained ia 
 the above reaction 3, the object being to convert the soluble cyanide into an 
 insoluble ferrocyanide of iron. In most cases of poisoning by hydrocyanic 
 acid there is, however, no time for the action of such an antidote, in conse- 
 quence of the rapidity of the action of the poison, and the treatment is chiefly 
 directed to the maintenance of respiration by artificial means. 
 
 About ten years ago, hydrogen dioxide was proposed as an antidote, by 
 which hydrocyanic acid is converted into the harmless oxamide, CONH 2 
 CONH 2 . A solution of hydrogen dioxide is introduced into the stomach and 
 then siphoned out. It is also used subcutaneously. In case a cyanide is the 
 poison, vinegar may be mixed with the hydrogen dioxide solution given inter- 
 nally in order to liberate the hydrocyanic acid. 
 
 Cyanogen derivatives obtained directly from nitrogen of the atmos- 
 
COMPOUNDS CONTAINING NITROGEN. 553 
 
 phere. When calcium carbide is heated 'to redness in contact with nitrogen, 
 calcium cyanamide is formed, thus : 
 
 CaC 2 + 2N = CN.NCa + C. 
 
 This substance is an excellent fertilizer, and is manufactured in large quanti- 
 ties and sold under the name of nitrolim or lime-nitrogen (Kalkstickstoff). It 
 is slowly decomposed in the soil by moisture and carbon dioxide into calcium 
 carbonate and cyanamide : 
 
 CN.NCa 4- H 2 -f CO 2 = CaCO 3 + CN.NH 2 . 
 The cyanide is further decomposed probably into urea : 
 CN.NH 2 -f H 2 = CO(NH 2 ) 2 . 
 
 Steam under high pressure converts all of the nitrogen of calcium cyanamide 
 into ammonia, which thus furnishes a method of obtaining ammonia from at- 
 mospheric nitrogen. 
 
 When mixed with sodium carbonate and fused, calcium cyanamide forms 
 sodium cyanide. By the action of acids on the calcium compound, cyanamide, 
 CN.NH 2 , is formed, which easily polymerizes to the beautifully crystallized 
 dicyandiamide, C 2 N 2 .N 2 H 4 , which is now made by the ton and used for various 
 purposes. It can very easily be made to unite with water to form urea, which 
 is manufactured thus in great quantities. 
 
 Barium carbide, when heated in nitrogen, acts differently from calcium car- 
 bide, forming barium cyanide, thus: 
 
 BaC 2 + 2N = Ba(CN) 2 . 
 
 Cyanic acid, HCNO, and Sulphocyanic acid, HCNS, are both 
 colorless acid liquids, the salts of which are known as cyanates and 
 mlpho-cyanates. These salts are obtained from alkali cyanides by 
 treating them with oxidizing agents or by boiling their solutions with 
 sulphur, when either oxygen or sulphur is taken up by the alkali 
 cyanide : 
 
 KCN + O = KCNO = Potassium cyanate. 
 
 KCN -f S = KCNS = Potassium sulphocyanate. 
 The acids themselves are obtained by indirect processes, as they 
 decompose when the salts are treated with mineral acids. Sulpho- 
 cyanates give with ferric salts a deep-red color, which is not affected 
 by hydrochloric acid, but disappears on the addition of mercuric 
 chloride. 
 
 Metallocyanides. Cyanogen not only combines with metals to 
 form true cyanides, which may be looked upon as derivatives of 
 hydrocyanic acid, but cyanogen also enters into combination with 
 certain metals (chiefly iron), forming a number of complex radicals, 
 Which upon combining with hydrogen form acids, or with basic 
 elements form salts. It is a characteristic feature of the compound 
 cyanogen radicals, thus formed, that the analytical characters of the 
 
554 CONSIDERATION OF CARBON COMPOUNDS. 
 
 metals (iron, etc.) entering into the radical are completely hidden. 
 Thus, the iron in ferro- or ferricyanides is not precipitated by either 
 alkalies, soluble carbonates, ammonium sulphide, or any of the com- 
 mon reagents for iron, and its presence can only be demonstrated by 
 these reagents after the organic nature of the compound has been 
 destroyed by burning it (or otherwise), when ferric oxide is left, 
 which may be dissolved in hydrochloric acid and tested for in the 
 usual manner. 
 
 The principal iron-cynogen radicals are ferrocyanogen [Fe u 
 (CN),, 1 ]*, and ferricyanogen [Fe^CNy] 111 . These two radicals con- 
 tain iron in the ferrous and ferric state respectively, and form, upon 
 combining with hydrogen, acids which are known as hydroferroeyanic 
 acid, H 4 Fe(CN) 6 (tetrabasic), and hydroferricyanic acid, H 3 Fe(CN) g 
 (tribasic) ; the salts of these acids are termed ferrocyanides and ferri- 
 cyanides. (For dissociation of these, see p. 549.) 
 
 Potassium ferrocyanide, Potassii ferrocyanidum, K 4 Fe(CN) 6 . 
 3H 2 O = 419.62 ( Yellow prussiate of potash). This salt is manu- 
 factured on a large scale by heating refuse animal matter (waste 
 leather, horns, hoofs, etc.) with potassium carbonate and iron (filings, 
 etc.). The fused mass is boiled with water, and from the solution 
 thus formed the crystals separate on cooling. 
 
 The nitrogen and carbon of the organic matter (heated as above 
 stated) combine, forming cyanogen, which enters into combination 
 first with potassium and afterward with iron. 
 
 Potassium ferrocyanide forms large, translucent, pale lemon-yellow, 
 soft, odorless, non-poisonous, neutral crystals, easily dissolving in 
 water, but insoluble in alcohol. 
 
 Analytical reactions : 
 
 1. Ferrocyanides heated on platinum foil burn and leave a residue 
 of (or containing) ferric oxide. 
 
 2. Ferrocyanides heated with concentrated sulphuric acid evolve 
 carbonic oxide ; with dilute sulphuric acid liberate hydrocyanic acid ; 
 with concentrated hydrochloric acid liberate hydroferroeyanic acid. 
 
 3. Soluble ferrocyanides give a blue precipitate with ferric salts 
 (Plate L, 5) : 
 
 3K 4 Fe(CN) 6 + 4FeCl 3 = 12KC1 + Fe 4 (FeC 6 N 8 ) 3 . 
 
 Potassium Ferric Potassium Ferric ferro- 
 
 ferrocyanide. chloride. chloride. cyanide. 
 
 The blue precipitate of ferric ferrocyanide, or Prussian blue, is 
 insoluble in water and diluted acids, soluble in oxalic acid (blue 
 
COMPOUNDS CONTAINING NITROGEN. 55 
 
 ink), and is decomposed by alkalies with separation of brown ferric 
 hydroxide and formation of potassium ferrocyanide. The addition 
 of an acid restores the blue precipitate. 
 
 4. Soluble ferrocyanides give with cupric solutions a brownish-red 
 precipitate of cupric ferrocyanide. (Plate III., 5.) 
 
 5. Soluble ferrocyanides produce, with solutions of silver, lead, and 
 zinc, white precipitates of the respective ferrocyanides. 
 
 6. Ferrocyanides give with ferrous salts a white precipitate of 
 ferrous ferrocyanide, soon turning blue by absorption of oxygen. 
 (Plate I., 4.) 
 
 Potassium ferricyanide, K 3 Pe(CN) G (Red prussiate of potash). Ob- 
 tained by passing chlorine through solution of potassium ferrocyanide: 
 
 K 4 Fe(CN) 6 -f Cl = KC1 + K 3 Fe(CN) 6 . 
 
 Potassium Chlorine. Potassium Potassium 
 
 ferrocyanide. chloride. ferricyanide. 
 
 While apparently this decomposition consists merely in a removal 
 of one atom of potassium from one molecule of potassium ferro- 
 cyanide, the change is actually more complete, as the atoms arrange 
 themselves differently, the iron passing also from the ferrous to the 
 ferric state. 
 
 Potassium ferricyanide crystallizes in red prisms, soluble in water. 
 It forms, with ferrous solutions, a blue precipitate of ferrous ferricy- 
 anide, or TurnbuWs blue : 
 
 2K 3 Fe(CN) 6 + 3FeSO 4 = 3K 2 SO 4 + Fe 3 Fe 2 (CN) 12 . 
 
 With ferric solutions no precipitate is produced by potassium ferri- 
 cyanide, but the color is changed to a deep brown. 
 
 Sodium nitroferricyanide, Na 2 Fe(CN) 5 N0.2H 2 O. (Sodium nitroprusside.) 
 This is a salt of nitroferricyanic acid, which is obtained by the action of nitric 
 acid on potassium ferrocyanide. Potassium nitrate is crystallized out by con- 
 centrating and cooling the solution, which is then neutralized by sodium car- 
 bonate, and the sodium salt crystallized. Addition of alcohol increases the 
 separation of potassium nitrate. The salt forms large ruby-red crystals, solu- 
 ble in 2.5 parts of water and in alcohol. The aqueous solution decomposes on 
 standing. It serves as a delicate test for soluble sulphides (but not free H 2 S), 
 giving a purple color which quickly passes into violet. It is also used as a test 
 for acetone (Legal's test). 
 
 Cyanides and isocyanides of organic radicals. Only one form of hydro- 
 cyanic acid and of metallic cyanides is known, but among organic cyanide* 
 two isomeric forms exist, known respectively as cyanides or nitrites, and isocyan- 
 ides or carbylamines. Experiments show that the constitution of these com- 
 pounds is represented by the formulas : 
 
 R-C=N, 
 
 Cyanide. Isocyanide. 
 
556 CONSIDERATION OF CARBON COMPOUNDS. 
 
 In one case the organic radical is in combination with carbon ; in the other, 
 with nitrogen. These compounds are apparently esters of hydrocyanic acid, 
 but they behave quite differently from esters, as they do not yield alcohols or 
 metallic cyanides on treatment with alkalies. 
 
 Cyanides or nitriles. These may be formed by heating together iodides 
 of hydrocarbon radicals with potassium cyanide : 
 
 CH 8 I + KCN = CH 3 CN + KI. 
 
 The cyanides are volatile liquids or solids. When heated with water in 
 presence of mineral acids or alkalies, they yield organic acids, thus : 
 
 CH 3 .CN + 2H 2 = CH 3 .C0 2 H 4- NH 3 . 
 Methyl Acetic acid, 
 
 cyanide. 
 
 This is an important reaction, as it furnishes a simple means of introducing 
 carboxyl into compounds, thus forming organic acids. For this reason the 
 cyanides are called nitriles of the acids, just as the acid oxides are called an- 
 hydrides of the corresponding acids. Thus, methyl cyanide is called aceto- 
 nitrile, because it yields acetic acid. In fact, the ammonium salts of organic 
 acids, by abstraction of water, yield cyanides : 
 
 CH S .CO 2 NH 4 = CH 8 .CN + 2H 2 O. 
 
 Isocyanides or carbylamines. These compounds are distinguished by a 
 disgusting odor. They are formed by heating silver cyanide, instead of potas- 
 sium cyanide, with iodides of hydrocarbon radicals, thus : 
 
 CH 3 I + AgCN = CH 3 NC + Agl. 
 
 It is strange, and as yet not explained, why hydrocarbon iodides produce 
 cyanides with potassium cyanide, and isocyanides with silver cyanide. 
 
 Isocyanides are also formed by heating together chloroform, primary amines, 
 and an alkali, as shown above in the paragraph on amines. 
 
 The isocyanides behave differently from the cyanides when heated with 
 water and acids, thus : 
 
 CH 3 NC + 2H 2 O = CH 3 NH 2 + HCO 2 H. 
 
 Methyl Methyl Formic 
 
 isocyanide. amine. acid. 
 
 Isosulphocyanates or mustard oils. The difference in structure between 
 sulpho- and iso-sulphocyanates is expressed in the following formulas : 
 
 R S C^N, sulphocyanate. E N=C S, isosulphocyanate. 
 
 The organic sulphocyanides are of no importance here. The principal member 
 of the mustard oils is allyl-isosulphocyanate, C 3 H 5 NCS, one of the decomposi- 
 tion products of myronic acid. 
 
 Treated with water and alkali, mustard oils break down, thus : 
 
 C^NCS + 2H 2 = C 3 H 5 NH 2 + H 2 S + CO 2 . 
 
 This reaction is similar to that which takes place in case of isocyanides. (See 
 above.) 
 
 Myronic acid, C 10 H 19 NS. 2 10 , is found as the potassium salt, which is known 
 as sinigrin, in black mustard seed. When treated with solution of myrosin, a 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 557 
 
 substance also contained in mustard seed and acting as a ferment upon myronic 
 acid or its salts, potassium myronate is converted into dextrose, allyl mustard 
 oil, and potassium bisulphate. 
 
 KC 10 H 18 NS 2 10 == C 6 H 12 6 + C 3 H 5 NCS -f KHSO 4 . 
 
 Potassium Dextrose. Allyl mustard Potassium 
 
 myronate. oil. bisulphate. 
 
 Allyl mustard oil, C 3 H 5 NCS. Mustard oils are esters of isosulphocyanic 
 acid, HNCS. Ordinary mustard oil, obtained from sinigrin, as stated above, 
 contains the radical allyl, derived from the unsaturated hydrocarbon propylene, 
 C 3 H 6 . The univalent radical allyl is isomeric, but not identical, with the tri- 
 valent radical glyceryl, C 3 H 5 , derived from propane, C 3 H 8 . The difference may 
 be seen from the structural formulas : 
 
 CH 2 CH=CH 2 , allyl. CH 2 CH-CH 2 , glyceryl. 
 
 The triatomic alcohol glycerin, C 3 H 5 (OH) 3 , may be converted into the 
 monatomic allyl alcohol, C 3 H 5 OH, by various processes. From allyl alcohol 
 an artificial allyl mustard oil is manufactured. 
 
 Mustard oil is a colorless or pale yellow liquid, which has a very pungent 
 and acrid odor and taste. When brought together with ammonia, direct combi- 
 nation takes place and crystals of thiosinamine (allyl-thio-urea), CS.N 2 H 3 .C 3 H 5 , 
 are formed . 
 
 C 3 H 5 NCS + NH 3 = CS.N 2 H 3 .C 3 H 5 . 
 
 Allyl sulphide, (C 3 H 5 ) 2 S, is the chief constituent of the oil of garlic. 
 
 50. BENZENE SERIES. AROMATIC COMPOUNDS. 
 General remarks. It has been stated before that most organic com- 
 pounds may be looked upon as derivatives of either methane, CH 4 , 
 or benzene, C 6 H 6 , these derivatives being often spoken of as fatty and 
 aromatic compounds respectively. The term aromatic compounds 
 was given to these substances on account of the peculiar and fragrant 
 odor possessed by many, though not by all of them. Benzene and 
 
 QUESTIONS. What are the three chief forms in which nitrogen enters into 
 organic compounds? What are amines and amides; in what respects do they 
 resemble ammonia compounds ? What is cyanogen, what is dicyanogen, and 
 how is the latter obtained ? How does cyanogen occur in nature, and which 
 non-metallic elements does it resemble in the constitution of various com- 
 pounds ? Mention some reactions by which hydrocyanic acid is formed, and 
 state the two processes by which the official diluted acid is obtained. What 
 strength and what properties has this acid ? State the composition of pure 
 potassium cyanide and of the commercial article. How is the latter made ? 
 Give reactions for hydrocyanic acid and cyanides. Explain the constitution 
 and give the composition of ferro- and ferricyanides. Give composition, mode 
 of manufacture, and tests of potassium ferrocyanide. What is red prussiate 
 of potash, how is it obtained, and by what reactions can it be distinguished 
 from the yellow prussiate ? 
 
558 CONSIDERATION OF CARBON COMPOUNDS. 
 
 * 
 
 methane derivatives differ considerably in many respects, and, as a 
 general rule, aromatic compounds cannot be converted into fatty 
 compounds, or the latter into aromatic compounds, without suffering 
 the most vital decomposition of the molecule, and in many cases this 
 transformation cannot be accomplished at all. 
 
 On the average, aromatic compounds are richer in carbon than fatty 
 compounds, containing of this element at least G atoms ; when decom- 
 posed by various methods, aromatic compounds, in many cases, yield 
 benzene as one of the products ; most aromatic substances have anti- 
 septic properties, and none of them serves as animal food, although 
 quite a number are taken into the system in small quantities, as, for 
 instance, some essential oils, caffeine, etc. 
 
 While some aromatic compounds are products of vegetable life, 
 many of them (like benzene itself) are obtained by destructive distil- 
 lation, and are, therefore, contained in coal-tar, from which quite a 
 number are separated by fractional distillation. 
 
 Constitution. There is not known any benzene compound which 
 has less than six atoms of carbon. In all of the various decomposi- 
 tions and replacements which occur in the formation of benzene 
 derivatives, the six carbon atoms persist, like a unit. These condi- 
 tions have led chemists to look upon the six carbon atoms as being 
 joined together, forming a nucleus to which other atoms or groups 
 are attached, in all of the known aromatic compounds. Thus, in 
 benzene, C 6 H 6 , which is the fundamental or mother-substance of 
 these compounds, the six carbon atoms are joined to six atoms of 
 hydrogen. 
 
 If benzene were of the nature of a fatty compound, we should 
 expect to find its structure correspond to a formula of this kind : 
 
 H H 
 
 This representation would indicate that benzene ought to behave 
 like a highly unsaturated compound. Moreover, we should expect 
 to obtain two isomeric compounds by replacing either a centrally 
 located hydrogen atom or one occupying a terminal position. 
 
 As a matter of fact, benzene does not behave like an unsaturated 
 chain compound (although it can be caused to unite directly with 
 some elements), and by replacement of a hydrogen atom but one kind 
 of substitution product has ever been obtained. These facts lead us 
 to believe that benzene is not an unsaturated chain compound, and 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 559 
 
 
 
 that all the hydrogen atoms are equivalent ; in other words, the mole- 
 cule C 6 H 6 is perfectly symmetrical. 
 
 In view of these and many other facts the conclusion is that the 
 six carbon atoms in benzene are united into a cycle or ring, and that 
 each carbon atom is in combination with one hydrogen atom. This 
 view was first put forth by August KekulS in 1865. Graphically 
 the closed carbon chain and also benzene (usually referred to as 
 Kekul6's benzene hexagon) are represented thus : 
 
 1 H 
 
 c / 2 H \ C A C / H 
 
 3 H/ \C^ \ 
 
 i 
 
 This formula for benzene accounts for the facts mentioned above. 
 Moreover, if two hydrogen atoms are replaced by substituting atoms 
 or radicals, three isomeric products are obtained. 
 
 For instance, we know three different substances which have been 
 obtained by replacement of two hydrogen atoms in benzene by two 
 hydroxyl groups. This would indicate that it makes a difference, as 
 far as the properties of a compound are concerned, in which relative 
 position the introduced radicals stand to one another, and as a result 
 of a great deal of investigation it was found that the following 
 formulas represent the three relative positions which the two replac- 
 ing groups may occupy in a benzene molecule : 
 
 OH OH OH 
 
 H^ tf^ X)H H v ,C. 
 
 A > -* 
 
 \TT TT/ \C\4 > 
 
 H H OH 
 
 Ortho-position. Meta-position. Para-position. 
 
 1:2. 1:3. 1:4- 
 
 Designating the hydrogen atoms in benzene with numbers, thus : 
 
 122456 
 
 C 6 H H H H H H, the above 3 compounds show that in one case 
 the hydrogen atoms 1 and 2, in the second 1 and 3, in the third 1 
 and 4 have been replaced by OH. The compounds formed in this 
 way are distinguished as ortho-, ineta-, and para-compounds. 
 
560 
 
 CONSIDERATION OF CARBON COMPOUNDS. 
 
 The molecular formula of the above three compounds is C 6 H 6 O 2 , 
 apparently indicating benzene in combination with two atoms of 
 oxygen or dioxybenzene ; actually they are dihydroxy benzene. 
 
 Otfto-dihydroxy benzene, C 6 H 4 OHOH, or C 6 H 4 (OH) 2 1 : 2, is known 
 
 1 3 
 
 as pyro-catechin, wefa-dihydroxy benzene, C 6 H 4 OHOH, or C 6 H 4 (OH) 2 
 
 1 4 
 
 1:3, as resorcin, and >ara-dihydroxy benzene, C 6 H 4 OHOH, or 
 C 6 H 4 (OH) 2 1 : 4, as hydroquinone. 
 
 Benzene derivatives. The analogy existing between methane- 
 and benzene-derivatives may be shown by comparing the composition 
 of a few derivatives : 
 
 Methane, 
 
 CH 4 
 
 Benzene, 
 
 C 6 H 6 
 
 Methyl, 
 
 CH 3 
 
 Benzyl, 
 Phenyl, 
 
 }C 6 H 5 
 
 Ethane, 1 
 Methyl-methane, / 
 
 CH 3 .CH 3 
 
 Toluene, 
 Methyl-benzene, 
 
 }C 6 H 5 .CH 3 
 
 Methyl-hydroxide, \ 
 Methyl-alcohol, / 
 
 CH 3 OH 
 
 Phenyl-hydroxide, 
 Phenol, 
 
 } C 6 H 5 .OH 
 
 
 /OH 
 
 
 /OU 
 
 Glycerin, 
 
 C 3 H 5 ^OH 
 
 Pyrogallol, 
 
 
 
 X OH 
 
 
 SX OH 
 
 Acetic acid, 
 
 CH 3 .CO 2 H 
 
 Benzoic acid, 
 
 C 6 H 5 .CO 2 H 
 
 Acetic aldehyde, 
 
 CH 3 .COH 
 
 Benzoic aldehyde, 
 
 C 6 H 5 .COH 
 
 Ethyl-sulphonic acid, 
 
 S 2 \OH 5 
 
 Benzene-sulphonic 
 acid, 
 
 SO *\OH 5 
 
 Malonic acid, 
 
 CH / C 2 H 
 
 Phthalic acid, 
 
 C H / C 2 H 
 
 Tartaric acid, 
 
 C 2 H 2 /2 2H 
 
 Salicylic acid, 
 
 c H /'OH 
 
 Ethyl ether, 
 
 g:p H 
 
 Phenyl-ether, 
 
 f C 6 H 5 \ 
 lC 6 H 5 / 
 
 Methyl-ethyl ether, j 
 
 C 2 H 5 V 
 
 Methyl-phenyl 
 ether, anisol, 
 
 ic 6 H 5 3 ) 
 
 The following graphic formulas may serve to illustrate the consti= 
 tution of some aromatic compounds : 
 
 OH 
 
 J 
 
 ^ 
 
 A 
 
 Benzene, CH. 
 
 C0 2 H 
 
 r I 
 
 H 
 
 i 
 
 H 
 
 Phenol or carbolic acid, Benzoic acid, C 6 H 5 .CO9H. 
 C 6 H 5 .OH. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 
 NO, OH 
 
 561 
 
 H C 
 
 \ c x 
 
 
 II 
 
 H 
 
 H 
 
 Nitro-benzene, C 6 H 6 NO a . 
 
 CH 
 
 Toluene, methyl-benzene. 
 C 6 H 6 .CH 3 . 
 
 CH 3 
 
 H 
 
 H 
 
 Xylene, di-methyl-benzene, 
 
 CH, 
 
 H 
 
 C0 2 H 
 
 XC0 2 H 
 
 A 
 
 H 
 
 Resorcin, C e H 4 (OH) 2 . Phthulic acid, C H 4 (CO 2 H) a . 
 
 H 
 
 OH 
 
 L 
 
 J 
 
 OH 
 
 \ OH 
 
 H 
 
 OH 
 
 I 
 
 C0 2 ] 
 
 Pyrogallol, C 6 H 3 (OH) 3 . Galb'c acid, C 6 H 2 .CO 2 H.(OH),. 
 
 OH 
 H \A 
 
 OH 
 
 H 
 
 / 
 
 X CH 3 
 \H 
 
 H 
 
 H 
 
 / 
 
 H 
 
 Cresol, C 6 H 4 .CH 3 .OH. 
 
 CH 
 
 Salicylic acid, C 6 H 4 .CO 2 H.OH. 
 COH 
 
 \ 
 
 \^f 
 
 i 3 H 7 
 
 H 
 
 Cymene, methyl-propyl benzene. Thymol, C 6 H 3 CH 3 .C 8 H 7 .OH. Benzaldehyde, oil of bitter 
 C 6 H 4 CH 3 .C 3 H 7 . almond, C 6 H 6 .COH. 
 
 The preceding graphic formulas show in the first column (besides 
 nitro-benzene) a number of hydrocarbons, in the second column 
 phenols, obtained by introducing hydroxyl into the hydrocarbon 
 molecule, and in the third column chiefly aromatic acids, formed by 
 introducing carboxyl, CO 2 H, or carboxyl and hydroxyl. 
 
 Differences between aromatic and fatty compounds. Substitution pro- 
 ducts with nitric acid, sulphuric acid, bromine, hydrocarbon radicals, etc., are 
 much more easily formed and held much more strongly in aromatic compounds 
 than in fatty ones. The phenols, which in composition correspond to alcohols, 
 36 
 
562 CONSIDERATION OF CARBON COMPOUNDS. 
 
 are more acid than the fatty alcohols ; aromatic amines are less alkaline than 
 in the fatty series. The phenols do not form esters like the alcohols. 
 
 Fatty amines with nitrous acid yield alcoholic compounds ; aromatic amines 
 behave quite differently, viz., a new series of bodies, known as diazo compounds, 
 is formed. Fatty compounds are easily oxidized, while benzene is very stable 
 in the presence of oxidizing agents. 
 
 Benzene series of hydrocarbons. 
 
 By replacing the hydrogen atoms in benzene by methyl, CH 3 , a 
 series of hydrocarbons is formed having the general composition 
 C n H 2n _ 6 . To this benzene series belong : 
 
 Benzene . . . C 6 H 6 B. P. 80.5 C. 
 
 Toluene . . . C 7 H 8 = C 6 H 5 CH 3 110 
 
 Xylene . . . C 8 H 10 - = C 6 H 4 (CH 3 ) 2 141 
 
 Cumene . . . C 9 H 12 = C 6 H 8 (CH 3 ) 8 169 
 
 Tetra-methyl-benzene C 10 H U = C 6 H 2 (CH 3 ) 4 190 
 
 Penta-methyl-benzene C,,H 16 = C 6 H(CH 3 ) 5 231 
 
 Hexa-methyl-benzene Ci 2 H 18 = = C 6 (CH 3 ) 6 264 
 
 The first four members of this series are found in coal-tar ; the 
 last three have been obtained by synthetical processes. While but 
 one toluene is known, the higher members form quite a number of 
 isomeric compounds. Instead of adding two or more methyl groups 
 it is possible to add an ethyl group, C 2 H 5 , or even higher homologous 
 groups, thus producing a great many isomeric compounds. Thus, 
 cymene, C 10 H 14 , found in the oil of thyme, is not tetra-methyl-ben- 
 zene, but para-methyl-iso-propyl-benzene, C 6 H 4 CH 3 .C 3 H 7 . This com- 
 pound is of interest on account of its close relation to the terpenes 
 and camphors, which will be spoken of later. 
 
 Benzene, C 6 H 6 (Benzol). When coal-tar is distilled, products are 
 obtained which are either lighter or heavier than water, and by col- 
 lecting the distillate in water a separation into so-called light oil 
 (floating on the water) and heavy oil (sinking beneath the water) is 
 accomplished. Benzene is found in the light oil and obtained from 
 it by distillation after phenol has been removed by treatment with 
 caustic soda and some basic substances by means of sulphuric acid. 
 Pure benzene may be obtained by heating benzoic acid with calcium 
 hydroxide : 
 
 C 6 H 5 .CO 2 H -f- Ca(OH) 2 == CaCO 3 + H 2 O + C 6 H fl . 
 
 Experiment 67. Mix 25 grammes of benzoic acid with 40 grammes of slaked 
 lime and distil from a dry flask, connected with a condenser. Add to the dis- 
 tilled fluid a little calcium chloride and redistil from a small flask. The 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 563 
 
 product obtained is pure benzene. Notice that it solidifies when placed in a 
 freezing mixture of ice and common salt. Observe the analogy between Ex- 
 periments 67 and 51. In one case a fatty acid is decomposed by an alkali with 
 liberation of methane, in the other an aromatic acid with liberation of benzene, 
 tin- carbonate of the decomposing hydroxide being formed in both cases. 
 
 Pure benzene is a colorless, highly volatile liquid, having a peculiar, 
 aromatic odor and a specific gravity of 0.884 ; it boils at 80.5 C. 
 (177 F.) and solidifies at C. (32 F.) ; it is an excellent solvent 
 for fats, oils, resins, and many other organic substances. 
 
 Nitro-benzene, C 6 H 3 .NO 2 . When benzene is treated with concen- 
 trated nitric acid, or with a mixture of nitric and sulphuric acids, 
 nitro-benzene is formed . 
 
 C 6 H 6 + HN0 3 == C 6 H 5 N0 2 + H 2 O. 
 
 Experiment 68. Mix 50 c.c. of sulphuric acid with 25 c.c. nitric acid ; allow 
 to cool, place the vessel containing the mixture in water, and add gradually 5 
 c.c. of benzene, waiting after the addition of a few drops each time until the 
 reaction is over. Shake well until all benzene is dissolved and pour the liquid 
 into 300 c.c. of water. The yellow oil which sinks to the bottom is nitro- 
 benzene. It may be purified by washing with water and redistilling, after 
 removal of water and shaking with calcium chloride. 
 
 Nitro-benzene is an almost colorless or yellowish oily liquid, which 
 is insoluble in water, has a specific gravity of 1.2, a boiling-point of 
 205 C. (401 F.), a sweetish taste, highly poisonous properties, even 
 when inhaled, and an odor resembling that of oil of bitter almond, 
 for which it is substituted under the name of essence of mirbane. It 
 is manufactured on a large scale, and is used chiefly in the preparation 
 of aniline. Dinitro benzene is also known. 
 
 Toluene, C 6 H 5 CH 3 (Methyl benzene}. This was first obtained by dry distilla- 
 tion of balsam of tolu, whence its name. It occurs in coal tar, from which it 
 can be separated, but may also be made from benzene by using a reaction gen- 
 erally employed for the introduction of the methyl groups, thus: 
 
 C 6 H 5 Br + CH 3 Br + 2Na = C 6 H 5 CH 3 + 2NaBr. 
 
 Toluene, as well as the other hydrocarbon derivatives of benzene, possesses 
 properties of the fatty hydrocarbons as well as benzene properties. This is 
 quite natural, because of the fatty radicals present in the molecule. Thus, 
 when oxidized, toluene yields benzoic acid, C 6 H 5 CO 2 H, the methyl being 
 oxidized while the benzene ring is unchanged. 
 
 Xylenes, CeH^CHg^ (Dimethyl benzenes}. Three xylenes are found in coal- 
 tar, and are distinguished as ortho-, meta-, and para-xylene. They can be 
 made synthetically from toluene in the same manner as toluene is made from 
 benzene. When oxidized they yield ortho-, meta-, and para-phthalic acids, of 
 the composition C 6 H 4 (C0 2 H) 2 . 
 
564 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Cymene, C 10 H 14 or CgH^CH^.CgHy (para-methyl-isojjroj^-benzene). 
 This hydrocarbon occurs in the oil of thyme and in the volatile oils 
 of a few other plants ; it has also been made synthetically ; it is a 
 liquid of a pleasant odor, boiling at 175 C. (347 F.). 
 
 Cymene is of special interest, because it is closely related to the 
 terpenes and camphors, from all of which it may be obtained by 
 comparatively simple processes. 
 
 Amino compounds of benzene. 
 
 Aniline, Phenyl-amine, C 6 H 5 NH 2 . The constitution of amines, 
 to which class aniline belongs, has been considered in Chapter 49. 
 Aniline is found in coal tar and in bone-oil; it is manufactured on 
 a large scale by the action of nascent hydrogen upon nitro-benzene, 
 iron and hydrochloric acid being generally used for generating the 
 hydrogen. 
 
 Experiment 69. Dissolve 20 c.c. of nitro-benzene (this may be obtained 
 according to the directions given in Experiment 68, using larger quantities of 
 the material) in alcoholic ammonia and pass through this solution hydrogen 
 sulphide as long as a precipitate of sulphur is produced ; the reaction takes 
 place thus : 
 
 C 6 H 5 NO 2 -f 3H 2 S = C 6 H 5 NH 2 + 2H 2 O + 3S. 
 
 Evaporate on a water-bath to expel ammonium sulphide and alcohol ; add to 
 the residue dilute hydrochloric acid, which dissolves the aniline, but leaves any 
 unchanged nitro-benzene undissolved. Separate the nitro-benzene from the 
 aniline chloride solution, evaporate this to dryness, mix with some lime, in 
 order to liberate the aniline, which may be obtained by distillation from a dry 
 flask. 
 
 Pure aniline is a colorless, slightly alkaline liquid, having a pecu- 
 liar, aromatic odor, a bitter taste, and strongly poisonous properties. 
 It boils at 184.5 C. (364 F.). Like all true amines, it combines 
 with acids to form well-defined salts. 
 
 Aniline dyes. The crude benzene used in the manufacture of aniline 
 dyes is generally a mixture of benzene, C 6 H 6 , and toluene, C 7 H 8 . 
 This mixture is first converted into nitro-benzene, C 6 H 6 NO 2 , and 
 nitro-toluene, C 7 H 7 NO 2 , and then into aniline, C 6 H 5 NH 2 , and tolu- 
 idine, C 7 H 7 NH 2 . When these substances are treated with oxidizing 
 agents, such as arsenic oxide, hypochlorites, chromic or nitric acid, 
 etc., various substances are obtained which are either themselves dis- 
 tinguished by beautiful colors or may be converted into numerous 
 derivatives showing all the various shades of red, blue, violet, green, 
 etc. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 565 
 
 As an instance of the formation of an aniline dye may be men- 
 tioned that of roaaniline, which takes place thus: 
 
 C 6 H 7 N -f 2C 7 H 9 N + 30 : C 20 H 19 N 3 + 3H 2 O. 
 Aniline. Toluidine. Rosaniline. 
 
 Experiment 70. To some of the aniline obtained by performing Experiment 
 69 add a little solution of bleaching powder: a beautiful purple color is ob- 
 tained. Treat another portion with sulphuric acid to which an aqueous solu- 
 tion of potassium dichromate has been added : a blue color is produced. A 
 third quantity treat with solution of cupric sulphate and potassium chlorate: 
 a dark color is the result. 
 
 Acetanilide, Acetanilidum, C 6 H 5 .NH.(CH 3 CO) 134.09, (Anti- 
 febrine, Phcnylacdamide). The term anilide is used for derivatives 
 of aniline obtained from this compound by replacement of the am- 
 monia hydrogen (or amino hydrogen) by acid radicals. If the radical 
 introduced is acetyl, C 2 H 3 O, the resulting compound is acetanilide, 
 
 C* TT 
 
 the constitution of which is represented in the formula NH^p 6 TT 5 r\ 
 
 It is obtained by boiling together for one or two days equal weights 
 of pure aniline and glacial acetic acid, distilling and collecting the por- 
 tion which passes over at a temperature of about 295 C. (563 F.). 
 The distillate solidifies on cooling and may be purified by recrystalliza- 
 tion from solution in water. The chemical change taking place is this : 
 
 C 6 H 6 NH 2 + C 2 H 4 O 2 = C 6 H 5 .NH.C 2 H 3 O + H 2 O. 
 
 Pure acetanilide forms white odorless crystals of a silky lustre and a greasy 
 feeling to the touch. It fuses at 113 C. (235 F.) and boils at 295 C. (563 F.) ; 
 it is but slightly soluble in cold, much more soluble in hot water, readily solu- 
 ble in alcohol and ether ; the solutions have a neutral reaction and are not 
 colored by either concentrated sulphuric acid or by ferric chloride. 
 
 Analytical reactions: 
 
 1 . When 0.1 gramme of acetanilide is boiled for several minutes with 
 2 c.c. of hydrochloric acid, and to this solution are added 3 c.c. of an 
 aqueous solution of phenol (1 in 20) and 5 c.c. of a filtered, saturated 
 solution of bleaching powder, a brownish-red liquid is obtained which 
 turns deep blue upon supersaturation with ammonia water. 
 
 2. On heating 0.1 gramme of acetanilide with a few c.c. of concen- 
 trated solution (1 in 4) of potassium hydroxide, the odor of aniline 
 becomes noticeable ; on now adding chloroform, and again heating, 
 the disagreeable odor of the poisonous phenyl-isocyanide, C 6 H 5 NC, is 
 evolved (distinction from antipyrine). 
 
 3. A mixture of equal parts of acetanilide and sodium nitrite 
 
566 CONSIDERATION OF CARBON COMPOUNDS. 
 
 sprinkled upon concentrated sulphuric acid produces a bright-red 
 color. 
 
 Compound acetanilide powder, Pulvis acetanilidi compositus, is 
 a mixture of 70 parts of acetanilide, 10 parts of caffeine, and 20 parts of sodium 
 bicarbonate. It is one form of the numerous headache powders in the market, 
 in which acetanilide, the cheapest of the common antipyretics, is a common con- 
 stituent. Sodium bicarbonate increases the solubility of the acetanilide. 
 
 Methyl acetanilide C 6 H 5 .N.CH 3 .C 2 H 3 0, (Exalgin], may be made by the 
 acetylating of monomethyl-aniline. It occurs as a crystalline powder or in 
 large crystalline needles ; it is tasteless and almost insoluble in water. 
 
 Sulphanilic acid, Amline-para-sulphonic acid, C8H 4 .NH,.S0 3 H. Obtained 
 by heating 1 part of pure aniline oil with 2 parts of fuming sulphuric acid, 
 and purifying the product by crystallization. 
 
 C 6 H 5 .NH 2 + H 2 SO, = C 6 H 4 .NH 2 .SO 3 H + H 2 O. 
 
 It is a colorless crystalline substance, soluble in 182 parts of cold water. 
 When sulphanilic acid is acted upon by nitrous acid, it is converted into diazo- 
 benzol-sulphonic acid, C 6 H 4 N.N.SO 3 , which is of interest because it is used as a 
 reagent in Ehrlich's diazo-reaction in urinary analysis. 
 
 Diphenyl-amine, (C 6 H 5 ) 2 NH, is obtained by the destructive distillation of 
 triphenyl-rosaniline (aniline-blue) as a grayish crystalline substance, slightly 
 soluble in water, more soluble in acids. A 0.2 per cent, solution in diluted 
 sulphuric acid (forming diphenylainine sulphuric acid) is colored intensely 
 blue by nitric acid; also, temporarily by nitrous acid and, somewhat less 
 intensely, by hypochlorous, bromic, and iodic acids, and a number of other 
 oxidizing agents. 
 
 Diamino-benzene, Meta-phenylene-diamine, CgH^NHa^, is obtained by 
 the reduction of meta-dinitro-benzene as a grayish crystalline powder. It has 
 strongly basic properties, is somewhat soluble in water, readily soluble in alco- 
 hol or ether. It is a valuable reagent for nitrites, as it forms, with even traces 
 of nitrous acid, an intense yellow color. 
 
 Methylthionine hydro chloride, Methylthioninae hydrochlori- 
 dum, C 16 H 18 N 3 SC1 = 317.36 (Methylene blue). This is a very complex 
 dye obtained by treating dimethyl-paraphenylene-diamine, C 6 H 4 .- 
 (NH 2 )N(CH 3 ) 2 , in hydrochloric acid solution with hydrogen sulphide 
 and subsequently with ferric chloride. It occurs as a dark-green 
 powder or in prismatic crystals having a bronze-like lustre, readily 
 soluble in water and somewhat less so in alcohol, giving solutions of 
 a deep-blue color. Alkalies change the color of the aqueous solution 
 to a purplish shade, and in excess cause a precipitate of a dull-violet 
 color. It is incompatible with potassium iodide, and reducing agents 
 decolorize it. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 567 
 
 Methylene-blue should not be confounded with the commercial article, which 
 is often the zinc chloride double salt of methylthionine, is employed as a dye or 
 stain, and is unfit for medicinal purposes. The presence of zinc can be told by 
 incinerating 2 grammes of the substance and testing the ash in the usual way 
 for zinc. Methylene-blue should also not be confounded with methyl blue, 
 which is the sodium salt of triphenyl-pararosaniline-trisulphonic acid. A solu- 
 tion of the latter with alkalies changes to reddish-brown, 
 
 Methylene azure, C 18 H 18 N 3 S0 3 C1, is derived from methylene-blue by the ad- 
 dition of oxygen. It is present in "ripened" methylene-blue and almost 
 always in even the best specimens of the medicinal article. It may be detected 
 by adding ammonia to a solution of methylene-blue and then shaking with 
 ether ; the methylene-azure passes into the ether, which is colored red. 
 
 Diazo compounds of benzene. 
 
 When fatty amines are treated with nitrous acid the ammo group 
 is replaced by hydroxyl, thus : 
 
 C 2 H 5 .NH 2 + HONO = C 2 H 5 OH -f 2N + H 2 O. 
 
 When, however, an aromatic amine is treated with nitrous acid, 
 in acid solution, a new class of compounds is formed, known as 
 diazo-compounds, thus : 
 
 C 6 H 5 .NH 2 HC1 + HONO = C 6 H 5 .N a .Cl -f- 2H 2 0. 
 
 Aniline Diazo-benzene 
 
 hydrochloride. chloride. 
 
 The characteristic diazo grouping is expressed thus : R N 2 , and 
 this group combines with acid residues to form diazo-salts, such as 
 diazo-benzene nitrate, C 6 H 5 .N 2 .NO 3 , sulphate, C 6 H 6 .N 2 .SO 4 H, etc. 
 
 The diazo-compounds are colorless, crystalline, unstable, and even explosive 
 substances ; soluble in water, insoluble in ether. They are of great scientific 
 and technical importance, as they form the starting-point for a large class 
 of dyes. Diazo-compounds are decomposed by water, either in the cold or upon 
 heating, the N 2 group being usually replaced by the (OH) group, thus : 
 
 C 6 H 5 .N 2 .NO 3 + H 2 O = C 6 H 5 OH -f N 2 + HNO 3 . 
 
 It is thus possible to introduce hydroxyl into the benzene nucleus through the 
 medium of nitre-compounds, and obtain substances belonging to the class of 
 phenols. 
 
 Diazo-compounds have a marked tendency to react with other substances, 
 especially amino-compounds and phenols, to form a class known as azo-com- 
 pounds, which are characterized by having the group N = N in combina- 
 tion with two residues. Azobenzene, C 6 H 5 N = N C 6 H 5 , is the mother- 
 substance of all azo-compounds, most of which are highly colored, and many 
 are used as dyes. The formation of colored azo-compounds is involved in the 
 test for nitrites in drinking-water by meta-phenylene-diamine (see page 432), 
 which gives triamino-azobenzene, NH 2 .C 6 H 4 N = N C 6 H 3 (NH 2 ) 2 , a dye 
 which has been on the market since 1866 and known as Bismark brown ; also 
 
568 CONSIDERATION OF CARBON COMPOUNDS. 
 
 the test in which sulphanilic acid and alpha-naphthylamine are used. In 
 Ehrlich's Diazo Reaction for typhoid fever, it is believed that some unknown 
 phenolic or amino compound in the urine unites with the diazo-sulphanilic 
 acid reagent, and forms an azo-dye. Some of the indicators used in volumetric 
 analysis are azo-dyes, for example, methyl-orange (see page 410). Dimethyl- 
 amino-azobenzol, C 6 H 5 N = N C 6 H 4 .N(CH 3 ) 2 , is used to detect hydrochloric 
 acid in stomach contents. 
 
 Phenyl hydrazine, C 6 H 5 .NH.NH 2 . When diazo-compounds are reduced, 
 they yield derivatives of the mother-substance, H 2 N NH 2 , known as hydra- 
 zine, or diamine. Thus, diazo-benzene yields phenyl hydrazine. It is a 
 strongly basic substance and unites readily with acids to form salts ; it is a 
 colorless crystalline substance, sparingly soluble in water, but soluble in acids. 
 Phenylhydrazine is of interest because it is used in the manufacture of anti- 
 pyrine, and as a valuable reagent for the detection of aldehydes and sugars. 
 It combines with both classes of compounds, forming with aldehydes bodies 
 known as hydrazones, with sugars, osazones. Most of these compounds are solid 
 and crystalline; the crystalline structure often serves for identification. 
 
 Arsenic and phosphorus derivatives. A number of compounds of aro- 
 matic hydrocarbons containing arsenic and phosphorus, and having compo- 
 sitions similar to nitro-, azo-, and amino-compounds, are known. The simi- 
 larities are shown in the following table : 
 
 C 6 H 5 .NO 2 
 
 Nitrobenzene. 
 
 C 6 H 5 .N,C 6 H 5 
 
 Azobenzene. 
 
 C 6 H 5 .NH 2 
 
 Phenylamine. 
 
 C 6 H V P0 2 
 Phosphinobenzene. 
 
 C 6 K 5 .P 2 .C 6 H 5 
 
 Phosphobenzene. 
 
 C 6 H 5 .PH 2 
 
 Phenylphosphine. 
 
 C 6 H 5 AsO 2 
 
 Arsinobenzene. 
 
 C 6 H 5 .As 2 .C 6 H 5 
 
 Arsenobenzene. 
 
 
 Arsenobenzene, C 6 H 5 .As : As.C 6 H 5 , is obtained by the reduction of phenyl- 
 arsine oxide, C 6 H 5 .AsO, by phosphorous acid, as yellow needles. By oxidation 
 it is converted into phenylarsonic acid, C 6 H 5 .AsO(OH) 2 . 
 
 Sodium para-aminophenyl arsonate, NH 2 .C 6 H 4 .AsO(OH).ONa.3H 2 O (sodium 
 arsanilate, sodium aniline arsonate, atoxyl), is a white, odorless, crystalline salt, 
 soluble in about 6 parts of water, and having a faint salty taste. The aqueous 
 solution on standing assumes a yellowish tint. It is used in sleeping sickness 
 (trypanosomiasis), syphilis, malaria, etc. It should be given hypodermically, 
 and not by the mouth. Atoxyl is made by heating aniline arsenate to about 
 200 C. for several hours, when a reaction takes place analogous to that by 
 which para-amino-benzene sulphonic acid (sulphanilic acid) is formed by heat- 
 ing aniline sulphate : 
 
 C 6 H 5 NH 2 .(HO) 3 AsO = NH 2 .C 6 H 4 .AsO(OH) 2 + H 2 O 
 Aniline arsenate. Para-aminophenyl arsonic acid. 
 
 The sodium salt of this acid is atoxyl. 
 
 IKoxydiaminoarsenobenzene, ^ ) ^C 6 H 8 .Afl : As.C 6 H 3 <^^^ ffi. The 
 
 dihydrochloride ("bichloride," as it is called in the market) of this diamine 
 compound was prepared by Ehrlich and Bertheim, and was the 606th com- 
 pound made in a search for a specific remedy for germ diseases. It is known 
 as " 606," or salvarsan. The arsenic occupies the para position in the benzene 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 569 
 
 nucleus. This substance has basic properties due to the NH 2 groups, and 
 therefore unites with acids ; it also has acid properties due to the (OH) groups, 
 and forms salts with alkalies just as phenol does. 
 
 Salvarsan is a lemon-yellow powder, which comes in sealed tubes. It is 
 soluble in water with a decided acid reaction, due to hydrolysis and liberation 
 of hydrochloric acid. The sodium salt gives an alkaline reaction in solution, 
 due to hydrolysis and liberation of sodium hydroxide. The free base is insolu- 
 ble in water and is precipitated by the cautious addition of alkali to the solu- 
 tion of the hydrochloride, or of acid to the solution of the sodium compound. 
 For injections, either a suspension of the free base or a solution of the mono- 
 or di-sodium salt is prepared from salvarsan. 
 
 Hydroxyl derivatives of the benzene series. 
 
 Phenols are hydroxyl derivatives of benzene. The name is a gen- 
 eral one for all such compounds. Phenols are allied to the tertiary 
 fatty alcohols, as they contain the characteristic grouping = C OH. 
 According to the number of hydrogen atoms replaced by hydroxyl, 
 we find mono-, di-, and tri-hydroxy phenols, corresponding to the 
 similarly constituted alcohols. Phenols differ from common alcohols 
 in not yielding aldehydes or acids by oxidation. 
 
 Phenols are either liquid or solid, and often have a peculiar odor. Most of 
 them can be distilled without decomposition, and are readily soluble in alcohol 
 and ether ; some are readily soluble in water. Many are antiseptic, for example, 
 phenol, cresol, resorcin, thymol, etc. Many individual phenols are found in the 
 vegetable and animal kingdoms. Destructive distillation of complex carbon 
 compounds usually results in the formation of phenols among the products; 
 thus, wood-tar and coal-tar are rich in phenols. 
 
 Phenols act like weak acids, forming salts with caustic alkalies, which are 
 soluble in water and far more stable than the alcoholates. But they do not 
 decompose carbonates. 
 
 Phenols can be obtained readily by first preparing sulphonic acids, and fusing 
 the alkali salts of these with caustic soda or potash. The actions are shown in 
 the following equations, which relate to synthetic phenol : 
 
 C 6 H 6 + H 2 S0 4 C 6 H 5 S0 3 H + H 2 0. 
 
 Benzene 
 eulphonic acid. 
 
 C 6 H 5 SO 3 Na + NaOH C 6 H 5 OH. + Na 2 SO 3 . 
 
 Phenol. 
 
 The phenol is liberated from its alkali salt by an acid, and is purified by 
 further appropriate treatment. 
 
 Phenol, C 6 H 5 OH = 93.34 ( Carbolic acid, Phenyl hydroxide). Crude 
 carbolic acid is a liquid obtained during the distillation of coal-tar 
 between the temperatures of 170-190 C. (338-374 F.), and con- 
 taining chiefly phenol, besides cresol, C 7 H 7 OH, and other substances. 
 
570 CONSIDERATION OF CARBON COMPOUNDS. 
 
 It is a reddish-brown liquid of a strongly empyreumatic and dis- 
 agreeable odor. 
 
 By fractional distillation of the crude carbolic acid, the pure acid 
 is obtained, which forms colorless, interlaced, needle-shaped crystals, 
 sometimes acquiring a pinkish tint ; it has a characteristic, slightly 
 aromatic odor, is deliquescent in moist air, soluble in from 15 to 20 
 parts of water, and very soluble in alcohol, ether, chloroform, glycerin, 
 fat and volatile oils, etc. ; it has, when diluted, a sweetish and after- 
 ward burning, caustic taste; it produces a benumbing and caustic 
 effect, and even blisters on the skin ; it is strongly poisonous, and a 
 powerful disinfectant, preventing fermentation and putrefaction to a 
 marked degree ; fusing point of the official article not less than 40 C. 
 (104 F.); boiling point 188 C. (370 F.). 
 
 Phenol, though generally called carbolic acid, has a neutral or but 
 faintly acid reaction, and the constitution of a tertiary alcohol, but it 
 readily combines with strong bases, for instance, with sodium hy- 
 droxide, forming sodium phenoxide or sodium phenolate : 
 
 C 6 H 6 OH -f NaOH = C 6 H 6 OXa + H a O. 
 
 Phenol obtained by synthetical processes is now sold in a state of 
 great purity ; it has comparatively little odor. 
 
 Phenol is readily liquefied by a small amount of water and is 
 usually dispensed in this form. The Liquefied phenol of the U. S. P. 
 contains about 13.6 per cent, of water. 
 
 Phenol often becomes colored when exposed to air and light. This is due 
 to oxidation. When pure it remains colorless even in sunlight if it is kept in 
 an atmosphere of inert gases, as hydrogen, nitrogen, or carbon dioxide. The 
 rate of oxidation varies with the temperature, being rapid at the boiling-point 
 of phenol. The products of oxidation are quinol, quinone, and catechol, and 
 the principal colored compounds are probably quinone condensation products. 
 The formation of the intensely red substance called phenoquinone is probable. 
 Glass which most completely absorbs ultra-violet light retards the action of 
 oxygen on phenol in the greatest degree. 
 
 Phenol or carbolic acid coefficient (Rideal- Walker coefficient}. Bacte- 
 riological standardization of disinfectants was proposed in 1896 by C. G. Moor. 
 In 1903 Samuel Rideal and Ainslie Walker developed the method now in use, 
 which, with later improvements, is the best available in spite of some defects. 
 In this method carbolic acid is taken as the standard of comparison for other 
 disinfectants. The phenol or carbolic acid coefficient is the ratio of the strength 
 in which a given disinfectant kills a given organism to that of carbolic acid 
 which effects the same sterilization in the same time. The colon or typhoid 
 bacillus is employed in the experiments of comparison. 
 
 The meaning of the coefficient will appear clear from the following exam- 
 ple, which refers to a culture of bacillus pestis. A 1 in 40 formaldehyde solu- 
 tion was equivalent to a 1 in 110 solution of carbolic acid, both sterilizing in 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 571 
 
 ten minutes, but not in seven and a half minutes. Hence, carbolic acid coeffi- 
 cient of the formaldehyde in this instance was ^, or 0.36. 
 
 The laws of some states require the labels of substances sold as disinfectants 
 to state the carbolic acid coefficient. The following table shows the coefficients 
 and the relative money values of various disinfectants in the market: 
 
 Carbol' ' C St f the Quantity of dls ' 
 Disinfectant. acid " Infectant equivalent to 1 
 
 coefficient EngUsh gttll n f 98 per 
 
 cent, carbolic acid. 
 
 Carbolic acid, 98 per cent 1.00 $ 0.25 
 
 Chinosol . 0.30 127.87 
 
 Condy's fluid 0.90 2.00 
 
 Cyllin (a cresol) 11.00 0.08 
 
 Formaldehyde 0.30 4.40 
 
 Izal 8.00 0.12 
 
 Listerine 0.03 324.62 
 
 Lysoform 0.10 36.49 
 
 Lysol 2.50 0.76 
 
 Pearson's antiseptic 1.40 0.42 
 
 Sanitas 0.02 42.56 
 
 The coefficients of some other disinfectants are : sulphonaphthol, 2.2 ; zeno- 
 leum, 2.49 ; kreso, 2.5 ; chloronaphtholeum, 5.4 ; hyco, 19 ; Platt's chlorides, 3. 
 
 Antidotes. Alcohol is the best antidote ; it prevents the corrosive action of 
 phenol. But the stomach should be at once emptied and washed out, else the 
 phenol will be absorbed and then alcohol would prove worse than no antidote. 
 Soluble sulphates have been recommended on the supposition that harmless 
 phenolsulphonates are formed, but recent experimenters have asserted that 
 they are useless as an antidote. Hot applications to the extremities, hypo- 
 dermic injection of cardiac and respiratory stimulants, intravenous injection of 
 normal saline solution, and morphine to relieve pain, are valuable aids in phenol 
 poisoning. 
 
 Tests for phenol. 
 (Use an aqueous solution.) 
 
 1. It coagulates albumin and collodion. 
 
 2. It colors solutions of neutral ferric chloride intensely and per- 
 manently violet-blue. 
 
 3. Bromine water, added in excess, produces, even in dilute solu- 
 tions, a white precipitate of tri-brom-phenol, C 6 H 2 Br 3 OH, which has 
 been used medicinally under the name of Bromol. 
 
 4. Millon's reagent (see Index), heated to boiling with phenol solu- 
 tion, gives an intense red color on addition of a few drops of nitric 
 acid. 
 
 5. On heating with nitric acid it turns yellow, nitre-phenols being 
 formed. 
 
572 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Bismuth tribrom-phenolate, Bi 2 O 2 .OH.(OC 6 H 2 Br 3 ) (Xeroform},is a fine 
 yellow, nearly odorless and tasteless powder, insoluble in water or alcohol, but 
 soluble in 2 per cent, hydrochloric acid in the proportion of 30 : 100. It is incom- 
 patible with alkaline media and should not be heated above 120 C. It is a non- 
 irritant and non-toxic antiseptic, recommended as a substitute for iodoform. 
 
 Nitro-plienols. Mono-, di-, and trinitro-phenols are known. Mononitro- 
 phenol is formed by the action of dilute nitric acid on phenol ; the di- and tri- 
 nitro- derivatives are formed by further nitration. Mononitro-phenol is of in- 
 terest also because it is used in the manufacture of acetphenetidiu. 
 
 Acetphenetidin, Acetphenetidinum, C 6 H 4 .O(C 2 H 5 ).NH(C 2 H 3 O) = 
 177.79 (Phenacetin). When mononitro-phenol, C 6 H 4 .NO 2 .OH, is 
 treated with reducing agents, the oxygen of NO 2 is replaced by hy- 
 drogen, and amino-phenol, C 6 H 4 .OH.NH 2 , is formed. The methyl 
 ether of this compound, C 6 H 4 .O(CH 3 ).NH 2 , is known as anisidin, 
 and the ethyl ether, C 6 H 4 .O(C 2 H 5 ).NH 2 , as phenetidin. By the 
 action of glacial acetic acid upon para-phenetidin, one hydrogen atom 
 in NH 2 is replaced by acetyl, C 2 H 3 O, when para-acetphenetidin is 
 formed. The compound is used as an antipyretic under the name 
 of phenacetin. 
 
 It is a colorless, odorless, tasteless powder, sparingly soluble in 
 water, readily soluble in alcohol; it fuses at 135 C. (275 F.). 
 Fresh chlorine water colors a hot aqueous solution first violet, then 
 ruby-red. The same color is obtained by boiling 0.1 gramme of 
 phenacetin with 1 c.c. of hydrochloric acid for one minute, diluting 
 with 10 c.c. of water, filtering when cold, and adding 3 drops of 
 solution of chromic acid. 
 
 Acetphenetidin is the best-known one of a large number of derivatives of 
 para-aminophenol, known as the phenetidin series. These derivatives, as well 
 an acetphenetidin itself, are contained in many migraine and headache powders. 
 Lactophenin is lactyl-para-phenetidin, C 2 H 5 OC 6 H 4 NH.COCH(OH)CH 3 , a diffi- 
 cultly soluble white powder. Sal-ophen, saliphen, phenocoll, salocoll, etc., are 
 similar derivatives. 
 
 Trinitro-phenol, C 6 H 2 (NO,) 3 OH (Picric acid, Carbazotic acid). 
 This substance is formed by the action of nitric acid on various mat- 
 ters (silk, wool, indigo, Peruvian balsam, etc.), and is manufactured 
 on a large scale by slowly dropping phenol into fuming nitric acid. 
 Picric acid forms yellow crystals which are sparingly soluble in 
 water ; it has a very bitter taste, strongly poisonous properties, and 
 is used as a yellow dye for silk and wool and as a reagent for albumin. 
 While phenol has but slight acid properties, picric acid behaves like 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 573 
 
 a strong acid, forming salts known as picratcs, most of which an- 
 explosives. 
 
 Phenolsulphonic acid, C 6 H 4 (OH)SO 3 H (Sulphocarbolic acid). 
 There are three varieties of this acid, namely, ortho, meta, and para. 
 The ortho and para acid are most easily obtained. When pure phenol 
 is mixed with an equal weight of sulphuric acid in the cold, only the 
 ortho acid is formed : 
 
 C 6 H 5 OH + H 2 S0 4 : C 6 H 4 (OH)S0 3 H + H 2 O. 
 
 At 100 C. (212 F.) only the para acid results. Both varieties form 
 clear solutions with water, but differ from each other in the character 
 of their salts, both as regards solubility and form of the crystals. 
 They are monobasic acids. 
 
 Ortho-phenohulphonic acid (Sozolic acid, Aseptol) occurs on the 
 market as a 33 per cent, solution. It is a syrupy liquid, having a 
 reddish color and a feeble odor. It is used as an antiseptic. 
 
 Sodium phenolsulphonate, Sodii phenolsulphonas (Sodium sulpho- 
 carbolate), C 6 H 4 (OH)SO 3 Na -f 2H 2 O, and Zinc phenolsulphonate, Zinci 
 phenolsulphonas (Zinc sulphocarbolate), (C 6 H 4 (OH)SO 3 ) 2 Zn -f- 8H 2 O, 
 are official salts of para-phenolsulphonic acid. They are obtained by 
 precipitating a solution of barium para-phenolsulphonate by sodium 
 carbonate and zinc sulphate respectively, filtering off the precipitate 
 of barium carbonate or sulphate, and evaporating the filtrate to crys- 
 tallization. Both salts are readily soluble and have antiseptic and 
 astringent properties. 
 
 Sulphonic acid has been spoken of before, when it was shown that inercap- 
 tans are converted into compounds termed sulphonic acids. These acids may 
 be looked upon as derivatives of sulphurous acid, obtained from it by replace- 
 ment of hydrogen by radicals. The relation existing between carbonic and 
 sulphonic acids may be represented by the following formulas : 
 
 Carbonic acid, c CoH Sulphuric acid, SO 2\OH 
 
 Formic acid, CO \QH Sulphurous acid, SO *\OH 
 
 Acetic acid, CO \OH 3 Methyl -sulphonic acid, 
 
 Any compound CO^w Anv sulphonic acid, 
 
 carbonic acid, 
 
 According to this view, phenolsulphonic acid is represented by the formula, 
 
 so / Q>H 4 OH 
 5Ua \OH 
 
 Ichthyol, Sodium ichthyo-sulphonate, C.^H^Na-Pe. Ichthyol is the sodium or 
 ammonium salt of a complex sulphonic acid, obtained by the dry distillation 
 
574 CONSIDERATION OF CARBON COMPOUNDS. 
 
 of a bituminous mineral found in Tyrol. It is a brown, tar-like liquid, having 
 a disagreeable odor. 
 
 Cresol, C 7 H 7 OH==1O7.25. The official cresol is a mixture of the 
 three isomeric cresols, (C C H 4 .CH 3 .OH), or hydroxyl derivatives of 
 toluene, the ortho-, para-, and meta-cresol. The cresols bear the same 
 relation to toluene that phenol bears to benzene, and they resemble 
 phenol very closely in their properties. Cresol is a colorless or straw- 
 colored refractive liquid having a phenol-like odor. It is soluble in 
 60 parts of water, miscible with alcohol, ether, and glycerin in all 
 proportions. It boils at about 200 C. (392 F.). 
 
 Cresol is slightly soluble in water, hence it is often used in the form of emul- 
 sions, or dissolved with the aid of salts or of soap. Compound solution of cresol, 
 Liquor cresolis compositus, is a linseed-oil-soap solution of cresol, of 50 per cent, 
 strength. It is of much more definite composition than many commercial prep- 
 arations of similar nature. Lysol is about the same as the official solution. 
 The mixtures known as creolins usually contain impure cresol dissolved with 
 the aid of rosin soap. They usually form emulsions when diluted with water. 
 Solveol and solutol are solutions of cresol made with the aid of salts. Tri-cresol 
 (enterot) is said to contain 35 per cent, of ortho-cresol, 40 per cent, of meta-cresol, 
 and 25 per cent, of para-cresol, and is soluble to the extent of 2.2 to 2.55 per 
 cent, in water. A vast number of other similar solutions are on the market. It 
 is generally held that cresol is more toxic to bacteria than phenol is. Losophan 
 and europhen are iodine compounds of cresol. 
 
 Creosote, Creosotum. Two different preparations of this name 
 are sold in the market. One is coal-tar creosote and is chiefly an 
 impure carbolic acid. The official creosote is a liquid product of the 
 distillation of wood-tar, especially of beechwood-tar, which contains 
 sometimes as much as 25 per cent, of creosote ; it resembles carbolic 
 acid in many respects, especially in its antiseptic properties and its 
 action on the skin. It is a mixture of substances, but consists chiefly 
 of guaiacol, C 6 H 4 .OCH 3 .OH, and creosol, C 6 H 3 .CH 3 .OCH 3 .OH. 
 
 From carbolic acid beechwood creosote may be distinguished by 
 requiring as much as 150 parts of water for solution; by being 
 miscible with the official collodium in equal volumes without form- 
 ing a coagulum ; by not being solidified on cooling ; by not coloring 
 ferric chloride permanently ; and by its boiling-point, which rises 
 from 205 to 215 C. (401 to 419 F.). 
 
 Creosote carbonate (Creosotal] is a mixture of carbonic acid esters, anal- 
 ogous to guaiacol carbonate, prepared from creosote by passing a current of 
 carbonyl chloride into a solution of creosote in sodium hydroxide. It is a yel- 
 lowish, thick, clear, and transparent liquid, odorless, and has a bland oily taste. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 575 
 
 It is insoluble in water, but soluble in alcohol and in fixed oils. It is non-toxic 
 and non-irritant and is used as a substitute for creosote. 
 
 Guaiacol, C 6 H 4 .OH.OCH ;{ = 123.13, found in beechwood creosote to the 
 extent of from 60 to 90 per cent., is a derivative of the diatomic phenol catechol 
 (pyrocatechin), C 6 H 4 (OH) 2 , obtained from it by replacing a hydroxyl hydrogen 
 atom by methyl, CH 3 . Guaiacol is consequently monomethyl catechol. It is 
 a colorless, crystalline solid, melting at 28.5 C. (83.5 F.), or a colorless re- 
 fractive liquid, boiling at 205 C. (401 F.), and possessing a strong aromatic 
 odor. It is difficultly soluble in water, easily soluble in alcohol and ether. In 
 alcoholic solution ferric chloride produces an immediate blue color, changing 
 to emerald green, later to yellowish. It is obtained either synthetically or 
 from creosote. 
 
 Veratrol, C 6 H 4 (OCH 3 ) 2 , the dimethyl ether of catechol, is a colorless, 
 aromatic, oily liquid, having the same boiling-point as guaiacol. 
 
 A number of derivatives of guaiacol are in the market, being chiefly com- 
 pounds with acid radicals, such as the camphorate (guaiacamphol), carbonate, 
 benzoate (benzosol], cinnamate (styracot), phosphate, phosphite, salicylate 
 (guaiacol-salol), valerate (geosote), etc., one of which is official, namely, 
 
 Guaiacol carbonate, Guaiacolis carbonas, (C 7 H 7 O),.CO 3 , is prepared by satu- 
 rating guaiacol with sodium hydroxide, and treating this compound with car- 
 bonyl chloride, COC1 2 . It is a white crystalline powder, insoluble in water, 
 sparingly soluble in alcohol, soluble in ether and chloroform. 
 
 Creosol, C 6 H 3 .CH 3 .OH.OCH 3 , the second constituent of creosote, is the next 
 homologue to guaiacol i. e., the methyl-ether of dioxytoluene. 
 
 Eugenol, C 6 H 3 (OH)(OCH 3 ).C 3 H 5 . 4 : 3 : 1 = 162.86, is an unsaturated 
 aromatic phenol obtained from oil of cloves and other sources. It is a color- 
 less > or a pale yellow liquid, having a strongly aromatic odor of cloves. 
 
 Safrol, Safrolum, C 6 H 3 .C 3 H 5 .OOCH 2 , 1:3:4 = 180.86 (Shikimol, Allyl- 
 pyrocatcchol methylene ether), is found in oil of sassafras, oil of camphor, and 
 other volatile oils. It is a colorless liquid with a sassafras-like odor. 
 
 Thymol, C 10 H U O or C G H 3 .CH 3 .C 3 H 7 .OH 149.66 (Mdhyl-isopro- 
 pylphenol). Thymol is found in small quantities as a constituent of 
 the volatile oils of wild thyme, horse-mint, and a few other plants. 
 
 Thymol crystallizes in large translucent plates, has a mild odor, a warm, 
 pungent taste, melts at 50 C. (122 F.) and boils at 230 C. (446 F., It is now 
 largely used as an excellent and very valuable antiseptic, preference being 
 given to it on account of its comparative harmlessness when compared with 
 the strongly poisonous carbolic acid. 
 
 Thymol dissolved in moderately concentrated warm solution of potassium 
 hydroxide, gives on the addition of a few drops of chloroform a violet color, 
 which on heating soon changes into a beautiful violet-red. 
 
 Thymol iodide, Thymolis iodidum, (C 6 H,.CH 3 .C 3 H 7 .OI) 2 = 545.76 (Di- 
 
 thymol-diiodide, Aristol, Annidalin}. Obtained by the action of a solution of 
 
576 CONSIDERATION OF CARBON COMPOUNDS. 
 
 iodine in potassium iodide upon an alkaline solution of thymol. Condensation 
 of two molecules of thymol takes place with the introduction of two atoms of 
 iodine into its phenolic group. It is a bright, chocolate-colored, or reddish- 
 yellow, bulky powder, with a very slight aromatic odor; it contains 46.14 per 
 cent, of iodine and is used as a substitute for iodoform. 
 
 Resorcinol, C G H 4 (OH) 2 . 1:3 = 1O9.22 (Resorcin 9 Meta-dihydroxy- 
 benzene). It is formed by fusing different resins, such as galbanum, 
 asafoetida, etc., with caustic alkalies, but it is now made almost alto- 
 gether from benzene by heating the latter with fuming sulphuric acid 
 to 257 C., whereby benzene-meta-disulphonic acid, C 6 H 4 (SO 3 H) 2 , 
 is produced. The sodium salt of this acid is fused with sodium 
 hydroxide for several hours, forming sodium resorcin, C 6 H 4 (ONa) 2 . 
 The mass is dissolved in water, acidified, and extracted with ether, 
 which dissolves out the resorcin. This is further purified by sub- 
 limation and recrystallization. 
 
 Resorcinol is a white, or faintly-reddish, crystalline powder, having a some- 
 what sweetish taste and a slightly aromatic odor; it fuses at 119 C. (246 F.), 
 boils at 276 C. (529 F.), and is soluble in less than its own weight of water. 
 A dilute solution gives with ferrric chloride a bluish-violet color. Resorcinol, 
 when heated for a few minutes with phthalic acid in a test-tube, forms a yel- 
 lowish-red mass, which, when added to a dilute solution of caustic soda, forms 
 a highly fluorescent solution. Other fluorescent compounds are obtained by 
 heating resorcinol with very little sulphuric and either citric, oxalic, or tar- 
 taric acid, dissolving in a mixture of water and alcohol and supersaturating 
 the solution with ammonia. Resorcinol is largely used in the manufacture of 
 certain dyes. It must not be confused with the proprietary preparation of the 
 same name, composed of equal parts of resorcin and iodoform fused together. 
 
 Quinol, C 6 H 4 (OH) 2 .1 : 4 (Hydroquinone, Para-dihydrozy-benzene), is formed 
 by dry distillation of quinic acid (from Peruvian bark), by reduction of 
 quinone, and by fusing para-iodophenol with sodium hydroxide. It occurs 
 combined with sugar as the glucoside arbutin, in uva ursi (Bear-berry) leaves. 
 It forms small plates or hexagonal prisms, melting at 169 C., easily soluble in 
 hot water, alcohol, and ether. Oxidizing agents, such as ferric chloride, chlo- 
 rine, etc., convert it into quinone, C 6 H 4 O 2 . It is used as a developer in pho- 
 tography. 
 
 Solution of lead acetate gives a white precipitate with pyrocatechol, none 
 with resorcinol, and a precipitate only in the presence of ammonia with 
 hydroquinol. 
 
 Pyrogallol, Pyrogallic acid, C 6 H 3 .(OH) 3 . When gallic acid is 
 heated to 200 C. (392 F.) it is decomposed into carbon dioxide and 
 pyrogallol, a substance which is not a true acid, but a tri-hydroxy- 
 benzene i. e., a phenol. Pyrogallol crystallizes in colorless needles, 
 melts at 131 C. (268 F.), is easy soluble in water, ether, and alco- 
 hol. In alkaline solution it absorbs oxygen rapidly, assuming a red, 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 577 
 
 then reddish-brown and dark-brown color. Nitric acid also colors it 
 yellow, then brown, and this property is made use of in testing for 
 traces of nitric acid. Solutions of silver, gold, and mercury are 
 reduced by pyrogallol even in the cold. 
 
 Gallacetophenone or Gallactophenone, ^^< 3 obtained by 
 
 heating a mixture of pyrogallol, zinc chloride, and glacial acetic acid to 148 
 C. It is a crystalline powder of dirty flesh-color, soluble in water, introduced 
 to replace pyrogallol, which is poisonous. 
 
 Phloroglucinol, C 6 H 3 (OH) 3 . 1:3:5 (Phloroglucin, Symmetrical trihy- 
 droxy-benzene), results when resorcin and several resins, as gamboge, dragon's 
 blood, etc., are fused with potassium hydroxide. It forms colorless prisms, 
 melting at 218 C., very soluble in water and alcohol, and of a sweet taste. It 
 stains lignin red and, together with vanillin, is used to detect hydrochloric acid 
 in stomach contents. 
 
 Hydroxy-hydroquinone, C 6 H 3 (OH) 3 . 1 : 2 : 4, is the third trihydroxy- 
 benzene. It is an interesting fact that according to the theory as to the struc- 
 ture of the benzene molecule, three isomeric dihydroxy-benzenes and trihy- 
 droxy-benzenes should exist, and in each case three actually do exist. 
 
 Most of the phenols give colors with ferric chloride solution, and are acted 
 on by the oxygen of the air with formation of colored bodies. They are un- 
 stable toward oxidizing agents, forming in many cases carbon dioxide. The 
 di- and trihydroxyl derivatives are less stable than the simple phenols. The 
 same is true also of hydroxy acids of benzene, for example, salicylic and gallic 
 acids. 
 
 Aromatic alcohols and aldehydes. 
 
 Aromatic alcohols. These are aromatic derivatives of the fatty alcohols 
 i e., alcohols in which hydrogen of the fatty hydrocarbon residue is replaced by 
 a benzene derivative. The aromatic alcohols have the properties of true fatty 
 alcohols. 
 
 Benzyl alcohol, CJJ^CH V OH, is the simplest member of the class; it is 
 
 isomeric with cresol, C 6 H 4 <Q^ 3 , but has entirely different properties. Benzyl 
 
 alcohol is found in balsam of Peru and Tolu, mostly in combination with ben- 
 zoic or cinnamic acid. 
 
 Aromatic aldehydes. These are aromatic derivatives of the fatty alde- 
 hydes and behave in all respects like the latter ; thus they combine readily 
 with oxygen to form acids and behave generally like unsaturated compounds. 
 
 Benzaldehyde, Benzaldehydum, C 6 H 5 .COH = 1O5.25. This is 
 the simplest one of the aromatic aldehydes, and is produced artificially 
 or obtained from natural oil of bitter almonds or other oils. It is a 
 colorless, strongly refractive liquid, having a bitter-almond-like odor. 
 It is easily converted into benzoic acid by oxidation. 
 
 37 
 
578 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Oil of bitter almond, Oleum amyg-dalse amarse. Benzaldehyde 
 does not occur in a free state in nature, but is formed by a peculiar 
 fermentation of a glucoside, amygdalin, existing in bitter almonds, in 
 cherry-laurel, and in the kernels of peaches, cherries, etc., but not in 
 sweet almonds. The ferment causing the decomposition of amygdalin 
 is a substance termed emulsin, which is found in both bitter and 
 sweet almonds. As water is required for the decomposition, the 
 emulsin does not act upon the amygdalin contained in the same seed 
 until water is added, when the decomposition takes place as follows ; 
 
 C 20 H 27 NO n + 2H 2 = 2C 6 H 12 6 -f HCN + C 7 H 6 O. 
 Amygdalin. Water. Glucose. Hydrocyanic Benzaldehyde. 
 
 acid. 
 
 The oil is obtained by maceration of bitter almonds with water, 
 and subsequent distillation when it distils over with hydrocyanic 
 acid and steam, and separates as a heavy oil in the distillate. 
 
 It is an almost colorless, thin liquid of a characteristic aromatic 
 odor, a bitter and burning taste, and a neutral reaction. Pure benz- 
 aldehyde is not poisonous, but the oil of bitter almond is poisonous 
 on account of its containing hydrocyanic acid. 
 
 Sitter-almond water, Aqua amygdalae amarce, is made by dissolving 
 1 part of the oil in 999 parts of water. 
 
 Cinnamic aldehyde, Cinnaldehydum, C 6 H 5 .CH : CH.COH = 131.07 (Arti- 
 ficial oil of cinnamon, Cinnamyl aldehyde, Phenyl acrolein}. This aldehyde is 
 prepared synthetically, or is obtained from oil of cinnamon by extracting with 
 acid sodium sulphite. Cinnamic aldehyde is a colorless oil, having a cinna- 
 mon-like odor and a burning, aromatic taste. When exposed to the air it is 
 oxidized to cinnarnic acid. 
 
 Vanillin, Vanillhmm, C 6 H 3 .OH.OCH 3 .COH. 4:3:1 = 150.92 (Methylpro- 
 tocatechuic aldehyde}. Vanillin is the active constituent in vanilla bean, and is 
 made artificially in a variety of ways. One of these is the action of chloroform 
 and caustic potash on guaiacol. It occurs in white, crystalline needles, having 
 the odor and taste of vanilla, and melting at 80 to 81 C. It is soluble in 100 
 parts of cold and 15 parts of warm water, easily soluble in alcohol, ether, 
 chloroform, and dilute alkalies. It is extracted completely from its solution in 
 ether by shaking with a saturated aqueous solution of sodium bisulphite, from 
 which it may be precipitated by sulphuric acid ; it is also extracted by ammo- 
 nia water. 
 
