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V V |),..ijl.oJ I.." II'. J • 1. • CmilnA. l>.lin«t«L UH.,jtJV„l Wt.S,mfci,l. CONVERSATIONS * ON CHEMISTRY; IN WHICH THE ELEMENTS OF THAT SCIENCE > # ARE .„ FAMILIARLY EXPLAINED AND XUttstratett f>2 SEweritnettts, AJND SIXTEEN COPPER-PLATE ENGRAVINGS, * LIBRARY THE NINTH AMERICAN FROM THE -Epffflgg Afif fifg'MCT'WS OFFICE VISED, CORRECTED! 'ANtFENLARGED. 0EC.-8—1901 TO WHICH ARE NOW A EXPLANATIONS OF THE TEXT--QUESTIONS FOR EXERCISE—DI- RECTIONS FOR SIMPLIFYING THE APPARATUS, AND A VO-I CABULA.RY OF TERMS--TOGETHER WITH A LIST OF INTERESTING EXPERIMENTS. BY J. L. COMSTOCK, M. D. ?T ___ HARTFORD: OLIVER D. COOKE AND SONS. 1824. DISTRICT OF CONNECTICUT, SS. ♦ BE IT REMEMBERED, That on the twenty-ninth day L. S. of December, in the fortv sixth year of the Independence of the United States of America, Oliver D. Cooke, of the said District, hath deposited in this office the title of a Book, the right whereof he claims as proprietor, in the words following, to wit, " Conversations on Chemistry : in which the Elements of that science are familiarly explained and illustrated by experiments, and sixteen copperplate engravings. The eighth American from the sixth London edition, revised, corrected and enlarged. To which are now added, explanations of the text, questions for exercise, directions for simplfying the apparatus, and a vocabulary of terms; together with a list of interesting experiments. By Dr. J. L. Corn- stock." 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." v . : . - • ' 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, GL> ADVERTISEMENT OF THE AMERICAN EDITOR. THE familiar and agreeable manner in which the " Conversa- tions on Chemistry" are written, renders this one of the most pop- ular 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 adapted to the object of the work. In some respects, however, the English edition may be considered as objectionable. A book designed for the instruction of youth, ought if possible 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, doctrines 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. Bryan has not been suffi- ciently guarded. The brilliant discoveries of Sir Humphrey Davy, and his known eminenqe as a Chemical Philosopher, seem in many instances to have given his opinions an authority, which in the mind of the writer, 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 are designed to guard the pupil against adopting opinions which he will find either contradicted, or merely examined by most chemical writers. In addition to this, I have made such explanations of the text as I thought would assist the pupil in understanding what he read. In attempting to make this science popular, and of general utility, it is of great importance that the experiments come within the use of such instruments as are easily obtained. 1 have therefore given such directions on this subject as my former experience, as a lec- turer, with a small apparatus, taught me to believe would be of ser- vice. The questions, I believe, will be found to involve whatever is most important to be known throughout the work. The list of experiments was chiefly made up without referring to books; some few of them, however, are copied from Parke, Ac- cum, &c. Hartford, Ct. Jan. 1, 1822. 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 re- quired ; and she feels it the more necessary to apologize for the present undertaking, as her knowledge of the subject 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 pursuit. 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 knowledge of the sub- ject, slight as it was, gave her over others who had not enjoy- ed the same means of private instruction. Every fact or ex- periment 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 distinguished, seldom failed to produce on her mind the effect for which they wer© intended. Hence it was natural to infer, that familiar conversation was, in studies of this kind, a most useful auxiliary source of infor- mation ; and more especially to the female sex, whose educa- tion 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 acquainted with any book that could prove a substitute for it, she thought it might be useful for beginners, as well as satisfactory to her- self, to trace the steps by which she had acquired her little stock of chemical knowledge, and to record, in the form of dialogue, those ideas which she had first derived from conver- sation . But to do this with sufficient method, and to fix upon a mode of arrangement, was an object of some difficulty. After much PREFACE. V l hesitation, and a degree of embarrassment, which, probably, the most competent chemical writers have off en felt in common with the most superficial, a mode of division was adopted, which, though the most natural, does not always admit of being strictly pursued—It i- iU it of treating first of the simplest bod- ies, and then gradually rising to the most intricate compounds. It is not the author's intention to enter into a minute vindi- cation of this plan. But whatever may be its advantages or in- conveniences, 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 of- ten find it obscure or unsatisfactory ; for its various parts are so connected with each ofher as to form an uninterrupted 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 suppo- sed 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^ ex- planations 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 check- ed in her progress by the apprehension that such an attempt might be considered by some, either as unsuited to the ordinary pursuits ofher sex, or ill-justified by her own imperfect know- ledge of the subject. But, on the one hand, she felt encour- aged by the establishment of those public institutions, open to both sexes, foi the dissemination of philosophical knowledge, whi-h clearly prove that the general opinion no longer ex- cludes women from an acquaintance with the elements of science ; and, on the other, she flattered herself that whilst the impressions 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 perusing this work, that he is supposed to have previously acquired some slight know- ledge of natural philosophy, a circumstance so desirable, that the author has, since the original publication of this work, been induced to offer to the public a small tract, entitled " Conversations on Natural Philosophy," in" which the most essential rudiments of that science are familiarly explained. CONTENTS, CONVERSATION I. Page ON THE GENERAL PRINCIPLES OF CHEMISTRY. 1 Connection between Chemistry and Natural Philosophy.—Improv- ed State of modern Chemistry.—Its use in the Arts.—The gener- al Objects of Chemistry.—Definition of Elementary Bodies.—De- finition of Decomposition.—Integrant and Constituent Particles. ■—Distinction between Simple and Compound Bodies.—Classifi- cation of Simple Bodies.—Of Chemical Affinity, or Attraction of Composition.—Examples of Composition and Decomposition. CONVERSATION II. ON LIGHT AND HEAT. 15 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 Fl aids... Air Ther- mometer...Equal Diffusion ot Caloric...Coid a Negative Quality ...Professor Prevost's Theory of the Radiation of Heat...Profes- sor Pictet's Experiments on the Reflection of Heat...Mr. Leslie's Experiments on the Radiation of Heat. CONVERSATION III. CONTINUATION OF TI1E SUBJECT. 36, Of the. different Power of Bodies to Conduct Heat...Attempt to ac- count for this Power... Count Rumford's Opinion respecting the non-conducting P:wei of Fluids...Phenomena of Boiling...Of So- lution in general...Solvent Power of Water...Difference between Solution and Mixi.re ..Solvent Power of Caloric...Of Clouds, Rain, Dr. Wells'Theory of Dew, Evaporation, &c....Influence of Atmospherical Pressure on Evaporation...Ignition. CONVERSATION IV. ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT AND LA- TENT HEAT. 60 Of Specific Heat...Of the different Capacities of Bodies for Heat... Specific Heat, not perceptible by the Senses... How to "be ascer- tained ..Of 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 lee, CONTENTS. Vfi. and the Condensation of Elastic Fluids...Instances of Condensa- tion, and consequent Disengagement of Heat, produced by Mix- • tures, by the Slaking of Lime...General Remarks on Latent Heat ...Explanation of the Phenomena of Ether boiling, and Water freezing, at the same Temperature...Of the Production of Cold by Evaporation...Calorimeter...Meteorological Remarks. CONVERSATION V. ON THE CHEMICAL AGENCIES OF ELECTRICITY. 7R Of Positive and Negative Electricity...Galvani's Discoveries...Vol- taic Battery...Electrical Machine...Theory of Voltaic Excite- ment...Its Influence on the Magnetic Needle. CONVERSATION VI. ON OXYGEN AND NITROGEN. 89 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 Products of Combustion...Patent Lamps.. Decomposition of the Atmosphere by Respiration... Recomposition of the Atmosphere. CONVERSATION VII. ON HYDROGEN. 104 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 Forma- tion 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., * 123 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 ...Sulphurated Hydrogen Gas...Harrowgate, or Hydrosulphura- ted Waters...Phosphorus...Decomposition of Phosphorus...Histo- ry of its Discovery...Its Combustion in Oxygen Gas...Phosphoric Viii. CONTENTS. AcidL...Phosphorous Acid...Eudiometer...Combination of Phos- phorus with Sulphur...Phosphorated Hydrogen Gas ..Nomencla- ' tureof Binary Compounds...Phosphoret of Lime burning under. Water. CONVERSATION IX. ON CARBON. 134 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. 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, Metal-, by the Decomposition of Water... Power of Acids to promote this Effect...Oxydation of Metals by Acids...Metallic Neutral Salts...Previous Oxydation of the Metal requisite...Crystallization...Solution distinguished from Dissolution ..Five Metals susceptible of Acidification..Meteoric Stones...Alloys, Soldering, Plating, &c...Of Arsenic, and of the Caustic Effects of Oxygen...Of Verdigris,•Sympathetic Ink, &c... Of the new Metals discovered by Sir H. Davy. CONVERSATION XIII. ON THE ATTRACTION OF COMPOSITION. 173 Of the. Laws which regulate/the Phenomena of the Attraction of Composition...!. 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 cha- racterise Bodies in their separate slate, destroyed by Combina- tion...6. The Force of Attraction estimated by that which is re- quired by the separation of the Constituents...7. Bodies have amongst themselves different Degrees of Attraction...Of simple elective and double elective Attractions...Of quiescent and di- vellent Forces...Law of definite Proportions...Decomposition of Salts by Voltaic Electricity. v CONTENTS. IX. CONVERSATION XIV. ON ALKALIES. 183 Of the composition and general properties of the Alkalies...Of the new discovered Alkali or Lithion...Of Potash...Manner of pre- paring it...Pearlash...Soap...Carbonat of Potash...Chemical No- menclature.. .Solution 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.. .Ammonia- cal Gas...Composition of Ammonia...Hartshorn and Sal Volatile... Combustion of Ammoniacal Gas. CONVERSATION XV. ON EARTHS. 195 Compositioa 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...Baryte»...Limo ; its extensive chemical pro- perties and uses in the Aria...Magnesia...Strontian. CONVERSATION XVI. ~ ON ACIDS. 207 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 Decomposi- tion 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 PHOSPHATS. 212 Of the Sulphuric Acid...Combustion of Animal or Vegetable bodies by this Acid...Method of preparing it.. The Sulphurous Acid obtained 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 gene- ral.. .Sulphats...Sulphat of Potash, or .Sal Polychrjest...Cold pro- duced by the melting of salts.. Sulphat of Soda, or Glauber's salt ...Heat 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 Magnesia...Sulphat of Alumine, or Alum...Sulphat of Iron... Of Ink...Of the Phosphoric and Phosphorous Acids...Phosphorus obtained from bones...Phosphat of Lime. X. CONTENTS. CONVERSATION XVIII. of the nitric and carbonic acids ; or the combination op oxygen with nitrogen and with carbon, and of the ni- trAts and carbonats. 221 Nitrogen susceptible of various degrees of acidification...Of the Ni- tric Acid.*.Its Nature and Composition discovered by Mr. Cav- endish—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 trom Nitrat of Ammonia...Its singular effects on being respired ...Nitrats...of Nitrat of Potash, Nitre or Saltpetre...Of Gunpow- der... Causes of Detonation...Decomposition of Nitre...Deflagra- tion ..Nitrat of Ammonia...Nitrat of Silver...Of the Carbonic Acid...Formed by the combustion of Carbon...Constitutes a com- ponent part of the atmosphere...Exhaled in some caverns...Grot-. to del Cane.. Great weight of this Gas...Produced from calcare- ous stones by Sulphuric Acid...Deleterious effects of this Gas when respired...Sources whinh 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. ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MURIATIC ACIDS ; AND ON MURIATS. 23S On the Boracic Acid...Its decomposition, by Sir H. Davy...Its basis Boracium...Its Recomposition. .Its uses in the Arts...Borax or Borat of Soda...Of the Fluoric Acid...Obtained from Fluor; cor- rodes sjlicious 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...Combus- tion of bodies in this gas...It dissol es 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 fumigations...Its offensive smell, &c... Muriats...Muriat of Soda, or common salt...Muriat of Ammonia...Oxygenated Muriat of Potash...Detonates with Sul- phur, Phosphorus, &c...Experiment of burning Phosphorus under water by means of this salt and of Sulphuric Acid. CONVERSATION XX. ON THE NATURE AND COMPOSITION OF VEGETABLES. 250 Of organized bodies...Of the functions of Vegetables. .Of the ele- ments of Vegetables...Of the materials of Vegetables...Analysisof Vegetables... Of Sap... Mucilage or Gum... Sugar... Manna and Ho- ney...Gluten.,.Vegetable oils.. Fixed oils, Linseed, Nut,and Olive oils.. Volatile oils, forming Essences and Perfumes...Camphor Re- CONTENTS. XI. sins 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 painti.ig..Tan- nin ; its use in the arts of preparing Leather.. Woody Fihre..Vege- table Acids..The Alkalies and Salts contained in Vegetables. CONVERSATION XXI. ON THE DECOMPOSITION OF VEGETABLES. 268 Of fermentation in general—Of the saccharine fermentation, the product of which is sugar—Ot the vinous fermentation, the pro- duct of which is wine—Alcohol, or spirit of wine—Analysis of wine by distillation—Of brandy, rum, arrack, gin, &c—Tartrit of Potash, or Cream of Tartar—Liqueurs—Chemical properties of Alcohol—Its combustion—Of ether—Of the acetous fermenta- tion, the product of which is vinegar—Fermentation of bread—Of the putrid fermentation, which reduces vegetables to their ele- ments—Spontaneous succession of these fermentations—Of vege- tables said to be petrified—Of bitumens : Naphtha, Asphaltum, Jet, Coal, Succin, or Yellow Amber—Of Fossil wood, Peat and Turf. CONVERSATION XXII. HISTORY OF VEGETATION. 287 Connection 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 Materi- als by the Orgins of Plan-•?...Vegetable Heat...Of the Organs of Plants.. Of the Bark, consisting of Epidermis, Parenchyma, and Cortical Layers...Of Alburnum, or Wood...Leaves, Flowers, and Seeds. .Effects of the Season on Vegetation...Vegetation of Ever- greens in Winter. CONVERSATION XXIII. ON THE COMPOSITION OF ANIMALS. 304 Elements of Animals...Of the principal Materials of Animals, viz. Gelaiioe Albumen, Fibrine, Mucus...Of Animal Acids...Of An- imal Colours, Prussian Blue, Carmine, and Ivory Black. xa. CONTENTS. CONVERSATION XXIV. ON THE ANIMAL ECONOMY. ^14 Of the principal Animal Organs...Of Bofces, Teeth, Horns, Liga- ments, and Cartilage...Of the Muscles, constituting the Organs ot Motion...Of the Vascular System, forthe Conveyance ot fc luids... Of the Glands, for the Secretion of Fluids...Of the Nerves, con- ✓ stituting the Organs of Sensation...Of the (Cellular Substance which connects the several Organs...Of the hkin. CONVERSATION XXV. ON ANIMALIZATION, NUTRITION, AND RESPIRATION 322 Digestion...Solvent Power of the Gastric Juice...Formation of a Chyle...Its Assimilation, or Conversion into Blood...Of Respira- tion...Mechanical 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 PRODUCTS. 333 Of the Analogy of Combustion and Respiration... Animal Heat evolv- ed 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 Animal Body to resist the Effects of Heat...Cold Produced by Perspiration...Respiration of Fish and of Birds...Effects of Res- piration on Muscular Strength...Of several Animal Products, viz. Milk, Butter, and Cheese; Spermaceti; Ambergris; Wax; Lac; 'Suk; 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 no- tions of Natural Philosophy, 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. This is Chemistry, which is so closely connected with Natural Philo- sophy, that the study of the one must be incomplete without some knowledge of the other ; for, it is obvious that we can derive but a very imperfect 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., I am not disposed fo form a very favourable idea of Chemistry, nor do I e\ pec to derive much entertainment from it. I prefer the sciences which exhibit nature on a grand scale, to those that are con- fined to the minutiae of petty details. Can the studies which we have lately pursued, the general properties of matter, or the revolutions of the heavenly bodies, be compared to the mixing up of a few insignificant drugs ? I grant, however, there may be some entertaining experiments in chemistry, and should not dislike to try some of them : the distilling, for instance, of lavender, 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 entertain of its object. You confine the chemist's laboratory to the narrow precincts of the apothecary's and perfumer's shops, whilst it is subservient to an immense va- riety of other useful purposes. Besides, my dear, chemistry is by no means confined to works of art. Nature also has her GENERAL PRINCIPLES laboratory, which is the universe, and there she is inces- santly employed in chemical operations. You are surprised, Caroline ; but I assure you that the most wonderful and the most interesting phenomena of nature are almost all of them produced by chemical powers. What Bergman, in the intro- duction to his history of chemistry, has said of this science, will give you a more just and enlarged idea of it. The know- ledge of nature may be divided, fee observes, into three peri- ods. The first is that in which the'attention of men is occu- pied in learning the external forms and characters of objects, and this is called Natural History. In the second, they con- sider the effects of bodies acting on each other by their me- chanical power, as their weight and motion, and this consti- tutes the science of Natural Philosophy. The third period is that in which the properties and mutual action of the ele- mentary parts of bodies are investigated. This last is the science of Chemistry, and I have no doubt you will soon agree with me in thinking 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 en- large the sphere ofher ideas, and render the contemplation of nature a source of delightful instruction. CaroMtnp. If this is the case, I have certainly been much mistaken in the notion I had formed of chemistry. I own that I thought it was chiefly confined to the knowledge and prepa-' ration of medicines. Mrs. B. That is only a branch of chemistry which is called Pharmacy ; and, though the study of it is, no doubt, of great importance to the world at large, it belongs exclusively to professional men, and is therefore the last that I should advise you to pursue. Emily. But, did not the chemists formerly employ them- selves 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 mej might be'protracted to any desirable length, or their mortality pre vented. 2nd. The universal solvent, or a liquid which should dis solve every other substance. This it was supposed would lead to the grand discovery, viz. 3rd. The making of gold, or finding the philosopher's 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 OF CHEMISTRT. i Mrs. B. These were a particular set of misguided philo- sophers, who dignified themselves with the name of Alche- 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 com- plete a revolution, that, from an obscure and mysterious art, it is now become a regular and beautiful science, to which art is entirely subservient. It is true, however, that we.are indebted to the alchemists for many very useful discoveries, which sprung from their fruitless attempts to make gold, and which, undoubtedly, have proved of infinitely greater advan- tage to mankind than all their chimerical pursuits. The modern chemists, instead of directing their ambition to the vain attempt of producing any of the original substances in nature, rather aim at analysing 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 prodigiously to increase the luxuries as well as the necessaries of life. Emily. But I do not understand by what means chemistry can facilitate labour ; is not that rather the province of the mechanic ? Mrs. B. There are many ways by which labour may be rendered more easy, independently of mechanics ; but me- chanical inventions themselxes often derive their utility from a chemical principle. Thus that most wonderful of all ma- chines, the Steam-engine, could never have been invented without the assistance of chemistry. In agriculture, a chem- some degree, when we are told that the doctrine of transmutation, &c. was founded on a Theory, which in the 12th century, was con- sidered as plausible, as we consider many of ours at the present day, viz. That a perfect metal consisted of quicksilver and sulphur; these, when pure and united, formed gold. That all other metals contained a quantity of dross, which prevented the particles 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 perfection of gold; but many accidents comming between, change the mettalls, &c" See his book, printed in 1597, Chap. ii. C. 4 SENERAL PRINCIPLED ical knowledge of the nature 0/ soils, and of vegetation? may become highly useful; and, in those arts which relate to the comforts and conveniences of life, it would be endless to enumerate the. advantages which result from the study of this science. Caroline. But pray, tell us more precisely in what manner the discoveries of chemists have proved so beneficial to so- ciety ? 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 regard to method, we cannot expect to make any progress in chemistry. I wish to direct your observa- tion? 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 atten- tion. Emily. Well, then, let us now set to work regularly, I am very anxious to begin. Mrs. B. The object of chemistry is to obtain a knowledge1* of the intimate nature of bodies, and of their mutual action on each other. You find, therefore, Caroline, that this is no narrow or confined 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 na-* ture are composed of certain elementary principles, which' are not very numerous. Caroline. Yes ; 1 know that all bodies are composed of fire, air, earth, and water ; I learnt that many years ago. f Mrs. B. But you must now endeavour to forget it. I have already informed you what a great change chemistry has un- dergone since it has become a regular science. Within these thirty years especially, it has experienced an "entire revolu- tion, and it is now proved, that neither fire, air, earth, nor water, can be called elementary bodies.x For an elementary 1 body is one that has never been decomposed, that is to say,' separated into other substances ;^ and fire, air, earth, and wa-' ter, are all of them susceptible "of decomposition. Emily. I thought that decomposing a body was dividing1 OF CHEMISTRY. 5 it into its minutest parts. And if so, I do not understand why an elementary 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 ingredients, 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 is to separate from each other the various elementary substances of which it consists. Caroline. But flour, water, and other materials of bread, according to your definition, are not elementary substances. Mrs. B. No, my dear ; I mentioned bread rather as a fa- miliar comparison, to illustrate the idea, than as an example. The elementary substances of which a body is composed are cjdled the constituent parts of that body : in decomposing it, therefore, we separate its constituent parts. If, on the contrary,, we divide a body by chopping it to pieces, or even by grinding or pounding it to the finest powder, each of these small particles will stillconsist of a portion of the several consti- tuent parts of the whole body ; these are called the integrant parts ; do you understand the difference ? Emily, Yes, I think, perfectly. We decompose a bodv 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 inte- grant parts, it is not possible to decompose it. Such bodies are therefore called 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 elemen- tary principles. Caroline. But do not fire, air, earth, and water, consist. each of them, but of one kind of substance ? Mrs. B. No, my dear ; they are every one of them sus- ceptible of being separated into various simple bodies. In- stead of four, chemists now reckon no less than fifty seven elementary substances. 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 £ GENERAL PRINCIPLES deduced from the latest discoveries. After I have given you a list of the elementary 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. Excepting the more general agents of nature, heat, light, and electricity, 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 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 philosophical world. But to return to the list of simple bodies—these being usu- ally found in combination with oxygen, I shall class them ac- cording 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 elementary bodies whose properties I shall ex- plain 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 at- tention to the enumeration and classification of the simple bo- dies in general. They may be arranged as follows : CLASS I. Comprehending the imponderable agents, viz. HEAT, Or CALORIC, * 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 compos- ed of a metal, and yet not one among this number are known to have metallic bases. C. r Three of the alkalies only are known to have metallic bases. Q OF CHEMISTRY. LIGHT, ELECTRICITY. CLASS II. Comprehending agents capable of uniting with inflammable bodies, and in most instances of effecting their combustion. OXYGEN, CHLORINE, IODINE.* CLASS III. Comprehending bodies capable of uniting with orygen, and forming with it various compounds. This class may be divi- ded as follows: division 1. hydrogen, forming water. division 2. Bodies forming acids. nitrogen, . . forming nitric acid. sulphur, . . . forming sulphuric acid. phosphorus, . forming phosphoric acid. carron, . . forming carbonic acid. boracium, . • forming boracic acid. fluorium, . fmming fluoric acid. muriatium, . forming muriatic acid. division 3. Metallic bodies forming alkalies. potassium, . forming potash. sodium, . . forming soda. ammonium, . forming ammonia. lithium . . forming lithina.* * A majority of the most learned chemists, it is believed, have doubted whether chlorine and iodine were supporters of combustion, any farther than they contain oxygen. C. * This fourth alkali was discovered by Mr. Arfvredson, a Swedish chemist, so recently as the year 1818. GENERAL PRINCIPLES DIVISION 4. Metallic bodies forming earths. calcium, or metal forming lime. magnium, . . forming magnesia. barium, - . . forming barytes. strontium, . . forming strontites, silicium, .- . forming silex. alumium, . . forming alumine. yttrium, . . forming yttria. glucium . . forming glucina. zirconium, . forming zirconia.* thorinum, . forming thorina.t 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, zinc. tin, cadmium.|| ... * Subdivision 2. Brittle Metals. ARSENIC, ANTIMONY, BISMUTH, MANGANE , '* Of all these earths, three or four only have as yet been distinct- decomposed. f Thorina, anew earth discovered by Berzelius in 1816, in a mineral composed of fluoric acid and cerium. J 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, inal- terability, and great specific gravity, in an eminent degree. 4 Mercury, in its liquid state, cannot, of course, be called a malle- able metal. But when frozen, it possesses a considerable dee-rat"* malleability. ' 8 :W || A metal resembling tin; which was discovered in 1817, in an ore of zinc, by Mr. Stromeyer. OF CHEMISTRY. 9 SELENIUM,* ^ URANIUM, TELLURIUM, COLUMBIUM, Or TANTALIUM, COBALT, v, IRIDIUM, TUNGSTEN, OSMIUM, MOLYBDENUM, RHODIUM, TITANIUM, CERIUM.t CHROME, Caroline. Oh, what a formidable list I you will have much to do to explain it, Mrs. B.; for 1 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 hereafter this classification will appear quite clear, and, so far from perplexing you, will assist you m arranging your ideas. It would be a vain attempt to form a division which would appear perfectly clear to a beginner ; for you may ea- sily conceive that a chemical division being necessarily found- ed on properties with which you are almost wholly unac- quainted, it is impossible that you should at once be able to understand its meaning or appreciate its utility. But, before we proceed farther, it will be necessary to give you some idea of chemical attraction, a power on which the whole science depends. Chemical Attraction, or the Attraction of Composition, con- sists in the peculiar tendency which bodies of a different na- ture 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 attrac- tion, and the attraction of cohesion, or of aggregation, which you often mentioned 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 sim- ple 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, par- * Selenium was discovered a few years ago by Berzelius in the ferruginous pyrites of Fahlun in 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. f 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. 10 GENERAL PRINCIPLES tides 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 particles are con- nected into a single mass. Emily. The attraction of cohesion, then, is the power which unites the integrant particles of a body : the attraction of composition is that which combines the constituent parti- cles. Is it not so ? Mrs. B. Precisely: and observe that the attraction of cohesion unites particles of a similar nature, without chang- ing 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 attraction of composition, by combin- ing particles of a dissimilar nature, produces compound bo- dies, quite different from any of their constituents. If, for in- stance, I pour on the piece of copper, contained 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 com- bine with a particle of acid, and together they will form a new body, totally different from either the copper or the acid. Do you observe the internal commotion that already begins to take place ? It is produced by the combination of these two substances ;* and yet the acid has in this case to overcome not only the resistance which the 6trong cohesion of the par- ticles of copper opposes 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 to it as it would if the me'tal were suspend- ed in the liquid. Emily. The acid seems, however, to overcome both these obstacles 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 bo- dies will be completed. You may, however, already see how totally different this compound is from either of its ingredients. It is neither co- lourless, like the acid, nor hard, heavy, and yellow like the * 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. OF CHEMISfRY. 11 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 water with which the acid is diiuterl is evaporated, the compound will assume the form of regular crystals of a fine blue colour, and perfectly transparent.* Of these I can show you a spe- cimen, as 1 have prepared some for that purpose. Caroline. How very beautiful they are, in colour, form, and transparency ! Emily. Nothing can be more striking than this example of chemical attraction. Mrs. B. The term attraction has been lately introduced into chemistry as a substitute for the word affinity, to which some chemists 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 ; and this idea is not only imperfect, but erroneous, as it is generally particles of the most dissimilar na- ture, that have the greatest tendency to combine. Caroline. Besides, there seems to be no advantage in using a variety of terms to express the same meaning ; on the con- trary it creates confusion ; and as we are well acquainted with the term Attraction in natural philosophy, we had bet- ter 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 general 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 pre- ference 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 par- ticles (as you say was once supposed), yet, as it really ex- ists, it ought to be expressed. Mrs B. Well, let it be agreed that you may use the terms affinity, chemical attraction, and attraction of composition in- differently, provided you recollect that they have all the same meaning. Emily. I d© not conceive how bodies can be decomposed * These crystals are more easily obtained from a mixture of sul- phuric with a little nitric acid f f These crystals are sulphate of copper, or what is commonly known under the name of blue vitriol. C. 12 GENERAL PRINCIPLES by chemical attraction. That this power should be the means of composing 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 sepaiate its constituent parts, which, as we have just observed, cannot be done by mechanical means. ____ Emily. No : because mechanical means separate only the integrant 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 principles will be separated by means of the third body. Let us call two ingredients, of which the body i* composed, A and B. If we present to it another ingredi- ent C, which hns a greater affinity for B than that wh.ch unites A and B, it necessarily follows that B will quit A to combine with C. The new ingredient, therefore, has effect- ed a decomposition of the original body A B ; A has been lelt alone, are a new compound, B C, has been formed. Emily. We might, I think, use the comparison of two friends who 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. 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 ingredi- ents, copper and nitric acid ; we may do this by presenting to it a piece of iron, for which the acid has a stronger attrac- tion 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. j Caroline. So it is really ! but then i« 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 Bh CHEMISTRY. 13 acid which combines with the iron, and, in so doing, deposits or precipitates the copper on the surface of the blade. Emily. But cannot three or more substances combine to- gether, 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 attraction of several substances for each other is so equally balanced as to produce such complicated com- pounds * Caroline But, pray, Mrs. B., what is the cause of the chemical attraction of bodies for each other ? It appears to me mote extraordinary or unna^»ral, if I may use the expres- sion, than the attraction of cohesion, which unites particles of a similar nature. Mrs. B. Chemical attraction may, like that of cohesion or gravitation, be one of the powers inherent in matter, which, in our present state of knowledge, admits of no other satis- factory explanation than an immediate reference to a divine cause. Sir H. Davy, however, whose important discove- ries have opened such improved views in chemistry, has sug- gested an hypothesis which may throw great light upon that science. He supposes that there are two kinds of electrici- ty, with one or other of which all bodies are united. These we distinguish by the names of positive and negative electri- city ; those bodies are disposed to combine, which possess opposite electricities, as they are brought together by the attraction which these electricities, have for each other. But, whether this hypothesis be altogether founded on truth or not, it is impossible to question the great influ- ence of electricity in chemical combinations. Emily. So, that we must suppose that the two electrici- ties always attract each other, and thus compel the bodies in which they exist to combine ?| * Such compounds are quite numerous. They are called triple salts. Alum is one. It is composed of Alumine, potash, and sul- phuric acid. Tartar Emetic is another. It is composed of tartaric acid, potash and antimony. C. f 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 equilibrium, or in the same state of electricity, and consequently neither attract nor repel each other. If, therefore, chemical attraction depend* 1 14 GENERAL PRINCIPLES. Caroline. And may not this be also the cause of the at- traction of cohesion ? Mrs. B. No, for in particles of the same nature the same electricities must prevail, and it is only the different or oppo- site electric fluids that attract each other. Caroline. These electricities seem to me to be a kind of chemical spirit, which animates the particles of bodies, and draws them together. Emily. If it is known, then, with which of the electrici-' ties bodies are united, it can be inferred which will, and which will not, combine together 1 Mrs. B. Certainly. I should not omit to mention, that some doubts have been entertained whether electricity be re- ally a material agent, or whether it might not be a power in- herent in bodies, similar to, or perhaps identical with, at- traction. 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. Da- vy 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 princi- pal 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. QUESTIONS. What is the object of Chemistry? W hat is an elementary substance ? What is decomposition ? What is the difference between decomposition and division? What is a compound body ? What is the number of elementary substances ? What is the difference between attraction of cohesion, and attraction of composition? How can a compound body be decomposed ? What are the names and number of the simple bodies ?' on t)ie different electrical states of the particles, we are still at a loss how to account for their adhesion even after they are united. Thai celebrated Kepler accounted for the affinity of ^articles by suppos- ing each to have its likings and its antipalthies'^nd the power of choo-ing accordingly. This theory only wants our belief to make it satisfactory. C. LIGHT. 15 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 success- ively. You will begin 1 suppose with light ? Mrs. B. Respecting the nature of light we have little more than conjectures. It is considered by most philoso- phers as a real substance, immediately emanating from the sun, and from all luminous bodies, from which it is projected in right lines with prodigious velocity. Light however, being imponderable, it cannot be confined and examined by itself; and therefore it is to the effects it produces on other bodies, rather than to its immediate nature, that we must direct our attention. The connection between light and heat is very obvious ; indeed, it is such, that it is extremely difficult to examine the one independently 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. Mrs. B. I told you that fire was not now considered as a simple element. Whether light and heat be altogether dif- ferent 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 illustration of the separation of heat and light was long after pointed out by Dr. Herscbell. This philosopher discovered that these two agents were emitted in the rays of the sun, and that heat was less refran- gible than light ; for, in separating the different coloured rays of light 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 lea^t 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 delicate thermometer to distinguish the difference of the degree of heat within and without the spectrum. For in this experiment the heat is not totally separated from the light, each coloured ray retaining a certain portion of it. 16 LIGHT. though the greatest part is not sufficiently refracted to tail within the spectrum. Emily. I suppose, then, that these coloured rays which are the least refrangible, retain the greatest quantity of heat? Mrs. B. They do so. Emily. Though I 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 di- vided into the various coloured rays. Mrs. B. No doubt there must be some difference in the various coloured rays. Even their chemical powers are different. The blue rays, for instance, have the greatest ef- feet in separating oxygen from bodies, as was found by Scheele ; and there exists also, as Dr. Wollastcp has shown, rays more refrangible than the blue, which produce the same chemical effect, and, what is very remarkable, are invisible.* Emily. Do you think it possible that heat may be merely a modification of light ? Mrs. 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 contented 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 phosphorescence. Bodies that are possessed of this proper- ty, after being exposed to the sun's rays, appear luminous in the dark. The shells offish, the bones of land auimals, mar- ble, limestone, and a variety of combinations of earths, are more or less powerfully phosphorescent. 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 phospho- rescent nature ? Mrs. B. It is a very remarkable instance of phosphores-; cence in living animals ; this property, however, is not ex- * The violet rays have the power of imparting the magnetic virtue to steel. The process consists in intercepting all the rays except 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 extrem- ity. This is to oe done many times, and always towards the same extremity. After a while the needle acquires polarity. C. LIGHT. 11 clusively possessed 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 common to see animal matter in a dead state possessed of a phosphorescent quality ; seafish is often eminently so.* Emily. I have heard that the sea has sometimes had the appearance of being illuminated, and that the light is suppos- ed to proceed from the spawn of fishes floating on its surface. Mrs. B. This light is probably owing to that or some oth- er animal 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 chemi- cal compositions prepared for the purpose, the most common of which consists of oyster-shells and sulphur, and is known by the name of Canton's Phosphorus.! 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 connected with the chemical history of combustion, that I must defer all explanation of it till we come to the examina- tion of that process, which is one of the most interesting in chemical science. Light is an agent capable of producing various chemical changes. It is essential to the welfare both of the animal and vegetable kingdoms ; for men and plants grow pale and sickly if deprived of its salutary influence. It is likewise remark- able for its 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 op- tics we were taught to consider as the source and origin of colours, should have also the power of destroying them ? * The phosphorescence of dead animals is owing to the escape of phosphorus 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 3 parts of oyster shells calcined for an hour and pulverized with 1 part of sulphur. This is to be rammed into a crucible, which is to be kept at a red heat for one hour. On ex- posing 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 heat. C. 3* 18 FREE GALORIft, Caroline. It is a fact, however, that we every day expe- rience : you know how it fades the colours of linens and silks.,, Emily. Certainly. And I 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 properties of light can be accounted for only in their reference to compound bodies, it would be useless to de- tain you any longer on this subject ; we may therefore pas9 on to the examination of heat, or caloric, with which we are i somewhat better acquainted. • Heat and Light may be always distinguished by the dif- j ferent sensations they produce. Light affects the sense of sight; Caloric that of feeling ; the one produces Vision, the- other the sense of Heat. A Caloric is found to exist in a variety of forms or modifica- tions, 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 ? Mrs. 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, whatever may be its degree, or the source from which it is derived. Caroline. What then are the other modifications of ca- loric ? It must be a strange kind of heat that cannot be per- ceived by our senses. Mrs. B. None of the modifications of caloric should pro- perly be called heat; for heat, strictly speaking, is the sen- sation produced by caloric, on animated bodies ; this word, therefore, in the accurate language of science, should be con- fined to express the sensation. 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 confounding the cause and effect, that modern chemists ► adopted the new word caloric, to denote the principle which i'REE CALORIC 10 produces heat; yet they do not always, in compliance with. their own language, limit the word heat to the expression of the sensition, since they still frequently employ it in refer- ence to the other modifications of caloric which are quite in- dependent 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 pro- perties 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 particles, and not only separates them, but frequently drives them asunder 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 be- fore. 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. Preciaely. There is a continual struggle between the attraction of aggregation, and 'he expansive power of caloric ; and from the action of these two opposite forces, result all the various forms of matter, or degrees of consis- tence, 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, 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 at- traction of cohesion ; and the body, from a solid, is then con- verted 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 * If I touch a body at a higher temperature than my blind, I im- mediately receive a quantity of caloric from it, and at the sam#*in- stant 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. •1 20 FREE CALORIC. between the particles of the fluid, and drives them to such a dis;.uice from each other, that their attraction of aggregation, is wholly destroyed ; the liquid is then transformed into va- pour. - Airs. B. Very well; and this is precisely the case with boiling water, when it is converted into steam or vapour, and with all bodies that assume an aeriform state. Emily. I do not well understand the word aeriform ? Mrs. B. Any elastic fluid whatever, whether it be merely vapour or permanent air, is called aeriform. But each of these various states, solid, liquid, and aeriform, admit of many 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 melted glue, or melted metals, to that of ether, which is the lightest of all liquids. The different elastic fluids (with which you are not yet acquainted) are j 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 1 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! I knew that heat had this effect on bodies, but I did not imagine that it could be made so conspicuous. Mrs. B. By means of this instrument (called a Pyrome- ter) we may estimate, in 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 small iron bar ; I fix it to this apparatus, (Plate I. Fig. 1.) and then heat it by lighting the three lamps beneath it: when the bar expands, it increases in length as well as thickness ; and, as one end communi- cates with this wheel-work, whilst the other end is fixed and immoveable, no sooner does it begin to dilate than it presses against the wheel-work, and sets in motion the index, which points out the degrees of dilatation on the dial-plate. Emily. This is, indeed, a very curious instrument; but I do not understand the use of the wheels : would it not be PLJTE.I. Fio. 1. r«l.M.n,,r,fMrr„l.l*.XL«.nP,h,rni„v. IU3. *W „«*. C. /W„. ^.*.,Y.A. ftW*^ ,,,W fe/A. r.r. «w „/>„*,•,« „/„W5 ^«y ,W,W. 1 REE CALORIC. 21 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 ? Mrs. 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 in- creased in length, its motion would scarcely be perceptible ; but by means of the wheels it moves in a much greater pro- portion, which therefore renders the variations far more con- spicuous. By submitting different bodies to the test of the pyrome- ter, it is found that they are far from dilating in^he same pro- portion. Different metals expand in different degrees, and other kinds of solid bodies vary still more in this respect. But this different susceptibility of dilatation is still more re- markable in fluids than in solid bodies, as 1 shall show you. I have here 2 glass tubes, terminated at one end by large bulbs. We shall fill the bulbs, the one with spirit of wine, the other with water. I have coloured both liquids, in order that the effect may be 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 affected by heat: for scarcely any change is produced on it by the warmth of the hand. Mrs. B. True ; we shall now plunge the bulbs into hot water, (Plate I. Fig. 2.) 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 top of the tube, though the water has hardly be- jun to rise. Emily. The water now begins to dilate. Are not these ;lass tubes, with liquids rising within them, very like ther- nometers ? Mrs. B. A thermometer is constructed .exactly on the ame principle, and these tubes require only a scale to an- wer the purpose of thermometers ; but they would be ather awkward in their dimensions. The tubes and bulbs if thermometers, though of various sizes, are in general * In the absence of glass tubes terminated bv bu'^s, procure a air of tin cannisters, 3 inches high and two wide, soldered up all ound. In the middle of the top of each, have inserted a circular n spout, and into these cement glass tubes about 12 inches high. 'hese will answer every purpose. C 22 FREE CALORIC. much smaller than these ; the tube, too, is hermetically* closed, and the air excluded from it. The fluid most gene- rally used in thermometers is mercury, commonly called; quicksilver, the dilatations and contractions of which cones- pond more exactly to the additions, and subtractions, of cal- oric, 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 not requisite to ascertain the temperature with great precision, spirit of wine will answer the purpose equally well, and indeed in some respects better, as the ex- pansion of the latter is greater, and therefore more conspitf uous. This fluid is used likewise in situations and experi- ments in which mercury would be frozen ; for mercury be- comes 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.j A thermometer, therefore, consists of a tube.with a bulb, such as you see here, containing a fluid whose degrees of dl latation and contraction are indicated by a scale to which the i 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 at that temperature. The extreme points of the scales are not the same in all thermometers, nor are the degrees always divided in the same manner. In different countries philosophers have chosen to adopt differ- ent scales and divisions. The two thermometers most used are those of Fahrenheit, and of Reaumur ; the first is gener- ally preferred by the English, the latter by the French. Emily. The variety of scale must be very inconvenient, and I should think liable to occasion confusion, when Frent and English experiments are compared. * The tube is closed by holding the end over a spirit lamp until the glass is melted. This vv'ord is derved from Hermes, the Greek name for Mercury. He is said to have been the inventor of chern'l istry ; hence this is sometimes called the Hermetic art, and herme- tically, or chemically closed, is closed by heat or melting. C. f Spirit of wine is stated to have been frozen in England by ! >;fi< process which the author has preferred to keep secret. C. PLATE 11. THERMOMETER. Fie,. J. Fire zingffor'nt cfflfrtrr FREE CALORIC. 23 Mrs. B. The inconvenience is but very trifling, because the different gradations of the scales do not effect the prin- ciple upon which thermometers are constructed. When we know, for instance, that Fahrenheit's scale is divided into 212 degrees, in which 32° corresponds with the freezing point, and 212° with the point of boiling water ; and that Reaumur's is divided only into 80 degrees, in which 0° de- notes 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, thermometers are sometimes constructed with both these scales, one on either side of the tube ; so that the correspondence of the different degrees of the two scales is thus instantly seen. Here is one of these scales, (Plate II. Fig. 1.) by which you can at once perceive that each degree of Reaumur's cor- responds to 2 1-4 of Fahrenheit's division. But I believe the French have, of late, given the preference to what they call the centigrade scale, in which the space between the freezing and the boiling point is divided into 100 degrees. Caroline. That seems to me the most reasonable division, and I cannot guess why the freezing point is called 32°, or what advantage is derived from it. Mrs. B. There is really no advantage in it; and it ori- ginated in a mistaken opinion of the instrument-maker, Fah- renheit, who first constructed these thermometers. He mix- ed snow and salt together, and produced by that means a degree of cold which he concluded was the greatest 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 thermometers ? Mrs. B. I believe they are the only liquids now in use, though some others, such as linseed oil, would make tolerable thermometers : but for experiments in which a very quick and delicate test of the changes of temperature is required, air is the fluid sometimes employed. The bulb of air ther- mometers is filled with common air only, and its expansion and contraction are indicated by a small drop of any coloured li- quor, which is suspended within the tube, and moves up and down, according as the air within the bulb and tube expmds or contracts. But in general, air thermometers, hosveve! sensible to changes of temperature, are by no means accurate. in their indications. 24 FREE CALORIC. I can, however, show you an air thermometer of a very peculiar construction, which is remarkably well adapted for some chemical experiments, as it is equally delicate and ac- curate in its indications.* Caroline. It looks like a double thermometer reversed, the tube being bent, and having a large bulb at each of its ex- tremities. (Plate II. Fig. 2.) Emily. Why do you call it an air thermometer ? the tube contains a coloured 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 contraction of the air within the bulbs, which afford an indication of their relative tempeif ture. 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 il you reverse the experiment. But if, on the contrary, both tubes are of the same temper- ature, as is the case now, the coloured 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 thermo- meter cannot indicate the temperature of any particular body, or of the medium in which it is immersed : it serves only to point out the difference of temperature between the two bulbs, when placed under different circumstances. For this reason it hits been called differential thermometer. You will see hereafter to wha't particular purposes this instrument applies, Emily. But do common thermometers indicate the exact quantity of caloric contained either in the atmosphere, or in any body with which they are in contact ?t * Students in chemistry may amuse themselves with air therm*' meters of their own construction. Procure a flat vial, or inkstand with a wide mouth -. also a broken thermometer tube, the bulb be- ing 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 coloured liquid. Warm the bulb of the tube by hold- ing it in the hand, and in this state introduce the small end through the cork nearly to the bottom of the vial. The hand being removed from the bulb, the fluid will rise in the tube. The fluid will after- wards rise or fall as heat is applied to the vial or bulb. C. f The thermometer indicates the exact quantity of free calorfc present at the time and place of the experiment. Thus if a certatt quantity of heat is required to raise the mercury 20Q, double this FREE CALORIC 85 Mrs. B. No : first, because there are other modifications of caloric which do not affect the thermometer ; and, second- ly, because the temperature of a body, as indicated by the thermometer, is only relative. When, for instance, the thermometer remains stationary 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 quan- tity 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. Mrs. B. Let us compare a thermometer to a well, in which the water rises to different heights, according as it is more or less supplied by the spring which feeds it : if the depth of the well is unfathomable, it must be impossible to know the absolute quantity of 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 tjfne, and conse- quently know the precise quantity of its increase or diminu- tion, without having the least knowledge of the whole quanti- ty of water it contains.! Caroline. Now I comprehend it very well : nothing ap- pears to me to explain a thing so clearly as a comparison. Emily. But will thermometers bear any degree of heat ? Mrs. B. No: for if the temperature were much above the highest degree marked on the scale of the thermometer, the mercury would burst the tube in an attempt to ascend. And at any rate, no thermometer can be applied to tempera- tures higher than the boiling point of the liquid used in its quantity will raise it to 40°. All bodies contain a quantity of heat not appreciable by the thermometer, or sensible to the touch. This is called fixed or latent heat. This can sometimes be set free, as when we hammer a piece of cold iron it becomes hot. Thus the latent caloric is squeezed out of the iron by the contraction of its pores under the hammer, and then becomesyree caloric. C. f This passage may be expounded as follows. The unfathomable depth of the well signifies the absolute quantity of caloric, and which the thermometer does not measure ; because all bodies however cold, still contain caloric. Thus mercury freezes at 40'? below ze- ro, but still contains caloric, and so on. The rising and falling of the water signifies the greater or less quantity of free caloric as In- dicated by the thermometer. C. 4 26 FREE CALORIC. construction ; for the steam, on the liquid beginning to boil, would burst the tube. In furnaces, or whenever any very high temperature is to be measured, a pyrometer, invented by Wedgwood, is used for that purpose. It is made of a certain composition of baked clay, which has the peculiar property of contracting by heat, so that the degree of contraction of this substance indicates the temperature to which it has been exposed. Emily. But is it possible for a body to contract by heat ? I'thought that heat dilated all bodies whatever. Mrs. B. This is not an exception to the rule. You must recollect 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 this instrument are derived. This change, consists in a beginning fusion which tends to unite the parti- cles of clay more closely, thus rendering it less pervious or spongy.* Clay is to be considered as a spongy body, abounding in interstices or ^jores, from its having contained water when soft. These interstices are by heat lessened, and would by extreme heat be entirely obliterated. > Caroline. And bow do you ascertain the degrees of con- traction of Wedgwood's pyrometer ? Mrs. B. The dimensions of a 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 we quit the subject of expansion, I must observe to you that, as liquids expand more readily than solids, so elastic fluids, whether air or vapour, are the most expansible of all bodies. It may appear extraordinary, that all elastic fluids whatev- er, undergo the same degree of expansion from equal aug- mentations of temperature. Emily. I suppose, then, that all elastic fluids are of the same density ? Mrs. B. Very far from it; they vary in density, more than either liquids or solids. The uniformity of their ei- * According to the calculations of Saussure, the temperature ne- cessary to melt this clay is 1575° Wedgwood, which is a degree of heat greatly beyond our common furnaces It is therefore most probable that the clay contracts at lower temperatures by the lossg of moisture.. C. FREE CALORIC. 27 pansibility, 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 at- traction of cohesion, no such difference can be expected in elastic fluids, since in these the attraction 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 the ex- pansive force 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 pro- perties of free caloric. Free caloric always tends to diffuse itselfequally,thatis to say, when two bodies are of different temperatures, the warmer gradually parts with its heat to the colder, till they are both brought to the same temperature. Thus, when a thermometer is applied to a hot body, it receives caloric ; when to a cold one, it communicates part of its own caloric, and this communication coutinues until the thermometer and the body arrive at the same temperature. Emily. Cold, then, is nothing but a negative quality, sim- ply implying 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 be discovered. Caroline. But when I lay my hand on this marble table I feel it positively cold, and cannot conceive that there is any ealoric in it. Mrs. B. The cold you experience consists in the loss of caloric that your hand sustains in an attempt to bring its tem- perature to an equilibrium with the marble. If you lay a piece of ice upon it, you will find that the contrary effect will take place ; the ice will be melted by the heat which it ab- stracts from the marble. Caroline. Is it not in this case the air of the room, which, being 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 cannot be on the same principle as other fluids, since it has bo weight. 28 FREE CALORIC. Mrs. B. Very true, Caroline ; that is an excellent objec. tion. You might also with some propriety, object to the term equilibrium being applied to a body that is without weights but I know of no expression that would explain my meanu)» so well. You must consider it, however, in a figurative, ra- ther than in a literal 'sense: its strict meaning is an eqvd diffusion. We cannot, indeed, well say by what power it dif- fuses itself equally, though it is not surprising that it shouUI go from the parts which have the most to those which have the least. This subject is best explained by a theory sugge*. I ted by Professor Prevost of Geneva, which is now, 1 believe, generally adopted. According to this theory, caloric is Composed of particles perfectly separate from each other, every one of which I moves with a rapid velocity in a certain direction. Then] directions vary as much as imagination can conceive, the re;j suit of which is, that there are rays or lines of these particle moving with immense velocity in every possible direction Caloric is thus universally diffused, so that when any portiflD of space happens to be in the neighbourhood of another, whiehj oontains more caloric, the colder portion receives a quanti| of calorific rays from the latter, sufficient to restore an equi- librium of temperature. This radiation does not only take) place in free space, but extends also to bodies of every kind.* Thus you may suppose all bodies whatever constantly radia- ting caloric ; those that are of the same temperature give out and absorb equal quantities, so that no variation of tempera- ture is produced in them ; but when one body contains more free caloric than another, the exchange is always in favour of the colder body, until an equilibrium is effected ; this yo« found to be the case when the marble table cooled your band,] and again when it melted the ice. Caroline. This reciprocal radiation surprises me extreme- ly ; I thought from what you first said, that the hotter bodies alone emitted rays of caloric, which were absorbed by the colder ; for it seems unnatural that a hot body should receive] any caloric from a cold one, even though it should returns greater quantity, Mrs. B. It may at first appear so, but it is no more extras '■* This is true when applied to inanimate matter. But if a livfl animal is exposed to a degree of heat above the temperature ot ittl own body, it has the power of resistance; and though the heat be 100 degrees above that of the animal, it scarcely affects its temper* ture. C. 1 Mr. FICTETS' APPARATUS FOR THE REFLECTION OF MAT Ftf.l. A. A .fc'BJB. ConctH'C miri-ir* tiredon Hands. .(.Heated' Hultet //facedin the focus of die im'rrvi-A. WTIiermcmctrr uM its Mi /'hired i lirtiso'ft/ie mirivi-3. 1.2.3.4 Jti/yjv et" Caloric mJiatt'ny tivm die Mlet it tilling on the narmr A.-i.6.7.8 Tlu- .rami rai< irfiected rrvm t/i' i A. Hi die mirror B.S'JO.M.J2 The same reeiv re/lectce/ ir f/tf ntirwrB to tfie Thermometer. AL^L_ FREE CALORIC. 29 ordinary than that a candle should send forth rays of light to the sun, which, you know, must necessarily happen. Caroline. Well, Mrs. B—, I believe that I 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 yoifr own ; the loss of the caloric you part with in return, it is frue, 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 sustain an absolute loss of caloric. Emily. 4nil 'n t^s case we cannot be sensible of the small quantity of heat we receive in exchange from the colder bo- dy, because it serves only to diminish the loss. Mrs. B. Very well, indeed, Emily. Professor Pictet, of Geneva, has made some very interesting experiments, which prove not only that caloric radiates from all bodies whatever, but that these rays may be reflected according to the laws of optics, in the same manner as light. I shall repeat these ex- periments before you, having procured mirrors* fit for the purpose ; and it will afford us an opportunity of using the differential thermometer, which is particularly well adapted for these experiments.—I place an iron bullet, (Plate III. Fig. 1.) 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 direction, so as to fall on a similar mir- ror, which, you see, is placed opposite to the first, at the dis- tance 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 manner it is affec- ted 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 opposite 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 he planished with a hammer having a convex face, and afterwards polished with a piece of buckskin, and a little whiting. C. 30 FREE CALORIC. Emily. But would not the same effect take place, if the rays of 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 distance at which the bullet and the thermometer are from each other, that it would be almost imperceptible. The mirrors, you know, greatly increase the effect, by collecting a large quantity of rays into a focus ; place your hand in the focus of the mirror, and you will find 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 which it proceeds. Caroline. And the mirror which produces so much heat, by converging the rays, is itself quite cold. Mrs. B. The 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 themirroi presents to the rays, and, consequently, how much they are diffused in comparison to what they are at the focus, which is little more than a point, 1 think you can no longer wonder that the focus should be so much hotter than the mirror. The principal use of the mirrors in this experiment, is, to Drove that the calorific emanation is reflected in the same manner as light. Caroline. And the result, I think, is very conclusive. Mrs. B. The experiment may be repeated with a wax ta- per, instead of the bullet, with a view of separating the light from the caloric. For this purpose a transparent plate of glass must be interposed between the mirror« ; 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 experiment, that some few of the calorific rays pass through the glass together with the light, as the thermometer rises a little ; but, as soon as the glass is re- moved, and a free passage left to the caloric, it will rise corH ^iderably higher. % Emily. This experiment, as well as that of Dr. HerschelJ proves that light and heat may be separated ; for in the lat- ter experiment the separation was not perfect, any more than in that of Mr. Pictet. Caroline. I should like to repeat this experiment, with the difference of substituting a cold body instead of the hot one, to see whether cold would not be reflected as well a» heat. FREE CALORIC. 31 Mrs B. That experiment was proposed to Mr. Pictet by an incredulous philosopher like yourself, and he immediately tried it by substituting a piece of ice in the place of the heat- ed bullet. Caroline. Well, Mrs. B., and what was the result ? 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 cole! is not merely a negative quality, implying simply an inferior degree of heat? The cold 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 prooi of»the reflection of heat; this I shall endeavour to ex- plain to y#u. According to Mr. Prevost's theory, we suppose that all bodies whatever radiate caloric ; the thermometer used in these experiments, 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 sis it parts with, and no change of temperature is produced. But when we introduce a body of a lower tem- perature, such as a piece of ice, which 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 were to bring a large piece of ice into this room, the ice would in time be melted, by absorb- ing caloric from the general radiation which is going on throughout the room ; and, as it would contribute very little caloric in return for what is absorbed, the room would neces- sarily be cooled by it. Mrs. 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 bodies, 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 ex- planation. 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 received from it, that the fall of the 32 FREE CALORIC. mercury is occasioned : for the ice, far from emitting rays of cold, sends forth rays of caloric, which diminish the loss sus- tained by the thermometer. Let us say, for instance, that the radiation of the thermom- eter towards the ice is equal to 20, and that of the ice towards the thermometer to 10 : the exchange in favour of the ice is as 20 is to 10, or the thermometer absolutely loses 10, whilst the ice gains 10. Caroline. But if the ice actually semis rays of caloric to tfce thermometer, must not the latter fall still lower when the ice is removed ? Mrs. B. No : for the space which the ice occupied, ad- mits rays from all the surrounding bodies to pass through it;' and those being of the same temperature as the thermometer, will not affect it, because as much heat now retqjns to the thermometer as radiates from it. Caroline. I must confess that you have explained this in so satisfactory a manner, that I cannot help being convinced now that cold has no real claim to the rank of a positive being. Mrs. B. Before I conclude the subject of radiation, I must observe to you, that different bodies (or rather surfaces) pos- sess the power of radiating caloric in very different degreei Some curious experiments have been made by Mr. Leslie on this subject; and it was for this purpose that he invented the differential thermometer : with its assistance he ascer- tained that black surfaces radiate most, glass next, and polish- ed surfaces the least of all. Emily. Supposing these surfaces, of course, to be all of the same temperature. Mrs. B. Undoubtedly. 1 will now show you the verj simple and ingenious apparatus, by means of which he made . these experiments. This cubical tin vessel, or canister, has each of its side.* externally covered with different materials; the one is simply blackened ; the next is covered with white paper ; the third with a pane of 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 eachofits sides front it in succession. We shall begin with the black surface.* * The radiating power of different surfaces may be shown thus: Take a common half pint cup, scour one s;de bright, and paint ot smoke the other blank. Place this in the focus of the mirror, afl4 the thermometer will rise or fall as its sideg are changed. C FREE CALORIC. 33 Caroline. It makes the thermometer, which is in the focus of the other mirror, rise considerably.—Let us turn the pa- per surface towards the mirror. The thermometer fills a little, therefore of course this side cannot emit or radiate so much caloric as the blackened 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 polished tin surface it falls still lower : these two surfaces, therefore, radiate less and less. Caroline. 1 think I have found out the reason ofthis. Mrs. B. I should be very happy to hear it, for it has not yet (to my knowledge) been accounted for. 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 less proportion than the thermometer descends, as you will perceive if you now change the tin surface for the black one. Cara$fne. I was mistaken, certainly ; for the thermome- ter ris»s again now that the black surface fronts the mirror. Mrs. B. And yet the water in the vessel is still cooling, Caroline. . Emily. I am surprised that the tin surface should radiate the least caloric ; for a metallic vessel filled with hot water, a silver tea-pot, for instance, feels much hotter to the hand than one of black earthenware. Mrs. B. That is owing to the different power which va- rious bodies possess for conducting caloric, a property which we shall presently examine. Thus, although a metallic ves- sel feels warmer to the hand, a vessel ofthis kind is known to preserve the heat of the liquid within, better than one of any other materials ; it is for this reason that silver tea-pots make better tea than those of earthen-ware. Emily. According to these experiments, light-coloured dresses, in cold weather, should keep us warmer than black clothes, since the latter radiate so much more than the for- mer. 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 of caloric ; since it would imply thut ?ho*e bo- dies which radiate most, must ultim xely become •■.oldest. Suppose that we were to vary this experiment, by using ^ 34 FREE CALORIC. 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 dowi to the temperature of the room, the interchange of caloric between the canisters and the other bodies of the room being then equal, their temperatures would remain the same. Emily. I do not see why that should be the case ; for if different surfases 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 cer- tainly requires explanation. It is found by experiment that the power of absorption corresponds with and is proportional to that of radiation ; so that under equal temperatures, bodies compensate for the greater loss they sustain in consequence of their greater radiation by their greater absorption ; and if you were to make your experiment in an atmosphere heated like the canisters, to the temperature of boiling water, though it is true that the canisters would radiate in different degress, no change of temperature would be produced in them, be- cause they would each absorb caloric in proportion 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 w*uld. But the various bod- ies in the room would not, at a lower temperature, furnish either of the canisters with a sufficiency of caloric to com- pensate for the loss they undergo ; for, suppose the black canister to absorb 400 rays of caloric, whilst the metallic one 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 wha becomes of the surplus of calorific rays, which good radia- tors emit, and bad radiators refuse to receive : they must wan- der about in search of a resting place ? ' Mrs. B. They really do so : for they are rejected and sent back, or, in other words, reflected by the bodies which are bad radiators of caloric ; and they are thus transmitted" U other bodies which happen to lie in their way, by whiel FREE CALORIC. 