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CONVERSATIONS 
 
 CHEMISTRY; 
 
 IN WHICH THE 
 
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 ELEVENTH AMERICA*, FRO >, THE E ,,; IITn LONDQV , 
 
 TO WHICH AIII-: NOW ADDI.D, 
 
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 BY J. L. COMSTOCK, 31. I> 
 
 TOGETHER WITH A Ni^v ANr, , 
 
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 BY REV. Jit. BLAKE, A 
 
 HARTFORD: 
 
 PUBLISHED BY COOKE AND OO. 
 
 and 
 PACKARD AND BUTLBK. 
 
Mstrttt of <ottnecttcut, *8. 
 
 BE IT REMEMBERED, That on the second day of Oc. 
 L. S. tober, in the fifty-first year of the Independence of the 
 United States of America, Oliver D. Cooke and Co., of 
 the said District, have deposited in this office the title of a Book, the 
 right whereof they claim as proprietors, in (he words following, to wit, 
 " Conversations on Chemistry ; in which the Elements of that science 
 are familiarly explained and illustrated by experiments, and thirty- 
 eight engravings on wood. The tenth American from the eighth 
 London edition, revised, corrected, and enlarged. To which are now 
 added, explanations of the text, directions for simplifying the appara- 
 tus, and a vocabulary of terms; together with a list of interesting ex- 
 periments. By J. L. Comstock, M. D. Together with a new and ex- 
 tensive Series of Questions, by Rev. J. L. Blake, A. M. In conformity 
 to the act of the Congress of the United States, entitled, " An act for 
 the encouragement of learning, by securing the copies of Maps, Charts 
 and Books, to the authors and proprietors of such copies, during the 
 times therein mentioned." 
 
 CHAS. A. INGERSOLL, 
 Clerk of the District of Connecticut. 
 A true copy of record, examined and sealed by me, 
 
 CHAS. A. INGERSOLL, 
 Clerk of the District of Connecticut. 
 
ADVERTISEMENT l 
 
 OF THE AMERICAN EDITOR. 
 
 THE familiar and agreeable manner in which the "Conversations on Che- 
 mistry" are written, renders this one of the most popular treatises on the 
 subject which has ever appeared. The elegant and easy style also, in which 
 the authoress has managed to convey scientific instruction is peculiarly adap- 
 ted to the object of the work. 
 
 In some respects, however, the English edition may be considered as ob- 
 jectionable. A. book designed for the instruction of youth, ought, if possi- 
 ble, to contain none but established principles. 
 
 Known and allowed facts are always of much higher consequence than 
 theoretical opinions. To youth, particularly, by advancing as truths, doc- 
 trines which have arisen out of a theory not founded on demonstration, we 
 run a chance of inculcating permanent error. 
 
 In these respects we think that Mrs. Bryant has not been sufficiently guard- 
 ed. The brilliant discoveries of Sir Humphrey Davy, and his known emi- 
 nence as a Chemical Philos6pher, seem in many instances to have given his 
 opinions an authority, which, in the mind of the writt r, superseded further 
 investigation. Indeed, inferences are sometimes drawn from these opinions 
 which they hardly warrant. Under this view of the subject, a part of the 
 notes is designed to guard the pupil against adopting opinions which he will 
 find either contradicted, or merely examined by most chemical writers. Jn 
 addition to this, I have made such explanations of the text as I thought would 
 assist the pupil in understanding what he reads. 
 
 In attemptiug to make this science popular, and of general utility, it is of 
 great importance that the experiments come within the use of such instru- 
 ments as are easily obtained. I have therefore given such directions on this 
 subject, as my former experience as a lecturer, with a small apparatus, 
 taught me to believe would be of service. 
 
 The list of experiments was chiefly made up without re^rring to books : 
 some few of them, however, are copied from Parke, Accuw, &c. 
 
 REMARKS BY THE REV. MR. BLAKE. 
 
 The questions, in the present edition, are placed at the bottom of the sev- 
 eral pages to which they relate. This plan has been adopted in the Boston 
 edition of Conversations on Natural Philosophy, and is become very popular. 
 The advantages of it are too obvious to escape observation, and, of course, 
 to need being particularized. It will be seen that the questions are more 
 numerous than they were in the two first impressions from this copy. It 
 may b supposed by persons not acquainted with teaching, that they are too 
 numerous, as some of them are repeated in various forms, and others are 
 seemingly unimportant. But it is found necessary that scholars should be 
 examined on every page, and upon nearly every paragraph, whether there is 
 any thing very important or not. No small portion of learners will pass 
 over without study, all in which they are not to be questioned. Hence what 
 alight be called a system of questions would be quite insufficient. 
 
 15371843 
 
PREFACE. 
 
 IN venturing to offer to the public, and more particularly 
 to the female sex, an Introduction to Chemistry, the author, 
 herself a woman, conceives that some explanation may be 
 required ; and she feels it the more necessary to apologize 
 for the present undertaking, as her knowledge of the sub- 
 ject is but recent, and as she can have no real claims to the 
 title of chemist. 
 
 On attending for the first time experimental lectures, the 
 author found it almost impossible to derive any clear or satis- 
 factory information from the rapid demonstrations which are 
 usually, and perhaps necessarily, crowded into popular cour- 
 ses of this kind. But frequent opportunities having after- 
 wards occurred of conversing with a friend on the subject of 
 chemistry, and of repeating a variety of experiments, she be- 
 came better acquainted with the principles of that science, 
 and began to feel highly interested in its pursuits. It was 
 then that she perceived, in attending the excellent lectures 
 delivered at the Royal Institution, by the present Professor 
 of Chemistry, the great advantage which her previous know- 
 ledge of the subject, slight as it was, gave her over others 
 who had not enjoyed the same means of private instruction. 
 Every fact or experiment attracted her attention, and served 
 to explain some theory to which she was not a total stranger ; 
 and she had the gratification to find that the numerous and 
 elegant illustrations, for which that school is so much dis- 
 tinguished, seldom failed to produce on her mind the effect 
 for which they were intended. 
 
 Hence it was natural to infer, that familiar conversation 
 was, in studies of this kind, a most useful auxiliary source of 
 information ; and more especially to the female sex, whose 
 education is seldom calculated to prepare their minds for 
 abstract ideas, or scientific language. 
 
 As, however, there are but few women who have access 
 to this mode of instruction ; and as the author was not ac- 
 quainted with any book that could prove a substitute for it, 
 she thought it might be useful for beginners, as well as sat- 
 isfactory to herself, to trace the steps by which she had ac- 
 quired her little stock of chemical knowledge, and to record, 
 in the form of dialogue, those ideas which she had first de- 
 rived from conversation. 
 
 But to do this with sufficient method, and to fix upon a mode 
 of arrangement, was an object of some difficulty. After much 
 hesitation, and a degree of embarrassment, which, probably, 
 the most competent chemical writers have often felt in com- 
 mon with the most superficial, a mode of division was adopt- 
 
PREFACE. V 
 
 ed, which, though the most natural, does not always admit 
 of being strictly pursued it is that of treating first of the 
 simplest bodies, and then gradually rising to the most intri- 
 cate compounds. 
 
 It is not the author's intention to enter into a minute vindi- 
 cation of this phin. But whatever may be its advantages or 
 inconveniences, the method adopted in this work is such, 
 that a young pupil, who should only recur to it occasionally 
 with a view to procure information on particular' subjects, 
 might often find it obscure or unsatisfactory ; for its various 
 parts are so connected with each other as to form an unin- 
 terrupted chain of facts and reasonings, which will appear 
 sufficiently clear and consistent to those only who may have 
 patience to go through the whole work, or have previously 
 devoted some attention to the subject. 
 
 It will, no doubt, be observed, that in the course of these 
 Conversations, remarks are often introduced, which appear 
 much too acute for the young pupils, by whom they are sup- 
 posed to be made. Of this fault the author is fully aware. 
 But, in order to avoid it, it would have been necessary either 
 to omit a variety of useful illustrations, or to submit to such 
 minute explanations and frequent repetitions, as would have 
 rendered the work tedious, and therefore less suited to its 
 intended purpose. 
 
 In writing these pages, the author was more than once 
 checked in her progress, by the apprehension that such an 
 attempt might be considered by some, either as unsuited to 
 the ordinary pursuits of her sex, or ill-justified by her own 
 imperfect knowledge of the subject. But, on the one hand, 
 she felt encouraged by the establishment of those public in- 
 sititutions, open to both sexes, for the dissemination of philo- 
 sophical knowledge, which clearly prove that the general 
 opinion no longer excludes woman ironi an acquaintance 
 with the elements of science ; and, on the other, she flatter- 
 ed herself, that whilst the impression made upon her mind, 
 by the wonders of Nature, studied in this new point of view, 
 were still fresh and strong, she might perhaps, succeed the 
 better in communicating to others the sentiments she herself 
 experienced. 
 
 The reader will perceive, in perusiug this work, that he is 
 supposed to have previously acquired some slight knowledge 
 of Natural Philosophy, a circumstance so desirable, that the 
 author has, since the original publication of this work, been 
 induced to oiler to the public a small tract, entitled " Con- 
 versations on Natural Philosophy," in which the most es- 
 sential rudiments of that science are familiarly explained. 
 
CONTENTS. 
 
 CONVERSATION I. 
 
 ON THE GENERAL PRINCIPLES OF CHEMISTRY. 13 
 
 Connexion between Chemistry and Natural Philosophy Improved 
 state of modern Chemistry Its use in the Arts The general Ob- 
 jects of Chemistry Definition of Elementary Bodies Definition 
 of Decomposition Integrant and Constituent Particles Distinc- 
 tion between Simple and CompoundjBodies Classification of Sim- 
 ple Bodies Of Chemical Affinity, or Attraction of Composition 
 Examples of Composition and Decomposition. 
 
 CONVERSATION II. 
 
 ON LIGHT AND HEAT. 26 
 
 Light and Heat capable of being separated Dr. Herschel's Exper- 
 iments Phosphorescence Of Caloric Its two modifications 
 Free caloric Of the three different states of Bodies, solid, fluid, 
 and aeriform Dilatation of Solid Bodies Pyrometer Dilatation 
 
 of Fluids Thermometer Dilatation of Elastic Fluids Air 
 
 Thermometer Equal Diffusion of Caloric Cold a Negative 
 Quality Professor Prevost's Theory of the Radiation of Heat- 
 Professor Pictet's Experiments on the Reflection of Heat Mr. 
 Leslie's Experiments on the radiation of Heat. 
 
 CONVERSATION III. 
 
 CONTINUATION OF THE SUBJECT. 47 
 
 Of the different Power of Bodies to Conduct Heat Attempt to ac- 
 count for this Power Count Rumford's Opinion respecting the 
 non-conducting Power of Fluids Phenomena of Boiling Of So- 
 lution and Mixture Solvent power of Caloric Of Clouds, Rain, 
 Dr. Wells' Theory of Dew, Evaporation, c. Influence of At- 
 mospherical Pressure on Evaporation Ignition. 
 
 CONVERSATION IV. 
 
 ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT AND LATENT 
 HEAT. 69 
 
 Of Specific Heat Of the different Capacities of Bodies for Heat- 
 Specific Heat, not perceptible by the Senses How to be ascer- 
 tainedOf Latent Heat Distinction between Latent and Speci- 
 fic Heat Phenomena attending the Melting of Ice and the For- 
 mation of Vapour Phenomena attending the Formation of Ice, 
 
CONTENTS. VII 
 
 and the Condensation ofejastic Fluids Instances of Condensation, 
 and consequent Disengagement of Heat, produced by Mixtures, by 
 the Slaking of Lime General Remarks on Latent Heat Ex- 
 planation of the Phenomena of Ether boiling, and Water freezing, 
 at the same Temperature Of the Production of Cold by Evapora- 
 tion. 
 
 CONVERSATION V. 
 
 ON THE CHEMICAL AGENCIES OF ELECTRICITIES. 84 
 
 Of Positive and Negative Electricity Galvani's Discoveries Volta- 
 ic Battery Electrical Machine Theory of Voltaic Excitement 
 Its influence on the Magnetic Needle. 
 
 CONVERSATION VI. 
 
 ON OXYGEN AND NITROGEN. 95 
 
 The Atmosphere composed of Oxygen and Nitrogen in the State of 
 Gas Definition of Gas Distinction between Gas and Vapour 
 Oxygen essential to Combustion and Respiration Decomposition 
 of the Atmosphere by Combustion Nitrogen Gas obtained by 
 this process Of Oxygenation in general Of the Oxydation of 
 Metals Oxygen Gas obtained from Oxyd of Manganese De- 
 scription of a Water Bath for collecting and preserving Gases 
 Combustion of Iron Wire in Oxygen Gas Fixed and Volatile 
 Product of Combustion Patent Lamps Decomposition of the 
 Atmosphere by respiration Re-composition of the Atmosphere. 
 
 CONVERSATION VII. 
 
 ON HYDROGEN. 109 
 
 Of Hydrogen Of the Formation of Water by the combustion of 
 Hydrogen Of the Decomposition of Water Detonation of Hy- 
 drogen Gas Description of Lavoisier's Apparatus for the Form- 
 ation of Water Hydrogen Gas essential to the production of 
 Flame Musical tones produced by the Combustion of Hydrogen 
 Gas within a Glass Tube Combustion of Candles explained 
 Gas lights Detonation of Hydrogen Gas in Soap Bubbles Air 
 Balloons Meteorological Phenomena ascribed to Hydrogen Gas 
 Miners' Lamp. 
 
 CONVERSATION VIII. 
 
 ON SULPHUR AND PHOSPHORUS. 126 
 
 Natural History of Sulphur Sublimation Alembic Combustion 
 of Sulphur in Atmospheric Air Of Acidification in general No- 
 menclature of the Acids Combustion of Sulphur in Oxygen Gas 
 Sulphuric Acid Sulphurous Acid Decomposition of Sulphur 
 
Vlll CONTENTS. 
 
 Sulphuretted Hydrogen Gas Harrogale, or Hy.drosulphuretted 
 
 Waters Phosphorus Decomposition of Phosphorus History 
 
 of its Discovery Its combustion in Oxygen Gas Phosphoric 
 Acid Phosphorous Acid Eudiometer Combination of Phos- 
 phorus with Sulphur Phosphoretted Hydrogen Gas Nomencla- 
 ture of Binary Compounds Phosphoret of Lyme burning under 
 water. 
 
 CONVERSATION IX. 
 
 ON CARBON. 137 
 
 Method of obtaining pure Charcoal Method of making common 
 Charcoal Pure Carbon not to be obtained by Art Diamond 
 Properties of Carbon Combustion of Carbon Production of 
 Carbonic Acid Gas Carbon susceptible of only one Degree of 
 Acidification Gaseous Oxyd of Carbon Of Seltzer Water, and, 
 other mineral Waters Effervescence Decomposition of Water 
 by Carbon Of fixed and Essential Oils Of the Combustion of 
 Lamps and Candles Vegetable Acids Of the power of Carbon 
 to revive Metals. 
 
 CONVERSATION X. 
 
 ON METALS. 149 
 
 Natural History of Metals Of Roasting, Smelting, &c. Oxydation 
 of Metals by the Atmosphere Change of Colours produced by 
 different degrees of Oxydation Combustion of Metals Perfect 
 Metals burnt by Electricity only Some Metals revived by Car- 
 bon and other Combustibles Perfect Metals revived by Heat alone 
 Of the Oxydation of certain Metals by the Decomposition of 
 Water Power of Acids to promote this Effect Oxydation of Met- 
 als by Acids Metallic Neutral Salts Previous Oxydation of the 
 Metal requisite Crystallization Solution distinguished from Dis- 
 solution Five Metals susceptible of Acidification Meteoric Stones 
 Alloys, Soldering, Plating, &c. Of Arsenic, and of the Caustic Ef- 
 fects of Oxygen Of Verdigris, Sympathetic Ink, &c. Of the new 
 Metals discovered by Sir H. Davy. 
 
 CONVERSATION XL 
 
 ON THE ATTRACTION OF COMPOSITION. 171 
 
 Of the Laws which regulate the Phenomena of the Attraction of 
 Composition 1. It takes place only between bodies of a different 
 Nature 2. Between the most minute Particles only 3. Between 
 2, 3, 4, or more Bodies Of Compound or Neutral Salts 4. Pro- 
 duces a Change of Temperature 5. The Properties which char- 
 racterise Bodies in their separate state, destroyed by Combina- 
 tion 6. The Force of Attraction estimated by that which is re- 
 quired by the separation of the Constituents 7. Bodies hare 
 
CONTENTS. IX 
 
 amongst themselves different Degrees of Attraction Of simple elec- 
 tive and double elective Attractions Of quiescent and divellant For- 
 ces Law of definite Proportions Decomposition of Salts by Volta- 
 ic Electricity. 
 
 CONVERSATION XIV. 
 
 ON ALKALIES. 181 
 
 Of the composition and general properties of the Alkalies Of the 
 new discovered Alkali or Lithion Of Potash Manner of pepar- 
 ing it Pearlash Soap Carbonat of Potash Chemical Nomen- 
 clatureSolution of Potash Of Glass Of Nitrat of Potash, or 
 Saltpetre Effect of Alkalies on Vegetable Colours Of Soda Of 
 Ammonia, or Volatile Alkali Muriat of Ammonia Ammoniacal 
 Gas Composition of Ammonia Hartshorn and Sal Volatile 
 Combustion of Ammoniacal Gas. 
 
 CONVERSATION XV. 
 
 ON EARTHS. 191 
 
 Composition of the Earths Of their incombustibility Form the 
 bases of all Minerals Their Alkaline properties Silex ; its pro- 
 perties and uses in the Arts Alumine ; its uses in Pottery, &c. 
 Alkaline Earths Barytes Lime ; its extensive chemical proper- 
 ties and uses in the Arts Magnesia Strontian. 
 
 CONVERSATION XVI. 
 
 ON ACIDS. 202 
 
 Nomenclature of the Acids Of the Classification of Acids 1st Class 
 Acids of simple and known Radicals, or Mineral Acids 2d Class 
 Acids of double Radicals, or Vegetable Acids 3d Class Acids 
 of triple Radicals, or Animal Acids Of the Decomposition of Acids 
 of the 1st Class by combustible bodies. 
 
 CONVERSATION XVII. 
 
 OF THE SULPHURIC AND PHOSPHORIC ACIDS ; OR THE COMBINATIONS 
 OF OXYGEN WITH SULPHUR AND WITH PHOSPHORUS ; AND OF THE 
 SULPHATS AND PIIOSPHATS. 206 
 
 Of the Sulphuric Acid Combustion of Animal or Vegetable bodies 
 by this Acid Method of preparing it The Sulphurous .Acid ob- 
 tained in the form of Gas May be obtained from Sulphuric Acid 
 May be reduced to Sulphur Is absorbable by water Destroys 
 Vegetable colours Oxyd of Sulphur Of salts in general S-tfl- 
 phats Sulphat of Potash, or Sal Polychrest Cold produced by 
 the melting of salts Sulphat of Soda, or Glauber's salt Heat 
 
X CONTENTS. 
 
 evolved during the formation of salts Crystallization of salts 
 Water of Crystallization Efflorescence and Deliquescence of Salts 
 Sulphat of Lime, Gypsum, or Plaster of Paris Sulphat of Mag- 
 nesia Sulphat of Alumine, or Alum Sulphat of Iron Of Ink 
 Of the Phosphoric and Phosphorous Acids Phosphorus obtained 
 from bones Phosphat of Lime. 
 
 CONVERSATION XVIII. 
 
 OF THE NITRIC AND CARBONIC ACIDS J OR THE COMBINATION OF OX- 
 YGEN WITH NITROGEN AND WITH CARBON, AND OF THE NITRAT3 
 AND CARBONATS. 214 
 
 Nitrogen susceptible of various degrees of acidification Of the Nitric 
 Acid Its Nature and Composition discovered by Mr. Cavendish 
 Obtained from Nitrat of Potash Aqua Fortis Nitric Acid may be 
 converted into Nitrous Acid Nitric Oxyd Gas Its conversion into 
 Nitrous Acid Gas Used as an Eudiometrical test Gaseous Oxyd 
 of Nitrogen, or exhilarating Gas obtained from Nitrat of Ammonia 
 Its singular effects on being respired Nitrats Of Nitrat of Pot- 
 ash, Nitre or Saltpetre Of Gunpowder Causes of Detonation 
 Decomposition of Nitre Deflagration Nitrat of Ammonia Nitrat 
 of Silver Of the Carbonic Acid Formed by the combustion of 
 Carbon Constitutes a component part of the Atmosphere Exhal- 
 ed in some caverns Grotto del Cane Great weight of this Gas 
 Produced from calcareous stones by Sulphuric Acid Deleterious 
 effects of this Gas when respired Sources which keep up a supply 
 of this Gas in the atmosphere Its effects on vegetation Of the 
 Carbonats of Lime; Marble, Chalk, Shells, Spars, and Calcareous 
 Stones. 
 
 CONVERSATION XIX. 
 
 Qy THE BORHCIC, FLUORIC, MURIATIC, AND OXYGENATED MURIATIC 
 ACIDS J AND ON MURIATS. 226 
 
 On the Boracic Acid Its decomposition, by Sir H. Davy Its basis 
 Boracium Its Recomposition Its uses in the Arts Borax or Bo- 
 rat of Soda Of the Fluoric Acid Obtained from Fluor ; corrodes 
 siliceous earth ; its supposed composition Fluorine ; its supposed 
 basis Of the Muriatic Acid Obtained from Muriats Its gaseous 
 form Is absorbable by water Its Decomposition Is susceptible 
 of a stronger degree of Oxygenation Oxygenated Muriatic Acid 
 Its gaseous form and other properties Combustion of bodies in this 
 gas It dissolves Gold Composition of Aqua Regia Oxygenated 
 Muriatic Acid destroys all colours Sir H. Davy's Theory of the 
 nature of Muriatic and Oxymuriatic Acid Chlorine, used for 
 bleaching and for fumigation Its offensive smell, &c. Muriats 
 Muriatof Soda, or common salt Muriat of Ammonia Oxygena- 
 ted Muriat of Potash Detonates with Sulphur, Phosphorus, c. 
 Experiment of burning Phosphorus under water by means of this 
 *alt and of Sulphuric Acid. 
 
CONTENTS. XI 
 
 CONVERSATION XX. 
 
 OX THE NATURE AND COMPOSITION OF VEGETABLES. 238 
 
 Of organized bodies Of the functions of Vegetables Of the ele- 
 ments of Vegetables of the materials of Vegetables Analysis of 
 Vegetables Of Sap Mucilage or Gum Sugar Manna and 
 Honey Gluten Vegetable oils Fixed oils Linseed, Nut, and 
 Olive oils Volatile oils, forming Essences and Perfumes Cam- 
 phor Resins and Varnishes Pitch, Tar, Copal, Mastic, &c. 
 Gum, Resins Myrrh, Assafoetida, c. Caoutchouc, or Gum 
 Elastic Extractive colouring matter ; its use in the arts of dyeing 
 and painting Tannin ; its use in the art of preparing Leather 
 Woody Fibre Vegetable Acids The Alkalies and Salts contained 
 in Vegetables. 
 
 CONVERSATION XXI. 
 
 ON THE DECOMPOSITION OF VEGETABLES. 254 
 
 Of fermentation in general Of the saccharine fermentation, the pro- 
 duct of which is sugar Of the vinous fermentation, the product of 
 which is wine Alcohol, or spirit of wine Analysis of wine by dis- 
 tillation of brandy, rum, arrack, gin, c. Tartrlt of Potash, or 
 Cream of Turtar Liquers Chemical properties of Alcohol Its 
 combustion Of ether Of the acetous fermentation, the product of 
 which is vinegar Fermentation of bread Of ihe putrid fermenta- 
 tion, which reduces vegetables to their elements Spontaneous suc- 
 cession of these fermentations Of vegetables said to be petrified 
 Of bitumens ; Naphta, Asphaltum, Jet, Coal, Succin, or Yellow 
 Amber Of Fossil wood, Peat and Turf. 
 
 CONVERSATION XXII. 
 
 HISTORY OF VEGETATION. 271 
 
 Connexion between the Vegetable and Animal kingdoms Of Ma- 
 nures Of Agriculture Inexhaustible sources of Materials for 
 the purposes of Agriculture Of sowing Seed Germination of 
 the Seed Function of the Leaves of Plants Effects of light and 
 air on Vegetation Effects of water on Vegetation Effects of 
 Vegetation on the Atmosphere Formation of Vegetable Mate- 
 rials by the organs of Plants Vegetable Heat Of the organs of 
 Plants Of the Bark, consisting of Epidermis, Parenchyma, and 
 Cortical Layers Of Alburnum, or woodLeaves, Flowers, and 
 Seeds Effects of the season on Vegetation Vegetation of Ever- 
 greens in the Winter. 
 
 CONVERSATION XXIII. 
 
 Olf THE COMPOSITION OF ANIMALS. 287 
 
 Elements of Animals Of the principal Materials of Animals, viz. 
 
Xll CONTENTS. 
 
 Gelatine, Albumen, Fribrine, Mucus Of Animal Acids Of Ani- 
 mal Colours, Prussian Blue, Carmine, and Ivory Black. 
 
 CONVERSATION XXIV. 
 
 ON THE ANIMAL ECONOMY. 295 
 
 Of the principal Animal Organs Of Bones, Teeth, Horns, Liga- 
 ments, and Cartilage Of the Muscles, constituting the Organs of 
 Motion Of the Vascular System, for the conveyance of Fluids Of 
 the Glands for the secretion of Fluids Of the Nerves, constituting 
 the Organs of Sensation Of the Cellular substance, which connects 
 the several Organs Of the Skin. 
 
 CONVERSATION XXV. 
 
 ON ANIMALIZATION, NUTRITION, AND RESPIRATION. 302 
 
 Digestion' Solvent power of the Gastric Juice Formation of Chyle 
 Its Assimilation, or Conversion into Blood Of Respiration Me- 
 chanical Process of Respiration Chemical Process of Respiration 
 Of the Circulation of the Blood Of the Functions of the Arteries, 
 the Veins, and the Heart Of the Lungs Effects of Respiration on 
 the Blood. 
 
 CONVERSATION XXVI. 
 
 ON ANIMAL HEAT; AND OF VARIOUS ANIMAL PRODUCTIONS. 311 
 
 Of the Analogy of Combustion and Respiration Animal Heat evol- 
 ved in the Lungs Animal Heat evolved in the Circulation Heat 
 produced by Fever Perspiration Heat produced by Exercise 
 Equal temperature of Animals at all Seasons Power of the Ani- 
 mal Body to resist the Effects of HeatCold produced by Perspi- 
 ration Respiration of Fish and of Birds Effects of Respiration on 
 Muscular Strength. Of several Animal Products, viz. Milk, Butter, 
 and Cheese ; Spermaceti ; Ambergris ; Wax ; Lac ; Silk ; Musk ; 
 Civet ; Castor Of the putrid Fermentation Conclusion. 
 
CONVERSATIONS 
 
 ON 
 
 CHEMISTRY. 
 
 CONVERSATION I. 
 
 ON THE GENERAL PRINCIPLES OF CHEMISTRY. 
 
 Mrs. B. As you have now acquired some elementary notions 
 of NATURAL PHU.OSOPHV, I am going to propose to you another 
 branch of science, to which I am particularly anxious that you 
 should devote a share of your attention. T^iis is CHEMISTRY, 
 which is so closely connected with Natural Philosophy, that the 
 study of the one must be, incomplete without some knowledge of 
 the other ; for, it is obvious that we can derive hut a very imper- 
 fect idea of bodies from the study of the general laws by which 
 they are governed, if we remain totally ignorant of 'their intimate 
 nature. 
 
 Caroline. To confess the truth, Mrs. B., lam not disposed to 
 form a very favourable idea of chemistry, nor do I expect to derive 
 much entertainment from it. I prefer the sciences which exhibit 
 nature on a grand scale, to those that are confined to the minut :c 
 of petty details. Can the studies which we have lately pursued, 
 the general properties of matter, or the revolutions of the heaven- 
 ly bodies, be compared to the mixing up of a few insignificant 
 drugs ? I grant, however, there may be some entertaining experi- 
 ments in Chemistry, and should not dislike to try some of them 
 the distilling of lavender, for instance, or rose water 
 
 Mrs. B. I rather imagine, my dear Caroline, that your want of 
 taste for chemistry proceeds from the very limited idea you enter- 
 tain of its object. You confine the chemist's laboratory to the nar- 
 row precincts of the apothecary's and perfumer's shops, whilst it is 
 subservient to an immense variety of other useful purposes. Be- 
 sides, my dear, chemistry is by no means confined to works of art- 
 Nature also has her laboratory, which is the universe, and there she 
 is incessantly employed in chemical operations. You are surprised, 
 Caroline ; but I assure you, that the most wonderful and the most 
 
 1. With what other study is that of chemistry closely connected? 
 
 2. Why is the study of Natural Philosophy incomplete without 
 that of chemistry ? 
 
 3. What does Mrs. B. consider a chemical laboratory, in its most 
 extended signification ? 
 
 I 
 
14 GENEKAL PRINCIPLES 
 
 interesting phenomena of nature, are almost all of them produced 
 by chemical powers. What Berg-man, in the introduction to his 
 history of chemistry, has said of this science, will give you a more 
 just and enlarged idea of it. The knowledge of nature may be 
 divided, he observes, into three periods. The first is that in which 
 the attention of men is occupied in learning the external forms and 
 characters of object, and this is called Natural History. In the 
 second, they consider the effect of bodies acting on each other by 
 their mechanical power, as their weight and motion^ndj|his con- 
 stitutes the science of Natural Philosophy. The third period is 
 that in which the properties and mutual action of the elementary 
 parts of bodies are investigated. This last is the science of CHEM- 
 ISTRY, and I have no doubt you will soon agree with me in think- 
 ing it the most interesting. 
 
 You may easily conceive, therefore, that without entering into 
 the minute details of practical chemistry, a woman may obtain 
 such a knowledge of the science as will not only throw an interest 
 on the common occurrences of life, but will enlarge the sphere of 
 her ideas, and render the contemplation of nature a source of de- 
 lightful instruction. 
 
 Caroline. If this is the case, I have certainly been much mista- 
 ken in the notion 1 had formed of chemistry. I own that I thought 
 it was chiefly confined to the knowledge and preparation of medi- 
 cines. 
 
 Mrs. B. That is only a branch of Chemistry which is called 
 Pharmacy, and though the s'tudy of it is, no doubt, of great im- 
 portance to the world at large, it belongs exclusively to profession- 
 al men, and is therefore the last that I should advise you to pursue. 
 
 EmMy- But did not the chemists formerly employ themselves in 
 search of the philosopher's stone, or the secret of making gold?* 
 
 * The Alchymists had in view three great objects of discovery, 
 viz. 1st. The Elixir of health: by the use of which the lives of 
 men might be protracted to any desirable length, or their mortality 
 prevented. 2nd. The universal solvent, or a liquid which should 
 dissolve every other substance. This, it was supposed, would lead 
 to the grand discovery. 3rd. The making of gold, or finding the 
 philosophers stone. That men of sound and discriminating minds 
 on other subjects, should have spent their whole lives in pursuits so 
 chimerical, is to us wonderful indeed. But our wonder ceases in 
 some degree, when we are told thai the doctrine of transmutation, 
 fcc. was founded on a Theory, which, in the 12th century, was 
 considered as plausible, as we consider many of ours at the pres- 
 ent day, viz. That a perfect metal consisted of quicksilver and sul- 
 
 4. To what author docs Mrs. B. allude, in her introductory re- 
 ft. Into how many periods do.es Bergman divide the knowledge of 
 nature ? 
 
 6. Wha* is the first ? 
 
 7. What is the second ? 
 
 8. What is the third ? 
 
 9. What is that branch of chemistry called Pharmacy ? 
 
 1 0. What three great object* had the Alchymists in view ? 
 
OF CHEMISTRY. 
 
 15 
 
 JV/r.?. B. These were a particular set of misguided philosophers, 
 who dignified themselves with the name of Alchy mists, to distinguish 
 their pursuits from those of the common chemists, whose studies 
 were confined to the knowledge of medicines. 
 
 But since that period, chemistry has undergone so complete a 
 revolution, that, from an obscure and mysterious art, it is now be- 
 come a regular and beautiful science, to which art is entirely sub- 
 servient. It is true, however, that we are indebted to the alchy- 
 mists for many very useful discoveries, which sprung from their 
 fruitless attempts to make gold, and whiqfc, undoubtedly, have pro- 
 ved of infinitely greater advantage to mankind than ail their chi- 
 merical pursuits. 
 
 The modern chemists, instead of directing their ambition to the 
 vain attempt of producing any of the original substances in na- 
 ture, rather aim at analyzing and imitating her operations, and 
 have sometimes succeeded in forming combinations, or effecting 
 decompositions, no instances of which occur in the chemistry of 
 Nature. They have little reason to regret their inability to make 
 gold, whilst, by their innumerable inventions and discoveries, they 
 have so greatly stimulated industry and facilitated labour, as pro- 
 digiously to increase the luxuries as well as the necessaries of life. 
 
 Emily. ButI do not understand by what means chemistry can 
 facilitate labour ; is not that rather the province of the mechanic ? 
 
 JMrs. B. There are many ways by which labour may be render- 
 ed more easy, independently of mechanics ; but mechanical inven- 
 tions themselves often derive their utility from a chemical princi- 
 ple. Thus that most wonderful of all machines, the Steam-engine, 
 could never have been invented without the assistance of chemis- 
 try. In agriculture, a chemical knowledge of the nature of soils, 
 and of vegetation, is highly useful ; and, in those arts which re- 
 late to the comforts and conveniences of life, it would be endless to 
 enumerate the advantages which result frQtn the study of this sci- 
 ence. 
 
 Caroline. But pray, tell us more precisely in what manner the 
 discoveries of chemists have proved so beneficial to society ? 
 
 phur ; these, when pure and united, formed gold. That all other 
 metals contained a quantity of dross, which prevented the parti- 
 cles of these two substances from uniting. If, therefore, this dross 
 could be got rid of in the other metals, gold would be the result. 
 They believed also, that nature herself favoured this operation. 
 Thus Friar Roger Bacon, in his Mirror of Alchymy, says, " I must 
 tell you, that nature alwaies intendeth and striueth to the perfec- 
 tion of gold ; but many accidents comming between, change the 
 mettalls," &c. See his Book printed in 1597, chap. ii. C. 
 
 11. Who were formerly called Alchymists ? 
 
 12. Why did they assume this name ? 
 
 13. What is the object of modern chemistry ? 
 
 14. Can chemistry afford any assistance in manual labor ? 
 
 15. What are instances of it? 
 
 16. How is chemistry serviceable in agriculture ? 
 
 17. What opinion is said in the note, to have prevailed in tkel2th 
 century in relation to metals? 
 
16 GENERAL PRINCIPLES 
 
 Mrs. B. That would be an injudicious anticipation ; for you 
 would not comprehend the nature of such discoveries and useful 
 applications, as well as you will do hereafter. Without a due re- 
 gard to method, we cannot expect to make any progress in chem- 
 istry. I wish to direct your observations chiefly to the chemical 
 operations of Nature ; but those of art are certainly of too high 
 importance to pass unnoticed. We shall therefore allow them also 
 some share of our attention. 
 
 Emily. Well, then, let us now set to work regularly. I am very 
 anxious to begin. <p 
 
 Mrs. B. The object of chemistry is to obtain a knowledge of the 
 intimate nature of bodies, and their mutual action on each oth- 
 er. You find, therefore, Caroline, that this is no narrow or confin- 
 ed science, which comprehends every thing material within our 
 sphere. 
 
 Caroline. On the contrary, it must be inexhaustible ; and I am 
 at a loss to conceive how any proficiency can be made in a science 
 whose objects are so numerous. 
 
 Mrs. B. If every individual substance were formed of different 
 materials, the study of chemistry would, indeed, be endless ; but 
 you must observe that the various bodies in nature, are composed 
 of certain elementary principles, which are not very numerous. 
 
 Caroline. Yes ; I know that all bodies are composed of fire, air, 
 earth, and water ; I learnt that many years ago. 
 
 Mrs B. But you must now endeavour to forget it. I have al- 
 ready informed you what a great change chemistry has undergone 
 since it has become a regular science. Within these thirty years 
 especially, it has experienced an entire revolution, and it is now 
 proved that neither fire, air, earth, nor water, can be called ele- 
 mentary bodies. For an elementary body is one that has never 
 been decomposed, that is to say, separated into other substances ; 
 and fire, air, earth, and water, are all of them susceptible of de- 
 composition. 
 
 Emily. I thought that decomposing a body was dividing it into 
 its minutest parts. And if so, I do not understand why an elemen- 
 tary substance is not capable of being decomposed, as well as any 
 other. 
 
 Mrs. B. You have misconceived the idea of decomposition ; it 
 is very different from mere division. The latter simply reduces a 
 body into parts, but the former separates it into the various ingre- 
 dients, or materials, of which it is composed. If we were to take 
 a loaf of bread, and separate the several ingredients of which it is 
 made, the flour, the yeast, the salt, and the water, it would be very 
 different from cutting or crumbling the loaf into pieces. 
 
 Emily. I understand you now very well. To decompose a body 
 
 18. To what does Mrs. B. say it is necessary to pay regard in the 
 study of chemistry ? 
 
 19. Of what are the various bodies in nature composed ? 
 
 20. Of what was it formerly thought they were composed ? 
 
 2 1 . What is an elementary body ? 
 
 22. What is the difference between division and decomposition ? 
 
 23. What are instances of decomposition f 
 
OF CHEMISTRY. 17 
 
 is to separate from each other the various elementary substances 
 of which it consists. 
 
 Caroline. But flour, water, and other materials of bread, accord- 
 ing to your definition, are not elementary substances. 
 
 Mrs. B. No, rny dear; I mentioned bread rather as a familiar 
 comparison, to illustrate the idea, than as an example. 
 
 The elementary substances of which a body is composed are 
 called the constituent parts of that body ; in decomposing- it, there- 
 fore, we separate its constituent parts. If, on the contrary, we di- 
 vide a body by chopping it to pieces, or e\TOby grinding or pound- 
 ing it to the finest powder, each of these small particles will still 
 consist of a portion of the several constituent parts of the whole 
 body : these are called the integrant parts ; do you understand the 
 difference ? 
 
 Emily. Yes, I think perfectly. We decompose a body into its 
 constituent parts ; and divide it into its integrant parts. 
 
 Mrs. B. Exactly so. If, therefore, a body consists of only one 
 kind of substance, though it may be divided into its integrant parts, 
 it is not possible to decompose it. Such bodies are, therefore, call- 
 ed simple or elementary, as they are the elements of which all other 
 bodies are composed. Compound bodies are such as consist of more 
 than one of these elementary principles. 
 
 Caroline. But do not fire, air, earth, and water, consist, each of 
 them, but of one kind of substance ? 
 
 Mr*. B. JNo, my dear : they are every one of them susceptible 
 of being separated into various simple bodies. Instead of four, 
 chemists now reckon no less than fifty-seven elementary sub- 
 stances. The existence of most of these is established by the 
 clearest experiments ; but, in regard to a few of them, particularly 
 the most subtle agents of nature, heat, light, and electricity, there 
 is yet much uncertainty, and I can only give you the opinion which 
 seems most probably deduced from the latest discoveries. After 1 
 have given you a list of the e4ementary bodies, classed according 
 to their properties, we shall proceed to examine each of them sepa- 
 rately, and then consider them in their combinations with each 
 other. 
 
 Except the more general agents of nature, heat, light, and elec- 
 tricity, it would seem that the simple form of bodies is that of a 
 metal.* 
 
 Caroline. You astonish me ! I thought the metals were only one 
 
 * No actual discovery makes this probable. It is supposing that 
 all the gases, as oxygen, hydrogen, &c., as well as phosphorus, sul- 
 phur, and carbon, and several other substances are in part com- 
 posed of a metal, and yet not one among this number are known to 
 have metallic bases. C. 
 
 24. What are the constituent parts of a body ? 
 
 25. What are integrant parts of a body ? 
 
 26. How may com pound ixdies be defined ? 
 
 27. How many elementary substances are there ? 
 
 28. Concerning which three of them is there much uncertainty? 
 
 29. How is it proposed to examine these elementary substances' 1 
 
18 GENERAL PRINCIPLES 
 
 class of minerals, and that there were besides, earths, stones, rocks, 
 acids, alkalies, vapours, fluids, and the whole of the animal and 
 vegetable kingdoms. 
 
 Mrs. B. You have made a tolerably good enumeration, though I 
 fear not arranged in the most scientific order. All these bodies, 
 however, it is now strongly believed, may be ultimately resolved 
 into metallic substances.* Your surprise at this circumstance is 
 not singular, as the decomposition of some of them, which has been 
 but lately accomplished^has excited the wonder of the whole philo- 
 sophical world. 
 
 Cut to return to the list of simple bodies these being usually 
 found in combination with oxygen, I shall class them according to 
 their properties when so combined. This will, I think, facilitate 
 their future investigation. 
 
 Emily. Pray, what is oxygen ? 
 
 Mrs. B. A simple body ; at least, one that is supposed to be so, 
 as it has never been decomposed. It is always found united with 
 the negative electricity. It will be one of the first of the elementa- 
 ry bodies, whose properties I shall explain to you, and, as you will 
 soon perceive, it is one of the most important in nature ; but it 
 would be irrelevant to enter upon this subject at present. We 
 must now confine our attention to the enumeration and classifica- 
 tion of the simple bodies in general. They may be arranged as 
 follows : 
 
 CLASS I. 
 
 ^Comprehending the imponderable agents, viz : 
 
 .HEAT OR CAfcORIC, 
 LIGHT, 
 ELECTRICITY. 
 
 CLASS II. 
 
 Comprehending agents capable of uniting with inflammable 
 bodies, and in most instances of effecting their combustion. 
 
 OXYGEN, 
 
 CHLORINE, 
 
 lODlNE.f 
 
 * Three of the Alkalies only are known to have metallic bases. 
 
 f A majority of the most learned Chemists, it is believed, have 
 doubted whether Chlorine and Iodine were supporters of combus- 
 tion, any farther than they contain oxygen. C. 
 
 30. With what are simple bodies usually found in combination ? 
 
 31. With what are they always found united ? 
 
 32. Which of the elementary substances are included in the first 
 class ? 
 
 33. What ones does the second class include ? 
 
 34. What number of the alkalies are known to have metallic bases ? 
 
OF CHEMISTRY. 19 
 
 CLASS III. 
 
 Comprehending bodies capable of uniting with oxygen, and 
 forming with it various compounds. This class may be 
 divided as follows : 
 
 DIVISION 1. 
 HYDROGEN, forming water. 
 
 DIVISION 2. 
 
 Bodies forming acids. 
 NITROGEN, . . . forming nitric acid. 
 SULPHUR, .... forming sulphuric acid. 
 PHOSPHORUS, . . forming phosphoric acid. 
 CARBON, ... . . forming carbonic acid. 
 BORACIUM, . . . forming boracic acid. 
 FLUORIUM, . . . forming fluoric acid. 
 MURIATIUM, . . . forming muriatic acid. 
 
 DIVISION 3. 
 
 Metallic bodies forming alkalies. 
 POTASSIUM, . . . forming potasb. 
 
 SODIUM, forming soda. 
 
 AMMONIUM, ... forming ammonia. * 
 .LITHIUM, .... forming litbina.* 
 
 DIVISION 4. 
 
 Metallic bodies forming earths. 
 CALCIUM, or metal forming lime. 
 MAGNIUM, .... forming magnesia. 
 
 BARIUM, forming barytes, 
 
 STRONTIUM, . . . form ng strontites. 
 
 SILICIUM, forming silex, 
 
 ALUMIUM, .... forming alumine. 
 
 YTTRIUM, forming yttria. 
 
 GLUCIUM, forming glucina. 
 
 ZIRCONIUM, .... forming zirconia.f 
 THORINUM, . . . . forming thorina.}: 
 
 * This fourth alkali was discovered by Mr. Arfundson, a Swedish 
 chemist, so recently as the year 1818. 
 
 f Of all these earths, three or four only hare as yet been dis- 
 tinctly decomposed. 
 
 I Thorina, a new earth discovered by Berzelius in 1816, in a 
 mineral composed of fluoric acid and csjium. 
 
 35. What one makes the first division of the third class? 
 
 36. What ones make the second division of the third class ? 
 
 37. What ones make the third division of the third class ? 
 
 38. What ones make the fourth division of the third class ? 
 
20 GENERAL PRINCIPLES 
 
 DIVISION 5. 
 
 Metals, either naturally metallic, or yielding their oxygen to 
 carbon or to heat alone. 
 
 SUBDIVISION 1. 
 Malleable Metals. 
 
 GOLD, COPPER, 
 
 PLATINA, IRON, 
 
 PALLADIUM, LEAD, 
 
 SILVER,* NICKEL,, 
 
 MERCURY,f ZINC, 
 
 TIN, CADMIUM.^ 
 
 SUBDIV. 2. 
 
 Brittle Metals. 
 
 ARSENIC, ANTIMONY, 
 
 BISMUTH, MANGANESE, 
 
 SELENIUM,* <URANIUM, 
 
 TELLURIUM, COLUMBIUM Of TANTALIUM, 
 
 COBALT, IRIDIUM, 
 
 TUNGSTEN, OSMIUM, 
 
 MOLYBDENUM, RHODIUM, 
 
 TITANIUM, CERIUM. j] 
 
 CHROME, 
 
 * These first four metals have commonly been distinguished by 
 the appellation of perfect or noble metals, on account of their pos- 
 sessing- the characteristic properties of ductility, malleability, in- 
 alterability, and great specific gravity, in ,an eminent degree. 
 
 f Mercury, in its liquid state, cannot, of course, be called a mal- 
 leable metal. But when frozen, it possesses a considerable degree 
 of malleability. 
 
 f A metal resembling tin ; which was discovered in 1819, in an 
 ore of zinc, by Mr. Stromeyer. -. 
 
 $ Selenium was discovered a few years ago by Berzelius, in the 
 ferruginous pyrites' -of Fahlun, of Sweden. It has the metallic lus- 
 tre, but it does not conduct electricity, and is but a bad conductor 
 of caloric. It passes to the state of oxyde and acid, so that it might 
 perhaps more strictly be classed with sulphur. It may be distin- 
 guished by the smell of its vapour, which is that of horse radish. 
 
 || These last four or five metallic bodies are placed under this 
 class for the sake of arrangement, though some of their properties 
 have not been yet fully investigated. 
 
 39. What ones make the first part of the fifth division in the 
 third class ? 
 
 40. What ones make the second part of the fifth division in the 
 second class ? 
 
 41. Why have gold, platina, palladium, and silver, been tailed per- 
 fect or noble metals 3 
 
Or CHEMISTRY. 1 
 
 Caroline. Oh, what a formidable list ! you will have much to do 
 to explain it, Mrs. B. ; for I assure you it is perfectly unintelligible 
 to me, and I think rather perplexes than assists me. 
 
 Mrs. B. Do not let that alarm you, my dear ; I hope that here- 
 after this classification will appear quite clear, and, so far from 
 perplexing 1 you, will assist you in arranging- your ideas. It would 
 be in vain to attempt forming a division that would appear perfect- 
 ly clear to a beginner ; for you may easily conceive that a. chemi- 
 cal division being necessarily founded on properties with which 
 you are almost wholly unacquainted, it is impossible that you should 
 at once be able to understand its meaning or appreciate its utility. 
 
 But, before we proceed further, it will be necessary to give you 
 some idea of chemical attraction, a power on which the whole sci- 
 ence depends. 
 
 Chemical Attraction, or the Attraction of Composition, consists in 
 the peculiar tendency which bodies of a different nature have to 
 unite with each other. It is by this force that all the compositions, 
 and decompositions are effected. 
 
 Emily. What is the difference between chemical attraction, and 
 the attraction of cohesion, or of aggregation, which you often men- 
 tioned to us, in former conversations ? 
 
 Mrs. B. The attraction of cohesion exists only between particles 
 of the same nature, whether simple or compound ; thus it unites 
 the particles of a piece of metal which is a simple substance, and 
 likewise the particles of a loaf of bread which is a compound. The 
 attraction of composition, on the contrary, unites and maintains, in 
 a state of combination, particles of a dissimilar nature ; it is this 
 power that forms each of the compound particles of which bread 
 consists ; and it is by the attraction of cohesion that all these par- 
 ticles are connected into a single mass. 
 
 Emily, The attraction of cohesion, then, is the power which 
 unites the integrant particles of a body ; the attraction of compo- 
 sition that which combines the constituent particles. Is it not so ? 
 
 Mrs. B. Precisely ; and observe that the attraction of cohesion 
 unites particles of a similar nature, without changing their original 
 properties ; the result of such an union, therefore, is a body of the 
 same kind as the particles of which it is formed ; whilst the attrac- 
 tion of composition, by combining particles of a dissimilar nature, 
 produces compound bodies, quite different from any of their con- 
 stituents. If, for instance, I pour on the piece of copper, contain- 
 ed in this glass, some of this liquid (which is called nitric acid,) for 
 which it has a strong attraction, every particle of the copper will 
 combine with a particle of acid, and together they will form a new 
 body, totally different from either the copper or the acid. 
 
 42. Why do the divisions in chemical science appear unmeaning 
 to the young student ? 
 
 43. What is chemical attraction or the attraction of composition ? 
 
 44. What is the difference between chemical attraction and the 
 attraction of cohesion ? 
 
 45. What is the experiment mentioned as illustrating chemical 
 attraction ? 
 
 46. What will be the result if copper and nitric acid are put tch 
 gether ? 
 
22 GENERAL PRINCIPLES 
 
 Do rou observe the internal commotion that already begins lo 
 take place? It is produced by the combination of these two sub- 
 stances,* and yet the acid has in this case to overcome not only the 
 resistance which the strong cohesion of the particles of copper op- 
 poses to their combination with it, but also to overcome the weight 
 of the copper, which makes it sink to the bottom of the glass, and 
 prevents the acid from having such free access lo it as it would if 
 the metal were suspended in the liquid. 
 
 Emily, The acid seems, however, to overcome both these ob- 
 stacles without difficulty, and appears to be very rapidly dissolving 
 the copper. 
 
 Mrs. B. By this means it reduces the copper into more minute 
 parts than could possibly be done by any mechanical power. But 
 as the acid can act only on the surface of the metal, it will be some 
 time before the union of these two bodies will be completed. 
 
 You may, however, already see how totally different this com- 
 pound is from either of its ingredients. It is neither colourless, 
 like the acid, nor hard, heavy, and yellow like the copper. If you 
 tasted it, you would no longer perceive the sourness of the acid. 
 It has at present the appearance of a blue liquid ; but when the 
 union is completed, and the watt>r with which the acid is diluted, is 
 ^evaporated, the compound will assume the form of regular crystals 
 of a fine blue colour, and perfectly transparent.! Of these 1 can 
 jshowyou a specimen, as I have prepared some for that purpose. 
 
 Caroline. How beautiful they are, in color, form, and transpa- 
 rency ! 
 
 Emily. Nothing can be more striking than this example of chem- 
 ical attraction. 
 
 Mrs. B. The term attraction has been lately introduced into 
 chemistry as a substitute for the word affinity, to which some chem- 
 ists have objected because it originated in the vague notion that 
 chemical combinations depended upon a certain resemblance, 
 or relationship, between particles that are disposed to unite 5 and 
 
 * This hardly explains the process. A part of the oxygen of the 
 nitric acid unites with the copper; and in consequence of this loss 
 of oxygen, the nitric acid is converted into nitrous gas. It is the 
 escape of this gas through the water as it is formed that occasions 
 the commotion. C. 
 
 f These crystals are more easily obtained from a mixture of sul- 
 phuric with a little nitric acid. J 
 
 | These crystals are sulphat of copper, or what is commonly known 
 under the name of blue vitriol. C. 
 
 47. What has the acid in this experiment to overcome ? 
 
 48. On what part of a metal can the acid operate in this experi- 
 ment ? 
 
 149. What is the appearance of the compound substance thus for- 
 med: of copper and nitric acid ? 
 
 50. In the place of what term has chemical attraction been sub- 
 stituted ? 
 
 51. What is said in the note to produce the commotion when topper 
 and nitric acid are put together ? 
 
 5%. What was the objection to the term affinity ? 
 
OF CHEMISTRY. 
 
 this idea is not only imperfect, but erroneous, as it is generally 
 particles of the most dissimilar nature, that have the greatest ten- 
 dency to combine. 
 
 Caroline. Besides there seems to be no advantage in using a va- 
 riety of terms to express the same meaning ; on the contrary, it 
 creates confusion ; and as we are well acquainted with the term At- 
 traction in natural philosophy, we had better adopt it in chemistry 
 likewise. 
 
 Mrs. B. If you have a clear idea of the meaning, I shall leave 
 you at liberty to express it in the terms you prefer. For myself, 
 I confess that I think the word Attraction best suited to the gen- 
 eral law that unites the integrant particles of bodies; and Affinity 
 better adapted to that which combines the constituent particles as 
 it may convey an idea of the preference which some bodies have 
 for others, which the term attraction of composition does not so well 
 express. 
 
 Emily. So I think ; for though that preference may not result 
 from any relationship, or similitude, between the particles (as you 
 say was once supposed,) yet as it really exists, it ought to be ex- 
 pressed. 
 
 Mrs. B. Well, let it be agreed that you may use the terms affin- 
 ity, chemical attraction, and \attraction of composition, indifferently, 
 provided you recollect that they have all the same meaning. 
 
 Emily. I do not conceive how bodies can be decomposed by 
 chemical attraction. That this power should be the means of com- 
 posing them is very obvious ; but that it should at the same time, 
 produce exactly the contrary effect, appears to me very singular. 
 
 Mrs. B. To decompose a body is, you know, to separate its con- 
 stituent parts, which, as we have just observed, cannot be done by 
 mechanical means. 
 
 Emily. No ; because mechanical means separate only the inte- 
 grant particles ; they act merely against the attraction of cohesion, 
 and only divide a compound into smaller parts. 
 
 Mrs. B. The decomposition of a body is performed by chemical 
 powers. If you present to a body composed of two principles, a 
 third, which has a greater affinity for one of them than the two 
 first have for each other, it will be decomposed, that is, its two prin- 
 ciples will be separated by means of the third body. Let us call 
 two ingredients, of which the body is composed, A. and B. If we 
 present to it another ingredient C, which has a greater affinity for 
 B than that which unites A and B, it necessarily follows that B will 
 quit A to, combine with C. The new ingredient, therefore, has ef- 
 fected a decomposition of the original body A B ; A, has been left 
 alone, and a new compound B C, has been formed. 
 
 Emily. We might, I think, use the comparison of two friends, 
 wlio were very happy in each other's society, till a third disunited 
 them by the preference which one of them gave to the new comer. 
 
 53. Why does Mrs. B. prefer the term affinity ? 
 
 54. By what means cannot decomposition be effected? 
 
 55. How can a compound body be decomposed? 
 
 56. What illustration is given of the manner of decomposing a 
 body? 
 
24 GENERAL PRINCIPLES 
 
 Mrs. B. Very well. I shall now show you how this takes place 
 in chemistry. 
 
 Let us suppose that we wish to decompose the compound we have 
 just formed by the combination of the two ingredients, copper and 
 nitric acid ; we may do this by presenting to it a piece of iron, for 
 which the acid has a stronger attraction than for copper : the acid 
 will, consequently, quit the copper to combine with the iron, and 
 the copper will be what the chemists call precipitated, that is to say, 
 it will be thrown down in its separate state, and re-appear in its 
 simple form. 
 
 In order to produce this effect, I shall dip the blade of this knife 
 into the fluid, and when I take it out, you will observe that instead 
 of being wetted with a bluish liquid, like that contained in the glass, 
 it will be covered with a thin coat of copper. 
 
 Caroline. So it is really ! but then is it not the copper, instead 
 of the acid, that has combined with the iron blade? 
 
 Mrs. B. No ; you are deceived by appearances ; it is the acid 
 which combines with the iron, and in so doing, deposites or precip- 
 itates the copper on the surface of the blade. 
 
 Emily. But cannot three or more substances combine together, 
 without any of them being precipitated ? 
 
 Mrs. B. That is sometimes the case ; but, in general, the stronger 
 affinity destroys the weaker ; and it seldom happens that the at- 
 traction of several substances for each other is so equally balanced 
 as to produce such complicated compounds.* 
 
 Caroline. But pray, Mrs. B., what is the cause of the chemical 
 attraction of bodies for each other ? It appears to me more extraor- 
 dinary or unnatural, if I may use the expression, than the attraction 
 of cohesion, which unites particles of a similar nature. 
 
 Mrs B. Chemical attraction may, like that of cohesion or grav- 
 itation, be one of the powers inherent in matter, which, in our 
 present state of knowledge, admits of no other sBtisfactory explan- 
 ation than an immediate reference to a divine cause. Sir H. Da- 
 vy, however, whose important discoveries have opened such im- 
 proved views in chemistry, has suggested an hypothesis which may 
 
 * Such compounds are quite numerous. They are called triple 
 salts. Alum is one. It is composed of alumiue, potash and sul- 
 phuric acid. Tartar Emetic is another. It is composed of tartaric 
 acid, potash and antimony. C. 
 
 57. How can the substance formed of copper and nitric acid be 
 decomposed ? 
 
 58. Why will decomposition take place on the application of iron ? 
 
 59. What is precipitation ? 
 
 60. If it is the acid which combines with tbe iron, why is the 
 iron covered with a thin coat of copper in this experiment? 
 
 61. Do more than two simple substances ever unite in forming 
 the same compound ? 
 
 62. What are such compounds called ? 
 
 63. What are instances of them ? 
 
 64. What is one of the powers in addition to those mentioned by 
 philosophers which may be considered as inherent in bodies ? 
 
OF CHEMISTRY. 25 
 
 throw great light upon that science. He supposes that there are 
 two kinds of electricity, with one or other of which all bodies are 
 united. Theee we distinguish by the names of positive and nega- 
 tive electricity ; those bodies are disposed to combine, which pos- 
 sess opposite electricities, as they are brought together by the at- 
 traction which these electricities have for each other. But, whether 
 this hypothesis be altogether founded on truth or not, it is impossi- 
 ble to question the great influence of electricity in chemical com- 
 bination*. 
 
 Emily. So, that we must suppose that the two electricities al- 
 ways attract each other, and thus compel the bodies in which they 
 exist to combine r* 
 
 Caroline. And may not this be also the cause of the attraction 
 of cohesion ? 
 
 Mr. B. No, for in particles of the same nature the same elec- 
 tricities must prevail, and it is only the different or opposite elec- 
 tric fluids that attract each other. 
 
 Caroline. These electricities seem to me to be a kind of chemi- 
 cal spirit, which animates the particles of bodies, and draws them 
 together. 
 
 Emily. If it is known, then, with which of the electricities 
 bodies are united, it can be inferred which will, and which will 
 not, combine together ? 
 
 Mrs. B. Certainly. I should not omit to mention, that some 
 doubts have been entertained, whether electricity be really a ma- 
 terial agent, or whether it might not be a power inherent in bodies, 
 similar to, or perhaps identical with, attraction. 
 
 * There seems to be an objection to this theory as explained here. 
 When two bodies, one in the positive, the other in the negative 
 state of electricity are presented to each other, a mutual attraction 
 takes place, until they touch, or come within the striking distance, 
 so that the electric fluid can pass from the positive to the negative 
 body. When this is effected, they are said to be in a state of equi- 
 librium, or in the same state of electricity, and consequently nei- 
 ther attract nor repel each other. If, - therefore, chemical attrac- 
 tion depends on the different electrical states of the particles, we 
 are still at a loss how to account for their adhesion even after they 
 are united. The celebrated Kepler accounted for the affinity of 
 particles by supposing- each to have its likings and its antipathies, 
 and the power of choosing accordingly. This theory only wants 
 our belief to make it satisfactory. C. 
 
 65. How many kinds of electricity are there, and what are they 
 called? 
 
 66. What does Mrs. B. think has a great influence in effecting 
 chemical combinations ? 
 
 67. What is said of electricity in the note ? 
 
 68. What difficulty arises if we suppose chemical attraction to 
 depend upon the different electrical states of the particles ? 
 
 69. How does Kepler account for the affinity of particles ? 
 
 70. What doubts does Mrs. B. jinention as having been cnte.- 
 tained concerning electricity ? 
 
26 LIGHT. 
 
 Emily. But what, then, would be the electric spark which is 
 visible, and must, therefore, be really material ? 
 
 Mrs. B. What we call the electric spark, may, Sir H. Davy 
 says, be merely the heat and light, or fire produced by the chemical 
 combinations with which these phenomena are always connected. 
 We will not, however, enter more fully on this important subject 
 at present, but reserve the principal facts which relate to it to a 
 future conversation. 
 
 Before we part, however, I must recommend you to fix in your 
 memory the names of the simple bodies against our next interview. 
 
 CONVERSATION II. 
 
 ON LIGHT AND HEAT, OR CALORIC. 
 
 Caroline. We have learned by heart the names of all the simple 
 bodies which you have enumerated, and we are now ready to enter 
 on the examination of each of them successively. You will begin. 
 I suppose, with LIGHT i 
 
 Mrs. B. Respecting the nature of light we have little more than 
 conjectures. It is considered by most philosophers as a real sub- 
 stance immediately emanating from the sun, and from all luminous 
 bodies, from which it is projected in right lines with prodigious ve- 
 locity. Light, however, being imponderable, it cannot be confined 
 and examined by itself; and, therefore, it is to the effects it pro- 
 duces on other bodies, rather than to its immediate nature, that we 
 must direct our attention. 
 
 The connexion between light and heat is very obvious ; indeed, 
 it is such, that it is extremely difficult to examine the one inde- 
 pendently of the other. 
 
 Emily. But, is it possible to separate light from heat? I thought 
 they were only different degrees of the same thing, fire. 
 
 MrxTM? I told you that fire was not now considered as a simple 
 elemenf/ Whether light and heat be altogether different agents, or 
 not, I cannot pretend to decide ; but, in many cases, light may be 
 separated from heat. The first discovery of this was made by a 
 celebrated Swedish chemist, Scheele. Another very striking illus- 
 tration of the separation of heat and light was long after pointed 
 out by Dr. Hersche!!. This philosopher discovered that these two 
 agents were emitted- in the rays of the sun, and the heat was less 
 
 71. If electricity is a power inherent in bodies, what would the 
 electric spark be which is visible, and therefore, must be really 
 material ? 
 
 72. 'What do most philosophers consider light ? 
 
 73. With what is light obviously connected? 
 
 74- Can light and heal be separated ? 
 
 75. Who first discovered that they are not inseparably connect 
 ad? 
 
LIGHT. * ' 
 
 refrangible than light ; for, in separating the different coloured 
 rays of 1 ght by a prism, (as we did some time ago,) he found that 
 the greatest heat was beyond the spectrum, at a little distance from 
 the red rays, which, you may recollect, are the least refrangible. 
 
 Emily. I should like to try that experiment. 
 
 Mrs B. It is by no means an easy one : the heat of a ray of 
 light, refracted by a prism, is so small, that it requires a very deli- 
 cate thermometer to distinguish the difference of the degree of heat 
 within and'arilhoiil the spectrum. For in this experiment, ihe heat 
 is not totally separated from the light, each coloured ray retaining 
 a certain portion of it, though the greatest part is not sufficiently 
 refracted to fall within the spectrum. 
 
 Emily. I suppose, then, that those coloured rays which are the 
 least refrangible, retain the greatest quantity of heat ? 
 
 Mm. B. They do so 
 
 Emily. Though 1 no longer doubt that light and heat can be 
 separated, Dr Herschell's experiment does not appear to me to 
 afford sufficient proof that they are essentially different ; for light, 
 which you call a simple body, may likewise be divided into the 
 various coloured rays. 
 
 /Vrv. B. No doubt there must be some difference in the various 
 coloured rajs. Even their chemical powers are different. The 
 blue rays for instance, have the greatest effect in separating oxy- 
 gen from bodies, as was found by Scheele ; and there exists also, 
 as Dr Wollaston has shown, rays more refrangible than the blue, 
 which produce the same chemical effect, and, what is very re- 
 markable, are invisible.* 
 
 Kmily. Do \ou ihink it possible that heat may be merely a modi- 
 fication of light ? 
 
 J\lrs B. That is a supposition which, in the present state of 
 natural philosophy, can neither be positively affirmed nor denied. 
 Let us, therefore, instead of discussing theoretical points, be con- 
 tented with examining what is known respecting the chemical 
 effects of light. 
 
 Light is capable of entering into a kind of transitory union with 
 certain substances, and this is what has been called phosphores- 
 cence. Bodies that are possessed of this property, after being ex- 
 posed to the sun's rays, appear luminous in the dark. Th% shells 
 of fish, the bones of land animals, marble, limestone, and a variety 
 of combinations of earths, are more or less powerfully phosphores- 
 cent. 
 
 * The violet rays have the power of imparting the magnetic vir- 
 
 76. How can they be separated ? 
 
 77. Which of the coloured rays refracted by a prism, retain the 
 greatest quantity of heat ? 
 
 7. V hat effect have the blue rays on bodies ? 
 
 79. What power hove the violet rays as mentioned in the note ? 
 
 80. In what does the process consist . ? 
 
 81. I light capable of a union with other substances? 
 
 82. What is this union called ? 
 
 83. With what substances does this union mostly take place, io 
 the production of phosphorescence ? 
 
28 LIGHT. 
 
 Caroline. I remember being much surprised last summer with 
 the phosphorescent appearance of some pieces of rotten wood, 
 which had just been dug out of the ground ; they shone so bright 
 that I at first supposed them to be glow-worms. 
 
 Emily. And is not the light of a glow-worm of a phosphores- 
 cent nature ? 
 
 Mrs. B. It is a very remarkable instance of phosphorescence in 
 living animals ; this property, however, is not exclusively possess- 
 ed by the glow-worm. The insect called the lanthorn-fly, which 
 is peculiar to warm climates, emits light as it flies, producing in 
 the dark a remarkably sparkling appearance. But it is more com- 
 mon to see animal matter in a dead state possessed of a phosphores- 
 cent quality ; sea fish is often eminently so.* 
 
 Emily. I am rather surprised, Mrs. B., that you should have said 
 so much of the light emitted by phosphorescent bodies, without 
 taking any notice of that which is produced by burning bodies. 
 
 Mrs B. The light emitted by the latter is so intimately connect- 
 ed with the chemical history of combustion, that I must defer all 
 explanation of it till we come to the examination of that process, 
 which is one of the most interesting in chemical science. 
 
 Emily. 1 have heard that the sea has sometimes had the appear- 
 ance of being illuminated, and that the light is supposed to proceed 
 from the spawn of fishes floating on its surface. 
 
 Mrs. B. This light is probably owing to that or some other ani- 
 mal matter. Sea water has been observed to become luminous 
 from the substance of a fresh herring having been immersed in it ; 
 and certain insects, of the Medusa kind, are known to produce 
 similar effects. 
 
 But the strongest phosphorescence is produced by chemical com- 
 positions prepared for the purpose, the most common of which con- 
 sists of oyster-shells and sulphur, and is known by the name of 
 .Canton's Phosphorus. f 
 
 tue to steel. The process consists in intercepting all the rays ex- 
 cept this, and of throwing this, being first collected into a focus by 
 a lens, on the middle of a needle, and carrying it towards the ex- 
 tremity. This is to be done many times, and always towards the 
 same extremity. After a while the needle acquires polarity C. 
 
 * The phosphorescence of dead animals is owing to the escape of 
 tihosphorus in the form of phosphoretted hydrogen. This is set free 
 from its combination with the substance of the animal by the putre- 
 factive fermentation. C. 
 
 f To prepare this, mix three parts of oyster-shells calcined for an 
 hour and pulverized with one part of sulphur. This is to be rammed 
 into a crucible, which is to be kept at a red heat for one hour. On 
 
 84. What remarkable instances of phosphorescence in living ani- 
 mals are mentioned ? 
 
 85. To what is the phosphorescence of dead animals owing ? 
 
 86. How is it freed from its combination with the substance of tko 
 animal ? 
 
 87. What is the strongest phosphorescence, or how is it pro- 
 duced ? 
 
 88. How is this substance prepared ? 
 
LIGHT. 29 
 
 Light is an agent capable of producing various chemical changes. 
 It is essential to the welfare both of the animal and vegetable king- 
 doms ; for men and plants grow pale and sickly if deprived of its 
 salutary influence. It is likewise remarkable for us property of 
 destroying colour, which renders it of great consequence in the 
 process of bleaching. 
 
 Emily. Is it not singular that light, which in studying optics we 
 were taught to consider as the source and origin of colours, should 
 have also the power of destroying them ? 
 
 Caroline. It is a fact, however, which we every day experience ; 
 you know how it fades the colours of linens and silks. 
 
 Emily. Certainly. And 1 recollect that endive is made to grow 
 white instead of green, by being covered up so as to exclude the 
 light. But by what means does light produce these effects? 
 
 *Mrs. B. This I cannot attempt to explain to you until you have 
 obtained a further knowledge of chemistry. As the chemical pro- 
 perties of light can be accounted for only in their reference to com- 
 pound bodies, it would be useless to detain you any longer on this 
 subject ; we may, therefore, pass on to the examinaiion of heat, or 
 caloric, with which we are somewhat better acquainted. 
 
 HEAT and LIGHT may be always distinguished by the different 
 sensations they produce. Light effects the sense of sight , Caloric 
 that of feeling ; the one produces Vision, the other the sensation of 
 Heat. 
 
 Caloric is found to exist in a variety of forms or modifications, 
 and I think it will be best to consider it under the two following 
 heads, viz : 
 
 1. FREE OR RADIANT CALORIC. 
 
 2. COMBINED CALORIC. 
 
 The first, FREE or RADIANT CALORIC, is also called HEAT OF 
 TEMPERATURE ; it comprehends all heat which is perceptible to 
 the senses, and affects the thermometer. 
 
 " Emily. You mean, such as the heat of the sun, of fire, of candles, 
 of stoves ; in short, of every thing that burns ? 
 
 JV/r*. B. And likewise of things that do not burn, as, for instance, 
 the warmth of the body; in a word, all heat that is sensible, what- 
 ever may be its degree, or the source from which it is derived. 
 
 Caroline. What, then, are the other modifications of caloric ? It 
 
 exposing some of this to the sun's rays, it absorbs light, and will 
 shine in the dark. This shows that light can be separated from 
 beat C. 
 
 89. What does this experiment prove ? 
 
 90. To what is light essential, and what remarkable property 
 has it ? 
 
 91. What do optics teach us to consider the source and origin of 
 colours? 
 
 92. How may light and heat always be distinguished ? 
 
 93. Under what two heads is caloric considered ? 
 
 3* 
 
30 FREE CALOBIC. 
 
 must be a strange kind of heat that cannot be perceived by onr 
 senses. 
 
 Mrs. B. None of the modifications of caloric should properly be 
 called heat; for heat, strictly speaking, is the sensation produced 
 by caloric, on animated bodies ; this word, therefore, in the accu- 
 rate language of science, should be confined to express the sensa- 
 tion. But custom has adapted it likewise, to inanimate matter, and 
 we say the heat of an oven, the heat of the sun, without any reference 
 to the sensation which they are capable of exciting. 
 
 It was in order to avoid the confusion, which arose from thus con- 
 founding the cause and effect, that modern chemists adopted the 
 new word caloric, to denote the principle which produces heat ; yet 
 they do not always, in compliance with their own language, limit 
 the word heat to the expression of the sensation, since they still 
 frequently employ it in reference to the other modifications of ca- 
 loric which are quite independent of sensation.* 
 
 Caroline. But you have not yet explained to us what these other 
 modifications of caloric are. 
 
 Mrs. B. Because you are not acquainted with the properties of 
 free caloric, and you know that we have agreed to proceed with 
 regularity. 
 
 One of the most remarkable properties of free caloric is its power 
 of dilating bodies. This fluid is so extremely subtle, that it enters 
 and pervades all bodies whatever, forces itself between their parti- 
 cles, and not only separates them, but frequently drives them asun- 
 der to a considerable distance from each other. It is thus that 
 caloric dilates or expands a body so as to make it occupy a greater 
 space than it did before. 
 
 Emily. The effect it has on bodies, therefore, is directly contrary 
 to that of the attraction of cohesion ; the one draws the particles 
 together, the other drives them asunder. 
 
 Mrs. B. Precisely. There is a continual struggle between the 
 attraction of aggregation, and the expansive power of caloric ; 
 and from the action of these two opposite forces, result all the va- 
 rious forms of matter, or degrees of consistence, from the solid to 
 the liquid and aeriform state. And, accordingly, we find that most 
 bodies are capable of passing from one of these forms to the other, 
 
 * If 1 touch a body at a higher temperature than my hand, I im- 
 mediately receive a quantity of caloric from it, and at the same 
 instant feel the sensation called heat. The caloric then is the 
 cause of this sensation, and heat the effect of caloric passing into 
 my hand. C. 
 
 <94. What is free or radiant caloric ? 
 1-5, What is heat, strictly speaking ? 
 
 36. What is the difference between caloric and heat, as the terms 
 are used by chemists ? 
 
 97. What illustration of this is given in the note ? 
 
 98. What is one of the most remarkable properties of free ca- 
 loric? 
 
 99. What two forces are in direct opposition to each other ? 
 
 100. From what result all the various forms of matter, or degrees 
 pf consistence in bodies ? 
 
FREE CALORIC. 31 
 
 merely in consequence of their receiving different quantities of 
 caloric. 
 
 Caroline. That is very curious ; but I think I understand the 
 reason of it. If a great quantity of caloric is added to a solid body, 
 it introduces itself between the particles in such a manner as to 
 overcome, in a considerable degree, the attraction of cohesion ; 
 and the body, from a solid, is then converted into a fluid. 
 
 Mrs. B. This is the case whenever a body is fused or melted ; but 
 if you add caloric to a liquid, can you tell me what is the consequence ? 
 
 Caroline. The caloric forces itself in greater abundance between 
 the particles of the fluid, and drives them to such a distance from 
 each other, that their attraction of aggregation is wholly destroy- 
 ed ; the Ifquid is then transformed into vapour. 
 
 Mrs. B. Very well ; and this is precisely the case with boiling 
 water, when it is converted into steam or vapour, and with all bod- 
 ies that assume an aeriform stale. 
 
 Emily. I do not well understand the word aeriform. 
 
 Mrs. B; Any elastic fluid whatever ; whether it be merely va- 
 pour or permanent air, is called aeriform. 
 
 But each of these various states, solid, liquid, and aeriform, ad- 
 mit of different degrees of density, or consistence, still arising 
 (chiefly at least) from the different quantities of caloric the bodies 
 contain. Solids are of various degrees of density, from that of 
 gold, to that of a thin jelly. Liquids, from the consistence of melt- 
 ed glue, or melted metals, to that of ether, which is the lightest of 
 ail liquids. The different elastic fluids (with which you are not yet 
 acquainted) are susceptible of no less variety in their degrees of 
 density. 
 
 Emily. But does not every individual body also admit of different 
 degrees of consistence, without changing its state ? 
 
 Mrs. B. Undoubtedly ; and this I can immediately show you by 
 a very simple experiment. This piece of iron now exactly fits the 
 frame, or ring, made to receive it; but if heated red hot, it will no 
 longer do so, for its dimensions will be so much increased by the 
 caloric that has penetrated into it, that it will be much too large 
 for the frame. 
 
 The iron is now red hot ; by applying it to the frame, we shall 
 see how much it is dilated. 
 
 Emily. Considerably so indeed ! 1 knew that heat had this effect 
 on bodies, but did not imagine that it could be made so conspicuous. 
 
 101. What causes bodies to pass from one of these forms to th 
 other? 
 
 102. How would you explain the manner in which a solid is con- 
 verted into a liquid ? 
 
 103. If we add caloric to a liquid, what is the consequence ? 
 
 104. What is meant by the word aeriform ? 
 
 105. From what do the different degrees of density or consist- 
 ence arise? 
 
 106. Which is the lightest of all liquids ? 
 
 107. Are the elastic fluids susceptible of various degrees of den* 
 sity ? 
 
 108. Do bodies admit of different degrees of consistence without 
 changing their state ? 
 
FREE CALORIC. 
 
 Mrs. B. By means of this instrument (called a Pyrometer) we 
 
 may estimate, iu the most exact manner, the various dilatations of 
 
 any solid body by heat. The body we are now going to submit to 
 
 trial is this snail iron bar; i fix it to this apparatus, and then 
 
 Fig. ' Pyrometer. 
 
 I 
 
 A A, Bar of Metal. 1 2 3, Lamps burning. B B, Wheel work. C, Index. 
 
 heat it by lighting the three lamps beneath it ; when the bar ex- 
 pands, it increases in length as well as thickness; and, as one end 
 communicates with this wheel work, whilst the other end is fixed 
 and imm veable, no sooner does it begin to dilate than it presses 
 against the wheel worn, and sets in motion the index, which points 
 out the decrees of dilatation on the dial-plate. 
 
 Emily. This is, indeed, a very curious instrument ; hut I do not 
 understand the use of the wheels ; would it not be more simple, 
 and answer the purpose equally well, if the bar in dilating, pressed 
 against the index, and put it in motion without the intervention of 
 the wheels ? 
 
 .MM. B The use of the wheels is merely to multiply the motion, 
 and therefore render the effect of the caloric more obvious : for if 
 the index moved no more than the bar increased in length, its mo- 
 tion would scarcely be perceptible: but by means of the wheels 
 it moves in a much greater proportion, which therefore renders the 
 variations far more conspicuous. 
 
 By submitting different bodies to the test of the pyrometer, it is 
 found that they are far from dilating in the same proportion. Dif- 
 ferent metals expand in different degrees, an-1 other kinds of solid 
 bodies vary still rnor? in this respect. But this different suscepti- 
 bility of dilatation is still more remarkable in fluids than in solid 
 bodies as I shall show you. I have here two glass tubes, terminated 
 at one end by large bulbs. We shall fill the bulbs, the one with 
 
 109. What experiment proves that they do ? 
 
 1 10. What is the use of the Pyrometer? " 
 
 111. How would you explain figure I ? 
 
 1 12. What is the use of wheels in his instrument? 
 
 1 13. Does caloric expand all bodies in the same degree? 
 
 1 14. Which are most susceptible of dilatation, fluids or solids ? 
 
FREE CALORIC. 
 
 33 
 
 spirit of wiae, the other with water. 1 have colored both liquids, 
 in order that the effect maybe more conspicuous. The spirit of 
 wine, you see, dilates by the warmth of my hand as I hold the bulb.* 
 Emily. It certainly does, for I see it is rising into the tube. But 
 water it seems, is not so easily effected by heat ; for scarcely any 
 change is produced on it by the warmth of the hand. 
 
 Fig. 2. Mrs B. True ; we shall now plunge 
 
 the bulbs into hot water, and you will 
 see both liquids rise in the tubes ; but the 
 spirit of wine will ascend highest. 
 
 Caroline. How rapidly it expands ! 
 Now it has nearly reached the tube, 
 though the water has hardly begun to 
 rise. 
 
 Emily. The water now begins to dilate. 
 Are not these glass tubes, with liquids 
 rising within them, very like thermome- 
 ters ? 
 
 Mrs. B. A thermometer is construct- 
 ed exactly on the same principle, and 
 these tubes require only a scale to an- 
 swer the purpose of thermometers ; but 
 they would be rather awkward in their 
 dimensions. The tubes and bulbs of 
 thermometers, though of various sizes, 
 are in general much smaller than these ; 
 tne tube t00 ' is hermeticallyf closed, and 
 the air excluded from it. The fluid 
 most generally used in thermometers, is 
 BB Gia,... of mercury, commonly called quicksilver, 
 which hey ar.\^m". e d the dilatations and contractions of which 
 correspond more exactly to the additions 
 and subtractions of caloric, than those of any other fluid. 
 
 Caroline. Yet I have often seen coloured spirit of wine used in 
 thermometers. 
 
 Mrs. B. The expansions and contractions of that liquid are not 
 quite so uniform as those of mercury ; but in cases in which it is 
 
 * In the absence of glass tubes terminated by bulbs, procure a 
 pair of tin canisters, three inches high and two wide, soldered up all 
 round. In the middle of the top of each, have inserted a circular 
 tin spout, and into these cement glass tubes about twelve inches 
 high. These will answer every purpose. C. 
 
 f The tube is closed by holding the end over a spirit lamp until 
 the glass is melted. This word is derived from Hermes, the Greek 
 name for mercury. He is said to have been the inventer of chem- 
 istry ; hence this is sometimes called the Hermetic art, and hermet- 
 ically, or chemically closed, is closed by heat or melting. C. 
 
 115. What is the object of figure 2 ? 
 
 116. What fluid is generally used in thermometers? 
 
 117. Hw do the expansions and contractions of the spirits of 
 wine compare with those of mercury f 
 
34 FREE CALORIC. , 
 
 not requisite to ascertain the temperature with great precision, 
 spirit of wine will answer the purpose equally well, an 1 i ideed in 
 some respects better, as the expansion of the latter is greater, and 
 there r ore more conspicuous. This fluid is used likewise n situations 
 and experiments in which mercury would be frozen ; for mercury 
 becomes a solid body, like a piece of lead or any other metal, at 
 a certain degree of cold ; but no degree of cold has ever been 
 known to freeze spirit of wine * 
 
 A thermometer, therefore, consists of a tube with a bulb, such as 
 you see here, containing a fluid whose degrees of dilatation and 
 contraction are indicated by a scale to which the tube is fixed. 
 The degree which indicates the boiling point simply means that 
 when the fluid is sufficiently dilated to rise to this point, the heat is 
 such that water exposed to the same temperature will boil. When 
 on the other hand, the fluid is so much condensed as to sink to the 
 freezing point, we know that water will freeze al that temperature. 
 The extreme points of the scales are not the ^arne in all thermome- 
 ters, nor are the degrees always divided in the same manner. In 
 different countries philosophers have chosen to adopt different 
 scales and divisions. The two thermometers most used are those 
 of Fahrenheit, and of Reaumur; the first is generally preferred by 
 the English, the latter by the French. 
 
 Emily. The variety of scale must be very inconvenient, and I 
 should ihink liable 'o occasion confusion, when French and Eng- 
 lish exneriments ar< compared. 
 
 Mrs. B. The inconvenience is but very trifling, because the dif- 
 ferent gradations of the scales do not effect the princ pie upon 
 which thermometers are constructed. When we know, for in- 
 stance, that Fahrenheit's scale is divided into 212 degrees, in which 
 32 corresponds with iKe freezing point, and 2i2 with the point of 
 boiling w.iter ; and that Reaumur's is divided only into 80 degrees, 
 in which O c denotes the freezing point, and 80 that of boiling 
 water, it is easy to compare the two scales together, and reduce 
 the one into the other. But, for greater convenience, thermome- 
 ters are sometimes constructed with both these scales : one on 
 either side of the tuhe : so that the correspondence of the different 
 degrees of the two scales is thus instantly seen. Here is one of 
 these scales, (Tig. 3 ee next page,) by which yon can at once per- 
 ceive that each degree of Reaumur's corresponds to "2 1-4 of Fah- 
 renheit's division. Rut 1 believe the French have, of late, given 
 the preference to w v >al they call the centigrade scale, in which the 
 space between the freezing and the boiling point is divided into 100 
 degrees. 
 
 * Spirit of wine is stated to have been frozen in England by some 
 process which the author has preferred to keep secret. C. 
 
 _____ & 
 
 When is spirit of wine used ? 
 
 1 18. How would you describe a thermometer ? 
 
 1 19. What two thermometers are mostly used ? 
 1-20. How are thev graduated ? 
 
 121. What is the temperature of boiling water? 
 
 122. To what scale have the French been said to have preference ?' 
 
FREE CALORIC. 
 
 35 
 
 Fig. 3. 
 
 Tkerrnnmeter. 
 
 point 2io_E 
 
 Caroline. That seems to me 
 the most reasonable division, 
 and 1 cannot guess why the freez- 
 ing point is called 3/, or what 
 advantage is derived from it. 
 
 Mrs. B. There really is no 
 advantage in it ; and it originat- 
 ed in a mistaken opinion of the 
 instrument-maker, Fahrenheit, 
 who first constructed these ther- 
 mometers. He mixed snow and 
 salt together, and produced by 
 that means a degree of cold 
 which he concluded wasthegreat- 
 est possible, and therefore made 
 his scale begin from that point. 
 Between that and boiling water 
 he made 212 degrees, and the 
 freezing point was found to be 
 at 32. 
 
 Emily. Are spirit of wine, and 
 mercury, the only liquids used 
 in the construction of thermom- 
 eters ? 
 
 Mrs. B. I believe they are the 
 only liquids now in use, though 
 some others, such as linseed oil, 
 would make tolerable thermom- 
 eters ; but for experiments in 
 which a rery quick and delicate 
 test of the changes of tempera- 
 ture is required, air is the fluid 
 sometimes employed. The bulb 
 of air thermometers is filled with 
 common air only, and its expan- 
 sion aud contraction are indicat- 
 ed by a small drop of any col- 
 oured liquor, which is suspended 
 within the tube, and moves up 
 and down, according as the air 
 within the bulb and tube expands 
 or contracts. But in general, 
 air thermometers, however sen- 
 sible to changes of temperature, 
 are by no means accurate in 
 their indications. 
 
 I can, however, show you an air thermometer of a very peculiar 
 construction, which is remarkably well adapted for some chemical 
 
 123. Why was the freezing point in Fahrenheit's thermometer 
 fixed at 32 degrees ? 
 
 124. How are air thermometers constructed ? 
 
36 
 
 FREE CALORIC. 
 
 experiments, as it is equally delicate and accurate in its indica- 
 tions.* 
 
 Differential Thermom- t Caroline - It looks like a.doubk thermora- 
 , eter reversed, the tube being bent, and hav- 
 
 ing a large bulb at each of its extremities. 
 
 Emily. Why do you call it an air thermom- 
 eter ; the tube contains a colored liquid ? 
 
 Mrs. B. But observe that the bulbs are 
 filled with air, the liquid being confined to 
 a portion of the tube, and answering only 
 the purpose of showing, by its motion in the 
 tube, the comparative dilatation or contrac- 
 tion of the air within the btilbs, which afford 
 an indication of their relative temperature. 
 Thus if you heat the bulb A, by the warmth 
 of your hand, the fluid will rise towards the 
 bulb B, and the contrary will happen if you 
 reverse the experiment. 
 
 But if, on the contrary, both tubes are of 
 the same temperature, as is the case now, the 
 colored liquid, suffering an equal pressure 
 on each side, no change of level takes place. 
 Caroline. This instrument appears, indeed, 
 uncommonly delicate. The fluid is set in 
 motion by the mere approach of my hand. 
 
 Mrs. B. You must observe, however, that 
 this thermometer cannot indicate the tem- 
 perature of any particular body, or of the 
 medium in which it is immersed ; it serves only to point out the dif- 
 ference of temperature between the two bulbs, when placed under 
 different circumstances. For this reason it has been called differ- 
 ential thermometer. You will see hereafter to what particular 
 purposes this instrument applies. 
 
 Emily. But do common thermometers indicate the exact quan- 
 tity of caloric contained either in the atmosphere, or in any body 
 with which they are in contact ?f 
 
 * Students in chemistry may amuse themselves with air ther- 
 mometers of their own construction. Procure a flat vial or ink- 
 stand with a wide mouth ; also, a broken thermometer tube, the 
 bulb being entire. Fit a cork air tight to the vial, and pierce it 
 in the middle with a hot iron to admit the tube. Fill the vial about 
 half full of some colored liquid. Warm the bulb of the tube by 
 holding it in the hand, and in this state introduce the small end 
 through the cork neatly to the bottom of the vial. The hand be- 
 ing removed from the bulb, the fluid will rise in the tube. The flu- 
 id will afterwards rise or fall as heat is applied to the vial or bulb. 
 C. 
 
 f The thermometer indicates the exact quantity of free caloric. 
 
 125. What is said of air thermometers in the note ? 
 
 126. Which figure represents an air thermometer ? 
 
 127. Why has the air thermometer been called the differential 
 thermometer ? 
 
FREE CALORIC. <T, 
 
 Jlrs. X. No : first, because there are other modifications of ca 
 ioric which do not affect the thermometer ; and, secondly, because 
 the temperature of a body, as indicated by the thermometer, is 
 only relative. When, for instance, the thermometer remains sta- 
 tionary at the freezing point, we know that the atmosphere, (or 
 medium in which it is placed, whatever it may be) is as cold as 
 freezing water ; and when it stands at the boiling point, we know 
 that this medium is as hot as boiling water ; but we do not know 
 the positive quantity of heat contained either in freezing or boiling 
 water, any more than we know the real extremes of heat and cold ; 
 and consequently we cannot determine that of the body in which 
 the thermometer is placed.' 
 
 Caroline. I do not quite understand this explanation. 
 
 J\lrs. B. Let us compare a thermometer to a well, in which the 
 water rises to different heights, according as it is more or less sup 
 plied by the spring which feeds it ; if the depth of the well isun- 
 tathoraable. it must be impossible to know the absolute quantity oJ 
 water it contains ; yet we can with the greatest accuracy measure 
 the number of feet the water has risen or fallen in the well at any- 
 time, and consequently know the precise quantity of its increase 
 or diminution, without having the least knowledge of the whole 
 quantity of water it contains.* 
 
 Caroline. Now I comprehend it very well ; nothing appears to 
 me to explain a thing so clear as a comparison. 
 
 Emily. But will thermometers bear any degree of heat ? 
 
 .Mrs. B. No ; for if the temperature were much above the high- 
 est degree marked on the scale of the thermometer, the mercury 
 \vould burst the tube in an attempt to ascend. And at any rate, 
 no thermometer can be applied to temperatures higher than the 
 boiling point of the liquid used in its construction, for the steam, 
 on the liquid beginning to boil, would burst the tube. In furna- 
 ces, or whenever any very high temperature is to be measured, ;i 
 
 present at the time and place of the experiment. Thus if a cer 
 iain quantity of heat is required to raise the mercury 20, doublf 
 this quantity will raise it to 40. All bodies contain a quantity oi 
 heat not appreciable by the thermometer, or sensible to the touch. 
 This is called fixed or latent beat. This can sometimes be set free, 
 as when we hammer a piece of cold iron it becomes hot. Thu? 
 i he latent caloric is squeezed out of the iron by the contraction oi 
 tts pores under the hammer, and it then becomes free caloric. C 
 
 * This passage may be expounded as follows. The unfathoma- 
 ble depth of the well signifies the absolute quantity of caloric, 
 and which the thermometer does not measure ; because all bodies 
 
 128. Do common thermometers indicate the exact quantity of 
 caloric contained cither in the atmosphere, or in any body, with 
 which they come in contact ? 
 
 129. Why do they not ? 
 
 130. What comparison is made between a well and a thermom 
 ter ? 
 
 131. Why might not thermometers be applied to temperature . 
 higher than the boiling, point of the liquid used in their construe 
 'ion ? 
 
 t 
 
38 FREE CALORIC. 
 
 , pyrometer, invented by Wedgwood, is used for that purpose, li 
 is nrmcie of a certain composition of baked clay, which has the pe- 
 culiar property of contracting by heat, so that the degree of con- 
 traction of this substance indicates the temperature to which it has 
 been exposed. 
 
 Emily But is it possible for a body to contract by heat ? 1 thought 
 that heat dilated all bodies whatever. 
 
 JtfVv B. This is not an exception to the rule. You must recol- 
 lect that the bulk of the clay is not compared, whilst hot, with that 
 which it has when cold ; but it is from the change which the clay 
 has undergone by having been heated, that the indications of tbiV 
 instrument are derived. This change consists in a beginning fu- 
 sion, which tends to unite the particles of clay more closely, thus 
 rendering it less pervious or spungy.* 
 
 Ciayis to be considered as a spungy body, abounding in inter- 
 stices or pores, from its having contained water when soft. These 
 interstices a' e by heat lessened, and would by extreme heat be en- 
 tirely obliterated 
 
 Caroline And how do you ascertain he degrees of contraction 
 of Wedgwood's pyrometer ? 
 
 Mrs B. The dimensions of the piece of clay are measured by a 
 scale graduated on the side of a tapered groove, formed in a brass 
 ruler ; the more the clay is contracted by the heat, the further it 
 will descend into the narrow part of the tube. 
 
 Before.wequit the subject of expansion,! must observe to you, 
 that, as liquids expand more readily than solids, so elastic fluids, 
 wiftther air or vapour, are the most expansible of all bodies 
 
 If may appear extraordinary, that all elastic fluids whatever, un- 
 dergo the same degree of expansion from equal argumentation oi 
 temperature. 
 
 Emily. I suppose, then, that all elastic fluids are of the same den- 
 sity. 
 
 Jttrs. B. Very far from it ; they vary in density, more than ei- 
 ther liquids or solids. The uniformity of their expansibility, which 
 at first may appear singular, is, however, readily accounted for. 
 For if the different susceptibilities of expansion of bodies arise 
 from their various degrees of attraction of cohesion, no such dif- 
 
 bowever cold, still contain caloric. Thus mercury freezes at 40 
 below zero, but still contains caloric, and so on. The rising and 
 falling of the water signifies the greater or less quantity of free ca- 
 loric as indicated by the thermome!er.-C. 
 
 * According to the calculations of Saussure, the temperature 
 necessary to melt this clay is 1575 Wedgwood, which is a degree 
 of beat greatly beyond our common furnaces. It is therefore most 
 probable that the clay contracts at lower temperatures by the loss 
 of moisture. C. 
 
 132. Do all bodies however cold contain caloric ? 
 
 133. In what manner is it that clay appears to contract by heal : 
 
 134. What bodies are most expansible ? 
 
 135. Are all elastic fluids equally expanded from equal augmen- 
 fations of temperature ? 
 
 136. Are all elastic fluids of the same density ? 
 
FREE CALORIC. 30 
 
 Jbrencecan be expected in elastic fluids, since in these the attrac- 
 tion of cohesion does not exist, their particles being on the contrary 
 possessed of an elastic or repulsive power ; they will therefore all 
 be equally expanded by equal degrees of caloric. 
 
 Emily. True; as there is no power opposed to tbe expansive 
 ibrce of caloric in elastic bodies, its effect must be the same in all 
 of them 
 
 Mrs. B. Let us now proceed to examine the other properties ot 
 free caloric. 
 
 Free caloric always tends to diffuse itself equally ; that is to say, 
 when two bodies are of different temperatures, the warmer gradu- 
 ally parts with its heat to the colder, till they are both brought to 
 the same temperaure. Thus, when a thermometer is applied 'oa 
 hot body, it receives caloric ; when to a coKJ one, it commuicates 
 part of its own caloric, and this communication continues until the 
 thermometer and the body arrive at the same temperature. 
 
 Emily, ('old, then, is nothing but a negative quality, simply im- 
 plying the absence of heat 
 
 Mrs. B. Not the total absence, but a diminution of heat ; for we 
 know of no body in which some caloric may not he discovered. 
 
 Caroline. But when I lay my hand on this marble table, I feel 
 it positively cold, and cannot conceive that there is any caloric in 
 it. 
 
 Mrs. B. The cold you experience consists in the loss of caloric 
 that your hand sustains in an attempt to bring its temperature to 
 an equilibrium with the marble. If yon lay a piece of ice upon it, 
 you will find that a contrary effect will take place ; the ice wil! be 
 melted by the heat it abstracts from the marble A 
 
 Camline. Is it not in this case the air of the room, which bemg 
 warmer than the marble; melts the ice ? 
 
 Mrs. B. The air certainly acts on the surface which is exposed 
 to it, but the table melts that part with which it is in contact. 
 
 Caroline. But why does caloric tend to an equilibrium ? It can- 
 not he on the same principle as other fluids, since it has no weight . 
 Mr*. B. Very true, Caroline, that is an excellent objection. 
 You might also with some propriety, object to the it-r.n (<['<) ''-bri- 
 um bemg applied to a body that is without weight : but I know of 
 no expression that would explain my meaning so well. You must 
 consider it, however, in a figurative rather Uian a literal sen-e its 
 strict meaning is an equal diffusion. We cannot, indeed, well say 
 by what power it diffuses itself equally, though it is not surprising 
 that it should go from the parts which have the most to tho^e which 
 have the least The subject is best explained by a h^o, v su^gcs- 
 
 137. How then can their uniformity of expansibility be account- 
 ed for f 
 
 138 How does caloric tend to diffuse itself ? 
 139. How is this illustrated by a thermometer ? 
 140 What is cold ? 
 
 141. Do we know of any substance in which some caloric may 
 not be found ? 
 
 142. Why do some bodies feel cold if we lay ou-- hand upon them. 
 
 143. What objection is there to the term equilibrium, when 
 speaking of the equal diffusion of caloric ? 
 
10 FREE CALORIC. 
 
 led by Professor Prevost of Geneva, which is now, 1 believe, ges 
 crally adopted. 
 
 According to this theory, caloric is composed of particles per 
 iectly separate from each other, every one of which moves with a 
 rapid velocity in a certain direction. These directions vary as much 
 as imagination can conceive, the result of which is, that there are 
 rays or lines of these particles moving with immense velocity in 
 every possihle direction. Caloric is thus universally diffused, sc 
 that when any portion of space happens to be in the neighbourhood 
 of another, which contains more caloric, the colder portion re 
 ceives a quantity of calorific rays from the latter, sufficient to re 
 store an equilibrium of temperature. This radiation does not oniv 
 take place in free space, but extends also to bodies of every kind.* 
 Thus you may suppose all bodies whatever, constantly radiating ca- 
 loric ; those that are of the same temperature give out and absorb 
 equal quantities, so that no variation of temperature is produced in 
 them ; but when one body contains more free caloric than anoth- 
 er, the exchange is always in favour of the colder bod}^ until an 
 equilibrium is effected ; this you find to be the case when the mar- 
 ble table cooled your hand, and again when it melted the ice. 
 
 Caroline. This reciprocal radiation suprises me extremely ; I 
 thought, from what you first said, that the hotter bodies alone 
 emitted rays of caloric which were absorbed by the colder ; for ir 
 seems unnatural that a hot body should receive any caloric from o 
 cold one, even though it should return a great quantity. 
 
 Mrs. B. It may at first appear so, but it is no more extraordina- 
 ry than that a candle should send forth rays of light to the sun, 
 ivhjch, you know, must necessarily happen. 
 
 Caroline. Well Mrs. B., I believe that 1 must give up the point. 
 But I wish I could see these rays of caloric ; I should then have- 
 greater faith in them. 
 
 Mrs. B. Will you give no credit to any sense but that of sight : 
 You may feel the'rays of caloric which you receive from any body 
 of a temperature higher than your own ; the loss of the calorie 
 you part with in return, it is true, is not perceptible ; for as you 
 gain more than you lose, instead of suffering a diminution, you 
 are really making an acquisition of caloric. It is, therefore, only 
 when you are parting with it to a body of a lower temperature, 
 that you are sensible of the sensation of cold; because you then sus- 
 tain an absolute loss of caloric. 
 
 *This is true when applied to inanimate matter. But if a livetiu- 
 imal is exposed to a degree of heat above the temperature of its 
 own body, i( has the power of resistance ; and though the heat b< 
 100 degrees above that of the animal, it scarcely affects its temper- 
 ature.C. 
 
 144. What is professor Prevosl's theory of caloric ? 
 
 145. What remark respecting live animals u made in the note ? 
 
 146. Do all bodies constantly radiate caloric ? 
 
 147. If one body contain more free caloric than another, what i< 
 the consequence ? 
 
 148 Does a hot body receive caloric from a cold one ? 
 149. How does Mrs. B. answer the objection to the reciprocal 
 radiation of caloric between bodies of different temperature ' 
 ! M) What occasions the sensation of cold J 
 
FREE CALORIC. 
 
 41 
 
 Emily. And in this case we cannot be sensible of the small 
 juantity of heat we receive in exchange from the colder body, be- 
 cause if serves only to diminish the loss. 
 
 Mrs. B. Very well, indeed, Emily. Professor Pictet, of Gene- 
 va, has made some very interesting experiments, which prove not 
 only that caloric radiates from all bodies whatever, but ttattthflie 
 rays may be reflected, according to the laws of optics, in the same 
 manner as light. I shall repeat these experiments before you, hav- 
 ing procured mirrors* fit for the purpose ; and it will afford us an 
 opportunity of using the differential thermometer, which is partic- 
 ularly well adapted for these experiments. I place an iron bullet. 
 
 Fig. 5. 
 Mr. PicteFs Apparatus for the Reflection of Heat , 
 
 A A, and B B, Concave Mirror*, fixed on itands C, Heated Bul'et, placed in the d.cut it the 
 Mirror A. D, Thermometer, with its bulb placed in the 'ecus of the Mirror B. 234, rays 01 
 Caloric radiating from the Bullet, and falling on the Mirror A. 5673. the tame rays reflected 
 from the Mirror A to the .Mirror B. 9 10 1 1 12, the same rays reflected by the Mirror B. to the 
 Thejmometer. 
 
 about two inches in diameter, and heated to a degree not sufficient 
 to render it luminous, in the focus of this large metallic concave 
 mirror. The rays of heat which fall on this mirror are reflected, 
 agreeably to the property of concave mirrors, in a parallel direc- 
 tion, so as to fall on a similar mirror, which, you see, is placed op- 
 posite to the first, at the distance of about ten feet; thence the 
 rays converge to the focus of the second mirror, in which I place 
 one of the bulbs of this thermometer. Now, observe in what man- 
 ner it is affected by the caloric which is reflected on it from the 
 heated bullet The air is dilated in the bulb which we placed in 
 the focus of the mirror, and the liquor rises considerably in the op 
 posite leg. 
 
 * Mirrors made of common tinned iron show this experiment 
 very well. They may be 10 or 12 inches in diameter, and about 2 
 inches deep. They must be planished with a hammer having a 
 convex face, and afterwards polished with a piece of buckskin, and 
 -a little whiting. C. 
 
 151. What do Professor Pictet's experiments on caloric prove ? 
 
 152. What is the object of figure 5 ? 
 
 153. How would you explain the experiment represented in tlm 
 figure ? 
 
 4* 
 
12 FREE CALORIC. 
 
 Emily. But would not the same effect take place, if the rays 01 
 caloric from the heated bullet fell directly on the thermometer, 
 without the assistance of the mirrors ? 
 
 Mrs. B. The effect would in that case be so trifling-, at the dis- 
 tance at which the bullet and the thermometer are from each oth- 
 er, that it would be almost imperceptible. The mirrors, you 
 know, greatly increase the effect, by collecting a large quantity of 
 rays in a focus ; place your hand in the focus of the mirror, and you 
 will fed it much hotter there than when you remove it nearer to 
 the bullet. 
 
 Emily. That is very true ; it appears extremely singular to feel 
 the heat diminish in approaching the body from wnich it proceeds. 
 
 Caroline. v And the mirror which produces so much heat, by con- 
 verging the rays, is itself quite cold. 
 
 Mrs, B. Thfc same number of rays that are dispersed over the 
 surface of the mirror are collected by it into the focus ; but if you 
 consider how large a surface the mirror presents to the rays, and, 
 consequently, how much they are diffused in comparison to what 
 they are at the focus, which is a little more than a point, I think you 
 can no longer wonder that the focus should be so much hotter than 
 the mirror. 
 
 The principal use of the mirror in this experiment is, to prove 
 ihat the calorific emanation is reflected in the same manner as 
 light. 
 
 Caroline. And the result, I think, is very conclusive. 
 
 J\Irs. B. The experiment may be repeated with a wax taper in- 
 stead of the bullet, with a view of separating the light from the 
 caloric. For this purpose a transparent plate of glass must be in- 
 terposed between the mirrors ; for light, you know, passes with 
 great facility through glass, whilst the transmission of caloric is 
 almost wholly impeded by it. We shall find, however, in this ex- 
 periment, that some few of the calorific rays pass through the glass 
 together with the light, as the thermometer rises a little ; but, as 
 oon as the glass is removed, and free passage left to the caloric, it 
 will rise considerably higher. 
 
 Emily. This experiment, as well as that of Dr. HerscheH's, 
 proves that light and heat may be separated : for in the latter ex- 
 periment the separation was not perfect, any more than that of Mr. 
 Pictet. 
 
 Caroline. I should like to repeat this experiment, with the dif 
 ference of substituting a cold body instead of a hot one, to see 
 whether cold would not be reflected as Well a<? heat. 
 
 Mrs. B. That experiment was proposed to Mr. I^ictet by an in- 
 credulous philosopher like yourself, and he immediately tried it by 
 substituting a piece of ice in the place of a heated bullet. 
 
 Caroline. Well, Mrs. B-, and what was the result ? 
 
 154. Why do mirrors increase the effect in this experiment ? 
 
 155. Why does a metallic mirror feel cold when placed before 
 the fire? 
 
 156. What is the use of the mirror in the experiment ? 
 
 157. What substance almost wholly impedes the transmission of 
 caloric ? 
 
 158. What does this prove ? 
 
 1 59. What philosopher supf 
 
 pposed that cold might be reflected 
 
FBEE CALORIC. 48 
 
 Mrs. B. That we shall see ; I have procured some ice for the 
 purpose. 
 
 Emily. The thermometer falls considerably ! 
 
 Caroline. And does not that prove that cold is not merely a neg- 
 alive quality, implying- simply an inferior degree of heat f The 
 'old must be positive, since it is capable of reflection. 
 
 Mrs. B. So it at first appeared to Mr. Pictet ; but upon a little 
 consideration he found that it afforded only an additional proof of 
 the reflection of heat; this I shall endeavour to explain to you. 
 
 According to Mr. Provost's theory, we suppose that all bodies 
 whatever radiate caloric ; the thermometer used in these exper- 
 iments, therefore, emits calorific rays in the same manner as any 
 other substance. When its temperature is in equilibrium with that 
 of the surrounding bodies, it receives as much caloric as it parts. 
 with, and no change of temperature is produced. But when we 
 introduce a body of a lower temperature, such as a piece of ice, 
 vvhich parts with less caloric than it receives, the consequence is. 
 that its temperature is raised, whilst that of the surrounding- bodies 
 is proportionally lowered. 
 
 Emily. If, for instance, I was to bring a large piece of ice into 
 this room, the ice would' in time be melted, by absorbing caloric 
 irom the general radiation which is going on throughout the room ; 
 and as it would contribute very little caloric in return for what i^ 
 absorbed, the room would necessarily be cooled by it. 
 
 Jtfrs. B. Just so ; and as in consequence of the mirrors, a more 
 considerable exchange of rays takes place between the ice and the 
 thermometer, than between these and any of the surrounding bod- 
 ies, the temperature of the thermometer must be more lowered than 
 that of any other adjacent object. 
 
 Caroline. I confess I do not perfectly understand your explan- 
 ation. 
 
 Mrs. B. This experiment is exactly similar to that made with 
 the heated bullet ; for, if we consider the thermometer as the hot 
 body (which it certainly is in comparison to the ice,) you may then 
 easily understand that it is by the loss of the calorific rays which 
 the thermometer sends to the ice, and not by any cold rays receiv - 
 ed from it, that the fall of the mercury is occasioned ; for the ice, 
 far from emitting rays of cold, sends forth rays of caloric, which 
 diminish the loss sustained by the thermometer. 
 
 Let us say, for instance, that the radiation of the thermometer 
 towards the ice is equal to 10, and that of the ice towards the 
 thermometer to 20 ; the exchange in favor of the ice is as 20 i& 
 to 10, or the thermometer absolutely loses 10, whilst the ice gaini^ 
 10. 
 
 Caroline. But if the ice actually sends rays of caloric to the 
 thermometer, must not the latter fall still lower when the ice is re- 
 moved ? 
 
 Mrs. B. No ; for the space which the ice occupies, admits ray 
 
 160. What did his experiment prove ? 
 
 161. What is probable respecting the use of the thermometer in 
 this experiment, according to Mr. Prevost's theory ? 
 
 162. What similarity is there between this experiment and that 
 of the heated bullet? 
 
 163. Since the ice sends rays of caloric to the thermometer, wil ! 
 not the thermometer fall if the ice is removed ? 
 
44 FREE CALORIC. 
 
 from all the surrounding bodies to pass through it : and those being 
 of the same temperature as the thermometer, will not affect it, be- 
 cause as much heat now returns to the thermometer as radiates 
 from it. 
 
 Caroline. I must confess that you have explained this in so satis- 
 factory a manner, that I cannot help being convinced uow that cold 
 has no real claim to the rank of a positive being 
 
 Mrs. B Before I conclude the subject of radiation, I must ob- 
 serve to you, that different bodies (or rather surfaces,) possess the 
 power of radiating caloric in very different degrees. 
 
 Some curious experiments have been made b\ -r. Leslie on 
 this subject, and it was for this purpose that heinvented the differ- 
 ential thermometer ; with its assistance he ascertained that black 
 surfaces radiate most, glass next, and polished surfaces the least of 
 all. 
 
 Emily. Supposing these surfaces, of course, to be all of the same 
 temperature. 
 
 Mrs. B. Undoubtedly. I will now show you the very ingen- 
 ious apparatus, by means of which he made these experiments. 
 This cubical tin vessel, or canister, has each of its sides externally 
 covered with different materials ; the one is simply blackened ; 
 the next is covered with white paper ; the third with a pane oi 
 glass, and in the fourth the polished tin surface remains uncovered. 
 We shall fill this vessel with hot water, so that there can be no 
 doubt but that all its sides will be of the same temperature. Now 
 let us place it in the focus of one of the mirrors, making each of 
 its sides front it in succession. We shall begin with the black 
 surface.* 
 
 Caroline. It makes the thermometer which is in the focus of the 
 other mirror rise considerably. Let us turn the paper surface 
 towards the mirror. The thermometer falls a little, therefore oi 
 course, this side cannot emit or radiate so much caloric as the black- 
 ened side. 
 
 Emily. This is very surprising ; for the sides are exactly of the 
 same size, and must be of the same temperature. But let us try 
 the glass surface. 
 
 Mrs. B. The thermometer continues falling, and with the plain 
 surface it falls still lower ; these two surfaces therefore radiate les? 
 and less. 
 
 Caroline. I think I have found out the reason of this. 
 
 Mrs. B. I should be very happy to hear it, for it has not yet, (to 
 my knowledge) been accounted for. 
 
 * The radiating power of different surfaces may be shown thus. 
 Take a common half pint tin cup, scour one side bright, and paint 
 or smoke the other black. Place this in the focus of the mirror, 
 and the thermometer will rise or fall as its sides are changed. C. 
 
 164. Why will it not? 
 
 165. Do all surfaces radiate caloric in equal degrees ? 
 
 1 66. What surfaces radiate most caloric, and what ones least ? 
 
 167. What illustration is given of the different radiations of d if- 
 ferent surfaces? 
 
 168. How is it stated in the note, that the radiating power of dif- 
 ferent surfaces may be shown? 
 
FREE CALORIC- 45 
 
 Caroline. The water within the vessel gradually cools, and the 
 thermometer in consequence gradually falls. 
 
 .Mrs. B. It is true that the water cools, but certainly in much les? 
 proportion than the thermometer descends, as you will perceive it 
 you now change the tin surface for the black one. 
 
 Caroline. I was mistaken, certainly, for the thermometer rises 
 again now that the black surface fronts the mirror. 
 
 Mrs. B. And yet the water in the vessel is still cooling, Car- 
 oline. 
 
 Emily. I am surprised that the tin surface should radiate the 
 Jeast caloric, for a metallic vessel filled with hot water, a silver 
 tea-pot for instance, feels much hotter to the baud than one of black 
 earthenware. 
 
 Mrs. B. That is owing to the different power which various bod- 
 ies possess for conducting caloric, a property which we shall pre- 
 sently examine. Thus, although a metallic vessel feels warm to 
 the hand, a vessel of this kind is known to preserve the heat of the 
 liquid within, better than one of any other materials ; it is for thi^ 
 reason that silver tea-pots make better tea than those of earthen- 
 ware. 
 
 Emily. According-fto these experiments, light coloured dresses, 
 m cold weather, should keep us warmer than black clothes, since 
 the latter radiate so much more than the former. 
 
 Mrs. B. And that is actually the case. 
 
 Emily. This property, of different surfaces to radiate in different 
 degrees, appears to me to be at variance with the equilibrium oi 
 caloric ; since it would imply that those bodies which radiate most 
 must ultimately become coldest. 
 
 Suppose that we were to vary this experiment, by using two 
 metallic vessels full of boiling water, the one blackened, the other 
 not ; would not the black one cool the first ? 
 
 Caroline. True ; but when they were both brought down to the 
 temperature of the room, the interchange of caloric between thr 
 canisters and the other bodies of the room being then equal, their 
 temperature would remain the same- 
 
 Emily. I do not see why that should be the case ; for if different 
 surfaces of the same temperature radiate in different degrees when 
 heated, why should they not continue to do so when cooled down 
 to the temperature of the room ? 
 
 Mrs. B. You have started a difficulty, Emily, which certainly 
 requires explanation. It is found by experiment, that the powei 
 of absorption corresponds with, and is proportional to, that of radia 
 tion ; so that under equal temperatures, bodies compensate for the 
 
 169. Why will a silver tea-pot or any metallic vessel filled with 
 iiot water, feel much hotter to the hand than one of black earthen 
 ware ? 
 
 170. Why will a silver tea-pot make better tea than an earthen 
 one? 
 
 171. Why is a light colored dress warmer than a black one in 
 winter ? 
 
 ' 172. And why a light colored one colder than a black in the 
 summer ? 
 
 173. What difficulty is mentioned respecting the above theory o 4 " 
 <he radiation of caloric ? 
 
46 FREE CALORIC. 
 
 greater loss they sustain in consequence of their greater radiatiuu 
 by their greater 'absorption ; so that if you were to make your ex- 
 periment in an atmosphere heated like the canisters, to the tem- 
 perature of boiling water, though it is true that the canisters would 
 radiate in different degrees, no change of temperature would be 
 produced in them, because they would each absorb caloric in pro- 
 portion to their respective radiation. 
 
 Emily. But would not the canisters of boiling water also absorb 
 caloric in different degrees in a room of the common temperature : 
 
 Mrs. B. Undoubtedly they would But the various bodies in 
 the room would not, at a lower temperature, furnish either of the 
 canisters with a sufficiency of caloric to compensate for the loss 
 they undergo ; for, suppose a black canister to absorb 400 rays 
 of caloric, whilst the metallic <*>ne absorbed only 200 ; yet if the 
 former radiate 800, whilst the latter radiates only 400, the black 
 canister will be the first cooled down to the temperature of the 
 room. But from the moment the equilibrium of temperature has 
 taken place, the black canister, both receiving and giving out 400 
 rays, and the metallic one 200, no change of temperature will take 
 place. 
 
 Emily. I now understand it extremely well. But what becomes 
 of the surplus of calorific rays, which good radiators emit, and bad 
 radiators receive ? they must wander about in search of a resting- 
 place ! 
 
 Mrs. B They really do so; for they arerejected and sent back, 
 or, in other words, refected by the bodies tfhich are bad radiators 
 of caloric : and they are thus transmitted to other bodies which 
 happen to lie in their way. by which thej are either absorbed or 
 again reflected, according as the property of reflection, or that oi 
 absorption, predominates in hese bodies. 
 
 Caroline. I Jo not well understand the difference between radia- 
 ting and reflecting caloric, for the caloric that is reflected from a 
 body, proceeds from it 'in straight lines, and may surely be said to 
 radiate from it ? 
 
 -Mrs. B It is true that there at first appears to be a great analo- 
 gy between radiation and reflection, as they equally convey the 
 idea of the transmission of caloric. 
 
 But if you consider a little, vou will perceive that when a body 
 radiates caloric, the heat which it emits not only proceeds from, 
 but has its origin in the body itself Whilst when a bodv reflects 
 caloric, it parts with none of its own caloric, but only reflects that 
 which it receives from other bodies 
 
 Emily. Of this difference we hare very striking examples be- 
 fore us, in the tin vessel of water and the concave mirrors ; the 
 first radiates its own heat, the latter reflect the heal^ which they re- 
 ceive from other bodies 
 
 Carnline. Now that I understand the difference, it no longer 
 
 174. If different surfaces of the same temperature radiate in dif- 
 ferent degrees when heated, why do they not continue to do so 
 when cooled to the temperature of the room ? 
 
 175. What becomes of the surplus of caloric, which good radia- 
 tors emit and bad ones refusie to receive ? 
 
 176. What is the difference between the radiation and reflection 
 of caloric ? 
 
 J77. How would you illustrate this difference by example ~ 
 
FREE CALORIC. 47 
 
 surprises me that bodies which radiate, or part with their own ca- 
 ioric freely, should not have the power of transmitting with equal 
 facility that which they receive from other bodies. 
 
 Emily. Yet no body can be said to possess caloric of its own, if 
 all caloric is originally derived from the sun. 
 
 Jftrs. B. When I speak of a body radiating its own caloric, I 
 mean that which it has absorbed and incorporated either immedi- 
 ately from the sun's rays, or through the medium of any other sub- 
 stance. 
 
 Caroline, ft seems natural enough that the power of absorption 
 should be in opposition to that of reflection, for the more caloric a 
 body receives, the less it will reject. 
 
 Emily. And equally so that the power of radiation should cor- 
 respond with that of absorption. It is, in fact, cause and effect; 
 for a body cannot radiate heat without having previously absorbed 
 it ; just as a spring that is well fed flows abundantly. 
 
 Mrs. B. Fluids are in general very bad radiators of caloric ; and 
 air neither radiates nor absorbs caloric in any sensible degree. 
 
 We have not yet concluded our observations on free caloric. 
 But I shall defer, till our next meeting, what I have further to say 
 on this subject. I believe it will afford us ample conversation for 
 another interview. 
 
 CONVERSATION III. 
 
 CONTINUATION OF THE SUBJECT. 
 
 Mrs. B. IN our last conversation, we began to examine the if.u 
 lency of caloric to restore an equilibrium of temperature. This 
 property when once well understood affords the explanation of a 
 grreat variety of facts which appeared formerly unaccountable. 
 iTou must observe, in the first place, that the effect of this tenden- 
 cy is gradually to bring all bodies that are in contact, (o the same 
 temperature. Thus the fire which burns in the grafe, communi- 
 cates its heat from one object to another, till every part of the room 
 has an equal portion of it. 
 
 Emily. And yet this book is not so cold as the table on which it 
 lies, though both are at an equal distance from the fire, and actually 
 in contact with each other, so that according to your theory, they 
 should be exactly at the same temperature. 
 
 Caroline. And the hearth which is much nearer the fire than the 
 oarpet, is certainly the colder of the two. 
 
 Mrs. B. If you ascertain the temperature of these several bo- 
 
 1 78. When we speak of a body radiating its own caloric, what do 
 we mean ? 
 
 179. What are very bad radiators of caloric ? 
 
 180. Has caloric any effect upon thfiair? 
 
 181. What is the tendency of caloric ? 
 
 382. Do all substances at the same temperature feel equally varm 
 JT cold ? 
 
18 FKEE CALORIC. 
 
 dies by a thermometer (which is a much more accurate test 
 your feeling,) you will find that it is exactly the same. 
 
 Caroline. But if they are of the same temperature, why should 
 the one feel colder than the other ? 
 
 Mrs. B. The hearth and the table feel colder than the carpet or 
 the book, because the latter are not such good conductors of heat 
 as the former. Caloric finds a more easy passage through marble 
 and wood, than through leather and worsted ; the two former will 
 therefore absorb heat more rapidly from your hand, and consequent- 
 ly give it a stronger sensation of cold than the two latfer, although 
 they are all of them really of the same temperature. 
 
 Caroline. So, then, the sensation I feel on touching a cold body, 
 is in proportion to the rapidity with which my hand yields its heat 
 to that body. 
 
 Mrs. B. Precisely ; and if you lay your hand successively on 
 every object in the room, you will discover which are good, and 
 which are bad conductors of heat, by the different degrees of cold 
 which you feel. But in order to ascertain this point, it is necessa- 
 ry that the several substances should be of the same temperature, 
 which will not be the case with those that are very near the fire, or 
 those that are exposed to a current of cold air from a window or 
 door. 
 
 Emily. But what is the reason that some bodies are better con 
 ductors of heat than others ? 
 
 Mrs. B. This is a point not well ascertained. It has been con- 
 jectured that a certain union or adherence takes place between the 
 caloric and the particles of the body through which it passes. If 
 this adherence be strong, the body detains the heat, and parts with 
 it slowly and reluctantly; if slight, it propagates it freely and rap- 
 idly. The conducting power of a body is therefore, inversely, as its 
 tendency to unite with caloric. 
 
 Emily. That is to say, that the best conductors are those that 
 have the least affinity for caloric. 
 
 Mrs. B. Yes ; but the term affinity is objectionable in this case, 
 because, as that word is used to express a chemical attraction 
 ''which can be destroyed only by decomposition,) it cannot be ap- 
 plicable to the slight and transient union that takes place between 
 free caloric a'nd the bodies through which it passes ; an union 
 which is so weak, that it constantly yields to the tendency which 
 Caloric has to an equilibrium. Now you clearly understand, that 
 the passage of caloric, through bodies that are good conductors, is 
 much more rapid than through those that are bad conductors, and 
 that the former both give and receive it more quickly, and therc- 
 
 183. Why do they not? 
 
 184 What are instances of substances of the same temperature 
 producing different sensations of heat and cold ? 
 
 185. To what is the sensation proportional on touching one': 
 hand to a cold body ? 
 
 186. How can we ascertain which bodies are good conductors of 
 heat and which are not ? 
 
 187. Why are some bodies better conductors of heat than others ? 
 
 188. Will caloric pass quickest through good, or bad conduct 
 ors ? 
 
 189. Which gives and receives it most readily ? 
 
FREE CALORIC. 49 
 
 fore, in a given time more abundantly, than bad conductors, which 
 makes them feel either hotter or colder, though they may be in 
 fact, both of the same temperature. 
 
 Caroline. Yes, I understand it now ; the table and the book lying 
 upon it, being- really of the same temperature, would each receive 
 in the same space of time, the same quantity of heat from my hand, 
 were their conducting powers equal ; but as the table is the best 
 conductor of the two, it will absorb the heat from my hand more 
 rapidly, and consequently produce a stronger sensation of cold 
 than the book. 
 
 Mrs. B. Very well, my dear ; and observe, likewise, that if you 
 were to heat the table and the book an equal number of degrees 
 above the temperature of your body, the table, which before felt 
 the colder, would now feel the hotter of the two ; for, as in the first 
 case it took the heat most rapidly from your hand, so now it will im- 
 part heat most rapidly to it. Thus the marble table, which seems 
 to us colder than the mahogany one, will prove the hotter of t\\e 
 two to the ice ; for if it makes heat more rapidly from our hands, 
 which are warmer, it will give out heat more rapidly to the ice 
 which is colder. Do you understand the reason of these apparent- 
 ly opposite effects ? 
 
 Emily. Perfectly. A body which is a good conductor of caloric, 
 affords it a free passage ; so that it penetrates through that body more 
 rapidly than through one which is a bad conductor ; and conse- 
 quently, if if is colder than your hand, you lose more caloric, and if it 
 is hotter you gain more than a bad conductor of the same temperature. 
 
 Mm. B. But you must observe that this is the case only when the 
 conductors are either hotter or colder than your hand ; for, if you 
 heat different conductors to the temperature of your body, they will 
 all feel equally warm, since the exchange of caloric between bodies 
 of the same temperature is equal. Now, can you tell me why flan- 
 nel clothing, which is a very bad conductor of heat, prevents our 
 feeling cold? 
 
 Caroline. It prevents the cold from penetrating . . . 
 
 Mrs. B But you forget that cold is only a negative quality. 
 
