M- A A COMPENDIUM OF THE COURSE OF CHEMICAL INSTRUCTION IN THE MEDICAL DEPARTMENT OF THE UNIVERSITY OF PENNSYLVANIA. BY ROBERT HARE, M.D. PROFESSOR OF CHEMISTRY. IN TWO PARTS. PART I. COMPRISING THE CHEMISTRY OF HEAT AND LIGHT, AND THAT OF INORGANIC SUBSTANCES, USUALLY CALLED INORGANIC CHEMISTRY. FOURTH EDITION. WITH AMENDMENTS AND ADDITIONS. PHILADELPHIA: J. G. AUNER, No. 343 MARKET STREET John C. Clark, Printer. 1840. Aftnt* 14 zi5c PREFACE TO THE FIRST EDITION. Where a subject cannot be followed by a reader without study, it would seem unreasonable to expect that, without some assistance, it should be followed at a lecture. Under this impression, from the time that I became a lecturer, I applied myself so to improve and multiply the means and methods of experimental illustration, as to render manipulation easier, and the result more interesting and instructive. But notwithstanding all my efforts, there remained obstacles to be sur- mounted. However striking might be the experimental illustration of a property or principle, the rationale might be incomprehensible to a majority of my class, unless an opportunity for studying it were afforded them. Again, some of my contrivances, which greatly facilitated my experi- ments, were too complex to be understood without a minuteness of expla- nation, which, even if it were useful and agreeable to some of my hearers, might be useless and irksome to others; and to such minutiae I have not deemed it expedient to exact attention. A chemical class, in a medical school, usually consists of individuals, who differ widely with respect to their taste for chemistry, and in opinion as to the extent to which it may be practicable or expedient for them to learn it. There is also much disparity in the opportunities which they may have enjoyed, of acquiring some knowledge of this science, and of others which are subsidiary to its explanation. Hence a lecturer may expatiate too much for one portion of his auditors, and yet be too concise for another portion. While to the adept he may often appear trite, to the novice he may as often appear abstruse. Some pupils, actuated by a laudable curiosity, under circumstances per- mitting its indulgence, may desire an accurate knowledge of the apparatus by which my experimental illustrations are facilitated: other pupils may feel themselves justified, perhaps necessitated, not to occupy their time with the acquisition of any knowledge which is not indispensable to graduation. After some years' experience of the difficulties abovementioned, I came to the conclusion, that the time spent in the lecture room might be rendered much more profitable, if students could be previously apprized of the chain PREFACE. of ideas, or the apparatus and experiments, to be subjected to attention at each lecture; especially as the memory might afterwards be refreshed by the same means. In consequence of this conviction, the minutes of my course of instruction were printed; and subsequently a work, comprising engravings and descriptions of the larger portion of such of my apparatus and experiments, as could in this way be advantageously elucidated. En- couraged by the success of my plan, I am now preparing an edition which will be still more extensive. The work thus expanded, I have entitled " A Compendium of the Course of Chemical Instruction in the Medical School," &c. There will be much matter in the Compendium, respecting which I shall not question candidates at the examination for degrees. With the essence of the larger part, I shall undoubtedly expect them to be acquainted; but other portions have been introduced, that I may not be obliged to dwell upon them in my lectures, and that attention to them may be optional on the part of the students. To designate the portion of the work, respecting which candidates for degrees will not be questioned, I have had it printed in a smaller type, excepting where it was too much blended with subjects of primary importance to be separated. I wish it, however, to be under- stood, that I shall expect attention to the parts thus distinguished, bo far as they may be necessary to a comprehension of the rest. Thus, although I do not deem it to be a part of my duty to question a pupil on pneumatics, I shall expect him to understand the influence of atmospheric pressure upon chemical reaction, and in pneumato-chemical operations. One great and almost self-evident advantage, resulting from my under- taking, I have yet to mention; I allude to the instruction which students may derive from the Compendium, either before or subsequently to their attendance on my lectures, and especially during the period which inter- venes between their first and second course. PREFACE TO THE FOURTH EDITION. The suggestions, which were made in the Preface to the first edition of the Compendium, respecting the necessity of an appropriate text book, to aid and extend the instruction afforded by the course of chemical lectures, delivered in the Medical Department of the University of Pennsylvania, have acquired additional force since that Preface was written. During the twelve intervening years the boundaries of those portions of human knowledge over which Chemistry has established a rightful domain, have undergone an ex- tension commensurate with the time. It is, of course, proportionably more difficult to do justice to the whole of the wonderful region comprised within those boundaries in sixty lectures delivered within four months. Formerly, the attention of the student was alternately claimed by six professors; but latterly, the claims of a seventh professor have been added to those pre- viously established. Nevertheless, I am under the impression, that with the assistance which my text books are competent to afford, my course of lec- tures, brief as it is, may be more serviceable to a student who makes due use of those text books, than it could prove, were its duration doubled, with- out being associated with treatises made expressly for the purpose of ampli- fying the information partially afforded by my lectures, or of remedying their inevitable omissions. Having been prevented by indisposition from commencing this work as early as expedient, I am under the necessity of issuing that part which re- lates to Caloric, Light, and Inorganic Chemistry first. Dynamic Electri- city, comprising Galvanism or Voltaic Electricity, and Electro-magnetism, having been already issued, I shall in the next place republish my Treatise on Mechanical Electricity. Then to complete the new edition of my text books, only Organic Chemistry will remain to be reprinted. On this branch I hope to furnish a treatise before I reach that part of my course of lectures, in which it becomes the object of attention. I am in hopes that numbering the paragraphs, an excellent expedient re- sorted to by me for the first time in this edition, will be found advantageous to the reader, by rendering references from one part of the work to another less inconvenient, and consequently more frequent. \ CONTENTS. Page INTRODUCTION. Definition of Natural Philosophy, Chemistry, and Physiology - - 1 Of Chemical reaction - - - - - 2 Of repulsive reaction, or repulsion - - 2 I. CALORIC. Experimental proofs of a material cause of calorific repulsion 3 Expansion ...... 6 Expansion of solids - - - - - 6 Expansion of liquids - - - - - 8 Expansion of aeriform fluids - - - - 10 Thermometers - - - - - 10 Modification of the effects of caloric by atmospheric pres- sure - - - - - - 14 Capacities for heat, or specific heat - - 44 Slow communication of heat, comprising the conducting process and circulation - - - - 47 Quick communication of heat, or radiation - - 62 Means of producing heat, or rendering caloric sensible - 57 Means of producing cold, or rendering caloric latent - 68 States in which caloric exists in nature - - 74 II. Light - - - - - - - 75 Sources of light - - - - - 76 Heating, illuminating, and chemical properties of the rays 78 Polarization of light - - - - - 80 PONDERABLE MATTER. Of certain general properties of ponderable hatter and the means of ascertaining or investigating them - - 83 Sect. I. Chemical attraction - - - - - 83 Attraction of aggregation, or cohesion - - 83 Crystallization - - - - 84 Chemical affinity, or heterogeneous attraction - - 89 II. Definite proportions - - - - 93 Tables of chemical equivalents - - - - 94 Atomic theory - - - - - - 95 Chemical symbols - - - - 96 Atomic weights and symbols of the simple substances - 97 III. Specific gravity - - - - - - 98 Definition and discovery of the aeriform fluids called gases 105 INORGANIC CHEMISTRY; OR CHEMISTRY OF INORGANIC SUBSTANCES. Individual ponderable elements - - 110 Basacigew Elements - - - - 110 Sect. I. Oxygen - - - - - 110 II. Chlorine - - - - - - 117 Compounds of chlorine with oxygen - - - 123 Hypochlorous acid, or protoxide of chlorin* 124 VIM < OxXTENTS. Pago Euchlorine, or impure chlorous acid - j2^ Chloric acid - Oxychloric, or perchloric acid lone, or percmorii; auiu III. Bromine - 128 Compounds of bromine with oxygen and chlorine - 129 Bromic acid - Chloride of bromine - - i^n IV. Iodine - „ Compounds of iodine with oxygen - - "* Iodic, hyperiodic, and iodous acid - - ^ Chlorides and bromides of iodine - - ' 1^3 V. Fluorine ----- VI. Sulphur...... "* Compounds of sulphur with oxygen - - ' Z» Hyposulphurous acid - lA1 Sulphurous acid - - - :j: Hyposulphuric acid ... - 1« Sulphuric acid - - - " " « Chlorides, bromide, and iodide of sulphur - - 14" VII. Selenium.......J*° Compounds of selenium with oxygen - - - 141 VIII. Tellurium.......]*l Radicals ... - Non-metallic Radicals .... 1 Sect. I. Hydrogen - - - - - | Compounds of hydrogen with oxygen - - - lou Water.......15° Deutoxide or bioxide of hydrogen - - - 156 Compound of hydrogen with chlorine - - - 160 Chlorohydric or muriatic acid gas - - - 160 Old theory of the nature of chlorine and chlorohydric acid 165 Bromohydric acid .... - 165 Iodohydric acid - - - - - 165 Compounds of hydrogen with sulphur - - - 166 Sulphydric acid, or sulphuretted hydrogen - - 167 Polysulphide of hydrogen - - - - 170 Compounds of hydrogen with selenium and tellurium - 171 Selenhydric acid, or selenuretted hydrogen - - 171 Telluhydric acid, or telluretted hydrogen - - 171 II. Nitrogen or azote - - - - - 172 Atmospheric air - - - - - 174 Chemical compounds of nitrogen with oxygen - - 179 Protoxide of nitrogen, or nitrous oxide - - 179 Nitric oxide, or nitrous air 182 Hyponitrous acid .... - 183 Nitrous acid ------ 184 Theory of volumes - - - - - 187 Nitric acid - - - - - - 190 Nitroso-nitric acid - - - - - 192 Compounds of nitrogen with chlorine and iodine - - 195 Some points of chemical theory .... 195 Theories of combustion .... 196 Influence of the habitudes of chemical agents with the Voltaic series, on classification and nomenclature 198 Methods of distinguishing degrees of oxidizement, de- rived from the school of Lavoisier - - 199 Origin of the erroneous idea of an acidifying principle - 200 Acidity - - - - - 201 Alkalinity - - - - - - 202 Compounds of nitrogen with hydrogen - - - 204 CONTENTS. IX Page Ammonia, or the volatile alkali - - - 204 Ammonium --.... 208 Phosphorus - - - - - - -211 Compounds of phosphorus with oxygen - - - 214 Oxide of phosphorus - - - - - 215 Hypophosphorous acid .... 215 Phosphorous acid ..... 215 Phosphoric acid - - - - - 216 Chlorides of phosphorus - - - - - 217 Bromides and iodides of phosphorus - - - 217 Sulphides and selenides of phosphorus - - - 217 Compounds of phosphorus with hydrogen - - 218 Protophosphuretted hydrogen - - - . 218 Perphosphuretted hydrogen - - - - 218 Carbon - - - . . . 220 Compounds of carbon with oxygen - - - 224 Carbonic oxide ..... 224 Carbonic acid ------ 225 Oxalic acid - - - - - - 231 Mellitic acid ...... 232 Croconic acid - - - - - - 232 ' Compounds of carbon with oxygen and chlorine - - 232 Chloral - - - - - 232 Chloroxycarbonic acid ..... 233 Chlorides of carbon ..... 233 Bromide of carbon ..... 233 Iodides of carbon ---.-. 233 Sulphocarbonic acid, or bisulphide of carbon - - 234 Compounds of carbon with hydrogen - - - 234 Light carburetted hydrogen, or fire damp - - 236 Safety lamp ---... 236 Deutocarbohydrogen, or defiant gas - - - 237 Certain gaseous compounds formed by igniting gaseous elements of water with defiant gas, &c. - 238 Other varieties of carbohydrogen - - - 240 Bicarburet of hydrogen .... 240 Naphthaline ...... 240 Compounds of carbon with chlorine and hydrogen - 241 Compound of carbon With nitrogen ... 241 Bicarburet of nitrogen, or cyanogen - - - 241 Nomenclature of the compounds of cyanogen - 242 Cyanic, cyanuric, and fulminic acid - - 243 Chlorides, bromides, and iodides of cyanogen - 245 Sulphocyanogen - 245 Sulphocyanhydric acid .... 245 Cyanhydric or prussic acid ... - 246 Boron - - - - - - 249 Compound of boron with oxygen - - - 250 Boric or boracic acid - - - - - 250 Chloride of boron - - - - 251 Silicon - - - - - - - 251 Compound of silicon with oxygen - - - 253 Silica, or silicic acid ----- 253 Glass - - - - - - 254 Compounds of fluorine with hydrogen, boron, and silicon - 255 Fluohydric acid - - - - '- 256 Fluoboric acid - - - - - - 256 Fluosilicic acid ..... 257 Reaction of fluohydric acid with fluoboric and fluosilicic acid ,.---- 258 X CONTENTS. Page Sect. VII. Zirconion - - - - - - 259 Metallic Radicals ------- 259 Metals of the Earths Proper ... - - 264 Sect. I. Aluminium ------- 264 Alumina ------- 265 Chloride of aluminium ----- 268 II. Glucinium - - - - " " - 268 Glucina - - - - - - - 269 III. Yttrium - - - - - - - 269 Yttria.......269 IV. Thorium - - - - - - - 269 Thorina.......270 Metals of the Alkaline Earths ----- 270 Sect. I. Magnesium ------- 270 Magnesia ------ 270 II. Calcium, barium and strontium ... - 271 Evolution of calcium, barium and strontium - - 272 III. Lime, or calcia, the oxide of calcium ... 273 Baryta - - - - - - - 275 Strontia -.--•-- 277 Peroxides or bioxides of barium and strontium - - 277 Metals of the Alkalies, or Alkalieiable Metals - - - 278 Sect. I. Potassium ------- 278 II. Sodium - - - - - - - 279 Potash or potassa, and soda .... 280 Peroxides and suboxides of potassium and sodium - 283 III. Lithium - - - - - - - 284 Lithia.......284 Reaction of chlorine, bromine, iodine, fluorine, and cyanogen, with the metals of the earths and alkalies - 284 Reaction of sulphur, selenium, and tellurium, with the metals of the earths and alkalies - - - 288 Metals Proper ....... 289 Sect. I. Gold - - - - - - - 290 Compounds of gold with oxygen - - - - 291 Compounds of gold with the halogen class - - 292 Compounds of gold with sulphur - 292 II. Platinum - - - - - - - 293 Compounds of platinum with oxygen ... 294 Compounds of platinum with the halogen class - - 294 Compounds of platinum with sulphur ... 296 Power of platinum and other metals in a divided or spongy form to induce chemical reaction ... 296 III. Silver - - - - - - 297 Compounds of silver with oxygen ... 298 Compounds of silver with the halogen class - - 299 Compounds of silver with sulphur ... 299 IV. Mercury ------- 300 Compounds of mercury with oxygen ... 302 Reaction of acids with mercury and its oxides - - 303 Chlorides of mercury - 304 Bromides, iodides, fluorides, and cyanides of mercury - 307 Compounds of mercury with sulphur - - - 308 Phosphurets of mercury ----- 309 Combustion of mercury with chlorine - - - 309 V. Copper ..--... 3jo Compounds of copper with oxygen - - - 312 Compounds of the oxides of copper with acetic acid - 314 Compounds of copper with the halogen class - . 314 Compounds of copper with sulphur and selenium - 315 CONTENTS. XI Page VI. Lead - - - - - - - 315 Compounds of lead with oxygen ... - 316 Compounds of the protoxide of lead with acetic acid - 318 Carbonate of lead - - - - -318 Compounds of lead with the halogen class - - 319 Compounds of lead with sulphur and selenium - - 319 Sect. VII. Tin - - - - - - - - 320 Compounds of tin with oxygen ... - 320 Compounds of tin with the halogen class - - 321 Compounds of tin with sulphur and selenium - - 321 VIII. Bismuth - - - - - - - 322 Compounds of bismuth with oxygen ... 323 Compounds of bismuth with the halogen class - - 323 Compounds of bismuth with sulphur and selenium - 324 IX. Iron - - - - - - - 324 Compounds of iron with carbon, boron, silicon, and phos- phorus ...... 325 Compounds of iron with oxygen - - - 326 Reaction of iron with acids .... 328 Compounds of iron with the halogen class - - 329 Compounds of iron with sulphur and selenium - - 330 X. Zinc - - - - - - - 331 Compounds of zinc with oxygen - - - - 331 Compounds of zinc with the halogen class - - 333 Compounds of zinc with sulphur and selenium - - 333 XI. Arsenic ....... 334 Compounds of arsenic with oxygen ... 335 Compounds of arsenic with the halogen class - - 338 Compounds of arsenic with sulphur and selenium - 338 Compounds of arsenic with phosphorus and hydrogen - 339 Means of detecting arsenic in cases where poisoning is sus- pected by it - - - - - 340 XII. Antimony ------- 344 Sesquioxide of antimony ----- 345 Compounds of antimony with oxygen of minor importance 346 Compounds of antimony with the halogen class - - 347 Compounds of antimony with sulphur and selenium - 347 XIII. Metals proper of minor importance .... 350 Palladium - - - - - 350 Rhodium - - - - - - - 350 Iridium ------- 351 Osmium - - - - - - -351 Nickel - - - - - - - 351 Cadmium - - - - - - 352 Chromium -....- 352 Cobalt - - - - - - - 354 Columbium ...... 354 Manganese ...... 354 Molybdenum ... . - - 354 Titanium ...... 355 Tungsten ...... 355 Uranium ------- 355 Cerium ------- 355 Vanadium ...... 355 Salts .....--.. 356 Sect. I. Oxysalts - - - - - - - 359 Chlorates and hypochlorites .... 359 Oxychlorates ...... 364 Nitrates - - - - - - - 364 Nitrites and hyponitrites ----- 365 Xll CONTENTS. Sulphates Hyposulphates, sulphites, and Seleniates hyposulphites - - 365 - 366 - 366 Phosphates Phosphites Carbonates - - - 366 - 366 - 367 Borates - - » . . - 367 Silicates - - - 367 Sect. II. III. Cyanates and fulminates -Double oxysalts Sulphosalts Selenisalts and tellurisalts - ^- - 368 - 368 - 369 - 369 IV. Chlorosalts, bromosalts, iodosalts , and fluosal ts - - 370 V. Cyanosalts - - 370 DEFINITIONS OF CHEMISTRY. It is natural that a person whose attention may be directed to chemistry, should inquire of what does it treat, or how is it to be defined or distin- guished from other sciences ? Agreeably to the definition given in the second page of the Compendium, chemistry treates of those phenomena and operations of nature which arise from reaction between particles of inorganic matter. I subjoin several other definitions from some of the most celebrated modern writers on chemistry. Thomson defines chemistry to be " the science which treats of those events or changes in natural bodies, which are not accompanied by sen- sible motions." Henry conceives that " it may be defined, the science which investigates the composition of material substances, and the permanent changes of constitution, which their mutual actions produce." According to Murray, " it is the science which investigates the combi- nations of matter, and the laws of those general forces, by which these combinations are established and subverted." Brande alleges " that it is the object of chemistry to investigate all changes in the constitution of matter, whether effected by heat, mixture, or other means." According to Ure, " chemistry may be defined that science, the object of which is to discover and explain the changes of composition that occur among the integrant and constituent parts of different bodies." The definition given by Berzelius is as follows:—"Chemistry is the science which makes known the composition of bodies, and the manner in which they comport with each other." COMPENDIUM OF CHEMICAL INSTRUCTION, &c. INTRODUCTION. 1. The phenomena and operations of the material world appear to be dependent on certain properties in the parti- cles or masses of matter which enable them to exercise a reciprocal influence. Without this reciprocal action, which I would prefer to call reaction,* every particle or mass would be as if no other existed, and could itself have no efficient existence. 2. The reciprocal action or reaction, thus inferred to exist, may be distinguished as taking place between masses, between a mass and particles, and between particles only. 3. Reaction between masses^ is sublimely exemplified in the solar system, by that attraction between the sun and planets, by which they are made to revolve in their orbits. 4. Reaction between a mass and particles is exemplified by the reflection, refraction, and polarization of light. 5. Reaction between particles is exemplified by a fire, or the explosion of gunpowder. Definition of Natural Philosophy, Chemistry, and Physiology. 6. Natural Philosophy, in its most extensive sense, treats of physical reaction generally. In its more limited and * In Mechanics, acti6n is said to produce reaction; but in the case of an innate property, which mutually causes different portions of matter to be self attractive, or repellent, it is impossible to distinguish the agent from the reagent. From our first acquaintance with any bodies so situated, they may be said mutually to react, or to exercise reaction. t By the word mass, I mean a congeries of particles capable of producing some effect collectively, to which severally they would be incompetent. 