35 they are either absorbed or again reflected, according as the property of reflection, or that of absorption, predominates in these bodies. Caroline. I do not well understand the difference between radiating and reflecting caloric ; for the caloric- that is reflec- ted'from a body proceeds from it in straight lines, and may surely be said to radiate from it ? Mrs. B. It is true that ttrere at first appears to be a great analogy between radiation and reflection, as they equally con- vey the idea of the transmission of caloric. But if you consider a little, you will perceive that when a sody radiates caloric, the heat which it emits not only pro- :eeds from, but has its origin in the body itself. Whilst ivhen a body reflects caloric, it parts with none of its own ;aloric, but only reflects that which it receives from other )odies. Emily. Of this difference we have very striking examples >efore us. in the tin vessel of water, and the concave mir- rors ; the first radiates its own heat, the latter refleot the .ieat which they receive from other bodies. Caroline. Now, that I understand the difference, it no onger surprises me that bodies which radiate, or part with heir own c&loric freely, should not have the power of trans- mitting with equal facility that which they receive from other •odies. i Emily. Yet no body can be said to possess caloric of its wn, if all caloric is originally derived from the sun. Mrs. B. When I speak of a body radiating its own calo- ic, I mean that which it has absorbed and incorporated ither immediately from the sun's rays, or through the me- ium of any other substance. Caroline. It seems natural enough that the power of ab- srption should be in opposition to that of reflection, for the tore caloric a body receives, the less it will reject. Emily. And equally so that the power of radiation should ?rrespond with that of absorption. It is, in fact, cause and ffect ; for a body cannot radiate heat without having previ- nsly absorbed it ; just as a spring that is well fed flows Mindantly. Mrs. B. Fluids are in general very bad radiators of calo- 'c ; and air neither radiates nor absorbs'caloric in any sen- ble degree. We have not yet concluded our observations on free calo- c. But I shall defer, till our next meeting, what I have 36 FREE CALORIC. further to say on this subject. I believe it will afford us am- pie conversation for another interview. QUESTIONS. Is there an inseparable connection between light and heat >-Hovr ToTha^i^ttSToresence of dead animal matter owing? How do you distinguish heat and light from each other. What is free caloric ? What is combined or latent caloric ? , ■ , What is the difference between heat and caloric . What is the most remarkable effect of free caloric on bodies? Does heat expand all bodies in the same degree ? What is the temperature of boiling water ? Why cannot water be heated above a certain degree in the opei Why was the freezing point of Fahrenheit marked 32° ? Why do air thermometers indicate smaller changes of temperature thao others? . Can jou name any substance, or any known, condition ot a tub stance in which caloric is absent ? What is cold ? Why does a metallic mirror feel cold when placed before the nre W hat kind of a surface radiates most heat ? Why do metallic coffee pots retain the heat of the coffee longer thai earthen ones ? What becomes of the caloric radiated by a hot body ? What is the difference between the radiation and refection of cat ^ one: CONVERSATION III. CONTINUATION OF THE SUBJECT. Mrs. B. In our last conversation, we began to examine the tendency of caloric to restore an equilibrium "of temper- ature. This property, w4ien once well understood, affoti the explanation of a great variety of facts which appeared formerly unaccountable. You must observe, in the first phce, that the effect of this tendency is gradually to bring all bodies that are in contact to the same temperature. Thiifl the fire which burns in the grate, communicates its heat from one object to another, till every part of the room has as equal proportion of it. Emily. And yet this book is not so cold as the table ot which it lies, though both are it an equal distance from u* fire, and actually in contact with each other, so that, accorl FREE CALORIC. iug to your theory, they should be exactly of the same tem- perature. Caroline. And the hearth, which is much nearer the fire than the carpet, is certainly the colder of the two. Mrs. B. If you ascertain the temperature of these sev- era* bodies by a thermometer (which is a much more accu- rate test than your feeling), you will find that it is exactly the same. Cu-oline. 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 axe not such good con- ductors of heat as the former. Caloric finds a more easy passage through marble and wood, than through leather and wor-.ted ; the two former will therefore absorb heat more rapidly from your hand, and consequently give it a stronger sensation of cold than the two latter, 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,ifyou 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 you feel. • But in order to ascertain this point, it is necessary 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 bet- ter conductors of heat than others ? Mrs. B. This is a point not well ascertained. It has been conjectured 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 de- tains the heat, and parts with it slowly and reluctantly ; if slight, it propagates it freely and rapidly. The conducting power of a body is therefore, inversely, as its tendency to unite with caloric. fe Emily. That is to say, that tke best conductors are those l'that have the least affinity for caloric. Mrs. B. Yes ; but the term affinity is objectionable in this i'case, because, as that word is used to express a chemical at- traction (which can be r'^Voved only by decomposition), it icannot be applicable to the slight and transient union thai 5 38 JREE CAL0IC takes place between free caloric and 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 therefore, 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 conse- quently 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 nost rapidly from your hand, so it will now impart heat most rapidly to it. Thus the marble table, which seems to us colder than the mahogany one, will prove the hottar of the two to the ice : for, if it takes 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 apparently 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 con- ductor : and, consequently, if it is colder than your hand, you lose more caloric, and if it is hotter, you gain more than with a bad conductor of the same temperature. Mrs. 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 tempera- ture 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 flannel clothing, which is a very bad conductor of heat, prevents our feeling cold ? Caroline. It prevents thecold from penetrating .... Mrs. B. But you forget that cold is only a negative qual- ity- FREE CALORIC. 39 Caroline. True; it only prevents the heat of our bodies from escaping so rapidly as it would otherwise do. Mrs. 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 efficacious in keeping their temperature at the same degree, as it would prevent the free access of the exter- nal heat, by the difficulty with which it conducts it. Emily. This, I think, is very clear. Heat, whether ex- ternal or internal, cannot easily penetrate flannel ; therefoie in cold weather 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 greater 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 ; i this again will feel colder than flannel; and down, which is tone of the lightest, is at the same time one of the warmest [bodies.* hi Caroline. This is, I suppose, the reason that the plumage \ of birds preserves them so effectually from the influence of keold in winter ? li Mrs. B. Yes ; but though feathers in general are an ex- cellent preservative against cold, down is a kind of plumage .peculiar to aquatic birds, and covers their chest, which is the part most exposed to the water ; for though the surface of the water is not of a lower temperature than the atmosphere, yet, j]f)s it is a better conductor of heat, it feels much colder, conse- quently the chest of the bird requires a warmer covering than Ijiny other part of its body. Besides, the breasts of aquatic a[t»irds are exposed to cold, not only from the temperature of he water, but also from the velocity with which the breast tfthe bird strikes against it ; and likewise from the rapid eva- poration occasioned in that part by the air against which it , .trikes, after it has been moistened by dipping from time to ',.ime into the water. If you hold a finger of one hand motionless in a glass of s Vater, and at the same time move a finger of the other hand ipei ' ° 58'l *One reason why fur, down, &c. conduct heat so badly, is, that C^iey contain a large quantity of air, which is a worse conductor than , le materials themselves. C. ire £ 40 FREE CALORIC. swiftly through water of the same temperature, a different sensation will be soon perceived in the different fiQgers-* Most animal substances, especially those which Providence ha« assigned as a covering for animals, such as fur, wool, hair, skin, &c. are bad conductors of heat, and are, on that account, such excellent preservatives against the inclemency of winter, 'that our warmest apparel is made of these materials. Emily. Wood is, I dare say, not so good a conductor as metal, and it is for that reason, no doubt, that silver tea-pob 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 radi- ated more caloric than an earthen one. The silver pot is ia fact hotter to the hand when in contact with it; but it is be- cause its conducting power more than counterbalances its de- ficiency in regard to radiation. We have observed that the most dense bodies are m gen- eral the best conductors ; and metals, you know, are of thai class. Porous bodies, such as the earths and wood, are worse conductors, chiefly, I believe, on account of their pores being filled with arr ; for air is a remarkably bad conductor. Caroline. It is a very fortunate circumstance that air should be a bad conductor, as it tends to preserve the heat/ the body when exposed to cold weather. Mrs B. It is one of the many benevolent dispensations of Providence, in order to soften the inclemency of the seasons, and to render almost all climates habitable toman. In fluids of different densities, the power of conducting heat varies no less remarkably ; if you dip your hand into this ves- sel full of mercury, you will scarcely conceive that its tem- perature is not lower than that of the atmosphere. Caroline. Indeed I know not how to believe it, it feels so extremely cold.—But we may easily ascertain its true temper atue by the thermometer.-—It is really not colder than the air ;—the apparent difference then is produced merely by the difference of the conducting power in mercury and in air. Mrs. B. Yes ; hence you may judge how little thesentf of feeling is to be relied on as a test of the temperature» bodies, and how necessary a thermometer is for that purpflfj It has indeed been doubted whether fluids have the pow of conducting caloric in the same manner as solid bodies Count Rumford, a very few years since, attempted to profl * The reason seems to be, that the finger, when it i* still, wa' the wa!er in contact with it: while the one that is stirring is fl stantly exposed to fresh applications of cold. C, FREE CALORIC. 41 by a variety of experiments, that fluids, when at rest, were not at all endowefd with this property. Caroline. How is that possible, since they are capable of imparting 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 Rumford did not mean to say that fluid9 would not communicate their heat to solid bodies ; but only that heat does not pervade fluids, that is to say, is not trans- mitted from one particle of a fluid to another, in the same manner as in solid bodies. Emily. But when you heat a vessel of water over the fire, if the particles of water do not communicate heat to each oth- er, how does the water become hoi throughout? Mrs. B. By constant agitation. Water, as you have seen, expands by heat in the same manner as solid bodies ; the heated particles of water, therefore, at the bottom of the ves- — sel, become specifically lighter than the rest of the liquid, and consequently ascend to the surface, where, parting with some :of their heat to the colder atmosphere, they are condensed, and give way to a fresh succession of heated particles ascend- ing from the bottom, which having thrown off their heat at the surface, are in their turn displaced. Thus every particle is successively heated at the bottom, and cooled at the surface of the liquid ; but as the fire communicates heat more rapidly than the atmosphere cools the succession of surfaces, the whole of the liquid in time becomes heated. Caroline. This accounts most ingeniously for the propa- gation of heat upwards. But supposing you were to heat the ) jpper surface of a liquid, the particles being specifically ii ighter than those below, could not descend ; how therefore vould the heat be communicated downwards ? .^ Mrs B. If there were no agitation to force the heated sur- face downwards, Count Rumford assures us that the heat vould not descend. In proof of this he succeeded in making she upper surface of a vessel of water boil and evaporate, vhjle a cake of ice remained frozen at the bottom.* ,i Caroline. That is very extraordinary indeed ! j Mrs. B. It appears so, because we are not accustomed to leat liquids by their upper surface ; but you will understand his theory better if I show you the internal motion that takes I * Dr. Thomson says—"All fluids, however, are capable of con- noting-caloric ; for when the source of heat is applied to their sur- ice, the caloric gradually makes its way downwards, and the tem- perature of every stratum gradually diminishes from the surface to ?be bottom of the liquid." C. 42 FREE CALORIC. nlace in liquids when they experience a change of tempera- ture The motion of the liquid itself is indeed invisible front the extreme minuteness of its particles ; but it you mix with it any coloured dust, or powder, of nearly the same specific gravity as the liquid, you may judge of the internal motion of the latter by that of the coloured dust it contains.—Do you see the small pieces of amber moving about in the liquid cod- tained in this phial ? Caroline. Yes, perfectly. Mrs. B. We shall now immerse the phial in a glass othot water/and the motion of the liquid will be shown by that which it communicates to the amber. Emily. I see two currents, the one rising along the sides of the phial, the other descending in the centre ; but I do not understand the reason of this. Mrs.- B. The hot water communicates its caloric, through the medium of the phial, to the particles of the fluid nearest to the glass ; these dilate and ascend laterally to the surface, where, in parting with their heat, they are condensed, and in descending, form the central current. Caroline. This is indeed a very clear and satisfactory ex* periment; but how much slower the currents now move than they did at first ? Mrs. B. It is because the circulation of particles has near- ly produced an equilibrium ot temperature between the liquid in the glass and that in the phial. Caroline. But these communicate laterally, and I thought that beat in liquids could be propagated only upwards. Mrs. B. You do not take notice that the heat is imparted from one liquid to the other, through the medium of the phial itself, the external surface of which receives the heat from the water in the glass, whilst its internal surface transmitsi to the liquid it contains. Now take the phial out of the hot water, and observe the effect of its cooling. Emily. The currents are reversed ; the external current now descends, and the internal one rises.—I guess the reason of this change :—the phial being in contact with cold air in- stead of hot water, the external particles are cooled insteai of being heated ; they therefore descend and force up the central particles, which, being warmer, are consequet'')1 lighter. .Mrs. B. It is just so. Count Rumford hence infers, that no alteration of temperature can take place in a fluid, will an internal motion of its particles j and as this motion is pre FREE CALORIC. 43 duced only by the comparative levity of the heated particles, heat cannot be prop;tgated downwards. But though 1 believe that Count Rumford's theory »* to heat being incapable of pervading fluids i& not strictlv correct, yet there is, no doubt, much truth in his observation, that die communication is materially promoted by a motion ot the parts ; and this accounts for the cold that is found to prevail at the bottom of the lakes in Switzerland, which are fed by rivers issuing from the snowy Alps. The water of these rivers being colder, and therefore more dense than that of the lakes, subsides to the bottom, where it cannot be affected by the warmer temperature of the surface ; the motion of the waves may communicate this temperature to some little depth, but it can descend no further than the agitation ex- tends. Emily. But when the atmosphere is colder than the lake, the colder surface of the water will descend, for the very reason that the warmer will not. Mrs. B. Certainly ; and it is on this account that neither a lake, nor any body of water whatever, can be frozen until every particle 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 s frozen. * Emily. But if the temperature of the whole body of wa- ter be brought down to the freezing point, why is only the ; surface frozen ? Mrs. B The temperature of the whole body is lowered, rbut not to the freezing point. The diminution of heat, as you know, produces a contraction in the bulk of fluids, as well as of 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 temperature, 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 • severity, 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 af- fected by the external cold. Caroline. And the sea does not freeze, I suppose, because t[s depth is so great, that a frost never lasts long enough to ^4 FREE CALORIC. bring down the temperature of such a great body of watej to 40 degrees ? , Mrs. B. That is oue 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 degrees below the freezing point. When the caloric of fresh water, therefore, is imprisoned by the ice on its surface, the ocean still con- tinues throwing off heat into the atmosphere, which is a most signal dispensation of Providence to moderate the intensity 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 atmosphere would not be heated by the rays of the sun passing throngh it ? Mrs. B. Nor is it heated in that way. The pure atmos- phere is a perfectly transparent medium, which neither ra- diates, absorbs, nor conducts caloric, but transmits the rays of the sun to us without in any way diminishing their intensi- ty. 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 win- dows not heated then by the sun shining on them ? Mrs. 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 converging the rays to a focus will set combustible bodies on fire, without 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, there- fore, must retain some of the caloric radiated by the fire: Is it that the solar rays alone pass freely through glass with- out paying tribute ? It seems unaccountable that the radia- tion of a common fire should have power to do what the suns rays cannot accomplish. Mrs B. It is not because the rays from the fire have more power, but rather because they have less, that they heat glass and other transparent bodies. It is true, however, * 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 clearwater No effect on the temperature will be produced; but if an opake body, as a piece of cork, be introduced under the fociH) the water at this point instantly begins to boil. C. FREE CALORIC. 45 that as you approach the source of heat the rays being nearer each other, the heat is more condensed, and can produce ef- fects 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 ko easily done by culinary heat. Yet caloric emanated from burning bodies, which is commonly called culinary heat, has neither the intensity nor the velocity of solar rays. All caloric, we have said, is supposed to proceed originally from the sun ; but after having been incorporated with terrestrial bodies, and again given out by them, though its nature is not essen- tially altered, it retains neither the intensity nor the Velocity with which it first emanated from that luminary ; it has there- fore not the power of passing through transparent mediums, such as glass and water, without being partially retained by those bodies. Emily. I recollect that in the experiment on the reflec- tion of heat, the glass screen-which you interposed between the burning taper and the mirror, arrested the rays of calor- ic, 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, may be heated internally by a fire in the room f 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 sur- face of the earth would contribute very little towards warm- ing it. Emily. The radiation of heat is not confined to burning bodies ; for all bodies, you know, have that property : there- fore, not only every thing upon the surface of the earth, but the earth itself, must radiate heat; and this terrestrial caloric, not having, I suppose, sufficient power to traverse the atmos- phere, 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 terrestrial or culinary heat, though it cannot pass through the denser transparent mediums, such as glass or wa- ter, without loss, traverses the atmosphere completely ; so that all the heat which the earth radiates, unless it meet with ;louds* or any foreign body to intercept its passage, passes into the distant regions of the universe. * Every one has observed how oppressive the heat is on a foggy", o*-cloudy dav in the summer. The moisture of the fog absorbs the heat which the earth radiates, and throws it back upon the earth ■-',j;ain, aud upon us. C- 46 FREE CALORIC. 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 num- berless dispensations of Providence for our good. If all the heat which the earth has received from the sun since the creation, had been accumulated in it, its temperature by this time would, no doubt, have been more elevated than any hu- man being could have borne. Caroline. I spoke, indeed, very inconsiderately. But, s Mrs. B., though the earth, at such a high temperature, might i have scorched our feet, we should always have had a cool re- freshing air to breathe, since the radiation of the earth does not heat the atmosphere. Emily. The cool air would have afforded but very insuf- ficient refreshment, whilst our bodies were exposed to the burning radiation 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 atmos- phere 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 stra- tum of air is warmed by coming in contact with the earth. You may perceive this effect in a sultry day, if you attentive- j ly observe the strata of air near the surface of the earth: 1 they appear in constant agitation ; for though it is true the air itself is invisible, yet the sun shining on the vapours float- \ ing in it, render them visible, like the amber dust in the wa- ter. The temperature of the surface of the earth is there- fore the source from whence the atmosphere derives its heat, ' though it is communicated neither by radiation, nor transmit- ted from one particle of it to another by the conducting pow- er; 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. Emily. Since it is from the earth, and not the sun, that the ■J< FREE CALORIC. 47 atmosphere receives its heat, I no longer wonder that eleva- ted regions should be colder than plains and valleys. It wag always a subject of astonishment to me, that in ascending a mountain and approaching the sun, the air became colder in- stead 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, 1 should have supposed that heat would have accumulated in the upper regions of the atmos- phere, and that we should have felt the air warmer as we as- cended '! Mrs. B. The atmosphere, you know, diminishes in densi- ty, 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 tt will not ascend into the upper regions of the atmosphere until all the parts be- neath 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 winter on very high mountains, although they are almost constantly ex- posed to the heat of the sun's rays, being too much elevated to be often enveloped in clouds. Emily. These explanations are very satisfactory ; but al- low me to ask you one more question respecting the increas- ed levity of heated liquids. You said that when water was heated over the fire, the particles at the bottom of the vessel ascended as soon as heated, in consequence of their specific levity : why does not the same effect continue when the wa- ter boils, and is converted into steam ? and why does the steam rise from the surface, instead of the bottom of the li- quid ? Mrs. B. The steam or vapour does ascend from the bot- om, though it seems to arise from the surface of the liquid. tVe shall boil some water in this Florence flask, (Plate IV. Fig. 1.) in order that you may be well acquainted with the jrocess of ebullition : you will then see, through the glass, hat the vapour rises in bubbles from the bottom. We shall nakeitboil by means of a lamp, which is more convenient for his purpose than the chimney fire. Emily. I see some small bubbles ascend, and a great many 48 FREE 0AL0RI0. appear all over the inside of the flask : does the water be- gin to boil already ? Mrs. B. No : what you now see are bubbles of air, which were either dissolved in the water, or attached to the inner surface of the flask, and which, being rarefied by the heat, ascend in the water. Emily. But the heat which rarefies the air inclosed in the water, must rarefy the water at the same *ime ; thrrja- fore, if it could remain stationary in th<- water when both were cold, I do not understand why it should not when both are equally heated. Mrs. B. Air being much less dense than water, is more easily rarefied ; the former, therefore, expands to a great extent, whilst the latter continues to occupy nearly the same space ; for water dilates comparatively but very little with- out changing its state and becoming vapour. Now that the water in the flask begins to boil, observe what large bubbles rise from the bottom of it. Emily. 1 see them perfectly ; but I wonder that they have sufficient power to force themselves through the water. Caroline. They must rise, you know, from their specific levity, Mrs. B. You are right, Caroline ; bnt vapour has not ii all liquids (when brought to the degree of vaporization) the power of overcoming the pressure of the less heated sur- j face. Metals, for instance, mercury excepted, evaparate only from the surface ; therefore no vapour will ascend j from tl-.em till the degree of heat which is necessary to form it has reached the 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 begins to diffuse itself in the air., ., Mrs B. When the steam is first formed, it is so perfect* ly dissolved by caloric, as to be invisible. In order, how- ever, to understand this, it will be necessary for me to enter into some explanation respecting the nature of solution. Solution takf;s place whenever a body 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 te partake of its fluidity ; but in common solutions this happens without any decomposition, the body being only divided in- to its integrant particles by the fluid in which it is melted. FREE CALORIC. 49 Caroline. It is then a mode of destroying the attraction of aggregation. Mrs. B. Undoubtedly.—The two principal solvent fluids are water and caloric. You may have observed that if you melt salt in water it totally disappears, and theater remains clear and transparent as before ; yet though the union of these two bodies appears so perfect, it is not produced by any chemical combination ; both the salt and the water re- main unchanged ; and if you were to separate them by evap- orating the latter, you wpuld find the salt in the same state as before. Emily. I suppose that water is a solvent for solid bodies and caloric for liquids 1 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 dissolved by heat : thus metals, which are insoluble in water, can be dissolved by intense heat, be- ing first fused or converted into a liquid, and then rarefied into an invisible vapour. Many other bodies, such as salt, gums, &c. yield to either of these solvents. Caroline. And that, no doubt, is the reason why hot wa- ter will melt,them so much better than cold water? Mrs. B. It is so. Caloric may, indeed, be considered as having, in every instance, 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 specula- tion too far ; I should rather think that water and caloric unite their efforts to dissolve a body, and that the difficulty or facility of effecting this, depend both on the degree of attraction of aggregation to be overcome, and on the arrarige- ment 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 a^ water ? Mrs B. The solvent power of other liquids varies ac- cording to their nature, and that of the substances submitted to their action. Most of these solvents, indeed, differ essen- tially from water, as they do not merely separate the inte- grant particlos of the bodies which they dissolve, but attack their constituent principles by the power of chemical at- traction, thus producing a true decomposition. These more 50 FREE CALORIC. complicated operations we must consider in another place, and confine our attention at present to the solutions by water and caloric. Caroline. But there are a variety of substances which, when dissolvejLin water, make it thick and muddy, and de- stroy its transparency. 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 dis- appears and leaves the water transparent, whilst the chalk changes it into an opaque liquid like milk. Emily. And would lumps of chalk and salt produce simi- lar effects on water ? Mrs. B. Yes, but not so rapidly : salt is, indeed, soon melted though in a lump ; 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 reduced 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 respecting solutions, which is, that a fluid is not nearly so much increased 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 together 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, I shall fill with wa- ter, pouring 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 dissolved, you will observe that it is no longer full. Caroline. I shall try to add a little more salt.—But now, you see, Mrs. B. 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 salt it is capable of FREE CALORIC. 51 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 so obvious as that of water. Caloric, we may conceive, dissolves wa- ter, and converts it into 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 dissolved by caloric. But the air with which it comes in contact, being much colder than the vapour, the latter yields to it a quan- tity of its caloric. The particles of vapour being thus in a great 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. Caroline. That I understand very well. If you hold a cold plate over a tea-urn, the steam issuing from it will be immediately co^^rted 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 diffused in the air ? Mrs. B. It is not merely diffused, but is again dissolved by the aiF. Emily. The air, then, has a solvent power, like water and caloric ? Mrs. B. This was formerly believed to be the case. But it appears from more recent enquiries that the solvent power of the atmosphere depends solely upon the caloric contained in it. Sometimes the watery vapour diffused in the atmos- phere is but imperfectly dissolved, as is the case in the for- mation of clouds and fogs ; but if it gets into a region suffi- ciently 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 differ- ence between vaporization and evaporation. Water, when heated to the boiling point, can no longer exist in the form of water, and must necessarily be converted into vapour or 52 FREE CAL0RI6. 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 contains, 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 atmosphere damp. Mrs B. On the contrary, when the moisture is well dis- solved it occasions no humidity ; it is only when in a state of imperfect solution and floating in the atmosphere, in the form of watery vapour, that it produces dampness. This happens more frequently in winter than in summer ; for the lower the temperature of the atmosphere, the less water it can dissolve ; and in reality it never contains so much moisture as in a dry hot summer's day. Caroline. You astonish me ; But why, then, is the air so dry in frosty weather, when its temperature is at the lowest ? Emily. This, I conjecture, proceeds not so much from the moisture 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 atmospheric heat could not dissolve, produces what is called a hoar frost; for the particleWrescend in freez- ing, 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 phe- nomena of rain, of dew, &c. When moist air of a certain temperature happe'ns to pass through a colder region of the atmosphere, it parts with a portion of its heat to the sur- rounding air ; the quantity of caloric, therefore, which served to keep the water in a state of vapour, being dimin- ished, the watery particles approach each other, and form themselves 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 electri- * In cold climates, when 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. FREE CALORIC. 53 cal state, &c which may contribute 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 mi- nute drops from the atmosphere, precipitated by the cool- ness of the evening. Caroline. This precipitation is owing, I suppose, to the cooling 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 course 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 sodner 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. Towards evening, therefore, when the solar heat declines, and when after sun-set it entirely 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 being thus reduced, it is unable to retain so large a portion of wa- tery vapour, and deposits those pearly drops which we call : dew. Emily. If this be the cause of dew, we need not be ap- prehensive of receiving any injury from it ; for it can be de- posited only on surfaces 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 thi9 reason to be 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, whenever the dew is oo- 6* 54 FREE CALORIC. pious, there is a chill in the atmosphere which is not alwayi 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 agitation of the air be not considerable ; for when the wind is strong, it is found that less dew is deposited than in calm weather, especially if the atmosphere be loaded with clouds. These accumulations of moisture not only prevent the free radiation ot the earth towards the upper regions, but themselves radiate towards the earth ; for which reasons much less dew is formed than on fine clear nights, when the radiation 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. After sunrise the equilibrium of temperature between these two bodies is gradually restored by the solar rays passing* freely through the atmosphere to the earth ; and later in the morning the temperature of the earth gains the ascendancy, and gives out caloric to the air by contact, in the same manner as it re- ceives it from the air during the night. Can you tell me, now, why a bottle of wine taken fresh from the cellar (in summer particularly), will soon be cov- ered with dew ; and even the glasses into which the wine is poured will be moistened with a similar vapour ? Emily. The bottle being colder than the surrounding air, must absorb caloric from it ; the moisture, therefore, which *- that air contained becomes visible, and forms the dew which is deposited on the bottle. Mrs. B. Very well, Emily. Now, Caroline, can you inform me why, in a warm room, or close carriage, the con- trary effect takes place : that is to say, that the inside of the windows is covered with vapour ? Caroline. I have heard that it proceeds from the breath of those within the room or the carriage ; and I suppose it is occasioned by the windows which, being colder than the breath, deprive it of part of its caloric, and by this means convert it into watery vapour. Mrs. B. \o\x have both explained it extremely well. FREE CALORIC. 5i Bodies attract dew in proportion as they are good radiators of caloric, as it is this quality which reduces their tempera- ture below that of the atmosphere ; hence we find that little or no dt-w is deposited on rocks, sand, or water ; while grass; and living vegetables, to which it is so highly beneficial, at- tract it in abundance—another remarkable instance ot 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 ef- fects 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 be reduced in the evening, in comparison to that of the atmosphere. In the West In- dies especially, where the intense heat of the day is strongly contrasted with the coolness of the evening, the dew is pro- digiously abundant. During a drought, the dew is less plen- tiful, as the earth is not sufficiently supplied with moisture to be able to saturate the atmosphere. Caroline. I have often observed, Mrs. B., that when I walk out in frosty weather, with a veil over my face, my breath freezes upon it. Pray what is the reason of that ? Mrs. B. It is because the cold air immediately seizes on the caloric of your breath, and, by robbing it of its solvent, reduces it to a denser fluid, which is the wafery vapour that settles on your veil, and there it continues parting with its caloric till it is brought down to the temperature of the at- mosphere, and assumes the form of ice. You may, perhaps, have observed that the breath of ani- mals, or rather the moisture contained in it, is visible in damp weather, or during a fro.->t. In the former case, the atmos- phere being oversaturated with moisture, can dissolve no more. In the latter, the cob! condenses it into visible vapour ; and for the same reason, the steam arising from water that is warmer than the atmosphere, becomes visible. Have you never taken notice of the vapour rising from your hands af- ter having dipped them into warm water ? Caroline. Frequently, especially in frosty weather. Mrs. B. We have already observed that pressure is an obstacle to evaporation : there are liqiuds which contain so great a quantity of caloric, and whose particles consequently adhere so slightly together, that they may be rapidly conver- ted into vapour without any elevation of temperature, merely by taking off the weight of the atmosphere. In such liquids *6 FREE CALORIC. you perceive, it is the pressure of the atmosphere alone that connects their particles, and keeps them in a liquid state. Caroline. 1 do not well understand why the particles of su. 'i fluids should be disunited and converted into vapour, without any elevation of temperature, in spite of the attrac- tion of cohesion. . Mrs. B. It is because the degree of heat at which we usually observe these fluids is sufficient to overcome their attraction of cohesion. Ether is of this description ; it will boil and be converted into vapour, at the common tempera- ture 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 taken away, or heat applied ; and that it was for that reason so necessary to keep it carefully corked up 1 Mrs. B. it is true it will evaporate, but without ebulli- tion ; whaj 1 am now speaking of is the vaporization of ether, or its conversion into vapour by boiling. I am going to show you how suddenly the ether in this phial will be converted into vapour, by means of the air pump.—Observe with what rapidity the bubbles ascend, as I take off the pressure of the atmosphere. Caroline. It positively boils : how singular to see a liquid boil without heat I Mrs. B. Now I shall place the phial of ether in this glass, which it nearly fits, so as to leave only* a small space, which I fill with water ; and in this state I put it again under the re- ceiver. (Plate IV. Fig. 1.)*—You will observe, as I ex- haust the air from it, that whilst the ether boils, the water freezes. Caroline. It is indeed wonderful to see water freeze in contact with a boiling fluid ! Emily. 1 am at a loss to conceive how the ether can pass to the state of vapour without an addition of caloric. Does it not contain more caloric in a state of vapour, than in a state of liquidity ? * Two pieces of thin glass tubes, sealed at one end, might answer this 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 almost instantly in the same manner. The two glasses are placed over one other, with a few drops of water interposed between them, and the uppermost glass is filled with ether. After working the pump for a minute or two, the glasses are found to adhere strODgly together, and a thin layer of ice is seen between them. free caloric. 57 Mrs. B. It certainly does : for though it is the pressure of the atmosphere which condenses it into a liquid, it is by fore ing out the caloric that belongs to it when in an aeriform ™Kttty' J°n have, therefore, two difficulties to explain, Mrs B. First, whence the ether obtains the caloric neces- sary to convert it into vapour, when it is relieved from the pressure of the atmosphere ; and, secondly, what is the rea- son that the water, in which the bottle 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 caloric which the latter sustains, is the occasion of its freezing^* Mrs. B. You are perfectly right -Jmid if you look at the thermometer which I have placed in the water, whilst I am working the pump, you will see that every time bubbles of vapour are produced, the mercury descends ; which proves that the heat of the water diminishes in proportion as the ether boils. Emily. This I understand now very well ; but if the wa- ter 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 temperature, was always equal ; how, then, is it that the water, which was; originally of the same temperature as the ether, gives out caloric to it, till the water is frozen, and the ether made to boil ? Mrs. B. I suspected that you would make these objec- tions ; and, in order to remove them, I enclosed two ther- mometers 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 temperature is not destroyed ; for as the thermometer descends in the water, that in the ether sinks in the same manner ; so that both thermometers 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 exceedingly. 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 latejvt 58 free caloric heat : and that, I think, we must defer till our next inter- view. Caroline. I believe, Mrs. B., that you are glad to put off the explanation ; for it must be a veryr difficult point to ac- count for. Mrs. B. I hope, however, that I shall do it to your com- plete satisfaction. Emily. But before we part, give me leave to ask you one question. Would not water, as well as ether, boil with less heat, if deprived of the pressure of the atmosphere ? Mrs. B. Undoubtedly. You must always recollect that there are two forces to overcome, in order to make a liquid boil or evaporate ; the attraction of aggregation, and the weight of the atmolttkere. On the summit of a high moun- tain (as M. De Saussure ascertained 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 removed hy means of a good air-pump, and if water be placed in the ex- hausted receiver, it will evaporate so fast, however cold it may be, as to give it the appearance of boiling from the sur- face. But without the assistance of the air-pump, I can show you a very pretty experiment, which proves the effect of the pressure of the atmosphere in this respect. Observe, that this Florence flask is about half full of water, and the upper half of invisible vapour, the water being in the act of boiling. I take it from the lamp, and cork it carefully —the water, you see, immediately ceases boiling. I shall now dip the flask into a basin of cold water.! Caroline. But look, Mrs. B., the water begins to boil again, although 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 thermometer immersed in it remains stationary at 180 de- grees, which is about 30 degrees below the boiling point. When I took the flask from the lamp, 1 observed to you that the upper part of it was filled with vapour ; this being com- pelled to yield its caloric to the cold water, was again conden- * On the top of Mount Blanc, water boiled when heated only to 187 degrees, instead of 212 degrees. f The same effect may be produced by wrapping a cold wet linea cloth round the upper part of the flask. * In order to show how much the water cools whilst it is boiling, a thermometer, graduated 09 the tube itself, may be introduced into the bottle through the cork. free caloric. 59 sed into water. What, then, filled the upper 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, though it had lost many degrees of heat, it began boiling again the instant the vacuum was formed above it. The boiling has now ceas- ed, the temperature of the water 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 atmo- spheric pressure, at a temperature as low as 100 degrees ; and in a vacuum it boils at almost any temperature ; but wa- ter being a more dense fluid, requires a more considerable quantity of caloric to make it evaporate quickly, even when the pressure of the 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 ascer- tained by experiment; but at any rate this proportion must vary, according to the temperature of the atmosphere ; for the lower the temperature, the smaller must be the propor- tion of vapour that the atmosphere can contain. To conclude the subject of free caloric, I should mention Ignition, by which is jneant that emission of light which is produced in bodies at a very high temperature, and which is the effect of accumulated caloric. Emily You mean, I suppose, that light which is produ- ced 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 produced in the ignited body. All solid bodies, and most liquids, are susceptible of ignition, lor, in other words, of being heated so as to become luminous ; and it is remarkable that this takes place pretty nearly at the same temperature in all bodies, that is, at about 800 degrees of Fahrenheit's scale. Emily. But how can liquids attain so high a temperature, without being converted into vapour ? r Mrs. B. By means of confinement and pressure. Water „ "t 60 combined caloric. confined in a strong iron vessel (called Papin's digester,) cai have its temperature raised to upwards of 400 degrees. Sir James Hall has made some very curious experiments on the effects of heat assisted by pressure ; by means of strong gun- barrels, he succeeded in melting 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. I am surprised at that; for I thought that the force of steam was such as to destroy almost all mechanical resis- tance. Mrs. B. The expansive force of steam is prodigious ; but in order to subject water to such high temperatures, it is pre- vented by confinement from being converted into steam, and the expansion of heated water is comparatively trifling. But we have dwelt so long on the subject of free caloric, that we must reserve the other modifications of that agent to our next meeting, when we shall endeavour to proceed more rapidly. QUESTIONS. Why do some substances feel hotter, or colder, than others, at the same temperature? Do fluids conduct caloric downwards ? How are fluids heated when placed over a fire ? Why does water first freeze at the surface? Why does not the surface of the sea freeze ? Why does a fire heat glass, when the sun does not ? Whv, inthe summer, is it particularly hot in cloudy, or foggy wea- ther ? Why is the wind cooling to our bodies ? • Does water boil from the top, or bottom of the vessel ? What are the principal so/vent fluids ? What is the difference between solution and mixture ? Is a fluid increased in bulk by the solution of a solid? When is a solvent saturated? What is evaporation ? When does the air contain most moisture ? in winter or summer ? How do you account for the formation of dew ? Why is a glass of cold water covered with moisture in hot weather? Why does the evaporation of ether freeze water? How does ignition differ from combustion? CONVERSATION IV. ON COMBINED CALORIC, COMPREHENDING SPECI- FIC AND LATENT HEAT. Mrs. B. We are now to examine the other modification! of caloric. COMBINED CALORIC. 61 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 different 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 that it is impossible to discover the absolute quantity of caloric which bodies contain ? Mrs. B. True ; but at the same time I said that we were enabled to form a judgment of the proportions which bodies bore to each other in this respect. Thus it is found that, in order^o raise the temperature of different bodies the same number of degrees, different quantities of caloric are required for each of them. If, for instance, 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 temperature 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 body, will be heated soonest, and the milk, which is the largest, will require the longest time. Mrs. B. That explanation will not do ; for if the lead be the least in bulk, it offers also the least surface to the caloric, the quantity of heat therefore which can enter into it in the same space of time is proportionally smaller. • Emily. Why, then, do not the three bodies attain the tem- perature of the oven at the same time 1 Mrs. B. It is supposed to be on.account of the different capacity of these bodies for caloric. Caroline. What do you mean by the capacity of*a body for caloric ? Mrs. B. I mean a certain disposition of bodies to require . more or less caloric for raising their temperature to any de- gree of heat. ) Perhaps the fact may be thus explained : Let us put as many marbles into this glass as it will con- tain, and pour some sand over them—observe how the sand penetrates and lodges between them. We shall now fill an- other glass with pebbles of various forms—you see that they arrange themselves in a more compact manner than the mar- bles, which,Jjeing globular, can touch each other, by a single point only. * The pebbles, therefore, will not admit so much 6and between them ; and consequently one of these glasses 7 62 COMBINED CALOfUC 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 bodies of different kinds, and the sand the caloric contained in them ; and it appears- very plain, from this comparison, that one body may admit of more caloric between its particles than another. Mrs. B. You can no longer be surprised, therefore, that bodies of a different capacity for caloric should require dif- ferent proportions of that fluid to raise their temperatures , equally. Emily. But I do not conceive why the body that contains the most-caloric should not be of the highest temperature; that is to say, feel hot in proportion to the quantity of caloric it contains. * ( Mrs. B. The caloric that is employed in filling the capa- ; city of a body, 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. i Caroline. It appears to me very extraordinary that heat J should be confined in a body in such a manner as to be im- perceptible, j Mrs. B. If you lay your hand on a hot body, you feel only j the caloric which leaves it, and enters your hand ; for it is impossible that you should be sensible of that which remains in the body. The thermometer, in the same manner, is af- fected only by the free caloric whfch a body transmits to it, and not at all by that which it does not part 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 re- quires 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 contra- diction to call it heat, when it is so situated as to be incapable of producing that sensation. Yet this modification of caloric , is commonly called specific heat. Caroline. But it certainly would have been more correctte;1 have called it specific caloric. Emily. I do r ot understand how the term specif c applies to this modification of caloric ? Mrs. B. It expresses the relative quantity of caloric which different species of bodies of the samp weight and temperature are capable of containing. This modification is also frequent- COMBINED CALORIC. 63 ly called heat of capacity, a term perhaps preferable, as it explains better its own meaning. You now understand, 1 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 capaci- ty for caloric than the lead, a greater proportion of that fluid became insensible in those bodies : and the more slowly, therefore, their temperature was raised. Caroline. But might not this difference proceed from the different conducting powers of heat in these three bodies, since that which is the best conductor must necessarily attain the temperature of the ov$n first? Mrs. B. Very well observed, Caroline. This objection would be insurmountable, if we could not, by reversing the experiment, prove that the milk, the chalk, and the lead, ac- tually absorbed different quantities of caloric, and we know that if the different time they took in heating, proceeded mere- ly from their different conducting powers, they would each have acquired an equal quantity of caloric. Caroline. Certainly. But how can you reverse this ex- periment ? 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 celebrated Lavoisier has invented a machine to es- timate, upon this principle, the specific heat of bodies in a more perfect manner ; but I cannot explain it to you, till you are acquainted with the next modification of caloric. Emily. The more dense a body is, I suppose, the less is its capacity for caloric 1 Mrs. B. This is not always the Case with bodies of differ- ent nature; 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 be- 64 COMBINED caloric. tween the particles ; but, probably, also upon some peculiar constitution of the bodies, which we do not comprehend. ~ Emily. But, Mrs. B., it would appear to me more proper to compare bodies by measure, rather than by weight, in or- der 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 substances ; for equal weights may be composed of very different quantities? Mrs. B. You are mistaken, my dear : equal weight must contain equal quantities of matter ; ahd when we wish to know what is the relative quantity of caloric, which substan- ces of various kinds are capable of containing under the same temperature, we must compare equal weights, and not equal bulks, of those substances. Bodies of the same weight may undoubtedly be of very different dimensions ; but does not change their real quantity of matter. A pound of featheri does not contain one atom more than a pound of lead. Caroline. I have another difficulty to propose. It ap- pears to me, that if the temperature of the three bodies in the oven did not rise equally, they would never reach the same degree : the lead would always keep its advantage over the chalk and milk, and would, perhaps, be boiling before the others had attained the temperature of the oven. I think you might as well say that, hi the course of time, you and I 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 stationary ; for it would then give out as much heat as it would receive. You should recollect that the ex- change of radiating heat, between two bodies of equal tempe- rature, 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 loug as I live, I shall never cease io 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 required 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 other, in order to be equally satisfied. Mrs. B. Yes, that is very fair ; for the quantity of food necessary to satisfy their respective appetites, varies in the COMBINED caloric. tCJ 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 specific heat of bodies. Mrs. B. None at all . no more than satiety is a test of the quantity of food eaten. The thermometer, as I have repeat- edly said, can be affected only by free caloric, which alone raises the temperafure of bodies. But there is another mode of proving the existence of spe- cific 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 tem- perature 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 obtained. Thus, for instance, if you mix to- gether a pound of mercury, heated* at 60 degrees, and a pound of water heated at 100 degrees, the temperature ofthe mixture, instead of being 75 degrees, will be 80 degrees ; so that the water will have lost only 12 degrees, whilst the mercury will have gained 38 degrees ; from which you will conclude that the capacity of mercury for heat is less than that of water. Caroline. I wonder that mercury should have so little specific heat. Did we not see it was a much better conduct- or of heat than water ? Mrs. B. And it is precisely on that account that its spe- cific 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 to part with it to other bodies. But let us now proceed to utent heat. Caroline. And pray what kind of heat is that ? Mrs. B. It is another modification of combined caloric, which is so analogous to specific heat, that most chemists make no distinction between them ; but Mr. Pictet, in his Essay on Fire, has so clearly discriminated them, that I am induced to adopt his view ofthe subject. We therefore call latent heal that portion of insensible caloric which is employ- ed in changing the state of bodies ; that is to say, in convert- 7# GS COMBINED CALORIC. ing 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 increase of capacity for heat, in consequence of which it immediately ab- sorbs 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 modification latent caloric instead of latent heat, since it does not excite the sensation of heat.' Mrs. B. This modification of heat was discovered and named by Dr. Black long before the French chemists intro- duced the term caloric, and we must not presume to change it, as it is still used by much better chemists than ourselves. Besides, you are not to suppose that the nature of heat is al- tered by being variously modified : for if latent heat and spe- cific heat do not excite the same sensations as free caloric, it i is owing to their being in a state of confinement, which pre- vents them from acting upon our organs ; and consequently, 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 heat; for they are both of them im- prisoned and concealed in bodies. Mrs. B. Specific heat is that which is employed in filling the capacity of a body for caloric, in the state in which this body actually exists ; while latent heat is that which is em- ployed only in effecting a change of state, that is, in convert- ing bodies from a solid to a liquid, or from a liquid to an aeri- form state. But 1 think that, in a general point of view, both these modifications might be comprehended under the name of heat of capacity, as in both cases the caloric is equally en- gaged in filling the capacities 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 yoa at present,) to five or six degrees below the freezing pAint, as you will find indicated by the thermometer which is placed in it. We shall expose it to the heat of a lamp, and you will see the thermometer gradually rise, till it reaches the freez- ing point— Emily. But there it stops, Mrs. B., and yet the lamp burns just as well as before. Why is not its heat communi- cated to the thermometer ? COMBINED CALORIC. 6T Caroline. And the snow begins to melt; therefore it must be rising above the freezing point. Mrs. B. i he heat no longer affects the thermometer, be- cause 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 ofthe ice be melted. Caroline. Now it is all melted, and the thermometer be- gins to rise again. Mrs. B. Because the conversion of the ice into water being completed, the calorie 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 be- ginning to melt, though the lamp burns equally well. Mrs. 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 heat is required to raise its tempera- ture, and therefore the thermometer rises slower in the water than it did in the ice. Emily. True ; you said that a solid body always increas- ed its capacity for heat by becoming fluid, and this is an in- stance of it. Mrs. B. Yes ; and the latent heat is that which is absorb- ed 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 consideration. I have before observed to you, that though the thermometer 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 ofthe absolute quantity of heat in any body. We cannot tell how low it ought to fall by the privation of all heat, but an attempt has been made to infer it in the following manner. It has been found by experiment, that the capacity of water for heat, when compared with that of ice, is as 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 be added to it as much heat as would, if it did not melt it, raise its temperature 140 degrees.* This quantity of heat is * That is water contains 140 degrees of heat more than is indi- cated by the thermometer. C. 63 COMBINED CALORIC therefore absorbed, 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 consequently be 1260 degrees below 32 degrees.* This mode of investigating so curious a question is inge- nious, but its correctness is not yet established by similar cal- culations for other bodies. The points of absolute cold, in- dicated by this method in various bodies, are very remote from each other ; it is, however, possible, 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 phenomenon. ' Caroline. It is wonderfully curious ! The caloric is now busy in 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 va- pour ! Mrs. B. You see, my dear, how easily you have become acquainted with these modifications of insensible heat, which at first appeared so unintelligible. If, now, we were to re- verse these changes, and condense the vapour into water, and the water into ice, the latent heat would re-appear en- tirely, in the form of free caloric. Emily. Pray do let us see the effect of latent heat return- ing to its free state. .Mrs. B. For the purpose of showing this, we need simply conduct 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 ^This calculation was made by Dr. Irvine. Dr. Crawford after- wards placed the real zero at 1500 degrees below the 0 of Eahreo- heit. Still later, Mr. Dalton has 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 been demonstrated on this difficult question. C. COMBINED CALORIC. 69 method of heating liquids, has been turned to advantage, in several economical establishments. The steam kitchens, which are getting into such general use, are upon the same principle. The steam is conveyed through srpipe in a simi- lar manner, into the several vessels which contain the pro- visions to be dressed, where it communicates to them its la- tent caloric, and returns to the state of water. Count Rum- ford 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 caloric, he takes care also to turn the latent heat to advantage. It is thus that he is ena- bled 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 am so clear and plain, I cannot understand why they are not uni- versally used. Mrs. B. A long time is always required before innovations, however useful, can be reconciled with the prejudices of the vulgar. Emily. What a pity 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 ! Mrs. B. I believe, my dear, that there are as many nov- elties attempted to be introduced, the adoption of which would be prejudicial to society, as there are of those which would be beneficial to it. The well-informed, though by no means exempt from error, have an unquestionable advantage over the illiterate, in judging what is likely or not to prove serviceable ; and therefore we find the former more ready to adopt such discoveries as promise to be really advan- tageous, than the latter, who, having no other test of the value of a novelty but time and experience, at first oppose its introduction. The well-informed, however, are frequent- ly disappointed in their most sanguine expectations, and the prejudices of the vulgar, though they often retard the pro- gress of knowledge, yet sometimes, it must be admitted, prevent the propagation of error.—But we are deviating from our subject. We have converted steam into water, and are now to change water into ice. in order to render the latent heat sen- sible, as it escapes from the water on its becoming solid, 70 COMBINED CALORIC For this purpose we must produce a degree of cold that will make, water freeze. Caroline. That most be very difficult to accomplish in this warm room.* Mrs. B. Not so much as you think. There are certain chemical mixtures which produce a rapid change from the solid to the fluid state, or the reverse, in the substances com- bined, 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 to- gether, are melting rapidly ; beat therefore must-be absorbed by the mixture, and c»ld produced. Caroline. It feels even colder than ice, and yet the snow is melted. This is very extraordinary. *Afrs. B. The cause of the inten-se cold of the mixture is to be attributed to the change of a solid to a fluid states. The union of the snow and salt produces a new arrangement ©f their particles, in consequence of which they become li- quid ; and the quantity of caloric, required to effect this change, is seized upon by. the mixture wherever it can be obtained. This eagerness ofthe 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 its temperature 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, I 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 be 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 mer- cury sinks below the freezing point. Then agitate the water, or drop into it a small piece of ice, and it instantly shoots into crystals, and the thermometer rises. C. COMBINED CALORIC. 71 Mrs. B. That is always the case previous to the freezing of water when it is in a state of rest. Now it begins to con- geal, and you may observe that the thermometer again rises to the freezing point. Caroline. It appears to me very strange that the ther- mometer should rise the very moment that the water freezes • for it seems to imply that the water was oolder before it froze than when in the act of freezing. Mrs. B. It is so ; and after our long dissertation on this circumstance, I did not think it would appear so surprising to you. Reflect a little, and I think you will discover the rea- son of it. Caroline. It must be, no doubt, the extrication of latent heat, at the instant the water freezes, which raises the tem- perature. Mrs. B. Certainly : and if you now examine the ther- mometer, you will find that its rise was but temporary, and lasted only during the disengagement ofthe latent heat—now that all the water is frozen it falls again, and will continue to fall till the ice, and mixture are of an equal temperature. Emily. And can you show us any experiments in which liquids, by being mixed, become solid, and disengage latent heat ? Mrs. B. I could show you several, but you are not yet sufficiently advanced to understand them well.' I shall, how- ever, try one, which will afford you a striking instance ofthe fact. The fluid which you see in this phial consists of a quantity of a certain salt called muriat of lime, dissolved in water. Now, if I pour into it a few drops 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 escap- ing ; for the bottlejs warm, and the fluid is changed to a solid white substance like chalk !* Caroline. This is, indeed, the most curious experiment we hav*1 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 under- stand that.—But take care, Caroline, do not approach too near it, for it has a very pungent smell. * 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 water. The experiment succeeds well, if the water is saturated with the muriate. C. > 72 COMBINED CALORIC. 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 agitation till it became cold, as you may feel the phial is. Now when I take out the cork and let the air fall upon it, (for, being closed 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 of 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 ex- periment of the disengagement of latent heat. Mrs. B. The slaking of lime is another remarkable in- stance ofthe extrication of latent heat Have you never ob- served how quick-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 the lime that occasions its giving out la- tent heat; for the quick-lime, which is solid, is (if I recol- lect right) reduced to 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 sensi- ble form. Caroline. 1 always thought that the heat originated in the lime. It seems very strange that water,^and cold water too, should contain so 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 liquid. Mrs. B. It cannot properly be called ice, since ice implies a degree of cold, at least equal to the freezing point. Yet, as water, in combining with lirne, 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 observ- ed that it does not moisten or liquefy the lime in the smallest degree. , Emily. But, Mrs. B., the smoke that rises is white ; if it COMBINE* CAf.ORItf. 73 was only pure caloric which escaped, we might feel, but eonld not see it. Mrs. B. This white vapour is formed by some of the par- ticles 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. Yon cannot exactly say absorbs latent 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 vapour, absorb heat ; and that when the reverse takes place, heat is disengaged.* Emily. We can now, I think, account for the ether boil- ing, and the water freezing in vacuo, at the same tempera- ture, t Mrs. G. Let me hear how yon explain it. Emily. The latent heat, which the water gave out in freezing, was immediately absorbed by the ether, during its conversion into vapour ; and therefore, from a latent state in one liquid, it passed into a latent state in the other. Mrs. B. But this only partly accounts for the result of the experiment; it remains to be explained why the temper- ature of the ether, while in a state of ebullition, is brought down to the freezing temperature of the water —It is be- cause the ether, during its evaporation, reduces its own tem- perature, in the same proportion as that of the water, by converting its free caloric into latent heat ; so that, though one liquid boils, and 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 ? Mrs. B. The fact is, that it does, though much less rapid- ly than ether. Thus, for instance, you may often have ob- served, in the heat of summer, how much any particular spot may be "cooled by watering, though the water used for'lhat purpose be as warm as the air itself. Indeed so much cold .may be produced by the mere evaporation of water, that the inhabitants of India, by availing themselves of the most favour- able circumstances for this process which their warm climate it can afford, namely, the cool ofthe night, and situations most [Exposed to the night breeze, succeed in causing water to * This ruin, if not universal, admits of very feiv exceptions. i See page 50. •f 8 74 COMBINED CALORIC. freeze, though the temperature of the air be as high as 60 degrees. The water is put into shallow earthen trays, so as to expose an extensive surface to the process of evaporation, and in the morning, 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. How delicious it mu«t be to drink liquids so cold in those tropical climates! But, Mrs. B., could we not try that experiment ? ' Mrs. B. If we were in the country, I have no doubt but that we should be able to freeze water, by the same means, and under similar circumstances. But we can do it immedi- ately, upon a small scale, in this very room, in which the thermometer stands at 70 degrees. For this purpose we need only place some water in a little cup under the receiver of the air-plimp (Plate V. fig. 1.,) and exhaust the air from it. What will be the consequence, Caroline ?, Caroline. Of course the water will evaporate more quick- ly, since there will no longer be any atmospheric pressure on its surface: but will this be sufficient to make the water freeze ? Mrs. B. Probably not, because the vapour will not be car- ried off fast enough ; but this will-be accomplished without difficulty if we introduce into the receiver (fig. 1.,) in a sau- cer, or other large shallow vessel, some strong sulphuric acid, a substance which has a great attraction for water, whether in the form of vapour, or in the liquid state. This attraction is such that the acid will instantly absorb the mois- ture as it rises from the water, so as to make room for the formation of fresh vapour; this will of course hasten the rro- cess, and the cold produced from the rapid evaporation of the water, will, in a few minutes, be sufficient to freeze its surface.* We shall now exhaust the air from the receiver. Emilys Thousands of small bubbles already arise through the water from the internal surface ofthe cup ; what is the reason of this ? Mrs. B. These are bubbles of air which were partly at- tached to the vessel, and partly diffused in the water itself; arid they expand and rise inconsequence ofthe atmospheric pressure being removed. Caroline. See, Mrs. B. ; the thermometer in the cup is sinking fast; it has already descended to 40 degrees ! * This experiment was first devised by Mr. Leslie, and has since been modified in a variety of forms. j>LjTfi r. Mill. Fij.Z. Me?.I.Thr enrpitrnp Vmrff tor i/r. /„,,/„? ,^v,iniritt. C« na„rer vit/, nMuric acit/.Ii it ri/ersr e>r e,ert/tc/i c/tf ,i-ii/,„,,iri„ /jater. ])« stami /Jc t/re reer. toiei ify le/'.i tne>e/e ef^Wass. A a T/terr/icnieter. /•'/,>. 1. Dr. H7>/frstciit Ci-yvplionnt Fin S. Dr Jlercets /W e/~miner die fn,,//,. ;■„.. />;,..}.{.• j. ,/,, ,/irrVrent/rare., '*/■}„. J_ seen separate. COMBINED CALORIC. 75 Emily. The water seems now and then violently agitated on the surface, as if it were boiling; and yet the thermome- ter is descending fast! Mrs. B. You may call it boiling, if you please, for this ap- pearance is, as well as boiling, owing to the rapid formation of vapour: but here, as you have just observed, it takes place from the surface, for it is only when heat is applied to the bottom ofthe vessel that the vapour is formed there.—Now crystals of ice are actually shooting all over the surface of the water. Caroline. How beautiful it is ! The surface is now en- tirely frozen,—but 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 is frozen ; but it will then again begin to descend lower and lower, in conse- quence ofthe evaporation which goes on from the surface of the ice. Emily. This is a most interesting experiment ; but it would be still more striking if no sulphuric acid were re- quired. .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 evapo- ration alone, without the assistance of sulphuric acid. This tube, which, as you see (Plate V. fig. 2.,) is termin- ated at each extremity by a bulb, one of which is half full of water, is internally perfectly exhausted of air ; the conse- quence of this is, that the water in the bulb is always much disposed to evaporate. This evaporation, however, does not proceed sufficiently fast to freeze the water ; but if the emp- ty ball be cooled by some artificial mpans, so as to condense quickly the vapour 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 called this instrument Crynphorus. 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 ; but let us try the experiment. Emily. How will you cool the instrument ? You have neither ice nor snow. Mrs. B. True ; but we have other means of effecting this.* You recollect what an intense cold can be produced * This mode of making the experiment was proposed, and the particulars detailed, by Dr. Marcet, in the 34th vol. of Nicholson's Journal, p. I'9- ;c COMBINED CALORIC. by the evaporation of ether in an exhausted receiver. YVe shall inclose the bulb in this little bag of fine flannel (Plati: V. fig. 3.), then soak it in ether, and introduce it into the re- ceiver ofthe air-pump. (fig. 5.) For this purpose we shall find it more convenient to use a cryophorus of this shape (fig, 4.), as its elongated bulb passes easily through a brass plate which closes the top ofthe receiver. If we now exhaust the receiver quickly, you will see, in less than a minute, the wa- ter freeze in the other bulb, out ofthe receiver. Emily. The bulb already looks quite dim, and small drops of water are condensing on its surface. Caroline. And now crystals of ice shoot all over the wa- ter. 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 an}' further digression. Having advanced so far on the subject of heat, I may novr gave you an account ofthe calorimeter, an instrument invent- ed by Lavoisier, upon the principles just explained, for the purpose of estimating 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 asceitained, 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 ofthe 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 ofthe quantity of caloric which the body has given out in descending from a certain temperature to the feezing point. Caroline. In this apparatus, I suppose, the milk, chalk, and lead, would melt different quantities of ice, in proportion to their different 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 ofthe absolute quantity of heat contained in a body, than the thermometer : for though by means of it we extricate both the free and combined calo- ric, yet we extricate them only to a certain degree, which is the freezing point; and we know not how much they contais of either below that point. Emily. According to the theory of latent heat, it appear! to me. that the weather should be warm when it freezes, and cold in a thaw : for latent heat is liberated from every sub- stance that it freezes, and such a large supply of heat most COMBINED CALORIC. 