M. DE LA METHERIE, well acquainted with the later difcoveries, accustomed to experimental inquiries, and cautious in drawing his conclufions, has undertaken this important work; and, in the volumes before us, has given, in one view, the various facts that have been related by others, or difcovered by himself. Cultivating, as we learn from his preface, the sciences merely for their own fake, and being an enemy to all party fpirit, he has fought out the truth with diligence, and recorded. his discoveries with fidelity. He is far from believing that he, may not have committed errors. The opinions which he has adopted are deduced from facts only, and he is ready to retract them whenever other facts are difcovered, by which they may be invalidated.

The first objects of his attention are fire, light, and heat. We fhall briefly give the refults of his investigations on these abstruse fubjects, of which he treats in his firft fix chapters. He concludes,

That there exifts an ethereal matter, a fluid, of the greatest fubtility; which, when fet in motion by bodies in the ftate of ignition, produces light, in a manner fimilar to that by which the tremulous motion of the air caused by fonorous bodies, produces found: That this luminous fluid or ethereal matter is homogeneous, and ought to be claffed among thofe fubftances which are called elementary: That it is the fame with that which has been defcribed under the name of igneous fluid, or elementary fire*: That the primary particles (les molécules) of this fluid are fpherical, perfectly elaftic, and endowed with confiderable activity: That this fluid, combined with fome other principle more grofs than itfelf, probably pure air, in a fmall quantity, conftitutes the matter of heat; and that the matter of heat is a fluid poffeffed of the common properties of all other fluids; it penetrates all bodies that are expofed to it, as water penetrates porous fubftances that are plunged into it: in this flate, M. DE LA METHERIE, following other philofophers, calls it free or fenfible heat. It conftantly endeavours to preferve an equilibrium ; confequently a heated body placed near a cold body, will give, or part with, fo much heat, as to make an equilibrium, or equal degree of heat in each. This communication of heat is in proportion to the maffes of the bodies, if the bodies themfelves be homogeneous. Different bodies have a greater or lefs affinity to the matter of heat, and confequently are capable of taking different quantities of it. And in this ftate it is called latent or specific heat.

The matter of heat may combine itself with other bodies, and become one of their conftituent parts, and in that ftate he

*It is poffible that these two fluids may be different. M. DE LA METHERIE fuppofes them to be one and the fame, but capable of producing different effects.

APP. REV. Vol. LXXIX.

calls

calls it chaleur combinée, or caufticon; it is the fame principle which the ancients called calidum, or unctuofum, and what LeMERI, with feveral others, have denominated the matter of fire. Quick-lime, after having undergone a violent calcination, contains a great quantity of this caufticon or combined heat; the alkalies alfo, which have a great refemblance to lime, contain this fame principle, and to it M. DE LA METHERIE attributes their activity: the energy of acids is likewife attributed to the caufticon which enters their compofition.

The caufticon gives a great activity to all thofe bodies which contain it, but it cannot render them combustible; it is therefore different from the inflammable principle, or the principle of combuftion. M. DE LA METHERIE now comes to the grand queftion, which at this time has made a divifion among chemifts: Is the inflammable principle a distinct elementary substance, and a component part of combuftible bodies? or are combuftiole bodies fimple elementary fubftances?

STAHL thought that the inflammable principle was a diftinct fubftance, and that it might pafs from one body into another. This alfo is M. DE LA METHERIE's opinion. The caufticon, or the matter of heat, may combine itself with a certain quantity of air or of water, and it will then lofe part of its activity, and preferve only that primary quality of being able to produce fire or flame, on certain occafions. It then takes another name, viz. the inflammable principle. This principle is the inflammable air of the prefent chemifts, and the phlogifton of STAHL.

