Priestley and Lavoisier Readings

Priestley and Lavoisier Readings - 208 THE ENLIGHTENMENT...

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Unformatted text preview: 208 THE ENLIGHTENMENT AND ENTERPRISE dazzled with a brilliant light; but thick darkness still covers an immense stretch of the horizon. There are a few circumstances from which the philosopher can take consolation; but he is still afflicted by the spec- tacle of the stupidity, slavery, barbarism, and extrav- agance of mankind; and the friend of humanity can find unmixed pleasure only in tasting the sweet delights of hope for the future. >6=(->I- It is this most obscure and neglected chapter of the history of the human race, for which we can gather so little material from records, that must occupy the foreground of our picture; and whether we are con— cerned with a discovery, an important theory, a new legal system, or a political revolution, we shall endeavour to determine its consequences for the majority in each society. For it is there that one finds the true subject matter of philosophy, for all interme- diate consequences may be ignored except insofar as they eventually influence the greater mass of the human race. It is only when we come to this final link in the chain that our contemplation of historical events and the reflections that occur to us are true utility. Only then can we' appreciate men’s true claims to fame, and can take real pleasure in the progress of their reasons; only then can we truly judge the perfection of the human race. The idea that everything must be considered in relation to this single point of reference is dictated both by justice and by reason. Nevertheless one might be tempted to regard it as fantastic. But one would be wrong. To show this is so, we have only to cite two striking examples. The man who tills our soil owes his enjoyment to the commonest goods, which plentiftu supply his needs, to the long—continued labours of industry assisted by science: and his enjoyment of these goods can be traced back further, to the victory of Salamis, but for which the shadows of Oriental despotism threatened to engulf the earth. Similarly, the mariner who is preserved from shipwreck by precise obser- vations of longitude owes his life to a theory which can be traced back through a chain of truths to dis- coveries made in the school of Plato, and thereafter buried for twenty centuries in total disuse. 6.4 Joseph Priestley, Considerations on the Doctrine of Phlogiston and the ' Decomposition of Water Ioseph Priestley (1733—1804) came from a family of weavers and was raised as a Noncory‘ormist. He studied for the ministry and held a number of church positions during his life. He had little formal training in natural philosophy, but he came into contact with a number of people who were interested in the subject such as Matthew Thorner, a physician who had lectured on chemistry, and Benjamin Franklin. He worked on a large range of chemical topics, most significantly on the proper— ties of “airs.” He was a strong supporter of the phlogiston theory of combustion, and in this selec— tion defends phlogiston against the new oxygen theory presented by Antoine Lavoisier. CONSIDERATIONS ON THE DOCTRINE OF PHLOGISTON, AND THE DECOMPOSITION OF WATER There have been few, if any, revolutions in science so great, so sudden, and so general, as the prevalence of what is now usually termed the new system of chem~ istry, or that of the Antiphlogistians, over the doctrine of Stahl, which was at one time thought to have been the greatest discovery that had ever been made in the science. I remember hearing Mr. Peter Woulfe, whose knowledge of chemistry will not be ques- tioned, say, that there had hardly been any thing that deserved to be called a discovery subsequent to it. Though there had been some who occasionally expressed doubts of the existence of such a principle as that of phlogiston, nothing had been advanced that could have laid the foundation of another system before the labours of Mr. Lavoisier and his friends, from whom this new system is often called that of the French. This system had hardly been published in France, before the principal philosophers and chemists of England, notwithstanding the rivalship which has long subsisted between the two countries, eagerly adopted it. Dr. Black in Edinburgh, and as far as I hear all the Scots have declared themselves con- verts and what is more, the same has been done by Mr. Kirwan, who wrote a pretty large treatise in opposition to it. The English reviewers of books, I JOSEPH PRIESTLEY, DOCTRINE OF FHLOGISTON AND THE DECOMPOSITION OF WATER 209 perceive, universally favour the new doctrine. In America also, I hear of nothing else. It is taught, I believe, in all the schools on this continent, and the old system is entirely exploded. And now that Dr. Crawford is dead, I hardly know of any person, except my friends of the Lunar Society at Birming- ham, who adhere to the doctrine of phlogiston; and what may now be the case with them, in this age of revolutions, philosophical as well as civil, I will not at this distance answer for. It is no doubt time, and