7^7 warm the atmosphere ; whilst, during 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 freez- ing point ; otherwise the frost must cease. But if the quan- tity of latent heat extricated does not destroy the frost, it serves to moderate the suddenness ofthe change of temper- ature of the atmosphere, at the commencement both of frost and of a thaw. In the first instance, its extrication dimin- ishes the severity of the cold ; and, in the latter, its absorp- tion moderates the warmth occasioned by a thaw ; it even sometimes produces a discernible chill, at the breaking up of a 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 discussions, to which 1 am by no means competent. One circumstance, however, we can easily understand. When the air has passed over cold countries, it will probably ar- rive here at a 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 dis- tinct body, or, as I have heard, a peculiar kind of motion produced in bodies ? Mrs. B. As I before told you, there is yet much uncer- tainty as to the nature of these subtile agents. But I am in- clined to consider heat not as mere motion, but as a separate substance. Late experiments, too, appear to make it a com- pound body, consisting of the two electricities ; and in our next conversation I shall inform you of the principal facts on which that opinion is founded. QUESTIONS. What is understood by capacity for caloric? Have all bodies of the same weight the same capacity for caloric ? How is the capacity of bodies for heat ascertained ? What is the latent caloric ? How does latent caloric differ from specific caloric ? Why does not the thermometer rise in a warm room, when its buib is in a niece of ice ? 1 <<-v 78 COMBINED CALORIC. How much latent heat does water contain? Is the real zero known to exist ? How can ice be made in the summer? Why does the slaking of lime produce heat? CONVERSATION V. ON THE CHEMICAL AGENCIES OF ELECTRICITY.* Mrs. 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 essentia) connection with the phenomena of chemistry. Caroline. It is electricity, if 1 recollect right, which comes next in our list of simple substances ? Mrs. B. I have placed electricity in that list, rather from the necessity of classing it somewhere, than from any conviction that it has 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 simple 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 inher- ent 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. Caroline. Well, I must confes-, I do not feel nearly se interested in a science in which so much uncertainty prevails, as in those which rest upon established principles. I never was fond of electricity, because, however beautiful and cu- rious the phenomena it exhibits may be, the theories, by which they were explained, appeared 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 respec- tine it would now have been clearly explained. Mrs. B. That is a point which we are yet far from hav- ing attained. But, in spite of the imperfection of our theo- ries, you will be amply repaid by the importance and nov- * The electricity extricated by the metals is commonly ealled Galvanism. C. electro-chemistry. 79 elty of the subject. The number of new facts which have already been ascertained, and the immense prospect of dis- covery which has lately been opened to us, will, I hope, ultimately lead to a perfect elucidation of this branch of na- tural science ; but at present you must be- contented with studying the effects, and in some degree explaining the phe- nomena, without aspiring to a precise knowledge of the re- mote cause of electricity. You have already obtained some notions of electricity : in our present conversation, therefore, I shall confine my- self to that part of the science which is of late discovery, and is more particularly connected with chemistry. It wus a trifling and accidental circumstance which first gave rise to this new branch of physical science. Galvani, a professor of natural philosophy at Bologna, being engaged (about twenty years ago) in some experiments on muscular irritability, observed, that when a piece of metal was laid on the nerve of a frog, recently dead, whilst the limb supplied by that nerve rested upon some other metal, the limb sudden- ly 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 by connecting them by means of a metalic conductor. But without subjecting a frog to any cruel experiments, I can easily make you sensible of this kind of electiic action. Here is a piece of zinc, (one of the metals 1 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 tongue ;—very well;—now make the projecting parts of the metals touch each other, and you will instantly perceive a peculiar sensa- tion. Emily. Indeed I did ; a singular taste, and I think a de- gree of 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 by subsequent experiments, which proved that Galvanism (the name this newjjower had obtained) was nothing more than electricity. Gajvani sup- posed 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 80 ELECTRO-CHEMISTRY. depend on on the organs of the frog, but upon the electrical agency of the metal9, which is excited by the moisture of the animal, the organs of the frog being only a delicate test of the presence of electric influeuce. Caroline. 1 suppose, then, the saliva of the mouth an- swers the same purpose as the moisture of a frog, in exciting the electricity of the pieces of silver and zinc with which Emily tried the experiment on her tongue ? Mrs. B. Precisely. It does not appear, however, neces- sary that the fluid used for this purpose should be of animal nature. Water, and acids very much diluted by water, are found to be the most effectual in promoting the developement of electricity in metals ; and, accordingly, the original appar- atus 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 paper ^ impregnated with water ; and this instrument, from its ori- ginal inconvenient structure and limited strength, has gradu- i ally arrived at its present state of power and improvement, such as exhibited in the Voltaic battery. In this apparatus, a specimen of which you see before you (Plate IV. fig. 1,) the plates of zinc and copper are soldered together in pairs, each pair being placed at regular distances in wooden troughs, and the interstices being filled with fluid. 1 Caroline. Though you will not allow us to inquire into \ the precise cause of electricity, may we not ask in what manner the fluid acts on the metals so as to produce it ? Mrs. B. The action of the fluid on the metals, whether water or acid be used, is entirely of a chemical nature. But whether electricity is excited by this chemical action, or whether it is produced by the contact of the two metals, is . a point upon which philosophers do not yet perfectly agree. Emily. But can the mere contact of two metals, without any intervening fluid, produce electricity ? ■Mrs. B. Yes, if they are afterwards separated. It is an established fact, that when two metals are put in contact, and afterwards separated, 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 zinc and copper. Mrs. B. It is upon this principle that Volta and Sir H. Davy explain the phenomena of the pile ; but notwithstand- ing these two great authorities, many philosophers entertain i Altaic Hatte. jPLATjK. FI Fit/. ■£. Fit?. 4. ~\ 23 -i<5 G S^f-sii ^ 1 xV=§; Me?. 3 fllc'c In ca/ Marti itie. I'ir.-i \ t/tt a -li.-hlc:. U t7ic Cettdttctirr.-B. t/te-J?tttcr._C trie CAttitt. J-"ie7.I.} C-J-./'l/triir l/.n'tivy,V electro-chemistrv. 81 doubts on the truth of this theory. The chief difficulty which occurs in explaining the phenomena ofthe Voltaic bat- tery on this principle, is, that two such plates show no si-ns 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 al„ays continue so, being sol- dered together ; and they cannot, therefore, receive a suc- cession of charges. Besides, if we consider the mere dis- turbance of the balance of electricity by the contact of the plates, as the sole cause of the production of Voltaic electri- city, 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 of electrical fluid, though without any means of replenishing itself from other sources. This subject, it must be owned, is involved in too much obscurity to enable us to speak very decidedly in favour of any theory. But, in order to avoid perplexing you with different explanations, 1 shall confine myself to one which appears to me to be least encumbered with difficulties, and most likely to accord with truth.* This theory supposes the electricity to be excited by the chemical action of the acid on the zinc ; but you are yet such novices in chemistry, that 1 think it will be necessary to give you some previous explanation of the nature of this action. All metals have a strong attraction for oxygen ; and this element is found in great abundance, both in water and in acids. The action of the diluted acid on the zinc consists, therefore, in its oxygen combining with it, and dissolving its surface. Caroline. In the same manner, I suppose, as we saw an acid dissolve copper ? Mrs. B. Yes ; but in the Voltaic battery the diluted acid is not strong enough to produce so complete an effect ; it acts only on the surface of the zinc, to which it yields its oxygen, forming upon it a film or crust, which is a compound of the oxygen and the metal. * This mode of explaining the phenomena of the Voltaic pile is called the chemical theory of electricity, because it a.scribes the cause of these phenomena to certain chemical changes which take place during their appearance. The mode which is here sketched was long since suggested by Dr. Bostock, who has lately (1818) published " An Account of the History and Present State of Gal- vanism ■" which contains a fuller and more complete statement of his opinions, and those of other writers on the subject, than any of his former papers. ELECTRO-CHEMISTRY. Emily. Since there is so strong a chemical attraction be- tween oxygen and metals, I suppose they are naturally in different states of electricity. Mrs. B. Yes : it appears that all metals are united with the positive, and that oxygen is the grand source of the neg- ative electricity. 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 oxy- gen, 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 Voltaic battery more intelligible, to confine our attention at first to the effect produced on two plates only. (Plate IV. fig. 2.) If a plate of zinc be placed opposite to one of copper, or any other metal less attractive of oxygen, and the space be- tween them (suppose of half an inch in thickness,) be filled with an acid or any fluid capable of oxydating the zinc, the oxydated surface will have its capacity for electricity dimin- ished, so that a quantity of electricity will be evolved from that surface. This electricity will be received by the con- tiguous fluid, by which it will be transmitted to the opposite metallic surface, the copper, which is not oxydated, 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 com- munication with other bodies, the action of the acid, and further developement 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 allow- ed to communicate with other bodies ? Mrs. B. Precisely : the common electrical machine, when excited by the friction of the rubber, gives out both the pos- itive and negative electricities.—(Plate VI. fig. 3.) The positive, by the rotation of the glass cylinder, is conveyed' into the conductor, whilst the negative goes into the rubber^ * The acid arts upon the copper, but not so strongly as on the zinc Any two metals, one of which has a stronger attraction for oxygen than the other, will form the galvanic series G I ELECTRO-CHEMISTRY. 83 But, unless there is a communication made between the rub- ber and the ground, a very inconsiderable quantity of elec- tricity can be excited ; for the rubber, like the plates of the battery, has too small a capacity to admit of an accumulation of electricity. Unless, therefore, the electricity can pass out of the rubber, it will not continue to go into it, and, consequently, no additional accumulation will take place. Now, as one kind of electricity cannot be given out without the other, the developement of the positive electricity is stopped as well as that of the negative, and the conductor, therefore, cannot receive a succession of charges. Caroline. But does not the conductor, as well as the rub- ber, require a communication with the earth, in oider to get rid of its electricity ? Mrs B. No : for it is susceptible of receiving and con- taining a considerable quantity of electricity, as it is much larger than the rubber, and therefore has a greater capacity ; and this continued accumulation of electricity in the conduc- tor is what is called a charge. Emily. Bnt when an electrical machine is furnished with two conductors to receive the two electricities, I suppose no communication with the earth is required ? Mrs. B. Certainly not, until the two are fully charged ; for the two conductors will receive equal quantities of elec- tricity. Caroline. I thought the use ofthe chain had been to con- vey the electricity from the ground into the machine. Mrs. B. ?' That was the idea of Dr. Franklin, who suppos- ed that there was but one kind of electricity, and who, by the terms positive and negative (which he first introduced,) meant only different quantities of the same kind of electricity .* i he chain was in that 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 r. consider the chain as a vehicle to conduct the negative elec- i tricity into the earth. * The idea of Dr. Franklin was, that the positive state consisted in the presence, or accumulation ofthe electric fluid, and that the ne- 1 gative was merely its absence or diminution. Hence the terms used bv him to indicate theso states west: positive and negative. In this f chapter Mrs. B- has used these terms ofthe American Philosopher improperly, for plus and minus were never meant to signify two sort* of elect'icity, but only its presence or absence «v here authors have an01 *ted Dufay's theory, of two electricities, they have used the teniis, vitreous and resinous. C. 34 ELECTRO-CHEMISTRY. Emily. And are both kinds produced whenever electrici- ty is excited ? Mrs. B. Yes, invariably. If you rub a tube of glass with a woollen cloth, the glass becomes positive, and the cloth ne- gative.* If, on the contrary, you excite a stick of sealing- wax by the same means, it is the rubber which becomes pos- itive, and the wax negative. But with regard to the Voltaic battery, in order that the acid may act 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 think 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 tl.e purpose of carrying off the electricity, I admit ; but recollect, that though it is necessary to find a vent for the electritity, yet we must not lose it, sinre it is the power which we are endeavouring to obtain. In- stead, therefore, of conducting it into the ground, let u.» make the wires, trom either plate, meet : the two electricities will thus be brought together, and will combine and neutralize each other ; and as long as this communication continues, the two plates having a vent for their respective electricities, the action ofthe acid will go on freely and uninterruptedly. Emily. That is very clear, so far as two plates only are concerned ; but I cannot say 1 understand how the energy of the succession of plates, or rather pairs of plates, of which the Galvanic trough is composed, is propagated and accumu- lated throughout a battery ? Mrs. B. In order to show you how the intensity of the electricity is increased by increasing the number of plates, we will examine the action of four plates ; if you understand these, you will readily comprehend that of any number what- ever. In this figure (Plate VI. Fia;. 4.,) you will observe that the two central plates are united : they are soldered to- gether, (a* we observed in describing the Voltaic trough.) so a^ to form but one plate, which offers two different surfaces; the one of copper, the other of zinc. * 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. ELECTRO-CHEMISTRV. 85 Now you recollect, that, in explaining the action of two plates, we supposed that a quantity of electricity was evolved from the surface ofthe first zinc plate, in consequence ofthe 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, consequently, some accumulation of electricity takes place. When, therefore, the fluid in the next cell acts upon the zinc plate, electricity is extricated from it in larger quantity, and in a more concentrated form, than before. This concentrated electricity is again conveyed by the fluid to the next pair of plates, No. 4 and 5, when it is further increased by the action ofthe fluid in the third cell, and soon, to any number of plates, of which the battery may consist; so that the electrical energy will continue to accu- mulate in proportion to the number of double plates, the first zinc plate ofthe 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 undisturb- ed ? Mrs. B. No : for the action will soon stop, as was ex- plained before, unless a vent be given to the accumulated elec- tricities. This is easily done, however, by establishing a communication by means of the wires (Fig. 1.,) between the two ends ofthe 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 pro- gress. Emily. Is it the union ofthe two electricities which pro- duces 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 com- pound ofthe two electricities. Caroline. Yet, surely, caloric is very different from the electrical spark ? Mrs. B. The difference may consist, probably, only in in- tensity ; for the heat ofthe electric spark is considerably more intense, though confined to a very minute spot, than any heat we can produce by other means. Emily. Is it quite certain that the electricity of the Vol- taic battery is precisely ofthe same nature as that of the com- mon electrical machine ? 9 36 ELECTRO-CHEMISTRV. Mrs. B. Undoubtedly : the shock given to the human body, the spark, the circumstance of the same substances which are conductors ofthe one being also conductors of the other, and of those bodies, such as glass and sealing-wax, which are non-conductors ofthe one, being also non-conduct- ors of the other, are striking proofs of it. Besides, Sir H. Davy has shown, in his Lectures, that a Leyden jar, and a common electric battery, can be charged with electricity ob- tained from a Voltaic battery, the effect produced being per- fectly similar to that obtained by a common machine. Dr. Wollaston has likewise proved that similar chemical decompositions 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 electricities is essentially the same, as they show that the rubber ofthe common electrical machine, like the zinc in the Voltaic batte- ry, produces the two electricities by combining with oxygen. Caroline. But I do not see whence the rubber obtains oxy- gen, 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 partly 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 ofthe 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 sim- ilar, why not use the common machine for chemical decompo- * sitions ? Mrs. B. Though its effects are similar to those of the Vol- taic battery, they are incomparably weaker. Indeed, Dr. Wollaston, in using it for chemical decompositions, was obli- ged to act upon the most minute quantities of matter, and though the result was satisfactory in proving the similarity of its effects to those ofthe Voltaic battery, these effects were too small in extent to be in any considerable degree applicable to chemical decomposition. Caroline. How terrible, then, the shock must be from a Voltaic battery, since it is so much more powerful than an electrical machine ! Mrs. B. It is not nearly so formidable as you think ; at least it is by no means proportional to the chemical effect. The great superiority of the Voltaic battery consists in the ELECTRO-CHEMISTRY. 87 large quantity of electricity 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 chemical 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 machine will pass through any space of water. t Caroline. Would it not be possible to increase the inten- sity 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 electrical 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 communication through the fluids em- ployed. By increasing the number of plates of a battery, you in- crease its intensity, whilst, by enlarging the dimensions ofthe' plates, you augment its quantity ; and as the superiority of the battery over the common machine consists entirely in *he quantity of electricity produced, 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, howev- er, 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 ap- paratus was obtained by increasing the intensity, which, how- ever, still falls very far short of that ofthe common machine. I should not omit to mention, that a very splendid, and, at the same time, most powerful battery, was, a few 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 thousand double plates of zinc and copper, of six square inches in dimensions, arranged in troughs of Wedgwood-ware, each of which contains twenty of these plates. The troughs are furnished with a contriv- ance for lifting the plates out of them in a very convenient and expeditious manner.* * A model of this mode of construction is exhibited in Plate XIII. fig. 1. Note. In consequence of the discoveries of Prof. Hare, of Phil- adelphia, the present theory of galvanism must probably undergo v. HH ELECTRO-CHEMISTRV. Caroline. Well, now that we understand the nature ofthe action of the Voltaic battery, il 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 with any propriety introduce the subject of these discoveries till we come to them in the regular course of our studies. There is, however, a recent discovery respecting the Voltaic pile, which, though not immediately connected with chemistry, is too curious to be passed over in silence. It relates to the influence of electricity on magnetism, lately discovered by a Danish philosopher, Mr. Oersted. Caroline. WThat! animal magnetism ? I have often heard of magnetic tractors ; but I thought there was no truth in them. Mrs. B. Nor is there ; it is only the magnetic needle to which I allude. You already know something of the won- derful property of the magnetic 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 fact is this : If a Voltaic battery be so placed as to have its negative pole di- rected towards the south, and its positive one towards the '*■ north, a communication being at the same time established over the battery, between its two poles, by means of metal- lic wires ; and if a magnetic needle be suspended just above the wire, and in a parallel direction, the needle will imme- diately move round upon its pivot, its northern extremity directing itself towards the west, more or less, according to the energy of the pile, while, on the other hand, if the mag- netic needle be placed below the Voltaic conductor, it will likewise begin to move round, but its north pole will, in this case, point towards the east. 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- stances, has presented some new phenomena. This calorific prin- ciple is immensely increased, while the electric shock is hardly to be perceived. Prof. Hare has named this new apparatus calori- motor, or heat mover. The new views which he has been induced to offer, seem to be confirmed by the action of the colorimotor,viz. that galvanism is a compound of electricity and caloric This the- ory, it is obvious, will set aside many of the principles laid down in the foregoing chapter. An account of this theory, with a descrip- tion of the calorimotor, is published in Silliman's Journal, with Ob- servations by the Editor ; also in Hare's edition of Henry's, Chem- istry. C. OXYGEN AND NITROGEN. 89 Emily. How curious this is ? and pray how is this singu- lar effect explained ? Mrs. B. It is one of the most intricate points of natural science, and one upon which philosophers can yet offer'but very uncertain conjectures. Several of the most eminent scientific men, however, are earnestly engaged in investiga- ting the subject, and it is to be hoped, that some important discovery may yet be made. In the mean time they have al- ready ascertained many curious facts illustrative of the in- fluence which electricity and magnetism exert upon each other, one of the most striking of which is; that if a steel needle be placed transversely upon the conductor of a Vol- taic pile in action, the needle will, in a few seconds become magnetic, so as to be capable of attracting and repelling iron like magnets. Or if any portion of the conducting wire be turned into a spiral, and a needle laid within its coils, but so as not to touch them, it will immediately become magnetic, as I shall easily show you the first time we set the Voltaic pile in action ; for it is now too much exhausted to produce the effects in question. We shall therefore here terminate this conversation, which has been already sufficiently long and difficult. QUESTIONS. What kind of body is electricity ? How many metals are required to produce the galvanic action' Can galvanism be produced without water? \ How many kinds of electricity are there ? What were the ideas of Dr. Franklin on this subject? What is said to produce the heat of the electric fluid ? What is the difference between electricity and galvanism? What difference does it make in the action ofthe galvanic battery. whether you increase the number of plates, or enlarge their di mensions ? CONVERSATION VI. ON OXYGEN AND NITROGEN. Airs. B. To-day we shall examine the chemical proper ties of the atmosphere. Caroline. I thought that we were first to learn the nature of oxygen, which comes next in our table of simple bodies ? Mrs. B. And so you shall ; the atmosphere being com- 9* 99 OXYGEN AND NITROGEN. posed of two principles, oxygen and nitrogen, we shall proceed to analyse it, and consider its component parts sep- arately. Emily. I always thought that the atmosphere had been a very complicated" fluid, composed of all the variety of ex- halations from the earth. Mrs. B. Such substances may be considered rather as heterogeneous 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 «w the names of oxygen gas and nitrogen or azotic gas. Emily. Pray what is a gas ?* Mrs. B. The name of gas is given to any fluid capable of existing constantly in an aeriform state, under the pressure and at the temperature of the atmosphere. Caroline. Is not water, or any other substance, when evaporated by heat, called gas ? Mrs. B. No, my dear ; vapour is, indeed, an elastic fluid, and bears a strong resemblance to a gas ; there are, howev- er, 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 bv 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 elas- ticity to caloric ? Mrs. B. It is the prevailing opinion ; and the difference between gas and vapour is thought to depend on the differ- ent 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 com- bined. Emily. When yon speak, then, of the simple bodies oxy- gen and nitrogen, you mean to express those substances which are the bases of the two gases ? 4 Mrs. B. Yes, in strict propriety ; for they can properly be called gases only when brought to an aeriform state. * All kinds of air differing from the atmosphere, are called by this name. C. oxy»en and nitrogen. 91 Caroline. In what proportions are they combined in the atmosphere ? 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 esseutial b..th to respiration and combustion, while neither of these pro- cesses 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 composition of the atmosphere is not a great impedi- ment to breathing ? Mrs. B. We should breathe more freely than our lungs could bear, if we respired oxygen gas alone. The nitrogen is no impediment to respiration, and probably, on the contra- ry, answers some useful purpose, though we do not know in what manner it acts in that process. Emily. And by what means can the two gases, which compose the atmospheric air be separated ? Mrs. B. There are many ways of analysing the atmos- phere : the two gases may be separated first by combustion. Emily. You surprise me ! how is it possible that combus- tion should separate them ? Mrs. 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 prevails, and they have consequently all of them, an attraction for oxygen.|| *In 100 parts of the atmospheric air, there is 21 of oxygen and 79 of nitrogen. C. 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 excep- tion to this statement; but this subject cannot be discussed till the properties and nature of chlorine come under examination. J The hypothesis that combustion, as well as chemical affinity are electrical phenomena, was first proposed by Berzelius, of Stockholm. The theory is shortly this. In all cases, where the particles of bod- ies, have a chemical attraction for each other, they are in opposite states of electricity, and the force of their union is in proportion to the intensity of these electrical states, since it is this which forces them to unite. Thus the particles of an acid, and an alkali unite, because one is strongly negative, and the other strongly positive. In cases of combustion, these different states are still more intense, oxygen always being in the negative state, and the combustible in the positive, and when a union takes place, heat and light is the 92 OXYGEN AND NITROGEN. Caroline. That surprises me extremely ; how then are the combinations of the other bodies performed, if, according to your explanation of chemical attraction, bodies are suppo- sed only to combine in virtue of their opposite states of elec- tricity ? Mrs. B. Compound bodies, in which oxygen prevails over the other component parts, are also negative, but their 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 positive, but their positve energy is diminished in proportion to the quantity of oxygen which enters into their composition. Bodies, therefore, that are not already combined with oxy- gen, will attract it, and, under certain circumstances, will ab- sorb 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 ofthe gas, which is absorbed ; and the two electricities escaping, 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 oxy- gen from the atmosphere, and you will see what becomes of the caloric. Caroline. You are joking, Mrs. B.; you do not mean to decompose the atmosphere with a piece of dry stick ? Mrs. B. Not the whole body of the atmosphere, certain- ly ; but if we can make this piece of wood attract any quantity of oxygen from it, a proportional quantity of atmospherical air will be decomposed. 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 temperature is required for the commencement ofthe union ofthe oxygen and the wood. This elevation of temperature was formerly thought to be necessary, in order to diminish the cohesive attraction ofthe wood, an' betw^on the affinity of a body for oxygen and its combustibility ; but I think I understand it now perfectly. 94 OXYGEN AND NITROGEN. Mrs. B. Combustion, then, you see, is nothing more than the rapid combination of a body with oxygen, attended by the disengagement of light and heat. Emily. But are there no combustible bodies whose attrac- tion for oxygen is so strong, that they will combine with it, without the application of heat ? Caroline. That cannot be j otherwise we should see bodies burning spontaneously. Mrs. B. But there are some instances of this kind, such as phosphorus, potassium, and some compound bodies, which I shall hereafter make you acquainted with. These bodies, however, are prepared by art, for in general, all the combus- tions that could occur spontaneously, at the temperature of the atmosphere, have already taken place ; therefore new combustions cannot happen without the temperature of the body being raised. Some bodies, however, will 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 with the source of ■ caloric, the sooner will its temperature be raised to the de- gree necessary for it to burn. If you hold it near the fire, the same effect will be produced ;.but more time will be re- quired, as 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 electrrc energy of the wood, which is required to enable it to combine with the oxygen ? Mrs. B. The caloric which is gradually produced by the two electricities during combustion, keeps up the temperature , ofthe burning body ; so that when once combustion has be- gun, no further application of caloric is required. Caroline. Since 1 have learnt this wonderful theory of combpstion, 1 cannot help gazing at the fire ; and I can scarcely conceive that the heat and light, which I always sup- posed to proceed entirely from the coals, are really produced as much by the atmosphere. Emily. When you Wow the fire, you increase the combus- tion, I suppose, by supplying the coals with a greater quanti- ty of oxygen gas. Mr*. B. Certainly ; but of course no blowing will pro- duce combustion, unless the temperature ofthe coals be first raised. A single spark, however, is sometimes sufficient to J PLATBIW. tfy.2. Fly. 3. Pirpamtini cf axyam j/as. Pic 4. Tlo.'i f'cmbtisttrjrt or' CK 7rrli ct •iccy'tiir' t/t. iron uiie in oxygen or"a mj.i-r under a reeeirer. f-'iy.t.jiJietrrt w. ■ : standi Tir- S. ATFtirnace .B Hattfieu Bttort in the furnace .C /tbtertatri .11 Receiver ; dr. .fun' 1 r:\YW Sli, Ifper/cixtted on vliic/i t/ie Jteceiirer stanefs .Ftj.4. Ccmtuslicti ot OXYGEN AND NITROGEN. 95 produce that effect; for, as I said before, when once combus- eWa^h^ is efficient to Sere bP a femperatUre ^ reSt °f the body, provided that there be a free access of oxygen. It however sometimes happens that if a fare be ill made, it will be extinguished be- fore all the fuel is consumed, from the very circumstance of the combustion being so slow that the caloric disengaged is in- sufficient to keep up the temperature of the fuel. You must recollect that there are three things required in order to pro- duce combustion ; a combustible body, oxygen, and a temper- ature at which the one will combine with the other. Emily You said that combustion was one method of de- composing 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 ofthe atmosphere ? Mrs. B. It is necessary for this purpose to burn the body within a close vessel, which is easily done.—We shall intro- duce a small lighted taper (Plate VII. Fig. 1.) under this glass receiver, which stands in a basin over water, to prevent all communication with the external air.* Caroline. How dim the light burns already !—It is now extinguished. Mrs. B. Can you tell us why it is extinguished ? Caroline. Let me consider.—The receiver was full of atmospherical air ; the taper, in burning within it, must have combined with the oxygen contained in that air, and the calo- ric that was disengaged produced the light ofthe taper. But when the whole ofthe oxygen was absorbed, the whole of its electricity was disengaged; consequently no more caloric 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 disposed of, what remains under the receiver must be pure nitrogen gas. Mrs. B. There are some circumstances which prevent the nitrogen gas, thus obtained, from being perfectly pure ; but we may easily try whether the ox-ygen has disappeared, by putting another lighted taper under it.—You see how in- * To make a taper, melt some bees wax, and dip into it a striD of cotton cloth about an inch»wide, and before it is cold, twist it pretty hard. Cotton wick does better than the cloth A quart tumbler makes a good receiver. Two or three inches of the tape' c»d be fastened to a piece of wire, beot so that it will stand up. Thus the experiment is easily made. C 96 OXYGEN AND NITROGEN. stantaneously 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 animal under the receiver, it would immediately be suffocated. But that is an experi- ment which I 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 trans- parent and invisible, like common air. This cloudiness pro- ceeds from a variety of exhalations, which arise from the burning taper, the nature of which you cannot yet under- stand. Caroline. The water in the receiver has now risen a lit- tle above its level in the basin. What is the reason of this ? Mrs. B. With a moment's reflection, I dare say you would have explained it yourself. The water rises in con- sequence ofthe oxygen gas within it having been destroyed, or rather decomposed, by the combustion ofthe taper. Caroline. Then why did not the water rise immediately when the oxygen gas was destroyed ? Mrs. B. Becau.se the heat of the taper, whilst burning, occasioned a dilatation ofthe air in the vessel, and a produc- tion of carbonic acid, which at first counteracted this effect. Another means of decomposing the atmosphere is the oxy- genation of certain metals. This process is very analagous to combustion ; it is, indeed, only a more general term to ex- press the combination of a body with oxygen. Caroline. In what respect, then, does it differ from com- bustion ? Mrs. B. The combination of oxygen in combustion is al- ways accompaaied by a disengagement of light and heat; whilst this circumstance is not a necessary consequence of simple oxygenation. Caroline. But how can a body absorb oxygen without the combination ofthe two electricities which produce caloric ? Mrs. B. Oxygen does not always present itself in a gas- eous form ; it is a constituent part of a vast number of bodies, both solid and liquid, in which it exists in a state of greater density than in the atmosphere ; and from these bodies it may be obtained without much disengagement of caloric. It may likewise, in some cases, be absorbed from the atmos- phere without any sensible production of light and heat; for, if the process be slow, the caloric is disengaged in «uch small quantities, and so gradually, that it is not' capable of OXYGEN AND NITROGEN. 97 producing either light or heat. In this case the absorption of oxygen is called oxygenation or oxydation, instead of com- bustion, as the production of sensible light and heat is essen- tial 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 I should have thought that oxygen could never have penetrated such bodies. Mrs. B<. Their strong attraction for oxygen counterbalan- ces this obstacle. Most metals, however, require to be made red hot before 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 properly termed an oxyd; thus we have oxyd of lead, oxyd of iron, &c* Emily. And in the Voltaic battery, it is, I suppose, an ox- yd of zinc, that is formed by the union of the oxygen with that 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 to 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 or oxygenated Emily. Metals, when converted into oxyds, become, I suppose, negative. Mrs. B. Not in general ; because in most oxyds the pos- itive energy of the metal more than counterbalances the na- tive energy ofthe oxygen with which it combines. This black powder is an oxyd of manganese, a metal which has so strong an affinity for oxygen, that it attracts that sub- stance from 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 ofthe appearance of a metal. It is now heavier than it was before oxydation, in consequence ofthe additional weight ofthe oxy- gen with which it has combined. Caroline. I am very glad to hear that; for I confess I could not help having some doubts whether oxygen was real- ly a substance, as it is not to be obtained in a simple and pal- * Red lead and rust of iron. C. 10 98 OXYGEN AND NITROGEN. pable state ; but its weight is, I think, a decisive proof of its being a real body. 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 we not then have it in its palpable simple state ? Mrs. B. No ; for I can only separate the oxygen from the manganese, by presenting to it some other body, for which it has a greater affinity than for the manganese. Caloric afford- ing the two electricities is decomposed, and one of them uni- ting with the oxygen, restores it to the aeriform state. Emily. But you said just now, that manganese would at- tract oxygen from the atmosphere in which it is combined with the negative electricity ; how, therefore, can the oxy- gen have a superior affinity for that electricity, since it aban- dons it to combine with the manganese ? Mrs. B. I give you credit for this objection, Emily ; and the only answer I can make to it is, that the mutual affinities of metals for oxygen, and of oxygen for electricity, vary at different temperatures ; a certain degree of heat will, there- fore, dispose a metal to combine with oxygen, whilst, on the contrary, the former will be compelled to part with the lat- ter, 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. (Plate VII. fig. 2.) The retort containing the manganese you cannot see, as I have inclosed it in this furnace, where it is now red-hot. But, in order to make you sensible of the escape of the gas, which is itself invisible, I have connected the neck ofthe retort with this bent tube, the extremity of which is immersed in this vessel of water. (Plate VII. fig. 3.) Do 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 ? Mrs. B. We shall collect it in this receiver.—For this purpose, you observe, I first fill it with water, in order to ex- clude the atmospherical air ; and then place it over the bub- * 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 bend- ing 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. OXYGEN ANB NITROGEN. 99 bles which issue from 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, 1 suppose, from their specific levity ? Mrs. B. Yes ; for though oxygen forms rather a heavy gas, it is light compared to water. You see how it gradu- ally displaces the water from the receiver, it is now full of gas, and I may leave it inverted in water on this shelf, where 1 can keep the gas as long as I choose, for future ex- periments. This apparatus (which is indispensable 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 re- ceiver to rest upon under water, and the holes in it for the gas to pass into the receiver! I long to make some experi- ments with this apparatus. Mrs. B. I shall try your skill that way, when you have a little more experience. 1 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. Caroline. Really ! 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 affinity for oxygen. Mrs. B. Iron will, however, not burn in atmospherical air without a very great elevation of temperature ; but it is eminently combustible in pure oxygen gas ; and what will surprise you still more, it can be set on fire without any con. siderable rise of temperature. You see this spiral iron- wire. |—I fasten it at one end to this cork, which is made to fit an opening at the top of the glass receiver. (Plate VII. fig. 4.) Emily. I see the opening in the receiver ; but it is care- fully closed by a ground glass-stopper. * 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, wMl answer very well for a great variety of experiments on the gases. C f 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 oxygon is collected. A botile of white glass of a quart capacity does well ,■ .■ HYDROGEN. 107 the atmosphere ; for, in the first case, there is a chemical union and condensation ofthe two substances ; in the latter, they are simply mixed together in their gaseous state. You will find, however, that in some cases, nitrogen is quite as intimately connected with oxygen, as hydrogen is. But this is foreign to our present subject. Emily. Water, then, is an oxyd, though the atmospheri- cal air is not. Mrs. B. It is not commonly called an oxyd, though, ac- cording to our definition, it may, no doubt, be referred to that class of bodies. Caroline. I should like extremely to see water decompo- sed. Mrs. B. I can gratify your curiosity by a much more easy process than the oxydation of charcoal or metals ; the decom- position of water by these latter means takes up a great deal of lime, and is attended with much trouble ; for it is necessa- ry that the charcoal or metal should be made red hot in a fur- nace, that the water should pass over them in a state of vapour, that the gas formed should be collected over the water-bath, &c. In short, it is a very complicated operation. But the same effect may be produced with the greatest facility, by the action ofthe 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. Mrs. B. For this purpose I fill this piece of glass tube (Plate VIII. fig. l.) with water, and cork it up at both ends ; through one ofthe corks I introduce that wire ofthe battery which conveys the positive electricity ; and the wire which conveys the negative electricity is made to pass through the other cork, so that the two wires approach each other suffi- ciently near to give out their respective electricities. Caroline. It does not appear to me that you approach the wires so near as you did when you made the battery act by itself. Mrs. B. Water being a better conductor of electricity than air, the two wires will act on each other at a greater distance in the former than in the latter case. Emily. Now the electrical effect appears : I see small bubbles of air emitted from each wire. Mrs. B. Each wire decomposes the water ; the positive by combining with its oxygen, which is negative ; the nega- tive, by combining with its hydrogen, which is positive. Caroline. That is wonderfully curious 1 but what are the small bubbles of air ? 108 HYDROGEN. Mrs. B. Thos£ that appear to proceed from the positive wire, are the result ofthe decomposition ofthe water by that wire. That is to say, the positive electricity having combi- ned with some ofthe oxygen ofthe water, the particles of hy- drogen which were combined with that portion of oxygen are set at liberty, and appear in the form of small bubbles of gas or air. Emily. And I suppose the negative fluid, having in the same manner combined with some of the hydrogen of the wa- ter, the particles of oxygen that were combined with it, are set free, and emitted in a gaseous form. Mrs. B. Precisely so. But I should not forget to observe, that the wires used in this experiment are made of platina, a metal which is not capable of" combining with oxygen ; for otherwise the wire would combine with the oxygen, and the hydrogen alone would be disengaged. Caroline. But could not water be decomposed without the electric circle being completed ? If, for instance, you immer- sed only the positive wire in the water, would it not com- bine with the oxygen, and the hydrogen gas be given out ? Mrs. B. No ; for as you may recollect, the battery can- not act unless the circle be completed ; since the positive wire will not give out its electricity, unless attracted by that ofthe negative wire. Caroline. I understand it now.—But look, Mrs. B., the decomposition of tbe water which has been going on for some time, does not sensibly diminish 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 sin- gle drop of water is sufficient to produce thousands of 9uch small bubbles as those you now perceive. Caroline. But in this experiment, we obtain the oxygen and hydrogen* gases mixed together. Is there any means of procuring the two gases separately ? Mrs B. They can be collected separately with great ease, by modifying a little the experiment. Thus, if instead of one tube, we employ two, as you see here (c, d,) Plate VIII. fig. 2,) both tubes being closed 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 down- wards, 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 ofthe battery, and the other with HYDROGEN. loS the other end, the water in the tubes will be decomposed ; hydrogen will be given out round the wire in the tube con- nected with the positive end of the battery, and oxygen in the other; and these gases will be evolved exactly in the proportions which I have before mentioned, namely, two measures Of hydrogen for one of oxygen. We shall now be- gin the experiment, but it will be sometime before any sen- sible 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 decom- position of water by charcoal or metals is attended with so much inconvenience. Mrs. B. Water, may be decomposed by means ol metals without any difficulty ; but for this purpose the intervention of an acid is required. Thus, if we add some sulphuric acid (a substance with the nature of which you are not yet ac- quainted) 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 hrtsten the process. Of this I am going to show you an in- stance. 1 put into this bottle the water that is to be decom- posed, the metal that is to effect that decomposition by com- bining with the oxygen, and the acid which is to facilitate the combination ofthe metal and the oxygen. You will see with what violence these will act on each other.* Caroline. But what metal is it that you employ for this purpose ? Mrs. 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 upon by the acid, and is disposed to receive the oxy- * To obtain hydrogen, fit a cork air tight to an oi! 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 einc, granulated by melting, and pouring it into cold water. Then pour in half an ounce by measure of Milphuric acid, and immediately put the cork into its place, and plunge the other end of the tube under a receiver, or large tum- bler, filled with water, and inverted in the water-bath. The flask 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. 11 110 HYDROGEN. gen produced by the decomposition of the water, it necessa- rily follows that the greater is the surface, the more consid- erable is the effect. The bubbles which are now rising are hydrogen gas---- Caroliyie. How disagreeable it smells ! Mrs. B. It is indeed unpleasant, though I believe not par- ticularly 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 the water- bath. (Plate VIII. fig. 3.) Emily. How very rapidly the gas, escapes ! it is perfectly transparent, and without any colour whatever. Now the re- ceiver is full---- Mrs. B. We shall therefore remove it and substitute an- other in its place. But you must observe, that when the re- ceiver is full, it is necessary to keep it inverted with the mouth under water^ otherwise 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 re- ceiver, so that it can be taken out of the bath and conveyed any where ; the water in the saucer being equally effectual in preventing its escape as that in the bath. (Plate VIII. fig. 4.) Emily. I am quite surprised to see what a large quantity of hydrogen gas can be produced by so small a quantity of water, especially as oxygen is the principal constituent of water. Mrs. B. In weight it is ; but not in volume. For though # the proportion, by weight, is nearly eight parts of oxygen to one of hydrogen, yet the proportion of the volume ofthe gases is about one part 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 de: composed so hot! As the water changes from a liquid to ar gaseous form, cold should be produced instead of heat. Mrs. B. No ; for if one of the constituents of water is converted into a gas, the other becomes solid in combining with the metal. . Emily. In this case, then, neither heat nor cold should be produced ? Mrs. B. True ; but observe that the sensible heat which is disengaged in this operation, is not owing to the decompo- sition of the water, but to an extrication of heat produced * Hydrogen is about 13, times lighter than atmospheric air. C. HYDROGEN. Ill by the mixture of water and sulphuric acid. I will mix some water and sulphuric acid together in this glass, that you may feel the surprising quantity "of heat which is disengaged by their union—now take hold ofthe glass---- Caroline. Indeed I cannot ; it feels as hot as boiling wa- ter. I should have imagined there would have been heat enough disengaged to have rendered the liquid solid. Mrs. B. As, however, it does not produce that effect, we cannot refer this heat to the modification called latent heat. We may however, I think, consider it as heat of capacity, since the liquid is condensed by its loss ; and if you were to repeat the experiment, in a graduated tube, you would find the two liquids, when mixed, occupy considerably less space th in they did separately. But we will reserve this to an- other opportunity, and attend at present to the hydrogen gas which we have been producing. If I now set the hydrogen gas, which is contained in this receiver, at liberty all at once, and kindle it as soon as it comes in contact with the atmosphere, by presenting it to a candle, it will so suddenly and rapidly decompose the oxygen gas, by combining with its basis, that an explosion, or a deto- nation (as chemists commonly call it,) will be produced. For this purpose, I need only take up the receiver, and quickly present its open mouth to the candle——so..... Caroline. It produced only a sort of hissing noise, with a vivid flash 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 instance, 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 small orifice, from the sudden dilatation ofthe 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 ; fo*\ as I 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. Caroline. That is frue ; but I thought this was a different combination, 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. Put water certainly was produced ; for oxygen 112 HYDROGEN. is incapable of combining with hydrogen in any other pro- portions than those which form water ; therefore water must always be the result of their combination. If, instead of bringing the hydrogen gas into sudden con- tact 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 g is to burn in contact with the atmos- phere, the combustion goes on quietly and gradually at the point of contact, without any detonation, because the sur- faces 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, (Plate VIII. fig. 5.) is full of hydrogen gas, and is carefully corked. If I take out the cork without moving 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 en- tirely 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 procure a fresh supply of hydrogen gas, by putting into this bottle (Plate VIII. fig. 6,) iron-filings, water, and sulphuric acid, materials similar 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 rapid stream. Caroline. I hear already the hissing of the gas through the tube, and I can feel a strong current against my hand. Mrs. B. This current I am going to kindle with the can- dle—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 for- mer experiment ? Mrs. B. The combustion goes on uninterruptedly as long as the new gas continues to be produced. Now, if I invert this receiver over the flame, you will soon perceive its inter- nal surface covered with a very fine dew, which is pure water.—t * The levity of hydrogen is such, that if a vessel be filled with it, and kept inverted, it may be carried about the room, without its es- caping. The above experiment therefore may be made by bring- ing a small jar, or,tumbler of the gas over a lighted lamp. C. f The burning of a candle, lamp, wood, &c. always produces water. The tallow and oil contain hydrogen, and during combustion, it unites with the oxygen of the atmosphere. Hold a wide tube over a larnp> and it is soon covered with moisture. Wood contains hydrogen. C- nyjjROGLN 113 Caroline. Yes, indeed ; the glass is now quite dim with moisture ! How glad 1 am that we can see the water produ- ced 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 water would have escaped in the state of vapour, as it did in the former experiment. We have here, of course, obtain- ed but. a very small quantity of water ; but the difficulty of procuring a proper apparatus, with sufficient quantities of gases, prevents my showing it you on a larger scale. The composition of water was 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 ingenious apparatus, to perform with great accuracy, and upon a large scale, 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 globe 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; they burn together, that is to say, the hydrogen combines with the oxygen, the caloric is 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 o* water ever formed in this apparatus ? Mrs. B. Several ounces ; indeed, very nearly a pound, if I recollect right; but the operation lasted many days. Emily. This experiment must have convinced all the world ofthe truth ofthe discovery. Pray, if improper pro- portions ofthe gases were mixed and set fire to, what would be the result ? Mrs. B. Water would equally be formed, but there would be a residue of either one or other ofthe gases, because, as I have already told you, hydrogen and oxygen will combine only in the proportions requisite for the formation of water. Emily. Look, Mrs. B., our experiment with the Voltaic battery, (Plate VIII. fig. 2.) has made great progress ; a quantity of gas has been formed in each tube, but in one of them there is twice as much a* in the other. Mrs. B. Yes ; because, as I said before, water is compo- sed of two volumes of hydrogen to one of oxygen—and'if we should now mix these gases together and set fire to them by 11* 114 HYDROGEN. 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 combus- tion of hydrogen gas, which 1 shall show you, though I must acquaint you first, that 1 cannot well explain the cause of it. For this purpose, I must put some materials into our appara- tus, 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, I shall now kindle it with the taper. Emily. It burns exactly as it did before-—What is the cu- rious effect which you were mentioning ? Mrs. B. Instead of the receiver, by means of which we have just seen the drops of water form, we shall invert over the flame this piece of tube, which is about two feet in length, and one inch in diameter, (Plate VIII. fig. 7 ;) but you must observe that it is open at both ends. Emily. What a strange noise it produces ! something like the iEolian harp, but not so sweet. . Caroline. It is very singular, indeed ; but I think rather 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 sound, is not extraordinary ; but the sound here is so peculiar, that no other gas has a similar ef- fect. Perhaps it is owing to a brisk vibratory motion ofthe glass, occasioned by the successive formation and condensa- tion of small drops of water on the sides ofthe glass tube, anil the air rushing in to replace the vacuum formed.* Caroline. How very much this flame resembles the burn- ing of a candle. Mrs. B. The burning of a candle is produced by much the same means. A great deal of hydrogen is contained in candles, whether of tallow or wax. This hydrogen being converted into gas by the heat of the candle, combines with the oxygen of the atmosphere, and flame and water result from the combination. So that, in fact, the flame of a candle is owing to the combustion of hydrogen gas. An elevation of temperature, such as is produced by a lighted match or taper, is required to give the first impulse to the combustion ; but afterwards it goes on of itself, because the candle finds a sup- ply of caloric in the successive quantities of heat which re- sult from the union ofthe two electricities given out by the * This ingenious explanation was first suggested by Dr. Delarive. See Journals ofthe Royal Institution, vol. i. p. 259. HYDROGEN. 116 gases during their combustion. But there are other circum- stances connected with the combustion of candles and lamps, which I cannot explain to you till you are acquainted with carbon, which is one of their constituent parts. In general, however, whenever you see flame, you may infer that it is owing to the formation and burning of hydrogen gas*|' for flame is the peculiar mode ot burning hydrogen gas, which, with only one or two apparent exceptions, does not belong to any other combustible. Emily. You astonish me ! I understood that flame was the caloric produced by the union ofthe two electricities, in all combustions whatever ? Mrs. B Your error proceeded from your vague and in- correct 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, appeared to me to emit flame ; yet, as it was a simple metal, it could contain no hydrogen. Mrs. B. It produced a sparklibg, dazzling blaze of light, but no real flame. Emily. And what is the cause ofthe regular shape ofthe flame of a candle ? Mrs. B. The regular stream of hydrogen gas which ex- hales from its combustible matter. Caroline. But the hydrogen gas must, from its great levity, ascend into the upper regions ofthe atmosphere : why there- fore 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 oxy- gen, into watery vapour ; but in a state of such minute division as to be invisible. Caroline. I do not understand what is the use of the wick of a candle, since the hydrogen gas burns so well without it. Mrs. B. * The combustible matter of the candle must b<$ * 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 the combination besides flame and water is a quantity of carbonic acid. C 116 HYDROGEN. decomposed in order to emit the hydrogen gas ; and the wick is instrumental in effecting this decomposition. Its combus- tion first melts the combustible matter, and— Caroline. But, in lamps, the combustible matter is already fluid, and yet they also require wicks. Mrs. B. I 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 ; for you must have observed that the wick does not burn quite to the bottom. 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 ofthe wick which is immediately in contact with the can- dle, as to the part just above, so that the heat there is not sufficient to produce its decomposition : the combustion, therefore, begins 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, I hope, be soon adopted every where, I can perceive no wick at all. How are these lights managed ? Mrs. B. I am glad you have put me in mind of saying a few words on this very useful and interesting 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 quan- tities ? Mrs. 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-Carbonat, 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 highly inflammable ; and, inhum- ing, it emits that vivid light which you have so often observ- ed. Caroline. And does the process for procuring it require nothing but heating the coals, and conveying the gas through tubes ? * 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 which the wick passes, conducts off the heat. C. ■"•4?-#. tljtu jt: JFia.2. Apparatus f?r transterrirty gases from a Receiver inte> a Meia'e&r.^Fii?. 2. Apparatus /or Motility Soap iuiSles. HYDROGEN. 117 Mrs. B. Nothing else ; except that the gas must be made to pass, rnmediaU ly at its formation, through two or three large vessels of water,* in which it deposits some other in- gredients, 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 impurities, and tubes that convey it to the desired spot, being propelled with uni- form velocity through the tubes by means of a certain de- gree of pressure which is made upon the reservoir. 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, offices, and public places, it far surpasses any former iuvention : 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 generally desirable, either with respect to economy or convenience. It nr-ay, however, be considered as one of the happiest applications of chemis- try 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, I 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 with what ease and rapidity they will ascend, without the assistance of blow- ing, from the lightne.-s 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 requir- ed. There is you see, a similar stop-cock fastened to this bladder, which is made to fit that on the receiver. I screw them one on the other, and now turn the two cocks, to open a communication between the receiver and the bladder : then, by sliding the receiver off the shelf, and gently sinking it into the bath, the water rises in the receiver, and forces the gas into the bladder. (Plate IX. fig. 1.) * The ga« 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. 118 HYDROGEN. Caroline. Yes, I see the bladder swell as the water rises in the receiver. Mrs. B. 1 think that we have already a sufficient quan- tity m 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 gas into the soap and water, at the mouth of the pipe. (Plate IX. fig. 2.) V Emily. There is a bubble ; but it bursts before it leaves the mouth of the pipe. Mrs. B. 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. I 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 ? Mrs. B. No, they are perfectly air tight ; we shall suc- ceed presently, I dare say. Caroline. Now a bubble ascends ; it moves with the rapid- ity of a balloon. How beautifully it refracts the light. Emily. It has burst against the ceiling—yon succeed now wonderfully; but why do they all ascend and burst against the ceiling ? Mrs. B. Hydrogen gas is so much lighter than atmospheri- cal 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 pur- pose is very simple. It consists of a number of vessels, either jars or barrels, in which the materials for the forma- tion ofthe gas are mixed, each of these being furnished with a tube, and communicating with a long flexible pipe, which conveys the gas into the balloon. AW?/. But the fire-balloons which were first invented, and have been since abandoned, on account of their being to- HYDROGEN. 119 so dangerous, were constructed, I suppose, on a different principle. Mrs. B. They were filled simply with atmospherical air, considerably rarefied by heat; and the necessity of having a fire underneath the balloon, in order to preserve the rare- faction 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 filling soap-bubbles with a mix- ture of hydrogen and oxygen gases, in the proportions that form water ; and afterwards setting fire to them. Emily. '1 hey will detonate, I suppose ? Mrs. B. Yes, they will. As you have seen the method of transferring the gas from the receiver into the bladder, it is not necessary to repeat it. I have therefore provided a bladder which contains a due proportion of oxygen and hy- drogen 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---- Caroline. 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 lightning. Mrs. B. The combination of the two gases takes place during that instant of time that you see the flash, and hear the detonation. Emily. This has a strong resemblance to thunder and lightning.j Mrs. B. These phenomena, however, are generally of an electrical nature. Yet various meteorological effects may be attributed to accidental detonations of hydrogen gas in the atmosphere; for nature abounds with hydrogen : it consti- tutes a very considerable portion ofthe whole mass of water belonging to our globe, and from that source almost every body obtains it. It enters into the composition of all animal substances, and of a great number of minerals ; but it is most abundant in vegetables. From this immense variety of b^ies it is often spontaneously disengaged ; its great levity makes * 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. f The report is owing to the air, rushing in to fill the vacuum, cau- sed by the condensation of the two gases and the heat extricated at the same instant. C 120 HYBROCEN. it rise into the superior regions of the atmosphere ; and when, either by an electrical spark, or any casual elevation of temperature, it takes fire, it may produce such meteors or luminous appearances as are occasionally seen in the at- mosphere. Of this kind 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. Mrs. B. That probably is often the case, though it is not a necessary consequence ; for the water may be dissolved by the atmosphere, as it descends towards the lower regions, and remain there in the form of clouds. ' The application of electrical attraction to chemical pheno- mena is likely to lead to many very interesting discoveries in meteorology ; for electricity evidently acts a most important part in the atmosphere. This subject however, is, as yet, not sufficiently developed for me to venture enlarging upon it. The phenomena of the atmosphere are far from being well understood ; and even with the little that is known, I am but imperfectly acquainted. But before we take leave of hydrogen, I must not omit to mention to you a most interesting discovery of Sir H. Davy, which is connected with this subject. Caroline. You allude, 1 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 pur- pose it was intended to answer. Mrs. B. It often happpns in coal mines, that quantities of the gas called by chemists hydro-carbonat, or by the miners firedamp, (the same from which the gas-lights are obtained,) ooze out from fissures in the beds of coal, and fill the cavities in which the men are at work : and this gas being inflamma- ble, the consequence is, that when the men approach those places, with a lighted candle, the gas takes fire, and explo- sions happen, which destroy the men and horses employed in that part ofthe colliery, sometimes in great numbers. Emily. What tremendous accidents these must be I But whence does that gas originate ? Mrs. B. Being the chief product of the combustion of coal, no wonder that inflammable gas should occasionally ap- pear in situations 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 ; HYDROGEN. 121 and, therefore, those accumulations of gas may arise either , from combustions actually going on, or from former combus- tions, the gas having perhaps been confined there for ages. Caroline. And how does Sir H. Davy's lamp prevent those 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 ofthe lamp is shortly this : It was ascertained two or three years ago, both by Mr. Tenant, and by Sir Humphrey himself, that the com- bustion of inflammable gas could not be propagated through small tubes ; so that if a jet of an inflammable gaseous mix- ture, issuing from a bladder or any other vessel, through a small tube, be set fire to, it burns at the orifice ofthe 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 ever penetrate through the tube into the vessel from which the gas issues, so as to explode at once the whole ofthe 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 construction of a lamp ? Mrs. B. Nothing easier. You need only suppose a lamp enclosed 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 lanthorn be car- ried into an atmosphere capable of exploding, an explosion or combustion ofthe 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 explained, 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 ? Mrs. B. No ; in the early part of the inquiry a lamp of this kind was actually proposed ; but it was but a rude 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 perfection, at last conceived the happy idea that if the lamp were surrounded with a wire-work or wire-gauze, of a close texture, instead of glass or horn, the tubular contrivance I have just described would be entirely superseded, since each of the interstices ofthe gauze would act as a tube in preventing the propagation of explosions; so 12 122 HYDROGEN. that this pervious metallic covering would answer the various purposes of transparency, of permeability to air, and of pro- tection against explosion. This idea, Sir Humphrey immedi- ately submitted to the test of experiment, and the result has answered his most sanguine expectations, both in his laborato- ry and in the collieries 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 ofthe bowels ofthe earth one of the most valuable necessa- ries of life. Here is one of these lamps, every part of which vou will at once comprehend. (See Plate X. fig. 1.) Caroline. How very simple and ingenious ! But 1 do hot yet well see why an explosion taking place within the lamp snould not communicate to the external air around it, through the interstices ofthe wire ? Mrs. B. This has been and is still a subject of wonder, even to philosophers ; and the only mode they have of ex- plaining it is, that flame or ignition cannot pass through a fine wire-work, because the metallic wire cools the flame suffi- ciently 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. Emily. But I should expect the wire would often become red hot, by the burning ofthe gas wifhin the lamp. Mrs. B. And this is actually the case ; for the top of the lamp is very apt to become red hot. But fortunately, such inflammable gaseous mixtures as are found in the mines can- not be exploded by red hot wire, the intervention of actual flame being required for that purpose ; so that the wire does not set fire to the explosive gas around it. " Emily. I can understand that ; but if the wire be red hot, how can it cool the flame within, and prevent its passing through the g;-nze 1 . Mrs. B. t 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 interesting discovery, and one which shows at once the immense utility with which sci- ence may be practically applied to some ofthe most impor- tant purposes. FINITEX. /'rir.J.A..t/ie cistern containiiiff t/te ott.—B.the sctrt-j e}\ t.?/iic7i t/re aaetzg caae ur ttjrcc/ to trie cistertt —C.appertittr ten stt/fAiett/ ot'/.-Fj.a uitrr t£r trt'tttrittrty-l/tc totcti 'D.-F./tb to/trpause cy/ttte/er. Gr.rf e/ce-et/e- lkp.-Ftejt.2'. A. t/ta rvsttvoir *.**, water CZPcrctlain titie containing Carfivnt. A) furnace trirety/t v/ticn tht tube passes. _R Receiver£rt/u jras pttrWurce/. £ Itater lat/i. SULfHUR. 125 Let us return to the sulphur. You now perfectly understand 1 suppose, what is meant by sublimation ? Emily. I believe 1 do. Sublimation appears to consist in destroying, by means of heat, the attraction of aggregation of the particles of a solid body, which are thus volatilized ; and as soon as they lose the caloric which produced that effect, they are deposited in the form of a fine powder. Caroline. It seems to me to be somewhat similar to the transformation of water into vapour, which returns to its li- quid state when deprived of caloric. Emily. There is this difference, however, that the sul- phur does not return to its former state, since, instead of lumps, it changes to a fine powder. Mrs. B. Chemically speaking, it is exactly the same sub- stance, whether in the form of lump or powder. For if this powder be melted again by heat, it will, in cooling, be restor- ed to the same solid state in which it was before its sublima- tion. Caroline. But if there be no real change produced by the sublimation of the sulphur, what is the use of that operation. Mrs. B. It divides the sulphur into very minute parts, and thus 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 combustion, for the completion of which one circumstance only is wanting, the absorption of oxygen. Mrs. B. But that circumstance is every thing. No essen- tial alteration is produced in sulphur by sublimation ; whilst in combustion 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 result 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 tem- perature be considerably raised.—You see that it burns with a faint blueish 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 re- ceiver, a little above its level in the plate. Well, Emily, can you account for this ? Emily. I suppose Ahat the sulphur has absorbed the oxy- gen from the atmospherical air within the teceiver, 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. 12* 126 SULPHUR. Mrs. B. Your first conjecture is very right: but you are mistaken in the last; for nothing will be left in the cup.— The white vapour 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 combina- tion of oxygen and sulphur, producing a true gas, which would continue such under the pressure and at the tem- perature of the atmosphere, if it did not unite with the wa- ter 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 oxygen, which is the acidifying principle. And, indeed, the word oxygen is de- rived from two Greek words signifying to produce an acid. Caroline. Why then, is not water, which contains such a quantity of oxygen, acid ? Mrs. B. Because hydrogen, which is the other constitu- ent of water, is not susceptible of acidification. I believe it will be necessary, before we proceed further, to say a few words on the general nature of acids, though it is rather a deviation from our plan of examining the simple bodies sep- arately, before we consider them in a state of combination. 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 discernible by their sour taste, and by turning red most ofthe blue vegetable colours. These two proper- ties are common to the whole class of acids ; but each of them is distinguished by other peculiar qualities. Every acid con- sists of some particular substance, (which 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 sufficient 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 requisite to constitute it an oxyd. before it can combine with the greater quantity which is necessary to render it an acid. * 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, as in lemons, apples, &c. C. SULPHUR. 127 Caroline. Are all oxyds capable of being converted into acids ? S!'is- B- Very .far from '* 5 ^ is only certain substances which will enter into that peculiar kind of union with oxy- gen that produces acids, and the number of these is propor- tionally very small; but all burnt bodies may be considered as belonging either to the class of oxyds, or to that of acids. At a future period, we shall enter more at large into this sub- ject. 