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ART. I. Histoire de l'Academie, &c.-CONCLUSION of the History and Me. moirs of the Royal Academy of Sciences at Paris, for the Year 1768. Begun in the Appendix to our last Volume, Page 683.

Continuation of the CHEMICAL ARTICLE S. MEMÒIR II. On a Method of dying Silk, by Means of Cochineal, of

a bright and durable Scarlet Colour, &c. By M. Macquer.

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a very capital discovery and improvement made by that excellent chemift, in the art of dying. Drebel, a Dutch chemist, was the first who discovered the method of obtaining from cochineal, by the means of a dissolution of tin in aqua regia, a bright and solid scarlet colour, exceeding, in beauty and lustre, any that had before been produced, either by the bands of art, or even in the works of nature. Unfortunately however wooller ftuffs only, or those fabricated from animal substances of a fimilar kind, were found capable of receiving this beautiful and permanent dye. The artists, who endeavoured to apply this discovery to the dying of filk, cotton, or linnen, found, to their great astonishment, that though they employed the same ingredients, and followed the same process, the result, 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 fima plest of all tests, that of washing in water.

This fingular phenomenon, which has hitherto constantly dirconcerted the artists, who have tried many random experiments without effect, was of a nature to pique the curiosity of the cheAPP. Rev. Vol. xlvii,



mist and philofopher, who never rest when they find themselves foiled in their attempts to discover the causes of singular 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 likewise ftrongly excited to the subje&; and after many attempts, which were also unsuccessful, as they were founded on wrong principles, he has at length succeeded in the resolution of the problem : and that, by means of a very night variation in the common process, to which he was led by the tingevious experiments he made upon this occafion, and by the plausible theory which he deduced from them.

Palling over the detail here given of the steps by which he ar** rived at this discovery, we shall briefly relate the effential parts

of the process ; first premising a short view of the theory by which he was led to it.

From some of his experiments it appears that, on dropping a solution of tin in aqua regia into a decoction of cochineal, a bright scarlet precipitate, or lake, as it is termed by the painters, is formed by the earth or calx of the metal (diverted of its acid, now Jargely diluted with the water) greedily attracting, and combining itlelf with, the fæcula, or colouring matter of the cochineal. This precipitate however, on agitating the liquor, is capable of being suspended in it, and of being received into the

pores of woolen threads or stuffs immersed in it. The Author lupposed that silk 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 compacto ness of its substance or structure. He conjectured, however, that though the compound scarlet lake, or precipitate, atrea ing formed, could not be adınitted into the pores of the filk, the : colouring marrer of the cochineal, while in a state of foutis,

might probably find a ready admittance there, and unite with the solution of the tin, previously introduced into the substance of the filk: and the event justified his supposition.

He firft dipped a piece of filk into a faturated solution of tin in aqua ragia, somewhat weakened by the addition of a quantity of water, so small as to produce no precipitation of the earth of the metal. Having exprefled the liquor from the folk, and afterwards washed it in water, in order to free it from any superAuous part of the folution, he dipped it into a decoction of cochineal, quickened (as is usual in the dying of woollen cloths) with a finall quantity of cream of tartar. The filk immediately took a full and bright scarlet colour, which refifted all the tests ør proofs usually employed on wool,


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From the consequences attending this small variation in the maneuvre, the Author's rationale of it appears probable; and it seems evidently to follow, that his success was owing to the colouring process being carried on within the body of the silk. The filk, according to his theory, already containing the metal disfolved in the acid, was capable of receiving the colouring matter of the cochineal, likewise in a flate of solution ; though it could . not admit the said colouring matter into its pores, when previously united with the earth of the tin, in the form of a precipitate or lake, whose particles were too large to enter there.

