From the collection of the Z n z _ m o PreTinger i a Uibrary San Francisco, California 2006 FIRST PRINCIPLES CHEMIST RY, FROM THE PREFACE TO THE FIRST EDITION. THE object of this work is sufficiently indicated by its title. It has grown out of the exigencies of teaching, and has been received as the Text Book in the public lectures at Yale College. It is important that a work of this kind should contain only such matter as is actually taught to a class by recitations and lectures. 1* VI PREFACE. All fulness beyond this is unavailable to either teacher or pupil, and serves often to embarrass the one and to discourage the other. This is perhaps the reason why several works, otherwise excellent, have failed to answer the purpose for which they were written. The science of Chemistry has now reached the point where its First Principles can be presented by the teacher with almost mathe- matical precision. Chemistry has attractions of an economical and experimental character, which will always secure for it a place in every system of education. Without wishing to diminish its claims to attention on these grounds, the author urges the paramount advantages pos- sessed by his favorite science, as a study peculiarly fitted to train the mind to a methodi/.ed and logical habit of thought. If nothing more is to be derived from its study than the entertainment offered by brilliant phenomena, and a knowledge of convenient economical processes, the pupil will fail of its most important advantage. The beautiful philosophy, the perspicuous nomenclature, and lucid method of modern chemistry, are so obvious that they cannot fail to awaken the attention of every intelligent pupil, and carry him on his course of intellectual culture with rapid progress. * * * * The author has consulted all the best authorities within his reach, both in the standard systems of England and France, and in the scientific journals of this country and Europe. The works of Dan- iell, Graham, Brande, Kane, Fownes, Gregory, Faraday, Mitscher- lich, Berzelius, Dumas, Liebig, and Gerhardt, have all been used, as also the treatises of Dr. Hare and Prof. Silliman. The Organic Chemistry is presented mainly in the order of Lie- big in his Traite tie Chimie Organiqttf. The author takes pleasure in acknowledging the important aid derived in this portion of the work from his friend and professional assistant, Mr. THOMAS S. HUNT, whose familiarity with the philosophy and details of Chem- istry, will not fail to make him one of its ablest followers. The labor of compiling the Organic Chemistry has fallen almost solely upon him. If it shall be found to meet the wants of both teachers and pupils, and to promote the progress of Scientific Chemistry in this coun- try, the author will feel that he has not labored in vain. NEW HAVEN, December 1, 1646. TABLE OF CONTENTS. INTRODUCTION, Sources of Knowledge, Distinction between the an- cient and modern philo- sophy, . Physical and Intellectual Philosophy, General divisions of knowledge of nature, MATTER. General Properties of Matter, Molecules, or Atoms, Indestructibility of Matter, and Cohesion, Repulsion and Attraction, Elements and Impondera- ble Agents, The Three States of Mat- terthe Solid, the Flu- id, and the Gaseous, The Atmosphere and Laws of Gases, Air-Pump, Law of Mariotte, Barometer, Limits of the Atmosphere, Weight and Specific Gra- vity, Standards of Specific Gra- vity, PART I. PHYSICS. PAGE PAOK . n Specific Gravity of Solids, 30 e L3 The Hydrometer, . 39 lean- Specific Gravity of Gases, 41 ihilo- LIGHT, Sources and Nature, 41 11 Reflection, ... 43 ctual Refraction, . . 44 . 14 Prism and Analysis of our Light, ... 46 e, 15 Double Refraction, . 48 jrties Polarization, . . 49 . 18 Chemical Rays, . . 50 17 Spectral Impressions, . 51 atter, Phosphorescence, . 52 18 HEAT Sources, . . 53 mical Expansion, . . 55 19 Thermometers, . . 56 dera- Pyrometers, . . 62 . 20 Laws of Expansion, . 63 Mat- Unequal Expansion of Wa- Flu- ter, ... 65 5, 21 Communication of Heat, 67 Laws Conduction, . . 68 21 Convection of Heat, . 71 . 26 Radiant Heat, . . 72 . 27 Absorption, . . 73 29 Transmission of Heat, 74 >here, 32 Melloni's Experiments, 75 Gra- Specific Heat or Capacity, 78 . 33 Changes produced by Heat Gra- in the State of Bodies, . 34 Liquefaction, . . 79 quids, 35 | Freezing and Melting, 81, 52 Vlll CONTENT:?. Vaporization, (Boiling- Points,) ... 83 Cryophorus, . . 87 Elevation of Boiling-Points by Pressure, . . 88 The Steam Engine, . 90 Evaporation, . . 90 Maximum Density of Va- pors, ... 91 Diffusion of Gases, . 92 Dew Point, . . 93 . Hygrometers, . . 94 Spheroidal State of Bodies, 95 Liquefaction of Gases, 95, 96 j ELECTRICITY. Of Magnetism, 98 , Magnetics and Diamag- netics, . . . 102 | Electricity of Fnction, 103 Theories of Electricity, 105 PACK Electroscopes, . . 106 Electrical Machines, . 107 Leyden Jar and Electro- phorous, . . 108 Electricity of Chemical Action Galvanism, 109 Voltaic Pile, . . Ill Simple Voltaic Circle, 112 Compound Voltaic Circle, 113 Galvanic Batteries, . 115 Electro-Magnetism, . 116 Ampere's Theory, . 118 Electro-Magnetic Motions 121 Henry's Coils, . . 123 Secondary Currents, . 12 4 Electro-Magnetic Tele- graph, . . .127 Magneto-Electricity, . 130 Thermo-Electricity, . 131 PART II. CHEMICAL PHILOSOPHY. ELEMENTS AND THEIR LAWS OF COMBINATION, . 133 Combination by Weight, 134 Definite and Multiple Pro- portions, . . . 134 Equivalent Proportions, 135 Table of Chemical Equi- valents, . . . 136-7 Combination by Volume, 138 Chemical Nomenclature, 140 I Names of Compounds, 141 Chemical Symbols, . 145 Chemical Affinity, . 147 Atomic Theory, . . 151 Specific Heat of Atoms, 152 CRYSTALLIZATION, . . 152 Crystalline forms, . 155 Cleavage of Crystals, 158 Measurement of Crys- tals, . . .159 Isomorphism, . 161 CHEMICAL EFFECTS OF VOL- TAIC ELECTRICITY, . 163 Conditions of Voltaic De- composition, . . 164 Laws of Electrolysis, . 167 Voltameters, . . 168 Sustaining Batteries, . 169 " " Daniell's, 170 Grove's and Smee's Bat- teries, . . .171 Electro-Metallurgy, . 173 CONTENTS. PART HI. INORGANIC CHEMISTRY. PAGE NON-METALLIC ELEMENTS, 175 Classification, . . 175 1. Oxygen, ... 176 Management of Gases, 179 2. Chlorine, ... 181 Compounds of Chlorine with Oxygen, . 185 3. Bromine, . . . 188 4. Iodine, . . . 189 Compounds of Iodine with Oxygen, &c. . . 190 5. Fluorine, ... 191 6. Sulphur, ... 192 Compounds with Oxygen, 193 Sulphurous Acid, . 194 Sulphuric Acid, . 195 7. Selenium, ... 199 8. Tellurium, . . 200 9. Nitrogen, ... 200 Chemical History of the Atmosphere, . . 202 Compounds of Oxygen and Nitrogen, . 203 Nitrous Oxyd, . . 204 Nitric Oxyd, . . 205 Nitric Acid, . . 207 10. Phosphorus, . . 209 Compounds of Phospho- rus with Oxygen, . 211 Other Compounds of Phos- phorus, . . 212 11. Carbon, ... 213 Carbonic Acid, . 217 Carbonic Oxyd, . 220 Compounds of Carbon with the Chlorine Group, 222 Compounds of Carbon and Nitrogen, 12. Silicon, . Sicilic Acid, Fluorid of Silicon, 13. Boron, Boracic Acid, . 14. Hydrogen, 222 223 224 226 227 228 229 PAOK Nature of Hydrogen, 234 Compounds of Hydrogen, 235 Water, . . . 235 Eudiometry by Hydrogen, 240 Union of Hydrogen and Oxygen by platinum sponge, . . . 241 Oxyhydrogen Blowpipe, 242 Natural and Chemical His- tory of Water, . , 244 Peroxyd of Hydrogen, 246 Ozone, ... 247 Compounds of Hydrogen with II. and III. classes, 248 Action of Hydrogen with Chlorine, . . 248 Hydrochloric Acid, . 249 Hydrobromic Acid, . 252 Hydriodic Acid, . 253 Hydrofluoric Acid, . 254 Hydrosulphuric Acid, 255 Ammonia, . . 258 Phosphureted Hydrogen, 261 Light Carbureted Hydro- gen, ... 263 Olefiant Gas, . . 264 Combustion and Structure of Flame, . . 266 Lamps and Blowpipe, 271-2 Safety Lamp, . . 274 METALLIC ELEMENTS, . 275 General Properties of the Metals,. . . 276 Classification of Oxyds, 278 Theory of Salts, . 279 Classification of Metals, 281 15. Potassium, . . 282 Potash, ... 284 Salts of Potash, . 287 16. Sodium and Soda, . 292 Chlorid, &c. of Sodium, 293 Manufacture of Glass, 297 17. Ammonium, . . 298 Salts of Ammonium, . 299 CONTENTS. Hydrosnlphuret of Am- monia, . 18. Lithium, . 19. Barium, . . " . 20. Strontium, 21. Calcium and Lime, . 22. Magnesium and Magnesia, 306 23. Aluminium, Alums, Pottery, . 24. Glucinum; 25. Yttrium ; 26. Zirconium; 27. Thorium; 28. Cerium; 29. Lantanum, 30. Manganese, 31. Iron, Manufacture of Iron, . Oxyds of Iron, . 32. Chromium, 33. Nickel, . 34. Cobalt, . 35. Zinc, 36. Cadmium, 'AGE PAG* 37. Lead, . 324 300 38. Uranium, . . 326 301 39. Copper, . 326 3QJ 40. Vanadium ; 41. Tungsten; 303 42. Molybdenum ; 43. Co- 303 lumbium ; 44. Titanium, 327 306 45. Tin, . . 329 308 46. Bismuth, , . 331 309 47. Antimony 332 310 48. Arsenic, . 334 Arsenious Acid, White Arsenic 334 Detection of Arsenic as a 311 poison, . 336 312 49. Osmium, ... 338 314 50. Mercury, . 339 315 51. Silver, ... 342 316 52. Gold, ... 345 318 53. Platinum, 346 320 54. Palladium 348 321 55. Rhodium, ... 349 322 56. Iridium, . 349 323 PART IV. ORGANIC CHEMISTRY. INTRODUCTION, . . 350 General Properties of Or- ganic Bodies, . 350 Modes of Combination, 352 Equivalent Substitution, 352 Monobasic Acids, and Substitution by Resi- dues, . . . 353 Sesqui-salts, Direct Union, 354 Isomerism, . . 354 On the Density of Vapors, 355 Analysis of Organic Sub- stances, . . 357 ORGANIC COMPOUNDS AND PRO- DUCTS OF THEIR ALTERA- TION, . . . 362 Ammonia, . . . 362 Amides, . . . 363 THE GROUP OF ALCOHOLS, Alcohol, ... 364 Sulphur Alcohol, . 366 Action of Acids upon Al- cohol, . . . 366 Coupled Acids, . . 367 Nitric, Perchloric, Hydro- chloric Ethers, . 368-69 Acetene, Nitric Acetene, Sulphovinic Acid, 369-70 Carbovinic Acid, . 370 Silicic Ethers, Products of the decomposition of Sulphovinic Acid, 371 Sulphuric Ether, Letheon, 372 Olenant Gas, . . 373 CONTENTS. PAGE Dutch Oil, . . 374 Products of the Oxyda- tion of Alcohol, . 375 Acetic Acid, . . 376 Acetates, . . 377 Acetates of Lead, . 378 Wood-Spirit, or Methylic Alcohol, . . 380 Methylic Ethers, &c., 381 Oxydation of Wood-Spirit, 382 Formic Acid, . . 383 Amylic Alcohol, . 383 Amy lie Ethers, . . 384 Oxydation of Amylic Acid, 385 Ethal and Ethalic Acid, 385-6 On the Relations of the preceding Bodies, . 387 Bitter Almond Oil, Ben- zoilol, . . .388 Benzamide, Hydrobenza- mide, . . . 389 Benzoine, Benzene, Nitro- benzene, . . 390 Oil of Cumin, . . 390 Oil of Spirea, . . 391 Salicylol, Salicylic Acid, 391 Phenol, Oil of Cinnamon, 393 SUGAR, STARCH, AND ALLIED SUBSTANCES, . . 394 Products of the decompo- sition of the Sugars, 395 The Vinous Fermentation, 395 Lactic Acid, . . 396 Starch, . . .398 Dextrine, . . .399 Woody Fibre, . . 400 Xyloidine, Gun Cotton, Pyroxyline, 401 Transformation of Woody Fibre, Destructive Dis- tillation of Wood, . 403 Kreasote, Paraffine, Coal Tar, . . .404 Petroleum, . . 405 FATS AND THE SUBSTANCES DE- RIVED FROM THEM, . 405 Soaps, Glycerides, Acro- leine, . . . 406 Butyric Acid, Butyric Ether, . . .407 Margarine, Stearrne, Ole- ine, 409 Fatty Acids, Oleic Acid, Soaps, VEGETABLE ACIDS, . Oxalic Acid, Oxalate of Lime, Tartaric Acid, . Racemic, Malic, Citric, Tannic, Tannin, Gallic Acid, PAGE 410 411 412 412 412 414 414 415 416 417 418 VOLATILE OR ESSENTIAL OILS, 418 Oil of Turpentine, . 419 Camphene, . . 419 Juniper, Pepper, Lemon, &c. 419 Camphor, Borneo Cam- phor, Oil of Mustard, 420 Caoutchouc, Gum-Elastic, 420 Gutta Percha, . . 421 COLORING MATTERS, . 421 Quercitrine, Carthamine, Turmeric, . . 422 Hematoxyline, Carmine, Chlorophyle, Lecano- rine, Orcine, . . 422 Indigo, . . .423 Indigogene, Sulphindigotic Acid, Saxon Blue, . 424 Isatine, Chlorisatine, . 425 Isatyde, Indine, Ariilic Acid, . . .425 Chloranile, . . 426 ORGANIC BASES, OR ALKALOIDS. Constitution and characters 426 Anilene, Chloranilene, Ni- traniline, . . 427 Quinoline, Nicotine, Co- nine, Amarine, . 428 Cinchonine, . . 428 Morphine, Codeine, Nar- cotine, . . .429 Strychnine, Brucine, So- lanine, Veratrine, . 430 Aconitine, Sanguinarine, Theine, Caffeine, The- obromine, . . 431 OTHER VEGETABLE PRINCIPLES. Amygdaline, Asparagine, 432 Salicine, Saligenine, Sali- retine, . . .433 Helicine, Phloridzine, 434 Xll CONTENTS. THE CYANIDS, AND THE COM- POUNDS DERIVED FROM THEM. Hydrocyanic Acid, . 435 Cyanid of Potassium, . 436 Cyanogen, . . . 437 Cyanates, Cyanate of Po- tash, . . . 438 Urea, . . .439 Sulphocyanates, Mellon, 440 Melan, ... 440 Results of the Complica- tion of the Cyanids, 441 Cyanuric Acid, Melanine,441 Ammeline, Ammelide, 442 Complex Cyanids, Ferro- cyanids, Yellow Prus- siate of Potash, . 442 Ferro-cyanic Acid, Prus- sian Blue, Ferridcyanid of Potassium, . 444 Ferridcyanic Acid, . 445 Platino-cyanids, . . 445 Fulminates, Fulminate of Mercury, do. Silver, 446 ALCARSINE, AND THE BODIES DERIVED FROM IT. Alcarsine, Chlorarsine, 447 Kakodyle, Alcargene, 448 URIC ACID, AND THE PRO- DUCTS OF ITS DECOMPOSI- TION, .... 448 Allantoine, Alloxan, Al- loxantine, . . 449 Uramile, Murexide, Para- banic Acid, . . 450 Oxaluric Acid, . . 451 HIPPURIC ACID, . . 451 Glycocoll, Gelatine Su- gar, Relations of Gly- cocoll and Alcargene, 452 NUTRITIVE SUBSTANCES CON- TAINING NITROGEN, . 452 rxai Vegetable Albumen, Fi- brine, Caseine, &c. 452 Bread, Yeast, Animal Al- bumen, Fibrine,Caseine 453 Proteine, . . . 454 Gelatine, Chondrine, . 455 THE BLOOD. Red Globules, Hematine, Arterial Blood, 456 Chyle, . . .457 THE GASTRIC JUICE, . 457 Pepsine, the Saliva, . 458 THE BILE. Cholesterine, 453 Choleic Acid and Cho- leate of Soda, . . 458 THE URINE, ... 459 Calculi, . . .460 THE BRAIN AND NERVOUS MAT- TER, .... 460 Cerebric and Oleo-phos- phoric Acids, . 460 MILK AND BONES, . . 460 Analysis of Bones, . 461 NUTRITION OF PLANTS AND ANIMALS, . . . 462 The Food of Plants, . 462 Cellular Tissue,. . 463 Evolution of Oxygen, . 463 Soils, Inorganic Constitu- ents of Plants, . 463 Action of Humus, . 464 Growth of Air Plants, 464 Fertilizers, Ammonia,Gu- ano, . . . 465 The Digestive Function, 465 Assimilation of Fats, . 466 Waste of Tissues, . 466 Objects of Respiration, 467 Uses of Oxygen, . 467 Vital Heat, . . 467 Balance of Organic Na- ture, . . . 468 INDEX, . . . .471 FIRST PRINCIPLES OF CHEMISTRY, PART I. PHYSICS. INTRODUCTION. 1. OUR knowledge of nature begins with^experienceJ While this teaches us that like causes, under similar cir- cumstances, produce like effects, we also recognise as insepa- rable from our experience, the great principle that^cyery event must have a cause.) Man, " as the priest and interpreter of nature,"* seeks to extend his experience by experiment. Every experiment is byt a/question addressed to naturc^Jask- ing for an increase of knowledge ; and if we question her aright, we may be sure of a satisfactory answer. 2, ^bservation instructs us in a knowledge of the external forms of nature! and we thus acquire our first impressions of the various departments of Natural History. Our knowledge would, however, be very limited, without a constant effort (to extend our experience by experiment^ The ancient tjfreeks and Romans fwere learned and polished in the intel- lectual arts, and excelled in many branches of human know- ledge.^ Their ignorance, however, of the works of nature, and te laws by which they are regulated, was extreme ; and 1. What is the beginning of our knowledge of nature? What great principle do we recognise in connection with experience ? What is an experiment ? 2. What does observation teach ? How does it extend our knowledge ? What is said of the ancients ? Why did they fail ? "Homo naturae minister et interpret" Bacon. 14 INTRODUCTION. this was because |hcy failed to question her aright y because they overlooked the true connection between cause and etfect. The ancient philosophy Abounded in plausible arguments^ regarding those phenomena of nature which could not fail to arrest the attention of an intelligent people; but its reasonings were based on anl a priori assumption of a cause, and not upon an inductive inquiry alter facts and their connections. ) It failed to apply itself(to the careful collection and study or facts in order to science.} Facts in naturc(are the expression of the Divine willAin the government of the physical world. /The universe of matter is made up of facts,f which, observed, TTaced out, and arranged, lead us to the knowledge of certain laws and forces which proceed /(directly from the mind of God^ These are the " laws of Suture :'\>cicnce is but the exposition of them! and of science based upon such grounds, the ancient Philosophy was cotnpletcly ignorant. 3. It is important to distinguish. that knowledge /vhich is purely intellectual in its characters from that whicn results from observation and experience. Speaking of this subject, one of the most learned of living philosophers says : \J\ clever man, shut up alone, and allowed unlimited time, might reason out for himself all the truths of mathematics, by pro- ceeding from those simple notions of space and number, of which he cannot divest himself, withoutceasing to think ; but he could never tell, by any eflbrt of reasoning, what would become of a lump of sugar, if immersed in water, or what impression would be produced on the eye, by mixing the colors yellow and bluc.jf (Hersckel.) We may, however, with propriety doubt^whether there is any knowledge or philosophy so purely intellectual, or absolute, that it does not imply some previous recognition of physical facts.^ 4. The physical philosopher is also of nccpssity\gn intel- lectual philosopher^ The observation of factsubrms only the foundation of science,Vnd a fact isolated and unexplained has ( no scientific value. J The knowledge of physical laws deduced Characterize the ancient philosophy. On what was its reasoning based ? How did it fail ? What are facts ? How do we detect the laws and forces of nature ? From whence do these proceed ? What is science ? 3. What convenient distinction is named ? "What remark is quoted in illustration of this ? What doubt may we entertain 1 4. What is said of the physical philosopher / What of observation ? What of an isolated fact ? INTRODUCTION. 15 from the study of observed facts will enable the philosopher fro foretell the result of the possible combination of those raws'! and to assign reasons for apparent departures from them. In this way (discoveries are predicted and detailed 1 observation is anticipated, and called on to verify the alleged discovery. The perturbations of the planet Uranus ^ndicated the existence of some body in space heretofore unknown.," yWhen Le Verrier had reconciled these disturbances^Jwith the supposed influence of a new planet, and determined its ele- ments of motion, he had as truly discovered the remote sphere which now bears his name, as when the German astronomer, by pointing his telescope to the precise place in the heavens which Le Verrier had designated, announced to the world that the stupendous prediction was verified by observation. In like manner, a familiarity with chemical laws enables the chemist to (foretell the result of combinations ^vhich he has never investigated, and in some cases even to assign the con- stitution of bodies which he has never analyzed. 5. Our knowledge of nature is conveniently classified kinder three great divisions,! which are, Natural History, Mechanical Philosophy, and Chemistry. The first teaches fus the characters and arrangement of the various forms of animal and vegetable life and minerals, giving origin to the sciences of Zoology, Botany, and Mineralogy J Mechanical Philosophy (explains the laws which govern masses of matter, without considering of what that matter is composed./ It tells us how bodies fall to the earth, how liquids spout from an orifice ; it explains the power of the lever, the screw, and the inclined plane ; it teaches us the mechanical laws of the atmosphere and of the celestial bodies, the phenomena of tides and currents and the winds ; but it tells us nothing of the nature of the various substances of which it treats. I Chemistry begins where the natural sciences end J It teaches us the intimate and invisible constitution of bodies, and reveals to us the compounds which may be formed by the What does a knowledge of natural laws enable the philosopher to do ? What happens in this way ? Illustrate this in case of the perturba- tions of Uranus. When had Le Verrier truly made his discovery ? What can the chemist do ? 5. How is our knowledge of nature classified ? What does the first teach ? Mechanical philosophy teaches what ? Define the province of Chemistry. 16 MATTER. union of simple substances, and the laws of their combination. lit investigates the forces resident in matter,}and which are inseparable from our idea of molecular action, forces whose play produces the phenomena of Light, of Heat, and of Electricity. Chemistry also unfolds the\wonderful operations of animal and vegetable life,Jso far as their functions dej>cnd upon chemical laws, as in tne processes of respiration and digestion. While we now direct our attention to Chemistry, we naturally inquire,UVhat is Matter? ) I. MATTER. V 1. General Properties of Matter. G( Experience ^founded on the evidence of our senses, has convinced us of the existence of matter. We feel tin* resistance which it offers to our touch ; we sec that it has form, and occupies space, and hence we say it has extent ; and, lastly, we attempt to raise it, and we find ourselves opposed by a certain force which we call weight. Matter possesscsfextensionA Ix'cause it occupies some space. It islimpenetrablcj Ix.'causc one particle of matter cannot occupy the same space with another at the same time. It ha^ gravityjbecausc it olx'ys the law of universal gravitation. Whatever, therefore, possesses these three qualities, is matter. 7. Let us look at these qualities a little more attentively. The largest and most solid masses of matter, even entire mountains, may be ground down by mechanical force to dust so fine that the winds will bear it away ; but each minute particle still occupies some space, and we may imagine that a great multitude of smaller particles may still be formed from its further division. A grain of gold may be spread out so thin as to cover 600 square inches of surface on silver wire, and an ounce can in this manner be made to cover 1300 miles of such wire. One grain of green vitriol, What is its relation to the powers of matter ? It also unfolds what of life ? What inquiry naturally arises in commencing tho study of Chemistry ? G. What evidence have \ve of the existence of matter ? What three qualities are named as belonging to matter ? What is extension ? What is impenetrability ? What do we mean by weight? 7. If we reduce solid matter to dust, do we destroy its quality of extension ? Give an illustration in the case of gold, of the divisibi- lity of matter. GENERAL PROPERTIES OF MATTER. 17 (sulphate of iron) dissolved, and diffused in 20 million grains of water, will still be easily detected by the proper tests. The delicate perfume of musk, which is due to matter in an exceedingly fine state of division, has been known to remain for many years in a drawer or apartment, and still to emit very decided fragrance. Of course it had continued to give its appropriate odor during the whole time ; and, being invisible at first, we may form some idea of the wonderful minuteness of each particle. The organic world also presents us with beautiful exam- ples of the great divisibility of matter, in the remarkable forms of animalcules revealed by the microscope, many millions of which can be embraced in a single drop of water. Yet each of these inconceivably minute organisms has its own muscu- lar, digestive, and circulatory systems. How minute, then, the ultimate particles, of which many myriads must be con- tained in each animalcule ! It is, however, maintained, that matter is not infinitely divisible ; for none of the attributes of infinity can be predi- cated of that which is finite. 8. Molecules, or Atoms. Every mass of matter, how- ever minute, is composed of a vast number of extremely minute particles, which we call molecules,* or atoms. What- ever size these particles may possess, they are the centres of all the forces or powers whose united effect gives matter all its known properties. We can, however, form some idea of the relative size and weight of these molecules, as is made evident by the laws of chemical combination ; and the laws of crystallization also reveal the fact that they have an inherent difference of form, some being spherical while others are ellipsoidal. Give another illustration in the case of iron. A third case (the perfume) is mentioned. What illustration does the organic world offer ? Is matter then infinitely divisible ? 8. How is every mass com- posed ? What is a molecule ? What is said of them ? What do we know of their relations ? What further do the laws of crystal- lization show ? * Molecule, a diminutive, from moles, a mass. This term is pre- ferable to ' atom' or ' ultimate particle' as implying no theory, which both the others do. Atom is from a privative and temno, I cut, sig- nifying their supposed indivisibility. O * 18 MATTER. We know that matter of all sorts is influenced by the laws of universal gravitation. It is the constant operation of this law on matter which gives it the property that wo call weight, which is the measure of the force required to over- come the attraction of gravitation. This force, in the language of natural philosophy, is said to lx? directly as the quantity of matter, and inversely as the square of the distance. The weight of a hody is therefore dependent on the numt)cr of molecules or atoms which it contains. \^ 9. Indestructibility of Matter. No particle or aTofti of matter can ever be annihilated or destroyed. The same omni- potence which called it into being is required to destroy it. But, it may be asked, do we not see matter daily perishing before us in our fires, and vanishing in smoke and vapor? Its forms do indeed vanish from our sight, but it is not lost ; and we shall learn, when we come to attend to the beautiful phenomena of life, by how divine an arrangement the winds and the rains gather up their lost atoms, and restore them to the earth, thus clothing it with new beauty. 10. Cohesion. The power of gravitation just mentioned, acts alike on all matter, and at all distances. Hut the power which holds together the several particles of matter which form a solid mass, acts on particles of a like kind, and at insensible distances. This attraction of aggregation is called the force of cohesion, that power which we must overcome before we can reduce a piece of marble or lead to dust or smaller fragments. Opposed to this force, which would draw together and keep united all the particles of a body, we have the power of repulsion, whose tendency is to separate these particles from one another. In illustration of the first of these powers, if we press together two smooth surfaces of lead, clean and bright, as for example the halves of a bullet cut through, they will adhere or unite together so firmly as to require the power of several pounds weight to draw them apart. The plates of polished glass, What law influences all matter ? What property in bodies is due to this law ? On what does the weight of a body depend ? 9. What of .the destructibility of matter / What becomes of the matter burnt or turned into vapor ? Is it lost ? How shall we prove this ? 10. What other power of attraction is here mentioned ? How dif- fering from gravitation ? Among what particles exerted ? What is it called ? What opposing force have we ? Its tendency is what ? What example illustrates the attraction of aggregation ? GENERAL PROPERTIES OP MATTER. 19 also, which are prepared for large mirrors, if allowed to rest together, with their surfaces in close contact, have been known to unite so firmly as to break before they would yield to any effort to separate them. This is owing to the force of attraction between the particles of the same kind, called homogeneous attraction, or the attraction of ag- gregation. 11. Repulsion. We see the second of these opposing powers, namely, repulsion, in one of the common effects of HEAT. This power is able to overcome the strongest attrac- tion, and to separate, to a great distance, the particles before closely united. Heat will convert ice into water, and the water into invisible vapor. The most solid metals cannot resist its power ; and yet, when it ceases to operate, the an- tagonist power of attraction again draws the separated parti- cles together, and restores the^riginal form. 12. Chemical Attraction. Matter is, however, governed by another and yet more powerful force of attraction, namely, the power of affinity, or chemical attraction. It is unlike the power of gravity, because it acts only at invisible dis- tances, and is also unlike the power of cohesion, (attraction of aggregation,) because it exists only between particles of different kinds. Gravity acts on all matter and at all dis- tances. Cohesion acts only on the same kind of matter at insensible distances. Chemical affinity acts only between unlike particles at insensible distances. 13. The action of this marvellous power of chemical affi* mty, results in producing from two unlike particles or atoms of matter, a third body having no resemblance in any of its properties to either of the other two constituent particles. The compound molecule of the new body acts the part of a simple molecule, in its relation to other bodies. To follow out all the wonderful results of this power of affinity, and make ourselves acquainted with all the new bodies which are formed under its influence, constitutes the proper business of Another also ? What other name is there for this sort of attrac- tion ? 11. What does heat show us? How does it act? What changes will it produce on water ? If removed again, what happens ? 12. What other force, still, governs matter ? Differs from gravity and aggregation in what ? Contrast these three sorts of attraction by their actions. 13. What is the result of chemical affinity ? What properties has the third body? 20 MATTER. the chemist. To do this, we must first become familiar with a number of other important subjects. 14. Elements. If we could imagine a world to exist, com- posed wholly of lead or of iron, and capable of supporting human life, it would afford no opportunity for the study of the science of chemistry, which owes its existence to the fact that matter is various and not simple. We learn not onlv that there are different kinds of matter in the world, but also that nearly all the forms in which we see it in nature, or in which we make it combine by art, are capable of being reduced to a few sim- ple substances, which are called elements. An element is a form of matter which has hitherto resisted all attempts to ob- tain from it any thing more simple. The numl>cr of such bodies at present known is fifty-six, and of these all things arc made. The progress of science may show us, by improved methods of investigation, that jome of our elements are com- pounds, or, on the other hand, some new ones may be dis- covered. Water was one of the four elements of the ancients, (earth, air, fire, and water.) We now know that water is a compound of two gaseous elements, (oxygen and hydrogen.) Gold is an example of what we suppose to l>e an clement. We can alter its form by combining it with other substances, thus making it part of a new compound, but no process has ever enabled us to show that it is itself a compound. The process by which a body is shown to be compound, i.s called analysis ; and that by which the same body is repro- duced, by the direct union of its elements, is called synthesis. Where these two modes of proof arc united, the evidence obtained is of the very highest kind. 15. Imponderable Agents. Besides the elementary mat- ter of the world of which we have already spoken, there are certain other agents of so subtle a nature that they possess none of the common properties of matter. These are Light, Heat, and Electricity ; they are frequently called 14. What if the world were made of iron or lead ? To what docs chemistry owe its existence ? What do we learn of matter ? Arc things about us generally simple or compound ? In what sense is the term element used in chemistry ? Do we positively *now any element ? What illustration is named of the elements of the an- cients ? What is cold ? How can we alter its properties ? What is analysis ? What synthesis ? What is the best kind of proof in chemistry ? 15. What other agents are there besides those already mentioned ? What have they been called ? THE THREE STATES OF MATTER. 21 imponderable agents, because we have never been able to collect and weigh them. Of their real nature, it must be remembered, we know nothing. We shall treat of them as if they were matter, because the language of science accords with this mode of presenting their phenomena. Late investi- gations countenance the opinion that they are inseparably connected with the existence of matter, and should be classed philosophically with its general powers or forces. Chemical affinity has been considered identical with electricity. It is also considered as an established fact in science, that there exists, throughout all space, an extremely rare elastic medium, called ether, whose vibrations cause the phenomena of light. Whatever may be the ultimate fate of this opinion, it is found to accord with the most mathematical exactness with all the phenomena of optics. ., 2. The Three States fy Matter the Solid, Fluid, and Gaseous* 10. The three common conditions, or states, in which matter is known to us, are the solid, fluid, and gaseous. In- deed we may reduce them simply to solids and fluids, if we choose to consider fluids as of two sorts, elastic fluids, as air and vapor, and inelastic fluids, as water and other liquids. We have already hinted that these several states of matter depend on the power of heat. (11.) This cause will be more fully considered in the chapter on heat. 17. Properties of Solids. It is the distinguishing property of solids to have their particles bound together by so strong an attraction as in a great measure to destroy their power of moving among each other. No solid, however, not even gold and platinum, which are the most compact solids known, has its particles of matter so aggregated as to be incapable of some condensation. Blows, pressure, or a reduction of temperature, will condense almost all solids into a smaller bulk, and water may even be What of the nature of these ? What have we reason to believe ? What is said of a pervading ether ? 16. Name the three states of matter. Reduce them to two. Distinguish between the two classes of fluids, and give an example. What cause is suggested for these different states of bodies ? 17. What is said to be the distinguish- ing feature of solids? What is said of the most compact bodies? How can they be diminished in bulk? 22 MATTER. forced through the pores of gold, by very great mechanical pressure. AH solid bodies are, therefore, considered as porous, and their particles are believed to touch each other in comparatively few points. 18. Solids possess several other properties which may bo considered in one way or another as modifications of the power of cohesion. (10.) (1.) Hardness ; this property is possessed by solids in very various degrees, from the diamond, the hardest of all substances, to those solids which are so soft as to be easily scratched by the finger-nail, as lead and some minerals. Hardness has no connection with weight or densi- ty, for lead is more than three times as heavy as the diamond. (2.) Elasticity ; or the power of assuming their original form after being bent or compressed. It is found in all degrees of perfection, from glass and steel, which are almost perfectly clastic, to lead, which possesses none of this quality. (U.) Brittleness is often closely connected with the last property. If glass or steel be bent beyond a certain degree, it breaks suddenly: this point is the limit of their elasticity. (4.) Mal- leability, or the capability of being beaten by blows into thin leaves, is found in thn highest perfection in gold, and in a good degree in many other metals ; 300,000 leaves of gold are but an in h thick ; while an equal number of leaves of common letter paper would be several rods in thickness. (5.) Ductility and laminability are properties closely allied to malleability. Iron, for instance, unless heated, cannot be beaten like gold, but it may be drawn into fine iron wire (duc- tility) and plated by rollers into thin sheets, (laminability.) 19. Fluids. Fluids arc distinguished from solids by tho perfect freedom of motion among their particles. We havo said (16) that fluids may be divided into two classes; liquids, like water, and gases or vapors, like air and steam. The first is inelastic, or very nearly so; the second highly elastic. We will consider them separately. 20. Liquids press with equal force on all parts of a vessel What proof of the porousness of gold ? What of solids in general ? 18. Of what force are the several properties connected in this sec- tion modifications ? Enumerate these properties. What is hard- ness ? Give an example. Is it connected with weight or density ? (2) What is elasticity ? (3) Brittleness ? (I) Malleability ? Give an example and a comparison. (.">) How do ductility and laminabi- lity differ from malleability ? 19. Distinguish fluids from solids. Classify them. (16.) 20. How do liquids press on a containing vessel? THE THREE STATES OF MATTER. 23 containing them. If an attempt be made to condense water, for instance, in a tight vessel, the pressure exerted for this purpose will at once be felt in every part of the fluid, and on all sides of the containing vessel to the same degree as on the portion where the power is applied. Liquids are said to be inelastic ; but this is not strictly true, for water may be com- pressed, in the reft^d apparatus of CErsted, one part in 22,000 for every atmosphere of pressure, and the water in a vessel sunk to the depth of 1000 fathoms (6000 feet) in the sea, has been compressed to nineteen-twentieths of its origi- nal bulk. For all practical purposes, however, water and other fluids are inelastic, so that they may be applied to exert immense power in the hydrostatic press. 21. Capillary attraction is a property possessed by fluids as distinguished from solids. By this property, fluids will mount in small tubes (called capillary or hair tubes, from the hairlike fineness of the bore) to a considerable height against the power of gravity. It is this power which enables wood and other porous bodies to draw up into their pores any fluid with which they may come in contact. Water standing in a tumbler has its surface made concave, being raised by capillary attraction at the edges where it comes into contact with the glass. The capillary force is so great, that plugs of dry wood driven into holes bored for the purpose, in rocks, and then saturated with water, swell so much from the quantity of water drawn into the pores of the wood, (by capillary attrac- tion) as to burst open the rocks. By the same power, a lamp or candle draws up its supply of fuel. A solid bar of lead, bent like the letter U, and one end of it put into a vessel of quicksilver, (the only metal which is a fluid at common temperatures,) after some time becomes so saturated with the mercury by capillary action, as to convey it out of the vessel, like a syphon. When surfaces are wet by water or oil, or any other fluid, it is by virtue of this power ; and we see from this that the capillary power is closely connected with chemical affinity, Give an illustration. What is said of the elasticity of liquids ? What of that of water ? How may they be considered, however ? 21. What is capillarity ? Define the word. How is the power seen in a tumbler of water ? Also in lamps and candles ? Give an illustration of this power in wood. What experiment is mentioned with lead ? What is said of the wetting of surfaces ? 24 MATTER. (or heterogeneous attraction.) Mercury, for instance, will not wet or cover the surface of glass or the skin, nor of iron ; but it at once wets lead, tin, gold, silver, and many other metals. Glass can be wet by water only with some difficulty : oil, however, easily wets glass, and after this, water cannot be made to adhere to its surface at all. 22. The cohesion of the particles of a liquid for each other, is well shown by the globular form of the dew-drop : the power of cohesion, (or homogeneous attraction) tending to bring all the particles to a centre, produces a sphere. A soap-bubble is a beautiful example of the cohesive power of a thin film of liquid. Soap-water is more viscid, but not more coherent than pure water, and the bubble may l>o considered as a large drop of water, with all its interior removed, and the place supplied with air. The cohesive power of the particles of water in the film of the bubble is so great, that if the pipe be taken from the mouth before the bubble leaves it, a stream of air will be driven forcibly from^hc bore of the pipe, by the contraction of the film. ^^ 23. Elastic fluids are either gases or vapbrs. A gas is matter in a pertnancnf.li/ aerial form. A vapor is matter temporarily in an aerial form. The same physical laws govern both, and we will briefly review thorn. 24. The Atmosphere and Laws of Gases. We live on this planet at the bottom of a vast ocean of gaseous matter, which we call the air, or our atmosphere. It surrounds us everywhere, and presses upon us with a weight which, when stated in numbers, seems beyond belief. Under its influence, all operations, chemical as well as mechanical, arc performed. It penetrates deeply into the crust of the earth itself, and is largely dissolved in all its waters. Its chemical composition will be discussed in its proper place, when we come to con- sider the properties of the two elements of which it is princi- pally composed. How is it connected with capillarity ? Give an illustration in mercury, and in oil and water on glass. 22. How is the power of cohesion shown in liquids ? What is said of the soap-bubble ? How may we consider th.> bubble / What is said of the cohesive powor of the film? IIo'.v is this weil illustrated? 23. What are elastic fluids? (16 and 19.) Define a ea=. Define a vapor. 24. To \vhat is the air compared ? Wiiat i said of it ? Is it confined to the surface ? THE ATMOSPHERE. 25 25. It is usual to speak of a vessel or apartment which contains air only, as empty. It is easy to show, however, that the so-called empty space is in reality full, and that the matter it contains is just as capable of being weighed, trans- ferred, and rendered sensible by its resistance to other bodies, as any other form of matter. If we plunge a bell-glass or inverted tumbler into water, holding its mouth horizontally downwards, we shall find a resistance to its descent, which arises from the air confined within it. The water will rise in the vessel to a certain height, which varies with the degree of pressure we apply. The deeper we sink the glass, the higher will the water rise in its interior, and the less space will the air occupy : as we diminish the pressure, the air, by its elasticity, returns to its former dimensions, and entirely displaces the water. 26. Elasticity of the Air. Suppose the two tight-bot- tomed hollow cylinders a and 6, in the annexed figure, to be filled with air: if we fit a plug so tightly to the sides of both, that no air can pass between it and the sides of the cylinder, and then try to force down this plug by pressure on the , stem, we shall find a resistance to its downward motion. The plug, or piston as it is called, descends indeed, but with increasing resistance as it goes down ; and if the pressure be removed, it returns to its former position, suddenly and with force. We have thus demonstrated not only that the air is a material substance, offering resistance, but also, that it is an elastic substance, capable of compression to an indefinite extent, and of restoration to its former condition on the with- drawal of the pressure. 27. The elasticity of the air may also be shown by placing the piston in &, in the position represented in the drawing, the air beneath it being in the same state of pressure as that What is said of a so-called empty vessel ? How can we illus- trate the presence of air in an empty vessel '/ 26. Explain the mode by which the elasticity of the air is shown in this section. 27. How is its elasticity shown in the cylinder b (26) ? 3 26 MATTER. above ; if we now attempt to raise the piston, the air which before filled only one-half of the cylinder, will expand and fill the whole ; and this would be the case, if at the com- mencement of the experiment only one-thousandth part of the vessel contained air. The tension of the expanded portion, as it is termed, would then be only one-thousandth part of ordinary air at the earth's surface. We thus learn that air, and also many other gases, are perfectly elastic ; although, as we shall see further on, there are a number of gases which can, by great cold and pressure, be reduced to liquids, and some of them even to a solid form. 28. Air-Pump. The remarks just made serve also to ex- plain the principle and construction of the common air-pump, an instrument of great importance to science. In order to make an air-pump of one of the cylinders already described, it is necessary only to open a communication in the bottom of the cylinder, with some vessel from which we wish to remove the air, and also to open a hole in the piston commu- nicating with the external air. Each of the holes is covered with a little flap or lid of leather or oiled silk, fitting the orifice close- ly, and called a valve. Both these valves open freely in an upward direc- tion, but the lower one is tightly closed by the least downward pressure. In the an- nexed figure this arrangement is shown. We have a glass vessel, (called an air-receiver,) from which we wish to re- move the air. The receiver is made to fit tightly by its edges on the metallic plate, from which passes a tube forming a connection with the bottom of the cylinder, where, as shown in the above figure, the lower valve is placed. Suppose the How does half the air fill all the space ? To what extent will this occur ? What term expresses the degree of elasticity ? 28. What important instrument do the foregoing principles explain ? How may one of the cylinders a or b (26) be made into an air-pump? Explain the construction and use of the same in the figure. THE ATMOSPHERE. 27 piston to be in the place shown in the figure, and that we attempt to raise it by the rod : as it rises, the air beneath it expands, to fill the enlarged space, and with it the air in the glass vessel and tube also expands, while the little valve at the bottom allows the air to pass freely into the cylinder from the glass, to supply the vacancy occasioned by the rise of the piston. If we now press the piston down, the air beneath in the cylinder cannot return into the receiver by the lower valve which opens only upward, and, with the least downward pressure, closes the opening tight ; but the valve in the piston itself now opens outwardly, the air beneath passes out and escapes, while the piston descends freely to the bottom of the cylinder. We may now raise it again, when a fresh por- tion of air will come in from the glass vessel, and be again expelled through the piston-valve, when the piston is again pushed downwards. By continuing this process, we pump out the greater part of the air, as with a common pump we draw water from a well. We cannot, however, remove all the air in this way, because, as just explained, the smallest quantity of air will expand so as to fill the entire space. This process is called exhaustion. 29. Vacuum. The space thus produced by exhausting the air is called a vacuum, or empty space ; a perfect va- cuum, however, cannot be formed in this way, although the air-pump can produce an exhaustion which answers all the purposes of science and art. Many forms of the air-pump are in use, all, however, depending upon the principles ex- plained. One of the most common is that in which two pistons are so arranged (see fig. in 26) as to work up and down alternately, being moved by a winch and toothed wheel. Sometimes the cylinders are formed of heavy glass tubes, which enable the student to see the manner in which the pis- ton and valves move, and better to understand the operation. The air-pump depends entirely on the elasticity of the air for its successful operation. 30. Law of Mariotte. The volume or bulk of air at a given temperature, depends on the pressure to which it is subject, or, in other words, the volume of the air is always What raises the valves ? On pressing the piston down, why does not the air return ? How does the air beneath it escape ? What is the process compared to ? What is it called ? 29. What is tha empty space called ? Why cannot a perfect vacuum be formed ? 28 MATTER. 1 inversely as the pressure, while the density is directly as the pressure. This is called the law of Mariottc, who was the first accurately to demonstrate it by ex- periments. The annexed figure shows the simple apparatus used by him for this pur- pose. It is a glass tube turned up and scaled at the lower end : a graduated scale of equal parts is attached to it. Mercury is poured into the open end of this tube so as to rise; just to the first horizontal line, and a portion of air of the ordinary elasticity is thus^en- closed in the short limb of 9 inches. Now if mercury be poured into the longer leg, so that it may stand at 30 inches (33) above the level of the mercury in the snorter leg, it will press with its whole weight on the included air, which will then 1x3 found to occupy 4 inches, only half of its former space. If, iu like manner, the column of mercury 1x3 increased to twice this length, its pressure on the included air will be tri- pled, and the space occupied by it will be reduced to one-third, and so on in simple proportion. 31. Weight of the Atmosphere. It has been abundantly shown by the experiments already explained that the air has weight. The first movement of the air-pump will fix the air-glass on the plate ofthr pump, and after a tolerable exhaustion is produced, great force will be required to remove the jar, and the pump itself may often be lifted by it. The power that holds the air-jar down is only the weight of the air pressing upon the upper side of the glass, while that pressure is removed from the inside of the glass, by the action of the pump; an upward pressure is also exerted upon the under side of the board or plate of the pump, thus co-operating with the down- 30. What is meant by the volume of air ? On what does it de- pend ? State the law in precise terms. What is this law called ? Explain the apparatus which illustrates it. 31. How do we know that air has weight ? THE ATMOSPHERE. 29 ward pressure upon the glass receiver. The leather by which boys raise large stones and bricks, acts in the same way. The leather adheres to the stone only because the air is pressed out from the surfaces of contact, and rests with all its weight on the upper side. The difficulty which we experience in raising our feet from a wet clay soil, is due in a degree to the same cause ; and if the air could be perfectly removed from beneath our feet, we should be as firmly and immoveably planted on the earth as a well- rooted tree. The weight of the air is also well shown by the burst- ing of a piece of bladder-skin tied tightly over the mouth of an open jar on the plate of the air-pump. As the purnp is worked, the flat surface of the bladder becomes more and more concave, and at length bursts inward with a smart explosion. The same accident would befall the glass jars used on the air-pump, if they were not made of strong glass, and arched in form. Thin square glass bottles are blown purposely to show this, and burst under the air-pump, being either crushed inward by removing the air, or bursting outward by the expansion of the contained air, when they are surrounded by a vacuum. J^ 32. We can also determine the weight of the air by ex- hausting a small glass globe fitted by a stop-cock to the pump. Suppose such a globe to hold 100 cubic inches of air at the medium temperature and pressure : if we weigh it before and after exhaustion, we shall find, if the vacuum be perfect, that it has lost nearly 31 grains of weight, which it regains on allowing the air to enter; hence we learn that 100 cubic inches of air weigh about 31 grains. By using other gases besides air, we ascertain by a similar experiment their rela- tive weights and specific gravities, (49, and figure in the same section.) 33. Barometer. The Barometer* is an instrument by which, on principles just explained, we actually measure the What force holds down the receiver of the pump ? Explain the action of the leather " sucker." Why is it difficult to raise our feet in wet clay ? Give another experimental illustration of the weight of the air. 32. How may we illustrate its weight accurately? How much do 100 cubic inches weigh ? 33. What is the barome- ter ? Give its definition. * From the Greek, la^os, weight, and wietron, measure. 3* 30 MATTER. weight of the atmosphere. This instrument was invented A. D. 1643, by a celebrated Italian philosopher, named Torri- celli. Philosophers up to this time, when called to explain the phenomena of the atmosphere and the rise of water in a common pump, had contented themselves with sav- ing that " Nature abhors a vacuum ;" but a well- digger in Florence informed Torricelli, that he could raise water in a pump only 33 feet, and this philoso- pher at once reasoned, that if nature abhorred a va- cuum, there was no reason why she should cease to abhor it when it was more than 33 fat high. He in- ferred that this column of water must be equal in weight to the entire height of an atmospheric column of equal size. To prove this experimentally, it was only necessary to use a fluid so much heavier than water, as to bring the height of the column down to con- venient dimensions. Mercury, which is 13 times heavier than water, was the fluid selected. A strong glass tube about 3 (bet long, sealed at one end, was filled with mercury. The finger being placed on the open end as a stopper, the tube was inverted, and the mouth immersed in a small vessel of mer- cury. On withdrawing the finger, the mercury in the tube sank a certain distance, oscillated up and down, and finally came to rest nt the height of about 30 inches from the surface of the mercury in the outer vessel. The empty space atxjve the mercury is the most perfect vacuum that can be produced, and is called the Torricellian vacuum, in honor of the discoverer of the barometer. If water were em- ployed instead of mercury, it would require a tube about 33 feet long. 34. Determination of the Pressure of the Atmosphere. Water and mercury are supported at these respective Who discovered it, and when ? What explanation has been be- fore given of atmospheric pressure ? What observation did the well-digger of Florence make? How did Torricelli explain it? What simple experiment did he choose, to prove his inference ? Ex- plain the arrangement of apparatus in the figure. What happened in withdrawing the finger ? At about what height will the vibrating column of mercury stand ? What is the space above the mercury called ? If water were used, how long a tube would be required ? 31. What sustains the mercury or \vator, the tube being open at bottom? THE THREE STATES OF MATTER. 31 heights by the weight or pressure of the air on the surface of the fluid. Such a column of mercury becomes thus an exact counterpoise for the weight of the atmosphere. If the tube had the area of one inch exactly, and the mercury in the barometer tube stood at 30 inches, we should find that fifteen pounds of mercury would be required to fill ihe tube. The pressure of the air, then, on the surface of the mercury, is capable of supporting a column of that metal weighing fifteen pounds. This is also the weight of a column of air of the same size, reaching to the supposed limits of the atmosphere. Every square inch of the surface of land or sea is therefore subject to a pressure equal to fifteen pounds, or to a column of mercury 30 inches in height. A man of ordinary size has a surface of about 15 square feet, and he must consequently sustain a pressure on his body of about 15 tons. This pro- digious load he bears about with him unconsciously, because the mobility of the particles of air causes it to bear with equal force on every part of his body, beneath his feet as well as on his head, and in the inner cavities as well as on the outer surface ; if it were not so, great inconvenience and even death must result. We can easily feel the pressure of the atmosphere on our own persons, by placing one of our hands over the mouth of an air-jar, as is seen in the annexed figure, when a single stroke of the. pump will firmly fix the hand, which seems drawn in by what we are accustomed to call suction, but which we now see to be only the external pressure of the atmosphere. On letting the air in again, we cease to feel this sensation, because the balance or equi- librium of pressure is restored. 35. The pressure of the air at the surface is not a constant quantity. This is shown by the barometer, the mercury in which will be found to vary in height at different times as much as 2 or 2|. inches between one extreme and another. This variation arises from the fact, that the quantity of air How much mercury is a counterpoise to the atmosphere, and in how long a tube, of what diameter ? Whence we infer what about the pressure on the surface of every thing ? A man sustains what load of air ? Why are we unconscious of this, and why does it not crush us ? We can convince ourselves of the reality of this by what sim- ple experiment? What is meant by what we commonly call section ? 32 MATTER. varies from time to time at the same places, owing to meteo- rological causes which this is not the place to discuss ; but hence arises the value of the barometer as a weather-glass, and to show with precision the amount of atmospheric pressure at any given time. The barometer is also of great use in measuring the heights of mountains; because it will be seen from what has been already said, that the air at the level of the sea must weigh more than on a high hill, since the former is pressed down by and supports the weight of the entire atmosphere, while on the mountain top we have risen above a certain portion of the entire weight of the air. The air grows more and more rare as we ascend, and the ba- rometer falls in exact proportion. The inconvenience which travellers have experienced in ascending high mountains has, it is said on good authority, been very much exaggerated. The heart continues its action under a diminished external pressure, and no serious consequences, it is believed, ever follow, as the bursting of blood-vessels or lesion of the lungs, as some have asserted. On the summit of Chimborazo, Baron von Humboldt found that his barometer had sunk to 13 inches 11 lines, and the same philosopher descended into the sea in a diving-bell, until the mercurial column rose to 45 inches ; he consequently has safely experienced a change of 31 inches of pressure in his own person. Limits of the Atmosphere. A person who has risen in a balloon, or on a mountain, to the height of 2*705 miles, or 14,282 feet, has passed through one-half of the entire weight of the air, and finds his barometer to indicate this by standing at 15 inches. The upper limits of the atmosphere cannot be accurately determined, but it is sup- posed from the observations of astronomers to be about 45 miles high. We may judge, then, how extremely thin or rare the upper portions must be, when we have one-half of 35. Is the pressure of the air constantly the same ? How does the barometer show this? It varies how much? Arising from what cause ? What common name for the barometer is derived from its use? What other important use is made of the barometer? Whence its use for this purpose? What observations did Hum- boldt make on Chimborazo? What depth did he reach in the sea? How many inches of pressure has he personally experienced ? How high must one ascend in order to pass through half the weight of the air? Where will his barometer then stand" How high is the atmo sphere believed to extend? WEIGHT AND SPECIFIC GRAVITY. 33 its entire weight within less than three miles of the earth's surface. 3. Weight and Specific Gravity. 36. At every step of research the chemist must appeal to his balances. This instrument should possess a beam, in- flexible by the weight intended to be used, and should be delicately poised on a sharp edge of hardened steel, (called the knife-edge,) resting on a plate of agate, mounted on the summit of an upright pillar of brass. The beam should be so accurately made that it will assume a horizontal position when at rest, its index or pointer marking zero, on the small scale near the foot of the column. At each end of the beam is also a knife-edge supporting the scale-pan, and in a delicate balance there is always an adjustment by which, when the instrument is not in use, the beam is supported on points inde- pendent of the delicate knife- edge, which is thus saved from unneces- sary wear. A good ba- lance will turn readily with a weight of one- thousandth part of a grain, when each arm supports 'one thousand grains. In delicate weighing, a glass case is em- ployed to protect the balance from the fluctuations of the atmosphere. When accurate results are required with a balance whose arms are of unequal length, or which is from any cause inaccurate, the method adopted is to weigh the substance accurately in each pan, and to take the mean of the two weighings, which will give the true weight ; or the substance being placed in one pan, is counterpoised accu- rately by the addition of shot or bits of foil in the other : it is then removed, and its place supplied with known weights till the equilibrium is restored. The weights added give the weight of the substance. The above figure shows the form What do we infer of its rarity in the upper regions ? 36. To what instrument does the chemist constantly appeal ? Explain the construction of the balance. Its use. 34- MATTER. of a good balance, arranged for taking specific gravities. One pan is removed, and a shorter one (b) substituted, from which by a silk thread the substance (a) is supported in a glass of pure water, as explained in 41. It is always assumed, when the weights of substances arc stated in books of science, that the operation was performed at a given temperature by the thermometer; and 60 of Fahrenheit's scale is the point agreed upon, because that is about the usual temperature of the air; and if it be higher or lower, a corresponding allowance is made, because the bulk, and consequently the specific weight of bodies, differ with their temperature. This precaution is necessary only when we take the sj>ecific gravity of bodies, and not their absolute weights. 37. Density. The density of a body is a direct result of the law of gravity as already explained (8), the weight of a body being the measure of the force of gravity, which is directly proportioned to the quantity of matter. The greater the number of particles of a given kind within a given space, the greater the density of the body, or in the language of common life, the henrier it is. Now as bodies differ greatly in this particular, each body is said to have a specific gravity, or density, j>eculiar to itself. 38. Specif c Gravity. The specific gravity of a body is its weight, compared with that of some other body of exactly equal volume. We say that lead is heavier thnn cork ; by which we mean, that of equally sized pieces of these sub- stances, one is very many times heavier than the other; that is, there is very much more matter in the one than in the other under equal dimensions. As a difference in s|>ecific gravity in bodies is found to be accompanied by other important dif- ferences, we will give an account of the methods of deter- mining this character in liquids, solids, and in gases. 39. Standards of Specific Gravity. Pure water at a temperature of 60 is the substance which has been adopted as a standard of comparison for the specific gravity of all solid and liquid substances ; while the dry atmospheric 37. What is density? What law is it the result of? (8.) The density of a body, then, is the measure of what force? What is the density peculiar to each sort of matter called ? 38. Define Specific Gravity. What is meant when we say that one body is heavier than another? What is said of the importance of specific gravity? 39. Name the standard adopted for comparison of specific gravity? WEIGHT AND SPECIFIC^ GRAVITY. 35 air at 60 of Fahrenheit and 30 inches of the barometer is the standard assumed for all gases and vapors. Thus calling water 1, lead will be 1 1-445, or lead is nearly eleven and a half times as heavy as water. Cork is lighter than water, and must be expressed by a fractional number. Oil of vitriol (sulphuric acid) has a specific gravity of 1-847 when p'ure, or nearly twice as much as water. A pint measure of this dense liquid would weigh nearly twice as much as a similar measure of water ; while a pint of quicksilver would weigh thirteen and a half times as much as a pint of water, and a like measure of alcohol only about three-quarters as much, (0-794 being the specific gravity of alcohol.) We see now the necessity of knowing accurately the temperature of substances compared, at the time of weighing, as their bulk increases materially with every increase of temperature, and their specific gravity consequently diminishes. 40. Specific Gravity of Liquids. To measure the spe- cific gravity of liquids accurately, a small thin glass bottle is required, which holds a known weight of pure water at 60 when accurately filled. One thousand grains is a con- venient quantity for comparison ; but a smaller quantity is often more convenient, when we have but little of a substance, although it then requires a simple calculation to reduce it to the standard. The accompanying figure a shows such a bottle. To its neck a glass stopper is adapted, by grinding, which is perfo- rated by a small hole. The weight of the bot- tle is counterpoised by a small mass of lead, which is easily cut by a knife to the exact weight. This coun- terpoise is carefully preserved for this pur- ~V pose. The bottle is now ready for use ; it is filled with the fluid under examination, the stopper is carefully introduced, and the excess of the liquid gushes out Of solids and fluids. Also for gases and vapors. Mention the ex- amples given in the text. 40. Explain the method of finding the specific gravity of fluids, and the apparatus figured in this section. 36 % MATTER. through the small orifice. The exterior of the bottle is wiped dry, and its weight, when thus filled, is ascertained ; and if the bottle is graduated to 1000 grains of pure water at 60, the weight obtained is the specific gravity. For instance, if the fluid is pure ether, the 1000 gr. bottle, when filled, would weigh only 720 grains, and '720 is the specific gravity of ether. As, however, it may not be always convenient to procure a thousand-grain bottle, any glass phial may be converted into one, which will answer the piirjx>se very well. Suppose it to contain 376 grains of pure water: then, as 376 : 1000, so is the weight obtained to the specific gravity of the fluid. A little bottle like the annexed cut (ft) answers the same purpose, although in a less accurate manner than that with the perforated stopper. Its neck is quho narrow, v and the lines marked on it show the upper and lower surfaces / of the liquid in the neck. The quantity of pure water whicrw"" it holds at this point is learned from previous trial. 41. Specific Gravity of Solids. The dctermi nation <9i*" the specific gravity of solids is founded on the theorem first proved by Archimedes, that irhen a solid body is immersed in water, it loses a portion of its weight exactly equal to the weight of the tratcr displaced. The story in which it is stated that this philosopher detected the fraud of King Micro's goldsmith, in furnishing to the monarch, as a crown of pure gold, one made of a debased metal, is a good example of the practical value of this theorem. In fact, plunging an irregular solid into water, is the only mode by which we can easily and accurately measure the precise bulk of the body as compared with an equal bulk of water. For convenience in taking the specific gravities of solids, a small scale-pan is hung to one arm of the balance, (as shown in 36,) and the instrument brought to a |>erfect equi- librium. A hook is attached to the lower sur- face of this pan, for suspending a thread. It is required to take the specific gravity of the mineral quartz. If the bottle holds more than 1000 grains, what course is adopted ? 41. On what is the method for the specific gravity of solids founded ? State this theorem in precise terms. What anecdote is mentioned of Archimedes ? How do we proceed in taking the specific gravity of a solid ? Why does the specimen weigh less in water ? WEIGHT AND SPECIFIC GRAVITY. 37 The specimen is attached by a filament of raw silk, or a fine hair, with a noose at the end, to the hook, and the actual weight of the mass hanging in the air accurately determined. But, in order to have its weight as compared with water, we must know precisely how much a mass of water will weigh, which is just equal in bulk to the specimen. Now if we suspend it as it hangs from the scale-beam in a vessel of pure water, we shall displace just such a quantity of water as corresponds with the bulk of the crystals, and no more ; the water will buoy up the specimen by a weight just equal to a like bulk of water : in other words, the specimen will weigh less in water than it did in air ; and we must diminish the weight on the other side of the beam, to correspond with this loss of weight. If we now subtract from the weight in air, that which we have found to be its weight in water, the difference will evidently give us the weight of a bulk of water exactly equal to the bulk of our specimen. As water is the standard of comparison which has been adopted for spe- cific gravity, if we divide the actual weight of the substance in air by the weight of an equal bulk of water, we shall have the specific gravity sought. 42. We deduce the following rule for determining specific gravity. Subtract the weight in water from the weight in air, divide the weight in air by the difference thus found, and the quotient will be the specific gravity. A single example may serve to impress this simple but important subject on the mind of the learner : we find on trial that the Weight of the substance in air, is 357-95 grs. Weight of the substance in water, " 239-41 " Difference, ..... 118-54 sli = 3 ' 01 8 P ecific gravity.* How much less does it weigh ? 42. State the rule which is given for finding the specific gravity. Give an example on the black-board. (Note.) Explain the principles and use of Nicholson's Araeometer. Give an example of its use. * Nicholson's Arceometer. A cheap and convenient substitute for the balance is found in a little instrument represented in the annexed cut, and called Nicholson's Arceometer, which we will briefly de- scribe, v is a metallic ball or float having a descending hook, to which is hung a little weighted pan I to hold the substance which is 4 38 MATTER. 43. Substances which are lighter than water can have their specific gravity taken, by attaching to them any con- venient bit of metal which will sink them ; the weight of the substance is taken in air, and then the united weight, after attaching the piece of metal. The weight in water of both united is now taken, and the light body being detached, the weighing is repeated on the metallic body. 44. For this purpose we may also take some liquid in which the light body will just float, and then determine the specific gravity of the fluid by the bottle, (40,) which will give us at once the specific gravity of the solid. Thus, if we put a lump of wax into water, it will float above the surface; but 43. How can we take the specific gravity of substances lighter than water ? 44. Explain another method by the use of the speci- fic gravity bottle, and its principle. weighed in water ; the wire stem / supports a cup c. A mark t on the stem shows the point at which the whole apparatus will float in a tall vessel of water when a certain known weight (called the balance weight) is put in the cup r. The specimen under examination must not exceed in weight the balance- weight, this being the limit of the instrument. Sup- pose the limit to be 100 grains. To find by this in- strument the specific gravity of a substance, place it on c, and add weights till the instrument sinks to the mark t ; the added weight being subtracted from 100, gives the weight of the specimen in air. Now place the specimen in the pan /, and again add weights to c. As much more weight on c will now be required as corresponds to the weight of a bulk of water equal to the specimen, which it must be remembered is buoyed up by a power just equal to such weight. The difference of weight thus found will be the divisor of the weight of the specimen, and the quotient will be the specific gravity sought. This instrument is generally made of brass or tin-plate, but may be more elegantly made of glass. For example, put the specimen in Balance weight = 100-00 Weights added to sink instrument to t = 22-57 grs. Weight of specimen in air = 77-43 Specimen placed in lower pan requires ad- ditional weights = 35-43 77' 43 35.43 22-57= 12-86, the weight of a like bulk of water ; then ^^ = 6-02, the specific gravity sought. WEIGHT AND SPECIFIC GRAVITY. 39 in pure alcohol it will sink. If we dilute the alcohol by small doses of water, we shall soon find a point when the wax will just float, or rise and sink indifferently. The alcohol at this state of dilution has the same specific gravity as the wax, and this we find by the specific gravity bottle to be about 0-9. 45. If a substance is in powder or in small grains, its specific gravity is found by taking a known weight of it, and having introduced it into the specific gravity bottle for fluids, to fill it with pure water and weigh : the weight of the sub- stance being deducted from the weight of the whole contents of the bottle, the difference between the sum thus obtained and the weight of the water which the bottle alone will hold, corresponds with the difference between the weight of the sub- stance in air and water. For instance, we introduce 100 grains of a powdered mineral into a specific gravity bottle, holding 1000 grains of pure water, and fill the remaining space with water at 60. We might expect that we should have a weight of 1100 grains, but find only 1059, the place of some of the water being occupied by the powder introduced. The bottle holds, 1000 grains. Substance introduced weighs, 100 " 1100 Weight found, 1059 Difference, 41 100 ~4l = 2-044, the specific gravity sought. 46. If the substance is soluble in water, we must employ a fluid of known specific gravity, in which it is not soluble. For instance, sugar cannot be weighed in water, but in abso- lute or pure alcohol it can. The specific gravity being determined in a fluid whose specific gravity, as compared with water, is known, it is easy by a simple proportion to tell the specific gravity of the solid. 47. The Hydrometer* is an instrument of great use in determining the specific gravity of liquids without a balance. 45. If the substance is in powder, how do we proceed ? Give the example named in the text on the black-board. 46. If the sub- stance is soluble in water, how do we proceed ? 47. What is the hydrometer ? * From the Greek hudor, water, and mctron, measure. MATTER. It is simply a glass tube with a bulb blown on one end of it, containing a few shot to counterbalance the instrument, while a scale of equal parts is made of paper and introduced into the open end, which is then tightly sealed. This scale indi- cates the points to which the stem sinks when immersed in fluids of different densities. The fluid for convenience is placed in a tube or narrow jar ; the more dense the fluid, the less quantity will the hydrometer displace, while in a lighter fluid it will sink deeper. The zero point of the scale is always placed where the instrument will rest in pure water, after which the graduation is effected on a variety of arbi- trary scales, all of which can however be referred to the true specific gravity, by calculation. The scales of these instruments read either up or down, according as the fluid to be measured is either heavier or lighter than water. In case of alcohol, (it being lighter than water,) the graduation of the hy- drometer is made to indicate the number of parts of pure alcohol in a hundred parts of the liquid, absolute alcohol being 100, and water 0. The hydrometers of Baume (a French maker) are much used in the arts. These instruments are of the greatest service to the manufacturer, and when carefully made are sufficiently ac- curate for most purposes of the laboratory. They should always be proved by comparison with the balance before they are accepted as standards. For many purposes they are made of brass or ivory, as well as of glass. 48. Little balloons or bulbs of glass are frequently em- ployed to find, in a rough way, the density of fluids. When several of them are thrown in a fluid of known density, some will sink, some rise even with the surface, and others will just float. Those which just float are taken, and being marked, (as in the figure, with the density of the liquid Explain its principal use. What is the zero of its scale ? In case of alcohol how is it graduated ? How do we find the true specific gravity from the arbitrary scale ? -18. What are specific gravity bulbs ? How are they used ? Mention the case in which they are most useful. SOURCES AND PROPERTIES OF LIGHT. 41 which they represent,) are then used to determine the spe- cific gravity of liquids of unknown density. They are called specific gravity bulbs, and are of great service in ascertaining the density of gases reduced to a liquid by pressure in glass tubes, when, from the circumstances of the experiment, all the usual modes of ascertaining specific gravity are inappli- cable. The method described in 44 for finding the gravity of light substances, involves the same principle as that here given. 49. Specific Gravity of Gases. It remains only, under this head, to speak of the modes used for determining the specific gravity of gases and vapors. For this purpose a globe, or other conveniently formed glass vessel, holding a known quantity by measure, (usually 100 cubic inches) is carefully freed from air or moisture, by the air-pump or exhausting syringe, and is then filled with the gas or vapor in question, and at 60 Fahrenheit, and 30 inches of the barometer, (32), and weighed ; the weight of the apparatus filled with common air being previously known, the difference enables the experimenter to make a direct comparison. The an- nexed figure shows an apparatus for this purpose ; the globe (b) is provided with a stop-cock, (e), and fitted by a screw to the air-jar (a.) The jar is graduated so that the quantity of air or other gas entering may be known from the rise of the water in (a.) It is thus found that 100 cubic inches of pure dry air weigh 31-0117 grains, while the same quantity of hydrogen gas weighs only 2*14 grains, being about fourteen times lighter than air. II. LIGHT. 50. The physical phenomena of light properly belong to the science of Optics, a branch of natural philosophy not necessarily connected with chemistry. A knowledge of some of the laws of light is, however, required of the chemi- cal student, and the progress of discovery daily shows us What previous case involves the principle of the bulbs ? 49. How do we find the specific gravity of gases ? Explain the apparatus used. How much do we thus find the air to weigh ? 50. To what branch of science does light properly belong ? What is said of its chemical importance ? 4* 42 LIGHT. some new connection between the phenomena of light and chemical action. 51. Sources and Nature of Light. The sun is the great source of light, although we can show many minor and arti- ficial sources. Of the real nature of light we know nothing. Sir Isaac Newton argued that it was a material emanation from the sun and other luminous bodies, consisting of parti- cles so attenuated as to be wholly imponderable to our means of estimating weight, and having the greatest imaginable re- pulsion to each other. These particles, by his theory, are supposed to be sent forth in straight lines, in all directions, from every luminous body, and which, falling on the delicate nerves of the eye, produce the sense of vision. This is called the Newtonian or corpuscular theory of light. It is not now generally believed to 1x3 true, but the language of optical science is formed on the supposition of its correctness. The other view or theory of light, which is now generally accepted, is called the wave or undulatory theory. It is known that sound is conveyed through the air by a series of vibrations or waves, pulsating regularly in all directions, from the original source of the sound. In the same manner it is believed that light is conveyed to the eye by a series of unending and inconceivably rapid pulsations or undulations, imparted from the source of light to a very rare or attenuated medium, which is supposed to fill all space. This medium is called the luminiferous ether (15.) However difficult it may be to form any just comprehension of the ultimate or real nature of light, we do know many things about its properties, some of which may be enumerated, and briefly explained. 52. Properties of light. 1st. Light is sent forth in rays in all directions from all luminous bodies. 2d. Italics not themselves luminous become visible by the light falling on them from other luminous bodies. 3d/ The light which pro- ceeds from all bodies has the color of the body from which it comes, although the sun sends forth only white light. 4th. 51. Name the great source of light ? What do we know of its nature ? Give the theory of Newton. What is this theory com- monly called? What is said of its probability and truth? What is the now accepted doctrine ? Explain what is meant by the un- dulatory theory. What is it which is supposed to undulate ? What name is given to this medium ? 52. State what is known of light. 1st. Its rays. 2d. Of its luminousnoss. 3d. Of its color. REFLECTION. 4-3 Light consists of separate parts independent of each other. 5th. Rays of light proceed in straight lines. 6th. Light moves with a wonderful velocity, which has been computed by astronomical observations to be at least one hundred and ninety-five thousands of miles in a second of time. This velocity is so wonderful as to surpass our comprehension. Herschel says of it, that a wink of the eye, or a single motion of the leg of a swift runner, or flap of the wing of the swiftest bird, occupies more time than the passage of a ray of light around the globe. A cannon-ball at its utmost speed would require at least seventeen years to reach the sun, while light comes over the same distance in about eight minutes. 53. When a ray of light falls on the surface of any body, several things may happen. 1st. It may be absorbed and disappear altogether, as is the case when it falls on a black and dull surface. 2d. It may be nearly all reflected, as from some polished surfaces. 3d. It may pass through or be transmitted ; and 4th. It may be partly absorbed, partly re- flected, and partly transmitted. Bodies are said to be opake when they intercept all light, and transparent when they per- mit it to pass through them. But probably no body is either perfectly opake or transparent, and we see these properties in every possible degree of difference. Metals, which are among the most opake bodies, become partly transparent when made very thin, as may be seen in gold-leaf 09 glass, which transmits a greenish purple light, and in quicksilver, which gives by transmitted light a blue color slightly tinged with purple. To protect pictures formed by the daguerreo- type process, they are covered with a film of gold or copper, so thin as not to injure the impression, and yet it effectually prevents its removal by the touch. On the other hand, glass and all other transparent bodies stop the progress of more or less light. 54. Refection. Light is reflected according to a very 4th. Of its parts. 5th. Of its course. 6th. Of its velocity. Il- lustrate this by the examples named by Herschel. What is said of the speed of a cannon-ball ? 53. State what becomes of a ray of light falling on any surface. 1st. On a dull surface. 2d. On a polished surface. 3d. On a transparent. 4th. What else may hap- pen ? What is a transparent body ? What is an opake one? Are these qualities ever perfect ? What is said of the opacity of gold and quicksilver ? Of the gold and copper in the daguerreotype ? f>4. State the law of reflection. 44 LIGHT. simple law. In the annexed figure, if the ray of light fall from P' to P, it is thrown directly back to P' ; for this reason a per- son looking into a common mirror, ^ sees himself correctly, but his im- age appears to be as far behind the mirror as he is in front of it. If the ray fall from R to P, it will be reflected to R', and if from r, then it will go in the line r', and so for any other point. If we measure the angles R P P' and P' P R', we shall find them equal to each other, and so also the angles r P P' and P' P r'. These angles arc called re- spectively the angles of incidence and refection. We there- fore state that the angle of incidence is equal to the angle of reflection, which is the law of simple reflection. This law is as true of curved surfaces as it is of planes ; for a curved surface (like a concave metallic mirror) is considered as made up of an infinite number of small planes. " 55. Simple Refraction. If a ray of light falls perpendi- cularly on any transparent or uncrystallized surface, ns glass or water, it is partly reflected, partly scattered in all direc- tions, (which part renders the object visible,) and partly transmitted in the same direction from which it comes. If, however, the light come in any other than a perpendicular or vertical direction, as from R to A, on the surface of a thick slip of glass, as represented in the figure, it will not pass the glass in the line R A B, but will be bent or refract- ed at A, to C. As it leaves the glass at C, it again travels in a di- rection parallel to R A, its first course. Refraction, then, is the change of direction which a ray of light suffers on passing from a rarer to a denser medium, and the reverse. In passing from a rarer to a denser medium, (as from air to glass or water,) Draw the diagram on the board and demonstrate it. What is the angle of incidence ? What that of reflection ? How does this law apply to curved surfaces ? 55. What becomes of a ray of light when it falls perpendicularly on a transparent surface ? When obliquely ? Demonstrate it on the black-board from the diagram. Give the definition of the law of refraction. Which way is the ray bent ? AMOUNT OP REFRACTION. 4.5 the ray is bent or refracted towards a line perpendicular to that point of the surface on which the light falls, and from a denser to a rarer medium the law is reversed. A common experiment, in illustration of this law, is to place a coin in the bottom of a bowl, so situated that the observer cannot see the coin until water is poured into the vessel ; the coin then becomes visible, because the ray of light passing out of the water from the coin, is bent towards the eye. In the same manner, a straight stick thrust into water appears bent at an angle where it enters the water. 56. Amount of Refraction. The obliquity of the ray to the refracting medium, determines the amount of refraction. The more obliquely the ray falls on the surface, the greater the amount of refraction. A little modification of the last figure will make this clear. Let R A be a beam of light falling on a refracting medium, it is bent as before to R'. If we draw a circle about A as a centre, and a line a a, from the point a where the circle cuts the ray R at right angles, to the perpendicular passing through A, the line a a is called the sine of the angle of inci- dence ; while the line a' a' is called the sine of the angle of refraction. If a more oblique ray r, cuts the circle at 6, the line b b will be longer than the line a a, inasmuch as the angle b A a, is greater than the angle a A a. The line measuring the obliquity before refraction, when the ray passes into a denser medium, is always greater than that which measures it after, and is nearly one-third more in the case of water. This is called the index of refraction ; the refractive power of water is expressed by 1^ or 1-33, while common glass with a higher refractive power, has the index of refraction 1J or 1'5, and the diamond 2-239. In What two common illustrations of this law are named ? 56. What determines the amount of refraction ? Show how this can be demon- strated by an alteration of the last figure. What is the line a a called ? What is a a, called ? What is said of the line measuring the obliquity before refraction and after ? How much greater in the case of water? What is it called ? What is the refractive index of water ? 4-6 LIGHT. the larger works full tables will be found with the refractive indices of numerous substances. 57. Substances of an inflammable nature, or containing carbon, and those which are dense, have, as a general thing, a higher refracting power than others. Sir Isaac Newton observed that the diamond and water had both high refracting powers, and he sagaciously foretold the fact, which chemis- try has since proved, that both these substances had a com- bustible base, or were of an inflammable nature. We now know that the diamond is pure carbon, and that water has hydrogen, a combustible gas, as one of its constituents. 58. Prism. In the cases of sim- R 'plc refraction just explained the ray, afler leaving the refracting medium, goes on in a course parallel to its original direction, because the two sur- faces of the medium are parallel. If, however, we employ a tri- angular jjlass prism like the figure, or any other surfaces not parallel, the ray will be diverted permanently from its original direction after leaving the prism. As already explained, the ray R is bent towards a perpendicular to the surface, (which is the dotted line,) but on leaving the prism it is by the same law fur- ther refracted in the direction R'; and by altering the form of the surfaces we may thus send it in almost any direction, as in the common multiplying-glass, which gives as many im- ages as it has faces, and all in different directions. In this way it is that concave metallic mirrors concentrate and convex ones disperse a beam of liiiht. 59. Analysis of Light. By means of the prism we learn that a beam of sun- light is not simple white light, but a compound of seve- ral colors of the most vivid tints which can be im- agined. We are indebted to Sir Isaac Newton for this beau- u 57. What is said of inflammable substances ? What was Newton's conjecture about diamonds and water ? What uo we now know of. them ? 58. If the surfaces of the refracting medium are not parallel, how is the ray affected ? Explain this by the figure. Give an instance of the application. 59. What do we learn by means of the prism ? Who discovered this, and what is it called ? PRISMATIC COLORS. 47 tiful experiment, which is called Newton's Analysis of Light. A beam of sunlight from R, in the figure, falling from a small circular aperture in the shutter of a darkened room on a common triangular prism, is refracted twice, and bent up- ward towards the white screen R', placed at some distance from the prism, where it forms an oblong colored image, composed of seven colors. This image is called the pris- matic or solar spectrum. The light from flames of all kinds, the oxy-hydrogen blowpipe, and the electric spark, or galvanic light, is also compound in its nature, like that of the sun and other celes- tial bodies. 60. Prismatic Colors. The colors of the solar spectrum are in the following order, upwards : red, orange, yellow, green, blue, indigo, violet. These colors are of very dif- ferent refrangibility, and for this reason are presented in a broad surface, the red being the least refracted, and the violet the most. The seven colors of Newton, it is believed, are really composed of the three primitive ones, red, yellow, and blue. This idea is well expressed in the following diagram. The three primitive BLTnr . TKLt , w. RED. SOLAR SPECTRUM. colors each attain their greatest in- tensity in the spec- trum at the points marked at the sum- mit of the curves ; while the four other colors, violet, indi- go, green, and orange, are the result of a mixture, in the spectrum, of the other three. A portion of proper white light is also found in all parts of the spectrum, which cannot be separated by refraction. We may hence infer that there is a portion of each color in every part of the spectrum, but that each is most intense at the points where it appears Explain from the figure how this is done. Is the image on the screen circular ? What name is given to the image ? How many colors are in it ? Why do we say the light is analyzed ? Is light from other sources compound ? 60. Give the order of the colors in the solar spectrum. Why are these colors separated to different parts of the spectrum ? Which is most bent, and which least ? What are the three primitive colors ? Explain the diagram, and how the three united form the seven. Is each color pure, or mixed with some white light ? When most pure ? 48 LIGHT. strongest. The light is most intense in the yellow portion, and fades toward each end of the spectrum. Sir John Herschel has detected rays of greater refrangi- bility than the violet of the spectrum, which have a lavender color. They have this color after concentration, and are therefore not merely, as might be supposed, dilute violet rays. If the spectrum is formed by a beam of light passing through a slit not over -j^th of an inch in width, the image will be crossed by a number of dark lines, which always appear in the same relative position. These are called the Jlxed lines of the spectrum, and are much referred to as boundary lines in optical descriptions. These lines can be transferred to the sensitive papers used in photography. 61. Natural Color of Bodies. The color of bodies nature are due to the fact that their surfaces absorb all the light, except the color we recognise as belonging to each object. This property is to be ascribed to some cause in- herent in the nature of the substances. 62. Double Refraction. The refraction which we have just considered, belongs to all bodies which permit the pass- age of light. Rut in most crystalline substances, and all bodies having any regular internal structure, such as bone, shell, &c., there is another sort of refraction. By looking through such bodies in certain positions, two objects are seen instead of one, one by the ordinary, and the other by an ex- traordinary ray. This phenomenon is called Double refraction, and is best seen in the mineral called calc spar, or Iceland spar, which, when pure, is colorless and transparent, and breaks into regular rhombs, with brilliant faces. If a rhomb of this mineral be laid over a black line, we see a double image, as if there were in reality two lines.* This direction of the ray is owing to What is lavender light ? Describe the lines observed in the spec- trum. 61. Give the cause of the color of natural bodies. 62. How generally is simple refraction found in transparent bodies ? What bodies have another sort of refraction ? What is seen on looking through such bodies ? What is this property called ? In what best seen ? * A sharp line like p g, when seen through a rhomb of calc spar in the direc- tion of the ray R r, will seem to be dou- ble, a second parallel line m n, being seen at a short distance from it, and the dot o, will have its fellow e. In this case the light is represented as coining from R to r, and passing through the crys- POLARIZATION. 49 the interior crystalline structure of the mineral. Of the two beams into which the light is divided, one obeys the law of refraction already explained, while the other pursues an en- tirely different course. One is called the ordinary, and the other the extraordinary ray. 63. Polarization. The light which has passed one crys- tal of Iceland spar by extraordinary refraction, is no longer affected like common light. If we attempt to pass it through another crystal of the same substance, there will be no fur- ther subdivision, and only a greater separation of the two beams. This peculiar physical change is called polarization, as the light is supposed to assume a polar condition. Many other mineral substances also polarize light when cut into thin plates. The mineral called tourmaline has this property in a remarkable degree. The internal structure of this mineral is such, that a ray of light can pass through thin plates of it in one direction, but not in another ; as, for illus- tration, a thin blade may pass between the wires of a cage if held parallel to the interstices, but will of course be arrested if turned at right angles to them. In the annexed figure we have two thin plates of tour- maline placed par- allel to each other in the same direc- tion. A ray of light passes through both in the direction of R R', and apparently suffers no What is this property owing to ? Explain the figure in the note, on the board. 