In the feventh chapter, he refutes the opinion of MUSCHENEROECK, who thought cold a diftinct fubftance. He fhews that it is only a privation of fenfible heat; and he gives the known methods of augmenting it. The matter of heat continually combining itself with other fubftances, diminishes the quantity of fenfible heat; an exceffive degree of cold would then take place over the whole furface of the globe, if certain caufes did not exift that might counterbalance this effect. These caufes appear to M. DE LA METHERIE to be, the central heat, and the presence of the fun; and the examination of these causes forms the fubject of the next chapter.

Chap. IX. treats of fluids and bodies in an aëriform state. According to the doctrine here delivered, every folid body becomes fluid by the addition of the matter of heat, and if more heat be applied, the body affumes an aëriform ftate, fo that every fubftance may exift either in a ftate of folidity, of fluidity, or of vapours. The fubftance itself is nevertheless the fame in all these three ftates, although while folid it has the properties which conftitute folidity; while fluid, thofe which characterife Auidity; and when in an aeriform ftate, it obeys the general laws of claftic fluids; its nature ftill remains the fame, and only

affumes

affumes these three different ftates of existence, in proportion as it is combined with different quantities of the matter of heat.

Different bodies require different degrees or quantities of heat, to produce thefe different ftates of folidity, fluidity, and vaporofity*. Hence, by the natural degree of heat, fome fubftances are always in a folid, others in a liquid form, and others in the form of air or vapour.

M. DE LA METHERIE, having fhewn that any fubftance is preferved in an aëriform ftate, in confequence of the quantity of heat which it contains, proceeds to defcribe the following fpecies of air; viz. atmospheric, pure, inflammable, acid, impure, and nitrous.

The next object of the Author's attention is the electrical Aluid, which he supposes to be fire, the luminous fluid, or perhaps the matter of heat in violent motion, and combined with pure air. This opinion is given merely as a conjecture; he acknowleges that it is not demonftrated, but adds, that it is conformable to analogies deducible from known experiments.'

The two following chapters are employed in defcribing the inflammable phofphoric, and the inflammable fulphureous airs. The former is obtained from phofphorus, digefted with any of the deaerated alkalies, quick-lime, or metallic calces, and has the peculiar property of detonating with the fimple contact of pure or atmospheric air. The latter is the hepatic air of other authors, which, from many experiments here related, appears to be a combination of inflammable air with the fulphureous acid. The Author fuppofes that the cauflicon, or matter of heat, is the fubftance which unites them. The phosphoric inflammable air confifts of inflammable air united with the phosphoric acid, by means of the caufticon: but he does not pretend to give any account how the matter of heat acts, in forming these compounds.

The numerous difcoveries that have lately been made réfpecting aëriform fluids, have thrown new light on fome of the operations of vegetation; it is therefore neceffary that vegetation fhould have a chapter allotted to it in a treatife on airs. M. DE LA METHERIE defcribes the principal phenomena of vegetation, relates the experiments of PRIESTLEY, INGENHOUSZ, and other philofophers, compares them with his own, and proceeds to the analyfis of the different fubftances found in vegetables.

The fecond volume commences with a chapter on refpiration. We here find an objection to part of Dr. PRIESTLEY's theory; but it is founded on a misapprehenfion of the Doctor's mean

This is a new word; the fcience feems to want it, and we have ufed it, although without an authority.

Q92

ing.

