3J0

COCHINEAL.

less expensively; partly by the effect of its down, which enables it better to resist rainsand storms.

The wild cochineal, when it is bred upon the field nopal, loses in part the tenacity andquantity of its cotton, and acquires a size double of what it has on the wild opuntias.

It may, therefore, be hoped that it will be improved by persevering care in the rearing ofit, when it will approach more and more to fine cochineal.

The fine cochineal, when well dried and well preserved, should have a gray color,bordering on purple. The gray is owing to the powder, which naturally covers it, andof which a little adheres; as also to a waxy fat. The purple shade arises from thecolor extracted by the water in which they were killed. It is wrinkled with parallel fur-rows across its back, which are intersected in the middle by a longitudinal one ; tience,when viewed by a magnifier, or even a sharp naked eye, especially after being swollenby soaking for a little in water, it is easily distinguished from the factitious, smooth, .glistening, black grains, of no value, called East India cochineal, with which it is oftenshamefully adulterated by certain London merchants. The genuine cochineal has theshape of an egg, bisected through its long axis, or of a tortoise, being rounded like ashield upon the back, flat upon the belly, and without wings.

These female insects are gathered off the leaves of the nopal plant, after it has ripenedits fruit, a few only being left for brood, and are killed, either by a momentary immer-sion in boiling water, by drying upon heated plates, or in ovens: the last become of anash-gray color, constituting the silver cochineal, or jaspeada; the second are blackish,called negra, and are most esteemed, being probably driest; the first are reddish brown,and reckoned inferior to the other two. The dry cochineal being sifted, the dust, withthe imperfect insects and fragments which pass through, are sold under the name ofgrmdllo.

Cochineal keeps for a long time in a dry place. Hellot says that he has tried some130 years old, which produced the same effect as new cochineal.

We are indebted to MM. Pelletier and Caventou for a chemical investigation of cochi-neal, in which its coloring matter was skilfully eliminated.

Purified sulphuric ether acquired by digestion with it a golden yellow color, amountingby Dr. John to one tenth of the weight of the insect. This infusion left, on evaporation?a fatty wax of the same color.

Cochineal, exhausted by ether, was treated with alcohol at 40° B. After 30 infusion 5in the digester of M. Chevreul, the cochineal continued to retain color, although thealcohol had ceased to have any effect on it. The first alcoholic liquors were of a redverging on yellow. On cooling, they let fall a granular matter. By spontaneous evapo-ration, this matter, of a fine red color, separated, assuming more of the crystalline ap-pearance. These species of crystals dissolved entirely in water, which they tinged of

yellowish-red.

of

This matter has a very brilliant purple-red color; it adheres strongly to the sidesthe vessels ; it has a granular and somewhat crystalline aspect, very different, however?from those compound crystals alluded to above; it is not altered by the air, nor does 1sensibly attract moisture. Exposed to the action of heat, it melts at about thedegree centigrade (122° Fahr.). At a higher temperature it swells, up, and is deco®,posed with the production of carbureted hydrogen, much oil, and a small quantity 0water, very slightly acidulous. No trace of ammonia was found in these products.

The coloring principle of cochineal is very soluble in water. By evaporation?^^liquid assumes the appearance of sirup, but never yields crystals. It requires of (0matter a portion almost imponderable to give a perceptible tinge of bright purplish re ^a large body of water. Alcohol dissolves this coloring substance, but, as we h aV ^ grready stated, the more highly it is rectified the less of it does it dissolve. Sulphuric e - a gdoes not dissolve the coloring principle of cochineal; but weak acids do, possibly 0 - g ,to their water of dilution. No acid precipitates it in its pure state. This coloring I theciple, however, appears to he precipitable by all the acids, when it is accompanied ianimal matter of the cochineal. r th,

The affinity of alumina for the coloring matter is very remarkable. When tha . ^ e .newly precipitated, is put into a watery solution of the coloring principle, this I s 0 ^.diately seized by the alumina. The water becomes colorless, and a fine red lak e ^ ee ntained, if we operate at the temperature of the atmosphere ; hut if the liquor ccor d-hot, the color passes to crimson, and the shade becomes more and more violet?ing to the elevation of the temperature, and the continuance of the ebullition. aC tjon.

The salts of tin exercise upon the coloring matter of cochineal a remarks jjnuid.The muriatic protoxyde of tin forms a very abundant violet precipitate in m uriati cThis precipitate verges on crimson, if the salt contains an excess of acid. T ie „ e ]ati-deutoxyde of tin produces no precipitate, hut changes the color to scarlet-red. to

nous alumina be now added, we obtain acrimson by boiling.

fine red precipitate, which