63. How is the ray which has passed one crystal of calc spar affected by another ? What is this change called ? In what else is it seen ? How is it illustrated ? Explain the figures of the tourmaline plates. tal, it is split and emerges in two beams at e and o. The same effect would be produced if the light fell so as to strike any part of the imaginary plane A C B D, which diagonally divides the crystal, and is called its principal section. The axis or line drawn from A to B, is contained in this plane. But if we look through the crystal in a di- rection parallel to this plane (A C B D) there is only simple refrac- tion, and only one line is seen. 5 50 LIGHT. change : if however, these plates are so placed as to cross each other at right angles, as in the second figure, the ray of light is totally extinguished ; and four such points may be found in revolving one of the plates about the ray as an axis. 64. Light is also polarized when passed obliquely through a bundle of plates of thin glass, or mica, arranged as in the figure. The reflection of light from the surface of various substances is also productiveof polarization, at an angle which is peculiar to each substance, and hence called the angle of polarization. This angle on glass is found to be 5648'. The phenomena of polarized light are among the most attractive and important in the science of optics, but their study would lead us away from our pre- sent object. 65. Chemical Rays. Besides the rays of light in the so- lar spectrum which we have already noticed, and the rays of heat which we shall presently consider, there is still another class of rays, which, while they have a greater refrangibility than the violet, are also found by the delicate experiments of Herschel, to be present in every part of the solar spectrum : they have been sometimes called the chemical rayx, from the powerful effect which they produce in chemical combinations. They act in a manner altogether independent of the rays of heat. Chlorine and hydrogen gases are made to combine by them with explosive energy, while in diffuse light the union of these gases is slow and quiet. Many metallic salts are changed to a darker color by their action, as the chlorid and iodid of silver, facts which have been beautifully applied in the arts of photography by sensi- tive papers, and of the daguerreotype. The last depends on the sensitiveness of the iodid of silver to the action of the chemical or more luminous rays of the sun. This power in the non-luminous rays has been variously designated by the terms actinism, tithonicity, and energia. 66. The accompanying diagram will enable the student to 64. How else is light polarized ? How by reflection ? What is the angle called ? What is it for glass ? 65. What other class of rays is named ? How do they act ? Give examples of their effects. What arts are dependent on the chemical rays ? What has this power been called ? CHEMICAL RAYS. 51 obtain clearer views of our present knowledge in relation to this interesting subject, which has already made so many splendid presents to the arts. From A to B, we have the solar spectrum with the colors in the same order as already described, (60.) The greatest chemical power is at the vio- let, and the greatest heat at the red ray. At b another red ray is discovered, and at a is the lavender light. The luminous effects are shown by the curved line C, the maximum of light being found at the yellow ray. The point of greatest heat is at D, beyond the red ray, and d it gradually declines to the violet end, where it is entirely wanting, the other limit of heat being at c. The chemical powers are greatest about E, in the limits of the violet, and 2 gradually extend to d, where VIOLW, they are lost. They disap- INDI00 ' pear also entirely at C, the BLUB, yellow ray, which is neutral in ORKEN > this respect, attain another TKLLOW point of considerable power at *p N01 F, in the red ray, which gives ^i its own Color to photographic EXTREME RED, pictures ; and ceases entirely at e. The points Z>, C, , therefore, represent respective- ly the three distinct phenomena of Heat, Light, and Chemical Power. This last is believed to be quite independent of the other powers ; for all light may be removed from the spec- trum by passing it through blue solutions, and yet the chemi- cal power remains unaltered. \/ 67. Spectral Impressions. ificbnnection with the chemi- cal properties of light, we mention the curious fact that bodies have the power of impressing their images or pictures on each other in the dark, or on plates of polished metal and glass, in such a manner that these become at once visible, if the bright surface be breathed on or exposed to the vapor of Explain the diagram illustrating the points of greatest light, heat, and chemical action. What is found at Fon the scale ? Is the chem- ical power independent of light ? 67. What are spectral impressions ? 52 LIGHT. mercury, as in the daguerreotype. If a coin or medal is placed on a finely polished surface of sheet-copper or silver, and be left in a perfectly dark place for a few hours, (parti cularly if the plate has been warmed,) it will be found that on breathing upon or mercurializing the metallic surface, an image of the object will at once be brought out, and can be renewed in the same manner indefinitely. It is supposed that this eflect is owing to an invisible influence, passing be- tween the two objects, and producing a change in the condition of the surface, or the arrangement of its particles. Engrav- ings can be permanently copied in this way, and many curi- ous and instructive experiments performed, which our space will not permit us to describe. 68. Phosphorescence is a property possessed by some bodies of emitting a feeble light, often at ordinary tempera- tures. The diamond and some other substances, after being ex- posed to the rays of the sun, will emit light for some time in the dark. Fluor-spar, feld-spar, and some other minerals, give out a fine light of varied hues, when gently heated or scratched. Oyster-shells which have been calcined with lime and exposed to the sun-light, will shine in a dark place for a considerable time afterwards. The glow-worm, the fire-fly, rotten wood, decaying fish, and various marine animals, possess the same property in a greater or less degree. This and similar facts, have been made the basis of an argument by Dr. Draper, to sustain the opinion that there is, in addition to light, heat, and electricity, a fourth imponderable agent. This brief outline of the history of light, must impress the belief that this agent holds a most important place in main- taining the physical welfare of our planet. Plants, by aid especially of the yellow rays, transform the inorganic constituents of matter into living and growing or- ganisms, which appropriate their food, decompose and recom- pose various compounds in a manner which the chemist can never hope to imitate. How are they produced ? 68. What is phosphorescence ? What substances possess it ? What opinion has been based on such facts ? What is said of the importance of light ? How are fluids affected by it ? Which ray is effectual in vegetation ? SOURCES OP HEAT. 53 III. HEAT. 69. All our knowledge of heat is confined to its effects. We experience a sensation' on coming near to, or touching other bodies, which we call heat or cold, according as they have a higher or lower temperature than ourselves. This is the common use of the word. In chemical language, we mean by heat, the unknown cause of the effects produced by it on bodies, and not the sensation. We are as ignorant of the real nature of heat as we are of that of light. It is often called an imponderable agent, as has been before mentioned, because we can find no increase of weight in bodies by heat- ing them, nor any decrease in weight by cooling them. The changes which heat has power to work on matter are wonder- ful; and as it is one of the most important of chemical agents, we shall be well employed in the study of its phenomena. Without pausing, therefore, to consider any of the inge- nious theories which have been proposed regarding the nature of heat and its relations to matter, we will proceed to con- sider its sources and effects. 70. Sources of Heat. 1st. The sun is the great source of heat. His rays alone make the earth inhabitable ; with- out them, this world would be only a barren waste, and its waters would be as solid and unalterable as granite. All the combustible material on or in the earth, would not supply the want of the sun for a single day. 2d. Combustion is another source of heat. Our fires give us warmth, because the combustible part of the fuel takes on a new form of existence, combining chemically with one portion of the atmosphere, and evolving heat. This source of heat, then, is due to a change of state in bodies. The same cause we shall also see, further on, (111,) may sometimes be a source of cold, that is, of a diminution of heat. This source of heat is entirely limited by the amount of the substances suffering change, and ceases when the change is complete. 69. What do we know of the nature of heat? Distinguish be- tween its nature and our sensations. 70. Name the first source of heat. The 2d. Why does the fire warm us ? What limits this source of heat? 5* 54 HEAT. 3d. Friction is a third source of heat. Heat is generated by friction to an indefinite amount, as in the rubbing together of two limbs in a forest, moved by violent winds, by which it is said that so much heat has been excited as to set fire to large tracts of timber-land. Savage nations, by rubbing two sticks violently together, are accustomed to produce fire. Large plates of iron have been made to move slowly over each other, by water-power, thus producing heat enough to warm extensive buildings. The water beneath which cannon are bored becomes very hot, from the friction of the borer against the metal which it cuts. The principal thing to be remarked in reference to this source of heat is, that it seems to be without limit, so long as motion is continued ; and that the substances used to produce friction do not necessarily suffer any permanent change of state. The evolution of heat goes on, the substances acted on neither increasing nor dimin- ishing in quantity, while the body retains its chemical pro- perties unaltered. 4th. A fourth source is Electricity, and it is probably very closely allied to the second. The spark from the elec- trical machine, the galvanic current, and the lightning, are alike sources of heat. We might also mention the warmth of our own bodies, and the whole animal world, as another source of heat ; but it seems more than probable that animal heat is only the result of chemical changes going on in the process of respi- ration, and the other functions of the body, and as such be- Igngs to the second source, already mentioned. 5lh. Geology teaches us that the interior of the earth is in a state of intense ignition, amounting at times to fluidity, as is proveu 1 by the eruptions of lava from active volcanoes. All the excavations for mines and artesian* wells which have been made have shown, that as we descend, the temperature f of the earth constantly increases, after we have passed below What is said of friction ? Give examples of heat thus produced. What is said of electricity and animal heat ? What has geology taught? State the facts. Does heat from these various sources differ in kind ? * Artesian wells are borings made with an auger, usually to a great depth, and are so called from the province of Artois in France, where they were first made. EXPANSION. 55 the influence of the atmosphere. This increase amounts to about 1 of Fahrenheit's thermometer for every 40 or 45 feet of descent. The celebrated well of Grenelle, at Paris, (which is an artesian boring,) is 1794 feet deep, and its temperature is 82, which is 31 above the mean temperature of Paris; and the well at Mondorf, in the Duchy of Luxemburg, is 2200 feet deep, and the water rises with a temperature of 95 Fahrenheit. This increase of temperature, if continued at the same rate, would give us boiling water at about two miles from the surface. At ten miles, all solid substances would become intensely red ; and at thirty or forty, all known solids would be in a state of fusion. No doubt the central heat of the earth, escaping by insensible degrees to the surface, has had an important influence on its condition. From whatever source heat may be derived, its effects on matter are the same, and we will first consider one of its most general powers, namely, 1. Expansion. The effect of Heat in altering the dimen- sions of Bodies. 71. Heat has been called the antagonist of attraction: while the latter power acts to bind together the particles of matter, heat tends to separate them. We see about us mat- ter in the different forms of solids, liquids, and gases or vapors. Water presents a familiar instance of a substance known to us in all three of these states ; as a solid in ice, a liquid at common temperatures, and an invisible vapor at higher tem- peratures. The sole cause, so far as we know, of this change of state in water, is variation of temperature. 72. We have before seen (26) the remarkable power of elasticity in expanding air and other gases. Heat produces expansion in all bodies, even the most firm ; and this is so powerful as to set at defiance all attempts to restrain it. 73. To show the expansion of a solid, a bar of metal What is said of the well at Grenelle ? What would happen if the ratio of increase of temperature continued the same ? 71. Of what is heat the antagonist force ? Illustrate this. 72. What power of heat do we now consider ? 56 HEAT. is provided with a handle, (see an- nexed figure,) which at ordinary tem- peratures, exactly fits a gauge; on heating this over a spirit-lamp, or by plunging it into hot water, it will be so much swelled (expanded) in all its dimensions, as no longer to enter the gauge. On cooling it with ice, it will again not only enter freely, but with room to spare. The same fact is shown by a small cannon-ball, to which, when cold, a ring with a handle will exactly fit, but on heating the ball in the fire, the ring will no longer encircle it. 74. The expansion of a fuid may be shown by filling the bulb of a large tube a with colored fluid to a mark on the stem. On plung- ing the bulb into hot water, the fluid is seen to rise rapidly in the stem. If it be cooled by a mixture of ice and water, it is seen to sink considerably below the II " line. A similar bulb 6, filled with air, and having its lower end under water, is arranged as in the figure to show the |j3 JJ| expansion of air by heat. The warmth ^;x ^-Ipjg of the hand applied to the naked ball ^ JaS t^^Sfi w *^ k su ffi c i ent to cause bubbles of air ^^^ to escape from the open end through the water, and on removing the hand, the contraction of the air in the ball, from the cooling of the surface, will cause a rise of the fluid in the stem, correspond- ing to the volume of air expelled, as shown in the figure. The slightest change of temperature will cause this column of fluid to move, as the air expands or contracts. We thus prove experimentally that solids, fluids, and gases, expand by an increase, and contract by a decrease of temperature. 75. Thermometers. The law of expansion enables us to construct an instrument by which we can measure changes of temperature with accuracy. Such an instrument is the 73. Illustrate the expansion of a solid. 74. Illustrate expansion in a fluid ; (a) in water, (5) in a gas. 75. What instrument does the law of expansion give us ? EXPANSION. 57 Thermometer.* Hot and cold are terms of comparison only, and teach us nothing of the real difference of temperature which bodies may possess. If we place one hand in a vessel of iced water, and the other in moderately warm water, we at once perceive a strong contrast ; but if we suddenly plunge both hands into a third vessel of water at the common tempe- rature, our sensations are at once reversed ; the third vessel is warm as compared with ice- water, and cold as compared with the tepid water. The thermometer, however, enables us with the greatest ease to obtain accurate notions of these comparative temperatures. This valuable instrument was first constructed by Sanc- torio, an Italian philosopher, about A. D. 1590. Sanctorio's instrument was what is now called an air-thermom- ^^ eter, because a confined portion of air is employed to show the changes of temperature. The annexed figure shows the arrangement of the parts. A bulb of glass with a long stem is placed with its mouth downwards, in a vessel containing a portion of colored water. A part of the air is expelled from the ball by expansion, (74,) which causes the fluid to rise to a convenient point in the stem, to which is attached a scale of equal parts, with degrees or divisions marked by some arbitrary rule. Thus arranged, the instrument indicates with great deli- cacy any change of temperature in the surrounding air. The portion of air confined in the ball, when heated in any degree, expands, and pressing on the column of fluid in the stem drives it down, according to the amount of expansion or the degree of heat ; and the reverse results from a decrease of temperature ; the confined air then con- tracting occupies less room, and the fluid rises. The air- thermometer is very delicate, but is too limited in its range to supply the wants of science ; it has given place to the 76. Mercurial^ or Common Thermometer, which is now in every house. This instrument indicates changes of tem- What does this instrument enable us to do ? Illustrate the inaccu- racy of our sensations. Who invented the thermometer, and when ? Explain his instrument. 76. What instrument is now used in place of the air-thermometer ? * Named from the Greek thermos, warmth, and metron, measure. 58 HEAT. perature by the expansion of a fluid in a vacuum. It is form- ed of a small glass tube with a very fine bore, (a capillary tube, 21,) on one end of which is blown a small boll or bulb to contain the mercury, or other fluid with which it is filled. This instrument is made by a process which gives us a fine illustration of several principles already explained, which we will briefly describe. It would be impossible to pour any fluid (much less, mer- cury) into so small an opening as the fine hair-line of a thermometer-bore. If, however, we cautiously hold the ball of the lube in the flame of a small alcohol-lamp, the heat, expanding the air which it contains, will drive out a portion of it at the open end, which is held under the surface of a small quantity of mercury, and the air will be seen escaping in bubbles through it. Let us hold the tube as nearly hori- zontal as possible, and, still keeping its open end under the mercury, withdraw the ball from the heat ; as it gradually cools, the contraction of the remaining portion of the air within the ball, (27,) aided by the pressure of the air on the surface of the mercury, (33,) will cause the fluid to rise rapidly in the tube, and we shall presently see it fall, drop by drop, into the empty ball, until (if the process has been well performed) it is nearly filled. How shall we get rid of the remaining air in the ball and tube? Let us fit a small funnel or cone of paper to the open end of the tube, tie it securely there, and put into it a little mercury, which will quite cover the open end. Now place the ball in the lamp-flame again, and taking care not to heat the stem, cautiously warm the mer- cury, until the heavy fluid boils vigorously in the delicate glass ball. The air in the tube is driven out by the vapor of the boiling mercury, and is seen to escape in bubbles through the fluid metal in the paper funnel, which acts as a valve (28) to prevent its return. The whole space is now full of the invisible vapor of this dense metal, and once more withdraw- ing the ball from the heat, the vapor is condensed, and the pressure of the air on the surface of the mercury in the funnel, instantly forces it into the vacuum beneath, completely filling both ball and stem. The operation of thermometer- making is now completed by once more warming the ball, to expel any remaining portion of the air, and also, if necessary, Give the process of making a thermometer. EXPANSION. 59 a part of the mercury in the stem, and at the same instant the open end of the tube is sealed by a blow-pipe. On again cooling, the mercury contracts, and leaves a vacuum of the most- perfect description, (33.) We will explain presently how the thermometer may be fitted with a scale. Alcohol is also employed to fill thermometers which are to be used for estimating very low temperatures ; but mercury is the fluid preferred for all common cases, because of the great uniformity in its rate of expansion. In the arctic regions, the temperature, for many weeks together, is below the freezing point of mercury, and there alco- hol thermometers are indispensable. Pure alcohol has never been frozen. 77. Graduation of tyermometers. To make the ther- mometer of any va(ae as* an indicator of temperature, we must have a standard of comparison, by which two observers with different instruments, and in different parts of the globe, may compare the results of their observations. We are indebted to Sir Isaac Newton for suggesting the method of graduating thermometers. He knew that ice melted, and water boiled, always at the same temperatures at the level of the sea. By marking the place where the mercury of a thermometer stood, in boiling water, and also in a mixture of snow or ice with water, two fixed and immutable points are obtained, the boiling and freezing of water,* which were found by repeated trials, to be at the same relative distance in all good instruments. By dividing the space between these points into any number of equal parts, the instrument became complete, and its indications could be compared with those of any other, graduated on the same plan. 78. Thermometrical Scales. In this country and in Eng- land, Fahrenheit's scale is chiefly employed. It is unfortu- nate that there should be more than one thermometrical scale in What is used to fill thermometers to register extreme cold ? 77. How is one thermometer compared with another ? What is New- ton's mode of graduation ? How is the space between boiling and freezing divided ? * We shall see hereafter that, although the melting and freezing of water take place at the same temperature, under favorable cir- cumstances, yet that it is the melting of ice, and not the freezing of water, which gives invariably the constant temperature of 32 the freezing point being liable to some variation. 60 HEAT. 100 50 ; .10 use, because it is inconvenient to translate the terms of any other nation into our own. The scale or division of Celsius (a Swedish phi- losopher) is generally used at present in continental Europe, and is also called the Centigrade scale, because it divides the in- terval between the boiling and freezing of water into one hundred parts. Formerly the French used the graduation of Reaumur, which made 80 between boiling and freezing water. Fahrenheit (who was a citizen of Amsterdam) thought that he had found the true zero, or point of greatest possible cold, by means of a mixture of snow and salt. We now know that there is no such thing as an absolute zero* either of heat or cold. Fahrenheit divided his scale from his supposed zero to the boiling point of water into 212, which places the freezing of water at 32, and leaves 180 totwccn that point and the boil- ing of water. Both Celsius (Centigrade) and Reaumur made the freezing of water the zero of their scales. The degrees of Centi- grade are always marked in books C. ; of Reaumur R. ; and of Fahrenheit F., or Fahr. Therefore C.=0 R.=32F.; and 100C= 80R.= 180F. ; and keeping these propor- tions in mind, it is quite easy to translate the reading of one scale into the other. The figure annexed shows us at a glance the several scales compared. The one on the right, marked De Lisle, was the contrivance of a French astronomer 78. Name the principal thermometrical scales ? What number of * degrees did Celsius make between boiling and freezing water? How many are there in Reaumur's scale ? What was Fahrenheit's zero? How many degrees had he above zero to the boiling of water ? The word zero is from the Italian, and signifies < nothing,' and was applied to the thermometer in allusion to the supposed absence of all heat. EXPANSION. 61 who proposed to call boiling water zero, and read down- wards, by 150, to the freezing point. It is not used. We shall use only Fahrenheit's scale, which is so well understood in this country ; and a single example will show how we may convert the degrees of Centigrade or Reaumur into those of Fahrenheit. 100C.==80 R.=180F. is the same as 5C.= 4R.=9F. Fahrenheit's scale (180) is to that of Reaumur (100) as 9 is to 5. To reduce Centigrade to Fahrenheit, we can multiply by 9 and divide by 5, and add 32 to the quo- tient, and vice versa. Suppose we wish to know what 70C. is on Fahrenheit's scale ; we have the proportion 5:9:: 70 : 126. If we add 32, which is the difference between zero of F. and C., we have 126 + 32= 158, which is the number required, for70C.=158F. In stating thermometrical degrees, the sign + is used for points above zero, and for those below. 79. The Self-Registering Thermometer (often called, also, Six's Thermometer) is a form of the instrument contrived for the purpose of ascertaining the extremes of variations which may occur, as, for instance, during the night, or in sounding to great depths in the sea, or measuring the temperature of an artesian boring. It consists of two horizontal thermome- ters attached to one frame, as in the figure ; b is a mercurial thermometer, and measures the maximum temperature, by pushing forward, with the expansion of the column, a short piece of steel wire, of such size as to move easily in the bore of the tube ; it is left by the mercury at the remotest point reached by the expansion ; a is a spirit-of-wine thermometer, I and measures the minimum temperature. It contains a short cylinder of porcelain, shown in the figure, which retires with the alcohol on the contraction of the column of fluid, but does not advance on its expansion. To use the instrument, it is How are the degrees of one scale converted into another ? Give examples. 79. Explain Six's thermometer. What registers the maximum temperature ? 62 HEAT. necessary before every observation to incline it, and with a slight jar bring the cylinder of porcelain in a to the surface of the fluid. 80. The Differential Thermometer is a form of air-ther- mometer, (75^) with two bulbs on one tube, bent twice at right angles, and supported as shown in the figure ; a little sulphu- ric acid, water, or other fluid, partly fills the stem only, (shown by the cross-lines in the figure.) When the bulbs of this instrument are heated or cooled alike, no change is seen . ^^ in the position of the column, but the \& CJ^ i nstant an y inequality of temperature exists between them, as from bringing the hand near one of them, the column of fluid moves rapidly over the scale. A modification of this instrument, of great delicacy, was contrived by Dr. Howard of Baltimore, in which ether was used, the bulbs being vacuous of air. It is called a differential thermometer, be- cause it notes only differences of tem- perature, and not actual temperature. 81. Pyrometers. All common thermometers arc limited to comparatively low temperature*'. Mercury boils at about 660, above which we can judge of temperatures only by the expansion of solids. We have thermometers made with gases or vapors, and with fluids, and pyrometers made with solids. A Pyrometer* is an instrument for measuring high tem- peratures. The only instrument of this sort which we need mention, as it is the only one susceptible of accuracy, is Daniell's Register Pyrometer. It consists of a hollow case of black lead, or plumbago, into which is dropped a bar of metal, (platinum is preferable,) secured to its place by a strap of platinum and a wedge of porcelain. The whole is then heated, as for instance, by placing it in a pot of molten What the minimum ? 80. What is a differential thermometer I Why so called T 81. What is a pyrometer, and its use ? * From the Greek, pur, fire, and matron, measure. A very conve- nient form of pyrometer for illustration, is made by all instrument- makers, which shows the expansion of a metallic bar, heated by a spirit-lamp, moving an index like a clock-pointer. EXPANSION. 63 silver, whose temperature wo wish to ascertain. The metal bar ex- pands mueh more than the case of black lead, and being confined from moving in any but an up- ward direction, drives forward the arm of a lever, as shown in the figure, over a graduated arc, on which we read the degrees of Fah- renheit's scale ; (this graduation has been determined beforehand with great care.) This instrument gives very accurate results; by it the melting point of cast iron has been found to be 2786 F., and of silver I860 F. The highest heat of a good wind- furnace, is 3300 F. Having, to a sufficient extent, become acquainted with in- struments for measuring temperature, and with the principles of their construction, we can now proceed intelligently with our main subject. 82. Expansion of Solids and Liquids. (1.) Different solids expand differently with equal increase of temperature. (2.) The same solid expands equally for every equal addition of heat below 212. Between the freezing and boiling of water, 350 cubic inches of lead become 351 ; 800 of iron become 801 ; and 1000 of glass become 1001. Each solid, in fact, has a rate of expansion peculiar to itself. The same is true of liquids. 1000 parts of water between 32 and 212, expand to 1046 parts; and 1000 parts of quicksilver become 1080 parts. The expansions are gradual, both in solids and liquids, and on withdrawing the heat, they return with equal regularity to their former dimensions. Above 212, the expansion of both solids and liquids becomes irreg- ular and increases. 83. The unequal expansion of solids is well shown by joining firmly, by rivets, two bars, one of iron and one of brass, as in the figure. When they are heated, the brass ex- What is the principle of Daniell's pyrometer ? What are some of the results obtained by it ? 82. How do solids expand ? How with equal increments of heat ? Name some examples. Also some of liquids. Above 212 how do bodies expand ? 83. How is the unequal expansion of solids shown ? 64 HEAT. panding most, will cause the compound bar to bend, as shown ^^ ..-.. :.-J-J^L_:_^_I_J _ jL-A-^' .- v in the lower figure. If they are cooled by ice, the brass contracting most, will bend the united metals in an opposite direction. 84. The Compensation Pendulum gives a beautiful appli- cation of the law of unequal expansion to regulating the rate of rx time-pieces. The length of the pendulum X is altered by variations of temperature, and , II _ of course the rate of the clock is disturbed. A perfect compensation for this error is ob- tained by the use of a compound pendulum of brass and iron, or other two metals, ar- ranged as is shown in figure a, in such a manner that the expansion of one metal downwards will exactly counteract that of the other metal upwards ; thus keeping the ball of the pendulum at a uniform dis- tance from the point of suspension. The shaded bars represent the iron, and the light ones, the brass. The same object is accomplished by using mercury, as shown in figure &, contained in a glass or steel vessel at the end of the pendulum-rod. The expansion which lengthens the rod also increases the volume of the mercury ; this increase of bulk in the mercury raises the centre of gravity to an exactly compensating amount, and the clock remains unaltered in rate. Watches and chronometers are regulated by a like beautiful contrivance. The balance-wheel c, on whose uniform motion the regularity of the watcli or chronometer depends, is liable to a change of dimensions from heat or cold. If made smaller, it will move faster, and if larger, slower. To avoid this error, c the outside of the wheel is made of brass, the inside of steel, and cut at two opposite points ; one end of 84. How is the unequal expansion of metals used in regulating time-pieces ? How is the chronometer balance constructed ? EXPANSION. 65 each part is screwed to the arm, and the loose ends of the rim, being united by a screw, are drawn in or thrown out by the changes of temperature, in precise proportion to the amount of change ; thus perfectly adapting the revolution of the wheel to the force of the spring. The principle of this wheel will be seen in the compound bars. (83.) 85. Practical applications of the laws of expansion in solids are frequently made with great advantage in the arts. The rivets which hold together the plates of iron in steam- boilers are put in and secured while red-hot, and on cooling draw together the opposite edges of the plates with great power. The wheel- wright secures the parts of a carriage- wheel by a red-hot tire, or belt of iron, which being quickly quenched, before it chars the wood, binds the whole fabric together with wonderful firmness. The walls of the Con- servatory of Arts in Paris were safely drawn into a vertical position after they had bulged badly, by the alternate con- traction and expansion of large rods of-iron passed across it, and so secured by screw-nuts and heated by argand lamps as to draw the walls inward. Towers of churches and other buildings have been thrown down or otherwise injured by the expansion of large iron rods, (anchors,) built into the masonry with the design of strengthening them. The me- chanical arts are, in fact, full of beautiful applications of the principles of expansion. 86. Unequal Expansion of Water. The general law of expansion for nearly all solids and fluids, especially within the limits of the freezing and boiling points of water, is, that each solid or fluid expands or contracts an equal amount for every like increase and reduction of temperature, each body having its own rate of alteration (82.) There are, however, some exceptions to this law, of which water offers a remarkable example; the comfort, and even habitabilily of our globe, are in a great degree dependent on this exception to the ordinary laws of nature. We will briefly explain it, and the effects resulting from it. If we fill a large thermometer-tube or bulbed glass (like the one figured in 74, ) with water, and place it in a cold 85. Name some other practical applications of the same principle in the arts. 86. Explain the unequal expansion of water. 6* 66 HEAT. situation,* where we can observe the fall of the temperature by the thermometer, we shall see the column descend regu- larly with the temperakire, until it reaches 39*1 F., when the contrary effect will take place ; the water then begins suddenly to rise in the tube, by a regular expansion, until the temperature falls to 32, when so sudden an expansion takes place as to throw the water in a jet from the open orifice, and the ball at the same time is not unfrequently broken from the solidification of the water. If, on the other hand, we heat water in such an apparatus, commencing at 32, we shall find that, until the temperature rises to 40, the fluid, in place of expanding as we might expect, will actually contract. Water has, therefore, its greatest density at 39'l, and its density is the same for equal temjxjraturcs above and below this point; thus we shall find it having a similar density at 34 and 45, and this is true until it reaches the point of solidification at 32. 87. Beneficial Results. Let us now observe what useful end this curious irregularity in the expansion of water sub- serves. When winter approaches, the lakes and rivers, by the contact of the cold air, begin to lose their heat on the surface ; the colder water, being more dense, falls to the bottom, and its place is supplied by warmer water rising from below. A system of circulation is thus set in motion, and its tendency, if the mass of water is not too large, is to reduce the whole, gradually, to the same temperature throughout. When, however, the water has cooled to 39*1, this circulation is suddenly stopped by the operation of the law just explained : below this point the water no longer contracts by cooling, and of course does not sink, but on the contrary expanding, as before explained, it becomes relatively lighter, and remains on the surface ; the temperature of this layer or upj>cr stratum gradually falls, until the freezing point is reached and a film of ice is formed. But as ice is a very bad conductor, the heat now escapes with extreme slowness ; all currents tending At what temperature is it most dense ? How is it at equal tem- peratures above and below this point ? 87. Explain the use of the irregular expansion of water in its operation in nature. Why does not the heat of the water escape after the ice commences forming ? * A freezing mixture of salt and ice surrounding it will answer the purpose very well. COMMUNICATION OF HEAT. 67 to convey away the cooler parts of the water are arrested, and the thickness of the ice can increase only by the slow conduction through the film already formed ; the consequence is, that our most severe winters fail to make ice of any great thickness. Other causes, also, which we shall presently ex- plain, co-operate at all times to render the freezing of water a very slow process. If this irregularity did not exist, there is every reason to believe that the entire waters of the globe* would freeze solid : when any portion reached the point of congelation, all would become solid at once, like a mass of molten metal cooled in a crucible. We cannot fail to be im- pressed by the wisdom of that power, which not only frames great general laws for the government of matter, but also makes exceptions to them, when the welfare of His creatures requires them. 88. The expansion of all gases and vapors is the same for an equal degree of heat, and equal increments of heat produce equal amounts of expansion. This rate of expan- sion is not altered by any change in the compression or elas- tic force of the gas, and amounts to J^th part of the volume of the gas at for each degree of Fahrenheit's scale. When gases are near the point of compression at which they become liquid, this law becomes irregular. The expansion of air by heat, is one cause of winds and atmospheric currents. The trade-winds and other regular winds so well known to mariners, are the joint result of the motion of the earth on its axis, and the rise of heated air from the equatorial regions of the globe. 2. Communication/of Heat. Equilibrium of Temperature. 89. Equilibrium of Temperature. A healed body, like a red-hot camion-ball, cools when removed from the source What limits the thickness of ice ? What might happen but for this ? 88. What is the law of expansion in gases ? What irregularity does this law undergo ? What results from the expansion of atmo- spheric air ? 89. What is equilibrium of temperature ? Explain how a hot body may cool. (1.) (2.) (3.) * Sea-water above 32 is not subject to the exception, but it is below 28o. 68 HEAT. of heat; (1) by communicating its heat to the substance supporting it, (conduction ;) (2) by the contact of the atmo- sphere conveying it away, (convection ;) and (3) by direct radiation, or a transmission of rays of heat in all directions through the surrounding air, as light (52) is transmitted. All these causes act to withdraw the excess of heat from the heated body, which thus divides itself equally among surround- ing bodies according to their several powers of receiving it, until a perfect equilibrium of temperature is produced, the hot body has become cool, and the others have gained heat. In liquids or gases, this uniform diffusion or distribution of temperature takes place rapidly, localise of the mobility of their particles ; but in solids, much more slowly. Its dif- fusion has no connection with the conducting power of the fluids, however, which are among the worst of conductors. 90. Conduction of Heat. Each solid has its own pecu- liar power of conducting heat, but in all it is a progressive operation, the heat seeming to travel from particle to particle with greater or less rapidity, according to the conducting power of the solid. If we hold a pipe-stem or glass rod in the flame of a spirit-lamp or candlo, wo can heat it to red- ness within an inch of our fingers with no inconvenience ; but a wire of silver or copper would burn us in a very short time when at the distance of many inches from the flame. . ===ii===^= == This is owing to a difference inherent in O these solids, which we call conducting power. The progress of conducted heat in a solid is easily shown, as in the annexed figure, representing a rod of copper, to which are stuck by wax several marbles at equal distances ; one end is held over a lamp, and the marbles drop off, one by one, as the heat melts the wax ; that nearest the lamp falling first, and so on. If the rod is of copper, they all drop very soon ; but if a rod of lead or platinum is used, the heat is conveyed much more slowly. Little cones of various metals, and other substances, may be tipped How does the diffusion of heat take place in gases and liquids ? How in solids ? 90. Explain conduction in solids. What experi- ments are named in illustration of it ? COMMUNICATION OF HEAT. 69 with wax or bits of phosphorus,* as shown in the figure &, and placed on a hot surface. The wax will melt, or the phos- phorus inflame, at different times, according to the conduct- ing power of the various solids. Accurate experiments have been made, which have enabled us to arrange most solids in a table showing their conducting powers. The metals as a class are good conductors, while wood, charcoal, fire-clay, and similar bodies, are bad ones. Thus gold is the best conductor, and may be represented by the number 1000 ; then marble will be 23-5, porcelain 12, and fire-clay 11. Metals compared with each other are very different in conducting power. Thus Gold, 1000. Iron, 375. Silver, 973. Zinc, 363. Copper, Platinum, 898. 381. Tin, Lead, 304. 180. 91. The sense of touch gives us a good idea of the dif- ferent conducting power of various solids. All the articles in an apartment have nearly the same temperature ; but if we lay our hand on a wooden table, the sensation is very different from that we feel on touching the marble mantel or the metal door-knob. The carpet will give us still a different sensation. The marble feels cold, because it rapidly conducts away the heat from the hand ; while the carpet, being a very bad conductor, retains and accumulates the heat, and thus feels warm. Clothing is not itself warm, but being a bad conductor retains the heat of the body. A film of confined air is one of the worst conductors ; loose clothes are therefore warmer than those which fit closely. For the same reason, porous bodies, like charcoal, are bad conductors ; and a wooden handle enables us to manage hot bodies with ease. 92. The conducting power of fluids is very small. This is contrary to the general impression of people, who think, from the ease with which a tea-kettle boils, that liquids con- How are the different classes of bodies as conductors ? Name some examples. Give some examples from the table. 91. Explain the relation of our sense of touch to the conducting power of bodies. * If phosphorus is used, some screen must be employed to cut off the radiant heat, which will otherwise inflame it prematurely. 70 HEAT. duct heat with facility. A simple and instructive experiment will prove to us that the conducting power of fluids is very low. A glass, like that in the figure, is filled nearly to the brim with water. A thermometer- lube, with a large ball, is so arranged in it that the ball is just covered, and no more, with the water ; the stem passes out at the bottom through a tight cork, and has a little colored fluid, L, in it, which will of course move with any change of bulk in the air contained in the ball. Thus arranged, a pointer, I, marks exactly the position of one of the drops of inclosed fluid, and a little ether is poured on the surface of the water, and set on fire. The flame is intensely hot, and rests on the surface of the water ; the column of fluid at I is, however, unmoved, which would not be the case if any sensible quantity of heat had been imparted to the water. The warmth of the hand touching the ball will at once move the fluid at I, by ex- panding the air within. By heating a vessel of water on the top, then, we should never succeed in creating any- thing more than a superficial boiling; at the depth of a few inches the water would remain cold. 93. The conducting power of gases is also very small. Heat travels with extreme slowness through a confined por- tion of air (91.) This is a very different thing from the convection of heat in gases, which we will presently explain. Double windows and doors, and furring so called, of plas- tered walls, afford excellent illustrations of the slow conduction of heat through confined air. We have no proof that heat can be conducted in any degree by gases and vapors. To illustrate the relative conducting power of solids, fluids, and gases; if we touch a rod of metal heated to 1*20, we shall 92. How is the conducting power of fluids ? Give an experiment- al illustration. 93. How is it in gases ? Give illustrations. What comparative trial in solids, fluids, and gas, is named ? COMMUNICATION OF HEAT. 71 be severely burned; water at 150 will not scald us if we keep the hand still, and the heat is gradually raised ; while air at 300 has been often endured without injury. The oven-girls of Germany, clad in thick socks of woolen, to pro- tect the feet, enter ovens without inconvenience where all kinds of culinary operations are going on, at a temperature above 300 ; although the touch of any metallic article while there would severely burn them. 94. Convection of Heat. Fluids and gases are heated by what is termed Convection. Heat applied from beneath to a vessel containing water, heats the layer or film of particles in contact with the vessel. These ex- pand with the heat, and consequent- ly, becoming lighter, rise, and colder particles supply their place, which also rise in turn, and so the whole contents of the vessel come succes- sively into contact with the source of heat, and convey it away. This is well illustrated in the annexed figure, which shows how water acts in a vessel of glass, when heated at a point beneath by a spirit-lamp. Each particle in turn comes under the influence of heat, because of the per- fect mobility of the fluid, and the heat is thus conveyed to, and distributed throughout, the whole mass. A series of such currents exist in every vessel in which water is boiled, and they are rendered more evident, by throwing into it a few grains of some solid, (like amber,) so nearly of the same gravity of water, that it will rise and fall with the currents. A perpetual circulation is thus established in fluids, which serves to keep up the equi- librium of temperature in our globe. \ K S 95. In the air, and in all gases and vapors, the same thing happens. The earth is heated by the sun's rays, and the What is said of the oven-girls in Germany ? 94. How are fluids and gases heated ? Explain what is meant by convection of heat. Give an account of the experiment. 72 HEAT. film of air resting on the heated surface rises, or tends to rise, to be replaced by colder air. The rarified air may be easily seen on a hot day, rising from the surface of the earth, being made visible by its different refractive power. Hence arise many aerial currents and winds. The currents of the ocean are also influenced by the same cause. 96. Convection and conduction of heat will, therefore, be carefully distinguished from each other by the learner. Heat is, so to speak, transported rapidly in fluids by convection, while by conduction it travels slowly and progressively from particle to particle, within the limits of the body subject to it. 97. Radiant Heat. We have spoken of the sun's rays as composed of both light and heat ; these rays of heat proceed from all hot bodies, at all temperatures, for the slightest disturbance of the equilibrium of temperature will occasion their emission. Radiant heat is subject in all respects to the same laws, and possesses the same habitudes as light. It can pass through many substances ; it is subject to reflec- tion, absorption, refraction, and polarization. Radiation of heat takes place in a vacuum much more rapidly than in air, and is, therefore, quite independent of any conducting me- dium. 98. Reflection of heat is shown by the concave parabolic mirror. All rays of heat or light falling on this form of me- tallic mirror are collected atF, the focus, and a hot body placed in the focus will have its rajs sent forth in parallel straight lines, as shown in the figure. A second and simi- lar mirror may be so placed as to receive and collect in a focus all the rays proceed- ing from any body in the focus of the other, where they will become evident by their effect on the thermometer. If the hot body be a red-hot cannon-toll, and the mir- rors are carefully adjusted, so as to be ex- actly opposite each other in the same line, the accumulation of heat in the focus of the second mirror is such, as to inflame dry tinder, or gunpowder, even at twenty feet distance. This 95. Explain the origin of aerial and oceanic currents. 96. Con- trast the effects of convection and conduction. 97. What is radiant heat f From what bodies does it flow, and why ? What is said of its properties ? 98. Explain the reflection of heat, and the me- tallic mirrors. COMMUNICATION OF HEAT. 73 arrangement is shown in the annexed figure, and the experi- ment is a most strik- \ ing and satisfactory A C^ one. It is quite es- "^ sential that the mir- rors should be highly polished ; otherwise the heat, in place of being reflected to the second mirror, will be absorbed by the dull surface. A bright mirror will not become sensibly hotter from the near approach of the hot body, nearly the whole heat being re- flected ; but a black mirror will grow rapidly hot, and will then emit heat itself, by what has been called secondary radiation. 99. The formation of dew is owing to radiation, cooling the surface of the earth so rapidly, that the moisture of the air, which is always abundant in summer, is condensed upon it, as we see it on the outside of a tumbler of iced-water in a hot day. Radiation takes place more rapidly from the sur- face of grass and vegetation, than from dry stones or dusty roads : for this reason, plants receive abundant dew, while the barren sand has none. 100. Radiation of cold was formerly supposed to occur, because a mass of ice placed in the focus of one mirror, caused the thermometer in the other to fall. The true expla- nation of this is, that the thermometer, in this case, is the hot body, and parts with heat to melt the ice, and thus restore the equilibrium of temperature. Cold is merely the absence of heat, and is a negative, and not a positive quality. 101. Absorption of Heat. All black and dull surfaces absorb heat very rapidly when exposed to its action, and part with it again by secondary radiation. The sun shining on a person dressed in black, is felt with much more power than if he were dressed in white. The former color rapidly ab- sorbs heat, while from the latter a considerable part of it is reflected. The color of bodies has nothing to do with their radiating powers, and one colored cloth is as warm in winter as another, as regards the emission of heat. What experiment is shown by the mirrors ? What if they are dull or black ? 99. Explain dew. 100. Explain the supposed ra- diation of cold. 101. How does color affect absorption? 74- I1LAT. 102. The nature of the surface of bodies has the greatest eiTect on their several powers of radiation. Hot water in a bright tin canister, or a polished silver tea-pot, will remain hot very much longer than in a vessel with dull or roughened surfaces. A coating of lamp-black on the surface of a tin canister, placed in the focus of the mirror, will radiate live times more heat from boiling water than clean lead, and eight times more than bright tin, as proved by the differential thermometer. Bright metals have the lowest radiating power, and hence are selected to preserve heat in those substances which we wish to keep hot. For the same reason, tlicy are the worst vessels in which to heat a fluid. The effort to boil water in a bright cop|>er tea-kettle, is very tedious ; as soon, however, as the surface becomes sooty from the lire, the heat passes in rapidly. The nature and not the color of the sur- face affects radiation. A dull cast-iron stove radiates more heat than a polished sheet-iron one the openness of the pores and great number of points of the cast-iron materially aid its radiating power. 3. Transmission of Heat through Bcnlies. 103. The rays of heat from the sun, like the rays of light from the same luminary, pass through transparent substances with little change or loss. Radiant heat, however, from ter- restial sources, whether luminous or not, is in a great mea- sure arrested by many transparent substances. If the sun's rays be concentrated by a metallic mirror, the heat accom- panying them is so intense at the focus as to fuse copper and silver with ease. A pane of colorless window-glass inter- posed between the mirror and the focus, will not stop any considerable part of the heat. If the same mirror is presented to any other source of heat, however, (as the red-hot ball, 98,) the glass plate will stop nearly all the heat, although the light is undiminished. We thus distinguish two sorts of calorific rays, which are sometimes called Solar and Culina- ry Heat, and we discover that substances transparent to light Does it affect radiation ? 102. What chiefly affects radiating pow- er ? Give illustrations. 103. Give the distinction between rays of heat from the sun, and those from most terrestrial substances. How are the latter affected by glass and other transparent substances ? TRANSMISSION OF HEAT THROUGH BODIES. 75 are not, so to speak, transparent to heat in a like degree. This property is distinguished from transparency by the term Diathermancy* Bodies allowing the passage of the heat are said to be diathcrmous, while those allowing the passage of light are said to 1x3 diaphanous.^ Bodies which complete- ly arrest the passage of radiant heat are said to be adiather- mous. Bodies which are highly transparent or diaphanous, are often completely adiathermous, so that the transparency of a body is not connected with its diathermancy. Thus glass of various sorts arrests from 47 per cent, to 67 per cent, of the rays of heat, while common alum in per- fectly clear masses allows the passage of only 9 rays in 100. On the other hand, rock-salt stops only 8 rays in 100, 92 passing freely through. These facts are easily shown, when no other means are at hand, by placing a tablet of rock-salt and one of glass in a situation to be exposed to the heat of a fire. The glass will soon grow so hot as to burn the fingers, from the quantity of heat arrested by it, while the salt will hardly be affected. A large air-thermometer, or a delicate differential one, with one ball blackened, will also answer to make many of these changes of temperature evident, in the absence of the more delicate means explained in the next section. 104. Mellani's Apparatus. Nearly all the knowledge we possess on this interesting branch of science, we owe to the labors of a distinguished Italian philosopher, M. Melloni, who has invented a most beautiful apparatus, by which all these observations and discoveries have been made. Its general arrangement is represented in the annexed figure. The degree of heat is measured in this instrument, not by a ther- mometer, (which would be altogether too rude an indicator of such minute changes of temperature as are here shown,) What is Diathermancy ? What is meant by diaphanous ? What by adiathermous ? Are these properties united generally ? Give instances. * From the Greek, dia, through, and thermos, heat, in allusion to the passage of heat through substances. f From the Greek, dia, through, and phaino, to shine. 76 HEAT. but by what is called a tker mo-multiplier, or multiplier of heat. This is an arrangement of little bars of the two metals, antimony and bismuth, about fifty of which are soldered together by their alternate ends, the whole being with its case not more than 2^ inches long, by J to ^ of nn inch in diameter. The least difference of heat between the opposite ends of this little buttery will produce an electrical current capable of influencing a magnetic needle, in an instrument called a galvanometer. The needle of the galvanometer will move in exact accordance to the intensity of the heat. This is so delicate an instrument, that the radiant heat of the hand held near the battery will cause the needle to move some 10 over its graduated circle. In the figure, a is the source of heat, (an oil-lamp in this case,) b a screen having a hole to admit the passage of a bundle of rays ; c is the substance on which the heat is to fall ; d the thermo- multiplier, or battery, which is to receive the rays after they have passed through the substance c. Two wires connect the opposite members of this battery with the galvanometer *>, which, for steadiness, is placed on a bracket attached to the wall. Thus arranged, and with various delicate aids which we cannot now explain, a vast number of most instructive experiments have been made on radiant heat from different sources, and its effect ascertained on various substances. Four different sources of heat were employed: (1) the naked flame of an oil-lamp; (~) a coil of platinum wire heated to redness by an alcohol-lamp ; (3) a surface of blackened copper heated to 734, and (4,) the same heated to 212 by boiling water. The first two of these are luminous sources of heat, the last two not so. 104. Explain Melloni's apparatus from the figure. What sources of heat were used ? TRANSMISSION OF HEAT THROUGH BODIES. 77 The following table will show a few of the principal re- sults. Transmission of 100 rays of heat from Names of interposed substances, common c. g *S a thickness, 0-102. J3 ^ e S'S |i ll t O & u Rock-salt, transparent and colorless, . . 92 92 92 92 36 98 6 39 914 r> Rock-crystal 38 28 6 Rock-crystal, brown, 37 28 6 g 2 o o 8 Ice, pure and transparent, 6 Thus it appears that rock-salt is the only substance which permits an equal amount of heat from all sources to pass. In other cases the number of rays passing seem proportioned to the intensity of the source. M. Melloni has called rock- salt the glass of heat, as it permits heat to pass with the same ease that glass does light. It is supposed that the difference found by experiment in the diathermancy of bodies, is owing to a peculiar relation which the various rays of heat sustain to these bodies, exactly analogous to that difference in the rays of light which we call color. Thus all other bodies, except salt, act on heat as colored glasses act on light, entirely absorbing some of the colors, and allowing others to pass. Thus rock-salt may be said to be colorless as respects heat, while alum and ice are in the same sense almost black. Opake bodies, like wood and metals, entirely prevent the transmission of heat ; but dark-colored crystal is seen, by the table, to differ only 1 from white crystal, and even per- fectly black glass does not entirely stop all heat. 105. By cutting rock-salt into prisms and lenses, the heat from radiant bodies may be reflected, refracted, and concen- trated, like light, and doubly refracting minerals, like Iceland- spar, will polarize it. All these interesting results, however, we must pass without further notice. Give some illustrations of the results from the table. What has rock-salt been called, and why ? To what are the different powers of bodies in this respect supposed to be owing ? 105. What other attributes of light have been discovered in radiant heat, and how'/ 78 HEAT. 4. Specific Heat. Capacity of Bodies for Heat. )C 106. Specific heat is that amount of heat require/ to raise any body through a given number of degrees of tem- perature, as, c. g., 10. It is a remarkable fact, and one of great importance, that the same quantity of heat cannot raise different bodies through an equal number of degrees of tem- perature. If equal measures (say a pint) of mercury and water be exposed to the same source of heat, we shall find that the mercury will attain its highest temperature about Twice as soon as the water ; and on removal from the fire, it will cool in half the time. If a pint measure of water at 150 be mixed quickly with an equal measure of the same fluid at 50, the two measures of fluid will have the tempera- ture of 100, or the arithmetical mean of the two tempera- tures before mixture. If, however, we take one measure of water at 150, and an equal measure of mercury at 50, and rapidly mix them, we shall find that they will have the temperature of 118. The mercury has gained 68, and the water lost only 3*2, or about half as much. Hence we infer that the same quantity of heat can raise the temperature of mercury through twice as many degrees as that of water. We thus prove, by actual trial, that each body (solid, fluid, or gas) has its own relation to the amount of heat required to raise it a given number of degrees of heat, and this amount being peculiar to each body, is called its specific heat. As water is adopted as the standard of comparison for specific heats, the specific heat of mercury will be to water as 32 to 68, or nearly 0-47. It is more convenient to compare bodies by weight than by measure ; and hence if we divide the specific heat by measure (0'47) by the specific gravity of mercury, (13-5,) we obtain the number, 0*035, its specific heat, by a comparison of weights. The process just de- scri!)od for determining specific heat, is called the method of mixtures. 107. The method of mixtures can te used to obtain the specific heat of solids as well as fluids. Thus a bar of cop- per of a pound weight may be heated to a temperature of 400, and then put into a pound of water at 50; when the 106. What is specific boat ? Illustrate this in the case of mercury and water. Give tho specific heat of mercury by measure and weight. What is this method called ? CHANGES PRODUCED BY HEAT. 79 equilibrium is restored, both will have the temperature of 72. The copper has lost 228, and the water has gained 22. The specific heats being then as 228 : 22, that of the copper is found to be ^3% =0-095. Other methods have been used to determine specific heats, but it is foreign to our present purpose to describe them. The following table will show the specific heats of a number of substances : Water, 1-000 Copper, 0-095 Ether, 0-520 Lead, 0-031 Alcohol, 0-660 Gold, 0-032 Sulphuric Acid 0-333 Antimony, 0-0/51 Mercury, 0-033 Tin, 0-056 Silver, 0-057 Phosphorus, 0-118 Zinc, 0-095 Glass, 0-197 Iron, 0-114 Lime, 0-205 The specific heat is found to be most intimately connected with the chemical character of the substance, and many curi- ous and important inferences have been made from the study of these relations. We shall have occasion to refer to this subject again, in^ the chapter on Chemical Philosophy. 5. Changes produced by Heat in the state of Bodies. 108. Liquefaction. The change of a solid to a fluid is called liquefaction, and is always attended by a remarkable absorption of heat. Water is a substance familiarly known under all three states of solid, fluid, and gaseous ; and the melting of ice will furnish us a good instance of the pheno- mena which take place in the process of liquefaction. We have already seen that two equal measures of water at diffe- rent temperatures have, when mingled, a temperature which is the mean of their previous temperatures, (106.) If, how- ever, we take a pound of ice (solid water) at 32, and a pound of water at 212, we shall find, when the ice is melted, that the two pounds of water have the temperature of only 52 ; the ice gains only 20, while the water has lost 160. There are, then, 140 of heat lost in producing this change. We can take another mode of trial. Let us expose a pound 107. Is it used for solids, and how ? Give some examples from table. 108. What is liquefaction ? Explain and illustrate the change of ice to water. 80 HEAT. of ice at 32, and another pound of water at the same tempe- rature, to a constant source of heat, in two vessels every way alike, and note the changes of temj)erature by the thermome- ter. When the ice is all melted, we shall find that the water into which it is converted has still only the temperature of 32, while the other pound of water has risen from 3:2 to 172 ; here again we see the loss of 140 of heat used in converting the ice into water. We may reverse the last experiment, and lake equal weights of ice at 32 and water at 172, and mix them ; the ice will soon be all melted, and the mixture will have the temperature of only 32 : so that, in whatever way we may make the trial, we constantly observe the loss of 140 of heat. This is called the heat of fluidity, it being necessary to the existence of the water in a fluid state, and it is also designated latent heat, because it is lost, absorbed, or concealed, as it were, and no indication of it can be found by the thermometer. 109. Congelation. If a vessel filled with water at 52 be placed in an atmosphere of 32, it will rapidly cool down to 32 by the loss of 20 of temperature. After this, it will, as may be seen by the thermometer, remain at 32, until it is all converted to solid ice ; although we cannot doubt that it is all the while giving out a quantity of heat, which had before been insensible or latent. If the water had been ten minutes in cooling from 52 to 32, (or in losing 20,) then it would require one hour and ten minutes, or seven times as long, for it to become completely frozen. If, then, in equal times it lost equal degrees of heat, its latent heat will be 20 X 7=140, which is the same result as before. Thus it is by a wise order of Providence that the freezing and thawing of snow and ice are extremely slow and grad- ual processes. If water became solid at once on reaching 32, the water would be suddenly frozen to a great depth ; and if ice melted as quickly on reaching the same tempera- ture, the most sudden and dreadful floods would accompany these events, and the common changes of the seasons would be calamitous to human comfort and life. What amount of heat is in all these cases unaccounted for ? What is this lost heat called ? What becomes of it ? 109. State the phe- nomena observed in freezing. How do we then discover the same quantity of latent heat in water ? What reflection is hence drawn in the order of Providence ? LIQUEFACTION. 81 110. Freezing is a warming process. Water may bo cooled below its freezing point and still remain liquid, if its surface be covered with a thin film of oil, and if it is in a thin smooth vessel, kept quite still ; but the least disturbance will cause it, when in this situation, to become solid at once, and the temperature will immediately rise from 23 or 24 to 32. The freezing of a part has therefore given out heat enough to raise the temperature of the whole from 24 to 32, or through 8. In like manner, it is true that melting is a cooling pro- cess, although it seems paradoxical to say so. A solid can melt (become liquid) only by absorbing heat from surround- ing bodies, which must, of course, become cooler. Hence in part the cooling influence of an iceberg, which is often felt for many leagues, or of a large body of snow on a distant mountain. 111. Freezing mixtures, or the means used to produce artificial cold, owe their powers to the principles just ex- plained. Ice-cream is frozen by a mixture of snow or pounded ice with common salt. In this case the two solids are rapidly changed to fluids ; the ice is melted by the salt, and the salt is dissolved by the water from the melting ice. Both these operations absorb (or render latent) a large quantity of heat. The surrounding bodies are called on to supply the heat required, and the cream, in a thin metallic vessel, loses heat so rapidly from this cause, as to be soon turned to ice. The thermometer will fall in this operation to F. ; and this was the very experiment by whichf Fahrenheit (78) assumed that he had attained to a true zero of cold. Nitrate of ammonia dissolved in water at 46 will sink the temperature to zero, and the exterior of the vessel be- comes at once thickly covered with hoar-frost. Common saltpetre, (nitrate of potassa,) dissolved in water, lowers its temperature several degrees, and is therefore much used in the hot regions of Asia, where it abounds, for cooling wine. Mercury may be frozen by using a mixture of three parts of chloride of calcium, and two of dry snow ; this mixture will sink the temperature from +32 to 50. It should be di- vided into two pretty abundant portions ; the first of which 110. How is freezing a warming process ? Illustrate this. Why is melting a cooling process? 111. What are freezing mixtures? To what do they owe their power ? Give some examples. 82 HEAT. serves to cool down the mercury, and the second is used when the first is exhausted, and completes the work. But all other means of producing cold are insignificant, when compared to the power of solidified carbonic acid gas, in a vacuum, by means of which, Dr. Faraday has succeeded in obtaining a temperature of 175 below zero of Fahren- , heit's thermometer. \/112. The melting point of every substance is very uni- / fo*m, and each body has its own, which is often one of its / most characteristic marks. Thus it is the melting of ice, and not the freezing of water, that gives the constant tempera- ture of 32. By no contrivance can we raise the tempera- ture of ice above 32 ; nor can any other solid be heated above its melting point and remain a solid. Some substances, in melting, pass at once, like ice, to a state of perfect fluidity ; others have an intermediate pasty state. The following table contains the melting points of a few bodies at both ends of the scale : Mercury, 39 C Potassium, -f 13G Newton's Alloy,212 Tin, 412 Lead, 612 Zinc, 773 Silver, 1873 Gold, 2016 Cast Iron, 2786 Platina, (above) 3280 113. Diminution of volume in a body will cause a por- tion of the latent heat to become sensible. Thus, numerous blows will condense iron or gold, and so much heat will be evolved, that blacksmiths in this way sometimes kindle their fires. Water poured on quicklime combines with it, with the escape of much heat ; the water in this case taking on the solid form. Sulphuric acid and water, when mingled, give out great heat, and the bulk of the mixture is less than that of the two before mixing. Liquefaction is always a cooling process, and solidification a heating one, to all sur- rounding bodies. A certain quantity of heat may be consi- dered as necessary to preserve each body in its natural con- dition : if it be condensed, less is required, and it gives out What is the greatest cold thus produced ? 112. What is said of the melting points ? Name some examples of extremes from the table. 113. How does diminution of volume affect the latent heat of bodies ? Name some examples. VAPORIZATION. 83 the excess; and if expanded, it absorbs more. Dr. Black, of Scotland, was the first who made known to us the beau- tiful philosophy of latent heat, and the phenomena of lique faction and vaporization. 114. Difference between heat and temperature. It is easy to see, from what has been said, that the thermometer cannot tell us any thing of the amount of heat in a body, since the latent heat is quite insensible to any thcrmometrical test. We speak more properly, then, when we say that we know ' the temperature of a body, than to say we know its heat. 6. Vaporization. The boiling points of Bodies. 115. A continuance of the heat which melted the ice (1 08) into water, will turn the water into vapor or steam. The phenomena which attend this physical change are not less curious or instructive than the last. If we place a known quantity of water over a steady source of heat, we shall see the thermometer indicating each mo- ment a higher temperature, until, at 212, the fluid boils ; after which, the thermometer indicates no further change, but remains steadily at the same point until all the water is boiled away. Let us suppose that, at the commencement of the experiment, the temperature of the water was 02, and that it boiled in six minutes after it was first exposed to the heat : then the quantity of heat which entered into it each minute was 25, because 212, the boiling point, less 62, leaves 150 of heat accumulated in six minutes, or 25 each minute. Now if the source of heat continue uniform, we shall find that in forty minutes all the water will be boiled away ; and hence there must have flowed into the water, to convert it into steam, 25 X 40=1000. One thousand degrees of heat, therefore, have been absorbed in the process, and this constitutes the latent heat of steam. What we have already said on the latent heat of liquids will render this more clear. So much heat was imparted to the water, that if it had been a fixed solid, it would have been heated to red- ness ; and yet the steam from it, and the fluid itself, had during the whole time only a temperature of 212. Who first made known these laws? 114. Distinguish between heat and temperature. 115. What takes place when we heat water ? Explain the process and the amount of heat absorbed by boiling water ? What do you call this heat ? 84 HEAT. 116. The large amount of latent heat contained by steam, becomes again sensible on its condensation to water. This enables us to make great use of steam as a means of con- veying heat. The steam takes up a large quantity of heat, and transports it to the point where we wish it applied. gallon of water converted into steam, at the ordinary pressure of the atmosphere, will raise five gallons and a half of ice- cold water to the boiling point. In this way we can boil water in wooden tanks, heat large buildings by steam-pipes, and make numberless other useful applications of steam-heat in the arts. 117. The distillation of water (or any other fluid) affords a good illustration of the quantity of latent heat conveyed away in the vapor. In the arrangement here figured, a glass retort (R) is made to contain a quantity of water, which is boiled by a lamp below, the steam is conveyed by the bent neck to a receiving-vessel, in which it is condensed, being surrounded by cold water or ice poured into the dish placed to support it. After the water boils in the retort, its tempera- ture docs not rise any further, but the vapor con- veys the heat of the lamp over to the condenser. The water which surrounds it will grow rapidly hot from the latent heat of the steam, rendered sensible by its reconversion into water. For this reason the condensing water must be frequently changed. In metallic stills, the condenser is a long metallic tube, bent into a spiral, (called a worm,) and surrounded by cold water. 118. The latent heat of steam, which may be set down at about 1000, (although it is stated more accurately at 967,) 116. How does the latent heat of steam again become sensible? How much ice-cold water will one gallon turned to steam boil ? 117. How does the process of distillation illustrate this ? 118. How does the latent heat of steam compare with that of the vapor of other fluids ? VAPORIZATION. 85 is greater than that of any other known fluid. The latent heat of fluids has no connection with their boiling point ; since many liquids which boil at high temperatures have little latent heat, and the reverse. The annexed table shows the boiling points and latent heat of the vapor of several common liquids. Liquids. Boiling Point. Latent Heat of Vapor. Water, Alcohol, Ether, Petroleum, Oil of Turpentine, Nitric Acid, (strong,) Ammonia,* (liquid,) 212 172 96 320 314 248 140 967 442 302 178 178 532 837 119. Boiling or Ebullition takes place in a liquid when it becomes so hot that its vapor can rise in bubbles to the sur- face, and escape uncondensed by the atmospheric pressure, or the temperature of the fluid. The elasticity (or tension) of the vapor then becomes greater than the united pressure of the fluid and the air. When the boiling is vigorous, a great number of these bubbles of uncondensed vapor rise to the surface at the same instant, and the liquid is thrown into violent agitation. If a vessel containing cold water be heated suddenly, the lower surface receives the most heat ; bubbles of vapor are formed, and rise a little way, when, meeting the colder water, the vapor is at once condensed, and the liquid, before sustained by the elastic vapor, falls with a sudden jar on the bottom of the vessel, producing a series of little ex- plosions. This may be well seen in a glass flask suddenly heated by a lamp. When the heat is gradually applied, it is so evenly and quietly distributed that this effect is not per- ceived. The boiling point is much affected by the nature of the vessel. In a metallic vessel, water boils at 210 and 211. If a glass vessel be coated inside with shellac, water boils in it at 211; but if it be thoroughly cleaned with sulphuric Is latent heat connected with the boiling point ? Illustrate this from the table. 119. What is boiling ? Illustrate this. How does the nature of the vessel affect it ? * Specific Gravity, 0-945. 86 HEAT. acid, it may be heated to 221 or more, without the escape of bubbles. A few grains of sand, or a little fragment of wire, or a small piece of charcoal, will, however, at once equalize these differences, and cause the water to boil quietly at 212. This simple means will prevent the unpleasant jar from sudden escape of vapor, and frequent fracture of the glass vessel. 120. The pressure of the atmosphere determines the boil- ing point of fluids ; and when we speak of the boiling point, we always mean ebullition under the ordinary pressure of the air, or 30 inches of the barometer, (33.) It follows, there- fore, that by a diminution of pressure, water may be made to boil at a much lower temperature than 212. In ascend- ing high mountains, the boiling point falls with the elevation, from the diminished pressure of the air. On this account, a difficulty is experienced at the Hospital of Saint Bernard, on the Swiss Alps, in cooking eggs and other viands in boiling water. This place is 8400 feet above the sea, and water boils there at 196 ; on the summit of Mount Blanc, it boils at 187. We see that it is the temperature, and not the boil- ing which performs the cooking. The Rev. Dr. Wollaston contrived an instrument to determine the height of mountains by the boiling point. lie found an ascent of 530 feet to be equal to a decrease of 1 in the boiling point ; and with a thermometer having large spaces, accurately subdivided, T ^^ of a degree may be read. -^ 121. Boiling under Diminished Pressure. An experi- ment easily performed, gives a very good illustration of the I phenomena of boiling under diminished pressure. A small quantity of water is boiled in a glass retort, or in a bolt-head, like that in the following figure ; when the water has boiled a short time, a good cork, previously well fitted to the orifice, is firmly inserted, and the vessel removed from the heat. It may now be supported in an inverted position, with the mouth under water, as seen in the annexed figure. The boiling will still continue, and more rapidly than before ; and if we attempt to check it by cold water poured on the ball, we shall only cause it to boil more vehemently. A little hot water 120. What influences the boiling point ? Mention the boiling point of water on Mount Blanc, and the elevation necessary to produce 1 of difference in the boiling point. 121. Explain the experiment of Dolling under diminished pressure. VAPORIZATION. 87 will, however, at once arrest the ebullition of the confined fluid. In this case, the air is driven out of the vessel on the first boiling of the water, and as we close the orifice, while the steam is still issuing, there is only the vapor of water in the cavity. As this condenses from cooling, the pressure on the water diminishes, and it boils more easily from the heat it still contains ; the affusion of cold water, by pro- ducing a more perfect condensation, occasions a more violent ebullition. The hot water, however, increases the elasticity of the uncon- dcnsed vapor, and represses the boiling. These alterations can be produced as long as the water in the vessel is warmer than the cold water poured on it. When cold, the space over the water will be a good vacuum, and if we turn the water from the ball into the neck, it will fall like lead, with a smart blow and rattling sound. This is sometimes called the water-hammer. The perfection of the vacuum can be tested by withdrawing the cork under water ; the pressure of the atmosphere will then drive in a quantity of water, equal to the vacuum produced bv the first expulsion of the air. 122. Freezing and Boiling in a vacuum. A little ether under an air-jar on the plate of the air-pump will flash into vapor as soon as the pressure is removed by working the pump ; and water may be frozen by its own evaporation, over a good air-pump, arranged as in the figure. The water is contained in a watch- glass on a tripod, over a shallow dish of sulphuric acid, and the whole is covered by a low air-jar. On working the pump, the water evaporates so rapidly in the vacuum as to boil even at 72, its vapor is instantly absorbed by the sulphuric acid, and in this way both the sensible and latent heat are removed so rapidly, that the water is frozen solid while still apparently boiling. 123. The Cryophorus, or frost-bearer, offers another What principles are here brought into view ? How is the absence of the air made evident ? 122. How is water frozen in a vacuum? 88 HEAT. illustration of the same facts. This little instrument, invented by Dr. Wol- laston, is only a bulb of glass, containing a lit- tle water, and connected by a long bent tube with another bulb or protube- rance, which is empty ; the space over the water is a vacuum, the tube having been sealed when the water was boiling. On placing the empty stem in a freezing mixture of ice and salt, the vapor of the water is so rapidly condensed as to freeze the fluid in the ball which is remote from the freezing mixture. 124. Practical application of these facts is made in the arts on a large scale, in manufacturing sugar. The boiling of the syrup is performed in vacuo, in large pans of copper, holding several hundred gallons, the air and vapor being removed from the vessels by a steam-engine ; the syrup is thus rapidly boiled down at a temperature of 150 to 180, without any danger of burning. Vegetable extracts nre frequently made, and saline solutions boiled, in the same way. Nothing in the arts shows more clearly the value and beauty of scientific principles. 125. Elevation of the Boiling Point by Pressure. If water is boiled in a vessel, which can be closed after the escape of the atmospheric air, as in the brass boiler (a) of the annexed figure, we can easily submit it to any desired degree of pressure, and thus elevate the boiling point. This boiler is provided with a thermometer (c) whose ball is within the steam cavity ; and also with a barometer tube, (A,) which descends into some mercury, placed in the bot- tom. It is supported by a tripod (f) over a lamp, (f,) and a sf op-cock (d) cuts off the external air. As soon as the water in it boils, the steam accumulates, and, pressing on the mercury, forces it up the tube, against 'the imprisoned air. The relation of air to pressure has already been explained, (30.) When the mercury indicates 30 inches, or double the pressure of the air, the thermometer will indicate a temperature of 250 0< 5. In this way the boiling point of water ha 123. What is the cryophorus ? Explain the principle of its action. 121. What practical application is made of these facts ? 125. How does pressure affect the boiling point ? Explain the apparatus here figured. VAPORIZATION. 89 been raised to 429-34, or nearly to the melting point of tin; the pressure was then 375 pounds to the inch, or 25 atmospheres. Mr. Jacob Perkins heated steam so highly, that a jet of it set fire to combusti- ble bodies. 126. The clastic jwwer of steam :n contact with water is limited only by the strength of the contain- ing vessel: if steam l>e heated with- out water, (not in contact with i/,) then its elastic or expansive power is exactly like that of other gases or vaj>ors, (88.) 1 27. The increase of volume in changing from a liquid to a gaseous state is such, that 1 cubic foot of water becomes 1700 cubic feet of steam ; or a cubic inch of water becomes nearly a cubic foot of steam ; while 1 cubic foot of alcohol and ether yield, respectively 493 and 212 cubic feet of vapor. Water is, therefore, incomparably the best fluid from which to generate steam for a moving power ; for its higher boiling point is more than made up by the greater volume of its vapor, and the cost of fuel is in proportion to the la- tent heat of equal volumes of vapor. Thus water is superior to ether for this purpose, in the proportion of 2500 to 1000. The latent heat of steam diminishes as the heat rises, so that the heating power of steam at 400 is no greater than that of an equal volume at 212. These facts sre of the greatest value in the arts. What is the boiling point of water under 30 inches of mercury? How high has it been raised ? 126. How does elevation of tem- perature affect steam ? 127. What is the increase of volume from vaporization of water? Of alcohol ? Of ether? 8* 90 HEAT. / 128. The Steam-Engine. The principle of this appa- itatus is simple, and easily illustrated by the simple instrument a here figured, which was contrived by Dr. Wollaston. A glass tube (a), with a bulb to hold a little water, is fitted with a piston. A hole passes from the under side through the rod, and is closed by a screw at a. This screw is loosened to ad- mit the escape of the air, and the water is boiled over a lamp ; as soon as the steam issues freely from the open end of the rod, the screw is tighten- ed, and the pressure of the steam then raises the piston to the top of the tube; the experimenter withdraws it from the lamp, the steam is condensed, and the air pressing freely on the top of the piston forces it down again ; when the operation may be repeated by again bringing it over the lamp. In the common condensing engine, a cylinder (ci) is fitted with a solid piston, the rod of which moves through a tight packing in the cover, and to it the machinery is attached. A pipe (d) brings the steam from a boiler to the valve arrange- ment, (c,) by which the steam is admitted, alternately, to the top and bottom of the cylinder ; and also an alternate communication is opened with the condenser, (b.) Thus, when the steam enters at the top, (in the direction of the ar- row,) that at the bottom of the piston is driven through the lower opening to (b) where it is condensed. The valves are :noved at the proper time by the machinery. 129. Evaporation from the surface of liquids takes place 128. Explain the principles of the steam-engine from Dr. Wollas- ron's instrument. Explain the general structure of the condensing engine from the figure. VAPORIZATION. 91 at all temperatures, while ebullition, it will be remembered, occurs only at a particular temperature for each fluid. Even snow and ice waste by evaporation, at temperatures too low to melt them. Mercury rises in vapor, even at the temper- ature of 60 ; for Dr. Faraday found at that temperature that a slip of gold-leaf suspended in a close vessel was whitened by amalgamation with the vapor of the mercury. The state of the atmosphere as to dryness and pressure influences natural evaporation, which is greatly increased by heat and a rapid wind. It must be remembered that all the water which falls to the earth in snow and rain has arisen in evapo- ration. That natural evaporation takes place only from the surface is proved by its being en- tirely prevented by a film of oil on the surface of the fluid. 180. Influence of Pressure on Evaporation. If we introduce a few drops of water into the va- cuum above the mercury in a barometer tube (33), the level of the mercury will be reduced by the vaporization of a part of the water. The tension of the vapor is increased, by a rise of temperature : we may slip a larger tube over the barometer tube, the lower end of which dips under the mer- cury, and then fill the intervening space with hot water. The vapor of the confined water will force down the column of mercury in direct pro- portion to the temperature ; and by means of a thermometer and a scale of inches we can tell exactly the tension of the vapor of water for every temperature under 212. 131. Maximum Density of Vapors. If we nearly fill with mercury three barometer tubes closed at one end, and into the open end of one pour a little ether, into the second some alcohol, and into the third some water, and then invert them with their mouths beneath mercury, we shall see, on withdrawing the finger from the open end, that the 129. What is the difference between evaporation and ebullition ? 130. How does pressure affect evaporation ? How is the tension of vapor measured ? 92 HEAT. mercury will be depressed least by the water, more by the alcohol, and most of all by the ether, (about 10 inches at 60.) The addition of more of each fluid will have no effect in lowering the mercury, the tem- perature remaining the same. There is, therefore, a point of density of the vapor which cannot be passed without again con- verting it to a liquid. This is easily shown by inclining the tube containing the ether out of a vertical position ; the more nearly horizontal it becomes, the less ether can re- main in vapor, because the increased pressure forces it into a fluid state. The same fact is beautifully shown in the annexed figure, where the barometer-tube with ether is depressed in a deep cistern of mercury. The film of liquid ether on the surface of the mercury in the tube is seen to increase as the tube descends, until the ethereal va|>or is all reconverted to a fluid ; on diminishing the pressure of the finger, the liquid ether again flashes into vapor. The weight of 100 cubic inches of aqueous vapor at 212 in the greatest state of density ever obtained, is 14-90:2 grains; while the same at 32 is only '13(3 grains. The point of maximum density of a vapor is lowered by cold as well as by pressure, and when these two effects are united, we can convert many gases, which arc quite permanent at the com- mon pressure and temperature of the air, into liquids, and even to solids. 132. Diffusion of Gases and Vapors. The vapor of water will rise and fill a confined vessel of air, and have the same tension as if no air were present. It will take a longer time to do it, but as much will ultimately rise as if the space were a vacuum. The air seems to be an impediment only to the rapid rise of the vapor. On the same principle, prob- ably, is explained the curious and important fact, that, when different gases are in contact, they will not remain separate, 131. What is the maximum density of vapors ? Illustrate this from the figure. VAPORIZATION. 93 but will soon mingle uniformly, even against the force of gravity. Our atmosphere, for instance, is composed of two gases, the specific gravities of which are as 976 to 1130, and we might suppose that the heavier would be at ^ the bottom, as would be the case in two such liquids as water and oil. But they are found to be in a state of uniform mixture. If we connect together by a tube two bottles containing, one a light gas, hydrogen, and the other a heavier gas, oxygen, and place the light one uppermost, in a few hours we shall find them per- fectly commingled ; as may be proved by the fact, that the mixture will explode violently on touching a match to the open mouth of one of the vessels, which we know a mixture of these two gases will always do. The same efTect will take place through a very fine tube, or even through a plug of plaster-of-paris, or through a membrane, as of gold-beater's skin. The degree of condensation of the air or vapor has no effect in the operation of the law of the uniform diffusion of gases. 133. Dew-Point. Watery vapor is never absent from the """tir; but its quantity is very variable, depending on the causes 1 Already named, (129.) When the air is highly charged with humidity, it deposits dew on any substance colder than itself. A glass of iced water in summer is immediately covered with a coat of condensed vapor from the surrounding air. When a warm humid morning succeeds a cool night, we see the pavements and walls of the houses recking with deposited water, as if they had been drenched with rain. If we drop bits of ice into a tumbler of water having the same temper- ature with the air, and watch the fall of a thermometer placed in it, we can note with accuracy the temperature of the water, when it has cooled so far that dew begins to be deposited on the clean surface of the glass. This tempera- ture is called the dew-point ; and the number of degrees be- tween the temperature of the air, and of water cooled to that degree at which dew begins or ceases to be deposited, is an accu- rate indication of the actual dryness of the air. The nearer the dew-point is to the temperature of the air, the more moisture does it contain, and vice-versa. In this climate, in summer, this difference amounts often to 40 or more, and in India it 132. Mention the facts relating to the diffusion of vapors and gases. Illustrate this. 133. What is the dew-point ? How does it indicate the dryness or humrdity of the climate ? 94 HEAT. has been known to be as much as 61 ; that is, with an ex- ternal temperature of 90, the dew-point has been seen as low as 29. The amount of moisture in the air has a great influence on the indications of the barometer, and it is always requisite, in making barometrical observations, to make a correction for the tension of the vapor of water in the air. 134. Hygrometers* arc instruments to determine the amount of moisture in the air. One much used is called the wet bulb hygrometer, and consists of two sim- ilar delicate mercurial thermometers, the bulb of one of which is covered with muslin, and is kept constantly wet by wa- a ter, led on to it by a string from a tube in the centre. The evaporation of the water from the wet bulb reduces the temperature of that thermome- ter to which it is attached, in proportion to the dry ness of the air, and consequent rapidi- ty of evaporation. The other thermometer indicates the ac- tual temperature, and the dif- ference being noted, a mathematical formula en- ables us to determine the dew-point. But the most delicate and beautiful instrument for this use is that of Mr. Daniell, which is constructed on the principle of the cryophorus, (123.) It is represented in the annexed figure, (a.) The long limb ends in a bulb which is made of black glass, that the condensed vapor may be more easily seen on it. It contains a portion of ether, into which dips the ball of a small and delicate thermometer contained in the cavity of the tube. The whole instrument contains only the vapor of ether, air having been removed. The short limb carries an empty bulb, which is covered with muslin. On the support is another thermome- ter, by which we can observe the temperature of the air. When an observation is to be made by this instrument, a little ether is poured on the muslin : this evaporates rapidly, 134. What are Hygrometers ? Describe the wet bulb. Describe the Hygrometer of Prof. Daniell. From the Greek hitgros, moist, and metron, measure. VAPORIZATION. 95 and of course reduces the temperature of the other ball, (122.) As soon as this has fallen to the dew-point, the moisture collects and is easily seen on the black glass. At this instant, the temperature indicated by the thermometers is noted down, and the difference gives us the true dew-point. 135. The Spheroidal state of bodies, as it is called, is a curious and instructive instance of the low conducting power of vapors. When water or any other liquid is projected in drops on a surface, heated considerably alx>vc its boiling point, it will assume a spheroidal form, roll about with activity, and evaporate with extreme slowness. Water assumes this condition at 298 ; and a grain and a half of water in this state at 392 requires 3-30 minutes to evaporate : at a dull red heat, the same quantity will last 1*13 minutes, and at a bright red, 0-50, the rate of evaporation increasing with the temperature. The water, in these experiments, docs not touch or wet the hot surface, but is kept at a sensible dis- tance from it by the elastic force of an atmosphere of its own vapor. This vapor is a non-conductor, and its formation abstracts the sensible heat from the fluid ; so that, notwith- standing the proximity of the red-hot metal, the temperature of the fluid is found to be always lower than its boiling point, being, for water, 206, for alcohol, 168, and for ether, 91. A modification of this process enables us to perform the surprising experiment of freezing water in a white-hot crucible, by the aid of liquid sulphurous acid in the spheroidal state. 