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M. DE LA Metherie, well acquainted with the later dircoveries, accustomed to experimental inquiries, and cautious in drawing his conclusions, 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 discovered by himself. Cultivating, as we learn from his preface, the sciences merely for their own fake, and being an enemy to all party spirit, he has sought 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 discovered, by which they may be invalidated.
The first objects of his attention are fire, light, and heat. We fhall briefly give the results of his investigations on these abstruse fubje&s, of which he treats in his first fix chapters. He concludes,
That there exifts an ethereal matter, a Auid, of the greatest subtility ; which, when set in motion by bodies in the Itate of ignition, produces light, in a manner fimilar to that by which the tremulous motion of the air caused by sonorous bodies, produces found : That this luminous fluid or ethereal matter is homogeneous, and ought to be clafled among those substances which are called elementary : That it is the same with that which has been described under the name of igneous Auid, or elementary fire* : That the primary particles (les molécules ) of this fluid are spherical, perfectly elastic, and endowed with confiderable activity: That this Auid, combined with fome other principle more gross than itself, probably pure air, in a small quansity, conftitutes the matter of heat; and that the matter of heat is a fluid possessed of the common properties of all other fluids; ic penetrates all bodies that are exposed to it, as water penetrates porous fubftances that are plunged into it: in this state, M. de
LA METHERIE, following other philosophers, calls it free or fenfible heat. It constantly endeavours to preserve an equilibrium ; consequently a heated body placed near a cold body, will give, or part with, so much heat, as to make an equilibrium, or equal degree of heat in each. This communication of heat is in proportion to the masses of the bodies, if the bodies themselves be homogeneous. Different bodies have a greater or less affinity to the matter of heat, and consequently are capable of taking different quantities of it. And in this state it is called latent or specific heat.
The matter of heat may combine itself with other bodies, and become one of their constituent parts, and in that state he
* It is possible that these two fluids may be different. M.DE LA METHÈRIE supposes them to be one and the fame, but capable of producing different effects. APP, Rey. Vol. LXXIX. Ra
calls it chaleur combinée, or causticon; it is the same principle which the ancients called calidum, or unctuosum, and what LeMERI, with several others, have denominated the matter of fire. Quick-lime, after having undergone a violent calcination, contains a great quantity of this cauflicon or combined heat ; the alkalies also, which have a great resemblance to lime, contain this fame principle, and to it M. de la MeTHERIE attributes their a&ivity: the energy of acids is likewise attributed to the cauflicon which enters their composition.
The causticon gives a great activity to all those bodies which contain it, but it cannot render them combustible: it is therefore different from the inflammable principle, or the principle of combustion. M. de la Metherie now comes to the grand question, which at this time has made a division among chemifts : Is the inflammable principle a distinct elementary substance, and a component part of combuftible bodies ? or are combustible bodies simple elementary substances ?
STAHL thought that the inflammable principle was a diftinct substance, and that it might pass from one body into another. This also is M. DE LA Merherie'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 lose part of its activity, and preserve only that primary quality of being able to produce fire or fame, on certain occasions. It then takes another name, viz. the inflammable principle. This principle is the inflammable air of the present chemists, and the phlogision of STAHL.
In the seventh chapter, he refutes the opinion of MUSCHENEROECK, who thought cold a diftinct substance. He thews that it is only a privation of sensible heat; and he gives the known methods of augmenting it. The matter of heat continually combining itself with other substances, diminishes the quantity of sensible heat; an exceflive degree of cold would then take place over the whole surface of the globe, if certain causes did not exist that might counter balance this effect. These causes appear to M. DE LA METHERIE to be, the central heat, and the presence of the sun; and the examination of these causes forms the subject of the next chapter.
Chap. IX. treats of fluids and bodies in an zë:iform state. Ac. cording to the dodrine here delivered, every solid body becomes Auid by the addition of the matter of heat, and if more beat be applied, the body assumes an aëriform state, so that every substance may exist either in a state of solidity, of-Auidity, or of vapours. The substance itself is nevertheless the same in all these three ftates, although while solid it has the properties which constitute folidity; while fluid, those which characterise fluidity; and when in an zëriform ftate, it obeys the general laws of clastic Auids; its nature still remains the fame, and only
assumes these three different states 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 these different states of folidity, fluidity, and vaporofity *. Hence, by the natural degree of heat, Tome substances are always in a solid, others in a liquid form, and others in the form of air or vapour.
M, DE LA METHERIE, having thewo that any substance is preserved in an aëriform ftare, in consequence of the quantity of heat which it contains, proceeds to describe the following species of air ; viz. atmospheric, pure, inflammable, acid, impure, and nitrous.
The next object of the Author's attention is the electrical Auid, which he supposes to be fire, the luminous fuid, or perhaps the matter of heat in violeni motion, and combined with
This opinion is given merely as a conjecture; he acknowleges that it is not demonstrated, but adds, that it is conformable to analogies deducible from known experiments.'