of course opportunity of examination and discussion, that gives stability to any principles. But this new theory has not only kept its ground, but has been constantly and uniformly advancing in reputation, more than ten years, which, as the attention of so many persons, the best judges of everything relating to the subject has been unremittingly given to it, is no inconsiderable period. Every year of the last twenty or thirty has been of more importance to science, and especially to chemistry, than any ten in the preceding century. So firmly established has this new theory been consid- ered, that a new nomenclatm‘e, entirely founded upon it, has been invented, and is now almost in universal use; so that, whether adopt the new system or not, we are Luider the necessity of learning the new lan— guage, if we would understand some of the most valuable of modern publications. In this state of things, an advocate for the old system has but little prospect of Obtaining a patient hearing. And yet, not having seen sufficient reason to change my opinion, and knowing that free discus- sion must always be favourable to the cause of truth, I wish to make one appeal more to the philosophical world on the subject, though I have nothing materi- ally new to advance. For I cannot help thinking that What I have observed in several of my publications has not been duly attended to, or well understood. I shall therefore endeavour to bring into one view what appears to me of the greatest weight, avoiding all extraneous and unimportant matter; and perhaps it may be the means of bringing out something more decisive in point of fact, or of argument, than has hitherto appeared. No person acquainted with my philosophical publications can say that I appear to have been par- ticularly attached to any hypothesis, as I have fre— quently avowed a change of opinion, and have more than once expressed an inclination for the new theory, especially that very important part of it the decomposition of water, for which I was an advocate when I published the sixth volume of my experi— ments; though farther reflection on the subject has led me to revert to the creed of the school in which I was educated, if in this respect I can be said to have been educated in any school. However, Whether this new theory shall appear to be well founded or not, the advancing of it will always be considered as having been of great importance in chemistry, from the attention which it has excited, and the many new experiments which it has occasioned, owing to the just celebrity of its patrons and admirers. SECTION I OF THE CONSTITUTION OF METALS According to the doctrine of phlogiston, advanced by Becher and Stahl in the beginning of this century, and much simplified and improved since their time, metals, phosphorus, sulphur, and many other sub- stances which are supposed to contain it, are com- pounds, consisting of this principle, and another which may be called its base. Thus each of the metals contains phlogiston united to a peculiar calx, and sulphur and phosphorus consist of the same princi— ple and their respective acid, or the bases of them. But according to the antiphlogistic theory, all the metals are simple substances, and become calces by imbibing pure air; and sulphur and phosphorus are also simple substances, and become the acid of vitriol and of phosphorus by imbibing the same principle, called by them oxygen, or the principle, as it probably is, or universal acidity. As a proof that metals are simple substances, and that they become calces merely by imbibing air, they allege the case of mercury, which becomes the calx called precipitate per se by exposure to the atmos— phere in a certain degree of heat, and which becomes running mercury again by exposure to a greater degree of heat. They therefore think it impossible not to conclude, that in all other cases of calcination, as well as this, the only difference between the calx and the metal, is that the latter has parted with the air which it has imbibed. . But this is the case of only this particular calx of this metal, and there is another calx of the same metal, viz. that which remains after exposing turbith mineral to a red heat, which cannot be completely revived by any degree of heat, but may be revived in inflammable air, which it imbibes, or when mixed with charcoal, iron filings, or other substances sup- posed to contain phlogiston. And if this calx of mercury, or (supposing it to contain some acid of vitriol) this salt, necessarily requires some addition to constitute it a metal, all mercury must contain the same. For though with the same external appear- ance, the same metal may contain different propor— tions of any particular principle, as phlogiston, they must be denominated different substances, if some specimens contain this element, and others be wholly destitute of it. All, therefore, that can be inferred from the experiment with the precipitate per se is, that in this particular case, the mercury in becoming that calx imbibed air, without parting with any, or very little, of its phlogiston; and if we judge by the air expelled from the calces of metals