 Caroline. True, it only prevents the heat of our bodies from es- 
 caping so rapidly as it would otherwise do. 
 
 Jtfr.i B Now you have explained it right ; the flannel rather 
 keeps in the heat, than keeps out the cold. Were the atmosphere 
 of a higher temperature than our bodies, it would be equally effica- 
 cious in keeping their temperature at the same degree, as it would 
 prevent the free access of the external heat, by the difficulty with 
 which it conducts it. 
 
 Emily. This, I think, is very clear. Heat, whether external or 
 internal, cannot easily penetrate flannel ; therefore, in cold weather 
 
 190. If we lay our hand upon a table and a book both of the 
 *amc temperature, why does the table produce a stronger sensation 
 of cold than the book ? 
 
 191. Under what circumstances will good and bad conductors 
 feel equally warm to our flesh ? 
 
 192. Why does flaunel clothing prevent our feeling cold ? 
 
 193. Under what circumstances, or when would a flannel dress 
 produce a contrary effect in our feelings ? 
 
50 TREE CALOKIC. 
 
 it keeps us warm, and if the weather were hotter than our bodies, 
 it would keep us cool. 
 
 Jtfrs. B. The most dense bodies are, generally speaking, the best 
 conductors of heat ; probably because the denser the body the great- 
 er are the number of points or particles that come in conlaci with 
 caloric. At the common temperature of the atmosphere, a piece of 
 metal will feel much colder than a piece of wood, and the latter 
 than a piece of woollen cloth ; this again will feel colder than flan- 
 nel ; and down, which is one of the lightest, is at the same time one 
 of the warmest bodies.* 
 
 Caroline. This is, I suppose, the reason that the plumage of birds 
 preserves them so effectually from the influence of cold in winter? 
 
 Mrs. B. Yes ; but though feathers in general are an excellent 
 preservative against cold, down is a kind of plumage, peculiar to 
 aquatic <>irds, and covers their chest, which is the part most ex- 
 posed to the water ; for though the surface of the water is not of a 
 lower temperature than the atmosphere, yet it is a better conduc- 
 tor of heat, it feels much colder, consequently the chest of the bird 
 requires a warmer covering than any other part of its body. Be- 
 sides, the breasts of aquatic birds are exposed to cold, not only from 
 the temperature of the water, but also from the velocity with which 
 the breast of the bird strikes against it ; and likewise from the rap- 
 id evaporation occasioned in that part by the air against which it 
 strikes, after it has been moistened by dipping from time to time 
 into the water. 
 
 If you hold a finger of one hand motionless in a glass of water, 
 and at the same time move a finger of the other hand swiftly through 
 water of the same temperature, a different sensation will be soon 
 perceived in the different fingers, f 
 
 Most animal substances, especially those which Providence has 
 assigned as a covering for animals, such as fur, wool, hair, skin, 
 &c. are bad conductors of heat, and are, on that account, such ex- 
 cellent preservatives against the inclemency of winter, that our 
 warmest apparel is made of these materials. 
 
 * One reason, why fur, down, &c. conduct heat so badly, is, that 
 they contain a large quantity of air, which is a worse conductor 
 than the materials themselves. C. 
 
 f The reason seems to be, that the finger, when it is still, warms 
 the water in contact with it ; while the one that is stirring is con- 
 stantly exposed to fresh applications ^of cold C. 
 
 194. What bodies are generally considered the best conductors 
 of caloric ? 
 
 195. Why are dense bodies the best conductors . ? 
 
 196. If the surface of water is not of a lower temperature than 
 the atmosphere, why does it feel colder ? 
 
 197. Why are fur, hair, wool, and down, good preservatives 
 against the inclemency of winter f 
 
 198. Why are they bad conductors of caloric ? 
 
 199. If you hold a finger of one hand motionless in a glass of wa- 
 ter, and at the same time more a finger of tfte other hand swiftly 
 through water of the same temperature, why is a different sensation 
 produced ? 
 
FREE CALORIC. 
 
 ili/. Wood is, I dare say, not so good a conductor as metal, 
 > rid it is for that reason, no doubt, that silver tea-pots have always 
 wooden handles. 
 
 Mrs. B. Yes ; and it is the facility with which metals conduct 
 caloric that made you suppose that a silver pot radiated more calor- 
 ic than an earthen one. The silver pot is in fact hotter to the 
 hand when in contact with it ; but it is because its conducting pow- 
 er more than counterbalances its deficiency in regard to radiation. 
 
 We have observed that the most dense bodies are in general the 
 best conductors ; and metals you know, are of that class. Porous 
 bodies, such as the earths, and wood, are worse conductors, chiefly, 
 I believe, on account of their pores being filled with air ; for air is a 
 remarkably bad conductor 
 
 Caroline. It is a very fortunate circumstance that air should be 
 a bad conductor, :is it tends to preserve the heat of the body when 
 exposed to cold weather.. 
 
 Mrs. B. It is one of the many benevolent dispensations of Prov- 
 idence, in order to soften ihe incleme'ncy of the season, and to ren- 
 der almost all climates habitable to man 
 
 In fluids of different densities, the power of conducting heat va- 
 ries no less remarkably ; if YOU dip your hand into this vessel full 
 of mercury, you will scarcely conceive thai its temperature is not 
 lower than that of the atmosphere. 
 
 Caroline. Indeed I know not how to believe it, it feels so extreme- 
 ly cold. But we may easilv ascertain its true temperature by the 
 thermometer It is really not colder than the air: the apparent 
 difference then is produced merely by the difference of the conduct- 
 ing power in mercury and in air. 
 
 Jllrs. B. Yes ,- hence you may judge how little the sense of feel- 
 ing is to be relied on as a test of the temperature of bodies, and 
 how necessary a thermometer is for that purpose 
 
 It has indeed been doubted whether fluids have the power of con- 
 ducting caloric in the same manner as solid bodies* Count Rura- 
 ford a very few years since, attempted to prove by a variety of ex- 
 periments, that fluids when at.rest, were not at all endowed with 
 this property. 
 
 Caroline. How is that possible, since they are capable of impart- 
 ing cold or heat to us ; for if they did not conduct heat, they would 
 neither take it from, nor give it to us? 
 
 Mrs. B. Count Rumferd did not mean to say that fluids would 
 not communicate their heat to solid bodies ; but only that heat does 
 not pervade fluids, that is to say is not transmitted from one parti- 
 cle of a fluid to another, in the same manner as in solid bodies. 
 
 Emily. But when you heat a vessel <f water over the fire, if the 
 particles of water do not communicate heat to each other, how does 
 the water become hot throughout ? 
 
 200 Why does a silver tea-pot feel hotter to the hand than an 
 earthen one? 
 
 201. Why are wood and earths bad conductors of it ? 
 
 202. Have fluids of different densities the same power of con- 
 ducting caloric ? 
 
 203. Ought the sense of feeling to be relied on as a test of the 
 temperature of bodies? Why? 
 
50 FREE CALORIC. 
 
 it keeps us warm, and if the weather were hotter than our bodies, 
 it would keep us cool. 
 
 Mrs. B. The most dense bodies are, generally speaking, the best 
 conductors of heat ; probably because the denser the body the great- 
 er are the number of points or particles that come in contact with 
 caloric. At the common temperature of the atmosphere, a piece of 
 metal will feel much colder than a piece of wood, and the latter 
 than a piece of woollen cloth ; this again will feel colder than flan- 
 nel ; and down, which is one of the lightest, is at the same time one 
 of the warmest bodies.* 
 
 Caroline. This is, I suppose, the reason that the plumage of birds 
 preserves them so effectually from the influence of cold in winter? 
 
 Mrs. B. Yes ; but though feathers in general are an excellent 
 preservative against cold, down is a kind of plumage, peculiar to 
 aquatic oirds, and covers their chest, which is the part most ex- 
 posed to the water ; for though the surface of the water is not of a 
 lower temperature than the atmosphere, yet it is a better conduc- 
 tor of heat, it feels much colder, consequently the chest of the bird 
 requires a warmer covering than any other part of its body. Be- 
 sides, the breasts of aquatic birds are exposed to cold, not only from 
 the temperature of the water, but also from the velocity with which 
 the breast of the bird strikes against it ; and likewise from the rap- 
 id evaporation occasioned in that part by the air against which it 
 strikes, after it has been moistened by dipping from time to time 
 into the water. 
 
 If you hold a finger of one hand motionless in a glass of water, 
 and at the same time move a finger of the other hand swiftly through 
 water of the same temperature, a different sensation will be soon 
 perceived in the different fingers.f 
 
 Most animal substances, especially those which Providence has 
 assigned as a covering for animals, such as fur, wool, hair, skin, 
 &c. are bad conductors of heat, and are, on that account, such ex- 
 cellent preservatives against the inclemency of winter, that our 
 warmest apparel is made of these materials. 
 
 * One reason, why fur, down, &c. conduct heat so badly, is, that 
 they contain a large quantity of air, which is a worse conductor 
 than the materials themselves. C. 
 
 f The reason seems to be, that the finger, when it is still, warms 
 the water in contact with it ; while the one that is stirring is con- 
 stantly exposed to fresh applications .of cold -C. 
 
 194. What bodies are generally considered the best conductors 
 of caloric ? 
 
 195. Why are dense bodies the best conductors '. 
 
 196. If the surface of water is not of a lower temperature than 
 the atmosphere, why does it feel colder ? 
 
 197. Why are fur, hair, wool, and down, good preservatives 
 against the inclemency of winter ? 
 
 198. Why are they bad conductors of caloric ? 
 
 199. If you hold a finger of one hand motionless in a glass of wa- 
 ter, and at the same time move a finger of tlie other hand siviftly 
 through water of the same temperature^ why is a different sensation 
 produced ? 
 
FREE CALORIC. 
 
 51 
 
 Enrilu. Wood is, I dare say, not so good a conductor as metal, 
 nd it is for that reason, no doubt, that silver tea-pots have always 
 wooden handles. 
 
 Mrs. B. Yes ; and it is the facility with which metals conduct 
 caloric that made you suppose that a silver pot radiated more calor- 
 ic than an earthen one. The silver pot is in fact hotter to the 
 hand when in contact with it ; but it is because its conducting pow- 
 er more than counterbalances its deficiency in regard to radiation. 
 
 We have observed that the most dense bodies are in general the 
 best conductors ; and metals you know, are of that class. Porous 
 bodies, such as the earths, and wood, are worse conductors, chiefly, 
 I believe, on account of their pores being filled with air ; for air is a 
 remarkably bad conductor 
 
 Caroline. It is a very fortunate circumstance that air should be 
 a bad conductor, ^s it tends to preserve the heat of the body when 
 exposed to cold weather.. 
 
 Mrs. B. It is one of the many benevolent dispensations of Prov- 
 idence, in order to soften ihe incleme'ncy of the season, and to ren- 
 der almost all climates habitable to man 
 
 In fluids of different densities, the power of conducting heat va- 
 ries no less remarkably ; if >ou dip your hand into this vessel full 
 of mercury, you will scarcely conceive thai its temperature is not 
 lower than that of the atmosphere. 
 
 Caroline. Indeed I know not how to believe it, it feels so extreme- 
 ly cold. But we may easily ascertain its true temperature by the 
 thermometer It is really not colder than the air: the apparent 
 difference then is produced merely by the difference of the conduct- 
 ing power in mercury and in air. 
 
 Mrs. B. Yes ; hence you may judge how little the sense of feel- 
 ing is to be relied on as a test"of the temperature of bodies, and 
 how necessary a thermometer is for that purpose 
 
 It has indeed been doubted whether fluids have the power of con- 
 ducting caloric in the same manner as solid bodies Count Rum- 
 ford a very few years since, attempted to prove hy a variety of ex- 
 periments, that fluids when at .rest, were not at all endowed with 
 this property. 
 
 Caroline. How is that possible, since they are capable of impart- 
 ing cold or heat to us ; for if they did not conduct beat, they would 
 neither take it from, nor give it to us? 
 
 Mrs. B. Count Rumford did not mean to say that fluids would 
 not communicate their heat to solid bodies ; but only that heat does 
 Dot pervade fluids, that is to say is not transmitted from one parti- 
 cle of a fluid to another, in the same manner as in solid bodies. 
 
 Emily. But when you heat a vessel <>f water over the fire, if the 
 particles of water do not communicate heat to each other, how does 
 the water become hot throughout ? 
 
 200 Why does a silver tea-pot feel hotter to the hand than an 
 earthen one? 
 
 201 . Why are wood and earths bad conductors of it ? 
 
 202. Have fluids of different densities the same power of con- 
 ducting caloric ? 
 
 203. Ought the sense of feeling to be relied on as a test of thr 
 *emperature of bodies? Why? 
 
54 FREE CALORIC. 
 
 of the water has risen to the surface to give off its caloric to the colder 
 atmosphere ; therefore the deeper a body of water is, the longer 
 will be the time it requires to be frozen. 
 
 Emily. But if the temperature of the whole body of water be 
 brought down to the freezing point, why is only the surface frozen r 
 
 Mrs. B. The temperature of the whole body is lowered, but not to 
 the freezing point The diminution of heat, as you know, produces 
 a contraction in the bulk of fluids, as well as ot solids This effect, 
 however, does not take place in water below the temperature of 40 
 degrees, which is 8 degrees above the freezing point. At that tem- 
 perature, therefore, the internal motion, occasioned by the increased 
 specific gravity of the condensed particles, ceases ; for when the 
 water at the surface no longer condenses,it will no longer descend, 
 and leave a fresh surface exposed to the atmosphere ; this surface- 
 alone, therefore, will be further exposed to its severit} ,and will soon 
 be brought down to the freezing point, when it becomes ice, which 
 being a bad conductor of heat, preserves the water beneath a long 
 time, from being affected by the external co'd. 
 
 Caroline. And the sea does not freeze, 1 suppose, because its depth 
 is so great, that a frost never lasts long enough to bring down the 
 temperature of such a great body of water to 40 degrees ? 
 
 Mrs. B That is one reason why the sea, as a large mass of water, 
 does not freeze. But, independently of this, salt water does not 
 freeze till it is cooled much below 32 degrees, and with respect to 
 the law of condensation, salt water is an exception, as it condenses 
 even many degree* below the freezing point. When the caloric of 
 fresh water, therefore, is imprisoned by the ice on its surface, the 
 ocean still continues throwing off heat into the atmosphere, which 
 is a most signal dispensation of Providence to moderate the intensi- 
 ty of the cold in winter. 
 
 Caroline. This theory of the non-conducting power of liquids, 
 does not, I suppose, hold good with respect to air, otherwise the at- 
 mosphere would not be heated by the rays of the sun passing 
 through it ? 
 
 Mrs. B. Nor is it heated in that way. The pure atmosphere is a 
 perfectly transparent medium, which neither radiates, absorbs, nor 
 conducts caloric, but transmits the rays of the sun to us without in 
 any way diminishing their intensity. ' The air is therefore not more 
 heated, by the sun's rays passing through it, than diamond, glass, 
 water, or any other transparent medium * 
 
 Caroline. That is very extraordinary ! Are glass windows not 
 heated then by the sun shining on them ? 
 
 * To show still better that transparent media are not heated by 
 the rays of the sun, throw the focus of a burning lens into a vessel 
 of clear water. No effect on the temperature will be produced ; 
 but if an opake body, as a piece of cork be introduced under the 
 focus, the water at this point instantly begins to boil. C. 
 
 213. Why does water first freeze at the surface ? 
 
 214. Why does not the surface of the sea freeze? 
 
 215. What moderates the intensity of the cold in winter? 
 
 216. Is the atmosphere heated by the rays of the sun passing 
 through it ? 
 
 217. What experiment mentioned in the note, proves that transpa- 
 rent media are not heated by the rays of the sun ? 
 
FREE CALORIC. OO 
 
 Jlrs. B. No ; not if the glass be perfectly transparent. A most 
 Convincing proof that glass transmits the rays of the sun without 
 being heated by them, is afforded by the burning lens, which by con- 
 verging the rays to a focus will set combustible bodies on fire, 
 withou 1 its own temperature being raised. 
 
 Emily. Yet, Mrs. B., if I hold a piece of glass near the fire, it is 
 almost immediately warmed by it ; the glass therefore must retain 
 some of the caloric radiated by the fire. Is it that the solar rays 
 alone pass freely through the glass without paying tribute ? It seems 
 unaccountable that the radiat on of a common fire should have 
 power to do what the sun's rays cannot accomplish. 
 
 Mrs. B. It is not because the rays from the fire havemore power, 
 but rather because they have less, that they heat glass and other 
 transparent bodies. It is true, however, t fiat as you approach the. 
 source of heat the rays being nearer each other, the heat is more 
 condensed, and can produce effects of which the solar rays, from 
 the great distance of their source, are incapable Thus we should 
 find it impossible to roast a joint of meat by the sun's rays, though 
 it is so easily done by culinary heat Yet caloric emanated from 
 burning bodies which is commonly called culinary heat, has neither 
 the intensity nor the veloc.t> of *olar rays. All caloric, we have 
 said, is supposed to proceed originally from the sun : but after hav- 
 ing been incorporated with terrestrial bodies, and again given out 
 by them, though its nature is not essentially altered, it retains nei- 
 ther the intensity nor the velocity with which it first emanated from 
 that luminary; it ha therefore not the power of passing through 
 transparent mediums, such as glass and water, without being par- 
 tially retained by those bodies. 
 
 Emily. I recollect that in the experiment on the reflection of 
 heat, the glass screen which you interposed between the burning 
 taper and mirror, arrested the rays of caloric, and suffered only 
 those of light to pass through it. 
 
 Caroline Glass windows, then, though they cannot be heated by 
 the sun shining on them, ma' be heated internally hy a fire in the 
 room ? But, Mrs. B , since the atmosphere is not warmed by the 
 solar rays passing through it, how does it obtain heat ? for all the 
 fires that are burning on the surface of the earth would contribute 
 very little towards warming it. 
 
 Emily. The radiation of heat is not confined to burning bodies ; 
 for all bodies, you know, have thai property : therefore, not only 
 every thing upon the surface of the earth, but the earth itself, must 
 radiate heat ; and this terrestrial caloric, nipt having, T suppose, suf- 
 ficient power to traverse the atmosphere, communicates heat to it. 
 
 Mrs. B. Your inference is extremely well drawn, Emily : but the 
 foundation on which it rests is not sound : for the fact is, that terres- 
 trial or culinary heat, though it cannot pass through the denser 
 transparent mediums, such as glass or water, without loss, traverses 
 the atmosphere completely ; so that all the heat which the earth 
 
 218. What is culinary heat ? 
 
 219 Why does fire heat glass, when the sun does not ? 
 220. To what experiment is allusion here made illustrative of 
 this subject 
 
>6 FEE CALORIC. 
 
 radiates, unless it meet with clouds* or any foreign body to inter- 
 cept its passage, passes into the distant regions of the universe. 
 
 Caroline What a pity that so much heat should be wasted ! 
 
 Mrs. B. Before you are tempted to object to any law of nature, 
 reflect whether it may not prove to be one of the numberless dis- 
 pensations of Providence for our good If all the heat which the 
 earth has received from the sun since the creation, had been accu- 
 mulated in it, its temperature by this time would, no doubt, have 
 been more elevated than any human being could have borne. 
 
 Caroline. 1 spoke, indeed, very inconsiderately. But, Mrs. B., 
 though the earth, at such a high temperature, might have scorched 
 our feet, we should always have had a cool refreshing air to breathe, 
 since the radiation of the earth does not heat the atmosphere 
 
 Enuly. The cool air would have afforded but very insufficient 
 refreshment, whilst our bodies were exposed to the burning radia- 
 tion of the earth. 
 
 Mrs. B. Nor should we have breathed a cool air : for though it is 
 true that heat is not communicated to the atmosphere by radiation ; 
 yet the air is warmed by contact with heated bodies, in the same 
 manner as solids or liquids. The stratum of air which is immediately 
 in contact with the earth is heated by it ; it becomes specifically 
 lighter, and rises, making way for another stratum of air, which is, 
 in its turn heated and carried upwards; and thus each successive 
 stratum of air is warmed by coming in contact with the earth. You 
 -may perceive this effect in a sultry day. if you attentively observe 
 the^strata of air near the surface of the earth ; they appear in con- 
 stant agitation ; for though it is true the air itself is invisible, yet the 
 sun shining on the vapour-- floating in it, render them visible, like 
 the amber dust in the water. The temperature of the surface of 
 the earth is therefore the source from whence the atmosphere de- 
 rives its heat, though it is communicated neither by radiation, nor 
 transmitted from one particle of it to another by the conducting 
 power ; but every particle of air must come in contact with the 
 earth, in order to receive heat from it. 
 
 Emily. Wind, then, by agitating the air, should contribute to 
 cool the earth and warm the atmosphere, by bringing a more rapid 
 succession of fresh strata of air in contact with the earth ?, and yet 
 in general wind feels cooler than still air 
 
 Mrs. B. Because the agitation of the air carries off heat from the 
 surface of our bodies more rapidly than still air, by occasioning a 
 greater number of points of contact in a given time. 
 
 * Every one has observed how oppressive the heat is on a foggy, 
 or cloudy day in the summer. The moisture of the fog absorbs the 
 heat which the earth radiates, and throws it back upon the earth 
 again, and upon us. C. 
 
 221. What becomes of the heat which the earth radiates? 
 
 222. What would be the effect if all the heat which the earth has 
 received from the sun,since the creation, had been accumulated in it? 
 
 223. Why, in summer, is it particularly hot in cloudy, or foggy 
 weather ? 
 
 224. How is the air heated, if not as has been said, by the rays of the 
 sunpassing through i/? 
 
 225. Why is the wind cooling to our bodies ? 
 
TREE CALOIIK . 
 
 57 
 
 Emily. Since it is from the earth, and not the sun, that the at- 
 mosphere receives its heat, T uo longer wonder that elevated regions 
 should be colder than plams and valleys. Jt was always a subject 
 of astonishment to me, that in ascending a mountain and approach- 
 ing the su i the air became colder instead of being more heated. 
 
 Mrs. B. At the distance of about a hundred millions of miles, 
 which we are from the sun, the approach of a few thousand feet 
 makes no sensible difference, whilst it produces a very considerable 
 effect with regard to the warming of the atmosphere at the surface 
 of the earth 
 
 Caroline. Yet as the warm air arises from the earth, and the 
 cold air descends to it, I should have supposed that heat would have 
 accumulated in the upper regions of the atmosphere, and that we 
 should have felt the air warmer as we ascended. 
 
 Mrs. B. The atmosphere you know, diminishes in density, and 
 consequently in weight, as it is more distant from the earth ; the 
 warm air. therefore, rises only till it meets with a stratum of air of 
 its own density ; and it will not ascend into the upper regions o r the 
 atmosphere until all the parts beneath have been previously heated. 
 The length of summer, even in warm climates, does not heat the air 
 sufficiently to melt the snow which has accumulated during the win- 
 ter on very high mountains although they 
 are almost constantly exposed to the heat 
 of the sun's rays, being too much eleva- 
 ted to be often enveloped in clouds. 
 
 Emily. These explanations are very 
 satisfactory ; but allow me to ask you one 
 mote question respecting the increased 
 levity of heated liquids. You said tiiat 
 when water was heated over the fire, the 
 particles at the bottom of the vessel as- 
 cended as soon as heated, in consequence 
 of their specific levity ; why does not the 
 same effect continue when the water boils 
 and is converted into steam ? and why 
 does the steam arise i'rom the surface, in- 
 stead of the bottom of the liquid ? 
 
 Mrs. B The steam or vapour does as- 
 cend from the bottom, though it seems to 
 arise from the surface of the liquid. We 
 shall boil some water in this Florence 
 flask, (Fig. G.) in order that you n>ay be 
 well acquainted with the process of ebul- 
 lition : you will then see, through the 
 glass, that the vapour rises in bubbles 
 from the bottom. We shall make it boil 
 by means of a lamp, which is more con- 
 venient for this purpose than the chimney 
 fire. 
 
 oiling water in a flask 
 Patent Lamp. 
 
 220. Why is it colder on high hills and mountains than it is in 
 valleys, since the former are nearer the sun than the latter, and 
 >ince also it is the nature of the air to rise as it becomes warmed ? 
 
 2-27. What illustration is mentioned to shew that the air is not 
 heated by the sun's rays passing through it ? 
 
 223, Does water boil from the top, or from the bottom of a vessel ? 
 
FREE CALORIC. 
 
 Emily. I see some small bubbles ascend, and a great many appear 
 all over the inside of the flask ; does the water beg-in to boil already: 
 
 Mrs. B. No ; what you now see are bubbles of air, which were 
 either dissolved in tbe'water, or attached to the innersurface of the 
 flask, and which, being rarefied by the heat, ascend in the water. 
 
 Emily. But the heaf which rarefies the air inclosed in the water 
 must rarefy the water at the same time; therefore, if it could re- 
 main stationary in the water when boh were cold, I do not under- 
 stand why it should not when both are equally heated. 
 
 Mrs. B. Air being- much less dense than water, is more easily 
 rarefied ; the former, then fore, expands to a great extent, whilst 
 the latter continues to ocruov nearly the same space ; for the wa- 
 ter dilates comparatively *>ut very little without changing its >Uatc 
 and becoming vapour. " Now that the water in the flask begins to 
 boil, observe what large bubbles rise from the bottom of it. 
 
 Emily. I see them perfectly ; but I wonder that they have suffi- 
 cient power to force themselves through the water. 
 
 Caroline. They must ri^e, you know, f om their specific levity. 
 
 Mrs. B. You are right. Caroline : but vapour has not in all li- 
 quids (when brought to the degree of vaporization) <he power of 
 overcoming t>ie pressure of the less heated surface. Metals, for in- 
 stance, mercury excepted. evaporate only from the surface : there- 
 fore no vapour will ascend from them till the degree of heat which 
 is necessary to form it has reached the 4 surface ; that is to say, till 
 the whole of the liquid is brought to a state of ebullition. 
 
 Emily. I have observed that steam, immediately issuing from the 
 spout of a tea-kettle, is less visible than at a further distance from 
 it, yet it must be more dense when it first evaporates, than when 
 it bearins to diffuse itself in the air. 
 
 Mrs. B. When the steam is first formed, it is so perfectly dissolv- 
 eu by caloric, as to be invisible fn order, however, to understand 
 this, it will be necessary for me to enter into some explanation re- 
 specting the nature of SOLUTION. Solution takes place whenever a 
 ^ody is melted in a fluid. In this operation the body is reduced to 
 such a minute state of division by the fluid, as to become invisible 
 in it and to partake of its fluidity ; but in common solutions thi^ 
 happens without any decomposition, the body being only divided in- 
 to its integrant particles bv the fluid in whirh it is melted. 
 
 Caroline. It is then a mode of destroying the attraction of aggre- 
 gation 
 
 Mrs B Undoubtedly. the two principal solvent fluids are wa- 
 ter and caloric. You mav hav observed 'hat if you melt -alt in wa- 
 ter it totally disappears and the water remains clear and transpa- 
 rent as before ; yet though the union of these bodies appears so 
 perfect, it is not produced by srlTy chemical combination ; both the 
 
 229. What causes those bubbles which ascend, and those which 
 gather on the inside of a vessel when water is heating ? 
 230 Why is air more easily rarefied than water ? 
 
 231. When water begins to boil why do large bubbles rise from 
 the bottom ? 
 
 232. Has vapour always the power of overcoming the pressure 
 of the less heated surface ? 
 
 233. What substances evaporate only from the surface ? 
 
 234. When does solution take place ? 
 
 235. What are the two principal solvent fluids ? 
 
FREE CALORIC, 59 
 
 ialt and the water remain unchanged ; and if you were to separate 
 them by evaporating the latter, you would find the salt in the same 
 state as before. 
 
 Emily. I suppose that water is a solvent for solid bodies, and ca 
 ioric for liquids ? 
 
 Mrs. B. Liquids of course can only be converted into vapour by 
 caloric. But the solvent power of this agent is not at all confined 
 to that class of bodies ; a great variety of solid substances are dis- 
 solved by heat ; thus metals, which are insoluble in water, can be 
 dissolved by intense heat, being first fused or converted into a li- 
 quid and then rarefied into an invisible vapour. Many other bod- 
 ies, such as salt, gums, &c. yield t<> either of these solvents. 
 
 Caroline. And that, no doubt, is the reason why hot water will 
 melt them so much better than cold water. 
 
 Mrs. B. It is so. Caloric may, indeed be considered as having 
 in every instanre, some share in the solution of a body by water, 
 since water, however low its temperature may be, always contains 
 more or less caloric. 
 
 Emily. Then, perhaps, water owes its solvent power merely to 
 the caloric contained in it. 
 
 Mrs. B. That, probably, would be carrying the speculation too 
 far ; I should rather think that water and caloric unite their efforts 
 to dissolve a body, and that4he difficulty or facility of effecting this, 
 depend both on the degree of attraction of aggregation to be over- 
 come, and on the arrangement of the particles which are more or 
 less disposed to be divided and penetrated by the solvent. 
 
 Emily. But have not all liquids the same solvent power as water: 
 
 Mrs. B. The solvent power of other liquids varies according to 
 their nature, and that of the substances submitted to their action. 
 Most of these solvents, indeed, differ essent-ally from water, as they 
 do not merely separate the integrant particles of the bodies which 
 they dissolve, but attack their constituent principles by the power 
 of chemical attraction, thus producing a true decomposition These 
 more complicated operations we must consider in another place, and 
 confine our attention at present to the solutions by water and ca- 
 loric. 
 
 Caroline. But there are a variety of substances which, when dis- 
 solved in water, make it thick and muddy, and destroy its transpa- 
 rency. 
 
 Mrs. B. In this case it is not a solution, but simply a mixture. 
 I shall show you the difference between a solution and a mixture, 
 by putting some common salt into one glass of water, and some 
 powder of chalk into another ; both these substances are white, but 
 their effect on the water will be very different. 
 
 Caroline. Very different, indeed ! The salt entirely disappears 
 
 236. After salt has been dissolved in water, can they be separated 
 so as to have the salt in the same state, as before it was dissolved ? 
 By what means ? 
 
 237. Has caloric any influence in the solution of a body by water. 
 
 238. On what does the difficulty or facility of dissolving bodies 
 depend ? 
 
 239. Have all liquids the same solvent f<>wer as water ? 
 
 240. How do these solvents differ ff' 11 water ? 
 
 241. What is the difference bet*** 611 a solution and a mixture 
 
CO TREE CALORIC. 
 
 and leave the water transparent, whilst the chalk changes it into 
 an opaque liquid like milk. 
 
 Emily. And would lumps of chalk and salt produce similar effects 
 on water " 
 
 Mrs. B. Yes, but not so rapidlv : salt is, indeed, soon melted, 
 though in a lamp : but chalk, which does not mix so readily with 
 water would require a much greater length of time ; I therefore 
 preferred showing you the experiment with both substances redu- 
 ced to powder, which does not in any respect alter their nature, but 
 facilitates the operation merely by presenting a greater quantity of 
 surface to the water. 
 
 I must not forget to mention a very curious circumstance res- 
 pecting solution, which is, that a fluid is not nearly so much in- 
 creased in bulk by holding a body in solution, as it would be, by 
 mere mixture with the body. 
 
 Caroline. How is that possible ? for two bodies cannot exist to- 
 gether in the same space. 
 
 Mrs. B. Two bodies may, by condensation, occupy less space 
 when in union than when separate, and this I can show you by an 
 easy experiment. 
 
 This phial which contains some salt, 1 shall fill with water, pour- 
 ing it in quickly, so as not to dissolve much of the salt ; and when 
 it is quite full I cork it. If I now shake, the phial till the salt is dis- 
 solved, you will observe that it is no longer full. 
 
 Caroline. I shall try to add a little more salt. But now you see 
 Mrs. U. the water runs over. 
 
 Mrs. B. Yes ; but observe that the last quantity of salt you put 
 in remains solid at the bottom and displaces the water ; for it has 
 already melted all the sail it is capable of holding in solution. This 
 is called the point of saturation; and the water in this case is said to 
 be saturated with salt. 
 
 Emily. I think I now understand the solution of a solid body by 
 water perfectly ; but I have not so clear an idea of the solution of a 
 liquid by caloric. 
 
 Mrs. B. It is probably of a similar nature ; but as caloric is an 
 invisible fluid, its action as a solvent is not *o obvious as that of wa- 
 ter. Caloric, we may conceive, dissolves water and converts it in- 
 to vapour by the same process as water dissolves salt ; that is to say, 
 the particles of water are so minutely divided by the caloric as to 
 become invisible. Thus, you are now enabled to understand why 
 the vapour of boiling water, when it first issues from the spout of a 
 kettle is invisible ; it is so, because it is then completely dissolv- 
 ed by caloric. But the air with which it comes in contact, being 
 much colder than the vapour, the latter yields to it a quantity of 
 its caloric. The particles of vapour being thus in a good measure 
 deprived of their solvent, gradually collect, and become visible in 
 the form of steam, which is water in a state of imperfect solution; 
 and if you were further to deprive it of its caloric, it would return 
 to its original liquid state. 
 
 242. Are fluids equally increased in bulk by the solution and the 
 mixture of a solid ? 
 
 243. What experiment nroves that they are not ? 
 
 244. When is a solvent sa ura t e d ? 
 
 245. Why is vapour less visii^ on fj rs t rising f r0 m a liquid, than 
 after having ascended a distance from it ? 
 
FREE CALORIC. 61 
 
 C&roline. That I understand very well. If you hold a gold plate 
 over a tea-urn, the steam issuing from it will be immediately con- 
 verted into drops of water by parting with its caloric to the plate ; 
 but in what state is the steam when it becomes invisible by being 
 liffused in the air? 
 
 Mrs. B. It is not merely diffused, but is again dissolved by the air. 
 Emily. The air, then, has a solvent power, like water and caloric. 
 Mrs. B. This was formerly believed to be the case. But it ap- 
 pears from ino-e recent enquiries that the solvent power of the at- 
 mosphere depends solely upon the caloric contained in it Sometimes 
 the watery vapour diffused in the atmosphere is but imperfectly dis- 
 solved, as is the case in the formation of clouds and fogs ; but if it 
 gets into a region sufficiently warm, it becomes perfectly invisible. 
 Emily. Can any water be dissolved in the atmosphere without 
 having been previously converted into vapour by boiling? 
 
 Mrs. B. Unquestionably : and this constitutes the difference 
 between vaporisation and evaporation Wat?>r, when heated to the 
 boiling point, can no longer exist in the form of water, and must 
 necessarily be converted into vapour or steam, whatever may be 
 > the state and temperature of the surrounding medium ; this is called 
 vaporization. But the atmosphere, by means of the caloric it con- 
 tains, can take up a certain portion of water at any temperature, 
 and hold it in a state of solution. This is simply evaporation. Thus 
 the atmosphere is continually carrying off moisture from the sur- 
 face of the earth, until it is saturated with it. 
 
 Caroline. This is the case, no doubt, when we feel the atmos - 
 phf tedamp. 
 
 Mrs. B. On the contrary, when the moisture is well dissolved it 
 occasions no humidity ; it is only when in a state of imperfect so- 
 lution and floating in the atmosphere, in the form of watery vapour, 
 that it produces dampness. This happens more frequently in win- 
 ter than in summer ; for the lower the temperature of the atmos- 
 phere, the less water it can dissolve ; and in reality it never con- 
 tains so much moisture as in a dry, hot, summer's day. 
 
 Caroline. You astonish me ; but why. then, is the air so dry ia 
 frosty weather, when its temperature is" at the lowest ? 
 
 Emily. This, I conjecture, proceeds not so much from the mois- 
 ture being dissolved, as from its being frozen ;* is not that the case .' 
 Mrs. B. It is ; and the freezing of the watery vapour which the 
 
 * In cold climates, where there is not a cloud to be seen, and the 
 sun rises in all his glory, the air is sometimes full of little particles 
 of ice glistening in every direction, and forming a most beautiful 
 spectacle. This is owing to the condensation, and freezing of the 
 particles of water in the air, by the intense cold. C. 
 
 246. Upon what does the solvent power of the atmosphere depend.' 
 
 247. What causes fogs ? 
 
 248. What is the difference between vaporation and evaporizationr 
 249 Why does the atmosphere sometimes feel damp ? 
 
 250. When does the atmosphere contain most moisture, in sum. 
 mer or winter ? 
 
 251. Why is the air so dry in frosty weather . ? 
 
 252. How is frost produced ? 
 
 6 
 
62 FREE CALORIC, 
 
 atmospheric heat could not dissolve, produces what is called a hoar 
 frost ; for the particles descend in freezing 1 , and attach themselves 
 to whatever they meet with on the surface of the earth. 
 
 The tendency of free caloric to an equilibrium, together with its 
 solvent power, are likewise connected with the phenomena of rain, 
 of dew, &c. When most air of a certain temperature happens to 
 pass through a cold region of the atmosphere, it parts with a por- 
 tion of its heat to the surrounding air ; the quality of caloric, there- 
 fore, which served to keep the water in a state of vapour, being di- 
 minished, the watery particles approach each other, and form them- 
 selves into drops of water, which, being heavier than the atmosphere 
 descend to the earth. There are also other circumstances, and 
 particularly the variation in the weight of the atmosphere, the 
 changes which take place in its electrical state, &c. which may 
 cont ibute to the formation of rain This, however, is an intricate 
 subject, into which we cannot more fully enter at present. 
 
 Emily. In what manner do you account for the formation of dew ? 
 
 Mrs. B. Dew is a deposition of watery particles or minute drops 
 from he atmosphere, precipitated by the coolness of the evening. 
 
 Caroline This precipitation is owing, I suppose, to the cooling 1 
 of the atmosphere, which prevents its retaining so great a quantity 
 of watery vapour in solution as during the heat of the day. 
 
 Mrs. B. Such was, from time immemorial, the generally received 
 opinion respecting the cause of dew : but it has been very recently 
 proved by a <fljfcrse of ingenious experiments of Dr Wells, that the 
 deposition of dew is produced by the cooling of the surface of the 
 earth, which he has shown to take place previously to the cooling 
 of the atmosphere ; for on examining the temperature of a plot of 
 grass just before the dew-fall, he found that it was considerably 
 colder than the air a few feet above it, from which the dew was 
 shortly after precipitated. 
 
 Emily. But why should the earth cool in the evening sooner than 
 the atmosphere ? 
 
 Mrs. B. Because it parts with its heat more readily than the air; 
 the earth is an excellent radiator of caloric, whilst the atmosphere 
 does not possess that property, at least in any sensible degree. To- 
 wards evening> therefore, when the solar heat declines, and when 
 after sun set it entirety ceases, the earth rapidly cools by radiating 
 heat towards the skies; whilst the air has no means of parting with 
 its heat but by coming into contact with the cooled surface of the 
 earth, to which it communicates its caloric. Its solvent power be- 
 ing thus reduced, it is unable to retain so large a portion of watery 
 vapour, and deposits those pearly drops which we call dew. 
 
 Emily. If this be the cause of dew, we need not be apprehensive 
 of receiving any injury from it ; for it can be deposited only on sur- 
 faces that are colder than the atmosphere, which is never the case 
 with our bodies. 
 
 Mrs. B. Very true ; yet I would not advise you for this reason to 
 
 253 How is rain formed ? 
 
 254. In what manner do you account for the formation of dew ? 
 
 255. To what is the precipitation owing that takes place in the 
 production of dew ? 
 
 256. Why does the earth cool sooner in the evening than the at- 
 mosphere ? 
 
 257. What ill effects may result from dew to health ? 
 
FREE CALORIC. 63 
 
 he too confident of escaping all the ill effects which may arise from 
 exposure to the dew ; for it may be deposited on your clothes, and 
 chill you afterwards by its evaporation from them. Besides, when- 
 ever the dew is copious, there is a chill in the atmosphere which is 
 not always safe to encounter. 
 
 Caroline. Wind, then, should promote the deposition of dew, by 
 bringing a more rapid succession of particles of air in contact with 
 the earth, just as it promotes the cooling of the earth and warming 
 of the atmosphere during the heat of the day ? 
 
 Mrs. B. This may be the case in some degree, provided the agi- 
 tation of the air be not considerable ; for when the wind is strong, 
 it is found that less dew is deposited than in calm weather, especial- 
 ly if the atmosphere be loaded with clouds. These accumulation? 
 of moisture not only prevent the free radiation of the earth towards 
 the upper regions, but themselves radiate towards the earth ; for 
 which reasons much less clew is formed than on fine clear nights, 
 when the ra-liaiion of the earth passes without obstacle through the 
 atmosphere to the distant regions of space, whence it receives no 
 caloric in exchange. The dew continues to be deposited during the 
 night, and is generally the most abundant towards morning when 
 the contrast between the temperature of the earth, and that of the 
 air is greatest. V\er sunrise the equilibrium of temperature be- 
 tween those two bodies i<* gradually restored by the solar rays pass- 
 ing freely through the Umosphere to the earth ; and later in the 
 morning the temi>eratur<> of the earth gain* the jascendancy, and 
 gives out caloric to the air by contact, in the same manner as it re- 
 ceives it from the air du- ing the night. 
 
 ( 'an you tell me. now, why a bottle of wine taken fresh from the 
 cellar (in summer particularly,) 'Will so >n he covered with dew; 
 and even the glares imo which the wine is poured will be mois- 
 tened with a similar vapour ? 
 
 Emily. The bottle being colder than the surrounding air, mnst 
 absor > caloric -from it ; the moisture iherefore, which thataircon- 
 tained becomes visible, and forms th^dew which is deposited on 
 the bottle. 
 
 Mrs. B. Very well Em:lv. Now, Caroline, can you inform me 
 why, in a warm room or close carriage, the contrary effect takes 
 place : that is to say, that the inside of the windows is covered with 
 vapour ? 
 
 Caroline. I have heard that it proceeds frprn the breath of those 
 \vithi -i the room or the carnage ; and I suppose it is occasioned by 
 the windows which, being colder than the breatlr,<jj|u)rive it of part 
 of its caloric, and by this means convert it into watenfcvapour. 
 
 Mrs B. Yon have borh explained it extremely wepPlr Bodies at- 
 
 258. % >V hen does win. promote the deposition of dew ? 
 
 259. Why does more Jew accumulate in a clear night than when 
 it is cloudy ? 
 
 260. When is the dew most abundant, and why is it then most 
 abundant ? 
 
 2U. Why is a tumbler or bottle filled with cold water covered 
 with moisture in a warm day ? 
 
 2b2. Why in a warm room or in a close carriage does moisture 
 collect on the inside of the windows ? 
 
 263. Why does less dew collect on rocks and sands, than on grass 
 ^nd vegetables ? 
 
34 FREE CALORIC, 
 
 tract dew in proportion as they are good radiators of caloric, as it is 
 this quality which reduces their temperature below that of the at 
 mosphere ; hence we find that little or no dew is deposited on 
 rocks, sand, or water ; while grass and living vegetables, to which 
 it is so highly beneficial, attract it in abundance another remark- 
 able instance of the wise and bountiful dispensations of Providence, 
 Emily. And we may again observe it in the abundance of dew in 
 summer, and in hot climates, when its cooling effects are so much 
 required ; but I do not understand what natural cause increases 
 the dew in hot weather ? 
 
 Mrs. B. The more caloric the earth receives during the day, the 
 more it will radiate afterwards, and consequently the more rapidly 
 its temperature will he reduced in the evening, in comparison to 
 that of the a mosphere. In the West Indies especially, where the 
 intense heat of the day is strongly contrasted with the coolness of 
 the evening, the dew is prodigiously abundant. During a drought, 
 the dew i less plentiful, as the earth is not sufficiently supplied 
 with moisture to be able to saturate the atmosphere. 
 
 Caroline. \ have oft'-n observed, Mrs. B., that when 1 walk out 
 in frosty weather, with a veil over my face, my breath freezes upou 
 it. Pray what is the reason of that ? 
 
 Mrs. B. It is because the cold air immediately seizes on the calo- 
 ric of your breath, and, by robbing it of its solvent, reduces it to a 
 denser fluid, which is the watery vapour that settles on your veil, 
 and thfire it continues parting with its caloric till it is brought down, 
 to the temperature of the atmosphere, and assumes the form of ice. 
 You may, perhaps, have observed that the breath of animals, or 
 rather the moisture contained in it, is visible in Hamp weather, or 
 during a trost. In the former case, the atmosphere being oversatu- 
 rated with moisture can dissolve no more. In the latter, the cold 
 condenses it into visible vapour ; and for the same reason, the steam 
 arising from water that'is warmer than the atmosphere, becomes 
 risible. Have you never taken notice of the vapour rising from 
 your hands after having dipped them into warm water ? 
 Caroline. Frequently, especially in frosty weather. 
 Mrs. B. v e have already observed that pressure is an obstacle 
 to evaporation : there are liquids which contain so great a quantity 
 of caloric, and whose particles consequently adhere so slightly to- 
 gether, that they may be rapidly con verted into vapour without any 
 elevation of temperature, merely by taking off the weight of the at- 
 mosphere. In such liquids you perceive, it is the pressure of the 
 atmosphere alone that connects their particles, and keeps them m 
 a liquid state. 
 
 Caroline. I do not well understand why the particles of such flu 
 ids should be disunited and converted into vapour, without any el 
 evation of temperature, in spite of the attraction of cohesion. 
 Mrs. B. It is because the degree of heat at which we usually 
 
 264. Why does more dew collect in summer and in cold climates, 
 than in winter and warm climates ? 
 
 265. Why is there a small quantity of dew in a time of drought : 
 
 266. Why is the moisture contained in the breath of animals vi 
 sible in damp weather, or during a frost ? 
 
 267. How are certain liquids, which contain a great degree of ca 
 loric, converted into vapour, without any increase of temperature r 
 
FREE CALORIC. 
 
 observe these fluids is sufficient to overcome their attraction of co- 
 hesion. Ether is of this description ; it will boil and be converted 
 into vapour, at the common temperature of the air, if the pressure 
 of the atmosphere be taken off. 
 
 Emily. I thought that ether would evaporate without either the 
 pressure of the atmosphere being 1 taken awav, or heat applied ; and 
 that it was for that reason so necessary to keep it carefully corked 
 up. 
 
 Mrs. B. It is true it will evaporate, but without ebullition : what 
 I am now speaking- of is the vaporization of ether, or its conversion 
 into vapour by boiling. I am going to show you how suddenly 'he 
 ether in this phial will be converted into vapour, by means of the 
 air pump. Observe with what rapidity the bubbles ascen-l, as 1 
 take off the pressure of the atmosphere. 
 
 Caroline. It positively boils : how singular to see a liquid boil 
 without heat ! 
 
 Mrs B. Now I Fig 7 
 
 shall place the phial Pneumatic Pump. 
 
 of ether in this glass, 
 which it nearly fills, 
 so as to leave only a 
 small space,which I 
 All with water ; and 
 in this state I put it 
 again under the re- 
 ceiver.* You will 
 observe, as I ex- 
 haust the air from 
 it, that whilst the 
 ether boils, the wa- 
 ter freezes ! 
 
 Caroline. It is in- 
 deed wonderful to 
 see water freeze in 
 contaci with a boil- 
 ing fluid! 
 
 Emily. I am at a 
 loss to conceive how 
 the ether can pass to 
 the state of vapour, 
 without an addition 
 
 Ether evaporated, and water frezpn ii: the air pump. A 
 r. B. Gla 
 
 he air pump. 
 -~. C. Th 
 
 Fig. 7. 
 Of Caloric. DOCS it P*al of Ether. B. Glan vessel containing water 
 
 not contain more onrt . one in th * EUwr - lb 
 
 caloric in a state of vapour, than in a state of liquidity ? 
 
 * Two pieces of thin glass ftibes, sealed at one end, might answer 
 iliis purpose better. The experiment, however, as here described, 
 is difficult, and requires a very nice apparatus. But if, instead of 
 phials or tubes, two watch glasses be used, water may be frozen al- 
 most instantly in the same manner The two glasses were placed 
 over oneanother,with a few drops of water interposed between them, 
 and the uppermost glass is filled with ether After working the 
 
 268. How can ether be made to boil without the application of 
 caloric ? 
 
 269. How is the experiment made ? 
 
H> PHEE CALORIC. 
 
 Mrs. #. It certainly does : for though it is the pressure of the 
 atmosphere which condenses it into a liquid, it is by forcing- out the 
 caloric that belongs to it when in an aeriform state. 
 
 Emily. You have therefore, two difficulties to explain. Mr*. E. 
 First, whence the ether obtains the caloric necessary to convert it 
 into vapour, when it is relieved from the pressure of the atmosphere; 
 and, secondly, what is the reason that the water, in which the bot- 
 tle of ether stands, is frozen ? 
 
 Caroline. Now, I think I can answer both these questions. The 
 ether obtains the addition of caloric required, from the water in the 
 glass ; and the loss of the caloric which the latter sustains, is the oc- 
 casion of its freezing. 
 
 Mrs. B. You are perfectly right ; and if you look at the ther- 
 mometer which I have placed in the water, whilst 1 am working 
 the pump, you will see that every time bubbles of vapour are pro- 
 duced, the mercury descends ; which proves that the heat of the 
 water diminishes in proportion as the ether boils. 
 
 Emily. This 1 understand now very well; but if the water freezes 
 in consequence of yielding its caloric to the ether, the equilibrium 
 of heat must, in this case be totally destroyed. Yet you have told 
 us, that the exchange of caloric between two bodies of equal lem- 
 perature, was always equal ; how, then, is it that the water, which 
 was originally of the same temperature as the ether, gives out calo- 
 ric to it, till the water is frozen and the ether made to boil ? 
 
 J\lrs B. I suspected that you would make these objections ; and, 
 in order to remove them, 1 enclosed two thermometers in the air- 
 pump ; one of which stands in the glass of water, the other in the 
 phial of ether; and you may see that the equilibrium of tempera- 
 ture is not destroyed ; for as the thermometer descends in the wa- 
 ter, that in the ether sinks in the same manner ; so that both ther- 
 mometers indicate the same temperature, though one of them is in 
 a boiling, the other in a freezing liquid. 
 
 Emily. The ether, then, becomes colder as it boils ? This is so 
 contrary to common experience, that I confess it astonishes me ex- 
 ceedingly. 
 
 Caroline. It is, indeed, a most extraordinary circumstance. But 
 pray how do you account for it ? 
 
 Mrs. B. I cannot satisfy your curiosity at present ; for before 
 we can attempt to explain this apparent paradox, it is necessary to 
 become acquainted with the subject of LATENT HEAT : and that, I 
 think, we must defer till our next interview 
 
 Caroline. I believe, Mrs. B., that you are glad to put off the ex- 
 planation ; for it must be a very difficult point to account for. 
 
 Mrs. B. I hope, however, that 1 shall do it to your complete sat 
 isfaction. 
 
 Emily. But before we part, give m% leave to ask you one ques- 
 
 270 fn what state does ether exist when the pressure of the at- 
 mosphere is taken off? 
 
 271 Why does the evaporation of ether freeze water ? 
 
 272. What experiment is made with water and ether, and two 
 thermometers ? 
 
FREE CALORIC. i')"i 
 
 tiou. Would not water, as well as ether, boil with less heat, if de- 
 prived of the pressure of the atmosphere ? 
 
 B. Undoubtedly You must always recollect that then 
 are two forces to overcome, in order to make a liquid boil or evap- 
 01 aie ; the- attract on of aggregation, and the weight of the atmos- 
 phere On the summit of a high mountain (as M. De Saussure as- 
 certained on Mount Blanc,) much less heat is required to make 
 water boil, than in the plain where the weight of the atmosphere is 
 greater.* Indeed, if the weight of the atmosphere be entirely re- 
 moved b^ means of a good air pump, and if water be placed in the 
 exhausted receiver, it will evaporate ^o last, however* cold it may 
 be, as to give it the appearance of boiling from the surface. But 
 without the assistance of the air-pump. I can show you a very pret- 
 ty experiment, which proves the effect 6f the pressure of the at- 
 mosphere in this respect. 
 
 Observe that this Florence flask is about half full of water, and 
 the upper half of invisible vapor, the water facing in the act or bail- 
 ing. I take it from the lamp, and cork it carefully the water, you 
 see. immediately ceases boiling. 1 shall now dip the flask into a 
 ba^in -f cold water.f 
 
 Caroline. But look Mrs B. the water begins to boil again, al- 
 though the cold water must rob it more and more of its caloric ! 
 What can be the reason of that ? 
 
 Mrs. B. Let us examine its temperature. You see the thermom- 
 eter immersed in it remains stationary at 180 degrees, which is 
 about 30 degrees below the boiling point. When I took the flask 
 from the lamp, I observed to you that the upper part of it was fill- 
 ed with vapor ; this being compelled to yield its caloric to the cold 
 water, was again condensed into water. What then filled the up- 
 per part of the flask ? 
 
 Emily. Nothing ; for it was too well corked for the air to gain 
 admittance, and therefore, the upper part of the flask must be a 
 vacuum. 
 
 Mrs. B. The water below, therefore, no longer sustains the 
 pressure of the atmosphere, and will consequently boil at a much 
 lower temperature. Thus you see, (hough it had lost many degrees 
 of heat, it began boiling again'the instant the vacuum was formed 
 above it. The boiling has now ceased, the temperature of the water 
 
 * On the top of Mount Blanc, water boiled when heated only to 
 137 degrees, instead of 212 degrees. 
 
 f The same effectmay be produced by wrappinga cold wet linen 
 cloth round the upper part of the flask. In order to show you how 
 much the water cools whilst it is boiling,a thermometer graduated on 
 the tube itself, may be introduced into the bottle through the cork.-C 
 
 273. What two forces are to be overcome in order to make a li- 
 quid boil or evaporate ? 
 
 274. Why does it require the application of less caloric to boil 
 water on a high mountain than on low land ? 
 
 275. What is the appearance of water when placed in an ex- 
 hausted receiver ? 
 
 276. What experiment is mentioned to show how the boiling 1 of 
 liquids is effected by atmospherical pressure ? 
 
G8 FREE CALORIC. 
 
 being still farther reduced; if it had been ether instead of water, it 
 would have continued boiling- much longer, for ether boils under 
 the usual atmospheric pressure, at a temperature as low as 100 de- 
 grees ; and in a vacuum it boils at almost any temperature; but 
 water being- a more dense fluid, requires a more considerable quan- 
 tity of caloric to make it evaporate quickly, even when the press- 
 ure of (he atmosphere is removed. 
 
 Emily. What proportion of vapour can the atmosphere contain 
 in a state of solution ? 
 
 Mrs B I do not know whether it has been exactly ascertained 
 by experiment ; but at any rate this proportion must vary, accord- 
 ing so the temperature of the atmosphere ; for the lower the tem- 
 per Uure, the smaller must be the proportion of vapor that the at- 
 mosphere can contain. 
 
 To conclude the subject of free caloric, I should mention Ignition, 
 by which is meant that emission of light which is produced in Bod- 
 ies at a very high temperature, and which is the effect of accumu- 
 lated caloric 
 
 Emily. You mean, I suppose, that light which is produced by a 
 burning body. 
 
 Mrs. B. No ; ignition is quite independent of combustion. 
 Clay, chalk, and indeed all incombustible substances may be made 
 red hot. When a body burns, the light emitted is the effect of a 
 chemical change which takes place, whilst ignition is the effect of 
 caloric alone, and no other change than that of temperature is pro- 
 duced in tile ignited body. 
 
 All solid bodies, and most liquids, are susceptible of ignition, or 
 in other words, of being heated so as to become luminous ; and it is 
 remarkable that this takes place pretty nearly at the same tempera- 
 ture in all bodies, that is, at about 800 degrees of Fahrenheit's scale. 
 
 Emily. But how can liquids attain so high a temperature, without 
 beintr converted into vapour? 
 
 Mrs. B. By means of confinement and pressure. Water confin- 
 ed in a strong iron vessel (called Papin's digester.) can have its 
 temperature raised to upwards of 400 degrees. Sir James Hall has 
 made some very curious experiments on the effect of heat assisted 
 by pressure; by means of strong gun barrels, he succeeded in melt- 
 ing a variety of substances which were considered as infusible ; and 
 it is not unlikely that, by similar methods, water itself might be 
 heated to redness. 
 
 Emily. 1 am surprised at that ; for I thought that the force of 
 steam was such as to destrov almost all mechanical resistance. 
 
 Mrs. B. The expansive force of steam is prodigious ; but in or- 
 der to subject water to such high temperature, it is prevented by 
 confinement from being converted into steam, and the expansion ol 
 
 277. What proportion of vapour can the atmosphere contain in a 
 state of solution ? 
 
 278. What is meant by ignition ? 
 
 279. How does ignition vary from combustion ? 
 
 280. Are liquids susceptible of ignition ? 
 
 281. At what temperature does ignition take place? 
 
 282 How can they attain so high a temperature, without being- 
 converted into vapour ? 
 283. What experiments were made by Sir James Hall ? 
 
COMBINED CALORIC. 
 
 69 
 
 heated water is comparatively trifling 1 . But we have dwelt so long 
 on the subject of free caloric, that we must reserve the other mod- 
 ifications of that agent to our next meeting 1 , when we shall endeav- 
 or to proceed more rapidly. 
 
 CONVERSATION IV. 
 
 ON COMBINED CALORIC, COMPREHENDING SPECIFIC AND LA- 
 TENT HEAT. 
 
 Mm. B. We are now to examine the other modifications of ca- 
 loric 
 
 Caroline. I am very curious to know of what nature they can 
 be ; for I have no notion of any kind of heat that is not perceptible 
 to the senses. 
 
 Mrs. B. In order to enable you to understand them, it will be 
 necessary to enter into some previous explanations. 
 
 It has been discovered by modern chemists, that bodies of a dif- 
 ferent nature, heated to the same temperature, do not contain the 
 same quantity of caloric. 
 
 Caroline. How could that be ascertained ? Have you not told 
 us tha 1 it is impossible to discover the absolute quantity of caloric 
 which bodies contain ? 
 
 Mrs. B. True ; but at the same time I said tUat we were enabled 
 to form a judgment of the proportion which bodies bore to each oth- 
 er'in this respect Thus it is ound that, in order to raise the tem- 
 perature of different bodies -he same number of degrees, different 
 quantities of caloric are required for each of them. If for in- 
 stance, you place a pound of lead, a pound of chalk, and a pound 
 of milk, in a hot. oven, they will be gradually heated to the tempe- 
 rature of the oven ; but the lead will attain it first, the chalk next, 
 and the milk last. 
 
 Caroline. That is a natural consequence of their different bulks ; 
 the lead being the smallest bodv, will be heated soonest, and the 
 milk, which is the larg-est, will require the longest time. 
 
 Mrs. B That explanation will not do; for if the lead be the 
 least in bulk, it offers also th> least surface to the caloric, the quan- 
 tity of heat therefore, which can enter into it in the same space of 
 time i- proportionally smaller. 
 
 Emily \ Why, then, do not the three bodies attain the temperature 
 of the oven at the same time ? 
 
 Mrs. B It is supposed to be on account of the different capaci- 
 ties of these bodies for caloric. 
 
 Caroline. Whai do you mean by the capacity of a body for ca- 
 loric ? 
 
 284. Do bodies of a different nature heated to the same tempera- 
 ture contain equal quantities of caloric ? 
 
 285. What facts illustrative of this case mentioned of lead ; chalk 
 and milk ? 
 
<0 COMBINED CALORIC. 
 
 Mrs. B. I mean a certain disposition of bodies to require more or 
 less caloric for raising their temperature to any degree of heat. 
 Perhaps the fact may be thus explained : 
 
 Let us put as many marbles into this glass as it will contain, and 
 pour sand over them observe how the sand penetrates and 
 lodges between them- We shall now fill another glass wiih pebbles 
 of various forms you see that they arrange themselves in a more 
 compact manner than the marbles, which being globular, can touch 
 each other by a single point only. The pebbles, therefore, will not 
 admit so much sand between them ; and consequently one of these 
 glasses will necessarily contain more sand than the other, though 
 both of them be equally full. 
 
 Caroline. This I understand perfectly. The marbles and the 
 pebbles represent two bod;es of different kinds, and the sand, the 
 caloric contained in (hem ; and it appears very plain, from this com- 
 parison, that one body mav admit of more caloric between its par- 
 ticles than another. 
 
 Mrs. B. You can no longar be surprised, therefore, that bodies of 
 a different capacity for calo ic should require different proportions 
 of that fluid to raise their temperatures equally. 
 
 Emily, But I do not conceive why the body that contains the 
 most caloric should n-it be of the highest temperature ; that is to 
 say. feel hot in proportion to the quantity of caloric it contains. 
 
 Mm B The caloric that is employed^ filling the capacity of a 
 bodv is not free caloric ; but is imprisoned as it were, in the body, 
 and is therefore, imperceptible ; for we can feel only the caloric 
 which the body parts with, and not that which it retains. 
 
 Caroline. It appears to me very extraordinary, that heat should 
 be confined in a body in such a manner as to be imperceptible. 
 
 Mrs. B. If you lay your hand on a hot body, you feel only the 
 caloric which leaves it. and enters your hand ; for it is imnossible 
 that you should be sensible of that which remains in the body The 
 thermometer in the same manner, is effected only by the free calor- 
 ic which a body transmits to it, and not at all by that which it does 
 , not parl with. 
 
 Caroline. I begin to understand it: but I confess that the idea of 
 Insensible heat is so new and strange to me, that it requires some 
 time to render it familiar. 
 
 Mrs. B Call it insensible caloric, and the difficulty will appear 
 much less formidable. It is indeed a sort of contradiction to call it 
 heat, when it is so situated a- to be incapable of producing that sen- 
 sation. Yet this modification of caloric is commonly called spiLcrr- 
 ic HEAT 
 
 Caroline But it certainly would have been more correct to have 
 called it specific caloric 
 
 28e>. What is to be understood by the capacity of a body for ca- 
 loric ? 
 
 287 How is this fact explained ? 
 
 28H. Why do not bodie that contain most caloric feel hot m pro 
 portion to the quantity of caloric they contain ? 
 
 289. When a body' transmits caloric to a thermometer, is the 
 thermometer effected by what remains in the body ? 
 
 290. What is the imperceptible heat which bodies contain called : 
 
COMBINED CALORIC 71 
 
 Emily. I do not understand how the term specific applies to this 
 modification of caloric. 
 
 rs B. It expresses the relative quantity of caloric which dif- 
 ferent species of bodies of the same weight and temperature are ca- 
 pable of containing 1 . This modificatioH is also frequently called 
 heat of capacity, a term perhaps preferable, as it explains better its 
 own meaning. 
 
 You now understand, I suppose, why the milk and chalk required 
 a longer portion of time than the lead, to raise their temperature to 
 that of the oven ? 
 
 Emily. Yes ; the milk and chalk having a greater capacity for 
 caloric than the lead, a greater proportion of that fluid became in- 
 sensible in those bodies ; and the more slowly, therefore, their tem- 
 perature was raised. 
 
 Caroline. But might not this difference proceed from the differ- 
 ent conducting powers of heat in these three bodies, since that which 
 is the best conductor must necessarily attain the temperature ot" 
 the oven first ? 
 
 Mrs. B Very well observed, Caroline. This objection would bo 
 insurmountable if we could not, by reversing the experiment, prove 
 that the milk, the chalk, and the lead, actually absorbed different 
 quantities of caloric, and we know that if the different time they 
 took in heating, proceeded merely from their different conducting 
 powers, they would each- have acquired an equal quantity of caloric^ 
 
 Caroline. Certainly But how can you reverse this experiment ? 
 
 Mrs B. It may be done by cooling the several bodies to the 
 same degree, in an apparatus adapted to receive and measure the 
 caloric which they give out. Thus, if you plunge them into three 
 equal quantities of water, each at the same temperature, you will 
 be able to judge of the relative quantity Of caloric which the three 
 bodies contained, by that, which, in cooling, they communicated to 
 their respective portions of water ; for the same quantity of caloric 
 which they each absorbed to raise their temperature, will abandon 
 them in lowering it : and, on examining the three vessels of water, 
 you will find the one in which you immersed the lead to be the 
 least heated ; that which held the chalk will be the next ; and that 
 which contained the milk will be heated the most of all. The cel- 
 ebrated Lavoisier has invented a machine to estimate, upon this 
 principle, the specific heat of bodies in a more perfect manner ; but 
 I cannot explain it to you, till you are acquainied with the next 
 modification of caloric. 
 
 Emily* The more dense a body is, I suppose, the less is its capa- 
 city for caloric ? 
 
 Mrs. B. This is not always the case with bodies of different na- 
 ture ; iron, for instance, contains more specific heat than tin, though 
 it is more dense. This seems to show that specific heat does not 
 merely depend upon the interstices between the particles ; but 
 
 291. Do all bodies of equal weight contain the same capacity for 
 caloric ? 
 
 292. How is the experiment of the heated lead, chalk, and milk 
 explained ? 
 
 293. How can we ascertain the capacity of a body for caloric ? 
 
 294. On what is the capacity of caloric chiefly depending ? 
 
7'2 COMBINED CALORIC. 
 
 probably, also upon some peculiar constitution of the bodies, wljick 
 we do not comprehend. 
 
 Emily- But, Mrs. B., it would appear to me more proper to com- 
 pare bodies by measure, rather than by weight, in order to estimate 
 their specific heat. Why, for instance should we not compare pints 
 of milk, of chalk and of lead, rather than pounds of those substan- 
 ces ; for equal weights may be composed of very different quanti- 
 ties ? 
 
 Mrs. B. You are mistaken my dear; equal weight must contain 
 equal quantities of matter ; and when we wish to know what is the 
 relative quantity of caloric, which substances of various kinds are 
 capable of containing under the same temperature, we must com- 
 pare equal weights, aud not equal bulks, of those substances. Bo- 
 dies of the same weight may undoubtedly be of very different di- 
 mensions ; but this does not 'change their real quantity of matter. 
 A pound of feathers does not contain one atom more than a pound 
 of lead. 
 
 Caroline. I have another difficulty to propose. It appears to me 
 that if the temperature of the three bodies in the oven did noi rise 
 equally, they would never reach the same degree, the lead would 
 always keep its advantage over the chalk and milk, and would, per- 
 haps, be boiling Before the others had attained the temperature of 
 the oven. 1 think you might as well say that in the course of time, 
 you and 1 shall be of the same age. 
 
 Mrs. B. Your comparison is not correct, Caroline. As soon as 
 the lead reached the temperature of the oven, it would remain sta~ 
 tionary ; for it would then give out as much heat as it would receive. 
 You should recollect that the exchange of radiating heat, between 
 two bodies of equal temperature, is equal ; it would be impossible, 
 therefore, for the lead to accumulate heat after having attained the 
 temperature of the oven ; and that of the chalk and milk, therefore, 
 would ultimately arrive at the same standard. Now I fear that this 
 will not hold good with respect to our ages, and that as long as I 
 live, I shall never cease to keep my advantage over you. 
 
 Emily. I think that I have found a comparison for specific heat, 
 which is very applicable Suppose that two men of equal weight 
 and bulk, but who require different quantities of food to satisfy 
 their appetites, sit down to dinner, both equally hungry ; the one 
 would consume a much greater quantity of provisions than the oth- 
 er, in order to be equally satisfied. 
 
 Mrs. B. Yes, that is very fair ; for the quantity of food necessa- 
 ry to satisfy their respective appetites, varies in the same manner 
 as the quantity of caloric requisite, to raise equally the temperature 
 of different bodies. 
 
 Emily. The thermometer, then, affords no indication of the spe- 
 cific heat of bodies. 
 
 Mrs. B. None at all ; no more than satiety is a test of the quan- 
 tity of food eaten. The thermometer, as I have repeatedly said, can 
 
 295 Why are not bodies compared by measure rather than 
 weight to estimate their specific heat ? 
 
 296. If different bodies have different capacities for caloric, why 
 do they not rise to different temperatures in the same atmosphere ? 
 
 297. Does the thermometer afford any indication of the specific 
 lieat of bodies ? 
 
FREE CALORIC. 73 
 
 L>e affected only by free caloric which alone raises the temperature 
 of bodies. 
 
 But there is another mode of proving the existence of specific heat 
 which affords a very satisfactory illustration of that modification. 
 This, however, I did not enlarge upon before, as I thought it might 
 appear to you rather complicated. If you mix two fluids of different 
 temperatures, let us say the one at 50 degrees, and the other at 100 
 degrees, of what temperature do you suppose the mixture will be ? 
 
 Caroline. It will be, no doubt, the medium between the two, that 
 is to say, 75 degrees. 
 
 Mrs. B, That will be the case if the two bodies happen to have 
 the same capacity for caloric ; but if not, a different result will be ob- 
 tained. Thus, for instance, if you mix together a pound of mercury, 
 heated at 50 degrees, and a pound of water heated at 100 degrees, 
 the temperature of the mixture, instead of being Th degrees, will be 
 80 degrees ; so that the water will have lost only 12 degrees, whilst 
 the mercury will have gained 3K degrees ; from which you will con 
 elude that the capacity of mercury for heat is less than that of water 
 
 Caroline. I wonder that the mercury should have so tittle specific 
 heat. Did we not see it was a much better conductor of heat than 
 water ? 
 
 Mrs. B. And it is precisely on that account that its specific heat 
 is less. For since the conductive power of bodies depends, as we 
 have observed before, on their readiness to receive heat and part 
 with it, it is natural to expect that those bodies which are the worst 
 conductors should absorb the most caloric before they are disposed 
 [o part with it to other bodies. Bullet us now proceed to latent heat. 
 
 Caroline. And pray what kind of heat is that ? 
 
 Mrs. B. It is another modification of combined caloric, which i^ 
 so analogous to specific heat, that most chemists make no distinc- 
 tion between them ; but Mr. Pictet, in his Essay on Fire, has so 
 clearly discriminated them, that I am induced to adopt his view ol 
 the subject. We therefore call latent heat that portion of insensi- 
 ble caloric which is employed in changing the state of bodies ; thai 
 is to say, in converting solids into liquids, or liquids into vapour. 
 When a body changes its state from solid to liquid, or from liquid 
 to vapour, its expansion occasions a sudden and considerable in- 
 crease of capacity for heat, in consequence of which it immediately 
 absords a quantity of caloric, which becomes fixed in the body it 
 has transformed ; and, as it is perfectly concealed from our senses, 
 it has obtained the name of latent heat. 
 
 Caroline. I think it would be much more correct to call this mo- 
 dification latent caloric instead of latent heat, since it does not ex- 
 cite the sensation of heat. 
 
 Mrs. B. This modification of heat was discovered and named by 
 Dr. Black long before the French chemists introduced the term calo- 
 ric, and we must not presume to change it, as it is still used by much 
 
 298. What other method is mentioned as proving the existence 
 of specific heat ? 
 
 299. What will be the result as to temperature, if mercury bear- 
 ed at 50, and water heated at 1 00 degrees be mixed together ? 
 
 300. Why has mercury so little specific heat? 
 
 301. What is latent caloric ? 
 
 302. What does the conversion of a solid to a liquid occasion? 
 
74 COMBINED CALORIC. 
 
 better chemists than ourselves. Besides, you are not to supposf 
 that the nature of heat is altered by being variously modified : for if 
 latent heat and specific heat do not excite the same sensations as 
 free caloric, it is owing to their being in a state of confinement, 
 which prevents them from acting upon our organs ; and conse- 
 quently, as soon as they are extricated from the body in which they 
 are imprisoned, they return to their state of free caloric. 
 
 Emily. But I do not yet clearly see in what respect latent heat 
 differs from specific beat ; for they are both of them imprisoned 
 and concealed in bodies. 
 
 Mrs- B. Specific heat is that which is employed in filling the ca- 
 pacity of a body for caloric, in the state in which this body actually 
 exists ; while latent heat is that which is employed only in affecting 
 a change of state, that is, in converting bodies from a solid to a li- 
 quid, or from a liquid to an aeriform state. But I think, that in a 
 general point of view, both these modifications might be compre- 
 hended under the name of heat of capacity, as in both cases the ca- 
 loric is equally engaged in filling the capacity of bodies. 
 
 I shall now show you an experiment, which I hope will give you 
 a clear idea of what is understood by latent heat. 
 
 The snow which you see in this phial has been cooled by certain 
 chemical means, (which I cannot well explain to you at present,) 
 to five or six degrees below the freezing point, as you will find in- 
 dicated by the thermometer which is placed in it. We shall expose 
 it to the heat of a lamp, arid you will see the thermometer gradual- 
 ly rise, till it reaches the freezing point- 
 
 Emily. But there it stops, Mrs. B., and yet the lamp burns just 
 as well as before. Why is not its heat communicated to the ther- 
 mometer ? 
 
 Caroline. And the snow begins to melt ; therefore it must be ri- 
 sing above the freezing point. 
 
 Mrs. B. The heat no longer affects the thermometer, because it 
 is wholly employed in converting the ice into water. As the ice 
 melts, the caloric becomes latent in the new formed liquid, and 
 therefore cannot raise its temperature; and the thermometer will 
 consequently remain stationary, till the whole of the ice be melted. 
 
 Caroline. Because the conversion of the ice into water being 
 completed, the caloric no longer becomes latent ; and therefore the 
 heat which the water now receives raises its temperature, as you 
 find the thermometer indicates. 
 
 Emily. But I do not think that the thermometer rises so quickly 
 in the water as it did in the ice, previous to its beginning to melt 
 though the lamp burns equally well. 
 
 303. What is the consequence if latent and specific heat are ex- 
 tricated from the body in which they are imprisoned ? 
 304- What is the difference between specific heat and latent heat? 
 
 305. By what name is it thought they may both be called ? 
 306a. Why does not the thermometer rise in a warm room when 
 
 its bulb is in a piece of ice ? 
 
 306. In what experiment may be seen the existence of latent heat? 
 
 307. Why does the thermometer begin to rise as soon as the ice 
 to mel ted? 
 
COMBINED CALORIC. 75 
 
 Jtirs. B. That is owing to the different specific heat of ice and 
 water. The capacity of water for caloric being greater than that 
 of ice, more beat is required to raise its temperature, and therefore 
 the thermometer rises slower in the water than it did in the ice. 
 
 Emily. True ; you said that a solid body always increased its ca- 
 pacity for heat by becoming fluid, and this is an instance of it. 
 
 Mrs. B. Yes ; and the latent heat is that which is absorbed in 
 consequence of the greater capacity which the water has for heat, 
 in comparison to ice. 
 
 I must now tell you a curious calculation founded on that consi- 
 deration. I have before observed to ymi, that though the thermo- 
 meter shows us the comparative warmth of bodies, and enables us 
 to determine the same point at different times and places, it gives 
 us no idea of the absolute quantity of heat in any body. We cannot 
 tell how low it ought to fall by the privation of all heat, but an at- 
 tempt has been made to inter it in the following manner. It has 
 been found by experiment, that the capacity of water for heat, 
 when compared with that of ice, isaa 10 to 9 ; so that, at the same 
 temperature, ice contains one tenth of caloric less than water. By 
 experiment, also, it is observed, that in order to melt ice, there must 
 he added to it as much heat as would, if it did not melt it, raise its 
 temperature 140 degrees.* This quantity of heat is, therefore, ab- 
 sorbed, when the ice, by being converted into water, is made to 
 contain one ninth more caloric than it did before. Therefore 140 
 degrees is a ninth part of the heat contained in ice at 30 degrees ; 
 and the point of zero, or the absolute privation of heat, must conse- 
 quently be 1260 degrees below 31 degrees.f 
 
 This mode of investigating so curious a question is ingenious, but 
 its correctness is not yet established by similar calculations for other 
 bodies. The points of absolute cold, indicated by this method in va- 
 rious bodies, are very remote from each other ; it is however, possi- 
 ble, that this may arise from some imperfection in the experiments. 
 
 Caroline. It is indeed very ingenious but we must now attend 
 to our present experiment. The water begins to boil, and the 
 thermometer is again stationary. 
 
 Mrs. B. Well, Caroline, it is your turn to explain the phenom- 
 enon. 
 
 * That is, water contains 140 degrees of heat more than is indi- 
 cated by the thermometer. C 
 
 f This calculation was made by Dr. Irvine- Dr Crawford af- 
 terwards placed the real zero at 1500 degrees below the Oof Fah- 
 renheit. Still later, Mr. Dalton ha* turned his attention to the 
 same subject The mean of His experiments places the real zero 
 6000 degrees below the freezing point. All this goes to show that 
 very little has yet b*en demonstrated on this difficult question. C. 
 
 308. Why does the thermometer rise slower in the water than it 
 did in the ice ? 
 
 309. Since a thermometer does not indicate the absolute quanti- 
 ty of caloric contained in any body, what is its use ? 
 
 310 How much latent heat does wa'er contain ? 
 
 311. How much heat must be added to ice in order to melt it ? 
 
 3 1 2. What was proposed by Dr. Crawford^ and by Dr. Dalton > 
 as to fixing the real zero ? 
 
76 COMBINED CALORIC. 
 
 Caroline. It is wonderfully curious ! The caloric is now busy iu 
 changing the water into steam, in which it hides itself, and becomes 
 insensible. This is another example of latent heat, producing a 
 change of form. At first it converted a solid body into a liquid, and 
 now it turns the liquid into vapour ! 
 
 Mrs. B. You see, my dear, how easily you have become acquain- 
 ted with these modifications of insensible heat, which at first ap 
 peared so unintelligible. If, now, we were to reverse these chan- 
 ges, and condense the vapour into water, and the water into ice. 
 the latent heat would re-appear entirely, in the form of free caloric. 
 
 Emily. Pray do let us see the effect of latent heat returning to 
 its free slate. 
 
 Mrs. B. For the purpose of showing this, we need simply con- 
 duct the vapour through this tube into this vessel of cold water? 
 where it will part with its latent heat and return to its liquid form. 
 
 Emily. How rapidly the steam heats the water ! 
 
 Mrs. B. That is because it does not merely impart its free caloric 
 to the water, but likewise its latent heat. This method of heating 
 liquids, has been turned to advantage, in several economical estab- 
 lishments. The steam kitchens, which are getting into such gene- 
 ral use,are upon the same principle. The steam is conveyed through 
 a pipe in a similar manner, into the several vessels which contain 
 the provisions to be dressed, where it communicates to them its lat- 
 ent culoric and returns to the state of water. Count Rumford 
 makes great use of this principle in many of his fire-places : his 
 grand maxim is to avoid all unnecessary waste of caloric, for which 
 purpose he confines the heat in such a manner, that not a particle of 
 it shall unnecessarily escape ; and while he economises the free ca- 
 loric, he takes care also to turn the latent heat to advantage. It is 
 thus that he is enabled to produce a degree of heat superior to that 
 which is obtained in common fire places, though he employs less fuel, 
 
 Emily When the advantages of such contrivances are so clear 
 and plain, T cannot understand why they are not universally used. 
 
 Jt/r*. B. A long 1 ime is always required before innovations, how* 
 ever useful, can be reconciled with the prejudices of the vulgar. 
 
 Emily. What a pily it is that there should be a prejudice against 
 new inventions : how much more rapidly the world would improve 
 if such useful discoveries were immediately and universally adopted! 
 
 JV/rs B. T believe, my dear, that there areas many novelties at- 
 tempted to be introduced, the adoption of which would be prejudi- 
 cial to society, ns there are of those which would be beneficial to it. 
 The well-informed, though by no mesns exempt from error, have an 
 unquestionable ad vantage over the illiterate, in judging- what is like- 
 ly or not to prove serviceable ; and therefore we find the foimer 
 mo?e ready to adopt such discoveries as promise to be really advan- 
 tageous, than the latter, who, having no other t^st of the value of a 
 novelty but time and experience, at first oppose its introduction. 
 
 313. What is that heat called which produces a change of form 
 ID bodies ? 
 
 314. How may latent heat be converted into free caloric : 
 
 315. In what experiment may be st-en the effect of latent heat 
 returning to its free state ? 
 
 316. What is the advantage of Count Rumford's improved fire 
 places ? 
 
COMBINED CALORIC. 
 
 77 
 
 The well informed, however, are frequently disappointed in their 
 most sanguine expectations, and the prejudices of the Tulgar, 
 though they often retard the progress of knowledge, yet sometimes, 
 it must be admitted, prevent the propagation of error. But we are 
 deviating from our subject. 
 
 We have converted steam irjto water, and are now to change 
 water into ice, in order to render the latent heat sensible, as it es- 
 capes from the water on its becoming solid. For this purpose we 
 must produce a degree of cold that will make water freeze. 
 
 Caroline. That must be very difficult to accomplish in this warm 
 room. 
 
 Mrs B. IV ot so much as you think. There are certain chemic- 
 al mixtures which produce a rapid change from the solid to the flu- 
 id state, or the reverse, in the substances combined, in consequence 
 of which change latent heat is either extricated or absorbed. 
 Emily. I do not quite understand you. 
 
 Mrs. B. This snow and salt, which you see me mix together, 
 are melting rapidly ; heat therefore must be absorbed by the mix- 
 ture, and cold produced. 
 
 Caroline. It feels even colder than ice, and yet the snow is melt- 
 ed. This is very extraordinary. 
 
 Mrs. B. The cause of the intense cold of the mixture is to be at- 
 tributed to the change of a solid to a fluid state. The union of the 
 snow and salt produces a new arrangement of their particles, in 
 consequence of which they become liquid ; and the quantity of 
 caloric, required to effect this change, is seized upon by the mix- 
 ture whenever it can be obtained This eagerness of the mixture 
 for caloric, during its liquefaction, is such that it converts part of 
 its own free caloric into latent heat, and it is thus that the tempera- 
 ture is lowered. 
 
 Emily. Whatever you put in this mixture, therefore, would 
 freeze ? 
 
 Mrs B. Yes ; at least any fluid that is susceptible of freezing at 
 that temperature. 1 have prepared this mixture of salt and snow 
 for the purpose of freezing the water from which you are desirous 
 of seeing the latent heat escape. I have put a thermometer in the 
 glass of water that is to he frozen, in order that you may see how 
 it cools. 
 
 Caroline The thermometer descends, but the heat which the 
 water is now losing is its free, not its latent heat 
 
 Mrs. B. Certainly ; it does not part with its latent heat till it 
 changes its state and is converted into ice. 
 
 Emily. But here is a very extraordinary circumstance ! The 
 thermometer has fallen below the freezing point, and yet the water 
 is not frozen.* 
 
 * To make this experiment striking, the glass containing the wa- 
 ter and thermometer ought to be kept perfectly still until the mercu- 
 ry sinks below the freezing point. Then agitate the water, or drop 
 
 <6l 7. How is latent heat rendered sensible ? 
 
 318. How can water be made to freeze in a warm room ? 
 
 319. Why is a mixture of snow and salt so intensely cold ? 
 
 320. When does water part with its latent heat ? 
 
 7* 
 
~8 COMBINED CALORIC, 
 
 Mrs. B. That is always the case previous to the freezing of wa- 
 ter when it is in a state of rest. Now it begins to congeal, and you 
 may observe that the thermometer again rises to the freezing point. 
 
 Carolitie It appears to me very strange that the thermometer 
 should rise the very moment that the water freezes ; for it seems to 
 imply that the water was colder before it froze than when in the 
 act of freezing. 
 
 Mrs B. It is so ; and after our long dissertation on this circum- 
 stance. I did not think it would appear so surprising to you. Re- 
 flect a little, and 1 think you will discover the reason of it 
 
 Caroline- It must be, no doubt, the extraction of latent heat, at 
 the instant the water freezes, which raises the temperature. 
 
 Mrs. B. Certainly : and if you now examine the thermometer, 
 you will find that its rise was but temporary, and lasted only during 
 the disengagement of the latent heat now that all the water is fro- 
 zen it falls again, and will continue to fall till the ice and mixture 
 are all of an equal temperature. 
 
 Emily. And c*n you show us anv experiments in which liquids., 
 by being mixed, become solid and disengage latent heat? 
 
 Mrs. B. I could show you sf-veral, but you are not yet sufficient 
 iy advanced to understand them well. I shall, however, try one, 
 which will afford you a striking instance of the fact. The fluid wh ch 
 you see in this phial consists of a quantity of a certain salt called 
 murint of lime, dissolved in water. Now, if I pour into it a few dropt: 
 of this other fluid, called sulphuric acid, the whole, or very nearly 
 the whole, will be instantaneously converted into a solid mass. 
 
 Emily. How white it turns ! I feel the latent heat escaping ; for 
 the bottle is warm, and the fluid is changed to a solid white sub- 
 stance like chalk !* 
 
 Caroline. This is, indeed, the most curious experiment we have 
 seen yet. But pray what is that white vapour which ascends from 
 the mixture ? 
 
 Mrs. B. You are not yet enough of a chemist to understa|j| that 
 But take care, Caroline, do not approach too near it, for it has a 
 very pungent smell. 
 
 I shall show you another instance similar to that of the water, 
 which you observed to become warmer as it froze. I have in this 
 phial a solution of a salt called sulphat of soda, or Glauber's salt, 
 made very strong, and corked up when it was hot, and kept without 
 
 into it a small piece of ice, and it instantly shoots into crystals, and 
 the thermometer rises. C. 
 
 * The sulphuric acid by its stronger affinity for the lime, takes it 
 from the muriatic acid, unites with it, and forms sulphate of lime. 
 The solidity is owing to the insolubility of this last substance in wa- 
 ter. The experiment succeeds well, if the water is saturated with 
 he muriate. C. 
 
 321. Why does water become colder before freezing than it is in 
 he act of freezing ? 
 
 322. What example can you give of liquids becoming solid, by 
 being mixed, and disengaging latent heat ? 
 
 324. How is this effect accounted/or in the note ? 
 324. What other instance of the extrication of latent heat is giv 
 eu, and how is it produced ? 
 
COMBINED CALORIC. 7!f 
 
 agitation till it became cold, as you may feel the phial is. Now 
 when 1 take out the cork and let the air fall upon it, (for being clo- 
 sed when boiling, there was a vacuum in the upper part,) observe 
 that the salt will suddenly crystallize. 
 
 Caroline Surprising- ! how beautifully the needles of salt have 
 shot through the whole phial ! 
 
 Mrs. B Yes, it is very remarkable; but pray do not forget the 
 object ot the experiment . Feel how warm the phial has become by 
 the conversion of part of the liquid into a solid 
 
 Emily. Quite warm, I declare! this is a most curious experiment 
 of the disengagement of latent heat. 
 
 Mrs. B The slaking of lime is another remarkable instance of 
 the extrication of latentheat. Have you never observed howquick- 
 lime smokes when water is poured upon it, and how much heat it 
 produces ? 
 
 Caroline Yes ; but I do not understand what change of state 
 takes place in (he lime that occasions its giving out latent heat ; for 
 the quick-lime, which is solid, is (if I recollect right) reduced tu 
 powder by this operation, and is, therefore, rather expanded than 
 condensed. 
 
 Mrs. B. It is from the water, not the lime, that the latent heat 
 is set free. The water incorporates with, and becomes solid in the: 
 lime ; in consequence of which the heat, which kept it in a liquid 
 state is disengaged, and escapes in a sensible form. 
 
 Carolina I always thought that the heat originated in the lime. 
 It seems very strange that water, and cold water too, should con- 
 tain &o much heat. 
 
 Emily. After this extrication of caloric the water must exist in a 
 state of ice in the lime, since it parts with the heat which kept it li- 
 quid. 
 
 Mrs. B. It cannot properly be called ice, since ice implies a de- 
 gree of cold, at least equal to the freezing point Yet, as water, in 
 combining with lime, gives out more heat than in freezing, it must 
 be in a state of still greater solidity in the lime than it is in the form 
 of ice ; and you may have observed that it does not moisten or liqui- 
 fy the lime in the smallest degree. 
 
 Emily. But, Mrs B. the smoke that rises is white ; if it was on- 
 ly pure caloric which escaped, we might feel, but could not see it. 
 
 Mrs. B. This white vapor is formed by some of the particles of 
 lime in a state of fine dust, which are carried off by the caloric. 
 
 Emily. In all changes of state, then, a body either absorbs or 
 disengages latent heat ? 
 
 Mrs. B. You cannot exactly say absorbs Intent heat, as the heat 
 becomes latent only on being confined in the body ; but you may 
 say, generally, that bodies in passing from a solid to a liquid form, 
 or from the liquid state to that .of vapor, absorb heat ; and that 
 when the reverse takes place heat is disengaged.* 
 
 * * This rule, if not universal, admits of very few exceptions. 
 
 3 1 25. What other instance is mentioned of the extrication of la- 
 tent heat ! 
 
 326. Whence proceeds the heat in the slaking of lime ? 
 
 327. Why is the smoke that rises in the slaking of lime, white - 
 
 328. When do bodies absorb heat ? 
 When is heat disengaged ? 
 
SO COMBINED CALORIC. 
 
 Emily. We can now, I think account for the ether boiling, and 
 the water freezing in vacuo, at the same temperature-! 
 Mrs. B. Let me hear how you explain it 
 
 Emily. The latent heat which the water gave out in freezing, 
 was immediately absorbed by the ether, during Us conversion into 
 vapor ; and therefore, from a latent state in one liquid, it passes 
 into a latent state in the other. 
 
 Mrs. B. But this only partly accounts for the result of the ex- 
 periment; "it remains to be explained why the temperature of the 
 ether, while in a state of ebullition, is brought dowu to the freezing 
 temperature of water. It is because the ether, during its evapora- 
 tion, reduces its own temperature, in the same proportion as that of 
 the water by converting its free caloric into latent heat ; so that 
 though one liquid boils, arid the other freezes, their temperatures 
 remain in a state of equilibrium. 
 
 Emily. But why does not water, as well as ether, reduce its own 
 temperature by evaporating f 
 
 Mrs. B. The fact is, That it does, though much less rapidly than 
 ether. Thus, for instance you may often have observed, in the heat 
 of summer, how much any particular spot m-..y be cooled by water- 
 ing, though the water used for that purpose be as warm as the air 
 itself. Indeed so muc':i cold m <y be produced by the mere evapo- 
 ration of water, that the inhabitants of India, by availing themselves 
 of the most favorable circumstances for this "process which their 
 warm climate can afford, namely, the cool of the night, and situa- 
 tions most exposed to the night breeze, succeed m causing water 
 to freeze though the temperature of the air be as high as 60 de- 
 grees. The water is put into shallow earthen trays, so as to expose * 
 an extensive surface to the process of evaporation, and in the morn- 
 ing, the water is found covered with a thin cake of ice. which is 
 collected in sufficient quantity to be used for purposes of luxury. 
 
 Caroline. Flow delicious it must be to drink liquids so cold in 
 those tropical climates ' But, Mrs. B. could we not try that exper- 
 iment ? 
 
 Mrs. B If we were in the country, I have no doubt but that we 
 should be able 'o freeze vvater, by the same means, and under sim- 
 ilar circumstances. But we can do it immediately, upon a small 
 scale, in this very room, in which the thermometer stands at 70 de- 
 grees For this purpose we need only place some water in a little 
 cup under the receiver of th^ air-pump, Fig. 8, and exhaust the air 
 from it. What will be the consequence, Caroline? 
 
 Caroline. Of course the water will evaporate more quickly, since 
 there will no longer be an atmospheric pressure on its surface ; 
 but will this be sufficient to rnnke the water freeze ? 
 Mrs. B. Probably not. because the vapor will not be carried off 
 
 f See page 65. 
 
 329. Why does water freeze and ether boil in vacuo ? 
 
 330. Why does the ground become cooled by watering in sum- 
 mer, though the water used be as warm as the air itself? 
 
 331. How is ice often produced in India, where the temperature 
 is not below 60 degrees ? 
 
 332. How is water made to freeze under a glass receiver, as il- 
 lustrated in figure 8 ? 
 
COMBINED CALORIC. 
 
 81 
 
 last enough ; but this will be accomplished without difficulty if we 
 introduce into the receiver, Fig. 8, in a saucer, or other large shal- 
 low vessel some strong sulphuric acid, a substance which has a 
 great attraction for water, whether in the form of vapor or in the 
 liquid state. This attraction is such that the acid will instantly ab- 
 sorb the moisture as it rises from the water, so as to make room for 
 Fig. 8. 
 
 _ S. The air pomp and receiver for Mr. Leslie's experiment. C. a saieer with lulphuri'- 
 *J. H. a glais or earthen cup containing water. D. a ttand (or the cup with its lgt made f 
 S'ass. A. A Thermometer. 
 
 the formation of fresh vapor ; this will of course hasten the pro- 
 cess, and the cold produced from the rapid evaporation of the wa- 
 ter, will in a few minutes, be sufficient to freeze its surface.* We 
 "shall now exhaust the air from the receiver. 
 
 Emily. Thousands of small bubbles already arise through the 
 water from the internal surface of the cup ; what is the reason ol 
 this ? 
 
 Mrs B.~ These are bubbles of air which were partly attached to 
 the vessel, and partly diffused in (Vie water itself ; and they expand 
 and rise in consequence of the atmospheric pressure being removed. 
 
 Caroline. See, Mrs. B. ; the thermometer in the cup is sinking 
 fast : it has already descended to 40 degrees ! 
 
 Emily The water now and then violently agitated on the surface 
 as it it were boiling ; and yet the thermometer is descending fast ! 
 
 Mrs. B. You may call it boiling if you please, for this appear- 
 rn.ce i% as wrll as boiling, owing to the rapid formation of vapor ; 
 but here, as you have just observed, ittakes place from the surface,* 
 for it is only when heat is applied to the bottom of the vessel that the 
 vapor is formed there. Now crystals of ice are actually shooting 
 all over the surface of the water. 
 
 * This experiment was first devised by Mr. Leslie, and has since 
 been modified in a variety of forms. 
 
 333. When the air is exhausted from the receiver why do bub 
 hies rise through the water from the internal surface of the cup ? 
 334. Why does the water appear as if boiling- ? 
 
COMBINED CALORIC. 
 
 Caroline. How beautiful it is ! The surface is now entirely fro- 
 zenbut the thermometer remains at 32 degrees. 
 
 Mrs. B. And so it will, conformably with our doctrine of latent 
 heat, until the whole of the water be frozen ; but it \v\\\ then again 
 begin to descend lower and lower, in consequence of the evapora- 
 tion which goes on from the surface of the ice. 
 
 Emily. This is a most interesting experiment ; but it would be 
 s ill more striking if no sulphuric acid were required. 
 
 Mrs. B. I will show you a freezing instrument, contrived by Dr. 
 Wollaston, upon the same principle as Mr. Leslie's experiment, by 
 which water may be frozen by its own evaporation alone, without 
 the assistance of sulphuric acid. 
 
 Fig. 9 
 
 This tube, which, as you Dr< Walla8tOD ' 8 Cryo P horu. 
 
 see is terminated at each 
 extremity by a bulb, one 
 of which is half full of wa- 
 ter,is internally perfectly' 
 exhausted of air; thecon- 
 sequence of this is, that the water in the bulb, is always much dispo- 
 sed to evaporate. This evaporation, however, does not proceed suf- 
 icienlly, fast to freeze the water ; but if the empty ball be cooled 
 by some artificial means, so as to condense quickly the vapor which 
 rises from the water, the process may be thus so much promoted as 
 to cause the water to freeze in the other ball. Dr. Wollaston has 
 oalled this instrument Cryophnrus. 
 
 Caroline. So that cold 
 seems to perform here 
 the same part which the 
 sulphuric acid acted in 
 Mr. Leslie's experi- 
 ment ? 
 
 Mrs B. Exactly so ; 
 put let us try the ex- 
 periment. 
 
 Emity. Howwiilyou 
 cool the instrument ? 
 You have neither ice 
 nor snow. 
 
 Mrs B. True; but 
 we have ot her means of 
 effecting this.* You re- 
 collect what an intense 
 cold can be produced 
 by the evaporation of e- 
 therin an exhausted re- 
 ceiver. We shall in- 
 
 No 3. (Fig. 10.) Dr. Marcel's mode of using- the Cryopho- 
 ruB. No. I, and V, the different parr* of No. 3, 
 seen separate. 
 
 * This mode of making the experiment was proposed, and the 
 particulars detailed, by Dr. Marcet, in the 34th vol. of Nicholson's 
 Journal p. 119. 
 
 335 Hew long m this i-Xi eriment will the thermometer remain 
 at 3 ; ^ iegrees, or at the freezing 1 point ? 
 
 336. Why will it begin and continue to descend as soon as all the 
 water is frozen ? 337. What is the object of figures 1,2, and 3 ; 
 
COMBINED CALOHIC. 83 
 
 close the bulb in this little bag of fine flannel, (Fig 1 . 1.) then soak 
 it in ether, and introduce it inro the receiver of the air-pump. (Fig. 
 3.) For this purpose we shall find it more convenient to use a cryo- 
 phorusof this shape, (Fig. 2.) as its elongated bulb passes easily 
 through a brass plate which closes the top of the receiver. If we 
 now exhaust the receiver quickly, you will see in less than a minute, 
 the wafer freeze in the other bulb out of the receiver. 
 
 Emily. The bulb already looks quite dim, and small drops of wa- 
 ter are condensing on its surface. 
 
 Caroline. And now crystals of ice stioot all over the water This 
 is, indeed, a very curious experiment ! 
 
 Mrs. B. You will see, some other day, that, by a similar method, 
 even quicksilver may be frozen. But we cannot at present indulge 
 in any further digression. 
 
 Having advanced so far on the subject of heat, I may now give 
 you an account of the calorimeter, an instrument invented by La- 
 voisier, upon the principles just explained, for the purpose of esti- 
 mating the specific heat of bodies. It consists of a vessel, the inner 
 surface of which is lined with ice, so as to form a sort of hollow globe 
 of ice, in the midst of which the body, whose specific heat is to be 
 ascertained, is placed. The ice absorbs caloric from this body, till 
 it has brought it down to the freezing point ; this caloric converts 
 into water a certain portion of ice which runs out through an aper- 
 ture at the bottom of the machine ; and the quantity of ice changed 
 to water is a test of the quantity of caloric which the body has given 
 out in descending from a certain temperature to the freezing point. 
 
 Caroline. In this apparatus, I suppose, the milk, chalk,' and lead, 
 would melt different qnantites of ice, in proportion to their differ- 
 ent capacities for caloric. 
 
 Mrs. B. Certainly ; and thence we are able to ascertain, with 
 precision their respective capacities for heat. But the calorimeter 
 affords us no more idea of the absolute quantity of heat contained 
 in a body, than the thermometer ; for though by means of it we 
 extricate both the free and combined caloric, yet we extricate 
 them only to a certain degree, which is the freezing point ; and we 
 know not how much they contain of either helow that point. 
 
 Emily. According to the theory of latent heat, it appears to me 
 lhat the weather should be warm when it freezes, and cold in a thaw ; 
 for latent heat is liberated from every substance that it freezes, and 
 such a large supply of heat must warm the atmosphere; whilst du- 
 ring a thaw, that very quantity of free heat must be taken from the 
 atmosphere and return to a latent state in the bodies which it thaws. 
 
 Mrs. B. Your observation is very natural ; but consider that in 
 a frost the atmosphere is so much colder than the earth, that all the 
 caloric which it takes from the freezing bodies,is insufficient to raise 
 its temperature above the freezing point ; otherwise the frost must 
 cease. But if the quantity of latent heat extricated does not destroy 
 the frost, it serves to moderate the suddenness of the change of tern- 
 
 338. Can quicksilver be frozen ? 
 
 339. What is the calorimeter, and what is its use ? 
 
 340. Of what does it consist ? 
 
 341. Does the calorimeter indicate the absolute quantity of heat 
 contained in a body ? 
 
 342. What effect is produced on the temperature of the atmos- 
 here, by the attraction of latent heat from the winter frosts ; 
 
84 COMBINED CALORIC. 
 
 perature of the atmosphere, at the commencement both of frost and 
 of a thaw. ID the first instance, its extrication diminishes the sever- 
 ity of the cold ; and in the latter, its absorption moderates the 
 warmth occasioned by a thaw ; it even sometimes produces a dis- 
 cernible chill, at the breaking up of frost. 
 
 Caroline. But what are the general causes that produce those 
 sudden changes in the weather, especially from hot to cold, which 
 we often experience ? 
 
 Mrs. B. This question would lead us into meteorological discus- 
 sions, to which I am by no means competent. One circumstance, 
 however, we can easily understand. When the air has passed over 
 cold countries, it will probably arrive here at the temperature much 
 below our own, and then it must absorb heat from every object it 
 meets with, which will produce a general fall of temperature. 
 
 Caroline. But pray, now that we know so much of the effects of 
 heat, will you inform us whether it is really a distinct body, or, as I 
 have heard, a peculiar kind of motion produced in bodies ? 
 
 Mrs. B. As I have before told you, there is yet much uncertain- 
 ty as to the nature of these subtle agents. But I am inclined to 
 consider heat not as mere motion, but as a separate substance. 
 Late experiments, too, appear to make it a compound body, con- 
 sisting of the two electricities : and in our next conversation I shall 
 inform you of the principal facts upon which that opinion is founded. 
 
 CONVERSATION V. 
 
 ON THE CHEMICAL AGENCIES OF ELECTRICITY.* 
 
 Jtfrs. B. Before we proceed further, it will be necessary to give 
 you some account of certain properties of electricity, which have 
 of late years been discovered to have an essential connexion with 
 the phenomena of chemistry. 
 
 Caroline. It is ELECTRICITY, if I recollect right, which comes 
 next in our list of simple substances ? 
 
 Mrs. B. I have placed electricity in that list, rather from the ne- 
 cessity of classing it some where, than from any conviction that ithr.s 
 a right to that situation ; for we are as yet so ignorant of its intimate 
 nature, that we are unable to determine, not only whether it is sim- 
 ple or compound, but whether it is in fact a material agent; or, as 
 Sir H. Davy has hinted, whether it may not be merely a property 
 inherent in matter. As, however, it is necessary to adopt some 
 hypothesis for the explanation of the discoveries which this agent 
 has enabled us to make, I have chosen the opinion, at present most 
 prevalent, which supposes the existence of two kinds of electricity, 
 distinguished by the name of positive and negative electricity. 
 
 * The electricity extricated by the metals is commonly called 
 Galvanism. 
 
 343. What is heat now supposed to be ? 
 
 344. What subject is to be considered in this conversation ? 
 
 345. What are the uncertainties as to the nature of electricity ' 
 
 346. Flow many kinds of electricitv are there ? 
 
 347. What are they called ? 
 
ELECTRO-CHEMISTRY. 
 
 Caroline. Well, I must confess, I do not feel nearly so interested 
 in a science in which so much uncertainty prevails as in thost 
 which rest upon established principles. I never was fond of elec- 
 tricity, because, however beautiful and curious the phenomena it 
 exhibits may be, the theories, by which they were explained, ap- 
 peared to me so various, so obscure and inadequate, that I always 
 remained dissatisfied. I was in hopes that the new discoveries in 
 electricity had thrown so great a light on the subject, that every 
 thing respecting it would now have been clearly explained. 
 
 Mrs. B. That is a point which we are yet far from having attain- 
 ed. But, in spite of the imperfection of our theories, you will be 
 amply repaid by the importance and novelty of the subject. Thi 
 number of new facts which have already been ascertained, and tin. 
 immense prospect of discovery which has lately been opened to us, 
 will, I hope, ultimately lead to a perfect elucidation of this branch 01 
 natural science ; but at present you must be contented with study- 
 ing the effects, and in some degree explaining the phenomena, with 
 out aspiring to a precise knowledge of the remote cause of electri- 
 city. 
 
 You have already obtained some notions of electricity ; in out 
 present conversation, therefore, I shall confine myself to that part 
 of the science which is of late discovery, and is more particularly 
 connected with chemistry. 
 
 It was a trifling and accidental circum'stance which first gave rise 
 to this new branch of physical science. Galvani, a professor of nat- 
 ural philosophy at Bologna, being engaged (about 20 years ago) 
 in some experiments on muscular irritability, observed, that when a 
 piece of rnetal was laid on the nerve of a frog, recently dead, whilst 
 the limb supplied by that nerve rested upon some other metal, the 
 limb suddenly moved, on a communication being made between the 
 two pieces of metal. 
 
 Emily. How is this communication made ? 
 
 Mrs. B. Either by bringing the two metals into contact, or bj 
 connecting them by means of a metallic conductor. But without 
 subjecting a frog to any cruel experiments, I can easily make you 
 sensible of this kind of electric action. Here is a piece of zinc, 
 (one of the metals I mentioned in the list of elementary bodies) 
 put it under your tongue, and this piece of silver upon your tongue, 
 and let both the metals project a little beyond the tip of the touguo 
 very well ; now make the projecting parts of the metals touch 
 each other, and you will instantly perceive a peculiar sensation. 
 
 Emily. Indeed I did ; a singular taste, and I think a degree oi 
 heat ; but I can hardly describe it. 
 
 Mrs. B. The action of these two pieces of metal on the tongue is, 
 I believe precisely similar to that made on the nerve of a frog. I 
 shall not detain you by a detailed account of the theory by which 
 Galvani attempted to explain this fact, as it was soon overturned 
 
 348. What is the difference between electricity and Galvanism .' 
 
 349. From whom did Galvanism receive its name ? 
 
 35Q. What gave rise to the branch of physical science called 
 Galvanism ? 
 
 351. What simple experiment is mentioned ; that can be made up- 
 m the tongue to illustrate this subject ? 
 
 8 
 
$6 ELECTKO-CHEMISTR1'. 
 
 by subsequent experiments, which proved that Galvanism (the name 
 this new power had obtained)was nothing more than electricity. 
 Galvani supposed that the virtue of this new agent resided in the 
 nerves of the frog ; but Volta, who prosecuted this subject with 
 much greater success, showed that the phenomena did not depend 
 on the organs of the frog, but upon the electrical agency of the 
 metals, which is excited by the moisture of the animal, the organs 
 of the frog being only a delicate test of the presence of electric in- 
 fluence. 
 
 Caroline. I suppose, then, the saliva of the mouth answers the 
 same purpose as the moisture of a frog, in exciting the eUctricity 
 of the pieces of silver and zinc, with which Emily tried the exper- 
 iment on her tongue ? 
 
 Mfr.s. B Precisely. It does appear, however, necessary that 
 the lluid used for this'purpose should be of animal nature. Water, 
 and acids very much diluted by water, are found to be the most ef- 
 fectual in promoting the developement of electricity m metals ; and 
 accordingly the original apparatus which Volta first constructed 
 for this purpose consisted of a pile or succession of plates of zinc and 
 copper, each pair of which was connected by pieces of cloth or pa- 
 per impregnated with water; and this instrument, from its original 
 inconvenient structure and limited strength, has gradually arrived 
 at i-is present state of power and improvement, such as exhibited in 
 the Voltaic batter;. In this apparatus, a specimen of which you 
 see before you, Fig. II. 
 
 the plates Of Zinc Voltaic Battery. 
 
 and copper are 
 
 being placed at 
 regular distan- 
 ces in wooden 
 troughs and the 
 interstices being 
 fitted with fluid. 
 
 Carotene. Though y.-,n will not allow us to inquire into the pre- 
 cise cause of electricity may we not ask in what manner the fluid 
 acts on the metals so as to produce it ? 
 
 Jtfr.t. n. The action of the fluid on the metals, whether water or 
 acid be used, is entirely of a chemical nature. But whether elec- 
 tricity is excited by. this chemical action, or whether it is produced 
 by the contact of the two metals, is a point upon which philoso- 
 pher? do not yet perfectly aqrree. 
 
 Emily, But can the mere contact of two metals, without any in- 
 tervening fluid, produce electricity ? 
 
 Mrs. B. Yes, if they are afterwards separated. It is an establish- 
 
 352. How did Galvani account for the moving of the limb on a 
 communication being made between the two metals? 
 
 353. What was the true cause of it ? 
 
 354. What metals are used in the production of galvanic action" 
 35. Which figure represents a Voltaic battery ? 
 
 356. Can galvanism be produced without water ? 
 
ELECTRO-CHEMISTRY. 
 
 ed fact that when two metals are put in contact, and afterwards sep- 
 arated, that which has the strongest attraction for oxygen exhibits 
 signs of positive, the other of negative electricity. 
 
 Caroline. It seems, then, but reasonable to infer that the power 
 of the Voltaic battery should arise from the contact of the plates of 
 xinc and copper. 
 
 Mrs. B. It is upon this principle that Volta and Sir H. Davy ex- 
 plain the phenomena of the pile ; but notwithstanding these two 
 great authorities, many philosophers entertain doubts on the truth 
 of this theory. The chief difficulty which occur- in explaining the 
 phenomena of (he Voltaic batiery <-n thi- principle is tha uvo 
 such plates show no signs of different states of electricity whilst in 
 contact, but only on being separated after contact Now. in the 
 Voltaic battery, those plates that are in contact always continue so, 
 being soldered together ; and they cannot, therefore receive a >uc- 
 cession of charges. Besides, if we consider the mere disturb mce 
 of the balance of electricity ">y the contact of the piates. a> the sole 
 cause of the production of Voltaic electricity, it remains to be 
 explained how this disturbed balance becomes an inexhaustible 
 source of electrical energy capable of pouring forth a constant and 
 copious supply o electrical fluid, though wit!, rut any means ot re- 
 plenishing- itself from other sources This ^iject it must be own- 
 ed, is involved in too much obscurity to enableus to speak ver- de- 
 cidedly in favor )f any theory But in order to avoid perplexing 
 you with different explanations, I sh^ll confine myself to oru 
 apnears to me (o be least encumbered frith difficulties, and most 
 likel\ to accord with truth.* 
 
 This then -v supposes the electricity to he excited by th chemic- 
 al action of tiie acid on the zinc ; but you are-yet *uch novices in 
 chemistry, that I think it will be necessary to give yon some previ- 
 ous exolanalion of the nature of this ;>ct;on 
 
 All metals have a strong attraction for oxygen ; and this element 
 is found in great abundance, both in water and :n acids. The ac- 
 tion of the diluted acid on the zinc consists ihe;?fore, in i!s 
 combining with it, and dissolving its surf ice. 
 
 Caroline. In the same manner, I suppose, as we saw an acid dis- 
 solv ^ copper? 
 
 Mrs. B. Yes : but in the Voltaic battery the diluted acjd is not 
 strong enough to produce so complete an effect ; it acts only on the 
 
 * This mode o explaining the phenomena of the Volr ic 
 called ihe chemical theory of electricity, bee -use it a-.rrr.es the 
 cause of these phenomena to ascertain chemical changes which take 
 place during t:eir appearance*. The mode which fetched 
 
 was long since suggested by Dr Bostock, who has lately (i;i8) 
 published " An account of the History and Present State of Gnlvm- 
 ism ;" which contains a fuller and more complete statement of his 
 opinions and those of other writers on the subject, t!i 
 former papers. 
 
 357. What established fact in galvanic experiments is mentioned : 
 
 358. What two chemists have explained the phenomena 01 the 
 Voltaic battery, as proceeding solely from the contact of the two 
 metals ? 
 
 35 ( ) t For what have all metals strong attraction ? 
 
ELECTRO-CHEMISTRY. 
 
 surface of the zinc, to which it yields its oxygen, forming upon it 3 
 film or crust, which is a compound of the oxygen and the metal. 
 
 Emily. Since there is so strong a chemical attraction between ox- 
 ygen and metals, I suppose they are naturally in different states of 
 electricity. 
 
 Mrs. B. Yes ; it appears that all metals are united with the pos- 
 itive, and that oxygen is the grand source of the negative electri- 
 city. 
 
 Caroline. Does not, then, the acid act on the plates of copper, as 
 well as on those of zinc ?* 
 
 Mrs. B. No ; for though copper has an affinity for oxygen, it is 
 less strong than that of zinc ; and therefore the energy of the acid 
 is only exerted upon the zinc. 
 
 It will be best I believe, in order to render the action of the Vol- 
 taic battery more intelligible, to confine our attention at first to the 
 effect produced on two plates only. (Fig. 12.) 
 
 If a plate of zinc be placed opposite to one of copper, or Fig. 12. 
 any other metal less attractive of oxygen, and the space VoiuicBat 
 between them (suppose of half an inch in thickness,) be fil- te17 ' 
 led with an acid or any fluid capable of oxydating the zinc, * 
 the oxydated surface will have its capacity for electricity 
 diminished, so that a^fuantity of electricity will be evolv- 
 ed from that surface. This electricity will be received 
 by the contiguous fluid, by which it will be transmitted to 
 the opposite metallic surface, the copper, which is not ox- 
 ydated, and is therefore disposed to receive it ; so that the 
 copper plate will thus become positive, whilst the zinc 
 plate will be in the negative state. 
 
 This evolution of electrical fluid, however, will be very 
 limited ; for as these two plates admit of but very little ac-. 
 cumulation of electricity, and are supposed to have no communica- 
 tion with other bodies, the action of the acid, and further develop- 
 ment of electricity, will be immediately stopped. 
 
 Emily. This action, I suppose, can no more continue than that 
 of a common electrical machine, which is not allowed to communi- 
 cate with other bodies ? 
 
 Mrs. B. Precisely ; the common electrical machine when excit- 
 ed by the friction of. the rubber, gives out both the positive and neg- 
 ative electricities. (Fig. 13.) The positive, by the rotation of the 
 ^lass cylinder, is conveyed into the conductor, whilst the negative 
 goes into the rubber. But, unless there is a communication made 
 between the rubber and the ground, a very inconsiderable quantity 
 
 * The acid acts upon the copper, but not so strongly as on the 
 /.inc. Any two metals, one of which has a stronger attraction for 
 oxygen than the other, will form the galvanic series. C. 
 
 360. What is the grand source of negative electricity ? 
 
 361. Why in the Voltaic battery is the energy of the action ex- 
 erted only upon the zinc ? 
 
 362. How would you explain the principle of the Voltaic battery 
 by Fig. 12 ? 
 
 363. How would you describe the mode of collecting electricity 
 in the common electrical machine? . 
 
 364. Why must the rubber be connected with the ground ? 
 
ELECTRO-CHEMISTRY. 
 
 89 
 
 of electricity can be excited ; for the rubber like thf plates of the 
 batterv. has too small a capacity to admit of an accumulation of 
 electricity. Unless, therefore, the electricity can pt^s out of the 
 rubber, it will not continue to sro into it, and consequently, no ad- 
 ditional accumulation will take place. Now, as one k<nd of elec- 
 tricity crxnnnt he given out without the other, the developernent of 
 the positive electricity is stopped as well as that of tho negative, and 
 the conductor, therefore, cannot receive a successor, of charges. 
 13. Electrical Machine. 
 
 Fig:. 13. A, the Cylinder. B, the Conductor, R, the Kabber. C, the Chtio. 
 
 Caroline. But docs not the conductor, as well as the rubber, re- 
 quire communication with the earth, in order to t n<! of its 
 electricity f 
 
 Mrs. B. No ; for it is susceptible of receiving and containing a 
 considerable quantity of electricity, as it is much larg r than the 
 rubber, and therefore has a greater capacity; and Ui-s com ;.ued 
 accumulation of electricity in the conductor is what is called a 
 charge. 
 
 Emily. But when an electrical machine is furnished with two 
 conductors to receive the two electricities, I suppose no communi- 
 cation with the earth is required? 
 
 Mrs. B. Certainly not, until the two are fully charged ; for the 
 two conductors will receive equal quantities of electricity. 
 
 Caroline. I thought the use of the chain had been to convey the 
 electricity from the ground into the machine. 
 
 Mrs.B. That was the idea of Dr. Franklin, who supposed that 
 there was but one kind of electricity, and who by the terms posi- 
 tive and negative (which he first introduced.) meant only different 
 quantities of the same kind of electricity.* The chain was in that 
 
 * The idea of Dr. Franklin was, that the positive state consisted 
 
 365. What is called a charge in the use of the common electrical 
 machine ? 
 
 366. What was Dr. Franklin's opinion concerning electricity ? 
 
90 ELECTRO-CHEMISTRY. 
 
 case supposed to convey electricity from the ground through the 
 rubber into the conductor. But as we have adopted the hypothesis 
 of two electricities, we must consider the chain as a vehicle to con- 
 duct the negative electricity into the earth. 
 
 Emily. And are both kinds produced whenever electricity is ex- 
 oited ? 
 
 Mrs. B. Yes, invariably. If you rub a tube of glass with a wool- 
 Hen cloth, the glass becomes positive, and the cloth negative.* If, 
 m the contrary, you excite a stick of sealing- wax by the same means. 
 <tis the rubber which becomes positive, and the wax negative. 
 
 But with regard to the Voltaic battery, in order that the acid may 
 ict freely on the zinc, and the two electricities be given out without 
 interruption, some method must be devised, by which the plates 
 may part with their electricities as fast as they receive them. Can 
 you (hink of any means by which this might be effected ? 
 
 Emily. Would not two chains or wires, suspended from either 
 plate to the ground, conduct the electricities into the earth, and thus 
 answer the purpose ? 
 
 Mrs. B. It would answer the purpose of carrying off the electri- 
 city, I admit ; but recollect, that though it is necessary to find a 
 vent for the electricity, yet we must not lose it, sinoe it is the pow- 
 er we are endeavoring to obtain. Instead, therefore, of conduct- 
 ing it into the ground, let us make the wires, from either plate, 
 meet ; the two electricities will thus be brought together, and will 
 combine and neutralize each other ; and as long as this communi- 
 cation continues, the two plates having a vent for their respective 
 electricities, the action of the acid will go on freely and uninter- 
 ruptedly. 
 
 Emily. That is very clear, so far as two plates only are concern- 
 ed ; but I cannot say 1 understand how the energy of the succes- 
 sion of plates, or rather pairs of plates, of which the Galvanic trough 
 is composed, is propagated and accumulated throughout a battery ? 
 
 in the presence, or accumulation of the electric fluid, and that the 
 negative was merely its absence or diminution. Hence the terms 
 'used by him to indicate these states were positive and negative. In 
 this chapter Mrs. B. has used these terms of the American Philoso- 
 pher improperly, for plus and minus were never meant to signify 
 two sorts of electricity, but only its presence or absence. Where 
 authors have adopted Dufay's theory of two electricities, they have 
 used the terms, vitreous and resinous. C. 
 
 * Most probably, because the glass takes the electric, fluid from 
 the cloth. Indeed, we conceive there is about the same reason for 
 believing that the negative state is the absence of the electric fluid 
 as there is for believing that cold is the absence of heat. C. 
 
 367. What is the use of the chain in the common electrical ma- 
 rjiine ? 
 
 368. Are negative and positive electricity always produced when 
 electricity is excited ? 
 
 369. What is necessary in the Voltaic battery, that the two elec- 
 tricities be given out without interruption ? 
 
 370. In what manner do two pieces of wire produce this effect : 
 
ELECTRO-CHEMISTRY. 
 
 91 
 
 -\frs. B. In order to show you how the intensity of the electrici- 
 ty is increased by increasing the number of plates, we will exam- 
 ine the action of four plates ; if you understand these, you will 
 readily comprehend that of any number whatever. 
 
 Fig. 14. Voltaic Battery. 
 
 In this figure you will observe that the 
 two central plates are united ; they are 
 soldered together, (as we observed in 
 describing the Voltaic trough,) so as to 
 form but one plate, which offers two 
 different surfaces ; the one of copper, 
 the other of /inc. 
 
 Now you recollect, that, in explaining 
 the action of two plates, we supposed 
 that a quantity of electricity was evolved 
 from the surface of the first zinc plate, in 
 consequence of the action of the acid, and- 
 was conveyed by the interposed fluid to the copper plate No. 2, 
 which thus became positive. This copper plate communicates its 
 electricity to the contiguous zinc plate, No 3, in which, conse- 
 quently, some accumulation of electricity takes place. When, 
 therefore, the fluid in the next cell acts upon the zinc plate, elec- 
 tricity is extricated from it in larger quantity, and in a more con- 
 centrated form, than before. This concentrated electricity is again 
 conveyed by the fluid to the next pair of the plates, No. 4 and 5, 
 when it is further increased by the action of the fluid in the third 
 cell, and so on, to any number of plates, of which the battery may 
 consist , so that the electrical energy will continue to accumulate 
 in proportion to the number of double plates, the first zinc plate of 
 the series being the most negative, and the last copper plate the 
 most positive. 
 
 Caroline. But does the battery become more and more strongly 
 charged, merely by being allowed to stand undisturbed ? 
 
 Mrs. B. No : for the action will soon stop, as was explained be- 
 fore, unless a vent be given to the accumulated electricities. This 
 is easily done, however, by establishing a communicationjby means 
 of the wires (See Fig. 11,) between the two ends of the battery ; 
 these being brought into contact, the two electricities meet and 
 neutralize each other, producing the shock and other effects of 
 electricity : and the action goes on with renewed energy, being no 
 longer obstructed by the accumulation of the two electricities 
 which impeded its progress. 
 
 Emily. Is it the union of the two electricities which produces the 
 electric spark ? 
 
 Mrs. B. Yes ; and it is, I believe, this circumstance which gave 
 rise to Sir H. Davy's opinion, that caloric may be a compound of 
 the two electricities. 
 
 Caroline. Yet, surely, caloric is very different from the electoral 
 
 Mrs. B. The difference may consist, probably, only in intensity ; 
 
 371. How would you explain figure 14 ? 
 
 372. How would you explain figure 14, which represents the 
 Voltaic battery, so as to produce the electric spark : 
 
 373. What does Sir II. Davy suppose-caloric to be ? 
 
02 ELECTRO-CHEMISTRY. 
 
 for the heat of the electric spark is considerably more intense 
 though confined to a very minute spot, than any heat we can pro- 
 duce by other means. 
 
 Emily. Is it quite certain that the electricity of the Voltaic 
 battery is precisely of the same nature as that of the common elec- 
 trical machine? 
 
 Mrs. B. Undoubtedly; the shock given to the human body, the 
 spark, the circumstance of the same substances which are conduct- 
 ors of the one, being also conductors of the other, and of those bodies, 
 such as glass and sealing- wax, which are non conductors of the one, 
 being also non conductors of the other, are striking proofs of it. 
 Besides, Sir H. Davy has shown, in his Ijectures. thai a Leyden jar, 
 and a common electric battery , can be charged with electricity 
 obtained from a Voltaic battery, the effect produced being perfect- 
 ly similar to that obtained by a common machine. 
 
 Dr. VVollaston has likewise proved, that similar chemical decom- 
 positions are effected by the electric machine and by the Voltaic 
 battery; and has made other experiments which render it highly 
 probable, that the origin of both electric-ties is essentially the same, 
 as they show that the rubber of the common electrical machine, 
 like the zinc in the Voltaic battery, produces the two electricities, 
 by combining with oxygen. 
 
 Caroline But I do not see whence the rubber obtains oxygen, for 
 there is neither acid nor water used in the common machine ; and I 
 always understood that the electricity was excited by the friction. 
 
 Mrs. B It appears that by friction the rubber obtains oxygen 
 from the atmosphere, which is par ly composed of that element. The 
 oxygen combines with the amalgam of the rubber, which is of a 
 metallic nature, much in the same way as the oxygen of the acid 
 combines with the zinc in the Voltaic battery, and it is thus that 
 the two electricities are disengaged. 
 
 Caroline But if the electricities of both machines are similar, 
 why not use the common machine for chemical decompositions ? 
 
 Mrs. B. Though its effects are similar to those of the Voltaic 
 battery, they are incomparably weaker. Indeed Dr. Wollaston, in 
 using it for chemical decompositions, was obliged to act upon the 
 most minute quantities of matter, and though the result was satis- 
 factory in proving the similarity of its effects to those of the Voltaic 
 battery, these effects were too small in extent to be in any consid- 
 erable degree applicable to chemical decompositions. 
 
 Caroline. How terrible, then, a shock must be from a Voltaic 
 battery, since it is so much more powerful than an electrical ma- 
 chine. 
 
 Mrs. B. It is not nearly so formidable as you think ; at least it is 
 
 374. How does the degree of heat in the electric spark compare 
 with that produced by other means ? 
 
 375. What proves that the electricity in the Voltaic battery is of 
 the same nature as that of the common electrical machine ? 
 