The two following chapters are employed in describing the inflammable phosphoric, and the inflammable sulphureous airs. The former is obtained from phosphorus, digefted with any of the deaë:ated 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 supposes that the cauflicon, or matter of heat, is the substance which vnites them. The phosphoric inflammable air consists of inflammable air united with the phosphoric acid, by means of the cauflicon: but he does not pretend to give any account how the matter of heat acts, in forming these compounds.
The numerous discoveries that have lately been made respecting aëriform Auids, have thrown new light on some of the operations of vegetation ; it is therefore necessary that vegetation should have a chapter allocred to it in a treatise on airs. M. DE LA Metherie describes the principal phenomena of vegetation, relates the experiments of Priestley, INGENHOUSZ, and other philosophers, compares them with his own, and proceeds to the analysis of the different substances found in vegetables.
The second volume commences with a chapter on respiration. We here find an objection to part of Dr. PRIESTLEY's theory; but it, is founded on a misapprehension of the Doctor's mean
• This is a new word; the science seems to want it, and we have used it, although without an authority. Q9 2
ing. M. de la Metherie says, Dr. Priestley's experie 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 same phlogiston cannot change pure air into acid, and into impure air. It is therefore neceffary that there should be two causes to produce these two effects. And the Author proceeds to ascertain these causes. Now Dr. PRIESTLEY says, that the air vitiated by breathing is phlogisticated, or, as M. DE LA METHERIE calls it, impure air, and contains no acid air, This mistake has frequently been made both by foreigners and natives; and we have often mentioned it : see Rev. vol. Ixi. P. 384. In this chapter, the Author also attacks Dr. Crawford's theory of animal heat; he says, “The heat which the blood acquires in the lungs cannot be wholly attributed to this cause [viz. the deposition of absolute heat by the pure air]; the greatest part of it is owing to the augmentation of the motion which the blood receives in that viscus. This acceleration is in the proportion of the mass of the lungs to that of the whole body, because the blood of the aorta, which goes to every part of the body, paffcs in the same time through the lungs; and the circulation, thus accelerated, produces the heat.' This is an extraordinary paragraph: In the first place, the Author confounds absolute with sensible heat; and the distinction between them forms the very basis 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 lastly, the argument which the Author uses to prove the increased motion of the blood in the lungs, dire@ly proves the contrary. We hall add alio, that we doubt whether the blood which goes to every part of the body passes in the same time through the lungs.
M. DE LA METHERIE's opinion is, that in the act of respiration, the pure air produces these three effects; ist, it deposits fome heat in the lungs ; 2dly, it receives from the blood a certain principle ; 3dly, it combines itself in part with the animal Auids. He does not, however, give a satisfactory account how these effects are produced,
The next chapter is entitled De l'Animalisation. The Author here thews, that the component parts of vegetables are charged into those of animals; for all animals, either immediately or mediately, derive their nouril ment from vegetables : and the five following chapteis are employed in describing and analysing milk, lymph, animal oils, animal acids, and animal and vegetable coal (charbon).
No natural operation has so much excited the attention of chemists as fermentation ; which M. DE LA METHERIE divides into two species; one, forming compounds, as that which produces wine, bread, vinegar, &c, and in vegetables and animals elaborates their juices, and forms of them an astonishing variety of different substances: the other species is that which decomposes the subftances produced by the former,
From experiments, it appears that these fubftances are absolutely necessary for producing the spirituous fermentation in must or wort, viz. ift, sugar; 2dly, tartar; 3dly, the extractive part *, all diluted with a proper quantity of water. Fera mentation also requires the free access of the air. M. DELAME. THERIE thinks that pure air is absorbed by all liquors that undergo a vinous fermentation ; part of it is changed into acid air, and the remainder into impure air: the specific heat of the pure air is then disengaged. But the Author cannot allow all the sensible heat perceivable in a fermenting mass to be produced by this cause alone, because certain substances, as hay stacked too green, will become excessively hot, and even take fire without the access of pure air. He therefore accounts for the heat of fermenting bodies in the following manner: One of the most ordinary causes of heat is friction; now in all fermenting mafies a considerable intestine motion exists, which producing a friction among the parts of the mass, muft necessarily occasion heat. Beside, many of the fermenting substances contain a great quantity of combined heat, which, during their decompofition, is disengaged ; and, hence, another source of heat. But let us return to the process.
The pure air being absorbed, augments the first motion ; the acid of tartar, being by the action of the pure air disengaged, acts on the other principles of the must, viz. the saccharine and oily parts, as all acids do on these subliances : hence a decompofition, effervescence, and disengagement of airs, &c. Part of the airs which are thus disengaged, viz. the acid, pure, inHammable, and impure airs, combine themselves, either with each other, or with the absorbed air and the matter of heat; and from this combination arise (naissent) the new products which we find to be the result 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 essential produce of this fermentation is spirit, which is a compound, conlisting of tartareous acid, saturated with inAammable air.
Such is the fubftance of M. DE LA METHere'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, hy macerating or boiling them in water.