640

DYEING AND CALICO PRINTING.

blood is effe< 5 ted as follows :—The fresh blood is collected in circular, flat-bottomed basins with perpendicular sides, 14 inches in diameter and 4 deep,and containing about 2 gallons. In these the blood is let stand, withoutstirring, for two to six hours until coagulated. Filters are provided similarin form to the coagulating basins, but rather wider. Their bottoms andsides are pierced with holes 2.J inches in diameter. These filters are linedwith a dense, compaft cotton or linen cloth. The serum is first decantedinto the filter. The filtered serum is received into a depositing vessel. Thishas in its bottom a hole fitted with a cork through a perforation, in which aglass tube slides up and down. As long as the serum is not perfedlly clearthe upper mouth of this tube is kept above the level of the liquid, but whenall subsidence is at an end, which may be in twelve to fourteen hours, thetube is drawn down so that its upper end comes below the level of the serum.By gradually sliding the tube downwards as required the serum, as far asclear, may be drawn off with even less disturbance than by a syphon. Theclear serum is evaporated down to dryness at a very gentle heat, and mayserve instead of egg-albumen for fixing light and bright colours.

The clot is next thrown upon the filter and cut up into small pieces. Thecoloured serum which runs through is not mixed with the clear, but is receivedby itself into the subsiding vessel, and treated in the same manner asdescribed above. Its clearest portion is likewise evaporated to dryness, andserves for fixing dark and heavy shades. The blood of five oxen yields 2 lbs.of dry, colourless albumen. That of twenty sheep or thirty-four calves pro-duces the same quantity.

The majority of the pigment colours used in this style have been alreadydescribed (see p. 150), but we have yet to notice certain brown and blackcolouring matters.

Among these are —

Several metallic sulphurets.

Brown oxides and Vandyke brown.

Substances, such as Umber, Terra de Sienna, Cologne earth, &c.

Lampblack.

The black or brown metallic sulphurets have been occasionally applied totissues. Among the methods of fixing them may be mentioned the im-pregnating of the tissue with a soluble metallic salt, precipitable by sul-phuretted hydrogen. The pieces are first passed into a solution containingsolutions of lead, &c., and then are placed in an atmosphere of sulphurettedhydrogen; or the salts of such metals as lead, copper, mercury, cadmium,mixed with hyposulphite of soda, are printed on the tissue, and the lattersteamed ; the hyposulphite becomes decomposed into sulphate, and a sulphideof the metal is fixed.

Although lampblack is not used as a pigment to produce blacks, it isoccasionally employed for solid greys. The lampblack is, previously to use,thoroughly purified by washing with caustic soda-lye to remove empyreumaticmatters, and is next generally mixed with its own weight of ultramarine toobtain, by fixing with blood, a good grey ; or it may be used with ochre,chrome-yellow, and other similar substances to produce various shades.Lampblack grey resists strong chemical reagents. Its use is more general