We shall only further observe that, tho' the arts may bitherto perhaps have derived their chief advancement from casual or random trials of workmen, chere can be no doubt that their further improvement is principally to be expected from preconcerted experiments, that lead the way, as in the present case, to a scientific 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 singular properties of antimony, and the present very extensive use 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 interesting both to the philosophical chemist and to the physician. We cannot however even briefly specify, much less enter into any detail of the various experiments made by M. de Laflone, and here related, on this mineral substance. We shall observe, nevertheless, that the discovery of several new and fingular products, or neutral falts, having the reguline or metallic part of the antimony for their basis, has been the result of

his inquiries. The principal drift of the Author's experiments · appears to have been the discovery of a method of procuring

the most intimate solution of the active part of the antimony in the acid of tartar. In one of his processes, that concrete, united with half its own weight of the sedative salt, is thereby changed with it into a soluble tartar; three parts of wbich boiled in water with one part of the glass of antimony, dissolve the glass almost entirely, and form with it a kind of gummy salt, exceedingly foluble, and greatly preferable to the common tartar emetic. Some other preparations are likewise given, which are bere said to be more constant in their effects than the lastmentioned medicine, and even to be invariable in their operation. Among the various products described in this memoir, there is a sale of the gummy kind, formed by a solution of the diaphoretic antimony, not wholly deprived of its phlogiston, which LI 2


is said to operate as a mild purgative. The medicinal propers ties however of these new combinations remain to be accurately ascertained by further experiments and observations,

In the laft article of this class is given the analysis of a mineral water at Vaugirard, which contains nothing interefting.

ANATOM X. This class contains only one memoir, in which M. Daubeston endeavours to explain the very particular and complex mechanism, by which the act of rumination is performed by cer. tain animals; the nature of which had not yet been properly understood. At the end of this memoir the Author warmly ex. presies his disapprobation of what appears to us a very fingular pra&ice among the French husbandmen; who, with much care, and at a needless expence, house their theep in warm Atables during the winter, through the appreherfion that these animals would suffer from the cold of that feason. In order to encourage and incite them to a more rational practice, he affures them of his having a&tually kept abroad, during the whole preceding winter, by way of experiment, a fmall flocks belonging to himself; not only without injury to the Sheep, but manifestly to their advantage. He declares his intention to continue this practice for the future ; takes great pains to recommend this proposed innovation to the farmers; and seems to speak of the general adoption of it among them as an event not likely to be brought about without some difficulty !

GEOMETRY and ALGÉB R A. The first of these classes 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 short paper of M. du Séjour on an analytical subject.

ASTRONOMY. MEMOIR I. On the Elements of the Variation in the inclination of

the second Satellite of Fupiter, and of the Libration of its Nodes. By M. Maraldi.

We have given some account of the Author's former inquiries on this subject, 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 prosecute this interesting subject, and has here completed his whole desigo ; giving in this memoir the ultimate result of all his calculations, followed by a particular account of all the aftronomical observations at large, on which his determinations are foupded, and which amount to above a thousand. In this collection the time, place, ftace of the weather, name of the observer, and the magnifying power, or quality of the telescope, are distinctly specified with regard to every eclipse contained in it. He has every where compared the resulys with the tables of M. Bailly, founded and calculated on the Newtonian theory; with which they agree, exclutive 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 leas inclination of the orbit of the second satellite to that of Jupiter, at the beginning of the years 1672, 1702, 1732, and 1762, to have been nearly 2o. 48'. that its greatest inclination, at the distance 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 said inclination, and that of the node, is 30 years; and that the mean place of the ascending node is in 13° 52'. of Aquarius. On these new elements the Author has constructed 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 likewise calculated a considerable number of eclipses; wherein the small differences, almost always less than a minute, between his cale culations and actual observations, furnish a very satisfactory proof of the accuracy of the computus, and the justice 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 singular derangement or irregularity in the motion of the planec Sucurn, lately discovered by the Author. This irregularity is of fuch a nature, that it is impoflible to reconcile the ancient and modern observations on any single daypothesis, or to make them correlpond to the same tables. Nevertheless, as it is necessary to have exact tables of this planet, both on account of che calculating ephemerides in general, as well as for the particular purpose of finding the longitude at sea, by taking the disa tance of the moon from this planet, as from a known point, M. de la Lande has constructed tables, which are here given, formed on certain new elements, and founded on particular data or affumptions. These, he affirms, represen; the opposi tions of Saturn, for 30 years past, with such precision, that the calculations founded upon them do not differ from actual ob servations a fingle minute. Their accusacy may likewise, he adds, safely be depended upon, as to all the common purposes of astronomy, for some years to come. This is the utmost that can be expected in the present case; as neither the period, the laws, or the cause of this irregularity are yer known or as. counted for.

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