ing. M. DE LA METHERIE fays, Dr. Prieftley's experi ments prove, that the blood imparts to the pure air a principle which vitiates it, and changes it into acid air and impure air. Dr. PRIESTLEY thinks these effects are owing to phlogiston. But the fame phlogifton cannot change pure air into acid, and into impure air. It is therefore neceffary that there fhould be two causes to produce these two effects.' And the Author proceeds to afcertain thefe caufes. Now Dr. PRIESTLEY fays, that the air vitiated by breathing is phlogifticated, or, as M. DE LA METHERIE calls it, impure air, and contains no acid air. This miftake has frequently been made both by foreigners and natives; and we have often mentioned it: fee Rev. vol. lxi. P. 384. In this chapter, the Author alfo attacks Dr. Crawford's theory of animal heat; he fays, The heat which the blood acquires in the lungs cannot be wholly attributed to this cause [viz. the depofition of abfolute heat by the pure air]; the greateft part of it is owing to the augmentation of the motion which the blood receives in that vifcus. This acceleration is in the proportion of the mass of the lungs to that of the whole body, becaufe the blood of the aorta, which goes to every part of the body, paffes in the fame time through the lungs; and the circulation, thus accelerated, produces the heat.' This is an extraordinary paragraph: In the first place, the Author confounds abfolute with fenfible heat; and the diftinction between them forms the very bafis of Dr. Crawford's theory: Secondly, it is by no means proved that the motion of the blood in the lungs is greater than that in the rest of the body: And laftly, the argument which the Author ufes to prove the increased motion of the blood in the lungs, directly proves the contrary. We fhall add alfo, that we doubt whether the blood which goes to every part of the body paffes in the fame time through the lungs.

M. DE LA METHERIE's opinion is, that in the act of refpiration, the pure air produces thefe three effects; 1ft, it depofits fome heat in the lungs; 2dly, it receives from the blood a certain principle; 3dly, it combines itfelf in part with the animal Huids. He does not, however, give a fatisfactory account how thefe effects are produced.

The next chapter is entitled De l'Animalifation. The Author here fhews, that the component parts of vegetables are changed into thofe of animals; for all animals, either immediately or mediately, derive their nourishment from vegetables and the five following chapters are employed in defcribing and analyfing milk, lymph, animal oils, animal acids, and animal and vegetable coal (charbon).

No natural operation has fo much excited the attention of chemifts as fermentation; which M. DE LA METHERIE divides

into two fpecies; one, forming compounds, as that which produces wine, bread, vinegar, &c. and in vegetables and animals elaborates their juices, and forms of them an aftonishing variety of different fubftances: the other fpecies is that which decomposes the subftances produced by the former.

From experiments, it appears that thefe fubftances are abfolutely neceffary for producing the fpirituous fermentation in muft or wort, viz. ift, fugar; 2dly, tartar; 3dly, the extractive part*, all diluted with a proper quantity of water. Fermentation also requires the free accefs of the air. M. DE LA METHERIE thinks that pure air is abforbed by all liquors that undergo a vinous fermentation; part of it is changed into acid air, and the remainder into impure air: the fpecific heat of the pure air is then difengaged. But the Author cannot allow all the fenfible heat perceivable in a fermenting mafs to be produced by this caufe alone, because certain fubftances, as hay ftacked too green, will become exceffively hot, and even take fire without the accefs of pure air. He therefore accounts for the heat of fermenting bodies in the following manner: One of the most ordinary caufes of heat is friction; now in all fermenting maffes a confiderable inteftine motion exifts, which producing a friction among the parts of the mafs, muft neceffarily occafion heat. Befide, many of the fermenting fubftances contain a great quantity of combined heat, which, during their decompofition, is difengaged; and, hence, another fource of heat. But let us return to the process.

The pure air being abforbed, augments the firft motion; the acid of tartar, being by the action of the pure air difengaged, acts on the other principles of the muft, viz. the faccharine and oily parts, as all acids do on thefe fubftances: hence a decompofition, effervefcence, and difengagement of airs, &c. Part of the airs which are thus difengaged, viz. the acid, pure, inflammable, and impure airs, combine themselves, either with each other, or with the abforbed air and the matter of heat; and from this combination arife (naiffent) the new products which we find to be the refult of fermentation. The operation however must be stopped in due time; for if it is continued too long, the airs will all be diffipated, a total decompofition will take place, and nothing will remain but a vapid liquor. The effential produce of this fermentation is fpirit, which is a compound, confifting of tartareous acid, faturated with inflammable air.

Such is the fubftance of M. DE LA METHERIE's theory of vinous fermentation. From a number of curious experiments,

*By the term la partie extractive, the Author means whatever can be extracted from plants, by macerating or boiling them in water. Q93

it