136. Liquefaction and Solidification of Gases. We have said that, by the united aid of cold and pressure, many gases have been made fluid, and even solid. No degree of mere pressure, not even 50 atmospheres, (or 750 Ibs. to the square inch,) can alone produce this result. By combining the two agents, Dr. Faraday has succeeded in reducing fifteen aeriform bodies to the liquid or solid state. The simple appa- ratus required for many of these results, is only a small tube of glass, bent as in the figure, at an obtuse angle, in which are placed the materials for generating the gas ; for instance, 135. What is meant by the spheroidal state ? How does it illus- trate these principles ? Explain the experiments mentioned in this paragraph. Is the temperature of the fluid in this state as high as its boiling point ? 136. How are gases made fluid or solid ? 96 HEAT. powdered bicarbonate of soda and water in one end, and sul- phuric acid in the other, to generate carbonic acid gas ; they are separately introduced, and the tube then sealed by the blow-pipe. On reversing the position of the tube, the acid can be made to run down on the carbonate of soda, and the carbonic acid gas will be set free, but cannot escape from the tube. The empty end is then placed in a freezing mixture, and the gas is condensed into a liquid by its own pressure. Some hazard attends these experiments, and the operator should be protected by gloves and a mask of wire-gauze ; for the tubes occasionally burst under the enormous pressure, and might wound him severely. Car- bonic acid treated in this way becomes a clear transparent crystalline solid, at temperatures below 71, at which point it melts into a perfect limpid fluid, which is not so heavy as the solid. M. Cagniard de la Tour has shown, that at a certain temperature and pressure, a liquid becomes a clear transparent vapor, or gas, having the same bulk as the liquid. At this temperature, or one a little greater, no additional pressure, however great, would convert the gas into a liquid. Dr. Faraday thinks that this state comes on with carbonic acid at about 90, and with a pressure above 50 atmospheres. 137. Liquefaction and Solidification of Carbonic Acid. M. Thilorier has contrived an apparatus for condensing carbonic acid on a large scale. The arrangement is shown in the accompanying figure ; g is the generator of the gas, a strong cast-iron vessel, hung by centres on a frame, (J ;) in it is put the requisite quantity of carbonate of soda and water, and a tube (a) of copper, holding an equivalent amount of strong sulphuric acid ; the cap is strongly screwed in, and the position of the apparatus inverted, by turning it over in the frame ; the acid then runs out among the carbonate of soda, and an enormous pressure is generated by the succes- sive portions of gas evolved ; after a time, when no more gas is produced, the generator is connected by a metallic tube with the receiver, (r ;) stop-cocks of peculiar construction are fixed on the top of both vessels, and being opened, the liquefied gas collects in r, which is cooled by a freezing mix- ture for the purpose of condensing it. In this way, several charges of the condensed carbonic acid gas are accumulated Explain the process. What has M. Cagniard de la Tour shown ? 137. Describe M. Thilorier's apparatus for condensing carbonic acid. ELECTRICITY. 97 in r. It can then be drawn off by a jot (j) secured to the top, which enters a metallic box, (&,) having perforated wooden han- dles. The rapid evaporation of the condensed gas here absorbs so much heat from the rest, that a considerable portion is convert- ed to a fine white solid, like dry snow. The author has repeat- edly formed balls of this snow of considerable size. When thus made solid, it wastes away very slowly, and may be handled, and moulded with ease. If suffered to rest on the hand, however, it destroys the vitality of the flesh, like a hot iron. It is now in a condition analogous to bodies in the spheroidal state, (133;) being surrounded by an atmosphere of its own vapor, the radiation of heat to it from surrounding bodies is cut off, and it acquires the very low temperature of 148. If it is wet with ether in a capsule containing mercury, the latter is frozen solid, and can then be hammered with a wooden mallet, and drawn out like lead. If it is moistened with ether in vacuo, with certain precautions, the greatest degree of cold yet observed is produced; viz: 174 below zero of Fahrenheit. The greatest cold before known was 148, and the greatest natural cold ever recorded by man was 60, which was found by Captain Ross in his polar voyages. We now see how entirely the gaseous, liquid, and solid states of bodies are dependent on heat and pressure. It is more than probable that all the bodies now known to us as permanent gases may be reduced to the fluid or solid state, by means similar to those which have already been used. IV. ELECTRICITY. ^-V^^ y 138. Tnere is a remarkable power inherent in all things, which yte call electricity,* and which, so far as we know, What temperature has been reached by aid of this condensed gas ? How is the lowest artificial temperature found ? What do we now see from these facts ? * From the Greek, electron, amber, the substance in which this 9 98 ELECTRICITY. is inseparable from matter. It has been classed with light and heat, as an imponderable agent, and is doubtless very closely related to, if not identical with these forces, the three being, perhaps, only modifications of one and the same power. It is so intimately connected with matter, as to be evolved, in some form or degree, with every change, either mechanical or chemical, which matter undergoes. As was said of heat, (69,) we know it only by its effects, as manifested on or through matter. We shall consider this power under its most remarkable forms of existence or manifestation, regarding them all, however, as modifications of one and the same thing. These are (1,) the Electricity of Magnetism ; (2,) that of Friction, or Statical Electricity ; (3,) that of Chemical Action, Galvanism, or Voltaism, called also, Dynamical Electricity ; and (4,) Thermo-electricity, or Electricity from Heat. 1. Magnetic Electricity, or Magnetism. 139. Lode-stone.* A kind of iron-ore has been known from remote antiquity which has the property of at- tracting to itself small particles of iron, and which is called the lode-stone. By contact, it can impart its virtues to iron and steel, and also in a slight degree to cobalt and nickel. As it abounded in Magnesia, (a province of ancient Lydia,) it was called by Pliny, magnes, and hence the name magnet. A bar or needle of steel, which has received the magnetic ^ influence, when suspended on a point, as in the figure, will be found to have a directive tend- ency, by which one end turns invariably to the north. The terms, -j- and , (plus and minus,) are also used to indicate the north and south poles. The needle is, therefore, said to have polarity, and the end turning north is commonly called the north pole, and the other end the south 138. What is said of electricity ? How is it classed ? How divided, (1 ?) (2?) (3 ?) (4 ?) 139. What is the lode-stone ? power was first noticed by the ancients, more than 600 years B. O Modern philosophers have given the name of the substance to the unknown power. * Sometimes spelt improperly load-stone. It is from the Saxon, laden, to lead or direct. MAGNETIC ELECTRICITY. 99 pole. If we bring the north end of a magnetic bar near to the similar end of the suspended needle, ^ j^. -^ the latter will move away, as indicated by the ' arrows, being repelled by the similar power of the bar. If, however, we bring the end N, towards the opposite end of the needle S, it will be attracted to the bar, and strive to move as near to it as possible. The reverse is, of course, true of the opposite end of the bar. If, in place of a mag- netic bar, we had used a bar of unmagnetic iron, we should have found both ends of the suspended needle equally, but less powerfully, attracted by it. We thus learn, (1,) that the magnet has polarity, and (*ar in iron- filings, we shall find only the ends attracting a tuft of the metallic particles, while the middle is free. If two magnetic bars, however, like the figure, are placed together, ( + and ,) and a sheet of paper laid over them, they will attract iron filings scattered on the paper, in the way represented in the figure ; here a pair of central poles have power to attract the iron, which the middle part of the simple bar had not. The particles of iron arrange themselves in what arc called magnetic curves. If the paper is jarred, this effect is rendered more striking. 14*2. Artificial Magnets are made of all forms, tin- most common being the so called horse-shoe magnet, U shaped like the annexed figure. It is found that the power of magnets is much increased by uniting 111. How arc permanent magnets made ? How is the power sup- posed to be distributed ? Why have the polos more power than the centre? If two bars are laid together, how is it? 142. What Ibrms are given to artificial magnets ? MAGNETIC ELECTRICITY. 101 several thin plates of hardened steel, each of which is sepa- rately magnetized. A bar of soft iron, called the keeper, is placed across the poles of a u magnet, to prevent it from losing power; and if it be made to hold a weight nearly equal to its power, it will be found to gain strength daily, and in like manner to lose its magnetism if unemployed. >ended on the horizontal bar, (,) so as to move in a vertical plane, instead of horizontally, as in the compass-needle. The graduated vertical circle (r) is placed in the magnetic meridian, and the needle then assumes, in this latitude,* the position shown in the figure, dipping down at an angle of 73 26'-7. Over the magnetic equator it would stand horizontal, being equally attracted in both directions. At either magnetic pole it would be ver- tical. The horizontal variation of the needle, its dip, and the intensity of the polar attraction, are subject to daily and local changes, from the fluctuation in the amount or direction of this force ; and daily and even hourly observations have now 143. What is said of the earth's magnetism ? How is it shown ? Is the magnetic pole coincident with the pole of revolution ? What is dip, and what variation ? Are they constant ? * Lat. 41 IS', Ion. 17 58', in September, 1839. 9* 10*2 ELECTRICITY. for several years been made in all parts of the world, to determine with accuracy the limit of these variations, and the laws which govern them. 144. Magnetism from the earth is induced in ail bars of steel or iron, which stand long in a vertical position. Tongs and blacksmiths' tools are often found to be magnetized. A bar of iron held in the magnetic meridian, and at the proper dip, becomes immediately magnetic from the induction of the earth; and the effect may be hastened by striking it on the t'iul with a hammer; the vibration seems to aid in inducing the magnetic force. The tools used in boring and cutting iron are generally found to be magnets. 145. Magnetics and Diamagnetics, Dr. Faraday, in 1845, made the important discovery that all solid and fluid sub- stances were subject to the influence of a powerful magnet, but in a manner different from tint in which iron and nickel are influenced by the magnetic force. We shall presently see (166) that a bar of iron suspended on a pivot will take a place at right angles to the direction of the magnetic or gal- vanic current, or will come to rest in the equator of magnetic force. Now a bar of bismuth, or a stick of phosphorus, under the same circumstances, will act in a manner precisely the reverse of the iron, and will come to rest in the magnetic or polar plain 1 . All bodies, which under the magnetic power net like iron, are called magnetics, while those which re- semble bismuth in their behavior -under the same circum- stances, arc called diamaguctics. A few bodies of each class are enumerated in the following list, where we observe that iron and bismuth are at the extremes, each standing as the type of its own class, while air and vacuum occupy the zero, or neutral point of quiescent inactivity. Iron, nickel, cobalt, manganese, palladium, crown-glass, platinum, osmium, air and vacuum, arsenic, ether, alcohol, gold, water, mer- cury, flint-glass, tin, heavy-glass, antimony, phosphorus, bismuth. It is a curious sight to see a piece of wood, or of lit. How are bars of iron and steel affected by the earth's mag- netism ? 115. What was Faraday's discovery in 1815 ? Into what two classes are bodies divided in reference to their behavior under magnetic influence? Of which is iron the type ? Of which is bis- muth ? How are the classes contrasted ? Enumerate a few of each class. Is this action confined to metals ? Mention snm< singular examples. KLKCTRrCITY OF FRICTION. 103 beef, or an apple, or n bottle of water, repelled by a magnet ; or taking ihe leaf of a live and hanging it up between the poles, to observe it lake an equatorial position. 2. Electricity of Friction ; or Statical Electricity. 140. Electricity is rro/rrrf by several of the same causes which we have already (60) named as sources of heat. Friction excites it abundantly ; chemical action still more It attends animal life, and is powerfully exhibited in som. 1 animals, as in the torpedo, and electrical eel : heat evolves it, and wo have reason to believe that the sun's rays are jx^r- petually exciting electrical currents in the earth. Like heat, it neither adds to or subtracts from the weight of matter : but unlike heat, it produces no change in dimensions, and does not atlivt the power of coltesion in bodies. In |towerful discharges, however, it overcomes cohesion by rending or fusion. All matter is subject to its influence, and it can be transferred from an excited body to one previously in a neu- tral stale. 147. Electrical Excitement. If we briskly rub a glass tube with warm and dry silk, and bring it near to any light substance, as a leather susjxnuled by a thread, a flock of cotton, some shreds of silk, or, as in the figure, to two balls of pith, suspended on a hook by delicate wire, the light substances will at first be strongly attracted to the tube, but in an instant will fly oil" again, as if repelled by some unseen force, and any further effort to attract them to the excited glass will only cause their further removal. Ivach separate thread of silk and each pith-hall seems to retreat as far as possible from the jjlass tube and from : ho other threads. An artificial head of hair or shreds of dry paper shows this in a striking manner, when placed on the conductor of an excited electrical machine. Each hair stands 14i>. How is electricity evolved f Contrast 147. Explain The first facts in electrical excitement pith-ball* and head of hair affected t it with heat. How are the 104. ELECTRICITY. aloof from every other, as if instinct with hatred. If now, in the place of the glass tube, we use a stick of sealing-wax, rubbed with dry flannel, and present this to the pith-ball which has been excited by the glass tube, we shall find a very strong attraction manifested between them ; the light substance previously excited by the glass, will move to the ex- cited resin much more actively than a substance not previously excited in this way ; and two substances separately excited, one by the glass and the other by the resin, will attract each other with equal power. One of these is called vitreous, and the other resinous electricity. These simple phenomena form the basis of all electrical science. ^J 148. Electrical Polarity. We see in the facts just stated /a strong resemblance between the two sorts of electrical ex- / citement and the opposite powers of the magnet. The vitreous is to the resinous electricity as the north pole of a magnet is to the south. Hence we call the vitreous the positive elec- tricity, and the resinous the negative electricity. Each par- ticle of matter thus influenced by electrical excitement must have polarity, like the mag- netic needle, attracting and repelling, accord- ing as it is acted on by like or unlike forces. Thus a row of pith-balls, as in the figure, will all become excited b induction, or influence, and the signs plus and minus wi explain how they stand related to each other. Magnetism, as it is usually understood, is confined to two or three metals ; while electricity can, with proper precautions, be excited in all substances. We cannot conceive of one sort of electrical excitement existing without the other ; thus the glass tube is -f , but the silk which rubs it is , and vice versa, the resin is , but the flannel is -f . 149. Electrical Equilibrium. All cases of electrical ex- citement are due to a disturbance of the electrical equilibrium, or balance of power, which, aside from disturbing causes, If wax is used in place of glass, what happens ? What are these two electricities called ? 148. What analogy do we see between the two electricities and the magnet ? What names do we give to them ? Can one sort of electricity exist without the other ? 149. What is electrical equilibrium ? ELECTRICITY OF FRICTION. 105 naturally exists among surrounding bodies; and the intensity of the electrical action is directly proportioned to the amount of that disturbance. The more unlike in electrical state a body becomes to surrounding substances, the more energetic will be the display of electrical power. The opposite states are, however, always in such proportion as exactly to neu- tralize each other in any two substances which have been mutually excited, as glass and the silk rubber. 150. Theories of Electricity. Two theories have been proposed to explain the ordinary phenomena of electricity. The first is that proposed by our distinguished countryinnn, Dr. Franklin, (and called the Franklinian hypothesis,} which is very simple and ingenious. It supposes that thorn is a simple, subtle, and highly elastic fluid, which pervades all matter. This fluid is self-repellent, but attracts all matter, or its ultimate particles; these particles of matter are con- sidered as also self-repellent, when deprived of or possessing more than their natural quantity of electricity, and as natu- rally attracting when they are in opposite conditions. In the natural state of bodies, this fluid is uniformly distributed, and its increase or diminution produces electrical excitement. Accordingly, when a glass tube is rubbed with a silk hand- kerchief, the electrical equilibrium is disturbed, the glass acquires more than its natural quantity, and is over-charged, the silk possesses less, and is under-charged. The second hypothesis is that of Du Fay, who conjectured that electrical phenomena were due to two highly elastic, imponderable fluids, the particles of which are self-repellent, but attractive of each other. These two fluids exist in all unexcited bodies in a state of combination and neutralization, when no electrical phenomena are seen. Friction occasions the separation of the fluids, and the electrical excitement in a body continues until an equal amount of opposite electricity to that excited has been restored to it. According to Dr. Franklin's theory, the two states are denominated positive and negative ; according to Du Fay, they arc distinguished as vitreous and resinous. We can use either of these terms indifferently, however, without commit- ting ourselves to either theory, both of which cannot be true. The real use of such terms is, to enable us to obtain clearer 150. Name the two theories of electricity. What is the Frank- linian hypothesis ? What is Du Fay's view ? What are these two theories called / 106 ELECTRICITY. notions of the relation of the several phenomena ; and the hypothesis which they express serves as a thread of phi- losophy hy which we connect our separate facts. 151. Conductors and Insulators of Electricity. The pith-balls or glass tubes, which have been electric-ally excited, return to a natural state very slowly indeed, if left untouched, in dry air. But the hand, or a metallic rod, will at once restore them to the unexcited state, while dry silk, glass, and resin, will not remove the excitement. Bodies are, therefore, divided into conductors and non-conductors of elec- tricity, or, more properly, into good and bad conductors. The electrical discharge takes place through good conductors, (as the metals,) with an inconceivable velocity, which can be compared only to the velocity of light. Among good conductors, in the order of their conducting power, are the metals, charcoal, plumbngo, and various fused chlorids, strong acids, water, damp air, vegetable and animal bodies ; among imperfect conductors are spermaceti, glass, sulphur, fixed oils, oil of turpentine, resin, ice, diamond, and dry gases. The latter substances are also called insulators, because by their aid we can insulate or confine electricity. 15*2. Electroscopes, or Electrometers. The kind of elec- trical excitement in a body is ascertained by a very simple apparatus, called an electroscope. The pith-balls (147) serve this purpose very well. We excite them by electricity of a known kind, as of an excited glass tube brought into actual contact with them, and then we bring near them the body whose electrical state we wish to learn : if they are still further repelled, we conclude that the body in question has vitreous or positive electricity; but if they arc attracted, we conclude that the reverse is true. The gold-leaf electrometer is, however, a much more sensitive and delicate test of electrical ex- citement, and consists of two leaves of gold, suspended in an air-jar, and communicating by a wire with a small plate of brass ; the approach to this plate of a body in any degree excited, will occasion an immediate movement of the gold-leaves, from which we can tell the nature of the What is the use of such theories? 151. What are conductors ? What are insulators ? Name some of each. 152. What is an elec- troscope ? How do we, by means of it, ascertain the kind of elec- tricity ? ELECTRICITY OF FRICTION. 107 excitement, as above described, having previously imparted to the gold leaves a particular kind of electricity. 153. The Electrical Machine. The principle of the common electrical machine will be easily understood, after what has been said. Two forms of this machine are in com- mon use, the cylinder and the plate machine : a good view of the latter is presented in the annexed figure ; d is a wheel of plate- glass, turned on an axis by a handle. The electricity is excited by the friction of two cushions or rubbers, (e, e,) which press against the plate, and are covered with a soft amalgam of mercury, tin, and zinc, which greatly heightens the effect. The rubbers are connected with the earth by a metallic chain, (b.) The excited glass delivers its electricity to several sharp points of wire attached to the bright brass arms, and connected with the great conductor, (a.) The conductor and plate are perfectly insulated by glass supports. When thus arranged, and the machine is turned, bright sparks of a violet color, forming lines like lightning, will dart with a sharp sound to any conducting substance brought near to the great conductor. This is positive electricity. If nega- tive electricity be wanted, we must insulate the rubbers, and, connecting the conductor with the earth, draw the sparks from the rubber. Every care must be taken in the use of an electrical appa- ratus, to keep it clean and smooth, and particularly free from moisture. Dust acts as so many points to discharge the fluid, and moisture deposits itself in a thin film over the insu- lators, and prevents the accumulation of power. 153. Explain the electrical machine. How is negative electricity obtained ? What care is to be used in keeping an electrical machine ? 108 ELECTRICITY. 154. The Lcyden Jar, or l r ia/, is the simple means by which the experimenter collects and transfers a portion of the electricity evolved by his machine, and applies it to the purposes of experiment. The Loydcn-jar, (so called from the place where it was first invented,*) is only a glass bottle, covered inside and out with tin-foil up to the line seen in the figure. A brass ball communicates by a wire and chain with the interior coating, the mouth being stopped by a cover of dry wood. On approaching the ball to the conductor of the electrical machine, when in action, a series of vivid sparks will l>e received by it, and a great accumulation of vitreous electricity takes place in the interior, provided the exterior be not insulated. On forming a connection by a con- ductor between the interior and exterior surfaces, the equilibrium is at once restored by a rush of the opposing forces, accompanied with a brilliant flash of artificial lightning, and, if the hand of the operator is the conducting medium, a violent shock is felt, commonly known as the electrical shock. A series of such jars arranged so as to be charged by one machine, is called an electrical battery. 155. The Eh'ctrojrfiorus^ is a convenient mode of obtain- ing an electrical spark, when no electrical machine is to be had, and consists of a shallow tray or dish of tin, (or a wooden box,) the size of a dining plate, partly filled with melted shellac, (a,) or some other resinous preparation, made as smooth as possible. A disc of brass (b) with a glass handle is provided, and the bed of resin is rubbed with a dry flannel or cat-skin; this excites negative electricity, and the metal disc is then laid on the excited surface, and touched with the finger. A coating of 154. What is the Leyden-jar, and how used ? 155. What is an electrophorus, and how made and used ? * This instrument, attributed to one Cunaeus, of Leyden, in 1746, has done as much for statical electricity as has the pile of Volta for galvanism. f From the Greek, electron, and pkero, I carry. ELECTRICITY OF CHEMICAL ACTION. 109 positive electricity is induced on it, and it may be raised by the handle, and discharged by a conductor, giving a vivid spark, sufficient to explode gases. The resinous electricity not being conducted away from the shellac, the spark may be repeated as long as the excitement lasts. 156. A jet of high steam issuing from a locomotive or other insulated steam-boiler, will, with certain precautions, give a stream of electrical sparks more powerful than any electrical machine. This has been called hydro-electricity, and is produced by the friction of the hot steam on the edges of the orifice from which the steam issues. 157. Thunder and Lightning. These common natural phenomena arc due to the passage of electricity from one cloud to another, or from a cloud to the earth, which is usually attended with a brilliant flash and loud explosion. Dr. Franklin first suggested and proved the lightning of the atmosphere to 1x3 the same thing as the machine electricity, and contrived an electrical kite by which he drew the lightning of the clouds to the earth.* In a thunder-storm the electri- cal cloud, the intervening air, and the earth, represent respectively the inner and outer coatings of the Leyden-jar ; the air being the non-conductor through which the discharge finally takes place. / 3. Electricity of Chemical Action^ Galvanism, or Voltaism. 159. We have found /the electricity of friction, or ma- chine electricity, to be endued with great energy, passing with a vivid spark through a considerable thickness of dry air, and capable of being insulated by non-conductors, so as to be easily transferred and managed, as in the Leyden-jar. Moreover, we know that dryness and insulation from the earth are essential to its excitation, by artificial means. We shall now see how strongly in these, as well as in many other respects, it is contrasted with the sort of electricity 156. What is said of the electricity of high steam ? 157. What are thunder and lightning ? How are the conditions of a thunder-storm like the Leyden-jar '/ What was Franklin's discovery about lightning ? 158. What leading properties have we observed in machine electri- city? " Eripuit ccelis fulmen sceptrumque tyrannis." 10 110 ELECTRICITY. which is the product of chemical action, and best known "as Galvanism, or Voltaism.* 159. Origin and Discovery of Galvanism. Accident led to the origin of the science oT galvanism in 1790.J Gal- vanij observed that the freshly prepared legs of a frog were convulsed, when brought within the influence of a powerful electrical machine in action. He at once believed that he had discovered in electricity the secret spring of life and nervous power. Volta, however, reasoned, that the convulsions were in no way con- nected with animal life, but that the muscular contractions were excited in the legs of the frog by induction from the active machine; this effect being produced through the influ- ence of two metals, which, at the time, were in contact with the naked flesh. This ex- periment is easily repeated on the legs of a frog, from which the skin has been recently stripped. They arc? suspended by a silver or platinum wire, or a wire of any metal, passed under the crural nerves, which are easily found, by gently separating the large muscles of the legs at a. A slip of zinc, bent so as to touch at the same time the toes and the wire of suspension, will occasion violent convulsions in the legs. This irritability is lost soon after death. 159. When, how, and by whom, was galvanism discovered ? Explain the experiment with the frog's legs. * This sort of electrical excitement is, also, frequently called the "electricity of contact," because actual contact of the metals em- ployed was supposed to be required. It is likewise called dynami- cal electricity, (from f/Hnami*, power,) and " current affinity." f Accident, properly considered, never discovered any philosophical principle. The minds of philosophers had been ripening for fifty years for Volta's discovery, and the twitching of the frog's legs, like Newton's apple, was only the spark which fired the train that had been long laid. t Prof. Galvani lived at Bologna, in Italy, and Volta of Pavia waa his nephew and pupil ; although Galvani made the first observations, Volta offered the true explanation of the observations of his uncle, and by rational experiments supported it against powerful opposition. Voltaism would, therefore, seem to be a more just term for the science than galvanism. ELECTRICITY OF CHEMICAL ACTION. Ill 160. Voltaic Pile. Volta sagaciously reasoned, that the same effects could be produced with simple metals and a fluid, or substances saturated with a fluid. The truth of this conjecture is easily verified, by placing on the tongue a silver coin, and beneath it a slip of zinc, or a cent of copper. On touching the edges of the two metals so situated, we per- ceive a mild flash of light and a sharp prickling sensation, or twinge, giving notice of the production of a voltaic cur- rent. Volta arranged a series of copper and silver coins in a pile, with cloths wet in a saline or acid fluid between them. The arrangement is seen in the figure. The copper (c) and zinc (z) alter- nate with the wet cloth between. The pile begins with z and ends with c. On establish- ing a metallic communication between these extremes by a wire, a current of electricity flows in the direction of the arrow on the wire.* If one hand be placed on each end of the pile, a shock will be experienced, simi- lar in some respects to that from the electrical machine, and yet very unlike it. If the pile has many members, on touching the wires communicating between the extremes, the shock is very intense, and a vivid spark will be produced, which is increased if points of prepared charcoal are attached to the ends of the wires. The con- ducting wires held together will grow hot, and if a short piece of small platina wire is interposed, it will be heated to bright redness. Such is an outline of the remarkable discovery of Volta, whose pile was made known to the world in 1800. The principle involved in this arrangement is unaltered, although moie manageable and extensive forms of apparatus have supplied the place of the pile. 160. What was Volta's reasoning ? What instrument did he in- vent, and when ? How was it constructed? What is its action? * The terms fluid or current ', are used in obedience to custom; but the learner should remember, that the ' fluid' is only an ideal one, as we have no evidence of its existence, and the wire which communicates the electrical influence does not carry any fluid, as a pipe carries water. There is not a particle of evidence as to the real nature of the electrical excitement produced by the action of acid water on different metals. All we know is, that so long as such action lasts, there is a constant production of an electrical excitement or influence, which we call a current. 112 ELECTRICITY. 161. Simple Voltaic Circle. A voltaic current is established whenever we bring two dissimilar metals, (as copper, silver, or platina, with zinc or iron,) into contact in an acid or saline fluid. Thus if we place a slip of copper in a glass of acid water, and be- side it in the same vessel a slip of amalga- mated* zinc, as long as the two metals do not touch there will be no action, but on touching the upper ends of the two slips of metal, a vigorous action will commence, bubbles of gas will be rapidly given off from the copper, while the zinc will be gradually dissolved in the acid water. This action will be arrested at any moment, on separating the two metals. The end of the zinc in the acid is -f, or positive, and that in the air , or negative; the copper has the reverse signs. These relations are expressed in the figures by the signs -f and , and by the direction of the arrows showing how the -f electricity of the zinc passes to the of the copper in 1 the acid ; while the bubbles of gas (hydrogen) r> - ^9 /set free at the + end of the zinc, travel over and are delivered at the of the copper. The second figure shows how the current may \K established by wires, without the di- rect contact of the slips. In this case the wires (as in the pile, 160) carry the influence in the direction of the arrows, and the existence of the current and its positive and negative characters may be shown by the effect produced by it on a small magnetic needle, which 161. What is a simple voltaic circle? Explain the electrical relations of zinc and copper, in and out of the acid. What is amalgamation? Is contact of the metals in the vessel necessary ? Explain the second figure. What determines the direction of the current? * Amalgamated zinc, is zinc which has been rubbed over with mercury; this is done by dipping common sheet or cast zinc into a dilute acid, and while the surface is still being acted on, rubbing it with mercury, which will at once cover the surface with a resplen dent surface of quicksilver. Pure zinc does not need amalgamation, but all commercial zinc is impure, and the object of the amalgamation is to cover over the impurities, (mostly iron and charcoal,) and re- duce the surface to perfect electrical uniformity, so that it shall be all positive, and not a mixture of positive and negative. ELECTRICITY OF CHEMICAL ACTION. 113 will be influenced by the wires carrying the current, just as by the magnet ; being attracted or repelled according as it is above or below the wire, and in either case endeavoring to place itself at right angles to the conducting wire, (166.) The direction of the voltaic current (and of course the + or qualities of the metals from which it is evolved) de- pends entirely on the nature of the chemical action produced. Thus, if in the arrangement just described, strong ammonia were used, in place of the dilute acid, all the relations of the metals and the fluid would be reversed, since the action would then be on the copper. The chemical effects of the voltaic circle will be considered in- the chapter on chemical philosophy. G.t*y- | VAt^? 162. The CopipdAtif^roltaic Circle. If^Sh-pkcfe of one cell, as just described, we arrange scveral/Gf the same sort, like the three in the figure, not forming any direct metallic communication be- tween the members of the same cell, but only between those of different cells, then we shall find (attending to the signs -f and ) that the positive electricity of the first copper will be exactly neutralized by the nega- tive of the zinc of the next cell, and so on ; and we shall have at the terminal wires only the same quantity of elec- tricity which we had in a single cell ; all the opposite electricities of the intermediate members being exactly neutralized.* 163. Quantity and Intensity. We learn the remarkable fact from this statement, that, no matter how much we may increase the number of the members in the voltaic circle, the quantity of electricity passing in the current is equal only If ammonia were used, how would it be ? 162. What is a com- pound voltaic circuit? How are the members united? Explain the relations from the signs -{- and . What do we thus dis- cover ? * This form of apparatus was called the crown of cups, (Couronne tie tasses,) being arranged in a circle. 10* 1H ELECTRICITY. to that evolved by a single cell. But the current which has passed through a number of similar cells has acquired an intensity exactly proportioned to the number. Thus no single cell, however large, would ever afford electricity of a tension sufficiently high to decompose water, or give the slightest shock to the animal frame. Hut the increase of size of the individual plates will enable us to produce much greater effects of induced magnetism, and to accumulate heat to a surprising extent.* These effects are said to depend on the quantity of electricity, while the other class depend on greater intensity given to a smaller amount of electricity, bv extending the series. The electricity always Hows, both in simple and compound circles, from the zinc to the copper, in the fluid of the battery ; and from the copper to the zinc, out of the battery. This is important to be remembered, since the zinc is called the electro-positive element of the voltaic series, although out of the fluid it is negative ; and consequently, in voltaic decom- position, that element which goes to the zinc pole is called the electro-positive element, being attracted by its opposite force; while the clement going to the copper is called, for the same reason, the elcctro-negatire. The compound circle, reduced to the simplest form of expression, would be Copper zinc -fluid copper zinc. Here the copper end is negative and the zinc positive but the two terminal plates are in no way concerned in the effect ; so that, throwing them out of the question, we bring it to the state of the simple circle, which is simply Zinc -fluid copper ; and here we find the zinc end negative, and the copper end positive. 163. Explain what is meant by quantity and intensity. What ad- vantage is there in multiplying the series, if no more electricity is evolved ? What happens from the use of large plates ? How does the current always flow in the battery ? How out of it ? What electrical names then have the copper and zinc ? Reduce the com- pound circle to its simple form of expression. * Hare's calon'motor, or heat-mover, is constructed on this principle. ELECTRICITY OF CHEMICAL ACTION. 164. Galvanic batteries are very various in form, but all involve the same principle. Besides those already men- tioned, we may briefly name a few others; and, (1,) Mr. Cruickshank's, called the " trough battery," is formed of double plates of copper and zinc sol- dered together, and cemented into a mahogany trough, so ns to form a series of tight cells, into which the acid fluid is poured ; the effect is greatest at the first moment of contact of the acid and plates, + and the operator must hasten to complete his experiments before the power has materially de- clined. (2.) To avoid this inconvenience, Dr. Wollaston contrived the annexed arrangement, where the copper is bent so as to surround the zinc, thus doubling the surface compared with the last; the metallic connections are made to a bar of wood, by means of which the whole series may be easily raised and lowered, in the porcelain or earthen-ware trough, having a separate cell for each pair. (3.) Dr. Hare, of Philadelphia, first informed us that separate cells were not required for each pair of plates, and that by packing an arrangement similar to Wollaston's, in a frame, with varnished paste-boards between the members, to prevent any metallic contact, a large number of members might be instantaneously immersed and raised again from the acid fluid at one movement. The greatest economy of power is thus gained, and the effects are truly surprising. Such an arrangement is called a deflagrator, from the energy with which it deflagrates or burns the metals and other combustible substances. There is a battery of this kind in the Laboratory of Yale College, consisting of nine hundred 164. Mention some of the forms of battery. (I.) Cruickshanks', and its disadvantages. (2.) Wollaston's improvement. 116 ELECTRICITY. members, 4-X12 inches, each zinc being surrounded by a copper case, and the whole packed as above described in twelve frames, and all immersed at one movement. The fluid used to excite this battery is usually dilute sulphuric acid, (1 part acid to 14 or 16 of water by weight.) Its deflagrations are ex- tremely splendid and energetic, and the arch of light (A in the an- nexcd figure) given out at its poles, be- tween points of char- coal, (C C,) has often been five or six inches in length. The power of such an instrument in chemical decomposition is very great. There are many other forms of voltaic battery, but wo have not space to mention any more, except those which will be named when we treat of the chemical effects of galvanism. As more knowledge of chemical terms than the student is now supposed to possess would be required to make them intelligible, they arc described under the head of chemical philosophy. 165. Effects of Voltaic Electricity. These are con- veniently classified under the heads, (1,) Electrical, (54,) Luminous, (3,) Calorific, (4,) Electro-magnetic, (5,) Chemi- cal, (6,) Physiological. Of these, the first three and the last have received as much attention as our limits will permit. The fifth will 1*3 considered alVr we have become somewhat familiar with the principles of chemical philosophy. We have then to consider, briefly, the fourth effect of voltaic electricity, Electro- Magnetism. 166. If a wire conveying a voltaic current is brought above, and parallel to, a magnetic needle, (as shown in figure a,) the latter is invariably affected, as if the poles of another magnet had been brought near, (130.). If the current is (3.) Hare's deflagrators, and their great superiority. 165. How are the effects of voltaic electricity classed ? 166. How is the mag- netic needle affected by the voltaic current ? ELECTRO-MAGNETISM. 117 flowing, as indicated by the arrow on the wire, say to the north, then the north pole of the needle will turn to the east; if the current is flowing south, it will turn to the west. If the line carrying the current is placed beneath the needle, the same effect is produced as if the current had been re- versed ; the needle turns in the opposite way to what it does when the wire is above. The effort of the needle is to place itself at right angles to the wire, as if influenced by a tangential force. If the wire is bent in a rectangle, as in figure 6, and wound with silk or cot- ton, to prevent metallic contact, and the lateral passage of the current from wire to wire, then it is evident that any current which may be flowing over the wire will have to pass com- pletely around the needle, and the effect which is produced will be in proportion to the number of turns made by the wire, since its influence' is multiplied by the number of turns. In this way we can make a very feeble current give decided indications. Prof. (Ersted, of Copenhagen, in 1819, first made known the law of electro- magnetic attraction and repulsion ; since which time the progress of this branch of science has been very rapid. 167. Galvanoscopes, or (Galvanometers, are instruments by which we measure the force and direction of a galvanic or voltaic current, which is often a most important thing to be known. The prin- ciple of the last arrangement is here ap- plied. In order to free the magnetic needle from the directive tendency which it receives from the earth's magnetism, two needles are used, with their unlike poles placed opposite to each other, (see fig. a,) one within and the other above the coil. They will then hang suspended by the silk fibre which supports them, What is the effect of the needle ? If the wire is bent into a rect- angle, what is the effect ? Who discovered the first law of electro- magnetism, and when ? 167. What are galvanoscopes ? 118 ELECTRICITY. with no tendency to swing in any direction, since they are wholly occupied with their own attractions and repulsions, and their directive power is neutralized ; consequently, they are free to move with the slightest in- fluence of any current passing through the coil. Such an arrangement is called an astatic needle.* To give it greater delicacy, and prevent the currents of air from moving it, a glass shade (fig. b) is placed over it, and the movements of the needle arc read on the graduated circle.f For the purpose of elementary explanation of the principles of electro- magnetism, such a needle as that figured in the last section will answer. The tendency of the galvanometer-needle, it will be remembered, is always to place itself at right angles to the direc- tion of the electrical current, that position being the equator of the attracting and repelling powers, and consequently a point of equilibrium. 168. Am^re's Theory. The discovery of the first law of electro-magnetic influence by (Ersted, attracted great attention; and in 1820, M. Ampere, a French philosopher, made the suggestion that the magnetism of the earth was due to the influence of the sun's rays, which, falling on the earth, might be considered as encircling it in an unending series of spiral lines, producing in it the phenomena of magnetic in- duction, (140.) The discovery, by CErsted, of the magnetic influence of an electric current, (166,) led him to conjecture, that if such a current was made to pass in a spiral about any conductor, it would become magnetic. This idea led to the discovery of the phenomena of the 1G9. Helix.\ A wire coiled in the form here represented, Explain the figures. What is an astatic needle ? 168. State Ampere's theory. * From the Greek, astatox, just balanced. f It was a galvanometer such as this which was referred to as being used in Melloni's apparatus, (104.) t So called from the Greek, kelisso, to twist round ; Latin, helix, in allusion to the coiling of a vine about a tree. ELECTRO-MAGNETISM. 119 and made the medium of communication for a voltaic current, becomes capable of manifesting very strong magnetic influence on any conductor placed in its axis. A delicate steel needle, laid in the helix, will be drawn to the centre and held suspended there, without material support, like Mahomet's fabled coffin. If the needle is of steel, the magnetism it thus receives will be retained by it ; but if it be of soft iron, it is a magnet only while the current is passing ; brass, lead, copper, or any other metallic conductor, can in this way be made to mani- fest temporary magnetic power. The more closely the helix is wound, and the more revolutions it makes, the more pow- erful is the magnetism which it can induce, (166.) It is essential that the wire of which it is formed should be insu- lated from contact with itself, by being wound with silk or cotton, or coiled in an open spiral, as in the figure. A short and stout wire of lead or copper, connecting the poles of a single cylinder battery, when excited, becomes strongly magnetic, as may be seen by the bundle of iron-filings which it will then attract; each filing becomes itself a magnet, and the whole surround the wire in a beautiful tuft or festoon. The moment the connection between the poles is broken, they all fall, and the wire has not power to lift a single par- ticle of iron. 170. De la Rive's Ring. We infer, therefore, that the helix itself has polarity, and this is beautifully proved by the arrangement represented in the an- nexed figure, called De la Rive's ring, which is simply a small wire helix, whose ends are attached to the little battery of zinc and copper con- tained in a glass tube, and the whole made to float on the surface of a basin of water, by means of a large cork, through which the glass tube is thrust. On exciting this small battery by a little dilute acid, poured into the 169. What discovery did Ampere's theory lead to ? What is a helix, and its action? How does a stout wire in the poles of a bat- tery show the spiral or tangential direction of the current? 170. What does De la Rive's ring show ? Explain it. If 120 ELECTRICITY'. tube, and placing the apparatus on the water, it will at once assume a polar direction, as if it were a compass-needle, the axis of the helix being in the magnetic meridian ; and it will then obey the influence of any other magnet brought near it, manifesting the ordinary attractions and repulsions. _V-*"" 171. Electro-magnets, We may avail ourselves of* the principle of the helix to manufacture artificial magnets ; if steel wires are introduced, as before stated, (169,) within the helix, they become permanent magnets, while soft iron is made only temporarily so. The position of the poles may be determined by a little reflection from what has been already said. If the helix is wound from left to right, the poles will be the reverse of their position if the winding was from right to left ; a reversal of the direction of winding will be the same as changing the poles. By reversing the wind- ing in the middle of the helix, we shall establish two sets of poles ; and if it is twice reversed, three sets will be pro- duced, and so on ; we can also reverse the polarity of our magnet at will, by changing it end for end in the helix, or by reversing the direction of the current. Obvious as was the conclusion to which these principles lead, Prof. Henry, of Prince- ton, was the first who attempted to apply them to the production of large magnets, from soft iron wound with successive short coils of covered wire, as in the figure. In this way, he succeeded in producing the most powerful magnets which have been made. One on his plan, now in the Laboratory of Yale College, has lifted 2500 pounds. In these magnets the wire is insulated, and wound in short coils of 60 to 100 feet, the opposite ends of which are connected with the oppo- site poles of the battery. A small battery was used in one of his experiments, consisting of two con- centric cylinders of copper soldered into a cup, to hold half a pint of dilute acid, with a zinc cylinder immersed in it. With this, 650 pounds were sustained by the magnetism induced in a bar of soft iron, two inches square, twenty 171. How is the principle of the helix applied to making artificial magnets ? If the helix is reversed ? If twice reversed ? Mention Prof. Henry's magnets. Hour much have they been made to lift ? ELECTRO-MAGNETISM. 121 inches long, and bent into the horse-shoe form. This was wound with 540 feet of insulated copper bell-wire, in nine separate coils of 60 feet each. With a larger battery, the same magnet sustained 750 pounds. A very small electro- magnet has been made to lift 420 times its own weight. 172. The Magic Circle. The reader must remember that the magnetism of soft iron, induced from the voltaic current, is not the result of contact between the helix or coil and the iron ; but this effect is produced through an intervening space of air, or other material which is non-con- ducting to ordinary electricity, or galvan- ism. The annexed figure shows two small semicircles of soft iron, forming a ring when united, and fitted with handles ; a small coil of insulated wire, (R,) placed within the soft iron circle, will cause the induction of magnetism in it, the moment the terminal wires (a b) are connected with a small battery. The rings of iron and of wire are quite distinct, and may be moved about in each other ; the soft iron semicircles seem bound together as if by magic, and hence the apparatus has been called the magic circle. Fifty or sixty pounds are easily sustained by such an apparatus made of iron about half an inch in diameter. 173. Electro-Magnetic Motions. The great magnetic power induced in soft iron, early suggested its application to the moving of machinery. As yet, however, we have produced nothing which can take the place of steam or water, as a moving power. The causes of failure cannot well be explained in this place, as they involve some chemical reasoning which would be in anticipation of our knowledge. Faraday was the first who succeeded in producing mo- tion by the mutual action of magnets and conductors. It is quite impossible to name, much less describe, even a tenth 172. Is electro-magnetism the result of contact ? Illustrate this from the magic circle. 173. Has the great power of electro-magnets been made available for use ? Who first produced electro-magnetic motion ? 11 122 ELECTRICITY. part of the ingenious and instructive forms of apparatus which have been contrived by various experimenters, for producing motion. Ampere's Rotating Battery is an instructive form of appa- ratus, and one of the first contrived. In this, a small double cylinder or cup of copper is hung by a pivot over and around the pole of a U magnet, standing as represented in the sectional figure on pole S. This holds the dilute acid, into which the zinc cylinder (Z) dips, which is suspended on another pivot so as to hang freely. As soon as the acid water is poured into the cup, a current of electricity will flow (161) from ihc zinc to the copper, over the wire and through the pivot to the zinc again. The zinc and copper are in the con- dition of two conductors, conveying an electric current in opposite direc- tions, and being under the influence of the poles of the magnet, (166,) and free to move, they revolve in opposite directions. If each pole is thus provided, the cups and zincs on each will revolve difFerently. 174. Page's Revolving Armature* One of the simplest forms of the electro-magnetic engine is that figured on the next page, in which an electro-magnet (M) is fixed on a stand, with its poles in an upright position. A brass wheel is so placed over it, that three bars or armatures of soft iron, (A,) which divide the circumference, may pass very near to the poles of the magnet, as the wheel turns. The arrangement is such, that the revolution of the wheel shall break the Describe Ampere's rotating battery. 174. What is Page's re- volving armature, and how does it operate ? Dr. C. G. Page of the Patent Office, Washington, is the author of numerous ingenious electro-magnetic machines, [for an account of which see the American Journal of Science, passim,] and is one of the most successful cultivators of this science. His apparatus, with much other useful matter, will be found described and figured in a useful work called Davis's Manual of Magnetism, 18mo. Boston, 1842. Several of the figures here given are from Mr. Davis's book. ELECTRO-MAGNETISM. 123 connection between the battery and the electro-magnet, three times in every revolution. Tin's is accomplished by the wire (B) which plays upon three pins of wire, in the little disc seen upon the horizontal axis of the wheel. As often as these pins touch the wire, (B,) the circuit is completed, and the soft iron (M) becomes a magnet. As soon, how- ever, as this contact is broken, M ceases to be a magnet. Now this happens three times in every revo- lution of the wheel, and the breaking of contact is so contrived that it always happens just when one of the soft iron armatures (A) comes over the poles of the electro-magnet. The bars (A) being each in suc- cession strongly attracted to the poles of the magnet, cause the wheel to move, and the revolution, being once established, is kept up with great velocity. If the magnetism in M was not destroyed by the contact- breaker, (B,) at the very time when A comes over the poles the revolution would be arrested by the strong attraction of 4hc magnet for the armature. 175. Henry 1 s Coils. When an electrical current from a single pair of plates is passed through a long conductor, as a spiral of copper ribbon, or a long bell-wire, it will be found, at the moment of breaking the contact between the conductor and the battery, that vivid sparks will appear, and a feeble shock will be felt if the moistened fingers grasp the naked conductors. A long conductor then supplies the place of an increased number of plates in a voltaic series, and to some degree imparts the quality of intensity (163) to a current of quan- tity. A flat spiral of copper ribbon one hundred feet long, wound with cotton, and varnished, shows these effects well. A magnetic needle will be powerfully affected by this coil while the current is passing ; the N. or S. pole being drawn 175. What is the effect of Henry's coils on the voltaic current ? 124 ELECTRICITY. toward the centre, (see the figure,) according to the direction of the current, the reversal of the current producing a reversal in the direction of the needle. The oppo- site sides of the spiral of course produce opposite eflects on the needle. Its axis, it will be seen, is the same as that of the helix, (169,) and it will in like manner produce magnetism. The mag- netism is, however, to be distin- guished from the new effects excited by the passage of the feeble current through the coiled conductor, on breaking con- tact, i. e ., the vivid spark and the shock. The latter is feeble with 100 feet of copfHT ribbon, and becomes more intense (178) if the length of the conductor l>e increased, the battery remaining the same ; but the sparks are diminished by lengthening the conductor. The increase of intensity in the shock is, however, limited by the increased resistance or diminished conduction of the wire, which finally counteracts the influence of the increasing length of the current. On the other hand, if the battery power be increased, the coil remain- ing the same, these actions diminish. This class of phe- nomena has been attributed to the induction of a current upon itself. Prof. Henry first observed the eflects here described, and has made an extended series of researches on this species of induction, as well as that mentioned in the next section. 176. Secondary Currents. If a long coil of fine insulate^ wire be brought within a small distance of the flat spiral, figured in the last section, a new species of induction will be detected in the coil of fine wire. The arrangement used by Prof. Henry is seen in the annexed figure. A small sus- taining battery (L) is connected with the flat spiral of copper ribbon, (A,) by wires from the battery cups, (Z and C.) This communication is broken at will, by drawing the end of one of the battery wires (Z) over the rasp on the spiral. When the coil of fine wire (W) is in the position indicated What does the long conductor imitate ? How is the magnetic needle affected by the flat spiral ? How are the two effects of shock and spark related to the length of the conductor ? To what are these effects attributable ? 176. What are secondary currents ? Explain the arrangement here figured, and the effects. ELECTRO-MAGNETISM. 125 in the figure, and the hands grasp the conductors at the ex- tremities, a violent shock is felt by the person holding the conductors, as often as the circuit is broken by the passage of the wire over the rasp. When the coil (W) contains several thousand feet of wire, the shocks are too intense to be borne. As this induction takes place through an inter- vening space of air, or non-conductors, we can, by placing the spiral (A) against a division- wall or the door of a room, give shocks to a person in another room, who grasps the conductors of the wire coil, (W,) arid brings it near to the wall on the side opposite to A. This effect is produced as if by magic, without a visible cause. A screen or disc of metal introduced between the two coils will cut off this inductive influence, by itself becoming the medium of an in- creased current. But if it be slit by a cut from the centre to the circumference, as a b in the figure, the induction of an intense current in W is the same as if no screen were present. Discs or screens of wood, glass, paper, or other non-conductors, offer no im- pediment to this induction. 177. Induced currents of the third, fourth, and fifth order. If the wires from W be connected with another flat spiral, and it with a second coil of fine wire, and so on, a series of currents will be induced in each alternation of coils. The secondary intense current in B, will induce a quantity current in the second flat spiral, (C ;) and a second fine wire coil (W) will induce a tertiary intense current, and so on. These currents have been earned to the ninth order, de- creasing each time in energy by every removal from the When is the shock felt by the person holding the ends of the fine wire ? What magical modification of the experiment is mentioned ? How do screens of metal affect the induction ? How, if they are slit ? How, if of non-conducting substances ? 126 ELECTRICITY. original battery current. The polarity, or direction of these secondary currents, alternates, commencing with the sec- ondary. Thus the current ot the battery is -f ; and the .secondary current is -f ; the current of the third order is ; the current of the fourth order is -}- ; and the current of the fifth order is . These alternations are marked in the figure above. 173. Compound Electro-magnetic Machine. Hy com- bining and modifying the results just briefly enumerated, a great numljcr of ingenious and beautiful electro-magnetic machines have been produced, founded on the principle of the flat spiral, secondary intense currents, nnd induced magnetism. One of these, contrived by r Or. Page, is figured in the margin. In this little machine, a short coil of stout in- sulated copper \\ire forms a helix, within which some straight soft iron wires (M) are placed. The bat- tery current is made to pass through this stout wire, by which 'means magnetism is induced (1C9) in the soft iron. The conducting wires are so arranged beneath the board, that the glass cup (C) containing some mercury is in connection with the battery. Tho bent wire (W) dips into this mercury, and also by a branch into B, and when in the position shown in 177. Explain the induced currents of the third, fourth, and fifth order, and their several polarities. 178. How are the principles of 175 and 176 combined in the instruments here figured ? Where ia the magnetism ? ELECTRO-MAGNETISM. 127 the figure, the current from the battery will flow uninter- ruptedly. As soon, however, as the battery connection is completed, M becomes strongly magnetic, and draws to itself a small ball of iron on the end of P; this moves the whole wire (P W) and raises the point out of the mercury, (C;) as the wire leaves the mercury, a brilliant spark is seen on its surface, (176;) the contact being thus broken with the bat- tery, M ceases to receive induced magnetism, and the ball (P) being consequently no longer attracted to M, the wire (VV) falls by its gravity to the position in the figure. This again establishes the battery connection, and the same effects just described recur; thus the bent wire (W) receives a vibratory motion, and at each vibration a brilliant spark is seen at C, and M becomes magnetic. It remains only to mention that the short quantity wire is surrounded by a fine intensity wire, 2000 to 3000 feet long, having no metallic connection with the battery or quantity wire, with its ends terminating in two binding screws on the left of the board. The fine wire receives a secondary induced current like the coil, (W, 176,) which, if touched, produces the most intense shocks at each vibration of the wire. 179. The filectro-inagnctic telegraph is a contrivance which very happily illustrates the application of abstract scientific principles and discovery to the wants of society. The inconceivably rapid passage of an electrical current over a metallic conductor, was discovered by Watson in 1747, and this discovery gave the first hint of the possibility of using electricity as a means of telegraphic communication. Numerous attempts were made very early after this discovery to construct a telegraph to be worked by ordinary electricity, but from difficulties inherent in the mode, these attempts were attended with only very partial success. The discovery of electro-magnetism by Oersted, in 1820, (166) supplied the necessary means of successful construction. Many plans have since been proposed for accomplishing this object, most of which have failed from a want of simplicity in construction and notation, and from consequent inefficiency. Superior to all others in these essential conditions of success, is the beau- tiful contrivance patented by Prof. Morse in 1837, which we will now briefly describe. When is the spark, and when the shocks 1 179. What suggested the electrical telegraph ? What discovery gave the means of success ? 128 ELECTRICITY. The successful operation of the electric telegraph depends on the fact, that an electro- magnet can be created ut any point, no matter how distant from us, provided a good metallic communication is established by conducting wires between the battery and the distant station. There is no difficulty in understanding how the power of the battery on our table may, by long wires, be made to move any electro-magnetic ma- chine on the other side of the room, or in an adjoining apart- ment. We have only to extend this idea to places distant from each other, 100, or 1000, or 10,000 miles, and we have a conception of the magnetic telegraph. The machinery required is of the simplest kind. In the accompanying figure we have a view of its most essential parts. It is called the telegraphic register. A simple electro-magnet, (m m,) with its poles upward, receives its induced magnetism (171) from n current of electricity conducted by the wires (W W) from the distant station. Suppose that the battery which excites this current is in Washington, and the electro-magnet is in Boston. As soon as the circuit is completed by the union of the poles in Washington, m m becomes a magnet, and draws to its poles an armature or bar of soft iron (a) on the lever, (/.) The motion of this lever starts a spring which sets in motion the clock arrangement, (c.) This clock machinery, in con- sequence of the weight attached to it, will, when once set in On what does the operation of the telegraph depend ? Explain the apparatus as here figured. ELECTRO-MAGNETISM. 129 motion, continue to move. As soon as it begins to move, the bell (6) is rung by the machinery, to warn the superintendent that he is about to receive a communication. The immediate object of the clock machinery is to draw forward a narrow ribbon of paper, (p p,) in the direction of the arrows, and to cause it to advance with a regular motion. The paper ribbon passes by the end of the pen lever, (/,) in which is a steel point, (s,) that indents the paper whenever this end of the lever is thrown upwards by the attraction of the armature (a) to the magnet, (m.) If m m were constantly magnetized, the mark made by the point (a) would be a continuous line. Hut we have before seen that we can make and discharge an electro-magnet as often and as fast as we please ; the instant, therefore, the circuit (w tr) is broken by the operator at the battery in Washington, m m erases to be a magnet, and lots go the iron armature, (a,) when the point (s) of the lever falls, so as no longer to mark the paper. The circuit being renewed, the point marks again ; and this may be repeated as often as the operator at Washington pleases. The length of time that the circuit is closed, will be exactly registered in the corresponding length of the mark made by 5. The com- pleting of the circuit is performed by touching a spring on the operator's table, which establishes a metallic communi- cation between the poles of the battery. A touch will pro- duce a dot, a continued pressure a long line, and intermitting repeated touches a series of dots and short lines. This enables the operator to mark the paper at Boston with :i series of dots and lines, so arranged as to form a telegraphic alphabet, by means of which he can easily and rapidly com- municate his thoughts. To complete the arrangement, the operator in Boston must have his own battery in connection with another similar register in Washington. In practice only one wire is used with each register, the circuit being completed by connecting the other pole of the battery with the moist earth by means of a buried metallic plate and a wire. The remarkable observation that the earth could be used in this manner as a part of the circuit, was made by Steinheil, in Germany, in 1837. Such is a brief account of one of the most remarkable discoveries of modern times; What is the object of the clock-work ? How does the point mark the paper ? What relation is there between the length of the marks and the battery circuit ? How are the conducting wires arranged ? 130 ELECTRICITY. many particulars arc purposely omitted, to avoid confusion in the main idea. The paper ribbon (p) is supplied from a large coil not shown in the figure. This telegraph makes a permanent record of the communication sent, and is thus independent of the presence or attention of the attendant. If it were possible to unite the antipodes by telegraphic wires, no measurable time would be required to make communi- cations, such is the inconceivable rapidity of electrical currents. One curious fact connected with the operation of the tele- graph, is the induction of atmospheric electricity upon the wires to such an extent, as often to cause the machines at the several stations to record the approach of a thunder-storm. This induction occasions a serious inconvenience in working the telegraph, not unattended with danger to the operators. The electricity thus induced on the wires may, howevejf, be withdrawn by points of metal in communication with the earth, and placed at a suitable distance from the conductor. 180. Magneto- Electricity. As we have seen effects pro- duced from galvanism, which exactly resemble those of ordi- nary machine electricity, and the magnetic influence, so, conversely, we might expect the production of electrical effects from the magnet. The electrical current from a single galvanic pair, we have seen, produces magnetism in a spiral wire at right angles with its own course ; so the induction of magnetism in soft iron from a permanent mairnet, in like What is said of the atmospheric electricity ? 180. What is mag- neto-electricity ? THERMO-ELECTRICITY. 131 manner, produces an electrical current at right angles to itself in the wire coiled on the armature. This class of phenomena was discovered by Faraday in 1831, and our countryman, Mr. J. Saxton, soon contrived a machine very similar to the ono of which a figure is here given, called a Magneto-electrical Machine. This consists of a powerful magnet, (S,) secured to a board, with its poles so situated that an armature, formed of two large bundles of insulated copper wire, (W,) wound on soft iron axes, may be revolved on an axis before its '" |K)les, by the multiplying wheel, (M.) A current of electricity is thus induced in VV, just as in the flat coils, the permanent magnet here taking the place of the flat spiral, (176.) The current excited in VV is led off by conductors to the binding screws, (p and n,) the continuity of the current being broken (in imitation of the rasp in 176) by a contrivance at b on the axis, called a break-piece, which is made / ' by alternate ribs of metal (c) and ivory (i) as in *~ the annexed figure ; the current is broken by the ivory and renewed by the metal, and at every break the per- son whose hands grasp the conductors secured to p and n feels a sharp shock, which may be graduated at will by the rapidity of the revolutions of M, and by the adjustment of the break, (b.) A long and fine wire say 3000 feet of wire fa of an inch in diameter is required to produce shocks and chemical decompositions. A shorter and stouter wire, as 250 feet of wire fa or fa inch in diameter, will produce no shock, but will deflagrate the metals powerfully, and produce a secondary current of induction in soft iron. We thus imitate in magnetism the effects produced from a voltaic current, (163 ;) the short and stout wire of the armature is the simple circuit of large plates ; the long and fine wire is like the com- pound circuit of smaller plates. 4. Thermo-Electricity, or the Electrical current excited by Heat. 181. If two metals unlike in crystalline structure and conducting power are united by solder, and the point of their union is heated or cooled, an electrical current will be ex- Who discovered this class of phenomena, and when ? What is magneto-electricity the converse of? Explain Saxton's machine. Explain the relations of the quantity and intensity wire to the simi- lar effects of the voltaic battery. 132 ELECTRICITY. cited, which will flow from the heated point to the metal which is the poorer conductor. Bismuth and antimony are such metals, being bad conduc- tors, and unlike in. crystalline structure. If two bars of these metals arc united, as in the figure, and the point (c) is warmed by a lamp, a current will be set in motion which will flon from b to , as in the figure. The compus: needle may be thus affected, as by the vol. air current, (166.) For this purpose two bars may be merited MS in the figure, and their j'.nction being heated by a lamp, the needle will swing, in eonseqiir.icc of the electrical current oxci'ed by the heat. When several such are joined, we have a greatly in." /eased effect, as will be remcmbcrc'd in the thermo- electric pile in Melloni's apparatus, (1C4.) Thermo-electric effects are not confined to metals, for they may bo produced from other solids, and even from fluids ; and a single metal, as an iron wire, which has been twisted or bent abruptly, will originate a thermo-electric current when the distorted part is greatly heated. The rank of the principal metals in the thermo-electric series is as follows, beginning with the positive: bismuth, mercury, platinum, tin, lead, gold, silver, '/inc, iron, antimony. When the junction of any pair of these is heated, the current passes from that which is highest to that which is lowest in the list, the ex- tremes affording the most powerful combination. If we pass a feeble current of electricity through a pair of antimony and bismuth, the temperature of the system rises, if the current passes from the former to the latter ; but if from the bismuth to the antimony, cold is produced in the compound bar. If the reduction of temperature is slightly aided artificially, water contained in a cavity in one of the bars may be frozen. Thus we see that as change of tempe- rature disturbs the electrical equilibrium, so conversely the disturbance of the latter produces the former. 181. What is thermo-electricity 7 In what substances is it ex- cited ? What metals are here named ? Which way does the current flow ? Are these effects confined to metals ? Are two metals essential ? Enumerate the order of some metals producing thermo- electric effects. What experiment is stated the converse of the foregoing ? CHEMICAL PHILOSOPHY. 133 PART II. CHEMICAL PHILOSOPHY. I. ELEMENTS AND THEIR LAWS OF COMBINATION. 182. Number and Classification of Elements. We have already defined the chemical sense of the word Element, (14,) and mentioned that there are fifty-six such substances at present known to us. There are also several other sub- stances which have been lately proposed as elements of the metallic class, about which, however, we know so little, that they are not included in our list, (188.) About forty of the elements have the peculiar lustre, and other properties of metals, and it is customary to divide the elements into two great classes the metallic and the non-metallic. This con- venient distinction is not, however, strictly accurate, since there are several elements which, like tellurium, carbon, arsenic, silicon, &c., seem to possess an intermediate character. Only fourteen of the elementary bodies are of common occurrence, and of these the atmosphere, water, and the great bulk of the planet are composed. The remainder are comparatively rare, and are known only to the chemist. But the same laws of combination apply to the whole, and we shall best accomplish our present object by discussing the first principles of chemical philosophy, and illustrating them by a selection of facts, rather than by attempting the task of giving too much detail. 183. State in which the elements exist. At common temperatures, and when set free from combination, nearly all the elements are solids. Two, mercury and bromine, are fluids, and five are gases, namely, chlorine, fluorine, hydrogen, oxygen, and nitrogen. A few only of the elements are naturally found in a free or uncombined state, among which we may name oxygen, nitrogen, carbon, sulphur, and nine or ten metals. All the rest exist in combination with each other, and so completely concealed or disguised as to be known only to the chemist. 182. How many elements do we know ? How are these usually divided ? How many are found as principal constituents of the globe? 183. In what state do the elements exist? Which are fluids ? Which are gases ? Which are free or uncombined ? In what state are the others ? 12 134- ELEMENTS AND THEIR LAWS OF COMBINATION. 1. Combination by Weight. 184. The laws by which the elements unite to form com- pounds, arc included in the four following propositions. 1st LAW. A compound of two or more elements is always formed by the union of certain definite and unalterable pro- portions of its constituent elements. This is the law of definite proportions. 2d LAW. When two bodies unite in more proportions than one, these proportions bear some simple relation to each other. This is the law of multiple proportions. 3d LAW. When a body (A) unites with other bodies, (B, c, D, &c.,) the proportions in which H, c, and D, unite with A, will represent in numbers the proportions in which they will unito among themselves, in case such union takes place. This is the law of equivalent proportions. 4th LAW; The combining proportion of a compound body is the sum of the combining weights of its several elements. This is the law of the combining numbers of compounds. These four laws are the foundation of all chemical science, and should receive the attention which their great importance demands. We will briefly illustrate their meaning, which will be done, however, more effectually by the constant use we shall have to make of them, on almost every succeeding page of this treatise. 185. Definite Proportions. Analysis shows us that a given compound is always formed of certain elements in defi- nite proportions, and that no change can take place in the number or proportion of its constituent elements, without destroying its peculiar character, and forming a new sub- stance. Thus, in nine grains of water there are eight grains of oxygen and one grain of hydrogen. Any attempt to form water from any other proportion of its elements would be useless. Constancy of composition is essential to the being of chemical compounds. 186. Multiple Proportions. If a body (A) unites with a body (B) in more proportions than one, thus producing more 18 1. State the first law of combination. What is this law called ? What is the second law? What is this law called? What is the third law, and what called ? The fourth, and what called ? What is said of these laws ? 185. What has analysis shown ? Illustrate this? COMBINATION BY WEIGHT. 135 than one compound of the two elements, these proportions bear a simple relation to each other. (1.) We may have a series of compounds represented by A-j-B : A-f 2B : A-J-3B : A + 4B : A + 5B : in which one, two, three, four, and live parts by weight of B, unite with one part of A, forming five separate and distinct compounds. Several examples of this law will be found in the following pages. (2.) In place of the simple ratio of numbers here explained, we may have another series of compound bodies, whose elements bear to each other an intermediate ratio. Thus the expressions, 2A-f3B : 2A + 5B : 2A + 7B : represent a scries of com- pounds, of which our .future studies will afford us several cases. ^ 187. Equivalent -Proportions. This jpayoe considered as the most important law in chernic*tphilosoph*y, and its discovery and application have been the great cause of the rapid advance of modern chemistry. Chemical analysis has shown that the body, oxygen, can form one definite com- pound, or more than one, with every other clement yet dis- covered, except perhaps fluorine. The compounds of oxy- gen with the elements being perfectly definite, (18.3,) can all be expressed in numbers, which numbers will truly ex- press the combining weights of the several bodies. For the sake of illustration, let us assume that it requires eight parts by weight of oxygen to unite with each of the other elements, and that these eight parts require various weights of the several elements. We can then make a table which shall correctly express these numerical relations. 6 parts of carbon. Thus, 8 parts of oxygen unite with- 1 part of hydrogen. 35-41 parts of chlorine. 108-12 of silver. 27-14 of iron. 101-27 of mercury. 16-09 of sulphur. And we might go on thus through the whole list of ele- mentary substances, analyzing their several compounds with oxygen, and setting down the combining numbers of each in one table. The few examples given above are, however, . 186. Illustrate the law of multiple proportions. 187. Illustrate the law of equivalent proportions. What is said of oxygen ? What is assumed for illustration ? How do other bodies stand related to oxygen ? How has this been determined ? 136 ELEMENTS AND THEIR LAWS OF COMBINATION. sufficient for our purpose. Oxygen is selected as the term of comparison for the other bodies, because it almost uni- versally unites with the several other elements. The number 8 is attached to it, because hydrogen, which is made the unit in our books, enters into combination in a smaller proportion than any other body. We might with equal propriety make oxygen unity, when hydrogen would be expressed by a fractional number. But taking oxygen as fl, all the other numbers expressing the combining weight of each element have been determined with great care, by often repeated analyses. Let it be understood, then, that if any of the Ixxlies in the table should form compounds with each other, the weights in which they will unite will be in the exact pro- portion of the numbers severally affixed to them. Thus, if hydrogen unites with chlorine to form a new compound, (hydro-chloric acid,) it will require one part of hydrogen to 85*41 parts of chlorine to form such compound. One pound of hydrogen will unite to 85*41 pounds of chlorine, and will form 36-41 pounds of the compound. Any excess or de- ficiency of either of the dements will make no difference with the result, and the above law will in all cases be found strictly true. If sulphur and mercury unite to form a third body, it will be only in the proportion of the numbers 16-09 and 101-J6; and if sulphur unite with iron, it will be as 16-09 : 27-14. We see then that the several numbers arc truly the equivalents of each other, as they are all the equivalent of oxygen, and are, therefore, most appropriately called cquiva lent proportions, or equivalent numbers. 188. Table of Chemical Equivalents. In the following table, the equivalent or combining numbers of all the ele- mentary bodies are given in accordance with the latest and best authorities. Two columns of combining proportions are given; in the first, hydrogen, and in the second, oxygen, is used as the unit of comparison. Because hydrogen enters into combination with other bodies in a smaller weight than any other known element, it has generally been used in Great Britain and in this country as the basis of the scale of Illustrate this in the case of hydro-chloric acid. If there is an excess or deficiency of either element, what then? What term is most appropriate to express this ? 188. What does the table show us ? What is said of the hydrogen scale, and why has it been used ? COMBINATION BY WEIGHT. 137 equivalent numbers. It was also believed, and is still, by some good chemists, that the numbers expressing the com- bining weights of all bodies would be found, on more accurate research, to be simple multiples of the unit of hydrogen. If this view were correct, it would give us the great convenience of avoiding fractional numbers. But the most rigid experi- ments have failed to prove this idea to be true, and as it has no necessary foundation in the nature of things, we are not at liberty to adopt it. Berzelius, and most European chemists, assume oxygen as 100; and the second column of figures in the table gives the equivalents according to this scale. TABLE OF ELEMENTARY SUBSTANCES, WITH THEIR EQUIVALENTS AND SYMBOLS. H=l, H=l, Sym- or Sym- or bol.* Oxv.=SOxy.= 100 bol. Oxy.=8 Oxy.=100 Aluminium, Al 1369i 171.17 Manganese, Mn 2767 34589 Antimony, Sb(l) 129 04 161290 Mercury, Hg(6) 101-26 126,582 Arsenic, A a 7521 94008 Molybdenum, Mo 47-88 598.52 Barium, Ba 6855 Nickel, Ni 2959 36968 Bismuth, Bi 7095 886 97 Nitrogen, N 1406 175.75 Boron, B 1090 136-20 Osmium, Os 99-56 124449 Bromine, Br 7826 97831 Oxygen, O 8- 100 Cadmium, Cd 5.574 69677 Palladium, Pd 5327 66.590 Calcium, Ca 20 2.50 Phosphorus, P 3138 39228 Carbon, C 6 75- Platinum, PI 9868 123350 Cerium, Ce 4503 574.70 Potassium, K(7) 3919 48992 Chlorine, CI 3541 44265 Rhodium, R 52 11 65139 Chromium, Cr 2814 351-82 .Selenium, Se 3957 494-58 Cobalt, Co 2952 36899 Silicon, Si 22 18 27731 Columbium. Cm 18459 230743 Silver, Ag(8) 108-12 135161 Copper, Didymium, Cu(2) Di 3165 39570 Sodium Strontium, N.,0, 2327 4:<-78 29090 54729 Fluorine, F 18-70 233-80 Sulphur, s 1609 201.17 Glucinurn, O 2650 &31 26 Tellurium, Te 64.14 80176 Gold, Au(3) 99.44 1243 Thorium, Th 5959 74490 Hydrogen, H 1 1-25 Tin, Sn(10) 5882 73.5 29 Iodine, I 12636 157950 Titanium, Ti 2429 30369 Iridium, Ir 9868 123350 Tungsten, W(ll) 9464 1183 Iron, Fe(4) 2714 33921 Vanadium, V 6855 85689 Lantnnum. Ln Uranium, U 60 750- Lead, Pb(5) 10356 129450 Yttrium, Y 3220 402.51 Lithium, L 643 80 33 Zinc, Zn 3300 41250 Mapnesium, Mp 12-67 158-35 Zirconium, Zr 3362 42020 * In the symbols, the Latin names of the elements are employed. Eleven of these are not in common use, viz : (1.) Stibium, (2.) Cu- prum, (3.) Aurum, (4.) Ferrum, (5.) Plumbum, (6.) Hydrargyrum, (7.) Kalium, (8.) Argentum, (9.) Natrium, (10.) Stannum, (11.) Wolframium, (from the mineral, Wolfram.) Columbium is fre- quently represented by the symbol Ta, from Tantalum, a name by which the European chemists distinguish this metal. 12* 138 CLEMENTS AND THEIR LAWS OF COMBINATION. It is obvious that the numlicrs of the oxygon scale are just twelve and a half times as largo as those in the hydrogen scale; consequently, dividing the oxygen equivalents by 12*5 will give the hydrogen numbers, and multiplying the latter by the same sum will give us the oxygen numbers. 189. Combining Numbers of Compounds. It has been stated that the equivalent or combining proportion of a com- pound body is always the sum of the combining equivalents of its elements. Strict experiment has established this im- portant law, which will receive constant illustration as we go on ; at present, however, we must accept it as truth, and not anticipate, by attempting to give examples which cannot be well understood until we have become somewhat familiar with chemical language, symbolic illustration, and the laws ofaffinitv. / J. Combination by Volume. 190. (raseous bodies, whether elementary or compound, combine not only in accordance with the laws just explained, but also according to a peculiar law of their own, whereby certain volumes of each are required. The volumes in which gaseous bodies unite, are either 1 to 1 , or 1 to 2, or 1 to 3, &c. Thus water is formed of 2 volumes or measures of hydrogen, and 1 volume of oxygen. In combining, these three volumes are condensed into two. If we take oxygen, hydrogen, chlorine, and nitrogen, in the proportions by weight in which they combine, or measure the volumes t^ey occupy as gases, a very obvious relation will be observed between them ; the volume of oxygen being exactly one half that of each of the others. Thus, 8 grains of oxygen occupy 23-3 cubic inches. 1 grain of hydrogen, 46-7 35-41 grains of chlorine, 46-2 14-06 grains of nitrogen, 46-5 ' How is one scale translated into the other ? [Note. If the learner can commit the table to memory with the hydrogen equivalents and symbols, it will be of great service to him hereafter.] 189. What is said of combining numbers of compounds? 190. How else than by weight do the gases combine ? Illustrate this. What relation is seen between the equivalent weights and volumes of bodies ? Name some examples. COMBINATION BY VOLUMP. 139 The same is true of compound gases, and also all bodies which can be raised in vapor, as sulphur, iodine, and mercury. Solids, which combine with gases, arc subject to the same law. Sulphur has -j- the volume of oxygen, and mercury 4 times. 191. We can state this truth in another form. If we call the weight of a volume of oxygen 1000, then an equal volume of hydrogen will weigh 0-06*25, and these numbers will represent the relative specific gravity of the gases. But in water, two volumes of hydrogen unite with one of oxygen, and we must, therefore, double the above hydrogen number, 2 X -0626 = 0-125. Now these numbers, 1000 and 0-125, are exactly the equivalent numbers on the oxygen scale, 100- and 12-5, or making hydrogen unity, then we have 100-0-i- 12-5 = 8 ox., and 0-125-M2-5=1 hyd. This re- lation between the specific gravity of gaseous bodies and their combining number, or chemical equivalents, is uni- versally true, and we might give a long table including these relations ; but the following examples will answer : Gases and vapors. Specific Gravities. Chemical I quivalents. By weight. Air =1. Hydrogen=l. By volume. Hydrogen, Nitrogen, Oxygen, Chlorine, Iodine vapor, Bromine vapor, Mercury vapor, Sulphur vapor, 0-069 1 1- 0-972 14-03 1-111 16- 2-470 35-64 8-701 126-30 5-393 78- 6-969 101. 6-648 j 96-54 100 or 1 100 or 1 50 or J- 100 or 1 100 or 1 100 or 1 200 or 2 16-66 or 1- 14-06 8- 35-41 126-36 78-26 101-27 16-09 When the numbers ki the second column are the same as the equivalents, (or with only a fractional difference,) then a volume represents an equivalent. The other numbers are multiples of the equivalent. Thus, 2x8= 16, the number for the density of oxygen, and sulphur 16x6 = 96, the density of sulphur vapor. 192. Conclusions. (1.) If we know the proportions by volume in which two gases combine, and also their specific What of compound gases and solids ? 191. State this truth in another form. Is this relation of density and combining numbers general? Name some of the examples in the table. 192. What conclusions are drawn from the previous statements? 1st? 2d ? 3d? 4th? 140 ELEMENTS AND THEIR LAWS OF COMBINATION. gravities, we can calculate the composition of the compound by weight. (2.) Or we can foretell the density of a com- pound by knowing the volumes and specific gravities of its elements. (3.) If we know the volume and specific gravity of one of the two elements of a compound, and of the com- pound itself, we can then calculate its composition by weight. (4.) If we know the specific gravity and composition of a compound by weight, we can then calculate its composition by volume. Many examples will be found in elementary chemistry of the practical application of these rules. 3. Chemical Nomenclature and Symbols. 193. Names of the Elements. Some of the elementary bodies have been known from the remotest antiquity, and were in common use long before the science of chemistry was heard of. Thus several metals, as Copper, (Cuprum,) Gold, (Aurvm,) Iron, (Fcrrum,) Mercury, (Hydrargyrum,) Silver, ( Argentum,) IxMid, (Plumbum,) Tin, (Stannum,) have long been known either by the names we now give them, or by those Latin terms of which our Knglish names are translations. No descriptive meaning is conveyed by such terms as these, nor by such as Sulphur and Carbon. The alchemists named the metals after the various planets. Thus, Gold was called Sol, the Sun ; Silver, Luna, the Moon ; Iron, Mars ; Lead, Saturn ; Tin, Jupiter ; Quick- silver, Mercury ; and Copper, Venus. Hence formerly the astronomical signs or symbols of these planets were em- ployed by alchemists and mineralogists to represent the names of these metals, and they are still in use in some countries. Several of the elements have been named from some prominent or distinguishing physical property of color, taste, or smell, which they possess : thus Bromine is so called from the Greek word bromos, fetor ; Chlorine, from chloros, green, in allusion to its greenish color ; Chromium, from chroma, color, because it makes highly colored compounds, as chrome-yellow ; Glucinum, from glukus, sweet, from the sweet taste of its salts ; Iodine, from ton, a violet, and eidos, 193. Whence have some of the elements, as copper, &c., received their names =' What did the alchemists call the metals? On what other principles have some been named ? Give instances. CHEMICAL NOMENCLATURE AND SYMBOLS. 141 in the likeness of; and so for many others. Another class of names has been contrived from what was supposed to be the characteristic attribute of the body in combination. Thus, Oxygen was so named because many of its compounds are acids, from the Greek, ojws, acid, and gennao, I produce. Hydrogen is from hudor, water, and gennao, I produce. We might thus go through the whole list, but fc is unnecessary, as we shall have again to give the etymology of these words when we speak of each element. 194. Names of Compounds. All chemical compounds derive their names from one or more of their constituents, according to certain fixed and simple rules, which we must very briefly explain. When two elements unite, the compound is called binary, from 6i?, twice ; thus water, sulphuric acid, oxyd of silver, and oxyd of iron, are binary compounds. Compounds of binary combinations with each other, as of sulphuric acid with soda, forming sulphate of soda, or Glauber's salts, (and the salts, generally so called,) are called ternary compounds, (from ter, thrice.) Com- pounds of salts with each other, (as in the case of alum, which is a compound of sulphate of potash and sulphate of alumina,) are named quaternary compounds, from quatuor, four. 195. All the compounds of oxygen with the other ele- ments are called cither oxyds or acids. Thus, water in chemical language is the oxyd of hydrogen ; the chemical name of potash is the oxyd of potassium. It has been be- fore stated, that oxygen forms compounds with all the other elements, (187.) Some of these compounds have what we commonly call acid* properties: thus, the compounds of oxygen and sulphur are called acids, and not oxyds. Oxyds are divided into two classes ; (a) neutral oxyds, like water ; 194. How are compounds named ? What are binary compounds ? What ternary? What quaternary? 195. What are the oxygen compounds called ? Give instances. How are oxyds described ? Notes. What are acids ? What alkalies ? What bases ? * Acids are known by their taste in some cases, and by their power of turning the vegetable blues to red; but more particularly by their power of uniting with and saturating alkalies and other bases. 142 ELEMENTS AND THEIR LAWS OF COMBINATION. (b) alkaline* oxyds and bases,f like potash, alumina. When the same element unites with oxygen in more than one pro- portion, (184, 2d,) forming two or more oxyds, then they are distinguished by the Greek prefix, proto, (protos, first,) applied to that body which has the least portion of oxygen, which is called the protojcyd ; deuto, (deuteros, second,) is prefixed to the next degree of oxidation, giving us the term dent ox yd ; trito, (tritos, third,) to the body containing still more oxygen than the deiitox yd. The oxyd which contains the largest dose of oxygen with which the body is known to unite, is also called the peroxyd, from the Latin, per, which is a par- ticle of intensity in that language. Thus there are two oxyds of hydrogen, the protoxyd (water) and the peroxyd ; there arc three oxyds of manganese; (1.) the protoxyd, (2.) the deutoxyd, (3.) the peroxyd of manganese. Some oxyds arc formed in the proportion of 2 to 3, or once and a half. Such oxyds are distinguished by the term se&quioxyds, from the numeral scsf/t/i, (once and a half.) Certain inferior oxyds are called xuboxydx. 190. The binary compounds of chlorine, and some other elements which resemble oxygen in their manner of combi- nation, and in their relations to electrical decomposition, are also distinguished in the same manner as oxygen. Thus, with the other elementary l>odtes : Chlorine forms Chlorids. Bromine " Rromids. Iodine " lodids. Fluorine " Fluorids. Oxygen " Oxyds. 197. The binary compounds of sulphur analogous to the oxyds are called sulphurets, and not sulphids. The prefix Explain the terms expressing different degrees of oxydation, and their use. l.tf, proto. 2salts is sometimes expressed by the Greek prefix di, twice; thus, the dichromatc of lead has twice as much of the l>ase lead as the chroma te of lead. 201. (3.) Quaternary Compounds. The double salts are named from their bases ; thus alum, which is formed of sul- phate of alumina and sulphate of potash, is called double sulphate of alumina and potash. The chlorid of potassium and platinum is another double salt, formed from the union of a chlorid of platinum and chlorid of potassium. 