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DYEING AND CALICO PRINTING.

conditions of the atmosphere and daylight, but nothing quite definite is knownin this respedt.

Carmine-lake is a substance of a beautiful red colour, and is obtained bythe addition of an alkali to a deco&ion of cochineal mixed with alum. Thissubstance was known before cochineal was discovered, and was made atFlorence from kermes,—hence the name of Florentine lake, still in use.Cochineal is also met with in commerce in the state of cake. Although veryrarely thus brought to Europe, a parcel reached France some years ago fromCordova, in South America: it was in the shape of solid, round, shiny, deepred-coloured cakes, containing five-sixths of the ordinary colouring matter ofcochineal; the rest consisting of broken-up pieces of the inseft (Coccus Cacti)mixed with vegetable matter.

Without being in the least adulterated, cochineal differs in richness ofcolouring matter, according to its origin. Sometimes parcels reach theEuropean market which have been partly exhausted with boiling water andre-dried: this fraud is always accompanied by the loss of the naturally-adhering down of the insedl, and in order to reproduce the appearance thereofthe inse&s are, before, being quite dry, placed in casks along with some whitepowder or other,—as, for instance, white lead, sulphate of* baryta, or Frenchchalk. In order to detedt this sophistication it is only requisite to place thecochineal in cold water for some time, when such adhering powders willbecome detached, sink to the bottom of the vessel, and may be analysed afterdecantation of the water. Partly exhausted cochineal is always more deeplywrinkled, and does not, when placed in water, take up moisture equally; aportion of the insetts (grains, as they are termed by the brokers) float, andothers become only partly submerged. Various methods have been proposedfor determining the richness of cochineal in colouring matter. M. Robiquetdoes this comparatively in the following manner :—One part by weight ofcochineal is five times successively exhausted with water, and the solutionsobtained are decolourised by a solution of io parts of bleaching-powder: thismethod is obviously faulty, for the good reason that the decoftion of cochinealcontains other organic matters beside the colouring material, and the oxidisingadtion of the hypochlorite of lime is partly expended upon these substances.By Anthon’s method a known volume of a solution of alum is applied to pre-cipitate completely a decodtion of cochineal, and a standard sample of thatware is used for comparing the results. Penny’s method is based upon theready oxidation of the colouring matter of cochineal (carminic acid) by thered prussiate of potassium (ferricyanide) in the presence of an alkali; i grm.of pulverised cochineal is dissolved in 36 grms. of a weak solution of causticpotassa; this solution is diluted with 24 grms. of water, and there is nextadded by drops a standard solution of ferricyanide of potassium, containing5 grms. of that salt to the litre of water, until the purplish-red colour of theoriginal solution be converted into a brownish-yellow.

Since carminic acid is completely precipitated by neutral acetate of lead,M. Bloch proposes the use of a standard solution of that salt for estimatingquantitatively the acid alluded to ; unfortunately the reagent proposed precipi-tates a variety of other substances likewise.

Those who apply cochineal for dyeing test its goodness by a dyeing process,executed on the small scale, as for madder, taking 1 grm. of the ware; or they