rendered cauftic, in confequence of the acidum pingue combined with it.

We shall add only another inftance, to illuftrate Mr. Meyer's hypothefis. When a calcareous earth has been diffolved in the nitrous acid, we may precipitate it either in a mild or a cauftic ftate, according as we apply to the folution either a mild or a cauftic alcali. In both these cafes, the nitrous acid leaves the earth to unite with the alcali; but in the first of them, according to the English theory, the fixed air leaves the mild alcali, and unites with the precipitated earth in the form of limeftone: whereas in the latter, the earth is precipitated in a cauftic ftate, or in that of quicklime; as its fixed air had been expelled from it on the addition of the nitrous acid; and as the cauftic alcali has no fixed air to furnish it with.-To this fimple explication Mr. Meyer opposes the following, nearly as fimple, and which has no other defect than that it is merely hypothetical.

He affirms that, in the laft-mentioned procefs, (viz. where the cauftic alcali, for inftance, is employed) there are two neutral folutions :-that of the alcaline falt, neutralifed with the acidum pingue; and that of the chalk, neutralised by the nitrous acid:-that a double decompofition takes place; the nitrous acid leaving the earth, and uniting with the alcali; while at the fame time the acidum pingue deserts the cauftic aleali, and unites with the earth, which is now rendered cauftic in its turn. When a mild alcali has been employed, the calcareous earth is precipitated in a mild ftate; because, the mild alcali cannot furnish it with any of the acidum pingue which fhould render it cauftic.-In general, that caufticity in lime and cauftic alcalis, which the English philofophers have afcribed to the expulfion or absence of fixed air, Mr. Meyer invariably attributes to the acquifition and presence of his hypothetical acid.

His doctrine however was attacked, and the English system defended, in the year 1769, by M. Jacquin, a Profeffor at Vienna, in a Latin differtation, entitled, "A chemical Examination of M. Meyer's Doctrine of the Acidum Pingue, and of Dr. Black's Doctrine concerning the Phenomena of fixed Air, with regard to Lime. M. Lavoifier greatly commends this work for the method and perfpicuity obfervable in it; though it does not contain many new facts.

The German hypothefis had made a rapid progress throughout Germany; it had been adopted by chemifts of reputation, and even began to be taught publickly in the schools, when its inventor died. He was fucceeded however by a most zealous difciple, in M. Crans; whofe prepoffeffion for M. Meyer's acidum pingue feems to have made him blind to the moft evident and conftant appearances. The experiments related by him,

Ne

in his work publifhed at Leipfic in the year 1770, in fupport of the new acid, and in oppofition to the doctrine of fixed air, as maintained by Dr. Black, are fuch as must aftonish every one who has been fufficiently converfant in the fubject. vertheless, M. Lavoifier, many of whofe own experiments afford a complete refutation of the greater part of them, relates them with all the phlegm of an indifferent hiftorian. They fcarce indeed deserve a regular refutation: we fhall only there fore, on the authority of M. Lavoifier, collect a few of M. Crans's fingular conclufions; condenfing them into the form of propofitions, with a few remarks of our own annexed.

The great lofs of fubftance fuftained by limeftone and other calcareous earths in the fire is principally owing to the expulfion of a great quantity of water.-This affertion is totally deftitute of proof, and is contradicted by daily experience; more particularly by fome of the Author's experiments, the refult of which will be hereafter given.

Limestone, after calination, does not lose its property of effervescing with acids.-M. Crans quotes in proof of this affertion the teftimonies of Du Hamel, Geoffroy, Homberg, and Pott, and his own conftant experience. It requires however no other answer than a flat contradiction; fuppofing the ftone to be perfectly calcined, and that, by effervefcence, the Author means the expulfion of feemingly aerial bubbles.

Quicklime, after being expofed to the air a confiderable time, is fo far from refuming the fixed air which it is supposed to have loft, and becoming milder, that it acquires even a greater degree of cauflicity. by fuch expofure.-Neither this or the two following affertions require any comment.

