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DYEING AND CALICO PRINTING .
Messrs. Brooke, Simpson, and Spiller have introduced into commerce alac-dye superior to that imported from India. Their improvement consists intreating stick-lac with weak ammonia, and adding to this solution chloride oftin, when a fine red insoluble matter is formed, and precipitates. This iscollerted, and is ready for use. These different preparations are chiefly appliedfor dyeing woollen fabrics scarlet; 2 to 3 parts produce the same effect as1 part of cochineal. In order to neutralise the influence of the alumina, alarger proportion of tin solution is required to be added to the acidified dye-liquor.
The India Museum (India Office, Westminster), contains a very completeand valuable collertion of all the substances here described, and also of variousproducts which are never met with in the European trade, belonging to thisclass of materials.
What is, or at least was, known as Polish grain, Coccus polonicus, or Polishkermes, is an insert living on the roots of the Scleranthus , a plant growingwild, in various parts of Central Europe, in a sandy soil. This insert—of thesize of a peppercorn, exhibiting a purplish-red colour—was formerly gatheredabout the middle of June, but now it is altogether forgotten, having been dis-placed by cochineal.
As far as the colouring matters of genuine cochineal and stick-lac have beeninvestigated, it appears that, if not identical, they at least agree closely intheir properties. Cochineal owes its tinrtorial properties to a red acid, solublein water. Within the body of the living insert the colouring matter is present,not in the state of solution, but as small granules grouped around a largercolourless nucleus, in state of suspension, in the midst of a colourless liquid.The insert is richest in this substance just before the period of laying eggs.This acid, though in an impure state, was first isolated by MM. Pelletier andCaventon, who called it carmine, considered it to be a nitrogenous matter, andexpressed its formula by C8H I3 N0 5 . Arppe, Warren de la Rue, and HugoMuller proved it to be an acid, and found that in a perfectly pure state it doesnot contain any nitrogen, though it is accompanied by nitrogenous matters,which render its purification very difficult. According to the authors justnamed, the pure substance in the amorphous state consists of Ci 4 Hi 4 08>Carminic acid in crystals, as obtained by Dr. Schiitzenberger, consists ofC 9 H80 5 ; but Dr. Schaller, who also obtained this acid in a crystalline state,represents this composition as CgHsOg. Dr. Schiitzenberger found, more-over, that the colouring matter exists in cochineal in two degrees of oxidation;to one of these the formula C 9 Hs0 5 belongs, and to the other C 9 Hs07»Schaller’s formula being intermediate. Schiitzenberger, however, desires thatthese researches should be taken up by some one, in order to settle this pointdefinitively.
Carminic acid may be obtained readily in the crystalline state by the fol-lowing process:—Cochineal is exhausted first with ether, which removes fattymatters, and next with boiling water. The red liquid is precipitated with neutralacetate of lead, slightly acidified with acetic acid. The bluish-violet precipi-tate which falls carries down all the colouring matter, and the filtrate is nearlycolourless. When well washed with hot water the precipitate consists chieflyof carminate and phosphate of lead, mixed with a small quantity of nitro-genous matter, a larger portion of which is found in the filtrate, which, on