 376 How do the rubber of the common electrical machine and 
 the zinc in the Voltaic battery produce the two electricities ? 
 
 377. How does the rubber obtain oxygen, in the use of the com- 
 mon electrical machine ? 
 
 378. Why is not the common electrical machine used for chemi- 
 cal decompositions ? 
 
ELECTRO-CHEMISTRY. 93 
 
 by no means proportional to the chemical effect. The great supe- 
 riority of the Voltaic battery consists in the large quantity of elec- 
 tricity that passes : but in regard to the rapidity or intensity of the 
 charge, it is greatly surpassed by the common electrical machine. 
 It would seem that the shock or sensation depends chiefly upon the 
 intensity ; whilst, on the contrary, for chemicar purposes, it is 
 quantity which is required. In the Voltaic battery, the electricity, 
 though copious, is so weak as not to be able to force its way through 
 the fluid which separates the plates, whilst that of a common ma- 
 chine will pass through any space of water. 
 
 Caroline. Would it not be possible to increase the intensity of 
 the Voltaic battery till it should equal that of the common machine}? 
 
 Mrs. B. It can actually be increased till it imitates a weak elec- 
 trical machine, so as to produce a visible spark when accumulated 
 in a Leyden jar. But it can never be raised sufficiently to pass 
 through any considerable extent of air, because of the ready com 
 munication through the fluids employed. 
 
 By increasing the number of plates of a battery, you increase its 
 intensity, whilst, by enlarging the dimensions of the plates, you aug- 
 ment its quantity and as the superiority of the battery over the 
 common machine consists entirely in the quantity of electricity pro- 
 duced, it was at first supposed that it was the size, rather than the 
 number of plates that was essential to the augmentation of power. 
 It was, however, found upon trial, that the quantity of electricity 
 produced by the Voltaic battery, even when of a very moderate 
 size, was sufficiently copious, and that the chief advantage in this 
 apparatus was obtained by increasing the intensity, which, hower- 
 er, still falls very far short of that of the common machine. 
 
 I should not ornit to mention, that a very splendid, and, at the 
 same time, most powerful battery, was affew years ago, constructed 
 under the direction of Sir H. Davy, which he repeatedly exhibited 
 in his course of electro-chemical lectures. It consists of two thou- 
 sand double plates of zinc and copper, of six square inches in di- 
 mensions, arranged in troughs of Wedgwood-ware, each of which 
 contains twenty of these plates. The troughs are furnished with a 
 contrivance for lifting the plates out of them in a very convenient 
 and expeditious manner.* 
 
 * A model of this mode of construction is exhibited in (Fig. 15.) 
 NOTE. In consequence of the discoveries of Prof. Hare, of Phil- 
 adelphia, the present theory of galvanism must probably undergo a 
 radical change. This gentleman has invented a new method of ex- 
 tricating the voltaic influence, by so connecting the plates, that in 
 effect only two great surfaces of the metals are presented to each 
 other. By this arrangement, the galvanic action on different sub- 
 
 379. In what does the superiority of the Voltaic battery consist ? 
 
 380. In what respect does the common electrical machine surpass 
 the Voltaic battery ? 
 
 381. What is the difference in the action of the Voltaic batter}-, 
 whether the number of plates is increased or their size is enlarged ? 
 
 382. How extensive was the large battery constructed by Sir II. 
 Davy ? 
 
 383. What American chemist has distinguithed himself by discovtr 
 its in galvanism ? 
 
94 
 
 ELECTRO-CHEMISTRY. 
 
 Caroline. Well, now that we understand the nature of the action 
 of the Voltaic battery, I long to hear an account of the chemical 
 discoveries to which it has given rise. 
 
 Mrs. B. You must restrain your impatience, my dear, for I cannot 
 wit 1 : nny propriety introduce the subject of these discoveries till we 
 come to them In the regular course of our studies. There is, how- 
 ever, a recent discovery respecting the Voltaic pile, which, though 
 not immediately connected with chemistry, is too curidus to be pass- 
 ed over in silence. It relates to tht- influence of electricity on mag- 
 netism, lately discovered by a Danish philosopher. Mr. Oersted. 
 
 Caroline. What ! animal magnetism ? have often heard of mag- 
 net^- !r*^'->rs ; bu< I thoug 1 t th-e was no truth in them. 
 
 ^ Mrs. J5. Nor is there ; it is only the magnetic needle to which I 
 allude. You already know something of the wonderful property of 
 the :nagiie t; r; needle to direct one of its extremities towards the 
 north; and you may easily conceive how interesting any new fact 
 relating to this truly mysterious agent, must be to science. The 
 principal f;I t is this ; If a Voltaic battery be so placed as to have its 
 negative pole directed towards the south and its positive one towards 
 the north a communication being at the same time established over 
 the battery, bel ween its two poles, by means of metallic wires ; and 
 if a magnetic needle be suspended just above the wire, and in a par- 
 allel direction, the needle will immediately move round upon its 
 
 stanoes,has presented some npiw phenomena This calorific principle 
 is immensely increased, while the electric shock is hardly to be per- 
 ceived. Praf, Hare has named this new apparatus calorimotor, or heat 
 mover. The new views which he has been induced to offer, seem to 
 be confirmed by 
 the action of the 
 ealorimotor. viz. 
 that galvanism is a 
 
 _W*Nte _ _ ~V>^^. 
 
 4r 
 
 compound of elec 
 tricity and calo : - 
 ic. This theory,* 
 it is obvious, will 
 set aside many of 
 the principles laid 
 down in the fore- 
 going chapter. 
 
 Anaccountof this 
 theory, with a de- 
 scHntion o f ^6 
 calorimotor, is 
 published in Silli- 
 man's Journal, 
 with observations 
 by fhe Editor; al- 
 so in Hare's edi- 
 tion of Chemis- 
 try. C. 
 
 Fig 5. V 
 
 Fig. 15. 
 
 >ltaic Battery of improved t 
 out of the 
 
 >nstruction with the plates 
 
 
 a. To what does the recent discovery made by Mr. Oersted relate 
 
 b. What is the principal fact connected with this discovery ? 
 324. What does Mr. Hare suppose Galvanism to be ? 
 
OXYGEN AND NITROGEN. 95 
 
 >ivot, its northern extremity directing itself towards the west, more 
 >r less according to the energy of the pile, while on the other hand, 
 f the magnetic needle be placed below the Voltaic conductor, it* 
 vill likewise begin to move round, hut its north jpole will, in this 
 ;ase point towards the east* 
 
 y&Qvr curious this is ! and pray how is this singular effect 
 ix plained ? 
 
 Mis. B. It is one of the most intricate points or natural science, 
 md one upon which philosophers can yet offer but very uncertain 
 :onjectures. Several of the most eminent scientific men, however, 
 ire earnestly engaged in investigating the subject, and it is to be 
 loped, that some impor ant discovery may yet be made. In the 
 nean time they have already ascertained many curious facts illus- 
 rative of the influence which electricity and magnetism exert upon 
 ;ach other, one of the most striking of which is, that if a steel needle 
 >e placed transversely upon the conductor of a Voltaic pile in action, 
 he needle will, in a few seconds, become magnetic, so as to be ca- 
 )able of attracting and repelling iron like magttets. Or if any por- 
 ion of the conducting wire be turned into a spiral, and a needle 
 aid within its coils, but so as not to touch them, it will immediately 
 lecome magnetic, as I shall easily show you the 6rst time we set the 
 Voltaic pile in action ; for it is nov too much exhaust eii to produce 
 :he effects in question. We shall therefore here terminate this con- 
 rersation, which has been already sufficiently long and difficult. 
 
 CONVERSATION VI. 
 
 ON OXYGEN AND NITROGEN. 
 
 Jlfr*. B, To-day we shall examine the chemical properties of 
 
 ATMOSPHERE. W+ 
 
 Caroline. I thought that we were first to learn the nature of ox- 
 VGEN which conies next in our table of simple bodies ? 
 
 Mrs. B. And so you shall ; the atmosphere being composed of 
 two principles, OXYGEN and NITROGEN, we shall proceed to analyse 
 it, and consider its component parts separately. 
 
 Emily. I always thought that the atmosphere had been a very 
 complicated fluid, composed of all the variety of exhalations from 
 the earth. 
 
 Mrs. B. Such substances may be considered rather as heterogene- 
 ous and accidental, than as forming any of its component parts ; and 
 the proportion they bear to the whole mass is quite inconsiderable. 
 
 ATMOSPHERICAL AIR is composed of two gases, known by the 
 names of OXYGEN GAS and NITROGEN or AZOTIC GAS. 
 
 Emily. Pray what is a gas ?* 
 
 * All kinds of air differing from the atmosphere are called by this 
 name. C. 
 
 c. What other facts have been observed on this subject ? 
 385. Of what is the atmosphere composed ? 
 
96 OXYGEN AKD NITROGEV* 
 
 Mrs. B. The name of gas is given to any fluid capable of exist- 
 ing 1 constantly in an aeriform state, under the pressure and at the 
 ^emperature of the atmosphere. 
 
 Caroline. Is no| water, or any other substance, when evaporated 
 by heat, called gas ? 
 
 Mrs.B. No my dear; vapour is, indeed, an elastic fuid, and 
 bears a strong resemblance to a gas : there are, however, several 
 points in which they essentially differ, and by which you may always 
 distinguish them. Steam, or vapour, owes its elasticity merely to a 
 high temperature, which is equal to that of boiling water. And it 
 differs from boiling water only by being united with more caloric, 
 which as we before explained, is in a latent state. When steam is 
 cooled, it instantly returns to the form of water ; but air, or gas, 
 has never yet been rendered liquid or solid, by any degree of cold. 
 
 Emily. But does not gas, as well as vapour, owe its elasticity to 
 caloric ? 
 
 Mrs. B. It is the prevailing opinion ; and the difference between' 
 gas and vapour is thought to depend on the different manner, in 
 which caloric is united with the basis of these two kinds of elastic . 
 fluids. In vapour it is considered as in a latent state ; in gas, it is 
 supposed to be chemically combined. 
 
 Emily. When you speak, then,. of the simple bodies oxygen and 
 nitrogen, you mesn to express those substances which are the bases 
 of the two gases ? 
 
 Mrs. B. Yes, in strict propriety ; for they can properly be called 
 gases, only when brought to an aeriform slate. 
 
 Caroline. In what proportions are they combined in the atmos- 
 phere ? 
 
 Mrs. B. The oxygen gas constitutes a little more than one-fifth, 
 and the nitrogen gas a little less than four- fifths.* When separated, 
 they are found to possess qualities totally different from each other. 
 For oxygen gas is essential both to respiration and combustion, 
 while neither of these processes can be performed in nitrogen gas. 
 
 Caroline. But if nitrogen gas is unfit for respiration, how does it 
 happen that the large proportion of it which enters into the compo- 
 sition of the atmosphere is not a great impediment to breathing : 
 
 Mrs. B. We should breathe more freely than our lungs could 
 bear, if we respired oxygen gas alone. The nitrogen is no impedi- 
 ment to respiration, and probably on the contrary, answers some 
 nGeOil purpose, though we do not know in what manner it acts ia 
 that process. 
 
 * In 100 parts of the atmospheric air, there is 21 of oxygen and 
 79 of nitrogen. C. 
 
 386. What is a gas ? 
 
 387. What is the difference between vapour and gas ? 
 
 388. To what does vapour owe its elasticity ? 
 
 389. To what do the gases owe their elasticity ? 
 
 390. When may oxygen and nitrogen be called gases ? 
 
 391. What is an essential difference between oxygen and nitro- 
 gen, when separated ? 
 
 392. If nitrogen gas is unfit for respiration, how does it happen, 
 that the large proportion of it, which enters into atmospheric air. 
 does not cause an impediment in breathing ? 
 
OXYGEN AND NITROGEN. 07 
 
 Kmily. And by what means can the two gases, which compose 
 'he atmospheric air be separated ? 
 
 Mrs. B. There are many ways of analysing tbe atmosphere : the 
 two gases may be separated first by combustion? 
 
 Emily- You surprise me ! how is it possibjfc that combustion 
 should separate them ? 
 
 J)frs. B, I should previously inform you, that till within a few 
 years, oxygen was supposed to be the only simple body naturally 
 combined with negative electricity. Sir H. Davy has since added 
 chlorine and iodine to that number, but they are bodies of inferior 
 importance. In all the other elements the positive electricity pre- 
 vails, and they have consequently, all of them, an attraction for 
 oxygen.ff 
 
 Caroline. That surprises mfe extremely ; how then are the com- 
 binations of the other bodies performed,^, according to your expla- 
 nation of chemial attraction, bodies are supposed only to combine 
 in virtue of their opposite states of electricity ? 
 
 Mrs. B. Compound bodies, iu which oxygen prevails over the 
 other component parts, are also negative, but tbeir negative energy 
 is greater or less in proportion as the oxygen predominates. Those 
 compounds into which oxygen enters in less proportion than the 
 other constituents, are positivfr, but their positive energy is dimi- 
 nished in proportion to the quantity of oxygen which enters into 
 their composition. 
 
 Bodies, therefore, that are not already combined with oxygen, 
 will attract it, and, under certain circumstances, will absorb it from 
 the atmosphere, in which case the nitrogen gas will remain alone, 
 and may thus be obtained in its separate state. 
 
 Caroline. I do not understand how a gas can be absorbed ? 
 
 Mrs. B. It is only the oxygen, or basis of the gas, which is absorL 
 
 f If chlorine or oxymuriatic gas be a simple body, according to 
 Sir H. Davy's view of the subject, it must be considered as an ex- 
 ception to this statement ; but this subject cannot be discussed till 
 the properties and nature of chlorine come under examination. 
 
 f The hypothesis that combustion, as well as chemical affinity are 
 electrical phenomena, was first proposed by Berzelius, of Stock- 
 holm. The theory is shortly this. In all cases, where the particles 
 of bodies have a chemical attraction for each other, they are in op- 
 posite states of electricity, and the force of their union is in propor- 
 tion to the intensity of these electrical states, since it is this which 
 forces them to unite. Thus the particles of an acid and an alka! , 
 unite, because one is strongly negative and the other strongly posi- 
 tive. In case of combustion, these different states are still more in 
 tense, oxygen always being in the negative state, and the combusti- 
 ble in the positive, and when a union takes place, heat and light is 
 
 393. Can the two gases that compose the atmospheric air be se- 
 parated ? 
 
 394. In what proportions are oxygen and nitrogen combinedin & 
 mogpheric air ? 
 
 395. What causes negative electricity ? 
 
 396. How can combustion separate them ? 
 
 397. How is caloric produced in combustion ! 
 
 398. What is the theory of combustion proposed by Berzelitts f 
 
98 OXYGEN AND NITROGEN. 
 
 ed ; and the tiro electricities escaping 1 , that is to say, the negative 
 from the oxygen, the positive from the burning body, unite and 
 produce caloric. 
 
 Emily. And what, becomes of this caloric ? 
 Mrs. B. We shall make this piece of dry wood attract oxygen 
 from the atmosphere, and you will see what becomes of the caloric. 
 Caroline. You are joking, Mr. B. : you do not mean to decom- 
 pose the atmosphere with a piece of dry stick ? 
 
 Mrs. B IN ot the whole body of the atmosphere, certainly ; but if 
 we can make this piece of wood attract any quantity of oxygen 
 from it, a proportional quantity of atmospherical air will be decom- 
 posed. 
 
 Caroline. If wood has so strong an attraction for oxygen, why 
 does it not decompose the atmosphere spontaneously ? 
 
 Mrs. B. It is found by experience, that an elevation of tempera 
 ture is required for the commencement of the union of the oxygen 
 and the wood. 
 
 This elevation of temperature was formerly thought to be neces- 
 sary, in order to diminish the cohesive attraction of the wood, and 
 enable the oxygen to penetrate and combine with it more readily. 
 But since the introduction of the new theory of chemical combina- 
 tion, another cause has been assigned, and it is now supposed that 
 the high temperature, by exalting the electrical energies of bodies, 
 and consequently their force of attraction, facilitates their combi- 
 nation. 
 
 Emily. If it is true that caloric is composed of the two electrici- 
 ties, an elevation of temperature must necessarily augment the 
 electric energies of bodies. 
 
 Mrs. B. I doubt whether that would be a necessary consequence ; 
 for admitting this composition of caloric, it is only by being decom- 
 posed that electricity can be produced. Sir H. Davy, however, in 
 his numerous experiments, has found it to be an almost invariable 
 rule, that the electrical energies of bodies are increased by elevation 
 of temperature. 
 
 What means, then, shall we employ to raise the temperature of 
 the wood, so as to enable it to attract oxygen from the atmosphere ? 
 Caroline. Holding it near the fire, I should think, would answer 
 the purpose. 
 
 Mrs. B. It may, provided you hold it sufficiently close to the fire ; 
 for a very considerable elevation of temperature is required. 
 
 Caroline. It has actually taken fire ; and yet I did not let it touch 
 the coals, but I held it so very close that I suppose it caught fire 
 merely from the intensity of the heat. 
 Mrs.- B. Or you might say, in other words, that the caloric which 
 
 the consequence. This theory is not well proved, nor generally 
 adopted. C. 
 
 399. If wood has a strong attraction for oxygen, why does it not 
 decompose the air spontaneously ? 
 
 400. Why is it necessary to heat a combustible substance to make 
 it burn ? 
 
 401. Are the electrical energies of bodies increased by elevation 
 of temperature ? 
 
 402. Why will a piece of wood when held near the fire, burn, 
 although it does not touch (he coals ? 
 
OXYGEN AND NITROGEN. 
 
 ' he wood imbibed, so much elevated its temperature, and exalted 
 its electric energy, as to enable it to attract oxygen very rapidly 
 irom the atmosphere. 
 
 Emily: Does the wood absorb oxygen while it is burning f 
 
 Mrs. B. Yes ; and the heat and light are produced by the union 
 >f the two electricities which are set at liberty, in consequence of 
 the oxygen combining with the wood 
 
 Caroline You astonish me ! the heat of a burning body proceeds 
 then as much from the atmosphere as from the body itself? 
 
 Mrs. B. It was supposed that 'he caloric given out during corn- 
 bus ion, proceeded entirely, or nearly so, from the decomposition 
 of the oxygen gas; but according to Sir H Davy's new view ot 
 the subject, both the oxygen gas and the combustible body concur 
 in supplying the heat and light, by the union of their opposite elec- 
 tricities. 
 
 Emily. I have not yet met with any thing in chemistry that has 
 surprised or delighted me so much as this explanation of combus- 
 tion. I was at first wondering what connexion there <;ould be be- 
 tween the affinity of a body for oxygen and its combustibility ; but 
 1 think I understand it now perfectly. 
 
 J\lrs B. Combustion, then, you see, is nothing more than the 
 rapid combination of a body with oxygen, attended by the disen- 
 gagement of lisfht and heat. 
 
 Emily. But are there no combustible bodies whose attraction for 
 ox\grn is so strong, that they will combine with it, without the ap- 
 plication of heat ? 
 
 Caroline That cannot be ; otherwise we should see bodies bur- 
 ning spontaneously. 
 
 W> < B But there are some instances of (his kind, such as phos 
 phorus potassium, and some compound bodies, which I shall here- 
 after rnakeynu acquainted with. These bodies, however, are pre- 
 pared by art, for in general, all the combustions that could occur 
 .spontaneously, at the temperature of the atoiosphere, have already 
 taken place ; therefore new combustions cannot happen without 
 the temperature of the body being raised. Some bodies, however, 
 wiP burn at a much lower temperature than others. 
 
 Caroline But the common way of burning a body is not merely 
 to approach it to one already on fire, but rather to put the one in 
 actual contact with the other, as when I burn this piece of paper by 
 holding it in the flame of the fire. 
 
 Mrs. B. The closer it is in contact wijh the source of caloric, 
 the sooner will its temperatur-- be raiseoT to the degree necessary 
 for it to burn If you hold it near the fire, the same effect will be 
 produced ; but more time will be required, a you found to be the 
 case with the piece of stick. 
 
 Emily. But why is it not necessary to continue applying caloric 
 throughout the process of combustion, in order to keep up the elec- 
 tric energy of the wood, which is required to enable it to combine 
 with the oxygen ? 
 
 403. When a substance burns, what does it absorb ? 
 
 404. How are heat and light produced ? 
 
 405. What is combustion ? 
 
 406. Why do not bodies burn spontaneously ? 
 
 407. What are instances of combustion without a previous in- 
 crease of temperature ? 4 
 
OXYGEN AND NITROGEN. 
 
 Mrs. B. The caloric which is gradually produced by the two 
 electricities during combustion keeps up the temperature of the 
 burning body ; so that when once combustion has begun, no fur- 
 ther application of caloric is required. 
 
 Caroline. Since I have learnt this wonderful theory of combus- 
 tioo, I cannot help gazing at the fire ; and I can scarcely conceive 
 that the heat and light, which I always supposed to proceed entire- 
 ly from the coals, are really produced as much by the atmosphere. 
 
 Emily. When you blow the fire, you increase the combustion, I 
 suppose, by supplying the coals with a greater quantity of oxygen 
 gas. 
 
 Mrs. J3. Certainly ; but of course no blowing will produce com- 
 bustion, unless the temperature of the coals be first raised. A siu- 
 gje spark, however, is sometimes sufficient to produce that effect ; 
 for, as I said before, when once combustion has commenced, the 
 caloric disengaged is sufficient to elevate the temperature of the 
 rest of the bod\ , provided that there be a free access of oxygen. 
 It however sometimes happens that if a fire be ill made, it will be 
 extinguished before all the fuel is consumed, from the very circum- 
 stance of the combustion being so slow that the caloric disengaged 
 is insufficient to keep up the temperature of the fuel. You must re- 
 collect that there are three things required in order to produce 
 eombustion ; a combustif le body, oxygen, and a temperature at 
 which the one will combine with the other. 
 
 JZmtty You said that combustion was one method of decompos- 
 ing- the atmosphere, and obtaining the nitrogen gas, in its simple 
 state ; but how do you secure this gas, and prevent it from mixing 
 with the rest of the atmosphere ? 
 
 Mrs. B. It is necessnry for this purpose to 
 burn the body within a close vessel, which is 
 easily done. We shall introduce a small light- 
 ed taper under this glass receiver, which stands 
 ba.in ove. w^ter, to prevent allcommuni- 
 '\ with he external air.* 
 .Caroline. How dim the light burns already ! 
 
 Hovy extinguished. 
 p Mrs. B. Can you tell us why it is extin- 
 
 ed ? 
 
 Caroline. Let me consider. The receiver 
 ?vas full of atmospheri<Jl air ; the taper, in 
 
 Combustion c: a taper under i. 
 receiver. 
 
 * To make a taper, melt some bees wax. and dip into it a strip ot 
 cotton cloth about an inch wide, and before it is cold. t\vist it pretty 
 
 408. Why is it not necessary to continue- applying caloric 
 throughout the process of combustion, in order to keep up the elec- 
 tric energv of the wood, which is required to enable it to combine 
 with the oxygen ? 
 
 409 Why does blowing the fire increase combustion ? 
 
 410. Why will fire be sometimes extinguished before all the wood 
 ;i consumed ? jgp 
 
 411. What three things are necessary to produce combustion . 
 
 412. Why will a burning taper placed under a glass receiver, us 
 n figure 16, soon become extinguished ? 
 
OXYGEN AND NITROGEN. lOl 
 
 burning within it, must have combined with the oxygen contained 
 in that air. and the caloric that was disengaged produced the light 
 of the taper But when the whole of the oxygen was absorbed, the 
 \vhole of its electricity was disengaged ; consequently no more ca- 
 Joric could be produced, the taper ceased to burn, and the flame 
 was extinguished. 
 
 Mrs. B. Your explanation is perfectly correct. 
 
 Emily. The two constituents of the oxygen gas being thus dis- 
 posed of, what remains under the receiver must be pure nitrogen 
 gas. 
 
 tA/r.?. B. There are some circumstances which prevent the nitro- 
 gen gas thus obtained, from being perfectly pure ; but we may 
 easily try whether the oxygen has disappeared, by putting another 
 lighted taper under it. You see how instantaneously the flame is 
 extinguished, for want of oxygen to supply the negative electricity 
 required for the formation of caloric ; and were you to put an ani- 
 mal under the receiver, it would be immediately suffocated. But 
 thai is an experiment which 1 do not think your curiosity will tempt 
 you to try. 
 
 Emily. Certainly not. But look, Mrs. B., the receiver is full of 
 a thick white smoke. Is that nitrogen gas ? 
 
 Mrs. B. No, my dear ; nitrogen gas is perfectly transparent and 
 invisible, like common air This cloudiness proceeds from a vari- 
 ety of exhalations, which arise from the burning taper, the nature of 
 which you cannot yet understand. 
 
 Caroline. TJie water in the receiver has now risen a little above 
 its level in the basin. What is the reason of this ? 
 
 Mm B. With a moment's reflection, I dare say you would have 
 explained it yourself The water rises in consequence of the oxy- 
 gen g-as within it having been destroyed or rather decomposed, by 
 the combustion of the taper. 
 
 Caroline. Then why did not the water rise immediately when the 
 oxygen" gas was destroyed? 
 
 Mrs. B. Because the heat of the taper, whilst burning, occasion- 
 ed a dilatation of the air in the vessel, and a production of carbonic 
 acid, which at first counteracted this effect. 
 
 Another means of decomposing the atmosphere is the oxygenation 
 of certain metals. This process is very analagous to combustion ; 
 it is, indeed, only a more general term to express the combination 
 of a body with oxygen. 
 
 Caroline. In what respect, then, doeyi^iffer frotn combustion ? 
 
 Mrs. B. The combination of oxygen il^Rmbustion is always ac 
 
 hard. Cotton wick does better than the ctotl* .A quart tumbler 
 makes a good receiver. Two or three incites otvle taper can be 
 fastened to a piece of wire, bent so that it wiftstand up. Thus the 
 experiment is easily made. C. 
 
 413. How long will it burn thus placed under^teceiver ? 
 
 414. What would be the consequence if an a&pal.were placed 
 under the receiver ? Why ? 
 
 415. What is another method of decomposing the air ? 
 
 416. In what respect does oxygenation differ from the decompo- 
 sition of air by combustion? 
 
 S* 
 
LOO OXYGEN AND KITROGErs < 
 
 companied by a disengagement of light and heat ; whilst this en 
 cumstance is not a necessary consequence of simple oxygenation. 
 
 Caroline. But how can a body absorb oxygen without the com- 
 bins 'ion of the two electricities which produce caloric ? 
 
 Mrs. B. Oxygen does not always present itself iu a gaseous form ; 
 it is a constituent part of a vast number of bodies, both solid and li- 
 quid, in which it exists in a state of greater density than in the at- 
 inosphere; and f om these bodies it may be obtained without much 
 diseng;temei w of caloric. It may likewise, in some cases be ab- 
 sorbed irorn the atmosphere without any sensible production of light 
 aid heat ; for, if the process be slow, the caloric is disengage..- in 
 i small quantities and so gradually, that it is not capable of pro- 
 ducing either light or heat. In this case the absorption of oxygen 
 is caller' oxygenation or oxydation, instead of combustion, as the pro- 
 duction ofsensiblo light arid heat is essential to the latter. 
 
 Emily. I wonder that metals can unite with oxygen ; for, as they 
 are so dense, their attraction of aggregation must be very great ; 
 and 1 should have thought that oxygen could never have penetrated 
 such bodies. 
 
 Mrs. B. Their strong attraction for oxygen counterbalances this 
 obstacle. Most metajs, however, require to be made red hot, be- 
 fore they are capable of attracting oxygen in any considerable 
 quantity. By this combination they lose most of their metallic 
 properties, and fall into a kind of powder, formerly called calx, but 
 now much more rroperly termed zuoxyd ; thus we have oxyd of 
 tead< oxyd of iron, &c.* 
 
 Emily. And in the Voltaic battery, it is, I suppose, an oxyd of 
 ^inc, that is formed by the union of the oxygen withrthat metal. 
 
 Mrs. B. Yes, it is 
 
 Caroline. The word oxyd, then, simply means a metal combined 
 with oxygen 
 
 Mrs. B. Yes ; but the term is not confined (o metals, though 
 chiefly applied to them Any body whatever, that has combined 
 with a certain quantity of oxygen, either by means of oxydation, or 
 combustion, is called an oxyd, and is said to be oxydated oroxygena- 
 >ed. 
 
 Emily. Metals, when converted into oxyds, become, I suppose, 
 negative. 
 
 Mrs. B. Not in general ; because in most oxyds the positive en- 
 ergy of the metal, more than counterbalances the native energy of 
 the oxygen with which^jjpmbines. 
 
 This black powder is an oxyd of manganese, a metal which has so 
 
 * Red Leaded husi of Iron. C. 
 
 417. Does oxygg always exist in a gaseous state ? 
 
 418. When is f absorption of oxygen called oxygenation, or 
 oxydation ? 
 
 419. How ca|roxygen penetrate metals, since their attraction oi 
 aggregation is so great ? 
 
 420. What is the chemical name for red lead and rust of iron ? 
 
 421. What is an oxyd ? 
 
 422. If oxyds are a combination of metals and oxygen, why are 
 not negative ? 
 
OXYGEN ASD XITROGEX. 103 
 
 strong an affinity for oxygen, that it attracts that substance fpom 
 the atmosphere at any known temperature; it is therefore never 
 found in its metallic form, but always in that of an oxyd; in which 
 state, you see it has very little of the appearance of a metal. It is 
 now heavier than it wakbefore oxydr.tion,in consequence of the ad- 
 ditional weight of the oxygen, with which it has combined. 
 
 Caroline. 1 am very glad to hear that ; for I confess I coukl not 
 help having -ome doubts whether oxygen was really a substance, as 
 it is not to be obtained in a simple and palpable staUL: but its we; 
 is, 1 think, a decisive proof of its being a real boc^* 
 
 Mrs. B. It is 'easy to estimate its weight, by separating it from 
 the manganese, and finding how much the latter has lost. 
 
 Emily. But if you can take the oxygen from the metal, shall 
 not then have it in its palpable simple state ? 
 
 rs. B. No ; for I can only separate the oxygen from the man- 
 ganese, by presenting to itsomeothe" body, for which it has a great- 
 er affinity than for the manganese. Caloric affording the two elec- 
 tricities is decomposed, and one of them uniting with the oxygen, 
 restores it to the aeriform state. 
 
 Emily. But you said just now, that manganese would attract ox- 
 ygen from the atmosphere in which it is combined witli the nega- 
 tive electricity ; how, therefore, can the oxygen have a superior 
 affinity for th^t electricity, since it abaudons'it to combine with the 
 manganese? 
 
 Mrs. B. I give you credit for this objection, Emily ; and the on- 
 ly answer 1 can*nake to it is, that the mutual affinities of metals for 
 oxvgen, and of oxygen for electricity, vary at different tempera- 
 tures; a certain degree of heat will, therefore, dispose a metal to 
 combine with .oxygen, whilst on the contrary, the former will be 
 compelled to part with the latter, when the temperature is further 
 increased. I have put some oxyd of manganese into a retort, 
 which is an earthen vessel with a bent neck, such as you see here. 
 (See Fig 17, No. 1.) The retort containing the manganese you can- 
 not see, as 1 have enclosed it in this furnace, where it is now red-hot. 
 But, in order to mak' vou sensible of the escane of the gas, which 
 is itself invisible, I have connected the neck of the retort with 
 bent tube, the extremity of which is immersed in a vessel of water. 
 (See Fig. 17, No. 2.) bo you see the bubbles of air rise through 
 the water? 
 
 Caroline Perfectly. This, then, is pure oxygen gas? What a 
 pity it should be lost. Could you not preserve it ? 
 
 *To collect oxygen gas, take an oil flask, and having fitted a cork 
 to it, pierce the cork so as to admit a bent glass tube ; (the bending 
 is done over a spirit lamp.) Put into the flask some black oxyd of 
 manganese, and pour on sulphuric acid enough to make it into a 
 paste. Then put in the cork and tube, and having connected the 
 other end of the tube with a receiver, in, the tub of water, apply the 
 heat of an Argand lamp. C. 
 
 423. How can it be determined that oxygen has weight? 
 
 424. How can oxygen be separated from manganese after having- 
 been oxydated ? 
 
 4 C 25. How may pure oxygen be collected ? 
 
 4*26. How would you describe the experiment represented in fi^- 
 ure 1 7 ? 
 
104 
 
 OXYGEN AND NITROGEN, 
 Fig. 17. 
 
 No. 1. A, retort on a stand. No. 2. A, Furnace. B, Earthen Retort in the furnao . 
 (-, Water Bath. D .Receiver. E E, Tube conveying the gas from the Retort through the 
 water into the Receiver. F F F, Shelf perforated on which the Receiver stands. 
 
 Mrs. B We shall collect it in this receiver. For this purpose, 
 you observe, I first fill it with water, in order to exclude the at- 
 mospherical air ; and then place it over the bubbles which issue 
 Irom the retort, so as to make them rise through the water to the 
 upper part of the receiver. 
 
 Emily The bubbles of oxygen gas rise, I suppose, from their 
 specific levity ? 
 
 J\lrs B \ r es ; for though oxygen forms rather a heavy gas, it 
 is light compared to water. You see how it gradually displaces the 
 water from the receiver. It is now full of gas, and I may leave it 
 inverted in water on this shelf, where I can keep the gas as long as 
 I choose, for future experiments. This apparatus (which is indis- 
 pensable in all experiments in which gases are concerned) is called 
 a water- bath.* 
 
 Caroline. It is a very clever contrivance, indeed ; equally simple 
 and useful. How convenient the shelf is for the receiver to rest 
 upon under water, and the holes in it for the gas to pass into the re- 
 ceiver ! I long to make some experiments with this apparatus. 
 
 Mrs. B. 1 shall try your skill that way, when you have a little 
 more experience. I am now going to show you an experiment, 
 which proves, in a very striking manner, how essential oxygen is 
 to combustion. You will see that iron itself will burn in this gas, 
 in the most rapid and brilliant manner. 
 
 * A common large sized wash-tub,with a board 4 or 5 inches wide 
 fixed through the middle, and about 6 inches from the top, and filled 
 with water, will answer very well for a great variety of experiments 
 on the gases. C. 
 
 427. How does the weight of oxygen gas compare with that of 
 water ? 
 
 428. How may the great tendency of oxygen to produce combus 
 tion, be preyed ? 
 
OXYGEX AXU NITKOGEIV. 
 
 Caroline. ReoRy ! I did not know that it was possible to burn iron, 
 
 Emily. Iron is a simple body, and you know, Caroline, that all 
 simple bodies are naturally positive, and therefore must have an af- 
 finity for oxygen. , . 
 
 Mrs. B. Iron will, however, not burn in atmospherical air will 
 out a very great elevation of temperature ; but it is eminently com- 
 bustible in pure oxj-gen gas; and what will surprise you still more, 
 it can he set on fijre without any considerable rise of temperature. 
 You see this spiral iron wire.* I fasten it at one end to this cork, 
 which is made to fill an opening at the top of the gtess receiver. 
 
 Fig. 1C. 
 
 Emily. 1 see the opening in the receiver; 
 but it is carefully closed by a ground glass- 
 stopper. 
 
 Mrs. B. That is in order to prevent the gas 
 from escaping ; but I shall take out the stop- 
 per, and put in the cork, to which the wire 
 hangs. Now I mean to burn this wire in the 
 oxygen gas, but I must fix a small* piece of 
 lighted tinder to the extremity of it in order 
 to give the first impulse to combustion ; for, 
 however powerful oxygen is in pro'rnoting 
 combustion, you must recollect that it cannot 
 take place without some elevation of tempera- Combustion of iron wire in 
 ture> I shall now introduce the wire into the C3iysen " 
 
 receiver, by quickly changing the stoppers. 
 
 Caroline. Is there no danger of the gas escaping while you 
 change the stoppers ? 
 
 Mrs. B. Oxygen gas is a little heavier than atmospherical air, 
 therefore it will not mix with it very rapidly ; and if I dotiot leave 
 the opening uncovered, we shall not lose any 
 
 Caroline. Oh, what a brilliant and beautiful flame ! 
 
 Emily. It is as white and dazzling as (he sun ! Now a piece of 
 the meited wire drop? to the- bottom ; I fear it is extinguished ; but 
 no, it burns again as bright as ever. 
 
 Mrs. B. It will burn till the wire is entirely consumed, provided 
 the oxygen is not first expended ; for you know it can burn only 
 while there is oxygen to combine with it. 
 
 Caroline. I never saw a more beautiful light. My eyes can 
 hardly bear it ! How astonishing to think that all this caloric was 
 contained in the small quantity of gas and iron that was' enclosed 
 in the receiver ; and that without prod/icing any visible heat ! 
 
 Emily. How wonderfully quick combustion goes on in pure oxy- 
 
 * The combustion of steel, as a watch spring, is much more vivid 
 than that of iron. This affords a very beautiful experiment, and 
 is easily made after the oxygen is collected. A bottle of white glass 
 of a quart capacitv does well as a receiver. An inch of water at 
 the bottom will prevent its breaking. C. 
 
 429. Why have all simple bodies an affinity for oxygen ? 
 
 430. Will iron burn in oxygen gas without an elevation of tcm 
 perature ? 
 
 431. Which is lightest, oxygen gas or atmospherical air ? 
 
 432. How long will a piece of iron burn in oxygen gas ? 
 
100 
 
 OXYGEN AND NITfcOGEN. 
 
 gen gas ! But pray, are these drops of burnt iron as heavy as the 
 wire was before ? 
 
 Mrs. B. They are even heavier ; for the iron in burning, has ac- 
 quired exactly (he weight of the oxygen which has disappeared, 
 and is now combined with it. It has become an oxyd of iron. 
 
 Caroline. I do not know what you mean by saying that the oxy- 
 gen has disappeared, Mrs. B , for it was always invisible. 
 
 Mrs. B True, my dear; the expression was incorrect. But 
 though you could not see the oxygen gas, I believe you had no doubt 
 of its presence as the effect it produced on the wire was sufficiently 
 evident. 
 
 Cimline Yes, indeed ; ye.t you know it was the caloric, and not 
 the ox \gen gas itself, that dazzled us so much. 
 
 Mrs B You are not quite correct in your turn, in saying the 
 caloric dazzled you ; for caloric is invisible ; it effects only the sense 
 of feeling ; it was the light which dazzled you. 
 
 Caroline. True; but light and caloric are such constant com- 
 panions, that it is difficult to separate them, even in idea. 
 
 Mrs B. The easier it is to "confound them, the more careful you 
 should be in making the distinction 
 
 Caroline. But why has the water now risen and filled part of the 
 receiver ? 
 
 Mrs. B. Indeed, Caroline, 1 did not suppose you would have ask- 
 ed *-)ch a question ! I dare say, Emily, you can answer it. 
 
 Emily Let me reflect . . The oxvgen has combined with the 
 wire; the caloric has escaped ; consequently nothing can remain 
 in the receiver, and the water will rise to fill the vacuum. 
 
 Caroline. I wonder that I did not think of that. 1 wish that we 
 bad we'ghed the wire and the oxvgen gas before the combustion ; 
 we might then have found whether the weight of the oxyd was equal 
 to that of both. 
 
 Mrs.B. You might try the experiment if you particularly wish- 
 ed it ; but I can assure .you that, if accurately performed, it never 
 fails to show that the additional weight of the oxyd is precisely equal 
 to that of the oxygen absorbed, whether the process has been a real 
 combustion or a simple oxygenation. 
 
 Caroline. But this cannot be tht- case with all combustions in 
 general ; for when any substance is burnt in the common air so far 
 from increasing in weight, it is evidently, diminished, and sometimes 
 entirelv consumed. 
 
 Mrs. B But what do you men by the expression consumed? You 
 cannot suppose that the smallest particle of any subs;ance <n nature 
 can be actually destroyed. A compound body is decomposed by 
 combustion ; some of its constituent parts fly off in a gaseous form, 
 while others remain in a concrete state ; the former are called the 
 volatile* the latter the fixed products of combustion. But if we col- 
 led the whole of them, we sh^ll Always find that thev exceed the 
 
 433. Why will the component parts of a compound body that has 
 been decomposed by combustion, weigh more than the compound 
 body did ? 
 
 434. What is the impropriety in saying that a person is dazzled 
 by caloric ? 
 
 435. Can a particle of any substance be actually destroyed r 
 
 436. What is the fixed product in combustion ? 
 
 437. What is the volatile product in combustion ? 
 
OXYGEN AND NITROGEN. 107 
 
 weight of the combustible body, by that of the oxygen which has 
 Combined with them during combustion. 
 
 Emily. In the combustion of a coal fire, then, I suppose that the 
 ashes are what would be called the fixed product, and the sraoke 
 the volatile product ? 
 
 Mrs. B. Yet when the fire burns best, and the quantity of vola- 
 tile products should be the greatest, there is no smoke ; how can 
 you account for that ? 
 
 Emily. Indeed 1 cannot ; therefore I suppose that I was not right 
 in my conjecture. 
 
 Mrs. B. Not quite; ashes as you supposed, are a fixed product 
 of combustion ; but smoke, properly sjjeaking, is not one of the vt>- 
 latile products, as it consists of some minute undecomposed particles 
 of coals which are carried off by the heated air without being 
 burnt, and are either deposited in the form of soot, or dispersed by 
 the wind. Smoke, therefore, ultimately becomes one of the fixed 
 products of combustion. As you may easily conceive that the 
 stronger the fire is, the less smoke is produced, because the fewer 
 particles escape combustion. On this principle depends the inven- 
 tion of Argand's Patent Lamps ; a current of air is made to pass 
 through the cylindrical wick of the lamp, by which means it is so 
 plentifully supplied with oxygen, that scarcely a particle of oil es- 
 capes combustion, nor is there any smoke produced. 
 
 Emily. But what then are the volatile products of combustion ? 
 
 Mrs. B. Various new compounds with which you are not yet ac- 
 quainted, and which being converted by caloric either into vapour 
 or gas, are invisible : but they can be collected, and we shall exam- 
 ine them at some future period. 
 
 Caroline. There are then other gases, besides the oxygen and ni- 
 trogen gases. 
 
 Mrs. B. Yes, several ; any substance that can assume and main- 
 tain the form of an elastic fluid at the temperature of the atmos- 
 phere, is called a gas. We shall examine the several gases in their 
 respective places ; but we must now confine our attention to those 
 which compose the atmosphere. 
 
 I shall show you another method of decomposing the atmosphere, 
 which is very simple. In breathing, we retain a portion of the ox- 
 ygen, and expire the nitrogen gas ; so that if we breathe in a clos- 
 ed vessel, for a certain length of time, the air within it will be de- 
 prived of its oxygen gas. Which of you will make the experiment ? 
 
 Caroline. I should be very glad to try it. 
 
 Mrs. B. Very well; breathe several times through this glass tube* 
 into the receiver with which it is connected, until you feel that your 
 breath is exhausted. 
 
 Caroline. 1 am quite out of breath already ! 
 
 Mn. B. Now let us try the gas with a lighted taper. 
 
 Emily. It is very pure nitrogen gas, for the taper is immediately 
 extinguished. 
 
 Mrs. B. That is not a proof of its being pure, but only of the ab- 
 sence of oxygen, as it is that principle alone which can produce 
 combustion, every other gas being absolutely incapable of it.* 
 
 * This does not agree with the opinion that chlorine and iodine 
 are simple bodies, since they are both supporters of combustion. -C 
 
 438. Why is there no smoke when the fire burns best ? 
 
 439. How can the atmosphere be decomposed by breathing c 
 
108 OXYGEN AND NITROGEN. 
 
 Emily. In the methods which you have shown us, for decompo- 
 sing the atmosphere, the oxygen always abandons the nitrogen ; 
 but is there no way of taking the nitrogen from oxygen, so as to 
 obtain the latter pure from the atmosphere? 
 
 Mrs B. You must observe, that whenever oxygen is taken from 
 the atmosphere, it is by decomposing the oxygen gas ; we cannot do 
 the same with the nitrogen gas, because nitrogen has a stronger af- 
 finity for caloric than for any other known principle ; it appears 
 impossible, therefore, to separate it from the atmosphere by the pow- 
 er of affinities. But if we cannot obtain the oxygen gas by this 
 means, in its separate state, we have no difficulty {as you have seen) 
 to procure it in its gaseous fprm, by taken it from those substances 
 that have absorbed it from the atmosphere, as we did with the oxyd 
 of manganese. 
 
 Emily. Can atmospherical air be recomposed, by mixing due 
 proportions of oxygen and nitrogen gases ? 
 
 Mrs. B. Yes : if about one part of oxygen gas be mixed with 
 about four parts of nitrogen gas, atmospherical air is produced.* 
 Emily. The air, then, must be an oxyd of nitrogen ? 
 Mrs. B. No, my dear'; for it requires a. chemical combination 
 between oxygen and nitrogen in order to produce an oxyd ; whilst 
 in the atmosphere these two substances were separately combined 
 with caloric, forming two distinct gases, which are simply mixed in 
 the formation of the atmosphere. 
 
 I shall say nothing more of oxygen and nitrogen, at present, as 
 we shall continually have occasion to refer to them in our future 
 conversations. They are both very abundant in nature; nitrogen 
 is the most plentiful 'in the atmosphere, and exists also in all animal 
 substances ; oxygen forms a constituent part both of the animal and 
 vegetable kingdoms, from which it may be obtained by a variety of 
 chemical means. But it is now time to conclude our lesson. I am 
 afraid you have learnt more to-day than you will be able to remem- 
 ber. 
 
 Caroline. 1 assure you that I have been too much interested in 
 it, ever to forget it. In regard to nitrogen there seems to be but 
 little to remember ; it makes but a very insignificant figure in com- 
 parison to oxygen, although it composes a much larger portion of 
 the atmosphere. 
 
 Mrs. B. Perhaps this insignificance you complain of, may arise 
 from the compound nature of nitrogen, for though I have hitherto 
 considered it as a simple body, because it is not known in any nat- 
 ural process to be decomposed, yet from some experiments of Sir H. 
 Davy, there appears to be reason for suspecting that nitrogen is a 
 
 *The proportion of oxygen in the atmosphere varies from 21 to 
 
 22 per cent. 
 
 440. Why may not oxygen be taken from.the atmosphere so as to 
 leave the nitrogen pure ? 
 
 441. How can atmospheric air be. produced by the union of oxy- 
 gen and nitrogen ? 
 
 442. Why is not the union that takes place between oxygen and 
 nitrogen in the production of atmospheric air, an oxyd ? 
 
 443. Where do oxygen and nitrogen exist? 
 
 444. Is nitrogen a simple or a compound substance ? 
 
HYDROGEN. 109 
 
 compound body, as we shall see afterwards. But even in its simple 
 =tate it will not appear so insignificant when you are better ac- 
 quainted with it ; for though it seems to perform but a passive part 
 in the atmosphere, and has no very striking properties, when con- 
 sidered in- its separate state, yet you will see by and by what a very 
 important agent it becomes, when combined with other bodies. But 
 no more of this at present; we must reserve it for its properplace. 
 
 CONVERSATION VII. 
 
 ON HYDROGEN. 
 
 Caroline. The next simple bodies we come to are CHLORINE and 
 roDiNE. Pray what kind of substances are these ? Are they also 
 invisible ? 
 
 Mrs. 8. No ; for chlorine, in the state of gas, Las a distinct 
 greenish color, and is therefore visible ; and iodine, in the same 
 state, has a beautiful claret-red colour. These bodies, 1 have al- 
 ready informed you, are, like oxygen, endowed with the negative 
 electricity ; but the explanation of their properties, implies various 
 considerations, which you would not yet be able to understand ; we 
 shall therefore defer their examination to some future conversation, 
 and we shall go on to the next simple substance, HYDROGEN, which 
 we cannot, any more than oxygen, obtain in a visible or palpable 
 form. We are acquainted with it only in its gaseous state, as we 
 are with oxygen and nitrogen. 
 
 Caroline. But in its gaseous state it cannot be called a simple 
 substance, since it is combined with heat and electricity ? 
 
 Mrs. B. True, my dear ; but as we do not know in nature, of any 
 substance which is not more or less combined with caloric and elec- 
 tricity, we are apt to say that a substance is in its pure state when 
 combined with those agents only. 
 
 Hydrogen was formerly called inflammable air, as it is extremely 
 combustible, and burns with a great flame. Since the invention of 
 the new nomenclature, it has obtained the name of hydrogen, which 
 is derived from two Greek words, the meaning of which is to pro- 
 ffuce water 
 
 Emily And how does hydrogen produce water ? 
 
 Mrs. B. By its combustion. Water is composed of 89 parts, by 
 weigh . of oxygen, combined with 11 parts of hydrogen ; or of two 
 parts, by bulk, of hydrogen gas, to one part of oxygen gas. 
 
 Caroline. Really ! is it possible that water should be a combina- 
 tion of two gases, and that one of these should be inflammable air ! 
 Hydrogen must be a most extraordinary gas that will produce both 
 fire and water. 
 
 Emily. But I thought you said that combustion could take place 
 in no gas but oxygen. 
 
 445. Of what color are chlorine and iodine ? 
 
 446. What d'-es the term hydrogen signify ? 
 
 447. What was it formerly called ? 
 
 448. How does hydrogen produce water? 
 
 449. In what proportions do oxygen and hydrogen combine to 
 produce water? 10 
 
110 HYDROGEN, 
 
 Mrs. B. Do you recollect what the process of combustion con- 
 sists in ? 
 
 Emily. In the combination of a body with oxygen, with disen- 
 gagement of light and heat. 
 
 Mrs. B. Therefore when 1 say that hydrogen is combustible, I 
 mean that it has an affinity for oxygen ; but, like all other combusti- 
 ble substances, it cannot burn unless supplied with oxygen, and also 
 heated to a proper temperature. 
 
 Caroline. The simply mixing 1 1 parts of hydrogen, with 89 parts 
 of oxygen gas, will not. therefore, produce \vater. 
 
 Mrs B. No; water being a much denser fluid than gases, in or- 
 der to reduce these gases to a liquid, it is necessary to diminish the 
 quantity of caloric or electricity which maintains them in an elastic 
 form. 
 
 Emily. That I should think might be done by combining the 
 oxygen and hydrogen together ; for in combining, they would give 
 out their respective electricities in the form of caloric, and by this 
 means would be condensed. 
 
 Caroline. But you forget, Emily, that in order to make the oxy- 
 gen and hydrogen combine, you must begin by elevating their tem- 
 perature, which increases, instead of diminishing, their electric en- 
 ergies. 
 
 Mrs B. Emily is, however, right ; for though it is necessary to 
 raise their temperature, in order to make them combine, as that 
 combination affords them the means of parting with their electrici- 
 ties, it is eventually the cause, of the diminution of electric energy. 
 
 Caroline. You love to deal in paradoxes to-day, Mrs. B, Fire, 
 then, produces water. 
 
 Mrs. B. The combustion of hydrogen gas certainly does; but 
 you do not seem to have remembered the theory of combustion so 
 well as you thought you would Can you tell me what happens in 
 the combustion of hydrogen gas ?. 
 
 Caroline. The hydrogen combines with the oxygen, and their op- 
 posite electricities are disengaged in the form of caloric. Yes, I 
 think I understand it now by the loss of this caloric, the gases are 
 condensed into a liquid. 
 
 Emily. Water, then, I suppose, when it evaporates and incorpo- 
 rates with the atmosphere, is decomposed, and converted into hy- 
 drogen and oxygen gases. 
 
 Mrs. B. No, my dear there you are quite mistaken : the de- 
 composition of water is totally different from its evaporation; for 
 in the latter case (as you should recollect) water is only in a state of 
 very minute division ; and is merely suspended in the atmosphere, 
 without any chemical combination, and without any separation of 
 its constituent parts. As long as these remain combined, they form 
 WATER, whether in a state of liquidity, or in that of an elastic fluid, 
 as vapor, or under the solid form of ice. 
 
 450. When it is said that hydrogen is combustible, what is inten- 
 ded ? 
 
 451. Will imply mixing, eighty five parts of oxygen and fifteen 
 of hydrogen, produce water ? 
 
 452. What is necessary ? 
 
 453. What happens in the combustion of hydrogen gas ? 
 
 454. What is the difference between the decomposition and evap- 
 oration of water ? 
 
HYDROGEN. 
 
 Ill 
 
 In our experiments on latent heat, you may recollect that we 
 aused water successively to pass through these three forms, merely 
 by an increase or diminution of caloric, without employing any 
 power of attraction, or effecting any decomposition 
 
 Caroline. But are there no means of decomposing water ? 
 Mrs.B. Yes several; charcoal, and metals, when heated red hot, 
 will attract the oxygen from water, in the same manner as they will 
 from the atmosphere. 
 
 Caroline, Hydrogen, I see, is like nitrogen, a poor dependant 
 friend of oxygen, which is continually forsaken for greater favorites. 
 Mrs B The connection, or friendship, as you choose to call it, 
 is much more intimate between oxygen ;md hydrogen, in the state 
 of water, than between oxygen and nitrogen, in the atmosphere ; 
 for. in the first case, there is a chemical union and condensation of 
 the two substances ; in the latter, they are simply mixed together 
 in their ga-eous state. You will find, however, that in some cases, 
 nitrogen is quite as intimately connected with oxygen, as hydrogen 
 is. Hut this is foreign to our present subject. 
 
 Emily. Water, then, is an oxyd, though the atmospherical air is 
 not. 
 
 JMrs. B. It is not commonly called an oxyd, though, according to 
 our definition, it may, no doubt, be referred to that class of bodies, 
 Caroline. I should like extremely to see water decomposed. 
 Jl/rs. B. I can gratify your curiosity by a much more easy pro- 
 cess than the ox\dation of charcoal or metals; the decomposition 
 of water by these latter means takes up a great deal of time, and is 
 attended with much trouble ; for it is necessary that the charcoal 
 or metal should be made red hot in a furnace, that the water should 
 pass over them in a state of vapour, that the gas f >rmeu an; 
 collected over the water bath, &c. In short, it is a very complica- 
 ted oueration But the same effect nr^ be produced with the great- 
 est facility, by the action of the Voltaic battery, which this will give 
 me an opportunity of exhibiting. 
 
 Caroline. I am very glad of that, for I longed to see the power of 
 this apparatus in decomposing bodies. 
 
 Jttrs. B. For this pjirpose I fill this piece of flass tube with wa- 
 ter, and cork it 
 up ai both ends ; 
 rough one of 
 i he corks 1 intro- 
 duce that wire 
 of the battery, 
 which conveys 
 the positive elec- 
 tricity ; and the 
 
 Fiff IK. 
 
 Apparatus for tbe decomposition of water by the Voltaic Baunry. 
 
 455. What are the means of decomposing water? 
 
 456. What is the difference between the union of oxygen and ni- 
 trogen, and the union of oxygen and hydrogen ? 
 
 457. Ma\ water be considered an oxyd ? 
 
 458. What is the inconvenience of decomposing water by the ox- 
 ydation of charcoal or metals ? 
 
 459. How may water be decomposed by the use of the Voltaic 
 battery , 
 
wire which conveys the negative electricity is made to pass through 
 the other cork, so that the 'wo wires approach each other sufficient- 
 ly near to give out their respective electricities. 
 
 Caroline* It does no: ai pear to me that you approach the wires 
 so near as you did when 3 on made the battery act by itself. 
 
 Mrs B Water being a better conductor of electricity than air, 
 the two wires will a on each other at a greater distance in the for- 
 mer, than in the lat'.er case 
 
 Emily. Now th electrical effect appears ; I see small bubbles 
 of air emitted from each wire. 
 
 Mrs.B. Esc ! - wire decomposes the water ; the positive by com- 
 bining with irs oxygen, which is> negative ; the negative by com- 
 bining with i' hydrogen, which is positive. 
 
 Caroline. That is wonderfully curious ! but what are the small 
 bubbles of air ? 
 
 Mrs.B Those that appear to proceed from the positive wire, 
 are the u suit of the decomposition of the water by that wire. That 
 is to say the positive electricity having combined with some of the 
 oxygen of the water, the particles of hydrogen which were combin- 
 ed with that portion of oxygen are set' at liberty, and appear in the 
 form of small bubbles of gas or air. 
 
 Emily, And T suppose the negative fluid, having in the same 
 manner combined with some of the hyirogen of the water, the par- 
 ticles of oxygen that were combined with it, are set free, and emit- 
 ted in a gaseous form. 
 
 Mm. B. Precisely so. But I should not forget to observe, that 
 the wires used in this experimentare made of platina, a metal which 
 is not capable o f combining ith oxygen ; for otherwise the wire 
 "Wou!;^ combine vrith the oxygen, and the hydrogen alone would be 
 disengaged. 
 
 Caroline. But could not water be decompo^H without the elec- 
 tric circle being completed ? If, for instance, you immersed on'y the 
 positive wire in the water, would it not combine with the oxygen, 
 and the hydrogen gas be given out ? 
 
 Mrs. B. No; for as you may recollect, the battery cannot act 
 unless i he circle be completed ; since the positive wire will not give 
 out its electricity, unless aiuaced by that of the negative wire. 
 
 Caroline. I understand it now. But look, Mrs. B., the decompo- 
 sition of the water v, hich has been going on for some time, does not 
 sensibly drninish its quantity what is the reason of that ? 
 
 Mrs. B. Because the quantity decomposed is so extremely small. 
 If you compare the density of water with that of the gases into 
 which it is resolved you must be aware that a single drop of water 
 is sufficient to produce thousands of such small bubbles as those you 
 now perceive. 
 
 Caroline. But in this experiment, we obtain the oxygen and hy- 
 drogen gases mixed together. Is there any means of procuring the 
 two gases separately^ 
 
 Mrs. B. They can be collected separately with great ease by 
 
 460. Which is the best conductor ot electee- y, water or air ? 
 
 461. What remarkable property has platina ? 
 
 462. Wh> cannot water be decomposed unless the electric circle 
 is completed ? 
 
HYDROGEN. 113 
 
 ifcodify ing a little the experiment Thus, if instead of one tube, we 
 employ two, as you see here (c, d,) (Fig. 19,) both tubes being clos- 
 Fig. 19. ed at one end, and open at the other ; and 
 
 if after filling these tubes with water, we 
 place them standing in a glass of water (e) 
 with their open end downwards, you will 
 see that the moment we connect the 
 wires (a, b,) which proceed upwards from 
 the interior of each tube, the one with one 
 end of the battery, and the other with the 
 other end, the water in the tubes will be 
 decomposed ; hydrogen will be given out 
 round the wire in the tube connected with 
 the positive end of the battery, and oxy- 
 gen in the other , and these gases will be 
 
 Apparatus for decomposing Ur ? V lved ^actly in the proportions which 
 
 1.7 voltaic Electricity and obtaining I have before mentioned, namely, two 
 
 the gases separate. measures of hydrogen for one of oxygen. 
 
 We shall now begin the experiment, but 
 
 it will be some time before any sensible quantity of the gases can 
 be collected. 
 
 Emily. The decomposition of water in this way, slow as it is, is 
 certainly very wonderful ; but I confess that I should be still more 
 gratified, if you could show it us on a larger scale, and by a quicker 
 process. I am sorry that the decomposition of water by charcoal 
 or metals is attended with so much inconvenience. 
 
 Mrs. B. Water may be decomposed by means of metals without 
 any difficulty ; but for this purpose the intervention of an acid is re- 
 quired Thus, if we add *me sulphuric arid (a substance with the 
 nature of which you are not jet acquainted) to the water which the 
 metal is to decompose, the acid enables the metal to combine with 
 the oxygen of the water so readily and abundantly, that no heat is 
 required to hasten the process. Of this I am going to show you an 
 instance. I put into this bottle the water that is to be decomposed, 
 ^fie metal that is to effect that decomposition by combining with the 
 oxygen, and the acid which is to facilitate the combination of the 
 metal and the oxygen. You will see with what violence these will 
 act on each other. * 
 
 * To obtain hydrogen, fit a cork airtight to an oil flask, and pierce 
 it with a burning iron, to admit a tube. The tube may be of glass, 
 lead, or tin, bent to a convenient shape, and put into the opening- 
 made by the hot iron. Pour into the flask about a gill of water, and 
 drop into it about an ounce of zinc, granulated by rnelling, and 
 pouring it into cold water. Then pour in half an ounce by measure 
 of sulphuric acid, and immediately put the cork into its place, and 
 plunge the other end of the tube under a receiver, or large tumbler, 
 filled with water and inverted in the water bath. The gask grows 
 hot and the gas begins to rise, the instant the acid is poured in ; a 
 place therefore must previously be prepared to set it ; and if nothing- 
 better is at hand, a bowl, with a cloth in it, to prevent breaking 
 the flask, and set at a convenient height will do very well. C. 
 
 463. How can water be decomposed so as to procure the tw" 
 gases separate ? 
 
 464. How may water be decomposed by means of iron filio^s 
 
 10* 
 
114 
 
 HYDROGEN. 
 
 Caroline. But what metal is it that you employ for this purposed 
 
 Jtfrs. B. It is iron ; and it is used in the state of filings, as these 
 present a greater surface to the acid than a solid piece of metal. 
 For as it is the surface of the metal which is acted u\ on by the arid, 
 and is disposed to receive the oxygen produced by ihe decomposi- 
 tion of the water, it ueoessan \ follows that the greater is the sur- 
 face, the more considerable is the effect. The bubbles which arc 
 now rising on the hydrogen gas 
 
 Caroline. How disagreeable it smells ! 
 
 J\Jrs. B. It is indeed unpleasant, though I believe not particularly 
 hurtful. We shall not, however, suffer any more to escape, as it 
 will be wanted for experiments. I shall therefore collect it in a 
 glass-receiver, by making it pass through this bent tube, which will 
 conduct it into Ihe water-bath (Fig. 20. No. I.) 
 Fig. 20. 
 
 1. Apparatus for preparing and collecting hydrogon as. 2. Receiver full of hydrogen gas 
 inverted over mater. 
 
 Emily. How very rapidly the gas escapes ! it is perfectly trans- 
 parent and without any colour whatever. Now the receiver is full. 
 
 JMrs B. We shall therefore remove it and substitute another in 
 its place. But you must observe, that when the receiver is full,W 
 is necessary to keep it inverted with the mouth underwater, other- 
 wise the gas would escape. And in order that it may not be in the 
 way, I introduce within the bath, under the water, a saucer, into 
 which I slide the receiver, so that it can be taken out of the bath 
 and conveyed any where ; the water in the saucer being equally ef- 
 fectual in preventing its escape as that in the bath. (Fig. 20. No. 2.) 
 
 Emily. I am quite surprised to see what a large quantity of hy- 
 drogen gas can be produced by so small quantity of water, especi- 
 ally as oxygen is the principal constituent of water. 
 
 Mrs. B. In weight it is; but not in volume. For though the pro- 
 portion, by weight, is nearly eight parts of oxygen to one of hydro- 
 gen, yet the proportion of the volume of the gases is about one part 
 
 465. Why are iron filings, in this experiment, better than a solid 
 piece of metal ? 
 
 466. How may hydrogen g-as be collected as the water is decom- 
 posed ? 
 
 467. What are the proportions of oxygen and hydrogen in water > 
 
HVDROGEN. 115 
 
 of oxygen to-two of hydrogen; so much heavier is the former than 
 the latter.* 
 
 Caroline. But why is the vessel in which the water is decomposed 
 so hot ? As the water changes from a liquid to a gaseous form, cold 
 should be produced instead of heat. 
 
 Jtfr.v. B. No : for if one of the constituents of water is cjnverted 
 into gas, the other becomes solid in combining with the m< ;al. 
 
 Emily. In this case, then, neither heat nor cold should be produ- 
 ced ? 
 
 Mrs. B. True ; but observe that the sensible heat which is dis- 
 engaged in this operation, is not owii.g to the decornposrion of the 
 water, but to an extrication of heat produced by the mixture of wa- 
 ter and sulphuric acid. I will mix some water and sulphuric acid 
 together in this glass, that you may ted the surprising quantity of 
 heat which is disengaged by their union now take hoL f the grlass. 
 
 Caroline Indeed 1 cannot ; it feels as hot as boiling water. I 
 should have imagined th-.-re would have been heat enough disenga- 
 ged to have rendered the ! quid solid. 
 
 .Airs B. %s, however, ! does not produce that effect, we cannot 
 refer this heat to die modification called latent bent. We may 
 however, I think, consider it as heat of capacity, since the liquid is 
 condensed by its loss ; and if >. ou were to repeat the experiment, in 
 a graduated tube, you would tmd the two liquids when mixed, oc- 
 cupy considerably less space th^u they did separately. But we will 
 res, rve this to another opportunity, and attend at present to the 
 hydrogen gas which we have been producing. 
 
 If I no v set the hydrogen gas which is contained in this receiver 
 at liberty all at once, and^indle it as soon as it comes in contact 
 with the atmosphere, by presenting it to a candle, it will so sudden- 
 ly and rapidly decompose the oxygen gas, by combining with its ba- 
 sis, that an explosion or a detonation (as chemist 1 - commonly call it) 
 \villbe produced For this purpose,! need only take up thereceiv- 
 
 and quickly present its open mouth to the candle so . . . 
 Caroline. It produced only a sort of hissing noise, with a vivid 
 h of light I had expected a much greater report. 
 Mrs. B. And so it would have been, had the gases been closely 
 confined at the moment they were made to explode. If, for in- 
 stance, we were to put in this bottle a mixture of hydrogen gas and 
 atmospheric air ; and if, after corking the bottle, we should kindle 
 the mixture by a very fine orifice, from the sudden dilatation of the 
 gases at the moment of their combination, the bottle must either 
 fly to pieces, or the cork be blown out with considerable violence. 
 
 Caroline But in the experiment which we have just seen, if you 
 did not kindle the hydrogen gas, would it not equally combine with 
 the oxygen ? 
 
 Mrs, B. Certainly not : for, as 1 have just explained to you, it is 
 necessary that the oxygen and hydrogen gases be burnt together, 
 in order to combine chemically and produce water. 
 
 * Hydrogen is about 13 times lighter than atmospheric air. C. 
 
 468. How much lighter is hydrogen than common air ? 
 
 469. How can hydrogen gas be made to produce an explosion 
 with a loud report ? 
 
 470. How can the experiment named be varied so as to produce 
 loud report? 
 
110 
 
 Caroline. That is true ; but I thought this was a different com 
 bination, for I see no water produced. 
 
 Mrs. B. The water resulting from this detonation was so small 
 in quantity, and in such a state of minute division, as to be invisible. 
 But water certainly was produced ; for oxygen is incapable of com- 
 bining with hydrogen in any other proportions than those which 
 form water ; therefore, water must always be the result of their 
 combination. 
 
 If, instead of bringing the hydrogen gas into sudden contact with 
 the atmosphere, (as we did just now,) so as to make the whole of it 
 explode the moment it is kindled we allow but a very small surface 
 of gas, to burn in contact with the atmosphere, the combustion goes 
 on quietly and gradually at the point of contact, without any deto- 
 nation, because thesur r aces brought together are too small for the 
 immediate union of the gases. The experiment is a very easy one. 
 This phial, with a narrow neck. (Fig. 2i,No. I.) is full of hydrogen 
 gas, and is carefully corked. If I take out the cork without mo- 
 ving the phial, and quickly approach the candle to the orifice, you 
 
 will see how different the result will be * 
 
 Emily. How prettily it burns, with a blue flame ! 
 The flame is gradually sinking within the phial 
 now it has entirely disappeared. But does not this 
 combustion likewise produce water ? 
 
 Mrs. B. Undoubtedly. In order to make the 
 formation of the water sensible to you I shall pro- 
 cure a fresh supply of hydrogen gas, by putting into 
 this bottle (Fig. 2!. No. 2.) iron filings, water, and 
 sulphuric acid, rnaterials^imilar to those which we 
 have just used for the same purpose. I shall then 
 cork up the bottle, leaving only a small orifice in 
 the cork, with a piece of glass tube fixed to it, 
 through which the gas will issue in a continued ra- 
 pid stream. 
 
 Carolina. I hear already the hissing of the galfl 
 through the tube, and I can feel a strong currefl 
 against my hand. 
 Mrs B This current 1 am going to kindle with 
 
 the candle see how vividly it burns 
 
 Emily. It burns like a candle with a great flame. 
 But why does this combustion last so much longer 
 than in the former experiment * 
 
 Mm. B. The combustion goes on uninterruptedly 
 tin? the formation ofas long- as the new gas continues to be produced. 
 water by the combus-j^y if I invert this rcceiverovcr the flame, you will 
 
 lion of bydrcg-en gas. 
 
 * The levity of hydrogen is such, (hat if a vessel be filled with it. 
 and kept inverted, 'it may be carried about the room without its es- 
 caping 1 . The above experiment therefore may be made by bring- 
 ing a small jar, or tumbler of gas over a lighted lamp.- C. " 
 
 471. Can oxygen and hydrogen combine in any other propor- 
 tions than to produce water ? 
 
 472. What is represented in figure 21 ? 
 
 473. How can it be made to burn like a candle ? 
 
 474. If an inverted receiver filled with hydrogen gas be held over 
 the flame of a lamp, what will be seen on its internal surface f 
 
 i. si 
 
 of bydren gas. 2 
 Apparatus for illustra- 
 
HYDROGEN, 117 
 
 soon perceive its internal surface covered with a very fine dew. 
 which is pure water.* 
 
 Caroline. Yes, indeed ; the glass is now quite dim with moist- 
 ure ! How glad I am that we can see the water produced by this 
 combustion. 
 
 Emily. It is exactly what I was anxious to see ; for I confess I 
 was a little incredulous. 
 
 Mrs B. If I had not held the glass bell over the flame, the wa- 
 ter would have escaped in the state of vapour, as it did in the former 
 experiment We have here, of course, obtained but a very small 
 quantity of water ; but the difficulty of procuring a proper appara- 
 tus, with sufficient quantities of gases, prevents my showing it you 
 on a larger scale. 
 
 Tne composition of water wan discovered about the same period, 
 both by Mr. Cavendish, in this country, and by the celebrated- 
 French chemist, Lavoisier. The latter invented a very perfect 
 and ir,--enious apparatus,to perform with great accurac) , and upon a 
 large scaie, the formation of water by the combination of oxygen, 
 and hydrogen gases. Two tubes, conveying due proportions, the 
 one of oxygen the other of hydrogen gas, are inserted at opposite 
 sides of a large glo^e of glass previously exhausted of air ; the two 
 streams of gas are kindled within the globe, by the electrical spark, 
 at the point where they come in contact ; thev burn together, that 
 'is to say, the hydrogen' combines wilh the oxygen, the caloric i^set 
 at liberty, and a quantity of water is produced, exactly, equal in 
 weight to that of the two gases introduced into the globe. 
 
 Caroline And what was the greatest quantity of water ever 
 formed in this apparatus ? 
 
 Mrs. B. S -veral ounces ; indeed, very nearly a pound, if I recol- 
 lect right ; but the operation lasted many days. 
 
 Emi'y. This exoeriment must hnve convinced all the world of 
 the truth of the discovery. Pray if improper proportions of the 
 gases were mixed and set fire to. what would be the result ? 
 
 ^fc-.v. B Water *ouid f qually be formed, hut there would be a 
 r^Bie of either one or other of the gases, because, as I have al- 
 reaw fold you, hydrogen and oxygen will combine only in the pro- 
 portions requisite for the formation of vvater 
 
 Emily. Look, Mrs. B., our experiment with the Voltaic battery, 
 (See Fig. 19,) has made great progress ; a quantity of gas has been 
 formed in each tube, but in one of (hem there is tw'ice as much as in 
 in the other 
 
 Jl/r* B Yes ; because, as I said before, water is composed of 
 
 * The burning of a candle, lamp, wood, &c. always produces wa- 
 ter. The tallow and oil contain hydrogen, and during combustion, 
 it unites with the oxygen of the atmosphere. Hold a wide tube 
 over a lamp, and it is soon covered with moisture. Wood contains 
 hydrogen C. 
 
 475 How is water produced by the. burning of a candle, lamp&c.: 
 
 476. What chemists discovered the composition of water ? 
 
 477. How would you describe the apparatus invented by Lavoi 
 sker for converting oxygen and hydrogen gases into waier? 
 
 478. What would be the result if other proportions of oxygen 
 and hydrogen gas were mixed than is proper for the production of 
 water ? 
 
118 
 
 HYDROGEN. 
 
 i.wo volumes of hydrogen to one of oxygen and if we should now 
 mix these gnses together and set fire to them by an electrical spark, 
 both gases would entirely disappear, and a small quantity of water 
 would be formed. 
 
 There is another curious effect produced by the combustion of 
 hydrogen gas, which 1 shall show you, though I must acquaint you 
 first, that I cannot well explain the cause of it. For this purpose, I 
 must put some materials into our apparaius, in order to obtain a 
 stream of hydrogen gas, just as we have done before. The process 
 is already going on, and the gas is rushing through the tube, 1 shall 
 now kindle it with the taper. 
 
 Emily. It burns exactly as it did before "VVhat is the curious 
 effect which you are mentioning ? 
 
 JMrs. B. Instead of the receiver, by means of which we have 
 just seen the drops of water form, we shall invert over ihe flame this 
 piece of tube, which is about iwo feet in length, and one inch in diam- 
 (Fig. 22.) eter but you must observe that it is open at boll; ends. 
 Emily. What a strange noise it produces ! something 
 like tho JEolian harp, but not so sweet. 
 
 Caroline. It is very singular indeed ; butl think rath- 
 er too powerful to be pleasing And is not this sound 
 accounted for " 
 
 Mrs. B. That the percussion of glass, by a rapid 
 stream of gas, should produce a <ound, is not extraordi- 
 nary ; but the sound here is so peculiar, that no other 
 gas has a similar effect. Perhaps it is owing to a brisk 
 vibratory moiion of the glass, occas,i ned by the succes- 
 sive formation and condensation of small drops of water 
 on the sides of the glass tube, and the air rushing in to 
 replace the vacuum formed.* 
 
 Caroline. How very much this flame resembles the 
 burning of a candle. 
 
 Jftrs. B The bu rning of a candle is produced by much 
 the same me^ns A great deal of hydrogen is contatffcd 
 in candles, whetherof tallow or wax This hydrogedlll- 
 ing converted into gas by the heat of the candle, dom- 
 bines with the oxyffen of the atmosphere, and flame and 
 w-.iter re in 14 from the combination. So that in fact, the 
 A aratus Aflame of a candle is owing to the combustion of hydrogen 
 product* Har-eas. An elevation of temperature, such as is produced 
 wonic sounds hy^ a lighted match or tap-r is required to give the first 
 In, dro^njT impulse to the combustion ; but afterwards it goes on oi 
 itself because the candle finds a supply of caloric in the successive 
 quantities of heat which result from the union of the two electrici- 
 ties given out by the gases during- theircombustion. But there arc 
 other circumstances connected with the combustion of candles and 
 lamps, which I cannot explajn to you till you are acquainted witl 
 carbon, which is one of their constituent parts. In general, howev- 
 er, whenever you see flame, you may infer that it is owing to tin 
 
 * This ingenious explanation was first suggested by Dr. Delarive. 
 See Journals of the Royal Institution, vol. i p. 259. 
 
 479. What curious experiment is exhibited in figure 22 : 
 -ISO. How is a common candle made to burn ? 
 
HYDROGEN. 
 
 119 
 
 formation and burning of hydrogen gas*f ; for flame is the pecu- 
 liar mode of burning hydrogen gas, which with only ooe or two ap- 
 parent exceptions, does not belong to any other combustible. 
 
 Emily. You astonish me ! I understood that flame was the calo- 
 ric produced by the union of the two electricities, in all combus- 
 tions whatever ? 
 
 Mrs. B. Your error proceeded from your vague and incorrect 
 idea of flame ; you have confounded it with light and caloric in 
 general. Flame always implies caloric, since it is produced by the 
 combustion of hydrogen gas ; but all caloric does not imply flame. 
 Many bodies burn with intense heat without producing flame. 
 Coals, for instance, burn with flame, until all the hydrogen which 
 they contain is evaporated ; but when they afterwards become red 
 hot, much more caloric is disengaged than when they produce 
 flame. 
 
 Caroline. But the iron wire, which you burnt in oxygen gas, ap- 
 peared 'o me to emit flame ; yet, as it was a simple metal, it could 
 contain no hydrogen. 
 
 Mrs. B. It produced a sparkling, dazzling blaze of light, but no 
 real flame. 
 
 Emily. And what is the cause of the regular shape of the flame 
 of a candle ? 
 
 Mrs B. The regularsteam of hydrogen gas, which exhales from 
 its combustible matter. 
 
 Caroline. But the hydrogen ga r . must, from its great levity, as- 
 cend into the upper regions of the atmosphere ; why, therefore, 
 does not the flame continue to accompany it ? 
 
 Mrs. B. The combustion of the hydrogen gas is completed at the 
 point where the flame terminates : it then ceases to be hydrogen 
 gas, as it is converted, by its combination with oxygen, into watery 
 vapour ; but in a state of such minute division as to be invisible. 
 
 Caroline. I do not understand what is the jase of the wick of a. 
 candle, since the hydrogen gas burns so well without it. 
 
 'iWrs. B. The combustible matter of the candle must be decom- 
 posed in order to emit the hydrogen gas : and the wick is instru- 
 mental in effecting this decomposition. Its combustion first melts 
 the combustible matter, and 
 
 Caroline. But, in lamps, the combustible matter is already fluid, 
 and yet they also require wicks. 
 
 Mrs. B. \ am going to add, that afterwards, the burning wick 
 (by the power of capillary attraction) gradually draws up the fluid 
 to the point where combustion takes place ; foi you must have ob- 
 served that the wick does not burn quite to the bottom. 
 
 *Or rather hydro carbonat, a gas composed of hydrogen and car- 
 bon, which will be noticed under the head Carbon. 
 
 f The candle also contains carbon, which gives brilliancy to the 
 flame, and the product of combination besides flame and water is 
 a quantity of carbonic acid. C. 
 
 48 1 . What is said in the note of the burning of a candle ? 
 
 482. What is flame? 
 
 483. How long will coals burn with flame ? 
 
 484. To what is the regular shape of the flame of a candle owing : 
 
 485. If the flame of a candle is produced by Hydrogen gas, why 
 is the wick necessary ? 
 
120 HYDROGEN. 
 
 Caroline. Yes ; but I do not understand why it does not. 
 Mrs. B. Because the air has not so free an access to that part ol 
 the wick which is immediately in contact with the candle as to the 
 part just above, so that the heat there is not sufficient to produce 
 its decomposition ; the combustion, therefore, begirt a little above 
 this point.* 
 
 Caroline. But, Mrs. B., in those beautiful lights, called gas 
 lights, which are now seen in so many streets, and will, 1 hope, be 
 soon adopted every where, I can perceive no wick at all. How 
 are these lights managed ? 
 
 Mrs. B. 1 am glad you have put me in mind of saying a few 
 words on this very useful and important improvement. In this mode 
 of lighting, the gas is conveyed to the extremity of a tube, where 
 it is kindled and burns as long as the supply continues. There is 
 therefore, no occasion for a wick, or any other fuel whatever. 
 Emily. But how is this gas procured in such large quantities ? 
 JMrs. B. It is obtained from coal, by distillation. Coal, when 
 exposed to heat in a close vessel, is decomposed ; and hydrogen, 
 which is one of its constituents, rises in the state of gas, combined 
 with another of its component parts, carbon, forming a compound 
 gas, called Hydro-Carhonat* the nature of which we shall again 
 have an opportunity of noticing when we treat of carbon. This 
 gas, like hydrogen, is perfectly transparent, invisible, and h ghly 
 inflammable ; and, in burning, it emits that vivid light which you 
 have so often observed . 
 
 Caroline. And does (he process for procuring it require nothing 
 but heating the coals, and conveying the gas through tubes ? 
 
 Mrs. B. Noihmg else, except that the gas must be made to pass, 
 immediately at its formation, through two or three large vessels of 
 water.f in which it deposits some oiher ingredients, and especially 
 water, tar. and oil, which also arise from the distillation of coals. 
 The gas-light apparatus, therefore, consists simply in a large iron 
 vessel, in which the coals are exposed to the heat of a furnace,- 
 some reservoirs of water, in which the gas deposits its impuritiqfc, 
 and tubes that convey it to tho desired spot, being propelled with 
 uniform velocity through the tubes by means of a certain degree of 
 pressure which is made upon the reservoir. 
 
 * In the burning of a candle, the reason why combustion does not 
 take place in immediate contact with the tallow, is, that the caloric 
 is here employed in converting a solid into a fluid, as explained in 
 the conversation on free caloric. In the burning of a lamp if the 
 same thing takes place, it is because the metallic tube through 
 vrhich t'.ia wick passes, conducts off the heat. C. 
 
 f The gas is passed through one vessel of slacked lime and water 
 to absorb the carbonic acid gas, with which it is always more or 
 less mixed, when first distilled. C. 
 
 486. Why is it that the wick of a candle does not burn to the bot- 
 tom? 
 
 487. How are gas lights made to burn without wicks ? 
 
 488. What is the gas called, used in lighting the streets of some 
 large cities ? 
 
 489. How is it obtained ? 
 
 490. Of what does the gas light apparatus consist ? 
 
HYDROGEN. 12l 
 
 Emily. What an admirable contrivance ! Do you not think, Mrs. 
 B., that it will soon be universally adopted? 
 
 Mrs. B* Most probably ; for the purpose of lighting streets, offi- 
 ces, and public places, it far surpasses any former invention : but in 
 regard to the interior of private houses, this mode of lighting has not 
 yet been sufficiently tried to know whether it will be found gene- 
 rally desirable, either with respect to economy or convenience. It 
 may, however, bo considered as one of the happiest applications of 
 chemistry to the comforts of life; and there is every reason to sup- 
 pose that it will answer the full extent of public expectation. 
 
 I have another experiment to show you with hydrogen gas, which, 
 1 think, will entertain you. Have you ever blown bubbles with 
 soap and water ? 
 
 Emily. Yes, often, when I was a child ; and I used to make them 
 float in the air by blowing them upwards. 
 
 Mrs. B. We shall fill some bubbles with hydrogen gas, instead 
 of atmospheric air, and you will see wilh what ease and rapidity 
 they will ascend, without the assistance of blowing, from the light- 
 ness of the gas. Will you mix some soap and water, whilst I fill 
 this bladder with the gas contained in the receiver which stands on 
 the shelf in the water bath ? 
 
 Caroline. What is the use of the brass-stopper and turn-cock at 
 the top of the receiver? 
 
 Mrs. B. It is to afford a passage to the gas, when required. There 
 is, you see, a similar stop-cock fastened to this bladder, which is 
 made to fit on the receiver. I screw them one on the other, and 
 now turn the two cocks, to open a communication between the re- 
 ceiver and the bladder ; then, by sliding the receiver off" the shelf, 
 and gently sinking into the bath, the water rises in the receiver, 
 and forces the gas into the bladder. (Fig. 23, No. 1.) 
 
 Caroline. Yes. I see the bladder swell as the water rises in the 
 receiver. 
 
 Jtfrs. B. I think that we have already a sufficient quantity in the 
 bladder for our purpose ; we must be careful to stop both the cocks 
 before we separate the bladder from the receiver, lest the gas should 
 escape. Now I must fix a pipe to the stopper of the bladder, and by 
 dipping its mouth into the soap and water, take up a few drops : then 
 I again turn the cock, and squeeze the bladder, in order to force the 
 
 rs into the soap and -water, at the mouth of the pipe. (Fig. 23, No. 
 ) 
 
 Emily. There is a bubble ; but it bursts before it leaves the 
 mouth of the pipe. 
 
 Mrs J3. We must have patience and try again ; it is not so easy 
 to blow bubbles by means of a bladder, as simply with the breath. 
 
 Caroline. Perhaps there is not soap enough in the water. 1 should 
 have had warm water ; it would have dissolved the soap better. 
 
 Emily. Does not some of the gas escape between the bladder and 
 the pipe ? 
 
 491. What is said of lighting streets, offices, and public places 
 with this gas ? 
 
 492. How can bubbles of soap and water be made to float in the airr 
 How can these bubbles be made so as to explode on setting fire 
 
 to them? (Seepage 123.) 
 
 493. What is represented in 23, No. 1 and 2? 
 
 11 
 
No. 1. 
 
 Apparatus for transferring gases from a Receiver into a bladder. No. 2. Apparatus for 
 blowing Soap bubbles. 
 
 Mrs. B. No ; they are perfectly air tight; we shall succeed pre- 
 sently, I dare say. 
 
 Caroline. Now a bubble ascends ; it moves with the rapidity of a 
 balloon. How beautifully it refracts the light. 
 
 Emily. It has burst against the ceiling you succeed now won- 
 derfully ; but why do they all ascend and burst against the ceiling? 
 
 Mrs. B. Hydrogen gas is so much lighter than atmospherical air, 
 that it ascends rapidly with its very light envelope, which is burst 
 by the force with which it strikes the ceiling. 
 
 Air-balloons are filled with this gas, and if they carry no other 
 weight than their covering,would ascend as rapidly as these bubbles. 
 
 Caroline. Yet their covering must be much heavier than that of 
 these bubbles ? 
 
 Mrs. B. Not in proportion to the quantity of gas they contain. 
 i do not know whether you have ever been present at the filling of 
 a large balloon. The apparatus for that purpose is very simple. 
 It consists of a number of vessels, either jars or barrels, in which the 
 materials for the formation of the gas are mixed, each of these be- 
 ing furnished with a tube, and communicating with a long flexible 
 pipe which conveys the gas into the balloon. 
 
 Emily. But the fire-balloons which were 6rst invented, and have 
 been since abandoned, on account of their being so dangerous, 
 were constructed, I suppose, on a different principle. 
 
 Mrs. B. They were filled simply with atmospherical air, consider- 
 
 494. With what are air balloons filled ? 
 
 495. What is the apparatus for filling a large balloon with hydro- 
 gen g-as ? 
 
 496. With what were fire balloons filled ? 
 
 497. Why were they abandoned ? 
 
HYDROGEN. 1550 
 
 ably rarefied by heat ; and the necessity of having a fire underneath 
 the balloon, in order to preserve the rarefaction of the air within it, 
 was the circumstance productive of so much danger. 
 
 If you are not yet tired of experiments, I have another to show 
 you. It consists in fii!.ing soap-bubbles with a mixture of hydrogen 
 and oxygen gases, in the proportions that form water ; and after- 
 wards setting fire to them. 
 
 Emily. They will detonate, I suppose. 
 
 Mrs. B. Yes. they will. As you have seen the method of trans- 
 ferring the gas from the receiver into the bladder, it is not necessa- 
 ry to repeat it. I have therefore provided a bladder which contains 
 a due proportion of oxygen and hydrogen gases, and we have only 
 to blow bubbles with it. 
 
 Caroline. Here is a fine large bubble rising shall I set fire to it 
 with a candle ? 
 
 Mrs. B. If you please^- 
 
 Carcline. Heavens, what an explosion !* It was like the report 
 of a gun: I confess it frightened me much, I never should have 
 imagined it could be so loud. 
 
 Emily. And the flash was as vivid as lighting. 
 
 JUrs. B. The combination of the two gases take place during 
 that instant of time that you see the flash, and hear the detonation. 
 
 Emily. This has a rteong resemblance to thunder and light ning.f 
 
 Mrs. 3. These phllKnena, however, are generally of an electri- 
 cal nature. Yet various meteoroligical effects may be attributed 
 to accidental detonations of hydrogen gas in the atmosphere ; for 
 nature abounds with hydrogen ; it constitutes a very considerable 
 portion of the whole mass of water belonging to our globe, and from 
 that source almost every body obtains it. It enters into the com- 
 position of all animal substances, and of a great number of minerals; 
 but it is most abundant in vegetables. From this immense variety 
 of bodies it is often spontaneously discharged ; its great levity 
 makes it rise into the superior regions of the atmosphere ; and 
 when, either by an electrical spark, or any casual elevation of tem- 
 perature, it takes fire, it may produce such meteors or luminous 
 appearances as are occasionally seen in the atmosphere. Of this 
 k;nd are probably those broad flashes which we often see on a 
 summer evening, without hearing any detonation. 
 
 Emily. Every flash, I suppose, must produce a quantity of water? 
 Caroline. And this water, naturally, descends in the form of rain. 
 Mrt. B. That probably is often the case, though it is not a neces- 
 
 * In making this experiment, always be careful to turn the stop- 
 cock, or detach the bubble completely from the pipe before it is set 
 fire to ; otherwise a sad accident may happen from the gas taking 
 fire in the bladder. C, 
 
 | The report is owing to the air, rushing in to fill the vacuum, 
 caused by the condensation of the two gases, and the heat extrica- 
 ted at the same instant. C. 
 
 408. How can bubbles be made of soap and water so as to ex- 
 plode with a loud reporf, on setting fire to them ? 
 
 499. To what is it snid in the note lh.nl the report is owing ? 
 
 500, In what substances is hydrogen most abundant? 
 591. How may heat lightning be accounted for ? 
 
124 HYDROGEN. 
 
 sary consequence ; for the water may be dissolved by tbe atmos- 
 phere, as it descends towards the lower regions, and remain there 
 in the form of clouds. 
 
 The application of electrical attraction to chemical phenomenais 
 likely to lead to many very interesting- discoveries in meteorology ; 
 for electricity evidently acts a most important part in the atmos- 
 phere. This subject, however, is, as yet, not sufficiently developed 
 for me to venture enlarging upon it. The phenomena of the atmos- 
 phere are far from being well understood : and even with the little 
 that is known, 1 am but imperfectly acquainted. 
 
 But before we take leave of hydrogen, I must not omit to men- 
 tion to you a most interesting discovery of Sir H. Davy, which is 
 connected with this subject. 
 
 Caroline. You allude. I suppose, to the new miner's lamp, which 
 has of late been so much talked of. I have long been desirous of 
 knowing what that discovery was, and what purpose it was intend- 
 ed lo answer. 
 
 Mrs. B. It often happens in coal-mines, that quantities of the gas 
 called by chemists hydro carbonat, or by the miners^re damp, (the 
 same from which the gaslights are obtained,) ooze out from the fis- 
 sures in the beds of coal, and fill the cavities $4 which the men are 
 at work ; and this gas being inflammable, th* consequence is, that 
 when the men approach those places, with aflpited candle, the gas 
 takes fire, and explosions happen, which dest%y themen and horses 
 employed in that part of the colliery, sometimes in great numbers. 
 
 Emily. What tremendous accidents these must be ! But whence 
 does that gas originate ? 
 
 Mrs. B. Being the chief product of the combustion of coal, no 
 wonder that inflammable gas should occasionally appear iu situa- 
 tions in which this mineral abounds, since there can be no doubt 
 that processes of combustion are frequently taking place at a great 
 depth under the surface of the earth ; and, therefore, these accumu- 
 lations of gas may arise either from combustions actually going on, 
 or frorn former combustions, the gas having perhaps been confined 
 there from ages. 
 
 Caroline. And how does Sir H. Davy's lamp prevent tho$e 
 dreadful explosions ? 
 
 Mrs. B. By a contrivance equally simple and ingenious; and 
 one which does no less credit to the philosophical views from which 
 it was deduced, than to the philanthropic motives from which the 
 inquiry sprung. The principle of the lamp is shortly this : It was 
 ascertained two or three years ago, both by Mr. Tenant, and by Sir 
 Humphrey himself, that the combustion of inflammable gas could 
 not be propagated through small tubes ; so that if a jet of an inflam- 
 mable e-aseous mixture, issuing from a bladder, or any other vessel, 
 through a small tube, be set fire to, it burns at the orifice of the 
 tube, but the flame never penetrates into the vessel. It is upon this 
 fact that Sir Humphrey's safety lamp is founded. 
 
 Emily. But why does not the flame never penetrate through tbe 
 
 502. Is it supposed that the subject of meteorology is well under- 
 stood ? 
 
 503. What disastrous effects often happen in coal-mines ? 
 
 504. Whence does the hydrogen gas in mines originate ? 
 
 505. Upon what discovery of Mr. Tenant and Sir H. Davy was 
 the miner's safety lamp founded ? 
 
HYDROGEN. 125 
 
 tube into the vessel from which the gas issues, so as to explode at 
 once the whole of the gas ? 
 
 Mrs. B. Because, no doubt, the inflamed gas is so much cooled 
 in its passage through a small tube as to cease to burn before the 
 combustion reaches the reservoir. 
 
 Caroline. And how can this principle be applied to the construc- 
 tion of a lamp ? 
 
 Mrs. LS. Nothing easier. You need only suppose a lamp enclo- 
 sed all round in glass or horn, but having a number of small open 
 tubes at the bottom, and others at the top, to let the air in and out. 
 Now, if such a lamp or lauihorn be carried into an atmosphere ca- 
 pable of exploding, an explosion or combustion of the gas will take 
 place within the lamp ; and although the vent afforded by the tubes 
 will save the lamp from bursting, yet from the principle just ex- 
 plained, the combustion will not be propagated to the external air 
 through the tubes, so that no farther consequence will ensue. 
 Emily. And is that all the mystery of that valuable lamp r 
 Mrs. B. No ; in the early part of the inquiry, a lamp of this kind 
 was actually proposed ; but it was but a rt.de sketch compared to 
 its present state of improvement. Sir H. Davy, after a succession 
 of trials, by which he brought his lamp nearer and nearer to per- 
 fection, at last conceived the happy idea that if the lamp were sur- 
 rounded with a wire-wick or wire-gauze, of a close texture, instead 
 of glass or horn, the tubular contrivance have just described 
 would be entirely superseded, since each of the insterstices of the 
 gauze would act as a tube in preventing the propagation of explo- 
 sions : so that this pervious metallic covering would answer the va- 
 rious purposes of transparency, of permeability to air and of pro- 
 tection against explosion. This idea, Sir Humphrey immediately 
 submitted to the test of experiment, and the result has answereti 
 his most sanguine expectations, both in his laboratory and in the 
 colleries where it has already been extensively tried. And he has 
 now the happiness of thinking that his invention will probably be 
 the means of saving every year a number of lives, which would 
 have been lost in digging out of the bowels of the earth one of the 
 most valuable necessaries of life. Here is one of these lamps, every 
 part of which you will at once comprehend. (Fig. 24.) 
 
 Caroline. How very simple and ingenious ! But I do not yet well 
 see why an explosion taking place within the lamp, should not 
 communicate to the external air around it, through the interstices 
 of the wire? 
 
 .Mrs. n. This has been and is still a subject of wonder, even to 
 philosophers ; and the only mode they have of explaining it is, that 
 flame or ignition cannot pass through a fine wire work, because 
 the metallic wire cools the flame sufficiently to extinguish it in 
 passing through the gauze. This property of the wire-gauze is 
 quite similar to that of the tubes which I mentioned on introducing 
 the subject ; for you may consider each interstice of the gauze as 
 an extremely short tube of a very small diameter. 
 
 , \ ., * : _,. 
 
 506. Why does not flame penetrate through a tube that conveys 
 fcydrc-gen gas so as to produce an explosion ? 
 
 507. How would you describe the miner's lamp ? 
 
 508. What is the use of the miner's lamp ? 
 
 509. Which figure represents the miner's lamp ? 
 
 11* 
 
126 
 
 SULPHUR. 
 
 Fig. 24. 
 
 Emily. But I should expect the 
 wire would often become red hot, by 
 the burning of thegas within the lamp. 
 
 Mrs. B. And this is actually the 
 case ; for the top of the lamp is very 
 apt to become red hot. But fortun- 
 ately, such inflammable, gaseous mix- 
 tures as are found in the mines cannot 
 be exploded by the red hot wire, the 
 intervention of actual flame being re- 
 quired for that purpose ; so that the 
 wire does not set fire to the explosive 
 gas around it. 
 
 Emily. 1 can understand that; but 
 if the wire be red hot, how can it cool 
 the flame within, and prevent its pas- 
 sing through the gauze ? 
 
 Mrs. B. The gauze, though red hot, 
 is not so hot as the flame by which it 
 has been heated; and as metallic 
 wire is a good conductor, the heat 
 does not much accumulate in it, as it 
 passes off quickly to the other parts of 
 the lamp, as well as to any contiguous 
 bodies. 
 
 Caroline. This is indeed a most in- 
 teresting discovery, and one which 
 shows at once the immense utility 
 w it.b which science may be practical-* 
 Jy applied to some of the most impor- 
 tant purposes. 
 
 CONVERSATION VIII. 
 
 ON SULPHER AND PHOSPHORUS. 
 
 Jtfr*. B. Sulphur is the next sub- 
 stance that comes under our consid- 
 eration. It differs in one essential 
 point from the preceding, as it exists 
 in a solid form at the temperature of 
 the atmosphere. 
 
 Caroline. I am glad that we have at 
 last a solid body to examine : one that A. the cut. containing. -H. B. the 
 we can see and touch. Pray, is it not""" r trrew h y winch the p U z- e<* *6*td 
 with sulphur that the points of match- t o . 1 tbe r ' i>t( a r * .^^"^ 'TJ^D* 
 es arc covered, to make them easilyr. the wire\^z7cyiLaT. m Gf aubitcp. 
 kindle ? 
 
 510. What is necessary to produce explosions in inflammable 
 gaseous mixtures ? 
 
 511. In what state does sulphur exist ? 
 
SULPHUR. 
 
 127 
 
 Mrs. B. Yes, it is ; and you therefore, already know, that sulphur 
 is a very combustible substance. It is seldom discovered in nature 
 in a pure unmixed state ; so great is its affinity for other substances 
 that it is almost constantly found combined with some of them. It 
 is most commonly united with metals, under various forms, and is 
 separated from them by a very simple process. It exists, likewise, 
 in many mineral waters, and some vegetables yield it in various pro- 
 portions, especially those of the cruciform tribe. It is also found 
 in animal matter ; in short, it may be discovered, in greater or less 
 quantity in the mineral, vegetable, and animal kingdoms.* 
 
 Emu'//. I have heard of Jlowers of sulphur are they the produce 
 of any plant ? 
 
 Mrs. B. By no means ; they consist of nothing more than com- 
 mon sulphur reduced in a very fine powder by a process called 
 sublimation. You sec some of it in this phial ; it is exactly the 
 same substance as the lump of sulphur, only its color is a paler yel- 
 low, owing to its state of very minute division. 
 Emily. Pray what is sublimation ? 
 
 Mrs. B. It is the evaporation, or more properly speaking, the 
 volatilization of solid substances, which, in cooling condense again 
 into a concrete form. The process, in this instance, must be per- 
 formed in a closed vessel, both to prevent combustion, which would 
 lake place if the access of air were not carefully precluded, and 
 likewise, in order to collect the substance after the operation. As it 
 is rather a slow process we shall not try the experiment now ; but 
 you will understand it perfectly if I show you the apparatus used for 
 the purpose, (fig. 25.) Some lumps of sulphufare put into a receiver 
 Fig. 25. of this kind, which is called a. cucurbit. 
 
 Fts shape you see somewhat resembles 
 that of a pear, and is open at the top, so 
 as to adapt itself exactly to a kind of con- 
 ical receiver of this sort, called the head. 
 The cucurbit, thus covered with its head 
 is placed over a sand-bath ; this is nothing 
 more than a vessel full of sand, which is 
 kept heated by a furnace, such as you see 
 here, so as to preserve the apparatus in a 
 moderate and uniform temperature. The 
 sulphur then soon begins to melt, and im- 
 mediately after this a thick white smoke 
 rises, which is gradually deposited within 
 the head, or upper part of the apparatus, 
 where it condenses against the sides, 
 somewhat in the form of vegetation, 
 whence it has obtained the name of flow- 
 ers of sulphur. This apparatus, which 
 is called an a/rw/>ir, is highly useful in 
 all kinds of distillations, as you will see 
 
 * The sulphur of commerce is chiefly obtained in the vicinity of 
 
 Sublinution of Sulphur. 
 A, AUml-ic. U, Sand-bulb. 
 C. Furnace. 
 
 512. In what may it be found ? 
 
 513. How do the flowers of sulphur differ from sulphur in a solid 
 5! 4. What is sublimation? [stater 
 
 515. What does figure 25 represent ? 
 
 516. From what is the name " Flowers of sulphur*' derived ? 
 
128 SULPHUS. 
 
 when we come to treat of those operations. Alembics are not 
 commonly made of glass, like this wti>ch is applicable only to dis- 
 tillation upon a very small scale. Those used in manufactures are 
 generally made of copper, and are of course considerable larger. 
 The general construction, however, is always the same, although 
 their shape admits of some variation. 
 
 Caroline. What is the use of that neck, or tube, which bends 
 down from the upper piece of the apparatus ? 
 
 J\lrs. B. It is of no use in sublimations ; but in distillations (the 
 general object of which is to evaporate, by heat, in closed vessels 
 the volatile parts of a compound body, and to condense them again 
 into a liquid,) it serves to carry off the condensed fluid, which oth- 
 erwise would fall back into the cucurbit. But this is rather foreign 
 to our present subject. Let us return to the sulphur. You now 
 perfectly understand 1 suppose, what is meant by sublimation? 
 
 Kmily. 1 believe I do. Sublimation appears to consist in de- 
 stroying by means of heat, the attraction of aggregation of the par- 
 ticles of a solid body, which are thus volatilized ; and as soon as 
 they lose the caloric which produced that effect, they are deposited 
 iu the form of a fine powder. 
 
 Caroline. It seems to me to be somewhat similar to the transfor- 
 mation of water into vapor, which returns to its liquid state when 
 deprived of caloric. 
 
 Emily. There is this difference, however, that the sulphur doea 
 not return to its former state, since instead of lumps, it changes to 
 a fine powder. 
 
 J\frs. B. Chemically speaking, it is exactly the same sumbstance, 
 whether in the form of lump or powder. For if this powder be 
 melted again by he;it, it will, in cooling, be restored to the same 
 olid state in which it was before its sublimation. 
 
 Caroline. But if there be no real change produced by the subli* 
 mation of the sulphur, what is the use of that operation ? 
 
 Jfrs. B. It divides the sulphur into very minute parts, and thu* 
 disposes it to enter more readily into combination with other bodies, 
 It is used also as a means of purification. 
 
 Caroline. Sublimation appears to me, like the beginning of com- 
 bustion, for the completion of which one circumstance only is want- 
 ing, the absorption of oxygen. 
 
 Mrs. B. But that circumstance is every thing. No essential al- 
 teration is produced in sulphur by sublimation ; whilst in combus- 
 tion it combines with the oxygen, and forms a new compound totally 
 different in every respect from sulphur in its pure state. We shall 
 now burn some sulphur, and you will see how very different the re 
 
 volcanoes, or in volcanic countries, where it is brought up from the 
 bowels of the earth by sublimation. An inferior kind is obtained 
 by the distillation of pyrites. C. 
 
 5 1 7. What effect is produced if the flowers of sulphur are melted ? 
 
 518. If no real change is produced by the sublimation of sulphur, 
 what is the use of that operation ? 
 
 619. What is the difference between the sublimation and combus- 
 tion of sulphur? 
 
 i>20. If sulphur is burnt what will be the result ? 
 
SULPHUR. 129 
 
 suit will be. For this purpose I put a small quantity of flowers of 
 sulphur into this cup, and place it in a dish, into which I have poured 
 a little water; I now set fire to the sulphur with the point of this 
 hot wire ; for its combustion will not begin unless its temperature 
 be considerably raised. You see that it burns with a faint bluish 
 flame ; and as I invert over it this receiver, white fumes arise from 
 'the sulphur, and fill the vessel. You will soon perceive that the 
 water is rising- within the receiver, a little above its level in the 
 plate. Well, Emily, can you account for this ? 
 
 Emily. I suppose that the sulphur has absorbed the oxygen from 
 the atmospherical air within the receiver, and that we shall find 
 some oxygenated sulphur in the cup. As for the white smoke, I 
 am quite at a loss to guess what it may be. 
 
 Jllrs. B. Your first conjecture is very right ; but you are mis- 
 taken in the last ; for nothing will be left in the cup. The white 
 vapor is the oxygenated sulphur, which assumes the form of an 
 elastic fluid of a pungent and offensive smell, and is a powerful acid. 
 Here you see a chemical combination of oxygen and sulphur, pro- 
 ducing a true gas, which would continue such under the 1 pressure 
 and at the temperature of the atmosphere, if it did not unite with 
 the water in the plate, to which it imparts its acid taste, and all 
 its acid properties. You see now with what curious effects the 
 combustion of sulphur is attended. 
 
 Caroline. This is something quite new ; and I confess that I do 
 not perfectly understand why the sulphur turns acid. 
 
 Mrs. B. It is because it unites with the oxygen, which is the 
 acidifying principle. And indeed, the word oxygen is derived from 
 two Greek words signifying to produce an add. 
 
 Caroline. Why, then, is not water which contains such a quan- 
 tity of oxygen, acid ? 
 
 JV/r.?. B. Because hydrogen, which is the other constituent of 
 water, is not susceptible of acidification. I believe it will be ne- 
 cessary before we proceed further, to say a few words on the gen- 
 eral nature of acids, though it is rather a deviation from our plan of 
 examining the simple bodies separately, before we consider them 
 in a state of combustion. 
 
 Acids may be considered as a peculiar class of burnt* bodies, 
 which during their combustion or combination with oxygen, have 
 acquired very characteristic properties. They are chiefly discern- 
 ible by their sour taste, and by turning red most of the blue veget- 
 able colors. These two properties are common to the whole class 
 of acids; but each of them is distinguished by other peculiar qual- 
 .ties. Every acid consists of some particular substance, (which 
 
 * This might mislead the student. The acids are not all of them 
 formed by burning. All the vegetable acids, as the citric, malic 
 &c. exist ready formed ; some of them are contained in fruits, 
 in lemons, apples, &c.~ C. 
 
 521. What is the acidifying principle? 
 
 522. What does the term oxvgen signify ? 
 
 523. Tf oxygen is the acidifying principle, why does not water 
 become acid, since it contains so much of that gas ? 
 
 524. Of what do acids consist? 
 
130 SULPHUR. 
 
 constitutes its basis, and is different in each,) and of oxygen, which 
 is common to them all 
 
 Emily. But I do not clearly see the difference between acids and 
 oxyds. 
 
 Mrs. B. Acids were in fact oxyds, which, by the addition of a 
 certain quantity of oxygen, have been converted into acids. For 
 acidification, you must observe always implies previous oxydation, 
 as a body must have combined with the quantity of oxygen requis- 
 ite to constitute it an ox\d, before it can combine with the greater 
 quantity which is necessary to render it an acid. 
 
 Caroline. Are all oxyds capable of being converted into acids? 
 
 Mrs B. Very far from it ; it is only certain substances which will 
 enter into that peculiar kind of union with oxygen that produces 
 acids, and the number of these is proportionally very small ; but all 
 burnt bodies may be considered as belonging either to the class of 
 oxyds, or that of acids. At a future period, we shall enter more 
 at large into this subject. At present I have but one circumstance 
 further to point out to your observation respecting acids ; it is, that 
 most of them are susceptible of two degrees of acidification, ac- 
 cording to the different quantities of oxygen with which their basis 
 combines. 
 
 Emily. And how are these two degrees of acidification distin- 
 guished ? 
 
 Mrs. B. By the peculiar properties which result from them. 
 The acid we have just mnde is the first or weakest degree of acidi- 
 fication, and is called sulphurews acid if it were fully saturated 
 with oxygen it would be called sulphuric acid. You must therefore 
 remember, that in this, as in all acids, the first degree of acidifica- 
 tion is expressed by the termination in ous the stronger by the 
 termination in ic. 
 
 Caroline. And how is the sulphuric acid made ? 
 
 Mrs. B. By burning sulphur over water v in pure oxygen gas,, 
 and thus rendering its combustion much more complete. I have 
 provided some oxygen gas for this purpose ; it is in that bottle, but 
 we must first decant the gas into the glass receiver which stands on 
 the shelf in the bath, and is full of water. 
 
 Caroline. Pray, let me try to do it, Mrs. B. 
 
 .Mr.?. B. It requires some little dexterity hold the bottom com- 
 pletely under water, and do not turn the mouth upwards, till it is 
 immediately under the aperture in the shelf through which the gas 
 is to pass into the receiver, and then turn it up gradually. Very 
 -well ; you have only to let a few bubbles escape, and that must be 
 expected at a first trial. Now I shall put this piece of sulphur in- 
 to the receiver,through the opening at the top, and introduce along 
 with it a small piece of lighted tinder to set fire to it. This requires 
 to be done very quickly, lest the atmospherical air should obtain en- 
 trance and mix with the pure oxygen gas. 
 
 Emily. How beautifully it burns ! 
 
 Caroline. But it is already buried in the thick vapour. This, I 
 suppose, is sulphuric acid ? 
 
 525. What is the difference between oxyds and acids? 
 
 526. Are all oxyds capable of becoming acids ? 
 
 527. What is the difference between sulphureous acids and sul- 
 phuric acids ? 52tt. How is sulphuric acid obtained ? 
 
SULPHUR. 131 
 
 Emily. Are these acids always in a gaseous state ? 
 
 Mrs. B. Sulphureous acid, as we have already observed, is a per- 
 manent gas, and can be obtained in a liquid form only by condensing 
 it in water. In its pure state, the sulphureous acid is invisible, and 
 it now appears in the form of a white smoke, from its combining 
 with the moisture. But the vapour of the sulphuric acid, which you 
 have just seen to rise during the combustion, is not gas, but only a 
 vapour, which condenses into liquid sulphuric acid, by losing its ca- 
 loric. It appears, however, from Sir II. Davy's experiments, that 
 this formation and condensation of sulphuric acid requires the pres- 
 ence of water, for which purpose, the vapour is received into cold 
 water, which may afterwards be separated from the acid by the 
 evaporation. 
 
 Sulphur has hitherto been considered as a simple substance ; but 
 Sir H. Davy has suspected that it contains a small portion of hy- 
 drogen, and perhaps also of oxygen. 
 
 On submitting sulphur to the action of a Voltaic battery, he ob- 
 served, that the negative wire gave out hydrogen ; and the existence 
 of hydrogen in sulphur was rendered still more probable by his ob- 
 serving that a small quantity of water was produced during the 
 combustion of sulphur. 
 
 Emily. And pray of what nature is sulphur when perfectly pure ? 
 
 Mrs. B. Sulphur has probably never been obtained perfectly free 
 from combination, so that its radical may possibly possess proper- 
 ties very different from those of common sulphur. It has been sus- 
 pected to be of a metallic nature ; but this is mere conjecture. 
 
 Before we quit the subject of sulphur, I must tell you that it is 
 susceptible of combining with a great variety of substances, and 
 especially with hyrogen, with which you are already acquainted. 
 Hydrogen gas can dissolve a small portion of it. 
 
 Emily. What ! can a gas dissolve a solid substance? 
 
 Mrs. B. Yes ; a solid substance may be so minutely divided by 
 heat, as to become soluble in gas ; and of this there are several in- 
 stances. But you must observe, that, in the present case, a chemi- 
 cal union or combination of the sulphur with the hydrogen gas is 
 produced. In order to effect this, the sulphur must be strongly 
 heated in contact with the gas ; and the heat reduces the sulphur to 
 such a state of extreme division, and diffuses it so thoroughly with 
 the gas, that they combine and incorporate together. And as a proof 
 that there must be a chemical union between the sulphur and the 
 gas, it is sufficient to remark that they are not separated when the 
 sulphur loses the caloric by which it was volatilized. Besides, it is 
 evident, from the peculiar fetid smell of this gas, that it is a new 
 compound totally different from either of its constituents ; it is call- 
 ed sulphuretted hydrogen gas, and is contained in great abundance 
 in sulphureous mineral waters. 
 
 Caroline. Are not the Harrogate waters of this nature? 
 
 629. Are sulphureous and sulphuric acids always in agaseous state? 
 
 630. What was Sir H. Davy's opinion concerning sulphur? 
 
 531. What is sulphur in its pure state? 
 
 532. Can a gas dissolve a solid substance ? 
 
 533. How can it be done ? 
 
 534. How is it known that the union between hydrogen gas and 
 sulphur is a chemical union ? 
 
 535. What is the product of this union called? 
 
132 PHOSPHORUS. 
 
 Mrs. B, Yes; they ure naturally impregnated with sulphuretted 
 hydrogen gas, and there are many other springs of the same kind, 
 which show that this gas must often be formed in the bowels of the 
 earth by spontaneous processes of nature. 
 
 Caroline. And could not such waters be made artificially by im- 
 pregnating common water with this gas ? 
 
 Mrs. B. Yes ; they can be so well imitated, as perfectly to re- 
 semble the Harrogate waters. 
 
 Sulphur combines likewise with phosphorus, and with the alka- 
 lies, and alkaline earths, substances with which you are yet unac- 
 quainted. We cannot, therefore, enter into these combinations at 
 present. In our next lesson we shall treat of phosphorus. 
 
 Emily. May we not begin that subject to-day ; this lesson has 
 been so short ? 
 
 Mrs. B. I have no objection, if you are not tired. What do you 
 say, Caroline ? 
 
 Caroline. I am as desirous as Emily of prolonging the lesson to- 
 day, especially as we are to enter on a new subject; for I confess 
 that sulphur has not appeared to me so interesting as the other sim- 
 ple bodies. 
 
 Jtfrs. B. Perhaps you may find phosphorus more entertaining. 
 You must not, however, be discouraged when you meet with some 
 parts of a study less amusing than others ; it would answer no good 
 purpose to select the most pleasing parts, since if we did not proceed 
 with some method, in order to acquire a general idea of the whole, 
 we could scarcely expect to take interest in any particular subjects. 
 
 PHOSPHORUS, 
 
 PHOSPHORUS is considered as a simple body ; though, like sulphur, 
 it has been suspected of containing hydrogen It was not known by 
 the earlier chemists. It was first discovered by Brandt, a chemist of 
 Hamburg, whilst employed in researches after the philosopher's 
 stone ; but the method of obtaining it remained a secret till it was a 
 second time discovered both by Kunckle and Boyle,in the year 1680. 
 You see a specimen of phosphorus in this phial ; it is generally 
 moulded into small sticks of a yellowish color, as you find it here. 
 
 Caroline. I do not understand in whit the discovery consisted : 
 there may be a secret method of making an artificial composition ; 
 but how can you talk of making a composition which naturally exists ? 
 
 Jtfr*. B. A body may exist in nature, so closely combined with 
 other substances, as to elude the observation of chemists, or render 
 it extremely difficult to obtain it in its separate state. This is the 
 case with phosphorus, which is so intimately combined with other 
 substances, that its exi&tence remained unnoticed till Brandt dis- 
 covered the means of obtaining it free from other combinations. It 
 is found in all animal substances, and is now chiefly extracted from 
 
 536. What is there which shows that this gas is sometimes form- 
 ed spontaneously in the bowels of the earth ? 
 
 537. By whom was phosphorus discovered ? 
 
 538. What is the appearance of it ? 
 
 539. How is phosphorus obtained ? 
 
PHOSPHORUS. 133 
 
 bones, by a chemical process. It exists also in some plants, that bear 
 a strong analogy to animal matter in their chemical composition. 
 
 Emily. But is it never found in its pure separate state ? 
 
 JUrs. B. Never ; and this is the reason why it remained so- long 
 undiscovered. 
 
 Phosphorus is eminently combustible ; it melfs and takes fire at 
 the temperature of one hundred degrees, and absorbs in its com- 
 bustion, nearly once and a half its own weight of oxygen. 
 
 Carriline. What ! will a pound of phosphorus consume a pound 
 and a half of oxygen ? 
 
 Mrs. B. So it appears from accurate experiments. 1 can show 
 you with what violence it combines with oxygen, by burning some 
 of it in that gas. We must manage the experiment in the same man- 
 ner as we did the combustion of sulphur. You see I am obliged to 
 cut this little bit of phosphorus under water, otherwise there would 
 be danger of its taking fire by the heat of my fingers. I now put 
 it into the receiver, and kindle it by means of a hot wire. 
 
 Emily. What a blaze ! 1 can hardly look at it. I never saw any 
 thing so brilliant. Does it not hurt your eyes, Caroline ? 
 
 Caroline. Yes; but still I cannot help looking at it. A prodi- 
 gious quantity of oxygen must, indeed, be absorbed, when so much 
 light and caloric are disengaged ! 
 
 Mrs. B- In the combustion of a pound of phosphorus, a sufficient 
 quantity of caloric is set free, to melt upwards of a hundred pounds 
 of ice ; this has been computed by direct experiments with the ca- 
 lorimeter. 
 
 Emily. And is the result of this combustion, like that of sulphury 
 an acid ? 
 
 Jlfrs. B. Yes ; phosphoric acid. And had we duly proportioned 
 the phosphorus and the oxygen, they would have been completely 
 converted into phosphoric acid, weighing together, in this new state, 
 exactly the sum of their weights separately. The water would have 
 ascended into the receiver, on account of the vacuum formed, and 
 would have filled it entirely. In this case, as in the combustion of 
 sulphur, the acid vapor formed is absorbed and condensed in the 
 water of the receiver. But when this combustion is performed with- 
 out any water or moisture being present, the acid then appears in 
 the form of concrete whitish flakes, which are, however, extremely 
 ready to melt upon the least admission of moisture. 
 
 Emily. Does phosphorus, in burning in atmospherical air, pro- 
 duce like sulphur, a weaker sort of the same acid ? 
 
 Mrs. B. No ; but it burns in atmosperical air, nearly at the same 
 temperature as in pure oxygen gas ; and it is in both cases so strong- 
 ly disposed to combine with the oxygen, that the combustion is per- 
 fect and the product similar : only in atmospherical air, being less 
 rapidly supplied with oxygen, the process is performed in a slow 
 
 546. Why was it for along time undiscovered ? 
 
 541. At what temperature wilt it melt and take fire ? 
 
 542. What proportion of oxygen will phosphorus consume, com- 
 pared with its own weight ? 
 
 543. How much caloric will the combustion of a pound of phos- 
 phorus set free ? 
 
 544. What is the result of the combustion of phosphorus.!! 
 
 12 
 
134 PHOSPHORUS. 
 
 Caroline. But is there no method of acidifying 1 phosphorus in a 
 slighter manner, so as to form phosphorus acid ? 
 
 Mrs. B. Yes, there is. When simply exposed to the atmosphere, 
 phosphorus undergoes a kind of slow combustion at any tempera- 
 ture above zero. 
 
 Emily, Is not the process in this case rather an oxydation than a 
 combination ? For if the oxygen is too slowly absorbed for a sen- 
 sible quantity of light and heat to be disengaged, it is not a true 
 combustion. 
 
 Mrs. B. The case is not as you suppose ; a faint light is emitted, 
 which is very discernible in the dark ; but the heat evolved is not 
 sufficiently strong to be sensible ; a whitish vapour arises from this 
 combustion, which, uniting with water, condenses into liquid phos- 
 phorus acid. 
 
 Caroline. Is it not very singular that phosphorus should burn at 
 so low a temperature in atmospherical air, whilst it does not burn 
 in pure oxygen without the application of heat? 
 
 Mrs. B. So it at first appears. But this circumstance seems to 
 be owing to the nitrogen gas of the atmosphere. This gas dissolves 
 small particles of phosphorus, which being thus minutely divided and 
 diffused in the atmospherical air, combines with the oxygen, and un- 
 dergoes this slow combustion. But the same effect does not take 
 place in oxygen gas, because it is not capable of dissolving phospho- 
 rus ; it is therefore necessary, in this case, that heat should be ap- 
 plied to effect that division of particles, which, in the former instance, 
 is produced by Ihe nitrogen. 
 
 Emily. I have seen letters written with phosphorus, "which are 
 invisible by day-light, but may be read in the dark by their own 
 light. They look as if they were written with fire ; yet they do 
 not seem to burn. 
 
 Mrs.B. But they do really burn ; for it is by their slow combus- 
 tion that the light is emitted ; and phosphorus acid is the result of 
 this combustion. 
 
 Phosphorus is sometimes used as a test to estimate the purity of 
 atmospherical air. For this purpose, it is burnt in a graduated tube, 
 called an Eudiometer (fig. 26.) and the proportion f oxy- F j 2 6. 
 gen in the air examined is deduced from the quantity of air Eud j " mete r 
 which the phosphorus absorbs ; for the phosphorus will ab- 
 sorb all the oxygen, and the nitrogen alone will remain. 
 
 Emily. And the more oxygen is contained in the atmos- 
 phere, the purer, I suppose, it \% esteemed ? 
 
 Mrs. B. Certainly. Phosphorus, when melted combines 
 with a great variety of substances. With sulphur it forms 
 a compound so extremely combustible that it immediately 
 takes fire on coming in contact with the air. It is with this 
 composition that phosphoric matches are prepared which 
 kindle as soon as they are taken out of their case and are 
 exposed to the air. 
 
 545. Why will phosphorus burn at so low a temperature in at- 
 mospherical air, when it does not burn in pure oxygen without the 
 application of heat ? 
 
 ,>46. For what is phosphorus sometimes used? 
 
 547. What instrument is used for this purpose, and how is the 
 purity of the air ascertained by it ? 
 
 548. How are phosphoric matches made ? 
 
PHOSPHORUS. 135 
 
 Emily. I have a box of these curious matches; but I ha^e ob- 
 served that, in very cold weather, they will not take fire without 
 being previously rubbed. 
 
 Mrs. B. By rubbing- them you r raise ,their temperature ; for you 
 know, friction is one of the means of extricating heat. 
 
 Emily Will phosphorus, like sulphur, combine with hydrogen gas? 
 
 Mrs. B. Yes ; and the compound gas which results from this 
 combination has a smell still more fetid than the sulphuretted hy- 
 drogen ; it resembles that of garlic. 
 
 The phosphorelted hydrogen gas has this remarkable peculiarity, 
 that it takes fire spontaneously in the atmosphere at any tempera- 
 ture. It is thus, probably, that are produced those transient flames 
 or flashes of light, called by the vulgar Will-of-lhe-Wisp, or, more 
 properly, Ignes-fatui^ which are often seen in church. yards, and 
 places where the putrefactions of animal matter exhale phosphorus 
 and hydrogen gas. 
 
 Caroline. Country people, who are so much frightened by those 
 appearances, would be soon reconciled to them if they knew from 
 what a simple cause they proceed. 
 
 Mrs. B. There are other combinations of phosphorus that have 
 also very singular properties, particularly that which results from 
 its union with lime. 
 
 Emily. Is there any name to distinguish the combination of two 
 substances, like phosphorus and lime, neither of which are oxygen, 
 and which cannot therefore produce either an oxyd or an acid ? 
 
 Mrs. B. The names of such combinations are composed from 
 those of their ingredients, merely by a slight change in their termi- 
 nation. Thus, the combinat on of sulphur with lime is called a sul~ 
 phuret, and that of phosphorus, a phosphuret of lime.* This latter 
 
 * Phosphuret of lime is a very curious substance. To make it, 
 take a thin glass tube, 6 or 8 inches long, and less than half an inch 
 in diameter ; if it is closed at one end, so much the better, but a cork 
 will do. N ear the closed end put a piece of phosphorus half an inch 
 long. Then put in by means of a slick or wire, holding the tube 
 horizontally, thirty or forty pieces of newly hurned quick lime, 
 about the size of split peas, lettjng the lowest remain two or three 
 inches from the phosphorus. Then stop the other end of the tube 
 loosely, and place the part containing the quick-lime, in a Hed of 
 charcoal, so contriving it that a candle or red hot iron can be brought 
 under the part where the phosphorus lies. Kindle a fire by means 
 of bellows, and heat the lime red hot, without melting the phoapho- 
 rus, which may be kept cool by a wet rag ; when this is done, bring 
 the hot iron or candle under the phosphorus, so as to make it pass 
 through the quick-lime in the form of v.fcpour. Cork up the phos- 
 phuret of lime for use. C. 
 
