Изображения страниц
PDF
EPUB

ences, which distinguish the radical from the acetous acid, such as the superior affinity of the former to alkalies, its forming with them a more perfect combination, and its resifting more powerfully the action of heat. M. BERTHOLLET Thews moreover how the acetous acid may acquire these properties, when it is converted into radical vinegar.

III. Concerning the Preparation of Caustic Aikali, its Crypiala lization, and its Action on Spirit of Wine. By the same. The experiments related in this Memoir, were defigned to obtain a caustic alkali, disengaged from the foreign mixtures of effervescent alkali, calcareous earth, iron, &c. which it generally contains.

IV. New Reflections on the Augmentation of Weight, which Sulphur and Poofphorus acquire in Combullion, and the Cause to which this Augmentation is owing. By M. LAVOISIER. This ingenious academician attributes the augmentation of weight, which the phosphorus acquires when it is burned in vital (i. 6. depblogisticated) air, to the absorption and fixation of this air; and this opinion, which he founded upon experiments, was published in different memoirs several years ago. M. Bergman, in a new edition of his Differtation on elective Attractions, mentions the experiments of the academician, but combats the con. clusions he deduces from them. He acknowledges, that pbafphorus, as also sulphur, and several other substances acquire an augmentation of weight in combustion ; but he observes, at the same time, that the specific heat of the acids, that are formed, is greater than that which the phosphorus poffefied; and it is to this augmentation of specific heat that he attributes the augmentation of weight observable in the experiments of M. LAVOISIER. He, moreover, ascribes the diminution of the vital air, in which the combustion is effectuated, to the combination of the vital air with the phlogitoo in the production of heat; and in this he adopts the opinion of SCHEELE.

To the opinions of these two respectable adversaries, M. LAVOISIER opposes several new experiments and ingenious reasonings, in the Memoir now before us. From these it appears, that the quantity of heat disengaged from 92 grains of burning phosphorus, however considerable it may appear, has no sensible weight, none that can be ascertained even with the ashitance of the most exad instrumenis; and, consequently, that the principle of treat is not composed, as these two celebrated chemifts affirm, of vital air and phlogiston, fince a body which has weight cannot enter the con potition of a body that has little or none; it appears, also, from the experiments and reasonings of this academician, that the very great augmentation of weighi, which the phosphorus affumes in combustion (and which is nearly in the proportion of 150 to 100) cannot be explained by

the the fixation of the heat, without building upon fuppofitions that are evidently false, and are, moreover, con radiced by palpable facts. M. LAVOISIER therefore stands firm in the conciu uns he formerly drew from the experiments above-mentioned, and ftill maintains, that phosphorus, as also sulphur, and several other substances, absorb, in combuftion, 'vital air, or rather decompose it, that they seize upon its basis, and that the maiter of heat, which is extremely abundant in viral air, becomes free, by the new combination which its basis has undergone, and communicates icrelf to all the surrounding bodies. He likewise thinks that these explications, lo remarkable for their fimplicity, would have been long since adopted by cbemists, had they not been prepossessed with a notion of the existence of a phlogistic principle, of which, fays be, no clear idea has been hitherto given, which every one defines in his own way, and which the same chemift often defines differently, according to the nature of the facts he is to explain and account for. This is a sharp attack upon phlogiston; but it receives a deadly blow, or, át least, such a wound, as it will be difficult to heal, in the following Memoir.