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, according to the different quantities of oxygen with which their basis combines. Emily. And how are these two degrees of acidification distinguished ? Mrs. B. By the peculiar properties which result from them. The acid we have just made is the first or weakest degree pf acidification, and is called sulphureous acid; if it were fnlly saturated with oxygen it would be called sulphu- ric acid. You must therefore remember, that in this, as in all acids, the first degree of acidification is expiessed 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, 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 re- ceiver which stands on the shelf in the bath, and is full of water. Caroline. Pray, let me try to do it, Mrs. B. Mrs. B. It requires some little dexterity—hold the bot- tle completely under water, and do not turn the mouth up- wards, till it is immediately under the aperture in the ^helf, through which the gas is to pass into the receiver, and then turn it up gradually.—Very well ; you have only let a few bubbles escape, and that must be expected at a first trial.— Now I shall put this piece of sulphur into 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 being done very quickly, lest the atmospherical air should ob- tain entrance and mi? with the pure oxygen gas. Emily. How beautifully it bums ! Caroline. But it is already buried in the thick vapour. This, I suppose, is solphurie acid? Emily. Are these acids always in a gaseous state ? Mrs. B. Sulphureous acid, as we have already observed, 128 SULPHUR. is a permanent gas, and can be obtained in a liquid form only by condensing it in water. In its pure state, the sulphure- ous acid is invisible, and it now appears in the form of a white smoke, from its combining with the moisture. But the va- pour of sulphuric acid, which you have just seen to rise dur- ing the combustion, is not a gas. but only a vapour, which condenses into liquid sulphuric acid, by losing its caloric. It appears however from Sir H. Davy's experiments, that this formation and condensation of sulphuric acid requires the presence of water, for which purpose the vapour is received into cold water, which may afterwards be separated from the acid by evaporation. Sulphur has hitherto been considered as a simple substance; but bir H. Davy has suspected that it contains a small por- tion of hydrogen, and perhaps also of oxygen. On submitting sulphur to the action ofthe Voltaic battery, he observed that the negative wire gave out hydrogen ; and the existence of hydrogen in sulphur was rendered still more probable by his observing that a small quantity of water was produced during the combustion of sulphur. Emily. And pray of what nature is sulphur when perfect- ly pure ? Mrs. B. Sulphur has probably never been obtained per- fectly free from combination, so that its radical may possibly possess properties very different from those of common sul- phur. It has been suspected 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 substan- ces, and especially with hydrogen, with which you are alrea- dy 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 divi- ded by heat, as to become soluble in gas: and of this there are several instances. But you must observe, that, in the pre- sent case, a chemical 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 th*> gas ; the heat reduces the sulphur to such a state of extreme divi- sion, and diffuses it so thoroughly thr<. i;h 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. Be- sides, it is evident, from the peculiar fetid smell of this gas* PHOSPHORUS. 129 that it is a new compound totally different from either of its constituents ; it is called sulphuretted hydrogen gas, and is contained in great abundance in sulphureous mineral waters. Caroline. Are not the Harrogate waters of this nature ? Mrs. B. Yes ; they are naturally impregnated with sul- phuretted hydrogen gas, and there are many other springs of the same kind, which shows that this gas must often be form- ed in the bowels of the earth by spontaneous processes of na- ture. Caroline. And could not such waters be made artificially by impregnating common water with this gas ? Mrs. B. Yes ; they can be so well imitated, as perfectly to resemble the Harrogate waters. Sulphur combines likewise with phosphorus, and with the alkalies, and alkaline earths, substances with which you are yet unacquainted. We cannot, therefore, enter into these combinations at present. In our next lesson we shall treat ef phosphorus. Emily. May we not begin that subject to-day ; this lesson has been so short ? Dfy-s. 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 les- son to-day, especially as we are to enter on a new subject; for I confess that sulphur has not appeared to me so interest- ing as the other simple bodies. Mrs. B. Perhaps you may find phosphorus more enter- taining. 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 or- der 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 hydrogt*. It was not known by the earlier chemists. It was first discov- ered by Brandt, achemist of Hamburgh, whilst employed in researches after the philosopher's stone ; but the m iiiod of obtaining it remained a secret till it was a second time dis- covered both by Kunckel 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 colour, as you find it here. 130 PHOSPHORUS. Caroline. I do not understand in what the discovery con- sisted : there may be a secret method of making an artificial composition ; but how can you talk of making a substance which naturally exists ? Mrs. 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 always so intimately combined with other substances, that its existence remained unnoticed till Brandt discovered the means of obtain- ing it free from other combinations. It is found in all animal substances, and is now chiefly extracted fiom bones, by a chemical process. It exists also in some plants, that bear a strong analogy to animal matter i#n their chemical composi- tion. Emily. But is it never found in its pure separate state ? M^s. B. Never ; and this is the reason that it remained so long undiscovered. Phosphorus is eminently combustible : it melts and takes fire at the temperature of one' hundred degrees, and absorbs in its combustion nearly once and a half its own weight of"pxy- gen. Caroline. What! will a pound of phosphorus consume a pound and a half of oxygen ? Mrs.' B. So it appears from accurate experiments. I can show you with what violence it combines with oxygen, by burning some of it in that gas. We must manage the experi- ment in the same manner as we did the combustion of sulphur. You see I am obliged to cut this little bit of phosphorus un- der water, otherwise there would be danger of its taking fire by the heat of my fingers. I now put it into the receiver, and k-indle it by means of a hot wire. Emily. What a blaze ! I can hardly look at it. I never saw any thing so brilliant. Does it not hurt your eyes, Car- oline ? Caroline. Yes : but still I cannot help looking at it. A prodigious quantity of oxygen must, indeed, be absorbed, when x > 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 ex- periments with the calorimeter. Emily. And is the result of this combustion, like that of sulphur, an acid ? Mrs. B. Yes : phosphoric acid. And had we duly pro- portioned the phosphorus and the oxygen, they would have PHOSPHORUS, 131 been completely converted into phosphoric acid, weighing together, m th.s new state, exactly the sum of their weights separately. The water would have ascended into the receiv- er, on account, ofthe vacuum formed, and would have filled it entirely. In this case, as in the combustion of sulphur, the acid vapour formed is absorbed and condensed imthe water of the receiver. But when this combustion is performed with- out any water or moisture being present, the acid then ap- pears in the form of concrete whitish flakes, which are, how- ever, extremely ready to melt upon the least admission of moisture. Emily. Does phosphorus, in burning in atmospherical air. produce, like sulphur, a weaker sort ofthe same acid ? Mrs. B. No : for it burns in atmospherical air, nearly at the same temperature as in pure oxygen gas ; and it is in both cases so strongly disposed to combine with the oxygen, that the combustion is perfect, and the product similar ; only in atmospherical air, being less rapidly supplied with oxygen-, the process is performed in a slower manner. Caroline. But is there no method of acidifying phospho- rus in a slighter manner, so as to form phosphorous acid ? Mrs. B. Yes, there is. When simply exposed to the at- mosphere, phosphorus undergoes a kind of slow combustion at any temperature above zeto. Emily. Is not the process in this case rather an oxydation than a combination"? For ifthe oxygen is too slowly absorb- ed for a sensible 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 phosphorous 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 w ithout the application of heat ? Mrs B. So it at first appears. But this circumstance seems t° be owing to the nitrogen gas of the atmosphere. This gas dissolves small particles of phosphorus, which be- ing thus minutely divided and diffused in the atmospherical air, combines with the oxygen, and undergoes this slow com- bustion.,, But the same effect does not take place in oxvgen gas, beoausf it is not capable of dissolving phosphorus ; it is therefore necessary, in this c-v.sh, that heat should be applied to effect that division of particles, which, in the former in- stance, is produced by the nitrogen. % 132 PHOSPHORUS. 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 combustion that the light is emitted ; and phosphorous acid is the result of this combustion. Phosphorus is sometimes used as a test to estimate the pu- rity of atmospherical air. For this purpose, it is burnt in a graduated tube, called an Eudiometer (Plate XI. fig. 2.), and the proportion of oxygen in the air examined is deduced from the quantity of air w hich the phosphorus absorbs ; for the phosphorus will absorb 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 is 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 com- position that phosphoric matches are prepared, which kindle as soon as they are taken out of their case and are exposed to the air. Emily. I have a box of these curious matches ; but I have observed that, in very cold weather, they will not take fire without being previously rubbed. Mrs. B. By rubbing them you raise their temperature -, for, you know, friction is one of the means of extricating heat. Emily. Will phosphorus, like sulphur combine with hy- drogen gas ? Mrs. B. Yes ; and the compound gas which results from this combination has a smell still more fetid than the sulphur- etted hydrogen ; it resembles that of garlic. The phosphoretted hydrogen gas has this remarkable pe- culiarity, that it takes fire spontaneously in the atmosphere, at any temperature. It is thus, probably, that are produced those transient flames, or flashes of light, called by the vul- gar Will-of the-Wisp, or, more properly, Ignes-fatui, which are often seen in church-yards, and places where the putre- factions of animal matter exhale phosphorus and hydrogen gas. Caroline. Country people, who are so much frightened by those appearances, would soon be 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. PHOSPHORUS. l>j 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 termination. Thus the combination of sulphur with lime is called a sulphuret, and that of phosphorus, a phosphu- ret of lime* This latter compound, I was going to say, has the singular property of decomposing water, merely by being thrown into it. It effects this by absorbing the oxygen of water, in consequence of which bubbles of hydrogen gas as- cend, holding in solution a small quantity of phosphorus. Emily. These bubbles then are phosphoretted hydrogen gas? Mrs. 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 pro- perly speaking, the phosphuret of sulphur ? Mrs. B. Yes : but the phenomenon appears more extra- ordinary 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 issue from it. Caroline. Cannot we try the experiment ? Mrs. B. Very easily ; but we must do it in the open air ; for the smell of the phosphoretted hydrogen gas is so ex- tremely fetid, that it would be intolerable in the house. But * Phosphuret of lime is a very curious substance. To make it, take a thin glass tube,6or8 inches long, and less than half an inch*in diameter; if it isclosed at oneend, so much the better, but acork will do. Near the closed end put a piece of phosphorus half an inch long. Then put in by means of a stick or wire, holding the tube horizon- tally-, thirty or forty pieces of newly burned quick-lime, about the size of split peas, letting ihe lowest remain 2 or 3 inches from the phosphorus. Then stop the other end ofthe tube loosely, and place the part containing the quick-lime, in a bed of charcoal, so contri- ving 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 phosphorus, which may be kept cool bv a wet. rag ; when this is done, bring the hot iron or can- dle undor the phosphorus, so as to make it pass through-the quick- lime in the form of vapour. Cork upAhe phos.phuret of lime for use. C. 13 134 PHOSPHORUS. before we leave the room, we may produce, by another pro- cess, some bubbles ofthe same gas, which are much less of- fensive. There is in this little glass retort a solution of potash in water; I add to it a small piece of phosphorus. We must now heat the retort over the lamp, after having engaged its neck under water—you see it begins to boil; in a few min- utes 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 complicated, I fear, to be made perfectly intelligible to you at present. In a few words, the reciprocal action of the potash, phos- phorus, caloric, and water are such, that some ofthe water is decomposed, and the hydrogen gas thereby formed carries off some minute particles of phosphorus, with which it forms phosphuretted hydrogen gas, a compound which spontane- ously takes fire at almost any temperature. 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 va- pour, which are produced by the combustion of hydrogen and phosphorus. QUESTIONS. Where is sulphur obtained ? How does.brimstone differ from the flowers of sulphur ? What is sublimation ? When sulphur is burned, what is the product ? From whence is phosphorus obtained ? What is the result of its combustion ? How are the phosphorus and phosphoric acid formed ? Does phosphoric combine with hydrogen.? What are the singular properties of phosphuret of lime r CQNVERSATjpi IX. ON CARB(|f. Caroline. To-day, Mrs. B., I believe we are to learn the. nature and properties of carbon. This substance is quite new to me ; I never heard it mention^ before. Jlfrs. B. Not so new as you imagine ; for carbon is no: CARBON. 13* thing more than charcoal in a state of 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 chem- ical processes by which a simple body is obtained in a state of purity, consist in unmaking the compound in which it is contained, in order to separate from it the simple substance in question. The method by which charcoal is usually ob- tained, is, indeed, commonly called making it ; but, upon ex- amination, you will find this process to consist simply in sep- arating it from other substances with which it is found com- bined in nature. Carbon forms a considerable part ofthe solid matter of all organized 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 re- mains, is charcoal. Caroline. But if heat be applied to the wood in order to evaporate the oil and water, will not the temperature of the charcoal be raised so as to make it burn ? and if it combines with oxygen, can we any longer call it pure ? M?s. B. I was going to add, that, in this operation, the air must be excluded. Caroline. How then can the vapour ofthe 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 ofthe retort, the evaporable part ofthe wood will escape through its neck, into which no air can penetrate, as long as the heated vapour continues to fill it. And if it be wished to collect these volatile products ofthe wood, this can easily be done by introducing the neck ofthe 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 pro- cess. Emily. I have seen the process of making charcoal. The wood is ranged on the ground in a pile of a pyramidical form, with a fire underneath ; the whole is then covered with clay, a few holes only being left for the circulation of air. Mrs. B, These holes are closed as soon as the wood ia 136 carbox. fairly lighted, so that the combustion is checked, or at least continues but in a very imperfect manner ; but the heat pro- duced by it is sufficient to force out and volatilize, through the earthy cover, most part ofthe oily and watery principles ofthe 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 contains about five per cent, of hydro- gen ; 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 I dare say will surprise you.—This ring, which I wear on my finger, owes its brilliancy 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 car- bon in a crystallized state. Emily. That is astonishing ! Is it possible to see two things apparently 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 chiefly 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 dia- mond and cotton are composed, why should they not be manufactured, or imitated, by some chemical process, which would render them much cheaper, 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 knowjn of what these bodies consist, since every thing which we are acquainted with in nature is formed from the various simple substances that we have enumerated. But you must not suppose that a know- ledge of the component parts of a body will in every case enable us to imitate it. It is much less difficult to deco'm- , pose bodies, and discover of what materals they are made, than it is to recompose them. The first of these processes is called analysis, the last synthesis. When we are able to as- certain the nature of a substance by both these methods, so that the result of one confirms that of the other3 we obtaia CARBON. 137 the most complete knowledge of it that we- are capable of acquiring. This is the case with water, with the atmosphere, with most ofthe oxyds, acids, and neutral salts, and with 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 imitated by the aid of chemistry ; but it did not appear to me absurd to suppose that chemists might attain a perfect imi- tation of inanimate nature. Mrs. B. They have succeeded in this point in a variety of instances ; but, as you justly observe, the principle of life, or even the minute and intimate organization of the vegetable kingdom, are secrets that have almost entirely eluded the researches of philosophers ; 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, unor- ganized substaace, might be, one would think, perfectly ins- table by art. Mrs. B. It is sometimes as much beyond our power to obtain a simple body in a state of perfect purity, as it is to imitate a complicated combination ; for the operations by which nature separates bodies are frequently as inimitable as those which she uses for their combination. This is the case with carbon ; all the efforts of chemists to separate it entirely from other substances have 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 diamond. Here is some charcoal in the purest state we can procure it : you see that it is a very black, brit- tle, 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 invariably re-- mains at the bottom ofthe vessel, after all the other parts of the vegetable are evaporated. Emily' Yet carbon is, no doubt, combustible, since you 138 CARBON. say that charcoal would absorb oxygen, if air were admitted during its preparation. \ Caroline. Unquestionably. Besides, you know, Emily, how much it is used in cooking. But pray what is the rea- son that 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 I 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 retains some remains of the various oth- er component parts of vegetables, and hydrogen particularly, which accounts for the flame in question. Caroline. But what becomes of the carbon itself during its combustion ? Mrs. B. It gradually combines with the oxygen ofthe at- mosphere, 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 condensable vapour, but a per- manent elastic fluid, which always remains in the state of gas, under any pressure and at'-any temperature. The nature of this acid was first ascertained by Dr. Black, of Edinburgh; and, before the introduction ofthe new nomenclature, it was QnUedJixed air. It is now distinguished by the more appro- priate 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, car- bon 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 ide;. of the basis of the ox- ygen, hydrogen, and nitrogen gases, the existence of which, as real bodies, you seemed to doubt, because 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 carbon. 139 not appear to be essential to carbon, and it is pure carbon, and not charcoal, that we must consider as the basis of car- bonic acid. We shall make some carbonic acid, and, in or- der to hasten the process, we shall burn the carbon in ox- ygen gas. Emily. But do you mean, then, to burn diamond ? Mrs. B. Charcoal will answer the purpose still bet'er, being softer and more easy to inflame ; besides, the experi- ments on diamond are rather expensive. Caroline. But is it possible to burn diamond ? Mrs.' B. Yes, it is ; and in order to effect this combuston, nothing 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. It has longsbeen known as a combus- tible substance, but it is within these few years only that the product of its combustion has been proved to be pure carbo- nic acid. This remarkable discovery is due to Mr. Ten- nant. Now let us try to make some carbonic acid. Will you, Emily, decant some oxygen gas from this large jar into the receiver in which we are to burn the carbon ; and I shall in- troduce this small piece of charcoal, with a little lighted tin- der, which will e necessary to give the first impulse to the combustion. -* Emily. I car "onceive how so small a piece of tinder, and that but jus 1, can raise the temperature of the carbon sufficiently to sw fire to it; for it can produce scarce- ly 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 ij not more brilliant; it does not give out near so much light or caloric as phosphorus, or sulphur. Yet since it combines with so much oxygen, why is not a proportional quantity of light and heat disengaged from the decomposition ofthe ox- ygen gas, and the union of its electricity with that ofthe char- coal ? Mrs. B. It is not surprising that less light and heat should be liberated in tiiis than in almost any other combustion, since the oxygen, instead of entering into a solid or liquid combination, as it does in the phosphoric and sulphuric acids, is employed in formiug another elastic fluid ; it therefore parts with less of its caloric. MO CARBON. 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 ofthe degree of solidity in which oxygen is combined in a burnt body, by the quantity of caloric liberated during its combustion ? , Mrs. B. Yes ; provided that you take into the account the quantity of oxygen absorbed by the combustible body, and observe the proportions which the caloric bears to it. Caroline. But why should the water, after the combus- tion of carbon, rise in the receiver, since the gas within it re- tains an aeriform state ? Mrs. B. Because the carbonic acid gas is gradually ab- sorbed by the water ; and this effect would be promoted by shaking, the receiver. Emily. The charcoal is now extinguished, though it is not nearly consumed ; it has such an extraordinary avidity for oxygen, I suppose, that the jeceiver did not contain enough to satisfy the whole. Mrs. B. Tint is certainly the case: for if the combus- tion were performed in *,he exact proportions of 28 parts of carbon to 72 of oxygen, both these ingredients would disap- pear, and 100 parts of carbonic acid wTould be produced. Caroline. Carbonic acid must be a very strong acid, since it contains so great a proportion of oxygen ? Mrs. B. That is a very natural inference; yet it.is er- roneous. 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 bodies into strong acids, will only be sufficient simply to oxydate others. Caroline. Since this acid is so weak, I think chemists should hive 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 converted into a gas, by uniting with a smaller proportion of oxygen ; but as this gas does not possess any ,'cid proper- tie3 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 brriatne, as it contain* so much oxygen ? Mrs. B. On the contrary, it is extremely pernicious. Ox CARBON. 141 ygen, when in a state of comi.iuation with other substances, loses, m ;ti:n>).st every instance, its resp.cable properties, and the salubrious effects which it has on the animal economy when in its uuconfiued state. Carbonic acid is not only unfit for respiration, but extremely 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 consid- er that a charcoal fire produced carbonic acid gas.—Can this gas be condensed into a liquid ? Mrs. B. No : 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 impiegnated with it, in a very strong degree, by the assistance of agitation and pressure, as I am going to show you. I shall detant some carbonic acid gas in- to this bottle, which I fill first with water, in order to ex- clude 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 allow- ed to stand over it for some time. The bottle is now about h.ilffull of carbonic acid gas, and the other half is still occu- pied by the water. By corking the bottle, and then violent- ly shaking it, in fhie way, I can mix the gas and water togeth- er.—Now will you taste it ? , Emily. It has if distinct acid taste. Caroline. Yes, it is sensibly sour, and appears full of lit- tle bubbles. Mrs. B. It possesses likewise all the other properti s of acids, but 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 that which is produced by nature, it was found to contain 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 advan- tage, since they may be prepared stronger or weaker, as oc- casion requires. Caroline. It thought I had tasted 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 H2 CARBON. 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 condensed, 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 im- pregnated with carbonic acid. It requires a particular ap- paratus 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 Selt- zer water a very small quantity of soda, and of a few other saline or earthy ingredients, which will remain in the water, though it should be kept uncorked for any length of time. Caroline. I 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 solution, besides the gaseous acid, a particular saline sub- stance, called soda, which imparts to the water certain me- dicinal qualities. Caroline. But how can these waters be so wholesome, since carbonic acid is so pernicious ? Mrs. B. A gas, we may conceive, though very prejudi- cial to breathe, may be beneficial to the stomach.—But it would The 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 forgot 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 alto-. gether obtained by artificial means. They have been lately used medicinally, particularly on the continent, where, lun- derstand, they have acquired some reputation. Emily. If I recollect right, Mrs. B., you told us that car- bon was capable of decomposing water ; the affinity between oxygen and carbon must, therefore, be greater than between oxygen and hydrogen ? Mrs. B. Yes ; but this is not the case, unless their tem- perature be raised to a certain degree. It is only when car- bon 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 extin- guish the combustion ; for the coals of wood, (both of which CARBON. 143 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 diminnti.m of heat thus produced is such, that the combustible matter loses the power of decomposing the wa- ter, 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 oif the water by the carbon during the conflagration. Mrs. B. Certainly.—The apparatus which you see here (Plate XI. fig. 3.), 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 hy- drogen gas, which results from this decomposition, is collect- ed in the receiver. But the hydrogen thus obtained is far from being pure ; it retains in solution a minute portion of carbon, and co >tains also a quantity of carbonic acid. This renders it heavier than pure hydrogen gas, and gives it some peculiar properties : it is distinguished by the name of car- bonated hydrogen gas. Oaroline. 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 ofthe oxygen (proceeding from the decom- posed water) with the carbon, which, you-know, makes car- bonic acid. Caroline. True : I should have recollected that.—The product ofthe decomposition of water by red-hot charcoal, therefore, is carbonated hydrogen gas, and carbonic acid gas. Mrs. B. You are perfectly right, now. Carbon is frequently found combined with hydrogen in a ?tnte of solidity, especially in coals, which owe their combus- tible 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 mentioned when speaking of the gas-lights, the hydrogen gas produced by the burningof coals is not pure : for, during the 144 CARBON. combustion, particles of carbon are successively volatilized with the hydrogen, with which they form whal^ i3 called a hydro-carbonat, which is the principal product of this com- bustion. Carbon is a very bad conductor of heat ; for this reason, it is employed (in conjunction with other ingredients) for coating furnaces and other chemical apparatus. Emily. Pray what is the use of coating furnaces ? Mrs. B. In most cases in which a furnace is used, it is ne- cessary 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 fur- nace with a kind of plaster, composed of materials that are bad conductors of heat. Carbon, combined with a small quantity of iron, forms a compound called plumbago, or black-lead, of which pencils are made. This substance, agreeably to the nomenclature, is « carburet of iron. Emily. Why, then, is it called black-lead ? Mrs. B. It is an ancient name given to it by ignorant peo- ple, from its shining metallic appearance ; but it is certainly a most improper name for it, as there is not a particle of lead in the composition. There is only one mine of this mineral, which, is in Cumberland * It is supposed to approach as 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 extremely small pro- portion of carbon, acquires very remarkable properties: this is steel. Caroline. Really ; and yet steel is much harder than iron ? Mrs. B. But carbon is not ductile like iron, and therefore m'ay 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 de- pends upon some chemical cause, I cannot pretend to decide. But there is a subsequent operation, 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 ;-' She means in England. Black lead is found in a great variety of places in this country. *"'. / CARBON. Ur> the composition of a vast number of natural productions ; such, for instance, as all the various kinds of oils, which re- sult from the combination of carbon, hydrogen, and caloric, in various proportions. Emily. I thought that carbon, hydrogen, and caloric3 formed carbonated hydrogen gas. Mrs. B. That is the case when a small portion of carbonic acid gas is held jn solution by hydrogen gas. Different pro- portions of the same principles, together with the circum- stances of their union, produce very different combinations ; of this you will see innumerable examples. Besides, we are not now talking of gases, but of carbon and hydrogen, com- bined only with a quantity of caloric, sufficient to bring thera 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 state 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 Hot turn to fat when cold ? Mrs. B. Not at the common temperature of the atmos- phere, because they retain too much caloric to congeal at that temperature ; but if exposed to a sufficient degree of cold, their latent heat is extricated, and they become solid fat sub stances. Have you never seen salad-oil frozen in winter ? Emily. Yes ; but it appears to me in that state very dif- ferent from animal fat. Mrs. B. The essential constituent parts of either vegeta- ble or animal oils are the same, carbon and hydrogen; their variety arises from the different proportions of these sub- stances, 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 mat- ter, the other with the delicate perfume of a flower. The difference of fixed oils, and volatile or essential oilst consists also in the various proportions of carbon and hydro- gen. Fixed oils 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 essen- tial oils. The essential oils (which comprehend the whole class of essences and perfumes) are lighter ; they contain more equal proportions of carbon and hydrogen, and are vo- latilized or evaporated without being decomposed. Emily. When you say that one kind of oil will evaporate, 14 146 - CARBON. and the other be decomposed, you mean, I suppose, by the application of heat? Mrs. B. Not necessarily ; for there are oils that will eva- porate slowly at the common temperature ofthe atmosphere ; but for a more rapid volatilization, or for their decomposi- tion, the assistance of heat is rectuired.* Caroline. I shall now remember, I think, that fat and oil are really the same substances, both consisting of carbon and hydrogen ; that in fixed oils the carbon preponderates, and heat produces a decomposition ; while, in essential oils, the proportion of hydrogen is greater, and heat produces a vola- tilization only. Emily. I suppose the reason why oil burns so well in lamps, is because its two constituents are so combustible ? Mrs. B. Certainly ; the combiistion of oil is just the same as that of a candle ; if tallow, it is only oil in a concrete state ; if wax, or spermaceti, its chief chemical ingredients are still hydrogen and carbon. Emily. I wonder, then, there should be so great a differ- ence between tallow and wax ? Mrs. B. I must again repeat, that the same substances, in different 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 applicable to the present case ; for tallow and wax are far from being very dissimilar ; the chief differ- ence consists in the wax being a purer compound of carbon and hydrogen than the tallow, which retains more of the gross particles of animal matter. The combustion of a 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 com- bustion goes on ; and the constituent parts of the oil being thus separated, the carbon unites with a portion of oxygen from the atmosphere to form carbonic acid gas, whilst the hydrogen combines with another portion of oxygen, and forms with it water.— The products, therefore, of the combustion ef oils, are water and carbonic acid gas. * 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 of cas- tor, kc. do not evaporate. Hence a good test ofthe purity of es- sential oil, is, to let a drop fall on paper. If a grease-spot remains after a few minutes, it is adulterated with some fixed oik C. CARBON. - 147 Caroline. But we see neither water nor carbonic acid pro- duced 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. Em- ily is perfectly correct iu her explanation, and I am very much pleased with it. All the vegetable acids consist of various proportions 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 oxyds. Caroline. I am extremely delighted with all these new ideas ; but, at the same time, I cannot help being apprehen- sive that I may forget many of them. Mrs. B~. I would advi*e 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, 1 shall lend you the heads or index, which I occasionally consult for the sake- of preserving some method and arrangement in these conversations. Unless you follow some such plan, you cannot expect to retain nearly all that you learn, how great soever be the impression it may make on you at first. Emily. I will certainly follow your advice.—Hitherto 1 have found that I recollected, pretty well, -what you have taught us ; but the history of carbon is a more extensive sub- ject than any ofthe simple bodies we have yet examined. Mrs. B. I have little more to say on carbon at present ; but hereafter you will see that it performs a considerable part in most chemical operations. Caroline. That is, 1 suppose, owing to its entering into (lie composition of so great a variety of substances ? Mrs. B. Certainly ; it is the basis, as you have seen, of all vegetable matter ; and you will find that it is very essen- tial to the process of animalization. But in the mineral king- dom, also, particularly 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 sub- stance from many oxjigenated or burnt bodies, and thus de- oxygenate, or unburn tnem, and restore them to their original combustible state. Caroline. 1 do not understand how a body can be unburnt, and restored to its original state. This piece of tinder, for instance, that has been burnt, if by any means the oxygen 14S METALS. ivere 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 sub- stances, as you observed in a former conversation. Mrs. B. A compound body is decomposed by combustion in a way which generally precludes the possibility of restor- ing it to its former state ; the oxygen, for instance, does not become fixed in the tinder, but it combines with its volatile parts, andilies off in the shape of gas, or watery vapour. You see, therefore, how vain it would be to attempt the re- composition of such bodies. But, with regard to simple bo- dies, or at least bodies whose component parts are not dis- turbed by the process of oxygenation or deoxygenation, it is often possible to restore them, after combustion, to their ori- ginal state.—The metals, for instance, undergo no other al- teration by combustion than a combination with oxygeD ; therefore, when the oxygen is taken from them, they return to their pure metallic state. But 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 simple bodies that come next under consideration. QUESTIONS. What is carbon ? Under what form does crystallized charcoal appear r Why does charcoal burn without a blaze ? What becomes of carbon during its combustion ? Is it possible to burn a diamond ? What is the product of its combustion ? Does carbon unite with more than one proportion of oxygen ? Is it safe to breathe carbonic acid ? Why does a small quantity of water increase the flame of a fire: What is the composition ot black lead ? How may the adulteration of volatile oil be detected? What are the products of a burning candle or lamp ? , How does carbon restore oxydated substances to their combustible state ? v v CONVERSATION X. ON METALS. • Mrs. B. The metals, which we are now to examine, are bodies of a very different nature from those which we have hitherto considered. They do not, like the bases of gases, elude the observation of our senses ; for, they, are the most METALS. 149 brilliant, the most ponderous, and the most palpable substan-- ces in nature. Caroline. I doubt, however, whether the metals will ap- pear to us so interesting, and give us so much entertainment, as those mysterious 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, ofthe interesting discoveries which were a few years ago made by Sir H. Da- vy respecting this class of bodies. By the aid ofthe 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 acquainted. But the acquaintance, you will soon perceive, is but very superficial; and I trust that 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 sel- dom found naturally in their metallic form : they are gene- rally more or less oxygenated, or combined with sulphur, earths, or acids, and are often blended Vith 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 ofthe 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 quantity of metal, combined with various earthy substances, with which they form minerals of different nature and appearance, which are called ores. Caroline. I 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 ofthe roasting and smelting of lead ; but, I confess, that I do not understand in what these operations Consist. Mrs. B. .xoasting is the process by which the volatile parts ofthe ore are evaporated : smelting, that by which the pure metal is afterwards separated from the earthy remains ef the ore. This is done by throwing the whole into a fur- nace, and mixing with it certain substances that will combine with the earthy parts and other foreign ingredients ofthe 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 14* 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, pre- vents the air from having any further influence on the mass ; so that neither combustion nor oxygenation can take place. Caroline. Are all the metals equally combustible ? Mrs. B. No ; their attraction for oxygen varies extremely. There are some that will combine with it only at a very high temperature, or by the assistance, of acids ; whilst there are others that oxydate spontaneously, and with great rapidity, even at the lowest temperature ; such is, in particular, man- ganese, which scarcely ever exists in the metallic state, as it immediately absorbs oxygen on being exposed to the air, and crumbles to an oxj'd in the course of a few hours. Emily. Is not that the oxyd from which you extracted the oxygen 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 tem- perature ofthe atmosphere ? Mrs. B. They all do, more or less, excepting gold, sil- ver, and platina." Copper, lead, and iron, oxydate slowly in tLe air, and cover themselves with a sort of rust, a process which depends on the gradual conversion of the surface into an oxyd. This rusty surface preserves the interior metal from oxydation, as it prevents the air from coming in contact/with it. Strictly 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 por- tion of carbonic acid. Emily. When metals oxydate from the atmosphere with- out an elevation of temperature, some light and heat, I sup- pose, 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 consider how extremely slow, and, indeed, how im- perfectly, most metals oxydate by mere exposure to the at- mosphere. For the quantity of oxygen with which metals are capable of combining, generally depends upon their tem- perature ; and the absorption stops at various points of oxy- dation, according to the degree to which their temperature is raised. UETALS. lil 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 oxygen. Mrs. B. Certainly. When the metal oxygenates with sufficient rapidity for light and heat to become sensible, com- bustion actually takes place. But this happens only at very high temperatures, and the product is nevertheless an oxyd ; for though, as 1 have just said, metals will combine with dif- ferent proportions of oxygen, yet with the exception of only ■five of them, they are not susceptible of acidification. Metals change colour during the different degrees of oxy- dation which they undergo. Lead, when lieated in contact with the atmosphere, first becomes grey ; if its temperature be then raised, it turns yellow, and a still stronger heat chan- ges it to red. Andit is even capable of astronger degree of oxydation, in which the oxyd is puce coloured. Iron become! successively a green, brown, and white oxyd. Copper chan- ges 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 uni- ted 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 remarka- ble circumstance, that if you burn metals rapidly, the light or flame they emit during combustion partakes ofthe colours which the oxyd successively assumes. Caroline. How is that accounted for, Mrs. B., since light does not proceed from the burning body, but from the de- composition of the oxygen gas ? Mrs. B. The correspondence of the colour of the light with that of the oxyd which emits it, is, in all probability, owing to some particles of the metal which are volatilized and carried off by the caloric. Caroline.. It is then a sort of metallic gas. Emily. Why is it reckoned so unwholesome to breathe the air of a place in which metals are melting ? Mrs. B. Perhaps the notion is too generally entertained. But it is true with respect to lead, and some other noxious metals, because, unless care be taken, the particles of the oxyd which are volatilized by the heat are inhaled with the breath, and may produce dangerous effects. I must show you some instances ©f the combustion of met- 1 5~ miCXMJCIt als ; it would require the heat of a furnace to make them barn in the common air, but if we supply 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, par- ticularly if the experiment be tried upon a small scaled—I begin by lighting this piece of charcoal with the candle, and then increase the rapidity of its combustion by blowing upon it with a blow-pipe. (Plate XII. fig. 1.) Emily. That I do not understand ; for it is not every kind of air, but merely oxygen gas, that produces combustion.—- Now you said that in breathing we inspired, but did not ex- pire oxygen gas. Why, therefore, should the air which you breathe through the blow-pipe promote the combustion of the charcoal ? Mrs. B. Because the air, which has but once passed through the lungs", isyet but little altered, a small portion only of its oxygen being destroyed ; so that a great deal more is gained by increasing the rapidity ofthe current, by means ofthe blow-pipe, than is lost in consequence of the air pass- ing 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 some iron filings on it, and supply them with a current of oxygen gas, by means - of this apparatus, (Plate XII. fig. 2.) which consists simply of a closed tin cylindrical vessel, full of oxygen gas, with tw» 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 issuing 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. B. The process is, in fact, the same; there is only some difference in the mode of conducting it. Let us burn some tin in the same manner—you se,e that it is equally comr bustible.—Let us now try some copper— Caroline. This burns with a greenish flame ; it is, I sup- pose, owing to the colour 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. Uold, silver, and plaUna} are incapable of being oxydated by PLATB^m. ^pjoaratus tor the combustion or" nit tals by mrtvis of oJcyyot you recollect, the zinc plates of the Voltaic battery are oxydated by the acid and water, much more effectually than by water alone. Caroline. And I have often observed that if I drop vine- gar, lemon, 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 oxy- gen ; from the atmosphere, from water, and from acids. Mrs. B. The two first you have already witnessed, and I shall now show you how metals take the oxygen from an acid. This bottle contains nitric acid ; I shall pour some of it over this piece of copperleaf....... 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 the greatest part of its oxygen, is converted into a weaker acidr 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 answer that question yourself. * Lead is capable of decomposing water, and when suffered to stand long in a vessel of this metal, it becomes poisonous. When used merely to convey water, there is but little danger. G. METALS. 151 Caroline. Perhaps it is that the oxvgen enters into the metal in a more solid state than it existed in the acid, in conse- quence of winch caloric is disenga^iid. Mrs. B. If the combination ofthe oxygen and the metal results from the union of their opposite electricities, of course caloric mu-t be given out. Emily. The effervescence is over ; therefore I suppose that the metal is now oxydated. Mrs. B. Yes. But there is another important connection between metals and acids, with which I must now make you acquainted. Metals, when in the state of oxyds, are capable of being dissolved by acids, in this operation they enter into a chemical combination with the acid, and form an entirely new compound. Caroline. But what difference is there between the oxy- dation and the dissolution ofthe metal by ah acid ? Mrs. B. In the first case, the metal merely combines with a portion of oxygeu taken from the a^id, which is thus partly deoxygenated, as in the instance you have just seen ; in the second case, the metal, after being previously oxydated, is actually dissolved in the acid, and enters into a chemical com- bination with it, without producing any further decomposition or effervescence.—This complete combination of an oxyd and an aeid 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 remem- ber that the metals are incapable of entering into this combi- nation with acjds, unless they are previously oxydated ; therefore, whenever you bring a metal in contact with an acid, if will be first oxydxted and afterwards dissolved, provi- ded that there be a sufficient quantity of acid for both opera- tions. 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 ofthe water oxydates 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 cunts of oxyd are suc- cessively formed, and rapidly dissolved by the acid, which continues combining with the new-formed surfaces of oxyd till the. whole ofthe metal is dissolved. During this process the hydrogen gas ofthe water is disengaged, and flies off with ef- fervescence. 15 158 METALS. Emily. Was not this the manner in which the sulphuric • acid a>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 r off the covering of oxyd, as it is formed, prepares a fresh sur- face of metal to act upon the water. « Caroline. The acid here seems to act a part not very dif- ferent from that of a scrubbing-brush.—But pray would not this be a good method of cleaning metallic utensils ? Mrs. B. Yes ; on some occasions a weak acid, as vinegar, is used for cleaningcopper. 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 af- terwards wiped off, otherwise it would produce fresh oxyd. Caroline. Let us watch the dissolution of the copper in the nitric acia ; for I am very impatient to see the salt that is to result from it. The mixture is now of a beautiful blue co- lour ; but there is no appearance of the formation of a salt; it seems to be a tedious operation. Mrs. B. The crystallization of the salt requires some length of time to be completed ; if, however, you are so im- patient, 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 i few days since. by the oxydation of iron filings through the assistance of sul- phuric 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 hydrogen escaped alone. Mrs. B. Very well ; the result, therefore, was a com- pound salt, formed by the combination of sulphuric acid with oxyd of iron. It still remains in the vessel in which the ex- periment 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 decomposi- tion ofthe water; 2dly, the oxydation of the metal; and 3dly, the formation of a compound salt. Caroline. Here it is, Mrs. B.—What beautiful green crys- tals ! But we do not perceive any crystals in the solution of copper in nitrous acid ? Mrs. B. Because the salt is now suspended in the water METALS. 159 which the nitrous acid contains, and will remain so till it is de- posited, in consequence of rest and cooling. Emily. I am surprised that a body so opaque as iron can be converted into such tianspareut crystals- Mrs. B. It is the union with the acid that produces the transparency ; for if the pure metal were melted, and after- wards permitted to cool and crystalize, it would be found just as opaque as before. Emily. I do not understand the exact meaning of crystalli- zation. Mrs. B. You recollect that when a solid body is dissolv- ed, 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 ofthe bo- dy will, on the water being evaporated, again unite into d so- lid mass, by the force of their mutual attraction. But when the body is dissolved by caloric alone,'nothing more is neces- sary, in order to make1 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 dur- ing 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 ofthe 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 forget to observe, that heat and water may unite their solvent powers : and, in this case, crystallization may be has- tened by cooling, as well as by evaporating the liquid. Caroline. But if the body dissolved is of a volatile nature, will it not evaporate w ith the fluid ? Mrs. B. A crystallized body held in solution only by wa- ter 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 crystalliz- ing from their watery solution, always retain a small portion of water, which remains confined in the crystal, in a solid form, and does not reappear unless the body loses its crystalline state.' This is called the water of crystallization. But you * 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. 160 METAL. must observe, that whilst a body may be separated from its solution in water or caloric simply by cooling or by evapora- tion, an acid can be taken from a metal with which it is com- bined only by stronger affinities, which produce a decompo- sition. Emily. Are the perfect metals susceptible of being dis- solved and converted into compound salts by acids ? Mrs. B. Gold is acted upon by only one acid, the oxygen- ated muriatic, a very remarkable acid, which, when in ite most concentrated 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 solv- ent 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. I 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 convert- ed into acids. Caroline. Acids are connected with metals in such a varie- ty of ways, that I am afraid of some confusion in remember- ing 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 compound salts : and lastly, several ofthe , metals are themselves susceptible 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 combine. They are most of them, in their simple State, capable of uniting 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 py- rites, from which certain kinds of mineral waters, as those of Harrogate, derive their chief chemical properties. In this combination, the sulphur, together with the iron, have so strong an attraction for oxygen, that they obtain it both from the air and from water, and by condensing it in a solid form, produce the heat which raises the temperature ofthe water in such a remarkable degree. Emily. But if pyrites obtain oxygen from water, that wa- ter must slider a decomposition, and hydrogen gas be evolved. METALS. 161 Mrs. B. That is actually the case in the hot springs al- luded to, which give out an extremely fetid ga9, composed of hydrogen, impregnated with sulphur. Caroline. If I recollect right, steel and plumbago, which you mentioned in the last lesson, are both carburets of iron. Mrs. B. Yes ; and they are the only carburets of much eonsequence. A curious combination of metals has lately very much at- tracted the attention ofthe scientific world : 1 mean the me- teoric stones which fall from the atmosphere. They consist principally of native or pure iron, which is never found in that state in the bowels ofthe earth;* and contain also a small quantity of nickel and chrome, a combination likewise new in the mineral kingdom. These circumstances have led many ecientific 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. I have heard much of these stones, but I be- lieve many people are of opinion that they are formed on the surface of the earth, and laugh at their pretended celestial origin. - Mrs B. The fact of their falling is so well ascertained, that I think no person who has at all investigated the subject, can now ent rtain any doubt of it. Specimens of these stones have been discovered in all parts ofthe world, and to each of them some tradition or story of its fall has been found con- nected. And as the analysis of all those specimens affords precisely the same results, there is strong reason to conjecture that they all proceed from the same source. It is to Mr. Howard that philosophers are indebted for having first ana- lysed these stones, and directed their attention to this inter- esting subject. * 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 earth One found by Prof. Pallas in Siberia weighed lbOO lbs. Another found in South America is said to weigh 30,000 lbs. &c. These have been suspected to be of meteoric origin, though nothing is known, which makes this certain. Those stones which are known bevond a doubt to have fallen from the atmosphere, have a very dif- ferent composition. These genernlly contain the following ingredi- ents, 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, Sic. in every age since the Christian era, and in almost every part of the world. C. 15* 162 ' , METAL?, Caroline. But pray, Mrs. B., how can solid masses of iron and nickel be formed fron the atmosphere, which consists of the two airs, nitrogen and oxygen ? Mrs. B. I 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 al- loys ; 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 composed 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 ignorant workmen, it is iron plated with tin, which renders it more durable, 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 should 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 suspect- ed 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 fusible 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 ofthe same ■ature ? Mrs. B. In the operation of plating, two metals are united, ©ne being covered with the other, but without the interven- tion of a third : iron or copper may thus be covered with gold or silver. Emily. 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 state at the temperature ofthe atmosphere. AH me- HETALS. 163 tals are fusible at different degrees of heat, and they have likewise each the property of freezing or becoming solid at a certain fixed temperature. Mercury congeals only at seventy- two degrees below the freezing point. Emily. That is to say, that in order to freeze, it requires a temperature of seventy-two degrees colder than taat at which water freezes. Mrs. B. Exactly so. Caroline. But is the temperature ofthe atmosphere ever so low as that ? Mrs. B. Yes, often in Siberia ; but happily never in this part ofthe globe. Here, however, mercury may be congeal- ed by artificial cold ; I mean such intense cold as can be pro- duced by some chemical mixtures, or by the rapid evapora- tion of ether under the air pump.* Caroline. And can mercury be made to boil and evapo- rate ? Mrs. B. Yes, like any. other liquid ; only it requires a much greater 'degree of heat. At the temperature of six hundred degrees, 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 the^m 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 sub- stance 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 discovered by the Rev. Mr. Gregor, in the tin- mines of Cornwall ; columbium or tantalium, which has lately been discovered by Mr. Hatchett ; and osmium, iridium, pal- ladium, and rhodium, all of which Dr. W7ollaston and Mr. Tennant 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 Swe- den, 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 pro- perties this substance seems to hold a medium between 'the * By a process analogous to that described, page 75, of this work. IM METALS. combustibles and the metals. It bears in particular a strong analogy to sulphur. Caroline. Arsenic has been mentioned amongst the metals, I had no notion that it belonged to hat class of bodies, for 1 ^had never seen it but as a powder, and never thought of it but as a most deadly poison. Mrs. B. In its pure metallic state, I believe, it is not so poisonous ; but it has such a^great affinity for oxygen, that it absorbs it from the atmosphere at its natural temperature: you, have seen it, therefore, only in its state of oxyd, when, from its combination with oxygen, it has acquired its very poisonous properties. ' Caroline. Is it possible that oxygen can impart poisonous qualities ? That valuable substance which produces light and fire, and which all bodies in nature are so eager to obtain ? Mrs.B. Most ofthe 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 general, oxygen, in a concrete state, appears to be particularly destructive in its effects on flesh or any animal matter ; and those oxyds are must caustic that have an acrid, burning taste, which proceeds from the metal having but a slight affinity for oxygen, and therefore easily yielding it to the flesh, which it corrodes and destroys. Emily. What is the meaning of the v.ord caustic, which you have just used ? Mrs. B. It expresses that property which some bodies possess, of disorganizing and destioying animal matter, by operating a kind of combustion, or at least a chemical decom- position. You must often have heard of caustic used to burn warts, or other animal excrescences ; most of these bodies ewe their destructive power to the oxygen with which they are combined. The common caustic, called lunar caustic, is a compound formed by the union of nitric acid and silver ; anffit 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 exyds, as they contain a greater proportion of oxygen ? Mrs. B. Some ofthe acids are ; but the caustic property of a body depends not only upon the quantity of oxygen which it contains, but also upon its slight affinity for that prin- ciple, and the consequent facility with which it yields it. Emily. Is not this destructive property of oxygen ac- counted for ? Mrs. B. It proceeds probably frdm the strong attraction •f oxygen for hydrogen ; for if the one rapidly absorb the METALS 165 other from the animal fibre, a disorganization of the sub- stance must ensue. Emily. Caustics are, then, very properly^said to burnthe flesh, since the combination of oxygen and hydrogen is an ac- tual combustion. Caroline. Now, I think, this effect would be more prop- erly termed 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 contained in the atmosphere burn us ? Mrs. B. Because it is in a gaseous state, and has a greater attraction for its electricity than for the hydrogen of our bo- dies. Besides, 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. 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 nature of its oxygen. Mrs. B. Your hand dees notdecompose 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 quit- ting it« state of water to act upOn your hand. You must not forget that oxyds are caustic in proportion as the oxygen ad- heres slightly to them. Emily. Since the oxyd of arsenic is poisonous, its acid, I suppose, isfu'ly as much so ? Mrs B. Yes ; it is one ofthe strongest poisons in nature. Emily. There is a poison called verdigris, which forms on buss 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 oxy- gen ? Mrs. B. It is produced by the intervention of oxygen for verdi;rris is a compound salt formed by the union of vine- gar and copper ; it is a beautiful green colour, and much used in painting. J 66 METAXS. Emily. But, I believe, verdigris is often formed on cop- per when no vinegar has been in contact with it. Mrs. B. Not real verdigris, but other salts, somewhat re- sembling 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 wa- ter on this piece of tin-foil, and then some of the salt.—Now observe that I fold it up suddenly, andpress it into one lump. Caroline. What a prodigious vapour issues from it—and sparks of fire 1 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 ofthe oxygen ofthe salt rapidly entering in- to a closer eombination with the tin. There is also a beautiful green salt too curious to be omit- ted ; it is produced by the combination of cobalt with muriat- ic acid, which has the singular property of forming what is called sympathetic intc. Characters written with this solution are invisible when cold, but when a gentle heat is applied, they assume a fine bluish green colour. Caroline. I think one might draw very curious landscapes with the assistance of this ink ; I would first make a-water- colour drawing of a winter-scene, in which the trees should be leafless, and the grass scarcely green ; I would then trace all the verdure with the invisible ink, and whenever I chose 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, 1 roust introduce to your acquaintance the curious metals which Sir H. Davy has recently discovered. The history of these extraordinary bodies is yet so much in its infancy, that I shall confitie mvself 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 discov- eries, than to enter into a minute account of particular bodies or experiments. Caroline. But I have heard that these discoveries, how- ever splendid and extraordinary, are not very likely to prove ef any great benefit to ihe world, as they are rather objects •f curiosity than of use* Mrs. B. Such may be the illiberal conclusions of the ig- METALS. 167 narant and narrow-minded ; but those who can duly estimate the advantages ot 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 present subject; for some of the new metals have already proved eminently useful as chelnical agenti, 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 alka- lies, the earths, and three ofthe acids, all of which had been hitherto considered as undecompoundable or simple bodies. When Sir H. Davy first turned his attention to the effects ot the Voltaic battery, he tried its power on a variety of com- pound bodies, and gradually brought to light a nu'mber ofnew and interesting facts, which led the way to more important discoveries. It would be highly interesting to trace his steps in thi* new department of science, but it would lead us too far from our principal object. A general view of his most remarkable disoverie» is ill that 1 can aim at, or that you could, at present, understand. The facility with winch compound bodies yielded to the Voltaic electricity, iuduced him to make trial of its effects on substances hitherto considered as simple, but which he sus- pected of being compound, and his researches were soon •rowned with the most complete 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 sobstance gave out an elastic fluid at the positive wire, which was ascertained to be oxygen, and at the negative wire, small globules of a very high metallic lustre, very similar in appearance to mercury ; thus proving that potash, which had hitherto 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 platina, as they were when you decomposed water ; for if of iron, the oxygen would have combined with the wire, in- stead of appearing 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 seea 1US METALS. / it, as iX is the metal which we burnt in contact with sulphur. Emily. What is the liquid in which you keep it ? Mrs B. ltis.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 oxy- gen," that it will not only absorb it from the air, but likewise from water, or any body whatever that contains it. Emily. This, then, is one of the bodies that oxydates spontaneously without the application of heat. Mrs. B. Yes ; and it has this remarkable peculiarity, that it attracts oxygen much more rapidly from water than from air ; so that when thrown into water, however cold, it actual- ly 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-cohverted 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 ofthe simple 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 bet- ter in water than in air ? Caroline. I do not think so : for" if the attraction of potas- sium 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 sup- plied by water than by air. Mrs. B. That cannot, however, be precisely the reason, for when potassium is introduced under water, without con- tact of air, the combustion is not so rapid, and, indeed, in that case, there is no luminous appearance ; but a violent action takes place, much heat is excited* the potash is regenerated, and hydrogen gas is evolved. Pctassi tm is so eminently combustible, that instead of re- quiring, like other metals, an elevation of temperature, itwill burn rapidly 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. Mrs B. This hole contains a solution of potash : for the alkali being extremely soluble, disappears in the water at the i METALS. 169 instant it is produced. Its presence, however, may be easily ascertained, alkalies having the property of changing p_aper, stained with turmeric, to a red colour ; it 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 had always been supposed incapable of sup- porting combustion, as we were unacquainted with any sub- stance that had a greater attraction for oxygen than carbon. Potassium, however, readily decomposes this gas, by absorb- ing its oxygen, as I shall show you. This retort i? filled with carbonic acid gas. 1 will put a small piece of potassium in it; but for this combustion a slight elevation of tempeialure is required, for which purpose 1 shall hold the retort over the lamp. Caroline. Now it has taken fire and burns with violence ! It has burst the retort. Mrs. 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 its surface. Mrs. B. You are right. This metal is perfectly fluid at the temperature 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 being about six, when water is reckoned at ten ; so that this metal is actually light- er than any known fluid, even than ether. Potassium combines with sulphur and phosphorus, forming sulphurets and phosphurets ; it likewise forms alloys with several metals, and amalgamates with mercury. Emily. But can a sufficient quantity of potassium be ob- tained, by means of the Voltaic battery, to admit of all its properties and relations to other bodies being satisfactorily ascertained ? Mrs. B. Not easily ; but I must not neglect to inform you chat 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. Davy had obtained, attempted to separate po- taesium from its combination with oxygen, by common chem- 16 170 METALS. ical means, and without the aid of electricity. They caused red-hot potash in a state of fusion to filter through iron turn- ings in an iron tube, heated to whiteness. Their experiment was crowned with the most complete success ; more potassi- um was obtained by this single operation, than could have been collected in many weeks by the most diligent use of the Voltaic battery. Emily. In this experiment, 1 suppose the oxygen quitted its combination with the potassium to unite with the iron turnings ? Mrs. B. Exactly so ; and thus the potassium was obtained in its simple state. From that time it has become a most convenient and powerful instrument of deoxygenation in chemical experiments. This important improvement, en- grafted on Sir H. Davy's previous discoveries, served but to add to his glory, since the facts which he had established, when possessed of only a few atoms of this curious substance, and the accuracy of his analytical statements were all confirm- ed when an opportunity occurred of repeating his experi- ments upon this substance, which can now be obtained in un- limited quantities. Caroline. What a satisfaction Sir H. Davy must have felt, when by an effort of genius 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 which Sir H. Davy submitted to the influence of the Voltaic battery was Soda, the other fixed alkali, which yielded to the same powers of decomposi- tion ; from this alkali, too, a metallic substance was obtained, very analogous in its properties to that which had been dis- covered in potash ; Sir H. Davy has called it sodium. It is rather heavier than potassium, though considerably lighter than water ; it is not so easily fusible as potassium. -Encouraged by these extraordinary results, Sir H. Davy oext performed a series of beautiful experiments on Ammonia, or the.volatile alkali, which, from analogy, he was led to sus- pect might also contain oxygen. This he soon ascertained to be the fact, but he has not yet succeeded in obtaining the basis of ammonia in a separate state ; it is from analogy, and from the power which the volatile alkali has, in its gaseous form, to oxydate iron, and also from the amalgams which can be obtained from ammonia by various processes, that the proofs of that alkali being also a metallic oxyd are deduced. Thus, then, the three alkalies, two of which had always ■- been considered as simple bodies, have now lost all claim to METALS. 171 that title, and I have accordingly classed the alkalies amongst the compounds, whose properties we shall treat of jn a future conversation. Emily. What are the other newly discovered metals which yOu have alluded to in your list of simple bodies ? Mrs. B. They are the metals ofthe earths 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 ap- pearance, a kind of earthy substance. Mrs. B. They have, besides, several features of resem- blance with metallic oxyds ; Sir H. Davy had, therefore, great reason to be sanguine in his expectations of decompo- sing them, and he was not disappointed. He could not, how- ever, succeed in obtaining the basis of the earths in a pure separate state ; but metallic alloys wore formed with other metals, which sufficiently proved the existence of the metal- lic basis of the earths. The last class of new metallic bodies which Sir II. Davy discovered was obtained from the three nndecompounded acids, the boracic, the fluoric, and the muriatic acids ; but as you are entirely unacquainted with these bodies, I shall re- serve the account of their decomposition till we come to treat of their properties as acids. Thus in the course of two years, by the unparalleled ex- ertions of a single individual, chemical science has assumed a new aspect. Bodies have been brought to light which the human eye never before beheld, and which might have re- mained 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 energetic 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 proved that all the earths, and, in fact, the solid surface of this globe, are metallic bodies mineralized by oxy- gen, and as our planet has been calculated to be considerably 172 MB; ALS. more dense upon the whole than it is on the surface, it us reasonable to suppose that the interior of the earth is com- posed of a metallic mass, the surface of which only has been mineralized by the atmosphere. The eruptions of volcanoes, those stupendous problems of nature, admit now of an easy explanation.* For if the bow- els of the earth are the grand recess of these newly discov- ered inflammable bodies, whenever water penetrates into them, combustions and explosions roust take place ; and it is remarkable that the lava which is thrown out, is the very kind of substance which might be expected Jto result from these combustions. I must new take my leave of you ; we have had a very long conversation to-day, and I hope you will be able to re- collect what you have learnt. At our next interview we shall enter on a new subject. QUESTIONS. How many metals are there.' Name them. Where are the metals found ? Are all the metals combustible ? What are oxides? What use is made of metallic oxides ? How is the most intense heat produced ? Do the metals oxydate on being exposed to the air ? When a metal dissolves in an acid, what causes the heat ? What state must a metal be in before it can be dissolved by an acid What is crystallization ? Do any of the metals combine with so much oxygen as to become acids ? At what degree of cold does mercury become solid ? From whence do. the metallic oxides derive their poisonous qualities ? What peculiarities have the new metals, discovered by Sir H. Davy ? * It is always easy to form a theory. But an explanation of these " stupendous problems of nature," we believe has not yet been de- monstrated to the satisfaction of all, though great learning and im- mense labour 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 consist of supposition piled on supposition; there being as yet no proof that the crust of the earth is formed only of these two ele- ments, c. ON THE ATTRACTION OF COMPOSITION. 