202. The chemical nomenclature, when once understood, enables us after a little use to form, in most cases, from the mere name of the compound substance, a correct idea of its 199. Sulphur acids and hydrogen acids arc how named ? 200. How are salts named ? Give examples. How are the species named ? What is a bi and scsqui sulphate ? What meaning has the prefix di ? 201. (3.) How are double salts named ? Give examples. * In strict uniformity to rule, the term chlorohydric is correct, but use has established the other. The same remark is true of bromo- hydric, fluohydric, and iodohydric acids. CHEMICAL NOMENCLATURE AND SYMBOLS. 145 composition, and of the proportions of its constituents. This great advantage is possessed by no other science, and cannot be too highly estimated. There are a good many compounds, however, that have been discovered of late years, for which this nomenclature provides no names. But we have certain written expressions, by means of which we can convey an idea of all chemical compounds with a mathematical precision and great convenience. 203. Chemical Symbols of the Elements. In the table of Elementary Bodies (188) the " symbols" of the several elements will be found opposite to their names. The sym- bols are merely the first letter of each name, or the first two, when more than one element begins with the same letter ; thus O stands for oxygen, and Os for Osmium ; P stands for Phosphorus ; PI for Platinum, and Pd for Palladium. The second letter in all such cases is small, a capital letter being uniformly used for the first. The Latin names are invariably used for the abbreviation, and for this reason there are eleven symbols, unlike the common names of the elements they represent. (See note to 188.) Prof. Berzelius contrived the system of symbols now in use, and by a happy thought he made each symbol represent not merely the substance for which it stands, but one equivalent of each substance. Thus O stands not for oxygen in general, but for one equivalent of that element; or, hydrogen being unity, for the number 8. O and 8 are therefore interchangeable expressions, while O 2 , O 3 , &c., represent 2x8 and 3x 8, or 16 and 24, according to the second law of chemical combination, (184.) Compounds are represented by using merely the symbols, and sometimes uniting them by the sign of addition, (4--) Thus water will be represented by HO or II -fO, which means one equivalent of each clement, 1 + 8 = 9, which is the combining number of water. Protoxyd of lead is thus written PbO, or Pb + O. 204. When more than one equivalent of an element is in combination, we then prefix a number expressing it, like an algebraic co-efficient, (as 5O,) or the number may be applied 202. What great advantage has the chemical nomenclature ? 203. What are chemical symbols ? Give examples. What names are abbreviated ? Whose contrivance are the symbols ? For what does the symbol stand? Illustrate. How are compounds repre- sented ? Give examples on the black-board. 13 146 ELEMENTS AND THEIR LAWS OF COMBINATION. above on the right, (as O\) or below on the right, (as O 5 ;) each of these expressions means five equivalents of oxygen. We can write nitric acid N5O, or NO 5 , or NO 3 , the latter being the usual mode; sometimes, but not often, the + or comma (,) is used between them, as N-f O s , or N,O 5 . Such expressions are called formula;; thus the formula for sulphuric acid is SO 3 , or S-fO 3 , from which we know that the combining number of sulphuric acid is 16-f^ 3 , or 16 + 24 = 40. When two compounds unite to form a new body, the sign -for(,) is used between them; thus, sul- phate of oxyd of iron is written FcO + SO 3 , or FeO,SO 3 . The small figures apply only to the letters to which they are attached ; larger figures used before the compound, apply to the whole formula ; thus, 3SO 3 means three equivalents of sulphuric acid ; but the sign + prevents the passage of this meaning beyond the sign. Thus 2FcO-fSO a means two equivalents of oxyd of iron and one of sulphuric acid ; in order to make the figures apply to both, we must write it 2(FcO + SO,,) cir 2(FeO,SO 3 .) In chemical symbols, the oxygon, or element most nearly resembling it, (i. c. the electro-negative element,) is placed last ; the base (or electro-positive element) being placed first. Thus we say SO 3 for dry sulphuric acid, and not O 3 S. A com- pound of sulphuric acid (SO 3 ) and water contains 2 equiva- lents of water, only one of which is however chemically combined as a base with the acid. We can make this apparent to the reader in constructing the formula thus, HO,SO 3 -f IIO; the comma signifies a closer union than the +, and the first equivalent of water is in intimate union with the acid, forming a sulphate of water, while the second portion is combined with this sulphate. Compounds which contain water, like common sulphuric acid, nitric acid, and many mineral bodies, are termed hydrous. 205. The symbols are sometimes abbreviated still further, to simplify the expression of very complex combinations. This is done by expressing one equivalent of oxygen by a 204. How is more than one equivalent expressed ? Show the different modes in which nitric acid is expressed ? How is the union of compounds expressed ? Tell the difference between the small and large figures. Which element is placed first in symbols ? Illustrate. How can we make the peculiar construction of hydrous sulphuric acid seen / What are hydrous bodies? CHEMICAL AFFINITY. 147 dot, two by two dots, &o. Thus S signifies the same as SO 3 , (dry sulphuric acid.) Common crystallized alum is written in full, thus, Al A,3S0 3 + KO,S0 3 + 24HO. We can conveniently condense this long expression ; thus AlS 3 -fKS + 24H. The short line under the Al signifies two equivalents of the base. Sometimes the double equivalent of base is denoted by a black letter, thus, Al, in place of the line beneath. In Berzelius's original symbols the short line is made through the type in the lower half. Sulphur is in like manner signi- fied by a comma ; thus, bisulphuret of iron, Fe,S 2 , may be more shortly written Fe. The constant use of these sym- bolic expressions in the elementary chemistry will soon familiarize the learner with their use and meaning. They have contributed very much to the progress of the science, and arc invaluable as a ready means of comparing as well as expressing the composition of compound bodies. 4. Chemical Affinity. 206. We have already explained (12 and 13) what is meant by chemical affinity, as the power which unites two or more unlike bodies to form a third substance, whose properties differ from those of its constituents. Chemical affinity, or the capability of union, is not possessed alike by all bodies. Oxygen, as before stated, is the only element capable of forming chemical compounds with all other ele- ments. Carbon can unite with oxygen, sulphur, hydrogen, and some other bodies, but no compound has been formed between it and gold, silver, fluorine, aluminium, iodine, bro- mine, &c. It is, therefore, said to have no affinity for these bodies, or no capability of union with them. The power of union among bodies, or affinity, is exceedingly different in degree, and is much affected by many circumstances. Thus 205. Illustrate on the black-board the abbreviation of symbols in the case of alum. How is sulphur in combination signified by symbols ? 206. What is chemical affinity ? Is it equal in all bodies ? Illustrate by examples. 148 ELEMENTS AND THEIR LAWS OF COMDIXATION. a body A may unite with a body B, forming a third body AB ; but if a body C had been present, A might have so much more affinity for C than it has for B, as to unite with it, forming AC, while B would remain unailectcd. For example, sulphuric acid and soda will unite to form Glau- ber's salts, or sulphate of soda ; but if soda and baryta had Ixjth been present, and sulphuric acid were added, only the sulphate of baryta (or heavy spar) would be formed, and the soda would remain disengaged, unless there was sulphuric acid enough to satisfy all the baryta and soda too. This is what is sometimes called elective affinity, as if the acid selected the baryta rather than the soda. 207. The more unlike, ns a general thins, any two txxhes arc in chemical properties, the stronger is their disposition to unite. The metals, as a class, have very little disposition to unite with each other, and when they do so it is not generally in chemical proportions. But they do unite with oxygen, chlorine, sulphur, &c., forming fixed and determinate com- (MHinds. The alkalies, j)otash and soda, form no proper compound with each other, and their alkaline properties arc not altered by sucli union. Sulphuric and nitric acid may be mingled in any proportion, but no new compound is formed, and the mixture is still acid. But if the (xjtash and soda IKJ put with the nitric and sulphuric acid, separately, and in their combining proportions, the result will be two compound Ixidies, having neither acid nor alkaline properties. If the nitric acid is added to its equivalent of potash, we shall have saltpetre, or nitrate of potassa, while the sulphuric acid in like manner will unite with its equivalent of soda, forming sulphate of soda, or Glauber's salts. 208. Solution is the result of a feeble affinity, but one in which the properties of the dissolved body arc unaltered ; thus, sugar is dissolved in all proportions in water or alcohol, and a drop of the solution may IKJ mingled in an ocean of water. Camphor is soluble in alcohol, in any proportion, but the addition of water to the solution will cause the cam- phor to be thrown down. Gum is soluble in water, but not in alcohol. We have already seen, that the solution of What is meant by "elective affinity" 207. What principal condition of affinity is named ? Illustrate this. 208. What is said of solution ? CHEMICAL AFFINITY. 149 various salts in water would produce cold (111) from the change of state in the hody dissolved. 200. The circumstances which modify the action of affinity are numerous, some of which we may briefly notice. We have said (16) that chemical affinity existed only among unlike particles, and at insensible distances. Intimate con- tact among particles is, therefore, in the highest degree necessary to promote chemical union. Any circumstance which favors such contact will increase the activity of, or disposition to, chemical combination. Solution brings par- ticles near together, and leaves them free to move among each other ; substances in a state of solution have, therefore, an opportunity to unite, which they do not possess when solid. Hence the old maxim, " Corpora non agunt nisi sint soluta." Carbonate of soda and tartaric acidj for example, both in a dry state, will never unite ; but the addition of water will at once, by dissolving them, bring about a union. Heat will often cause union to take place, being, in fact, a most powerful means of solution. Sand or silica will not unite with soda or potash by contact or aqueous solution, but if the mixture in proper proportions is strongly heated, union takes place and glass is formed. Sulphur will not unite with cold iron, but if the iron be heated to redness, or the sulphur melted, a vigorous union takes place, and a sulphuret of iron results. Cohesion (10) is strongly opposed to chemical union, or affinity, and any means which will overcome it will promote the union of the elements. Solution and heat both act by overcoming cohesion ; and the fine mechanical division of a body, or pulverization, does the same. 210. Bodies in the nascent* state (as it Js called) will often unite, when under ordinary circumstances no affinity is seen between them. Thus hydrogen and nitrogen gases, under ordinary circumstances, do not unite if mingled in the same vessel ; but when these two gases are set free at the same time, from the decomposition of some organic matter, 209. What circumstances modify or are essential to affinity ? How does solution favor it ? Illustrate. How does heat favor it ? Illus- trate. How does cohesion affect it ? What counteracts cohesion ? 210. What of bodies in the nascent state ? Illustrate this. * From nascens, being born, or in the moment of formation. 13* 150 I:LI:.MI:NTS AND THEIR LAWS OF COMBINATION. they readily unite, forming ammonia. The same is true of carbon under the same circumstances, which will then unite in a great variety of proportions with hydrogen and nitrogen, although no such union can l>c ('fleeted among these bodies separately. 1*11. The quantity of matter, as well as the order and condition in which substances may be presented to each other, often exerts an important influence on the power of affinity. Thus vapor of water, when passed through a gun- barrel heated to redness, will be decomposed, the oxygen uniting with the iron, while the hydrogen escapes at the other end of the tube. On the contrary, if hydrogen gas is passed over oxyd of iron in a tube heated to redness, the oxygen of the ox yd unites with the hydrogen, leaving metallic iron, while steam (formed from the union of the hydrogen with the oxygen from the iron) issues from the open end of the tube. Numerous examples of this sort might be given, where the play of affinities seems to be determined by the prcjKUidcrancc of one sort of matter over another, or by the peculiar con- dition of the resulting compounds, as regards insolubility, or the power of vapori/ation. 212. The presence of a third body often causes a union, or the exertion of the* force of affinity, when this third body takes no part in the changes which happen. Thus, oxygen and hydrogen gases may he mingled without any combination taking place between them, although a strong affinity exists. If, however, a portion of platinum in a state of very fine division (spongy platinum) be introduced into the mixture, union takes place, sometimes slowly, but more often with an explosion, the platinum being at the same time heated to redness from ihe rapid union of the gases which takes place in its pores. Advantage is taken of this fact in constructing the common instrument for lighting tapers by a stream of hydrogen falling on spongy platinum. No change is suffered in this case by the platinum, which seems to act by its presence only. Berzclius has proposed the term catalysis, from the Greek kata, bv, and luo, to loosen, to express the peculiar power which some bodies possess of aiding chemical changes by their presence merely. We shall have occasion 211. What of quantity of matter ? Give an example. 212. What is meant by the influence of presence ? Illustrate this. What other term expresses these cases ? ATOMIC THEORY. 151 to refer to this subject again. The case of the platinum is much more intelligible than many other instances of con- tact-union and decomposition of which chemistry offers ex- amples, since it appears to act by its power of condensation, to bring the particles within combining distance. 5. Atomic Theory. 213. We have already (7 and 8) said something of atoms as being the smallest conceivable state in which matter exists. As all ponderable matter is assumed to be formed by an aggregation of a series of these atoms, the interesting question at once arises, do the chemical equivalents or combining weights of the several elements express the relative weights of their atoms? Dr. Dalton first proposed the view now universally accepted, which assumes this to be the fact. All that has been said in this chapter on the combining weights of bodies, &c., has been the result of rigorous chemical in- vestigation, and is capable of demonstrable proof. Dallon's hypothesis of the relative weights of ultimate atoms is only theoretical, but has been found to conform in a remarkable degree to the results of experience. We may feel some good degree of certainty in the belief that we know the actual re- lation of weight between the ultimate atoms or molecules of the elements. There is no doubt that tho atom of sulphur is two times heavier than that of oxygen ; but we know nothing of their actual weight. 214. We can now, perhaps, better understand why the equivalent numbers of bodies should always be multiples of each other. If the atom of oxygen be represented by eight, (and we cannot conceive of an atom as being divided,) then any compound containing more than one atom of oxygen, must have twice, thrice, or four times eight, and so on. On this view of atoms, all the four great laws of chemical com- bination (184) receive a remarkable corroboration, as a little reflection will show. The atomic weight of a body is there- fore as correct an expression as its equivalent weight, or combining proportion. We might easily illustrate this theory to the senses in a gross way, by a series of spheres so marked as to represent the several atoms of elementary 213. What is the atomic theory? 214. What help does it give in understanding chemical facts ? 152 CRYSTALLIZATION. bodies, the union of which would show the compound re- sulting from the union of atoms. 6. Specif c Heat of Atoms. 215. Specific heat has already been explained, (106.) If in place of comparing equal weights of different bodies together, we take them in atomic proportions, we shall find tin- numbers representing the sj>ecific heat of lead, tin, zinc, enpper, nickel, iron, platinum, sulphur, and mercury, to l>e identical ; while tellurium, arsenic, silver, and gold, although equal to each other, will be twice that of the nine previous Ixxlies, and iodine and phosphorus will be lour times as much. Tin; general conclusion drawn from these and other similar facts is, that the atoms of all simple substances have the same capacity for heat. The specific heat of a Ixuly would thus aflord the means of fixing its atomic weight. There can b<; no doubt of the truth of this in numerous cases, but experiments arc still wanting to show it to be universally true. Compound atoms have in some cases been shown to have the same relations to heat as the simple. This is true of many of the carbonates, and some sulphates. A more minute discussion of the atomic theory would be out of place in this work. II. CRYSTALLIZATION. 1. Nature of Crystallization and Primary Forms of Crystals. 216. Nature of Crystallization. The forms of living nature, both animal and vegetable, are determined by the laws of vitality, and are generally bounded by curved lines and surfaces. Inorganic or lifeless matter is fashioned by a different law. Geometrical forms, bounded by straight lines and plane surfaces, take the place in the mineral kingdom which the more complex results of the vital force occupy in the animal and vegetable world. The power which de- termines the forms of inorganic matter is called crystallization. 215. What relation has specific heat to the atomic theory ? 216. What parallel is drawn between the forces of living and inorganic nature. NATURE OP CRYSTALLIZATION. 153 A crystal is any inorganic solid, bounded by plane surfaces symmetrically arranged, and possessing a homogeneous structure. Crystallization is, then, to the inorganic world, what the power of vitality is to the organic; and viewed in this, its proper light, the science of crystallography rises from the low station of being only a branch of solid geometry, to occupy an exalted philosophical position. We sec, therefore, the importance of devoting a brief space to this subject in con- sidering the general principles of Chemical Philosophy. The cohesive force in solids (10) is only an exertion of crystalline forces, and in this sense no difference can be established between solidification and crystallization. The forms of matter resulting from solidification may not always be regular, but the power which binds together the molecules is that of crystallization. 217. Circumstances influencing Crystallization. Solu- tion is one of the most important conditions necessary to crystallization. Most salts and other bodies are more soluble in hot than in cold water. A saturated hot solution will usually deposit crystals on cooling. Common alum and Glauber's salts are examples of this. Solution by heat or fusion also allows of crystallization, as is seen in the crys- talline fracture of zinc and antimony. Sulphur crystallizes beautifully on cooling from fusion, and so do bismuth and some other substances. The slags of iron furnaces and scoria? of volcanic districts present numerous examples of minerals finely crystallized by fire. The glass, which cools slowly after long fusion, in the clay fire-pots of our glass- houses, has often beautiful star-formed opaque white crystals found in it, and the whole mass of the glass sometimes becomes crystalline and opaque. Blows and long continued vibration produce a change of molecular arrangement in masses of solid iron and other bodies, resulting often in the formation of broad crystalline plates. Rail-road axles are thus frequently rendered unsafe. In short, any change which can disturb the equilibrium of the particles, and permits any freedom of motion among them, favors the re-action of the polar or axial forces, (218,) and promotes crystallization. What is crystallization said to be ? What is the cohesive force? 217. Name some circumstances which influence crystallization. CRYSTALLIZATION. - 1 |3 ^ r V V y / Magnetism influences and promotes crystallization. When , ^.,,.y ^ ~/z\ nitrate of mercury on a glass plate is \ placed over the poles of an electro- magnet, as in the figure, crystalliza- tion takes place in the curved lines here shown. By substituting a plate of copper for the glass, it is curiously etched in the magnetic curves by the acid of the silver salt. These experi- ments may be much varied by the ingenuity of the learner. The observations of Mr. R. Hunt have given us much new information on this point. 218. Polarity of Molecules. The laws of crystallization show that the molecules (or ultimate particles of matter) have polarity. That is, these molecules have three imaginary axes passing through them, whose terminations, or poles, are the centre of the attractions (10) by which a series of similar particles are attracted to each other to form a regular solid. These molecules are either spheres (a) or ellipsoids, (r,) and the three axes (N. S.) are always either the fundamental axes or the diameters of these particles. In the sphere (a) these axes are always of equal length, and at right angles to each other, and the forms which can result from the aggre- gation of such spherical particles can be only symmetrical solids, such as the cube and its allied forms. The cube drawn about the sphere a may be supposed to be made up of a great number of little spheres (b) whose similar poles unite N. and S. In the ellipsoid (c) all the axes may vary in length, giving origin to a vast diversity of forms. All What is said of the power of magnetism in this respect? 218. What do the laws of crystallization show ? What are the axes of molecules ? What forms have the molecules of bodies ? What forms can come from the spherical particles ? How may the struc- ture of the cube be shown ? How are the axes of the ellipsoid ? PRIMARY FORMS OF CRYSTALS. 155 matter not subject to the vital force is endowed with such polarity inherent in its molecules.* 219. Crystalline Forms. The mineral kingdom presents us with the most splendid examples of crystals ; yet, in the laboratory we can imitate the productions of nature, and in many cases produce beautiful forms from the crystallization of various salts, which have never been observed in nature. The learner who is ignorant of the simple laws of crystal- lography, sees in a cabinet of crystals an unending variety and complexity of form, which at first would seem to baffle all attempts at system or simplicity. Numerous as the natu- ral forms of crystals are, however, they may be all reduced to six classes, comprising only thirteen or fourteen forms, which are called the primary forms, because all other crys- talline solids, however complex or varied, may be formed from them by certain simple laws. 220. Primary forms. The first class of primary forms includes the cube, (1,) the octahedron, (2,) and the dodeca- hedron, (3.) The faces of the cube are equal squares. The eight solid an- gles are similar, and also the twelve edges. The three 1 2 3 axes are equal, (aa, bb, cc,) and connect the centres of opposite faces. The regular octahedron (2) consists of two equal four-sided pyramids, placed base to base. The six solid angles are equal, and so also the edges, which, as in the cube, are twelve in number. The plane angles are 60, and the interfacial 109 28' 16". The axes connect the opposite angles ; they are equal, and intersect at right angles. To what matter do these axial attractions belong ? 219. How are the complex forms of crystals arranged and simplified? 220. Describe the first class of primary forms. * We thus see that atoms or molecules are, as before remarked, only the centres of several forces, whose aggregate results we call matter. Under the influence of heat, the crystallogenic attraction loses its polarity and force, and the body becomes liquid or gaseous. The return to a solid state can occur again only when the attractions become polar or axial. 156 CRYSTALLIZATION. This class is also called the monomctric, (mono*, one, and metron, measure,) the axes being equal. 221. The second class includes the square prism, (4,) and square octahedron, (o.) In the square prism (-4) the eight solid angles are right angles, and similar, as in the culie. The eight basal edges are similar, but differ from the four lateral. The two basal laces are squares, the four lateral are parallelograms. The axes connect the centres of oppo- site faces, and intersect at right varv in the length of the vertical MM 1- 'cS s~\ : Square prisms 4 angles. axis, (ohedron, (14.) The three lateral axes arc equal, and intersect at angles of 00 ; they connect the centres of opposite lateral edges. This will be seen on placing a rhombohedron in position and looking down upon it from above. The six lateral edges will be found to be arranged around the vertical axis, hke the sides of a hexagonal prism. 220. The mutual relations of the primary forms are well shown in the foregoing arrangement. Thus, in each of the six classes, the first named solid alone is, pro|>erly considered, a primary form, the others in each class being frequently found as secondaries to these. The six fundamental forms are the cube, square prism, right rectangular prism, oblique rhombic prism, or right rhornboidal prism, oblique rhomboi- ^^ / .s required. The eye at P, looking ^\^/ / at the face (b c) of the crystal, ^HJMV observes a reflected image of M, /Si in the direction P N. The crys- ^/ Mmam ta l ma y now be so turned that the N * same image is seen reflected in the next face, (b a,) and in the same direction, (P N.) To effect this, the crystal must be turned until a b has the present position of b c. The angle d b c measures, therefore, the number of degrees through which the crystal must be turned. But d b c subtracted from 180 equals the required angle of the crystal a b c ; consequently, the crystal passes through a number of degrees, which, subtracted from 180, gives the required angle. When the crystal is attached to a graduated circle, which should move with it, we have the goniometer of Wollaston. In the annexed figure, a is such a circle of 4>rass, graduated to half de- grees, and hung by the axis 6, on which it moves with d fl IHINLy^ K rcat steadiness. This axis is perforated from end to end for the passage of a closely fitting rod or central axis, on one end of which is the bent joint, (rf,) carrying the crys- tal, (f.) By the head c, and the arrangement at d, the crystal is adjusted without moving the graduated wheel ; and when this is accomplished in such a manner that the eye of the observer placed over the crystal, as at P, can see a clear image of a line on the wall, (M,) or a window-bar, in each face successively, then the graduated wheel (which stands when at rest at zero of the vernier e) is made to revolve, and with it the crystal, until the mark or window-bar is distinctly seen in the second face. The number of degrees and parts of a degree which correspond to the angle required, are thus obtained directly by the movement of the wheel, which was How is this principle used in Wollaston's instrument ? ISOMORPHISM. 161 beforehand placed with 180 opposite to the zero on the vernier. The movement of the wheel is, therefore, in fact, a subtraction of the angle d b c from 180. The great advan- tage of this instrument is, that we can by its aid obtain very precise results, and often on crystals too small to be held in the fingers and applied to a common goniometer. A small 'magnifier is sometimes attached to the instrument, to render it more complete. 230. In measurements by the goniometer, a knowledge of the following simple principle in mathematics will be found of great value. " The sum of the three angles of a triangle equals 180," or " The sum of the angles of a polygon equals twice as many right angles as the polygon has sides less two" If the figure has six sides, then it contains 2x (6 2) = 8 right angles, or 8 X 90=720.* 4. Isomorphism.^ 231. Identity of crystalline form was formerly supposed to indicate an identity of chemical composition. We now know that certain substances may replace each other in the constitution of compounds, without changing their crystalline form. This property is called isomorphism, and those bases which admit of mutual substitution are termed isomorphous. Chemistry furnishes us many examples of these isomorphous bodies. Thus alumina and peroxyd of iron replace each other indefinitely. The carbonate of iron and carbonates of lime and magnesia are also examples, as the common sparry iron, (spathic iron,) which is a carbonate of iron, in which a large portion of carbonate of lime sometimes crystallizes, without producing any change of form in the mineral. Oxyd of zinc and of magnesia, oxyd of copper and protoxyd of iron, also take the place each of the other in compounds, without any alteration of crystalline form. When those bodies unite 230. State the principles in this section regarding triangles and polygons. Give an example. 231. What is isomorphism ? Name some examples. * The subject of crystallography cannot be further illustrated here ; but the learner who desires to pursue it is referred to the highly philosophical treatise on Mineralogy by Mr. J. D. Dana, from which we derive the substance of the foregoing. f Isos, equal, and morpke, form. u* 162 CRYSTALLIZATION. with acids to form salts, the resulting compounds have the same crystalline form, and if they have the same color, are not to be distinguished from each other by the eye. In double salts, like common alum, these relations arc also found. The sulphate of iron may take the place of sulphate of alumina in common alum, and -no change of form will occur; and soda may, in like manner, replace the potash. In fact, all the similar compounds of isomorphous bodies have a great resemblance to each other, in general appearance and chemical properties. The two bases in a double salt are, however, never taken from the same group of isomorphous bodies. 232. A knowledge of this law is of great importance to the chemist, and often enables him to explain, in a satisfactory manner, apparent contradictions and anomalies, and to decide many doubtful points. It is supposed that the elements whose compounds are isomorphous, arc also so themselves. M. Scheerer has noticed the curious and important fact, that in compounds containing magnesia, protoxyd of iron, and other bases of the 6th family below, a part of the base may be wanting without a change of crystalline form, pro- vided that this be replaced by a quantity of water which con- tains three times as much oxygen as this part of the base. For example, the compounds Mg'Si, Mg*Si + 311 and MgSi + 6H, in accordance with this principle, are isomorphous. Thus, chrysolite and serpentine may be isomorphous, and much light is shed on the relations of hydrous and anhydrous minerals. A more full discussion of this subject does not belong to our restricted limits, and we can only mention, in conclusion, the group of isomorphous bodies named by Prof. Graham in his " Elements." 1st Family ; Chlorine, Iodine, Bromine, Fluorine. 2d Family ; Sulphur, Selenium, Tellurium. 3d Family; Phosphorus, Arsenic, Antimony. 4th Family; Barium, Strontium, Lead. 5th Family ; Silver, Sodium, Potassium, Ammonium. 6th Family ; Magnesium, Manga- nese, Iron, Cobalt, Nickel, Zinc, Copper, Cadmium, Alumi- nium, Chromium, Calcium, Hydrogen. What of salts of isomorphous bases ? Is it found in double salts ? 232. What six families of isomorphous bodies are named? ELECTRO-CHEMICAL DECOMPOSITION. 163 233. Dimorphism.* Some substances have two forms, under both of which they are found. Thus common calc- spar (carbonate of lime) generally occurs in rhombohedrons, (224, 13,) but in arragonite (which is only pure carbonate of lime) it is seen as a rhombic prism, (221, fig 6.) III. CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. 1. Electro- Chemical Decomposition. 234. In discussing the electricity of chemical action, (158,) allusion was made to the power possessed by this species of electricity to produce or modify chemical decomposition. Having now become somewhat familiar with the elementary constitution of matter, and the laws of chemical combination, we can the more intelligently proceed to a very brief review of the chemical effects of voltaic electricity. 235. Decomposition of Water. Water was the first sub- stance on which the decomposing power of the battery was observed, soon after the discoveries of Galvani and Volta were made known in England. When two gold or platinum wires are connected with the opposite ends of the battery, and held a short distance asunder in a cup of water, a train of gas-bubbles will be seen rising from each, and escaping from the surface of the water. With an arrange- ment of two glass tubes placed over the plati- num poles, as figured in the margin, we can collect these bubbles as they rise, and shall soon find that the gas given off from the plate is twice the volume of that obtained from the -f plate. When the tubes are of the same size, this difference of volume becomes at once evident to the eye. By examining these gases, (as will be explained in the elementary ~~ chemistry,) we shall find them, respectively, pure hydrogen and pure oxygen, in the exact proportion of two volumes of the former to one of the latter, (190.) By no modification of the arrangement can we cause 233. What is dimorphism ? 234. Why is electro-chemical de- composition treated in this place ? 235. Mention the facts occurring in the decomposition of water. How is this made more striking ? In what proportion do the gases rise ? Can we change this pro- portion ? * From disy two, and morphe, form. 164 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. this process to vary ; the hydrogen invariably appears on the side, and oxygen on the -f- side. Water, then, is not only decomposed by the voltaic current, but that decomposition takes place in the proportions (185) of the equivalents of the elements, and these elements seek opposite poles of the battery. j:J6. The experimental researches in electricity by Mr. Faraday, have shed much light on this subject; and his virws being now generally adopted, it will be unnecessary for us to discuss the opinions formerly advanced by Volta, Davy, and others, which are very interesting and important in the history of the science, but do not now form part of its first principles. Mr. Faraday's researches required the intro- duction of certain new terms, some of which we will now explain, as we shall find them more convenient than any others. (1.) The terminal wires or conductors of a battery are often termed the poles, as if they possessed some attractive power by which they draw bodies to themselves, as a magnet attracts iron. Mr. Faraday has shown that this notion is a mistake, and that the terminal wires act merely as a path or door to the currents, and he therefore calls them electrodes, from electron and odos, a way. The electrodes are any surfaces which convey an electric current into and out of a decomposable liquid. The term electrolyses, from electron, and the Greek verb luo, to unloose, is used to express decom- position ; and the substances suffering decomposition are termed electrolytes. Thus, the experiment mentioned in the last section is a case of electrolysis, in which water is the electrolyte. The elements of an electrolyte are called ions, from the Greek participle ion, going, since the elements go to the -f or electrode. The electrodes arc distinguished ns the anode and the cathode, from ana, upwards, and odos, way, or the way in which the sun rises; and kala, down- wards, and odos, or the way in which the sun sets ; the anode is -f , and the cathode . We will now briefly consider the *J37. Conditions of Electro-Chemical Decomposition. (1.) All compounds are not electrolytes, that is, they are not directly decomposable by the voltaic current. Many bodies, What do we infer ? 230. What is said of Faraday's researches ? What did they require ? What does he call the poles, and why? Explain the terms electrode, electrolysis, and electrolyte. What are ions? 237. Are all compounds electrolytes? ELECTROCHEMICAL DECOMPOSITION. 165 however, not themselves electrolytes, are decomposed by a secondary action. Thus, nitric acid is decomposed in the electrical circuit by the secondary action of the nascent (210) hydrogen, which, uniting with one equivalent of the oxygen, again forms water and nitrous acid. Sulphuric acid is not an electrolyte, while hydrochloric acid is ; and the nascent chlorine from the latter attacks the -f electrode, if it be of gold. (2.) Electrolysis cannot happen unless the fluid be a con- ductor of electricity ; and no solid body, however good a conductor, has ever been thus decomposed. A plate of ice, however thin, interposed between the electrodes, will entirely prevent the passage of the power ; but the electrolysis will proceed as soon as the least hole melts in the ice, through which the power can pass. Fluidity is therefore a very essential condition of electrolysis. The fluidity may be that of heat, or of solution; thus, the chlorids of lead, silver, and tin, are not electrolysed in a solid state, but when fused they are decomposed with ease. (3.) The ease of electro-chemi- cal decomposition seems in a good degree proportioned to the conducting power of the fluid. Thus, pure water is by no means a good conductor, and its electrolysis is difficult ; but the addition to it of a few drops of sulphuric acid, or of some other soluble conductor, greatly promotes the ease with which it is decomposed. (4.) The amount of electrolysis is directly proportioned to the quantity of electricity which passes the electrodes. (5.) The binary compounds of the elements, (194,) as a class, are the best electrolytes. Water and iodid of potassium are instances ; while sulphuric acid, which has three equivalents of base to one of acid, is not an electrolyte. No two elements seem capable of forming more than one electrolyte. (6.) Most of the salts are resolvable into acid and base. Thus, sulphate of soda is resolved into sulphuric acid, which appears at the -f electrode, and will there redden a vegetable blue ; and the soda which appears at the electrode will restore the previously reddened blue ; so that by reversing the direction of the current, these striking effects are also reversed. Give examples. What is the second condition of electrolysis ? Give examples. (3.) To what is the ease of electrolysis pro- portioned ? (4.) To what is its amount owing ? (5.) What class of compounds are the best electrolytes ? Give examples. (6.) What of salts ? Give examples. 166 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. 233. (7.) A single ton, as bromine, for instance, has no disposition to pass to cither of the electrodes, and the current has no effect upon it. There can be no electrolysis except when a separation of ions takes place, and the separated elements go one to each electrode. (8.) There is no such thing, in fact, (as has been often supposed,) as an actual transfer of ions from one part of the fluid to either electrode. In the case of water, for example, (235,) oxygen is given out on one side and hydrogen on the other. In order that tin's may be the case, there must be water between the electrodes. We cannot believe that the separation of the elements takes place at the electrode where one clement is evolved, and that the other travels over unseen to the opposite electrode. \Vc may, however, conceive of water in its quiet state, as repre- sented by the annexed diagram, 11IJ1])' each molecule being firmly united by polar attractions (21 S) to every other, and that the electrolytic force of the electric current lias power to disturb this polar equilibrium, each molecule being similarly atlected. In this case the electrolysis will proceed from particle to particle through the whole chain of affinities, decomposing and recomposing, unti4 the ultimate particle on each sidr, having no polar force to neutralize it, escapes at that electrode which has a polarity opposite to itself. This explanation may be better understood, perhaps, by inspecting the second diagram, which represents a series of compound molecules of water undergoing electrolysis, the H and O being eliminated at the opposite extremities. The same explanation will be found to serve for all other cases of electrolysis, both simple and secondary. 1239. (9.) A surface of water, and even of air, has been shown capable of acting as an electrode, proving that the contact of a metallic conductor with the decomposing fluid is not essential. The discharge from a powerful electrical 238. (7.) What is said of a single ion? (8.) What of the transfer of ions ? Give the explanation offered of the decomposition of water. 239. (9.) What is said of electrolysis without metallic con- ductors ? Explain the experiment of the electrolysis of sulphate of Boda by the electrical machine. ELECTRO-CHEMICAL DECOMPOSITION. 167 machine (153) was made to pass from a sharp point through air to a pointed piece of litmus paper moistened with sulphate of soda, and then to a second piece of turmeric paper simi- larly moistened. This discharge had power to effect a true electrolysis ; the blue litmus was reddened by the sulphuric acid set free from the sulphate of soda, while the yellow turmeric was turned brown by the alkaline soda from the same salt. 240. (10.) Electrolysis takts place in a series of com- pounds in the precise order of their equivalents. I'hus if wine-glasses are arranged in a series, and in one is placed sulphate of soda, in another acidulated water, in another iodid of potassium, and in another hydrochloric acid, and if the whole series be connected together by siphon tubes, or moistened lampwick, passing from glass to glass, and a powerful galvanic current be then passed through them, electrolysis will occur in all, but not in an equal degree. It has been proved by accurate experiment, that the decom- position which ensues is in exact proportion to the equivalents of each substance. In other words, we may say it requires one equivalent of electricity to decompose one equivalent of an electrolyte, formed from the union of an equivalent of acid and another of base. Conversely, from the fact that an equivalent of electricity is required to decompose any com- pound, it is proved that the opposite elements of this compound, in uniting, will disengage the same equivalent of electricity. 241. (11.) The passage of a current within the cells of a voltaic battery (2G2) depends also upon the decomposition in each cell, equally with that between the platinum electrodes. The same phenomena which we notice in the decomposing cell (235) take place also in each battery cell. Water is decomposed, and the hydrogen is given off from the positive plate, while the oxygen combines with the zinc, and thus escapes detection. Therefore, no fluid not an electrolyte is suitable to excite a battery. Acid water acts, for this purpose, only by the decomposition of the water, and oxydation of the zinc. The presence of the acid is useful only so far as it combines with the oxyd of zinc constantly accumulating on 240. How does electrolysis occur in a series of compounds ? In other words, what do we say ? Conversely, what ? 241. How does a current pass in the cells of a battery ? What happens in each cell ? What is requisite in the fluid used to excite a battery ? How does acid water act in the battery ? 168 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. '9 , us, =Jm ""- \W 'U*y (he zinc plate, which must be removed as fast as formed, in order to keep up a steady flow of electricity. 2. From what has been said, we can see that a decom- posing cell interjKwsed in the circuit will give us an exact account of amount of electri- city flowing. Such an instrument has been called by Faraday a voltameter, (measurer of voltaic electricity,) and is figured in the margin, (a.) It differs from the decom|K>sing cell, (235,) in being a single cell, and having a ground glass tube at top bent twice, o as to deliver the accumu- lating gases into a graduated air-vessel, in which their volume is measured. A more simple form of the apparatus is easily con- st ructed, as shown in 6, which is a short piece of glass tube, with two corks and a bent tube, (t.) Tho elect nxJc's /* p pass through the corks, arid should terminate in broad plates of platinum foil. A common form of the instrument is seen in the annexed figure, which has only one tube, and that is graduated. When this is filled with the mixed gases, and a lighten! match is applied to the open end, the two elements unite again, with a loud explosion and vivid flash. If the apparatus is so arranged that this can be done over water without access of air, the fluid rushes up to fill the vacuum occasioned by the re-union of the elements in the formation of water. 243. The theories which have been proj)oscd to account for electro-chemical 242. What is a voltameter ? What does it show ? Explain the figures. When the mixed gases are fired, what happens ? SUSTAINING BATTERIES. 169 decomposition and the action of the voltaic circuit, we cannot discuss here, any further than to say that the chemical theory first proposed by Dr. Wollastun is now generally accepted. Volta argued that the contact of different metals was essential to the production of a current. The researches of Faraday, however, in confirming the chemical view of Wollaston, have completely disproved the contact theory. A very simple experiment by Faraday illustrates this statement. A slip of amalgamated sheet zinc bent at a right angle is hung in a glass of dilute acid ; on it is laid a folded piece ,-- of bibulous paper moistened with iodid of jxrtas- sium. A platinum plate, with an attached wire of the same metal, is now placed in the acid water, but not in contact with the zinc ; the sharpened end of the wire is bent, so as to touch the moistened paper, and very soon it is discolored by a brown spot made by the free iodine, liberated from the electro-chemical decomposition of the iodid of potassium, with which the paper is moistened. There is no contact of metals, and the current is excited only from the decomposition of the iodid out of the cell, and of the water in it. A very strong argument in favor of the chemical theory has been before mentioned, (161,) that the direction of the current is always determined by the nature of the chemical action the metals most acted on being always positive. Professor Herzelius, in view of the facts of electricity, considers all chemical action as the result of opposite electrical states in the elements and their compounds. We have now made all the explanations that are necessary to enable us to understand the principles and construction of 2. Sustaining Batteries. Vi44. Local action. In the old forms of batteries made of copper and zinc unamalgamatcd, (164,) there is always a great amount of local action in each cell, arising from the impurity of the zinc. We have before explained how, by amalgamating the zinc with mercury, it is reduced to a state of electrical uniformity, (161, note.) In order to have a constant voltaic current of equal power, not only the evils 243. What two theories have been proposed to account for the electrical phenomena of electrolysis ? What simple experiment disproves the contact theory ? 244. What are sustaining batteries? 15 170 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. arising from local action must be avoided, but also, in some degree, the weakening of the acid solution. Batteries so con- structed as to meet these difficulties, are called sustaining batteries, or constant batteries. We will first mention DaniclPs Constant Battery. This truly philo- sophical instrument (a vertical section of which is annexed) is made up of an ex- + terior circular cell of copper, (-f,) three and a half inches in diameter, which serves both as a containing vessel and as a nega- tive element ; a porous cylindrical cup of earthen-ware, (1% fig. 6,) (or the membrane of an ox-gullet,) is placed within the copper cell, and a solid cylinder of amalgamated zinc ( 7.) within the porous cup. The outer cell (c) is charged by a mixture of eight parts of water and one of oil of vitriol, saturated with blue vitriol, (sulphate of copper.) omc of the solid sulphate is also suspended on a perforated shelf, or in a gauze bag, to keep up the saturation, is filled with the same acid water, but without Any number of cells so arranged arc easily The; inner the copper salt. (/>) connected together by binding screws, as in the . figure the c of one pair to the z of the next, 9 and so on. This instrument, when arranged and charged as here descrilK-d, will give out no gas. The hydrogen from the decomposed water is not given otF in bubbles on the copper side, as in all forms of the simple circuit of zinc and copper; because the sulphate of copper there present is decomposed by the circuit, atom for atom, with the decomposed water, and the hydrogen takes the atom of o.xyd of copper, appropriating its oxygen to form water again, and metallic copper is deposited on the outer cell. No action of any sort results in this battery, when properly arranged, until the poles are joined. Ten or twelve such cells form the most active, constant, and least costly battery which can be procured. 245. Explain PanirlFs Battery from the fignre. What is its principle of action / What becomes of the hydrogen 7 When does this batterv act ? SUSTAINING BATTERIES. 171 246. Grove's Battery. Professor Grove, of London, has contrived another compound sustaining battery, of great power, and most remarkable intensity of action. The metals used are platinum and amalgamated zinc. _ \ A vertical section of this battery is shown in the "N annexed figure. The platinum ( -f- ) is placed in a porous cell of earthenware, containing strong nitric acid. This is surrounded by the amalga- mated zinc ( ) in an outer vessel of dilute sul- phuric acid, (six to ten parts water to one of acid, by measure.) The platinum, being the most costly metal, is here surrounded by the zinc, in order to economize its surface as much as possible. In this battery the hydrogen of the decomposed water on the zinc side enters the nitric acid cell, decomposes an equivalent of the acid, forming water with one equivalent of its oxygen, while the deutoxyd of nitrogen is given out as a gas, and coming in contact with the air is converted into nitrous acid fumes. No other form of battery can be compared with this for intensity of action. A series of four cells (the platinum foil being only three inches long and half an inch wide) will decompose water with great rapidity ; and twenty such cells will evolve a very splendid arch of light from points of prepared charcoal, and deflagrate all the metals very powerfully. It is rather costly, and troublesome to manage, as are all batteries with double cells and porous cups. The author has contrived a very efficient form of the same battery, in which mineral carbon (plumbago) is substituted for the platinum ;* and the carbon battery of Bunsen is constructed on the same principles, and produces most brilliant effects. But all other batteries yield in sim- plicity and ease of management to that contrived by Mr. Smee. 247. Smee's Battery is formed of zinc and silver, and needs but one cell and one fluid to excite it. The silver plate (S) is prepared by coating its surface with platinum, thrown down on it by a voltaic current, in the state of fine 246. What is Grove's Battery ? How does it differ from the last ? How does it act? What is its energy? 247. What is Smee's Battery? * American Journal of Science, (1st series,) vol. xliii, p. 393. 172 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. division, which is known as platinum-black. The object of this is to prevent the adhesion of the liberated hydrogen to the polished silver. Any polished smooth surface of metal will hold bubbles of gas with great obstinacy, thus preventing in a measure the contact between the fluid and the plate by the interposition of a film of air-bubbles. The roughened surface produced from the deposit of platinum- black entirely prevents this. The zinc plates (z z) in this battery arc well amal- gamated, and face both sides of the silver. The three plates are held in position by a clamp at top, (&,) and the interposition of a bar of dry wood (w) prevents the passage of a current from plate to plate. Water, acidulated with one-seventh its bulk of oil of vitriol, or, for less activity, with one- sixteenth, is the exciting fluid. The quantity of electricity excited in this battery is very great, but the intensity is not as great as in those compound batteries just described, where there is a double electrolysis, and of course a double intensity acquired. This battery is perfectly constant, does not act until the poles are joined, and, without any attention, will maintain a uniform flow of power for days together. A plate of lead, well silvered, and then coated with platinum-black, will answer equally as well, and indeed better than a thin plate of pure silver. This battery is recommended over every other for the student, as comprising the great requisites of cheapness, ease of management, and constancy. A How is the silver plate prepared ? What is the use of the pla- tinum-black ? How is this battery excited ? What acts as well a.9 silver ? What recommends this batterv over others ? ELECTRO-METALLURGY. 173 form of it, well calculated for the student's laboratory, is here shown, which is a porcelain trough with many cells. This battery is the one universally employed in electro-metallurgy. 3. Electro-metallurgy. 248. The depositing of metals by electrical agency seems to have been suggested by Daniell's battery. It has been remarked, that the copper of the sulphate of copper in the outer cell of that battery is deposited in a metallic state. The procuring of a pure metal in a perfectly malleable state, by means of a current of electricity, is a most important fact, and has given rise to a new and valuable art, which is every day extending its applications. We thus accomplish, in fact, a cold casting of copper, silver, gold, zinc, and many other metals ; and a new field of great extent has been thus opened for the application of metallurgic processes. The very simple apparatus re- quired to show these results experimentally, is represented in the annexed figure. It is nothing, in fact, but a single cell of Daniell's battery. A glass tumbler, (S,) a common lamp-chimney, (P,) with a bladder-skin tied over the lower end and filled with dilute acid, is all the apparatus required. A strong solution of sulphate of copper is put in the tumbler, (S,) and a zinc rod (Z) in P ; the moulds, or casts, (?n, m,) are seen suspended by wires attached to the binding screw of Z. Thus arranged, the copper solution is slowly decomposed, and the metal is evenly and firmly deposited on wz, m. A perfect reverse copy of m is thus obtained in solid malleable copper. The back of m is protected by varnish, to prevent the adhesion of the metallic copper to it. In this manner the most elabo- rate and costly medals are easily multiplied, and in the most accurate manner. In practice, casts are made in fusible metal of the object to be copied, and the operation is con- ducted in a separate cell, containing only the sulphate of copper, one of Smee's batteries supplying the power. The 248. What first suggested electro-metallurgy ? What is required in order to obtain several metals in the metallic state ? Explain the process for obtaining the copy of a medal. 15* 174 CHEMICAL EFFECTS OF VOLTAIC ELECTRICITY. art is also now extensively applied to plating in gold and silver from their solutions ; the metals thus deposited adhering perfectly to the metallic surface on which they are deposited, provided these be quite clean and bright. Many details in these processes, very needful to the successful practice of the art, are necessarily omitted here. The reader is referred for further information to Mr. Smee's excellent " Elements of Electro-Metallurgy," or Walker's " Electro- type Manipulation," re-published at Philadelphia. 249. We have now finished our preliminary view of those great powers of nature, whose operations we see to a greater or less extent in every chemical process. It may be thought that we have devoted too large a space to the topics already discussed ; but the author is convinced, from long observation, that if the principles of chemical philosophy are well acquired by the student, but little difficulty will be experienced in afterwards pursuing, even alone, and without the aid of a teacher, the wide detail of elementary chemistry. In entering on the execution of the remaining portion of our task, it is with the full understanding that no attempt is made on our part at presenting even a complete outline of the countless facts of elementary chemistry. Only such selections will be made from them as are deemed most in point to illustrate and enforce the principles already laid down, and to increase our familiarity with the philosophy of chemistry. It is hoped that this course will be satisfactory to both teacher and pupil, and the apology implied in this remark is intended to explain any apparent deficiencies which may be seen on the suc- ceeding pages. The complete and philosophical treatises of Turner, Kane, and Graham, are all excellent works of reference for the more advanced student. 249, What is said of the importance of chemical philosophy? PART III. INORGANIC CHEMISTRY. CLASSIFICATION OF ELEMENTS. 250. A natural order and perspicuous classification is of the greatest service to the student in any department of science. We will not discuss the various modes which have been adopted in chemistry for arranging the elementary bodies and their compounds, since such discussions can have but little value while we are unacquainted with the characters and affinities of the bodies which we propose to classify. It is usual to divide elementary bodies into two great groups, the non-metallic and metallic elements. This convenient arrangement is founded on characters which in a general and popular sense are correct and easily distinguished, but which fail in several cases to afford any accurate distinction. No one can doubt to which classes, for example, gold and sulphur should be respectively referred ; but it is impossible to say why carbon and silicon are not as well entitled to be classed in the same group with the metals as tellurium and arsenic, if we except the single character of lustre. While there- fore we retain these general divisions, we should not hesitate to depart from them whenever by so doing we can present the facts of elementary chemistry in a clearer and more im- pressive manner. We will discuss the first division of elementary bodies in the following order : C i The only element \yhich forms com- CLASS i. < 1. Oxygen. V pounds with all others, and the type of ( } electro-negative bodies. 1 Four elements very similar in all their 2. Chlorine, sensible properties, and forming similar CLASS n. 3. Bromine, [compounds with the metals, and whose 4. Iodine, [acid compounds with oxygen, are also 5. Fluorine. similar, and have the constitution ex- J pressed by RO, R0 4 , RO 5 , RO 7 .* 250. What is the value of classification in science ? What is necessary in order to understand a classification ? How are the ele- ments usually divided ? What is said of this division ? What exam pies are quoted in illustration ? Give the classification in the text. Name the bodies in the second class. Why are they associated ? * R signifies an atom of either of the electro-positive bodies. 176 INORGANIC CHEMISTRY. 6. Sulphur, CLASS in. 4 7. Selenium, 8. Tellurium. CLASS iv. CLASS v. CLASS vi. 9. Nitrogen, 10. Phosphorus. These stand in close relation with the preceding, while their compounds with the metals are more similar to the oxyds of those metals than are the analogous compounds of the second class. The oxy- gen acids have the formula ROj, ROa. This group properly includes also arsenic and antimony, which are, how- ever, from convenience, discussed else- > where. The four form similar com- pounds with oxygen, RO, R0 3 , RO 5 , and peculiar gaseous compounds with hydrogen, RHa. r , 1 These three bodies are similar, non-vola- 11. car ion, I ^ combustible baseS) and a i ike in form . }*' J mcon > fing feeble acids with oxygen, having the ' J formula RO 3 . 1 This highly electro-positive body is 14 H d lunlike any of the preceding, and has r analogies with the succeeding group (^ J of metals. 251. We will consider these several classes separately. The compounds which each element forms with those before it, will be taken up in order ; and we shall then be better able to understand the relation of each element to its associates in the same group. The several classes, too, will then be better understood in the analogies which unite, and the differences which separate them. CLASS I. 1. OXYGEN. Equivalent, 8. Symbol, O. Density, 1*105. 252. History and Importance. This gaseous element was first discovered by Dr. Priestly, in 1774, and in the following year by M. Schcele, a Swedish chemist. Before this discovery, all gaseous bodies were considered as modifi- cations of common air, and oxygen was called vital air, What bodies form the third class? What other two bodies properly belong in the fourth class ? How are these all related ? What of their hydrogen compounds ? What bodies are associated in the fifth class ? What element stands alone in the seventh class ? What are its affinities ? 251. How will they be discussed ? 252. When and by whom was oxygen discovered ? OXYGEN. 177 dephlogisticated air, &c. But Lavoisier proposed the name of oxygen,(hom oxus,acid 9 ) as bethought it the parenfrofall acids. This is the most interesting and important of- the elements. It forms more than one-fifth part of the atmosphere, and eight-ninths of the waters of the globe by weight, and consti- tutes at least one-third part of the crust of the planet. By its means combustion and life are sustained, and it has the widest range of affinities of all known substances. 253. Preparation. This gas may be obtained pure from many substances which* contain it ; but it is most easily and economically prepared by the decomposition, by heat, of the salt called chlorate of potash. Chloric acid contains five equivalents of oxygen, and the composition of the salt which it forms with potash is ClOj, KO*. By heat, all the oxygen, both in acid and base, (six equivalents,) is given off, and we have left KC1, or the dry chlorid of potassium. The arrangement of apparatus for this purpose is shown- in the annexed figure. One- tenth part by weight of pure oxyd of man- ganese is mingled with a convenient portion of chlorate of potash in a small glass flask, (a,) to which a bent glass tube is fitted by a cork. This tube conveys the gas to the open mouth of the in- verted air-jar, which is filled with water. The heat of the lamp beneath decom- poses the salt, and pure oxygen gas is freely given off, which escapes through the tube and displaces the water from the air-jar. By aid of the oxyd of manganese, the chlorate is What is said of its abundance and importance ? In what pro- portion does it exist in air, water, and the earth ? 253. How do we obtain pure oxygen ? Explain the use of manganese with the chlo- rate. Why is the chlorate of potash able to yield so much oxygen ? * One ounce of chlorate of potash will yield 543 cubic inches of pure oxygen gas, of more than \\ gallons. The constituents are in equivalent proportion, Chlorine 35-41, Potassium 39-19, and Oxygen 48. 178 NON-MET ALL 1C ELEMENTS. quietly decomposed, and the gas comes over gradually; while without it the operation proceeds with almost explosive energy, the whole gas being given off at nearly the same instant. The glass flask (a) is protected from fusion by the thin metallic cup (c), in which is some dry sand. 254. Oxygen is often made also from the peroxyd of manganese, heated strongly in a gun-barrel or iron bottle, from which a tube conveys the gas to the water-trough, or gas-holder. The gas from this source is not quite pure, having usually a little carbonic acicHvith it. One pound of peroxyd of manganese will yield about seven gallons of oxygen gas, and the process is recommended by its cheap- ness. Oxygen gas is alsa conveniently obtained by the action of sulphuric acid on the peroxyd of manganese, in which case an apparatus similar to that above figured is employed. Many other substances yield oxygen, as the oxyds of lead and mercury, or the nitrates of potash and soda, when heated alone in a suitable vessel. Bichromate of potash with sulphuric acid may also be employed for the same purpose. 255. Properties and Experiments. Oxygen, when pure, is a transparent, colorless gas, which no degree of cold or pressure has ever reduced to a liquid state. It is a little heavier than the atmosphere, its density being, compared to air, as 1-1057 : 1-000. One hundred cubic inches of the dry gas (32 and 49) weigh 34-29 grains. Its most remarkable O property is the energy with which it supports com- bustion. Any body which will burn in common air, burns with greatly increased splendor in oxygen gas. A newly extinguished candle or taper, which has the least fire on the wick, will instantly be rekindled in oxygen, and burn in it with great beauty. A quart of this gas in a narrow-mouthed bottle, will easily relight a candle fifty times. A bit of charcoal bark with the least spark of ignition on it, attached to a wire and lowered into a jar of this gas, will burn with intense brilliancy as long as any of the gas remains. A steel watch-spring tipped with a piece of burning match, and lowered into a jar of pure oxygen gas, bursts into the most 254. How is oxygen made from manganese ? What is the yield ? What other modes are mentioned ? 255. Describe the properties of oxygen. Explain the combustion of the watch-spring. OXYGEN. 179 magnificent combustion ; the oxyd of iron which is formed falls down in burning globules, like glowing meteors, which fuse them- selves into the glazed surface of an earthen plate, (as in the figure,) although covered with an inch of water. If, as often happens, a motion of the spring throws a glo- bule of this fused oxyd against the side of the glass vessel, it melts itself into the substance of the glass, or if that is thin, goes through it. This is one of the most brilliant and instructive experiments in chemistry. If the orifice at top is closed air-tight, and water is poured into the plate from a pitcher, we shall find, as the experiment proceeds, that the water will rise in the jar as the gas is consumed ; and if we could collect and weigh the globules of oxyd of iron, we should f;nd in them an increase of weight equal to the weight of the oxygen consumed. 256. It affects life when breathed, by quickening the circulation of the blood, and causing an excitement, which soon results in general inflammatory symptoms and death. In an atmosphere of pure oxygen we should live too fast. It exerts, however, no specific poisonous influence, being, when used in moderation, altogether salutary, and often resorted to, to inflate the lungs of drowned persons, and not unfrequently with the most beneficial results. The blood is constantly brought into contact with the air in the lungs, and it is the oxygen in the air which is the active agent in rendering it fit to sustain life. As this is the first gaseous body we have had occasion to mention, we will make a few remarks on the Management of Gases. 257. Pneumatic Troughs. Gases not absorbed by water, are always collected in a vessel of water called a pneumatic trough ; the figure in 253 shows a small neat one made of glass ; but for practical purposes they are usually made, like the one on the next page, of japanned copper, of tin plate, 256. How does oxygen affect life ? Is it poisonous or salutary ? 257. What is a pneumatic trough ? 180 NON-METALLIC ELEMENTS. or wood, to hold several gallons of water. The essential parts are the well (W) in which the air-jars are filled, and a shelf (S) covered with about an inch of water. A groove W Hllllflllll 1 1 or channel (d) is made in the shelf, to allow the end of the gas-pipe to dip under the air-jar. If nothing better is at hand, a common wooden tub e turned out, while the remainder has the form of long, slender, confused prisms, as in the annexed figure. This dillerence of form is the result of tempe- rature. Sulphur melts at 226, and from that point to 2SO is a clear amber-colored fluid. At about 320 it begins to thicken and grow reddish, and from that point to about 480 it is so stiff that the vessel containing it may be turned over without spilling it. In this state it copies seals, medallions, &c., very perfectly, and is 2S2. Give the natural history of sulphur. 283. What are its principal properties? Describe its crystallization and fusion. SULPHUR. 193 much used for this purpose. At 482 it becomes more fluid, and remains so until it reaches its boiling point at 601. It is very volatile, and sublimes readily even below its boiling point, forming flowers of sulphur. This is the method used to purify it from the earthy matters found with it. It is also cast into long cylinders, and is then called roll sulphur. When cold it has no odor, and the warmth of the hand causes it to crackle, from a disturbance of its crystalline structure. By warmth and friction it acquires its weM known brimstone smell. It is eminently a non-conductor of electricity, and is easily excited to give negative electrical sparks by friction. Sulphur is insoluble in water, and tasteless. It is dissolved by oil of turpentine, and some other oils, and more readily in sulphuret of carbon. Its vapor is soluble in vapor of alco- hol, but fluid alcohol docs not dissolve solid sulphur. 284. In its chemical relations it much resembles oxygen. It forms sulphurcts with most of the elements that form oxyds, and these sulphurets often unite to form bodies analogous to salts, as the oxyds do. Bcrzelius with much reason argues that its binary combinations, from their analogy to the oxyds, should be called sitlphids, and not sulphurets. Its uses are well known. It is one of the essential ingre- dients of gunpowder, and is the basis of all kinds of matches. Nearly all the sulphuric acid used in the arts is made from it. The gas arising from its combustion is employed in bleaching straw and woolen goods ; and in medicine it has a specific power in certain obstinate cutaneous diseases. Compounds of Sulphur with Oxygen. 285. With oxygen it unites in several proportions. It burns in common air with a pale blue flame, and gives the well known odor of a burning match, forming only sulphurous acid, which is its lowest compound with oxygen. Tho com- pounds of sulphur and oxygen are numerous, but only two of them are of sufficient importance to engage our attention at present, viz : Is it volatile ? Has it odor when cold ? How does it act as an electric ? In what is it soluble ? 284. What are its chemical relations ? Why is it associated with oxygen ? Name its uses. 285. What compounds does it form with oxygen ? 17 194- NON-METALLIC ELEMENTS. Combination by weight. Symbol. Sulphur. Oxygen. Sulphurous acid, SO 2 16-09 16 Sulphuric acid, S0 3 16-09 24 286. (1.) Sulphurous acid, (SO 2 .) This is the sole pro- duct of the combustion of sulphur in common air or pure oxygen gas. But for experiment it is prepared by the action of sulphuric acid (SO 3 ) with heat on copper clippings or mercury, in a glass retort. One equivalent of oxygen is retained by the metal, and the other two with the sulphur are given off as sulphurous acid. Sulphurous acid is one of the gases which must be collected over mercury, or by displace- ment of air in dry vessels. Its high specific gravity renders it easy to do the latter. 287. Properties. This is a colorless gas, having a density of 2-21 : 100 cubic inches of it weigh 68-69 grains. It has a very pungent, suffocating odor, quite insufferable, and it at once extinguishes flame. A lighted candle lowered into a jar containing it is extinguished, and the edges of the flame, as it expires, are tinged with green. A solution of blue litmus or blue cabbage turned into a jar of the gas is at first reddened by the acid, and then bleached. Water absorbs 37 times its volume of sulphurous acid, forming a strongly acid fluid. Its avidity for moisture is so great that it forms an acid fog with the water in the atmosphere, and a bit of ice slipped under a jar of it on the mercurial cistern is instantly melted ; the water absorbs the gas, and the mercury rises to fill the jar. Its bleaching power is only temporary. Articles bleached by it after a time regain their previous color. 288. Sulphurous acid is easily condensed by cold and pressure into a fluid having a specific gravity of 1*45, which becomes a crystalline, transparent, colorless solid at 105. The solid is heavier than the liquid, and sinks in it. By volume, sulphurous acid contains one volume of oxygen and volume of sulphur vapor, (191,) condensed into one volume. Sulphurous acid forms a series of salts with bases, which are called sulphites. 28G. How is sulphurous acid formed? How is it collected? 287. Give its properties. Does it support the combustion of a- candle ? How does it affect vegetable colors ? Is it dissolved^ by water ? What of its avidity for moisture ? Does it bleach perma- nently ? 288. Does it become liquid ? At what temperature is it solid ? Give its composition by volume. SULPHUR. 195 289. (2.) Sulphuric acid, (SO 3 , HO.) This acid is one of the most important compounds known ; its affinities are very powerful, and no class of bodies is better understood by chemists than the sulphates. In the arts great use is made of sulphuric acid, many millions of pounds of it being annually consumed in manufacturing nitric and muriatic acids, the sul- phate of copper, and alum, and in the processes of dyeing. It is not formed by the direct union of its elements, since we have seen that only sulphurous acid can result from the combustion of sulphur in air. Sulphurous acid must be oxydized to form sulphuric acid. 290. This may be done by passing a mixture of sulphu- rous acid with common air over spongy platinum, heated to redness in a tube, when there will issue from the open end of the tube a mixture of sulphuric acid in vapor, with nitrogen from the air. In the arts, however, this process cannot be used ; but sulphuric acid is made on a large scale by bringing together sulphurous acid, (SO 2 ,) nitrous acid, (NO 4 ,) and water, (HO,) all in a state of vapor, in a large chamber or room, when sulphurous acid (SO 2 ) passes to a higher state of oxydation (SO 3 ) at the expense of one half the oxygen of the nitrous acid, (NO 4 ,) which thus- becomes reduced to the state of the deutoxyd of nitrogen, (N0 2 .) The arrangement employed is repre- sented in the an- nexed figure. A A is a chamber fifty feet or more long, lined on all sides with sheet lead. A very large leaden tube (B) opening into one end of the chamber, communicates with a furnace. Its lower end rests in a gutter (o o) of dilute acid, to prevent the effects of 289. What is said of the importance of sulphuric acid ? What are its chief uses in the arts ? How is it formed ? 290. How may sulphurous acid be oxydized ? How is it done in the arts ? Of what use are the nitric and nitrous acids, in this process ? Describe the arrangement of the leaden chamber. 196 NON-METALLIC ELEMENTS. too much heat, and the escape of the vapors. The sulphur is intioduced by a door (c) to an iron pan, and a fire built beneath, (n.) The heat melts the sulphur, which burns in a current of air passing over it, and the sulphurous acid thus formed enters the chamber in company with air and the vapors of nitric acid set free from small iron pans standing over the sulphur, and containing the materials to evolve nitric acid, (sulphuric acid and saltpetre.) A small steam- boiler (e) furnishes a jet of steam (x) as required, and a quantity of water covers the floor, which is inclined so as to be deepest at h. A chimney with a valve or damper (p) allows the escape of spent and useless gases. Things being thus arranged, the chamber receives a constant supply of sulphurous acid, common air, nitric acid-vapor, and steam. These react on each other ; the nitric acid (NO 5 ) gives up a part of its oxygen to the sulphurous acid, forming nitrous acid, (NO 4 ,) and finally the deutoxyd of nitrogen, (NO 2 .) The last substance in contact with air gaihs another equiva- lent of oxygen, to form nitrous acid anew, which is again destined to be deoxydized by a fresh portion of sulphurous acid. In this way a small quantity of nitric acid can be made to oxydize an indefinite amount of sulphurous acid ; serving the purpose, as it were, of a carrier of oxygen from the atmospheric air to the sulphurous acid. Meanwhile the water on the floor of the chamber grows rapidly acid ; and when it has attained a specific gravity of about 1'5, it is drawn off and concentrated by boiling, first in open pans of lead until it becomes strong enough to corrode the lead, and afterwards in stills of platinum until it has a density of about 1-8, in which state it is sold in carboys, or large bottles packed in boxes. 291. The process of forming sulphuric acid is easily illustrated in the class-room, by an arrangement of apparatus like that shown in the adjoining figure. Two flasks (a b) are so connected by bent tubes with a large bottle, that from one (a) sulphurous acid, and from the other (b) nitric oxyd What vapors enter the chamber ? What use is made of steam ? What receives and condenses the vapors ? Explain the successive changes which take place in the chamber. How can a small quan- tity of nitric acid answer the purpose ? How is the acid water from the chamber concentrated? 291. How can we illustrate this process in the class-room ? SULPHUR. 197 gases (304) are made to pass into the middle bottle, the inner surface of which is slightly moistened. By blowing in occasionally at c, the spent gases are ejected at d, and fresh air introduced. Under these circumstances the interior of the central vessel is soon covered with a white crys- talline solid, which' appears to be a compound of sul- phurous acid and nitrous acid, (SO 2 ,NO 4 .) This substance is decomposed by a larger quantity of water into sulphuric acid and hyponitrous acid, and as it is known to be formed in the leaden chambers in large quantities, it is supposed to have an important influence in the production of sulphuric acid. 292. Sulphuric acid unites with water in four proportions ; namely, Nordhausen acid, Oil of vitriol, Acid of sp. gr., 1-78, Acid of sp. gr., 1'63, 2(S0 3 )HO S0 3 ,HO S0 3 ,HO-fHO S0 3 ,HO + 2H 293. The most concentrated sulphuric acid, however, is made by distilling dry sulphate of iron in earthenware retorts, at a red heat, when the acid of the salt with half an equivalent of water comes over in vapor, and is condensed in earthen tubes. It is a dark-brown, oily fluid, of the specific gravity of 1*9, or nearly twice as heavy as water, and with such an avidity for water as to hiss like hot iron 'when dropped into it. This sort of acid is made at Nord- hausen, in Saxony, and is commonly called the Nordhausen sulphuric acid. It has the 'composition of 2SO 3 ,HO = 89-19. When it is put in a retort and moderately heated, a white crystalline product is obtained from it, which is dry, or anhy- Explain the arrangement and reaction. What is the composition of the white crystalline compound ? How does water affect it ? 292. What compounds does sulphuric acid form with water? 293. How is the strongest sulphuric acid made ? What is its character ? its strength ? its formula ? What is it called ? 17* 198 NON-METALLIC ELEMENTS. drous sulphuric acid, (SO 3 .) Common sulphuric acid, when as strong as possible, has still one equivalent of water, as above. It also unites with two equivalents, (SO 3 ,lIO-f HO,) with a specific gravity of 1-780. When acid of this strength is exposed to a temperature of 32, it freezes in large crys- tals. Great heat is generated from the mixture of strong sulphuric acid and water, and a diminution of bulk attends the mixture. When exposed to a temperature of 15, sul- phuric acid freezes ; and at 620 it boils, giving off a dense white vapor. It is intensely acid to the taste, and deadly, if by any accident it is swallowed, corroding and burning the organs with intense heat. It blackens nearly all inorganic matters, charring or burning them like fire. Its strong dis- position for water enables us to employ it in desiccation, and in the absorption of aqueous vapor, (122.) 294. The silky anhydrous compound (SO 3 ) obtained from the distillation of Nordhausen acid, (2SQj,-f-HO,) does not possess acid properties when dry, but water at once changes it to common sulphuric acid. It has therefore been inferred that sulphuric acid cannot exist without water, or that water is essential to the acid property. In this case it is supposed that the oxygen of the water joins that already with the sul- phur, (forming SO 4 ,) while the new compound thus produced unites with hydrogen, forming SO 4 H. Some writers prefer to express the composition of sulphuric acid in this way, because it commits them to no theory, but is merely a state- ment of the number of atoms of each element in the com- pound, without attempting to decide how the elements may be united. 295. Chlorid of sulphur is prepared by passing dry chlorine over melted sulphur. It is a volatile, deeply-colored liquid, of a disagreeable odor, boils at 280, and has a density of 1-687. It consists of two equivalents of sulphur and one of chlorine, (S 2 C1.) It is decomposed by water. There are also bromids and iodids of sulphur, which how- ever possess very little interest. Give the composition of the common sulphuric acid. At what strength and temperature does it freeze ? When mingled with water, what happens ? Give other properties of sulphuric acid. 294. Is the silky compound acid ? To what does the common acid owe its acid properties ? What view is given of the possible arrangement of its atoms ? 295. What compounds of sulphur are here named ? SELENIUM. 199 7. SELENIUM. Equivalent, 39'57. Symbol, Se. Density, 4*3. 296. History and Properties. This element was dis- covered by Berzelius in 1818, and named by him from selene, the moon. It is associated in nature with sulphur in some kinds of iron pyrites, and also at the Lipari Islands combined with sulphur and accompanied by other volcanic products. It closely resembles sulphur in most of its properties, as well as in its natural associations. At common temperatures it is a brittle solid, opake, and having a metallic lustre like lead, but in powder it is of a deep red color. Its specific gravity is between 4*3 and 4-32. It softens at 212, and may then be drawn out into red colored threads ; at a little higher temperature it melts completely, and boils at 650 r giving a deep yellow vapor without odor. It is insoluble. When heated in the air, it combines with oxygen and gives out a disagreeable and strong odor, like putrid horse-radish. Before the blowpipe, on charcoal, it burns with a pale blue flame, and -Jg- of a grain, so heated, will fill a large apart- ment with its odor. It is a non-conductor of heat and of electricity. 297. The compounds of selenium with oxygen are three, two of which are acids analogous to sulphurous and sulphu- ric acids. Their composition is, Composition by weight. Symbol. Selenium. Oxygen. Oxyd of selenium, SeO 39-57 8 Selenious acid, . SeO 2 39-57 16 Selenic acid, Se0 3 39.57 24 298. Oxyd of selenium is formed when selenium is heated in the air. It is a colorless gas, and possesses the strong odor before mentioned. Selenious acid is a white and very soluble body, procured by the action of nitric acid on selenium. It is distinctly acid, and can be sublimed 296. When, where, and by whom was selenium discovered ? Give its properties. What physical property most distinguishes it ? 297. What are its compounds with oxygen? 298. Characterize these compounds. (1.) The oxyd; (2.) Selenious acid. 200 NON-METALLIC ELEMENTS. without change of properties. Selenic acid is formed by oxydizing selenium with nitrate of potash, and it may also be formed by the action of nitric acid on selenium. It strongly resembles sulphuric acid in its acid properties and compounds. Both selenious and selenic acids form salts with the alkalies and bases, every way similar to the sulphites and sulphates. With sulphur, selenium forms a sulphuret which is found native among volcanic products. 8. TELLURIUM. Equivalent, 64-14. Symbol, Te. 299. Tellurium is a very rare substance, more analogous to sulphur in its chemical relations than to the metals, with which it is usually classed. It is found native or alloyed with gold, and is also combined with bismuth, silver, &c., in several very rare minerals, as telluric bismuth, graphic tellurium, and aurotellurite. When pure, it is a tin-white, brittle substance, with a metallic lustre, and a density of 6-26. It melts at low red- ness, is very volatile, and is a bad conductor of heat and electricity. It burns when strongly heated in the air, and forms tellurous acid, TcO a . Telluric acid, (TeO 3 ) can also be formed from tellurous acid, by a process which need not now be described. CLASS IV. 9. NITROGEN, OR AZOTE.* Equivalent, 14-06. Symbol, N. Density, -972. 300. Preparation and History. This gas forms four- fifths of the air we breathe, and is an essential constituent of most organic substances. It enters into a great variety of combinations. (3.) Selenic acid. 299. What is tellurium? Give its properties. What acids does it form ? 300. Give the symbol and equivalent of nitrogen. * So called from a, privative, and zoe, life, frem its deadly effects. Nitrogen is from nitrnm, nitre, and gannao, I form. NITROGEN. 201 It is most easily procured for purposes of experiment from the atmosphere, by withdrawing the oxygen of the air by phosphorus. This is easily done by burning some phosphorus in a floating capsule, in an air-jar over the pneumatic cistern. The strong affinity of phosphorus for oxygen enables it to withdraw every trace of this element, leaving be- hind nitrogen nearly pure, con- taining about -5^ of phosphorus and the vapors of phosphorus, ^ with the snow-white phosphoric acid which the water soon absorbs. The first combustion of the phosphorus expels a portion of the air by expansion ; but as the combustion proceeds the water rises in the jar, showing a considerable absorption. Pure nitrogen is also easily obtained from fused nitrate of ammonia by aid of a bit of zinc, which is lowered by a wire passing through the cork of the tubulure, so as to bring the zinc into contact with the fused salt. As soon as the protoxyd of nitrogen begins to be set free, oxyd of zinc is formed, and nitrogen evolved, NO-f Zn=ZnO + N. Other processes may be used, such as passing air over cuttings of copper in a tube heated to redness, and the action of nitric acid on lean animal muscle ; but the method first named will best suit our purposes. 301. Properties of Nitrogen. Nitrogen is best described by saying that its properties are entirely negative. It is a fixed gas, which no degree of cold and pressure has ever liquefied. It cannot support combustion, nor life ; yet it is not poisonous, and kills merely by exclusion of air. It has neither taste nor smell. It is a little lighter than air, having a density of '972. It does not combine directly with any element, although by indirect methods it enters into powerful combinations with several. In the air, it seems to act the part of a diluent, and is not, properly speaking, in chemical combination with the oxygen there present ; the atmosphere is regarded as a mixture of the two gases, diffused through each other, (132.) How is it prepared ? 301. What are its properties ? Does it support life and combustion ? Is it poisonous ? Does it directly combine with other elements ? How does it act in common air ? 202 NON-METALLIC ELEMENTS. 1. The Chemical History of the Atmosphere. 302. We have already (24) given a sufficient account of the mechanical or physical properties of the atmosphere and the laws of gases, and need not repeat them here. The number and proportion of the constituents of the atmosphere are constant, although their union is only mechanical. Repeated analyses have shown that atmospheric air is always formed of nitrogen, oxygen, watery vapor, a little carbonic acid, traces, perhaps, of carbureted hydrogen, and a small quantity of ammonia. The air on Mount Blanc, or that taken in a balloon by Gay Lussac from 21,735 feet above the earth, has the same chemical composition as that on the surface, or at the bottom of the deepest mines. The carbonic acid being liable to changes in quantity from local causes, is found to vary slightly. To the constituents already named, we may add the aroma of flowers and other volatile odors, and those unknown mysterious agencies which affect health, and are called miasmata. We may state the composition of the atmosphere in 100 parts, to be - By weight. By measure. Nitrogen, 77 parts. 79-19 Oxygen, 23 20-81 100 100-00 To this we must add from 3 to 5 measures of carbonic acid in 10,000 of air; a variable quantity of aqueous vapor, and a trace of ammonia. Nitric acid has also been some- times found in small quantity in rain-water, formed in the air by the electrical discharges of thunder-clouds, and washed out by the rains. 100 cubic inches of dry air weigh 31*011 grains. 303. Analysis of Air. The oxygen of the air is ab- stracted by all substances having an affinity for it, with the same ease as if nitrogen were not present. The experiments described in 300 are one mode of analyzing air. The term 302. Describe the chemical composition and properties of the air. Do the proportions vary ? Which constituents may vary ? Give its constitution by weight and measure. How much carbonic acid is there in it ? What do 100 cubic inches weigh? 303. How is the air analyzed ? NITROGEN. 203 eudiometry has been applied to processes for determining the purity of the air, from words signifying " a good condition of the air." One of the sim- plest means of analyzing the atmosphere, consists in removing the oxygen by the slow combustion of phosphorus. For this purpose the arrangement is made, as in the annexed figure, by sustaining a stick of phosphorus on a wire in a confined portion of air, contained in a graduated glass tube, whose open end is beneath water. A gradual absorption takes place, and in about twenty-four hours the water ceases 'to rise in the tube, by which we know that the phosphorus has removed all the oxygen. The water absorbs the resulting phosphorous acid, and we may read off, by the graduation on the tube, the amount of gas removed. A narrow-necked bolt-head shows this result in a more striking manner in the class-room, the large volume of air in the ball causing a very appreciable rise of water in the stem during the course of a lecture. When speaking of hydrogen, we will mention another method of eudiometry. The agency of the air in combustion and respiration will also be explained under the appropriate heads. From this mechanical mixture of oxygen and nitrogen, we pass to the 2. Compounds of Oxygen and Nitrogen. 304. Nitrogen unites with Oxygen, forming five com- pounds, three of which are acids. Their names and con- stitution are thus expressed : Combination by weight. Protoxyd of nitrogen, (nitrous oxyd,) Symbol. NO Nitrogen. 14-06 Oxygen. 8 Deutoxyd of nitrogen, (nitric oxyd,) N0 2 14-06 16 Hyponitrous acid, N0 3 14-06 24 Nitrous acid, NO 4 14-06 32 Nitric acid, N0 5 14-06 40 What is eudiometry ? Give a simple mode of illustrating the analysis of air. 304. Name the compounds of oxygen with nitrogen. Give their composition on the black-board. 204 NON-METALLIC ELEMNETS. This group of compounds is generally considered as one of the most instructive examples of the law of multiple pro- portions (184) in the whole range of chemical affinities, and our attention is arrested by the fact, that the same elements which form our salubrious air, should, by mere change of proportions, unite to form the corrosive and deadly acids of nitrogen. 305. Protoxyd of Nitrogen, (NO,) Nitrous Oxyd, or Laughing Gas. This gaseous compound of nitrogen is best prepared by heating nitrate of ammonia (NH 3 , N0 5 ) in a glass flask by the aid of a spirit-lamp. The arrangement is here shown ; the gas is given off at about 400 to 500, and is delivered by the bent tube to an air-jar on the pneumatic trough. The nitrate of ammonia, which is a crystalline white salt formed by neuralizing dilute nitric acid by carbonate of ammonia, is so constituted as to be resolved by heat alone, into nitrous oxyd and water; thus, NH 4 O, NO 3 , become by heat 4HO + 2NO. The hydrogen in the ammonia takes so much oxygen from the nitric acid three equivalents as is required to form three equivalents of water, and the nitrogen, both of the acid and ammonia, unites with the remaining oxygen to form the gas in question. Consequently the equivalents of these elements show us that 71 grains of nitrate of ammonia will yield 44 grains of nitrous oxyd and 27 grains of water. Care must be taken not to heat this salt too highly, as it then yields nitric oxyd and nitrous acid fumes. If a red cloud towards the close of the operation is seen to rise, the heat must be abated. 306. Properties. Nitrous oxyd is a colorless gas, with a faint, agreeable odor, and a sweetish taste. With a pres- sure of fifty atmospheres at 45 F. it becomes a clear liquid, and at about 150 below zero freezes into a beautiful, clear, crystalline solid. By the evaporation of this solid, a degree 305. How is protoxyd of nitrogen prepared ? What caution is needed ? 306. What are the properties of this gas ? Has it been solidified, and at what temperature ? NITROGEN. 205 of cold may be produced far below that of the carbonic acid bath (137) in vacua, (or lower than 174 F.) It evap- orates slowly, and does not freeze, like carbonic acid, by its own evaporation. The specific gravity of nitrous oxyd is 1-525; 100 cubic inches of it weigh 47*29 grains. Cold water absorbs about its own volume of this gas. It cannot, therefore, be long kept over water, but may be collected in vessels filled with warm water over the water-trough. It supports the combustion of a candle, and sometimes re-lights its red wick with almost the same promptness as pure oxygen. Phosphorus burns in it with great splendor. With an equal bulk of hydrogen, it forms a mixure that explodes with violence by the electric spark or a match ; the residue is pure nitrogen, the oxygen forming water with the hydro- gen. 307. Its most remarkable property, and that from which it derives the name of * laughing gas? is its intoxicating power on the system. For this purpose it is breathed when pure or diluted with air, through a wide tube, connected with a silk or elastic-gum bag or with a gas-holder, and may be inhaled and exhaled several times, until giddiness comes on, and a feeling of joyous or boisterous exhilaration. This is shown by a disposition to laughter, a flow of vivid ideas and poetic imagery, and often by a strong disposition to muscular exertion. These sensations are usually quite transient, and pass away without any resulting languor or depression. In a few cases dangerous consequences have followed its use, and it should be employed with great caution. In at least one case,* at Yale College, it produced a permanent restoration of health and joyous exhilaration of spirits which continued for months. Its effects, however, in different individuals are various. 308. Deutoxyd or Binoxyd of Nitrogen, Nitric Oxyd. This gas is easily prepared by adding strong nitric acid to How does the solid gas behave ? Is this an absorbable gas ? 307. What is its most remarkable property ? How does it affect the sys- tem ? Are its effects uniform ? 308. How is binoxyd of nitrogen formed ? * In another case consumptive symptoms resulted, which continued for years, although not eventually fatal. 