 ,0 CO 
 
 Ooumarin, C 6 H,( the anhydride of ortho-hydroxy-cinnamic 
 
 X CH=CH, 
 
 acid, is found in the Tonka bean and resembles vanillin in odor. It forms 
 white, shining prisms, melting at 67 C., and soluble in 400 parts of cold, 45 
 parts of hot water, and in 7.5 parts of alcohol ; easily soluble in ether. 
 
 An aqueous solution of vanillin is turned blue by a few drops of ferric chlo- 
 ride solution, coumarin is not. An aqueous solution of coumarin, unlike va- 
 
BENZESE SERIES. AROMATIC COMPOUNDS. 579 
 
 nillin, forms a precipitate when iodine in potassium iodide is added in excess, 
 at first brown and flocculent, and afterward, on shaking, forming a dark-green 
 curdy clot. 
 
 " Extracts of vanilla," made not from the vanilla bean, but consisting of 
 alcoholic tinctures of synthetic vanillin or coumarin, can readily be detected by 
 evaporating off the alcohol, making up the original volume with water, and 
 acidifying with acetic acid. A reddish-brown precipitate of resin is formed in 
 the case of a true extract, but none in the artificial. The filtrate from this 
 resin gives a copious precipitate with basic lead acetate solution, the artificial 
 extract gives none. 
 
 Vanillin has been found adulterated with benzoic acid, acetanilide, boric 
 acid, terpin hydrate, and coumarin. 
 
 Acids of the benzene series. 
 
 These are derivatives in which one or more carboxyl groups 
 (COOH ) have replaced hydrogen in the benzene molecule. Benzoic 
 acid is the simplest, and bears the same relation to benzene as acetic 
 acid bears to methane. Many of these acids are found as natural 
 products, but the carboxyl group may be introduced by various reac- 
 tions, of which the following are the principal ones : 
 
 1. Oxidation of benzene compounds containing fatty hydrocarbon 
 radicals or substituted radicals : 
 
 C 6 H 5 CH 2 OH + 20 = C 6 H 5 COOH + H 2 O. 
 
 2. Hydrolysis of a cyanide by heating with dilute acid : 
 
 C 6 H 5 CN + 2H 2 O = C 6 H 5 COOH + NH 3 . 
 
 3. The treatment of alkali salts of phenols with carbon dioxide 
 (see Salicylic Acid). 
 
 Benzoic acid, Acidum benzoicum, HC 7 H 5 O 2 or C 6 H 5 CO 2 H = 
 121.13. Found in benzoin and some other resins; also in combination 
 with other substances in the urine of herbivorous animals; it is 
 obtained from benzoin by heating it carefully, when the volatile 
 benzoic acid sublimes. It is now also manufactured from toluene, 
 which is first converted into benzo-trichloride (trichlormethyl-ben- 
 zene) by passing chlorine into hot toluene : 
 
 C 6 H 6 CH S + 6d == C 6 H 5 CC1 3 + 3HC1. 
 
 Benzo-trichloride, when treated with water under pressure, yields 
 benzoic and hydrochloric acids, thus: 
 
 C 6 H 5 CC1 3 + 2H 2 : : C 6 H 5 C0 2 H + 3HC1. 
 
 Benzoic acid forms white, lustrous scales or friable needles, which 
 are but slightly soluble in cold water, but easily soluble in alcohol. 
 
580 CONSIDERATION OF CARBON COMPOUNDS. 
 
 ether, oils, etc. Shaken in solution with hydrogen dioxide, benzoic 
 acid is converted into salicylic acid. 
 
 Benzoic acid, prepared by sublimation from gum benzoin, has a 
 slight aromatic odor resembling that of benzoin ; the acid obtained 
 synthetically is odorless. 
 
 Benzoic acid, when neutralized with an alkali, gives a flesh-colored 
 or reddish precipitate of ferric benzoate on the addition of a neutral 
 solution of ferric chloride. 
 
 By neutralizing benzoic acid with either ammonium hydroxide, 
 sodium hydroxide, or lithium carbonate, the official salts ammonium 
 benzoate, NH 4 C 7 H 5 O 2 , sodium benzoate, NaC 7 H 5 O 2 .H 2 O, and lithium 
 benzoate, LiC 7 H 5 O 2 , are obtained. The three salts are white, soluble 
 in water, and have a slight odor of benzoin. 
 
 Benzoic acid and its derivatives, taken internally, are eliminated in the 
 urine as hippuric acid, C 6 H 5 CO.NH.CH 2 COOH (benzoyl-amino-acetic acid), 
 and its derivatives. 
 
 Many halogen, nitro- and amino-benzoic acids exist which are interesting 
 in pure and technical chemistry. 
 
 Ethyl para-amino-benzoate, C 6 H 4 (NH 2 )(COOC 2 H 5 ) (Anesthesiri), is a 
 local anesthetic, introduced as a substitute for cocaine. It is a white, odorless, 
 tasteless powder, melting at 90 to 91 C., almost insoluble in cold and diffi- 
 cultly soluble in hot water. It is soluble in 6 parts of alcohol. When placed 
 on the tongue it produces a sensation of numbness. 
 
 Benzoyl chloride, C 6 H 5 .COC1, is obtained by distilling benzoic acid with 
 phosphorus pentachloride. It is a colorless, irritating oil, boiling at 200 C., 
 slowly decomposed by cold water, but more stable than acetyl chloride. It 
 acts on hydroxyl compounds, forming benzoic acid esters, thus : 
 
 C 6 H 5 .COC1 + C 6 H 5 OH C 6 H 5 COOC 6 H 5 + HC1. 
 
 Phenyl benzoate. 
 
 This process of introducing the benzoyl radical is known as " benzoylation." It 
 is greatly facilitated when carried out in the presence of alkali. 
 
 Benzosulphinide, Saccharin, Benzosulphinidum, C 6 H 4 .CO.SO 2 .- 
 NH = 181.77 (Anhydro-ortho-sulphamide-benzoic acid, Benzoyl sul- 
 pJionic-imide). This substance is a derivative of benzoic acid, 
 C 6 H 5 .CO 2 H, obtained by the discoverers from toluene by the trans- 
 formations indicated in the following formulas : 
 
 CH 3 
 
 ,CH 3 /COOH /CO, 
 
 C.H / __> C.H/ _> C 6 H / >NH. 
 
 -\so a jra, NSCVNH, Nao/ 
 
 Other methods of preparing saccharin have been devised. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 581 
 
 Saccharin is a white, crystalline, odorless powder. It is but sparingly 
 soluble in water, requiring about 250 parts for solution ; this solution is 
 slightly acid and has an extremely sweet taste, which is yet perceptible when 
 saccharin is dissolved in 125,000 parts of water, which shows that it is about 
 500 times sweeter than cane-sugar, a solution of which in 250 parts of water is 
 yet perceptibly sweet. Saccharin is soluble in alcohol and ether, and it is this 
 latter property which is made use of in testing sugar (or other substances in- 
 soluble in ether) for saccharin. The substances are treated with ether, which 
 is filtered off and evaporated, when the saccharin may be recognized by its 
 taste in the residue. 
 
 Saccharin forms very soluble and well-crystallizing salts with the alkalies, 
 which are also intensely sweet ; they are articles of commerce. The sodium 
 salt is known as soluble saccharin or krystallose. Saccharin is known in the 
 British Pharmacopoeia as Glusidum (Gluside), and in commerce as glucusimide, 
 saccharol, saccharinol, saccharinose, agucarine, etc. A number of preparations, 
 such as antidiabetin, contain saccharin. Dulcin or sucrol, another very sweet 
 substance, is para-phenetol-carbamide. 
 
 Phthalic acid, C 6 H 4 QQg Of the aromatic polybasic 
 
 acids, the dibasic acids are the most important. They are called 
 phthalic acids in allusion to the fact that one of them can be obtained 
 from naphthalene. Theoretically, three dibasic acids are possible and 
 all are known. When mixed with lime and distilled they yield 
 benzene. 
 
 Phthalic acid can be obtained by the oxidation of derivatives of 
 benzene containing two side-chain hydrocarbons in the ortho-position, 
 but it is manufactured by oxidizing naphthalene by hot fuming sul- 
 phuric acid with the help of a catalytic agent, as mercury. The sul- 
 phuric acid loses oxygen to the naphthalene and forms sulphur diox- 
 ide, which escapes in great quantities. Enormous quantities of phthalic 
 acid are employed in the manufacture of synthetic indigo. It is a 
 crystalline white substance, readily soluble in hot water, alcohol, and 
 ether. When heated it decomposes, yielding water and phthalic 
 anhydride, which latter sublimes in long needles : 
 
 Phthalic anhydride. 
 
 Iso-phthalic acid (Meta-phthalic acid), C 6 H 4 (COOH) 2 1 : 3, may be obtained by 
 oxidizing benzene derivatives containing two side-chains in the meta-position, 
 and from rosin by oxidation with nitric acid. It is difficultly soluble in water 
 and does not give an anhydride when heated. 
 
 Terephthalic acid (Para-phthalic acid), C 6 H 4 (COOH). 2 l : 4, can be formed by 
 
582 CONSIDERATION OF CARBON COMPOUNDS. 
 
 oxidation of turpentine and in other ways. It is nearly insoluble in water, 
 alcohol, and ether, and does not yield an anhydride. 
 
 Phenolphthalein. When phthalic anhydride is heated with phenols 
 and concentrated sulphuric acid, a class of substances is obtained 
 known as phthaleins. The simplest of these is phenolphthalein, the 
 composition of which is shown in the following reaction : 
 
 C6Hl \co >0 + 2C6H5 - OH = C 
 
 Phthalic anhydride. Phenol. Phenolphthalein. 
 
 It occurs as a creamy-white powder or crystals, soluble in 600 parts 
 of water and in 10 parts of alcohol. It dissolves in alkaline solu- 
 tions with a beautiful red color, and is used as a sensitive indicator in 
 acidimetry and alkalimetry. Acids destroy the red color by reform- 
 ing the colorless phenolphthalein from its salts. Taken internally, it 
 acts as a purgative, but appears to possess no further physiological 
 action. For adults the average dose is 0.1 to 0.2 Gm., given as 
 powder, in cachets, capsules, or pills. In obstinate cases 0.5 Gm. 
 doses may be given. 
 
 Resordnolphthalein or fluorescein is obtained by heating phthalic anhydride 
 and resorcinol at 210 C. with zinc chloride as a dehydrating agent. It is a 
 reddish-brown substance which exhibits an intense yellowish-green fluores- 
 cence in an alkaline solution, hence its name. By treatment with bromine it 
 forms tetrabromfluorescein, the potassium salt of which is the dye known as 
 eosin, C 20 H 6 O 5 Br 4 K 2 . This is a valuable stain for animal and plant tissues. In 
 dilute solution it shows a beautiful rose tint. 
 
 Phenolsulphonephthalein, C 6 H 4 ^gQX) . This substance is anal- 
 
 ogous to phenolphthalein, and may be obtained in a similar manner 
 by heating together phenol and the anhydride of orthosulphobenzoic acid, 
 
 C H / CO \ 
 6 4 \cjn /^> which is analogous to the anhydride of phthalic acid. The 
 
 source of the anhydride of sulphobenzoic acid is saccharin. 
 
 Phenolsulphonephthalein is a red or brownish-red powder, soluble in alcohol, 
 but not in ether. It is slightly soluble in cold water, giving a deep yellow 
 color to the solution, but readily soluble in alkalies, the mono-sodium salt 
 having a bordeaux red color, while with excess of alkali the solution has a 
 beautiful purple color similar to that of phenolphthalein in alkaline solution. 
 It is used as a diagnostic test of renal efficiency by injecting 6 Mgm. in the 
 form of the mono-sodium salt. The test depends upon the fact that normal 
 kidneys excrete 40 to 60 per cent, of the dose during the first hour after its 
 first appearance in the urine, whereas kidneys not functioning properly 
 excrete a much smaller per cent. The readings are made by means of a 
 colorimeter. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 583 
 
 Hydroxy-acids of the benzene series. 
 
 These derivatives, which are known also as phenol-acids, contain 
 the (OH) and (COOH) groups in the benzene nucleus, and accord- 
 ingly possess the properties of phenols and acids. The hydrogen of 
 the (OH) group as well as that of the (COOH) group can be replaced 
 by a metal or hydrocarbon radical. The radical introduced into the 
 (COOH) group is easily removed by saponification, as in the case of 
 any ethereal salt, whereas that introduced into the (OH) group is not. 
 
 The simplest hydroxy-acids are those containing one (OH) group 
 and one (COOH) group. There are three such acids, namely, ortho-, 
 meta-, and para-hydroxy-benzoic acid. Of these, the ortho acid, 
 known better as salicylic acid, is the most important. 
 
 Salicylic acid, Acidum salicylicum, HC 7 H 5 O 3 or C 6 H 4 OH.CO 2 H 
 = 137. Derived from benzene by introducing one hydroxyl and 
 one carboxyl radical. It is found in several species of violet, and in 
 the form of methyl salicylate in the wintergreen oil (oil of Gaul- 
 theria procumbens). May be obtained by fusing potassium hydroxide 
 with salicin. 
 
 Nearly all salicylic acid used medicinally or otherwise is obtained by syn- 
 thesis. The first step is the conversion of phenol into sodium pheiiolate by 
 treatment with sodium hydroxide, thus : 
 
 C 6 H 5 OH + NaOH = C 6 H 5 ONa + H 2 O. 
 
 Sodium phenolate is next dried and treated with carbon dioxide, when direct 
 combination takes place and sodium phenol carbonate is formed, thus : 
 
 C 6 H 5 ONa + C0 2 -a NaC 6 H 5 C0 3 . 
 
 Sodium Sodium phenol 
 
 phenolate. carbonate. 
 
 Sodium phenol carbonate is isomeric with sodium salicylate and is actually 
 converted into the latter compound by being heated to 130 C. (266 F.), in 
 tightly closed vessels, or in vessels through which carbon dioxide passes. 
 
 Salicylic acid is a white, solid, odorless substance, having a sweet- 
 ish, slightly acrid taste, and an acid reaction ; it is soluble in 308 parts 
 of water and in 2 parts of alcohol ; it fuses at about 157 C. (315 F.), 
 and sublimes slowly at 100 C. (212 F.) and rapidly at 140 C. 
 (281 F.). It is a valuable antiseptic. 
 
 By the action of the alkali hydroxides on salicylic acid, the various 
 salts may be obtained, as, for instance, sodium salicylate, NaC 7 H 5 O 3 , 
 ammonium salicylate, NH 4 C 7 H 5 O 3 > and lithium salicylate, LiC 7 H 5 O 3 > 
 
584 CONSIDERATION OF CARBON COMPOUNDS. 
 
 all of which are official. They are white salts, readily soluble in 
 water. In the presence of free alkali, the solutions absorb oxygen 
 from the air and become colored. Solutions of salicylates are incom- 
 patible with acids, salicylic acid being precipitated. 
 
 Bismuth subsalicylate is official and has approximately the com- 
 position, C 6 H 4 (OH)CO 2 BiO. It is a white, amorphous or crystalline, 
 odorless and tasteless powder, permanent in the air, and almost insol- 
 uble in water. Alcohol or ether extracts salicylic acid, with decom- 
 position of the salt. 
 
 Strontium salicylate, (C 6 H 4 (OH)CO 2 ) 2 Sr + 2H 2 O, which is official, 
 is a white crystalline powder, odorless, and having a sweetish saline 
 taste. It is soluble in 18 parts of water and 66 parts of alcohol. It 
 is incompatible with ferric salts, mineral acids, quinine salts in solu- 
 tion, spirit of nitrous ether, sulphates and carbonates, and sodium 
 phosphate in powder. 
 
 Mercuric salicylate, C&H^QQ /Hg, is prepared by heating on a water- 
 bath 21.5 parts of yellow mercuric oxide, 15 parts of salicylic acid, and a little 
 water until the mixture is perfectly white. It occurs as a white, amorphous 
 powder, tasteless, and neutral to litmus paper, slightly soluble in water or alco- 
 hol, but soluble in solutions of sodium hydroxide and sodium carbonate, form- 
 ing a double salt. It is soluble also in warm solutions of chlorides, bromides, 
 and iodides. It is used as a disinfectant, and as a remedy in syphilis and in 
 certain skin diseases. 
 
 Analytical reactions. 
 
 1. Add to solution of salicylic acid or its salts ferric chloride: a 
 reddish-violet color is produced, yet noticeable in solutions containing 
 1 part of salicylic acid in 500,000 parts of water. 
 
 2. Add some cupric sulphate : a bright green color will result. 
 
 3. Dissolve some salicylic acid or sodium salicylate in methyl alco- 
 hol and add one-fourth the volume of sulphuric acid. Heat gently 
 and set aside for a few minutes. On reheating, the odor of methyl 
 salicylate is developed. 
 
 Aspirin, C6H 4 .0(CH 3 CO)COOH (Acetyl-salicylic acid ), is obtained by the 
 prolonged action of acetic anhydride on salicylic acid at about 150 C. It forms 
 colorless needles, melting at 135 C., odorless, and of an acidulous taste, solu- 
 ble in 100 parts of water and freely in alcohol or ether. Boiling water or 
 alkalies decompose it, liberating acetic acid. 
 
 Salicin, C 13 H 18 7 . This glucoside is found in several species of Salix (wil- 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 585 
 
 low), and is mentioned here because it splits into glucose and salicylic alcohol, 
 C 6 H 4 .OH.CH 2 OH, when boiled with dilute acids: 
 
 C 13 H 18 7 + H 2 = C 6 H 12 6 + C,H 8 O r 
 
 Salicylic alcohol is converted by chromic acid into salicylic aldehyde, C 6 H< 
 OH.COH, which by further oxidation is converted into salicylic acid. 
 
 Salicin forms white, silky, shining needles, which are soluble in less than an 
 equal weight of water, have a neutral reaction and a very bitter taste. 
 
 Salicin sprinkled upon concentrated sulphuric acid produces a red color. 
 Boiled with very dilute hydrochloric acid for a few minutes, and this solution 
 nearly neutralized with sodium carbonate, a violet color is produced on the 
 addition of a drop of ferric chloride solution. 
 
 Methyl salicylate, Methylis salicylas, CH 3 ,C 7 H 5 3 or C 6 H 4 (OH)COOCH S 
 
 1 ". 2 = 150.92. Oil of wintergreen is chiefly methyl salicylate, a nearly color- 
 less liquid with a characteristic, strongly aromatic odor. It is made by the 
 method so extensively used in the manufacture of esters, viz., by heating of 
 salicylic acid with methyl alcohol in the presence of sulphuric acid. (See 
 above reaction 3 of salicylic acid, ) It is also found in many other volatile oils, 
 especially in oil of betula 
 
 Phenyl salicylate, Salol, Phenylis salicylas, C 6 H 5 .C 7 H 5 O 3 or 
 C 6 H 4 (OH)COOC 6 H 5 1:2 = 212.47. This ester is a white, crystalline, 
 almost tasteless powder, which is nearly insoluble in water, readily 
 soluble in alcohol, ether, and benzol, and fuses at 42 C. (107.4 F.). 
 It is used as an antiseptic and antipyretic. 
 
 Salol heated with potassium hydroxide solution causes its decom- 
 position into phenol, which can be recognized by its odor, and potas- 
 sium salicylate, from which crystalline salicylic acid will separate 
 upon supersaturating the liquid with hydrochloric acid. An excess 
 of bromine-water produces a white precipitate in an alcoholic solution 
 of salol. 
 
 Salol is made by the action of suitable dehydrating agents upon a 
 mixture of phenol and salicylic acid : 
 
 C 6 H 5 OH -f HC 7 H 5 3 = C 6 H 5 .C 7 H 5 3 + H 2 O. 
 
 A more simple method for its manufacture consists in the heating 
 of salicylic acid between 220 and 230 C. (428 and 446 F.) in an 
 atmosphere of carbon dioxide, in a flask with a long, narrow neck. 
 The reaction is this : 
 
 Anisic acid, O 6 H 4 <j^| (Para-methoxy-benzoic acid), is isomeric with 
 methyl salicylate, but, unlike the latter, it is not saponified when heated with 
 
586 CONSIDERATION OF CARBON COMPOUNDS. 
 
 alkalies. This is due to the fact that the methyl group is combined as in an 
 ether. The ether groups, as OCH 3 , OC 2 H 5 , OC 6 H 5 , etc., are often called methoxy, 
 ethoxy, phenoxy, etc. Anisic acid is formed by the oxidation of anethol, 
 
 OOH 
 
 3 , an ether contained in oil of anise. 
 
 Gallic acid, Acidum gallicum, HC 7 H 5 O 5 -f H 2 O or C 6 H 2 (OH) 3 .- 
 CO 2 H + H 2 O = 186.65. Obtained by exposing moistened nut-galls 
 to the air for about six weeks, when a peculiar fermentation takes 
 place, during which taimic acid is converted into gallic acid, which 
 is purified by crystallization. The crystals contain one molecule of 
 water, which may be expelled at 100 C. (212 F.). It is a white, 
 solid substance, forming long, silky needles ; it has an astringent and 
 slightly acidulous taste and an acid reaction ; it is soluble in about 
 100 parts of cold or in 3 parts of boiling water, also readily soluble 
 in alcohol, but sparingly in ether and chloroform ; it gives a bluish- 
 black precipitate with ferric salts, and does not coagulate albumin, 
 nor precipitate alkaloids, gelatin, or starch (difference from tannic 
 acid). A piece of potassium cyanide added to solution of gallic acid 
 produces a deep rose-color. 
 
 Bismuth subgallate, a salt which is somewhat variable in composition, is 
 official. It is a yellow, amorphous, insoluble powder, known as Dermatol. 
 
 Tannic acid, Acidum tannicum, C 13 H 9 O 7 .COOH = 319.66 
 (Gallotannic acid, Digallic acid). There are a number of tannic 
 acids, or tannins, found in various parts of different plants (oak-bark, 
 nut-galls, cinchona, coffee, tea, etc.), the properties of which are not 
 quite identical. All tannins, however, are amorphous, have a faint 
 acid reaction and strongly astringent properties; they all precipitate 
 albumin and most of the alkaloids ; they give with ferric salts a dark- 
 colored solution or precipitate, the color being dark green or dark 
 blue ; they form with animal substances compounds which do not 
 putrefy. Use is made of this property in the process of tanning 
 i. e., converting hides into leather. 
 
 The official or tannic acid is obtained by extracting nut-galls with 
 ether and alcohol, and evaporating the solution ; it forms light-yel- 
 lowish, amorphous scales, having a faint and characteristic odor, a 
 strongly astringent taste, and an acid reaction ; it is easily soluble in 
 water and diluted alcohol. 
 
 Analytical reactions : 
 
 1. To solution of tannic acid add ferric chloride: a blue-black pre- 
 cipitate falls, soluble in large excess of tannic acid with violet color 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 587 
 
 If ferric chloride is added in excess, the black precipitate dissolves in 
 it with green color. 
 
 2. Add a few drops of potassium hydroxide : a brown coloration 
 results. 
 
 3. To a dilute solution (1 in 100) of tannic acid add a small quan- 
 tity of lime-water. A pale bluish-white, flocculent precipitate is 
 formed, which is not dissolved on shaking (difference from gallic acid), 
 but becomes more copious and of a deeper blue than pinkish by the 
 addition of an excess of lime-water. 
 
 4. Tannic acid precipitates solutions of gelatin, albumin, gelatinized 
 starch, tartar emetic, and most of the alkaloids. 
 
 The Naphthalene series. 
 
 Naphthalene, Naphthalenum, C 10 H 8 = 127.10. The constitution 
 of all benzene derivatives considered so far may be explained by the 
 introduction of radicals in benzene. Naphthalene and its derivatives 
 must be assumed to be formed by the union of two benzene residues 
 in such a way that they have two carbon atoms in common, as repre- 
 sented in these formulas : 
 
 H H H OH 
 
 H \ C A C A C / H 
 
 <J <!! <" 
 
 P/*\0/ W \0/\H H/ H c / \c^ \H 
 
 j. i A 1 
 
 Naphthalene, Ci H 8 . Naphthol, Ci H T .OH. 
 
 Naphthalene has been mentioned as a product of the destructive distillation 
 of coal, and is obtained from that portion of coal-tar which boils between 180 
 and 220 C. (356 and 428 F.). This distillate is treated with caustic soda and 
 then with sulphuric acid and distilled with water vapor. 
 
 When pure, naphthalene forms colorless, lustrous crystalline plates, having 
 a penetrating, but not unpleasant, odor and a burning, aromatic taste. It fuses 
 at 80 C. (176 F.), and boils at 218 C. (424 F.), but volatilizes slowly at ordi- 
 nary temperature, and readily with water vapor. It is only sparingly soluble 
 in water, but easily soluble in alcohol, ether, chloroform, etc. Impure naph- 
 thalene assumes, when exposed to light, a reddish or brownish color. Naph- 
 thalene is converted into phthalic acid by oxidizing agents. 
 
 Derivatives of naphthalene. While benzene yields only one kind 
 of mono-substitution product, naphthalene yields two varieties in 
 every case. Thus, there are two mono-hydroxy derivatives (naph- 
 
588 CONSIDERATION OF CARBON COMPOUNDS. 
 
 thol), two mono-amino derivatives (naphthylamine), etc. This is 
 exactly what would be expected if the formula for naphthalene given 
 above be true. The 8 hydrogen atoms in the molecule fall into two 
 groups of 4 each, the atoms of each group bear the same relation to the 
 molecule, but different from the relation that the atoms of the other 
 group bear. This is shown in the following formulas, in which the 
 hydrogen atoms are designated in a manner that permits of reference 
 in the formulas for the derivatives of naphthalene : 
 
 Ha 3 Ha 8H HI 
 
 /3 3 H .a X Hj3 7H (X H2 
 
 \ c / \ c / 
 
 o 
 
 x^C s /G^ /C\ ^C\ 
 
 \H3 
 
 II II 
 
 Ha' 2 Ha 1 H 5 H 4 
 
 In the first formula, hydrogen atoms , a 1 , a 2 , a 3 are alike, and , 
 /5 1 , /5 2 , /5 s are alike, but bear a different relation from that of the a 
 hydrogen atoms. In the second formula, the corresponding groups 
 are 1, 4, 5, 8 and 2, 3, 6, 7. The mono-substitution products in which 
 the a hydrogen is replaced, are known as alpha- or a-derivatives, the 
 others as beta- or ^-derivatives. 
 
 Theoretically, the number of di- and tri-substitution products of 
 naphthalene is very large. Thus, ten di-chlor and fourteen tri-chlor 
 derivatives are possible, and all are known. Such facts as these leave 
 very little doubt as to the truth of the structural formula of naphtha- 
 lene as given above. 
 
 Naphthol, C 10 H 7 OH = 142.98. This monatomic phenol bears to 
 naphthalene the same relation as phenol to benzene /. <?., hydroxyl 
 replaces hydrogen in the respective hydrocarbons. Two isomeric 
 naphthols, the alpha- and beta-naphthol, are known, which differ in 
 their physical properties and in their physiological action. The 
 naphthol which is used medicinally is beta-naphthol, a solid compound 
 crystallizing in thin, shining plates, having an odor similar to phenol 
 and a sharp, pungent taste. It fuses at 122 C. (252 F.), boils at 
 286 C. (547 F.), is soluble in about 1000 parts of cold, or 75 parts 
 of boiling, water ; and readily soluble in alcohol, ether, chloroform, 
 and fatty oils. The aqueous solution is colored greenish by ferric 
 chloride. A few drops of iodine solution added to an aqueous solution 
 of beta-naphthol, followed by an excess of alkali solution, should pro- 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 589 
 
 duce no color, but if alplia-naphthol is present, an intensely violet 
 color is produced. 
 
 Naphthol occurs in coal-tar, but it is prepared synthetically from 
 naphthalene in the same manner in which phenol is prepared from 
 benzene. When concentrated sulphuric acid is heated with naphthalene 
 for several hours at 200 C., the beta-sulphonic acid is formed, C 10 H 7 - 
 SO 3 H ; during the early stage of the process, and particularly at 80- 
 90 C., much alpha-sulphonic acid is formed, but at a higher temper- 
 ature this is converted into the beta variety. The sodium salt of the 
 beta acid is fused with sodium hydroxide, forming sodium naphthol 
 and sodium sulphite. By treating the former with an acid, beta-naph- 
 thol is liberated, which must be further purified. 
 
 Microeidine, C 10 H 7 .ONa, is the name given to sodium naphthol. 
 ItS aqueous solution is used as a disinfectant for cleansing dental 
 instruments. 
 
 Alpha-naphthol is obtained in the same manner as the beta product, from 
 the sodium salt of alpha-naphthalene sulphonic acid. It forms lustrous needles, 
 melting at 95 C. and boiling at 278-280 C. It is more readily soluble in water 
 than beta-naphthol, and is said by one author to be three times more powerful 
 as an antiseptic and only one-third as poisonous as the beta compound. It is 
 official in the French Pharmacopoaia. Most authorities state, however, that it is 
 more poisonous than beta-naphthol. It has been used as a test for sugar in urine 
 and is employed in the preparation of certain azo dyes, as is also beta-naphthol. 
 
 The naphthols act in general like the phenols, but the (OH) group reacts 
 more readily than in the phenols. Thus, it can easily be replaced by the amido 
 (NH 2 ) group. Naphthols readily form sulphonic acids, of which many are 
 known and are used in the manufacture of azo dyes. The 1, 4, naphthol-sul- 
 phonic acid is used most. 
 
 Beta-naphthol benzoate, C 6 H 5 COOC 10 H 7 (Benzoyl-naphthol},\& obtained by the 
 action of benzoyl chloride on beta-naphthol at 170 C. It is a white crystalline 
 powder, melting at 107 C., tasteless, odorless, and insoluble in water, but solu- 
 ble in alcohol, chloroform, and hot ether. It splits into beta-naphthol and 
 benzoic acid in the intestines. 
 
 Beta-naphthol-bismuth (Orphol] has approximately the composition, C 10 H 7 O.- 
 Bi 2 O 2 (OH), and is said to be formed by the action of an alkaline solution of 
 naphthol on a solution of bismuth nitrate in dilute glycerin. It is a light- 
 brown, odorless, almost tasteless powder, insoluble in alcohol as well as water. 
 In the intestines it splits into naphthol and bismuth hydroxide. 
 
 Alpha-amino-naphthalene, C 10 H 7 .NH 2 (Alpha-nap hthy famine], is obtained by 
 the reduction of the corresponding nitro-naphthalene, the chief product of the 
 action of nitric acid on naphthalene in the cold. It is also formed by heating 
 alpha-naphthol with the ammonia compound of zinc chloride. It melts at 
 50 C., has a pungent odor, and turns red in contact with air. It is easily 
 soluble in alcohol, and forms crystalline salts with acids, the solutions of which 
 with oxidizing agents give a blue precipitate, which soon turns red. 
 
590 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Beta-amino-naphthalene, C 10 H 7 .NH 2 (Beta-naphthy famine), is easily obtained 
 by heating beta-naplitbol with the ammonia compound of zinc chloride to 210C. 
 It forms pearly scales, soluble in hot water, ordorless, and melting at 112C. It 
 does not give a colored compound with oxidizing agents. 
 
 Naphthionic acid, C 10 H 6 (NH 2 )SO 3 H (1, 4, Naphthylamine-sulphonic add). A 
 number of sulphonic acids are formed when the naphthylarnines are treated with 
 sulphuric acid, some of which are valuable in the preparation of dyes. The 
 sodium salt of naphthionic acid is used in making congo red, which has the 
 
 composition : 
 
 C 6 H 4 .N 2 .C 10 H 5 (NH 2 )S0 3 Na. 
 
 C 6 H 4 .N 2 .C 10 H 5 (NH 2 )S0 3 Na. 
 
 Four mono-sulphonic acids are formed when beta-naphthylamine is treated 
 with sulphuric acid. 
 
 Santonin, Santoninum, C 15 H 18 O 3 = 244.29, is an anhydride of 
 santonic acid, C 15 H 20 O 4 . As several reactions point to a relationship 
 between this acid and naphthalene, santonin is mentioned in this place. 
 
 Santonin is the active principle of wormseed, the unexpanded 
 flowerheads of Artemisia, from which it is obtained by extraction 
 with alcohol and lime-water, and decomposition of the soluble com- 
 pound of lime and santonin by an acid. Santonin crystallizes in 
 colorless prisms, which turn yellow on exposure to light ; it is but 
 sparingly soluble in water, more soluble in alcohol and ether. 
 
 Santonin taken internally confers upon the urine a dark color re- 
 sembling the color of urine containing bile; upon heating such urine 
 it turns cherry-red or crimson, the color disappearing on the addition 
 of an acid, and reappearing on neutralization. 
 
 Analytical reactions : 
 
 1. Santonin added to alcoholic solution of potassium hydroxide 
 produces a bright-red liquid which gradually becomes colorless. 
 
 2. To 1 c.c. of sulphuric acid add a few drops of ferric chloride 
 solution and a crystal of santonin : on heating, a dark-red color is 
 produced, changing into violet-brown. 
 
 Aromatic compounds containing- nitrogen in the cycle. 
 
 Pyrrol, C 4 H 4 NH. During the destructive distillation of certain 
 nitrogenous matters (chiefly bones), a liquid known as bone-oil is ob- 
 tained, which contains a number of nitrogenous basic subtances, 
 among which pyridine and pyrrol are found. Pyrrol has but weak 
 basic properties, is insoluble in water, and has an odor like chloroform. 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 591 
 
 A solution of pyrrol in alcohol, treated with iodine in the presence 
 of oxidizing agents, such as ferric chloride, deposits after some time 
 crystals of tctra-iodo pyrrol. This compound is official under the 
 name of iodol, iodolum, C 4 I 4 NH = 566.17. It is a pale-yellow, crys- 
 talline powder, almost insoluble in water, soluble in 9 parts of alcohol, 
 1 to 2 parts of ether, and 15 parts of fatty oils; it is, when pure, 
 tasteless and odorless, and contains of iodine 88.97 per cent. 
 
 Antipyrine, Antipyrina, C U H 12 N 2 O = 186.75 (Phenyl-dimethyl- 
 isopyrazolon). When phenyl-hydrazine is heated with diacetic ether, 
 CH 3 CO.CH 2 .COOC 2 H 5 , a substance is formed known as phenyl- 
 methyl-isopyrazolon. 
 
 In this compound a second hydrogen atom may be replaced by 
 methyl, when phenyl-dimethyl-isopyrazolon is formed, which is the 
 substance to which the name antipyrine has been given. 
 
 Antipyrine is a white, crystalline, odorless powder, having a slightly bitter 
 taste; it fuses at 113 C. (235 F.), is soluble in less than its own weight of 
 water, in 1 part of alcohol, in 1 part of chloroform, but only in 50 parts of 
 ether. 
 
 The structure of antipyrine and its relation to pyrrol and isopyrazoltm inay 
 be shown by the constitutional formulas: 
 
 HC CH HC CH HC CH 2 
 
 H S JH I JH HH. 
 
 NH NH NH 
 
 Pyrrol. Pyrazol. Pyrazolin. 
 
 HC CH 2 HC=:CH CH 3 C= 
 
 i!r co HN co 
 
 co 
 
 NC 6 H 5 
 
 Pyrazolon. Isopyrazolon. Phenyl-dimethyl- 
 
 isopyrazolon. 
 
 Analytical reactions : 
 
 1. 0.2 gramme of antipyrine dissolves in 2 c.c. of nitric acid with- 
 out change of color. On heating slightly the liquid assumes a yellow, 
 then an intense red color. 
 
 2. 12 c.c. of a 1 per cent, solution of antipyrine treated with 0.1 
 gramme of potassium nitrite solution yield a colorless solution, which 
 turns intensely green on the addition of 1 c.c. of dilute sulphuric acid. 
 In a more concentrated solution green crystals of isonitroso-antipyrine 
 form on standing. 
 
592 CONSIDERATION OF CARBON COMPOUNDS. 
 
 3. The addition of ferric chloride to solution of antipyrine causes 
 a deep-red color, changing to yellow on the addition of sulphuric 
 acid. 
 
 4. Mercuric chloride, as well as tannic acid, produces a white pre- 
 cipitate. 
 
 Incompatibilities. In addition to those indicated in the above tests, the 
 following may be mentioned : A mixture of antipyrine and calomel produces 
 a poisonous organic mercury compound ; with phenol, even in dilute aqueous 
 solution, an oily mass is formed; rubbed with sodium salicylate, a pasty mass 
 is produced, in solution, however, there seems to be no eftect ; with beta-naph- 
 thol, a moist mixture results ; rubbed with chloral hydrate, an oil is produced. 
 On the other hand, antipyrine increases the solubility in water of caffeine and 
 the quinine salts. 
 
 Salipyrin is antipyrine salicylate, obtained by direct combination of anti- 
 pyrine and salicylic acid. It is a white odorless powder, with a harsh, sweetish 
 taste, and is almost insoluble in water. 
 
 Resopyrin is a compound of antipyrine and resorcin. Hypnal is a com- 
 pound of antipyrine and chloral hydrate. Pyramidon is a dimethyl-amido 
 substitution product of antipyrine. Ferripyrine is a combination of anti- 
 pyrine and ferric chloride. Many other combinations are known. 
 
 Antipyrine is a constituent of many " migraine powders." 
 
 Pyridine, C 5 H 5 N. This substance has been mentioned above as 
 being a constituent of bone-oil. Other substances have been isolated 
 from this oil and have been found to form a homologous series : 
 
 Pyridine, C 5 H 5 N Lutidine, C 7 H 9 N 
 
 Picoline, C 6 H 7 N Colliding C 8 H U N 
 
 Pyridine is of special interest, because it has been found that sev- 
 eral of the alkaloids, such as quinine, cinchonine, etc., when oxidized, 
 yield acids containing nitrogen, which bear to pyridine the same 
 relation that benzoic acid bears to benzene, or that acetic acid bears 
 to methane. 
 
 Thus, when nicotine is treated with oxidizing agents, nicotinic 
 acid, C 6 H 5 NO 2 , is obtained, which, when distilled with lime, breaks 
 up into pyridine and carbon dioxide, thus : 
 
 C 6 H 5 N0 2 = C 5 H 5 N + C0 2 . 
 
 The relation of nicotinic acid to pyridine, of benzoic acid to ben- 
 zene, acetic acid to methane, may be shown thus : 
 
BENZENE SERIES. AROMATIC COMPOUNDS. 593 
 
 CH 3 .H C 6 H 6 .H C 6 H 4 N.H 
 
 Methane. Benzene. Pyridine. 
 
 CH 3 .C0 2 H C 6 H 5 .C0 2 H C 5 H 4 N.CO 2 H. 
 
 Acetic acid. Benzoic acid. Nicotinic acid. 
 
 Pyridine is also obtained together with another basic substance, 
 termed quinoline, C 9 H 7 N, by distilling quinine or cinchonine with 
 potash. These observations, showing an intimate relationship between 
 alkaloids and the pyridine and quinoline bases, have led to numerous 
 experiments made with the view of either solving the problem of 
 making alkaloids synthetically, or of obtaining substances which 
 might have physiological actions similar to those of the alkaloids. 
 The result of these efforts has been the introduction into the materia 
 medica of quite a number of new remedies. 
 
 Pyridine is a colorless liquid, having a sharp, characteristic odor, 
 strongly basic properties, and a boiling-point of 116 C. (241 F.). 
 
 Quinoline, C 9 H 7 N ( Chinoline), has been mentioned above as a product of the 
 distillation of quinine with potash ; it may also be obtained by the action of 
 sulphuric acid upon a mixture of aniline, nitro-benzene, and glycerin. It is, 
 like pyridine, a colorless liquid, but its aromatic odor is less pleasant and its 
 basic properties are less marked than those of pyridine. Boiling-point 237 C. 
 (458 F.). 
 
 The constitution of pyridine and quinoline is supposed to correspond to 
 benzene and naphthalene respectively, one of the groups CH having been re- 
 placed by an atom of nitrogen, thus : 
 
 H H H H H 
 
 ! 
 
 C X /Cx //CH HQ, /(\ 
 
 ^/ ^^ ^c x x 
 
 HC\ /CH H 
 
 \N/ 
 
 H H H 
 
 Pyridine. Quinoline. Isoquinoline. 
 
 Isoquinoline is very similar to quinoline, but differs slightly in its proper- 
 ties. Like quinoline it is closely related to a number of alkaloids, especially 
 those of the opium group. It is found together with quinoline among the bases 
 of coal-tar and bone-oil. 
 
 Kairine, C 10 H 13 .NO.HC1. The name kairine has been given to the hydro- 
 chloride of methyl-oxychinoline hydride. It is a white, crystalline, odorless 
 powder, soluble in 6 parts of water or in 20 parts of alcohol. 
 
 Thalline, C 10 H n NO (Tetra-hydro-paramethyt-oxy quinoline). Quinoline serves 
 
 in the manufacture of thalline, a white, crystalline substance, which has an 
 
 aromatic odor, fuses at 40 C. (104 F.) and is soluble in water, alcohol, and 
 
 ether. The most characteristic feature of the substance is that it is colored 
 
 38 
 
594 CONSIDERATION OF CARBON COMPOUNDS. 
 
 intensely green by various oxidizing agents, such as ferric chloride and others. 
 Some of the salts of thalline, chiefly the sulphate, tartrate, and tannate, have 
 been used medicinally. 
 
 51. TERPENES AND THEIR DERIVATIVES. 
 
 The group of hydrocarbons of the general formula (C 5 H 8 ) X , found 
 largely in the volatile oils, has been called by the generic word ter- 
 penes, but this term has been more specifically applied to the sub- 
 group C 10 H 16 . According to the molecular complexity this group has 
 been classified into : 
 
 Hemiterpenes C 5 H 8 , 
 
 Terpenes proper Ci H l6 , 
 
 Sesquiterpenes C 15 H 24 , 
 
 Diterpenes C 20 H 32 , 
 
 Polyterpenes (C 10 H 16 ) X . 
 
 Isopene is the only representative of the hemiterpenes found in a 
 volatile oil, and does not occur naturally, but is formed by the de- 
 structive distillation of rubber or gutta percha. The terpenes proper 
 and sesquiterpenes are among the principal constituents of the vola- 
 tile oils. The diterpenes and higher polyterpenes are more rarely 
 found and but little studied. 
 
 Volatile or essential oils. The term essential oil is more a phar- 
 maceutical than chemical term, and is used for a large number of 
 
 QUESTIONS. What is the difference between fatty and aromatic compounds, 
 and from which two hydrocarbons are they derived ? From what source is 
 benzene obtained, how can it be made from benzoic acid, and what are its 
 properties ? Give the graphic formulas of benzene, nitro-benzene, phenol, 
 thymol, benzoic acid, and salicylic acid. Mention methane derivatives which 
 have a constitution analogous to that of the substances mentioned. Give com- 
 position, properties, and mode of manufacture of, and tests for carbolic acid. 
 What relation exists between benzoic acid and oil of bitter almond? What is 
 the source of amygdalin, to which class of substances does it belong, and what 
 are the products of its decomposition under the influence of emulsin ? Explain 
 the process for the manufacture of salicylic acid, and state its properties. 
 Give composition and properties of naphthalene and naphthol. Give tests for 
 tannin, state the source from which it is derived and for what it is used. From 
 what, and by what process, is aniline obtained; what is its composition and 
 what its constitution? How are aniline dyes manufactured from aniline? 
 State the properties and some reactions characteristic of antipyrine. What 
 is saccharin, and what are its properties ? State the composition of iodol. 
 
TERPENES AND THEIR DERIVATIVES. 595 
 
 liquids obtained from plants, and having in common the properties 
 of being volatile, soluble in ether and alcohol, almost insoluble in 
 water, and having a distinct and in most cases even highly charac- 
 teristic odor. They stain paper as do fats or fat oils, from which 
 they differ, however, by the disappearance after some time of the 
 stain produced, while fats leave a permanent stain. 
 
 The specific gravity of volatile oils ranges generally between 0.85 
 and 0.99. Being nearly insoluble in, and specifically lighter than, 
 water, they will float on it. The water, however, retains in most 
 cases enough of the oils to assume their odor (medicated waters). 
 Most volatile oils are optically active, turning the plane of polarized 
 light either to the right or left. While chemically pure oils are 
 colorless, many, even when freshly prepared, have a distinct color; 
 some are pale yellow, dark yellow, reddish or reddish brown, while 
 a few are green or blue. The oils generally darken with age, espe- 
 cially when exposed to light and air, the atmospheric oxygen acting 
 on them and converting the oils often into a sticky and resinous mass. 
 
 Volatile oils are found in different parts of plants, and are the 
 principles imparting to the respective plants their characteristic odor. 
 The extraction of volatile oils from plants is accomplished generally 
 by distilling with water the vegetable matter containing the oil, the 
 oil passing over with the steam and floating on the surface of the 
 condensed water. In some instances mechanical pressure is used for 
 the separation, as in case of the oils of orange, lemon, bergamot, etc. 
 In other cases the oils are extracted by suitable solvents, or special 
 methods are used. 
 
 In their chemical composition essential oils differ widely ; some are 
 compound ethers (oil of wintergreen is methyl salicylate), others are 
 aldehydes (oil of bitter almonds is benzaldehyde), but most of them 
 are hydrocarbons of the aromatic series, or mixtures of them, often 
 associated with oxygen derivatives, alcohols, phenols, ketones, alde- 
 hydes, esters, etc. 
 
 Oil of doves. The principal constituent of this oil is eugenol, C 8 H S .C 3 H,. 
 OCH 3 .OH, a monatomic phenol ; a sesquiterpene, C 15 H 24 , culled caryophylleue 
 is also present. 
 
 Oil of cinnamon consists chiefly of cinnamic aldehyde, C 6 H 5 CH.CHCOH, 
 a compound which has been prepared synthetically. Oil of cinnamon also 
 contains cinnamyl acetate, C 9 H 9 .C,H 3 O 2 , and a small amount of cinnamic acid 
 C 8 H 8 2 . 
 
 Oil of peppermint. The oils found in the market differ widely from one 
 another, and there is no other volatile oil containing so many different con- 
 
596 CONSIDERATION OF CARBON COMPOUNDS. 
 
 stituents ; as many as seventeen having been found in one sample. Besides 
 three different terpenes and one sesquiterpene, were found acetaldehyde, acetic 
 acid, isovalerianic acid, amyl alcohol, menthol, menthon, C 10 H 18 0, menthyl 
 acetate, C 10 H 19 O.C 3 H 3 0, and others. 
 
 Terpenes, C 10 H 16 . The terpenes are widely distributed in the 
 vegetable kingdom, especially in the coniferse and varieties of citrus, 
 etc., and are found in the volatile oils obtained from the individual 
 plants. The terpenes are readily acted upon by many agents and 
 hence undergo numerous changes. One of these changes is polym- 
 erization i. e., conversion into compounds of the composition C^H^ 
 and CjjoHgg, which may be effected by heating a terpene in a sealed 
 tube, or by shaking it with concentrated sulphuric acid or with cer- 
 tain other substances. Many of them also show a great tendency to 
 pass into more stable isomers under certain conditions i. e., when 
 acted on by acids. Gaseous chlorine acts violently upon them, and 
 bromine and iodine convert many of them into cymene. Many ter- 
 penes are therefore closely related to cymene, C 10 H 14 , and may be con- 
 sidered as dihydrocymene ; others, however, show a quite different 
 structure. They are oxidized quite readily with the formation of a 
 number of organic acids, and unite with gaseous hydrochloric acid to 
 form mono- or dihydrochlorides. With bromine they often form 
 characteristic tetrabromides, C 10 H 16 Br 4 . They readily yield com- 
 pounds with nitrosyl chloride, of the formula C 10 H 16 .NOC1, known 
 as nitrosochlorides, and with the oxides of nitrogen compounds of 
 the formulas C 10 H 16 .N 2 O 3 and C 10 H 16 .N 2 O 4 , known as nitrosites and 
 nitrosates respectively. The terpenes are almost all optically active, 
 and most of them exist both in dextro- and in Isevorotatory modifi- 
 cations. 
 
 Pinene is the chief constituent in most of the volatile oils obtained 
 from the coniferse, and is also found largely in other volatile oils. 
 
 Oil of turpentine, C 10 H 16 , is chiefly composed of pinene. It is a 
 thin, colorless liquid of a characteristic aromatic odor, and an acrid, 
 caustic taste ; it is insoluble in water, soluble in alcohol, and an excel- 
 lent solvent for resins and many other substances. When treated 
 with hydrochloric acid gas direct combination takes place and a white 
 solid substance of the composition C 10 H 16 HC1 is formed, which is 
 known as pinene hydrochloride, or artificial camphor, on account of 
 its similarity to camphor both in appearance and odor. 
 
 Experiment 7L Through 10 or 20 c.c. of oil of turpentine pass a current of 
 hydrochloric-acid gas for some time, or until a quantity of a solid substance 
 
TERPENES AND THEIR DERIVATIVES. 597 
 
 has separated. Collect this substance, which is artificial camphor, upon a filter ; 
 notice its characteristic odor. Heat some of it; hydrochloric acid is set free. 
 
 Camphene is the only solid hydrocarbon of the terpene group, and occurs in 
 the oil from Pinus Sibirica. It is obtained by heating the above pinene hydro- 
 chloride with alcoholic potash. 
 
 Limonene is the principal constituent of orange oil, and is found in a large 
 number of other oils, as the dextro modification. Laevolimonene occurs in 
 pine-needle oil. 
 
 Dipentene is the inactive modification of limonene, and can be prepared by 
 heating pineiie, camphene, sylvestrene, or limonene to 250-270 C. for several 
 hours. 
 
 Terebene, Terebenum, consists chiefly of dipentene with other hydrocar- 
 bons, and is obtained from oil of turpentine by mixing it with sulphuric acid, 
 distilling, washing the distilled oil with soda solution, redistilling, and collect- 
 ing the portions which pass over at a temperature of 155-165 C. (311- 
 329 F.). Terebene resembles oil of turpentine in most respects, but has not 
 the unpleasant odor of this oil. 
 
 Sylvestrene is found in Swedish and Russian oil of turpentine. 
 
 Phellandrene is widely distributed in volatile oils; notably in the water- 
 fennel oil and eucalyptus oil. 
 
 Sesquiterpenes, C 15 H 24 . These are likewise widely distributed in 
 the vegetable kingdom, and are very similar in their general proper- 
 ties to the terpenes proper, but have a higher boiling-point. Of 
 those, well characterized, may be mentioned : cadinene, from oil of 
 cade and a large number of other volatile oils ; caryophyttene, from oil 
 of cloves ; humulene, from oil of hops ; santolene y from oil of sandal- 
 wood; cedrene, from oil of cedarwood ; and zingiberene, from oil of 
 ginger. 
 
 Rubber, Elastica (Caoutchouc) is the dried milky juice found in 
 quite a number of trees growing in the tropics. It consists chiefly 
 of hydrocarbons of the terpene series, having a very large molecular 
 weight and a complex molecular structure. 
 
 The commercial article is yellowish-brown, has a specific gravity 
 of 0.92 to 0.94, is soft, flexible, insoluble in water and alcohol, 
 but soluble in carbon disulphide, ether, chloroform, and benzene. It 
 is not acted upon by dilute mineral acids ; concentrated nitric and 
 sulphuric acid, as well as chlorine, attack it after a time. It is hard 
 and tough in the cold ; when heated it becomes viscous at 125 C. 
 (257 F.), and fuses at 170-180 C. (347-356 F.) to a thick liquid, 
 which, on cooling, remains sticky, and only regains its original char- 
 acter after a long time. 
 
 Vulcanized rubbw is India-rubber which has been caused to enter 
 
598 CONSIDERATION OF CARBON COMPOUNDS. 
 
 into combination with from 7 to 10 per cent, of sulphur by heating 
 together the two substances to a temperature of 130-150 C. (266- 
 302 F.). Vulcanized rubber differs from the natural article by 
 possessing greater elasticity and flexibility, by resisting the action of 
 solvents, reagents and atmosphere to a higher degree, and by not 
 hardening when exposed to cold. 
 
 Hard rubber, vulcanite, or ebonite, is vulcanized rubber, containing 
 from 20 to 35 per cent, of sulphur, and often also tar, white-lead, 
 chalk, or other substances. It is hard, tough, and susceptible of a 
 good polish. 
 
 Preservation of rubber. Various substances have been recommended 
 for preserving articles of rubber. For undeteriorated rubber, it is said that a 
 3 per cent, solution of either phenol or aniline is the best, while for deterior- 
 ated rubber, or such as has been exposed many times to boiling water, a 1 per 
 cent, solution of potassium pentasulphide is best, the restorative properties of 
 the latter depending on the absorption of the sulphur from the pentasulphide. 
 The articles are immersed in the solutions in vessels of appropriate shape. It 
 has been observed that black rubber immersed in the aniline solution under- 
 goes an increase in volume. For example, rubber tubing shows a marked in- 
 crease in length. 
 
 Gutta-percha is the concrete juice of a tree Isonaudra gutta. It 
 resembles india-rubber both in composition and properties. At ordi- 
 nary temperature it is a yellowish or brownish, hard, somewhat 
 flexible, but scarcely elastic substance ; when warmed it softens, and 
 is plastic above 60 C. (140 F.) ; at the temperature of boiling-water 
 it is very soft. It is insoluble in water, alcohol, dilute acids and 
 alkaline solutions ; soluble in oil of turpentine, carbon disulphide, 
 and chloroform. 
 
 Oxygen derivatives of terpenes. 
 
 Stearoptens or camphors are substances closely related to the 
 terpenes and to cymene both in physical and chemical properties; 
 while terpenes are liquid, camphors are crystalline solids. Borneo 
 camphor has the composition C 10 H 18 O, while the camphor found 
 in the camphor-trees of China and Japan has the composition 
 C 10 H 16 0. 
 
 Camphor, Camphora, C ]0 H 16 O (LaurinoT), forms white, translucent 
 masses of a tough consistence and a crystalline structure ; it has a 
 characteristic, penetrating odor and poisonous properties ; in the pres- 
 ence of a little alcohol or ether it may be pulverized ; it is nearly 
 insoluble in water, but soluble in alcohol, ether, chloroform, etc. ; 
 boiled with bromine it forms the monobromated camphor, carnphora 
 
TERPENES AND THEIR DERIVATIVES. 599 
 
 monobromata, C, H 15 BrO, a white crystalline substance having a mild 
 camphoraceous odor and taste. Heating with nitric acids converts 
 camphor into camphoric add, acidum camphoricum, CgH^CO.,!!)^ 
 a colorless, crystalline, fusible substance having an acid taste ; it is 
 slightly soluble in water, readily in alcohol and ether. 
 
 Cineol. Eucalyptol, C 10 Hi 8 0, is found in the volatile oils of different species 
 of eucalyptus, as also in the oils of some other plants. It is liquid at the ordi- 
 nary temperature, but solidifies when cooled to a little below the freezing-point 
 of water. It has an aromatic, distinctly camphoraceous odor. 
 
 Menthol, C 10 H 19 OH (Mint-camphor). Found together with a ter- 
 pene in oil of peppermint, and separates in crystals on cooling the oil. 
 Menthol is nearly insoluble in water, fuses at 43 C. (109 F.), and 
 boils at 212 C. (414 F.). It has the characteristic odor of pepper- 
 mint. 
 
 Terpin hydrate, Terpini hydras, C 10 H 20 O 2 .H 2 O, is the hydrate of 
 the diatomic alcohol terpin, and is formed from pinene under the 
 influence of alcohol and nitric acid. It forms colorless crystals, melt- 
 ing at 117 C. (243 F.), is readily soluble in alcohol, but sparingly 
 soluble in water, ether, or chloroform. 
 
 Resins are obtained, together with the essential oils, from plants. 
 Mixtures of a resin and a volatile oil are known as oleo-resins, while 
 mixtures of a resin or oleo-resins and gum are known as gum-resins. 
 The name balsam is also used for a certain group of oleo-resins. 
 
 The resins are mostly amorphous, brittle bodies, insoluble in water, 
 but soluble in alcohol, ether, fatty and essential oils ; they are fusible, 
 but decompose before being volatilized ; they all contain oxygen and 
 exhibit somewhat acid properties. 
 
 Turpentine, the oleo-resin of the conifers, contains besides the oil of 
 turpentine a resin called colophony, rosin, or ordinary resin, consisting 
 chiefly of the anhydride of abietic acid, C 44 H 64 O 5 . 
 
 Copaiva balsam consists of a volatile oil and a resin, the latter 
 being principally copaivic acid, C 20 H 30 O 2 . 
 
 Of fossil resins may be mentioned amber and asphalt, the latter 
 having most likely been formed from petroleum. 
 
 QUESTIONS. What substances are known as terpenes : where are they found 
 in nature? Give the composition of the principal groups of terpenes. Men- 
 tion the general properties of essential oils, and name some of the important 
 ones. What is the source of rubber ; how is it converted into vulcanized and 
 hard rubber ? State the composition and properties of camphor. 
 
600 CONSIDERATION OF CARBON COMPOUNDS. 
 
 52. ALKALOIDS. 
 
 General Remarks. The basic substances found in plants are 
 grouped together under the name of alkaloids, this term signifying 
 alkali-like, in allusion to the alkaline or basic properties of these 
 substances. They show their derivation from ammonia to a more or 
 less marked degree, as, for instance, in their power to combine with 
 acids to form well-defined salts, to combine with platinic chloride to 
 form insoluble double compounds, etc. 
 
 The compounds formed by the direct combination of alkaloids with 
 acids are, in the case of oxygen acids, named like other salts of these 
 acids, for instance, sulphates, nitrates, acetates, etc. In the case of 
 halogen acids, however, a different method has been adopted, because 
 it would be incorrect to apply the terms chlorides and bromides to 
 substances formed not by the combination of chlorine or bromine with 
 other substances, nor by the replacement of hydrogen in the respective 
 hydrogen acids of these elements, but by direct combination of these 
 acids with the alkaloids. The terms hydrochloride and hydrobromide 
 have been adopted by the U. S. P. for the compounds obtained by 
 direct union of alkaloids with hydrochloric and hydrobromic acids. 
 Formerly the terms hydrochlorate and hydrobromate were used. 
 
 Alkaloids are found in the leaves, stems, roots, barks, and seeds of 
 various plants ; it often happens that a certain alkaloid is found in 
 the different species of one family, and it is often the case that 
 
 various alkaloids of a similar composition are found in the same plant. 
 
 General properties of alkaloids: 
 
 1 . They combine with acids to form well-defined salts, and are set 
 free from the solutions of these salts by alkalies and alkali carbonates. 
 
 2. In most cases those containing no oxygen are volatile liquids, 
 those containing oxygen are non-volatile solids. 
 
 3. The volatile alkaloids have a peculiar disagreeable odor, remind- 
 ing of ammonia ; the non-volatile alkaloids are odorless. 
 
 4. Most solid alkaloids fuse at a temperature above 100 C. (212 
 F.) without decomposition, but are decomposed when the heat is 
 raised much beyond the fusing-point. 
 
 5o Most alkaloids are insoluble, or nearly so, in water, but soluble 
 in alcohol, chloroform, benzene, acetic ether, and many also in ether. 
 
 6. The hydrochlorides, sulphates, nitrates, acetates (and most other 
 salts) of alkaloids are either soluble in water, or in water which has 
 been slightly acidulated, and also in alcohol ; but they are insoluble, 
 or nearly so, in ether, acetic ether, chloroform (except veratrine and 
 
ALKALOIDS. 601 
 
 narcotine), amyl alcohol (except veratrine and quinine), benzene, and 
 benzin. 
 
 7. The solid alkaloids, as well as their salts, may be obtained in a 
 crystalline state. 
 
 8. Most alkaloids are white, have a very strong, generally bitter, 
 taste, and act very energetically upon the animal system. 
 
 9. From the aqueous solutions of alkaloid salts, the solid alkaloids 
 are precipitated by alkali hydroxides, in an excess of which reagents 
 some alkaloids (morphine, for instance) are soluble. Alkali car- 
 bonates and bicarbonates liberate all, and precipitate most alkaloids ; 
 not precipitated by bicarbonates are strychnine, brucine, veratrine, 
 atropine, and a few rare alkaloids. 
 
 Most alkaloids give precipitates with tannic acid, picric acid, 
 phospho-molybdic acid, potassium mercuric iodide; and the higher 
 chlorides of platinum, gold, and mercury. These precipitates are 
 similar in properties and composition to those formed with ammonia. 
 
 Most alkaloids give beautiful color reactions when treated with 
 oxidizing agents, such as nitric acid, chloric acid, chromic acid, ferric 
 chloride, chlorine water, etc. 
 
 A decinormal solution of mercuric-potassium iodide, HgI 2 .(KI) 2 , made by 
 dissolving 13.546 grammes mercuric chloride and 49.8 grammes potassium 
 iodide in 1000 c.c of water, is known as Mayer's solution. This precipitates all 
 alkaloids, forming with them white or yellowish-white, generally crystalline 
 compounds. The solution has been used for volumetric determination of alka- 
 loids, but the method is now discarded, as the results are not accurate. (In 
 most cases the alkaloid replaces the potassium in the potassium-mercuric iodide.) 
 
 Phospho-molybdic acid, mentioned above as a reagent for alkaloids, is pre- 
 pared as follows : 15 grammes ammonium molybdate are dissolved in a little 
 ammonia water and diluted with water to 100 c.c. This solution is poured 
 gradually into 100 c.c. of nitric acid, specific gravity 1.185, and to this mixture 
 Is added a warm 6 per cent, solution of sodium phosphate as long as a precipi- 
 tate is produced. This precipitate is collected on a filter, washed and dissolved 
 in very little sodium hydroxide solution ; the solution is evaporated to dryness, 
 further heated until all ammonia has been expelled and the residue dissolved 
 in 10 parts of water. To this solution is added a quantity of nitric acid suffi- 
 cient to redissolve the precipitate which is formed at first. This reagent gives 
 precipitates not only with the alkaloids, but also with the salts of potassium 
 and ammonium. 
 
 General mode of obtaining 1 alkaloids. The disintegrated veg- 
 etable substance (bark, seeds, etc.) is extracted with acidified water, 
 which dissolves the alkaloids. When the alkaloid is volatile, it is 
 obtained from this solution by distillation, after having been liberated 
 by an alkali. 
 
602 CONSIDERATION OF CARBON COMPOUNDS. 
 
 volatile alkaloids are precipitated from the acid solution by 
 the addition of an alkali, and the impure alkaloid thus obtained is 
 purified by again dissolving in an acid and reprecipitating, or by dis- 
 solving in alcohol and evaporating the solution. 
 
 As the quantity of alkaloids in plants, and consequently in the aqueous 
 extract made from them, is often so small that the precipitation process gives 
 unsatisfactory results, a second method known as the shaking-out process is often 
 employed for the separation of alkaloids. In using this process the con- 
 centrated aqueous extract, to which a suitable alkaline precipitant has been 
 added, is agitated with a liquid (such as chloroform) not miscible with water 
 and acting as a solvent upon the alkaloids. The operation is performed in an 
 apparatus known as separator or separatory funnel, consisting of a globular or 
 cylindrical glass vessel, provided with a well-fitting stopper and an outlet-tube 
 containing a glass stopcock. Having introduced into this vessel the extract 
 and solvent, the latter is made to dissolve the alkaloids present by a rapid 
 rotation of the separator. As the aqueous solution and the solvent do not mix, 
 but form two distinct layers one above the other, they may be conveniently 
 separated by opening the stopcock until the heavier liquid has run out. By 
 evaporation of the liquid, used as a solvent, the alkaloids may be obtained in a 
 more or less pure condition. 
 
 Assay methods. As the medicinal value of many drugs, such as opium, 
 cinchona bark, etc., as also that of the galenical preparations, such as tinctures, 
 extracts, etc., obtained from such drugs, depends chiefly on the alkaloids pres- 
 ent, and as the quantity of the alkaloids in drugs varies considerably, the 
 U. S. P. gives specific assay methods for the estimation of the percentage of the 
 alkaloids contained in drugs or in certain preparations. 
 
 These assay methods must be closely followed by the analyst, as otherwise 
 results may be obtained which are either too high or too low. This is due to 
 the fact that these methods in many cases do not give absolutely correct results, 
 but give results sufficiently accurate for all practical purposes, provided the 
 directions of the Pharmacopeia are closely followed. To bring about a 
 standard and uniformity in alkaloidal strength is the object of these assay 
 methods. 
 
 Antidotes. In cases of poisoning by alkaloids the stomach-pump and emetics 
 (zinc sulphate) should be applied as soon as possible ; astringent liquids may be 
 given, because tannic acid forms insoluble compounds with most of the alkaloids. 
 In some cases special physiological antidotes are known, and should be used. 
 
 Detection of alkaloids in cases of poisoning 1 . The separation 
 and detection of poisonous alkaloids in organic matter (food, contents 
 of stomach, etc.), especially when present in very small quantities, as 
 is generally the case, is one of the most difficult tasks of the toxi- 
 cologist, and none but an expert who has made himself thoroughly 
 familiar with the methods of discovering minute quantities of organic 
 poisons in the animal system should undertake to make such an 
 
ALKALOIDS. 
 
 PLATE VI 
 
 norphine treated with nitric acid. 
 
 Morphine treated with solution of 
 ferric chloride. 
 
 Codeine treated with bromine water 
 and ammonia water. 
 
 
 
 Quinine treated with chlorine water 
 and ammonia water. 
 
 Strychnine treated with sulphuric 
 acid and potassium dicbromate. 
 
 Brucine treated with nitric acid and 
 with sodium thiosulphate. 
 
 Physostigmine treated successively 
 
 with ammonia water, alcohol, acetic acid, 
 and again with ammonia water. 
 
 Veratrine treated with sulphuric acid. 
 
 A Jfofit&Co Litli Bulttntorr, . \(d 
 
ALKALOIDS. 603 
 
 analysis in case legal proceedings depend on the result of the 
 chemist's report. 
 
 Of the various methods applied for the separation of alkaloids from organic 
 matter, the following may be mentioned : 
 
 The substance to be examined is properly comminuted (if this be necessary) 
 and repeatedly digested at 40 to 50 C. (104 to 122 F.) with water slightly 
 acidulated with sulphuric acid. The filtered liquids (containing the sulphates 
 of the alkaloids) are evaporated over a water-bath to a thin syrup, which is 
 mixed with three or four times its own volume of alcohol ; this mixture is 
 digested at about 35 C. (95 F.) for several hours, cooled, filtered, and again 
 evaporated nearly to dryness. (By this treatment with alcohol many substances 
 soluble in the acidified water, but insoluble in diluted alcohol, are eliminated 
 and left on the filter, while the alkaloids remain in solution as sulphates.) 
 
 A little water is now added to the residue, and this solution, which should yet 
 have a slight acid reaction, is shaken with about three times its own volume of 
 acetic ether, which dissolves some coloring and extractive matters, but does not 
 act upon the alkaloid salts. The two strata of liquids which form on standing 
 in a tube are separated by means of a pipette, and the operation is repeated, if 
 necessary, i. e., if the ether should have been strongly colored - 
 
 The remaining acid aqueous solution is next slightly supersaturated with 
 sodium carbonate, which liberates the alkaloids. Upon now shaking the solu- 
 tion with acetic ether, all alkaloids are dissolved in this liquid, which, after 
 being separated from the aqueous solution, leaves upon evaporation, at a low 
 temperature, the alkaloids generally in a sufficiently pure state for recognition 
 by special tests. It may, however, be necessary to purify the residue further 
 by neutralizing with an acid, allowing to crystallize in a watch-glass, and sep- 
 arating the small crystals from adhering mother-liquor. 
 
 The above method for detecting alkaloids in the presence of organic matter 
 generally answers the requirements of students. 
 
 The practical toxicologist has in most cases of poisoning some data (deduced 
 from the symptoms before death, or from the results of the post-mortem exam- 
 ination) pointing to a certain poison, which, of course, facilitate his work con- 
 siderably. 
 
 Classificati9n of alkaloids. While the constitution of many alka- 
 loids has as yet not been determined, others have been shown to be 
 derivatives, or to contain the nuclei of either pyridine, quinoline, or 
 isoquinoline. Closely related to pyridine are the liquid bases coniine, 
 nicotine, and sparteine, as also the solid alkaloids atropine, cocaine, 
 ecgonine, and others. Among alkaloids derived from quinoline are 
 those found in cinchona bark and in nux vomica. Related to iso- 
 quinoline are the opium alkaloids. 
 
 The pyridine group of alkaloids. 
 
 The close relationship between pyridine and some of the vegetable 
 alkaloids may be shown by considering their structure, which is this : 
 
604 CONSIDERATION OF CARBON COMPOUNDS. 
 
 CH CH 2 CH 2 
 
 /% /\ /\ 
 
 HC CH H 8 C CH 2 H 2 C CHa 
 
 II I II I I 
 
 HC CH H,C CH 2 H 2 C CHC 3 H T 
 
 N NH NH 
 
 Pyridine. Piperidine. Coniine. 
 
 Piperidine has been made by adding 6 atoms of hydrogen to pyri- 
 dine by means of sodium and alcohol ; coniine, which is propyl-piperi- 
 dine, was the first true alkaloid prepared artificially. 
 
 Piperin, Piperina, C 17 H 19 NO 3 =-- 283.04. This compound is found 
 in black and white pepper. While it is isomeric with morphine, it 
 differs widely from it in all its properties. It can hardly be called 
 an alkaloid, as it has no alkaline reaction, is but feebly basic, and does 
 not show the general alkaloidal reactions. The U. S. P. emphasizes 
 this by giving to piperin the ending in and not ine, which is used for 
 all true alkaloids. It forms colorless or pale yellowish crystals 
 which are, when first put in the mouth, almost tasteless, but produce 
 on prolonged contact a sharp, biting sensation. 
 
 Piperin dissolves in concentrated sulphuric acid with a dark blood- 
 red color, which disappears on dilution with water. Treated with 
 nitric acid it turns rapidly orange, then red. 
 
 Coniine, C 8 H 17 N, occurs in conium maculatum (hemlock), accom- 
 panied by two other alkaloids. It is a colorless, oily liquid, having 
 a disagreeable, penetrating odor. 
 
 Pilocarpine, O U H 16 N 2 O 2 . Found in the leaflets of pilocarpus 
 species. The alkaloid crystallizes with difficulty ; its solutions in 
 ether, alcohol, or water have an alkaline reaction. It is a white, 
 crystalline powder, which dissolves in fuming nitric acid with a 
 faintly greenish tint. The aqueous solution is precipitated by most 
 of the common reagents for alkaloids. The hydrochloride and nitrate 
 are official. 
 
 Nicotine, C 10 H 14 N 2 . Tobacco leaves contain from 2 to 8 per cent, 
 of nicotine, which is a colorless, oily liquid, having a caustic taste 
 and a disagreeable, penetrating odor. It gives with hydrochloric 
 acid a violet, with nitric acid an orange, color. 
 
 Sparteine, C 15 H 26 N 2 . This alkaloid, found in scoparius (broom, 
 Irish broom), is a colorless, oily liquid, turning brown on exposure 
 to air and light. It has a slight aniline-like odor. 
 
ALKALOIDS. 605 
 
 Sparteine sulphate, Ci 5 H 26 N. 2 H 2 S0 4 + 5H 2 0, is obtained by saturating the 
 alkaloid with sulphuric acid ; it is a colorless, crystalline salt, readily soluble 
 in water. An ethereal solution of the salt, to which a few drops of ammonia 
 water have been added, deposits, on the addition of an ethereal solution of 
 iodine, minute dark greenish-brown crystals. 
 
 The tropine group of alkaloids. 
 
 Atropine, Atropina, C^H^NOs = 287.O4 (Daturine). Obtained 
 from Atropa belladonna. It is a white, crystalline powder, having a 
 bitter and acrid taste and an alkaline reaction ; it is sparingly soluble 
 in water, but very soluble in alcohol and chloroform. The commer- 
 cial article generally contains a small quantity of hyoscyamine. 
 Atropine sulphate, (CtfH^NO^.ELjSO^ is a white, crystalline powder, 
 easily soluble in water. 
 
 Analytical reactions : 
 
 1. Atropine dissolves in concentrated sulphuric acid without color. 
 This solution is not colored by nitric acid (difference from morphine), 
 and not at once by potassium dichromate (difference from strychnine). 
 " 2. A mixture of atropine and nitric acid, when evaporated to dry- 
 ness over a water-bath, leaves a yellow residue, which turns violet on 
 the addition of a few drops of an alcoholic solution of potassium 
 hydroxide and a fragment of the same reagent. 
 
 3. On warming a mixture of atropine and concentrated sulphuric 
 acid a pleasant odor, reminding of roses and orange flowers is evolved. 
 The addition of a few fragments of potassium dichromate changes 
 this odor to that of bitter almond. 
 
 4. Solutions of atropine dilate the pupil of the eye to a marked 
 extent. 
 
 Homatropine, C 16 H 21 NO 3 . This alkaloid is obtained by the con- 
 densation of tropine and mandelic acid. The hydrobromide is offi- 
 cial. It is a white crystalline powder, and resembles atropine in its 
 mydriatic properties. 
 
 Hyoscyamine, C 17 H 23 NO 3 . Found in small quantities together 
 with hyoscine in the seeds of Hyoscyamus niger (henbane), and in 
 some other plants belonging to the solanaceae. 
 
 Hyoscyamine resembles atropine closely in most of its chemical, 
 physical, and physiological properties, but the corresponding salts of 
 the two alkaloids crystallize in different forms ; the hydrobromide and 
 sulphate are official. 
 
606 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Hyoscyamine differs from atropine by yielding with gold chloride 
 a precipitate which, when recrystallized from a hot aqueous solution, 
 acidified with hydrochloric acid, deposits lustrous, golden-yellow 
 scales. 
 
 Hyoscine, C 17 H 21 NO 4 . Found together with hyoscyamine in 
 Hyoscyamus. The alkaloid is known only in an amorphous, semi- 
 solid state, but the salts, of which the hydrobromide is official, crys- 
 tallize readily. Hyoscine evaporated to dryness on a water-bath with 
 a few drops of fuming nitric acid leaves a nearly colorless residue 
 which turns violet on the addition of some alcoholic solution of 
 potassium hydroxide. 
 
 Scopolamine hydrobromide, C 17 H 21 NO 4 HBr3H 2 O, is the hydro- 
 bromide of an alkaloid obtained from plants of the Solanacese, and is 
 chemically identical with hyoscine hydrobromide. 
 
 Cocaine, Cocaina, C 17 H 21 NO 4 = 3OO.92. This alkaloid is found 
 in the leaves of the South American shrub Erythroxylon coca, in 
 quantities varying from 0.15 to 0.65 per cent. It is a white crystal- 
 line powder, soluble in about 600 parts of water, easily soluble in 
 alcohol, ether, and chloroform ; it fuses at 98 C. (208 F.). A frag- 
 ment of cocaine placed on the tongue causes the sensation of numb- 
 ness without acrid or bitter taste ; the solution in water is faintly bitter. 
 
 Cocaine heated with acids in sealed tubes is decomposed into methyl alcohol, 
 benzoic acid, and ecgonine, showing it to be methyl-benzoyl-ecgonine : 
 
 C 12 H 21 NO 4 + 2H 2 O = CH 3 HO + G 6 H 5 CO 2 H + C 9 H 15 NO 3 . 
 Cocaine. Methyl alcohol. Benzoic acid. Ecgonine. 
 
 Ecgonine is found in the coca leaves as benzoyl-ecgonine, C 9 H I5 (C 7 H 5 0)N0 3 
 + 4H 2 O ; this is a white, crystalline substance from which cocaine may be 
 obtained by heating it with methyl-iodide. The mother-liquors obtained in 
 the manufacture of cocaine from the leaves contain the alkaloid in an amor- 
 phous state and possibly one or two other alkaloids, one of which has been 
 named hygrlne. Whether these alkaloids are contained in the coca-plant, or 
 are products of the decomposition of cocaine, are questions not yet decided. 
 
 Of the various salts of cocaine, the hydrochloride, C 17 H 21 NO 4 HC1, 
 is official. This salt crystallizes from alcohol in short, anhydrous 
 prisms; from aqueous solution, however, with two molecules of water, 
 which are completely expelled at a temperature of 100 C. (212 F.). 
 The anhydrous salt fuses at 190 C. (374 F.) and is readily soluble 
 in water ; this salt solution has a somewhat more bitter taste than the 
 alkaloid itself. 
 
ALKALOIDS. 607 
 
 Analytical reactions : 
 
 1. Cocaine salts are precipitated from an aqueous solution as fol- 
 lows : Platinum chloride produces a yellowish-white, mercuric chlo- 
 ride a white nocculent, picric acid a yellow pulverulent, the alkali 
 carbonates and hydroxides a white precipitate, which latter is soluble 
 in ammonia. 
 