1 2 INTRODUCTION. usual acceptation, it treats of those phenomena and ope- rations of nature, which arise from reaction between masses, or between a mass and particles. 7. Chemistry treats of the phenomena and operations of nature, which arise from the reaction between the particles of inorganic matter. 8. Physiology treats of the phenomena and operations, which arise from the reaction of the masses or atoms of organic or living bodies. OF CHEMICAL REACTION. 9. Reaction between particles, or chemical reaction, is distinguished into repulsive reaction or repulsion, and attractive reaction or attraction. OF REPULSIVE REACTION OR REPULSION. A Priori Proofs that there must be a Matter in which Re- pulsion exists as an Inherent Property. 10. Matter may be defined to be that which has proper- ties. We know nothing of matter directly. It is only with its properties that we have a direct acquaintance. It is from our perception of matter, through the powers or properties by which it affects our senses, that we believe in its existence. 11. The existence of repulsion and attraction is as evi- dent as that of the matter which, in obedience to their successive predominancy, may be seen either to cohere, in solids, with great tenacity, or to fly apart with explosive violence in the state of a vapour. The existence of re- pulsion and attraction being proved, it must be admitted that they are properties of matter; since the existence of a property, independently of matter, is inconceivable. But being of a nature to counteract each other, the repellent and attractive powers cannot coexist in particles of the same kind, and consequently must belong to particles of different kinds. There must, therefore, be a matter en- dowed with repulsion, distinct from that which is endowed with attraction. 12. I conceive that the phenomena of chemistry demon- strate that there are at least the three following properties, which, from their obvious incompatibility, cannot belong to the same elementary particles. INTRODUCTION. 3 13. 1st. An innate property of reciprocal attraction. 14. 2d. An innate property of counteracting attraction directly, by imparting reciprocal repulsion. 15. 3d. An innate property of imparting an attraction; variable in its force, and limited and contingent in its du- ration. 16. I presume that there must be at least three different kinds of matter, to each of which, one of the properties thus specified innately appertains. 17. The permanent and unvarying attractive power is exemplified by gravitation, and, as modified by circum- stances, by tenacity, or cohesion. 18. It resides, undoubtedly, in every kind of matter en- dowed with weight, and consequently in all that is consi- dered as material by the mass of mankind. 19. It must likewise act between each of those impon- derable principles which I am about to mention, and all other matter, whether ponderable or imponderable. 20. The power of imparting reciprocal repulsion to ponderable matter is supposed by chemists generally to belong to certain imponderable material reciprocally repul- sive particles, constituting the cause of heat, called ca- loric. 21. The power of indirectly counteracting attraction, and substituting for it a contingent and variable attraction, appears to belong to electricity. Light also appears to exercise a modifying influence. 22. Thus we have reason to infer the existence of at least three imponderable substances—electricity, caloric, and light—each consisting of particles reciprocally repul- sive, yet attractive of other matter, and probably more or less attractive of each other. OF CALORIC. Experimental Proofs of the Existence of a material Cause of Calorific Repulsion. 23. It has been ascertained that ice melts and water freezes at the temperature of 32° of Fahrenheit's thermo- meter. If at this temperature, which is called the freezing point, ice in a divided state, as in that of snow for in- stance, be mingled with an equal weight of water at 172°, 4 INTRODUCTION. the ice will be melted, and the resulting temperature will be 32°; but if equal weights of water be mingled at those temperatures, the mixture will have the mean heat of 102°. 24. It follows that a portion of heat becomes latent in the aqueous particles during the liquefaction of the ice, sufficient to raise an equal weight of water one hundred and forty degrees. In this case the ice is supposed to combine with material calorific particles, innately endowed with a power of reciprocal repulsion, and likewise with that of combining with ponderable matter. Hence water is considered as a combination of ponderable particles, endowed with a reciprocally attractive power, and impon- derable particles endowed with a reciprocally repellent power; so that, in obedience to the power last mentioned, the compound atoms, instead of cohering as in the solid state, move freely among each other, forming consequently a liquid. 25. In all cases of liquefaction or fusion which have been examined, analogous results have been observed; whence it is generally believed that whenever a solid is converted into a liquid, its particles unite with a portion of the material cause of heat, which becomes latent, as in the case of ice in melting. The evidence is equally strong in favour of the inference that in passing from the liquid to the aeriform state, ponderable matter combines with, and renders latent even a larger quantity of heat in proportion to its weight, than in cases of liquefaction. 26. When, by means of a thermometer, we observe the rise of temperature in water exposed to a regular heat, as when placed in a cup upon a stove, we find that nearly equal increments of heat are acquired in equal times, until the boiling point is attained. Subsequently, the cup being open so as to allow the steam to escape freely, no further rise of temperature will be found to ensue; but in lieu of it, steam will be evolved more or less copiously, in propor- tion to the activity of the fire. Since from the time the water boils it ceases to grow hotter, it may be fairly pre- sumed that the steam generated during the ebullition, al- though of a temperature no higher than 212°, contains, in a latent state, the caloric which meanwhile enters the liquid. This presumption is fully justified by the fact, that if any given weight of steam be received in a quantity of CALORIC. 5 cool water ten times heavier, it will cause in it a rise of temperature of nearly one hundred degrees. 27. The heat which would raise ten parts of water to 100 degrees, would, if concentrated into one of those parts, raise it to 1000 degrees nearly, which is about equal to a red heat. It follows, therefore, that as much heat is ab- sorbed in producing steam, as would render the water of which it consists red-hot, if prevented from assuming the aeriform state. 28. These facts and deductions induce chemists general- ly to believe that the cause of calorific repulsions is mate- rial ; that it consists of a fluid, of which the particles are self-repellent, while they attract other matter; that by the union of this fluid with other matter, a repulsive property is imparted, which counteracts cohesion, so as to cause, successively, expansion, fusion, and the aeriform state; and further, that it is by the afflux of the calorific matter that the sensation of heat is produced, while that of cold results from its efflux. Acceptation of the term Caloric. 29. If we place a small heap of fulminating mercury upon the face of a hammer, and strike it duly with another hammer, an explosion will ensue so violent as to cause a visible indentation in the steel surface. This explosion, agreeably to the premises, can only be explained by sup- posing the evolution of a great quantity of the material cause of heat. Were an equal quantity of red-hot sand to be suddenly quenched with water, the effect would be com- paratively feeble. We may, therefore, infer that the ful- minating powder, though cold, contains more of the cause of heat than a like quantity of red-hot sand. Hence it would follow from using the word heat in the sense both of cause and effect, that there is more heat in a cold body than in a hot one, which in language is a contradiction. On this account it was considered proper by the chemists of the Lavoisierian school, to use a new word, caloric, to . designate the material cause of calorific repulsion. Experimental Illustration. 30. A portion of fulminating mercury exploded between two hammers. 6 IMPONDERABLE SUBSTANCES. ORDER PURSUED IN TREATING OF CALORIC. Expansion.—Modification of the effects of Caloric by Atmos- pheric Pressure.—Capacities for Heat, or Specific Heat.-— Slow Communication of Heat, comprising the Conducting Pro- cess and Circulation.—Quick Communication of Heat, or Ra- diation.—Means of producing Heat, or rendering Caloric sen- sible.—Means of producing Cold, or rendering Caloric latent. —States in which Caloric exists in Nature. EXPANSION. OF THE EXPANSION OF SOLIDS, LIQUIDS, AND ELASTIC FLUIDS, AND ON THE OPPONENT AGENCY OF ATMOSPHERIC AND OTHER PRESSURE. Expansion of Solids. 31. A ring and plug, which when cold fit each other, cease to do so when either is heated; and a tire when red- hot is made to embrace a wheel otherwise too large for it. Pyrometer, in which the Extension, in length, of a Metallic Bar is ren- dered sensible by a Combination of Levers. 32. The influence of temperature on the length of a metallic wire may be rendered evident by means of the instrument, of which fig. 1, in the oppo- site engraving is a representation. 33. WW, represents a wire, beneath which is a spirit lamp consisting of a long, narrow, triangular vessel of sheet copper, open along the upper angle, so as to receive and support a strip of thick cotton cloth, or a suc- cession of wicks. By the action of the screw at S the wire is tightened, and by its influence on the levers, the index I is raised. The spirit lamp is then lighted and the wire enveloped with flame. It is of course heated and expanded, and, allowing more liberty to the levers, the index upheld by them falls. 34. By the action of the screw the wire may be again tightened, and, the application of the lamp being continued, will again, by a further expan- sion, cause the depression of the index; so that the experiment may be repeated several times in succession. 35. Since this figure was drawn, I have substituted for the alcohol lamp the more manageable flame of hydrogen gas, emitted from a row of aper- tures in a pipe supplied by an apparatus for the generation of that gas. See fig. 2. 36. If, while the index is depressed by the expansion, ice or cold water be applied to the wire, a contraction immediately follows so as to raise the index to its original position. 37. Metals are the most expansible solids, but some are more expansible than others. 38. The following table, abstracted by Turner from that furnished by Lavoisier, will show the increase of bulk obtained by glass and various me- tals in rising in temperature from 32° to 212°. Instrument for demonstrating the Power of Caloric in expanding a Metallic Rod. CO 6 (Page 6.) 976717668835756�55���6231�53�442�2752886328�97�24���77348�65�83146296�73030927422�298157459�526467 8038�3 CALORIC. 7 Mmes ofSuhstances. ^"ll^^ Glass tube without lead, mean of three specimens - - 1-1115 of its length. English flint glass,........1-1248 Copper,..........1-581 Brass, mean of two specimens,......1-532 Soft iron, forged,........1-819 Iron wire,..........1-812 Untempered steel,........1-927 Tempered steel,........1-807 Lead,..........1-351 Tin of India, - '- - ,......1-516 Tin of Falmouth,.......•- 1-462 Silver,..........1-524 Gold, mean of three specimens,.....1-602 Platinum, determined by Borda,.....1-1167 39. Pyrometers have been made of platinum, in one of which, invented by Daniell, changes in the length of a cylinder of this metal, arising from temperature, are made sensible by the motion of a lever associated with it, and which acts as an index. In the other, a bulb is formed of platinum, and the degree of heat is inferred from the quantity of air expelled. 40. The use of this air pyrometer is burdened by the necessity of mea- surement and calculation to ascertain the result. This might be very much facilitated by the use of a sliding rod and air-gauge. The retraction of the rod might be made to compensate the expulsion of air, while divisions well made on it would indicate the quantity. Experimental Illustration of the different Expansibility of Metals. 41. That the expansibility of one metal may exceed that of another, may be rendered apparent by soldering to- gether, face to face, two thin strips, one iron the other brass. On exposure to heat, the compound strip, thus constituted, assumes the shape of an arch. The brass, which is the more expansible metal, forms the outer and of course larger curve. Supposed Exception to the Law that Solids expand by Heat in the case of Clay, which contracts in the Fire. 42. The phenomena do not justify us in considering the contraction of clay from heat as an exception to the ge- neral law. In the first instance clay shrinks by losing water, of which the last portions are difficult to expel. In the next place a chemical union takes place between the principal ingredients, silica and alumina, which is rendered more complete in proportion to the duration and intensity of the fire. It may be presumed that the vitreous com- 8 IMPONDERABLE SUBSTANCES. pound, which would result from a complete fusion and combination of the constituents, would be as expansible as other vitreous substances. Experimental Illustration. 43. The contraction produced by heat in cylinders of clay shown by means of the ingenious but inaccurate pyro- meter of Wedgwood. Expansion of Liquids or non-elastic Fluids. 44. The word fluid applies to every mass that will flow, distribute itself equally in obedience to its own weight or self-repulsion. 45. Ponderable fluids are either elastic or non-elastic. Latterly the term liquid has been employed to designate those fluids which are, like water, alcohol, and oil, devoid of elasticity, a property which, in due time, I shall define and illustrate. Liquids are expanded when their Temperature is raised, and some Liquids are more expansible than others. CALORIC. 9 46. Let two glass vessels be provided with bulbs and necks of the same shape and dimensions as represented in the preceding figure. Let one of them, that on the left for instance, be supplied with as much alcohol as will occupy it to the level designated by the letters O O. Let the ves- sel on the right be occupied with water to the same level, the height of the liquid in each being made to correspond with a little fillet of white paper secured about the neck. Under each vessel, place equal quantities of charcoal, burn- ing with a similar degree of intensity; or preferably, sur- round the bulbs simultaneously with hot water in an oblong vessel of suitable dimensions. The liquids in each vessel will be expanded so as to rise into the necks; but the alco- hol will rise to a- greater height than the water. 47. The dilatation of the following liquids, by a change of temperature from 32° to 212°, is as follows—alcohol 1-9, nitric acid 1-9, fixed oils 1-12, sulphuric ether 1-14, oil of turpentine 1-14, sulphuric or muriatic acid 1-17, brine 1-20, water 1-23 nearly, mercury about 1-55. 48. The rate of expansion for liquids increases with the temperature; as if their particles, by becoming more re- mote, lost some of their ability to counteract the repulsive influence of caloric. 49. The number associated with each of the substances in the following list, shows its melting point as estimated by Fahrenheit's scale. One degree of DanielPs pyrometer, (39) by which the temperatures above 600° were measured, is calculated to be equal to seven of Fahrenheit. 50. Cast iron 3479°, gold 2590°, silver 2233°, brass 1869°, antimony 810°, zinc 648°, lead 606°, bismuth 497°, tin 442°, sulphur 218°, beeswax 142°, spermaceti 112°, phos- phorus 108°, tallow 92°, olive oil 36°, milk 30°, blood 25°, sea water 27i°, oil of turpentine 14°, mercury—39°, nitric acid—452°, sulphuric ether—46°. Exception to the Law that Liquids expand by Heat. 51. The bulk of water diminishes with the temperature, until it reaches 39° nearly. Below this point, it expands as it grows colder, and in freezing increases in bulk one- ninth. This wonderful exception to the law that liquids expand by heat, appears to be a special provision of the Deity for the preservation of aquatic animals; for were 2 10 IMPONDERABLB SUBSTANCES. water to increase in density as it approaches the point of congelation, the upper stratum would continue to sink as refrigerated in bodies of water below 39°, as well as in others. Hence a whole river, lake, or sea might, in high latitudes, be rendered too cold for animal life; and finally be so far converted into ice, as not to thaw during the ensuing summer. Subsequent winters co-operating, the whole might be consolidated so as never to thaw. But in consequence of the peculiarity in question, the cold- est stratum, in a body of water below 39°, remains at top, until, if the cold be adequate, congelation ensues. The buoyant sheet of ice, which results in this case, forms effec- tively a species of winter clothing to the water beneath it; and, by augmenting with the frost, opposes an increas- ing obstacle to the escape of caloric from the water which it covers. Expansion of Aeriform Fluids. 52. Aeriform fluids are much more expansible than liquids. In order, however, to appreciate the changes of bulk which they may be observed to sustain, it is neces- sary to understand the influence which the pressure of the atmosphere has upon their density, independently of tempe- rature. The simple influence of heat, in expanding them, may be illustrated by holding a hot iron over the thermo- meter of Sanctorio, represented in the following figure. Thermometers. 53. The invention of the thermometer is ascribed to Sanctorio. The principle of that form of the instrument which he contrived may be understood from the following article. CALORIC. 11 Expansion of Air illustrated by the Air Thermometer of Sanctorio on a large Scale. 54. The bulb of a matrass is support- ed by a ring and an upright wire with its neck downwards, so as to have its orifice beneath the surface of the water in a small glass jar. A heated iron being held over the ma- trass, the contained air is so much in- creased in bulk, that, the vessel being inadequate to hold it, a partial escape from the orifice through the water ensues. On the removal of the. hot iron, the residual air regains its pre- vious temperature, and the portion expelled by the expansion is replaced by the water. 55. If in this case the quantity of air expelled be so regulated, that when .the remaining portion returns to its previous temperature, the liquid rises about half way up the stem, or neck, the apparatus will constitute an air thermometer. For whenever the tem- perature of the external air changes, the air in the bulb of the matrass must, by acquiring the same temperature, sustain a corresponding increase or diminution of bulk, and consequently, in a proportionate degree, influ- ence the height of the liquid in the neck. As elastic fluids are dilated equably, in proportion to the temperature, and are also much more expan- sible than liquids, this thermometer would be very accurate, as well as pre-eminent in sensibility, were it not influenced by atmospheric pressure as well as temperature. On this account, however, it was never of much utility. Subsequently, liquids were resorted to, and the instrument assumed the form now generally employed, the principle of which is explained. (45.) 56. In the following pages I shall give engravings and descriptions of the form of the thermometer used in the laboratory, of the self-registering thermometer, of the differential thermometer, and of an apparatus which illustrates the difference between it and Sanctorio's thermometer. 57. Agreeably to the example of my predecessor and preceptor Dr. Woodhouse, I have been accustomed to exhibit to my class the blowing and filling of a thermometer. Of this process an account is subjoined. 58. The tubes used in constructing thermometers are made at almost all the glass houses, having usually a capillary perforation. They are made by rapidly drawing out a hollow glass globe while red-hot, by which means it is changed into a long cylindrical string ot glass, in the axis of which a perforation exists, in consequence of the cavity of the globe. When a thermometer tube is softened by exposure to a flame, excited by a blow-pipe, a bulb may be blown upon it. While the bulb is still warm, the other end of the tube is immersed in mercury, or in spirit, according to the purposes for which the instrument is intended. As the bulb cools, the air within it contracts, and thus allows the liquid to enter, in obedience to the pressure of the atmosphere. The bulb thus becomes partially supplied with the liquid, which is next boiled in order to expel all the air from the cavity of the bulb and perforation. 