and other circumstances, there are few, if any, of them but contain more or less of phlogiston. I would observe in this place, that it is asserted by some very able chemists, that if the precipitate per se be made with proper attention, it will be revived without yielding any air. This is also the case with miniurn when fresh made. But this is owing, I doubt not, to their wanting water, which I deem to be essential to the constitution of every kind of air; so that they both contain the element of dephlogisti- cated air, though, for want of water, it is not able to assume that form. That mercury may have the same external appearance, and all its essential properties, and yet contain different proportions of something that enters into it, is evident from the phenomena of its solution in the nitrous acid, and the revival of its calx in inflammable air. According to the old theory, there is a loss of some part of its phlogiston in the solution of mercury in the nitrous acid, since nitrous air is procured in the process. And though it may be revived from its precipitates by mere heat, yet if it be revived in a vessel of inflammable air, it will imbibe it in great quantities. Mercury revived in these cir- cumstances must contain more phlogiston than that which is revived from the same calx by mere heat. But though mercury revived by mere heat after a solution in nitrous acid must have a deficiency of phlogiston, and when it is revived from precipitate per se in inflammable air must contain a redundancy of the same principle, yet there will hardly be a doubt but that, in all chemical processes, it would exhibit the same phenomena. THE ENLIGHTENMENT AND ENTERPRISE In all other cases of the calcination of metals in air, which I have called the phlogistication of the air, it is not only evident that they gain something, which adds to their weight, but that they likewise part with something. The most simple of these processes is the exposing [of] iron to the heat of a burning lens in confined air, in consequence of which the air is diminished, and the iron becomes a calx. But that there is something emitted from the iron in this process is evident from the strong smell which arises from it. If the process be continued, inflammable air will be produced, if there be any moisture at hand to form the basis of it. From this it is at least probable, that, as the process went on in an uniform manner, the same substance, viz. the basis of inflammable air, was continually issuing from it; and this is the sub- stance, or principle, to which we give the name of phlogiston. That the effect of this process is not, as the antiphlogistians assert, the mere separation of the dephlogisticated from the phlogisticated air in that of the atmosphere, I have proved in a course of experiments, in which I have shown that a consider— able part of the phlogisticated air that is found after this process is formed in the course of it, by the union of the phlogiston from the iron with the dephlogisticated air. And if the calcination of the iron in this process be always attended with the loss of some constituent part of it, the same is, no doubt, the case with all other calcinations of the same metal, and also those of all other metals. And farther, if the metals be compound substances, containing phlogis- ton united to some base, the same is the case with sulphur and phosphorus, because they become acids when they are used in the same process. According to the antiphlogistic theory, the inflammable air that is produced in the solution of metals in any acid comes wholly from the water combined with it, and not at all from the metal dis- solved. But the advocates for this theory do not seem to have attended to one necessary consequence of this supposition. According to their own principles, water consists of eighty—seven parts of oxygen, to only thirteen of hydrogen, in every hundred, which is nearly seven times as much of the former as of the latter. Consequently, since nothing but hydrogen escapes in the process, there must remain, from this decomposition of the water, seven times as much oxygen in the solution. But both Mr. Lavoisier and Mr. de la Place say, what I doubt not is strictly true, ANTOINE LAVOISIER, ELEMENTS OF CHEMISTRY that after the process the acid will saturate exactly the same quantity (they do not say more) of alkali, that it would have done before; whereas, with the addition of so much oxygen, it ought to saturate con- siderably more. If the oxygen from the decomposi- tion of the water do not join that in the acid, what becomes of it? If this case be analogous to that of the supposed decomposition of water by hot iron, the oxygen ought to be lodged in the iron, and compose finer cinder (magnetic oxide of iron). But this substance is not soluble in vitriolic acid, if that be employed in the experiment; and when it is dissolved in the marine acid, it does not dephlogisticate it, as minium, and other substances containing oxygen, do. It is evident, therefore, that there is no addition of oxygen in this process, consequently no decomposi- tion of water in the case, and that the inflammable air must