 2. To a cocaine solution, strongly acidified with hydrochloric acid, 
 add some potassium dichromate, when an orange-colored crystalline 
 precipitate of cocaine chromate forms. 
 
 3. Add 1 c.c. of a 3 per cent, solution of potassium permanganate 
 to 1 centigramme of cocaine hydrochloride dissolved in 2 drops of 
 water; a violet precipitate forms which appears brownish-violet when 
 collected on a filter. 
 
 4. Boil a small quantity of cocaine solution for a few minutes with 
 dilute sulphuric acid ; neutralize carefully with potassium hydroxide 
 and then add a few drops of ferric chloride solution. A pale, brownish- 
 yellow precipitate of basic ferric benzoate will form. 
 
 Substitutes for cocaine. Several synthetics have been introduced to 
 take the place of cocaine. Some of these are the following : 
 
 Alypin, (CH 3 ) 2 N.CH 2 .C(C 2 H 5 )(C 6 H 5 COO).CH 2 .N(CH 3 ) 2 .HC1, is the hydro- 
 chloride of the benzoyl-ethyl-tetramethyldiamido derivative of secondary 
 propyl alcohol. It is a white hygroscopic powder, very soluble in water and 
 alcohol, of a neutral reaction and bitter taste. It is a local anesthetic, claimed 
 to be equal to cocaine, but not a mydriatic, and less toxic than cocaine. It is 
 used externally in a 10 per cent, solution and hypodermically in a 1 to 4 per 
 cent, solution. 
 
 Beta-eucaine hydrochloride, C 5 H 7 N.(CH 3 )3( CeHsCOO^HCl, is a salt of 
 trimethyl-benzoyl-hydroxypiperidine. It is a white powder, soluble in 20 
 parts of water and in 14 parts of alcohol. Its solutions can be boiled without 
 change, and are precipitated by alkalies or carbonates. It is a local anesthetic 
 like cocaine, but weaker, and does not dilate the pupil or contract the blood- 
 vessels. It is used in a 2 to 3 per cent, solution in the eye, and 5 to 10 per 
 cent, solution or ointment on other parts. 
 
 Holocaine hydrochloride, CH 3 ,C( :N.CeH 4 .OC 2 H5)(.NH.C 6 H 4 .OC 2 H 5 )JICl, 
 
 is the salt of a basic condensation product of paraphenetidin and acetparaphe- 
 netidin (phenacetin). It forms colorless, neutral or faintly alkaline crystals, 
 odorless, slightly bitter, and producing transient numbness on the tongue. It 
 is soluble in 50 parts of water, easily in alcohol. The solution is precipitated 
 by alkalies and carbonates and the alkaloidal reagents. Porcelain should be 
 used in making solutions, as alkali from glass causes a turbidity. 
 
 The salt is a local anesthetic like cocaine, but having a quicker effect and 
 antiseptic action. A 1 per cent, solution is employed. It is more toxic than 
 cocaine. 
 
608 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Pelletierine tannate of the U. S. P. is a mixture of the tannates of four 
 alkaloids (ptmicine, iso-punicine, inethyl-punicine, and pseudo-punicine) ob- 
 tained from Punica Granatum. 
 
 The quinoline group of alkaloids. 
 
 Cinchona alkaloids. The bark of various species of cinchona 
 contains a number of alkaloids, of which the most important are 
 quinine, cinchonine, quinidine, and cinchonidine. These alkaloids 
 exist in the bark in combination with a peculiar acid, termed kinie 
 acid. The quantity and relative proportion of the alkaloids vary 
 widely in different barks, but the official bark should contain not less 
 than 5 per cent, of total alkaloids, and at least 4 per cent, of anhy- 
 drous ether-soluble alkaloids. 
 
 Quinine, Quinina, C 20 H 24 N 2 O 2 .3H 2 O = 375.46. This formula 
 represents the official alkaloid, but it is also known anhydrous, and 
 in combination with either one or two molecules of water. The 
 anhydrous quinine is a resinous substance, while the crystallized 
 quinine is a white, flaky, amorphous or crystalline powder, having 
 a very bitter taste and an alkaline reaction. It is nearly insoluble in 
 water, but soluble in alcohol, ether, ammonia water, chloroform, and 
 dilute acids. When heated to about 57 C. (134 F.) it melts ; at 
 100 C. (212 F.) it loses 2 molecules of water, the remainder being 
 expelled at 125 C. (257 F.). 
 
 Quinine sulphate, Quininse sulphas, (C 20 H 24 N 2 O 2 ) 2 H 2 SO 4 .7H 2 O 
 = 866.15. This salt, containing two molecules of the alkaloid in 
 combination with one of sulphuric acid and seven of water, is the 
 common form of quinine sulphate. It forms snow-white, silky, light 
 and fine, needle-shaped crystals, fragile and somewhat flexible, making 
 a very light and easily compressible mass ; it has a very bitter taste 
 and a neutral reaction ; it is soluble in 720 parts of cold and in 30 
 parts of boiling water ; soluble in 65 parts of alcohol, but nearly 
 insoluble in ether and chloroform ; it readily dissolves in diluted 
 sulphuric or hydrochloric acid. 
 
 Quinine bisulphate, Quininse bisulphas, C 20 H 24 N 2 O 2 .H 2 SO 4 .7H 2 O 
 = 544.33. This salt is formed when the common sulphate is dis- 
 solved in an excess of diluted sulphuric acid. It crystallizes in color- 
 less, silky needles, has a strongly acid reaction, and is soluble in 8.5 
 parts of water. 
 
ALKALOIDS. 609 
 
 Quinine hydrochloride, C 20 H 24 N 2 O 2 .HC1.2H 2 O =393.76. 
 Quinine hydrobromide, C 20 H 24 N,O 2 -HBr.2H 2 O = 420.06. 
 Quinine salicylate, 2(C 20 H2 4 N 2 O 2 .C 7 H 6 O 3 )H 2 O = 935.54. 
 
 The above three salts are obtained by treating quinine with the respective 
 acids ; they are white, crystalline substances ; the first two are easily, the sali- 
 cylate is sparingly soluble in water. 
 
 Iron and quinine citrate is a scale compound obtained by dissolving ferric 
 hydroxide and quinine in citric acid, evaporating, etc. 
 
 Analytical reactions : 
 
 1. Quinine or its salts, dissolved in water or in dilute acids, give, 
 after having been shaken with fresh chlorine water, or bromine 
 water, an emerald-green color on the addition of ammonium hydrox- 
 ide. (Plate YL, 4.) 
 
 The reaction is readily shown by treating 10 c.c. of a solution 
 (about 1 in 1500) with 2 drops of bromine water, and then with an 
 excess of ammonia water. The green color is due to the formation 
 of thalleioquin. 
 
 2. Solutions of quinine, treated with chlorine water, then with 
 fragments of potassium ferrocyanide, turn pink, then red on the 
 addition of ammonium hydroxide not in excess. 
 
 3. Solutions of quinine give with ammonia water a white pre- 
 cipitate of quinine, which is readily dissolved in an excess of 
 ammonia. The precipitate is also soluble in about twenty times its 
 own weight of ether (the other cinchona alkaloids requiring larger 
 proportions of ether for solution). 
 
 4. Most solutions of quinine, especially when acidulated with sul- 
 phuric acid, show a vivid blue fluorescence. 
 
 5. Neutral solutions of quinine are precipitated by alkaline oxa- 
 lates. 
 
 6. Quinine and its salts form colorless solutions with concentrated 
 sulphuric acid. A dark or red color indicates the presence of other 
 organic substances. 
 
 Quinidine, C 20 H 24 N 2 O 2 . Isomeric with quinine; it gives, like the 
 latter, a green color with chlorine water and ammonia, and forms 
 fluorescent solutions. Unlike quinine, it is precipitated from neutral 
 solutions by potassium iodide. 
 
 Cinchonine, C 19 H 22 N 2 O. This alkaloid is found in cinchona bark 
 in quantities varying from 0.5 to 3 per cent. It crystallizes without 
 water, forming white needles ; it is almost insoluble in water, soluble 
 
 39 
 
610 CONSIDERATION OF CARBON COMPOUNDS. 
 
 in 116 parts of alcohol or in 163 parts of chloroform, readily soluble 
 in dilute acids. 
 
 By dissolving the alkaloid in sulphuric acid is obtained: 
 Cinchonine sulphate, Cinchonince sulphas, (C 19 H 22 N 2 O) 2 H 2 SO 4 .2H 2 O. 
 It is a white, crystalline substance. Cinchonine differs from quinine 
 by its greater insolubility in ether, by its insolubility in ammonia 
 water, by not forming fluorescent solutions, and by not giving a 
 green color with chlorine water and ammonia. 
 
 Analytical reactions: 
 
 " 1. Chlorine water added to the solution of a cinchonine salt pro- 
 duces a yellowish-white precipitate insoluble in excess of ammonia. 
 
 2. Potassium ferrocyanide solution added to a neutral solution of 
 cinchonine produces a white precipitate soluble in excess of the re- 
 agent. Upon adding an acid to this solution a golden-yellow 
 precipitate is formed. 
 
 3. With alkali hydroxides, carbonates, and bicarbonates, cincho- 
 nine salts form white precipitates insoluble in ammonia. 
 
 Cinchonidine, C^H^N^p. An alkaloid isomeric with cinchonine; 
 soluble in 75 times its weight in ether. The sulphate, which crystal- 
 lizes with 3 molecules of water, is official. 
 
 Strychnine, Strychnina, C^H^N^ = 331.73. This alkaloid is 
 found, together with brucine, in the seeds and bark of different 
 varieties of Strychnos, and is generally obtained from nux vomica. 
 Strychnine is a white, crystalline powder, having an intensely bitter 
 taste, which is still perceptible in solutions containing 1 in 700,000. 
 It is nearly insoluble in water and in ether, soluble in chloroform 
 and in dilute acids. 
 
 Strychnine has strong basic properties and is one of the most 
 powerful poisons known, one-quarter of a grain having caused death 
 within a few hours. 
 
 By dissolving it in sulphuric acid or nitric acid the official strych- 
 nine sulphate, strychnines sulphas, (C 21 H 22 N 2 O 2 ) 2 .H 2 SO 4 .5H 2 O, or 
 strychnine nitrate, strychnince nitras, (C 21 H 22 N 2 O 2 .HNO 3 ), is obtained. 
 
 Analytical reactions : 
 
 1. Strychnine dissolves in sulphuric acid and nitric acid without 
 color. 
 
 j^2. A fragment of potassium dichromate, drawn through a solution 
 of strychnine in concentrated sulphuric acid, produces momentarily a 
 blue, then brilliant violet color, which slowly passes to cherry-red, 
 
ALKALOIDS. 611 
 
 then to rose-pink, and finally to yellow. This reaction may still be 
 noticed with -g^-g^ grain of strychnine (Plate VI., 5). 
 
 3. Sonnemchein's ted. When to a very small quantity of strych- 
 nine, dissolved in a drop of sulphuric acid, some ceroso-ceric oxide is 
 added, and the mixture is stirred with a glass rod, a deep-blue color 
 is produced, changing soon to violet, and finally remaining cherry- 
 red. One part of strychnine in one million parts of water can thus 
 be recognized. The reagent may be made by heating cerium oxalate 
 to redness and dissolving it in 30 times its weight of sulphuric 
 acid. 
 
 4. Solutions of strychnine give with diluted solution of potassium 
 dichromate a yellow, crystalline precipitate, which, when collected, 
 washed, and heated with concentrated sulphuric acid, shows the play 
 of colors described in test 2. A play of colors similar to the above 
 is shown under identical conditions by mixtures of other alkaloids ; 
 for instance, by morphine containing 10 per cent of hydrastine. 
 
 5. Neutral solutions of strychnine give yellow precipitates with 
 the chlorides of gold and platinum and with picric acid; a white 
 precipitate with mercuric chloride, potassium hydroxide, and with 
 chlorine-water ; a greenish-yellow precipitate with potassium ferro- 
 cyanide. 
 
 Brucine, C 23 H 26 N 2 O 4 .4H 2 O. This alkaloid is found associated 
 with strychnine in various species of Strychnos. It is readily soluble 
 in alcohol, amyl alcohol, and chloroform, but sparingly soluble in 
 cold water and in ether. 
 
 Analytical reactions : 
 
 1. To 1 c.c. of water add 5 drops of nitric acid and 5 milligrammes 
 of brucine ; a deep blood-red color results. Heat the liquid until it 
 has assumed a yellow color, then add 9 c.c. of cold water and a few 
 milligrammes of sodium thiosulphate (or a small crystal of stannous 
 chloride) ; a beautiful amethyst or violet color results (Plate VI., 6). 
 
 2. Fresh chlorine water, added drop by drop to a concentrated 
 brucine solution, produces a red color, turning violet, and becoming 
 colorless on addition of an excess of chlorine. 
 
 Veratrine, Veratrina. This is a mixture of alkaloids obtained 
 from the seed of Asagraa officinalis. It is a white, amorphous, rarely 
 crystalline powder, highly irritating to the nostrils ; nearly insoluble 
 in water, readily soluble in alcohol. 
 
 Analytical reactions : 
 
 1. Concentrated sulphuric acid causes with veratrine first a yellow, 
 
612 CONSIDERATION OF CARBON COMPOUNDS. 
 
 then reddish-yellow, intense scarlet, and, finally, violet-red color. 
 (Plate VI., 8.) The yellow or orange-red solution exhibits, by re- 
 flected light, a greenish fluorescence. 
 
 2. Veratrine, when heated with concentrated hydrochloric acid, 
 dissolves with a blood-red color. 
 
 3. Bromine water colors veratrine violet. 
 
 4. Veratrine forms with nitric acid a yellow solution. 
 
 The isoquinoline group of alkaloids. 
 
 Opium is the concrete, milky exudation obtained, in the Orient, 
 by incising the unripe capsules of papaver somniferum, poppy. 
 Chemically, opium is a mixture of a large number of substances, 
 containing besides glucose, fat, gum, albumin, wax, volatile and 
 coloring matter, meconic acid, etc., not less than sixteen or eighteen 
 different alkaloids, many of which are, however, present in minute 
 quantities. 
 
 Ordinary opium should contain not less than 9 per cent., and when 
 dried at 85 C. (185 F.) not less than 12 per cent, nor more than 
 12.5 per cent, of morphine, to be the official article. Dried and pow- 
 dered opium, after having been exhausted with purified petroleum 
 benzene (which dissolves chiefly the narcotine, but not the morphine 
 salts), is the deodorized opium of the U. S. P. 
 
 Morphine, Morphina, C 17 H 19 NO 3 .H 2 O = 303 (Morphia). A 
 white crystalline powder, or colorless, shining, prismatic crystals, 
 odorless, of a bitter taste, and an alkaline reaction to litmus ; almost 
 insoluble in ether and chloroform, very slightly soluble in cold 
 water, soluble in 300 parts of cold, and 36 parts of boiling, alcohol ; 
 heated for some time at 100 C. (212 F.) it becomes anhydrous ; at 
 254 C. (489 F.) it melts, forming a black liquid. 
 
 The following salts are official : 
 
 Morphine acetate, Morphines acetas, C 17 H 19 NO 3 .C,H 4 O 2 .3H 2 O. 
 
 Morphine hydrochloride, Morphinse hydrochloridum, C 17 H 19 NO 3 .HC1.3H 2 O. 
 Morphine sulphate, Morphinae sulphas, (C n H 19 NO 3 ) 2 H 2 SO 4 .5H 2 O. 
 
 The above three salts are white, and soluble in water. 
 
 Analytical reactions : 
 
 1. Morphine or a morphine salt sprinkled upon nitric acid assumes 
 an orange-red color, and then produces a reddish solution, gradually 
 changing to yellow. (Plate VI., 1.) 
 
 ^,2. Neutral solution of ferric chloride causes a blue color with 
 morphine or with neutral solutions of morphine salts ; the color is 
 
ALKALOIDS. 613 
 
 changed to green by an excess of the reagent, and is destroyed by 
 free acids or alcohol, but not by alkalies. (Plate VI., 2.) 
 
 3. A fragment of iodic acid added to a strong solution of a mor- 
 phine salt is decomposed, with liberation of iodine, which imparts a 
 violet color to chloroform upon shaking the latter with the mixture. 
 
 4. A mixture of 2 parts of morphine and 1 part of cane-sugar 
 added to concentrated sulphuric acid gives a rose-red color. 
 
 5. Morphine dissolves in cold, concentrated sulphuric acid, forming 
 a colorless solution, which, after standing for several hours, turns 
 pink or red on the addition of a trace of nitric acid. 
 
 6. Aqueous or acid solutions of morphine salts are precipitated by 
 alkaline hydroxides ; the precipitated morphine is soluble in potas- 
 sium or sodium hydroxide, but not in ammonium hydroxide. 
 
 7. Neutral solutions of morphine afford yellow precipitates with 
 the chloride of gold or platinum, with potassium chromate or dichro- 
 mate, and with picric acid, but not with mercuric chloride. 
 
 Heroin, C 17 H 17 (C 2 H 3 O 2 ) 2 NO, is diacetyl-raorphine, obtained by heating 
 morphine with acetyl chloride. It is a white powder, having a bitter taste, 
 alkaline reaction, and practically insoluble in water, easily soluble in hot alco- 
 hol. It readily forms salts with acids, the one usually employed being the 
 hydrochloride, which is a white powder, of bitter taste, soluble in 2 parts of 
 water and in alcohol. It is precipitated by alkalies, carbonates, and alkaloid 
 reagents. 
 
 Apomorphine, C 17 H 17 NO 2 . When morphine is heated for some 
 hours with an excess of hydrochloric acid, under pressure to 150 C. 
 (302 F.), it loses water and is converted into apomorphine, a crys- 
 talline alkaloid valuable as an emetic. 
 
 Apomorphine hydrochloride, C 17 H 17 NO 2 .HC1 (U. S. P.), is a grayish- 
 white salt which turns greenish when exposed to light and air. 
 
 Analytical reactions : 
 
 1 . Nitric acid produces a deep purple color fading to orange. 
 
 2. Sulphuric acid containing a trace of nitric acid produces a blood- 
 red color fading to orange. 
 
 3. Sulphuric acid containing a trace of selenious acid produces a 
 dark blue color, fading to violet, then turning black. 
 
 4. Sulphuric acid containing a trace of ferric chloride produces a 
 pale blue color. 
 
 Codeine, Codeina, C 18 H 21 NO 3 .H 2 O =- 314.83. A white crystalline 
 powder, sparingly soluble in cold water, easily soluble in alcohol and 
 chloroform. It is neutral to litmus and has a faintly bitter taste. 
 
614 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Codeine has been found to be morphine methyl-ether, and is made 
 synthetically by heating morphine with methyl-iodide. 
 
 Codeine combines with acids to form salts soluble in water, of which 
 the following are official : 
 
 Codeine phosphate, Codeinae phosphas, C 18 H 21 NO 3 .H 3 PO4.2H 2 O. 
 Codeine sulphate, Codeinse sulphas, (C 18 H 21 NO 3 ) 2 .H 3 SO 4 .5H 2 O. 
 
 Analytical reactions : 
 
 1. On adding to 5 c.c. of an aqueous solution of codeine (1 : 100) 
 10 drops of bromine water, shaking so as to redissolve the precipitate 
 formed, and adding after a few minutes some ammonia water, the 
 liquid assumes a claret-red tint. (Plate VI., 3.) 
 
 2. Codeine heated with sulphuric acid containing a drop of nitric 
 acid gives a blood-red color. 
 
 3. Codeine, dissolved in sulphuric acid, forms a colorless liquid, 
 which, upon being warmed with a trace of ferric chloride, becomes 
 deep blue. 
 
 4. Crystals of codeine sprinkled upon nitric acid assume a red 
 color, but the acid will acquire only a yellow, not a red color. (Dif- 
 ference from morphine.) 
 
 5. Sulphuric acid containing a trace of selenious acid gives a green 
 color, changing rapidly to blue, and then slowly back to grass-green. 
 
 Dionin, C 19 H 2 30 3 N.HC1 4- H 2 0, is the hydrochloride of the ethyl ester of 
 morphine, which is similar to codeine, the methyl ester of morphine, and is 
 prepared in the same manner as the latter. It is a white, odorless, slightly 
 bitter powder, soluble in 7 parts of water and 2 parts of alcohol ; insoluble in 
 ether and chloroform. It is distinguished from morphine salts by its insolu- 
 bility in excess of alkali. Some authorities claim that it possesses no advan- 
 tage over codeine. 
 
 Narcotine, C 22 H 23 N0 7 , and Narceine, C 23 H 27 N0 8 .3H.,0, are white crystalline 
 opium alkaloids, which are almost insoluble in water, soluble in alcohol. 
 Concentrated sulphuric acid forms with narcotine a solution which is at first 
 colorless, but turns yellow in a few minutes, and purple on heating. Narceine 
 dissolves in concentrated sulphuric acid with a gray-brown color, which changes 
 to red when heated. 
 
 Stypticin, C 12 H 13 3 N.HC1 ( Cotarnine hydrochloride), is a salt of cotarnine, 
 an oxidation product of narcotine, similar to hydrastinine. Cotarnine is ob- 
 tained by boiling narcotine for a long time with water, or by heating it with 
 dilute nitric acid. Stypticin is a yellow powder, soluble in water and in alco- 
 hol. Its solution gives, with iodine solution, a brown precipitate of cotarnine 
 periodide. It is a hemostatic, analgesic, and uterine sedative. 
 
ALKALOIDS. 615 
 
 Meconic acid, C 7 H 4 O 7 .3H 2 O. A tribasic acid, characteristic of 
 opium, in which it exists to the extent of 3 or 4 per cent., most 
 likely combined with the alkaloids. It is a white, crystalline sub- 
 stance, soluble in water and alcohol. 
 
 Meconic acid forms with ferric chloride a blood-red color, which is 
 not affected by dilute acids or by mercuric chloride (different from 
 ferric sulphocyanate), but disappears on the addition of stannous 
 chloride and of the alkali hypochlorites. This test may be used in 
 cases of poisoning to decide whether opium or morphine is present. 
 
 Hydrastine, Hydrastina, C 21 H 21 N0 6 = 380.32. Found together with ber- 
 berine in the rhizome of Hydrastis Canadensis (golden seal) in quantities vary- 
 ing from 0.1 to 0.2 per cent. Hydrastine crystallizes in four-sided, colorless 
 prisms ; it fuses at 131 C. (268 F.), is insoluble in water and benzin, soluble 
 in about 2 parts of chloroform, 124 parts of ether, and 135 parts of alcohol at 
 the ordinary temperature. 
 
 Hydrastine answers to all the. general tests for alkaloids; treated with con- 
 centrated sulphuric acid it shows a yellow color, turning red, then purple on 
 heating. Concentrated nitric acid produces a yellow color, changing to orange. 
 The fluorescence noticed in solutions of hydrastine or its salts is due to pro- 
 ducts formed from it by oxidation. While hydrastine itself crystallizes very 
 readily, especially from solutions in acetic ether, its salts can scarcely be 
 obtained in crystals. 
 
 Hydrastinine, C 11 H 11 NO 2 . When hydrastine is treated with 
 oxidizing agents it is converted into hydrastinine, the hydrochloride 
 of which is official. This salt has a pale-yellow color, a bitter, saline 
 taste, and is soluble in 0.3 part of water, and also readily soluble in 
 alcohol, but difficultly soluble in ether or chloroform. A dilute 
 aqueous solution of the salt (up to about 1 in 100,000) has a decided 
 blue fluorescence. 
 
 Berberine, C 20 H 17 N0 4 . Found in a number of plants (Berberis Tulgaris, 
 Hydrastis Canadensis, etc.) belonging to entirely different families. It is a 
 yellow, crystalline substance, soluble in 7 parts of alcohol, 18 parts of water, 
 insoluble in ether, chloroform, and benzene. 
 
 Berberine not only forms well-defined, readily crystallizing salts with acids, 
 but it also enters into combination with a number of other substances, as, for 
 instance, with alcohol, ether, chloroform, etc. Some of these compounds crys- 
 tallize well, as for instance, berberine-chloroform, C 20 H 17 NO 4 .CHC1 3 . 
 
 The xanthine alkaloids. 
 
 Caffeine and theobromine are xanthine derivatives and are closely 
 connected with uric acid. They show the properties of alkaloids to 
 a much less degree than the majority of the compounds considered in 
 this chapter ; they do not act on red litmus and are but feebly basic. 
 
616 CONSIDERATION OF CARBON COMPOUNDS. 
 
 Theobromine has been obtained from xanthine, C 5 H 4 N 4 O 2 (a base found in 
 animal liquids), by treating its lead compound with methyl-iodide, CH 8 I, when 
 lead iodide and dimethyl-xanthine are formed. By introducing a third methyl 
 group into the molecule of theobromine trimethyl-xanthine, i. e., caffeine or 
 theine is formed. These facts show the close relationship between the active 
 principles of the vegetable substances used so extensively in the preparation 
 of the beverages, coffee, tea, and chocolate. And again, these principles show 
 a relationship to a series of substances (such as xanthine, uric acid, and others) 
 which are found in animal fluids. 
 
 Caffeine, Caffeina, C 8 H 10 N 4 O 2 .H 2 O or C 5 H(CH 3 ) 3 N 4 O 2 .H 2 O = 
 210.64 (Trimethyl-xanthine, Theine, Guaranine), occurs in coffee, tea, 
 Paraguay tea, and a few other plants. It forms fleecy masses of long, 
 flexible, silky needles, which are soluble in about 45 parts of water 
 and in 53 parts of alcohol ; it has a slightly bitter taste and a neutral 
 reaction. 
 
 Caffeine is dissolved by sulphuric acid without color ; when evapo- 
 rated to dryness with hydrochloric acid and a little potassium chlorate 
 the mass assumes a purple color on holding it over ammonia-water. 
 
 Two volumes of a saturated solution of caffeine in water mixed 
 with one volume of mercuric chloride solution form after a short time 
 large crystals of caffeine-mercuric chloride. 
 
 Oitrated caffeine (U. S. P.) is obtained by adding caffeine to a solu- 
 tion of citric acid and evaporating the mixture to dryness. 
 
 Theobromine, C 7 H 8 N 4 O 2 (Dimethyl-xanthine^). Found in the seeds 
 of Theobroma cacao, a tree growing in the tropics. It is white, crys- 
 talline, sparingly soluble in cold water, alcohol, and ether, volatilizes 
 without decomposition at 290 C. (554 F.), has a neutral reaction, 
 but forms with acids well-defined salts. 
 
 Theobromine sodium salicylate, C 7 H 7 N 4 O 2 .Na -f C 7 H 5 O 3 .Na (Diure- 
 tin), is a double salt of theobromine-sodium and sodium salicylate. It is 
 obtained by dissolving in water molecular proportions of sodium hydroxide, 
 theobromine, and sodium salicylate, and evaporating the solution to dryness. 
 It is a white powder, containing 50 per cent, of theobromine, readily soluble in 
 water, and easily decomposed by exposure to carbon dioxide or by acids. It is 
 incompatible with acids, bicarbonates, borates, phosphates, ferric salts, chloral, 
 etc. Its effects are like those of theobromine, but it has the advantage of 
 greater solubility. 
 
 Unclassified alkaloids. 
 
 Physostigmine, C 15 H 21 N 3 O 2 (Eserine). Found in the seeds of 
 Physostigma venenosum (Calabar bean). The pure alkaloid does not 
 crystallize well, is almost tasteless, and assumes gradually a reddish 
 tint. The sulphate and salicylate are official. Both are white or 
 yellowish-white crystalline powders, which have a bitter taste. The 
 sulphate is readily, the salicylate sparingly soluble in water. 
 
ALKALOIDS. 617 
 
 Analytical reactions : 
 
 1. Five milligrammes of physostigmiue dissolved in 2c.c. of 
 ammonia water yield a yellowish -red liquid which, on evaporation 
 on a water-bath, leaves a blue or bluish -gray residue, soluble in 
 alcohol, forming a blue solution. Upon supersaturation with acetic 
 acid this becomes violet and exhibits a strong reddish fluorescence. 
 The violet solution leaves on evaporation a residue which is first 
 green and afterward blue. (Plate VI., 7.) 
 
 2. Physostigmine or its salts give with calcium oxide and water a 
 red liquid which turns green on heating. 
 
 Aconitine, Aconitina, C 34 H 47 NO n . Found in various species of 
 aconitum to the amount of about 0.2 per cent. It is a white crystal- 
 line powder, requiring for solution 3200 parts of water or 22 parts 
 of alcohol. 
 
 Aconitine is one of the most poisonous substances known and 
 should never be tasted except in highly diluted solutions, which cause 
 a characteristic tingling sensation when brought in contact with the 
 mucous surfaces of the tongue. A dilute aqueous solution is precipi- 
 tated by alkalies, tannic acid, mercuric potassium iodide, but only 
 concentrated solutions yield precipitates with platinic chloride, mer- 
 curic chloride, and picric acid. 
 
 Any soluble salt of aconitine in dilutions of 1 : 1000 produces 
 with a drop of potassium permanganate solution a blood-red precipi- 
 tate of aconitine permanganate. 
 
 Colchicine, Colchicina, C^H^NOg = 396.23. This alkaloid is 
 obtained from Colchicum. It is a pale yellow amorphous powder or 
 leaflets, having a very bitter taste. It is soluble in 22 parts of water 
 and very soluble in alcohol and chloroform. It melts at 142 C. 
 (288 F.). Sulphuric acid produces a citron-yellow color, changed 
 to greenish-blue, then to red, and finally to yellow by the further 
 addition of nitric acid. Excess of potassium hydrate changes this 
 to red. 
 
 Ptomaines (Putrefactive or cadaveric alkaloids). It has been 
 known for a long time that vegetable, and more especially animal 
 matter, when in a state of decomposition (putrefaction) acts generally 
 as a poison, both when taken as food or when injected under the skin. 
 Though many attempts had been made to isolate the poisonous pro- 
 ducts, this was not accomplished successfully until the years 1873 to 
 
618 CONSIDERATION OF CARBON COMPOUNDS. 
 
 1876, by Francesco Selmi, of Italy. He demonstrated that a great 
 number of basic substances can be extracted from putrid matter by 
 treating it successively with ether, chloroform, amyl alcohol, and 
 other solvents. He also showed that these substances resemble vege- 
 table alkaloids in many respects, and assigned to them the name 
 ptomaines, derived from TITS/MO, that which is fallen i. e., a cadaver. 
 Although Selmi did not succeed in isolating any of the ptomaines 
 completely (he experimented with extracts only) his investigations 
 stimulated other scientists, and by the united efforts of many workers 
 our knowledge of ptomaines has now advanced so far, that general 
 statements can be given in regard to their origin, composition, phys- 
 ical and chemical properties, action upon the animal system, etc. 
 
 Formation of ptomaines. It has been shown in Chapter 41 that 
 albuminous substances under favorable conditions undergo a decom- 
 position termed putrefaction. Presence of moisture, a suitable tem- 
 perature, and the action of a ferment are the essential factors in 
 putrefaction. The ferments are living organized beings, termed 
 germs, bacteria, bacilli, microbes, organized ferments, etc. 
 
 It is during the growth, development, and multiplication of these 
 micro-organisms that the decomposition of the albuminous sub- 
 stances into simpler forms of matter takes place. A full explanation 
 of the exact mode of the formation of decomposition-products from 
 organic matter by the action of bacteria has not been furnished yet, 
 but we do know that ptomaines are found among these products. 
 We also know that certain bacteria split up organic molecules in a 
 certain direction, i. e., with the formation of certain products. We 
 also know that while micro-organisms live chiefly in dead organic 
 matter, they also have the power of existing and multiplying in the 
 living organism, causing the decomposition of living tissues, often 
 with the formation of ptomaines. 
 
 General properties of ptomaines. Ptomaines resemble veg- 
 etable alkaloids in all essential properties. Some contain carbon, 
 hydrogen, and nitrogen only, corresponding to the volatile alkaloids, 
 such as coniine and nicotine, while others contain oxygen also, corre- 
 sponding to the fixed alkaloids. 
 
 Ptomaines and alkaloids both have the basic properties and the 
 power to combine with acids to form well-defined salts ; they have in 
 common a number of characteristic reactions, such as the formation of 
 precipitates with the chlorides of platinum, mercury, gold, as also 
 with tannic acid, phospho-molybdic acid, picric acid, etc. ; and both 
 
ALKALOIDS. 619 
 
 show corresponding solubility and insolubility in the various solvents 
 generally used for the extraction of alkaloids. 
 
 Ptomaines not only possess the general characters of true alka- 
 loids, but even the often highly characteristic color-tests of the latter 
 are in some cases almost identical with those of ptomaines. Thus, 
 ptomaines have been found which resemble in their chemical 
 properties as well as in their physiological action upon the animal 
 system, the alkaloids morphine, atropine, strychnine, coniine, digi- 
 taline, etc. 
 
 Many attempts have been made to find some characteristic prop- 
 erties by which to differentiate between the putrefactive and the 
 vegetable alkaloids, but practically without results. It is true that 
 most vegetable alkaloids are optically active, while ptomaines are 
 inactive, but it does not often happen that ptomaines are obtained in 
 such quantities as to permit of an exact determination of optical 
 properties. 
 
 Under these conditions it is evident that the toxicologist has a most 
 difficult task, when called upon to examine a body (especially when 
 already in a state of decomposition) for alkaloidal poisons. How 
 many times, in former years, chemists may have unjustly claimed the 
 presence of poisonous vegetable alkaloids in material given them for 
 examination, we cannot say, but we do know of a number of cases 
 of recent date in which such claims were shown to be based upon 
 errors, made in consequence of the close analogy between ptomaines 
 and alkaloids. 
 
 While the poisonous properties of some ptomaines are well marked, 
 others are more or less inert. The poisonous ptomaines are now 
 often termed toxines, in order to distinguish them from the inert 
 basic products of putrefactive changes. 
 
 The toxines are of special interest to the physician, because it is 
 now known that infectious diseases are caused by the poisonous prod- 
 ucts formed by the growth, multiplication, and degeneration of micro- 
 organisms in the living body. This statement is of far-reaching im- 
 portance, as it opens a new field for investigation in connection with 
 the treatment of infectious diseases. 
 
 Non-poisonous ptomaines. A number of these basic substances 
 have been known for a long time. Some of them are also formed by 
 other processes than those of putrefaction, and the term ptomaines 
 may, therefore, not well be chosen for all of them. However, the 
 
620 CONSIDERATION OF CARBON COMPOUNDS. 
 
 close relationship between these substances unites them into a natural 
 group, of which the following members may be mentioned: 
 
 Methylamine, NH 2 .CH 3 , the simplest organic base that can be formed, has 
 been found in decomposing herring, pike, haddock, poisonous sausage, cultures 
 of comma bacillus on beef-broth, etc. It is an inflammable gas of strong ain- 
 moniacal odor. 
 
 Dimethylamine, NH(CH 3 ) 2 , has been found in putrefying gelatin, decom- 
 posing yeast, poisonous sausage, etc. It is, like the former, a gas at ordinary 
 temperature. 
 
 Trimethy famine, N(CH 3 ) 3 , has been shown for a long time to occur in some 
 animal and vegetable tissues. Its presence has been demonstrated in leaves 
 of chenopodium, in the blood of calves, in human urine, etc., but it also occurs 
 as a product of putrefaction in yeast, meat, blood, ergot, etc. It is a liquid, 
 possessing a strong, fish-like odor. Boiling-point 9 C. (48 F.). 
 
 Ethylamine, NH 2 .C 2 H 5 ; DiSthylamine, NH.(C 2 H 5 ) 2 ; Triethylamim, N.(C 2 H 5 ) 3 ; 
 Propylamine, NH 2 .C 3 H 7 ; Neuridme, C 5 N 2 H 14 , are other non-poisonous volatile 
 ptomaines belonging to the amine group, while of the non-volatile amides 
 may be mentioned : My dine, C 8 H U NO ; Pyocyanine, C U H U NO 2 ; Betaine, C 5 H 13 
 N0 3 , etc. 
 
 Poisonous ptomaines. While no strict line of demarcation can 
 be drawn between poisonous and non-poisonous substances, the fol- 
 lowing list of ptomaines embraces those which cause serious dis- 
 turbances when brought into the animal system : 
 
 Isoamylamine, C 5 H 13 N, a colorless, strongly alkaline liquid, has been found 
 in putrefying yeast and in cod-liver oil . It is strongly poisonous, producing 
 rigor, convulsions, and death. 
 
 Cadaverine, C 5 H U N 2 , occurs very frequently in decomposing animal tissues, 
 and seems to be a constant product of the growth of the comma bacillus, 
 irrespective of the soil on which it is cultivated. It is a syrupy liquid, pos- 
 sessing an exceedingly unpleasant odor, resembling that of coniine. The sub- 
 stances which have been described by various scientists as " animal coniine " 
 were most likely cadaverine. This base is not very poisonous, but is capable 
 of producing intense inflammation, necrosis, and suppuration in the absence of 
 bacteria. 
 
 Neurine, C 5 H 13 NO, is a base which has been obtained by boiling protagon 
 with baryta, and has been formed by synthetical processes. It also occurs, 
 however, frequently in decomposing meat. It is exceedingly poisonous, even 
 in small doses. Atropine possesses a strong antagonistic action toward neurine, 
 and the injection of even a small quantity is sufficient to dispel the symptoms 
 of poisoning by neurine. 
 
 Choline, C 5 H 15 NO 2 , has been found in animal tissues, in a number of plants 
 (hops, ergot, Indian hemp, white mustard, etc.), and in putrid matters. It is 
 much less poisonous than neurine. 
 
 Mytilotoxine, C 6 H 15 NO 2 , is the poison found in poisonous mussels. It has a 
 strong paralysis-producing action, resembling curara in that respect. 
 
ALKALOIDS. 621 
 
 Typhotoxine, C 7 H 17 NO 2 , is looked upon as the specific toxic product of the 
 activity of Koch-Eberth's typhoid bacillus. The poison throws animals into a 
 paralytic or lethargic condition, so that they lose control over the muscles and 
 fall down helpless. Simultaneously frequent diarrhoeic evacuations take place, 
 and death follows in from one to two days. 
 
 Tetanine, C 13 H 30 N 2 O 4 , has been obtained from cultures of tetanus microbes, 
 from the amputated arm of a tetanus patient, and from the brain and nerve 
 tissues of persons who died from tetanus. It produces in animals the symp- 
 toms characteristic of tetanus, such as tonic and clonic convulsions. While 
 mice and rabbits are strongly affected by tetanine, dogs and horses seem to be 
 but slightly susceptible to its action. 
 
 Mydatoxine, C 6 H 13 NO 2 , has been obtained from human internal organs which 
 were kept for four months at a temperature varying from 9 to -f 5C. (16 
 to 41 F.). It is an alkaline syrup, which does not possess strong toxic 
 properties. 
 
 Tyrotoxlcon. The composition of this highly poisonous ptomaine has not 
 been established yet. It has been found in decomposing milk, in poisonous 
 cheese, ice-cream, and cream-puffs. 
 
 Spasmotoxine. Composition yet unknown. Obtained from cultures of the 
 tetanus-germ on beef-broth. Produces violent convulsions. 
 
 Leucomaines. The basic substances formed in the living tissues 
 by retrograde metamorphosis, during normal life, are known as leuco- 
 maines, in contradistinction to the ptomaines, or basic products of 
 putrefaction. To the group of leucomaines belong many substances 
 known long ago, such as creatine, creatinine, xanthine, guanine, and 
 others. Most of these bodies are non-poisonous, but some have been 
 discovered of late, possessing strong poisonous properties. The 
 accumulation of these substances in the body, because of incomplete 
 excretion or oxidation, produces auto-intoxication. The more impor- 
 tant leucomaines will be mentioned in the physiological part. 
 
 QUESTIONS. State the general physical and chemical properties of alka- 
 loids. Give a general method for the extraction and separation of alkaloids 
 from vegetables. Mention the chief constituents of opium. Mention the prop- 
 erties of morphine and its salts; give tests for them. Mention the principal 
 alkaloids found in cinchona bark. State the physical and chemical properties 
 of quinine and cinchonine. Which of their salts are official, and by what tests 
 may these alkaloids be recognized and distinguished from each other? Give 
 tests for strychnine, brucine, atropine, and veratrine. What is the chemical 
 relationship between xanthine, caffeine, and theobromine ? Mention proper- 
 ties of, and give tests for, cocaine. Mention the characteristic physical, chem- 
 ical, and physiological properties of ptomaines. 
 
VII. 
 PHYSIOLOGICAL CHEMISTRY. 
 
 53. PROTEINS. 
 
 General remarks. Physiological chemistry is that part of chem- 
 istry which has more especially for its object the various chemical 
 changes which take place in the living organism of either plants or 
 animals. It considers the chemical nature of the different substances 
 used as "food/' follows up the changes which this food undergoes 
 during its absorption and assimilation in the organism, and treats, 
 finally, of the products eliminated by it. The chemical changes tak- 
 ing place in the organism are either normal (in health) or abnormal 
 (in disease). The abnormal products formed under abnormal condi- 
 tions are generally termed " pathological " products. 
 
 Of the three classes of organic compounds, viz., fats, carbohydrates, 
 and proteins, from which our food-supply is chiefly derived, the first 
 two have been considered in the part on Organic Chemistry, while the 
 study of proteins is taken up in this chapter. 
 
 Occurrence in nature. Proteins form the chief part of the solid 
 and liquid constituents of the animal body ; they occur in blood, 
 tissues, muscles, nerves, glands, and all other organs ; they are also 
 found in small quantities in nearly every part of plants, and in larger 
 quantities in many seeds. They have never yet been formed by arti- 
 ficial means, but are almost exclusively products of vegetable and 
 animal life. 
 
 General properties. The word protein (formerly proteid) re- 
 fers to a member of that group of substances which consist, so 
 far as is known at present, essentially of combinations of a-amino- 
 
 623 
 
624 PHYSIOLOGICAL CHEMISTRY. 
 
 acids l and their derivatives, e. g. y a-amino-acetic acid or glycocoll ; 
 a-amino-propionic acid or alanine ; phenyl-a-amino-propionic acid or 
 phenylalanine ; guanidine-amino- valeric acid or arginine, etc., and are, 
 therefore, essentially polypeptides. The various proteins resemble one 
 another closely in their properties. Their composition is so complex 
 that, as yet, no chemical formula has been assigned to them with any cer- 
 tainty; they all contain carbon, hydrogen, oxygen, and nitrogen; most 
 contain sulphur, several phosphorus, and some iron. Various other 
 metallic and non-metallic elements have been found in certain proteins. 
 
 Nearly all proteins are amorphous, non-diffusible, colorless, odor- 
 less, nearly tasteless, and non-volatile. When heated under such 
 conditions that the volatile products formed are not burnt at all, or 
 only partially, a disagreeable odor is noticed, due chiefly to ammonia 
 derivatives. Proteins vary in solubility ; all are optically active, 
 most of them being laevorotatory, while haemoglobin and the nucleo- 
 proteins are dextrorotatory. Proteins are distinguished by the ease 
 with which they undergo chemical change under the influence of 
 reagents, ferments, or variations in temperature ; they all undergo 
 the process of putrefaction, which has been considered in Chapter 41. 
 
 By boiling with dilute acids or alkalies, and also by the action of 
 certain enzymes, the proteins undergo hydrolytic cleavage, forming 
 many simpler compounds. (The terms hydrolytic cleavage and 
 hydrolysis -will be explained more fully later on ; they refer to a 
 splitting up of complex molecules, while water or its constituents are 
 taken up at the same time.) 
 
 Classification. The classification here used is the one which has 
 been adopted by the American Society of Biological Chemists and 
 the American Physiological Society, and is as follows : 
 
 I. SIMPLE PROTEINS. a, Albumins; b, Globulins; c, Glutelins ; 
 d, Prolamines, or Alcohol-soluble proteins; e, Albuminoids; f, His- 
 tones ; g, Protamines. 
 
 II. CONJUGATED PROTEINS. a, Nucleoproteins ; b, Gtycoproteins ; 
 c, Phosphoproteins ; d, Haemoglobins ; e, Lecithoproteins. 
 
 III. DERIVED PROTEINS : 
 
 1. Primary protein derivatives: a, Proteans ; b, Metaproteins ; c, 
 Coagulated proteins. 2. Secondary protein derivatives : a, Proteases; 
 b, Peptones; c, Peptides. 
 
 1 Greek letters are, in some cases, used to indicate the position of substituting groups in a 
 molecule. In organic acids, the carbon atom next to the carboxyl group (COOH) is designated 
 by a, the next one by /3, the next one by y, etc. Thus, lactic acid is a-hydroxy-propionic 
 acid, CH 3 .CHOH.COOH; alanine is a-amino-propionic acid, CH 3 .CHNH 2 .COOH; glycocoll is 
 a-amino-acetic acid, CH 2 NH 2 .COOH ; hydracrylic acid is -hydroxy-propionic acid, CH 2 OH.- 
 CH 2 COOH. 
 
PROTEINS. 625 
 
 I. Simple proteins. 
 
 These are protein substances which yield only a-amino-acids or 
 their derivatives by hydrolysis. 
 
 The simple proteins occur in all animal and vegetable organisms. 
 In the animal body they are the most prominent solid constituents 
 of the muscles, glands, and blood-serum, and are found to a greater 
 or less extent in all tissues, secretions, and excretions. The percent- 
 age composition of simple proteins is as follows : 
 
 Carbon 50.0 to 55.0 per cent. 
 
 Hydrogen 6.5 " 7.3 " 
 
 Nitrogen 15.0 " 18.0 " 
 
 Oxygen 21.0 " 24.0 
 
 Sulphur 0.3 " 2.5 " 
 
 A few simple proteins contain phosphorus to the extent of 0.42 
 0.85 per cent., and a few contain also a trace of iron. 
 
 The nitrogen of proteins is split off in four forms, viz., as ammo- 
 nia, as diamino-acids, as monami no-acids, and as a guanidine residue. 
 Part of the nitrogen is easily split off as ammonia by the action of 
 alkalies. 
 
 By boiling proteins with alkalies, part of the sulphur is split off 
 as sulphide, while the remainder can be obtained as sulphate, after 
 fusing the residue with potassium nitrate and sodium carbonate. As 
 about one-half of the total sulphur present is obtained by each opera- 
 tion, it is assumed that there are at least two atoms of sulphur in the 
 protein molecule. 
 
 When acted upon by enzymes or other hydrolytic agents, the 
 simple proteins form first proteins of lower molecular weight, which 
 are diffusible and not coagulated by heat. By the prolonged action 
 of certain ferments (trypsin, bacteria, etc.), or by long boiling with 
 acids, they give rise to the formation of amino-acids (tyrosine, leucine, 
 aspartic, and glutamic acids), of the hexone bases (lysine, arginine, 
 histidine), and a number of undefined bodies. 
 
 In solubility the simple proteins vary ; some are soluble in water, 
 others only in water containing either acids, alkalies, or certain 
 neutral salts, while yet others are insoluble. The soluble proteins 
 are converted into insoluble modifications by the action of heat or 
 certain reagents. This change is called coagulation, and is distin- 
 guished from precipitation by the fact that proteins when once coagu- 
 lated cannot return to their original condition. The temperature at 
 which coagulation takes place depends on the nature of the protein 
 present, the reaction of the solution, and the presence of neutral salts. 
 40 
 
626 PHYSIOLOGICAL CHEMISTRY. 
 
 An alkaline solution of a protein will not coagulate on boiling ; a neutral 
 solution will do so partially ; a solution showing an acid reaction will be 
 coagulated completely on boiling, provided the quantity of neutral salt present 
 be not too small, and the protein solution not too dilute. 
 
 Tests for simple proteins. 
 
 a. Coagulation or precipitation tests. 
 
 (Use a solution made by dissolving white of an egg in about 10 parts of a 
 2 per cent, sodium chloride solution.) 
 
 1. Heat test. To 5 c.c. of protein solution add a few drops of 
 dilute acetic acid, and heat. The protein is completely coagulated. 
 
 2. Heller's test. Place 1 c.c. of nitric acid in a test-tube, and allow 
 a few c.c. of protein solution to flow down the side of the tube, taking 
 care that the liquids do not mix. A white, opaque ring of coagu- 
 lated protein forms at the line of junction. (Strong sulphuric, 
 hydrochloric, and metaphosphoric acids coagulate proteins in the 
 same way.) 
 
 3. To 5 c.c. of protein solution add solution of cupric sulphate ; 
 repeat with solutions of mercuric chloride, lead acetate, and silver 
 nitrate. In all cases coagulation takes place. (These reactions 
 explain the use of proteins, such as the white of egg, as antidotes in 
 cases of poisoning by metallic compounds.) 
 
 4. To 5 c.c. of protein solution add a few drops of acetic acid and 
 some potassium ferrocyanide solution ; coagulation takes place. 
 
 5. Saturate 10 c.c. of protein solution with ammonium sulphate ; 
 all proteins are precipitated except peptones. 
 
 6. Solutions of picric, trichloracetic, phosphotungstic, phospho- 
 molybdic, tannic, taurocholic, and nucleic acids, potassium mercuric 
 iodide, alcohol, all precipitate proteins under special conditions. 
 
 b. Color tests. 
 (Use any dry protein.) 
 
 1. Xanthoproteic reaction. Heat a small quantity of protein with 
 concentrated nitric acid ; the protein, or the solution, turns yellow. 
 Allow it to cool, and add an excess of ammonia : the color changes 
 to orange. (Plate VIII., 1.) 
 
 This reaction is due to the presence of the tyrosine and the trypto- 
 phane radicals in the protein molecule. 
 
 2. Milton's reaction. Pour a few c.c. of water on a small quantity 
 of protein ; add 1 c.c. of Millon's reagent, and boil : a purple-red 
 color develops. (Millon's reagent is made by dissolving 10 grammes 
 
PROTEINS. 627 
 
 of mercury in the same weight of pure nitric acid, and adding to the 
 cool solution 2 volumes of water.) This reaction is given by tyrosine. 
 
 3. Biuret reaction. Boil a small quantity of protein with 5 c.c. 
 of solution of sodium hydroxide, and after cooling add one or two 
 drops of dilute solution of cupric sulphate : a violet to pink color is 
 obtained, according to the amount of copper solution and the nature 
 of the protein. (Plate VIII., 2.) (It may be necessary to heat the 
 solution before a distinct color appears.) 
 
 This reaction is given by biuret, hence its name. 
 
 Boil a small quantity of protein in a test-tube with absolute alcohol ; filter, 
 wash with absolute alcohol, then with ether, and use the dry material for the 
 following tests. 
 
 4. Adamkieivicz's reaction. Dissolve a small quantity of the pro- 
 tein by boiling with glacial acetic acid. Allow to cool, and, holding 
 the test-tube in an inclined position, let 2 c.c. of concentrated sul- 
 phuric acid flow down the side of the tube. A violet or purple 
 color develops where the liquids meet. 
 
 This reaction is due to tryptophane, and is produced by an impurity 
 in the acetic acid used, i. e., glyoxylic acid, CHO COOH (Hopkins- 
 Cole). A few drops of a dilute solution of glyoxylic acid can be 
 added when the acetic acid used fails to give a positive test. 
 
 5. Lieberman's reaction. To some of the dry protein add concen- 
 trated hydrochloric acid : the protein turns deep blue to violet. On 
 standing, the color fades. Probably due to tryptophane. 
 
 Many of the above color-reactions will be given by the cleavage-products 
 of proteins, and by various other substances, but the proteins alone will 
 respond to all of the five tests. 
 
 (a) Albumins. These substances are soluble in water and are pre- 
 cipitated from their aqueous solution by large quantities of mineral 
 acids and by saturation of their solution with ammonium sulphate. 
 In a solution containing 1 per cent, of neutral salt they are coagulated 
 between 60 and 75 C. (140 and 167 F.). 
 
 They include ovalbumin (white of egg) ; serum-albumin of blood- 
 serum and serous fluids ; lactalbumin of milk ; and vegetable albumins. 
 
 (b) Globulins. These compounds are insoluble in water, but dis- 
 solve in water containing from 0.5 to 1 per cent, of some neutral salt. 
 The solution coagulates on heating, is precipitated by saturation with 
 magnesium sulphate or sodium chloride, and by the addition of an 
 equal volume of saturated solution of ammonium sulphate. Globulins 
 are precipitated if the salt be removed from their solution by dialysis. 
 
628 PHYSIOLOGICAL CHEMISTRY. 
 
 Serum- or para-globulin of blood, lacto-globulin of milk, and 
 fibrinogen are globulins. 
 
 (c) Glutelins are simple proteins insoluble in all neutral solvents, 
 but readily soluble in very dilute acids and alkalies. They occur in 
 abundance in the seeds of cereals. 
 
 (d) Prolamines or alcohol-soluble proteins. These are soluble 
 in 70 to 80 per cent, alcohol, and in dilute acids and alkalies, but in- 
 soluble in water, absolute alcohol, and other neutral solvents. Similar 
 to glutelins, they are found chiefly in the vegetable kingdom. For 
 instance, zein is found in maize, gliadin in wheat, hordein in barley, 
 etc. 
 
 (e) Albuminoids. Simple proteins which possess essentially the 
 same chemical structure as the other proteins, but are characterized 
 by great insolubility in all neutral solvents. They occur chiefly as 
 constituents of the skeleton, of the skin and its appendages, and 
 exist, as a rule, in an insoluble condition. To the albuminoids 
 belong : Keratins, elastin, collagen, and a few other substances. 
 
 Keratins occur as the principal constituents of the horny por- 
 tion of the skin and its appendages. A special keratin, neurokeratin, 
 is found in the nervous system. The keratins contain proportion- 
 ately more sulphur than other proteins, part of it in very loose com- 
 bination. The darkening of the hair by the use of a lead comb, 
 forming black lead sulphide, is due to the action of this sulphur. 
 The products of deep cleavage of the keratins are the same as those 
 of the proteins, but with relatively greater quantities of the sul- 
 phurized products, mainly in the form of cystine. 
 
 Keratins dissolve slowly in cold caustic alkalies, more rapidly on 
 heating. They are insoluble in water, alcohol, ether, and in gastric 
 and pancreatic juices. They give the xanthoproteic, biuret, and 
 Millon's reactions. 
 
 Elastin occurs in the connective tissue, particularly in yellow 
 elastic fiber; it contains very little sulphur (less than 0.5 per cent.), 
 and yields on deep cleavage the same products as simple proteins, 
 giving, however, glycocoll, little glutamic acid, and no aspartic acid. 
 
 Elastin is insoluble in water and in cold solutions of caustic alka- 
 lies ; it dissolves slowly in alkalies on boiling and in cold sulphuric 
 acid ; it is easily dissolved by warm nitric acid, as also by the action 
 of proteolytic enzymes. It shows the same color-reactions as the 
 keratins. 
 
 Collagen occurs in the fibre of connective tissue. Ossein, the 
 chief organic constituent of bone, is a collagen; and chondrin, a 
 
PROTEINS. 629 
 
 constituent of cartilage, is collagen mixed with a small quantity of 
 other material. 
 
 On boiling with water (more readily with acidified water) collagen 
 is converted into gelatin, while the latter, when heated to 130 C. 
 (266 F.), is converted into collagen. (Collagen may, therefore, be 
 considered an anhydride of gelatin.) 
 
 Gelatin yields no tryptophane, no tyrosine, and contains a rather 
 small percentage of sulphur. 
 
 Reticulin, occurring in reticular tissue, and skelatins, forming the skeletal 
 tissues of invertebrates, are classed with the albuminoids. 
 
 (/) Histones. Soluble in water and insoluble in very dilute 
 ammonia, and, in the absence of ammonium salts, insoluble even in 
 an excess of ammonia ; yield precipitates with solutions of other pro- 
 teins. On hydrolysis they yield a large number of amino-acids, 
 among which the basic ones predominate, such as arginine and histi- 
 dine, while others of them are absent (cystine, tyrosine). 
 
 (g) Protamines. Simpler polypeptides than the proteins included 
 in the preceding groups. They are soluble in water, uncoagulable by 
 heat, have the property of precipitating aqueous solutions of other 
 proteins, possess strong basic properties, and form stable salts with 
 strong mineral acids. They are the simplest natural proteins. 
 
 II. Conjugated proteins. 
 
 Substances which contain the protein molecule united to some 
 other molecule or molecules otherwise than as a salt. 
 
 (a) Nucleoproteins. These are compounds of one or more pro- 
 tein molecules with nucleic acid. They occur chiefly in the cell 
 nuclei, but are found also in the protoplasm. Nucleoproteins yield, 
 on digestion with pepsin, a simple protein, usually a histone or a pro- 
 tamine, and nuclein. Nuclein is generally but not always resistant 
 to peptic digestion. On treatment with caustic alkali it is split into 
 protein and nucleic acid, which is the important portion of the 
 nucleoproteins. This nucleic acid consists of a carbohydrate group 
 linking together nitrogenous bases and phosphoric acid. As there 
 are many different nucleic acids these constituent groups vary within 
 certain limits. The carbohydrates may be pentose or hexose. The 
 nitrogenous bases may be one or more purine bodies (guanine, adenine, 
 etc.) or pyrimidine derivatives (thymine, cytosine, uracil). The phos- 
 phoric acid is said to be metaphosphoric acid. The purine bodies in 
 nucleins are the origin of the uric acid of human urine. 
 
630 PHYSIOLOGICAL CHEMISTRY. 
 
 The nucleoproteins give all the color reactions, are soluble in water con- 
 taining a small quantity of alkali, and are precipitated from this solution by 
 acetic acid. "They are dextro-rotatory. 
 
 (6) Glycoproteins. Compounds of the protein molecule, with a 
 substance or substances containing a carbohydrate group other than a 
 nucleic acid. This carbohydrate group is capable of reducing cupric 
 oxide. Several groups of glycoproteins are differentiated as follows : 
 
 Mucins are secreted by the larger mucous glands of the body, 
 by certain mucous membranes, and are found also in the connective 
 tissue and umbilical cord. The mucins are soluble in water con- 
 taining a little alkali. The solution is mucilaginous, and with acetic 
 acid gives a precipitate insoluble in an excess of the acid. This 
 precipitate is not formed in the presence of 5 to 10 per cent, of 
 sodium chloride. The solution is not coagulated by heat nor pre- 
 cipitated by potassium ferrocyanide. An acid solution containing 
 salts is precipitated by tannic acid, and a similar neutral solution by 
 alcohol, as also by salts of heavy metals. Mucins when pure are 
 acid in reaction, and give the protein color-reactions. 
 
 Mucoids are certain mucin-like substances, such as colloid and 
 ovomucoid, and differing from the mucins in solubility and certain 
 other physical properties. The mucoids are not precipitated by 
 acetic acid. 
 
 Chondroproteins (chondromucoid, amyloid) yield chondroitin- 
 snlphuric acid as one of the decomposition-products. This latter 
 has the power to reduce cupric oxide and to precipitate proteins ; it 
 is sometimes found in the urine. 
 
 Chondromucoid occurs in cartilage; it resembles the mucins in 
 solubility and other properties. 
 
 Amyloid occurs pathologically as an infiltration in the spleen, liver, 
 kidneys, and other organs. Amyloid is insoluble without decomposi- 
 tion. It gives the biuret, xanthoproteic, Millon's, and Adamkiewicz's 
 reactions. 
 
 The reactions with the following coloring-matters are characteristic for 
 amyloid : It is colored red by aniline-green ; also red by methyl-aniline iodide, 
 especially after the addition of acetic acid ; violet or blue by iodine and sul- 
 phuric acid ; and reddish-brown or violet by iodine. 
 
 (c) Phosphoprotein. Compounds of the protein molecule with 
 some, as yet undefined, phosphorus-containing substance other than 
 a nucleic acid or lecithin. Caseinogen, the principal protein con- 
 stituent of milk, belongs to this group. 
 
PROTEINS. 631 
 
 (d) Haemoglobins. Compounds of the protein molecule, with 
 hseinatin or some similar substance. Haemoglobins form the coloring- 
 matters of the blood. On hydrolysis they yield a simple protein and 
 a substance called haemochromogen, which contains iron and is read- 
 ily oxidized to hsematin. (Further discussion under Blood.) 
 
 (e) Lecithoproteins. Compounds of the protein molecule with 
 lecithins, which will be considered later. (See Index for lecithins.) 
 
 III. Derived proteins. 
 
 These substances are derivatives of proteins, and are obtained from 
 them by hydrolytic changes of various kinds, e. g., through the action 
 of acids, alkalies, heat, or enzymes. 
 
 1. Primary protein derivatives. 
 
 Derivatives of the protein molecule apparently formed through 
 hydrolytic changes which involve only slight alterations of the pro- 
 tein molecule. 
 
 (a) Proteans. Insoluble products which apparently result from 
 the incipient action of water, very dilute acids, or enzymes on pro- 
 teins originally soluble. 
 
 (6) Metaproteins. Products of the further action of acids and 
 alkalies, whereby the molecule is so far altered as to form products 
 soluble in very weak acids and alkalies, but insoluble in neutral 
 fluids. The two principal metaproteins are the alkali metaprotein or 
 alkali albuminate and the acid metaprotein or acid albuminate. 
 
 Alkali metaprotein is formed when native proteins are acted upon 
 by alkalies to such an extent that part of the nitrogen, and occasion- 
 ally sulphur also, is eliminated from the molecule. The change 
 takes place slowly at the ordinary temperature, more rapidly on 
 heating. 
 
 Acid metaprotein is obtained by digesting a native protein with 
 dilute acid. 
 
 Alkali and acid metaproteins (album inates) have certain properties 
 in common. Both are insoluble in water or neutral salt solution, but 
 easily soluble in the presence of a small amount of either an acid or 
 an alkali. The solution does not coagulate on boiling, but is com- 
 pletely precipitated when neutralized. A solution in dilute acid is 
 also precipitated by saturation with magnesium sulphate, ammonium 
 sulphate, or sodium chloride, while a solution in alkali is not precipi- 
 tated by similar treatment. Although agreeing in many reactions, 
 alkali and acid metaproteins are essentially different. Thus the 
 
632 PHYSIOLOGICAL CHEMISTRY. 
 
 alkali metaproteins have decided acid properties, as can be shown by 
 the fact that on the addition of calcium carbonate they dissolve in 
 water with the liberation of carbon dioxide, a property not possessed 
 by acid metaproteins. 
 
 As part of the nitrogen is eliminated during the formation of alkali 
 metaproteins, the latter cannot be converted into acid metaproteins by 
 treatment with acids ; the reverse change, however, may be brought 
 about. 
 
 (c) Coagulated proteins. Insoluble products, which result from 
 the action of heat on their solutions, or from the action of alcohols on 
 the protein. The nature of the process of coagulation is unknown ; 
 the result is the formation of protein substances insoluble without 
 decomposition. In the liver and other glands coagulated proteins 
 have been found. Hard-boiled white of egg and fibrin are coagu- 
 lated proteins. 
 
 The temperature of coagulation is constant for any certain protein ; 
 it is, however, considerably modified by the presence or absence of 
 acids, alkalies, and salts in the solution. Fractional coagulation by 
 gradual heating of a solution of several proteins aifords a rough means 
 of separation. 
 
 2. Secondary protein derivatives. 
 
 Products of the further hydrolytic cleavage of the protein mole- 
 cule by acids, alkalies, superheated steam, or enzymes. 
 
 (a) Proteoses. Soluble in water, uncoagulated by heat, and pre- 
 cipitated by saturating their solutions with ammonium sulphate or 
 zinc sulphate. 
 
 Primary proteoses (protalbumoses) are precipitated by one-half 
 saturation with ammonium sulphate. 
 
 Secondary proteoses (deutero-albumoses) are precipitated by com- 
 plete saturation with ammonium sulphate. 
 
 There are several subdivisions of primary and secondary proteoses, 
 viz., hetero-proteoses, dysproteoses, the different properties of which 
 are not definite. 
 
 (6) Peptones. Soluble in water, uncoagulated by heat, and not 
 precipitated by saturating their solutions with ammonium sulphate. 
 They are the result of the digestion of proteins ; their solutions in 
 water are readily diffusible. The peptones are divided into anti-pep- 
 tones, hemi-peptones, and ampho-peptones. Here, again, the proper- 
 ties of the different classes are not definite. 
 
 The proteoses and peptones give a biuret reaction showing more 
 red color than the natural proteins. 
 
PROTEINS. 633 
 
 (c) Peptides. Definitely characterized combinations of two or more 
 ami no -acids, the carboxyl group of one being united with the amino 
 group of the other with the elimination of a molecule of water. The 
 peptones are peptides or mixtures of peptides, the latter term being 
 at present used to designate those of definite structure, such as poly- 
 peptides, dipeptides, etc. 
 
 Products of proteolysis. 
 
 Proteolysis is the change effected in proteins during their diges- 
 tion, and is brought about by the action of bodies termed proteolytic 
 agents, or enzymes. The products formed vary in quantity and com- 
 position with the nature of the proteins and enzymes, and depend 
 also on the condition under which the changes take place. While 
 the compounds grouped together as proteins differ widely in their 
 properties, yet the end-products of any proteolysis will be comprised 
 in a few amino-acids and nitrogenous bases. This would indicate that 
 there exists a close relation between the different proteins, the differ- 
 ence being due more to the atomic arrangement within the molecule 
 than to the quality and quantity of the elements present in protein 
 molecules. 
 
 These decomposition products of proteins are : 
 
 (1) Monamino-acids : 
 
 Glycocoll (amino-acetic acid), CH 2 .NH 2 .CO 2 H. 
 
 Alanine (aminopropionic acid), C 2 H 4 .NH 2 .CO 2 H. 
 
 Valine (amino-iso-valeric acid), C 4 H 8 .NH 2 .CO 2 H. 
 
 Aspartic acid (aminosuccinic acid), C 2 H 3 .NH 2 .(CO 2 H) 2 . 
 
 Glutamic acid (amino-pyrotartaric acid), C 3 H 5 .NH 2 .(CO 2 H) 2 . 
 
 Phenylalanine (phenyl-amino-propionic acid), C 6 H 5 .C 2 H 3 .NH 2 .CO 2 H. 
 
 Iso-leucine (amino-methyl-ethyl-propionic acid), C 6 H 10 .NH 2 .CO 2 H. 
 
 Leucine (amino-caproic acid), C 5 H, .NH 2 .CO 2 H. 
 
 Serine (amino-oxypropionic acid), C 2 H 3 (OH).NH 2 .CO 2 H. 
 
 Proline (pyrrolidine-carboxylic acid), C 4 H 7 .NH.CO 2 H. 
 
 Oxyproline (oxypyrrolidine-carboxylic acid), C 4 H 7 O.NH.CO 2 H. 
 
 Tryptophane (indol-amino-propionic acid), C U .H ]2 N 2 O 2 . 
 
 Cystine (disulphide of aminothio-propionic acid (cysteine), (C 2 H 3 S.NH 3 .- 
 
 C0 2 H) 2 . 
 Tyrosine (oxyphenyl-amino-propionic acid), C 8 H 8 O.NH 2 .CO 2 H. 
 
 (2) Diamino-acids (hexone bases) : 
 
 Arginine (guanidine-aminovaleric acid), C 6 H, 4 N 4 O 2 . 
 Histidine (amino-iimdazol-propionic acid), C 6 H 9 N 3 O 2 . 
 Lysine (diamino-caproic acid), C 6 H 14 N 2 O 2 . 
 
 An enormous amount of work is being done in the attempt to solve 
 the protein molecule by studying these substances (proteoses, peptones, 
 
634 PHYSIOLOGICAL CHEMISTRY. 
 
 peptides, ammo-acids) obtained by proteolysis. They are successively 
 simpler, more soluble, and more diffusible as the proteolysis proceeds. 
 The constitution of many of these simpler decomposition products has 
 now been well substantiated (amino-acids). It has been found pos- 
 sible to make a beginning in the synthesis of protein by forming com- 
 binations of amino-acids, linking the carboxyl group of one to the 
 amino group of another, with the elimination of a molecule of water. 
 This procedure can be repeated, and substances have been formed 
 containing thirty-six or more amino-acid molecules. These substances 
 are apparently entirely analogous to the peptides derived from the 
 proteins, as some of them give a biuret test, are acted upon by prote- 
 olytic enzymes (erepsin), and have other common properties. It is 
 probable, therefore, that this grouping is one of the many forms of 
 combination that must be present in the protein molecule. While all 
 of these amino-acids have been found in protein, they are not neces- 
 sarily all present in any one protein, and in different proteins they 
 are present in markedly different proportions. Experimental work 
 is beginning only now to show the significance of these differences 
 in the proteins. The molecular weights of the proteins cannot be 
 determined by any known methods, and the actual structural consti- 
 tution is entirely unknown. 
 
 As leucine and tyrosine are readily isolated (see Pancreatic Diges- 
 tion), their more important properties are stated here. 
 
 Tyrosine, C 6 H 4 .OH.C 2 H 3 (NH 2 )CO 2 H (Para-oxyphenyl-amino-pro- 
 pionic acid). This is obtained from all proteins, except collagen and 
 reticulin, by trypsin digestion, by prolonged boiling with dilute acids 
 or alkalies, by fusion with alkaline hydroxides, and by putrefaction. 
 Tyrosine is generally found with leucine ; both these substances have 
 nearly the same physiological properties and pathological significance. 
 They occur in the intestine during the digestion of proteins, and, patho- 
 logically, they are found in atheromatous cysts, in pus, in abscess and 
 gangrene of the lung, in the urine during yellow atrophy of the liver, 
 and in phosphorus poisoning. 
 
 Tyrosine crystallizes in colorless, fine, silky needles, often tufted 
 (Fig. 81). It is very slightly soluble in water, more so in the pres- 
 ence of alkalies and mineral acids, insoluble in alcohol and ether. 
 (For a method of preparing tyrosine and leucine from proteins, see 
 Pancreatic Digestion.) 
 
PROTEINS. 635 
 
 Analytical reactions of tyrosine. 
 
 1. Place a few crystals of tyrosine on a slide, and warm gently ; 
 they do not melt. (Crystals of fatty acids found in pus resemble 
 tyrosine in general appearance, but melt when heated, and are insolu- 
 ble in hydrochloric acid.) 
 
 2. To a very small quantity of tyrosine add water and a few drops 
 of Millon's reagent. On boiling, the mixture turns rose red ; and 
 on standing a deeper red color develops. (All phenols and their 
 derivatives show this reaction.) 
 
 3. Peria's reaction. Place a small quantity of tyrosine upon a 
 watch-glass, add a few drops of concentrated sulphuric acid, and 
 heat for half an hour over a boiling water-bath. Allow it to cool and 
 pour into 15 c.c. of water contained in a porcelain evaporating dish. 
 Warm, neutralize with powdered barium carbonate, filter while hot, 
 evaporate the filtrate to a few cubic centimeters, and add a very 
 dilute ferric chloride solution : a violet color appears. 
 
 Leucine, C 5 H 10 .NH 2 .CO 2 H (Amino-caproie acid). This is a con- 
 stant product of the cleavage of proteins. It is easily soluble in 
 hot water, less so in cold water, soluble in alcohol, insoluble in ether. 
 It is easily soluble in acids and alkalies, forming crystalline com- 
 pounds with mineral acids. When impure, leucine crystallizes in 
 rounded lumps which often show radiating striations (Fig. 80). 
 AVhen pure it forms white, glittering, flat crystals. 
 
 Analytical reactions of leucine. 
 
 1. Heat slowly in a dry test-tube a very small portion of leucine ; 
 it sublimes in the form of woolly flakes. If heated above its melting- 
 point, 170 C. (338 F.), it decomposes into carbon dioxide and 
 amylamine, the latter substance having a characteristic odor. The 
 
 reaction is this : 
 
 C 6 H 13 N0 2 = C0 2 + C B H u NH a . 
 
 2. Heat a little leucine in a dry test-tube, add a piece of caustic 
 soda and a few drops of water. Heat until the caustic soda melts, 
 when ammonia is given off. Allow to cool, dissolve in a little water, 
 and acidulate with dilute sulphuric acid : the odor of valeric acid is 
 noticeable. (Leucine, by this treatment, takes up oxygen and de- 
 composes into valeric acid, ammonia, and carbon dioxide.) 
 
 3. Dissolve a little leucine in water, decolorize if necessary with 
 animal charcoal, filter, render alkaline with caustic soda, and add 
 2 drops of cupric sulphate solution. The cupric hydroxide which is 
 
636 PHYSIOLOGICAL CHEMISTRY. 
 
 precipitated at first dissolves on shaking, giving a blue solution which 
 is not reduced on heating. 
 
 4. Sherer's reaction (applicable only to very pure leucine). Evapo- 
 rate carefully to dryness on a platinum foil a small portion of leucine 
 with a few drops of nitric acid. The residue is almost transparent, 
 and turns yellow or brown on the addition of caustic alkali. If this 
 mixture be again carefully concentrated, an oil-like drop is obtained, 
 which runs over the foil in a spheroidal state. 
 
 Hydrolysis. 
 
 In the animal body a certain kind of decomposition, called hydro- 
 lysis or hydrolytic cleavage, is particularly prominent. By cleavage 
 is meant the breaking up of a complex molecule into simpler ones, for 
 example, the splitting up of dextrose into alcohol and carbon dioxide : 
 
 C 6 H 12 O 6 == 2C 2 H 5 OH + 2CO 2 , 
 
 When the splitting is accompanied by the decomposition of water 
 and the taking up of its constituents by the decomposition-products, 
 it is known as hydrolytic cleavage or hydrolysis. The special kind 
 of hydrolysis is sometimes indicated by adding the suffix " lysis " to 
 a root designating the nature of the substance decomposed, as pro- 
 teolysis for hydrolytic cleavage of proteins. A familiar example of 
 this kind of cleavage is the inversion of cane-sugar by boiling with 
 acidified water : 
 
 C 12 H 22 O n + H 2 : : C 6 H 12 6 + C 6 H 12 6 , 
 
 Hydrolytic cleavage, as has been shown, can be brought about out- 
 side the body by heat, with or without the aid of acids or alkalies, 
 and by the action of certain substances called enzymes. 
 
 Enzymes (ferments). 
 
 Enzymes, as mentioned in Chapter 41, are substances that decom- 
 pose others without themselves undergoing permanent change, i. e., 
 they are catalysts. The activity of all enzymes is impeded by accu- 
 mulation of the products of the fermentation. The activity of enzymes 
 is controlled by the temperature and character of the solution in 
 which they act. There is a certain temperature at which every 
 enzyme is most active the "optimum" temperature. A higher 
 temperature first impairs, and then destroys its activity. All enzymes 
 are destroyed by heating to 100 C. (212 F.) with water. Cooling 
 impairs their activity ; but even after freezing they regain their 
 power when carefully brought to the proper temperature. Some act 
 
PROTEINS. 637 
 
 best in neutral, others in either acid or alkaline, solution of certain 
 concentration. The action of enzymes is in many cases reversible. 
 Thus, ethyl butyrate is split by lipase into ethyl alcohol and butyric 
 acid ; and under certain conditions lipase will produce the opposite 
 effect and cause the combination of alcohol and butyric acid with the 
 formation of ethyl butyrate. 
 
 As it has been shown that living " organized ferments " owe their 
 activity to the enzymes which they secrete, there is less stress laid 
 now upon the distinction between organized and unorganized fer- 
 ments, and the term ferment is reserved mainly for yeast. 
 
 The chemical composition of the enzymes is not known. As yet, 
 no enzyme has been prepared in the pure state ; they may be extracted 
 from the cells by means of water and glycerin. The solution in 
 glycerin is very stable. When in solution they are easily obtained 
 by precipitation of some other substance from the same solution, the 
 enzyme being carried down with the precipitate. The activity of 
 their solution is generally destroyed by heating to 80 C. (176 F.). 
 
 The quantitative estimation of enzymes is based on the amount of 
 decomposition-products formed, or the amount of material decom- 
 posed in a given time and under certain conditions. 
 
 Enzymes occur widely distributed in animal and vegetable organ- 
 isms, and possess great diversity of function. At present, enzymes 
 are classified according to the nature of the changes they produce ; 
 the more prominent groups are : 
 
 Amylases or amylolytic enzymes, converting starches into simple 
 sugars : ptyalin, amylopsin, malt, diastase. 
 
 Proteases or proteolytic enzymes, converting proteins into peptone or 
 simpler compounds : pepsin, trypsin. 
 
 Steatases or steatolytic enzymes, splitting fats : steapsin. 
 
 Invertases or inverting enzymes, splitting sugar : invertin. 
 
 Coagulases or coagulating enzymes, converting soluble proteins into 
 insoluble forms : rennin. 
 
 Oxidases or oxidizing* enzymes. Oxidases produce oxidation in 
 the presence of oxygen, peroxidases (catalases), only in the presence 
 of a peroxide. Oxygenases are theoretical enzymes, capable of first 
 combining with oxygen and then transferring it to some other sub- 
 stance. 
 
 Of glucoside-splitting enzymes has been mentioned, in Chapter 50, 
 emulsin or synaptase, which decomposes amygdalin, while myrosin 
 acts on sinigrin found in mustard seed. 
 
