534

DYEING AND CALICO PRINTING.

sulphuric acid, which, combining with the alkali, leaves the stannic acid (oxideof tin) deposited in the fibre.

In dyeing cotton yarn is extensively used for a variety of colours, especiallyfor the anilines. Its application to the warps of mixed piece goods requiresmuch caution. The sulphur present in the wool or worsted is very apt toreadt upon tin presented in an alkaline solution, thus turning the fibre an un-pleasant brownish colour. The only way of avoiding this mischief is to workat the lowest possible temperature, to make the solution very dilute, and notneedlessly to prolong the mordanting process.

Some printers consider it advantageous to form double salts of the stannicand some other acid, and to employ them in place of the ordinary stannates.Mercer and Blyth patented the arsenio-stannates and phospho-stannates ofpotash, soda, and ammonia. The arsenio-stannate of soda can be made bydissolving ij lbs. of the arseniate of soda in i gallon of stannate of sodaliquor at 50° Tw. The benefit to be derived from such admixtures or com-pounds is somewhat doubtful. In 1852 James Higgin patented an alumino-stannate to be used in place of the ordinary stannate. This alumino-stannateis prepared by adding to stannate of soda in solution, aluminate of sodaalso in solution, in such proportion that for every 14 lbs. of metallic tin in thestannate there shall be 1 lb. of alumina. The patentee proposes also to addchloride of aluminium to the chlorides of tin used in printing or dyeing.

Silico-stannates have been used experimentally, but the results wereunsatisfactory.

Alumina Mordants.

Several compounds of aluminium are highly important as mordants. Themajority of these have been incidentally described in the foregoing chapters,as potash-alum, ammonia-alum, sulphate of alumina, acetate of alumina,nitrate of alumina, muriate of alumina (aluminic chloride) oxalate of alumina,hyposulphite of alumina, &c. Tartrate of alumina is rarely used as such,but it is formed in the dye-bath whenever alum and cream of tartar are usedtogether.

Aluminate of Soda, called also alkaline-pink mordant, was formerly pre-pared when wanted by adding an excess of caustic soda to a solution of alumor of sulphate of alumina. The mixture is kept at a boil until the precipitateformed at first is entirely re-dissolved. Sulphate of soda, and, if commonalum was used, sulphate of potash, were always present. It is now sold in thesolid state, and containing very little foreign matter. As its name implies, itis used by printers as a mordant for pinks. The calico, after treatment withthe aluminate, is passed through a solution of chloride of ammonium orchloride of zinc, by the adtion of which alumina is deposited on the fibre.

Aluminate of soda is as yet little used among dyers. Though alkaline it iscapable of fixing colours upon wool, which cannot be blackened by the re-action, as in case of the stannates and plumbates. Indeed, with judiciousmanagement the aluminate of soda can be made to produce every effectderivable from alum, and, in addition, certain) others, which the latter isincapable of yielding.

Aluminate of potash is similar in its action to the soda salt, but being morecostly is rarely used. Mixed with oil it has been proposed as a mordant forcotton to be dyed with madder. The shades obtained were fast but dull.