173 CONVERSATION XIII. ON THE ATTRACTION OF COMPOSITION Mrs. B. Having completed our examination of the simple or elementary bodies, we are now to proceed to those of a compound nature ; but, before we enter on this extensive subject, it will be necessary to make you acquainted with the principal laws by which chemical combinations are governed. You recollect, I hope, what we formerly said of the na- ture of the attraction of composition, or chemical attraction, or affinity, as it is also called ? Emily. Yes, 1 think, perfectly ; it is the attraction that subsists between bodies of a different nature, which occasions them to combine and form a compound, when they come in contact; and, according to Sir H. Davy's opinion, this effect is produced by the attraction of the opposite electricities, which prevail in bodies of different kinds. Mrs. B. Very well: your definition comprehends the first law of chemical attraction, which is, that it takes place only between bodies of a different nature; as, for instance, be- tween an acid and an alkali ; between oxygen and a met- al, &c. Caroline. That we understand of course ; for the attrac- tion between particles of a similar nature is that of aggrega- tion, or cohesion, which is independent of any chemical power. Mrs. B. The second law of chemical attraction is, that it takes place only between the most minute particles of bodies; therefore, the 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 inferred ; for the finer the particles ofthe two substan- ces are, the more easily and perfectly they will come in con- tact 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 for them to act on each other ; and that, in order to produce the ex- treme division requisite for a chemical action, one, if not both ofthe bodies, should be in a fluid state. There are, howev- er, a few instances in which two solid bodies, very finely puT- 16* , 174 ON THE ATTRACTION verized, 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 ofthe constituents has, I believe, been either liquid or aeriform. In combustions, for instance, the oxygen is taken from the atmosphere, in which it existed in the state of gas ; and whenever we have seen acids combine with metals or with alkalies, they were either in a liquid or an aeriform state. Mrs. B. The third law of chemical attraction is, that it tan take place between two, three, four, or even a greater num- ber of bodies. Caroline. Oxyds and acids are bodies composed of two constituents, but I recollect no instance ofthe combination of a greater number of principles. Mrs. B. The compound salts, formed by the union ofthe metals with acids, are composed of three principles. And there are salts formed by the combination ofthe 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 aame implies a knowledge ofthe composition ofthe salt. The three alkalies, the alkaline earths, and the metals, are called salifiable bases or radicals; and the acids, salifying principles. The name of each salt is composed both of that ofthe acid and the salifiable 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 ad- ded for the specific distinction of the salt; if it be potash, it will compose a sulphat of potash ; if ammonia, sulphat of am- monia,-he. Emily. The crystals which we obtained from the combi- nation of iron and sulphuric acid were therefore sulphat of iron ? Mrs. B. Precisely ; and those which we prepared by dis- solving copper in nitric acid, nitrat of copper, and soon.—But this is not all; ifthesaltbe formed by that class of acids which ends in ous, (which you know indicates a less degree * This is the case with animate of ammonia and Quicklime* (A OF COMPOSITION. 175 af oxygenation,) the termination of the name of the salt will be in it, as sulphit of potash, sulphit 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. 'J heir real number cannot he ascertained, since it increases every day. But we must not proceed further in the investigation of the compound salts, until we have com- pleted the examination of the nature of the ingredients of which they are composed. The fourth law of chemical attraction is, that a change of temperature always takes place at the moment of 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 ofthe bodies for heat, which always takes place when the combination is attended with an increase of density, but more especially when the compound passes from the liquid to the solid form. I shall now show you a striking instance of a change of tempe- rature from chemical union, merely by pouring some nitrous acid on this small quantity of oil of turpentine—the oil will in- stantly combine with the oxygen of the acid, and produce a considerable change of temperature. Caroline. What a blaze ! The temperature ofthe oil and the acid must be greatly raised, indeed, to produce such a violent combustion. Mrs. B. There is, however, a peculiarity in this combus- tion, which is, that the oxygen, instead of being derived from the atmospheric alone, is principally supplied by the acid it- self. Emily. And are not all combustions instances ofthe change of temperature produced by the chemical combination of two bodies ? Mrs. B. Undoubtedly ; when oxygen loses its gaseous form, in order to combine with a solid body, it becomes con- densed, and the caloric evolved produces the elevation of temperature. The ^-pecific gravity of bodies is at the same time altered by chemical combination ; for in consequence of a change of capacity for heat, a change of density must be produced. Caroline. ' That was the ease with the sulphuric acid and water, which, by being mixed together, gave out a great deal of heat, and increased in density. Mrs. B. < The fifth law of chemical attraction is, that the properties which characterise bodies, when separate, are alter- ed or destroyed by their combination. 176 ON THE ATTRACTION Caroline. Certainly ; what, for instance, can be so differ ent from water as the hydrogen and oxygen gases ? Emily. Or what more unlike sulphat of iron, than iron or sulphuric 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 constituents 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 in- stance, 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 attraction 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 comparatively ascertained by experiment, and can be repre- sented by numbers which express, at least by approximation, the relative degrees of attraction. The seventh law is, that bodies have amongst themselves dif- ferent degrees of attraction. Upon this law, (which you may have discovered yourselves long since,) the whole science of chemistry depends ; for it is by means ofthe various degrees of affinity which bodies hive for each other, that all the chem- ical compositions and decompositions are effected. Every chemical fact or experiment is an instance ofthe same kind ; and whenever the decomposition of a body is performed by the addition of any single new substance, it is said to be ef- fected 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 princi- ples, which would not, each separately, perform the decom- position. In this case, there are two new compounds formed inconsequence of a reciprocal decomposition and recomposi- tion. All instances of this kind are called double elective at- tractions. Caroline. I confess I do not understand this clearly. Mrs. B. You will easily comprehend it bv the assistance of this diagram, in which the reciprocal forces of attraction are represented by numbers : OF COMPOSITION. 177 Original Compound. Sulphat of Soda. Result Nitrat of Soda Soda 8 Sulphuric Acid Result 7 Divellent^Attractions 6-13 I S"1Phat ' ofLime Nitric Acid 4 Lime 12 Original Compound. Nitrate ofLime. 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 the sulphuric acid attract each other by a force which is superior, and (by way of supposition) is represented by the nnmber 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. Mrs. B. If, on the other hand, we endeavour to decom- pose this salt by nitric acid, which tends to combine with so- da, 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 elective attraction, there- fore, can we accomplish our purpose. But let us previously combine together 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 com- pound to the sulphat of soda, a decomposition will ensue, be- cause the sum ofthe forces which tend to preserve the two salts in their actual state is not equal to that ofthe forces which tend to decompose them, and to form new combinations. The nitric acid, therefore, will combine with the soda, and the sulphuric acid with the lime.* ' * Suppose we say thus. The sulphuric acid attracts soda with a 178 ON THE ATTRACTION Caroline. I understand you now very well. This double effect takes place because the numbers 8 and 4, which rep- resent the degrees of attraction ofthe constituents of the two original salts, make a sum less than the numbers 7 and 6, which represent the degrees of attraction ofthe two new com- pounds that will in consequence be formed. Mrs. B. Precisely so. Caroline. But what is the meaning of quiescent and divel- lent forces, which are written in the diagram ? Mrs. B. Quiescent forces are those which tend to pre- serve compounds 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 doc- trine of chemical attractions, which have been laid down as rules by modern 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 uniform operation of elective at- traction, and has advanced the opinion, that, in chemical com- binations, the changes which take place, and the proportions in which bodies combine, depend not only u|>on the affinities, but, also, in some degree, on the respective quantities 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 ofthe same materials ? Mrs. B. On the contrary, it is found that a remarkable uniformity prevails, as to proportions, between the ingredi- ents of bodies of similar composition. Thus water, as you may recollect to have seen in a former conversation, is com- posed of two volumes of hydrogen gas to one of oxygen, and this is always found to be precisely the proportion of its con- stituents, from whatever source the water be derived. The same uniformity prevails with regard^ to the various salts ; the acid and alkali, in each kind of salt, being always found to stronger force than it does lime, and soda has a stronger affinity for sulphuric acid than it has for nitric acid. It is plain then, that nei- ther lime nor nitric acid alone will decompose the iulpfhat of soda. Novv if we unite the nitric acid and lime, we form nitmte of lime. But the nitric acid has not so strong an affinit) for the nrne as it has for soda. On mixing the two salts in solution, therefore, tire 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 OF COMPOSITION. 179 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, asthe other.* Emily. If the proportions in which bodies combine are so constant and so well defined, how can Mr. Berthollet's remark be reconciled with this uniform system of combination ? Mrs. B. Great as that philosopher's authority is in chem- istry, it is now generally supposed that his doubts on this sub- ject were, in a great degree, groundless ; and that the excep- tions he has observed in the laws of definite proportions,'7iave been only apparent, and may be accounted for consistently with those laws. Emily. I think I now understand this law of definite pro- portions very well, so far as it regards the gases, such as oxy- gen and hydrogen, in the instance you have just mentioned ; but in the case of acids and alkalies, when the bodies are ei- ther liquid or solid, I do not conceive how their bulks or vol- umes can be measured in order to ascertain the proportion in which they combine ? Mrs. B. Your question is quite in point : the fact is, that the law of combination, by volume, does not prevail in regard to liquids and solids. In these, we must leave the circum- stance of bulk entirely out of consideration. It is to their weight that we must attend, in determining the proportions * The student already understands, that in chemical combina- tions the union takes place only between the particles, or atoms, of substances. These atoms, it is supposed are indivisible, being the ultimate particles of which bodies are composed. In chemical com- binations, then, where substances are capable of uniting in only one proportion, this must be atom to atom. Thus oxygen and hydrogen unite only in the proportions of 100 of the former to 750 of the latter by weight. Here an atom of oxygen unites to an atom of hydrogen to form water ; but the atoms 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- nese, will unite to 14, 28, 42, or 56 of oxygen, but not with anv in- termediate quantity, as with 12, 20, 60, &c. This law of definite proportions, so far as is known, holds good, where the resulting compound differs widely from either of the substances of which it is composed, as in the salts, compound minerals, &c. The theory of definite proportions is explained by supposing that a substance which we shall call A, unites with another substance B, atom to atom, and that this 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 ofB. C ISO ON THE ATTRACTION in which they combine ; and, accordingly, if we take the combining substances in a state of perfect purity, and ascer- tain with great accuracy, once for all, the proportion.-, by weight, in which they Unite, we shall find that in every other instance in which these substances have an opportunity of combining, they will unite in the same proportions, and in no other—unless it be in such proportions that one of the bod) s shall be, in weight, exactly double, triple, or quadruple what it was in the former combination. Caroline. This requires a good deal of attention to be well understood ; and 1 should like to have it illustrated by some particular examples of these different combinations. 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 nitrogen, by combining with one volume of oxygen, forms the substance 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, 1 may mention, as an example, the case of the salt called sulphat of potash, in which a given weight of potash may combine with two different proportions of sulphuric acid ;. but the quantit}' of acid in one case is ex- actly double what it is in the other. Emily. And pray what can be the cause of this singular uniformity in the law of combination ? Mrs. B. Philosophers have not been able to give us any decisive information upon this point ; but they have attemp- ted 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, (and 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 interme- diate combination would be obtained ? Mrs. B. Yes : but the nature of the atom is incompatible with the idea of any farther division ; sinre the chemical atom is the smallest quantity which chemistry can obtain. and such as no mechanical means can possibly subdivide. Caroline. And pray, what k the use of all this doctrine of definite proportions ? Mrs. B. It is very considerable ; for it enables chemists to form tables, by which they can see at one^glance the < im- position of all the bodies which have been accurately analy- • F COMPOSITION 181 zed, and ascertain in an instant what quantity of one body will be necessary to decompose a certain quantity of another ; and, in general, such tables serve to present, in one view, the result of any chemical decomposition, and the quantities of the new compounds formed ; by which means, a consider- able saving of labour is gained, either in enabling us to cal- culate 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 must not run the risk of entering into difficulties which might confuse your ideas, and throw more obscurity than interest upon this abstruse part of the philosophy of chemistry.* Caroline. Pray, Mrs. B., can you decompose a salt by means of electricity, in the same way as we decompose wa- ter ? Mrs. B. Undoubtedly : and I am glad this question oc- curred 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, ind the alkali by the negative wire. Emily. But how can you render that decomposition per- ceptible ? Mrs. B. By placing in contact with the extremities of each wire, in the solution, pieces of paper stained with cer- tain vegetable colours, which are altered by the contact of an acid or an alkali. Thus this blue vegetable [(reparation called litmus, becomes red when touched by an acid ; and the juice of violets becomes green by the contact of an alk )li. But the experiment can be made in a much more distinct manner, by receiving the extremities of ihe wire* into differ- * This would have been the proper place for meutioning Dr Wol- Iaston's scale of cheinic-l equivalents; but the subjoc' has been thought to imply some considerations not sutficicntlv 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 this senile, and the peculiar pronerhYs which it possesses, though not verv easily described, may be readily understood on inspecting the instrument, which should be in the hands of every chemical student. v 17 . ' ■ ia2 ON THE ATTRACTION ent 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 com- pleted ; how can the effect be produced ? Mrs. B. You are right; I ought to have added that the two vessels must be connected together by some interposed substance capable of conducting electricity. A piece of moistened cotton-wick answers this purpose very well. You see that the cotton (Plate XIII. fig. 2. c.) has one end im- mersed in one glass, and the other end in the other, so as to establish a communication between any fluids contained in them. We shall now put into; each of the glasses a little glauber salt, or sulphat of soda, (which consists of an acid and an alkali,) 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 bat- tery, thus .... Caroline. The wires are already giving out small bubbles : is this owing to the decomposi'ion of the salt? Mrs. B. No : these are bubbles produced by the decom- position ofthe 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, I 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 experiment in this manner :■—These three glasses (fig. 3. f, g, h,) are, as in the former instance, connected together by wetted cotton, but the middle one alone contains a saline solution, the two others containing only distilled water, col- oured as before by vegetable infusions*. Yet, on making the connection with the battery, 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 be 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, fig. 4,) an alkaline solution, the glauber salt being placed into the FLJTE.LW '■ / K/caic Battel of tiiiinvoea' conduction wlh the Tlatcsout of tlic Cel* ^^S»-^«^/^T^ **< FoltaicMattery. OP COMPOSITION. 183 negative glass (1) and the positive glass (i) containing only water. The acid will be attracted by the positive wire (m) and will actually appear in the vessel (i) after passing through the alkaline solution (k) without combining with it, although, you know, acids and alkalies are so much disposed to com- bine. But this conversation has already much exceeded our usual limits, and we cannot enlarge more upon this interesting subject at present. QUESTIONS. What is the attraction of composition ? What is the kind of attraction which brings acids and alkalies to unite? What are the seven laws of chemical attraction ? What are the salifiable bases ? What are the salifiable principles? How do salts ending in ate differ from those ending in ite ? How do acids ending in ic differ from those ending ioous? How are chemical compositions, and decompositions effected ? What is meant by quiescent and divellant forces ? When acids and alkalies unite in several proportions, what relations do these proportions hear to each other? When a salt is decomposed by galvanism, at which pole does the acid appear ? CONVERSATION XIV. ON ALKALIES. Mrs. B. Having now given you some idea ofthe laws by which chemical attractions are governed, we may proceed to the examination 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 bodies composed of only two principles. The sulphurets, phosphurets, carburets, &c. are of this de- scription ; 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 184 ALKAL1L5. are three, viz. potash, soda, and ammonia. The two first are called^ared alkalies* because they exist in a solid form at the temperature, of the atmosphere, and require a great heat to be volatilised. They consist, as you already know, of metallic bases combined with oxygen. In potash, the pro- portions are about eighty-six parts of potassium to fourteen of oxygen ; and in soda, seventy-seven parts of sodium to twen- ty-three of oxygen. The third alkali, ammonia, has been distinguished by the name of volatile alkali, because its natu- ral form is that of gas. Its composition is of a more compli- cated nature, of which we shall speak hereafter. Some ofthe earths bear so strong a resemblance in their properties to the alkalies, that it is difficult to kuow under which head to place them. The celebrated French chemist, Fourcroy, has classed two of them (barytes and stronites) with the alkalies ; but as lime and magnesia have almost an equal title to that rank, I think it better 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 al- kaline 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 de- compose it, is entitled to the appellation of caustic. I he al- kalies, 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 absorb- ing these substance? from animal matter 'hat 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 viu,- » lets, and other blue vegetable infusions, to green ; and have, * 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 cattedpeta/ite; bni has since been detected in some other minerals. Though this alkali resem- bles potash and soda in its general properties, yet it has decidedly an alkaline substance of its own, capable of forming different snlts with the acids, and having in particular the property of combining witk much greater proportions of acid than the other alkalies. FOTASH. 185 in general, a very great tendency to unite with acids, although the respective qualities of these two classes of bodies form a remarkable contract. We shall examine the result of the combination of acids and alkalies more particularly hereafter. It will be sufficient at present to inform you, that whenever acids are brought in contact with alkalies, or alkaline earths, they unite with a re- markable eagerness, and form compounds perfectly different from either of their constituents ; these bodies are called neutral or compound salts. The dry white powder which yoirsee 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 at- mosphere, 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 is never found in its pure sepa- rate 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 volatilised by combustion. Caroline. But you once said, that after all the volatile parts of a vegetable were evaporated, the substance that re- mained was charcoal ? Mrs. B. I am surprised that you should still confound the processes of volatilisation and combustion. In order to procure charcoal, we evaporate such parts as can be reduced to vapour by the operation of heat alone ; but when we burn the vegetable, we burn the carbon also, and convert it into carbonic acid gas. Caroline. That is true ; I hope I shall make no more mistakes in my favourite theory of combustion. Mrs. B. Potash derives its name from the pots in which the vegetables, 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 oPa wood fire, then, are potash, since they are vegetable ashes ? Mrs. 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 vegetables, 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 imperfect state in which it is 17* 186 P0TA5SL used in the arts, is much more complicated than simple com- bustion. It was once deemed impossible to separate it en- tirely from all foreign substances, and it is only in chemical 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- ush, which is of great efficacy in taking out grease, in washing linen, &c. ; for potash combines readily with oil or fat, with which it forms a compound well known to you under the name of soap. Caroline. Really! Then I should think-it would be bet- ter to wash all linen with pearl-ash than with soap, as, in the latter case, the alkali being already combined with oil, must be less efficacious in extracting grease. Mrs. 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 cannot 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 pur- pose. Caustic potash, as we already observed, acts on the skin, and animal fibre, in virtue of its attraction for water and oil, and converts all animal matter into a kind of saponaceous Emily. Are vegetables the only source from which pot- ash can be derived ? Mrs. B. No.: for, though far most abundant in vegetables, it is by no means confined to that class of bodies, being found als© on the surface of the earth, mixed with various minerals, especially with earths and stones, whence it is supposed to be conveyed into vegetables bv the roots ofthe plant. It is also met with; though in very small quantities, in some ani- mal 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 compound salt, formed by the union of carbonic acid with potash. Mrs.B. Very true ; you see how admirably the nomen- clature of modern chemistry is adapted to assist the memory ; when you hear the name of a compound, you necessarily learn what are its constituent parts ; and when you are ac- POTASH. 187 Huamted with these constituents, you can immediately name the compound which they liw-n. Caroline. Pray how were oodies arranged and distin- guished before this nomenclature was introduced ? Mrs. B. Chemi>try was then a much more difficult study ; for every substance hid an arbitrary n sme, which it derived either from the person who discovered it, as Glauber's salts for instance ; or from some other circum-tance relative to it, though quite unconnected with its real nature, us potash. These names have been retained for some of the simple bodies ; for as this class is not numerous, and therefore can e '.sily be remembered, it has not been thought necessary to change them.. Emily. Yet I think it would have rendered the new no- menclature more complete to have-methodized the names of the elementary, as well as ofthe compound bodies, though it could not have been done in the same manner. But the names ofthe simple substances might have indicated their na- ture, or, at least, some of their principal properties ; and if, like the acids and compound salts, all the simple bodies had a similar 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 the old and new terms. Mrs. B. Butyou are not aware of the difficulty of introdu- cing 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 lea«t exceptionable, were not left as an introduction to the new ones, lew people would have had industry and perseverance enough to submit to the study of a completely new language ; and the inferior 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, Lavoisier and his colleagues, who invented the new nomenclature, thought it most prudent to leave a few links ofthe old chain; in order to connect it with the new one. Besides, you may easily conceive the inconvenience which might arise from giving a regular nomenclature to substance*, the simple nature of which is always uncertain ; for the new names might, per- haps, have proved to have been founded in error. - And, in- deed, cautious as the inventors of the modern chemical lan- guage 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 188 POTASH. bodies, those names have been so contrived as to indicate one of the chief properties of the body in question ; this is the case with oxygen, which, as I explained to you, signifies generator of acids ; and hydrogen generator of water.* If all the elementary bodies had a similar termination, 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 retur 1 to the alkalies.—We shall now try to melt some of this caustic potash in a little water, as a circumstance occurs during 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 theory of latent heat, according to which heat is disenga- ged when fluids become solid, and cold produced when solids are melted ? Mrs. B. i 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 may be explained thus : When water first comes in contact with the potash, it produces an effect similar to the slaking of lime, that is, the water is solidified in combining with the potash, and thus loses its la- tent heat ; this is the heat that you now feel, and which is, therefore, produced, not by the melting of the solid, but by / the solidification of the fluid. But when there is more water than the potash can absorb and solidify, the latter then yields to the solvent power of the water ; and if we do not perceive the cold produced by its melting, it is because it is counter- balanced by the heat previously disengaged.! A very remarkable property of potash is the formation ef glass by its fusion with silicious earth. You are not yet ac- quainted 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 apd flint are chiefly composed of it; alone, it is infusible, but mixed with potash, it melts when exposed to the heat of a furnace, combines with the alkali, and runs into glass. * It may here be observed, fhat, even with regard to these two bodies, the nomenclature is become exceptionable, since it is now- found that oxygen is one ofthe constituents of alkalies as well as of acids, and that hydrogen enters into the composition of some of the acids, and in particular ofthe 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 separate state. roTASH. 189 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,! Airs. B. The transparency, or opacity of bodies, does not, I conceive, depend so much on their intimate nature, as upon the arrangement of their particles : we cannot have a more striking instance 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, and which, in all probability, derives its beautiful transparency from the peculiar 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. Airs. B. It is by no means an easy operation to make per- fect glass ; for if the sand or flint, from which the silicious earth is obtained, be mixed with an\ metallic p; rtieJes, or other substance, which cannot be vitrified, the glass will be discoloured, or defaced, by opaque sperks. Caroline. That I suppose, is the reason whv object? so often appear irregular and distorted through a common glass window. Airs. B. This species of imperfection proceeds, I 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 containing 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 irregular refraction of the rays of light which pass thr -ugh it. Another species o.f 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 silex (which are as two to one) not being carefully observed ; the glass, in those cases, will be liable to alteration from the action ofthe air, of salts, and es- pecially o acids, which will effect its decomposition by com- bining with the potash, and forming compound salts Emily. What an extremely useful substance potash is ! Mrs. B. Besides the great importance of potash \<\ the^ manufactures of glass and soap, it is of ve.y con«ider-tHe utility in many ofthe other arts, and in its combinations with several acids, particularly the nitric, with which it forms saltpetre. 150 SODA. Caroline. Then saltpetre must be a nitrat of potash. But we are not yet acquainted with the nitric acid. Mrs. B. We shall therefore defer entering into the par- ticulars 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 strongly resembles potash ; indeed, so great is their similitude, that they have been long confounded, and they can now scarcely be distinguished, except by the difference ofthe 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^he waters ofthe 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 ofthe neutral salts. Soda may be obtained from common salt ; but the easiest and most usual method of pro- curing it is by the combus'ion of marine plants, an operation perfectly analogous to that by which potash is obtained from vegetables. Emily. From what does soda derive its name ? r Mrs. B. From a plant called by us soda, and by the Arabs kali, which affords it in great abundance. Kali has, indeed, given its name to the alkalies in general. * 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 glass- es may be inverted for a moment. Then pour the tincture into each, and theone containing the acid will appear a most beautiful red, anil the other as beautiful a green. C. AMMONIA. 151 Caroline. Does soda form glass and soap in the same man- ner as potash ? Airs. B. Yes, it does ; it is of equal importance in the arts, and is even preferred to potash for some purposes ; but you will not be able to distinguish their properties, till we ex- amine 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 ofthe same nature as hartshorn ? Mrs. B. Yes, it is? as you will see by-and-bye. This alkali is seldom found in nature in its pure state ; it is most commonly extracted from a compound salt, called sal ammo- niac, which was formerly imported from Ammonia a region of Libya, from which both these salts and the alkali derive their names. The crystals contained in this bottle are speci- mens of this salt, which consists of a combination of ammonia and muriatid acid. Caroline. Then it should be called muriat of ammonia; for though I am ignorant what muriatic acid is, yet I know that its combination with ammonia cannot bat 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 altogether ; and it is still sold under that name by druggists, though by scientific chemists it is more properly called muriate of ammonia. Caroline. Both the popular and the common name should be inscribed on labels—this would soon introduce the new nomenclature. Emily. By what means can the ammonia be separated from the muriatic acid ? Mrs. B. By chemical attractions; but this operation is too complicated for you to understand till you are better ac- quainted with the agency of affinities. Emily. And when extracted from the salt, what kind of substance is ammonia ? Mrs. B. Its natural form, at the temperature ofthe atmos- phere, when free from combination, is that of gasj and in this state it is called ammoniacal gas. But it mixes verv rea- dily 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 princi: pies does it consist ? Mrs. B. It was discovered a few years since, bv Berthol- let, a celebrated French chemist, that it consisted of about 192 AMMONIA. one part of hydrogen to four parts of nitrogen. Having heat- ed ammoniacal gas under a receiver, by causing the electrical spark to pass repeatedly through it, he found that it increased considerably in bulk, lost all its alkaline properties, and was actually cor.verted into hydrogen and nitrogen gases ; and from the latest and most accurate experiments, the propor- tions appear to be, one volume of nitrogen gas to three of ©xygen gas.* Caroline. Ammonia, therefore, has not, like the two other alkalies, a metallic basis ? Mrs. B. It is believed that it has, though it is extremely difficult to reconcile that idea with what 1 have just stated of its chemical nature. But the fact is, that although this sup- posed metallic basis of ammonia has never been obtained distinct and separate, yet both Professor Berzelius> of Stock- holm, and Sir H. Davy, have succeeded in forming a combi- nation of mercury with the basis of ammonia, which has so much the appearance of an amalgam, that it strongly corro- borates the idea of ammonia having a metallic basis.t But these theoretical points are full of difficulties and doubts, and it would be useless to dwell any longer upon them. Let es therefore return to the properties of volatile alkali. Ammoniacal gas is considerably lighter than oxygen gas, and only about half the weight of atmospherical air. It possesses most ofthe 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 can be collected in a receiver over mer- cury only. Caroline. 1 do not understand this. Mrs. B. Do you recollect the method which we 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 instantaneously absorbed by it. We ran therefore neither use water for that purpose, nor any other liquid of * It ought to be hydrogen gas. C. f This amalgam is easily obtained, by placing a globule of mercu- ry upon a piece of muriat, or carbonat of ammonia, and electrifying this globule by the Voltaic battery The srlobule instantlv begins to exoand to three or four times its former size, and becomes much less fluid, thonsrh without losing its metallic lustre, a change which is ascribed to the metallic basis of ammonia uniting with the mercu- ry. This is an extremely curious experiment. AMMONIA. Vili which water is a component part; so that; in orde"r to collect this gas, we are obliged to have recourse to mercury, (a li- quid 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 beginning of the conversation—hartshorn ; it is the ammoniacal gas escaping from the water which gives it so powerful a smell.* Emily. But there is no appearance of effervescence is hartshorn. Mrs. 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 impregnated with immoniacal 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 take place if it was not coun- teracted 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 account 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, be- tween the opposite effects, I should have supposed the ori- ginal temperature would have been preserved. Mrs. B. But you have forgotten to take into the account- * To obtain ammoniacal gas, mix together equal parts of muriate of ammonia, and dry burnt lime ; after pulverizing each separately, 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 heat- ed in a retort in tne same way. To collect and retain the gas with- out a mercurial bath, fix a receiver or bottle in an inverted position, and connect to the retort a tube, which introduce up into the re- ceiver so that it nearly reaches the bottom. As the gas comejs over, its levity is such, that it fills the upper part of the receiver first, gradually driving out the air, and taking its place. To keep it for any considerable time, the receiver must be stopped. A pretty ex- periment may be made by introducing up into the receiver with the ammonia, some muriatic gas. Both gases are invisible until thev are brought together, when they unite, forming a dense white cloud, and fall down in the solid form of muriate ofammonia.- The muriatic gas is obtained by pouring sulphuric acid on common salt, and ap- plying the heat of a lamp. It may be sent up into the receiver «• the way above described or ammonia. C. 18 194 AMMONIA. the rarefaetion ofthe water (or melted ice) by the impregna- tion of the gas ; and this is the cause ofthe cold which is ulti- mately produced. Caroline. Is the sal volatile (the smell of which so strongly resembles hartshorn) likewise a preparation of ammonia ? Mrs. B. It is carbonat of ammonia dissolved in water; and which, in its concrete state is commonly called salts of hartshorn. Ammonia 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 with water.—Oil and acids are very excellent antidotes for alkaline poisons ; can you guess why ? Caroline. Perhaps, because the oil combines with the al- kali, and forms soap, and thus destroys its caustic properties • and the acid converts it into a compound salt, which, I sup- pose, is not so pernicious 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 ? Mrs. B. So far from it, that it is contained in, and may be extracted from, all animal substances whatever. Hydrogen and nitrogen are two of the chief constituents of animal mat- ter ; it is therefore not surprising that they should occasional- ly meet and combine in those proportions that compose am- monia. But this alkali is more frequently generated by the \ spontaneous decomposition of animal substances ; the hydro- gen and nitrogen gases that arise from putrified bodies com- bine 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 prin- cipally extracted from this salt, can also be produced by a great variety of other substances. The horns of cattle, es- pecially 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 substance whatever, yields it by decomposition. We shall now lay aside the alkalies, however important the subject may be, till we treat of their combination with aei«k The next time we meet, we shall examine the earths. EARTHS. 195 QUESTIONS. What are the alkalies? What is their composition ? What are the general properties of the alkalies ? On what does the causticity of the alkalies depend ? To what colour do the alkalies change the vegetable blues r From whence is potash obtained ? What is the chemical name of potash ? What is its composition ? Why is heat disengaged when water is poured on caustic potash What is the result when potash is melted with silex? What is the chemical name of salt petre ? What is its composition ? From whence does soda derive its name ? How is it obtained ? How does soda differ from potash ? Why is the volatile alkali called ammonia ? From what is it extracted? By what means can ammonia be separated from the muriatic acid ■: Under what form does it appear when pure ? What is the composition of ammonia? How can ammoniacal gas be retained for experiments without a mercurial bath ? How do you account for the production of cold, when ice is melted with ammoniacal gas ?« What is the substance used in smelling bottles, called hartshorn ? What is formed when ammonia unites with oil ? From what class of substances can ammonia be extracted r CONVERSATION XV. ON EARTHS. Mrs. B. The earths, which we are to-day to examine. are nine in-number : SILEX, STRONTITES,* ALUMINE, YTTR1A, BARVTES,* OLUCINA, LIME,* ZIRCONIA. MAGNESIA,* * 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 remembered, was supposed to have formed an amalgam with mer- cury, and on this account was supposed to have had a metallic basis. 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 th« blow-pipe, charged with oxygen and hydrogen, was led to believe he had obtained their metallic bases. But as his experiments have been repeated at the Royal Institution without success, it is now understood that the Dr. must have been mistaken. C. 196 EARTHS. The last three are of late discovery : their properties arc but imperfectly known ; and, as they have not yet been ap- plied to use, it will be unnecessary to enter into any particu- lars respecting them ; we shall confine our remarks, there- fore to the first five. They are composed, as you have al- ready learnt, of a metallic basis combined with oxygen ; and, from this circumstance, are incombustible. Caroline. Yet I have seen turf burnt in the country, and it makes an excellent fire ; the earth becomes red hot, and pro- duces 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 inter- mixed with it. The caloric, which is produced by the com- bustion of these substances, makes the earth red hot, and this being a bad conductor of heat, retains its caloric a long time ; but were you to examine it when cooled, you would find that it had not absorbed one particle of oxygen, nor suffered any alteration from the fire. Earth is, however, from the cir- cumstance just mentioned, an excellent radiator of heat, and owes its utility, when mixed with fuel, solely to that proper- ty. It is in this point of view that Count Rumford has recom- mended balls of incombustible substances to be arranged in fire-places, and mixed with the coals, by which means the ca- loric disengaged by the combustion of the latter i? more per- fectly reflected into the room, and an expense of fuel is saved. Emily. I expected that the list of earths would be mueb 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 ; for barytes, strontites, and the others of late discov- ery, 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, marble^ chalk, slate, sand, flint, and all kinds of stones, from the precious jewels to the commonest pebbles ; in a word, all the immense variety of mineral products, may be referred to some of these earths, either in a simple state, or combined the one with ihe other, or blended with other ingredients. Caroline. Precious stones composed of earth I That seems very difficult to conceive. Emily. Is it more extraordinary than that the most pre- cious of all jewels, diamond, should be composed of carbon 1 But diamond forms an exception, Mrs. B. ; for, though a stone, it is not composed of earth. EARTHS. 197 Mrs. B. I did not specify the exception, as 1 knew you were so well acquainted with it. Besides, I would call a dia- mond 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. Mrs. B. We are very far from understanding all the se- cret resources of nature ; but 1 do not think the spontaneous formation of the crystals, which we call precious stones, one ofthe 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, transparency, and beauty, for which they are so much admired ; and renders them in appearance so totally different from their rude and primitive ingredients. Caroline. But how does it happen that they are spontane- ously dissolved, and afterwards crystallized ? Mrs. B. The scarcity of many kinds of crystals, as rubies, emeralds, 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 dribbles 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 crystalliza- tion is more regular and perfect, in proportion as the evapo- ration ofthe solvent is slow and uniform ; nature, 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 transparency, by admitting a free passage to the rays of light; but I cannot understand why crystallized earths should assume such beautiful colours as most of them do. Sapphire, for instance, is of a celestial blue ; ruby, a deep rod; topaz, a brilliant yellow ? Mrs. B. Nothing is more simple than to suppose that the arrangement of their particles is such, as to transmit some of the coloured rays of light, and to reflect others, in which case the stone must appear ofthe colour of the rays which it re- flects. But besides, it frequently happens that the colour of a stone is owing to a mixture of some metallic matter. 18* 198 EARTHS. Caroline. Pray, are the different kinds of precious atones each composed of one individual earth, or are they formed of a combination of several earths ? Mrs. B. A great variety of materials enters into the com- position of most of them ; not only several earths, but some- times salts and metals. The earths, however, in their sim- ple state, frequently form very beautiful crystals ; and, in- deed, it is in that state only that they can be obtained perfect- ly pure. Emily. Is not the Derbyshire spar produced by the crys- tallization 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 con- fusedly blended together, as you may jud e 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 state in which they are commonly found, and which, it less pleasing to the eye, is far more interesting by its utility. All the earths are more or less endowed with alkaline pro- perties ; but there are four, barytes, magnesia, lime, and strontites, which are called alkaline earths, because they pos- sess those qualities 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, likje them, susceptible of a considerable degree of causticity, and are acted upon in a similar manner by chemical tests.—The remaining earths, silexand alumine, with one or ,two others of late discovery, are in some degree more earthy, that is to say, they possess more completely the properties common to all the earths, which are, insipidity, dryness^ un- alterableness in the fire, infusibility, &c. Caroline. Yet, did you not tell us that silex, or silicious earth, when mixed with an alkali, was fusible, and run into glass ? Mrs. B. Yes, my dear; but the characteristic properties of earths, which I have mentioned, are to be 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 * The Derbj'shire spar is composed of lime and fluoric acid: bence it is called fiuate of lime. The colours are owing to inter- mixture with metallic oxides. It is a very beautiful mineral, and instead of being op^ike, it is generally translucent, or nearly trans- parent. C. SILEX. 199 these general properties, each earth has its own specific characters, by which it is distinguished from any other sub- stance. Let us therefore review them separately. Silex, or silica, abounds in flint, sand, sand-stone, agate, jasper, &c. ; it forms the basis of many precious stones, and particularly of those which strike fire with steel. It is rough to the touch, scratches and wears away metals ; it is acted upon by no acid but the fluoric, and is not soluble in water by any known process ; but nature certainly dissolves it by means with which we are unacquainted, and thus pro- duces a variety of silicious crystals, and amongst these rock crystal, which is the purest specimen of this earth. Sile* appears to have been intended by Providence to form the so* lid basis ofthe globe, to serve as a foundation for the origin* al mountains, and give them that hardness and durability which has enabled them to resist the various revolutions which the surface of the earth has successively undergone. From these mountains silicious rocks have, during the course of ages, been gradually detached by torrents of water, and brought down in fragments ; these, in the violence and rapid* ity of their descent, are sometimes crumbled to sand, and in this state form the beds of rivers and ofthe sea, chiefly com- posed of silicious materials. . Sometimes the fragments are broken without being pulverised by their fall, and assume the form of pebbles, which gradually become rounded and polished. Emily. Pray what is the true colour of silex, which forms such a variety of different coloured subtances ? Sand is brown, flint is nearly black, and precious stones are of all co- lours. Mrs. B. Pure silex, such as is found only in the chemist's laboratory, is perfectly white, and the various colours which it assumes in the different substances you have just mention- ed, proceed from the different ingredients with which it is mixed in them. Caroline. I wonder that silex is not more valuable, since it forms the basis of so many precious stones.* Mrs. B. You must not forget that the yalue we set upon precious stones depends in a great measure upon the scarci- ty with which nature affords them ; for, were those produc- tions either common or perfectly imitable by art, they would no longer, notwithstanding their beauty, be so highly esteem- ed. But the real value of silicious earth, in many of the * The bases of some of the most costly gems, as sapphire, ruby and topaz, are alumine. C ^00 ALUMINE. most useful arts, is very extensive. Mixed with clay, it forms the basis of all the various kinds of earthenware, from the most common utensils to the most refined ornaments. Emily. And we must recollect its importance in the forma- tion of glass with potash. Mrs. B. Nor should we omit to mention, likewise, many other important uses of silex, such as being the chief ingredi- ent of some ofthe most durable cements, of mortar, &c. I said before that silicious earth combined with no acid but the fluoric ; it is for this reason that glass is liable to be at- tacked by that acid only, which, from its strong affinity, to si- lex, forces that substance from its combination with the pot- ash, and thus destroys the glass. We will nowhasien to proceed to the other earths, for I am rather apprehensive of your growing weary of this part of our subject. Caroline. I confess that the history of the earth is not quite so entertaining as that ofthe 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 omission would throw great obscurity on our gen- eral outline of chemical 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 &lum, of which it forms the basis. Caroline. But it ought/to be just the contrary, Mrs. B. ; the simple body should give, instead of taking, its name from the compound. Airs. B. That is true ; but as the compound salt was known long before its basis was discovered, it w,as very na- tural that when the earth was at length separated from the acid, it should derive its name from the compound from wnich it was obtained. However, to remove your scruples, we will call the salt according to the new nomenclature, sulphat of alumine. From this combination, alumine 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 nattire it is found chiefly in clay, which contains a considerable pro- portion of this earth ; it is very abundant in fullers' earth, slate, and a variety of other mineral productions. There is indeed scarcely any mineral substance more useful to man- kind than alumine. In the state of clay, it forms large strata of the earth, gives consistency to the soil of valleysr and of all low and damp spots, such as swamps and marshes. The beds of lakes, ponds, and springs, are almost entirely of ALUMINE. 201 clay ; instead of allowing of the filtration of water, as sand Joes, it forms an impenetrable bottom, and by this means wa- ter 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 reser- voirs of water were bedded by soma hard stone, or rock, which the water could not penetrate'. Mrs. B. That is not the £ase ; 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 tit for corn, owe their consistence in a great measure to alumine : this earth it therefore used to improve sandy or chalky soils, which do not retain a suflicient quaptity of water for the purpose of vegetation. Alumine is the most essential ingredient in all potteries. It enters into the composition of brick, as well as that ofthe finest porcelain : the addition of silex and water hardens it, renders it susceptible 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 certain 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 js,* I believe, ne- cessary for the composition of porcelain, as well as a finer kind of clay ; and these materials are, no doubt, more care- fully prepared, and curiously wrought, in the one case than in the other. Porcelain owes it beautiful semi-transparency to a commencement of vitrification. Emily. But the commonest earthernware, though not transparent, is covered with a kind of glazing. Mrs. B. That precaution is equally necessary for use as for beauty, as the ware would be liable to be spoiled and cor- roded by a variety of substances, if not covered with a coat- ing of this kind. In porcelain it consists of enamel, which is a fine white opake glass, formed of metallic oxyds, sand, salts, and such other materials as are susceptible of vitrifica- tion. The glazing of common earthenware is made chiefly of oxyd of lead, or sometimes merely of salt, which, when * 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 feldspar. Its composition is silex and alumine, silex being the predominant ingredient. C 202 BARYTES. thinly spread over earthen vessels, will, at a certain heat, run into opaque glass. Caroli7ie. And of what nature are the colours which are used for painting porcelain ? Mrs. B. They are all composed of metallic oxyds ; s* that these colours, instead of receiving injury from the ap- plication of fire, are strengthened and developed by its ac- tion, which causes them to undergo different degrees of oxy- dation. Alumine and silex are not only often combined by art, but they have in nature a very strong tendency to unite, and are found combined, in different proportions, in various gems and other minerals. Indeed, many of the precious stones, such as ruby, oriental sapphire, amethyst,* &c. consist chiefly of alumine. We may now proceed to the alkaline earths. I shall say but a few words on Barytes, as it is hardly ever used, ex- cept in chemical 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 attraction for acids ; this last proper- ty it possesses to such a degree, particularly with regard to the sulphuric acid, that it will always detect its piesence in any substance or combination whatever, by immediately uni- ting with it, and forming a sulphafof barytes. This renders it a very valuable chemical test- It is found pretty abun- dantly in nature in the state of carbonet,t 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 slightly as the last. Lime is strongly alkaline. In natnre 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 substan- ces, with which it forms the common lime-stone ; but it is separated in the kiln from these ingredients, which are vol- atilized whenever a sufficient degree 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 * The amethyst is almost entirely composed of silex. C. f The native carbonate of barytes is a rare mineral. It is a viru- lent poison. The sidphateot barytes is found in considerable abun- dance. C. BARYTES. 203 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, we're it all exposed to the atmosphere, it would absorb both moisture and carbonic acid gas from it, and be soon slaked. Here i« also some 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 ex- cessively hot!—It swells, and now it bursts and crumbles t© powder, while the water appears to produce no kind of alter- ation on the lime stone. Mrs. 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 pro- duces this prodigious disengagement of heat, the cause of which I formerly explained to you : do you recollect it ? Emily. Yes ; you said that the heat did not proceed from the lime, 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 crum- bled, as you see, it will then gradually be diffused in the wa- ter, till it will at length be dissolved in it, and entirely dis- appear ; but for this purpose it requires no less than 700 times its weight of water. This solution is called lime-wa- ter.* Caroline. How very small, then, is the proportion of lime dissolved ! 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, I believe, for the purpose of combining with and neutralizing the superabundant acid which it meets with in the stomach. Emily. I am 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 in- visible, and, therefore, will not, in the least degree impair the transparency of the solvent ? I said that the attraction of lime for carbonic acid was so strong, that it would absorb it from the atmosphere. We *To make lime-water, take a piece of well burned lime, about the size of a hen's egg, put it into an earthen dish, and sprinkle wa- ter on it, till it falls into powder : Then pcur on two quarts of boiling water, and stir it several times, after the lime fcas settled pour off the clear water and cork it up for use. C 204 LIME. may see this effect by exposing a glass of lime-water to the air : the lime will then separate from the water, combine" with the carbonic acid, and re-appear on the* surface in the form of a white film, which is earbonat of lime, commonly called chaU. 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 appear on the surface of the wateT : but it is far from resembling hard solid cbalk. Mrs. B. That is owing to its state of extreme division : in a little 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-waier into this glass tube, and, by breathing re- peatedly into it, you will soon perceive a precipitation of chalk. 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 re-appears when convert- ed into chalk ; but you must take notice of a very singular circumstance", which is, that chalk is soluble in water impreg- nated with carbonic acid. Caroline. It is very curious, indeed, that carbonic acid gas should render lime soluble in one instance, and insoluble in the other! Mrs. 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. Mrs. B. I shall now pour an additional quantity of the SeltzerVater into the lime-water.— Emily. How singular ! The cloud is redissolved, and the liquid is again transparent. Mrs. 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, there- fore, which I introduced into the lime-water, was employed in forming the carbonat of lime, which remained visible, until an additional quantity of carbonic acid dissolved it. Thws, you see, when the lime and carbonic acid are in proper pre- MAGNESIA. 205 portions lo form chalk, the white cloud appears; but when the acid predominates, the chalk is no sooner formed than it is dissolved. ( Caroline. That is now the case ; but let us try whether a further addition of lime-water will again precipitate the chalk. Emily. It does, indeed ! The cloud re-appears, because, I suppose, there is now no more ofthe carbonic acid than is- necessary to form chalk ; and, in order to dissolve the chalk, a superabundance of acid is required. Mrs. B. We have, 1 think, carried this experiment far enough ; every repetition would but exhibit the same appear- ances. Lime combines with most of the acids, to which the car- bonic (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 state ; 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 likewise in the animal and the vegetable creations. Emily. And in the arts is not lime of very great utility ? Airs. B. Scarcely any substance more so ; you know that it is a most essential requisite in building, as it constitutes the basis of all cements, such as mortar, stucco, plaster, kc. Lime is also of infinite importance in agriculture ; it light- ens and warms soils that are too cold and compact, in conse- quence of too great a proportion of clay.—But it would be endless to enumerate the various purposes for which it is em- ployed ; 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. Airs. B. It is in the state of carbonat that magnesia is usu- ally employed medicinally ; it then differs but little in ap- pearance 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 extremely 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, amianthus, and more particularly in a certain lime stone, which has been dig. covered by Mr. Tennant, to contain it in very great quanti- ties. It does not attract and solidify water, like lime: but when mixed with water and exposed to the atmosphere, it 19 206 MAGNESIA. slowly absorbs carbonic acid from the latter,.and thus loses its causticity. Its chief use in medicine is, likethatof lime, de- rived from its readiness to combine w',r> and neutralize, the acid which it meets with in the stomach. Emily. Yet, you said that it was taken in the state of car- bonat, in which case it has already combined with an acid 1 Mrs. B. Yes ; but the carbonic is the last of all the acids in the order of affinities ; it will therefore yield the magne- sia to any ofthe others. It is, however, frequently taken in its caustic state as a remedy 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 ? Mrs. B. Because there is a spring in the neighbourhood of Epsom, which contains this salt in great abundance. The last alkaline earth which we have to mention 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 eo little use in the arts, that it will not be necessary to enter into any particulars respecting it. One of the remarkable characteristic proper- ties of strontites is, that its salts, when dissolved in spirit of wine, tinge the flame of a deep red, or blood colour. QUESTIONS. What is the number of earths, and what their names ? Why are they incombustible ? What costly substances do the earths compose ? With what are the gems coloured ? Which are the alkaline earths ? What substances contain silica in the greatest abundance -: What is the composition of Derbyshire spar ? What are the important uses of silex ? From whence does alumine derive its name ? From what substance is this earth obtained ? In what kind of soil does it occur most abundantly ; Is jt useful in the arts, or otherwise, and for what purposes : Name the alkaline earths. Of what use is barytes'? Has it any remarkable properties ? In what respect does caustic lime differ from lime-stone ? What is the process of making quick-lime? What effect does the air produce on quick-lime ? What effect has water on it ? What is the cause ofthe heat, when lime is sprinkled with water3 Does it dissolve in water, and in what proportion ■' What is the process of making lime-water ? For what has lime a remarkable affinity ? Acins. 207 Why does lime-water turn white on breathing into it ? Of what use is lime in the arts ? Of what use is it in agriculture ? What are the principal uses of magnesia ? Does it attract water ? In what state is it used in medicine ? What does it form when combined with sulphuric acidr? Is strontian of any use ? What are its peculiarities ? CONVERSATION XVI. ON ACIDS. Mrs. B. We may now proceed to the acids. Of the.me- tallic oxyds, you have already acquired some general notions. This subject though highly interesting in its details, is not of sufficient importance to our concise view of chemistry, to be particularly treated of; but it i9 absolutely necessary that you should be better acquainted with the acids, and likewise with their combinations with the alkalies, which form the triple compounds, called neutral salts. The class of acids is characterised by very distinct proper- ties. They all change blue vegetable infusions to a red co- lour : they are more or less sour to the taste ; and have a general tendency to combine with the earths, alkalies, and metallic oxyds. You have, I believe, a clear idea of the nomenclature by which the base (or radical) of the acid, and the various de- grees of acidification, are expressed ? Emily. Yes, 1 think so ; the acid is distinguished by the name of its base, and its degree of oxydation, that is the quan- tity of oxygen it contains, by the termination of that name in ous or ic ; thus sulphureous acid is that formed by the small- est proportion of oxygen combined with sulphur ; sulphuric acid is that which results from the combination of sulphur with the greatest quantity of oxygen. Mrs. B: A still greater latitude may, in many cases, be allowed to the proportions of oxygen that can be combined with acidifiable radicals ; for several of these radicals are sus- ceptible of uniting with a quantity of oxygen so small as to be insufficient to give them the properties of acids ; in these ca- ses, therefore, they are converted into oxyds. Such is sul- phur, which, by exposure to the atmosphere with a degree of heat inadequate to produce inflammation, absorbs a small pro- portion of oxygen, which colours it red or brown. This, 208 ACIOi. therefore, may be considered as a first degree of oxygenation of sulphur ; the 2d converts it into sulphureotw acid ; the 3d into the sulphuric acid ; and, 4thly, if it was foand capable of combining with a still larger proportion of oxygen, it would then be termed superoxygenated sulphuric acid. Emily. Are these various degrees of oxygenation com- mon to all the acids ? Mrs. B. No ; they vary much in this respect :- some are suseeptihle of only one degree of oxygenation : others, ef two or three ; there are but very few that will admit of more. Caroline. The modern nomenclature must be of immense advantage in pointing out so easily the nature of the acids, and their various degrees of oxygenation. Mrs. B. Till lately many of the acids had not been de- composed ; but analogy afforded so strong a proof of their compound nature, that I could never reconcile myself to classing them with the simple bodies, though this division has been adopted by several chemical writers. At present the muriatic and the fluoric, are the only acids which have not had their bases distinctly separated. Caroline. We have heard of a great variety of acids ; - pray how many are there in all ? Mrs. B. I believe there are reckoned at present thirty- four, and their number is constantly increasing as the science improves ; but the most important, and those to which we. shall almost entirely confine our attention, are but few. I shall however, give you a general view of the whole : and then we shall more particularly examine those that are the most essential. This class of bodies was formerly divided into mineral, ve- getable, and animal acids, according to the substances from which they were commonly obtained. Caroline. That, I should think, must have been an excel- lent arrangement; why was it altered ? Mrs. B. Because, in many cases, it produced confusion. In which class, for instance, would you place carbonic acid 1 Caroline. Now I perceive the difficulty. I should be at a loss where to place it, as you have told us that it exists in the animal, vegetable, and mineral kingdoms. Emily. There would be the same objection with respect to phosphoric acid, which, though obtained chiefly from bones, can also, you said, be found in small quantities in stones, and likewise in some plants. Mrs. B. You see, therefore, the propriety of changing this mode of classification. These objections do not exist in the present nomemclature y for the composition and nature ACIDS. 209' }■ Acids, of known and simple bases. of each individual acid is in some degree pointed out, instead of the class of bodies from which it is extracted ; and, with regard to the more general division of acids, they are classed under these three heads : First, Acids of known or supposed simple bases, which are formed by the union of these bases with oxygen. They are the following : The Sulphuric Carbonic Nitric Phosphoric Arsenical Tungstenic Molybdenic Boracic Fluoric Muriatic This class comprehends the most anciently known and most important 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 consequently consist of triple combinations. These are the vegetable acids, whose common radical is a compound of hy- drogen and carbon. Caroline. But if the basis of all the vegetable acids be the same, it should form but one acid ; it" may indeed com- bine with different proportions of oxygen, but the nature of the acid must be the same. Airs. B. The only difference that exists in the basis 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 dis- similar. 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 portion of hydro- gen or of carbon The Acetic Oxalic Tartarous Citric Malic . Gallic * Mucous Benzoic Succinic Camphoric Suberic The names of these acids are, Acids, of double bases being of veget- able origin. 19* 210 ACIDS. > Acids, of triple bases, or animal acids. The 3d class of acids consists of those which have triple radicals, and are therefore of a still more compound nature. This class comprehends the animal acids, which are, The Lactic "| Prussic Formic Bombic Sebacic Zoonic Lilhic I have given you this summary account or enumeration of the acids, as you may find it more satisfactory to have at once an outline 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 animal and vegetable kingdoms. The acids of simple and known radicals are in most instan- ces capable 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 oT 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 oxy- gen by which it was acidified on the metal. And again, if we pour some acid on a compound combustible substance, (we shall try it on this 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 colour of the wood to blacks How is that ? Mrs. 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 atmosphere, or from any other source, the chemical effect on the wood is the same. 'In the case of real combustion, wood becomes black, because it is ?edueed to the state of charcoal by the evaporation of its other constituents. But can you tell me the reason why wood turns black when burnt by the application of an acid ? Caroline. First, tell me what are the ingredients of wood ? Mrs. 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, combines with the hydrogen ofthe wood, to form water •. ACIDS. 211 and that the carbon of the wood, remaining alone, appears of its usual black colour. Mrs. B. Very well indeed, my dear ; that is certainly the most plausible explanation. Emily. Would not this be a good method of making char- coal ? Mrs. B. It would be an extremely expensive, and, I be- lieve, very imperfect method ; for the action of the acid on the wood, and the heat produced by it, are far from suflicient 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 ? Mrs. B. They are vegetable acids, whose bases are com- posed of 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 little of their oxygen to the wood, and produce a stain upon it; but the carbon will not be sufficiently uncovered to as- sume its black colour. Indeed, the several mineral acids themselves possess this power of charring wood in very dif- ferent degrees. Emily. Cannot vegetable acids be decomposed, by any combustibles ? Mrs. B. No : because their radjcal is composed of two substances which have a greater attraction for oxygen than any known body. Caroline. And are those strong acids, which burn and de- compose wood, capable of producing similar effects on the skin aud flesh of animals ? Mrs. B. Yes ; all the mineral acids, and one of them more especially, 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 cf nitrogen and other substances in animal matter, which pre- vents the separation of carbon from being so conspicuous. QUESTIONS, What is an acid ? What are the general properties of the acids ? What is meant by the radical of an acid ? What substance unites to the radical to form an acid ? How does the language of chemistry distinguish the stronger froca the weaker acid ? What term is used to denote the first degree of oxygenation ? When a radical unites with another proportion of oxygen after that denoted bv ic, wh>t term is used ? 212 OP THE SVLPHURIC Are all the acids capable of equal degrees of oxygenation r What is the number of acids ? v, How many kinds of acids are there ? Name the acids which are known to have simple bases. Which are called mineral acids ? Of what are the radicals of the vegetable acids composed. Why do these acids differ, when composed of the same radicals > What are the names of the vegetable acids ? Name the acids with triple radicals. . What is their composition, and from whence are they obtained^ By what means can the acids of simple radicals be decomposed . Why does sulphuric acid change the colour of wood to black ? Why do not vegetable acids produce the same effect? What is the reason the vegetable acids are not decomposed by com- bustibles ? ., < • .t i tt Do the mineral acids have the same effect upon the skin that they do on wood ? If they do not what is the reason ? CONVERSATION XVII. OF THE SULPHURIC AND PHOSPHORIC ACIDS; OR THE COMBINATIONS OF OXYGEN WITH SULPHUR AND PHOSPHORUS ; AND OF THE SULPHATS AND PHOSPHATS. Mrs. B. In addition to the general survey which we have taken of acids, 1 think you will find it interesting to examine individually, a few of the most important of them, and like- wise some of their principal combinations with the alkalies, alkaline earths, and metals. The first of these acids, in point of importance, is the svlphuric, 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 as sulphuric acid. What resemblance or connection can there be between oil of vitriol and this acid ? Airs. B. Vitriol is the common name for sulphat of iron, a salt which is formed by the combination of sulphuric acid and iron ; the sulphuric acid was formerly obtained by dis- tillation from this salt, and it very naturally received its name from the substance which afforded it. Corpline. But it is still usually called oil of vitriol ? Mrs. B. Yes: a sufficient length of time has not yet elapsed, since the invention ot 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 bot- tle from the chemists, oil of vitriol was inscribed on the AND SULPHUREOUS ACIDS. 21£ label ; but, as I knew you were very punctilious in regard to the nomenclature, I changed it, and substituted the words sulphuric acid. Emily. This acid has neither colour nor smell, but it ap- pears 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 t« that name, as it does not contain either hydrogen or carbon, which are the essential constituents of oil. Mrs. B. Certainly ; and therefore it would be the more absurd to retain a name which owed its origin to such a mis- taken analogy. Sulphuric acid, in its purest state, would probably be a concrete substance, but its attraction for water is such, that it is impossible to obtain that acid perfectly free from it ; it is, therefore, always seen in a liquid form, such as you here find it. One of the most striking properties of sulphuric acid is that of evolving a considerable quantity of heat when mixed with water ; this I have already shown you. Emily. Yes, I recollect it: but what was the degree of heat produced by that mixture ? ' \ Mrs. B. The thermometer may be raised by it to 300 de grees, which is considerably above the temperature of boil- ing water. Caroline. Then the water may be made to boil in that mixture ? Mrs. B. Nothing more easy, provided that you employ sufficient quantities^ acid and of water, and in the due pro- portions. The greatest heat is produced bj' a mixture of one part of water to four of the acid : we shall make a mix- ture of these proportions, and immerse in it this thin glass tube, which is full of water. Caroline. The vessel feels extremely hot, but the water/ does not boil yet. Mrs. B. You must allow some time for the heat to pene- trate the tube, and raise the temperature of the water to the boiling point— Caroline. Now it boils—and with increasing violence. Mrs. B. But it will not continue boiling long : for the mixture gives out heat only while the particles of the water and the acid are mutually penetrating each other : as soon as the new arrangement of these particles is effected, the mix- ture will gradually cool, and the water return to its formed temperature. 2U OP THE SULPHWRIC You have seen the manner in which sulphuric acid decom- poses all combustible substances, whether animal, vegetable, or mineral, and burns them by means of its oxygen ? Caroline. Iliave very unintentionally repeated the ex- periment on ray gown, by letting a drop ofthe acid fall upon it, and it has made a stain, which, I suppose, will never wash out. Mrs. B. No, 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 stop- per, 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 mat- ter ; and, as far as the decomposition of the skin of your fin- ger is effected, there is no remedy ; but by washing it im- mediately m water, you will dilute the acid, and prevent any further injury. Caroline. It feels extremely hot, I assure you. Airs. B. You have now learned by experience, how cau- tiously this acid must be used. You will soon become ac- quainted with another acid, the nitric, which, though it pro- duces less heat on the skin, destroys it still quicker, and makes upon it an indelible stain. You should never handle any substances of this kind, without previously dipping your fingers in water, which will weaken their caustic effects. But, since you will not repeat the experiment, I must put in the stopper, for the acid attracts the moisture from'the atmos- phere, which would destroy its strength and purity. Emily. Pray, how can sulphuric acid be extracted from sulphat of iron by distillation ? Mrs. B. The process of distillation, you know, consists in separating substances from one another by means of their different degrees 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 of forming acids by the combustion of their radicals is known, why should not this method be used for making sulphuric acid ? Mrs. B. This is actually done in most manufactures ; but the usual method of preparing sulphuric acid does not consist in burning the sulphur in oxygen gas (as we formerly did by way of experiment,) but in heating it together with another AND SULPHUREOUS ACIDS. 