18 206 NON-METALLIC ELEMENTS. clippings of sheet copper, contained in a bottle arranged with two tubes like the annexed figure ; a little water is first put with the copper cuttings, and the nitric acid poured in at the tall funnel tube until brisk effervescence comes on. In this case the copper is oxydized by a part of the oxygen of the acid, and the oxyd thus formed is dissolved by another por- tion of acid. The nitrogen in union with the two equivalents of oxygen is given off as nitric oxyd, which, not being absorbed by water, may be collected over the pneu- matic-trough. Many other metals have the same action with nitric acid. 309. Properties. Nitric oxyd is a transparent, colorless gas, tasteless and inodorous, but excites a violent spasm in the throat when an attempt is made to breathe it. It has never been condensed into a liquid. Its specific gravity is 1*039, and 100 cubic inches weigh 32-22 grains. It contains equal measures of oxygen and nitrogen uncondensed. A lighted taper is instantly extinguished when immersed in it, but phosphorus previously well inflamed will burn in it with great splendor. When this gas comes into contact with the air, deep red fumes are produced, by its union with the oxygen of the air to form nitrous acid. If to a tall jar, nearly filled with nitric oxyd, standing over the well of the cistern, pure oxygen gas be turned up, deep blood-red fumes instantly fill the vessel, much heat is generated, and a rapid absorption results from the solution of the red nitrous acid vapors in the water of the cistern. If both gases are pure and in the right proportions, the absorption will be complete, and no gas left in the vessel. If purple cabbage- water, made green by an alkali, is used to fill the air-jar, the acid formed at once turns the vegetable infusion to a lively red. 310. Hyponitrous Acid, (NO 3 .) This is a thin mobile liquid, formed from the mixture of four measures of deut- oxyd of nitrogen with one measure of oxygen, both perfectly 309. What are its properties ? Is it respirable ? Is it condensa- ble ? Give its specific gravity and its composition by volume. Does it support combustion ? What is its action with oxygen ? What finr* experiment is named ? H10. What is hyponitrous acid? NITROGEN. 207 dry, and exposed after mixture to a temperature below zero of Fahrenheit. It has an orange red vapor, and at common temperatures is green, but at zero is colorless. Water decom- poses it, forming nitric acid and deutoxyd of nitrogen. Its most interesting compound is that formed with sulphurous acid in the manufacture of sulphuric acid, (290,) as already described. 311. Nitrous Acid, (NO 4 .) We have already anticipated the mode of forming this compound and its properties in de- scribing the deutoxyd of nitrogen. Whenever the latter body is brought into contact with the air, red nitrous acid fumes are formed. By decomposing the nitrate of lead in an earthen retort nitrous acid and oxygen are obtained and the former may be condensed in a very cold receiver. In this state it is a nearly colorless fluid, which becomes yellow and finally red as the temperature rises. It boils at 82, and is decomposed by water, nitric acid and deutoxyd of nitrogen being formed. This body, although considered as an acid, is not very well characterized. The red color of the strong, fuming nitric acid of commerce, is due to the presence of nitrous acid dissolved in the fluid. 312. Nitric Acid, Aqua Fortis, (NO 5 HO.) This powerful and important acid is bet- ter known than any other R of the compounds of nitro- gen. It is best obtained by decomposing either the nitrate of soda or of pot- ash, (saltpetre,) by strong sulphuric acid. The ar- rangement of apparatus required is seen in the adjoining cut. The re- tort ( R ) con-tains the nitre in small crystals, and should be supported in a sand-bath ; or if the salt does not exceed a pound or two, a naked fire an- What compound of it have we already described? 311. What is said of nitrous acid ? How can it be obtained ? Can it be mixed with water ? 312. How is nitric acid formed ? Describe the arrangement of apparatus and the proportions of the materials. 208 NON-METALLIC ELEMENTS. swers very well. To it is added about twice its weight of strong oil of vitriol. The sulphuric acid takes the place of the nitric, forming bisulphate of soda or potash, and the strong nitric acid distils over to the receiver, which is kept cool by water or ice. No luting of any kind must be employed about its neck. The retort becomes very hot, and the whole operation is a critical one. The dense red vapors of nitrous acid which appear in the early stage of the process disappear entirely after a time, and are again renewed toward its close. When the deep blood-red vapors prevail, and but little acid condenses in the neck of the retort, the heat is remitted and the receiver dis- connected ; the bisulphate of potash is then in a state of quiet fusion and intensely hot, (about 600 F.) When nearly cold it may be gradually dissolved by hot water, but the retort is generally sacrificed in the operation. The strongest nitric acid is produced only when equal weights of sulphuric acid and nitre are used. 313. Properties. Nitric acid thus obtained is a highly colored, red, fuming, and very corrosive acid, of great energy. The color is due to nitrous and hyponitrous acid, the pure nitric acid being colorless, with a specific gravity of 1*5, and boiling at 248. It stains the skin yellow, and acts violently on most organic matters and metals. Poured on powdered recently ignited charcoal, deflagration speedily ensues, and warm oil of turpentine is at once inflamed by it. 314. One equivalent of water is essential to the character of nitric acid, (NO 5 , HO,) the simple NO S being an unknown substance. The strongest nitric acid has nine parts of water to 54 of real acid. Like sulphuric acid, it has several definite combinations with water, which freeze and boil at very different temperatures. Strong aqua fortis freezes at about 50 below zero, but when diluted with one-half water it freezes at 1-|. The green hydrated nitrous acid freezes into a bluish white solid. 315. It oxydizes other substances very powerfully, from the great amount of oxygen it contains. It is the usual What changes are noticed as the process goes on ? When is the process arrested ? 313. What are rts properties ? What gives it its ordinary color ? How does it effect the skin, the metals and char- coal ? 314. Is the anhydrous nitric acid known ? What is the com- position of the strongest nitric acid ? Is it ever frozen, and at what temperature ? 315. How does it affect other bodies ? PHOSPHORUS. 209 solveift of most of the metals, when we would carry them to the condition of peroxyds. In all such cases, the binoxyd of nitrogen is formed, (NO 2) ) which at once produces red fumes in the air. It forms a large class of salts, (nitrates,) all of which are soluble in water. This makes it difficult to detect the presence of this acid. It however decolorizes a solution of indigo in sulphuric acid, which is the common test for the presence of nitric acid ; and with a drop or two of hydrochloric acid it dissolves gold leaf. 10. PHOSPHORUS. Equivalent, 31-38. Symbol, P. Density, 1-77. 316. History. Phosphorus is an element nowhere seen free in nature, but it exists largely in the animal kingdom, combined with lime, forming bones, and it is found also in other parts of the body. In the mineral kingdom it exists in several well known forms, particularly in the mineral called apatite, which is a phosphate of lime. It is introduced into the animal system by the plants used as food, whose ashes contain a notable quantity of phosphate of lime. It was dis- covered in 1669 by Brandt, an alchemist of Hamburg, while engaged in seeking for the philosopher's stone, in human urine. Its name implies its most remarkable property, (phos, light, and phero, I carry.) 317. Preparation. Phosphorus is now procured in im- mense quantities from burnt bones, for the manufacture of friction matches. The bones are calcined until they. are quite white; they are then ground to a fine powder, and fifteen parts of this are treated with thirty parts of water and ten of sulphuric acid : this mixture is allowed to stand a day or two, and is then filtered, to free it from the insoluble sulphate of lime, formed by the action of the oil of vitriol on the bones. The clear liquid (which is a soluble salt of lime and phos- phoric acid) is then evaporated to a syrup, and a quantity of powdered charcoal added. The whole is then completely dried in an iron vessel and gently ignited. After this, it is introduced into a stoneware or iron retort, to which a wide tube of copper is fitted, communicating with a bottle in which 316. What is phosphorus ? When and by whom discovered ? What existence has it in nature? 317. How is it prepared? De- scribe the process of procuring it. 18* 210 NON-METALLIC ELEMENTS. is a little water, that just covers the open end of the tube ; a small tube carries the gases given out to a chimney or vent. The retort being very gradually heated, the charcoal decom- poses the phosphoric acid, carbonic acid and carbonic oxyd gases are evolved, and free phosphorus flows down the tube into the bottle, where it is condensed. The operation is a criti- cal one, and often fails from the break- ing of the retort. Splendid flashes of light are constantly given out during the operation, from the escape of phos- phureted hydrogen. The crude phos- phorus thus obtained is purified by melting under water, and it is then cast into glass tubes, where it is allowed to cool, forming the sticks in which it is sold. 318. Pure phosphorus is a yellowish semi-transparent solid, which cuts like wax, is brittle at 32, and then shows a crystalline fracture. It has a density of I'll. It is insolu- ble in water, but dissolves in several oils, in ether, alcohol, and in sulphuret of carbon : from the last it crystallizes in regular dodecahedrons, (220.) It melts at 108 into a color- less liquid, and boils at 650, forming a colorless vapor of a density of 4-327. 319. Phosphorus is exceedingly inflammable, being easily set on fire by the heat of the hand, and great caution is re- quired in managing it. It must be kept under water, to which alcohol enough may be added to prevent its freezing in winter. If exposed to the "air, it wastes slowly away, forming phos- phorous acid, and in the dark it is seen to be luminous. The vapor which then comes from it, has a strong garlic odor, which does not belong either to the pure phosphorus or its acid compounds. A little olefiant gas, the vapor of ether, or any essential oil, will entirely arrest the slow oxydation of phosphorus in air. The presence of nitrogen or hydrogen seems to be essential to this operation, as in pure oxygen, phosphorus does not form phosphorous acid at common tem- 318. What is its usual condition ? In what is it soluble ? How is its density when solid and in vapor ? 319. What of its inflamma- bility ? How is it kept ? How does air affect it ? What substances arrest its slow combustion ? How does it burn in oxygen ? PHOSPHORUS. 211 peratures. It burns in pure oxygen gas with great splendor, forming one of the most brilliant experiments in chemistry. For this purpose it is suspended in a metallic spoon, in a dry globe, filled with oxygen by displacement of air, as already described. 1. Compounds of Phosphorus with Oxygen. 320. The compounds of phosphorus with oxygen are four in number, and may be understood from the following list. Composition by Weight. Symbol. Phosphorus. Oxygen. Oxyd of phosphorus, P 2 O 62-76 Hypophosphorous acid, PO 31-38 8 Phosphorous acid, P0 3 31-38 24 Phosphoric acid, P0 5 31-38 40 321. Oxyd of phosphorus is formed when a stream of oxygen gas is allowed to flow from a tube upon phosphorus under warm water. The phosphorus burns under water and forms a brick-red powder, which is the oxyd in question, with much unburnt phosphorus. This oxyd is also formed when phosphorus is kept for a long time under water ; the sticks then become coated with the red oxyd. By heat, this oxyd is decomposed into phosphorous and phosphoric acids. 322. Hypophosphorous acid is very little known, and we need not describe its mode of formation. Its salts are all sol- uble in water, and it is a powerful deoxydizing agent. 323. Phosphorous Acid. When some sticks of phospho- rus are placed in a funnel, and its mouth covered, a delicate stream of white vapor is seen to descend from the lower end of the tube, which may be collected in a tall foot-glass. These vapors are phosphorous acid, formed from the slow combustion of the phosphorus by the oxygen of the air. It is also formed when phosphorus is burnt in a very limited supply of oxygen gas. In both cases it soon takes another dose of oxygen from the air, and becomes a mixture of phos- phorous and phosphoric acids. When first made, phosphorous acid is a dry white powder, having a very strong affinity for water, which it absorbs togethei 320. Name the compounds of phosphorus with oxygen, and give the formulas? 321. Describe the oxyd, its formation and properties. How does heat affect it ? 322.* What of hypophosphorous acid ? 323. How is phosphorous acid formed ? What are its properties ? 212 NON-METALLIC ELEMENTS. with oxygen from the air, and gradually becomes phosphoric acid. Its solution is sour, and it forms well determined salts, (phosphites.) 324. Phosphoric acid is formed when phosphorus is burned in a copious supply of dry air, as in the experiment for obtaining nitrogen, (300,) or that of phosphorus in dry oxygen, (319.) When wanted in large quantity, it is prepared from the ashes of bones treated with sulphuric acid, as already described. This solution is first freed from lime and magne- sia, and is then evaporated to dryncss and ignited, when the sulphuric acid is driven off and phosphoric acid remains behind melted, and solidifies on cooling into a colorless glass, which is then called glacial phosphoric acid. Phosphoric acid is also formed by the action of very strong nitric acid on phosphorus ; but the operation is a dangerous one, and should be attempted only on very small quantities of phosphorus, and with extreme caution. 325. Phosphoric acid is a powerful acid, having an in- tensely sour taste, and all the attributes belonging to an acid. It has, when dry, a very strong affinity for water, and unites with it almost explosively, forming, according to circum- stances, three distinct compounds, or phosphates of water, whose constitution is as follows : Monobasic phosphate of water, or metaphosphoric acid, HO-f-PQv Bibasic phosphate of water, or pyrophosphoric acid, 2HO-f-P0 5 . Tribasic phosphate of water, or common phosphoric acid, 3HO + P0 5 . Each of these three phosphates of water is the source of a distinct series of salts with bases. The class of salts most generally known is that formed from the last phosphate of water, or the tribasic phosphates. The reader can consult Dr. Graham's Elements of Chemistry for a fuller account of this subject, which our limits prevent our giving in more detail. 2. Compounds of Phosphorus, with Members of the II. Class. 326. (1.) Chlorids of Phosphorus. Of these there are two, the perchlorid, (PC1 5 ,) and sesquichlorid, (PCI 3 .) The 324. How is phosphoric acid formed? How from bones? 325. Describe its properties. How does water affect it ? Give its com- pounds with water. Which is common phosphoric acid ? PHOSPHORUS. 213 first is formed when phosphorus is introduced into a jar of dry chlorine, where it inflames and lines the sides of the vessel with a white matter, which is the perchlorid of phos- phorus. This compound is.very unstable, and when put in water both it and the water suffer decomposition, and hydro- chloric and phosphoric acids result. 327. (2.) Bromids of Phosphorus. Two of these com- pounds are also known, and are easily formed by mingling small quantities of the elements in a flask filled with dry carbonic acid gas ; they immediately react on each other, evolving heat and light, and form the protobromid of phospho- rus, (PBr 3 ,) which is a brown fluid, easily decomposed by water ; and the perbomid of phosphorus, (PBr 5 ,) which is a volatile yellowish white solid, that sublimes on the sides of the flask and is easily fused by gentle heat into a red fluid. It is decomposed by water into phosphoric and hydrobromic acids. 328. (3.) lodids of Phosphorus. These elements com- bine in three proportions, forming protiodid of phosphorus, (PI,) sesquiodid of phosphorus (PI 3) ) and the periodid of phosphorus, (PI 5 .) The union of these elements is accom- plished with energy by simple contact in a dry state. Their compounds are not important. 329. (4.) Sulphuret of Phosphorus. Sulphur unites with phosphorus with prodigious violence, frequently with a dangerous explosion, and more than 30 or 40 grains of the latter cannot be safely put with the sulphur. Seleniuret of phosphorus is formed in the same manner as the last, and is similar to it in all its properties. CLASS V. THE CARBON GROUP. 11. CARBON. Equivalent, 6. Symbol, C. Specific gravity in vapor, Q'4t2l. Solid in the diamond, 3-52. 330. History. Charcoal and mineral coal, which are the two common forms of carbon, have been known from 326. Name the chlorids of phosphorus. 327. How many bromids of phosphorus are there ? How are they formed ? 328. How many iodids of phosphorus, and how formed ? 329. What is said of the union of sulphur and phosphorus ? What of its seleniuret ? 214. NON-METALLIC ELEMENTS. the remotest times of history. Its great importance in the daily wants of society, makes it one of the most interesting of the elementary bodies, and our interest in it is not dimin- ished from the fact that the charcoal and mineral coal which we use as fuel, and the black lead of our pencils, are essentially the same thing with that rare and costly gem, the diamond. The three distinct and very dissimilar forms of existence which this element assumes, give us one of the best examples known of the allotropism (264) of bodies. We will very briefly mention the principal characters of the three forms of carbon (1,) the diamond, (2,) graphite or plumbago, (4,) mineral coal and charcoal. 331. The diamond is pure carbon crystallized. It takes the forms of the regular system, or first crystalline class, (220,) of which the annexed figures are some of its common modifications. Its crystalline faces are often curved, as in the second figure. The diamond is the hardest of all known substances, and can be scratched or cut only by its own dust. The solid angles of this mineral, formed by the union of curved planes, are much used, when properly set, for cutting glass, which is done with great ease and precision. It has a specific gravity of 3-52, and the highest value of any kind of treasure. The most esteemed diamonds are colorless, and of an inde- scribable brilliancy ; this gem has also a peculiar lustre known as the * adamantine lustre.' They are often slightly colored, of a yellowish, rose, blue, or green, and even black tint. The largest known diamond belongs to the Great Mogul, and when found weighed 2769-3 grains, or nearly six ounces : it has the form and size of half a hen's egg. The most highly valued diamond in the world is called the Pitt diamond, and was sold to the Duke of Orleans for 130,000. It weighs less than an ounce. This was the gem which Napoleon mounted in 330. Give the equivalent and density of carbon. What is here said of carbon ? What three forms of carbon are named ? 331. What is the diamond? What forms does it occur under ? Describe it as noticed in the text. What is the native source of the diamond ? CARBON. 215 the hilt of his Sword of State. The diamond is usually found in the loose sands of rivers, and is generally accompanied by gold and platinum. Its native rock is supposed to be a pecu- liar flexible kind of sandstone, called itacolumite ; and it is sometimes found loosely imbedded in a ferruginous conglo- merate in Brazil. A few diamonds have been found in the United States. 332. From its high refractive power (56) the diamond is supposed to be of vegetable origin. The sun's light seems to be absorbed by the diamond, for it phosphoresces most beautifully for some time in a dark place, after it has been exposed to the sun. It is a non-conductor of heat and elec- tricity, and is very unalterable by any chemical means. It is infusible, and not attacked by acids or alkalies. But heated to redness in the air, it is totally consumed, and the sole product of its combustion is carbonic acid gas, which alone is sufficient proof that diamond is pure carbon. 333. (2.) Graphite or Plumbago. This form of carbon is sometimes improperly called " black lead" but it does not contain a trace of lead in its composition, and bears no re- semblance to it, except that both have been used to mark upon paper. This peculiar mineral is found in the most ancient rocks, as well as with those of a more modern era. It is also fre- quently found in company with coal, and is sometimes formed artificially, as in the fusion of cast iron. It almost always contains a trace, and sometimes several per cent, of iron, which is however foreign to it; otherwise it is pure carbon. It is very much used for making pencils, and the coarser sorts are manufactured into very useful and refractory melt- ing pots. The most valued plumbago for the finest drawing pencils, has been brought chiefly from the Borrowdale mine in Cumberland, England ; but it is a common mineral in this country, as, for instance, at Sturbridge in Massachusetts, and many other places. It is sometimes found crystallized in flat six-sided prisms, a form altogether incompatible with that of the diamond. It is soft, flexible, and easily cut ; feels greasy 332. What origin has the diamond been supposed to have, and why ? What are its relations to heat, light, and electricity ? How affected by chemical means? What does affect it? 333. What is plumbago ? How found ? What use is made of it ? How does it crystallize ? What are its physical properties? How does intense heat affect it ? 16 NON-METALLIC ELEMENTS. and marks paper. It is quite incombustible by all ordinary means, but burns in oxygen gas, forming only carbonic acid gas, and leaving a red ash of oxyd of iron. 334. (3.) Coal. The vast beds of mineral carbon, known to us as anthracite, bituminous coal, brown coal, and lignite, are all of them nearly pure carbon. Of the first two of these, no country has such abundant and excellent supplies as the United States. These accumulations of fuel are the remains of the ancient vegetation of the planet, which, long anterior to the creation of man, a bountiful Pro- vidence laid away in the bowels of the earth for his future use. Bituminous coal differs from anthra'cite only in having a quantity of bituminous matter united with it, which in the anthracite has been driven off by heat and pressure. 335. Charcoal from wood is the carbonized skeleton of the woody fibre which is found in all plants. The best charcoal is made by heating sticks of wood in tight iron vessels, without contact of air, until all gases and vapors cease to be given off. A great quantity of acetic acid, tar, and oily matters, with water, are given out, and a jetty black, brittle, hard charcoal is left behind, which is a perfect copy of the form of the origin.il wood. It is a non-conductor of heat, but conducts electricity almost as well as a metal. It is a very unchangeable substance, insoluble in water, acids, or alkalies, suffers little change from long exposure to air and moisture, and does not yield to the most intense heat to which it can be subjected. 336. Charcoal has the property of absorbing gases to a most remarkable degree, at common temperatures. A frag- ment of recently heated charcoal, of a convenient size to be introduced under a small air-jar over the mercurial cistern, will soon take up many times its own volume of air, as will appear by the rise of the mercury in the air-jar. In this case it absorbs more oxygen than nitrogen, the residual air having only eight per cent, of oxygen in it. On heating, it again parts with the gas it has absorbed. The power of absorption seems to depend entirely on the natural elasticity of the gas, and not at all on its affinity for carbon. Those 334. What is coal ? How does anthracite differ from bituminous coal ? 335. What is charcoal ? How is the best made ? What are its powers of ronduction ? Is it a changeable substance ? 336. What is said of its power of absorbing gases ? What gases are most absorbed by it ? CARBON. 217 gases that are most easily reduced to a fluid condition by cold and pressure, are most abundantly absorbed by charcoal. Charcoal from hard wood with fine pores has this property in the highest degree. Thus charcoal from box-wood freshly prepared, will absorb of ammoniacal gas 90 times its own volume ; of muriatic acid gas 85 times ; of sulphureted hy- drogen 81 times ; of nitrous oxyd 40 times ; of carbonic acid 32 times ; of oxygen 9*25 times ; of nitrogen 1*5 times ; and of hydrogen 1'75 times its own volume. 337. Charcoal also has the power of absorbing the bad odors and coloring principles of most animal and vegetable substances. Tainted meat is made sweet by burying it in powdered charcoal, and foul water is purified by being strain- ed through it. The highly colored sugar syrups are com- pletely decolorized by being passed through sacks of animal charcoal, (bone black,) prepared by igniting bones. It also precipitates bitter principles, resins, and astringent substances from solution. Common ale or porter becomes not only colorless, but also in a good degree deprived of its bitter principles, by being heated with and filtered through animal charcoal. This property is lost by use, and regained by heating it afresh. Its power of absorption seems similar to that possessed by spongy platinum, (212.) Hydrogen, in small quantity, is very obstinately retained in the pores of charcoal, and water is consequently always produced from the combustion of carbon in pure oxygen gas. Carbon has a greater affinity for oxygen at high temperatures than any other known substance, and for this reason it is useful in reducing oxyds of iron and other oxyds to the metallic state. 1. Compounds of Carbon with Oxygen. 338. Carbon unites with oxygen in two proportions, to form carbonic oxyd and carbonic acid, whose composition is thus expressed : Composition by weight. Symbol. Carbon. Oxygen. Carbonic oxyd, CO 6 8 Carbonic acid, C0 2 6 16 What rule regulates this ? Mention some instances of the amount of absorption. 337. How does it affect bad odors and vegetable colors ? What else does it also remove ? To what is this analogous ? What is said of its affinity for oxygen ? 338. Name the compounds of carbon with oxygen and their composition. 19 218 NON-METALLIC ELEMENTS. 339. Carbonic Acid. (CO 2 .) History. This is the sole product of the combustion of the diamond or any pure car- bon in the air, or oxygen gas. It was first recognised and described by Dr. Black, in 1757, under the name of fxed air. This philosopher proved that limestone and magne- sian rocks contained a large quantity of this gas in a state of solid combination with the earths, and also that it was freely given out in the processes of fermentation, respiration, and combustion. 340. Preparation. Carbonic acid is easily procured by treating any carbonate with a dilute acid. Carbonate of lime, in the form of marble powder, is usually employed for this purpose ; it is put with a little water'into a wide-mouth- ed bottle, (ft,) (like that used in 308 ;) sulphuric or hydro- chloric acid is turn- ed in at the tube funnel, when the gas is set free with effer- vescence, and es- capes through the bent tube. If it is wished to have the gas dry, it is passed over dry chlorid of calcium in the hori- zontal tube t, which completely removes every trace of moisture from it. Its weight enables us to collect it in dry bottles (a) by displacement of air, as in the case of chlorine, (260.) No heat is required, and the acid is added in small successive portions, the gas being freely evol- ved at each addition. If the gas is not required dry, the long chlorid of calcium tube may be dispensed with. When ob- tained by the action of monohydrated nitric acid on carbonate of ammonia, the carbonic acid evolved retains a white cloudy appearance, even after passing through water, which renders it visible, a point of some importance in experiments with this gas. This gas can also be collected over the pneumatic trough, not being absorbed by water so rapidly but that it may be thus managed well enough for experimental purposes. 339. Give the history of carbonic acid. 310. How is it prepared ? Ho*v is it dried ? Ho\v may it be colbcted ? CARBON. 219 341. Properties. At the common temperature and pressure, carbonic acid is a colorless, transparent gas, with a pungent and rather pleasant taste and odor. At a tempe- rature of 32, and a pressure of 30 to 36 atmospheres, it is condensed into a clear limpid liquid, not as heavy as water, which freezes by its own evaporation into a white, snow-like substance. We have already described (137) the apparatus and process by which this interesting experiment is performed. Carbonic acid is about once and a half as heavy as common air, having a specific gravity of 1*524 ; and 100 cubic inches, therefore, weigh 47*26 grains. 342. Cold water recently boiled absorbs about its own volume of carbonic acid gas, but with pressure much more will be taken up, in quantity exactly proportioned to the pressure exerted. The solution has a pleasant acid taste, and temporarily reddens blue litmus paper. The ' soda water,' so much used as a beverage, is usually only water strongly impregnated with carbonic acid, the soda being generally omitted in its preparation. The effervescence of this, as well as of small beer and sparkling wines, is due to the escape of this gas. Natural waters have usually more or less of this gas dissolved in them ; and some mineral springs, like the Saratoga and Ballston springs, and the Seltzer water, are highly charged with carbonic acid. 343. Carbonic acid instantly extinguishes a burning taper lowered into it, even when mingled with twice or three times its bulk of air. Fresh lime-water agitated with this gas, rapidly absorbs it, becoming at the same time milky, from the production of the insoluble carbonate of lime. In this way the presence of carbonic acid is easily detected, and this gas distinguished from nitrogen. 344. Death follows the inspiration of carbonie acid, even when largely diluted with air. It kills by a specific poisonous influence on the system resembling some narcotics, and is unlike nitrogen (291) in this particular, which kills only by exclusion of air, as waiter drowns. Instances of death from sleeping in a close room where a charcoal fire is 341. What are the properties of carbonic acid ? At what tempe- rature and pressure does it solidify ? What is its gravity ? 342. How much of it does water absorb ? What is said of the solution ? Ts it found in natural waters ? 343. How does it affect combustion ? What test is there for it? 344. How does it affect life when breathed ? Is it poisonous ? 220 NON-METALLIC ELEMENTS. burning, and from descending into wells which contain car- bonic acid, are lamentably frequent. The latter accident may always be avoided by taking the obvious precaution to lower a burning candle into the well before going into it, when if the candle burns, all may be considered sale, but its being extinguished is certain evidence that the well is unsafe. Wells containing carbonic acid may often be freed from it by lowering a pan of recently heated charcoal into the well, which will soon absorb thirty-five times its bulk of this gas, (336,) thus removing the evil. 345. Numerous natural sources evolve large quantities of carbonic acid, particularly in volcanic districts. It abounds also, in common with gases to be mentioned hereafter, in coal mines; it is produced abundantly by those explosions, which are so often fatal in the mines, and kills by its poi- sonous influences those who may esoape the explosion. The Grotto del Cane, in Italy, (dog's grotto,) is a noted instance of the natural occurrence of this gas. It is always present in the air, (302,) being given off by the respiration of all animals, and besides the other sources already named, is an invariable product of all common cases of combustion. All the carbon which plants secrete in the process of their developemcnt, is derived either from the carbonic acid of the atmosphere, which they decompose by the aid of sun-light by their green leaves, retaining the carbon and returning the pure oxygen to the air; or it is absorbed by their rootlets and then decomposed by the sun's light at the surface of the leaf. 346. Carbonic acid is formed of equal volumes of its two constituent gases condensed into one. For this reason the air suffers no change of bulk from the enormous quan- tities of this gas which are hourly formed and decomposed on the earth. This acid unites with alkaline bases, forming an important class of salts, (the carbonates,) which are all decomposed by any stronger acid, with the escape of car- bonic acid. 347. Carbonic Oxyd, (CO.) Preparation. This gas is produced in several ways. (1.) By passing carbonic acid How may these accidents be avoided ? 345. What natural sources of it are named ? Is it in the air ? Whence do plants get their carbon ? 346. Give its composition by volume. What class of salts does it form ? 317. How is carbonic oxyd prepared ? First ? CARBON. . 221 over fragments of coal heated to redness in an iron tube, the oxygen gains another equivalent of carbon, and carbonic oxyd results. (2.) Oxalic acid, (C 2 O 3 ,HO-|-2HO,) when treated with five or six times its weight of strong sulphuric acid, is decomposed, the acid takes the water of the oxalic acid, and a gas escapes, which is formed of equal measures of carbonic acid and carbonic oxyd. C 2 O 3 yield CO and CO 2 . Carbonic acid is absorbed by standing over water, or by agitation of the gas with an alkali, and the carbonic oxyd is left pure. (3.) The best method is that recommended by Dr. Fownes, which is to mingle in a capacious retort eight or ten parts of sulphuric acid with one part of dry finely powdered yellow prussiate of potash. The salt is entirely decomposed by a gentle heat, yielding an abundant volume of pure carbonic oxyd. 348. Properties. This is a colorless, almost inodorous gas, burning with a beautiful pale blue flame, such as is often seen on a freshly fed coal fire. Its specific gravity is a little less than that of air, or *973 ; and 100 cubic rhches of it weigh 30-20 grains. It is not absorbed by water, does not render lime-water milky, and explodes feebly with oxygen. It is not irrespirable, but is even more poisonous than carbonic acid, producing a state of the system resembling profound apo- plexy. This gas is very largely produced in the process of reducing iron from its ore in the high furnace. Carbonic oxyd is formed of half a volume of oxygen and one volume of carbon, or two volumes of carbon and one of oxygen condensed into two volumes. 349. Carbonic oxyd combines with chlorine and some other elementary bodies, forming compounds in which it appears to act the part of an element. Its union with chlorine is pro- duced by the influence of light, nd the product is called phos- gene gas. This is a pungent, highly odorous, suffocating body, possessing acid properties, and decomposed by water. 2. Compounds of Carbon with the Chlorine Group. 350. The compounds of oxygen and carbon already mentioned are the most important which carbon forms with Second ? third ? Which mode is preferred ? 348. What are its properties ? What is its density ? How does it affect life ? In what art is it largely produced ? 349. What compound does it form with chlorine ? What is its name ? 19* 222 NON-METALLIC ELEMENTS. the first class of the non-metallic elements. But there are certain others which we will briefly mention. They are Composition by weight. Symbol. Chlorine. Carbon. Chlorid of carbon, CC1 35-41 6 Perchlorid of carbon, C 2 C1 3 106-23 12 Dichlorid of carbon, C 2 C1 35-41 12 Sulphur. Bisulphuret of carbon, 82 32-18 6 351. The chlorids of carbon are obtained from the action of chlorine on a peculiar body formerly called Dutch liquid,* produced from the union of chlorine, hydrogen, and carbon. We shall refer any further mention of these compounds to the organic chemistry. 352. Bisulphuret of carbon is produced by passing the vapor of sulphur over fragments of recently prepared char- coal, heated to redness in a porcelain tube, which is so inclined that the heavy volatile fluid may run down in vapor and be condensed in an ice-cold vessel filled with water. This product is redistilled, to purify it. 353. Properties. Bisulphuret of carbon, when pure, is a colorless liquid, but has usually a yellowish tint; its power of refracting light is very remarkable. It has a most dis- gusting odor, and boils at 110. Its density is 1'27, and in vapor 2-68. It dissolves sulphur, phosphorus, and iodine, these bodies being deposited again in beautiful crystals by the evaporation of the sulphuret of carbon. It burns in the air at about 600, with a pale blue flame. It forms an ex- plosive mixture with oxygen, and a combustible one with binoxyd of nitrogen. It dissolves easily in alcohol and ether, and is precipitated again by water. 3. Compounds of Carbon with Nitrogen. 354. Carbon forms an unimportant compound with phos- phorus, but with nitrogen it unites to form one of the most remarkable compound bodies known to chemists. This is 350. What other compounds are named of carbon with oxygen ? 351. What are the chlorids of carbon ? 352. How is the bisulphuret of carbon prepared ? 353. What are its properties ? What does it dissolve ? In what is it soluble ? 351. What is cyanogen ? * From its being discovered at Harlem, in Holland, by an asso- ciation of Dutch chprrmts. SILICON. 223 called cynanogen, and is composed of one equivalent of nitro- gen and two of carbon, or NC 2 . Although a compound, it acts in all respects like an element, entering into combina- tion with the same energy with which elements unite. Its production and properties are referred to the organic chem- istry, where it can be better understood. 12. SILICON. Equivalent, 22-18. Symbol, Si. Density in vapor, (hypo- thetical,) 15-29. 355. Common quartz, or rock crystal and gun-jlint, are very familiar substances ; these are the compound of sili- con and oxygen, known as silica, or silicic acid. Silicon is, however, a substance very rarely seen, even by chemists, because it never occurs in nature, and is very difficult to prepare. Silica, its compound with oxygen, is, next to oxygen, the most abundant, and one of the most important substances known. It is calculated that it forms one-sixth part of the crust of the globe. 356. Preparation of Silicon. Silica retains its oxygen so powerfully that it is very difficult to separate it and leave the pure silicon. Silicon may be procured, however, by an indirect process, which is to decompose the double fluorid of silicon and potassium, (2SiF 3 -f 3KF.) This is a white powder, like starch, and very sparingly soluble in water. To decompose this, it is mixed with about its own weight of the metal potassium cut in small pieces, and put in a test tube of hard glass, which is then heated over a lamp. As soon as the tube is heated on the bottom to redness, a vivid ignition is seen to take place, and to spread through the whole mass. The residue after this ignition, when cool, is treated with water, which dissolves all the fluo- rid of potassium that has been formed in the process, leaving behind the silicon. Thus the ('2SiF 3 + 3KF) acted on by 6K give 9KF and 2Si. How does it act ? Where do we consider it ? 355. Of what is silicon the basis ? Is it a natural substance ? How abundant is silica? 356. How is silicon prepared ? Give the reaction. 224 NON-METALLIC ELEMENTS. 357. Properties. Silicon is a dark nut-brown powder, without metallic lustre, and a non-conductor of electricity. Heated in air or oxygen it burns, forming silica. If heated in a close vessel, it shrinks and becomes more dense. Be- fore ignition it is soluble in hydrofluoric acid, but after this it is insoluble, and is incombustible in the air or oxygen gas. It seems then to resemble the graphite variety of carbon. These two diverse conditions of silicon are probably con- nected with the two states in which silica occurs. This element has been often called a metal, and. named accordingly silicium ; but if power to conduct electricity, and the posses- sion of a metallic lustre, are attributes of a metal, silicon has no claim to be so classed. Its real affinities are more with carbon. Compounds of Silicon. 358. The known compounds of silicon are not numerous; those mentioned in this section are Composition. Symbol. Silicon. Oxygen. Silicic acid, (silica,) SiO 3 22-18 24 Chlorine. Chlorid of silicon, SiCl 3 22-18 106-23 Bromine. Bromid of silicon, SiBr 22-18 234-78 Fluorid of silicon, SiF 3 22-18 56-10 ' Sulphur. Sulphuret of silicon, SiS 3 (probably) 22-18 66-27 The similarity of composition in these bodies is a remark- able circumstance, as will be seen at a glance by inspecting their formulas. 359. Silicic acid or Silica, (SiO 3 .) This oxyd of sili- con exists abundantly in nature in the form of rock crystal, agate, common uncrystallized quartz, silicious sand, &c. ; it also enters largely into combination with other substances to form the rock masses of the globe. It is a very hard sub- stance, easily scratching glass, and is difficult to reduce to a powder; its specific gravity is 2-66. It is infusibb alone, 357. What are its properties ? How does heat affect it ? What two states of it are noticed ? To what are these analogous ? Why not consider it a metal ? 358. What compounds of silicon are named ? 359. What is silicic acid ? Give its properties. SILICON. 225 except by the power of the compound blowpipe. It dissolves with effervescence in fused carbonate of 'soda or potash ; the effervescence being due to the escape of carbonic acid from the alkali, which is replaced by the silicic acid. No acid (except the hydrofluoric) has any effect on silica. When in its finest state of division it is still harsh and gritty to the touch or between the teeth. 360. Silica is known in two very unlike conditions its insoluble or common condition, and its soluble or hydrous state. When silica is dissolved in a fused alkali, and then again this silicated alkali in a strong acid, as the hydrochloric, we obtain on evaporating the solution to a small bulk, a trem- ulous gelatinous mass, which is soluble silica. If an excess of alkali is used, the silicate formed is soluble in water, and is sometimes called the liquor of flints. If this soluble silica is dried, it is again reduced to its insoluble condition. Most natural waters contain some small portion of soluble silica ; it has been often seen in this state in mines ; and on breaking open silicious pebbles, the central parts are sometimes semi- fluid and gelatinous. The hot waters of the great geysers in Iceland, and of other hot springs, also dissolve large quanti- ties of silica, probably aided by alkaline matter. Agates, chalcedony, cornelian, &c. have been deposited from the sol- uble state. It is in this condition, no doubt, that silica enters the substance of many vegetables, as, for instance, the reeds and grasses, which have often a thick crust of silica on their bark. It also produces most beautiful petrifactions of natu- ral objects, as corals, shells, arid many vegetables, completely replacing the organic matters, and turning them into solid quartz or elegant chalcedonies and agates. 361. The uses of silica in the arts are very important. It is the basis of all glass, being fused with alkalies to form this useful and beautiful substance, (see glass and pottery,) and also of porcelain and all kinds of potters' ware. In chemistry its uses are chiefly confined to certain analytical operations of no importance to our present object. 362. It is called an acid, from the power it has of acting the part of a powerful acid at high temperatures. At ordi- What dissolves it ? 360. What two unlike conditions of silica are named ? How is the soluble condition produced ? How do we find it in nature ? What function does it discharge ? 361. What are the uses of silica ? 362. Why is it called an acid ? 226 NON-METALLIC ELEMENTS. nary temperatures its insolubility renders its acid properties insensible to all our usual tests lor acids. When by a suffi- cient temperature it is rendered soluble, we sec its acid char- acter very distinctly in the ease with which it completely saturates the most powerful alkalies. 363. Chlorid of silicon is formed by passing a current of dry chlorine gas over silicon heated to redness in a tube of porcelain or glass ; or, more simply, by employing, in place of silicon, the finely powdered silica, mixed with powdered charcoal in the same tube, and treated in the same manner. The carbon takes the oxygen of the silica at the high temper- ature, and the chlorine unites with the silicon to form a very volatile chlorid of silicon, which is condensed in a cold receiver, while the excess of chlorine, and the carbonic oxyd formed in the process, escape as gases. The chlorid of sili- con is a colorless liquid, denser than water, and boils at 124. Water decomposes it, forming hydrochloric acid and silica. There is a bromid of silicon possessing the same properties and formed in an exactly similar manner. 364. Fluorid of silicon, (fluosilicic acid.) The affinity existing between fluorine and silicon is one of the strongest known to chemists. We have already mentioned this while speaking (280) of fluorine. Fluorid of silicon may be pro- cured by heating a mixture of powdered flour-spar and quartz with strong oil of vitriol : Fluor-spar. Silica. Sul. arid. Sul. lime. Water. Fluorid silicon. 3CaF -f SiO3 -f 3(SO3,HO) = 3(CaO, SO 3 ) + 3HO + SiF 3 . Being rapidly absorbed by water, it must be collected over mercury. It forms dense white vapors with the moisture of the air, as soon as it comes in contact with it. 365. Properties. This is a dense, colorless gas, having a specific gravity of about 3-60, air being 1 : it has lately been rendered fluid by Dr. Faraday, with a cold of 160 be- low zero, and a pressure of about nine atmospheres. When this gas is passed into a vessel of water, it is decomposed, each bubble becomes incrusted in a shell or sack of pure silica, and retains its form more or less as it rises through Why are its acid properties concealed ? 363. How is chlorid of silicon formed ? What are its properties ? 364. How is fluorid of silicon formed ? Give the reaction on the black-board. Is it ab- sorbed ? 36/5. Give its properties. How does it behave in contact with water ? BORON. 227 the water, which soon becomes milky, from the quantity of finely divided silica suspended in it. Meanwhile the water becomes a solution of hydrofluosilicic acid, 2(SiF 3 ) -f- 3HF, which is formed from the decomposition of one-third of the fiuorid of silicon, giving silica and hydrofluoric acid, which last unites with the remaining fluorid of silicon, and dissolves in water. The fluosilicic acid gas should not be passed directly into water, but the tube should dip under the surface of a portion of mercury in the bottom of the bottle holding the water ; if this precaution is neglected, the open end of the tube soon becomes plugged up with silica, and the gas bottle may burst. This acid solution is decomposed by heat. It forms almost insoluble salts (double fluorids) vfith the metals potassium and sodium, and hence is of value in separating these substances from their solutions. 366. Silicon, when heated with sulphur, unites with it, forming a sulphuret, which is a white earthy compound, (SiS 3 .) It is decomposed by water into silica and sulphureted hydrogen. 13. BORON. Equivalent, 10' 90. Symbol, B. Density in vapor, (hypo- thetical,) -751. 367. The only compound of boron commonly known is borax, a salt much used in the arts. Boracic acid (its compound with oxygen) is found in the waters of certain lagoons or lakes in Tuscany, from which large quantities of it are introduced to commerce. This acid, accompanied by sulphur and selenium, is also sublimed among the volcanic products of the volcanoes at the Lipari islands, and in other similar places. 368. Boron is prepared by a process very similar to that which produces silicon. The double fluorid of boron and potassium being treated with potassium in an iron vessel heated to redness, gives us KF, BF 3 + 3K=4KF + B. The boron remains as a dark olive-green powder, after the soluble fluorid has been dissolved out by water. Heated in What reaction takes place? What caution is required? 366. What is the sulphuret of silicon ? 367. Give the equivalent and symbol for boron. How is it found associated in nature ? 368. How is boron prepared ? 228 NON-METALLIC ELEMENTS. air to about 600, it burns brilliantly, producing boracic acid. It does not conduct electricity, is insoluble in water and all other neutral fluids. Heated out of contact with air, it suf- fers no change. It is easy to see how similar these charac- ters are to those possessed by carbon and silicon. Compounds of Boron. 369. The compounds of boron mentioned under this head are Composition by weight. Symbol. Boron. Oxygen. BoAcic acid, B0 3 10-90 24 Chlorine. Chlorid of boron, BC1 3 10-90 106-23 Fluorine. Fluorid of boron, BF1 3 10-90 56-10 Sulphur. Sulphuret of boron, 683 10-90 48-27 370. Boracic acid, as just mentioned, is found native, and is also produced, when boron is burnt in oxygen or common air. It is easily prepared by decomposing common borax (borate of soda) dissolved in about 4 parts of hot water, with one-third its weight of sulphuric acid. Sulphate of soda is formed and boracic acid set free, which, being nearly insolu- ble in cold water, is deposited in pearly scales as the solution cools. When quite cold, the supernatant fluid is poured off, and the white scales washed with cold water. This is a hydrate of boracic acid, BO 3 + 3HO. Half this water of crystallization is expelled at 212 ; when it melts into a fusible glass, which is brittle and clear when cold. Boracic acid is little soluble in cold, but readily in hot water ; and its watery solution cannot be evaporated without the steam carrying away a large portion of the acid. The glassy acid is, however, quite fixed, even at a red heat. Alcohol dis- solves boracic acid, and the solution burns with a peculiar and quile characteristic green color. Its acid powers are feeble ; its salts (borates) being all decomposed even by weak acids. It turns blue litmus to a port-wine color, but What are its properties ? To what is it likened? 369. Name the compounds of boron in this section. 370. How is boracic acid formed ? What are its properties ? What is the glacial acid ? Can the watery solution be evaporated ? What is its proper solvent ? What characteristic property has it '( What of its acid characters ? HYDROGEN. 229 does not redden it, and affects yellow turmeric paper like an alkali, turning it brown. 371. It is used in the arts to promote the fusion of other bodies, which it does in a remarkable degree, by the fusi- bility of all its salts. It is also much used as a flux in blow- pipe operations and in the laboratory. 372. Chlorid of boron is formed in the same manner as the chlorid of silicon, boracic acid being used in place of silica. It is a dense, colorless, transparent gas at ordinary temperatures, having a specific gravity of 4-09 ; and by cold and pressure it may be reduced to a fluid. It has a pungent, acid smell, and forms thick vapors in the air. It is absorbed by water, and is collected over mercury. 373. Fluorid of boron. The same process by which fluorid of silicon is prepared yields fluorid of boron, by sub- stituting boracic for silicic acid. The gas is similar, and has a density of 2'362, and an avidity for water which causes it to form dense fumes in the air. It is decomposed by water, hydrofluoboric acid being formed, which is per- fectly analogous to hydrofluosilicic acid. 374. The sulphuret of boron is a white powder formed from the combustion of boron in the vapor of sulphur, and is quite similar to the sulphuret of silicon. It is decomposed by water, boracic acid and sulphureted hydrogen being formed. CLASS VI. HYDROGEN. Equivalent, I. Symbol, H. Density, 0-069. 375. History. Hydrogen was first described as a dis- tinct gas by the English chemist Cavendish, in 1766, and was called by him inflammable air. It had previously been confounded with other combustible gases, several of which had been long known. Hydrogen exists abundantly in nature as a constituent of water, whence its name, (193.) It is also a constituent of nearly all animal and vegetable 371. Of what use is boracic acid ? 372. What is said of the chlorid of boron ? 373. What of the fluorid ? To what are it and the chlorid similar ? 374. What of the sulphuret of boron ? 375. Give the equivalent, symbol, and density of hydrogen. When and by whom was hydrogen discovered ? In what manner does it exist in nature > 20 230 NON-METALLIC ELEMENTS. substances, in which it exists in such proportions to oxygen as to form water during the combustion of these bodies." 376. Preparation. This gas is best prepared for use by the action of dilute sulphuric acid on zinc or iron. Zinc is usually preferred as yielding a purer gas. The acid is diluted with four or five times its bulk of water, and the operation may be conducted in a glass retort, or more conveniently in the small way by using a gas bottle (a) con- taining the zinc in small fragments, to which the dilute acid is turned through the tube funnel, (b.) The shorter tube (f) with a flexible joint conveys the gas to the air-jar, (e,) standing in the cistern, (g.) No heat is required in this operation. An ounce of zinc yields 615 cubic inches of hydrogen gas. When it is required in large quantity, a leaden pot or stone jar, properly fitted, and holding a gallon or more, is used to contain the requisite charge of materials, and the gas is stored for use in a gas-holder such as has already been described and figured, ( 258. ) Zinc is readily granulated, by being turned when melted, into cold water. 377. Properties. Hydrogen when pure is a clear color- less gas, which no amount of cold and pressure yet obtained, has reduced to a liquid form. It refracts light very power- fully, and has the highest capacity for heat of any known gas. It is inodorous and tasteless, and may be breathed without inconvenience when mingled with a large quantity of common air. It cannot, however, support respiration alone, and an animal plunged in it soon dies of suffocation. Water 376. How is it prepared ? Describe the process. 377. Give the properties of hydrogen mentioned in this section. Is it poisonous ? HYDROGEN. 231 absorbs only about one and a half per cent, of its bulk of pure hydrogen gas. The voice of a person who has breathed it acquires for a time a peculiar shrill squeak. 378. Hydrogen is the lightest of all known forms of mat- ter, being sixteen times lighter than oxygen, and fourteen times and a half as light as common air. 100 cubic inches of it weigh only 2-14 grains. Soap-bubbles blown with it from a bladder rise rapidly in the air ; and it is usually em- ployed to fill balloons, being the lightest gas which can be pro- duced, and the cheapest, if we except common coal gas. A turkey's crop, well cleansed, makes a good balloon on a small scale, for the class-room, and very beautiful small balloons (from 1^ to 5 feet diameter) are prepared in Paris of gold- beaters' skin. Hydrogen is so named from the fact that it forms water by its union with oxygen. (Hudor, water, and gennao, to form.) 379. Hydrogen is the most attenuated form of matter with which we are acquainted. We have reason to suppose the molecules of this body to be smaller than those of any other now known to us. Dr. Faraday, in his attempts to liquefy this gas, found that it would leak and escape through an apparatus which was quite tight to other gases. Thus hydrogen leaked freely with a pressure of 27 or 28 atmospheres, through stop-cocks that were perfectly tight with nitrogen at 50 or 60 atmos- pheres. This extreme tenuity, together with the remarkable law of diffusion of gases already explained, (132,) renders it unsafe to keep this gas in any but perfectly tight vessels. A small crack in a bell jar, quite too narrow to leak with water, will soon render the hydrogen with which it may be filled explosive. The superiority in diffusive power which hydrogen has over com- mon air, is well seen in what is called Mr. Gra- ham's diffusion tube, of which a figure is annexed. A glass tube 11 or 12 inches long and of convenient size, has a tight plug of dry plaster of Paris at the upper end, and How does it affect the voice ? 378. What is said of its density ? What do 100 cubic inches weigh ? For what purpose is it used ? Give the meaning of the word hydrogen. 379. What is said of the molecules of hydrogen ? What was the result of Dr. Faraday's experiments on it ? How is its tenuity evident from the law of diffusion ? Explain the diffusion tube. 232 NON-METALLIC ELEMENTS. being filled with dry hydrogen by displacement of air, and its lower end put into a glass of water, the hydrogen escapes so rapidly through the plaster plug, that the water is seen to rise in the tube, so as in a few moments to replace nearly all the hydrogen, and the remaining portion of gas is found to be explosive. Hydrogen also enters into combination in a smaller proportionate weight than any known body, (188,) and con- sequently has been chosen as the unit of the scale of equiva- lents. Sounds are propagated in hydrogen with but little more power than in a vacuum. 380. Hydrogen is a most eminently combustible gas, taking fire from a lighted taper, which is instantly extin- guished by being plunged into the gas. It burns with a very faint light and a bluish white flame. Its extreme levity requires this experiment to be performed in an inverted ves- sel like the annexed figure. A dry bottle with its mouth downward is well suited to collect this gas by dis- placement of air, as the heavier gases are collected (260) by the reverse position. When lighted, the gas burns quietly at the mouth of the bottle ; and the extinguished taper may be relighted by the flame at the mouth. If the bottle is suddenly re- versed after the gas has burned awhile, the remain- ing gas being mixed with common air, will burn explosively with a single flash. Three of the most remarkable properties of hydrogen arc thus shown by one experiment, viz : its extreme levity, its combustibility, and its explosive union with oxygen. If this gas is incautiously mingled with common air, or much more with pure oxygen, a severe explosion results when the mixture is fired. The eyes or limbs of inex- perienced operators have thus too often paid the forfeit by the explosion of gas vessels. Particular caution is required not to collect any gas from the vessel in which it is generated until all the common air is expelled, as well from the genera- tor, as from the receiving-vessel or gas-holder. 381. Pure hydrogen is not yielded by the methods before Why was hydrogen chosen as the unit of the scale of equivalents ? How are sounds propagated by it? 380. What of the combustibility of hydrogen ? How does it burn ? What three remarkable proper- ties of hydrogen may be shown in one experiment, and how ? What caution is given about collecting gases ? 381. Why is hydrogen not pure when obtained by the mode described ? HYDROGEN. 233 described. The gas, when obtained from iron, has always a peculiar and offensive odor, due in a measure to the pre- sence of a volatile oil, formed by the gas with the carbon always found in iron. That yielded by the use of zinc is also somewhat impure, both having a portior of the metals dissolved in the gas, which tinge the flame. Traces of sulphureted hydrogen and car- bonic acid are akn usually found in hydrogen, being formed from the impurities in the metals by which the gas is evolved. Some of these impurities, and particularly the vapor of the acid, which is carried over mechanically, are removed by passing the gas through a second bottle containing an alkaline solution, in water or alcohol. It is generally advisable to pass gases through a portion of water or some other fluid which will remove from them their impurities. 382. Water is the sole product of the combustion of hydrogen in common air, or in oxygen gas. The combustion of a jet of hydrogen, and the production of water from this combus- tion, and certain musical tones, are all neatly shown by an arrangement like the annexed figure. The gas is generated in the bottle a, and a perforated cork at the mouth has a small glass tube, from the narrow end of which the stream of hydrogen is lighted. An open glass tube (&) held over this flame, is at once bedewed by the water produced in the combustion, and a musical tone is gene- rally given out, by the interruption which the flame suffers from the rapid current of air, ascending through the tube, which causes it to flicker, and being momentaril) extinguished, there occur a series of little explosions. The pitch of the note pro- With what is it contaminated ? How may it be purified ? 382. What is the product when hydrogen is burnt in air or oxygen ? De- scribe the philosopher's lamp and the musical tones with hydrogen. 20* 234 NON-METALLIC ELEiMENTS. duced depends on the length and size of the glass tube, and the size of the jet of hydrogen, which should be small. If the jet is fitted to the gas-holder, we can modulate the tone by turning the key of the stop-cock regulating the supply of gas. The little gas bottle (a) with a small jet is often called " the philosopher's lamp." 1. Nature of Hydrogen. 383. The real nature of Hydrogen was for a long time not well understood. It was associated, with oxygen and chlorine, because it was supposed to bear the same relations to hydrochloric acid that oxygen bears to sulphuric and chloric acids. Dr. Kane insisted on the highly electro-posi- tive nature of hydrogen ; and, to prove to the satisfaction of chemists that this gaseous body was in reality more nearly allied to iron, zinc, copper, and manganese, than to any other class of bodies, he showed that the compounds of hydro- gen with oxygen, chlorine, iodine, sulphur, &c., were almost universally electro-positive in combination, and possessed basic characters, derived from the pre-eminent electro-positive energies of hydrogen itself. It is now the belief of nearly all philosophical chemists, that hydrogen is most closely allied to the metals, particularly to zinc and copper ; that the chlorids, iodids and fluorids of hydrogen, although they pos- sess the characters which we assign to acids, resemble in many. respects the chlorids, iodids, &c., of the same metals; that in fact hydrogen is a metal, exceedingly volatile, proba- bly standing in that respect in the same relation to mercury that mercury does to platinum, but still possessed of all truly chemical peculiarities of the metallic state, and no more deprived of the common-place qualities of lustre, hardness, or brilliancy, than is the mercurial atmosphere which fills the apparently empty space in the barometer tube.* The vapor of mercury, and of other volatile metals, is like hydrogen a non-conductor of heat and electricity ; but we cannot on this account deny their metallic character. We must not forget that hydrogen may yet, by sufficient cold and pressure, bo 383. What is said of the nature of hydrogen? To what is it compared ? What is the present opinion of chemists about hydrogen ? What analogous cases have we in the volatile metals ? * Dr. Kane's Elements, page 409, English edition. HYDROGEN. 235 made solid or fluid, when doubtless we shall see its resem- blance in physical, as well as we now do in chemical charac- ters, to the metals. The propriety of giving hydrogen the place in our classification which it occupies, will now be more apparent to those who have usually seen it placed next to oxygen. 2. Compounds of Hydrogen with . Oxygen. 384. There are two known compounds of hydrogen with oxygen, viz : Composition by weight. Symbol. Hydrogen. Oxygen. Water, (the oxyd of hydrogen,) HO 1 Binoxyd of hydrogen, HOz 1 16 The first of these is the most remarkable compound known, whether we contemplate it in its purely chemical relations, or in reference to the wants of man and the present condition of the globe. 385. Water. The reader has already been made familiar with the composition of water, as formed by the union of two volumes of hydrogen and one of oxygen. Frequent mention has been made of it in the foregoing pages of this work, as an illustration of the principles of combination and decomposition. We cannot properly understand the produc- tion of hydrogen by any process, without studying at the same time the constitution of water. In examining the com- pounds of hydrogen and oxygen, as in all other chemical in- vestigations, we can pursue the subject either analytically or synthetically ; that is, we can either form the compounds by the direct union of the elements, or we can decompose these compounds, and thus gain a knowledge of their consti- tution. 386. The Decomposition of Water. The simplest case of the decomposition of water is that where metallic potas- sium is employed, which is directly oxydized by the water, hydrogen being evolved. The reaction is K-f HO KO-f H, which last is given off. 387. The voltaic decomposition of water has already been described, (235,) and we need not repeat it here. It 384. What are the compounds of hydrogen and oxygen ? Give their composition. 385. What is said of the constitution of water ? How can we proceed in studying the compounds of hydrogen and oxygen ? 386. What is the simplest case of the decomposition of water ? 236 NON-METALLIC ELEMENTS. is, however, by far the most satisfactory means of decom- position which we possess, since both elements of the water are evolved in a pure form and in exact atomic propor- tions. In fact this is a complete ex- perimentum crucis, being both analysis and synthesis ; for we may so arrange the single tube apparatus, that the mix- ed gases from the electrolysis of water may be fired by the ignition of the wires, as soon as a sufficient volume of the mixture has been collected. A com- plete absorption follows the explosion, and the gases again go on collecting. The oxygen which is dissolved in water from the air, always makes this experi- ment, when accurately performed, seem to show a very slight excess in the oxygen. 388. The decomposition of water by heat in the manner here figured is one of the best methods of analyzing water, both from its satisfactory results, and its cheapness and ease of accomplishment. An iron tube, (as a gun-barrel,) or a tube of porcelain, c, is laid horizontally over a fire, or heated in a furnace to full redness. The tube con- tains clean turnings of iron, or better, a bundle of clean iron wire of known weight. A small retort (a) holding a little water is boiled by a spirit lamp at the moment when the iron is at a full red heat ; the vapor of the water coming into contact with the heated iron, is decomposed, the oxygen is retained by the iron, forming oxyd of iron, and the hydro- gen is given off from the tube,y, which may be made to con- duct it, either to the pneumatic trough, or to a gas-holder like the one already figured, (258.) For every eight grains of weight acquired by the iron, 46 cubic inches of hydrogen, weighing one grain, have been evolved. 387. What is the voltaic mode of decomposition ? 388. Describe the method of decomposing water by heat. What is the reaction in this case ? How much hydrogen do we get for eight grains of gain in the iron ? HYDROGEN. 237 389. The iron in this case is evidently substituted for the hydrogen, taking its place with the oxygen to form the oxyd of iron, while the hydrogen is set free. The oxyd of iron resulting from this action is the same black oxyd which the smith strikes off in scales under the hammer, being a mixture of protoxyd and peroxyd. This case of affinity is an interesting one, because it is seemingly reversed when, under the same circumstances, we pass a stream of hydro- gen over oxyd of iron, by means of which the iron is reduced to the metallic state, and water is produced. It will be remembered that we cited this instance, (211,) while speaking of the influence of quantity of matter in determin- ing the nature of the chemical changes which might take place among bodies. 390. The decomposition of water by zinc or iron in the ordinary mode of procuring hydrogen can now be satisfac- torily explained. As already stated, dilute sulphuric acid is added to fragments of zinc, or to iron filings, and hydrogen gas is given off abundantly with effervescence. The action continues until either the zinc or acid is all consumed, or until there is no longer water enough to dissolve the resulting sulphate of zinc. Thus we take Zn + SO 3 +HO, and we obtain H+(SO 3 + ZnO.) In other words, the zinc has taken the place before occupied by hydrogen, while the oxygen of that atom of water has united with the zinc, to form oxyd of zinc. * The acid dis- solves this oxyd as fast as it is formed, thus making a con- stantly renewed surface of clean metal. The water serves to dissolve the sulphate of zinc as fast as it is formed. Zinc 389. What is the action of the iron in this case ? What oxyd is formed ? 390. How is the decomposition of water by zinc explained ? Give the reaction. How is it in case we employ hydrochloric acid ? (Note.) What does the acid do, and what the water ? How do the electrical relations affect this change ? *We can state this reaction in much more simple terms, by em- ploying hydrochloric acid in place of sulphuric acid : we have then Hydrochloric acid-}- zinc. Hydrogen -fchlorid of zinc. HCl-fZn and obtain H + ZnCl. In this case there is no oxydation, for the same change is made when dry hydrochloric acid is used, and consequently no compound con- taining oxygen is present. 238 NON-METALLIC ELEMENTS. and iron decompose water even without the aid of an acid, but only with great slowness, and the action ceases as soon as the metal is covered by the coating of the oxyd thus formed, which protects it from further corrosion. A dilute acid removes this coating of oxyd, and also aids, no doubt, in establishing such electrical relations as to make the zinc highly electro-positive. That this is the fact, seems quite pro- bable, because pure zinc is hardly affected by dilute acids, and we have already noticed the effects of amalgamation (161, note) in rendering the zinc incapable of decomposing water. 391. It was formerly said that the presence of an acid in water with zinc disposed the zinc to decompose the water, because the acid was ready to take up the oxyd as soon as formed. This was called a case of disposing affinity. But there can be no oxyd of zinc to exert this influence on the acid, until the water is decomposed ; so that the idea that the acid disposed the zinc to decompose the water is quite futile. We find a much simpler and more probable explanation in the foregoing section. 392. The recompo&ition or formation of water from its elements may be effected in a variety of ways. A mixture of oxygen and hydrogen gases will never unite under ordi- nary circumstances of temperature, &c. ; but the passage of an electric spark through them, or the application of red-hot flame, or intensely heated wire, will produce an explosive union, destructive to the containing vessel, unless the gas is in extremely small quantities. If this mixture is made in exact atomic proportions, and the gases are pure, the result of the explosion will be a com- plete condensation ; but usually one of the gases is in slight excess. 393. This explosion may be safely made in a tube of very strong glass, holding only one or two cubic inches of the mixed gases. This tube is usually graduated into parts of a cubic inch, and is fitted with two wires for the passage of the spark, which come near to each other, but do not touch. A gas pistol of metal, (a,) like the figure, gives a perfectly safe method of performing this experiment, being 391. What is said of disposing affinity ? 392. How is the recom- position of water effected ? COMPOUNDS OF HYDROGEN. 239 filled with the mixed gases and stopped with a cork, (o ;) a smart explosion follows the passage of the spark, and the cork is forcibly driven out by the expansion of the uniting gases, accompanied by flame. A bladder filled with the mixed gases in atomic proportions, will be blown into shreds with a deafening explosion, by the application of a match to a pin-hole made in its side. Soap- bubbles filled from a bag of the explosive mixture will, from their lightness, rise rapidly, and may be exploded by a match or candle. In all these cases the sole result is the production of water ; but, being in the form of vapor, it escapes unseen. 394. The formation of water may be proved by burning a jet of hydrogen in a dry vessel of oxygen, or even of com- mon air. For this purpose the jet of the compound blow- pipe is introduced into a large dry globe of glass, and the supply of the two gases regulated by the stop-cocks. The interior of the globe is immediately bedewed with the vapor of water produced in the combustion, which rapidly collects in drops on the sides of the vessel, and runs down to the bottom. No question in science has excited more inquiry and research, than the constitution of water. Re- peated trials, both analytical and synthetical, often on a most liberal scale and long continued, have been made to prove it ; and the uniform result of the best experiments has been, that 8 parts by weight of oxygen require 1 part by weight of hydrogen to form 9 parts of water, and that 2 volumes of hydrogen saturate 1 volume of oxygen. 395. Hydrogen is frequently employed in eudiometry, or in the analysis of gases. For this purpose a known volume of hydrogen is mingled with a given amount of the gas to be analyzed, and the mixture is exploded by electricity in a graduated tube of glass, or some other similar form of apparatus. The figure of a very good form of eudiometer invented by Dr. Ure, is here annexed. It is a U tube of stout glass ten or twelve inches long, the shorter limb of which is closed, and graduated into decimals of a cubic inch. 393. How may this conveniently be done ? Name some other similar experiments. 394. How is the water produced in these ex- periments made manifest ? Describe the experiment. 395. How is hydrogen used in eudiometry ? 240 NON-METALLIC ELEMENTS. Two wires of platinum, for the passage of the spark, arc fused into the glass near the top. When it is to be used, it is filled with dry mercury, by placing it horizon- \ N tally in the mercury trough, and a conve- nient portion of the mixture of the gas to be examined with hydrogen is then intro- duced. The thumb is placed over the open end, and by adroit management all the mixture is transferred to the closed end of the tube, and by forcing out a portion with a rod, thrust into the open end, the mercury is made to stand at the same level in both limbs. These adjust- ments being made, the whole bulk of the mixture is read on the graduation, and while the thumb is firmly held over the open end of the tube, an electrical spark is made to explode the gases. The air between the thumb and the mercury acts like a spring to break the force of the explosion ; and afterwards, on removing the thumb, the weight of the atmosphere forces the mercury into the shorter leg, to supply the partial vacuum occasioned by the union of the gases. Proper allowances being made for tem- perature and pressure, the quantity of residual gas is read on the graduation, and a calculation can then be made of the amount of oxygen present. If the gas contains carbon, carbonic acid would be formed, and must be absorbed by an alkali. 396. The union of oxygen and hydrogen can however be effected slowly and quietly without any explosion, or visible combustion. This may be done by passing the mixed gases through a tube heated below redness, when combination takes place, without explosion. This result is accomplished at a still lower temperature, if the tube contains coarsely pow- dered glass or sand. We see in this case the operation of that remarkably power of surface (212) once or twice alluded to before ; and we will now mention a still more remarkable instance of the same action. 397. Power of platinum in promoting the union of Oxy- Describe lire's eudiometer. How is it used ? 396. How is the quiet union of hydrogen and oxygen accomplished ? 397. How does platinum produce this result ? COMPOUNDS OF HYDROGEN. 24-1 gen and Hydrogen. Professor Dobereiner of Jena, many years ago, (in 1824,) observed that platinum in the state of fine division, known as spongy platinum, would cause an immediate union of these gases. The common instrument employed for lighting tapers is made by taking advantage of this principle. A little spongy pla- tinum is formed into a ball, like the annexed figure, and mounted on a ring of wire which slips within the cup (d) on the top of gas-holder, (a, second fig.) The gas is generated by the action of dilute acid in the outer vessel (a) on a lump of zinc (z) hang- ing in the inner vessel, (jf,) and is let out at pleasure by the cock, (c,) issuing in a stream on the spongy platinum. The latter is at once heated to redness by the stream of hy- drogen, which is condensed within its pores to such a degree that it combines with a portion of oxygen, always present in the sponge by atmospheric absorption. The union of these gases is always attended by intense heat, and, as a consequence, the platinum at once ^o\vs with redness, and the hydrogen i$ ihflamed. After some time the sponge loses this property 1o a certain extent, but it is again restored by being well ^ignited. When the spongy platinum is mixed with clay and sal-ammoniac and made into balls, its effects are less intense, and such balls are often used in analysts to cause t^ gradual combination of gases. 398. Dr. Farada^ has sliowB v however, that it is by no means essential that the platinum should be in the spongy form in order to effect the result. Clean slips of platinum foil, and even of gold and palladium, can produce the union of hydrogen and oxygen. For this purpose the platinum is cleaned in hot sulphuric acid, washed thoroughly with pure water, and hung inja jar of the mixed gases. Combination then takes place so Vapidly as to cause at every instant a sen- sible elevation of thS water in the jar. If the metal is very thin, it sometimes becomes hot enough during the process of combination to glow, or even to explode the gases. What common instrument illustrates this ? In what state is the platinum ? How is the heat produced ? 398. What has Dr. Faraday shown about platinum ? How is it cleaned ? What follows its im- mersion in the mixed gases ? 21 242 NON-METALLIC ELEMENTS. 399. The same effect of platinum in causing combination is seen in other bodies besides oxygen and hydrogen. Sev- eral mixtures of carbon gases will act with platinum in the same way, and the vapors of alcohol or ether may be oxydized by a coil of platinum wire hung from a card in a wine-glass containing a few drops of either of these fluids. The coil of wire is heated to redness in a lamp, and while still hot is hung in the glass; it then retains its red-hot condition as long as any vapor of ether or alcohol remains. In this case, only the hydrogen of the ether or alco- hol is oxydized, and the carbon is unaffect- ed ; a peculiar irritating ethereal odor is given off, which affects the nose and eyes unpleasantly. Little balls of plati- num sponge suspended over the wick of an alcohol lamp will glow after the lamp is extinguished. This is a common toy at the instrument-makers. 400. Compound or oxyhydrogcn blowpipe. The heat pro- duced by the combustion of oxygen and hydrogen, in atomic proportions, is the most intense that can be obtained by artificial means. Dr. Hire of Philadelphia was the first who succeeded in forming an instrument to burn these gases together safely, which Professor Silliman called " the com- pound blowpipe." The invention was afterwards appropri- ated by Dr. Clark in England. Tkj? arrangement of this instrument is such, that the two gases are brought from separate gas-holders, by flexible tubes, so as to deliver at the same time two volumes of hydrogen, and one of oxygen gas, the hydrogen gas tube terminating in a hollow cylindri- cal jet, inside of which passes the jet of oxygen gas. Thus arranged, the gases come in contact only at the moment of combustion, and all danger of explosion .is avoided. The flame from the compound blowpipe differs from the common flame of a lamp or candle, by I eing, so to speak, an entire cone of ignited aerial matter, instead of being (like a lamp flame) ignited only on the outside ; (see flame and com- bustion.) Numerous modifications of the compound blowpipe 399. What further case of surface action is instanced? 400. What is the compound blowpipe, and by whom invented ? How is it arranged ? How does its flame differ from that of a common lamp ? COMPOUNDS OF HYDROGEN. 243 are in use, the most important of which we will barely men- tion. That most generally adopted, and the most safe, is to store the gases in separate holders, and bring them, as just mentioned, by distinct tubes to a common jet. 401. Two bags of gum-elastic cloth answer very well to hold the two gases, and are fitted after the fashion of a bellows, with a hinge on one side. This is the mode usually adopted in the arrange- ment of the hydroxygen microscope. The effects of the compound blow- pipe may also be safely produced by passing a stream of oxygen from a gas-holder through the flame of a spirit-lamp, (tr,) as is seen in the annexed figure. The jet is regula- ted by the cock, (,) and the Tamp flame supplies the hydrogen. 402. The mixed gases in atomic proportions are some- times forced by a condensing syringe into a very strong me- tallic box, from which they issue by their own elasticity. To prevent the danger of an explo- sion, a contrivance is employed called " Hcm- ming's safety tube," which is a brass tube six or eight inches long, filled with fine brass wire, closely packed, and having a conical rod of brass forcibly driven into their centre, by which the wires are very closely crowded together. This forms in fact a great number of small metallic tubes, through which the gas must pass. It is a property of such small tubes entirely to arrest the progress of flame, as we shall see under the compounds of carbon and hydrogen. (469.) The jet is screwed to one end of this tube, and the other end is connected with the holder of the mixed gases. Several severe explosions, it is said, have occurred, even with all these precautions ; so that if the mixed gases are used at all, 401. What arrangements are adopted for this instrument ? How may oxygen be employed alone ? 402. How are the mixed gases used alone ? What is Hemming's tube of safety ? 244 NON-METALLIC ELEMENTS. it should be only in a bag or bladder, the bursting of which can be attended with no danger. 403. The effects of the compound blowpipe arc very re- markable. In the heat of its focus the most refractory metals and earlhs arc fused, or dissipated in vapor. Plati- num, which docs not melt in the most intense furnace of the arts, here fuses with the rapidity of wax, and is even volatili- zed. By the adroit management of the keys, which a little practice soon teaches, we can either reduce metallic oxyds, or oxydize substances still more highly. The flame of the mixed gases falling on a cylinder of prepared lime, adjusted to the focus, produces the most intense artificial light known. This is sometimes called the Drummond light. It is now extensive- ly employed in distant night signals, and can be seen further at sea than any other light. Much use is also made of it as a substitute for the sun's light in optical experiments, which is a most important fact in the experimental sciences. All optical results can be more conveniently shown by the oxyhy- drogen light than by the sun ; and thus many instructive ex- periments can 1x3 exhibited to an evening audience, or on a dark day. The galvanic focus alone, among artificial sources of light, equals it. 3. Natural and Chemical History of Water. 4*04. Water when pure is a colorless, inodorous, tasteless fluid, which conducts heat and electricity very imperfectly. It refracts light powerfully, and is almost incapable of com- pression. We have made so much use of water as an exam- ple, in illustration of the laws of heat, &c., in the first part of this volume, that the reader must already be familiar with many of its attributes. Its greatest density, it will be remem- bered, (86,) is found to be at 39-5, or, more exactly, 39-83. It is the standard of comparison (38) for all densities of solids and liquids. In the form of ice, its density is 0*92, and it freezes at 32. One imperial gallon of water weighs 70,000 grains, or just ten pounds. The American standard gallon holds, at 39-83 Fahr., 58,372 American troy grains of pure 403. What are the effects of the compound blowpipe ? What is the Drummond light ? What use is made of it ? 404. Give the pro- perties of pure water. Of what is it the standard ? How much does the imperial gallon hold ? How much the American ? COMPOUNDS OF HYDROGEN. 24-5 distilled wafer. One cubic inch at 00 and 30 inches baro- meter weighs 252-458 grains, which is 815 times as much as a like bulk of atmospheric air. One hundred cubic inches of aqueous vapor, at 212 and 30 inches barometer, weigh 14*96 grains, and its specific gravity is 0-6202. 405. Water boils under ordinary circumstances at 212; but we have seen (119) that its boiling point was very much affected by the nature of the vessel. Since the first part of this volume was printed we are lately informed, that water may be heated even to 275, provided it be perfectly free from air, and that this is the case even in a vacuum. It evaporates at all (129) temperatures. 406. Pure water is never found on the surface of the earth, for the purest natural waters contain small quanties of earthy or saline matters which they have dissolved from the rocks and soil. Moreover, all good water that which is fit for the use of man has a considerable quantity of carbonic acid and atmospheric air dissolved in it, and without which it would be flat and unpalatable. Many mineral springs, besides the saline matters they hold in solution, are highly charged with sulphureted hydrogen, carbonic acid gas, and other gases derived from decomposition, in the strata through which they pass. 407. Pure icater can be procured only by distillation, and it is a substance of such indispensable importance to the chemist, that every well furnished labratory is provided with means for its abundant preparation. A copper still, well tinned, and connected with a pure block-tin worm or conden- ser, answers very well to produce the common supply. But very accurate operations require it to be again distilled in clean vessels of hard glass. The solvent powers of pure water are in some cases much greater than of common water. 408. The solvent powers of water far exceed those of any other known fluid. Nearly all saline bodies are, to a greater or less extent, dissolved by water, and heat generally aids this result. In the case of common salt, however, and a few other bodies, cold water dissolves as much as hot. Gases are What is the weight of a cubic inch of water ? 405. What is the boiling point of water ? What departures from this law are named ? 406. What does common water contain ? Why is it never pure ? 407. How is pure water obtained ? 408. How are the solvent powers of water ? Give examples. 21* 246 NON-METALLIC ELEMENTS. nearly all absorbed or dissolved in cold water, and some of them to a very great extent, while others, as hydrogen and common air, are very little taken up. They are all expelled again by boiling. - Hot water dissolves many bodies which are quite insoluble in cold, especially when aided by small portions of alkaline matter. The waters of the hot springs in Iceland and in Arkansas deposit much silicious matter before held in solution ; and Dr. Turner found that common glass was dissolved in the chamber of a steam-boiler at 300, and stalactites of silicia were formed from the wire basket in which the glass was suspended. This is a subject of great importance in many geological speculations. 409. The powers of water as a chemical agent are very various and important. From its neutral, mild, and salutary character, we are accustomed to regard it only as a negative substance, possessed of little energy, while it is in fact one of the most important chemical agents in our possession. Besides its solvent powers, we know that it combines with many substances, forming a large class of hydrates; hy- drate of lime and potash are examples. It is also, as we have seen, (292,) essential to the acid properties of common sulphuric, phosphoric, and nitric a/ids, acting here the part of a much more energetic base than in the hydrates. It forms an essential part in the composition of many neutral salts, and can be replaced in composition by other neutral saline bodies; while as water of crystallization it discharges still another important and distinct function, the crystalline forms of many salts being quite dependent on its presence in atomic proportions. 410. Peroxyd or Binoxyd of Jfydrogen. This curious compound was discovered in 1818 by M. Thenard. It is difficult of preparation by any process ; but that lately recom- mended by M. Pelouze is the best. It consists in decompos- ing the peroxyd of barium by exactly as much very cold solution of hydrofluoric acid, (fluosilicic or phosphoric acid may be used as well,) as will saturate the base, the whole being precipitated as fluorid of barium. The reaction may be expressed thus : How does hot water act in this respect ? Mention facts. 409. What are the powers of water as a chemical agent ? How does it act in sulphuric acid, &c. ? How in many salts ? 410. What is the peroxyd of hydrogen ? By whom, and when discovered ? How is it prepared ? COMPOUNDS OP HYDROGEN. 247 Peroxyd of barium. Hydrofluoric acid. Fiuorid of barium. Peroxyd of Hydrogen BaO 2 + HF BaF + HO 2 . The pcroxyd of hydrogen remains dissolved in the water, which is freed from the insoluble fluoric! of barium by filtra- tion, and then evaporated in the vacuum of an air-pump by the aid of the absorbing power of sulphuric acid. 411. Properties. The properties of this body are very remarkable. When as free from water as possible, it is a syrupy liquid, colorless, almost inodorous, transparent, and possessed of a very nauseous, astringent, and disgusting taste. Its specific gravity is 1*453, and no degree of cold has ever reduced it to the solid form. Heat decomposes it with effer- vescence and the escape of oxygen gas. It can be preserved only at a temperature below 50. The contact of carbon and many metallic oxyds decompose it, often explosively, and with evolution of light. No change is suffered by many bodies which decompose it ; but several oxyds, as those of iron, tin, manganese, and others, pass to a higher state of oxydation. Oxyd of silver, and generally those oxyds which lose their oxygen at a high temperature, are reduced to a metallic state by this decomposition. When diluted, and especially when acidulated, the peroxyd of hydrogen is more stable. This body is dissolved by water in all proportions, bleaches litmus paper, and whitens the skin. None of its compounds are known, nor docs it seem to have any tendency to combine with other bodies. 412. Ozone. There is a remarkable body given off* during the electrolysis of water, having a peculiar odor, and very volatile. The same odor is perceived when a series of electrical sparks is passed through a confined portion of air ; and lastly, when phosphorus is slowly oxydized in a large volume of air, a peculiar odor is perceived, which is identical with the foregoing, and does not belong either to phosphorus or any of its compounds. This is the ozone of Professor Schonbein, of which much has been said in the scientific journals. It bleaches powerfully, and converts many pro- toxyds (as those of calcium and barium) to peroxyds, and sulphurous to sulphuric acid. It is decomposed by heat, water, and oxygen, like peroxyd of hydrogen ; and the latest Explain the reaction. 4 11. 'What are its properties ? 412. What remarkable body is named in connection with binoxyd of hydrogen ? How is it produced ? What are its properties ? What is its real nature ? 248 NON-METALLIC ELEMENTS. opinion is, that ozone is an allotropic condition (415) of oxygen, analogous to the double condition of chlorine, and many other elements. Oa and O/3 may be employed to ex- press these two states. 4. Compounds of Hydrogen with the II. and III. Classes. 413. The eminently electro-positive character of hydro- gen causes it to form well characterized and analogous com- pounds with all the members of the oxygen group. These binary compounds have frequently been called the hydracids, in distinction from those acid bodies already considered, which, in parity of language, have been called the oxacids. It is however more in accordance with facts and the principles of a philosophic classification, to look upon these bodies as having in reality the same essential characters as the chlorids, bromids, iodids, &c., of other highly electro- positive bases. We have already remarked, (199, note,) that the principles of our nomenclature require all these bodies to be called after their electro-negative elements, i. e. chlorohydric, bromohydric, &c. ; but common usage having established the other names, we shall not on the present occasion depart from them. The compounds of hydrogen to be considered under this head are Composition by weight. Symbol. Hydrogen. Chlorine. Hydrochloric acid, HC1 1 35-41 Bromine. Hydrobromic acid, HBr 1 78-26 Iodine. Hydriodic acid, HI 1 126-36 Fluorine. Hydrofluoric acid, HF 1 18-70 Sulphur. Hydrosulphuric acid, HS 1 16-09 Selenium. Hydroselenic acid, HSe 1 39-57 Tellurium. Hydrotelluric acid, HTe 1 64-14 414. Action of Hydrogen with Chlorine. These bodies have a very powerful affinity for each other, and combine 413. What is said of the compounds of hydrogen with the oxygen group ? How are the hydracids now looked upon ? Enumerate these, and give their formulas and constitution on the board. What is re- markable in this group ? 414. What of the affinity of chlorine and hydrogen ? COMPOUNDS OF HYDROGEN. 249 under ordinary circumstances, when mixed in the gaseous state. Their affinity is such as to enable chlorine to decom- pose water (264) and appropriate its hydrogen. In this way chlorine becomes one of the most powerful oxydizing agents known, since the nascent oxygen given off during the decomposition of water attacks any third body which may be present that is capable of combining with it. 415. The combination of hydrogen with chlorine de- pends on the action of light. We have already remarked that light, (264,) and especially the violet ray, gives chlorine the power to decompose water. Chlorine prepared in the dark, and mingled with hydrogen, the mixture being also kept in the dark, will not combine with hydrogen nor decom- pose water, and the two bodies seem altogether indifferent to each other. It has been long known that the direct rays of the sun would cause the explosive union of this mixture ; and Dr. Draper has shown that chlorine gas which has been exposed alone and dry to the sun's light, has acquired the power of forming this explosive union with hydrogen, even in the dark, and retains it for some time. The result of this union is hydrochloric acid. We see in this fact the best proof of the double state which chlorine can assume, (allotropism,) and which it possesses in common with several other bodies. In its passive state, (as prepared in the dark,) it actually replaces hydrogen in the constitution of many organic bodies, or, in other words, assumes an electro- positive condition. The effect of the sun's light is to confer a new state upon it, probably by a new arrangement of its molecules, (218,) by which its character is completely changed. It then becomes highly electro-negative. We have then in chlorine an instance of an element capable of acting in opposite characters under different circumstances. 416. Hydrochloric Acid, Chlorid of Hydrogen, Mu- riatic Acid. This compound is formed from the action of dilute sulphuric acid on common salt, or chlorid of sodium. The reaction may be thus described : NaCl + SO 3 ,HO=: (NaO, SO) -f C1H. No process is more simple. A little heat is required, and How is it shown? How does chlorine assist in oxydation ? 415. On what does the combination of hydrogen and chlorine depend ? Explain this as illustrated. How does chlorine appear to us under this view ? 416. How is hydrochloric acid formed ? What other names has it ? 250 NON-METALLIC ELEMENTS. the gas being entirely absorbed by water, must be collected over mercury, or in dry vessels by displacement of air. 417. Properties. Chlorid of hydrogen is a gas having a density of 1-269. It is colorless, has the greatest avidity for water, forms an acid fog by combining with the moisture of the air, which attacks the skin, has a most suffocating effect in respiration, and greatly irritates the eyes. It is by no means, however, so unpleasant as chlorine. With a pressure of 26-30 atmospheres, at 32, it becomes a colorless liquid, which no degree of cold yet employed has solidified. 