 549. Will phosphorus combine with hydrogen ? 
 
 550. What remarkable peculiarity has phosphoretted hydrogen 
 gas ? 
 
 551. How is it supposed that the Jgnes-fatui are produced ? 
 
 552. What is the combination of phosphorus with lime, called '" 
 
136 PHOSPHORUS. 
 
 compound, I was going to say, has the singular property of decom- 
 posing water, merely by being thrown into it. It effects this by ab- 
 sorbing the oxygen of water, in consequence of which, bubbles ot 
 hydrogen gas ascend, holding in solution a small quantity of phos- 
 phorus. 
 
 Emily. These bubbles then are phosphorelled hydrogen gas ? 
 
 Jftrs. B. Yes ; and they produce the singular appearance of a 
 flash of fire issuing from water, as the bubbles kindle and detonate 
 on the surface of the water, at the instant that they come in contact 
 with the atmosphere. 
 
 Caroline. Is not this effect nearly similar to that produced by the 
 combination of phosphorus and sulphur, or, more properly speak- 
 ing, the phosphuret of sulphur ? 
 
 Mrs. B. Yes ; but the phenomenon appears more extraordinary 
 in this case, from the presence of water, and from the gaseous form 
 of the combustible compound. Besides, the experiment surprises 
 by its great simplicity. You only throw a piece of phosphuret of 
 lime into a glass of water, and bubbles of fire will immediately is- 
 sue from it. 
 
 Caroline. Cannot we try the experiment ? 
 
 Jftrs. B. Very easily ; but we must do it in the open air : for 
 the smell of the phosphoretted hydrogen gas is so extremely fetid, 
 that it would be intolerable in the house. But before we leave the 
 room, we may produce by another process, some bubbles of the 
 same gas, which are much less offensive. 
 
 There is in this little glass retort a solution of potash and water ; I 
 add to it a small piece of phosphorus. We must now heat the re- 
 tort over the lamp after having engaged its neck under water you 
 see it begins 10 boil ; in a few minutes bubbles will appear, which 
 take fire and detonate as they issue from the water. 
 
 Caroline. There is one and another. How curious it is ! But 
 I do not understand how this is produced. 
 
 Mrs. B. It is the consequence of a display of affinities too com- 
 plicated. I fear, to be made perfectly intelligible to you at present. 
 
 In a few words, the reciprocal action of the potash, phosphorus, 
 caloric, and water are such, that some of the water is decomposed, 
 and the hydrogen gas thereby formed carries off some minute par- 
 ticles of phosphorus, with which it forms phosphoretted hydrogen 
 gas, a compound which spontaneously takes fire at almost any tem- 
 perature. 
 
 Emily. What is that circular ring of smoke which slowly rises 
 from each bubble after its detonation ? 
 
 Mrs. B. It consists of water and phosphoric acid in vapor, which 
 are produced by the combustion of hydrogen and phosphorus. 
 
 553. What singular peculiarity has the phosphoret of lime ? 
 
 554. What will be the consequence if a piece of phosphoret of 
 lime is thrown into the water ? 
 
 555 Why is it necessary that this experiment be made in the 
 open air ? 
 
 556. What will be the consequence if phosphorus be added to a 
 solution of potash in water, and the whole heated over a fire ? 
 
CARBON. 137 
 
 CONVERSATION IX. 
 
 ON CARBON. 
 
 Caroline. To-day, Mrs B., I believe we are to learn the nature 
 and properties of CARBON. This substance is quite new to me ; 1 
 never heard it mentioned before. 
 
 Mrs, B. Not so new as you imagine ; for carbon is nothing- more 
 than charcoal in a state or purity, that is to say, unmixed with any 
 foreign ingredients. 
 
 Caroline. But charcoal is made by art, Mrs. B., and how can a 
 body consisting of one simple substance be fabricated ? 
 
 Mrs. B. You again confound the idea of making a simple body 
 with that of separating it from a compound. The chemical proces- 
 ses by which a simple body is obtained in a state of purity, consist 
 in unmaking the compound in which it is contained, in order lo sep- 
 arate from it the simple substance in question. The method by 
 which charcoal is usually obtained, is, indeed, commonly called 
 making it ; but upon examination, you will find this process to con- 
 sist simply in separating it from other substances with which it is 
 found combined in nature. 
 
 Carbon forms a considerable part of the solid matter of all organ- 
 ized bodies ; but it is most abundant in the vegetable creation, and 
 it is chiefly obtained from wood. When the oil and water (which 
 are other constituents of vegetable matter) are evaporated, the 
 black, porous, brittle substance that remains, is charcoal. 
 
 Caroline. But if heat be applied to the wood in order to evaporate 
 the oil and water, will not the temperature of charcoal be raised so 
 as to make it burn ? and if it combines with oxygen, can we any 
 longer call it pure ? 
 
 Mrs. B. I was going to add, that, in this operation, the air must 
 be excluded. 
 
 Caroline. How then can the vapor of oil and water fly off? 
 
 Mrs. B. In order to produce charcoal in its purest state, (which 
 is, even then, but a less imperfect sort of carbon,) the operation 
 should be performed in an earthen retort. Heat being applied to 
 the body of the retort, the evaporable part of the wood will escape; 
 through its neck, into which no air can penetrate, as long as the 
 healed vapour continues to fill it. And if it be wished tocollect these, 
 volatile products of the wood, this can easily be done by introducing 
 the neck of the retort into the water bath apparatus, with which you 
 are acquainted. But the preparation of common charcoal, such as 
 is used in kitchens and manufactures, is performed on a much larger 
 scale, and by an easier and less expensive process. 
 
 Emily. I have seen the process of making charcoal. The wood 
 is ranged on the ground in a pile of pyramidieal form, with a fire 
 underneath ; the whole is then covered with clay, a few holes only 
 being left for the circulation of air. 
 
 557. What is carbon ? 
 
 558. In what consists the chemical process by which a 
 body is obtained in a slate of puritv ? 
 
 559. In what is charcoal found in most abundance ? 
 
 12* 
 
138 ARSON. 
 
 Mrs. B. These holes are closed as soon as the wood is fairly light- 
 ed, so that the combustion is checked, or at least continues but in a 
 very imperfect manner ; but the heat produced by it is sufficient to 
 force out and volatilize, through the earthy cover, most part of the 
 oily and watery principles of the wood, although it cannot reduce 
 it to ashes. 
 
 Emily. Is pure carbon as black as charcoal ? 
 Mrs. B. The purest carbon we can prepare is so ; but chemists 
 have never yet been able to separate it entirely from hydrogen. Sir 
 H. Davy says, that the most perfect carbon that is prepared by art 
 contain? about five per cent, of hydrogen ; he is of opinion that if 
 we could obtain it quite free from foreign ingredients, it would be 
 metallic, in common with other simple substances. 
 
 But there is a form in which charcoal appears, that 1 dare say will 
 surprise you. This ring, which I wear on my nger, owes its bril- 
 liancy to a small piece of carbon. 
 
 Caroline. Surely you are jesting, Mrs. B. 
 Emily. I thought your ring was diamond. 
 
 Mrs. B. It is so. 'But diamond is nothing more than carbon in a 
 crystallized state. 
 
 Emily. That is astonishing \ Is it possible to see two things ap- 
 parently more different than diamond and charcoal ? 
 
 Caroline. It is indeed, curious to think that we adorn ourselves 
 with jewels of charcoal ! 
 
 Mrs. B. There are many other substances, consisting chefly of 
 carbon, that are remarkably white. Cotton, for instance, is almost 
 wholly carbon. 
 
 Caroline. That, I own, I could never have imagined ! But pray, 
 
 Mrs. B., since it is known of what substance diamond and cotton 
 
 are composed, why should they not be manufactured, or imitated, 
 
 % <by some chemical process, which would render them much cheap- 
 
 er, and more plentiful than the present mode of obtaining them ? 
 
 Mrs. B. You might as well, -my dear, propose that <we should 
 make flowers and fruit, nay, perhaps, even animals by a chemical 
 process : for it is known of what these bodies consist, since every 
 thing which w are acquainted with in nature is formed from the va- 
 rious simple substances that we have enumerated. But you must 
 not suppose that a knowledge of the component partsof a body will 
 in every case enable us to imitate it. It is much less difficult to de- 
 compose bodies, and discover of 'what materials they are made, than 
 it is to recompose them. The first of these processes is catted analy- 
 sis, the last synthesis. When we are able to ascertain the nature of 
 a substance by both these methods, so that the result of one confirms 
 that of the other, we obtain the most complete knowledge of it that 
 we are capable of acquiring. This is the case with water, with the 
 atmosphere, withtnost of the oxyds, acids, and neutral salts, and with 
 
 560. How is charcoal in its purest state produced ? 
 
 561. What is the common method -of ^producing charcoal? 
 
 562. What did Sir H. Davy suppose carbon would be, if free 
 from foreign ingredients f 
 
 563. What does charcoal become on being crystallized ? 
 
 564. What white substance is thene consisting chiefly of carbon ? 
 
 565. What is to be understood by the terms analysis and synlher 
 sis as used by chemists ? 
 
CARBON. 139 
 
 many other compounds. But the more complicated combinations 
 of nature, even in the mineral kingdom, are in general beyond our 
 reach, and any attempt to imitate organized bodies must ever prove 
 fruitless ; their formation is a secret which rests in the bosom of the 
 Creator. You see, therefore, how vain it would be to attempt to 
 make cotton by chemical means. But, surely, we have no reason 
 to regret our inability in this instance, when nature has so clearly 
 pointed out a method of obtaining it in perfection and abundance. 
 
 Caroline. I did not imagine that the principle of life could be im- 
 itated by the aid of chemistry ; but it did not appear to me absurd 
 to suppose that chemists might attain a perfect imitation of inani- 
 mate nature. 
 
 Mrs. B. They have succeeded in this point in a variety of instan- 
 ces ; but, as you justly observe, the principle of life, or even the 
 minute and intimate organization of the vegetable kingdom, are se- 
 crets that have almost entirely eluded the researches of philoso- 
 phers : nor do I imagine that human art will ever be capable of 
 investigating them with complete success. 
 
 Emily. But diamond, since it consists of one simple, unorgani- 
 zed substance, might be,one would think, perfectly tmitable by art. 
 
 Mrs. B. It is sometimes as much beyond our p'ower to obtain a 
 simple body in a state of perfect purity, as it is to imitate a compli- 
 cated combination ; for the operations by which nature separates 
 bodies are frequently as inimitable as those which she uses for their 
 combination. Thisis the case with carbon ; all the efforts for chem- 
 ists to separate it entirely from other substances Uave been fruitless, 
 and in the purest state in which it -can be obtained by art, it still 
 retains a portion of hydrogen, and probably of some other foreign 
 ingredients. We are ignorant of the means which nature employs 
 to crystallize it. It may probably be the work of ages, to purify, 
 arrange, and unite the particles of carbon in the form of a diamond. 
 Here is some charcoal, in the purest state we can procure it ; you 
 see that it is a very black, brittle, light, porous substance, entirely 
 destitute of either taste or smell. Heat, without air, produces no 
 alteration in it, as it is not volatile ; but on the contrary, it invari- 
 ably remains at the bottom of the vessel, after all the other parts of 
 the vegetables are evaporated. 
 
 Emily. Yet carbon is, no doubt, combustible, since you say that 
 charcoal would absorb oxygen, if air were admitted during its pre- 
 paration. 
 
 Caroline. Unquestionably. Besides, you know, Emily, how much 
 it is used in cooking. But pray what is the reason tbat charcoal 
 burns without smoke, whilst a wood fire smokes so much ? 
 
 Mrs. B. Because, in the conversion of wood into charcoal, the 
 volatile particles of the former have been evaporated. 
 
 Caroline. Yet 1 have frequently seen charcoal burn with flame ; 
 therefore, it must, in that case contain some hydrogen. 
 
 Mrs. B. You should recollect that charcoal, especially that which 
 is used for common purposes, is not perfectly pure. It generally 
 
 566. In what cases is obtained the most perfect knowledge of the 
 nature of compound bodies ? 
 
 567. Have means ever been discovered to crystallize carbon ? 
 
 568. What is the reason that charcoal burns without smoke ? 
 
140 CARBON. 
 
 retains some remains of theTarious other component parts of veg- 
 etables, and hydrogen particularly, which accounts for the flame in 
 question. 
 
 Caroline. But what becomes of the carbon itself during- its com- 
 bustion ? 
 
 Mrs. B. It gradually combines with the oxygen of the atmos- 
 phere, in the same way as sulphur and phosphorus, and, like those 
 substances, it is converted into a peculiar acid, which flies off in a 
 gaseous form. There is this difference, however, that the acid is 
 not, in this instance, as in the two cases just mentioned, a mere 
 condensible vapour, but a permanent elastic fluid, which always 
 remains in the state of gas, under any pressure and at any tempera- 
 ture. The nature of this acid was first ascertained by Dr. Black, 
 of Edinburgh ; and, before the introduction of the new nomencla- 
 ture, it was called jlxed air. It is now distinguished by the more 
 appropriate name of carbonic acid gas. 
 
 Emily. Carbon, then, can be volatilized by burning, though by 
 heat alone, no such effect is produced ? 
 
 Mrs. B. Yes ; but then it is no longer simple carbon, but an acid 
 of which carbon forms the basis. In this state, carbon retains no 
 more appearance of solidity or corporeal form than the basis of any 
 other gas. And you may, I think, from this instance, derive a more 
 clear idea of the basis of the oxygen, hydrogen, and nitrogen gases, 
 the existence of which, as real bodies, you seemed to doubt, be- 
 cause they were not to be obtained simply in a solid form. 
 
 Emily. That is true : we may conceive the basis of the oxygen 
 and of the other gases, to be solid, heavy substances, like carbon; 
 but so much expanded by caloric as to become invisible. 
 
 Caroline. But does not the carbonic acid gas partake of the 
 blackness of charcoal ? 
 
 Mrs. B. Not in the least. Blackness, you know, does not ap- 
 pear to be essential to carbon, and it is pure carbon, and not char- 
 coal, that we must consider as the basis of carbonic acid. We 
 shall make some carbonic acid, and, in order to hasten the process, 
 we shall burn the carbonic in oxygen gas. 
 
 Emily. But do you mean, then, to burn diamond ? 
 
 Mrs. B. Charcoal will answer the purpose still better, being 
 softer and more easy to inflame ; besides the experiments on dia- 
 mond are rather expensive. 
 
 Caroline. But is it possible to burn diamond? 
 
 Mrs. B. Yes, it is ; and in order to effect this combustion, noth- 
 ing more is required than to apply a sufficient degree of heat by 
 means of the blow-pipe, and of a stream of oxygen gas. Indeed, it 
 is by burning diamond that its chemical nature has been ascertained, 
 
 569. From what does the flame in the burning of charcoal pro- 
 ceed ? 
 
 570. In the combustion of charcoal what becomes of the carbon ? 
 
 571. What is the gas called formed by the combination of carbon 
 and oxygen ? 
 
 572. Why does not carbonic acid gas partake of the blackness 
 of charcoal, if prepared from that material ? 
 
 573. How has the chemical nature of diamonds been ascertained ? 
 
CARBON. 141 
 
 It has long been known as a combustible substance, but it is with- 
 in these few years only that the product of its combustion has been 
 proved to be pure carbonic acid. This remarkable discovery is 
 due to Mr. Tennant. 
 
 Now let us try to make some carbonic acid. Will you,JEmily, 
 decant some oxygen gas from this large jar into the receiver in 
 which we are to burn the carbon ; and 1 shall introduce this small 
 piece of charcoal, with a little lighted tinder, which will be neces- 
 sary to give the first impulse to combustion. 
 
 Emily. I cannot conceive how so small a piece of tinder, and that 
 but just lighted, can arise the temperature of the carbon sufficiently 
 to set fire to it ; for it can produce scarcely any sensible heat, and 
 it hardly touches the carbon. 
 
 Mrs. B. The tinder thus kindled has only heat enough to begin 
 its own combustion, which, however, soon becomes so rapid in the 
 oxygen gas, as to raise the temperature of the charcoal sufficiently 
 for this to burn likewise, as you see is now the case. 
 
 Emily. I am surprised that the combustion of carbon is not more 
 brilliant ; it does not give out near so much light or caloric as 
 phosphorus, or sulpher. Yet since it combines with so much oxy- 
 gen, why is not a proportional quantity of light and heat disengaged 
 from the decomposition of the oxygen gas, and the union of its 
 electricity with that o f the charcoal ? 
 
 .Mrs. B. Is it not surprising that less light and heat should be li- 
 berated in this than in almost any other combustion, since the ox- 
 ygen, instead of entering iuto a solid or liquid combination, as it 
 does in the phosphoric and sulphuric acids, is employed in forming 
 another elastic fluid ; it therefore parts with less of its caloric. 
 
 Emily. True ; and, on second consideration, it appears, on the 
 contrary, surprising that the oxygen should, in its combination 
 with carbon, retain a sufficient portion of caloric to maintain both 
 substances in a gaseous state. 
 
 Caroline. We may then judge of the degree of solidity in which 
 oxygen is combined in a burnt body, by the quantity of caloric li- 
 berated during its combustion ? 
 
 JWrs. B. Yes; provided that you take into the account the quan- 
 tity of oxygen absorbed by the combustibe body, and observe the 
 proportions which the caloric bears to it. 
 
 Caroline. But why should the water, after the combustion of car- 
 bon, rise in the receiver, since the gas within it retains an aeriform 
 state ? 
 
 J\Irs. B. Because the carbonic acid gas is gradually absorbed by 
 the water ; and this effect would be promoted by shaking the re- 
 ceiver. 
 
 Emily. The charcoal is now extinguished, though it is not nearly 
 consumed ; it has such an extraordinary avidity for oxygen, I sup- 
 pose, that the receiver did not contain enough to satisfy the whole. 
 
 Mrs B. That is certainly the case ; for if the combustion were 
 
 574. What is the production of their combustion ? 
 
 575. Why is so little light and heat disengaged in the combustion 
 of carbon ? 
 
 576. Does carbon unite with more than one proportion of oxy- 
 gen ? 
 
142 CARBON. 
 
 performed in the exact proportions of "2H parts of carbon to 72 of 
 oxygen, both these ingredients would disappear, and 100 parts of 
 carbonic acid would be produced. 
 
 Caroline. Carbonic acid must be a very strong- acid, since it con- 
 tains so great a proportion of oxygen ? 
 
 Mrs. B. That is a very natural inference ; yet it is erroneous. 
 For the carbonic is the weakest of all the acids. The strength of 
 an acid seems to depend upon the nature of its basis, and its mode 
 of combination, as well as upon the proportion of the acidifying 
 principle. The same quantity of oxygen that will convert some bod- 
 ies into strong acids, will only be sufficient simply to oxydate others. 
 
 Caroline. Since this acid is so weak, I think chemists should 
 have called it the carbonous, instead of the carbonic acid. 
 
 Emily. But, I suppose, the carbonous acid is still weaker, and is 
 formed by burning carbon in atmospherical air. 
 
 Mrs. B. It has been lately discovered, that carbon may be con- 
 verted into a gas, by uniting with a small proportion of oxygen ; 
 but as this gas does not possess any acid properties, it is no more 
 than an oxyd ; it is called gaseous oxyd of carbon. 
 
 Caroline. Pray is not carbonic acid a very wholesome gas to 
 breathe, as it contains so much oxygen ? 
 
 Mrs. B. On the contrary, it is extremely pernicious. Oxygen, 
 when in a state of combination with other substances, loses, in al- 
 most every instance, its respirable properties, and the salubrious 
 effects which it has on the animal economy when in its unconfined 
 state. Carbonic acid is not only unfit for respiration, but extreme- 
 ly deleterious if taken into the lungs, 
 
 Emily. You know, Caroline, how very unwholesome the fumes 
 of burning charcoal are reckoned. 
 
 Caroline. Yes ; but to confess the truth, I did not consider that 
 a charcoal fire produced carbonic acid gas. Can this gas be con- 
 densed into a liquid ? 
 
 Mrs. B. ISo : for, as I told you before, it is a permanent elastic 
 fluid. But water can absorb a certain quantity of this gas, and can 
 even be impregnated with it, in a very strong degree, by the assis- 
 tance of agitation and pressure, as I am going to show you. I shall 
 decant some carbonic acid gas into this bottle, which I fill first with 
 water, in order to exclude the atmospherical air; the gas is then 
 introduced through the water, which you see it displaces, for it will 
 not mix with it in any quantity, unless strongly agitated, or allowed 
 to stand over it for some time. The bottle is now about half full of 
 carbonic acid gas, and the other half is still occupied by the water. 
 By corking the bottle, and then violently shaking it, in this way, I 
 can mix the gas and water together. Now will you taste it ? 
 
 Emily. It has a distinct acid taste. 
 
 Caroline. Yes, it is sensibly sour, and appears full of little bubbles. 
 
 Mrs. B. It possesses likewise all the other properties of acid, but 
 
 577. On what does the strength of an acid depend ? 
 
 578. Why is not carbonic acid good for respiration, since it con- 
 tains a large quantity of oxygen ? 
 
 579. Why are the fumes of burning charcoal reckoned unwhole- 
 some ? 
 
 580. How can water be impregnated with carbonic gas ? 
 
 581. What is Seltzer found to be, on analysis ? 
 
CARBON. 143 
 
 of course, in a less degree than the pure carbonic acid gas, as it is 
 so much diluted by water. This is a kind of artificial Seltzer water. 
 By analysing 1 that which is produced by nature, it was found to con- 
 tain scarcely any thing more than common water impregnated with 
 a certain proportion of carbonic acid gas. We are therefore able to 
 imitate it by mixing those proportions of water and carbonic acid. 
 Here, my dear, is an instance in which, by a chemical process, we 
 can exactly copy the operations of nature ; for the artificial Seltzer 
 waters can be made in every respect similar to those of nature ; in 
 one point, indeed, the former have an advantage, since they may 
 be prepared stronger or weaker, as occasion requires. 
 
 Caroline. I thought I had lasted such water before. But what 
 renders it so brisk and sparkling ? 
 
 Mrs. B- This sparkling or effervescence, as it is called, is always 
 occasioned by the action of an elastic fluid escaping from a liquid ; 
 in the artificial Seltzer water it is produced by the carbonic acid, 
 which being lighter than the water in which it was strongly conden- 
 sed, flies off with great rapidity the instant the bottle is uncorked ; 
 this makes it necessary to drink it immediately. The bubbling 
 that took place in this bottle was but trifling, as the water was but 
 very slightly impregnated with carbonic acid. It requires a partic- 
 ular apparatus to prepare the gaseous artificial mineral waters. 
 
 Emily. If, then, a bottle of Seltzer water remains for any length 
 of time uncorked, I suppose it returns to the state of common water ? 
 
 Mrs. B. The whole of the carbonic acid gas, or very nearly so, 
 will soon disappear: but there is likewise in Seltzer water a very 
 small quantity of soda, and a few other saline or earthy ingredi- 
 ents, which will remain in the water, though it should be kept un- 
 corked for any length of time. 
 
 Caroline. 1 have often heard of people drinking soda-water. 
 Pray what sort of water is that ? 
 
 Mrs. B. It is a kind of artificial Seltzer water, holding in solu- 
 tion, besides the gaseous acid, a particular saline substance, called 
 soda, which imparts to the water certain medicinal qualities. 
 
 Caroline. But how can these waters be so wholesome, since car- 
 bonic acid is so pernicious : 
 
 Mrs. B. A gas, we may conceive, though very prejudicial to 
 breathe, may be beneficial to the stomach. But it would be of no 
 use to attempt explaining this more fully at present. 
 
 Caroline. Are waters never impregnated with other gases ? 
 
 Mrs. B. Yes ; there are several kinds of gaseous waters. I for- 
 got to tell you that waters have, for some years past, been prepared, 
 impregnated both with oxygen and hydrogen gases. These are not 
 an imitation of nature, but are altogether obtained by artificial 
 means. They have been lately used medicinally, particularly on the 
 continent, where, I understand, they have acquired some reputation. 
 
 Emily. If I recollect right, Mrs. B., you told us that carbon was 
 
 582. How is the brisk and sparkling appearance in Seltzer water 
 occasioned ? 
 
 583. What is soda -water ? 
 
 584. How can these waters be wholesome, since carbonic acid 
 is so pernicious ? 
 
 585. What other gaseous waters have been prepared, and for 
 what purpose? 
 
144 
 
 CARBON. 
 
 capable of decomposing water ; the affinity between oxygen and car- 
 bon must, therefore, be greater than between oxygen and hydrogen ? 
 
 Mrs. B. Yes ; but this is not the case, unless their temperature 
 be raised to a certain degree. It is only when carbon is red-hot, 
 that it is capable of separating the oxygen from the hydrogen. 
 Thus, if a small quantity of water be thrown on a red-hot fire, it 
 will increase rather than extinguish the combustion ; for the coals 
 of wood, (both of which contain a quantity of carbon,) decompose 
 the water, and thus supply the fire both with oxygen and hydrogen 
 gases. If, on the contrary, a large mass of water be thrown over 
 the fire, the diminution of heat thus produced is such, that the com- 
 bustible matter loses the power of decomposing the water, and the 
 fire is extinguished. 
 
 Emily. I have heard that fire-engines sometimes do more harm 
 than good, and that they actually increase the fire when they cannot 
 throw water enough to extinguish it. It must be owing, no doubt, 
 to the decomposition of the water by the carbon during the confla- 
 gration. 
 
 Mrs. B. Certainly. The apparatus which you see here (fig. 27,) 
 
 Decomposition of water by Carbon. 
 
 .A. Retort containing water. B. Lamp to beat the water. C. C. Porcelain tube containing Car- 
 bon. D. Furnace through which the tube passes. E. Receiver for the gas produced. F. Water bath. 
 
 may be used to exemplify what we have just said. It consists in a 
 kind of open furnace, through which a porcelain tube, containing 
 charcoal, passes. To one end of the tube is adapted a glass retort 
 with water in it ; and the other end communicates with a receiver 
 placed on the water bath. A lamp being applied to the retort, and 
 the water made to boil, the vapour is gradually conveyed through 
 the red-hot charcoal, by which it is decomposed ; and the hydrogen 
 gas, which results from this decomposition, is collected in the re- 
 ceiver. But the hydrogen thus obtained is far from being pure ; it 
 retains in solution a minute portion of carbon and contains also a 
 quantity of carbonic acid. This renders it heavier than pure hy- 
 drogen gas, and gives it some peculiar properties : it is distinguish- 
 ed by the name of carbonated hydrogen gas. 
 
 587. Why will a small quantity of water thrown upon a fire in- 
 crease rather than diminish it ? 
 
 588. How would you describe the experiment made by the use 
 of figure 27? 
 
 89. What is the gas called produced in the experiment ? 
 
CARBON. 145 
 
 Caroline. And whence does it obtain the carbonic acid that is 
 mixed with it ? 
 
 Emily. I believe I can answer that question, Caroline. From 
 the union of the oxygen (proceeding 1 from the decomposed water) 
 with the carbon, which, you know, makes carbonic acid. 
 
 Caroline. True : I should have recollected that. The product 
 of the decomposition of water by red-hot charcoal, therefore, is car- 
 bonated hydrogen gas, and carbonic acid gas. 
 
 Mrs. B. You are perfectly right, now. 
 
 Carbon is frequently found combined with hydrogen in a state of 
 solidity, especially in coals, which owe their combustible nature to 
 these two principles. 
 
 Emily. Is it the hydrogen, then, that produces the flame of coals? 
 
 Mrs. B. It is so ; and when all the hydrogen is consumed, the 
 carbon continues to burn without flame. But again, as I mention- 
 ed when speaking of the gas-lights, the hydrogen gas produced by 
 the burning of coals is not pure ; for, during the combustion, par- 
 ticles of carbon are successively volatilized with the hydrogen, with 
 which they form what is called a hydro-carbonat, which is the prin- 
 cipal product of the combustion. 
 
 Carbon is a very bad conductor of heat ; for this reason, it is 
 employed (in conjunction with other ingredients) for coating furna- 
 ces and other chemical apparatus. 
 
 Emily. Pray what is the use of coating furnaces ? 
 
 Mrs. B. In most cases in whjch a furnace is used, it is necessary 
 to produce and preserve a great degree of heat, for which purpose 
 every possible means are used to prevent the heat from escaping by 
 communicating with other bodies, and this object. is attained by 
 coating over the inside of the furnace with a kind of plaster, com- 
 posed of materials that are bad conductors of heat. 
 
 Carbon, combined with a small quantity of iron, forms a com- 
 pound called plumbago, or black lead, of which pencils are made. 
 This substance, agreeably to the nomenclature, is a carburet of iron. 
 
 Emily. Why, then, is it called black-lead ? 
 
 Mrs. B. It is an ancient name given to it by ignqrant people, 
 from its shining metallic appearance ; but it is certainly a most im- 
 proper name for it, as there.is not a^particle of lead in the composi- 
 tion. There is only one mine of this mineral, which is in Cumber- 
 land.* It is supposed to approach a.s,nearly to pure carbon as the 
 best prepared charcoal does, as it contains only five parts of iron, 
 unadulterated by any other foreign ingredients. There is another 
 carburet of iron, in which the iron, though united only to an ex - 
 
 * She means in England. Black lead is found in a.great variety 
 of places in this country. C. 
 
 590. By what is the flame of burning coals occasioned ? 
 
 591. Why is carbon used for coating furnaces and other chemi- 
 cal apparatus ? 
 
 592. Of what is black lead made ? 
 
 593. Why is it called black lead ? 
 
 594. What is steel? 
 
 13 
 
1 46 CARBON. 
 
 tremely small proportion of carbon, acquires very remarkable .pro- 
 perties : this is steel. 
 
 Caroline. Really ; and yet steel is much harder than iron ? 
 
 J\]rs. B. But carbon is not ductile like iron, and therefore may 
 render the steel more brittle, and prevent its bending so easily. 
 Whether it is that the carbon, by introducing itself into the pores 
 of the iron, and, by filling- them makes the metal both harder and 
 heavier; or whether this change depends upon some chemical 
 cause, 1 cannot pretend to deci'de. But there is a subsequent ope- 
 ration, by which the hardness of steel is very much increased, 
 which simply consists in heating the steel till it is red-hot, and then 
 plunging it into cold water. 
 
 Carbon, besides the combination just mentioned, enters into the 
 composition of a vast number of natural productions : such, for in- 
 stance, as all the various kinds of oils, which result from the com- 
 bination of carbon, hydrogen, and caloric, in various proportions. 
 
 Emily. 1 thought that carbon, hydrogen, and caloric, formed car- 
 bonated hydrogen gas. 
 
 Mrs. B. That is the case when a small portion of carbonic acid 
 gas is held in solution by hydrogen gas. Different proportions of 
 the same principles, together with the circumstances of their union, 
 produce very different combinations ; of this you will see innume- 
 rable examples. Besides, we are not now talking of gases, but of 
 carbon and hydrogen, combined only with a quantity of caloric, 
 sufficient to bring them to the consistency of oil or fat. 
 
 Caroline. But oil and fat are not of the same consistence? 
 
 Mrs. B. Fat is only congealed oil ; or oil, melted fat. The one 
 requires a little more heat to maintain it in a fluid slate than the 
 other. Have you never observed the fat of meat turned to oil by 
 the caloric it has imbibed from the fire ? 
 
 Emily. Yet oils in general, as salad-oil, and lamp-oil, do not turn 
 to fat when cold ? 
 
 Mrs. B. Not at the common temperature of the atmosphere, be- 
 cause they retain too much caloric to congeal at that temperature ; 
 but if exposed to a sufficient degree of cold, their latent heat is ex- 
 tricated, and they become solid, fat substances. Have you never 
 seen salad-oil frozen in winter ? 
 
 Emily. Yes ; but it appears to me in that state very different 
 from animal fat. 
 
 Mrs. B. The essential constituent parts of either vegetable or an- 
 imal oils are the same, carbon and hydrogen ; their variety arises 
 from the different proportions of these substances, and from other 
 accessory ingredients that may be mixed with them. The oil of a 
 whale, and the oil of roses, are, in their essential, constituent parts, 
 the same ; but the one is impregnated with the offensive particles of 
 animal matter, the other with the delicate perfume of a flower. 
 
 The difference of fixed oils, and volatile or essential oils, consists 
 also in the various proportions of carbon and hydrogen. Fixed oils 
 
 695. To what is the hardness of steel owing ? 
 
 596. What is the difference between fat and oil ? 
 
 597. What are the essential constituent parts of oil ? 
 
 598. What is the difference between offensive animal and fragrant 
 vegetable oil ? 
 
CARBON. 1 
 
 are those which will not evaporate without being decomposed ; this 
 is the case with all common oils, which contain a greater proportion 
 of carbon than the essential oils. The essential oils (which com- 
 prehend the whole class of essences and perfumes) are lighter ; they 
 contain more equal proportions of carbon and hydrogen, and are 
 volatilized or evaporated without being decomposed. 
 
 Emily. When you say that one kind of oil will evaporate, and the 
 other be decomposed, you mean, I suppose, by the application of 
 heat ? 
 
 Mrs. B. Not necessarily ; for there are oils :hat will evaporate 
 slowly at the common temperature of the atmosphere ; but for a 
 more rapid volatil. -.ation, or for their decomposition) the assistance 
 of heat is required.* 
 
 Caroline. I shall now remember, 1 think, that fat and oil are re- 
 ally the same substances, both consisting of carbon and hydrogen ; 
 that in fixed oils the carbon preponderates, and heat produces a de- 
 composition ; while, in essential oils, Hie proportion of hydrogen is 
 greater, and heat produces a volatilization only. 
 
 Emi l y. 1 suppose the reason why o.l burns so well in lamps, is 
 because its two constituents are so combustible ? 
 
 Mrs. B. Certainly ; the combustion of oil is just the same as that 
 of a candle ; if tallow, it is only oil in a concrete stale ; if wax, or 
 spermaceti, its chief chemical ingredients are still hydrogen and 
 carbon. 
 
 Emily. I wonder, then, there should be so great a difference be- 
 tween tallow and wax ? 
 
 Mrs.B. I must again repeat, that the same substances, in differ- 
 ent proportions, produce results that have sometimes scarcely any 
 resemblance to each other. But this is rather a general remark 
 that I wish to impress upon your minds, than one which is applica- 
 ble to the present case ; for fallow and wax are far from being very 
 dissimilar; the chief difference consists in the wax beng a purer 
 compound of carbon and hydrogen than the tallow, which retains 
 more of the gross particles of animal matter. The combustion of 3 
 candle, and that of a lamp, both produce water and carbonic acid 
 gas. Can you tell me how these are formed : 
 
 Emily. Let me reflect . . . Both the candle and lamp burn by 
 means of fixed oil this is decomposed as the combustion goes on ; 
 and the constituent parts of the oil being thus separated, the carbon 
 unites with a portion of oxygen fioin the atmosphere to form carbo- 
 nic acid gas, whilst the hydrogen combines with another portion of 
 
 *The volatile or essential oils evaporate when exposed to the air. 
 Hence the odour which oil of lavender, peppermint. &c. give out. 
 The animal oils, and what are called expressed oils, as that ofcastor, 
 &c. do not evaporate. Hence a good test of the purity of essential 
 oil, is, to let a drop fall on paper. If a grease-spot remains after a 
 few minutes, it is adulterated with some fixed oil. C. 
 
 599. What are fixed oils ? 
 
 600. What are essential oils ? 
 
 601. Why will oil burn so well in lamps ? 
 
 602. In what does the difference between tallow and wax consist 
 
 603. How may the adulteration of volatile oil be detected? 
 
 604. What are the products of the combustion of oils ? 
 
148 CAEBON. 
 
 oxygen and forms with it water The products, therefore, of the 
 combustion of oils, are water and carbonic acid gas. 
 
 Caroline. But we see neither water nor carbonic acid produced 
 by the combustion of a candle. 
 
 Mrs. B. The carbonic acid gas, you know, is invisible, and the 
 water being in a state of vapour, is so likewise. Emily is perfectly 
 correct in her explanation, and I am very much pleased with it. 
 
 All the vegetable acids consist of various proponions of carbon 
 and hydrogen, acidified by oxygen. Gums, sugar, and starch, are 
 likewise composed of these ingredients ; but, as the oxygen, which 
 they contain is not sufficient to convert them into acids, they are 
 classed with the oxyds, and called vegetable oxyd. 
 
 Caroline. 1 am extremely delighted with all these new ideas ; 
 but, at the same time, I cannot help being apprehensive that I may 
 forget many of them. 
 
 Mrs. B. 1 would advise you to take notes, or, what would answer 
 better still, to write down, after every lesson, as much of it as you 
 can recollect. And, in order to give you a little assistance, I shall 
 lend you the heads or index, which I occasionally consult for the 
 sake of preserving some method and arrangement in these conver- 
 sations. Unless you follow some such plan, you cannot expect to 
 retain nearly all that you learn, how great soever be the impress- 
 ion it may make on you at first. 
 
 Emily. 1 will certainly follow your advice. Hitherto I have 
 found that I recollected pretty well, what you have taught us ; bat 
 the history of carbon is a more extensive subject than any of the 
 simple bodies we have yet examined. 
 
 JMrs. B. I have little more to say on carbon at present ; but 
 hereafter you will see that it performs a considerable part in chem- 
 ical operations. 
 
 Caroline. That is, I suppose, owing to its entering into the com- 
 position of so great a variety of substances ? 
 
 Mrs. B. Certainly ; it is the basis, as you have seen, of all vege- 
 table matter; and you will find that it is very essential to the pro- 
 cess of animalization. But in the mineral kingdom, also, particu- 
 larly in its form of carbonic acid, we shall discover it combined 
 with a great variety of substances. 
 
 In chemical operations, carbon is particularly useful, from its 
 very great attraction for oxygen, as it will absorb this substance 
 from many oxygenated or burnt bodies, and thus de- oxygenate, or 
 unburn them,"\tnd restore them ta their original combustible state. 
 
 Caroline. I do not understand how a body can be unburnt, and re- 
 stored to its original state. This piece of tinder, for instance, that 
 has been burnt, if by any means oxygen were extracted from it, 
 would not be restored to its former state of linen ; for its texture is 
 destroyed by burning, and that must be the case with all organized 
 or manufactured substances, as you observed in a former conversa- 
 tion. 
 
 Mrs. B. A compound body is decomposed by combustion in a way 
 which generally precludes the possibility of restoring it to its former 
 state ; the oxygen, for instance, does not become fixed in the tinder, 
 
 605. Of what do the vegetable acids consist ? 
 
 606. How does carbon restore oxydated substances' to their com- 
 bustible state? 
 
METALS. 149 
 
 but it combines with its volatile parts, and flies off in the shape of 
 gas or watery vapour. You see, therefore, how vain it would be to 
 attempt the recomposition of such bodies. But, with regard to sim- 
 ple bodies, or at least bodies whose component parts are not dis- 
 turbed by the process of oxygeuation or deoxygenation, it is often 
 possible to restore them, after combustion, to thoir original state. 
 The metals, for instance, undergo no other alteration by combustion 
 than a combination with oxygen ; therefore, when the oxygen is 
 taken from them, they return to their pure metallic state. Bat I 
 shall say nothing further of this at present, as the metals will furnish 
 ample subject for another morning ; and they are the class of sim- 
 ple bodies that come next under consideration. 
 
 CONVERSATION X* 
 
 ON METALS, 
 
 Mrs. B. The METAI.S, which we are now to examine, are bodies 
 of a very different nature from those which we have hitherto con- 
 sidered. They do not, like the bases of gases, elude the observa- 
 tion of our senses ; for, they are the most brilliant, the most pon 
 derous, and the most palpable substances in nature. 
 
 Caroline. I doubt, however, whether the metals will appear to us 
 so interesting, and give us so much entertainment, as those myste- 
 rious elements which conceal themselves from our view. Besides, 
 they cannot afford so much novelty : they are bodies with which 
 we are already so well acquainted. 
 
 Mrs. B. You are not aware, my dear, of the interesting discove- 
 ries which were a few years ago made by Sir H. Davy, respecting 
 this class of bodies. By the aid of the Voltaic battery, he has obtained 
 from a variety of substances, metals before unknown, the properties 
 of which are equally new and curious. We shall begin, however, by 
 noticing those metals with which you profess to be so well acquain- 
 ted. But the acquaintance, you will soon perceive, is hut very super- 
 ficial, and 1 trust you will find both novelty and entertainment in 
 considering the metals in a chemical point of view. To treat of this 
 subject fully, would require a whole course of lectures ; for metals 
 form of themselves a most important branch of practical chemistry. 
 We must, therefore, confine ourselves to a general view of them. 
 These bodies are seldom found naturally in their metallic form : they 
 are generally more or less oxygenated, or combined with sulphur, 
 earths, or acids, and are often blended with each other. They are 
 found buried in the bowels of the earth in most parts of the world, but 
 chiefly in mountainous districts, where the surface of the globe has 
 been disturbed by earthquakes, volcanoes, and other convulsions of 
 nature. They are spread in strata or beds, called veins, and these 
 veins are composed of a certain quality of metal, combined with 
 
 607. What alteration do metals undergo from combustion ? 
 
 608. What is the subject of this Conversation ? 
 
 609. Are metals generally found in their pure metallic state ? 
 
 610. In what state are they usually found to exi^t? 
 
 611. In what places are they chiefly discovered ? 
 
 13* 
 
 
150 METALS. 
 
 various earthy substances, with which they form minerals of differ- 
 ent nature and appearance, which are called ores. 
 
 Caroline. 1 now feel quite at home, for my father has a lead mine 
 in Yorkshire, and I have heard a great deal about veins of ore, and 
 of the roasting and smelting of lead ; but, I confess, that I do not 
 understand in what these operations consist. 
 
 Mrs. B. Roasting is the process by which the volatile parts of the 
 ore are evaporated ; smelting, that by which the pure metal is af- 
 terwards separated from the earthy remains of the ore. This is 
 done by throwing the whole into a furnace, and mixing it with cer- 
 tain substances that will combine with the earthy parts and other 
 foreign ingredients of the ore ; the metal being the heaviest, falls 
 to the bottom, and runs out by proper openings in its pure metallic 
 state. 
 
 Emily, You told us in a preceding lesson, that metals had a great 
 affinity for oxygen. Do they not, therefore, combine with oxygen, 
 when strongly heated in the furnace,and run out in the state of oxyds? 
 
 Mrs. B. No ; for the scoriae, or oxyd, which soon forms on the 
 surface of the fused metal, when it is oxydable, prevents the air 
 from haying any further in6uence on the mass ; so that neither 
 combustion nor oxygenation can take place. 
 
 Caroline. Are all the rnetals equally combustible ? 
 
 Mrs. B. No ; their attraction for oxygen varies extremely. 
 There are some that will combine with it only at a very high tem- 
 perature, or by the assistance of acids ; whilst there are others that 
 oxydate spontaneously, and with great rapidity, even at the low- 
 est temperature ; such is, in particular, manganese, which scarcely 
 ever exists in the metallic state, as it immediately absorbs oxygen 
 ori being exposed to the air, and crumbles to an oxyd in the course 
 of a few hours. 
 
 Emily. Is not that the oxyd from which you extracted the oxy- 
 gen gas ? 
 
 Mrs. B. It is : so that, you see, this metal attracts oxygen at a 
 low temperature, and parts with it when strongly heated. 
 
 Emily. Is there any other metal that oxydates at the tempera- 
 ture of the atmosphere ? 
 
 Mrs. B. They all do, more or less, excepting gold, silver, and 
 platina. 
 
 Copper, lead, and iron, oxydate slowly in the air, and cover them- 
 selves with a sort of rust, a process which depends on the gradual 
 conversion of the surface into an oxyd. This rusty surface pre- 
 serves the interior metal from oxydation, as it prevents the air 
 from coming in contact with it. Strickly speaking, however, the 
 word rust applies only to the oxyd, which forms on the surface of 
 iron, when exposed to air and moisture, which oxyd appears to be 
 united with a small portion of carbonic acid. 
 
 612. How are they refined ? 
 
 613. What prevents the combustion and oxygenation of metal** 
 when in a state of fusion ? 
 
 614. Are all rnetals equally combustible ? 
 
 615. To what is their difference in this respect owing ? 
 
 616. Do metals oxydate on being exposed to the air? 
 
 617. By what is the rust occasioned that lakes place ofl coppr 
 and iron ? 
 
METALS. 151 
 
 4. 
 
 Emily. When metals oxydate from the atmosphere without an 
 elevation of temperature, some light and heat, I suppose, must be 
 disengaged, though not in sufficient quantities to be sensible. 
 
 Mrs. B. Undoubtedly ; and, indeed, it is not surprising that, in 
 this case, the light and heat should not be sensible, when you con- 
 sider how extremely slow, and, indeed, how imperfectly, nfost met- 
 als oxydate by mere exposure to the atmosphere. For the quantity 
 of oxygen with which metals are capable of combining, generally 
 depends upon their temperature ; and the absorption stops at va- 
 rious points of oxydation, according to the degree to which their 
 temperature is raised. 
 
 Emily. That seems very natural ; for the greater the quantity of 
 caloric introduced into a metal, the more will its positive electricity 
 be exalted, and consequently the stronger will be its affinity for ox- 
 ygen. 
 
 Mrs B. Certainly. When the metal oxygenates with sufficient 
 rapidity for light and heat to become sensible, combustion actually 
 takes place. But this happens only at very high temperatures, 
 and the product is nevertheless an oxyd ; for though, as I have just 
 said, metals will combine with different proportions of oxygen, yet 
 with the exception of only five of them, they are not susceptible of 
 acidification. 
 
 Metals change color during the different degrees of oxydation 
 which they undergo. Lead, when heated in contact with the at- 
 mosphere, first becomes grey ; if its temperature be then raised, 
 it turns yellow, and a still stronger heat changes it to red. And it is 
 even capable of a stronger degree of oxydation, in which the oxyd 
 is puce colored. Iron becomes successively a green, brown and 
 white oxyd. Copper changes from brown to blue, and lastly green. 
 
 Emily. Pray, is the white lead with which houses are painted, 
 prepared by oxydating lead ? 
 
 Mrs. B. Not merely by oxydating, but by being also united with 
 carbonic acid. It is a carbonat of lead. The mere oxyd of lead is 
 called red lead. Litharge is another oxyd of lead, containing less 
 oxygen. Almost all the metallic oxyds are used as paints. The 
 various sorts of ochres consist chiefly of iron more or less oxydated- 
 And it is a remarkable circumstance, that if you burn metals rap- 
 idly, the light or flame they emit during combustion partakes of the 
 colours which the oxfrf successively assumes. 
 
 Caroline. How is that accounted for, Mrs. B., since light does 
 not proceed from the burning body, but from the decomposition of 
 the oxygen gas ? 
 
 Mrs. B. The correspondence of the color of the light, with that 
 of the oxyd which emits it, is, in all probability, owing to some par- 
 ticles of the metal which are volatilized and carried off by the caloric 
 
 618. Are light and heat disengaged when metals oxydate from 
 the atmosphere, without an elevation of temperature? 
 
 619. Why are they not perceived ? 
 
 620. What changes of colour do lead, iron, and Copper undergo 
 during their different degrees of oxydation ? 
 
 621. How is common white lead obtained ? 
 
 622. For what purpose are most of the metallic oxyds used ? 
 
 623. How are yellow paints or ochres obtained, or of what are 
 tb&j composed ? 
 
152 
 
 METALS. 
 
 Caroline. It is then a sort of metallic gas. 
 
 Emily. Why is it reckoned so unwholesome to breathe the air of 
 p ace where metals are melting ? 
 
 Mrs.B. Perhaps the notion is too generally entertained. But it 
 s true with respect to lead, and some other noxious metals, because 
 unless care be taken, the particles of the oxyd which are volatiliz- 
 ed by the heat are inhaled with the breath, and may produce dan- 
 gerous effects. 
 
 Fig. 28. I must show you some 
 
 instances of the combus- 
 tion of metals; it would re- 
 quire the heat of a furnace 
 to make them burn in the 
 common air, but if we sup- 
 ply them with a stream of 
 oxygen gas, we may easily 
 accomplish it. 
 
 Caroline. It will still, I 
 suppose, be necessary in 
 some degree to raise their 
 temperature ? 
 
 Mrs. B. This, as you 
 shall see, is very easily 
 done, particularly if the 
 experiment be tried upon 
 a small scale. I begin by 
 lighting this piece of char- 
 coal with the candle, and 
 then increase the rapidity 
 of its combustion by blow- 
 ing upon it with a blow- 
 pipe. (Fig. 28, No. I.) 
 
 Emily. That 1 do not 
 understand ; for it is not 
 every kind of air, but 
 merely oxygen gas, that 
 
 produces combustion. 
 
 Now you said that in brea- 
 thing we inspired, but did 
 not expire oxygen gas. 
 Why, therefore, should the 
 air which you breathe thro' 
 the blow-pipe promote the 
 combustion of the char- 
 coal ? 
 
 Mrs. B. Because the 
 
 air, which has but once 
 
 Aprantus for the connection of metah by meant of oxygen , , , ,1 I,,-,, 
 
 gM. No. 1. Igniting charcoal with a taper and blow-pipe, passed through the lUUgS, 
 
 No. 2. Combustion of metals by means of a blow-pipe con-lS TCt but little altered, a 
 ying a stream of oxygen gas from a gaS-holder. small portion Only of its OX- 
 
 ygen being destroyed ; so that a great deal more is gained by in- 
 creasing the rapidity of the current, by means of the blow pipe, than 
 
 624. Why is it reckoned unwholesome to breathe the air of a 
 place in which metals are melting ? 
 
 625. What gas produces combustion ? 
 
METALS. 153 
 
 is lost in consequence of the air passing once through the lungs, as 
 you shall see 
 
 Emily. Yes, indeed, it makes the charcoal burn much brighter. 
 Mrs. B. Whilst it is red hot, I shall drop s^jme iron filings on it, 
 and supply them with a current of oxygen gas, by means of this 
 apparatus, (Fig. 28, No. 2.) which consists simply of a closed tin 
 cylindrical vessel, full of oxygen gas, with two apertures and stop- 
 cocks, by one of which a stream of water is thrown into the vessel 
 through a long funnel, whilst by the other the gas is forced out 
 through a blow-pipe adapted to it, as the water gains admittance. 
 Now that I pour water into the funnel, you may hear the gas issu- 
 ing from the blow-pipe. I bring the charcoal close to the current, 
 and drop the filings upon it 
 
 Caroline. They emit much the same vivid light as the combustion 
 of the iron wire in oxygen gas. 
 
 Mrs. &. The process is, in fact, the same ; there is only some 
 difference in the mode of conducting it. Let us burn some fin in 
 the same manner you see that it is equally combustible. Let us 
 now try some copper 
 
 Caroline. This burns with a greenish flame ; it is, I suppose, ow- 
 ing to the color of the oxyd ? 
 Emily. Pray, shall we not also burn some gold ? 
 Mrs. B. That is not in our power, at least, in this way. Gold, 
 silver, and platina, are incapable of being oxydated by the greatest 
 heat that we can produce by the common method. It is from this 
 circumstance, that they have been called perfect metals. Even 
 these, however, have an affinity for oxygen ; but their oxydation or 
 combustion can be performed only by means of acids, or by electri- 
 city. 
 
 The spark given out by the Voltaic battery produces at the point 
 of contact, a greater degree of heat than any other process ; and it 
 is at this very high temperature only that the affinity of these met- 
 als for oxygen will enable them to act on each other. 
 
 I am sorry that 1 cannot show you the combustion of the perfect 
 metals by this process, but it requires a considerable Voltaic battery. 
 You will see these experiments performed in the most perfect man- 
 ner, when you attend the chemical lectures of the Royal Institution. 
 But in the mean time I can, without difficulty, show you an ingen- 
 ious apparatus lately contrived for the purpose of producing intense 
 heats, the power of which nearly equals that of the largest Voltaic 
 batteries. It simply consists, you see, in a strong box, made of iron 
 or copper, (Fig. 29.) to which may be adapted the air-syringe or 
 condensing pump, and a stop-cock, terminating in a small orifice 
 similar to that of a blow- pipe. By working the condensing syringe 
 up and down in this manner, a quantity of air is accumulated in the 
 vessel, which may be increased to almost any extent, so that, if we 
 now turn the stop-cock, the condensed air will rush out, forming a 
 jet of considerable force ; and if we place the flame of a lamp in the 
 current, you will see how violently the flame is driven in that direc- 
 
 626. What is represented by figure 28 ? 
 
 627. What metals have been called perfect ? 
 
 628. Why have they been thus called ? 
 
 629. What is represented by figure 29'? 
 
ndensed air. B, the condensing syringe, 
 for oxygen. D, the moveable jet 
 
 Caroline. It seems to be exactly the same effect as that of a blow- 
 pipe worked by the mouth, only much stronger. 
 
 Emily. Yes ; and the instrument has this additional advantage, 
 that it does not fatigue the mouth and lungs like the common blow- 
 pipe, and requires no art in blowing. 
 
 Mrs. B. Unquestionably ; but yet this blow-pipe would be of 
 very limited utility*, if its energy and power could not be greatly 
 ncreased by s^me other contrivance. Can you imagine any mode 
 of producing such an effect? 
 
 Entity. Could not the reservoir be charged with pure oxygen 
 instead of common air, as in the case of the gas-holder? 
 
 Mrs. B. Undoubtedly ; this is precisely the contrivance I allude 
 bo. The vessel need only be supplied with air from a bladder full 
 of oxvjen, instead of the air of the room, and this, you see, may 
 be easily done by screwing the bladder on the upper part of the syr- 
 inge, so that, in working the syringe, the oxygen gas is forced from 
 the bladder into the condensing vessel. 
 
 Caroline. With the aid or^tffis small apparatus, therefore, we could 
 obtain the same effects as tbdse we have just produced with the gas- 
 holder, by means of a column of water forcing the gas out of it. 
 
 Mrs. B. Yes ; and much more conveniently so. But there is 
 s mode of using this apparatus, by which more powerful effects 
 still may be obtained. It consists in condensing in the reservoir, 
 not oxygen alone, but a mixture of oxygen and hydrogen in the ex- 
 act proportion in which they unite to produce water ; and then kin- 
 
 630. How could the reservoir in that figure be supplied with pure 
 oxygen ? 
 
 631. How is the most intense heat produced ? 
 
METALS. 155 
 
 die the jet formed by the mixed gases. The heat disengaged by this 
 combustion, without the help of any lamp, is probably the most in- 
 tense known ; and various effects are said to have been obtained 
 from it which exceed all expectation. 
 
 Caroline. But why should we not try this experiment ? 
 
 Mrs. B. Because it is not exempt from danger;* the combustion 
 (notwithstanding various contrivances which have been resorted to 
 with a view to prevent accident) being apt to penetrate into the in- 
 side of the vessel, and to produce a dangerous and violent explosion. 
 We shall, therefore, now prodeed to our subject. 
 
 Caroline. I think you said the oxyds of metals could be restored 
 to their metallic state ? 
 
 Mrs. B. Yes; thi* operation is called reviving a metal. Metals 
 are in general capable of being revived by charcoal, when heated 
 red hot, charcoal having a greater attraction for oxygen than the 
 metals. You need only, therefore, decompose, or unbuin theoxyd 
 by depriving it of its oxygen and the metal will be restored to its 
 pure state. 
 
 Emily. But will the carbon, by this process, be burnt, and be 
 converted into carbonic acid ? 
 
 Mrs. B. Certainly. There are other combustible substances to 
 which metals of a high temperature will part with their oxygen. 
 They will also yield it to each other, according to their several 
 degrees of attraction for it ; and if the oxygen goes into a more 
 dense state in the metals which it enters, than it existed in that which 
 it quits, a proportional disengagement of caloric will take place. 
 
 Caroline. And cannot the oxyds of gold, silver, and platina, 
 which are formed by means of acids or of the electric fluid, be re- 
 stored to their metallic state ? 
 
 Mis. B. Yes, they may, and the intervention of a combustible 
 body is not required ; heat alone will take the gxygen from them, 
 convert it into gas, and revive the metal. 
 
 Emily. You said that rust was an oxyd of iron ; how is it, then, 
 that water, or merely dampness, produces it, which you know, it 
 very frequently does on steel grates, or any iron instruments ? 
 
 * Hydrogen and oxygen may be burned together with the most 
 perfect safety by means of the compound blow-pipe, an instrument 
 invented by Prof. Hare, of Philadelphia. Instead of mixing the 
 gases in the same reservoir, they are kept separate until they meet 
 at the point of combustion. An account of this blow-pipe is given 
 by Prof. Silliman, in his edition of Henry's chemistry, together with 
 a list of experiments made with it on various substances. This was 
 the first notice of any experiment made by burning the two gases 
 together, for the purpose of obtaining an intense heat. C. 
 
 632. How may oxygen and hydrogen be burned together with 
 tafety f 
 
 633. What is called reviving a metal ? 
 
 634. By wlmt are metals revived ? 
 
 635. What effect is produced on the carbon which is used to re- 
 vive a metal ? 
 
 636. Can the oxyds of the perfect metals be restored to their 
 metallic state ? 
 
 537. By what means? 
 
156 METALS. 
 
 Mrs. B. In that case the metal decomposes the water, or damp- 
 ness (which is nothing but water in a state of vapour,) and obtains 
 the oxygen from it. 
 
 Caroline. I thought that it was necessary to bring metals to a 
 very high temperature to enable them to decompose water. 
 
 Mrs. B. It is so, if it is required that the process should be per- 
 formed rapidly, and if any considerable quantity is to be decomposed. 
 Rust, you know, is sometimes months in forming, and then it is only 
 the surface of the metal that is oxy dated. 
 
 Emily. Metals, then, that do not rust, are incapable of spontane- 
 ous oxydation, either by air or water ? 
 
 Mrs. B. Yes ; and this is the case with the perfect metals, which 
 on that account, preserve their metallic lustre so well. 
 
 Emily. Are all metals capable of decomposing water, provided 
 their temperature be sufficiently raised ? 
 
 Mrs. B. No ; a certain degree of attraction is requisite, besides 
 the assistance of heat. Water, you recollect, is composed of oxy- 
 gen and hydrogen ; and, unless the affinity of the metal for oxygen 
 be stronger than that of the hydrogen, it is in vain that we raise its 
 temperature, for it cannot take the oxygen from the hydrogen. 
 Iron, zinc, tin, and antimony, have a stronger affinity for oxygen 
 than hydrogen has, therefore these four metals are capable of de- 
 composing water. But hydrogen, having an advantage over all the 
 other metals with respect to its affinity for oxygen, it not only with- 
 holds. its oxygen from them, but is even capable, under certain cir- 
 cumstances, of taking the oxygen from the oxyds of these metals. 
 
 Emily. I confess that I do not quite understand why hydrogen can 
 take oxygen from those metals which do not decompose water. 
 
 Caroline. Now I think I do perfectly. Lead, for instance, will 
 not decompose water, because it has not so strong an attraction for 
 oxygen as hydrogen has. Well, then, suppose the lead to be in a 
 state of oxyd ; hydrogen will take the oxyd from the lead, and unite 
 with it to form water, because hydrogen has a stronger attraction 
 than oxygen has for lead, and it is the same with all the other metals 
 which do not decompose water. 
 
 Emily. I understand your explanation, Caroline, very well ; and 
 I imagine that it is. because lead cannot decompose water that it is 
 so much employed for pipes for conveying that fluid.* 
 
 Mrs.JZ. Certainly; lead is, on that account, particularly appro- 
 priate to such purposes ; whilst, on the contrary, this metal, if it 
 was oxydable by water, would impart to it very noxious qualities, 
 as all oxyds of lead are more or less pernicious. 
 
 * Lead ist capable of decomposing water, and when suffered to 
 stand long in a vessel pf -this metal, it becomes poisonous. When 
 used merely to convey water, there is but little danger. C. 
 
 630. If rust is an oxyd of iron, why is it that water or dampness 
 causes it ? 
 
 639. Do the metals oxydateon being exposed to the air? 
 
 640. Why will not the perfect metals rust ? 
 
 641. What metals are capable of decomposing water>? 
 42. Why cannot all metals decompose water ? 
 
METALS. 157 
 
 But with regard to the oxydation of metals, the most powerful 
 mode of effecting it, is by means of acids. These, you know, con- 
 tain a much greater proportion of oxygen than either air or water ; 
 and will, most of them, easily yield it to metals. 
 
 Thus, you recollect, the zinc plates of the Voltaic battery are ox- 
 ydated by the acid and water, much more effectually than by water 
 alone. 
 
 Caroline. And I have often observed that if I drop vinegar, lem- 
 on, or any acid on the blade of a knife, or on a pair of scissors, it 
 will immediately produce a spot of rust. 
 
 Emily. Metals have, then, three ways of obtaining oxygen ; from 
 the atmosphere, from water, and from acids. 
 
 Mrs. B. The two first you hare already witnessed, and I shall 
 now show you how metals take the oxygen from an acid. This bot- 
 tle contains nitric acid ; I shall pour some of it over this piece of 
 copper leaf .... 
 
 Caroline. Oh, what a disagreeable smell ! 
 
 Emily. And what is it that produces the effervescence, and that 
 thick yellow vapour ? 
 
 Mrs B. It is the acid, which, being abandoned by th egreatest 
 part of its oxygen, is converted into a weaker acid, which escapes 
 in the form of gas. 
 
 Caroline. And whence proceeds this heat ? 
 
 Mrs. B. Indeed, Caroline, I think you might now be able to an- 
 swer that question yourself. 
 
 Caroline. Perhaps it is that the oxygen enters into the metal in a 
 more solid state than it existed in the acid, inconsequence of which 
 caloric is disengaged. 
 
 Mrs. B. If the combination of the oxygen and the metal results 
 from the union of their opposite electricities, of course caloric must 
 be given out. 
 
 Emily. The effervescence is over ; therefore I suppose that tb 
 metal is now oxydated. 
 
 Mrs. B. Yes. But there is another important connexion be- 
 tween metals and acids, with which I must now make you acquaint- 
 ed. Metals, when in a state of oxyds, are capable of being dissolv- 
 ed by acids. In this operation they enter into a chemical combi- 
 nation with the acid, and form an entirely new compound. 
 
 Caroline. But what difference is there between the oxydation 
 and the dissolution of the metal by an acid ? 
 
 Mrs. B. In the first case, the metal merely combines with a por- 
 tion of oxygen taken from the acid, which is thus partly deoxygen- 
 atcd, as in the instance you have just seen ; in the second case the 
 metal, after being previously oxydated, is actually dissolved in the 
 
 643. What is the most powerful mode of oxydating metals i 
 
 644. From what do metals obtain oxygen ? 
 
 645. When a metal dissolves in acid, what causes the efferves- 
 cence ? 
 
 646. To what is the heajowing, when a metal is dissolved in acid ? 
 
 647. What state must a metal be in before it can be dissolved by 
 an acid ? 
 
 648. How can metal then be dissolved ? 
 
 649. What is the difference between the oxydation and be disso- 
 lution of a metal by an acid ? 
 
 14 
 
158 METALS. 
 
 acid, and enters into a chemical combination with it, without pro- 
 ducing any further decomposition or effervescence. This complete 
 combination of an oxyd and an acid forms a peculiar and important 
 class of compound salts. 
 
 Emily. The difference between an oxyd and a compound salt, 
 therefore, is very obvious ; the one consists of a metal and oxygen ; 
 the other of an oxyd and an acid. 
 
 Mrs. B. Very well ; and you will be careful to remember that 
 the metals are incapable of entering- into this combination with acids, 
 unless they are previously oxydated ; therefore whenever you bring 
 a metal in contact with an acid, it will be first oxydated, and after- 
 wards dissolved, provided that there be a sufficient quantity of acid 
 for both operations. 
 
 There are some metals, however, whose solution is more easily 
 accomplished by diluting the acid in water; and the metal will, in 
 this case, be oxydated, not by the acid, but by the water, which it 
 will decompose. But in proportion as the oxygen of the water ox- 
 ydates the surface of the metal, the acid combines with it, washes it 
 off and leaves a fresh surface for the oxygen to act upon ; then other 
 coats of oxyd are successively formed, and rapidly dissolved by the 
 acid, which continues combining with the new formed surfaces of 
 oxyd till the whole of the metal is dissolved. During this process the 
 hydrogen gas of the water is disengaged,and flies off with effervesence. 
 
 Emily. Was not this the manner in which the sulphuric acid as- 
 sisted the iron filings in decomposing water ? 
 
 Mrs. B. Exactly ; and it is thus that several metals, which are 
 incapable alone of decomposing water, are enabled to do it by the 
 assistance of an acid, which, by continually washing off the covering 
 of oxyd, as it is formed, prepares a fresh surface of metal to act upon 
 the water. 
 
 Caroline. The acid here seems to act a part not very different 
 from that of a scrubbing brush. But pray, would not this be a good 
 method of clensing metallic utensils ? 
 
 Mrs. B. Yes ; on some occasions a weak acid, as vinegar, is 
 used for cleaning copper. Iron plates, too, are freed from the rust 
 on their surface by diluted muriatic acid, previous to their being 
 covered with tin. You must remember, however, that in this mode 
 of cleaning metals the acid should be quickly afterwards wiped off, 
 otherwise it would produce fresh oxyd. 
 
 Caroline. Let us watch the dissolution of the copper in the nitric 
 acid : for I am very impatient to see the salt that is to return from 
 it. The mixture is now of a beautiful blue color ; but there is no 
 appearance of the formation of a salt ; it seems to be a tedious ope- 
 ration. 
 
 Mrs. B. The crystallization of the salt requires some length of 
 time to be completed ; if, however, you are so impatient, I can easily 
 show you a metallic salt already formed. 
 
 Caroline. But that would not satisfy my curiosity half so well as 
 one of our own manufacturing. 
 
 Mrs. B. It is one of our own preparing that I mean to show you. 
 When we decomposed water a few days since, by the oxydation of 
 
 650. What is the difference between a compound salt and an oxyd 
 
 651. Why are acids good in cleaning rust from metals? 
 
 652. What caution is necessary in cleaning metals by acids ? 
 
METALS. 159 
 
 iron filings through the assistance of sulphuric acid, in what did the 
 process consist ? 
 
 Caroline. In proportion as the water yielded its oxygen to the 
 iron, the acid combined with the new formed oxyd, and the hydro- 
 gen escaped alone. 
 
 Jftrs. B. Very well ; the result, therefore, was a compound salt, 
 formed by the combination of sulphuric acid with oxygen of iron. 
 It still remains in the vessel in which the experiment was performed. 
 Fetch it, and we shall examine it. 
 
 Emily. What a variety of processes the decomposition of water, 
 by a metal and an acid, implies : 1st, the decomposition of the water ; 
 2dly, the oxydation of the metal; and 3dly, the formation of a com- 
 pound salt. 
 
 Caroline. Here it is, Mrs. B. Iteiat beautiful green crystals ! But 
 we do not perceive any crystals inkhe solution of copper in nitrous 
 acid. 
 
 Mrs. B. Because the salt is now suspended in the water which the 
 nitrous acid contains, and will remain so till it is deposited, in con- 
 sequence of rest and cooling. 
 
 Emily. I am surprised that a body so opaque as iron can be con- 
 verted into such transparent crystals. 
 
 Mrs. B. It is the union with the acid that produces the transpa- 
 rency ; for if the pure metal were melted, and afterwards permitted 
 to cool and crystallize, it would be found just as opaque as before. 
 
 Emily. 1 do not understand the exact meaning of crystallization. 
 
 Mrs. B. You recollect that when a solid body is dissolved, either 
 by water or caloric, it is not decomposed : but that its integrant 
 parts are only suspended in the solvent. When the solution is made 
 in water, the integrant particles of the body will, on the water being 
 evaporated, again uniie into a solid mass, by the force of tbeir mu- 
 tual attraction. But when the body is dissolved by caloric alone, 
 nothing more is necessary, in order to make its particles re-unite, 
 than to reduce its temperature. And, in general, if the solvent, 
 whether water or caloric, be slowly separated by evaporation or by 
 cooling, and care taken that the particles be not agitated during 
 their re-union, they will arrange themselves in regular masses, each 
 individual substance assuming a peculiar form or arrangement ; 
 and this is what is called crystallization. 
 
 Emily. Crystallization, therefore, is simply the re-union of the 
 particles of a solid body which has been dissolved in a fluid.* 
 
 Mrs. B. That is a very good definition of it. But I must not for- 
 get to observe, that Aectfand water may unite tbeir solvent powers 
 and in this case^ crystallization may be hastened by cooling, as wel 
 as by evaporating the liquid. 
 
 Caroline. But if the body dissolved is of a volatile nature, will it 
 not evaporate with the fluid ? 
 
 * Not exactly, because the particles of the fluid make a part of 
 the crystal. Crystallization is that process by which the particles 
 of bodies unite to form solids, of certain, and regular shapes. C. 
 
 653. What processes does the decomposition of water by a metal 
 and an acid imply ? 
 
 654. What causes crystallized iron to be transparent ? 
 a. What is crystallization ? 
 
 
160 METALS. 
 
 Mrs. B. A crystallized body held in solution only by water is 
 scarcely ever so volatile as the fluid itself; and care must be taken 
 to manage the heat so that it may be sufficient to evaporate the 
 water only. 
 
 I should not omit also to mention that bodies, in crystallizing from 
 their watery solution, always retain a small portion of water, which 
 remains confined in the crystal, in a solid form, and does not re-ap- 
 pear unless the body loses its crystalline state. This is called the 
 water of crystallisation. But you must observe, that whilst a body 
 may be separated from its solution in water or caloric simply by cool- 
 ing or>y evaporation, an acid can be taken from a metal with which 
 ; it is combined only by stronger affinities, which produce a decom- 
 position. 
 
 Emily. Are the perfect metals susceptible of being dissolved and 
 converted into compound salts by acids ? 
 
 Mrs. B. Gold is acted upon by only one acid, the oxygenated 
 muriatic, a very remarkable acid, which, when it is most concen- 
 trated state dissolves gold or any other metal, by burning them 
 rapidly. 
 
 Gold can, it is true, be dissolved likewise by a mixture of two 
 acids, commonly called aqua.regia ; but this mixed solvent derives 
 that property from containing the peculiar acid which I have just 
 mentioned. Platina is also acted upon by this acid only ; silver is 
 dissolved by nitric acid. 
 
 Caroline. 1 think you said that some of the metals might be so 
 strongly oxydated as to become acid ? 
 
 Mrs. B. There are five metals, arsenic, molybdean, chrome, 
 tungsten, and columbium, which are susceptible of combining with 
 a sufficient quantity of oxygen to be converted into acids. 
 
 Caroline. Acids are connected with metals in such a variety of 
 ways, that I am afraid of some confusion in remembering them. In 
 the first place, acids will yield their oxygen to metals. Secondly, 
 they will combine with them in their state of oxyds, to form com- 
 pound salts ; and lastly, several of the metals are themselves sus- 
 ceptible of acidification. 
 
 Mrs. B. Very well ; but though metals have so great an affinity 
 for acids, it is not with that class of bodies alone that they will com- 
 bine. They are most of them, in their simple state, capable of uni- 
 ting with sulphur, with phosphorus, with carbon, and with each 
 other; these combinations, according to the nomenclature which 
 was explained to you on a former occasion, are called sulphurets, 
 phosphorets, carburets, &c. 
 
 The metallic phosphorets offer nothing very remarkable. The 
 sulphurets form the peculiar kind of mineral called pyrites, from 
 which certain kinds of mineral waters, as those of Harrogate, derive 
 
 655. What is the water of crystallization ? 
 
 656. Are the perfect metals susceptible of being dissolved and 
 converted into compound salts by acids ? 
 
 657. Can any of the metals combine wffi so great a quantity of 
 oxygon as to become acids ? 
 
 658. With what other substances besides acids, will metals com- 
 bine ? 
 
 650. What are the combinations of the metals with each other 
 called? 
 
METALS. 161 
 
 their chief chemical properties. In this combination, the sulphur, 
 together with the iron, have so strong an attraction for oxygen, that 
 they both obtain it from the air and from water, and by condensing 
 it in a solid form, produce the heat which raises the temperature of 
 the water in such a remarkable degree. 
 
 Emily. But if pyrites obtain oxygen from water, that water must 
 suffer a decomposition, and hydrogen gas be evolved. 
 
 Mrs. B. That is actually the case in the hot springs alluded to, 
 which give out an extremely fetid gas, composed of hydrogen, im- 
 pregnated with sulphur. 
 
 Caroline. If I recollect right, steel and plumbago, which you men- 
 tioned in the last lesson, are both carburets of iron. 
 
 Mrs. B. Yes; and they are the only carburets of much conse- 
 quence. 
 
 A curious combination of metals has lately very much attracted 
 the attention of the scientific world : 1 mean the meteoric stones 
 which fall from the atmosphere. They consist principally of native 
 or pure iron, which is never found in that state in the bowels of the 
 earth ;* and contain also a small quantity of nickel and chrome, a 
 combination likewise new in the mineral kingdom. 
 
 These circumstances have led many scientific persons to believe 
 that those substances have fallen from the moon, or some other 
 planet, while others are of opinion either that they are formed in the 
 atmosphere, or are projected into it by some unknown volcano on 
 the surface of our globe. 
 
 Caroline. 1 have heard much of these stones, but I believe many 
 people are of opinion that they are formed on the surface of the 
 earth, and laugh at their pretended celestial origin. 
 
 J\lrs. B. The fact of their falling is so well ascertained, that I 
 think no person who has at all investigated the subject, can now 
 entertain any doubt of it. Specimens of these stones have been dis- 
 covered in all parts of the world, and to each of them some tradition 
 or story of its fall has been found connected. And as the analysis of 
 all those specimens afford precisely the same results, there is strong 
 
 * This seems to be a mistake. Several localities of native iron, 
 found in veins are pointed out by authors. In several instances 
 large blocks of native iron have been found on the surface of the 
 fearth. One found by Prof. Pallas in Siberia, weighed 16001bs. 
 Another found in South America, is said to weigh 30,000 Ibs. &c. 
 These have been suspected to be of meteoric origin, though nothing 
 is known, which makes this certain. Those stones which are known 
 beyond a doubt to have fallen from the atmosphere, have a very dif- 
 ferent composition. These generally contain the following ingre- 
 dients, viz. iron, nickel, chrome, oxide of iron, sulphur, silex, lime, 
 magnesia, and alumine. The iron rarely amounts to a quarter of 
 the whole. Accounts are recorded of the falling of stones, sulphur, 
 c. in every age since the Christian era, and in almost every part 
 of the world. C. 
 
 660. Which are the most important carburets ? 
 
 651. Of wbnt do the meteoric stones which have attracted so 
 much attention from the scientific world, consist ? 
 
 662. What opinions have been entertained as to the origin o/ 
 these stones? 14* 
 
162 METALS. 
 
 reason to conjecture that they all proceed from the same source. 
 It is to Mr. Howard that philosophers are indebted for having first 
 analysed these stones, and directed their attention to this interest- 
 ing subject. 
 
 Caroline. But pray, Mrs. B., how can solid masses of iron and 
 nickel be formed from the atmosphere, which consists of the two 
 airs, nitrogen and oxygen ? 
 
 Mrs B. 1 really do not see how they could, and think it much 
 more probable that they fall from the moon, or some other celestial 
 body. But we must not suffer this digression to take up too much 
 of our time. 
 
 The combinations of metals with each other are called alloys ; 
 thus brass is an alloy of copper and zinc ; bronze of copper and tin,&c. 
 
 Emily. And is not pewter also a combination of metal ? 
 
 Mrs. B. It is. The pewter made in this country is mostly com- 
 posed of tin, with a very small proportion of zinc and lead. 
 
 Caroline. Block-tin is a kind of pewter, I believe ? 
 
 Mrs.B. Properly speaking, block-tin means tin in blocks, or 
 square massive ingots ; but in the sense in which it is used by igno- 
 rant workmen, it is iron plated with tin, which renders it more dur- 
 able, as tin will not so easily rust. Tin alone, however, would be too 
 soft a metal to be worked for common use, and all tin vessels and 
 utensils are in fact made of plates of iron, thinly coated with tin, 
 which prevents the iron from rusting. 
 
 Caroline. Say rather, oxydating, Mrs. B. Rust is a word that 
 ought to be exploded in chemistry. 
 
 Mrs. B. Take care, however, not to introduce the word oxydate 
 instead of rust, in general conversation ; for you would probably 
 not be understood, and you might be suspected of affectation. 
 
 Metals differ very much in their affinity for each other ; some 
 will not unite at all, others readily combine together, and on this 
 ^property of metals the art of soldering depends. 
 
 Emily. What is soldering .'? 
 
 .Mrs. B. It is joining two pieces of metal together, by a more fu- 
 sible metal interposed between them. Thus tin is a solder for lead ; 
 brass, gold, or silver, are solder for iron, &c. 
 
 Caroline. And is not plating metals something of the same nature? 
 
 Mrs..B. In the operation of plating, two melals are united, one 
 being covered with the other, but without the intervention of a 
 third ; iron or copper may thus be covered with gold or silver. 
 
 $mily. Mercury appears to me of a very different nature from 
 the other metals. 
 
 Mrs. B. One of its greatest peculiarities is, that it retains a fluid 
 gtate at the temperature of the atmosphere. All metals are fusible 
 at different degrees of heat, and they have likewise each the proper- 
 ty of freezing or becoming solid at a certain fixed temperature. 
 
 663. Who first analysed these stones ? 
 
 664. What are the combinations of metals with each other called? 
 6,65. Of what is brass an alloy ? 
 
 666. Of what is pewter composed ? 
 
 667. What 'is block-tin ? 
 
 668. On what <!oes the art of .soldering depend ? 
 
METALS. 163 
 
 Mercury congeals only at seventy-two degrees below the freezing 
 point. 
 
 Emily. That is to say, that in order to freeze, it requires a tem- 
 perature of seventy-two degrees colder than that at which water 
 freezes. 
 
 Mrs. B. Exactly so. 
 
 Caroline. Bnt is the temperature of the atmosphere ever so low 
 as that ? 
 
 Mrs. B. Yes, often in Siberia ; but happily never in this part of 
 the globe. Here, however, mercury may be congealed by artifi- 
 cial cold ; I moan such intense cold as can be produced by some 
 chemical mixtures or by the rapid evaporation of ether under the 
 air pump.* 
 
 Caroline. And can mercury be made to boil and evaporate ? 
 
 Mrs. B. Yes, like any other liquid ; only it requires a much 
 greater degree of heat. At the temperature of six hundred de- 
 grees, it begins to boil and evaporate like water. 
 
 Mercury combines with gold, silver, tin, and with several other 
 metals ; and, if mixed with any of them in a sufficient proportion, 
 it penetrates the solid metal, softens it, loses its own fluidity, and 
 forms an amalgam, which is the name given to the combination of 
 any metal with mercury, forming a substance more or less solid, 
 according as the mercury or the other metal predominates. 
 
 Emily. In the list of metals there are some whose names I have 
 never before heard mentioned. 
 
 Mrs. B. Besides those which Sir H. Davy has obtained, there are 
 several that have been recently discovered, whose properties are 
 yet but little known, as for instance, titanium, which was discover- 
 ed by the Rev. Mr. Gregor in the tin-mines of Cornwall ; colum- 
 bium or tantalium, which haslately been discovered by Mr. Hatch- 
 ett ; and osmium, iridium, palladium, and rhodium, all of which 
 Dr. Wollaston and Mr, Tenant found mixed in minute quantities 
 with crude platina, -and the distinct existence of which they proved 
 by curious and delicate experiments. More recently still Professor 
 Berzelius has discovered in a pyritic ore, at Fahlun, in Sweden, a 
 metallic substance, which he has called selenium, and which has the 
 singular peculiarity of assuming the form of a yellow gas when 
 heated in close vessels. In some of its properties this substance 
 seems to hold a medium between the combustibles and the metals. 
 It bears in particular a strong 1 analogy to sulphur. 
 
 Caroline. Arsenic has been mentioned amongst the metals, I had 
 no notion that it belonged to that class of bodies, for I had never 
 seen it but as a powder, and never thought of it but as a most dead- 
 ly poison. 
 
 Mrs. /?_ In its pure metallic state, 1 believe it is not so poisonous^ 
 but it has such a great affinity for oxygen, that it absorbs it from the 
 atmosphere as its natural temperature ; you have seen it therefore, 
 
 * By a process analogous to that described, page 81, of this work 
 
 669. At what temperature will mercury congeal ? 
 
 670. At what temperature will it boil and evaporate ? 
 
 671. What is the combination of a metal with mercury called? 
 
 672. What metals have been recently discovered ? 
 
 673. What is the natural state of arsenic ? 
 
164 METALS. 
 
 only in its slate of oxyd, when, from its combination with oxygen, 
 it has acquired its very poisonous properties. 
 
 Caroline. Is it possible that oxygen can impart poisonous quali- 
 ties ? That valuable substance which produces light and fire, and 
 which all bodies in nature are so eager to obtain ? 
 
 Mrs. B. Most of the metallic oxyds are poisonous, and derive 
 this property from their union with oxygen. The white lead, so 
 much used in paint, owes its pernicious effects to oxygen. In gen- 
 eral, oxygen, in a concrete state, appears to be particularly des- 
 tructive in its effects on flesh or any animal matter : and^those oxyda 
 are most caustic that have an acrid, burning taste, which proceeds 
 from the metal having but a slight affinity for oxygen, and therefore 
 easily yielding to the flesh, Which it corrodes and destroys. 
 
 Emily. What is the meaning of the word caustic ', which you 
 have just used ? 
 
 Mrs. B. It expresses that property which some bodies possess, of 
 disorganizing and destroying animal matter, by operating a kind of 
 combustion, or at least a chemical decomposition. You must often 
 have heard of caustic used to burn warts, or other animal excres- 
 cences ; most of these bodies owe their destructive power to the 
 oxygen with which they are combined. The common caustic call- 
 ed lunar caustic, is a compound formed by the union of nitric acid 
 and silver ; and it is supposed to owe its caustic qualities to the 
 oxygen contained in the nitric acid. 
 
 Caroline. But, pray, are not acids still more caustic than oxyds, 
 as they contain a greater proportion of oxygen? 
 
 Mrs, B. Some of the acids are ; but the caustic property of a 
 body depends not only upon the quantity of oxygen which it con- 
 tains, but also upon its slight affinity for that principle, and the con- 
 sequent facility with which it yields it. 
 
 Emily. Is not this destructive property of oxygen accounted for ? 
 
 Mrs. B. It proceeds probably from the strong attraction of ox- 
 ygen for hydrogen ; for if the one rapidly absorb the other from the 
 animal fibre, a disorganization of the substance must ensue. 
 
 Emily. Caustics are, then, very properly said to burn the flesh, 
 since the combination of oxygen and hydrogen is an actual com- 
 bustion. 
 
 Caroline. Now, I think, this effect would be more properly term- 
 ed an oxydation, as there is no disengagement of light and heat. 
 
 Mrs. B. But there really is a sensation of heat produced by the 
 action of caustics. 
 
 Emily. If oxygen is so caustic, why does not that which is con- 
 tained in the atmosphere burn us ? 
 
 Mrs. B. Because it is in a gaseous state, and has a greater at- 
 traction for its electricity than for the hydrogen of our bodies. Be- 
 sides, should the air be slightly caustic, we are in a great measure 
 sheltered from its effects by the skin : you know how much a 
 wound, however trifling, smarts on being exposed to it. 
 
 674. From what do metals derive their poisonous properties ? 
 
 675. What is a caustic ? 
 
 676. On what does the caustic property of a body depend ? 
 
 677. How is this destructive property of oxygen accounted for? 
 
 678. If oxygen is of a caustic tendency, why does not that burn 
 us, which is contained in the atmosphere ? 
 
METALS. 165 
 
 Caroline. It is a curious idea, however, that we should live in a 
 slow fire. But, if the air was caustic, would it not have an acrid 
 taste? 
 
 Mrs. B. It possibly may have such a taste ; though in so slight 
 a degree, that custom has rendered it insensible. 
 
 Caroline. And why is not water caustic ? When I dip my hand 
 into water, though cold, it ought to burn me from the caustic na- 
 ture of its oxygen. 
 
 Mrs. B. Your hand does not decompose the water ; the oxygen 
 in that state is much better supplied with hydrogen than it would 
 be by animal matter, and, if its causticity depend on its affinity for 
 that principle, it will be very far from quitting its state of water to 
 act upon your hand. You must not forget that oxyds are caustic 
 in proportion as the oxygen adheres slightly to them. 
 
 Emily. Since the oxyd of arsenic is poisonous, its acid, I suppose, 
 is fully as much so ? 
 
 Mrs. B. Yes, it is one of the strongest poisons in nature. 
 Emily. There is a poison called verdigris, which forms on brass 
 and copper when not kept very clean ; and this I have heard, is an 
 objection to these metals being made into kitchen utensils. Is this 
 poison likewise occasioned by oxygen ? 
 
 Jtt rs. B. It is produced by the intervention of oxygen, for verdi- 
 gris, is a compound salt formed by the union of vinegar and cop- 
 per ; it is a beautiful green colour, and much used in painting. 
 
 Emily. But, I believe, verdigris is often formed on copper when 
 no vinegar has been in contact with it. 
 
 Mrs. R. Not real verdigris, but other salts, somewhat resembling 
 it, may be produced by the action of other acids on copper. 
 
 The solution of copper in nitric acid, if evaporated, affords a salt 
 which produces an effect on tin that will surprise you, and I have 
 prepared some from the solution we made before, that I might show 
 it to you. I shall first sprinkle some water on this piece of tin-foil, 
 and then some of the salt. Now observe that I fold it up suddenly, 
 and press it into one lamp. 
 
 Caroline. What a prodigious vapour issues from it and sparks 
 of fire, I declare ! 
 
 Mrs. B. I thought it would surprise you. The effect, however, 
 I dare say you could account for, since it is merely the consequence 
 of the oxygen of the salt rapidly entering into a closer combination 
 wifh the tin. 
 
 There is also a beautiful green salt too curious to be omitted ; it 
 is produced by the combination of cobalt with muriatic acid, which 
 has the singular property of forming what is called sympathetic ink. 
 Characters written wtih this solution are invisible when cold, but 
 when a gentle heat is applied, they assume a fine bluish green col- 
 our. 
 
 Caroline. I think one might draw very curious landscapes with 
 the assistance of this ink ; I would first make a water-colour draw- 
 
 679. Why is not water caustic ? 
 
 680. What is verdigris ? 
 
 681. What experiment is made with a piece of tin-foil and a solu- 
 tion of copper in nitric acic ? 
 
 682. What is called sympathetic ink ? 
 
 683. What are the peculiarities of this ink ? 
 
166 METALS. 
 
 ing of a winter scene, in which the trees would be leafless, and the 
 grass scarcely green ; 1 would then trace all the verdure with the 
 invisible ink, and whenever I choose to create spring, I should hold 
 it before the fire, and its warmth would cover the landscape with a 
 rich verdure. 
 
 Mrs. B. That will be a very amusing experiment, and I advise 
 you by all means to try it. 
 
 Before we part, I must introduce to your acquaintance the curi- 
 ous metals which Sir H. Davy has recently discovered. The histo- 
 ry of these extraordinary bodies is yet so much in its infancy that I 
 shall confine myself to a very short account of them ; it is more 
 important to point out to you the vast, and apparently inexhaustible 
 field of research which has been thrown open to our view by Sir H. 
 Davy's memorable discoveries, than to enter into a minute account 
 f of particular bodies or experiments. 
 
 Caroline. But I have heard that these discoveries, however splen- 
 did and extraordinary, are not very likely to prove of any great 
 benefit to the world, as they are rather objects of curiosity than of 
 use. 
 
 Mrs. B. Such may be the illiberal conclusions of the ignorant 
 and narrow-minded ; but those who can duly estimate the advanta- 
 ges of enlarging the sphere of science, must be convinced that the 
 acquisition of every new fact, however unconnected it may at first 
 appear with practical utility, must ultimately prove beneficial to 
 mankind. But these remarks are scarcely applicable to the pres- 
 ent subject ; for some of the new metals have already proved emin- 
 ently useful as chemical agents, and are likely soon to be employed 
 in the arts. For the enumeration of these metals, I must refer you 
 to our list of simple bodies ; they are derived from the alkalies, the 
 earths, and three of the acids, all of which had been hitherto con- 
 sidered as undecompoundable, or simple bodies. 
 
 When Sir H. Davy first turned his attention to the effects of the 
 Voltaic battery, he tried its power on a variety of compound bodies, 
 and gradually brought to light a number of new and interesting 
 facts, which led the way to more important discoveries. It would 
 be highly interesting to trace his steps in this new department of 
 science, but it would lead us too far from our principal object. A 
 general view of his most remarkable discoveries is all that 1 can aim 
 at, or that you could, at present, understand. 
 
 The facility with which compound bodies yielded to the Voltaic 
 electricity, induced him to make a trial of its effects on substances 
 hitherto considered as simple, but which he suspected of being com- 
 pound, and his researches were soon crowned with the most com- 
 plete success. 
 
 The body which he first submitted to the Voltaic battery, and 
 which had never yet been decomposed, was one of the fixed alkalies 
 called potash. This substance gave out an elastic fluid at the pos- 
 itive wire, which was ascertained to be oxygen, and at the negative 
 wire, small globules of a very high metallic lustre, very similar in 
 
 684. What induced Sir H. Davy to try the effects of the Voltaic 
 battery on substances till then considered simple ? 
 
 685. What was the first substance which he submitted to the 
 Voltaic battery ? 
 
 686. What was the effect ? 
 
METALS. 167 
 
 appearance to mercury ; thus proving- that potash, which had hith- 
 erto been considered as a simple incombustible body, was in fact, 
 a metallic oxyd ; and that its incombustibility proceeded from its 
 being already combined with oxygen. 
 
 Emily. I suppose the wires used in this experiment were of plati- 
 na, as they were when you decomposed water; for if of iron, the 
 oxygen would have been combined with the wire, instead of appear- 
 ing in the form of gas. 
 
 Mrs. B. Certainly ; the metal however, would equally have 
 been disengaged. Sir H. Davy has distinguished this new substance 
 by the name of POTASSIUM, which is derived from that of the alkali, 
 from which it is procured. I have some small pieces of it in this 
 phial, but you have already seen it, as it is the metal which we 
 burnt in contact with sulphur. 
 
 Emily. What is the liquid in which you keep it ? 
 
 Mrs. B. It is naptha, a bituminous liquid, with which I shall 
 hereafter make you acquainted. It is almost the only fluid in which 
 potassium can be preserved, as it contains no oxygen, and this 
 metal has so powerful an attraction for oxygen, that it will not only 
 absorb it from the air, but likewise from water, or any body what- 
 ever, that contains it. 
 
 Emily. This, then, is one of the bodies that oxydates spontane- 
 ously without the application of heat. 
 
 Mrs. B. Yes : and it has this remarkable peculiarity, that it at- 
 tracts oxygen much more rapidly from water than from air : so that 
 when thrown into water, however cold, it actually bursts into flame. 
 I shall now throw a small piece, about the size of a pin's head, on 
 this drop of water. 
 
 Caroline. It instantaneously exploded, producing a little flash of 
 light! This is, indeed, a most curious substance ! 
 
 Mrs. B. By its combustion it is re-converted into potash ; and 
 as potash is now decidedly a compound body, I shall not enter into 
 any of its properties till we have completed our review of the sim- 
 ple bodies ; but we may here make a few observations on its basis, 
 potassium. If this substance is left in contact with air, it rapidly 
 returns to the state of potash, with a disengagement of heat, but 
 without any flash of light. 
 
 Emily. But is it not very singular that it should burn better in 
 water than in air? 
 
 Caroline. I do not think so ; for if the attraction of potassium 
 for oxygen is so strong ,that it finds no more difficulty in separating 
 it from the hydrogen in water, than in absorbing it from the air, it 
 will no doubt, be more amply and rapidly supplied by water than 
 by air. 
 
 Mrs. B. That cannot, however, be precisely the reason, for when 
 potassium is introduced under water, without contact of air, the 
 combustion is not so rapid, and, indeed, in that case there is no lu- 
 minous appearance; but a violent action takes place, much heat 
 is excited, the potash is regenerated and hydrogen gas is evolved. 
 
 637. What did this prove? 
 
 688. What is this new substance called? 
 
 689. What fluid contains no oxygen ? 
 
 690. What remarkable peculiarity has potassium? 
 
 691. How may potassium be recomposed ? 
 
 692. What will be the result if potassium is put under water 
 without being in contact with air ? 
 
168 METALS. 
 
 Potassium is so eminently combustible, tbat instead of requiring, 
 like other metals, an elevation of temperature, it will burn rap- 
 idly in contact with water, even below the freezing- point. This you 
 may witness by throwing- a piece on this lump of ice. 
 
 Caroline. It again exploded with flame, and has made a deep 
 hole in the ice. 
 
 JWrs. B. Thistle contains a solution of potash : for the alkali 
 being extremely' soluble, disappears in the water the instant it is 
 produced. Its presence, however, may be easily ascertained, alka- 
 lies having the properties of changing paper, stained with turmeric, 
 to a red colour; if you dip one end of this slip of paper into the 
 hole in the ice, you will see it change colour ; and the same, if you 
 wet it with the drop of water in which the first piece of potassium 
 was burnt. 
 
 Caroline. It has indeed changed the paper from yellow to red. 
 
 Mrs, B. This metal will burn likewise, in carbonic acid gas, a 
 gas that has always been supposed incapable of supporting combus- 
 tion, as we were unacquainted with any substance that had a great- 
 er attraction for oxygen than carbon. Potassium, however, readi- 
 ly decomposes this gas by absorbing its oxygen, as I shall show you. 
 This retort is filled with carbonic acid gas. 1 will put a small 
 piece of potassium in it ; but for this combustion a slight elevation 
 of temperature is required, for which purpose I shall hold the retort 
 aver the lamp. 
 
 Caroline. Now it has taken fire and burns with violence ! It has 
 burst the retort. 
 
 Jflrs. B. Here is a piece of regenerated potash ; can you tell me 
 why it has become so black? 
 
 Emily. No doubt it is blackened by the carbon, which, when its 
 oxygen entered into combination with the potassium, was deposited 
 on it surface. 
 
 Mrs. B. You are right. This metal is perfectly fluid at the tem- 
 perature of one hundred degrees ; at fifty degrees it is solid, but 
 soft and malleable; at thirty-two degrees it is hard and brittle, and 
 its fracture exhibits an appearance of confused crystallization. It 
 is scarcely more than half as heavy as water ; its specific gravity be- 
 ing about six, when water is reckoned at ten ; so that this metal is 
 actually lighter than any known fluid, even than ether. 
 
 Potassium combines with sulphur and phosphorus, forming sul- 
 phurets and phosphorets ; it likewise forms alloys with several met- 
 als, and amalgamates with mercury. 
 
 Emily. But can a sufficient quantity of potassium be obtained, by 
 means of the Voltaic battery, to admit of all its properties and rela- 
 tions to other bodies, being satisfactorily ascertained ? 
 
 Jflrs. B. Not easily ; but I must not neglect to inform you that a 
 method of obtaining this metal in considerable quantities, has since 
 been discovered. Two eminent French chemists, Thenard and 
 Gay Lussac, stimulated by the triumph which Sir H. Da<vy hadob- 
 
 693. At how low a temperature will potassium burn in contact 
 with water ? 
 
 694. Why, until the discovery of potassium, had carbonic acid- 
 gas been considered incapable of supporting combustion? 
 
 695. How does potassium decompose this gas? 
 
 696. What metal is lighter than any known fluid? 
 
METALS. 169 
 
 tamed, attempted lo separate potassium from its combination with 
 oxygen, by common chemical means, a'nd without the aid of elec- 
 tricity. They caused red-hot potash in a state of fusion, to filter 
 through iron turnings HI an iron tube, heated to whiteness. Their 
 experiment was crowned with the most complete success ; more 
 potassium was obtained by a single operation, than could have been 
 collected in many weeks by the most diligent use of the Voltaic 
 battery. 
 
 Emily. In this experiment, I suppose the oxygen quitted its com- 
 bination with the potassium, to unite with the iron turnings ? 
 
 Mrs. B. Exactly so ; and thus the potassium was obtained in its 
 simple state. Ftom that time it has become a most convenient and 
 powerful instrument of deox^genation in chemical experiments. 
 This impor'ant improvement, engrafted on Sir H. Davy's previous 
 discoveries, served but to add to h;s glory, since she lads which he 
 had established, when possessed only of a few atoms of this curious 
 substance, and the accuracy of his analytical statements were all 
 confirmed, when an opportunity occurred of repeating his experi- 
 ments upon this substance, which can now be obtained in unlimited 
 quantities. 
 
 Caroline. What a satisfaction Sir H. Davy must have felt, when 
 by mn effort ofgemus, he succeeded in bringing to light, and actually 
 giving, existence to these .curious bodies, which without him might 
 perhaps have ever remained concealed from our view ? 
 
 Mrs. B. The next substance wliich Sir H. Davy submitted to the 
 influence of the .Voltaic battery, was Soda, the other fixed alkali, 
 which yielded to the same powers of decomposition ; from this alkali, 
 too, a metallic substance was obtained, very analogous in its proper- 
 ties to that which had been discovered in potash ; Sir H. Davy haul 
 called it SODIUM. It is rather heavier than potassium, though con- 
 siderably lighter than water; it is not so easily fusible as potassium. 
 
 Encouraged by these extraordinary results, Sir H Davy next 
 performed a series of beautiful experiments on Ammonia, or the vo- 
 latile alkali, which, from analog}, he was led to suspect might also 
 contain oxygen. This be soon ascertained to be the- fact,. but be 
 has not yet succeeded in obtaining the basis of ammonia in a sepa- 
 rate state ; it is from analogy, and from the power which (he volatile 
 alkali has, in its gaseous form, to oxydate iron, and also from the 
 amalgams which can be obtained from ammonia by. various process- 
 es, that the proofs of alkali being also a metallic oxyd are deduced. 
 
 Thus, then, the three alkalies, two of which had always been con- 
 sidered as simple bodies, have now lost all claim to that title, and I 
 -have accordingly classed the alkalies amongst .the compounds, 
 whose properties I shall treat of in a future conversation. 
 
 Emily. What are the other newly discovered metals which you 
 have alluded to in your list of simple bodies ? 
 
 697. How may potassium be obtained in large quantities ? 
 
 698. In the experiment for obtaining potassium, why did the ox- 
 ygen quit that substance ? 
 
 699. What was the next substance submitted to the influence of 
 the ..Voltaic battery ? 
 
 700. -What was the effect ? 
 
 70.1. What is the substance produced by the decomposition of 
 Sodaxalied ? 
 
 15 
 
170 METALS. 
 
 Mrs. B. They are the metals of the earth which became next the 
 object of Sir H. Davy's researches ; these bodies,had never yet been 
 decomposed, though they were strongly suspected, not only of being 
 compounds, but of being- metallic oxyds. From the circumstance 
 of their incombustibility, it was conjectured, with some plausibility, 
 that they might possibly be bodies that had been already burnt. 
 
 Caroline. And metals, when oxydated, become, to all appear- 
 ance, a kind of earthy substance. 
 
 Mrs. B. They have, besides, several features of resemblance with 
 metallic oxyds ; Sir H.Davy had, therefore, great reason to be 
 sanguine in his expectations of decomposing them; and he was not 
 disappointed. He could not, however, succeed in obtaining the ba- 
 sis of the earths in a pure separate state ; but metallic alloys were 
 formed with other metals, which sufficiently proved the existence 
 of the metallic basis of the earths. 
 
 The last class of new metallic bodies which Sir H. Davy discov- 
 ered, was obtained from the three undecorn pounded acids, the bora- 
 cic, the fluoric, and the muriatic acids ; but as you are entirely un- 
 acquainted with these bodies, 1 shall reserve the account of their 
 decomposition, till we come to treat of their properties as-acids. 
 
 Thus in the course of twoyears, by the unparalleled exertions of 
 a single individual, chemical science has assumed a new aspect. 
 Bodies have been brought to light which the human eye never be- 
 fore beheld, and which might have remained eternally concealed 
 under their impenetrable disguise. 
 
 It is impossible, at the present period, to appreciate, to their full 
 extent, the consequences which science or the arts may derive from 
 these discoveries ; we may, however, anticipate the most important 
 results. 
 
 In chemical analysis, we are now in possession of more energet- 
 ic agents of decomposition than were ever before known. 
 
 In geology, new views are opened, which will probably operate a 
 revolution in that obscure and difficult science. It is already prov- 
 ed that all the earths, and, in fact, the solid surface of this globe, 
 are metallic bodies mineralized by oxygen, and as our planet has 
 been calculated to be considerably more dense upon the whole than 
 it is on the surface, it is mere reasonable to suppose that the interi- 
 or of the earth is composed of a metallic mass, the surface of which 
 only has been mineralized by the atmosphere. 
 
 The eruptions of volcanoes, thosestupendous problems of nature, 
 
 admit now of an easy explanation.* For if the bowels of the earth 
 
 are the grand recess of these newly discovered inflammable bodies, 
 
 ' whenever water penetrates into them, combustions and explosions 
 
 * It is always easy to form a theory. But an explanation of the^e 
 " stupendous problems of nature," we believe has not yet been de- 
 monstrated to the satisfaction of all, though great learning and im- 
 
 702. What peculiarities have the new metals, discovered by Sir 
 
 ; H. Davy ? 
 
 703. What reason had Sir H. Davy for supposing the metals 
 might be decomposed ? 
 
 704. What are earths supposed to be ? 
 
 705. What is supposed to form the principal interior part of. oar 
 
ON THE ATTRACTION OF COMPOSITION. 171 
 
 must take place ; and it is remarkable that the lava which is thrown 
 out, is the very kind of substance which might be expected to re- 
 sult from these combustions. 
 
 I must now take tny leave of you ; we have had a very Ion? con- 
 versation to-day, and I hope you will be able to recollect what you 
 have learnt. At our next interview, we shall enter on a new sub- 
 ject. 
 
 CONVERSATION XIII. 
 
 ON THE ATTRACTION OP COMPOSITION. 
 
 Mrs. J5. Having completed our examination of the simp'e or el- 
 ementary bodies, we are now to proceed to those of a compound 
 nature ; but,, before w< enter on this extensive subject, it will be 
 necessary to make you acquainted with the principal Jaws by which 
 chemical combinations are governed. 
 
 You recollect, I hope, what we formerly said of the nature of the 
 attraction of composition, or chemical attraction, or affinity, as it 
 is also called. 
 
 Emily. Yes, I think, perfectly; it is the attraction that subsists 
 between bodies of a different nature, which occasions them to com- 
 bine and form a compound, when they come in contact ; and, ac- 
 cording to Sir H. Davy's opinion, this effect is produced by the 
 attraction of the opposite electricities, which prevailed in bodiesof 
 different kinds. 
 
 Mrs. B. Very well ; your definition comprehends the first law 
 of chemical attraction, which is, l\\at it takes place only between bod- 
 ies of a different nature ; as, fur instance, between an acid and an 
 alkali; between oxygen and a metal, &c. 
 
 Caroline. That we un 'erstand of course ; for the attraction be- 
 tween particles of a s.trnl .r nature is that of aggregation, or cohe- 
 sion, which is independent of anv chemical power. 
 
 Mrs. B. Thesecond law of chemical attraction, is, that it tdket 
 place only between the most minute particles of bodies ; therefore, the 
 
 mense labor has been bestowed on the subject! If the " easy ex- 
 planation" is founded on the data here proposed, viz. that the solid 
 surface of our globe consists of nothing except metals and oxygen, 
 such a theory in the present state of knowledge, must chiefly con- 
 sist of supposition piled on supposition ; there being as yet no proof 
 that the crust of the earth is formed only of these two elements. 
 C. 
 
 706. How are volcanoes accounted for ? 
 
 707. What do you understand by the attraction of composition ? 
 708 What cause does Sir H. Davy assign for the attraction be- 
 tween bodies of a different nature ? 
 
 709. What is the first law of chemical attraction ? 
 
 710. What is the attraction between particles of a similar na- 
 ture called ? 
 
 711. What the second law of chemical attraction f 
 
172 ON THE ATTRACTION 
 
 more you divide the particles of the bodies to be combined, the 
 more readily they act upon each other. 
 
 Caroline. That is again a circumstance which we might have in- 
 ferred; for the finer ihe particles of the two substances are, the 
 more easily and perfectly they willcomein contact with each other, 
 which must greatly facilitate their union. It was for this purpose, 
 you said, that you used iron filings, in preference to wires or pieces 
 of iron, for the decomposition of water. 
 
 Mrs. B. It was once supposed that no mechanical power could 
 divide bodies into particles sufficiently minute/or them 10 act on 
 each other ; and that, in order to produce the extreme division re- 
 quisite for a chemical action, one, if not both of the bodies, should 
 be in a fluid slate. There are, however, a few instances in which 
 two solid bodies, very finely pulverized, exert a chemical action on 
 one another;* but such exceptions to the general rule are very 
 rare indeed. 
 
 Emily. In all the combinations that we have hitherto seen, one 
 of the constituents has, 1 believe, been either liquid or aeriform. 
 In combustion, for instance, the oxygen is taken from the atmos- 
 phere, in which it existed in a state of gas ; and whenever we 
 have seen acids combine with metals or with alkalies, they were 
 Cither in a liquid or an aeriform state. 
 
 Mrs. B. The third law of chemical attraction is, that it can take 
 place between two, three, four, or even a greater number of bodies. 
 
 Caroline. Oxydsand acids are bodies composed of two constitu- 
 ents, but 1 recollect rid instance of the combination of a greater 
 number of principles. 
 
 Mrs. B. The compound salts, formed by the union of the met- 
 als with acids, are composed of three principles. And there are 
 salts formed by the combination of the alkalies with the earths 
 which are of a similar description. 
 
 Caroline. Are they of the same kind as the metallic salts ? 
 
 Mrs. B. Yes ; they are very analogous in their nature, although 
 different in many of their properties. 
 
 A methodical nomenclature, similar to that of the acids, has been 
 adopted for the compound salts, Each individual salt derives its 
 name from its constituent parts, so that every name implies a 
 knowledge of the composition of the salt. 
 
 The three alkalies, the alkaline earths, and the metals, are called 
 salilable bases or radic.als, and the acids, snlifying principhs. The 
 name of each salt is composed both of (hat of the acid and the salifi- 
 able base ; and it terminates in at or it according to the degree of the 
 oxygenation of the acid. Thus, for instance, all those salts which 
 are formed by the combination of the sulphuric acid with any of the 
 salifiable bases, are Called sulphats, and the name of the radical is 
 
 *This is the case with muriate of ammonia and quick lime. C. 
 
 712. What is necessary in order that chemical action take place 
 between different bodies ? 
 
 713. What the third law of chemical attraction ? 
 
 714. How are con pound salts formed ? 
 
 71?. What are called salifiable bases or radicals ? 
 
 716. What are called salifying principles ? 
 
 717. How do salts ending in ate differ from those ending in etc ? 
 
OF COMPOSITION. 173 
 
 added for the specific distinction of the salt ; if it be potash, it will 
 compose a sulphat of potash, ; if ammonia, sulphat of ammonia, &c. 
 Emily. The crystals which we obtained from the combination of 
 iron and sulphuric acid were therefore sulphat of iron. 
 
 Mrs. B. Precisely ; and those which we prepared by dissolving 
 copper in nitric acid, nitrat of copper, and so on. But this is not 
 all ; if the salt be formed by that class of acids which end in ous, 
 (which you know indicates a less degree of oxygenation) the termi- 
 nation of the name of the salt will be in it, as sulphit of potash, sul- 
 phit of ammonia, &c. 
 
 Emily. There must bean immense number of compound salts, 
 since there is so great a variety of salifiable radicals, as well as of 
 salifying principles. 
 
 *Mrs. B. Their real number cannot be ascertained, since it in- 
 creases every day. But we must not proceed further in the investi- 
 gation of the compound salts, until we have completed the exami- 
 nation of the nature of the ingredients of which they are composed. 
 
 The fourth law of chemical attraction is, that o 'change of 'temper- 
 ature always takes place at the moment tf combination. This arises 
 from the extrication of the two electricities in the form of caloric, 
 which always occurs when bodies unite ; and also sometimes in 
 part from a change of capacity in the bodies for hent, which always 
 takes place when the combination is attended with an increase of 
 density, but more especially when the compound passes from the li- 
 quid to the solid form. I shall now show you a striking instance of 
 a change of temperature from chemical union, merely by pouring 
 some nitrous acid on this small quantity of oil of turpentine, the oil 
 will instantly combine with the oxygen of the acid, and produce a 
 considerable change of temperature. 
 
 Caroline. What a blaze ! The temperature of the oil and the 
 acid must be greatly raised, indeed, to procure such a violent com- 
 bustion. 
 
 Mrs. B. There is, however, a pecuHarity in this combustion, 
 which is, that the oxygen, instead of being derived from the atmos- 
 pheric air alone, is principally supplied by the acid itself. 
 
 Emily. And are not all combustions instances of the change of 
 temperature produced by the chemical combination of two bodies? 
 
 Jlrs. B. Undoubtedly ; when oxygen loses its gaseous form, in 
 order to combine with a solid body, it becomes condensed, and the 
 caloric evolved produces the elevation of temperature. The spe- 
 cific gravity of bodies is at the same time altered by chemical com- 
 bination ; for in consequence of a change of capacity for heat, a 
 changeof density roust be produced. 
 
 Caroline. That was the case with the sulphuric acid and water, 
 which, by being mixed together, gave out a great deal of heat, 
 and increased in density. 
 
 718. How do acids ending in ic differ from those ending in ous ? 
 
 719. What is the fourth law of chemical attraction ? 
 
 720. From what does the changeof temperature arise ? 
 
 721. What is an instance of increase of temperature from chem- 
 tcal union ? 
 
 722. Is the specific gravity of bodies affected by chemical com- 
 bination? 
 
 15* 
 
174 OX THE ATTRACTION 
 
 Mrs. B. The fifth law of chemical attraction is, that the proper- 
 ties which characterize bodies, when separate, are altered or destroy- 
 ed by their combination. 
 
 Caroline. Certainly ; what, for instance, can be so different from 
 water, as the hydrogen and oxygen gases ? 
 
 Emily. Or what more unlike sulphat of iron, than iron or sul- 
 phuric acid ? 
 
 Mrs. B. Every chemical combination is an illustration of this 
 rule. But let us proceed 
 
 The sixth law is, that the force of chemical affinity between the con- 
 stituents of a body, is estimated by that which is required for their 
 separation. This force is not always proportional to the facility 
 with which bodies unite ; for manganese, for instance, which you 
 know, is so much disposed to unite with oxygen, that it is never 
 found in a metallic state, yields it more easily than any other metal. 
 
 Emily. But, Mrs. B.,you speak of estimating the force of attrac- 
 tion between bodies, by the force required to separate them ; how 
 can you measure these forces ? 
 
 Mrs. B. They cannot be precisely measured, but they are com- 
 paratively ascertained by experiment, and can be represented by 
 numhers which express, at least by approximation, the relative de- 
 grees of attraction. 
 
 The seventh law is, that bodies have amongst themselves different de- 
 grees of attraction. Upon this law, (which you may have discover- 
 ed yourselves, long since,] the whole science of chemistry depends, 
 for it is by means of the various degrees of affinity which bodies 
 have for each other, that all the chemical compositions and decom- 
 positions are effected. Every chemical fact or experiment is an 
 instance of the same kind ; and whenever the decomposition of a 
 body is performed by the addition of any single new substance, it is 
 said to be effected by simple elective attractions. But it often happens 
 that no simple substance will decompose a body, and that, in order 
 to effect this, you must offer to the compound a body which is itself 
 composed of two, or sometimes three principles, which would not, 
 each separately, perform the decomposition. In this case there aro 
 two new compounds formed in consequence of a reciprocal decom- 
 position and recomposition. All instances of this kind are called 
 double elective attractions. 
 
 Caroline. I confess I do not understand this clearly. 
 
 Mrs. B. You will easily comprehend it, by the assistance of this 
 diagram, in which the reciprocal forces of attraction are represent* 
 ed by numbers : 
 
 723. What is the fifth law of chemical attraction ? 
 
 724. What is the sixth law of chemical attraction ? 
 
 725. What is the seventh law of chemical attraction ? 
 
 726. Upon what does the whole science of chemistry depend ? 
 
 727. What is a simple elective attraction ? 
 
 728. What is a double elective attraction ? 
 
or COMPOSITION 4 175 
 
 Original Compound. 
 Sulphatof Soda. 
 
 Result. 
 Nitrat 
 of Soda 
 
 Soda 8 Sulphuric Acid 
 
 < 
 
 Result. 
 
 7 DivelUnt Attractions 6-13 Y Sulphat 
 
 of Lime 
 
 Nitric Acid 4 Lime 
 12 
 
 Original Compound. 
 ISitrate of Lime. 
 
 We here suppose that we are to decompose sulphat of soda; that 
 is, to separate the acid from the alkali ; if for this purpose, we add 
 some lime, in order to make it combine with the acid, we shall fail 
 in our attempt, because the soda and Ihe sulphuric acid attract each 
 other by a force which is superior, and, (by way of supposition) is 
 represented by the number 8 ; while the lime tends to unite with 
 this acid by an affinity equal only to the number 6. It is plain, 
 therefore, that the sulphat of soda will not be decomposed, since a 
 force equal to 8 cannot be overcome by a force equal only to 6. 
 
 Caroline. So far, this appears very clear. 
 
 JMrs. B. If on the other hand we endeavour to decompose thi 
 alt by nitric acid, which tends to combine with soda, we shall be 
 equally unsuccessful, as nitric acid tends to unite with the alkali by 
 a force equal only to 7. 
 
 In neither of these cases of simple electire attraction, therefore, 
 can we accomplish our purpose. But let us previously combine 
 tog-ether the lime and nitric acid, so as to form a nitrate of lime, a. 
 compound salt, the constituents of which are united by a power 
 equal to 4. If then we present this compound to the sulphat of so* 
 da, a decomposition will ensue, because the sum of the forces which 
 tend to preserve the two salts in their actual slate, is not equal to 
 that of the forces which tend to decompose them, and to form new 
 combinations. The nitric acid, therefore, will combine with th* 
 and the sulphuric acid with the lime.* 
 
 * Suppose we say thus. The sulphuric acid attracts soda with a 
 stronger force than it does lime* and toda has a stronger affinity for 
 sulphuric add than it has for nitric acid. It is plain then, that nei* 
 ther lime nor nitric acid alone will decompose the sulphat of soda. 
 Now if we unite the nitric acid and lime, wo form nitrate of lime. 
 
 729- What is represented in the diagram ? 
 
 730. What it said in the note of the subject of this diagram f 
 
176 ON THE ATTRACTION 
 
 Caroline. I understand you now very well. This double effect 
 takes place because the numbers 8 and 4, which represent the de- 
 grees of attraction of ihe constituents of the two original salis, make 
 a sum less than the numbers 7 and 6, which represent the degrees 
 of attraction of the two new compounds that wiil io consequence 
 be formed. 
 
 Mrs. B. Precisely PO. 
 
 Caroline. But what is the meaning of quiescent and divellent for- 
 ces, which are written in the diagram ? 
 
 Mrs. B. Quiescent forces nre those which tend to preserve com- 
 pounds in a state of rest, or such as they .actually are ; divellent 
 forces, those which tend to destroy that state of combination, and 
 to form new compounds. 
 
 These are the principal circumstances relative to the doctrine of 
 chemical attractions, which have r>een laid down as rules by mod- 
 ern chemists : a few others might be mentioned respecting the 
 same theory, but of less importance, and such as would take us too 
 far from our plan. I should however, not omit to mention that Mr. 
 Berthollet, a celebrated French chemist, has questioned the uni- 
 form operation of elective attraction, and has advanced the opinion 
 that, in chemical combinations, the changes which take place and 
 the proportions in which bodies combine, depend not only upon the 
 affinities, but, also, in some degree, on the respective qualities of 
 the substances concerned, on the heat applied during the process, 
 and some other circumstances. 
 
 Caroline. In that case, I suppose, there would hardly be two 
 compounds exactly similar, though composed of the same materials ? 
 
 Mrs. B. On the contrary it is found that a remarkable uniformity 
 prevails, as to proportions, between the ingredients of bodies of 
 similar composition. Thus water, as you may recollect to have 
 seen in a former conversation, is composed of two volumes of hy- 
 drogen gas to one of oxygen, and tin's is always found to be precise- 
 ly the proportion of its constituents, from whatever source the wa- 
 ter be derived. The same uniformity prevails with rerrard to the 
 various salts ; the acid and alkali, in each kind of salt, being always 
 found to combine in the same proportions. Sometimes, it is true, 
 the same acid, and the same alkali are capable of making two dis- 
 tinct kinds of salts : but in all these cases it is found that one of the 
 salts contains just twice, or in some instances, thrice as much acid, 
 or alkali, as the other.* 
 
 But the nitric acid has not so strong an affinity for the lime as it has 
 for soda. On mixing the two t salts in solution therefore, the nitric 
 acid quits the lime, and combines with the soda. This leaves the 
 sulphuric acid and the lime free and uncombined ; they then unite 
 and form sulphat of lime. C. 
 
 * The student already understands, that in chemical combinations 
 the union takes place only between the particles, or atoms, of sub- 
 
 731. What are quiescent forces ? 
 
 732. What are divellent forces ? 
 
 733. VVhat was the opinion of Berthollet upon chemical combi- 
 nations ? 
 
 734. What remarkable uniformity is found to exist in chemical 
 combinations ? 
 
OP COMPOSITION. 177 
 
 Emily, If the proportions in which bodies combine are so con- 
 stint and so welt defined, how can Mr. Berthollet's remark be re* 
 conciled with this uniform system of combination ? 
 
 Mrs. B. Great as that philosopher'* authority is in ghemistry, it 
 is now generally supposed that his doubts on this subject were, in a 
 great degree, groundless ; and that the exceptions he has observed 
 in the laws of definite proportions, have been only apparent, and 
 may beaccounfed for consistently with those laws. 
 
 Emily. I think I now understand this law of de6nite proportions 
 very well, so far as it regards the gases, sueh as oxygen ind hydro- 
 gen, in the instance you have just mentioned ; but in the case of 
 acids and alkalies, when -the bodies are either liquid or solid. I do 
 not conceive how their bulks or volumes can be measured in order 
 to ascertain the proportion in which they combine. 
 
 Jllrs. B. Your question is quite in point ; the fact is, that (he law 
 of combination by volume^ does not prevail in regard to liquids and 
 solids. In these, we must leave the circumstance of bulk entirely 
 out of consideration. It is to their weight that we must attend, in 
 determining the proportions in which they combine ; and, according- 
 ly, if we take the combining substances in a state of perfect purity, 
 an 1 ascertain with great accuracy, once for all, the proportions by 
 toeighi, in which they unite, we shall find that in every other instance 
 in which these substances have an opportunity of ..combining, they 
 w-il unite in the same proportions, and in no other unless it be in 
 su :h proportions that one of the bodies shall be. in weight, exactly 
 lr. ible, triple, or quadruple what it was in the former combination. 
 
 stances. These atoms, it is supposed, are indivisible, being the ul- 
 tir iate particles of which bodies are composed. In chemical com- 
 bi lations, then, where substances a- e capable of uniting in only one 
 proportion, this must beatom to atom. Thus oxygen and hydrogen 
 uriteorily in the proportions of loO of the former to 750 of the lat- 
 te by weight. Here an atom of oxygen unites to an atom of hy- 
 drogen to form water ; but the afons of oxygen are seven and an 
 half times heavier than those of hydrogen. 
 
 When substances unite in several proportions, the second and 
 third are always multiples of the first. Thus 100 parts of manga- 
 nr.se will unite to 14, 28.42, or 56 of oxygen, but not with any in- 
 termediate quantity, as with 12, 20, 60, &c. This law of definite 
 proportions, so far as is known, holds good, where the resulting 
 cc opound differs widely from either of the substances of which it 
 is composed, as in the salts, compound minerals. Sfc. The theory 
 of definite proportions is explained bv supposing that a substance 
 which we shall call A., unites with another substance, B., atom to 
 atom, and that ibis forms a certain compound. When they unite in 
 the second proportion, two atoms of B. unite to one of A., and this 
 forms another compound, and so on, until the atoms of A. can unite 
 to no more of B. C. 
 
 735. In what proportions do oxygen and hydrogen unite to form 
 water ? 
 
 736. How much heavier is oxygen than hydrogen ? 
 
 737. When acids and alkalies unite in several proportions, what 
 relation do these proportions bear to each other ? 
 
178 ON THE ATTRACTION 
 
 Caroline* This requires a good deal of attention to be well un- 
 derstood ; and I should like to have it illustrated by some particu- 
 lar examples of these different combinations. ^(^^^H 
 
 Mrs. B. Nothing- easier than to satisfy you in this respect. For 
 instance, with regard to bulk, nitrogen gas is capable of combining 
 with oxygen gas, in different proportions ; thus, one volume of ni- 
 trogen, by combining with one volume of oxygen, forms the sub- 
 stance called nitrous gas ; with two volumes of oxygen, it forms 
 nitrous acid- gas, &c. And with regard to solids and liquids, the 
 proportions of which are estimated by weight, I may mention, as 
 an exanYple, the case of the salt called sulpha t of potash, in which 
 a given weight of potash may combine with two different propor- 
 tions of sulphuric acid ; but the quantity of acid in one case is ex- 
 actly double what itHf in the other. 
 
 Emily. And pray what can be the cause of this singular unifor- 
 mity in the law of'combmiation ? 
 
 Mrs. B. Philosophers have not been able to give us any decisive 
 information upon this point ; but they have attempted to explain it 
 in the following manner : since chemical combination takes place 
 between the most minute particles of bodies, may we not suppose 
 that the smallest particles or portions in which bodies combine, (nd 
 which we may. call chemical atoms,} are capable of uniting together 
 one to one, or sometimes one to two, or one to three, &c., but that 
 they cannot combine in any intermediate proportion. 
 
 Emily. But if an atom was broken into two, an interrnediatecom- 
 bination would be obtained ? 
 
 Mrs. B. Yes; but the nature of the atom is incompatible with 
 the idea of any farther division ; since the chemical atom is the 
 smallest quantity which chemistry can obtain, and such as no me- 
 chanic means can possibly subdivide. 
 
 Caroline. And pray, what is the use of all this doctrine of defi- 
 nite proportions ? 
 
 Mrs. B. Ilia very considerable ; for it enables chemists to form 
 tables, by which they can see at one glance the composition of all 
 the bodies which have been accurately analyzed, and ascertain in 
 an instant what quantity of one body will be necessary to decom- 
 pose a certain quantity of another ; and, in general, such tables 
 serve to present, in one view, the result of any chemical decompo- 
 sition, and the quantities of the new compounds formed ; by which 
 means, a considerable saving of labor is gained, either in enabling 
 us to calculate beforehand the results of any manufacturing opera- 
 tions; or in estimating those obtained in analytical processes. But 
 I perceive the subject is becoming rather too intricate for us. We 
 roust not run the risk of entering into difficulties which might con- 
 fuse your ideas, and throw more obscurity than interest upon this 
 abstruse part of the philosophy of chemistry.* 
 
 * This would have been the proper place for mentioning Dr. 
 Wollaston's scale of chemical equivalents; but the subject has been 
 thought to imply some considerations not sufficiently elementary for 
 the purpose of this book. It may, however, be just mentioned, that 
 the principal object of this scale is to give a tabular view of the 
 proportions in which the several acids and bases combine in forming 
 their respective salts, and likewise to indicate the equivalent com- 
 pounds which result from their decomposition. The great utility of 
 
OP COMPOSITION. 179 
 
 ' 
 
 Caroline. Pray, Mrs. B., can you decompose a salt by means of 
 electricity, in the same way as we decompose water ? 
 
