COCHINEAL.

311

, co l? r mg principle the name carminium has been given, because it forms the

Da Sf °* pigment called carmine.

■ihe process followed in Germany for making carmine, which consists in pouring acertain quantity of solution of alum into a decoction of cochineal, is the most simple of. > and affords an explanation of the formation of carmine, which is merely the carmi-*jium and the animal matter precipitated by the excess of acid in the salt, which has takendown with it a small quantity of alumina; though it appears that alumina ought not tohe regarded as essential to the formation of carmine. In fact, by another process, called?y ^ le name of Madame Cenette of Amsterdam , the carmine is thrown down, by pouringinto the decoction of cochineal a certain quantity of the binoxalate of potash. When car-bonate of soda is added, then carminated lake also falls down. That carmine is a triplecompound of animal matter, carminium, and an acid, appears from the circumstance thatliquors which have afforded their carmine, when a somewhat strong acid is poured intothem, yield a new formation of carmine by the precipitation of the last portions of thedoimal matter. But whenever the whole animal matter is thrown down, the decoctions,although still much charged with the coloring principle, can afford no more carmine.

Uc h decoctions may be usefully employed to make carminated lakes, saturating thea cid with a slight excess of alkali, and adding gelatinous alumina. The precipitatesbtained on adding acids to the alkaline decoctions of cochineal, are therefore trueAmines, since they do not contain alumina; but the small quantity of alumina whichjs thrown down by alum in the manufacture of carmine, augments its bulk and weight.5 gives, besides, a greater lustre to the color, even though diluting and Weakening it alittle.

The carmines found in the shops of Paris were analyzed, and yielded the same pro-Ucts. They are decomposed by the action of heat, with the diffusion at first of a veryr ° n g smell of burning animal matter, and then of sulphur. A white powder remained,°unting to about one tenth of the matter employed, and which was found to be alu-a * Other quantities of carmine were treated with a solution of caustic potash, whichI)oir ^^ sso ^ vec ^ them, with the exception of a beautiful red powder, not acted on by

a $n and concentrated acids, and which was recognised to be red sulphuret of mercurv'Vermilion. This matter, evidently foreign to the carmine, appears to have been ad-in order to increase its weight.

the ^ ^ rece ^' n 3 observations and experiments seem calculated to .throw some light onbatf art scarlet and crimson. The former is effected by employing a cochineal

which there have been added, in determinate proportions, acidulous tartrate ofknow aii< ^ n * tr o-murialic deutoxyde of tin. The effect of these two salts is now welln * The former, in consequence of its excess of acid, tends to redden the color,nt fi °t P re< ?ipitate ^ along with the animal matter; the latter acts in the same manner,c arm - “V i ts excess of acid, then by the oxyde of tin which falls down also with thete nc j me ant * animal matter, and is fixed on the wool, with which it has of itself a strongsh a{ j e nc .T to combine. MM. Pelletier and Caventou remark, that Cf to abtain a beautifulis i n ’ muriate of tin ought to be entirely at the maximum of oxvdizement; and itth e nr a state that ^ must exist in the solution of tin prepared according to

We°i^ 0r ^ 0ns P rescr ibed in M. BerthollePs treatise on dyeing.”this saltT^ See w ky> ia dyeing scarlet, the employment of alum is carefully avoided, asless to h r^ S to conver t tbe shade to a crimson. The presence of an alkali would seemv^ouldhe ^ eaie ?* The alkali Would occasion, no doubt, a crimson-colored bath; but itshould th GaS ^ case t0 res t° re l be color, by using a large quantity of tartar. We

matter anH^^ 6 ’ P rocure l ^ ie advantage of having a bath better charged with coloringpoint. £ an ^mal substance. It is for experience on the large scale to determine this^uitish > S t0 ear lhy salts, they must be carefully avoided; and if the waters be se-. Tooitl W °^ be a reason for adding a little alkali.

lo boil the^ Cr } mson ’ ^ is sufficient, as we know, to add alum to the cochineal bath, or°f l ’ n j since 0 ') 1 et C ' otb * n a ^ um water. It is also proper to diminish the dose of the saltThe alkal* 1S ^ ount ^ to counteract the action of the alum,liaisons by th' ° U ” bt to be rejected as a means of changing scarlet to crimson. In fact,°f acids. ^ lS P rocess cannot be permanent colors, as they pass into reds by the action

ain Uionia and^ ^ on G r °tthuss, carmine may be deprived of its golden shade by^ade known S fyr rr enl tleatment with acetic acid and alcohol. Since this fact wascanning. ’ -Herschel, color makj^^at Halle, has prepared a most beautiful

cochinea]. whicl/h^h’ 1 ' Ia '’ eStJ,s . ^ ustoms have lately detected a system of adulteratinghe house in Lomj aS “ e ? a • lract i se( i for many years upon a prodigious scale by a mercan-‘ appears that the^ * • ave analyzed about 100 samples of such cochineal, from whichgenuine article is moistened with gum-water, agitated in a box or