 Not infrequently the enzymes of the body are secreted in an inac- 
 
638 PHYSIOLOGICAL CHEMISTRY. 
 
 tive state, and are then spoken of as zymogens or pro-enzymes. These 
 zymogens become active in the presence of certain supplementary 
 substances. These substances are called kinases if of organic nature, 
 and activators if of inorganic nature. Thus, enterokinase is the kinase 
 of trypsinogen, converting it into trypsin, while hydrochloric acid is 
 the activator of pepsinogen, converting it into pepsin. 
 
 While enzymes will be fully considered later, the following two 
 are mentioned here because they furnish official preparations. 
 
 Pepsin is one of the active principles of gastric juice, capable of 
 converting albumin, in the presence of hydrochloric acid, into soluble 
 peptones. While pure pepsin is not known, a number of preparations 
 containing more or less of this ferment are sold as pepsin. They are 
 obtained by dhTerent processes of extraction from the glandular layer 
 of fresh stomachs from healthy pigs. 
 
 Pepsin, U. S. P., should be either a fine, white, or yellowish-white, 
 amorphous powder, or consist of thin, pale yellow or yellowish, 
 transparent or translucent grains or scales. It should be capable 
 of digesting not less than 3000 times its own weight of freshly 
 coagulated and disintegrated egg albumin. 
 
 Experiment 72. Use the U. S. P. process for the valuation of pepsin, as fol- 
 lows : " Mix 9 c.c. of diluted hydrochloric acid with 291 c.c. of distilled water, 
 and dissolve the pepsin in 150 c.c. of the acid liquid. Immerse a hen's egg, 
 which should be fresh, during fifteen minutes in boiling water ; remove the 
 pellicle and all of the yolk ; rub the white, coagulated albumin through a clean 
 No. 40 sieve. Reject the first portion that passes through the sieve, and place 
 10 Gin. of the succeeding portion in a wide-mouthed bottle of 100 c.c. capacity. 
 Add 20 c.c. of the acid liquid, and with the aid of a glass rod tipped with cork 
 or black rubber tubing, completely disintegrate the albumin ; then rinse the rod 
 with 15 c.c. more of the acid liquid and add 5 c.c. of the solution of pepsin. 
 Cork the bottle securely, invert it three times, and place it in a water-bath that 
 has previously been regulated to maintain a temperature of 52 C. (125.6 F.). 
 Keep it at this temperature for two and one-half hours, agitating every ten 
 minutes by inverting the bottle once. Then remove it from the water-bath, 
 add 50 c.c. of cold distilled water, transfer the mixture to a 100 c.c. graduated 
 cylinder, and allow it to stand for half an hour. The deposit of undissolved 
 albumin should not then measure more than 1 c.c. 
 
 "The relative proteolytic power of pepsin stronger or weaker than that just 
 described may be determined by ascertaining through repeated trials the 
 quantity of the above pepsin solution required to digest, under the prescribed 
 conditions, 10 grammes of boiled and disintegrated egg albumin. Divide 15,000 
 by this quantity expressed in c.c. to ascertain how many parts of egg albumin 
 one part of the pepsin will digest." 
 
 Pancreatin, U. S. P. This preparation is a mixture of the 
 enzymes existing in the pancreas of warm-blooded animals, and is 
 
CHEMICAL CHANGES IN PLANTS AND ANIMALS. 639 
 
 usually obtained from the fresh pancreas of the hog. It consists 
 principally of amylopsin, myopsin, trypsin, and steapsin. It is a 
 yellowish or grayish, almost odorless powder, soluble in water to the 
 extent of 90 per cent., insoluble in alcohol. It has the power to 
 digest proteins, and should convert not less than twenty-five times its 
 own weight of starch into sugar. 
 
 Experiment 73. Introduce 7.5 grammes of starch into a flask, add 120 c.c. 
 of distilled water, and boil until a translucent mixture results. Cool the 
 resulting paste to 40.5 C. (105 F.), and add to it 0.3 gramme of pancreatin, 
 previously dissolved in about 10 c.c. of distilled water at 40.5 C. (105 F.). 
 Shake the flask well, maintaining the temperature of the mixture at 40.5 C. 
 (105 F.) during five minutes ; at the end of this time all of the starch should 
 be converted into substances soluble in water, and a thin liquid be produced. 
 Mix 2 drops of tenth-normal iodine V. S. with 60 c.c. of distilled water, and 
 add to it 2 drops of the warm converted starch solution ; no color should result, 
 or, at most, a wine-red color, showing the presence of dextrin and maltose. 
 The appearance of a blue or purple color indicates the presence of unconverted 
 starch and that the pancreatin is below the standard i. e., that of converting 
 not less than 25 times its own weight of starch into substances soluble in water. 
 
 54. CHEMICAL CHANGES IN PLANTS AND ANIMALS. 
 
 Difference between vegetable and animal life. As a general 
 rule, it may be stated that the chemical changes in a plant are pro- 
 gressive or constructive, in an animal regressive or destructive. That is 
 to say, plants take up as food a small number of inorganic substances 
 of a comparatively simple composition, convert them into organic 
 substances of a more and more complicated composition with the 
 simultaneous liberation of oxygen, while animals take up as food 
 these organic vegetable substances of a complex composition, assim- 
 ilating them in their system, where they are gradually used (burned 
 up) and finally discharged as waste products, which are identical (or 
 nearly so) with those substances serving as plant food. 
 
 QUESTIONS. To which class of substances is the term protein applied, and 
 which elements enter into their composition? How are proteins classified, and 
 how do these groups differ from each other? Describe the five color-reactions 
 of proteins. Mention the conditions necessary for the coagulation of a protein 
 solution by heat ; and state how coagulation differs from precipitation. De- 
 scribe the products of proteolysis. Describe the nucleoproteins. Give a full 
 description of the nature and action of enzymes. State the composition and 
 properties of tyrosine and leucine. Define hydrolytic cleavage. Mention two 
 enzymes that are official; state their sources and their function in the process 
 of digestion. 
 
640 PHYSIOLOGICAL CHEMISTRY. 
 
 Plant food. Waste products of animal life. 
 
 Carbon dioxide. Carbon dioxide. 
 
 Water. Water. 
 
 Ammonia, NH 3 . Urea, CO(NH 2 ) 2 . 
 
 Nitrates, MzNO 3 . Urates, MzC s H 2 N 4 O 3 . 
 
 f Calcium. f Calcium. 
 
 Phosphates , | M ium _ Phosphates | , M ium . 
 
 Sulphates - of Sodi(]m Su phates . of godium 
 
 Chlorides ) potassium ^ Chlondes J Pw^ium. 
 
 It should be remembered that no sharply defined line of demarca- 
 tion can be drawn between plants and animals. Synthetic processes 
 occur in the body of animals, and cleavage processes take place in 
 some plants. However, in the animal organism the processes of oxi- 
 dation and cleavage are predominant, while in plants those of deoxi- 
 dation and synthesis are prevalent. 
 
 Formation of organic substances by the plant. As shown in 
 the preceding table, plants take up the necessary elements for organic 
 matter from a comparatively small number of compounds. All carbon 
 is derived from carbon dioxide ; hydrogen chiefly from water ; oxygen 
 from either of the two substances named, as well as from the various 
 salts ; nitrogen either from ammonia, or from nitrates or nitrites ; 
 while sulphur and phosphorus are derived from sulphates and phos- 
 phates respectively. These substances are taken into the plant chiefly 
 by the roots, the assimilation of the necessary mineral constituents 
 being facilitated by an acid secretion (discharged from the roots) 
 which has a tendency to render these salts, present in the soil and 
 surrounding the roots, soluble. 
 
 Water having absorbed more or less of carbon dioxide, of ammonia 
 or ammonium salts, and of nitrates, phosphates, and sulphates of 
 potassium, calcium, etc., enters the plant through the roots by a simple 
 process of diffusion, and is carried to the various green parts of the 
 plant (chiefly to the leaves), where, under the influence of sunlight, a 
 chemical decomposition and the formation of new compounds take 
 place, the liberated oxygen being discharged directly through the 
 leaves into the atmosphere. 
 
 It is difficult to explain fully the process of the formation of highly complex 
 organic compounds in the plant, because we know so little in regard to the 
 intermediate products which are formed. However, it is fair to assume that 
 the various compounds above mentioned as plant food are first decomposed 
 (with liberation of oxygen) in such, a manner that residues or unsaturated 
 radicals are formed, which combine together. From these compounds, pro- 
 
CHEMICAL CHANGES IN PLANTS AND ANIMALS. 641 
 
 duced at first, more complicated ones will be formed gradually by replacement 
 of more hydrogen, oxygen, or other atoms by other residues. 
 
 The following equations, while not showing the various radicals and inter- 
 mediate compounds formed, may illustrate some of the results obtained by the 
 plant in forming organic compounds : 
 
 C0 2 + H 2 == H 2 CO 3 
 
 H 2 CO 3 O = H 2 C0 2 = Formic acid. 
 2C0 2 + H 2 = H 2 C 2 5 
 
 H 2 C 2 O 5 O = H 2 C.,O 4 = Oxalic acid. 
 6C0 2 + 6H 2 = C 6 H 12 18 
 
 C 6 H 12 O 18 12O = C 6 H 12 O 6 = Glucose. 
 10C0 2 + 8H 2 = C 10 H 16 28 
 
 Ci H 16 O, 8 28O = C 10 H 16 = Oil of turpentine. 
 10C0 2 + 4H 2 + 2NH 3 =* C, H 14 O 24 N 2 
 
 C 10 H U 24 N 2 24O = C 10 H U N 2 = Nicotine. 
 
 The above formulas show that the formation of organic compounds in the 
 plant is always accompanied by the liberation of oxygen, and it may be stated, 
 as a general rule, that no organic substance (produced in nature) contains a 
 quantity of oxygen sufficient to convert all carbon into carbon dioxide and all 
 hydrogen into water, which fact also explains the combustibility of all organic 
 substances. 
 
 Why it is that the living plant has the power of forming organic substances 
 in the manner above indicated, we know not, and we know very little even in 
 regard to the means by which the living cell accomplishes this formation, fcut 
 we do know that sunlight furnishes the kinetic energy necessary in the forma- 
 tion of complex substances from the simpler ones. This kinetic energy is 
 transformed into the potential energy, or chemical tension, of the new com- 
 pounds and of the liberated oxygen. 
 
 Animal food. Those substances which when taken into the body 
 yield energy, build tissue, or prevent the consumption of tissue, 
 without injury to the organism, are called animal foods. The food 
 taken by animals is (beside water and a few of its mineral con- 
 stituents) all derived from vegetables, but it is taken from them 
 either directly or indirectly ; in the latter case it has been taken pre- 
 viously into and assimilated by other animals, as in case of food 
 taken in the form of meat, milk, eggs, etc. While some animals 
 (herbivora) feed upon vegetable, and some (carnivora) upon animal 
 food exclusively, others are capable of taking and assimilating either. 
 
 The fact that animal food is derived from vegetable matter renders 
 it superfluous to state that the elements taking an active part in the 
 formation of either vegetable or animal matter are identical. Of the 
 total number of the elements, only 15 are found as necessary con- 
 stituents of the animal body. These elements are carbon, hydro- 
 gen, oxygen, nitrogen, sulphur, phosphorus, chlorine, iodine, fluorine, 
 silicon, calcium, magnesium, sodium, potassium, and iron. A few 
 
 41 
 
642 PHYSIOLOGICAL CHEMISTRY. 
 
 other elements, such as aluminum, manganese, copper, etc., are some- 
 times found in the animal system, but they cannot be looked upon 
 as normal or necessary constituents. 
 
 , The various kinds of animal food are derived chiefly from three 
 groups of organic substances, viz., carbohydrates (sugars, starch, etc.), 
 fats, and proteins or nitrogenous substances. The inorganic sub- 
 stances, such as phosphates, chlorides, etc., required by the animal in 
 the construction of bones, for the liberation of hydrochloric acid in 
 the gastric juice, etc., are generally found as constituents of various 
 kinds of food or are derived from drinking water. Milk contains all 
 the necessary organic or inorganic constituents ; bread is rich in phos- 
 phates, which latter are also found in smaller or larger quantities in 
 nearly all kinds of vegetable and animal food. 
 
 Through the food are supplied those compounds which supply the 
 constituents that replace the exhausted material of the living cells, 
 and by chemical changes their inherent potential energy is converted 
 into the heat of the body and into the kinetic energy used in work- 
 ing the living mechanism. While the nitrogenous substances have 
 primarily the task of continuously replacing the wear and tear of the 
 nitrogenous tissues, they also serve, together with non-nitrogenous 
 food, to yield the animal heat, as also muscular and other power for 
 the work which the body performs. To a certain extent the different 
 nutrients can do the work of one another. Thus, the body can burn 
 protein in place of fats or carbohydrates, but neither of the latter can 
 replace the protein in building or repairing tissue. On the other 
 hand, the fats and carbohydrates, while being consumed, protect the 
 proteins. 
 
 To some extent, the animal body may be regarded as a complicated machine, 
 in which the potential energy, supplied by the food, is converted into actual 
 energy of heat and mechanical labor. The main difference is that in our 
 machines the fuel serves as the source of energy only, while in the body the 
 food is mainly changed first into tissue (thus building up and renewing the 
 body constantly), serving as fuel afterward. While in the best steam-engine 
 only one-tenth of the fuel is utilized as mechanical work, one-fifth of the energy 
 of the food is realized in the human body. 
 
 Heat and muscular power are forms of energy developed by the 
 consumption of food in the body. The amount of energy developed 
 is the measure of the food value of any nutrient, and the unit of 
 value is the calorie. 
 
 While each individual substance generates a definite number of 
 calories during combustion, for practical purposes it is sufficiently 
 accurate to estimate the average amount of heat and energy in 1 
 
CHEMICAL CHANGES IN PLANTS AND ANIMALS. 
 
 643 
 
 pound of either proteins or carbohydrates as 1860 calories, while 
 that in a pound of fat is equal to 4220 calories. 
 
 It is important to notice that carbohydrates and fats are oxidized 
 to carbon dioxide and water, thus producing the theoretical yield of 
 energy in the body, while only part of the protein molecule is reduced 
 to carbon dioxide and water, the remainder appearing as urea and 
 other nitrogenous bodies possessing latent energy, which must be sub- 
 tracted from the theoretical heat value of the protein. 
 
 Composition and fuel values of several important food materials are 
 given in the following table: 
 
 
 
 Water. 
 
 Proteins. 
 
 Fats. 
 
 Carbohy- 
 drates. 
 
 Mineral 
 matter. 
 
 Value of 1 
 pound in 
 calories. 
 
 Bread . . 
 Wheat flour 
 Oatmeal 
 Kice . . 
 White beans 
 Dried peas . 
 Potatoes 
 Sweet potatoes 
 Turnips 
 Milk 
 
 32.0 
 12.5 
 
 7.6 
 12.4 
 12.6 
 12.3 
 
 78.9 
 71.1 
 89.4 
 87 
 
 9.0 
 11.0 
 15.1 
 7.4 
 23.1 
 26.7 
 2.1 
 1.5 
 1.2 
 36 
 
 2.0 
 1.1 
 7.1 
 0.4 
 2.0 
 1.7 
 0.1 
 0.4 
 0.2 
 40 
 
 56.0 
 74.9 
 68.2 
 79.4 
 59.2 
 56.4 
 17.9 
 26.0 
 8.2 
 47 
 
 1.0 
 0.5 
 2.0 
 0.4 
 3.1 
 2.9 
 1.0 
 1.0 
 1.0 
 07 
 
 1300 
 1645 
 1850 
 1630 
 1615 
 1565 
 375 
 530 
 185 
 325 
 
 Butter 
 Cheese, full cream 
 Cheese, skimmed milk 
 Egg 
 
 10.5 
 30.2 
 41.3 
 738 
 
 1.0 
 
 28.3 
 38.4 
 149 
 
 85.0 
 35.5 
 68 
 10.5 
 
 0.5 
 
 1.8 
 8.9 
 
 3.0 
 4.2 
 
 4.6 
 08 
 
 3615 
 2070 
 1165 
 721 
 
 Beef, sirloin 
 Mutton, shoulder 
 Veal, shoulder . 
 Pork, fresh .... 
 
 60.0 
 58.6 
 68.8 
 50.3 
 
 18.5 
 18.1 
 20.2 
 16.0 
 
 20.5 
 22.4 
 9-8 
 32.8 
 
 
 
 1.0 
 0.9 
 1.2 
 
 0.9 
 
 1210 
 1260 
 790 
 1680 
 
 The relative proportions in which the two kinds of food are taken 
 by animals depend upon the nature of the animal and upon its par- 
 ticular condition of existence. 
 
 Below are given in column A the daily quantity of food required 
 to maintain a grown person in good health, with neither loss nor 
 gain in weight, while the figures in column B refer to the quantities 
 of food for a working man of average height and weight. 
 
 Proteins 125 grammes. 
 
 Fats 79 
 
 Carbohydrates . . . .485 " 
 Inorganic salts . . . .25 " 
 
 Water 2600 
 
 Equivalent to 3050 calories. 
 
 The above nutrients will be furnished by a diet consisting of 1.5 
 
 B. 
 
 130 grammes. 
 85 " 
 400 
 
 30 " 
 2600 " 
 3800 calories. 
 
644 PHYSIOLOGICAL CHEMISTRY. 
 
 to 2 pounds of bread, 10 to 14 ounces of lean beef, 2 to 3 ounces of 
 butter, with 2 quarts of water. 
 
 Digestibility. In providing a diet, it must be borne in mind that 
 the digestibility of a food is more a measure of its nutritive value than 
 its elementary composition. Different foods show great differences 
 in the rapidity and completeness with which they are absorbed. 
 Thus eggs, fresh meat, white bread, and butter are absorbed and 
 assimilated more readily than pork, rye bread, potatoes, green vege- 
 tables, and bacon. 
 
 By digestibility of food many different conditions are, or may be, implied. 
 Some of these, as the ease with which a certain food is digested, the time re- 
 quired for the process, the influence of different substances and conditions on 
 digestion, and the effects on health and comfort, are so dependent upon indi- 
 vidual peculiarities, that no definite rule for the measurement of food-digesti- 
 bility can be established. Fortunately, the most important factor, viz., the 
 amount digested, can be determined accurately by experiment. The method 
 consists in analyzing and weighing both the food consumed and the feces 
 excreted, the difference being taken as the amount digested. 
 
 In general it can be said that animal protein is easily and completely di- 
 gested, while protein of vegetable food is less so. Thus, of the protein contained 
 in potatoes, whole wheat, and rye flour, one-fourth, or more, may escape diges- 
 tion, and thus be rendered useless as nourishment. About 5 per cent, of fats 
 escape digestion, while carbohydrates are, in general, completely digested, 
 cellulose being the only exception. 
 
 In adjusting a diet, it is important to provide sufficient protein for the build- 
 ing and repair of tissue, and enough of other materials to furnish the body 
 with heat and energy for the work to be performed. A proper diet for a grown 
 person doing moderate work should provide about 3500 calories of energy with 
 a nutritive ratio of from 1 : 4 to 1 : 6. 
 
 The nutritive ratio is the ratio of the protein to the sum of all the other 
 nutritive ingredients. The fuel value of fats is two and a quarter times that 
 of proteins and carbohydrates, that of the two latter being considered to be 
 alike. In calculating the nutritive ratio, the quantity of fats is multiplied by 
 2.25, and the product added to the weight of carbohydrates. The sum divided 
 by the weight of protein gives the nutritive ratio. 
 
 If less protein be administered than is needed for repair, although a sufficient 
 number of calories be provided, more nitrogen will be excreted in the urine 
 than is contained in the food. When the protein is given in sufficient quantity 
 to replace the worn tissues, sufficient calories being also provided for, a nitroge- 
 nous equilibrium is established i. e., the nitrogen excreted equals the nitrogen 
 administered. Should more protein than is necessary be administered, with 
 sufficient calories, then more nitrogen is excreted and thereby the equilibrium, 
 as far as nitrogen is concerned, is rapidly re-established. 
 
 During the periods of growth and convalescence from acute disease the pro- 
 teins can be increased in the body by increase of protein food. The nitrogenous 
 equilibrium is then less rapidly re-established, as nitrogenous matter is utilized 
 
CHEMICAL CHANGES IN PLANTS AND ANIMALS. 645 
 
 in the construction of new tissue. When the quantity of food absorbed is 
 greater than is required for repair and energy, the carbohydrates are converted 
 into fat, and this, with the excess of fat from the food, is stored up in the 
 fatty tissue of the body, to be drawn upon whenever needed. In starvation no 
 tissue decreases as much as the fatty. The fatty tissue of the animal body is a 
 depot where, during proper alimentation, nutritive material of great value is 
 stored, to be given off as it may be needed. 
 
 Nutrition. In the process of nutrition five phases may be distin- 
 guished, viz. : Digestion, absorption, anabolism, catabolism, and excre- 
 tion of waste products. These processes are commonly spoken of 
 collectively as metabolism. 
 
 Digestion is the process of converting food material into dialyzable 
 compounds, or into other forms of matter capable of absorption. Ab- 
 sorption is the mechanical process of transferring the digested mate- 
 rials from the alimentary canal into the circulation. Anabolism 
 includes the synthetic changes taking place after they are absorbed 
 until they have become a part of living cells. Catabolism includes 
 those destructive changes which take place chiefly in consequence of 
 oxidation, the oxygen being supplied during the process of respira- 
 tion. Excretion of waste products is the discharge of that material 
 which is no longer needed in the system. 
 
 Digestion. It has been stated before that foods are divided into 
 two classes, inorganic and organic, and that the latter are subdivided 
 into proteins, carbohydrates, and fats. As a rule, the inorganic foods 
 are taken into the body without chemical change. Before the organic 
 foods can be absorbed they have to undergo digestion. This is the 
 process by which organic compounds capable of acting as foods are so 
 altered that they may be absorbed. The process of digestion will be 
 fully considered in a later chapter. 
 
 Absorption, anabolism, catabolism, excretion. While these subjects, 
 particularly absorption and excretion, are considered later under the 
 various organs concerned (see Index), a brief statement of the changes 
 in the various food-stuffs, subsequent to their absorption, is made 
 here. 
 
 Carbohydrates. The carbohydrates, mainly as dextrose, are carried 
 from the intestine by the portal system to the liver, where the bulk 
 of them is dehydrated and converted into glycogen. Some of the 
 dextrose is changed into glycogen by the muscle, and in this organ 
 and the liver a reserve-supply of glycogen is stored up. This gly- 
 cogen forms the most readily available source of energy for the body. 
 When used it is first split into dextrose, and then oxidized to carbon 
 dioxide and water, passing probably through a lactic acid stage. The 
 
646 PHYSIOLOGICAL CHEMISTRY. 
 
 sugar metabolism is so carefully controlled and is influenced by so 
 many factors that the details are not clear. The question has been 
 largely studied by observation of cases of spontaneous and experi- 
 mental diabetes. This term implies much more than a mere glyco- 
 suria ; hyperglucsemia (excessive amount of sugar in the blood) must 
 be present, and there is a profound change in the handling of carbo- 
 hydrates by the body, as well as some derangement of the protein and 
 fat metabolism. The pancreas plays an important role and furnishes 
 an internal secretion from the islands of Langerhans, which probably 
 enables the muscle to split and oxidize the glycogen as it needs it. 
 The muscle is thus involved, as well as the liver, in sugar control. 
 The adrenal is thought perhaps to control the transportation of sugar 
 in the body, for example, its removal from the liver to the muscle ; 
 while the thyroid seems to have an inhibitory action upon both the 
 pancreas and the adrenal. Phloridzin produces an increased perme- 
 ability of the kidney to sugar, but not a true diabetes. 
 
 Fats. Shortly after the emulsified fats reach the blood through 
 the thoracic duct from the intestine, there occurs a peculiar change in 
 them whereby they become dialyzable, soluble in water, and insoluble 
 in ether. The nature of this change is entirely obscure. The fats 
 are deposited in the body as fats and form a reserve store of potential 
 energy. A small proportion is synthesized into the lecithins. While 
 the fat of any animal tends to remain true to the composition charac- 
 teristic of that animal, there is so little change in fat during digestion 
 that it is possible to recognize, in the tissue of the animal, foreign fats 
 which have been introduced with the food. The fat of the body is 
 derived primarily from the fat of the food, but is also formed in con- 
 siderable amount from carbohydrates. The location of this transfor- 
 mation of carbohydrate to fat is unknown. There is a possibility that 
 protein also may form fat, as it can undoubtedly form sugar, which 
 might be further changed to fat. Experiments in feeding foreign 
 fats have shown that the so-called fatty degenerations of the liver, 
 etc., are not transformations of protein into fat, but that the fat is 
 brought by the blood and deposited in the diseased organ. When fat 
 is burned it is first saponified. The final products are carbon dioxide 
 and water. The acetone bodies of the urine are believed to represent 
 steps in the incompleted oxidation of the fats. 
 
 Proteins. After the proteins enter the portal blood as native pro- 
 teins they pass through the liver, probably with little change, and 
 are distributed to the tissues. Here a part enters into the repair or 
 the growth of the protein tissues (" tissue protein "), while a part is 
 
CHEMICAL CHANGES IN PLANTS AND ANIMALS. 647 
 
 immediately broken down without actually being incorporated by the 
 tissues ("circulating protein"). This is evidenced by the marked 
 increase in the nitrogenous excretion which appears shortly after 
 protein ingestion. It is important to notice that carbohydrate and 
 fat can replace one another in the diet, but that neither can replace 
 protein to more than a slight extent. Indeed, it has very recently 
 been shown that not all proteins have the same nutritive value (Os- 
 borne and Mendel). Thus, an animal can thrive upon a single pro- 
 tein, such as casein, egg-albumen, or glutenin (wheat). It will live, 
 but will not grow to maturity upon gliadin (wheat) or hordein (bar- 
 ley) alone. It will not even live upon zein (maize). This difference 
 in typical proteins is undoubtedly due to differences in the amino- 
 body content of the protein. Zein contains no lysine or tryptophane. 
 It has long been known that the albuminoid substance, gelatin, con- 
 taining no tryptophaue and no tyrosine, cannot replace protein. 
 
 It is believed that these deficiencies in amino-acids make it im- 
 possible for the organism to build up its native protein from such 
 material. 
 
 The specific waste products of protein (meat) metabolism, the 
 nitrogenous excreta, appear mainly in the urine, and will for the 
 most part be considered in that connection, while the formation of 
 urea and certain other substances will be discussed with the liver. 
 
 Respiration. The most important changes in respired air are the 
 changes in the quantities of oxygen and carbon dioxide. Pure air, 
 after being dried, contains, by volume, of oxygen 20.8 per cent., of 
 nitrogen 79.2 per cent., and a quantity of carbon dioxide (0.04 per 
 cent.) so small that it need not be considered. When 100 volumes of 
 air have been breathed once, it gains a little more than four parts of 
 carbon dioxide and loses a little more than five parts of oxygen ; so 
 that the composition of 100 volumes of inspired air, when expired, is, 
 after being dried, oxygen 15.4 parts, nitrogen 79.2 parts, and carbon 
 dioxide 4.3 parts by volume. 
 
 Much the greater portion of the oxygen lost from respired air 
 enters into combination with the haemoglobin ; a small portion is 
 absorbed by the blood-serum. The immediate source of the carbon 
 dioxide is the blood, in which it exists partly in simple solution and 
 partly in a loose combination with hemoglobin. 
 
 The blood is the common carrier of the body : from the alimentary 
 canal it receives ultimately all the food material ; from the lungs it 
 receives oxygen ; these it carries to the tissues for their sustenance ; 
 
648 PHYSIOLOGICAL CHEMISTRY. 
 
 from the tissues it receives the products of catabolism, and carries 
 them to their proper organs of elimination. 
 
 The bright red color of the arterial blood is due to oxyhaBmoglobin. 
 A large portion of this oxygen absorbed by the haemoglobin is given 
 up to the tissues as the blood passes through the capillaries, and we 
 have then the reduced hemoglobin, to which is due the dark color of 
 the venous blood. 
 
 In almost the reverse manner, the hemoglobin takes up carbon from 
 the tissues and conveys it to the lung. It is important to note that 
 carbon dioxide, in distinction from carbon monoxide, is not attached to 
 hemoglobin in the same manner in which the oxygen is attached. It 
 has been shown that the dark color of the venous blood is not due to 
 the presence of carbon dioxide, but to a decrease of the oxygen. 
 
 The details of the manner in which oxidation in the animal body is induced 
 and how it proceeds are not known. In some way the atmospheric oxygen, 
 which under ordinary conditions has no action on the proteins, fats, and carbo- 
 hydrates, is so changed as to become active. It is commonly believed that the 
 process is carried on by enzymes, some of which (peroxidases) have been actually 
 demonstrated, while others (oxygenases) are merely hypothetical (see page 637). 
 
 Waste products of animal life. The changes which the food 
 suffers after having been absorbed by the animal system are ex- 
 tremely complicated, and far from being thoroughly understood. 
 Numerous products and organs are formed and nourished from and 
 by the blood ; among them muscular, nerve, and brain substance, ex- 
 cretions and secretions, 1 such as milk, saliva, bile, gastric and pan- 
 creatic juice, etc., together with bones, teeth, hair, and many others. 
 
 Most of these substances (some secretions, such as milk and others, 
 excepted) suffer a constant oxidation in the system, and are finally 
 eliminated as waste products ; in regard to the intermediate com- 
 pounds formed in the tissues we know little, but it is highly probable 
 that the reduction of the complicated food material to the simple 
 forms of the waste products is very gradual. There are three chan- 
 nels through which the waste products are given off; they are the 
 lungs, the skin, and the kidneys. By the lungs are eliminated 
 chiefly carbon dioxide and some water, by the kidneys urine (which 
 is a weak aqueous solution of urea, uric acid, urates, phosphates, 
 chlorides, and sulphates of calcium, magnesium, sodium, potassium, 
 etc.), and by the skin are constantly eliminated carbon dioxide and 
 water, and during the process of sweating also more or less of the 
 constituents of urine. 
 
 1 An excretion consists of material detrimental to the organisms, and removed from it by 
 certain glands. A secretion contains peculiar compounds especially elaborated by the glands 
 for the purpose of serving certain requirements of the organism or its offspring. Thus, urea 
 and sweat are excretions, while pepsin and milk are secretions. 
 
ANIMAL FLUIDS AND TISSUES. 649 
 
 There is also excretion through the intestinal tract. 
 
 Chemical changes after death. After the death of either a 
 plant or an animal, a chemical decomposition commences which finally 
 results in the formation of those inorganic compounds from which 
 the plant originally derived its food, viz., carbon dioxide, water, 
 ammonia, sulphates, phosphates, etc. This decomposition of a dead 
 body is generally a simultaneous fermentation or putrefaction, aided 
 by decay or slow combustion. 
 
 There are numerous intermediate products formed, which differ 
 according to the nature of the decomposing substance, or according 
 to the conditions (degree of temperature, amount of moisture and air 
 present, etc.) under which the decomposition takes place. 
 
 During the decomposition of dead vegetable matter (especially of 
 moist wood) the intermediate products are frequently called humus, 
 which substance (or better, mixture of substances) forms the chief 
 part of the organic matter in the soil. 
 
 During the decomposition of dead animals, the sulphur is first 
 eliminated as hydrogen sulphide, and a number of other intermediate 
 products have been shown to be formed ; among them certain organic 
 bases called ptomaines or cadaveric alkaloids, substances which have 
 been spoken of in Chapter 52. The decomposition of organic matter 
 may be prevented under conditions which have been mentioned here- 
 tofore in connection with putrefaction. 
 
 55. ANIMAL FLUIDS AND TISSUES. 
 
 Constituents of the animal body. The animal body consists 
 mainly of three kinds of matter, viz., water, organic, and inorganic 
 matter. It contains of water about 70 per cent., of organic matter 
 25 per cent., and of inorganic matter about 5 per cent. The water 
 may be determined by drying a weighed quantity in an air-bath at a 
 temperature of 100 to 105 C. (212-221 F.); the organic matter 
 is estimated by burning the dried substance, and the inorganic matter 
 
 QUESTIONS. What is the difference between vegetable and animal life from 
 a chemical point of view ? Mention the chief substances serving as plant food. 
 Explain the formation of organic substances in the plant. What elements 
 enter into the animal system as necessary constituents? The members of which 
 three groups of organic substances are chiefly used as food by animals? Give 
 a full explanation of respiration. Explain the term calorie, and state the use 
 made of it in valuation of food. Which points should be considered in the 
 selection of a diet? What are the waste products of animal life, and through 
 which channels are they eliminated? What is the final result of the decom- 
 position of dead plants or animals ? 
 
650 PHYSIOLOGICAL CHEMISTRY. 
 
 (ash) by weighing the residue. Some of the elements which are left 
 in the inorganic residue have, however, been actually constituents of 
 organic compounds ; iron, for instance, w r hich is left in the ash, has 
 been chiefly a constituent of haemoglobin ; sulphur, left as a sulphate, 
 may have been a constituent of albumin, etc. 
 
 The complex nature of the various organic matters has been referred 
 to in the preceding chapter, and will be more fully considered below; 
 but it may be mentioned here, that some of these organic substances 
 (or groups of substances) may be separated by a successive treatment 
 of the animal matter with various solvents. Thus, by treating with 
 ether or carbon disulphide, all fats may be extracted ; by then treat- 
 ing with alcohol and water successively other substances (generally 
 termed extractive matter or extractives) are dissolved, which may be 
 obtained by evaporating the solution. 
 
 The relative quantities of the three constituents in some of the 
 animal fluids and tissues is shown in the following table : 
 
 
 Water. 
 
 Organic and 
 volatile matter. 
 
 Inorganic resi- 
 due (ash). 
 
 Saliva .... 
 
 . 99.50 
 
 0.32 
 
 0.18 
 
 Gas trie juice 
 
 . 9943 
 
 0.33 
 
 0.24 
 
 Pancreatic juice . 
 
 . 90.97 
 
 8.18 
 
 0.85 
 
 Bile .... 
 
 85.92 
 
 13.30 
 
 0.78 1 
 
 Chyle .... 
 
 . 91.80 
 
 7.40 
 
 0.80 
 
 Lymph 
 
 . 91 80 
 
 7.40 
 
 0.80 
 
 Pus .... 
 
 . 87.00 
 
 12.20 
 
 0.80 
 
 Cows' milk . 
 
 . 87.00 
 
 12.25 
 
 0.75 
 
 Human milk 
 
 . 86.80 
 
 12.85 
 
 0.35 
 
 Blood . . . . 
 
 . 79.50 
 
 19.70 
 
 0.80 
 
 Blood- corpuscles . 
 
 . 54.60 
 
 44.68 
 
 0.72 
 
 Blood- serum 
 
 . 90.50 
 
 8.68 
 
 0.82 
 
 Urine . 
 
 . 95.70 
 
 3.00 
 
 130 
 
 Bone (varies widely) . 
 
 . 22.00 
 
 26.00 
 
 52.00 
 
 Dentine 
 
 . 10.00 
 
 2500 
 
 6500 
 
 Enamel 
 
 0.40 
 
 3.60 
 
 96.00 
 
 Among the extractives are found creatine and creatinine, urea, uric 
 acid, organic salts, etc. After the fatty matter and the extractives 
 have been removed there remains an elastic and somewhat horny 
 mass, which consists chiefly of proteins (albumin, fibrin, globulin, etc.). 
 
 The complete separation of all substances is extremely difficult on 
 account of the great similarity in properties of many of these sub- 
 stances, and the rapid changes which they suffer when acted upon by 
 solvents or chemical agents. 
 
 As the nature or composition of many of the inorganic salts present 
 in the animal tissues is changed during the burning off of the organic 
 
 1 The metals in combination with the biliary acids are not included. 
 
ANIMAL FLUIDS AND TISSUES. 651 
 
 matter, it is necessary to determine them either in the aqueous solution 
 (extract) or by subjecting the animal matter to dialysis, by which process 
 they may be more or less completely separated from the organic matter, 
 which is left in the dialyzer, while the salts pass through the membrane. 
 
 Blood. Two kinds of blood are distinguished, the arterial or oxi- 
 dized and the venous or deoxidized blood. Arterial blood as it is 
 present in the system, or immediately after it has been drawn from 
 the body, is a red liquid of an alkaline reaction and a specific gravity 
 of about 1.055. Upon examination under the microscope blood is 
 seen to consist of a colorless fluid, called plasma, in which float small 
 globules or corpuscles, which make up about 40 per cent, of the whole 
 volume of blood. These corpuscles are of three varieties, viz., red 
 and white corpuscles, and blood-plates. The red corpuscles of blood, 
 or erytkrocytes, which give to the blood its color, are biconcave, cir- 
 cular, non-nucleated disks, about ^W of an inch in diameter. When 
 viewed through the microscope they are of a faint greenish-yellow 
 color, while en masse they show the color of arterial blood. The 
 white corpuscles of blood, or leucocytes, are round or irregularly shaped 
 nucleated cells ; they are devoid of coloring-matter, and are far less 
 numerous than the red corpuscles. The blood-plates are colorless, 
 oval, round, or lenticular disks, measuring generally less than one- 
 half of the diameter of red corpuscles. 
 
 Specific gravity. This varies in healthy adults between 1.046 and 
 1.067, but under pathological conditions may vary between 1.025 
 and 1.068. 
 
 The specific gravity can be determined by permitting a drop of blood to fall 
 into a mixture of chloroform and benzol presenting a specific gravity of about 
 1.055. If the drop sinks to the bottom, more chloroform must be added ; if it 
 floats on the surface, benzol has to be added until it floats midway in the 
 liquid. The specific gravity of the mixture, which is now identical with that 
 of the blood, is determined by a delicate hydrometer. 
 
 Reaction. The alkaline reaction of blood is due to the presence 
 of sodium bicarbonate, NaHCO 3 , and disodium phosphate, Na 2 HPO 4 , 
 both of which have a weak alkaline reaction. "While blood reacts 
 alkaline to litmus, it is neutral to phenol phthalein, and according to 
 the newer concept of alkalinity (an excess of dissociated hydroxyl 
 ions over the dissociated hydrogen ions present) it is nearly neutral. 
 For clinical purposes it is still regarded as alkaline, and the extent 
 of this alkalinity to litmus or lacmoid has some importance. There 
 are no very satisfactory methods of titration. That one most used 
 (Dare) depends upon the disappearance of the spectrum of hsemo- 
 
652 PHYSIOLOGICAL CHEMISTRY. 
 
 globin as a solution of blood is gradually neutralized. Tartaric acid, 
 2^^, is the acid used, and the addition of acid is made by means of a 
 specially devised pipette until the two absorption bands become no 
 longer visible through the spectroscope. 
 
 The alkalinity of the blood may be estimated by mixing 5 c.c. of freshly 
 drawn blood with about 45 c.c. of a 0.25 per cent, solution of ammonium 
 oxalate (which prevents coagulation) and titrating this mixture with a |^ solu- 
 tion of tartaric acid, using as an indicator lacmoid paper soaked in a concen- 
 trated solution of magnesium sulphate. 
 
 For clinical purposes, where often but small quantities of blood are avail- 
 able, the following method may be used. The blood is drawn into a capillary 
 pipette up to the mark etched on the stem; the pipette is next tilted to 
 admit a bubble of air into the bore, and then ^ sulphuric acid is drawn in to 
 the mark. The exactly equal volumes of blood and acid thus obtained are 
 transferred to a watch-glass, well mixed, and a drop of the mixture then 
 tested with lacmoid paper. If an acid or alkaline reaction be shown, the 
 operation is repeated with weaker or stronger acid until the resulting mixture 
 is neutral. 
 
 Odor. The peculiar odor of blood, differing widely in different 
 animals, is due chiefly to the presence of certain volatile fatty acids. 
 Addition of sulphuric acid renders the odor more distinct. 
 
 The composition of blood. The following table, taken from Howell, 
 lists the more important constituents of blood-plasma : 
 
 f Fibrin ogen. 
 
 I Paraglobulin. { Euglobulin. 
 Proteins. -< <- Pseudoglobulm. 
 
 Serum-albumin. 
 [ Nucleo-protein. 
 Fats. 
 Sugar. 
 Urea. 
 
 Jecorin. 
 Extractives. ^ Glucuronic acid< 
 
 Lecithin. 
 Cholesterin. 
 Lactic acid. 
 
 Chlorides "| f Sodium. 
 Carbonates I j Potassium. 
 lts ' 1 Sulphates j of -j Calcium. 
 
 Phosphates \ I Magnesium. 
 
 L Iron, 
 f Internal secretions. 
 
 Enzymes. { ^P as ^ 
 Enzymes and unknowns. ^ Glycolase, etc. 
 
 I Immune bodies (amboceptors). 
 Complements. 
 I Opsonins. 
 
ANIMAL FLUIDS AND TISSUES. 653 
 
 The proteins of blood-plasma. There are three important proteins 
 in blood-plasma : serum-albumin, serum -globulin (paraglobulin), and 
 fibrinogen. Of the other proteins described, the nucleo-protein seems 
 to be the best founded. As fibrinogen is directly concerned in the 
 clotting of blood, it will be described in that connection. The albumin 
 and the globulin of the blood are typical members of their respective 
 classes, and possess all the qualifications of these classes and of pro- 
 teins in general. They are found together also in the lymph and in 
 various other fluids of the body. There is some evidence that the 
 albumin is in reality made up of two or three different albumins, 
 while the globulin can be divided into two portions by fractional pre- 
 cipitation. Thus, on adding saturated ammonium sulphate solution 
 to plasma, all the globulin will be precipitated before the sulphate 
 solution amounts to 50 per cent, of the resulting mixture. The 
 so-called euglobulin will precipitate between 28 and 36 per cent, 
 of saturation with ammonium sulphate, and the pseudoglobulin 
 between 36 and 44 per cent. Under these conditions no albu- 
 min will be cast down. If, however, solid ammonium sulphate be 
 now added to the point of saturation, all of the albumin will be 
 precipitated. 
 
 Coagulation. When blood leaves the body and is allowed to stand 
 a while, it will be seen that the entire mass has coagulated /. e., has 
 been converted into a semi-solid, gelatinous material known as the 
 blood-clot, or the placenta sanguinis. Later it will be observed that 
 a small quantity of straw-colored liquid, known as the blood-serum, 
 appears on top of the clot. While the latter shrinks in volume the 
 quantity of serum increases, the clot finally floating in the liquid, 
 which itself ultimately gelatinizes in consequence of the coagulation 
 of the serum-albumin. Clot consists of fibrin holding in its meshes 
 blood-corpuscles, which may be removed by washing the clot in a 
 stream of water. 
 
 The coagulation of blood can be prevented in various ways. After 
 the injection of albumose into a vein of a dog the blood does not coag- 
 ulate on leaving the body. If the blood be drawn directly into a sat- 
 urated solution of magnesium sulphate, in the proportion of 3 to 1, 
 or into a solution of potassium oxalate, so that the mixture contains at 
 least 1 per cent, of oxalate, no coagulation takes place. The plasma 
 obtained from such blood is known as peptone, salt, and oxalate plasma, 
 respectively. 
 
 Coagulation of blood may be retarded by rapidly cooling it. If 
 the blood of a horse, whose blood always coagulates slowly, be re- 
 
654 PHYSIOLOGICAL CHEMISTRY. 
 
 ceived into a cold, narrow glass cylinder, and allowed to stand at 
 C., the blood may be kept fluid for several days. The corpuscles 
 will deposit in a red layer from the plasma. 
 
 It may readily be shown that the clotting of blood is due to a 
 change of some kind which converts the soluble protein fibrinogen 
 into an insoluble form called fibrin. Fibrinogen is one of the globu- 
 lins, it coagulates at a temperature of from 50 to 60 C., and is pre- 
 cipitated by half- saturation with sodium chloride. It is present also 
 in lymph. 
 
 It is well known that the clotting of fibrinogen is produced by an 
 organic substance formerly called fibrin-ferment, but preferably called 
 thrombin, as it is probably not an enzyme. It is also known that this 
 thrombin is active only in the presence of calcium salts ; that is, that 
 inactive thrombin (prothrombin or thrombogen) is changed by cal- 
 cium into the active form. It is, however, possible to remove the 
 calcium from activated thrombin without impairing its activity ; 
 therefore the calcium does not enter directly into the conversion of 
 fibrinogen into fibrin. 
 
 As calcium is present in all blood, it is evident that in cir- 
 culating blood either prothrombin must not be present as such, 
 or, if present, its activation by the calcium must be prevented by 
 some antagonistic substance (antithrombin), for otherwise clotting 
 would occur within the blood-vessels, which does not happen under 
 normal conditions. Accordingly, there are two theories to explain 
 these facts. 
 
 Morawitz believes that in order to convert prothrombin into throm- 
 bin, not only calcium but also a secondary organic substance (throin- 
 bokinase) must be present, and that this thrombokinase is furnished 
 to blood which has escaped from the blood-vessels by the injured 
 leucocytes and platelets. The other view, to which Howell inclines, 
 is that prothrombin is transformed into thrombin by calcium salts 
 alone, and that this change is prevented by the antithrombin of 
 the circulating blood, and that when the blood is shed the injured 
 cells set free a zymoplastic substance which counteracts the anti- 
 thormbin and leaves the calcium free to convert the prothrombin 
 into thrombin. 
 
 The different methods of preventing the clotting of blood 
 are to be explained thus : The cooling of blood probably pre- 
 vents the formation of the thrombokinase, or the thromboplas- 
 tic substances, by preserving the cells intact. The addition of 
 
ANIMAL FLUIDS AND TISSUES. 655 
 
 oxalate solution removes the calcium salts by precipitation. The 
 injection causes the production of antithrombin in the injected 
 animal. 
 
 Blood-serum differs from plasma only in containing no fibrinogen 
 and much active thrombin. 
 
 Experiment 74. (Separation of the proteins of blood-plasma and of blood-serum.) 
 
 a. Fibrinogen. To 5 c.c. of salt or oxalate plasma add an equal volume of 
 saturated solution of sodium chloride. Fibrinogen is precipitated, carrying 
 with it the prothrombin. Filter and preserve the nitrate for the separation of 
 albumin and globulin, as detailed below. 
 
 Dissolve the fibrinogen and protlirombiu in a little dilute salt solution, add 
 an excess of calcium chloride, and keep the mixture at 40 C. for a few minutes. 
 Shreds of fibrin are formed and precipitated. 
 
 b. To 25 c.c. of blood-settim, contained in a mortar, add 20 grammes of 
 ammonium sulphate and rub with a pestle until the fluid is saturated with 
 the salt. Filter through dry filter-paper, acidulate the filtrate with acetic 
 acid, and boil. No change occurs, as both proteins have been precipitated 
 completely. 
 
 c. To 25 c.c. of blood-serum add 25 c.c. of a saturated solution of am- 
 monium sulphate; filter; and wash with a saturated solution of the salt. 
 Under this treatment only serum-globulin is precipitated, while serum- 
 albumin is kept in solution. Heat the filtrate to boiling: serum-albumin 
 is coagulated. Place some of the residue left on the filter (globulin) in a 
 test-tube and pour water on it; the protein dissolves by virtue of the small 
 quantity of salt adhering to it. Heat the solution to boiling : coagulation 
 takes place. 
 
 d. Saturate 25 c.c. of serum with magnesium sulphate : serum-globulin is 
 precipitated, serum-albumin remains in solution. 
 
 Serum-albumin and serum- globulin give the ordinary protein reactions. 
 
 A quick method to obtain fibrin is to stir or whip blood with twigs im- 
 mediately after it has been shed. Under these conditions the fibrin 
 does not entangle the blood-corpuscles, but separates as a stringy mass, 
 which adheres to the twigs used for stirring. The remaining part, being 
 made up of the corpuscles suspended in the serum, is designated as defibrin- 
 ated blood. 
 
 Red blood-corpuscles when wet contain of water, 54.63 per cent. ; 
 haemoglobin, 41.1 per cent.; other proteins, 3.9 per cent.; fats 
 (chiefly cholesterin and lecithin), 0.37 per cent. The quantity of 
 water in corpuscles varies widely, and most likely ranges in healthy 
 blood from 76 to 80 per cent. Dried corpuscles contain about 90 
 per cent, of haemoglobin. 
 
 While red blood-corpuscles can be broken up (laked) by the 
 addition of various substances to the blood, the simplest way is by 
 
656 PHYSIOLOGICAL CHEMISTRY. 
 
 the addition of water, which reduces the osmotic pressure of the 
 plasma, and consequently causes the salts of the corpuscles to attract 
 an excess of water, whereby the corpuscle is ruptured and its con- 
 stituents go into solution. In order to avoid this action on the blood- 
 cells and a similar action on the tissue cells, it is customary in sur- 
 gical procedures, and especially in intravenous injections, to use a 
 solution of equal osmotic pressure with the blood. Such a solution 
 is the "normal salt solution" made up usually of 0.9 per cent, sodium 
 chloride in distilled water, which is the simplest solution that has 
 been found to have no very deleterious effect. 
 
 Blood-pigments. The haemoglobins or blood-pigments are the 
 chief constituents of red blood-corpuscles ; they contain from 0.4 to 
 0.6 per cent, of iron, and show a slight difference in composition ; 
 when in powder form they all have a blood-red or brick-red color; 
 they all crystallize, but not with equal facility. Hemoglobin is the 
 substance which carries oxygen to the various tissues, as described in 
 the previous chapter. It belongs to the class of conjugated proteins. 
 
 Experiment 75. Pour some freshly drawn venous blood into four volumes of 
 a saturated solution of sodium sulphate contained in a vessel which stands in 
 ice ; mix and set aside for several hours ; no coagulation occurs and the cor- 
 puscles settle to the bottom of the vessel. Pour off the supernatant liquid, 
 collect the sediment on a filter, and wash it first with cold solution of sodium 
 sulphate and then with water. 
 
 Prepare haemoglobin from these corpuscles as follows : agitate the collected 
 mass violently with small quantities of ether until the corpuscles are nearly 
 dissolved ; allow the liquid to settle, filter, render the filtrate slightly acid with 
 acetic acid, and add alcohol as long as the precipitate first formed continues to 
 dissolve ; cool the red solution to C. (32 F.) for several hours, when crystals 
 of haemoglobin will form ; collect these on a filter and wash with an ice-cold 
 mixture of alcohol and water. 
 
 Hcemoglobin, also called reduced hcemoglobin, occurs only in small 
 quantity in arterial blood, in larger quantity in venous blood, and is 
 almost the only coloring-matter in the blood after asphyxiation. A 
 solution of hemoglobin has a most remarkable attraction for oxygen, 
 with which it enters into a molecular combination, forming oxyhazmo- 
 globin. The power of hemoglobin to take up oxygen depends on 
 the iron it contains. The solution of oxy hemoglobin will give up 
 oxygen to reducing agents or when subjected to a sufficiently low 
 oxygen pressure. It is due to this property of the oxyhernoglobin 
 that arterial blood gives up oxygen to the tissue. 
 
ANIMAL FLUIDS AND TISSUES. 657 
 
 Mdhcrmogtobin is a transformation-product of oxyhsemoglobin found 
 in sanguinous transudates and cystic fluids ; it also occurs in the urine 
 during haematuria and haemoglobin uria; and in the blood and urine 
 after poisoning with potassium chlorate, amyl nitrite, alkali nitrates, 
 and several other bodies. 
 
 Hcemochromogen. When haemoglobin is acted upon by acids, alka- 
 lies, etc., it is split into globin (a histone) and hsemochrornogen. The 
 latter forms only about ^V of the haemoglobin molecule, contains all 
 of the iron present, and consequently the group to which the oxygen 
 is attached when oxyhsemoglobin is formed. In the presence of 
 oxygen haemochromogen is rapidly converted into haematin. 
 
 Ilcematin. Just as haemochromogen is split from haemoglobin, 
 haematin is derived from oxyhaemoglobin. It is a comparatively 
 simple substance, having the formula C 34 H 34 N 4 FeO 5 . It is found in 
 the feces after hemorrhage in the intestine, and also after a diet con- 
 sisting largely of red meats. Haematin has been found in urine after 
 poisoning with arsenetted hydrogen. Haematoporphyrin (^H^N^Oj 
 is obtained when haematin is hydrolyzed. 
 
 Haematoporphyrin occurs in traces in normal urine ; it is found in 
 greater quantity in urine after the use of sulphonal. Haematopor- 
 phyrin is isomeric with the bile-pigment bilirubin, and a pigment 
 closely resembling urobilin has been obtained by the action of reduc- 
 ing agents on haematoporphyrin. It is noteworthy that this substance 
 does not contain iron. 
 
 Carbon monoxide haemoglobin is a molecular combination of one 
 molecule of haemoglobin and one molecule of carbon monoxide. The 
 combination is stronger than that between oxygen and haemoglobin and 
 this explains the poisonous action of carbon monoxide, which causes 
 death by replacing the oxygen of the blood. A similar and even 
 more stable chemical combination is formed with haemoglobin by 
 nitric oxide. 
 
 Carbon dioxide haemoglobin (carbo-hwmoglobin). Haemoglobin has 
 the property of forming an unstable compound with carbon dioxide, 
 the CO 2 is, however, not attached to the same portion of the molecule 
 as that to which the oxygen (in oxy haemoglobin) is attached. Thus, 
 the presence of carbon dioxide does not prevent the absorption of 
 oxygen by haemoglobin, which is in great contrast to the action of 
 carbon monoxide, and is important in the process of respiration. 
 
 Spectroscopic examination. The different haemoglobins are distinguished 
 chiefly by their absorption -spectra. In the following description the violet end 
 of the spectrum is assumed to be on the observer's right. 
 42 
 
658 
 
 PHYSIOLOGICAL CHEMISTRY. 
 
 a. Oxyh&moglobin. Dilute 10 c.c. of blood with 90 c.c. of water, and filter. 
 Place part of the solution in a glass vessel with parallel sides and examine 
 with a spectroscope. When the solution is so concentrated the spectrum 
 will probably be entirely shut off as far as the yellow or orange, but on gradu- 
 ally diluting with water a spectrum is finally seen which shows two absorption - 
 bands to the right of the D line. The right-hand band is broader, fainter, and 
 less sharply denned than the other, and the color of the light which emerges 
 from the left limb of the left hand is yellow. When the solution is further 
 diluted the bands disappear simultaneously. (Fig. 72, a.} 
 
 b. Reduced haemoglobin. When a solution of oxy haemoglobin is treated with 
 a reducing agent the coloring-matter loses oxygen and is changed to hsemo- 
 
 FIQ. 72. 
 
 Yellow 
 
 Qreen 
 
 Cyan-blue 
 
 Absorption-spectra of blood constituents, a, oxyhaemoglobin. 
 6, reduced haemoglobin, c, methsemoglobin. d, haematine. e, 
 reduced hsematine. /, hsematoporphyrin. g, carbon monoxide 
 haemoglobin. 
 
 globin. Stokes' fluid is the most suitable reagent for reducing, and is prepared 
 as follows: Dissolve 3 grammes of selected crystals of ferrous sulphate in cold 
 water and add a cold aqueous solution of 2 grammes of tartaric or citric acid. 
 Make up with water to a volume of 100 c.c., and immediately before using add 
 ammonia-water until the precipitate which forms at first is redissolved. 
 
 Prepare a solution of oxyhsemoglobin which will show the characteristic ab- 
 sorption-bands. Allow a few drops of Stokes' fluid to flow into the solution, when 
 its color changes to a purple or violet, and the spectrum shows a single broad 
 
ANIMAL FLUIDS AND TISSUES. 659 
 
 diffused and poorly defined band, as though two oxyhsemoglobin bands had 
 gone together and had been displaced to the left (Fig. 72, 6). When the solu- 
 tion is agitated with air its color changes to bright red and the spectrum again 
 shows oxy haemoglobin. 
 
 c. Methcemoglobin. To a dilute solution of blood add a drop or two of a 
 freshly prepared 10 per cent, solution of potassium ferricyanide. The color of 
 the solution becomes brown. Add just enough sulphuric acid to give a slightly 
 acid reaction and examine spectroscopically, when the spectrum is seen repre- 
 sented in Fig. 72, c. On rendering the solution slightly alkaline and adding 
 a few drops of Stokes' fluid the methaenioglobin changes to haemoglobin, and 
 on agitating with air into oxyhsemoglobin. These changes can easily be fol- 
 lowed with the spectroscope. 
 
 d. Add hcematin. To a few drops of undiluted blood add a drop or two of 
 acetic acid. The haemoglobin is broken up into a histon called globin, and a 
 non-protein substance called hsemin. The solution which results is almost 
 black, but on diluting with water is seen to be red. The spectrum has a band 
 in the red, almost coincident with the band shown by methsemoglobin in 
 neutral or acid solution. 
 
 e. Alkaline hcematin. To a portion of acid hsematin solution add sodium 
 hydroxide until the precipitate which forms has redissolved. The solution 
 will be alkaline and, if properly diluted, will show a poorly defined band to 
 the left of the D line. It is usually observed, however, that the entire spec- 
 trum is absorbed except the red. (Fig. 72, d.) 
 
 f. Reduced hcematin (Hsemochromogen). Reduce a portion of alkaline 
 haematm solution with Stokes' fluid, and after properly diluting examine 
 Bpectroscopically. Two sharply defined dark bands are seen between D 
 and E, which seem to be coincident with the bands produced by oxyhaemoglo- 
 bin. It will be- noted, however, that the light which emerges on the left of the 
 left band is plainly green. By diluting the solution with water the band on 
 the right may be made to disappear, while the other band is still very dark. 
 (Fig. 72, e .) 
 
 g. Hcematoporphyrin. Add a drop of blood to a few c.c. of concentrated 
 sulphuric acid, mix well, dilute with water, and render alkaline with sodium 
 carbonate. The spectroscope shows four bands. (Fig. 72, /.) 
 
 h. Carbon monoxide hcemoglobi?i. Pass a slow current of carbon monoxide 
 (illuminating-gas, containing carbon monoxide, may be used) through 50 c.c. 
 of blood until its color is bright red. Examined spectroscopically, the bands 
 seen occupy nearly the same position as those of oxy haemoglobin, but they do 
 not disappear on treatment of the solution with Stokes' fluid. (Fig. 72. g.) 
 
 On adding to 10 c.c. of carbon monoxide haemoglobin solution 15 c.c. of a 
 20 per cent, solution of potassium ferrocyanide the mixture shows a bright-red 
 color. On treating oxyhsemoglobin solution in the same way, it assumes a 
 grayish-brown or green color. 
 
 Examination of blood-stains. Blood-stains may be recognized, 
 after having been washed off with as little water as possible, by the 
 following methods : 
 
 1. Examine the reddish fluid under the microscope for blood cor- 
 puscles. 
 
660 PHYSIOLOGICAL CHEMISTRY. 
 
 2. Evaporate a drop of the fluid on a microscope slide with a 
 minute fragment of sodium chloride, cover with a cover-glass, allow 
 a drop of glacial acetic acid to enter from the side and warm gently ; 
 abundant crops of hsemin crystals are seen under the microscope 
 after cooling. 
 
 3. Add a drop of the fluid to some freshly prepared tincture of 
 guaiacum in a test-tube and float on the surface of an ethereal solu- 
 tion of hydrogen dioxide ; a blue ring forms at the junction of the 
 ethereal solution and the guaiacum. (Blood is, however, not the only 
 substance showing this reaction. 
 
 4. The spectroscope shows bands characteristic of haemoglobin. 
 
 5. The biologic blood-test. This test depends upon the fact that 
 animals (rabbits) injected with human blood-serum will develop a 
 specific antibody. This antibody is present in the blood-serum of 
 the injected animal and is termed a " precipitin," because it produces 
 a visible precipitate when the serum of the animal is mixed with a 
 solution of human blood-serum. As the technique is very intricate, 
 and the results are worthless unless carefully controlled, no details 
 can be given here. Positive results can be obtained with blood or 
 blood-stains many years old. Human protein of other origin (milk, 
 semen, etc.) and protein from the higher anthropoid apes will also 
 give positive results. 
 
 The immune bodies of the blood-serum. When foreign protein 
 is introduced into an animal by injection or, as in disease, by infection 
 with bacteria, it is found that there is a response on the part of the 
 animal which causes the presence of certain substances (immune 
 bodies, antibodies) in the circulating blood. These have a specific 
 action upon the foreign protein. To this class belong agglutinins, 
 lysins, etc. Agglutinins are capable of causing an agglutination or 
 clumping of the corresponding bacteria. They have proved of great 
 clinical value in the diagnosis of typhoid fever by means of the Widal 
 reaction. This test consists in observing microscopically or macro- 
 scopically a mixture of active typhoid bacilli and the blood-serum of 
 the patient. If agglutinins are present, and the bacteria are clumped 
 within a certain time by a certain dilution of serum, it is shown that 
 the patient has, or in some cases has had, typhoid fever. Bacterio- 
 lysins are antibodies capable of dissolving the corresponding bacteria. 
 Opsonins are capable of producing some change in bacteria, whereby 
 it becomes possible for the leucocytes of the blood to ingest them 
 (phagocytosis). They are normally present in varying amounts. It 
 is manifest that these bodies form a part of the defensive mechanism 
 
ANIMAL FLUIDS AND TISSUES. 661 
 
 of the body. They have so far not been of great assistance thera- 
 peutically, but promise to be of great value in the prophylaxis of 
 certain diseases, as in the typhoid vaccination by injections of killed 
 cultures of B. typhosus. 
 
 In this connection it is important to note that bacteria form several 
 classes of toxins or poisons. Ptomaines are produced by the effect 
 of bacteria upon the medium in which they are growing. Bacterial 
 toxins are substances which, in distinction to ptomaines, are elab- 
 orated by the bacteria within the bacterial cells. These are substances 
 of doubtful chemical structure and are divided into two classes : (1) 
 Endotoxins, toxins existing mainly in connection with the bacterial 
 cell, going into solution with difficulty and possessing in such solution 
 only a moderately poisonous action. (2) Soluble toxins, readily re- 
 moved from the bacterial cell by solution and giving a solution of 
 strong toxic action. 
 
 It has been found that an animal which has been treated with bac- 
 teria-producing soluble toxins has present in its blood a specific anti- 
 body which is capable of neutralizing the toxin of the corresponding 
 bacteria. This substance is called an antitoxin and protects, from 
 the poisonous effects of the toxin, not only the original animal (active 
 immunity), but also other animals into which the antitoxin-containing 
 serum may be injected (passive immunity). This production of 
 passive immunity has been widely used in the treatment of diphtheria 
 and the prophylaxis of tetanus. In other bacterial diseases, such as 
 typhoid and streptococcus infections, where the toxins present are 
 mainly endotoxins, the production of an antitoxin conferring passive 
 immunity has not been successful. 
 
 In the case of some of these antibody reactions it is found that a 
 third substance is necessary. This substance is commonly called the 
 complement ; and in this connection the antibody is termed the am- 
 boceptor, and the foreign protein the antigen. The amboceptor and 
 the complement are both present in the blood-serum. Complement 
 is an unstable substance present in all fresh blood, and is not specific, 
 that is, it will enable any amboceptor to act upon the corresponding 
 antigen. Amboceptor is fairly stable, is usually present only in re- 
 sponse to the introduction of some antigen, and is specific, that is, it 
 will act only upon its corresponding antigen. 
 
 As amboceptor will act upon antigen only in the presence of com- 
 plement, the presence or absence of complement in a solution may 
 readily be shown by mixing the solution with a suitable amboceptor 
 and antigen, when the presence of complement is shown by the occur- 
 
662 PHYSIOLOGICAL CHEMISTRY. 
 
 rence of the interaction of the amboceptor and antigen, while its ab- 
 sence is shown by the failure of the reaction. The reagents com- 
 monly used are red blood-corpuscles and the corresponding haemolysin 
 (amboceptor), since the interaction is shown by a visible change, 
 haemolysis, and if no reaction occurs the mixture remains unchanged. 
 
 This procedure is used in the Wassermann reaction for syphilis. 
 If a mixture be made of the blood-serum of a syphilitic patient, an 
 emulsion of animal lipoids, and complement, it is found that the com- 
 plement becomes absorbed or fixed, so that if the mixture be tested 
 for complement by the addition of red blood-corpuscles and the cor- 
 responding haemolysin, no haemolysis will occur. If, on the other 
 hand, the patient has not syphilis, no fixation of complement will 
 occur, the complement will be left free to act, and will produce hae- 
 molysis when the corpuscles and haemolysin are added. 
 
 Ehrlich, in explaining his theory of immunity, begins by describ- 
 ing the cell as consisting of a certain group of atoms forming an 
 essential nucleus which is combined with several different groups of 
 atoms, called side-chains, varying in composition and structure. 
 
 Each of these side-chains has atoms arranged in such a way that 
 they present affinities for combining with groups of atoms of nutrient 
 or other material circulating in the animal fluids. These groups he 
 calls receptors, and the arrangement of atoms, by virtue of which 
 combination occurs, a haptophore group. 
 
 Thus, specific lysis is due to the action of a complement on a spe- 
 cific cell through a specific amboceptor, the chemical reaction being 
 due to the presence, in the chemical structure of the cell, of a re- 
 ceptor having a group of atoms haptophorous with a group of atoms 
 of the amboceptor, which, in turn, has a group haptophorous with one 
 of the complement. 
 
 Lymph is a clear, colorless, or slightly yellow liquid of a faint 
 alkaline reaction ; in composition it closely resembles blood-serum. 
 It contains less protein, particularly less fibrinogen, the salts and ex- 
 tractives are present in about the same amount. Lymph coagulates 
 more slowly and less firmly than blood. The term " chyle " is applied 
 to the lymph of the lacteals and thoracic duct when it is clouded by 
 the fat absorbed from the food in the intestine. 
 
 Bone is chemically distinguished from other tissues by the large 
 quantity of inorganic salts which it contains. Dried bones contain 
 about 31 per cent, of organic matter combined with 69 per cent, of 
 mineral matter. Different bones (and even different parts of the same 
 
ANIMAL FLUIDS AND TISSUES. 663 
 
 bone) of the same person differ somewhat in composition ; more- 
 over, the bones of a child contain somewhat more of organic matter 
 than those of a grown person, as may be shown by the following 
 analyses of the corresponding bone in children and a grown person : 
 
 Child one year. Child five years. Man twenty-five years. 
 
 Organic matter, 43.42 per cent. 32.29 per cent. 31.17 per cent. 
 
 Tricalcium phosphate, 48.55 " 59.74 " 58.95 " 
 
 Magnesium phosphate, 1.00 " 1.34 " 1.30 " 
 
 Calcium carbonate, 5.79 " 6.00 " 7.08 " 
 
 Soluble salts, 1.24 0.63 " 1.50 " 
 
 Ferric phosphate, Traces. Traces. Traces. 
 
 Frequently human bones contain calcium fluoride, which substance, 
 to the amount of 1 to 2 per cent., is a normal constituent of the 
 bones of many animals. The organic matter of bone is ossein, a 
 collagen, yielding gelatin on boiling with dilute hydrochloric acid. 
 
 Experiment 76. Pour upon 3 grammes of bone 10 c.c. of water, and then 
 10 c.c. of hydrochloric acid. (Notice that carbon dioxide is liberated.) The 
 dilute acid dissolves the mineral constituents of the bone, leaving the organic 
 matter (ossein) as a swollen mass, which retains the shape of the bone. 
 
 Decant the acid solution, and to part of it add an excess of ammonia, then 
 acidify with acetic acid. The greater part of the precipitate formed by am- 
 monia will dissolve. The insoluble part contains traces of silica, but is chiefly 
 ferric phosphate, most of which is derived from the blood in the bone. Filter 
 and test portions of filtrate for phosphoric acid with ammonium molybdate 
 and for calcium with ammonium oxalate. Dissolve the washed precipitate on 
 the filter with a little hydrochloric acid, and test for phosphoric acid as above, 
 and for iron with potassium ferrocyanide. (The detection of the mineral con- 
 stituents of bone may be carried out with the ash left from incinerating bone.) 
 
 Wash the ossein, obtained above, first with water, then with dilute solution 
 of sodium carbonate, and finally with water again. Put the washed ossein in 
 a beaker with a little water and boil until most of the ossein has been dissolved. 
 Neutralize, if necessary, with sodium carbonate, and filter while hot into a test- 
 tube. On standing, the solution gelatinizes more or less completely. Ossein 
 is converted into gelatin by this treatment. 
 
 Gelatin. The purest commercial form of gelatin is known as 
 isinglass, prepared from the sounds or air-bladders of certain fishes ; 
 it is much used as an article of food in creams and jellies. An 
 impure gelatin, prepared from animal refuse (hoofs, bones, hides, etc.), 
 forms common glue, and its solution in acetic acid is sold as liquid 
 glue. In a pure state gelatin is a colorless or slightly yellowish, 
 transparent, tasteless mass. The presence of gelatin often prevents 
 the formation of precipitates by holding them in suspension in a 
 finely divided state, so that they may pass through filter-paper. 
 
664 PHYSIOLOGICAL CHEMISTRY. 
 
 The nutritive value of gelatin is discussed under Metabolism 
 (page 646). 
 
 As gelatin contains no tyrosiue and no tryptophane, it will be 
 found that the results obtained with the xanthoproteic and Mil Ion 
 tests below are only faintly positive, being due to impurities. 
 
 Tests for gelatin. Pour upon a gramme of gelatin 25 c.c. of water and allow 
 to stand twenty-four hours. The gelatin now is swollen, but not dissolved. 
 Decant the water, add 8 c.c. of distilled water, heat over a water-bath until the 
 gelatin dissolves, then cool. To the gelatinous mass, thus obtained, add about 
 50 c.c. of water and heat again until dissolved. Use this solution for the fol- 
 lowing tests : 
 
 1. Add tannin, or hydrochloric acid and phosphotungstic acid: voluminous 
 precipitates are formed. 
 
 2. Boil a portion with one-third its volume of nitric acid : a faint-yellow 
 color is produced, showing the presence of an aromatic radical. 
 
 3. Add caustic potash and a little cupric sulphate : a blue to violet color 
 appears without a trace of red. (Difference from albumoses and peptones.) 
 
 4. Boil with Millon's reagent: a faint pink or red color. (Difference from 
 proteins in general.) 
 
 5. Add bromine-water: a heavy yellow precipitate is formed, possessing 
 tough, adhesive properties. 
 
 6. Add a few drops of acetic acid and boil ; add acetic acid and potassium 
 ferricyanide ; add mercuric chloride. Precipitation takes place in neither case. 
 (Difference from simple proteins.) 
 
 Note that gelatin solidifies on cooling and becomes liquid again on 
 the application of heat (difference from proteins in general). 
 
 Teeth consist of three distinct tissues, viz., dentine, forming the 
 chief mass, in its interior being the pulp cavity ; enamel, investing 
 the crown and extending some distance down the neck ; and cement, 
 covering the fangs. The composition of cement is almost the same as 
 that of bone, its organic and inorganic constituents having the rela- 
 tive proportions of 30 : 70. 
 
 Dentine contains less water than bone and is also poorer in organic 
 matter. The following table gives the composition of the dentine of 
 an adult woman and man respectively : 
 
 Woman. Man. 
 
 Organic matter ossein and vessels . . . 27.61 20.42 
 
 Calcium phosphate 66.72 67.54 
 
 Calcium carbonate 3.36 7.97 
 
 Magnesium phosphate 1.08 2.49 
 
 Soluble salts, chiefly sodium chloride . . 0.83 1.00 
 
 Fat 0.40 0.58 
 
 Enamel is distinguished by the very small proportion of water and 
 
ANIMAL FLUIDS AND TISSUES. 665 
 
 organic matter contained in it. Its average composition may be thus 
 stated : 
 
 Water and organic matter 3,5 
 
 Calcium phosphate and traces of fluoride .... 86.9 
 
 Magnesium phosphate 1.5 
 
 Calcium carbonate ........ 8.0 
 
 Tartar is the name given to the substance which deposits from 
 alkaline saliva on the teeth. It is of a grayish, yellowish, or brown- 
 ish color, and consists chiefly of calcium phosphate, with a little 
 carbonate, but contains also bacteria and other organic matter, salts 
 of the alkalies, and silica. 
 
 Hair, nails, horns, hoofs, feathers, epithelium, are nearly iden- 
 tical in composition. They all contain cholesterin and nitrogenous 
 substances termed keratins, which are probably not distinct chemical 
 compounds, but mixtures of several substances similar in composition 
 and properties. 
 
 Cholesterin fats are very resistant to the action of putrefactive bacteria, and 
 the occurrence of these fats in combination with the keratins serves as a pro- 
 tection to the skin surface from the attacks of the ever-present bacteria. 
 
 Muscle. The chemical composition of the various morphological 
 elements of striated muscle is not definitely known. Fresh, inactive 
 muscle has an amphoteric reaction i. e., it colors red litmus-paper 
 faintly blue, and blue litmus-paper slightly red. After activity or 
 death the reaction becomes acid. If the blood is removed from 
 muscle immediately after death, and the muscle is then quickly cut 
 and frozen, an alkaline fluid can be pressed out, the muscle-plasma, 
 which contains the proteins of muscle. Muscle-plasma coagulates 
 spontaneously, separating a protein body, myosin, and yielding a 
 serum, muscle-serum. A similar change takes place in the muscle 
 shortly after death, causing the hardening of the muscle observed in 
 rigor mortis. 
 
 The more important constituents of muscle are considered here 
 without attempting a morphological distinction. 
 
 Proteins of muscle. There is at present no generally accepted view 
 as to the nature of the essential proteins of muscle tissue. This is 
 due largely to the many different names given them, which are in 
 almost hopeless confusion. It seems certain that there are at least 
 two proteins in living muscle which have the power of coagulating 
 after death. V. Fiirth calls the less abundant of these myosin and 
 its coagulated form myosin fibrin ; the second he calls myogen, and 
 
666 PHYSIOLOGICAL CHEMISTRY. 
 
 says that it is converted first into an intermediate stage, and finally 
 into myogen fibrin. Myosin belongs to the globulins and myogen 
 resembles the albumins. The coagulation of these proteins appears 
 to take place spontaneously, as no enzyme has been satisfactorily 
 demonstrated. The process is probably not analogous to the clotting 
 of fibrinogen. 
 
 Carbohydrates of muscle. There are present in muscle varying 
 amounts of dextrose and glycogen, which form probably the most 
 important source of energy for the work of the muscle. The dex- 
 trose is brought by the blood-stream, and any excess over the amount 
 needed for immediate use is converted into glycogen by the muscle, 
 and "is held in reserve in this form. When a muscle does work, i. e., 
 when it contracts, the glycogen is split again into dextrose, which is 
 then oxidized with a resulting liberation of energy. It is possible to 
 show that the carbon dioxide of the muscle is increased in amount, 
 and that there is also a formation of lactic acid. It is believed that 
 this lactic acid represents an incomplete oxidation of the sugar. In 
 the burning of dextrose by the muscle tissue, an internal secretion or 
 hormone produced by the pancreas is believed to play an important 
 part. 
 
 Muscle extractives. The extractive bodies of the muscle are 
 important, and are both nitrogenous and non-nitrogenous. Among 
 the first, creatine, the xanthine bases, urea, and uric acid deserve men- 
 tion. Non-nitrogenous extractives always present are inosite, gly- 
 cogen, sugar, and lactic acid. 
 
 Creatine (Meihyl-guanidine-acetic acid), NH = ^\TC/ip 2 TT \ p TT o 
 
 =C 4 H 9 N 3 O 2 , occurs in muscles of vertebrates, in the brain, blood, 
 transudates, and the amniotic fluid. When pure, it forms colorless, 
 transparent, rhombic prisms. The crystals are soluble in 75 parts 
 of cold, much more soluble in hot water, slightly soluble in alcohol, 
 insoluble in ether. The solution is neutral to litmus, though creatine 
 is a weak base, combining with some of the acids to form crystal- 
 line salts. Creatine may be obtained by the action of cyanamide on 
 sarcosine (methyl-glycocoll). 
 
 dride of creatine, and may be obtained by boiling creatine with acids, 
 when a molecule of water is split off. Vice versd, creatinine may 
 be converted into creatine. Creatinine is readily soluble in water 
 and alcohol, but nearly insoluble in ether ; it crystallizes in colorless 
 
 
ANIMAL FLUIDS AND TISSUES. 667 
 
 prisms ; the solution is slightly alkaline to litmus. Creatinine is a 
 strong base, forming well-defined salts ; it also forms an insoluble 
 double compound with zinc chloride, for which reason the latter is 
 often used to precipitate creatinine. The occurrence of creatinine 
 in urine will be considered later. 
 