12 IMPONDERARLE SUBSTANCES. The orifice being again depressed into the liquid, when the whole becomes cold the liquid will fill the cavity of the bulb. This result will be hereafter fully explained and illustrated. The open end of the tube being now heated, is drawn out into a filament with a capillary perforation. The bulb being raised to a temperature above the intended range of the thermometer, so as to expel all the superabundant liquid, the point is fused so as to seal the orifice hermetically, or in other words so as to be perfectly air-tight. In the next place, the bulb is to be exposed to freezing water, and the point to which the liquid reaches in the capillary perforation-marked. In like manner the boiling point is determined, by subjecting the bulb to boiling water. The distance between the freezing and boiling points, thus ascertained, may be di- vided according to the desired graduation. 59. The scale of Reaumur requires 80 divisions, that of Celsius 100, Fahrenheit's 180. The graduation of Celsius is the most rational; that of Fahrenheit the least so, although universally used in Great Britain and the United States. The degrees of these scales are to each other obviously, as 80, 100, and 180; or as 4, 5, and 9. Hence it is easy to convert the one into the other by the rule of three. 60. It should, however, be observed that the scales of Celsius and Reaumur com- mence at the freezing of water, all above that being plus, all below it minus; while the scale of Fahrenheit commences at thirty-two degrees below freezing. Hence in order to associate correctly any temperature noted by his thermometer with theirs, we must ascertain the number of degrees which the mercury is above or below freezing, and convert this number into one equivalent to it by their gradua- tion ; and conversely, after changing any number of degrees of theirs into his, we must consider the result as indicating the number of degrees above or below 32 on his scale. 61. The process above described for the construction of a thermometer, is equally applicable whether the bulb be filled with alcohol or mercury. Each of these liquids has peculiar advantages. Mercury expands most equably. Equal divisions on the scale of the mercurial thermometer will more nearly indicate equal incre- ments or decrements of temperature. Mercury also affords a more extensive range ; as it does not boil below 656°, nor freeze above—39°, of Fahrenheit's thermometric scale. 62. Alcohol, being more expansible than mercury, is more competent to detect slight changes. It boils at 176° of Fahrenheit, and for its congelation is alleged to require—90° of the same scale. As this temperature is below any ever observed in nature, and can only be attained by an extremely difficult process, latterly disco- vered by Bussier, it can hardly ever happen that an alcoholic thermometer will not be found competent to measure any degree of cold which chemists have a motive for determining. Besides those above mentioned, a thermometric scale has been used in Russia, which bears the name of its author, Delisle. In this, zero is at the boiling point of water, and five of his graduations are equal to six of Fahrenheit's. Laboratory Thermometer. 63. The thermometers used in laboratories, are usually con- structed so as to have a portion of the wood or metal, which defends them from injury and receives the graduation, to move upon a hinge, as represented in the adjoining figure. 64. This enables the operator to plunge the bulb into fluids, without introducing the wood or metal, which would often be detrimental either to the process or to the instru- ment, if not to both. 65. The scale is kept straight by a little bolt on the back of it, when the thermometer is not in use. Self-registering Thermometer. CALORIC. 13 66. This figure represents a self-registering thermometer. It comprises necessarily a mercurial and a spirit thermometer, which differ from those ordinarily used, in hav- ing their stems horizontal and their bores round; also large enough to admit a cylin- der of enamel in the bore of the spirit thermometer, and a cylinder of steel in the bore of the mercurial thermometer. Both the cylinder of enamel and that of steel must be as nearly of the same diameter with the perforations in which they are respec- tively situated, as is consistent with their moving freely in obedience to gravity, or any gentle impulse. 67. In order to prepare the instrument for use, it must be held in such a situation, as that the enamel may subside as near to the end of the alcoholic column as possible, yet still remaining within this liquid. The steel must be in contact with the mer- cury, but not at all immersed in it. 68. On this account the bulbs of the thermometers are placed at opposite ends of the plate upon which they are secured; so that when this plate is made to stand up on one end, in such manner as to have the bulb of the mercurial thermometer lower- most, that of the spirit thermometer will be uppermost. Under these circumstances, impelled by gravity, the steel cylinder will subside upon the surface of the mercurial column, while the cylinder of enamel will sink within the little column of spirit, which retains it, till it reaches the surface of that column. The instrument being, after this object is attained, suspended in a horizontal position, as represented in the figure, if in consequence of its expansion by heat, the mercury advance into the tube, the steel moves before it; but should the mercury retire during the absence of the observer, the steel does not retire with it. Hence, the maximum of temperature, in the interim, is discovered by noting the graduation opposite the end of the cylin- der nearest the mercury. The minimum of temperature is registered by the enamel, which retreats with the alcohol when it contracts, but, when it expands, does not advance with it. The enamel must retire with the alcohol, since it lies at its mar- gin, and cannot remain unmoved in the absence of any force competent to extricate it from a liquid, towards which it exercises some attraction. But when an opposite movement takes place, which does not render its extrication from the liquid neces- sary to its being stationary, the enamel does not accompany the alcohol. Hence the minimum of temperature, which may have intervened during the absence of the ob- server, is discovered by ascertaining the degree opposite the end of the enamel near- est to the end of the column of alcohol. o Leslie's Differential Thermometer. 69 This instrument consists of a glass tube nearly in the form of the letter U, with a bulb at each termination. In the bore of the tube there is some liquid, as,for instance, coloured sulphuric acid, alcohol, or ether. When such an instrument is exposed to any general alteration of temperature in the surrounding medium, as in the case of a change of weather, the air in both bulbs being equal- ly affected, there is no movement produced in the fluid; but the opposite is true, when the slightest change of temperature exclusively affects one of the bulbs. Any small bodies situated at different places in the same apartment warmed by a fire, will show a diversity of temperature, when severally applied to the different bulbs. 14 IMPONDERABLE SUBSTANCES. Difference between an Air Thermometer and a Differential Thermometer, illustrated upon a large Scale. 70. The adjoining figure represents an instrument, which acts as an air thermometer, when the stopple S is removed from the tubulure in the coni- cal recipient, R; because in that case, whenever the density of the atmos- phere varies either from changes in temperature, or barometric pressure, hereafter to be explained, the extent of the alteration will be indicated by an increase or diminution of the space occupied by the air in the bulb, B, and of course by a corresponding movement of the liquid in the stem, T. But when the stopple is in its place, the air cannot, within either cavity of the instrument, be affected by changes in atmospheric pressure: nor can changes of temperature which operate equally on both cavities, produce any movement in the liquid which sepa- rates them. Hence, under these cir- cumstances, the instrument is compe- tent to act only as a differential ther- mometer. MODIFICATION OF THE EFFECTS OF CALORIC BY ATMOS- PHERIC PRESSURE. Digression to demonstrate the Nature and Extent of Atmospheric Pressure. Experimental Proof that Air has Weight. 71. The air being allowed to replenish an exhausted globe, while suspended from a scale beam and accurately counterpoised, causes it to preponderate. 72. By a temporary communication with an air pump, by means of a screw with which it is furnished, a glass globe is exhausted of air. It is then suspended to one arm of a scale beam, and accurately counterpoised. Being thus pre- pared, if by opening the cock the air be al- lowed to re-enter the globe, it will preponde- rate; and if a quantity of water, adequate to restore the equilibrium, be introduced into a small vessel, duly equipoised by a counter- weight applied to the other arm of the beam, the inequality in bulk of equal weights of air and water will be satisfactorily exhibited. / CALORIC. 15 Definition of Elasticity. 73. The power which bodies have to resume their shape, position, or bulk on the cessation of constraint, is called elasticity. The degree in which any body possesses this power is not to be estimated by the force, but by the perfection of its recoil. A coach spring is far more powerful, but is not more elastic, than a watch spring. 74. Elasticity is erroneously spoken of as a varying property in the air, which, in common with aeriform fluids in general, appears to be always perfectly elastic. 75. As a property distinguishing aeriform fluids from liquids, elasticity conveys the idea of a power in a given weight of a fluid to expand or to contract with the space in which it may be confined, producing at the same time a pressure on the internal surface of the cavity, or any object within it, inversely as the space. The Existence and Extent of the Pressure of the Atmosphere experimentally demon- strated. PRELIMINARY PROPOSITION. 76. For the pressure of any fluid on any area assumed within it, the pressure of a co- lumn of any other fluid may be substituted, making it as much higher as lighter, as much lower as heavier; or in other words, the heights are inversely as the gravities. Experimental Illustration in the case of Mercury and Water. C HI i I lli J 1 ill 26 I iff f^ ~ ii illlirTfnifMfflB — 1-5 •1-0 ^mmKH^^^ 77. If into a tall glass jar, such as is represented in the adjoining figure, a glass cylinder, C, (like a large glass tube open at both ends) were introduced—on filling the jar with water, this liquid would of course rise in the cylin- der to the same height as in the jar; but, if, as in the figure, be- fore introducing the water, the bottom of the jar be covered with a stratum of mercury, two inches deep, so as to be sufficiently above the open end of the cylinder, it must be evident that the water will be prevented from entering the cylinder by the interposition of a heavier liquid. But as the pressure of the water on the mer- cury outside of the cylinder is unbalanced by any pressure from water within the cylinder, the mercury within will rise, until, by its weight, the external pres- sure of the water is compensated. When this is effected, it will be seen, on comparing, by means of the scale, S, the height of the X__- . two liquids, that for.every inch of 1 "' ■' ~ W elevation acquired by the mer- j||||j|g||p^ cury, the water has risen more EE=r-T- than a foot; since the weight of mercury is to that of water, as 13.6 to 1. 16 IMPONDERABLE SUBSTANCES. 78. It may be demonstrated that the pressure of the column of mercury is exactly equivalent to that of a column of water having the same base, and an altitude equal to that of the water in the jar, by filling the cylinder with water. It will then be seen, that, when the water inside of the cylinder is on a level with the water on the outside, the mercury within the cylinder is also on a level with the mercury without. 79. It is, therefore, obvious, that the elevation of the column of mercury, within the tube, is produced by the weight or pressure of the water without, and measures the extent of that pressure on the lower orifice of the tube. The Illustration extended to the case of Liquids lighter than Mercury. 80. Let there be four jars, each about four inches in diameter, and more than thirty inches in height, severally occupied by mercury to the depth of about two inches. In the axis of each jar, let a tube be placed, of about one inch and a half in diame- ter, and about one-fourth taller than the jar, with both ends open, and the lower orifice under the surface of the mercury. On pouring water into the jars, the mer- cury rises in the tubes, as the water rises in the jars; but the mercury rises as much less than the water as it is heavier. 81. The mercurial columns in this case, as in the preceding experiment, owe their existence to the pressure of the surrounding water, and by their height measure the extent of that pressure on the areas of their bases respectively. They may be considered as substituted severally for the aqueous columns, which would have en- tered the tubes had not the mercury been interposed. Accordingly, water being poured into one of the tubes, the mercury in that tube subsides to a level with the mercury without, when the water poured into the tube reaches the level of the water without. 82. The three remaining columns of mercury may be considered as substituted, in water, for columns of water, and being as much lower as heavier are found ade- quate to preserve the equilibrium. 83. It remains to be proved that other fluids, heavier or lighter than water, may in like manner be substituted for the columns of mercury, and of course for the water of which the mercury is the representative. CALORIC. 17 84. Into the three tubes, in which, by the addition of water to the jars, columns of mercury are sustained, pour severally, ether, alcohol, (differently coloured, so that they may be distinguished) and a solution of sulphate of copper, until the mercurial columns, within the tubes, are reduced to a level with the mercury without. It will be found that the column formed by the cupreous solution is much lower than the surface of the water on the outside of the tube; that the opposite is true of the column of alcohol; and that the ether, still more than the alcohol, exceeds the sur- rounding water in elevation. 85. While it is thus proved that columns of mercury, ether, alcohol, and of a saline liquid may, in water, be substituted for columns of this liquid; it is also appa- rent that they must be as much higher as lighter, as much lower as heavier; or in other words, their heights must be inversely as their gravities. Torricellian Experiment. 86. Pursuant to the law which has been above illustrated, that the pressure of one fluid may be substituted for that of another, provided any difference of weight be compensated by a corresponding difference in height; if, in lieu of water, the mer- cury were pressed by air on the outside of the tubes, unbalanced by air within, co- lumns of the metal would be elevated, which would be in proportion to the height and weight of the air thus acting upon it. 87. In order to show that the air exercises a pressure on the mercury outside of the tubes, analogous to that exercised by water in the experiments just described, it is only requisite that this external pressure be unbalanced by the pressure of air within the tube. This desideratum is obtained by filling, with mercury, a tube about three feet in length, open at one end and closed at the other, and covering the open end with the hand, until it be inverted and merged in a vessel containing some of the same metal, without allowing any air to enter. A mercurial column of about 30 inches in height will remain in the tube, supported by the pressure of the sur- rounding air, and an index of its weight. This is a case obviously analogous to that of the mercurial columns, supported by the pressure of water in the experi- mental illustration above given. 88. The tube may be supposed to occupy either of the three posi- tions, represented in the drawing. The mercury, in each position, preserves the same degree of ele- vation, its surface being always in the same horizontal plane, or level, whether upright or inclined. Or we may suppose three tubes, filled with mercury, and inverted in a vessel, nearly full, of the same metal, to be placed in the positions represented in the draw- ing. The upper surfaces of the columns of mercury in each tube, will be found always coincident with the same horizontal plane, however different may be the an- gle which they make with the horizon. And the horizontal plane, in which their surfaces are thus found, will be between 28 and 31 inches above the surface of the mercury in the vessel. The line,L, with which the mercury in each of the tubes is on a level, represents a cord rendered horizontal, by mak- ing it parallel with the surface of the mercury in the reservoir. 3 18 IMPONDERABLE SUBSTANCES. Additional Illustration of Atmospheric Pressure. 89. I trust that the preceding illustrations are well adapted to convey a clear concep- tion of atmospheric pressure; but as it some- times happens, fortuitously, that when truth cannot get access to the mind under one form, it may reach it in another, even when less eligible, I subjoin the following illustra- tion, which, though less amusing, and asso- ciating with it fewer instructive phenomena, is more brief, and perhaps, equally conclu- sive. 90. If a tube, recurved into a crook at one end so as to form a syphon, with legs of very unequal length, and both ends open, have the crook lowered into water, as in the adjoining figure, the fluid will of course, rise within the tube to the same height as without. But if, before the crook is sunk in the fluid, it be occupied by mercury, the water will enter the tube, only so far as the pressure which it exerts upon the mercury in the short leg of the syphon, is competent to raise the mercury in the long leg. 91. This pressure, or the effort of the water to enter the tube, is obviously measured by the height to which it forces the mercury, in the long leg of the syphon, above the mercurial surface in the short leg. The height will of course be greater or less, in proportion to the depth to which the lower surface of the mercury may be sunk. It will also be greater or less, according as the fluid in which it is immersed is heavier or lighter. Hence, as water is about 820 times heavier than air, a depth of 820 inches in air would displace the mercury as much as one inch in water. 92. Let us imagine a tube recurved at one end, similarly to the one represented in the foregoing figure, the crook likewise occupied by mercury, to have the upper orifice as completely above the atmosphere, as the orifice of the tube is above the water in the jar. The mercury, in the short leg of the syphon, thus situated, would be evidently exposed to a pressure, caused by the air analogous to that sustained from water, in the case of the tube, as already illustrated; and this pressure of the air would, as in the case of the water, be measured by the rise of the mercury in the long leg of the syphon. 93. Yet to realize this experiment with a syphon reaching above the atmosphere, it is obviously impossible; but, as the only motive for giving such a height to the syphon is to render the mercury in the long leg inacessible to atmospheric pressure, if this object can be otherwise attained, the phenomenon may be exhibited in the case of the atmosphere without any material deviation. 94. In fact, to protect the mercury in the long leg from atmospheric pressure, we have only to seal the orifice of that leg, and, through the orifice of the other, to fill the syphon with mercury, before we place it in a vertical position. We shall then find that the pressure of the air on the mercury, in the open leg of the syphon, will support a column of this metal in the other leg of nearly thirty inches, though occa- sionally varying from 28 to 31 inches. Inferences respecting the Weight of the Atmosphere from the preceding Experiments. 95. Supposing the base of the column of mercury, sustained by the atmosphere, as demonstrated in the preceding articles, were equivalent to a square inch, the total weight of the column would be about fifteen pounds. This of course represents the weight of that particular column of air only, whose place it has usurped; and as, for every other superficial inch on the earth's surface, a like column of air exists, the earth must sustain a pressure from the atmosphere, equal to as many columns of mercury, 30 inches high, as could stand upon it; or equal to a stratum of mercury of the height just mentioned, extending all over the surface of the globe. CALORIC. 19 96. It has been shown that the heights of heterogeneous fluids, reciprocally resist. ing each other, are inversely as their gravities; or, in other words, that they are as much higher as lighter, as much lower as heavier. The height of the column of air which, by its pressure, elevates the mercury, must, therefore, be as much greater than the height of the column of mercury, as the weight of the mercury is greater than the weight of the air, supposing the air to be of uniform density. Mercury is 11152 times heavier than air, and of course the height of the atmosphere would be (if uniform in density) 11152 X 30 inches = 27880 feet; supposing 30 inches to be the height of the mercurial column supported. 