 Mrs. B. Undoubtedly : and 1 am glad this question occurred to 
 you, because it gives me an opportunity of showing you some very 
 interesting experiments on the subject. 
 
 If we dissolve a quantity, however small, of any salt in a glass of 
 water, and if we plunge into it the extremities of the wires, which 
 proceed from the two ends of -the Voltaic battery, the salt will be 
 gradually decomposed, the acid being attracted by the positive, and 
 the alkali by the negative wire. 
 
 Emily. But how can you render that decomposition perceptible? 
 
 Mrs. J5, By placing in contact with the extremities of each wire, 
 in the solution, pieces of paper stained with certain vegetable co- 
 lours, which are altered by the contact of an acid or an alkali. 
 Thus this blue vegetable preparation called litmus, becomes red 
 when touched by an acid ; and the juice of violets becomes green 
 by the contact of an alkali. 
 
 But the experiment can be made in a much more distinct manner, 
 by receiving the extremities of the wires into different vessels, so 
 that the alkali shall appear in one vessel, and the acid in the other. 
 
 Caroline. But then the Voltaic circle will not be completed ; 
 how can the effect ^e produced ? 
 
 Mrs. B. You are right ; I ought to have added that the two ves- 
 sels must be connected together by some interposed substance, capa- 
 ble of conducting electricity. A piece of moistened cotton wick an- 
 swers this purpose very well. You see that the cotton has one end 
 Fig. 31. 
 
 
 f Chemical de 
 
 omposition by the Voltaic Battery. 
 
 immersed in one glass, and the other end in the other, so as to estab- 
 lish a communication- between any fluids contained in them. We 
 
 this scale, and the peculiar properties which it possesses, though not 
 very easily described, may, be readily understood on inspecting the 
 instrument, which should be in the hands of every chemical student. 
 
 ,738. Can a salt be decomposed by means of electricity ? 
 ^739. When a salt is decomposed by Galvanism, at which .pole 
 lubes the acid appear ? 
 "740. How would you explain Fig. 31 f 
 
180 ON THE ATTRACTION 
 
 shall now put into each of the glasses a little glauber salt, or sulphat 
 of soda, (which consists of an acid and alkuli,) and then we shall 
 fill the glasses with water, which will dissolve the salt. Let us now 
 connect the glasses by means of the wires, (e. d.) with the two ends 
 of the battery, thus .... 
 
 Caroline. 'The wires are already giving out small bubbles : is this 
 owing to the decomposition of tl e salt? 
 
 Mrs. B. No : these are bubbles produced by the decomposition 
 of the water, as you saw in the former experiment. In order to 
 render the separation of the acid from the alkali, visible, I pour into 
 the glass (a) which is connected with the positive wire, a few drops 
 of a solution of litmus, which the least quantity of acid turns red ; 
 and into the other glass, (b) which is connected with the negative 
 wire, 1 pour a few drops of the juice of violets .... 
 
 Emily. The blue solution is already turning red all round the 
 'Wire. 
 
 Caroline. And the violet solution is beginning to turn green. 
 This is indeed very singular ! 
 
 Mrs. B. You will be still more astonished when we vary the ex- 
 periment in this manner These three glasses (f, g, h,) are, as in 
 Fig. 32. the former instance, 
 
 connected together by 
 wetted cotton, but the 
 middle one alone con- 
 tains a saline solution, 
 the two others contain- 
 ing only distilled water, 
 coloured as before by 
 vegetable infusions. 
 Yet, on making the coo* 
 
 nect '. on ^ ^ fa 
 
 ry, the alkali will appear in the negative glass, (h,) and the acid in 
 the positive glass (f,) though neither of them contained any saline 
 matter. 
 
 Emily. So that the acid and alkali must he conveyed right and 
 left from the central glass, into the other glasses, by means of the 
 -connecting moistened cotton ? 
 
 Mrs. B. Exactly so ; and you may render the experiment still 
 more striking by putting into the central glass (k,) an alkaline solu. 
 Fig. 33. tion, the glauber salt be- 
 
 . -, m. ' n placed into the ne- 
 ' ^^^^ K ^n&v * WL galive glass< ^ and tbe 
 
 positive glass, (i) con- 
 tain ing only water. The 
 acid will be attracted by 
 the positive wire, (m) 
 and will actually appear 
 in the vessel (i,) after 
 passing through -the al- 
 
 Ltanee. of Chemical decon,po,ition b, the Voltaic Batter,. .^IJne^olution (k) W> tft , 
 
 out combining with it, although, you know, acids and alkalies 
 o much disposed to combine. But this conversation has alre are 
 _ ad.v 
 
 741. How will you explain the experiment illustrated in Fig. 32? 
 . '742. How will you explain the experiment illustrated in Fig. 33? 
 
ALKALIES. 181 
 
 much exceeded our usual limits, and we cannot enlarge more up- 
 on this interesting subject at present. 
 
 CONVERSATION XIV. 
 
 ON ALKALIES. 
 
 Mrs. B. Having now given you some idea of the laws by which 
 chemical attractions are governed, we may proceed to the examina- 
 tion of bodies which are formed in consequence of these attractions. 
 
 The first class of compounds that present themselves to our notice, 
 in our gradual ascent to the most complicated combinations, are bo- 
 dies composed of only two principles. The sulphurets, phosphorets, 
 carburets, &c. are of this description ; but the most numerous and 
 important of these compounds are the combinations of oxygen with 
 the various simple substances with which it has a tendency to unite. 
 Of these you have already acquired some knowledge, but it will be 
 necessary to enter into further particulars respecting the nature and 
 properties of those most deserving our notice. Of this class are the 
 ALKALIES and the EARTHS, which we shall successively examine. 
 
 We shall first take a view of the alkalies, of which there are three, 
 viz. POTASH, SODA, and AMMONIA. The two first are czlledjixed al- 
 kalies,* because they exist in a solid form at the temperature of the 
 atmosphere, and require a great heat to be volatilized. They consist 
 as you already know, of metallic bases combined with oxygen. ID 
 potash, the proportions are about eighty-six parts of potassium, to 
 fourteen of oxygen ; and in soda, seventy-seven parts of sodium to 
 twenty-three of oxygen. The third alkali, ammonia, has been dis- 
 tinguished by the name of volatile alkali, because its natural form is 
 that of gas. Its composition is of a more complicated nature, of 
 which we shall speak hereafter. 
 
 Some of the earths bear so strong a resemblance in their proper- 
 ties to the alkalies, that it is difficult to know under which head to 
 place them. The celebrated French chemist, Fourcroy, has classed 
 
 * It has already been stated that a third fixed alkali has lately been 
 discovered by Mr. Arfvredson, which has been called lithion. It was 
 first found in a Swedish mineral called pelalite : but has since been 
 detected in some other minerals. Though this alkali resembles pot- 
 ash and soda in its general properties, yet it has decidedly an alkaline 
 substance of its own, capableof forming different salts with the acids, 
 and having in particular the property of combining with much 
 greater proportions of acid than the other alkalies. 
 
 743. What is the first class of compounds which present them- 
 se lves to our notice ? 
 
 744. Which are instances of this description ? 
 
 745. What are the alkalies? 
 
 746. Why are potash and soda called fixed alkalies? 
 
 747. Of what do the flexed alkalies consist ? 
 
 748. Why is ammonia called volatile? 
 
 16 
 
182 POTASH. 
 
 two of them (barytes and strontites) with the alkalies; but as lime 
 and magnesia have almost an equal title to that rank, I think it bet- 
 ter not to separate them, and therefore have adopted the common 
 method of classing- them with the earths, and of distinguishing them 
 by the name of alkaline earths. 
 
 The general properties of alkalies are, an acrid burning taste, a 
 pungent smell, and a caustic action on the skin and flesh. 
 
 Caroline. I wonder they should be caustic, Mrs. B., since they 
 contain so little oxygen. 
 
 Mrs. B. Whatever substance has an affinity for any one of the 
 constituents of animal matter, sufficiently powerful to decompose it, 
 is entitled to the appellation of caustic. The alkalies, in their pure 
 state, have a very strong attraction for water, for hydrogen, and for 
 carbon, which, you know, are the constituent principles of oil, and it 
 is chiefly by absorbing these substances from animal matter that 
 they effect its decomposition ; for, when diluted with a sufficient 
 quantity of water, or combined with any oily substance, they lose 
 their causticity. 
 
 But to return to the general properties of alkalies they change, 
 as we have already seen, the colour of syrup of violets, and other blue 
 vegetable infusions to green ; and have, in general, a very great 
 tendency to unite with acids, although the respective qualities of 
 these two classes of bodies form a remarkable contrast. 
 
 We shall examine the result of the combination of acids and alka- 
 lies more particularly hereafter. It will be sufficient at present to 
 inform you, that whenever acids are brought in contact with alka- 
 lies or alkaline earths, they unite with a remarkable eagerness, and 
 form r compounds perfectly differentjfrom either of their constituents ; 
 these bodies are called neutral or compound salts. 
 
 The dry white powder which you see in this phial is pure caustic 
 POTASH ; it is very difficult to preserve it in this state, as it attracts, 
 with extreme avidity, the moisture from the atmosphere, and if the 
 air were not perfectly excluded, it would, in a very short time, be 
 actually melted. 
 
 Emily. It is then, I suppose, always found in a liquid state? 
 Mrs. B. No ; it exists in nature in a great variety of forms and 
 combinations, but it is never found in its pure separate state ; it is 
 combined with carbonic acid, with which it exists in every part of 
 the vegetable kingdom, and is most commonly obtained from the 
 ashes of vegetables, which are the residue that remains after all the 
 other parts have been volatilized by combustion. 
 
 Caroline. But you once said, that after all the volatile parts of a 
 vegetable were evaporated, the substance that remained was char- 
 coal ? 
 
 Mrs. B. I am surprised that you should still confound the processes 
 of volatilization and combustion. In order to procure charcoal, we 
 evaporate such parts as can be reduced to vapour by the operation 
 
 749. What are the general properties of alkalies ? 
 
 750. On what does the caustic property of alkalies depend ? 
 
 751. To what colour do the alkalies change the vegetable blues ? 
 
 752. How are neutral or compound salts formed ? 
 
 753. What would be the consequence if caustic potash were not 
 secluded from the air , ? 
 
POTASH. AOO 
 
 of heat alone ; but when we burn the vegetable, we burn the carbon 
 also, and convert it into carbonic acid gas. 
 
 Caroline. That is truest hope I shall make no more mistakes in 
 rny favourite theory of combustion. 
 
 Jflrs. B. Potash derives its name from the pots in which the re- 
 g-etables, from which it was obtained, used formerly to be burnt ; the 
 alkali remained mixed with the ashes at the bottom, and was thence 
 called potash. 
 
 Emily. The ashes of a wood fire, then, are potash, since they are 
 vegetable ashes? 
 
 JWrs. B. They always contain more or less potash, but are very 
 far from consisting of that substance alone, as they are a mixture of 
 various earths and salts which remain after the combustion of ve- 
 getables, and from which it is not easy to separate the alkali in its 
 pure form. The process by which potash is obtained, even in the im- 
 perfect state in which it is used in the arts, is much more complica- 
 ted than simple combustion. It was once deemed impossible to se- 
 parate it entirely from all foreign substances, and it is only in che- 
 mical laboratories that it is to be met with in the state of purity in 
 which you find it in this phial. Wood-ashes are, however, valuable 
 for the alkali which they contain, and are used for some purposes 
 without any further preparation. Purified in a certain degree, they 
 make what is commonly called pearl-ash, which is of great efficacy 
 in taking out grease, in washing Unep, &c.; for potash combines rea- 
 dily with oil or fat, with which it forms a compound well known to 
 you under the name of soap. 
 
 Caroline. Really ! Then 1 should think it would be better to wash 
 all linen with pearl-ash than with soap, as in the latter case, the al- 
 kali being already combined with oil, must be less efficacious in ex- 
 tracting grease. 
 
 JMrs. B. Its effects would be too powerful on fine linen, and 
 would injure its texture ; pearl-ash is therefore only used for that 
 which is of a strong, coarse kind. For the same reason, you can- 
 not wash your hands with plain potash ; but, when mixed with oil 
 in the form of soap, it is soft as well as cleansing, and is therefore 
 much better adapted to the purpose. 
 
 Caustic potash, as we already observed, acts on the skin, and ani- 
 mal fibre, in virtue of its attraction for water and oil, and converts 
 all animal matter into a kind of saponaceous jelly. 
 
 Emily. Are vegetables the only source from which potash can be 
 derived ? 
 
 Mrs. B. No : for though far most abndant in vegetables, it is by 
 no means confined to that class of bodies, being found also on the 
 surface of the earth, mixed with various minerals, especially with 
 earths and stones, whence it is supposed to be conveyed into vege- 
 tables by the roots of the plant. It is also met with, "though in very 
 
 754. From what is potash obtained ? 
 
 755. From what is the term potash derived ? 
 
 756. Of what do wood-ashes consist ? 
 
 757. How will soap assist in cleansing clothes from grease or oil ? 
 
 758. Why may not pearl ash be used for the purpose, without 
 being made into soap ? 
 
 759. Is potash confined to vegetables ? 
 
184 POTASH. 
 
 small quantities, in some animal substances. The most common state 
 of potash is that of carbonat ; I suppose you understand what that is ? 
 
 Emily. I believe so ; though I do not recollect that you ever 
 mentioned the word before. If I am not mistaken, it must be a com- 
 pound salt, formed by the union of carbonic acid with potash. 
 
 Mrs. B. Very true; you see how admirably the nomenclature of 
 modern chemistry is adapted to assist the memory ; when you hear 
 the name of a compound, you necessarily learu what are its consti- 
 tuent parts; and when you are acquainted with these constituents, 
 you can immediately name the compound which they form. 
 
 Caroline. Pray how were bodies arranged and distinguished be- 
 fore this nomenclature was introduced ? 
 
 Jtfrs. B. Chemistry was then a much more difficult study ; for 
 every substance had an arbitrary name, which it derived from the 
 person who discovered it, as Glauber's salts for instance ; or from 
 some other circumstance relative to it, though quite unconnected 
 with its real nature as potash. 
 
 These names have been retained for some of the simple bodies ; 
 for as this class is not numerous, and therefore can easily be re- 
 membered, it has not been thought necessary to change them. 
 
 Emily. Yet I think it would have rendered the new nomenclature 
 more complete to have methodized the names of the elementary, as 
 of the compound bodies, though it could not have been done in the, 
 same manner. But the names of the simple substances might have 
 indicated their nature, or, at least, some of their principal proper- 
 ties ; and if, like the acids and compound salts, all the simple bodies 
 bad asimilar termination, they would have been immediately known 
 as such. So complete and regular a nomenclature would, I think, 
 have given a clearer and more comprehensive view of chemistry 
 than the present, which is a medley of (he old and new terms. 
 
 Mrs. B. But you are not aware of the difficulty of introducing 
 into science an entire set of new terms ; it obliges all teachers and 
 professors to go to school again, and if some of the old names, that 
 are least exceptionable, were not left as an introduction to the new 
 ones, few people would have had industry and perseverance enough 
 to submit to the study of a completely new language ; and the infe- 
 rior classes of artists, who can only act from habit and routine, would, 
 at least for a time, have felt material inconvenience from a total 
 change of their habitual terms. From these considerations, Lavoi- 
 sier and his colleagues, who invented the new nomenclature, thought 
 it most prudent to leave a few links of the old chain, in order to con- 
 nect it with the new one. Besides, you may easily conceive the in- 
 convenience which might arise from giving a regular nomenclature 
 to substances, the simple nature of which is always uncertain; for 
 the new names might, perhaps, have proved to have been founded in 
 
 760. What is the most common state of potash? 
 
 761. What is carbonat? 
 
 762. How were bodies arranged and distinguished before the new 
 nomenclature was introduced ? 
 
 763. Why have the old chemical names been retained? 
 
 764. What inconvenience might arise from giving a regular no- 
 menclature to substances, the nature of which is uncertain ? 
 
POTASH. ISO 
 
 error. And, indeed, cautious as the inventors of tbe modern che- 
 mical language have been, it has already been found necessary to 
 modify it in many respects. In those few cases, however, in which 
 new terms have been adopted to designate simple bodies, those 
 names have been so contrived as to indicate one of the chief proper- 
 ties of the body in question ; this is the case with oxygen, which, as 
 I explained to you, signifies generator of acids ; and hydrogen go 
 nerator of water.* If all the elementary bodies had a similar ter- 
 mination, as you propose, it would be necessary to change the name 
 of any that might hereafter be found of a compound nature, which 
 would be very inconvenient in this age of discovery. 
 
 But to return to the alkalies. We shall now try to melt some of 
 this caustic potash in a little water, as a circumstance occurs du- 
 ring its solution very worthy of observation. Do you feel the heat 
 that is produced ? 
 
 Caroline. Yes, I do ; but is not this directly contrary to our theo- 
 ry of latent heat, according to which heat is disengaged wben fluids 
 become solid, and cold produced when solids are melted? 
 
 Mrs. B. The latter is really the case in all solutions; and if the 
 solution of caustic alkalies seems to make an exception to the rule, 
 it does not, I believe, form any solid objection to the theory. The 
 matter iay be explained thus : When water first comes in contact 
 with the potash, it produces an effect similar to the slacking of lime, 
 that is, the water is solidified in combining with the potash, and thus 
 loses Hs iatent heat ; this is the heat that you now feel, and which is, 
 therefore, produced not by the melting of the solid, but by thejglidi- 
 ficatiou of the fluid. But when there is more water than the potash 
 can absord and solidify, the latter then yields to the solvent ^^er 
 of the water; and if we do not perceive the oold produced by its 
 melting, it is because it is counter-balanced by the beat previously 
 disengaged. f 
 
 A very remarkable property of potash is the formation of glass by 
 its fusion with silicious earth. You are net yet acquainted with this 
 last substance, further than its being in the list of simple bodies. It 
 is sufficient, for the present, that you should know that sand and flint 
 are chiefly composed of it ; alone, it is infusible, but mixed with pot- 
 
 * It may here be observed, that even with regard to these two 
 bodies, the nomenclature is become exceptionable, since it is now 
 found that oxygen is one of the constituents of alkalies as well as of 
 acids, and in particular of the muriatic. 
 
 f This defence of the general theory, however plausible, is liable 
 to some obvious objections. The phenomenon might, perhaps, be 
 better accounted for, by supposing that a solution of alkali in water 
 has less capacity for heat than either water or alkali in their sepa- 
 rate state. 
 
 705. In the few cases where new names have been adopted to de- 
 signate simple substances, how have these names been contrived ? 
 
 766. What interesting circuimtaBce occurs if caustic potash is 
 melted in water? 
 
 767. How is glass made? 
 
 768. ]f caustic potash i$ put in water, why it heat disengaged? 
 
 !<* 
 
186 POTASH. 
 
 ash, it melts when exposed to the heat of a furnace, combines with 
 the alkali, and runs into glass. 
 
 Caroline. Who would ever have supposed that the same substance 
 which converts transparent oil into such an opaque body as soap, 
 should transform that opaque substance, sand, into transparent 
 glass ? 
 
 J\frs. B. The transparency, or opacity of bodies, does not, I con- 
 ceive, depend so much on their intimate nature, as upon the ar- 
 rangement of their particles : we cannot have a more striking in- 
 stance of this, than is afforded by the different states of carbon, 
 which, though it commonly appears in the form of a black, opaque 
 body, sometimes assumes the most dazzling, transparent form in 
 nature, that of diamond, which, you recollect, is carbon, which 
 in all probability, derives its beautiful transparency from the pecu- 
 liar arrangement of its particles during their crystallization. 
 
 Emily* I never should have supposed that the formation of glass 
 was so simple a process as you describe it. 
 
 Mrs. B. It is by no means an easy operation to make perfect 
 glass ; for if the sand or flint, from which the silicious earth is ob- 
 tained, be mixed with any metallic particles, or other substance, 
 which cannot be vitrified, the glass will be discoloured, or defaced, 
 by opaque specks. 
 
 Caroline. That 1 suppose, is the reason why objects so often ap- 
 pear irregular and distorted through a common glass window. 
 
 Mrs. B. This species of imperfection proceeds, 1 believe, from 
 another cause. It is extremely difficult to prevent the lower part 
 of the vessels, in which the materials of glass are fused, from con- 
 taining a more dense vitreous matter than the upper, on account of 
 the heavier ingredients falling to the bottom. When this happens, 
 it occasions the appearance of veins or waves in the glass, from the 
 difference of density in its several parts, which produces an irregu- 
 lar refraction of the rays of light which pass through it. 
 
 Another species of imperfection sometimes arises from the fusion 
 not being continued for a length of time sufficient to combine the 
 two ingredients completely, or from the due proportion of potash 
 and sttex (which are as two to one] not being carefully observed ; 
 the glass, in those cases, will be liable to alteration from the action 
 of the air, of salts, and especially of acids which will effect its de- 
 composition by combining with the potash, and forming compound 
 
 Emily. What an extremely useful substance potash is ! 
 
 Mrs. B. Besides the great importance of potash in the manufac- 
 tures of glass and soap, it is of very considerable utility in many of 
 the other arts, and in its combinations with several acids, particu- 
 larly the nitric, with which it forms saltpetre. 
 
 769. On what does the opacity of bodies depend ? 
 
 770. To what does a diamond owe its transparency ? 
 
 771. What is the occasion of the veins or waves discovered on 
 eorne glass ? , . f 
 
 772. What other imperfection sometimes occurs in the reading of 
 
 glass ? 
 
 773. Of what does saltpetre consist? 
 
AMMONIA. 187 
 
 Caroline. Then saltpetre must be anitrat of potash. But we are 
 not yet acquainted with the nitric acid. 
 
 Mrs. B. We shall therefore defer entering into the particulars of 
 these combinations till'we come to a general review of the compound 
 salts. In order to avoid confusion, it will be better at present to 
 confine ourselves to the alkalies. 
 
 Emily. Cannot you show us the change of colour which you said 
 the alkalies produced on blue vegetable infusions ? 
 
 Mrs. B. Yes, very easily. I shall dip a piece of white paper 
 into this syrup of violets, which, you see, is of a deep blue, and 
 dyes the paper of the same colour. As soon -as it is dry, we shall 
 dip it into a solution of potash, which, though itself colourless, will 
 turn the paper green.* 
 
 Caroline. So it has, indeed ! And do the other alkalies produce a 
 similar effect? 
 
 Mrs. B. Exactly the same. We may now proceed to SODA, 
 which, however important, will detain us but a very short time ; as 
 in all its general properties it very stroHgh resembles potash ; in- 
 deed, so great is their similitude, that t-hey have been long confound- 
 ed, and they can now scarcely be distinguished, except by the dif- 
 ference of the salts which they form with acids. 
 
 The great source of this alkali is the sea, where, combined with 
 a peculiar acid, it forms the salt with which the waters of the ocean 
 are so strongly impregnated. 
 
 Emily. Is not that the common table salt ? 
 
 Mrs. B. The very same ; but again we must postpone entering 
 into the particulars of this interesting combination, till we treat of 
 the neutral salts. Soda may be obtained from common salt ; but 
 the easiest and most usual method of procuring it is by the combus- 
 tion of marine plants, an operation perfectly analogous to that by 
 which potash is obtained from vegetables. 
 
 Emily. From what does soda derive its name ? 
 
 Mrs. B. From a plant called by us SODA, and by the Arabs KALI, 
 which affords it in great abundance. Kali has, indeed, given ita 
 name to the alkalies in general. 
 
 Caroline. Does soda form glass and soap in the same manner as 
 potash ? 
 
 * A very pretty experiment on the change of colours may be 
 made as follows : Make a tincture, by pouring boiling water on red 
 cabbage and let it stand a while. Put it into a phial. The colour 
 will be purple. Take two wine glasses, and into 'one put a few 
 drops of sulphuric acid, and into the other the same quantity of a 
 strong solution of potash. So little of either will do, that the glasses 
 may be inverted for a moment. Then pour the tincture into each, 
 and the one containing the acid will appear a most beautiful red, 
 and the other as beautiful a green. C. 
 
 774. What is the chemical name of saltpetre ? 
 
 775. How may blue vegetable colours be turned green ? 
 
 776. How does soda differ from potash ? 
 77T7. What is *the great sourc* of soda? 
 
 778. How maysoda be obtained? 
 
 779. 'From what does soda derive its name? 
 
188 AMMONIA. 
 
 Mrs. B. Yes, it does ; it is of equal importance in the arts, and is 
 even prefered to potash for some purposes ; but you will not be able 
 to distinguish their properties, till we examine the compound salts 
 which they form with acids ; we must therefore leave soda for the 
 present, and proceed to AMMONIA, or the VOLATILE ALKALI. 
 
 Emily. I long- to hear something of this alkali ; is it not of the 
 same nature as hartshorn ? 
 
 Mrs. B. Yes, it is, as you will see bye-and-bye- This alkali is 
 seldom found in nature in its pure state ; it is most commonly extrac- 
 ted from a compound salt,called sal. ammoniac, which was formerly 
 imported from Ammonia, a region of Lybia, from which both these 
 salts and the alkali derive their names. The crystals contained in 
 this bottle are specimens of this salt, which consist of a combina- 
 tion of ammonia and muriatic acid. 
 
 Caroline. Then it should be called muriat of ammonia ; for though 
 I am ignorant what muriatic acid is, yet I know that its combina- 
 tion with ammonia cannot but be so called ; and I am surprised to 
 see sal. ammoniac inscribed on the label. 
 
 Mrs. B. That is the name by which it has been so long known, 
 that the modern chemists have not yet succeeded in banishing it al. 
 together ; and it is still sold under that name by druggists, though by 
 scientific chemists it is more properly called muriat of ammonia. 
 
 Caroline* Both the popular and common name should be inscribed 
 on labels this would soon introduce the new nomenclature. 
 
 ily. By what means can the ammonia be separated from the 
 latic acid ? 
 
 Irs. B. By chemical attractions ; but this operation is too com- 
 plicated for you to understand till you are better acquainted with 
 the agency of affinities. 
 
 Emily. And when extracted from the salt, what kind of sub- 
 stance is ammonia P 
 
 Mrs. B. Its natural form, at the temperature of the atmosphere, 
 when free from combination, is that of gas ; and in this state it is 
 called ammoniacalgas. But it mixes very readily with water, and 
 can be thus obtained in a liquid form. 
 
 Caroline. You said that ammonia was more complicated in its 
 composition than the other .alkalies ; pray of what principles does 
 it consist ? 
 
 Mrs. J31c It was discovered a few years since,by Berthollet, a cel- 
 ebrated French chemist, that it consisted of about one part of hydro- 
 gen to four parts of nitrogen. Having heated ammoniacal gas un- 
 der a receiver, by causing the electrical spark to pass repeatedly 
 through it, he found that it increased considerably in bulk, lost all 
 ite alkaline properties, and was actually converted into hydrogen and 
 nitrogen gases ; and from the latest and most accurate experiments 
 
 780. Can glass and soap be formed from soda as well as from potash ? 
 
 781. From what does ammonia derive its name ? 
 
 782. From what is it mostly obtained ? 
 
 783. What is the proper chemical name of this volatile alkali ? 
 
 784. How can ammonia be separated from muriatic acid ? 
 
 785. How is ammoniacal gas obtained ? 
 
 786. Under what form does it appear when pure ? 
 
 787. Of what principles does ammonia consist ? 
 
AMMONIA. 189 
 
 the proportions appear to be, one volume of nitrogen gas, to three 
 of oxygen gas.* 
 
 Caroline. Ammonia, therefore, has not, like the two other alka- 
 lies, a metallic basis. 
 
 Mrs. B. It is believed that it has, though it is extremely difficult 
 to reconcile that idea with what I have just stated of its chemical 
 nature. But the fact is, that although this supposed metallic basis 
 of ammonia has never been obtained distinct and separate, yet both 
 Professor Berzelius, of Stockholm, and Sir H. Davy, have suc- 
 ceeded in forming a combination of mercury with the basis of am- 
 monia which has so much the appearance of an amalgam, that it 
 strongly cqrroborates the idea of ammonia having a metallic basis.J 
 But these theoretical points are full of difficulties and doubts, ana 
 it would be usteless to dwell any longer upon them. 
 
 Let us therefore return to the properties of volatile alkali. Am- 
 moniacal gas is considerably lighter than oxygen gas, and only 
 about half the weight of atmospherical air. It possesses most of the 
 properties of the fixed alkalies ; but cannot be of so much use in 
 the arts on account of its volatile nature. It is, therefore, never 
 employed in the manufacture of glass, but it forms soap with oils 
 equally as well as potash and soda ; it resembles them likewise in 
 its strong attraction for water ; for which reason it ca n be collected 
 in a receiver over mercury only. 
 
 Caroline. I do not understand this. 
 
 Mrs. B. Do you recollect the method which was used to collect 
 gases in a glass receiver over water? 
 
 Caroline. Perfectly. 
 
 Mrs. B. Ammoniacal gas has so strong a tendency to unite with 
 water, that instead of passing through that fluid, it would be in- 
 stantaneously absorbed by it. We can therefore neither use water 
 for that purpose nor any other liquid of which water is a compo- 
 nent part ; so that in order to collect this gas, we are obliged to 
 have recourse to mercury, (a liquid which has no action upon it,) 
 and a mercurial bath is used instead of a water bath, such as we 
 employed on former occasions. Water impregnated with this gas 
 is nothing .more than the fluid which you mentioned at the begin- 
 ning of the conversation hartshorn^ it is the ammoniacal gas es- 
 caping from the water which gives it so powerful a smell.J 
 
 * It ought to be hydrogen gas. C. 
 
 f This amalgam is easily obtained, by placing a globule of mer- 
 cury upon a piece of muriat, or carbonat of ammonia, and electri- 
 fying this globule by the Voltaic battery. The globule instantly 
 begins to expand to three or four times its former size, and becomes 
 much less fluid, though without losing its metallic lustre, a change 
 which is ascribed to the metallic basis of ammonia uniting with 
 the mercury. This is an extremely curious experiment. 
 
 J To obtain ammoniacal gas, mix together equal parts of muriate 
 of ammonia, and dry burnt lime ; after pulverizing each separately, 
 
 788. Has ammonia a metallic basis ? 
 
 789. What is the specific gravity cf ammoniacal gas ? 
 
 790. How does ammonia resemble potash and soda ? 
 
 79 1 . Why cannot ammonia be collected in a receiver over water ? 
 
 792. What is hartshorn ? 
 
190 AMMONIA. 
 
 Emily. But there is no appearance of effervescence in hartshorn. 
 
 J\frs. B. Because the particles of gas that rise from the water 
 are too subtle and minute for their effect to be visible. 
 
 Water diminishes in density, by being 1 impregnated with ammoni- 
 acal gas ; and this augmentation of bulk increases its capacity for 
 caloric. 
 
 Emily. In making hartshorn, then, or impregnating water, with 
 ammonia, heat must be absorbed and cold produced ? 
 
 Mrs. B. That effect would lake place if it was not counteracted 
 by another circumstance ; the gas is liquefied by incorporating 
 with the water, and gives out its latent heat. The condensation of 
 the gas more than counterbalances the expansion of the water 
 therefore, upon the whole, heat is produced. But if you dissolve 
 ammoniacal gas with ice or snow, cold is produced. Can you ac- 
 count for that ? 
 
 Emily. The gas in being condensed into a liquid, must give out 
 heat ; and, on the other hand, the snow or ice in being rarefied 
 into a liquid, must absorb heat ; so that between the opposite ef- 
 fects, I should\have supposed the original temperature would have 
 been preserved. 
 
 Jlfrs. B. But you have forgotten to take into the account the 
 rarefaction of the water, (or melted ice,) by the impregnation of the 
 gas, and this is the cause of the cold which is ultimately produced. 
 
 Caroline. Is the sal volatile (the smell of which so strongly re- 
 sembles hartshorn) likewise a preparation of ammonia ? 
 
 Mrs. J3* It is carbonat of ammonia dissolved in water ; and which 
 in its concrete state, is commonly called salts of hartshorn. Am- 
 monia is caustic, like the fixed alkalies, as you may judge by the 
 pungent effects of hartshorn, which cannot be taken internally, nor 
 applied to delicate external parts, without being plentifully diluted 
 
 rub them together in a mortar ; put them into a retort, and apply 
 the heat of a lamp. Or, the common spirit of sal ammoniac may be 
 heated in a retort in the same way. To collect and retain the gas 
 without a mercurial bath, fix a receiver or bottle in an inverted 
 position, and connect to the retort a tube, which introduce up into 
 the receiver, so that it nearly reaches the bottom. As the gas 
 comes over, its levity is such, that it fills the upper part of the re- 
 ceiver first, gradually driving out the air, and taking its place. To 
 keep jjt for any considerable time, the receiver must be stopped. A 
 pretty experiment may be made by introducing- up into the receiver 
 with the ammonia, some muriatic gas. Both gases are invisible 
 until they are brought together, when they unite, forming a dense 
 white cloud and fall down in the solid form of muriate of ammonia. 
 The muriatic gas is obtained by pouring sulphuric acid on common 
 salt, and applying the heat of a lamp. It may be sent up into the 
 receiver in the way above described, or ammonia. C. 
 
 793. What change is produced on water by being impregnated 
 with ammoniacal gas ? 
 
 794. Why is cold produced if ammooiacal gas is dissolved with 
 snow or ice ? 
 
 795. How can ammonical gas be retained for experiment! without a 
 mercurial baik ? 
 
 796. What is sal volatile:? 
 
EARTHS. 191 
 
 with water. Oil and acids are very excellent antidotes for alkaline 
 poisons ; can you guess why ? 
 
 Caroline. Perhaps, because the oil combines with alkali, and 
 forms soap, and thus destroys its caustic properties : and the acid 
 converts it into a compound salt, which, I suppose, is not so perni- 
 cious as caustic alkali. 
 
 Mrs. B. Precisely so. 
 
 Ammoniacal gas, if it be mixed with atmospherical air, and a 
 burning taper repeatedly plunged into it, will burn with a large 
 flame of a peculiar yellow colour. 
 
 Emily. But, pray, tell me, can ammonia be procured from this 
 Lybian salt only ? 
 
 Jttrs. B. So far from it, that it is contained in, and may be ex- 
 tracted from, all animal substances whatever. Hydrogen and 
 nitrogen are two of the chief constituents of animal matter ; it it 
 therefore not surprising that they should occasionally meet and 
 combine in those proportions that compose ammonia. But this 
 alkali is more frequently generated by the spontaneous decomposi- 
 tion of animal substances ; the hydrogen and nitrogen gases that 
 arise from putrefied bodies combine and form the volatile alkali. 
 
 Muriat of ammonia, instead of being exclusively brought from 
 Lybia, as it originally was, is now chiefly prepared in Europe, by 
 chemical processes. Ammonia, although principally extracted 
 from this salt, can also be produced by a great variety of other 
 substances. The horns of cattle, especially those of deer, yield it 
 in abundance, and it is from this circumstance that a solution of 
 ammonia in water has been called hartshorn. It may likewise be 
 procured from wool, flesh, and bones ; in a word, any animal sub- 
 stance whatever, yields it by decomposition. 
 
 We shall now lay aside the alkalies, however important the sub- 
 ject may be, till we treat of their combination with acids. The 
 next time we meet, we shall examine the earths. 
 
 CONVERSATION XV. 
 
 ON EARTHS. 
 
 Mrs. B. The EARTHS, which we are to-day to examine, are nine 
 in number. 
 
 SILEX, 8TRONTITE8,* 
 
 * There is less evidence that these four earths are composed of 
 metallic bases than there is in the case of ammonia, which it will be 
 
 797. Why are oils and acids good antidotes for alkaline poisons ? 
 
 798. From what can ammonia be procured ? 
 
 799. What are the chief constituents of animal matter? 
 
 800. Why has a solution of ammonia in water been called harts- 
 horn ? 
 
 801. How many earths are there ? 
 
 802. What are their names ? 
 
192 EAKTHS. 
 
 
 
 ALUMINE, TTTRIA, 
 
 BARYTES,* GLUCINA, 
 
 LIME,* ZIRCON1A. 
 MAGNESIA, 
 
 The last three are of Jate discovery ; their properties are but 
 imperfectly known ; and as they have not yet been applied to use, 
 it will be unnecessary to enter into any particulars respecting them. 
 We shall confine our remarks, therefore, to the first five. They are 
 composed, as you have already learnt, of a metallic basis combined 
 with oxygen ; and from this circumstance are incombustible. 
 
 Caroline. Yet 1 have seen turf burnt in the country, and it makes 
 an excellent fire ; the earth becomes red hot, and produces a very 
 great quantity of heat. 
 
 Mrs B. It is not the earth that burns, my dear, but the roots, 
 grass, and other remnants of vegetables that are intermixed with it. 
 The caloric, which is produced by the combustion of these sub- 
 stances, makes the earth red hot, and this being a bad conductor 
 of heat, retains its caloric a long time ; and were you to examine 
 it when cool, you would find that it had not absorbed one particle 
 of oxygen, nor suffered any alteration from the fire. Earth is, how- 
 ever, from the circumstance just mentioned, an excellent radiator 
 of heat, and owes its utility, when mixed with fuel, solely to that 
 property. It is in this point of view that Count Rumford has re- 
 commended balls of incombustible substances to be arranged in fire 
 places, and mixed with the coals, by which means the caloric dis- 
 engaged by the combustion of the latter is more perfectly reflected 
 into the room, and an expense of fuel is saved. 
 
 Emily. 1 expected that the lists of earths would be much more 
 considerable. When I think of the immense variety of soils, I am 
 astonished that there is not a greater number of earths to form them. 
 
 Mrs. B. You might, indeed, almost confine that number to four; 
 fdr barytes, strontites, and the others of late discovery, act but so 
 small a part in this great theatre, that they cannot be reckoned as 
 essential to the general formation of the globe. And you must not 
 confine your idea of earths to the formation of soil ; for rock, mar- 
 ble, chalk, slate, sind, flint, and all kinds of stones, from the pre- 
 cious jewels to the commonest pebbles ; in a word, all the immense 
 
 remembered, was supposed to have formed an amalgam with mer- 
 cury, and on this account was supposed to have had a metallic, ba- 
 sis. Of the other earths no one except Dr. Clarke, of Cambridge, 
 Eng., has pretended to offer any but conjectural evidence of their 
 metallic nature. This gentleman, on subjecting them to the heat of 
 the blow-pipe, charged with oxygen and hydrogen, was led to be- 
 lieve he had obtained their metallic bases. But as his experiments 
 have been repeated at the Royal Institution without success, it ia 
 now understood that the Dr. must have been mistaken. C. 
 
 803. Of what are the earths composed ? 
 
 804. Why are the earths incombustible ? 
 
 805. Why then is turf used for fuel in some countries ? 
 
 806. Why is the earth a good radiator of heat ? 
 
 807. What is said of barytes and strontites, as constituting a part 
 of the globe ? 
 
EARTHS. 193 
 
 variety of mineral products, may be referred to some of these 
 earths, either in a simple state, or combined the one with the other, 
 or blended with other ingredients. 
 
 Caroline. Precious stones composed of earth ! That seems very 
 difficult to conceive. 
 
 Emily. Is it more extraordinary than that the most precious of 
 all jewels, diamond, should be composed of carbon ? But diamond 
 forms an exception, Mrs. B. ; for, though a stone, it is not com- 
 posed of earth. 
 
 Mrs. B. I did not specify the exception, as I knew you were so 
 well acquainted with it. Besides, I would call a diamond a mineral 
 rather than a stone, as the latter term always implies the presence 
 of some earth. 
 
 Caroline. I cannot conceive how such coarse materials can be 
 converted into such beautiful productions. 
 
 JWrs. B. We are very far from understanding 1 all the secret re- 
 sources of nature ; but I do not think the spontaneous formation of 
 the crystals, which we call precious stones, one of the most difficult 
 phenomena to comprehend. 
 
 By the slow and regular work of ages, perhaps of hundreds of 
 ages, these earths may be gradually dissolved by water, and as 
 gradually deposited by their solvent in the undisturbed process of 
 crystallization. The regular arrangement of their particles, during 
 their re-union in a solid mass, gives them that brilliancy, transpa- 
 rency, and beauty, for which they are so much admired ; and ren- 
 ders them in appearance so totally different from their rude and 
 primitive ingredients. 
 
 Caroline. But how does it happen that they are spontaneously 
 dissolved, and afterwards crystallized ? 
 
 Jllrs. B. The scarcity of many kinds of crystals, as rubies, erne- 
 raids, topazes, &c., shows that their formation is not an operation 
 very easily carried on in nature. But cannot you imagine that 
 when water holding in solution some particles of earth filters 
 through the crevices of hills or mountains, and at length dripples 
 into some cavern, each successive drop may be slowly evaporated, 
 leaving behind it the particle of earth which it held in solution? 
 You know that crystallization is more regular and perfect, in pro- 
 portion as the evaporation of the solvent is slow and uniform ; na- 
 ture, therefore, who knows no limit of time, has, in all works of this 
 kind, an infinite advantage over any artist who attempts to imitate 
 such productions. 
 
 Emily. I can now conceive that the arrangement of the particles 
 of earth during crystallization, may be such as to occasion transpa- 
 rency, by admitting a free passage to the rays of light ; but I can- 
 not understand why crystallized earths should assume such beauti- 
 ful colours as most of them do. Sapphire, for instance, is of a ce- 
 lestial blue ; ruby, a deep red ; topaz, a brilliant yellow ? 
 
 808. What valuable substance do the earths compose ? 
 
 809. Is it deemed difficult to understand the spontaneous forma- 
 tion of crystal ? 
 
 810. What does the scarcity of many kinds of crystals show ? 
 
 811. How may it be supposed that they are formed ? 
 
1 94 EARTHS. 
 
 Mrs. B. Nothing 1 is more simple than to suppose that the ar- 
 rangement of (heir particles, is su-feh, as to transmit some of the 
 coloured rays of light, and to refiYct others, in which case the stone 
 must appear of the colour of the lays which it reflects. But be- 
 sides, it frequently happens that the colour of a stone is owing- to 
 a mixture of some metallic matter. 
 
 Caroline. Pray, are the different hinds of precious stones each 
 composed of one individual earth, or are they formed of a combina- 
 tion of several earths ? 
 
 Mrs. B. A great variety of materials enters into the composition 
 of most of them ; not only several earths, but sometimes salts and 
 metals. The earths, however, in their simple st'nte, frequently 
 form very beautiful crystals ; and, indeed, it is in that stite only 
 that they can be obtained perfectly pure. 
 
 Emily. Is not the Derbyshire spar produced by the crystalliza- 
 tion of earths, in the way you have just explained ? I have been in 
 some of the subterraneous caverns where it is found, which are 
 similar to those you have described. 
 
 Mrs. B. Yes ; but this spar is a very imperfect specimen of 
 crystallization;* it consists of a variety of ingredients confusedly 
 blended together, as you may judge by its opacity, and by the 
 various colours and appearances which it exhibits. 
 
 But, in examining- the earths in their most perfect and agreeable 
 form, we must not lose sight of that stale in which they are com- 
 monly found, and which, if less pleasing- to the eye, is far more in- 
 teresting by its utility. 
 
 All the earths are more or less endowed with alkaline proper- 
 ties ; but there are four, barytes, magnesia, lime, and strontites, 
 which are called alkaline earths^ because they possess those quali- 
 ties in so great a degree, as to entitle them, in most respects, to the 
 rank of alkalies. They combine and form compound salts with 
 acids, in the same way as alkalies ; they are, like them, susceptible 
 of a considerable degree of causticity, and are acted upon in a simi- 
 lar manner by chemical tests. The remaining earths, silex and 
 aiumine, with one or two others of late discovery, are in some de- 
 gree more earthy, that is to say, they possess more completely the 
 properties common to all the earths, which are insipidity, dryness, 
 unalterableness in the fire, infusibility, &c. 
 
 Caroline. Yet, did you not tell us that silex, or siliceous earth, 
 when mixed with an alkali, was fusible, and run into glass ? 
 
 Mrs. B. Yes, my dear ; but the characteristic properties of earths, 
 
 * The Derbyshire spar is composed of lime andyZuortc acid ; hence 
 t is called /wa/e of lime. The colours are owing to intermixture 
 with metallic oxides. It is a very beautiful mineral, and instead of 
 being opaque, it is generally translucent, or nearly transparent. C. 
 
 812. Whence may it be supposed they receive their beautiful 
 colours? . 
 
 813. Wha.t is an instance of simple earths in a state of crystal- 
 lization ? 
 
 814. What is the composition of Derbyshire spar * 
 
 815. What are alkaline earths? 
 
 816. Why are they so called? 
 
 817. What properties are common to all earths ? 
 
SILEX. 195 
 
 which I have mentioned, are to he considered as belonging to them 
 in a state of purity only ; a state in which they are very seldom to 
 be met with in nature. Besides these general properties, each earth 
 has its own specific characters, hy which it is distinguished from 
 any other substance. Let us, therefore, review them separately. 
 
 Sri.EX, or SILICA, abounds in flint, sand, sand-stone, agate, jas- 
 per, &c. ; it forms the basis of many precious stones, and particu- 
 larly of those which strike fire with steel. It is rough to the touch, 
 scratches and wears away metnis ; it is acted upon by no acid but 
 the fluoric, and it is not soluble in water by any known process; but 
 nature certainly dissolves it by means with which we are unac- 
 quainted, and thus produces a variety of siliceous crystals, and 
 amongst these, rock crystal, which is the .purest specimen of this 
 earth. Silex appears to have been intended by Providence to form 
 the solid basis of the globe, to serve as the foundation for the origi- 
 nal mountains, and give trem that hardness and durability which 
 has enabled them lo resist the various revolutions which the surface 
 of the earth hi ive'y undergone. From these mountains 
 
 silicious rocks hare, during tl>e couise of ages, been gradually de- 
 tached by torrents of water, and brought down in fragments ; these, 
 in the violence arid ripidily of their descent, are sometimes crum- 
 bled to sand, an I in rhi- state form the beds of rivers and of the sea, 
 chiefly composed of sil.ceous materials. Sometimes the fragments 
 are broken without being pulverized by their fall, and assume the 
 form of pebbles, which gradually become rounded and polished. 
 
 Emily. Prav, whar is the true colour of silex, which forms such a 
 variety of different coloured Mibslances ? Sand is brown, flint is 
 nearly black, and precious st mcs are of all colours. 
 
 J\lrs B. Pure silex, such a- is found only in the chemist's labo- 
 ratory, is perfectly white, and the varieus colours which it as r --:imes 
 in the different substances von hwe just mentioned, proceed from 
 the different ingredients with which it is mixed in them. 
 
 Caroline. I wonder thai silex is not more valuable, since it forms 
 the basis of so many precious stones.* 
 
 Mrs. B. You must not forget that the value we set upon precious 
 stones depends in a great measure upon the scarcity with which 
 nature affords thorn ; for, were those productions either common or 
 perfectly imitable by art, they would no longer, notwithstanding 
 their beauty, be so highly esteemed. But the real value of siliceous 
 earth in many of the rno-t u-eful arts, is very extensive. Mixed 
 with clay, it forms the basis of all the various kinds of earthern 
 ware, from the most c ..\nrnon utensils to the most refined ornaments. 
 
 Emily. And we must recollect its importance in the formation of 
 glass with potash, 
 
 Mrs. B. Nor should we omit to mention, likewise, many other 
 
 * The bases of some of the most costly gems, as sapphire, ruby, 
 and topaz, are alumine. C. 
 
 818. In what is silex chieflv found ? 
 
 819. What is tie purest specimen of silex? 
 
 820. What is the colour of silex ? 
 
 821. Upon what does the value of precious stones depend? 
 
 822. For what important uses is silex chiefly valuable ? 
 
196 ALUMINE. 
 
 important uses of silex, such as being the chief ingredient of some 
 of the most durable cements, of mortar, &c. 
 
 I said before that siliceous earth combined with no acid but the 
 fluoric ; it is for this reason that glass is liable to be attacked by 
 that acid only, which, from its strong affinity to silex, forces that 
 substance from its combination with the potash, and thus destroys 
 the glass. 
 
 We shall now hasten to proceed to the other earths, for I am ra- 
 ther apprehensive of your growing weary of this part of our subject. 
 
 Caroline. 1 confess that the history of the earths is not quite so 
 entertaining as that of the simple substances. 
 
 Mrs. B. Perhaps not ; but it is absolutely indispensable that you 
 should know something of them ; for they form the basis of so 
 many interesting and important compounds, that their total omis- 
 sion would throw great obscurity on our general outline of chemi- 
 cal science. We shall, however, review them in as cursory a 
 manner as the subject can admit of. 
 
 ALUMINE derives its name from a compound salt called alum, of 
 which it forms the basis. 
 
 Caroline. But it ought to be just the contrary, Mrs. B.; the sim- 
 ple body should give, instead of taking, its name from the compound. 
 
 Mrs. B. That is true ; but as the compound salt was known long 
 before its basis was discovered, it was very natural that when the 
 earth was at length separated from the acid, it should derive its 
 name from the compound from which it was obtained. However, 
 to remove your scruples, we will call the s>alt according to the new- 
 nomenclature, sulphat of alumine. From this combination, alu- 
 mine may be obtained in its pure state ; it is then soft to the touch, 
 makes a paste with water, and hardens in the fire. In nature it is 
 found chiefly in clay, which contains a considerable proportion of 
 this earth ; it is very abundant in fullers' earth, slate, and a variety 
 of other mineral productions. There is indeed scarcely any mine- 
 ral substance more useful to mankind than alumine. In the state 
 of clay, it forms large strata of the earth, gives consistency to the 
 fiorl of valleys, and of all low and damp spots, such as swamps and 
 marshes. The beds of lakes, ponds, and springs, are almost en- 
 tirely of clay ; instead of allowing of the nitration of water, as sand 
 does, it forms an impenetrable bottom, and by this means water is 
 accumulated in the caverns of the earth, producing those reservoirs 
 whence springs issue, and spout out at the surface. 
 
 Emily. I always thought that these subterraneous reservoirs of 
 water were bedded by some hard stone, or rock, which the water 
 could not penetrate. 
 
 Mrs. B. That is not the case ; for in the course of time water 
 would penetrate, or wear away silex, or any other kind of stone, 
 while it is effectually stopped by clay, or alumine. 
 
 The solid compact soils such as are fit for corn, owe their consist- 
 
 823. How, and why does the fluoric acid destroy glass ? 
 
 824. Why is it necessary to understand the nature of the earths ? 
 
 825. From what does alumine derive its name ? 
 
 826. What is the sulphat of alumine ? 
 
 827. In what is alumine chiefly found ? 
 
 828. In what kind of soil does it occur most abundantly ? 
 
BARYTES. 197 
 
 ence in a great measure to alnmine ; this earth is therefore used to 
 improve sandy or chalky soils, which do not retain a sufficient quan- 
 tity of water for the purpose of vegetation. 
 
 Alumine is the most essential ingredient in all potteries. It en- 
 ters into the composition of brick, as well as that of the finest porce- 
 lain : the addition of silex and water hardens it, renders it suscept- 
 ible of a degree of vitrification, and makes it perfectly fit for its 
 various purposes. 
 
 Caroline. I can scarcely conceive that brick and china should 
 be made of the same materials. 
 
 Mrs. B. Brick consists almost entirely of baked clay ; but a cer- 
 tain proportion of silex is essential to the formation of earthen or 
 stone ware. In the common potteries sand is used for that purpose 
 a more pure silex is,* I believe, necessary for the composition of 
 porcelain, as well as a finer kind of clay ; and ihese materials are, 
 no doubt, more carefully prepared, and curiously wrought, in the 
 one case than in the other. Porcelain owes its beautiful semi- 
 transparency to a commencement of vitrification. 
 
 Emily. But the commonest earthenware, though not transparent, 
 is covered with a kind of glazing. 
 
 Mrs. B. That precaution is equally necessary for use as for beau- 
 ty, as the ware would be liable to be spoiled and corroded by a va- 
 riety of substances, if not covered with a coating of this kind. In 
 porcelain it consists of enamel, which is a fine white opaque glass, 
 formed of metallic oxyds, sands, salts, and such other materials as 
 are susceptible of vitrification. The glazing of common earthen- 
 ware is made chiefly of oxyd of lead, or sometimes merely of saU, 
 which, when thinly spread over earthen vessels, will, at a certain 
 heat, run into opaque glass. 
 
 Caroline. And of what nature are the colours which are used for 
 painting porcelain ? 
 
 Mrs. B. They are all composed of metallic oxyds ; so that these 
 colours, instead of receiving injury from the application of fire, are 
 strengthened and developed by its action, which causes them to 
 undergo different degrees of oxydation. 
 
 Alumine and silex are not only often combined by art, but they 
 have in nature a very strong tendency to unite, and 'are found com- 
 bined, in different proportions, in various gems and other minerals 
 Indeed, many of the precious stones, such as ruby, oriental sapphire 4 , 
 amethyst,f &c. consist chiefly of alumine. 
 
 We may now proceed to the alkaline earths. I shall say but a few 
 words on B ARYTES, as it is hardly ever used, except in chemical 
 
 * Porcelain clay, of which china ware is made, is found among 
 granite rocks, and seems to owe its origin to the decomposition of a 
 mineral called fddspar. Its composition is silex and alumine, si- 
 lex being the predominant ingredient. C. 
 
 f The amethyst is almost entirely composed of silex. C. 
 
 829. What is the use of alumine for purposes of vegetation ? 
 
 830. What is the use of it in wrks of art ? 
 
 831. To what is the transparency of porcelain owing ? 
 
 832. Of whal is the glazing of common earchen-vrare made ? 
 
 833. What is the nature of the colours which ar ; e used for paint- 
 ing porcelain ? 
 
 m 
 
198' LIME. 
 
 laboratories. It is remarkable for its great weight, and its strong 
 alkaline properties, such as destroying animal substances, turning 
 green some blue vegetable colours, and showing a powerful attrac- 
 tion for acids ; this last property it possesses to such a degree, par- 
 ticularly with regard to the sulphuric acid, that it will always de- 
 tect its presence in any substance or combination whatever, by im- 
 mediately uniting 1 with it, and forming a sulphat of barytes. This 
 renders it a very valuable chemical test. It is found pretty abun- 
 dantly in nature in the state of carbonat,* from which the pure 
 earth can be easily separated. 
 
 The next earth we have to consider is LIME. This is a substance 
 of too great and general importance to be passed over so lightly as 
 the last. 
 
 Lime is strongly alkaline. In nature it is not met with in its 
 simple state, as its affinity for water and carbonic acid is so great 
 that it is always found combined with these substances, with which 
 it forms the common lime-stone ; but it is separated in the kiln from 
 these ingredients, which are volatilized whenever a sufficient de- 
 gree of heat is applied. 
 
 Emily. Pure lime, then, is nothing but lime-stone, which has been 
 deprived, in the kiln, of its water and carbonic acid ? 
 
 Mrs. B. Precisely : in this state it is called quick-lime, and it is so 
 caustic, that it is capable of decomposing the dead bodies of animals 
 very rapidly, without their undergoing the process of putrefaction. 
 I have here some quick-lime, which is kept carefully corked up in a 
 bottle to prevent the access of air ; for were it all exposed to the at- 
 mosphere, it would absorb both moisture and carbonic acid gas from 
 it, and be soon slaked- Here is also soine lime stone we shall 
 pour a little water on each, and observe the effects that result from 
 it. 
 
 Caroline. How the quick-lime hisses ! It is become excessively 
 hot ! It swells, and now it bursts and crumbles to powder, while 
 the water appears to produce no kind of alteration on the lime- 
 stone. 
 
 J\Irs. B. Because the lime-stone is already saturated with water, 
 whilst the quick-lime, which has been deprived of it in the kiln, 
 combines with it with very great avidity, and produces this prodi- 
 gious disengagement of heat, the cause of which I formerly ex- 
 plained to you ; do you recollect it ? 
 
 Emily. Yes ; you said that the heat did not proceed from the lim o 
 
 "* The native carbonat of barytes is a rare mineral. It is a viru- 
 lent poison. The sulphat of barytes is found in considerable abun- 
 dance. C. 
 
 834. For what is barytes remarkable? 
 
 835. For what is it valuable ? 
 
 836. Where is it abundantly found ? 
 
 837. What is the reason that lime is not found in its simple state? 
 
 838. How does lime-stone differ from pure lime? 
 
 839. What effect will quick-lime have upon the dead bodies of 
 animals ? 
 
 840. What effect does the air produce on quick-lime ? 
 
 841. What effect has water on it ? 
 
 842. Why will not water have an effect on lime-stone as .well as 
 quick-lime ? 
 
BARYTES. 199 
 
 but from the water which was solidified, and thus parted with its 
 heat of liquidity. 
 
 Mrs.B. Very well. If we continue to add successive quantities 
 of water to the lime, after being- slaked and -crumbled, as you see, 
 it will then gradually be diffused in the water, till it will at length 
 be dissolved in it, and entirely disappear ; but for this purpose it 
 requires no less than 700 times its weight of water. This solution 
 is called lime water.* 
 
 Caroline. How very small, then, is the proportion of lime dissol- 
 ved ! 
 
 Mrs.B. Barytes is also of very difficult solution ; but it is much 
 more soluble in the state of crystals. The liquid contained in this 
 bottle is lime-water : it is often used as a medicine, chiefly, 1 be- 
 lieve, for the purpose of combining with and neutralizing the super- 
 abundant acid which it meets with in the stomach. 
 
 Emily. I arn surprised that it is so perfectly clear : it does .not 
 at all partake of the whiteness of the lime. 
 
 Mrs. B. Have you forgotten that, in solutions, the solid body is 
 so minutely subdivided by the fluid as to become invisible, und 
 therefore, will not, in the least degree impair the transparency of 
 the solvent ? 
 
 I said that the attraction of lime for-carbonic-acid tv8 so strong, 
 that it would absorb it from the atmosphere. We may see this effect 
 by exposing a glass of lime-waier to the air ; the lim? will then se- 
 parate from the water, combine with the carbonic acid, and re ap- 
 pear on the surface in the form of a white film, which is carbonat 
 of lime, commonly called chalk. 
 
 Caroline. Chalk is, then, a compound salt ! I never should have 
 supposed that those immense beds of chalk, that we see in many 
 parts of the country were a salt. Now the white film begins to ap- 
 pear on the surface of the water : but it is far from resembling hard 
 solid chalk. 
 
 Jflrs. B. That is owing to its state of extreme division : in a lit- 
 tle time it will collect into a more compact mass, and subside at the 
 bottom of the glass. 
 
 If you breathe into lime-water, the carbonic acid, which is mixed 
 with the air that you expire, will produce the same effect. It is an 
 experiment very easily made : I shall pour some lime-water into 
 this glass tube, and, by breathing repeatedly into'it, you will soon 
 perceive a precipitation of chalk. 
 
 * To make lime-water, take a piece of well burned lime, about 
 ze of a hen's eg^g, put it into an earthen dish, and sprinkle wa- 
 tt it, till it falls into powder : Then pour on two quarts of boil- 
 m ,,,, and stir it several times, after the lime has settled ; pour 
 ; clear water and cork it for use. C. 
 
 \ ^ Why is heat disengaged when water is put upon quick-lime? 
 #44. How much water does it take to dissolve lime ? 
 
 845. Is Barytes easily dissolved in water ? 
 
 846. W hy does not lime-water partake of the-whiteness of lime ? 
 
 847. For what has lime a very strong attraction ? 
 
 846. Why does a white film collect on the surface of lime-water 
 on being exposed to the air ? 
 
 849. Why will lime- water turn white if you breathe into it ? 
 
20Q 
 
 Emily- I see already a small white cloud formed. 
 
 Mrs. B. It is composed of minute particles of chalk ; at present 
 it floats in the water, but it will soon subside 
 
 Carbonat of lime, or chalk, you see, is insoluble in water, since 
 the lime which was dissolved reappears when converted into chalk; 
 but you must take notice of a very singular circumstance, which 
 is, that chalk is soluble in water impregnated with carbonic acid. 
 
 Caroline. It is very curious, indeed, that carbonic acid and gas 
 should render lime soluble in one instance, and insoluble in the 
 other ! 
 
 JMrs. B. I have here a bottle of Seltzer water, which you know, 
 is strongly impregnated with carbonic acid ; let us pour a little of 
 it into a glass of lime water. You see that it immediately forms a 
 precipitation of carbonat of lime ? 
 
 Emily. Yes, a white cloud appears. 
 
 Jftrs.B. I shall now pour an additional quantity of the Seltzer 
 water into the lime water. 
 
 Emily. How singular ! The cloud is re-dissolved, and the liquid 
 is again transparent. 
 
 Mis.B. All the mystery depends upon this circumstance, that 
 carbonat of lime is soluble in carbonic acid, whilst it is insoluble in 
 water; the first quantity of carbonic acid, therefore, which 1 intro- 
 duced into the lime water, was employed in forming the carbonat 
 of lime, which remained visible, until an additional quantity of car- 
 bonic acid dissolved it. Thus, you see, when the lime and carbonic 
 acid are in proper proportions to form chalk, the white cloud ap- 
 pears ; but when the acid predominates, the chalk is no sooner 
 formed than it is dissolved. 
 
 Caroline. That is now the case; bullet us try whether a further 
 addition of lime- water will again precipitate the chalk. 
 
 Emily. It does, indeed! The cloud re-appears, because, I sup- 
 pose, there is now no more of the carbonic acid than is necessary 
 to form chalk; and, in order to dissolve the chalk, a superabun- 
 dance of acid is required. 
 
 Mrs. B. We have, I think, carried this experiment far enough; 
 every repetition would but exhibit the same appearance. 
 
 Lime combines with most of the acids, to which the carbonic (as 
 being the weakest) readily yields it ; but these combinations we 
 shall have an opportunity of noticing more particularly hereafter. 
 -It unites with phosphorus, and with sulphur, in their simple stale: 
 in short, of all the earths lime is that which nature employs most 
 frequently, and most abundantly, in its innumerable combinations. 
 It is the basis of all calcareous earths and stones ; we find it like- 
 wise in the animal and vegetable creations. 
 
 Emily. And in the arts is not lime of very great utility ? 
 
 JHrs. B. Scarcely any substance more so ; you know that it is a 
 
 850. What is the chemical name of chalk ? 
 
 851. What is the process of making lime-water . ? 
 
 852. How may chalk be dissolved ? 
 
 85a What will be the result if Seltzer water be poured into 
 .lime-water ? 
 
 854. What is the basis of all calcareous earths and stones? 
 
 855. Of what use is lime in thejirts ? 
 
MAGNESIA. 201 
 
 most essential requisite in building, as it constitutes the basis of all 
 cements, such as mortar, stucco, plaster, &c. 
 
 Lime is also of infinite importance in agriculture ; it lightens and 
 warms soils that are too cold and compact, in consequence of too 
 great a proportion of clay. But it would be endless to enumerate 
 the various purposes for which it is employed ; and you know enough 
 of it to form some idea of its importance ; we shall therefore, now 
 proceed to the third alkaline earth* MAGNESIA. 
 
 Caroline. I am already pretty well acquainted with that earth ; 
 it is a medicine. 
 
 Mrs. B. It is in the state of carbonat that magnesia-is usually 
 employed medicinally; it then differ but little in appearance from 
 its simple form, which is that of a very fine light white powder. It 
 dissolves in 2000 times its weight of water, but forms with acids ex- 
 tremely soluble salts. It has not so great an attraction for acids 
 as lime, and consequently yields them to the latter. It is found in 
 a great variety of mineral combinations, such as slate, mica, ami- 
 anthus; and more particularly in a certain lime-stone, which has 
 been discovered by Mr. Tenant to contain it in very great quan- 
 tities. It does not attract and solidify water, like lime ; but when 
 mixed with water and exposed to the atmosphere, it slowly absorbs 
 carbonic acid from the latter, and thus loses its causticity. Its chief 
 use in medicine is, like that of lime, derived from its readiness to 
 combine with, and neutralize, the acid which it meets with in the 
 stomach. 
 
 Emily. Yet, you said that it was taken in the state of carbonat, 
 in which case, it has already combined with an acid ? 
 
 Jlfr*. B. Yes ; but the carbonic is the last of all the acids in the 
 order of affinities ; it will therefore yield the magnesia to any of the 
 others. It is, however, frequently taken in its caustic state as a rem- 
 edy for flatulence. Combined with sulphuric acid, magnesia forms 
 another and more powerful medicine commonly called Epsom salt. 
 
 Caroline. And properly, sulphat of magnesia, I suppose ? Pray, 
 how did it obtain the name of Epsom salt ? 
 
 Jtfrs. B. Because there is a spring in the neighborhood of Epsom 
 which contains this salt in great abundance. 
 
 The last alkaline earth which we have to metftion is STRONTIAN, 
 or STRONTITES, discovered by Dr. Hope a few years ago, It so 
 strongly resembles barytes in its properties, and is so sparingly 
 found in nature, and of so little use in the arts, that it will not be 
 necessary to enter into any particulars respecting it. One of this re- 
 markable characteristic properties of strontites is, that its salts, 
 when dissolved in spirit of wine, tinge the flame a deep red, or 
 blood color. 
 
 856. Of what use is lime in agriculture ? 
 
 857. What is the simple form of magnesia ? 
 
 858. Does it attract water ? 
 
 859. What is its chief use in medicine ? 
 
 860. In what state is it used in medicine ? 
 
 861. What does it form combined with sulphuric acid ? 
 
 862. Why is the sulphat of magnesia called Epsom salt ? 
 863 Is strontian of any use ? 
 
 864. What is one of the remarkable properties of strontites ? 
 

 r :~ 
 
204 
 
 ACIDS. 
 
 Acids of known and simple bases. 
 
 The Sulphuric 
 
 Carbonic 
 
 Nitric 
 
 Phosphoric 
 
 Arsenical 
 
 Tungstenic 
 
 Molybdenic 
 
 Boracic 
 
 Fluoric 
 
 Muriatic 
 
 This class comprehends the most anciently known and most im- 
 portant acids. The sulphuric, nitric, and muriatic, were formerly, 
 and are still frequently called mineral acids. 
 
 2dly. Acids that have double or binary radicals, and which con- 
 sequently consist of triple combinations. These are the vegetable 
 acids, whose common radical is a compound of hydrogen and carbon. 
 Caroline. But if the basis of all the vegetable acids be the same 
 it should form but one acid ; it may indeed combine with different 
 proportions of oxygen, but the nature of the acid must be the same. 
 Mrs. B. The only difference that exists in the bases of vegetable 
 acids, is the various proportions of hydrogen and carbon from 
 which they are severally composed. But this is enough to produce 
 a number of acids apparently very dissimilar. That they do not 
 however, differ essentially, is proved by their susceptibility of being 
 converted into each other, by the addition or subtraction of a por- 
 tion of hydrogen of carbon. The names of these acids are, 
 The Acetic 
 
 Oxalic 
 
 Tartarout 
 
 Citric 
 
 Mnlic 
 
 Gallic 
 
 Mucous 
 
 Bensoic 
 
 Succinic 
 
 Camphoric 
 
 Suberic ^ 
 
 The 3d class of acids consist of those which have triple radicals, 
 and are therefore of a still more compound nature. This class com- 
 prehends the animal acids, which are, 
 
 Acids of double bases,being of vegetable origin. 
 
 The Lactic 
 Prussic 
 
 f OTWVtC 
 
 Bombic 
 Sebacic 
 Zoonic 
 Lithic 
 
 J- Acids, qf 
 J 
 
 triple bases, or animal acids. 
 
 878. What are their names ? 
 
 879. What ones of this class are called mineral acidt? 
 
 880. What ones make the second division ? 
 
 681. What is the common radical of vegetable acids ? 
 
 882. What is the difference in the bases of vegetable acids ? 
 
 883. What are the names of the vegetable acids ? 
 
 884. What ones make the third division of acids? 
 
 885. Name the acids with triple radicals ? 
 
ACIDS. 205 
 
 I have given you this summary account or enumeration of the 
 acids, as you may find it mo: e satisfactory to have at once an out- 
 line or a general notion of the extent of the subject : but we shall 
 now confine ourselves to the first class, which requires our more 
 immediate attention ; and defer the few remarks which we shall 
 have to make on the others, till we treat of the chemistry of the ani- 
 mal and vegetable kingdoms- 
 
 The acids of simple and known radicals are in most instances ca- 
 pable of being decomposed by combustible bodies, to which they 
 yield their oxygen. If, for instance, I pour a drop of sulphuric acid 
 on this piece of iron, it .will produce a spot of rust ; you know what 
 it is ? 
 
 Caroline. Yes; it is an oxyd, formed by the oxygen of the acid 
 combining with the iron. 
 
 .Mrs. B. In this case you see the sulphur deposits the oxygen by 
 which it was acidifie 1 on the melal. And again, if we pour some 
 acid on a compound combustible substance, (we shall try it on (his 
 piece of wood) it will combine with one or more of the constituents 
 of that substance, and occasion a decomposition. 
 
 Emily. It has changed the cc lour of the wood to black. How is 
 that ? 
 
 JMrs. B. The oxygen deposited by the acid has burnt it ; you 
 know that wood in burning becomes black before it is reduced to 
 ashes. Whether it derives the oxygen which burns it from the at- 
 mosphere, or from any other source, the chemical effect on the 
 wood is the same. In the case of real combustion, \rood becomes 
 black, because it is reduced to the state of charcoal by the evapora- 
 tion of its other constituents. But can you tell me the reason w.hy 
 wood turns black when burnt by the application of an acid ? 
 
 Caroline. First tell me what are the ingredients of wood r 
 
 Jtfrs. B. Hydrogen and carbon are the chief constituents of 
 wood, as of all other vegetable substances. 
 
 Caroline. Well, then, I suppose that the oxygen of the acid com- 
 bines with the hydrogen of the wood, to form "water ; and that the 
 carbon of the wood, remaining alone appears of its usual black col- 
 our. 
 
 J\Irs. B. Very well indeed, my dear; that is certainly the most 
 plausible .explanation. 
 
 Emily. VVould not this be a good method of making charcoal ? 
 
 J\lrs. B. It would be an extremely expensive, and I believe very 
 imperfect method ; for the action of the acid on the wood, and the 
 heat produced by it, are far from sufficient to deprive the wood of 
 all its evaporable parts. 
 
 Caroline. What is the reason that vinegar, lemon, and the acid 
 of fruits, do not produce this effect on the wood ? 
 
 Jtfrs. B. They are vegetable acids, whose bases are composed of 
 
 836. How can acids of simple radicals be decomposed? 
 
 887. If a drop of sulphuric acid falls on a piece of iron, why does 
 it produce rust ? 
 
 888. .Why does acid turn wood black? 
 
 889. Why does wood become black in real combustion? 
 
 890. What are the chief constituents of wood ? 
 
 G91. Why do not vinegar, lemon $ and the other vegetable acida 
 produce the same. effect on wood ? 
 
 18 
 
206 OF THE SULPHURIC 
 
 hydrogen and carbon; the oxygen, therefore, will not be disposed 
 to quit this radical, where it is already united with hydrogen. The 
 strongest of these may, perhaps, yield a liille of their oxygen to the 
 Wood, and produce a stain upon it but the carbon will not be suffi- 
 ciently uncovered to assume its black colour. Indeed, the several 
 mineral acids themselves possess this power of charring wood in 
 very different degrees. 
 
 Emily. Cannot vegetable acids be decomposed, by any combus- 
 tibles ? 
 
 Jttrs. B. No : because their radical is composed of two substan- 
 ces which have a greater attraction for oxygen than any known bo- 
 dy. 
 
 Caroline. And are those strong acids, which burn and decom- 
 pose wood, capable of producing similar effects on the skin and 
 flesh of animals ? 
 
 JK/rv. B. Yes ; all the mineral acids, and one of them more es- 
 pecially, possess powerful caustic qualities. They actually corrode 
 and destroy the skin and flesh ; but they do not produce upon these 
 -exactly the same alteration they do on wood, probably because 
 there is a great proportion of nitrogen and other substances in ani- 
 mal matter, which prevents the separation of carbon from being so 
 conspicuous. 
 
 CONVERSATION XVII. 
 
 OP THE SULPHURIC ANf) PHOSPHORIC ACIDS ; OR THE COM- 
 BINATIONS OF OXYGEN WITH SULPHUR AND PHOSPHORUS. J 
 AND OF THE SULPHATS AND PHOSPHATS. 
 
 rs. B. In addition to the general survey which we have taken 
 of acids, I think you will find it interesting to examine individually, 
 a few of the most important of them, and likewise some of tbeir 
 principal combinations with thealkalies, alkaline earths, and metals. 
 The first of these acids, in point of importance, is the SULPHURIC, 
 formerly called oil of vitriol 
 
 Caroline. I have known it a long time by that name, but had no 
 idea that it was the same fluid assulphuric acid. What resemblaqce 
 or connection can there be between oil of vitriol and this acid ? 
 
 Jtfr.?. .8. Vitriol is the common name for sulphat of iron,^. salt 
 which is formed by the combination of sulphuric acid and iron : ihe 
 sulphuric acid was formerly obtained by distillation from this salt, 
 and it very naturally received its name from the substance which 
 afforded it. 
 
 892. Why cannot vegetable acids hedecomposed by combustibles? 
 893* Do the mineral acids have the same effect on the skin and 
 flesh of animals as on wood ? 
 
 B94. If they do not what is the reason ? 
 
 895. What is the proper chemical name of oil of vitriol ? 
 
 896. Why was it called oil of vitriol? 
 
AND SULPHURIC ACIDS. 207 
 
 Caroline. But it is still usually called oil of vitriol ? 
 
 Mrs.B. Yes: a sufficient length of time has not yet elapsed, 
 since the invention of the new nomenclature, for it to be generally 
 disseminated; but, as it is adopted by all scientific chemists, there 
 is every reason to suppose that it will gradually become universal. 
 When I received this bottle from the chemists, oil of vitriol was in- 
 scribed on the label ; but as I knew you were very punctilious in re- 
 gar ] to the nomenclature, I changed it, and substituted the words 
 sulphuric arid. 
 
 Emily. This acid has neither colour nor smeU, but it appears 
 much thicker than water. 
 
 Mrs. B. It is nearly twice as heavy as water, and has, you see, 
 an oily consistence. 
 
 Caroline. And it is probably from this circumstance that it has 
 been called an oil ; for it can have no real claim to that name, as it 
 does not contain either hydrogen or carbon, which are the essential 
 constituents of oil. 
 
 fl/rs. B. Certainly, and therefore, it would be the more absurd 
 to re! .in a name which owed its origin to such a mistaken Analogy. 
 
 Snl: huric acid, in its purest state would probably be a concrete 
 Fubstunce, but its attraction for water is such, that it is impossible 
 toohtuin that acid perfectly free from it: it is, therefore, always 
 seen in a liquid form, such us you here find it. One' of the most 
 striking properties of sulphuric acid is that of evolving a considera- 
 ble qnintity of heat when mixed with water; this 1 have already 
 shout! you. 
 
 Emily. Yes, I recollect it ; but what was the degree of heat pro- 
 duced by that mixture ? 
 
 Jllr*. B. The thermometer rnny be raised by it to 300 degrees, 
 which is considerably above the temperature of boiling water. 
 
 Ctirnline. Then the water may be made to boil in that mixture? 
 
 JIT .?. B. Nothing more easy, provided that you employ sufficient 
 quantities of acid and of water, and in th- due proportions. The 
 greyest heat is produce^ by a mixture of one part of water to four 
 of the acid ; we shall nuk- a mixture of these proportions, and 
 immerse in it this thin glass tube, which is full of water. 
 
 Cnmline. The vessel feels extremely hot, but the water does not 
 boil \e\. 
 
 J\/Jrs. B. You must allow some time for the heat to penetrate the 
 tube, and raise the temperature of the water to the boiling point 
 
 Caroline. Now it boils -and with increasing violence. 
 
 jfrrt. B. But it will not continue boiling long: for the mixture 
 gives out heat only while t'>e particles of the water and the acid are 
 mutually penetrating each other ; as soon as the new arrangement 
 
 897. What is the colour and smell of this acid? 
 89tf. What is its weight? 
 
 899. What would sulphuric acid be in its purest state ? 
 
 900. What is the consequence of mixing it with water ? 
 
 901. What is one of its most striking properties ? 
 
 902. How high may a thermometer be raised by it ? 
 
 903. In what proportions must sulphuric acid and water be mix- 
 ed in order to produce the greatest degree of heat ? 
 
 904. Why does the mixture of sulphuric acid, and water give out 
 heat only for so short a time ? 
 
208 OP THE SULPHURIC 
 
 of these particles is affected, the mixture will gradually cool, and 
 the water return to its former temperature. 
 
 You have seen the manner in which sulphuric acid decomposes 
 all combustible substances, whether animal, vegetable, or mineral, 
 and burns them by means of its oxygen ? 
 
 Caroline. I have very unintentionally repeated the experiment 
 on my gown, by letting a drop of the acid fall upon it, and it has 
 made a stain, which I suppose will never wash out. 
 
 Jllrs. B. JSo, certainly ; for before you can put it into water, the 
 spot will become a hole, as the acid has literally burnt the muslin. 
 
 Caroline, So it has indeed ! Well, I will fasten the stopper, and 
 put the bottle away, for it is a dangerous substance Oh, now I 
 have done worse still, for I have spilt some on my hand ! 
 
 Mrs. B. It is then burned, as well as your gown, for you know 
 that oxygen destroys animal as well as vegetable matter; and as 
 far as the decomposition of the skin of your finger is effected, there 
 is no remedy ; but by washing it immediately in water, you will di- 
 lute the acid, and prevent any further injury. 
 - Caroline. It feels extremely hot, I assure you. 
 
 Mrs. B. You have now learned by experience, how cautiously 
 this acid must be used. You will soon become acquainted with 
 another acid the nitric, which, though it produces less heat on the 
 skin, destroys it still quicker, and makes upon i' an indelible stain. 
 You should never handle any substances of this kind without pre- 
 viously dipping your fingers into water, which will weaken their 
 caustic effect. But, since you will not repeat the experiment, I 
 must put in the stopper, for the acid attracts the moisture from the 
 atmosphere, which would destroy its strength and purity. 
 
 Emily. Pray, how can sulphuric acid be extracted from sulphat 
 of iron by distillation? 
 
 Jars. B. The process of distillation, you know consists in sepa- 
 rating substances from one another by means of their different de- 
 grees of volatility, and by the introduction of a new chemical agent, 
 caloric. Thus, if sulphat of iron be exposed in a retort to a proper 
 degree of heat, it will be decomposed, and the sulphuric acid will 
 be volatilized. 
 
 Emily But now that the process for forming acids by the com- 
 bustion uf their radicals is known, why should not this method be 
 used for making sulphuric acid ? 
 
 Mis. B. This is actually done inmost manufactures; but the 
 usual method of preparing sulphuric acid does not consist in burn- 
 ing the sulphur in oxygen gas (as we formerly did by way of ex- 
 periment,) but in heating it together with another substance, nitre, 
 which yields oxygen in sufficient abundance to render the combus- 
 tion in common air rapid and complete. 
 
 Caroline. This substance, then, answers the same purpose as ox- 
 ygen gas? 
 
 Mrs. B. Exactly. In manufactures the combustion is performed 
 in a leaden chamber, with water at the bottom, to receive the va- 
 pour and assist its condensation. The combustion is however, never 
 so perfect but that a quantity of sulphureous acid is formed at the 
 
 905. How does sulphuric compare with nitric acid ? 
 
 906. In what consists the process of distillation? 
 
 907. How is sulphuric acid obtained ? 
 
AND SULPHUREOUS ACIDS. 209 
 
 same time ; for, if you recollect that the sulphureous acid, accord- 
 ing to the chemical nomenclature, differs from the sulphuric only 
 by containing less oxygen. 
 
 From its own powerful properties, and from the various combina- 
 tions into which it enters, sulphuric acid is of great importance m 
 many of the arts. 
 
 It is used also in medicine in a state of great dilution ; for were 
 it taken internally, in a concentrated slate, it would prove a most 
 dangerous poison. 
 
 Caroline. I am sure it would burn the throat and stomach. 
 
 Mrs. B. Can you think of any thing that would prove an anti- 
 dote to this poison ? 
 
 Caroline. A large draught of water to dilute it. 
 
 Mrs. B That would certainly weaken the caustic power of the 
 acid, but it would increase the heat to an intolerable degree. Do 
 you recollect nothing that would destroy its deleterious properties 
 more effectually ? 
 
 Emily. An Alkali might, by combining with it ; but, then, a pure 
 alkali is itself a poison, on account of its causticity. 
 
 Mrs. B. There is no necessity that the alkali should be caustic. 
 Soap, in which it is combined with oil ; or magnesia, either in tb 
 state of carbonat, or mixed with water, would prove the best anti- 
 dote. 
 
 Emily. In those cases then, I suppose, the potash and the mag- 
 nesia would quit their combinations to form salts with the sulphuric 
 acid ? 
 
 Mrs. B. Precisely. 
 
 We may now make a few observations on the sulphureous acid, 
 which we have found to be the product of sulphur slowly and im- 
 perfectly burnt. This acid is distinguished by its pungent smell, 
 and its gaseous form. 
 
 Caroline. Its aeriform state is, I suppose, owing to the smaller 
 proportion of oxygen, which renders it lighter than sulphuric acid ? 
 
 Mrs. B. Probably ; for by adding oxygen lo the weaker acid, 
 it may be converted into the stronger kind. But this change of 
 state may also be connected with a change of affinity with regard 
 to caloric 
 
 Emily. And may sulphureous acid be obtained from sulphuric 
 acid by a diminution of oxygen ? 
 
 Mrs. B. Yes ; it can be done by bringing any combustible sub- 
 stance in contact with the acid. This decomposition is most easily 
 performed by some of the acids ; these absorb a portion of the oxy- 
 gen from the sulphuric acid, which is thus converted into the sul- 
 phureous, and flies off in its gaseous form. 
 
 Caroline. And cannot the sulphureous acid itself be decomposed 
 and reduced lo sulphur? 
 
 Mrs. B. Yes; if this gas be heated in contact with charcoal, the 
 oxygen of (he gas will combine with it, and the pure sulphur will 
 be regenerated. 
 
 908. How does sulphureous acid differ from sulphuric ? 
 
 909. What would prove the best remedy to a person who had 
 swallowed sulphuric acid ? 
 
 910. Flow may sulphureous acid be obtained ? 
 
 91 1. How can the sulphuric acid be changed to the sulphureous ? 
 
 912. How can sulphureous acid be reduced to sulphur ? 
 
 18* 
 
210 OF THE SULPHUREOUS ACID. 
 
 Sulphureous acid is readily absorbed by water ; and in this liquid 
 state it is found particularly useful in bleaching linen and woollen 
 cloths, and is much used in manufactures for those purposes. I 
 can show you its effect in destroying colours, by taking out vegeta- 
 ble stains I think I see a spot on your gown, Emily, on which we 
 may try the experiment. 
 
 Emily. It is the stain of mulberries ; but I shall be almost afraid 
 of exposing my gown to the experiment, after seeing the effect 
 which the sulphuric acid produced on that of Caroline 
 
 Mrs. B. There is no such danger from the sulphureous ; but the 
 experiment must be made with great caution, for during the forma- 
 tion of sulphureous acid by combustion, there is always some sul- 
 phuric produced. 
 
 Caroline. But where is your sulphureous acid ? 
 
 Mrs. B. We may easily prepare some ourselves, simply by burn- 
 ing a match ; we must first wet the stain with water, and now hold 
 it in this way, at a distance over the lighted match; the vapour 
 that arises from it is sulphureous acid, and the stain, you see, gradu- 
 ally disappears. 
 
 Emily. I have frequently taken out stains by this means, with- 
 out understanding the nature of the process. But why is it neces- 
 sary to wet the stain before it is exposed to the acid fumes ? 
 
 Mrs. B* The moisture attracts and absorbs the sulphureous 
 acid ; and it serves likewise to dilute any particles of sulphuric acid 
 which might injure the linen. 
 
 Sulphur appears to be susceptible of a third combination of oxy- 
 gen, in which the proportion of the latter is too small to render the 
 sulphur acid. It acquires this slight oxygenation by mere exposure 
 to the atmosphere, without any application of heat ; in this case 
 the sulphur does not change its natural form, but is only discolour- 
 ed, being changed to red or brown, a state in which it may be 
 considered an oxyd of sulphur. 
 
 Before we take leave of the sulphuric acid, we shall say a few 
 words of its principal combinations. It unites with all the alkalies, 
 alkaline earths and metals, to form compound salts. 
 
 Caroline. Pray, give me leave to interrupt you for a moment : 
 you have never mentioned any other salts than the compound or 
 neutral salts ; is there no other kind ? 
 
 Mrs. B. The term salt has been used, from time immemorial, as 
 a kind of a general name for any substance that has savour, odour, 
 is soluble in water, and crystallizable, whether it be of an acid, an 
 alkaline or compound nature : but the compound salts alone retain 
 that appellation in modern chemistry. 
 
 The most important of the salts formed by the combinations of the 
 sulphuric acid, are, first, sulphat of potash, formerly called sal poly- 
 ehrest : this is a very bitter salt, much used in medicine ; it is found 
 in the ashes of most vegetables, but it may be prepared artificially 
 by the immediate combination of sulphuric acid and potash. This 
 
 913. What important use is made of this acid ? 
 
 914. What is the easiest process for making this acid ? 
 
 915. How would you describe a third combination of sulphur 
 with oxygen ? 
 
 916. With what does sulphuric acid unite ? 
 
 917. What is the meaning of the term salt? 
 
OF THE SULPHATS. 211 
 
 salt is easily soluble in boiling- water. Solubility is, indeed, a prop- 
 erty common to all salts ; and they always produce cold in melting- 
 
 Emily. That must be owing to the caloric which they absorb in 
 passing- from a solid to a fluid form. 
 
 Mrs. B. That is, certainly, the most probable explanation. 
 
 Sulphat of Soda, commonly called Glauber's salt, is another me- 
 dicinal salt, which is still more bitter than the preceding-. We must 
 prepare some of these compounds, that you may observe the phe- 
 nomena which take place during- their formation. We need only 
 pour some sulphuric acid over the soda which I have put into this 
 glass. 
 
 Caroline. What an amazing- heat is disengaged ! I thought you 
 said that cold was produced by the melting of salts? 
 
 Mrs. B. But you must observe that we are now making, not melt- 
 ing, a salt. Heat is disengaged during the formation of compound 
 salts, and a faint light is also emitted, which may sometimes be per- 
 ceived in the dark. 
 
 Emily. And is this heat and light produced by the union of the 
 opposite electricities of the 'alkali and the acid r 
 
 Mrs. B. No doubt it is, if that theory be true. 
 
 Caroline. The union of an acid and an alkali is then an actual 
 combustion ? 
 
 Mrs.B. Not precisely, though there is certainly much analogy 
 in these processes. 
 
 Caroline* Will this sulphat of soda become solid ? 
 
 .Mr*. B. We have not, I suppose, mixed the acid and the alkali 
 in the exact proportions which are required for the formation of 
 the salt, otherwise the mixture would have been almost immediate- 
 ly changed to a solid mass ; but in order to obtain it in crystals, as 
 you bee it in this bottle, it would be necessary first to dilute it with 
 water, and afterwards to evaporate the water, during which opera- 
 tion the salt would gradually crystallize. 
 
 Caroline. But of what use is the addition of ivater, if it is after- 
 wards to be evaporated ? 
 
 Mrs. B. When suspended in water, the acid and the alkali ar 
 more at liberty to act on each other, their union is more complete, 
 and the salt assumes the regular form of crystals during the slow 
 evaporation of its solvent. 
 
 Sulphat of soda liquefies by heat and effloresces in the air. 
 
 Emily* Pray what is the meaning of the word effloresces? I do 
 not recollect your having mentioned it before. 
 
 Mrs. B. A salt is said to effloresce when it loses its water of crys- 
 tallization on being exposed to the atmosphere, and is thus gradual- 
 ly converted into a dry powder : you may observe that these crys- 
 tals .of sulphat of soda are far from possessing the transparency 
 which belongs to their crystalline state ; they are covered with a 
 white powder, occasioned by their having been exposed to the at- 
 mosphere, which has deprived their surface of its lustre, by absorb- 
 ing its water of crystallization. Sails are, in general, either efflor- 
 escent or ddique&cent : this latter property is precisely the reverse of 
 
 918. Why do the salts produce cold in melting ? 
 
 919. By what name is the sulphat of soda called ? 
 
 920. How can sulphat of soda be formed ? 
 
 921. What is the signification of the word effloresces ? 
 
212 OF THE SULPHATS. 
 
 the former ; that is to ssy, deliquescent salts absorb water from the 
 atmosphere, and are moistened and gradually melted by it. Muriat 
 of lime is an instance of great deliquescence. 
 . Emily But are there no salts that have the same degree of at- 
 traction for water as the atmosphere, and that will consequently 
 not be affected by it ? 
 
 Mrs. B. Yes: there are many such salts, as, for instance, com- 
 mon salt, sulphat of magnesia, and a variety of others. 
 
 Sulphat oflimeis very frequently met with in nature, and consti- 
 tutes the well known substance called gypsom or plaster of paris. 
 
 Sulphat of magnesia, commonly called Lpsomsalt, is another very 
 bitter medicine, which is obtained from sea- water and from several 
 spring's, or may be prepared by the direct combination of its ingre- 
 dients 
 
 We hare formerly mentioned sulphat ofalumine as constituting 
 the common alum; it is found in nature chiefly in the neighborhood 
 of volcanoes, and is particularly useful in the arts, from its strong 
 astringent qualities. It is chiefly employed by dyers and calico- 
 printers, to fix colours ; and is used also in the manufacture of 
 some kinds of leather. 
 
 Sulphuric acid combines also with the metals. 
 
 Caroline. One of these combinations, sulphat of iron, we are al- 
 ready well acquainted with. 
 
 Mrs.B. This h the most important metallic salt formed by sul- 
 phuric acid, and the only one which we shall here notice. It is of 
 great use in the arts ; and in medicine, it affords a very valuable 
 tonic ; it is of this salt that most of those preparations called steel 
 medicines are composed. 
 
 Caroline. But does any carbon enter into these compositions to 
 form steel ? 
 
 Mrs. B. Not an atom : they are, therefore, very improperly cal- 
 ted steel ; but it is the vulgar appellation, and medical men them- 
 selves often comply with the general custom. 
 
 Sulphat of iron may be prepared, as you have seen, by dissolving 
 iron in sulphuric acid : but is generally obtained from the natural 
 production called Pyrites, which being a sulphuret of iron, requires 
 only exposure to the atmosphere to be oxydated, in order to form 
 the salt ; this, therefore, is much the most easy way of procuring 
 it on a large scale. 
 
 Emily. I am surprised to find that both acids and compound salts 
 are generally obtained from their various combinations, rather than 
 from the immediate union of their ingredients. 
 
 Mrs. E>. Were the simple bodies always at hand, their combina- 
 tions would naturally be the most convenient method of forming 
 compounds ; but you must consider that, in most instances, there is 
 great difficulty and expense in obtaining the simple ingredient from 
 
 92?. What is the signification of the word deliquescent ? 
 
 923. What substance is frequently found in nature, the same a* 
 sulphat of lime ? 
 
 924. From what is the sulphat of magnesia obtained ? 
 
 925. Where is the sulphat of ahimine chiefly found? 
 
 926. For what purpose is it used? 
 
 927. From what is the sulphat of iron obtained ? 
 
 928. How is sulphat of iron manufactured in the large way ? 
 
OF THE STJLPHATS. 213 
 
 their combinations ; it is, therefore, often more expedient to procure 
 compounds from the decomposition of other compounds. But, to 
 return to the sulphat of iron. There is a certain vegetable acid 
 called gallic acid, which has the remarkable property of precipitat- 
 ing this salt black I shall pour a few drops of the gallic acid into 
 this solution of sulphat- of iron 
 
 Caroline. It is become as black as ink ! 
 
 Mrs B. And it is ink in reality. Common writing ink is a pre- 
 cipitate of sulphat of iron by gallic acid ; the black color is owing 
 to the formation of gallat of iron, which being insoluble, remains 
 suspended in the fluid. 
 
 This acid has also the property of altering the color of iron in 
 its metallic state. You may frequently see its effect on the blade of 
 a knife, that has been used to cut certain kinds of fruits. 
 
 Caroline. True; and that is, perhaps, the reason that a silver 
 knife is preferred to cut fruits ; the gallic acid, i suppose, does not 
 act upon silver. Is this acid found in all fruits ? 
 
 Mrs. B. It is contained, more or less, in the rind of most fruits 
 and roots, especially the radish, which, if scraped with a steel or iron 
 knife, has its*bright red color changed to a deep purple, the knife 
 being at the same time blackened. But the vegetable substance 
 in which the g'allio acid most abounds, is nutgall, a kind of ex- 
 cresence that grows on oaks, and fr&m which the acid is commonly 
 obtained for its various purposes. 
 
 Mrs B. We now come to the PHOSPHORIC and PHOSPHOROUS 
 ACIDS. In treating of phosphorus, you have seen how these acids 
 may be obtained from it by combustion. 
 
 Emily. Yes ; but I should be much surprised if it was the usual 
 method' of obtaining them, since it is so very difficult to procure 
 phosphorus in its pure state. 
 
 Mrs. B. You are right, my dear ; the phosphoric acid, for gene- 
 ral purposes, is extracted from bones, in which it is contained in the 
 state of phosphat of lime ; from this salt the phosphoric acid is sepa- 
 rated by means of the sulphuric, which combines with the lirne. In 
 its pure state, phosphoric acid is either liquid or solid, according to 
 its degree of concentration. 
 
 Among the salts formed by this acid, phosphat of lime is the only 
 one that affords much interest ; and this, we have already observed, 
 constitutes the basis of all bones. It is also found in very small 
 quantities in some vegetables. 
 
 929. How may the sulphat of iron be turned black ? 
 
 930. Why is a knife turned black in cutting fruit ? 
 
 931. In what vegetable substance does gallic acid mostly abound? 
 
 932. Where is the phosphat of lime found ? 
 
214 ON THE NITRIC 
 
 CONVERSATION XVIII. 
 
 OF THE NITRIC AND CARBONIC ACIDS ; OR THE COMBINATIONS 
 OF OXYGEN WITH NITROGEN AND CARBON ; AND OF THE 
 NITRATS AND CARBONATS. 
 
 Mrs. B. I am almost afraid of introducing- the subject of the 
 JRTITRIC ACID, as I am sure that I shall be blamed by (. aroline for 
 not having made her acquainted with it before.. 
 
 Caroline. Whj so, Mrs. B. ? 
 
 Mrs. B. Because you have long known its radical, which is ni- 
 trogen, or azote; and in treating- of that element, i -lid not even 
 hint that it was the basis of an acid. 
 
 Caroline. And what could be your reason for not mentioning this 
 acid sooner ? 
 
 Mrs. B. I do not know whether you will think the reason suffi- 
 ciently good to afcquit me ; but the omission, I assure yon, did not 
 proceed from negligence. You may recollect that nitrogen was one 
 of the first simple bodies which we examined ; you were then igno- 
 rant of the theory of combustion, which 1 believe was* for the first 
 time, mentioned in that lesson; and therefore it would have been 
 in vain, at that time, to have attempted to explain the nature and 
 formation of acids. 
 
 Caroline. 1 wonder, however, that it never occurred to us to in- 
 quire whether nitrogen could be acidified ; for, as we knew it was 
 classed among the combustible bodies, it was natural to suppose that 
 it might produce an acid. 
 
 Mrs. B. That is not a necessary consequence ;*/or it might com- 
 bine with oxygen only in the degree requisite to form an oxyd. But 
 jou will find that nitrogen is susceptible of various degrees of oxy- 
 genation, some of which convert it merely into an oxyd, and others 
 give it all the acid properties. 
 
 The acids, resulting from the combination of oxygen and nitro- 
 gen, are called the NITROOS and NITRIC acids. We will begin with 
 the nitric, in which nitrogen is in the highest state of oxygenation. 
 This acid has so powerful an attraction for water lhat it has never 
 been obtained perfectly free from it. But water may be so strongly 
 impregnated with it as to form an exceedingly powerful arid solu- 
 tion. Here is a bottle of this acid, which you see, is quite limpid. 
 
 Caroline. What a strong offensive smell it has ! 
 
 Mrs. B. This acid confains a greater abundance of oxygen than 
 any other ; but it retains it w>'h very little force. 
 
 Emily. Then it must be a powerful caustic, both from the facility 
 with which it parts with its oxygen, and the quantity which it affords. 
 
 933. What is the radical of nitric acid ? 
 
 934. What acids are formed by the combination of nitrogen and 
 oxygen ? 
 
 935. How does nitric acid naturally exist ? 
 
 936. How does this compare with oilier acids as to the quantity 
 of oxygen contained in it ? 
 
 937. To what is the gfeat causticity of nitric acid owing ? 
 
I 
 
 AND NITROUS ACTDS. 215 
 
 Mn. B. Very well, Emily ; both causes and effects are exactly 
 such as you describe ; nitric acid burns and destroys all kinds of 
 organized matter. It even sets fire to some of the most combustible 
 substances. We shall pour a little of it over this piece of dry 
 warm charcoal* you see it inflames it immediately ; it would do 
 the same with oil of turpentine, phosphorus, and several other very 
 combustible bodies. This shows you how easily this acid is decom- 
 posed by combu-tible bodies, since these effects must depend upon 
 the absorption of its oxygen. 
 
 Nitric acid has been used in the arts from time immemorial ; but 
 it is only within these twenty-five years that its chemical nature has 
 been ascertained. The celebrated Mr. Cavendish discovered that 
 it consisted of about 10 paits of nitrogen and 25 of oxygen. f These 
 principles, in their gaseous state, combine at a high temperature; 
 and this may be effected by repeatedly passing the electoral spark 
 through a mixture of the two gases. 
 
 Emily. The nitrogen and oxygen gases, of which the atmosphere 
 is composed, do not combine I suppose, because their temperature 
 is not sufficiently elevated. 
 
 Caroline. But in a thunder-storm, when the lightning repeatedly 
 passes through them, may itnot produce nitric acid ? We should be 
 in a strange situation, if a violent storm should at once convert the 
 atmosphere into nitric acid. 
 
 Mrs. B. There is no danger of it, my dear : the lightning can af 
 feet but a very small portion of the atmosphere, and though it wer 
 occasionally to produce a little nitric acid, it never could happen to 
 such an extent as to be perceivable. 
 
 Emily. But how could the nitric acid be known, and used, before 
 the method of combining its constituent was discovered ? 
 
 Mrs. B. Previous to that period the nitric acid was obtained, 
 and it is indeed still extracted, for the common purposes of art, 
 from the compound salt which it forms with pot-ash, commonly call- 
 ed nitre. 
 
 Caroline. Why is it so called ? Pray, Mrs. B., let these old un- 
 meaning names be entirely given up, bj us at least; and let us call 
 this salt nitrat of pot-fish. 
 
 * To inflame charcoal, a stronger acid than that sold at the shops 
 is necessary. The experiment with oil, turpentine, and phospho- 
 rus, succeeds, if about a sixth part of sulph. acid is added to the ni- 
 tric acid. The experiment with the turpentine requires caution. 
 The vial containing the acid must be tied to a stick, a yard or two 
 long, the operator pouring it into a small quantity of the turpentine 
 standing at a distance. C. 
 
 f The proportion stated by Sir H. Davy, in his Chemical Re- 
 searches, is as 1 to 2,389. 
 
 938. What is the reason why nitric acid inflames charcoal, oil of 
 turpentine, &c. ? 
 
 939. What are the proportions of oxygen and nitrogen in nitric 
 acid ? 
 
 940. What is the reason, that the oxyqen and nitrogen of which 
 the atmosphere is composed, do not combine and form nitric acid ? 
 
 941. Why, does not lightning produce Uug elevation of lempera- 
 ture ? 
 
216 ON THE NITRIC 
 
 Mrs. B. With all my heart; but it is necessary that I should, at 
 least, mention the old names, and more especially those which are 
 yet in common use ; otherwise, when you meet with them, you 
 would not be able to understand their meaning. 
 
 Emily. And how is the acid obtained from this salt ? 
 
 Mrs. B. By the intervention of sulphuric acid, which combines 
 with the pot-ash, and sets the nitric acid at liberty. This I can 
 easily show you, by mixing some nitrat of potash and sulphuric acid 
 in this retort, and heating it over a lamp ; the nitric acid will come 
 over in the form of vapour, which we shall collect in a glass bell. 
 This acid diluted in water, is commonly called aquafortis, if Car- 
 oline will allow me to mention that name. 
 
 Caroline. 1 have often heard that aqua fortis will dissolve almost 
 all metals ; it is no doubt because it yields its oxygen so easily. 
 
 Mrs. B. Yes ; and from this powerful solvent property, it deriv- 
 ed the name of aqua fortis, or strong water. Do you not recol- 
 lect, that weoxydated, and afterwards dissolved, some copper in this 
 acid ? 
 
 Emily. If 1 remember right, the nitrat of copper was the first in- 
 stance you gave us of a compound salt. 
 
 Caroline. Can the nitric acid be completely decomposed and con- 
 verted into nitrogen and oxygen ? 
 
 Emily. That cannot be the case, Caroline ; since the acid can b& 
 decomposed only by the combination of its constituents with other 
 bodies. 
 
 Mrs. B. True ; but caloric is sufficient for this purpose. 
 
 By making the acid pass through a red hot porcelain tube, it is 
 decomposed ; the nitrogen and oxygen regain the calorie which 
 they had lost in combining, and are thus both restored to their gas- 
 eous state. 
 
 The nitric, acid may also be partly decomposed, and is by this 
 means converted into NITROUS ACID. 
 
 * Caroline. This conversion must be easily effected, as the oxygen 
 is so slightly combined with the nitrogen. 
 
 Mrs. B. The partial decomposition of nitric acid is readily ef- 
 fected by most metals; but it is sufficient to expose the nitric acid to 
 a very strong light to make it give out oxygen gas,and thus be con- 
 verted into nitrous acid. This latter acid appears in various degrees 
 of strength, according to the proportions of nitrous acid gas and 
 water of which it is composed ; the strongest ,is a yellow color, as 
 you see in this bottle. 
 
 Caroline. How it fumes when the stopper is -taken out'! 
 
 Jtfrs. B. The acid exists naturally in a gaseous state, and is here 
 so strongly concentrated in water, that it is constantly escaping. 
 
 Here is another bottle of nitrous acid, which, you see, is of an or- 
 ange red : this acid is weaker, that is, contains a smaller quantity of 
 the acid gas ; and with a still less proportion of the gas it is of an 
 
 942. How is nitric acid obtained from the nitrate of potash ? 
 
 943. What is the common name of nitric acid diluted in water? 
 044. What is the propriety of the name aqua fortis? 
 
 945. How may nitric acid be decomposed ? 
 
 946. How can nitrous acid be formed ? 
 
 947. How may the color of water be effected by the different 
 portions of nitrous acid with^hich it is combined ? 
 
AND NITROUS ACIDS. 217 
 
 olive-green colour, as it appears in this third bottle. In short, the 
 weaker the acid, the deeper is its colour. 
 
 Nitrous acid acts still more powerfully on some inflammable sub- 
 stances than the nitric. 
 
 Emily. I am surprised at that, as it contains less oxygen. 
 
 Mrs. B. But, on the other hand, it parts with its oxygen much 
 more readily : you may recollect that we once inflamed oil with 
 this acid. 
 
 The next combinations of nitrogen and oxygen form only oxyds 
 of nitrogen, the first of which is commonly called nitrous air ; or 
 more properly nitric oxyd gas.* This may be obtained from nitric 
 acid, by exposing the latter to the action of metals, as in dissolving 
 them it does not yield the whole of its oxygen, but retains a portion 
 of this principle sufficient to convert it into this peculiar gas, a spe- 
 cimen of which 1 have prepared, and preserved with this inverted 
 glass bell. 
 
 Emily. It is-a-perfectly invisible elastic fluid. 
 
 Mrs. B. Yes ; and it may be kept any length of time in this man- 
 ner over water, as it is not, like the nitric and nitrous acids, absorb- 
 able by it. It is rather heavier than atmospherical air, and is inca- 
 pable of supporting either combustion or respiration. I am going 
 to incline the glass gently on one side, so as to let some of the gas 
 escape 
 
 Emily. How very curious ! It produces orange fumes like the 
 nitrous acid ! that is the more extraordinary, as the gas within the 
 glass is perfectly invisible. 
 
 Mrs. B. It would give me much pleasure if you could make out 
 the reason of this curious change, without requiring any further 
 explanation. 
 
 Caroline. It seems, by the colour and smell, as if it were convert- 
 ed into nitrous acid gas ; yet that cannot be, unless it combines 
 with more oxygen ; and how can it obtain oxygen the very instant 
 it escapes from the glass ? 
 
 Emily. From the atmosphere, no doubt. Is it not so, Mrs. B. ? 
 
 Mrs. B. You have guessed it ; as soon as it comes in contact with 
 the atmosphere, it absorbs from it the additional quantity of oxygen, 
 necessary to convert it into nitrous acid gas. And, if I now remove 
 the bottle entirely from the water, so as to bring at once the whole 
 of the gas in contact with the atmosphere, this conversion will ap- 
 pear still more striking. 
 
 Emily. Look, Caroline, the whole capacity of the bottle is in- 
 stantly tinged of an orange colour ! 
 
 Mrs. B. Thus you see, it is the most easy process imaginable to 
 
 * To procure nitrous air, put into a retort some filings, or shav- 
 ings of copper, on which pour nitric acid, diluted with four or five 
 parts of water ; then apply the beat of a lamp, and receive the gas in 
 the usual way, over water. C. 
 
 948. Why does nitrous acid act more powerfully on some inflam- 
 mable substances than nitric acid ? 
 
 949. How can nitrous air, or nitric oxyd gas be obtained-? 
 
 950. How can this gas be preserved ? 
 
 951..Kowcan nitrous oxyd gas be converted yx to nitrous -cwl 
 ? 
 
218 OF THE NITRIC 
 
 convert nitrous oxydgns, into nitrous acid gas. The property of at- 
 tracting oxygen from the atmosphere, without any elevation of tem- 
 perature, has occasioned this gaseous oxjd being used as a test, for 
 ascertaining the degree of purity of the atmosphere. I am going to 
 show you how it is applied to this purpose. You see this graduated 
 glass tube, which is closed at one end, (see fig. 30,) I first fill it with 
 water, and then introduce a certain measure of nitrous gas, which, 
 not being absorbable by water, passes through it, and occupies the 
 upper part of the tube. I must now add rather above two-thirds of 
 oxygen gas, which will just be sufficient to convert the nitrous oxyd 
 gas into nitrous acid gas. 
 
 Caroline. So it has ! I saw it turn of an orange colour ; but it 
 immediately afterwards disappeared entirely, and the water, you 
 see, has risen, and almost filled the tube. 
 
 Mrs. B. That is because the acid gas is absorbable by wafer, 
 and in proportion as the gas impregnates the water, the latter rises 
 in the tube. When the oxygen gas is very pure, and the required 
 proportion of nitrous oxyd gas very exact, the whole is absorbed by 
 the water ; but if any other gas be mixed with the oxygen, instead 
 of combining with the nitrous oxygen, it will remain and occupy the 
 upper part of the tube : or if the gases be not in the. dye proportion, 
 there will be a residue of that which predominates. Pefore we leave 
 this subject, 1 must not forget to remark that nitrous acid may be 
 formed, by dissolving nitrous oxyd gas in nitric ^cid. This solution 
 may be effected simply, by making bubbles of nitrous oxyd gas pass 
 through nitric acid. 
 
 Emily. That is to say, that nitrogen at its highest degree of oxy- 
 genation, being mixed with nitrogen at its lowest degree of oxy- 
 genation, will produce a kind of intermediate substance, which is 
 nitrous r..cid. 
 
 J\Irs- B. You h?.ve stated the fact with great precision. There 
 are various other methods of preparing nitrous oxyd, and of obtain- 
 ing it from compound bodies ; but it is not necessary to enter into 
 these, particulars. It remains for me only to mention another curi- 
 ous modification of oxygenated nitrogen, which has been distinguish- 
 ed by the name of gaseous oxyd of nitrogen. It is but lately that 
 this gas has been accurately examined, and its properties have been 
 investigated chiefly by Sir H. Davy. It has obtained also the name 
 of exhilarating gas, from the very singular property which that gen- 
 tleman has discovered in it, of elevating the animal spirits, when in- 
 haled into the lungs, to a degree sometimes 'resembling delirium or 
 intoxication. 
 
 Caroline. It is respirable, then? 
 
 Emily. It can scarcely be called respirable, as it would not sup- 
 port life for anv length of time ; but it may be breathed for a few 
 moments without any other effects, than the singular exhilaration of 
 spirits I have just mentioned. It affects different people, however, 
 in a v?ry different manner. Some become violent, even outrage ou 
 
 952. On what principle can nitrous air be applied, to test the pu- 
 rity of the atmosphere ? 
 
 953. What is the process? 
 
 954. By what other name is the exhilarating gas called ? 
 
 955. And -why is it called exhilarating gas ? 
 
AND NITROUS ACIDS. 
 
 219 
 
 others experience a languor attended with faintness; but most agree 
 in opinion, that the sensations it excites are extremely pleasant. 
 
 Caroline. I thought I should like to try it how do you breathe it? 
 
 Mrs. B. By collecting the gas in a bladder, to which a short tube 
 with a stop-cock, is adapted ; this is applied to the niou'h with one 
 hand, whilst the nostrils are kept closed with the other, in order that 
 the common air may have no access. You then alternately inspire, 
 and expire the gas,' till you perceive its effects. But I cannot con- 
 sent to your making the experiment ; for the nerves are sometimes 
 unpleasantly affected by it, and I would not run any risk of that 
 kind. 
 
 Emily. I should like, at least, to see some body breathe it ; but 
 pray by what means is this curious gas obtained ? 
 
 Mrs. B. Jt ia procured from nif.rnt of ammonia.* an arti6cial 
 salt, which yields this gas on the application of a gentle heat. I have 
 put some of the salt into a retort, and by the aid of the lamp the gas 
 will be extricated. 
 
 Caroline. Bubbles of air begin to escape through the neck of the 
 retort into the water apparatus ; will you not collect them ? 
 
 Mrs. B. The gas that first comes over need not be preserved, as 
 it consists of little more than common air that was in the retort ; 
 
 * To make nitrate of ammonia, take some nitric acid, or aqua 
 fortis dilute it with four or five quarts of water ; put it into a shal- 
 low earthen dish, and throw in pieces of carhonate of ammonia, un- 
 til the effervescence ceases. Evaporate about one third of the liquor 
 by a gentle heat, and sot it away to crystallize. The crystals are 
 Gug sirivieu prisms. To procure the m.'Vm/' .';.X<>7 r T.'!?7" r ^* n 
 gas, and to try its effects by respiration, the following simple appa- 
 ratus may be used, where a better is not ni hand. Put some nitrate 
 of ammonia into an oil flask, having first fitted to it a cork an:i o-lass 
 tube, bent so as to go under the receiver in the water hath Then 
 apply the gentle heat of a lamp. 
 
 For a receiver, fill a large jug with water, and invert it in the 
 water bath ; having fitted to the jug a cork, having two holes made 
 through it with a burning ir0h ; into one of these holes put a glass 
 tube open at both ends, and nearly long enough to reach the bottom 
 of the jug. Providea large bladder furnished with a short tube tied 
 to it. When the jug is nearly filled with the gas, remove and set it 
 upright, by passing the hand'under its mouth then put in the cork 
 and tube, the other opening in the cork being closed When you 
 wish to breathe the gas, bikp the stopper out of the cork, arid pass 
 in the tube attached to the bladder. Then by means of a small tun- 
 nel, pour water into the jug through the long'tube, until it drives out 
 gas enough to fill the bladder. Mrs. B. describes the manner of 
 breathing it. 
 
 Caution. Let the gas stand an hour or two over water before it is 
 breathed C. 
 
 956. How is this gas breathed ? 
 
 957. How is this gas obtained : 
 
 958. When do chemical decompositions and combinations take 
 place, during the formation nf this gas from nitrate of ammonia? 
 
 959. What caution is necessary before it is breathed ? 
 
220 OF THE NITRIC 
 
 besides there is always in this experiment, a quantity of watery va- 
 pour which must come away before the nitrous oxyd appears. 
 
 Emily. Watery vapour? Whence does that proceed ? There is no 
 water in nitrat of ammonia ? 
 
 Mrs. B. You must recollect that there is in every salt a quantity 
 of water of crystallization, which may be evaporated by heat alone. 
 But, besides this, water is actually generated in this experiment, as 
 you will see presently. First tell me, what are the constituent parts 
 of nitrat of ammonia ? 
 
 Emily. Ammonia, and nitric acid ; this salt, therefore, contains 
 three different elements, nitrogen and hydrogen, which produce the 
 ammonia; and oxygen, which, with nitrogen, forms the acid. 
 
 Mrs. B. Well then, in this process the ammonia is decomposed; 
 the hydrogen quits the nitrogen to combine with some of the oxygen 
 of the nitric acid, and forms with it the watery vapour which is now 
 coming orer. VVhen that is effected, what will you expect to find ? 
 
 Emily. Nitrous acid instead of nitric acid, and nitrogen instead 
 of ammonia. 
 
 Mrs. B. Exactly so ; and the nitrous acid and nitrogen combine 
 and form the gaseous oxyd of nitrogen, in which the proportion of 
 oxygen is 37 parts to 63 of nitrogen. 
 
 You may have observed, that for a little while no bubbles of air 
 have come over, and we have perceived only a stream of vapour 
 condensing as it issued into the water. Now bubbles of air again 
 make their appearance, and I imagine that by this time all the wa- 
 tery vapour is come away, and that we may begin to collect the gas. 
 We may try whether it is pure, by filling a phial with it, and plung- 
 ing a taper into it yes, it will do now,- for the taper burns brighter 
 than in the common air, and with a greenish flame. 
 
 Caroline. But how is that? I thought no gas would su-pport com- 
 bustion but oxygen or chlorine. 
 
 Mrs. B. Or any gas that contains oxygen, and is ready to yield 
 it, which is the case with this in a considerable degree ; it is not 
 therefore, surprising that it should accelerate the combustion of the 
 taper. 
 
 You see that the gas is now produciii in great abundance ; we 
 shall collect a large quantity of it, and I dare say that we shall find 
 some of the family who will'be curious to make the experiment of 
 respiring it. Whilst this process is going on, we may take a gene- 
 ral survey of the most important combinations of the nitric and ni- 
 trous acids with the alkalies. 
 
 The first of these is nitrat of potash, commonly called nitre, or 
 saltpetre. 
 
 Caroline. Is not that the salt with which gunpowder is made ? 
 
 Mrs. B. Yes. Gunpowder is a mixture of five parts of nitrat to 
 one of sulphur, and one of charcoal Nitre, from its great proper- 
 
 960. W hat are the constituent parts of nitrat of ammonia ? 
 
 961. What is the process of making nitrous oxide? 
 
 962. How is the gaseous oxyd of nitrogen formed ? 
 
 963. How can it be determined when it is pure ? 
 
 964. What is the common name of nitrat of potash ? 
 
 965. Of what is gunpowder made ? 
 
AND- NITROUS ACIDS, 221 
 
 tion of oxygen, and from the facility with which it yields it, is the 
 basis of the most detonating compositions. 
 
 Emily. But what is the cause of the violent detonation of gun- 
 powder when set on fire ? 
 
 Mrs. B. Detonation may proceed from two causes ; the sudden 
 formation or destruction of an elastic fluid. Jn the first case, when 
 either a solid or liquid is instantaneously converted into an elastic 
 fluid, the prodigious and sudden expansion of the body strikes the 
 air with great violence, and this concussion produces the sound 
 called detonation. 
 
 Caroline. That I comprehend very well ; but how can a similar 
 effect be produced by the destruction of a gas ? 
 
 Mrs. B. A gas can be destroyed only by condensing it to a liquid 
 or solid state ; when this takes place suddenly, the gas, in assuming 
 a new and compact form, produces a vacuum, into which the sur- 
 rounding air rushes with great impetuosity ; and it is by that rapid 
 and violent motion that the sound is produced. In all detonations, 
 therefore, gases are either suddenly formed or destroyed. In that 
 of gunpowder^ can you tell me which of these two circumstances 
 takes place ? 
 
 Emily. As gunpowder is a solid, it must, of course, produce the 
 gases in its detonation ; but how, I cannot tell. 
 
 Mrs. B. The constituents of gownpowder, when heated to a cer- 
 tain degree, enter into a number of new combinations, and ar 
 instantaneously converted into a variety of gases, the sudden ex- 
 plosion of which gives rise to the detonation. 
 
 Caroline. And in what instance does the destruction or condensa- 
 tion of gases produce detonation ? 
 
 Mrs. B. I can give you one with which you are well acquainted ; 
 the sudden combination of the oxygen and hydrogen gases. 
 
 Caroline. True; I recollect perfectly that hydrogen detonates 
 with oxygen when the two gases are converted into water. 
 
 Mrs. B. But let us return to the nitrat of potash. This salt is 
 decomposed when exposed to heat, and mixed with any combusti- 
 ble body, such as carbon, sulphur, or metals, these substances oxy- 
 dating rapidly at the expense of the nitrat. I must show you an in- 
 stance of this. I expose to the fire some of the salt in a small iron 
 ladle, and, when it is sufficiently heated, add to it some powdered 
 charcoal ; this will attract the oxygen from the salt, and be con- 
 verted into carbonic acid. 
 
 Eanily. But what occasions that crackling noise, and those vivid 
 flashes that accompany it? 
 
 Mrs. B. The rapidity with which the carbonic acid gas is formed, 
 occasions a succession of detonations, which, together with the 
 emission offlame, is called deflagration. 
 
 Nitrat of ammonia we have already noticed, on account of the 
 gaseous oxyd of nitrogen which is obtained from' it. 
 
 966. Why is nitre the basis of most detonating compositions ? 
 
 967. What is the cause of the detonation of gunpowder, when 
 fire is set to it ? 
 
 968- What causes the detonation when a gas is destroyed ? 
 
 969. In what instance does the destruction or condensation of 
 gases produce detonation ? 
 
 970. When is the nitrat of potash decomposed ? 
 
 19* 
 
222 
 
 CARBONIC ACID. 
 
 Nilrat of silver, is the lunar caustic, so remarkable for its de- 
 stroying 1 animal fibre, for which purpose it is often used by sur- 
 geons. We have said so much on former occasions, on the mode 
 in which caustics act on animal matter, that I shall not detain you 
 any longer on this subject. 
 
 We now come to CARBONIC ACID, which we have already had 
 many opportunities of noticing-. You recollect that this acid may 
 be formed by the combustion of carbon, whether in its imperfect 
 state of charcoal, or in its purest form of diamond. And it is not 
 necessary, for this purpose, to burn the carbon in oxyen gas, as we 
 did in the preceding- lecture ; for you need only light a piece of 
 charcoal, and suspend it under a receiver on the water bath. The 
 charcoal will soon be extinguished, and the air in the receiver will 
 be found mixed with carbonic acid. The process, however, is 
 much more expeditious if the combustion be performed in pure 
 oxygen gas. 
 
 Caroline. But how can you separate the carbonic acid, obtained 
 in this manner, from the air with which il is mixed ? 
 
 JUrs. B. The readiest mode is to introduce under the receiver a 
 quantity of caustic lime, or caustic alkali, which soon attracts the 
 whole carbonic acid to form a carbonat. The alkali is found in- 
 creased in weight, and the volume of the air is diminished by a 
 quantity equal to that of the carbonic acid which was mixed with it. 
 
 Emily. Pray, is there no method of obtaining pure carbon from 
 carbonic acid ? 
 
 JWrs. B. For a long time it was supposed that carbonic acid was 
 not decompoundable ; but Mr. Tennant discovered, a few years ago, 
 that this acid may be decomposed by burning phosphorus in a closed 
 vessel with carbonat of soda or carbonat of lime ; the phosphorus 
 absorbs the oxygen from the carbonat, whilst the carbon is sepa- 
 rated in the form of a black powder. This decomposition, however, 
 is not effected simply by the attraction of the phosphorus for oxygen, 
 since it is weaker than that of charcoal ; but the attraction of the 
 alkali or lime for the phosphoric acid, unites its power at the same 
 time. 
 
 Caroline. Cannot we make the experiment ? 
 
 Mrs. B. Not easily ; it requires being performed with extreme 
 nicety, in order to obtain any sensible quantity of carbon, and the 
 experiment is much too delicate for me to attempt it. But there 
 can be no doubt of the accuracy of Mr. Tennant's results ; and all 
 chemists now agree, that one hundred parts of carbonic acid gas 
 consists of about twenty-eight parts of carbon to seventy-two of 
 oxygen gas. But if you recollect, we decomposed carbonic acid 
 gas the other day by burning potassium in it. 
 
 Caroline. True, so we Jid ; and found the carbon precipitated 
 on the regenerated potash. 
 
 Mrs. B. Carbonic acid gas is found very abundantly in nature ; 
 it is supposed to form about one thousandth part of the atmosphere, 
 
 971. What is nitrat of silver ? 
 
 972. What gas is produced by the burning of charcoal in oxy- 
 gen gas ? 
 
 973. How is carbonic acid formed ? 
 
 974. And how can carbon be obtained from carbonic acid ? 
 
 975. What portion of the atmosphere does this gas form ? 
 
 976. How is the carbonic acid gas in the atmosphere produced ? 
 
CARBONIC ACID. 223 
 
 and is constantly produced by the respiration of animals ; it exists 
 in a great variety of combinations, and is exhaled from many natu- 
 ral decompositions. It is contained in a state of great purity in 
 certain caves, such as the Grotto del Cane, near Naples. 
 
 Emily. I recollect having read an account of that grotto, and of 
 the cruel experiments made on the poor dogs, to gratify the curiosi- 
 ty of strangers. But I understood that the vapour exhaled by the 
 cave was called fixed air, 
 
 Mrs. B. That is the name by which carbonic acid was known 
 before its chemical composition was discovered. This gas is more 
 destructive of life than any other ; and if the poor animals that are 
 submitted to its effects are not plunged into cold water as soon as 
 they become senseless, they do not recover. It extinguishes flame 
 instantaneously. I have collected some in this glass, which I will 
 pour over the candle.* 
 
 Caroline. This is extremely singular it seems to extinguish the 
 light as it were by enchantment, as the gas is invisible. I never 
 should have imagined that gas could have been poured like a liquid. 
 
 Mrs. B. It can be done with carbonic acid only, as no other gas 
 is sufficiently heavy to be susceptible of being poured out in the 
 atmospherical air without mixing with it. 
 
 Emily. Pray, by what means did you obtain this gas ? 
 
 Mrs. B. I procured it from marble. Carbonic acid gas has so 
 strong an attraction for all the alkalies and alkaline earths, that 
 these are always found in nature in the state of carbonats. Com- 
 bined wilh lime, this acid forms chalk, which may be considered as 
 the basis of all kinds of marbles, and calcareous stones. From these 
 substances carbonic acid is easily separated, as it adheres so slight- 
 ly to its combinations, that the carbonats are all decomposable by 
 any of the other acids. I cart easily show you how I obtained this 
 gas ; I poured some diluted sulphuric acid over pulverized marble 
 in this bottle, (the same which we used the other day to prepare 
 hydrogen gas,) and the gas escaped through the the tube connected 
 with it ; the operation still continues, as you may perceive 
 
 Emily Yes, it does ; there is a great fermentation in the glass 
 vessel. What singular commotion is excited by the sulphuric acid 
 taking possession of the lime, and driving out the carbonic acid ? 
 
 Caroline. But did the carbonic acid exist in a gaseous state in 
 the marble ? 
 
 Mrs. B. Certainly not ; the acid, when in a slate of combina- 
 tion is capable of existing in a solid form. 
 