 Experiment 77. a. Preparation of creatine. Digest 400 grammes of finely 
 divided lean beef with 500 c.c. of water at a temperature of 50 C. (122 F.) ; 
 filter the mass through cloth, press out well, and repeat the operation twice 
 with 1000 c.c. of water, bringing the mixture to the boiling-point each time ; 
 then evaporate the mixed filtrates to about one liter. (In place of the liquid 
 extract, thus obtained, a solution of commercial extract of beef may be used.) 
 Acidify the solution with acetic acid, heat to boiling, and filter off the coagu- 
 lated proteins ; to the cold filtrate add basic lead acetate as long as a precipitate 
 is formed, filter and precipitate excess of lead by passing hydrogen sulphide 
 through the solution. Finally filter, evaporate filtrate over a water-bath to a 
 syrup, and set aside. After a day or two crystals of creatine will be found, 
 which, if too highly colored, may be redissolved in water, decolorized with 
 bone-black, and recry stall ized. 
 
 b. Conversion of creatine into creatinine. Heat 0.5 gramme of creatine with 
 10 c.c. of dilute sulphuric acid for half an hour over a water-bath ; then dilute 
 with 25 c.c. of water and add a sufficient quantity of powdered barium car- 
 bonate to neutralize the acid. Next filter, evaporate the filtrate to about 5 c.c., 
 and use this solution of creatinine for the following tests : 
 
 1. To a few drops of the solution add an equal volume of an alcoholic solu- 
 tion of zinc chloride. Creatinine zinc chloride, (C 4 H 7 N 3 O) 2 .ZnCl a , crystallizes 
 in warty lumps, composed of fine needles or prisms. 
 
 2. Weyl's reaction. Add, drop by drop, a freshly prepared, dilute solution 
 of sodium nitroprusside, Na 2 Fe(CN) 5 lS T O, until the solution is colored yellow; 
 then add drop by drop a dilute solution of sodium hydroxide : a fine transient 
 ruby-red color is obtained which soon passes into yellow. Acidulate solution 
 with acetic acid and warm : solution turns green, then blue, the color being 
 due to the formation of Prussian blue. 
 
 3. To a very dilute solution of creatine add a trace of an aqueous solution 
 of picric acid and render faintly alkaline: the solution turns intensely red. 
 
 Xanthine bases are a group of nitrogenous substances produced in 
 the organism as the result of the cleavage of nucleins. They are 
 closely related to one another, as also to uric acid, from which they 
 may be obtained by synthetic processes. Indeed, an increased secre- 
 tion of uric acid follows their ingestion as food. While eleven 
 xanthine bases have been isolated from the cell, only four (xanthine, 
 hypoxanthine, guanine, and adenine) are found in the muscle. Con- 
 jointly the xanthine bases are also termed alloxur bases or purine 
 bases. The first named refers to the fact that the nucleus of xanthine 
 bases is assumed to be made up of the carbon-nitrogen nuclei of 
 alloxsm, C 4 H 2 N 2 O 4 (an oxidation-product of uric acid), and wea, 
 
668 PHYSIOLOGICAL CHEMISTRY. 
 
 CN 2 H 4 O. When the two nuclei occur joined together into one 
 nucleus the latter is known as the purine-nueleus. Purine itself is a 
 hypothetical compound containing this nucleus. 
 
 N C 
 
 C 
 
 u 
 
 N/~1 XT /""I TT 
 
 O JN =Url 
 
 II II 
 
 N x C C N. HC C NH. 
 
 ' U-> : 1J-N> H - 
 
 Alloxan Urea Purine 
 
 nucleus, nucleus. nucleus. 
 
 By oxidation, or by replacement of hydrogen atoms in purine with 
 the radicals OH, NH 2 , NH, or by introducing the methyl group, 
 CH 3 , the different purine bases or allied compounds have been 
 formed. These bodies are also closely related to the vegetable bases 
 caffeine and theobromine, and also to uric acid, as shown in the fol- 
 lowing table : 
 
 Purine 
 
 Hypoxanthine (oxypurine) .... C 5 H 4 N 4 O 
 
 Xanthine (di-oxy purine) ..... C 5 H 4 N 4 O 2 
 
 Uric acid (tri-oxy purine) ..... C 5 H 4 N 4 O 3 
 
 Heteroxan thine (methyl-xan thine) . . . C 5 H 3 (CH 3 )N 4 Oj 
 Paraxanthine (dimethyl-xanthine) \ . 
 
 Isomeric with theobromine / ' ' M^CH^I^O, 
 
 Caffeine (trimethyl-xan thine) .... C 5 H(CH 3 ) 3 N 4 O 2 
 
 Adenine (amino-purine) ..... C 5 H 3 (NH 2 )N 4 
 
 Guanine (amino-oxypurine) .... C 5 H 3 (NH 2 )N 4 O 
 
 Carnine (dimethyl-uric acid) .... C 5 H 2 (CH 3 ) 2 N 4 O, 
 
 Uric acid and the xanthine bases take up water and yield qualitatively the 
 same decomposition-products when treated with fuming hydrochloric acid 
 under pressure, viz., ammonia, carbon dioxide, glycocoll, and formic acid. 
 
 Xanthine and hypoxanthine (sareine) occur generally together, 
 though in small quantities, in urine and in almost all tissues. In 
 larger quantity they are found in the meat-extracts. When pure 
 these bodies are colorless powders, almost insoluble in water, alcohol, 
 and ether. With acids they form crystallizable salts, and with silver 
 nitrate double compounds, which are employed in the separation of 
 the bases from fluids. 
 
 Phosphocarnic acid is a glyco-nucleoprotein, occurring in muscle ; it yields 
 on hydrolysis succinic acid, carbon dioxide, phosphoric acid, a carbohydrate, 
 and carnic acid, a protein almost identical with peptone. It forms soluble 
 compounds with the alkaline earths, and also an iron compound (carniferrin) 
 soluble in alkalies ; these properties serve as a means to carry these metallic 
 compounds through the body. (Lacto-phosphocarnic acid is an analogous 
 compound found in milk.) 
 
ANIMAL FLUIDS AND TISSUES. 669 
 
 Muscle pigment. Muscle, even when completely freed from blood, has a red 
 color, due to a pigment which is some slight modification of blood haemoglobin. 
 
 Of non-nitrogenous bodies found in muscle, inosite and sarcolactic acid, which 
 have been previously considered, deserve mention. 
 
 Experiment 78 (Preparation of sarcolactic add). Dissolve 20 grammes of 
 commercial meat-extract in 200 c.c. of water, add basic lead acetate as long as 
 a precipitate is formed ; filter and evaporate filtrate to a syrupy consistence. 
 Then add 200 c.c. of 96 per cent, alcohol ; filter and evaporate the filtrate to 
 dry ness over a water-bath. Dissolve the residue in 40 c.c. of water and 20 c.c. 
 of sulphuric acid. Extract this solution twice with an equal volume of ether 
 in a separatory funnel. Filter the ethereal solutions and evaporate the ether 
 with proper precautions. The residue, consisting of a colorless liquid, is sar- 
 colactic acid, to which apply : 
 
 Uffelmann's test for lactic acid. To an aqueous solution add a few drops of 
 Uffelmann's reagent (10 c.c. of a 2 per cent, solution of carbolic acid in 
 water, to which a few drops of ferric chloride solution have been added). A 
 yellow color is produced. 
 
 Inorganic constituents of muscle are chiefly mono- and dipotassium 
 phosphate, with smaller portions of sodium bicarbonate, salts of 
 magnesium and calcium, some iron salts, and traces of sulphates 
 and chlorides. 
 
 Meat- extracts are of two kinds, those from which the proteins and peptones 
 have been removed, and those containing besides proteins large quantities of 
 the basic extractives. Articles of the first class are destitute of nutritive 
 value, and the second derive no nutritive value from the extractive con- 
 stituents. The physiological effect of the flesh bases seems to be in the direc- 
 tion of nerve stimulants, and for this reason they are to be classed with tea 
 and coffee as adjuncts to food, not as true foods. 
 
 The thyroid gland contains iodine in some form of protein com- 
 bination, known as thyro-iodine ; this compound contains 9.3 per 
 cent, of iodine. 
 
 Desiccated thyroid glands, Glandulae thyroideae siccae. Numerous 
 extracts of the thyroid are upon the market. The preparation of the Pharma- 
 copoeia is the cleaned, dried, and powdered glands of the sheep, freed from fat. 
 It is a yellowish amorphous powder, partially soluble in water. 
 
 Thyreoidectin and rodagen are unofficial preparations prepared respectively 
 from the blood and from the milk of animals from which the thyroids have 
 been removed. Their action is stated to be exactly the opposite of that of the 
 thyroid preparations. 
 
 The thyroid gland, and also the adrenals, have some influence on sugar 
 metabolism, which is not yet understood. 
 
 The suprarenal glands contain a substance which has the power of con- 
 stricting the blood-vessels of the body, and thus causing a great but transient 
 rise in blood-pressure. This substance has been found to be methylamino- 
 ethanol-dioxy-benzol, C 6 H 3 (OH) 2 .CH(OH).CH 2 .NH.CH 3 . It is used particu- 
 
670 PHYSIOLOGICAL CHEMISTRY. 
 
 larly to produce local anaemia, and is called by various names : suprarenalm, 
 suprarenin, adrenalin, epinephrin. 
 
 Desiccated suprarenal glands, Glandulae suprarenales siccse. These 
 are the cleaned, dried, and powdered suprarenal glands of the sheep or ox, 
 freed from fat. A light-yellowish, amorphous powder, partially soluble in 
 water. 
 
 Brain consists of so many individual parts that the analysis of it 
 as a whole is of little value, and to separate these parts successfully 
 is a task not yet accomplished. Brain, as a whole, contains lecithin, 
 cholesterin, protagon, and many other substances, some of which are 
 distinguished by the large quantity of phosphorus they contain. 
 
 The gray matter contains albumin, globulin, nucleoprotein, and nuclein. 
 Neurokeratin forms the neuroglia. In the white matter is found protagon, a 
 very complex substance containing nitrogen and phosphorus. It yields on 
 hydrolysis a lecithin, fatty acid, and cerebroside. The cerebrosides are nitro- 
 genous substances free from phosphorus, yielding on hydrolysis galactose, 
 sometimes called brain-sugar. Fused with caustic potash, or boiled with nitric 
 acid, they form palmitic or stearic acids. Three cerebrosides are known: 
 cerebrin, kerasin, and encephalin. 
 
 The term " lipoids :> is applied to an indefinite group of organic substances, 
 which are, like the fats, soluble in ether and alcohol. These substances are 
 present in many kinds of tissue, and are particularly abundant in the brain 
 and in nerve fibres. The more important membranes are cholesterin and the 
 phosphorized fats (phosphatides, lecithins). The cerebrosides are also classed 
 here. The function of these substances is entirely unknown. Their abun- 
 dance in brain tissue is the basis of the well-known theory that the anaesthesia 
 produced by ether and chloroform is due to the solvent action of these sub- 
 stances upon the lipoids. 
 
 Lecithins, C^H^NPOg or C 42 H 84 NPO 9 . Lecithin, one of the con- 
 stituents of bile, is a member of the group of substances generally 
 termed phosphorized fats or lecithins. These bodies are highly com- 
 plex in composition, and may be looked upon as fats formed f Von/ 
 glycerin-phosphoric acid by substitution of hydrogen atoms with two 
 fatty acid radicals and a base, choline. 
 
 Glycerin-phosphoric acid, C 3 H 5 <^ QpQ 2 QTj\ ^ s obtained by the 
 
 action of glycerin on phosphoric acid, when combination takes place 
 with elimination of water, thus : 
 
 C 3 H 5 (OH) 3 + H 3 P0 4 C 3 H 5 (OH) 2 .H 2 P0 4 + H 2 O. 
 
 Glycerin-phosphoric acid is a syrupy liquid yielding easily soluble 
 salts, some of which are used medicinally. The hydroxyl hydrogen 
 is replaceable by acid radicals and the hydrogen of phosphoric acid 
 by bases. Thus, by introducing the radicals of stearic acid and 
 of choline distearyl-lecithin is obtained of the composition, C 3 H 5 
 (C 18 H 35 2 ) 2 .HP0 4 .C 2 H 4 N(CH 3 ) 3 OH. 
 
ANIMAL FLUIDS AND TISSUES. 671 
 
 Choline (Trimethyl-oxyetJiyl-ammonium hydroxide), N(CH 3 ) 3 .C 2 H 5 O.OH, has 
 been mentioned as one of the ptomaines. It is a colorless fluid of oily con- 
 sistency, has strongly basic properties, and is extremely unstable. By removal 
 of the elements of water choline is converted into the strongly poisonous 
 substance neurine, mentioned on page 620. On the other hand, choline by 
 oxidation is converted into muscarine, a ptomaine even more poisonous than 
 neurine. 
 
 Cholesterin, C 27 H 45 OH. This substance has been classed by 
 physiologists among the fats, because it is greasy and soluble in 
 ether, but its chemical constitution is that of an alcohol. It is found 
 chiefly in bile, but also in blood, nerve-tissue, brain, contents of the 
 intestines, feces, etc. ; its presence in certain vegetables, as pease, 
 beans, etc., has also been demonstrated. Cholesterin combines with 
 fatty acids to form fats. 
 
 Cholesterin crystallizes in colorless, rhombic plates, which are 
 insoluble in water, alkalies, and dilute acids, but soluble in ether. It 
 sometimes forms in the organism solid masses, known as biliary cal- 
 culi or gall-stones, some of which are almost pure cholesterin. 
 
 Cholesterin is an unsaturated, secondary alcohol, and a derivative 
 of the terpenes. 
 
 Reactions of cholesterin: 
 
 1. Place a small quantity of cholesterin on a slide, moisten with a 
 drop of 80 per cent, sulphuric acid, and cover with a cover-glass. 
 Allow a little iodine solution to run in under the cover-glass and 
 examine it with the microscope. The cholesterin crystals pass through 
 many shades of colors, gradually becoming brown or violet or clear 
 blue. 
 
 2. Evaporate, in a shallow porcelain dish, a small quantity of 
 cholesterin Avith hydrochloric acid containing a trace of ferric chloride. 
 A blue residue is formed. 
 
 QUESTIONS. What three kinds of matter are found as constituents of the 
 animal body, and how can they be determined quantitatively? Mention the 
 chief constituents of blood, and state those which predominate in serum and 
 in the corpuscles respectively. What substances cause the clotting of blood, 
 and what explanation can be given ? How may blood-stains be recognized ? 
 What are the characteristics of the different haemoglobins? Describe methods 
 for determining the specific gravity and the alkalinity of blood. How can the 
 proteins of blood-serum be separated ? Mention the principal constituents of 
 muscles, bone, teeth, and hair. State the properties and reactions of creatine 
 and gelatin. What is the composition of glycerin-phosphoric acid, and in 
 what form of combination does it exist in the body? 
 
672 PHYSIOLOGICAL CHEMISTRY. 
 
 56. DIGESTION. 
 
 General remarks. It has been stated that foods are divided into 
 two classes, inorganic and organic, and that the fetter are subdivided 
 into proteins, carbohydrates, and fats ; and also that the term diges- 
 tion refers to the process by which organic foods are altered in such 
 a manner that they may be absorbed. 
 
 The process of digestion is both mechanical and chemical. By 
 the mechanical part of the process the food-material is disintegrated, 
 propelled along the alimentary canal, and mixed with the different 
 digestive secretions. These latter cause a chemical change, usually 
 hydrolysis, of the food, converting it into soluble and easily absorb- 
 able substances. For convenience of study the process is divided 
 into salivary, gastric, and intestinal digestion ; and the secretions 
 and chief alterations of the nutrients in these portions of the tract are 
 considered separately. It should be remembered, however, that these 
 three processes are closely interdependent, and any disturbance of 
 function, mechanical or chemical, in one part of the digestion will 
 disturb and derange all. 
 
 Salivary digestion. The first part of the process of digestion is 
 accomplished in the mouth, and consists in the breaking up of the 
 food by the teeth and mixing it with saliva, the process being known 
 as mastication. In addition, the saliva, to a limited extent, converts 
 starch into maltose. This action of the saliva is due to its ferment 
 ptyalin. Other functions of the saliva are to keep the mucous mem- 
 brane of the mouth moist and to lubricate the food bolus. 
 
 Saliva is the mixed secretion of the parotid, submaxillary, sub- 
 lingual, and buccal glands. The quantity secreted in a day varies 
 from 600 to 1500 c.c. The flow is easily excited by reflex stimula- 
 tion, as by the smell or sight of food, or by chewing of some insolu- 
 ble substance. Saliva appears as a viscid, frothy, tasteless, inodor- 
 ous liquid, of a sp. gr. of 1.002 to 1.008. The reaction to litmus is 
 generally slightly alkaline, but may become acid under pathological 
 conditions. Saliva as it appears in the mouth contains food particles 
 and numerous micro-organisms. The average composition of saliva 
 is as follows : 
 
 Water 99.49 
 
 Mucin and epithelium 0.13 
 
 Fatty matter 0.11 
 
 Ptyalin, maltase, and other organic matter . . . .0.12 
 Salts 0.15 
 
 The salts are alkali and earthy phosphates, carbonates and chlo- 
 rides, and potassium sulphocyanate. The latter occurs in variable 
 
DIGESTION. 673 
 
 quantity in the saliva of different individuals. Pathologically, saliva 
 may contain sugar in diabetes, melanin in Addison's disease, bile- 
 pigment in icterus. Leucine and urea have been found in saliva 
 during uremia. The iodides and some other drugs are habitually 
 secreted by the salivary glands. This function is used in measuring 
 the rapidity of absorption. 
 
 Ptyalin, the diastatic enzyme, occurs in the saliva of all animals 
 except the pure carnivora. It is characterized by its action in con- 
 verting starch into sugar. It acts best at 40 C. (104 F.) in a 
 neutral solution, although it is active in a weak alkaline solution, 
 and also in acid solution up to 0.2 per cent, of mineral acid. 
 
 The conversion of starch into sugar by ptyalin is a progressive hydrolysis. 
 The first change is the formation of soluble starch, which gives a blue color 
 with iodine. Soluble starch is split into maltodextrin and erythrodextrin ; the 
 latter gives a red color with iodine. These dextrins are next split and yield 
 maltose, maltodextrin, and achroodextrin, which are not colored by iodine. 
 From achroodextrin more maltodextrin and maltose are derived, and finally 
 the hydrolysis results in the formation of maltose with some maltodextrin. 
 The maltose is converted into glucose by the action of the enzyme maltase. 
 
 Experiment 79. Mix intimately 1 gramme of starch with 10 c.c. of water, 
 pour this mixture into 90 c.c. of boiling water and stir until a smooth paste is 
 formed. Place 10 c.c. of paste in a test-tube, heat to 40 C. (104 F.), add 1 
 c.c. of saliva and 1 c.c. of 1 per cent, solution of sodium carbonate, mix well, 
 and keep at the stated temperature. At the expiration of one minute take out 
 a drop of the mixture, place it on a white plate, and add a drop of dilute 
 iodine solution. The mixture will turn blue. Eepeat testing the mixture, 
 which is to be kept at the same temperature, every minute until iodine has no 
 longer any effect on the solution, indicating the conversion of all starch into 
 simple sugars. With normal saliva the color reaction will cease within six 
 minutes ; a longer time would indicate an insufficient quantity of ptyalin in 
 the saliva used for the experiment. 
 
 When the solution no longer is affected by iodine add to 1 c.c. of solution 6 
 c.c. of alcohol : a precipitate of dextrin is formed. Allow the digestion to 
 proceed for half an hour, then heat some of the digested mixture with Feh- 
 ling's solution: the formation of red cuprous oxide shows the conversion of 
 starch into glucose. 
 
 Action of adds and alkalies on salivary digestion. In each of three test-tubes, 
 A, B, and C, place 5 c.c. of starch paste, prepared as above, and 1 c.c. of saliva. 
 To A add 3 c.c. of 0.25 per cent, hydrochloric acid ; to B add 3 c.c. of 1 per 
 cent, sodium carbonate. Keep the tubes at 40 C., and note the time required 
 for the disappearance of the iodine color reaction with the contents of each 
 tube. The reaction will disappear first in B, then in C, and finally in A. 
 
 In order to obtain saliva for experimental purposes a small glass 
 rod or a piece of rubber should be placed in the mouth. This will 
 stimulate the flow of saliva, which is to be collected and filtered. 
 
 43 
 
674 PHYSIOLOGICAL CHEMISTRY. 
 
 General tests for mixed saliva. 
 
 1. Allow a few c.c. of saliva to stand a day or two : a cloudiness 
 will be observed, due to the precipitation of calcium carbonate, which 
 has been held in solution by carbon dioxide. 
 
 2. Acidify saliva with acetic acid : a precipitate of mucin is formed 
 insoluble in an excess of the acid. 
 
 3. Apply the xanthoproteic, Millon's, and biuret reactions for 
 proteins (see page 626). 
 
 4. Acidify with acetic acid and add ferric chloride : a red color, 
 due to the formation of ferric sulphocyanide, is produced. 
 
 Gastric digestion. The food, after mastication, passes through 
 the oesophagus into the stomach. Here the mass is kneaded by the 
 contractions of the muscular wall of the stomach and is acted on by 
 the gastric juice. By this treatment with the aid of the fluids 
 ingested the food is converted into a turbid liquid, known as chyme. 
 A small portion of the digested mass is absorbed through the stomach 
 wall, but most of the food, after being completely acted upon, passes 
 through the pylorus into the duodenum. 
 
 Gastric juice is a liquid secreted by the follicles of the stomach. 
 It can be obtained, in a fairly normal condition, either from animals 
 (dogs) or from man, by the aid either of gastric fistulse or of the 
 stomach-pump. It is a thin, nearly colorless liquid, having a some- 
 what sour taste, an acid reaction, and a specific gravity varying from 
 1.002 to 1.003. The total solids are about 0.5 per cent., nearly one- 
 half being inorganic salts, chiefly the chlorides and phosphates 
 of alkali and alkaline earth metals. The organic matter present, 
 and amounting to about 0.3 per cent., is chiefly pepsin and a little 
 mucin. 
 
 The secretion of gastric juice is not continuous, and is brought 
 about by chemical irritation of the gastric mucuous membrane or by 
 psychic influence. A strong desire for food will cause a flow of the 
 juice ; chemical irritation, as by the alkaline mass of food and saliva, 
 causes a slower but more continuous flow. The quantity of juice 
 secreted during digestion varies with the quantity and quality of the 
 food. 
 
 The average composition of pure gastric juice may be approxi- 
 mately stated thus : 
 
 Water 99. 26 per cent. 
 
 Pepsin and other organic matter . . . .0.30 
 Rennin . y 
 
 Free hydrochloric acid .... 0.22 
 
 Alkali chlorides 20 
 
 Phosphates of calcium, magnesium, and iron . 0.02 
 
DIGESTION. 675 
 
 The acidity of gastric juice is due chiefly to hydrochloric acid, 
 present in quantities varying from 0.1 to 0.3, or even 0.4 per cent.; 
 to a slight extent also to organic acids and acid salts. The presence 
 of free acid in gastric juice cannot be demonstrated until about 
 twenty minutes after the swallowing of food ; this is due to the 
 power of proteins to form compounds with hydrochloric acid. During 
 this time the ptyalin of saliva is active in the hydrolysis of starch. 
 The gastric juice is the only secretion of the body containing free 
 acid. The mode of production of the hydrochloric acid is not under- 
 stood. While it is known that it is derived from the chlorides of the 
 blood, the details of the process are not yet worked out. The function 
 of the acid is to activate the enzymes of the stomach which are se- 
 creted in the zymogen state, and to aid in peptic digestion. It also 
 has a marked antiseptic action upon the contents of the stomach and 
 upper intestine. Organic acids, chiefly lactic, are frequently found in 
 the stomach, but these are not secreted in the gastric juice itself, but 
 are produced by some fermentative action from the food after it has 
 entered the stomach. Lactic acid is never found in a normal stomach 
 unless it was present in the food before ingestion. It is often present 
 in cases of gastric stagnation with a decreased hydrochloric output. 
 These cases may be either benign or, more often, malignant in origin. 
 Thus, the persistent occurrence of lactic acid with a diminution or 
 absence of hydrochloric acid is an indication of serious disturbances, 
 possibly of cancer of the stomach. 
 
 The origin of the lactic acid is the carbohydrate food ; other food 
 material may of course produce other organic acids (e. g., butyric acid 
 from butter). 
 
 The enzymes of gastric juice. The two important enzymes of the 
 stomach are pepsin and rennin, which are secreted in an inactive or 
 zymogen form, and are activated by the hydrochloric acid of the gas- 
 tric juice. In addition to these there is probably a lipolytic enzyme 
 (gastric lipase) present. In the cardiac end of the stomach the reaction 
 does not become acid for some time after digestion commences, and the 
 ptyalin of the saliva continues its action on the starches during this time. 
 
 Digestive action of gastric juice. The conversion of proteins into 
 peptone is a progressive reaction due to the action of pepsin in hydro- 
 chloric acid solution. Simple proteins are first changed into syn- 
 tonin, an acid albuminate ; this is split into compounds known as 
 primary proteoses (proto-proteoses, protalbumoses). By further action 
 these primary proteoses form secondary proteoses (deutero-proteoses, 
 deutero-albumoses), which are finally split, forming peptones. 
 
676 PHYSIOLOGICAL CHEMISTRY. 
 
 Peptone is the end-product of gastric digestion, is diffusible, and 
 is not further changed by pepsin. The intermediate products exist 
 at the same time in gastric digestion, their relative quantities depend- 
 ing on tiie length of time the action has progressed. 
 
 While it is believed that gastric digestion normally carries the de- 
 composition of proteins no further than this, it is possible to split 
 proteins into the amino-bodies by pepsin-hydrochloric acid digestion 
 outside of the body. 
 
 Compound proteins are split by gastric juice, the simple proteins 
 formed being digested as above stated. The nucleoproteins yield a 
 peptone free from phosphorus, the nuclein split off being unchanged. 
 Collagen is first converted into gelatin, which then forms successively 
 an acid albumin, proto-proteose, deutero-proteose, and gelatin-peptone. 
 Elastin is changed slowly, while keratins are not changed at all. 
 
 Rennin is a milk-curdling enzyme present in all normal human 
 gastric juice. It is absent in chronic catarrh of the stomach and 
 other diseases. Its presence in gastric juice is shown by its action 
 on milk, and will be considered in the article on clinical examination 
 of gastric juice. 
 
 Absorption in the stomach. It has been shown that the stomach is 
 able to absorb sugars, peptones, salts, and some drugs. However, 
 the absorption is not extensive unless concentrated solutions are 
 present, and probably plays no great part in normal metabolism. 
 
 Experiment 80. (Artificial gastric digestion.) Dissolve 2 grammes of scale 
 pepsin in 1000 c.c. of 0.4 per cent, hydrochloric acid. To this solution add 
 about 250 grammes of protein. The protein material may be fresh or dried 
 blood-fibrin, the meat- residue from the preparation of creatine (Experiment 77), 
 or the whites of 18 eggs, previously boiled and finely divided. The fresh fibrin 
 or the egg-albumin may be added directly to the digestive fluid. The meat- 
 residue or dried fibrin should first be boiled with a liter of water, containing 
 1 c.c. of hydrochloric acid, until the material gelatinizes ; it must be cooled 
 before mixing it with the digestive fluid. Keep mixture in a thermostat at a 
 temperature of 40 C. (104 F.) for ten days. Filter the solution, heat the 
 filtrate to 50 C. (122 F.), and neutralize with sodium carbonate, when syntonin 
 is precipitated. 
 
 Evaporate filtrate from syntonin to about 200 c.c., adding sodium carbonate 
 if necessary to keep solution neutral during evaporation, filter, and saturate 
 solution with ammonium sulphate, when protease is precipitated, while peptone 
 remains in solution. 
 
 To purify the proteose, dissolve the precipitate in water, heat to boiling, and 
 add barium carbonate until all ammonium sulphate is decomposed. Filter, 
 evaporate filtrate to a small volume, and pour solution into double the volume 
 of 95 per cent, alcohol, when proteose is precipitated as a sticky mass. To 
 obtain it as a powder, allow the mass to remain in contact with the alcohol for 
 
DIGESTION. 677 
 
 two hours, transfer to absolute alcohol for one hour, and then to ether for an 
 hour; then collect on a filter and dry between filter-paper. The proteose thus 
 obtained is a mixture of primary and secondary proteoses. 
 
 Use an aqueous solution of this proteose for the following tests : Acidulate 
 a portion with acetic acid and add an equal volume of saturated solution of 
 sodium chloride. The solution becomes cloudy, clearing again when heat is 
 applied, and becoming cloudy again when cool. (Characteristic of proteoses.) 
 Other portions of the solution use for the xanthoproteic, Millon's, and biuret 
 reactions. 
 
 Proteoses will give positive precipitation tests with acetic acid and ferro- 
 cyanide, and with trichloracetic acid. Peptones will give negative results with 
 the same tests. 
 
 To obtain peptone, the filtrate from the proteose is heated and 20 grammes 
 of ammonium sulphate are added to remove traces of proteose. The filtrate, 
 after being concentrated by evaporation, is treated with barium carbonate, 
 alcohol and ether, exactly as directed above for proteose. Use some of the 
 peptones for the xanthoproteic, Millon's, and biuret reactions. 
 
 Clinical examination of gastric juice. The chemical examina- 
 tion of gastric juice, or of contents of stomach, is now considered of 
 great importance in the diagnosis of diseases of the stomach. The 
 juice for examination is obtained as follows : On an empty stomach, 
 the patient partakes of a test-meal, consisting usually of bread and 
 water, and an hour after or later (depending upon the form of meal 
 administered) the contents of the meal are withdrawn by means of a 
 stomach-tube. The liquid is filtered and used for further examina- 
 tions. These examinations consist of the following determinations : 
 a. reaction ; b. presence of free acids ; c. presence of free hydro- 
 chloric acid ; d. presence of lactic and other organic acids ; e. total 
 acidity ; /. estimation of free acids ; g. estimation of free hydrochloric 
 acid ; h. estimation of combined hydrochloric acid ; i. estimation of 
 total organic acids ; j. presence of pepsin and pepsinogen ; k. presence 
 of renuin and rennin zymogen ; I, detection of proteins ; m, detection 
 of carbohydrates. 
 
 In case a sufficient supply of gastric juice cannot be obtained for the reac- 
 tions below, the student should prepare the following solutions : A. A 0.25 per 
 cent, hydrochloric acid ; B. A mixture of 10 parts of A and 40 parts of water; 
 C. A solution of 0.8 gramme of lactic acid in 100 c.c. of water ; D. A 2 per 
 cent, solution of albumose in water. Make reactions b and c with solution A, 
 repeat with B, and with a mixture of 1 part of B and 2 parts of D. 
 
 a. Reaction. This should be, and in all normal juices is, distinctly 
 acid to litmus-paper. 
 
 6. Free acids. The presence of free acids is detected by congo-red 
 paper. This paper is prepared by soaking unsized paper in a 1 per 
 cent, aqueous solution of congo-red, and drying. If a drop of juice 
 
678 PHYSIOLOGICAL CHEMISTRY. 
 
 is placed upon the paper, the presence of free acids is indicated by 
 the change of color from red to blue ; if the blue color is intense, 
 free hydrochloric acid is present. (Neither combined hydrochloric 
 acid nor acid salts, such as acid phosphates, act on congo-red.) 
 
 c. Free hydrochloric acid. There are a number of reagents for the 
 detection of free hydrochloric acid. The more important of these 
 are : tropaeolin 00, phloroglucin-vanillin, resorcin, and dimethyl- 
 amino-azobenzol. 
 
 Tropceolin 00. Dissolved in water, the 1 per cent, brownish -yel- 
 low solution of tropaeolin 00 (diphenylamine-orange) is changed to a 
 brown-red or deep-red color upon the addition of juice containing 
 free hydrochloric acid. Upon gentle evaporation and heating a lilac 
 color is produced. The same reaction may be made with filter-paper, 
 soaked for some time in an alcoholic solution of the reagent, allowed 
 to dry, and used as test-paper. Hydrochloric acid turns this paper 
 brown, and upon heating the brown color changes to blue. (The 
 paper does not keep unchanged over a month.) 
 
 Phloroglucin-vanillin. This reagent is made by dissolving 2 parts 
 of phloroglucin and 1 part of vanillin in 30 parts of alcohol. It is 
 a very sensitive and reliable agent for the detection of free hydro- 
 chloric acid. ^Five drops of the solution mixed with an equal quan- 
 tity of gastric filtrate are gently heated over a Bunsen flame. On 
 complete evaporation a distinct red color or tinge appears in the 
 presence of not less than 0.01 per cent, of hydrochloric acid. The 
 formation of cherry-red crystals indicates the presence of large quan- 
 tities of the acid. Organic acids have no action on this reagent. 
 
 Resorcin. This reagent is equally as sensitive as, and more stable 
 than, phloroglucin-vanillin. The solution is obtained by dissolving 
 5 parts of resublimed resorcin and 3 parts of cane-sugar in 100 parts 
 of dilute alcohol. The manner of testing with this reagent is the 
 same as described above for phloroglucin-vanillin ; a bright-red tinge 
 or color appears, even when very small quantities of free hydrochloric 
 acid are present. 
 
 Dimeihyl-amido-azobeMzol. A 0.5 per cent, solution of this substance 
 in alcohol is mixed with a few drops of the stomach contents, and in 
 the presence of as little as 0.002 percent, of free hydrochloric acid a 
 cherry-red color develops. 
 
 d. Lactic acid. (Use solution C.) Uffelmann's reagent answers 
 best for detecting this acid. It is made by adding 1 or 2 drops of 
 ferric chloride solution to 10 c.c. of a 1 per cent, carbolic acid solu- 
 tion, and diluting this solution with water until it assumes an 
 
DIGESTION. 679 
 
 amethyst-blue color. To 2 c.c. of this solution an equal volume of 
 gastric juice is added. In the presence of at least 0.01 per cent, of 
 lactic acid the liquid assumes a pure yellow color. As the presence 
 of too much hydrochloric acid (or even of some other substances) 
 prevents the change, it is well to shake (in doubtful cases) 10 c.c. 
 of juice with 50 c.c. of ether, evaporating the ethereal solution 
 to dryness, dissolving the residue in a few drops of water, and 
 adding to this solution, which contains the lactic acid, the above 
 reagent. 
 
 Butyric acid changes Uffelmann's reagent to brownish yellow. 
 Butyric and acetic acids may be recognized by their odor. 
 
 It has been mentioned that the total acidity of gastric juice is due to acid 
 salts, organic acids, free and combined hydrochloric acid. Clinically it is 
 sometimes necessary to estimate the acidity due to each. This is done by the 
 following method. 
 
 e. Total acidity. This is best determined by titration with an 
 alkali ; the estimation is conducted as follows : To 10 c.c. of the 
 filtered liquid a few drops of phenolphthalein solution are added, and 
 to the mixture deci-normal potassium hydroxide solution is slowly 
 added from a burette until the liquid assumes a slight reddish tint, 
 which does not disappear on stirring. 
 
 It is customary to express the acidity in percentages, according to 
 the quantity of deci-normal potassium hydroxide used. Thus, 52 
 per cent, acidity would indicate that every 100 c.c. of gastric fil- 
 trate are exactly neutralized by 52 c.c. of deci-normal potassium 
 hydroxide. 
 
 Though the total acidity is due to a mixture of free and combined 
 hydrochloric acid, organic acids, and acid salts, it is frequently 
 expressed as hydrochloric acid. As 1 c.c. of deci-normal alkali 
 solution corresponds to 0.003618 gramme of HC1, the number of 
 c.c. of alkali used multiplied by the factor stated, gives the grammes 
 of HC1 in the 10 c.c. of juice used. Suppose 5.2 c.c. of alkali were 
 required; this would correspond to 5.2 X 0.003618, equal to 0.0188 
 gramme of HC1 in 10 c.c., or to 0.188 per cent. 
 
 /. Estimation of free acids. Both free hydrochloric and organic 
 acids change the bright-red color of congo-red to blue, while alkalies 
 restore it to red. Acid salts, such as acid phosphates, have no effect 
 on this indicator. If, therefore, a titration of 10 c.c. of filtered gas- 
 tric juice, to which enough of congo-red solution has been added to 
 impart a distinct blue color, is made (as above described for total 
 acidity), then the number of c.c. of deci-normal potassium hydroxide 
 
680 PHYSIOLOGICAL CHEMISTRY. 
 
 solution used to restore the red color indicates the quantity of free 
 acid present. The calculation is made as above mentioned. 
 
 g. Estimation of free hydrochloric acid. The use of dimethyl- 
 ami no-azobenzol as an indicator for free hydrochloric acid has been 
 mentioned above. For quantitative work 10 c.c. of gastric filtrate 
 are mixed with 5 drops of the dimethyl-amino-azobenzol solution, 
 and this mixture is titrated with ^ sodium hydroxide solution. The 
 disappearance of the reddish color indicates when the reaction is 
 completed. The difference between the estimation of total free acids 
 (/) and that of free hydrochloric acid (g) indicates the quantity of 
 organic acids present. 
 
 h. Estimation of combined hydrochloric acid. To 10 c.c. of gas- 
 tric juice add 3 drops of a 1 per cent, alizarin solution and titrate 
 with YQ alkali until the solution assumes a clear violet color. The 
 acidity thus determined is due to free hydrochloric acid, acid salts, 
 and organic acids. The difference between the results of titration 
 with alizarin (A) and with phenol-phthalein (e) shows acidity due to 
 combined hydrochloric acid, while the difference between the titra- 
 tion with alizarin (h) and that with dimethyl-amino-azobenzol shows 
 acidity due to organic acids and acid salts. 
 
 i. The total organic acids, free and combined, may be determined 
 by neutralizing 10 c.c. of gastric juice, using phenolphthalein as an 
 indicator, evaporating the neutral solution to dryness and incinerating 
 the residue. By this operation the organic acids are converted into 
 carbonates, which are titrated with ^ acid, and from the result the 
 quantity of organic acid is calculated, usually as lactic acid. 
 
 j. Pepsin and pepsinogen. In case free acid is present, 10 c.c. of 
 gastric juice are placed in a beaker, and a small bit of dried fibrin 
 or a lamella of blood albumin (Merck), is added, and the beaker 
 placed in a thermostat at a constant temperature of 38 to 40 C. 
 (100 to 104 F.). Pepsin is indicated by the rapid solution of the 
 flake of albumin. If free hydrochloric acid is absent, the juice is 
 rendered acid with a drop of this acid and then tested in the manner 
 described. 
 
 k. Rennin enzyme and rennin zymogen. Rennin is tested for as 
 follows : 10 c.c. of gastric juice are exactly neutralized with deci- 
 normal alkali and mixed with an equal volume of neutral unboiled 
 milk. The mixture is placed in a thermostat at 38 C. (100 F.). 
 If a casein coagulum is formed in ten to fifteen minutes, the coagula- 
 tion is due to the rennin enzyme. 
 
 Rennin zymogen is detected thus: 10 c.c. of gastric juice are 
 
PLATE VII 
 
 INDICATORS FOR ALKALIES AND ACIDS. 
 
 Litmus. 
 
 Congo red. 
 
 3 
 
 Phenolphthalein. 
 
 
 flethy 1- orange ; Dimethj I-amido- 
 azobenzol ; Tropseolin D. 
 
 5 
 
 Alizarin for acids. 
 
 I ffelmann's test for lactic acid. 
 
 Gunzburg's phloroglucin- vanillin 
 test or Boas' resorcin test for free hy- 
 drochloric acid. 
 
 Methyl-violet. 
 
 Haematoxylin. 
 
 A ffocn & Co Lie/i. Baltimore., .Wd. 
 
 The colors on the left indicate alkaline, those on the right acid reaction. 
 For explanation see page in Index. 
 
DIGESTION. 681 
 
 rendered feebly alkaline and mixed with 2 c.o. of a 1 per cent, 
 solution of calcium chloride and 10 c.c. of milk. If the rennin 
 zymogen be present, a heavy cake of casein is precipitated in a few 
 minutes. 
 
 1. 'Detection of proteins. Of these, syntonin, albumoses, and pep- 
 tones are to be looked for. Syntonin : The gastric filtrate is exactly 
 neutralized, whereupon a cloudiness or precipitate is formed, which 
 is soluble both in alkalies and in acids. Albumoses: These are pre- 
 cipitated by a saturated solution of ammonium sulphate, while pep- 
 tones remain in solution. Peptones : These are recognized by the 
 biuret-test. The juice is rendered strongly alkaline with potassium 
 hydroxide and a few drops of a cupric sulphate solution (1 in 1000) 
 are added. A red color indicates the presence of peptones. 
 
 ra. Detection of carbohydrates. Starch is recognized by the blue 
 color produced by iodine solution (1 iodine, 2 potassium iodide, 100 
 water). The reaction is less marked in proportion to the amount of 
 starch converted into dextrin and sugar. 
 
 Erythrodextrin gives a mahogany-brown color, and achroodextrin 
 remains unchanged by the iodine solution. Inasmuch as sugar is 
 present in the test-meal itself, it is useless to test for this substance. 
 
 Intestinal digestion. The changes in food taking place in the 
 small intestine are much more complex and far-reaching than those 
 occurring in the stomach. Little or no absorption takes place from 
 the stomach, and the alterations in the food brought about by the 
 gastric juice can be considered as being largely preparatory for the 
 action of the digestive fluids of the intestine. The close dependence 
 of one part of the process of digestion on the other is shown by the 
 normal effect of the entrance of chyme into the duodenum. The 
 acid chyme causes a reflex secretion of the pancreatic juice, the bile, 
 and the intestinal juice, the digestive fluids of the intestine. These 
 fluids are all alkaline, and are secreted in sufficient quantity to neu- 
 tralize the chyme and to provide the degree of alkalinity most suit- 
 able for the action of the ferments which complete the process of 
 digestion. A slight increase of the acidity of the gastric contents is 
 followed by an increase in the secretion of the digestive fluids of the 
 intestine. Intestinal digestion depends upon three secretions : (1) 
 the pancreatic juice ; (2) the bile ; (3) the succus entericus, the secre- 
 tion of the intestine. 
 
 Pancreatic secretions. The secretions of the pancreas are of 
 two kinds, an external, the pancreatic juice, which flows into the 
 
682 PHYSIOLOGICAL CHEMISTRY. 
 
 intestine, and an internal secretion, which passes directly into the 
 blood, and has a governing power over the metabolism of sugar and 
 the conversion of glycogeu into sugar by the liver. 
 
 Pancreatic juice. There is no thoroughly reliable analysis of this 
 highly complex liquid on record. It is an alkaline liquid containing 
 from 3 to 6 per cent, of solids, two-thirds of which are of organic, 
 one-third of inorganic nature. Among the organic constituents are 
 a number (certainly three, probably four) of enzymes : 1. Amylopsin 
 converts starch into sugar (this action is more energetic than that of 
 ptyalin) ; 2. Trypsin converts proteins into peptones (this action takes 
 place in alkaline, but not in acid solution, as in case of pepsin) ; 3. 
 Steapsin decomposes fats into glycerin and fatty acids ; 4. A milk- 
 curdling enzyme. The inorganic solids are chiefly alkali chlorides 
 and carbonates, with some calcium, magnesium, and iron phosphates. 
 
 The quality of the food has an unmistakable influence on the com- 
 position of the juice and on the quantity of the different enzymes. 
 Thus, the juice is always richest in diastatic enzyme after a bread 
 diet, and richest in steapsin after a meal consisting of much fat. 
 
 The secretion of pancreatic juice is thought to be caused by stimuli 
 reaching the pancreas by two routes : (1) nervous stimuli by the sym- 
 pathetic nerves; (2) chemical stimuli by the blood-stream. The 
 chemical substance concerned is termed secretin, and is formed in the 
 intestine as soon as hydrochloric acid is admitted from the stomach 
 during the course of digestion. The HC1 acts upon a substance 
 normally present (prosecretin), transforming it to secretin, which is 
 absorbed and carried by the blood to the pancreas. Secretin belongs 
 to the class of bodies called hormones. 
 
 The trypsin of the pancreatic juice is for the most part secreted in 
 an inactive or zymogen state (trypsinogen), and becomes active when 
 it meets the kinase of the intestine (enterokinase). The other enzymes 
 (amylopsin, steapsin) are secreted mainly in the active condition. 
 
 Amylopsin (diastase) is closely related to ptyalin, and converts raw 
 or boiled starch into erythrodextrin, achrobdextrin, and finally into 
 maltose and dextrose. The dextrose is probably formed by the in- 
 vertin of the intestinal juice. 
 
 Experiment 81. (Diastatic action of pancreatin.) Dissolve 1 gramme of pan- 
 creatin in 500 c.c. of water, and after standing at 40 C. (104 F.) for two hours 
 filter the solution. Mix in a test-tube equal volumes of the solution and starch 
 paste, prepared as directed in Experiment 79, and heat at 40 C. (104 F.). 
 Notice that the material gradually* becomes transparent, reduces Fehling's 
 solution, and is not colored blue by iodine solution. Repeat the experiment 
 with a boiled solution of pancreatin, and notice that it has no effect on starch, 
 
DIGESFION. 683 
 
 the enzyme having been destroyed by heat. (The pancreatin solution itself 
 should be tested with Fehling's solution, as the commercial article is frequently 
 adulterated with sugar.) 
 
 Steapsin (lipase) splits the neutral fats into fatty acids and glycerin. 
 The liberated fatty acids combine with alkali of the pancreatic juice, 
 forming soap. The action of lipase is materially aided by the pres- 
 ence of bile, although it is not understood how this occurs. 
 
 Experiment 82. (Fat-splitting action of steapsin.} (Fresh pancreas must be 
 used for the experiment.) Shake about 2 grammes of butter with a few c.c. of 
 lukewarm water, to which a drop of caustic soda solution has been added. 
 After cooling shake with an equal volume of ether, pour the ethereal solution 
 on a watch-glass and allow the ether to evaporate. To the neutral butter fat 
 thus obtained add a piece of fresh pancreas the size of a pea, mix the materials 
 intimately by rubbing, and place in a thermostat at 40 C. (104 F.). After a 
 few minutes the odor of butyric acid will be recognized. 
 
 Shake a gramme of butter fat, obtained as above, with about 5 c.c. of luke- 
 warm water, render slightly alkaline with sodium carbonate, using rosolic acid 
 as an indicator, add some fresh pancreas converted into a thin paste by grind- 
 ing with water, and keep the mixture at 40 C. (104 F.) for twelve hours. 
 Notice that the mixture turns yellow, due to the acid liberated from the butter 
 fat. The experiment when made with boiled pancreas does not show liberation 
 of acid. 
 
 Trypxin breaks down proteins by a series of changes almost iden- 
 tical with those produced by pepsin. It is, however, most active in 
 an alkaline medium, and has a more rapid and complete action than 
 that of pepsin. The digestions by pepsin and trypsin are to a certain ex- 
 tent supplementary to each other, for it is found that proteins subjected 
 to both are more thoroughly decomposed than by either one alone. 
 Under normal conditions it is probable that tryptic digestion produces 
 a considerable amount of amino-bodies, and that the remainder of the 
 peptones and proteoses are split up by the intestinal enzyme, erepsin. 
 
 Experiment 83. (Artificial tryptic digestion.} To 250 grammes of protein add 
 a solution of 5 grammes of sodium carbonate, 3 grammes of pancreatin, and 
 5 c.c. of chloroform. Keep in a thermostat at 40 C. (104 F.) for ten days. 
 Then filter off a few c.c. of the liquid and add bromine-water. A violet color 
 is produced, due to tryptophane. Acidify the digested mixture with acetic 
 acid, boil, filter, evaporate filtrate to 150 c.c., and allow to stand in a cool 
 place. In a few hours crystals of tyrosine will be deposited. Decant the 
 mother-liquor and purify the tyrosine by recrystallizing from a solution con- 
 taining a little ammonia. Use the crystals to test for tyrosine (see Index). 
 
 Evaporate the mother-liquor from the tyrosine to a thin syrup, add 200 c.c. 
 of hot alcohol, allow the mixture to cool, and filter. Evaporate the filtrate to 
 dryness, dissolve the residue in water, and boil with freshly prepared lead 
 hydroxide. Allow to cool, filter, free the filtrate from lead by means of 
 
684 PHYSIOLOGICAL CHEMISTRY. 
 
 hydrogen sulphide, and evaporate to a small volume. The leucine which is 
 precipitated on standing is best separated from the mother-liquor by placing 
 the mass on a plate of porous clay. Use the crystals to make reactions for 
 leucine (see Index). 
 
 Bile, secreted by the liver, is a thin, transparent liquid of a golden- 
 yellow color, and a specific gravity of 1.020 ; it has a very bitter taste 
 and an alkaline reaction ; it varies widely in composition, the total 
 solids ranging from 9 to 17 per cent., being always highest after a 
 meal ; its composition, moreover, is highly complex ; the following is 
 an average of five analyses of bile from subjects with healthy livers : 
 
 Water 91.68 per cent. 
 
 Mucus and pigment 1.29 " 
 
 Taurocholate of sodium 0.87 
 
 Glycocholate of sodium 3.03 " 
 
 Fat . 0.73 
 
 Soaps . . 1.39 " 
 
 Cholesterin 0.35 " 
 
 Lecithin 0.53 
 
 Bile obtained after death is of a brownish-yellow color ; freed from 
 mucus it will remain undecomposed for an almost indefinite period. 
 The mucus may be separated by the addition of diluted alcohol and 
 subsequent filtration. 
 
 The quantity of bile discharged daily by a grown person may be 
 put at from 1000 to 1700 c.c., or from 23 to 47 ounces, but a con- 
 siderable quantity of this discharged bile is reabsorbed in a changed 
 form by the intestines; only a small amount of bile matters (in a 
 decomposed state, however) is contained in the feces. 
 
 Bile is to be regarded both as a secretion and an excretion, as will 
 be seen below in the statements concerning its constituents. It has 
 long been believed that bile is an intestinal antiseptic. Its action is, 
 however, weak and probably unimportant, as it has been found that 
 certain bacteria (B. typhosus, B. coli) grow well in media containing 
 bile. 
 
 Biliary pigments. Several pigments have been found in bile, but 
 it is probable that only two, bilirubin and biliverdin, occur in normal 
 bile. 
 
 The bile-pigments are formed in the liver from haemoglobin by a 
 process in which the iron is split off and retained in the organism. 
 While the pigments of the bile are regarded as waste products of 
 metabolism, a certain portion of them is absorbed in the intestine, is 
 excreted again by the liver, and also by the kidneys (as urochrome 
 and urobilin). That portion which passes out with the feces is re- 
 duced to stercobilin (isomeric with urobilin). 
 
DIGESTION. 685 
 
 Bilirubin, C 16 H 18 N 2 O 3 , is a reddish-yellow pigment derived from 
 hsematin, which it resembles. It is sparingly soluble in water, 
 alcohol, and ether, readily soluble in hot chloroform and carbon 
 disulphide. 
 
 Biliverdin, C 32 H 36 N 4 O 8 , is a green powder existing in green biles ; 
 it is formed from bilirubin by mild oxidation. 
 
 Tests for biliary coloring-matters. A reaction known as Gmelin's 
 test may be applied in different ways : 
 
 1. Place into a test-tube a few c.c. of a chloroform solution of 
 bilirubin, and pour down the side of the inclined tube an equal 
 volume of yellow nitric acid in such a manner that the liquids do 
 not mix. At the line of junction colored rings appear, being green 
 nearest the solution of the coloring-matter, and progressively blue, 
 violet, red, and yellow. (Plate VIII., 7.) 
 
 2. Place on a white porcelain slab a few drops of the solution and 
 alongside of it a drop of yellow fuming nitric acid. On causing 
 the two liquids to come in contact a play of colors as above is seen 
 at the junction. 
 
 3. Expose an alkaline solution of bilirubin to the air in an open 
 vessel ; it turns green, owing to the formation of biliverdin. The 
 latter answers also to Gmelin's test. 
 
 Biliary acids. Glycocholic acid, C^H^NOg, and taurocholic acid, 
 C 26 H 45 NO 7 S, exist as sodium salts in the bile^bf man and most 
 animals. Both salts may be obtained as colorless crystals, which 
 dissolve in water, forming solutions with an acid reaction and an 
 intensely bitter taste. Both acids are easily decomposed by heating 
 with alkalies or with dilute acids, also by the action of putrefying 
 material or by chemical changes taking place in the intestines. In 
 all these cases are formed cholic acid, C 24 H 40 O 2 , and a second product, 
 which in the case of glycocholic acid is glycocoll, amino-acetic acid, 
 CH 2 .NH 2 .CO 2 H, and in the case of taurocholic acid, taurine, amino- 
 ethyl-sulphonic acid, NH 2 .C 2 H 4 .SO 3 H. 
 
 These acids are formed in the liver, and very likely from some 
 protein material ; the mode of formation is, however, not known. As 
 in the case of the bile-pigments, the bile acids in part represent waste 
 material, while a part is reabsorbed by the intestine. The physio- 
 logical activity of bile acids is concerned mainly with the fats ; they 
 aid the saponification by lipase, and promote the absorption of fat 
 (probably by their solvent action). They are believed to hold the 
 cholesterin of the bile in solution. 
 
686 PHYSIOLOGICAL CHEMISTRY. 
 
 Test for biliary acids. The biliary acids and their salts show a 
 characteristic reaction known as Pettenkofer's test. This reaction is 
 shown by adding very little cane-sugar to the liquid substance under 
 examination, and adding concentrated sulphuric acid in such a 
 manner that the temperature does not rise above 70 C. (158 F.). 
 In the presence of biliary acids a beautiful cherry-red color is devel- 
 oped, which gradually changes to dark reddish-purple. The red 
 liquid when examined spectroscopically shows two absorption-bands, 
 one at F, the other near E, between D and E. Bile acids are not 
 the only substances which show the colors of Pettenkofer's test, but 
 the spectroscopic examination will clear up doubtful cases. 
 
 Experiment 84. Evaporate ox-bile to a thick syrup, digest it with 5 parts of 
 pure, cold alcohol for two hours, and filter. Mix the filtrate, which contains 
 sodium glycocholate and taurocholate, with freshly prepared animal charcoal, 
 boil and filter ; evaporate to dryness in a water-bath, redissolve in the smallest 
 possible amount of pure alcohol, and add ether until the solution becomes 
 markedly turbid. A white, crystalline mass is deposited in a few hours or days ; 
 this is known as Planner's crystallized bile, and is a mixture of the two sodium 
 salts mentioned. 
 
 Dissolve the mass in a small volume of water, adding a little ether and then 
 dilute sulphuric acid; glycocholic acid crystallizes out in shining needles. 
 Taurocholic acid is easiest prepared by using -dog's bile, which contains no 
 glycocholic acid. 
 
 Apply the Pettenkofer test to the glycocholic acid obtained. 
 
 Cholesterin and lecithin in the bile are present in considerable 
 amount. They are regarded here as waste products. 
 
 Siiiary calculi consist chiefly of cholesterin, and in addition they 
 contain bile-pigment, the bile acids combined with calcium, calcium 
 soaps, and calcium carbonate. 
 
 Experiment 85. (Examination of biliary calculi.} Boil the freshly powdered 
 stones with water to remove bile, filter, and extract the dry residue with a 
 mixture of alcohol and ether. Filter, and evaporate the filtrate to a small 
 volume, when crystals of cholesterin will be deposited. Purify the crystals by 
 dissolving them in boiling alcohol to which a fragment of sodium hydroxide 
 has been added, and treating the mixture in a separatory funnel with ether. 
 By evaporation of the ethereal solution cholesterin is obtained in a pure con- 
 dition. Apply the tests for the same (see Index). 
 
 The residue of the calculi, insoluble in ether and alcohol, consists of the 
 inorganic salts and bile-pigments. Dissolve the salts by pouring dilute hydro- 
 chloric acid over the contents in the filter, and show in filtrate the presence of 
 calcium by neutralizing with ammonia, acidifying with acetic acid, and adding 
 ammonium oxalate, when calcium oxalate is precipitated. To a portion of the 
 hydrochloric acid solution add potassium ferrocyanide ; sometimes a red pre- 
 cipitate is formed, due to the presence of traces of copper in the calculus. 
 
DIGESTION. 687 
 
 The residue left on the filter consists of bilirubin. Purify it by washing 
 with water, drying, and heating the mass with chloroform. On filtering and 
 evaporating the solution in a watch-glass rhombic plates or prisms of bilirubin 
 are left, which examine microscopically, and to which apply the tests men- 
 tioned above. 
 
 Succus entericus. The small intestine secretes several important 
 enzymes : erepsin, which acts mainly upon the proteoses and peptones, 
 splitting them into peptides and amino-bodies; inverting enzymes act- 
 ing upon the disaccharides (invertase, maltase, lactase) ; and entero- 
 kinase, which is necessary for tryptic digestion. In addition the 
 small intestine forms the prosecretin, from which the stimulating 
 hormone secretin is derived and carried to the pancreas. The succus 
 intestinalis is alkaline, and aids in neutralizing the acid from the 
 stomach. 
 
 Fermentative and putrefactive changes. In addition to the 
 alterations brought about by the digestive enzymes, the food also 
 undergoes fermentative and putrefactive changes, due to the action 
 of bacteria, always present in the intestine. Some of these bacteria 
 convert carbohydrates into acetic, butyric, lactic, and succinic acids, 
 while carbon dioxide, methane, and hydrogen are also liberated. 
 Certain fats probably form neurine and similar toxic substances. 
 By putrefaction of proteins are formed : phenol, several aromatic 
 derivatives, notably indole and skatole, volatile fatty acids, carbon 
 dioxide, methyl-mercaptan, and hydrogen sulphide. 
 
 As intermediate products, the bacteria convert to some extent the 
 food material into the same substances which are formed by the 
 action of pancreatic juice ; these products, however, are not useful 
 to the organism, but are only intermediate stages of far-reaching 
 decompositions. The end-products of bacterial action pass out of 
 the intestine in the feces and as flatus, or are absorbed and carried 
 to the liver, where most of the aromatic compounds are conjugated 
 with potassium acid sulphate, and in this form are secreted in the 
 urine. Thus the quantity of aromatic sulphates in the urine is a 
 measure of putrefaction in the intestine. 
 
 Absorption in the small intestine. It seems advisable under 
 this heading to follow in outline the foodstuffs from their ingestion 
 to their delivery into the circulation. 
 
 The carbohydrates are first acted upon by the saliva, ptyalin split- 
 ting the starches into maltose, and maltase splitting the maltose into 
 dextrose. While this action continues for some time in the cardiac 
 end of the stomach, it is, in all, not very extensive. There is no 
 
688 PHYSIOLOGICAL CHEMISTRY. 
 
 gastric enzyme acting upon carbohydrates, but a small amount of the 
 simple sugars may be absorbed here. In the intestine the starches 
 are energetically attacked by the amylopsin (diastase) of the pancreas, 
 and the disaccharides are converted into the monosaccharides by the 
 inverting enzymes of the succus entericus. In this manner almost 
 all of the starch and sugar of the food is normally reduced to the 
 hexose form, the greater part being dextrose, with some laevulose, 
 galactose, and pentose (from cane-sugar, milk-sugar, and various vege- 
 tables respectively). These simple sugars are absorbed by the small 
 intestine, transferred as such to the blood-stream, carried directly to 
 the liver by the portal vein, and here stored up as glycogen. If an 
 excessive amount of sugar, particularly a simple sugar, be eaten, it is 
 absorbed more rapidly than the organism is able to care for it, and it 
 will appear unchanged in the urine (alimentary glycosuria, Icevulo- 
 suria, etc.). The exact mechanism of this fact is not known. It is 
 commonly believed that the liver is unable to convert more than a 
 certain amount of sugar into glycogen, hence there results an exces- 
 sive quantity of sugar in the blood, which excess is excreted by the 
 kidneys. The amount of sugar which can be eaten at one time with- 
 out a resulting excretion is termed the assimilation limit of that sugar. 
 The assimilation limit differs for the different sugars and in different 
 individuals. 
 
 Fats undergo less digestive change than either carbohydrates or 
 proteins. Their digestion occurs mainly in the intestine, and consists 
 primarily of a saponification into glycerin and fatty acid by the lipase 
 of the pancreas. The biliary fatty acids combine with the alkali of 
 the intestinal contents to form soaps, which produce an emulsification 
 of the neutral fat still present. This emulsification is believed to be 
 of importance in offering a greater surface of fat for the action of the 
 lipase. The bile has two important actions in fat digestion, the bile 
 salts aid the action of the lipase and also act as solvents for both the 
 fatty acids and the soaps. It is believed now that little or no fat is 
 absorbed in the form of an emulsion, and that the greater part is 
 taken up as glycerin and fatty acid (soap). The glycerin is, of 
 course, readily soluble, while the fatty acid is very likely in solution 
 with the bile salts. Apparently the glycerin and fatty acid are at 
 once resynthesized in the mucous membrane of the intestine to neutral 
 fat and passed into the lacteals as an emulsion, which, in turn, is 
 carried to the general circulation by the thoracic duct. 
 
 Proteins are digested by three enzymes, pepsin (stomach), trypsin 
 (pancreas), and erepsin. The three carry out what is fundamentally 
 
DIGESTION. 689 
 
 the same process. The pepsin action is exerted mainly to effect the 
 earlier actions, i. e., the change from protein through primary and 
 secondary proteose to peptone ; the erepsin is concerned mainly with 
 the later transformation from peptone to polypeptide and amino- 
 bodies (arnino-acids), while the action of trypsin is important through- 
 out the entire decomposition. The general course and ultimate results 
 of protein digestion are now fairly clear, and it is universally accepted 
 that proteins are absorbed in the form of the amino-bodies or, perhaps, 
 in part as fairly simple polypeptides, the protein nuclei of Abder- 
 halden. The digestion of protein is believed to have a deeper signifi- 
 cance than (as in the case of the carbohydrates and fats) the mere pro- 
 duction of soluble and dialyzable substances. As the protein material 
 absorbed by the intestine is converted again to protein, and as the 
 ingested (foreign) protein must give rise to a different (native) 
 protein, it is easy to see that this change must be much more readily 
 carried out if the foreign protein is first split into its component parts, 
 the amino-bodies. Abderhalden believes that not all the protein is 
 necessarily split entirely to amino-acids, but part may remain in the 
 polypeptide form and serve as a nucleus to which the other amino- 
 bodies may be added which are needed for the production of the 
 native protein. The native protein thus formed is conveyed by the 
 portal system to the liver. 
 
 Absorption in large intestine. As the large intestine secretes no 
 enzymes, the only digestive action here is due to the enzymes which 
 have been brought down from above. This is probably not of any 
 great moment, as experimental work has shown that, with the excep- 
 tion of water, there is little absorption by the large intestine. It is, 
 however, true that clinical work with rectal feeding shows that per- 
 sons may be sustained to a certain extent by rectal injections of pre- 
 digested food mixtures. 
 
 Feces consist of the unabsorbed material from the food, the waste 
 material excreted from the blood, detached epithelium, and the secre- 
 tions of the intestine. The odor depends largely on the indole and 
 skatole, to a less degree on valeric and butyric acids, and on hydro- 
 gen sulphide present. The quantity and composition of feces passed 
 depend on the nature of the food and the energy of the digestive 
 powers. A grown person in normal condition discharges from 100 
 to 250 grammes (4 to 9 ounces) daily. A diet rich in animal proteins 
 causes the quantity of feces to be small, while a diet rich in vegetable 
 44 
 

 . 
 
 . 
 
 . 77. 3 per cent. 
 23 " 
 
 es 
 
 biliary, 
 residue 
 
 and coloring-matters . 
 of food 
 
 . 5.4 
 . 1.8 " 
 . 1.5 
 . 1.8 
 . 5.2 
 4.7 
 
 690 PHYSIOLOGICAL CHEMISTRY. 
 
 and starchy foods increases the quantity. An approximate analysis 
 of the feces of a healthy adult shows : 
 
 Water 
 
 Mucin 
 
 Proteins 
 
 Extractives 
 
 Fats 
 
 Salts 
 
 The proteins, other than mucin, are chiefly keratins and nucleins. 
 The principal salts are ammonium-magnesium phosphate, calcium 
 carbonate, calcium and magnesium phosphate. The bile-pigment 
 normally is stercobilin, derived from bilirubin by reduction. 
 
 A large proportion of the feces consists of bacteria. The micro- 
 scopic examination of feces for intestinal parasites and bacteriological 
 examinations are of great value in clinical work. The significance 
 of the chemical findings are not yet well understood except in a few 
 instances (e. g., presence of blood and bile). 
 
 Experiment 86. (Chemical examination of feces.} 
 
 a. Reaction. Normally the reaction of feces is slightly alkaline to litmus. 
 
 b. Fat. Extract the feces with ether and evaporate the ethereal solution. 
 Mix a portion of the residue with potassium acid sulphate and ignite ; in the 
 presence of neutral fat the characteristic odor of acrolein is noticed. Dissolve 
 another portion of the residue in a mixture of alcohol and ether which has 
 been colored blue-violet by alkanet (a dye derived from a plant of the same 
 name, and used as .an indicator for certain acids) ; a red color indicates the 
 presence of fatty acids. (The occurrence of large amounts of fats or fatty acids 
 in the feces may be the result of the ingestion of an excessive quantity of fat, 
 or of imperfect digestion and absorption due to pathological conditions.) 
 
 c. Mucin. Mix the feces with lime-water, allow to stand for several hours, 
 filter, and acidify filtrate with acetic acid. A precipitate indicates mucin. To 
 verify the nature of the precipitate, boil it with dilute hydrochloric acid for an 
 hour, then neutralize, and heat with Fehling's solution. A red precipitate 
 proves the substance to have been mucin. (Mucin occurs in the feces in con- 
 siderable quantity whenever there is catarrh of the large intestine, and in cases 
 of membranous enteritis.) 
 
 d. Albumin. Mix the feces with water, acidify with acetic acid, and filter, 
 est the clear filtrate by adding potassium ferrocyanide. Albumin, when 
 
 present, coagulates. (Albumin is found in the feces of typhoid fever patients.) 
 
 e. Proteose and peptone. Make a thin paste of feces with water, boil, and 
 ;er while hot. To the filtrate add lead acetate, filter, and apply the biuret 
 
 aon. (Proteose and peptone are found in the feces whenever much pus is 
 produced in the intestine.) 
 
 / Carbohydrates. Boil the residue, left from the extraction with ether (6), 
 
DIGESTION. 691 
 
 with water, filter, and evaporate filtrate to a small volume. Test the liquid for 
 sugar with Fehling's solution, and for dextrin and starch with iodine. 
 
 g. Blood. When the blood in the feces is derived from the lower portion 
 of the intestine the red color is so characteristic that further examination is 
 unnecessary. When the blood comes from the upper intestine and the pig- 
 ment has been altered, it becomes necessary to make a spectroscopic examina- 
 tion or the ha3min test, for which see page 658. For the spectroscopic exami- 
 nation, the feces are extracted with water containing a little acetic acid, and 
 the liquid is extracted with ether. If blood is present, the ethereal solution 
 is brownish red. Evaporate the solution to dryness and dissolve the residue in 
 water containing a little sodium hydroxide. The solution is haematin in alka- 
 line solution, and will show the characteristic bands, Fig. 72, e. Hrematin may 
 occur in feces physiologically as a result of a meat diet ; pathologically, it is' 
 found after hemorrhage into the intestine from any source. 
 
 Occult blood is the name given to traces of blood occurring in the feces after 
 small hemorrhages from ulcer of the stomach or duodenum. Its presence is 
 shown as follows : Extract 10 grammes of feces with 25 c.c. of ether to remove 
 fat. To the residue add 5 c.c. of glacial acetic acid and then extract again 
 with 20 c.c. of ether. To this ethereal extract add a little powdered guaiac 
 and then 1 or 2 c.c. ozonized turpentine. A blue color develops on shaking 
 and standing, rendered more intense by the addition of chloroform. 
 
 Klunge's aloin test may be used in place of the guaiac reaction. Mix the 
 acetic acid and ether extract of feces, obtained as above, with 1 or 2 c.c. of tur- 
 pentine, and add immediately about 1 c.c. of a 2 per cent, solution of aloin in 
 70 per cent, alcohol. In the presence of blood the fluid rapidly becomes bright 
 red in color. 
 
 h. Bile-pigments. Shake the feces with a saturated solution of mercuric 
 chloride, filter, and add chloroform. A rose color develops at the junction of 
 the fluids in the presence of urobilin, which is the normal bile-pigment of 
 feces. (The absence of bile-pigment in the feces indicates disease of the liver 
 or obstruction to the flow of bile.) 
 
 Extract feces with chloroform, and to the chloroform solution apply Gmelin's 
 test for bile-pigments. (The presence of bilirubin or biliverdin in the stools 
 of adults indicates catarrh of the intestine.) 
 
 i. Bile acids. Extract feces with alcohol and evaporate the filtrate to dryness. 
 Dissolve the residue in water containing a little sodium hydroxide, and to the 
 solution apply Pettenkofer's test. (Normally, bile acids are completely absorbed, 
 therefore their presence in feces is pathological.) 
 
 j. Ferments. Extract the feces with glycerin, precipitate the solution with 
 alcohol, and dissolve the precipitate in water. To part of the solution add a 
 little starch paste, keep the mixture at 40 C. (104 F.) for several hours, and 
 test for glucose. A positive test indicates the presence of diastatic enzyme. 
 Digest another portion of the solution at the stated temperature with coagu- 
 lated protein and a little sodium carbonate. Filter and apply the biuret 
 reaction, which, if positive, indicates the presence of proteolytic ferment. 
 (The various digestive enzymes are found in the feces when there is diarrhoea 
 resulting from inflammation of the upper intestine.) 
 
 Jc. Inorganic constituents are determined in the usual manner after drying and 
 incinerating the feces. Present are chiefly earthy phosphates, silica, sodium 
 chloride and sulphate, iron compounds, etc. 
 
692 PHYSIOLOGICAL CHEMISTRY. 
 
 Fecal calculi. Feces sometimes contain hard masses, known as 
 coproliths and enteroliths. Coproliths are inspissated feces. Entero- 
 liths usually consist of concentric layers of earthy phosphates and 
 insoluble soaps around a nucleus of a piece of bone, a fruit-stone, 
 etc. Pancreatic stones consist of calcium phosphate and carbonate 
 without cholesterin or bile-pigment. Intestinal sand is the name 
 given to certain small calculi occurring in the feces. They are com- 
 posed of magnesium and calcium soaps, cholesterin, bile-pigment, 
 salts of magnesium, and some of the hydroxy acids, such as succinic 
 acid. The clinical significance of these concretions is not definitely 
 known. 
 
 The liver. The anatomical relations of the liver indicate the im- 
 portance of this organ in assimilation, digestion, and excretion. The 
 digestive function of the liver, which is comparatively slight, and the 
 excretory function are carried out largely by means of the bile. The 
 digestive properties of bile have been considered. 
 
 While it is probable that the liver has some action on the protein 
 material brought to it by the portal system directly after its digestion 
 and absorption in the intestine, this has not been proved. It is, how- 
 ever, known that the main nitrogenous excretion of the body, the 
 urea of the urine, is formed here, and is merely excreted by the 
 kidneys. The mechanism of this urea production is not clear. It is 
 likely that the waste nitrogen is brought to the liver in the form of 
 ammonium salts (carbonate or carbamate), and by it is transformed 
 into urea. Liver tissue has the power of producing such a change 
 under experimental conditions, but it has not been proved that the 
 process occurs normally in this manner. In birds the main nitrog- 
 enous excretion, uric acid, has also been shown to be formed in the 
 liver. 
 
 Glycogen is one of the most important constituents of the liver, and 
 undoubtedly represents a storage supply of carbohydrate material. It 
 is derived for the most part directly from the carbohydrates of the 
 food which have been split in the intestine, absorbed as dextrose and 
 laevulose, and carried directly to the liver by the portal vein. Here 
 these simple sugars are converted into the more complex glycogen by 
 a process of dehydration. It is probable that some of the simple as 
 well as the conjugate proteins can also form sugar and, hence, gly- 
 cogen. Some of the sugar excreted in diabetes is certainly derived 
 from the proteins. It is not clear, however, that such a change takes 
 place under normal conditions. The question with regard to the fats 
 is in somewhat the same condition. It has been shown that glycogen 
 
DIGESTION. 693 
 
 can be derived from glycerin ; hence it can be derived from the fats 
 which contain glycerin, but whether it is normally derived from the 
 fats is not known. When the tissues are in need of sugar to supply 
 them with a source of energy, the glycogen of the liver is split and 
 is distributed by the blood-stream in the form of dextrose. This is 
 seen especially clearly in the case of the muscles, which require a 
 large amount of sugar, and have also the power of storing up a local 
 supply very much as the liver stores up a general supply for he 
 whole body. It is found that in starvation, and particularly in 
 starvation with extensive muscular work, that the store of glycogen 
 in both the liver and the muscles is rapidly exhausted. 
 
 Indole and skatole, formed by putrefaction in the intestine, are 
 
 brought to the liver by the portal vein. Indole, C 6 H / NH ">CH, 
 
 is oxidized, forming indoxyl, C 8 H 7 NO, which combines with potas- 
 sium acid sulphate, with elimination of water, forming indoxyl 
 potassium sulphate, C 8 H 6 NKSO 4 , which is excreted in the urine. 
 Skatole, methyl-indole, C 6 H 4 (CCH 3 CH)NH, is similarly converted 
 into the oxidation product skatoxyl, C 9 H 9 NO, and skatoxyl potassium 
 sulphate, C 9 H 8 NKSO 4 . These substances appear in the urine as the 
 conjugate or ethereal sulphates. 
 
 The formation of glycogen from sugar has been mentioned, and its physical 
 properties were considered in Chapter 48. 
 
 Experiment 87. (Preparation of glycogen.} Digest 50 grammes of fresh liver 
 with 500 c.c. of boiling water containing about 5 c.c. of acetic acid. Strain 
 the liquid through muslin. The solution contains besides glycogen some pro- 
 tein, which remove by concentrating the liquid to a small volume and adding 
 alternately a few drops of hydrochloric acid and of potassium mercuric iodide 
 as long as a precipitate is formed. Filter and mix filtrate with 2 volumes of 
 alcohol, when glycogen is precipitated ; purify it by pouring off the super- 
 natant liquid and washing it with 65 per cent, alcohol by decantation. Then 
 cover with absolute alcohol, let stand for an hour, collect the glycogen on a 
 filter, and dry between filter-paper. 
 
 Tests for glycogen. 
 
 1. Dissolve some glycogen in warm water : an opalescent solution 
 resembling soluble starch solution is formed. 
 
 2. To a portion of solution add iodine solution : a reddish-brown 
 color resembling the one produced by erythrodextrin is produced. 
 
 3. Heat some of the solution with Fehling's solution : no change 
 occurs. 
 
 4. Acidify solution with hydrochloric acid, boil a few minutes, 
 
694 PHYSIOLOGICAL CHEMISTRY. 
 
 cool, and neutralize. Divide solution, and heat one portion with 
 Fehling's solution, when the formation of a red precipitate indicates 
 the conversion of glycogen into dextrose. To the second portion add 
 iodine : no change. 
 
 5. To some glycogen solution add about half its volume of saliva, 
 keep the mixture at 40 C. (104 F.) for about ten minutes, and test 
 part of solution with iodine, the other portion with Fehling's solu- 
 tion. The results show that glycogen has been changed as in 
 previous test. 
 
 The liver has also a neutralizing function, by virtue of which it 
 retains and renders innocuous various toxins and putrefactive pro- 
 ducts which are absorbed by the intestine. 
 
 57. MILK. 
 
 General properties. Milk is the secretion of the mammary 
 glands, the presence of which is characteristic of mammalia. The 
 milk of different animals differs somewhat in composition, but it 
 always contains all the constituents necessary for a normal develop- 
 ment of the various tissues, liquids, organs, etc., of the young 
 mammal, which generally feeds exclusively upon milk for a shorter 
 or longer period of its early life. 
 
 Milk is an opaque, aqueous solution of casein, albumin, lactose, and 
 inorganic salts, holding in suspension small globules of fat, invested, 
 most likely, with coatings of casein or with some other albuminous 
 envelope. The reaction of woman's milk and that of the herbivora 
 is normally alkaline, but that of carnivora is acid. Its specific 
 gravity ranges from 1.029 to 1.033, but may in extreme cases vary 
 between 1.018 and 1.045. 
 
 Experiment 88. a. Examine milk microscopically ; notice the variously sized 
 globules of fat, and compare the appearance of milk, cream, and skimmed milk. 
 
 b. Test with sensitive litmus-paper the reaction of fresh cows' milk and of 
 milk that has been exposed to the air for a day or two. The former will be 
 alkaline or amphoteric, due to the presence of mono- and di-calcium phos- 
 
 QUESTIONS. What is the active principle of saliva, and how does it act on 
 starch? Explain the process of the absorption of protein. State the compo- 
 sition of gastric juice, explain its physiological action, and describe methods 
 for determining its chief constituents. What substances are formed during the 
 conversion of a simple protein into peptone? What are the functions of ^pan- 
 creatic juice? State the composition of the different kinds of calculi found in 
 feces. How are fats digested and absorbed ? State the general properties of 
 bile and mention its chief constituents ; describe Gmelin's and Pettenkofer's 
 tests. What are the principal constituents of feces ? State properties and re- 
 actions of glycogen. 
 