97. Hence the atmosphere, if of the same density throughout as on the surface of the earth, would not extend much above the elevation ascribed to the highest moun- tains. 98. But as the pressure of the atmosphere causes its density, it may be demon. strated that, the heights increasing in arithmetical progression, the densities will decrease in geometrical progression. Thus at an elevation of three miles, the air being, by observation, half as dense as upon the earth's surface: . , At 6 miles it will be \ At 21 miles it will be t^i^-r'" 9 - - - - * 24 - --- m 12 J 27 .... _i La m m m Tr At 5T2 15 .... ^ 30 --- - T^ 18 Tp>* B"4 or rarer than we can render it by the finest air pump. These results have been verified, to a considerable extent, by actual observation. 99. It is reasonable to suppose that there is a degree of rarefaction, at which the weight of the ponderable particles of the air will be in equilibrio with the repulsive power of the caloric united with them. Beyond the distance from the earth's sur- face at which there should be such an equilibrium, the air could not exist Hence it is inferred that the extent of our atmosphere is limited. Of the Water Pump. 100. The admission of the atmosphere is necessary to the suction of the water from a receiver. Air may be removed from close vessels by the same process. Water rises by the pressure of the atmosphere; air presses out by its own elasticity. Mechanism and Action of the Suction Pump rendered evident by means of a Model with a Glass Chamber. Difference between pumping an Elastic Fluid and a Liquid, illus- trated by an appropriate Contrivance. 101. A little suction pump is constructed, with a chamber C C, of glass, which Sermits the action of its piston, P, and valves to be seen. Below the pump is a ollow glass globe filled with water. This globe communicates with the pump by a tube, visibly descending from the lower part of the pump, through an aperture in the globe, till it nearly reaches the bottom. This tube is luted air-tight into the aper- ture by which it enters the globe. Its orifice, next the chamber, is covered by a valve opening upwards. In the axis of the piston there is a perforation, also covered by a valve opening upwards. 102. If the piston, P, be moved alternately up and down as usual in pumping, as often as it rises its valve will shut close; so that if nothing passes by the sides of the Siiston nor enters into the chamber of the pump from below, a vacuum must be brmed behind the piston. Under these circumstances, it might be expected that the water would rise from the globe through the lower valve, and prevent the forma- tion of a vacuum. But being devoid of elasticity, and, therefore, incapable of self- extension beyond the space which it occupies, the water does not rise into the chain. ber of the pump, so long as by means of the cock, C, of the recurved pipe, PP, com- munication with the external air is prevented. But if this cock be opened during the alternate movement of the piston, a portion of the water will mount from the globe into the chamber at each stroke of the piston. The opening of the cock per- mits the atmosphere to press upon the fluid in the globe, and to force it up the tube leading to the pump chamber, as often as the chamber is relieved from atmospheric pressure by the rise of the piston. As soon as the piston descends, the valve over the orifice of the tube shuts, and prevents the water from returning into the globe. It is of course forced through the perforation in the piston, so as to get above it. 20 IMPONDERABLE SUBSTANCES. When the piston rises, the valve over its perforation being shut, it 'lifts the portion of water above this valve until it runs out at the nozzle of the pump; while the chamber, below the piston, receives another supply from the globe. But if after all the water has been pumped from the globe, the pumping be continued with the cock closed, a portion of air will be removed from the globe at each stroke, until the resi- due be so much rarefied, as, by its elasticity, no longer to exert against the valve, closing the tube, sufficient pressure to lift it, and thus to expand into the vacuity formed behind the piston, as often as it rises. 103. The rarefaction thus effected in the air remaining in the globe, is rendered strikingly evident, by causing the orifice of the curved tube to be under the surface of some water in an adjoining vase, while the cock is opened. The water rushes from the vase into the exhausted globe with great violence; and the extent of the rarefaction is demonstrated by the smaiiness of the space within the globe which the residual air occupies, after it is restored to its previous density by the entrance of the water. (Page 21.) CALORIC. 21 Description of a Chemical Implement. \104. The operation of sucking up a liquid through a quill, arises from the partial removal of atmospheric pressure from within the quill by the muscular power of" the mouth. There is a great analogy between the mode in which suction is ef- fected by the mouth, and that in which a liquid is made to rise into the bulb of an implement which I am about to describe, and which is very useful for withdrawing small portions of liquids from situations from which otherwise they cannot be removed without inconvenience. 105. This instrument is constructed by duly attaching a bag of caoutchouc to the neck of a glass bulb with a long tapering perforated stem. 106. In order to withdraw from any vessel into which the stem will enter, a portion of any contained liquid, it is only necessary to compress the bag so as to exclude more or less of the air from within it; then to place the orifice of the stem be- low the surface of the liquid, and allow the bag to resume its shape. Of course, the space within it becoming larger, the air must be rarefied, and inadequate to resist the pressure of the atmosphere, until enough of the liquid shall have entered to restore the equilibrium of density between the air within the bag and the atmosphere. The air within the bag cannot, however, fully resume its previous density; since the column of the liquid counteracts, as far as it goes, the atmospheric pressure. Indeed, this counteracting influence is so great in the case of mercury, that the instrument cannot be used with this liquid. It is however the only substance, fluid at ordinary temperatures, which is too heavy to be drawn up into the bulb of the instrument in question, when fur- nished with a stout bag. Of the Air Pump. Difference between the Air Pump and the Water Pump. 107. The action of the air pump is perfectly analogous to that of the water pump; as there is no difference between pumping water and pumping air, excepting that which arises from the nature of the fluids; the one being elastic, the other, in common with liquids in general, almost destitute of elasticity. 108. In the air pump, as in the water pump, therefore, there is a chamber, and an upper and lower valve, which operate in the same manner as the valves of the water pump already described. Description of a large Air Pump with Glass Chambers. 109. The opposite engraving represents a very fine instrument of large size, ob- tained from Mr. Pixii, of Paris. 110. From the figure, it must be evident that this pump has two glass chambers. They are unusually large, being nearly three inches in diameter inside. The lower valve, V, is placed at the end of a rod, which passes through the packing of the piston. Hence, during the descent of the piston, the friction of the packing against the rod, causes it to act upon the valve with a degree of pressure adequate to prevent any escape of air, through the hole which it closes, at the bottom of the chamber. The air included between the piston and the bottom of the chamber, is, therefore, by the descent of the piston, propelled through a channel in the axis of the piston, covered by a valve opening upwards. When the motion of the piston is re- versed, the air cannot, on account of the last mentioned valve, return again into the cavity which the piston leaves behind it. But in the interim, the same friction of the packing, about the rod, which had caused it to press downwards, has now, in consequence of the reversal of the stroke, an opposite effect, and the valve V is lifted as far as a collar on the upper part of the rod will permit. The rise, thus permitted, is just sufficient to allow the air to enter the chamber through an aperture which the valve had closed, and which communicates by means of a perforation with a hole in the centre of the air pump plate, and of course with the cavity of the receiver, RR, placed over the plate. The reaction of the air in the perforation and pump chamber 22 IMPONDERABLE SUBSTANCES. being diminished, the air of the receiver moves into the chamber until the equili- brium of density is restored between the two cavities. The chamber will now be as full of air as at first; but the air with which it is replenished is not so dense as before, as the whole quantity in the receiver and the chamber scarcely exceeds that which had existed, before the stroke, in the receiver alone. By the next downward stroke, the air which has thus entered the chamber is propelled through the valve hole in the piston. Another upward stroke expels this air from the upper portion of the chamber; and the valve attached to the rod being again uplifted, the portion of the chamber, left below the piston, is supplied with another complement of air from the receiver: and thus a like bulk of air is withdrawn at every stroke of the pump. I say a like bulk of air, since the quantity necessarily varies with the density of the air in the vessel subjected to exhaustion. This density is always directly as the quantity of air remaining; of course it finally becomes insignificant. Thus when the quantity, in the receiver, is reduced to one-hundredth of what it was at first, the weight of air removed, at each stroke, will be one-hundredth of the quantity taken at each stroke when the process began. 111. I have explained the action of one chamber only, as that of the other is ex- actly similar, excepting that while the piston of one descends, that of the other rises. 112. The gauge represented in the engraving, is one which I have contrived upon a well known principle. It consists of a globular vessel to hold mercury, supported upon a cock. The mercury is prevented from entering the perforation in the cock, by a tube of iron, surmounted by a smaller one of varnished copper, which passes up into a Torricellian glass tube till it reaches near the top. The glass tube opens at its lower extremity, under the surface of the mercury in the globe. The exhaustion of this tube, and that of any vessel placed over the air pump plate, proceed simulta- neously, and consequently the mercury is forced up from the globe into the glass tube to an altitude commensurate with the rarefaction. 113. By inspecting a scale, SS, behind the glass tube, the height of the mercury is ascertained. In order to make an accurate observation, the commencement of the scale must be duly adjusted to the surface of the mercury in the globe. On this account it is supported by sliding bands on an upright square bar, between the glass cylinders. 114. The receiver, RR, represented on the air pump plate, is one which I usually employ in exhibiting the artificial aurora borealis. The sliding wire, terminated by a ball, enables the operator to vary the distance through which the electrical corus- cations are induced. Experimental Illustrations of the Elastic Reaction of the Air. Air occupying a small Portion of a Cavity, rarefied so as to fill the whole Space. 115. Air is dependent on its own weight for its density, and enlarges in bulk in proportion as the space allotted to it is enlarged. s-~ < Expulsion of a Liquid by the Rarefaction of Air. 122. A flask, half full of water, is inverted in another vessel, having some water at the bottom, and both are placed, under a bell glass, on the plate of an air pump. As the bell is exhausted by the action of the pump, the air included in the flask enlarges its bulk, finally occu- pying the whole cavity, and partially escaping from the orifice through the water in the lower vessel. When the atmosphere is allowed to re-enter the bell, the water rises into the flask, so as to occupy as much more space than at first, as the air occupies less, in consequence of a portion having escaped as abovementioned. Experimental Proofs of the Weight of the Atmosphere. Atmospheric Pressure on the Hand. 123. If, as represented in this figure, the air be ex- hausted from a vessel covered by the hand, its re- moval will be found almost impracticable: for, sup- posing the opening which the hand closes to be equal to five square inches, at 15 lb. per square inch, the pressure on it will evidently be seventy-five pounds. Bladder ruptured by the Weight of the Atmosphere. 124. Let there be a glass vessel open at both ends, as represented in this figure. Over the upper opening let a bladder be stretched and tied, so as to produce an air-tight juncture. For every square inch of its super- ficies, the bladder thus covering the opening in the vessel sustains a pressure of about 15 pounds. Yet this is productive of no perceptible effect; because the atmosphere presses upwards against the lower surface of the bladder, as much as downwards upon the upper surface. But if the vessel be placed upon the plate of an air pump, so that, by exhaustion, the atmosphe- 24 IMPONDERABLE SUBSTANCES. lie pressure downwards be no longer counteracted by its pressure upwards, the blad- der will be excessively strained, and usually torn into pieces. 125. When the bladder is too strong to be broken by the unassisted weight of the air, a slight score with the point of a penknife will cause it to be ruptured not only where the score is made, but in various other parts, so that it will, at times, be torn entirely from the rim of the vessel. The Hemispheres of Otho Guericke, the celebrated Inventor of the Air Pump. 126. Two brass hemispheres are so ground to fit each other at their rims as to form an air- tight sphere when united. One of the hemispheres is furnished with a cock, on which is a screw for attaching the whole to the air pump. Being by these means exhausted, the cock closed, and the ring, R, screwed on to the cock, great force must be exerted, before the hemispheres can be separated. Bottle broken by Exhaustion of the Air from within. 127. Proof that a square glass bottle may be broken by atmospheric pressure on the outside, as soon as it ceases to be counteracted by the resistance of the air within. 128. The mouth of a square bottle being placed over the hole in an air pump plate, so as to be suffi- ciently tight for exhaustion, a few strokes of the air pump, by withdrawing the air from the interior, causes the bottle to be crushed. 129. A stout globular glass vessel, with an aper- ture at top, is placed over the bottle, to secure the spectators from the fragments. Bottle broken by Exhaustion of the Air from without. 130. The elastic reaction of the air, confined within a square bottle, will burst it, as soon as relieved from the counteracting weight of the atmosphere. 131. If a thin square bottle, so sealed that while unbroken the contained air cannot escape, be placed within the receiver pf an air pump, the exhaustion of the receiver will, by removing the pressure which counteracts the elastic reaction of the con- fined air, cause the bottle to be fractured. The Height of the Column of Mercury which balances the Atmosphere, shown by Exhaustion. 132. R, fig. 1, is a hollow glass cylinder, about 33 inches in height, and 2£ inches in diameter, into the upper end of which a brass gallows screw, G, is cemented; so that by means of the flexible pipe communicating with the air pump plate, A, the cylinder may be exhausted. The mouth of the cylinder being immersed in mercury in the vase, the metal, as the exhaustion proceeds, rises in the cylinder, until it CALORIC. 25 reaches more or less nearly to the height at which it stands in a Torricellian tube, accordingly as the pump may be more or less perfect. Barometric Column of Mercury lowered by Exhaustion. 133. It has been shown that in a tube void of air, a mercurial column may be sup- ported at the height nearly of thirty inches; and this has been alleged to result from the pressure of the atmosphere on the surface of the mercury on the outside of the tube. 134. In order to verify this allegation, let a tube, fig. 2, supporting within it a column of mercury, be placed under a competent receiver upon the air pump plate. 135. It will be found that, as the air is withdrawn from the receiver, the mercury in the tube will subside, and, if the exhaustion be carried far enough, will sink to a level with the mercury on the outside. 136. If, while this experiment is performing, a communication exist between the air pump and the cylinder, R, employed in the preceding experiment, the mercury will rise in the cylinder, while it falls in the tube; thus proving that the force which is required to remove the air from the outside of the tube and lower the mercury within it, is adequate to raise in the cylinder a mercurial column equal in height to that which is reduced. 1 2G IMPONDERABLE SUBSTANCES. Of the Barometer Gauge. 137. While I am upon the subject of atmospheric pressure, it appears to me expedient to give a de- scription of an instrument which, in several of my illustrations, is employed to ascertain the quantity of air within a receiver. 138. It consists of a barometer tube, 33 inches in height, supported in a vertical position by a pedes- tal, and a strip of wood, G G. Attached to the latter is a brass scale, by which 30 inches is divided into 500 equal parts. The gauge tube is surmounted by a ferrule and gallows screw, by the aid of which a flexible leaden pipe, P, communicates with the bore of the tube. By means of the valve cock and gallows screw at V, this pipe may be made to com- municate also with the cavity to be measured, the valve cock enabling us to suspend the communica- tion when desirable. The lower orifice of the glass tube, T, is covered by mercury in a broad shallow receptacle, D. Supposing the cavity, under these circumstances, to be exhausted, and the communi- cation with the bore of the glass tube open, the ex- tent of the exhaustion, or, in other words, the quantity of air withdrawn, will be exactly in pro- portion to the rise of the mercury as indicated by the scale; and consequently, reversing the operation, the fall of the mercury, as indicated by the scale, will show the quantity of air which may be intro- duced. If we count the degrees upwards from the surface of the mercury in the receptacle, D, their number will show the quantity of air withdrawn. If we count the degrees downwards from the level of the top of the mercurial column in the barometer, the number will indicate the exact quantity of gas in the cavity examined. In short, the quantity taken out, or introduced,.is always measured by the num- ber of degrees which the mercury rises or falls in consequence. It is preferable to have two scales, one beginning above, the other below. 139. This gauge may be employed to indicate the quantity of air in any cavity. It only requires accuracy in the divisions of the scale, and in the adjustment of zero to the proper level. As the height of the mercurial column in the barometer varies with those changes of atmospheric pressure which it is employed to indicate, there- fore, in counting downwards, care must be taken to place the commencement of the scale on a level with the upper end of a column of mercury in a good barometer, at the time. To facilitate this adjustment, I have occasionally placed a Torricellian tube by the side of the gauge tube. The top of the column of the mercury in the Torricellian tube is then the proper point for the upper zero. As the strip of wood to which the scale is attached slides upon the iron rod, R, the scale may be fixed at a proper height by a set screw.* 140. As a perfect vacuum cannot be produced by means of an air pump, in order to wash out of a receiver all traces of atmospheric air, it is necessary that portions of the gas to be substituted should be repeatedly introduced, and as often removed by exhaustion.t 141. The rise of the mercury in the tube, by diminishing the quantity in the re- ceptacle, D, will cause the surface of it to be lower; but the breadth of this vessel is so great, and the descent of the mercurial surface in it so inconsiderable that no error worthy of attention is thus produced. 142. It is proper to mention that the cavity of the tube ought to be so small in proportion to that of the receiver, as to create no error worthy of attention. * Both the gauge tube and the rod, R, should be longer than they are represented in the figure. t One gas may be employed to wash another out of a cavity, in a mode analogous to that in which water may wash out alcohol, or alcohol water. CALORIC. 27 Apparatus for illustrating the Difference between the Lifting and Forcing Pumps. 