876 COCHINEAL 



bordering on purple. The grey is owing to the powder which naturally covers the 

 insects, of which a little adheres, and to a waxy fat. The purple shade arises from 

 the colour extracted by the water in which they were killed. The grain is wrinkled 

 with parallel furrows across its back, which are intersected in the middle by a longi- 

 tudinal one : hence, when viewed by a magnifier, or even a sharp naked eye, especially 

 after being swollen by soaking for a short time in water, it is easily distinguished from 

 the factitious, smooth, glistening, black grains, of no value, called East India cochineal, 

 with which it is often shamefully adulterated by certain London merchants. The 

 genuine cochineal has the shape of an egg, bisected through its long axis, or of a 

 tortoise, being rounded like a shield 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 

 ripened its fruit, a few only being loft for brood : they are killed either by a momentary 

 immersion in boiling water, by drying upon heated plates or in ovens : the last become 

 of an ash-grey colour, 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, with the imperfect insects and fragments which pass through, are 

 sold under the name of Granillo. Cochineal keeps for a long time in a dry place. 

 Hellot says that he has tried some 130 years old, which produces the same effect as 

 new cochineal. 



We are indebted to MM. Pelletier and Caventou for a chemical investigation of 

 cochineal, in which its colouring matter was skilfully eliminated. 



Purified sulphuric ether acquired by digestion with it a golden-yellow colour, 

 amounting, according to Dr. John, to one-tenth of the weight of the insect. This 

 infusion left, on evaporation, a fatty wax of the same colour. 



Cochineal, exhausted by ether, was treated with alcohol at 40 B. After 30 

 infusions in the digester of M. Chevreul, the cochineal continued to retain colour 

 although the alcohol had ceased to have any effect on it. The first alcoholic liquors 

 were of a red verging on yellow. On cooling, they let fall a granular matter. By 

 spontaneous evaporation, this matter, of a fine red colour, separated, assuming more 

 of the crystalline appearance. These species of crystals dissolved entirely in water, 

 which they tinged of yellowish red. 



This matter has a very brilliant purple-red colour ; it adheres strongly to the sides 

 of the vessels ; it has a granular and somewhat crystalline aspect, very different, 

 however, to those compound crystals alluded to above ; it is not altered by the air, 

 nor does it sensibly attract moisture. Exposed to the action of heat, it melts at about 

 50 (122 F.). At a higher temperature it swells up, and is decomposed with the 

 production of carburetted hydrogen, much oil, and a small quantity of water, very 

 slightly acidulous. No trace of ammonia was found in these products. 



The colouring principle of cochineal is very soluble in water. By evaporation, the 

 liquid assumes the appearance of syrup, but never yields crystals. It requires of this 

 matter a proportion almost imponderable to give a perceptible tinge of bright purplish 

 red to a large body of water. Alcohol dissolves this colouring substance, but, as we 

 have already stated, the more highly it is rectified, the less of it does it dissolve. 

 Sulphuric other does not dissolve the colouring principle of cochineal ; but weak acids 

 do, possibly owing to their water of dilution. No acid precipitates it in its pure state. 

 This colouring principle, however, appears to be precipitable by all the acids when it 

 is accompanied by the animal matter of the cochineal. 



The affinity of alumina for the colouring matter is very remarkable. When that 

 earth, newly precipitated, is put into a watery solution of the colouring principle, 

 this is immediately seized by the alumina. The water becomes colourless, and a fine 

 red lake is obtained, if we operate at the temperature of the atmosphere ; but if the 

 liquor has been hot, the colour passes to crimson, and the shade becomes more and 

 more violet, according to the elevation of the temperature, and the continuance of 

 the ebullition. 



The salts of tin exercise upon the colouring matter of cochineal a remarkable 

 action. The proto-chloride of tin forms a very abundant violet precipitate in the 

 liquid. This precipitate verges on crimson, if the salt contains an excess of acid. 

 The bi-chlorido of tin produces no precipitate, but changes the colour to scarlet-red. 

 If gelatinous alumina be now added, we obtain a fine red precipitate, which does 

 not pass to crimson by boiling. 



To this colouring principle the name carminic acid has been given. It forms the 

 basis of the beautiful pigment called carmine. A very complete examination of tho 

 colouring matter of the cochineal insect has been made by Dr. Warren De La Eue. 

 See CARMINE. 



IThe carmines found in the shops of Paris have been analysed, and all yielded the same 