MILK. 
 
 695 
 
 phate ; the latter will be acid, because lactic acid has been formed by the 
 fermentation of milk-sugar. 
 
 c. Boil some fresh milk; no coagulum, but a scum is formed. After re-, 
 moval of the scum it is reformed on boiling. Repeat the experiment with 
 milk that has stood some time ; a coagulum is formed. 
 
 Composition. The average composition of various kinds of milk 
 is given below, but it must be remembered that milk not only differs 
 in certain species, but also in the same animal at different times ; 
 for instance, the quality and quantity of food taken, as also various 
 physiological changes, have decided influence upon the milk secreted. 
 
 Human milk. 
 
 Cows' milk. 
 
 Variations. Average. 
 
 Variations. Average. 
 
 Water . 
 
 90.8 to 
 
 85.3 
 
 88.30 
 
 90.2 to 83.7 
 
 86.70 
 
 Casein and albumin 
 
 1.4 to 
 
 2.5 
 
 2.00 
 
 3.3 to 
 
 5.5 
 
 4.40 
 
 Fat (butter) . 
 
 3.0 to 
 
 3.8 
 
 3.40 
 
 2.8 to 
 
 4.5 
 
 3.65 
 
 Lactose 
 
 4.0 to 
 
 8.0 
 
 6.00 
 
 3.0 to 
 
 6.0 
 
 4.50 
 
 Inorganic salts 
 
 0.2 to 
 
 0.4 
 
 0.30 
 
 0.7 to 
 
 0.8 
 
 0.75 
 
 Goat. 
 
 Sheep. 
 
 Ass. 
 
 Mare. 
 
 Cream. 
 
 Water . 
 
 86.0 
 
 83.3 
 
 90.6 
 
 90.6 
 
 56 
 
 to 71 
 
 Casein and albumin 
 
 3.8 
 
 5.4 
 
 2.7 
 
 2.2 
 
 4 
 
 to 3 
 
 Fat (butter) . 
 
 5.2 
 
 5.3 
 
 1.0 
 
 1.1 
 
 35 
 
 to 22 
 
 Lactose 
 
 4.3 
 
 5.2 
 
 5.3 
 
 5.8 
 
 4 
 
 to 3 
 
 Inorganic salts 
 
 0.7 
 
 0.8 
 
 0.4 
 
 0.3 
 
 0.7 
 
 to 0.7 
 
 Skimmed 
 milk. 
 
 Condensed . 
 milk. 
 
 Buttermilk. Curd. 
 
 Whey. 
 
 Water . 
 
 90.6 
 
 25 
 
 15.0 
 
 90.2 
 
 59.4 
 
 93.5 
 
 Casein and albumin 
 
 3.1 
 
 14 
 
 2.2 
 
 4.1 
 
 27.7 
 
 0.8 
 
 Fat (butter) . 
 
 0.8 
 
 10 
 
 82.0 
 
 1.0 
 
 6.4 
 
 0.3 
 
 Lactose 
 
 4.8 
 
 49 1 
 
 0.3 
 
 3.7 
 
 5.0 
 
 4.5 
 
 Inorganic salts . . 
 
 0.7 
 
 2 
 
 0.5 
 
 0.7 
 
 1.5 
 
 0.6 
 
 Lactic acid . 
 
 
 . . 
 
 . . 
 
 0.3 
 
 . . 
 
 0.3 
 
 The inorganic salts consist chiefly of calcium or sodium phosphate 
 and sodium and potassium chloride, but contain also some magnesium 
 and iron. The proteins consist mainly of casein with some albumin, 
 the proportion being in cows' milk about as 6 to 1, in woman's milk 
 as 3 tc 4. 
 
 Besides the constituents mentioned in the above analyses, milk also 
 contains a very small quantity of extractives, among which are found 
 urea, creatine, lecithin, citric acid, phospho-carnic acid, etc. The 
 principles which give to milk its peculiar odor have not yet been 
 conclusively pointed out. The gaseous constituents of milk are 
 mainly carbon dioxide, oxygen, and nitrogen : 100 volumes of milk 
 
 i Including cane-sugar added by the manufacturer. 
 
696 PHYSIOLOGICAL CHEMISTRY. 
 
 contain of carbon dioxide 7.06, of oxygen 0.1, of nitrogen 0.7 
 volumes. 
 
 Milk contains several enzymes, whose natures vary with their 
 sources. One of these, an oxidizing ferment (oxidase, catalase), is a 
 constant constituent, and is of importance because its absence shows 
 that the milk has been heated for preservation. 
 
 The presence of an oxidizing ferment in milk can thus be shown : Shake 10 
 c.c. of milk with 1 c.c. of tincture of guaiac, 5 c.c. oil of turpentine, and 5 c.c. 
 of solution of hydrogen dioxide. A blue color is developed when the ferment 
 is present. 
 
 Milk-proteins. The proteins of milk are caseinogen, lactoglobulin ^ 
 and ladalbumin. Lactoglobulin and lactalbumin closely resemble the 
 globulin and albumin of the blood-serum, and are believed to be de- 
 rived from them with little constitutional change. Caseinogen is, on 
 the other hand, a specialized protein containing phosphorus and be- 
 longing to the group of phospho-proteins. It is present in milk 
 either in solution or perhaps in combination with phosphates in a 
 partially insoluble form, and this combination may be responsible for 
 some of the opacity of the milk. When milk is acted upon by rennin 
 there is a coagulation of the caseinogen and the formation of a clot. 
 It may readily be shown that this process takes place in two steps. 
 First, the caseinogen is changed by the rennin to a form called para- 
 casein. This substance remains in solution, and the nature of the 
 change is not understood. In the second stage the paracasein forms 
 a combination with the calcium salts of the milk and is precipitated 
 as casein (calcium-casein). The calcium enters only in the second 
 step and has no part in the formation of paracasein. The significance 
 of this coagulation of milk in the stomach is not known. It is fre- 
 quently stated that a peptone is split off from the caseinogen in the 
 production of paracasein. The process may be hydrolytic in nature, 
 and a preliminary step in the digestion of caseinogen. As implied 
 above, no coagulation will take place if the calcium salts be removed 
 from the milk. 
 
 Caseinogen occurs only in milk ; it is a phospho-protein, yielding 
 on hydrolysis a pseudonuclein. When dry it is a fine, white powder, 
 insoluble in water, but soluble in dilute salt solution and in water 
 containing a little alkali. 
 
 Caseinogen resembles the alkali albuminates in dissolving in water in the 
 presence of calcium carbonate with evolution of carbon dioxide. The solution 
 is precipitated by hydrochloric and acetic acids, the precipitate being soluble 
 in slight excess, and reprecipitated by a large excess of the acid. The solution 
 
MILK. 697 
 
 in lime-water is not precipitated by phosphoric acid, but an opaque fluid is 
 obtained containing casein and calcium phosphate in suspension. The solu- 
 tion is precipitated by alum, zinc sulphate, cupric sulphate, etc. Caseinogen 
 solutions are not coagulated by heat, but, like milk, are covered with a scum. 
 
 Experiment 89. (Preparation of casein.} To a mixture of 400 c.c. of milk 
 and 1 liter of water add gradually enough (but not more) of acetic acid to pre- 
 cipitate the casein, which also carries down the fat. Decant the liquid, then 
 filter, first through muslin, then through paper, reserving liquid for Experi- 
 ment 93. Wash the coagulum well with water, press it as dry as possible, 
 then grind it with 100 c.c. of alcohol, and allow to stand for an hour. Filter, 
 dry the coagulum between filter-paper, place it with 200 c.c. of ether into a 
 stoppered bottle and let stand for a day. Collect the precipitate on a filter and 
 add filtrate to the alcoholic filtrate from above; the mixture will be used for 
 Experiment 92. Rub the casein in a mortar until the ether is evaporated. 
 To purify it from fat, mix with water and add drop by drop a 1 per cent, 
 solution of sodium hydroxide until the greater part of the casein is dis- 
 solved. The mixture, which should not be alkaline after thoroughly stirring 
 it, is then filtered, when some fat and suspended matter is left behind, while a 
 fairly clear filtrate is obtained. Acidify faintly with acetic acid, wash the 
 precipitated casein with water, alcohol, and ether, and dry between paper. 
 
 Tests for casein. 
 
 1. Apply the xanthoproteic, Millon's, and biuret reactions. 
 
 2. Dissolve casein in a 1 per cent, solution of sodium carbonate; 
 neutralize with acetic acid, when casein is precipitated. 
 
 3. Mix some casein in a mortar with freshly precipitated cal- 
 cium carbonate and water. Casein dissolves, while carbon dioxide 
 is liberated. 
 
 4. Dissolve casein in lime-water and add dilute phosphoric acid 
 until the solution is neutral. No precipitate is formed, but the 
 liquid becomes turbid. 
 
 5. Heat a mixture of casein with sodium carbonate and potassium 
 nitrate in a crucible (or dry test-tube) until all organic matter has 
 been destroyed. Dissolve mass in water, acidify with nitric acid, 
 filter, and add ammonium molybdate. A yellow precipitate is formed, 
 showing the presence of phosphorus in the casein. 
 
 Experiment 90. (Separation of the proteins.} Saturate 20 c.c. of fresh milk with 
 powdered sodium chloride: a precipitate consisting of caseinogen and fat is 
 formed. Filter, wash the precipitate with saturated solution of sodium 
 chloride, rub the moist precipitate with 20 c.c. of water, allow to stand for 
 twenty-four hours, and filter. The solution contains caseinogen in the 
 same condition in which it is found in milk. To a portion of the solution 
 add acetic acid : casein is precipitated. To another portion add a solution of 
 rennin and some calcium chloride, heat to 40 C. (104 F.) for a short time, 
 when a precipitate of paracasein is formed. 
 
 Saturate the filtrate from caseinogen and fat with magnesium sulphate : 
 
698 PHYSIOLOGICAL CHEMISTRY. 
 
 lactoglobulin is precipitated. The filtrate contains lactalbumin, which can be 
 precipitated by saturating the solution with ammonium sulphate. 
 
 Experiment 91. (Action of rennin on milk.} To 20 c.c. of milk add 4 c.c. of 
 a 0.1 per cent, solution of rennin, mix well, and digest at 40 C. (104 F.). 
 A coagulum consisting of casein and fat soon forms, while an aqueous fluid 
 (whey), containing proteins, milk-sugar, salts, and extractives, is pressed out. 
 After adding a drop or two of acetic acid heat a portion of the whey to boiling : 
 a voluminous coagulum of simple proteins is formed. 
 
 Eepeat the above experiment with milk from which, by the addition of 2 
 c.c. of a 1 per cent, solution of ammonium oxalate, the calcium salts have 
 been removed. No coagulum occurs until calcium chloride is added in a 
 quantity sufficient to precipitate any ammonium oxalate left in solution, and 
 to furnish the calcium salt required for precipitation. 
 
 Kepeat again, boiling the mixture in order to destroy the rennin before the 
 addition of the calcium solution ; clotting will occur, showing that calcium is 
 necessary only for the precipitation, not for the interaction between the casein- 
 ogen and the rennin. 
 
 Milk-fat. It has been mentioned above that the fat of milk is 
 held in suspension as small globules, which are surrounded by a 
 protein envelope. The latter prevents the solution of fat when 
 ether is added directly to milk. If, however, a few drops of caustic 
 alkali be added with the ether, then the envelope will be destroyed 
 and the fat dissolves. Whenever a precipitate occurs in milk the fat 
 is carried down with the insoluble substance and the envelope is 
 generally destroyed. The fat of milk is a mixture of the glycerides 
 of several fatty acids, chiefly of palmitic and oleic, with small quan- 
 tities of butyric, caproic, caprylic, and stearic acids. Butter fat may 
 be recognized by liberating the butyric acid, which has a character- 
 istic odor. 
 
 Experiment 92. (Liberation of butyric acid.) Use the mixed ethereal and 
 alcoholic filtrate from Experiment 89. Allow the ether to evaporate spon- 
 taneously, and add to the alcoholic solution of butter fat about 5 grammes 
 of potassium hydroxide. Heat the mixture on a water-bath until a drop of 
 it is found to be completely soluble in water, indicating complete saponifica- 
 tion. Evaporate until odor of alcohol has disappeared; add 30 c.c. of dilute 
 sulphuric acid, when the fatty acids are set free and butyric acid can be recog- 
 nized by its odor. 
 
 Butter. Even in the thickest varieties of cream there is no cohe- 
 sion between the fat globules, while in butter the fat has actually 
 cohered. This change is accomplished by violently agitating (churn- 
 ing) the cream, when the fat particles gradually combine with each 
 other, while the liquid (buttermilk) separates. 
 
 Chemically, butter is a milk-fat, containing a certain proportion^ 
 
MILK. 699 
 
 15 or 16 per cent., of water, besides traces of casein, salts, coloring- 
 matter, etc. For curing butter, common salt is often used ; the 
 quantity added should not exceed 5 per cent. 
 
 The composition of buttermilk has been given above ; when 
 freshly obtained from sweet cream it is a pleasant drink and a whole- 
 some food. 
 
 Milk-sugar. Lactose. The general properties of milk-sugar 
 have been mentioned on page 534. By hydrolysis it yields two 
 simple sugars, dextrose and galactose ; when boiled with nitric acid, 
 saccharic and mucic acids are formed, the latter being a characteristic 
 product of the oxidation of galactose. Solutions of milk-sugar are 
 dextrorotatory. Lactose occurs occasionally in the urine of preg- 
 nant women, and also in the urine after ingestion of large quantities 
 of milk-sugar. 
 
 Experiment 93. (Preparation of milk-sugar.) Use the aqueous filtrate obtained 
 in Experiment 89. Free the solution from the remaining proteins by boiling 
 and filtering; evaporate to about 75 c.c., when calcium phosphate will be 
 deposited. Filter, evaporate to a syrup, and set aside, when crystals of lactose 
 will be formed. The crystals may be purified by treating their solution with 
 bone-black aud recrystallizing. 
 
 Tests for milk-sugar. 
 
 1. To solution of milk-sugar apply Fehling's, Trornmer's, Moore's, 
 Boetger's, and Nylander's tests, for which see Index. 
 
 2. Add ammonio-silver nitrate and a drop of sodium hydroxide. 
 A mirror of metallic silver forms on heating the mixture. 
 
 3. Indigo-test. To a dilute solution add enough indigo-carmine to 
 produce a blue color, and render alkaline with sodium carbonate. 
 On heating, the blue solution becomes successively red, yellow, and 
 colorless, or nearly so, in consequence of the deoxidizing power of 
 the lactose. Pour the cooled solution repeatedly from one test-tube 
 into another; the colors are reproduced in reverse order in con- 
 sequence of the absorption of oxygen. 
 
 4. As grape-sugar responds to the above tests, the fermentation- 
 test may be used for distinguishing between the two sugars. Fill 
 two fermentation tubes with glucose and lactose solution, respectively ; 
 add yeast, let stand in a warm place, and notice that a gas rises from 
 the glucose, but not from the lactose solution. 
 
700 PHYSIOLOGICAL CHEMISTRY. 
 
 Physical and chemical changes in milk on standing. 
 
 After leaving the body milk undergoes physical and chemical 
 changes. The principal physical change is the separation of milk 
 into two layers : the upper, cream, contains practically all the fat, 
 and its proportionate quantity of other constituents; the lower, 
 skimmed milk, is almost fat-free. By removing varying quantities 
 of skimmed milk by siphon or otherwise, the proportion of fat in the 
 remainder of the milk is increased. 
 
 Of chemical change, occurs, particularly on standing in a warm 
 place, conversion of lactose into lactic acid through lactic acid fer- 
 mentation. The reaction of milk then becomes acid, the casein coag- 
 ulates and separates as a solid white curd carrying with it fat. The 
 remaining thin, transparent liquid, whey, contains all the inorganic 
 salts, that portion of lactose which has not been decomposed, as also 
 the lactic acid formed. 
 
 There has recently been an extensive use of milk which has been 
 fermented by the Bacillus Bulgaricus, a powerful lactic acid pro- 
 ducer. This use has been based upon the belief of Metchnikoff that 
 acid-producing bacteria are antagonistic to the putrefactive bacteria 
 which are normally present in the intestine, hence the milk is advised 
 in cases of intestinal disorder. 
 
 Milk also undergoes another peculiar fermentation, by which it is 
 converted into a thick, ropy, gelatinous mixture. 
 
 The decomposition of the milk-sugar and with it the "curdling" 
 may be prevented 1, by chemical treatment with alkaline salts or 
 antiseptics ; 2, by physical treatment, such as cooling or icing, boil- 
 ing and aeration ; 3, by condensation or evaporation, with or without 
 the addition of a preservative agent. All these systems of preserva- 
 tion, however, are subject to serious disadvantages because they either 
 interfere with the natural constitution and properties of the milk, or 
 because they serve their purpose for too limited a time. 
 
 The addition of alkalies such as lime-water, sodium carbonate or 
 bicarbonate, does not prevent the lactic fermentation, but prevents 
 the action of the liberated acid on the casein by forming a lactate of 
 calcium or sodium. 
 
 Milk preservatives. The chemical changes in milk are best pre- 
 vented by cleanliness and preservation at a low temperature. Various 
 antiseptics, such as salicylic acid, boric acid, formaldehyde, benzoic 
 acid, etc., are added to milk with the view of preventing decomposi- 
 tion. While the small quantities used appear to be harmless, yet 
 
MILK. 701 
 
 there can be no doubt that the continued use of milk containing these 
 preservatives is detrimental to health, especially in the case of human 
 nurslings. For this reason many countries, States, and cities prohibit 
 legally the use of preservatives. 
 
 Tests for preservatives in milk. 
 
 Formaldehyde. Float a mixture of 10 c.c. of milk and 10 c.c. of water in a 
 test-tube, on concentrated sulphuric acid made pale yellow by addition of 
 ferric sulphate. A blue to violet color at the line of junction shows the pres- 
 ence of formaldehyde. Pure milk gives a greenish color. 
 
 Salicylic acid. Acidify 25 c.c. of milk with acetic acid, boil, and filter. Ex- 
 tract the nitrate with an equal volume of ether. Shake the ether extract with 
 a dilute (straw-colored) solution of ferric chloride, On separating, the aqueous 
 solution shows a reddish-violet color when salicylic acid is present. 
 
 Benzole acid. Proceed as in the foregoing test, but shake the filtrate with 
 an equal volume of solution of hydrogen dioxide before extracting with ether. 
 By this treatment benzoic acid is converted into salicylic acid, which is then 
 tested for by ferric chloride. 
 
 Boric acid and borax. A few drops of the filtrate obtained as in the prece- 
 ding test are mixed with a drop of strong hydrochloric acid and a drop of satu- 
 rated alcoholic solution of turmeric. The mixture is evaporated to dryness on 
 a water-bath, and a drop of ammonia added to the residue when cold. A dull- 
 green stain shows the presence of boric acid or borax. 
 
 In addition to the test for chemical preservatives, commercial milk 
 is now examined by bacteriological methods, the number and, if pos^ 
 sible, the character of the organisms being determined. By extreme 
 care in the production of milk it is possible to keep the count lower 
 than 30,000 per cubic centimeter ("certified milk"). A cheaper 
 method of producing good milk is by heating the milk for a certain 
 time to a temperature below the boiling-point, which will kill all the 
 pathogenic and many of the non-pathogenic bacteria. This method 
 is commonly called " pasteurization." It has the disadvantage that 
 the digestibility of the milk is lessened, an important point in infant 
 feeding. 
 
 Experiment 94. (Analysis of milk?) As the proportion of fat varies at dif- 
 ferent periods of the milking, it is necessary to secure a sample from the well- 
 mixed yield of milk. a. Determine the specific gravity of milk, cream, and 
 skimmed milk by means of the lactometer (a urinometer answers the purpose). 
 
 b. Fat. Determine the total butter fat by using Babcock's method, which is as 
 follows : Place 10 c.c. of milk into a small, specially constructed bottle provided 
 with a long, slender, graduated neck ; add 2 c.c. of a mixture of ainyl alcohol 
 37, methyl alcohol 13, and hydrochloric acid 50 parts; then fill the bottle grad- 
 ually with sulphuric acid. Place the bottle in a centrifugal machine and 
 rapidly revolve for three minutes, when the fat is forced to the top of the 
 mixture. Add enough warm water to float the separated fat into the neck, 
 when the exact percentage can be read on the scale. A special form of bottle, 
 
702 PHYSIOLOGICAL CHEMISTRY. 
 
 arranged for small quantities, is manufactured for the examination of human 
 milk. 
 
 c. Total protein. Separate the skimmed milk from the cream of the sample 
 under observation. Dilute the skimmed milk with 4 parts of water and with 
 this solution fill Esbach's albuminometer (see Index) to the mark U, add 
 Esbach's reagent to R, and allow to stand 24 hours. Multiply the reading by 
 5; the result gives the number of grammes per liter. Skimmed milk is used 
 in order to avoid the fat which would be carried down with the protein if 
 whole milk were used. 
 
 d. Albumin and globulin. Dilute 25 c.c. of milk with 15 c.c. of water in a 50 
 c.c. flask, heat on a water-bath to 38 to 40 C. (100 to 104 F.), and add very 
 gradually a saturated solution of potassium alum until a rapidly subsiding 
 coagulum of casein forms. Add water to make 50 c.c., filter, and estimate the 
 simple proteins (albumin and globulin) in the filtrate by means of the albu- 
 minometer, as above, multiplying the reading on the instrument by 2. Another 
 method for the estimation of total protein or of the simple protein depends on 
 the accurate determination of nitrogen in milk or in milk after the removal of 
 casein. The percentage of nitrogen multiplied by 6.25 gives the percentage of 
 protein.) 
 
 e. Determination of milk-sugar. Lactose can be estimated by titration with 
 Fehling's solution ; for details of the operation see chapter on Urine-analysis. 
 A second method depends on the rotatory power of lactose : milk is freed from 
 protein and then examined by the polarimeter. 
 
 /. Determine total solids, as well as all other constituents, by following the 
 directions given above. 
 
 Human milk. The quantitative differences between human milk 
 and cows' milk have been shown in the table on page 695 ; they con- 
 sist chiefly in this, that human milk contains only about one-half the 
 quantity of protein and of inorganic salts, but one-third more of 
 lactose, as compared with cows' milk. In addition, it may be said 
 that human milk is richer in lecithin ; moreover, the proteins of 
 human milk differ from those of cows' milk. When human milk 
 is treated with acids or rennin, casein or paracasein is formed less 
 readily than by treating cows' milk in the same way. The precipi- 
 tates show marked physical differences from one another. Casein 
 from human milk is easily and completely soluble in gastric juice, 
 and human paracasein is precipitated in a loose and flocculent form, 
 which is much more readily digested than the tough and more 
 compact masses from cows' milk. The casein of human milk shows 
 a lower percentage of carbon, nitrogen, and phosphorus, but a higher 
 percentage of hydrogen, sulphur, and oxygen, than casein of cows' 
 milk. Finally, opalisin, a protein rich in sulphur, is found in human 
 milk exclusively. 
 
 Modified milk, used for infant feeding, is cows' milk, the composition of 
 which has been changed so as to resemble that of human milk. The quantity 
 
URINE AND ITS CONSTITUENTS. 703 
 
 of fat is increased by adding cream, or by removing part of the lower layer 
 from milk which has separated into two layers (top milk). This mixture is 
 diluted with water to lower the percentage of protein ; milk-sugar and lime- 
 water are then added in different proportions, according to the quantity desired. 
 Although the difference in the composition of human and cows' milk is con- 
 siderable, the fuel value of both is nearly the same, about 315 calories to the 
 pound of milk. 
 
 58. URINE AND ITS CONSTITUENTS. 
 
 Excretion of urine. It has been explained in a former chapter 
 how blood absorbs the digested food as chyle, how this is acted upon 
 by the atmospheric oxygen in the lungs, and how this arterial blood, 
 while passing through the system, deposits proteins and other sub- 
 stances, receiving in exchange the products formed by the oxidation 
 of the various tissues. These products are either gases (chiefly car- 
 bon dioxide), liquids (chiefly water), or solids held in solution by the 
 water. These waste materials must necessarily be eliminated from 
 the system, and this result is accomplished principally by the kidneys. 
 
 The urine is the most important animal excretion ; in it are elimi- 
 nated the nitrogenous waste materials as well as most of the water 
 and soluble mineral substances. A study of the composition of the 
 urine will give important information regarding metabolism, the 
 nature of the chemical processes taking place within the body, as 
 also of the condition of the urinary organs. 
 
 General properties. Normal human urine, when in a fresh state, 
 is a clear, transparent aqueous liquid, of a lighter or deeper amber 
 color, having a peculiar, faintly aromatic odor, a bitter, saline taste, 
 a distinct acid reaction on blue litmus-paper, and a specific gravity 
 heavier than water (averaging about 1.020). 
 
 In urine, shortly after cooling, especially if it be concentrated, a 
 light, cloudy film of mucus is formed, which slowly sinks to the 
 bottom ; the acid reaction gradually increases, small yellowish-red 
 
 QUESTIONS. Mention the five principal constituents of milk. To what 
 group of compounds does casein belong, how is it obtained, and what are its 
 reactions? Give tests for milk-sugar, and state how it may be distinguished 
 from grape-sugar. What physical and chemical changes does milk suffer on 
 standing? Describe the processes used for preserving milk; what are their 
 advantages and disadvantages? Give approximately the quantities of the 
 chief components of cream, skimmed milk, butter, buttermilk, curd, whey, and 
 cheese ; also state how the materials are obtained from milk. Describe the 
 advantages of the combined use of the lactometer and creamometer in testing 
 milk. What are the differences between human and cows' milk ? What is 
 paracasein? Give a process for the complete quantitative analysis of milk. 
 
704 PHYSIOLOGICAL CHEMISTRY. 
 
 crystals of acid urates, or uric acid, are deposited. In this condition 
 the urine may often continue unchanged for several weeks, provided 
 the temperature be low. If, however, the temperature be above the 
 mean, decomposition speedily takes place. The urine is then found 
 to be covered with a thin, shining, and frequently iridescent mem- 
 brane, fragments of which sink gradually to the bottom. The urine 
 then becomes turbid, acquires a pale color, its reaction becomes alka- 
 line, and it begins to develop a nauseous ammoniacal odor, due to the 
 products formed by the decomposing action of certain microorganisms 
 (chiefly bacterium ureaB and micrococcus urea?) upon urea, which is 
 converted into ammonium carbonate and ammonium carbamate. The 
 change from an acid to an alkaline urine causes the precipitation of 
 earthy phosphates, ammonium-magnesium phosphate, ammonium 
 urate, etc. 
 
 Points to be considered in the analysis of urine. They are : 
 
 1. Color, odor, general appearance whether clear, smoky, cloudy, 
 turbid, etc. 
 
 2. Reaction whether acid, neutral, or alkaline to test-paper. 
 
 3. Specific gravity, and amount for twenty-four hours. 
 
 4. Examination of sediments, microscopically and chemically. 
 
 5. Chemical examination for the various normal and abnormal 
 constituents. 
 
 Samples of urine should always be drawn from the well-mixed and 
 exactly measured quantity of the total urine discharged in twenty- 
 four hours. 
 
 If the specimen cannot be examined promptly it should be pre- 
 served in a stoppered bottle by the addition of a very small amount 
 of chloroform (3 to 5 c.c. to one liter of urine). 
 
 Color. Normal urine is generally pale yellow or reddish yellow, 
 but it may be as colorless as water, or as dark brownish-black as 
 porter ; a reddish and smoky tint generally indicates the presence of 
 blood, and a brownish-green suggests the presence of the coloring- 
 matter of bile. 
 
 The nature of the normal coloring-matters of urine is as yet 
 doubtful ; the existence of three separate pigments has been demon- 
 strated ; they have been named urobilin, urochrome, and uroerythrin, 
 and, most likely, are products of the decomposition of biliary mat- 
 ters. Numerous other substances, such as indican, occur occasionally 
 in the urine, and produce various colors, especially when the urine is 
 exposed to air and light, or when acted on by reagents. 
 
URINE AND ITS CONSTITUENTS. 705 
 
 Urochrome is the yellowish pigment of urine ; the quantity excreted, 
 as far as known, has no clinical significance. It is probably a deriva- 
 tive of bilirubin. 
 
 Uroerythrin is a red pigment, and causes the pink color often seen 
 in urinary sediments. It occurs in very minute quantity in normal 
 urine, and is increased by muscular activity, profuse sweating, ex- 
 cessive eating, alcohol excess, digestive disturbance, circulatory dis- 
 turbance of the liver, malaria, pneumonia, and many other patho- 
 logical conditions. Whenever present in sufficient quantity to give 
 a rose color to the sediment or to the precipitate produced by adding 
 barium chloride to the urine, uroerythrin is excreted in increased 
 quantity. 
 
 Urobilin y a reddish-brown pigment, occurs normally in very small 
 quantity, but it increases considerably whenever there is great de- 
 struction of haemoglobin in the body (internal hemorrhage, pernicious 
 anemia, poisoning by antipyrine), in cirrhosis of the liver, and dur- 
 ing high fever. When present in excessive quantity urobilin colors 
 the urine a dark brownish-red, and the foam shows a yellow or yel- 
 lowish-brown color. 
 
 It is thought to be usually present in the condition of a chromogen, 
 called urobilinogen, producing the pigment urobilin after being acted 
 upon by light or by an acid. 
 
 The presence of urobilin can be demonstrated by the spectroscopic exam- 
 ination of urine to which a small amount of hydrochloric acid has been added. 
 It may be necessary to let this mixture stand a short time, or to dilute it, or to 
 examine the amyl alcohol extract. The characteristic spectrum shows a 
 single band between B. and F. Urine containing urobilin will give a green 
 fluorescence on the addition of 1 per cent, zinc chloride, if it has been previ- 
 ously made alkaline with ammonia and filtered. 
 
 Abnormal coloring-matters are chiefly those of blood, bile, and of 
 certain vegetables and drugs. 
 
 Blood-pigment is usually present alone as methaemoglobin in hgemo- 
 globinuria, and associated with the red blood-corpuscles in haematuria. 
 Bile-pigment will be discussed later. 
 
 The ingestion of rhubarb, senna, or santonin produces a bright 
 yellow color in the urine which becomes red on the addition of an 
 alkali. Methylene-blue is excreted by the kidneys and colors the 
 urine blue. Urines which become very dark on standing occur after 
 the ingestion of phenol, in cases of melanotic sarcoma (melanogen), 
 and in alkaptonuria, an unexplained pathological condition in which 
 
 45 
 
706 PHYSIOLOGICAL CHEMISTRY. 
 
 homogentisic acid and uroleucic acid (alkapton) are excreted by the 
 kidneys. 
 
 Odor. The normal odor of fresh urine is characteristic, and is 
 sometimes spoken of as aromatic; it is not known by what substance 
 or substances this odor is caused. The arnmoniacal and putrescent 
 odor which urine acquires on standing is due to the products of de-' 
 composition formed, chiefly ammonia. 
 
 A number of substances taken internally and separated by the kidneys from 
 the blood, cause the urine to assume a characteristic odor ; aromatic substances 
 especially impart such odors; oil of turpentine gives an odor reminding of 
 violets, and the odor of cubebs, copaiba, asparagus, garlic, valerian, and other 
 substances is promptly transferred to the urine of persons using these drugs 
 internally. A sweetish smell sometimes attends the presence of large quantities 
 of sugar in urine. 
 
 Volume. The amount of urine in twenty-four hours varies greatly 
 under physiological conditions. It is usually between 900 and 1500 c.c. 
 It is influenced very largely by the amount of water ingested, by 
 sweating, by diarrhoea, etc. It is decreased in acute nephritis, in- 
 creased in chronic nephritis, diabetes mellitus, and diabetes insipidus. 
 
 Reaction. This is generally acid in healthy urine which has been 
 recently passed, but may become neutral or alkaline within a short 
 period, by decomposition of urea and formation of ammonium car- 
 bonate and carbamate. The acid reaction of urine is due to mono- 
 sodium ortho-phosphate, NaH 2 PO 4 , and to free organic acids. These 
 organic acids have not as yet been identified. 
 
 While urine shows an acid reaction generally, it may have a neutral 
 or even alkaline reaction. In many cases this alkaline reaction points 
 to decomposition of urea in the bladder, but it may be due also to the 
 elimination of alkali carbonates, derived from food taken or drugs 
 administered. 
 
 Thus, the alkali tartrates, citrates, acetates, etc., have (after diges- 
 tion) a tendency to neutralize the urine, and an excess of them is 
 eliminated as carbonate. 
 
 To distinguish between the harmless alkaline reaction caused by 
 fixed alkalies and the alkaline reaction produced by decomposition of 
 urea, a piece of red litmus-paper may be used. If this, after having 
 been moistened with the urine, remains blue on drying (by warming 
 gently) the reaction is due to the fixed alkalies ; if the red color 
 reappears, the alkaline is due to ammonia compounds. 
 
 This distinction possesses no importance in urine which has become 
 alkaline on standing. 
 
URINE AND ITS CONSTITUENTS. 
 
 707 
 
 FIG. 73. 
 
 Urine sometimes is amphoteric in its reaction, i. e., it colors red litmus-paper 
 faintly blue, and blue litmus-paper slightly red. This condition is caused most 
 likely by the simultaneous presence of monosodium orthophosphate, NaH 2 PO 4 , 
 which has an acid, and of disodium orthophosphate, NaH 2 PO 4 , which has an 
 alkaline, reaction. 
 
 The acidity of the urine is best determined in the following manner 
 (Folin) : 25 c.c. of urine are shaken in a flask with 15 to 20 grammes 
 of powdered potassium oxalate, 1 to 2 
 drops of phenolphthalein (J per cent, 
 solution in alcohol) are added, and the 
 mixture titrated at once with $ sodium 
 hydroxide. The end-reaction is the for- 
 mation of a distinct pink color. The 
 acidity of the urine is usually expressed 
 in terms of -^ acid or alkali for twenty- 
 four hours. 
 
 The oxalate is added to precipitate 
 calcium, and thus avoid the deposition 
 of calcium phosphate as the mixture 
 becomes alkaline. It also reduces the 
 error due to ammonium. 
 
 Specific gravity. The normal spe- 
 cific gravity of an average amount of 
 1500 c.c. of urine passed in twenty-four 
 hours is about 1.020, but it varies, even 
 in health, from 1.012 to 1.030 or more. 
 A specific gravity above 1.030 may 
 indicate the presence of sugar, larger 
 quantities of which may cause the spe- 
 cific gravity to rise to 1.050. Albumi- 
 nous urine is frequently of low specific 
 gravity, 1.010 to 1.012, especially in 
 chronic nephritis. 
 
 It should be remembered that the 
 specific gravity of urine considered 
 separately from the quantity of urine passed in twenty-four hours is 
 of no value, and that in some diseases (for instance in acute nephritis 
 with albuminuria) the specific gravity of albuminous urine may be as 
 high as 1.030, while a diabetic urine may have a specific gravity of 
 1.025, or less, in consequence of a large volume passed. 
 
 The determination of the specific gravity of urine is generally accom- 
 
 Urinometer. 
 
708 PHYSIOLOGICAL CHEMISTRY. 
 
 plished by the urinometer, which is a small hydrometer indicating spe- 
 cific gravity from zero (or 1000) to 60 (or 1060). (See Fig. 73.) As 
 the temperature influences the density of liquids, a urinometer can 
 only give correct results at a certain degree of temperature, which is 
 generally marked upon the instrument. 
 
 Composition. Urine is chiefly an aqueous solution of urea and 
 inorganic salts, containing, however, always some uric acid, coloring-, 
 and other organic matters. 
 
 Urine also contains gaseous constituents, amounting to about 16 
 per cent, by volume ; these gases are chiefly carbon dioxide (88 per 
 cent.) and nitrogen (11 per cent.), with very little oxygen (1 per cent.). 
 
 The quantity of urine passed in a day also varies widely, an adult 
 discharging from 500 to 2300 c.c. in twenty-four hours ; a normal 
 average quantity is about 1000 to 1500 c.c. (about 36 to 54 ounces). 
 The quantity of total solids contained in this urine varies from 55 to 60 
 grammes (840 to 920 grains), and about one-half of this quantity is urea. 
 
 As many of the .so-called pathological constituents of urine are 
 actually present in minute quantities in normal urine, it is difficult to 
 make an absolute distinction between physiological and pathological 
 constituents. Below is given a working classification of the more 
 important constituents, regarding as normal those whose presence may 
 readily be shown by clinical tests. Accordingly, indican, for ex- 
 ample, is placed with the normal bodies, while acetone is placed with 
 the pathological substances, though both are normally present in 
 small amounts. 
 
 Normal constituents. 
 Urea. 
 Ammonia. 
 
 Nitrogen as 
 
 Creatinine. 
 
 Uric acid. ( Xanthine bases. 
 Other bodies < Allantoin. 
 
 ( Hippuric acid. 
 Chlorine as chlorides. 
 
 Phosphorus as phosphoric acid. ( ( 1 ) Inorganic (K, Na, etc.). 
 
 Sulphur as { Neutral sul P lmr - (2) Organic (ethereal). 
 
 (Oxidized sulphur = sulphates: \ Indole (indican). 
 Sodium, } Skatole. 
 
 Potassium, I . . [ Phenol. 
 
 Calcium, Combined with acids. 
 
 Magnesium, I 
 Oxalic acid. 
 Pigments. 
 Enzvmes. 
 
URINE AND ITS CONSTITUENTS. 709 
 
 Pathological constituents. 
 
 f Serum albumin. 
 Serum globulin. 
 
 Albumose (proteose). 
 Proteins : 
 
 Peptone. 
 
 Bence-Jones albumin. 
 . Haemoglobin. 
 
 Carbohydrates : 
 
 Glycuronic acid. 
 
 Glucose (dextrose). 
 
 Levulose. 
 
 Maltose. 
 
 Lactose. 
 
 Pentose. 
 
 f /3-oxy-butyric acid. 
 Acetone bodies -j Diacetic acid. 
 I Acetone. 
 
 Biliary acids, biliary pigments. 
 
 Melanin. 
 
 Alkapton. 
 
 Unknown body or bodies giving the Ehrlich diazo-reaction. 
 
 Determination of total solids. An approximate determination 
 of total solids may be deduced from the specific gravity of the urine, 
 as it has been found that the last two figures of the specific gravity 
 of urine, multiplied by 2.2, correspond to the number of grammes in 
 1000 c.c. of urine. If, for instance, 1450 c.c. of urine, of a specific 
 gravity of 1 .018, have been discharged in twenty-four hours, then the 
 quantity of total solids in 1000 c.c. will be 18 X 2.2, or 39.6 grammes ; 
 and in 1450 c.c., 57.42 grammes. 
 
 A more exact method of determining the total solids in urine is the evapora- 
 tion of about 10 c.c. in a weighed platinum dish over a water-bath (or, better, 
 under the receiver of an air-pump over sulphuric acid), until it is found that no 
 more loss in weight ensues on continued exposure of the dish in the drying 
 apparatus. By now reweighing the dish, plus contents, and deducting from 
 the weight that of the empty dish, the weight of total solids is found. This 
 determination has practically no clinical value. 
 
 Determination of inorganic constituents. The platinum dish 
 containing the known quantity of total solids is exposed to the action 
 of a non-luminous flame, and the heat continued until all organic 
 matter has been destroyed and expelled. By reweighing now, and 
 deducting the weight of the platinum dish, plus ash, from the weight 
 
710 PHYSIOLOGICAL CHEMISTRY. 
 
 of the dish, plus total solids, the quantity of total organic matter is 
 determined ; and by deducting weight of dish from weight of dish 
 plus ash, the total quantity of inorganic matter is found. 
 
 The analysis of the ash is effected by the methods given in con- 
 nection with the consideration of the various acid and basic constitu- 
 ents themselves. Chlorine is determined by precipitating the solution 
 of the ash in nitric acid with silver nitrate, sulphuric acid by barium 
 chloride, phosphoric acid by ammonium molybdate, calcium by ammo- 
 nium oxalate, potassium by chloroplatinic acid, iron by potassium 
 ferrocyanide, etc. 
 
 As the methods outlined above are too involved for clinical w r ork, 
 no details are given. Modern methods for quantitative urinary analy- 
 sis are practically all volumetric, and will be described for the various 
 constituents of the urine. 
 
 Nitrogen in the urine. The nitrogen in the urine is derived di- 
 rectly from protein metabolized. As only a small part of the nitro- 
 gen is excreted in the feces and sweat, the estimation of the urinary 
 nitrogen is the most commonly used procedure for determining the 
 amount of protein broken down in the body. The total nitrogen 
 varies from 10 to 16 grammes a day, and, as indicated above, varies with 
 the protein metabolism. Thus it is increased with a heavy meat diet, 
 with fever, in diabetes, etc. The approximate distribution of the 
 urinary nitrogen is : 
 
 Urea 85 per cent. 
 
 Ammonia 5-6 per cent. 
 
 Creatinine 4 per cent. 
 
 Uric acid 0.5-1 per cent. 
 
 Other nitrogen 3-5 per cent, (hippuric acid, xanthine 
 
 bases, etc.). 
 
 The estimation of nitrogen alone has little clinical value, but it is 
 frequently done in order to find the percentage of ammonia, which is 
 very valuable. The method used is the customary Kjeldahl method 
 (p. 445), using the Gunning mixture of sulphuric acid, sodium sul- 
 phate, and copper sulphate. 
 
 Normal nitrogenous constituents of urine. The more important are 
 urea, uric acid, ammonia, creatiniiie (creatine). Less important are 
 the xanthine bases, hippuric acid, etc. 
 
 Urea, Carbamide, CO(NH 2 ) 2 , or CO li <^ *. Urea, the most im- 
 portant constituent of urine, is the chief nitrogenous end-product of 
 the metabolism of proteins in the body, and carries off by far the 
 
URINE AND ITS CONSTITUENTS. 711 
 
 largest quantity of all nitrogen ingested with the food. From 85 to 
 86 per cent, of the total nitrogen of the urine is found in urea, the 
 formation of which in the liver has been considered heretofore. Urea 
 has never yet been found as a product of vegetable life, but is found 
 as a normal constituent of the urine of the mammalia, and in smaller 
 quantity in the excrement of birds, fishes, and some reptiles. It 
 occurs in small quantities also in blood, muscular tissue, lymph, per- 
 spiration, and many other animal fluids. Pathologically urea may 
 appear in all fluids and tissues. 
 
 When pure, urea crystallizes from an aqueous solution in colorless 
 prisms ; it is colorless, and has a cooling, bitter taste ; it easily dis- 
 solves in water, the solution having a neutral reaction ; it fuses when 
 heated at 130 C. (266 F.), but decomposes at a higher temperature, 
 giving off ammonia gas and water, while a number of other sub- 
 stances are formed at the same time. A pure solution of urea does 
 not decompose at ordinary temperature, but on boiling, and especially 
 under pressure, it takes up water, and is decomposed into ammonia 
 and carbon dioxide, or into ammonium carbonate : 
 
 CO(NH 2 ) 2 4- 2H 2 = C0 2 + 2NH 3 + H 2 O = (NH 4 ) 2 CO 3 . 
 
 The same decomposition takes place in urine under the influence 
 of a bacterial enzyme, if the temperature be not too low. 
 
 A solution of urea is decomposed by the action of chlorine or 
 bromine with generation of hydrochloric (or hydrobromic) acid, car- 
 bon dioxide, and nitrogen : 
 
 CO(NH 2 ) 2 + 6C1 + H 2 = 6HC1 + CO 2 + 2N. 
 
 Alkali hypochlorites or hypobromites cause a similar decomposi- 
 tion, upon which is based the quantitative estimation of urea. 
 
 Urea forms with acids definite salts, and with certain oxides and 
 salts definite compounds. 
 
 Urea is formed artificially by numerous decompositions, as, for instance : 
 
 a. By a process similar to the one taking place in the animal system, viz.} 
 by limited oxidation of albuminous substances by potassium permanganate. 
 
 b. By oxidation of uric acid in the presence of water : 
 
 4 3 + H 2 + O = CO(NH 2 ) 2 + 
 Uric acid. Urea. Alloxan. 
 
 c. By the action of caustic alkalies upon creatine : 
 
 C 4 H 9 N,O 2 + H 2 O = CO(NH 2 ) 2 + C 3 H 7 NO 2 . 
 Creatine. Urea. Sarcosine. 
 
 d. By the molecular transformation of ammonium cyanate, which tahea 
 place when its solution is evaporated and allowed to crystallize : 
 
 NH 4 .CXO = CO(NH 2 ) 2 . 
 
712 PHYSIOLOGICAL CHEMISTRY. 
 
 e. By the action of carbonyl chloride, COC1. 2 , on ammonia : 
 COC1 2 + 2NH 3 = : 2HC1 + CO(NH 2 ) 2 . 
 /. By the action of ammonia on ethyl carbonate : 
 
 (C 2 H 5 ) 2 C0 3 + 2NH 3 2C 2 H 5 OH + CO(NH 2 ) 2 . 
 
 Urea may be obtained from urine by evaporating it to the consist- 
 ence of a syrup and mixing the cooled residue with an equal volume 
 of nitric acid, when crystals of urea nitrate, CO(NH 2 ) 2 .HNO 3 , form, 
 which may be decomposed by barium carbonate into urea and barium 
 nitrate : 
 
 2[CO(NH 2 ) 2 .HNO 3 ] + BaCO 3 = 2CO(NH 2 ) 2 + Ba(NO 3 ) 2 + CO 2 + H 2 O. 
 
 Experiment 95. Evaporate about 200 c.c. of urine to a syrupy consistence, 
 allow to cool, place the vessel containing the syrup in ice and add slowly with 
 stirring a volume of nitric acid equal to that of the evaporated urine. Set 
 aside for twenty-four hours, collect the crystalline mass of urea nitrate on a 
 filter, wash with very little cold water, allow to drain well, dissolve in hot 
 water, and, while the solution boils gently, add small quantities of potassium 
 permanganate until the solution is colorless. To the hot solution add freshly 
 precipitated barium carbonate as long as carbon dioxide escapes. Filter and 
 evaporate the solution to dryness over a water-bath ; boil the mass with alco- 
 hol, which dissolves the urea, but does not act on the barium nitrate. Allow 
 the urea to crystallize from the alcoholic solution. 
 
 Reactions of urea. There are no very characteristic reactions by 
 which urea can be well recognized. From organic mixtures it is 
 separated by digesting them with from 3 to 4 volumes of alcohol in 
 the cold ; the filtered liquid is evaporated to dryness and extracted 
 with alcohol, which again is evaporated. The dry residue may be 
 tested for urea as follows : 
 
 1. Dissolved in a few drops of water, the addition of an equal 
 quantity of colorless nitric acid causes the formation of white, shin- 
 ing, crystalline plates or prisms of urea nitrate. 
 
 2. If a strong solution of oxalic acid is added, instead of nitric 
 acid, rhombic plates of urea oxalate form. 
 
 3. The residue (or urea) heated in a test-tube to about 160 C. 
 (320 F.) until no more vapors of ammonia are evolved, leaves a 
 substance termed biuret, C 2 H 6 N 3 O 2 , which, upon the addition of a few 
 drops of potassium hydroxide solution and a drop of cupric sulphate 
 solution, causes the solution of the cupric hydroxide with a reddish- 
 violet color. 
 
 Determination of urea. The amount of urea in twenty-four hours 
 is normally from 25 to 35 grammes. The greater part of it is derived 
 
URINE AND ITS CONSTITUENTS. 713 
 
 from the exogenous protein metabolism, and the total quantity is 
 thereby largely affected by the diet. It is increased by a meat diet, 
 as is the total nitrogen output ; it is decreased in fever. In disease 
 of the two organs most concerned with urea elimination, the liver 
 (formation) and the kidney (excretion), it is usually, though not always, 
 decreased. 
 
 The quantitative estimation of urea in urine may be effected by 
 various methods, of which but one will be mentioned, because it re- 
 quires less time and less skill in manipulation than most other 
 methods. This determination is based upon the fact that urea is 
 decomposed by alkali hypobromites into carbon dioxide, water, and 
 nitrogen : 
 
 CO(NH 2 ) 2 + 3(NaBiO) = SNaBr + CO, + 2H 2 O + 2N. 
 
 The liberated nitrogen is collected, and from its volume the weight 
 of the urea is calculated. The carbon dioxide is absorbed by the 
 excess of alkali present. The hypobromite solution must be prepared 
 freshly by making the following mixture of: 
 
 (a) 1 volume of a solution containing bromine, 125 grammes ; 
 sodium bromide, 125 grammes; water, 1 liter. 
 
 (6) 1 volume of 22.5 per cent, sodium hydroxide solution. 
 
 (c) 3 volumes of water. 
 
 2NaOH + 2Br = NaBr + NaOBr -t H 2 O. 
 
 Of the many instruments recommended for the determination of urea, the 
 latest modification of Doremus' apparatus (Fig. 74) is most convenient. The 
 operation is carried out thus : Some urine is poured into B, while the stopcock 
 C is closed and then opened for a moment so as to fill its lumen. After having 
 washed the tube A with water, it is filled with the hypobromite solution. From 
 the tube B, previously filled with urine. 1 c.c. (or less if much urea is present) 
 is allowed to mix with the hypobromite solution, and after the reaction is com- 
 pleted the reading is taken. The degrees marked upon the tube A indicate 
 directly the number of grammes of urea contained in -the quantity of urine 
 employed. 
 
 Albumin must be removed, if present, and for careful work the specimen 
 must contain not more than 1 per cent, of urea, which can be readily accom- 
 plished by diluting a second specimen. 
 
 For careful work this method is not sufficiently accurate, and the Folin 
 method should be used. 
 
 Experiment 96. Determine urea in urine by the above-described methods. 
 
 Ammonia in the urine. Ammonia is normally present in the 
 urine in small amount, representing about 5 or 6 per cent, of the total 
 nitrogen. The amount seems dependent upon two factors : the ability 
 of the organism to convert the waste nitrogen from the proteins into 
 
714 
 
 PHYSIOLOGICAL CHEMISTRY. 
 
 urea, and the necessity of neutralizing the acid radicals of the urine 
 which are normally in excess of the basic radicals. Accordingly, 
 the urinary ammonia is increased when the urea-forming apparatus is 
 deficient /. e., in certain disease of the liver. It is likewise increased 
 in the presence of an abnormal excess of acid e. g., the acidosis of 
 diabetes and of the pernicious type of vomiting in pregnancy. As 
 the absolute amount of ammonia in the urine is greatly modified by 
 
 FIG. 74. 
 
 Doremus' ureometer. 
 
 the amount of total nitrogen, it is necessary to estimate the amounts 
 of each in order to obtain the important point the ammonia fraction 
 of the total nitrogen. 
 
 Estimation of ammonia in the urine. The ammonia in a measured 
 amount of urine is set free by the addition of sodium carbonate. By 
 means of a suitable closed system of apparatus and an ordinary suc- 
 tion pump a current of air is carried through this mixture and 
 allowed to bubble up through a measured amount of sulphuric acid. 
 At the end of an hour and a half all of the ammonia will have been 
 
VRINE AND ITS CONSTITUENTS. 715 
 
 carried over, and the excess of acid is titrated with ~ sodium hydroxide 
 with alizarin as an indicator. 
 
 Creatinine is normally present in urine to the amount of 1 or 2 
 grammes in twenty-four hours. It is believed to be derived from the 
 creatine of muscle, and mainly from the body muscle, not the food. 
 Its significance is still much disputed, as an accurate method of esti- 
 mation has been only comparatively recently devised (Folin, 1905). 
 Creatine is not normally present in urine. 
 
 Creatinine is best recognized in the urine by removing the phos- 
 phates and coloring-matter by milk of lime, concentrating the filtrate 
 by evaporation, and applying the tests mentioned before. As crea- 
 tinine is a reducing agent, its presence in urine will influence the tests 
 for sugar based on its deoxidizing power. 
 
 Make tests 2 and 3 of Experiment 77, to show the presence of creatinine in 
 urine. 
 
 NH CO 
 
 Uric acid, H 2 C 5 H 2 N 4 O 3 . 2.6.8. Oxypurine, CO C-NH^ 
 
 ,co. 
 
 NH C NH X 
 
 Uric acid is found in small quantities in human urine, chiefly in com- 
 bination with sodium, potassium, and ammonium, but also with cal- 
 cium and magnesium. In larger proportions, uric acid is found in 
 the excrement of birds, mollusks, insects, and chiefly of serpents, the 
 solid urine of the latter consisting almost entirely of uric acid and 
 urates. It is also found in Peruvian guano. The proportion of uric 
 acid to urea in human urine is normally between 1 : 50 and 1 : 70. 
 The normal amount for twenty-four hours is about 0.7 gramme. 
 
 Pure uric acid is a white, crystalline, tasteless, and odorless sub- 
 stance, almost insoluble in water, requiring 1900 parts of boiling and 
 15,000 parts of cold water for its solution; it is also insoluble, or 
 nearly so, in alcohol and ether. The great insolubility of uric acid 
 causes its separation in the solid state, both in the bladder and in the 
 tissues. 
 
 It is believed that uric acid is derived by oxidation from the purine 
 bodies of the nucleins, and is increased when there is an increase in 
 nuclein metabolism. That coming from the tissue nucleins is termed 
 " endogenous " uric acid; that from the food nucleins is termed 
 " exogenous." While uric acid is formed synthetically in the liver 
 of birds, such a synthesis has not been proved for man. It seems 
 probable that most of the waste nitrogen in birds, as in man, is con- 
 verted into urea ; but is further changed to uric acid for excretion. 
 
716 PHYSIOLOGICAL CHEMISTRY. 
 
 The exogenous uric acid is increased on a diet rich in nucleopro- 
 teins (sweetbreads) ; the endogenous uric acid, being derived mainly 
 from the muscles and the leucocytes, is increased after exercise, in 
 leukaemia, etc. 
 
 Experiment 97. (Preparation of uric acid.) Add 100 c.c. of hydrochloric 
 acid to 1 liter of urine and set aside for a day. Collect the highly colored 
 crystals of uric acid, wash with water, transfer them to a beaker with a little 
 water, heat, and add enough sodium hydroxide to dissolve the crystals. Decol- 
 orize the solution of sodium urate with boneblack, filter while hot, acidify with 
 hydrochloric acid, and allow to crystallize. Examine the crystals microscop- 
 ically and chemically. 
 
 Tests for uric acid. 
 
 1. Murexide test. Place a few fragments of uric acid in a porcelain 
 dish, add a drop of nitric acid, and carefully evaporate over a flame. 
 To the dry residue add a drop of ammonia- water, which produces a 
 beautiful purplish-red color. (Plate VIII., 4.) 
 
 To distinguish from xanthine and guanine, add a drop of caustic 
 soda, when the red changes to a deep blue color. Moisten with water 
 and evaporate to dryness, when the color disappears. With xanthine 
 or guanine the color persists. 
 
 For the following tests use solution of sodium urate prepared by dissolving 
 uric acid in warm water with the aid of sodium carbonate. 
 
 2. Schif's reaction. Place a drop of the solution on a piece of 
 filter-paper previously moistened with silver nitrate. A dark stain 
 is formed, due to the reduction of the silver salt. 
 
 3. Boil with Fehling's solution. A gray precipitate is formed when 
 uric acid, a reddish precipitate when the copper solution, is in excess. 
 (The reaction shows the necessity of exercising judgment in drawing 
 conclusions when testing for sugar in urine with reducing agents.) 
 
 4. Add magnesia-mixture and then silver nitrate. Uric acid is 
 precipitated as a gelatinous magnesia-silver salt. (This reaction may 
 be used to precipitate uric acid from urine, especially in those cases 
 in which hydrochloric acid fails to precipitate the acid.) 
 
 Quantitative estimation of uric acid. Of the many methods de- 
 scribed for this purpose, the one which is based on the separation of 
 uric acid and its subsequent titration with potassium permanganate 
 is best adapted for the needs of the physician. It is carried out 
 thus : 
 
 Uric acid is precipitated by ammonium sulphate as ammonium 
 urate, which is filtered off and isolated. On the addition of sul- 
 
URINE AND ITS CONSTITUENTS. 717 
 
 phuric acid, uric acid is set free and the amount is titrated with ^ 
 potassium permanganate solution. 
 Reagents used : 
 
 1. Ammonium sulphate, 500; uranium acetate, 5; acetic acid 
 (10 per cent.), 60 ; water, 650. 
 
 2. Ammonium sulphate, 10 per cent, solution. 
 
 3. f-Q potassium permanganate. . 
 
 To 100 c.c. of urine add 25 c.c. of reagent 1 ; let stand until the 
 precipitate has settled (five to ten minutes) and filter through two 
 folded filter-papers. To 100 c.c. of filtrate add 5 c.c. of concentrated 
 ammonia water and let stand for twenty-four hours. Pour off the 
 supernatant fluid through a filter and collect on it the precipitate of 
 ammonium urate with the aid of some 10 per cent, ammonium sul- 
 phate ; wash with the same solution for a short time. Open the 
 filter and collect the precipitate in a beaker with about 100 c.c. of 
 water. Add 15 c.c. of concentrated sulphuric acid, which will dis- 
 solve it. Titrate at once (while hot) with potassium permanganate 
 -/-$. The end-reaction is the first trace of rose color present through- 
 out the beaker after the addition of two drops of the reagent in 
 excess. 
 
 Calculation : As there is used in the titration only of the original 
 amount of urine (taking 100 c.c. of the first filtrate, not the whole 
 125 c.c.), J of the result of the titration is the amount of permanga- 
 nate which would correspond to 100 c.c. of urine. Each cubic centi- 
 meter of the permanganate corresponds to 0.00375 gramme of uric 
 acid from which it is simple to calculate the amount of uric acid 
 present in the urine. 
 
 Correction : As ammonium urate dissolves to the extent of 0.003 
 gramme in 100 c.c., this amount must be added for every 100 c.c. of 
 urine. 
 
 Xanthine bodies. The xanthine bodies are normally present in 
 urine in small amount. Those present in largest amount are para- 
 xanthine, heteroxanthine, and methylxanthine, which arise from the 
 similar bodies, caffeine, theobromine, and theophylline, in the food. 
 Otherwise the origin and significance of the purine bodies are thought 
 to be the same as those of uric acid. 
 
 Allantoin (glyoxyldiureide), C 4 H 6 N 4 O 3 , is normally present in 
 minute amounts in adults, more abundantly in the newborn. While 
 it will reduce Fehling's solution, the amount present is never suf- 
 ficient to give a positive test. 
 
 Hippuric acid, CgHgNOj (Benzoyl-glycocoll, Benzoyl-amino-acetic 
 
718 PHYSIOLOGICAL CHEMISTRY. 
 
 acid), is a normal constituent of human urine, but is found in much 
 larger quantities in the urine of herbivora. Its constitution is 
 CH 2 .NH CO 2 H, 
 
 | and is the result of the combination of glycocoll 
 
 C 6 H 5 CO 
 
 and benzoic acid. This synthesis occurs in the kidney. Hay, and 
 especially aromatic herbs, contain benzoic acid, or compounds having 
 a similar composition, and a portion of these compounds is eliminated 
 in hippuric acid. Administration of benzoic acid increases the amount 
 of hippuric acid in urine. 
 
 When pure, hippuric acid crystallizes in transparent, colorless, 
 odorless prisms, which have a bitter taste, and are sparingly soluble 
 in water. 
 
 Experiment 98. (Preparation of hippuric acid.} To 400 c.c. of horse's urine 
 add some milk of lime, heat, filter, evaporate the filtrate to a small volume, 
 and acidify with hydrochloric acid. The calcium hippurate which had been 
 formed is decomposed and the liberated hippuric acid separates either at once 
 or on standing. If too highly colored, dissolve crystals in hot water contain- 
 ing some ammonia, decolorize solution with boneblack, filter, acidify with 
 hydrochloric acid, and recrystallize. Examine crystals microscopically and 
 chemically. 
 
 Tests for hippuric acid. 
 
 1. Heat in a dry test-tube : a sublimate of benzoic acid is formed 
 and the odor of hydrocyanic acid is noticed. 
 
 2. To solution add ferric chloride : a brown precipitate is formed. 
 
 3. Heat the dry acid with calcium hydroxide in a test-tube : ben- 
 zene and ammonia are evolved. 
 
 4. Evaporate to dryness with a few drops of nitric acid : an intense 
 odor of nitrobenzene is evolved. 
 
 Chlorides in urine. Chlorides are present in larger amount than 
 any other inorganic constituent. As sodium chloride is the most 
 abundant, the total quantity is usually expressed in terms of sodium 
 chloride, and normally amounts to 10 to 15 grammes in twenty-four 
 hours. While the origin of the chlorides is in the ingested food, they 
 bear some relation to the body metabolism, which as yet is not un- 
 derstood. In nephritis there is a retention of chlorides, particularly 
 with the development of oedema. In pneumonia there is a great 
 decrease in the chlorides, with a return to normal amounts at, or even 
 slightly before, the crisis. The significance of these facts is not 
 known. 4 
 
 Qualitative test for chlorides. To a few c.c. of urine, acidified with 
 nitric acid, add a few c.c. of 5 per cent, silver nitrate solution. A 
 
URINE AND ITS CONSTITUENTS. 719 
 
 white precipitate of silver chloride forms. By comparing the result 
 with that obtained with a known normal urine, a rough estimate 
 can be gotten as to the amount of chlorides present. 
 
 Estimation of chlorides. The chlorides in a measured amount of 
 urine are precipitated by the addition of an excess of silver nitrate 
 solution of known strength. The silver chloride is removed and the 
 amount of silver nitrate remaining in solution is determined by the 
 method given on page 427. The following solutions are used : (1) 
 Silver nitrate of such strength that 1 c.c. corresponds to 0.01 gramme 
 of sodium chloride. (2) Potassium sulphocyante of such strength that 
 1 c.c. corresponds to 1 c.c. of the silver solution. (3) Ammonio- 
 ferric alum, saturated solution. 
 
 To 10 c.c. of urine in a 100 c.c. graduated flask add 4 c.c. of con- 
 centrated nitric acid and 50 c.c. of distilled water. Add 15 c.c. of 
 the silver solution and dilute the mixture to the 100 c.c. mark, shak- 
 ing well. Filter off 50 c.c. and titrate with the sulphocyanate solu- 
 tion, after adding 3 c.c. of ammonio-ferric alum. The result multi- 
 plied by 2 shows the number of cubic centimeters of silver nitrate 
 which was in excess. The difference between this number and 15 
 is the number of cubic centimeters of silver nitrate which corresponds 
 to the chloride content of the 10 c.c. of urine. 
 
 Phosphoric acid is found in urine, in part (about two-thirds) com- 
 bined with alkalies, and in part (about one-third) with lime and 
 magnesia. These phosphates have in acid or neutral urine the com- 
 position NaH 2 PO 4 , CaH 4 (PO 4 ) 2 , MgH 4 (PO 4 ) 2 ; in amphoteric urine, 
 in addition to the above, there occur Na 2 HPO 4 , CaHPO 4 , MgHPO 4 ; 
 in alkaline urine compounds of the composition Na 2 HPO 4 , CaHPO 4 , 
 MgHPO 4 , Na 3 PO 4 , Ca 3 (PO 4 ) 2 , Mg s (PO 4 ) 2 , MgNH 4 PO 4 may be pres- 
 ent. A small quantity is present as glycerin-phosphoric acid. 
 
 The phosphates in urine amount normally to about 3 grammes of 
 P 2 O 5 in twenty-four hours. They are derived mainly from the food, 
 and to a much smaller amount from the body protein. They are in- 
 creased in certain cases of diabetes, and are decreased in most of the 
 fevers. The determination of the phosphatic output has little clinical 
 importance. 
 
 On adding any alkali the phosphates of calcium and magnesium 
 (generally termed earthy phosphates) are precipitated ; the phosphates 
 of sodium or possibly potassium remain dissolved, and may be pre- 
 cipitated as magnesium ammonium phosphate by the addition of 
 magnesia mixture. 
 
720 PHYSIOLOGICAL CHEMISTRY. 
 
 Experiment 99. ( Volumetric determination of phosphoric acid.) Soluble 
 uranium salts give with phosphates a dirty-white precipitate of uranium phos- 
 phate : Na 2 HPO 4 + UO 2 (NO 3 ) 2 = UO 2 HPO 4 + 2NaNO 3 . The precipitate is 
 soluble in mineral acids, insoluble in acetic acid. Tincture of cochineal is not 
 affected by uranium phosphate, but is colored greenish by soluble uranium 
 salts. These reactions are used for determining phosphoric acid, thus : 
 
 Make up a solution of sodium acetate, 100 grammes ; acetic acid (glacial), 
 30 grammes ; and water to make 1000 c.c. 
 
 Prepare a volumetric solution of nitrate or acetate of uranium so adjusted 
 that 1 liter is equivalent to 5 grammes of P 2 O 5 . To 100 c.c. of filtered urine 
 add 5 c.c. of the acetate solution and a few drops of solution of cochineal. Heat 
 to boiling and titrate with uranium solution until the liquid assumes a green 
 color. The number of c.c. required multiplied by 0.005 indicates the quantity 
 of P 2 O 5 in the urine used. 
 
 Sulphur in the urine. Sulphur is present in the urine in three 
 forms : 
 
 Neutral (unoxidized) sulphur ; cystine, etc. 
 Oxidized (acid) sulphur : 
 
 a. Inorganic (preformed) sulphates, Na, K, etc. 
 
 b. Ethereal (conjugate) sulphates ; sulphuric acid in combination 
 
 with skatole, indole, phenol, etc. 
 
 The origin of the urinary sulphur is the protein metabolism, while 
 a small portion may arise from the ingested sulphates. The total 
 amount has little clinical importance. It is increased in fever and 
 with a meat diet. The inorganic sulphates are largely in excess, 
 their amount being about ten times that of the ethereal sulphates. 
 
 Experiment 100. 1. Demonstrate neutral sulphur by adding HC1 to urine 
 with a fragment of zinc ; hydrogen sulphide will be evolved and will blacken 
 lead acetate paper. 
 
 2. Demonstrate inorganic sulphates by adding barium chloride solution to 
 urine acidified with acetic acid ; a white precipitate of barium sulphate will 
 form. Filter this solution ; and, 
 
 3. Demonstrate ethereal sulphates by adding HC1 and barium chloride solu- 
 tion to the filtrate. On boiling the organic sulphates will be broken up and a 
 second precipitate of barium sulphate will form. 
 
 Neutral sulphur in the urine. While there is normally present 
 about 10 per cent, of the total sulphur in this form, the bodies which 
 contain it are so far almost unknown. Sulphocyanates are found 
 in small amounts. 
 
 Pathologically the best known body is cystine, which is believed 
 to indicate an inability on the part of the body to completely break 
 down the protein residues. 
 
 Cystine, diamino-dithw-dipropionic acid, ^' 2 is 
 
URINE AND ITS CONSTITUENTS. 721 
 
 secreted by the members of some families, and seems to be without 
 pathological significance, except that it may be deposited in the 
 bladder and form calculi. 
 
 Cystine is insoluble in water, alcohol, and ether, but is readily soluble in 
 ammonia- water ; boiled with solution of sodium hydroxide a sulphide of sodium 
 is formed which stains silver black. Cystine crystallizes in characteristic regu- 
 lar six-sided tablets, and is best recognized microscopically in the precipitate 
 formed by adding acetic acid to urine. Inorganic sulphates of sodium, potas- 
 sium, and magnesium are present, but possess no great interest. 
 
 Ethereal sulphates. As the conjugated substances (phenol, para- 
 cresol, skatole, indole, etc.) are formed in the intestine as putrefac- 
 tion products of the proteins, and are conjugated (in the liver) merely 
 for excretion, the resulting organic sulphates are increased whenever 
 the intestinal putrefaction is increased. The estimation of these 
 bodies as sulphates is, however, seldom carried out, as the increase is 
 important only when it is marked, and it is simpler to show an in- 
 crease of the non-sulphate portion. The indican tests are commonly 
 made use of in this connection. 
 
 Indican, indoxyl-sulphuric add, C 8 H 7 NSO 4 , 
 
 / NH \ 
 
 C 6 H <^ ^CH This compound is not identical with the 
 
 X C^_O SO 2 .OH. 
 
 indican found in woad and a few other plants. The vegetable indican 
 is a glucoside, C 26 H 31 NO 7 , yielding by fermentation, among other 
 products, dextrose and indigo-blue, C 16 H 10 N 2 O 2 . The latter is iden- 
 tical with the indigo obtained from indoxyl-sulphuric acid, which 
 decomposes into sulphuric acid (or a salt of it), and indoxyl, which 
 latter, by oxidation, yields indigo, thus : 
 
 C 8 H 6 KNSO, + H,0 = C 8 H 7 NO + KHSO 4 
 
 Potassium Indoxyl. 
 
 indoxy 1-sul ph ate. 
 
 2(C 8 H 7 NO) + 2O = C 16 H 10 N 2 2 -f 2HjO 
 Iiidoxyl. Indigo. 
 
 The source and formation of indican in the body have been men- 
 tioned. In urine it occurs normally to the extent of 0.002 per cent., 
 while pathologically the quantity may be much greater. Indican is 
 pale yellow, but is easily converted into indigo-blue, and it is this 
 property which is used for its detection. 
 
 Tests for indican. 
 
 1. Mix equal volumes of urine and strong hydrochloric acid ; then 
 add drop by drop a solution of bleaching-powder until the maximum 
 
 Afi 
 
722 PHYSIOLOGICAL CHEMISTRY. 
 
 of color is attained ; add chloroform, which is colored blue. (Care 
 should be taken to add the hypochlorite slowly, as an excess destroys 
 the color ; highly colored urine should be decolorized with basic lead 
 acetate ; in doubtful cases the mixture of urine, hydrochloric acid, one 
 or two drops of bleach ing-powder solution, and chloroform should 
 be set aside for several hours.) 
 
 2. ObermayeSs test depends on the conversion of indican into indigo 
 by ferric chloride ; and as this reagent has no further action on indigo, 
 the method has a great advantage over the previous ones. The test 
 is made by following the directions given in the above test, using an 
 equal volume of strong HC1 containing 0.2 per cent, of ferric 
 chloride and no bleaching-powder solution. 
 
 Indigo-red appears in the urine in the same conditions in which 
 indican is found. It is recognized by Rosenbach's reaction : Urine 
 is boiled, and, while it is still boiling, nitric acid is added drop by 
 drop, when a deep red color appears if indigo-red is present. The 
 foam on shaking the test-tube is bluish red. 
 
 Skatole (skatoxyl-sulphuric acid) is rarely present in the urine. Its 
 formation is analogous to that of indole. 
 
 Phenol, C 6 H 5 OH, and paracresol, C 6 H 4 .CH 3 .OH, occur in urine 
 in combination with potassium acid sulphate. The combined quan- 
 tity of the two substances is about 0.002 per cent. The quantity is 
 increased during intestinal putrefaction from all causes (except simple 
 obstruction), when there is absorption of pus from abscess or wounds, 
 and after ingestiou of carbolic acid. 
 
 Experiment 101. (Determination of phenol.} 
 
 a. Qualitative determination. Render alkaline 100 c.c. of urine with sodium 
 carbonate, evaporate to a syrup, add 20 c.c. of hydrochloric acid, and distill. 
 To the distillate apply the tests for phenol. 
 
 b. Quantitative determination. To 500 c.c. of urine add 25 c.c. of hydrochloric 
 acid and distill 200 c.c. Neutralize distillate with sodium hydroxide, in order 
 to convert benzoic and possibly other acids present into salts, and again distill 
 200 c.c. Determine the quantity of phenol in the distillate by means of deci- 
 normal bromine solution, as directed on page 424. 
 
 Pyrocatechin, ortho-dioxy benzene, C 6 H 4 (OH) 2 , occurs in urine as 
 pyrocatechin sulphuric acid. It is derived from the putrefaction of 
 vegetable food, and is found in large quantity in urine after taking 
 carbolic acid. Urine containing pyrocatechin turns dark on exposure 
 to air, especially if it is made alkaline. 
 
 To show the presence of pyrocatechin, add a little sulphuric acid 
 to the urine, boil, and when cool extract with ether. Evaporate the 
 ether, dissolve the residue in a little water, and apply tests. 
 
URINE AND ITS CONSTITUENTS. 723 
 
 Tests for pyrocatechin. 
 
 1 . Add dilute ferric chloride solution : a green color is evolved. 
 Add a little tartaric acid and then ammonia : the green color changes 
 to violet, but on acidifying with acetic acid the green color reappears. 
 
 2. Add sodium hydroxide : the solution turns green, brown, and 
 black. 
 
 3. Add lead acetate : pyrocatechin is precipitated as a lead com- 
 pound. 
 
 4. Show that Fehling's solution and ammonio-silver nitrate solu- 
 tion are reduced by pyrocatechin, but that it does not act on alkaline 
 bismuth solution. 
 
 Sodium, potassium, calcium, and magnesium occur in the urine 
 mainly as inorganic salts. They are derived from the food. The 
 amount present is not important clinically. 
 
 Oxalic acid. The source of this acid in urine is unknown. Many 
 vegetables and fruits contain oxalates, which, after ingestion, are 
 secreted to a great extent unchanged. That oxalic acid occurs as a 
 metabolic product is shown by its excretion during starvation, and 
 also when the diet is exclusively protein and fat. It is believed that 
 the protein, and not the fat, is concerned here. An increased elimi- 
 nation of oxalic acid occurs in diabetes, icterus, and in the condition 
 called oxaluria. 
 
 Enzymes in urine. Pepsin has been shown to be present in small 
 amount in normal urine ; lipase and a diastase have been found in a 
 few cases. 
 
 Pathological constituents. While the normal constituents of 
 urine, and especially the quantity excreted in twenty-four hours, 
 give valuable information in regard to the whole process of metab- 
 olism taking place in the body, pathological constituents often show 
 with great precision abnormal conditions existing in the body, and 
 the qualitative or quantitative determination of pathological con- 
 stituents is therefore a valuable aid in diagnosing disease. Of patho- 
 logical constituents are of chief interest the proteins (albumin, globu- 
 lin, albumoses, peptones), sugars, and the constituents of blood or 
 bile. But many other substances occur at times, and should not 
 be overlooked in the examination. To these substances belong 
 acetone, diacetic acid, melanin, a compound giving the diazo-reac- 
 tion, etc. 
 
724 PHYSIOLOGICAL CHEMISTRY. 
 
 Proteins in urine. Albumin in urine is always serum-albumin, 
 and is usually associated with serum-globulin. The pathological con- 
 dition is termed albuminuria. While transient albuminuria may 
 follow severe muscular or mental strain, cold baths, etc., and leave 
 no permanent effect, it must always be regarded as a pathological 
 condition. The most common cause of continued albuminuria is or- 
 ganic disease of the kidneys, acute and chronic nephritis, or even 
 chronic passive congestion. It occurs in all severe febrile conditions, 
 in- blood diseases (pernicious anemia, leukemia), after chloroform and 
 ether anaesthesia, and after many poisons (cantharides, phenol, etc.). 
 Albumin is present in all urines containing blood or pus arising from 
 any portion of the urinary tract. 
 
 Tests for albumin. 
 
 1. Heat and acid. Heat to boiling the upper portion of urine in a 
 test-tube. If a cloud appears it is due to albumin or phosphates. 
 The lower cold urine serves as a guide for comparison. If no cloud 
 forms, albumin may or may not be present ; in any case add a few 
 drops of 5 per cent, acetic acid until the reaction is acid boiling 
 again after each drop. A cloud already present, due to phosphates, 
 will disappear; one due to albumin will become more distinct. In 
 case albumin is present, but has not already been coagulated, it will 
 form a cloud on the addition of the acid, showing that there was not 
 sufficient acid present originally, the urine being either neutral or 
 alkaline. The test is made more delicate by the addition of one-eighth 
 of the volume of the urine of saturated salt solution, which should 
 always be done with very dilute urines. It is important to avoid an 
 excess of the acid, as the coagulated albumin may go into solution 
 again. If the test is made with the addition of salt solution, it is 
 extremely delicate and rarely misleading. The acetic acid may be 
 replaced Ijy nitric acid, with which an excess of acid is less to be 
 feared, and fa to y 1 ^ volume of concentrated acid can be added. 
 With nitric acid the urine should not be boiled after the acid has 
 been added. 
 