143. The process by which the water is drawn into the chamber is the same in the case of the forcing as in that of the lifting pump. In the lifting pump, L, the water which has entered the chamber during the ascent of the piston, passes through the piston during its descent, and is lifted by it when the motion is reversed. In the forcing pump, F, the piston, being imperforate, forces, in descending, the water into the adjoining air vessel, A, whence its regress is prevented by a valve, V. The stroke being repeated, the water accumulates in the air vessel, compressing the con- tained air, until it reacts upon the water with sufficient force to cause an emission of this liquid through the jet pipe, J J, commensurate with the supply. Of Condensation. 144. It has been shown that, in consequence of the elasticity of the air, the quan- tity of this fluid, in any close vessel, may be diminished until the residual portion has, by the action of the air pump, become too rare to escape in opposition to the very slight resistance made by the valves. It remains to show that, in consequence of the same property, by an operation the converse of that of the air pump, the air in any adequate vessel may be made many times more dense than it would other- wise be. Of the Condenser. 145. The instrument employed for the purpose of condensing air is called a con- denser. 146. The air pump was illustrated by its analogy with the suction pump. There is the same analogy between the condenser and the forcing pump. In the air pump, the valve between the chamber and receiver opens towards the chamber; in the case of the condenser a corresponding valve opens towards the receiver. 147. Besides the valve thus placed between the chamber and receiver, there is in each pump another valve. In the air pump, the air passes this second valve only 28 IMPONDERABLE SUBSTANCES. when the piston moves so as to lessen the vacancy between it and the bottom of the chamber; in the condenser, the air passes only when the piston moves so as to en- large the vacancy. In other respects these machines are so much alike, that the one might be used for the other. In my experimental illustrations, I shall have occasion to employ instruments which serve either to exhaust or to condense, according to the aperture selected for making a communication with the receiver. FlO. 1. 148. Fig. 1, in the adjoining engraving, represents a condenser. It consists of a brass cylinder, A A, ground internally, so as to be perfectly cylindrical. Into this a piston, B, is fitted by means of oiled leathers packed between screws, repre- sented in the figure, and turned in the lathe, so as to enter the chamber in obedi- ence to considerable force. At the lower end of the rod, a perforation, C C, may be seen, which commences at the lower ex- tremity, rises vertically until it gets above the packing, and then passes out at right angles to its previous direction through the rod of the piston. Just above where it commences, a cavity, D, may be observed, which is left for the upper valve. This valve is formed of a strip of oiled leather tied over a brass knob represented within the cavity. 149. The upper and lower valves are ex- actly alike; hence, a good idea of either may be obtained from fig. 2, which affords a separate view of the lower valve. 150. The action of the condenser is as follows. When the piston is drawn up, all the air within the chamber gets below the packing through the perforation, C C, and the upper valve, which opens downwards with ease so as to afford a passage. When the piston descends, the air included in the chamber cannot get by the leather packing. The upper valve at the same time shuts so as to prevent it from getting through the perforation, C C. It has therefore to proceed through the lower perforation, E. The piston being drawn up again, the valve at E shuts and prevents a return of the air expelled, while the air of the chamber again gets below the piston as in the first instance. Thus, at every stroke, the contents of the chamber are discharged through the lower valve, while its retrocession from any receiver into which it may pass is prevented by the valve, E. 151. As the quantity of air in the vessel increases, the force requisite to drive the piston home becomes greater; and it has to descend farther, ere the air within the chamber exceeds in density that in the receiver, so far as to open the lower valve. Influence of Pressure on the Bulk of Air, and of its Density on its Resistance. 152. Air lessens in bulk as the pressure which it sustains augments; and the resist- ance arising from its elasticity is augmented, as the quantity confined in the same space is increased, or the confining space diminished. 153. For the illustration of this proposition, I have devised the apparatus repre- sented in the opposite engraving. 154. If mercury be poured into the air-tight vessel, A, through the tube, T T, which passes perpendicularly into this vessel until it touches the bottom; as the air in the vessel cannot escape, it is gradually reduced in bulk, but at the same time re- acts upon the surface of the metallic liquid with a force which becomes greater, in proportion as its bulk is lessened. Hence an increasing mercurial column will bo upheld, which by its height indicates the resistance. When the air in the vessel has been reduced to half its previous bulk, the height of the mercury in the tube will be about 30 inches, or equal to that of the mercury in the barometer at the time of Apparatus for illustrating the Influence of Pressure on the Bulk of Air. T (Page 28.) CALORIC. 29 performing the experiment. Thus it is shown, that when air is condensed into half the space which it occupies under the pressure of the atmosphere, its reactive power is doubled, being adequate to support a column of mercury equal to the pressure of the atmosphere, in addition to that pressure. It follows that the quantity of air oc- cupying any space is as the pressure, and is always to that of an equal bulk of the atmosphere, as the height of the column of mercury which the said air can support in a Torricellian tube, is to the height of the mercury in the barometer: and like- wise, that the resistance of air increases with the diminution of the including space ; or, vice versa, that the space which a given weight of air is capable of occupying, lessens as the pressure increases. 155. It remains to be shown that the resistance of air to compression increases as the quantity in any space increases. 156. If, by means of the condenser, C, (the valve cock, v c, and the cock, c, being open,) air be injected into the vessels, A and B at the same time, it will be found that the liquid in the vase, V, will mount into the flask, F, and that when the pres- sure is adequate to cause the air in this to be reduced to half its previous volume, the mercury in the tube, TT, will have the same height as in the previous experi- ment; because the density of the air, and of course its quantity and reactive power, are doubled in one case no less than in the other. 157. The communication between the condenser and the receiver, A, is suspended during the first mentioned experiment, by closing the valve ccck, v c. This cock is opened during the action of the condenser in the second experiment; and like- wise another cock at c, which serves to intercept the communication between the condenser and the receiver, B. Mechanical Action of the Lungs in Respiration illustrated. 158. The elevation of the sternum rarefies the air within the cavity of the thorax. Consequently, the atmospheric pressure not being adequately resisted, the external air rushes through the trachea into the lungs, dilating all the cells. The depression of the sternum and consequent diminution of the cavity cause the air which had thus entered, or an equivalent portion, to flow out. For the illustration of the pro- cess here described, I have contrived the apparatus represented below. 159. A tall receiver, R, with an orifice, O, is placed in a globe containing water, 30 IMPONDERABLE SUBSTANCES. so that about two-thirds of the receiver are occupied by this liquid, the remainder with air, whilst a bladder is so suspended from the orifice as not to touch the water. 160. The atmosphere has access to the cavity of the bladder through its neck, and through the orifice O of the receiver, but not to the space A, between the outside of the bladder and the inside of the receiver. 161. It may be assumed as an obvious consequence of the preceding experiments, (154, 156) that the pressure, exerted by any given quantity of air, is inversely as the confining space; or in other words, that the pressure increases as the space lessens, and diminishes as the space enlarges. 162. When a cavity to which the atmosphere has no access is enlarged, the density of the contained air is proportionably diminished. When any cavity is di- minished, the density of the contained air is proportionably increased. But if the atmosphere, meanwhile, have access to the cavity, it will by its influx or efflux tend to preserve the equilibrium of density and pressure between the air of the cavity and the external medium. These consequences are well known to ensue, from an al- ternate enlargement and diminution of capacity, during the working of an air pump, a condenser, or bellows. 163. In like manner the elevation of the receiver, R, enlarging the cavity within it unoccupied by water, causes the air to rush in through the orifice, O ; and the re- versal of the motion, reducing the cavity, causes the air to rush out through the same aperture. The bladder is so situated as to receive all the air that enters, and to supply all that is expelled. Hence when the receiver is lifted, the bladder is in- flated, and when lowered to its previous position, the bladder resumes its original dimensions. 164. Supposing the space, A, between the outside of the bladder and the inside of the receiver, to represent the space between the outside of the lungs and the inside of the thorax, the cavity of the bladder representing the cavities of the lungs, and the orifice, O, performing the part of the trachea and nostrils, the explanation, above given, will be as applicable to the apparatus by which nature enables us to breathe, as to that employed in the preceding illustration. EXPANSION OF ELASTIC FLUIDS. 165. Having by means of the preceding digression ex- plained the nature and extent of atmospheric pressure, I shall proceed to show the important influence exercised by it in all chemical processes in which elastic fluids are concerned. 166. It has been demonstrated (54) in illustrating the principle of Sanctorio's thermometer, that the bulk of the air in any space varies with the temperature. 167. It has been shown that the same effect may be produced by variations in atmospheric pressure. (115, 119, 120, 122.) 168. It follows that the volume of elastic fluids is in- versely as the pressure and directly as the heat. In other words, the less the pressure and the greater the heat, the larger their bulk; and vice versa, the less the heat, and the greater the pressure, the less their bulk. 169. Agreeably to the observations of JDalton, Gay-Lussac, and Crich- ton, 1000 parts of atmospheric air, in rising from the temperature of 32° to 2123, will expand so as to measure 1375 parts nearly, or, T^th of the bulk which it would have at 32°, for each degree of heat which it may re- ceive. CALORIC. 31 170. Having, therefore, any given bulk of dry air, 100 cubic inches for instance at 60°, to find its bulk at any other temperature, suppose at 80°, wc must in the first place consider that 480 parts at 32° would at 60°, adding one part for every degree above 32°, be 508 parts; and would by a proportionate increase, become at 80°, 528 parts. But if 508 parts at G0° become 528 at 80°, what will 100 parts at 60° become when heated to 80°. 508 : 528 : : 100 : 103.9 171. It has been inferred by the same distinguished philosophers, that all aeriform substances, whether gases or vapours, are expanded by heat at the same rate as dry atmospheric air, if they be not in contact with any vaporizable matter, in the liquid or solid state, which by vaporizing or con- densing may vary the result. Theory of Expansion. 172. The expansion of matter, whether solid, liquid, or aeriform, by an increase of temperature, may be thus explained. 173. In proportion as the temperature within any space is raised, there will be more caloric in the vicinity of the particles of any mass contained in the space. The more caloric in the vicinity of the particles, the more of it will combine with them; and in proportion to the quantity of caloric thus combined, will they be actuated by that reciprocally repellent power, which, in proportion to its intensity, regulates their distance from each other. 174. There may be some analogy between the mode in which each ponderable atom is surrounded by the caloric which it attracts, and that in which the earth is surrounded by the atmosphere; and as in the latter case, so probably in the former, the density is inversely as the square of the dis- tance. 175. At a height at which the atmospheric pressure does not exceed a grain to the square inch, suppose it to be doubled, and supported at that in- creased pressure by a supply of air from some remote region; is it not evident that a condensation would ensue in all the inferior strata of the atmosphere, until the pressure would be doubled throughout, so as to be- come at the terrestrial surface, 30 pounds, instead of the present pressure of 15 pounds? Yet the pressure at the point from which the change would be propagated would not exceed two grains per square inch. 170. In like manner, it may be presumed that the atmospheres of caloric are increased in quantity and density about their respective atoms, by a slight increase in the calorific tension of the external medium. Demonstration that Atmospheric Pressure opposes and limits Chemical Action, where Elastic Fluids are to be generated or evolved. Of Vaporization. 177. Water would boil at a lower temperature than 212°, if the atmospheric pressure was lessened; for when it 32 IMPONDERABLE SUBSTANCES. has ceased to boil in the open air, it will begin to boil again in an exhausted receiver. Those who ascend mountains find that for every 530 feet of elevation, the boiling.point is lowered one degree of Fahrenheit's thermometer. It is, in fact, lowered or raised rVfoth of a degree for every tenth of an inch of variation in the height of the mercury in the barometer. Ebullition from diminished Pressure. 178. The adjoining figure represents a vessel of water boiling within a receiver, in consequence of the diminution of pressure by exhaustion. Culinary Paradox.—Ebullition by Cold. 179. A matrass, half full of water, be- ing heated until all the contained air is superseded by steam, the orifice is closed so as to be perfectly air-tight. The matrass is then supported upon its neck, in an in- verted position, by means of a circular block of wood. A partial condensation of the steam soon follows from the re- frigeration of that portion of the glass which is not in contact with the water. The pressure of the steam upon the liquid of course becomes less, and its boiling point is necessarily lowered. Hence it begins again to present all the phenomena of ebullition, and will continue boiling sometimes for nearly an hour. 180. By the application of ice, or of a sponge soaked in cold water, the ebullition is accelerated; because the aqueous vapour which opposes it, is in that case more ra- pidly condensed; but as the caloric is at the same time more rapidly ab- stracted from the water by the increased evolution of vapour to replace that which is condensed, the boiling will cease the sooner. CALORIC. 33 Improved Apparatus for showing the Culinary Paradox. 181. This figure illustrates a new and in- structive method of effecting ebullition by cold. 182. The apparatus consists principally of a glass matrass, with a neck of about three feet in length, tapering to an orifice of about a quarter of an inch in diameter. The bulb is bulged inwards in the part directly oppo- site the neck, so as to create a cavity capa- ble of holding any matter which it may be desirable to have situated therein. In addi- tion to the matrass, a receptacle holding a few pounds of mercury is requisite. The bulb of the matrass being rather less than half full of water, and this being heated to ebullition, the orifice should be closed by the finger, defended by a piece of gum-elas- tic, and depressed below the surface of the mercury; the whole being supported as re- presented in the figure. Under these cir- cumstances, the mercury rises as the tempe- rature of the water declines, indicating the consequent diminution of pressure within the bulb. Meanwhile, the decline of pressure lowering the boiling point of the water, the ebullition continues till the mercury rises in the neck nearly to the height of the mercury in the barometer. 183. By introducing into the cup formed by the bulging of the bulb, cold water, alcohol, ether, or ice, the refrigeration, the diminution of pressure, and the ebullition, are all simultaneously accelerated; since these results are reciprocally dependent on each other. Experimental Proof that some Liquids would be permanently aeriform, if Atmospheric Pressure were removed. 184. The power of certain liquids, common ether for instance, to assume in vacuo, at ordinary tempe- ratures, the aeriform state, in opposition even to the pressure of a column of mercury, may be shown by the following experiment. 185. A glass funnel is ground to fit air-tight into the neck of a glass decanter, so that the stem of the funnel may reach nearly to the bottom of the decan- ter, as represented in the adjoining cut. The decan- ter is filled with mercury, with the exception of a small portion of the neck, which is occupied by ether. The stem of the funnel is then introduced into the neck of the decanter, so as to be air-tight; and the whole be- ing included in a receiver, the air is withdrawn by a pump. The ether converted into vapour will force the mercury to rise from the decanter, through the stem, into the wider part of the funnel. 186. Rationale.—The attraction between the ponderable particles of the ether, and those of caloric, can be indulged only in opposition to the reci- procally repulsive power of the latter; since one tends to rarefy the caloric, 5 34 IMPONDERABLE SUBSTANCES. J the other to condense it into the limited space occupied by the ether. It follows that the caloric cannot combine with the ponderable matter beyond the point at which the repulsive power becomes equal to the attractive. But the repulsion exercised by the same number of particles of caloric will be greater as the space is less, and vice versa. The larger, therefore, the space occupied by the ponderable particles of the ether, the more caloric may combine with them, without rendering its reciprocally repulsive power paramount to its attraction for them. 187. The removal of atmospheric pressure, by allowing the ponderable particles to occupy a larger space, enables them to combine with that addi- tional quantity of caloric which is necessary to the aeriform state. 188. This explanation may, of course, be extended to the ebullition of other liquids in vacuo, at temperatures lower than those at which they boil in the air. It is obviously applicable to the two preceding illustra- tions. Boiling Point elevated by Pressure. 189. Into a small glass matrass, with a bulb of about an inch and a half in diameter and a neck of about a quarter of an inch in bore, in- troduce nearly half as much ether as would fill it. Closing the orifice with the thumb, hold the bulb over the flame of a spirit lamp, until the effort of the generated vapour to escape becomes difficult to resist. Removing the matrass to a sufficient distance from the lamp, lift the thumb from the orifice. The ether, previously qui- escent, will rise up in a foam, produced by the rapid extrication of its vapour. 190. This experiment may be performed with less risk, by plunging the matrass in hot water, instead of heating it by a lamp. 191. Having supplied a small flask with a quantity of mercury, sufficient to cover the bottom to about an inch in depth, let there be a glass tube so introduced through the neck, and luted air-tight, as to extend nearly an inch below the mercurial surface. If the flask thus prepared, be duly heated, the ether will be proportionably vapourized, and the generated vapour pressing on the mercury, will cause a column of this metallic liquid to rise within the tube, and thus to in- dicate and measure the pressure. It is necessary to discontinue the heat, when the mercurial column ap- proaches the upper orifice of the tube, in order to pre- vent the metal from overflowing. High Pressure Boiler. (Page 35.) 031�9956 CALORIC. 35 High Pressure Boiler. 192. That the temperature of steam increases with the pressure, may be demonstrated by means of a small boiler, such as is represented in the opposite engraving. 