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Hiftoire de l'Academie, &c.-CONCLUSION of the Hiftory and Memoirs of theRoyal Academy of Sciences at Paris, for the Year 1768. Begun in the Appendix to our laft Volume, Page 683.
Continuation of the CHEMICAL ARTICLES.
MEMOIR II. On a Method of dying Silk, by Means of Cochineal, of a bright and durable Scarlet Colour, &c. By M. Macquer.
HIS Memoir of Mr. Macquer's contains the hiftory of
T a very capital discovery and improvement made by that
excellent chemift, in the art of dying. Drebel, a Dutch chemist, was the first who difcovered the method of obtaining from cochimeal, by the means of a diffolution of tin in aqua regia, a bright and folid fcarlet colour, exceeding, in beauty and luftre, any that had before been produced, either by the hands of art, or even in the works of nature. Unfortunately however woollen ftuffs only, or those fabricated from animal fubftances of a fimilar kind, were found capable of receiving this beautiful and permanent dye. The artifts, who endeavoured to apply this difcovery to the dying of filk, cotton, or linnen, found, to their great aftonishment, that though they employed the fame ingredients, and followed the fame procefs, the refult, with regard to filk particularly, was nothing more than the production of a weak and dirty colour, resembling that of the lees of wine, or the skin of an onion; and which would not stand the fimpleft of all tests, that of washing in water.
This fingular phenomenon, which has hitherto conftantly dif concerted the artifts, who have tried many random experiments without effect, was of a nature to pique the curiofity of the che LI
APP. Rev. Vol. xlvii.
ift and philofopher, who never reft when they find themselves foiled in their attempts to discover the causes of fingular appearances. Accordingly M. du Fay and M. Hellot, who had long been employed, by order of the French ministry, in the improvement of the art of dying, have laboured, though ineffectually, to clear up this chemical difficulty. The atten tion of the Author was likewife ftrongly excited to the subject; and after many attempts, which were alfo unfuccefsful, 25 they were founded on wrong principles, he has at length fucceeded in the refolution of the problem: and that, by means of a very flight variation in the common procefs, to which he was led by the ingenious experiments he made upon this occafion, and by the plaufible theory which he deduced from them. Paffing over the detail here given of the fteps by which he arrived at this difcovery, we fhall briefly relate the effential parts of the process; firft premising a fhort view of the theory by which he was led to it.
From fome of his experiments it appears that, on dropping a folution of tin in aqua regia into a decoction of cochineal, a bright fea let precipitate, or lake, as it is termed by the painters, is formed by the earth or calx of the metal (divested of its acid, now largely diluted with the water) greedily attracting, and combining itself with, the facula, or colouring matter of the cochineal. This precipitate however, on agitating the liquor, is capable of being fufpended in it, and of being received into the pores of woollen threads or stuffs immersed in it. The Author fuppofed that filk did not acquire a proper dye from the fame liquor, because the particles of this precipitate were too large to be received into its pores, on account of the compactnefs of its fubftance or structure. He conjectured, however, that though the compound fcarlet lake, or precipitate, alreay ́formed, could not be admitted into the pores of the filk, the colouring matter of the cochineal, while in a flate of folution, might probably find a ready admittance there, and unite with the flution of the tin, previously introduced into the fubftance of the filk: and the event juftified his fuppofition.
He firft dipped a piece of filk into a faturated folution of tin in aqua regia, fomewhat weakened by the addition of a quantity of water, fo fmall as to produce no precipitation of the earth of the metal. Having exprefled the liquor from the filk, and afterwards wafhed it in water, in order to free it from any fuperAuous part of the folution, he dipped it into a decoction of cochineal, quickened (as is ufual in the dying of woollen cloths) with a finmall quantity of cream of tartar. The filk immediately took a full and bright fcarlet colour, which refifted all the tests or proofs ufually employed on wool.
From the confequences attending this fmall variation in the manæuvre, the Author's rationale of it appears probable; and it feems evidently to follow, that his fuccefs was owing to the colouring process being carried on within the body of the filk. The filk, according to his theory, already containing the metal diffolved in the acid, was capable of receiving the colouring matter of the cochineal, likewise in a state of felution; though it could not admit the faid colouring matter into its pores, when pre.viously united with the earth of the tin, in the form of a precipitate or lake, whofe particles were too large to enter there.
We fhall only further obferve that, tho' the arts may hitherto perhaps have derived their chief advancement from cafual or random trials of workmen, there can be no doubt that their further improvement is principally to be expected from preconcerted experiments, that lead the way, as in the prefent cafe, to a fcientific theory; which becomes, in its turn, the fruitful germ of new and useful discoveries. MEMOIR III. New Experiments and Enquiries, relating to the Combination of the concrete Acid of Tartar with Antimony. By M. de Laffone.