come from the decomposition of the iron. 4-36-3- On the whole, I cannot help saying, that it appears to me not a little extraordinary, that a theory so new, and of such importance, overturning every thing that was thought to be the best established chem— istry, should rest on so very narrow and precarious a foundation, the experiments adduced in support of it being not only ambiguous, or explicable on either hypothesis, but exceedingly few. I think I have recited them all, and that on which the greatest stress is laid, viz. that of the formation of water from the decomposition of the two kinds of air, has not been sufficiently repeated. Indeed, it requires so difficult and expensive an apparatus, and so many precau- tions in the use of it, that the frequent repetition of the experiment cannot be expected; and in these cir- cumstances the practiced experimenter cannot help suspecting the accuracy of the result, and conse— quently the certainty of the conclusion. But I check myself. It does not become one in a minority, and especially of so small a minority, to speak or write with confidence; and though I have endeavoured to keep my eyes open, and to be as attentive as I could to every thing that has been done in this business, I may have overlooked some cir- cumstances which have impressed the minds of others, and their sagacity is at least equal to mine. The phlogistic theory is not without its difficul- ties. The chief of them is that we are not able to ascer— 211 tain the weight of phlogiston, or indeed that of the oxygenous principle. But neither do any of us pretend to have weighed light, or the element of heat, though we do not doubt but that they are prop- erly substances, capable by their addition, or abstrac- tion, of making great changes in the properties of bodies, and of being transmitted from one substance to another. 6.5 Antoine Lavoisier, Elements of Chemistry Antoine—Laurent Lavoisier (1743—94) was born into a wealthy family of lawyers. He began his higher education in law, following in his father’s footsteps, but was attracted to Science, particularly chemistry. He gained an associate position in the Academic des Sciences in 1768, deciding to devote his life to science. In 1789, Lavoisier published his most influential book, Traité élémentaire de chirnie (Elements of Chemistry). This brought together all aspects of his work, introducing his nomenclature, his experimental system and appa~ ratus, his methods and standards of measurement, and an extensive compilation of all elements and compounds recognized under his system. Widely read and quickly translated, it gave the deathblow to the phlogiston theory. This selection looks at one of his important instruments developed with the physicist Pierre Laplace, the calorimeter, used to quantify heat. CHAPTER III DESCRIPTION OF THE CALORIMETER, OR APPARATUS FOR MEASURING CALORTc The calorimeter, or apparatus for measuring the rel— ative quantities of heat contained in bodies, was described by M. de la Place and me in the Memoirs of the Academy for 1780 If, after having cooled any body to the freezing point, it be exposed in an atmosphere of 25° (88.25”), the body will gradually become heated, from the surface inwards, till at last it acquire the same tem- perature with the surrounding air. But, if a piece of ice be placed in the same situation, the circumstances are quite different; it does not approach in the small— est degree towards the temperature of the circum- 212 THE ENLIGHTENMENT AND ENTERPRISE ambient air, but remains constantly at Zero (32°), or the temperature of melting ice, till the last portion of ice be completely melted. This phenomenon is readily explained, as, to melt ice or reduce it to water, it requires to be com- bined with a certain portion of caloric; the whole caloric attracted from the surrounding bodies, is arrested or fixed at the surface or external layer of ice which it is employed to dissolve, and combines with it to form water; the next quantity of caloric com— bines with the second layer to dissolve it into water, and so on successively till the whole ice be dissolved or converted into water by combination with caloric, the very last atom still remaining at its former tem- perature, because the caloric has never penetrated so far as long as any intermediate ice remained to melt. Upon these principles, if we conceive a hollow sphere of ice at the temperature of Zero (32°) placed in an atmosphere 10° (545°), and containing a sub— stance at any degree of temperature above freezing, it follows, first, that the heat of the external atmos— phere cannot penetrate into the internal hollow of the sphere of ice; secondly, that the heat of the body placed in the hollow of the sphere cannot penetrate outwards beyond it, but will be stopped at the inter- nal surface, and continually employed to melt suc- cessive layers of ice, until the temperature of the body be reduced to Zero (32°), by having all its superabundant caloric above that temperature carried off by the ice. If the whole water, formed within the sphere of ice during the reduction of the temperature of the included body to Zero, be care- fully