215 substance, nitre, which yields oxygen in sufficient abundance to render the combustion in common air rapid and complete. Caroline. This substance, then, answers the same pur- pose as oxygen gas ? Mrs. B. Exactly; In manufactures the combustion is performed in a leaden chamber, with water at the bottom, to receive the vapour and assist its condensation. The com- bustion is, however, never so perfect but that a quantity of sulphureous acid is formed at the same time ; for you recol- lect that the sulphureous acid, according to the chemical no- menclature, differs from the sulphuric only by containing less oxygen. From its own powerful properties, and from the various combinations into which it enters, sulphuric acid is of great importance in many ofthe arts. It is used also in medicine in a state of great dilution ; for were it taken internally, in a concentrated state, it would prove a most dangerous poison. Caroline. 1 am sure it would burn the throat and stomach. Mrs. B. Can you think of any thing that would prove an antidote to this poison ? Caroline. A large draught of water to dilute it. Mrs. B. That would certainly weaken the caustic power ofthe acid, but it would increase the heat to an intolerable degree. Do you recollect nothing that would destroy its de- leterious properties more effectually ? Emily. An alkali might, by combining with it; but, then, a pure alkali is itself a poison, on account of its cauticity. Mrs. B. There is no necessity that the alkali should be caustic. Soap, in which it is combined with oil; or magne- sia, either in the state of carbonat, or mixed with water, would prove the best antidote. Emily. In those cases then, I suppose, the potash and the magnesia would quit their combinations to form salts with the sulphuric acid ? Mrs. B. Precisely. We may now make a few observations on the sulphureoMs acid, which we have found to be the product of sulphur slow- ly and imperfectly 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 bulphur/c acid ? Airs. B. Probably ; for by adding oxygen to the weaker acid, it may be converted into the stronger kind. Bat this 216 •F THE SULPHUREOUS ACID. change of state may also be connected with a change of affini- ty with regard to caloric. Emily. And may sulphureous acid be obtained from sul- phuric acid by a diminution of oxygen ? Airs. B. Yes ; it can be done by bringing any combusti- ble substance in contact with, the acid. This decomposition is most easily performed by some ofthe metals ; these absorb a portion of the oxygen from the sulphuric acid, which is thus converted into the sulphureons, and.flies off in its gase- ous form. Caroline. And cannot the sulphureous acid itself be de- composed and reduced to sulphur ? Mrs. B. Yes ; if this gas be-beated in contact with char- coal, the oxygen ofthe gas will combine with it, and the pure sulphur will be regenerated* 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 co- lours, by taking out vegetable stains—I think 1 see a spot on your gowp, 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 Car- oline— Mrs. B. There is no such danger from the sulphureous ; but the experiment must be made with great caution, for du- ring the formation of sulphureous acid by combustion, there is always some sulphuric produced. Caroline. But where is your sulphureous acid ? Mrs. B. We may easily prepare some ourselves, simply by burning a match ; we must first wet the stain with water, and now hold it in this way, at a little distance, over the light- ed match : the vapour that arises from it is sulphureous acid, and the stain, you see, gradually disappears. Emily. I fiave frequently taken out stains by this means, * without understanding the nature of the process. But why is it necessary to wet the stain before it is exposed to the acid fumes ? Mrs. B. The moisture attracts and absorbs the sulphure- ous acid ; and it serves likewise to dilute any particles of sul- phuric acid which might injure the linen. Sulphur appears to be susceptible of a third combination with oxygen, in which the proportion of the latter is too small to render the sulphur acid. It acquires this slight oxy- genation by mere exposure to the atmosphere, without any OF THE SULPHATS. 217 application of heat; in this case, the sulphur does not change its natural form, but is only discoloured, being changed to red or brown, a state in which it may be considered as 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 mo- ment : 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 imme- morial, as a kind of general name for any substance that baa savour, odour, is soluble in water, and crysUllizable, wheth- er it be of an acid, an alkaline, or compound nature ; but the compound salts alone retain that appellation in modern chem- istry. The most important of the salts, formed by the combina- tions of the sulphuric acid, are, first, sulphat of potash, for- merly called sal polychrest: 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 combina- tion of sulphuric acid and potash. This salt is easily soluble (in boiling water. Solubility is, indeed, a property common to all salts ; and they always produce cold in melting. Emily. That must be owing to the caloric which they ab- sorb 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 medicinal salt, which is still more bitter than the preceding We must prepare some of these compounds, that you may ob ssrve the phenomena which take place during their forma- tion. We need only pour some sulphuric acid over the soda which I have put into this glass. Caroline. What an amazing heat is ' disengaged !---1 thought you said that cold was produced by the melting of salts ? Mrs. B. But you must observe that we are now making, not melting a salt. Heat is disengaged during the formation of compound salts, and a faint light is also emitted, which maf sometimes be perceived in the dark. Emily. And is this heat and light produced by the union of the opposite electricities of the alkali and the acid ? Airs. B. No doubt it is, if that theory be true. Caroline. The union of an acid and an alkali is then .*» actual combustion ? 20 218 OF THE SULFHATS. Mrs. B. Not precisely, though there is certainly much analogy in these processes. Caroline. Will this sulphat of soda become solid ? Mrs. 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 immediately changed to a solid mass ; but, in order to obtain it in crystals, as you see it in this bottle, it would be necessary first to dilute it with water, and afterwards to evap- orate the water, during which operation the salt would grad- ually crystallize. Caroline. But of what use is the addition of water, if it is afterwards to be evaporated ? Mrs. B. When suspended in water, the acid and the al- kali are 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 wa- ter of crystallization on being exposed to the atmosphere, and is thus gradually converted into a dry powder : you may observe that these crystals 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 atmosphere, which has de- prived their surface of its lustre, by absorbing its water of crystallization. Salts are, in general, either efflorescent or deliquescent: this latter property is precisely the reverse of th? former; that is to say, deliquescent salts absorb water from the atmosphere, and are moistened and gradually melted by it. Muriat of lime is an instance of great de- liquescence. Emily. But are there no salts that have the same degree of attraction for water as the atmosphere, and that will con- sequently not be affected by it ? Mrs. B. Yes ; there are many such salts, as, for instance, common salt, sulphat of magnesia, and a variety of others. Sulphat of lime is very frequently met with in nature, and constitutes the well-known substance called gypsum or plas- ter of Paris. Sulphat of magnesia, commonly called Epsom salt, is an- other very bitter medicine, which is obtained from sea-water and from several spring, or may be prepared by the direct combination of its ingredients. 0E THE SULPHATS. 2iy We have formerly mentioned sulphat of alumine as consti- tuting the common alum ; it is found in nature chiefly in the neighbourhood of volcanoes, and is particularly useful in the arts, from its strong astringent qualities. It is chiefly em- ployed by dyers and calico-printers, to fix colours ; and i6 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 already well acquainted with. Airs. B. This is the most important metallic salt formed by sulphuric acid, and the only one that 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 pre- parations called steel medicines are composed. Caroline. But does any carbon enter into these composi- tions to form steel ? Mrs. B. Not an atom : they are, therefore, very impro- perly called steel : but it is the vulgar appellation, and medi- cal men themselves often comply with the general custom. Sulphat of iron may be prepared, as you have seen, un- 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 com- pound salts are generally obtained from their various combi- nations, rather than from the immediate union of their ingre- dients. Mrs. B. Were the simple bodies always at hand, their combinations 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 ingredients from their combinations ; it is, therefore, often more expedient to procure compounds from the de- composition of other compounds. But, to return to the sul- phat of iron.—There is a certain vegetable acid called gallic acid, which has the remarkable property of precipitating this salt black—I shall pour a few drops ofthe gallic acid in- to 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 precipitate of sulphat of iron by gallic acid ; the black colour is owing to the formation of gallat of iron, which be- ing insoluble, remains suspended in the fluid. This acid has also the property of altering the colour o 220 PHOSPHORIC AND PHOSPHORUS ACIDS. 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 sup- pose, does not act upon silver.—Is this acid found in all fruits 1 Airs. 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 colour changed to a deep purple, the knife being at the same time blackened. But the vegetable substance in which the 'gallic acid most abounds, is nutgall, a kind of excrescence that grows on oaks, and from which the acid is commonly obtained for its various purposes. Mrs. B. We now come to the phosphoric and phospho- rous 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 diffi- cult to procure phosphorus in its pure state. Airs. B. ' You are right, my dear ; the phosphoric acid, for general purposes, is extracted from bones, in which it is con- tained in the state of phosphat of lime : from this salt the phosphoric acid is separated by means of the sulphuric, which combines with the lime. In its pure state, phosphoric acid is either liquid or solid, according to its degree of con- centration. Among the salts formed by this acid, phosphat of lime is the only one that affords much ? re rest; and this, we have al- ready observed, constitutes the basis of all bones. It is also found in very small quantities in some vegetables. QUESTIONS. What is the chemical name of oil of vitriol r What is the colour and smell of sulph. acid ? What is its specific gravity ? What is the consequence of mixing it with water r What is the process for obtaining sulph. acid ? What the best antidote, when a quantity is swallowed.' How can the sulphuric acid be changed to the sulphurous ? What use is made of sulphurous acid ! What is the easiest process for making this acid ? Define what the term salt means. What is the chemical name and composition of Glauber's Salt I How can sulphate of soda be formed ? What qualities in the salts are denoted by the terms efflorescent and deliquescent? OF THE NITRIC AND NITROUS ACIDS. 221 From whence comes sulph. of alumine? What are its principal uses ? How is sulphate of iron manufactured in the large way ? What substance strikes a black colour with sulph. of iron? Why does the cutting of an apple turn the blade of the knife black ? Where is phosphate of lime chiefly found ? CONVERSATION XVIII. OF THE NITRIC AND CARBONK ACIDS : OR THE COM- BINATIONS OF OXYGEN WITH NITROGEN AND CAR- BON ; AND OF THE NITRATS AND CARBONATS. Airs. B. I am almost afraid of introducing the subject of the nitric acid, as I am sure that I shall be blamed by Car- oline for not having made her acquainted with it before. Caroline. Why so, Mrs. B. ? Mrs. B. Because you have long known its radical, which is nitrogen, or azote ; and in treating of that element, I did not even hint that it was the basis of an acid. Caroline. And what could be your reason for not mention - ing this acid sooner ? Mrs. B. I do not know whether you will think the reason sufficiently good to acquit me ; but the omission, I assure you, did not proceed from negligence, You may recollect that nitrogen was one of the first simple bodies which we ex- amined ; yon were then ignorant of the theory of combus- tion, which I 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. I wonder, however, that it never occurred to us to inquire whether nitrogen could be acidified : for, as we knew it was classed among the combustible bodies, it was na- tural to suppose that it might produce an acid. Mrs. B. That is not a necessary consequence : for it might combine with oxygen only in the degree requisite to form an oxyd. But you will find that nitrogen is susceptible of various degrees of oxygenation, some of which convert it merely into an oxyd, and others give it all the acid proper- ties. The acids, resulting from the combination of oxygen and nitrogen, are called the nitrous 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 that it has never been obtained perfectly free from it. OF THE NITRIC But water may be so strongly impregnated with it as to form an exceedingly powerful acid solution. 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 contains a greater abundance of oxy- gen than any other ; but it retains it with very little force. Emily. Then it must be a powerful caustic, both from the facility with which it parts with its oxygen, and the quan- tity which it affords. Mrs. B. Very well, Emily ; both cause and effect are ex- actly such as you describe : nitric acid burns and destroys all kinds of organised 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 decomposed by com- bustible bodies, since these effects must depend upon the ab- sorption of its oxygen. Nitric acid has been used in the arts from time immemo- rial ; 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 parts of nitrogen and 25 of oxygen.| These principles, in their gas- eous state, combine at a high temperature ; and this may be effected by repeatedly passing the electrical spark through a mixture ofthe two gases. Emily, The nitrogen and oxygen gases, of which the at- mosphere is composed, do not combine, I suppose, because their temperature is not sufficiently elevated. Caroline. But in a thunder-storm, when the lightning re- peatedly passes through them, may it not 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 light- ning can affect but a very small portion of the atmosphere, and though it were occasionally to produce a little nitric acid, it never could happen to such an extent as to be perceivable. * To inflame charcoal, a stronger acid than that sold at the shops is necessary. The experiment with ol. turpentine and phosphorus, succeeds, if about a sixth part of sulph. acid is added to the nitric 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 email quantity of the turpentine, standing at a distance. C. f The proportion stated by Sir H. Davy, in his Chemical Re- yearcaes, is aa lto 2,389. AND nitrous acids. 22o Emily. But how could the nitric acid be known, and used, before the method of combining its constituents was discov- ered ? Mrs. B. Previous to that period the nitric acid was obtain- ed, and it is indeed still extracted, for the common purposes of art, from the compound salt which it forms with potash, commonly called nitre. Caroline. Why is it so called ? Pray, Mrs. B., let these old unmeaning names be entirely given up, by us at least; and let us call this salt nitrat of potash. 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 potash, and sets the nitric acid at liberty. This 1 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 Caroline will allow me to mention that name. Caroline. I 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 derived the name of aqua fortis, or strong water. Do you not recollect that we oxychted, and afterwards dissolved, some copper in this acid ? Emily. If I remember right, the nitrat of copper was the first instance you gave us of a compound salt. Caroline. Can the nitric acid be completely decomposed and converted into nitrogen and oxygen ? Emily. That cannot be the case, Caroline ; since the acid can be decomposed only by the combination of its constitu- ents 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 legain the calor- ic which they had lost in combining, and are thus both re- stored to their gaseous state. The nitric acid may also be partly decomposed, and is by this means converted into nitrous acid. 224 OF THE NITRIC Caroline. This conversion must be easily effected, as the oxygen is so slightly combined with the nitrogen. Airs. B. The partial decomposition of nitric acid is readi- ly effected 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 converted into nitrous acid. This latter acid appears in various degrees of strength, according to the pro- portions of nitrous acid gas and water of which it is composed ; the strongest is a yellow colour, as you see in this bottle. Caroline. How it fumes when the stopper is taken out! Mrs. 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 orange red; this acid is weaker, that is, contains a smaller quantity of the acid gas ; and with a still less pro- portion of the gas it is of an olive-green colour, as it appears in this third bottle. In short, the weaker the acid, the deep- er is its colour. Nitrous acid acts still more powerfully on some inflamma- ble substances 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 inflam- ed oil with this acid. The next combinations of nitrogen, and oxygen form only oxyds of nitrogen, the first of which is commonly called ni- trous 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 specimen of which 1 have prepared, and preserved with this inverted glass bell. Emily. It is a perfectly invisible elastic fluid. Airs. B. Yes ; and it may be kept any length of time in this manner over water, as it is not, like the nitric and nitrous acids, absorbable by it. It is rather heavier than atmospher- ical air, and is incapable of supporting either combustion or respiration. I am going to incline the glass gently on one side, so as to let some ofthe gas escape— Emily. How very curious!—It produces orange fumes * 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 heat of a lamp, and receive the gaB in the usual way, over water. C. ANB NITROUS ACIDS. 22a 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 requiiing any further explanation. Caroline. It seems, by the colour and smell, as if it were converted 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 wa- ter, so as to bring at once the whole of the gas into contact with the atmosphere, this conversion will appear still more striking— Emily. Look, Caroline, the whole capacity of the bottle is instantly tinged of an orange colour ! Mrs. B. Thus, you see, it is the most easy process ima- ginable to convert nitrous oxyd gas into nitrous acid gas. The property of attracting oxygen from the atmosphere, without any elevation of temperature, has occasioned this gaseous oxyd being used as a test for ascertaining the degree ot puri- ty of the atmosphere. I am going to show you how it is ap- plied to this purpose.—You see this graduated glass tube, which is closed at one end, (Plate X. fig. 2.)—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 ofthe tube. I must now add rather above two-thirds of oxygen gas, which will just be sufficient to convert the nitrous oxyo* gas into nitrous acid gas. Caroline. So it has !—I saw it turn of an orange colour ; but it immediately afterwards disappeaied entirely, and the water, you see, has risen, and almost filled the tube. Mrs. B. That is because Ihe acid gas is absorbable by water, and in proportion as the gas impregnates the water, the latter ri«es in the tube. When the oxygen gas is very pure, and the required proportion of nitrous oxyd gas very exact, th-2 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 arr1 occupy the upper part of the tube ; or if the gases I * not in the due proportion, there will be a residue of that which predominates.—Before we leave this subject. I must not forget to remark that nitrous 226 OF THE NITRIC acid may be formed by dissolving nitrous oxyd gas in nitric acid. This solution may be effected simply by making bub- bles of nitrous oxyd gas pass through nitric acid. Emily. That is to say, that nitrogen at its highest degree of oxygenation, being mixed with nitrogen at its lowest de- gree of oxygenation, will produce a kind of intermediate substance, which is nitrous acid. Mrs. B. You have stated the fact with great precision.—- There are various other methods of preparing nitrous oxyd, and of obtaining it from compound bodies ; but it is not ne- cessary to enter into these particulars. It remains for me only to mention another curious modification of oxygenated nitrogen, which has been distinguished by the name of gase- 9us oxyd of nitrogen. It is but lately that this gas has been accurately examined, and its properties have been investiga- ted chiefly by Sir H. Davy. It has obtained also the name of exhilarating gas, from the very singular property which that gentleman has discovered in it, of elevating the animal spirits, when inhaled into the lungs, to a degree sometimes resem- bling delirium or intoxication. Caroline. Is it respirable, then ? Airs. B. It can scarcely be called respirable, as it would not support life for any length of time ; but it may be breath- ed for a few moments without any other effects than the sin- gular exhilaration of spirits I have just mentioned. It affects different people, however, in a very different manner. Some become violent, even outrageous ; others experience a lan- guor, 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 mouth 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 per- ceive its effects. But I cannot consent to your making the experiment; for the nerves are sometimes unpleasantly af- fected 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 ? Airs. B. It is procured from nitrat of ammonia,* an artifi- * To make nitrate of ammonia, take some nitric acid, or aquafor- tis—dilute it with four or five parts of water ; put it into a shallow earthen dish, and throw in pieces of carbonate of ammonia, until the effervescence ceases. Evaporate about one third of the liquor AND NITROUS ACIDS. 227 cial 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 a 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 ? s~ Mrs. B. The gas that first comes over need not be pre- served, as it consists of little more than common air that was in the retort ; besides, there is always in this experiment, a quantity of watery vapour 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 evapora- ted by heat alone. But, besides this, water is actually gen- erated 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 nitro- gen, forms the acid. Mrs. B. Well then, in this process the ammonia is de- composed ; 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 cominir over. When that is ef- fected, what will you expect to find ? by a gentle heat, and set it away to crystallize. The crystals are long striated prisms. To procure the nitrous oxide or exhilarating gas, and to try its effects by respiration, the following simple appa- ratus may be used, where a better is not at hand. Put some nitrate of ammonia into an oil flask, have first fitted to it a cork, and glass tube, bent so as to go under the receiver in the water bath. 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 iron ; into one of these holes put a glass tube open at both ends, and nearly long enough to reach the bottom of the jug. Provide a large bladder furnished with a short tube tied to it. When the jng 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, take the stopper out of the cork, and pass in the tube attached to the bladder. Then by means of a small tunnel, pour water into the j'lg through the long tube, until it drives out gas enough to fill the bladder. Mrs. B. describes the manner of breathing it. Caution. Eet the gas stand an hour or two over water before it it breathed. C. .^28 OF THE NITRIC Endly. Nitrous acid instead of nitric acid, and nitrogen instead of ammonia. Mrs. B. Exactly so ; and the nitrous acid and nitrogen eombine, and form the gaseous oxvd of nitrogen, in which the proportion of oxygen is >7 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 bub bles ot air again make their appearance, and I imagine that by this time all the watery v ipour 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, antl plunging a taper into it—yes, it will do now, for the taper burns brighter than in the com- mon air, and with a greenish flame. Caroline. But how is that ? I thought no gas would sup- port combustion but oxygen or chlorine. Mrs. B. Op 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 produced 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 general survey of the most important com- binations of the nitric and nitrous 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 nitre to one of sulphur, and one of charcoal.—Nitre, from its great proportion of oxygen, and from the facility with which it yields it, is the basis of the most detonating compo- sitions. Emily. But what is the cause of the violent detonation •f gunpowder when set fire to ? Mrs. B. Detonation may proceed from two causes ; the sudden formation or destruction of an elastic fluid. In the first case, when either a solid or liquid is instantaneously converted into an elastic fluid, the prodigious and sudden ex- pansion 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 ©F THE NITRATS. 229 a liquid or solid state ; when this takes place suddenly, the gas, in assuming a new and compact form, produces a vacu- um, into which the surrounding air rushes with great impet- uosity ; 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 oY these two circumstances takes place ? Emily. As gunpowder is a solid, it .must, of course, pro- duce the gases in its detonation ; but how, I cannot tell. Mrs. B. The constituents of gunpowder, when heated to a certain degree, enter into a number of new combinations, and are instantaneously converted into a variety of gases, the sudden explosion of which gives rise to the detonation. Caroline. And in what instance does the destruction or condensation of gases produce detonation ? Mrs. B. I can give you one with which you are well ac- quainted ; the sudden combination of the oxygen and hydro- gen gases. Caroline. True ; I recollect perfectly that hydrogen de- tonates with oxygen when the two gases are converted into water. Airs. B. But let us return to the nitrat of potash.—This salt is decomposed when exposed to heat, and mixed with any combustible body, such as carbon, sulphur, or metals, these substances oxydating rapidly at the expense of the nitrat. I must show you an instance of this.—I expose to the fire some of the salt in a small iron ladle, and,ewhen it is suffi- ciently heated, add to it some powdered charcoal ; this will attract the oxygen from the salt, and be converted into car- bonic acid.— Emily. But what occasions that crackling noise, and those vivid flashes that accompany it ? Airs. B. The rapidity with which the carbonic acid gas is formed, occasions a succession of small detonations, which, together with the emission of flame, is called deflagration. Nitrat of ammonia we have already noticed, on account of the gaseous oxyd of nitrogen which is obtained from it. Nitrat of silver is the lunar caustic, so remarkable for its destroying animal fibre, for which purpose it is often used by surgeons. 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 21 930 CARBONIC acid. its imperfect state of charcoal, or in its purest form of dia- mond. And it is not necessary, for this purpose, to burn the carbon in.oxygen 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 ex- tinguished, 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 it is mixed ? Mrs. B. The readiest mode is to introduce under the re- ceiver a quantity of caustic lime, or caustic alkali, which soon attracts the whole carbonic acid to form a carbonat.— The alkali i9 found increased in weight, and the volume of the air is diminished by a quantity equal to that of the car- bonic acid which was mixed with it. Emily. Pray is there no method of obtaining pure carbon from carbonic acid ? Mrs. 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 burn- ing 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 separated in the form of a black powder. This decomposition, however, is not effect- ed simply by the attraction of the phosphorus for oxygen, 9ince it is weaker than that of charcoal ; but the attraction of the alkali or lime for the phosphoric acid, unites its pow- er 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 at- tempt it. But there can be no doubt of the accuracy of Mr. Tennant's results ; and all chemists now agree, that one hun- dred 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 did ; and found the carbon pre- cipitated on the regenerated potash. Mrs. B. Carbonic acid gas is found very abundantly in na ture ; it is supposed to form about one thousandth part ot the atmosphere, and is constantly produced by the respiration of animals ; it exists in a great variety of combinations, and i< CARBONIC ACID. 234 exhaled from many natural 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 grat- ify the curiosity of strangers. But I understood that the va- pour exhaled by this cave was called fixed air. Mrs. B. That is the name by which carbonic acid wag 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 extin- guish the light as it were by enchantment, as the gas is invis- ible. 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 pour- ed 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. Combined with lime, this acid forms chalk, which may be considerod as the basis of all kinds of marbles, and calcareous stones. From these substances carbonic acid is easily separated, as it adheres so slightly to its combinations, that the carbonats are all decomposable by any of the other acids. I can 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 pre- pare hydrogen gas,) and the gas escaped through 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 ! * 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. 232 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 state of com- bination, is capable of" existing in a solid form. Caroline. Whence, then, does it obtain the caloric ne- cessary to convert it into gas ? Mrs. B. It may be supplied in this case from the mixture of sulphuric acid and water, which produces an evolutio n o heat, even greater than is required for the purpose ; since, as you may perceive by touching the glass vessel, a consider- able 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 disengag- ed 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, be- cause 1 think I can put you in a way of doing it yourself. Is carbonic acid combustible ? ' Caroline. Why, no—because it is a body which has beea already burnt ;* it is carbon only, and not the acid that is combustible. Mrs. B. Well, and what inference do you draw from this 1 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 variety of other combustible bodies. Indeed, Mrs. B., you are very ungenerous ; you are not sat- isfied with convincing me that my objections are frivolous, but you oblige me to prove them so mys,elf. Mrs. B. You must confess, however, that I make ample amends for the detection of error, when 1 enable you to dis- cover the truth. You understand, now, I hope, that carbon- ic acid is equally produced by the decomposition of chalk, or by the combustion of charcoal. These processes are cer- * Not burnt in the common acceptation of the word. The car- bon is already united to oxygen^ and therefore has no affinity for it. In the artificial production of carbonic acid, the carbon is burnt. C. CARBONIC ACID. 233 tainly of a very different nature ; in the first case the acid is already formed, and requires nothi.ig more than heat to re- store 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 ex- cuse 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 com- bined ? Mrs. B. The question is, indeed, not very easy to an- swer ; but I conceive that the general carbonization of calca- reous matter may have been the effect of a general combus- tion,* occasioned by some revolution of our globe, and pro- ducing an immense supply of carbonic acid, with which the calcareous matter became impregnated ; or that this may have been effected by a gradual absorption of carbonic acid from the atmosphere. But this would lead us to discussions which we cannot indulge in, without deviating loo much from our subject. Emily. How does it happen that we do not perceive the pernicious effects ofthe 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 oth- er substances, that contain carbon. Airs. B. And also the breath of animals. Caroline. The breath of animals ? I thought you said that this gas was not at all respirable, but on the contrary; ex- tremely poisonous. Mrs. B. So it is ; but although animals cannot breathe in carbonic acid gas, yet, in the process of respiration, they have the power of forming this gas in their lungs ; so that the air which we expire, or reject from the lungs, always contains a certain proportion of carbonic acid, which is much greater than that which is commonly found in the atmosphere. Caroline. But what is it that renders carbonic acid such a deadly poison ? Mrs. B. The manner in which this gas destroys life, * This idea is at random. We cannot account for the origin of carbonic acid in its native state any better tnan we can for oxygen. It cannot be the product of combustion, since it existed before the growth of combustible materials. C. 21* 234 CARBONIC ACID. seems to be merely by preventing the access of respirable air, for carbonic acid gas, unless very much diluted with com- mon air, does not penetrate into the lungs, as the windpipe ac- tually contracts and refuses it admittance.—But we must dis- miss 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 veget- ables as it is to that of animals ? Mrs. B. If a vegetable be completely immersed in it, I believe it generally proves fatal to it ; but mixed in certain proportions with atmospherical air, it is on the contrary, very favourable to vegetation. You remember, I suppose, our mentioning the mineral wa- ters, both natural and artificial, which contain carbonic acid gas ? Caroline. You mean the Seltzer water ? Mrs. B. That is one of those which are the most used ; there are, however, a variety of others into which carbonic acid enters as an ingredient : all these waters are usually dis- tinguished by the name of acidulous or gaseousmineral waters. The class of salts called 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 de- tail. The state of carbonat is the natural state of a vast num- ber of minerals, and particularly of the alkalies 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 separating them from this acid, that they acquire that causticity and those striking qualities which I have formerly described. All marbles, chalks, shells, calcareous spars, and limestones of every de- scription, are neutral salts, in which lime, their common basis, has lost all its characteristic properties. • Emily. But if all these various substances are formed by the union of lime with carbonic acid^ whence arises their di- versity of form and appearance ? Mrs. B. Both from the different proportions of their com- ponent parts, and from a variety of foreign ingredients which may be occasionally blended with them : the veins and co- lours of marbles, for instance, proceed from a mixture of me- tallic substances ; silex ahd alumine also frequently enter into these combinations. The various carbonats, therefore, which I have enumerated, cannot be considered as pure unadultera- ted neutral salts, although they certainly belong to that das* of bodies. G0KACIC ACID. 235 QUESTIONS. What acids are formed by the combination of nitrogen and oxygen ? What acid contains the greatest proportion of oxygen? Explain the reason why nitric acid inflames charcoal, ol. turpen- tine, &c. How is nitric acid obtained, and from what substance ? How can nitric, be converted into nitrous, acid ; and what is the cause of the change ? Why does nitric acid act with peculiar energy on combustibles ? How can nitrous air be procured from nitric acid, and what is the principle ? How is nitrous air converted into nitrous acid gas ? On what principle can nitrous air be applied to test the purity ofthe atmosphere ? What is the process ? How is the exhilarating gas procured ? Describe the process of making nitrate of ammonia. ' What caution is necessary before it is breathed ? When do chemical decompositions and combinations take place du- ring the formation of this gas from nitrate of ammonia? Why is nitrate of potash used in making gun powder, rather than any other salt ? What causes the detonation when gun powder is fired? What gas is formed when charcoal is burned in oxygen gas ? By what method can charcoal be procured from carbonic acid ? What portion of the atmosphere is formed of this gas ? By what means is this gas procured for experiment? From whence came the immense quantity of carbonic acid contain- ed in limestone rocks ? In what manner does this gas destroy life ? What effect does it have on vegetation ? What are the waters called which contain this gas? What are the salts called which are partly composed of this gas ? How extensive is this class of salts, and under what forms do they chiefly occur in nature ? CONVERSATION XIX. UN THE BORACIC, FlLuORIC, MURIATIC, A?sD OXY- GENATED MURIATIC ACIDS; AND ON MURIATS.— ON IODINE AND IODIC ACID. Mrs. B. We now come to the three remaining acids with simple bases, the compound nature ef which, though long suspected, has been but recently proved. The chief of these is the muriatic ; but I shall first describe the two oth- ers, 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, but for the 236 BORACIC ACID. use of manufactures we have always received it from the re- mote cbuntry of Thibet, where it is found in some lakes, combined with soda. It is easily separated from the soda by sulphuric acid, and appep.rs in the form of shining scales, as you see here. Caroline. I am glad to meet with an acid which we need not be afraid to touch ; for I perceive, from your keeping it in a piece of paper, that it is more innocent than our late ac- quaintance, the sulphuric and nitric acids. Mrs. B. Certainly ; but being more inert, you will not find its properties so interesting. However its decomposi- tion, and the brilliant spectacle it affords when its basis again unites with oxygen, atones for its want of other 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 positive wire gave out oxygen, and on the nega- tive wire was deposited a black substance, in appearance re- sembling 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 quantities, by exposing the acid to a great heat in an-iron gun- barrel. A third method of decomposing the boracic acid consisted in burning potassium in contact with it in vacuo. The pot- assium attracts the oxygen from the acid, and leaves its basis in a separate state. The recomposition of this acid I shall show you by burn- ing some of its basii, 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 beau- tiful sparks it throws out! Airs. 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 bora- cic 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 common- ly called borax. This salt has a peculiar power of dissolving metallic oxyds, and of promoting the fusion of substances ca- pable of being melted ; it is accordingly employed in vari- ous metallic arts ; it is used, for example, to remove the ox- FLUORIC ACID. 237 yd from the surface of metals, and is often employed in the assaying of metallic ores. Let us now proceed to the fluoric acid. This acid is obtained from a substance which is found frequently in mines, and particularly in those of Derbyshire, called^wor, a name which it acquired from the circumstance of its being used to render the ores of metals more fluid when heated. Caroline. Pray is not this the Derbyshire spar, of which so many'ornaments are made ? Mrs. B. The same ; but though it has long been employ- ed for a variety of purposes, its nature was unknown until Scheele, the great Swedish chemist, discovered that it con- sisted 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 condensed in water, ascends in the form of gas. A very peculiar property of this acid is its union with silicious earths, which I have already men- tioned. If the distillation of this acid is performed in glass vessels, they are corroded, and the silicious part ofthe glass comes over, united with the gas ; if water is then admitted, part of the silex is deposited, as you may observe in this 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 covered 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 engravings.* Mrs. B. But you could not have it in a glass bottle ; for in that case the acid would be saturated with silex, and inca- pable of executing an engraving ; the same thing would hap- * 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, drawings are easily and beautifully made on glass. C. 238 MURIATIC ACID. pen were the acid kept in vessels of porcelain or earthen- ware : this acid must therefore be both prepared and pre- served in vessels of silver. If it be distilled from floor 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 intensely corrosive substance known. This seems to be the acid combined with a little water. It may be called hydrofluoric acid; and Sir H. Davy has been led, from some late experiments on the subject, to consider pure fluoric acid as a compound of a certain unknown princi- ple, which he calls fluorine, with hydrogen. Sir H. Davy has also attempted to decompose the fluoric acid by burning potassium in contact with it; but he has not yet been able, by this or any other method, to obtain its ba- sis in a distinct separate state. We shall conclude our account of the acids with that of the muriatic acid, which is, perhaps, the most curious and interesting of all of them. It is found in nature combined with soda, lime and magnesia. Muriat of soda is the common sea-salt ; and from this substance the acid is usually disen- gaged by means of the sulphuric acid. The natural state of the muriatic acid is that of an invisible permanent gas, at the common temperature of the atmosphere ; but it has a re- markably strong attraction for water, and assumes the form of a whitish cloud whenever it meets any moisture to com- bine with. This acid is remarkable for its peculiar and very pungent smell, and possesses, 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 at- traction 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 acid gas, of itself in- visible, but made apparent by combining with the moisture of the atmosphere. Emily. Have you not any of the pure muriatic acid gas ? Mrs. 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 MURIATIC ACID. 239 moisture of the atmosphere, that it is converted into this dewy vapour. Mrs. B. Certainly ; and for the same 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 attempted to decompose it, than the other two undecompoun- ded acids. It is singular that potassium will burn in muriatic acid, and be converted into potash, without decomposing the acid, and the result of this combustion is a muriat 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 oxydate the potassium ? Mrs. B. The potassium, in this process, obtains oxygen from the moisture with which the muriatic acid is always combined, and, accordingly, hydrogen, resulting from the de- composition of the moisture, 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 bat- tery, because 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 ob- served that the presence of water appeared always neces- sary to develope the acid properties, so that acids are not even capable of reddening vegetable blues if they have been carefully deprived of moisture. This remarkable circum- stance led him to suspect, that water, instead of oxygen, may be the acidifying principle ; but this he threw out rather as a conjecture than as an established point. Sir H. Davy obtained very cnrious 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 pre- senting to his view the basis ofthe muriatic acid, of which he was in search ; and he was at last induced to form an opin- ion respecting the nature of this acid, which I shall presently explain. Emily. Is this acid susceptible of different degrees of oxygenation ? Airs. B. Yes : for though it cannot be deoxygenated, yet we may add oxygen to it. Caroline. Why, then, is not the least degree of oxygena- tion of the acid called the muriatous, and the higher degree the muriatic acid ? 242 OXY-MURIATIC ACID. in the same manner in oxy-muriatic acid gas ; but I have not prepared a sufficient quantity of it, to show the combustion of all hese bodies. Caroline. There are several jars ofthe gas yet remaining. Mrs. B. We must reserve these for future experiments. The oxy-muriatic acid does not, like othe¥ifbids, redden the blue vegetable colours ; but it totally destroys all colour, and turns' vegetables perfectly white. Let us collect some vegetable substances to put into this glass, which is full of gas. Emily. . Here is a sprig of myrtle— Caroline. And here some coloured paper— Mrs. #t We shall also put in this piece of scarlet riband, and a rose— Emily. Their colours begin to fade immediately. But how does the gas produce this effect ? Mrs. B. The oxygen combines with the colouring matter of these substances, and destroys it ; that is to say, destroys the property which these colours had of reflecting only one kind of rays, and renders them capable of reflecting them all, which, you know, will make them appear white. Old prints may be cleaned by this acid, for the paper will be 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 ofthe oxy-muriatic acid has lately been ena- ployed in manufactures in a variety of bleaching processes; but for these purposes the gas must be dissolved in water, as the acid is thus rendered much milder and less powerful in its effects ; for, in a gaseous state, it would destroy the tex- ture, as well as the colour of the substance submitted to its action. Caroline. Look at the things which we put into the gas ; they have now entirely lost their colour? Airs. B. The effect ofthe acid is almost completed ; arid if we were to examine the quantity that remains, we should find it to consist chiefly of muriatic acid. The oxy-muriatic acid has been used to purify the air in fever 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 has been sub- mitted to its influence will no longer generate that disorder. Caroline. Indeed, I think the remedy must be nearly as bad as the disease ; the oxy-muriatic acid has such a dread- fully suffocating smell. Mrs. B. It is certainly extremely offensive^: but by keep- ing the mouth shut, and wetting the nostrils with liquid ammo- OXV-MURIATIC ACID. 243 nia, in order to neutralize the vapour as it reaches the nose, its prejudicial effect"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 vapour of ni- tric acid, which iftfltorcely less efficacious for this purpose, is not at all prej^^pal, it is usually preferred on such occa- sions. Caroline. You have not told us yet what is Sir H. Davy's new opinion respecting the nature of muriatic acid, to which you alluded a few minutes ago ? Mrs. B. True ; I avoided noticing it then, because you could not have understood it without some previons know- ledge ofthe oxy-muriatic-acid, which I have but just introdu- ced to your acquaintance. Sip-H. Davy's idea is, that muriatic acid, instead of being a compound, consisting of an unknown basis and oxygen, is formed by the union of oxy-muriatic 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 ; bait according to Sir H. Davy's hypothesis, oxy muriatic gas is considered as a simple body, which con- tains no oxygen—as a substance of its own kind, which has a great analogy to oxygen in most of its properties, though in others it differs entirely from it —According to this view of the subject, the name of oxy-muriatic acid can no longer be proper, and therefore Sir H. Davy has adopted that of chlo- rine, or chlorine gas, a name which is simply expressive of its greenish colour ; and in compliance with that philosopher's theory, we have placed chlorine in our table among the sim- ple bodies. Caroline. But what was Sir H. Davy's reason for adopting an opinion so contrary to that'which had hitherto prevailed? Mrs. B. Theigflfe many circumstances which are favour- able to the new ddftrTne ; but the clearest and simplest fact in its support is, 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 con- sidered as perfectly conclusive ? Mrs. B. Not so decisive as it appears at first sight; be- cause it is argued by those who «till incline to the old doc- trine, that muriatic acid gas, however dry it may be, always contains a certain quantity of water, which is supposed essen- tial to its formation. So that, in the experiment just mention- ed, this water is supplied by the'union of the hydrogen gas with the oxygen ofthe oxy-muriatic acid ; and therefore the 244 MURIATS. mixture resolves itself into the base of muriatic acid and wa- ter, that is, muriatic acid gas. ^^ Caroline. I think the old theory must be the true one ; for otherwise how could you explain the_ formation of oxy- muriatic gas, from a mixture of muriatic^^and oxyd of man- ganese ? ^^P Mrs. B. Very easily ; you need only suppose that in this process the muriatic acid is decomposed ; its hydrogen unites with the oxygen 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 con- taining no oxygen ? Mrs. B. We need only suppose that combustion is the result of intensechemical action ;* so that chlorine, like oxy- gen, in combining with bodies, forms compounds which have less capacity for caloric than their constituent principles, and, therefore, caloric is evolved at the moment of their combina- tion. Emily. If, then, we may explain every thing by either theory, to which ofthe two shall we give the preference ? Airs. B. It will, perhaps, be better to wait for more deci- sive proofs, if such can be obtained, before we decide posi- tively upon the subject. The new doctrine has certainly gained ground very rapidly, and may be considered as gene- rally established ; but a few competent judges still refuse their assent to it, and until that theory is established beyond all doubt, it may be as well for us still occasionally to use the language to which chemists have long been accustom- ed.—But let us proceed to the examination of salts formed by muriatic acid. Among the compound^alts.formed by muriatic acid, the muriat of soda, or common salt, is the mJBfciteresting.t The uses and properties of'tms salt are too wen knqwnto require * " Intense chemical action," neither explains the process, nor indeed conveys to the mind any definite idea. The views of Sir FT. Davy on the composition of chlorine, are combatted by many ofthe 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 chemis- try. C. f According to Sir H. Davy's views of the nature of the muriat- ic and oxy-muriatic acids, dry muriat of soda is a compound of sodi- um and chlorine, for it may be formed by the direct combination of oxy-muriatic gas and sodium. In his opinion, therefore, what we commonly call muriat of soda, contains neither soda nor muriatic acid. MURIATS. 245 much comment. Besides the pleasant flavour it imparts to the food, it is very wholesome, when not used to excess, as it assists the process of digestion. Sea-water is the great source from which muriat of soda is extracted by evaporation. But it is also found in large solid masses in the bowels of the earth, in England, and in many other parts ofthe 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. Mrs. B. Crystallization depends, as you may recollect, on the slow and regular reunion 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. Muriat of ammonia is another combination of this^acid, which we have already mentioned as the principal source from which ammonia is derived. I can at once show you the formation of this salt by the im- mediate 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 pla- ced in the jar in which these gases are mixed, you would per- ceive that some heat is at the same time produced. Emily. The effects of chemical combinations are, indeed, wonderful !—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 phenomena which nature seldom exhibits to our view ; but the most common of her operations are as wonderful, and it is their frequency 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 muriat of ammonia which you once show- ed us! Mrs. 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. 22* 246 OXY-MURIATS. We now proceed to the ozy-muriats. In this class of salts the oxy-muriat of potash* is the most worthy of our atten- tion, for itd striking 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 increase of oxygen by combining with potash ? Mrs. B. It does not really acquire an additional quantity of oxygen, but it loses some of the muriatic acid, which pro- duces the same effect, as the acid which remains is propor- tionably super-oxygenated.t If this salt be mixed, and merely rubbed together with sulphur, phosphorus, charcoal, or indeed any other combus- tible, it explodes strongly. Caroline. Like gun-powder, I suppose, it is suddenly con- verted into elastic fluids ? Mrs. B. Yes : but with this remarkable difference, that no increase of temperature, any further than is produced by gentle friction, 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 converted into muriatic acid gas ; whilst the char- coal, 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 combinations, I do not understand of 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 ef- fects. Yon see I mix an exceedingly small quantity of the salt with a little powdered charcoal, in this Wedgwood mor- tar, and rub them together with the pestle— * Oxy-muriat of potash is prepared by passing chlorine through a solution of potash in water. The process is long and difficult. C. f According to Sir H. Davy's new views, just explained, oxy- muriat of potash is a compound of chlorine with oxygen and oxyd ef potassium. OXY-MURIATS. 247 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 quan- tity of solid substance may produce a very great volume of gases ; and it is the sudden evolution of these which occa- sions the sound. Emily. Would not oxy-muriat of potash make stronger gun-powder than nitrat of potash ? Airs. B. Yes ; but jthe 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, I think ; for the common gun-powder is q'uite 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 nev- er attempt to repeat it by yourselves. I throw a small piece of phosphorus into this glass of water ; then a little oxy-mu- riat of potash : and lastly, I pour in (by means of this funnel, so as to bring it in contact 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 phosphorus takes fire and burns from the bottom of the wa- ter. Emily. How wonderful it is to see flame bursting out un- der water, and r;sing through it! Pray, how is this accoun- ter for ? Mrs. B. Cannot you find it out, Caroline ? • Emily. Stop—I think I can explain it. Is it not because the sulphuric acid decomposes the salt by combining with the potash, so as to liberate the oxy-muriatic acid gas by which the phosphorus is set on fire ? Mrs. B. Very well, Emily ; and with a little more reflec- tion you would have discovered another concurring circum- stance, which is, that an increase of temperature is produced by the mixture of the sulphuric acid and water, which assists in promoting the combustion of the phosphorus. I must, before we part, introduce to your acquaintance the newly 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 com- bustion like oxygen and chlorine ? Mrs. B. It is ; and although it does not so generally dis- engage light and heat from inflammable bodies, as oxygen and ^chlorine do, yet it is capable of combining with most of them ; and sometimes, as in the instance of potassium and phospho- 248 * OXY-MVRIATS. rus, the combination is attended with an actual appearance of of light and heat. Caroline. But what sort of a substance is iodine : what is its form and colour ? Mrs. B. It is a very singular body, in many respects. At the ordinary temperature of the atmosphere, it commonly appears in the form of blueish 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 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. How curious! They seem to melt, and the tube immediately fills with the beautiful violet vapour. But look, Mrs. B., the same scales are now appearing at the other end of the tube. Mrs. B. This is,.in fact, a sublimation of iodine, from one part ofthe tube to another; but with this remarkable pecul- iarity, 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 ofthe gas that iodine has obtained its name Caroline. But how is this curious substance obtained ? Ms. B. It is found in the ley of ashes, ot sea-weeds, after the soda has been separated by crystallization ; and it is dis- engaged by means of sulphuric acid, which expels it from the alkaline ley in the form of a violet gas, which may be collec- ted and condensed in the way which you have just seen.— This interesting discovery was made in the year 1812, by M. Courtois, a manufacturer of saltpetre at Paris. Caroline. And pray, Mrs. B., what is the proof of iodine being a simple body ? 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 bod- ies, in a manner analogous to oxygen and chlorine. The mo9t curious of these combinations 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 OXY-MURIATS. 249_ 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. QUESTIONS. What is the basis of boracic acid ? What is the composition of borax ? What are its uses ' From whence is Jluoric acid obtained? W hat are its peculiar properties? Describe the method of etching on glass. With what is muriatic acid chiefly found combined ? AV"hat is the natural state in which this exists? How can this gas be confined wit^ut a mercurial bath? What is the basis of muriatic acid? m Is this acid capable of combining with different proportions of oxy- gen ? Why is not the least degree of oxygenation called the muriatous acid ? How is oxy-muriatic acid obtained ? ^» Explain the reason why metals inflam^^Bbgas. W hy does a mixture of nitric, and mu^Kcali^lissolve gold, when neither of them will do it alone? ^h &JP^- Why does oxy-muriatic acid turn thevtl^mlof vegetables while? Of what use is this acid in the arts? -4^_ Why is oxy-muriatic acid lately called chlorine? What are the reasons for supposing that chlorine is a simple sub- stance ? What are the reasons for supposing that it is not a simple substance? From whence, and by what process is muriate of soda obtained ? What two gases, when mixed, form muriate of ammonia? Describe ihe experiment. W hat are the peculiar properties of oxy-.muriate of potash ? Why does it explode on being rubbed with charcoal, sulphur, &c. What gases are generated at the moment of explosion with char- coal ? -Explain the changes which take place, and the cause of - the detonation. How can phosphorus be set on fire at the bottom of a vessel of wa- ter ? and how do you account for it ? What are the peculiarities of iodine? How can you show the violet coloured gas ? From whence is iodine obtained? Why is it considered a simple body : 250 COMPOSITION CONVERSATION XX. ON THE NATURE AND COMPOSITION OF VEGET- ABLES. Mrs. B. We have hitherto treated only of the simplest combinations of elements, such as alkalies, earths, acids, compound salts, stones, &c. ; all of which belong to the min- eral kingdom. It is time now to turn our attention to a more complicated class of compounds, that of organized bodies, which will furnish us with a new source of instruction and amusement. . Emily. By organized bodies, I suppose you mean the ve- getable and animal creation ? I have however, but a very vague idea of,the word organization, and I have often wished to know more precisely what it means. Mrs. B. Organized bodies are such as are endowed by nature with vario^ parts, peculiarly constructed and adapted to perform certain functions connected with life. Thus you may observe, that mineral compounds are formed by the sim- ple effect of mechanical or chemical attraction, and may ap- pear to some to be, in^i great measure, the productions of chance ; whilst orgajfcgL bodies bear the most striking and impressive marksjfl K and are eminently distinguished^ by that unknown JH If, called life, from which the vari- ous organs derive die power of exercising their respective functions. Caroline. But in what manner does life enable these or- gans 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. We must content ourselves 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 vague and unsatisfactory idea of an unknown agent. Caroline. And yet I think I can fqrm a very clear idea of life. Mrs. B. Pray let me hear how you would define it 1 Caroline. It is perhaps more easy to conceive than to ex- press—let me consider—Is not life the power which enables both the animal 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 OF VEGBTABLES. 251 the effects which the unknown cause produced, without giving us any notion of the cause itself. Emily. Yes, Caroline, yof* have told us what life does, but you have not told us what it is. Airs. B. We may study its operations j but we should puzzle ourselves 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 bo- dies ; these we shall find distinguished from the mineral crea- tion, not only by their more complicated nature, but by the power which they possess within themselves, of forming new chemical arrangements of their constituent parts, by means of appropriate organs. Thus, though all vegetables are ulti- mately composed of hydrogen, carbon,' and oxygen, (with a few other occasional ingredients,) they separate and combine these principles, by their various organs, in a thousand ways, and form, with them, different kinds of juices and solid parts, which exist ready made in vegetables, and may, therefore, be considered as their immediate materials. These are : Sap, Resins, Mucilage, Gum Resins, Sugar, Balsams, Fecula, Caoutchouc. Gluten, Extractive colouring Matter, Fixed Oil, Tannin, Volatile Oil, Woody Fibre, Camphor, Vegetable Acids, fyc. Caroline. What a long list of names ! I did not suppose that a vegetable was composed of half so many ingredients. Mrs. B. You must not imagine that every one of these materials is formed in each individual plant. I only mean to say, that they are all derived exclusively from the vegetable kingdom. Emily. But does each particular part ofthe plant, such as the root, the bark, the stem, the seeds, the leaves, consists of one of these ingredients only, or of several of them combined together ? Mrs. B. I believe there is no part of a plant which can be said to consist solely o£ any one particular ingredient ; a certain number of vegetable materials must always be com- bined for the formation of any particular part, (of a seed for instance,) and these combination* are carried on by sets of vessels, or minute onjans, which select from other parts, and bring together, the several principles required for the deve- 252 COMPOSITION lopement and growth of those particular parts which they are intended to form and to maintain. And are not these combinations always regulated by the laws of chemical attraction ? Airs. B. No doubt; the organs of plants cannot force principles to combine which have no attraction for each oth- er ; nor can they compel superior attractions to yield to those of inferior power ; they probably act rather mechanic- ally, by bringing Into contact such principles, and m such pro- portions, as will, by their chemical combination, form the va- rious vegetable products. Caroline. We may then consider each of these organs as a curiously constructed apparatus, adapted for the perform- ance of a variety of chemical processes. Airs. B. Exactly so. As long as the "plant lives and thrives, the carbon, hydrogen, and oxygen, (the chief constit- uents of its immediate materials,) are so balanced and connect- ed together, that they are not susceptible of entering into oth- er combinations ; but no sooner does death take place, than this state of equilibrium is destroyed, and new combinations produced. Emily. But why should death destroy it ? for these, princi- ples must remain in the same proportions, and consequently, 1 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 attrac- tions succeeds, similar to that which would take place in min- eral or unorganized matter. Emily. It is this order of attractions, I suppose, that de- stroys 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 ? Airs. B. ~ And that, you know, is never the case : plants may be partially preserved for some time after death, by dry- ing ; but in the natural course of events they all return to the state of simple elements ; ;>. wise and admirable dispensa- tion of Providence, by which dead plants are rendered fit to enrich the soil, and become subservient to the nourishment of living vegetables. Caroline. But we are talking ofthe dissolution of plants, before we have examined them in their living state. Mrs. B. That, is true, my dear. But 1 wished to give yoo a general idea ofthe nature of vegetation, before we en- tered into particulars. Besides, it is not so irrelevant as you OP VEGETABLES. ".53 suppose to talk of vegetables in their dead state, since we cannot analyze them without destroying life ; and it is only by hastening to submit them to examination, immediately af- ter they have ceased to live, that we can anticipate their na- tural decomposition. There are two kinds of analysis of whi-h 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 consists 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 on- ly, as the organs by which the various secretions or separa- tions 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 ofthe plant. The basis of this juice, which the roots suck up from the soil, js water ; this holds in solution the various other ingredients required by the several parts ofthe plant, which are gradu- ally secreted from the sap by the different organs appropria- ted to that purpose, as it passes them in circulating through the plant. Mucus, or mucilage, is a vegetable substance, which, like all the 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 ? Airs. 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 arable ; it forms the chief nourishment ofthe natives of those parts, who obtain it in great quantities from incisions which they make in the trees. Caroline. 1 did not know that gum was eatable. Airs. B. There is an account of a whole ship's compa- ny being saved from starving by feeding on the cargo, which was gum Senegal, I should not, however, imagine, that it would be either a pleasant or a particularly eligible diet to those who have not, from their birth, been accustomed to it. It is, however, frequently taken medicinally, and considered as very nourishing. Several kinds of vegetable acids may be obtained, by particular processes, from gum or mucilage, the principal of which is called the mucous acid. 23 234 COMPOSITION Sugar is not found in its simple state in plants, but is alway* mixed 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 exclusively from the sugar-cane ? Mrs. B. Because it is both most abundant in that plant, and most easily obtained from it. Besides, the sugars produ- ced by other vegetables differ a little in their nature. During +he 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 ex- tent. 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 exact- ly like common sugar.* Emily. Pray, in what manner is sugar obtained from the sugar-cane ? Mrs. B. The juice of this plant is first expressed by pass- ing 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 standing 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 un- dergoes another operation to be refined and converted into loaf sugar. For this purpose it is dissolved in water, and af- terwards purified by an animal fluid called albumen. White of eggs chiefly consist of this fluid, which is also one of the constituent parts of blood ; and consequently eggs, or bul- lock's blood, are commonly used for this purpose. The albuminous fluid being diffused through the syrup, combines with all the solid impurities contained in it, and * Some foreign chemists (M. M. Kirkoff, Braconnot. fe.) havq found that if starch be boiled for a long time in water containing one-fortieth part of sulphuric acid, and evaporated down to a cer- tain consistence, the solution of starch concretes, in cooling, into a solid brownish mass, which has the taste and other general proper- ties of sugar. During this paocess, no gas is disengaged, and the acid is not decomposed. OF VEGETA1IES. 255 rises with them to the surface, where it forms a thick scum ; the clear liquor is then again evaporated to a proper consis- tence, and poured into moulds, in which, by a confused crys- tallization, 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 matter. Caroline. I am very glad to hear that the blood that ie used to purify sugar does not remain in it; it would be a dis- gusting idea. I 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 ac- count of the process in detail. But the principal improve- ment relates to the mode of evaporating the syrup, in order to bring it to the consistency of sugar. Instead of boiling Hie 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 little 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 economisal improvements. Emily. And pray how are sugar-candy and barley-sugar prepared ? Mrs, B. Candied sugar is nothing more than the regular crystals, obtained by a 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, and, like all other vegetable substances, resolved into carbonic acid and hydro- gen. The formation and the decomposition of sugar afford many very interesting particulars, which we shall fully exa- mine, after having gone through the other materials of veget- ables. We shall find that there is reason to suppose that sugar is not, like the other materials, secreted from the sap by ap- propriate 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. I thought that honey was in some measure an ani- mal substance, as it is prepared by the bees. 256 COMPOSITION Airs. B. It is rather collected by them from flowers, and conveyed to their store-houses, the hives. It is the wax only that undergoes a re a I alteration in the body of the bee, and is thence converted into an animal substance.* Manna is another kind of s.igar, which is united with a nau- seous extractive matter, to which it owes its peculiar taste and colour. It exudes like gum from various trres in hot climates, some of which have their leaves gb.zed by it. The next of the vegetable materials is fecula; 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 ve- getable ; butthiit of one particular grain is become a favour- ite and most common food of a large part of mankind. Emily. Yea allude, I suppose, to bread, which is made of wheat flour ? Mrs. B. Yes. The fecula of wheat contains also another vegetable 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 sup- posed tc be owing to the viscous 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 resemblance ; 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 carbon in various proportions. They are of two kinds, fixed and volatile, both of which we formerly mentioned. Do you remember in what the difference between fixed and vol- atile oil consists ? Emily. If I recollect rightly, the former are decomposed by beat, whilst the latter are merely volatilized by it. Mrs. B.- Very well. Fixed oil is contained only in the seeds of plants, excepting in the olive, in which it "is produ- ced in, and expressed from, the fruit. We have already ob- served that seeds contain also fecula ; these two substances, united with a little mucilage, form the white substance con- tained in the seeds or kernels of plants, and is destined for * 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 beeswax itself is not an animal substance, is clear from its analy- sis. G. OP VEGETABLES. 257 the nourishment of the young plant, to which the seed gives birth. The milk of almonds, which is expressed from the seed of that name, is composed of these 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. Nat 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 ? Airs. B. Animal oils most commonly ; but the preference given to them is owing to their being less expensive ; for ve- getable oils burn equally well, and are more pleasant, as their smell is not offensive. 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 lamp, which may not be sufficiently favourable to a perfect combustion ; but there is certainly a defect in the nature of oil itself, which renders it necessary for the best constructed lamps to be occasionally trimmed. This defect arises from a portion of mucilage which it is extremely dif- ficult to separate from the oil, and which being a bad combus- tible, gathers round the wick, and thus impedes its combus- tion, and consequently dims the light. Caroline. 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 1 think I once before explained to you. The oil rises be- tween the fibres ofthe cotton by capillary attraction, and the heat of the burning wick volatilizes it, and brings it succes- sively to the temperature at which it is combustible. Emily. I suppose the explanation which you have given with regard 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 circumstance just explained, the common sorts of oils are not very highly combustible, so that the heat pro- duced 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. Wax candles, then, contain no incombustible matter, since they do not require snuffing ? Airs. B. Wax is a much better combustible than t Mow, but still not perfectly so, since it likewise contains son r*ar- 23* 258 COMPOSITION tides 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, 1 wonder that they should require so great an elevation of temperature before they begin to burn ? Airs. B. Though fixed oils will not enter into actual com- bustion below the temperature of about four hundred de- grees,* yet they will slowly absorb oxygen at the common temperature of the atmosphere. Hence arises a variety of changes in oils which modify their properties and uses in the arts. If oil simply absorbs, and combines with oxygen, it thick- ens 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 alteration ofthe oil consists not only in the addition of a certain quantity of oxygen, but in the diminution ofthe hydrogen. These oils are distinguish- ed 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 contin- ually use them in painting. But 1 do not understand why the acquisition of oxygen on one hand, and a loss of hydrogen on the other, should render them drying. Mrs. 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 subtract- ed ; or from this additional quantity of oxygen giving rise to new combinations, in consequence of which the most fluid parts ofthe oil are liberated and volatilized. For the purpose of painting, the drying quality of oil is fur- ther 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 peculiar acid is formed, called the sebacic acid. Caroline. Since the nature and composition of oil is so * 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 temperature than 600. C. OF VE6ETABLES. 259 well known, pray could not oil be actually made, by combin- ing its principles ? Mrs. B. 