193. A glass tube, of about five feet in height, and of half an inch in bore nearly, is secured into an aperture in a very strong iron boiler, so as to be air-tight, and so as to be concentric with the axis of the boiler. Within the boiler the tube descends in such manner as to pass through the water with which it is supplied, and to terminate close to the bottom, be- neath a small quantity of mercury purposely introduced. On the opposite side of the boiler, a tube, not visible in the engraving, descends into it. This tube consists of about two inches of a musket barrel, and is closed at bottom. The object of it is to contain some mercury, into which the bulb of a thermometer may be plunged for ascertaining the temperature. 194. When the fire has been applied during a sufficient time, the mercury will rise in the glass tube so as to be visible above the boiler; and con- tinuing to rise during the application of the fire, it will be found that, with every sensible increment in its height, there will be a corresponding rise of the mercury in the thermometer. 195. In front of the tube, as represented in the figure, there may be ob- served a safety valve with a lever and weight for regulating the pressure. It has been found that, when the effort made by the steam to escape, in opposition to the valve thus loaded, is equal to about fifteen pounds for every square inch in the area of the aperture, the height of the column of mer- cury, C C, raised by the same pressure, is about equal to that of the co- lumn of this metal, usually supported by atmospheric pressure in the tube of a barometer. 196. Hence the boiler, under these circumstances, is conceived to sustain an unbalanced pressure equivalent to one atmosphere; and for every addi- tional fifteen pounds per square inch, required upon the safety valve to re- strain the steam, the pressure of an atmosphere is alleged to be added. To give to steam at 212 degrees, or the boiling point, such an augmentation of power, a rise of 38 degrees is sufficient, making the temperature equal to 250 degrees. To produce a pressure of four atmospheres about 293 de- grees would be necessary. Eight atmospheres would require nearly 343 degrees. 197. When by means of the cock an escape of steam is allowed, a cor- responding decline of the temperature and pressure ensues. 198. If the steam, as it issues from the pipe, be received under a portion of water of known temperature and weight, the consequent accession of heat is surprisingly great, when contrasted with the accession of weight derived from the same source. It has in fact been ascertained that one measure of water, converted into aqueous vapour, will, by its condensa- tion, raise about ten measures of water in the liquid form one hundred degrees. Of the Incompetency of a Jet of High Steam to scald at a certain Distance from the Aperture. 199. Much attention has been excited by the observation, that the hands may be enveloped in a jet of vapour from a high pressure boiler without 36 IMPONDERABLE SUBSTANCES. inconvenience, at a certain distance from the aperture through which it escapes. Experimental Demonstration. 200. The fact that the hand may be immersed without injury in a jet of steam while issuing from a boiler, if not too near the aperture, experimentally demonstrated. 201. Rationale.—Since the temperature, density, and pressure, which form the distinguishing attributes of high steam, cannot be sustained with- out confinement, steam ceases to be high steam as soon as it is liberated. Consequently, a jet from a high pressure boiler is essentially no more than a copious jet of aqueous vapour at the heat of boiling water. 202. The only distinguishing characteristic, derived from its previously superior temperature and density, is a greater velocity of efflux. Without any superiority of temperature, the high pressure jet is propelled into the atmosphere with a momentum, which cannot be given to low steam. Hence the rapid refrigeration to which the former is subjected, at a sufficient dis- tance from the place of its efflux to admit of an extensive diffusion in the atmosphere. Illustration of the Process by which Thermometers are supplied with the Liquids used in their construction. 203. A globe, with a long cylindrical neck, situated as in the preceding figure, and containing a small quantity of water, being subjected to the flame of a lamp, the water, by boiling, will soon fill the cavity of the globe and neck with steam. When this is accomplished, bubbles of air will cease to escape from the orifice of the neck through the water in the vase. 204 The apparatus being thus prepared, on removing the lamp, the water will quickly rush from the vase into the vacuity arising from the condensation of the steam within the globe. 455 CALORIC. 37 Explosive Power of Steam. 205. If a glass bulb, hermetically sealed while containing a small quantity of water be suspend- ed by a wire over a lamp flame, an explosion soon follows, with a violence and noise which are sur- prising, when contrasted with the quantity of water by which they are occasioned. 206. Rationale.—Supposing that the bulb were, in the first instance, merely filled with steam, without any water in the liquid form, the explana- tion of this phenomenon would be comprised in the theory of expansion, already suggested. (173.) In that case, the effort of the steam to enlarge itself, would be nearly in direct arithmetical proportion to the temperature; but water being present in the li- quid form, while the expansive power of the steam, previously in existence, is increased, more steam is generated with a like increased power of expansion. It follows that the increments of heat being in arithmetical proportion, the explosive power of the confined vapour will increase geometrically, being actually doubled as often as the temperature is augmented 38°. (196.) Interesting Experiments with respect to Vaporization under extreme Pres- sure, by M. Cagniard de la Tour, and Mr. Perkins. 207. Agreeably to some experiments performed by M. Cagniard de la Tour, in which liquids were exposed to heat in very stout tubes, vaporiza- tion was performed in a space which was to that previously occupied,— 'Ether, as 2 to 1, producing a pressure of 33 atmos- pheres. Alcohol, as 3 to 1, producing a pressure of 119 atmos- pheres. Water, as 4 to 1, producing a pressure greater than that caused by the alcohol. In the case of 208. Mr. Perkins alleges that a small iron boiler of great strength may be heated red-hot while holding a portion of water, and that if, under these circumstances, an aperture be opened of \ of an inch in diameter, the steam will not escape, although upon a reduction of temperature, it will rush out with great violence. 209. It was inferred that the repulsion between the particles of the caloric in union with the water, and those in union with the metallic ring bounding the aper- ture, was paramount to the pressure tending to produce the expulsion of the steam. 210. I am unable to reconcile this experiment with one which I performed by heating to incandescence, in a forge fire, a tube of iron, of which the bore was less than i of an inch, while, by means of a cock, a communication with a high pressure boiler was made. Under these circumstances, the steam was not prevented from escaping through the pipe. 211. It appears to be sufficiently proved that the quantity of caloric combined with a given weight of steam is always the same, whatever may be its temperature; the sensible heat increasing and the latent heat diminishing as the density and pressure are augmented. Cold and Cloudiness arising from Rarefaction. 212. Incipient rarefaction in the air of a receiver is usually indicated by a cloud, which disappears when the exhaustion has proceeded beyond a certain point. A delicate thermometer placed in the receiver, shows that a decline of temperature 38 IMPONDERABLE SUBSTANCES. accompanies this phenomenon. We may, therefore, infer that the cloud is the con- sequence of refrigeration. If the suggestions be correct which were made (Theory of Expansion, 175) respecting the mode in which caloric exists in atmospheres around the particles of ponderable matter, it will not be difficult to understand why afiriform fluids should absorb more caloric, in proportion as their consti- tuent particles are enabled, by a diminution of pressure, to become more remote. Hence, by rarefaction, the capacity of air is increased, and cold is produced, which condenses the aqueous vapour until its sensible heat is restored by an accession of caloric from the surrounding medium. (184.) Cold produced by the Palm Glass. 213. In forming the bulbs severally at the ends of the glass tube represented in this figure, one is furnished with a perforated pro- jecting beak. By warming the bulbs, and plunging the orifice of the beak into alcohol, a portion of this liquid enters, as the air within contracts in returning to its previous tempera- ture. The liquid, thus introduced, is to be boiled in the bulb which has no beak, until the whole cavity of the tube and of both bulbs, not occupied by liquid alcohol, is filled with its steam. While in this situation, the end of the beak is to be shortened and sealed, by sub- jecting it to the flame excited by a blowpipe. 214. As soon as the instrument becomes cold, the steam, which had filled the space vacant of liquid alcohol, condenses, and with the exception of a slight portion of vapour, which is always emitted by liquids when relieved from atmospheric pres- sure, a vacuum exists within the bulb. 215. The instrument, thus formed, has been called a palm glass; because the phe- nomenon which it exhibits is seen by grasping one of the bulbs, so as to bring it completely into contact with the palm of the hand. One of the bulbs being thus situated, and while surcharged with the alcohol, and held in the position represented in the figure, both the liquid and vapour are propelled from it into the other bulb. This phenomenon combines the characteristics of the differential thermometer, (69,) with those of the culinary paradox, (179,) being the joint effect of the expansion, and evolution of vapour, in one part of the apparatus, and its contraction and condensa- tion in another. The phenomena are precisely similar, whether we warm the lower bulb, or cool the upper one by means of ice. The motive for recurring to the expe- riment here is to state that, as soon as the last remnant of the liquid is forced from the bulb in the hand, a striking sensation of cold is experienced by the operator. 216. This cold has been attributed generally to an increase of the capacity of the residual vapour for caloric in consequence of its attenuation. The analogy is evi- dent between this phenomenon and that above described, as taking place in the re- ceiver of an air pump; in either case refrigeration results from a diminution of density. Cold consequent to relaxation of Pressure. 217. Cold is produced whether a diminution of density arise from relieving con- densed air from compression, or from subjecting air of the ordinary density to rare- faction. A cloud similar to that which has been described as arising in a receiver partially exhausted, may usually be observed in the neck of a bottle recently uncork- ed, in which a quantity of gas has been evolved in a state of condensation by a fer- menting liquor. CALORIC. 39 218. The apparatus represented in the annexed figure, shows the influence of relaxed pressure on the capacity of air for heat and moisture. 219. A glass vessel with a tubulure and a neck has an air thermometer fastened air-tight by means of a cork into the form- er, while a gum-elastic bag is tied upon the latter. Before closing the bulb, the inside should be moistened. Under these circumstances, if the bag, after due com- pression by the hand, be suddenly re- leased, a cloud will appear within the bulb, adequate, in the solar rays, to pro- duce prismatic colours. At the same time the thermometer will show that the compression is productive of warmth, the relaxation of cold. 220. The cloud which has been shown to arise (212,) in air suddenly rarefied, has been much insisted upon of late, by Mr. Espy, as illustrating a meteorological pro- cess, which he considers as the principal cause of rain storms. This induced me to make some experiments in order to elucidate this subject. 221. Large globes, each containing about a cubic foot of space, furnished with thermometers and hygrometers, were made to communicate, respectively, with re- servoirs of perfectly dry air, and of air replete with aqueous vapour.* The cold ultimately acquired by any degree of rarefaction, appeared to be the same, whether the air was in the one state or the other; provided that the air, replete with aqueous vapour, was not in contact with liquid water in the vessel subjected to exhaustion. When water was present, in consequence of the formation of additional vapour, and a consequent absorption of caloric, the cold produced was nearly twice as great as when the air was not in contact with liquid water; being nearly as 9 to 5. 222. Under the circumstances last mentioned, the hygrometer was motionless ■ whereas, when no liquid water was accessible, the space, although previously satu- rated with vapour, by the removal of a portion of it together with the air which is withdrawn by the exhaustion, acquires a capacity for more vapour; and hence the hygrometer, by an abstraction of one-third of the air, revolved more than sixty de- rees towards dryness. But when a smaller receiver (after being subjected to a iminution of pressure of about ten inches of mercury, so as to cause the index of the hygrometer to move about thirty-five degrees towards dryness) was surrounded by a freezing mixture, until a thermometer in the axis of the receiver stood at three degrees below freezing, the hygrometer revolved towards dampness, until it went about ten degrees beyond the point at which it rested when the process commenced. 223. It appears, therefore, that the dryness produced by the degree of rarefaction employed is more than counterbalanced by a freezing temperature. 224. As respects the heat imparted to the air above mentioned, the fact, that the ultimate refrigeration in the case of air replete with vapour, and in that of anhy- drous air, was equally great, and that when water was present the cold was greater in the damp vessel, led to the idea, that the heat arising under such circumstances could not have much efficacy in augmenting the buoyancy of an ascending column of air: but when, by an appropriate mechanism, the refrigeration was measured by the difference of pressure at the moment when the exhaustion was arrested, and when the thermometer had become stationary, it was found coeteris paribus, that the reduction of pressure arising from cold was at least one-half greater in the anhy. drous air, than in the air replete with vapour. This difference seems to be owing to a loan of latent heat made by the contained moisture, or transferred from the appa- * The hygrometers were constructed by means of the beard of the avena sensitiva, or wild oat, also called animated oat. 40 IMPONDERABLE SUBSTANCES. ratus by its intervention, which checks the refrigeration; yet, ultimately, the whole of the moisture being converted into vapour, the aggregate refrigeration does not differ in the two cases. 225. Agreeably to Dalton's tables, at 70° the quantity of moisture in 31 grains or 100 cubic inches of air, is 551-1000ths of a grain. The space allotted to this weight of vapour being doubled, it would remain uncondensed at 45° F., being associated with the same weight, but double the volume, of air; but at 32°, notwithstanding the doubling of the space, only 356-1000ths of a grain would remain in the aeriform state; of course 551 — 356 = 195-1000ths, or nearly 2-10ths of a grain, would be precipitated. 226. The latent heat given out by the condensation of this vapour, would heat, as is well known, 1000 times its weight of water, or 195 grains, one degree; or 31 grains 195-31ths = 6.29 degrees; and as the capacity of air for heat is only one- fourth of that of water, it would heat 31 grains of air 6.29 X 4 = 25.16, or nearly 25° F. As air, at 32° F., expands l-480ths for each additional degree, the difference of bulk, arising from the heat received, as above calculated, would be 25-480ths, or l-19ths nearly. 227. When air, replete with aqueous vapour, was admitted into a receiver par- tially exhausted, and containing liquid water, a copious precipitation of moisture en- sued, and a rise of temperature greater than when perfectly dry air was allowed to enter a vessel containing rarefied air in the same state. In the instance first men- tioned, a portion of vapour arises into the place of that which is withdrawn during the partial exhaustion. Hence when the air, containing its full proportion of va- pour, enters, there is an excess of vapour which must precipitate, causing a cloud, and an evolution of latent heat from the aqueous particles previously in the aeriform Btate. As the enlargement of the space occupied by a sponge, allows, proportiona- bly, a larger quantity of any liquid to enter its cells, so any rarefaction of the air when in contact with water, consequent on increase of heat or diminution of pres- sure, permits a proportionably larger volume of vapour to associate itself with a given weight of the air. When, subsequently, by the afflux of wind replete with aqueous vapour, the density of the aggregate is increased, a portion of the vapour equivalent to the condensation must be condensed, giving out latent heat, excepting so far as the heat thus evolved, being retained by the air, raises the dew point. 228. Hence, whenever a diminution of density of the air inland causes an influx of sea air to restore the equilibrium, there may result a condensation of aqueous va- pour, and evolution of heat, tendino- to promote an ascending current. This process being followed by that which Mr. Espy has pointed out, of the transfer of heat from vapour to air, during its ascent to the region of the clouds, and consequent precipi- tation of moisture, is probably among the efficient causes of those non-electrical rain storms, during which water from the Gulf of Mexico, or from the Atlantic, is trans- ferred to the soil of the United States. Of the Influence of the Atmosphere in promoting Evapora- tion. 229. It has been seen that by its pressure the atmo- sphere opposes vaporization; yet a free access of air is found indispensable in the desiccation of hay, or in the evaporation of water or other solvents. It was at one time generally conceived that evaporation resulted from an affinity between the liquid and the air, analogous to that between water and sugar, or alcohol and resin; but in consequence of the observations of several distinguished philosophers, a different view of this subject has been lat- terly entertained. It has in fact been ascertained that the quantity of aqueous vapour, in any space having sufficient access to liquid water, is always directly as the tempera- ture, whether there be a plenum or a vacuum, or whatever may be the density of the air simultaneously present. CALORIC. 41 230. It has been alleged that a current of atmospheric particles promotes evaporation, only by removing the ne- cessity to which the vapour would otherwise be exposed, of diffusing itself through the atmospheric interstices to a greater distance. 231. Nevertheless, it appears to me that the influence of a current of atmospheric air, in promoting evaporation, is greater than can be reasonably thus accounted for. 232. It is difficult to conceive that the elements of at- mospheric air should have no affinity for those of liquids; or that, if such affinity exist, it should not promote the process of evaporation. Nothing can be more certain than that evaporation is accelerated in proportion to the extent to which contact may be induced between the aeri- form and liquid particles. Hence when surfaces, moistened with such volatile liquids as sulphuret of carbon, or the more volatile ethers, are exposed to the wind, or to a blast, intense cold is produced by the accelerated evaporation. It is well known that the direction of the wind becomes evident from the sensation of coldness, experienced in that part of the wetted finger on which it blows. With the re- frigerating influence of a breeze, when the skin is moistened by perspiration, we are all familiar. 233. The processes of evaporation, and vaporization in the sense of ebullition, cannot be confounded in practice, however they may be identified agreeably to prevailing theories. In either case, heat is requisite, though much less is necessary in that of evaporation; but other things being equal, the process last mentioned, is accelerated in proportion to the extent of surface exposed to the air, while ebullition takes place in proportion to the surface exposed to the fire, without access of air. It only requires that the vapour generated should have an aperture sufficient to allow of its escape, without increase of pressure. Hence evaporating vessels are made broad and shallow, while boilers may be made deep with narrow openings. Cold produced by the Evaporation of Ether when accelerated by a Current of Air. 234. The cold, produced by evaporation accelerated by a current of air, may be advantageously shown by subject- ing a thermometer bulb simultaneously to a jet of ether, 6 12 IMPONDERABLE SUBSTANCES. and a blast from a bellows, so that the aerial and ethereal particles may be thoroughly mingled just before reaching the bulb. Water may be frozen in a bulb thus refrige- rated. 