collected, the weight of the water will be exactly proportional to the quantity of caloric lost by the body in passing from its original temperature to that of melting ice; for it is evident that a double quantity of caloric would have melted twice the quantity of ice; hence the quantity of ice melted is a very exact measure of the quantity of caloric employed to produce that effect, and consequently of the quantity lost by the only substance that could possibly have supplied it. I have made this supposition of What would take place in a hollow sphere of ice, for the purpose of more readily explaining the method used in this species of experiment, which was first conceived by M. de la Place. It would be difficult to procure such spheres of ice, and inconvenient to make use of them when got; but, by means of the following apparatus, we have remedied that defect. I acknowledge the name of Calorimeter, which I have given it, as derived partly from Greek and partly from Latin, is in some degree open to criticism; but, in matters 0f science, a slight deviation from strict etymology, fer the sake of giving distinctness of idea, is excusable; and I could not derive the name entirely from Greek without approaching too near to the names 0f known instruments employed for other purposes. The calorimeter is represented in P1. VI. It is shown in perspective at Fig. 1 and its interior struc- ture is engraved in Fig. 2 and 3, the former being a horizontal, and the latter a perpendicular section. Its capacity or cavity is divided into three parts, which, for better distinction, I shall name the interior, middle, and external cavities. The interior cavity fiff, Fig. 4 into which the substances submitted to exper~ irnent are put, is composed of a grating or cage of iron wire, supported by several iron bars; its opening or mouth LM, is covered by the lid HG, of the same materials. The middle cavity b11111], Fig. 2 and 3 is intended to contain the ice which surrOLmds the inte- rior cavity, and which is to be melted by the caloric of the substance employed in the experiment. The ice is supported by the grate mm at the bottom of the cavity, under which is placed the sieve mi. These two are represented separately in Fig. 5 and 6. In proportion as the ice contained in the middle cavity is melted, by the caloric disengaged from the body placed in the interior cavity, the water runs through the grate and sieve, and falls through the conical funnel ccd, Fig. 3 and tube xy, into the receiver F, Fig. 1. This water may be retained or let out at pleasure, by means of the stop-cock ll. The external cavity Hana, Fig. 2 and 3 is filled with ice, to prevent any effect upon the ice in the middle cavity from the heat of the surrounding air, and the water produced from it is carried off through the pipe ST, which shuts by means of the stop-cock 1‘. The whole machine is covered by the lid FF, Fig. 7 made of tin painted with oil colour, to prevent rust. When this machine is to be employed, the middle cavity bbbb, Fig. 2 and 3; the lid GH, Fig. 4 of the interior cavity; the external cavity Hana, Fig. 2 and 3; and the general lid FF, Fig. 7 are all filled with pounded ice, well rammed, so that no void spaces remains and the ice of the middle cavity is allowed to drain. The machine is then opened, and the sub— stance submitted to experiment being placed in the interior cavity, it is instantly Closed. After waiting till the included body is completely cooled to the freez- ANTOINE LAVOISIER, ELEMENTS OF CHEMISTRY 213 ing point, and the whole melted ice has drained from the middle cavity, the water collected in the vessel F, Fig. 1 is accurately weighed. The weight of the water produced during the experiment is an exact measure of the caloric disengaged during the tooling of the included body, as this substance is evidently in a similar situation with the one formerly mentioned as included in a hollow sphere of ice; the whole caloric disengaged is stopped by the ice in the middle cavity, and that ice is preserved from being affected by any other heat by means of the ice contained in the general lid, Fig. 7, and in the external cavity. Experiments of this kind last from fifteen to twenty hours; they are sometimes accelerated by covering up the substance in the interior cavity with well drained ice, which hastens its cooling. The substances to be operated upon are placed in the thin iron bucket, Fig. 8, the cover of which has an opening fitted with a cork into which a small ther- mometer is fixed. When we use acids, or other fluids capable of injuring the metal of the instruments, they are contained in the matras, Fig. 10, which has a similar thermometer in a cork fitted to its mouth and which stands in the interior cavity upon the small cylindrical support RS, Fig. 10. It is absolutely requisite that there be no com— munication between the external and middle cavities of the calorimeter, otherwise the ice melted by the influence of the surrounding air, in the external cavity, would mix with the water produced from the ice of the middle cavity, which would no longer be a measure of the caloric lost by the substance