 Caroline. Whence, then, does it obtain the caloric necessary to 
 convert it into gas ? 
 
 * Merely pouring it over a candle, will not extinguish it. Put a 
 short piece of candle, or taper, into the bottom of a deep tumbler, 
 and then pour in the gas, and the flame goes out as quickly as 
 though you poured in water. C. 
 
 977. By what name was this known before its chemical com- 
 position was discovered ? 
 
 978. By what means is this gas procured for experiment ? 
 97<>. Of what is chalk formed ? 
 
 980. What is the basis of all kinds of marble and calcareous earths ? 
 
 981. How may carbonic acid be obtained from marble ? 
 
224 CARBONIC ACID. 
 
 Mrs. B. It may be supplied in this case from the mixture of sul- 
 phuric acid and water, which produces an evolution of heat, even 
 greater than is required for the purpose ; since, as you may per- 
 ceive by touching the glass vessel, a considerable quantity of the 
 caloric disengaged becomes sensible. But a supply of caloric may 
 be obtained also from a diminution of capacity for heat, occasioned 
 by the new combination which takes place ; and, indeed, this must 
 be the case when other acids are employed for the disengagement 
 of carbonic acid gas, which do not, like the sulphuric, produce heat 
 on being mixed with water. Carbonic acid may likewise be dis- 
 engaged from its combinations by heat alone, which restores it to 
 its gaseous state. 
 
 Caroline. It appears to me very extraordinary that the same gas 
 which is produced by the burning of wood and coal should exist 
 also in such bodies as marble and chalk, which are incombustible 
 substances. 
 
 .Mrs. B. I will not answer that objection, Caroline, because I 
 think I can put you in the way of doing it yourself. Is carbonic 
 acid combustible? 
 
 Caroline. Why, no because it is a body which has been already 
 burnt ;* it is carbon only, and not the acid that is combustible. 
 Mrs. B. Well, and what inference do you draw from this ? 
 Caroline. That carbonic acid cannot render the bodies with which 
 it is united combustible ; but that simple carbon does, and that it is 
 in this elementary state that it exists in wood, coals, and a great va- 
 riety of other combustible bodies. Indeed, Mrs. B., you are very 
 ungenerous ; you are not satisfied with convincing me that my ob- 
 jections are frivolous, but you oblige me to prove them so myself. 
 
 J\Irs. t B. You must confess, however, that I make ample amends 
 for the detection of error, when 1 enable you to discover the truth. 
 You understand, now, I hope, that carbonic acid is equally produced 
 by the decomposition of chalk, or by the combustion of charcoal. 
 These processes are certainly of a very different nature ; in the first 
 case the acid is already formed, and^ requires nothing more than 
 heat to restore it to its gaseous state ; whilst in the latter, the acid 
 is actually made by the process of combustion. 
 
 Caroline. I understand it now, perfectly. But I have just been 
 thinking of another difficulty, which, I hope, you will excuse my ' 
 not being able to remove myself. How does the immense quantity 
 of calcareous earth, which is 'spread all over the globe, obtain the 
 carbonic acid with which it is combined ? 
 
 Mrs. B. The question is, indeed, not very easy to answer ; but I 
 
 * IN ot burnt in the common acceptation of the word. The carbon 
 is already united to oxygen, and therefore has no affinity for it. In 
 the artificial production of carbonic acid, the carbon is burnt. C. 
 
 982. Whence does carbonic acid obtain the caloric necessary 
 toconvert it into gas ? 
 
 9B3. Will carbonic acid render a body combustible ? 
 
 984. It might be thought that carbonic a<;id could not be obtairi- 
 ed from substances so unlike as chalk and carbon how is this ob- 
 jection answered ? 
 
 985. How do the processes of obtaining carbonic acid from the 
 decomposition of chalk, and the combustion of charcoal differ ? 
 
CARBONIC ACID. 225 
 
 conceive that the general carbonization of calcareous matter maj" 
 have been the effect ofa general combustion,* occasioned by some 
 revolution of our globe, and producing an immense supply of car- 
 bdoic acid, with which the calcareous matter became impregnated; 
 or that this may have been effected by a gradual absorption of car- 
 bonic acid from the atmosphere. But this would lead us todiscus- 
 sions which we cannot indulge in, without deviating too much from 
 our subject. 
 
 Emily. How does it happen that we do not perceive the perni- 
 cious effects of the carbonic acid which is floating: in the atmosphere? 
 
 Mrs. B. Because of the state of very great dilution in which it 
 exists there. But can you tell me, Emily, what are the sources 
 which keep the atmosphere constantly supplied with this acid ? 
 
 Emily. I suppose the combustion of wood, coals, and other sub- 
 stances that contain carbon. 
 
 Mrs B. And also, the breath of animals. 
 
 Caroline. The breath of animals ? I thought you said that the 
 gas was not at all respirable, but on the contrary, extremely poi- 
 sonous. 
 
 Mrs. B. So it is ; but although animals cannot breathe in car- 
 bonic acid gas, yet in the process of respiration, they have the pow- 
 er of forming this gas in their lungs ; sp that the air which we ex- 
 pire, or reject from the lungs, always contains a certain proportion 
 of carbonic acid, winch is much greater than that which is commen- 
 Jy found in the atmosphere. 
 
 Caroline. But what is it that renders carbonic acid such a dead- 
 ly poison ? 
 
 Mrs. B. The manner in which this gas destroys life, seems to be 
 merely by preventing the access of respirable air ; for carbonic 
 acid gas, unless very much diluted with common air, does not pen- 
 etrate into the lungs, as the windpipe actually rontracts and refu- 
 ses it admittance. But we must dismiss this subject at present, as 
 we shall have an opportunity of treating of respiration much more 
 fully, when we come to the chemical functions of animals. 
 
 Emily. Is carbonic acid as destructive to the life of vegetables as 
 it is to that of animals ? 
 
 Mrs. B. If a vegetable be completely immersed in it, 1 believe 
 it generally proves fatal to it ; but mixed in certain proportions 
 with atmospherical air, it is on the contrary, very favourable to ve- 
 getation. 
 
 * This idea is at random. We cannot account for the origin of 
 carbonic acid in its native state any better than ve c?.n for oxygen. 
 It cannot be the product of combustion, since it existed before the 
 growth of combustible materials. C. 
 
 986. How does marble and calcareous earth obtain its grea 
 quantity of carbonic acid ? 
 
 987. Why do we not experience the pernicious effects of the car- 
 bonic acid in the atmosphere? 
 
 988. How is the atmosphere supplied with this acid ? 
 
 989. Why is carbonic acid gas so destructive to animal life ? 
 
 990. What effect does it have on vegetation ? 
 
226 BORACIC ACID. 
 
 You remember, I suppose, our mentioning 1 the mineral waters, 
 both natural and artificial, which contain carbonic acid gas? 
 
 Caroline. You mean the Seltzer water ? 
 
 Mrs.B. That is one of I hose which are most used; there are, 
 however, a variety of others into which carbonic acid enters as an 
 ingredient: all these waters are usually distinguished by the name 
 of acidulous or gaseous mineral waters. 
 
 The class of salts ca.led carbonats is the most numerous in nature; 
 we must pass over them in a very cursory manner, as the subject 
 is far too extensive for us to enter" on it in detail. The state of car- 
 bonat is the natural siate of a vast number of minerals, and partic- 
 ularly of the a'kalies and alkaline earths, as they have so great an 
 attraction for the carbonic acid, that they are almost always found 
 combined with it ; and you may recollect that it is only by separa- 
 ting- them from this acid, that they acquire causticity and those 
 striking- qualities which I have formerly described. All marbles, 
 chalks, shells, calcareous spars, and limestones of every descrip- 
 tion, are neutral s ills, in which lime, their common basis, has lost 
 all its characteristic properties. 
 
 Emily. But if all these various substances are formed by the un- 
 ion of lime with carbonic acid, whence arises their diversity of 
 ibr<t, and appearance ? 
 
 -Mrs. B Both from the different proportions of iheir component 
 parts, and from a variety of foreign ingredients which may be oc- 
 casionally blended with them ; the veins and colours of marbles, 
 for instance, proceed from a mixture of metallic substances ; silex 
 and alumine also frequently enter into these combinations. The 
 various carbonats, therefore, which I have enumerated, cannot be 
 considered as pure arid unadulterated neutral salts, although they 
 certainly belong to that class of bodies, 
 
 CONVERSATION XIX. 
 
 ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MU- 
 RIATIC ACIDS ; AND ON MURIATS. ON IDOINE AND IODIC 
 
 ACID. 
 
 Mrs.B. We now come to the three remaining acids with simple 
 bases, the compou id nature of which, though long suspected, has 
 been but recenth proved. The chief of these is the muriatic ; 
 
 991. What are the waters called, into which this gas enters as an 
 ingredient ? 
 
 992. What are the salts formed by the acid of this gas ? 
 
 993. flow extensive is this class of salts, and under what forms 
 do they chiefly occur in nature ? 
 
 994. If hme is the common basis of marbles, ehalks, shells, cal- 
 careous spars, and iime stones, why is there such a diversity in 
 their form nnd appearance ? 
 
 995. Prom what do the veins and colours of marble proceed ? 
 
BORACIC ACID. 227 
 
 but I shall first describe the two others, as their bases have been 
 obtained more distinctly than that of the muriatic acid. 
 
 You may recollect I mentioned the BORACIC ACID. This is found 
 very sparingly in some parts of Europe, hut for the use of manufac- 
 tures we have always received it from the remote country of Thi- 
 bet, where it is found in some lakes, combined with soda. It is ea- 
 sily separated from the soda by sulphuric acid, and appears in the 
 form of shining- scales, as you see here. 
 
 Caroline. I am glad to meet wuh an acid which we need not be 
 afraid to touch ; for I perceive from your keeping 1 it in a piece of 
 paper, that it is more innocent than our late acquaintance, the sul- 
 phuric and nitric acids. , 
 
 Mrs. B. Certainly ; but being more inert, you will not find its 
 properties so interesting. However its decomposition, and the 
 brilliant spectacle it affords when its basis again .unites with oxy- 
 gen, atones for its want of btlier striking qualities. 
 
 Sir H. Davy succeeded in decomposing the boracic acid, (which 
 had till then, been considered as undecompoundable,) by various 
 methods. On exposing this acid to the Voltaic battery, the posi- 
 tive wire gave out oxygen, and on the negative wire was deposited 
 a black substance, in appearance resembling charcoal. This was 
 the basis of the acid, which Sir H. Davy has called Boracium or 
 Boron. 
 
 The same substance was obtained in more considerable quanti- 
 ties by exposing the acid to a great heat in an iron gun barrel. 
 
 A third method of decomposing the boracic acid consisted in burn- 
 ing potassium in contact with it in vacuo. The potassium attracts 
 the oxygen from the acid, and leaves its basis in a separate state. 
 
 The recomposition of this acid I shall show you by burning some 
 of its basis, which you see here, in a retort full of oxygen gas. The 
 heat of a candle is all that is required for this combustion. 
 
 Emily. The light is astonishingly brilliant, and what beautiful 
 sparks it throws out ! 
 
 J\lrs. B. The result of this combustion is the boracic acid, the 
 nature of which, you see, is proved, both by analytic and synthetic 
 means. Its basis has not, it is true, a metallic appearance ; but it 
 makes very hard alloys with other metals. 
 
 Emily. But pray, Mrs. B, for what purpose is the boracic acid 
 used in manufactures? 
 
 Mrs. B. Its principal use is in conjunction with soda, that is, in 
 the state of borat of soda, which in the arts is commonly called bo- 
 rax. This salt has a peculiar power of dissolving metallic oxyds, 
 and of promoting the fusion of substances capable of being melted ; 
 it is accordingly employed in various metallic arts ; it is used, for 
 example, to remov the oxyd from the surface of metals, and is of- 
 ten employed in the assaying of metallic ores. 
 
 Let us now proceed to the FLUORIC Acre. This acid is obtained 
 from a substance which is found frequently in mines, and particd- 
 
 996. Where is the boracic acid obtained ? 
 
 997. What is the composition of borax ? 
 
 998. What is the basis of this acid ? 
 
 999. For what purpose is the boracic acid used in manufactures ? 
 > 1000. From what is- the fluoric acid .obtained ? 
 
228 FLUORIC ACID. 
 
 larly in those of Derbyshire, called^wor, a name which it acquired 
 from the circumstance of its being- used to render the ores of met- 
 als more fluid when heated 
 
 Caroline. Pray, is not this the Derbyshire spar, of which so ma- 
 ny ornaments are made ? 
 
 Mrs. B. The same ; but though it has long been employed fora 
 variety of purposes, its nature was unknown until Scheele, the great 
 Swedish chemist, discovered that it consisted of lime united with a 
 peculiar acid, which obtained the name of fluoric acid. It is easily 
 separated from the lime by the sulphuric acid, and unless condens- 
 ed in water, ascends in the form of gas. A very peculiar property 
 of this acid, is its union with siliceous earths, which I have already 
 mentioned. It the distillation of this acid is performed in glass ves- 
 sels, they are corroded, and the siliceous part of the glass comes 
 over, united with the gas ; if water is then admitted, part of the si- 
 lex is deposited, as you may observe in the jar. 
 
 Caroline. I see white flakes forming on the surface of the water; 
 is that silex ? 
 
 Mrs. B. Yes, it is. This power of corroding glass has been used 
 for engraving, or rather etching upon it. The glass is first cover- 
 ed with a coat of wax, through which the figures to be engraved are 
 to be scratched with a pin ; then pouring the fluoric acid over the 
 wax, it corrodes the glass where the scratches have been made. 
 
 Caroline. I should like to have a bottle of this acid to make en- 
 gravings.* 
 
 Jftrs. B. But you could not have it in & glass bottle ; for in that 
 case the acid would be saturated with silex, and incapable of exe- 
 cuting an engraving ; the same thing would happen were the acid 
 kept in vessels of porcelain or earthenware ; this acid must there- 
 fore be both prepared and preserved in vessels of silver. 
 
 If it be distilled from fluor spar and vitrolic acid, in silver or leaden 
 vessels, the receiver being kept very cold during the distillation, it 
 assumes the form of a dense fluid, and in that state is the most in- 
 tensely corrosive substance -known. This seems to be the acid com- 
 
 *A bottle of fluoric acid is not easily obtained. To make etch- 
 ings on glass, first cover the glass with a thin coat of bees wax 
 
 This is done by warming it over a lamp, and passing the wax over 
 the surface. Then make the drawing by cutting through the wax 
 quite down to the glass. To do the etching in the small way, take 
 a lead or tin cup, and on the bottom place about a table spoonful of 
 pulverized fluor spar, and on this pour sulphuric acid enough to 
 moisten it place the glass on the cup as a cover, with the side to 
 be etched downward then set the cup in warm water, or warm 
 the bottom over a lamp, taking care not to melt the wax. In 15 or 
 20 minutes or more, the etching will be done. In this -way, draw- 
 ings are easily and beautifully made on glass. C. 
 
 1001. From what does it derive its name ? 
 
 1002. By what other name is this acid called ? 
 
 1003. Of what does it consist? 
 
 1004. What singular effect does it have on glass 
 
 1005. How could you describe the method of etching on glass? 
 , 1006. la what kind of vessels may it be preserved? 
 
MURIATIC ACID. 229 
 
 bined with a little water. It may be called hydro-Jluic acid ; and 
 Sir H. Dary has been led, from late experiments on the subject, to 
 consider pure fluoric acid as a compound of a certain unknown prin- 
 ciple, which he calls^worme, with hydrogen. 
 
 Sir H. Davy has also attempted to decompose the fluoric acid by 
 burning potassium in contact wi'h it ; but he has not yet been able 
 by this or any other method, to obtain its basis in a distinct separate 
 state. 
 
 We shall conclude our account of the acids wilh that of the MURI- 
 ATIC ACID, which is, perhaps, the most curious and interesting of all 
 of them. It is (ound in nature combined with soda, lime, and mag- 
 nesia. Muriat of soda is the common sea salt ; and from this sub- 
 stance the acid is usually disengaged by means of the sulphuric acid. 
 The natural stale of the muriatic acid is that of an invisible, perma- 
 nent gas, at the common temperature of the atmosphere ; but it has 
 a remarkable strong attraction for water, and assumes the form of a 
 whitish cloud whenever it meets any moisture to combine with. This 
 acid is remarkable for its peculiar and very pungent smell and pos- 
 sesses, in a powerful degree, most of the acid properties. Here is a 
 bottle containing muriatic acid in a liquid state, 
 
 Caroline. And how is it liquefied ? 
 
 Mrs. B By impregnating water with it ; its strong attraction for 
 water makes it very easy to obtain it in a liquid form. Now, if I 
 open the phial, you may observe a kind of vapour rising from it, 
 which is muriatic r.cid gas, of itself invisible, but made apparent by 
 combining with the moisture of the atmosphere. 
 
 Emily. Have you not any of the pure muriatic acid gas ? 
 
 J\Irft. B. This jar is full of that acid in its gaseous state it is 
 inverted over mercury instead of water, because, being absorbable 
 by water, this gas cannot be confined by it. 1 shall now raise the 
 jar a little on one side, and suffer some of the gas to escape. You 
 see that it immediately becomes visible in the form of a cloud. 
 
 Emily. It must be, no doubt, from its uniting with the moisture of 
 the atmosphere, that it is converted into this dewy vapour. 
 
 Mrs.B. Certainly; and for the s^me reason, that is to say, its 
 extreme eagerness to unite with water, this gas will cause snow to 
 melt as rapidly as an intense fire. 
 
 This acid proved much more refractory, when Sir H- Davy at- 
 tempted to decompose it, than the other two undecomposed acids. 
 It is singular that potassium will burn in muriatic acid, and be con- 
 verted into potash, without decomposing the acid and the result of 
 this combustion is a murial of potash ; for the potash as soon as it is 
 regenerated, combines with the muriatic acid. 
 
 Caroline. But how can the potash be regenerated if the muriatic 
 acid does not <-xydale the potassium ? 
 
 Jttrs. B. The potassium in this process, obtains oxygen from the 
 moisture with which the muriatic acid is always combined, and, ac 
 
 1007. What did Sir H. Davy call this acid ? 
 
 1008. Where is muriatic acid found ? 
 
 1009. What is the natural state? 
 
 1010. How is it liquefied ? 
 
 10 1 1. How can this gas be confined without a mercurial bath ? 
 
 1012. Wh it effect will muriatic acid gas have on snow ? 
 
 1013. Why will it meh snow ? 
 
 20 
 
230 OXY-MURIATIC ACID. 
 
 cordingly, hydrogen, resulting 1 from the decomposition of the mois- 
 ture, is invariably evolved. 
 
 Emily. But why not make these experiments with dry muriatic acid? 
 Mrs. B. Dry acids cannot be acted on by the Voltaic battery, be- 
 cause acids are non-conductors of electricity, unless moistened. In 
 the course of a number of experiments, which Sir H. Davy made 
 upon acids in a state of dryness, he observed that the presence of 
 water appeared always necessary to develope the acid properties, so 
 that acids are not even capable of reddening- vegetable blues iithey 
 have been carefully deprived of moisture. This remarkable cir- 
 cumstance led him to suspect, that water, instead of oxygen, may be 
 the Acidifying 1 principle ; but this he threw out rather as a conjec- 
 ture than as an established point. 
 
 Sir H. Davy obtained very curious results from burning- potassium 
 in a mixture of phosphorus and muriatic acid, and also of sulphur 
 and muriatic acid ; the latter detonates with great violence. All his 
 experiments, however, failed in presenting to his view the basis of 
 the muriatic acid, of which he was in search ; and he was at last in- 
 duced to form an opinion respecting the nature of this acid, which 
 I shall presently explain. 
 
 Emily. Is this acid susceptible of different degrees of oxygenation ? 
 Mrs, B. Yes ; for though it cannot be deoxygenated, yet we may 
 add oxygen to it. 
 
 Caroline. Why, then, is not the least degree of oxygenation of 
 the acid called the muriatous, and the higher degree the muriatic 
 acid ? 
 
 Mrs. B. Because, instead of becoming, like other acids, more 
 dense, and more acid by an addition of oxygen, it is rendered, on the 
 contrary, more volatile, more pungent, but less acid, and less absorb- 
 able by'water. These circumstances, therefore, seem to indicate 
 the propriety of making an exception to the nomenclature. The 
 highest degree of oxygenation of this acid has been distinguished by 
 the additional epithet of oxygenated, or, for the sake of brevity, ory, 
 so that it is called oxygenated or oxy-muriatic acid. This likewise 
 exists in a gaseous form, at the temperature of the atmosphere ; 
 it is also susceptible of being absorbed by water, and can be con- 
 gealed, or solidified, by a certain degree of cold. 
 
 Emily. And how do you obtain the oxy-muriatic acid ? 
 Mrs. B. In various ways ; but it may be most conveniently ob- 
 tained by distilling liquid muriatic acid over oxyd of manganese, 
 which supplies the acid with the additional oxygen. One part of the 
 acid being put into a retort, with two parts of the oxyd of manga- 
 nese, and the heat of a lamp applied, the gas is soon disengaged, and 
 
 1014. Why cannot dry acids be acted on by the Voltaic battery ? 
 
 1015. What is the basis of muriatic acid ? 
 
 1016. Is this acid capable of combining with different propor- 
 tions of oxygen ? 
 
 1017. Why is not the least degree of oxygenation called the mu- 
 riatous acid ? 
 
 10 1 8. What is the highest degree of oxygenation of this acid called ? 
 
 1019. How is the oxy-murialic acid obtained ? 
 
OYY-MTJRIATIC ACID. 231 
 
 may be received over water, as it is but sparingly absorbed by it. 
 I have collected some in this jar * 
 
 Caroline. It is not invisible, like the generality of gases ; for it is 
 of a yellowish color. 
 
 J\frs. B. The muriatic acid extinguishes flame, whilst, on the 
 contrary, the oxy-muriatic makes the flame larger, and gives it a 
 dark red color. Can you account for this difference in the two acids ? 
 
 Emily. Yes, I think so ; the muriatic acid will not supply the 
 flame with the oxygen necessary for its support ; but when this 
 acid is further oxygenated, it will part with its additional quantity 
 of oxygen, and in this way support combustion, f 
 
 Mrs. B This is exactly the case : indeed the oxygen added to 
 the muriatic acid, adheres so slightly to it, that it is separated by 
 mere exposure to the sun's rays. This acid is decomposed also by 
 combustible bodies, many of which it burns, and actually inflames, 
 without any previous increase of temperature. 
 
 Caroline. That is extraordinary indeed ! I hope you mean to in- 
 dulge us with some of these experiments ? 
 
 Mrs. B. I have prepared several glass jars of oxy muriatic acid 
 gas for that purpose. In the first we shall introduce some Dutch 
 gold leaf Do you observe that it takes fire : 
 
 Emily. Yes, indeed it does how \vonderful it is ! It became im- 
 mediately red hot, but was soon smothered in a thick vapor. 
 
 Caroline. What a disagreeable smell ! 
 
 Mrs. B. We shall try the same experimeat with phosphorous in 
 another jar of this acid. You had better keep your handkerchief to 
 your nose when I open it now let us drop into it this little piece of 
 phosphorus 
 
 Caroline. It burns really ; and almost as brilliantly as in oxygen 
 gas ! Out what is most extraordinary, these combustions take place 
 without the metal or phosphorus being previously lighted, or even 
 in the least heated. 
 
 Mrs. B. All these curious effects are owing to the very great fa- 
 cility with which this acid yields oxygen to such bodies as are 
 strongly disposed to combine with it. It appears extraordinary in- 
 deed to see bodies, and metals in particular, melted down and in- 
 flamed by a gas, without any increase of temperature, either of the 
 gas, or of the combustible. The phenomenon, however, is, you see, 
 well accounted for. 
 
 Emily. Why did you burn a piece of Dutch gold leaf rather than 
 a piece of any other metal ? 
 
 Mrs. B. Because, in the first place, it is a composition of metals 
 
 * Breathing only a few bubbles of the gas is attended with bad 
 sometimes with dangerous consequences. The young chemist, 
 therefore, had better not undertake to make it. C. 
 
 f According to this new theory of chlorine, as will be explained 
 at the end of this conversation, this combustion is effected in con- 
 sequence of the union of chlorine (or oxy-muriatic acid) with the 
 hydrogen of the combustible body. 
 
 10*20. Why will the muriatic acid extinguish flame, and oxy-mu- 
 riatic acid make it larger, giving it a dark red color ? 
 
 1021. Why will some combustible bodies burn in this acid with- 
 out any previous increase of temperature ? 
 
232 OXY-MURIATIC ACID. 
 
 (consisting 1 chiefly of copper) which burns readily ; and I use a thin 
 metallic leaf in preference lo a lump of metal, because it offers to 
 the action of the gas but a small quantity of matter under a large 
 surface. Filing's, or shavings, would answer the purpose nearly as 
 well; but a lump of metal, though the surface would ox y date with 
 great rapidity, would not take fire. Pure gold is not inflamed by 
 6xy-muriatic acid gas, but it is rapidly oxydated, and dissolved by 
 it ; indeed, this acid is the only one that will dissolve gold. 
 
 Emily. This, I suppose, is what is commonly called aqua rfgia, 
 which you know is the only thing that will act upon gold. 
 
 Mm. B. This is not exactly the case either; for aqua regia is 
 composed of a mixture of muriatic acid and nitric acid. But, in 
 fact, the result of this mixture is the formation of oxy-muriatic 
 acid, as the muriatic acid oxygenates itself at the expense of the 
 nitric; this mixture, therefore, though it bears the name of ni/ro- 
 muriatic -I c^d, acts on gold merely in virtue of the oxy-muriatic 
 acid which it contains. 
 
 Sulphur, volatile oils, and many other substances, will burn in the 
 same manner in oxy-muriatic acid gas; but I have not prepared a 
 sufficient quantity of it, to show combustion of all these bodies. 
 
 Caroline. There are several jars of the gas yet remaining. 
 
 Mrs. B. We must reserve these for future experiments. The 
 oxy-muriatic acid does not, like other acids, redden the blue vege- 
 table colors ; but it totally destroys all color, and turns vegetables 
 perfectly white. Let us collect some vegetable substances to put 
 into this glass which is full of gas. 
 
 Km' hi Here is a sprig of myrtle 
 
 Curofi'ie. And here some colored paper 
 
 Mrs. B. We shall also put in this piece of scarlet riband, and a 
 rose 
 
 Emily. Their colors begin to fade immediately. But how does the 
 gas produce this effect ? 
 
 J\lrfi. B. The oxygen combines with the coloring matter of these 
 substances, and destroys it ; that is to say, destroys the property 
 which these colors had of reflecting only one kind of rays, and ren- 
 ders them capable of reflecting them all, which, you know, will 
 make them appear white. Old prints may be cleaned bv this acid, 
 for the paper will he whitened without injury to the impression, as 
 printer's ink is made of materials (oil and lamp black) which are 
 not acted upon by acids. 
 
 This property of the oxy-muriatic acid has lately been employed 
 in manufactures in a variety of bleaching processes ; but for these 
 purposes the gas must be dissolved in water, as the acid is thus ren- 
 dered much milder and less powerful in its effects ; for in a gaseous, 
 
 Bv what aci I is gold oxydated and dissolved ? 
 
 1023 Why does a mixture of nitric, and muriatic acids dissolve 
 gold, when neither of them will do it alone? 
 
 10-24. What effect does the oxy-muriatic acid have on vegetable 
 colors ? 
 
 1025. Why does it produce this effect? 
 
 1026. Why is it, that the paper of old prints may be cleansed by 
 this acid, without any injury to the impression? 
 
 J027. Of what use is the oxy-muriatic acid in manufactures? 
 
OXY-MURIATIC ACID. 233 
 
 state, it would destroy the texture, as well as the color of the sub- 
 stance submitted to its action. 
 
 Caroline Luok at the things which we put into the gas; they 
 have LIOVV entirely lost their color ! 
 
 Mrs. 13. The effect of the acid is almost completed ; and if we 
 were to examine the quantity that remains, we should find it to con- 
 sist chiefly of muriatic acid. 
 
 The ox} -muriatic acid'has been used to purify the air in fevei 
 hospitals and prisons,as it burns and destroys putrid effluvia of every 
 kind. The infection of the small-pox is likewise destroyed by this 
 gas, and matter that lias been submitted to its influence will DO 
 longer generate that disorder. 
 
 Caroline. Indeed, I think the remedy must be nearly as bad as 
 the disease; the oxy-muriatic acid hns such a dreadfully suffocat- 
 ing smell. 
 
 Mrs. B. It is certainly extremely offensive ; but by keeping the 
 mouth shut, and wetting the nostrils with liquid ammonia, in order 
 to neutralize the vapor as it reaches the nose, its prejudicial effects 
 may be in some degree prevented. At any rate, however, this mode 
 of disinfection can hardly be used in places that are inhabited. And 
 as the vapor of nitric acid, which is scarcely less efficacious for this 
 purpose, is not at all prejudicial, it is usually preferred on such oc- 
 casions. 
 
 Caroline. You have not told us yet what is Sir H. Havy's new 
 opinion respecting the nature of muriatic acid to which you alluded 
 a few minutes ago ? 
 
 Mrs. B. True: f avoided noticing it then, because you could not 
 have understood it without some previous knowledge of the oxy-mu- 
 riatic acid, which I have but just introduced to your acquaintance. 
 
 Sir H. Da-yy's idea is, that muriatic acid, instead of being acorn- 
 pound, consisting of an unknown basis and oxygen, is formed by the 
 union of .oxy-muriatrc gas with hydrogen. 
 
 Emily. Have you not told us just now that oxy-muriatic gas was 
 itself a compound of muriatic acid and oxygen ? 
 
 Mrs. B. Yes ; but according to Sir H. Davy's hypothesis, oxy- 
 muriatic gas is considered as a simple body, whi'ch contains no oxy- 
 gen as a substance of its own kind, which has a great analogy to 
 oxygen in mxjst of its properties, though in others it differs entirely 
 from it. According to this view of the subject, the name of oxy-mu- 
 riaiic acid can no longer be proper, and therefore, Sir H. Davy has 
 adopted that of chlorine, or 'chlorine gas, a name which is simply 
 expressive of its greenish color ; and in compliance with that phi- 
 losopher's theory, we have placed chlorine in our table among the 
 simple bodies. 
 
 Caroline. But what was Sir H. Davy's reason for adopting an 
 opinion so contrary to that which had -hitherto prevailed ? 
 
 Mrs. B. There are many circumstances Vhich are favorable to 
 the new doctrine : bnt the clearest and simplest fact >n its support is, 
 
 1028. For what medicinal purposes has it been used ? 
 
 1029. How may the inconvenience of the osy-friuriatic acid be 
 prevented ? 
 
 1030. What does Sir H. Davy suppose rnuria'iip acid to be ? 
 
 1031. Why is oxy-muriatic acid lately called chlorine ? 
 
 20* 
 
234 MURIATS. 
 
 that if hydrogen gas and oxy- muriatic gas be mixed together, both 
 these gases disappear, and muriatic acid gas is formed. 
 
 Emily. That seems to be a complete proof; is it not considered 
 as perfectly conclusive? 
 
 Mrs B. IN ot so decisive as it appears at first sight ; because it is 
 argued by those who still incline to the old doctrine, that muriatic 
 acid gas, however dry it may be, always contains a certain quantity 
 of water, which is supposed essential to its formation. So that, in 
 the experiment just mentioned, this water is supplied by the union 
 of the hydrogen gas with the oxygen of the oxy-muriatic acid ; and 
 therefore the mixture resolves itself into the base of muriatic acid 
 and water, that is, muriatic acid gas. 
 
 Caroline. I think the old theory must be the true one ; for other- 
 wise how could you explain the formation of oxy-muriatic gas, from 
 a mixture of muriatic acid and oxyd of manganese ? 
 
 Mrs. B Very easily ; you need only suppose that in this process 
 the muriatic add is decomposed ; its hydrogen unites with the oxy- 
 gen of the manganese to form water and the chlorine appears in its 
 separate state. 
 
 Emily. But how can you explain the various combustions which 
 take place in oxy-muriatic gas, if you consider it as containing no 
 oxygen ? 
 
 Mrs. B. We need only suppose that combustion is the result of 
 intense chemical action ;* so that chlorine, like oxygen, is combin- 
 ing with bodies, forms compounds which have less capacity for ca- 
 loric than their constituent principles, and, therefore, caloric is 
 evolved at the moment of their combination. 
 
 Emily. If, then, we may explain every thing by either theory, to 
 which of the two shall we give the preference ? 
 
 Mrs. B. It will, perhaps, be better to wait for more decisive 
 proofs, if such can be obtained, before we decide positively upon the 
 subject. The new doctrine has certainly gained ground very rapidly, 
 and may be considered as generally established ; but a few competent 
 judges still refuse their assent to it, and until that theory is establish- 
 ed beyond all doubt, it may be as well for us still occasionally to use 
 the language to which chemists have long been accustomed. But 
 let us proceed to the examination of salts formed by muriatic acid. 
 
 Among the compound salts formed by muriaticacid, Ihemuriat of 
 soda, or common salt, is the most interesting.f The uses and pro- 
 
 * " Intense chemical action," neither explains the process, nor 
 indeed conveys to the mind any definite idea. The views of Sir H. 
 Davy on the composition of chlorine, are comhatted by many of the 
 first chemists in England, as well as in this country. The inquisi- 
 tive reader may become acquainted with the grounds of dispute on 
 both sides by referring- to Cooper's edition of Thomson's chem- 
 istry. C. 
 
 f According to Sir H. Davy's view of the nature of the muriatic 
 and oxy-muriatic acids, dry muriat of soda is a compound of sodium 
 
 1032. What are the reasons for supposing that chlorine is not a 
 simple substance ? 
 
 1033. How are the combustions in oxy-muriatic acid explained, 
 if it does not contain oxygen ? 
 
 1034. What is said on the subject in the note ? 
 
MURIATS. 235 
 
 perties of this salt are too well known to require much comment. 
 Besides the pleasant flavour it imparts to the food, it is very whole- 
 some, when not used toexcess, as it assists in the process of digestion. 
 Sea-water is the great source from which muriat of soda is ex- 
 tracted bv evaporation. But it is also found in large solid masses in 
 the bowels of the earth, in England, and in many other parts of the 
 world. 
 
 Emily. I thought that salts, when solid, were always in the state 
 of crystals ; but the common table salt is in the form of a coarse 
 white powder. 
 
 JWrs. B. ( rystallization depends, as you may recollect, on the 
 slow and regular re-union of particles dissolved in a fluid ; common 
 sea-salt is only in a state of imperfect crystallization, because the 
 process by which it is prepared is not favourable to the formation 
 of regular crystals. But if you dissolve it, and afterwards evaporate 
 the water slowly, you will obtain a regular crystallization. 
 
 Jlfuriat of ammonia is another combination of this acid, which we 
 have already mentioned as the principal source from which ammo- 
 nia is derived. 
 
 1 can at once show you the formation of this salt by the immedi- 
 ate combination of muriatic acid with ammonia. These two glass jars 
 contain, the one muriatic acid gas, the other ammoniacal gas, both 
 of which are perfectly invisible now, if I mix them together, you 
 see they immediately form an opaque white cloud, like smoke. If 
 a thermometer was placed in the jar in which these gases are mixed, 
 you would perceive that some heat is at the same time produced. 
 
 Emily. The effects of chemical combinations are, indeed, won- 
 derful ! How extraordinary it is that two invisible bodies should 
 become visible by their union ! 
 
 Mrs. B. This strikes you with astonishment, because it is a phe- 
 nomenon which nature seldom exhibits to our view ; but the most 
 common of her operations are as wonderful, and it is their frequen- 
 cy only that prevents our regarding them with equal admiration. 
 What would be more surprising, for instance, than combustion, were 
 it not rendered familiar by custom ? 
 
 Emily. That is true. But pray, Mrs. B., is this white cloud the 
 salt that produces ammonia ? How different it is from the solid mu- 
 riat of ammonia which you once showed us ! 
 
 J\Irs. B. It is the same substance, which first appears in the state 
 of vapour, but will soon be condensed by cooling against the sides 
 of the jar, in the form of very minute crystals. 
 
 We now proceed to the oxy muriats. In this class of salts the oxy- 
 muriat of potash,* is the most worthy of our attention, for its striking 
 
 and chlorine, foi*it may be formed by the direct combination of oxy - 
 muriatic gas and sodium. In his opinion, therefore, what we cdm- 
 raonly call muriat of soda, contains neither soda nor muriatic acid. 
 * Oxy-muriat of potash is prepared by passing chlorine through a 
 solution of potash in water. The process is long and difficult. C. 
 
 1035. Where is the muriat of soda obtained? 
 
 1036. On what does crystallization depend ? 
 
 1037. Why is common salt in a:ntate of imperfect crysallization ? 
 
 1038. Of what is the muriat of ammonia a combination ? 
 
 1039. What two gases, when mixed, form muriat of ammonia ? 
 
236 OXY-MURIATS. 
 
 properties. The acid, in this state of combination, contains a still 
 greater proportion of oxygen than when alone. 
 
 Caroline. But how can the oxy-muriatic acid acquire an in- 
 crease of oxygen by combining with potash ? 
 
 Mrs. B. It does not really acquire an additional quantity of oxy- 
 gen, but it loses some of the muriatic acid, which produces, the 
 same effect, as the acid which remains is proportionably super- 
 oxygenated. 
 
 If this salt be mixed, and merely rubbed together with sulphur) 
 phosphorus, charcoal, or indeed any other combustible, it explodes 
 strongly. 
 
 Caroline. Like gun-powder, 1 suppose, it is suddenly converted 
 into elastic fluids ? 
 
 Mrs. B. Yes : but with this remarkable difference, that no in- 
 crease of temperature, any further than is produced by gentle fric- 
 tion, is required in this instance. Can you tell me what gases are 
 generated by the detonation of this salt with charcoal ? 
 
 Emily. Let me consider-.... The oxy-muriatic acid parts with 
 
 its excess of oxygen to the charcoal, by which means it is convert- 
 ed into muriatic acid gas ; whilst the charcoal, being burnt by the 
 oxygen, is changed to carbonic acid gas. What becomes of the 
 potash I cannot tell. 
 
 Mrs. B. That is a fixed product which remains in the vessel. 
 
 Caroline. But since the potash does not enter into the new com- 
 binations, I do not understand what use it is in this operation. 
 Would not the oxy-muriatic acid and the charcoal produce the 
 same effect without it ? 
 
 Mrs. B. No ; because chlorine (or oxy-muriatic acid) does not 
 unite with charcoal, unless oxygen be added to it, and this oxygen 
 is supplied by the potash. 
 
 I mean to show you this experiment, but I would advise you not 
 to repeat it alone ; for if care be not taken to mix only very small 
 quantities at a time, the detonation will be extremely violent, and 
 may be attended with dangerous effects. You see I mix an exceed- 
 ing small quantity of the salt with a little powdered charcoal, in this 
 Wedgwood mortar, and rub them together with the pestle 
 
 Caroline. Heavens ! How can such a loud explosion be produced 
 by so small a quantity of matter ? 
 
 Mrs B. You must consider that an extremely small quantity of 
 solid substance may produce a very great volume of gases ; and it 
 is the sudden evolution of these which occasions the sound. 
 
 * According to Sir H. Davy's new views, just explained, oxy- 
 muriat of potash is a compound of chlorine with oxygen and oxyd 
 of potassium. 
 
 1040. What are the peculiar properties of oxy-muriat of potash ? 
 
 1041. Why will the oxy-muriat of potash explode if mixed and 
 rubbed together with sulphur, phosphorus, charcoal, or any other 
 combustible substance ? 
 
 1042. What gases are generated by the detonation of this salt 
 with charcoal ? 
 
 1043. Why would not the same effect be produced by the oxy- 
 muriatic acid and charcoal without the potash ? 
 
OXY-MURIATS. 237 
 
 Emily. Would not oxy muriat of potash make stronger gun- 
 powder than nitrat of potash ? 
 
 Mrs.B. Yes ; but the preparation, as well as the use of this salt, 
 is attended with so much danger, that it is never employed for that 
 purpose. 
 
 Caroline. There is no cause to regret it, 1 think ; for the com- 
 mon gun-powder is quite sufficiently destructive. 
 
 Mrs. B. I can show you a very curious experiment with this 
 salt ; but it must again be on condition that you will never attempt 
 to repeat it by yourselves. 1 throw a small [> ; ece of phosphorus 
 into this glass of water; then a little oxy-muriat of potash; and 
 lastly, I pour in (by means of this funnel, so as to bring- it in con- 
 tact with the two other ingredients at the bottom of the glass) a 
 small quantity of sulphuric acid 
 
 Caroline. This is, indeed, a" beautiful experiment ! The phospho- 
 rus takes fire and burns from the bottom of the watt r. 
 
 Emily. How wonderful it is to see flame bin-sting flnt under wa- 
 ter, and rising through it ! Pray, hov/ is this accounted for ? 
 
 Mrs. B. Cannot you find il out, Caroline ? 
 
 Emily. Stop I think 1 can explain it. Is it not because the 
 sulphuric acid decomposes the salt by combining with '.he potash, 
 so as to liberate the oxy-muriatic acid gas by which the phospjiorus 
 is set OP fire ? 
 
 Mrs. B. Very well, Emily ; and with a little more reflection you 
 would have discovered another concurring circumstance, which is, 
 that an increase of temperature is produced by the mixture of the 
 sulphuric acid and water, which assists in promoting the combus- 
 tion of the phosphorus. 
 
 I must, before we part, introduce to your acquaintance the new- 
 ly discovered substance, IODINE, which you may recollect we 
 placed next to oxygen and chlorine in our table of simple bodies. 
 
 Caroline. Is this also a body capable of maintaining combustion 
 like oxygen and chlorine ? 
 
 Mrs. B. It is ; and although it does riot so generally disengage 
 light and heat from inflammable bodies, as oxygen and chlorine do, 
 yet it is capable of combining with most of ihein : and sometimes, 
 as in the instance of potassium and phosphorus, the combination is 
 attended with an actual appearance of light and heat 
 
 Caroline. But what sort of substance is iodine ; what is its form 
 and colour? 
 
 Mrs B. It is a very singular body, in many respects. At the or- 
 dinary temperature of the atmosphere, it commonly appears in the 
 form of bluish-black crystalline scales, such as you see in this tube. 
 
 Caroline. They shine like black lead, and some of the scales have 
 the shape of lozenges. 
 
 Mrs. B. That is actually the form which the crystals of iodine 
 
 1044. From what may a stronger gun-powder than that now 
 used be made ? 
 
 1045. Why is it not used ? 
 
 1046. Flow may phosphorus be set on fire in water? 
 
 1047. Why is this effect produced ? 
 
 1048. How does iodine differ from oxygen and chlorine? 
 
 1049. How does iodine appear ? 
 
238 COMPOSITION 
 
 often assume. But if we*heat them gently by holding the tube 
 over the flame of a candle, see what a change takes place in them. 
 
 Caroline, ilowcuiious! They seem to melt, and the tube im- 
 mediately fills with the beautiful violet vapour. But look, Mrs. B., 
 :he same scales are now appearing at the other end of the tube. 
 
 JWrs. B. This is, in fact, a sublimation of iodine, from one part 
 of the tube to another ; but wilh this remarkable peculiarity, that 
 while in the gaseous state, iodine assumes that bright violet colour, 
 which as you may already perceive, it loses as the tube cools, and 
 the substance resumes its usual solid form. It is from the violet 
 colour of the gas that iodine has obtained its name. 
 
 Caroline. But how is this curious substance obtained ? 
 
 Mrs. B. It is found in the ley of ashes, of sea-weeds, after the 
 soda has been separated by crystallization ; and it is disengaged 
 by means of sulphuric acid, which expels it from the alkaline ley 
 in the form of a violet gas, which may be collected and condensed 
 in the way which you have just seen This interesting discovery 
 was made in the year 1812, by M. Courtios, a manufacturer of salt- 
 petre at Paris. 
 
 Caroline. And pray, Mrs. B., what is the proof of iodine being a 
 simple bod}' ? 
 
 Mrs, B. It is considered as a simple body, both because it is not 
 capable of being resolved into other ingredients ; and because it is 
 itself capable of combining with other bodies, in a manner anala- 
 gous to oxygen and chlorine. The most curious of these combina- 
 tions is that which it forms with hydrogen gas, the result of which 
 is a peculiar gaseous acid. 
 
 Caroline. Just as chlorine and hydrogen gas form muriatic acid. 
 In this respect chlorine and iodine seem to bear a strong analogy 
 to each other. 
 
 Mrs. B. That is indeed the case ; so that if the theory of the 
 constitution of either of these two bodies be true, it must be true 
 also in regard to the other ; if erroneous in the one, the theory 
 must fall in both. 
 
 But it is now time to conclude ; we have examined such of the 
 acids and salts as I conceived would appear to you most interesting. 
 I shall not .enter into any particulars respecting the metallic acids, 
 as they offer nothing sufficiently striking for our present purpose. 
 
 CONVERSATION XX. 
 
 ON THE NATURE AND COMPOSITION OF VEGETABLES. 
 
 Mrs. B. We have hitherto treated only of the simplest combina- 
 tion of elements, such as alkalies, earths, acids, compound salts, 
 
 1050. How can you show the violet coloured gas ? 
 
 1051. From what does iodine obtain its name ? 
 105*2. How is iodine obtained ? 
 
 1053. Why is iodine reckoned a simple body ? 
 
 1054. In what respect do chlorine and iodine resemble each other? 
 J055. What are the simplest combinations of elements ? 
 
OF VEGETABLES. i 239 
 
 stones, &c.: all of which belong- to the mineral kiiycykflt is time 
 now to turn our attention to a more complicated cla^jrqigJHh pounds. 
 that of ORGANIZED BODIES, 'which will furnish usmhapH?w source 
 of instruction and amusement.* ' J? ' 
 
 Emily. By organized bodies, [ suppose you meajyffie vegetable 
 and animal creation ? 1 have, however, but a ve'rjjKague idea of 
 the \vord organization, and 1 have often wished to loH^more f.re- 
 cisely what it means. 
 
 Mrs. B. Organized bodies are such as are endowed by nature 
 with various parts, peculiarly constructed and, adapted to perform 
 certain functions connected with life. Thus yo^j may observe, that 
 mineral compounds are formed by the simple effect of mechanical 
 or chemical attraction, and may appear to some to be, in a great 
 measure, the productions of chance ; whilst organized bodies bear 
 the most striking and impressive marks of design, and are eminent- 
 ly distinguished by that unknown principle, called life, from which 
 the various organs derive the power of exercising their respective 
 functions. 
 
 Caroline. But in what manner does life enable these organs to 
 perform their several functions ? 
 
 Mrs. B. That is a mystery which, I fear, is enveloped in such 
 profound darkness, that there is very little hope of our ever being 
 able to unfold it. \\ernustcontentourselves with examining the 
 effects of this principle ; as for the cause, we have been able only 
 to give it a name, without attaching any other meaning to it, than 
 the vagtie and unsatisfactory idea of an unknown agent. 
 
 Caroline. And yet I think I can form a very clear idea of life. 
 Mrs B Pray let me hear how you would define it ? 
 Caroline. It is, perhaps, more easy to conceive, than to express 
 let me consider Is not life the power which enables both the ani- 
 mal and the vegetable creation to perform the various functions 
 which nature has assigned to them ? 
 
 Mrs. B. I have nothing to object to your definition ; but you will 
 allow me to observe, that you have only mentioned the effects 
 which the unknown cause produces, without giving us any notion 
 of the cause ijself. 
 
 Emily. Yes, Caroline, you have told us what life does, but you 
 have not told us what it is. 
 
 Mrs. B. We may study its operations ; but we should puzzle our- 
 selves to no purpose by attempting to form an idea of its real nature. 
 We shall begin with examining its effects in the vegetable world, 
 which constitutes the simplest class of organized bodies ; these we 
 shall find distinguished from the mineral creation, not only by their 
 more complicated nature, but by the power which they possess with- 
 in themselves, of forming new chemical arrangements of their con- 
 stituent parts, by means of appropriate organs. Thus, though all 
 vegetables are ultimately composed of hydrogen, carbon, and oxy- 
 gen, (with a few other occasional ingredients,) they separate and 
 
 1056. What are organized bodies? 
 
 1057. How do they differ from inorganic matter ? 
 J058. What is life in its philosophical acceptation ? 
 
 1059. What is the simplest class of organized bodies ? 
 
 1060. Of what are vegetables mostly composed ? 
 
240 COMPOSITION 
 
 ;. * 
 
 combine th&ee principles, by their various organs, in a thousand 
 ways, andioTn, with them, different kinds of juices and solid parts, 
 which exist readjs made in vegetables, and may, therefore, be con- 
 sidered as their immediate materials. 
 These are : 
 
 Sap,- Resins, 
 
 Murage, Gum Resins, 
 
 Sugar, ' Balsams, 
 
 Fecula, Caoutchouc, 
 
 Gluten, Extractive colouring Matter, 
 
 Fixed Oil, Tannin, 
 
 Volatile Oil, Woody Fibre, 
 
 Camphor. Vegetable Acids, ike. 
 
 Caroline. VV hat a long 1 list of names! I did not suppose that a ve- 
 getable was composed of half so many ingredients. 
 
 J\lrs. B. You must not imagine that every one of these materials 
 is formed in each individual plant. 1 only mean to say, that they are 
 all derived exclusively from the vegetable kingdom. 
 
 Emily. But does each particular part of the plant, such as the 
 root, the bark, (he stem, the seeds, and leaves, consist of one of 
 these ingredients only, or of several of them combined -together ? 
 
 Jtfrs. B. I believe there is no part of a plant which can be said to 
 consist solely of any one particular ingredient ; a certain number 
 of vegetable materials must always be combined for the formation 
 of any particular part, (of a seed for instance,) and these combina- 
 tions are carried on by sets of vessels, or minute organs, which se- 
 lect from other parts, and bring together, the several principles re- 
 quired for the developement and growth of those particular parts 
 which they are intended to form and to maintain. 
 
 Emily. And are not these combinations always regulated by the 
 laws of chemical attraction ? 
 
 J\frs. B. No doubt : the organs of plants cannot force principles 
 to combine which have no attraction for each other ; nor can they 
 compel superior attractions to yield to those of inferior power ; they 
 probably act rather mechanically, by bringing into contact such 
 principles, and in such proportions, as will, by their chemical com- 
 bination, form the various vegetable products. 
 
 Caroline. We may then consider each of these organs as a curi- 
 ously constructed apparatus, adapted for the performance of a va- 
 riety of chemical processes. 
 
 Ji/Lrs. B. Exactly so. As long as the plant lives and thrives, the 
 carbon, hydrogen, and oxygen, (the chief constituents of its imme- 
 diate materials,) are so balanced and connected together, that they 
 are Dot susceptible of entering into other combinations ; but no 
 sooner does death take place, than this state of equilibrium is de- 
 stroyed and new combinations produced. 
 
 1061. "What are the ingredients of vegetables ? 
 
 1062. Is it. to be supposed that all these ingredients exist in a sin- 
 gle vegetable ? 
 
 1053. And does any vegetable or any part of one consist solely 
 of a single one of these ingredients ? 
 
 1064. By what are the combinations in the vegetable kingdom 
 regulated ? 
 
 1065. How may the organs of plants be considered ? 
 
OF VEGETABLES. 241 
 
 Emily. But why should death destroy it ? for these principles must 
 remain in the same proportions, and consequently, I should suppose, 
 in the same order of attractions? 
 
 Mrs. B. You must remember, that in the vegetable, as well as in 
 the animal kingdom, it is by the principle of life that the organs are 
 enabled to act ; when deprived of that agent or stimulus, their power 
 ceases, and an order of attractions succeeds, similar to that which 
 would take place in mineral or unorganized matter. 
 
 Emily. In this order of attractions, 1 suppose, that destroys the 
 organization of the plant after death ; for if the same combinations 
 still continued to prevail, the plant would always remain in the state 
 in which it died ? 
 
 Mrs. B. And that, you know, is never the case ; plants may be 
 partially preserved for some time after death, by drying ; but in the 
 natural course of events they all return, to the state of simple ele- 
 ments; a wise and admirable dispensation of Providence, by which 
 dead plants are rendered fit to enrich the soil, and become subser- 
 vient to the nourishment of living vegetables. 
 
 Caroline. But we are talking of the dissolution of plants, before 
 we have examined them in their living state. 
 
 JV/r. B. That is true, my dear. But I wished to give you a gen- 
 eral idea of the nature of vegetation, before we entered into par- 
 ticulars. Besides, it is not so irrelevant as you suppose to talk of ve- 
 getables in their dead state, since we cannot analyze them without 
 destroying life ; and it is only by hastening to submit them to ex- 
 amination, immediately after they have ceased to live, that we can 
 anticipate their natural decomposition. There are two kinds of ana- 
 lysis of which vegetables are susceptible ; first,that which separates 
 them into their immediate materials, such as sap, resin, mucilage, 
 &c. ; secondly, that which decomposes them into their primitive 
 elements, as carbon, hydrogen, and oxygen. 
 
 Emily. Is there not a third kind of analysis of plants, which con- 
 sists in separating their various parts, as the stem, the leaves, and 
 the several organs of the flower ? 
 
 Mrs. B. That, my dear, is rather the department of the botanist ; 
 we shall consider these different parts of plants only, as the organs 
 by which the various secretions or separations are performed ; but 
 we must first examine the nature of these secretions. 
 
 The sap is the principal material of vegetables, since it contains 
 the ingredients that nourish every part of the plant. The basis of 
 this juice, which the roots suck up from the soil, is water ; this holds 
 in solution the various other ingredients required by the several 
 parts of the plant, which are gradually secreted from the sap by the 
 different organs appropriated to that purpose, as it passes them in 
 circulating through the plant. 
 
 J\Iucus, or mudlagCy is a vegetable substance, which, like all the 
 
 1066. Why should death destroy vegetable combination^? 
 
 1067. What is an admirably wise dispensation of Providence in 
 regard to the nature of plants ? 
 
 1068. Of how many kinds of analysis are vegetables susceptible ? 
 
 1069. What is the first ? 
 
 1070. What is the second ? 
 
 1071. What is the principal material of vegetables 3 
 
 1072. What is the basis of this juice ? 
 
 21 
 
242 COMPOSITION 
 
 others, is secreted from the sap ; when in excess, it exudes from the 
 trees in the form of gum. 
 
 Caroline. Is that the gum so frequently used instead of paste or 
 glue ? 
 
 Mrs. B. It is ; almost all fruit trees yield some sort of gum, but 
 that most commonly used in the arts is obtained from a species of 
 acacia-tree, in Arabia, and is called gum arabic ; it forms the chief 
 nourishment of the natives of those parts, who obtain it in great 
 quantities from incisions which they make in the trees. 
 Caroline. I did not know that gurn was eatable. 
 Mrs. B. There is an account of a whole ship's company being 
 saved from starving by feeding on the cargo, which was gum sen- 
 egal. I should not, however, imagine, that it would be either a plea- 
 sant or a particularly eligible diet to those who have not, from their 
 birth, been accustomed to it. It is, however, frequently taken me- 
 dicinally, and considered as very nourishing. Several kinds of ve- 
 getable acids may be obtained, by particular processes, from gum 
 or mucilage, the principal of which is called the mucous acid. 
 
 Sugnr is not found in its simple state in plants, but is always mix- 
 ed with gum, sap, or other ingredients : this saccharine matter is to 
 be met with in every vegetable, but abounds most in. roots, fruits, 
 and particularly in the sugar cane. 
 
 Emily. If all vegetables contain sugar, why is it extracted ex- 
 clusively from the sugar-cane ? 
 
 Mrs. B. Because it is both most abundant in that plant, and 
 most easily obtained from it. Besides, the sugars produced by other 
 vegetables differ a little in their nature. 
 
 During the late troubles in the West Indies, when Europe was 
 but imperfectly supplied with sugar, several attempts were made to 
 extract it from other vegetables, and very good sugar was obtained 
 from parsnips and from carrots ; but the process was too expensive 
 to carry this enterprize to any extent. 
 
 Caroline. I should think that sugar might be more easily obtained 
 from sweet fruits, such as figs, dates, &c. 
 
 Mrs. B. Probably ; but it would be still more expensive, from 
 the high price of those fruits, and it would not be exactly like com- 
 mon sugar.* 
 
 Emily. Pray, in what manner, is sugar obtained from the sugar- 
 cane ? 
 
 * Some foreign chemists (MM. Kirkoff, Braconnot, &c.) have 
 found that if starch be boiled for a long time in water containing 
 one fortieth part of sulphuric acid, and evaporated down to a certain 
 ' consistence, the solution of starch concretes, in cooling, into a solid 
 brownish mass, which has the taste and other general properties of 
 sugar. During this process, no gas is disengaged, and the acid is 
 not decomposed. 
 
 1073. 'What is the mucilage of vegetables ? 
 
 1074. What uses are made of mucilage or gum ? 
 
 1075. In what state does sugar naturally exist ? 
 
 1076. In what does it mostly abound ? 
 
 1077. If it is found in all vegetables, why is it extracted from su- 
 gar cane only ? 
 
OF VEGETABLES. 243 
 
 Mrs. B. The juice of this plant is first expressed by passing it 
 between two cylinders of iron. It is then boiled with lime-water, 
 which makes a thick scum rise to the surface. The clarified liquor 
 is let off below, and evaporated to a very small quantity, after 
 which it is suffered to crystallize by starraing in a vessel, the bottom 
 of which is perforated with holes, that are imperfectly stopped in 
 order that the syrup may drain off. The sugar obtained' by 'this 
 process is a coarse, brown powder, commonly called raw or moist 
 sugar; it undergoes another operation to be refined and converted 
 into loaf sugar. For this purpose it is dissolved in water, and after- 
 wards purified by an animal fluid called albumen. White of eggs 
 chiefly consists of this fluid, which is also one of the constituent parts 
 of blood : and consequently eggs, or bullock's blooij, are commonly 
 used for this purpose. 
 
 The albuminous fluid being diffused through the syrup, combines 
 with all the solid impurities contained in it, and rises with them to 
 the surface where it forms a thick scum ; the clear liquor is then 
 again evaporated to a proper consistence, and poured into moulds, 
 in which, by a confused crystallization, it forms loaf sugar. But an 
 additional process is required to whiten it ; to this effect the mould 
 is inverted, and its open base is covered with clay, through which 
 water is made to pass ; the water slowly trickling through the sugar 
 combines with and carries off the colouring mater. 
 
 Caroline. I am very glad to hear that the blood that is used to 
 purify sugar does not remain in it ; it would be a disgusting idea, t 
 have heard of some improvements by the late Mr. Howard in the 
 process of refining sugar. Pray what are they ? 
 
 Mrs. B. It would be much too long to give you an account of the 
 process in detail. But the principal improvement relates to the mode 
 of evaporating the syrup in order to bring it to the consistency of 
 sugar. Instead of boiling the syrup in a large copper, over a strong 
 fire, Mr. Howard carries off the water by means of a large air pump, 
 in a way similar to that used in Mr. Leslie's experiment for freezing 
 water by evaporation ; that is, the syrup being exposed to a vacuum, 
 the water evaporates quickly, with no greater heat than that of a lit- 
 tle steam, which is introduced round the boiler. The air-pump is of 
 course of large dimensions, and is worked by a steam engine. A 
 great saving is thus obtained, and a striking instance afforded of the 
 power of science in suggesting useful economical improvements. 
 
 Emily. And pray how are sugar-candy and barley-sugar pre- 
 pared ? 
 
 Mrs. B. Candied sugar is nothiug more than the regular crystals, 
 obtained by slow evaporation from a solution of sugar. Barley- 
 sugar is sugar melted by heat, and afterwards cooled in moulds of 
 a spiral form. 
 
 Sugar may be decomposed by a red heat, land, like all other ve- 
 getable substances, resolved into carbonic acid and hydrogen. The 
 formation and the decomposition of sugar afford many very inter- 
 esting particulars, which we shall fully examine after having gone 
 
 1078. In what manner is sugar obtained from sugar-cane ? 
 
 1079. How is sugar refined or converted into loaf sugar ? 
 
 1080. What is Mr. Howard's improvement for refining sugar ? 
 
 1081. How is sugar-candy and barley-sugar prepared ? 
 
 1082. How may sugar be Decomposed, and what is the product ? 
 
244 COMPOSITION 
 
 through the other materials of vegetables. We shall find that there 
 is reason to suppose that sugar is not like the other materials, se- 
 creted from the sap by appropriate organs ; but that it is formed by 
 a peculiar process with which you are not yet acquainted. 
 
 Caroline. Pray, is not honey of the same nature as sugar ? 
 
 Mrs. B. Honey is a mixture of saccharine matter and gum. 
 
 Emily. 1 thought that honey was in some measure an animal sub- 
 stance, as it is prepared by the bees. 
 
 Mrs. B. It is rather collected by them from flowers, and convey- 
 ed to their store-houses, the hives. It is the wax only that under- 
 goes a real alteration in the body of the bee, and is thence convert- 
 ed into an animal substance.* 
 
 Manna is another kind of sugar, which is united with a nauseous 
 extractive matter, to which it owes its peculiar taste andcolour. It 
 exudes like gum from various trees in hot climates, some of which 
 have their leaves glazed by it. 
 
 The next of the vegetable materials is/eew/a-; this is the general 
 name given to the farinaceous substance contained in all seeds, and 
 in some roots, as the potatoe, parsnip, &c. It is intended by nature 
 for the first aliment of the young vegetable ; but that of one parti- 
 cular grain is become a favourite and most common food of a large 
 part of mankind. 
 
 Emily. You allude, I suppose, to bread, which is made of wheat 
 flour ? 
 
 Mrs. B. Yes. The feculaof wheat contains also another vege- 
 table substance which seems peculiar to that seed, or at least has not 
 as yet been obtained from any other. This is gluten, which is of a 
 ( sticky, ropy, elastic nature ; and it is supposed to be owing to the 
 viscious qualities of this substance, that wheat-flour forms a much 
 better paste than any other. 
 
 Emily. Gluten by your description, must be very like gum ? 
 
 Mrs. B. In their sticky nature they certainly have some resem- 
 blance ; but gluten is essentially different from gum in other points, 
 and especially in its being insoluble in water, whilst gum, you 
 know, is extremely soluble. 
 
 The oils contained in vegetables all consist of hydrogen and car- 
 bon in various proportions. They are of two kinds^arerf and vola- 
 tile, both of which we formerly mentioned. Do you remember in 
 what the difference between fixed and volatile oil consists ? 
 
 Emily. If I recollect rightly, the former are decomposed by heat, 
 whilst the latter are merely volatilized by it. 
 
 _^ * 
 
 * It was the opinion of Huber, that the bees prepared the wax from 
 honey and sugar. There is, however, found on the leaves of some 
 plants a substance, having all the properties of wax ; and that bees- 
 wax itself is not an animal substance, is clear from its analysis. C. 
 
 1083. Of what does honey consist ? 
 
 1084. What is said of the wax of bees ? 
 
 1085. What is manna ? 
 
 1086. What is the fecula of vegetables ? 
 
 1087. What is gluten : 
 
 1088. How does gluten differ from gum ? 
 
 1089. Of what do vegetable oils consist ? 
 
 1090. What is the difference between fixed and volatile oils ? 
 
OF VEGETABLES. 245 
 
 Mrs. B. Very well. Fixed oil is contained only in the seeds ct 
 plants, excepting in the olive, in which it is produced in, and ex- 
 pressed from, the fruit. We have already observed that seeds con- 
 tain also fecula ; these two substances,united with a little mucilage, 
 form the white substance contained in the seeds or kernels of plants , 
 and is destined for the nourishment of the youeg plant, to which the 
 seed gives birth. The milk of almonds, which is expressed from 
 the seed of that name, is composed of those three substances. 
 
 Emily. Pray, of what nature is the linseed oil which is used in 
 painting ? 
 
 Mrs. B. It is a fixed oil, obtained from the seed of flax. Nut 
 oil, which is frequently used for the same purpose, is expressed 
 from walnuts. 
 
 Olive oil is that which is best adapted to culinary purposes, 
 
 Caroline. And what are the oils used for burning? 
 
 Mrs. B. Animal oils, most commonly ; but the preference given 
 to them is owing to their being less expensive ; for vegetable oils 
 burn equally well, and are more pleasant, as their smell is not of- 
 fensive. 
 
 Emily. Since oil is so good a combustible, what is the reason 
 that lamps so frequently require trimming ? 
 
 Mrs. B. This sometimes proceeds from the construction of the 
 lamps, which may not be sufficiently favourable to a perfect com- 
 bustion ; but there is certainly a defect in the nature of oil itself, 
 which renders it necessary for the best constructed lamps to be oc- 
 casionally trimmed. This defect arises from a portion of mucilage 
 which it "IE extremely difficult to separate from the oil, and which 
 being a bad combustible, gathers round the wick, and thus im- 
 pedes its -combustion, and consequently dims the light. 
 
 Carotins. But will not oils burn without a wick ? 
 
 Mrs. B. Not unless their temperature be elevated to five or six 
 hundred degrees ; the wick answers this purpose, as I think I onc< 
 before explained to you. The oil rises between the fibres of the 
 cotton by capillary attraction, and the heat of the burning wick 
 volatilizes it, and brings it success! v sly to the temperature at which 
 it is combustible. 
 
 Emily. I suppose the explanation which you have given with re- 
 gard to the necessity of trimming lamps, applies also to candles, 
 which so often require snuffing ? 
 
 Mrs.B, I believe it does ; at least in some degree. But besides 
 the circumstances just explained, the common sorts of oils are not 
 very highly combustible, so that the heat produced by a candle, 
 which is a coarse kind of animal oil, being insufficient to volatilize 
 them completely, a quantity of soot is gradually deposited on the 
 wick, which dims the light, and retards the combustion. 
 
 Caroline. Wa-x candles, then, contain no incombustible matter, 
 sicfce they do not require snuffing ? 
 
 1091. From what part of plants are fixed oils obtained ? 
 
 1092. From what is linseed oil obtained ? 
 
 1093. What oil.<* best for burning ? 
 
 1094. Since oil is a good combustible, what is the reason tha ; : 
 iamps require so frequeut trimming ? 
 
 1095. What is the use of wicks in lamps ? 
 
 \ 1096. Why do candles more than lamps require trimming ? 
 
246 COMPOSITION 
 
 Mrt. B. Wax is a much better combustible than tallow, but 
 still not perfectly so, since it likewise contains some particles that 
 are unfit for burning ; but when these gather round the wick, 
 (which in a wax light is comparatively small,) they weigh it down 
 on one side, and fall off together with the burnt part of the wick. 
 
 Caroline. As oils are such good combustibles, I wonder that they 
 should require so great an elevation of temperature before they be- 
 gin to burn ? 
 
 Mrs. B. Though fixed oils will not enter into actual combustion, 
 below the temperature of about four hundred degrees,* yet they 
 will slowly absorb oxygen at the common temperature of the at- 
 mosphere. Hence arises a variety of change in oils which modify 
 their properties and uses in the arts. 
 
 If oil simply absorbs, and combines with oxygen, it thickens and 
 .changes to a kind of wax. This change is observed to take place 
 on the external parts of certain vegetables, even during their life. 
 But it happens in many instances that the oil does not retain all 
 ' the oxygen which it attracts, but that part of it combines with, or 
 burns the hydrogen of the oil, thus forming a quantity of water, 
 which gradually goes off by evaporation. In this case, the altera- 
 tion of the oil consists not only in the addition of a certain quantity 
 of oxygen, but in the diminution of the hydrogen. These oils are 
 distinguished by the name of drying oils. Linseed, poppy, and nut 
 ' oils, are of this description. 
 
 Emily. I am well acquainted with drying oils, as I continually 
 use them in painting. But I do not understand why the acquisi- 
 tion of oxygen on one hand, and the loss of hydrogen on the other, 
 should render them drying. 
 
 Jllrs. B. This, I conceive, may arise from two reasons ; either 
 from the oxygen which is added being less favourable to the state 
 of fluidity than the hydrogen, which is subtracted ; or from this 
 additional quantity of oxygen giving rise to new combinations, in 
 consequence of which the most fluid parts of the oil are liberated 
 and volatilized. 
 
 For the purpose of painting, the drying quality of oil is further 
 increased by adding a quantity of oxyd of lead to it, by which 
 means it is more rapidly oxygenated. 
 
 The rancidity of oils is likewise owing to their oxygenation. In 
 this case, a new order of attraction takes place, from which a pe- 
 culiar acid is formed, called the sebacic acid. 
 
 Caroline. Since the nature and composition of oil is so well 
 known, pray, could not oil be actually made, by combining its prin- 
 ciples ? 
 
 * This statement is too low. None of the fixed oils boil at a less 
 temperature than 600 degrees, nor will they burn until converted 
 into vapour ; consequently they cannot burn at a lower tempera- 
 ture than 600. C. 
 
 1097. Why are wax better than tallow candles ? 
 
 1098. What elevation of temperature is necessary in order to 
 burn oil ? 
 
 1099. What are the principal drying oils ? 
 
 1100. Why will the oxyd of lead increase the drying quality 
 ofdils? 
 
 flOJi To what is the rancidity of oil owing ? 
 
OF VEGETABLES. 247 
 
 .Mrs. J5. That is by no means a necessary consequence ; for 
 there are innumerable varieties of compound bodies which we can 
 decompose, although we are unable to reunite their ingredients. 
 This, however, is not the case With oil, as it has very lately been dis- 
 covered that it is possible to form oil, by a peculiar process, from 
 the action of oxygenated muriatic acid gas on hydro-carbonate.* 
 
 We now pass to the volatile or essential oils. These form the basis 
 of all the vegetable perfumes, and are contained, more or less, in 
 every part of the plant excepting the seed ; they are, at least, never 
 found in that part of the seed which contains the embryo plant. 
 Emily. The smell of flowers, then, proceeds from volatile oil ? 
 Mrs. B. Certainly ; but this oil is often most abundant in the 
 rind of fruits, as in oranges, lemons, &c., from which it may be ex- 
 tracted by the slightest pressure ; it is found also in the leaves of 
 plants, and even in the wood. 
 
 Caroline. Is it not very plentiful in the leaves of mint, and of 
 thyme, and all the sweet smelling herbs ? 
 
 Jlfr*. B. Yes : remarkably so ; and in geranium leaves also, 
 which have a much more powerful odour than the flowers. 
 
 The perfume of sandal fans is an instance of its existence in wood. 
 In short, all vegetable odours or perfumes are produced by the 
 evaporation of particle's of these volatile oils. 
 
 Emily. They are, I suppose, very light, and of very thin consist- 
 ence, since they are volatile ? 
 
 Mrs. B. They vary very much in this respect, some of them be- 
 ing as thick as butter, whilst others are as fluid as water. In order 
 to be prepared for perfumes, or essences, these oils are first proper- 
 ly purified, and then, either distilled with spirit of wine, as is the 
 case with lavender water, or simply mixed with a large proportion 
 of water, as is often done with regard to peppermint. Frequently, 
 also, these odoriferous waters are prepared merely by soaking the 
 plants in water, and distilling. The water then comes over im- 
 pregnated with the volatile oil. 
 
 Caroline. ^Such waters are frequently used to take spots of 
 grease out (|Pcloth, or silk : how do they produce that effect ? 
 
 Mrs. B. B^combining with the substance that forms these stains ; 
 for volatile oils, and likewise the spirit in which they are distilled 
 will dissolve wax, tallow, spermaceti, and resins ; if, therefore, the 
 
 * Hydro- carbonate, is also called olcfiant or oil making gas, on 
 account of the supposed property here mentioned. But later ex- 
 periments have shown that the substance it forms with chlorine, is 
 not an oil, but a kind of ether, hence it is now known under the 
 name of chloric ether. C. 
 
 1102. Is there any known method of making oil by combining 
 its principles r 
 
 1 103. What forms the basis of vegetable perfumes? 
 
 1104. In what part of the plant are the volatile or essential oils 
 contained ? 
 
 1 105. From what proceeds the smell of flowers ? 
 
 1 106. How sire volatile oils obtained ? 
 
 1107. Why will water mixed with vegetable oils assist in re- 
 moving spots of grease from cloth ? 
 
COMPOSITION 
 
 spot proceeds from any of those substances, it will remove it. In- 
 sects of every kind have a great aversion to perfumes, so that vola- 
 tile oils are employed with success in museums for (he preserva- 
 tion of stuffed birds and other species of animals. 
 
 Caroline. Pray, does not the powerful smell of camphor proceed 
 from a volatile oil ? 
 
 Mrs. B. Camphor seems to be a substance of its own kind, re- 
 markable by many peculiarities. But if not exactly of the same 
 nature as volatile oil, it is at least very analagous to it. It is ob- 
 tained chiefly from the camphor-tree, a species of laurel which 
 grows in China, and in the Indian isles, from the stem and roots of 
 which it is extracted.* Small" quantities have also been distilled 
 from thyme, sage, and other aromatic plants ; and it is deposited in 
 pretty large quantities by some volatile oils after long- standing. It 
 is extremely volatile and inflammable. It is insoluble in watery but 
 is soluble in oils, in which state, BS well as in its solid form, it is fre- 
 quently applied to medicinal purposes. Amongst the particular 
 properties of camphor, there is one too singular to be passed over 
 in silence. If you take a small piece of camphor, and place it on 
 the surface of a basin of pure water, it will immediately begin to 
 move round and round with great rapidity ; but if you pour into 
 the basin a single drop of any odiferous fluid, it will instantly put a 
 stop to this motion. You can at any time try so simple an experi- 
 ment ; but you must not expect that I shall be able to account for 
 the phenomenon, as nothing satisfactory has as yet been advanced 
 forjts explanation, 
 
 Caroline. It is very singular indeed ; and I will certainly make 
 the experiment. Pray, what are resins, which you just now men- 
 tioned ? 
 
 Mrs. B. They are volatile oils, that have been acted on, and pe- 
 culiarly modified, by oxygen. 
 
 Caroline. They are, therefore, oxygenated volatile oils ? 
 
 Mrs. B. Not exactly ; for the process does not appear to consist 
 so much in the oxygeination of the oil, as in the combustion of a por- 
 tion of its hydrogen, and a small portion of its carbon. For when 
 resins are artificially made by the combination of volatile oils with 
 oxygen, the vessel in which the process is performed is bedewed 
 with water, and the air included within it is loaded with carbonic 
 acid. 
 
 Emily. This process must be, in some respects, simlar to that for 
 preparing drying oils ? 
 
 Mrs. B- Yes ; and it is by this operation that both of them acquire 
 a great degree of consistence. Pitch, tar, and turpentine, are the 
 most common resins ; they exude from the pine and fir trees. Co- 
 
 * Camphor comes chiefly from Japan. It is obtained by distilling 
 the wood of the laurus camphora^ or camphor tree, with water, in 
 'large iron pots, with earthen caps stuffed with straw. The cam- 
 phor sublimes and concretes upon the straw. C. 
 
 1 108. From what is camphor obtained ? 
 
 1 109. Is camphor contained in other plants ? 
 
 1110. What is the method of obtaining it? 
 
 11 11. What remarkable peculiarity has camphor ? 
 
 1112. W hat are resins ? 
 
OF VEGETABLES. 
 
 249 
 
 pal, mastic and frankincense, are also of this class of vegetable sub- 
 stances. 
 
 Emily. Is it of these resins that the mastic and copal varnishes 
 so much used in painting are made ? 
 
 Mrs. B. Yes. Dissolved either in oil or in alcohol, resins form 
 varnishes. From these solutions they may be precipitated by wa- 
 ter, in which they are insoluble. This I can easily show you. 
 you will pour some water into this glass of mastic varnish, it will 
 combine with the alcohol in which the resin is dissolved, and the 
 latter will be precipitated in the form of a white cloud. 
 
 Emily. It is so. And yet how is it that pictures or drawings, var- 
 nished with this solution, may safely be washed with water ? 
 
 Mrs. B. As the varnish dries, the alcohol evaporates, and the dry 
 varnish or resin which remains, not being soluble in water, will not 
 be acted on by it. 
 
 There is a class of compound resins, called gum resins, which are 
 precisely what their name denotes, that is to say, resins, combined 
 with mucilage. Myrrh and assafoetida are of this description. 
 
 Caroline. Is it possible that a substance of so disagreeable a smell 
 as assafcetida can be formed from a volatile oil ? 
 
 Mrs. B. The odour of volatile oils is by no means always grateful. 
 Onions and garlic derive their smell from volatile oils, as well as ro- 
 ses and lavender. 
 
 There is still another form under which volatile oils present them- 
 selves, which is that of balsams. These consist of resinous juices 
 combined with a peculiar acid, called the benzoic acid. Balsams 
 appear to have been originally volatile oils,* the oxygenation of 
 which, has converted one part into a resin, and the other part into 
 an acid, which combined together, form a balsam ; such are the 
 balsams of Peru, Tolu, &c. 
 
 We shall now take leave of the oils and their various modifica- 
 tions, and proceed to the next vegetable substance which is caoutch- 
 ouc. This is a white, milky, glutinous fluid, which acquires consis- 
 tence and blackens in drying, in which state it forms the substance 
 with which you are so well acquainted, under the name of gurn- 
 elastic. 
 
 Caroline. I am surprised to hear that gum- elastic was ever white, 
 or ever fluid ! And from what vegetable is it procured ? 
 
 Mrs. B. It is obtained from two or three different species of trees 
 in the East Indies, and South America, by making incisions in the 
 stem. The juice is collected as it trickles from these incisions, and 
 moulds of clay, in the form of little bottles of gum-elastic, are dipped 
 
 * This is an erroneous idea. Balsams are original and peculiar 
 substances, and consist chiefly of resinous matter in a semifluid 
 state. The benzoic acid is most probably formed during the pro- 
 cess by which it is obtained. C. 
 
 1 1 13. What are the most common resins ? 
 
 1114. Of what are mastic and copal varnishes made 
 
 1115. What will be the consequences if water be poured into a 
 vessel containing mastic varnish? 
 
 1116. What are gum resins ? 
 
 1117. What are balsams? 
 
 1118. From what is caoutchouc obtained ? 
 
 1119. What are its uses ? 
 
250 COMPOSITION 
 
 into it. A layer of this juice adheres to the clay and dries onit ; 
 and several layers are successively added by repeating- this till the 
 bottle is of sufficient thickness. It is then beaten to break down 
 the clay which is easily shaken out. The natives of the countries 
 where this substance is produced, sometimes make shoes and boots 
 of it by a similar process, and they are said to be extremely pleasant 
 and serviceable, both from their elasticity, and their being water- 
 proof. 
 
 The substance which comes next in our enumeration of the im- 
 mediate ingredients of vegetables, is extractive matter. This is a 
 term which, in a general sense, may be applied to any substance ex- 
 tracted from vegetables ; but it is more particularly understood to 
 relate to the extractive coloring matter of plants. A great variety 
 of colors are prepared from the vegetable kingdom, both for the 
 purposes of painting and of dying ; all the colors called lakes are 
 of this description ; but they are less durable th\n mineral colors, 
 for by long exposure to the atmosphere, they either darken or turn 
 yellow. 
 
 Emily.. I know that in painting, the lakes are reckoned far less 
 durable colors than the ochres ; but what is the reason of it ? 
 
 Mrs. B. The change which takes place in vegetable colors is 
 owing chiefly to the oxygen of the atmosphere slowly burning their 
 hydrogen, and leaving, in some measure, the blackness of the car- 
 bon exposed. Such change cannot take place in ochre, which is 
 altogether a mineral substance. 
 
 Vegetable colors have a stronger affinity for animal than for veg- 
 etable substances ; and this is supposed to be owing to a small quan- 
 tity of nitrogen, which they contain. Thus, silk and worsted will 
 take a much finer vegetable dye than linen and cotton. 
 
 Caroline. Dying, then, is quite a chemical process ? 
 
 Mrs. B. Undoubtedly. The condition required to form a good 
 dye is, that the -coloring matter should be precipitated, or fixed, 
 on the substance to be dyed, and should form a compound not solu- 
 ble in the liquids to which it would probably be exposed. Thus, for 
 instance, printed or dyed linens or cottons mast be able to resist 
 the action of soap and water, to which they must necessarily be sub- 
 ject in washing ; and woollens and silks should withstand the action 
 of grease and acids, to which they may accidentally be exposed. 
 
 Caroline. B ut if finen and cotton have not a sufficient affinity for 
 coloring matter, how are they made to resist the action of washing, 
 which they a ways do when they are well printed ? 
 
 Mrs. B. When the substance to be dyed has either no affinity 
 for the coloring matter, or not sufficient power to retain it, the com- 
 bination is effected or strengthened, by the interven-tion of a third 
 substance, called a mordant, or basis. The mordant must have a 
 
 1 120. What is the extractive matter of vegetables ? 
 
 1 121. What are the colors called prepared from vegetables ? 
 
 1122. To what is the change which takes place in vegetable col- 
 ors owing ? 
 
 1123. Why have vegetable colors a stronger affinity for animal 
 than for vegetable substances ? 
 
 1 124. What is necessary that vegetable colors be durable ? 
 
 1125. What are mordants and their uses .? 
 
OP VEGETABLES. 
 
 251 
 
 strong- affinity both for the coloring matter and the substance dyed, 
 by which means it causes them to combine and adhere together. 
 
 Caroline. And what are the substances that perform the office of 
 thus reconciling- the two adverse parties ? 
 
 Mrs. B. The most common mordant is sulphat of alumine, or 
 alum. Oxyds of tin and iron in the state of compound salts, are 
 likewise used for that purpose. 
 
 Tannin is another vegetable ingredient of great importance in the 
 arts. It is obtained chiefly from the bark of trees ; but it is found 
 also in nut-galls, and in some other vegetables. 
 
 Emily. Is that the substance commonly called tan, which is used 
 in hot-houses f 
 
 Mrs. B. Tan is the prepared bark in which the peculiar substance, 
 tannin is contained. But the use of tan in hot-houses is of much 
 less importance than the operation of tanning, by which skin is 
 converted into leather. 
 
 Emily. Pray how is this operation performed ? 
 
 Mrs. B. Various methods are employed for this purpose, which 
 all consist in exposing skin to the action of tannin, or of substances 
 containing this ; ; inciple in sufficient quantities, and disposed to 
 yield it to the sktu. The most usual way is to infuse coarsely pow- 
 dered oak bark i; water, and to keep the skin immersed in this in- 
 fusion for a certs n length of time. During this process, which is 
 slow and gradual, the skin is found to have increased in weight, and 
 to have acquired a considerable tenacity and impermeability to wa- 
 ter. This effect may be much accelerated by using strong satura- 
 tions of the tanning principle, (which can be extracted from bark,) 
 instead of employing the bark itself. But this quick mode of pre- 
 paration does not appear to make equally good leather. 
 
 Tannin is contained in a great variety of astringent vegetable 
 substances, as galls, the rosetree, and wine ; but it is no where so 
 plentiful as in bark. All these substances 3 ield it to water, from 
 which it may be precipitated by a solution of isinglass or glue, with 
 which it strongly unites and forms an insoluble compound. Hence 
 its valuable property of combining with skin (which consists chiefly 
 of fflue,) and of enabling it to resist the action of water. 
 
 Emily. Might we not see that effect by pouring a little melted 
 isinglass into a glass of wine, which you say contains tannin ? 
 
 Mrs. B. Yes. 1 have prepared a solution of isinglass for that 
 very purpose. Do you observe the thick, muddy precipitate ? That 
 is the tannin combined with the isinglass. 
 
 Caroline. This precipitate must then be of the same nature as 
 the leather? 
 
 Mrs. B. It is composed of the same ingredients ; but the organ- 
 ization and texture of the skin being wanting, it has neither the 
 consistence nor the tenacity of leather. 
 
 1 126. What substances are commonly used as mordants ? 
 
 1127. From what is tannin obtained ? 
 
 11 28. What are its uses ? 
 
 1129. What is the process of converting skins into leather, by 
 the use of tanning ? 
 
 1 130. Why does tanning cause skins on being changed to leather, 
 to be impervious to water ? 
 
 1131. How does a solution of isinglass in water differ from leather? 
 
252 COMPOSITION 
 
 Caroline. One might suppose that men who drink large quanti- 
 ties of red wine, stand a chance of having the coats of their stom- 
 achs coverted into leather, since tannin has so strong an affinity 
 for skin. 
 
 Mrs. B. It is not impossible but that the coats of their stomachs 
 may be, in some measure, tanned or hardened by the constant use 
 of this liquor ; but you must remember that where a number of 
 other chemical agents are concerned, and above all, where life ex- 
 ists, no certain chemical inference can be drawn. 
 
 I must not dismiss this subject, without mentioning a recent dis- 
 covery of Mr. Hatchett, which relates to it. This gentleman found 
 that a substance very similar to tannin, possessing all its leading 
 properties, and actually capable of tanning leather, may be produc- 
 ed by exposing carbon, or any substance containing carbonaceous 
 matter, whether vegetable, animal, or mineral, to the action of ni- 
 tric acid.* 
 
 Caroline. And is not this discovery very likely to be of use to 
 manufactures? 
 
 Mrs. B. That is very doubtful, because tannin, thus artificially 
 prepared, must probably always be more expensive than that which 
 is obtained from bark. But the fact is extremely curious, as it af- 
 fords one of those very rare instances of chemistry being able to im- 
 itate the proximate principles of organized bodies. 
 
 The last of the vegetable materials is woody fibre it is the hard- 
 est part of plants. The chief source from which this substance is 
 derived, is wood, but it is also contained, more or less, in every solid 
 part of the plant. It forms a kind of skeleton of the part to which 
 it belongs and retains its shape after all the other materials have dis- 
 appeared. It consists chiefly of carbon united with a small portion 
 of salts, and the other constituents common to all vegetables. 
 
 Emily. It is of woody fibre then, that the common charcoal is 
 made ? 
 
 Mrs. B. Yes. Charcoal, as you may recollect, is obtained from 
 wood by the separation of all its evaporable parts. 
 
 Before we take leave of the vegetable materials, it will be proper 
 at least to enumerate the several vegetable acids which we either 
 have had or may have occasion to mention. I believe I formerly 
 told you that their basis or radical, was uniformly composed by hy- 
 drogen and carbon, and that their difference consisted only in the 
 various proportions of oxygen which they contained. 
 
 * To make artificial tannin, Mr. Hatchett used 100 grains of char- 
 coal with 500 of nitric acid, diluted with twice its weight of water. 
 This mixture was heated, and then suffered to digest for two days ; 
 more acid was then added, and the digestion continued until the 
 charcoal was dissolved. This solution being evaporated to dry ness, 
 leaves a dark brown mass. This is the tannin in question. Its taste 
 is bitter and highly astringent. C. 
 
 1132. What discovery was made by Mr, Hatchett ? 
 
 1133. How did he prepare artificial tannin? 
 
 1134. What is woody fibre? 
 
 1135. Of what does it chiefly consist ? 
 
 1136. From what is charcoal made ? 
 
OF VEGETABLES. 253 
 
 The following are the names of the vegetable acids : 
 The Mucous acid obtained from gum or mucilage ; 
 Suberic, - from cork ; 
 
 Camphoric, 
 .Benzole 
 Gallic 
 Malic 
 Citric 
 
 from camphor; 
 from balsams : 
 from galls, bark, &c. 
 from ripe fruits ; 
 from lemon juice ; 
 
 Oxalic - from sorrel 
 
 Succinir. - from amber ; 
 
 Tartarous - from tartrit of potash ; 
 
 Acetic - from vinegar. 
 
 They are all decomposable by heat, soluble in water, and turn ve- 
 getable blue colours re/i. The succinic, the tartarous, and the ace- 
 tous acids, are the productions of the decomposition of vegetables ; 
 we shall, therefore, reserve their examination for a future period. 
 
 The oxalic acid, distilled from sorrel, is the highest term of vege- 
 table acidification ; for, if more oxygen be added to it, it loses its 
 . vegetable nature, and is resolved into carbonic acid and water; 
 therefore, though all the other acids may be converted into the ox- 
 alic by an addition of oxygen, the oxalic itself is not susceptible of 
 a further degree of oxygenation : nor can it be made by any che- 
 mical processes, to return to a state of lower acidification.* 
 
 To conclude this subject, 1 have only to add a few words on tfte 
 gallic acid. 
 
 Caroline. Is not this the same acid before mentioned, which forms 
 ink, by precipitating sulphat of iron from its solution ? 
 
 Mrs. B. Yes. Though it is usually extracted from galls, on ac- 
 count of its being^most abundant in that vegetable substance, it 
 may also be obtained from a great variety of plants. It constitutes 
 what is called the astringent principle of vegetables ; it is generallv 
 combined^vith tannin, and you will find that an infusion of tea, cof- 
 fee, bark, red wine, or any vegetable substance that contains the 
 astringent principle, will make a biack precipitate with a solution 
 of sulphat of iron. 
 
 Caroline. But pray what are galls ? 
 
 Mrs. B- They are excrescences which grow on the bark of young 
 
 * Oxalic acid may be formed artificially. Put one ounce ofwhite 
 sugar, powdered, into a retort, and pour on three ounces of nitric 
 acid. When the solution is over, make the liquor boil, and when it 
 acquires a reddish brown colour, add three ounces more of nitric 
 acid. Continue the boiling until the fumes cease, and the colour of 
 the liquor vanishes. Then let the liquor be poured into a wide ves- 
 sel, and on cooling, white slender crystals will be formed. These 
 are oxalic acid. C. 
 _^_ , . _i . 
 
 1 137. What are the names of the vegetable acids ? 
 
 1138. What is the composition of the basis of these acids ? 
 
 1139. What general quality have all vegetable acids ? 
 
 1 140. What is the highest term of vegetable acidification ? 
 
 1141. What acid is called the astringent principle of vegetables ? 
 
 1 142. From what is it usually extracted ? 
 
 .1 V What are the galls that yield this acid ? 
 
254 COMPOSITION 
 
 oaks, and are occasioned by an insect which wounds the bark of 
 trees, and lays its egg's in the aperture. The lacerated vessels of 
 the tree then discharge their contents, and form an excrescence, 
 which affords a defensive covering for these eggs. The insect, when 
 come to life, first feeds on this excrescence, and sometime after- 
 wards eats its way out, as it appears from a hole which is formed in 
 all gall-nuts that no longer contain .an insect. It is in hot climates 
 only that strongly astringent gall nuts are found ; those which are 
 used for the purpose of making ink are brought from Aleppo. 
 
 Emily. But are not the oak apples which grow on the leaves of 
 the oak in this country of a similar nature ? 
 
 Mrs. B' Yes; only they are an inferior species of galls, contain- 
 ing less of the astringent principle, and therefore less applicable to 
 useful purposes. 
 
 Caroline. Are the vegetable acids never found but in their pure 
 uncombined state? 
 
 Mrs. B. By no means ; on the contrary, they are frequently met 
 with in the state of compound salts ; these, however, are in gene- 
 ral not fully saturated with the salifiable bases, so that the acid pre- 
 dominates ; and in this state, they are called acidulous salts. Of 
 this kind is the salt- called cream of tartar. 
 
 Caroline. Is not th salt of lemon commonly used to take out 
 ink-spots and stains, of this nature ? 
 
 J\lrs. B. No; that salt consists of the oxalic acid, combined, with 
 a little potash. It is found in that state in sorrel. 
 
 Caroline. And pray how does it take out ink-spots ? 
 
 JWrs. B. By uniting with the .iron, and rendering it soluble in 
 water. 
 
 Besides the vegetable materials which we have enumerated, a va- 
 riety of other substances, common to the three kingdoms, are found 
 in vegetables, such as potash, which was formerly supposed to be- 
 long exclusively to plants, and .was, in consequence, called the ve- 
 getable alkali. 
 
 Sulphur, phosphorus, earths, and a variety of metallic oxyds, are 
 also found in vegetables, but only in small quantities. And we meet 
 sometimes with neutral salts, 'formed by the, combination . of these 
 ingredients. 
 
 CONVERSATION XXI. 
 
 ON THE DECOMPOSITION OF VEGETABLES. 
 
 Caroline. The account which you have given us, Mrs. B., of the 
 materials of vegetables, is doubtless, very instructive ; but it does 
 
 1144. In what climates are strongly astringent gall-nuts found ? 
 
 1145. Are the,vegetable acids never found but in their pure un- 
 combined state ? 
 
 1 f4G. : How does the oxalic acid remove ink-spots ? 
 1147. What gubetances common, to the three kingdoms arefoun<J 
 rn vegetables? 
 
OF VEGETABLES, 
 
 255 
 
 not completely satisfy my curiosity. I wish to know how plants ob- 
 tain the principles from which their various materials are formed ; 
 by what means these are converted into vegetable matter, and how 
 they are connected with the life of the plant. 
 
 Mrs. B. This implies nothing- less than a complete history of the 
 chemistry and physiology of vegetation, subjects on which we have 
 yet but very imperfect notions. Still I hope that I shall be able, in 
 some measure, to satisfy your curiosity. But, in order to render the 
 subject more intelligible, 1 must first make you acquainted with the 
 various changes which vegetables undergo, when the vital power 
 no longer enables them to resist the common laws of chemical at- 
 traction. 
 
 The composition of vegetables being more complicated than that 
 ohninerals, the former'more readily undargo chemical changes than 
 the latter ; for the greater the variety of attractions, the more easi- 
 ly is the equilibrium destroyed, and a new order of combinations in- 
 troduced. 
 
 Emily. I am surprised that vegetables should be so easily suscep- 
 tible of decomposition : for the preservation of the vegetable king- 
 dom is certainly far more important than that of minerals. 
 
 Mrs. B. You must consider, on the other hand, how much more 
 easily the former is renewed than the latter. The decomposition of 
 the vegetable takes place only after the death of the plant, which, 
 in the common course of nature, happens when it has yielded fruit 
 and seeds to propagate its species. If, instead of thus finishing its 
 career, each plant was to retain its form and vegetable state, it 
 vould become an useless burden to the earth and its inhabitants. 
 When vegetables, therefore, cease to be productive, they cease to 
 live, and nature then begins her process of decomposition, in orde 
 to resolve them into ther chemical constituents, hydrogen, carbon 
 and oxygen ; those simple and primitive ingredients, which she 
 keeps in store for all her combinations. 
 
 Emily. But since no system of combination can be destroyed ex- 
 cept by the establishment of another order of attractions, how can 
 the decomposition of vegetables reduce them to their simple ele- 
 ments ? 
 
 .Jftri. B. Tt is a very long process, during which a variety of new 
 combinations are successively established, and successively destroy- 
 ed ; but, in each of these changes, the ingredients of vegetable 
 mattef tend to unite in a more simple order of compounds, till 
 they are at length brought to their elementary state, or, at least, to 
 their most simple order of combinations. Thus you will find that 
 vegetables are in the end almost entirely reduced to water and car- 
 bonic acid ; the hydrogen and carbon dividing the oxygen between 
 them so as to form with it these two substances. But the variety of 
 intermediate combinations that take place during the several stages 
 
 1148. Why do vegetables more readily undergo chemical chan 
 ges than minerals ? 
 
 1 149. When do vegetables become decomposed ? 
 
 1150. Into what are vegetables reduced by decomposition ? 
 
 1151. Since no system of combination can be destroyed, except 
 by the establishment of another order of attractions, how can the de- 
 composition of vegetables reduce them to their simple elements ? 
 
256 DECOMPOSITION 
 
 of the decomposition of vegetables, present us with a new set of 
 compounds, well worthy of our examination. 
 
 Caroline. How is it possible that vegetables, while putrefying, 
 should produce any thing worthy of observation ? 
 
 Mrs. B. They are suscceptible of undergoing certain changes 
 before they arrive at the state of putrefaction, which is the final 
 term of decomposition ; and of these changes we avail ourselves for 
 particular and important purposes. But, in order to make you un- 
 derstand this subject, which is of considerable importance, I must 
 explain it more in detail. 
 
 The decomposition of vegetables is always attended by a violent 
 internal motion, produced by the disunion of one order of particles, 
 and the combination of another. This is called FERMENTATION. 
 There are several periods at which this process stops, so that a state 
 of rest appears to be restored, and the new order of compounds fair- 
 ly established. But, unless means be used to secure these new 
 combinations in their actual state, their duration will be but tran- 
 sient, and a new fermentation will take place, by which the com- 
 pound last formed will be destroyed ; and another, and less complex, 
 will succeed. 
 
 Emily. The fermentations, then, appear to be only the successive 
 steps by which a vegetable descends to its final dissolution. 
 
 Mrs. B. Precisely so. Your definition.is perfectly correct. 
 
 Caroline. And how many fermentations, or new arrangements, 
 does a vegetable undergo before it is reduced to its simple ingre- 
 dients ? 
 
 Mrs. B. Chemists do not exactly agree in this point ; but there 
 are, I think, four distinct fermentations, or periods, at which the 
 decomposition of vegetable matter stops and changes its course. 
 But every kind of vegetable matteris not equally susceptible of un- 
 dergoing all these fermentations. 
 
 There are likewise several circumstances required to prodoce 
 fermentation. Water, and a certain degree of heat are both essen- 
 tial to this process, in order to separate the particles, and thus weak- 
 en their force of cohesion, that the new chemical affinities may be 
 brought into action. 
 
 ,i Caroline. In frozen climates, then, how can the spontaneous de- 
 composition of vegetables take place ? 
 
 Mrs. B. It certainly cannot ; and, accordingly, we find scarcely 
 any vestiges of vegetation where a constant frost prevails. 
 
 Caroline. One. would imagine that, on the contrary, such spots 
 would be covered with vegetables ; for since they cannot be decom- 
 posed, their number must always increase. 
 
 Mrs. B. But, my dear, heat and water are quite as essential to 
 the formation of vegetables, as they are to their decomposition. Be- 
 sides, it is from the dead vegetables, reduced to their elementary 
 principles, that the rising generation is supplied with sustenance. 
 No young plant, therefore, can grow, unless its predecessors contri- 
 bute both to its formation and support ; and these not only furnish 
 
 1152. What is the process called, that disunites and decomposes 
 he elements of vegetables ? 
 
 1153. What are the fermentations ? 
 
 1154. How many kinds of fermentation are there?. 
 
 1155. What is necessary to produce fermentation ? 
 
OF VEGETABLES. 
 
 257 
 
 the seed from which the new plant springs, but likewise the food by 
 which it is nourished. 
 
 Caroline. Under the torrid zone, therefore, where water is never 
 frozen, and the heat is very great, both the processes of vegetation 
 and of fermentation must, I suppose, be extremely rapid ? 
 
 Mrs. B. Not so much as you imagine ; for in such climates great 
 part of the water which is required for these processes is in an aeri- 
 form state, which is scarcely more conducive either to the growth 
 or formation of vegetables than that of ice. In those latitudes, there, 
 fore, it is only in low, damp situations, sheltered by woods from the 
 sun's rays, Uat the smaller tribes of vegetables can grow and thrive 
 during the dry season, as dead vegetables seldom retain water 
 enough to produce fermentation, but are on the contrary, soon dried 
 up by the heat of the sun, which enables them lo Desist that process ; 
 so that it is not till the fall of the autumnal rain;- (which are very vio- 
 lent in such climates,) that spontaneous fermentation can take place. 
 
 The several fermentations derive their names from their principal 
 products. The first is called the saccharine fermentation, because 
 its product is sugart 
 
 Caroline. But sugar, you have told us, is found in all vegetables ; 
 it cannot, therefore, be the product of their decomposition. 
 
 Mrs. B. It is true that this fermentation is not confined to the 
 decomposition of vegetables, as it continually takes place during 
 their life ; and, indeed, this circumstance has till lately prevented it 
 from being considered as one of the fermentations, and the forma- 
 tion of sugar, whether in living or dead vegetable matter, is so ev- 
 idently a new compound, proceeding from the destruction of the 
 previous order of combinations, and essential to the subsequent fer- 
 mentations, that it is now, I believe, generally esteemed the first 
 step, or necessary preliminary to decomposition, if not an actual 
 commencement of that process. 
 
 Caroline. I recollect your hinting to us that sugar was supposed 
 not to be secreted from the sap, in the same manner as mucilage, 
 fecula, oil, and the other ingredients of vegetables. 
 
 Mrs. B. It is rather from these materials, than from the sap itself, 
 that sugar is formed ; and it is developed at particular periods, as 
 you may observe in fruits, which become sweet in ripening, some- 
 times even after they have been gathered. Life therefore is not es- 
 sential to the formation of sugar, whilst, on the contrary, mucilage, 
 fecula, and the other vegetable materials that are secreted from the 
 sap by appropriate organs, whose powers immediately depend on 
 the vital principle, cannot be produced but during the existence of 
 that principle. 
 
 Emily. The ripening of fruits is then their first step to destruc- 
 tion as well as their last towards perfection ? 
 
 Mrs. B. Exactly. A process analagous to the saccharine fer- 
 
 1157. What in the torrid zone prevents the processes of vegeta- 
 tion and fermentation from being rapid ? 
 
 1158. From what do the several fermentations derive their names? 
 
 1159. Why is the first of them called a saccharine fermentation ? 
 
 1160. Why was not sugar formerly considered a fermentation? 
 
 1161. Why is it at present considered a fermentation ? 
 
 1162. From what parts of Vegetables is sugar formed ? 
 
 09* 
 
258 DECOMPOSITION 
 
 mentation takes place also during the cooking of certain vegeta- 
 bles. This is the case with parsnips, carrots, potatoes, &c., in 
 which sweetness is developed by heat and moisture; and we know 
 that if we carry the process a little farther, a more complete decom- 
 position would ensue. The same process takes place also in seeds 
 previous to their sprouting. 
 
 Caroline. How do you reconcile this to your theory, Mrs. B. 
 Can you suppose that decomposition is the necessary precursor of 
 life? 
 
 Mrs, B. That is indeed the case. The materials of the seed must 
 be decomposed, and the seed disorganized, before a plant can sprout 
 from it. Seeds, besides the embryo plant, contain (as we have al- 
 ready observed] fecula, oil, and a little mucilage. These substan- 
 ces are destined for the nourishment of the future plant; but they 
 undergo some change before they can be fit for this function. The 
 seeds, when buried in the earth, with a certain degree of moisture 
 and of temperature, absorb water, which dilates them, separates 
 their particles, and introduces a new order of attractions, of which 
 sugar is the product. The substance of the seed is thus softened, 
 sweetened, and converted into a sort of white, milky pulp, fit for 
 the nourishment of the embryo plant. 
 
 The saccharine fermentation of seeds is artificially produced, for 
 the purpose of making malt, by the following process: A quantity 
 of barky is first soaked in water for two or three days: the water 
 being afterwards drained off, the grain heats spontaneously, swells, 
 bursts, sweetens, shows a disposition to germinate, and actually 
 sprouts to the length of an inch, when the process is stopped by put- 
 ting it into a kiln, where it is well dried at a gentle heat. In this 
 state \\ is crisp and friable, and constitutes the substance called 
 malt, which is the principal ingredient of beer. 
 
 Emily. But I hope you will tell us how malt is made into beer ? 
 
 Mrs. B. Certainly ; but i must first explain to you the nature of 
 the second fermentation, which is essential to that operation. This 
 is called the vinous fermentation, because its product is wine. 
 
 Emily. How very different the decomposition of vegetables is 
 from what I had imagined ! The products of their disorganization 
 appear almost superior to those which they yield during their state 
 of life and perfection. 
 
 Mrs. B. And do you not, at the same time, admire the beautiful 
 economy of Nature, which, whether she creates, or whether she 
 destroys, directs all her operations to some useful and benevolent 
 purpose ? H appears (hat the saccharine fermentation is extremely 
 favorable, if not absolutely essential, as a previous step, to the vinous 
 fermentation ; so that if sugar be not developed during the life of the 
 plant, the saccharine fermentation must be artificially produced be- 
 
 1163. What process analagous to saccharine fermentation takes 
 place during the cooking of certain vegetables ? 
 
 1164. How would you describe this fermentation in seeds prior 
 to germination ? 
 
 1 165. How is saccharine fermentation exhibited in the making of 
 malt? 
 
 1166. Why is the second fermentation called vinous ? 
 
 1167. Why does barley resist the vinous fermentation until it has 
 gone through the saccharine 
 
OF VEGETABLES. 
 
 259 
 
 fore the vinous fermentation can take place. This is the case with 
 barley, which does not }ield any sugar until it is made into malt ; 
 and it is in that state only that it is susceptible of undergoing- the 
 vinous fermentation by which it is converted into beer. 
 
 Caroline. But if the product of the vinous fermentation is always 
 wine, beer cannot have undergone that process, for beer is certain- 
 ly not wine. 
 
 Mrs. B. Chemically speaking, beer may be considered as the 
 wine of grain. For it is the product of the fermentation of malt, 
 just as wine is that of the fermentation of grapes, or other fruits. 
 
 The consequence of the rinous fermentation is the decomposition 
 of the saccharine matter, and the formation of a spiritous liquor from 
 the constituents of the sugar. But in order to promote this ferment- 
 ation, not only water and a certain degree of heat are necessary, but 
 some other vegetable ingredients, besides the sugar, as fecula, mu- 
 cilage, acids, salts, extractive matter, &c. all of which seem to con- 
 tribute to this process, and give to the liquor its peculiar taste. 
 
 Emily. It is, perhaps, for this reason, that wine is not obtained 
 from the fermentation of pure sugar ; but that fruits are chosen for 
 that purpose, as they contain not only sugar, but likewise the other 
 vegetable ingredients which promote the vinous fermentation, and 
 give the peculiar flavour. 
 
 Mrs. B. Certainly. And you must observe, also, that the relative 
 quantity of sugar is not the only circumstance to be considered in the 
 choice of vegetable juices for the formation of wine ; otherwise the 
 sugar-cane would be best adapted for that purpose. It is rather the 
 manner and proportion in which the sugar is mixed with other vege- 
 table ingredients that influences the production and qualities of wine. 
 And it is found that the juice of the grape not only yields the most 
 considerable proportion of wine, but that it likewise affords it of the 
 most grateful flavour. 
 
 Emily. I have seen a vintage in Switzerland, and I do not re- 
 collect that heat was applied, or water added, to produce the fer- 
 mentation of the grapes. 
 
 Mrs. B. The common temperature of -the atmosphere in the cel- 
 lars in which the juice of the grape is fermented is sufficiently warm 
 for this purpose ; and as the juice contains an ample supply of water, 
 there is no occasion for any addition of it. But when fermentation is 
 produced in dry malt, a quantity of water must necessarily be added. 
 
 Emily. But what are precisely the changes that happen during 
 the vinous fermentation ? 
 
 Mrs. B. The sugar is decomposed, and its constituents are re- 
 combined into two new substances : the oce a peculiar liquid sub- 
 stance, called alcohol or spirit of wine, which remains in the fluid ; 
 the other, carbonic acid gas, which escapes duringth&ferrnentation. 
 Wine, therefore, as I before observed, in a genentl point of view, 
 may be considered as a liquid, of which alcohol constitutes the essen- 
 
 1 168. What is the consequence of the vinous fermentation ? 
 
 1 169. What is necessary* to produce this fermentation ? 
 
 1 1 70. Why are grapes chosen for wine instead of put e sugar ? 
 1171 What is to be considered in the choice of vegetable juices 
 
 for the formation of wine ? 
 
 1172. What are the changes that happen during the vinous fer- 
 mentation ? 
 
260 DECOMPOSITION 
 
 tial part. And the variety of strength and flavour of the different 
 kinds of wine, are to be attributed to the different qualities of the 
 fruits, from which they are obtained, independently of the sugar, 
 
 Caroline. 1 am astonished to hear that so powerful a liquid as spir- 
 it of wine should be obtained from so mild a substance as sugar. 
 
 Mrs. B. Can you tell me in what the principal difference consists 
 between alcobol and sugar? 
 
 Caroline. Let me reflect ; Sugar consists of carbon, hydrogen, 
 and oxygen. If carbonic acid be subtracted from it, during the for- 
 mation of alcohol, the latter will contain less carbon and oxygen 
 than sugar does ; therefore hydrogen must be the prevailing prin- 
 ciple of alcohol. 
 
 Mrs.B. It is exactly so. And this vdry large proportion of hy- 
 drogen accounts for the lightness and combustible properly of alco- 
 hol, and of spirits in general, all of which consist of alcohol vari- 
 ously modified. 
 
 Emily. And can sugar be recomposed from the combination of 
 alcohol and carbonic acid ? 
 
 Mrs. B. Chemists have never been able to succeed in effecting 
 this ; but from analogy I should suppose such a recom position possi- 
 ble. Let us now observe more particularly, the phenomena that 
 take place during the vinous fermentation. At the commencement 
 of this process, heat is evolved, and the liquor swells considerably 
 from the formation of the carbonic acid, which is disengaged in such 
 prodigious quantities as would be fatal to any pers'on who should una- 
 wares inspire it ; an accident which has sometimes happened. If the 
 fermentation be stopped by putting the liquor into barrels, before 
 the whole of the carbonic acid is evolved, the wine is brisk, like 
 Champagne, from the carbonic acid imprisoned in it, and it tastes 
 sweet, like cider, from the sugar not being completely decomposed. 
 
 Emily. But I do not understand why heat should be evolved du- 
 ring this operation. For, as there is a considerable formation of gas 
 in which a proportionable quantity of heat must become insensible, 
 I should have imagined that cold, rather than heat, would have 
 been produced. 
 
 Mrs. B. It appears so on first consideration ; but you must recol- 
 lect that fermentation is a complicated chemical process ; and that, 
 during the decompositions andrecompositioos attending it, a quanti- 
 ty of chemical heat may be disengaged, sufficient both to develope 
 the gas, and to effect an increase of temperature. When the fer- 
 mentation is completed, the liquid cools and subsides, the efferves- 
 cence ceases, and the thick, sweet, sticky juice of the fruit, is con- 
 verted into a clear, transparent, spirituous liquor, called wine. 
 
 Emily. How much I regret not having been acquainted with 
 the nature of the vinous fermentation, when I had an opportunity 
 of seeing the process. 
 
 Mrs^ B. You have an easy method of satisfj ing yourself in that 
 
 1 1 73. What is the principal difference between sugar and alcohol ? 
 
 1 174. Can sugar be recomposed by the combination of alcohol 
 and carbonic acid ? 
 
 1 175. What takes place at the commencement of the vinous fer- 
 mentation ? 
 
 1 176. Why is Champagne wine so brisk? 
 
 1 177. What process is analagous to the making of wine? 
 
OF VEGETABLES. 
 
 261 
 
 respect by observing the process of brewing 1 , which in every essen- 
 tial circumstance, is similar to that of making wine, and is really a 
 very curious chemical operation. 
 
 Although we cannot actually make wine at this moment, it will be 
 easy to show you the mode of analyzing it. This is done by distil- 
 lation. When wine of any kind is submitted to this operation, it is 
 found to contain brandy, water, tartar, attractive colouring matter 
 and some vegetable acids. I have put a little Port wine into this 
 
 alembic of glass, & 
 on placing the lamp 
 under it, you will 
 soon see the spirit 
 and water succes- 
 sively come over 
 
 Emily. But you 
 do not mention al- 
 cohol amongst the 
 products of the dis- 
 tillation of wine ; 
 and yet that is its 
 most essential in- 
 gredient. 
 
 Mrs. B. The al- 
 cohol is contained 
 in the brandy which 
 is now coming over 
 and dropping from 
 the still. Brandy is 
 nothing more than 
 a mixture of alcohol 
 and water ; and in 
 order to obtain the 
 alcohol pure, we ; 
 must again distil it 
 from brandy 
 
 (Fig. 34.) 
 
 Ai Alembic. B. Lamp. C. Wine. 
 
 Caroline. I have just taken a drop on my finger ; it tastes like 
 strong brandy, but it is without colour, whilst brandy is of a deep 
 yellow. 
 
 Mrs. B. It is not so naturally ; in its pure state, brandy is colour- 
 less, and it obtains the yellow tint you observe, by extracting the 
 colouring matter from the new oaken casks in which it is kept. But 
 if it does not acquire the usual tinge in this way, it is the custom to 
 colour the brandy used in this country artificially with a litte burnt 
 sugar, in order to give it the appearance of having been long kept. 
 
 Caroline. And is rum also distilled from wine? 
 
 . B. By no means ; it is distilled from the sugar cane, a plant 
 which contains so great a quantity of sugar, that it yields more al- 
 cohol than almost any other vegetable. After the juice of the cane 
 has been pressed out for majiing sugar, what still remains in the 
 bruised cane is extracted by water, and this watery solution of su- 
 gar is fermented, and produces rural, 
 
 __ _ ________ _ t _ :-. _ _ 
 
 1 1 78. When wine is distilled what is the product ? 
 
 1179. What is brandy? 
 
 1180. From what does brandy obtain its colouring.? 
 
 1181. From what and how is rum, distilled I 
 
262 DECOMPOSITION 
 
 The spiritous liquor called arack is in a similar manner distilled 
 from the product of the vinous fermentation of rice. 
 
 Emily. But rice has no sweetness ; does it contain any sugar ? 
 
 Mrs. B. Like barley, and most other seeds, it is insipid until it 
 has undergone the saccharine fermentation ; and this, you must re- 
 collect, is always a previous step to the vinous fermentation in those 
 vegetables in which sugar is not already formed. Brandy may, in 
 the same manner, be obtained from malt. 
 
 Caroline. You mean from beer, I suppose ; for the malt must 
 have previously undergone the vinous fermentation. 
 
 Mrs. B. Beer is not precisely the product of the vinous ferment- 
 ation of malt. For hops are a necessary ingredient for the forma- 
 tion of that liquor ; whilst brandy is distilled from pure fermented 
 malt. But brandy, no doubt, might be distilled from beer, as well 
 as from any other liquor that has undergone the vinous fermenta- 
 tion : for since the basis of brandy is alcohol, it may be obtained 
 from any liquid thaLcontains that spiritous substance. 
 
 Emily. And pra * from what vegetable is the favourite spirit of 
 the lower orders of the people, gin, extracted ? 
 
 Mrs. B. The spirit (which is the same in all fermented liquors) 
 may be obtained from any kind of grain ; but the peculiar flavour 
 which distinguishes gin is' that of juniper berries, which are distilled 
 together with the grain. 
 
 I think the brandy contained in the wine which we are distilling, 
 must, by this ti^e, be ajl come over. Yes taste the liquid that is 
 now dropping from the alembic. 
 
 Caroline. It is perfectly insipid, like water. 
 
 Mrs.B. It is water, which as I was telling you, is the second 
 product of wine, and comes over after all the spirit, which is the 
 lightest part, is distilled. The tartar, and extractive colouring 
 matter we shall find in a solid form at the bottom of the alembic. 
 
 Emily. They look very much like the lees of wine. 
 
 Mrs. B And in many respects, they are of a similar nature, for 
 lees of wine consist chiefly of tartrit of potash ; a salt which exists 
 in the juice of the grape, and in many other vegetables, and is de- 
 veloped only by the vinous fermentation. During this operation, it 
 is precipitated, and deposits itself on the internal surface of the 
 cask in which the wine is contained. It is much used in medicine, 
 and in various arts, particularly dying, under the name of cream of 
 t&tlar, and it is from this salt that the tartarous acid is obtained. 
 
 Caroline. But the medicinal cream of tartar is in appearance, 
 quite different from those dark coloured dregs; it is perfectly 
 colourless. 
 
 Mrs. B. Because it consists of the pure salts only, in its crystal- 
 lized form ; whilst in the instance bafore us, it is mixed with the 
 deep coloured extractive matter, and other foreign ingredients* 
 
 Emily. Pray, cannot we now obtain pure alcohol from the bran- 
 dy which we have distilled ? 
 
 "Mrs. B. We might; but the process would be tedious ; for in 
 order to obtain alcohol perfectly free from water, it is necessary to 
 distil, or, as the .distillers call it, rectify it several times. You must 
 
 1 182. From what and how is gin distilled ? 
 
 1183. What is the origin of the cream of tartar ? 
 
 1184. From what may alcohol be obtained ? 
 
OF VEGETABLES. 263 
 
 therefore, allow me to produce a bottle of alcohol that has been 
 thus purified. This is a very important ingredient, which has many 
 striking properties, besides its forming the basis of all spiritous 
 liquors. 
 
 Emily. It is alcohol, I suppose, that produces intoxication ? 
 JWrs. B. Certainly ; but the stimulus and momentary energy it 
 gives to the system, and the intoxication it occasions when taken 
 in excess, are circumstances not yet accounted for. 
 
 Caroline. I thought that it produced these effects by increasing 
 the rapidity of the circulation of the blood ; for drinkuig. wine or 
 spirits, I have heard always quickens the pulse. 
 
 Jftrs. B. No doubt ; the spirit by stimulating the nerves increases 
 the action of the muscles ; and the heart, which is one of the strong- 
 est muscular organs, beats with augmented vigour, and propels the 
 blood with accelerated quickness. After such a strong excitation 
 the frame naturally suffers a proportional degree of depression, so 
 that a state of debility and languor, is the invariable consequence 
 of intoxication. But though these circumstances are well ascer- 
 tained, they are far from explaining why alcohol should produce 
 such effects. 
 
 Emily. Liqueurs are the only kind of spirits which I think plea- 
 sant. Pray, of what do they consist ? 
 
 Mrs. B. They are composed of alcohol, sweetened with syrup, 
 and flavoured with volatile oil. 
 
 The different kinds of odoriferous spiritous waters are likewise 
 solutions of volatile oil in alcohol, as lavender, water, eau de Co- 
 longe, &c. 
 
 The chemical properties of alcohol are important and. numerous. 
 It is one of the most powerful chemical agents, and is particularly 
 useful in dissolving a variety of substances, which are soluble nei? 
 ther by water nor heat. 
 
 Emily. We have seen it dissolve copal and mastic to form var- 
 nishes ; and these resins are certainly not soluble in water, since 
 water precipitates them from their solution in alcohol. 
 
 Mrs. B. I am happy to find that you recollect these circum- 
 stances so well. The same experiment affords also an instance of 
 another property of alcohol, its tendency to unite with water ; for 
 the resin is precipitated in consequence of losing the alcohol, which 
 abandons it frem its preference^for w.ater. It is intended also, as 
 you may recollect, with -the s,ame peculiar circumstance of a dis- 
 engagement of heat, and consequent diminution of bulk, which we 
 have supppsed to be produced by a mechanical penetration of par- 
 ticles, by which latent heat is forced out. 
 
 Alcohol unites thus readily not only with resins and with water, 
 but with oils and balsams ; these compounds .form the extensive 
 class of elixirs, tinctures, quintessences, &JG. 
 
 Emily. I sjuppose that alcohol must be highly combustible, since 
 it contains so large a proportion of hydrogen. 
 
 1185. What is the intoxicating principle in spiritous liquors ? 
 
 1186. How does -it produce this effect ? 
 
 1187. What are the different .kinds, ,pf odoriferous spiritous wa- 
 ters ? 
 
 1188. What are some of the most peculiar uses of alcohol? 
 ,1189. Why are brandy and other spiritous liquors so combusti&le ? 
 
264 DECOMPOSITION 
 
 Mrs. B. Extremely so ; and Ut will burn at a very moderate 
 temperature. 
 
 Caroline. I Lave often seen both brandy and spirit of wine burnt ; 
 they produce a great deal of flame, but not a proportional quantity 
 of heat, and no smoke whatever. 
 
 Mrs. B. The last circumstance arises from their combustion be- 
 ing complete ; and the disproportion between the flame and heat 
 shows you that^ these are by no means synonymous. 
 
 The great quantity of.flarne proceeds from the combustion of the 
 hydrogen, to which you know that manner of burning is peculiar. - 
 Have you not remarked also, that brandy arid alcohol will burn 
 without wick? They take fire at so low a temperature, that this 
 assistance is not required to concentrate the heat and volatilize the 
 fluid. 
 
 Caroline. I have sometimes seen brandy burnt by merely heating 
 it in a spoon. 
 
 Mrs. B. The rapidity of the combustion of alcohol, may, how- 
 ever, be prodigiously increased by first volatilizing. An ingenious 
 instrument has been c > istructed on this principle to answer the 
 purpose of a blow-pipe, which may be used for melting glass, or other 
 chemical purposes, it consists of a small metallic vessel, (fig. 35,) 
 of a spherical shape, Fig. 35. 
 
 which contains the alco- Alcohol Blowpipe. 
 
 hoi, and is healed by the 
 lamp beneath it ; as sq.on 
 as the alcohol is vola- 
 tilized, it passes thro' the 
 spout of the vessel, and 
 issues just above the 
 wick of the lamp which 
 immediately sets fire to 
 the stream of vapour, as 
 I shall show you.* 
 
 Emily. With what 
 amazing violence it 
 burns ! The flame of I 
 alcohol, in the state of 
 vapour, is,I fancy,much D The , _ E The ve , gel in which the A]cchol ig boi] . 
 
 hotter than When the J Dff F. Safety valve. G. The inflamed jet or gleam of al- 
 Spirit is merely burnt coho1 Creeled towards a glass tube H. 
 
 in a spoon. 
 
 Mrs. B. Yes ; because in this way the combustion goes on much 
 quicker, and, of course, the heat is proportionally increased. Ob- 
 
 * A spirit lamp, which answers very .well for bending small glass 
 tubes, may be .constructed by almost any one. Take a low vial 
 with a wide mouth, fit a cork to it, and pierce the cork to admit a 
 piece of glass tube, the bore of which is about the size of a^ large 
 
 1190. Why is 110 smoke produced when brandy or spirit of wine 
 is burnt ? 
 
 1191. Why will brandy and alcohol burn without a wick ? 
 
 1192. How would you describe the experiment represented in 
 fig. 35? 
 
 1193. Huow would you describe the, spirit lamp ? 
 
OF VEGETABLES. 265 
 
 serve its effect on this small glass tube, the middle of which I pre- 
 sent to the extremity of the flame, where the heat is greatest. 
 
 Caroline. The glass, in that spot, is become red hot, and bends 
 from its own weight. 
 
 Mrs. B. 1 have now drawn it asunder, and am going to blow a 
 ball at one of the heated ends ; but 1 must previously close it up 
 and flatten it with this little metallic instrument, otherwise the 
 breath would pass through the tube without dilating any part of it. 
 Now Caroline, will you blow strongly into the tube whilst the 
 closed end is red hot ? 
 
 Emily. You blow too hard; for the ball suddenly dilated ton 
 great size, and then burst into pieces. 
 
 Mrs. B. You will be more expert another time ; but I must cau- 
 tion you, should you ever use this blow-pipe, to he very careful that 
 the combustion of the alcohol does not go on with too great vio- 
 lence, for I have seen the flame sometimes dart out with such force 
 as to reach the opposite wall of the room, and set the paint on fire. 
 There is, however, no danger of the vessel bursting, as it is provi- 
 ded with a safety tube, which affords an additional vent for the va- 
 pour of alcohol when required. 
 
 The products of the combustion of alcohol consist in a great pro- 
 portion of water, and a small quantity of carbonic acid. There is 
 no smoke or fixed remains whatever. How do you account for 
 that, Emily ? 
 
 Emily. 1 suppose that the oxygen which the alcohol absorbs in 
 burning, converts its hydrogen into water, and its carbon into car- 
 bonic acid gas, and thus it is completely consumed. 
 
 Mrs. B. Very well. Ether, the lightest of all fluids, and with 
 which you are well acquainted, is obtained from alcohol, of which 
 it forms the lightest and most volatile part. 
 
 Emily. Ether, then, is to alcohol, what alcohol is to brandy. 
 
 Mrs. B. No ; there is an essential difference. In order to ob- 
 tain alcohol from brandy, you need only deprive the latter of its 
 water; but for the formation of ether, the alcohol must be decom- 
 posed, and one of its constituents partly subtracted. I leave you to 
 guess which of them it is. 
 