418. This gas dissolves largely in cold water, forming an acid solution, which is the common muriatic acid of com- merce, or spirit of salt of the shops. At common tempera- tures water will absorb nearly 420 times its own bulk of muriatic acid gas. The solution is a powerful acid, of great use in the arts and in the chemical laboratory. It may be prepared pure by an arrangement of appa- ratus like the figure. The common salt is con- tained in a large flask (a) which is fitted with a cork having two tubes, one of which (b) bends over and dips into the middle bottle, (c,) which contains a little water to wash the gas. The last bottle (d) is filled with pure water, kept cool by ice or a freezing mixture ; the gas, after being wash- ed in the middle bottle, (c,) passes by the second bent tube (e) to the last bottle, where it is absorb- ed. Sulphuric acid, equal in weight to the salt employed, is turned in successive portions upon the salt through the recurved 417. What is its condition ? What its properties ? 418. How much of this gas does water absorb ? What is the solution called ? Explain the apparatus by which it is made. COMPOUNDS OF HYDROGEN. 251 funnel tube (f) shown on a larger scale in the second figure. This is called a safety tube ; it is bent twice on itself, and has a ball blown on one of the turns. When a liquid is poured in at the funnel-top, it must rise as high as the turn, before it can pass down into the flask, and a por- tion of the fluid is therefore always left behind in the bend, which serves as a valve against the entrance of air, and also effectually prevents an explosion of the flask in case the tube of delivery should become stop- ped. It acts also as a safety tube against the danger of absorption, and the rushing back of the fluid in the bottles by atmospheric pressure, in case the gas in the flask, should cease to be given out. This accident, which not unfrequently happens, is also provided for by the large open tube (g) in the middle bottle through which the bent tube descends into the fluid, which is at the same time open to the air. This arrangement completely prevents the loss of the product in the last bottle, (d t ) which, in case of a stoppage of the gas, would otherwise, by the partial vacuum resulting, be all driven back into the first bottle, and finally into the flask. The joints about the corks are made tight by a little yellow wax melted over them by a warm iron rod. Heat is applied by means of the furnace, (o,) or by a lamp. This same apparatus may be employed in making solutions of all the absorbable gases, and is so simple as to be within the means of the humblest laboratory ; the essential parts being only wide-mouthed bottles, glass tubes, a gas bottle or flask, and a few corks. 419. Pure hydrochloric acid is a colorless, highly acid, fuming liquid, having a specific gravity of 1*8 when satu- rated ; it then contains 42 parts in a hundred of real acid. Its purity is tested by its leaving no residue on evaporating a drop or two on clean platinum, and by its giving no milkiness when a solution of chlorid of barium is added to it, [sulphuric acid.] Neutralized by ammonia, it ought not to become black when hydrosulphuret of ammonium is added, [iron.] It may always be obtained pure, by diluting the acid of com- merce until it has the specific gravity of 1*11, and distilling. The product is colorless and pure, having the same density. What is the action and use of the safety tube ? 419. What are the characters of pure hydrochloric acid ? How is it purified ? 252 NON-METALLIC ELEMENTS. The commercial acid is always impure, and colored yellow by free chlorine, iron, and organic matters. A solution of nitrate of silver detects the presence of a soluble chlorid, or of hydrochloric acid, by forming with it a white curdy pre- cipitate of chlorid of silver, which is soluble in ammonia, but insoluble in acids or water. This acid is an electrolyte, (236, 1,) and is also decomposed by ordinary electricity. A mixture of muriatic acid gas with oxygen, passed through a red-hot tube, produces water and chlorine. 420. Tiie uses of hydrochloric acid are very numerous. Its decomposition by oxyd of manganese affords the easiest mode of procuring chlorine. It dissolves a great number of metals forming chlorids, from which these metals may be obtained in their lowest state of oxydation. In chemical analysis and the daily operations of the laboratory it is of indispensable use. Mingled with half its own volume of strong nitric acid, it makes the deeply-colored, fuming and corrosive aqua regia. This mixed acid evolves much free chlorine, which in its nascent state has power to dissolve gold, platinum, &c., forming chlorids of those metals, and not nitromuriates, as was formerly supposed. As soon as all the chlorine is evolved, this peculiar power of the aqua regia is lost. 421. Hydrochloric acid is made in the arts in immense quantities, especially in England, where the carbonate of soda is largely made from common salt, (chlorid of sodium,) by the action of sulphuric acid. The vast volumes of chlorid of hydrogen which are evolved in this process, are by law required to be condensed, to avoid the injury to vegetation and health formerly experienced, from their being allowed to escape into the atmosphere. In this way, hydrochloric acid is made as an incident to other processes, in such quan- tifies as to overstock tho market. 422. Hydrobramic Acid Bromid of Hydrogen. Hy- drogen and bromine do not act upon each other in the gaseous state, even by the aid of the sun's light ; but a red heat or the electric spark causes union, only among those particles, however, which are in immediate contact with the heat, the action not being general. Hydrobromic acid may What impurities have the commercial acids ? How are they de- tected ? 420. What are its uses ? What is aqua regia ? What use has it, and on what dependent ? 421. What is said of the abundance of this acid? 422. Kow do hydrogen and bromine at .together ? COMPOUNDS OF HYDROGEN. 253 be prepared by the reaction of moist phosphorus on bromine in a glass tube. The gas given off must be collected over mercury. It is composed, like hydrochloric acid, of equal volumes of its elements not condensed. Its specific gravity is 2*731, and it is condensed by cold and pressure into a liquid. In its sensible properties it bears a close resemblance to hydrochloric acid. With the nitrates of silver, lead, and mercury, it gives white precipitates similar to the chlorids. It has a strong avidity for water, and dissolves largely in it, giving out much heat during the absorption. The saturated aqueous solution has the same reactions as the dry acid, and fumes with a white cloud in contact with air. It dissolves a large quantity of free bromine, acquiring thereby a red tint. 423. Hydriodic AcidIodid of Hydrogen. This body may be formed by the direct union of its elements at a red heat, but is more easily prepared by acting on iodine and water with phosphorus, by which means the gas is given out in large quantities. The action of phosphorus and iodine is violent and dangerous, but may be regulated and made safe by putting a little powdered glass between each layer of phosphorus and iodine. Phosphoric acid is formed and remains in solution, while the hydriodic acid gas is given out, and may be collected over mercury, or dissolved in water. The dry gas has a great avidity for water. Its specific gravity is 4-385, air = 1 ; being formed like the two last of one volume of each element uncon- densed. Cold and pressure reduce it to a clear liquid, which, at 60 Fahr., freezes into a colorless solid, having fissures running through it like ice. It forms a very acid fluid by solution in water, which has, when saturated, a specific gravity of 1-7, and emits white fumes. The aqueous solution is also prepared by transmitting a current of hydrosulphuric acid through water in which free iodine is suspended. The gas is decomposed, sulphur set How is hydrobromic acid prepared ? What character has it ? 423. How is hydriodic acid prepared ? What is the reaction ? What are the properties of the gas ? How else may the aqueous solution be prepared ? 22 254 NON-METALLIC ELEMENTS. free, and hydriodic acid produced, which is purified from free hydrosulphuric acid by boiling, and from sulphur by filtration. 424. The aqueous hydriodic acid is easily decomposed by exposure to the air, iodine being set free. It forms characteristic, highly colored precipitates with most of the metals, particularly with lead, silver, and mercury. Bro- mine decomposes it, and chlorine decomposes both hydro- bromic and hydriodic acids, thus showing the relative affinities of these bodies for hydrogen. This acid is a valuable reagent ; its presence in solution is easily detected by a cold solution of starch with a few drops of strong nitric or sulphuric acid, which instantly gives the fine charac- teristic blue of the iodid of starch. 425. Hydrofluoric Acid, or Fluorid of Hydrogen, is obtained from the decomposition of fluor-spar by strong sul- phuric acid. The operation must be performed in a retort of pure lead, silver, or platinum, and requires a gentle heat. The fluorine leaves the lime and joins the hydrogen of an atom of water in the acid, forming hydrofluoric acid, while sulphate of lime remains behind ; or, expressed in symbols, Fluorid of Sul. acid. Sul. lime. Fluorid of calcium. hydrogen. CaF + S0 3 , HO S0 3 , CaO + HF The fluor-spar must be pure, and especially free from silica. 426. Propertied. Hydrofluoric acid is a gas which at 32 is condensed into a colorless fluid, with a density of 1*069, which can be preserved as a fluid even at higher temperatures in well stopped bottles of silver or lead. Its avidity for water is extreme, and when brought in contact with it, the acid hisses like red-hot iron. Its aqueous solution, as well as the vapor of the acid, attacks glass very powerfully, and is often used to etch it, as, for example, in marking the test bottles in the laboratory, or biting in designs traced in wax on the surface of glass plates. It is a powerful acid, with a very sour taste, neutralizes alkalies, 42-1. What properties has the aqueous hydriodic acid ? What are the mutual relations of iodine, bromine, and chlorine, as shown by their compounds with hydrogen ? How is the presence of hydriodic acid detected ? 425. What is hydrofluoric acid'? Explain the reac- tion by which it is produced. 426. What are the properties of this body ? What is its most remarkable affinity ? COMPOUNDS OF HYDROGEN. 255 and permanently reddens blue litmus. On some of the metals its action is very powerful ; it unites explosively with potassium, evolving heat and light. It attacks and dissolves, with the evolution of hydrogen, certain bodies which no other acid can affect, such as silicon, zirconium, and columbium. Silicic, titanic, columbic, and molybdic acids are also dissolved by it. 427. Hydrofluoric acid is a most dangerous body to experiment with. It attacks all forms of animal matter with wonderful energy. The smallest drop of the concentrated acid produces ulceration and death, when applied to the tongue of a dog. Its vapor floating in the air is very corro- sive, and should be carefully avoided. If it falls, even in small spray, on the skin of the hand or any part of the body, it produces a malignant ulcer, which it is very difficult to cure. Any considerable quantity of it would prove fatal. For this reason it is quite inexpedient for unexperienced persons to attempt its preparation. By using a weaker sulphuric acid, however, and having water in the condenser, no risk is incurred. As before remarked, it attacks silica more pow- erfully than any other body, and their mutual affinity is one of the most powerful known to us. This fact puts us in possession of an admirable mode of analyzing silicious min- erals, when we do not wish to fuse them with an alkali. By exposing the fine powder of the moistened mineral to the vapor of the hydrofluoric acid, all the silica is taken up and carried away as hydrofluosilicic acid gas, (364.) 428. The hydrofluoric acid was formerly called fluoric acid, and the fluor spar, a fluate of lime. We now know that this mineral is a Jluorid of calcium, in exact analogy with the chlorid of sodium, and a very numerous class of similar binary compounds, with which our study of the metals will familiarize us. 429. Hydrosulphuric Acid Sulphureted Hydrogen. When the protosulphuret of iron or the sulphuret of antimony is treated with a dilute acid, effervescence occurs, and a gas is given out having a most disgusting fetid odor, which at once reminds us of the nauseous smell of bad eggs. This What are its relations to the metals ? What acids are dissolved by it ? 427. How does it affect animal matter ? What caution is given ? What analytical use is named for this acid ? 428. What was this acid formerly called ? What more exact knowledge do we now possess ? 429. What is hydrosulphuric acid, and how set free ? 256 NON-METALLIC ELEMENTS. is sulphuretcd hydrogen gasj one of the most useful reagents to the chemist, especially in relation to the metallic bodies. 430. Properties. This gas is colorless, and less offensive in quantity than when the air is contaminated with only a trace. It burns with a pale blue flame like that of sulphur, water and sulphurous acids being the products. If oxygen is mingled with it, and the mixture ignited, or touched with a match, it explodes with a shrill sound, sulphur is deposited, and water formed. When the oxygen is in the proportion of 150 measures to 100 of sulphurcted hydrogen, the combus- tion is complete, and only sulphurous acid and water are formed. Strong nitric acid and chlorine gas also decompose it, and sulphur is set free. It has a specific gravity of 1-171, and 100 cubic inches of it weigh 36-33 grains. At a tem- perature of 50, it is made liquid by a pressure of 14-5 atmospheres, and at 122 Kahr., it freezes into a white confused crystalline solid, not transparent, and which is much heavier than the fluid, sinking in it readily. 431. Cold water dissolves its own volume of sulphurcted hydrogen, and acquires its peculiar odor and properties. When recently prepared, it takes the place of the gas ns a test ; but it is so easily decomposed by contact with the air, with the deposition of sulphur, that it cannot long be kept on hand. The student should always have at hand in the laboratory a little gas bottle, like the figure, holding some fragments of protosulphuret of iron, to which, when the gas is wanted, a little water is added and then a few drops of oil of vitriol. Effervescence ensues, and the gas is delivered by the bent tube, into any solution which we desire to treat with it. 432. Properties and Uses. This gas posesses the pro- perties of an acid; its aqueous solution reddens litmus paper, and it forms compounds with many bases. It precipitates What other name has it ? 430. What are its properties ? How does it smell ? Is it combustible ? How does it burn when mingled with oxygen ? Is it condensable to a fluid ? 431. How much of it will water dissolve ? What properties has the solution ? What ob- jection to its use ? What mode is preferred for using this reagent ? 432. How is it seen to be an acid ? What are its properties and uses? COMPOUNDS OF HYDROGEN. 257 from solution all the metals whose sulphurets are insoluble in water, often giving the most characteristic precipitates. It thus enables the chemist to effect many separations of metals with ease and certainty, and, as before remarked, is one of his most valuable reagents. Its presence in solution is at once detected by its blackening the salts of lead. Characters drawn on paper with a solution of the acetate of lead, are quite colorless ; but a stream of sulphureted hydrogen at once causes them to stand forth in deep black, its action producing the dark sulphuret of lead. 433. It occurs in solution in many mineral springs, giving the water highly valuable medicinal characters. Such springs are much resorted to in this country, as at Avon, N. Y., and the sulphur springs of Virginia. The disgust at first felt at drinking these nauseous waters is soon overcome, and those patients who take them in large quantity soon observe the gas to penetrate their whole system and exude in their perspiration. Silver coin, and other silver articles in the pockets of such persons are soon completely blackened by the coating of sulphuret of silver formed on their surface. 434. Although salutary when used in the stomach, it has been found to be a deadly poison to the more delicate animals, even when present in the air in only a small quantity. The operative chemist is, however, in the habit of breathing it with impunity, for the atmosphere of an active laboratory is often impregnated with iL 435. When sulphurous acid and sulphureted hy- drogen gas are brought together in a common re- ceiving vessel, mutual de- composition ensues, and the sulphur of both is thrown down in a yellow cloud, which attaches it- self to the sides of the vessel. The same ar- How does it act with the metals ? How is its presence detected ? 433. How does this gas occur in nature ? What use is made of sul- phureted waters ? 434. What is said of the effect of this gas on the system of animals ? 435. What is the reaction when sulphuric acid and hydrosulphuric acid gases are mingled ? 22 * 258 NON-METALLIC ELEMENTS. rangement of apparatus which was employed for illustrating the formation of sulphuric acid, will answer in this experi- ment, substituting the materials for sulphurated hydrogen in the flask, (b.) 436. Hydroselenic Acid Seleniurcted Hydrogen. This body is quite similar to the foregoing, and is formed in the same manner by decomposing the protosclcniuret of any of the more easily oxydized metals, with a weak acid. Its properties and reactions are very similar to those of the hydrosulphuric acid. It is absorbed by water, turns the skin brown, and irritates the mucous membrane. Tellureted Hydrogen is evolved when an alloy of tin and tellurium is acted on by muriatic acid: it reddens lit- mus paper, dissolves in water, and possesses the general habitudes of sulphureted hydrogen. 5. Compounds of Hydrogen with Class III. 437. The compounds which hydrogen forms with the nitro- gen group, are strongly contrasted in chemical and physical characters with the remarkable natural family which has just engaged our attention. The latter are all acid, and gen- erally in an eminent degree. The compounds of hydrogen with the nitrogen group are, on the contrary, either neutral or strongly basic, forming a series of salts or peculiar com- pounds with the hydracids before named ; thus furnishing a strong reason for the propriety of the arrangement which we have adopted in our classification. The compounds named under this head, are Composition by weight. Symbol. Nitrogen. Hydrogen. Ammonia, NH 3 14-06 3 Phosphorus. Phosphureted hydrogen, PH 3 31-38 3 438. Ammonia, and the other compounds of nitrogen and hydrogen, might with propriety be treated under organic chemistry, since hydrogen and nitrogen do not, by any 436. What is hydroselenic acid, and how allied to the last body ? 437. What is said of the compounds of the hydrogen with the nitro- gen group ? What compounds are named ? Give their symbols and composition. 438. Where might ammonia be more properly treated of ? COMPOUNDS OP HYDROGEN. 259 direct means, unite as gases, and all the compounds of am- monia may ultimately be traced back to an organic origin. Ammonia is almost invariably one of the products of the decomposition of those organic matters which contain nitro- gen ; and we shall see, when we come to study these bodies, that their elements are so arranged, that we might expect such a result. Ammonia is however so important a body in relation to the metals, and, in fact, as a reagent in nearly all chemical experiments, that we shall find it more convenient to become acquainted with it here, than at a later period of our studies. 439. History. Sal ammoniac and the watery solution of ammonia have been long known, and probably were in use among the ancients. The very name of ammonia indi- cates its antiquity.* The sal-ammoniac, sulphate of ammo- nia, and ammonia-alum are found among the products of volcanoes. Free ammonia is exhaled from the foliage and found in the juices of certain plants, in the perspiration of animals, in iron rust and absorbent earths. Rain water also contains a small quantity of ammoniacal salts, washed out of the atmosphere ; and the guano so much valued as a manure, is rich in various ammoniacal compounds. 440. Preparation. Ammonia is best prepared for use by decomposing one of its saline compounds, as the sal-am- moniac, by an alkali and heat. For this purpose equal parts of dry powdered sal-ammoniac and freshly slaked dry lime are well mingled and heated in a glass, or if the quantity is considerable, in an iron vessel. The lime takes the hydro- chloric acid, forming a chlorid of calcium, and ammonia is given out as a gas. 441. Properties. The dry gas is colorless, having the very pungent smell so well known as that of ' hartshorn.'' It is, when undiluted, quite irrespirable, and attacks the eyes, mouth, and nose powerfully. It is alkaline, and has fre- quently been called the volatile alkali. Being very rapidly absorbed by water, it must be collected over mercury or in 439. What is known of the antiquity of ammonia? What ammo- niacal compounds are found native ? What other natural sources of ammonia are named ? 440. How is ammonia prepared ? 441. What are the properties of this gas ? * From Amman, an epithet by which Jove was known, and ammos, sand, in allusion to the Egyptian desert of Ammon, where sal-ammo- niac was first obtained. 260 NON-METALLIC ELEMENTS. inverted dry vessels. It does not support the combustion of a candle, and does not burn itself, although a small jet of the gas will burn in pure oxygen, and the flame of the candle, as it goes out, is slightly enlarged with a yellowish fringe. Mixed with an equal volume of oxygen, it explodes with the electric spark, yielding water and free nitrogen. The dry gas passed through a red-hot tube is completely decomposed ; iiOO measures of the gas yielding 400 measures after decom- position, which by analysis is found to consist of 300 measures of hydrogen and 100 of nitrogen. The specific gravity of dry ammonia is therefore (192) 0-5893, and 100 cubic inches weigh 15-23 grains. By pressure it is easily con- verted into a liquid, which freezes at 103 Fahrenheit, producing a white translucent crystalline solid, which is heavier than the liquid. 442. The solution of this gas in water (called aqua am- monitp, and sometimes improperly liquid ammonia) is easily prepared, and possesses all the peculiar properties of the gas. This is best made by an arrangement like the annexed figure, called Woulfe's apparatus. This consists essentially of the gas bottle (a,) which contains the materials to generate the gas, and is placed over a furnace. Three three-necked bot- tles (b c d) are all connected with a by a scries of bent tubes, (t t i i). The gas in passing from a by t, must go through a portion of water in 6, where it is absorbed. It is prevented from escaping by a tube in the middle orifice, (o,) which has its lower end dipping 3 little way into the water of each bottle. The effect of this is to cause a column of liquid to How does it affect combustion ? How is it analyzed ? What is its constitution by weight and volume ? What is its density ? How does cold affect it ? -142. How is aqua ammoniac prepared ? Ex- plain Woulfe's apparatus anJ its mode of action. COMPOUNDS OF HYDROGEN. 261 play up and down in o, as the pressure of the gas varies. Each tube, (i) has a shorter end not reaching the fluid. Things being thus arranged, and the tightness of all the joints and corks being secured by bees-wax, the gas bubbles through o, until the water can absorb no more ; it then passes on to c, and then to df, saturating each in turn. In the last vessel is a little mercury under which the bent tube (i) dips, with the design of cfeating a slight pressure on the whole appa- ratus, as is indicated by the height of the column of water in ooo. It only remains to keep the whole (b c d) cold, and the water in the bottles will then soon become saturated with the gas. The first bottle, is usually contaminated by foreign matters, and is rejected. Under sulphuret of ammonium will be found a more simple form of the same apparatus formed of common wide-mouthed bottles. 443. The saturated aqueous solution of ammonia has a specific gravity of about U'875, is colorless and transparent, and exhales the gas abundantly ; when it is of this density it contains 32 per cent, of real ammonia. It must be kept in tight bottles, to prevent the loss of strength and the absorp- tion of carbonic acid gas from the air. It has all the charac- ters of an alkali, it saturates the most powerful acids, and forms a series of salts which are all soluble in water, and are volatilized at a red heat. It boils vehemently at 130, and freezes at about 40 below zero. It browns yellow turmeric paper temporarily, but the original color returns as the gas evaporates. 444. The presence of ammonia is always recognised by its odor, by its action on turmeric or blue cabbage paper, (which last it turns green,) and especially by the white cloud of muriate of ammonia which is formed on bringing a rod moistened with hydrochloric acid near it. 445. Hydrogen and Phosphorus Phosphureted Hy- drogen. This gaseous body is formed when the phosphuret of calcium, or of some other alkaline metal, is acted upon by water ; but is more conveniently prepared by employing quick-lime recently slaked, water, and a few sticks of phos- phorus, in a small retort, the ball of which is nearly filled with the mixture. A gentle heat generates the gas, which vVhat properties ? 443. What gravity has the saturated aqueous solution? What characterizes its salts? 444. How is ammonia recognised ? 445. What is phosphorated hydrogen, and how prepared 7 262 NON-METALLIC ELEMENTS. breaks from the surface of the water (beneath which the beak of the retort dips very slightly) in bubbles, that inflame spontaneously as they reach the air, rising in beautiful wreaths of smoke, which float in concentric, expanding rings This gas loses its spontaneous inflammability by standing a time over water, a body not yet obtained in a separate form being deposited. A few drops of ether or oil of turpentine destroy this property, but a very little nitrous acid restores it. 446. Properties. This gas has a disgusting, heavy odor, like putrid fish, which is far more annoying than sul- phureted hydrogen. It is transparent and colorless, has a bitter taste, and if dry may be kept unchanged either in the light or dark. It is deadly when breathed. When procured as just described, it acts very violently with oxygen gas. If bubbles of it are allowed to enter a jar of oxygen, each bubble burns with a most brilliant light and a sharp ex- plosion. The mixture of even a very small quantity with oxygen would be quite hazardous. 447. Phosphureted Hydrogen is neither alkaline nor acid, but it has more resemblance to an alkali than to an acid, since it forms, with several metallic chlorids, compounds analogous to those which ammonia yields with the same bodies. It also combines with hydrobromic and hydriodic acids, forming colorless crystalline salts, which are decom- posed by water. 448. Three Phosphurets of Hydrogen have been distin- guished, which have the formulas PH, PH 2 , and PH 3 . The What remarkable property has the fresh gas ? Is this property constant ? 446. What are its characters ? How does it react with oxygen ? 447. Is this gas alkaline or acid ? What compounds analogous to salts does it form ? 448. How many and what phos- phurets of hydrogen are known ? COMPOUNDS OF HYDROGEN. 263 last is the pure gas, the second is the spontaneously in- flammable body, and the first is a solid. 6. Compounds of Hydrogen with the Carbon Group. 449. Carbon and hydrogen unite to form a vast number of compounds, all of which, directly or indirectly, are the product of organic life, and will therefore (with two excep- tions) be discussed more properly in the organic chemistry. 450. The carlo-hydrogens, as these bodies are often called, are sometimes solids at common temperatures, as paraffine and nephthaline ; or liquids, as the oils of turpen- tine, lemons, and naphtha. Two of them are gases, and being also products of the mineral kingdom, they may be properly discussed under inorganic chemistry. We refer to the Composition by weight. Symbol. Carbon. Hydrogen. Light carbureted hydrogen gas, CHg 6 2 Olefiant, or heavy carbureted hydrogen gas, CaHg 12 2 451.. Light Carbureted Hydrogen Gas; Marsh Gas; Fire Damp ; or Di-carburet of Hydrogen, This gas occurs abundantly in nature, being formed nearly pure by the decomposition of vegetable matter under water. The bubbles which rise, when the leaves and mud of a stagnant pool or lake are stirred, are light carbureted hydrogen, with about $ of carbonic acid. It is also evolved in large quantity in coal mines, but is then accompanied by several other gases. In the salt regions of this country it is given out abundantly with olefiant gas from some of the artesian wells bored for salt water. It is also sometimes blown out in a strong blast from fissures in the earth ; and it forms a part of the gas employed to light cities, 452. Preparation. This gas may be prepared artificially by mixing equal parts of acetate of soda, and solid hydrate 449. What is said of the number and nature of the compounds of carbon and hydrogen ? Of what are they the product ? 450. How do the carbo-hydrogens present themselves ? What two are referred to? Give their formulas and composition. 451. What other names has the light carbureted hydrogen ? What natural supplies have we of it ? 452. How is it prepared ? 264? NON-METALLIC ELEMENTS. of potash, with one and a half parts of quicklime. The mix- ture is strongly heated in a retort, when the gas, perfectly pure, is disengaged abundantly, and may be collected over water. The hydrate of potash decomposes the acetic acid at a high heat, and takes from it two equivalents of carbonic acid, while two equivalents of marsh gas are given off; thus: Acetic acid, C 4 H 3 3 ( _ j Carbonic acid, 2 eq C 2 O 4 Water, H O f ) Marsh gas, 2 eq C 2 H4 C 4 H 4 4 C 4 H 4 O The use of the lime is to keep the potash from acting on the glass retort. 453. Properties. This gas has a density of -5595, and 100 cubic inches of it weigh 17.41 grains. It is composed of one volume of carbon and two volumes of hydrogen, or six parts by weight of the former to two of the latter. It is neutral, inodorous, tasteless, and respirable without poison- ous effects. Water absorbs very little of it, and it has not been condensed into a liquid. Twice its bulk of oxygen burns it completely, with a loud explosion, forming water and an equal volume of carbonic acid. In the air it burns quietly with a bright yellow flame, giving the same products. It is not easily decomposed ; but at a red heat, in a porce- lain tube, it deposits carbon and gives out hydrogen. With moist chlorine in the sun-light, it forms carbonic and hydro- chloric acids, but is not affected by it in the dark. 454. Olefiant Gas, or heavy Citrbureled Hydrogen Gas. This gas was discovered in 1796, by an association of Dutch chemists, who gave it the name of olefiant, because it forms a peculiar oil-like body with chlorine. It is prepared by mixing strong alcohol with five or six times its weight of oil of vitriol in a capacious retort, and applying heat to the mixture. The action is complicated and cannot be well explained at this time. Ether distils over soon after the heat is applied, and with it, the olefiant gas which may be collect- ed over water. The alcohol becomes carbonized, froths up very much, and carbonic and sulphurous acids are given off Give the reaction. 453. What is the density and composition of this gas ? Give its general properties. How does it act with chlorine. 454. When, and by whom, was olefiant gas discovered 1 Whence its name ? How is it prepared ? What is the result ? COMPOUNDS OF HYDROGEN. 265 towards the close of the process. The gas can be purified by passing it first through a wash-bottle containing a solution of potash, and then through oil of vitriol ; the potash removes the acid vapors, and the oil of vitriol retains the ether. 455. Properties. Olefiant gas is a neutral, colorless, tasteless gas, nearly inodorous, and having a density of 0-981, 100 cubic inches of it weighing 30-57 grains. It burns with a most brilliant white light, and evolves much free carbon. Its splendid combustion makes it a favorite subject of experiment. With an equivalent quantity of oxygen gas, it explodes with a tremendous detonation, which is too severe even for very strong glass vessels. Bubbles of the mixture may be exploded by a burning paper, as they rise from beneath the surface of water. It is decomposed by passing through tubes heated to redness, -and much carbon is deposited. This effect happens in the iron retorts of city gas Works, in which crusts of pure carbon, sometimes of great thickness, accumulate from the decomposition of the gas. 456. As already remarked, this gas forms a remarkable compound with chlorine ; the gases unite (2 volumes of chlorine and 1 of defiant) by simple contact, the dense oily liquid collects on the side of the air-jar and surface of the water, and may be received as it falls in a basin placed for the purpose under the jar. If two measures of chlorine and one of olefiant gas be fired as soon as the mixture is made, by a candle, or lighted match, from the open mouth of the jar, the hydrogen of the olefiant unites with the chlorine, and all the carbon of the former is set free in a dark cloud, filling the vessel. 457. Coal gas and resin gas are much used for illumi- nating cities ; they are formed chiefly of light carbureted hy- drogen and olefiant gas, with some other volatile hydrocar- bons. Their illuminating power is in proportion to the amount of olefiant gas contained in the mixture. Numerous products from the destructive distillation of coal and resin 455. What properties has olefiant gas ? How does it burn ? How does it act with oxygen ? How is it decomposed ? What happens in large gas retorts ? 456. How does olefiant gas act with chlo- rine? If the mixture is at once fired, how does it act? 457. For what are coal and resin gases used ? On what depends their illumi- nating power ? 23 266 NON-METALLIC ELEMENTS. require to be removed before the gas is fit for use. It is accordingly washed in milk of lime to free it from sulphu- reted hydrogen and carbonic acid, and sometimes with dilute sulphuric acid to remove ammonia. Tar and soluble oils are condensed by passing the gas through a series of iron pipes in water, which is done before it goes to the lime purifiers. The gas from oil has a higher illuminating power, and needs no purification when well prepared. A natural supply of coal gas, composed of light carbureted hydrogen and defiant gas, is used to illuminate the village of Fredonia, N. Y. ; and some of the salt works in Kenawha, Va., are heated by the burning gas conducted for the purpose under the kettles. Vast volumes of this gas are given off from the Artesian borings in those regions. 458. Hydrogen combines with boron, forming a combus- tible gas, which bucns with the green flame peculiar to the compounds of boron, and deposits boracic acid. Its compo- sition and properties are not known. From analogy we might suspect the existence of a series of borurets of hydro- gen, and possibly siliciurets of the same element. 7. Combustion and the Structure of Flame. 459. Combustion is the disengagement of light and heat, which accompanies chemical combination. Nearly all our operations being performed in presence of the oxygen of the atmosphere, the term combustion has come to be restricted, in a popular sense, to the union of bodies with oxygen, when heat and light are accompaniments of such union. Combustible bodies, in the common sense of the term, are those which burn (i. e., unite with oxygen with heat and light) under ordinary circumstances. Thus, carbon, sulphur, and phosphorus, are among the elementary combustibles ; and tar, oils, wood, &c., are compound combustibles. Oxygen being possessed of stronger affinities than any other elementary body, forms compounds with those bodies which are burned in it, which are no longer combustible ; thus iron which has been burnt (i. e. oxydized) in oxygen gas, (255,) How are they purified ? What natural supplies of coal gas are named ? 458. What compound of hydrogen and boron is named ? 459. What is combustion ? What popular restriction has arisen in the use of this term ? What is commonly meant by combustible bodies? What is said of bodies which have been burnt in oxygen ? COMBUSTION AND FLAME. 267 is no longer capable of a similar change, because we have no other body, which, at common temperatures, can remove the oxygen from combination. Iron will also burn brilliantly in sulphur vapor, forming a compound, (protosulphuret of iron,) which is incombustible in an atmosphere of sulphur vapor, but which will still burn in oxygen gas. This is only saying that the affinities (i. e. the electro- negative qualities) of oxygen are more powerful than those of sulphur. 460. The division of elementary bodies into combustibles and supporters of combustion, was proposed by Doctor Thomson, and that classification has prevailed with English and American authors to a great extent. This principle is radically defective as a guide to any philosophical arrange- ment of bodies, since it seizes on a single phenomenon ac- companying chemical union, and disregards most of those natural analogies which group the elements into distinct classes. It has been remarked by an old writer on chemistry, that " combustion is the grand phenomenon of chemistry." It would be more conformable to truth to say, that affinity is the grand phenomenon of chemistry, and that its exertion is sometimes accompanied by the evolution of heat and light. The attentive student has already, it is hoped, found sufficient grounds, in the arguments and illustrations which have been presented, to admit the existence of a higher chemical philosophy than that of combustibles and sup- porters. 461. In all cases of combustion the action is reciprocal. Hydrogen burns in common air ; but if a stream of oxygen is thrown into a jar of hydrogen, through a small aperture at the top, when the latter is burning, the flame is carried down into the body of the jar, and the oxygen will continue to burn in the hydrogen, as it issues from the jet. In this case the oxygen may be said to be the combustible, and the hydrogen the supporter. The simple statement in both cases is, that oxygen and hydrogen combine together, and combustion that is, the disengagement of light and heat Illustrate this. 460. What is said of the division of bodies into combustibles and supporters of combustion? Why is this principle of classification radically deficient? 461. What is said of the re- ciprocal action of combustion ? Illustrate this by a jet of oxygen in hydrogen gas. 268 NON-METALLIC ELEMENTS. is the consequence.* The diamond burns in oxygen gas; but the latter is as much altered by the union as the former, and we cannot therefore say whether the oxygen or the carbon is the most burnt. Heat and light attend this union ; but the carbon of the human body is as truly burnt in the lungs by the atmospheric oxygen, as is the fuel of our fires ; and the product of the combustion, the carbonic acid thrown out by the lungs at every exhalation, is the same thing which is discharged at the mouth of a furnace. In the case of the animal body, the combustion is so slow that no light is evolved, and only that degree of heat (98 to 100) which is essential to vitality. We cannot- deny that there is in this case a real combustion, and yet it does not answer to our usual definition, since no light is evolved. The term combustion must have, then, a chemical sense vastly more comprehensive than its popular meaning. The rust which slowly corrodes and destroys our strongest fixtures of iron, and the gradual process of decay which reduces all structures of wood to a black mould, are to the chemist as truly cases of combustion, as those more rapid unions with oxygen which arc accompanied by the splendid evolution of light and heat. 462. The heat produced by combustion has received no satisfactory explanation. All we can say is, that any change of state in a body is accompanied by an alteration of tem- perature. When two liquids become solid, we can better understand why heat should be produced, (109.) But why the union of carbon and oxygen, to form a gas, should evolve such intense heat as to fuse the most refractory bodies, is more than has been explained. It will be remembered that chemical combination was pointed out as one of the sources of heat, and that it is strictly limited to the amount of matter suffering change. 463. The temperature at which bodies become luminous in diffuse daylight is considered to be about 1000. Gases, however, can be heated much higher without being luminous ; The burning of the diamond. What is said of those eases where no light or heat accompanies the change? 462. How is the heat of combustion explained ? 463. At what temperature do bodies become luminous ? How is it with gases ? * DanielPs Introduction to Chemical Philosophy, p. 322. COMBUSTION AND FLAME. 269 indeed, it is probable that no degree of heat whatever would make common air or any other gas visible. We may heat a combustible gas, like the olefiant, to a point when it will take fire in the air. This we do, in fact, when we touch it with the flame of a candle. The current of heated air ascending from an argand lamp chimney is invisible ; but a thin wire held in it will at once glow with bright redness, showing that the air is highly heated. A few bodies, when intensely heated in the air, suffer no change ; such are gold, platinum, palladium, and other metals not easily oxydized. The term incandescence expresses the condition of such bodies, and varies in intensity with the degree of heat. A white heat is considered equal to about 3000. A much lower temperature will inflame most combustible bodies, and the combustion, when once begun, is continued without further addition of outward heat, as is seen in our common fires. The at- mosphere in such cases supplies all that is required to con- tinue the combustion. 404. The structure of fame deserves our particular attention. Flame is ignited, combustible, aerial matter. All these conditions are needed to constitute flame, as a moment's attention will show. The flame can burn only in contact with the air, and must therefore consist of an exterior ring or shell of flame, and an interior cone of uninflamcd combustible matter. A common candle or lamp shows those conditions per- fectly. The wick draws up the tallow or oil, which is converted into a volatile hydrocarbon, as soon as it touches the ignited portion of the wick, or hot atmosphere of flame. This combustible can burn only in contact with oxygen ; and that the interior portion (a) is actually inflam- mable gas, is very easily proved, since it can be led out by a small glass tube, (&,) and set fire to from its other end. How is the high temperature of heated air made evident ? How high is the temperature of whiteness ? 464. What is flame ? How does flame burn ? Illustrate this in the case'of the common candle. How is tha interior portion seen to be combustible ? 23* 270 NON-METALLIC ELEMENT?. In like manner, by bringing a sheet of platinum foil over the 'flame of a large spirit-lamp, it will be heated to redness in a ring, while the centre will remain black, showing that the interior is comparatively cold, and the exterior intensely hot. Phosphorus may be placed on the expanded wick of a large alcohol-lamp, or on a tuft of cotton wet with alcohol, and after kindling, it can be at once extinguished, by setting fire to the alcohol, which, rising in a voluminous flame, envelops the phosphorus in an atmosphere that cannot sustain its combustion, and consequently it ceases to burn, but commences again as soon as the air comes in contact with it. 4ti5. The temperature of fame is much higher than that of ignited solids, even when the color of the flame is very feeble, as of alcohol or pure hydrogen. The quantity of light which flames emit is dependent on the presence of minute particles of solid matter, which glow with the intense heat, and reflect a strong light. This result is experienced when the flame of the oxyhydrogen blowpipe falls on lime or platina ; and the brilliant focus of the galvanic light is probably filled with the vapor of volatilized carbon, or of the metals suffering combustion. The carbohydrogen gases burn with such intense brilliancy, on account of the minute particles of carbon derived from the decomposition of the gas by the heat, which burn in the air, and thus give the strong light peculiar to these compounds. \Vhon the particles of free carbon become too numerous, and there is not oxygen enough to burn them, the flame smokes. A common tallow candle is in this con- dition, and is therefore a very im- perfect means of illumination. The various contrivances in common use, as argand and solar lamps, &c., have for their object to raise the temperature of the flame so high, by a full supply of oxygen, as to leave no carbon Illustrate this by phosphorus. 465. What is said of the tempera- ture of flame ( On what does the luminousness of flame depend ' Illustrate this. When the free carbon becomes too abundant, what happens 1 How do thp argand and solar burners improve the quality of flame COMBUSTION AND FLAME. 271 unburnt. The quantity of light thus obtained from the same quantity of oil is greatly increased, and all inconveniences from smoke and bad odors avoided. The common laboratory lamp illustrates this principle, as seen in the sectional figure. It will be observed that there is a central opening vertically through the lamp, which allows a column of air to draw up within the circular wick, and the flame is thus doubled, as compared with the common spirit- lamp, or candle. 466. The student who resides where gas is used for illumination, possesses a ready means of procuring a very powerful and economical heat, which he can command at pleasure, by regulating its intensity with a stop-cock. It is always ready and can be left for any length of time. With a mica chimney and a moveable foot connected with a flexible gas-pipe, the gas-lamp may be placed where the con- venience of the operator re- quires. A small glass spirit-lamp with a close cover to pre- vent evaporation, is an indispensable convenience even in the humblest laboratory. 467. Dr. C. T. Jackson has contrived a modification of the common argand spirit-lamp, which is the most powerful lamp-furnace in use. This invention consists in applying the principle of the mouth-blowpipe to the argand-lamp, and is accomplished by forcing a blast of air or of pure oxygen gas from a bellows, into the bottom of a tube within that which carries the circular wick. The arrangement is such, that the blast issues in a narrow ring concentric with the wick and in close contact with it. The wick is turned up pretty high, and the lower orifice of the argand tube stopped with a cork, when the blast is in use. By this lamp 600 grains of carbonate of soda are readily fused in a platinum crucible, and many operations accomplished which usually require a furnace heat. The supply of air or gas is regula- ted by a screw on the bottom of the blast tube, and the bel- lows to supply the blast is placed beneath the table and worked What is the principle of this structure ? 466. What is the gas- lamp ? 467. Describe Dr. Jackson's lamp. 272 NON-METALLIC ELEMENT?. convert the by the foot. If the intense heat is not wanted, the lower orifice is opened, and the lamp then hecomes only a power- ful argand. The chimney of this lamp must be made of mica, to withstand the heat. 468. The mouth-blowpipe enables us flame of a corn- mon candle or lamp into a pow- erful furnace. By the blast from the jet of the blow- pipe, the operator turns the flame in a horizontal direction upon the object of experiment, at the same time that he sup- plies to the interior cone of combustible matter a further quantity of oxygen. The flame suffers a remarkable change of appearance as soon as the blast strikes it, and the inner blue point has very different chemical effects from the exterior or yellow point. Immediately before the exterior flame is a stream of intensely heated air, which is capable of powerfully oxydizing a body held in it, and this point is therefore called the oxydizing fame. The inner or blue point is called the reducing flame, and in it all metallic oxyds capable of reduction are easily reduced to the metallic state or a lower degree of oxydation. Between the outer and inner flames is a point of most intense heat, where refractory bodies are easily melted. Charcoal is generally employed to support bodies before the blowpipe flame, when we would heat them in contact with carbon. Forceps of pla- tinum are used to hold the substance when it is to be heated alone ; and a small wire of the same metal, with a little loop bent on one end, is used to hold a globule of fused car- bonate of soda, or other flux, when we wish to submit a body to the action of such reageants. The art of blowing an un- intermitting stream is soon acquired, by breathing at the same 468. What does the mouth-blowpipe accomplish ?. Describe the flame. How does the blast affect it 1 Distinguish between the reducing and the oxydizing flames. COMBUSTION AND FLAME. 273 time through the mouth and nostrils ; and an experienced operator will blow a long time without fatigue. No instrument is more useful to the chemist and mineralogist than the mouth-blowpipe. By its means we may in a few moments submit a body to all the changes of heat, or the action of rea- geants, which can be accomplished with a powerful furnace.* 469. The temperature of flame may be so reduced by bringing cold metallic bodies near it as to be extinguished. On this simple fact rests the power of the " safety lamp" of Sir Humphrey Davy to protect the life of the miner. If a narrow coil of copper wire be brought over a candle or lamp so as to encircle it, the flame will be extinguished ; but if the wire be heated previously to redness, the flame con- tinues to burn. The same effect will be produced by a small metallic tube. A wire held in the flame is seen to be sur- rounded with a ring of non-luminous matter. If many wires, in the form of a gauze, are brought near the flame of a can- dle, it will be cut off and extinguished above ; only a current of heated air and smoke will be seen ascending, while the flame continues to burn beneath and heats the wire gauze red- hot in a ring, marking the limits of the flame. The flame may be relighted above the gauze, -and will then burn as usual, as seen in the second figure. Sir Humphrey Davy found that a wire gauze would in all cases arrest the progress of flame, and that a mix- // . ture of explosive gases y)v could not be fired through it. A wire gauze is only a series of very short square tubes, and their power to arrest flame comes from the fact that 469. How do cold metallic bodies affect flame ? What valuable instrument is based on this fact ? How does wire gauze affect flames ? What may the wire gauze be considered ? What temperature do the carbohydrogens require for their combustion ? * The student would do well to consult " Berzelius on the Blow- pipe," translated by J. D. Whitney. Boston, 1845 ; Ticknor & Co. j 12mo. pp. 237, 274 NON-METALLIC TLEMKNTS. they cool the gases below their point of ignition. Providen- tially, the heat required to ignite the carbon gases is much higher than that which will produce the union of oxygen and hvdrogen. 470. Safety Lamp. The explosion of inflammable gases in coal mines has destroyed thousands of those whose duties required them to submit to the exposure. To avoid these lamentable accidents, Davy invented the miner's lamp, which is only a common lamp surrounded by a cage of wire gauze completely enclosing the flame. When this lamp is placed in an explosive atmosphere, the gas enters the cage, enlarges the flame on the wick, and burns quietly, the gauze effectually preventing the pas- sage of the flame outwards. We thus enter the camp of the enemy, disarm him, and make him labor for us. The miner is not only protected by this instrument, but is rendered conscious of his danger, by the enlargement of his flame. As long as the lamp can burn, it is sale to stay, as an irrespirablc atmosphere would extinguish the flame. The powerful blast of wind which sometimes sweeps through the mines may render the lamp unsafe, by forcing the flame against the gauze, until it is heated so hot as to inflame the external atmosphere. This accident is prevented by the addition of a glass to cover the sides, the air being admitted from below through flat gauze discs. 471. The phenomena of the safety lamp may be easily illustrated by the teacher, with a large bell glass placed over a naked lamp and left open beneath. Hydrogen may be admitted from below by a gas-pipe, when the atmosphere soon becomes explosive and goes ofT, extinguishing the lamp. The miners lamp under the same circumstances, will first burn with an enlarged flame, and then go out quietly, as soon as the air can no longer support the combustion. 470. For what use was the miner's lamp contrived ? How is it constructed ? How does it indicate the state of the atmosphere in the mine? 471. How are the phenomena of the safety lamp illus- trated ? METALLIC ELEMENTS. 275 II. METALLIC ELEMENTS. 1. General Properties of Metals. 472. The number of the metallic elements is about forty-two, or three times the number of the non-metallic bodies, which have already engaged our attention. If we include five lately proposed new metals, we shall have forty-seven bodies in this class. Of all this number, however, a few only are of con- siderable interest, while many (at least half) are totally un- known in common life. The minerals which contain several of the rare metals, in combination with various substances, are among the most uncommon specimens of mineralogical cabinets. 473. A metal is a body which conducts electricity and heat, which is opaque, and has a peculiar brilliancy, known as the metallic lustre. It has been before remarked (251) that metallic lustre is the only property which belongs pecu- liarly and solely to this class of bodies. A metal, when submitted in solution to electrolysis, is always given out at the negative side of the battery, and is therefore a positive electric. Any body which possesses these general properties is a metal, according to our present notions of the metallic character. We see every variety in some of these charac- ters. Some metals are almost without lustre, as manganese, whife others, like gold and silver, may stand as examples of perfection in this as well as in all other metallic properties. Opacity is not complete even in gold and mercury, as already mentioned, (53.) Some metals are perfectly malleable when cold, as silver, gold, lead, and tin ; others are malleable when hot, as iron, platinum, &c., and are not without this property, though in a less degree, even when cold. Some, like zinc, are larninable at a moderate heat, but brittle above and below it ; others, like antimony, are brittle at all temperatures short of fusion. We have already explained (18) the properties of brittleness, malleability, ductility, and laminability. The tenacity of metals depends much on their relations to these 472. What is the number of metallic elements ? How many of these are of much importance ? 473. What is a metal ? How do they act in electrolysis ? What variety is seen in the metallic character ? Is opacity perfect in them? Mention their characters. 276 METALLIC ELEMENTS. properties. Iron is an example of great tenacity and duc- tility, while in malleability it is much inferior to gold and silver. 474. The tenacity of metals is compared by using wires of the same size of different metals, and ascertaining how much weight they will sustain. Iron is the most tenacious, and lead the least.- Wires are drawn through * * smooth conical holes in a steel plate, each succeeding hole being a little less than its pre- decessor. In this way wires of extreme fine- ness may be drawn from several of the ductile metals. Dr. Wollaston succeeded, by a pecu- \ .* liar method, in making a gold wire so small ^-' that 530 feet of it weighed only one grain ; it was only y^TT ^* an mc h m diameter; and a platinum wire was made by the same philosopher, of not more than -j^^ of an inch. Metals passed repeatedly through the rolling- mill, or wire plate, become stiff and brittle, but are again made soft by heating them to redness and cooling them slowly. This is called annealing. Copper is annealed by plunging the red-hot metal into cold water, while the same treatment renders iron and steel extremely hard. 475. The fusibility and density of metals differ very much. Platinum is at once the most dense of all bodies, being 21 to 21 -5, and also one of the most infusible. Gold is next in density, (19-26,) but fuses at 2016 F. Palladium, uranium, cobalt, nickel, iron, molybdenum, manganese, colurnbium, tungsten, and titanium, are all infusible below 3000, (the heat of the most powerful air furnace ; and most of these are altogether infusible. In density, sodium and potassium occupy the lowest points, (-972 and -865,) being less in density than water, and they also fuse at the low temperature of 190 and 136. 476. Metals vary also in volatility as much as in other properties. Mercury boils at 662, and arsenic, tellurium, cadmium, zinc, potassium, and sodium, are also volatile at 474. How is the tenacity of metals compared ? Explain the use of the wire plate. How fine have wires of gold and platinum been made? What is annealing? How is it accomplished in different metals ? 475. How do the density and fusibility of metals com- pare ? 476. How do metals compare in volatility by heat ? Mention some of the volatile ones. GENERAL PROPERTIES OF METALS. 277 temperatures below a red heat. It is not impossible that all the metals would be volatile, if we could heat them highly enough ; but many of them, as gold, platinum, silver, &c., may be exposed to the highest heat of a wind-furnace with- out change. Some metals assume a semi-fluid or pasty con- dition before melting, such as platinum and iron, both of which can be welded or made to unite without solder, when in this soft state ; lead, potassium, and sodium, can be welded in the cold, as also can mercury, when it is frozen. In cooling from fusion, some metals crystallize beautifully, of which bismuth is an example, while others, as gold and platina, are not commonly seen in the crystalline form. 477. The metals are rarely found in their metallic state in nature. Their characters are generally masked under some form of combination with oxygen or sulphur. Thus, iron is perhaps never seen in a malleable form in mines. The masses of malleable iron found on the surface of the earth are probably all of meteoric origin, having fallen through the atmosphere to the earth. Some metals, as gold, silver, platinum, copper, bismuth, and a few others, are frequently found native, or in the malleable form, either pure or alloyed with each other. An alloy is the union of two metals, as of copper an3SO3 + KO,SO 3 -f 24HO, (205;) it dissolves in 18 parts of cold water, and the solution has an acid reaction. 569. Alum and Acetate of Alumina are largely employed in the arts of dyeing and tanning. Alumina combines with coloring matters, and seems to form a bond of union be- tween the fibre of the cloth and the color. In this it is said to act the part of a mordant. When alum is added to the solution of a coloring matter, and the alumina is precipitated with an alkali, all the coloring matter is thrown down with What are its properties ? How is its hydrate described ? What difference is there in the two forms of alumina ? How is alumina distinguished by tests ? 568. What is the sulphate of alumina ? What are alums? Give the formula of common alum. 569. In what art is alum much used ? How does it act with colors ? What are lakes ? 310 METALLIC ELEMENTS. it and forms what is called lake. The common lake used in water-coloring is" derived from madder treated in this way. Carmine is a lake made from cochineal. 570. Silicates of Alumina. This is the most extensive and important class of the aluminous salts, and comprises a great number of interesting minerals. Feldspar, (A1 2 O 3 , 3SiO 3 -r-KO,SiO 3 ,) which is one of the chief components of granite and granitic rocks, is of this class, and has the com- position of an anhydrous alum, the sulphuric acid being replaced by the silicic. Kyanite and Sillimanite are simple basic silicates of alumina. Albite is a salt having soda in place of the potash in feldspar, while spodumene and petalite are similar compounds, with a portion of the soda replaced by lithia. Many other similarly constituted compounds are found among minerals, some of which are hydrous and others anhydrous, and varied by frequent substitution of peroxyd ot iron, or other isomorphous bases, for the alumina. 571. Pottery. The decomposition of feldspar and other aluminous minerals and rocks, gives origin to the clays which are so important in the art of pottery. Decomposed feldspar forms porcelain clay, commonly called kaolin. The undecomposed mineral is often ground up to mix with the materials for porcelain. The feldspar of Middletown, Ct., and Wilmington, Delaware, is used in large quantities for this purpose. The difference between porcelain and earthen ware, con- sists in the partial fusion of the materials of the former by the heat of the furnace, which gives it the semi-transparency and great beauty for which it is so highly prized. The glaze in porcelain is formed of a more fusible mixture of the same materials, put over the articles as a wash, after they have been once through the furnace ; (in which state they are called biscuit ware ;) they are then baked again at a heat which fuses the glaze, but which does not soften the body of the ware. 572. The painting of porcelain is an art requiring a refined knowledge of chemistry. All the colors used in this art are 570. What is the most important class of alumina compounds ? Give the composition and properties of feldspar. 571. What is the origin and composition of clays ? Of what material is porcelain composed ? How does it differ from earthen ware ? Of what does the glaze consist ? GLUCINCM, YTTRIUM, &C. 311 metallic oxyds, which are put on after the ware has been once baked. The colors result from compounds formed by the metallic oxyds with alumina by fusion, and do not ap- pear until after the baking. Metallic gold is put on in the form of an oxyd, and the steel lustre is produced by metal- lic platinum. 24. GLUCINUM. 25. YTTRIUM. 26. ZIRCONIUM. 27. THORIUM. 28. CERIUM. 29. LANTANUM. 573. All these metals are so rare as to be known only to chemists. Their oxyds occur in several minerals, nearly all of which are among the most uncommon specimens in min- eralogical collections. Glucina, (24,) or the sesquioxy,d of glucinum, (G 2 O 3 ,) is the most abundant, being found to the amount of 17 per cent, in the gems, beryl, emerald, and chrysoberyl. It very much resembles alumina, and is named in allusion to the sweet taste of its salts. Yttria, (25,) the oxyd of yttrium, (YO,) is a white earthy powder, form- ing sweetish salts, but differing from alumina and glucina in not being redissolved like them in an excess of potash and soda : this earth is found in the minerals yttro-cerite, gadoli- nite, and yttro-tantalite. Zirconia, (26,) sesquioxyd of zir- conium, (Zr 2 O 3 ,) which is the earth of the zircon or hyacinth, much resembles alumina, but differs from it and from gluci- cina, yttria, and thorina, by being precipitated from its solutions, as an insoluble sulphate, by boiling with solution of sulphate of potash. Thorina, (27,) the oxyd of thorium, is found in only one or two very rare minerals, as in thorite and monazite ; its specific gravity is 9, being much higher than any other earth. Cerium, (28,) and Lantanum, (29.) The oxyds of these two rare metals are invariably associated with each other, and also with that of another metal, didy- mium, not yet fully described ; they are found only in some very rare minerals, as cerite, allanite, monazite, &c. The oxyd of cerium forms beautiful yellow salts, while the oxyd of lantanurn forms equally beautiful rosy compounds ; the latter has been named in allusion to its having been long con- cealed or hidden under cerium, with which it is associated. 572. How is porcelain colored ? 573. What six metals included in this section ? In what mineral is glucina found ? Describe yttria. In what mineral is zirconia found ? What are its properties ? What is said of thorium ? With what is cerium always associated ? 312 METALLIC ELEMENTS. CLASS IV. METALS WHOSE OXYDS FORM POWERFUL BASES. 30. MANGANESE. Equivalent^ 27-67. Symbol, Mn. Density, 8. 574. Manganese is never found as a metal in nature, but may be produced from its black oxyd by a high heat with charcoal. Metallic manganese is a gray brittle metal, not magnetic, and resembles some varieties of cast iron. It dis- solves rapidly in sulphuric acid with escape of hydrogen. Manganese in the form of the black oxyd is an important and pretty common metal. Its great use is for producing chlorine, (260,) and in the manufacture of glass, where it acts by its oxygen to decolorize the compound. 575. The oxyds of manganese are numerous ; we give the formulas of six, and there are possibly one or two more, viz : protoxyd, MnO ; sesquioxyd, (or braunite,) Mn 2 O 3 ; peroxyd, or deutoxyd, (pyrosulite,) MnO 2 ; red oxyd, (haus- mannite,) Mn 3 O 4 ; manganic acid, Mn0 3 ; hypermanganic acid, Mn 2 O 7 . The Protoxyd is a green-colored powder, formed from heating the carbonate of manganese in hydrogen. It is a powerful base, attracts oxygen from the air, and is the base of the beautiful rose-colored salts of manganese. The sesquioxyd or braunite occurs crystallized in octahe- drons, and forms belonging to the dimetric system. The Hydrated Sesquioxyd (manganite) is a finely crystal- lized mineral in long black prisms, found in superb speci- mens at Ilfeld, in the Hartz. In powder the sesquioxyd is brown ; it is decomposed by hydrochloric acid with the evo- lution of chlorine, but sulphuric acid combines with it to form a sesquisulphate, which yields a purple double salt with sul- phate of potash, (manganese alum,) isomorphous with the corresponding salt of alumina. This salt is, however, very easily decomposed by a gentle heat. 574. What is said of manganese ? What form of it is most com- mon ? For what is it used ? 575. How many and what oxyds of manganese are named ? Which is the base of the rose-colored salts ? What is the sesquioxyd ? What is the hydrated sesquioxyd ? What is said of the sulphate of the sesquioxyd ? MANGANESE. 313 576. The Perosyd is the most common ore of manganese, and has a high commercial value. It is found abundantly at Bennington, Vt., and other places in this country. When crystallized it is called pyrolusite, and beautiful specimens of this mineral have been observed at Salisbury and Kent, Conn., among the iron ores. 577. Manganic Acid is known only in combination, gen- erally as manganate of potash. This is best formed by mixing equal parts of finely powdered black oxyd of manganese and chlorate of potash with rather more than one part of hydrate of potash dissolved in a very little water. This mixture when evaporated is heated to a point short of redness, and a dark green mass is formed which contains manganate of potash. In this case the manganese obtains oxygen from the chlorate of potash, and the manganic acid thus formed combines with potash, giving a salt in green crystals. This salt, dissolved in water, gives a brilliant emerald-green solution, which almost immediately changes color, being in quick succession green, blue, purple, and finally crimson-red, and has thence been called chameleon mineral. This last color is due to the presence of permanganic acid, which, however, cannot be separated from its combinations, but forms a salt with potash in beautiful purple crystals. The compounds of per- manganic acid are more stable than the manganates. The salts of these acids are respectively isomorphous with sul- phates and perchlorates, (SO 3 and CI 2 O 7 .) 578. The chlorids of manganese (MnCl and Mn 2 Cl 3 ) correspond to the protoxyd and sesquioxyd. The chlorid is formed abundantly in acting on black oxyd of manganese, (260,) with hydrochloric acid. The mixed solution of chlo- rids of iron and manganese is evaporated to dryness, and then heated to dull redness. The chlorid of manganese is then dissolved out from the dry mass, leaving the insoluble protoxyd of iron behind. It has a beautiful pink tint, and deposits tabular rose-colored crystals on evaporation. It is soluble in alcohol, and fusible by heat. The sesquichlorid is formed by solution of sesquioxyd in cold hydrochloric acid, but is decomposed by a gentle heat and evolves chlorine. 576. Which is the most common ore of manganese ? Where and how is it found? 577. Describe manganic acid and the curious salt it forms with potash. What is the changeable compound called ? What is said of the salts of manganic and permanganic acid ? 578. Describe the chlorids of manganese. 27 314 METALLIC ELEMENTS. 579. The salts of manganese are numerous, and in a chemical view quite important. Sulphate of manganese is a very beautiful rose-colored salt, isomorphous with sulphate of magnesia. It is used to give a fine brown dye to cloth, being decomposed by a solution of bleaching-powder, which forms the brown peroxyd in the fibre of the stuffs. 31. IRON. Equivalent, 27.14. Symbol, Fe. Density, 7*8. 590. Iron is found mallcabh, and alloyed with nickel, in large masses of meteoric origin. One of these, discovered in Texas, weighs 1635 pounds, and is now in Yale College Cabinet. It is not certain that malleable iron of terrestrial origin has yet been discovered -in nature. Iron is the most abundant and most important metal known to man. Its ores are found everywhere, and often in immediate connection with the coal and limestone necessary to reduce them to the metallic state. There is no soil, and scarcely any mineral, which does not contain some proportion of the oxyd of iron. 581. Pure iron is difficult to prepare. The purest iron of commerce is always contaminated with a portion of silicon and carbon. When quite pure it is nearly white, quite soft, perfectly malleable, and the most tenacious of all metals. Its density is 7*8, which may be a little in- creased by hammering. It crystal- lizes in forms of the first class, as is beautifully shown in the crystalline structure of the meteoric iron. It fuses with extreme difficulty, first becom- ing soft or pasty, in which state it is welded. When intensely heated in air or oxygen gas it combines with oxygen, burning with brilliant light and numerous scintillations, and is converted into oxyd of iron, (255.) Iron also attracts oxy- gen at common temperatures, forming rust. This does not 579. What is said in general of the salts of manganese ? 580. What is the equivalent of iron ? How is malleable iron found ? What is said of its abundance and value ? 581. Give the properties of iron. What is said of its fusion and welding? How does it be- have with oxvcen ? IRON. 315 happen in dry air, but the presence of moisture, and particu- larly of a little acid vapor, very much promotes its formation. Iron decomposes water very rapidly at a red heat, hydrogen being evolved. It is the chief medium of magnetism, being powerfully attracted by the magnet, and also itself suscepti- ble of this influence. 582. The chief ores of iron are, (1,) brown hematite or hydrous peroxyd, from which the best iron is made. (2.) The red hematite and specular iron or peroxyd. (3.) Clay iron stone, which is an impure carbonate of iron, or carbon- ate of iron with carbonate of lime and magnesia. This is the nodular ore of the coal formations. (4.) Black or mag- netic oxyd of iron, which is the ore of the iron mountains of Missouri and of Sweden. 583. The reduction of the ores of iron to the metallic state is performed in large furnaces called high or blastfur- naces. These are built of stone, in a conical form, 30 to 50 feet high, and lined internally with the most refractory fire-bricks. The furnace is divided into the throat, the fire-room, (6,) the boshes, (e,) (that portion sloping inward,) the crucible, (,) and the hearth, (h.) The blast of air supplied from very large blowing cylinders is introduced by two or three tuyere pipes (aa) near the bottom. In the most improved furnaces, the air-blast is heated by causing it to pass a \ through a series of pipes in the upper portion of the furnace, so as to have a temperature of 500 or more when it enters the furnace. When the furnace is brought into action, it is first heated with coal only, for about 24 hours ; and then is charged alternately with proper proportions of coal, roasted ore, and lime for flux, until it is quite full. When once brought into action, the blast is kept up for months or even years, until 582. What ores of iron are enumerated ? 583. How is the reduc- tion of iron effected ? Describe the high furnace. What is the hot blast ? 316 METALLIC ELEMENTS. the furnace requires repairing. The ore is reduced on the boshes, and in the upper part of the crucible, and the melted metal collects on the hearth, covered by the molten flux, which is a glass formed by the fusion of the lime used and the earthy parts of the ore. From time to time, the iron is drawn olF by an opening previously stopped with clay, and run into rude open moulds in sand. This is cast iron, and is of various qualities, according the various character of the ore, and the working of the furnace. If malleable bar iron is wanted, the cast-iron is again melted, in what is called the puddling furnace, where it is stirred about by an iron rod, in contact with oxyd of iron, and a current of heated carbonic oxyd from the high furnace. It gradually becomes stiff and pasty from the burning out of the carbon, and from some molecular change not well understood. It is finally raised in a rude ball and placed under the blows of a huge tilt-hammer, when the scoria is pressed out and the particles made to cohere. It grows tenacious by a repetition of this process, being cut up and piled or faggoted and reheated several times, until it is finally made into tough and fibrous metal. 584. Steel is formed from refined iron by heating in con- tact with charcoal in close vessels, (called cementation.) It gains from one to two per cent, of carbon, becomes fusible, and can be tempered according to the use for which it. is designed. 585. The oxyds of iron are four, viz: (1,) protoxyd, (FeO;) (2,) sesquioxyd, commonly called peroxyd, (FejOa ;) (3,) black oxyd, (magnetic oxyd,) (Fe 3 O 4 ,) and (4) ferric acid, (Fc0 3 .) (1.) The Protoxyd of Iron is a powerful base which is unknown in nature except in combination. It saturates acids completely and is isomorphous with a large class of bodies, of which zinc and magnesia are examples, (232.) This oxyd is thrown down from its solutions by potash, as a whitish bulky hydrate, that soon gains another dose of oxy- gen from the air becoming brown, and finally red. Its salts when soluble have a styptic taste like ink and a greenish color. What is the operation of the furnace ? What is cast iron ? How is malleable iron made from cast iron ? 584. What is steel ? 585. What are the oxyds of iron ? Give their formulas. Describe the protoxyd. IRON. 317 586. (2.) The Peroxyd of Iron is found native in the beautiful specular iron of Elba, and also in the red and brown hematites. It is slightly acted on by the magnet, and after ignition is almost insoluble in strong acids. It is iso- morphous with alumina, and is generally associated with it in soils and many minerals. It is often of a brilliant red, and as ochre of various tints is much used as a pigment. Am- monia precipitates it from its solutions as a bulky red hydrate. 587. (3.) Black Oxyd of Iron is familiarly known in the common magnetic iron ore and native lode-stone. It crystal- lizes in octahedrons. It forms no salts. The fiery cinders or scales thrown off under the smith's hammer are this oxyd. (4.) Ferric Acid is a new compound, corresponding to manganic acid, discovered by M. Fremy. A ferrate of pot- ash is formed, when one part peroxyd of iron and four parts of nitre are heated to full redness in & covered crucible for an hour. The ferrate of potash is dissolved out of the porous mass by ice-cold water. The solution has a deep amethys- tine color, and is easily decomposed by heat. A soluble salt of baryta precipitates ferric acid as a beautiful red ferrate of baryta, which is permanent. The chlorids of iron (FeCl and Fe 2 Cl 3 ) correspond to the protoxyd and sesquioxyd (peroxyd) of the same base. The latter is often used in medicine and may be formed by satu- rating hydrochloric acid with freshly prepared peroxyd of iron. The protiodid of iron is also a valuable medicine. 588. The sulphurets of iron are found native, and are well known as pyrites. The protosulphuret is easily formed artificially, by fusing sulphur with iron-filings ; they ignite with a vivid combustion, (459,) and protosulphuret of iron is formed, which is much used in preparing sulphureted hydro- gen. Yellow iron pyrites and white iron pyrites are dimorphous forms of the bisulphuret, (FeS 2 ;) the first is one of the most common of crystallized minerals. The mag- netic sulphuret, magnetic pyrites, corresponds in composition to the magnetic oxyd. 586. How is the peroxyd known ? 587. What is the black oxyd ? What is ferric acid ? What chlorids of iron are named ? What oxyds do they correspond to ? 588. What are the sulphurets of iron 1 For what is the protosulphuret used ? What is the name of the ordinary sulphuret ? 27* 318 METALLIC ELEMENTS . Of the salts of iron, the green rtriol or protosul- phate (FeO, SO 3 -f 7HO) is the most important. It is made in immense quantities, as at Stafford, Vt., from the decompo- sition of iron pyrites, which furnishes both the acid and the base. This salt crystallizes beautifully, and is much used as the basis of all black dyes and ink, and in the manufacture of prussian blue. It is called copperas in the arts. Persul- phate of iron is a sulphate of the |>ero.\yd, (Fe-Os + tfSOg.) Carbonate of iron occurs in nature as spathic iron ore, which is isomorphous with carbonate of lime. A variety of steel is made directly from this ore without cementation, (o^-l.) It is formed artificially by precipitating a solution of sulphate by an alkaline carbonate, and is used in medicine. The presence of a salt of iron is easily detected by the fine blue (prussian blue) formed on adding prussiate of potash to the solution ; an infusion of galls gives a black color (ink) to solutions of iron. 32. cnROMirM. Efimvalent, 28-14. Symbol, Cr. Density, 0. 590. Chromium in combination irith iron is rather an abundant substance, particularly in this country, bcin^ Ibund as chromic iron at iinrchills, near Baltimore, Lancaster Co., Pa., and in other places. The beautiful red chromate of lead is also a natural product in iSil>eria. The metal, from its great affinity for oxygen, is very difficult to procure. It is n hard, almost infusible substance, resembling cast-iron, nearly insoluble in acids, and does not decompose water. I may be oxydizcd by fusion with nitre, but does not change in the air. 591. Chromium forms five compounds with oxygen; of which the sesquioxyd (Cr 2 O 3 ) and chromic acid (CrO,) are the most important. Chromium bears the strongest analogy in its chemical character to manganese and iron. The per- fect identity of constitution in the oxyds of these three metals is shown in the following tabular arrangement : 589. Which of the salts of iron are named as very important ? How and where is it made in this country ? What is the carbonate and for what used ? 590. Give the equivalent and symbol of chro- mium. How is it found associated? What of the metal? 591. What compounds does chromium form with oxygen ? CHROMIUM. 319 Acids. Protoxyd. Sesquioxyd. Black oxyd. x Manganese forms, MnO MmQs M n 3 O4 MnOa Mn 2 O 7 . Iron forms, FeO Fe 2 O 3 Fe 3 O 4 FeO 3 Chromium forms, CrO CraOa Cr 3 4 CrO 3 Cr 2 O 7 . The Protoxyd of Chromium has only very lately been formed by M. Peligot, and is a strong base. It acts in com- bination like the protoxyd of iron, with which it is isomor- phous. 592. The Sesquioxyd of Chromium is easily prepared, by treating a boiling and rather dilute solution of bichromate of potash, with an excess of hydrochloric acid, and then with small successive portions of alcohol or sugar, until it assumes a fine emerald green tint. Ammonia in slight excess will now throw down the hydrated oxyd as a bulky pale green precipitate, soluble in acids. When this precipitate is dried, it shrinks very much, and on ignition suddenly undergoes a vivid incandescence and becomes deep green. The sesqui- oxyd of chromium is a feeble base like those of iron and alumina, and may replace them in combination, as in the for- mation of chrome alum with sulphate of potash. All the salts of this oxyd are either emerald green or bluish purple. It imparts a rich tint of green to glass and porcelain, and is the cause of the color of the emerald. The Protochlorid of Chromium (CrCl) is obtained as a white and very soluble substance by the action of dry hydro- gen gas on the following compound. The Sesqvichlorid (Cr 2 C1 3 ) is prepared by passing chlorine gas over an ignited mix- ture of the sesquioxyd and charcoal. It forms a crystalline sublimate of a peach-blossom color, and is insoluble in water. The sesquioxyd dissolves in hydrochloric acid, but the hydra- ted chlorid thus obtained is decomposed by heat. 593. Chromic Acid (CrO 3 ) is readily formed by treating a cold and concentrated solution of bichromate of potash with one and a half parts of sulphuric acid. The mixture when cold deposits brilliant ruby-red prisms of chromic acid. The sulphate of potash in solution above, may be turned off, and the chromic acid dried on a porous brick, being carefully With what metals is it closely allied ? How is this relation shown ? Give the comparative formulas of the oxyds of manganese, iron, and chromium. What is said of the protoxyd ? 592. How is the sesquioxyd prepared ? What are \ts properties and analogies ? 593. How is chromic acid prepared * What are its properties ? 320 METALLIC ELEMENTS. covered with a glass to prevent access of organic matters, which at once decompose it. If a little of this acid bo thrown into alcohol or ether, the violence of the action is such as to set fire to the mixture. Chromic acid forms numerous salts, which are all highly colored. 594. The Chromate of Potash and the Bichromate are both familiar examples. The first, (KG, CrO 3 ) is formed on a very large scale by decomposing the native chromic iron with nitrate of potash, by aid of heat. Chromate of potash is dissolved out from the ignited mass, and crystal- lizes in anhydrous yellow crystals. It is isomorphous with sulphate of potash, dissolves in two parts of cold water, and is the source of all the preparations of chromium. Bichromate of Potash (KO, 2CrO 3 ) is formed by adding sulphuric acid to a solution of the yellow chromate, when half the |>otash is removed, and the bichromate crystallizes by slow evaporation in brilliant red crystals of a rhombic form, which are soluble in ten parts of cold water. 595. Chromate of Lead Chrome Yellow (PbO,CrO 3 ,) is the well-known pigment prepared by precipitating the nitrate or acetate of lead by a solution of chromate or bichro- mate of potash. Chrome Green is the oxyd of chrome, pre- pared in a particular way. Chlorochromic Acid (CrO^Cl) is a deep red volatile liquid resembling bromine, which appears when equal weights of common salt and bichromate of potash are intimately mixed, and heated in a retort with three parts of sulphuric acid. The chlorochromic acid distils over, filling the receiver with a superb ruby-red vapor. Water decom- poses it, forming chromic and hydrochloric acids. 33. NICKEL. Equivalent, 29*59. Symbol, Ni. 596. Nickel is rather a rare metal, but may be prepared from the speiss or crude nickel of commerce. It is white and malleable, having a density of 8'27, and fuses above 3000. It is not easily oxydized, and is one of the two or Describe the chlorids of chromium. ,"594. How is chromate of potash formed T Bichromate of potash is how formed ? 595. What is chrome yellow ? What chrome green ? Describe chlorochromic acid. 596. In what state does nickel occur in nature ? COBALT. 321 three magnetic metals ; magnets may be made of it nearly as powerful as those of iron. Nickel is almost always found alloyed in masses of meteoric iron. In this country it has been obtained at Chatham, Ct. as an arseniuret, and also at Mine la Motte, in Missouri, as an earthy oxyd associated with cobalt. A beautiful green hydrous oxyd of nickel has been found lately in Lancaster Co., Pa., having the composi- tion NiO + 2HO. There are two oxyds of nickel. The protoxyd (NiO) is prepared by precipitating a solution of nickel by caustic pot- ash, which gives a grass-green hydrated oxyd, which by heat loses its water and becomes gray. The oxyd of nickel is isomorphous with magnesia, and has been obtained crys- tallized in regular octahedrons. The salts of this oxyd have a fine green color, which they impart to their solutions. The peroxyd of nickel (NiO 3 ) is a dull black powder, of no particular interest. 597. The Sulphate of Nickel (NiO,SO 3 + 7HO) is a fine- ly crystallized salt occurring in green prisms, which lose their water of crystallization by heat. It forms beautiful well crystallized double salts, with the sulphates of potash and ammonia. Oxalic acid precipitates an insoluble oxalate of nickel from the solution of the sulphate, and the metallic nickel is easily obtained from the oxalate by heat. Nickel is chiefly employed in making German silver, a white malleable alloy, composed of copper 100, zinc 60, and nickel 40 parts. 34. COBALT. Equivalent, 29-52. Symbol, Co. 598. Cobalt is a metal almost always associated with nickel, and closely resembling it in many of its reactions. When pure it is a brittle reddish white metal, with a density of 8'53, and melts only at very high temperatures. It is generally said to be magnetic, but is not so when quite pure. It dissolves with difficulty in strong sulphuric acid, and is not oxydized in air. It forms two oxyds every way analogous to those of nickel. Its protoxyd is a grayish pink powder, very soluble in hydrochloric acid, and forming pink salts. This oxyd occurs native. Describe its properties. What are its oxyds ? In what form does the protoxyd crystallize ? 597. Describe the sulphate and oxalate of nickel. What is the composition of German silver ? 598. Wha* are the characters of cobalt ? 322 METALLIC ELEMENTS. The Chlorid of Cobalt (CoCl) is formed by dissolving the oxyd in hydrochloric acid. The solution is pink, and when verv dilute may be used as a blue sympathetic ink, which may be made green by mixing a little chlorid of nickel. Writing made with this on paper is colorless when cold, but becomes of a fine blue or green when gently warmed, and loses its color again on cooling. The salts of cobalt and nickel are isomorphous with those of magnesia. They are not thrown down by sulphureted hydrogen, but give blue or green precipitates with potash, soda, and their carbonates. The same precipitates with ammonia are soluble in excess of that reagent. Oxyd of cobalt imparts a splendid blue to glass, and the pulverized glass of this color is called smalt and powder blue. Zajfre is an impure oxyd of cobalt used to give the fine blue color to common earthen ware. 35. ZINC. fyuivalent, 33. Symbol, Zn. Density, 6-86. 599. Zinc is an important and rather common metal. It is not found native, but a peculiar red oxyd of zinc abounds at Sterling, Xesv Jersey, and calamine or carbonate of zinc is found abundantly in many places. The ores of zinc are reduced by heat and charcoal, in large crucibles closed at top, but having an iron tube descending from near the top, through the bottom, and terminating in a vessel of water. The metal being volatile, rises and escapes by the tube into the water. This is called distillation by descent. 600. Zinc is a bluish white metal, easily oxydized in the air, and crystallizes in broad foliated laminae, well seen in the fracture of an ingot of the commercial article. It is called spelter in the arts, and is used chiefly to alloy copper in forming brass. Zinc is not a malleable metal, at ordinary temperatures, but at a temperature of between 250 and 300 it becomes quite malleable, and is then rolled into sheet zinc. At 400 it is again quite brittle, and may be granula- What interesting experiment is mentioned with the chlorid ? With what metal is the oxyd of cobalt and its salts isomorphous ? What use is made of the oxyd of cobalt ? 599. How is zinc reduced from its ores ? 600. What are its properties ? At what temperature is it malleable ? CADMIUM. 323 ted by blows of the hammer ; at 773 it melts, and if air has access to it, it takes fire, and burns rapidly with a bril- liant whitish green flame, giving off flakes of white oxyd of zinc, sometimes called lana philosophica. It is completely volatile at a red heat. The Chlorid of Zinc, ZnCl, is a salt easily prepared when zinc is dissolved in hydrochloric acid, hydrogen being evolved. Sulphuret of Zinc, Blende, ZnS, occurs native in the forms of the first crystallographic class, and is colored yel- low, brown, and black. This is one of the ores of zinc (called black Jack) from which the metal is obtained. The oxyd (ZnO) is a white powder, insoluble in water, but easily dissolved in all acids, forming a series of salts, of which the most important is Sulphate of Zinc, or White Vitriol, ZnO, SO 3 -f 7HO. - This salt has the same form as the sulphate of magnesia, and looks extremely like it. It dissolves in 2^ parts of cold water, and forms double salts with the sulphates of ammo- nia and potash. It is a powerful emetic. Sulphuret of ammonium throws down a characteristic white precipitate of sulphuret of zinc from its neutral solu- tions. 36. CADMIUM. Equivalent, 55'74. Symbol, Cd. Density, 8'65. 601. Cadmium is generally found associated with zinc, and is almost as volatile as mercury. It is quite malleable, white, and harder than tin. It fuses at 442, and volatilizes at a temperature a little above this. It is not easily oxydiz- ed, and is but slightly soluble in hydrochloric or sulphuric acids. Nitric acid dissolves it with ease, forming a salt from which sulphureted hydrogen throws down a very char- acteristic orange-yellow sulphuret. This compound is also found native and crystallized, (greenockite.) Its oxyd (CdO) is a bronze powder, formed by igniting the nitrate or carbonate. Is it combustible ? Describe the sulphuret. What is said of the sulphate ? 601. What are the properties of cadmium ? Describe its sulphuret. 324 METALLIC ELEMENTS. 37. LEAD. Equivalent, 103-56. Symbol, Pb. Density, 11-35. 602. This useful and familiar metal occurs in boundless profusion in this country, chiefly as galena, or sulphuret of lead, from which the metal is easily obtained by smelting the ore with a limited amount of fuel, at a low heat. The car- bonate, phosphate, chromate, and arscniate, are also natural salts of lead much prized by the mineralogist. Lead is a bluish gray metal, very soft and ductile, but not very tena- cious ; it oxydizes in the air quite rapidly, forming a coat of oxyd, or carbonate, which protects it from further corrosion. Its density is 11-35, and it fuses at 612; when melted it combines rapidly with oxygen from the air, forming either protoxyd, or red oxyd, according to the heat. Lead is slowly acted upon by soft or rain water, and in some cases by hard water ; so that it is unsafe to use water- pipes of lead, unless it has been proved by experiment that the particular water in question . does not act on this metal. It is a deadly poison, at least in the form of carbonate, which is generally produced under these circumstances. Lead does not easily dissolve in dilute acids, except in nitric, with which it forms a soluble salt : strong sulphuric acid dissolves it when heated, forming a nearly insoluble sulphate of lead. There are three oxyds of lead, of which only the protoxyd has basic properties. 603. Protoxyd of Lead ; Litharge, PbO. This oxyd is a yellow powder, formed by slowly oxydizing lead, with heat. It is slightly soluble in water, and the solution is alkaline. It fuses easily, and then dissolves silica with great rapidity; hence its use in glazing pottery, (571,) and in the manufacture of glass, (535.) It forms a large class of definite salts, which have often a sweet taste, as is seen in the acetate or sugar of lead. The sesqnioxyd has the formula PbaOa, and is a reddish yellow insoluble powder. The Pcroxyd, PbO 2 , is prepared by acting on the red lead 602. What is the chief ore of lead ? Describe the metal. How does water affect lead ? 603. Describe the protoxyd of lead. The other oxyds. What use is made of litharge ? LEAD. 325 with nitric acid ; it is a puce-colored body which acts the part of an acid, withi bases forming salts. 604. Red Oxyor Red Lead, Pb 3 O 4 . This is a com- mon pigment, ancHs formed when melted lead is exposed to a temperature of 600 or 700. It is of variable constitution, according to the temperature at which it is prepared. Acted on by hydrochloric acid, it evolves chlorine, and with sul- phuric acid, oxygen is given off. It is preferred to litharge for glass making. The chlorid and iodid of lead possess no particular interest ; the latter crystallizes in beautiful yellow scales from its so- lution in hot water. The sulphuret of lead is the native galena already mentioned, and occurs in brilliant cleavable cubes. Sulphureted hydrogen throws down a black sulphu- ret from all soluble salts of lead, being the best test of its presence. 605. Zinc precipitates it from its solutions by electrical action (248) in beautiful crystalline plates of metallic lead, which assume a branching form, often an inch or two in length, and hence called the lead tree, or arbor saturni, from the alche- rnistic name of this metal. The acetate or nitrate may be employed ; an ounce of the salt is dis- solved in two quarts of water, and a piece of clean zinc suspended in it by a thread ; the pre- cipitation is gradual, and occupies one or two days. The arrangement is seen in the annexed figure. 606. Carbonate of Lead ; White Lead ; PbO,CO 2 . This salt is found beautifully crystallized in nature, but is prepared artificially in very large quantities, for the purposes of a paint. This pigment is obtained by casting lead in very thin sheets, which are then rolled up into a loose scroll and placed in a pot over a small quantity of vinegar, and so arranged as not to project above the pot, nor touch the vinegar. Many thousands of these pots are arranged in successive layers over each other, with boards between, and the interstices filled with spent tan, or fermenting stable dung, which gives a gentle heat to the acid. After a time the lead is completely converted into an opake white crust 605. How is metallic lead produced from its solution ? 606. How is the carbonate prepared, and for what is it used ? 28 326 METALLIC ELEMENTS. of carbonate. The theory of this process will be explained when we describe the acetates of leadJjj|prganic chemistry.) White lead is now largely adulterated bjLulphate of baryta, but the fraud may be easily detected b^iissolving the car- bonate in an acid, when the sulphate of baryta will be left behind. Carbonate of lead is highly poisonous. 38. URANIUM. 607. This is a very rare substance, found only in pitch- blende, uranite, and a few other rare minerals. Its chemical history is, however, possessed of considerable interest. There are three oxyds of uranium, viz., UO 2 , U 2 3 , and U 4 O 6 . The metal is usually obtained as a dark powder, but can be condensed into a white malleable form. It forms beautiful yellow salts. The phosphate of uranium and cop- per (uranite) is one of the most beautiful of minerals. 39. COPPER. Equivalent, 31-65. Symbol, Cu. Density, 8-895. 608. Copper has been in familiar use since the times of Tubal Cain, and is one of the most important metals to the wants of society. It is often found in the metallic state. The metallic copper of Lake Superior is associated with na- tive silver, and small proportions of silver are also often alloy- ed with the copper. One mass from this region now at Washington, weighs over 3000 pounds. Its most usual ores are the red oxyd of copper and the copper pyrites, or sul- phuret of copper and iron. The blue and green malachites, or carbonates of copper, and several other salts of this metal, are also found in the mineral kingdom. Copper is very malleable, and is the only red metal except titanium. It fuses at 1996, and has a density of 8-895, which may be in- creased to 8-95 by hammering. It does not change in dry air, but in moist air becomes covered with a green coat of carbonate. It is stiffened by hammering or rolling, and softened again by heating and quenching in water. It may be drawn into very fine wire, which is an excellent conduc- tor of heat and electricity, and is much used in electro-mag- netism, and for the telegraphic conductors. Nitric acid is the proper solvent of copper, sulphuric and G07. What is said of uranium? 