 2. Nitric acid test. About 20 c.c. of clear urine are placed in a 
 conical test-glass of about 50 c.c. capacity ; from 5 to 10 c.c. of nitric 
 acid are added by means of a pipette in such a manner that the acid 
 flows slowly from the pipette, which is carried to the bottom of the 
 vessel. Operating carefully, two distinct layers of liquid are obtained, 
 and in the presence of albumin a distinct white cloud will appear at 
 
URINE AND ITS CONSTITUENTS. 725 
 
 the zone of contact, the extent and intensity of the cloud varying 
 with the quantity of albumin present. Very small quantities of 
 albumin cannot be detected at once, but will appear on standing, the 
 cloudiness extending gradually upward. A distinct ring from 1 to 2 
 cm. above the zone of contact, and appearing within five to ten 
 minutes after the addition of nitric acid, was formerly thought to be 
 due to uric acid, and was called the urate ring. It is believed now 
 to be in some cases composed of protein material. In urines contain- 
 ing a high percentage of urea, a ring may form at the plane of con- 
 tact, consisting of urea nitrate, which is distinctly crystalline in 
 appearance. Following the ingestion of turpentine and various bal- 
 sams, this test may show a precipitate of resinous acids at the junc- 
 tion of urine and acid, which is recognized by its solubility in alcohol 
 or ether. Albumoses produce a ring which dissolves on heating and 
 reappears on cooling. 
 
 At the zone of contact a change in color is generally noticed. In 
 normal urine this varies from pale red to intense brick red ; in biliary 
 urine a color- play similar to the colors of the rainbow may be noticed, 
 while the presence of indican is indicated by a violet or blue tint. 
 It is important to distinguish between color rings and precipitate 
 rings. 
 
 3. Trichlor acetic acid may be used for the detection of albumin by 
 dropping a fragment into a few cubic centimeters of urine contained 
 in a test-tube. As the acid dissolves, a cloudy ring forms in the pres- 
 ence of albumin, which is not dissolved on warming. 
 
 4. Potassium ferrocyanide test. 5 to lOc.c. of cold urine are acidu- 
 lated with 5 to 10 drops of acetic acid, and to the mixture are added 
 a few drops of solution of potassium ferrocyanide. In the presence 
 of even traces of albumin a turbidity is caused. A precipitate which 
 dissolves on heating is due to albumose. This test is extremely deli- 
 cate, especially when modified so as to allow a few cubic centimeters 
 of diluted acetic acid, to which a few drops of potassium ferrocynaide 
 solution had been added, to flow down the side of the test-tube con- 
 taining the urine. A decided turbidity at the point of contact of the 
 two liquids shows albumin. 
 
 In case the addition of acetic acid to the cold urine should cause a 
 turbidity (which may be due to mucin or nucleo-albumin) it must be 
 filtered before adding the potassium ferrocyanide. 
 
 In the above methods the manipulations and precautions are mi- 
 nutely described, in order to detect small quantities or even traces of 
 albumin. When albumin is abundantly present, there is no difficulty 
 
726 PHYSIOLOGICAL CHEMISTRY. 
 
 whatever in its detection, as heat will precipitate it in most cases from 
 an acid, neutral, or sometimes even alkaline urine ; the precipitate 
 should, however, always be tested by the addition of a few drops of 
 nitric acid, and the previous addition of a few drops of acetic acid is 
 also advisable. 
 
 Quantitative estimation of albumin. The average amount of 
 albumin present in acute cases of albuminuria is 0.1 to 0.5 per cent., 
 rarely over 1 per cent., though it may rise to 4 per cent. An 
 approximate method for the comparative estimation of albumin is to 
 precipitate it (with the precautions above given) in a graduated test- 
 tube by heat and setting aside for twelve (or, better, for twenty-four) 
 hours. At the end of that time the proportion of the coagulated 
 albumin which has collected at the bottom of the fluid is noticed. If 
 the albumin occupy one-fourth, one-sixth, one-tenth of the height of 
 the liquid, there is said to be one-fourth, one-sixth, or one-tenth of 
 albumin in the urine. If, however, at the end of twelve or twenty- 
 four hours scarcely any albumin has collected at the bottom, there is 
 said to be a trace. 
 
 The volumes of coagulated albumin indicate the following quantities of dry 
 albumin : 
 
 Slight turbidity indicates about 0.01 per cent. 
 
 & of tbe tube is filled 0.05 " 
 
 r V " " ....... 0.10 " 
 
 j * 0.25 
 
 I " " ....... 0.50 " 
 
 " " ....... 1.00 " 
 
 Complete coagulation . 2 to 3 " 
 
 Esbach's albuminometer (Fig. 75) is a conveniently arrnnged tube for deter- 
 mining approximately the quantity of albumin. The tube is rilled with urine to 
 U, and then with the reagent to R. The reagent is a solution containing 1 
 gramme of picric acid and 2 grammes of citric acid in 100 c.c. of water. After 
 having filled the tube it is closed with a stopper, inverted twelve times, and set 
 aside for twenty-four hours. At the end of that time the albumin will have 
 settled down, when the amount pro mille in grammes may be directly read off 
 from the scale. 
 
 Tsuchiya's reagent possesses many advantages over Esbach's, and is used in 
 the same manner. It is, Phosphotungstic acid, 1.5 grammes; hydrochloric 
 acid (concentrated), 5 c.c.; alcohol, 95 c.c. 
 
 A better method of exactly estimating the amount of albumin is its 
 complete separation and weighing, as described below. 
 
 Experiment 102. Acidify 100 c.c. of clear albuminous urine with acetic acid ; 
 heat to the boiling-point in a water-bath for half an hour, and filter through a 
 
URINE AND ITS CONSTITUENTS. 
 
 727 
 
 small filter, previously dried at 110 C. (230 F.) and weighed ; wash with boil- 
 ing water to which a little ammonia water has been added (to remove uric 
 acid and urates), then with pure water until the filtrate is not rendered turbid 
 any longer by silver nitrate, next with pure alcohol, and finally with ether. 
 Dry filter and contents at 110 C. (230 F.) and weigh. 
 
 As it may happen that the precipitated albumin encloses earthy phosphates, 
 it is well to burn filter with contents in a platinum crucible, and to deduct the 
 weight of the remaining inorganic residue (less the weight of the filter ash) 
 from that of the albumin. 
 
 Serum-globulin is detected by rendering the urine alkaline with 
 ammonia water, filtering off the precipitate of phosphates, and add- 
 ing to the clear filtrate an equal volume of a saturated 
 solution of ammonium sulphate. The appearance of a FIG. 75. 
 precipitate indicates globulin. 
 
 Albumoses answer to the nitric acid test and the 
 potassium ferrocyanide test for albumin ; the precip- 
 itate formed by these reagents dissolves on heating, 
 but reappears on cooling. Albumoses are further rec- 
 ognized thus : To the urine strongly acidified with hydro- 
 chloric acid is added an equal volume of a saturated so- 
 lution of sodium chloride. On boiling, serum-albumin, 
 if present, is precipitated and filtered off while hot. 
 Albumoses separate from the filtrate on cooling. 
 
 The solution, filtered while hot, gives a red biuret 
 reaction. As albumose is frequently present in albu- 
 minuria, its demonstration is important only in the 
 absence of albumin. Albumosuria occurs with the 
 absorption of purulent exudates, in acute yellow atrophy 
 of the liver, and in other conditions. 
 
 Peptones are not uncommonly present in the urine aibuminometer. 
 in albumosuria, but are rarely present alone. Peptonuria 
 exists when it is possible to obtain a red biuret reaction after the 
 careful removal of protein and albumose. Both here and in the case 
 of albumosuria urobilin may mislead one when the biuret reaction is 
 tried. It may be removed by extraction with alcohol. 
 
 Bence- Jones body is present in the urine in certain cases of 
 bone disease (multiple myeloma). It is thought to be a unique 
 albumin and not an albumose, as held by the earlier view. It is 
 coagulated in urine acidified with acetic acid on heating to 50 or 
 60 C., and redissolves as the temperature reaches the boiling-point. 
 It is very rarely present. 
 
 Esbach's 
 
728 PHYSIOLOGICAL CHEMISTRY. 
 
 Nucleo-albumin. If the ring occurring in Heller's test some dis- 
 tance above the place of contact becomes more distinct when the 
 urine is diluted, it is believed to be of protein origin, and has been 
 called nucleo-albumin, mucin, euglobulin, Morner's body, etc. Its 
 true nature is not yet known. The cloud produced by acetic acid 
 in the cold is believed to be due to the same body. As urates may 
 be precipitated in both of these methods, it is important to rule them 
 out by diluting the urine, when the precipitate due to urates will not 
 appear. True nucleo-albuminuria is rare. 
 
 Blood. The presence of blood in urine manifests itself generally, 
 unless the amount be too slight, by a blood-red or brow r nish color 
 with a bluish, smoky, or greenish tint, and deposits a red or reddish- 
 brown sediment after standing. As a general rule, all constituents 
 of blood, including the corpuscles, are present (haematuria), but in 
 some cases only haemoglobin (methaemoglobin) is found (haemoglobin- 
 uria). 
 
 The tests for blood depend either on the microscope, spectroscope, 
 or on chemical changes. By the microscope is examined the deposit 
 which forms on standing ; almost unaltered blood-corpuscles may be 
 found, or they may be much swollen, decolorized, and deformed. 
 
 Haematuria is common and occurs in diseases of the kidney (acute 
 nephritis, stone, tuberculosis, trauma) ; similar conditions of the ure- 
 ters and bladder ; general conditions (malignant forms of smallpox, 
 malaria, etc. ; haemophilia). 
 
 Haemoglobinuria occurs occasionally in severe fevers (scarlet fever, 
 yellow fever) ; after severe burns or exposure to cold ; in certain 
 poisonings (potassium chlorate, carbon monoxide). It is always pre- 
 ceded by haemoglobinaemia, i. 6., the presence of free haemoglobin in 
 the circulating blood. The spectroscope shows the absorption-bands 
 of the blood-pigments, for which see Fig. 72. 
 
 Tests for blood in urine. 
 
 1. Render alkaline with sodium hydroxide and boil. In the pres- 
 ence of blood coloring-matter the precipitate of phosphates produced 
 is colored red. In a urine containing other coloring-matters (bile- 
 pigments, etc.) the test may be misleading ; in such cases, filter off 
 the precipitate, wash, and dissolve it in acetic acid. In the presence 
 of blood-pigment the solution becomes red, but the color gradually 
 disappears on exposure to air. 
 
 2. Allow a mixture of freshly prepared tincture of guaiacum and 
 
URINE AND ITS CONSTITUENTS. 729 
 
 ozonized oil of turpentine to flow down the side of a test-tube in 
 such a manner as to form a distinct layer above the urine. A white 
 ring, gradually turning blue, will appear at the surface of contact. 
 (Ozonized oil of turpentine is oil which has been exposed to air for 
 some time ; in place of it may be used peroxide of hydrogen or a 
 mixture of this compound with ether.) 
 
 3. Add a little of a solution of egg-albumin to 100 c.c. of urine, 
 heat to boiling, and filter off the coagulum, which has taken up the 
 hsematin. Mix the precipitate in a mortar with 20 c.c. of absolute 
 alcohol and a few drops of sulphuric acid, transfer to a flask, heat 
 to boiling, and filter. After cooling, render alkaline with sodium 
 hydroxide, reduce with ammonium sulphide, and examine spectro- 
 scopically for reduced ha3matin. (Fig. 72.) 
 
 The direct spectroscopic examination of urine is generally unsatisfactory > 
 because it often contains a number of substances giving absorption spectra. 
 
 Carbohydrates in urine. Dextrose (glucose) in urine is normally 
 present in minute amount. When the amount is sufficient to give 
 the customary reduction tests, the condition is spoken of as glyco- 
 suria. If dextrose be eaten in large amount the body is unable to 
 burn all of it, and a temporary glycosuria results. This is called ali- 
 mentary glycosuria and is not a serious condition. The amount of 
 sugar, the " assimilation limit," which can be ingested without the 
 appearance of the sugar in the urine, differs for the different sugars 
 and differs in different individuals. A more serious condition, per- 
 sistent glycosuria, exists in diabetes when the body is unable to carry 
 on the normal sugar metabolism. In this disease the amount of dex- 
 trose in the urine may be very large, and frequently dextrose is 
 present, even when the patient is on a carbohydrate-free diet. In 
 both of these conditions the glycosuria is secondary to an increase 
 in the dextrose content of the blood, while in experimental " phlorid- 
 zin diabetes " the change is in the kidneys, and there is no increase 
 in the dextrose of the blood. 
 
 There are many tests by which dextrose can be detected. They 
 depend chiefly on the following properties of dextrose, viz. : 1, to act 
 as a deoxidizing or reducing agent upon certain metallic oxides (cop- 
 per, bismuth, silver, mercury) in the presence of alkalies ; 2, to pro- 
 duce a yellow or brown color when in contact with alkalies, slowly 
 in the cold, rapidly on heating ; 3, to ferment with yeast ; 4, to unite 
 with phenyl-hydrazine to a crystalline compound; 5, to have the 
 power of rotating the plane of polarization to the right. 
 
730 PHYSIOLOGICAL CHEMISTRY. 
 
 Tests. 
 
 1. Trommer's test. A few drops (2-4) of a 5 per cent, solution of 
 cupric sulphate are added to about 5 to 8 c.c. of urine in a test-tube 
 and then an equal volume of potassium (or sodium) hydroxide solu- 
 tion is added. The alkaline hydroxide precipitates both earthy phos- 
 phates and cupric hydroxide, the latter, however, dissolving (espe- 
 cially if sugar be present) in the excess of the alkali, producing a 
 beautiful blue transparent liquid. (If no sugar is present, the color 
 is less blue, but more of a greenish hue.) The liquid is now heated, 
 when, if sugar be present, a yellow precipitate of cuprous hydroxide 
 is formed which subsequently loses its water and becomes the red 
 cuprous oxide, which falls to the bottom or adheres to the sides of 
 the test-tube. (Plate VIII., 5.) 
 
 In drawing conclusions from the above test, it should be remem- 
 bered that a change of color does not indicate sugar ; that a precipi- 
 tate of earthy phosphates must not be mistaken for cuprous oxide ; 
 and that substances other than sugar may deoxidize cupric oxide at 
 the temperature of 100 C. (212 F.). 
 
 A disadvantage of Trommer's test is the formation of black cupric 
 oxide whenever too much copper solution is used in proportion to the 
 sugar present. The formation of the black oxide, which may mask 
 a small quantity of cuprous oxide, is avoided in the next test. 
 
 2. Fehling's test differs from Trommer's test in merely using a pre- 
 viously mixed reagent instead of producing this reagent, as it were, 
 in the urine by adding to it cupric sulphate and an alkaline hydroxide 
 successively. This reagent, known as Fehling's solution, or as alkaline 
 cupric tartrate volumetric solution, is made by mixing exactly equal 
 volumes of the below-mentioned copper solution and the Rochelle 
 salt solution at the time required. 
 
 Copper solution : 
 
 Crystallized cupric sulphate 34.64 grammes. 
 
 Water, sufficient quantity to make .... 500 c.c. 
 
 Rochelle salt solution : 
 
 Potassium sodium tartrate 173 grammes. 
 
 Potassium hydroxide . . . . . . .125 " 
 
 Water, sufficient quantity to make .... 500 c.c. 
 
 Both solutions are preserved in small well-stoppered bottles, and 
 mixed only at the time needed, because the mixture is apt to decom- 
 pose when kept some time. 
 
 The addition of sodium-potassium tartrate in Fehling's solution prevents the 
 precipitation of cupric hydroxide by the alkaline hydroxide. This action is anal- 
 
URINE AND ITS CONSTITUENTS. 731 
 
 ogous to the formation of the soluble scale compounds of iron, where the pre- 
 cipitation of ferric hydroxide is also prevented by tartaric or other organic acids. 
 
 The test is made by heating in a test-tube 10 c.c. of Folding's solu- 
 tion which has been diluted with 2 to 5 volumes of water and add- 
 ing drop by drop the suspected urine ; if the latter contains larger 
 quantities of sugar, a yellow or red precipitate of cuprous hydroxide 
 and oxide will be produced very readily ; if but small quantities are 
 present, the reaction will appear only on standing for some time. 
 
 Haines' test is a modification of Fehling's test. The reagent is as 
 follows : " Dissolve 30 grains of cupric sulphate in \ ounce of water, 
 add \ ounce of glycerin and then 5 fluidounces of liquor potassse." 
 The advantage of the reagent is that it is very stable. It should be 
 used by boiling about 1 drachm in a test-tube, adding 8 to 10 drops 
 of the suspected urine, and again bringing to a boil. In the presence 
 of sugar a precipitate of cuprous oxide is thrown down. 
 
 3. Botgcr's bismuth test consists in adding to a mixture of equal 
 volumes of urine and potassium (or sodium) hydroxide solution a few 
 grains of subnitrate of bismuth and boiling for half a minute. If 
 sugar be present, a gray or dark -brown, finally black, precipitate of 
 bismuthous oxide, Bi 2 O 2 , or of metallic bismuth is formed. If but 
 very little sugar is present, the undecomposed excess of bismuthic 
 nitrate (or bismuthic hydroxide) mixes with the metallic bismuth, 
 imparting to it a gray color ; the test should then be repeated with a 
 smaller amount of the bismuth salt. (Plate VIII., 6.) 
 
 The above test may be advantageously modified by using a bismuth 
 solution instead of the powder. The solution known as Nylander's 
 reagent is made by dissolving 2 grammes of bismuth subnitrate, 4 
 grammes of Rochelle salt, and 10 grammes of sodium hydroxide in 
 90 c.c. of water, and filtering. One-half c.c. of this solution is heated 
 with about 5 c.c. of urine, when, in the presence of sugar, a brown 
 or black precipitate will form after a few minutes 7 boiling. 
 
 If the urine contains hydrogen disulphide (sometimes produced by decom- 
 position of certain urinary constituents), black bismuth sulphide will be formed, 
 which may be mistaken for metallic bismuth ; albumin itself may be the cause 
 of the formation of alkaline sulphides : the previous complete separation of 
 albumin is therefore indispensable. 
 
 4. Moore's or Heller's test is made by heating urine with about 
 one-fourth its volume of solution of potassium hydroxide. In the 
 presence of sugar the color of the mixture will deepen to a dark yel- 
 low or brown, and the depth of color is a fair indication of the quan- 
 
732 PHYSIOLOGICAL CHEMISTRY. 
 
 tity of sugar present. In case but a slight change takes place in 
 color, it is well to compare it with that of an unchanged specimen 
 of the urine. 
 
 5. Fermentation test. This is based upon the decomposition of 
 dextrose by yeast with the generation of carbon dioxide. A piece 
 of yeast about the size of a pea is ground up in urine and the mixture 
 used to fill a fermentation tube. The tube is then kept for twenty- 
 four hours at a fairly constant temperature of 22 to 28 C. If dex- 
 trose be present, fermentation will commence within twelve hours 
 and will manifest itself by the formation of carbon dioxide gas, which 
 will collect at the upper end of the long arm of the tube. 
 
 The urine and the fermentation apparatus should be sterilized by heat to 
 destroy any gas-producing bacteria present. For a control of the test, two 
 more fermentation tubes should be prepared, one with a mixture of a glucose 
 solution and yeast (to determine that the yeast is efficient),, and another with 
 sterilized water and yeast (to show that the yeast itself does not generate 
 
 The disadvantages of this process are the length of time required for its per- 
 formance, the unreliability of the ferment, and the fact that small quantities 
 of sugar (less than 0.5 per cent.) evolve so little carbon dioxide that a doubt 
 may be felt as to the presence of sugar at all. 
 
 6. The pTienyl-Tiydrazine test. To 10 c.c. of urine in a test-tube, 
 add phenyl-hydrazine hydrochloride, 0.4 gramme and sodium ace- 
 tate, 1 gramme, warm until dissolved, adding water, if necessary, and 
 keep in a boiling water-bath for half an hour. Filter while hot, and 
 allow to cool slowly. The presence of dextrose will be shown by the 
 deposition of yellow crystals, which are seen with the microscope to 
 be needles arranged in sheaves. This precipitate is an osazone 
 (phenyl-dextrosazone) and melts at 205 C. Pentoses and maltose 
 give similar osazones, as do lactose and glycuronic acid. The latter 
 are rarely present in sufficient amount to give a positive test with the 
 urine directly. The melting-points are of value in recognizing the 
 different osazones. 
 
 7. Polariscopic test. Before urine can be examined by the polari- 
 scope it should be freed from proteins and from the greater part of 
 coloring-matters by precipitation with neutral lead acetate. The 
 sensitiveness of the test depends on the construction of the instru- 
 ment, but even the best polarimeters do not show traces of sugar, 
 for which reason it is generally useless to apply the test unless sugar 
 has been indicated bv other tests. 
 
URINE AND ITS CONSTITUENTS. 
 
 733 
 
 The following table shows the tests for distinguishing dextrose 
 from other reducing agents occurring in the urine : 
 
 
 Fehling's test. 
 
 Bismuth test. 
 
 Fermenta- 
 tion test. 
 
 I'hfiivl-hv- Polarisropic 
 drazine test. test. 
 
 Dextrose . 
 
 Reduction 
 
 Reduction 
 
 Positive 
 
 Positive 
 
 f Dextro- 
 
 
 
 
 
 
 \ rotatory 
 
 Pentoses . 
 
 Reduction 
 
 Reduction 
 
 Negative 
 
 Positive 
 
 ( Dextro- 
 \ rotatory 
 
 Lactose 
 
 Reduction 
 
 Reduction 
 
 Negative 
 
 Positive 
 
 f Dextro- 
 1 rotatory 
 
 Laevulose . 
 
 Reduction 
 
 Reduction 
 
 Positive 
 
 Positive 
 
 f Lsevo- 
 
 
 (partial) 
 
 
 
 
 \ rotatory 
 
 
 
 
 
 
 !Laevo-ro- 
 
 Glycuronic acid 
 
 Reduction 
 
 Reduction 
 
 Negative 
 
 Positive 
 
 tatoryin 
 
 
 
 
 
 
 urine 
 
 Alkaptonic acids 
 Uric acid . 
 Creatinine 
 Pyrocatechin 
 
 Reduction 
 Reduction 
 Reduction 
 Reduction 
 
 Negative 
 Negative 
 Negative 
 Negative 
 
 Negative 
 Negative 
 Negative 
 Negative 
 
 Negative 
 Negative 
 Negative 
 Negative 
 
 Inactive 
 Inactive 
 Inactive 
 Inactive 
 
 Allantoin . 
 
 Reduction 
 
 Negative 
 
 Negative 
 
 Negative 
 
 Inactive 
 
 Quantitative estimation of sugar. By far the best method is 
 the decomposition of a copper solution of a known strength, and 
 Fehling's solution prepared as stated above, answers this purpose 
 well. 
 
 1000 c.c. of Fehling's solution, containing 34.64 grammes of crys- 
 tallized cupric sulphate, CuSO 4 .5H 2 O, are decomposed by 5 grammes 
 of grape-sugar, or 1 c.c. of solution by 0.005 of grape-sugar. 
 
 To make the quantitative determination, operate as follows : 10 c.c. 
 of Fehling's solution are poured into a porcelain dish of about 200 c.c. 
 capacity, placed over a flame. The copper solution is diluted with 
 about 40 c.c. of water, and heated to boiling ; to the boiling liquid, 
 urine (which has been previously diluted with 9 parts of water) is 
 added from a burette very gradually, until the blue color of the solu- 
 tion has disappeared, and there remains, upon subsidence of the 
 cuprous oxide, an almost colorless, clear liquid. A filtered portion 
 of this liquid, acidified with hydrochloric acid, should not give a 
 reddish-brown precipitate with potassium ferrocyanide (a precipitate 
 would show that all copper had not been precipitated, and that more 
 urine was needed), while a second portion of the filtered fluid should 
 not produce a red precipitate on boiling with a few drops of Fehling's 
 solution (a precipitate would indicate that too much urine had been 
 added, in which case the operation has to be repeated). 
 
 The calculation of the amount of sugar present is easily made. 
 10 c.c. of Fehling's solution are decomposed by 0.05 gramme of 
 sugar ; this quantity must, therefore, be contained in the number of 
 
734 PHYSIOLOGICAL CHEMISTRY. 
 
 c.c. of urine used. Suppose 30 c.c. of urine, diluted with 9 parts of 
 water, or 3 c.c. of pure urine, have been required to decompose the 10 
 c.c. of Fehling's solution, then 3 c c. of urine contain of grape-sugar 
 0.05 gramme, or 100 c.c. of urine 1.666 grammes, according to the 
 proportion : 
 
 3 : 0.05 : : 100 : x 
 
 1 = 1.666. 
 
 If the urine contains but very little sugar, it may be used directly 
 without diluting it, or instead of diluting it with 9 parts of water, it 
 may be diluted with 4 volumes or with an equal volume of water. 
 
 In using Fehling's solution for the volumetric estimation of lactose, 
 it should be remembered that 1 c.c. of solution is decomposed by 
 0.0067 gramme of lactose. 
 
 Modified Fehling method (Rudisch and Celler). The only change is 
 in diluting the 10 c.c. of Fehling solution with 40 c.c. of 50 per 
 cent, potassium stilphocyanate instead of with 40 c.c. of water. The 
 end-reaction here is the same, i. e., the disappearance of the blue. As 
 there is no precipitate to obscure the end-point, the estimation is 
 readily made and the method is an improvement over the original 
 procedure. As the same amount of Fehling's solution is used, the 
 calculation is carried out in the same way. 
 
 Harvey G. Beck has devised the following method : 
 
 The apparatus used consists of a suitable beaker ; four centrifugal tubes 
 graduated at 2 c.c. ; a pipette of 2 c.c. capacity, graduated into twentieths c.c., 
 and a wire tube-holder to support the tubes when placed in the beaker. A 
 centrifuge will greatly facilitate the work. 
 
 The procedure is as follows : The beaker, one-third full of water, is placed 
 over a.Bunseu flame, and the four centrifugal tubes, after being filled to the 
 graduation mark (2 c.c.) with standard Fehling's solution, are placed in the 
 tube-holder and suspended in the beaker. The tubes are numbered respectively 
 1, 2, 3, and 4, according to their position in the tube-holder. The urine is added 
 from the pipette in quantities of twentieths c.c., as follows: fa to No. 1, -fa to 
 No. 2, fa to No. 3, and -fa to No. 4. The tubes, after being thoroughly shaken, 
 are suspended in boiling water for at least three minutes, when they are removed 
 and either set aside in the tube-stand until the cupric oxide is precipitated, or 
 centrifugalized in order to hasten precipitation. If all the tubes still show a 
 blue color, the urine is increased to ^, -fa, $%, and fa respectively, by adding 
 fa e.c. to each tube, and the foregoing steps are repeated. This process is con- 
 tinued until one, or more, of the tubes is completely decolorized. The first tube 
 in the series in which the blue color has entirely disappeared is noted; the 
 number of twentieths c.c. required to reduce it, divided into twenty, gives the 
 percentage of sugar present. 
 
 Estimation by fermentation can be readily done, using specially 
 graduated tubes, which can be read directly in percentages of dextrose. 
 
URINE AND ITS CONSTITUENTS. 735 
 
 Estimation by means of the polariscope furnishes the quickest method ; 
 the details cannot be given here. 
 
 Other carbohydrates in urine. Laevulose is rarely present in the 
 urine; in almost all of the cases dextrose is also presen t(diabetes). 
 Laevulosuria should be suspected when a urine reduces copper solu- 
 tions, rotates polarized light to the left or not at all, and shows no 
 Ia3vorotation after being fermented. 
 
 Lsevulose reduces copper and bismuth solutions, ferments with 
 yeast, is laevorotatory, and forms the same osazone with phenyl- 
 hydrazine as is formed by dextrose. 
 
 Maltose is very rarely present in urine. Such urines show a 
 higher percentage of sugar with the polariscope than with Fehling's 
 solution. 
 
 Lactose occurs in the urine of lactating women, and occasionally 
 in the urine of persons on an exclusive milk diet. It gives a delayed 
 and incomplete Fehling test, reduces Nylander's solution, does not 
 ferment with yeast, rotates polarized light to the right. While it 
 forms a yellow osazone with phenyl-hydrazine, the amount present in 
 the urine is rarely sufficient to give a positive test. 
 
 Pentoses, C 5 H 10 O 5 , occur in many fruits and vegetables as complex 
 carbohydrates, known as pentosanes. When taken into the body the 
 pentosanes are split and pentose is excreted in the urine. Consid- 
 erable pentose is found in the urine of persons addicted to the use 
 of morphine. Pentoses owe their chief importance to the similarity 
 of their reactions to those of glucose. Normally, the quantity of 
 pentose in the urine is not such as to interfere with the reactions for 
 sugar. 
 
 Pentoses reduce Fehling's and bismuth solutions ; they are dextrorotatory ; 
 with phenyl-hydrazine they form a crystalline compound, melting between 
 153 and 158 C. (307 and 317 F.). Pentoses do not ferment with yeast, and 
 are characterized by responding to Tollen's orcin reaction. This is made by 
 adding 3 c.c. of a saturated solution of orcin in hydrochloric acid to 5 c.c. of 
 urine previously decolorized with boneblack. In the presence of pentose a 
 green color develops on heating, beginning at the top and gradually extending 
 through the mixture. 
 
 Glycuronic acid, CHO.(CHOH) 4 .CO 2 H. Glycuronic acid occurs 
 in normal urine in minute amount. It is an oxidation product of 
 glucose, and is usually present in the form of the conjugated glycu- 
 ronates, i. e., glycuronic acid linked to aromatic bodies (phenol, cresol, 
 etc.). It is increased after the taking of camphor, chloral, menthol, 
 and other substances, which produce aromatic substances in the urine 
 
736 PHYSIOLOGICAL CHEMISTRY. 
 
 to which the glycuronic acid is linked. The amount usually present 
 is not sufficient to reduce Fehling's solution, unless the boiling is con- 
 tinued for a long time. The conjugate glycuronates are Isevorotatory. 
 
 Glycuronic acid reduces Fehling's and bismuth solutions, forms an osazone 
 melting at 115 C. (239 F.), does not ferment with yeast, and is dextrorotatory. 
 5 c.c. of urine containing glycuronic acid when decolorized with boneblack, 
 mixed with an equal volume of hydrochloric acid and 0.025 phloroglucin, de- 
 velops a deep-red color on heating. (This reaction is also shown by pentoses ; 
 glycilronic acid does not give the orcin reaction.) 
 
 Acetone, diacetic and /3-oxy-butyric acids. These substances, 
 commonly called the " acetone bodies/' are believed to be due to an 
 abnormal metabolism of fat, though the protein metabolism may also 
 be concerned. As can be seen from the following reactions acetone 
 is derived from diacetic acid, and diacetic acid from /9-oxy -butyric 
 acid : 
 
 CH 3 CH(OH).CH 2 .COOH + O = CH 3 .CO.CH 2 COOH + H 2 O 
 /3-oxy-butyric acid. Diacetic acid. 
 
 CH 3 .CO.CH 3 .COOH = CH 3 .CO.CH 3 -f CO 2 
 Acetone. 
 
 As oxy-butyric acid and diacetic acid are unstable, acetone is the 
 first of these bodies to appear in the urine, and it is only as the 
 pathological conditions increase that diacetic and finally oxy-butyric 
 acid are found. Acetone is, indeed, normally present in minute 
 amounts, and is always increased in the presence of the other two. 
 As these bodies have the same origin, their presence has the same sig- 
 nificance, the higher members showing merely a graver aspect. 
 
 They are increased, in many conditions : with a carbohydrate-free 
 diet, in any cachectic condition, in many types of fever. They are 
 markedly increased in diabetes. 
 
 The more severe cases of acetonuria are also referred to as acido- 
 sis (acid intoxication). The term emphasizes, of course, not the acid 
 excreted in the urine, but the acid remaining in the system. In 
 order to neutralize this abnormal acidity without using the fixed 
 alkali of the body the organism converts less nitrogen into urea 
 than is normally done, and uses it as an alkali in the form of ammonia. 
 Thus the proportion of the urinary nitrogen in the form of ammonia 
 is increased in acidosis, becoming even 40 per cent., the normal being 
 5 or 6 per cent. This percentage is the best index of the severity of 
 the condition. 
 
 Acidosis is most common in diabetes and pernicious vomiting of 
 pregnancy, and indicates the danger of coma. 
 
URINE AND ITS CONSTITUENTS. 737 
 
 Legal's test for acetone. To 25 c.c. of urine add an equal volume of a strong, 
 freshly-made solution of sodium nitroprusside, and then a few drops of sodium 
 hydroxide solution. In the presence of acetone a red color develops, which, on 
 addition of an excess of acetic acid, becomes darker red. (Compare WeyPs 
 reaction for creatinine.) 
 
 Acetone may also be recognized in the following manner : 500 c.c. of urine 
 are acidified with a few drops of hydrochloric acid and distilled. To the dis- 
 tillate a few drops of iodine solution (1 iodine, 2 potassium iodide, 100 water) 
 and of potassium hydroxide are added. If acetone is present, a characteristic 
 yellowish- white precipitate of iodoform is formed. 
 
 Diacetic acid is recognized by adding to the urine drop by drop a 
 fairly strong solution of ferric chloride, filtering off any precipitate 
 of phosphate, and adding more ferric chloride, when in the presence 
 of diacetic acid a deep-red color is produced, which disappears on 
 boiling. The test should also be made with an ethereal extract, ob- 
 tained by shaking urine previously acidified with sulphuric acid with 
 ether ; the ferric chloride solution, on being agitated with the ethereal 
 extract, becomes red. (As salicylic acid and a number of other sub- 
 stances give a red or violet color with ferric chloride, care must be 
 taken not to confound diacetic acid with these substances.) 
 
 The detection of /3-oxy-butyric acid is difficult, and is rarely done 
 in clinical work. Its presence is probable when urine, after being 
 fermented, still contains a tavorotatory body. 
 
 Bile may be present in the urine in any case of jaundice. 
 
 Detection of bile-pigment. The presence of bile in urine is gen- 
 erally indicated by a decided color, which varies from a deep brown- 
 ish-red to a dark brown ; the foam of such urine (produced by shak- 
 ing) has a distinct yellow color, and a piece of filtering-paper or a 
 piece of linen dipped into the urine assumes a yellow color, which 
 does not disappear on drying. 
 
 The further detection of bile depends upon the reactions of the 
 biliary coloring-matters or biliary acids. 
 
 Tests for bile. 
 
 1. Gmelin's test for biliary coloring-matters has been considered, 
 and may be applied to urine either by allowing a small quantity 
 of nitric acid, containing some nitrous acid, to flow down the sides 
 of a test-tube (containing the urine) in such a manner that the two 
 fluids do not mix, or by placing upon a porcelain plate a few drops 
 of the urine, near it a few drops of nitric acid, to which one drop of 
 sulphuric acid has been added, and allowing the two liquids to ap- 
 proach gradually. In both cases (if bile-pigment is present) a play of 
 
 47 
 
738 PHYSIOLOGICAL CHEMISTRY. 
 
 color is seen at the point of union between the two fluids, the colors 
 changing from green to blue, violet-red, and yellow or yellowish- 
 green. While the appearance of the green at the beginning is indis- 
 pensable to prove the presence of bile, the presence of all the other 
 colors is not essential. (Plate VIII., 7.) 
 
 The above test may be made in a somewhat modified form by mix- 
 ing the urine with a concentrated solution of sodium nitrate, and 
 pouring down the sides of the test-tube concentrated sulphuric acid in 
 such a manner as to form two distinct layers ; the colors are seen at 
 the point of contact as above. 
 
 If the urine be very dark in color, it should be diluted with water 
 before applying the above tests. 
 
 2. Add a few drops of sodium carbonate solution to the urine until 
 it has a distinct alkaline reaction, then add calcium chloride and 
 shake well. The precipitated calcium carbonate carries down the 
 pigments and leaves the urine nearly colorless or of its normal color. 
 Collect the precipitate on a filter, wash, and transfer it with alcohol 
 to a test-tube. Dissolve by the addition of hydrochloric acid and 
 boil the clear solution, when it turns green. Allow to cool and add 
 nitric acid, when the green solution turns blue, violet, and red. 
 (This test may show the presence of biliary coloring-matters when 
 Gmelin's test fails to do so, and is recommended when the urine con- 
 tains a large amount of indican.) 
 
 While bile acids are always present with bile-pigment in urine, 
 their demonstration is usually difficult. 
 
 Pettenkofer's test for biliary acids is made by dissolving a few 
 grains of cane-sugar in urine contained in a test-tube, and allowing 
 concentrated sulphuric acid to trickle down the side of the inclined 
 test-tube ; a purple band is seen at the upper margin of the acid, and 
 on slightly shaking the liquid becomes at first turbid, then clear, and 
 almost simultaneously it turns yellow, then pale cherry-red, dark 
 carmine-red, and finally a beautiful purple violet. The temperature 
 must not be allowed to rise much above 38 C. (100 F.). 
 
 As many substances (other than biliary acids) show a similar 
 reaction, it is often necessary to separate the bile acids by the process 
 described in connection with the consideration of bile itself. 
 
 In case the quantity of biliary constituents is so small that they 
 cannot be noticed by the tests mentioned, the urine should be shaken 
 with about one-fourth of its volume of chloroform, which dissolves 
 the biliary matters. Some of this solution is dropped upon blotting 
 paper, and after evaporation a drop of red fuming nitric acid is 
 
PHYSIOLOGICAL REACTIONS. 
 
 PLATE VIII. 
 
 Xanthoproteic Reaction. 
 
 Biuret Reaction. Most albumins sho^ 
 the color on the left, peptones that on th< 
 right. 
 
 Indican Reaction. 
 
 Murexid Test for uric acid. 
 
 Fehling's Test for sugar. 
 
 6 
 
 Botger's bismuth Test for sugar. 
 
 Gmelin's Test for biliary colorin 
 matters. 
 
 8 
 
 Diazo Reaction. 
 
 Affoen&Ca Litti Bultiinorf, ,\td. 
 
 For explanation of reactions see page in Index. 
 
URINE AND ITS CONSTITUENTS. 739 
 
 placed in the centre of the remaining stain, when concentric color 
 rings appear. The second portion of chloroform solution is evap- 
 orated and the residue used for making the reactions, as described 
 above. 
 
 Melanin (melanogen), the black pigment of the skin of the negro, has been 
 found in the urine of persons suffering from melanotic cancer and certain wast- 
 ing diseases. Urine containing melanin darkens on standing, turns black on 
 the addition of either nitric or chromic acid, and forms with bromine-water a 
 yellow precipitate rapidly turning dark. 
 
 Alkaptonic acids. Two of these acids occur in the urine of certain 
 otherwise healthy persons, and seem to be without clinical signifi- 
 cance. The acids are : Jiomogentisic acid, dioxphenyl-acetic acid, 
 C 6 H 3 (OH) 2 .CH 2 .CO 2 H, and uroleucic acid, dioxyphenyl-lactic acid, 
 C G H 3 (OH) 2 .C 2 H 3 .OH.C0 2 H. 
 
 Both acids reduce Fehling's solution, as also ammoniacal silver nitrate solu- 
 tion, but not bismuth solution ; they are optically inactive, do not form an 
 osazone, and do not ferment with yeast. 
 
 To test for alkaptonic acids, the urine should be acidified with hydrochloric 
 acid and then extracted with ether. The ethereal solution is evaporated, the 
 residue dissolved in water, and heated with Millon's reagent. In the presence 
 of alkaptonic acids a purple-red color is observed. 
 
 Diazo-reaction. Some abnormal constituent (which has not yet 
 been isolated) is found in the urine of certain diseases. The presence 
 of this unknown substance is indicated by a very characteristic reac- 
 tion with diazo-benzene-sulphonic acid, which compound is produced 
 by the action of nitrous acid on sulphanilic acid. Two solutions are 
 required : a. 5 grammes of sulphanilic acid dissolved in a mixture 
 of 50 c.c. of hydrochloric acid and 1000 c.c. of water; 6. a 0.5 
 per cent, solution of sodium nitrite. To perform the reaction 50 
 parts of a and 1 part of b are mixed, and equal volumes of the reagent 
 and of urine are mixed in a test-tube and saturated with ammonia. 
 In those cases in which the reaction is positive the solution assumes 
 a carmine-red color, which, on shaking, must also be visible in the 
 foam. If the test-tube is allowed to stand twenty-four hours, a 
 greenish precipitate is formed. Normal urine, thus treated, shows a 
 deep-yellow or orange to orange-red color; the precipitated phos- 
 phates as well as the foam are colorless. On Plate VIII., 8, the 
 color of the diazo-reaction is represented. Normal urine may show 
 the orange-red on the left, but the carmine-red on the right is char- 
 acteristic of the diazo-reaction. 
 
 If, instead of mixing the urine and reagent with ammonia water, 
 
740 PHYSIOLOGICAL CHEMISTRY. 
 
 the latter be allowed to float on the mixture, a carmine-red ring will 
 form at the zone of contact, when the reaction is positive. 
 
 It was formerly held that this test is pathognomonic of typhoid 
 fever. Later work has, however, shown that it usually is present in 
 typhoid fever and measles ; it is frequently present in erysipelas, 
 pneumonia, scarlet fever, diphtheria, and pulmonary tuberculosis ; it 
 is rarely present in acute rheumatic fever and cerebrospinal men- 
 ingitis. 
 
 It is, however, of much value in the diagnosis of typhoid fever, and 
 is thought to indicate a bad prognosis in pulmonary tuberculosis. 
 
 Functional tests of the kidney. Many attempts have been made 
 to find a substance which, when injected into the body, would be 
 excreted by the kidney in such a manner that examination of the 
 urine would show the ability of the kidneys to carry on their func- 
 tion of excretion. Among the substances tried are methylene-blue, 
 salicylic acid, and phloridzin. By far the most suitable substance 
 has recently been found in phenolsulphonephthalein (Geraghty- 
 Rowntree). This substance has no poisonous action, and is excreted 
 very rapidly by normal kidneys. It produces a red color in alkaline 
 solution, and its amount may thus be readily estimated by noting the 
 extent to which a standard solution must be diluted to produce the 
 same depth of color. It is somewhat more accurate to use a special 
 instrument, a colorimeter. After the injection of this drug (0.006 
 gramme) the unchanged drug will, under normal conditions, appear 
 in the urine in from five to eleven minutes, 50 per cent, is excreted 
 during the first hour, and from 60 to 80 per cent, during the first and 
 second hour together. 
 
 In diseases of the kidneys the initial appearance is delayed and the 
 hourly output is decreased. 
 
 Urinary deposits (sediments). Normal urine is always clear, but 
 occasionally, and particularly in abnormal conditions, it is turbid. 
 
 Urine may be turbid when passed, and this indicates an excess 
 of mucus, or the presence of renal epithelium, pus, blood, chyle, 
 semen, bile, fat-globules, or phosphates or urate of sodium in excess, 
 etc. A turbidity subsequent to the passage of the urine is generally 
 due to the precipitation of phosphates or urates, or it may result 
 from fermentation or decomposition. Either of the substances named 
 will form a deposit on standing. 
 
 When such a deposit is to be examined, a few ounces of the urine 
 should be set aside for several hours in a tall, narrow, cylindrical 
 
URINE AND ITS CONSTITUENTS. 
 
 741 
 
 glass or whirled in the centrifuge for a few minutes ; when the 
 sediment has collected at the bottom the supernatant urine may !><> 
 decanted, or the sediment may be taken out by means of a pipette 
 for examination. 
 
 Sediments are either organized or unorganized. To the first 
 belong: mucus, blood, pus, fat, urinary casts, epithelium, sprrmato- 
 zoids, fungi, infusoria, etc. ; to the second belong : uric acid, urates, 
 calcium oxalate, phosphate, or carbonate, magnesium-ammonium 
 phosphate, cystine, hippuric acid, etc. 
 
 The chemical examination of any urinary sediment should always 
 be preceded by a microscopical examination, which latter is in many 
 
 FIG. 76. 
 
 Various forms of uric acid crystals. (Finlayson.) 
 
 cases the only way of determining the nature of the sediment, espe- 
 cially of the organized substances. 
 
 Organized sediments. Red blood-corpuscles appear under the 
 microscope as reddish, circular disks, sometimes laid together in 
 strings. If seen in profile, they appear biconcave. 
 
 Pus cells (leucocytes) appear as round granular cells, in which the 
 nucleus frequently is not made out until dilute acetic acid is added. 
 
 Epithelial cells, from the urinary tubules, ureter, bladder, vagina, 
 etc. Their place of origin is frequently difficult to determine. 
 
 Casts. Hyaline, waxy, finely granular, coarsely granular, pus 
 casts, blood casts, epithelial casts. 
 
 Unorganized sediments, (a) In acid urine. Uric acid is deposited 
 in colored crystals from acid urine ; it is not dissolved by heat, nor 
 
742 
 
 PHYSIOLOGICAL CHEMISTRY. 
 
 by acetic or hydrochloric acid, but dissolves on the addition of caustic 
 potash and burns on platinum foil without leaving a residue ; it is 
 recognized by the murexide test. Uric acid crystallizes in many forms, 
 usually in rhombs with rounded corners, the so-called "whetstone 
 crystals." The crystals are usually brow 7 n. The sediment has a 
 
 FIG. 77. 
 
 Calcium oxalate crystals. (Finlayson.) 
 
 red crystalline appearance (" brick-dust "), and occurs in any concen- 
 trated, strongly acid urine. 
 
 Add urates (Na, K) form a voluminous sediment, amorphous under 
 the microscope, of a yellowish-brown or reddish color. This is the only 
 sediment which dissolves on heating. 
 
 FIG. 78. 
 
 Crystalline phosphates. (Finlayson.) 
 
 Calcium oxalate is rarely found in more than microscopic amounts. 
 The crystals are peculiarly clear, and have a double envelope, or 
 sometimes a dumb-bell appearance. 
 
 Magnesium-ammonium phosphate, or triple phosphate, MgNH 4 .- 
 PO 4 .6H 2 O, is found generally in triangular prisms with bevelled. 
 
URINE AND ITU CONSTITUENTS. 
 
 743 
 
 ends, but sometimes also in star-shaped, feathery crystals, due to the 
 partial dissolving of the first type. These crystals are most abundant 
 in alkaline urine, but are also present in faintly acid urines. They 
 dissolve in acetic acid. 
 
 (b) In alkaline urine. Ammonium-magnesium phosphate (vide supra). 
 
 FIG. 79. 
 
 Ammonium urate crystals. (C. E. Simon.) 
 
 Calcium and magnesium phosphates. These are basic phosphates. 
 They form the commonest sediment in alkaline urine, are amorphous, 
 dissolve with acetic acid, but not with heat. 
 
 FIG. 80. 
 
 y- 
 
 Crystals of leucine (different forms). (Crystals of creatinine-zinc chloride resemble the 
 leucine crystals depicted at a.) The crystals figured to the right consist of comparativelj 
 impure leucine. (Charles.) 
 
 (c) In ammoniacal urine. Ammonium-magnesium phosphate (vide 
 
 supra). 
 
 Ammonium urate is found, generally associated with amorphous or 
 crystalline phosphates, in urine which has become ammoniacal. 
 crystalline globules are generally covered with spinous excrescences, 
 which give them the characteristic "thorn-apple" appearance, and 
 have a yellow color. They are soluble in acetic acid. 
 
744 
 
 PHYSIOLOGICAL CHEMISTRY. 
 
 The following crystals occur only in abnormal urines : 
 Leucine, or amino-caproic acid, C 6 H n (XH 2 )O 2 , and Tyrosine, 
 C 9 H U NO 3 , are but rarely met with in urinary deposits. Leucine is 
 found either as rounded lumps, showing but little crystalline structure, 
 
 FIG. 81. 
 
 Tyrosine crystals. (Charles.) 
 
 or as spherical masses, exhibiting fine radial striation. Tyrosine 
 appears generally in fine, long, silky needles, forming bundles or 
 rosettes. 
 
 Cystine occurs occasionally as a grayish, crystalline deposit, form- 
 
 FIG. 82. 
 
 Crystals of cystine spontaneously voided with urine. (Roberts.) 
 
 ing transparent six-sided plates ; it also occurs in calculi. The latter 
 may be recognized by the chemical properties mentioned below, or by 
 dissolving a little in hydrochloric acid and neutralizing with ammonia, 
 when cystine is reprecipitated and shows the characteristic six-sided 
 plates under the microscope. 
 
URINE AND ITS CONSTITUENTS. 745 
 
 Urinary calculi are solid deposits of various sizes formed from 
 the urine within the kidney, ureter, bladder, and urethra. They 
 may contain all the constituents of urine which occur as sediments, 
 and also certain pathological constituents deposited around an organic 
 framework. 
 
 Calculi are cal led primary when formed in unchanged urine, and secondary 
 when they are formed in urine which has undergone decomposition. Uric 
 acid, calcium oxalate, calcium carbonate, xanthine, and cystic calculi are 
 primary formations, while ammonium urate, phosphatic and urostealith calculi 
 3,re secondary. 
 
 During the development of a calculus the original deposit may be covered 
 by a layer of a different material, which in turn may be covered by another 
 substance. For this reason a simple stone may be converted into a compound 
 one. In this way a primary stone, by irritation of the bladder producing 
 cystitis, accompanied by alkaline fermentation, causes a deposition of phos- 
 phates, and is converted into a secondary calculus. The further action of the 
 alkaline urine may dissolve the primary calculus, replacing it with phosphates. 
 
 In examining calculi it is necessary to make a section through the 
 centre of the calculus and scrape off a little from each layer, the 
 portions being examined separately. They may be found to be alike 
 (simple calculi) or unlike (compound or mixed calculi) in composi- 
 tion. The following scheme serves for a qualitative examination of 
 calculi. Heat some of the powdered calculus on platinum foil, when 
 the material will either burn and char without a flame (A), or burn 
 with a flame (B), or will not burn at all (C). (It should be remem- 
 bered that a calculus generally contains a little organic matter, so that 
 slight carbonization is always to be expected on heating it.) 
 
 A. To the material burning without a distinct flame apply the 
 murexide test. If affirmative, uric acid or urates are indicated. 
 Heat some powder with potassium hydroxide; a strong odor of 
 ammonia proves the calculus to consist of ammonium urate; a nega- 
 tive result shows it to be uric acid. If the murexide test was nega- 
 tive, test for xanthine. The powder wall dissolve in nitric acid 
 without effervescence, leave on evaporation a yellow residue, turning 
 orange with alkali and red on heating. 
 
 B. Material burning with a distinct flame may either be soluble 
 in alcohol and ether (urostealith) or insoluble in these solvents, but 
 soluble in potassium hydroxide solution on heating (fibrin), or soluble 
 both in hydrochloric acid and in caustic alkalies (cystine). Urostea- 
 lith burns with a yellow flame and emits the odor of burning resin. 
 Fibrin burns also with a yellow flame, but emits odor of burnt 
 feathers. Cystine burns with a pale-blue flame, emitting a peculiar 
 
746 PHYSTOLOGICAL CHEMISTRY. 
 
 sharp odor. On evaporation of its solution in ammonia it separates 
 in characteristic six-sided plates. 
 
 C. Material which does not burn may consist of calcium car- 
 bonate, calcium oxalate, or phosphates. Calcium carbonate shows 
 effervescence with all acids, and the solution, after being neutralized, 
 is precipitated by ammonium oxalate. Calcium oxalate does not 
 effervesce with hydrochloric acid directly, but does so after being 
 heated, when carbonate is formed and is tested for as such. The 
 presence of phosphates is indicated by the presence of a yellow pre- 
 cipitate, produced in the solution in nitric acid by ammonium molyb- 
 date. When the phosphates, on heating with caustic potash, evolve 
 ammonia gas, magnesium ammonium phosphate is present ; when the 
 test is negative the calculus consists of calcium phosphate, which can 
 be verified by dissolving the powder in hydrochloric acid, neutral- 
 izing with ammonia, redissolving the precipitate in acetic acid, and 
 adding ammonium oxalate, when a white precipitate is formed. 
 
 Most common are calculi of uric acid ; often met with are those of 
 urates, phosphates, and oxalates ; rarely, however, those of xanthine, 
 cystine, fibrin, and urostealith. 
 
 QUESTIONS. What is urine, where and by what process is it formed in the 
 animal body, and what is its function? Mention the general physical and 
 chemical properties of urine. Give the composition of human urine, and state 
 by what conditions the composition is influenced. State the composition and 
 properties of urea. By what process is urea formed in the animal body, and 
 how can it be obtained artificially ? Describe a process by which urea may be 
 estimated quantitatively in urine. In what forms is uric acid found in urine, 
 and what are its properties? Describe the murexide test. How can uric acid 
 be determined quantitatively in urine? What is hippuric acid, and by what 
 tests may it be recognized ? What points are to be considered, and what sub- 
 stances determined, in the analysis of normal and abnormal urine? What is 
 the color of urine, and what are the chief causes influencing the color ? What 
 is the specific gravity of healthy urine, how is it determined, and how is the 
 total amount of solids approximately calculated from the specific gravity? 
 Describe the different tests by which albumin may be recognized, and state the 
 precautions necessary in making these tests. How may the quantity of al- 
 bumin in urine be determined approximately, and also accurately? Describe 
 the various tests for sugar. On what principles are they based, and how can 
 sugar be distinguished from other reducing substances occurring in urine? 
 How is sugar determined quantitatively ? By what tests are biliary pigments 
 and acids recognized in urine? What is the nature of urinary sediments, and 
 by what means are they recognized? What are urinary calculi generally com- 
 posed of, and by what simple tests can their nature be determined? 
 
APPENDIX. 
 
 TABLE OF WEIGHTS AND MEASURES. 
 
 Measures of length. 
 
 1 
 
 millimeter 
 
 = 
 
 0.001 
 
 meter 
 
 = 0.0393/ 
 
 1 
 
 centimeter 
 
 
 
 0.01 
 
 meter 
 
 = 0.3937 
 
 1 decimeter 
 
 0.1 
 
 meter 
 
 = 3.937 
 
 1 
 
 meter 
 
 
 
 
 = 39.37 
 
 1 
 
 decameter 
 
 = 
 
 10 
 
 meters 
 
 = 32.8083 
 
 1 
 
 hectometer 
 
 = 
 
 100 
 
 meters 
 
 = 328.083 
 
 1 
 
 kilometer 
 
 r=r 
 
 1000 
 
 meters 
 
 = 0.6213' 
 
 1 
 
 1 
 
 yard or 36 
 inch 
 
 inches 
 
 = 0.9144 
 = 25.4 
 
 inch. 
 
 inches. 
 
 inches. 
 
 feet. 
 
 feet. 
 
 mile. 
 
 meter. 
 
 millimeters. 
 
 1 milliliter 
 1 centiliter 
 1 deciliter 
 1 liter 
 1 decaliter 
 1 hectoliter 
 1 kiloliter 
 1 U. S. gallon 
 1 imperial gallon 
 1 minim 
 1 fluidrachm 
 1 fluidounce 
 1 liter 
 
 Measures of capacity. 
 
 1 c.c. == 0.001 liter = 
 
 10 c.c. = 0.01 liter = 
 
 100 c.c. = 0.1 liter = 
 1000c.c. 
 
 = 10 liters = 
 
 = 100 liters = 
 
 = 1000 liters = 
 
 0.0021 
 0.0211 
 0.2113 
 1.0567 
 2.6417 
 26.417 
 264.17 
 3785.43 
 4543.5 
 0.06 
 3.70 
 29.57 
 33.81 
 
 U. S. pint. 
 
 U. S. pint 
 
 U. S pint. 
 
 U. 8. quart. 
 
 U. S. gallons. 
 
 U. S. gallons. 
 
 U. S. gallons. 
 
 c.c. 
 
 c.c. 
 
 c.c. 
 
 c.c. 
 
 c.c. 
 
 fluidounces. 
 
 Weights. 
 
 1 milligram 
 
 = 
 
 0.001 
 
 gramme 
 
 1 centigram 
 
 = 
 
 0.01 
 
 gramme 
 
 1 decigram 
 
 = 
 
 01 
 
 gramme 
 
 1 gramme 
 
 
 
 
 1 decagram 
 
 = 
 
 10 
 
 grammes 
 
 1 hectogram 
 
 = 
 
 100 
 
 grammes 
 
 1 kilogram 
 
 =. 
 
 1000 
 
 grammes 
 
 1 kilogram 
 
 
 
 
 1 grain Troy 
 
 
 
 
 1 drachm Troy 
 
 
 
 
 1 ounce Troy 
 
 
 
 
 1 ounce avoirdupois 
 
 1 pound avoirdupois 
 
 0.015 grain 
 
 0.154 grain 
 
 1.543 grain 
 
 15.432 grains 
 
 154.324 grains 
 
 0.268 pound Troy. 
 2.679 pounds Troy. 
 2.2046 pounds avoirdupois. 
 0.0648 gramme. 
 3.888 grammes. 
 31.103 grammes. 
 28.350 grammes. 
 453.592 grammes. 
 
 (747) 
 
748 APPENDIX. 
 
 Commercial weights and measures of the U. A. 
 
 1 pound avoirdupois = 16 ounces. 
 
 1 ounce = 437.5 grains. 
 
 1 gallon = 231 cubic inches. 
 
 1 gallon = 4 quarts = 8 pints. 
 
 1 pint of water weighs 7291.2 grains at a temperature of 15.6. 
 
 Apothecarie^ weights. 
 
 The apothecaries' ounce is of the same value as the now obsolete English Troy 
 ounce. 
 
 1 ounce 8 drachms 480 grains. 
 
 1 drachm 3 scruples 60 grains. 
 
 1 scruple 20 grains. 
 
 1 ounce 31.103 grammes. 
 
 1 grain 64.799 milligrams. 
 
 Apothecaries' fluid measures. 
 
 These are derived from the U. S. gallon ; the liquid pint of this gallon is identical 
 in value with the apothecaries' pint. 
 
 1 pint 16 fluidounces 7680 minims. 
 
 1 fluidounce = 8 fluidrachms 480 minims. 
 
 1 fluidrachm 60 minims. 
 
 Jewelers' weight. 
 1 carat = 0.205 gramme 3.163 grains. 
 
TABLE OF ELEMENTS AND ATOMIC WEIGHTS. 
 
 On the basis H^= 1 (U. S. P., VIII.) and O = 16 (International \\Vights, 1912). 
 
 Name. 
 
 Atomic weights. 
 Symbol. H==1 Q==16 
 
 Name. Symbol 
 
 Atomic weights. 
 H = 1 = 16 
 
 Aluminum 
 
 . . Al 
 
 26.9 
 
 27.1 
 
 Neodymium . . 
 
 .Nd 
 
 142.5 
 
 144.3 
 
 Antimony . . 
 
 . . Sb 
 
 119.3 
 
 120.2 
 
 Neon 
 
 . Ne 
 
 19.9 
 
 20.2 
 
 Argon . . . 
 
 A 
 
 39.6 
 
 39.88 
 
 Nickel 
 
 Ni 
 
 58.3 
 
 58.68 
 
 Arsenic . . . 
 
 . . As 
 
 74.4 
 
 74.96 
 
 Nitrogen . . . 
 
 .N 
 
 13.93 
 
 14.07 
 
 Barium . 
 
 Ba 
 
 136.4 
 
 137.37 
 
 Osmium 
 
 Os 
 
 189.6 
 
 ion q 
 
 Bismuth . . 
 
 . . Bi 
 
 206.9 
 
 208 
 
 Oxygen .... 
 
 .O 
 
 15.88 
 
 1 *7U. 7 
 
 16 
 
 Boron 
 
 B 
 
 10.9 
 
 ]1 
 
 "P?i 1 1 Q f\ i n m 
 
 Pd 
 
 10^ 7 
 
 lOfi 7 
 
 Bromine . . 
 
 . . Br 
 
 79.36 
 
 79.92 
 
 i .1 1 i.u 1 1 1 in i 
 
 Phosphorus . . 
 
 JTil 
 
 . P 
 
 J.UO. t 
 
 30.77 
 
 -lUv). / 
 
 31.04 
 
 Cadmium . . 
 
 . . Cd 
 
 111.6 
 
 112.4 
 
 Platinum . . . 
 
 .Pt 
 
 193.3 
 
 195.2 
 
 Caesium . . . 
 
 . . Cs 
 
 131.9 
 
 132.81 
 
 Potassium . . . 
 
 . K 
 
 38.86 
 
 39.1 
 
 Calcium . . 
 
 . . Ca 
 
 39.8 
 
 40.07 
 
 Praseodymium 3 
 
 . Pr 
 
 139.4 
 
 143.6 
 
 Carbon . . . 
 
 . . C 
 
 11.91 
 
 12 
 
 Radium .... 
 
 . Ra 
 
 223 
 
 226.4 
 
 Cerium . . . 
 
 . . Ce 
 
 139.2 
 
 140.25 
 
 Rhodium . . . 
 
 .Rh 
 
 102.2 
 
 102.9 
 
 Chlorine . . 
 
 . . Cl 
 
 35.18 
 
 35.46 
 
 Rubidium . . . 
 
 .Kb 
 
 84.8 
 
 85.45 
 
 Chromium 
 
 . . Cr 
 
 51.7 
 
 52 
 
 Ruthenium . . 
 
 .Ru 
 
 100.9 
 
 101.7 
 
 Cobalt . . . 
 
 . . Co 
 
 58.56 
 
 58.97 
 
 Samarium . . . 
 
 .Sm 
 
 148.9 
 
 150.4 
 
 Columbium 1 . 
 
 . . Cb 
 
 93.3 
 
 93.5 
 
 Scandium . . . 
 
 .80 
 
 43.8 
 
 44.1 
 
 Copper . . . 
 
 . . Cu 
 
 63.1 
 
 63.57 
 
 Selenium . . . 
 
 . 8e 
 
 78.6 
 
 79.2 
 
 Erbium 
 
 Er 
 
 164.8 
 
 167.7 
 
 Silicon .... 
 
 . Si 
 
 28.2 
 
 28.3 
 
 J; luorine 
 
 F 
 
 18.9 
 
 19 
 
 Silver 
 
 As 
 
 107.12 
 
 107.88 
 
 Gadolinium 
 
 17 
 
 . . Gd 
 
 155.8 
 
 157.3 
 
 Sodium .... 
 
 ' -"o 
 
 .Na 
 
 22.88 
 
 23 
 
 Gallium . . 
 
 . . Ga 
 
 69.5 
 
 69.9 
 
 Strontium . . . 
 
 .Sr 
 
 86.94 
 
 87.63 
 
 Germanium . 
 
 . - Ge 
 
 71.9 
 
 72.5 
 
 Sulphur .... 
 
 .S 
 
 31.83 
 
 32.07 
 
 Glucinum 2 . 
 
 . . Gl 
 
 9.03 
 
 9.1 
 
 Tantalum . . . 
 
 . Ta 
 
 181.6 
 
 181.5 
 
 Gold .... 
 
 . . Au 
 
 195.7 
 
 197.2 
 
 Tellurium . . . 
 
 .Te 
 
 126.6 
 
 127.5 
 
 Helium - . . 
 
 . .He 
 
 3.99 
 
 3.99 
 
 Terbium . . . 
 
 .Tb 
 
 158.8 
 
 159.2 
 
 Hydrogen . . 
 
 . . H 
 
 1.00 
 
 1.008 
 
 Thallium . . . 
 
 . Tl 
 
 202.6 
 
 204 
 
 Indium . . . 
 
 . . In 
 
 113.1 
 
 114.8 
 
 Thorium . . . 
 
 . Th 
 
 230.8 
 
 232.4 
 
 Iodine 
 
 I 
 
 125.9 
 
 126.92 
 
 Thulium . . 
 
 .Tm 
 
 169.7 
 
 168.5 
 
 Iridium . 
 
 Tr 
 
 mK 
 
 1Q<J 1 
 
 Tin 
 
 . Sn 
 
 118.1 
 
 119 
 
 Iron .... 
 
 . ir 
 . . Fe 
 
 .O 
 
 55.5 
 
 -L/O. i. 
 
 55.84 
 
 Titanium . . . 
 
 .Ti 
 
 47.7 
 
 48.1 
 
 Krypton . . 
 
 . . Kr 
 
 81.2 
 
 82.92 
 
 Tungsten . . . 
 
 . W 
 
 182.6 
 
 184 
 
 Lanthanum . 
 
 . . La 
 
 137.9 
 
 139 
 
 Uranium . . . 
 
 .U 
 
 236.7 
 
 238.5 
 
 Lead .... 
 
 . . Pb 
 
 205.35 
 
 207.1 Vanadium . 
 
 . V 
 
 50.8 
 
 51 
 
 Lithium . . . 
 
 . . Li 
 
 6.98 
 
 6.94 Xenon . 
 
 . Xe 
 
 127 
 
 130.2 
 
 Magnesium . 
 
 Mg 
 
 24.18 
 
 24.32 
 
 Ytterbium . . 
 
 . Yb 
 
 171.7 
 
 172 
 
 Manganese 
 
 . Mn 
 
 54.6 
 
 54.93 
 
 Yttrium .... 
 
 . Yt 
 
 88.3 
 
 89 
 
 Mercury . . 
 
 Hg 
 
 198.5 
 
 200.6 
 
 Zinc 
 
 . Zn 
 
 64.9 
 
 65.87 
 
 Molybdenum 
 
 . . Mo 
 
 95.3 
 
 96 
 
 Zirconium . . . 
 
 . Zr 
 
 89.9 
 
 90.6 
 
 1 Also called Niobium, 
 
 Nb. 2 Also called Beryllium, Be. 3 Also called Didymium, Di. 
 
 749 
 
INDEX. 
 
 A. 
 
 ABSOLUTE temperature, 47 
 
 weight, 32 
 
 zero, 48 
 Absorption, 676, 687, 689 
 
 by charcoal, 39 
 
 by liquids, 39 
 
 by solids, 40 
 
 spectra, 61 
 Acacia, 536 
 Accumulator, 320 
 Acetanilide, 565 
 Acetates, 503 
 Acetic aldehyde, 491 
 
 anhydride, 505 
 
 ether, 522 
 Acetone, 494 
 
 in urine, 736 
 Aceto-nitrile, 555 
 Acetoximes, 541 
 Acetphenetidin, 572 
 Acetyl chloride, 505 
 
 oxide, 505 
 Acetylene, 473 
 Acid, abietic, 599 
 
 acetic, 500 
 
 glacial, 501 
 
 mono-, di-, and trichlor-, 504 
 
 acetyl-salicylic, 584 
 
 acrylic, 494 
 
 amino-acetic, 544 
 
 ammo-formic, 545 
 
 amino-succinamic, 543, 546 
 
 amino-succinic, 543 
 
 anisic, 585 
 
 arabic, 536 
 
 arsenic, 349 
 
 arsenous, 348 
 
 aspartic, 546 
 
 barbituric, 547 
 
 benzoic, 579, 701 
 
 beta-oxybutyric, 736 
 
 boric or boracic, 187, 701 
 
 bromic, 240 
 
 butyric, 505 
 
 cacodylic, 478 
 
 camphoric, 599 
 
 carbamic, 269, 545 
 
 carbazotic, 572 
 
 carbolic, 569 
 
 carbonic, 180 
 
 chloric, 237 
 
 Acid, chlorpplatinic, 235, 367 
 chromic, 308 
 citric, 516 
 cyanic, 553 
 diacetic, 736 
 dichromic, 308 
 digallic, 586 
 disulphuric, 212 
 ethyl-sulphuric, 521 
 formic, 500 
 fulminic, 541 
 galactonic, 532 
 gallic, 586 
 glacial acetic, 501 
 
 phosphoric, 226 
 gluconic, 531 
 
 glycerin-phosphoric, 448, 670 
 glycocholic, 685 
 glycolic, 511 
 glycuronic, 735 
 hippuric, 717 
 homogentisic, 739 
 hydrazoic, 170 
 hydriodic, 242 
 hydrobromic, 239 
 hydrochloric, 232 
 hydrocyanic, 548 
 hydroferricyanic, 554 
 hydroferrocyanic, 554 
 hydrofluoric, 244 
 hydrofluosilicic, 186 
 hydroxy-acetic, 511 
 hydroxy-propionic, 511 
 hypobromous, 240 
 hypochlorous, 236 
 hyponitrous, 173 
 hypophosphorous, 223 
 hyposulphurous, 213 
 indoxyl-sulphuric, 721 
 iodic, 243 
 lactic, 511 
 malic, 512 
 malonic, 508 
 manganic, 303 
 meconic, 615 
 metaboric, 187 
 metaphosphoric, 226 
 met-arsenic, 349 
 met-arsenous, 348 
 meta-stannic, 363 
 molybdic, 368 
 mucic, 532 
 muriatic, 232 
 
 751 
 
752 
 
 INDEX. 
 
 Acid, myronic, 556 
 naphthionic, 590 
 naphthylamine sulphonic, 590 
 nicotinic, 593 
 nitric, 174 
 
 ionic explanation of liberation 
 
 of, 195 
 
 nitro-hydrochloric, 235 
 nitro-muriatic, 235 
 nitrosyl-sulphuric, 209 
 nitrous, 173 
 
 estimation by metaphenylene- 
 
 diamine, 432 
 oleic, 506 
 oxalic, 508 
 palmitic, 506 
 parabanic, 547 
 perchloric, 238 
 perchromic, 310 
 permanganic, 303, 305 
 persulphuric, 214 
 phenolsulphonic, 573 
 phosphocarnic, 668 
 phospho-molybdic, 601 
 phosphoric, 226 
 phosphorous, 225 
 phthalic, 581 
 picric, 572 
 prussic, 548 
 pyrogallic, 576 
 pyrophosphoric, 226 
 pyrosulphuric, 212 
 pyrotartaric, 508 
 racemic, 513 
 rosolic, 410 
 saccharic, 531 
 salicylic, 583, 701 
 salts, definition of, 122 
 santonic, 590 
 sarcolactic, 511, 669 
 silicic, 186 
 sozolic, 573 
 stannic, 362 
 stearic, 506 
 succinic, 508 
 sulphanilic, 566 
 sulphocarbolic, 573 
 sulphocyanic, 553 
 sulpho-vinic, 521 
 sulphuric, 208 
 sulphurous, 206 
 tannic, 586 
 tartaric, 512 
 
 isomerism of, 513 
 tauro-cholic, 685 
 tetraboric, 187 
 thiosulphuric, 213 
 triazoic, 170 
 trichlor-acetic, 504 
 uric, 715, 741 
 
 estimation of, 716 
 uroleucic, 739 
 valeric, 505 
 Acidic oxides, 117 
 
 Acidimetry, 412 
 
 Acids, activity or strength of, 200 
 
 alkaptonic, 739 
 amino-, 544 
 aromatic, 579 
 definition of, 117 
 detection of, 391 
 
 dissociation theory applied to, 199 
 fatty, 496 
 
 monobasic, 496 
 
 hydroxy-, organic, 510 
 
 ions formed by, 200 
 
 thio-, 212 
 Aconitine, 617 
 Acrolein, 493 
 
 phenyl, 578 
 Acrylic aldehyde, 493 
 Actinic waves, 56 
 Actinium, 84 
 Action, catalytic, 154 
 
 contact, 154 
 
 endothermic, 91 
 
 exothermic, 91 
 
 reversible, 114 
 Activators, 638 
 Activity, optical, 67 
 Adamkiewicz's reaction, 627 
 Adhesion, 37 
 Adrenalin, 670 
 Affinity, chemical, 92 
 After-damp, 184 
 Agglutinins, 660 
 Agucarine, 581 
 Air, analysis of, 166 
 
 expired, 182 
 
 liquefaction of, 166 
 Alabaster, 277 
 
 Albumin, tests for, in urine, 726 
 Albuminoids, 628 
 Albuminometer, Esbach's, 726 
 Albumins, 627 
 Alcohol, 482 
 
 absolute, 483 
 
 allyl, 486 
 
 amyl, 486 
 
 benzyl, 577 
 
 denatured, 485 
 
 diluted, 483 
 
 ethyl, 482 
 
 methyl, 482 
 
 salicylic, 584 
 Alcoholic liquors, 485 
 Alcoholometers, 34 
 Alcohols, 479 
 
 aromatic, 577 
 
 primary, secondary, and tertiary, 
 479 
 
 sulpho-, 495 
 
 thio-, 495 
 Aldehyde, acetic, 491 
 
 acrylic, 493 
 
 benzoic, 577 
 
 cinnamic, 578 
 
 formic, 490 
 
INDEX. 
 
 753 
 
 Aldehyde, methylprotocatechuic, 578 
 Aldehydes, 489 
 
 aromatic, 577 
 Aldoses, 530 
 Aldoximes, 541 
 Alkali-metals, remarks on, 255 
 
 summary of tests, 272 
 Alkalimeter, 34 
 Alkalimetry, 412 
 Alkaline-earth metals, 277 
 
 summary of tests, 285 
 Alkaloids, 600 
 
 antidotes for, 602 
 
 cadaveric, 617 
 
 classification, 603 
 
 detection of, in poisoning, 602 
 Alkyl, definition of, 474 
 Alkylene, definition of, 474 
 Allantoin, 717 
 Allotropic modifications, 129 
 
 silver, 331 
 Allotropy, 129 
 Alloxur bases, 667 
 Alloys, 253, 323 
 
 aluminum, 286 
 
 antimony, 358 
 
 arsenic, 347 
 
 bismuth, 327 
 
 copper, 323 
 
 dental, 254, 337 
 
 gold, 366 
 
 iron, 294 
 
 lead, 319 
 
 manganese, 303 
 
 manufacture of, 254 
 
 platinum, 367 
 
 pot-metal, 254 
 
 properties of, 254 
 
 silver, 331 
 
 tin, 323 
 
 zinc, 313, 323 
 Allyl alcohol, . 486 
 
 iodide, 486 
 
 isosulphocyanate, 556 
 
 mustard oil, 557 
 
 sulphide, 557 
 
 thio-urea, 557 
 Alpha-derivatives, 588, 624 
 
 -naphthol, 589 
 
 -naphthylamine, 589 
 Alum, ammpnio-ferric, 299 
 
 ammonium, 287 
 
 burnt, 287 
 
 chrome, 310 
 
 definition of an, 286 
 
 iron, 299 
 
 potassium, 287 
 Alumina, 287 
 Aluminates, 288 
 Aluminum, 285 
 
 acetate, 287 
 
 alloys of, 286 
 
 and ammonium sulphate, 287 
 
 and potassium sulphate, 287 
 
 48 
 
 Aluminum-bronze, 286 
 
 carbide, 466 
 
 chloride, 289 
 
 hydroxide, 287 
 
 oxide, 286, 288 
 
 silicate, 289 
 
 sulphate, 288 
 Alypin, 607 
 Amalgams, 253, 337 
 
 dental, 337 
 Amber, 599 
 Amboceptors, 661 
 Amides, 543 
 Amine, di- and triethyl-, 620 
 
 di- and trimethyl-, 620 
 
 diphenyl-, 566 
 
 ethyl, 620 
 
 isoamyl, 620 
 
 methyl, 620 
 
 propyl, 620 
 Amines, 541 
 
 primary, secondary, and tertiary, 
 
 542 
 
 Amino-acids, 544 
 Aminoform, 543 
 Ammeter, 77 
 Ammonia, 167 
 
 albuminoid, 431 
 
 aromatic spirit of, 269 
 
 determination by Nessler's solu- 
 tion, 431 
 
 from atmospheric nitrogen, 553 
 
 in urine, 714 
 
 ionic explanation of liberation of, 
 194 
 
 liniment, 526 
 
 water, 169 
 Ammonium, 268 
 
 acetate, 503 
 
 acid urate, 743 
 
 -amalgam, 268 
 
 benzoate, 580 
 
 bromide, 270 
 
 carbamate, 269 
 
 carbonate, 269 
 
 chloride, 269 
 
 hydrogen sulphide, 270 
 
 hydroxide, 169 
 
 iodide, 270 
 
 molybdate, 368 
 
 nitrate, 270 
 
 persulphate, 214 
 
 phosphate, 270 
 
 salicylate, 583 
 
 sesquicarbona '?, 269 
 
 sulphate, 270 
 
 sulphide, 270 
 
 sulphydrate, 270 
 
 urate, 743 
 
 valerate, 506 
 Amorphism, 21 
 Ampere, 77 
 Amperemeter, 77 
 Amphoteric reaction, 707 
 
754 
 
 INDEX. 
 