V. Reflexions on Phlogiston, designed as an Illufiration of the Theory of Combullion and Calcination, published in 1977. By the same. In this extensive Memoir, which occupies no Jels than 34 quarto pages, the ingenious academician illustrates and confirms his theory by new experiments and considerations which, at the same time, tend to thew the fallacy of some prevailing opinions with respect to the nature of the inflammable principle, and the phenomenon of combustion. It is more especially his design, here, to Mew that the phlogision of Stahl is an imaginary entity, of which he has gratuitously suppoied the existence in metals, sulphur, phosphorus, and all combustible bodies, and that the phenomena of combustion and calcination may be accounted for, and explained, much more ealily and simply, without the supposed phlogiston, than with it. For this purpose be carries us back to the times anterior lo STAHL, when the principal phenomena of combustion were unknown, and takes particular notice of the important discoveries of that emia nent chemist, which he appreciates with accuracy and applause; but he exposes the defects, and the variations, of his hypothesis, relative to the inflammable principle of phlogiston, and endeavours to evince its total insufficiency, even in the advantageous form under which Macquer exhibits it, to explain the phenomena of combustion and calcination, with some of which it is totally incompatible. He afterward considers the attempts made by the acute Baumé, to improve Stabi's doctrine, and more particularly to account for the augmentation of weight in calcined metals, when they are deprived of their phlogiston, by

fuppofing supposing the place of the phlogiston occupied by pure fire. And here he shews that M. Baumé attributes to the element of fire, a degree of weight, which is very considerable, and which is po. fitively contradicted by palpable facts and experience. He thews, moreover, the insuperable objections to M. Baumé's hypothesis, furnished by the experimenis, which, of late years, have been made on heat, in England, France, and Sweden. These objections, which have also disconcerted the hypothefis of Stohl, were felt by Macquer : he did not, however, despair of reconciling the recent experiments, whence they were deduced, with the doctrine of phlogiston. For this purpose, he imagined a new Theory, which is presented in a very ingenious and plausible manner, in the second edition of his Chemical Dictionary, under the articles phlogiston and calcination. But while he seemed to defend the doctrine of Stahl, and yet continued to employ the term phlogison, he exhibited a theory, which is neither that of Stabl, nor of any other chemist, but is peculiar to himself. Instead of the phlogistón, or infammable principle of Stahl, which is fupposed to be a compound of the element of fire and an earthy element, he substituted the peculiar fubfiance of light, fixed, mediately or immediately, in metals, sulphur, coal, phosphorus, and other combustible bodies or compounds, of which it is cne of the principles, and deprived, while in this fate of fixation, of its mobility, and of the other properties, which distinguish it, when it is disengaged.

M. LAVOISIER enters into a long, laborious, and acute review of this theory: he acknowledges that it furnishes answers to a great number of objections to the doctrine of phlogiston, that could not be solved on the hypothesis of Stahl in its prie mitive form, together with explications of many phenomena, of which, on that hypothefis, no satisfactory account could be given. Of these advantages of Macquer's new theory, he gives a circumftantial, candid, and elegant enumeration : but he shews, nevertheless, thai, in a mulcitude of cases, it is absolutely defi. cient, and that the new forms and properties of the phlogiston, which it exhibiis, are proved chimerical, by evident facts and experiments. His proofs are drawn from a great number of experiments made by himself, and also from those of Messrs. Crawfurd, Wilke, and De la Place; and they will, we believe, be deemed by many, who peruse this Memoir with attention, a full sefutation of the system of Macquer in particular, and of the doctrine of phlogiston in general. It is certain, that phlogiston, as employed in the writings of the chemists, is a vague, precarious, iil-defined principle, a perfect Proteus, which changes its form every moment, and, in a great number of chemical exo plications, is in contradiction with itself. It is reprelented as the principle of colours, and yet it is a known fact, that the

more

more metallic calces are deprived of phlogiston, the more are their colours heightened and invigorated. Sometimes it is represented as a heavy substance; at others, as deftitute of weight or gravitv. At one time, it is a free fire, palles through the pores of veffels, explains the phenomena of Causticity and transparence; at another, it is a fire combined with an earthy element, which cannot pass through the pores of veílels, and by which the non caufticity, and opacity, of bodies, are to be accounted for, and explained.

The Academician, after having attacked the principle of phlogiston, establishes, as a preparation for his reflections on combustion and calcination, the principle, of what he calls, an igneous fluid, the substance or matter of heat and fire. He acknowledges that this principle, is, in a certain degree, also hypothetical; but by acute, clear, and judicious oblervations on the phenomena and effcets of heat, he proves, that it is ne. cessary to suppose the existence of such a particular Auid. The theory which he builds on this principle, is clear, consistent, and consonant to observation and experience; but, for a farther account of it, we must refer our readers to the Memoir, which is, in every point of view, a masterly production.