608. In what state eroxyd at a very moderate heat. (2.) The scsquioxyd is a grayish powder, which has been but little examined. (3.) The peroxyd is found native in the beautiful crystallized tin stone. It may be obtained in a soluble, and an insoluble condition. When the pcrchlorid is precipitated by an alkali, the bulky white precipitate of hydrated peroxyd which appears, is easily soluble in acids ; but if tin is acted on by an excess of moderately strong nitric acid, a white insoluble powder is formed, which is not acted on by the strongest acids. Heat converts both into a lemon-yellow powder, which dissolves in alkalies, but not in acids, and which is known as stannic acid ; it reddens test-paper, and forms salts. The putty used to polish stone and glass is the peroxyd of tin. 616. Protochlorid of Tm, which is prepared by dissolving tin in hot hydrochloric acid, is a powerful deoxydizing agent, and reduces the salts of silver, mercury, platinum, &c., to the metallic state. The anhydrous protochlorid is formed by heating protochlorid of mercury with powdered tin. 617. Perchlorid of Tin is a dense fuming liquid, long known as the fuming liquor of Labavius. It is formed by distilling a mixture of 1 part of powdered tin and 5 of corrosive sublimate. The tin mordant used by the dyers is formed by dissolving tin in hydrochloric acid, with a little nitric, at a low temperature, or by passing chlorine gas through the protochlorid. The sulphurets of tin correspond to the chlorids. The bisulphuret (aurum musivum) is used as a bronze color for imitating gold in ornamental painting and printing. How does strong nitric acid affect it ? 615. What oxyds of tin are there ? What is the protoxyd ? Describe the peroxyd. What two modifications of it are named ? How does heat affect them ? What is putty ? 616. How is protochlorid of tin employed as a reagent ? 617. What is perchlorid of tin, and how prepared ? What is the tin mordant ? What sulphurets of tin are there ? BISMUTH. 331 The alchemistic name for this metal was Jove, and the preparations of tin are still called Jovial preparations. 46. BISMUTH. Equivalent, 70-95. Symbol, Bi. Density, 9-82. 618. Bismuth is found native, and also in combination with other substances. Native bismuth is found at Monroe, Conn. It is a brittle, highly crystalline metal, of a red- dish white color, with a density of 9-82, and fuses at 497. It is obtained in large and beautiful cubical crystals, by per- forating the crust of a mass which is just cooling from a state of fusion in a crucible, and pouring out the still fluid interior. The vessel will be lined with a multitude of brilliant crystals. It dissolves in nitric acid, but like other metals of this class, does not decompose water under any circumstances. 619. Two oxyds of bismuth are known. The protoxyd (BiO) is formed by gently igniting the subnitrate, and is a yellowish powder, easily soluble in acids, and is the base of all the salts of bismuth. It is, however, a very feeble base, since even water decomposes its salts. The peroxyd (Bi 2 O 3 ) is not of much interest. 620. The Nitrate of Bismuth (BiO,NO 5 -f 3HO) is the most interesting of its salts. It may be obtained from a strong solution in large transparent crystals, which are decomposed by water. It is a striking and instructive experiment, to turn the solution of the nitrate of bismuth into a large quantity of water, when it is immediately decomposed, with the production of a copious white precipitate of subnitrate of bismuth. This is owing to the superior basic power of the water, which takes a part of the nitric acid. The white precipitate is a basic nitrate, (BiO,NO 5 -f 3BiO,HO.) 621. The alloy of bismuth known as Newton's fusible metal, is formed of 8 parts bismuth, 5 parts lead, and 3 parts tin, and melts below 212. It is much used in taking casts of medals. The expansion of bismuth in cooling, renders it a valuable constituent of alloys, where sharpness of impression in casting is important. 618. What is the color and fusibility of bismuth ? Describe its crystals, and the mode of obtaining them. 619. How many oxyds has this metal ? 620. What is the most interesting property of the nitrate ? 621. What is the composition of Newton's fusible metal ? 332 METALLIC ELEMENTS. 47. ANTIMONY. Equivalent, 129-04. Symbol, Sb, (Stibium.) Density, 6-7. 622. This metal is derived chiefly from its native sul- phuret, which is a rather abundant mineral. The metal is obtained by fusing the sulphuret with iron-filings, or car- bonate of potash, which combines with the sulphur and sets free the metal. It is a white brilliant metal with a blue tint, forming broad rhomboidal crystalline plates. It is very brit- tle, and like bismuth may be reduced to a fine powder. It fuses at about 1000, or low redness, and at a higher heat is volatilized. It dissolves in hot hydrochloric acid, but nitric acid converts it into the insoluble white antimonic acid. Its alloy with lead is type-metal, which, like the alloys of bismuth, gives very sharp casts, by reason of the expan- sion from crystallization, it suffers in solidifying, although it is remarkable that both of the constituent metals shrink when cast separately. Finely powdered antimony is inflamed in chlorine gas, forming the perchlorid. 623. Three compounds of- antimony and oxygen are known, viz : (1.) Oxyd of Antimony, SbO 3 . This oxyd may be ob- tained by digesting the precipitate from chlorid of antimony by water, with carbonate of potash or soda, or by burning antimony in a red-hot crucible. It is n fawn-colored insol- uble powder, anhydrous, and volatile when highly heated in a close vessel. Boiled with cream of tartar, (acid tartrate of potash,) it forms the well-known tartar emetic, which may be obtained in crystals from the solution. The Glass of Antimony is an impure fused oxyd, prepared for the purpose of making tartar emetic. Heated in air, this oxyd gains another equivalent of oxygen, and forms 624. (2.) Antimonious Acid, SbO 4 . This is a gray pow- der, not volatile, insoluble in acids, unless recently precip- itated. Its hydrate reddens litmus paper, and combines with alkalies. (3.) Antimonic Acid, SbO 5 , is formed as already stated, 622. How is antimony obtained ? What are its properties ? 623. How many compounds does antimony form with oxygen ? 624. De- scribe the two acids of antimony. ANTIMONY. 333 when antimony is digested in an excess of strong nitric acid. It dissolves in alkalies, with which it forms definite salts, that are again decomposed by acids, hydrate of antimonic acid being thrown down. The hydrate loses its water be- low a red heat, becoming a crystalline fawn-colored powder, and by a higher heat one equivalent of oxygen is expelled, antimonious acid being formed. 625. There are chlorids and sulpkurets of antimony, cor- responding to the oxyd and to antimonic acid. The Terchlorid, Butter of Antimony, SbCl 3 , is made by distilling the residue of the solution of sulphuret of antimony in strong hydrochloric acid. When a drop of the distilled liquid forms a copious white precipitate on falling into water, the receiver is changed, and the pure chlorid is collected. It is a highly corrosive fuming fluid, and by cooling forms a crystalline deliquescent solid. It is used in medicine as a caustic. Water decomposes it, but it dissolves in hydro- chloric acid unchanged ; water poured into the solution throws down a bulky precipitate which is a mixture of oxyd and chlorid of antimony, and has long been known by the name of powder of algaroth. The bromid of antimony is a crystalline volatile com- pound. 626. The Ter sulphuret of Antimony, SbS 3 , constitutes the common commercial sulphuret, and the beautiful crystallized native mineral. The Pentasulphuret of Antimony, SbS 5 , is formed by boil- ing the tersulphuret with potash and sulphur, and throwing down the compound in question by an acid, as a golden yel- low sulphuret, known by the name of sulphur auratum, or golden sulphur of antimony. More generally, how- ever, the decomposition on adding an acid, as above, gives us the oxy sulphuret of antimony, (SbS 3 + SbO 3 ) which is a characteristic reddish-orange precipitate. This is the sub- stance known as kermes mineral, and is an article of the older medical practice. The solution of sulphuret of anti- mony in caustic potash and sulphur, is a case in which sul- phuret of potassium is a sulphur base, and sulphuret of anti- mony, a sulphur acid. 625. Describe the terchlorid and its decomposition. 626. What is said of the chlorids and sulphurets ? What is formes mineral? 334 METALLIC ELEMENTS. 48. ARSENIC. Equivalent, 75-21. Symbol, As. Density, 5-884. 627. Metallic Arsenic is found native in thick crusts, called testaceous arsenic, evidently deposited by sublimation. It is however more usually obtained from roasting the ores of cobalt, nickel, and iron, with which metals it is often combined, forming arseniurels. The vapors of arsenious acid given out in the roasting, are condensed in a long hori- zontal chimney, or in a dome constructed for the purpose ; the first product being purified by a second sublimation. Arsenic is a brilliant steel-gray metal, brittle, and easily crystallized. It cannot be sublimed unchanged in presence of air, but may be so in close vessels, at a temperature of 356, without previously melting. Its vapor has a very powerful garlic-like odor, like phosphorus. This metal is known by druggists under the absurd name of cobalt, and is sold in powder to destroy flies. Metallic arsenic is easily obtained by subliming the common white arsenic with black flux, (489,) in a vessel of hard glass, like a cologne vial or oil bottle. The metal forms a brilliant black crust in the upper and cooler parts of the vessel. Arsenic forms two compounds with oxygen. 628. Arsenious Acid White Arsenic Rafs Bane, AsO 3 . This well known and fearful poison is formed as just stated, when metallic arsenic is sublimed in air, or when any of the ores of arsenic are roasted. This acid is what is usually known as arsenic in commerce. When newly sublimed, it is a hard transparent glass, brittle, and with a density of 3'7. It slowly changes to a white opake enamel. As sold in commerce, it is usually reduced to a white powder, rarely found without adulteration. It sublimes at 380, without change, and crystallizes in brilliant octa- hedrons, as may be well seen by heating a small quantity in a glass tube. Its vapor is inodorous, but if sublimed from charcoal it gives the peculiar garlic odor of metallic arsenic, being reduced to that state. It is soluble in about 10 parts of hot water, and is almost tasteless, with a faint sweetish 627. How is arsenic obtained, and what are its properties ? 628 Describe arsenious acid. ARSENIC. 335 flavor, which renders it the more dangerous poison, since no warning is given to the victim who takes it, as in case of most other metallic poisons. The solution in water is acid to test-paper, and deposits nearly all its arsenic in crystals, on cooling. Hydrochloric acid dissolves it, as also do alkalies, which however do not form crystallizable salts with it. The best antidote to the poisonous effects of arsenic is the hydrated peroxyd of iron, freshly precipitated, and used in its gelatinous condition. 629. Arsenic Acid, As0 5 . This acid is formed by adding nitric acid to the solution of white arsenic, in hydro- chloric acid, as long as any red vapors of nitrous acid show themselves, and then carefully evaporating the solution to entire dryness ; a white porous subcrystalline. mass remains, which is slowly soluble in water. Its solution is a powerful acid, quite similar in chemical characters to phosphoric acid. The analogy is so great that there is a complete similarity in constitution, and even in external appearance, between all the salts of these two acids. For every tribasic phosphate we have an arseniate, not only similar in constitution, but iso- morphous, and so resembling it in all its external properties as not to be distinguished by the eye. Thus the tribasic phosphate of soda, (528,) and the tribasic arseniate of soda, are Phosphate of soda, PO 6 ,2NaOHO -f 24Aq. Arseniate of soda, AsO 5 ,2NaOHO -f 24 Aq. These, and many other facts, lead to the opinion that the elements are themselves isomorphous, and in fact arsenic has no claim to the metallic character but its lustre, being in chemical properties and natural affinities associated with phosphorus. 630. The Chlorid of Arsenic (AsCl 3 ) is a fuming volatile liquid, decomposed by water, and very poisonous. The bromid and iodid are both crystallizable solids, also decom- posed by water. The sulphurets of arsenic are natural compounds, used as pigments, and also in pyrotechny. The first, AS 2 , is a red transparent body called realgar, and AsS 3 is the golden yellow orpiment. Both these substances are found native, 629. How is arsenic acid obtained ? To what other acid is it allied, and how ? What is the real character of arsenic ? 630. Describe the sulphurets. 336 METALLIC ELEMENTS. and as usually associated, they are brought from Koordistan in Persia, and from China. The higher sulphurets may be formed,, which are AsO 5 and AsO 9 ; the former is the product thrown down by sulphureted hydrogen in a solution of arse- nic. All but the highest of these compounds are sulphur acids. 631. Arseniureted Hydrogen. This is perhaps the most deadly poison known. Jt is a gas produced by the action of dilute sulphuric acid on an alloy of zinc and arsenic, or by the evolution of hydrogen in presence of arsenic or arsenious acid. This gas is readily absorbed by a solution of sulphate of copper, and precipitates an arseniuret of that metal. It burns with a peculiar blue flame, and deposits metallic arsenic or arsenious acid. Marsh's test for arsenic depends on the generation of this gas. 632. Detection of Arsenic as a Poison. The fearful use which is made of this terrible poison in destroying human life, renders it of the first moment that we should know easy and certain process for its detection. Accordingly we find that very numerous methods have been proposed for this purpose, a few of which we will briefly mention. When a fluid, or other substance free from organic matter, is to be examined for arsenic, there are many tests which we can apply. (1.) Sulphureted hydrogen throws down the yellow sulphuret in acidulated solutions of arsenious acid ; this is redissolved by ammonia, and again precipitated by acids. (2.) Nitrate of silver produces a yellow precipitate of arsenite of silver in solutions of arsenious acid, if a trace of ammo- nia is present ; but the precipitate does not appear in an acid solution, and an excess of ammonia dissolves it. (3.) Sul- phate of copper gives a brilliant green precipitate of arsenite of copper, (Scheele's green,) in alkaline solutions of arse- nious acid, which precipitate is redissolved by ammonia in excess. (4.) A clean slip of metallic copper placed in a solution of arsenious acid, is soon coated with a gray deposit of metallic arsenic ; this is known as Remsch's test. 633. All these tests taken collectively, constitute to the mind of the chemist a perfect demonstration of the presence of arsenic ; but they are liable to many objections arising from the presence of organic matters, of impurity in reagents, 631. What are the characters of arseniureted hydrogen ? 632. What are some of the means of detecting the presence of this poison ? ARSENIC. 337 and from the possible presence of other metallic matters, as antimony, which forms a brick-red or yellowish sulphuret, and cadmium, whose sulphuret much resembles orpiment. It is therefore always demanded in judicial investigations, that no proof of the presence of arsenic shall avail except that of sublimed metallic arsenic. 634. Reduction of Arsenic. When it is possible to obtain from the suspected substance any grains of arsenious acid, these are carefully selected for the purpose of examination. If not, the yellow sulphuret obtained from the suspected solution by sulphureted hydrogen is employed, to produce the metallic arsenic. Either of these substances is introduced into a small tube of hard glass, drawn out at the lower part as here represented, and the narrow part of the tube is then filled with black flux to the shoulder, (a.) Its interior being wiped out, the flame of a small spirit-lamp is applied to the upper part of the mixture to expel any moisture it may contain, which is next carefully removed by bibulous paper. The flux is then gradually heated to redness from a to 6, and the heat slowly carried down below &, until the lower part of the tube is fully red. If any arsenic is present it is sublimed, and deposited in a brilliant ring just above the shoulder, as seen in the figure. For further proof, the tube may be drawn off at a in the lamp-flame, and the metallic arsenic vola- tilized by the heat until it is all converted into arsenious acid, which a magnifier shows to be in brilliant white octahedral crystals. 635. But the most common and most difficult case of testing for arsenic is when the fluids of the stomach, ejected by the patient, or the stomach itself and its contents, are to be examined. The organic matters present in all such cases, render the liquid tests quite worthless, and oblige us to have recourse to a method of which a brief sketch only can be presented. The suspected fluid, and the solid parts cut small, are placed in a large porcelain capsule with a con- siderable quantity of pure hydrochloric acid, and as much water as will make the mixture thin. This mixture is 633. What other bodies resemble it in its reactions ? 634. How are we to obtain it in a metallic state ? 635. How do we ascertain its presence when mixed with organic matters ? 29 338 METALLIC ELEMENTS. heated on a water-bath, and while hot, small portions of 20 or 30 grains of chlorate of potash are added to the mixture, at short intervals. The chlorine evolved by this treatment completely decomposes the organic matters, and the final result is the production of a yellow transparent fluid, which can easily be filtered. From this, sulphureted hydrogen in excess will throw down all arsenic, antimony, &c., which may be present ; and after resolution and reprecipitation, the suspected sulphuret of arsenic may be reduced in the same way as has been just described. Another mode of reduction, however, is much to be preferred, where cyanid of potassium is employed in the reduction tube, in place of the black flux, with about three parts dry carbonate of soda, and the sulphuret. 636. Marsji's test is one which is very convenient, sim- ple, and if used with care, satisfactory in most cases. It depends on the formation of arseniureted hy- drogen. The suspected substance is placed in a flask with the materials to generate hydrogen, (376.) This gas, as it issues from a jet, is set on fire, and if arsenic is present in the mix- ture, the flame burns with a peculiar blue light, and a clean plate of mica or porcelain held over it, is at once blackened by a film of metallic arsenic. The annexed figure shows a convenient form of this apparatus. The materials for hydrogen and the suspected body are put in the lower bulb, and dilute sul- phuric acid being turned into the upper bulb, hydrogen gas is generated, and may be delivered at will by the stop-cock and jet. Extremely minute traces of arsenic may be detected by this test. Antimony presents a some- what similar spot, but may easily be distinguished from arse- nic by a practised eye. It must be observed that all the reagents employed in this apparatus, the zinc, the acid, and even the glass of the vessel, may contain arsenic. 49. OSMIUM. 637. Osmium (Os, 99-56) is one of the rare metals which are associated with platinum. It has a density of 10-, 636. Describe Marsh's test. What objections are there to his method ? 637. With what body is osmium associated ? MERCURY. 339 and is of a white-bluish color, neither fusible, nor volatile, but takes fire in the air, forming osmic acid, (OsO 4) ) which is volatile and poisonous. Osmium forms four oxyds, viz : OsO, Os 2 O 3 , OsO 2 , and OsO 4 . Osmiate of potash is formed when the metal is fused with nitre. Osmium combines with sulphur and phosphorus, and has the same number of sulphu- rets as of oxyds and chlorids. CLASS VI. NOBLE METALS, WHOSE OXYDS ARE RE- DUCED BY HEAT ALONE. 50. MERCURY. Equivalent, 101-26. Symbol, Hg, (Hydrargyrum.) Den- sity, 13-5. 638. This is the only metal which is fluid at ordinary temperatures. It is found as native or running mercury in Spain and Carniola, and also as cinnabar or sulphuret of mer- cury, but it is a rather rare and costly metal. It has never been found in this country. The alchemists supposed it to be silver enchanted, (quick-silver,) and made many efforts to obtain from it the solid silver it was supposed to contain. Pure mercury is a silver-white, fluid metal, unchanged by air, and very brilliant. Cooled below 40, as when frozen by carbonic acid, (137,) it solidifies, and is then as malle- able as lead. It crystallizes at this degree of cold in cubes. It boils at 660, and forms a colorless, very dense vapor. Even at 60, a very rare vapor of metallic mercury (129) rises from it. If heated in the air at above 600, it slowly passes to the condition of red oxyd of mercury, which is its highest combination with oxygen. 639. The uses of mercury are numerous and important in the arts, and also in medicine. It forms alloys (amal- gams) with many other metals ; with tin it constitutes the brilliant coating of glass mirrors, (called silvering,) and it is of indispensable importance in procuring gold and silver from their ores. Its use in filling thermometers and baro- meters (76) has already been described. What are its properties ? What oxyds does it form ? What is the sixth class of metals ? 638. How is mercury found in nature ? What are its properties ? 639. What are the uses of this metal ? 340 METALLIC ELEMENTS. Nitric acid dissolves mercury very rapidly even in the cold ; hydrochloric acid scarcely acts on it, and sulphuric only by the aid of heat, when it forms an insoluble sul- phate of mercury, evolving sulphurous acid, (286.) The equivalent of mercury is often stated at 202-52, on the sup- position that the gray oxyd is the protoxyd ; but this seems to be more properly considered as a suboxyd, and the real protoxyd as the red oxyd. On this view the equivalent is stated at 101-26. Mercury may be so finely divided as to lose its metallic appearance entirely ; as in blue pill, mercurialized chalk, (creta cum hydrargyro,) and mercurial ointment, which do not, as has sometimes been stated, contain the suboxyd of mercury, but only mercury in a state of very minute mechan- ical division. 640. The Gray, or Suboxyd of Mercury ', Hg 2 O, is formed by digesting calomel in caustic potash, or by adding the same reagent to a solution of the nitrate of the suboxyd of mercury. It is an insoluble, dark gray powder, which is easily decomposed into metallic mercury and the red oxyd. The Red Oxyd, or Protoxyd, Red Precipitate, HgO, is prepared in the large way by heating the nitrate very cau- tiously, until it is quite decomposed, and a brilliant red crys- talline powder is left. It may also be formed by heating metallic mercury for a long time in a glass vessel nearly closed, and in this form is the preparation to which the old name of red precipitate per se was applied. Heat decom- poses this oxyd into oxygen and metallic mercury. It is, like the oxyd of lead, slightly soluble in water, and gives to it an alkaline reaction. It is a dangerous corrosive poison. 641. The chlorids of mercury correspond to the oxyds, and are both very important compounds. (1.) The Subchlorid of Mercury, (Calomel,) Hg 2 Cl, is a well known medicine, and is easily formed by precipitating a solution of subnitrate with common salt. A white, insolu- ble, tasteless powder falls, which is the calomel. Even strong acids when cold do not affect it ; but it is instantly de- composed by alkalies and the suboxyd produced. Heat How do acids act upon it ? 610. How many oxyds does mercury form ? Describe the preparation of the red oxyd ? 641. How many chlorids are there ? How is calomel prepared ? MERCURY. 341 sublimes it unchanged. Its complete insolubility at once distinguishes this safe and mild substance from the highly poisonous (2.) Corrosive Sublimate, or Chlorid of Mercury, HgCl. This salt is most economically prepared by the double de- composition of sulphate of mercury, by common salt, which by simple interchange gives corrosive sublimate and sulphate of soda, (HgO, SO, + NaCl=HgCl + NaO,SO 8 .) The chlo- rid is also formed by dissolving the red precipitate in hot chlorohydric acid. Corrosive Sublimate is a very heavy crystalline body, soluble in about 15 parts of cold water, and in two or three parts of hot, giving a solution which pos- sesses the most distressing and nauseous metallic taste, and is a deadly poison. It is soluble in alcohol and ether. It melts and sublimes a little below 600. Albumen com- pletely precipitates it, and the whites of eggs are therefore an antidote for this poison. For the same reason it is, doubtless, that timber and animal substances are preserved from decay, as in the kyanizing process, by steeping in solu- tion of corrosive sublimate. The albuminous portions of wood suffer decay sooner than the vegetable fibre, and these are rendered completely indestructible in the process of Mr. Kyan, which is now in use in our national ship-yards. 642. There are two iodids of mercury, Hg 2 l and Hgl. The second is a brilliant scarlet-red precipitate, formed by adding solution of iodid of potassium or hydriodic acid to a solution of corrosive sublimate. The iodid is at first yel- low, but soon passes by a molecular change into the splendid scarlet crystalline powder before noticed. It cannot be used as a pigment on account of its instability. 643. Two sulphurets of mercury, Hg 2 S and HgS, exist, the first of which is formed when sulphureted hydrogen is passed through a solution of subnitrate of mercury, and is a black powder. The sulphuret, HgS, or cinnabar, is formed when the nitrate of mercury (nitrate of the red oxyd) is treated with sulphureted hydrogen. It is a black precipi- tate, but turns red when sublimed, and forms the familiar What is the process for obtaining corrosive sublimate ? How does it differ from calomel ? Describe the antidote for this poison and its effect upon it. What uses are made of chlorid of mercury ? 642. Describe the iodid of mercury. 643. How many sulphurets of mercury are there ? 29* METALLIC ELEMENTS. pigment vermillion. This is the common ore of the quick- silver mines. 644. The nitrates of mercury. The action of nitric acid on mercury varies with the temperature and the strength of the acid. In the cold, dilute nitric acid dissolves mer- cury, forming a neutral nitrate of the suboxyd ; but if the mercury is in excess, a salt is deposited in large and trans- parent white crystals, which is a nitrate with excess of base. If hot and strong, the nitrate of the red oxyd is formed, which is a very soluble salt not crystallizable. A basic salt of this oxyd may also be formed, which is decomposed by water. 645. Sulphate of Mercury (HgO SO 3 ) results as an in- soluble, white, subcrystalline powder, by the action of the strong acid on metallic mercury, (286,) sulphurous acid being evolved. Boiling water decomposes this salt, removing a part of its acid, by which a yellow basic sulphate is formed, known as turpeth mineral. Its composition is 3HgO, SO 3 . The sulphate of the gray oxyd, Hg 2 O> SO 3 , is formed as a crystalline white powder by treating a solution of subnitrate of mercury with sulphuric acid. It is slightly soluble in water. 646. Ammonia produces many interesting compounds with the salts of mercury, of which the white precipitate, as it is called, is best known. This falls when chlorid of mer- cury in solution is treated with ammonia in excess, and is considered as a double amide and chlorid of mercury, HgCl and HgNH 2 . All the compounds of mercury are volatile at a red heat, and those which are soluble, whiten a slip of clean copper by depositing metallic mercury on its surface. 51. SILVER. Equivalent, 108-12. Symbol, Ag, (Argentum.) Density, 10-5. 647. The mines of Mexico and the Southern Andes furnish most of the silver of commerce, although many mines of this metal are found in Spain, Saxony, and the What is vermillion ? 644. How are the nitrates of mercury ob- tained ? What is the 'nature of the nitrate of 'the red oxyd ? 645. How is the sulphate formed ? 646. What is the nature of white pre- cipitate ? What are the characteristics of mercurial compounds ? 647. From what sources is silver obtained ? SILVER. 343 Hartz mountains. Galena, or the native sulphuret of lead, is also a constant source of silver, as it is rarely quite free from this precious metal. Silver is often found native, and also in combination with sulphur. The brilliant lustre and white color of this valuable metal are familiar to all. It is perfectly ductile and malleable, and in hardness stands between gold and copper. For the pur- poses of economy and in coinage it is essential to alloy it with about -^ part of copper, to render it sufficiently stiff and hard. Pure silver melts at 1873, and when melted absorbs sev- eral times its volume of oxygen gas, which it parts with again on cooling. This renders silver a difficult metal to cast, and occasions the little projections and roughness usu- ally seen on silver which has been melted. Silver is obtained pure from its solution in nitric acid by precipitation with metallic copper, as a finely divided crystal- line powder ; or by decomposing its chlorid by fusion with two parts of dry carbonate of potash. Nitric acid dissolves silver in the cold with great rapidity, and if it contains any gold, this is left undissolved as a brown powder. Hydrochloric acid scarcely acts on silver, and sulphuric acid only when hot, forming the sulphate of silver, which is sparingly soluble in water. 648. Silver is parted from galena, by a process called cupellation, or fusing at a white heat the pulverized galena and a certain quantity of metallic lead, on a little thick cup or cupel of bone-ashes, in a muffle exposed to a current of air. The lead oxydizes and is absorbed, while the silver is left in a brilliant metallic button on the cupel. In the large way this process is much facilitated by the fact that the alloy of silver and lead is more fusible than pure lead, and the latter on cooling separates from the former, which may be drawn off, and contains all the silver. This small portion is cupelled, while the great bulk of the lead is returned to the arts uninjured. 649. Three oxyds of silver are known by chemists ; the suboxyd, Ag 2 O ; the protoxyd, AgO ; and the peroxyd, AgO 2 . We will now notice only the protoxyd. This is formed when the solution of silver in nitric acid is saturated What are the characteristics of pure silver ? 648. How is it sepa- rated from lead ? 649. Describe the preparation and character of oxyd of silver. 344 METALLIC ELEMENTS. with caustic potash, or when the chlorid of silver recently precipitated is digested in a solution of caustic potash of den- sity 1'3. It is a dark brown or black powder, if prepared by the first mode, or quite black and dense by the second process. It is a base forming well defined salts. Ammonia dissolves it readily, and it is also somewhat soluble in water, to which it gives an alkaline reaction. It is easily reduced by heat alone. Its solutions are at once detected by the bulky white curdy precipitate which they form with hydro- chloric acid or with common salt. This white precipitate turns dark by exposure to light. 650. Chlorid of Silver, AgCl, is formed, as just remarked, when any soluble salt of silver is treated with a soluble chlorid or with hydrochloric acid. This substance fuses at a moderate red heat into a transparent pale yellow fluid, which is horny and tough when solid, and hence called horn silver, a form in which this metal is sometimes found in mines. It is easily reduced to the metallic state by the nascent hydrogen generated when zinc is acted on by dilute sulphuric acid in contact with the chlorid. Pure silver and chlorid of zinc result ; or, it may be reduced by fusion with twice its weight of carbonate of soda or potash. The iodid and bromid of silver are, like the chlorid, insolu- ble in water, and very sensitive to light. The Daguerreotype and calotype (62) are both dependent on the sensitiveness of these compounds to light, for the accuracy and beauty of their results. The sulphurets of silver are found native, and the tarnish which blackens silver articles on long exposure, is formed by sulphureted hydrogen in the air. 651. The Nitrate of Silver, AgO, NO 5 , is a salt which crystallizes in beautiful flattened tables of a hexagonal form, which dissolve in half their weight of hot water. By heat it fuses, and when cast in cylindrical moulds forms the slender sticks called lunar cavstic, so much used by the sur- geon. Its solution has a disgusting metallic taste even when very dilute, and is a most delicate test of the presence of chlorine or any of its compounds. It blackens rapidly in 650. Describe the chlorid. How can it be reduced ? What are the relations of the silver compounds to light ? What is the action of sulphureted hydrogen on silver ? 651. Describe the nitrate. What are its reactions ? GOLD. 345 contact with organic matter when exposed to the light, and forms an indelible ink, which is much used in marking linen. Solution of cyanid of potassium will remove the stain produced by nitrate of silver. Metallic copper at once throws down metallic silver from the nitrate, and solu- tion of nitrate of copper is formed. Mercury precipitates metallic silver from a dilute solution, in beautiful tree-like forms, called arbor Diana. Ammonia, by acting on pre- cipitated oxyd of silver, forms a fulminating compound. It is extremely hazardous to deal with, as it explodes even when wet. 52. GOLD. Equivalent, 09.44. Symbol, Au. Density, 19-26. 652. This valuable metal is found only in the metallic or native state, being very widely diffused in small quantities in the older rocks. From these, by the action of various causes, it finds its way into the sand of rivers, and is dis- tributed in small quantities, in many wide-spread deposits of coarse gravel or shingle, as on the eastern flanks of the Ural Mountains, and over a wide belt of country in Virginia, the Carolinas, Georgia, and Alabama. These diluvial de- posits furnish nearly all the gold of commerce, by a process of washing, and amalgamation with mercury. Large masses of gold sometimes occur, as one of twenty-eight pounds in North Carolina, and in Siberia a mass was found, now in the Imperial Cabinet of St. Petersburg, weighing nearly eighty English pounds. Generally, however, k occurs only in minute grains. It is also found in veins of quartz, in compact limestone, and distributed in iron pyrites. Native gold is usually alloyed with silver. 653. Gold is distinguished by its splendid yellow color, its brilliancy, and freedom from oxydation, by its extreme malleability and ductility, by its high specific gravity, (19-26 to 19-5,) and by its indifference to nearly all reagents. It fuses at 2016 F., and is dissolved only by aqua regia, (420,) by nascent cyanogen, and by selenic acid. The first is the solvent commonly known, and the solution contains the perchlorid of gold. What is the arbor Diana ? 652. How does gold occur in nature ? How is it obtained? 653. Describe this metal. What is its usual solvent ? 346 METALLIC ELEMENTS. 654. Gold forms two very unstable oxyds, (Au 2 O and Au 2 3 ,) which are decomposed, even by light. Two cor- responding chlorids exist. The perchlorid is a very deli- quesgent salt, forming a red crystalline mass, soluble in ether, alcohol, and water. Metallic gold is deposited in elegant crystalline crusts from the ethereal solution of the chlorid. Ammonia throws down from solutions of gold' an olive-brown powder, (fulminating gold,) which when dry explodes with heat, or by percussion. 655. The solution of protosulphate of iron throws down gold from its solutions in a very fine brown powder, which is green, as seen by transmitted light, when diffused in water. The protochlorid of tin forms a characteristic purple pre- cipitate in gold solutions, called the purple of cassius, which is used in porcelain painting, and is probably a compound of the oxyds of tin and gold. Gilding of ornamental work is usually performed by gold leaf; but other metals are gilded either by applying it as an amalgam with mercury, the mercury being afterwards expelled by heat, or preferably by the now process of galvanic gilding from a solution of the cyanid of gold and potassium, (248.) Gold wash, as it is called, is applied by a mixture of carbonate of soda or potash in excess, with oxyd of gold, in which small articles cleansed in nitric acid are boiled, and thus become perfectly covered with a very thin film of gold. 53. PLATINUM. Equivalent, 98.68. Symbol, PI. Density, 19.70 to 21-23. 656. Platinum is a very remarkable metal, and if abundant would be extensively useful in domestic economy. It is found native in the gold workings in South America and in Siberia, on the eastern slope of the Urals. No ore of platinum is known, except its alloy with gold, and with iridium, osmium, and rhodium. Platinum is a white metal, between tin and steel in color, but harder than gold or silver, and unless quite pure, is, when unannealed, nearly as hard as palladium. A very little rhodium or iridium renders it more gray in color, and 654. How many oxyds of gold are there ? Describe the per- chlorid. 655. What tests distinguish gold ? How is gilding effected ? 656. Where is platinum found ? PLATINUM. 347 much harder. If pure it is very malleable, especially when hot, and can then be imperfectly welded. Its ductility and tenacity are remarkable ; but its most valuable property is its infusibility, which is so great that the thinnest platinum foil may be safely exposed to the most intense heat of a wind-furnace. It is soluble only by aqua regia, but alloys readily with lead, iron, and other base metals, so that great care is needed in using platinum vessels, not to heat them in contact with any metal or metallic oxyd with which they combine ; caustic potash, and phosphoric acid in contact with carbon, will also act upon platinum, at a red heat. This is a most useful metal to the chemist, and vessels of platinum are quite indispensable in the operations of analysis. Large retorts or boilers are made of it for the use of manu- facturers of sulphuric acid, which sometimes hold sixty or more gallons. In Russia it has been employed in coinage, for which by its great density and hardness it is well suited. When recently fused by the compound blowpipe or the gal- vanic focus, its density is about 19'9, which is increased to 21-5 by pressure and heat. 657. Platinum is obtained pure by digesting crude plati- num in aqua regia, and adding to the deep brown liquid a solution of chlorid of ammonium ; this throws down an orange- colored precipitate, which is a double chlorid of platinum and ammonium. This precipitate is reduced by heat to the metallic state, a porous dull brown mass, commonly known as platinum sponge. All the platinum of commerce is treated in this way. The sponge is condensed in steel moulds by heat and pressure, and when compact enough to bear the blows of the hammer, is heated and forged until it is perfectly tough and homogeneous. Spongy platinum is a very remarkable substance, having, as already noticed, (397,) power to cause the combination of hydrogen and oxygen, and to effect other chemical changes without being itself altered. Platinum black is a still more curious form of metallic platinum, and is formed by electrolyzing a weak solution of chlorid of platinum, when the black powder of platinum will appear on the negative electrode. The silver plates in Smee's battery (247) are prepared in this way. It is also Describe its characters and uses. 657. How is it obtained from its ores ? What is platinum black, and what are its properties ? 348 METALLIC ELEMENTS. prepared by adding an excess of carbonate of soda, with sugar, to a solution of chlorid of platinum, and gradually heating the mixture to near 212, stirring it meanwhile. The black powder which falls is afterwards collected and dried. This powder has the property of causing union among gaseous bodies as, for example, the elements of water to a greater degree than the spongy platinum. 658. Platinum forms two oxyds, and two chlorids, viz : P1O, P10 2 , and P1C1, PICI 2 . The oxyds are prepared from the chlorids by precipitation with alkalies, and are very unsta- ble. The protochlorid is prepared by heating the bichlorid to 450, when chlorine is evolved and it is left as a greenish- gray insoluble powder. The bichlorid of platinum is the usual soluble form of platinum, and is always formed when platinum is digested in aqua regia. It is prepared pure by dissolving spongy platinum in this menstruum, and cautiously expelling the acid by evaporation, at a moderate temperature. It gives a rich orange solution both in alcohol and water ; and forms soluble salts of much interest, with many metallic chlorids. Those with the alkaline metals are the most im- portant. The double chlorid of platinum and potassium is a very sparingly soluble salt, (P1CI 2 ,PC1,) which falls as a yellow highly crystalline precipitate when chlorid of plati- num is added to a solution of chlorid of potassium. The double chlorid of sodium and platinum (PlCl 2 NaCl + 6HO) is on the other hand very soluble, and forms large beautiful yellowish-red crystals in a dense solution. Potash and soda are most easily separated, by the different solubility of their double chlorids. The double chlorid of ammonium and platinum (P1C1 2 NH 4 CI) is the orange precipitate before named, and is the only test required to determine with perfect cer- tainty the presence of platinum in a solution. 54. PALLADIUM. Equivalent, 53-27. Symbol, Pd. Density, 11-8. 659. This very rare metal is usually found associated with ores of platinum. It is also found alloyed with gold 658. How is the bichlorid prepared ? Describe the double chlorids of platinum and the alkalies, their preparation and characteristics. 659. What is the symbol and equivalent of palladium ? RHODIUM, IRID1UM. 349 and silver in Brazil. It is a grayish-white metal, rather more brilliant than platinum, ductile, malleable, and extreme- ly infusible. It is, however, fused by the compound blowpipe. It gains a blue tarnish like steel by heating in the air, which it loses by a white heat. In hardness it is equal to fine steel, and it does not lose its elasticity and stiffness by a red heat. Its density varies from 10-5 to 11/8, and it suffers no change by exposure in the air. These qualities would render it a very valuable metal if it could be obtained in a sufficient quantity. Nitric acid dissolves it slowly, but aqua regia more rapidly. It forms two oxyds and two corresponding chlorids. 55. RHODIUM. Equivalent, 52-4. Symbol, R. Density, 10-8. 660. This is another metal associated with the ores of platinum, and is obtained by a process which need not be described here. It is a reddish-white metal, as fusible as iridium, and in hardness, ductility, and malleability, is much like it. Its density is probably about 10-8. (Hare.) 56. IRIDIUM. Equivalent, 98-68. Symbol, Ir. Density, 21-8. 661. Iridium is also associated with the ores of platinum in the native alloy called iridosmine, or osmiuret of iridium, which is left in black shining scales as a residuum, after digesting platinum ores in aqua regia. Iridium when ob- tained pure and fused, is susceptible of a fine polish, has a pale antimonial whiteness and the fracture of cast-iron. It is somewhat ductile, as hard as unannealed steel, and fuses under the compound blowpipe. . It is the densest body known, being as high as 2T80. (Hare.) The native alloy is much more infusible than the pure iridium, being, in fact, one of the most infusible bodies known ; it is very hard, and is used to point gold pens. Four oxyds and four chlorids have been described. Describe its properties? 660. What is said of rhodium ? 661. With what metal is iridium associated ? What is its density and hardness ? 30 PART IV. ORGANIC CHEMISTRY.* INTRODUCTION. 1. General Properties of Organic Bodies. 662. Definition. Organic chemistry is confined to the study of those bodies which are the products of life, and to the changes which they suffer by the action of other sub- stances. 663. The constituents of organic bodies are compara- tively few, but the results produced by their various combi- nations are wonderfully complex and numerous. Oxygen, nitrogen, carbon, and hydrogen, differently arranged and combined, compose nearly all the bodies found in the vege- table and animal kingdoms. Sulphur, phosphorus, and per- haps iron, occasionally occur, however, in these products ; and by the action of various reagents we are enabled to combine with organic substances, or with the products of their decomposition, chlorine, bromine, iodine, and various other bodies. In this way a great number of new com- pounds are produced, which come within the province of or- ganic chemistry as above defined. 664. Both animals and vegetables contain salts of potash, soda, lime, magnesia, and iron, with sulphuric, phosphoric, and silicic acids, and chlorine. Animals also secrete phosphate and carbonate of lime, to form their bones, as in quadrupeds, and their external coverings, as in the mollusca. These salts have been already described under their proper heads, in the inorganic chemistry, and their relations to life will be con- sidered in the section on the nutrition of animals and plants. 665. A strictly philosophical distinction cannot be estab- lished between organic and inorganic chemistry, as it will be seen from the statements already made, that these two * The questions at the foot of each page will be omitted in the remaining portion of the work, in the belief that both teacher and pupil will, by the time they reach this point, have become so familiar with the subject and with each other, as to render the questions no longer important, while the space which they occupy can be better employed. GENERAL PROPERTIES OF ORGANIC BODIES. 351 departments shade into each other so gradually, that the line of division must of necessity be somewhat arbitrary. Formerly it was considered as a distinctive mark of or- ganic compounds, that they could not be artificially formed at will, from a combination of their constituents. This distinction is, however, no longer exclusively true, since we are now able to form urea from cyanic acid and ammo- nia, both of which may be derived from the reaction of the mineral ingredients. By peculiar processes we have also been able to form numerous other bodies which are the products of organic life. They are, however, comparatively simple in their composition, and occur in nature only as secretions of organized bodies.* No art can ever enable us to produce the simplest organized tissue, as a cell or a fibre. 666. An important characteristic of organized bodies is the complexity of their composition, and their high equiv- alent numbers. In mineral compounds we rarely have any thing more intricate than a salt of two or three bases ; as for example, common alum, (568,) which may be resolved into sulphuric acid, alumina, potash, and water, each of which contains oxygen and a base. These constituents may be again combined to form the original alum. 667. The substance called gelatine, which is a principal constituent of the cellular tissue in animals, has the formula C 48 H 41 N 7 Oi 8 . By the action of heat, or other agents, we are able to resolve this complex body into ammonia, water, and other compounds, which are very much more sim- ple than gelatine. And these again we may decompose into their constituent elements. But by no power at our command, can we join the dissevered elements to form ge- latine anew. This peculiarity of organization is dependent on the vital force, which modifies the chemical affinities of bodies in a manner that we can never hope to imitate. While, therefore, in the study of mineral chemistry we can usually avail ourselves of the evidence to be obtained from both analy- sis and synthesis, (14,) in organic chemistry we must gener- ally be content with the former of these methods of proof. 668. Organic bodies possess the further peculiarity, that carbon is almost invariably one of their constituents, and * Organized bodies, or organisms, are distinguished by having a structure, which is the result of life ; this, organic bodies do not necessarily possess. For example, horn and skin are organisms, while gum and fat are simply organic bodies. 352 ORGANIC CHEMISTRY. associated in such proportions with oxygen, nitrogen, and hydrogen, that when the body is burned, these last combine with it to form carbonic acid and carbureted hydrogen ; and also among themselves, producing water and ammonia ; while any excess of carbon remains behind as charcoal. Organic substances have for this reason been defined by some writers as those bodies which char or blacken by heat. 2. Modes of Combination. 669. The different combinations presented by organic bodies may be reduced to three classes, and the laws which govern these will equally apply to all chemical compounds. These three modes of combination are termed, (1,) equiva- lent substitution ; (2,) substitution by residues, and (3,) direct union. 670. (1.) Equivalent Substitution. - The statement of this law is that one or more equivalents of any element in a compound, may be replaced by the same number of equiva- lents of another element. For example, acetic acid, C 4 H 4 O 4 , by the action of chlorine gas loses three equivalents of hydro- gen, which go to form hydrochloric acid, and takes in their place three equivalents of chlorine, which are substituted for the hydrogen. The new product, (chloracctic acid, C 4 CI 3 HO 4 ,) closely resembles acetic acid in its properties. Chlorine can then replace hydrogen, and the same power is possessed by bromine and iodine. 671. Alcohol, which has the formula C 4 HcO 2 , may have its oxygen replaced by sulphur, yielding sulphur-alcohol, C^Sa. Selenium and tellurium, which bear the closest resemblance in all their properties to sulphur, (250, iii.) can in the same manner replace oxygen. We see then that hydrogen may be replaced by chlorine, bromine, and iodine ; and oxygen by sulphur, selenium, and tellurium. 672. Where acetic acid acts upon metallic zinc, hydrogen is evolved and acetate of zinc (C 4 H 3 ZnO 4 ) is formed ; a com- pound in which an equivalent of zinc replaces one of hydro- gen. When this acid acts upon oxyd of zinc the acetate is also formed, while water is produced by the union of the oxygen of the oxyd with the hydrogen of the acid. Many chemists suppose that the acid contains water (thus C 4 H 3 O 3 -f HO,) which is decomposed in the one case, and displaced by the oxyd in the other : but we cannot separate water from the acid and obtain the compound C 4 H 3 O 3 , and indeed, we MODES OF COMBINATION. 353 have, no proof of the existence of such a compound. The view just stated, explains the constitution equally as well as the old one, and avoids all hypothesis. 673. From acetic acid we may form a great number of salts in which an equivalent of metal replaces one of hydro- gen, and the chloracetic acid yields a corresponding series. These constitute a genus, of which acetic acid is the type, and the various salts species. Thus Acetic acid, C 4 H 4 O 4 Chloracetic acid, C 4 C1 3 H0 4 Acetate of potash, C 4 H 3 KO 4 Chloracetate of potash, C 4 C1 3 K0 4 Acetate of silver, C 4 H 3 AgO 4 Chloracetate of silver, C 4 Cl 3 AgO In some compounds we can successively replace one, two, and even five equivalents of hydrogen by chlorine, or bromine, without deranging the molecular structure of the compound m other words, without destroying its type. 674. In tne acetic and many other acids, but one equiva- lent of hydrogen can be replaced by a metal, so that the salts contain but one equivalent of base ; these acids are therefore called monobasic acids. In tartaric acid, C 8 H 6 O, 2 , two equiva- lents of hydrogen may be thus replaced, and a salt obtained of the formula C 8 H 4 M a O 12 , M standing for any metal. These two equivalents may be replaced by two different metals, as by potassium and sodium, C 8 H 4 KNaO 12 ; and salts may also be formed in which but one equivalent of the hydrogen is replaced, as C 8 H 5 KO 12 . These are acid salts, having an acid reaction, and are still capable of neutralizing alkalies. Acids like the tartaric are called bibasic, and are distinguished both by yielding acid salts and by combining with two bases. Tribasic acids are also known, which contain three equiva- lents of hydrogen, replaceable by a metal ; they can form three kinds of salts, in which one, two, and three equivalents of a metal are substituted for the same number of hydrogen. The two first of these salts are acid, the third is neutral. 675. (2.) Substitution by Residues. When nitric acid, NHO 6 =NO 3 H-HO, acts upon the body called benzene, C 12 H 6 , two equivalents of its oxygen combine with the hydrogen of the benzene to form 2HO, and the residues unite to produce a new body, nitrobenzide, C 12 H 5 NO 4 , or C 12 H 4 NHO 4 . Acetic acid and alcohol unite in the same way to form acetic ether, C 4 H 4 O 4 +C 4 H 6 O 2 2HO=C 8 H 8 O 4 . In these compounds the acids cannot be discovered by the usual tests. 30* 354- ORGANIC CHEMISTRY. From these and a great number of similar cases, we deduce the law, that in these reactions, a portion of the oxygen of one body combines with the hydrogen of the other to form water, which is set free, while the residues unite. In the formation of nitrobenzide NHO 6 O 2 is sub- stituted for H 2 in the benzene. This principle explains in a simple manner many reactions in chemistry, and admits of a great number of applications, some of which we shall mention in their appropriate places. 676. The student is now prepared to understand the formation of the sesqui-salts. In those salts, which corres- pond to oxyds with one equivalent of oxygen, the metal re- places the hydrogen, equivalent for equivalent ; thus acetic acid is C 4 H 4 O 4 , and acetate of iron, C 4 H 3 FeO 4 ; but three equivalents of acetic acid react with one of sesquioxyd of iron to form one of sesquiacetate of iron and three of water ; three equivalents of hydrogen are removed, and but two of iron combined in their place. One equivalent of sesquiacetate of iron contains C 12 H 9 Fe 2 O 12 , while three of the acetate equal C, 2 H 9 Fc 3 O, 2 . The reaction which produces this seeming anomaly is readily explained : the three equivalents of oxgen in the sesquioxyd Fo 2 O 3 unite with three of the hydrogen of the acid, to form 3HO, and the residue Fe 2 replaces H 3 . 677. (3.) The third mode of combination in compounds is that of direct union, as when chlorine and sodium unite to form common salt. We have in organic chemistry examples of this mode in the vegetable alkalies which unite directly with acids and metallic salts ; also in some organic products which combine in the same manner with chlorine. 3. Isomerism. 678. We have first seen that acetic acid may have its hydrogen replaced by chlorine, while the characters of the compound remain unaltered. From this and similar in- stances we are led to conclude that the properties of com- pounds depend rather upon the peculiar arrangement of their constituent atoms than upon their kind : and moreover that the same proportions of the same elements may by a different mode of union form compounds widely differing in their characters. Such is really the case ; there are many in- stances of substances which, possessing the same composition and equivalent, are yet perfectly distinct in their properties. ON THE DENSITY OF VAPORS. 355 The formic ether of alcohol, and the acetic ether of wood spirit, are represented by the same formula, i. e. C 6 H 6 O 4 , but are very different in respect of many of their properties ; from the manner of their formation and the products of their decomposition, we have evidence of a difference in the arrangement of their molecules. Substances which have the same equivalent composition, but which differ in their properties, are called isomeric, or more definitely metameric bodies.* 679. Another form of isomerism is that in which the relative proportions of the elements being the same, one sub- stance has double or triple the equivalent of the other. The oil of bitter almonds and benzoine may both be represented by 0,411602, but the equivalent of the last is double that of the oil, and its real formula is C28H 12 O 4 . This relation is called polymeric, and benzoine is said to be polymeric of bitter almond oil. The compounds of carbon and hydrogen present many remarkable instances of isomerism ; olefiant gas, C 4 H 4 , buty- rene, C 8 H 8 , naphtene, C 16 H, 6 , and cetene, C^H^, have the same proportions of carbon and hydrogen, and each of these is polymeric of these before it. The equivalents of tlrese bodies are determined from an examination of their com- binations with other substances, or from the density of their vapors. 4. On the density of vapors. 680. It has been already shown that bodies unite in certain proportions by volume as well as by weight, (190,) and that where a condensation follows the union, it is always one- third, one-half, or some other simple proportional to the sum of the. volumes of its constituents. The vapor of water contains two volumes of hydrogen, and one of oxygen, con- densed one-third, and its specific gravity is equal to one-half the sum of the specific gravities of its constituents, thus 69-3 is the density of hydrogen, air being 1000, and on the same scale the density of oxygen is 1109-3, then * Isomerism, from isos, equal, and meros, measure, may be employed to designate all cases in which the same elements exist in the same relative proportions ; while metamerism, from meta, by, and meros, implies that the proportions of the elements are not only relatively but absolutely the same. The term polymerism, from polus, many, and meros, is explained by the examples given in (679.) 356 ORGANIC CHEMISTRY. Two volumes of hydrogen, 2 X 69-3 = 138' 6 One " oxygen, = 1109-3 Two " water, = 1247-9 One " " = 623-9 Now the specific gravity of the vapor of water at the normal temperature and pressure (120 and 131,) is 620-1, air being 1000, consequently if we know (192) the com- bining volume of any vapor, or the volume of its elements and its density, we can calculate the number of equivalents of each element in the compound, or in other words we can ascertain its formula. For example, olefiant gas has a specific gravity of 971, air being 1000, and it is composed of equal equivalents of carbon and hydrogen; one volume of it contains One volume of carbon vapor,* = 832-0 Two volumes hydrogen, 2 X 69-3 = 138-6 Yielding one volume of olefiant gas, 970-6 As we know from its compounds that the equivalent of this gas is represented by four volumes, its formula must be C 4 H 4 . The vapor of butyrene has a density of 1926 ; and as its combining volume is the same as olefiant gas, its formula will be C 8 Hg. Cetene, C^H^, has a density eight times that of olefiant gas. 681. The determination of the density of vapors is of great importance: in case of some volatile organic com- * As carbon is not volatile, the density of its vapor cannot be de- termined directly ; in its gaseous compounds, however, we know that it must assume the gaseous form. Now carbonic acid contains a volume of oxygen equal to its own ; if then from the number ex- pressing its specific gravity, we deduct that of oxygen, we shall have the specific gravity of the carbon vapor. The density of carbonic acid is 1525-2 air 1000 Deduct oxygen, 1109-3 We have the density of carbon vapor, 415-9 If we assume that the acid contains two volumes of oxygen gas and one of carbon, (CO 2 ) condensed into two volumes, the density of the vapor will be 415-9 X 2 831-8. It is not improbable, how- ever, that the acid may consist of equal volumes of carbon vapor and oxygen condensed one-half; in which case the density of tne former will be 415-9, and its volume the same as hydrogen ; two volumes corresponding to an equivalent. ANALYSIS OF ORGANIC SUBSTANCES. 357 pounds which form no combinations with other substances it is the only means of ascertaining their constitution and equivalent. The process is very simple; the method em- ployed in case of gases has been already described, (49.) When the substance is a liquid or solid, it is introduced into a narrow-necked glass globe of the form represented in the annexed figure, the weight of which is care- fully ascertained. The globe is held by means of its handle firmly attached by wire, beneath the surface of an oil or water-bath, and then heated to some degrees above the boiling-point of the substance. When this is all volatilized and the globe is filled with the vapor, the open and projecting end of the globe's neck is sealed by the flame of a spirit lamp ; and at the same time, the temperature of the bath is noted. When the globe is cooled it is again weighed, and the end of the neck broken off beneath the surface of mercuy, which rushes up and fills the vacuous vessel. The mercury is then carefully measured. The capacity of the vessel and its weight being thus ascertained, we can find the weight of a volume of vapor at the observed temperature, and by an easy calculation can determine what would be its volume at the ordinary temperature, (88) ; its weight com- pared with that of the same volume of air gives the specific gravity required. ANALYSIS OF ORGANIC SUBSTANCES. 682. The ultimate analysis of organic substances is of great importance ; for as we are unable to form them by a direct combination of their elements, a correct understanding of their composition and of the nature of the changes which they undergo, must depend entirely on the results of their analysis. The equivalent of many substances is so large, that a change of one-hundredth part in the proportions, gives to the compound entirely distinct properties. Great refine- ment is consequently necessary in analysis, to enable us to detect the minute differences in composition,.and such have been the care and skill with which the subject has been studied, that we have now arrived at a surprising accuracy in operations of this kind. 358 ORGANIC CHEMISTRY. 683. In theory, the process of organic analysis is ex- ceedingly simple^ If any organic substance, as sugar, for example, is heated with a body capable of yielding oxygen, such as the oxyd of copper, lead, or any other easily re- ducible metal, it is completely decomposed ; the carbon and hydrogen take oxygen from the metallic oxyd, and are wholly converted into carbonic acid and water. From the weight of these, it is easy to calculate the amount of carbon and hydrogen in the body, and if it contains no other element except oxygen, this is known by the loss. But notwith- standing the theoretical simplicity of the process, its execution is exceedingly difficult, and very many precautions are ne- cessary to insure accuracy. It is not the object of this work to explain all the precautions necessary to the successful per- formance of analytical operations, but merely to give an outline of the method pursued, and a general idea of the means employed. For more particular information the student is referred to an excellent memoir on this subject, by Baron Liebig, published in a separate volume. 684. The operation is performed in a combustion tube of hard glass, about 12 inches in length, and from -j^- to -f^ of an inch in diameter. One end is drawn out to a point, turned aside and sealed. Oxyd of copper prepared from the nitrate (609) is generally employed for the combustion. Just before using it, it is heated to redness, in order to expel the moisture which it readily attracts from the atmosphere ; the combustion tube is then about two-thirds filled with the hot oxyd. The substance to be analyzed having been care- \ Oxyd. Mixture. Oxyd. fully desiccated, five or six grains of it are weighed out in a tube with a narrow mouth, in order to prevent the absorption of moisture. It is then rapidly mixed in a dry porcelain mortar, with the greater portion of the oxyd from the tube, to which it is again transferred, and the tube is then nearly filled up with pure oxyd. The relative portions of the oxyd and mixture are shown in the figure above. 685. However carefully the mixture has been made, a ANALYSIS OF ORGANIC SUBSTANCES. 359 little moisture will have been absorbed from the air, which must be removed by the following arrangement. To the end of the combustion tube is fitted, by means of a cork, a long tube filled with chlorid of calcium, and to this is attached a small air-pump. The combustion tube is covered with hot sand, and the air slowly exhausted. After a short time, the stopcock is opened, and the air allowed to enter, thoroughly dried by its passage over the chlorid of calcium. It is again exhausted, and this process repeated four or five times, by which the mixture is completely dried. The annexed figure shows the arrangement for this purpose. 686. The tube is now ready for the combustion, and is placed in the furnace repr sented in tl accompanying figure. It is constructed of sheet iron, and fitted with a series of sup- porters at short distances from each other, to prevent the tube from bending when softened by heat. The furnace is placed on a flat stone or tile, with the front slightly inclined downwards. The quantity of water formed in the process is estimated by a light tube, represented in the annexed figure, which is filled with ^__-n t , tfjuMupM^ii i ajjISLL calcium, and after having been very carefully weighed, is attached by a well dried and closely fitting cork, to the end of the combustion tube. To determine the carbonic acid, a small five-bulbed tube of peculiar form, called Liebig's 360 ORGANIC CHEMISTRY. potash bulb, and represented in the annexed figure, is used. It is charged for this pur- pose with a solution of caustic potash of a specific gravity about 1-25, with which the three lower bulbs are nearly filled. Its weight is determined with great exactness, and it is then attached to the chlorid of calcium tube, by a little tube of gum elastic, which is held fast by a silken cord. The whole arrange- ment is shown below. The tightness of the junction is as- certained by drawing a few bubbles of air through the end of the potash tube, so that the liquid will be raised a few inches above the level on the other side ; if this level remains the same for some minutes, the whole apparatus is tight. 687. Heat is now applied by means of ignited charcoal placed around the anterior portion of the tube, and when this is red-hot, the fire is gradually extended along the tube, by means of a moveable screen, represented in the figure. This must be done so slowly as to keep a moderate and uni- form flow of gas through the potash solution. When the whole tube is ignited, and gas no longer escapes, the closed end of the combustion tube is broken off, and a little air drawn through the apparatus to remove all the remaining products of combustion. The tubes are then detached, and from the increase of weight in the chlorid of calcium tube, the amount of water, and hence that of hydrogen, is deduced. The carbon is determined from the increase in weight of the potash bulbs, by a simple calculation. 688. Volatile fluids are analyzed by enclosing them in a narrow-necked bulb of thin glass, filled with the fluid in the same mode as thermometers, (76.) The weight of the empty tube is first ascertained ; the fluid is introduced, the neck sealed, the weight being again ascertained, and the ANALYSIS OF ORGANIC SUBSTANCES. 361 difference gives the weight of the fluid. The neck of the bulb is then broken by a file mark at a, dropped into the closed end of the combustion tube, and covered with oxyd of copper, which should nearly fill the tube. When this is heated to redness, a gentle heat ap- plied to the portion of the combustion ( tube containing the volatile fluid, sends it in vapor over the ignited oxyd, completely burning it. The products of its combustion are estimated as before. 689. Fatty bodies and others which contain much car- bon and a small quantity of hydrogen, are more perfectly burned by employing chromate of lead in place of the oxyd of copper. This substance does not readily attract moisture from the atmosphere, like oxyd of copper, and is consequently better when the hydrogen is to be determined accurately. The chromate of lead (595) is prepared for use by heating it until it begins to fuse, and when cool reducing it to powder. 690. When nitrogen is a constituent of organic bodies, it is determined by placing in one end of the combustion tube, about three inches of carbonate of copper, secured in its place by a plug of asbestus ; and then the nitrogenous body is introduced, mixed with oxyd of copper. The re- maining space in the combustion tube is filled with turnings of metallic copper. The air is then withdrawn by an air- pump, and a gentle heat applied to the carbonate of copper, which evolves carbonic acid, and drives out all remaining traces of common air. The tube is now heated as usual, and the gases evolved are collected in a graduated air-jar, over mercury. When the combustion is finished, heat is again applied to the carbonate of copper, and another portion of carbonic acid expelled, which drives out all the nitrogen from the tube. The use of the copper turnings is to decom- pose any traces of nitric oxyd, which may be formed in the process. The carbonic acid is removed from the air-jar, by a strong solution of potash, and pure nitrogen remains, which is measured with the usual precautions, and from its volume the weight is easily determined. 691. Another and a preferable mode of determining nitro- gen, is that of Will and Varrentrapp, which is founded on f he fact that when a body containing nitrogen is heated with an excess of caustic potash, or soda, all the nitrogen is 31 362 ORGANIC CHEMISTRY. evolved in the form of ammonia, and may be thus estimated, by conducting it into hydrochloric acid. 692. Chlorine is determined in the analysis of organic compounds, by passing the vapor over quick lime heated to redness in a combustion tube; chlorid of calcium is formed, which is afterwards dissolved in water, and the chlorine pre- cipitated by nitrate of silver. From the weight of the chlorid of silver, the amount of chlorine is calculated. 693. Sulphur is a rare constituent of organic compounds. Its presence is detected by fusion with nitre and carbonate of soda, or by digestion with nitric acid. Sulphuric acid is thus formed, and is precipitated as sulphate of baryta, from the weight of which, that of the sulphur is determined. In the analysis with oxyd of copper, a small tube of peroxyd of lead is introduced between the chlorid of calcium tube and the potash apparatus, to absorb the sulphurous acid which is evolved. ORGANIC COMPOUNDS AND PRODUCTS OF THEIR ALTERATION. AMMONIA, NH 3 . 694. The properties of ammonia and of its salts have been already described, (43S.) It is a constant product of the decomposition of all organic matters which contain nitrogen ; and carbonate of ammonia is obtained in large quantities in the dry distillation of horns, bones, and other animal substances. When any nitrogenous organic substance is heated with an excess of hydrate of potash, its carbon is oxydized by the oxygen of the water, and all the nitrogen combining with the hydrogen is evolved in the form of ammonia. 695. An equivalent substitution (438) of chlorine, bromine, or iodine, may be made for the hydrogen of ammo- nia, as in the production of interesting compounds. Thus when a jar of chlorine is inverted in a solution of an ammo- niacal salt, the gas is absorbed and a heavy yellow oily fluid separates, which is known as chlorid of nitrogen, NC1 3 : it is formed from ammonia by the substitution of chlorine for its hydrogen. This is a most explosive and dangerous body. Even a gentle heat, the contact of phosphorus, fat oils, and many other agents, cause it to be decomposed with a very violent explosion. Bromine forms an analogous compound, (NBr 3 .) AMMONIA. 363 The reaction of ammonia with iodine, (when these two sub- stances are triturated together,) produces a compound in which two of its equivalents of hydrogen are replaced by iodine, giving us the formula, NI 2 H. It is a heavy black powder, which can hardly be dried from the ammoniacal liquor, without explosion, and which the slightest friction causes to be decomposed with a violent detonation. These bodies may be called tri-chlorinized and bin-iodized ammonia. Potassium when heated in dry ammonia displaces one equivalent of hydrogen, forming NH 2 K. This is an olive- green mass, which is resolved by water into ammonia and potash, NH 2 K + HO==NH 3 KO. 696. Ammonia is largely absorbed by many metallic salts, and forms with them definite crystalline compounds ; for example, the salts of silver, copper, and zinc combine with two equivalents of ammonia: but the affinity which holds the ammonia is feeble, and it may be often expelled from these combinations by a gentle heat. In some instances, however, the action is different ; thus when ammonia is added to a solution of chlorid of mercury, a white precipitate is formed, which appears to be a compound of HgCl with NH 2 Hg, corresponding to the potassium compound just described, HgCl + NH 3 = NH 2 Hg + HC1. The hydrochloric acid combines with another portion of ammonia to form sal- ammoniac. When a solution of ammonia is digested with calomel (HgaCl) a black powder is formed, the composition of which may be represented by Hg 2 Cl -f NH 2 Hg 2 . This reaction is like the last ; the chlorine unites with one equiva- lent of hydrogen, which is replaced by the residue Hg 2 . These are examples of the substitution by residues, (675.) 697. Amides. The action of ammonia upon many orga- nic substances containing oxygen is peculiar ; one, two, or three of its equivalents of hydrogen combine with the oxygen of the organic body, and the residues unite. Compounds are thus produced in which NH 2 , NH, or N replace the whole or a part of the oxygen of the organic compound. To these the name of amides has been given. Neither ammonia nor the organic matter can be detected in such compounds by the usual tests, but by the aid of acids and heat they take up the elements of water and reproduce the original substances ; the ammonia combining with the acid, while the organic body is set free. When the organic substance forming the amide is an acid, a similar change is effected by a solution of an 364 ORGANIC CHEMISTRY. alkali ; the regenerated acid forms a salt with the alkali, and ammonia escapes. 698. The amides of monobasic acids are derived from one equivalent of the acid and one of ammonia, by the loss of two equivalents of water. The bibasic acids afford two amides corresponding to their neutral and acid salts. (674.) These may often be formed by the action of heat upon the ammoniacal salts, which are resolved into water and an amide. Thus the oxalate of ammonia, when heated, loses four equivalents of water and is converted into oxamide, C 4 H 2 O 8 -f 2NH 3 (oxalate of ammonia) = 4HO -f C 4 H 4 N ? O 4 . This is a neutral insoluble body, which is converted into oxalic acid and ammonia by solutions of both alkalies and acids. The acid oxalate of ammonia, C 4 H 2 O 8 + NH 3 , loses in the same manner two equivalents of water and yields oxamic acid, C 4 H 3 NO 6 . This is a monobasic acid, and yields a series of salts ; it is, however, a proper amide, and is decomposed by the same agents as oxamide. When boiled for some time with water it takes up the elements of two equivalents, and is converted into acid oxalate of ammonia. THE GROUP OF ALCOHOLS AND THE PRODUCTS OF THEIR ALTERATION. ALCOHOL, C 4 H 6 O 2 . 699. This important substance is a product of the fermen- tation of sugar, and is contained in all fermented liquors. ALCOHOL. 365 From these it is obtained by distillation. A convenient appa- ratus for condensing the vapor of alcohol, ether, and other volatile products of distillation, is represented in the foregoing figure. The general arrangement is similar to the usual dis- tillatory apparatus, (117.) The neck of the retort passes into a large glass tube, which is encased by an outer one of metal closely adapted by corks at its ends to the glass tube, leaving a water-tight cavity between the two, which is filled with cold water by a tube entering near the lower end and terminating in a funnel at a higher level, where water is sup- plied from a small tank with a cock. An orifice near the upper end of the condenser permits the water to escape when it has risen to a higher level in the upper tube. This arrange- ment, (called from its inventor a " Liebig's condenser") secures an uninterrupted flow of cold water into the condenser as fast as the heated water escapes from the upper end, and the most volatile vapors are easily condensed to fluids in such an apparatus. If necessary, iced water can be employed. Alcohol thus distilled, still retains fifteen per centum of water. This is removed by digestion with quick lime or chlorid of calcium, which appropriate the water, and another distillation yields anhydrous or absolute alcohol. 700. Pure alcohol is a colorless fluid, with a specific gra- vity of *795, and boils at 173 F. It has a pungent and agreeable taste, and a fragrant odor. It is very combustible, and burns with a pale blue flame without smoke, which ren- ders it very useful as a source of heat in chemical processes. The action of alcohol on the system, is well known as that of a powerful and dangerous stimulant. It is largely used in the operations of the arts, the preparation of medicines, and the processes of chemistry. Its solvent powers are very great ; the volatile oils and resins are dissolved by it, as well as many acids and salts, the caustic alkalies, and a large number of other substances. The specific gravity of the vapor of alcohol is 1600, air being 1 000 ; and its equivalent is represented by four vol- umes, oxygen being one. It is composed of 4 volumes of carbon vapor, 4 X '832 = 3-3280 12 " hydrogen, 12 X -0693 = -8316 2 oxygen, 2 X 1-1093 = 2-2186 Equal to four volumes of alcohol vapor, 6-3782 Of which one volume weighs, 1-5946 31* 366 ORGANIC CHEMISTRY. 701. Sulphur Alcohol, Mercaptan, C 4 H C S 2 . This singu- lar compound is alcohol in which sulphur replaces the oxygen. It is a colorless and very volatile fluid, and has a very pow- erful odor, resembling onions. It acts upon oxyd of mercury with great violence ;* water is formed, and a white crystal- line substance, which is C 4 H 5 IIgS 2 . Analogous compounds may be obtained by its means with other metallic oxyds, and the term mercaptides has been used to distinguish them. Mercaptan is a fine example of the equivalent substitution of sulphur for oxygen in organic compounds. Mercaptan may be procured by saturating a solution of caustic potash, (den- sity of 1-3,) with sulphureted hydrogen gas, arrd distilling this in a retort with an equal volume of sulphovinate of time of the same density. The regulated temperature of a salt bath, and a Liebig's condenser are necessary, and the mercaptan is separated by a funnel from the accompanying water, which collects with it in the cold condenser. Action of Acids upon Alcohol. 702. Ethers. The action of acids upon alcohol is highly important in relation to chemical theory, and has been very attentively studied. When a monobasic acid acts upon alcohol a combination takes place, with the elimination of two equiva- lents of water. The resulting compounds are called ethers, and have been considered as stilts, in the formation of which alcohol minus one equivalent of water plays the part of a metallic oxyd. Unlike saline combinations, however, the acids of the ethers cannot be recognised by the usual tests: for example, oxalic ether does not produce any precipitate in the solutions of a salt of lime, while all the oxalates precipi- tate lime from its solutions as insoluble oxalate. When heated with the solution of a fixed alkali, the ethers take up the elements of two equivalents of water, regenerating alcohol and the acid. This change is sometimes effected by boiling with water. 703. A bibasic acid reacts in the same manner with two equivalents of alcohol and the separation of four equivalents of water. Thus oxalic acid, C 4 H 2 O 8 , and two of alcohol, 2C 4 H 6 O 2 , yield one equivalent of oxalic ether and four of water, C, 2 H 10 O 8 +4HO. Often, however, the reaction is dif- ferent; an equivalent of the acid acts upon but one equivalent * Whence its name, Mercy-riitm eapt ans. ALCOHOL. 367 of alcohol, and produces an acid ether which is capable of neutralizing bases to form salts. These are called vinic acids, and are monobasic ; e. g. oxalovinic and sulphovinic acids. If we represent the residue C 4 H 6 O 2 H 2 by E, the composition of these compounds may be represented thus Oxalic acid, C 4 H 2 8 Oxalic ether, C 4 H 2 * Oxalovinic acid, C 4 H 2 -j , 6 In these compounds the residue represented by E replaces two equivalents of oxygen. 704. Tribasic acids in the same way form neutral ethers with three equivalents of alcohol, or bibasic acids, with one equivalent. The power of forming vinic acids or acid ethers with alcohol, belongs only to those acids which are polybasic ; and the study of these reactions has shown us that several acids usually considered as monobasic are really bibasic acids. Thus the sulphuric yields with alcohol sulphovinic acid with wood-spirit, (a compound closely allied to alcohol in its chemical relations,) a corresponding acid, and a neutral ether. Agreeably to this view the formula of sulphuric acid must be doubled thus S 2 H 2 O 8 = 2SHO 4 , or 2SO 3 HO. It will be remembered that this acid forms both neutral and acid salts, as well as salts with two fixed bases, and is for this reason also to be considered bibasic, (674.) Carbonic acid is in the same way bibasic, since it forms neutral and acid carbonates, and yields with alcohol carbonic ether, and car- bovinic acid. Nitric acid on the other hand yields a neutral ether with one equivalent of alcohol ; it never forms acid or double salts, and is an example of a monobasic acid. The vinic acids and those formed in a similar manner are conveniently designated as coupled acids. 705. In these coupled acids, as in the neutral ethers, the original acid cannot be detected by the usual tests. The sul- phovinate of baryta is a very soluble salt, while the sulphate of the same base is a very insoluble compound. When heated with hydrate of potash, the sulphovinates assume the elements of water, and regenerate the acid and alcohol. It will be observed that the ethers present many analogies to the amides in formation and composition, as well as in the mode of their decomposition by alkalies. The similarity of origin will be seen by comparing the oxalic ether arid amides 368 ORGANIC CHEMISTRY. Oxamide, C 4 H 2 N 2 O 4 = Oxalic ether, C, 2 H 10 O 8 C 4 H 2 O 8 + 20,1^02 4HO Oxamicacid, C 3 H 3 N0 6 C4H 2 O 8 + NH3 2 HO Oxalovinijc acid, CgHeOg = C 4 H 2 O 8 + C 4 H 6 O2 2HO The neutral ether and amide are derived from one equiva- lent of the acid, and two of ammonia or alcohol, by the loss of four equivalents of water ; and the oxamic and oxalovinic acids, which are monobasic, are in like manner formed from an equivalent of the bibasic acid and one of ammonia or alcohol, by the abstraction of two of water. 706. Nitric Ether, C 4 H 5 N0 6 . This compound is formed by distilling equal parts of strong nitric acid and alcohol with a few grains of urea. The action of nitric acid upon alcohol is very violent. Nitrous acid is formed, which de- composes the ether, and gives rise to a variety of products ; but a little urea prevents this, and the distillation proceeds quietly, yielding nitric ether and water, C 4 H 6 O 2 + NHO 6 r= 2HO -\- C 4 H 5 NO 6 . It is a colorless liquid of a very sweet taste, is insoluble in water, has a specific gravity of 1*1 12, and boils at 185 F. The vapor explodes by a mod- erate heat. When this ether is mixed with a solution of potash in dilute alcohol, it reassumes the elements of water, and yields alcohol and nitrate of potash. 707. Perchloric Ether, C 4 HCI 6 . This is an extremely explosive compound, which is produced from the distillation of a concentrated solution of perchlorate and sulphovinate of barytes, in equivalent proportions. So long as the salts re- main in solution no reaction occurs, but as soon as they become solid a reciprocal decomposition ensues, and a sweet ethereal liquid collects in the receiver. This is the compound which has been called perchloric ether by Messrs. Hare and Boye.* It is a transparent colorless liquid, heavier than water, with a pungent agreeable smell, and very sweet taste, which leaves a biting impression on the tongue, similar to that of oil of cinnamon. It explodes by ignition, friction, or percus- sion, sometimes with no assignable cause, and with such pecu- liar violence that the smallest drop of it, when exploded upon an open porcelain plate, will shatter it into fragments. It is unsafe to operate with it unless protected by gloves and a close mask with thick glass eye-holes, and with the intervention of a moveable wooden screen. It dissolves in alcohol, and an *American Journal of Science, (1st Series,) vol. 42, p. 62. ALCOHOL. 369 alcoholic solution of potash added to the solution of the ether in alcohol decomposes it, with the production of in- soluble perchlorate of potash. 708. Hydrochloric Ether, C 4 H 5 CI. This substance is obtained by saturating alcohol with hydrochloric acid gas, when the ether passes over, and must be condensed by a freezing mixture, C 4 H C O 2 + HC1=C 4 H 5 C1 + 2HO. It is a colorless, very volatile liquid, with a pungent aromatic odor, and is slightly soluble in water. It has a specific gravity of -873, and boils at 52 F. With a solution of potash it is decom- posed like all the other ethers, and yields chlorid of potassium and alcohol. 709. Hydrobromic Ether, C 4 H 5 Br. When a mixture of alcohol, bromine, and phosphorus is distilled, hydrobromic acid is formed, which reacts with the alcohol to form hydro- bromic ether. It is a volatile fluid, heavier than water, and closely resembles the hydrochloric ether. Hydriodic Ether, C 4 H 5 I, is obtained by substituting iodine for bromine in the last process. It is a colorless liquid, of specific gravity 1-92, and boils at 160. 710. Acetene, C 4 H 6 . When hydrochloric ether is decom- posed by potassium, chlorid of potassium is formed, and a white crystalline compound, which is C 4 H 5 K. " This is decomposed by water, into water and a volatile oily liquid, which is C 4 H 6 . To this the name of acetene is given. The bodies formed by the action of hydrochloric, hydrobromic, and hydriodic acids upon alcohol, and which have just been described as ethers, may be viewed as acetene, in which an equivalent of hydrogen is replaced by chlorine, bromine, or iodine. A peculiar compound formed by the action of nitric or nitrous acid upon alcohol, may be viewed as a derivative of acetene. Nitric Acetene; Nitrous Ether; Hyponitric Ether, C 4 H 5 NO 4 . The red vapors evolved by the action of nitric acid upon starch, are rapidly absorbed by dilute alcohol, with the evolution of heat, and the present compound passes off in vapor and may be condensed. It is a pale yellow fluid, of a very fragrant odor of apples ; it has a specific gravity of -947, and boils at 62. This substance is re- garded by many as the ether of hyponitric acid, but it does not appear to yield alcohol and a hyponitrate by the action of potash, as it should do if it were like the ethers. It results from the action of NO 3 +C 4 H e O 2 =:HO-f C 4 H 5 NO 4 i 370 ORGANIC CHEMISTRY. and may oe regarded as derived from acetene and nitric acid, by the abstraction of 2HO. This substance is formed among many others, when alcohol is acted on by nitric acid, and an alcoholic solution of the impure product constitutes the sweet spirits of nitre, used in medicine. It was formerly obtained by distilling a mixture of nitre with sulphuric acid and alcohol. 711. Sulphovinic Acid, C 4 H 6 S 2 O 8 . The proper sulphu- ric ether, with two equivalents of alcohol, has not been obtained. When equal weights of alcohol and sulphuric acid are mixed and heated to boiling, sulphovinic acid is formed, and remains in the fluid ; the mixture is allowed to cool, diluted with water, and neutralized with chalk. The excess of sulphuric acid forms an insoluble sulphate with the lime, while the soluble sulphovinate of lime remains in solu- tion, and is obtained in crystals by evaporation and cooling. It forms beautiful colorless prisms, which have the composi- tion C 4 H 5 CaS 2 O p -f 2aq ; they lose the water in a dry atmosphere. The sulphovinate of potash is obtained by de- composing the lime salt with carbonate of potash. If carbonate of baryta is substituted for chalk in neutral- izing the acid mother-liquor, sulphovinate of baryta may be obtained in fine crystals. From a solution of this salt, dilute sulphuric acid precipitates all the baryta, and a solution of sulphovinic acid is obtained, which may be concentrated in vacuo. It forms a sour syrupy liquid, which is decom- posed by a gentle heat, (or even by too much concentration,) into alcohol and sulphuric acid. 712. Sulphovinic acid is derived from one equivalent of sulphuric acid, and one of alcohol, by the abstraction of the elements of two equivalents of water, S 2 H 2 O 8 + C 4 H 6 O 2 = C 4 H 6 S 2 O 8 + 2HO, and in its decomposition it reassumes the 2HO. When a sulphovinate is distilled with hydrate of pot- ash, it yields alcohol and a sulphate of potash; if, in place of hydrate of potash, the hydrosulphuret is employed, sulphur alcohol is obtained; C 4 H 6 S 2 O 8 + KSHS = C 4 H 6 S 2 + S 2 HK0 8 . (701.) When a sulphovinate is distilled with any salt, as ace- tate of lime, a double exchange ensues ; the acetic acid takes the place of sulphuric and forms acetic ether, while sulphate of lime remains. 713. Carbovinic Acid. When carbonic acid acts upon a solution of potash in absolute alcohol, crystals of car- bovinate of potash are formed ; they have the composition ALCOHOL. 371 C 6 H 5 KO 6 . This acid cannot be isolated. The carbonic -ether is formed by the action of potassium upon oxalic ether. It is a colorless liquid, which contains C ]0 H JO O 6 , and by the action of potash takes up the elements of water, and yields alcohol and carbonate of potash. By the action of sulphuret of carbon upon an alcoholic solution of potash we obtain sulphurized carbovinate of potash, in which sulphuret of carbon acts the part of carbonic acid. The acid is an oily liquid, of a sour and bitter tasle ; its formula is CgH^OgS^ =carbovmic acid, C 6 H 6 O 6 , in which four equivalents of oxygen are replaced by sulphur. From the yellow color of some of its salts it was originally de- scribed under the name of xanthic acid. Phosphovinic acid is formed by the reaction of one equiva- lent of tribasic phosphoric acid and one of alcohol. It is a bibasic acid, and in its general characters resembles sulpho- vinic acid. Arsenic acid forms an allied compound, the arsenovinic acid. 714. Silicic Ethers. Two ethereal compounds are formed by the reaction of chlorid of silicon upon alcohol. They are odorant and volatile liquids, of a pungent taste ; one has the formula C 12 Hi 5 SiO fi , and contains the elements of one equiva- lent of silicic acid and three of alcohol, minus the elements of water. The formula C 4 H 5 Si 2 O 7 is ascribed to the other, and both of them are slowly decomposed by water, and rapidly by alkalies into alcohol and silicic acid. When ex- posed to moist air in vessels partially closed, they deposit silicic acid in beautiful transparent masses, resembling the finest rock-crystal. By the action of the chlorid of boron upon alcohol, two boracic ethers are produced similar in composition and properties to the last : they burn with a fine green flame, which is characteristic of the combustion of an alcoholic solution of boracic acid boracic ether being formed by this combustion, and in the distillation of alcohol with boracic acid. (370.) Products of the decomposition of Sulphovinic Acid. 715. Ether. When dilute sulphovinic acid is heated to boiling, it is decomposed into sulphuric acid and alcohol, but when a mixture of equal weight of sulphuric acid and alcohol is boiled, water is evolved, and a liquid which may be repre- sented as C 4 H 5 O. In the first of these cases, the sulphovinic acid takes up the elements of two equivalents of water, and 372 ORGANIC CHEMISTRY. regenerates alcohol and the acid ; but in the second, this acid, when decomposed at the boiling-point of the liquid, about 300 F., assumes the elements of but one equivalent of water, and evolves the new compound ether. The best pro- portions for preparing this ether, are five parts of alcohol of 90 percent., and eight of ordinary sulphuric acid. The mixture is placed in a flask, (a,) through the cork of which is intro- duced a thermometer (d) and two tubes, one of which (c) conveys away the vapors to a condenser, and the other (b) is connected with a reservoir of alcohol. The mixture is heated to the boiling-point (about 300 F.) and care- fully maintained at that temperature. Alcohol is now admitted through the tube 6, in a quantity sufficient to pre- serve the original level of the liquid in the retort, the supply being regulated by a stopcock. During the whole ope- ration the liquid must be kept violently boiling, and the alcohol is then com- pletely decomposed into ether and water, which distil over together, and condense in the receiver. With these precautions the process may be carried on for a long time, the only limit to it being, that the acid is slowly volatilized, in combination with a portion of the alcohol. The ether which floats on the water in the receiver, is separated, and purified by distilling with a little caustic potash. This reaction is explained, by the fact that sulphovinic acid is formed when the mixture is heated to 285, and decomposed at a temperature a few degrees above it, if the liquid is boiling. The alcohol, as it flows into the boiling mixture through the tube 6, reduces the temperature at the point of contact, so that sulphovinic acid is formed, and a portion of the water elininated is immediately volatilized. As soon as the newly formed acid mixes with the boiling liquid, it is decomposed and ether is evolved. The result is, that with each equiva- lent of ether, one of water is volatilized so that, in effect, the alcohol is resolved into these substances. This body is the sulphuric ether of commerce, and so ALCOHOL. 373 well known in medicine. But it should be carefully distin- guished from those compounds, which like nitric ether, con- tain the elements of an acid. Ether is a colorless limpid fluid, having the specific gravity of '725. It boils at 96, and evaporates rapidly at ordinary temperatures, producing by its evaporation intense cold. Its taste and odor are pungent, penetrating, and peculiar. It is very combustible, and on account of its volatility should never be brought near a flame, as the vapor, when mixed with air, is very explosive. The ether of the shops is never pure, but contains alcohol, and as it is only sparingly soluble in water, may be purified by agitating it with its volume of this fluid, which combines with the alcohol, while the ether floats on the surface. Ether is considerably used as a medicine ; internally as a powerful stimulant ; and externally as a refrigerant, from the cold produced by its evaporation. The inhalation of vapor of ether mingled with atmospheric air, produces in the patient a kind of intoxication, which is soon followed by a state of stupor, in which the subject is insensible to external impressions. It has been lately em- ployed under the name of letheon, and with wonderful suc- cess, to produce insensibility during surgical operations. Pure ether is essential for this purpose, and may be obtained by washing the commercial article, as above described. The honor of this application so important in alleviating human suffering, belongs entirely to this country, having been first suggested by Dr. Charles S. Jackson, of Boston, and applied successfully by Mr. Morton, dentist, of the same city. The density of the vapor of ether is 2581, being equal to that of two volumes of alcohol vapor, less one of water. If we regard four volumes of vapor as representing its equivalent, its formula will be CgH^Og, but this formula is usually halved, which gives C 4 H 5 O. 716. Sulphur eted Ether, C 4 H 5 S, is a compound obtained by the reaction of hydrochloric ether with sulphuret of po- tassium, C 4 H 5 C14-KS=C 4 H 5 S + KC1. It is a colorless vola- tile liquid, with an odor resembling that of garlic. Selenium and tellurium in like manner replace the oxygen of ether, (C 4 H 5 O,) giving us analogous seleniureted and sulphureted ethers, (C 4 H 5 Se and C 5 H 5 Te.) 717. Olefant Gas, C 4 H 4 . This product is formed when alcohol is mixed with so much sulphuric acid, that the mix- 32 3/4 ORGANIC CHEMISTRY. lure does not boil below 320. The sulphovinic acid then no longer takes up an equivalent of water in its decomposition ; but is directly resolved into sulphuric acid and olefiant s;as, C 4 H 6 S 2 O 8 = S 2 H 2 O 8 +C 4 H 4 . This is essentially the process already described for obtaining this gas, (454,) but a more elegant way of preparing it, is by an arrangement similar to that used for producing ether. Sul- phuric acid is diluted with nearly one half its weight of water, so that its boiling-point is between 320 and 330, and being heated in the flask a to ebullition, the vapor of boiling alcohol is introduced from the flask d by the tube 6, which dips a little way in the acid. In this process, we may suppose that sulphovinic acid is formed with the escape of two equivalents of water in vapor, and is immediately decomposed into sulphuric acid and olefiant gas: an equivalent of alcohol yields C 4 H 4 -f 2HO. The gas is thus obtained quite pure, and the process may be continued for any length of time. 718. When olefiant gas is mingled with its own volume of chlorine, combination ensues, and a heavy oily liquid is obtained of a sweet and pungent taste. This compound was discovered by an association of Dutch chemists, and is hence often called the oil of the Dutch chemists ; its formula is C 4 H 4 C1 2 . The action of chlorine gas, aided by the sun's rays, will successively replace the hydrogen of this compound. The different products are C 4 H 5 CI, C 4 H 4 C1 2 , C 4 H 3 C1 3 , C 4 H 2 C1 4 , C 4 HC1 5 and C 4 C1 6 . A similar series is formed, and in a simi- lar manner, from the hydrochloric ether, C 4 H 5 C1. These two series of bodies, although represented by the same formulas, are quite different in properties, and are interesting examples of isomerism. The final product of the action of chlorine upon both series of compounds is the chlorid of carbon, C 4 Hg. This is a white crystalline solid of an aromatic odor, like camphor ; it melts at 320, and at a temperature a little above this, may be distilled unaltered. It is scarcely com- bustible, and is unchanged by acids or alkalies. When its vapor is passed through a porcelain tube heated to redness, it is resolved into chlorine gas and a new compound, ALCOHOL. 