358

DYEING AND CALICO PRINTING.

alcohol to an aqueous solution of that salt. According to Schaller, carminateof soda may be obtained in crystals from its aqueous solution ; its formula is

^Na^ 4 } Nascent hydrogen reduces solutions of carminic acid, but the

red colour returns on contact with air.

The decodfcions of cochineal behave, to some extent, differently with re-agents, this difference being due to the presence of nitrogenous substancesand phosphates. The following are the characteristic reactions of a decoCtionof cochineal:—Acids turn the colour to a yellowish-red, the fieriest shadebeing produced by oxalic acid, and cause a slight precipitate ; alkalies turnthe colour violet; lime-water gives a violet-coloured precipitate ; alum turnsthe colour first red, and then gives a precipitate ; chloride of aluminium,reddish-violet precipitate, the supernatant liquid being amaranth-coloured;chloride of tin turns the colour yellowish, forming a cherry-red precipitate;chloride of tin (as usually met with in the trade), violet precipitate ; bichlorideof tin turns the colour to scarlet; sulphate of iron gives first a violet-grey,and next a precipitate ; acetate of iron, a brown-coloured precipitate, turningto olive ; sulphate of copper and lead salts, violet-coloured precipitates;proto-nitrate of mercury, a precipitate exhibiting the colour of dregs of wine;per-nitrate of mercury, a brownish-red precipitate ; sulphate of zinc, deepviolet precipitate ; cream of tartar, salt of sorrel, and alum, yield each redprecipitates, constituting the carmine of commerce.

Ammoniacal Cochineal.—When a solution of carminic acid in ammoniais for some time left to itself a modification takes place, whereby the acidcombines intimately with the elements of ammonia, there being formed anamide or an amidated acid : this fad, long since known, has been utilised forthe preparation of a new colouring matter, termed ammoniacal cochineal, orcarminamide. This colouring matter does not produce red and scarletcolours, but violets, amaranths, and mauves, and the adtion even of oxalicacid in excess does not turn the colour of this pigment to yellowish-red.With bichloride of tin a deep violet, not a scarlet, precipitate is formed.There are met with in commerce two different kinds of ammoniacal cochineal,in cakes and in paste ; the former is prepared by digesting for three months,in a closed vessel, 3 parts of ammonia and 1 part of ground cochineal. Theliquor is decanted, and then is added to four-tenths of its weight of gelatinousalumina. This magma is evaporated in a copper basin, so as to expel allammoniacal smell, when the thickish mass is cut up into the shape of cakes,and dried. The paste is prepared in a similar manner, but the operation onlylasts eight days ; the liquor is evaporated to two-thirds of its bulk, and noalumina is added : this paste is one-third less rich in colouring matter. Dr.Schiitzenberger states that the colouring matter of the ammoniacal cochinealof commerce, and also that obtained by the diredt adtion of ammonia uponcarminic acid, contains nitrogen in another form than that of an ammoniacalsalt; and the formula of this compound is CgHgN0 4 .

The substance known as carmine is a preparation of cochineal, exhibiting avery bright red colour ; it is met with in commerce as an almost impalpablepowder, or as cakes packed in thin glazed paper or in small boxes; it is alsosold mixed up with white of egg, gelatin, or isinglass solution : the value ofthis substance depends upon various causes, but its beauty and the fineness of