VI. Concerning the Astion of Fire, animated by vital (or dephlo. gisticated) Air, on the most refrailory Mineral Subslances. By the same. Our readers have already seen some of the remarkable effects that have been produced by this Academician's new method of fusing bodies, long deemed infusible and refractory. These have been mentioned in our Sixty-fifth volume *, aş ailo the agent and instrument employed in these operations, namely, dephlogisticated air, and an hydraulic bellows. In the present Memoir, M. LAVOISIER has communicated to the Academy a series of his experiments, made, with this agent, on the most refractory mineral substances. His manner of proceeding, in the greatest part of them, was as follows: he made a small cavity in a large piece of coal, which he lighted with the flame of a waxcandle, directed by a tube ; he placed in the hollow of the coal, thus lighted, the substance on which the operation was to be performed, and thus presented it to the current of vital air.

These experiments were rade on earths and fiones--on saline fubflances-on fulphur and bituminaand on metallic fubfiances, Each of these general divifions are subdivided into particular classes, and the various effects, produced by our author's new agent on the substances that belong to each cleifs, are here deIcribed in a very perspicuous and interesting manner. We can only give the general results of these experiments. The following are those relative to simple earths, and their combinations:

[blocks in formation]

1. Among the simple earths, three are absolutely infusible : the calcareous, the magnerian, and heavy earths.-II. Rockcryftal is susceptible of only a very inconsiderable mollification, which is almost imperceptible, and may be imputed to the small portion of clay combined with it.-III. The quartz, and all quartzous and filiceous stones, differ from rock.cryftal, as they are all susceptible of being very sensibly mollified by the action. of an intensely ardent fire. - IV. Argillaceous earth, even in its greatest state of purity, is, alone and without addition, susceptible of fusion. - V. The three calcareous earths (the ordinary, the magnesian, and the heavy) in whatever proportions they are mixed together, do not communicate their fusibility to each other, but form, each, a kind of peculiar quick-lime, which falls into efflorescence in the air, and is extinguished, with heat, by the addition of water.-VI. The mixtures of the two other earths, either with each other, or with one of the three calca. reous earths, form compounds, which are vitrifiable, and pro: duce glass, more or less tranfparen:-and a very small quantity of calcareous earth is sufficient to communicate io quartzous earth, or earth of alum, a very great degree of fusibility.

From M. LAVOISIER's experiments on saline subfiances, it appeared, First, that phosphoric tartar is the most fixed of all salts, and is therefore proper to be employed as a diffolvent in experiments, made at the flame of an ordinary tube, or at the fire of a coal, animated by vital air.. Secondly, that marine lalo is entirely volatilized, without decomposition, at a certain de gree of intense heat. The case is the same with fixed vegetable alkali, fixed mineral alkali, and borax, which are diffipated in a few moments, with great facility.--Thirdly, that all salts are decomposed by being in contact with coal,- that their acid is converted into sulphur,--and that the basis remains visible, and retains all its properties.

The expo!ure of sulphur and bitumina to the action of fire animated by vital air, exhibits no other phenomenon, than a quick and rapid combustion.

The experimenis, made on metallic substances, furnished the academician with the following results : 1. All metallic fube stances, except platina, become volatile at the degree of fire produced by the action of vital air ; but the fixity of gold and filver is incomparably greater than that of other metals :--11, All metallic substances may be divided into two clasies ; of which one contains those that are incombuftible, such as platina, gold, filver, and mercury; the other, those which burn with a vie sible Aame. - Ili. The combustion of iron is p.culiarly remarkable, and is accompanied with a rapid ebullition, which emies iparks to a considerable distance, resembling exactly the sparks of a fire-work.-IV, A current of vital (or depniogisti

cated)

« ПредыдущаяПродолжить »