235. Agreeably to the principle above illustrated, (217) that when air is liberated from a state of compression, cold ensues, 1 have lately contrived a new mode of ex- hibiting the vaporization of ether, so as to freeze water on a more extensive scale, and on a much more striking manner than heretofore. Between the lower part of a very strong vessel of sheet iron, capable of holding 40 gallons, and the "hydrant" pipes by which our city is supplied with water, a communication is made by means of a pipe and cock, so as to be opened or closed at pleasure. The vessel is previous- ly filled with air, by allowing it to discharge any water which it may hold through a cock. Under these circumstances, on opening the communication with the hydrant pipes, the air within the vessel may be subjected to a pressure of more than one atmosphere. (154.) If by means of a suitable leaden pipe, furnished with a cock, and terminating with a capillary orifice, the air be allowed to blow into some ether and water contained in a thin capsule, the ether will be rapidly vaporized, and the water soon frozen. 236. In this experiment, in lieu of hydric (sulphuric) ether, we employ the new form of hyponitrous ether which I have lately discovered, the congelation will be more rapidly accomplished. 237. It will hereafter be shown, that, by analogous causes, when solid carbonic acid is thrown into ether, a refrigeration is produced by which mercury may be rapidly frozen. Definition of Vapour by Berzelius. 238. Berzelius objects to the use of the v#ord vapour as implying a condensible aeriform fluid. He uses it in the sense in which English authors employ the word fog, or cloud. Vapour and steam were originally, and still are used in this sense, yet the fluid which is used to propel steam engines, and to which they owe their distinguishing name, can only consist of water in the aeriform state in which it is by the distinguished Swede designated as aqueous gas. Johnson defines steam to be the smoke or vapour of any thing hot and moist. Of course steam smoke and va- pour have in some cases been used synonymously. I have elsewhere mentioned that before Black's discoveries and inferences were published, atmospheric air was the only aeriform fluid whose existence was recognised. Hence the use of the words steam and vapour has grown with our knowledge, and consequently the names applied to visible steam or vapour have been extended to mean the invisible aeri- form fluids from which it is produced by refrigeration. I have some repugnance to designating by a common epithet, permanent gases, and the condensible elastic fluids produced from liquids above their boiling points. I do not see that any dis- advantage arises from the customary use of the word vapour to designate the latter. Of the Opponent Influence of Pressure on the Extrication of Gaseous Substances from a state of Combination. 239. When one of the ingredients of a solid or liquid is prone to assume the aeriform state, its extrication will be more or less easily effected, in proportion as the pressure of the air is diminished or increased. CALORIC. 43 Escape of Carbonic Acid from Carbonate of Lime subjected to an Acid, promoted by Exhaustion and checked by Condensation. 240. If a tall cylindrical jar, containing a car- bonate undergoing the action of an acid, be placed under a receiver, and the air withdrawn by an air pump, the effervescence will be augmented. But if, on the other hand, the same mixture be placed under a receiver, in which the pressure is increased by condensation, the effervescence will be dimi- nished. In the one case, the effort of the carbonic acid to assume the gaseous state is repressed; in the other, facilitated. Hence the advantage of condensation in the process for manufacturing car- bonic acid water. Beyond an absorption of its own bulk of the gas, the affinity of the water is inadequate to subdue the tendency of the acid to the aeriform state; but when, by mechanical pressure, a great number of volumes of the gas are condensed into the space ordinarily occupied by one, the water combines with as large a volume of the condensed gas, as if there had been no con- densation. Improved Apparatus for showing the Influence of Pressure on Effervescence. 241. A cylindrical receiver, about 30 inches in height, and 3 inches in diameter, is supported on a wooden block, W, between upright iron rods, RR. each at the lower end, riveted to a plate of iron beneath the block, and, at the upper end, a screw cut and furnished with a nut. By means of these screws and nuts thus formed, and an intervening cross bar, B, a brass disk. D, is pressed upon the rim of the re- ceiver. The disk is so ground to fit to the rim of the glass, as that, with the aid of some beeswax duly softened by lard, an air-tight juncture may be made. In the middle of the disk there is an aperture, from which proceeds a stout tube, wilh a cock on each side, severally furnished with gallov/s screws, by means of which lead pipes may be made to communicate with an air pump on one side, and a con- denser on the other. The tube is also surmounted by a cock, into which a glass funnel is cemented. Before closing the receiver, some solid carbonate in pieces must be introduced so as to occupy about one-third of the cavity. For this purpose I have employed carbonate of ammonia, calcareous spar in fragments, and latterly clam shells. In either of these substances, carbonic acid and lime are the principal ingre- dients. The carbonate being introduced, and the disk fastened into its place, as re- presented in the figure, diluted muriatic acid may be added, by means of the funnel and cock, in quantity sufficient to cover the carbonate. 242. In consequence of the superior affinity of chlorine for the calcium, and of hy- drogen for the oxygen, (in the oxide of calcium or lime) the carbonic acid is expelled in the gaseous form, causing a perceptible effervescence or foaming of the liquid. If, under these circumstances, by means of the air pump, the atmospheric pressure within the receiver be lessened, the effervescence increases strikingly. On the other hand, if, by closing the communication with the air pump, and opening that with the condenser while this is in operation, the pressure be increased, it will be seen that the effervescence is diminished proportionably. 243. This experiment is much facilitated by the employment of an air pump, which I have contrived, by which we can either exhaust or condense at pleasure. 244. Agreeably to experiments performed by Faraday, when the reaction between an acid and a carbonate is made to take place in a stout tube hermetically sealed, the acid mav be separated in the liquid form. According to the more recent obser- vations of Thilorier, this result has been attained upon a large scale, and one por- tion of the resulting liquid has been found to be partially frozen, by the caloric ab- stracted by the vaporization of the other portion. 44 IMPONDERABLE SUBSTANCES. 245. Thilorier's process, as improved by Mitchell and others, will be hereafter il- lustrated and explained. 246. By analogous means various substances, naturally gaseous, have been liquefied by Faraday, as will be mentioned in treating of those substances. L>47. All the cases of liquefaction alluded to, are referable to the law that the power of any matter to pass to the aeriform state is, ceteris paribus, less in proportion as the pressure is greater. Of the Screw Rod and Plate Frame, employed in the preceding and many other Experiments. 248. The means by which the glass receiver, employed in the preceding experi- ment, is upheld and rendered air-tight by the rods, R R, the wooden block, W, the bar, B, and circular plate or disk, D, is one to which I shall resort frequently in the course of my experiments. Hence, to avoid unnecessary recurrence to analogous description, I shall in future designate as a screw rod and plate frame, that portion of the apparatus above described, which consists of the block, bar, plate, and screw rods* 249. The glass in this case is made quite true by grinding on a large lap wheel, such as is employed by lapidaries. The same object is effected in the case of brass plates without grinding, by turning them in a lathe with a slide rest, and by a tool with a fine pyramidal point. OF CAPACITIES FOR HEAT, OR SPECIFIC HEAT. 250. The power of equal weights of different substances, at the same temperature, in cooling or warming a liquid at a temperature different from their own, will be found very unequal. Thus the effect of a given weight of water being 1000, the effect of the like weight of glass will be 137, of copper 94, tin 51, lead 29, iron 110, gold 29, pla- tinum 31, zinc 92, silver 55. If equal weights of water and mercury, at different temperatures, be mixed, the effect on the water will be no greater than if, instead of the mer- cury, Tfth of its weight of water, at the same temperature as the mercury, had been added; and it takes twice as much mercury by measure as of water heated to the same point to have the same influence. 251. The term specific heat is usually employed to de- signate the quantity of caloric in a body in proportion to its weight or bulk, as specific gravity is used to convey an idea of weight compared with bulk. 252. In the process above described, the specific heats of substances are found in order to estimate their capaci- ties; the one being necessarily as the other, and the same series of numbers expressive of either. Modification of the screw rod and plate frame are represented in the en referred to page 28. (153.) ' CALORIC. 45 Apparatus for illustrating Capacities for Heat. 253. Let the vessels A, B, and C, be supplied with water through the tube, T, which communicates with each of them by a horizontal channel in the wooden block. The water will rise to the same level in all. Of course the resistance made by the water in each vessel to the entrance of more of this liquid will be the same, and will be measured by the height of the column of water in the tube, T. Hence, if the height of this column were made the index of the quantity received by each vessel, it would lead to an impression that they had all received the same quantity. But it must be obvious that the quantities severally received will be as different as are their horizontal areas. Of course we must not assume the resistance, ex- erted by the water within the vessels against a further accession of water from the tube, as any evidence of an equality in the portions previously received by them. 254. In like manner the height of the mercury in the thermometer shows the resistance which substances, whose temperature it measures, are making to any further accession of caloric; but it does not indicate the quantities, respectively received by them, in attaining the temperature in question. This varies, in them, in proportion to their attraction for this self-repellent fluid; as the quantities of water received by the vessels, A, B, C, are varied in the ratio of their respective areas. 255. Rationale.—It may be conjectured that this diversity in the power of substances, equally hot or cold, in influencing temperature, is due to a difference in their capacity to attract caloric, in consequence of which it probably forms denser atmospheres about the atoms of some substances, than it does about those of others. / 256. An analogy has already been suggested to exist between the man- ner in which these calorific atmospheres surround atoms, and that in which the earth is surrounded by the air; and also the mode has been suggested in which changes of temperature in the external medium would operate upon the density of such atmospheres. Supposing these preliminary sugges- tions correct, it would follow that the quantity of caloric absorbed or given out at each exterior change of temperature, by any one congeries of atoms, would be to that absorbed or given Out by any other congeries, as the pre- vious condensation of caloric in the one, is to its previous condensation in the other. (173,174, 175, 176.)* * A notice of the doctrine of Petit and Dulong that the capacities of all elemen- tary atoms for heat are the same, will be deferred till 1 have treated of atomic pro- portions 46 IMPONDERABLE SUBSTANCES. Of the Specific Heat of Gaseous Bodies. 257. It was suggested by Lambert and Pictet, and the suggestion was after- wards sanctioned by Dalton, that space may have a capacity for caloric. Consistently with this idea the quantity of caloric in a given space should always be the same whatever may be the gaseous fluid occupied by it. This is consistent with the fact that all the gases have the same capacity for heat, and all undergo a like expansion, in consequence of a like increase of temperature. Agreeably to this view of the case, the cold produced by rarefaction, as in the experiment with the exhausted receiver (212) or the palm glass, (215,) the heat consequent to the compression of air (219) arises from the caloric in the air or vapour, being too little for the space allotted to the air in one case, and too great for that allotted in the other. This idea seems to have been abandoned in consequence of an experiment performed by Gay Lussac. This eminent chemist having made a Torri- cellian vacuum within a tall cylindrical glass receiver, about 3 inches in diameter and 39 in height, found that when the mercury employed was made to rise or sink in the vacant space so as alternately to enlarge or di- minish it, no consequent variation of the temperature took place, since a delicate air thermometer, of which the bulb was included, indicated no change. It appeared, nevertheless, that when a minute quantity of air was admitted, any increase or diminution of the void space, consequent to the rise or fall of the mercury, was as productive, as the same thermometer showed, of a corresponding increase, or diminution, of sensible heat. Hence it has been inferred that a perfectly void space has no capacity for heat, the changes of temperature, consequent to the rarefaction or conden- sation of aSriform fluids, being altogether caused by corresponding changes in the capacity of those fluid.s for caloric. But as a perfect vacuum must liberate heat with perfect facility, it appears to me that the caloric should be absorbed by the mercury as rapidly as this metal could be made to en- croach upon the space occupied by the calorific particles, and that, conse- quently, no palpable condensation of them could be effected by the above described process resorted to by Gay Lussac. 258. Admitting that, for equal weights, the specific heat of air is seven times as great as that of mercury, that of space being the same by the premises, there could not have been a capacity greater than that of about 200 grains of the metal, whereas a very small stratum of this metal, equal to one-fourth of an inch, would, in the apparatus employed, amount to more than a pound. 259. The following experiments appear to me to be irreconcilable with the idea that the heat acquired by air entering a space does not arise from the specific heat of the space. When a receiver was exhausted so as to reduce the interior pressure to one-fourth of that of the atmosphere, and one-fourth was suddenly admitted, so as to lower the mercurial column in a gauge from about 22^ inches to 15 inches, heat was produced; and however the ratio of the entering air to the residual portion was varied, still there was a similar result. 260. When the cavity of the receiver was supplied with the vapour of ether, or with that of water, so as to form, according to the Daltonian hy- pothesis, a vacuum for the admitted air, still heat was produced by the lat- ter, however small might be the quantity, or rapid the readmission. When the receiver was exhausted, until the tension was less than that of aqueous vapour at the existing temperature, so as to cause the water to boil, as in the Cryophorus, or Leslie's experiment, still the entrance of T06tf7 of the quantity requisite to fill the receiver caused the thermometer to rise a tenth CALORIC. 47 of a degree. An alternate motion of the key of the cock, through one-fourth of a circle, within one-third of a second of time, was adequate to produce the change last mentioned. 261. The fact, that heat is produced, when to air, rarefied to one-fourth of the atmospheric density, another fourth is added, seems to me to be irre- concilable with the idea, that this result arises from the compression of the portion of air previously occupying the cavity, since the entering air must be as much expanded as the residual portion is condensed. 262. As, agreeably to Dalton, a cavity occupied by a vapour acts as a vacuum to any air which may be introduced, I infer that when a receiver, after being supplied with ether or water, is exhausted so as to remove all the air, and leave nothing besides aqueous or ethereal vapour, the heat, ac- quired by air admitted, cannot be ascribed, consistently, to the condensa- tion of the vapour. 263. It was ascertained by De la Rive and Marcet, that when the bulb of a thermometer is subjected to a jet of air while entering an exhausted receiver, that the instrument shows that refrigeration takes place. But if the jet be allowed to continue, a rise of temperature ensues. Hence it was inferred by them, that in the first instance there is refrigeration, and a con- sequent absorption of caloric; and subsequently an evolution of this prin- ciple, in consequence of the condensation of the air, which at the first moment of its influx, had been refrigerated. It appears to me, nevertheless, that in my experiments above described, the effect upon the thermometer was too rapid, and the quantity of the entering air too minute, to allow it to be refrigerated by rarefaction in the first place, and yet afterwards to be so much condensed as to become warm by the evolution of caloric. OF THE SLOW COMMUNICATION OF HEAT, COMPRISING THE CONDUCTING PROCESS AND CIRCULATION. Of the Conducting Process in Solids. 264. It is well known that if one end of a piece of metallic wire, as a common pin for instance, be held in a candle flame, the other end soon becomes too hot for the fingers. It is also known that the heated irons, used in soldering and other processes in the arts, have usually wooden handles, which do not become unpleasantly warm, when the irons within them are hot enough to blister the hands. This inferior power of wood in conducting heat is also well exemplified by the handles of silver tea-pots, which are sometimes altogether of wood; in other in- stances principally of metal, small portions of wood inter- vening. In either case, the facility with which the heat is propagated in the comparatively thin metallic socket, is strongly contrasted with the difficulty which it experiences in permeating the wood. 265. An inferiority of conducting power, when com- pared with metals, is also displayed by common bone, whalebone, ivory, porcelain, and especially glass. 48 IMPONDERABLE SUBSTANCES. Inequality of Conducting Power, experimentally illustrated. 266. Let there be four rods, severally of metal, wood, glass, and whalebone, each cemented into a ball of sealing-wax. Let each rod, at the end which is not cemented to the wax, be successively exposed to the flame excited by a blow pipe. It will be found, that the metal becomes quickly heat- ed throughout, so as to fall off from the wax; but the wood or whalebone may be destroyed, and the glass bent by the igni- tion, very near to the wax, without melting it so as to liberate them. Additional Illustration. 267. The following method of illustrat- ing the diversity of conducting power, pos- sessed by different substances, has been suggested by an analogous process described in Silliman's Chemistry. 268. Rods similar in diameter and length, and consisting severally of lead, tin, iron, copper, wood, and ivory, are made to pass from side to side, through a vessel of sheet copper, in the shape of an oblong parallelopiped. Each rod extends on one of the sides, to an equal distance beyond the ves- sel. By these means, when the vessel is filled with boiling water, equal portions of each rod being situated within the boiler, they are all exposed to an equal degree of heat. It is presumed that under these circumstances the conducting power will be nearly in the inverse ratio of the time necessary to communicate to the equidistant ends of the rods, a heat adequate to cause the ignition of similar pieces of phosphorus, simultaneously placed upon them, before the application of the boiling water. Rationale of the Fracture of Glass or Porcelain by Heat. 269. The fracture of glass or porcelain, exposed to fire, is the conse- quence of an inferior conducting power; as the heat is not distributed with quickness enough to produce a uniform expansion. Hence glass is as liable to crack by heat, in proportion as it is thinner. It may be divided by a heated iron, by a string steeped in oil of turpentine and inflamed, or by the heat generated by friction. (322, &c.) Of the Conducting Power of various Metals. 270. Metals are by far the best conductors of caloric. There are, how- ever, scarcely two that conduct it equally well. Despretz has ascertained by exact experiments, that the conduct- 271. ing power of the following metals is in the ratio of the sub Gold, Silver, Copper, Platinum, Iron, Zinc, oined numbers. 