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 discovered that it is possible to form oil, by a peculiar process, from the action of oxygenated muriat- ic 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 ofthe plant excepting the seed ; they are, at least, never found in that part ofthe 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 extracted 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 ? Mrs. B. Yes ; remarkably so ; and in geranium leaves also, which have a much more powerful odour than the flow- ers. The perfume of sandal fans is an instance of its existence in wood. In short, all vegetable odours or perfumes are pro- duced by the evaporation of particles of these volatile oils. Emily. They are, I suppose, very light, and of very thin consistence, since they are volatile ? Mrs. B. They vary very much in this respect, some of them being as thick as butter, whilst others are as fluid as water. In order to be prepared for perfumes, or essences, these oils are first properly purified, and then either distilled with spirit of wine, as in 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 impreg- nated with the volatile oil. Caroline. Such waters are frequently used to take spots * Hydro-carbonate, is also called olefiant or oil making gas, on account of the supposed property here mentioned. But later ex- periments hav? 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. 260 COMPOSITION of grease out of cloth, or silk ; how do they produce that effect ? _- Mrs. B. By 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 res- ins ; if, therefore, the spot proceeds from any of these sub- stances, it will remove it. Insects of every kind have a great aversion of perfumes, so that volatile oils are employed with success in museums for the preservation 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, remarkable by mmy peculiarities. But if not exactly ofthe same nature as volatile oil, it is at least very analogous to it. It is obtained chiefly from the camphor-tree, a species of lau- rel 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 aromat- ic plants ; and it is deposited in pretty large quantities by some volatile oils after long standing. It is extremely vola- tile and inflammable. It is insoluble in water, but is soluble in oils, in which state, as well as in its solid form, it is fre- quently applied to medicinal purposes. Amongst the partic- ular properties of camphor, there it 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 b »sin of pure water, it will immediately begin to mpv^ round and round with great ra- pidity ; but if you pour into the basin a single drop of any odoriferous fluid, it will instantly put a stop to this motion. You can at any time try so very simple an experiment ; but you must not expect that I shall be able to account for the phenomenon, as nothing satisfactory has yet been advanced for its explanation. Caroline. It is very singular indeed ; and I will certainly make the experiment. Pray what are resins, which you just now mentioned ? Airs. B. They are volatile oils, that have been acted on, and peculiarly modified, by oxygen. Caroline. They are, therefore, oxygenated volatile oils ? Airs. B. Not exactly : for the process does not appear to consist so much in the oxygenation ofthe oil, as in the com- *■ Camphor comes chiefly from Japan. It is obtained by distil- . 5ing the wood ofthe 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. OF VEGETABLES. 261 bustion of a portion of its hydrogen, and a small portion of its carbon. For when resins are artificially made by the com- bination of volatile oils with oxygen, the vessel in which the process is performed is bedewed with water, and the air in- cluded within it is loaded with carbonic acid. Emily. This process must be, in some respects, similar to that for preparing drying oils ? Airs. B. Yes ; and it is by this operation that both of them acquire a greater degree of consistence. Pitch,\tar, and tur- pentine, are the most common resins ; they exude from the pine and fir trees. Copal, mastic, and frankincense, are also of this class of vegetable substances. Emily. Is it of these resins that the mastic and copal var- nishes, so much used in painting, are made ? Airs. B. Yes. Dissolved either in oil, or in alcohol, re- sins form varnishes. From these solutions they may be pre- cipitated by water, in which they are insoluble. This I can easily show you.—If 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 win. be precipitated in the form of a white cloud. , Emily. It is so. And yet how is it that pictures or draw- ings, varnished 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 solu- ble 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 snr>ell as assafoetida 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 roses and lavender. There is still another form under which volatile oils pre- sent themselves, which is that of balsams. These consist of resinous juices combined with a peculiar acid, called the ben- zoic acid. Balsams appear to have been originally volatile oils,* the oxygenation of which has converted one part into a * 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 process by which it is obtained. C 2.62 COMPOSITION resin, and the other part into an acid, which, combined to- gether, form a balsam- such are the balsams of Peru, To- lu, &c. We shall now take leave ofthe oils and their various mod- ifications, and proceed to the next vegetable substance, which is caoutchouc. This is a white, milky, glutinous fluid, which acquires consistence, and blackens in drying, in which state it forms the substance with which you are so well acquainted, under the name of gum-elastic. * Caroline. I am surprised to bear that gum-elastic was ever' white, or ever fluid ! And from what vegetable is it pro- cured ? 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 into it. A layer of this juice adheres to the clay and dries on it: 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 coun- tries 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 immediate ingredients of vegetables, is extractive matter. This is a term, which, in a general sense, may be applied to any substance extracted from vegetables ; but it is more par- ticularly understood to relate to the extractive colouring mat- ter of plants. A great variety of colours are prepared from the vegetable kingdom, both for the purposes of painting and of dying ; all the colours called lakes are of this description ; but they are less durable than mineral colours, for, by long exposure to the atmosphere, they either^ darken or turn yel- low, Emily. I know that, in painting, the lakes are reckoned far less durable colours than the ochres ; but what is the rea- son of it ? Mrs. B. The change which takes place in vegetable col- ours is owing chiefly to the oxygen of the atmosphere slowly burning their hydrogen, and leaving, in some measure, the blackuess of the carbon exposed. Such change cannot take place in ochre, which is altogether a mineral substance. Vegetable colours have a stronger affinity for animal than for vegetable substances ; and this is supposed to be owing to • F VEGETABLES. 263 a small quantity 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 colouring matter should be precipita- ted, or fixed, on the substance to be dyed, and should form a compound not soluble in the liquids to which it will probably be exposed. Thus, for instance, printed or dyed linens or Cottons must be able to resist the action of soap and water, to which they must necessarily be subject in washing ; and wool- lens and silks should withstand the action of grease and acids, to which they may accidentally be exposed. Caroline. But if linen and cotton have not a sufficient af- finity for colouring matter, how are they made to resist the action of washing, which they always do, when they are well printed' Mrs. B. When the substance to be dyed has either no af- finity for the colouring matter, or not sufficient power to re- tain it, the combination is effected, or strengthened, by the intervention of a third substance, called a mordant, or basis. The mordant must have a strong affinity both for the colour- ing matter and the suhstance 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 v eatables. Emily. Is that the substance commonly called tan, which is used in hot-houses ? 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 s tanning, by which skin is converted into leather. Emily. Pray how is this operation performed ? Airs. B. Various methods are employed for this purpose, which all consist in exposing skin to the action of tannin, or of substances containing this principle, in sufficient quanti- ties, and disposed to yield it to the skin. The most usual way is to infuse coarsely powdered oak bark in water, and to keep the skin immersed in this infusion for a certain length of time. During this process, which is slow and gradual, The 264 COMPOSITION skin is found to have increased in weight, and to have acquir ed a considerable tenacity and impermeability to water. This effect may be much accelerated by using strong saturations of the tanning principle (which, can be extracted from bark,) instead of employing the bark itself. But this quick mode of preparation does not appear to make equally good leather. Tannin is contained in a great variety of astringent vegeta- ble substances, as galls, the rosetree, and wine ; but it is no where so plentiful as in bark. All these substances yield 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 com- bining with skin (which consists chiefly of glue,) and of en- abling 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. I have prepared a solution of isinglass for that very purpose.—Do you observe the thick, muddy pre- cipitate ?—That is the tannin combined with the isinglass. Caroline. This precipitate must then be of the same na- ture as the leather ? Mrs. B. It is composed of the same ingredients ; but the organization and texture of the skin being wanting, it has neither the consistence nor the tenacity of leather. Caroline. One might suppose that men who drink large quantities of red wine, stand a chance of having the coats of their stomachs converted 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 exists, no certain chemical inference can be drawn. I must not dismiss this subject, without mentioning a re- cent discovery of Mr. Hatchett, which relates to it. This gentleman found that a substance very similar to tannin, pos- sessing all its leading properties, and actually capable of tan- ning leather, may be produced by exposing carbon, or any substance containing carbonaceous matter, whether vegetable, animal, or mineral, to the action of nitric acid.* * 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, a*id the digestion continued until the OF VEGETABLES ^65 Caroline. And is not this discovery very likely to be of use to manufactures ? Mrs. B. That is very doubtful, because tannin, thus ar- tificially prepared, must probably always be more expensive than that which is obtained from bark. But the fact is ex- tremely curious, as it affords one of those very rare instances of chemistry being able to imitate the proximate principles of organized bodies. The last ofthe vegetable materials is woody fibre ; it is the hardest 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 ofthe part to which it belongs, and retains its shape after all the other materials have disappeared. 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 char- coal is made ? Mrs. B. Yes. Charcoal, as you may recollect, is ob- tained 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 of hydrogen and carbon, and that their difference consisted only in the various proportions of oxygen which they contained. The following are the names ofthe vegetable acids : The Mucous acid, obtained from gum or mucilage ; Suberic - - from cork ; Camphoric - from camphor; Benzoic - - from balsams ; Gallic - - from galls, bark, &c. Malic - <- from ripe fruits ; Citric - - from lemon juice ; Oxalic - - from sorrel ; Succinic - - from amber; Tartarous - - from tartrit of potash ; Acetic - - from vinegar. They are all decomposable by heat, soluble in water, and turn vegetable blue colours red. The succinic, the tartarous, charcoal was dissolved. The solution being evaporated to dryness, leaves a dark brown mass. This is the tannin in question, lis *aste is bitter and highly astringent. C. 24 266 COMPOSITION and the acetous acids, are the products 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 vegetable 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 oxalic by an addition of oxygen, the oxalic itself is not susceptible of a further degree of oxygenation; nor can it be made, by any chemical processes, to return to a state of lower,acidification.* To conclude this subject, I have only to add a few words on the gallic acid..... Caroline. Is not this the same acid before mentioned, which forms ink, by precipitating sulphat of iron from its so- lution ? Mrs. B. Yes. Though it is usually extracted from galls, on account of its being most abundant in that vegetable sub- stance, it may also be obtained from a great variety of plants. It constitutes what is called the astringent principle of "vege- tables ; it is generally combined with tannin, and you will find that an infusion of tea, coffee, bark, red wine, or any vegeta- ble substance that contains the astringent principle, will make a black 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 oaks, and are occasioned by an insect which wounds the bark oftrees, and lays its eggs in the aperture. The la- cerated vessels ofthe 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 afterwards 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 ofthe oak in this country of a similar nature ? * Oxalic acid may be formed artificially. Put one ounce of white 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. OF VEGETABLES. 267 Mrs. B. Yes ; only they are an inferior species of gajls, containing 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 fre- quently met with in the state of compound salts ; these, however, are in general not fully saturated with the salifiable bases, so that the acid predominates ; and, in this state, they are called acidulous salts. Of this kind is the salt called cream of tartar. Caroline. Is not the salt of lemon commonly used to take out ink-spots and stains, of this nature ? Mrs. B. No; that salt consists of the oxalic acid, combin- ed with a little potash. It is found in that state in sorrel. Caroline. And pray how does it take out ink spots ? Mrs. B. By uniting with the iron, and rendering it soluble in water. Besides the vegetable materials which we have enumera- ted, a variety of other substances, common to three kingdoms, are found in vegetables, such as potash, which was formerly supposed to belong exclusively to plants, and was, in conse- quence, called the vegetable alkali. Sulphur, phosphorus, earths, and a variety of metallic ox- yds, are also found in vegetables, but only in small quantities. And we meet sometimes with neutral salts, formed by the combination of these ingredients. QUESTIONS. What are the organized bodies, and how do they differ from inor- ganic matter ? Define what life is. What constitutes the simplest class of organized bodies ? Of what are vegetables chiefly composed ? What are the materials of vegetables ? Is any part of a plant composed of a single ingredient ? Why do vegetables decompose, when the principle of life is extin- guished ? Vegetables are susceptible of two kinds of analysis, what is the ob- ject of each ? What is mucilage, and what are its uses ? Can gum be used as food ? What proportion of vegetables contain sugar? In what manner is sugar obtained from the sugar cane ? How does honey differ from sugar ? What is fecula? What is gluten ? 268 DECOMPOSITION How many kinds of vegetable oils are there ? Prom what part of plants are fixed oils obtained ? What are the principal drying oils ? On what does this quality depend ? Why do painters add oxyd of lead to their oils ? To what is the rancidity of oil owing ? Is there any known method of making oil by combining its princi- ples ? How do volatile differ from fixed oils I How are volatile oils obtained ? When they are adulterated with fixed oils, bow can the fraud be detected ? From whence does camphor come, and from what is it extracted ? What is the method of obtaining it ? Is camphor contained in other plants ? What are resins ? How are varnishes prepared ? What are gum-resins ? What are balsams ? Give some account of caoutchouc or gum-elastic What is extractive matter ? What is the condition required to form a good dye ? Explain the nature and uses of mordants. What substances are commonly used as mordants ? What is tannin? How is artificial tannin made ? W hat is woody fibre ? Of what is it chiefly composed ? What are the names of the vegetable acids ? What is the composition ofthe bases of these acids " What is the gallic acid ? W hat are galls, and hpw are they formed ? How does the oxalic acid remove ink spots ? CONVERSATION XXL ON THE DECOMPOSITION OF VEGETABLES. Caroline. The account which yon have given us, Mrs. B., ofthe materials of vegetables, is, doubtless, very instructive ;. but it does not completely satisfy my curiosity. I wish to know how plants obtain the principles from which their vari- ous materials are formed ; by what means these are convert- ed into vegetable matter, and how they are connected with the life ofthe plant. Mrs. B. This implies nothing less than a complete histo- ry of the chemislry and physiology of vegetation, subjects on which we have yet but very imperfect notions. Still 1 hope that 1 shall be able, in some measure, to satisfy your curiosi OF VEGETABLES. 269 ty. But, in order to render the subject more intelligible, I 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 attrac- tion. The composition of vegetables being more complicated than that of minerals, the former more readily undergo chem- ical changes than the latter : for the greater the variety of attractions, the more easily is the equilibrium destroyed, and a new order of combinations introduced. Emily. I am surprised that vegetables should be so easi- ly susceptible of decomposition; for the preservation of the vegetable kingdom 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 ofthe vegetable takes place only after the death ofthe 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 would 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 order to resolve them into their chemical constituents, hy- drogen, carbon, and oxygen ; those simple and primitive in- gredients, which she keeps in store for all her combinations, Emily. But since no system of combination can be de- stroyed except by the establishment of another order of at- tractions, how can the decomposition of vegetables reduce them to their simple elements 1 Airs. B. It is a very long process, during which a variety of new combinations are successively established and succes- sively destroyed ; but, in each of these changes, the ingredi- ents of vegetable matter tend to unite in a more simple order of compounds, till they are at length brought to their element- ary state, or, at least, to their most simple order of combina- tions. Thus you will find that vegetables are in the end al- most entirely reduced to water and carbonic acid ; the hydro- gen and carbon dividing the oxygen between them, so as to form with it these two substances. But the variety of inter- mediate combinations that take place during the several sta- ges ofthe decomposition of vegetables, present us with a new let of compounds, well worthy of our examination. 24* 270 BEX Caroline. How is it possible that vegetables, while putre- fying, should produce any thing worthy of observation ? Mrs. B. They are susceptible 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 understand this subject, which is of eonsiderable 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 or- der 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 re- stored, and the new order of compounds fairly established. But, unless means be used to secure these new combinations in their actual state, their duration will be but transient, and a new fermentation will take place, by which the compound last formed will be destroyed ; and another, and less com- plex, 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 cor- rect Caroline. And how many fermentations, or new arrange- ments, does a vegetable undergo before it is reduced to its simple ingredients ? 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 matter is not equally susceptible of undergoing all these fermentations. There are likewise several circumstances required to pro- duce fermentation. Water and a certain degree of heat are both essential to this process, in order to separate the parti- cles, and thus weaken their force of cohesion, that the new chemical affinities may be brought into action. Caroline. In frozen climates, then, how can the sponta- aeons decomposition 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 can- not be decomposed, their number must always increase. Mrs* B. But, my dear^ heat and water are quite as es- \tv VCjKiH.1 All L, 113. 2*1 sential to the formation of vegetables, as they are to their decomposition. Besides, it is from the dead vegetables, re- duced to their elementary principles, that the rising genera- tion is supplied with sustenance. No young plant, therefore, can grow unless its predecessors contribute both to its forma- tion and support ; and these not only furnish 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 proces- ses 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 k required for these proces- ses is in an aeriform state, which is scarcely more conducive either to the growth or formation of vegetables than that of ice. In those latitudes, therefore, it is only in low damp situations, sheltered by woods from the sun's rays, that the smaller tribes of vegetables can grow and thrive during the dry season, as dead vegetables seldom retain water enough to produce fermentation, but arer on the contrary, soon dried up by the heat of the sun, which enables them to resist that process ; so that it is not till the fall of the autumnal rains (which are very violent 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 fer- mentation, because its product is sugar. Caroline. But sugar, you have told us, is found in all ve- getables ; it cannot, therefore, be the product of their de- composition. 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 formation of sugar, whether in living or dead vegetable matter is, so evidently a new compound, proceeding from the destruction ofthe previous order of com- binations, and essential to the subsequent fermentations, that it is now I believe generally esteemed the first step, or ne- cessary preliminary to decomposition, if not an actual com- mencement of that process. Caroline. I recollect your hinting to us that sugar wa» supposed not t© be secreted from the sap, in the same mai- mer as mueilage, fecula, oil, and the other ingredients of ve getabiess 272 de Mrs. B. It is rather from these materials, than from the sap itself, that sugar is formed; and it is developed at par- ticular periods, as you may observe in fruits, which become sweet in ripening, sometimes even after they have been gath- ered. Life* therefore is not essential to the formation of su- gar, whilst, on the contrary, mucilage, fecula, and the other vegetable materials that are secreted from the sap by appro- priate 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 destruction, as well as their last towards perfection ? Mrs. B. Exactly.—A process analagous to the saccharine fermentation takes place also during the cooking of certain vegetables. 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 decomposition would ensue. The same pro- cess 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 ofthe seed must be decomposed, and the seed disorganized, before a plant can sprout from it. Seeds, besides the embrio plant, contain (as we have already observed) fecula, oil, and a lit- tle mucilage. These substances are destined for the nour- ishment 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 embrio plant. The saccharine fermentation of seeds is artificially pro- duced, for the purpose of making malt, by the following pro- cess :—A quantity of barley 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 putting it into a kiln, where it is well dried at a gentle heat. In this state it is crisp and friable, and constitutes the substance called malt, which is the principal ingredient of beer, OF VEGETABLES. 273 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 vegeta- bles is from what 1 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 ?—It appears that the sac- charine fermentation is extremely favourable, if not abso- lutely essential, as a previoys step, to the vinous fermenta- tion ; so that if sugar be not developed during the life ofthe plant, the saccharine fermentation must be artificially pro- duced before the vinous fermentation can take place. This is the case with barley, which does not yield any sugar un- til 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 certainly not wine. Mrs. B. Chemically speaking, beer may be considered as the w ine of grain. For it is the product of the fermentation of malt, justas wine is that ofthe fermentation of grapes, or ether fruits. The consequence ofthe vinous fermentation is the decom- position ofthe saccharine matter, and the formation of a spir- itous liquor from the constituents of the sugar. But in or- der to promote this.fermentation, not only water and a certain degree of heat are necessary, but some other vegetable ingre- dients, besides the sugar, as fecula, mucilage, acids, salts, ex- tractive matter, &c, all of which seem to contribnte to this process ; and give to the liquor its peculiar taste. Emily. It is, perhaps, for this reason that wine is not ob- tained 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 forma- 274 DECOMPOSITION tion of wine ; otherw ise 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 vegetable ingredients that influences the production and qualities of wine. And it is found that the juice ofthe grape not only yields the most considerable proportion of wine, but that it likewise affords it ofthe most grateful flavour. Emily. I have seen a vintage in Switzerland, and I do not recollect that heat was applied, or water added, to produce the fermentation ofthe grapes. Mrs. B. The common temperature ofthe atmosphere in the cellars in which the juice ofthe grape is fermented is suf- ficiently 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 quan- tity 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 recombined into two new substances ; the one a peculiar liquid substance, called alcohol, or spirit of wine, which re- mains in the fluid ; the other, carbonic acid gas, which es- capes during the fermentation. Wine, therefore, as I before observed, in a general point of view, may be considered as a liquid, of which alcohol constitutes, the essential part. And the varieties of strength and flavour of the different kinds of wine, are to be attributed to the different qualities ofthe fruits, from which they are obtained, independently ofthe sugar. Caroline. Ian* astonished to hear that so powerful a li- quid as spirit of wine should be obtained from so mild a sub- stance as sugar. Airs. B. Can you tell me in what the principal difference consists between alcohol and sugar ? Caroline. Let me reflect;—Sugar consists of carbon, hy- drogen, and oxygen. If carbonic acid be subtracted from it, during the formation of alcohol, the latter will contain less carbon and oxygen than sugar does ; therefore hydrogen must be the prevailing principle of alcohol. Mrs. B. It is exactly so. And this very large proportion of hydrogen accounts for the lightness and combustible pro- perty of alcohol, and of spirits in general, all of which consist of alcohol variously modified. Emily. And can sugar be recnmposed from the combina- tion 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 re- 05 VEGETABLES. 275 composition possible. , Let us now observe more particularly, the phenomena that takes place during the vinous fermenta- tion. At the commencement of this process, heat is evolved, and the liquor swells considerably from the formation ofthe carbonic acid, which is disengaged in such prodigious quan- tities as would be fatal to any person who should unawares inspire it ; an accident which has sometimes happened. If the fermentation be stopped by putting the liquor into barrels, before the whole ofthe 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 evol- ved during 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 recollect that fermentation, is a complicated chemical process ; and that, during the decompositions and recomposi- tions attending it, a quantity of chemical heat may be disen- gaged, sufficient both to develope the gas, and to effect an in- crease of temperature. When the fermentation is comple- ted, the liquid cools and subsides, the effervescence ceases, and the thick, sweet, sticky juice of the fruit is converted in- to a clear, transparent, spirituous liquor, called wine. Emily. How much 1 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 satisfying yourself in that respect, by observing the process of brewing, which, in every essential 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 distillation. When wine of any kind is submitted to this operation, it is found to contain brandy, water, tartar, extractive colouring matter, and some vegetable acids. I have put a little port wine into this alembic of glass (Plate XIV. fig. 1.), and on placing the lamp under it, you will soon see the spirit and water successively come over— Emily. But you do not mention alcohol amongst the pro- ducts of the distillation of wine ; and yet that is its most es- sential ingredient. Mrs. B. The alcohol is contained in the brandy which is now coming over, and dropping from the still. Brandy is 276 DECOMPOSITION nothing more than a mixture of alcohol and water ; and m order to obtain the alcohol pure, we mus£ again distil it from brandy. 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 colourless, 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 little burnt sugar, in order to give it the appearance of having been long kept. Caroline. And is rum also distilled from wine ? Mrs. 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 alcohol than almost any other vegetable. After the juice ofthe cane has been pressed out for making sugar, what still remains in the bruised cane is extracted by water, and this watery solution of sugar is fermented, and produces rum. The spirituous liquor called arack is in a similar manner distilled from the product ofthe 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 recollect, 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 fermentation of malt. For hops are a necessary ingredient for the formation of that liquor ; whilst brandy is distilled from pure fermented malt. But brandy might, no doubt, be distilled from beer, as well as from any other liquor that has undergone the vinous fermentation ; for since the basis of brandy is alcohol, it may be obtained from any liquid that contains tfiat spirituous substance. Emily. And pray, from what vegetable is the favourite spirit ofthe lower orders of 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. OF VEGETABLES. 277 I think the brandy contained in the wine which we are dis- tilling, must, by this time, be all 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 lighest part, is distilled. The tartar, and ex- tractive colouring matter we shall find,in a solid form at the bottom ofthe alembic. Emily. They look very like the lees of wine. Mrs. B. And in many respects, they are of a similar na- ture, for lees of wine consist chiefly of tartrat of potash ; a salt which exists in the juice ofthe grape, and in many other vegetables, and is developed 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 dyeing, under the name of cream of tartar, and it is from this salt that the taitarous acid is obtained. Caroline. But the medicinal cream of tartar is in appear- ance quite different from these dark coloured dregs ; it is perfectly colourless. Airs. B. Because it consists of the pure salts only, in its crystallized form ; whilst in the instance before us, it is mixed with the deep-coloured extractive matter, and other foreign ingredients. Emily. Pray cannot we now obtain pure alcohol from the brandy 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, therefore, allovv 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 spirituous liquors'. Emily. It is alcohol. I suppose, that produces intoxication. Mrs. B. Certainly ; but the stimulus and momentary en- ergy it gives to the system, and the intoxication it occasions when taken in excess, are circumstances not yet accounted for. Caroline. 1 thought that it produced these effects by in- creasing the rapidity of the circulation of the blood ; for drinking wine or spirits, I have heard, always quickens the pulse. Airs. B. No doubt ; the spirit, by stimulating the nerves, increases the action ofthe muscles ; and the heart, which is 25 278 DECOMPOSITION one of the strongest 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 ascertained, they are far from' explaining why alcohol should produce such effects. Emily. Liqueurs are the only kind of spirits which I think pleasant. 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 spirituous waters are likewise solutions of volatile oil in alcohol, as lavender water, eau de Cologne, &c. The chemical properties of alcohol are important and nu- merous. It is one ofthe most powerful chemical agents, and is particularly useful in dissolving a variety of substances, which are soluble neither by water nor heat. Emily. We have seen it dissolve copal and mastic to form varnishes?; and these resins are certainly not soluble in wa- ter, since water precipitates them from their solution in at cohol. Airs. B. I am happy to find that you recollect these cir- cumstances so wjell. The same experiment affords also an instance of another property of alcohol,—its tendency to unite w ith water ; for the resin is precipitated in consequence of losing the alcohol, which abandons it from its preference for water. It is attended also, as you may recollect, with the same peculiar circumstance of a disengagement of heat,, and consequent diminution of bulk, which we have supposed to be produced by a mechanical penetration of particles, by whieh 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, &c. Emily. 1 suppose that alcohol must be highly combustible, since it contains so large a proportion of hydrogen. Airs. B. Extremely so ; and it will burn at a very mode- rate temperature. Caroline. I have often seen both brandy and spirit of wine burnt ; they produce a great deal of flame, but not a propor- tional quantity of heat, and no smoke whatever. Mrs. B. The last circumstance arises from their combus- tion being complete ; and the disproportion between the flame and heat shows you that these are by no means synonymous. OF VEGETABLES. 279 The great quantity of flame proceeds from the combustion ofthe hydrogen, to which, you know, that manner of burning is peculiar.—Have you not remarked also, that brandy and alcohol will burn without a wick ?—They take fire at so low a temperature, that this assistance is not required to concen- trate the heat and volatilize the fluid. Caroline. I have sometimes seen brandy burnt by merely heating it in a spoon. Mrs. B. The rapidity ofthe combustion of alcohol, may, however, be prodigiously increased by first volatilizing it. An ingenious instrument has been constructed on this princi- ple to answer the purpose of a blow-pipe, which may be used for melting glass, or other chemical puropses. It consists of a small metallic vessel (Plate XIII. fig. 2.) of a spherical shape, which contains the alcohol, and is heated by the lamp beneath it ; as soon as the alcohol is volatilized, it passes through 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 alcohol, in the state of vapour, is, I fancy, much hotter than when the spirit is merely burnt in a spoon. Mrs. B. Yes ; because in this way the combustion goes on much quicker, and, of course, the heat is proportionally increased.—Observe its effect on this small glass tube, the middle of which I present 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. I have uow drawn it asunder, and am going to- blow a ball at one ofthe heated ends : but I 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 bio wed too hard ; for the ball suddenly dila- ted1 to a great size, and then burst into, pieces. Mrs. B. You will be more expert another time ; but I * A spirit lamp, which answers verv 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 goosequill. Let the tube rise an inch br two above the cork—pass some cotton wick through the tube- -then fill the vial with alcohol, and put the cork and tube in their places. The lamp is then ready. 280 DECOMPOSITION must caution you, should you ever use this blow-pipe, to be very careful that the combustion of the alcohol does not go on with too great violence, for I have seen the flame some- times dart out with such force as to reach the opposite wall ofthe room, and set the paint on fire. There is, however, no danger of the vessel bursting, as it is provided with a safety tube, which affords an additional vent for the vapour of alcohol when required. The products of the combustion of alcohol consist in a great proportion of water, and a small quantity of carbonic acid. There is no smoke or fixed remains whatever.—Fow do you account for that, Emily ? Emily. I suppose that the oxygen which the alcohol ab- sorbs in burning, converts its hydrogen into water, and its carbon into carbonic acid gas, and thus it is completely con- sumed. 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 bran- Mrs. B. Np ; there is an essential difference, in order to obtain alcohol from brandy, you need only deprive the latter of its water ; but for the formation of ether, the alco- hol must be decomposed, 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 alcohol, and hydrogen is the lightest of all its ingredients : nor do I suppose that it can be oxygen, as alcohol contains so small a proportion of that principle ; it is, therefore, most probably, carbon, a diminution of which would not fail to render the new compound more volatile. Mrs. B. You are perfectly right. The formation of ether consists simply in subtracting from the alcohol a certain proportion of carbon ; this is effected by the action ofthe sulphuric, nitric, or muriatic acids, on alcohol. The acid and carbon remain at the bottom ofthe vessel, whilst the de- carbonized alcohol flies off in the form of a condensable va- pour, which is ether. «, Ether is the most inflammable of all fluids, and burns at so low a temperature that the heat evolved during its combus- tion is more than is required for its support, so that a quanti- ty of ether is volatilized, which takes fire, and gradually in- creases the violence ofthe combustion. ^ Sir Humphrey Davy has lately discovered a very singular fact respecting the vapour of ether. If a few drops of ether OF VEGETABLES. 281 be poured into 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 ? Airs. B. This is owing to a very peculiar property ofthe vapour of ether, and indeed of many other combustible gas- eous bodies. At a certain temperature lower than that of ignition, these vapours undergo a slow and imperfect com- bustion, which does not give rise, in any sensible degree, to the phenomena of light and flame, and yet extricates a quan- tity of caloric sufficient to re-act upon the wire and make it red hot, and the wire in its turn keeps up the effect as long as the emi-sion 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 tune, 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. If this lamp be lighted for a mo- ment, and blown out again, the wire, after ceasing for an in- stant 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 con- sumed in this peculiar manner. Caroline. That is extiemely curious. But why should not an iron or silver wire produce the same effect ? Airs. B. Because either iron or silver, being much better conductors of heat than platina, the heat is carried off too fast by those metals to allow the accumulation of caloric ne- cessary to produce the effect in question. Ether is so light that it evaporates at the common temper- ature of the atmosphere ; it is therefore necessary to keep it confined by a well ground glass stopper. No degree of cold known has ever frozen it.* Caroline. Is it not often taken medicinally? Airs. B. Yes ; it is one of the most effectual antispasmo- dic medicines, and the quickness of its effects, as such, proba- bly 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, * Ether freezes, and shoots into crystals at 46Q below the zero of Fahrenheit. C 25* 282 DECOMPOSITION like that of spiritous liquors, becomes prejudicial, and, if taken to excess, it produces effects similar to those of intox- ication. We may now take our leave ofthe 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 sugir and fermenta- ble bodies into alcohol and carbonic acid, which gives rise both to the formation of wine, and of all kinds of spirituous liquors. Airs. B. We shall now proceed to the acetous jermenta- tion, which is thus called, because it converts wine into vine- gar, by the formation of the acetous acid, which is the basis or radical,of vinegar. Caroline. But is not the acidifying principle ofthe acetous acid the same as that of all other arids, oxygen ? . Mrs. B. Certainly : and on .that account the contact of air is essential to this fermentation, as it affords the necessa- ry supply of oxygen. Vinegar, in order to obtain pure ace- tous acid from it, must be distilled and rectified by certain processes. Emily. But pray, Mrs. B., is not the acetous acid fre- quently formed without this fermentation taking place ? Is it not, for instance, contained in acid fruits, and in every sub- stance that becomes sour ? Airs. B. No, not in fruits ; you confound it with the citric, the malic, the oxalic, and other vegetable acids, to which living vegetables owe their acidity. But whenever a vegeta- ble substance turns sour, after it has ceased to live, the ace- tous acid is developed by means of the acetous fermentation, in which the substance advances a step towards its final de- composition. Amongst the various instances of acetous fermentation, that of bread is usually classed. Caroline. But the fermentation of bread is produced by yeast; how does that effect it ? Mrs. B. It is found by experience that any substance that has already undergone a fermentation, will readily excite it in one that is susceptible of that process. If, for instance, you mix a little vinegar with wine, that is intended to be acidi- fied, it will absorb oxygen more rapidly, and the (process be completed much sooner, than if left to ferment spontaneously. Thus yeast, which is a product of the fermentation of beer, is used to excite and accelerate the fermentation of malt, OF VEGETABLBS. 283 which h 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 fermenta- tion, why is it not sour 1 Mrs. B. It acquires a certain savour which corrects the heavy insipidity of flour, and may be reckoned a first degree of acidification ; or if the process were earried further, the bread would become decidedly acid. There are, however, some chemists who do not consider the fermentation of biead 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 combinations. All vegetables spontaneously under- go this fermentation after death, provided there be a sufficient degree of heat and moisture, 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 fermenta- tion previous to this last; or do they immediately suffer the putrid fermentation ? Mrs. B. That depends on a variety of circumstances, such as the degrees of temperature and of moisture, the na- ture of the plant itself, &c. But if you were carefully to follow and examine the decomposition of plants from their death'to their final dissolution, you would generally find a sweetness developed in the seeds, and a spirituous flavour in the fruits (which have undergone the saccharine fermenta- tion,) previous to the total disorganization and separation of the parts. Emily. I have sometimes remarked a kind of spirituous taste in fruits that were over ripe, especially oranges, and this was just before they became rotten. Mrs. B. It was then the vinous fermentation which had succeeded the saccharine, and had you followed up these changes attentively, you would probably have found the, spirituous taste followed by acidity, previous to the fruit pas- sing to the slate of putrefaction. When the leaves fall from the trees in autumn, they do not (if there is no great moisture in the atmosphere) imme- diately undergo a decomposition, but are first dried and with- ered ; as soon, however, as the rain sets in, fermentation commenees, their gaseous products are imperceptibly evol- ved into the atmosphere, and their fixed remains mixed with their kindred earth. 284 BEC0MP0SITI0N Wood, when exposed to moisture, also undergoes the pu- trid fermentation and becomes rotten. Emily. But I have heard that the dry rot, which is so liable to destroy the beams of houses, is prevented by a cur- rent of air ; and yet you said that air was essential to the pu- trid fermentation ? Mrs. 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 the rotting of wood is prevented or stopped by the free access of air. What is commonly called dry rot, however, is not, 1 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 va- riety 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 fixed products, consisting of carbon, small quantities of salts, potash, &c. form a kind of vegetable earth, which makes very fine manure, as it is composed of those elements which form the immediate materials of plants. Caroline. Pray are hot vegetables sometimes preserved from decomposition by petrification ? 1 have seen very cu- rious specimens of petrified vegetables, in which state they perfectly preserve their form and organization, though in appearance they are chafiged to stone. Mrs. B. That is a kind of metamorphosis, which, now that you are tolerably well versed in the his ory 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 chang- ed to a substance m 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 vegetable is destroyed, its place is supplied by a particle of silicious earth, conveyed thither by the water. In the course of time the vegetable is entirely destroyed, but the silex has completely.replaced it, having assumed its form and apparent texture, as if the vegetable itself were changed to stone. OF VEGETABLES. 285 Qaroline. That is very curious-! and I suppose that pet- rified animal 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 reduced, as we find they are, by decomposi- tion, to their constituent elements, but cannot be changed to elements which do not enter into their composition. There are, however, circumstances which frequently pre- vent the regular and final decomposition of vegetables : as, for instance, when they are buried either in the sea, or in the earth, where they cannotundergo the putrid fermentation for want of air. In these cases they are subject to a peculiar •hange, by which they are converted into a new class of compounds, called bitumens. ' , Caroline. These are substances I never heard of before. Mrs. B. You will find, however, that some of them are very familiar to you. Bitumens are vegetables so far de- composed as to retain no organic appearance ; but their or- igin is easily detected by their oily nature, their combusti- bility, the products of their analysis, and the impressions of the forms of leaves, grains, fibres of wood, and even of ani- mals, which they frequently bear. They are sometimes of an oily, liquid consistence, as the substance called naptha* 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 colour 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 vegeta- ble matter, mixed with the remains of marine animals and ma- rine salts, and occasionally containing a quantity ofsulphuret of iron, commonly called pyrites. * Petrifactions are of two kinds, viz. silicious, 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. * Naptha appears to be the only fluid in which oxygen does not exist; hence it* property of preserving potassium which has so strong an affinity for oxygen as to absorb it from all other fluids. It however loses this property by exposure to the atmosphere, proba- bly because it absorbs a small quantity of air, or moisture. it is again restored by distillation. C. 286 DECOMPOSITION OF VEGETABLES. Emily. It is, I suppose, the earthly, the metallic, and the saline parts of coals, that compose the cinders or fixed pro- ducts of their combustion ; whilst the hydrogen and carbon, which they derive from vegetables, constitute their volatile products. Caroline. Pray is not coke, (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 Goals. It consists of coals reduced to a substance analogous to charcoal, by the evaporation of their bituminous parts. Coke, therefore, is composed of carbon, with some earthy and saline ingredients. Succin, oi'yellow amber, is a bitumen which the ancients sailed electrum, from whence the word electricity is derived, as that substance is peculiarly, and was once supposed to be exclusively, electric'. It is found either deeply buried in the bowels ofthe earth, or 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 succinic. Emily. That oil I have sometimes used in painting, as it is reckoned to change less than the other kinds of oils. Mrs. B. The last class of vegetable substances that have changed their nature are fossil-wood, peat, and Jurf. These are composed of wood and roots of shrubs, that are partly de- composed by being exposed to moisture under ground, and yet, in some measure, preserve their form and organic ap- pearance. The peat, or black earth of the moors, retains but few vestiges ofthe roots to which it owes its richness and combustibility, these substances being 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 answers the pur- pose 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 vege- tation. We shall reserve this subject, therefore, for our next interview, when I expect that it will furnish us with ample matter for another conversation. s QUESTIONS. What are the elements into which vegetables are reduced by natural decomposition ? What is the process called which disunites and decomposes the ele- ments of vegetables ? * Hr>w many kinds offermentation are there? What circ umstances are necessary to induce this process ? VEGETATION. 287 Give some account ofthe saccharine fermentation. What is the process of making malt? What changes do the ingredients of the barley undergo to form malt? What is the second fermentation called? Why does barley resist the vinous fermentation until it has gone through the saccharine ? What changes take place among the ingredients present, during1 the vinous fermentation ? What is the principal difference between alcohol and sugar? When wine is distilled, what is the product? How does sugar differ from starch ? What difference is there between gin and brandy ? What is the origin of cream of tartar? On what does the intoxicating quality of liquors depend? What is the composition of alcohol? Describe the spirit lamp. How is ether obtained? How does it differ from alcohol ? What is the effect of the acetous fermentation ? What is the reason that wine, or cider, when corked tight, does not turn to vinegar ? What kind of fermentation is excited by the yeast to make bread ? What is the final operation of nature to reduce vegetables to their elements ? How are petrifactions formed ? What are bitumens, and how are they formed ? Why does naptha preserve potassium ? What is asphaltum? What is coal, and what are its ingredients? How does coke differ from coal? What is amber, and where is it found ? 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 the means of vegetation alone that mineral substances are introduced into the animal system ; since, generally speaking, it is from vege- tables that all animals ultimately derive their sustenance. Caroline. I do not understand that; the human species subsists as much on animal as on vegetable food. Airs. B. That is true ; but you do not consider that those that live on animal food, derive their sustenance equally, though not so immediately, from vegetables. The meat which we eat is formed from the herbs of the field, and the prey of carnivorous animals, proceeds, either directly or indi- 288 VEGETATION. rectly, from the same source. It is, therefore, through thii channel, that the simple elements become a part ofthe ani- mal frame. We should in vain attempt to derive nourish- ment from carbon, hydrogen, and oxygen, either in their sep- arate state, or combined in the mineral kingdom ; for it is on- ly by being united in the form of vegetable combination that they become capable of conveying nourishment. Emily. 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 ve- getable creation does not exhibit more wisdom in that admira- ble system of organization, by which it is enabled to answer its own immediate ends of preservation, nutrition, and propa- gation, than in its grand and ultimate object of forming those arrangements and combinations of principles, which are so well adapted for the nourishment of animals. Emily. But 1 am very curious to know whence vegetables obtain those principles which form their immediate materi- als ? Airs. 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 1 know on this subject I will endeavour to ex- plain to you. The soil, which, at first view, appears to be the aliment of vegetables, 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 with- out any earth or soil.* * The opinjon that water is the only food of plants, was adopted by the learned on this subject in the 17th century; and many expe- riments were made which seemed to prove that this was the truth. Among others was a famous one by Van Helmout, which for a long time was supposed to have established the point beyond all doubt. He planted a willow which weighed five pounds, in an earthen ves- sel containing 200 lbs. of dried earth. This vessel was sunk into the ground, and the tree was watered, sometimes with distilled, and sometimes with rain water. At the end of five years the willow weighed 169 lbs. ; and on weighing the soil, dried as before, it was found to have lost only two ounces. Thus the willow had gained 164 lbs, and yet its food had been only water. The induction from this experiment was ob- vious. Plants live on pure water. This, therefore, was the gene- ral opinion, until the progress of chemistry detected its fallacy.— Bergman, in 1773, 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 water con- taining about a grain of earth. So that this experiment by no means proved that the willow lived on water alone. Since this fime a great variety of experiments have been made for the purpose VEGETATION. 289 Caroline. Of that we have an instance in the hyacinth and other bulbous roots, which will grow andblossom beautifully in glasses of water. But I confess I should think it would be difficult to rear trees in a similar manner. Airs. B. No doubt it would, as it i6 the burying of the roots in the earth that supports the stem of the tree. But this office, besides that of affording a vehicle for food, is far the most important part which the earthy portion ofthe soil performs in the process of vegetation ; 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 necessary to be so attentive to the preparation ofthe soil ? Mrs. B. In order to impart-to it those qualities which render it a proper vehicle for the food ofthe plant. Water is the chief nourishment 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. Cal- careous 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 a carbonat of lime. Dif- ferent 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 of deciding what was the food of plants. In the cotirse of these, it has been found, that although seeds do vegetate in pure distilled wa- ter, yet the plant is weakly, and finally dies before the fruit is ma- tured. It is pretty certain then, that earth is absolutely necessary to the growth of plants, and that a part of their food is^takeu from the soil, Indeed, the well known fact, that a soil is worn out by a long succes- sion of crops, and finally becomes sterile, 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 a 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 purity the atmosphere. Thus it is seen that plants obtain their food from the earth, from walrr. and from the air. C. 26 290 VEGETATION. 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 ? Airs. B. Manure consists of all kinds of substances wheth- er of vegetable or animal origin, which have undergone the putrid fermentation, and are consequently decomposed, or nearly so, into their elementary principles. And it is requi- site that these vegetable matters should be in a state of decay, or approaching decomposition. 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 I ask you, what is the utility of supplying the soil with,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 decomposition 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 that 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 with wood. Caroline. But how is it that animal substances are reck- oned to produce the best manure ? Does it not appear much more natural that the decomposed elements of vegetables should be the most appropriate to the formation of new ve- getables ? Mrs. B. The addition of a much greater proportion of nitrogen, which constitutes the chief difference between ani- mal and vegetable matter, renders the composition of the for- mer more complicated, and consequently more favourable t© decomposition. Indeed, the use of animal substances is chiefly to give the first impulse to the fermentation of the vegetable ingredients that enter into 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 not make good manure. The heat produced by the fermentation of manure is another circumstance which is ex- tremely favourable to vegetation ; yet this heat would be too * But what is the use of all this, if " water is the chief nourish- ment of vegetables ?" C. VEGETATION. 29i great if the manure was laid on the ground during 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 de not knowTiow to remove. Since all organized bodies are, in the common course of nature, ultimately reduced to their ele- mentary state, they must necessarily in that stale enrich the soil, and afford food for vegetation. How is it, then, that agriculture, which cannot increase the quantity of those ele- ments that are required to manure the earth, can increase its produce so wonderfully as is found to be the case in all culti- vated countries ? Mrs. B. It is by suffering none of these decaying bodies to be dispersed and 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 vegeta- tion, or for that ofthe particular seed which is to be sown. Thus, if the soil 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. On soils thus im- proved, manures will act with 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 gene- rally diffused through it, to destroy the weeds which might appropriate 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 spontaneously 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 advantage of cultivation, 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 there- fore, the more populous the earth becomes, the less it will produce. Mrs. B. Your reasoning is very plausible ; but experi- ence every where contradicts the inference you would draw from it; since we find that the animal and vegetable king 292 VEGETATION. doms, instead of thriving, as you would suppose, at each oth- er's expense, always increase and multiply together. For yon should recollect that animals can derive the elements of which they are formed only through the medium of vegeta- bles. And "you must allow that your conclusion would be vali ! 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 believe that a much greater proportion of these principles than is required for such purposes, remains either in an ele- mentary state, or engaged in a less useful mode of combina- tion in the mineral kingdom. Possessed of such immense re- sources as the atmosphere and the waters afford us, for oxy- gen, 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 perfec- tion as to require the whole of what these resources could supply. Nature, however, in thus furnishing us with an inexhausti- ble stock 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 pointing 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 dis- covering the readiest method of obtaining the several princi- ples, 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 surprised that you do not mention the earth itself, as it contains abundance of coals, which are chiefly composed of carbon. Mrs. B. Though coals abound in carbon, they cannot, on account of their hardness, and impermeable texture, be im- mediately subservient to the purposes of vegetation ; and, we find, on the contrary, 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 de- rive from that source can be but very trifling, and must en- tirely depend on local circumstances. Caroline. Perhaps the smoky atmosphere of London is VEGETATION. 293 the cause of vegetation being so forward and so rich in its vicinity ? Airs. B. I rather believe that this circumstance proceeds from the very ample supply of manure, assisted, perhaps, by the warmth and shelter which town affords. Far from at- tributing any good to the smoky atmosphere of London, I confess I like to anticipate the time when.we shall have made such progress in the art of managing combustion, that every particle of carbon will be consumed, and the smoke destroy- ed at the moment of its production. We may then expect to * hive the satisfaction of seeing the atmosphere of London as clear 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, provided we are but industrious in applying them to the best advantage by improving the art of agricul- ture, no limits can be assigned to the fruits that we may ex- pect to reap from our labours. Caroline. Yes : I am perfectly satisfied in that respect, and 1 can assure you that I feel already much more interested in the progress and improvement of agriculture. Emily. I have frequently thought that the culture of the land was not considered as a concern of sufficient importance. Manufactures always take the lead : and health and innocence are frequently sacrificed to the prospect of a more profitable employment. It has often grieved me to see the poor man- ufacturers crowded together in close rooms, and confined for the whole day to the most uniform and sedentary employment, instead of being engaged in that innocent and salutary kind of labour, which Nature seems to have assigned to man for the immediate acquirement of comfort, and for the preservation of his existence. I am sure that you agree with me in think- ing so, Mrs. B. ? Airs. 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 man is sufficient to produce food for several, those whose industry is not required in til- lage 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 accommodation which the artificer prepares. Such 26* 294 VEGETATION. are the happy effects which naturally result from civilized society. It would be wiser, therefore, to endeavour to im- prove the situation of those who are engaged in manufactures, than to indulge in vain declamations on the hardships to which they are too frequently exposed. But we must not yet take our leave of the subject of agri- culture ; 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 ab- solutely necessary to its germination ; the earth must, there- fore, lie loose and light over it, in order that the air may pen- etrate. Hence the use of ploughing and digging, harrowing and raking, &c. A certain degree of heat and moisture, such as usually takes place in the spring, is likewise necessary. 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. Airs. B. Do you forget, my dear, that the young plant derives its existence from the destruction of the seed, and that it is actually by the saccharine fermentation that the lat- ter is decomposed ? Caroline. True ; I wonder that I did net recollect that. The temperature and moisture required for the germination of the seed is then employed in producing the saccharine fermentation within it ? Airs. B. Certainly. But, in order to understand the na- ture of germination, you should be acquainted with the differ- ent parts of which the seed is composed. The external covering or envelope contains, besides '^Rserm ofthe future plant, the substance which is to constitute its first nourish- ment ; this substance, which is called t'uc parenchyma, con- sists of fecula, mucilage, and oil, as we f&rmeriy observed. The seed is generally divided into two compartments, cal- led lobes or cotyledons, as is exemplified by this bean (Plate XV. fig. 1.)—the dark 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 plumula, 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 number in different seeds : some have only one, as wheat, oats, barley, and all the grasses; some have three, others six. But most seeds, as for instance, all the varieties of beans, have two cotyledons. When the seed is buried in the earth, at any temperature above 40 de- grees, it imbibes water, which softens and swells the lobes ; Fit/.* Fit,. 2. Fit/. J. FLATE^V. Fit,. 4. Garni nation. -ApparaVJs to illustrate tlic nifclianu-ni of l>/y Jt<«liWr. /iV.-3. A. b Cofy/ettmu.^C PluiiuJa .-T>Saa'tc/e .^lip. 1. A.K Cctyieclerv.-C J'tuiriulri ._1> ItaJtWc <5. A.A Cln'3 Jeff. RMrSaer rr/>menta„, trie /untie. C Mrt/i/rr reprr-eetitintr tlie DixpAruj&m. VEGETATION. 295 it then absorbs oxygen, which combines with some of its car- bon, and is returned in the form of carbonic acid. This loss of carbon increases the comparative proportion of hydrogen and oxygen in the seed, and excites the saccharine fermenta- tion, by which the parenchymatous matter is converted into a kind ef 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 fermenta- tion. 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 transformed into leaves.—If we go into the garden, we shall probably find some seeds in the state which I have de- scribed. Emily. Here are some lupines that are just making their appearance above ground. Mrs. B. We shall take up several of them to observe their different degrees of progress in vegetation. Here is one that has but recently burst its envelope—do you see the little radicle striking downwards ? (Plate XV. fig. 2.) In this the plumula is not yet visible. But here is another in a greater state of forwardness—the plumula or stem, has risen out ofthe ground, and the cotyledons are converted into seed- leaves. (Plate XV. fig 3.) Caroline. These leaves are very thick and clumsy, and unlike the other leaves, which I perceive are just beginning to appear. Mrs. B. It is because they retain the remains of the pa- renchyma, 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 (Plate XV. fig. 4.) the radicle had sunk deep into the earth, and sent out several shoots, each of which is fur- nished with a mouth to suck up nourishment from ?the soil ; the function ofthe original leaves, therefore, being no longer required, they are gradually decaying, and the plumula is be- come a regular stem, shooting out small branches, and spread- ing its foliage. Emily. There seems to be a very striking analosy between a seed and an egg ; both require an elevation of temperature to be brought to life ; both at first supply with aliment the 29b VEUETATIUW. organized being which they produce ; and as soon as this has attained sufficient strength to procure its own nourishment, the egg-shell breaks, whilst in the plant the seed leaves fall off. Mrs. B. There is certainly some resemblance between these processes ; and when you become acquainted with ani- mal chemistry, you will frequently be struck with its analogy to that of the vegetable kingdom. As soon as the young plant feeds from the soil it requires the assistance 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 surface of the foliage of plants is ad- mirably 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 con- sistence, which is fit to be assimilated to its several parts. Emily, Vegetation, then, must be essentially injured by destroying the leaves of the plant ? Mrs. B. Undoubtedly ; it not only diminishes the trans- piration, but also the absorption by the roots ; for the quan- tity x»f sap absorbed 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 xas it begins to derive its nourishment from the soil ; and, ac- cordingly, you will find that those lupines which haVe drop- ped their seed-leaves, and are no longer fed by the paren- chyma, have spread their foliage, in order to perform the office just described. But I should inform you that this function of transpiration seems to be confined to the upper surface of the leaves, whilst, on the contrary, the lower surface, which is more rough and uneven, and furnished 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 preser- vation. Light is essential to the developement of the colours, and to the thriving ofthe plant. You may have often ob- served 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 towards 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 damp- ness of the evening air ? VEGETATION. 297 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. Mrs. B. At least not in the same manner; but they cer- tainly derive some principles from the atmosphere, and yield others to it. Indeed, it is chiefly owing to the action ofthe atmosphere and the vegetable kingdom on each other, that the air continues always fit for respiration. But you will under- stand this better when I have explained the effect of water on plants. 1 have said that water forms the chief nourishment of plants : it is the basis not only ofthe sap, but of all the vegetable juices. Water is the vehicle which carries into the plant the various salts and other ingredients required for the formation and sup- port of the vegetable 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 co- louring matter, &c, whilst a portion ofthe oxygen enters in- to the formation of mucilage, of fecula, of sugar, and of veget- able acids. But the greater part of the oxygen, proceeding from the decomposition ofthe water is converted into a gase- ous state by the caloric disengaged from the hydrogen during its condensation in the formation ofthe vegetable materials.— In this state the oxygen is transpired by the leaves of plants when exposed to the sun's rays. Thus you find that the decom- position 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 by the numerous oxygenations, combustions, and respirations, that are constant- ly taking place on the surface of the globe.* * 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 con- verted into the several parts of the plant. But it has been demon- strated, that most, if not all the oxygen emitted by the leaves, is obtained by the decomposition of air, instead of water, as here sta- ted. If leaves are exposed to the rays of the sun, while under com- 298 VEGETATION^ Emily. What a striking instance of the harmony of na- ture ! Mrs. B. And how admirable the design of Providence., who makes every different part ofthe creation thus contribute to the support and renovation of each other ! But the intercourse ofthe vegetable and animal kingdoms, through the medium ofthe atmosphere, extends still further. Animals, in breathing, not only consume the oxygen ofthe 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 car- bon for its own purposes, and returns the oxygen for our's.* Caroline. How interesting this is ! I do not know a more beautiful illustration ofthe wisdom which is displayed in the laws of nature. Airs. B. Faint and imperfect as are the idea9 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 na- ture 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 wise dispensations of Provi- dence, to veil the splendour of a glory with %vhich we should be overpowered. But it is well suited to a rational being to explore, step by step, the works ofthe creation, to endeav- our to connect them into harmonious systems ; and, in a word, to trace, in the chain of beings, the kindred ties and benevo- lent design which unites its various links, and secures its pre- servation. Caroline. But of what nature are the organs of plants which are endued with such wonderful powers ? Mrs. B. They are so minute that their structure, as well mon 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 emitted. Now atmospheric air, always contains a quantity of car- bonic acid gas, and experiments show, that plants give out oxygen in some proportion to the quantity of this gas contained in the wa- ter. The fact then seems to be, that plants absorb carbonic acid, that this is decomposed by some unknown process ; the plant re- taining the carbon while the oxygen is given out. C. * 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 nfght they absorb water, and oxygen gas, and give out carbonic acid. C. VEGETATION. ■2Q0 as the mode in which they perform their functions, generally elude our examination ; but we may consider them as so ma- ny vessels or apparatus appropriated to perform, with the as- sistance of the principle of life, certain chemical processes, by means of which these vegetable compounds are generated. We may, however, trace the tannin, resins, gum, mucilage, and some other vegetable materials, in the organized arrange- ment of plants, in which they form the bark, the wood, the leaves, flowers, and seeds. The bark is composed of the epidermis, the perenchyma, and the cortical layers. The epidermis is the external covering ofthe plant. It is a thin transparent membrane, consisting of a number of slen- der 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 stems of corn and of seeds, it is composed of a thin coating of silicious earth, which accounts for the strength and hardness of those long and slender stems. Sir H. Davy was led to the discovery ofthe silicious nature ofthe epider- mis 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 if to be almost entirely silicious.* Caroline. With iron, then, a cane, I. suppose, will strike fire very easily ? Airs. B. 1 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 affinity for water, tends to preserve the plant from the destructive effects of violent rains, severe Climates, or inclement seasons, to which this species of vegetables is peculiarly exposed. Ei-nily. Besin 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 unnecessary expenditure of moisture. The parenchyma is immediately beneath the epidermis ; it is that green rind which appears when you strip a branch of any tree or shrub of its external coat of bark. The pa- renchyma is not confined to the ste * or branches, but extends over every part of the plant. It forms the green matter of * In the scouring rush, [Epiisctum hyemale) the silicious epider- rn|c; 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. 