 Amygdalin, 578 
 Amyl alcohol, 486 
 
 nitrite, 523 
 Amylases, 637 
 Amylene, 472 
 
 hydrate, 486 
 Amyloid, 537, 630 
 Amylopsin, 682 
 Analysis, 151 
 
 of air, 166 
 
 definition of, 371 
 
 gas, 427 
 
 gravimetric, 402 
 
 milk, 701 
 
 proximate, 443 
 
 qualitative, 371 
 
 of organic compounds, 442 
 
 quantitative, 371, 402 
 
 spectroscopic, 62 
 
 ultimate or elementary, of organic 
 compounds, 442 
 
 volumetric, 402 
 
 water, 429 
 Analytical chemistry, 371 
 
 reactions. See Tests. 
 
 ionic explanation of, 200 
 Anesthesin, 580 
 Anethol, 584 
 Anhydride of acids, 117, 141 
 
 acetic, 505 
 
 arsenic, 349 
 
 arsenous, 348 
 
 chromic, 308 
 
 phthalic, 581 
 
 Anhydrous, definition of, 152 
 Aniline, 564 
 
 -blue, 566 
 
 dyes, 564 
 Animal charcoal, 280 
 
 fluids and tissues, 649 
 
 food, 641 
 Anions, 190 
 Annealing, 252 
 Annidalin, 575 
 Anode, 75, 190 
 Antibodies, 660 
 Antidiabetin, 581 
 Antidotes to acetic acid, 502 
 
 alkalies, 257 
 
 alkaloids, 602 
 
 antimony, 361 
 
 arsenic, 358 
 
 barium, 284 
 
 copper, 326 
 
 hydrochloric acid, 233 
 
 hydrocyanic acid and its salts, 552 
 
 hydrogen sulphide, 214 
 
 lead, 322 
 
 mercury, 345 
 
 nitric acid, 177 
 
 oxalic acid, 509 
 
 phenol, 571 
 
 phosphorus, 222 
 
 silver, 334 
 
 Antidotes sulphuric acid, 212 
 
 zinc, 317 
 Antifebrin, 565 
 Antigen, 661 
 Antimonites, 359 
 Antimony, 358 
 
 alloys, 358 
 
 and potassium tartrate, 361, 515 
 
 black, 358 
 
 butter of, 360 
 
 chlorides, 360 
 
 crude, 358 
 
 golden sulphuret of, 360 
 
 oxides, 359 
 
 oxychloride, 360 
 
 spots, difference from arsenic, 357 
 
 sulphides, 359 
 
 sulpho-salts, 359 
 Antimonyl chloride, 360 
 Antipyrine, 591 
 
 derivatives, 592 
 
 incompatibles, 592 
 
 isonitroso, 592 
 Antiseptics, 457 
 i Antitoxin, 661 
 | Apatite, 219 
 I Apomorphine, 613 
 Apparatus for qualitative analysis, 371 
 
 quantitative analysis, 403-407 
 Apparent weight, 32 
 Aqua fortis, 174 
 
 regia, 235 
 Argentum, 330 
 
 Crede, 331 
 Argol, 512 
 Argon, 166 
 Argonin, 334 
 Argyrol, 334 
 Aristol, 575 
 Armature, 74, 78 
 Aromatic acids, 579 
 
 alcohols, 577 
 
 aldehydes, 577 
 
 compounds, 557 
 
 containing arsenic and phos- 
 phorus, 568 
 difference from fatty, 558, 561 
 
 hydroxy-acids, 583 
 Arsenetted hydrogen, 350 
 Arsenic, 346 
 
 alloys of, 347 
 
 chloride, 347 
 
 detection in cases of poisoning, 357 
 
 group of metals, remarks on, 346 
 summary of tests, 368 
 
 and mercury iodide, 351 
 
 pentoxide, 349 
 
 spots distinguished from anti- 
 mony, 357 
 
 sulphides, 347, 350 
 
 trioxide, 348 
 Arsenobenzene, 568 
 Arsenous anhydride, 348 
 
 iodide, 351 
 
INDEX. 
 
 755 
 
 Arsenous oxide, 348 
 Arsine, 350 
 Artiads, 104 
 Asbestos, 272 
 Asepsis, 458 
 Aseptol, 573 
 Asparagine, 546 
 Asphalt, 599 
 Aspirin, 584 
 Atmospheric air, 165 
 
 pressure, 36 
 Atomic theory, Dalton's, 96 
 
 weight, definition, 98 
 
 determination of, 105 
 Atomicity, 103 
 Atoms, definition, 98 
 Atoxyl, 568 
 Atropine, 605 
 Attraction, capillary, 37 
 
 molecular, 19 
 Auric chloride, 366 
 Auripigment, 347 
 Avogadro's law, 30 
 Azo compounds, 567 
 
 dyes, 567 
 
 B. 
 
 BABBIT-METAL, 323 
 Bacillus bulgaricus, 700 
 Baking-powders, 264 
 
 -soda, 264 
 Balsam, 599 
 
 copaiva, 599 
 Barite, 283 
 Barium, 283 
 
 carbonate, 283 
 
 chloride, 283 
 
 cyanide from barium carbide, 553 
 
 dioxide, 283 
 
 nitrate, 284 
 
 oxide, 283 
 
 platinocyanide, 368 
 
 sulphate, 283 
 Barley sugar, 533 
 Barometer, 34 
 Basalt, 286 
 Bases, activity of, 201 
 
 definition of, 118 
 
 dissociation theory applied to, 
 200 
 
 organic, 541 
 
 Basic salts, definition of, 122 
 Battery, storage, 320 
 B< inuerel rays, 84 
 Beer, 486 
 Beet-sugar, 533 
 Bell-metal, 323 
 
 Bence-Jones body in urine, 727 
 Benzaldehyde, 577 
 Benzene, 562 
 
 diamino-, 566 
 
 nitro-, 563 
 
 series of hydrocarbons, 562 
 
 Benzene theory, 558 
 Benzin, 468 
 Benzol, 562 
 
 hexahydroxy-, 532 
 Benzosulphinide, 580 
 Benzoyl chloride, 580 
 
 -ecgonine, 606 
 
 -naphthol, 589 
 Benzoylation, 580 
 Benzyl alcohol, 577 
 Berberine, 615 
 Beta-derivatives, 588, 624 
 
 -eucaine hydrochloride, 607 
 
 -naphthol, 588 
 bcnzoate, 589 
 -bismuth, 589 
 
 -naphthylamine, 590 
 Betaine, 620 
 Bettendorf's test, 354 
 Bile, 684 
 
 detection in urine, 737 
 Biliary acids, 685 
 
 calculi, 686 
 
 pigments, 684 
 Bilirubin, 685 
 Biliverdin, 685 
 Bismark brown, 567 
 Bismuth, 327 
 
 alloys, 327 
 
 and ammonium citrate, 518 
 
 beta-naphthol, 589 
 
 citrate, 517 
 
 nitrate, 328 
 
 oxides of, 327 
 
 oxy-, or subcarbonate, 329 
 or subchioride, 330 
 subnitrate, 328 
 subsalts, 328 
 
 subgallate, 586 
 
 subsalicylate, 584 
 
 tribrom-phenolate, 572 
 Bismuthyl salts, 328 
 Biuret, 712 
 
 reaction, 627 
 Black antimony, 358 
 
 -ash, 263 
 
 -lead, 178 
 
 -wash, 337 
 
 Bleaching-powder, 280 
 Blood, 651 
 
 coagulation of, 653 
 
 in urine, 728 
 
 occult, 691 
 
 -pigments, 656 
 
 plasma, 652 
 
 -serum, immune bodies of, 660 
 
 -stains, examination of, 659 
 Blue mass, 336 
 
 pill, 336 
 
 Prussian, 301, 554 
 
 stone, 325 
 
 Turnbull's, 301, 555 
 
 vitriol, 325 
 Boiling, 52 
 
756 
 
 INDEX. 
 
 Boiling-point, 53 
 
 determination of, 54 
 
 of solutions, 161 
 Bonds, double and triple, 471 
 Bone, 662 
 
 -ash, 279 
 
 -black, 279 
 
 -oil, 590 
 Borax, 187, 266 
 
 glass, 266 
 
 in milk, 701 
 Boroglycerin, 487 
 Boron, 187 
 
 trioxide, 187 
 
 Botger's bismuth test, 731 
 Boyle's law, 26 
 Brain, 670 
 Brandy, 486 
 Brass, 323 
 Braunite, 303 
 Bricks, 289 
 
 Bright line spectra, 61 
 Brimstone, 205 
 Erin's process, 138 
 British gum, 536 
 Brittleness, 26 
 Bromalin, 543 
 Brom-ethane, 478 
 Bromine, 239 
 
 deci-normal solution, 424 
 
 iodide, 243 
 Bromoform, 477 
 Bromoformin, 543 
 Bromol, 571 
 Bronze, 323 
 Brucine, 611 
 Butter, 525, 698 
 
 -milk, 695 
 
 of antimony, 360 
 
 C. 
 
 CACODYL, 478 
 
 oxide, 478 
 Cadaverine, 620 
 Cadinene, 597 
 Cadmium, 318 / 
 Caesium, 267 
 
 salts, 268 
 Caffeine, 616 
 
 citrated, 616 
 Calamine, 312 
 Calcined magnesia, 273 
 
 plaster, 279 
 Calcium, 277 
 
 acid phosphate, 279 
 
 bromide, 280 
 
 carbide, 281 
 
 carbonate, 278 
 
 chloride, 280 
 
 cyanamide, 553 
 
 glycerin-phosphate, 489 
 
 hydroxide, 278 
 
 hypochlorite, 281 
 
 Calcium hypophosphite, 280 
 
 oxalate, 508, 742 
 
 oxide, 277 
 
 phosphate, 279 
 
 sulphate, 279 
 
 sulphide, 281 
 
 superphosphate, 279 
 Calc-spar, 277 
 
 Calculations, chemical, 100, 111, 139 
 Calculi, biliary, 671 
 
 fecal, 692 
 
 urinary, 745 
 Calomel, 338 
 
 Caloric value of foods, 642 
 Calorie, 48 
 Calorimeter, 49 
 Camphene, 597 
 Camphor, 598 
 
 artificial, 596 
 
 mint-, 599 
 
 monobromated, 598 
 Cane-sugar, 533 
 Caoutchouc, 597 
 Capillary attraction, 37 
 Caramel, 531 
 Carat, definition of, 366 
 Carbamide, 546, 710 
 Carbide, 178 
 
 aluminum, 466 
 
 calcium, 281 
 Carbinol, 479, 482 
 Carbohydrates, 528, 729 
 
 classification of, 529 
 Carbolic acid, 569 
 
 coefficient, 570 
 Carbon, 178 
 
 dioxide, 180 
 
 ionic explanation of liberation 
 of, 195 
 
 disulphide, 217 
 
 monoxide, 183 
 
 silicide, 186 
 
 tetrachloride, 474 
 Carbonic oxide, 183 
 Carbonyl chloride, 184 
 Carborundum, 186 
 Carboxyl, 496 
 Carboxylic acids, 496 
 Carbylamines, 555 
 Carniferrin, 668 
 Caryophyllene, 595 
 Casein, 696 
 
 silver-, 334 
 Caseinogen, 696 
 Catalysis, 154 
 Cathode, 75, 82, 190 
 
 rays, 83 
 
 Cations, 83, 190 
 Caustic, lunar, 332 
 
 mitigated, 332 
 
 potash, 256 
 
 soda, 262 
 Cedrene, 597 
 Celestite, 282 
 
INDEX. 
 
 757 
 
 Celluloid, 538 
 Cellulose, 536 
 
 nitrates of, 537 
 Celsius thermometer, 46 
 Cement, 290 
 
 Centigrade thermometer, 46 
 Cerebrosides, 670 
 Cerite, 291 
 Cerium oxalate, . 291 
 Chains, definition of, 449 
 Chalk, 277 
 Charcoal, animal, 280 
 
 reduction test, 212 
 Charles' law, 45 
 Chelene, 478 
 Chemical affinity, 92 
 
 calculations, 100, 111, 139 
 
 changes after death, 649 
 
 in plants and animals, 639 
 
 effects of light, 68 
 
 energy, 91, 142 
 
 equations, definition, 110 
 types of, 113 
 
 equilibrium. 114 
 
 formulas, 99 
 
 reaction, definition, 92 
 
 work, 142 
 Chemistry, analytical, 371 
 
 definition of, 18 
 
 organic, 440 
 
 physiological, 623 
 
 thermo-, 143 
 Chile saltpeter, 266 
 Chinoline, 593 
 Chloral, 492 
 
 hydrated, 493 
 Chloralamide, 544 
 Chloralformamide, 544 
 Chlorate of potash, 258 
 Chloride of lime, 280 
 
 nitrogen, 243 
 Chlorinated lime, 280 
 
 soda, 237 
 Chlorine, 230 
 
 compound solution of, 232 
 
 iodides, 243 
 
 oxides of, 235 
 
 water, 232 
 Chloroform, 474 
 Choke-damp, 184 
 Cholesterin, 527, 671 
 Choline, 620, 671 
 Chondrin, 628 
 Chondromucoid, 630 
 Chondroproteins, 630 
 Chromates, discussion of, 308 
 Chrome alum, 310 
 
 -iron ore, 306 
 
 -yellow, 311 
 Chromic anhydride, 308 
 
 chloride, 309 
 
 hydroxide, 310 
 
 oxide or sesquioxide, 309 
 
 salts, 309 
 
 Chromite, 306 
 Chromium, 306 
 
 and ammonium sulphate, 310 
 
 and potassium sulphate, 310 
 
 trioxide, 308 
 Chyme, 674 
 Cinchona alkaloids, 608 
 Cinchonidine, 610 
 Cinchonine, 609 , 
 Cineol, 599 
 Cinnabar, 335, 342 
 Cinnamic aldehyde, 578 
 Cinnamyl acetate, 595 
 Clay, 289 
 
 Cleavage, hydrolytic, 453 
 Coagulases, 637 
 Coal, 467 
 
 -oil, 468 
 
 -tar, 470 
 Cobalt, 312 
 
 blue glass, 312 
 Cocaine, 606 
 
 substitutes, 580, 607 
 Codeine, 613 
 
 Coefficient of expansion, 48 
 Cognac, 486 
 Cohesion, 19 
 Cohesive gold, 365 
 Colchicine, 617 
 Collagen, 628 
 Collargol, 331 
 
 ointment, 331 
 Collodion, 538 
 
 medicated, 538 
 Colloidal silver, 331 
 
 solution, 331 
 Colloids, 41 
 Colloxylin, 538 
 Colophony, 599 
 Color, 56 
 
 Columbian spirit, 482 
 Combining weights of elements, 95 
 Combustion, 141 
 
 spontaneous, 141 
 Commutator, 78 
 Complement, 661 
 Compound acetanilide powder, 565 
 
 definition, 88 
 
 effervescing powder, 515 
 
 solution of cresol, 574 
 
 spirit of ether, 522 
 Conduction of heat, 49 
 Conductivity, 197 
 Conductors of electricity, 69 
 Congo red, 411 
 Coniine, 604 
 
 Constitutional formulas, 123 
 Contact action, 154 
 Convection, 50 
 Copaiva balsam, 599 
 Copper, 323 
 
 acetate, 504 
 basic, 504 
 
 aceto-arsenite, 504 
 
758 
 
 INDEX. 
 
 Copper alloys, 323 
 
 ammonio-compounds of, 325 
 
 arsenate, 352 
 
 arsenite, 352 
 
 oxides, 324 
 
 carbonate, 325 
 
 -glance, 323 
 
 ions of, 326, 327 
 
 pyrites, 323 
 
 sulphate, 325 
 Copperas, 298 
 Coproliths, 692 
 Corpuscles or electrons, 85 
 Corrosive chloride of mercury, 339 
 
 sublimate, 339 
 Corundum, 286 
 Cotarnine, 614 
 Cotton, collodion, 538 
 
 medicated, 537 
 Coumarin, 578 
 Cream, 700 
 
 of tartar, 514 
 Creatine, 546, 666 
 Creatinine, 546, 666, 715 
 Crede's ointment, 331 
 
 silver, 331 
 Creolins, 574 
 Creosol, 575 
 Creosotal, 574 
 Creosote, 574 
 
 carbonate, 574 
 Cresol, 574 
 
 Critical temperature, 141 
 Cryoscopic method, 160 
 Crystal systems, 22 
 Crystallization, 20 
 Crystalloids, 41 
 Crystals, 20 
 
 acicular, 25 
 
 clinometric, 22 
 
 laminar, 25 
 
 orthometric, 22 
 
 prismatic, 25 
 
 tabular, 25 
 
 Cupellation of gold, 364 
 Cuprous compounds, remarks on, 
 323 
 
 oxide, 324 
 Curd, 700 
 Currents, alternating, 78 
 
 dynamo-electrical, 78 
 
 faradic, 79 
 
 induced, 78, 79 
 
 interrupted, 79 
 
 magneto-electric, 78 
 
 secondary, 79 
 Cyanamide, 553 
 Cyanides, detection in poisoning, 552 
 
 double salts, 551 
 
 organic, 555 
 Cyanogen, 548 
 
 complex radicals of, 553 
 
 compounds, 547 
 
 dissociation of, 549 
 
 Cyanogen compounds obtained from 
 
 atmospheric nitrogen, 552 
 Cymene, 564 
 Cystine, 545, 720, 744 
 Cystogen, 543 
 
 D. 
 
 DALTON'S atomic theory, 97 
 
 Daniell's cell, 75 
 
 Daturine, 605 
 
 Decay, 454 
 
 Decomposition by electricity, 90 
 
 heat, 87 
 
 light, 90 
 
 mutual action of substances, 90 
 
 with formation of a precipitate, 
 
 116, 193 
 
 volatile product, 116, 194 
 Decrepitation, 377 
 Deflagration, 378 
 Deliquescence, 152 
 Denaturants, 485 
 Denatured alcohol, 485 
 Density, 33 
 Dental alloys, 337 
 Dentine, 664 
 Deodorizers, 457 
 Deoxidation, 147 
 Deoxidizing agents, 147 
 Derivatives, definition of, 451 
 Dermatol, 586 
 Desiccator, 404 
 Destructive distillation, 453 
 Detection of acids, 391 
 
 special remarks, 398 
 Dextrin, 536 
 Dextrorotation, 67 
 Dextrose, 530 
 Diads, 103 
 Dialysis, 40 
 Dialyzed iron, 298 
 Diamine, 169 
 Diamino-benzene, 566 
 Diamond, 178 
 Diastase, 534 
 Diazo-compounds, 567 
 
 -reaction, Ehrlich's, 568, 739 
 Dichlor-methane, 474 
 Dichromates, discussion of, 308 
 Dicyandiamide, 553 
 Dicyanogen, 548 
 Diethylene diamine, 543 
 Diffusion, 40 
 
 of gases, 42 
 
 rate of, for different substances, 40 
 Digestion, 645, 672 
 
 gastric, 674 
 
 intestinal, 681 
 
 salivary, 672 
 Dimethyl benzene, 563 
 Dimorphism, 22 
 Dionin, 614 
 Dipentene, 597 
 
INDEX. 
 
 759 
 
 Diphenyl-amine, 566 
 Disaccharides, 529, 533 
 Disinfectants, 457 
 Disinfection by formaldehyde, 491 
 Dispersion of light, 59 
 Displacement, 113 
 Dissociation, 172 
 
 electrolytic, 189 
 
 of acids and bases, 199 
 
 of formic acid and its homologues, 
 507 
 
 table of degree of, 203 
 Distillation, 53 
 
 destructive, 453 
 
 fractional, 462 
 Dithymol-diiodide, 575 
 Diuretin, 616 
 Divisibility, 28 
 Dolomite, 272 
 Donovan's solution, 351 
 Double decomposition, 113 
 
 refraction, 63 
 
 salts, definition of, 122 
 Drinking-water, 149 
 Drying oils, 525 
 Ductility, 26 
 Dulcin, 581 
 
 Dulong and Petit's law, 107 
 Dumas method for determination of 
 
 nitrogen, 445 
 Dyes, aniline, 564 
 
 azo, 567 
 Dynamite, 488 
 
 E. 
 
 EARTH metals, 286 
 
 summary of tests, 292 
 Earthenware, 289 
 Ebonite, 598 
 Ecgonine, 606 
 Effervescence, 152 
 Efflorescence, 152 
 Ehrlich's theory of immunity, 662 
 Elasticity, 26 
 Elastin, 628 
 Electric circuit, 76 
 
 current, 76 
 
 discharge through gases, 83 
 
 energy, 72 
 
 conversion of, 80, 82 
 
 furnace, 80 
 
 induction, 71 
 
 insulators, 69 
 
 light, 82 
 
 motors, 78 
 
 poles, 75 
 
 spark, 71, 83 
 
 units, 76 
 Electrical machines, 71, 78 
 
 potential, 76 
 
 tension, 76 
 Electricity, 69 
 
 by chemical action, 74 
 
 Electricity by magnet ism, 77 
 
 conductors of, (>!) 
 
 current, 72 
 
 duality of, 70 
 
 frictional, 69 
 
 galvanic, 74 
 
 nature of, 72 
 
 negative, 70 
 
 positive, 70 
 
 resinous, 70 
 
 static, 71 
 
 vitreous, 70 
 
 voltaic, 74 
 Electro-chemical equivalents, 197 
 
 series of metals, 198 
 Electrodes, 75, 82 
 
 polarized, 198 
 Electrolysis, 82, 195 
 
 electromotive force required for, 
 198 
 
 secondary changes in, 196 
 Electrolytes, 82 
 Electrolytic dissociation theory, 189 
 
 solution tension, 319 
 Electromagnetism, 77 
 Electromagnets, 77 
 Electromotive force, 76 
 Elements, classification of, 125 
 
 combining weights of, 95 
 
 definition, 88 
 
 metallic, 247 
 
 classification of, 251 
 derivation of names, 247 
 melting-points, 248 
 occurrence in nature, 250 
 properties of, 252 
 specific gravity of, 249 
 tune of discovery, 249 
 valence of, 250 
 
 natural groups of, 125 
 
 non-metallic, 126, 135 
 
 derivation of names, 135 
 time of discovery, 136 
 valence of, 136 
 
 periodic system of, 128, 130 
 
 physical properties of, 129 
 
 relative importance of, 124 
 Emanation, 87 
 Emerald green, 504 
 Emery, 286 
 Empirical formulas, 446 
 
 solution, 407 
 Emulsin, 578 
 
 Emulsion, definition of, 152 
 Emulsions, 524 
 Enamel, 664 
 Endosmosis, 40 
 Endothermic actions, 91 
 Energy, 19 
 
 chemical, 142 
 Enterol, 574 
 Enteroliths, 692 
 Enzymes, 456, 636 
 Eosin, 582 
 
760 
 
 INDEX. 
 
 Epithelial cells, 687 
 Epithelium, 665 
 Epsom salt, 274 
 Equations, chemical, 110, 113 
 
 thermal, 143 
 Equilibrium, chemical, 11'4 
 
 ionic, 192 
 
 effect hi chemical reactions, 
 192 
 
 nitrogenous, 644 
 Equivalence, 102 
 
 Equivalents of volumetric solutions, 
 416, 419, 422, 426 
 
 electro-chemical, 197 
 Erepsin, 687 
 Erythrite, 529 
 Erythrose, 528 
 Esbach's albuminometer, 726 
 Eserine, 616 
 Essence of mirbane, 563 
 Essential oils, 594 
 Esters, 518 
 Ethane, 466 
 
 halogen derivatives, 477 
 Ethene, 472 
 Ether, 50, 520 
 
 acetic, 522 
 
 diacetic, 591 
 
 ethyl, 520 
 
 hydrobromic, 478 
 
 luminiferous, 50 
 
 methyl, 522 
 -ethyl, 522 
 
 nitrous, 523 
 
 sulphuric, 520 
 Ethereal salts, 518 
 Ethers, 518 
 
 compound, 518 
 
 mixed, 519 
 Ethoxy, 586 
 Ethyl acetate, 522 
 
 alcohol, 482 
 
 amine, 620 
 
 bromide, 478 
 
 carbamate, 545 
 
 chloride, 477 
 
 iodide, 478 
 
 nitrite, 523 
 
 assay of, 429 
 
 oxide, 520 
 
 para-amino-benzoate, 580 
 Ethylene, 472 
 
 dichloride, 472 
 
 series of hydrocarbons, 472 
 Eucalyptol, 599 
 Eudiometer, 427 
 Eugenol, 575 
 Euphorin, 545 
 Europhen, 574 
 Evaporations, 52 
 Exalgin, 566 
 
 Excretion, definition, 649 
 Exothermic actions, 91 
 Expansion, coefficient of, 48 
 
 Explosive gelatin, 488 
 Extension, 18 
 
 Extraction, definition of, 157 
 Extractive matter, 650 
 of muscle, 666 
 
 F. 
 
 FAHRENHEIT thermometer, 46 
 Faraday's laws, 197 
 Fats, 523, 646 
 Fatty acids, 496 
 
 oils, 523 
 Feathers, 665 
 Fecal calculi, 692 
 Feces, 689 
 
 examination of, 690 
 Fehling's solution, 730 
 
 test, 730 
 Feldspar, 286 
 Fermentation, 455 
 Ferments, hydrolytic, 636 
 
 organized, 455 
 
 soluble or unorganized, 455 
 
 unorganized, 636 
 Ferrates, 296 
 Ferric acetate, 503 
 
 ammonium sulphate, 299 
 
 chloride, 297 
 
 tincture of, 297 
 
 citrate, 518 
 
 hydroxide, 296 
 
 with magnesium oxide, 296 
 
 hypophosphite, 300 
 
 oxide, 295 
 
 phosphate, 300 
 
 soluble, 300, 518 
 
 pyrophosphate, soluble, 300, 518 
 
 subsulphate, 300 
 
 sulphate, 299 
 
 tartrate, 516 
 Ferricyanogen, 554 
 Ferripyrine, 592 
 Ferrocyanogen, 554 
 Ferro-manganese, 303 
 Ferrous acetate, 503 
 
 ammonium sulphate, 299 
 
 bromide, 298 
 
 carbonate, 300 
 
 saccharated, 300 
 
 chloride, 296 
 
 hydroxide, 295 
 
 iodide, 298 
 
 oxide, 295 
 
 phosphate, 300 
 
 sulphate, 298 
 
 exsiccated, 299 
 
 sulphide, 298 
 Fertilizers, 279 
 Fibrinogen, 654 
 
 Fineness of gold, definition, 365 
 Fire-damp, 184, 466 
 Fixed oils, 524 
 Flame, 184 
 
1XDEX. 
 
 761 
 
 Flame tests, 261, 379 
 Flashing-point, 469 
 Fleitmann's test, 355 
 Flowers of sulphur, 205 
 
 of zinc, 313 
 Fluorescein, 582 
 Fluorine, 244 
 Fluor-spar, 244 
 Food, animal, 640 
 
 composition and fuel values, 642 
 
 digestibility of, 643 
 
 plant, 638 
 Force, definition of, 19 
 
 vital, 439 
 Formaldehyde, 490 
 
 disinfection, 491 
 
 in milk, 701 
 
 para-, 490 
 Formalin, 490 
 Formamide, 544 
 Formin, 543 
 Formulas, constitutional, 123, 447 
 
 empirical, 446 
 
 graphic, 123, 447 
 
 molecular, 99, 446 
 
 rational, 447 
 
 structural, 447 
 Fowler's solution, 349 
 Fractional distillation, 462 
 Frauenhofer lines, 62 
 Freezing-mixtures, 44 
 
 -point method, Raoult's, 109 
 
 -points of solutions, 160 
 Fructose, 532 
 
 Functional test of kidney, 740 
 Fusel oil, 486 
 Fusion, change of volume by, 52 
 
 latent heat of, 52 
 
 -point, 51 
 
 G. 
 
 GALACTOSE, 532 
 Galena, 318 
 
 argentiferous, 330 
 Gallacetophenone, 577 
 Gall-stones, 671 
 Galvanic electricity, 76 
 Galvanized iron, 313 
 Gamma derivatives, 624 
 Gas, analysis of, 427 
 
 definition of, 26 
 
 elasticity of a, 26 
 
 illuminating, 469 
 
 laughing, 172 
 
 natural, 467 
 
 olefiant, 472 
 
 tension of a, 26 
 
 volume, reduction of a, 428 
 
 water-, 184 
 
 Gases, absorption by charcoal, 39 
 by liquids, 39 
 by platinum, 39 
 
 diffusion of, 42 
 
 Gases, ionic explanation of liberation of, 
 194 
 
 solution of, 159 
 
 weight of, 34 
 Gasoline, 468 
 Gastric digestion, 675 
 
 juice, 674 
 
 examination of, 677 
 Gay-Lussac's law, 100 
 Gelatin, 663 
 
 -dynamite, 488 
 
 explosive, 488 
 German silver, 323 
 Germicides, 457 
 Gin, 486 
 Glass, 289 
 
 borax, 266 
 
 cobalt, 312 
 
 soluble, 186 
 Glauber's salt, 264 
 Gliadin, 628 
 Globin, 657 
 Globulins, 627 
 Glonoin, 487 
 Glucosan, 531 
 Glucose, 530 
 Glucosides, 539 
 Glucusimide, 581 
 Glue, 663 
 Gluside, 581 
 Glutelins, 628 
 Glycerides, 524 
 Glycerin, 487 
 
 phosphates, 488 
 
 trinitrate, 487 
 Glycerites, 487 
 Glycerol, 487 
 Glycerose, 528 
 Glycine, 544 
 Glycocoll, 544 
 Glycogen, 539, 692 
 Glycols, 479 
 Glycoproteins, 630 
 Glycozone, 155 
 Gmelin's test, 685, 737 
 Gold, 363 
 
 alloys, 366 
 
 and potassium cyanide, 364 
 
 and sodium chloride, 366 
 
 chlorides, 366 
 
 cohesive, 365 
 
 fineness of, 365 
 
 refining by cupellation, 364 
 parting, 364 
 quartation, 365 
 
 Golden sulphuret of antimony, 360 
 Goulard's extract, 504 
 Graham's law of diffusion, 42 
 Gram-atom, 407 
 Gram-molecule, 407 
 Granite, 286 
 Grape-sugar, 530 
 Graphic formulas, 123 
 Graphite, 178 
 
762 
 
 INDEX. 
 
 Gravimetric methods, 403 
 
 Gravitation, 31 
 
 Green iodide of mercury, 340 
 
 vitriol, 298 
 Group-reagents, 382 
 Guaiacamphol, 575 
 Guaiacol, 575 
 
 carbonate, 575 
 
 derivatives, 575 
 
 -salol, 575 
 Guanidine, 546 
 Guaranine, 616 
 Gum arabic, 536 
 
 British, 536 
 
 -resins, 599 
 Gun-cotton, 537 
 
 -metal, 323 
 Gunpowder, 258, 538 
 
 smokeless, 538 
 Gutta-percha, 598 
 Gutzeit's test, 354 
 
 modified, 354 
 Gypsum, 279 
 
 H. 
 
 ELEMATIN, 657 
 
 Hsematoporphyrin, 657 
 Haematoxylin, 410 
 Haemin crystals, 659 
 Haemoglobin carbon monoxide com- 
 pound, 657 
 Haemoglobins, 631 
 Haemolysis, 662 
 Haine's test, 731 
 Hair, 665 
 Halogens, 230 
 Haptophore group, 662 
 Hardness, 25 
 Hartshorn, spirit of, 169 
 Hausmannite, 303 
 Heat, 43 
 
 bright red, 48 
 
 conduction of, 49 
 
 convection of, 50 
 
 dark red, 48 
 
 decomposition by, 87 
 
 effects, 45 
 
 incipient red, 48 
 white, 48 
 
 latent, 44 
 
 mechanical equivalent of, 48 
 
 of neutralization, 203 
 
 of solution, 158 
 
 radiation of, 50 
 
 rays? 50 
 
 sources of, 44 
 
 specific, 49 
 
 waves, 51 
 
 white, 48 
 
 yellow, 48 
 Heavy spar, 283 
 Hedonal, 545 
 
 Helianthin, 411 
 
 Helium, 167 
 
 Heller's test, 626, 731 
 
 Hematite, 293 
 
 Hemiterpenes, 594 
 
 Henry's law, 159 
 
 Hepar, 212, 378 
 
 Heptads, 103 
 
 Heroin, 613 
 
 Hexads, 103 
 
 Hexamethylenamine, 543 
 
 Hexone bases, 633 
 
 Histidine, 630 
 
 Histones, 629 
 
 Holocaine hydrochloride, 607 
 
 Homatropine, 605 
 
 Homologous series, 450 
 
 Hoofs, 665 
 
 Hordein, 628 
 
 Hornblende, 286 
 
 Horns, 665 
 
 Humidity, 165 
 
 Humulene, 597 
 
 Humus, 649 
 
 Hydracids, 117 
 
 Hydrastine, 615 
 
 Hydrastinine, 615 
 
 Hydrazine, 169 
 
 Hydrazones, 568 
 
 Hydrocarbons, benzene series, 561 
 
 ethylene series, 472 
 
 general remarks, 462 
 
 halogen substitution products, 
 473 
 
 methane or paraffin series, 464 
 
 terpene series, 594 
 
 unsaturated, 470 
 Hydrogen, 144 
 
 arsenide, 350 
 
 dioxide, 153 
 
 nascent, 148 
 
 peroxide, 153 
 
 phosphide, 229 
 
 phosphoretted, 229 
 
 sulphide, 214 
 Hydrolysis, 201, 453, 636 
 Hydrolytic cleavage, 453, 636 
 
 ferments, 636 
 Hydrometers, 34 
 Hydroquinone, 576 
 
 hydroxy-, 577 
 Hydroxides, 119, 151 
 Hydroxyl, 119 
 Hydroxylamine, 169 
 Hygrine, 606 
 Hygrometers, 166 
 Hygroscopic, 152 
 Hyoscine, 606 
 Hyoscyamine, 605 
 Hypertonic solutions, 163 
 Hypnal, 592 
 Hypochlorites, 237 
 Hypotonic solutions, 163 
 Hypoxanthine, 668 
 
INDEX. 
 
 7C3 
 
 ICELAND spar, 63 
 Ichthyol, 573 
 Illuminating gas, 469 
 
 oil, 468 
 
 Imino-compounds, 542 
 Immunity, Ehrlich's theory of, 662 
 Impurities, detection of, 433 
 Indestructibility, 42 
 India-rubber, 597 
 Indican, 721 
 Indicators, 410 
 
 ionic explanation of action, 411 
 Indigo, 721 
 
 -red, 722 
 Indole, 693 
 Indoxyl, 721 
 Induction, 71 
 
 coil, 79 
 
 voltaic, 78 
 Ink, blue, 554 
 
 indelible, 333 
 Inosite, 532 
 Internal energy, 91 
 Intestinal digestion, 681 
 
 sand, 692 
 Inversion, 533 
 Invertases, 637 
 Iodide of nitrogen, 243 
 
 sulphur, 243 
 lodimetry, 421 
 Iodine, 240 
 
 chlorides of, 243 
 
 compounds of nitrogen, 244 
 
 Lugol's solution, 242 
 
 pentoxide, 243 
 
 sulphide of, 243 
 
 tincture of, 241 
 
 decolorized, 270 
 lodoform, 477 
 lodoformin, 543 
 lodol, 591 
 Ionic equations, 192 
 
 equilibrium, 192 
 
 mechanism of solution, 217 
 lonization constant, 192 
 
 theory of, 190 
 Ions, 75, 190 
 
 composition of, 190 
 
 independence of, 199 
 Iridium, 368 
 Iron, 292 
 
 acetates, 503 
 
 alloys, 294 
 
 alum, 299 
 
 and ammonium sulphates, 299 
 
 and potassium oxalates, 510 
 
 and quinine citrate, 518 
 
 and strychnine citrate, 518 
 
 bar-, 294 
 
 bisulphide, 293 
 
 bromide, 263, 298 
 
 Iron carbonate, 300 
 
 saccharated, 300 
 
 cast-, 293 
 
 chlorides, 296 
 
 citrate, 518 
 
 dialyzed, 298 
 
 galvanized, 313 
 
 -group of metals, 292 
 
 summary of tests, 316 
 
 hydroxides, 293 
 
 hypophosphite, 300 
 
 iodide, 298 
 
 monoxide or suboxide, 293 
 
 ores, 293 
 
 oxides, 293, 295 
 
 oxychloride, 298 
 
 perchloride, 297 
 
 phosphate, 300 
 
 soluble, 300, 518 
 
 pig-, 293 
 
 protochloride, 296 
 
 pyrites, 293 
 
 pyrophosphate, soluble, 518 
 
 reduced, 295 
 
 rust, 294 
 
 scale compounds of, 516, 518 
 
 sesquichloride, 297 
 
 subsulphate, 300 
 
 sulphates, 298 
 
 sulphide, 298 
 
 tartrate, 516 
 
 tersulphate, 299 
 
 trioxide, 296 
 
 wrought-, 294 
 Isocholesterin, 527 
 Isocyanides, organic, 555 
 Isomerism, 451 
 Isomorphism, 22 
 Iso-nitriles, 555 
 Isonitroso compounds, 540 
 Isoquinoline, 593 
 Is-osmotic solutions, 163 
 Isosulphocyanates, 556 
 Isotonic solutions, 163 
 
 K. 
 
 KAIRINE, 593 
 
 Kaolin, 289 
 
 Kelene, 478 
 
 Kelp, 241 
 
 Keratins, 628 
 
 Kerosene, 468 
 
 Ketones, 494 
 
 Ketoses, 530 
 
 Ketoximes, 541 
 
 Kidney, functional test of, 740 
 
 Kieserite, 274 
 
 Kinases, 638 
 
 Kjeldahl determination of nitrogen, 
 
 445 
 
 Koppeschaar's solution, 424 
 Krystallose, 581 
 
764 
 
 INDEX. 
 
 L. 
 
 LABARRAQUE'S solution, 237 
 Lactalbumin, 696 
 Lactoglobulin, 696 
 Lactometers, 34 
 Lactophenin, 572 
 Lactose, 534, 699 
 Lakes, 288 
 Lanolin, 527 
 Lapis infernalis, 332 
 
 lazuli, 290 
 Lard, 525 
 Latent heat, 44 
 
 of fusion, 52 
 of vaporization, 54 
 Laughing gas, 172 
 Laurinol, 598 
 Law, Avogadro's, 30 
 
 Boyle's, 26 
 
 Charles', 45 
 
 Dulong and Petit's, 107 
 
 Gay-Lussac's, 100 
 
 Graham's, 42 
 
 Henry's, 159 
 
 Mariotte's, 26 
 
 Mendelejeff's, 126 
 
 Newton's, 31 
 
 Ohm's, 77 
 
 Raoult's, 161 
 
 of atomic heats, 107 
 
 of combination by volume, 100 
 
 of constancy of composition, 93 
 
 of correlation of energies, 42 
 
 of equivalents, 102 
 
 of mass action, 116 
 
 of multiple proportions, 94 
 
 of specific heats, 107 
 
 of the conservation of energy, 
 
 42 
 Laws of electrolysis, Faraday's, 197 
 
 of osmotic pressure, 163 
 Lead, 318 
 
 acetate, 503 
 basic, 503 
 tribasic, 504 
 
 alloys, 319 
 
 arsenate, 350 
 
 carbonate, 321 
 
 chloride, 322 
 
 chromate, 322 
 
 dioxide or peroxide, 319 
 
 group metals, 318 
 
 summary of tests, 344 
 
 iodide, 321 
 
 nitrate, 321 
 
 oleate, 526 
 
 oxide, 319 
 
 phosphate, 322 
 
 plaster, 526 
 
 red oxide, 319 
 
 subacetate, 503 
 
 sugar of, 503 
 
 sulphate, 322 
 
 Lead sulphide, 318 
 
 -water, 504 
 
 white, 321 
 
 Leblanc's process, 263 
 Lecithins, 670 
 Lecithoproteins, 631 
 Legal's test, 737 
 Leucine, 546, 635, 744 
 Leucomaines, 621 
 Levorotation, 67 
 Levulose, 532 
 Lieberman's reaction, 627 
 Light, 56 
 
 chemical effects of, 68, 90 
 
 dispersion of, 59 
 
 infra-red, 56 
 
 plane-polarized, 64 
 
 rays, 57 
 
 reflection of, 57 
 
 refraction of, 58 
 
 ultra-violet, 56 
 
 waves, 56 
 Lignin, 536 
 Lignite, 467 
 Lime, 277 
 
 acid phosphate of, 279 
 
 air-slaked, 277 
 
 chloride of, 280 
 
 chlorinated, 280 
 
 -kilns, 277 
 
 liniment, 526 
 
 milk, of 278 
 
 nitrogen, 553 
 
 phosphate of, 279 
 
 sulphurated, 281 
 
 superphosphate of, 279 
 
 -water, 278 
 Limestone, 277 
 Limonene, 597 
 Liniments, 526 
 
 Linkage, double and triple, 471 
 Lipase, 683 
 Lipoids, 670 
 Liquids, absorption of gases by, 40 
 
 definition of, 26 
 Litharge, 319 
 Lithium, 267 
 
 benzoate, 580 
 
 bromide, 267 
 
 carbonate, 267 
 
 citrate, 517 
 
 hydroxide, 267 
 
 phosphate, 267 
 
 salicylate, 583 
 Litmus paper, 410 
 
 solution, 410 
 Liver, function of, 692 
 Lodestone, 296 
 Losophan, 574 
 Lugol's solution, 241 
 Lunar caustic, 332 
 Lupulin, 486 
 Lymph, 662 
 Lysine, 628 
 
INDEX. 
 
 765 
 
 Lysins, 660 
 Lysol, 574 
 
 M. 
 
 MAGNESIA alba, 273 
 
 calcined, 273 
 
 milk of, 273 
 Magnesite, 272 
 Magnesium, 272 
 
 ammonium phosphate, 742 
 
 carbonate, 273 
 
 citrate, 517 
 
 nitride, 274 
 
 oxide, 273 
 
 sulphate, 274 
 
 effervescent, 274, 517 
 Magnetic field, 74 
 
 iron ore, 73, 293 
 Magnetism, 73 
 Malachite, 323 
 Malleability, 26 
 Malonyl urea, 547 
 Malt, 534 
 Maltose, 534 
 Manganese, 303 
 
 alloys, 303 
 
 carbonate, 303, 306 
 
 oxides of, 302 
 
 spar, 303 
 Manganous hydroxide, 306 
 
 hypophosphite, 304 
 
 sulphate, 304 
 Mannite, 529 
 Mannose, 532 
 Mariotte's law, 26 
 Marsh-gas, 466 
 Marsh's test, 355 
 Mass, definition of, 18 
 
 -action, law of, 116 
 Massicot, 320 
 Matches, safety, 222 
 Matter, action of heat on, 28 
 
 definition of, 18 
 
 fundamental properties of, 18 
 
 radiant, 85 
 Mayer's solution, 601 
 Measures, metric, 32 
 Meat-extracts, 669 
 Mechanical equivalent of heat, 48 
 Meerschaum, 272 
 Melanin, 739 
 Melitose, 534 
 Melting-point, 51 
 
 determination of, 52 
 Membranes, semipermeable, 162 
 Mendelejeff's periodic law, 126 
 Menthol, 599 
 Mercaptans, 495 
 Mercurial ointment, 336 
 
 plaster, 336 
 Mercuric ammonium chloride, 342 
 
 chloride, 339 
 
 compounds, remarks, 336 
 
 Mercuric cyanide, 551 
 fulminate, 541 
 iodide, 340 
 nitrate, 341 
 oxide, 337 
 
 oxy- or subsulphate, 341 
 and potassium iodide, 341 
 and sodium chloride, 339 
 salicylate, 584 
 sulphate, 341 
 sulphide, 335, 342 
 Mercurous chloride, 338 
 
 compounds, remarks, 336 
 iodide, 340 
 nitrate, 341 
 oxide, 337 
 sulphate, 341 
 Mercury, 335 
 
 ammoniated, 342 
 and arsenic iodide, 351 
 complex salts of, 345 
 cyanide, 551 
 fulminate, 541 
 iodides, 340 
 mass of, 336 
 mild chloride of, 338 
 oxides of, 337 
 oxy cyanide, 551 
 proto- or subchloride of, 338 
 purification of, 336 
 salts, action of ammonia on, 343 
 with chalk, 336 
 Meta-compounds, 559 
 Metaldehyde, 492 
 Metals, 247 
 
 alkali-, remarks on, 255 
 
 summary of tests, 272 
 of alkaline earths, 277 
 
 summary of tests, 285 
 of the arsenic group, remarks on, 
 346 
 
 summary of tests, 369 
 classification of, 251 
 derivation of names, 247 
 earth group, summary of tests, 292 
 electro-chemical series of, 198 
 iron group, remarks, 292 
 
 summary of tests, 316 
 lead group, remarks, 318 
 
 summary of tests, 344 
 manufacture of, 253 
 melting-points of, 248 
 noble and base, 253 
 occurrence in nature, 250 
 properties of, 252 
 remarks on tests for, 274 
 separation of, 385 
 specific gravities of, 249 
 time of discovery, 249 
 valence of, 250 
 Metamerism, 451 
 Meta-phenylene-diamine, 566 
 Metaproteins, 631 
 Met-arsenites, 348 
 
766 
 
 INDEX. 
 
 Metathesis, 113 
 Methaemoglobin, 657 
 Methane, 466 
 
 halogen derivatives of, 474 
 
 series of hydrocarbons, 464 
 Methoxy, 586 
 Methyl acetanilide, 566 
 
 alcohol, 482 
 
 amine, 620 
 
 benzene, 563 
 
 blue, 567 
 
 chloride, 474 
 
 ether, 522 
 
 -ethyl ether, 522 
 
 -glycocoll, 545 
 
 hydroxide, 482 
 
 -orange, 410 
 
 salicylate, 585 
 Methylated spirit, 482 
 Methylene azure, 567 
 
 -blue, 566 
 
 chloride, 474 
 
 Methylthionine hydrochloride, 566 
 Mica, 286 
 Microcidine, 589 
 Microcosmic salt, 380 
 Milk, 694 
 
 analysis, 701 
 
 certified, 701 
 
 changes on standing, 700 
 
 clotting, 696 
 
 cows', 695 
 
 -fat, 698 
 
 human, 702 
 
 modified, 702 
 
 of lime, 278 
 
 of magnesia, 273 
 
 of sulphur, 205 
 
 preservatives, 700 
 
 -proteins, 696 
 
 skimmed, 700 
 
 -sugar, 534, 699 
 Millon's reaction, 626 
 Mineral waters, 149 
 Minium, 320 
 Mint-camphor, 599 
 Mirbane, essence of, 563 
 Mispickel, 347 
 Modified Gutzeit's test, 354 
 Mohr's salt, 299 
 Molecular formulas, 99, 446 
 
 motion, 43 
 
 theory, 28 
 
 weight, definition, 99 
 
 determination of, 108 
 
 weights, relation to densities of 
 
 gases, 108 
 Molecules, 99 
 Molybdates, 368 
 Molybdenum, 368 
 Monads, 103 
 Monazite sand, 291 
 Monosaccharides, 529 
 Monsel's solution, 300 
 
 Moore's test, 731 
 
 Mordants, 288 
 
 Morphine and its salts, 612 
 
 diacetyl-, 613 
 Mortar, 278 
 
 hydraulic, 290 
 Mucins, 630 
 Mucoids, 630 
 Murexid test, 716 
 Muscarine, 671 
 Muscle, 665 
 
 extractives, 666 
 
 sugar, 532 
 Musculin, 666 
 Mustard oils, 556 
 Mydatoxine, 621 
 Mydine, 620 
 Myosin, 666 
 Myosinogen, 666 
 Myrosin, 556 
 Mytilotoxine, 620 
 
 N. 
 
 NAILS, 665 
 Naphthalene, 587 
 
 amino-, 589 
 
 derivatives, 587 
 Naphthol, 588 
 Naphthylamines, 589 
 Narceine, 614 
 Narcotine, 614 
 Nascent hydrogen, 148 
 
 state, 148 
 Natural gas, 467 
 Nessler's solution, 341, 374 
 
 estimation of ammonia by, 431 
 Neuridine, 620 
 Neurine, 620 
 Neurodin, 545 
 
 Neutral substances, definition of, 120 
 Neutralization, 119, 202 
 
 equivalents, 416 
 
 heat of, 203 
 
 ionic explanation of, 202 
 Newton's law, 31 
 Nickel, 312 
 Nicol's prisms, 65 
 Nicotine, 604 
 Niter, 258 
 
 cubic, 266 
 Nitriles, 555 
 Nitro-benzene, 563 
 
 -cellulose, 537 
 
 compounds, 540 
 
 -glycerin, 487 
 
 -phenols, 572 
 Nitrogen, 164 
 
 chloride, 244 
 
 compounds in urine, 710 
 
 determination by Dumas or abso- 
 lute method, 445 
 Kjeldahl method, 445 
 soda-lime, 445 
 
INDEX. 
 
 767 
 
 Nitrogen iodide, 244 
 
 oxides of, 170 
 Nitrolim, 553 
 Nitrometer, 429 
 Nitroso compounds, 540 
 Nitrous ether, 523 
 
 oxide, 172 
 Nomenclature, 131 
 Non-metallic elements, 135 
 Nordhausen oil of vitriol, 212 
 Normal salt solution, physiologic, 656 
 
 salts, definition of, 121 
 
 solutions, 407 
 
 equivalents of, 416, 419, 422, 
 
 426 
 
 Nucleoproteins, 629 
 Nutrition, 645 
 Nylander's reagent, 731 
 
 0. 
 
 OBERMAYER'S test, 722 
 Ohm, 76 
 Ohm's law, 77 
 Oil, bitter almond, 578 
 bone-, 590 
 cinnamon, 595 
 
 artificial, 578 
 cloves, 596 
 fusel, 486 
 illuminating, 468 
 of garlic, 557 
 of vitriol, 208 
 peppermint, 595 
 phosphorated, 222 
 turpentine, 596 
 wintergreen, 585 
 Oils, drying and non-drying, 525 
 essential or volatile, 594 
 fatty, 523 
 fixed, 523 
 mustard, 556 
 Oleates, 507 
 Olefiant gas, 472 
 Olefins, 472 
 Olein, 524 
 Oleo-resins, 599 
 Opalisin, 702 
 Opium, 612 
 Opsonins, 660 
 Optic axis, 63 
 Optical activity, 67 
 Organic chemistry, 440 
 
 compounds, action of heat upon 
 
 453 
 
 classification of, 460 
 elementary analysis of, 442 
 elements in, 440 
 general properties 441 
 various modes of decomposi 
 
 tion, 452 
 cyanides, 555 
 ispcyanides, 555 
 Organized ferments, 455 
 
 Orphol, 589 
 Orpiment, 347 
 Ortho-compounds, 559 
 Osazones, 530, 568 
 Osmose, 40 
 Osmotic cells, 162 
 
 pressure, 162 
 Ossein, 628 
 Oxalates, 509 
 Oxalyl urea, 547 
 Oxidases, 637 
 
 Oxidation, definition of, 141 
 Oxides, acid-forming or acidic, 117 
 
 basic, 141 
 
 definition of, 141 
 
 neutral, 141 
 Oxidimetry, 417 
 Oxidizing agents, 142 
 Oximes, 541 
 Oxyacids, 117 
 Oxygen, 137 
 Oxy haemoglobin, 656 
 Oxypurine, 715 
 Ozone, 142 
 
 thermochemistry of, 144 
 
 P. 
 
 PAINTER'S colic, 322 
 Palladium, 367 
 Palmitin, 524 
 Pancreatic juice, 682 
 
 secretions, 682 
 
 stones, 692 
 Pancreatin, 638 
 Paracasein, 696 
 Para-compounds, 559 
 Paraffin, 469 
 
 series of hydrocarbons, 464 
 Paraformaldehyde, 490 
 Paraldehyde, 492 
 Parchment paper, 537 
 Paris green, 352, 504 
 Parting of gold, 364 
 Pasteurization, 701 
 Pearl-white, 329 
 Peat, 467 
 
 Pelletierine tannate, 608 
 Pentads, 103 
 Pental, 472 
 Pentosanes, 735 
 Pentoses, orcin reaction, 735 
 Pepsin, 638 
 Peptides, 633 
 Peptones, 632 
 Peria's reaction, 635 
 Perissads, 104 
 Petrolatum, 469 
 Petroleum, 468 
 
 -benzin, 468 
 
 Pettenkofer's test, 686, 738 
 Phellandrene, 597 
 Phenacetin, 572 
 Phenetidin, 572 
 
768 
 
 INDEX. 
 
 Phenetidin derivatives, 572 
 Phenol, 569 
 
 amino-, 572 
 
 coefficient, 570 
 
 determination in urine, 722 
 
 nitro-, 572 
 
 titration of, 424 
 
 tri-brom-, 571 
 
 trinitro-, 572 
 
 Phenolphthalein, 410, 582 
 Phenolsulphonphthalein, 582 
 Phenoxy, 586 
 Phenylacetamide, 565 
 
 acrolein, 578 
 
 -amine, 564 
 
 hydrazine, 568 
 
 salicylate, 585 
 Phloroglucinol, 577 
 Phosgene, 184 
 Phosphides, 221 
 Phosphine, 229 
 Phosphoprotein, 630 
 Phosphorated oil, 222 
 Phosphoretted hydrogen, 229 
 Phosphorite, 219 
 Phosphorus, 219 
 
 antidotes to, 222 
 
 detection of, 222 
 
 determination in organic com- 
 pounds, 445 
 
 oxides of, 223 
 
 oxychloride, 229 
 
 pentachloride, 229 
 
 pills of, 222 
 
 red or amorphous, 221 
 
 spirit of, 222 
 
 trichloride, 229 
 Photography, 333 
 Phthaleins, 582 
 Phthalic anhydride, 581 
 Physical properties of elements, 129 
 Physics, definition of, 17 
 Physiological chemistry, 623 
 Physostigmine, 616 
 Pilocarpine, 604 
 Pinene, 596 
 
 hydrochloride, 596 
 Piperazine, 543 
 Piperidine, 543 
 Piperin, 604 
 Pitch-blende, 84 
 Plant food, 640 
 Plaster, calcined, 279 
 
 lead, 526 
 
 of Paris, 279 
 Platinic ammonium chloride, 367 
 
 chloride, 367 
 Platinum, 367 
 
 alloys, 367 
 
 and barium cyanide, 368 
 
 black, and sponge, 367 
 
 absorption of gases by, 39 
 Plumbago, 178 
 Poirier's orange 3P, 411 
 
 Polariscope, 65 
 Polarization, 63 
 Polarized electrodes, 198 
 Polonium, 84 
 Poly-amines, 543 
 Polymerism, 451 
 Polymorphism, 22 
 Polysaccharides, 529, 535 
 Polyterpenes, 594 
 Porcelain, 289 
 Porosity, 36 
 Porter, 486 
 Pot-metal alloys, 254 
 Potash, bichromate or red chromate of, 
 307 
 
 caustic, 256 
 
 chlorate of, 258 
 
 crude, 256 
 
 red prussiate of, 555 
 
 yellow chromate of, 307 
 
 prussiate of, 554 
 Potassium, 255 
 
 acetate, 503 
 
 acid or bitartrate, 514 
 oxalate, 509 
 
 and antimony tartrate, 515 
 
 arsenite, 349 
 
 bicarbonate, 257 
 
 bisulphate, 259 
 
 bromide, 260 
 
 carbonate, 257 
 
 chlorate, 258 
 
 chromate, 308 
 
 citrate, 517 
 
 cyanate, 553 
 
 cyanide, 550 
 
 dichromate, 307 
 
 ferrate, 296 
 
 ferricyanide, 555 
 
 ferrocyanide, 554 
 
 gold cyanide, 364 
 
 hydroxide, 256 
 
 hypophosphite, 259 
 
 iodide, 259 
 
 iron oxalates, 510 
 
 manganate, 305 
 
 mercuric iodide, 341 
 
 nitrate, 258 
 
 oxide, 257 
 
 percarbonate, 257 
 
 perchlorate, 238 
 
 permanganate, 305 
 
 persulphate, 214 
 
 sodium tartrate, 515 
 
 sulphate, 259 
 
 sulphite, 259 
 
 sulphocyanate, 553 
 
 tartrate, 515 
 
 tetroxalate, 509 
 Powder of Algaroth, 360 
 Precipitate, definition of, 116 
 Precipitation, definition of, 121 
 
 ionic explanation of, 193c 
 Precipitins, 660 
 
769 
 
 Preston salt, 269 
 Principle of Archimedes, 34 
 Prismatic spectrum, 59 
 Prisms, 58 
 
 Nicol's, 65 
 Pro-enzymes, 638 
 Prolamines, 628 
 Proof-spirit, 484 
 Propylamine, 620 
 Protagon, 670 
 Protalbumoses, 632 
 Protamines, 629 
 Protargol, 334 
 Proteans, 631 
 Proteases, 637 
 Proteids. See Proteins. 
 Proteins, 623 
 
 alcohol-soluble, 628 
 
 classification of, 624 
 
 coagulated, 632 
 
 conjugated, 629 
 
 decomposition products, 633 
 
 derived, 631 
 
 simple, 625 
 Proteolysis, 633 
 Proteoses, 632 
 Prussian blue, 554 
 Prussiate of potash, red, 555 
 
 yellow, 554 
 Ptomaines, 617 
 Ptyalin, 673 
 Purine bases, 667 
 Putrefaction, 555 
 Pycnometers, 34 
 Pyocyanine, 620 
 Pyramidon, 592 
 Pyridine, 592 
 Pyrites, 293 
 Pyrocatechin, 575 
 
 tests for, in urine, 723 
 Pyrogallol, 576 
 Pyrolusite, 303 
 Pyroxylin, 537 
 Pyrozone, 155 
 Pyrrol, 590 
 
 tetra-iodo, 590 
 
 Q 
 
 QUANTIVALENCE, 102 
 
 Quartation of gold, 365 
 Quartz, 186 
 Quick-lime, 277 
 Quicksilver, 335 
 Quinidine, 609 
 Quinine, 608 
 
 salts, 608 
 Quinol, 576 
 Quinoline, 593 
 
 iso-, 593 
 
 R. 
 
 RADIATION of heat, 50 
 Radical, compound, 122 
 definition of, 122, 448 
 
 49 
 
 Radio-activity, 84 
 Radium, 84, 284 
 
 bromide and chloride, 285 
 Raoult's freezing-point method, 161 
 Rays, Becquerel, 84 
 
 cathode, 83 
 
 of heat, 50 
 
 of light, 57 
 
 Rontgen, 83 
 
 Reaction, reversible, 114 
 Reagents, list of, 374 
 
 use of, in analysis, 376 
 Realgar, 347 
 
 Reaumur thermometer, 46 
 Receptors, 662 
 Recording thermometers, 47 
 Red lead, 320 
 
 prussiate of potash, 555 
 Reduced iron, 295 
 Reducing agents, 147 
 Reduction, 147 
 Reflection of light, 57 
 Refraction, double, 63 
 
 of light, 58 
 Reinsch's test, 353 
 Rennin, 673 
 
 Residue, definition of, 122 
 Resins, 599 
 
 gum-, 599 
 
 oleo-, 599 
 Resopyrine, 592 
 Resorcin, 576 
 Resorcinol, 576 
 
 -phthalein, 582 
 Respiration, 647 
 Reticulin, 629 
 Reversed spectra, 62 
 Reversible actions, 114 
 Reversion, 533 
 Rhigolene, 468 
 
 Rideal-Walker coefficient, 570 
 Rigor mortis, 665 
 Rochelle salt, 515 
 Rock, phosphatic, 280 
 Rodagen, 669 
 Rontgen rays, 83 
 Rosaniline, 565 
 Rosin, 599 
 Rosolic acid, 410 
 Rouge, 296 
 Rubber, 597 
 
 preservation, 598 
 
 vulcanized, 597 
 Rubidium, 267 
 
 salts, 268 
 Ruby, 286 
 Ruhmkorf coil, 79 
 Rum, 486 
 
 SACCHARIN, 580 
 
 soluble, 581 
 
 Saccharinol, 581 
 
770 
 
 INDEX. 
 
 Saccharinose, 581 
 Saccharol, 581 
 Saccharose, 533 
 Safety matches, 222 
 Safrol, 575 
 Sal ammoniac, 269 
 
 sodse, 263 
 
 volatilis, 269 
 Salicin, 584 
 Saliform, 543 
 Salipyrin, 592 
 Saliva, 672 
 Salol, 585 
 Salt cake, 263 
 
 common, 262 
 
 of lemon, 509 
 
 of sorrel, 509 
 
 Preston, 269 
 Saltpeter, 258 
 
 Chile, 266 
 Salts, acid, definition of, 121 
 
 basic, definition of, 121 
 
 definition of, 120 
 
 double, definition of, 122 
 
 ethereal, 518 
 
 hydrolysis of, 201 
 
 ions of, 201 
 
 normal, definition of, 121 
 
 reaction to litmus, 121, 201 
 
 various methods of obtaining, 120 
 Salvarsan, 568 
 Santolene, 597 
 Santonin, 590 
 Saponification, 525 
 Sapphire, 286 
 Sarcine, 668 
 Sarcosine, 545 
 Scale compounds, 516 
 Scheele's green, 352 
 Schiff's reaction, 716 
 
 for formaldehyde, 490 
 Schweinfurt green, 352, 504 
 Schweizer's reagent, 537 
 Scopolamine hydrobromide, 606 
 Secretin, 682 
 Secretion, definition, 649 
 Sediment, definition of, 116 
 Seidlitz powders, 515 
 Selenium, 217 
 
 Semi-permeable membranes, 162 
 Serpentine, 272 
 Sesquiterpenes, 597 
 Sherer's reaction, 636 
 Shikimol, 575 
 Shot alloy, 347 
 Silica, 186 
 Silicates, 186, 286 
 Silicon* 186 
 
 carbide, 186 
 dioxide, 186 
 fluoride, 186 
 Silver, 330 
 
 allotropic forms of, 331 
 alloys of, 331 
 
 Silver, ammonio-chloride of, 335 
 
 compounds of, 335 
 bromide and iodide, 335 
 -casein, 334 
 chloride, 332 
 colloidal, 331. 
 
 complex compounds of, 334 
 Crede's, 331 
 cyanide, 551 
 fulminate, 541 
 German, 323 
 mirror, 514 
 nitrate, 332 
 
 moulded, 332 
 oxide, 333 
 tartrate, 514 
 vitellin, 334 
 Sinigrin, 556 
 Skatole, 693, 722 
 Skeletins, 629 
 Slag, 293 
 Slate, 286 
 Soap, 525 
 Soapstone, 272 
 Soda ash, 263 
 baking-, 264 
 bichromate of, 307 
 caustic, 262 
 -lime, 443 
 washing, 263 
 Sodium, 262 
 
 acetate, 503 
 -ammonium-hydrogen-phosphate, 
 
 380 
 
 arsanilate, 568 
 arsenate, 349 
 benzoate, 580 
 bicarbonate, 264 
 bisulphite, 264 
 borate, 266 
 bromide, 266 
 cacodylate, 478 
 carbonate, 263 
 
 monohydrated, 264 
 chlorate, 266 
 chloride, 262 
 citrate, 517 
 cobaltic nitrite, 374 
 cyanide, 551, 553 
 dichromate, 307 
 glycerin-phosphate, 489 
 and gold chloride, 366 
 hydroxide, 262 
 hypochlorite, 237 
 hypophosphite, 266 
 hyposulphite, 265 
 ichthyo-sulphonate, 573 
 iodide, 266 
 
 mercuric chloride, 339 
 met-arsenite, 348 
 metastannate, 363 
 -naphthol, 588 
 nitrate, 266 
 nitrite, 266 
 
ISDEX. 
 
 771 
 
 Sodium nitroferricyanido, 555 
 
 nitroprusside, 555 
 
 perborate, 189 
 
 peroxide, 263 
 
 phenolate, 570 
 
 phenolsulphonate, 573 
 
 phosphate, 265 
 
 effervescent, 265 
 exsiccated, 265 
 
 potassium tartrate, 515 
 
 pyrophosphate, 265 
 
 salicylate, 583 
 
 stannate, 363 
 
 sulph-antimonite, 359 
 
 sulphate, 264 
 
 sulphite, 264 
 
 sulphocarbolate, 573 
 
 tetrathionate, 213 
 
 theobromine salicylate, 616 
 
 thiosulphate, 265 
 Solder, 319 
 
 Solids, definition of, 19 
 Solubility, definition of, 158 
 
 table of, 396, 397 
 Soluble ferments, 455 
 Solute, 158 
 Solution, colloidal, 331 
 
 complex or chemical, 151 
 
 definition of, 151, 157 
 
 heat of, 158 
 
 ionic mechanism of, 217 
 
 of gases, 159 
 
 saturated, 151 
 
 simple, 151 
 
 tension, 319 
 
 Solutions, boiling- and freezing-points 
 of, 160 
 
 hyper- and hypotonic, 163 
 
 is-osmotic or isotonic, 163 
 Solutol, 574 
 Solvay process, 263 
 Solveol, 574 
 Somnoform, 478 
 Sonnenschein's test, 611 
 Sources of heat, 44 
 Sparteine, 604 
 Spasmotpxine, 621 
 Spathic iron ore, 293 
 Specific gravity, 32 
 
 heat, 49 
 
 weight, 32 
 Spectroscope, 59 
 Spectrum, 59 
 
 continuous, 61 
 Spermaceti, 520 
 Spirit, 482, 486 
 
 Columbian, 482 
 
 methylated, 482 
 
 of ammonia, aromatic, 269 
 
 of ether, 522 
 
 compound, 522 
 
 of glonoin, 488 
 
 of glyceryl trinitrate, 488 
 
 of hartshorn, 169 
 
 Spirit of Mindererus, 503 
 
 of nitrous ether, 523 
 assay of, }_".) 
 
 of phosphorus, 222 
 
 proof-, 484 
 
 wood-, 482 
 Stannic chloride, 363 
 
 hydroxide, 362 
 
 oxide, 362 
 
 sulphide, 363 
 Stannous chloride, 363 
 
 hydroxide, 362 
 
 oxide, 362 
 
 sulphide, 363 
 Starch, 535 
 
 iodized, 536 
 
 solution, 421 
 Stassfurt salts, 256 
 Steapsin, 683 
 Stearin, 524 
 Stearoptens, 598 
 Steatases, 637 
 Steel, 294 
 
 Stereo-isomerism, 452 
 Sterilization, 458 
 Stibnite, 358 
 Stokes' fluid, 657 
 Stoneware, 289 
 Storage battery, 320 
 Stout, 486 
 Strontianite, 282 
 Strontium, 282 
 
 chloride, bromide, and iodide, 282 
 
 hydroxide, 282 
 
 nitrate, 282 
 
 oxide, 282 
 
 salicylate, 584 
 Strychnine, 610 
 Stypticin, 614 
 Sublimation, 21 
 Substitution, 450 
 Succus entericus, 687 
 Sucrates, 534 
 Sucrol, 581 
 Sugar, cane-, 533 
 
 estimation in urine, 733 
 
 fruit-, 532 
 
 grape-, 531 
 
 muscle-, 532 
 
 of lead, 503 
 
 of milk, 534 
 Sulph-antimonites, 359 
 
 -arsenates, 351 
 Sulpho-alcohols, 495 
 Sulphonal, 495 
 Sulphonethylmethane, 496 
 Sulphonmethane, 495 
 Sulphur, 204 
 
 determination in organic com- 
 pounds, 445 
 
 dioxide, 206 
 
 flowers of, 205 
 
 iodide of, 243 
 
 milk of, 205 
 
772 
 
 INDEX. 
 
 Sulphur, oxides of, 206 
 
 precipitated, 206 
 
 sublimed, 206 
 
 trioxide, 208 
 
 washed, 206 
 Sulphurated lime, 281 
 Sulphuretted hydrogen, 214 
 Sulphuric anhydride, 208 
 
 ether, 520 
 
 Sulphurous anhydride, 206 
 Supersaturation, definition of, 158 
 Suprarenal glands, desiccated, 669 
 Surface-action, 36 
 
 tension, 38 
 
 Sweet spirit of niter, 523 
 Sylvestrene, 597 
 Symbols of compounds, 99 
 
 of elements, 99 
 Synthesis, 151 
 
 T. 
 
 TABLE of solubility, 396, 397 
 
 Talc, 272 
 
 Tallow, 525 
 
 Tannin, 585 
 
 Tannon, 543 
 
 Tannopin, 543 
 
 Tartar, 665 
 
 cream of, 514 
 crude, 512 
 emetic, 361, 515 
 Taurine, 546 
 Tellurium, 217 
 Temperature, 44, 46 
 absolute, 47 
 critical, 141 
 kindling, 142 
 Tempering, 252 
 Tenacity, 26 
 Tension, 26 
 
 of saturated water-vapor, 53 
 Terebene, 597 
 Terpenes, 594 
 Terpin hydrate, 599 
 Test, charcoal reduction, 212 
 
 definition of, 155 
 Tests for acetanilide, 565 
 acetic acid, 503 
 albumin in urine, 723 
 aluminum, 290 
 ammonium compounds, 271 
 antimony, 361 
 antipyrine, 591 
 apomorphine, 613 
 arsenic, 351 
 atropine, 605 
 barium, 284 
 bile, in urine, 737 
 biliary acids, 686 
 pigments, 685 
 bismuth, 329 
 blood in urine, 728 
 boric acid and borates, 188 
 
 Tests for brucine, 611 
 
 calcium, 281 
 
 carbohydrates in urine, 730 
 
 carbonates, 183 
 
 casein, 697 
 
 chloral, hydrated, 493 
 
 chlorates, 238 
 
 chloroform, 476 
 
 cholesterin, 671 
 
 chromium, 311 
 
 cinchonine, 610 
 
 citric acid, 517 
 
 cocaine, 607 
 
 codeine, 614 
 
 copper, 326 
 
 creatinin, 667 
 
 dextrose, 531 
 
 ethyl alcohol, 485 
 
 fats and fatty acids, 526 
 
 ferrocyanides, 554 
 
 fluorides, 244 
 
 formaldehyde, 490 
 
 gelatin, 664 
 
 glycerin, 487 
 
 glycogen, 693 
 
 gold, 366 
 
 hippuric acid, 718 
 
 hydrobromic acid and bro- 
 mides, 240 
 
 hydrochloric acid and chlo- 
 rides, 234 
 
 hydrocyanic acid, 551 
 
 hydrogen dioxide, 155 
 
 sulphide and sulphides, 
 216 
 
 hypochlorites, 238 
 
 hypophosphites, 224 
 
 indican, 721 
 
 iodine and iodides, 242 
 
 iron, 301 
 
 lead, 322 
 
 leucine, 635 
 
 manganese, 305 
 
 magnesium, 276 
 
 mercury, 343 
 
 metals, remarks on, 274 
 
 metaphosphoric acid, 226 
 
 milk-sugar, 699 
 
 morphine, 612 
 
 nitric acid and nitrates, 176 
 
 nitrous acid and nitrites, 173 
 
 oxalic acid, 509 
 
 phenol, 571 
 
 phosphates, 228 
 
 phosphites, 225 
 
 physostigmine, 617 
 
 potassium, 260 
 
 preservatives in milk, 701 
 
 pyrocatechin, 723 
 
 pyrophosphates, 226 
 
 quinine, 609 
 
 salicylic acid, 584 
 
 santonin, 590 
 
 silicic acid and silicates, 186 
 
L\DI-:X. 
 
 773 
 
 Tests for silver, 334 
 
 simple proteins, 626 
 sodium, 267 
 strontium, 282 
 strychnine, 610 
 sugar, in urine, 729 
 sulphuric acid and sulphates, 
 
 211 
 sulphurous acid and sulphites, 
 
 208 
 
 tannic acid, 586 
 tartaric acid, 514 
 thiosulphates, 213 
 tin, 363 
 tyrosine, 635 
 urea, 712 
 uric acid, 716 
 veratrine, 611 
 zinc, 315 
 Tetanine, 621 
 Tetrachlor-methane, 474 
 Tetrads, 103 
 Tetra-iodo-pyrrol, 591 
 Tetronal, 496 
 Thalleioquin, 609 
 Thalline, 593 
 Theine, 616 
 Theobromine, 616 
 
 sodium salicylate, 616 
 Theory, atomic, 96 
 
 of equivalents, 102 
 molecular, 28 
 Thermal equations, 143 
 Thermo-chemistry, 143 
 Thermodin, 545 
 Thermometers, 46 
 Thio-alcohols, 495 
 Thiosinamine, 557 
 Thymol, 575 
 
 iodide, 575 
 Thyreoidectin, 669 
 Thyro-iodine, 242, 669 
 Thyroid glands, desiccated, 669 
 Tin, 362 
 
 alloys, 323 
 chlorides, 363 
 hydroxides, 362 
 oxides, 362 
 perchloride, 363 
 -plate, 362 
 protochloride, 363 
 -stone, 362 
 sulphides, 363 
 
 Tincture of ferric chloride, 297 
 of iodine, 241 
 
 decolorized, 270 
 Titer, 412 
 Titration, 403, 411 
 Tollen's orcin reaction, 735 
 Toluene, 563 
 Tourmaline, 63 
 Toxines, 619 
 
 bacterial, 661 
 endo-, 661 
 
 Toxines, soluble, 661 
 Triads, 103 
 Tribrom-methane, 477 
 Trichloraldehyde, 492 
 Trichlor-methane, 474 
 Tri-cresol, 574 
 Triiodo-methane, 477 
 Trinitro-phenol, 572 
 Trional, 496 
 Triple linkage, 471 
 Trommer's test, 730 
 Tropseolin D, 411 
 Trypsin, 683 
 Tryptophan, 684 
 Turnbull's blue, 301, 555 
 Turpentine, 599 
 Turpeth mineral, 341 
 Type metal, 318, 358 
 Typhotoxine, 621 
 Tyrosine, 634, 744 
 Tyrotoxicon, 621 
 
 U. 
 
 UFFELMANN'S test, 669 
 
 Ultramarine, 290 
 
 Unguentum Cred6, 331 
 
 Urates, 742 
 
 Urea, 546, 710 
 
 compounds, 546 
 determination of, 712 
 manufacture of, 553 
 
 Ureids, 547 
 
 Ureometer, Doremus', 714 
 
 Urethane, 545 
 
 Urinary calculi, 745 
 sediments, 740 
 
 Urine, 703 
 
 albumin in, estimation, 726 
 alkaptonic acids in, 739 
 ammonia in, estimation, 713 
 analysis of, 704 
 carbohydrates in, 729 
 chlorides in, estimation, 719 
 composition of, 708 
 estimation of sugar in, 733 
 
 Urinometer, 707 
 
 Uritone, 543 
 
 Urobilin, 705 
 
 Urochrome, 705 
 
 Uroerythrin, 705 
 
 Urotropin, 543 
 
 V. 
 
 VALENCE, 102 
 Vanillin, 578 
 
 distinction from coumarin, 578 
 Vaseline, 469 
 Veratrine, 611 
 Veratrol, 575 
 Verdigris, 504 
 Vermilion, 342 
 Veronal, 547 
 
774 
 
 INDEX. 
 
 Vinegar, 502 
 Vital force, 439 
 Vitriol, blue, 325 
 
 green, 298 
 
 white, 315 
 Volatile oils, 594 
 Volhard's solution, 427 
 Volt, 77 
 Voltaic electricity, 74 
 
 induction, 78 
 Volumetric methods, 406 
 
 solutions equivalents of, 416, 419, 
 
 422, 426 
 Vulcanite, 598 
 Vulcanized rubber, 597 
 Vulcanizers, 80 
 
 W. 
 
 WASHING soda, 263 
 Wassermann reaction, 662 
 Waste products of animal life, 648 
 Water, 148 
 
 analysis, 429 
 
 bitter almond, 578 
 
 of crystallization, 152 
 
 distilled, 150 
 
 drinking-, 149 
 
 -gas, 184 
 
 hard, 149, 181 
 
 lead-, 504 
 
 mineral, 149 
 
 soft, 149 
 
 -vapor, tension of, 53 
 Waves, actinic, 56 
 
 of heat, 51 
 
 infra-red, 56 
 
 light, 56 
 
 ultra-violet, 56 
 Wax, 520 
 Weight, absolute, 32 
 
 apparent, 32 
 
 atomic, definition of, 98 
 
 definition of, 31 
 
 specific, 32 
 
 metric, 32 
 
 molecular, 99 
 Welsbach mantle, 291 
 Weyl's reaction, 667 
 Whey, 700 
 Whiskey, 486 
 White arsenic, 348 
 
 -lead, 321 
 
 I White precipitate, 342 
 
 vitriol, 315 
 Widal's reaction, 660 
 Will-Varrentrap determination of nitro- 
 gen, 445 
 Wine, 486' 
 Witherite, 283 
 Wood-naphtha, 482 
 
 -spirit, 482 
 Wool-fat, 527 
 Work, chemical, 142 
 
 X. 
 
 XANTHINE, 668 
 
 alkaloids, 615 
 
 bases, 667 
 
 bodies, 717 
 
 Xanthoproteic reaction, 626 
 Xeroform, 572 
 Xylenes, 563 
 
 Y. 
 
 YELLOW prussiate of potash, 554 
 -wash, 338 
 
 Z. 
 
 ZEIN, 628 
 Zinc, 312 
 
 acetate, 503 
 
 alloys, 313, 323 
 
 amalgam, 313 
 
 -blende, 312 
 
 bromide, 314 
 
 carbonate, 314 
 
 chloride, 314 
 
 flowers of, 313 
 
 hydroxide, 313 
 
 iodide, 314 
 
 oxide, 313 
 
 oxy chloride, 314 
 
 oxy phosphate, 314 
 
 phenolsulphonate, 573 
 
 silicate, 312 
 
 sulphate, 315 
 
 sulphocarbolate, 573 
 
 valerate, 506 
 
 -white, 313 
 Zincates, 317 
 Zingiberene, 597 
 Zymogens, 638 
 
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8656 
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 10th ed. 
 
 Simofi, W. 
 
 Manual of chem 
 Siiion & Base. 
 
 Library of the 
 University of California Medical School and Hospitals