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at a small diftance from Plombieres, may be of eminent use in this refpect. The foap-rock of Cornwall has long been used in the Worcester manufactory of china-ware, &c. poffibly by Mr. Wedgwood.

Mem. II. A Defcription of Two Mines of Earth-Coal in the Franche Comté, and in Alface, together with Experiments made on the Product of thefe Mines. By Mefirs. GUETTARD and LAVOISIER. The analysis of these coals yielded no volatile alkali, which is commonly derived from thefe fubftances. Thefe diverfities, in the principles of coals, indicate an effential difference in their origin, in the nature of the bodies which contri buted to their formation, or in the kinds of alteration which these bodies have undergone. But what that difference is-ignoramus, fay the Academicians.

Mem. III. Obfervations on the Red Mine of Copper. By M. SAGE. From feveral facts related in this Memoir, the acute Academician concludes, that the red mine of copper is no more than calx of copper, the copper itself deprived of its phlogiston. Accordingly this mine, reduced, yields feventy pounds of metal from the hundred, and is entirely diffolved in volatile alkali, ta which it gives a blue colour. These chemical results confirm M. SAGE's obfervation.

CHEMISTRY.

Mem. I. General Confiderations on the Nature of Acids, and on the Principles or Elements of which they are compofed. By M. LAVOISIER. In this very curious and elaborate Memoir, the celebrated Academician difplays his analytical talent to great advantage; and though vain are all attempts to come at material elements in their abfolute fimplicity, yet a ftep forwards, now and then, is ftill fomething, and may lead to discoveries of moment. The chemifts, indeed, having fucceffively learned, that their pretended elements turn out compound fubftances, are grown more modeft in their views than in days of yore. They understand by elements only the bodies, which we cannot decompofe, and which confequently muft pafs for elements with refpect to us. Nevertheless, as feveral of thefe fubftances indicate marks of a primitive formation effected by Nature, or of a decompofition executed by means which we can neither difcern nor imitate, they are juftly excluded from the clafs of elements, but regarded as principles, beyond which it is not attempted to carry the analysis of the fubftances which they compofe. But the analysis of thefe fubftances is itself one of the most attracting objects of chemistry: it furnishes problems difficult to folve, but of which, nevertheless, the obfervation of Nature proves the folution poffible: thus, at each epocha, which enriches chemistry with new means of analyfing, fubftances formerly confidered as

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elements

elements are excluded from that clafs, and are placed in the rank of compounds.

Acids, at least feveral of them, are regarded not as elements, because they are known to be formed and deftroyed, but as principles of great fimplicity which reject analyfis. The theory of airs has, of late years, given us fome hope, however, of carrying analysis a step farther than it has hitherto advanced. From the experiments that have been made on the airiform fluids that escape from bodies, it is evident, that fuch of these substances as are difengaged in the decompofition of an acid may be known, and fubjected to the examination of chemifts.

It was on the nitrous acid that the first trials were attempted; and M. LAVOISIER recalls here his experiments formerly made before the Academy, from which it appeared, that this acid was compofed of nitrous air and vital air, or what Dr. Prieftley calls dephlogisticated air; as alfo, that this latter entered as a conftituent part into the compofition of feveral acids. New and multiplied experiments have carried him a step farther; and, in the prefent Memoir, he maintains, that pure and vital air is the conftituent principle of acidity in general. And as acidity is a property which is common to all kinds of acids, and produces analogous effects and phænomena in them all, he supposes, that acids, if they are neither regarded as fimple fubftances, nor as the fame effential acid differently modified, derive their acid quality from one common principle, which he chufes to call the acidifying, or (if a Greek term fhould be preferred) oxiginous principle. This principle, combined with coaly fubftances, produces the chalky acid or fixed air; combined with fulphur, it forms the vitriolic acid; combined with nitrous air, it forms the nitrous acid; combined with Kunckel's phosphorus, it forms the phosphoric acid; and combined with fugar, it forms the acid of that fubftance.