The fingular properties of antimony, and the prefent very extenfive ufe of the tartar emetic in medicine, which is one of its most certain and efficacious preparations hitherto known, render an enquiry both into the chemical and medicinal properties of that mineral, and of its different preparations, peculiarly interefting both to the philofophical chemift and to the phyfician. We cannot however even briefly fpecify, much less enter into any detail of the various experiments made by M. de Laffone, and here related, on this mineral fubftance. We shall obferve, nevertheless, that the difcovery of feveral new and fingular products, or neutral falts, having the reguline or metallic part of the antimony for their bafis, has been the refult of his inquiries. The principal drift of the Author's experiments appears to have been the difcovery of a method of procuring the most intimate folution of the active part of the antimony in the acid of tartar. In one of his proceffes, that concrete, united with half its own weight of the fedative fait, is thereby changed with it into a foluble tartar; three parts of which boiled in water with one part of the glafs of antimony, diffolve the glass almost entirely, and form with it a kind of gummy falt, exceedingly foluble, and greatly preferable to the common tartar emetic. Some other preparations are likewife given, which are here faid to be more conftant in their effects than the lastmentioned medicine, and even to be invariable in their operation. Among the various products defcribed in this memoir, there is a falt of the gummy kind, formed by a folution of the diaphoretic antimony, not wholly deprived of its phlogiston, which
is faid to operate as a mild purgative. The medicinal properties however of these new combinations remain to be accurately afcertained by further experiments and obfervations.
In the laft article of this clafs is given the analysis of a mineral water at Vaugirard, which contains nothing interefting. ANATOM Y.
This clafs contains only one memoir, in which M. Daubenton endeavours to explain the very particular and complex mechanifm, by which the act of rumination is performed by certain animals; the nature of which had not yet been properly understood. At the end of this memoir the Author warmly expreffes his difapprobation of what appears to us a very fingular practice among the French husbandmen; who, with much care, and at a needlefs expence, houfe their fheep in warm tables during the winter, through the apprehenfion that thefe animals would fuffer from the cold of that feafon. In order to encourage and incite them to a more rational practice, he affures them of his having actually kept abroad, during the whole preceding winter, by way of experiment, a fmall flock belonging to himself; not only without injury to the sheep, but manifeftly to their advantage. He declares his intention to continue this practice for the future; takes great pains to recommend this propofed innovation to the farmers; and feems to speak of the general adoption of it among them as an event not likely to be brought about without some difficulty!
GEOMETRY and ALGEBRA.
The first of thefe claffes contains only an addition made by M. Fontaine to his memoir on Tautochronous Curves, printed in the volume of the Academy for the year 1734; and the fecond, a fhort paper of M. du Sejour on an analytical fubject.
MEMOIR I. On the Elements of the Variation in the Inclination of the fecond Satellite of Jupiter, and of the Libration of its Nodes. By M. Maraldi.
We have given fome account of the Author's former inquiries on this fubject, in the Appendix to our 42d volume, page 503, . extracted from the volume of the Memoirs for the year 1765. Since that time M. Maraldi has continued, to profecute this interefting fubject, and has here completed his whole defign; giving in this memoir the ultimate refult of all his calculations, followed by a particular account of all the aftronomical obfervations at large, on which his determinations are founded, and which amount to above a thousand. In this collection the time, place, ftate of the weather, name of the obferver, and the magnifying power, or quality of the telescope, are diftinctly (pecified with regard to every eclipfe contained in it. He has every where compared the reful with the tables of M. Bailly, founded and cal
culated on the Newtonian theory; with which they agree, ex-. clutive of a very few exceptions. It may perhaps be agreeable just to mention the final results of this important and laborious undertaking.
M. Maraldi determines the leaf inclination, of the orbit of the fecond fatellite to that of Jupiter, at the beginning of the years 1672, 1702, 1732, and 1762, to have been nearly 2°. 48. that its greatest inclination, at the diftance of 15 years respectively, that is, at the beginning of the years 1687, 1717, and 1747, was 3° 48'. that accordingly the period of the libration of the faid inclination, and that of the node, is 30 years; and that the mean place of the afcending node is in 13°. 52. of Aquarius. On thefe new elements the Author has conftructed tables, in which are given the quantity of the libration, the true inclination, and the true place of the node, for every year of the period. By means of these tables he has likewife calculated a confiderable number of eclipfes; wherein the small differences, almoft always lefs than a minute, between his calculations and actual obfervations, furnish a very fatisfactory proof of the accuracy of the computas, and the juftice of the elements on which it is founded. MEMOIR II. On the Elements of the Orbit of Saturn. By M. de la Lande.
In the Appendix to the volume of our work, referred to in the preceding article (page 499) we announced to the public a fingular derangement or irregularity in the motion of the planet Saturn, lately difcovered by the Author. This irregularity is of fuch a nature, that it is impoffible to reconcile the ancient and modera obfervations on any fingle hypothefis, or to make them correspond to the fame tables. Nevertheless, as it is neceffary to have exact tables of this planet, both on account of the calculating ephemerides in general, as well as for the particular purpose of finding the longitude at fea, by taking the dif tance of the moon from this planet, as from a known point, M. de la Lande has conftructed tables, which are here given, formed on certain new elements, and founded on particular data or affumptions. Thefe, he affirms, reprefen; the oppofitions of Saturn, for 30 years paft, with fuch precifion, that the calculations founded upon them do not differ from actual obfervations a fingle minute. Their accuracy may likewife, he adds, fafely be depended upon, as to all the common purposes of aftronomy, for fome years to come. This is the utmost that can be expected in the prefent cafe; as neither the period, the laws, or the cause of this irregularity are yet known or ac counted for.