20

DYEING AND CALICO PRINTING .

Dr. Calvert proposes to utilise the different action exercised by mineral acidsupon vegetable and animal fibre as a means of distinguishing them in mixedtissues. When a piece of woven fabric, whose warp consists of cottonthread, is soaked in dilute sulphuric or hydrochloric acid and dried at 212 0 ,the cotton thread is readily torn asunder, whilst the woollen thread remainsas strong as before. This plan is applied on a large scale to worn-out fabriccomposed partially of wool, in order to recover the wool for use again in makingsimilar fabrics or for working up into cloth. What is now known as vegetableparchment is made by soaking unsized paper (cellulose in the state of felt) forhalf a minute in concentrated sulphuric acid, and then washing it in largequantities of water, to the last of which ammonia has been added, when itassumes the aspeCt and consistence of an animal membrane. Gun-cotton con-sists of cellulose which has been aCted upon by very strong nitric acid or by amixture of concentrated sulphuric and nitric acids. An aqueous liquid con-taining ammoniacal solution of oxide of copper in sufficient quantity willdissolve cellulose, which can, however, be precipitated from it by acids withouthaving suffered any chemical change, but with the entire loss of its organicstructure. Gun-cotton is not soluble in this reagent, which is called from thename of its discoverer, Schweitzer’s. Cellulose is blackened by fluoride ofboron, but gun-cotton is not. Caustic and carbonated alkalies do not aCt uponcellulose even when warm, either in dilute or moderately strong solutions.According to M. Schwartz, cotton tissues placed in milk of lime are per-ceptibly weakened and deprived of their tensile strength unless they are keptfrom all contact with air. When submitted to the action of concentratedsolutions of caustic alkalies either at the ordinary or a higher temperature,cellulose swells and becomes disintegrated. The action is, however slow,especially with cellulose in a very compact and condensed form and freefrom incrustating matter, as, for instance, the so-called vegetable ivory(Phytelephas macrocavpa ), an intrinsically pure and highly condensed form ofcellulose. When a mixture of cellulose and a highly concentrated solutionof caustic potash are heated in a pure silver basin to about 662°, a simultaneousformation occurs of formiate, acetate, and carbonate of potassa, with evolutionof hydrogen gas and vapours of methylic alcohol (wood spirit). Chlorine gasand hypochlorous acid (hypochlorites, bleaching-powder) in a state of aqueoussolution are not injurious to cellulose nor weakening to fibre, especially ifnot used at too high a temperature. In a more concentrated state and ata higher temperature chlorine and the above-mentioned preparations of itare highly deleterious, dissolving, burning, or destroying the celluloseentirely, and breaking up the fibre. According to Dr. Gladstone, cellulose willcombine with caustic potassa, but water decomposes the combination, whichis stable enough in absolute alcohol.

Having thus examined and pointed out the properties of cellulose, atten-tion will next be turned to those kinds of vegetable fibre which are employed ona large scale, beginning with that one which is the most important of all froma manufacturing and commercial point of view, namely, cotton.