submit— ted to experiment. When the temperature of the atmosphere is only a few degrees above the freezing point, its heat can hardly reach the middle cavity, being arrested by the ice of the cover, Fig. 7, and of the external cavity; but, if the temperature of the air be under the degree of freezing, it might cool the ice contained in the middle cavity, by causing the ice in the external cavity to fall, in the first place, below zero (32°). It is therefore essential that this experiment be carried on in a temperature somewhat above freezing: Hence, in time of frost the calorimeter must be kept in an apartment carefully heated. It is likewise necessary that the ice employed be not under zero (32°), for which purpose it must be pounded and spread out thin for some time in a place of a higher temperature. The ice of the interior cavity always retains a certain quantity of water adhering to its surface, which may be supposed to belong to the result of the experiment; but as, at the beginning of each experi- ment, the ice is already saturated with as much water as it can contain, if any of the water produced by the caloric should remain attached to the ice, it is evident that very nearly an equal quantity of what adhered to it before the experiment must have run down into the vessel F in its stead; for the inner surface of the ice in the middle cavity is very little changed during the experiment. By any contrivance that could be devised, we could not prevent the access of the external air into the interior cavity when the atmosphere was 9" or 10° (52° or 54°) above zero. The air confined in the cavity being in that case specifically heavier than the external air, escapes downwards through the pipe xy, Fig. 3, and is replaced by the warmer external air, which, giving out its caloric to the ice, becomes heavier, and sinks in its turn; thus a current of air is formed through the machine, which is the more rapid in proportion as the external air exceeds the internal in temperature. This current of warm air must melt a part of the ice, and injure the accuracy of the experiment: We may, in a great degree, guard against this source of error by keeping the stop-cock u continually shut; but it is better to operate only when the temperature of the external air does not exceed 3° or at most 4° (39° to 41°); for we have observed, that, in this case, the melting of the interior ice by the atmospheric air is perfectly insensible so that we may answer for the accuracy of our experi- ments upon the specific heat of bodies to a fortieth part. We have caused make two of the above described machines; one, which is intended for such experiments as do not require the interior air to be renewed, is precisely formed according to the description here given; the other, which answers for experiments upon combustion, respiration, &c. in which fresh quantities of air are indispensably nec- essary, differs from the former in having two small tubes in the two lids, by which a current of atmos- pheric air may be blown into the interior cavity of the machine. It is extremely easy, with this apparatus, to determine the phenomena which occur in operations where caloric is either disengaged or absorbed. If we wish, for instance, to ascertain the quantity of caloric which is disengaged from a solid body in cooling at certain number of degrees, let its temperature be 214. THE ENLIGHTENMENT AND ENTERPRISE raised to 80° (212°); it is then placed in the interior cavity jjfi, Fig. 2 and 3 of the calorimeter and allowed to remain till we are certain that its temperature is reduced to zero (32°); the water produced by melting the ice during its cooling is collected, and carefully weighed; and this weight, divide by the volume of the body submitted to experiment, multiplied into the degrees of temperature which it had above zero at the commencement of the experiment, gives the proportion of what the English philosophers call specific heat. Fluids are contained in proper vessels, whose specific heat has been previously ascertained, and operated upon in the machine in the same manner as directed for solids, taking care to deduct, from the quantity of water melted during the experiment, the proportion which belongs to the containing vessel. If the quantity of caloric disengaged during the combination of different substances is to be deter- mined, these substances are to be previously reduced to the freezing degree by keeping them a sufficient time surrounded with pounded ice; the mixture is then to be made in the inner cavity of the calorimeter, in a proper vessel likewise reduced to zero (32°); and they are kept enclosed till the temper— ature of the combination has returned to the same degree: The quantity of water produced is a measure of the caloric disengaged during the combination. To determine the quantity of caloric disengaged during combustion and during animal aspiration, the combustible bodies are burnt, or the animals are made to breathe in the interior cavity, and the water produced is carefully collated. Guinea pigs, which resist the effects of cold extremely well, are well adapted for this experiment. As the continual