He afferts that, on diffolving a calcareous earth in the nitrous acid, and then precipitating it by means of alcalis, the precipitated earth will equally effervefce with acids; whether the precipitation were affected by the cauftic or the common fixed alcali.

He further affirms that, on diffolving mild calcareous earths, and quicklime, in acids, the quicklime fometimes last more weight than the mild calcareous earth: Nay, not content with this fingular affertion, M. Crans even affirms that the mild calcareous earth fometimes even acquired an additional weight, in confequence of the effervefcent process!

Thefe affertions are fo contradictory to experience, and the fyftem founded upon them is fo groundlefs, that we have been principally induced to collect them as a ftriking example of the delufion which a predilection for a preconceived and favourite hypothefis will produce in the minds of thofe who adopt and maintain it. The favourers of the German herefy refift the plain teftimony of their fenfes; in order to fet up an ens rationis, a mere creature of the imagination, in oppofition to a real fub

ftance,

tance, which falls under the cognifance of almoft every one of our senses.

After giving an account of M. de Smeth's experiments and obfervations on the fubject of Elaftic Vapours, &c. contained in a Latin differtation in 410. publifhed at Utrecht in 1772; the Author dwells minutely on the numerous and interesting difcoveries made by Dr. Prieftly on this fubject; his account of which is taken from the Doctor's first communication of them to the Public, in the Philofophical Tranfactions. On this part of the work we need not dwell; and fhall only obferve that the Tranflator has confiderably improved it, by correcting feveral of the Author's mistakes; either by altering the text, or by fubjoining additional notes. This hiftorical part is terminated by an account of the various obfervations, relative to the fubject of this treatife, which have been published by Mefirs. Du Hamel, Rouelle, Bouquet, and Baumé.

In the fecond part of his work the Author proceeds to relate his own original experiments. That we may give the Reader a general view of the nature and defign of them, we shall subjoin the titles of the chapters in which they are related.

Chap. 1. Of the Existence of an elastic fixable Fluid in calcareous Earths, and the Phenomena refulting from the Abfence of it in Lime. Chap. 2. Of the Existence of an claftic fixable Fluid in the fixed and volatile Alcalis, and if the Means by which they may be deprived f it. Chap. 3. Of the Precipitation of calcareous Earth, diffolved in nitrous Acid, by Alcalis in a Caufiic, and in a mild State. Chap. 4. Of the Combination of the elaftic Fluid of calcaneus Earth and Alcalis with metallic Subflances by Precipitation. Chap. 5. Of the Exiflence of elaftic fixable Fluid in the metallic Calces. Chap. 6. Of the Combination of elaftic Fluid with metallic Subflances by Calcination. Chap 7. Experiments en elaftic Fluid disengaged from effervefcent Mixtures, and from metallic Reductions. Chap. 8. Of Some Properties of Water impregnated with elaftic Fluid Separated from effervefcent Mixtures, or metallic Reductions. Chap. 9. Of the burning of Phofphorus, and the Formation of its Acid. Chap. 10. Experiments on Combustion and Detonation in Vacuo. Chap. 11. On Air in which Phofphorus has been burnt.

Though it may appear a work of fupererogation, to endeavour to determine the refpective merits of the fyftem of Dr. Black and the English philofophers, and that of the Germanfchool, with refpect to the true caufe of the caufticity of lime and alcaline falts; yet the Author employs the three first chapters in relating the experiments which he made to ascertain this point. They are conducted with a degree of method and precifion which do not leave the leaft room for cavil on the fubject. They derive indeed their principal value from the strict at

tention

tention which he pays to the circumftances of weight and meas fure in the greater part of his proceffes relative to this inquiry. From fome of these related in the first chapter it results that Ico pound weight of chalk contains about 31 pounds 15 ounces of elastic fluid, 15 pounds 7 ounces of water, and only 52 pounds 10 ounces of earth; and that poffibly the chalk contains more elastic fluid and lefs earth. He afterwards proves, with equal evidence and precifion, that the fame elastic fluid, to which chalk and other calcareous earths owe their mildness, conftitutes a confiderable part of the fubftance of fixed and volatile alcaline falts; and that all these bodies owe their caufticity principally to their being deprived of this component principle; and not to the acceffion of any supposed acidum pingue.

