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into the country; fince that period its ufe hasbecome more and more general, not only inEurope , but in various parts of Afia, and as al-moft the whole of this valuable commodity isftill raifed in Mexico, Peru , and the adjoiningSpanilh fettlcments, it becomes every year anobject of more fedulous cultivation than before.
The wild cochineal (gratia fylveftra) feedsUpon mold of the fpecies of cacti that are na-tives of Mexico , requires no particular care orattendance, and may be gathered fix times inthe year, there being fo many generations ofthis infect in a twelvemonth: the time of col-letting the cochineal is juft before the femaleproduces its young, as the animal perilhes im-mediately afterwards. The cultivated cochineal(grana fina) is fuppofed to have originated fromthe wild kind: but this opinion appears verydoubtful. If it be granted that the fuperior fizeof the former, and its want of thofe long whitehairs or down which cover the latter may bethe effedt of domeftication, there ftill remaintwo other diftindtive characters which appearto be original; thefe are, its feeding only uponone fpecies of cactus, the cochenillifer, or nopal,and its producing only three broods or gene-rations in the year. The management of thecochineal infect is fimple, but requires incef-fant attention. At the third annual gatheringof cochineal a certain number of females areleft adhering to branches of the nopal, whichare then broken off and kept carefully undercover during the rainy feafon; when this Isover, the flock of cochineal thus preferved byeach cultivator is diftributed over the wholeplantation of nopals, where they foon multiplywith great rapidity. In the fpace of twomonths the firlt crop is gathered by detachingthe infedts with a blunt knife, after which theyare put into bags and dipped in hot water tokill them, and finally dried in the fun, bywhich they lofe about two-thirds of theirweight. The proportion of colouring mattercontained in equal portions of the cultivatedcochineal, the wild cochineal of Mexico and aninferior kind from St. Domingo, is as eighteen,eleven, and eight. 1 The average quantity offine cochineal annually confumed in Europe amounts, according to Dr. Bancroft, to 600,000lbs. When thoroughly dry it experiences nochange from long keeping in clofe packages:Hellot affirms that he ufed fome which was 130years old, and found it as good as if it hadbeen quite frefh.
The colouring matter of cochineal may be* Bcrthollet on Dying, II. p. 169.
extradted either by water or. alcohol. The al-coholic folution is of a deep crimfon colour,and on .evaporation leaves a tranfparent refidu-um of a deep red, which has the appearance ofa refin. The aqueous folution or decodtion ofcochineal is of a violet crimfon colour, and thisif evaporated flowly to the confidence of anextradt, and then digefled in alcohol, com-municates to this menftruum a colour fimilarto the preceding fpirituous folution, a refiduumof the colour of wine lees being leit behind.
The aqueous decodtion of cochineal if mixedwith a little fulphuric acid affunies a red colour,inclining to yellowifh, and a fmall quantity of afine red precipitate is thrown down. Muriaticacid produces nearly the fame change of colour,but occafions no precipitate. A folution oftartar changes the cochineal decoction to a yel-lowifh red, and a fmall quantity of a pale-redprecipitate is flowly deposited: the fupernatantliquor is yellow, but on the addition of a little'alkali it becomes purple, the precipitate beingat the fame time rediffolved. Alum brightensthe colour of the infufion and gives it a redderhue -, a crimfon precipitate is depofited, and thefupernatant liquor retains a fimilar tinge. Amixture of alum and tartar produces a brighterand more lively colour, inclining to yellow : aprecipitate is thrown down, but much palerand Iefs in quantity than where alum alone isufed. Nitrio-muriat of tin throws down a co-pious crimfon fediment, not a particle of colour-ing matter remaining in the liquor. Sulphatof iron forms a brownifh-violet precipitate, andthe fupernatant liquor is of a dilute yellowifh-brown. Sulphat of zinc forms a deep violet,and acetite of lead a purple-violet precipitate,the liquor in both cafes being perfectly colour-lefs. Sulphat of copper changes the colour ofthe decodtion to violet, and a fmall fediment ofthe fame colour very flowly fubfides.
Cochineal is ufed either as the bafis of thatfine pigment called carmine and lake-red, or asa dying drug to tinge wool and filk, either fear-let or crimfon, or the finer kinds of violet.
The preparation of carmine and lake-red isfo valuable a procefs, and one fo eafily keptfecret, and its perfection depends fo much onnicety of manipulation, that none of the pub-Iifhed methods in all probability will afford itof the very belt quality. The following is per-haps the beft of thofe which have yet beenmade public, and if carefully purfued will yielda pigment greatly fuperior to the carmine thatis generally met with. 1 *
* Alyoa Cours dc Chimie, II. p. 174,