300 VEGETATION. the leaves, and is composed of tubes filled with a peculiar juice. . , 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 converted into wood. Emily. But through what vessels does the sap ascend ? Airs. B. That function is performed by the tubes of the alburnum or wood, which is immediately beneath the corti- cal 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 disposed in layers, from the number of which the age ofthe tree may be compu- ted, anew one being produced annually by the conversion of the bark into wood. The oldest, and consequently most in- ternal part ofthe alburnum, is called heart wood ; it appears to be dead, at least no vital functions are discernible in it. It is through the tubes ofthe living alburnum that the sap rises. These therefore, spread into the leaves, and there communi- cate with the extremities ofthe vessels ofthe cortical layers, into which they pour their contents. Caroline. Of what use, then, are the tubes ofthe paren- chyma, 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 in different parts of the sime individual plant: they are sometimes saccharine, as in the sugar-cane, some- times resinous, as in firs and evergreens, sometimes of a milky appearance, as in the laurel. Emily. I have often observed, that in breaking a young shoot, or in bruising a leaf of laurel, a milky juice will ooze out 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 * Turpentine is obtained as described in the text. But tar and pitch are obtained by a very different method. A conical cavity is VEGETATION 301 durability of this species of wood is chiefly owing to the resi- nous nature of its peculiar juices. The volatile oils have, in a great measure, the same preservative effects, as they defend the parts with which they are connected, from the attack of insects. This tribe seems to have as great an aversion to perfumes, as the human species have delight jn 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 aromatic woods, are, on this account, of great dura- bility. Emily. But the wood of the oak, which is so much es- teemed for its durability, has, I believe, no smell. Does it derive this quality from its hardness alone ? Mrs. B. Not entirely ; for the chesuut, though considera- bly harder and firmer than the oak, is not so lasting. The durability ofthe oak, is, I believe, in a great measure, owing to its having very little heart wood, the alburnum preserving its vital functions longer than in other trees. Caroline. If incisions are made into the alburnum and cortical layers, may not the ascending and descending sap be procured in the same manner as the peculiar juice is from the vessels ofthe parenchyma ? Mrs. B. Yes ; but in order to obtain specimens of these fluids, in any quantity, the experiment must he 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 ofthe tree. From the bark the sap will flow much more plentifully than from the wood, as the ascending sap is much more liquid, more abun- dant, 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 proportion of solid matter, which retards its motion. It does not appear that there is any excess of descending sap, as none ever exudes from the roots of plants ; this process, 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 driven out, and runs into the cavity, and finally into the re- servoir. Tar is a mixture of resin, empyrcumatic oil, charcoal, and acetic acid. The colour is derived from the charcoal. Pitch is made by boiling tar, by which its more volatile parts are driven off. Ke. 27 302 VEGETATION. therefore, seems to be carried on only in proportion to the waiits ofthe plant, and the sap descends no further, and in no greater quantity, than is required to nourish the several or- gans. Therefore, though the sap rises and descends in the plant, it does not appear to undergo a real circulation. The last of U e orsans of plants, is the flower. Or blossom, which produces the fruits and seed. These may be consider- ed as the ultimate purpose of nature in the vegetable creation. From fruits and seeds animals derive both a plentiful source of immediate nourishment, and an ample provision for the reproduction ofthe same means of subsistence. The seed which forms the final product of mature plants, we have already examined, as constituting the first rudiments of future vegetation. These are the principal organs of vegetation, by means of which the several chemical processes which are carried on during the life ofthe plant are performed. Emily. But how are the several principles which enter into the composition of vegetables, so combined, by the or- gans of the piant, as to be converted into vegetable matter ? Mrs. B. By chemical processes, no doubt ; but the appa- ratus in which they are performed, is so extremely minute as completely to elude our examination. W7e can form an opinion, therefore, only by the result of these operations. The sap is evidently composed of water, absorbed by the roots, and holding in solution the various principles which it derives from the soil. From the roots the sap ascends through the tubes ofthe alburnum into the stem, and thence branches out to every extremity of the plant. Together with the sap circulates a certain quantity of carbonic acid, which is gradually disengaged from the former by the internal heat ofthe plant. Caroline. What ? have vegetables a peculiar heat, analo- gous to animal heat ? Airs. B. It is a circumstance that has long been suspected ; but late experiments have decided beyond a doubt that vege- table heat is considerably above that of unorganized matter in winter, and below it in summer. The wood of a tree, in its interior, is about sixty degrees, when the thermometer is at seventy or eighty degrees in the air. And the bark, though so much exposed, is seldom below forty in winter. It is from the sap, after it has been elaborated by the leaves, that vegetables derive their nourishment ; in its pro- gress through the plant from the leaves to the roots, it depo- sits in the several sets of vessels with which it communicates, the materials on which the growth and nourishment of each VEGETATION. 303 plant depends. It is thus that the various peculiar juices, saccharine, oily, mucous, acid, and colouring, are formed ; as also the more solid parts, fecula, woody fibre, tannin, resins, concrete salts : in a word, all the immediate materials of ve- getables, as well as the organized parts, of plants, which latter, besides the power of secreting these from the sap, for the general purpose ofthe plant, have also that of applying them to their own particular nourishment. Emily. But why should the process of vegetation take place only at one season of the year, whilst a total inaction prevails during the other ? Mrs B. Me it is such an important chemical agent, that its effect, as such, might perhaps alone, account for the im- pulse which the spring gives to vegetation. But, in order to explain the mechanism of that operation, it has been supposed that th<- warmth of spring dilates the vessels of plants, and produces ,\ kind of v icuum, into which the sap (which had remained in .1 state of inaction in the trunk during the winter) rises ; th;s is followed by the aso ?nt 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 termi- nates its .uTimer career ; but when the c>M weather sets in, the fibres and vessels contract, the leaves wither, and are no longer able to perform their office of transpiration ; and as thi- secetion 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 inaction during the winter ; or the onlv internal motion tint takes place, is that of a small quantity of resinous juice, which slowly rises from the stem into the branches, and enlarge* their buds during the winter. Caroline. Yet, in evergreens, vegetation must continue throughout the year. Mrs. B. Yes ; but in winter it goes on in a very imper- fect mariner, compared to the vegetation of spring and sum- mer. We have dwelt much longer on the history of vegetable chemistry than I 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 ac- count ofthe fermentations for the conclusion : for the decom- position of vegetables naturally follows their death, and can hardlv, it seems, be introduced with so much propriety at any oth^r period.' Ahs. B. It is difficult to determine at what point precise- ly it may be most eligible to enter on the history of vegeta- 304 COMPOSITION tion ; every part of the subject is so closely connected, and forms such an uninterrupted chain, that it is by no means easy to divide it. Had I begun with the germination ofthe seed, which, at first view, seems to be the most proper arrange- ment, I could not have explained the nature and fermentation of the seed, or have described the changes which manure must undergo, in order to yield the vegetable elements. To understand the nature of germination, it is necessary, I think, previously to decompose the parent plant, in order to become 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 ofthe subject. QUESTIONS. From whence do all animals ultimately derive their sustenance.' From whence do plants derive their food? Will plants live on pure water ? Why do animal substances make the best manure ? What part of the seed are the cotyledons ? What is the radicle ? What is the plumule ? What purpose do each of these answer during germination? What office do the leaves of plants perform during their growth ?• What different functions do the two sides of the leaves perforin ? What is essential to the developement of the colours of plants? Why is air necessary to the growth of plants ? In what way does animal and vegetable life mutually support each other? Through what vessels does the sap of plants ascend ? What is the distinction between alburnum, and heart-wood ? How is pitch, tar, and turpentine obtained ? Why do vegetables grow, only during the warm season ? CONVERSATION XXIII. i ON THE COMPOSITION OF ANIMALS. Mrs. B. We have now come to the last branch of chem- istry, which comprehends the most complicated order of com- pound 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 animals ultimately derive their nour- ishment from.vegetables, the chemistry of this order of beings OF ANIMALS. 305 must consist merely in the conversion of vegetable into ani- mal matter. Airs. B. Very true ; but the manner in which this is ef- fected is, in a great measure, concealed from our observation. This process is called animalization, and is performed by pe- culiar organs. The difference of the animal and vegetable kingdoms does not, however, depend merely on a different arrangement of combinations. 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 matters. But these are not essential to the formation of animal matter. Caroline. Animal compounds contain, then, four funda- mental principles ; oxygen, hydrogen, carbon, and nitrogen ? Airs. B. Yes ; and these form the immediate materials of animals, which are gelatine, albumen, and jibrine* Emily. Are those all ? 1 am surprized that animals should be composed of fewer kinds of materials than vegetables ; for thev appear much more complicated in their organization. Airs. B. Their organization is certainly more perfect and intricate, and the ingredients that occasionally enter into their composition are more numerous. But notwithstanding the wonderful variety observable in the texture ofthe animal or- gans, 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. Animal substances being the most complicated of all natural compounds, are most easi- ly susceptible of decomposition, as the scale of attractions in- creases in proportion to the number of constituent principles. Their analysis is, however, both difficult and imperfect ; for as they cannot be examined in their living state, and are lia- ble to alteration immediately after death, it is probable that, when submitted to the investigation of a chemist, they are always more or less altered in their combinations and proper- ties, from what they were, whilst they made part ofthe living animal. Emily. The mere diminution of temperature, which they experience by the privation of animal heat, must, I should suppose, be sufficient to derange the order of attractions that existed during life. * These arc the principal ingredients of the soft parts. But in addition to these animal substances contain colouring matter of blood, mucous, su/phur, phosphorus, earths, alkalies, oils, acids, re- sins, and several others, which it is unnecessary to specify. C. on* 306 COMPOSITION Mrs. B. That is one of the causes, no doubt ; bat there are many other circumstances which prevent us from study- ing the nature of living animal substances. We must, there- fore, 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, form the basis of all the various parts of the animal system : either solid, as the skin.- flesh, nerves, membranes, cartilages, and bones ; or fluid, as blood, chyle, milk, mucus, the gastric and pancreatic juices, bile, perspiration, saliva, tears, Sac. Caroline. Is it not surprising that so great a variety of sub- stances, and so different in their nature, should yet all arise from so few materials, and from the same original elements 1 Airs. 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 com- posed. Thus, in considering the chemical nature of the cre- ation in a general point of view, we observe that it is through- out composed of a very smattnumber of elements. Butwhen 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 ; whilst in the vegetable and animal kingdoms, the attractions are peculiarly and regu- larly 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 another ; so that the three kingdoms are in- timately connected, and constantly contributing to the preser- vation of each other. Emily. There-is, however, one very considerable class of elements, which seems to be confined to the mineral kingdom : I mean nvetdls. 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 organized bodies. Phosphorus, however, is almost entirely confined to the 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. It may be obtained from thes'e sub tances, by means of boiling^water, under the forms of glue, size, isinglass, and transparent jelly. OF ANIMALS. 307 Caroline. But these are of a very different nature ; they cannot, therefore, be all pure gelatine. Airs. B. Not entirely, but very nearly so. Glue* is ex- tracted 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 offish ; 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, ad- ded 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 ? Airs. B. Yes. Gelatine may be obtained from almost any animal substance, as it enters more or less into the composi- tion of all of them. The process for obtaining it is extremely simple, as it consists merely in boiling the substance which contains it with water. The gelatine dissolves in water, and may be attained of any degree of consistence or strength, by, evaporating this solution. Bones in particular produce it very plentifully, as they consist of phosphat of lime, combin- ed 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 jell> may be more easily extracted by the water. It is of hartshorn 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 ? Mrs. B. And (what is more surprising) it is from the ge- latine 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 or- der 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 nitrogen combined in the form of ammonia. So that the first operation is a mere separation of ingredients, whilst the second requires a chem- ical decomposition. * Bones, muscles, tendons, ligaments, membranes, and skins, all of them yield glue. But the best is nade from the skins of old ani- mals. C. 308 ^.COMPOSITION Caroline. But when jelly is made from hartshorn shavings, what becomes ofthe phosphat of lime which constitutes the other part of bones ? Mrs. B. It is easily separated by straining. But the jelly is afterwards more perfectly purified, and rendered transpa- rent, by adding white of egg, which being coagulated by heat, rises to the surface along with ary impurities. Emily.. 1 wonder that bones .ire not used by the common people to make jelly ; a great deal of wholesome nourishment, might, 1 should suppose, be procured from thern, though the jelly would perhaps not be quite so good as if made fiom hartshorn shavings. Airs. 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 excusable. Besides, it requires a prodi- gious quatitity of tuel to dissolve bones and obtain the gelatine from them. The solution of bones in water is greatly promoted by an accumulation of heat. 1 his may be effected by means ot an extremely strong metallic vessel, called Papin,s digester, in which the bones and water are enclosed, without any possi- bility ofthe steam making its escape. A heat can thus be ap- plied much superior to that of boiling water ; and bones, by this means, are completely reduced to a pulp." But the pro- cess still consumes too much fuel to be generally adopted among the lower classes. Caroline. And why should not a manufacture be estab- lished for grinding or macerating bones, or at least for redu- cing them to thestate of shavings, when I suppose they would dissolve as readily as hartshorn shavings ? Airs. B. They could not be collected clean for such a purpose ; but they ar.? 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 sediment ? Airs. B. No : nor does it so much as require clarifying, as it consists 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 perfection in the culinary laboratory, by*that very able and most useful chemist, the cook. Caroline. To what an immense variety of purposes chem- istry is subservient! OF ANIMALS. 309 Emily. It appears, in that respect, to have an advantage over most 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 inspires a general curiosity, and a desire of inquiring into the nature of every object. ' Caroline. I suppose that soup is likewise composed of ge- latine ; for, when cold, it often assumes the consistence of jelly- Mrs. B. Not entirely ; for though soups generally con- tain a quantity of gelatine, the most essential ingredient is a mucous or extractive matter, a peculiar animal substance, very soluble in .water, which has a strong taste, and is more nourishing than gelatine. The various kinds of portable soup consist of this extractive matter in a dry state, which, in or- der to be made into soup, requires only to be dissolved in water. Gelatine, in its solid state, is asemiductile transparent sub- stance, without either taste or smell.—When exposed to heat, in contact with air and water, it first swells, then fuses, and finaMy burns. You may have seen the first part of this ope- ration performed in the carpenter's glue-pot. Caroline. But you said that gelatine had no smell, and glue lias a very disagreeable one. Mrs. B. Glue is not pure gelatine : as it is not designed for eating, it is prepared without attending to the state ofthe ingredients, which are more or less contaminated by parti- cles that have become putrid. Gelatine, may be precipitated from its solutions in water, by alcohol.—We shall try this experiment with a glass of warm jelly.—You see that the gelatine subsides by the un- ion of the alcohol and the water Fmily. How is it, then, that jelly is flavoured with wine, without producing any precipitation ? Airs. B. B- cause the alcohol contained in wine is already combined with water, and other ingredients, and is, therefore, no*t at liberty to act upon the jelly as when in its separate state. Gelatine is sob-hie both in acids and in alkalies : the former, you know, aie frequently used to season jellies. Caroline. Among the combinations of gelatine we must not forget one which you formerly mentioned ; that with tan- nin, to form leather. Airs. B. True ; but you must observe that leather can be produced only by gelatine in a membranous state ; for though pure gelatine and tannin will produce a substance chemically similar to leather, yet the texture ofthe skin is 310 COMPOSITION requisite to make it answer the useful purposes of that sub- stance. The next animal substance we are to examine is alb.umen ; this, although constituting a part ofmostof,the animal com- pounds, is frequently found insulated in the animal system ; the white of egg, for instance, consists almost entirely of al- bumen : the substance that composes the nerves, the serum, or white part ofthe blood, and the curds of milk, are little else than albumen variously modified. *ln its most simple state, albumen appears in the form of a transparent viscous fluid,'possessed of no distinct ta^te or smell; it coagulates at the low temperature of 165 degrees ; and, when once solidified, it will never return to its fluid state. Sulphuric acid and alcohol are each of them capable of co- agulating 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 ob- served, that if the spoon 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 hydro- gen gas, which has the property of tarnishing silver. We may now proceed to fibrine. This is an insipid and inodorous substance, having somewhat the appearance of fine white threads adhering together: it is the essential constitu- ent of muscles, or flesh, in which it is mixed with and soften- ed by gelatine. It is insoluble both in water and alcohol, but sulphuric acid converts it into a substance very analogous to gelatine. These are the essential and general ingredients of animal matter ; but there are other substances, which, though not peculiar to the animal system, usually enter into its compo- sition, 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 vege- table oils ? Airs B. Not the same, but very analogous. The chief , difference 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 a few animal acids, that is to say, acids peculiar OF ANIMALS. 311 to animal matter, from which they are almost exclusively ob- tained. 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 formic acid, from ants. The lactic acid, from the whey of milk. The sebacic. frtern oil or fat. Those produced during the decomposition of animal sub- stances by heat, are the prussic and zoonic acids. This last is produced by the roasting of meat, and gives it a brisk fla- vour. Caroline. The class of animal acids is not very extensive. Mrs. B. No : rnx. ire tney, generally speaking, of great importance. The prussic acid* I think, the only one suffi- ciently interesting to require any further comment. It can be formed by an aHifnial process without the presence of any .tnimal matter ; it .nay likewise be obtained from a va- riety of vet;'-tables, particularly those of the narcotic kind, such as poppies, l.-nel, &.c. But it is commonly obtained from blood, by si.ondy heating that substance with cans ic potash ; the alk'di attracts the acid from the blood, and forms with it a prussiiit of potash. From this state of combination the prussic non! can be obtained pure by means of other sub- stances which have the power of separating it from the al- kali. F.mily. But if this acid does not exist ready formed in blood, how can the alkali attract it from thence ? Mrs. B. It is the triple b;\«i.- only of this acid that exists in the blood ; and this is developed and brought to the state * Prussic acid can be obtained from Prussian blue (prass'if, have been offered to ac- 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. 336 ON ANIMAL HEAT. 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. Not if the person is in a good state of health ; for the additional caloric is then carried off by the perspira- tion which succeeds. Emily. What admirable resources nature has provided for us ! By the production of animal heat she has enabled us to keep up the temperature of our bodies above that of in- animate objects : and whenever this source becomes too abun- dant, the excess is carried off by perspiration. Mrs. B. It is by the same law of nature that we are en- abled, in all climates, and in all seasons, to preserve our bodies 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 Eng- land, and in the West-Indies. Mrs. B. Yes, I do ; at least if you speak of the tempera- ture 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 temperatureof your body, ' you will scarcely perceive any difference in its indication, whatever may be the difference of temperature of theatmos- phere. Caroline. And when I feel overcome by heat, I am really not 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 tem- perature of the atmosphere, his body is certainly a little warmer than 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 per- spiration. It is chiefly the external parts that are warmer, and I am sure you will be^surprised to hear that the internal temperature of the body scarcely ever descends below nine- ty-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 ON ANIMAL HEAT. 337 that of inanimate bodies, because an excess of caloric is car- ried off by perspiration. Caroline. But the temperature of the atmosphere, and, consequently, that of inanimate bodies, is surely never so high as that of animal heat. Mrs. B. I beg your pardon. In the East and West In- dies, and sometimes in the southern parts of Europe, the at- mosphere is frequently above ninecy-eight degrees, which is the common temperature of animal heat. Indeed, even in this country, it occasionally happens that the sun's rays, set- ting full on an object, elevate its temperature above that point. In illustration ofthe power which our bodies have to re- sist the effects of external heat, Sir Charles Blagden, with some other gentlemen, made several very curious experi- ments. He remained for some time in an oven heated to a temperature not much inferior to that of boiling water, with- out suffering any other inconvenience than a profuse perspir- ation, which he'supported by drinking plentifully, Emily. He could scarcely consider the perspiration as an inconvenience, since it saved him from being baked by giving vent to the excess of caloric. Caroline. I always thought, I 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 pro- duced in consequence of a quantity of caloric being carried offin a latent state ; this is the case with perspiration, and it is in this way that it affords relief. It is on that account, also, that we are so apt to catch cold, when in a state of profuse perspiration. It is for the same reason that tea is often re- freshing in summer, though it appears to heat you at the mo- ment you drink it. Emily. And in winter, on the contrary, tea is pleasant on account of its heat. Airs. B. Yes ; for we have then rather to guard against a deficiency than an excess of caloric, arid 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 per- spiration, conjointly "with the chill occasioned by the cold draught produce 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 338 ON ANIMAL HEAT. will counteract the effects of the cold drink, and the danger will be removed. You may, however, contrary to the com- mon 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 state of great perspiration, and on condition that you keep yourself in gen- tle exercise afterwards. Emily. But since we are furnished with such resources against the extremes of heat or cold, I should have thought that all climates would have been equally wholesome. Mrs. B. That is true, in a certain degree, with regard to those who have been accustomed to them from birth ; for we find that the natives of those climates, which we consider as 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 because the animal economy does not easily accustom itself to considerable 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 ? Mrs. B. Because, if more heat be carried off by the at- mosphere than the circulation can supply, the cold will finally prevail, the heart will cease to beat, and the animal will be frozen. And, likewise, 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 destruc- tive influence. Caroline. Fish, I suppose, have no animal beat, but only partake ofthe temperature ofthe water in whieh.they live.j Emily. And their coldness, no doubt, proceeds from their not breathing. Mrs. B. AH kinds of fish breathe more or less, though in a much smaller degree than land animals. Nor 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. * The common notion on this subject is certainly the most safe. A person heated, and almost exhausted by exercise on a hot day, ought never 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. f Animals belonging to the order Cetae of Naturalists, though they inhabit the sea, breathe atmospheric air, and have hot, red blood. This order includes the whales, dolphins, narwals, &c. C. ON ANIMAL HEAT. 338 Caroline. But how can fish breathe under water ? Mrs. B. They breathe by means of the air which is dis- solved in the water ; and if you put them into water, deprived of air by boiling, they are soon suffocated. If a fish is confined in a vessel of water closed from the air,, it soon dies ; and any fish put in afterwards would be killed immediately, 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 supposed to owe the peculiar firmness and strength of their muscles, by which they are enabled to sup- port the violent exertion of flying. This difference between birds and fish, which may be con- sidered as the two extremes ofthe scale of muscular strength, is well worth observing. Birds, residing constantly with the atmosphere, surrounded by oxygen, and respiring it in greater proportions than any other species of animals, are endowed with a superior degree of muscular strength4 whilst the mus- cles offish, on the contrary, are flaccid and oily ; these ani- mals are comparatively feeble in their motions, 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 strongly characteristic of that species of animals, and which relaxes and softens the small quantity of fibrine which their muscles contain. Caroline. But, Mrs. B., there are some species of birds that frequent both elements, as, for instance, ducks and other water fowl. Of what nature is the flesh of these ? Mrs. B. Such birds, in general, make but little use of their wings ; if they fly, it is but feebly, and only to a short dis- tance. Their flesh, too, partakes of the oily nature, and even in taste sometimes resembles that offish. 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 de- ficient in muscular strength ? Airs. 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 par- take, therefore, ofthe soft oily nature of fish ; indeed, many «f them are amphibious, as frogs, toads, and snakes, and very 340 ON ANIMAL PRODVCTS. few of them find any difficulty in remaining a length of 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 pecu- liar element, and their organs of respiration being compara- tively larger than in other classes of animals. I have now given you a short account ofthe principal ani- mal functions. However interesting the subject may appear to you,, a filler investigation of it would, I fear, lead us too far from our object. Emily. Yet I shall not quit it without much regret; for of all the applications of chemistry, these appear to me the most curious and most interesting. Caroline. But, Mrs: B., I must remind you that you pro- mised to give us some account of the nature of milk. Mrs. B True. There are several other animal produc- tions that deserve likewise to be mentioned. We shall begin with tii'ilk, which is certainly the most important and the most interesting of all the animal secretions. Milk, like all other animal substances, ultimately yields by analysis, 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 point- ed out. Caroline. Yes ; it is this salt which serves to nourish the tender bones of the suckling. Mrs. B. To reduce milk to its elements, would be a very complicated, 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 for 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 ofthe milk, gradually rises to the surface. It is of this, you know, that butter is made, which is nothing more than oxygenated cream. Caroline. Butter, then, is somewhat analogous to the waxy substance formed by the oxygenation of vegetable oil. Mrs. B. Very much so. Emily. But is the cream oxygenated by churning ? * Amphibious animals have the power of suspending respiration •or a considerable time. It is in consequence of this, that they are enabled to live under water. C. ON ANIMAL PRODUCTS. 34* Mrs. B. Its oxygenation commences* previous to churn- ing, merely by standing exposed to the atmosphere, from which it absorbs oxygen. The process is afterwards comple- ted by churning ; the violent motion which this operation oc- casions brings every particle of cream in contact with the at- mosphere, and thus facilitates its oxygenation. Caroline. But the effect of churning, I have often observ- ed in the dairy, is to separate the cream into two substances, butter and butter-milk. Mrs. B. That is to say, in proportion as the oily particles ofthe cream become oxygenated, they separate from the oth- er constituent parts of the cream in the form of butter. So by churning you produce, on the one hand, butter, or oxy- genated oil ; and, on the other, butter-milk, or cream depriv- ed of oil. But if you make butter by churning new milk in- stead of cream, the butter-milk will then be exactly similar in its properties to creamed or skimmed milk. Caroline. Yet butter-milk is very different from common skimmed milk. Airs. B. Because you know it is customary, in order to save time and labour, to make butter from cream alone. In this case, therefore, the butter-milk is deprived ofthe cream- ed milk, which contains both the curd and whey. Besides, in consequence ofthe milk remaining exposed to the atmos- phere during the separation ofthe 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 oxygenation ? Mrs. B. Animal oil is not so easily acidified as the other ingredients of milk. Butter, therefore, though usually made of sour cream, is not sour itself, because the oily part ofthe cream had not been acidified Butter, however, is suscepti- ble of becoming acid by an excess of oxygen ; it is then said to be rancid, and produces the sebacic 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 al- kaline solution, the alkali would separate the acid from the butter. * It is proper to mention that the oxygenation of cream, which is taken for granted in the above theory, is a disputed fact. 30* 342 ON ANIMAL PRODUCTIONS. Caroline. You said just now that creamed milk consisted of curd and whey. Pray how are these separated 1 Mrs. B. They may be separated by standing for a certain length of time exposed to the atmosphere ; but this decom- position may be almost instantaneously effected by the chemi- cal agency of a variety of substances. Alkalies, rennet,* and indeed almost all animal substances, decompose milk by com- bining with the curds. Acids and spirituous liquors, on the other hand, produce a decomposition by combining with the whey. In order, there- fore, to obtain 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 spirituous liquors. Emily. This is a very useful piece of information ; fori find white-wine whey, which I sometimes take when I have a cold, extremely 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. I 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. 1 can, however, safely point out to you a method of obtaining whey without either alkali, ren- net, or wine ; it is by substituting lemon-juice, a very small quantity of which will separate it from the curds. Whey, as an article of diet, is very wholesome, being re- markably light of digestion. But its effect, taken medicinally, is chiefly, I believe, to excite perspiration, by being drunk warm on going to bed. From whey a substance may be obtained in crystals by evaporation, called sugar of milk. This substance is sweet to the taste, and in its composition is so analogous to common sugar, that it is susceptible of undergoing the vinous fermen- tation. Caroline. Why then is not wine, or alcohol, made from whey ? Airs. B. The quantity of sugar contained in milk is so tri- fling, that it can hardly answer that purpose. I have heard * Rennet is the name given to a watery infusion of the coats of the stomach of a sucking calf. Its remarkable efficacy in promoting coagulation is supposed to depend on the gastric juice with which it is impregnated. ON ANIMAL PRODUCTS. 343 of only one instance of its being used for the production of a spirituous liquor, and this, is by the Tartan Arabs; their abundance of horses, as well as their scarcity of fruits, has in- troduced the fermentation of mares' milk, by which they pro- duce a liquor called koumiss. Whey is likewise susceptible of being acidified by combining with oxygen from the atmos- phere. It then produces the lactic acid, which you may re- collect 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 rennet, and yet this you have just told us is not the method of obtaining pure curds ? Mrs. B. Nor are pure curds so well adapted for the form- ation of cheese. For the nature, and flavour of the cheese depend, in a great measure, upon the cream or oily matter which is left in the curds ; so that if every particlo ot cream be removed from the curds, the cheese is scarcely eatable. Rich cheeses, such as Cream and Stilton 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 compound. 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 ofthe young animal, and equally destin- ed for that purpose. Mrs. B. There is, however, a very essential difference. The young animal is fermed, as well as nourished, by the contents ofthe egg-shell ; whilst milk serves as nutriment to the suckling, only after it is born. There are several peculiar animal substances which do not enter 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 ofthe whale, which, however, must undergo a certain preparation before it is in a fit state 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 it- self, but is generally feund floating on the surface ofthe sea. Wax, you know, is a concrete oil, the peculiar product of the bee, part of the eonstituents of which may probably be 344 ON ANIMAL PRODUCTS. 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 colour, but it is bleached by long exposure to the atmosphere, or may be instantaneously whitened by the oxy-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 formation ; it is the product of an insect, which collects ita ingredients from flowers, apparently for the purpose of pro- tecting its eggs from injury. It is formed into cells, fabrica- ted with as much skill as those ofthe honey'-comb, but dif- ferently arranged. The principal use of lac is in the manu- facture of sealing-wax, and in making varnishes and lacquers. Musk, 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 ob- tained ? -■ ' Airs. B. No. Far from it, for castor oil is a vegetable oil, expressed 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 ofthe 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 ox- ygen, 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 properties of which are but very little knowm. Emily. Before we conclude the subject of the animal economy, shall we not learn by -what steps dead animals re- turn to their elementary 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 albumen, fibrine, &c. are slowly reduced to the state of oxygen, hydrogen, 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 unorganized matter, to enter into the vegetable system. Hence they were transmitted to the ON ANIMAL PRODUCTS. 345 animal kingdom ; and from this they return again to their primitive simplicity, soon to re-enter the sphere of organiz- ed existence. When all the circumstances necessary to produce ferment- ation do not take place, animal, like vegetable matter, is lia- ble to a partial or imperfect decomposition, which converts it into a combustible substance very like spermaceti. 1 dare say that Caroline, who it so fond of analogies, will consider this as a kind of animal bitumen. Caroline. And why, sljould I not, since the processes which produce these substances are so similar ? Airs. B. There is, however, one consider«ble 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 ensues. This circumstance, of the occasional conversion of animal matter into a kind of sper- maceti, is of late discovery. A manufacture has in couse- quence 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 dif- ferent process to produce hartshorn, or, more properly, am- monia, and phosphorus ; 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 ofthe several kingdoms are frequently arrested in thei>' course, and variously modified, by human skill, which compels them to contribute, under new forms, to the neces- sities or luxuries of man. But all that we enjoy, whether produced by the spontane- ous operations of nature, or the ingenious efforts of art, pro- ceed alike from the goodness of Providence.—To God alone man owes the admirable faculties which enable him to im- prove and modify the productions of nature, no less than those productions themselves. In contemplating the works of the creation, or studying the inventions of art, let us, therefore, nevr forget the Divine Source from which they proceed ; and thus every acquisition of knowledge will prove a lesson of piety and virtue. QUESTIONS. What analogy is therebetween the effects of respiration, and those of combustion ? What is the principal source of animal heat ? What are the objections to Black's theory of animal heat 346 QUESTIONS. How are these objections obviated? What objections can be brought against Dr. Crawford s theory. What does Mr. Brodie's experiment prove ? What are the objections to Dr. Cooper's theory ? What are the objections against Dr. Philip's theory ? Why is the heat increased during a fever ? Why does not violent exercise greatly increase the temperature of the body ? * . , , On what principle is it that the temperature of the body remains the same in winter as in summer ? Is the temperature of a living animal raised by being exposed to a -heat, greater than that of its own body ? How is it proved that fish cannot live without air ? What effect does the respiration of a large or small quantity of air have on the museular powers of animals ? Why are amphibious animals enabled to remain a long time under water? What is the composition of milk ? What are the ingredients in milk ? What does cream absorb from the atmosphere to turn it into butter? Why does the butter-milk become sour when the butter separated from it is sweet ? What causes butter to become rancid ? What does rennet contain which causes the coagulation of milk? What is spermaceti ? What is ambergris ? By what process does dead animal matter return to i ts elementary state ? DESCRIPTION OF THE APHLOGISTIC, OR FLAME- LESS LAMP. BY DR. J. L. COMSTOCK, OF HARTFORD. IN the construction of this Lamp, the object is to keep a coil of wire in a state of ignition, without either flame 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 platina wire red hot, and instantly hold- ing it near the surface of some ether, placed in a wine glass, the wine was kept at a red heat as long as the experiment was continued. Whether Sir Humphrey pursued the subject any further, I am not informed. It is most probable, however, that he did not, as it is stated in a London paper ofthe last year, that Prof. Ure of Glasgow had determined the circumstances which modify the performance of the lamp, and that one construct- ed by him was in. full operation in that city (London) and had excited much public curiosity. This notice contained some directions, concerning the size of the wire, to be used, and the manner of coiling it. I have however seen no descrip- tion of this lamp which would enable one readily to construct 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 involves two conditions, which are absolutely requisite, viz. that we make use of a combustible substance which evapo- rates at a low degree of heat, and a metal which is a bad con- ductor of caloric. For the combustible, alcohol seems best suited to this purpose. Sulphuric ether, aside from its high price, and disagreeable smell, 1 have sometimes found to fail ; the ignition ceasing without any obvious cause. In regard to the metal, gold and silver, both fail in conse- quence of the rapidity with which they conduct caloric. Sil- ver, too, would soon be destroyed by the intense heat. Iron, although so bad a conductor, 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 con- ductor of caloric, and not easily oxidated at the highest tem- peratures. 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. Experience has shown that this size succeeds bet- ter than any other. If larger, the heat is carried off too f..st, and the ignition ceases. If much finer, it does not retain suf- 348 DESCRIPTION OF THE ficient heat at the lower part ofthe coil to keep up the evap- oration ofthe alcohol from the wick., The coiling of the wire, and the adjustment of the wick, are the most difficult parts ofthe construction. The coil, A. fig. 1. (frontispiece) is made by winding the wire round a piece of wood, cut of the proper size, and shape. - The size is determined 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 fig- ure. (I believe this is the best shape, though I have suc- ceeded as well when the coil was ofthe same shape through- out.) In winding the coil, it is best that the turns of the wire should come in contact. Afterwards it is to be gently ex- tended, 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 enters he tube. Us length half an inch, or a little less, containing from twenty to Thirty turns ofthe wire. The projection abov:. the tube is about one .xiif of the length. B. Fig. 1. is a glas= tube, containing a cotton wick, which by capillary attraction carries the alcohol up to the platina coil. The length of this is arbii.-ary, being from one to three or four inches. 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 the tube, and then introduced about half way into the coil, so as to come even with the top ofthe tube. This requires very nice ad- justment. If the wick is too high, the wire is rapidly cooled by the alcohol, and ignition ceases in a few moments. If too low, the evaporation by the heat of the wire is insufficient. If, however, the other parts are well constructed, a few tri- als will ensure success. Fig. 2. shows the lamp complete. The body of it is a low vial, or inkstand, capable of holding about two ounce?- of al- cohol. It is stopped accurately with a cork, which is cover- ed, for ornament, with tin foil. The aperture for admitting the tube and wick, is made with a hot iron. D. is a sma'l tube through which the alcohol is poured. A dropping tube is convenient for this purpose, but a small funnel is easily made by cutting off an jnch of t'19 neck of a broken retort, into which is pushed a cork, and throut/h this a small quill. Another orifice still, f::i lettin:: off the ai., 39 the alcohol goes in, may be ri><0. through «he cork. The orifices, of course, are to be stopped, to prevent evaporation, after the lamp is charged. ■irHL»019TIC LAM>. 349 Whea 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 con- tinue red hot until the alcohol is exhausted. The explanation why the ignition ofthe wire is permanent, seems to be sufficiently simple. Alcohol, when in the state of vapour, combines with oxygen with great facility. The temperature of the wire is first raised by the flame of the candle to about 600 degrees, Fahrenheit. 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 temperature at which the alcohol is combustible, so that one portion of alcohol by the absorption of oxygen, and the con- sequent extrication of heat, lays the foundation for the com- bustion of another portion ; and as the alcohol rises in a con- stant stream, so the effect is constant. The stream of vapour is much increased by the heat ofthe lower part of the coil, where it embraces the wick, and the temperature of the al- cohol is increased before it reaches the part ofthe 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 may be obtained from it, constitutes its utility. The proper matches for this purpose are prepared by dipping 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 beiug immediately obtained by merely touching a match to the platina coil, and then to the wick ofthe 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 be obtained at Mr. Gharles Hosmer's Variety Store, in this city. 31 A ^OCABUX.&RY 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 elementary bodies forming in general a class of silbstances, which are sour to the taste, and which unite with alkalies, and metallic oxides to foim salts. Jlcidules. Substances formed by the natural combination of some acids with a quantity of potash. The oxalic and tar- taric 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 pro- pensity 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 chang- ing their qualities. -------of composition. That force by which substances of different kinds combine, and form a third, which differs from either of the two first, before the combination. Thus muriatic acid and soda form common, salt. Albumen. Coagulable lymph. It is contained in animal sub- stances, 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 taste, 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. A VOCABULAR* OF CHEMICAL TERMS. 35l for the purpose of delecting 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. Jlrseniates. Salts formed by the combination of a base with the arsenic acid. Azote. This name is given by the French chemists to nitro- gen, which see. B. Balsams. Resinous, semi-fluid substances, which are obtain- ed 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. C- Calcareous. A chemical term formerly applied to describe chalk, marble, and all other combinations of lime with car- bonic acid. Calcination. The application of heat to saline, metallic, or other substances ; so regulated as to deprive them of mois- ture, &c. and yet preserve them in a pulverulent form. Caloric. The chemical term for the matter of heat. -------free. Is caloric in a separate state, or, if attached to other substances, not chemically united with them. ------latent. Is the term made use of to express that por- tion of caloric which is chemically united to any substance, so as to become a part of the said substance. Calorimeter. An instrument for ascertaining the quantity of caloric disengaged from any substance that may be the Ob- ject of experiment. Calx. An old term made use of to describe a metallic oxide. Camphorates. Salts formed by the combination of any base with the camphoric acid. 352 A VOflABWLARY Capillary. A term usually applied to the rise of the sap in vegetables, or the rise of any fluid in very small tubes ; ow- ing to a peculiar kind of attraction, 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 constituent parts. T hus plumbago, which is compo- sed of carbon and iron, is called carburet of iron. Causticity. That quality in certain substances by which they burn or corrode animal bodies to which they are applied. It js best explained by the doctrine of chemical affinity. Chalybeate. A term descriptive of those mineral waters which are impregnated with iron. Charcoal. Wood burnt in close vessels : it is an oxide of car- bon, and generally contains a small portion of salts and earth. Its carbonaceous matter may be converted by com- bustion 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 ending 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 substan- ces, excepting light and caloric, which prevents bodies from falling in pieces. Columbates. Salts formed by the combination of any base with the columbic acid. Combination. A term expressive of a true ehemical union of two ot more substances ; in opposition to mere mechani- cal mixture. Combustibles. Certain substances which are capable of com- bining more or less rapidly with oxygen. They are divi- ded by chemists into simple and compound combustibles. Combustion. The act of absorption of oxygen by combustible bodies from atmospheric or vital air. The word decom- bustion is sometimes used by the French writers to signify the opposite operation. Crucibles. Vessels of indispensable use in chemistry in the various operations of fusion by heat. They are made of baked earth, or metal, in the form of an inverted cone. OF CHEMICAL TERMS. 353 Crystallization. An operation of nature", in which various earths, salts, and metallic substances, pass from a fluid to a solid state, assuming certain determinate geometrical fig- ures, t -----------•----water of. That portion which is combined with salts in thr- act of crystallizing, and becomes a compo- nent part ofthe said saline substances. 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 melting them with lead. The process is called cupellation. D. Decomposition. The separation ofthe constituent principles of compound bodies by chemical means. Deflagration. The vivid combustion that is produced when- ever nitre, mixed with an inflammable substance, is exposed to a red heat. It may be attributed to the extrication of oxygen from the nitre, and its being transferred to the inflammable body ; as any of the nitrates or oxygenized muriates 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 attraction for that fluid. Deoxidize (formerly deoxidate.) To deprive a body of oxy- gen. Deoxidizement. A term made use of to express that opera- tion by which one substance deprives another substance of its oxygen. It is called unburning 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 substance in a liquid, with the application of heat. Digestor, Papin's. An apparatus for reducing animal or ve- getable substances 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 alco- hol. Thus we have dulcified spirit of nitre, dulcified spirit of vitriol, &c. 31* 354 A VOCABULARY E. Edulcoration. Expressive of the purification of a substance by washing with water. Effervescence. An intestine motion which takes place in cer- tain bodies, occasioned by the sudden escape of a gaseous substance. Efflorescence. A term commonly applied to those saline crys- tals which become pulverulent on exposure to the air, in consequence of the loss of a part ofthe water of crystalliza- tion. 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 gas- es. Vapour is called an elastic fluid ; gas, a permanently elastic fhiid. Elective Attractions. A term used by Bergman and others to designate what we now express by the words chemical af- finity. 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 matter 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 atmospheric air, owing to the chem- ical attraction ofthe latter for water. Eudiometer. An instrument invented by Dr. Priestley for determining the purity of any given portion of atmospheric air. The science of investigating the different kinds of gases is called eudiornetry. F. Fermentation. A peculiar spontaneous motion, which takes place in all vegetable matter when exposed for a certain time to a proper degree of temperature. Fibrine. That white fibrous substance which is left after freely washing the coagulum ofthe blood, and which chief- ly composes the muscular fibre. OF CHEMICAL TERMS. 355 Flowers. In chemical language, are solid dry substances re- duced to a powder by sublimation. Thus we have flowers of arsenic, of sal ammouiac, of sulphur, &.c. which are ar- senic, sal ammoniac, and sulphur, unaltered except in ap- pearance. Filiates. 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 fulmina- ting powders, which explode with a loud report by friction, or when slightly heated. Fusion. The state of a body which was solid in the tempera- ture ofthe atmosphere, 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 pheno- mena, resulting from different conductors of electricity pla- ced in different circumstances of contact; particularly the nerves ofthe 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 appara- tus contrived to measure, collect, preserve, or mix the dif- ferent 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 par- ticularly in the tendons 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. Oth- er 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 con- tains 7000 grains. 356 A VOCABULARY Granulation. The operation of pouring a melted metal into , water, in order to divide it into small particles for chemical purposes. Tin is thus granulated 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 wa- ter. It is generally expressed by decimals. Gums. Mucilaginous exudations from certain trees. Gum consists of lime, carbon, ogygen, hydrogen, and nitrogen, with a little phosphoric acid. H. Heat, matter of. See Caloric. Hermetically. A term applied to the closing ofthe orifice of a glass tube, so as to render it air-tight. Hermes, or Mer- cury, 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 ofwater. ------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 in- flammable air. Hydro-Carbonates. Combinations of carbon with hydrogen are described by this term. Hydro-carbonate gas is pro- cured from moistened charcoal by distillation. Hydrogenized sulphurets. Certain bases combined with sul- phuretted hydrogen. Hydro-Oxides. Metallic oxides combined with water. Hydrometers. Instruments for ascertaining the specific gravi- ty of spiritous liquors or other fluids. Hygrometers. Instruments for ascertaining the degree of moisture in atmospheric air. Hyperoxygenized. A term applied to substances which are combined with the largest possible quantity of oxygen. We have muriatic acid, oxygenized muriatic acid, and hy- peroxygenized muriatic acid. The latter can be exhibited only in combination. I. Inflammation. A phenomenon which takes place on mixing certain substances. The mixture of oil of turpentine with OF CHEMICAL TERMS. 357 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 chemi- cal affinity. Oil, for example, has no affinity "for water, unless it be previously combined with an alkali ; it then be- comes soap, and the alkali is said to be the intermedium which occasions the union. K. Kali. A genus of marine plants which is burnt to procure mineral alkali by afterwards lixiviating the ashes. L. Laboratory. A room fitted up with apparatus for the perfor- mance of chemical operations. Lactates. Salts formed by 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, Argand's. i.A kind of lamp much used for chemical experiments. It is made on the principle of a wind fur- nace, and thus produces a great degree of light and heat without smoke. Lens. A glass, convex on both sides, for concentrating the rays of the sun. It is employed by chemists in fusing re- fractory substances which cannot be operated upon by an ordinary degree of heat. 'Levigation. The grinding down of hard substances to an impalpable powder on a stone with a muller, or in a mill adapted to the purpose. Litharge. An oxide of lead which appears in a state of vitri- fication. 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 prevent the escape of gas or vapour in distilla- tion. M. Maceration. The steeping of a solid body in a fluid, in order to softeu it, without impregnating the fluid. 358 A VOCABULARY Malates. Salts formed by the combination of any base with malic acid. Malleability. That property of metals which gives them the capacity of being extended and flattened by hammering. It is probably occasioned by latent caloric. Massicot. A name given to the yellow oxide of lead, as mini- um 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 in acids. Mineral. Any natural substance of a metallic, earthy, or sa- line nature, whether simple or compound, is deemed a mineral. 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 solution. They are frequently termed Medicinal Waters. Molybdiates. Salts formed by the combination of any base with the molybdic acid. Mordants. Substances which have a chemical affinity for par- ticular colours ; they are employed by dyers as a bond to unite the colour with the cloth.inte put a grain or two of iodine. Warm the tube, (but not at that part where the iodine is,) and immediately cork it tight; the tube remains colourless, there being 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 a pulse glass, containing the iodine hermetically sealed, would be better. Such a little apparatus would be quite a curiosity to those who know nothing ofthe nature of iodine. See p. 248. 30. Write on paper with a solution of the nitrat 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 remains invisible ; but on exposure to the rays ofthe sun the characters turn yellow, and finally black, so that they are perfectly legible. Mr. Accum says, that this change of colour is owing to the partial reduction ofthe oxide of silver from the light expel- ling a portion 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 su- gar of lead: the writing will remain invisible. But on mois- tening the lin#s with a pencil, or feather dipped in water im- pregnated with sulphuretted hydrogen, the metal is revived, and the letters appear in metallic brilliancy. The author above cited, says, that in this instance, the hy- drogen ofthe sulphuretted hydrogen gas, abstracts the oxy- gen from the oxide of lead, and Gauses it to re-approach to Ihe metallic state ; at the same time, the sulphur ofthe sul- phuretted hydrogen gas combines with the metal thus regen- erated, and converts it into a sulphuret, which exhibits the metallic colour. i EXPERIMENTS. 373 32. Write on paper with a solution ofthe sulphate of cop- per. If this is strong, the writing will be of a faint green co- lour ; if weak, the characters are invisible. On holding the paper over a vessel containing some liquid ammonia, or if it be exposed to the action of this gas in any other way, the wri- ting assumes a beautiful blue colour. On exposing the paper to the sun, the colour disappears, because the ammonia evap- orates. 33. Put a small piece of phosphorus into a crucible, cover it closely with common chalk, so as to fill the crucible. Let another crucible be inverted upon it, and both subjected to the fire. When the whole has become perfectly red-hot, re- move them from the fire, and when cold, the carbonic acid of the chalk will have been decomposed, and the Black Char- coal, the basis ofthe acid, may be easily perceived amongst the materials* 34. Into a large glass jar, inverted upon a flat brick tile, and containing near its top a branch of fresh rosemary, or any other suchshrub, moistened with/water, introduce aflat, thick piece of heated iron, on which place some gum benzoin in gross powder. The benzoic 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 upontha leaves ofthe vegetable. This will serve as an ex- ample of Sublimation. 35. Mix a little acetate of lead with an equal portion of sulphate of zinc, both in fine powder; stir them together with a piece of glass or wood, and no chemical change will be perceptible : but if they be rubbed together 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, the experiment 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 be complete- ly ignited. 38. If a few pounds of a mixture ofiron filings and sulphur be made in paste with water, and buried in the ground for a few hours, thp water will be decomposed with so much ra- pidity, that combustion and flame will be the consequence. 39. For want of a proper glass vessel, a table spoonful of ether may be put into a moistened bladder, and the neck of 33 371 EXPERIMENTS. 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 ammonia, and stop the phial so as to exclude all atmospheric air. If left in this state, no solution of the cop- per 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 colourless. Let the stopper 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 colour, which it will recover only by the re-admission of air. These effects may thus be repeatedly produced. 41. If a spoonful of good alcohol and a little boracic acid be stirred 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 apiece of charcoal, attach a blow-pipe to a gasom- eter charged with oxygen gas, light the charcoal first with a bit of paper, and keep up the heat by pressing upon the ma- chine. When the metals get into complete fusion, the lead will begin to burn, and very soon will be all dissipated in a white smoke, leaving the silver in a state of purity. This experiment is designed to show the fixity ofthe noble metals. 43. Burn a piece of iron wire in a deflagrating jar of oxy- , gen 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 igni- ted sulphur be now introduced, this will also burn for alimit- ed time. Lastly, introduce a morsel of phosphorus, ancLcom- bustion will also follow in like manner. These experiments fchow 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 t. This will afford the most brilliant combustion under wa- fer 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 tritare, and they will instantly become fluid. 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 milkiness will EXPERIMENTS. 375 immediately be produced, more or less, according to the de- gree of its impurity. This is-a good , ckhod of ascertaining the purity of spring water. 47. To silver copper, or brass.—Clean the article intend- ed to be silvered, by means of dilute nitric acid, or bv scour- ing it with a mixture of common salt and alum. WThen it is perfectly bright, moisten a liitle of the powder, known in commerce by the name of silvering powder, with water, and rub it for some time on the perfectly cle?n surface of cop- per, or brass, which will become covered with a coat of me- tallic silver. It may afterwards be polished with soft leather. The silvering powder is prepared in the following manner : Dissolve some silver in nitric acid, and put pieces of copper into the solution ; 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 common salt, and half a drachm of alum. Another method : Precipitate silver from its solu- tion in nitric acid by copper, as before ; to half an ounce of this silver, add common salt and muriate of ammoniac, 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 previously boiled with acidulous tartarite of potash and alum, are to be rubbed ; after which they are to be made red-hot, and polished. 48. To prove that the air ofthe atmosphere always contains carbonic acid. This may be shewn by simply pouring any quan- tity of barytic water, or lime water, repeadedly from one ves- sel into another. The barytic water, when deprived ofthe contact of air, is perfectly transparent; but it instantly be- comes 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, seldom varies, except in the immediate vicinity of places where respiration and combustion are going on in the large way, and is about one hundredth part. INDEX; A Absorbent vessels, 317 Absorption of caloric, 84, 37 Acetic acid, 209, 265 Acetous fermentation, 282 acid, 266 Acidulous gaseous mineral wa- ters, 234 salts, 267 Acids, 207 Aeriform, 20 Affinity, 11,176 Agate, 199 Agriculture, 289 Air, 90 Albumen, 305 Alburnum, 301 Alchemists, 3 Alcohol, or spirit of wine, 274 Alembic, 124 Alkalies, 183 Alkaline earths, 184, 198 Alloys, 162 Alum, or sulphat of alumine, 200, 219 Alumine, 200 Alumium, 8 Amalgam, 263 Ambergris, 343 Amethyst, 202 Amianthus, 205 Ammonia, or yolatile alkali, 170, 184, 191 Ammoniacal gas, 191 how obtained, 193 Analysis, 136 of vegetables, 268 Animals, 304 Animal acids, 210 colours, 313 heat, 334 oil, 256, 310 Animalization, 305, 314 Antidotes, 203 Antimony, 8 Aqua fortis, 223 * regia, 160 ^ Arrack, 276 Argrand's Lamp, 102 Arsenic 8, 160, 164 Arteries, 317 Arterial blood, 226, 329 Aspbaltum, 285 Assafoetida, 261 Assimilation, 316 Astringent principle, 266 Atmosphere, 51, 89, 103 Atmospherical air, 90 Attraction of aggregation, or co- hesion, 10, 176• Attraction of composition, 11,173 Azote, or nitrogen, 221 Azotic gas, 90 B Balsams, 261 Balloons, 118 Bark, 299 Barytes, 195,202 Basis of acids, 121, 209 gases, 30 salts, 174 Beer, 272 Benzoic acid, 209, 265 Bile, 324 Birds, 317,339 Bismuth, 8 Bitumens, 285 Black lead, or plumbago, 144 Bleaching, 216 Blow-pipe, 139, 153 Blood, 328, 330 Blood-vessels, 330 Boiling water, 58 Bombic acid, 318, 344 Bones, 315, 345 Boracic acid, 235, 171 Boracium, 7, 236 Borat of soda, 234 Brandy, 275 Brass, 162 Bread, 283 Bricks, 201 Brittle metals, 8 378 INDEX. BroHze. 162 Butter, 340 Butter-milk, 341 C Calcareous earths, 202 stones, 231 Calcium, 7 Caloric, 18 absorption of, 35 conductors of, 37 combined, 60 expansive power of, 19,20 equilibrium of, 28 reflexion of, 34 radiation of, 28, 32 solvent power of, 49 capacity for, 62 Calorimeter, 76 Calx, 97 Camphor, 260 Camphoric acid, 209 Caoutchouc, 262 Carbonats, 186, 234 Carbonat of ammonia, 194 lead, 151 lime, 204 magnesia, 205 potash, 187 Carbonated hydrogen gas, 143 Carbon, 134 Carbonic acid, 138,229,230 Carburet ofiron, 144 Carmine, 313 Cartilage, 317 Castor, 344- Cellular membrane, 320 Caustics, 164 Chalk, 204, 234 Charcoal, 135 Cheese, 343 Chemical attraction, 9, 173 Chemistry, 2 - Chest, 325 China, 201 Chlorine, 7, 243 Chrome, 9, 161 Chvle, 318 Chyme, 324 Citric acid, 265, 209 » Circulation of the blood, 326 Civet, 344 Clay, 26,202 Coke, 286 Coal, 235 Cobalt, 9 Cochineal, 313 Cold, 29 from evaporation, 51, 55, 74 Colours of metallic oxpds, 151 Columbium, 9, 160 Combined caloric, 61 Combustion, 94 volatile products of, 102 fixed products of, 102 of alcohol, 278 of ammoniacal gas, 191 of boracium, 236 by oxymuriatic acid or chlorine, 240 of carbon, 139 of coals, 115, 143 of charcoal by nitric acid, 222 of candles, 114, 146 of diamonds, 139 of ether, 280 of hydrogen, 105, 112 ofiron, 99 of metals, 152 of oils, 146 of oil of turpentine by ni- trous acid, 175 of phosphorous, 130 ofsulphur,125 of potassium, 170 Compound bodies, 5, 183 or neutral salts, 185 Conductors of heat, 37 solids, 40 fluids, 41 Count Rumford's theory, 41 Constituent parts, 5 Copper, 8, 165 Copal, 261 Cortical layers, 299 Cotyledons, or lobes, 294 Cream, 340 Cream of tartar, or tartrit of pot- ash, 277 Cryophorus, 75 Crystallization, 159 Cucurbit, 124 Culinary heat, 45 Curd, 340 Cuticle, or epidermis, 320 Cyatfogen, 312 INDEX. 379 D Decomposition, 5, U of atmospherical air, 92, 95 of water by the Voltaic battery, 107 of salts by the Voltaie bat- tery, 181 of water by metals, 109, 337 by carbon, 143 of vegetables, 268 of potash, 169 of soda, 170 of ammonia, 170, 191 of\the boracic acid, 236 ofthe fluoric acid, 237 ofthe muriatic acid, 239 Deflagration, 229 Definite proportions, 179 Deliquescence, 218 Detonation, 111, 120 Dew, 53 Diamond, 136 Diaphragm, 325 Digestion, 323 Dissolution of metals, 81,157,149 Distillation, 124,214 of red wine, 276 Divellent forces, 178 Division, 5 • Drying oils, 258 Dyeing, 263 E Earths, 145 Earthen ware, 201 Effervescence, 141 Efflorescence, 218 Elastic fluids, 20 Electricity, 78, 83. 85 Electric machine, 82 Electro-magnetism, 88 Elective attractions 176 Elementary bodies, 5 Elixirs, tinctures, or quintescen- ces, 278 Enamel, 201 Epidermis of vegetables, 299 of animals, 320 Epsom salts, 206 Equilibrium of caloric, 27 Essences, 145, 259, 278 Essential, or volatile, oils, 145, 259 Ether, 56, 280 Evaporation, 51 Evergreens, 303 Eudiometer, 132 Expansion of caloric, 19 Extractive colouring matter, 262 F Falling stones, 161 Fat, 341 Feathers, 315 Fecula, 256 Fermentation, 270 Fibrine, 305, 310 Fire, 4, 15 Fish, 338 Fixed air, or carbonic acid, 138, 231 alkalies, 184 oils, 145, 256 products of combustion, 102 Flame, 115 Flint, 189, 199 Flower or blossom, 302 Fluoric aeid, 237 Fluorium, or Fluorine, 7, 238 Formic acid, 311 Fossil wood, 286 Frankincense, 261 Free or radiant caloric, or heat of temperature, 18 Freezing mixtures, 70 by evaporation. 56, 73 Frost, 52 Fruit, 302 Fuller's earth 200 Furnace, 144, 149 G Galls, 266 Gallat ofiron, 219 Gallic acid, 219, 266 Galvanism, 79 Gas, 90 Gas lights, 116 Gaseous oxyd of carbon, 140 nitrogen, 226 Gastric juice, 323 Gelatine, or jelly, 305, 306 Germination, 294 380 INDEX. Gin, 276 Glands, 319, 315 Glass, 188 Glauber's salts, or sulphat of so- da, 187 Glazing, 201 Ghicium, 8 Gluo, 307 Gluten, 256 Gold, 8, 160 Gum, 253 arabic, 253 elastic, or caoutchouc, 262 resins, 261 Gunpowder, 228 Gypsum, or Plaster of Paris, or sulphat of lime, 218 H Hair, 319 Harrogate water, 129 Hartshorn, 191, 193 Heart 325 wood, 300 Heat, 15, 18 of capacity, 63, 66 of temperature, II Honey, 256 Horns, 307, 315 Hydro-carbonat, 144,116 Hydrogen, 104 gas, 105. I and J. Jasper, 199 Ice,76 Jelly, 308 Jet, 285 Ignes fatui, 132 Ignition, 59 Imponderable agents, 6 Inflammable air, 105' Ink,219 Insects, 266 Integrant parts, 5 Iodine, 104, 247 Iridium, 9 Iron, 8, 155, 161 Isinglass, 307 Ivory black, 313 K Kali, 190 Koumiss, 343 L. Lac 3-14 Lactic acid, 311, 343 Lakes, colours, 262 Lamp without flame, 102, 347 Latent heat, 65. Lavender water, 278 Lead, 8, 151,156 Leather, 264, 309 Leaves, 296 Life, 250 Ligaments, 317 Light, 7, 18, 296 Lightning, 222 Lime, 202 water, 203 Limestone, 202 Linseed oil, 258 Liqueurs, 278 Liver, 319 Lobes, 294, 330 Lunar caustic, or nitrat of silver, 164, 229 Lungs, 328, 330 Lymph, 317 Lymphatic vessels, 317 M. Magnetic needle, 88 Magnesia, 205 Magnium, 8 Malic acid, 209, 265 Malt, 272 Malleable metals, 8 Manganese, 8, 150 Manna, 256 Manure, 290 Marble, 234 Marine acid, or muriatic acid, 238 Mastic, 261, 278 Materials of animals, 305 of vegetables, 250 Mercury, 8, 162 , new mode of freezing, 76, 163 Metallic acids, 160 oxyds, 150 Metals, 149 Meteoric stones, 161 Mica, 205 INDEX. 351 Milk, 314, 318 Minerals, 149 Mineral waters, 141, 209 acids, 209 Miner's lamp, 121 Mixture, 4Q Molybdena, 9, 160 Mordant, 263 Mortar, 205 Mucilage, 253 Mucous acid, 209, 253 membrane, 320 Muriatic acid, or marine acid, 238 Muriats, 244 Muriat of ammonia, 191, 245 lime, 71 soda, or common salt, 238,244 potash, 239 Muriatium, 7 Muscles of animals, 315 Musk, 344 # Myrrh, 261 N. Naphtha, 168, 285 Negative electricity, 13, 78, 83 Nerves, 319 Neutral, or compound salts, 20.7 Nickel, 8, 161 Nitre, or nitrat of potash, or salt- petre, 223, 228 Nitric acid, 221 Nitrogen, or azote, 90 gas, 89, 90 Nitro-muriatic acid, or aqua re- gia, 241 Nitrous acid gas, 225 air, or nitric oxyd gas, 224 Nitrats, 226 Nitrat of copper, 174 ammonia, 226,229 potash, or nitre, or salt- petre, 190,228 silver, or lunar caustic, 229 Nomenclature of acids, 126,207 compound salts, 174 Nomenclature of other binary oompounds, 132 Nut-galls, 220 Nut-oil, 258 Nutrition, 314 O. Ochres, 151 Oils, 145, 256 , Oil of amber, 286 ■-----vitriol, or sulphuric acid, 212 Olive oil, 257 Ores, 149 Organized bodies, 250 Organs of animals, 319 vegetables, 304 Osmium 8, 163 Oxalic acid, 209, 266 Oxyds, 97, 157 Oxyd of manganese, 150 iron, 97 lead, 151 sulphur, 217 Oxydation, or oxygenation, 156 Oxygen, 7, 126 gas, or vital air, 90 Oxy-muriatic acid, 240 Oxy-muriats, 246 Oxy-muriat of potash, 246 P. Palladium, 7,163 Papin's digester, 308 Parenchyma, 294, 299 Particles, 9 Pearl-ash, 186 Peat, 286 Peculiar juice of plants, 300 Perfect meials, 8, 153 Perfumes, 259 Perspiration, 332 Petrification, 285 Pewter, 162 Pharmacy, 2 Phosphat of lime, 220 Phosphorated hydrogen gas, 132 Phosphorescence, 17 . Phosphoric acid, 220 Phosphorus, 129 acid, 220 Phosphuret of lime, 133 sulphur, 133 Pitch, 299 Plaster, 265 Platina, 8, 155 Platina ignited by a lamp without flame, 102 * Plating, 162 382 in Plumbago, or black lead, 161 Plumula, 294 Porcelain, 201 Positive electricity, 13, 78, 83 Potassium, 167 Pottery, 201 Potash, 185 Precipitate, 12 Pressure of the atmosphere, 58, 59 Printers' ink, 242 Prussiat of iron,or Prussian blue, 312 potash, 311 Prussic acid, 311 Putrid fermentation, 283, 344 Pyrites, 219, 160 Pyrometer, 20, 26 Q. Quicklime, 202 Quiescent forces, 178 B Radiation «f caloric, 28 Prevost's theory, 29 Pictet's explanations, 31 Leslie's illustrations, 32 Radicals, 207, 210 Radicle, or "root, 294 Rain, £3 Rancidity, 258 Rectification, 277 Reflexion of caloric, 32, 29 Reptiles, 339 Resins, 260 Respfration, 324, 328 Reviving of metals, 154 Rhodium, 9,163 Roasting metals, 149 Rock crvstal, 199 Ruby, 197 Rum, 276 Rust, 150,155 S. - gaccharine fermentation, 271 Sal ammoniac, or muriat of am- monia, 191 polychrest, or sulphat of potash, 217 volatile, or carbonat of ammonia, 194 Salifiable bases, 174 Salifying principle J, 174 Saltpetre, or nitre, or nitrat of potash, 228 Salt, 217 Sand,199 • Sandstone, 199- Sap of plants, 272,253, 300 Sapphire, 197 Saturation, 51 Seas, temperature of, 43 Sebacir: acid, 258,311 Secretions, 331 Seeds of plants, 272, 302 Seltzer water, 142, 204 Senses, 320 Silex, or silica, 195, 199 Siliciurn, 8 Silk, 344 Silver, 152 Simple bodies, 5 Size, 307 Skin, 306, 320 Slaking of lime, 203 Slate, 200 Smelting metals, 149 Smoke, 102 Soap,186 Soda, 170, 190 wr.ter, 142 Sodium, 7,170 Soils, 289 Sold^r'ug, 162 Solubility, 217 Solution, 48 by the air, 49 of potash, 188 Specific heat, 62 Spermaceti, 343 Spirits, 275 Spirit lamp, Starch-sugar, 254 Steam, 60, 68 Steel, 144 Stomach, 323 Stones, 196 Stucco, 205 Strontites, 206 Strontium, 8 Suberic acid, 209, 265 Sublimation, 124 Succin, or yellow amber, 286 Succinic acid, 209, 265 INDEX. 383 Sugar, 255, 271 of milk, 342 Sulphats, 174 Super-oxygenated sulphuric a- cid, 208 Sulphat of alumine, or alum, 200, 219 barytes, 202 iron, 219 lime, or gypsum of plaster of Paris, 218 magnesia, or Epsom salt, 206, 218 - potash, or sal polychrest, 217 soda, or Glauber's salts, 217 Sulphur, 123 flowers Of, 124 Sulphurated hydrogen gas, 129 Sulphurets, 160 Sulphurous acid, 127, 215 Sulphuric acid, 213 Sympathetic ink, 166 Synthesis, 136 T. Tan, 263 Tannin, 264, 283 Tar, 247 Tartarous acid, 265 Tartrit of potash, 267 Teeth, 315 Telluriam, 9 Temperature, 18 Thaw, 76 Thermometers, 21 Fahrenheit's, 22 Reaumur's, 23 Centrigrade, 23 air, 23 differential, 24 Thunder, 119 Tin, 8 Titanium, 9, 163 Turf, 2'uG Turpentine, 175 Transpiration of plants, 296 Tungsten, 9, 160 V Vapour, 59, 68, 280 Vaporisation, 51 Varnishes, 261 Vegetables, 250 Vegetable acid, 251, 147 colours, 262 heat, 302 oils, 259 Veins, 321, 326 Venous blood, 327, 330 Ventricles, 327 Verdigris, 165 Vessels, 317 Vinegar, 282 Vinous fermentation, 273 Vital air, or oxygen gas, 90 Vitriol, or sulphat ofiron, 212 Volatile oils, 251, 256,25» products of combustion, 101 alkali, 184,191 Voltaic battery, 81, 149, 153, 169,181 U Uranium, 9 W Water, 105,113 decomposition of by elec- tricity, 113, 148 condensation of, 43 of the sea, 44 boiling, 47 solution by, 50 ofcrystalization, 159 Wax, 257, 343 Whey, 340 Wine, 273 Wood, 300 Woody fibre, 251,265 Wool, 315 Y Yeast, 282 Yttria, 195 Yttrium, 8 Z Zinc, 8 Zicornia, 195 Zincornium, 3 Zoonic aoid, 210, 311 '0- 3Ni:>ia3w jo Aavaan ivnouvn is* 3Ni3ia3w jo Aavaan ivnouvn NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIC 3NIDIQ3W jo Aavaan ivnouvn 3NiDia3w jo Aavaan ivnouvn U \ >4 i gk > % i NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE SNioiasw jo Aavaan ivnouvn 3NIDIQ3W JO Aava8IT IVNOUVN tfj. \, NATIONAL LIBRARY OF MEDICINE 'V ir/ V ,^' NATIONAL LIBRARY OF MEDICINE aNoiasw jo Aavaan ivnouvn /X^rt-X-S. ° 3NiDia3w jo Aavaan ivnouvn NATIONAL LIBRARY OF MEDICINE i - ,^t> ■% l'tX-w" X < r —Oft 0- x\^~ NATIONAL LIBRARY OF MEDICINE \ ^ in ^r te^ '^. 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