1000.0 973.0 898.0 381.0 374.3 363.0 CALORIC. 49 Tin, Lead, 303.9 179.6 Explanation of the Process by which Heat is supposed to be communi- cated in Solids. 272. I conceive that in solids, the stratum of atoms forming the surface first exposed to the heat, combining with an excess of this principle, divides it with the next stratum. The caloric received by the second stratum, is in the next place divided between the second and third stratum. In the mean time the first stratum has received an additional supply of caloric, which passes to the second and third stratum as in the first instance; while the quantity, at first received by them, is penetrating further into the mass. 273. It is I trust easy to conceive that, by the process thus suggested, ca- loric may find its way throughout any body, for the particles of which it may have sufficient affinity. Probably the superior conducting power of metals is due in great measure to a proportionably energetic affinity for caloric. 274. The conjectures, which I ventured to advance respecting the mode in which caloric may exist in atmospheres about atoms, seem to be pecu- liarly applicable to the case of metals, on account of their great expansi- bility by heat, and susceptibility of contraction by cold. (174.) 275. If caloric be not interposed in a dense repulsive atmosphere between metallic atoms, how can its removal cause that approximation of those atoms towards each other, without which the diminution of bulk invariably conse- quent to refrigeration could not ensue? Liquids almost destitute of Conducting Power. 276. That liquids are almost devoid of power to conduct heat, is proved by the inflammation of ether over the bulb of an air thermometer, protected only by a thin stratum of water. 277. The inflammation of ether upon the sur- face of water, as represented in this figure, does not cause any movement in the liquid included in the bore of the air thermometer at L, although the bulb is within a quarter of an inch of the flame. Yet the thermometer may be so sensi- tive, that touching the bulb, while under water, with the fingers, may cause a very perceptible indication of increased temperature. By placing the sliding index, I, directly opposite the end of the column of liquid in the stem of the thermo- meter, before' the ether is inflamed, it may be ac- curately discovered whether the heat of the flame causes any movement in it. 7 50 IMPONDERABLE SUBSTANCES. Communication of Caloric by Circulation. 278. That caloric cannot be communicated in liquids, unless it be so ap- plied as to cause a circulation of the particles, is demonstrated by the following experiment. 279. A glass jar, about 30 inches in height, is supplied with as much water as will rise in it within a few inches of the brim. By means of a tube descending to the bottom, a small quantity of blue colouring matter is introduced below the colourless water so as to form a stratum as represented at A, in the engraving. A stratum, differently coloured, is formed in the upper part of the vessel, as represented at B. A tin cap, supporting a hollow tin cylinder, closed at bottom, and about an inch less in diameter than the jar, is next placed as it is seen it in the engraving, so that the cylinder may be concentric with the jar, and descend about 3 or 4 inches into the water. 280. The apparatus being thus pre- pared, if an iron heater, H, while red- hot, be placed within the tin cylinder, the coloured water, about it, soon boils; yet neither of the coloured strata inter- mingles with the intermediate colourless mass; and on sliding the finger up- wards, while in contact with the glass, the heat will be found to have penetrated only a very small distance below the tin cylinder. But if the ring, R, be placed, while red-hot, upon the iron stand which surrounds the jar at S S, the portion of the liquid coloured blue, being opposite to the ring, will rise until it encounters the warmer, and of course lighter, particles, which have been in contact with the tin cylinder. Here its progress upwards is arrested; and, in consequence of the diversity of the colours, a well defined line of sepa- ration becomes conspicuous. 281. The phenomena of this interest- ing experiment may be thus explained. 282. If the upper portion of a vessel, containing a fluid, be heated exclusive- ly, the neighbouring particles of the fluid being rendered lighter by expan- sion, are more indisposed, than before, to descend from their position. But if the particles, forming the inferior strata of the fluid in the same vessel, be rendered warmer than those above them, their consequent expansion and CALORIC. 51 diminution of specific gravity causes them to give place to particles above them, which not being as warm, are heavier. Hence heat must be ap- plied principally to the lower part of the vessel, in order to occasion a uni- form rise of temperature in a contained fluid. 283. This statement is equally true, whether the fluid be aeriform or liquid, excepting that in the ease of aeriform fluids, the influence of pres- sure on their elasticity may sometimes co-operate with, and at others op- pose, the influence of temperature. Experimental Illustration of the Process by which Caloric is distributed in a Liquid until it boils. 284. On the first application of heat to the bottom of a vessel contain- ing cold water, the particles in con- tact with the bottom are heated and expanded, and consequently become lighter than those above them. They rise therefore, giving an opportunity to other particles to be heated and to rise in their turn. The particles which were first heated, are soon comparatively colder than those by which they were displaced, and, de- scending to their primitive situation, are again made to rise by additional heat and enlargement of their bulk. Thus the temperatures reversing the situations, and the situations the tem- peratures, an incessant circulation is maintained, so long as any one por- tion of the liquid is cooler than another, or in other words, till ebul- lition takes place; previously to which every particle must have combined with as much caloric as it can receive, without being converted into steam. 285. The manner in which caloric is distributed throughout liquids by circulation, as above described, is illustrated advantageously by an experi- ment contrived by Rumford, who first gave to the process the attention which it deserves. 286. Into a glass nearly full of water, as represented by the foregoing figure, small pieces of amber are introduced, which are in specific gravity so nearly.equal to water, as to be little influenced by gravitation.* The lowermost part of the vessel being subjected to heat while thus prepared, the pieces of amber are seen rising vertically in its axis, and after they reach the surface of the liquid, moving towards the sides, where the vessel is colder from the influence of the external air. Having reached the sides of the vessel, they sink to the bottom, whence they are again made to rise as before. While one set of the pieces of amber are at the bottom of the liquid, some are at the top, and others at intermediate situations; thus de- * As amber is rather heavier than water, it is expedient to add some sulphate of soda, to increase the specific gravity of the liquid. 52. IMPONDERABLE SUBSTANCES. monstrating the movements by which an equalization of temperature is ac- complished in liquids. 287. When the boiling point is almost attained, the particles being near- ly of the same temperature, the circulation is retarded. Under these cir- cumstances, the portions of liquid which are in contact with the heated sur- face of the boiler are converted into steam, before they can be succeeded by others; but the steam thus produced cannot rise far before it is con- densed. Hence the vibration and singing sound which is at this time ob- served. 288. According to an observation of Gay-Lussac, water boils in metal- lic vessels at a temperature nearly two and a half degrees lower than in those of earthenware. QUICK COMMUNICATION OF HEAT, OR RADIATION. 289. It must be evident that the heat which we receive from a fire in opposition to the draught, reaches us nei- ther by the conducting process nor by circulation. Actual contact is evidently indispensable to the passage of heat in either of these modes. The aeriform matter which is in contact with the embers, or the blaze of a fire, forms part of a current which tends rapidly towards the flue, as must be evident from the celerity with which the sparks which accompany it are propelled. The rapidity with which the aerial particles, heated by the fire, are thus carried up the chimney, far exceeds that with which caloric can be com- municated, in the opposite direction, either by the conduct- ing process or by circulation. 290. The caloric received from a fire under the circum- stances above mentioned, and which is analogous to that by means of which the culinary operations of toasting and roasting are accomplished, is called radiant caloric, or more usually, radiant heat. It has been called radiant, because it appears to emanate in radii or rays from every hot or even warm body, as light emanates from luminous bodies. 291. Radiant heat resembles light also in its susceptibi- lity of being reflected by bright metallic surfaces; in which case it obeys the same laws as light, and is of course lia- ble, in like manner, to be collected into a focus by concave mirrors. * Phosphorus ignited by Radiant Heat. (Page 53.) CALORIC. 53 Model for illustrating the Operation of Concave Mirrors. 5=3 292. The object of the model represented by this diagram, is to explain the mode in which two mirrors operate in collecting the rays of radiant heat emitted from one focus, and in concentrating them in another. 293. The caloric emitted by a heated body in the focus of the mirror, A, would pass off in radii or rays, lessening in intensity as the space into which they pass enlarges; or, in other words, as the squares of the dis- tances. But those rays which are arrested by the mirror, are reflected from it in directions parallel to its axis.* Being thus corrected of their divergency, they may be received, without any other loss than such as arises from mechanical imperfections, by the other mirror, which should be so placed that the. axis of the two mirrors maybe coincident; or, in other words, so that a line drawn through their centres, from A to B, may at the same time pass through their foci, represented by the little balls supported by the wires, W W. 294. The second mirror, B, reflects to its focus the rays which reach it from the first; for it is the property of a mirror, duly concave, to render parallel the divergent rays received from its focus, and to cause the parallel rays which it intercepts to become convergent, so as to meet in its focus. 295. The strings in the model are intended to represent the paths in which the rays move, whether divergent, parallel, or convergent. Phosphorus ignited at the distance of sixty feet by an incandescent Iron Ball. 296. The opposite engraving represents the mirrors which I employ in the ignition of phosphorus and lighting a candle by an incandescent iron ball. I have produced this result at sixty feet, and it might be always ef- fected at that distance, were it not for the difficulty of adjusting the foci with sufficient accuracy and expedition. I once ascertained that a mercurial thermometer, when at the distance last mentioned, rose to 110 degrees of Fahrenheit. 297. A tallow candle is so situated, that its wick, previously imbued with phosphorus, may be in the focus of one of the mirrors. A lamp being similarly situated with respect to the other mirror, it will be easy, by re- ceiving the focal image of the flame on any small screen, so to alter the arrangement, as to cause this image to fall upon the phosphorus. This being effected, the screen, S, placed between the mirrors, is lowered so as The axis of a mirror is in a line drawn from its centre through its true focus. 54 IMPONDERABLE SUBSTANCES. to intercept the rays. The iron ball being rendered white-hot is now sub- stituted for the lamp, and the screen being lifted, the phosphorus takes fire and the candle is lighted. Of the Diversity of Radiating Pmcer in Metals, Wood, Charcoal, Glass, Pottery, fyc. Diversity of Radiating Power experimentally illustrated. 298. At M, (see figure,) a parabolic mirror is represented. At B is a square glass bottle, one side of which is covered with tin foil, and another so smoked by means of a lamp as to be covered 'with carbon. Be- tween the bottle and mirror, and in the focus of the latter, there is a bulb of a differential thermometer, protected from receiving any rays directly from the bottle by a small metallic disk. The bottle being filled with boil- ing water, it will be found that the temperature in the focus, as indicated by the thermometer, is greatest when the blackened surface is opposite to the mirror, and least when the tin foil is so situated; the effect of the naked glass being greater than the one, and less than the other. 299. The worst radiators are the best reflectors, and the best radiators are the worst reflectors ; since the arrangement of particles which is fa- vourable for radiation is unfavourable for refection, and vice versa. 300. A polished brass andiron does not become hot when exposed from morning till night to a fire, so near that the hand placed on it is scorched intolerably in a few seconds. Fire places should be constructed of a form and materials to favour radiation: flues, of materials to favour the con- ducting process. To preserve heat in air or to refrigerate in water, vessels should be made of bright metal. In the latter case, the brightness is bene- ficial, only because the surface cannot be bright without being clean. If soiled, its communication with the liquid would be impeded. 301. Rationale.—Metals appear to consist of particles so united with each other, or with caloric, as to leave no pores through which radiant caloric can be projected. Hence the only portion of any metallic mass which can yield up its rays by radiation is the external stratum. CALORIC. 55 302. On the other hand, from its porosity, and probably also from its not retaining caloric within its pores tenaciously as an ingredient in its compo- sition, charcoal opposes but little obstruction to the passage of that subtile principle, when in the radiant form; and hence its particles may all be simultaneously engaged in radiating any excess of this principle with which a feeble affinity may have caused them to be transiently united, or in re- ceiving the rays emitted by any heated body, to the emanations from which they may have been exposed. We may account in like manner for the great radiating power of earthenware and wood. 303. For the same reason that calorific rays cannot be projected from the interior of a metal, they cannot enter it when projected against it from without. On the contrary, they are repelled with such force as to be re- flected without any perceptible diminution of velocity. Hence the superior efficacy of metallic reflectors. 304. It would seem as if the calorific particles which are condensed be- tween those of the metal, repel any other particles of their own nature which may radiate towards the metallic superficies, before actual contact ensues; otherwise, on account of mechanical imperfection, easily discernible with the aid of a microscope, mirrors could not be as efficacious as they are found to be in concentrating radiant heat. Their influence, in this respect, seems to result from the excellence of their general contour, and is not pro- portionably impaired by numberless minute imperfections. Radiation of Cold. 305. A thermometer placed in the focus of a mirror indicates a decline of temperature, in consequence of a mass of ice or snow being placed before it in the situation occupied by the bottle in the preceding figure. This change of temperature has been considered as demonstrating the radiation, and consequently the materiality of cold. For since the transfer of heat by radiation has been adduced as a proof of the existence of a material cause of heat, it is alleged that the transmission of cold by the same pro- cess ought to be admitted as equally good evidence of a material cause of cold. 306. The following is the explanation which I give of this phenomenon, agreeably to the opinion that cold is diminished heat. 307. I suppose that caloric exists throughout the sublunary creation, as an atmosphere held to the earth by the general attraction of all the matter in it, being in part combined with bodies in proportion to their affinities or capacities for it, and partly free. The particles of the free caloric I sup- pose incessantly to exert a self-repellent power, which increases with its density, as in the case of aeriform fluids. The repulsive power of caloric being in the ratio of the quantity, it follows that either a diminution or in- crease of temperature in any spot must equally produce a movement in the calorific particles; in the one case from the spot which sustains the change, in the other towards it. ' 308. Supposing the surface of a mirror to be subjected to the influence of a space in which a diminution of temperature has been produced, the rows of calorific particles between the mirror and the space will move into the space. The removal of one set of the calorific particles from the surface of the mirror, must make room for another set to flow into the situations thus vacated. The curvature of the surface of the mirror renders it more easy for those particles to succeed which lie in the direction of the focus. 56 IMPONDERABLE SUBSTANCES. Of the Observations and Apparatus of Melloni. 309. Dy means of a thermo-electric pile, and a galvanoscope or multi- plier, of extreme delicacy, Melloni has lately ascertained some interesting properties of heat-producing rays, which serve to show a marked diflerence, and, at the same time, a great analogy between them and the rays of light. 310. Let there be provided three transparent plates, severally of alum, rock salt,, and rock crystal or glass, each about an eighth or tenth of an inch thick; it will be found that the effect of the transmitted rays upon the pile, when unimpeded, being 30, that which takes place during the inter- position of the rock salt, will be 28, during the interposition of the rock crystal 15 or 16 ; while during the interposition of the alum the effect will only be two or three. 311. The effect of interposing a plate of smoky rock crystal, will, under the same circumstances, be equal to 14 or 15. 312. In other words, out of 30 parts, rock salt intercepts two parts of the influence of the radiant heat; rock crystal, whether smoky or clear, in- tercepts about half; while alum, or glass, intercepts nearly the whole. 313. If, in like manner, two pairs of plates be employed, one pair formed of a pane of green glass (impermeable to red rays,) and a plate of alum; the other pair formed of a pane of perfectly opake black glass, coupled with a plate of rock salt, it will be found that the first mentioned pair in- tercepts the calorific radiation entirely, while the other permits nearly one- third as much to pass, as when not interposed. 314. Hence it appears, that bodies, quite permeable by light, may en- tirely intercept radiant heat, while others, impermeable by light, allow the passage of radiant heat. Melloni designates the former as athermane, the latter as diathermane bodies. 315. It follows that permeability to heat-producing rays is not to be confounded with transparency. 316. Radiant heat has been found by Melloni to vary in its power of permeating bodies, according to the source from which it proceeds, and the media through which it may have passed. After passing through nitric acid, more will pass through alum than if received directly from the source. 317. Moreover certain media have, with respect to calorific rays, an in- fluence analogous to that which coloured media have with respect to light, in allowing some rays to pass, while others are arrested. 318. This property of the diathermane bodies, is called diathermansie. Rock salt seems to be a diathermane body, devoid of diathermansie. The last mentioned property lessens as the body is thinner, and may, as in the case of coloured media, be rendered null by an extreme tenuity. 319. The non-luminous calorific rays have been ascertained by Melloni, to be susceptible of refractions analogous to those of light. When the thermo-electric pile is so situated as that the rays of heat cannot directly reach it, by interposing a prism of rock salt, having a refracting an From + 50° to — 7°. 57 Water......1 ) Phosphate of soda - - - - 9) From + 50= to — 12°. G2 Diluted nitric acid - - - - 4 ^ Phosphate of soda - - 91 Nitrate of ammonia - - - - 6> From-f-50° to — 21°. 71 Diluted nitric acid - - - - 4) Sulphate of soda - - - -8) From + 50= to 0°. 50 Muriatic acid.....5 $ Sulphate of soda - - - -5*. From + 5

From any temp, to — 25°. Nitrate of ammonia - - - - 5i DU°uTedsulphuric"acid' ". "- '- l\ From + 32° to - 23°. 55 Snow Muriatic acid j" From + 32° to — 27°. 5