548

DYEING AND CALICO PRINTING.

water in alcohol, ether, &c. At full redness the sulphate of copper is decom-posed, the oxide of copper remaining in the form of a black powder.

Sulphate of copper is often found to be impure. The protosulphate of iron(copperas) is capable of crystallising along with blue vitriol, in a very consi-derable proportion, without any alteration in its form and colour. To detedtthe presence of iron the solution is boiled with a little nitric acid, and anexcess of ammonia is then added. If any iron is present, brown flocks willremain floating in the ammoniacal solution of copper. Zinc may be detected,along with manganese, magnesia, &c., by the process with sulphurettedhydrogen, as described under Nitrate of Copper. The sulphate of copper isused in resists for indigo-blues.

Copper salts have, within the last few years, met with a new application indyeing and printing aniline blacks, the sulphide being preferred by many.

The presence of copper, where not specially required, should be carefullyavoided, as its aftion is generally injurious, and even in minute traces it iscapable of modifying shades in an unexpected and puzzling manner. Withmadder it proves completely fatal, even in very small quantities. A piece ofsulphate of copper put into an indigo-vat throws it out of order, byoxidising the white indigo and sending it—in an insoluble state—to thebottom. This is a method of “ rattening,” not unknown in dye-works.

Tartar and Argols.

These substances, though not mordants, require a brief notice in addition tothe remarks made on p. 112. They occur in commerce in three principalStates,—white argol, red argol, and tartar. Good white argol is met with inflattish pieces, having on one side a distinctly crystalline texture, and on theother showing traces of the fibre of the wooden vessel in which it has beenallowed to crystallise. If a piece is broken the fraCture should look bright andcrystalline, and the bits, if shaken together in the hand, should ring likefragments of pots. Argol should melt slowly in the mouth with a pleasantlyacid, but not vinous taste. The powder should be white, faintly borderingupon pink or pinkish-grey. On the addition of dilute nitric acid no effer-vescence should be perceptible. An escape of gas shows the presence ofcarbonates, either of lime or of the alkalies. If a weighed portion of thesample is digested in dilute nitric acid, until everything soluble has been takenup, sand and organic matter will remain, and may be filtered off. Whenwashed, dried, and weighed, it should not exceed 2 per cent, though in adulte-rated samples it may reach 15 or 16. The dregs of white wines are now acommon sophistication. On drying they form small grey or reddish lumps, orclots, less brittle than argol, and without a trace of crystalline structure.This matter differs also in taste from argol, being very faintly acid.

The solution filtered from the organic matter and sand may be examinedfor other impurities. If the addition of a solution of chloride of bariumproduces a white turbidity or precipitate, sulphuric acid is present, showingthe probable existence of an alkaline sulphate (sulphate of soda) or of alumas a sophistication. It must, however, be remarked that the juice of thegrape contains a certain small amount of sulphate of potash. If the precipi-tate given by chloride of barium, however, is abundant, the sample cannot begenuine.