The Memoirs of M. LAVOISIER, in the preceding volumes, contain a part of his proofs in favour of these opinions. An examination of the circumftances which accompany the formation and decompofition of the acid of fugar, is more particularly the fubject of that now before us. The curious and nice experiment he employed in this examination is here amply and minutely related; we can only mention the effential parts of the operation and its refult. Nitrous acid being poured upon fugar, and diftilled on an open fire, there paffes firft nitrous air in great purity and ftrength, inflammable air, gafous air, and, finalJy, a portion of the nitrous acid which has not fuffered decompofition; the acid of fugar remains in the cucurbit. Thus the vital air, which difengaged itfelf from the nitrous air, combined itself with the fugar, and formed the faccharine acid; but the

gafous

gafous and inflammable airs which paffed, were produced by the decompofition of the acid of fugar; accordingly, this acid, in diftillation, is reduced to gafous air and inflammable air, leaving a coaly refiduum. As the gafous air is, according to the opinion of our Academician, a combination of the acidifying prin- . ciple with a coaly matter, the refult of this laft analyfis is, that fugar is no more than a compound of coaly matter fully formed, and inflammable air. M. LAVOISIER concludes this Memoir with announcing a feries of vegetable analyfes, which he intends to carry on in the fame method obferved in the analysis of fugar, and upon the fame principles. This is a new path opened in chemistry, in which the branch of that fcience, which treats of falts, instead of five or fix acids, which it formerly employed, has double that number already afcertained by our Academician, and will be followed, he thinks, by many more in time coming. In this very imperfect account of his long and elaborate Memoir, we cannot hope to have entirely avoided obfcurity; a part of this muft, however, be laid to the charge of the fubject, and the reft to the obligations we are under to brevity; fuppofing the author to pass free.

Mem. II. On the Decompofition of feveral neutral Salts, with Bafis of fixed and Volatile Alkalies, by the Marine Acid. By M. CORNETTE. It was proved, many years ago, by M. Baumé, that the nitrous acid decompofes vitriolated tartar and Glauber's falts, while the vitriolic acid decompofes alfo the prifmatic and the quadrangular nitre. This feeming paradox, which appears unfavourable to the doctrine of affinities, was confirmed by the experiments of M. Margraff, and thus became a kind of general rule. M. CORNETTE makes new fteps in the path, opened by the two abovementioned Academicians, and proposes to elucidate what has appeared uncertain, and to conciliate what may feem contradictory in their refults; and he comprehends, in this laborious undertaking, falts that have an earthy or a metallic bafis. This first Memoir treats only of the decompofition made by the marine acid, of vitriolic and nitrous falts, which have a basis of fixed vegetable or mineral alkali, or a basis of volatile alkali.

Mem. III. Second Memoir concerning the comparative Action of the Nitrous Acid and the Marine Acid upon Vitriolic Salts, with an earthy Bafis. By the fame.

Mem. IV. Obfervations on certain Saline Combinations of Iron. By M. DE LASSONE.

Mem. V. A new Method of effectuating, with accuracy, the PARTING in a great Number of Essays of Gold of different Degrees of Purity, and of applying, at one and the fame Time, this Operation to all the Effays, reunited, in One Matras. By M. TILLET. It is well known how greatly this ingenious Academician has contributed

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contributed to improve the method of feparating the imperfect metals that are united to gold and filver, and the new degrees of perfect on he has added to the operation of coppelling. The ope ration of parting, by which gold and filver are feparated from each other, has alfo employed his laborious attempts to render it more accurate than it has hitherto been; and he here lays down a new and effectual method to prevent the inconveniencies with which this nice and difficult operation is often attended.