The Author next proceeds to experiments on metals, precipitated from their folutions in acids, by calcareous earths, both mild and cauftic; and fhews that, in the first of these cafes particularly, the precipitates acquire a remarkable increase of weight; which appears to be owing to their attracting a confiderable portion of elaftic fluid. An augmentation is likewife perceived when the precipitation is effected by the cauftic earth; for which the Author accounts, by obferving that flaked lime ftill contains fome portion of elaftic fluid, which calcination has not been able to expel from it; as appears from one of his preceding experiments.

He next examines the phenomena attending the calcination of metals; and proves that a portion of elastic fluid is attracted from the atmosphere, fixed, and combined with them in that procefs; and that it produces that augmentation of weight which they acquire in calcination. His experiments fhew that when a metal paffes into the state of a calx, there is an abforption of this elaftic fluid; and that when the fame calx is reduced, or returns into the state of a metal, there is an effervefcence, which proceeds from a discharge of this fame fluid. His experiments like wife fatisfactorily evince that the calcination is nearly proportionable to this abforption; and that in proportion as the calcination proceeds, the diminution in the volume of the air contained in the glafs receiver under which the process is made, is nearly answerable to the augmentation of weight which the calx acquires.

By this title the Author defigns, in general, the elaftic fubftances generated or let loose from effervefcent mixtures, in the calcination of calcareous earths, the reduction of metallic calces, and other proceffes, without any particular appropriation of it to fixed air, or any other fpecies of elastic fluid.

6

In his subsequent chapters the Author fubje&s the elaftic fluid obtained from effervescent mixtures, and metallic reductions, to different trials, and obferves its effects on animals, burning bodies, &c. In the following obfervations on the burning of phofphorus, he fhews that this fubftance, which is known to acquire an increase of weight during combuftion, does not owe this augmentation to water or moisture attracted from the atmosphere; (though aqueous vapours, if fuch are at hand, unite with its acid) but derives it either from the air itself, or some other elastic Auid contained, in a certain proportion, in the air. Some other experiments of lefs confequence, on the combuftion of phosphorus in vacus, &c. terminate the volume.

To this work the Tranflator has added an Appendix containing two papers. The firft of thefe is a memoir read by M. La voifier before the Royal Academy of Sciences at Paris, on the nature of the principle which is combined with metals during their calcination, and which occafions the increase of their weight above fpoken of. In this memoir M. Lavoifier relates fome experiments made with the mercurius calcinatus, from which he expelled, by means of heat, and without addition, a large quantity of air, more pure even than the air in which we live." This air was, in reality, the pure or dephlogifticated air difcovered by Dr. Prieftley; who had before mentioned to M. Lavoifier at Paris his having extracted this fingular species of air from that calx*; the nature of which, as well as the compofition of atmospherical air he has fince fully explained in the fecond volume of his Obfervations. In the fecond of these papers, Mr. Henry has given a concife account of the results of Dr. Priestley's fuccessful inquiries into this curious and important fubject.

To the foregoing fummary of this work we fhall only add, that the Author has fhewn great ingenuity and addrefs in the imagining and conducting his experiments. His apparatus is indeed, in feveral inftances, very complex; but this quality it derives from his defire of reducing every fubject of examination to number, weight, and measure, and of giving all that degree of evidence and accuracy to his conclufions, of which phyfical experiments are fufceptible; efpecially in thofe cafes which had been particularly contefted. The Tranflator has done full juftice to his Author, whofe work he has likewife improved, as we have already hinted, both by occafional reformations of the text, and by the notes which he has added to it.

See Dr. Priestley's Experiments and Obfervations, vol. II. pag. 36 and 320.

Rev. Sept. 1776.

९

ART.