375 C 4 C1 4 , which is a volatile liquid, of the specific gravity of 1'55. If the vapor of this compound is passed repeatedly through a tube at a bright red heat, it is decomposed into chlorine and C 4 C1 2 . This body forms soft, silky crystals, which are vola- tile and combustible. Products of the Oxydation of Alcohol. 719. The first effect of oxydizing agents upon alco- hol, is to abstract two equivalents of its hydrogen, producing a body to which the name of aldehyde has been given.* This is produced by the action of nitric acid and various other substances, but is best obtained by the following pro- cess. Equal weights of powdered bichromate of potash and strong alcohol are introduced into a retort, and one and a half parts of sulphuric acid are gradually added through the tubulure ; a gentle heat is then applied, when a mixture of aldehyde and water distils over and may be condensed in a cold receiver. The impure product is mixed with ether, and saturated with ammonia, when a compound of aldehyde and ammonia separates in fine crystals. This, decomposed by dilute sulphuric acid, affords pure aldehyde. It is a colorless liquid, with a suffocating ethereal odor ; has a specific gravity of -790, and boils at 70 F. Its formula is C 4 H 4 2 = alco- hol C 4 H 6 O 2 ELj ; a solution of potash decomposes aldehyde, and forms a brown resinous substance, which is named aldehyde resin : this reaction enables us to detect the presence of aldehyde in liquids. When a solution of aldehyde, mixed with a little ammo- nia, is added to a dilute solution of nitrate of silver, and the mixture is heated : the silver is reduced, and lines the vessel with a brilliant metallic film which forms a perfect mirror. This fact has been successfully applied in the manufacture of mirrors. 720. Aldehyde cannot be preserved unchanged, even in sealed tubes, but is slowly changed into two polymeric com- pounds. One of these, elaldehyde, is a dense oily fluid, which has none of the properties of aldehyde. The den- sity of its vapor is three times that of aldehyde ; and its formula is 3C 4 H 4 O 2 = C^H^Og. The other body, metaldehyde, forms hard white prisms ; it is formed by the union of four * From alcohol de hydrogenatus. 376 ORGANIC CHEMISTRY. equivalents of aldehyde, and has the composition C 16 H, 6 O 8 . When aldehyde is exposed to the air, it gradually absorbs oxygen, and is converted into acetic acid. Acetic Acid, C 4 H 4 O 4 . This is the acid of vinegar ; and it is produced by the oxydation of alcohol, or aldehyde. The latter body combines directly with two equivalents of oxygen, C 4 H 4 O 2 + O 2 =C 4 H 4 O 4 . When alcohol is heated with a mix- ture of hydrate of potash and lime, hydrogen gas is evolved and acetate of potash is formed. The reaction is thus ex- plained : C 4 HA + KOHO==C 4 H 3 KO 4 + 4H. 721. Pure alcohol undergoes no change when exposed to the air alone ; but if its vapor mixed with air is brought into contact with platinum-black, it slowly unites with oxygen to form aldehyde, which readily absorbs another portion of oxy- gen, and produces acetic acid. The oxydating power of finely divided platinum has been before alluded to : it absorbs or condenses great quantities of gases and vapors in its pores, where they appear to be brought together in such a state that they readily react upon each other. 722. The formation of acetic acid may be beautifully shown by placing a little platinum-black in a watch-glass, by the side of a small vessel of alcohol, covering the whole with a bell-glass, and setting it in the sun-light. In a short time the vapor of acetic acid will condense on the sides of the glass, and run down in drops ; and if we occasionally admit fresh air by raising the bell-jar, the whole of the alco- hol will be acidified in a few hours. The change consists in the loss of two equivalents of hy- drogen, and the addition of two of oxygen. In the ordinary process for vinegar, alcoholic liquors, as wine and cider, are exposed to the air in open vessels. Although a mixture of pure alcohol and water does not absorb oxygen from the air, a small portion of any ferment, as vinegar already formed, or the substance called mother of vinegar, enables it to combine with oxygen. In this process, the essential thing is a free supply of air, and a proper temper- ature. In the manufacture of vinegar on the I large scale, this is secured by causing the liquor (b) to trickle from threads of cotton drawn through holes, over shavings of beech- wood previously soaked in vinegar, and con- tained in a large cask with holes in its sides, (c c c c,) so as ALCOHOL. 377 to admit a free circulation of air. Jn this way a vast surface is exposed, and the absorption of oxygen is very rapid, causing an elevation of 20 or 30 in the temperature. The liquid is passed through this apparatus four or five times in the course of twenty-four hours, in which time the change of the alcohol into vinegar is generally complete. The pro- duct is collected in the vessel a. 723. Acetic acid is also obtained by distilling wood in close vessels ; the volatile ingredients are expelled and char- coal alone remains ; the products are, besides carbonic acid and carbureted hydrogen, a large quantity of acetic acid, mixed with oily and tarry matters, from which it is separated mechanically. The acid thus prepared is known as pyrolig- neous acid, and is largely used in the arts of dyeing and calico-printing, but being contaminated by empyreumatic oils, is not fit for the purposes of domestic economy. By combining it with bases, salts are obtained, which, when de- composed, afford a pure acid. 724. By distilling dried acetate of soda with strong sul- phuric acid, a very concentrated acid is obtained, which, when exposed to cold, deposits crystals of pure acetic acid, C 4 H 4 O 4 . The pure acid is solid below 60 F. ; when liquid it has a specific gravity of 1-063, and boils at 248. It is perfectly soluble in water, alcohol, and ether ; it has a pun- gent fragrant odor and a very acid taste, and when applied to the skin is highly corrosive. The acid is monobasic ; all its salts are soluble in water. Acetates. 725. Acetate of Potash (C 4 H 3 KO 4 ), is easily prepared by neutralizing acetic acid with carbonate of potash. It is a very soluble deliquescent salt, and is employed in medicine. Acetate of soda (C 4 H 3 NaO 4 ), forms large crystals with six equivalents of water. It is prepared in large quantities from pyroligneous acid. The salt is healed to destroy the oily matter, and then affords by its decomposition a pure acid. Acetate of ammonia (C 4 H 4 O 4 +NH 3 ), is used in medicine by the name of the spirit of Mindereus. It is prepared by saturating acetic acid with ammonia, and is exceedingly soluble and volatile. The acetate of zinc is a beautiful white salt, and is employed as a tonic and astringent. The acetate of alumina is much used in dyeing ; it is obtained by dccom- 32* 378 ORGANIC CHEMISTRY. posing a solution of alum by one of acetate of lead ; sulphate of lead precipitates, and acetate of alumina with acetate of potash remains in solution. The acetate and sesqui-acetate of iron are prepared in a similar manner, and are largely employed in calico-printing and dyeing. The constitution of the sesqui-acetates has been already explained (676). 726. Acetate of Lead, C 4 H 3 Pb,O 4 . This salt is well known under the name of sugar of lead. It is prepared by dissolving oxyd of lead (litharge) in acetic acid, and crystal- lizes with three equivalents of water, which are expelled by gentle heat. It is a white salt, with a very sweet and astrin- gent taste, and is often employed as a medicine ; but is poi- sonous, and should be used internally with caution. The acetate of lead has a great tendency to combine with oxyd of lead, with which it forms several definite compounds. These are generally designated as basic salts, but should be carefully distinguished from the salts containing more than one equivalent of base, which are formed by bibasic and tribasic acids. In these last, the metal replaces the hydrogen of the acid, but in the basic acetates, the neutral salt combines directly with the oxyd. To distinguish them, the term sur- basic is applied, and the compound of the acetate with two equivalents of oxyd of lead is called the bi-surbasic acetate of lead. Three of these compounds are known, in which the acetate is combined with one-half, two, and five equivalents of oxyd. The second is the only one of importance. 727. Bi-surbasic Acetate of Lead, C 4 H 3 PbO 4 -f 2PbO. This salt, commonly called the tribasic acetate, is obtained by digesting a solution of six parts of the acetate with seven of litharge : the oxyd is dissolved, and the liquid affords, by evaporation, a salt crystallizing in long needles. It is also slowly formed when metallic lead is digested in an open vessel with a solution of the acetate, oxygen being absorbed from the air. The salt is very soluble in water, and its solution has an alkaline reaction : it is well known in pharmacy as Goulard's Extract, or solution of lead. When exposed to the air, it absorbs carbonic acid, and the two equivalents of oxyd of lead are precipitated as a carbonate. This reaction enables us to explain the formation of white lead, (606.) 758. A process frequently employed is to mix litharge and about T ^-oth of sugar of lead into a thin paste with water ; the mixture is gently heated, and a current of carbonic acid is passed through it. The acetate of lead dissolves a portion ALCOHOL. 379 of the oxyd to form the tribasic salt; this is immediately decomposed by the carbonic acid, which precipitates carbonate of lead, and leaves the acetate free to dissolve a new portion of oxyd. In this way the smallest quantity of the acetate is able to convert a large portion of the oxyd into carbonate, and at the end of the process to remain unaltered. 729. In the ordinary process, the plates of lead are ex- posed to the action of acetic acid, moisture, air, and carbonic acid from the fermenting tan. The lead immediately be- comes covered with a film of oxyd by the action of the air. This is dissolved by the vapor of acetic acid, and forms a solution of neutral acetate, which moistens the plates and gradually acts upon them, forming by the aid of the atmo- spheric oxygen, the basic acetate. This is decomposed by the carbonic acid, in the same manner as in the last process, and the neutral acetate is again set free to act upon the me- tallic lead ; the process goes on until all the lead is carbonated. In this way a small quantity of acetic acid will, under favor- able circumstances, convert a hundred times its weight of lead into carbonate in a few weeks. 730. Acetate of Copper, C 4 H 3 C 4 (X. This salt is quite soluble, and forms beautiful green crystals of the monoclinate system, containing one equivalent of water. The acetate of copper forms several surbasic salts which are insoluble in water. The fine green pigment called verdigris is a mixture of two or more of these ; all of these copper salts are very poisonous. The Acetate of Silver (C 4 H 3 AgO 4 ), crystallizes in white scales, and is the least soluble of the acetates. 731. Chloracetic Acid, C 4 C1 3 HO 4 . When acetic acid is placed in a vessel of chlorine gas, and exposed to the sun- light, three equivalents of its hydrogen are removed in the form of hydrochloric acid, and three of chlorine substituted in their place. The chloracetic acid closely resembles tne acetic, and its salts correspond to the acetates of the same bases. A solution of any chloracetate is decomposed by an amalgam of potassium : the chlorine is removed, and we obtain chlorid of potassium and ordinary acetate of potash. 732. Acetic Ether, C 8 H 8 O 4 . This is formed by the direct action of acetic acid on alcohol ; but is best obtained by distilling five parts of acetate of soda, eight of sulphuric acid, and three of alcohol. It is a very fragrant volatile liquid ; the odor of vinegar formed from fermented liquor is due to a little acetic ether. It contains the elements of one 380 ORGANIC CHEMISTRY. equivalent of alcohol, and one of acetic acid, less two of water, C 4 H 6 O 2 + C 4 H 4 O 4 =C 8 H 8 O 4 -f 2HO. 733. When acetic acid or acetates are decomposed by heat, a volatile liquid called acetone is obtained : it is derived from the elements of two equivalents of acetic acid, by the abstraction of two of carbonic acid gas and two of water, 2(C 4 H 4 O 4 )-(2CO 2 +2HO)=C 6 H 6 O2. The vapor of acetic acid, when passed through an ignited tube, is completely resolved into these substances. Acetone is a very volatile liquid, of specific gravity -793, and has a pungent and peculiar odor. It is readily soluble in water, alcohol and ether. When distilled with a mixture of chromate of potash and sulphuric acid, it yields acetic acid. By the action of an excess of potash upon an acetate, it is decomposed into carbonic acid and marsh gas, C 4 H 4 O 4 == 2CO 2 +C 2 H 4 , (451.) WOOD-SPIRIT, C 2 H 4 2 . 734. This substance is a product of the destructive dis- tillation of wood : when the crude pyroligneous acid (723) is saturated by lime and distilled, impure wood-spirit is obtained, and may be afterwards purified by repeated dis- tillations. It is a colorless liquid, of a peculiar and some- what unpleasant odor, and a hot pungent taste. It has a specific gravity of -798, and boils at 152; it is very com- bustible, and burns with a pale blue flame. Like alcohol, it mixes in all proportions with water. It is occasionally used in the arts for dissolving resins, and making varnishes ; and the pure wood-spirit has lately acquired some celebrity in the treatment of phthisis, under the name of wood-naphtha. This substance is known in commerce as pyroxylic spirit;* from its resemblance to alcohol, it has been called methylic alcohol,* and the name of methal is also employed. Wood-spirit is closely affined to alcohol in all its chemical relations. By the action of acids it gives rise to ethers, which in their properties and mode of formation are so similar to the corresponding bodies from alcohol, that what has been said of these will apply to them in every respect. With bibasic acids it forms methylic acids similar to the vinic. * Pyroxylic spirit, from pur, fire, and hulon, wood, in allusion to its origin ; and methylic alcohol, from metku, wine, and hulon : the wine or alcohol of wood. WOOD-SPIRIT. 381 735. The Nitric Methylic Ether, C 2 H 3 NO 6 , is formed by distilling wood-spirit with nitre and sulphuric acid. It is a heavy oily fluid, which by the action of a solution of potash takes up the elements of two equivalents of water, and yields nitrate of potash and wood-spirit. Its vapor, when heated to 250, explodes with great violence. Hydrochloric Methylic Ether, C 2 H 3 C1, is obtained in the form of a gas, having a sweet ethereal taste, and a specific gravity of 1*731. The compounds containing bromine and iodine are liquids. 736. Sulphuric Methylic Ether.- This compound, the analogue of which is unknown in the alcohol series, is obtained by distilling wood-spirit with eight or ten parts of sulphuric acid. It is a tasteless, oily fluid, which has an allia- ceous odor ; boils at 370, and has a specific gravity of 1-324. It is formed from an equivalent of sulphuric acid and two of wood-spirit, by the loss of four of water, S 2 H 2 O 8 -f-2C 2 H 4 O 2 ==C 4 H 6 S 2 O 8 + 4HO. By the action of boiling water it takes the elements of two equivalents of that liquid, and is in part decomposed, yielding wood-spirit and sulphomethylic acid, and by excess of caustic potash the decomposition is com- plete. By the action of ammonia a white crystalline com- pound is formed, which is called sulphamethylane ; one equivalent of the ether and one of ammonia, yield one equivalent of the new substance and one of wood-spirit, C 4 H 6 S 2 O 8 + NH 3 =C 2 H 5 NS 2 O 6 + C 2 H 4 O 2 . Its nature will be understood by referring to what we have said of the simi- larity between the ethers and amides, (705.) We have represented the former as derived from alcohol and an acid, by the loss of two equivalents of water ; and the amides, in the same manner, are formed from ammonia and an acid. Sulphamethylane is an ether- amide, and is formed from one equivalent of ammonia and one of wood-spirit, with one of a bibasic acid, by the separation of four of water ; it therefore corresponds to the neutral sulphuric methylic ether, and like it is decomposed by potash, taking up the elements of four equivalents of water, and yielding sulphuric acid, wood-spirit, and ammonia. 737. Sulphomethylic Acid, C 2 H : S 2 O 8 . This acid is ob- tained by a similar process to that for the sulphovinic, and like it is a monobasic acid, forming soluble salts with lime and baryta. It is, however, more permanent than the sulpho- vinic acid, and may be obtained in small crystals which arc very soluble in water. 382 ORGANIC CHEMISTRY. 738. When sulphomethylic acid is decomposed by heat, it undergoes a change similar to the sulphovinic acid, and evolves a colorless gas, which is wood-spirit, minus the ele- ments of one equivalent of water, C 2 H 4 2 HO = C 2 H 3 O. This corresponds precisely to the ether of alcohol, and is called wood ether, methylic ether or mether : it is not condensed by intense cold ; has a pungent taste and odor, and is soluble in water and alcohol. 739. In the same manner as hydrochloric ether may be considered as derived from acetene, which is alcohol minus two equivalents of oxygen, the corresponding compounds of wood-spirit may be derived from marsh gas, which is C 2 H 4 O 2 O 2 =C 2 H 4 . The name of formene is hence given to this gas. Several compounds formed from the action of chlorine and its congeners upon bodies of the alcohol and wood-spirit series, may be viewed as formene, in which a part of the hydrogen is replaced by chlorine, bromine, or iodine. Chloroform ; Tri-chlorinized Formene, C 2 HC1 3 . This is formed when alcohol or wood-spirit is distilled with a solu- tion of two or three parts of chlorid of lime, in twenty parts of water. It is a heavy oily liquid, nearly insoluble in water, which boils at 141, and has a specific gravity of 1'48. It has a very sweet and pungent taste, and its alcoholic solu- tion is employed in medicine under the name of chloric ether. Bromine forms a similar compound. lodiform ; Tri-iodized Formene, C 2 HI 3 , is obtained when iodine acts upon an alcoholic solution of potash. It crystal- lizes in bright yellow scales, and has a pungent aromatic taste. All of these compounds are decomposed by an alco- holic solution of hydrate of potash, affording a compound of the salt-radical with potassium, and formate of potash, C 2 HC1 3 + 4KO== 3KC1+ C 2 HK0 4 . When chloroform is exposed to the action of chlorine gas, aided by the sun's light, the remaining equivalent of hydro- gen is removed and a chlorid of carbon is obtained, C 2 C 4 1, or perchlorinized formene. Oxydation of Wood- Spirit. 740. When the vapor of wood-spirit mixed with air is exposed to the action of platinum-black, it loses hydrogen and absorbs oxygen, producing water and formic acid. This is derived from wood-spirit by a reaction exactly similar to that producing acetic acid from alcohol ; two equivalents of WOOD-SPIRIT. 383 hydrogen combine with oxygen to form water, and two of oxygen unite with the residue, (C 2 H 4 O 2 H 2 ) + O 2 =C 2 H 2 O4. The intermediate product of this reaction, corresponding to aldehyde, has not been obtained. When wood-spirit is heated with a mixture of hydrate of potash and lime, hydrogen gas is evolved, and formate of potash is produced. 741. Formic acid occurs as a secretion of the red-ant, (Formica rufa,) from whence it derives its name, and may be obtained by distilling the ants with water. It is also a product of the oxydation of sugar, and many other organic substances, and is best prepared by the following process. 800 grains of bichromate of potash and 300 of sugar, are dissolved in seven ounces of water. The mixture is placed in a retort, and one measured ounce of sulphuric acid very gradually added ; it is then distilled with a gentle heat, until three ounces of liquid are obtained. This is dilute formic acid, and may be used to form salts, which when decom- posed afford a strong acid. The pure acid is obtained by passing sulphureted hydrogen gas over dry formate of lead ; sulphuret of lead and formic acid are produced. The action is aided by a gentle heat, and the acid distils over. It is a colorless liquid, of specific gravity 1-235, which boils at 212, and at 32 crys- tallizes, like acetic acid, in shining plates. It fumes in the air, and has a very pungent odor, resembling that of ants ; it is powerfully acid and very corrosive, instantly blistering the skin. When this acid or its salts are heated with strong sulphuric acid, it is decomposed with the evolution of pure carbonic oxyd gas, C 2 H 2 O 4 =2CO + 2HO. When formic acid or a formate is heated with solutions of the noble metals, it reduces them, and is itself decomposed with the evolution of carbonic acid gas. The formates closely resemble the acetates. The formate of potash , C 2 HKO 4 , is very soluble. The formate of silver, C 2 HAgO 4 , crystallizes in scales ; when its solution is boiled, the silver is precipitated in the metallic state, while carbonic acid and carbonic oxyd gases escape, C 2 HAgO 4 Ag-f HO-f CO 2 +CO. AMYLIC ALCOHOL, Ci H 12 O 2 . 742. In the distillation of spirit made from potatoes, the last portions of the liquid are rendered milky by a peculiar oily substance which separates on standing, and to which the 384 ORGANIC CHEMISTRY. name of potato oil, or fusel oiZ, is given. It does not exist in the vegetable, but is a product of the fermentation, and is also found in the spirit obtained from the fermentation of raisins and the juice of beets. It is freed from alcohol by agitation with water, and is afterwards purified by distillation. When pure it is a colorless liquid, which is insoluble in water, has u specific gravity of -818, and boils at 269. It has a burning taste, and a pungent disagreeable odor, which excites coughing, and often distressing nausea. It closely resembles alcohol and wood-spirit in its chemical relations, ahd has hence received the name of amylic alcohol* or amylol. By the action of acids it yields ethers, which are similar to those derived from alcohol. 743. The Acetic Amylic Ether (C 14 H I4 O 4 ), is obtained by distilling potato oil with a mixture of acetate of potash and sulphuric acid. One equivalent of amylic alcohol, and one of acetic acid, yield one of the ether, and two of water ; C 10 H 12 O 2 + C 4 H 4 O 4 =C 14 H 14 O 4 + :2HO. It is a colorless fra- grant liquid, which is decomposed by an alcoholic solution of potash, forming acetate of potash and potato oil. Hydrochloric Amylic Ether (C 10 H,,C1), is formed when potato oil is distilled with hydrochloric acid. It may be viewed as a substitution product of valerene (C IO H I2 ), a body corresponding to acetene. By the action of nitric acid upon potato oil, a liquid is obtained corresponding to the hypo- nitrous ether from alcohol, which may be considered as nitric valerene. 744. With sulphuric acid, amylic alcohol forms a coupled acid which is quite similar to the sulphovinic, and is called sulphamylic acid. It is derived from one equivalent of sul- phuric acid and one of the amylic alcohol, by the abstraction of the elements of water ; and by the action of alkalies is decomposed with the regeneration of the potato oil and the formation of a sulphate. 745. The Amylic Ether or Amylether (C, H,,O), has been obtained, but its characters have not been studied. It appears to be formed by the distillation of sulphamylic acid. When potato oil is distilled with an excess of sulphuric acid, a volatile oily liquid is obtained, which is formed from the amylic alcohol by the abstraction of the elements of two * From amyhcm, starch, as it was supposed to be derived from the fermentation of the starch of the potatoes. AMYLIC ALCOHOL. 385 equivalents of water. It is called paramilene, and has the formula C 10 H 10 =C 10 H,2O2 2HO: it corresponds precisely to olefiant gas in the alcohol series. Oxydation of Amylic Alcohol or Potato Oil. 746. When this substance is exposed to the air, it slowly absorbs oxygen, and becomes acid : the change is effected much more rapidly when the oil is dropped upon platinum- black. The product of this oxydation is valerianic acid (C, H, O 4 ) : it is formed by a process similar to that yielding acetic acid. An equivalent of the oil loses two of hydrogen, which combine with exygen, producing water, and the residue takes two of oxygen to form the acid, C, Hi 2 O 2 -f 4O= C, H 10 O 4 -f 2HO. The acid is also formed with disengage- ment of hydrogen gas, when the oil is heated with hydrate of potash ; valerianate of potash is obtained, which is de- composed by distilling with dilute sulphuric acid. This acid is identical with that which exists in the Valeriana offi- cinalis, and is obtained by distilling the root of that plant with water. It is to this acid that the valerian owes its medicinal properties. Valerianic acid has been found in a free state in cheese, and it is to its presence that the flavor of old cheese is in part due. 747. Valerianic acid is a colorless oily fluid, which boils at 347, and has a specific gravity of '937. Its taste is sharp and acid, and its odor powerful and disagreeable, resembling that of valerian. Water dissolves a large quantity of it, and it is readily soluble in alcohol. Like the acetic and formic acids, it is monobasic : its salts are all soluble in water, and have a slight odor of valerian. 'The valerianate of potash is very soluble and deliquescent ; that of baryta (C IO H 9 BaO 4 ), crystallizes in fine transparent prisms. The valerianate of zinc (C, H 9 ZnO 4 ), is prepared by neutralizing the acid with carbonate of zinc, and crystallizes in white scales. It is em- ployed in medicine as a substitute for valerian, the peculiar medicinal powers of which it possesses in a high degree. By the action of chlorine upon this acid, a portion of its hydrogen is replaced, and trichlorinized valerianic acid is formed, which corresponds to the chloracetic acid. ETHAL, 748. This substance is obtained by the action of the hydrate of potash upon spermaceti : it is a white crystalline 33 386 ORGANIC CHEMISTRY. solid, which fuses at 118 : is insoluble in water, but soluble in alcohol, and may be volatilized without decomposition. In its chemical characters it is closely related to alcohol : by the action of perchlorid of phosphorus, it yields a com- pound which corresponds precisely to the hydrochloric ether from alcohol : it has the composition C^H^Cl. Ethal, when heated with sulphuric acid, combines with it to form a coupled acid, which is called the sulphocetic or sulphethalic : it is monobasic, and is formed precisely like the sulphovinic from one equivalent of sulphuric acid and one of ethal, by the abstraction of two of water. When ethal is distilled with anhydrous phosphoric acid, it loses the elements of two equivalents of water, and yields a carbo-hydrogcn, C^H^, which is called cetene, and is polymeric of olefiant gas. 749. The substance known as spermaceti or cetene, may be regarded as the aldehyde of ethal. It is found in immense cavities in the head of the sperm whale, where it is mixed with a portion of oil. The fluid parts arc removed by pressure, and the remaining oil dissolved by washing in a dilute solution of potash. Pure spermaceti fuses at 120, and forms in cooling radiated masses of beautiful crystalline plates with a pearly lustre. It is insoluble in water, but soluble in strong alcohol and ether. Its formula is C^H^C^, equal to ethal minus two equivalents of hydrogen. When fused with a gentle heat and mixed with hydrate of potash, it is decomposed, yielding ethal and the potash salt of ethalic acid, SC^A + KO,HO = C^HaA + C 32 H 31 KO 4 . 750. When ethal is heated with hydrate of potash to about 400, hydrogen gas is evolved, and ethalic acid is formed. The reaction is similar to that producing acetic acid from alcohol, (C^UA^U^ + O^CAO,. This is also obtained when a mixture of spermaceti and potash is heated to the same temperature : the aldehyde in this case simply takes two equivalents of oxygen to form the acid. The ethalic acid is a white solid, lighter than water ; it fuses at 131, and forms on cooling a brilliant radiated crystalline mass ; it is soluble in alcohol, but insoluble in water. This acid is monobasic : the ethalates with an alkaline base are soluble ; the others are insoluble in water. Ethalic acid belongs to a class of fatty acids yet to be described, and its character and relations will be again alluded to. RELATIONS OF THE PRECEDING BODIES. 387 On the Relations of the preceding Bodies. 751. The four classes of compounds last described have been shown to be nearly affined in their chemical characters : they may be viewed as members of a group of which common alcohol or spirits of wine is the representative, and may be designated by the common name of alcohols. They unite with sulphuric acid, with separation of the elements of water, to form coupled acids yield ethers by the action of other acids ; aldehydes by the abstraction of two equivalents of hydrogen ; monobasic acids which have the composition of the aldehydes plus two equivalents of oxygen, and hydro- carbons which correspond to the alcohols, minus two equivalents of water. Although the whole of these charac- teristics are not developed in any one of the group, they agree in a sufficient number to establish their close affinities. These relations, which depend upon similarity of constitution, are designated as homologous, and the alcohols are called homologues, or homologous bodies. This relation is to be carefully distinguished from analogy, which refers to external or accidental resemblance. To illustrate this by an example alcohol resembles acetone in being volatile, very combustible, and soluble in water, and ethal is like sperma- ceti in being solid, crystalline, and insoluble ; but these external resemblances are only analogies, and if we examine the constitution of the bodies, we shall find that the volatile, soluble alcohol, and the solid, crystalline ethal, are the bodies which are really affined to each other. 752. In the alcohols the oxygen is always equal to two equivalents, and the proportion of hydrogen is greater than that of the carbon by two; so that in effect their decom- position affords two equivalents of water, and a compound of equal equivalents of carbon and hydrogen. The acids derived from them all contain four of oxygen, and equal equivalents of the other elements. Wood-spirit, C2H 4 O 2 Formic acid, Alcohol, C 4 H 6 2 Acetic " C 4 H 4 O 4 Potato oil, CioHiaOa Valerianic acid, Ethal, C 32 H34O2 Ethalic " From these and many other instances we arrive at the important law that in a class of homologous bodies the pro- portion of oxygen is invariably the same ; and that the equi- valents of carbon and hydrogen bear a similar proportion to 388 ORGANIC CHEMISTRY. each other, being either equal, or varying by a common difference. The amount of nitrogen, when this element is present in homologues, is like the oxygen invariable: and when chlorine replaces hydrogen, it is subject to the same law as hydrogen itself; the like is true of sulphur replacing oxygen. BITTER ALMOND OIL, C 14 H 6 02. 753. Benzoilol, Essential Oil of Bitter Almonds. This oil does not exist ready formed in the almonds, but is pro- duced by the reaction of certain principles contained in the kernel when aided by the presence of water. It is obtained by bruising bitter almonds into a paste with water, and dis- tilling the mixture, when the oil passes over, with hydro- cyanic acid and other impurities. It is purified by redistilling it from a mixture of protochlorid of iron and lime. It is a colorless oily liquid, of a pungent burning taste, and very fragrant odor, like that of bruised bitter almonds. It boils at 356, but its vapor distils over with that of water at 212; its specific gravity is 1*073. It is often used in flavoring articles of food, but the crude oil which is sold for this pur- pose is exceedingly poisonous : from the experiments of Pereira it appears that the pure oil is harmless. Sulphureted Benzoilol. By the action of hydro-sul- phuret of ammonia upon bitter almond oil, its oxygen is re- placed by sulphur, and an insoluble powder is obtained of the formula C, 4 H 6 S 2 . Its decomposition by heat gives rise to a variety of new and curious products. 754. Chlorinized Benzoilol, C 14 H 5 C1O 2 . This is obtained by the action of dry chlorine gas upon the oil of bitter almonds. It is a colorless liquid, which is decomposed by alkalies, yielding a chlorid and a benzoato. By distilling this with bromid or iodid of potassium, similar compounds are obtained, in which bromine or iodine replaces an equivalent of hydrogen. The action of dry ammonia upon the chlorinized benzoilol yields hydrochloric acid, and a new substance, benzamide, C l4 lI 5 a0 2 + NH 3 =C H H 7 NO 2 + HC\. It is soluble in water, and crystallizes in beautiful prisms. It contains the elements of bcnzoate of ammonia minus two equivalents of water, and by the action of alkalies or acids takes up the elements of water and regenerates benzoic acid and ammonia, (697.) BITTER ALMOND OIL. 389 Hydi'obenzamide. When bitter almond oil is placed in a concentrated solution of ammonia, it is gradually converted into a white crystalline mass of this substance. It is formed from three equivalents of benzoilol and two of ammonia by the abstraction of the elements of six equivalents of water, 3(C 14 H 6 O 2 ) + 2NH 3 =C 42 H 18 N ? -f6HO. In this reaction the ammonia loses the whole of its hydrogen, which unites with the oxygen of the oil, and the residue (N 2 ) is substituted for O 6 . By the action of hydrochloric acid it takes up the ele- ments of water and regenerates the oil and ammonia ; the latter combines with the acid to form sal ammoniac. When boiled in a solution of potash it is converted into a metameric modification, which is no longer decomposed by acids, but unites directly with them, and neutralizes them. This sub- stance, which is an alkaloid, is also formed when ammonia is passed through an alcoholic solution of the oil of bitter almonds : it is called benzoline or amarine. 755. When bitter almond oil is exposed to the air, it rapidly absorbs oxygen, and is converted into a white crystalline substance, which is benzoic acid : this is formed by the com- bination of two equivalents of oxygen. The same effect is produced when the oil is heated with hydrate of potash : hydrogen gas is evolved, and benzoate of potash formed. A more abundant source of benzoic acid is found in benzoin, a fragrant resinous substance which is obtained from the Laurus benzoin. This contains a large quantity of the acid, which may be procured by exposure to a gentle heat, when the acid is volatilized, and condenses as a white sublimate. It is also obtained by boiling the benzoin with lime, which forms ben- zoate of lime ; hydrochloric acid added to the previously concentrated solution, precipitates the pure acid in crystalline plates. Benzoic acid forms light silky crystals of a pearly whiteness, and has a pleasant aromatic taste, very slightly acid. When pure it is inodorous, but generally has a little volatile oil adhering to it, which gives it a fragrant odor, like vanilla. It is volatile at a gentle heat, evolving a suffocating vapor, which condenses unchanged. It is very slightly soluble in cold, but more easily in hot water. The formula of benzoic acid is C J4 H 6 O 4 ; it is monobasic, and forms a large class of salts, which are of but little im- portance. When it is boiled for some time with strong nitric acid, nitrobenzoic acid is obtained. One equivalent of benzoic 33* 390 ORGANIC CHEMISTRY. acid and one of nitric acid lose the elements of two equiva- lents of water, and the residues unite. The new acid is monobasic, and resembles the benzoic in its properties. 756. Benzoine. When the crude oil of bitter almonds is mixed with an alcoholic solution of potash, it is gradually converted into a white crystalline substance, which is called benzoine. It is polymeric of the oil, and is formed by the union of two equivalents of it ; its formula is consequently QgHuO^ When the vapor of benzoine is passed through a red-hot tube, it is reconverted into bitter almond oil. 757. Benzene. The vapor of benzoic acid passed through a red-hot gun-barrel, is decomposed into carbonic acid and a new substance named benzene or benzole, which is C ]2 H 6 C, 4 H 6 O 4 =2CO 2 -}-C I2 H 6 . Benzene is more easily obtained by distilling benzoic acid with slaked lime, which combines with the carbonic acid. It is a colorless, fragrant liquid, which boils at 187, and has a specific gravity of '830. Benzene is formed when the fat oils are decomposed at a red heat, and is obtained in the manufacture of oil-gas for illumination. With fuming sulphuric acid, benzene yields a coupled acid, which is monobasic, and a neutral compound, sulphobenzide, containing the elements of two equivalents of benzene, and one of sulphuric acid, minus two of water. The action of nitric acid produces a dense oily liquid of a very sweet taste; it is nitrobenzene, C, 2 H 4 NO 4 , and is derived from one equiva- lent of benzene and one of nitric acid, by the abstraction of two equivalents of water. We may suppose that two equiv- alents of hydrogen in the benzene unite with two of oxygen from the acid, C 12 H 6 H 2 = C 12 H 4 and NHO 6 O 2 = NHO 4 . The residue of the acid is then substituted for the two equiv- alents of hydrogen in the benzene, thus, C ]2 H 4 NHO 4 . By the further action of fuming nitric acid, a crystalline compound, named binitrobenzene, is obtained. It is derived in the same manner as the last, by the action of another equivalent of the acid, and has the formula C 12 H 4 N 2 O 8 . OIL OF CUMIN. 758. The essential oil of the seeds of cumin, (Cuminum cyminum,) has the formula C^HjA, and when heated with hydrate of potash, is oxydized with the evolution of hydrogen, forming cuminate of potash. The cuminic add, C^H ffl O 4 , is white and crystalline, resembling the benzoic. Cuminol and OIL OF SPIREA ULMARIA. 391 curninic acid are homologues of benzoilol and the benzole acid. The acids in both instances are formed by fixing O 2 , and contain four equivalents of oxygen. It will be seen that in these oils the difference between the proportion of carbon and hydrogen is the same, and equals eight equivalents. OIL OF SPIREA ULMARIA, 759. Salicylol. This is obtained when the flowers of the Spirea ulmaria, (pride of the meadow,) are distilled with water; and is artificially formed by the oxydation of salicine, a process which will be described under that substance. Salicylol is a colorless fluid, of fragrant odor, like the flower of the spirea, and has a pungent taste. It has a specific gravity of 1-173, and boils at 380. By the action of metal- lic oxyds it yields compounds, in which an equivalent of hydrogen is replaced by a metal ; but in its other relations it does not resemble an acid. It does not pre-exist in the plant from which it is derived, but, like benzoilol, is formed in the process, by the reaction of principles not yet examined. It absorbs dry chlorine gas, and forms chlorinized sali- cylol, Ci 4 H 5 ClO 4 ; bromine and iodine yield similar com- pounds. Salicylol is metameric with benzoic acid. By the action of ammonia upon an alcoholic solution of the oil, hydrosalimide is formed. Like hydrobenzamide, it is derived from three equivalents of the oil and two of ammonia, by the abstraction of 6HO. Its formula is C 42 H 18 N 2 O 6 ; it crystallizes in brilliant yellow prisms, and is decomposed by both acids and alkalies, with the regeneration of the oil and ammonia. 760. Salicylic Acid, C I4 H 6 O C - This is formed from the oil by the union of two equivalents of oxygen : when sali- cylol is heated with hydrate of potash, the salicylate is formed ; this is decomposed by hydrochloric acid, which pre- cipitates the salicylic acid. It is white, crystallizable, volatile, and sparingly soluble in water, resembling benzoic acid. It is monobasic, and forms a large class of salts, which are of but little importance. 761. When a mixture of salicylic acid, sulphuric acid, and wood-spirit are distilled, the salicylic methylic ether is obtained. It contains the elements of one equivalent of the acid and one of the spirit, minus two of water, and by the action of alkalies is decomposed into a salicylate and wood- 392 ORGANIC CHEMISTRY. spirit. This ether is remarkable as constituting the oil of wintergreen, Gaultheria procumbens : it is obtained in large quantities by distilling the plant with water. When placed in a close vessel of strong ammonia it slowly dis- solves, and the liquid by evaporation yields wood-spirit, and finally crystals of salicylamide, which is an amide of salicylic acid, and contains the elements of salicylate of ammonia minus two of water. Like the other amides, it is readily decomposed by acids and alkalies, by the action of which it combines with the elements of water, and regene- rates the original compounds. The mode of its formation will be readily understood by referring to what has been said of the relations between the ethers and amides, (705.) The alcohol minus two equivalents of hydrogen, may be viewed as substituted for two of oxygen in the acid : the ammonia gives up two elements of hydrogen, regenerating the alcohol, and the residue takes the place occupied by the residue of the alcohol, producing an amide in place of the ether. The ethers of almost all acids yield amides in this way, by the action of ammonia. 762. By the action of strong nitric acid upon salicylic acid, nitrosalicylic acid is formed, by a reaction similar to that yielding the nitrobenzoic acid, (755.) It forms white crystals, very sparingly soluble in water. When fuming nitric acid is gradually added to the oil of wintergreen, the nitrosalicylic ether of wood-spirit is obtained ; it forms delicate yellow crystals, which are soluble in alcohol. 763. When salicylic acid is rapidly distilled, it is decom- posed into carbonic acid and phenol, C, 2 H 6 O2.C,tH 6 O 4 2CO 2 + C 12 HeA,. Phenol is found in the oil distilled from coal-tar, and according to Wohler constitutes the essential oil of Castoreum, a secretion of the beaver. It forms colorless crystals, which are liquefied by the least trace of moisture, and is generally obtained as hn oily fluid, of a burning taste, and pungent, disagreeable odor, resembling that of wood- smoke. With the alkalies it forms crystalline compounds, and has hence been considered an acid, and described by the name of carbolic acid. By the action of chlorine gas, five new products are obtained, in which one, two, three, four, or five equivalents of hydrogen are replaced by chlorine: these, like the original compound, act as acids. By the action of nitric acid, phenol yields a compound in which two equiv- alents of nitrous acid are united, as in binitrobenzene, (757.) OIL OF CINNAMON. 393 The final product of the action of nitric acid, is a substance in which the substitution of the hydrogen is complete, Ci 2 H G O 2 +3NHO 6 =C 12 3(NHO 4 )O 2 -f 6HO. The whole of the hy- drogen combines with the oxygen of the acid, and is replaced by the residue of the latter. This substance, which may be designated as tri-nitrophenol, has been described by different chemists as nitrophenisic, carbazotic, nitropicric, and picric acids. It is the final product of the action of nitric acid upon a great variety of organic substances ; an easy method of obtaining it is by boiling salicylic acid, or oil of wintergreen, with strong nitric acid, till all action has ceased, and the red vapors of nitric acid no longer appear. The excess of carbon in the salicylic acid is expelled in the form of carbonic acid. Nitrophenisic acid forms yellowish white crystalline scales, which are slightly soluble in water; the solution has a yellow color, and an intensely bitter taste.* Its salts have a yellow color, and explode violently when heated. The acid is monobasic, and if we represent the acid by C 12 H 3 N 3 O 14 , its potash salt will be C, 2 H 2 KN 3 O I4 ; this is a yellow crystalline powder, very sparingly soluble in water. Although this substance and the other derivatives of phenol yield salts with bases, they appear incapable of forming ethers or amides, and perhaps ought not to be considered as acids. OIL OF CINNAMON, C 18 H 9 O 2 . 764. Cinnamol. This fragrant oil is obtained by distilling the bark of cinnamon with water. It is a heavy fluid, soluble in water, and possesses in a high degree the taste and odor of cinnamon. When exposed to the air, it absorbs two equivalents of oxygen, and is converted into cinnamic acid, Ci S H 9 O 4 . Cinnamate of potash is formed with the evolution of hydrogen, when cinnamol is heated with hydrate of pot- ash. This acid is associated with the benzoic in the balsam of Tolu, and resembles it in its properties. When heated with nitric acid it is decomposed, and yields benzoic acid and benzoilol. * Whence the name picric, from the Greek pifrros, bitter. 394- ORGANIC CHEMISTRY. SUGAR, STARCH, AND ALLIED SUBSTANCES. 765. Under this head is included a class of substances of vegetable origin, which agree in containing carbon with oxy- gen and hydrogen in the proportions which form water. \Vhcn soluble, they are insipid or have a sweet taste, and arc generally nutritious. They are not volatile, and are readily decomposed by heat or other agents. 766. Sugars. These bodies are soluble in water, have a sweet taste, and by the process of fermentation yield alcohol and carbonic acid. Cane Sugar, C^HnO,,. This occurs in the juices of many plants, as the sugar-cane, maple, beet-root, and Indian corn. It is obtained by evaporating the juice to a syrup, when the sugar crystallizes in grains of a brownish color. It is obtained pure and white by redissolving it, and fil- tering the solution through animal charcoal, (337.) By the slow evaporation of a concentrated solution, it is obtained in fine transparent crystals, which are derived from an oblique rhombic prism ; in this state it constitutes rock-candy. It fuses at 356, and forms on cooling a vitreous mass, well known as barley sugar; this gradually becomes opaque, and changes into a mass of small crystals of ordinary sugar. Sugar is soluble in about one-third its weight of water, form- ing a thick syrup. It is insoluble in pure alcohol. 767. Grape Sugar; Glucose, C 12 Hj2O 12 + 2Aq. This sugar is found in the grape and many other fruits, and in honey. It is formed when cane sugar or starch is boiled with dilute sulphuric acid, and is a product in many other trans- formations. The urine in the disease called diabetes melli- tus contains a large quantity of grape sugar, which is formed from the starch and similar substances taken as food. Grape sugar is generally obtained as a white granular mass, which requires one and a half parts of cold water to dissolve it ; it is less sweet to the taste than cane sugar, and about two and a half times as much are required to give an equal sweetness to the same volume of water. When heated to '212, the two equivalents of water are expelled. "With sulphuric acid, grape sugar forms a coupled acid, the sul- phosaccharic. If a solution of grape sugar is mixed with a solution of potash, and then with a little sulphate of copper, the liquid becomes dark, and soon deposits suboxyd of copper in the form of a red powder. Cane sugar yields no precipi- SUGAR, STARCH, AND ALLIED SUBSTANCES. 395 tate until the solution is boiled. This test enable us to detect the 10 Q 00 part of grape sugar in a liquid. 768. Sugar of Milk ; Lactine, CAO w +2Aq.Th\s is found only in the whey of milk, and is obtained by evapo- rating it, and purifying the product by crystallization. Lactine forms semi-transparent prisms, soluble in six parts of cold water, and two and a half of boiling water ; it is much less sweet than cane or grape sugar. By a heat of 212 its water is expelled ; by boiling with dilute sulphuric acid, it combines with the elements of two equivalents of water, and is converted into grape sugar. 769. Mannite, C 6 H 7 6 . This substance is not a proper sugar, and is not susceptible of fermentation. It exists in the juice of celery and many sea-weeds ; and constitutes the principal part of the manna of the shops, which is the concen- trated juice of a species of ash. When this is dissolved in hot alcohol, the mannite is deposited by cooling. It forms delicate silky crystals, which are slightly sweet and very soluble in water. Products of the decomposition of the Sugars. 770. The vinous fermentation. When the juice of grapes or other fruits containing sugar is exposed to the air, a pecu- liar decomposition ensues, in which the sugar is resolved into carbonic acid gas and alcohol. A solution of pure sugar is not changed by exposure to the air ; but if there is added to it a little yeast, or the juice of any fruit in the state of fer- mentation, decomposition takes place, and carbonic acid and alcohol are formed. Many substances besides yeast will effect this change, as blood, albumen, or flour paste in a state of decomposition. It appears that the influence of a ferment depends on the condition rather than the kind of matter. Any nitrogenized substance capable of undergoing putrefac- tion produces the same effect, and we are to attribute this change, in the juice of fruits, to a small portion of albumi- nous matter present. The mode in which these substances act is not understood, but it is supposed that when in a state of decomposition, they are able to induce a similar state in ether substances with which they are in contact ; the equili- brium of the atoms in the compound is thus disturbed, and the elements arrange themselves in new forms. 771. The conversion of grape sugar into alcohol and car- bonic acid is very simple ; one equivalent of dry grape sugar, 396 ORGANIC CHEMISTRY. contains the elements of two equivalents of alcohol and four of carbonic acid gas : 2 equivalents of alcohol, 2 X (C 4 H 6 2 ) = C 8 Hi 2 4 4 " carbonic acid gas, 4 X CO 2 = C 4 O 8 I " grape sugar, Grape sugar is the only kind which is capable of this fer- mentation ; and although the others readily yield alcohol and carbonic acid, it is found that the first effect of the fer- ment is to transform them into grape sugar by the assimila- tion of the elements of water. Many juices of fruits readily become sour by exposure to the air, especially if the quantity of sugar which they con- tain, and consequently the portion of alcohol that can be formed, is small. But in these cases, the formation of the acid, which is the acetic, is probably preceded by that of alcohol. 772. When sugar is mixed with caseine (cheese curd) and exposed to a temperature of from 95 to 104, a peculiar fer- mentation takes place, which produces a slimy substance that renders the liquid viscid. The other products are mannite and lactic acid, C 6 H 6 O 6 . The gummy matter is identical in composition with sugar. Similar products are obtained when the juices of beets and carrots ferment at a high temperature. This has been termed the viscous fermentation. When caseine or any other animal matter in an advanced state of decomposition is employed, it induces the alcoholic fermentation ; but at an earlier stage of the decay the action is different, giving rise to lactic acid and mannite. When milk is exposed to a temperature from 95 to 104, it undergoes the vinous fermentation, and forms alcohol. It is well known that some nations prepare an intoxicating liquor by the fermentation of milk. In this process, a small quantity of acid is first formed, which converts the lactine into grape sugar. The elevated temperature promotes the decomposition of the caseine present, and thus enables it to produce this fermentation. Milk at ordinary temperatures becomes directly acid, without the previous formation of alcohol, and its sugar is then transformed into lactic acid. 773. Lactic Acid, C 6 H 6 O 6 . This acid may be obtained from sour milk, but is more easily prepared by thg fermenta- tion of sugar with caseine. Fourteen parts of cane sugar SUGAR, STARCH, AND ALLIED SUBSTANCES. 397 tire dissolved in sixty of water ; to the solution is then added four parts of the curd from milk, and five parts of chalk to neutralize the acid which is formed. This mixture is kept at a temperature of 77 to 86 F. for two or three weeks, or until it becomes a crystalline paste of lactate of lime. This is pressed in a cloth, dissolved in hot water, and filtered; the solution is then concentrated by evaporation. On cooling, it deposits the salt in crystals, which may be purified by re- crystallization. This process yields about thirteen and a half parts of the crystallized lactate, and a small quantity of mannite. The reaction is very simple ; one equivalent of dry grape sugar, C 12 H I2 O, 2 , contains the elements of two equivalents of lactic acid, 2(C 6 H 6 O 6 .) The mannite is the result of a secondary decomposition, and with certain pre- cautions, lactic acid is the only product. The carbonate of lime serves only to neutralize the acid formed. The lactate of lime may be decomposed by the careful addition of oxalic acid, which precipitates the lime, and the solution of lactic acid thus obtained, is concentrated by evaporation, and purified by solution in ether. It is a syrupy liquid, of specific gravity 1*215, and is strongly acid to the taste. 774. When lactic acid is heated to 482, a white crystal- line substance sublimes which is called lactide ; it is derived from the acid by the abstraction of the elements of two equi- valents of water, and has the formula C 6 H 4 O 4 . It is soluble in alcohol, but scarcely soluble in water ; by long continued boiling with it, however, it is converted into lactic acid. This acid is monobasic, and its salts are generally soluble and crystallizable. The lactate of lime (C 6 H 5 CaO 6 ) crystallizes in fine prisms, with five equivalents of water. The lactate of zinc is obtained by decomposing a hot concentrated solu- tion of lactate of lime by chlorid of zinc; the salt crystallizes in cooling in beautiful colorless prisms. The lactate of iron (C 6 H 5 FeO 6 ) is sparingly soluble in cold water, and may be prepared by a similar process ; it is employed in medicine. 775. When the mixture of sugar, chalk, and curd is kept at a higher temperature, about 90, a different action takes place ; hydrogen gas is evolved, and butyrate of lime is formed. This product will be afterwards described. The action of chromic acid upon sugar yields formic acid, (740.) Dilute nitric acid forms, with cane and grape sugar, saccharic acid, C,2H, O 14 ; it is bibasic ; strong nitric acid converts them into oxalic acid. 34 398 ORGANIC CHEMISTRY. 776. When sugar is added to a concentrated solution of three times its weight of hydrate of potash and heated, the mixture becomes brown, and hydrogen gas is evolved. When the action ceases, and the mass is cooled, dissolved in water, and distilled with dilute sulphuric acid, it yields formic and acetic acids, with a new acid, the metacetonic, which is obtained as a volatile liquid, with a pungent acid odor. It is monobasic, and has the formula CgHgO., : it is therefore a homologue of formic and acetic acids. A mixture of sugar and quick lime when distilled affords acetone, and an oily liquid called metacc.tone : this is related to the metacetonic acid as acetone is to the acetic, and yields that acid when distilled with a mixture of bichromate of potash and sulphuric acid. Mannite, starch, and gum, afford the same results with hydrate of potash and lime. 777. Gum, C 12 H 10 O| . This substance is best known in gum arable ; the gum which exudes from the cherry and plum, the mucilage of flaxseed, and many other plants, are identical with it. Gum is soluble in water, and forms a viscid solution, from which alcohol precipitates it unchanged. When boiled with dilute sulphuric acid, it is converted into grape sugar. With nitric acid, gum and milk sugar yield the mucic acid, which distinguishes them from all the other bodies of this class. The mucic acid is a white crystalline powder, which is sparingly soluble in water; it is bibasic, and is represented by the formula C, 2 H 10 O, 6 . It is consequently metameric with the saccharic acid, although quite different in its properties. 778. The Pectic Acid, which is extracted from many fruits, appears to be nothing but a modified form of gum, and yields grape sugar with dilute acids. It combines with lime and some other bases to form compounds, which have been described as pectates. Both gum and sugar have also the property of exchanging one or two equivalents of hy- drogen for lead, barium, or calcium, to form similar com- binations. 779. Starch, C, 2 H 10 O 10 . This substance exists in a great variety of vegetables. It is found in all the cereal grains, in the roots and tubers of many plants, as the potato, and in the bark and pith of various trees. It is obtained by bruising wheat and washing it in cold water, which holds the starch in suspension, and deposits it on standing. Potatoes furnish a large portion of starch by a similar process. The SUGAR, STARCH, AND ALLIED SUBSTANCES. 399 substances known as arrow-root, sa- lep, sago, and tapioca, are varieties of starch, obtained* from different plants, and sometimes altered by the heat employed in drying. When examined by the naked eye it is a white shining powder, but under the microscope is seen to consist of irregular grains, which have a rounded outline, and are composed of concentric layers, covered with an external mem- brane. The diameter of the grains of potato starch is about ^g- of an inch. Starch is insoluble in cold water, but if the mixture is heated, the globules swell, burst their envelopes, and form a transparent jelly, which is characterized by producing a deep-blue color with a solution of iodine. When the solution of starch is mixed with a little acid or an infusion of malt, and gently heated, it becomes very fluid, and is changed into dextrine* This has the same com- position as starch, but is very soluble in cold water, and is not colored blue by iodine. If starch is heated to 300 or 400, it is rendered soluble in water, and possesses all the properties of dextrine. In this state it is used in the arts as a substitute for gum, under the names of British Gum and leiocome. When dextrine is boiled for some time with dilute sulphuric acid, it is converted into grape sugar. It has been mentioned that grape sugar is formed in this way from starch ; but its formation is always preceded by that of dextrine. One part of starch may be dissolved in four parts of water, with about one-twentieth of sulphuric acid, and the mixture boiled for thirty-six or forty hours. The liquid is then mixed with chalk to separate the acid, and by evaporation and cooling affords pure grape sugar. Oxalic acid may be substituted for the sulphuric, with the same result. Starch sugar is extensively manufactured in Europe, and is often used to adulterate cane sugar. In this process the starch combines with the elements of two equivalents of water, C 12 H 10 10 + 2HO=C 12 H, 2 Oi 2 ; the acid is obtained at * So named, because when a beam of polarized light is passed through the solution, it causes the plane of polarization to deviate to the right hand. 400 ORGANIC CHEMISTRY. the end of the process quite unaltered, and one part of acid will saccharify one hundred of starch, by long continued boiling. Starch or dextrine unites with sulphuric acid to form a coupled acid ; and it is probable that this is first formed, and then destroyed by boiling : at the moment of decomposition, the liberated dextrine takes up the elements of water necessary for the formation of sugar. A small portion of the coupled acid is always found in the solution. 780. The action of an infusion of malt upon sugar is peculiar ; this substance is prepared from barley, by moistening the grain with water, and exposing it to a gentle heat till germination takes place, when it is dried in an oven at such a temperature as to destroy its vitality. The grain now contains a portion of starch sugar, and 'a small portion of a substance called diastase,* to which its peculiar properties are due. It is precipitated by alcohol from a concentrated infusion of malt, as a white flaky substance, which contains nitrogen, and is very prone to decomposition. When a little diastase is added to a mixture of starch and water, at a temperature of from 130 to 140, the starch is soon converted into dextrine, and in a few hours into grapo sugar. The action of an infusion of malt is due solely to the presence of a minute portion of this substance, one part of which will convert two thousand parts of starch into sugar. This effect appears to be due to a peculiar state of the diastase, which is a portion of the azotized matter of the grain in a modified form, and is analogous to that of ferments, already alluded to. 781. Woody Fibre; Cellulose, C 12 H 10 O 10 . This sub- stance is the solid insoluble part of vegetables, and remains when water, alcohol, ether, dilute acids and alkalies, have extracted from wood all its soluble portions. It is nearly pure in paper or old linen. Cellulose is identical in com- position with starch and dextrine, and by the action of strong sulphuric acid is dissolved and converted into that substance. This experiment is easily made with unsized paper or cotton ; to two parts of this, one part of the acid is very slowly added, taking care to prevent an elevation of temperature, which would char the mixture. In a few hours the whole is converted into a soft mass, which is soluble in water, and is * From the Greek diistemi,, to separate, because it separates the insoluble envelopes of the starch globules. SUGAR, STARCH, AND ALLIED SUBSTANCES. 401 principally dextrine. If the mixture is now diluted with water and boiled for three or four hours, the dextrine is com- pletely converted into grape sugar, which is obtained by neutralizing the acid with chalk, and evaporation. By this process paper or rags will yield more than their weight of crystallizable sugar. 782. The mutual convertibility of these different sub- stances is interesting in relation to many of the phenomena of vegetable life. The starch in the germinating seed is changed by the action of diastase into sugar, in which soluble form it seems better fitted for the nourishment of the embryo plant. In the growth of this, we have an example of the formation of cellulose from sugar, in which this substance assumes a structural form under the action of the vital force. This is a transformation from the unorganized to the organized, which mere chemical affinity can never effect. 783. Many unripe fruits, as the apple, contain a large quantity of starch, but no sugar. After the fruit is fully grown, the starch gradually disappears, and in its place we find grape sugar. This change constitutes the ripening of fruits, and as it is well known, will take place after they are gathered. In this process we have clearly a conversion of the starch into sugar, by the agency of the vegetable acids present in the fruit, a change which is the reverse of the previous one, and is probably independent of life. 784. Xyloidine ; Gun Cotton. When starch is rubbed in a mortar with nitric acid of specific gravity 1'5, it forms a gelatinous mass from which water precipitates xyloidine. When dry, it is a white powder, which takes fire at a low temperature and burns with great vivacity. Its composition is C 12 H 9 NOi 4 , and it is derived from starch, by the addition of one equivalent of nitric acid and the abstraction of the elements of two of water, C 12 H 10 O 10 + NHO 6 = C 12 H 9 NO 14 + 2HO. The nitric acid less O 2 may be viewed as repre- senting H 2 in the starch, and we may write the formula C 12 H 8 (NH0 4 )0 10 , (675.) The action of strong nitric acid upon woody fibre gives origin to another substance, which has lately attracted great attention as a substitute for gunpowder, under the name of gun cotton, and which Mr. Pelouze has called pyroxyline. Paper, saw-dust, or any other form of cellulose, by digestion in strong nitric acid, acquires a considerable increase of 34* 402 ORGANIC CHEMISTRY. weight, and is converted into this new substance ; but it is best obtained from cotton. The following is an outline of the process : one hundred grains of clean cotton are im- mersed for five minutes in a mixture of an ounce and a half of nitric acid of specific gravity 1*45 to 1-5, with the same measure of strong sulphuric acid ; it is then removed, care- fully washed in cold water from every trace of acid, and dried at a temperature which should not exceed 120. As thus prepared it preserves the form of the cotton unaltered, hut has less strength than the original fibre. It inflames by a very gentle heat ; sometimes under circumstances not well understood, it has been observed to take fire at 212 F. Its combustion is instantaneous, accompanied by an immense volume of flame, and it leaves not the slightest residue. When ignited in a confined space, it explodes with great violence : one-tenth of a grain is sufficient to shatter the strongest glass tube. Its power in propelling balls is about eight times greater than that of gunpowder. Its tremendous energy depends upon the fact that it is completely resolved, by its combustion, into aqueous vapor and permanent gases, which are carbonic oxyd, carbonic acid, and nitrogen. As these are much less noxious than the gases resulting from the combustion of gunpowder, the gun cotton will be found of great use in mining. Its analysis is very difficult, on account of its explosiveness ; but from the results of Pelouze and others, it appears to be derived from two equivalents of cellulose and five of nitric acid, with the abstraction of ten of water: 2C 12 H 10 O 10 = C^A,, + 5NHO 6 = C 24 H 15 NA -f 10HO. There are reasons for supposing that the equivalent of cellulose and all the allied substances should be doubled, and this substance will then be cellulose, CajfLjoO^, in which the residue of five equivalents of nitric acid replaces ten of hydrogen, which have formed water with the oxygen of the acid. Its formula may then be written C^H^NHO^O^. This formula requires that 100 parts of cellulose should yield 169-1 of pyroxyline, and experiment gives 170 to 172 parts. It is very difficult to dry it perfectly, for it is gradually decomposed at 212, and often explodes at that temperature : hence the analyses have invariably given a little more oxygen and hydrogen than the formula requires. Pyroxy- line, when pure, is soluble in the acetic ethers of alcohol and wood-spirit. SUGAR, STARCH, AXD ALLIED SUBSTANCES. 403 Transformation of Woody Fibre. 785. Byjhe action of atmospheric air and moisture, wood undergoes a slow decay, dependent on the absorption of oxy- gen, to which Liebig has applied the term eremacausis.* The carbon is converted into carbonic acid, while the oxygen and hydrogen of the lignine unite to form water. The resi- due is still found to contain oxygen and hydrogen in the original proportions, but the relative amount of carbon is continually increasing. For each equivalent of carbonic acid two of water are evolved. The final result of this pro- cess is a brown or black residue, which constitutes vegetable mould. Different products of this decomposition have been described under the names of humus, geine, ulmine, humic and ulmic acids. Nearly all of these bodies contain ammonia, for which they have a strong affinity ; this is in part absorbed from the air, but the late experiments of Mulder have shown that they have the power of forming ammonia from the nitrogen of the atmosphere. Pure humic acid moistened and placed in a close vessel filled with air, is found after some months to contain a considerable quantity of ammonia. The hydrogen evolved by a slow decomposition of the water, is brought into contact with nitrogen under such conditions, that they com- bine and produce the alkali. 786. The decomposition of wood, when buried in the ground and excluded from the action of the air, is very dif- ferent. The oxygen which it contains, gradually combines with the carbon to form carbonic acid, and substances are obtained, in which the proportion of carbon and hydrogen is greater than in the original fibre. Peat, lignite, and bitu- minous coal, are products of this decomposition. The car- bon and hydrogen in coal combine in various ways, and often generate vast quantities of gaseous carburets of hydrogen, (450.) Anthracite has resulted from the action of heat on bituminous coal, which has expelled all the volatile ingre- dients, and left a residue of nearly pure carbon. Destructive Distillation of Wood. The principal products of the decomposition of wood by * From erema, slow, and Jcausis, combustion, a term by which that chemist denotes those changes which take place in organic bodies from the gradual action of oxygen. 404 ORGANIC CHEMISTRY. heat, are acetic acid and pyroxylic spirits, and have been already described, (720, 734). Beside these a quantity of viscid tarry matter is obtained, which contains *nany very interesting compounds. 787. Kreasote. This substance occurs dissolved in the crude acetic acid from wood, and is separated and purified by a complicated process. It is a colorless oily fluid, which boils at 397, and has a specific gravity of 1-037 ; it has a peculiar and very persistent odor resembling that of smoke, and a powerful burning taste. It is soluble in about 100 parts of water, and the solution possesses powerful antiseptic qualities. Meat which has been soaked in it, is incapable of putrefaction,* and acquires a delicate flavor of smoke. The power of wood smoke to preserve flesh, is due to the presence of kreasote. It is a corrosive poison when taken in any quantity, but a little dilute solution is used medicinally, both internally and externally, as a styptic and antiseptic. It is often applied to the nerve of a decayed tooth, and in this may relieve the pain of tooth-ache, but its use requires care, for if brought in contact with the lining membrane of the mouth, it instantly destroys its vitality. 788. The composition of kreasote is C, 4 H 8 O 2 ; by the action of nitric, it yields nitrophenisic acid, (763). It com- bines with the alkalies to form crystalline compounds. Wood-tar contains several carburets of hydrogen, one of which, called eupione, is an oily, fragrant liquid, of the specific gravity -655, being the lightest liquid known. Its formula is, probably, C 6 H 6 . Paraffinc. This is a white crystalline substance, ob- tained from the less volatile portions of wood-tar. It crys- tallizes in delicate needles, which fuse at 110; it is soluble in alcohol and ether. Its formula is C 48 H 50 . Paraffine is obtained in large quantities by the dry distillation of bees- wax. 789. Coal Tar consists principally of a mixture of various hydrocarbons ; some of these are liquids and quite volatile, constituting what is called gas naphtha. Among the less volatile products, are two solid carburets of hydrogen, naphthalene, and paranaphthalene, or anthracene. The first of these is formed by the decomposition of many organic matters by heat. Its formula is C^Hg ; ft is volatile, and * Hence the name, from the Greek kreas, flesh, and soto, I preserve. FATS AND THE SUBSTANCES DERIVED THEREFROM. 405 forms beautiful pearly crystals of a fragrant odor. The action of chlorine, bromine, and nitric acid on naphthaline, gives rise to a great number of compounds, which have lately been studied by Laurent. They are formed by successive substitutions of the hydrogen by one or more of these sub- stances, and many metameric modifications of these bodies exist. Thus, the bichlorinized naphthaline, C 20 H 6 C1 2 , occurs in seven modifications, which are perfectly distinct in their characters. We are forced to suppose that these compounds owe their different properties to a different arrangement of their constituent atoms, and it is easy to see that, in this way, the number of possible combinations will be immense. More than twenty substances have been described, in which chlorine is in part substituted for the hydrogen of the naph- thaline. The final product of the action of chlorine is CaoClg, being a chlorid of carbon, which preserves the type of naphthaline. In addition to these, coal-tar contains a con- siderable proportion of phenol or carbolic acid, (763) and two organic alkaloids, named Icyanol and leukol. The watery products of the distillation of coal hold a large quantity of ammonia in solution, often combined with hydro- sulphuric and hydrocyanic acids. 790. Petroleum. In many parts of the world, an oily matter exudes from the rocks, or floats on the surface of springs. The principal sources of this substance are Amiano in Italy, Ava, and Persia, but it is found in many places in our own country. The well known Seneca Oil is an in- stance of this kind. Petroleum is a variable mixture of several bodies. By distillation, it yields a colorless liquid called naphtha, which is very light, volatile, and combustible. Its formula is C 6 H 5 . Naphtha occurs nearly pure in Italy and Persia, and is used for illumination. Petroleum contains a variety of other bodies, among which are paraffi?ie, and several resinous matters, formed perhaps by the oxydation of naphtha. These substances are probably derived from coal or other matters of vegetable origin. FATS AND THE SUBSTANCES DERIVED FROM THEM. Glycerides. 791. Under the general name of fats is included a large class of bodies of animal and vegetable origin, which are characterized by being insoluble in water, combustible, and 406 ORGANIC CHEMISTRY. volatile only at high temperatures with decomposition. Some of them, as the oils, are liquid at common temperatures, while others, as mutton tallow, require a heat of 120 for their fusion. When digested with water and an alkali, or a basic metallic oxyd, they take up the elements of water, and are resolved into acids, which unite with the base, forming the compounds called soaps, and a peculiar sweet substance to which the name of glycerine* is given. Glycerine is most easily prepared by heating a mixture of olive oil, oxyd of lead, and water. The oil is decomposed, and the acids form insoluble salts with the lead, while the glycerine is dissolved in the water; the solution is treated with sulphureted hydrogen to precipitate a little dissolved oxyd of lead, and evaporated in a water-bath. The formula of glycerine is C 6 H 8 O 6 . It is a colorless, syrupy liquid, of a very sweet taste, and is readily soluble in water and alcohol , it is not volatile, but when strongly heated is decomposed, evolving acetic acid, and other products, the most important of which is acroleine. This is obtained pure by distilling glycerine with anhydrous phosphoric acid; it is formed from it by the abstraction of the elements of four equivalents of water, C 6 H 8 O 6 4HO=C 6 H 4 O 2 , the formula for acroleine. It is a colorless liquid, having a powerful pungent odor, which irritates the eyes and nose exceedingly, and is the same smell that is evolved when fats are strongly heated. With sulphuric acid glycerine yields a coupled acid. 792. All of the fats contain the elements of one equivalent of glycerine, and two of an acid minus six equivalents of water. For example : palmitine yields, by the action of alkalies, ethalic acid and glycerine, and its composition may be expressed by (C 6 H 8 O 6 + 2C 32 H 32 4 )-6HO-C 70 H 66 O 8 . In its decomposition it takes up the elements of six equivalents of water, and regenerates glycerine and the acids. These sub- stances present some analogy to the ethers, (702,) and amides, (697,) in their mode of decomposition ; they are distinguished by the general name of glycerides. None of these are volatile without decomposition ; when distilled they yield some com- pound of carbon and hydrogen, a fatty acid, and acroleine ; the peculiar pungent odor of this last is characteristic of the glycerides. 793. The ethalic acid, which results from the decomposi- tion of palmitine, has been already noticed as a derivative of * From the Greek gliikus> sweet. FATS AND THE SUBSTANCES DERIVED THEREFROM. 407 one of the alcohols, and phocenine, another glyceride, yields, by its saponification, valerianic acid, which is a product of the oxydation of amylic alcohol. There are in addition to these a large number of fatty acids derived from the saponi- fication of glycerides, which are homologues of valerianic and ethalic acids, and these being the most important, will be first described. 794. Butyric Acid, C 8 H 8 O 4 . Butter is a mixture of several glycerides : the one to which it owes its agreeable flavor is called butyrine, and when saponified by an alkali yields butyric acid. It has been recently discovered that the fermentation of sugar under peculiar circumstances produces butyric acid, a fact referred to when describing sugar. A solution of sugar is mixed with a little curd of milk, and a sufficient quantity of chalk to saturate the acid which will afterwards be formed. The mixture is placed in a situation where the temperature is from 77 to 86 F. : the fermenta- tion is at first viscous, then lactic, and finally butyric : much hydrogen and carbonic acid gases are evolved, and the mix- ture emits a very unpleasant odor. After several weeks the evolution of gas ceases, and the liquid contains nothing but butyrate of lime. The operation succeeds best when con- siderable quantities are employed. The reaction is very simple. The sugar is probably first converted into grape sugar, one equivalent of which, C, 2 H, 2 O 12 :=C 8 H 8 O 4 + 4CO 2 + H 4 . This acid is easily procured by distilling the butyrate of lime with hydrochloric acid ; it must be digested with chlorid of calcium, and redistilled to obtain it free from water. Pure butyric acid is a limpid colorless liquid, which is dissolved in all proportions by water and alcohol, boils at 327, and has a specific gravity of '963. It has an odor resembling that of vinegar and strong butter, and an acid pungent taste. It is monobasic, and its salts are all soluble in water. The butyrate of lime (CgHyCaC},) dissolves readily in cold water, but its solubility diminishes as its temperature is elevated : at the boiling-point almost the whole of the salt separates in transparent prisms, which redissolve on cooling. Butyric Ether ', C 12 H 12 O 4 . This is formed with great facility by distilling a mixture of butyric acid and alcohol with sulphuric acid. It is a colorless liquid, slightly soluble in alcohol, and has an agreeable odor like pineapples. It is employed by distillers to flavor spirits. When a mixture of butyric acid and glycerine is heated with sulphuric acid, an 408 ORGANIC CHEMISTRY. oily liquid separates which appears to be butyrine, and yields butyric acid and glycerine by action of alkalies. It is the only glyceride that has been formed artificially. When butyrate of lime is distilled it affords butyrone, cor- responding to acetone (733), and a light colorless fluid called butyral. This has the formula C 8 H 9 O 2 , and sustains the same relation to butyric acid that aldehyde does to the acetic ; when exposed to the air it absorbs two equivalents of oxygen, and forms butyric acid. 795. The oil of the porj>oise contains a peculiar glyceride called phocenine ; by the action of alkalies it affords gly- cerine and valerianic acid (745), which has been described under the name of phoccnic acid. The saponification of butter affords, in addition to the butyric, the volatile acids called caproic, caprylic, and capric. They arc separated from each other and from butyric acid by the different solubility of their barytic salts. The caproic acid is C 12 H, 2 O 4 . It is an oily liquid, slightly soluble in water, and has an odor which resembles at the same time that of vinegar and of sweat. The caprylic (C I6 H I6 O 4 ) and the capric (C^H^O.,) arc volatile odorous acids closely resembling the caproic. The action of nitric acid upon castor oil and some other fats, yields a volatile oily acid of a fragrant odor called the t'TKuitkyJic : it is C 14 H 14 O 4 . The distilled water of the rose geranium (Pelargonium roscum) contains another oily acid allied to the last ; it is called pdargonic acid, and is C 18 H 18 O 4 . 796. The preceding acids are all volatile, odorous, more or less soluble in water, and although their boiling-points are often elevated, may be distilled over with its vapor. Their baryta and lime salts are soluble in water. The remaining acids in the series are solid, crystalline, inodorous, and in- soluble in water; their salts with a base of barium or calcium arc insoluble, while the potash and soda salts are very soluble in water, and are proper soaps. 797. The berries of the laurel, called Lavrus nobilis, con- tain a white crystalline glyceride called laurine, which, when sappnified, affords the lavric acid, C 24 H 2 ,O 4 . It is white and crystalline, and fuses at 88 : alcohol dissolves it readily, and the solution has a strongly acid reaction. The oil of the cocoanut yields, by saponification, cocinic ^H^O.! it is very fusible and resembles the last. The nutmeg contains a peculiar fat or glyceride called my- FATS AND THE SUBSTANCES DERIVED THEREFROM. 409 ristine, which yields, by the usual process, myristic acid, CasHagQ,. It resembles the preceding, and fuses at 120. The palm oil, which is the product of the nuts of the Elais guinensis, is a mixture of a fluid fat, oleine, with a solid crystalline substance called palmitine. This is the glyceride of ethalic acid, which has been described under the name of palmitic acid. 798. The solid fat of animals is composed of two solid glycerides, margarine and stearine, with a liquid called oleine.* The oil of olives and butter contains a portion of margarine. It is best obtained from animal tallow by dis- solving it in several times its volume of hot ether. The stea- rine crystallizes out on cooling, and after expelling the ether by evaporation, the margarine is obtained mixed with oleine, which may be removed by pressure between folds of blotting- paper. Pure margarine fuses at 116, and is very soluble in ether ; by the action of alkalies it yields glycerine and mar- garic acid. This acid is white, and crystallizes in pearly plates; it fuses at 140. Its composition is C^H^C^. 799. Stearine is obtained as a white crystalline mass, fusing at 130. It is almost insoluble in alcohol and cold ether. By saponification it yields the stearic acid ; this is very soluble in ether and alcohol, and melts at 167. Its formula is CggELjgO,!. The stearic ether is obtained by pass- ing hydrochloric acid gas through a hot solution of stearic acid in alcohol ; it is a white crystalline substance, soluble in alcohol, but insoluble in water ; it fuses at 88, and by a higher heat, is completely decomposed. It is the homologue of acetic and butyric ethers, and like them is decomposed by an alcoholic solution of potash, taking up the elements of two equivalents of water, and regenerating alcohol and stearic acid. The ethers of the other fatty acids may be formed by a process similar to that just described, and are much more fusible than the acids themselves. 800. Bees-wax may be regarded as the aldehyde of stearic acid ; its formula is CggHagOa, and it is consequently the homologue of spermaceti and butyral. When heated with hydrate of potash, hydrogen gas is evolved, and stearic acid formed. It is soluble in a solution of potash, and forms a * Stearine., from the Greek stear, tallow, and oleine, from elaion, oil. Margarine is named from margarites, a pearl, in allusion to the pearly lustre of its acid. 35 410 ORGANIC CHEMISTRY. kind of soap ; when boiled with a very concentrated potash ley, it yields stearic acid and a volatile crystalline substance, which appears to correspond to the ethol of spermaceti, and to be the alcohol of stearic acid. It has been regarded as a vegetable production, and col- lected by bees from plants; but recent experiments have satis- factorily shown that bees produce wax when fed upon pure sugar or honey ; it must, therefore, be a secretion of the insect. The berries of the Anamirta coculvs contain a peculiar glyceride, which by the action of alkalies yields the ana- mirtic acid. It closely resembles the preceding acids, and its composition is C^H^O.,. 801. The fatty acids already described, are homologues of formic and acetic acid ; they are monobasic, contain four equivalents of oxygen, with carbon and hydrogen in equal equivalents. This will be seen by arranging them in suc- cession. 1. Formic, C 2 H 2 O 4 11. 2. Acetic, C 4 H 4 O 4 12. Laurie, 3. Metacetonic, Ce He O 4 13. Cocinic, 4. Butyric, C* H 8 O 4 14. Myristic, 5. Valerianic, Ci Hi 4 15. 6. Caproic, C 12 Hi 2 O 4 16. Ethalic, C 32 H 32 O 4 7. Enanthylic, C U H )4 O 4 17. Margaric, C^H^A 8. Caprylic, Ci 6 Hi 6 O 4 18. Anamirtic, 9. Pelargonic, C IS Hj 8 O 4 19. Stearic, 10. Capric, The first, second, fifth, and sixteenth of these acids are de rived from alcohols already known, and the bodies corres- ponding to aldehyde in the fourth and nineteenth, have also been discovered ; we may regard all of them as the acids of a series of alcohols as yet unknown. In this group we observe a regular transition from the acetic and formic acids, through the butyric, valerianic, and other oily sparingly soluble acids, to the completely insoluble ethalic and stearic. The eleventh and fifteenth of the series are as yet unknown, but it is highly probable that they may yet be discovered, as well as others higher in the series. Three or four of those in the list have been described within as many years. The first two acids in the group which volatilizes without decomposition, exhibit a progressive increase of about 36 F. in their boiling-points; thus, the formic acid boils at 212, = 248,andthemetacetonic,at248-H FATS AND THE SUBSTANCES DERIVED THEREFROM. 411 802. Oleic Acid. The fluid portion of butter and animal fats consists principally of oleine ; and the vegetable and animal oils are composed of oleine and a little margarine, or other glycerides. It is obtained by exposing olive oil to cold, and separating the margarine which crystallizes out ; it is lighter than water, tasteless and inodorous. By the action of alkalies it yields glycerine and oleic acid. This resembles oleine itself, and has neither taste nor smell ; it rapidly absorbs oxygen from the air, and is altered. Its composition is CgeH^O^ and it is monobasic, forming, like the other fatty acids, soluble salts with the alkalies. When nitrous acid vapor is passed through oleic acid, it almost immediately solidifies into a crystalline mass of elaidic acid, which is purified by crystallization from alcohol. It forms superb crystals of a brilliant whiteness, fusing at 112. Its composition is precisely similar to oleic acid, of which it is a metameric modification. When oleic or elaidic acid is heated with hydrate of potash, hydrogen gas is evolved, and ethalate and acetate of potash are formed. If oleic acid is boiled for a few minutes with strong nitric acid, it is converted into margaric acid, which congeals on cooling : the reaction consists in the separation of two equivalents of carbon as carbonic acid gas. Stearic acid affords the margaric by a similar process. The prolonged action of nitric acid gives rise to the volatile acids of the preceding series. M. Redtenbacher has recently observed in the volatile products resulting from the action of nitric upon the oleic acid, all those from the acetic to the capric inclusive. The other fatty acids and wax yield the same products. 803. The residue of this process contains four soluble, crystallizable, bibasic acids, the succinic, CgH^Og, adipic, C, 2 H 10 Og, pimelic, Ci 4 H 12 O 8 , and suberic, C 16 H 14 O 8 . The suc- cinic acid was originally -obtained by distilling amber, a fossil resin, which occurs in recent geological formations. Succinic acid is soluble in water and alcohol ; when heated it fuses, and is decomposed into water and a neutral crystalline substance called succinide, C 8 H 4 O 6 , which when boiled with water is gradually reconverted into succinic acid. The other acids are of but little importance ; the suberic is a product of the action of nitric acid upon cork. When oleine or oleic acid is distilled, sebasic acid is obtained ; it is crystallizable, volatile, and soluble in water, and has the formula 412 ORGANIC CHEMISTRY. It is bibasic and homologous with the four preceding acids, in all of which the number of equivalents of hydrogen is less by two than the carbon, and the oxygen equal to eight equivalents. When these acids are fused with hydrate of potash, hydrogen gas is evolved, and salts of the volatile acids of the preceding groups are formed. The pimelic yields by this process valerianic acid ; carbonic acid is formed at the same time. 804. Soaps. The compounds of these acids are very important, and constitute the bodies generally known as soaps. These are mixtures of oleate, rnargarate, and stearatc of potash or soda, being formed from the saponiii- cation of mixed fats by these alkalies. The soft soaps con- tain potash, and the hard ones soda. All these compounds are readily decomposed by acids, which combine with the alkali and liberate the fatty acid. When we mix a solution of soap with the soluble salt of any other base, we obtain a precipitate which is an insoluble combination of the fatty acid with the base. Hence the power of salts of lime or magnesia to render water hard. The compounds of these acids with the oxyd of lead, constitute the lead plaster, or diachylon, so much used in surgery. A mixture of stearic and mar- garic acids, obtained by saponifying animal fats with lime, and decomposing the insoluble soap by hydrochloric acid, has been employed in the manufacture of candles. When a solid fat, as lard, is kept for a long time melted, especially if a little spirit of wine is mixed with it, the solid portions separate, on cooling, in crystalline grains : by subjecting this mass to pressure, the fluid part is separated, and the mixture of margarine and stearine thus obtained is used for the manu- facture of candles, while the fluid oleine constitutes what is called lard oil. Both of these products are now extensively manufactured in this country. VEGETABLE ACIDS. 805. Besides those vegetable acids already described, there are a number of others, most of which exist in saline combination in different plants. They are generally solid, crystallizable, soluble in water, and not volatile without decomposition. A few of the more important of them will bo noticed. 806. Oxalic Acid, C 4 H 2 O S , The salts of this acid exist VEGETABLE ACIDS. 413 in many vegetables : the agreeably sour taste of wood sorrel, Oxalis acetoselldy and other plants of the same genus, is due to the acid oxalate of potash which they contain. Oxalic acid is a product of the action of nitric acid upon sugar, starch, lignine, and many other organic substances. To prepare it, one part of starch is heated with eight parts of nitric acid, specific gravity 1*25. A violent action ensues, and much nitrous acid is evolved ; when this ceases, the solution is concentrated by evaporation, and on cooling yields a large quantity of crystals of 'oxalic acid, which are purified by washing in water, and recrystallization. Oxalic acid is colorless, very soluble in water, has a powerfully acid taste, and is very poisonous. It crystallizes with four equivalents of water, in forms belonging to the monoclinite system : by a gentle heat the water is expelled, and the dry acid, C 4 H 2 O 8 , remains ; this, by a careful appli- cation of heat, may be in part sublimed unchanged, but at a high temperature it is decomposed into formic acid, water, and carbonic oxyd and carbonic acid gases. When oxalic acid or an oxalate is heated with strong sulphuric acid, it is decomposed, and a mixture of equal volumes of carbonic acid and carbonic oxyd gases is evolved, C 4 H 2 O 8 =2CO 2 + 2CO + 2HO, (347.) 807. Oxalic acid is bibasic, and forms neutral salts in which two equivalents of its hydrogen are replaced by a metal, and acid salts with but one equivalent of fixed base. The neutral oxalate of potash (C 4 K 2 O 8 ) is a very soluble salt. The acid oxalate, commonly called binoxalate (C 4 HKO 8 ) is less soluble, and has an agreeable acid taste. It exists, as before stated, in the juice of the Oxalis 'icetosella, and is hence often distinguished as salt of sorrel ; it is used to remove iron stains from linen, which it does by forming a soluble salt with the iron. When this oxalate is dissolved in hydro- chloric acid, a salt separates on cooling which is commonly called a quadroxalate. Its composition is such that it may be regarded as a compound of equal equivalents of oxalic acid and the acid oxalate. The neutral oxalate of ammonia (C 4 H 2 O 8 2NH 3 ) crystallizes in fine prisms, and is much used in analytical chemistry. When exposed to heat, it is decom- posed, and yields, among other products, water and oxamide. This substance has been already described as the amide of oxalic acid, (698.) The acid oxalate yields in the same manner the acid amide, oxamic acid, which contains 35* 414 ORGANIC CHEMISTRY. C 4 H 2 O 8 ,NH 3 -2HO=C 4 H 3 NO 6 . When a solution of oxamic acid is boiled, it reassumes the elements of water and forms acid oxalate of ammonia. 808. The Oxalate of Lime (C 4 CaO 8 -f 4aq) is a very in- soluble salt, and occupies an important part in the vegetable economy, being secreted by a large number of plants, in the cells of which the microscope re- veals to us a great number of beautiful crystals of this substance ; this appearance is repre- sented in the annexed figure of a vessel from the bark of Torreya taxifolia. In many of the lichens, the oxalate of lime appears to re- place the woody fibre, and to be somewhat allied in its functions to the carbonates and phosphates of lime in the animal kingdom. The oxalates of the metals are generally insoluble. 809. Oxalic acid combines with two equivalents of the alcohols to form neutral ethers (703) ; they are obtained by distilling the alcohol and oxalic acid with a portion of sul- phuric acid. The oxalic methylic ether crystallizes finely ; those of spirit-of-winc and amylol are liquids. The oxalo- rinic is a coupled acid, which corresponds to the sulphovinic, (704.) AVhen oxalic ether is mixed with excess of ammonia, alcohol separates, and oxamide is formed ; but if ammonia is cautiously added, only half of the alcohol is eliminated, and a beautiful crystalline compound called oxamethane is ob- tained ; it is an ether-amide, like sulphamethylane, (736.) 810. Tartaric Acid, C 8 II 6 O, 2 . This acid exists in the juices of many fruits, particularly that of the grape, as an acid tartrate of potash. As this salt is almost insoluble in dilute alcohol, it is deposited, during the fermentation, in crystalline crusts known as crude tartar, or argol. It is decomposed by chalk to form a tartrate of lime ; this is mixed with an equivalent of sulphuric acid, which forms a sulphate, and liberates the tartaric acid. From a concentrated solution it crystallizes in fine rhombic prisms, very soluble in water and alcohol, and having a pleasant acid taste. Tartaric acid is bibasic, and often forms salts with two bases. 811. The Acid Tartrate of Potash, C 8 H 5 KO I2 , is obtained by purifying the crude tartar of wine, and generally appears as a white crystalline powder, known as cream of tartar. It is very little soluble in cold water, and has a slightly acid taste; it is extensively used in dyeing and in medicine. Tho VEGETABLE ACIDS. 415 neutral tartrate, C 8 H