renewal of air is absolutely necessary in such exper- iments, we blow fresh air into the interior cavity of the calorimeter by means of a pipe destined for that purpose, and allow it to escape through another pipe of the same kind; and that the heat of this air may not produce errors in the results of the experiments, the tube which conveys it into the machine is made to pass through pounded ice, that it may be reduce to zero (32°) before it arrives at the calorimeter. The air which escapes must likewise be made to pass through a tube surrounded with ice, precluded in the interior cavity of the machine, and the water which is reduced must make a part of What is col- lected, because the caloric disengaged from this air is part of the product of the experiment. It is somewhat more difficult to determine the specific caloric contained in the different gasses, on account of their small degree of density, for, if they are only placed in the calorimeter in vessels like other fluids, the quantity of ice melted is so small that the result of the experiment becomes at best very uncertain. For this species of experiment, we have contrived to make the air pass through two metallic worms, or spiral tubes; one of these, through which the air passes, and becomes heated in its way to the calorimeter, is contained in a vessel full of boiling water, and the other, through which the air circulates within the calorimeter to disengage its caloric, is placed in the interior cavity fifi‘f of that machine. By means of a small thermometer placed at one end of the second worm, the temperature of the air, as it enters the calorimeter, is determined, and its temperature in getting out of the interior cavity is found by another thermometer placed at the other end of the worm. By this contrivance we are enabled to ascertain the quantity of ice melted by determi- nate quantities of air or gas, while losing a certain number of degrees of temperature, and, conse— quently, to determine their several degrees of spe‘ cific caloric. The same apparatus, with some particu- lar precautions, may be employed to ascertain the quantity of caloric disengaged by the condensation of the vapours of different liquids. The various experiments which may be made with the calorimeter do not afford absolute conclu- sions, but only give us the measure of relative quan- tities; we have therefore to fix a unit, or standard point, from whence to form a scale of the several results. The quantity of caloric necessary to melt a pound of ice has been chosen as this unit; and, as it requires a pound of water of the temperature of 60° (167°) to melt a pound of ice, the quantity of caloric expressed by our unit or standard point is what raises a pound of water from zero (32°) to 60° (167°). When this unit is once determined, we have only to express the quantities of caloric disengaged from dif- ferent bodies by cooling a certain number of degrees, in analogous values: The following is an easy mode of calculation for this purpose, applied to one of our earliest experiments. We took 7 lib. 11 oz. 2 gros 36 grs. of plate-iron, cut into narrow slips and rolled up, or expressing the quantity in decimals, 7.707319. These, being heated in a bath of boiling water to about 78° (207.5“), were quickly introduced into the interior cavity of the ANTOINE LAVOISIER, ELEMENTS OF CHEMISTRY 215 calorimeter. At the end of eleven hours, when the whole quantity of water melted from the ice had thoroughly drained off, we found that 1.109795 poruids of ice were melted. Hence, the caloric disen— gaged from the iron by cooling 78° (1175") having melted 1.109795 pounds of ice, how much would have been melted by cooling 60° (135°)? This ques- tion gives the following statement in direct propor- tion, 78:1.10975zz602x = 0.85369. Dividing this quan- tity by the weight of the whole iron employed, viz. 7.7070319, the quotient 0.110770 is the quantity of ice which would have been melted by one potmd of iron whilst cooling through 60° (135°) of temperature. Fluid substances, such as sulphuric and nitric acids &c. are contained in a matras, Pl. VI, Fig. 9, having a thermometer adapted to the cork, with its Plate VI bulb inunersed in the liquid. The matras is placed in a bath of boiling water, and when, from the ther— mometer, we judge the liquid is raised to a proper temperature, the matras is placed in the calorimeter. The calculation of the products, to determine the specific caloric of these fluids, is made as above directed, taking care to deduct from the water obtained the quantity which would have been pro- duced by the matras alone, which must be ascer— tained by a previous experiment. The table of the results obtained by these experiments is omitted because not yet sufficiently complete, different cir- cumstances having occasioned the series to be inter- rupted; it is not, however, lost sight of; and we are less or more employed upon the subject every winter. Plate VI (continued) it 4-041: velar. ...
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Priestley and Lavoisier Readings - 208 THE ENLIGHTENMENT...

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