 Emily. It cannot be hydrogen, as ether is more volatile than al- 
 cohol, and hydrogen is the lightest of all its ingredients : m>r do I 
 suppose that it can be oxygen, as alcohol contains so small a propor- 
 tion of that principle ; it is, therefore, most probably, carbon, a di- 
 minution of which would not fail to render the new compound more 
 volatile. 
 
 Mrs. B. You are perfectly right. The formation of ether cpn- 
 
 sists simply in subtracting from the alcohol a certain proportion of 
 carbon ; this is effected by the action of the sulphuric, nitric, or 
 
 goosequill. Let the tube rise an inch or two above the cork 
 pass some cotton wick through the tube then fill the vial with al- 
 cohol, and put the cork and tube in their places. The lamp is then 
 ready. C. 
 
 1194. What is the composition of alcohol ? 
 
 1195. From what is ether obtained ? 
 
 1 196. How does it differ from alcohol ? 
 
 1 197. In what does the formation of ether consist ? 
 
 28 
 
266 DECOMPOSITION 
 
 riatic acids, on alcohol. The acid and carbon remain at the bot- 
 tom of the vessel, 1 whilst the decarbonized alcohol flies off in the 
 form of a condensable vapour, which is ether. 
 
 Ether is the most inflammable of all fluids, and burns at sa low a 
 temperature that the heat evolved during- its combustion is more 
 than is required for its support, so that a quantity of ether is volati- 
 lized, which takes fire, and gradually increases the violence of the 
 combustion. 
 
 Sir Humphrey Davy has lately discovered a very singular fact re- 
 specting- the vapour of ether. If a few drops of ether be poured in- 
 to a wine-glass, and a fine platina wire, heated almost to redness, be 
 held suspended in the glass, close to the surface of the ether, the 
 wire soon becomes intensely red hot, and remains so for any length 
 of time. We may easily try the experiment. 
 
 Caroline. How very curious ! The wire is almost white hot, and 
 a pungent smell rises from the glass. Pray how is this accounted 
 for? 
 
 Mrs. B. This is owing to a very peculiar property of the vapour 
 of ether, and indeed of many other combustible gaseous bodies. At 
 a certain temperature lower than that of ignition, these vapours un- 
 dergo a slow and imperfect combustion, which does not give rise, 
 in any sensible degree, to the phenomena of light and flame, -and 
 yet extricates a quantity of caloric sufficient to re-act upon the 
 wire, and make it red hot, and the wire in its turn keeps up the ef- 
 fect as long as the emission of vapour continues. 
 
 This singular effect, which is also produced by the alcohol, may 
 be-rendered more striking, and kept up for an indefinite length of 
 time, by rolling a few coils of platina. wire, of the diameter of from 
 about l-60th to l-70th of an inch, round the wick of a spirit-lamp. 
 I f this lamp be lighted for a moment, and blown out again, the wire, 
 after ceasing for an instant to be luminous, becomes red hot again, 
 though the lamp is extinguished, and remains glowing vividly, till 
 the whole of the spirit contained in the lamp has been evaporated 
 and consumed in this peculiar manner. 
 
 Caroline. This is extremely curious. But why should not an 
 iron or silver wire produce the same effect ? 
 
 Jllrs. B. Because either iron or silver, being much better con- 
 ductors of heat than platina, the heat is carried off too fast by those 
 metals to allow the accumulation of caloric necessary to produce 
 the effect in question. 
 
 Ether is so light that it evaporates at the common temperature of 
 the atmosphere ; it is therefore necessary to keep it confined by a 
 well ground glass stopper. No degree of cold known has ever fro- 
 zen it.* 
 
 * Ether freezes and shoots into crystals, at 46 below the zero of 
 Fahrenheit. C. 
 
 1 198. What is the most inflammable of all bodies ? 
 
 1199. What singular effect has Sir H. Davy lately discovered re- 
 specting the vapour of ether ? 
 
 1200. How may this effect be rendered more striking? 
 
 1201. Why would not an iron or silver wire produce the same 
 effect ? 
 
 1202. At what degree of cold will ether freeze ? 
 
OF VEGETABLES. 267 
 
 Caroline. Is it not often taken medicinally ? 
 
 Mrs B. Yes ; it is one of the most effectual antispasmodic medi- 
 cines, and the quickness of its effects, as such, probably depends on 
 its being instantly converted into vapour by the heat of the stomach, 
 through the intervention of which it acts on the nervous system. 
 But the frequent use of ether, like that of spiritous liquors, becomes 
 prejudicial, arid, if taken to excess, it produces effects similar to 
 those of intoxication. 
 
 We may now take our leave of the vinous fermentation, of which, 
 I hope, you have acquired a clear idea ; as well as of the several 
 products that are derived from it. 
 
 Caroline. Though this process appears, at first sight, so much 
 complicated, it may, I think, be summed up in a few words, as it 
 consists in the conversion of sugar and fermentable bodies into alco- 
 hol and carbonic acid, which gives rise both to the formation of 
 v?in, and of all kinds of spiritous liquors. 
 
 Mrs. B. We shall now proceed tb the acetous fermentation, which 
 is thus called, because it converts wine into vinegar, by the forma- 
 tion of the acetous acid, which is the basis or radical of vinegar. 
 
 Caroline. But is not the acidifying principle of the acetous acid 
 the same as that of all other acids, oxygen ? 
 
 Mrs. B. Certainly : and on that account the contact of air is es- 
 sential to this fermentation, as it affords the necessary supply of ox- 
 ygen. Vinegar, in order to obtain pure acetous acid from it, must 
 be distilled and rectified by certain processes. 
 
 Emily. But pray, Mrs. B. is not the acetous acid frequently 
 formed without this fermentation taking place f Is it not, for in- 
 stance, contained in acid fruits, and in every substance that be- 
 comes sour? 
 
 Mrs. B. No, not in fruits; you confound it with the citric, he 
 malic, the oxalic, and other vegetable acids, to which living vege- 
 tables owe their acidity. But whenever a vegetable substance 
 turns sour, after it has ceased to live, the acetous acid is developed 
 by means of the acetous fermentation, in which the substance ad- 
 vances a step towards its final decomposition. 
 
 Amongst the various instances of acetous fermentation that of 
 bread is usually classed. 
 
 Can t'ne. But the fermentation of bread is produced by yeast ; 
 how does that effect it ? 
 
 Mrs. B. It is found by experience that any substance (hat has 
 alreac/y undergone a fermentation, will readily excite it in one that 
 is susceptible of that process. If, for instance, you mix a little vine- 
 gar with wine, that is intended to be acidified, it will absorb oxygen 
 more rapidly, and the process be completed much sooner, than if lefy 
 to ferment spontaneously. Thus yeast, which is a product 0$' th c 
 fermentation of beer, is used to excite and accelerate the fermenta . 
 
 1203. How may the process of the vinous fermentation be ex- 
 pressed in a few words ? 
 
 1204. Why is the third fermentation called acetous ? 
 
 1205. Why is the contact of air necessary to produce the acetous 
 fermentation ? 
 
 1206. What is the reason that wine, or cider, when corked tight 
 does not turn to vinegar ? tflfe&s 
 
 1207. How is the fermentation of bread produced by yeast ? 
 
268 DECOMPOSITION 
 
 tion of malt, which is to be converted into beer, as well as that of 
 paste, which is to be made into bread. 
 
 Caroline. But if bread undergoes the acetous fermentation, why 
 is it not sour? 
 
 J\frs. B. It acquires a certain savour which corrects the heavy 
 insipidity of flour, and may be reckoned a first degree of acidifica- 
 tion, or if the process were carried further, the bread would become 
 decidedly acid. 
 
 There are. however, some chemists who do not consider the fer- 
 mentation of bread as being of the acetous kind, but suppose, that it 
 is a process of fermentation peculiar to that substance. 
 
 The putrid fermentation is the final operation of Nature and her 
 last step towards reducing organized bodies to their simplest combi- 
 nations. All vegetables spontaneously undergo this fermentation 
 after death, provided there be a sufficient degree of heat and mois- 
 ture, together with access of air ; for it is well known that dead 
 plants may be preserved by drying, or by the total exclusion of air. 
 
 Caroline. But do dead plants undergo the other fermentations 
 previous to this last ; or do they immediately suffer the putrid fer- 
 mentation ? 
 
 Jllrs. B. That depends on a variety of circumstances, such as the 
 degrees of temperature and of moisture, the nature of the plant itself, 
 &c. But if you were carefully to follow and examine the decompo- 
 sition of plants from their death to their final dissolution, you would 
 generally find a sweetness developed in the seeds, and a spiritous fla- 
 vour in the fruits (which have rndergone the saccharine fermenta- 
 tion, )previous to the total disorganization and separation of the parts. 
 
 Emily. I have sometimes remarked a kind of spiritous taste in 
 fruits that were over-ripe, especially oranges, and this was just be- 
 fore they became rotten. 
 
 JMrs. B. It was then the vinous fermentation, which had succeed- 
 ed the saccharine and had you followed up these changes attentive- 
 ly, you would probably have found the spiritous taste followed by 
 acidity, previous to the fruit passing to the state of putrefaction. 
 
 When the leaves fall from the trees in the autumn, they do not (if 
 there is no great moisture in the atmosphere) immediately undergo 
 a decomposition, but are first dried and withered : as soon, howev- 
 er, as the rain sets in, fermentation commences, their gaseous pro- 
 ducts are imperceptibly evolved into the atmosphere, and their fixed 
 remains mixed with their kindred earth. 
 
 Wood, when exposed to moisture, also undergoes the putrid fer- 
 mentation, and becomes rotten. 
 
 Emily. But I have heard that the dry rot, which is so liable to de- 
 stroy the beams of houses, is prevented by a current of air ; and yet 
 you'said that the air was essential to the putrid fermentation ? 
 
 J\lrs. B. True ; but it must not be in such a proportion to the 
 moisture as to dissolve the latter, and this is generally the case when 
 
 1208. Why then is it not sour ? 
 
 1209- What is the final fermentation id reducing organized bodies 
 to their simplest combinations ? 
 
 1210. What is mentioned of oranges, and other over- ripe fruit, as 
 illustrating the above principles of fermentation ? 
 
 1211 . .W^hat is said of the fermentation of leaves ? 
 
 1212. How may the dry rot be prevented f 
 
OF VEGETABLES. 269 
 
 the rotting of wood is prevented or stopped by the free access of air. 
 What is commonly called dry rot, however, is not, I believe, a true 
 process of putrefaction. It is supposed to depend on a peculiar kind 
 of vegetation, which, by feeding- on the wood, gradually destroys it. 
 
 Straw and all other kinds of vegetable matter undergo the putrid 
 fermentation more rapidly when mixed with animal matter. Much 
 heat is evolved during this process, and a variety of volatile products 
 are disengaged, as carbonic acid and hydrogen gas, the latter of 
 which is frequently either sulphurated or phosphorated. When all 
 these gases have been evolved, the 6xed products, consisting of car- 
 bon, small quantities of salts, potash, &c. form a kind of vegetable 
 earlh, which makes very fine manure, as it is composed of those ele- 
 ments which form the immediate materials of plants. 
 
 Caroline. Pray are not vegetables sometimes preserved from de- 
 composition by petrifaction ? 1 have seen very curious specimens of 
 petrified vegetables, in which state they perfectly preserve their form 
 and organization, though in appearance they are changed to stone. 
 
 Mrs. B. That is a kind of metamorphosis, which, now that you 
 are tolerably well versed in the history of mineral and vegetable 
 substances, I leave to your judgment to explain. Do you imagine 
 that vegetables can be converted into stone ? 
 
 Emily. No, certainly ; but they might, perhaps, be changed to a 
 substance in appearance resembling stone. 
 
 Mrs. B. It is not so, however, with the substances that are called 
 petrified vegetables ; for these are really stone, and generally of the 
 hardest kind, often consisting chiefly of silex. The case is this : 
 when a vegetable is buried under water, or wet in earth, it is slowly 
 and gradually decomposed. As each successive particle of the veg- 
 etable is destroyed, its place is supplied by a particle of siliciouB 
 earth, conveyed thither by the water. In the course of time the 
 vegetable is entirely destroyed, but the silex has completely re- 
 placed it, having assumed its form and apparent texture, as if the 
 vegetable itself were changed to stone. 
 
 Caroline. That is very curious ! and I suppose that petrified ani- 
 mal substances are of the same nature? 
 
 Mrs. B. Precisely. It is equally impossible for either animal or 
 vegetable substances to be converted into stone. They may be re- 
 duced, as we find they are, by decomposition, to their constituent 
 elements, but cannot'be changed to elements which do not enter 
 into their composition. 
 
 * Petrefactions are of two kinds, viz. siliceous, when flinty parti- 
 cles take the place of the original substance, and calcareous, where 
 the substance appears to be changed to lime-stone. The first kind 
 gives fire with steel, and the other effervesces with acids. C. 
 
 J213. On what is the dry rot supposed to depend ? 
 
 1214. Why will animal fnaUer,;mixed with straw and other 
 etable substances, hasten fermentation ? 
 
 1215. What are vegetable petrifactions 1 ? 
 
 1216. How are vegetable petrifactions formed-? 
 
 1217. How many kinds of petrifactions are there 1 ? 
 
 1218. What are they called, and what are their properties,? 
 
 23* 
 
U70 DECOMPOSITION OF VEGETABLES. 
 
 There are, however, circumstances which frequently prevent the 
 regular and final decomposition of vegetables : as for instance, when 
 they are buried either in the sea. or in the earth, where they cannot 
 undergo the putrid fermentation for want of air. In these cases 
 they are subject to a peculiar change, by which they are converted 
 *nto a new class of compounds, called bitumens. 
 
 Caroline. These are substances 1 never heard of before. 
 
 Mrs. B. You will find, however, that some of them are very fa- 
 miliar to you. Bitumens are vegetables so far decomposed as to re- 
 tain no organic appearance ; but their origin is easily detected by 
 their oily nature, their combustibility, the products of their analy- 
 sis, and the impression of the forms of leaves, grains, fibres of wood, 
 and even of animals, which they frequently bear. 
 
 They are sometimes of an oily, liquid consistence, as the sub- 
 stance called nnptha,* in which we preserved potassium ; it is a fine 
 transparent, colourless fluid, that issues out of clays in some parts of 
 Persia. But more frequently bitumens are solid, as asphaltum a 
 smooth, hard, brittle substance, which easily melts, and forms, in its 
 liquid state, a beautiful dark brown -color for oil painting. Jet, 
 which is of a still harder texture, is a peculiar bitumen, susceptible 
 of so fine a polish, that it is used for many ornamental purposes. 
 
 Coal is also a bituminous substance, to the composition of which 
 both the mineral and animal .kingdoms seem to concur. This most 
 useful mineral appears to consist chiefly of vegetable matter, mixed 
 with the remains of marine animals and marine salts, and occasion- 
 ally containing a quantity of sulphuret of iron, commonly called 
 pyrites. 
 
 Emily. It is, I suppose, the earthy, the metallic, and the saline 
 parts of coals, that compose the cinders or fixed products of their 
 combustion : whilst the hydrogen and carbon, which they derive 
 from vegetables, constitute their volatile products. 
 
 Caroline. Pray is not co/ce, (which I have heard is much used in 
 some manufactures,) also a bituminous substance ? 
 
 Mrs. B. No ; it is a kind of fuel artificially prepared from coals. 
 It consists of coals reduced to a substance analagous to charcoal by 
 the evaporation of their bituminous parts. Coke, therefore, is com- 
 posed of carDon, with some earthy and saline ingredients. 
 
 Succin, or yellow amber, is a bitumen which the ancients called 
 dectrum, from whence the word electricity is derived, as that sub- 
 stance is peculiarly, and was once supposed to be exclusively, elec^ 
 trie. It is found either deeply buried in the bowels of the earth, or 
 
 * Naptha appears to be the only fluid in which oxygen does not 
 exist ; hence its property of preserving potassium which has so strong 
 an affinity for oxygen as to absorb it from all other fluids. It how- 
 ever loses this property by exposure to the atmosphere, probably, 
 because it absorbs a small quantity of air, or moisture. It is again 
 restored by distillation.- C. 
 
 1219. What are bitumens, and how are they formed ? 
 
 1220. What is asphaltum ? 
 
 1221. What is jet? 
 
 1222. What is coal ? 
 
 1223. Flow does coke differ from coal ? 
 What is yellow amber ? 
 
VEGETATION. 271 
 
 floating on the sea, and is supposed to be a resinous body which has 
 been acted on by sulphuric acid, as its analysis shows it to consist 
 of an oil and an acid. The oil is called oil of amber : the acid the 
 succinnic. 
 
 Emily. That oil I have sometimes used in painting-, as it is reck- 
 oned to change less than the other kinds of oil. 
 
 Mrs. B. The last class of vegetable substances that have chang- 
 ed their nature are fossil-wood, peat, and turf. These are com- 
 posed of wood and roots of shrubs, that are partly decomposed by 
 being- exposed to the moisture under ground, and yet in some meas- 
 ure, preserve their form and organic appearance. The peat, or 
 black earth of the moors, retains but few vestiges of the roots to 
 which it owes its richness and combustibility, these substances be- 
 ing in the course of time, reduced to the state of vegetable earth. 
 But in turf the roots of plants are still discernible, and it equally an- 
 swers the purpose of fuel. It is the combustible used by the poor in 
 heathy countries, which supply it abundantly. 
 
 It is too late this morning to enter upon the history of vegetation. 
 We shall reserve this subject, therefore, to our next interview, 
 when I expect that it will furnish us with ample matter for another 
 conversation. 
 
 CONVERSATION XXII. 
 
 HISTORY OF VEGETATION. 
 
 Mrs. B. The vegetable kingdom may be considered as the link 
 which unites the mineral and animal creation into one common 
 chain of beings ; for it is through t^e means of vegetation alone that 
 mineral substances are introduced into the animal system ; since, 
 generally speaking, it is from vegetables that all animals ultimately 
 derive their sustenance 
 
 Caroline. I do not understand that ; the human species subsist as 
 much on animal as on vegetable food. 
 
 .Mrs. B. That is true ; but you do not consider that those that live 
 on animal food, derive their sustenance equally, though not so im- 
 mediately, from vegetables. The meat which we eat is formed 
 from the herbs of the field, and the prey of carniverous animals pro- 
 ceeds either directly or indirectly from the same source. It is, 
 therefore, through this channel, that the simple elements become a 
 part of the animal frame. We should in vain attempt to derive 
 nourishment from carbon, hydrogen, and oxygen, either in their 
 separate state or combined in the mineral kingdom ; for it is only by 
 
 1225. Where is it found ? 
 
 1226. What are fossil-wood, peat and turf? 
 
 1227. Why does naptha preserve potassium ? 
 
 1228. What is considered as uniting the mineral and animal cre- 
 ation ? 
 
 1229. From whence do all animals derive their sustenance ? 
 
 1230. In what state are carbon, hydrogen, and oxygen capable 
 x)f affording nourishment ? 
 
272 VEGETATION, 
 
 being united in the form of vegetable combination that they become 
 capable of conveying nourishment. 
 
 Em^ly. Vegetation, then, seems to be the method which Nature 
 employs to prepare the food of animals ? 
 
 Mrs. B. That is certainly its principal object. The vegetable 
 creation does not exhibit more wisdom in that admirable system of 
 organization, by which it is enabled to answer its own immediate 
 ends of preservation, nutrition and propagation, than in its grand 
 and ultimate object of forming those arrangements and combina- 
 tions of principles, which are so well adapted for the nourishment of 
 animals. 
 
 Emily. But T am very curious to know whence vegetables obtain 
 tho-e principles which form their immediate materials: 
 
 J\Irs. B. This is a point on which we are yet so much in the dark 
 that I cannot hope fully to satisfy your curiosity ; but what little I 
 know on this subject, 1 shall endeavor to explain to you. 
 
 The soil which at first view, appears lobe the element of vegeta- 
 bles, is found on a closer investigation, to be little more than the 
 channel through which they receive their nourishment ; so that it 
 is very possible to rear plants without any earth or soil.* 
 
 * The opinion that water is the only food of plants, was adopted 
 by the learned on this subject in the 17th century ; and many ex- 
 periments were made which seemed to prove that this was the 
 truth. Among others was a famous one by Van Helmout, which 
 fora long time was supposed to have established the point beyond 
 all doubt. He planted a willow which weighed five pounds, in an 
 earthen vessel containing 200 Ibs. of dried earth. This vessel was 
 sunk into the ground, and the tree was wateped, sometimes with 
 distilled, and sometimes with rain water. 
 
 At the end of five years the willow weighed 169 Ibs. ; and on 
 weighing the soil, dried as before, it was found to have lost only two 
 ounces. Thus'the* willow had gained 164 Ibs., and yet its food had 
 been only water. The induction from this experiment was obvious. 
 'Plants live on pure water. This, therefore, was the general opinion 
 until the progress of chemistry detected its fallacy. Bergman, in 
 1763, showed by some experiments, that the water which Van 
 Helmout had used, contained as much earth as could exist in the 
 tree at the end of the five years ; a pound of watercontained about 
 a grain of earth. So that 'this experiment by no means proved 
 that the willow lived orv water alone. Since this time a great 
 variety of experiments have been made for the purpose of deciding 
 what was the food of plants. In the course of these it has been 
 found, that although seeds do vegetate in pure distilled water, yet 
 the plant is weakly and finally dies before the fruit is matured. 
 
 It is pretty certain, then, that earth is absolutely necessary to the 
 growth of plants, and that a part of their foo4 is taken from the soil. 
 Indeed, the well known fact, that a soil is worn out by a long succes- 
 
 1231. Do vegetables receive their chief aliment from the soil in 
 which they grow ? 
 
 1232. What experiment was made by Helmout to ascertain the nour- 
 ithment of vegetables? 
 
 1233. What will be the condition of plants in-pure water only ? 
 
VEGETATION. 273 
 
 Caroline. Of that we have an instance in the hyacinth and other 
 bulbous roots, which will grow an'd blossom beautifully in glasses of 
 water. But I confess I should think it would be difficult to rear 
 trees in a similar manner. 
 
 Mrs. B No doubt it would, as it is the burying- of the roots in 
 the earth that supports the stern of the tree. But this office, besides 
 that of affording 1 a vehicle for food, is far the most important part 
 which the earthy portion of the soil performs in the process of ve- 
 getation ; for we can discover, by analysis, but an extremely small 
 proportion of earth in vegetable compounds. 
 
 Caroline. But if earths do not afford nourishment, why is it ne- 
 cessary to be so attentive to the preparation of the soil ? 
 
 Mrs. B. In order to impart to it those qualities which render it 
 a proper vehicle for the food of the plant. Water is the chief nour- 
 ishment of vegetables ; if, therefore the soil be too sandy, it will not 
 retain a quantity of water sufficient to supply the roots of the plants. 
 If, on the contrary, it abounds too much with clay, the water will 
 lodge in such quantities as to threaten a decomposition of the roots. 
 Calcareous soils are, upon the whole, the most favourable to the 
 growth of plants : soils are, therefore, usually improved by chalk, 
 which you may recollect, is carbonat of lime. Different vegetables 
 however, require different kinds of soils. Thus, rice demands a 
 most retentive soil ; potatoes, a soft sandy soil ; wheat, a firm and 
 rich soil. Forest trees grow better in fine sand, than in a stiff clay ; 
 and a light ferruginous soil is best suited to fruit trees. 
 
 Caroline. But pray what is the use of manuring the soil ? 
 
 Jlfrs. B. Manure consists of all kinds of substances whether of 
 vegetable or animal origin, which have undergone the putrid fer- 
 
 sion of crops, and finally becomes steril unless manured, is good 
 proof that plants do absorb something from it. 
 
 Saussure has shown that this is the fact, and also that the earth, 
 which is always found in plants, ^Is of the same kind, as that on 
 which they grow. Thus trees growing in a granitic soil, contain a 
 large proportion of silica, while those growing in calcareous soil, 
 contain little silica, but a great proportion of calcareous earth. 
 
 In addition to what plants absorb from the ground, there is no 
 doubt but they obtain a part of their nourishment from water and 
 air. Some experiments made at Berlin, show that wheat, barley, &c. 
 contain a quantity of earth though fed only on distilled water. 
 
 From the. air, plants absorb carbonic acid gas. The carbon they 
 retain, which forms the greatest part of their bulk. The oxygen is 
 emitted, and goes to purify the atmosphere. 
 
 Thus it is seen that plants obtain their food from the earth, from 
 water, and from the air. C. 
 
 1234. What facts did Saussure discover relating to this subject ? 
 1235 Whence do plants derive their food ? 
 
 1236. If earths do not afford nourishment, why is it necessary to 
 be so particular in enriching the soil ? 
 
 1237. What is the nourishment of vegetables ? 
 
 1238. What is the consequence to vegetables if the soil is too 
 .ndy ? 
 
 1239. What if it abounds too much with clay } 
 
274 VEGETATION. 
 
 mentation, and are consequently decomposed, or nearly so, into 
 their elementary principles. And it is requisite that these vegeta- 
 ble matters should be in a state of decay, or approaching- decompo- 
 sition. The addition of calcareous earth, in the state of chalk or 
 lime, is beneficial to such soils, as it accelerates the dissolution of 
 vegetable bodies. Now 1 ask you, what is the utility of supplying 
 the soil wiih these decomposed substances ? 
 
 Caroline. It is, I suppose, in order to furnish vegetables with the 
 principles which enter into their composition. For manures not 
 only contain carbon, hydrogen and oxygen, but by their decompo- 
 sition supply the soil with these principles in their elementary form-.* 
 
 *Mrs. B. Undoubtedly ; and it is for this reason that the finest 
 crops are produced in fields '.hat were formerly covered with woods, 
 because their soil is composed of a rich mould, a kind of vegetable 
 earth which abounds in those principles. 
 
 Emily. This accounts for the plentifulness of the crops produced 
 in America, where the country was, but a few years since, covered 
 wi'h wood- 
 
 Caroline. But how is it that animal substances are reckoned to 
 produce the best manure? Does it not appear much more natural 
 that the decomposed elements of vegetables should be the most ap- 
 propriate to the formation of new vegetables ? 
 
 Mrs. B. The addition of a much greater proportion of nitrogen, 
 which constitutes the chief difference between animal and vegeta- 
 ble matter, renders the composition of the former more complicated 
 and consequently more favourable to decomposition. 
 
 Indeed the use of animal substances is chiefly to give the first im- 
 pulse to the fermentation of the vegetable ingredients that enter in- 
 to the composition of. manures. The manure of a farm yard is of 
 that description ; but there is scarcely any substance susceptible of 
 undergoing the putrid fermentation, that will make good manure. 
 The heat produced b/ the fermentation of manure is another cir- 
 cumstance which is extremely favourable to vegetation; yet this 
 heat would be too great if the manure was laid on the ground dur- 
 ing the height of fermentation ; it is used in this state only for hot- 
 beds to produce melons, cucumbers, and such vegetables as require 
 a very high temperature. 
 
 Caroline. A difficulty has just occurred to me which I do not 
 know how to remove. Since all organized bodies are, in the com- 
 mon course of nature, ultimately reduced to their elementary state, 
 they must necessarily in that state enrich the soil, and afford food 
 for vegetation. How is it, then, that agriculture, which cannot in- 
 crease the quantity of those elements that are required to manure 
 the earth, can increase its produce so wonderfullj r , as is found to be 
 the case in all cultivated countries ? 
 
 * But what is the use of all this, if " water is the chief nourish- 
 ment of vegetables ?" C. 
 
 . What is the use of decomposed substances as is found in 
 manure? 
 
 1241. Why are the best crops produced on new lands, or where 
 they were recently covered with wood ? 
 
 . Why de animal substances make the best manure? 
 
VEGETATION. 275 
 
 > 
 
 Jfrs.B. It is by suffering- none of these decaying- bodies to be 
 dispersed an<) wasted, but in applying- them duly to the soil. It is 
 also by a judicious preparation of the soil, which consists in fitting- 
 it either for the general purposes of vegetation, or for that of the 
 particular seed which is to be sown. Thus, if thesoil t be too wet, it 
 may be drained ; if too loose and sandy it may be rendered more 
 consistent and retentive of water by the addition of clay or loam ; 
 it may be enriched by chalk, or any kind of calcareous earth. OQ 
 soils thus improved, manures will act wilh double efficacy ; and if 
 attention be paid to spread them on the ground at a proper season 
 of the year, to mix them with the soil, so that they may be general- 
 ly diffused through it, to destroy the weeds which might appropri- 
 ate these nutritive principles to their own use, to remove the stones 
 which would impede the growth of the plant, &c., we may obtain a 
 produce an hundred fold more abundant than the earth would spon- 
 taneously supply. 
 
 Emily. We have a very striking instance of this in the scanty 
 produce of uncultivated commons, compared to the rich crops of 
 meadows which are occasionally manured. 
 
 Caroline. But, Mrs. B., though experience daily proves the ad- 
 vantag-es of cultivatign, there is still a difficulty which I cannot get 
 over. A certain quantity of elementary principles exist in nature, 
 which it is not in the power of man either to augment or diminish. 
 Of these principles you have taught us that both the animal and 
 vegetable creation are composed. Now the more of them is taken 
 up by the vegetable kingdom, the less, it would seem will remain 
 for animals ; and therefore, the more populous the earth becomes, 
 the less it will produce. 
 
 J\Irs. B. Your reasoning is very plausible ; but experience ev- 
 ery where contradicts the inference you would draw from it ; since 
 we find that the animal and vegetable kingdoms, instead of thriving 
 as you would suppose, at each other's expense, always increase 
 and multiply together. For you should recollect that animals can 
 derivethe elements of which they arc formed only through the me- 
 dium of vegetables. And you must allow that your conclusion 
 would be valid only if every particle of the several principles that 
 could possibly be spared from other purposes, were employed in 
 the animal and vegetable creations. Now we have reason to be- 
 lieve that a much greater proportion of these principles than is re- 
 quired for such purposes, remains either in an elementary state, or 
 engaged in a less useful mode of combination in the mineral king- 
 dom. Possessed of such immense resources as the atmosphere and 
 the waters afford us, for oxygen, hydrogen and carbon, so far from 
 being in danger of working up all our simple materials, we cannot 
 suppose that we shall ever bring agriculture to such a degree of per- 
 fection as to require the whole of what these resources could supply. 
 Nature, however, in thus furnishing us with an inexhaustible stock 
 
 1243. How is it that agriculture, which cannot increase the 
 quantity of those elements that are required to manure the earth, so 
 greatly increases its vegetable products ? 
 
 1244. Of what are the vegetable and animal creation composed ? 
 
 1245. What objection is made to the principle stated for the in- 
 crease of vegetable productions ? 
 
 1246. How is this objection answered? 
 
276 VEGETATION. 
 
 of raw materials, leaves it in some measure to the ingenuity of man 
 to appropriate them to his own purposes. But, like a kind parent 
 she stimulates him to exertion, by setting- the example, and point- 
 ing out the way. For it is on the operations of nature that all the 
 improvements of art are founded. The art of agriculture consists, 
 therefore, in discovering the readiest method of obtaining the seve- 
 ral principles, either from their grand sources, air and water, or 
 from the decomposition of organized bodies ; and in appropriating 
 them in the best manner to the purposes of vegetation. 
 
 Emily, But, among the sources of nutritive principles, I am sur- 
 prised that you do not mention the earth itself, as it contains abun- 
 dance of coals, which are chiefly composed of carbon. 
 
 J\Irs B. Though coals abound in carbon, they cannot on ac- 
 count of their hardness and impermeable texture, be immediately 
 subservient to the purposes of vegetation ; and, we find, on the con- 
 trary, that coal districts are generally barren. 
 
 Emily. No ; but by their combustion, carbonic acid is produced ; 
 and this entering into various combinations on the surface of the 
 earth, may, perhaps, assist in promoting vegetation. 
 
 Mrs. B. Probably it may in some degree ; but at any rate, the 
 quantity of nourishment which vegetables may derive from that 
 source can be but very trifling, and must entirely depend on local 
 circumstances. 
 
 Caroline. Perhaps the smoky atmosphere of London is the cause 
 of vegetation being so forward and so rich in its vicinity ? 
 
 Mrs. B. I rather believe that thiscircumstance proceeds from the 
 very ample supply of manure, assisted, perhaps, by the warmth and 
 shelter, which the town affords. Far from attributing any good to the 
 smoky atmosphere of London, I confess 1 like to anticipate the time 
 when we shall have made such progress in the art of managing corn- 
 bastion that every particle of carbon will be consumed, and the 
 smoke destroyed at the moment of its production. We may then 
 expect to have the satisfaction of seeing the atmosphere of London 
 as qlear as that of the country. But to return to our subject: I hope 
 that you are now convinced that we shall not easily experience a 
 deficiency of nutritive elements to fertilize the earth, and that pro- 
 vided we are but industrious in applying them to the best advantage 
 by improving the art of agriculture, no limits can be assigned to 
 the fruits that we may expect to reap from our labours. 
 
 Caroline. Yes : I am perfectly satisfied in that respect, and I can 
 assure you that 1 feel already much more interested in the progress 
 and improvement of agriculture. 
 
 Emily. I have frequently thought that the culture of the laod was 
 not considered as a concern of sufficient importance. Manufactures 
 always take the lead; and health and innocence are frequently sa- 
 crificed to the prospect of a more profitable employment. It has 
 "often grieved me to see the poor manufacturers crowded together 
 
 s 1247. In what does the art of agriculture consist ? 
 
 1248. Why cannot coals be immediately subservient to the pur- 
 poses of vegetation ? 
 
 * 1249. Is there any occasion to apprehend a deficiency of nutritive 
 Clements to fertilize the earth ? 
 
 (250. What objection is made to manufactures ? 
 
VEGETATION. 
 
 277 
 
 in close roams, and confined for the whole day to the most uniform 
 and sedentary employment, instead of being 1 engaged in that inno- 
 cent and salutary .kind of labour, which Nature seems to have as- 
 signed to man for the. immediate acquirement of comfort, and for 
 the preservation of .his existence. .1 am sure .that you agree with 
 me in thinking so, Mrs B. 
 
 J\lrs B. I am entirely of your opinion, my dear, in regard to the 
 importance of agriculture ; but as the conveniences of life, which 
 we are all enjoying, are not derived merely from the soil, I am far 
 from wishing to depreciate manufactures. Besides, as the labour of 
 one mar. is sufficient to produce food for several, those whose in- 
 dustry is not required in tillage must do something in return for the 
 food that is provided, for them. They exchange, consequently, the 
 accommodations for the necessaries of life. Thus the carpenter and 
 the weaver lodge and clothe the peasant, who supplies them with 
 their daily bread. The greater stock of provisions, therefore, which 
 the husbandman produces, the greater is the quantity of accommo- 
 dation which the artificer prepares. Such are the happy effects 
 which naturally result from civilized society. It would be wiser, 
 therefore, to endeavor to improve the situation of those who are 
 engaged in manufactures, than to indulge m vain declamations on 
 the hardships to which they are too frequently exposed. 
 
 But we must not yet take our leave of the subject of agriculture ; 
 we have prepared the soil, it remains for us now to sow the seed. , 
 In this operation, we must be careful not to bury it too deep in the 
 ground, as the access of air is absolutely necessary to its germina- 
 tion ; the earth must, therefore, lie loose and light over it, in order 
 that the air may penetrate. Hence the use of ploughing and dig- 
 ging, harrowing and raking, &c. A certain degree of heat and 
 moisture, such as usually takes place in the spring, is likewise ne- 
 cessary. 
 
 Caroline. One would imagine you were going to describe the 
 decomposition of an old plant, rather than the formation of a new- 
 one ; for you have enumerated all the requisites of fermentation. 
 
 Mrs. B. Do you forget, my dear, that the young plant derives it<* 
 existence from the, destruction of the seed, and that it is actually by 
 the .saccharine fermentation that the latter is decomposed ? 
 
 Caroline. True; I wonder that I did not recollect that. The tem- 
 perature and moisture required for the germination of the seed is 
 then employed in pro.ducing the saccharine fermentation within it? 
 
 Mrs. 7?. Certainly. But, in order to understand the nature of 
 germination, you should be acquainted with tne different parts of 
 which the seed is composed. The external covering or envelope 
 contains, besides the germ of the future plant, the substance which 
 is to constitute its first nourishment : this substance> which is called 
 the parenchyma, consists of fecula, mucilage, and oil, as we former- 
 ly observed. 
 
 1251. For how many persons can one man, in agricultural, la- 
 bour, produce food ? 
 . 1252. Why is this a reason for encouraging manufacture,? ? 
 
 1253. What is the use of ploughing, digging, harrowing, raking. 
 ,<&.,, in agriculture ? , 
 
 24 
 
278 VEGETATION. 
 
 The seed is generally divided into two compartments, called lobat, 
 or cotyledons, as is exemplified by this bean, (Fig. 36,) the dark 
 (Fig. 36 ) coloured kind of string which divides the lobes is 
 called the radicle, as it forms the root of the plant, 
 and it is from a contiguous substance, called plu- 
 mula, which is enclosed within the lobes, that the 
 stem arises. The figure and size of the seed depend 
 very much upon the cotyledons ; these vary in num- 
 ber in different seeds; some have only one, as 
 wheat, oats, barley, and all the grasses ; some have 
 three, others six. But most seeds, as fof instance, all the varieties 
 of beans, have two cotyledons. When the seed is buried in the 
 earth, at any temperature above 40 degrees, it imbibes water, which 
 softens and swells the lobes ; it then absorbs oxygen, which com- 
 bines with some of its carbon, and is returned in the form of car- 
 bonic acid. This loss of carbon increases the comparative propor- 
 tion of hydrogen and oxygen in seed, and excites the saccharine 
 fermentation by which the parenchymatous matter is converted into 
 a kind of sweet emulsion. In this form it is carried into the radicle 
 by vessels appropriated to that purpose ; and in the meantime, the 
 fermentation having caused the seed to burst, the cotyledons are 
 rent asunder, the radicle strikes into the ground and becomes the 
 root of the plant, and hence the fermented liquid is conveyed to the 
 plumula, whose vessels have been previously distended by the heat 
 of the fermentation. The plumula being thus swelled, as it were, 
 by the emulsive fluid, raises itself and springs up to the surface of 
 the earth, bearing with it the cotyledons, which, as soon as they 
 come in contact with the air, spread'themselves, and are transform- 
 ed into leaves. If we go into the garden, we shall probably find 
 some seeds in the state in which I have described. 
 
 Emily* Here are some little lupines that are just making their 
 appearance above ground. 
 
 Mrs. t>. We shall take up several of them to observe their diffe- 
 rent degrees of progress in vegetation. Here is one that has but 
 recently burst its envelope do you see the little radicle striking 
 downwards? (Fig. 37. No. 1.) In this the plumula is not yet visi- 
 ble. But here is another in a greater state of forwardness the 
 plumula, or stem, has risen out of the ground, and the cotyledons 
 are converted into seed-leaves. (Fig. 37, No. 2.) 
 
 Caroline. These leaves are very thick and clumsy, and, unlike 
 'the other leaves, which 1 perceive are just beginning to appear. 
 
 Mrs. B. It is because they retain the remains of the parenchyma, 
 with which they still continue to nourish the young plant, as it has 
 not yet sufficient roots and strength to provide for its sustenance 
 from the soil. But, in this third lupine. (Fig. 37, No .3,) the radicle 
 had sunk deep into the earth, and sent out several shoots, each of 
 
 1254. What part of the seed is called cotyledons ? 
 
 1255. What part is called radicle? 
 
 1256. What part is called plumula ? 
 
 1357. At what temperature will seeds germinate ? 
 1258. How would you describe the process of germination in 
 ' seeds ? 
 
 J259. What do Nos. I and 2 of Fig. 37, represent ? 
 260. What daes No. 3, in -Fig. 37, represent ? 
 
VEGETATION. 
 
 279 
 
 which is furnished with a mouth 
 to suck up nourishment from 
 the soil ; (he function of the 
 original leaves, therefore, be- 
 ing- no longer required, they 
 are gradually decaying, and 
 the plumula is become a regu- 
 lar stem, shooting out small 
 branches, and spreading its 
 , foliage. 
 
 Emily. There seems to be a 
 very striking analogy between 
 a seed and an egg ; both require 
 an elevation of temperature to 
 be brought to life ; both at first 
 supply with aliment the organ- 
 ized being which they produce ; 
 and as this has attained suffi- 
 cient strength to procure its 
 own nourishment, the egg-shell 
 breaks whilst in the plant the 
 seed leaves fall off 
 
 Mrs. B. There is certainly 
 resemblance between 
 these processes; and when you 
 Fi ? . se and 37, NO. i. A B, Cotyied. c, En- become acquainted with ani- 
 
 velope. D, Radicle. Vig. 37, No. 2, A B, Cotyle- j -hprrmtrv VOI1 will fro 
 4ons. C, Plumula. D, Radicle. Fig. 37, No. 3, mal SII T' J U Wli 
 
 A B, Cotyledon. c.PLmuia. o, Radicle, quently be struck with its 
 
 analogy to that of the vegeta- 
 ble kingdom. 
 
 As soon as the young plant feeds from the soil, it requires the as- 
 sistance of leaves, which are the organs by which it throws off its 
 super-abundant fluid ; this secretion is much more plentiful in the 
 vegetable than in the animal creation, and the great extent of sur- 
 face of the foliage of plants is admirably calculated for carrying it 
 on in sufficient quantities. This transpired fluid consists of little 
 more than water. The sap, by this process, is converted into a 
 liquid of greater consistence, which is fit to be assimilated to its 
 several parts. 
 
 Emily. Vegetation, then, must be essentially injured by destroy- 
 ing the leaves of the plant. 
 
 Mrs. B. Undoubtedly ; it not only diminishes the transpiration, 
 but also the absorption by the roots ; for the quantity of sap ab- 
 sorbed is always in proportion to the quantity of fluid thrown off by 
 transpiration. You see, therefore, the necessity that a young plant 
 should unfold its leaves as soon as it begins to derive its nourish- 
 ment from the soil ; and, accordingly, yon will find that those 
 lupines which have dropped their seed-leaves, and are no longer 
 
 1261. What purposes do the leaves of vegetables answer during 
 their growth ? 
 
 1262. What will be the injury to vegetation if the leaves are de- 
 stroyed ? 
 
280 VEGETATION. 
 
 fed by the parenchyma, have spread their foliage, in order to per- 
 form the office just described. 
 
 But 1 should inform you that this function of transpiration seems 
 to be confined to the upper surface of the leaves, whilst on the con- 
 trary, the lower surface, which is more rough and uneven, and fur- 
 nished with a kind of hair or down, is destined to absorb moisture, 
 or such other ingredients as the plant derives from the atmosphere. 
 
 As soon as a young plant makes its appearance above ground, 
 light, as well as air, becomes necessary to its preservation. Light 
 is essential to the developement of the colours, and to the thriving 
 of the plant. You may have often observed what a predilection 
 vegetables had for the light. If you make any plants grow in a 
 room, they all spread their leaves and" extend their branches to- 
 wards the windows. 
 
 Caroline. And many plants close up their flowers as soon as it is 
 dark. 
 
 Emily. But may not this be owing to the cold and dampness of 
 the evening air? 
 
 Mrs. B. That does not appear to be the case ; for in a course of 
 curious experiments, made by Mr. Senebier, of Geneva, on plants 
 which he reared by lamp-light, he found that the flowers closed 
 their petals whenever the lamps were extinguished. 
 
 Emily. But, pray, why is air essential to vegetation ? Plants do 
 not breathe it like animals. 
 
 J\lrs. B. At least not in the same manner ; but they certainly 
 derive some principles from the atmosphere, and yield others to it. 
 Indeed, it is chiefly owing to the action of the atmosphere, and the 
 vegetable kingdom on each other, (hat the air continues always fit 
 for respiration. But you will understand this better when I have 
 explained the effect of water on plants. 
 
 I have said that water forms the chief nourishment of plants $ it 
 is the basis not only of the sap, but of all the vegetable juices. Wa- 
 ter is the vehicle which carries into the plant the various salts and 
 other ingredients required for the formation and support of the vege- 
 table system. Nor is this all : part of the water itself is decomposed 
 by the organs of the plant ; the hydrogen becomes a constituent part 
 of oil, of extract, of colouring matter, &c., whilst a portion of the 
 oxygen enters into the formation of mucilage, of fecula, of sugar, 
 and of vegetable acids. But the greater part of the oxygen pro- 
 ceeding from the decomposition of the water is converted into a gase- 
 ous state by the caloric disengaged from the hydrogen during its 
 condensation in the formation of the vegetable materials. In this 
 state the oxygen is transpired by the leaves of plants when exposed 
 to the sun's rays. Thus yon find that the decomposition of water, 
 by the organs of the plant, is not only a means of Supplying it with 
 its chief ingredient, hydrogen, but at the same time of replenishing 
 the atmosphere with oxygen, a principle which requires continual 
 renovation, to make up for the great consumption of it occasioned 
 
 1263. How does the under side of leaves differ from the upper 
 fc'de ? 
 
 H64. Of what use is light in the growth of vegetables ? 
 
 1265. Of what use is air in vegetation ? 
 
 1266. How are the various salts and other ingredients required for 
 the formation and support of the vegetable system carried into 
 plants ? 
 
VEGETATION. 281 
 
 by the numerous oxygenations, combustions, and respirations, that 
 are constantly taking place on the surface of the globe.* 
 
 Emily. What a striking instance of the harmony of nature I 
 
 Mrs. B. And how admirable the design of Providence, who 
 makes every different part of the creation thus contribute to the 
 support and renovation of each other ! 
 
 But the intercourse of the vegetable and animal kingdoms, 
 through the medium of the atmosphere extends still further. Ani- 
 mals, in breathing, not only consume the oxygen of the air, but load 
 it with carbonic acid, which, if accumulated in the atmosphere, 
 would, in a short time, render it totally unfit for respiration. Here 
 the vegetable kingdom again interferes ; it attracts and decomposes 
 the carbonic acid, retains the carbon for its own purposes, and re- 
 turns the oxygen for ours.f 
 
 Caroline. How interesting this is ! I do not know a more beauti- 
 ful illustration of the wisdom which is displayed in the laws of na^ 
 ture. 
 
 Jllrs. B. Faint and imperfect as are the ideas which our limited 
 perceptions enable us to form of divine wisdom, still they cannot 
 fail to inspire us with awe and admiration. What then, would be 
 our feelings, were the complete system of nature at once displayed 
 before us ! So magnificent a scene would probably be too great for 
 our limited comprehension ; and it is, no doubt, among the wisedis- 
 
 * The foregoing paragraph might mislead the student. Indeed it 
 seems to have been written without regard to proper authorities. 
 For instance, there is no proof that water is decomposed by the or- 
 gans of plants ; nor is it in the least degree probable that the oxy- 
 gen emitted by them owes its gaseous state, to the caloric set free 
 by the condensation of hydrogen. Authors on this subject agree 
 that the thickest veil covers the processes by which the sap is coo- 
 verted into the several parts of the plant. But it has been de- 
 monstrated, that most, if not all the oxygen emitted by the leaves, is 
 obtained by the decomposition of air, instead of water, as here stated.. 
 If leaves are exposed to the rays of the sun, while under common 
 water, they emit oxygen. But if the water is first deprived of its 
 air, by an air pump, or by boiling, not a particle of oxygen is emit- 
 ted. Now atmospheric air, always contains a quantity of carbonic 
 acid gas, and experiments show, that plants give out oxygen in 
 some proportion to the quantity of this gas contained in the water. 
 The fact then seems to be, that plants absorb carbonic acid, that 
 this is decomposed by some unknown process ; the plant retaining- 
 the carbon, while the oxygen is given out. C. 
 
 f It is a curious fact, demonstrated by experiments, that the 
 leaves of plants perform different offices at different periods of the 
 24 hours. During the day they give out water, absorb carbonic 
 acid, and emit oxygen gas ; but during the night they absorb wa- 
 ter, and oxygen gas, and give out carbonic acid. C. 
 
 1267. How do animal and vegetable life mutually support each 
 other ? 
 
 1268. What curious fact is staled of the leaves of vegetables in the 
 note? 
 
 1269. What in the organization of nature is particularly suited to 
 -Atonal powers of man ? 
 
 24* 
 
282 
 
 VEGETATION. 
 
 pensations of Providence, to veil the splendor of a glory with which 
 we should be overpowered. But it is well suited to a rational being 
 to explore, step by step, the works of the creation, to endeavor to 
 counect them into harmonious systems ; and, in a word, to trace, in 
 the chain of beings, the kindred ties and benevolent design which 
 unites its various links, and secures its preservation. 
 
 Caroline- But of what nature are the organs of plan Is which are 
 endued with such wonderful powers? 
 
 Mrs. B. They are so minute that their structure, as well as the 
 mode in which they perform their functions, generally elude our ex- 
 amination ; but we may consider them as so many vessels or appa- 
 ratus appropriated to perform, with the assistance of the principle 
 of life, certain chemical processes, by means of which these vegeta- 
 ble compounds are generated. We may, however, trace the tannin, 
 resins, gums, mucilage, and some other vegetable materials, in the 
 organized arrangement of plants, in which they form the bark, the 
 wood, the leaves, flowers, and seeds. 
 
 The bark is composed of the epidermis, the parenchyma^ and the 
 cortical layers. 
 
 The epidermis is the external covering of the plant. It is a thid 
 transparent membrane, consisting of a number of slender fibres, 
 crossing each other, and forming a kind of net work. When of a 
 white glossy nature, as in several species of trees, in the steins of 
 corn and" of seeds, it is corn posed of a thin coating of siliceous earth, 
 which accounts for the strength and hardness of those long and slen- 
 der stems. Sir H. Davy was led to the discovery of the siliceous 
 nature of the epidermis of such plants, by observing the singular 
 phenomenon of sparks of fire emitted by the collision of ratan canes 
 with which two boys were fighting in a dark room. On analysing the 
 epidermis of the cane, he found it to be almost entirely siliceous.* 
 
 Caroline. With iron, then, a cane I suppose, will strike fire very 
 easily ? 
 
 J\lrs. B. I understand that it will. In evergreens the epidermis 
 is mostly resinous, and in some few plants is formed of wax. The 
 resin, from its want of affinit}' for water, tends to preserre the plant 
 from the destructive effects of violent rains, severe climates, or in- 
 clement seasons, to which this species of vegetables is peculiarly 
 exposed. 
 
 Emily. Resin must preserve wood just like a varnish, as it is the 
 essential ingredient of varnishes. 
 
 Mrs. B. Yes; and by this means it prevents, likewise, all unne- 
 cessary expenditure of moisture. 
 
 The parenchyma is immediately beneath the epidermis; it is that 
 
 * In the scouring rush, (Equisetum hyemale) the siliceous epider- 
 mis is still more obvious. If drawn across a piece of soft metal, as 
 silver or copper, it cuts it like a file. It even makes an impression 
 on the hardest steel. C. 
 
 1270. Of what is bark composed? 
 
 1271. What is the epidermis ? 
 
 1272. In what manner was Sir H. Davy led to discover the sili- 
 ceous nature of the epidermis of particular plants ? 
 
 1273. How does resin tend to preserve the plant ? 
 3274. What is the parenchyma ? 
 
VEGETATION. 283 
 
 green rind which appears when ypu strip a branch of any tree or 
 ' shrub of its external coat of hark. The parenchyma is not confin- 
 ed to the stern or branches, but extends over every part of the plant. 
 It forms the green- matter of the leaves, and is composed of tubes 
 filled with a peculiar juige. 
 
 The cortical layers are immediately in contact with the wood ; 
 they abound with tannin and gallic acid, and consist of small vessels 
 through which the sap descends after being elaborated in the leaves. 
 The cortical layers are annually renewed, the old bark being con- 
 verted into wood. 
 
 Mrs. B. That function is performed by the tubes of the alber- 
 num or wood, which is immediately beneath the cortical layers. The 
 wood is composed of woody fibre, mucilage and resin. The fibres 
 are disposed in two ways : some of them longitudinally, and these 
 form what is called the silver grain of the wood. The others which 
 are concentric, are called the spurious grain. These last are dispos- 
 ed in layers, from the number of which the age of the tree may be 
 computed, a new one being produced annually by the conversion of 
 the bark into wood. The oldest, and consequently most internal part 
 of the albernum, is called heart wood ; it appears to be dead, at least 
 no vital functions are discernible in it. It is through the tubes of 
 the living albernum that the sap rises. These therefore, spread into 
 the leaves, and there communicate with the extremities of the ves- 
 sels of the cortical layers, into which they ponr their contents. 
 
 Caroline. Of what use, then, are the tubes of the parenchyma, 
 since neither the ascending nor descending sap passes through them ? 
 
 Mrs. B. They are supposed to perform the important function of 
 secreting from the sap the peculiar juices from which the plant 
 more immediately derives its nourishment. These juices are very 
 conspicuous, as the vessels which contain them are much larger 
 than those through which the sap circulates. The peculiar juices 
 of plants differ much in their nature, not only in different species 
 of vegetables, but frequently ia different parts of the same individual 
 plant; they are sometimes "saccharine, as in the sugar-cane, some- 
 times resinous as in firs and evergreens, sometimes of a milky ap- 
 pearance, as in the laurel. 
 
 Emily. I have often observed, that in breaking a young shoot, or 
 in bruising a loaf of laurel, a milky juice will ooze oui in great 
 abundance. 
 
 Mrs. B. And it is by making incisions in the bark, that pitch, tar, 
 and turpentine* are obtained from fir-trees. The durability of this 
 species of wood is chiefly owing to the resinous nature of its peculiar 
 
 * Turpentine is obtained as described iti the text. But tar and 
 pitch are obtained by a very different method. A conical cavity is 
 dug in the earth, at the bottom of.which is placed a reservoir. Over 
 this is piled billets of fir wood, forming a large pile. The pile is 
 covered with turf to smother the fire which is kindled at the top. As 
 the wood is heated, and gradually converted into charcoal, the tar is 
 
 1275. Through what docs the sap ascend ? 
 
 1276. Of what is the wood composed ? 
 
 1277. How are the fibres disposed ? 
 
 1278. Of what use are the tubes of the parenchyma ? 
 
 1279. How may pitch, tar, and turpentine be obtained ? 
 
284 VEGETATION. 
 
 juices. The volatile oils have, in a great measure, the same preserv- 
 ative effects, as they defend the parts with which they are connect- 
 ed, from the attack of insects. This tribe seems to have as great an 
 aversion to perfumes, as the human species have delight in them. 
 They scarcely ever attack any odoriferous parts of plants, and it is 
 not uncommon to see every leaf of a tree destroyed by a blight, 
 whilst the blossoms remain untouched. Cedar, sandal, and all ar- 
 omatic woods, are, on this account, of great durability. 
 
 Emily. But the wood of the oak, which is so much esteemed for 
 its durability, has, I believe, no smell. Does it derive this quality 
 from its hardness alone ? 
 
 JMrs. B. Not entirely ; for the chesnut, though considerably 
 harder and firmer than the oak, is not so lasting. The durability 
 of the oak, is, I believe, in a great measure, owing to its having 
 very little heart-wood, the albernum preserving its vital functions 
 longer than in other trees. 
 
 Caroline. If incisions are made into the albernum and cortical 
 layers, may not the ascending and descending sap be procured in 
 the same manner as the peculiar juice is from the vessel of the 
 parenchyma ? 
 
 JVrs. B. Yes ; but in order to obtain specimens of these fluids, in 
 any quantity, the experiment must be made in the spring, when the 
 sap circulates with the greatest energy. For this purpose a small 
 bent glass tube should be introduced into the incision, through 
 which the sap may flow without mixing with any of the other juices 
 of the tree. From the bark the sap will flow much more plentifully 
 than from the Wood, as the ascending sap is much more liquid, more 
 abundant and more rapid in its motion, than that which descends ; 
 for the latter having been deprived by the operation of the leaves 
 of a considerable part of its moisture, contains a much greater pro- 
 portion of solid matter, which retards its motion. It does not ap- 
 pear that there is any excess of descending sap, as none ever exudes 
 from the roots of plants ; this process, therefore, seems to be car- 
 ried on only in proportion to the wants of the plant, and the sap de- 
 scends no further, and in no great quantity, than is required to 
 nourish the several organs. Therefore, though the sap rises and 
 descends in the plant, it does not appear to undergo a real circula- 
 tion. 
 
 The last of the organs of plants, is the flower, or blossom, which 
 
 driven out and runs into the cavity, and finally into the reservoir. 
 Tar is a mixture of resin, empyreumatic oil, charcoal, and acetic acid. 
 The color is derived from the charcoal. Pitch is made by boiling 
 tar, by which its more volatile parts are driven off. C. 
 
 1280. On what are the durability of cedar, sandal, and all aromat- 
 ic woods depending? 
 
 1281. On what is the durability of oak depending ? 
 
 1282. Of what is tar said in the note to consist ? 
 
 1283. At what time in the year does the sap circulate with most 
 energy ? 
 
 1284. Why will sap flow more plentifully from the bark than 
 from the wood ? 
 
 J285. What is the ultimate purpose of nature in the vegetable 
 creation ? 
 
VEGETATION. 285 
 
 produces ihe fruits and seed. These may be considered as the ulti- 
 mate purpose of nature in the vegetable creation. From fruits and 
 seeds animals derive both a plentiful source of immediate nourish- 
 ment, and an ample provision for the reproduction of the same 
 means of subsistence. 
 
 The seed which forms the final product of mature plants, we 
 have already examined, as constituting the first rudiments of fu- 
 ture vegetation. 
 
 These are the principal organs of vegetation, by means of which, 
 the several chemical processes which are carried on during the life 
 of the plant are performed. 
 
 Emily. But how are the several principles which enter into the 
 composition of vegetables, so combined by the organs of the plant, 
 as to be converted into vegetable matter? 
 
 Mrs. B. By chemical processes, no doubt ; but the apparatus in 
 which they are performed, is so extremely minute as completely to 
 elude our examination. We can form an- opinion, therefore, only 
 by the result of these operations. 
 
 The sap is evidently composed of water, absorbed hy the roots 
 andholding in solution the various principles which it derives from 
 the soil. From the roots the sap ascends through the tubes of the 
 alburnum into the stem, and thence branches out to every extrem- 
 ity of the plant. Together with the sap circulates a certain quan- 
 tity of carbonic acid, which is gradually disengaged from the for- 
 mer by the internal heat of the plant. 
 
 Caroline. What? have vegetables a peculiar heat, analogous to 
 animal heat? 
 
 Mrs. B. It is a circumstance that has long been suspected ; but 
 late experiments have decided beyond a doubt that vegetable heat 
 is considerably above that of unorganized matter in winter, and 
 below it in summer. The wood of a free in its in erior, is about 
 sixty degrees when the thermometer is at seventy or eighty de- 
 grees in the air. And the bark, though so much exposed; is seldom 
 below forty in winter. 
 
 It is from the sap afte'r it has been elaborated by the leaves, that 
 vegetables derive their nourishment ; in its progress through the 
 plant from the leaves to the roots, it deposits in the several sets of 
 vessels with which it communicates, the materials on which the 
 growth and nourishment of each plant depends. It is thus that the 
 various peculiar juices, saccharine, oily, mucous, ai id, and colour- 
 ing, are formed ; as also the more solid parts, fecula, woody-fibre, 
 tannin, resins, concrete salts ; in a word all the immediate materi- 
 als of vegetables, as well us the organized parts of plants, which 
 latter, bes'ides the power of secreting these from the sap. for the 
 general purpose of the plant, have also that of applying them to 
 their own particular nourishment. 
 
 Emily. But why should the process ofvegetation take place only 
 
 1286. How are the several principles which enter into the com- 
 position of vegetables so combined by the organs of the plant as to 
 be converted into vegetable matter ? 
 
 1287. How does the temperature of vegetables compare with 
 that of unorganized matter ? 
 
 1288. How are the several pieces as well as more solid parts o* 
 vegetables formed ? 
 
286 VEGETATION. 
 
 at one season of the year, whilst a total inaction prevails during 
 the other ? 
 
 Mrs. B. Heat is such an important chemical agent, that its ef- 
 fect as such, might perhaps alone, account for the impulse which 
 the Spring- gives to vegetation. But, in order to explain the me- 
 chanism of that operation, it has "been supposed that the warmth of 
 spring dilates the vessels of plants, and produces a kind of vacuum, 
 into which the sap (which had remained in a state of inaction in the 
 trunk during the winter) rises ; this is followed by the ascent of the 
 sap contained in the roots, and room is 'thus made for fresh sap, 
 which the roots in their turn pump up from the soil. This process 
 goes on till the plant blossoms and bears fruit, which terminates its 
 summer career ; but when the cold weather sets in,fthe fibres and 
 ivessels contract, the leaves wither, and are no longer able to per- 
 form their office of transpiration ; and as this secretion stops, the 
 roots cease to absorb sap from the soil. If the plant be an annual, 
 its life then terminates ; if not, it remains in a state of torpid inac- 
 tion during the winter, or the only internal motion that takes place 
 is that of a small quantity of resinous juice, which slowly rises from 
 the stem into the branches, and enlarges their buds during the win- 
 ter. 
 
 Caroline. Yet, in evergreens vegetation must continue through- 
 out the year. 
 
 Mrs. B. Yes ; but in winter it goes on in, a very imperfect man- 
 ner, compared to the vegetation of spring and summer. 
 
 We have dwelt much longer on the history of vegetable chemis- 
 try than J had intended ; but we have at length, I think, brought 
 the subject to a conclusion. 
 
 Caroline. I rather wonder that you did not reserve the account 
 of the fermentations for the conclusioa ; for the decomposition of 
 vegetables naturally follows their death, and can hardly, it seems, 
 be introduced with so much propriety at any other period. 
 
 J\lrs. B. It is difficult to determine at what point precisely it may 
 be most eligible to enter on the history of vegetation ; every part 
 of the subject is so cloely connected, and forms such an uninter- 
 rupted chain, that it is !iy no means easy to divide it. Had J begun 
 with the germination of the seed, which, at first view seems to be 
 the most proper arrangement, I could not have explained the na- 
 ture and fermentation of the seed, or have described the changes 
 which manure must undergo, in order to yield the vegetable ele- 
 ments. To understand the nature of germination, it is necessary, I 
 think, previously to decompose the parent plant, in order to be- 
 come acquainted with the materials required for that purpose. I 
 hope, therefore, that, upon second consideration, you will find that 
 the order which I have adopted, though apparently less correct, is, 
 in fact, the best calculated for the elucidation of the subject. 
 
 1289. Why sViould the process of vegetation take place only in 
 warm weather ? 
 
 1290. What is the condition of vegetables called evergreens, in 
 the season of winter ? 
 
 1291. Why was not the fermentation of vegetables reserved for 
 the concluding part of what is said on this/ subject ? 
 
COMPOSITION OF ANIMALS. 287 
 
 CONVERSATION XXIH. 
 
 ON THE COMPOSITION OF ANIMALS. 
 
 . 
 
 . 
 
 Mrs. B. We have now come to the last branch of chemistry, 
 which comprehends the most complicated order ofcompound beings. 
 This is the animal creation, the history of which, cannot but excite 
 the highest degree of curiosity and interest, though we often fail in 
 attempting to explain the laws by which it is governed. 
 
 Emily. But since all animal ultimately derive their nourishment jf> t 
 from vegetables, the chemistry of this order of beings must consist^ 
 merely in the conversion of vegetable into animal matter. 
 
 Mrs. B. Very true ; but the manner in which this is effected is, 
 in a great measure, concealed from our observation. This pro- 
 cess is called animalisation, and is performed by peculiar organs. 
 The difference of ihe animal and vegetable kingdoms does not, 
 however, depend merely on a different arrangement of combina- 
 tions. A new principle abounds in the animal kingdom, which is 
 but rarely and in very small quantities found in vegetables ; this is 
 nitrogen. There is likewise in animal substances a greater and 
 more constant proportion of phosphoric acid, and other saline mat- 
 ters. But these are not essential to the formation of animal matter. 
 
 Caroline. Animal compounds contain, then, four fundamental 
 principles; oxygen, hydrogen,, carbon and nitrogen ? 
 
 Mrs. B. Yes; and these form the immediate materials of ani- 
 mals, which are gelatine, albumen, and^irme.* 
 
 Emily. Are those all ? I am surprised thatanimals should be com- 
 posed of fewer kinds of materials than vegetables ; for they appear 
 much more complicated in their organization. 
 
 Mrs. B. Their organization is certainly more perfect and intri- 
 cate, and the ingredients that occasionally enter into their compo- 
 sition are more numerous. But notwithstanding the wonderful va- 
 riety observable in the texture of the animal organs, we find that the 
 original compounds, from which all the varieties of animal matter 
 are derived, may be reduced to the three heads just mentioned. An- 
 imal substances being the most complicated of all natural com- 
 pounds, are most easily susceptible of decomposition, as the scale of 
 attractions increases in proportion to the number of constituent 
 principles. Their analysis is, however, both difficult and imper- 
 fect ; for as they cannot be examined in their living state, and are 
 liable to alteration immediately after death, it is probable that when 
 submitted to the investigation of a chemist, they are always more or 
 
 * These are the principal-mgredtents of the soft parts. But in 
 addition to these, animal substances contain colnuring matter of 
 blood, mucous, sulphur, phosphorus, earths, alkalies, oils, acids, rtsins, 
 and several others, which it is unnecessary to specify. C 
 
 1292. What forms the subject of the 23d conversation ? 
 
 1293. What is animalization ? 
 
 1294. What do animal compounds contain ? 
 
 1295. What are the immediate materials of animals ? 
 
 1296. On what account is the analysis of animal compounds diffi- 
 . G ult and imperfect ? 
 
288 COMPOSITION 
 
 less altered in their combinations and properties, from what they 
 were, whilst they made part of the living animal. 
 
 Emily. The mere diminution of temperature, which they experi- 
 ence by the privation of animal heat, must, 1 should suppose, be 
 sufficient to derange the order ofattractions, that existed during life. 
 
 J)Irs. B. That is one of the causes, no doubt; but there are many 
 other circumstances which prevent us from studying the nature of 
 living animal substances. We must, therefore, in a considerable 
 degree, confine our researches to the phenomena of these compounds 
 in their inanimate state. 
 
 These three kinds of animal matter, gelatine, albumen, and 
 fibrine, farm the basis of all the various parts of the animal system : 
 either solid, as the skin, Jlesh, nerves, membranes, cartilages, and 
 bones ; or fluid, blood, chyle, milk, mucous, the gastric and pancre- 
 atic juices, bile, perspiration, saliva, tears, <Sfc. 
 
 Caroline. Is it not surprising that so great a variety of substan* 
 ces, and so different in their nature, should yet all arise from so few 
 materials, and from the same original elements ? 
 
 Mrs. B. The difference in the nature of various bodies depends, 
 as I have often observed to you, rather on their state of combination, 
 than on the materials of which they are composed. Thus, in consi- 
 dering the chemical nature of the creation in a general point of view, 
 we observe that it is throughout cotnposed of a very small number 
 of elements. But when we divide it into the three kingdoms, we 
 find that, in the mineral, the combinations seem to result from the 
 union of elements casually brought together ; whilstin the veget- 
 able and animal kingdoms, the attractions are peculiarly and reg- 
 ularly produced by appropriate organs, whose action depends on 
 the vital principle. And we may further observe-, that by means of 
 certain spontaneous changes and decompositions, the elements of 
 one kind of matter become subservient to the reproduction of an- 
 other ; so that the three kingdoms ar intimately connected, and 
 constantly contributing to the preservation of each other. 
 
 Emily. There is, however, one very considerable class of ele- 
 ments, which seems to be confined to the mineral kingdom. I 
 mean metals. 
 
 Mrs. B. Not entirely; they are found, though in very minute 
 quantities, both in the vegetable and animal kingdoms. A small 
 portion of earths and sulphur enters also into the composition of or- 
 ganized bodies. Phosphorus, however, is almost entirely confined 
 to i\\Q animal kingdom ; and nitrogen, with but few exceptions, is 
 extremely scarce in vegetables. 
 
 Let us now proceed to examine the nature of the three principal 
 materials of the animal system. 
 
 Gelatine or jelly, is the chief ingredient of skin, and of all the 
 membranous -parts of animals. Tt may be obtained from these sub- 
 stances, by means of boiling water, under the forms of glue, sjze, 
 isinglass, and transparent jelly. 
 
 1297. On what does the difference of nature in various bodies 
 chiefly depend ? 
 
 1298. What is gelatine or jelly ? 
 
 1299. From what is it obtained ? 
 
 300. Under what forms does it exist when obtained ? 
 
OF ANIMALS. 289 
 
 Caroline. But these are of a very different nature ; they cannot, 
 therefore, be|all pure gelatine. 
 
 Mrs. B. Not entirely, but very nearly so. Glue* is extracted 
 from the skin of animals. Size is obtained either from skin in its 
 natural state, or from leather. Isinglass is gelatine procured from 
 a particular species of fish ; it is, you know, of this substance that 
 the finest jelly is made, and this is done by merely dissolving the 
 isinglass in boiling water, and allowing the solution to congeal. 
 
 Emily. The wine, lemon, and spices, are, I suppose, added only 
 to flavour the jelly ? 
 
 Mrs. B. Exactly so. 
 
 Caroline. But jelly is often made of hartshorn shavings, and of 
 calves' feet ; do these substances contain gelatine ? 
 
 J\lrs. B. Yes. Gelatine may be obtained from almost any ani- 
 mal substance, as it enters more or less into the composition of all 
 of them. The process for obtaining it is extremely simple, as it 
 consists merely in boiling the substance which contains it with wa- 
 ter. The gelatine dissolves in water, and may be obtained of v any 
 degree of consistence or strength, by evaporating this solution. 
 Bones in particular produce it very plentifully, as they consist of 
 phosphat of lime, combined or cemented by gelatine. Horns, 
 which are a species of bone, will yield abundance of gelatine. The 
 horns of the hart are reckoned to produce gelatine of the finest 
 quality ; they are reduced to the state of shavings, in order that the 
 jelly may be more easily extracted by the waters. It is of harts- 
 horn shavings that the jellies for invalids are usually made, as they 
 are of very easy digestion. 
 
 Caroline, it appears singular that hartshorn, which yields such a 
 powerful ingredient as ammonia, should at the same time produce 
 so mild and insipid a substance as jelly? 
 
 J>1rs. B. A-nd (what is more surprising) it is from the gelatine of 
 bones that ammonia is produced. You must observe, however, that 
 the processes, by which these two substances are obtained from 
 bones are very different. By the simple action of water and heat, 
 the gelatine is separated ; but in order to procure the ammonia, or 
 what is commonly called hartshorn, the bones must be distilled, by 
 which means the gelatine is decomposed, and hydrogen and nitro- 
 gen combined i;i the form of ammonia. So that the first operation 
 is a mere separation of ingredients, whilst the second requires a 
 chemical decomposition. 
 
 Caroline. But when jelly is made from hartshorn shavings, what 
 becomes of the phosphat of lime which constitutes the other part of 
 bones ? 
 
 * Bones, muscles, tendons, ligaments, membranes, and skips, all 
 mail.- 
 
 . of them yield glue. But the best is made from the skin of old ani- 
 . C. 
 
 130 1. From what is the best glue extracted? 
 
 1302. From what is isinglass obtained? 
 
 1303. What is the process of obtaining gelatine ? 
 
 1304. From what is the best gelatine obtained ? 
 
 1305. From what is ammonia produced ? 
 
 ^ 
 
290 COMPOSITION 
 
 J\lrs. B. It is easily separated by straining. But the jelly is after- 
 wards more perfectly purified, and rendered transparent, by adding 
 whites of eggs, which being coagulated by heat, rises to the sur- 
 face along with any impurities. 
 
 Emily. I wonder that bones are not used by the common people 
 to make jelly ; a great deal of wholesome nourishment, might, I 
 should suppose, be procured from them, though the jelly would per- 
 haps not be quite so good as if made from hartshorn shavings. 
 
 Mrs. B. There is a prejudice among the poor against a species of 
 food that is usually thrown to the dogs ; and as we cannot expect 
 them to enter into chemical considerations, it is in some degree ex- 
 cusable. Besides, it requires a prodigious quantity of fuel to dis- 
 solve bones and obtain the gelatine from them. 
 
 The solution of bones in water is greatly promoted by an accu- 
 mulation of heat. This may be effected by means of an "extremely 
 strong metallic vessel, called 'Papiri's digester, in which the bones 
 and water are enclosed, without any possibility of the steam making 
 its escape. A heat can thus be applied much superior to that of 
 boiling water ; and bones, by this means, are completely reduced 
 to a pulp. But the process still consumes too much fuel to be 
 generally adopted among the lower classes. 
 
 Caroline. And why should not a manufacture be established for 
 grinding or marcerating bones, or at least for reducing them to the 
 state of shavings, when, I suppose, they would dissolve as readily 
 as hartshorn shavings ? 
 
 Jt/r*. B. They could not be collected clean for such a purpose ; 
 but they are not lost, as they are used for making hartshorn, and 
 sal-ammoniac; and such is the superior science and industry of 
 this country, that we now send sal. ammoniac to the Levant, though 
 it originally came to us from Egypt. 
 
 Emily. When jelly is made of isinglass, does it leave no sedi- 
 ment ? 
 
 J\lrt. B. No : nor does it so much as require clarifying, as it con- 
 sists almost entirely of pure gelatine, and any foreign matter that is 
 mixed with it, is thrown off during the boiling in the form of scum. 
 These are processes which you may see performed in great per- 
 fection in the culinaoy laboratory, by that very able and most use- 
 ful chemist, the cook. 
 
 Caroline. To what an immense variety of purposes chemistry is 
 subservient ? 
 
 Emily. It appears, in rlhat respect, to have an advantage over 
 mtst other arts and sciences ; for these, very often have a tendency 
 to confine the imagination to their own particular object ; whilst 
 the pursuit of chemistry is so extensive and diversified, that it in- 
 spires a general curiosity and a desire of inquiring into the nature 
 of every object. 
 
 Caroline. I suppose that soup is likewise composed of gelatine ; 
 for, when cold, it often assumes the consistence of jelly. 
 
 Mrs. B. Not entirely ; for though soups generally contain a 
 
 1306. What becomes of the phosphat of lime when jelly is made 
 ifrom the shavings cf; hartshorn? 
 
 1307. What- obstacle is there to converting bones into gelatine 
 Tor food ? 
 
 1308. For what may bones be advantageously used ? 
 J309. Of what are soups composed ? 
 
OF ANIMALS. 291 
 
 quantity of gelatine, the most essential ingredient is a mucus, or 
 extractive matter, a peculiar animal substance, very soluble in wa- 
 ter, which has a strong taste, am! is more nourishing than gelatine. 
 The various kinds of portable soup consists of this extractive mat- 
 ter in a dry state, which, in order to be made into soup, requires 
 only to be dissolved in water. 
 
 Gelatine, in ite solid state, is a semiductile, transparent sub- 
 stance, without either taste or sjnell. When exposed to heat, in 
 contact with air and water, it first swells, then fuses, and finally 
 burns. You may have seen the first part of this operation per- 
 formed in the carpenter's glue-pot. 
 
 Caroline. But you said that gelatine had no smell, and glue has a 
 very disagreeable one. 
 
 Mrs. B. Glue is not pure gelatine : as it is not designed for eat- 
 ing, it is prepared without attending to the state of the ingredients, 
 which are more or less contaminated by particles that have be- 
 come putrid. 
 
 Gelatine may be precipitated from its solutions in water by alco- 
 hol. We shall try this experiment with a glass of warm jelly. 
 You see that the gelatine subsides by the union of the alcohol and 
 the water. 
 
 Emily. Flow is it, then, that jelly is flavoured with wine, without 
 producing any precipitation ? 
 
 Mrs. B. Because the alcohol contained in wine is already con> 
 bined with water and other ingredients, and is, therefore, not at 
 liberty to act upon the jelly as when in its separate state. Gela- 
 tine is soluble both in acids and in alkalies ; the former, you know, 
 are frequently used to season jellies. 
 
 Caroline. Among the combinations of gelatine we must not for- 
 get one which you formerly mentioned ; that with tannin, to form 
 leather. 
 
 Mrs. B. True; but you must observe that leather can be pro- 
 duced onlj r by gelatine in a membranous state ; for though pure 
 gelatine and tannin will produce a substance chemically similar to 
 leather, yet the texture of the skin is requisite to make it answer 
 the useful purposes of that substance. 
 
 The next animal substance we are to examine is albumen :. this, 
 although constituting a part of most of the animal compounds, is 
 frequently found insulated in the animal system ; the whites of eggs, 
 for instance, consists almost entirely of albumen : the substance that 
 composes the nerves, the serum, or white part of the blood, and the 
 curds of milk, are little else than albumen variously modified. 
 
 In its most simple state, albumen appears in the form of a trans- 
 parent, viscous fluid, possessed of no distinct taste or smell ; it co- 
 agulates at the low temperature of 165 degrees ; an(jl, when once 
 solidified, it will never return to its fluid state. 
 
 Sulphuric acid and alcohol are each of them capable of coagu- 
 
 1310. How does common glue differ from gelatine ? 
 
 1311. What effect will alcohol have on gelatine in water ? 
 
 1312. Why will not wine, which contains a portion of alcohol 
 produce precipitation, when put into jelly ? 
 
 1313. What is albumen ? 
 
 1314. At what temperature will it Coagulate ? 
 
292 COMPOSITION 
 
 lating albumen in the same manner as heat, as I am going to show 
 you. 
 
 Emily. Exactly so. Pray, Mrs. B., what kind of action is there 
 between albumen and silver ? I have sometimes observed, that of 
 the spooa with which I eat an egg happens to be wetted, it becomes 
 tarnished. 
 
 Mrs. B. It is because the white of an egg (and, indeed, albumen 
 in general) contains a little sulphur, which, at the temperature of 
 an egg just boiled, will decompose the drop of water that wets the 
 spoon, and produce sulphuretted hydrogen gas, which has the pro- 
 perty of tarnishing silver. 
 
 We may now proceed {ojibrine. This is an insipid and inodorus 
 substance, having somewhat the appearance of fine white threads 
 adhering together : it is the essential constituent of muscles, or 
 flesh, in which it is mixed with and softened by gelatine. It is in- 
 soluble both in water and alcohol, but sulphuric acid converts it 
 into a substance very analagous to gelatine. 
 
 These are the essential and general ingredients of animal mat- 
 ter ; but there are other substances, which though not peculiar to 
 the animal system, usually enter into its composition, such as oils, 
 acids, salts, &c. 
 
 Animal oil is the chief constituent of fat : it is contained in 
 abundance in the cream of milk, whence it is obtained in the form 
 of butter. 
 
 Emily. Is animal oil the same in its composition as vegetable 
 oils ? 
 
 Mrs. B. Not the same, but very analagous. The chief diffe- 
 rence is, that animal oil contains nitrogen, a principle which seldom 
 enters into the composition of vegetable oils, and never in so large 
 a proportion. 
 
 There are few animal acids, that is to say, acids peculiar to ani- 
 mal matter, from which they are almost exclusively obtained. 
 
 The animal acids have triple bases of hydrogen, carbon, and 
 nitrogen: Some of them are found native in animal matter ; others 
 are produced during its decomposition. 
 
 Those which we find ready formed, are, 
 
 The bombic acid, which is obtained from silk-worms. 
 
 The/ormic acid, from ants. 
 
 The lactic acid, from the whey of milk. 
 
 The sebacic, from oil or fat. 
 
 Those produced during the decomposition of animal substances 
 by heat, are the prussic and zoonic acids. This last is produced by 
 the roasting of meat, and gives it a brisk flavour. 
 
 Caroline. The class of animal acids is not very extensive. 
 
 Mrs. B. No ; nor are they, generally speaking, of great impor- 
 
 1315. Why is silver tarnished by the white of an egg ? 
 
 1316. What is fibrine? 
 
 1317. What is the difference between vegetable and animal oil? 
 131 tf. What are the bases of animal acids ? 
 
 1319. What are the names of those formed in animal substances 
 already formed ? 
 
 1320. What are those produced during the decomposition of ani- 
 m al substances ? 
 
OF ANIMALS. 293 
 
 tance. The prussic acid? I think the only one sufficiently interest- 
 ing to require any further comment. It can be formed by an arti- 
 ficial process without the presence of any animal matter; it may 
 likewise be obtained from a variety of vegetables, particularly those 
 of the narcotic kind, such as poppies, laurel, &c. But it is commonly 
 obtained from blood, by strongly heating that substance with caus- 
 tic poiash ; the alkali attracts the acid from the blood, and forms 
 with it a prussiat of potash. From this state of combination the 
 prussic acid can be obtained pure by means of other substances 
 which have the power of separating it from the alkali. 
 
 Emily. But if this acid does not exist ready formed in blood, how 
 ;an the alkali attract it from thence? 
 
 Mrs. B. It is the triple bases only of this acid that exists in the 
 c'ood ; and this is developed and brought to the state of acid, during 
 the combustion. The acid, therefore, is first formed, and it after- 
 wards combines with the potash. 
 
 Emily. Now I comprehend it. But how can the prussic acid be 
 artificially made ? 
 
 Mrs. B. By passing ammoniacal gas over red-hot charcoal ; and 
 hence we learn that the constituents of this acid are hydrogen, ni- 
 trogen, and carbon. The two first are derived from the volatile al- 
 kali, the last from the combustion of the charcoal. f 
 
 Caroline. But this does not accord with the system of oxygen be- 
 ing the principle of acidity. 
 
 Mrs. B. The coloring matter of Prussian blue is called an acid, 
 because it unites with alkalies and metals, and not from any other 
 
 * Prussic acid can be obtained from Prussian blue (prussiat of 
 iron) by the following process. Take 4 ounces of Prussian blue, 
 pulverize it finely, and mix with it 2 and a half ounces of red oxide 
 of mercury (red precipitate,) boil the mixture with 12 ounces of wa-j 
 ter in a glass vessel, frequently stirring it with a stick. Filter the 
 solution, which is a prussiat of mercury, and is formed by the trans- 
 fer of the prussic acid,, from the iron to the mercury. Put this solu- 
 tion into a retort, and add to it two ounces of clean iron filings and 
 six drachms of sulphuric acid, and distil off two and a half ounces of 
 prussic acid. This process requires a good apparatus, and ought not 
 to be undertaken by anyone who has not a knowledge of practical 
 chemistry. The fumes during the distillation ought carefully to be 
 avoided as poisonous. Prussic acid has of late been much used in 
 medicine, as a remedy, in consumption, hooping cough, &c. C. 
 
 f The basis of Prussic acid, has of late years, been ascertained 
 by M. Gay-Lussac, to be a combination of azote and carbon, which 
 he has called cyanogen. This compound, when combined with hy- 
 drogen, forms prussic acid, or, as it is now called, hydro-cyanic acid. 
 Pure cyanogen, in the state of gas, ma} he obtained from prussiat 
 of mercury by distillation. 
 
 1321. How is prussic acid obtained? 
 
 1322. How is it mentioned in the note that prussic acid can be ob- 
 tained from Prussian blue ? 
 
 1323. Does this acid exist already formed in the blood ? 
 
 1324. How is it ascertained that the constituents of prussic acid 
 are hydrogen, and nitrogen, and carbon ? 
 
 25* 
 
294 COMPOSITION OP ANIMALS. 
 
 characteristic properties of acids; perhaps the name is not strictly 
 appropriate. But this circumstance, together with some others of 
 the same kind, has induced several chemists to think that oxygen 
 may not be the exclusive generator of acids. Sir H. Davy, 1 have 
 already informed you, was led by his experiments on dry acids to 
 suspect that water might' be essential to acidity. And it is the 
 opinion of some chemists that acidity may possibly depend rather 
 on the arrangement than on the presence of any particalar princi- 
 ples. But we have not yet done with the prussic acid. It has a 
 strong affinity for metallic oxyds, and precipitates the solutions of 
 iron in acids of a blue color. "This is the Prussian blue, or prussia* 
 of iron, so much used in the arts, and with which 1 think you musv 
 be acquainted. 
 
 Emily. Yes, I am ; it is much used in painting, both in oil and in 
 water 'colors ; but it is not reckoned a permanent oil-color. 
 
 JVis. B. That defect arises, I believe, in general, from its being 
 badly prepared, which is the case when the iron is not so fully oxy- 
 dated as to forrri a red oxyd. For a solution of green oxyd of iron 
 (in which the metal is more slightly oxydated,) makes only a pale 
 green, or even a white precipitate, with prussiat of potash ; and this 
 gradually changes to blue by being exposed to the air, as I can im- 
 mediately show you. 
 
 Caroline. It already begins to assume a pale blue color. But 
 :hov7 does the air produce this change? 
 
 Mrs. B. By oxydating the iron more perfectly. If we pour some 
 nitrous acid on it, the blue color will be immediately produced, as 
 the acid will yield its oxygen to the precipitate, and fully saturate 
 it with this principle, as you shall see. 
 
 Caroline. It is very curious to see a color change so instantane- 
 ously. 
 
 J\lrs. B. Hence you perceive that Prussian blue cannot be a per- 
 manent color, unless prepared with red oxyd of iron, since by ex- 
 posure to the atmosphere it gradually darkens, and in a short time is 
 no longer in harmony with the other colors of the painting. 
 
 Caroline. But it can never become darker, by exposure to the 
 atmosphere, than the true Prussian blue, in which the oxyd is per- 
 fectly saturated. 
 
 Mrs. B. Certainly not. But in painting, the artist not reckon- 
 ing upon partial alterations in his colors, gives his blue tints that 
 particular shade which harmonizes with the rest of the picture. If, 
 afterwards, those tints become darker, the harmony of the coloring 
 must necessarily be destroyed. 
 
 Caroline. Praj of what nature is the paint, called carmine ?- 
 
 Mrs. B. It is an animal color, prepared from cochineal, an insect, 
 the infusion of which produces a very beautiful red.* 
 
 Caroline. Whilst we are on the subject of colors, I should like to 
 learn what ivory Hack is ? 
 
 * Carmine is obtained by precipitating the coloring matter from 
 an infusion of the insect by means of a solution of tin C. 
 
 1325. To what opinion was Sir H. Davy led respecting acidity ? 
 
 1326. Why is not Prussian blue a permanent oil color? 
 
 1327. In what way may Prussian blue be made a permanent color? 
 
 1328. From what is carmine prepared ? 
 
OF THE ANIMAL ECONOMY. 295 
 
 Mrs. B. It is a carbonaceous substance, obtained by the combus- 
 tion of ivory. A more common species of black is obtained from 
 the burning of bone. 
 
 Caroline. But during 1 the combustion of ivory or bone, the car- 
 bon, I should have imagined, must be converted into carbonic acid 
 gas, instead of this black substance ? 
 
 Mrs B. In this and in most combustions, a considerable part of 
 the carbon is simply volatilized by the heat, and again obtained con- 
 crete on cooling. This color, therefore ma}' be called the soot 
 produced by the burning of ivory or bone. 
 
 CONVERSATION XXIV. 
 
 OF THE ANIMAL ECONOMY. 
 
 Mrs. B. We have now acquired some idea of the various mate- 
 rials which compose the animal system ; but if you are curious to 
 know in what manner these substances are formed by the animal 
 organs from vegetable^ as well as from animal substances, il will be 
 necessary to have some previous knowledge of the nature and 
 functions of these organs, without which it is impossible to form any 
 distinct idea of the process of animalization and nutrition. 
 
 Caroline. I do not exactly understand the meaning of the word 
 animalization. 
 
 Mrs. B. Animalization is the process by which the food is am'w- 
 ilated, that is to say, converted into animal matter j and nutrition is 
 that by which the food thus assimilated is rendered subservient to 
 the purposes of nourishing and maintaining the animal system. 
 
 Emily. This, I am sure, must be the most interesting of all the 
 branches of chemistry ? 
 
 Caroline. So 1 think ; particularly as I expect that we shall hear 
 something of the nature of respiration, and of the circulation of 
 the blood ? 
 
 Mrs. B. Thes^ functions undoubtedly occupy a most important 
 place in the history of the animal economy. But I must previously 
 give you a very short account of the principal organs by which the 
 various operations of the animal system are performed. These are : 
 . The Bones, 
 
 Muscles, 
 Blood vessels, 
 Lymphatic vessels, 
 Glands, and 
 Nerves. 
 
 The bones ure the most solid part of the animal frame, and in a 
 great measure determine its form and dimensions. You recollect I 
 suppose what are the ingredients which enter into theircomposition. 
 
 1329. How is ivory black made ? 
 
 1330. What is the subject of the 24th conversation ? 
 
 1331. What is nutrition? 
 
 1332. What are the principal organs by which the various ope- 
 rations of the animal system are performed .' 
 
296 OF THE ANIMAL ECONOMY. 
 
 Caroline. Yes ; phosphat of lime, cemented by gelatine. 
 Mrs. B. During the earliest period of animal life, they consist 
 almost entirely of gelatinous membrane, having the form of the 
 bones, but of a loose spongy texture, the cells or cavities of which 
 are destined to be filled with phosphat of lime ; it is the gradual ac- 
 quisition of this salt which gives to the bones their subsequent 
 hardness and durability. Infants first receive it from their moth- 
 er's milk, and afterwards derive it from all animal and from most veg- 
 etable food, especially farinaceous substances, such as wheat-flour, 
 which contains it in sensible quantities. A portion of the phosphat, 
 after the bones of the infant have been sufficiently expanded and 
 solidified, is deposited in the teeth, which consist at first only of a 
 gelatinous membrane, or case, fitted for the reception of this salt ; 
 and which, after acquiring hardness within the gum, gradually pro- 
 trude from it. 
 
 Caroline. How very curious this is ; and how ingeniously nature 
 has provided for the solidification of such bones as are immediately 
 wanted, and afterwards for the formation of the teeth, which would 
 not only be useless, but detrimental in infancy. 
 
 Mrs. B. In quadrupeds, the phosphat of lime is deposited like- 
 wise in their horns, and the hair or wool with which they are gener- 
 ally clothed. 
 
 ID birds it serves also to harden the beaks and the quills of their 
 feathers. 
 
 When animals are arrived to a state of maturity, and their bones 
 have acquired a sufficient degree of solidity, the phosphat of lime 
 which is taken with the food is seldom assimilated, excepting when 
 the female nourishes her young ; it is then all secreted into the milk, 
 as a provision for the tender bones of the nursling. 
 
 Emily. So that whatever becomes superfluous in one being, is 
 immediately wanted by another ; and the child acquires strength 
 precisely by the species of nourishment which is no longer necessa- 
 ry to the mother. Nature is indeed, an admirable economist ! 
 
 Caroline. Pray, Mrs. B., does not the disease in the bones of 
 children, called the rickets, proceed from a deficiency of phosphat 
 of lime ? 
 
 Mrs. B. I have heard that this disease may arise from two causes ; 
 it is sometimes occasioned by the growth of the nmscles being too 
 rapid in proportion to that of the bones. In this case the weight 
 of the flesh is greater than the bones can support, and presses upon 
 them so as to produce a swelling of the joints, which is the great 
 indication of the rickets. 
 
 The other cause of this disorder is supposed to be an imperfect di- 
 
 1333. What are the ingredients that enter into the composition 
 of bones ? 
 
 1334. What gives to bones their hardness and durability ? 
 
 1 335. What is the state of bones in the early periods of animal life ? 
 
 1336. Whence is the phosphat of lime necossary in the formation 
 of bones obtained ? 
 
 1337. How are teeth formed? 
 
 1338. What gives the horns of quadrupeds and the beaks and 
 quills of birds their hardness ? 
 
 J339. When is the phosphat of lime assimilated in adult animals ? 
 1340. How is the disease called rickets occasioned ? 
 
OF THE ANIMAL ECONOMY. 297 
 
 gestion and assimilation of the food, attended with an excess of 
 acid, which counteracts the formation of phosphatof lime. In both 
 instances, therefore, care should be taken to alter the child's diet, 
 not merely by increasing- the quantity of aliment containing phos- 
 phat of lime, but a ' so n y avoiding all food that is apt to lurn acid on 
 the stomach, and to produce indigestion. But the best preserva- 
 tive against complaints of this kuj'l, is no doubt, good nursing: 
 when a child has plenty of air and exercise, the digestion and as- 
 similation will be properly performed, no acid will be produced to 
 interrupt these functions, and the muscles and bones will grow to- 
 gether in just proportions. 
 
 Caroline. I have often heard the rickets attributed to bad nurs- 
 ing, but I never could have guessed what connexion there was be- 
 tween exercise and the formation of the bones. 
 
 JWrs. B. Exercise is generally beneficial to all the animal func- 
 tions. If man is destined to labour for his subsistence, the bread 
 which he earns is scarcely more- essential to his health and preserv- 
 ation than the exertions by which he obtains it. Those whom 
 th: gifts of fortune have placed -above the necessity of bodily la- 
 bour, are compelled to take exercise in some mode or other, and 
 when they cannot convert it into an amusement, they must submit 
 to it aj a task, or their health will soon experience the effects of 
 their indolence. 
 
 Emily. That will never be my case ; for exercise, unless it be- 
 comes fatigue, always gives me pleasure ; and so far from being a 
 task, is to me a source of daily enjoyment. I often think what a 
 blessing it is, that exercise, which is so conducive to health, should 
 be so delightful ; whilst fatigue, which is rather hurtful instead of 
 pleasure, occasions painful sensations. So that fatigue, no doubt, 
 was intended to moderate our bodily exertions, as satiety puts a 
 limit to our appetites. 
 
 Mrs. B. Certainly. But let us not deviate too far from our sub- 
 ject. The bones are connected together by ligaments, which con- 
 sist of a white, thick flexible substance, adhering to their extremi- 
 ties so far as to secure the joints firmly, though without impeding 
 their motion. And the joints are, moreover, covered by a solid, 
 smooth, elastic white substance, called cartilage, the use of which 
 is to a).low, by its smoothness and elasticity, the bones to slide easily 
 over one another, so that the joints may perform their office without 
 difficulty or detriment. 
 
 Over'the bones the muscles are placed ; they consist of bundles 
 of fibres, which terminate in a kind of string, or ligament, by 
 which they are fastened to the bones. The muscles are the organs 
 of motion ; by their power of dilatation and contraction, they put 
 into action the bones, which act as levers in all motions of the body, 
 and form the solid support of its various parts. The muscles are 
 of various degrees of strength or consistence, in different species 
 of animals. The mammiferous tribe, or those that suckle their 
 young, seem, in this respect, to occupy an intermediate place be- 
 twt en birds and cold-blooded animals, such as reptiles and fishes. 
 
 Emily. The different degrees of firmness and solidity in the mus- 
 
 1341. What precaution may be taken against this disease ? 
 
 1342. How are the bones of an animal system confined together ? 
 
 1343. By what are the joints covered ? 
 
 1344. By what, are the organs of motion ? 
 
298 OF THE ANIMAL ECONOMY. 
 
 cles of these several species of animals, proceed, I imagine, fron 
 the different nature of the food on which they subsist. 
 
 Mrs. B. No, that is not supposed to be the case ; for the humai 
 species, who are of the mammiferous tribe, live on more substantia 
 food than birds ; and yet the latter exceed them in muscula 
 strength. We shall, hereafter, attempt to account for this differ 
 ence; but let us now proceed in the examination of the anima 
 functions. 
 
 The next class of organs is that of the vessels of the body, the of 
 fice of which is to convey the various fluids throughout the frame 
 These vessels are innumerable. The most considerable of then 
 are those through which the blood circulates, which are of twi 
 kinds ; the arteries which convey it from the heart to the extremi 
 ties of the body, and the veins which bring it back into the heart. 
 
 Besides these, there are a numerous set of small transparent ves 
 sels, destined to absorb and convey different fluids into the blood 
 they are generally called the absorbent or lymphatic vessels ; but i 
 is to a portion of them only, that the function of conveying int< 
 the blood the fluid called lymph is assigned. 
 
 Emily. Pray what is the nature of that fluid ? 
 
 Mrs. B. The nature and use of the lymph have, I believe, nevei 
 been perfectly ascertained ; but it is supposed to consist of mattei 
 that b?s been previously animalized, and which after answering th< 
 purpose for which it was intended, must, in regular rotation, mak< 
 way for the fresh supplies produced by nourishment, The lym 
 phatic vessels pump up this fluid from every part of the system, am 
 convey H into the veins to be mixed with the blood which' rum 
 through them, and which is commonly called venous blood. 
 
 Caroline. But does it not again enter into the animal systerr 
 through that channel ? 
 
 Mrs. B. Not entirely ; for the venous blood does not return intc 
 the circulation until it has underg-one a peculiar change, in whicfc 
 it throws off whatever is become useless. 
 
 Another set of absorbent vessels pump up the chyle from the 
 stomach and intestines, and convey it, after many circumvolutions] 
 into the great vein near the heart.* 
 
 Emily. Pray, what is chyle? 
 
 Mrs. B. It is the substance into which food is converted by di- 
 gestion. 
 
 Caroline. One set of the absorbent vessels, then, is employed in 
 bringing away the old material which are no longer fit for use : 
 whilst the other set is busy in conveying into the blood the new ma- 
 terials that are to replace them ? 
 
 * This is a mistake The chyle is conveyed into the trunk of the 
 absorbent system, called by anatomists the 'thoracic duct. This runs 
 in a serpentine direction along the internal side of the back bone, 
 up to the subclavian vein, which lies under the collar bone. Into 
 this vein the chyle is discharged, and mixes with the blood, and be- 
 fore it reaches the heart, it is converted into blood itself. C. 
 
 J345. For what purpose are the arteries ? 
 
 1346. For what purpose are the veins? 
 
 J347. What are lymphatic vessels? 
 
 1348. What is chyle? 
 
OF THE ANIMAL ECONOMY. 299 
 
 Emily. What a great variety of ingredients must enter into the 
 composition of the blood ! 
 
 Mrs. B. You must observe that there is also a great variety of 
 substances to be secreted from it. We may compare the blood to a 
 general receptacle or storehouse for all kinds of commodities, which 
 are afterwards fashioned, arranged, and disposed of, as circumstan- 
 ces require. 
 
 There is another set of absorbent vessels in females, which is dea- 
 tined to secrete milk for the nourishment of the young. 
 
 Emily. Pray is not milk very analagous in its composition to 
 blood ; for, since the nursing derives its nourishment from that 
 source only, it must contain every principle which the animal sys- 
 tem requires. 
 
 .Mrs. B. 'Very true. Milk is found, by its analysis, to contain the 
 principal materials of animal matter, albumen, oil, and phosphat of 
 lime; so that the suckling has but little trouble to digest and assi- 
 milate this nourishment. But we shall examine the composition of 
 milk more fully afterwards. 
 
 In many parts of the body, numbers of small vessels are collected 
 together in little bundles called glands, from a Latin word, mean- 
 ing acorn, on account of the resemblance which some of them bear 
 in shape to that fruit. The functions of the glands is to secrete, or 
 separate certain matters from the blood. 
 
 The secretions are not only mechanical, but chemical separations 
 from the blood; for the substances thus formed, though contained 
 in the blood, are not ready combined in that fluid. The secretions 
 are of two kinds ; those which form peculiar animal fluids, as bile, 
 tears, saliva, &c. ; and those which produce the general materials 
 of the animal system, for the purpose of recruiting and nourishing 
 the several organs of the body : such as albumen, gelatine, and 
 fibrine ; the latter may be distinguished by the name of nutritive 
 $ecretions. 
 
 Caroline. 1 am quite astonished to hear that all the secretions 
 should be derived from the blood. 
 
 Emily. 1 thought that the bile was produced by the liver. 
 
 JWrs. B. So it is ; but the liver is nothing more than a very large 
 gland, which secretes the bile from the blood. 
 
 The last of the animal organs which we have mentioned are the 
 nerves ; these are the vehicles of sensation, every other part of the 
 body being, of itself, totaily insensible. 
 
 Caroline. They must, then, be spread through every part of the 
 frame, for we are" every where susceptible of feeling. 
 
 Emily. Excepting the nails and the hair. 
 
 Jtfr*. B. And those are almost the only parts in which nerves 
 cannot be discovered. The common source of all the nerves is the 
 brain; thence they descend, some of them through different aper- 
 tures in the skull, but the greatest part through the backbone, and 
 extend themselves by innumerable ramifications throughout the 
 
 1349. To what may the blood be compared ? 
 
 1350. Of what does milk consist ? 
 
 1351. From what do the glands derivo their name ? 
 
 1352. What is their use? 
 
 1353. How many kinds of secretions- are there, and what are they ? 
 
 1354. What are the nerves ? 
 
 -4355. What is the common source of the nerves ? 
 
300 OF THE ANIMAL ECONOMY. 
 
 whole body. They spread themselves over the muscles, penetrate 
 the glands, wind round the vascular system, and even pierce into 
 the interior of the bones. It is most probable through them that the 
 communication is carried on between the mind and the other parts 
 of the body ; but in what manner they are acted on by the mind, 
 and made to react on the body, is still a profound secret. Many 
 hypotheses have been formed on this very obscure subject, but they 
 are all equally improbable, and it would be useless for us to waste 
 our time in conjectures on an inquiry, which, in all probability, is 
 beyond the reach of human capacity. 
 
 Caroline, But you have not mentioned those particular nerves 
 that form the senses of hearing, seeing, smelling, and tasting ? 
 
 Mrs. B. They are considered as being of the same nature as 
 those which are dispersed over every part of the body, and consti- 
 tute the general sense of feeling. The different sensations which 
 they produce, arise from their peculiar situation and connexion with 
 the several organs of taste, smell, and hearing. 
 
 Emily. But these senses appear totally different from that of feel- 
 ing ? 
 
 Mrs. B. They are all of them sensations, but variously modified 
 according to the nature of the different organs in which the nerves 
 are situated. For, as we have formerly observed, it is by contact 
 only that the nerves are affected. Thus odoriferous particles must 
 strike upon the nerves of the nose, in order to excite- the sense of 
 smelling; in the same manner that taste is produced by the parti- 
 cular substance coming in contact with the nerves of the tongue. 
 It is t'nus also that the sensation of sound is produced by the concus- 
 sion of the air striking against the auditory nerve; and sight is the 
 effect of the light falling upon the optic, nerve. These various sen- 
 ses, therefore, are affected only by the actual contact of the particles 
 of matter, in the same manner as that of feeling. 
 
 The different organs of the am'mal body, though easily separated 
 and perfectly distinct, are loosely connected together by a kind of 
 spongy substance, in texture somewhat resembling net-work, call- 
 ed the cellular membrane ; and the whole is covered by the skin. 
 
 The skin, as well as the bark of vegetables, is formed of three 
 coats. The external one is called the cuticle or epidermis; the se- 
 cond which is called the mucous membrane, is of a thin,, soft texture, 
 and consists of a mucous substance, which, in negroes is black, and 
 is the cause of their skin appearing of that colour. 
 
 Caroline. Is then the external skin of negroes white like ours ? 
 
 Mrs. B. Yes ; but as the cuticle is transparent, as well as porous, 
 the blackness of the mucous membrane .is visible through it. The 
 extremities of the nerves are spread over this skin, so that the sen- 
 sation of feeling is transmitted through the cuticle. The internal 
 covering of the muscles, which is properly the skin, is the thickest, 
 
 1356. How are the nerves made subservient to the purposes of 
 hearing, seeing, smelling, and tasting* ? 
 
 1357. By what are the different parts of the animal body connect- 
 ed together ? 
 
 1358. Of how many coats is the skin formed, and what are they 
 called? 
 
 1359. Where is the colour of the skin ? 
 
 ,1360. If the colour is in the second coat, why is it so easily.seen- ? 
 
OF THE ANIMAL ECONOMY. 301 
 
 the toughest, and the most resisting of the whole ; it is this mem r 
 brane which is so essential in the arts, by forming leather when 
 combined with tannin. 
 
 The skiu which covers the animal body, as well as those mem- 
 branes that form the coats of the vessels, consists almost exclusive- 
 ly of gelatine ; and is capable of being converted into glue, size, 
 or jelly. 
 
 The cavities between the muscles and the skin are usually filled 
 with fat, which lodges in the cells of the membranous net before 
 mentioned, and gives to the external form (especially in the human 
 figure) that roundness, smoothness, and softness, so essential to 
 beauty. 
 
 Emily. And the skin itself is, I think, a very ornamental part of 
 the human frame, both from the fineness of its texture, and the va- 
 riety and delicacy of its tints. 
 
 Mrs. B. This variety and harmonious gradation of colours, pro- 
 ceed, not so much from the skin itself, as from the internal organs 
 which transmit their several colours through it, these tints being 
 only softened and blended by the colour of the skin, which is uni- 
 formly of a yellowish white. 
 
 Thus modified, the darkness of the reins appears of a pale blue 
 colour, and the floridness of the arteries is changed to a delicate 
 pink. In the most transparent parts, the skin exhibits the bloom of 
 the rose, whilst where it is more opaque, its own colour predomin- 
 ates ; and at the joints, where the bones are most prominent, their 
 whiteness is often discernible. In a word, every part of the human 
 frame seems to contribute to its external ornament ; and this not 
 merely by producing a pleasing variety of tints, but by a peculiar 
 kind of beauty which belongs to each individual part. Thus it is 
 to the solidity and arrangement of the bones that the human figure 
 owes the grandeur of its stature, and its firm and dignified deport- 
 ment. The muscles delineate the form, and stamp it with energy 
 and grace, and the soft substance which is spread over them smooths 
 their ruggedness, and gives to the contour the gentle undulations 
 of the line of beauty. Every organ of sense is a peculiar and sep- 
 arate ornament ; and the skin, which polishes the surface, and 
 gives it that charm of colouring so inimitable by art, finally con- 
 spires to render the whole the fairest work of the creation. 
 
 But now that we have seen in what manner the animal frame is 
 formed, let us observe how it provides for its support, ?nd how the 
 several organs, which form so complete a whole, are nourished and 
 maintained. 
 
 This will lead us to a more, particular explanation of the internal 
 organs : here we shall not meet with so much apparent beauty, be- 
 cause these parts were not intended by nature to be exhibited to 
 view ; but the beauty of design, in the internal organization of the 
 animal frame, is, if possible, still more remarkable than that of the 
 external parts. 
 
 We shall deferthis subject till our next interview. 
 
 1361. Of what does the skin consist ? 
 
 1362. On what is the human complexion or colour depending be- 
 sides the skin ? 
 
302 ON ANIMALISATION. 
 
 CONVERSATION XXV. 
 
 ON ANIMALISATION, NUTRITION, AND RESPIRATION. 
 
 Mrs. B. We have now learnt of what materials the animal sys- 
 tem is composed, and have formed some idea of the nature of its or- 
 ganization. In order to complete the subject, it remains for us to 
 examine in what manner it is nourished and supported. 
 
 Vegetables, we have observed, obtain their nourishment from va- 
 rious substances, either in their elementary state, or in a very sim- 
 ple state of combination ; as carbon, water, and salts, which they 
 pump up from the soil ; and carbonic acid and oxygen, which they 
 absorb from the atmosphere. 
 
 Animals, on the contrary, feed on substances of the most compli- 
 cated kind ; for they derive their sustenance, some from the animal 
 creation, others from the vegetable kingdom, and some from both. 
 
 Caroline. And there is one species of animals, which, not satisfied 
 with enjoying eiiher kind of food in its simple state, has invented 
 the art of combining them together in a thousand ways, and of ren- 
 dering even the mineral kingdom subservient to its refinements. 
 
 Emily. Nor is this all ; for our delicacies are collected from the 
 various climates of the earth, so that the four quarters of the globe 
 are often obliged to contribute to the preparation of our simplest 
 dishes. 
 
 Caroline. But the ver) T complicated substances which constitute 
 the nourishment of animals, do not, 1 suppose, enter into the sys- 
 tem in their actual state of combination ? 
 
 Mrs. B. So far from it, that they not only undergo a new ar- 
 rangement of their parts, but a selection is made of such as are 
 most proper for the nourishment of the body, and those only enter 
 into the system, and are animalised. 
 
 Emily. And by what organs is this process performed ? 
 .Mrs. B. Chiefly by the stomach, which is the organ of digestion, 
 and the prime regulator of the animal frame. 
 
 Digestion is the first step towards nutrition. It consists in redu- 
 cing into one homogeneous mass the various substances that are 
 taken as nourishment ; it is performed by first chewing and mixing 
 the solid aliment with the saliva, which reduces it to a soft mass, in 
 which state it is conveyed into the stomach, where it is more com- 
 pletely dissolved by the gastric juice. 
 
 This fluid (which is secreted into the stomach by appropriate 
 glands) is so powerful a solvent, that scarcely any substances will 
 resist its action. 
 
 Emily. The coats of the stomach, however, cannot be attacked 
 by it, otherwise we should be in danger of having them destroyed 
 when the stomach was empty. 
 
 1363. What is the subject of the 25th conversation ? 
 
 1364. Do the substances which constitute the nourishment of an- 
 .imals enter into their system, in their actual state of combination ? 
 
 1365. Where is the digestion performed ? 
 
 1366. What is the first operation in digestion ? 
 
 1367. What office is performed by the gastric juice ? 
 
ON RESPIRATION. 303 
 
 Mrs. B. They are probably not subject to its action ; as long, at 
 least, as life continues. But it appears, that when the gastric jaice 
 has no foreign substance to act upon, it is capable of occasioning a 
 degree of irritation in the coats of the stomach, which produces the 
 sensation of hunger. The gastric juice, together with the heat and 
 muscular action of the stomach, converts the aliment into an uni- 
 form, pulpy mass, called chyme. This passes into the intestines, 
 where it meets w'ith the bile and some other fluids, by the agency of 
 which, and by the operation of other causes hitherto unknown, the 
 chyme is changed into chyle, a much thinner substance, somewhat 
 resembling milk, which is pumped by immense numbers of small 
 absorbent vessels spread over the internal surface of the intestines. 
 These, after many circumvolutions, gradually meet and unite into 
 large branches, till they at length collect the chyle into one vessel, 
 which pours its contents into the great vein near the heart, by which 
 means the food, thus prepared, enters into the circulation. 
 
 Caroline. But 1 do not yet clearly understand how the blood, thus 
 formed, nourishes the body and supplies all the secretions ? 
 
 Mrs. B. Before this can be explained to you, you must first allow 
 me to complete the formation of the blood. The chyle may, indeed, 
 be considered as forming the chief ingredient of blood: but this fluid 
 is not perfect until it has passed through the lungs, and undergone 
 (together with the blood that has already circulated) certain neces- 
 sary changes that are effected by RESPIRATION. 
 
 Caroline. I am very glad that you are going to explain the nature 
 of respiration : I have often longed to understand it; for though we 
 talk incessantly of breathing, 1 never knew precisely what purpose 
 it answered. 
 
 Mrs. B. It is, indeed, one of the most interesting processes ima- 
 ginable ; but in order to understand this function well, it will be 
 necessary to enter into some previous explanations. Tell me, 
 Emily, what do you understand by respiration? 
 
 Emily. Respiration, I conceive, consists simply in alternately in- 
 spiring air into the lungs, and expiring it from them. 
 
 Mrs. B. Your answer will do very well as a general definition. 
 But, in order to form a tolerably clear notion of the various phenom- 
 ena of respiration, there are many circumstances to be taken into 
 consideration. 
 
 In the first place, there are two things to be distinguished in res- 
 piration, the mechanical and the chemical part of the process. 
 
 The mechanism of breathing depends on the alternate expansions 
 and contractions of the chest, in which the lungs are contained. 
 When the chest dilates, the cavity is enlarged, and (he air rushes in 
 at the mouth, to fill up the vacuum formed by this dilatation ; when 
 it contracts, the cavity is diminished and the air forced out again. 
 
 1368. How is the sensation of hunger produced ? 
 
 1369. At what state of animalisation is the aliment called chyme : 
 
 1370. Into what is it next changed ? 
 
 1371. How does chyle differ from chyme ? 
 
 1372. What forms the chief ingredieut of blood? 
 
 1373. What is respiration I 
 
 1374. On what depends the mechanism of breathing? 
 
 1375. What takes place when the chest dilates ? 
 
 1376. What takes place when it contracts? 
 
304 
 
 ON RESPIRATION. 
 
 Caroline. 1 thought that it was the lungs that contracted and ex- 
 panded in breathing. 
 
 Mrs. B. They do likewise ; but their action is only the conse- 
 quence of that of tb.e chest. The lungs, together with the heart and 
 largest blood vessels, in a manner fill up the cavity of the chest : 
 they could not, therefore, dilate, if the chest did not previously ex- 
 pand ; and, on the other hand, when the chest contracts, it com- 
 presses the lungs, and forces the air out of them. 
 
 Caroline. The lungs, then, are like bellows, and the chest is the 
 power that works them. 
 
 (Fig. 35. 
 
 Mrs. B. PreCiSelv SO. Here is a CtirioUS^pparatus to illustrate the mechanism 
 
 little figure which will assist me in explain- 
 ing the mechanism of breathing. 
 
 Caroline. What a droll figure ! a little 
 head fixed upon a glass bell, with a bladder 
 tied over the bottom of it. 
 
 Mrs. B. You must observe that there is 
 another bladder within the glass, the neck 
 of which communicates with the mouth of 
 the figure this represents the lungs con- 
 tained within the chest ; the other bladder, 
 which you see is tied loose, represents a 
 muscular membrane, called the dia- 
 phragm, which separates the chest from 
 the lower part of the body. By the chest, 
 therefore, I mean that large cavity in the 
 upper part of the body contained within the 
 ribs, the neck, and the diaphragm ; this 
 membrane is muscular, and capahle of con- 
 traction and dilatation. The contraction 
 
 may be imitated by drawing the bladder 
 tight over the bottom of the receiver, as I 
 can easily do by squeezing it in my hand, 
 when the air in the bladder, which repre- 
 sents the lungs will be forced out through A A> olMiML B Bladderre . 
 
 the mOUth Of the figure. presentinglungs. C. Bladder re- 
 
 presenting the Diaphragm. 
 
 Emily. See, Caroline, how it blows the flame of the candle in 
 breathing ! 
 
 Mrs. B. By letting the bladder loose again, we imitate the dila- 
 tation of the diaphragm, and the cavity of the chest being enlarged, 
 the lungs expand, and the air rushes in to fill them. 
 
 Emily. This figure, I think, gives a very clear idea of the process 
 *)f breathing. 
 
 Mrs. B. It illustrates, tolerably well, the action of the lungs and 
 diaphragm ; but those are not the only powers concerned in the en- 
 largement or diminution of the cavity of the chest; the ribs are also 
 possessed of a muscular motion for the same purpose ; they are al- 
 ternately drawn in, edgeways, to assist the contraction, and stretch- 
 
 1377. On what does the expansion and contraction of the lungs 
 depend ? 
 
 1378. What part of the body is called the chest? 
 3379. How would you explaio figure 36 :? 
 
ON RESPIRATION. 805 
 
 ed out, like the hoops of a barrel, to contribute to the dilatation of 
 the chest. 
 
 Emily. 1 always supposed that the elevation and depression of 
 the ribs were the consequence, not the cause, of breathing. 
 
 Mrs. B. It is exactly the reverse. The muscular action of the 
 diaphragm, together with that of the ribs, are the causes of the con- 
 traction and expansion of the chest ; and the air rushing into, and 
 being expelled from the lungs, are only consequences of those actions* 
 
 Caroline. I confess that 1 thought the act of breathing began by 
 opening the mouth for the air to rush in, and that it was the air 
 alone, which, by alternately rushing in and out, occasioned .the di- 
 latations and contractions of the lungs and chest. 
 
 Mrs. B. Try the experiment of merely opening your mouth : 
 the air will not rush in, till by an internal muscular action you pro- 
 duce a vacuum yes, just so, your diaphragm is now dilated, and 
 the ribs expanded. But you will not be able to keep them long in 
 that situation. Your lungs and chest are already resuming their 
 former state, and expelling the air with which they had just been 
 filled. This mechanism goes on more or less rapidly : but, in gene- 
 ral, a person at rest and in health will breathe between fifteen and 
 twenty five times in a minute. 
 
 We may now proceed to the chemical effects of respiration ; but, 
 for this purpose, it is necessary that you should previously have 
 some notion of the circulation of the blood. Tell me, Caroline, 
 what do you understand by the circulation of the blood ? 
 
 Caroline. I am delighted that you have come to this subject ; for 
 it is one that has long excited my curiosity. But I cannqt conceive 
 how it is connected with respiration. The idea that I have of the 
 circulation is, that the blood runs from the heart through the veins 
 all over the tody, and back again to the heart 
 
 Mrs. B. I could hardly have expected a better definition from 
 you : it is, however, not quite correct ; for you do not distinguish 
 the arteries from the veins, which, as we have already observed, 
 are two distinct sets of vessels, each having its own peculiar func- 
 tions. The arteries convey the blood from the heart to the extre- 
 mities of the body ; and the veins bring it back into the heart. 
 
 This sketch will give you an idea of ,the manner in which some 
 of the principal veins and arteries of the human body branch out 
 of the heart, which may be considered as a common centre to both 
 sets of vessels. The heart is a kind of strong elastic bag, or mus- 
 cular cavity, which possesses a power of dilating itself, for the pur- 
 poses of alternately receiving and expelling the blood, in order to 
 carry on the process of circulation. 
 
 Emily. Why are the arteries in this drawing painted red, and the 
 veins purple ? 
 
 Mrs. B. It is to point out the difference of the colour of the blood 
 in these two sets of vessels. 
 
 1380. What office do the ribs perform ? 
 
 1381. What causes the contraction and expansion of the chest ? 
 
 1382. How many times will a person, well and at rest, breathe 
 ia a minute ? 
 
 1383. In what manner is the circulation of blood carried on .? 
 
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ON RESPIRATION. 307 
 
 small ramification*. Here it comes in contact* with the air which 
 we breathe. The action of the air on the blood in the lungs, is in- 
 deed,' concealed from our immediate observation ; but we are able 
 to form a tolerable accurate judgment of it from the changes which 
 it effects, not only in the blood, but also on the air expired. 
 
 The air, after passing through the lungs, is found to contain all the 
 nitrogen inspired, but to have lost part of its oxygen, and to have 
 acquired a portion of watery vapor, and of carbonic acid gas. 
 Hence it is inferred, that when the air comes in contact with the 
 venous blood in the lungs, the oxygen attracts from it the supera- 
 bundant quantity of carbon with which it has impregnated itself dur- 
 ing the circulation, and converts it into carbonic acid. This gas- 
 eous acid, together with the redundant moisture from the lungsf 
 being then expired, the blood is restored to its former purity, that is, 
 to the state of arterial blood, and is thus again enabled to perform 
 its various functions. 
 
 Caroline. This is truly wonderful ! of all that we have yet learn- 
 ed, I do not recollect any thing that has appeared to me so curious 
 and interesting. I almost believe that I should like to study anato- 
 my now, though I have hitherto had so disgusting an idea of it. 
 Pray, to whom are we indebted for these beautiful discoveries ? 
 
 Mrs. B. Priestly and Crawford, in this country, and Lavoisier, 
 in France, are the principal inventors of the theory of respiration. 
 Of late years the subject has been farther illustrated and simplified 
 by the accurate experiments of Messrs Allyn and Pepys. But th 
 still more important and more admirable d'iscovery of the circula- 
 tion of the blood was made long before by our immortal country- 
 man, Hervey. 
 
 Emily. Indeed, I never heard any thing that delighted me so 
 much as this theory of respiration. But I hope, Mrs. B., that you 
 will enter a little more into particulars before you dismiss so inter- 
 esting a subject. We left the blood in the lungs to undergo the 
 salutary change ; but how does it thence spread to all the parts of 
 the body? 
 
 Mrs. B. After circulating through the lungs, the blood is collect- 
 ed into four large vessels, by which it is conveyed into the left ven- 
 tricle of the heart, whence it is propelled to all the different parts 
 of the body by a large artery, which gradually ramifies into mil- 
 lions of small arteries through the whole frame. From the extremi- 
 ties of these little ramifications the blood is transmitted to the veins, 
 
 * Not in actual contact. In this case it is obvious there would be 
 nothing to confine the blood and .prevent its flowing out. The air 
 cells are separated from the blood vessels by an extremely thin 
 membrane. C. 
 
 f The quantity of moisture discharged by the lungs in 24 hours, 
 may be computed at eight or nine ounces. 
 
 1390. What effect does respiration have on the air we breathe? 
 139-1. What becomes of the blood when it has become purified in 
 circulating through the lungs ? 
 
 1392. Who were the inventors of the received theory of respi- 
 tion ? 
 
 1393. Who discovered the circulation of the blood? 
 
 1394. After the blood is purified in the lungs, how is it spread to 
 'the rarious parts of the body ? 
 
808 ON EESPIKATION. 
 
 which bring it back to the heart and lungs, 'to go 'round again and 
 again in the manner we have just described. You see, therefore, 
 that the blood actually undergoes two circulations ; the one, through 
 the lungs, by which it is converted into pure arterial blood ; the 
 other, a general circulation by which nourishment is conveyed to 
 every part of the body ; and these are both equally indispensable 
 to the support of animal life. 
 
 Emily. But whence proceeds the carbon with which the blood is 
 impregnated when it comes into the lungs ? 
 
 Mrs. B. Carbon exists in a greater proportion in blood than in 
 organized animal matter. The blood, therefore, after supplying its 
 various secretions, becomes loaded with an excess of carbon, which 
 is carried off by respiration ; and the formation of new chyle from 
 the food affords a constant supply of carbonaceous matter. 
 
 Caroline. I wonder what quantity of carbon may be expelled 
 from the blood by respiration in the course of 24 hours ? 
 
 Mrs. B. It appears by the experiments of Messrs., Allyn and 
 Pepys that about 40,000 cubic inches of carbonic acid gas, are emit- 
 ted from the lungs of a healthy person, daily ; which is equivalent 
 to eleven ounces of solid carbon every 24 hours. 
 
 Emily. What an immense quantity! And pray how much of 
 carbonic acid gas do we expel from our lungs at each respiration ? 
 
 Jftrs. B. The quantity of air which we take into our lungs at 
 -ach inspiration^ about40 cubic inches, which contains a little less 
 than 10 cubic inches of oxygen ; and of those 10 inches, one-eighth 
 is converted into carbonic acid gas on passing once through the 
 lungs,* a change sufficient to prevent air which has only been 
 breathed once from suffering a taper to burn in it. 
 
 Caroline. Pray how does air come in contact with the blood in 
 the lungs ? 
 
 Mrs. B. I cannot answer this question without entering into an 
 explanation of the nature and structure of the lungs. You re- 
 collect that the venous blood, on being expelled from the right ven- 
 tricle enters the lungs to go through what we may call the lesser 
 circulation ; the large trunk or vessel conveys its branches out, at 
 its entrance into the lungs, into an infinite number of very fine ram- 
 ifications. The wind -pipe, which conveys the air from the mouth 
 into the lungs, likewise spreads out into a correspond ing number of 
 air vessels, which follow the same course as the blood vessels, form- 
 ing millions of very minute air cells. These two sets of vessels are 
 so interwoven as to form a sort of net-work, connected into a kind 
 of spongy mass, in which every particle of blood must necessarily 
 come in contact with a particle of air. 
 
 * The bulk of carbonic acid gas formed by respiration, is exactly 
 the same as that of the oxjgen gas which disappears. 
 
 1395. Whence proceeds the carbon with which the blood is im- 
 pregnated on its return to the lungs ? 
 
 1396. What quantity of carbon is expelled from the blood by res- 
 piration in 24 hours ? 
 
 1397. What is the quantity of air we take into our lungs at each 
 respiration ? 
 
 1398. How does the air come-in contact with the blood in the 
 lungs ? 
 
ON RESPIRATION. 309 
 
 Caroline. But since the blood and the air are contained in differ- 
 ent vessels, how can they come in contact ? 
 
 Mrs. B. They act on each other through the membrane which 
 forms the coats of these vessv! ; for although this membrane pre- 
 vents the blood and the air from mixing together in the lungs, yet it 
 is no impediment to their chemical action on each other.* 
 
 Emily. Are the lungs composed entirely of blood vessels and air 
 vessels ? 
 
