This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Commercial cochineal is the dried, fecundated, female insect, Coccus cacti, Linne (Phylum Arthropoda, Class Insecta, Order Hemiptera).
The cochineal insects are indigenous to Central America and Mexico, where they live upon the fleshy branches of various species of Nopalea (Cactaceoe). The production of aniline dyes has, however, largely diminished the trade in cochineal, and at the present time the insects bred in the Canary Islands form the bulk of the commercial drug.
The insects are of a bluish red colour and very minute, measuring about a millimetre in length, and the male alone is provided with wings. After fecundation the female insects rapidly increase in size and develop abundance of a red colouring matter. They are then brushed off the plants and killed either by the fumes of burning sulphur or charcoal, or by hot water or stove heat. They are then dried in the sun (during which process they shrivel to about one-third of their size) and sifted to remove foreign fragments, etc. The number of harvests varies with the climate; in the Canary Islands there are generally two.
The dried cochineal insects of commerce are about 5 mm. long, oval in outline, flattish or slightly concave on one side and arched on the other. They are transversely wrinkled and a purplish black or greyish white colour, according to the variety (see below). They scarcely show any resemblance to insects, but when macerated in water they swell considerably, and then the three pairs of legs can be discerned. They are brittle, and easily reduced to a dark red or puce-coloured powder.
Cochineal contains up to 10 per cent. of a red colouring matter, carminic acid, which is obtainable in small, red prismatic crystals; it is soluble in water, alcohol, and in alkaline solutions. The drug also contains fat (about 10 per cent. and wax (about 2 per cent.), together with albuminoids, inorganic matter, etc.
The exact methods by which commercial carmine is produced are trade secrets; the preparation contains about 15 per cent. of water, 50 per cent. of carminic acid, 7 per cent. of ash, and about 20 per cent. of nitrogenous substances. It appears to be produced by precipitating infusions of cochineal by alum, in the presence of lime salts and either albumen or gelatin.
Two chief varieties of cochineal are recognised, viz. black grain and silver grain; the former are of a uniform purplish black colour, the latter greyish white. The greyish white colour of the silver grain is usually attributed to the waxy matter that covers the insects and has not been melted by heat; it appears, however, to be largely due to inorganic matter.
Cochineal is frequently adulterated by the addition of inorganic matter such as talc, barium carbonate and sulphate (for silver grain cochineal), or manganese dioxide, lead sulphide, magnetic iron sand, etc. (for black grain cochineal). These can readily be detected by means of the ash which should not exceed 6 per cent., genuine cochineal of good quality yielding generally about 2.5 per cent. Silver grain cochineal, heavily 'dressed,' may yield up to 50 per cent. of ash.