546

DYEING AND CALICO PRINTING.

Acetate of copper, commonly known as verdigris, occurs in commerce inseveral varieties. The common blue verdigris is a bibasic salt, formingdelicate, loose, blue scales and needles, which yield a blue powder. It con-sists of 2 (Cu0,C 4 H 3 Cu 04). It is prepared by packing wine-lees loosely incasks, with straw, till the acetous fermentation sets in. When that is endedthey are arranged in pots covered with straw in alternate layers, with alternatelayers of copper plates heated to the temperature of 40° C. These plateswhen used for the first time are previously moistened with a solution of theneutral acetate of copper and dried. At the end of about three weeks theplates are withdrawn, set upright to dry, dipped six or eight times in water inthe course of as many weeks, and again left to dry, during which operationthe verdigris continually swells up. It is then scraped off, and the plates areagain replaced alternately with fresh acid wine-lees, and the same operationsare repeated till the copper is corroded away.

Common green verdigris is a mixture of the sesqui-basic acetate of copper,with small but variable quantities of the bibasic and terbasic salts. It is pre-pared by repeatedly sprinkling copper plates with vinegar in a warm room.

In calico printing acetate of copper is used in solution, and is prepared by thedouble decomposition of sulphate of copper and sugar of lead. The followingmixture is often employed:—1 gallon of water at 160° F. ; 4 lbs. white sugarof lead ; 4 lbs. sulphate of copper. The ingredients are previously groundup, and the mixture is frequently stirred till the decomposition is complete,when the sulphate of lead is allowed to deposit, and the clear liquid is drawnoff. The respective proportions of sulphate of copper and of sugar of leadare varied in different establishments, some using 2 lbs. only, and others asmuch as 6 lbs. of sugar of lead to 4 lbs. of sulphate of copper. It is obviousthat where the smaller proportions of sugar of lead are used, the resultingsolution must contain a considerable quantity of sulphate of copper mixedwith the acetate.

The uses of verdigris are less extensive than was formerly the case. It isused in many catechu colours, in certain resists for indigo blues, and as anoxidising agent in a few steam colours. In black dyes for silks and for hats,and for printing blacks on silk goods, verdigris is also employed. Logwoodblues on wool are also dyed with an admixture of a salt of copper, generallyverdigris. The ACt George III., 20, which imposes a penalty of £20 for everypiece of cloth dyed blue by means of this process, is a curious specimen of thecommercial legislation of our forefathers, and is supposed to be still unrepealed.Verdigris figures in a great, variety of old dyeing receipts where its utility isexceedingly doubtful, or rather where its inutility has been satisfactorilydemonstrated.

Ammqmiuret of Copper.—On adding ammonia to solutions of the sul-phate, nitrate, or other salts of copper, a pale bluish-green precipitate is throwndown, which, on the addition of a larger quantity of ammonia, re-dissolves,forming a solution of an intense violet-blue. Cotton, steeped in this solution,swells up, becomes a jelly, and is finally liquefied. On the addition of anacid, however, the cotton is re-precipitated as a white powder, chemicallyunaltered, but having its fibrous structure destroyed. Dilute solutions of theammoniacal copper compound may be used for dyeing a pale green, by padding,drying, and finally washing.