 Mrs. B. I believe they are, with the addition only of nerves and 
 of a small quantity of the cellular substance before-mentioned, 
 which connects the whole into a uniform mass. 
 
 Emily. Pray, why are the lungs always spoken of in the plura! 
 number ? Ar6 there more than one ? 
 
 Mrs. B. Yes; for though they form but one organ, they really 
 consist of two compartments, called lobes, which are enclosed in sep- 
 arate membranes or bags, each occupying one side of the chest, and 
 being in close contact with each other, but without communicating 
 together. This is a beautiful provision of nature, in consequence of 
 which, if one of the lobes be wounded, the other performs the whole 
 process of respiration till the first is healed. 
 
 The blood, thus completed, by the process of respiration, form* 
 the most complex of all animal compounds, since it contains not on- 
 ly the numerous materials necessary to form the various secretions, 
 as saliva, tears, &c. but likewise all those that are required to nour- 
 ish the several parts of the body, as the muscles, bones, nerves,* 
 glands, &c.f 
 
 * It is not absolutely certain that the change which the blood un- 
 dergoes in the lungs is entirely owing to the loss of carbon ; since 
 experiments shew that any animal substance, eren the hand, when 
 confined in a portion of atmospheric air, lessens the quantity of ox- 
 ygen and produces a corresponding quantity of carbonic acid. It 
 is possible then, that the carbon produced by respiration, may be 
 owing merely to the contact between the air and the lungs. C. 
 
 f The process of secretion does not consist merely in the separa- 
 tion of certain materials from the blood by the secreting organ ; 
 but in many instances, entirely new products are formed, no traces 
 of which have been detected in the blood. For instance, the solid 
 matter of the bones is derived from the blood, yet not a particle of 
 phosphat of lime, (a substance composing the basis of the bone,) is 
 found in it. It appears, then, that the glands which are the organs 
 of secretion, have the power of producing from the ultimate atoms 
 of the blood, the variety of products peculiar to each. Thus, the 
 glands situated about the eyes secrete the tears, a saline, pellucid 
 fluid ; while the liver secretes from the same source, the bile, a 
 greenish, opake, bitter, and extremely nauseous substance. It is 
 most probable that we shall ever remain in profound ignorance, of 
 any mode of imitating these operations. 
 
 1399. If the blood and air are contained in separate vessels, how 
 can they come in contact ? 
 
 1400. Are the lungs entirely composed ot blood and air vessels ? 
 
 1401. Why are the lungs spoken of in the plural number? 
 
 1 402. What forms the most complex of all the animal compounds ? 
 
 1403. What is said of secretion in thenote ? 
 
310 ON RESPIRATION. 
 
 Emily. There seems to be a singular analogy between the blood 
 of animals and the sap of vegetables ; for each of these fluids con- 
 tains the several materials destined for the nutrition of the numer- 
 ous class of bodies to which they respectively belong. 
 
 Mrs. B. Nor is the production of these fluids in the animal and 
 vegetable systems entirely different ; for the absorbent vessels 
 which pump up the chyle from the stomach and intestines, may be 
 compared to the absorbents of the roots of plants, which suck up 
 the nourishment from the soil. And the analogy between the sap 
 and the blood may be still further traced, if we follow the latter in 
 the course of its circulation ; for in the living animal, we find every 
 where organs which are possessed of a power to secrete from the 
 blood and appropriate to themselves the ingredients requisite for 
 their support. 
 
 Caroline. But whence do these organs derive their respective 
 powers ? 
 
 Mrs. B. From a peculiar organization, the secret of which no 
 one has yet been able to unfold. But it must be ultimately by 
 means of the vital principle that both their mechanical and chemi- 
 cal powers are brought into action. 
 
 I cannot dismiss the subject of circulation without mentioning 
 perspiration, a secretion which is immediately connected with it, 
 and acts a most important part in the animal economy. 
 
 Caroline. Is not this secretion likewise made by appropriate 
 glands ? 
 
 Mrs. B. No ; it is performed by the extremities of the arteries, 
 which penetrate through the skin and terminate under the cuticle, 
 through the pores of which the perspiration issues. When this flu- 
 id is not secreted in excess, it is insensible, because it is dissolved 
 by the air as it exudes from the pores ; but when it is secreted 
 faster than it can be dissolved it becomes sensible, as it assumes its 
 liquid state. 
 
 Emily. This secretion bears a striking resemblance to the trans- 
 piration of the sap of plants. They both consist of the most fluid 
 parts, and both exude from the surface by the extremities of the 
 vessels through which they circulate. 
 
 Mrs. B. And the analogy does not stop there ; for, since it has 
 been ascertained that the sap returns into the roots of the plants, 
 the jesemblance between the animal and vegetable circulation is 
 become still more obvious. The latter, however, is far from being 
 complete, since, as we observed before, it consists only in a rising 
 and descending of the sap, whilst in animals the blood actually cir- 
 culates through every part of the system. 
 
 We have now, I think, traced the process of nutrition, fro-n the 
 introduction of the food into the stomach, to its finally becoming a 
 constituent part of the animal frame. This will, therefore, be a fit 
 period to conclude our present conversation. 
 
 What further remarks we have to make on the animal economy 
 shall be reserved for our next interview. 
 
 1404. What analogy is there between the blood of animals and 
 vegetables ? 
 
 1405. Whence do the several organs derive their respective 
 powers ? 
 
 1406. How does perspiration take place ? 
 
 1407. When is perspiration insensible ? 
 
 1408. When does it become sensible ? 
 
ON ANIMAL HEAT. 311 
 
 CONVERSATION XXVI. 
 
 ON ANIMAL HEAT ; AND ON VARIOUS ANIMAL PRODUCTS. 
 
 Emily- Since our last interview, I have been thinking much of 
 the theory of respiration ; and I cannot help being struck with the 
 resemblance which it appears to bear to the process of combustion. 
 For in respiration, as in most cases of combustion, the air suffers a 
 change, and a portion of its oxygen combines with carbon, pro- ' 
 ducing carbonic acid gas. 
 
 Mrs. B. I am much pleased that this idea has occurred to you ; 
 these two processes appear so very analagous, that it has been sup- 
 posed that a kind of combustion actually takes place in the lungs ; 
 not of the blood, but of the superfluous carbon which the oxygen 
 attracts from it. 
 
 Caroline. A combustion in our lungs ! that is a curious idea in- 
 deed ! But, Mrs. B., how can you call the action of the air on the 
 blood in the lungs combustion, when neither light nor heat are 
 produced by it ? 
 
 Emily. 1 was going to make the same objection. Yet I do not 
 conceive how the oxygen can combine with the carbon, and pro- 
 duce carbonic acid without disengaging heat ? 
 
 Mrs. B. The fact is that heat is disengaged.* Whether any light 
 be evolved, I cannot pretend to determine ; but that heat is pro- 
 duced in considerable and very sensible quantities is certain,; and 
 this is the principal, if not the only source of ANIMAL HEAT. 
 
 Emily. How wonderful that the very process which purifies and 
 elaborates the blood, should afford an inexhaustible supply of in- 
 ternal heat ? 
 
 Mrs. B. This is the theory of animal heat in its original simplici- 
 ty, such nearly as it was first proposed by Black and Lavoisier. It 
 appeared equally clear and ingenious ; and was at first generally 
 adopted. But it was objected on second consideration, that if the 
 whole of the animal heat was evolved in the lungs, it would necessa- 
 rily be much less in the extremities of the body, than immediately at 
 its source ; which is not found to be the case. This objection, how- 
 ever, which was by no means frivolous, is now satisfactorily removed 
 by the following consideration > Venous blood has been found by 
 
 * It has been calculated that the heat produced by respiration in 
 12 hours, in the lungs of a healthy person, is such as would melt 
 about 100 pounds of ice. 
 
 1409. What analogy is there between respiration and com- 
 bustion ? 
 
 1410. What is the principal source of animal heat ? 
 
 1411. What objection has been made to the hypothesis which 
 ascribes animal heat to respiration ? 
 
 1412. If the whole of animal heat is evolved in the lungs, why is 
 it not less at the extremities of the body than at its source? 
 
312 ON ANIMAL HEAT. 
 
 experiment to have less capacity for heat, than arterial blood ; 
 whence it follows that the blood, in gradually passing from the ar- 
 terial to the venous state, during the circulation, parts with a por- 
 tion of caloric, by means of which heat is diffused through every 
 part of the body.* 
 
 Emily. More and more admirable ! 
 
 Caroline. The cause of animal heat was always a perfect mystery 
 
 * This is substantially Dr. Crawford's theory of animal heat : and 
 that it is a most beautiful and ingenious one, cannot be denied. Sub- 
 sequent experiments have, however, proved its fallacy. Dr. John 
 Davy has shown that the difference of capacity for heat, between the 
 two kinds of blood is much less than was supposed by Dr. Crawford ; 
 the capacity of arterial being only one per cent above that of ve- 
 nous blood. Now it is obvious that this minute difference cannot ac- 
 count for animal temperature ; nor is it certain that even this small 
 quantity of heat is given out to the system. Another objection is 
 the result of an experiment of Mr. Brodie. This indeed seerns to 
 'settle the question that animal heat does not depend on any change 
 which the blood undergoes in the lungs. He found that on keeping 
 up an artificial respiration in the lungs of a decapitated animal, the 
 blood was changed from black to red, and carbonic acid was giv- 
 en out as usual ; but that the animal grew cold faster than another 
 dead one, where such artificial respiration was not kept up. 
 
 This, it is obvious would be the case, unless heat was caused by 
 respiration, as the air forced into the lungs would tend to cool the 
 animal. 
 
 Prof. Cooper, of Philadelphia, proposes another theory. " I see 
 no material difficulty," says he, " in accounting for the production 
 of animal heat from the doctrine of latent heat. The fluids of the 
 body are incessantly employed to renew the solids ; when a fluid 
 is converted into a solid , heat or caloric is precipitated. This takes 
 place every moment very gradually in every part of the system." 
 
 We are ignorant of the train of arguments by which the learned 
 Professor supports his theory. But, if on the one hand, the conver- 
 sion of a fluid into a solid produces heat, so it is equally well proved, 
 that the conversion of a solid into a fluid produces cold. Now the 
 solid parts of the body, after being deposited from the fluids, are 
 again converted into fluids by the absorbents. This theory, then, 
 accounts for the production of heat only when the deposition is 
 greater than the absorption, as during the growth of the system. 
 
 From some experiments, made by Mr. Brodie, and Dr. Philip, 
 they have been induced to believe that animal temperature depends 
 on the influence of the nerves. 
 
 In regard to this theory, it may be observed, that in some instan- 
 ces where the nervous influence seems to be suspended, the heat of 
 the part remains much the same as in health. 
 
 This subject has excited the attention of the learned and curiou 
 in all ages, and a great variety of theories hare been offered to acs 
 
 1413. What objection is there to Dr. Crawford's theory of animal 
 heat? 
 
 1414. What is Professor Cooper's theory of animal heat ? 
 
 1415. What was the opinion of Mr. Brodie, and Dr. Philip, on the 
 tubject of animal heat ? 
 
ON ANIMAL HEAT. * 313 
 
 to me, and I am delighted with its explanation. But, pray, Mrs. B., ' 
 can you tell ine what is the reaspn of the increase of heat that takes 
 place in a fever ? 
 
 Emily. Is it not because we then breathe quicker, and, there- 
 fore, more heat is disengaged in the system ? 
 
 Mrs. B. This may be one reason : but I should think that the 
 principal cause of the heat experienced in fevers, is that there is no 
 vent for the caloric which is generated in the body. One of the 
 most considerable secretions is the insensible perspiration ; this is 
 constantly carrying off c iloric in a latent state ; but during the hot 
 stage of a fever, the pores are so contracted, that all perspiration 
 ceases, and the accumulation of caloric in the bod]' occasions those 
 burning sensations which are so painful. 
 
 Emily. This is, no doubt, the reason why the perspiration which 
 often succeeds the hot stage of a fever, affords so much relief. If I 
 had kuown this theory of animal heat when 1 had the ferer last 
 summer, I think I should have found some amusement in watching 
 the chemical processes that were going on within me, 
 
 Cardtine. But exercise likewise produces animal heat, and that 
 must be quite in a different manner. 
 
 JYIrs. B. Not so much as you think ; for the more exercise you 
 take, the more the body is stitnul ited, and requires recruiting. For 
 this purpose, the circulation of the blood is quickened, the breath 
 proportionally accelerated, and consequently a greater quantity of 
 caloric evolved. 
 
 Caroline. True ; after running very fast, I gasp for breath, my 
 respiration is quick and hard, and it is just then that I begin to feel 
 hot. 
 
 Emily. It would seem, then, that violent exercise should produce 
 fever. 
 
 Mrs. B. Net if the person is in a good state of health ; for the 
 a Uiitional caloric is then carried off by the perspiration which suc- 
 ceeds. 
 
 Emily. What admirable resources nature hns provided for us ! 
 
 i" By the production of animal heat she has enabled us to keep up the 
 
 temperature of our bodies above that of inanimate objects ; and 
 
 whenever this source becomes too abundant, the excess is carried 
 
 off by perspiration. 
 
 Mrs. B. It is by the same law of nature that we are enabled, in 
 .all climates, and in all seasons, to preserve our bocHfcs of an equal 
 temperature, or at least very nearly so. 
 
 Caroline. You cannot mean to say that our bodies are of the 
 same temperature in summer, and in winter, in England, and in the 
 West Indies ! 
 
 count for it. We have seen none, however, to which insuperable 
 objections may not be brought. We must, therefore, at present 
 be contented with attributing the production of animal warmth to 
 the energies of the vital principle ; leaving it to future generations 
 to determine and define its immediate cause. C. 
 
 1416. What is the reason of heat in a fever? 
 
 1417. Why does exercise produce an increase of animal heat f 
 
 1418. Why does n,ot violent exercise produce fevers ? 
 
 27 
 
314 ON ANIMAL HEAT. 
 
 Mrs. B. Yes, I do ; at least if you speak of the temperature of 
 the blood, and the internal parts of the body : for those which are 
 immediately in contact with the atmosphere, such as the hands and 
 face, will occasionally get warmer, or colder, than the internal or 
 more sheltered parts. If you put the bulb of a thermometer in 
 your mouth, which is the best way of ascertaining- the real tempera- 
 ture of your body, you will scarcely perceive any difference in its 
 indication, whatever may be the difference of temperature of the 
 atmosphere. 
 
 Caroline. And when I feel overcome by heat, 1 am really Dot 
 hotter than when I am shivering- with cold ? 
 
 Mrs. B. When a person in health feels very hot, whether from 
 internal heat, from violent exercise, or from the temperature of the 
 atmosphere, his body is certainly a little warmer t'ran when he feels 
 very cold ; but this difference is much smaller than our sensations 
 would make us believe; and the natural standard is soon restored 
 by rest and by perspiration. It is chiefly the external parts that are 
 warmer 1 , and I am sure you will be surprised to hear that j,he inter- 
 nal temperature of the body scarcely ever descends below ninety- 
 five or ninety-six degrees, and seldom attains one hundred and four, 
 or one hundred and five degrees, even in the most violent fevers. 
 
 Emily. The greater quantity of caloric, therefore, that we receive 
 from the atmosphere in summer, cannot raise the temperature of 
 our bodies beyond certain limits, as it does that of inanimate bodies, 
 because an excess of caloric is carried off by perspiration 
 
 Caroline. But the temperature of the -atmosphere, and conse- 
 quently, th-at of inanimate bodies, is surely never so high as that of 
 animal heat. 
 
 Mrs. 2?. I beg your pardon. In the East and West Indies, and 
 sometimes in the southern parts of Europe, the atmosphere is fre- 
 quently above ninety-eight degrees, which is the common tempera- 
 ture of animal heat. Indeed, even in this country, it occasionally 
 happens that the sun's rays, setting full on an object, elevate its 
 temperature above that point. 
 
 In illustration of the power which our bodies have to resist the 
 effects of external beat, Sir Charles Blagden, with some other gen- 
 tlemen, made several very curious experiments. He remained for 
 some time in an oven heated to a temperature not much inferior to 
 that of boilin^water, without suffering any other inconvenience than 
 a profuse perspiration, which he supported by drinking plentifully. 
 Emily. He could scarcely consider the perspiration as an incon- 
 venience, since it saved him from being baked by giving vent to 
 the excess of caloric. 
 
 Caroline. I always thought, 1 confess, that it was from the heat 
 of the perspiration that we suffered in summer. 
 
 Mrs. B. You now find that you are quite mistaken. Whenever 
 evaporation takes place, cold, you know, is produced in conse- 
 quence of a quantity of caloric being carried off in a latent state ; 
 
 1419. Does the degree of animal heat vary with the change of 
 climate ? 
 
 1420. How is it that the temperature of the body remains essen- 
 tially the same in summer and winter, and in different climates ? 
 
 1421. What experiment was made by Sir Charles Blagden upon 
 this subject ? 
 
ON ANIMAL HEAT. 315 
 
 this is the case with p-r rspiration, and it is in this way that it affords 
 relief. It is on that account, also, that we are so apt to catch cold, 
 wheu in a state of profuse perspiration. It is for the same reason 
 that tea is most refreshing in summer, though it appears to heat you 
 at the moment you drink it. 
 
 Emily. And in winter, on the contrary, tea is pleasant on ac- 
 count of its heat. 
 
 Mrs. JB. Yes ; for we have then rather to guard against a defi- 
 ciency than an excess of caloric, and you do not find that tea will 
 excite perspiration in winter, unless after dancing, or any other 
 violent exercise. 
 
 Caroline. What is the reason that it is dangerous to eat ice after 
 dancing, or to drink any thing cold when one is very hot ? 
 
 Mrs.B. Because the loss of heat arising from the perspiration, 
 conjointly with the chill occasioned by the cold draught, produced 
 more cold than can be borne with safety, unless you continue to use 
 the same exercise after drinking that you did before ; for the heat 
 occasioned by the exercise will counteract the effects of ihe cold 
 drink, and the danger will be removed. You may, however, con- 
 trary to the common notion, consider it as a rule, that cold liquids 
 may at all times be drunk with perfect safety, however hot you 
 may feel,* provided you are not at the moment in a slate of great 
 perspiration, and on condition that you keep yourself in gentle ex- 
 ercise afterwards. 
 
 Emily. But since we are furnished with such resources against 
 the extremes of heat and cold, I should have thought that all cli- 
 mates would have been equally wholesome. 
 
 Jtfrs. B. That is true, in a certain degree, in regard to those who 
 have been accustomed to them from birth ; for we find that the na- 
 tives of those climates, which we consider the most deleterious, are 
 as healthy as ourselves ; and if such climates are unwholesome to 
 those who are habituated to a more moderate temperature, it is be- 
 cause the animal economy does not easily accustom itself to con- 
 siderable changes. 
 
 Caroline. But, pray, Mrs. B., if the circulation preserves the body 
 of an uniform temperature, how does it happen that animals are 
 sometimes frozen ? 
 
 JUrs B. Because, if more heat be carried off by the atmosphere 
 than the circulation can supply, the cold will finally prevail, the 
 
 
 * The common notion on this subject is certainly the most safe. 
 A person heated, and almost exhausted by exercise on a hot day, 
 ought nerer to drink any cold liquid, except in very small quanti- 
 ties at a time. Not a summer passes but we hear of deaths by 
 drinking cold water after violent exercise C. 
 
 1422. Why are we apt to take cold in a state of profuse perspira- 
 tion ? 
 
 1423. Why is hot tea refreshingln warm weather of summer ? 
 14-24. Why is not a quantity of caloric carried off by the use of 
 
 hot drink in winter, as well as summer? 
 
 1425- Why is it dangerous to drink cold water when in a state 
 of profuse perspiration ? 
 
 1426. If the circulation preserves the body of a uniform tempera- 
 ture, how does it happen that animals are sometimes frozen f 
 
316 ON ANIMAL HEAT. 
 
 heart will cease to beat, and the animal will be frozen. And, like- 
 wise, if the body remained long exposed to a degree of heat, greater 
 than the perspiration could carry off, it would, at least, lose the 
 power of resisting its destructive influence. 
 
 Caroline. Fish, I suppose, have no animal heat, but only partake 
 of the temperature of the water in which they live.* 
 
 Emily. And their coldness, no doubt, proceeds from their not 
 breathing ? 
 
 Mrs. B. All kinds of fish breathe more or less, though in a much 
 smaller degree than land animals. IN or are they entirely destitute 
 of animal heat, though, for the same reason, they are much colder 
 than other creatures. They have comparatively but a very small 
 quantity of blood, therefore but very little oxygen is required, and 
 a proportionally small quantity of animal heat is generated. 
 
 Caroline. But how can fish breathe underwater? 
 
 J\lrs. B. They breathe by means of the air which is dissolved in 
 the water ; and if you put them into water, deprived of air by boil- 
 ing, thsy are soon suffocated. 
 
 If a fish is confined in a vessel of water closed from the air, it 
 soon dies : ind any fish put in afterwards would be killed imme- 
 diately, as all the air had been previously consumed. 
 
 Caroline. Are there any species of animals that breathe more 
 than we do ? 
 
 Mrs. B. Yes ; birds, of all animals, breathe the greatest quantity 
 of air in proportion to their size ; and it is to this that they are sup- 
 posed to owe the peculiar firmness and strength of their muscles, by 
 which they are enabled to support the riolent exertion of flying. 
 
 This difference between birds and fish, which may be considered 
 as the two extremes of the scale of muscular strength, is well worth 
 observing. Birds, residing constantly with the atmosphere, sur- 
 rounded by oxygen, and respiring in greater proportions than any 
 other species of animals, are endowediwith a greater degree of mus- 
 cular strength, whilst the muscles offish, on the contrary, are flac- 
 cid and oily ; these animals are comparatively Yeeble in their mo- 
 tions, and their temperature is scarcely above that of the water in 
 which they live. This is, in all probability, owing to their imper- 
 fect respiration : the quantity of hydrogen and carbon, that is in 
 consequence accumulated in their bodies, forms the oil which is so 
 
 
 * Animals belonging to the order Cetae of Naturalists, though 
 they inhabit the sea, breathe atmospheric air, and have hot, red 
 blood. This order includes whales, dolphins, narwals, &c. C. 
 
 1427. Why are fish colder than land animals ? 
 
 1428. How can they breathe under water ? 
 
 1429. How can it be proved that fish cannot live without air ? 
 1430 What animals breathe the greatest-quantity of air accord- 
 ing to their size ? 
 
 1431. To what is the firmness and great strength of muscles in 
 birds owing ? 
 
 1432. To what is the oily nature of fish and amphibious animals 
 owing ? 
 
ON ANIMAL PRODUCTS. 317 
 
 strongly characteristic of that species of animals, and which relaxes 
 and softens the smail quantity of fibrine which their muscles contain. 
 
 Caroline. But, Mrs. B-, there are some species of birds that fre- 
 quent both elements, as, for instance, ducks and other water fowl. 
 Of what nature is the flesh of these ? 
 
 Jtfrs. B. Such birds, in general, make but little use of their 
 wings ; if they fly, it is but feebly, and only to a short distance. 
 Their flesh, too, partakes of the oily nature, and even in taste some- 
 times resembles that of fish. This is the case not only with the 
 various kinds of water fowls, but with all other amphibious animals, 
 as the otter, the crocodile, the lizard, &c. 
 
 Caroline. And what is the reason that reptiles are so deficient in 
 muscular strength ? 
 
 Mrs. B. It is because they usually live under ground, and seldom 
 come into the atmosphere. They have imperfect, and sometimes 
 no discernible organs of respiration ; they partake, therefore, of the 
 soft oily nature of fish; indeed many of them are amphibious, as 
 frogs, toads, and snakes, and very few of them find any difficulty in 
 remaining a length ot time under water.* Whilst, on the contrary, 
 the insect tribe, that are so strong in proportion to their size, and 
 alert in their motions, partake of the nature of birds, air being their 
 peculiar element, and their organs of respiration being compara- 
 tively larger than in other classes of animals. 
 
 I have now given you a short account of the principal animal 
 functions. However interesting the subject may appear to you, a 
 fuller investigation of it would, 1 fear, lead us too far from our ob- 
 ject. 
 
 Emily. Yet I shall not quit it without much regret ; for of all th 
 applications of chemistry, these appear to me the most curious and 
 most interesting. 
 
 Caroline. But, Mrs. B., I must remind you that you promised t(* 
 give us some account of the nature of milk. 
 
 Mrs. B. True. There are several other animal productions that 
 deserve likewise to be mentioned. We shall begin with milk, 
 which is certainly the most important and the most interesting of 
 all the animal secretions. 
 
 Milk, like all oilier animal substances, ultimately yields by analy- 
 sis, oxygen, hydrogen, carbon, and nitrogen. These are combined 
 in it under the forms of albumen, gelatine, oil, and water. But milk 
 contains, besides, a considerable portion of phosphat of lime, the 
 purposes of which I have already pointed out. 
 
 * Amphibious animals have the power of suspending respiration 
 for a considerable time. It is in consequence of this, that they are 
 enabled to live under water. C. 
 
 1433. What is the nature of the flesh of amphibious animals ? 
 
 1434. Why are reptiles so deficient in muscular strength ? 
 143,5. How are amphibious animals enabled to remain a long lime 
 
 under water ? 
 
 1436. What are the ingredients of milk ? 
 
 1437. Into what may milk be decomposed without any chemical 
 assistance ? 
 
 27* 
 
318 ON ANIMAL PRODUCTS. 
 
 Caroline. Yes ; it is this salt which serves to nourish the tender 
 bones of the suckling. 
 
 Jtfrs B. To reduce milk to its elements, would be a very com- 
 pligated. as well as useless operation ; but this fluid, without any 
 chemical assistance, may be decomposed into three parts, cream, 
 curds, and whey. These constituents of milk have but a very slight 
 affinity lor each other,and you find accordingly that cream separates 
 from milk by mere standing-. It consists chiefly of oil, which being 
 lighter than the other parts of the milk, gradually rises to the sur- 
 face. It is of this, you know, that butter is made, which is nothing 
 more than oxygenated cream. 
 
 Caroline. Butter, then, is somewhat analagous to the waxy sub- 
 stance formed by the oxygenation of vegetable oil. 
 
 Mrs. B. Very much so. 
 
 Emily. But is the cream oxygenated by churning ? 
 
 Mrs. B. Its oxygenation commences* previous to churning, 
 merely by standing exposed to the atmosphere, from which it ab- 
 sorbs oxygen. The process is afterwards completed by churning : 
 the violent motion which this operation occasions, brings every par- 
 ticle of cream in contact with the atmosphere, and thus facilitates 
 its oxvgenation. 
 
 Caroline. But the effect of churning, 1 have often observed in the 
 dairy, is to separate the cream into two substances, butter and but- 
 ter-mills. 
 
 Jllrs. B. That is to say, in proportion as the oily particles of the 
 cream become oxygenated, they separate from the other constitu- 
 ent parts of the cream in the form of butter. So by churning yon 
 produce, on the one hand, butter, or oxygenated oil ; and, on the 
 other, butter-milk, or cream deprived of oil. But if you make but- 
 ter by churning new milk instead of cream, the butter-milk will 
 then be exactly similar in its properties to cream or skimmed milk. 
 
 Caroline. Yet butter-milk is very different from common skim- 
 med milk. 
 
 Mrs. B. Because you know it is customary, in order to save time 
 and labor, to make butter from cream alone. In this case, there- 
 fore, the butter-milk is deprived of the creamed milk, which contains 
 both the curd and whey. Besides, in consequence of the rnilk re- 
 maining exposed to the atmosphere during the separation of the 
 cream, the latter becomes more or less acid, as well as the butter- 
 milk which it yields in churning. 
 
 Emily. Why should not the butter be equally acidified by oxyge- 
 nation ? 
 
 Mrs. B. Animal oil is not so easily acidified as the other ingredi- 
 ents of milk. Butter, therefore, though usually made of sour cream, 
 is not sour itself, because the oily part of the cream had not been 
 
 * It is proper to mention that the oxygenation of cream, which is 
 taken for granted in the above theory, is a disputed fact. C. 
 
 1437. What causes the cream to rise on the top ? 
 
 1438. What is the chemical name of butter? 
 
 1439. Why does churning convert cream to butter? 
 
 1440. When separation takes place in the cream, why is the bu 
 ter-milk sour and the cream sweet? 
 
ON ANIMAL PRODUCTS. 319 
 
 acidified. Butter, however, is susceptible of becoming 1 acid by an 
 excess of oxygen ; it is then said to be rancid, and produces the se- 
 bacic acid, the same as that which is obtained from fat. 
 
 Emily. If that be the case, might not rancid butter be sweetened 
 by mixing with it some substance that would take the acid from it? 
 
 Mrs. B. This idea has been suggested by Sir H. Davy, who 
 supposes, that if rancid butter were well washed in an alkaline so- 
 lution, the alkali would separate the acid from the butter. 
 
 Caroline. You said just now that creamed milk consisted of curd 
 and whey. Pray how are these separated ? 
 
 Mrs. B. They may be separated by standing fora certain length 
 of time exposed to the atmosphere ; but this decomposition may be 
 almost instantaneously effected by the chemical agency of a variety 
 of substances. Alkalies, rennet,* and indeed almost all animal sub- 
 stances, decompose milk by combining with the curds. 
 
 Acids and spiritous liquors, on the other hand, produce a decom- 
 position by combining with the whey. In order, therefore, to ob- 
 tain the whey pure, rennet or alkaline substances, must be used to 
 attract the curds from it. 
 
 But if it be wished to obtain the curds pure, the whey must be 
 separated by acids, wine, or other spiritous liquors. 
 
 Emily. This is a very usefel piece of information ; for I find 
 white-wine whey, which 1 sometimes take when I have a cold, ex- 
 tremely heating; now, if the whey were separated by means of an 
 alkali instead of wine, it would not produce that effect. 
 
 Mrs. B. Perhaps not But I would strenuously advise you not 
 to place too much reliance on your slight chemical knowledge in 
 medical matters. 1 do not know why whey is not separated from 
 curd by rennet, or by an alkali, for the purpose which you mention, 
 but I strongly suspect that there must be some good reason why 
 the preparation by means of wine is generally preferred. I can, 
 however, safely point out to you a method of obtaining whey with- 
 out either alkali, rennet or wine ; it is by substituting lemon jaice, 
 a very small quantity of which will separate it from the curds. 
 
 Whey, as an article of diet, is very wholesome, being remarkably 
 light of digestion. But its effect, taken medicinally, is chiefly, I 
 believe, toexcite perspiration, by being drunk warm on going to bed. 
 
 From whey a substance may be obtained in crystals by evapora- 
 tion, called sugar of milk. This substance is sweet to tbe taste, 
 and in its composition is so analogous to common sugar, that it is 
 susceptible of undergoing the vinous fermentation. 
 
 * Rennet is the name given to a watery infusion of the coats of 
 the stomach of a sucking calf. Its remarkable efficacy in promot- 
 ing coagulation is supposed to depend on the gastric juice with 
 which it is impregnated. 
 
 1441. What canses butter to become rancid ? 
 
 1442. How may rancid butter be made sweet ? 
 
 1443. How is milk from which the cream has been taken, decom- 
 posed, or converted into curd or whey ? 
 
 1444. How is pure whey obtained from milk ? 
 
 1445. How is pure curd obtained from it ? 
 
 1446. Why is whey as an article of diet, wholesome ? 
 J447. How is the sugar of milk obtained ? 
 
320 ON ANIMAL PRODUCTS. 
 
 Caroline. Why then, is not wine, or alcohol, made from whey ? 
 Mrs. B. The quantity of sugar contained in milk is so trifling, 
 that it can hardly answer that purpose. I have heard of only one 
 instance of its being-used for the production of a spiritous liquor and 
 this is by the Tartan Arabs : their abundance of horses, as well as 
 their scarcity of fruits, has introduced the fermentation of mares' 
 milk, by which they produce a liquor called koumi&s. Whey is 
 likewise susceptible of being acidified by combining with oxygen 
 from the atmosphere. It then produces the lactic acid, which you 
 may recollect is classed with the animal acids, as the acid of milk. 
 Let us now see what are the properties of curds. 
 Emily. I know that they are made into cheese ; but I have heard 
 that for that purpose they are separated from the whey, by the ren- 
 net, and yet, this you have just told us, is not the method of ob- 
 taining pure curds ? 
 
 Mrs. B. Nor are pure curds so well adapted to the formation of 
 cheese. For the nature and flavor of the cheese depend in a great 
 measure, upon the cream or oily matter which is left in the curds ; 
 so that if every particle of cream be removed from the curds, the 
 cheese is scarcely eatable. Rich cheeses, such as Cream and Stil- 
 ton cheeses, derive their excellence from the quantity, as well as 
 the quality of the cream that enters into their composition. 
 
 Caroline. I had no idea that milk was such an interesting com- 
 pound. In many respects there appears to me to be a very striking 
 analogy between milk and the contents of an egg, both in respect 
 to their nature and their use. They are, each of them, composed 
 of the various substances necessary for the nourishment of the 
 young animal, and equally destined for that purpose. 
 
 Jllrs. B. There is, however, a very essential difference. The 
 young animal is formed as well as nourished, by the contents of the 
 egg-shell ; whilst milk serves as nutriment to the suckling, only af- 
 ter it is born. 
 
 There are several peculiar animal substances which do not en- 
 ter into the general enumeration of animal compounds, and which, 
 however, deserve to be mentioned. 
 
 Spermaceti is of this class ; it is a kind of oily substance obtained 
 from the head of the whale, which, however, must undergo a cer- 
 tain preparation before it is in a fit slate to be made into candles. 
 It is not much more combustible than tallow, but it is pleasanter to 
 burn, as it is less fusible and less greasy. 
 
 Ambergris is another substance derived from a species of whale. 
 It is, however, seldom obtained from the animal itself, but is gener- 
 ally found floating on the surface of the sea. 
 
 Wax, you know, is a concrete oil, the peculiar product of the bee, 
 part of the constituents of which may probably be derived from 
 flowers, but so prepared by the organs of the bee, and so mixed 
 with its own substance, as to be decidedly an animal product. Bees' 
 wax is naturally of a yellow color but it is bleached by long expo- 
 sure to the atmosphere, or may be instantly whitened by the oxy- 
 
 1448. Do pure curds make good cheese ? 
 
 1449. On what does the quantity of cheese depend ? 
 
 1450. From what is spermaceti obtained ? 
 
 1451. What is ambergris ? 
 
ON ANIMAL PRODUCTS. 321 
 
 muriatic acid. The combustion of wax is far more perfect than 
 that of tallow, and consequently produces a greater quantity of light 
 and heat. 
 
 Lac is a substance- very similar to wax in the manner of its form- 
 ation ; it is the product of an insect, which collects its ingredients 
 from flowers, apparently for the purpose of protecting its eggs from 
 injury. It is formed into cells, fabricated with as much skill as 
 those of the honey comb, but differently arranged. The principal 
 use of lac is in the manufacture of sealing-wax, and in making var- 
 nishes and lacquers. 
 
 JtfwvA:, civet, and castor, are other particular productions, from 
 different species of quadrupeds. The two first are very powerful 
 perfumes ; the latter has a nauseous smell and taste, and is only 
 used medicinally. 
 
 Caroline. Is it from this substance that castor oil is obtained ? 
 
 Mrs. B. No. Far from it, for castor oil is a vegetable oil, ex- 
 pressed from the seeds of a particular plant ; and has not the least 
 resemblance to the medicinal substance obtained from the castor. 
 
 Silk is a peculiar secretion of the silk worm, with which it builds 
 its nest or cocoon. This insect was originally brought to Europe 
 from China. Silk in its chemical nature, is very similar to the 
 hair and wool of animals ; whilst in the insect it is a fluid, which is 
 coagulated, apparently by uniting with oxygen as soon as it comes 
 in contact with the air. The moth of the silk-worm ejects a liquor 
 which appears to contain a peculiar acid, called bombic, the proper- 
 ties of which are but very little known. 
 
 Emily. Before we conclude the subject of the animal economy, 
 shall we not learn by what steps dead animals return to their ele- 
 mentary state? 
 
 Mrs. B. Animal matter, although the most complicated of all 
 natural substances, returns to its elementary state by one single 
 spontaneous process, the putrid fermentation. By this, the albu- 
 men, fibrine, &c. are slowly reduced to the state of oxygen, hydro- 
 gen, nitrogen and carbon ; and thus the circle of changes through 
 which these principles have passed is finally completed. They first 
 quitted their elementary form, or their combination with unorgan- 
 ized matter, to enter into the vegetable system. Hence they were 
 transmitted to the animal kingdom ; and from this they return again 
 to their primitive simplicity, soon to re-enter the sphere of organ- 
 ized existence. 
 
 When all the circumstances necessary to produce fermentation 
 do not take place, animal, like vegetable matter, is liable to a par- 
 tial or imperfect decomposition, which converts it into a combusti- 
 ble substance very like spermaceti. I dare say that Caroline, who 
 is so fond of analogies, will consider this a kind of animal bitumen. 
 
 Caroline. And why should I not, since the processes which pro- 
 duce these substances are so similar? 
 
 Mrs. B. There is, however, one considerable difference ; the state 
 of bitumen seems permanent, whilst that of animal substances, thus 
 imperfectly decomposed, is only transient ; and unless precautions 
 be taken to preserve them in that state, a total dissolution infallibly 
 
 1452. How does wax compare with tallow for combustion ? 
 
 1453. What is lac? 
 
 1454. What account could you give of silk ? 
 
 1455. How does dead animal matter return to its original state ? 
 
322 
 
 APHLOGISTIC LAMP. 
 
 ensues. This circumstance, of the occasional conversion of animal 
 matter into a kind of spermaceti, is oflate discovery. A manufac- 
 ture has in consequence been established near Bristol, in which, by 
 exposing the carcasses of horses and other animals for a length of 
 time under water, the muscular parts are converted into this sper- 
 maceti-like substance. The bones afterwards undergo a different 
 process to produce hartshorn, or, more properly ammonia, and phos- 
 phorus ; and the skin is prepared for leather. 
 
 Thus art contrives to enlarge the sphere of useful purposes, for 
 which the elements were intended by nature , and the productions 
 of the several kingdoms are frequently arrested in their course, and 
 variously modified, by human skill, which compels them to contri- 
 bute, under new forms, to the necessities or luxuries of man. 
 
 But all that we enjoy, whether produced by the spontaneous ope- 
 rations of nature or the ingenious efforts of art, proceed alike from 
 the goodness of Providenre. To God alone man owes the admira- 
 ble faculties which enable him to improve and modify the produc- 
 tions of naiure, no less than (hose productions themselves. In con- 
 templating the worl<s,of the creation, or studying the inventions of 
 art, let us, thererefore, never forget the Divine Source from which 
 they proceed ; and thus every acquisition of knowledge will prove 
 a lesson of piety and virtue. 
 
 DESCRIPTION OF THE APHLOGISTIC, OR FLAMELESS 
 LAMP. 
 
 BY DR. J. L. COMSTOCK, OF HARTFORD. 
 
 Aphlogistic, or Flameless Lamp. 
 
 Fig. 1. -* . The Coil of Flatuia wire. B. The tflass tube cuntaj, 
 Tick. Fig. 2. The Lamp complete. I). The tube lor charging. 
 
 In the con- 
 struction of this 
 Lamp, the ob- 
 ject is to keep a 
 coil of wire in a 
 state of ignition, 
 without either 
 fl.une or smoke. 
 The principle 
 on which it is 
 constructed, I 
 believe, was first 
 discovered by 
 Sir H. Davy. 
 He, found that 
 on heating the 
 end of a piece of 
 plat ina wire red 
 hot, and instant- 
 jy holding it 
 near the surface 
 
 1456. What manufacture is it mentioned has recently .been form- 
 ed in Bristol ? 
 
APHLOGISTIC LAMP. 323 
 
 of some ether, placed in a wine glass, the wire was kept at a red 
 heat as long as the experiment was continued. 
 
 Whether Sir Humphrey pursued the subject any further, 1 am 
 not informed. It is most probable, however, dial he did not, as it 
 is stated in a London paper of the last year, that Prof. Ure of Glas- 
 gow, had determined the circumstances which modify the perform- 
 anceof tii-^lanna. uiMut one constructed by himwas in full opera- 
 tion in that city (London) and had excited much public curiosity. 
 This notice contained -oine directions, concerning- the size of the 
 wire, lo be used, and the manner of coiling it. I have however seen 
 no description of this lamp whicbMvould enable one readily to con- 
 struct it. The following may therefore, interest such readers, as 
 have seen an account of so curious a discovery. 
 
 The principle on which the aphlogistic lamp is constructed in- 
 volves two conditions, which are absolutely requisite, viz. that we 
 make use of a combustible substance which evaporates at a low de- 
 gree of heat, and a metal which is a bad conductor of caloric. For 
 the combustible, alcohol seems best suited to this purpose. Sulphu- 
 ricetk er, aside from its high price, and disagreeable smell, I have 
 sometimes found to fail ; the ignition ceasing without any obvious 
 cause. 
 
 In regard to the metal, gold and silver, both fail in consequence 
 of the rapidity with which they conduct caloric. Silver, too, would 
 soon be destroyed by theintense heat. Iron, although so bad a con- 
 ductor, as to remain ignited for a time, soon fails, being converted 
 into red oxide. Platina seems to be the only metal adapted to our 
 purpose, being a slow conductor of caloric, and not easily oxidated 
 at the highest temperatures. 
 
 This is to be drawn into wire of 56-1000 or 60-1000 of an inch in 
 diameter, being about the size of card, or brass wire, No. 26. Ex- 
 perience has shown that this size succeeds belter than any other. 
 If larger, the heat is carried off too fast, and the ignition ceases. If 
 much finer, it does not retain sufficient heat at the lower part of the 
 coil to keep up the evaporation of the alcohol from the wick. 
 
 The coiling of the wire, and the adjustment of the wick, are the 
 most difficult parts of the construction. 
 
 The coil, A. fig. -1. page 322, is made by winding the wire round 
 a piece of wood, cut of the proper size and shape. The size is de- 
 termined by the bore of the glass tube, allowing for the diameter of 
 the wire. The shape is plane cylindrical in that part which enters 
 the tube ; and slightly conical where it projects above the tube, as 
 seen in the figure. (1 believe this is the best shape, though I have 
 succeeded as well when the coil was of the same shape throughout.] 
 
 In winding the coil, it is best that the turns of the wire should 
 come in contact. Afterwards it is to be gently extended, so as to 
 leave the turns as nearly as possible to each other, without touching. 
 
 The diameter of the coil is about one sixth of an inch where it en- 
 ters the tube. Its length half an inch, or a little less, containing 
 from twenty to thirty turns of the wire. The projection above the 
 tube is about one half the length. 
 
 B. Fig. 1. is a glass tube, containing a cotton wick, which by ca- 
 pillary attraction carries the alcohol up to the platina coil. The 
 length of this is arbitrary, being from one to three or fourinches. 
 The bore is about the sixth of an inch, so as barely to admit the coil. 
 The wick, consisting of eight or ten threads, is first drawn through 
 
324 APHLOGISTIC LAMP. 
 
 the tube, and then introduced about half way into the coil, so as to 
 come even with the top of the tube. This requires very nice adjust- 
 ment. If the wick is too high the wire is rapidly cooled by the al- 
 cohol, and ignition ceases in a few moments. If too low, the evap- 
 oration by the heat of the wire is insufficient. If, however, the 
 other parts are well constructed, a few trials will ensure success. 
 
 Fig-. 2. shows the lamp complete. The body of it is a low vial or 
 inkstand, capable of holding about two ounces of alcohol. It is 
 stopped accurately with a cork, which is covered for ornament, 
 with tinfoil. The aperture for admitting the tube and wick, is made 
 with a hot iron. ^ 
 
 D. is a small tube through which the alcohol is poured. A (hop- 
 ping tube is convenient for (his purpose, but a small funnel is easily 
 made by cutting off an inch of the neck of a broken retort, into 
 which is pushed a cork, and through this a small quill. Another 
 orifice still, for Letting off the air, as the alcohol goes in, may be 
 made through the cork. The orifices, of course, are to be stopped, 
 to prevent evaporation, after the lamp is charged. 
 
 When the lamp is completed and charged, the alcohol is inflamed 
 by holding the coil in the blaze of a candle. After letting it burn for 
 a few minutes, the flame is blown out, when if every thing is properly 
 adjusted, the wire will continue red hot until the alcohol is exhausted. 
 
 The explanation why the ignition of the wire is permanent, seems 
 to be sufficiently simple. Alcohol when in the state of vapour, com- 
 bines with oxygen with great facility. The temperature of the wire 
 is first raised by the fla'me of the candle to about 600 degrees, Fah- 
 renheit. This degree of heat is such as to effect the combustion of 
 the alcohol with the oxygen of the atmosphere. When this is once 
 effected, the caloric extricated by the combustion of the alcohol, is 
 sufficient to keep the coil at a red heat, which again is the tempera- 
 ture at which the alcohol is combustible, so that one portion of alco- 
 hol by the absorption of oxygen, and the consequent extrication of 
 heat, lays the foundation for the combustion of another portion ; and 
 as the alcohol rises in a constant stream, so the effect is constant. 
 The stream of vapour is much increased by the heat of the lower 
 part of the coil, where it embraces the wick, and the temperature 
 of the alcohol is increased before it reaches the part of the coil 
 where combustion is effected. Sometimes the last, or upper turn of 
 the wire only is kept red hot. 
 
 This lamp, though one of the most curious inventions of the age, 
 is not merely a curiosity. The facility and certainty with which by 
 means of a match, a light maybe obtained from it, constitutes its 
 utility. The proper matches for this purpose are prepared by dip- 
 ping the common brimstone matches into a paste made by mixing 
 two parts of white sugar with one part of chlorate (oxy muriat) of 
 potash. The red French matches are of this kind, and answer the 
 purpose completely. 
 
 In cases where a light might be wanted, but a constant one would 
 be offensive, this lamp might be a great convenience ; a light being 
 immediately obtained by merely touching a match to the platina 
 coil, and then to the wick of the candle. Physicians or others who 
 are liable to be called up in the night would also find it convenient. 
 
 The aphlogistic lamp, with the proper matches, may he obtained 
 . at Mr. Charles Hosmer's Variety Store, in this City. 
 
A VOCABULARY 
 
 OF 
 
 CHEMICAL TERMS. 
 
 A. 
 
 Acetates. Compounds formed by the combination of a base with acetic acid. 
 
 Acids. Compounds formed by the combination of oxygen with certain ele- 
 mentary bodies, forming in general, a class of substances which are sour 
 to the taste, and which unite with alkalies and metallic oxyds to form salts. 
 
 Acidules. Substances formed by the natural combination of some acids 
 with a quantity of potash. The oxalic and tartanc acids are examples. 
 
 Aeriform fluids. Elastic fluids. Atmospheric air, and the gases are of this 
 kind. Their aeriform state is owing to the caloric with which their bases 
 are combined. 
 
 Affinity, chemical. A term used to express that peculiar propensity which 
 substances of different kinds have to unite with each other, as acids and 
 alkalies, &c. 
 
 of aggregation. That force is so called by which substances of the 
 
 same kind tend to unite, without changing their qualities. 
 
 -of composition. That force by which substances of different kinds 
 
 combine, and forma third, which differs from either of the two first, be- 
 fore the combination. Thus muriatic acid and soda form common salt. 
 
 Albumen. Coagulable lymph. It is contained in animal substances, as the 
 serum of the blood. The white of eggs is albumen. 
 
 Alcohol. Rectified spirit of wine. It is always the same, from whatever 
 kind of spirit it is distilled. 
 
 Alkalies* Peculiar substances which have a caustic burning taate, and a 
 strong tendency to combination, particularly with acids, and with water. 
 
 Alloys. A combination of any two metals, except mercury. Brass is an 
 alloy of copper and zinc. 
 
 Amalgam. A mixture of mercury with any other metal. 
 
 Analysis. Separation of the constituent parts of compounds, for the pur- 
 pose of detecting their composition. This is done by re-agents. 
 
 Annealing Rendering substances tough, which before were brittle. The 
 metals are annealed by heating them red hot, and then cooling them 
 gradually. 
 
 Arseniates. Salts formed by the combination of a base with the arsenic acid . 
 
 Azote. This name is given by the French chemists to nitrogen, which see. 
 
 B. 
 
 Balsams. Resinous, semi-fluid substances, which are obtained from certain 
 
 trees by making incisions. 
 Barometer. An instrument which indicates the variations of the pressure 
 
 of the atmosphere, as thermometers do of heat and cold. 
 Base. A term used by chemists to denote the substance to which an acid 
 
 is united to form a salt. Thus soda is the base of common salt. 
 Benzoates. Salts formed by the union of the benzoic acid with a base. 
 Blow-pipe. An instrument to increase and direct the flame of a lamp for 
 
 the analysis of minerals, and for other chemical purposes. 
 Borates. Salts formed by the combination of any base with the acid of borax. 
 
 Calcareous. A chemical term formerly applied to describe chalk, marble 
 and all other combinations of lime with carbonic acid. 
 
 28 
 
326 A VOCABULARY 
 
 Calcination. The armlication of heat to saline, metallic, or other substan- 
 ces ; so regulated <R to deprive them of moisture, &c, and yet preserve 
 them in a pulverulent form. 
 
 Caloric. The chemical term for the matter of heat. 
 
 free. Is caloric ifra separate state, or, if attached to other susbtan- 
 
 ces, not chemically united with them. 
 
 latent. Is the term made use of to express that portion of caloric 
 
 which is chemically united to any substance, so as to become apart of 
 the said substance. 
 
 Calorimeter. An instrument for ascertaining the quantity of caloric disen- 
 gaged from any substance that may be the object of experiment. 
 
 Galx. An old term made use of to describe a metallic oxide. 
 
 Camphor ates. Salts formed by the combination of any base with the cam- 
 phoric acid. 
 
 Capillary. A term usually applied to the rise of sap in vegetables, or the 
 rise of any fluid in very small tubes ; owing to a peculiar kind of attrac- 
 tion, called capillary attraction. 
 
 Carbon. The basis of charcoal. 
 
 Carbonates. Salts formed by the combination of any base with carbonic acid. 
 
 Carburets. Compound substances, of which carbon forms one of the con- 
 stituent parts. Thus plumbago, which is composed of carbon and iron, 
 is called carburet of iron. 
 
 Causticity. That quality in certain substances by which they burn or cor- 
 rode animal bodies to which they are applied. It is best explained by the 
 doctrine of chemical affinity. 
 
 Chalybeate. A term descriptive of those mineral waters which are impreg- 
 nated with iron. 
 
 Charcoal. Wood burnt in close vessels : it is an oxide of carbon, and gen- 
 erally contains a small portion of salts and earth. Its carbonaceous mat- 
 ter may be converted by combustion into carbonic acid gas. 
 
 Chlorine. A name lately given to the substance usually called oxy-muriatic 
 acid. Its compounds are called by the name of their bases with the end- 
 ing of ane. As phosphorane, sulphurane, &c. 
 
 Chromates. Salts formed by the combination of any base with the chromic 
 acid. 
 
 Citrates. Salts formed by the combination of any base with citric acid. 
 
 Coal. A term applied to the residuum of any dry distillation of animal or 
 vegetable matters. 
 
 Cohesion. A force inherent in all the particles of all substances, excepting 
 light and caloric, which prevents bodies from falling in pieces. 
 
 Coiumbates. Salts formed by the combination of any base with the colum- 
 bic acid. 
 
 Combination. A term expressive of a true chemical union of two or more 
 substances ; in opposition to mere mechanical mixture. 
 
 Combustibles. Certain substances which are capable of combining mere or 
 less rapidly with oxygen. They are divided by chemists into simple and 
 compound combustibles. 
 
 Combustion. The act of absorption of oxygen by combustible bodies from 
 atmospheric or vital air. The word decombustion is sometimes used by 
 the French writers to signify the opposite operation. 
 
 Crucibles. Vessels of indispensable use in chemistry in the various opera- 
 tions effusion by heat. They are made of baked earth, or metal, in the 
 form of an inverted cone. 
 
 Crystallization. An operation of nature, in which various earths, salts, 
 and metallic substances, pass from a fluid to a solid state, assuming cer- 
 tain determinate geometrical figures. 
 
 Crystallization, water of. That portion which is combined with salts in the- 
 act of crystallizing, and becomes a component part of the said saline sub- 
 stances. 
 
 Cupel. A vessel made of calcined bones, mixed with a small proportion of 
 clay and water. It is used whenever gold and silver are refined, by melt- 
 ing them with lead. The process is called cupellation. 
 
OF CHEMICAL TERMS. 327 
 
 D. 
 
 Decomposition. The separation of the constituent principles of compound 
 bodies by chemical means. 
 
 Deflagration. The vivid combustion that is produced whenever nitre, mix- 
 ed with an inflammable substance, is exposed to a red heat. It may be at- 
 tributed to the extrication of oxygen from the nitre, and its being trans- 
 ferred to the inflammable body ; as any of the nitrates or oxygenized mu- 
 riates will produce the same effect. 
 
 Deliquescence of solid saline bodies, signifies their becoming moist, or liquid, 
 by means of water which they absorb from the atmosphere in consequence 
 of their great attractions for that fluid. 
 
 Deoxidize, (formerly deoxidate.) To deprive a body of oxygen. 
 
 Deoxidizernent. A term made use of to express that operation by which one 
 substance deprives another substance of its oxygen. It is called unburn- 
 ing a body, by the French chemists. 
 
 Detonation. An explosion with noise. It is most commonly applied to the 
 explosion of nitre, when thrown upon heated charcoal. 
 
 Digestion. The effect produced by the continued soaking of a solid sob- 
 stance in a liquid, with the application of heat. 
 
 Digester, Papiri's. An apparatus for reducing animal or vegetable substan- 
 ces to a pulp or jelly expeditiously. 
 
 Distillation. A process for separating the volatile parts of a substance from 
 the more fixed, and preserving them both in a state of separation. 
 
 Ductility. A quality of certain bodies, in consequence of which they may 
 be drawn out to a certain length, without fracture. 
 
 Dulcification. The combination of mineral acids with alcohol. Thus we 
 have dulcified spirit of nitre, dulcified spirit of vitriol, &c. 
 
 E. 
 
 Edulcoration. Expressive of the purification of a substance by washing with 
 water. 
 
 Effervescence. An intestine motion which takes place in certain bodies, oc- 
 casioned by the sudden escape of a gaseous substance. 
 
 Efflorescence. A term commonly applied to those saline crystals which be- 
 come pulverulent on exposure to the air, in conseqnence of the loss of a 
 part of the water of crystallization. 
 
 Elasticity. A force in bodies, by which they endeavour to restore themselves 
 to the posture from whence they were displaced by an external force. 
 
 Elastic fluids. A name sometimes given to vapours and gases. Vapour is 
 called an elastic fluid ; gas, a permanently elastic fluid. 
 
 Elective Attractions. A term used by Bergmann and others to designate 
 what we now express by the words chemical affinity. When chemists 
 first observed the power which one compound substance has to decompose 
 another, it was imagined that the minute particles of some bodies had a 
 preference for some other particular bodies ; hence this property of mat- 
 ter acquired the term elective attraction. 
 
 Elements. The simple, constituent parts of bodies which are incapable of 
 decomposition ; they are frequently called principles. 
 
 Empyreuma. A peculiar and indescribably disagreeable smell, arising from 
 the burning of animal and vegetable matter in close vessels. 
 
 Ethers. Volatile liquids formed by the distillation of some of the acids with 
 alcohol. 
 
 Evaporation. The conversion of fluids into vapour by heat. This appears 
 to be nothing more than a gradual solution of the aqueous particles in at- 
 mospheric air, owing to the chemical attraction of the latter for water. 
 
 Eudiometer. An instrument invented by Dr. Priestley for determining the; 
 purity of any given portion of atmospheric air. The science of investiga- 
 ting the different kinds of gases is called eudiometry. 
 
 F. 
 
 Fermentation. A peculiar spontaneous motion which takes place in all vege- 
 table matter, when exposed for a certain time to a proper degree of tem- 
 perature. 
 
328 A VOCABULARY 
 
 flbrine. That white fibrous substance which is left after freely washing the 
 coagulum of the blood, and which chiefly composes the muscular fibre. 
 
 Flowers. In chemical language, are solid, dry substances, reduced to a pow- 
 der by sublimation. Thus we have flowers of arsenic, sal. ammoniac, of 
 sulphur, &c. which are arsenic, sal. ammoniac, and sulphur, unaltered ex- 
 cept in appearance. 
 
 Fluates. Salts formed by the combination of any base with fluoric acid. 
 
 Fluidity. A term. applied to all liquid substances. Solids are converted to 
 fluids by combining with a certain portion of caloric. 
 
 Flux. A substance which is mixed with metallic ore, or other bodies, to 
 promote their fusion ; as an alkali is mixed with silex in order to form glass. 
 
 Fulmination. Thundering, or explosion with noise. We have fulminating 
 silver, fulminating gold, and other fulminating powders, which explode 
 with a loud report by friction, or when s'ightly heated. 
 
 Fusion. The state of a body which was solid in the temperature of the at- 
 mosphere, and is now rendered fluid by the artificial application of heat. 
 
 G 
 
 Gallates. Salts formed by the combination of any base with gallic acid. 
 
 Galvanism. A new science which offers a variety of phenomena, resulting 
 from different conductors of electricity placed L in different circumstancea 
 of contact ; particularly the nerves of the animal body. 
 
 Gas. All solid substances when converted into permanently elastic fluids by 
 caloric, are called gases. 
 
 Gaseous. Having the nature and properties of gas. 
 
 Gasometer. A name given to a variety of utensils and apparatus contrived to 
 measure, collect, preserve, or mix the different gases. An apparatus of this 
 kind is also used for the purpose of administering pneumatic medicines. 
 
 Gelatine. A chemical term for animal jelly. It exists particularly in the ten- 
 dons and the skin of animals. 
 
 Gluten. A vegetable substance somewhat similar to animal gelatine. It is 
 the gluten of wheat flour which gives it the property of making good 
 bread, and adhesive paste. Other grain contains a much less quantity of 
 this nutritious substance. 
 
 Grain. The smallest weight made use of by chemical writers. Twenty grains 
 make a scruple: 3 scruples a drachm ; 8 drachms, or 480 grains make an 
 ounce; 12 ounces, or 5760 grains, a pound troy. The avoirdupois pound 
 contains 7000 grains. 
 
 Granulation. The operation of pouring a melted metal into water, in order 
 to divide it into small particles for chemical purposes. Tin is thus granu- 
 lated by the dyers before it is dissolved in the proper acid. 
 
 Gravity, specific. This differs from absolute gravity in as much as it is the 
 weight of a given measure of any solid or fluid body, compared with the 
 same measure of distilled water It is generally expressed by decimals. 
 
 Gums. Mucilaginous exudations from ctrtaia trees. Gum consists of lime, 
 carbon, oxygen, hydrogen, and nitrogen, with a little phosphoric acid. 
 
 Heat, matter of. See Caloric. 
 
 Hermetically. A term -applied to the closing of the orifice of a glass tube, so 
 as to render it air-tight. Hermes, or Mercury, was formerly supposed to 
 have been the inventor of Chemistry ; hence a tube which was closed for 
 chemical purposes, was said to be Hermetically or chemically sealed. It 
 is usually done by melting the end of the tube by means of a blowpipe. 
 
 Hydrogen. A simple substance ; one of the constituent parts of water. 
 
 gas. Solid hydrogen united with a large portion of caloric. It is 
 the lightest of all the known gases. Hence it is used to inflate balloons: 
 It was formerly called inflammable air. 
 
 Hydro-Carbonates. Combinations of carbon with hydrogen are described by 
 this term. Hydro-carbonate gas is procured from moistened charcoal by 
 distillation. 
 
 Hydrogenized sulphurets. Certain bases combined with sulphuretted hydro- 
 gen. 
 
 Hydro-Oxides. Metallic oxides combined with water. 
 
OF CHEMICAL TERMS. 329 
 
 Hydrometers. Instruments for ascertaining the specific gravity of spiritous 
 liquors or other fluids. 
 
 Hygrometers. Instruments for ascertaining the degree of moisture in at- 
 mospheric air. 
 
 Hypcroxygenized A term applied to substances which are combined with 
 
 - the largest possible quantity of oxygen. We have muriatic acid, oxygeni- 
 zed muriatic acid, and hyperoxygenized muriatic acid. The latter can 
 be exhibited only in combination. 
 
 Inflammation. A phenomenon which takes place on mixing certain sub- 
 stances. The mixture of oil of turpentine with strong nitrous acid is an 
 instance of this peculiar chemical effect. 
 
 Infusion, A simple operation to procure the salts, juices, and other virtues 
 of vegetables by means of water. 
 
 Intermediates. A term made use of when speaking of chemical affinity. Oil , 
 for example, has no affinity for water, unless it be previously combined 
 with an alkali , it then becomes soap, and the alkali is said to be the z'nter- 
 medinm which occasions the union. 
 
 K. 
 
 Kali. A genus of marine plants which is burnt to procure mineral alkal i 
 by afterwards lixiviating the ashes. 
 
 Laboratory. A room fitted up with apparatus for the performance of chem- 
 ical operations. 
 
 Lactates. Salts formed fey the combination of any base with lactic acid. 
 Lakes. Certain colours made by combining the colouring matter of cochineal 
 
 or of certain vegetables, with pure alumine, or with oxide of tin, zinc, &c. . 
 Lamp, Jlrgand's. A kind of lamp much used for chemical experiments. It 
 
 is made on the principle of a wind furnace, and thus produces a great de- 
 gree of light and heat without smoke. 
 Letts. A glass, convex on both sides, for concentrating the rays of the sun. 
 
 It is employed by -chemists in fusing refractory substances which cannot 
 
 be operated on by an ordinary degree of heat. 
 Levigation. The grinding down of hard substances to an impalpable paw- 
 
 der on a stone with a miller, or in a mill adapted to the purpose. 
 Litharge. An oxide of lead which appears in a state of vitrification. It is 
 
 formed in the process of separating silver from lead. 
 Lixiviation. The solution of an alkali or a salt in water, or in some other 
 
 fluid, in order to form a lixivium. 
 
 Lixivium. A fluid impregnated with an alkali or with a salt. 
 Lute. A composition for closing the junctures of chemical vessels to pre- 
 vent the escape of gas or vapour -in distillation. 
 
 M. 
 Maceration. The steeping of a solid body in a fluid, in order to soften it, 
 
 without impregnating the fluid. 
 
 Malates. Salts formed by the combination of any base with malic acid. 
 Malleability. That property of metals which g'ives them the capacity of 
 
 being extended and flattened by hammering. It is probably occasioned 
 
 by latent caloric. 
 Massicot. A name given to the yelio-w oxide of lead, as minium is applied 
 
 to the red oxide. 
 
 Matrass. Another name for a "bolt-head. 
 Menstruum. The fluid in which a solid body is dissolved. Thus water is a 
 
 menstruum for salts, gums, &c. and spirit of wine for resins. 
 Metallic Oxides. Metals combined with oxygen. By this process they are 
 
 generally reduced to a pulverulent form ; are changed from combustible to 
 
 incombustible substances ; and receive the property of being soluble m 
 
 acids. 
 Mineral. Any natural substance of a metallic, earthy, or saline nature^ 
 
 whether simple or compound, is deemed a mineral. 
 
 28* 
 
330 A VOCABULARY 
 
 Mineralizers. Those substances which are combined with metals in their 
 ores ; such are sulphur, arsenic, oxygen, carbonic acid, &c. 
 
 Mineralogy. The science of fossils and minerals. 
 
 Mineral Waters. Waters which hold some metal, earth, or salt, in solu- 
 tion. They are frequently termed Medicinal Waters. 
 
 Molybdiates. Salts formed by the combination of any base with the molyb- 
 dicacid. 
 
 Mordants. Substances which have a chemical affinity for particular col- 
 ours ; they are employed by dyers as a bond to unite the colour with the 
 cloth intended to be dyed. Alum is of this class. 
 
 Mucilage. \ glutinous matter obtained from vegetables, transparent and 
 tasteless, soluble in water, but not in spirit of wine. It chiefly consists of 
 carbon and hydrogen, with a little oxygen. 
 .^funites. Salts formed by the combination of any base with the mucous acid. 
 
 .Muffle. A semi-cylindrical utensil, resembling the tilt of a boat, made of 
 baked clay : its use is that of a cover to cupels in the assay furnace, to 
 prevent the charcoal from failing upon the metal, or whatever is the sub- 
 ject of experiment. 
 
 Muriates. Salts formed by the combination of any base with muriatic acid. 
 
 N. 
 
 Natron. One of the names for mineral alkali, or soda. 
 
 Neutralize. When two or more substances mutually disguise each other's 
 properties, they are said to neutralize one another. 
 
 Neutral Salt. A substance formed bj the union of an acid with an alkali, 
 an earth, or a metallic oxide, in such proportions as to saturate both the 
 base and the f cid. 
 
 Nitrates. Salts formed by the combination of any base with nitric acid. 
 
 Nitrogen. A simple substance, by the French chemists called azote. It 
 enters into a variety of compounds, and forms more than three parts in 
 four of atmospheric air. O. 
 
 Ochres. Various combinations of the earths with oxide, orcarbonate of iron. 
 
 Ores. Metallic earths, which frequently contain several extraneous mat- 
 ters; such as sulphur, arsenic, &c. 
 
 Oxalates. Salts formed by the combination of any base with oxalic acid. 
 
 Oxide. Any substance combined with oxygen, in a proportion not sufficient 
 to produce acidity. 
 
 Oxidize. To combine oxygen with a body without producing acidity. 
 
 Oxidizement The operation by which any substance is combined with ox- 
 ygen, in a degree not sufficient to produce acidity. 
 
 Oxygen. A. simple substance composing the greatest part of water, and 
 part of atmospheric air. 
 
 gas. Oxygen converted to a gaseous state by caloric. It is also 
 
 called vital air. It forms nearly one fourth of atmospheric air. 
 
 Oxygenize. To acidity a substance by oxygen. Synonymous with oxygen- 
 ate ; but the former is the better term. 
 
 O.rygenizement. The production of acidity by oxygen. 
 
 PeVicle. A thin skin which forms on the surface of saline solutions and otlj- 
 
 er liquors, when boiled down to a certain strength. 
 .Phlogiston. An old chemical name for an imaginary substance, supposed to 
 
 be a combination of fire with some other matter, and a constituent part of 
 
 all inflammable bodies, and of many other substances. 
 Phosphates. Salts formed by the combination of any base with phosphoric 
 
 acid. 
 Phosphites. Salts formed by the combination of any base with phosphorous 
 
 acid. 
 Phfjsphurets. Substances formed by an union with phosphorus. Thus we 
 
 have phosphuret of lirne, phosphuretted hydrogen, &c. 
 Plumbago. Carburet of iron, or the black lead of commerce. 
 Pneumatic. Any thing relating to the airs and gasses. 
 trough. A vessel filled in part with water or mercury, for the pur- 
 
OP CHEMICAL TERMS. 831 
 
 pose of collecting gases, so that they may be readily removed from one 
 vessel to another. 
 
 Precipitate. Any matter which, having been dissolved in a fluid, falls to 
 the bottom of the vessel, on the addition of some other substance capable 
 of producing a decomposition of the compound, in consequence of its at- 
 traction either for the menstruum or for the matter which was before 
 held in solution. 
 
 Precipitation. That chemical proces? by which bodies dissolved, mixed, 
 or suspended in a fluid, are separated from that fluid, and made to gravi- 
 tate to the bottom of the vessel. 
 
 Prussiates. Salts formed by the combination of any base with prussic acid. 
 
 Putrefaction. The last fermentative process of nature, by which organized 
 bodies are decomposed so as to separate their principles, for the purpose 
 of reuniting them by future attractions, in the production of new compo- 
 sitions. 
 
 Pyrites. An abundant mineral found on the English coasts, and elsewhere. 
 Some are sulphuretsof iron, and others sulphurets of copper, with a por- 
 tion of alumine and silex. The former are worked for the sake of the sul- 
 phur, and the latter for sulphur and copper. They are also called Mar- 
 casites anil Fire-stone. 
 
 martial. That species of pyrites which contains iron for its basis. 
 
 See a full account of these minerals in Henckel's Byritologia. 
 
 Pyrometer. An instrument invented by Mr. Wedgwood for ascertaining 
 the degrees of heat in furnaces and intense fires. See Philosophical tran- 
 sactions, vol. Ixii. and Ixiv. and Chemical Cavech. 
 
 Pyrophori. Compound substances which heat of themselves, and take fire on 
 "the admission of atmospheric air'. See an account of a variety of experi- 
 ments with these compositions in Wiegleb's Chemistry, quarto, p. 622, &c. 
 
 Q. 
 
 Quartz. A name given to a variety of siliceous earths, mixed with a small 
 portion of lime or alumine. Air. Kirwan confines the term to the purer 
 kind of silex. Rock crystal and the amethvst are species of quartz 
 
 R. 
 
 Radicals. A chemical term for the Elements of bodies ; which see. 
 
 compound. When the base of an acid is composed of two OP more 
 
 substances, it is said that the acid ts formed of a compound radical. The 
 sulphuric acid is formed with! a simple radical ; but the vegetable acids, 
 which have radicals composed of hydrogen and carbon, are said to be acids 
 with compound radicals. 
 
 Reagents. Substances which are added to mineral waters or other liquids 
 as tests to discover their nature and composition. 
 
 Receivers. Globular glass vessels adapted to retorts for the purpose of pre- 
 serving and condensing the volatile matter raised in distillation. 
 
 Rectification, is nothing more than the re-distilling a liquid to render it more 
 pure, or more concentrated, by abstracting a part of it onlv. 
 
 Reduction The restoration of metallic oxides to their original state of me- 
 tals ; which is usually effected by means ot charcoal and fluxes. 
 
 Refining. The process of separating the perfect metals from other metallic 
 substances by what is called cupellation. 
 
 Refrigeratory. A contrivance of any kind, which, by containing cold water, 
 answers the purpose of condensing the vapour or gas that arises in distil- 
 lation. A worm-tub is a refrigeratory. 
 
 Regulus. In its chemical acceptation, signifies a pure metallic substance, 
 freed from all extraneous matters. 
 
 Repulshn. A principle whereby the particles of bodies are prevented from 
 coming in actual contact. It is thought to be owing to caloric, which has 
 been called the repulsive power. 
 
 Resins. Veg' -table juices concreted by evaporation either spontaneously or 
 by fire. Their character is solubility in alcohol, and not in water. It seems 
 that they owe their solidity chiefly to their union with oxygen. 
 
 Retort. A vessel in the shape of a pear, with its neck bent downwards, us" 
 
A VOCABULARY 
 
 ed in distillation ; the extremity of which neck fits into that of another 
 bottle called a receiver. 
 
 Rock-costal. Crystallized silex. S. 
 
 Saccholates. Salts formed by the combination of any base with saccholac- 
 tic acid. 
 
 SaUfiable bases. All the metals, alkalies, and earths, which are capable of 
 combining wiih acids, and forming salts, are called salifiuble bases. 
 
 Saline. Partaking of the properties of salt. 
 
 Sails, neutral. A class of substances formed by the combination to satura- 
 tion of an acid with an alkali, an earth, or other salifiable base. 
 
 . triple. Sails formed by the combination of an acid with two bases or 
 
 radicals. The tartrate of soda and potass (Rochelle salt) is an instance 
 of this kind of combination. 
 
 Saponaceous. A term applied to any substance which is of the nature or 
 appearance of soap. 
 
 Saturation. The act of impregnating a fluid with another substance, till no 
 more can be received or imbibed A fluid which holds as much of any 
 substance as it can dissolve, is said to be saturated with that substance. 
 A solid may in the same way be saturated with a fluid. 
 
 Sebates. Salts formed by the combination of any base with sebacic acid. 
 
 Semi-Metal A name formerly given to those metals, which, if exposed to 
 the fire, are neither malleable, ductile, nor fixed. It is a term not used 
 by modern chemists. 
 
 Siliceous Earths. A term used to describe a variety of natural substances 
 which are composed chiefly of silex; as quartz, flint, sand, &c. 
 
 Simple Substances. Synonymous with Elements , which see. 
 
 Smelting. The operation of fusing ores for the purpose of separating the 
 metals they contain, from the sulphur and arsenic with which they are 
 mineralized, and also from other heterogeneous matter. 
 
 Solution. The perfect union of a solid substance with a fluid. Salts dissolv- 
 ed in water are proper examples of solution. 
 
 Spars. A name formerly given to various crystallized stones; such as the 
 fluor spar, the adamantine spar, &c. These natural substances are now 
 distinguished by names which denote the nature of each. 
 
 Stalactites. Certain concretions of calcareous earth found suspended like ici- 
 cles in caverns. They are formed by the oozing of water through the 
 crevices, charged with this kind of earth. 
 
 Steatites. A kind of stone composed of silex, iron, and magnesia. Also 
 called French chalk, Spanish chalk, and soap-rock. 
 
 Sub-Salts. Salts with less acid than is sufficient to neutralize their radicals. 
 
 Suberates. Salts formed by the combination of any base with the suberic acid. 
 
 Sublimation. A process whereby certain volatile substances are raised by 
 heat, and again condensed by cold into a solid form. Flowers of sulphur 
 are made in this way. The soot of our common fires is a familiar in- 
 stanee of this process. 
 
 Succinates Salts formed by the combination of any base with the succinic acid 
 
 Sulphates. Salts formed by the combination of any base with the sulphuric 
 acid. 
 
 Sulphites. Salts formed by the combination of any base with the sulphurous 
 acid. 
 
 Sulphures and Sulphurets. Combination f alkalies, or metals with sulphur. 
 
 Sulphuretted. A substance is said to be sulphuretted when it is combined 
 
 with sulphur. Thus we may say sulphuretted hydrogen, &c. 
 Super-Salts. Salts with an excess-ef acid, as the supertartrate of potass. 
 Synthesis. When a body is examined by dividing it into its component parts, 
 it is called analysis ; but when we attempt to prove the nature of a sub- 
 stance by the union of its principles, the operation is called synthesis. 
 
 T. 
 
 Tartrates. Salts formed by the combination of any base with the acid of tartar 
 Temperature. The absolute quantity of free caloric which is attached to any 
 body occasions the degree of temperature of that body. 
 
OF CHEMICAL TERMS. 333 
 
 Test. That part of a cupel which is impregnated with litharge in the opera- 
 tion of refining lead. It is also the name of whatever is employed in chem- 
 ical experiments to detect the several ingredients of any composition. 
 
 Test-Papers. Papers impregnated with certain chemical re-agents ; such as 
 litmus, turmeric, radish, &c. They are used to dip into fluids to ascertain 
 by a change of colours the presence of acids and alkalies. 
 
 Thermometer. An instrument to show the relative heat of bodies. Fahren- 
 heit's thermometer is that chiefly used in England. Other thermometers 
 are used in different parts of Europe. 
 
 Tinctures. Solutions of substances in spiritous menstrua. 
 
 Trituration. A chemical operation whereby substances are united by fric- 
 tion. Amalgams are made by this method. 
 
 Tubulated. Retorts which have a hole at the top for inserting the materials 
 to be operated upon without taking them out of the sand heat, are called 
 tubulated retorts. 
 
 Tungstates. Salts formed by the combination of any base with tungstic acid. 
 
 Vacuum. A space unoccupied by matter. The term is generally applied to 
 the exhaustion of atmospheric air by chemical or philosophical means. 
 
 Vapour. This term is used by chemists to denote such exhalations only as 
 can be condensed and rendered liquid again at the ordinary atmospheric 
 temperature, in opposition to those which are permanently elastic. 
 
 Vital Air. Oxygen gas. The empyrial or fire-air of Scheele, and the clephlo- 
 gisticated air of Priestly. 
 
 Vitrification. When certain mixtures of solid substances, such as silex and 
 alkali, are exposed to an intense heat, so as to be fused, and become glass 
 they are then said to be vitrified, or to have undergone vitrification. 
 
 Vitriols. A class of substances, either earthy or metallic, which are combi- 
 ned with the vitriolic acid. Thus there is vitriol of lime, vitriol of iron, 
 vitriol of copper, &c. These salts are now called Sulphates, because the 
 acid which forms them is called sulphuric acid. 
 
 Vitrinlated Tartar. The old name for sulphate of potass. 
 
 Volatile Alkali. Another name for ammonia. 
 
 Volatile Salts. The commercial name for carbonate of ammonia. 
 
 Volatility. A property of some bodies which disposes them to assume the 
 gaseous state. This property seems to be owing to their affinity for caloric. 
 
 Volume. A term made use of by modern chemists to express the space occu- 
 pied by gaseous t>r other bodies. 
 
 Union, chemical. When a mere mixture of two or more substances is made, 
 they are said to be mechanically united ; but when each or either sub- 
 stance Forms a component part of the product, the substances have form- 
 ed u chemical union. 
 
 w. 
 
 Water. The most common of all fluids, composed of 85 parts of oxygen, 
 and 15 of hydrogen. 
 
 mineral. Waters which are impregnated with mineral and other sub- 
 stances are known by this appellation. These minerals are generally held 
 in solution by carbonic, sulphuric, or muriatic acid. 
 
 Way, dry. A term used by chemical writers when treating of analysis or de- 
 composition. By decomposing in the dry way, is meant, by the agency of 
 fire. 
 
 Way, humid. A term used in the same mariner as the foregoing, but expres- 
 sive of decomposition in a fluid state, or by means of water, and chemical 
 reagents, or tests. 
 
 Welding' Heat. That degree of heat in which two pieces of iron or of plati- 
 na may be united by hammering. 
 
 Wolfram. An ore of tungsten containing also manganese and iron. 
 
 Worm Tub. A chemical vessel with a pewter worm fixed in the inside, and 
 in the intermediate space filled with water. Its use is to cool liquors du- 
 ring distillation. 
 
334 EXPERIMENTS. 
 
 Woulfe's apparatus. A contrivance for distilling the mineral acids and other 
 gaseous substances with little loss ; being a train of receivers with safety- 
 pipes, and connected together by tubes. 
 
 z. 
 
 Zaffre. An oxide of cobalt, mixed with a portion of silicious matter. It is 
 imported in this state from Saxony. 
 
 Zero. The point from which the scale of a thermometer is graduated. Thus 
 Celsius's and Reaumur's thermometers have their zero at the freezing 
 point, while the thermometer of Fahrenheit has its zero at that point at 
 which it stands when immersed in a mixture of snow and common salt. 
 
 LIST OF EXPERIMENTS. 
 
 IN making 1 up the following list of experiments, 1 have been care- 
 ful in general to select such as can be mnde with safety to the young 
 student ; where this is not the case the caution is mentioned. Most 
 of them require but very simple apparatus. Where any experi- 
 ment illustrates the text, a reference is made to the page. Some 
 of them are original, others t^-e borrowed. I have not, however, 
 deemed it necessary to cite authors. 
 
 1. To show that heat is not absorbed, but reflected by polished 
 metallic surfaces, hold a common new tin pan before the fire. The 
 pan will remain cold. See p. 41. 
 
 2. To show the power of a black surface to absorb caloric, 
 smoke or paint a black spot of the size of a dollar on the bottom of 
 a tin pan, and hold it towards the fire. On touching this spot, it 
 will be found hot, while the parts around it remain cold. See p. 
 46. 
 
 3. To make the upper part of a vessel of water boil, while there 
 is a cake of ice at the bottom. Into a glass tube put water enough 
 to occupy two inches. Freeze this, so as not to burst the tube, with 
 a freezing mixture, or by exposure to cold in winter. Then fill the 
 tube nearly full of wafer, and wind a flannel cloth several times 
 around the part containing the ice, so that the heat of the hand will 
 not melt it. Then hold the tube in an oblique direction over a 
 lamp, so as ,to heat tRe water an inch or two above the ice The 
 water will soon begin to boil, and by raising the tube a little ; at a 
 time, it will boil almost to the surface of the ice, without melting 
 it. See p- 52. 
 
 4- To show that some of the metals conduct caloric better than 
 others, procure wires of the same size and length, of gold, silver, 
 copper, iron, zinc, tin, &c. The wires may be 12 or 14 inches long. 
 Coat one end of each with bees wax, and put the other ends into a 
 vessel of hot water. The wax will melt first on the metal which is 
 the best conductor, and the comparative conducting powers are cal- 
 culated by the difference of time between the melting of the wax 
 on each. See p. 51. 
 
 5. The conducting powers of different substances in regard to ca- 
 loric, may be much more sensibly elucidated, by touching in cold 
 weather, a metal with one hand, and a piece of cork, wood, or cloth 
 with the other. Here the sensation of cold, to the hand which 
 touches the metal, is owing to the power which all metals have of 
 
EXPERIMENTS, 335 
 
 conducting 5 offbeat, more rapidly than any other class of substan- 
 ces. See p. 49. 
 
 6. To show that evaporation carries off caloric, moisten the bulb 
 of a thermometer tube with ether, by means of a hair pencil. The 
 mercury immediately begins to fall, and if the process be continu- 
 ed, may be brought down to the freezing- point, even in warm 
 weather. Whenever a fluid substance is converted into vapor, it 
 absorbs a quantity of caloric. In the present case, the ether takes 
 from the bulb of the thermometer, the caloric necessary to give it 
 the elastic form. Therefore, every new application of the ether 
 carries off successive portions of heat, and the mercury continues 
 to sink, until the bulb becomes so cold, as to absorb caloric from the 
 surrounding air, faster than it is carried off by the evaporation. This 
 is the reason why the mercury cannot be depressed below a certain 
 point by evaporation. The ether, although it assumes the elastic 
 form, does not receive the caloric necessary for this purpose from 
 the thermometer, but from the surrounding air. See p. 73. 
 
 7. To demonstrate that fluids boil at comparatively small degrees 
 of heat, when the pressure of the atmosphere is taken off, about half 
 fill with water a small retort, or Florence flask (common oil flask,) 
 and let it boil over a lamp. When the upper part is filled with steam 
 take it from the Inmp, and instantly cork it. airtight. If now it is 
 put into cold water, it begins to boil violently. ' If taken out of the 
 water, it stops boiling, and this may be done many times. This 
 curious method of making water boil by the application of cold, is 
 easily accounted for. When the flask is put into cold water, the steam 
 with which it was filled, is condensed and returns again to water. 
 This leaves a vacuum, in which water is converted into steam, or 
 boils, at a much lower temperature than in the open air. See p. 58. 
 
 8. If the above experiment is made by means of a small retort, a 
 very curious circumstance maybe observed: When the water is 
 cold, and consequently nearly a perfect vacuum is formed, if there- 
 tort is shaken, there is produced a sharp rattling noise, as though it 
 contained shot, instead of water, so that one would suppose by the 
 noise that the retort would be broken into a thousand parts at ev- 
 ery motion. This is owing to the weight with which the water falls 
 upon the glass, when there is no air to impede its motion. See p. 64. 
 
 9. Into a thin glass vessel pour an ounce or two of water, and 
 then pour in two drams of sulphuric acid; the glass will instantly 
 become too hot to be held in the hand. This experiment elucidates 
 the doctrine of latent heat. On mixing these two fluids, a chemic- 
 al combination takes place between their particles, in consequence 
 of which caloric is extracted at the same time their bulk is dimin- 
 ished. This also illustrates Dr. Black's law, that when substances 
 pass from a rarer to a denser state, caloric is g-iven out. If one 
 measure of sulphuric acid, and one of water, be mixed together, the 
 mixture will not again fill the measure twice. See p. 77. 
 
 10. To procure nitrogen, take a bell glass or larger tumbler, and 
 invert it over a short taper, set in a shallow dish of waiter. The ta- 
 per burns until it absorbs all the oxyg-en contained in the air under 
 the bell glass. What remains is nitrogen. If now, a lighted taper 
 be put under the bell glass, it will be instantly extinguished, show- 
 ing the absolute necessity of oxygen for the support of combustion, 
 See p. 100. 
 
 11. The formation of water by the burning of hydrogen may be 
 
386 EXPERIMENTS. 
 
 shown thus : Take a Florence flask and pour into it half a pint of 
 water, then put in about an ounce of granulated zinc, or the same 
 quantity of iron filings, and then pour in half an ounce by measure 
 of sulphuric acid. Have ready a cork, pierced with a burning iron, 
 and the stem of a tobacco pipe passed through the aperture. After 
 putting in the acid, put the cork in its place, and fix the flask up- 
 right by setting it in a bowl, surrounded by a cloth to make it stand 
 up and prevent its breaking. As the hydrogen is formed, it issues 
 through the stem of the tobacco pipe, at the end of which it is to be 
 fixed. If now a glass tube two or three feet long, and an inch or 
 two wide be passed on to the stem so as to include the flame within 
 its bore, the tube, in a few moments will be covered on the inside, 
 with moisture, b-ee p. 109. 
 
 If the orifice of the tube is quite small at the end where the gas is 
 fired, the above experiment serves to produce the musical tones. 
 See p. 118. 
 
 12. An exhibition of gas light my be made as follows : Into the 
 bowl of a common tabacco pipe put a piece of mineral, or what is 
 called sea-coal, and cover the coal closely with clay. When the 
 clay is dry, place the bowl in the fire and heat it slowly. In a few 
 minutes the gas, called carburreltcd hydrogen will issue from the 
 end of the pipe stem ; set fire to it with a candle, and it will burn 
 with a beautiful bright flame. This is the gas with which the streets, 
 factories, &c. are lighted in many of the European cities. 
 
 In the absence of mineral coal, a walnut, small piece of pine 
 knot, or butternut meat, &c. may take the place of coal. See p. 120. 
 
 13. The following gives an example of the manner in which sul- 
 phuric acid is formed. 
 
 Mix with a small quantity of the flowers of sulphur, about one 
 fifth part of finely pulverized nitre. Make a stand by hollowing 
 with a hammer a large button, and attaching wire to the eye, for 
 feet, so that the button will be two inches high ; or, by any other 
 means, place the sulphur and nitre about this height in a shallow 
 dish, containing an inch or two of water. Set fire to the mixture 
 with a hot iron, and immediately invert over it a bell glass, or large 
 tumbler^ The sulphur as it burns, absorbs oxygen from the air 
 contained under the bell glass, in a proportion which would consti- 
 tute sulphurotw acid. At the same time, the heat which this pro- 
 cess occasions, compels the nitre to give out another proportion 
 of oxygen, which is absorbed by the sulphurous acid, and this addi- 
 tional quantity of oxygen, constitutes sulphuric acid. Seep. 130. 
 
 14. Take three parts of nitre, two of potash, and one of sulphur, 
 fend mix them intimately, by rubbing in a mortar. This compound 
 is called fulminating powder. On placing a little of it on a shovel 
 over a hot fire, it explodes with great violence, and with a peculiarly 
 stunning report. 
 
 The combustion of phosphttrctled hydrogen in oxygen gas, af- 
 fords one of the most striking and beautiful among chemical exper- 
 iments. It is done as follows ; Take some phosphuret of lime, wrap 
 it in a paper and push it under a vessel, as a wide mouthed vial, filled 
 with water, and inverted on the shelf of the water bath. As soon as 
 the water penetrates through the paper so as to wet the phospburet of 
 lime, bubbles of phosphuretted hydrogen, begin to rise up through 
 the water. While this is going on, fill a strong glass vessel, as a 
 tumbler, or a piece of thick glass tube stopped at one end, with ox- 
 
EXPERIMENTS. 337 
 
 g^en gas. Invert this also on the shelf of the water bath. When 
 the phosphuretted hydrogen is collected, take the vessel containing 
 it in one hand, and that containing the oxygen in the other ; bring 
 the mouth of the former, by sinking it deeper in the water, under 
 the edge of the latter vessel, then by carefully depressing the bot- 
 tom of the vessel containing the phosphuretted hydrogen, let up a 
 bubble at a time into the oxygen gas. If this experiment is made 
 in a darkened room, the flashes of light appear astonishingly vivid 
 and beautiful. Seep. 135. 
 
 16. Take six or eight grains of oxy-muriate of potash, put it into 
 a mortar and drop in with it about a grain of solid phosphorus, cut 
 into two or three parts ; then rub them together with the pestle. 
 Very violent detonations are produced by these small quantities. 
 It is best, therefore, not to use more than is here mentioned at a 
 time. The hand, holding the pestle, ought always to be protected 
 with a glove or handkerchief. 
 
 17. To make liquid phosphorus, take an ounce vial and half fill it 
 with olive oil, put into the oil a piece of phosphorus of the size of a 
 pea; gradually heat the bottom of the vial, until the phosphorus is 
 melted, taking care to keep the thumb on the mouth ; then cork it 
 air tight. If this vial is first shaken, and then the cork be taken 
 out, it becomes luminous, first near the mouth, and gradually down 
 to the oil, at the bottom. The light which a bottle prepared in this 
 way gives, particularly if warmed, by holding it in the hand, is suffi- 
 cient to tell the hour of night by a watch. This luminous appear- 
 ance, when the cork is removed, is owing to the union of the oxy- 
 gen of rhe atmosphere with the phosphorus. It is slow combustion,, 
 attended with light, and most probably with some heat. 
 
 18. If drawings be made on silk with a solution of nitrate of sil- 
 ver, and the silk first moistened, is exposed to a stream of hydrogen 
 gas, or in any other way exposed to the action of this gas, the metal 
 is instantly revived, and the silk is covered with figures of silver. 
 See p. 155. 
 
 19. If a few drops of a solution of nitrate of silver in water, be 
 placed on a bright surface of copper, the silver is revived, and Drives 
 the copper a brilliant white coat of that metal. This is explained 
 on the principle of affinity. The copper has a stronger attraction 
 for the acid which composes a part of the nitrate of silver, than the 
 silver itself has. Therefore it attracts the acid from the silver, in 
 consequence of which this is received, and at the same time preci- 
 pitated on the copper. See p. 155. 
 
 20. Take a little of the white arsenic of the shops, and mix it with 
 some finely ground charcoal ; put the mixture into a small glass 
 lube closed at one end, and expose the part where the mixture is to 
 a moderate degree of heat gradually raised ; the arsenic will be re- 
 ceived, and will attach itself to the upper part of the tube, giving it 
 a brilliant metallic coat like quick silver. The arsenic may be 
 preserved in this state by stopping up the tube. See p. 155. 
 
 21. Dissolve a tea-spoonful of sugar of lead in a quart of rain 
 water. Put this into a decanter, or white glass bottle, and suspend 
 in it by means of a string a piece of zinc. The zinc decomposes 
 the acetate of lead by depriving it of its oxygen ; the consequence 
 is, that the lead is precipitated in the metallic state, on and around 
 the zinc, and forms a brilliant tree of metal. 
 
 22. Pour a solution of nitrate of silver into a glass vessel, and im- 
 
 29 
 
338 EXPERIMENTS. 
 
 merse a few slips of copper in it. In a short time, a portion of eop- 
 per will be dissolved, and all the silver precipitated in a metallic 
 form. If the solution which now contains copper be decanted into 
 another glass, and pieces of iron added to it, this metal will then be 
 dissolved, and the copper precipitated, yielding a striking instance 
 of peculiar affinities. See p. 176. 
 
 23. Ivory may be coated with silver by the following process : 
 Make a strong solution of nitrate of silver in pure water ; into this, 
 immerse a piece of ivory until it turns yellow ; then take it out and 
 immediately plunge it into a vessel of distilled water exposed to the 
 direct rays of the sun until it turns black. On rubbing it gently it 
 will appe'ar covered with a brilliant coat of silver, resembling a bar 
 of that metal. This curious effect is owing to the solar light which 
 decomposes the nitrate of silver, by taking the oxygen from it, 
 which flies off in the form of oxygen gas. 
 
 24. Through a vessel of lime water, recently made, pass bubbles 
 of carbonic acid gas by means of a bladder and tube, the lime water 
 instantly becomes white and turbid, and finally deposits a quantity 
 of carbonate of lime, in the form of powdered chalk. If now the water 
 be evaporated, a white powder remains which effervesces with 
 acids. If this powder is put into a retort, and sulphuric acid diluted 
 with water, is poured upon it, the beak of the retort being under a 
 vessel filled with water, the carbonic acid is again obtained, and the 
 salt remaining in the retort will be sulphate of lime or gypsum. 
 
 25. Mix one part of nitric acid with 5 or 6 parts of water in a vial; 
 into this put some copper filings, and in a few moments pour off the 
 liquid; it will be colourless. If now there be added some liquid 
 ammonia, another colourless fluid, the mixture becomes of an in- 
 tense and beautiful blue. Hence ammonia is a most delicate test 
 for the presence of copper, with which it strikes a deep blue co- 
 lour. See p. 187. 
 
 26. Put into a vial of pure water a few drops of the tincture of nut 
 galls, made by steeping the galls in water ; into another vial of pure 
 water put a grain or two of the sulphate of iron. If these colour- 
 less fluids are mixed, they instantly become black. Tincture of galls 
 is a most delicate test for the presence of iron, with which it strikes 
 a black. These two substances form the basis of ink. See p. 187. 
 
 27. Take two small glass jars, or tumblers, and fill one with car- 
 bonic acid gas, and the other with oxygen gas. Have them setup- 
 right with a cover on each. If a lighted taper be plunged into the 
 vessel containing the carbonic acid, it is extinguished instantly ; but 
 if it is immediately plunged into the other jar containing the oxy- 
 gen, it is as instantly lighted with a sort of explosion. See p. 236. 
 
 28. Put eight or ten grains of oxy-muriate. of potash into a tea-cup, 
 and then pour in two or three drachms of alcohol. If now about two 
 drachms of sulphuric acid is added, the mixture begins to dart forth 
 little balls of b4ue fire, and in a minute or two, the whole bursts 
 into flame. The alcohol is inflamed by the chlorine which is set 
 free from the salt, in consequence of the combination which takes 
 place between the potash and the sulphuric acid. See p. 236. 
 
 , 29. into a glass tube half an inch or an inch wide, two or three 
 inches long, with a bulb at the end, put a grain or two of iodine. 
 Warm the tube, (but not at that part where the iodine is,) and im- 
 mediately cork it tight ; the tube remains colourless, there being 
 
EXPERIMENTS. 339 
 
 only a few little specks here and there. If at any time the tube be 
 warmed at that part where the iodine is, it is instantly filled with a 
 gas of a most beautiful violet colour. If care is taken to keep the 
 tube well closed, so that the iodine does not escape, when it takes 
 the form of gas, this effect will always be produced whenever the 
 tube is warmed. A tube with two bulbs, like what is called apulse 
 glass, containing 1 the iodine hermetically sealed, would be better. 
 Such a little apparatus would be quite a curiosity to those who 
 know nothing of the nature of iodine. See p. 238. 
 
 30. Write on paper with a solution of the nilrat of silver, taking 
 care not to have it so strong as to destroy the paper. So long as it 
 is kept in the dark, or if the paper be closely folded, the writing re- 
 mains invisible.; but on exposure to the rays of the sun the charac- 
 ters turn yellow, and finally black, so that they are perfectly legible. 
 
 Mr. Accurn says, that this change of color is owing to the par- 
 tial reduction of the oxide of silver, from the light expelling a por- 
 tion of its oxygen ; the oxide therefore approaches to the metallic 
 .state ; for when the blackness is examined with a deep, or powerful 
 magnifier, the particles of metal may be distinctly seen. 
 
 31. Write on paper with a dilute solution of common sugar of 
 lead ; the writing will remain invisible. But on moistening the lines 
 with a pencil, or feather dipped in water impregnated with sulphu- 
 retted hvdrogen, the metal is revived, and the letters appear in me- 
 tallic brilliancy. 
 
 The author above cited, says, that in this instance, the hydrogen 
 of the sulphuretted hydrogen gas, abstracts the oxygen from the ox- 
 ide of lead, and causes it to re-approach to the metallic state ; at the 
 same time, the sulphur of the sulphuretted hydrogedfgas combines 
 with the metal thus regenerated, and converts it into a sulphuret 
 which exhibits the metallic color. 
 
 32. Write on paper with a solution of the sulphate of copper. If 
 this is strong, the writing will be of a faint green color ; if weak, 
 the characters are invisible. On holding the paper over a vessel 
 containing some liquid of ammonia, or if it be exposed to the action 
 of this gas in any other way, the writing assumes a beautiful blue 
 color. On exposing the paper to the sun, the color disappears, be- 
 cause the ammonia evaporates. 
 
 33. Put a small piece of phosphorus into a crucible, cover it close- 
 ly with common chalk, so as to fill the crucible. Let another cru- 
 cible be inverted upon it, and both subjected to the fire. When the 
 whole has become perfectly red-hot, remove them from the fire, and 
 when cold, the carbonic acid of the chalk will have been decompos- 
 ed, and the Black Charcoal, the basis of the acid, may be easily 
 perceived amongst the materials. 
 
 34. Into a large glass jar inverted upon a flat brick tile, and con- 
 taining near its top a branch of fresh rosemary, or any other such 
 shrub, moistened with water, introduce aflat, thick piece of heated 
 iron, on which place some gum benzoin in gross powder. The ben- 
 zoic acid, in consequence of the heat, will be separated, and ascend 
 in white fumes, which will at length condense, and form a most 
 beautiful appearance upon the leaves of the vegetable. This will 
 serve as an example of Sublimation. 
 
 35. Mix a little acetate of lead with an equal portion of sulphate 
 4f zinc, both in fine powder ; stir them together witlf a piece of 
 glass or wood, and no chemical change will be perceptible ; but if 
 
340 EXPERIMENTS. 
 
 they be rubbed tog-ether in a mortar, the two solids will operate on 
 each other; an intimate union will take place, and a fluid will be 
 produced. If alum or Glauber salt be used instead of sulphate of 
 zinc, theexperiment will be equally successful. 
 
 36. If the leaves of a plant, fresh gathered, be placed in the sun, 
 very pure oxygen gas may be collected. 
 
 37. Put a little fresh calcined magnesia in a tea-cup upon the 
 hearth, and suddenly pour over it as much concentrated sulphuric 
 acid as will cover the magnesia. In an instant sparks will be thrown 
 out, and the mixture will become completely ignited. 
 
 28. If a few pounds of a mixture of iron filings and sulphur be 
 made in paste with water, and buried in the ground for a few hours, 
 the water will be decomposed with so much rapidity, that combus- 
 tion and flame will be the consequence. 
 
 39. For want of a proper glass vessel, a table spoonfull of ether 
 may be put into a moistened bladder, and the neck of the bladder 
 closely tied. If hot water be then poured upon it, the ether will 
 expand, and the bladder become inflated. 
 
 40. Procure a phial with a glass stopper accurately ground into 
 it ; introduce a few copper filings, then entirely fill it with liquid am- 
 monia, and stop the phial so as to exclude all atmospheric air. If left 
 in this state, no solution of the copper will be effected. But if the 
 bottle be afterwards left open for some time, and then stopped, the 
 metal will dissolve, and the solution will be colorless. Let the stop- 
 per be now taken out, and the fluid will become blue, beginning at 
 the surface, and spreading gradually through the whole. If this blue 
 solution has not been too long exposed to the air, and fresh copper 
 filings be put in, again stopping the bottle, the fluid will once more 
 be deprived of its color, which it will recover only by the re-ad- 
 mission of air. These effects may thus be repeatedly produced. 
 
 41. If a spoonful of good alcohol and a little boracic acid be stir- 
 red together in a tea-cup, and then set on fire, they will produce a 
 beautiful green flame. 
 
 42. Alloy a piece of silver with a portion of lead, place the alloy 
 upon a piece of charcoal, attach a blow-pipe to a gasometer, charg- 
 ed with oxygen gas, light the charcoal first with a bit of paper, and 
 keep up the heat by pressing upon the machine. When the metals 
 get into complete fusion, the lead will begin to burn, and very soon 
 will be all dissipated in a white srnoke, leaving the silver in a state 
 of purity. This experiment is designed to show the fixity of the no- 
 ble metals. 
 
 43. Burn a piece of iron wire in a deflagrating jar of oxygen gas, 
 and suffer it to burn till it goes out of itself. If a lighted wax taper 
 be now let down into the gas, this will burn in it for some time, and 
 then become extinguished. If ignited sulphur be now introduced, 
 this will also burn for a limited time. Lastly, introduce a morsel of 
 phosphorus, and combustion will also follow in like manner. These 
 experiments show the relative combustibility of different substances. 
 
 44. Drop a piece of phosphorus, about the size of a pea, into a 
 tumbler of hot water, and from a bladder, furnished with a stop cock, 
 force a stream of oxygen gas directly upon it. This will afford the 
 most brilliant combustion under water that can be imagined. 
 
 45. Take an amalgam of lead and mercury, and another amalgam 
 of bismuth, let these two solid amalgams be mixed by triture, and 
 they will instantly become fluid. 
 
EYDEX. 841 
 
 46. Into distilled water drop a little spiritous solution of soap, no 
 chemical effect will be perceived ; but if some of the same solution 
 be added to hard-water, a milhiness will immediately be produced, 
 more or less, according to the degree of its impurity. This is a good 
 method of ascertaining the purity of spring water. 
 
 47. To silver copper or brass. Clean the article intended to be 
 silvered, by means of dilute nitric acid, or by scouring it with a 
 mixture of common salt and alum. When it is perfectly bright, 
 moisten a little of the powder, known in commerce by the name of 
 silvering powder., with water, and rub it for some time on the per- 
 fectly clean surface of copper, or brass, which will become covered 
 with a coat of metallic silver. It may afterwards be polished with 
 soft leather. 
 
 Thesilvering- powder is prepared in the following manner : Dis- 
 solve some silver in nitric acid, and put pieces of copper into the so- 
 lution ; this will throw down the silver in a state of metallic powder. 
 Take fifteen or twenty grains of this powder, and mix with it two 
 drachms of acidulous tartarite of potash, the same quantity of com- 
 mon salt, and half a drachm of alum. Another method : Precipi- 
 tate silver from its solution in nitric acid by copper, as before ; to 
 half an ounce of this silver, add common salt and muriate of ammo- 
 nia, of each two ounces, and one drachm of corrosive sublimate ; 
 rub them together, and make them into a paste with water. With 
 this, copper utensils intended to be silvered, that have been pre- 
 viously boiled with acidulous tartarite of potash and alum, are to be 
 rubbed ; after which they are to be made red-hot, and polished. 
 
 43. To prove that the air of , the atmosphere always contains car- 
 bonic acid. This may be shewn by simply pouring any quantity of 
 barytic water, or lime water, repeatedly 'from one vessel into an- 
 other. The barytic water when deprived of the contact of air, is 
 perfectly transparent ; but it instantly becomes milky, and a white 
 precipitate, which is carbonate of barytes, is deposited, when 
 brought into contact with it for a few minutes only. 
 
 The quantity of carbonic acid contained in the atmosphere, sel- 
 dom varies, except in the immediate vicinity of places where respi- 
 ration and*ombustion are going on in the large way, and is about 
 one hundwdth part. 
 
 INDEX. 
 
 A Agate, 195 
 
 Agriculture, 274 
 
 ABSORBENT vessels, 298 Air, 95 
 
 Absorption of caloric, 40, 45 Albumen, 287 
 Acetic acid, 252, 253 Alburnum, 283 
 
 Acetous fermentation, 267 Alchemists, i5 
 
 acid, 253 Alcohol, or spirit of wine, 259 
 
 Acidulous gaseous mineral wa- Alembic, 127 
 ters, 226 Alkalies, 181 
 
 salts, 254 Alkaline earths, 182, 194 
 
 Acids, 202 Alloys, 162 
 
 Aeriform, 31 Alum, or sulphat of aluraine. 
 
 Affinity, 23, 174 196, 212 
 
 29* 
 
342 INDEX. 
 
 Alumine, 196 Blood, 303, 305 
 
 Alumium, 19 Blood-vessels, 309 
 
 Amalgam, 163 Boiling water, 67 
 
 Ambergris, 320 Bombic acid, 292, 204 
 
 Amethyst, 197 Bones, 295 
 
 Amianthus, .201 Boracic acid, 204, 226 
 Ammonia, or volatile alkali, 169, Boracium, 19, 227 
 
 181, 188 Borat of soda, 227 
 
 Ammoniacal gas, 188 Brandy, 261 
 
 how obtained, 191 Brass, 162 
 
 Analysis, 138 Bread, 244 
 
 of vegetables, 241 Bricks, 197 
 
 Animals, 288 Brittle metals, 20 
 
 Animal acids, 292 Bronze, 162 
 
 colors, 294 Butter, 318 
 
 heat, 311 Butter-milk, 318 
 
 oil, 292 C 
 
 Animalization, 287, 295 Calcareous earths, 224 
 Antidotes, 191 stones, 223 
 
 Antimony, 20 Calcium, 20 
 
 Aqua fortis, 216 Caloric, 29 
 
 regia, 160 absorption of, 46 
 
 Arrak, 262 . conductors of, 48 
 
 Argand's lamp, 107 combined, 69 
 
 Arsenic, 20, 163, 165 expansive power of, 30, 
 
 Arteries, 298 31 
 
 Arterial blood, 306, 308 equilibrium of, 39 
 
 Asphaltum, 270 reflection of, 46 
 
 Assafoetida, 249 . radiation of, 40, 43 
 
 Assimilation, 297 solvent power of, 59 
 
 Astringent principle, 253 capacity for, 70 
 
 Atmosphere, 61, 95, 108 Calorimeter, 83 
 
 Atmospherical air, 95 Calx, 102 
 Attraction of aggregation, or co- Camphor, 240 
 
 hesion, 21, 171 Camphoric acid, 204, 253 
 Attraction of composition, 23, Caoutchouc, 240, 249 
 
 171 Carbonats, 226 
 
 Azote, or nitrogen, 214 Carbonat of ammonia, 290 
 Azotic gas, 95 lead, 150 
 
 B lime, 199 
 
 Balsams, 249 magnesia, 201 
 
 Balloons, 122 potash, 184 
 
 Bark, 282 Carbonated hydrogen gas, 144 
 
 Barytes, 192, 197 Carbon, 137 
 
 Basis of acids, 204 Carbonic acid, 142 
 
 gases, 30 Carburet of iron, 145 
 
 salts, 172 Carmine, 294 
 
 Beer, 258 Cartilage, 297 
 
 Benzoic acid, 204, 253 Castor, 321 
 
 Bile, 303 Cellular membrane, 300 
 
 Birds, 297 Caustics, 164 
 
 Bismuth, 20 Chalk, 199, 226 
 
 Bitumens, 270 Charcoal, 137 
 Black lead, or plumbago, 145 Cheese, 320 
 
 Bleaching, 210 Chemical attraction, 21 
 
 Blow-pipe, 140, 153 Chemistry, 13 
 
INDEX. 
 
 343 
 
 Chest, 304 
 
 China, 197 
 
 Chlorine, 18 
 
 Chrome, 20 
 
 Chyle, 298 
 
 Chyme, 303 
 
 Citric acid, 204, 253 
 
 Circulation of the blood, 205 
 
 Civet, 321 
 
 Clay, 38 
 
 Coke, 270 
 
 Coal, 270 
 
 Cobalt, 20 
 
 Cochineal, 274 
 
 Cold, 40 
 
 from evaporation, 80 
 Colours of metallic oxyds, 151 
 Columbium, 20 
 Combined caloric, 69 
 Combustion, 99 
 
 volatile products of, 107 
 
 fixed products of, 107 
 
 of alcohol, 263 
 
 of ammoniacal gas, 188 
 
 of boracium, 227 
 
 by oxy-muriatic acid, or 
 chlorine, 231 
 
 of carbon, 140 
 
 of coals, IIP, 145 
 
 of charcoal, by nitric acid, 
 215 
 
 of candles, 118, 147 
 
 of diamonds, 140 
 
 of ether, 266 
 
 of hydrogen, 109, 116 
 
 of iron, 105 
 
 of metals, 152 
 
 of oils, 147 
 
 of oil of turpentine by ni- 
 trous acid, 215 
 
 of phosphorus, 133 
 
 of sulphur, 128 
 
 of potassium, 168 
 Compound bodies, 17 
 
 or neutral salts, 182 
 Conductors of heat 48 
 
 solids, 50 
 
 fluids, 51 
 
 Count Rumford's theory, 
 
 51 
 
 Constituent parts, 17 
 Copper, 20, 165 
 Copal, 249 
 Cortical layers, 282 
 Cotyledons, or lobe, 278 
 
 Cream, 318 
 
 Cream of tartar, or tartrit of pot- 
 ash, 263 
 Cryophorus, 82 
 Crystallization, 159 
 Cucurbit, 127 
 Culinary heat, 55 
 Curd, 319 
 
 Cuticle, or epidermis, 300 
 Cyanogen, 293 
 
 D 
 Decomposition, 16 
 
 of atmospherical air, 98. 
 100 
 
 of water, by the Voltaic 
 battery, 112 
 
 of salts by the Voltaic bat- 
 tery, 179 
 
 of water by metals, 113 
 by carbon, 144 
 
 of vegetables, 254 
 
 of potash, 168 
 
 of soda, 169 
 
 of ammonia, 169 
 
 of the boracic acid, 227 
 
 of the fluoric acid, 228 
 
 of the muriatic acid, 229 
 Deflagration, 221 
 Definite proportions, 177 
 Deliquescence, 211 
 Detonation, 115, 123 
 Dew, 62 
 Diamond, 138 
 Diaphragm, 304 
 Digestion, 302 
 
 Dissolution of metals, 87, 15*3 
 Distillation, 127, 208 
 
 of red wine, 261 
 Divellent forces, 176 
 Division, 16 
 Drying oils, 246 
 Dyeing, 250 
 
 E 
 
 Earths, 181 
 Earthen-ware, 197 
 Effervescence, 157 
 Efflorescence, 211 
 Elastic fluids, 31 
 Electricity, 86, 90, 92 
 Electric machine, 88 
 Electo-magnetism, 94 
 Elective attraction, 174 
 Elementary bodies, 17 
 Elixirs, tinctures, or quintescen- 
 ces, 263 
 
344 
 
 IXDEX. 
 
 Enamel, 197 
 
 Epidermis of vegetables, 282 
 
 of animals, 300 
 Epsorn salts, 201 
 Equilibrium of caloric, 39 
 Essences, 147, 247 
 Essential or volatile oils, 147, 
 
 247 
 
 Ether, 65, 265 
 Evaporation, 61 
 Evergreens, 286 
 Eudiometer, 134 
 Expansion of caloric, 30 
 Extractive colouring- matter, 250 
 
 F 
 
 Falling stones, 161 
 Fat, 318 
 Feathers, 296 
 Fecula, 244 
 Fermentation, 356 
 Fibrine, 287, 292 
 Fire, 16, 26 
 Fish, 316 
 
 Fixed air, or carbonic acid, 140, 
 233 
 
 alkalies, 121 
 
 oils, 146, 245 
 
 products of combustion, 
 
 106 
 
 Flame, 119 
 Flint, 185, 195 
 Flower of blossom, 284 
 Fluoric acid, 228 
 Fluorium, or Fluorine, 28, 229 
 Formic acid, 292 
 Fossil wood, 271 
 Frankincense, 249 
 Free or radiant caloric, or heat 
 
 of temperature, 29 
 Freezing mixtures, 77 
 
 by evaporation, 65, 80 
 Frost, 62 
 Fruits 285 
 F uller's earth, 19G 
 Furnace, 145, 150 
 
 G 
 
 Galls, 253 
 Gallatof iron, 213 
 Gallic acid, 213, 253 
 Galvanism, 85 
 Gas, 95 
 Gas-lights, 120 
 
 Gaseous oxyd of carbon, nitro- 
 gen, 142, 217 
 Gastric juice, 302 
 
 Gelatine, or jelly, 287 288 
 
 Germination, 277 
 
 Gin, 262 
 
 Glands, 295, 299 
 
 Glass, 185 
 
 Glauber's salts, orsulphatof soda, 
 
 184 
 
 Glazing, 197 
 Glucium, 19 
 Glue, 189 
 Gluten, 244 
 Gold, 20, 160 
 Gum, 242 
 
 , arabic, 242 
 
 elastic, or caoutchouc, 249 
 
 resins, 249 
 Gunpowder, 221 
 
 Gypsum, or Plaster of Paris, or 
 sulphat of lime, 212 
 
 H 
 
 Hair, 299 
 
 Harrogate water, 132 
 Hartshorn, 188, 190 
 Heart, 305 
 
 wood, 283 
 Heat, 26 
 
 of capacity, 71, 74 
 
 of temperature, 29 
 Honey, 244 
 Horns, 289 
 
 Hydro- carbonat, 124, 145 
 Hydrogen, 109 
 
 gas, 110 
 
 I& J 
 
 Jasper, 195 
 Ice, 83 
 Jelly, 289 
 Jet, 270 
 Ignes fatui, 135 
 Ignition, 68 
 
 Imponderable agents, 18 
 Inflammable air, 109 
 Ink, 213 
 Insects, 254 
 Integrant parts, 17 
 Iodine, 109, 237 
 Iridium, 20 
 Iron, 20, 150, 161 
 Isinglass, 289 
 Ivory black, 294 
 
 K 
 
 Kali, 187 
 Koumiss, 320 
 
 Lac, 321 
 
INDEX. 
 
 345 
 
 Lactic acid, 292, 320 
 
 Lakes, colours, 250 
 
 Lamp without flame, 107, 322 
 
 Latent heat, 73 
 
 Lavender water, 263 
 
 Lead, 20, 151, 156 
 
 Leather, 251,291 
 
 Leaves, 280 
 
 Life, 239 
 
 Ligaments, 296 
 
 Light, 18 
 
 Lightning, 215 
 
 Lime, 198 
 
 water, 199 
 Limestone, 193 
 Linseed oil, 246 
 Liqueurs, 263 
 Liver, 299 , 
 Lobes, 278, 309 
 Lunar caustic, or nitrat of silver, 
 
 164, 222 
 Lungs, 307, 309 
 Lymph, 298 
 Lymphatic vessels, 293 
 
 M 
 
 Magnetic needle, 94 
 Magnesia, 201 
 Magnium, 19 
 Malic acid, 204, 253 
 Malt, 258 
 
 Malleable metals, 20 
 Manganese, 20, 150 
 Manna, 241 
 Manure, 274 
 Marble, 226 
 Marine acid, or muriatic acid, 
 
 229 
 
 Mastic, 249, 263 
 Materials of animals, 287 
 
 of vegetables, 239 
 Mercury, 20, 162 
 
 new mode of freezing, 83, 
 163 
 Metallic acids, 160 
 
 oxyds, 150 
 Metals, 149 
 Meteoric stones, 161 
 Mica, 201 
 Milk, 288, 299 
 Minerals, 150 
 Mineral waters, 143 
 
 acids, 203 
 Miners' lamp, 125 
 Mixture, 60 
 Molybdena, 20, 160 
 
 Mordant, 250 
 Mortar, 201 
 Mucilage, 241 
 Mucous acid, 204, 241 
 
 membrane, 300 
 Muriatic acid, or marine acid, 
 
 229 
 
 Muriats, 234 
 Muriat of ammonia, 188, 237 
 
 lime, 78 
 
 soda, or common salt, 187, 
 234 
 
 potash, 235 
 Muriatum, 19 
 Muscles of animals, 295 
 Musk, 321 
 Myrrh, 249 
 
 N 
 
 Naphtha, 270 
 
 Negative electricity, 25, 84, 88 
 Nerves, 299 
 
 Neutral, or compound salts, 20 
 Nickel, 20, 161 
 
 Nitre, or nitrat of potash, or salt- 
 petre, 215, 224 
 Nitric acid, 214 
 Nitrogen, or azote, 96 
 
 gas, 96 
 Nitro-muriatic acid, or aqua re- 
 
 gia, 160 
 Nitrous acid gas, 217 
 
 air, or nitric oxyd gas, 218 
 Nitrats, 221 
 Nitrat of copper, 165 
 
 ammonia, 219, 221 
 
 potash, or nitre, or salt- 
 petre, 215 
 
 silver, or lunar caustic, 
 
 222 
 Nomenclature of acids, 202 
 
 compound salts, 172 
 Nomenclature of other binary 
 
 compounds, 135 
 Nut-galls, 213* 
 Nut-oil, 245 
 Nutrition, 295 
 O 
 
 Ochres, 151 
 Oils, 146, 247 
 Oil of amber, 271 
 
 vitriol, or sulphuric acid, 
 
 206 
 
 Olive-oil, 245 
 Ores, 150 
 Organized bodies, 239 
 
346 
 
 INDEX. 
 
 Organs of animals, 299 
 
 vegetables, 239 
 Osmium, 20, 163 
 Oxalic acid, 204, 253 
 Oxyds, 102, 157 
 Oxyd of manganese, 105 
 
 iron, 102 
 
 lead, 151 
 
 sulphur, 201 
 
 Oxydation, or oxygenation ? 157 
 Oxygen, 18, 129 
 
 gas, or vital air, 95 
 Oxy-muriatic acid, 230 
 Oxy-muriats, 235 
 Oxy-muriat of potash, 235 
 
 P 
 
 Palladium, 20, 163 
 Papin's digester, 290 
 Parenchyma, 277, 283 
 Particles, 21 
 Pearl-ash, 183 
 Peat, 271 
 
 Peculiar juice of plants, 283 
 Perfect metals, 20, 153 
 Perfumes, 247 
 Perspiration, 310 
 Petrifaction, 269 
 Pewter, 162 
 Pharmacy, 14 
 Phosphat of lime, 213 
 Phosphorated hydrogen gas, 135 
 Phosphorescence, 28 
 Phosphoric acid, 213 
 Phosphorus, 132 
 
 acid, 213 
 Phosphuret of lime, 135 
 
 sulphur, 136 
 Pitch, 248 
 Plaster, 201 
 Platina, 20, 153 
 
 Platina ignited by a lamp with- 
 out a flame, 322 
 Plating, 16$ 
 
 Plumbago, or black lead, 16' J 
 Plurnula, 278 
 Porcelain, 197 
 
 Positive electricity, 25, 84, 88 
 Potassium, 168 
 Pottery, 197 
 Potash, 182 
 Precipitate, 24 
 Pressure of the atmosphere, 67, 
 
 Printers' Ink, 232 
 
 Prussiat of iron, or Prussian blue, 
 
 294 
 
 potash, 293 
 Prussic acid, 293 
 Putrid fermentation, 268,321 
 Pyrites, 2 1 2, 161 
 Pyrometer, 32 
 
 Q 
 
 Quicklime, 198 
 
 Quiescent forces, 176 
 R 
 
 Radiation of caloric, 89 
 
 Preyost's theory, 40 
 Pictet's explanations, 4 
 Leslie's illustrations, 44 
 
 Radicals, -202, 206 
 
 Radicle, or root, 278 
 
 Rain, 62 
 
 Rancidity, 246 
 
 Rectification, 262 
 
 Reflection of caloric, 40, 44 
 
 Reptiles, 317 
 
 Resins, 248 
 
 Respiration, 300, 303 
 
 Reviving of metals, 156 
 
 Rhodium, 20, 163 
 
 Roasting metals, 150 
 
 Rock crystal, 195 
 
 'Ruby, 193 
 
 Rum, 261 
 
 Rust, 150, 155 
 S 
 
 Saccharine fermentation, 257 
 
 Sal ammoniac, or muriat of am- 
 monia, 188 
 
 poly ch rest, or sulphat of 
 
 potash, 210 
 
 volatile, or carbonat of am- 
 monia, 190 
 
 Salifiable basis, 172 
 
 Salifying principles, 172 
 
 Saltpetre, or nitre, or nitrat of 
 potash, 220 
 
 Salt, 210 
 
 Sand, 195 
 
 Sandstone, 195 
 
 Sap of plants, 257, 241, 283 
 
 Sapphire, 193 
 
 Saturation, 60 
 
 Seas, temperature of, 54 
 
 Sebacic acid, 246 . 
 
 Secretions, 292 
 
 Seeds of plants, 258, 285 
 
 Seltzer water, 143, 200 
 
 Senses, 300 
 
INDEX. 
 
 347 
 
 Silex, or silica, 195, 191 
 
 Silicium, 19 
 
 Silk, 321 
 
 Silver, 153 
 
 Simple bodies, 18 
 
 Size, 289 
 
 Skin, 288 
 
 Slacking of lime, 300 
 
 Slate, 196 
 
 Smelting metals, 150 
 
 Smoke, 107 
 
 Soap, 183 
 
 Soda, 187, 169 
 
 water, 143 
 Sodium, 19, 169 
 Soils, 273 
 Soldering, 162 
 Solubility, 211 
 Solution, 58 
 
 by the air, 61 
 
 of potash, 185 
 Specific heat, 70 
 Spermaceti, 320 
 Spirits, 261 
 Spirit lamp, 364 
 Starch-sugar, 242 
 Steam, 68, 76 
 Steel, 146 
 Stomach, 302 
 Stones, 193 
 Stucco, 201 
 Strontites, 201 
 Strontium, 19 
 Suberic acid, 204, 253 
 Sublimation, 127 
 Succin, or yellow amber, 271 
 Succinic acid, 204, 253 
 Sugar, 240, 259 
 
 of milk, 319 
 Sulphats, 211 
 Super- oxygenated sulphuric 
 
 acid, 202 
 
 Sulphatofalumine,oralum, 196, 
 212 
 
 barytes, 198 
 
 iron, 212 
 
 lime, or gypsum, or plaster 
 of Paris, 212 
 
 magnesia, or Epsom salt, 
 201,212 
 
 potash, or salt polychrest, 
 210 
 
 soda, or Glauber's salts, 
 
 21 
 Sulphur, 126 
 
 Sulphur, flowers of, 127 
 Sulphuriated hydrogen gas, 131 
 Sulphurets, 160 
 Sulphureous acid, 130, 208 
 Sulphuric acid, 207 
 Sympathetic ink, 165 
 Synthesit, 138 
 
 T 
 
 Tan, 251 . 
 Tannin, 251 
 Tar, 248 
 
 Tartarous acid, 253 
 Taririt of potash, 254 
 Teeth, 296 
 Tellurium, 20 
 Temperature, 29 
 Thaw, 85 
 Thermometers, 34, 35 
 
 Fahrenheit's 34 
 
 Reaumer's, 34 
 
 Centrigrade, 34 
 
 air, 35 
 
 differential, 36 
 Thunder, 123 
 Tin, 20 
 
 Titanium, 20, 163 
 Turf, 270 
 Turpentine, 173 
 Transpiration of plants, 279 
 Tungsten, 20, 160 
 
 Vapour, 68, 76, 266 
 Vaporisation, 61 
 Varnishes, 249 
 Vegetables, 238 
 Vegetable ^acid, 240, 148 
 
 colors, 250 
 
 heat, 285 
 
 oils, 244 
 Veins, 301,306 
 Venous blood, 306, 308 
 Ventricles, 307 
 Verdigris, 165 
 Vessels, 298 
 Vinegar, 267 
 Vinous fermentation, 258 
 Vital air, or oxygen gas, 96 
 Vitriol, or sulphat of iron, 206 
 Volatile oils, 240, 244, 247 
 
 products of combustion, 
 106 
 
 alkali, 181, 188 
 
 Voltaic battery, 86, 149, 153, 16 ? 
 179 
 
 U 
 Uranium, 20 
 
348 INDEX. 
 
 W Wood, 283 
 
 Water, 109, 1 1 3 Woody fibre, 240, 252 
 decomposition of, by elec- Wool, 296 
 
 tricity,113 Y 
 
 condensation of, 54 Yeast, 267 
 
 of the sea, 54 Yttria, 192 
 
 boiling, 58 Yttrium, 19 
 solution by, 58 Z 
 
 of crystallization, 159 Zinc, 19 
 
 Wax, 320, 245 Zicornia, 192 
 
 Whey, 318 Zincornium, 19 
 
 Wine, 258 Zoonic acid, 204, 292, 
 

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