Mem. VI. A Report made to the Academy by the CHEMICAL CLASS, relative to the Gold that may be obtained from vegetable Earths and Afbes. This Report was defigned to terminate a difpute between the Count DE LAURAGUAIS and M. SAGE. The latter, in his Memoir read to the Academy the 23d of May 1778, gave an account of a feries of experiments. The refult was, that from an hundred pounds weight of garden vege table earth calcined, he had obtained two ounces and forty-four grains of gold, and from calcined mould one drachm and fiftyfix grains. Count LAURAGUAIS repeated the experiments of M. SAGE, and found the refults very different. Seconded by the fuffrage of two learned chemifts, whofe experiments agreed with his, he addreffed himself to the Academy, and defired they would appoint a commiffion to determine a matter which might be of great confequence, by preventing inconfiderate projectors from ruining themfelves by the expenfive purfuit of imaginary treasures. The Academy charged the Clafs of chemistry with this commiffion, and their report, inferted in this volume, exhibits a corrective to the experiments of M. SAGE, and a caution to the gold-feekers.

ASTRONOM Y.

Mem. I. In which the corrected Latitudes are applied to the Solution of feveral Geodetical Problems, and particularly to the Calcu lation of the Perpendicular to the Meridian, and of Loxodromics, on the Hypothefis of the elliptical Figure of the Earth. By M. DIONIS DU SEJOUR. This profound Aftronomer, after having hitherto applied his analytical methods to the problems which regard the determination of the celeftial motions, employs them here to the folution of thofe problems that regard the figure of the earth, confidered aftronomically. It is fully known that the earth is not a perfect sphere, but rather an oblate fpheroid, and may be confidered as a folid, formed by the revolution of an ellipfis. It is under this point of view that our Academician confiders it, after having fhewn, that the general canons he employs, may be extended to every other hypothefis, that is, to any figure which future obfervations may difcover, provided that it differ but little from a fphere. This Memoir, which contains 120 pages, is a very complete analytical theory of the figure of the earth aftro

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nomically

nomically confidered, and furnishes a new proof of the certainty, and alfo of the facility of analytical methods for the folution of aftronomical questions.

Mem. II. Concerning the Obliquity of the Ecliptic, determined by Obfervations made at the Royal Obfervatory at Paris, from 1739 to 1778. By M. CASSINI the fon. This curious Memoir is part of a great work undertaken by M. CASSINI, which is to contain a hiftory and an ample difcuffion of the aftronomical obfervations that have been made fince the royal obfervatory was founded. As feveral years muft elapfe before this work is finished, he propofes felecting from it the most interesting refults, and prefenting them to the public in the Memoirs of the Academy.

Mem. III. Second Memoir concerning the Spots in the Sun, containing different Obfervations of thefe Spots, together with the Pofitions which refult from them, and a Confirmation of the preceding refults. By M. DE LA LANDE. This is the continuation of a Memoir, prefented to the Academy in the year 1776, concerning the fpots in the fun, and the ufes that may be derived from the obfervation of them, in determining the pofition of the axis of that luminary, and the duration of his rotation. The firft part of the Memoir before us, contains an hiftorical and critical account of the first astronomers who obferved the fpots of the fun, fuch as Fabricius, Galileo, and Scheiner, who perceived them in 1611, of whom Galileo alone difcerned their real nature, and pointed out the manner in which they might be employed to afcertain the duration of the fun's rotation, and the pofition of his axis. In the following part of this Memoir M. DE LA LANDE relates and difcuffes a great number of obfervations of thefe fpots, fome anterior to his first Memoir, others which have been made fince its publication. Several of these obfervations agree with the period of twenty-five days and ten hours, which he has fixed for the revolution of the fun on his axis; but there are some which feem unfavourable to it. This difference he attributes to the changes which happen in the position or in the figure of these spots; but these changes form a real objection to his opinion concerning the caules of the fpots in the fun. He, indeed, acknowledges the difficulty, and, in the obfervation's of which he gives an account, relates equally what is favourable or unfavourable to the hypothefis of Mr. Wilson.

A fmall number of obfervations of a spot is fufficient to determine the pofition of the axis of the fun, and the duration of his rotation, so that, after fo many obfervations and researches, it may appear furprifing, that any uncertainty fhould remain on this head; but it must be confidered, that the diameter of the fun has only about thirty minutes, and that it is upon this fpace that we must judge of the variations of angles, which have an extent of 180 degrees. When this queftion fhall be decided,

fays

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