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DYEING AND CALICO PRINTING.

The process of ageing, as thus detailed, was in operation at Thornliebankin the autumn of 1856. About a year afterwards it began to be adopted byother printers, and now it is pretty generally used in the best arranged printingestablishments in Scotland and in Lancashire. The basic salts of aluminareadily yield to the textile fabric the excess of alumina they contain, andbecome thereby converted into neutral saturated salts. Heat and moisture, inthis case, aid the attradlion exerted by the porosity of the fibre. As regardsalkaline aluminates they are applied as mordants,—that is to say, the aluminathey contain is fixed to the fibre by (1), simple exposure to the open air, whenthe carbonic acid of the atmosphere saturating the alkali causes the depositionof alumina; (2), the cloth is passed through a very dilute acid solution, tooweak to re-dissolve the alumina, sour buttermilk being sometimes used forthat purpose in Switzerland and Holland ; (3), by causing the cloth to be passedthrough an aqueous solution of ammoniacal salt; alumina does not combinewith ammonia, which is of course hereby volatilised ; (4), by immersion in asolution of a metallic salt, the oxide of which forms an insoluble aluminatewith alumina.

The preparation of the red liquors as used for madder work has undergonea great number of variations and improvements since calico-printing anddyeing were first introduced into Europe. Many manufacturers use alum andwhite or brown acetate of lead as the chief ingredients ; others, again, applysulphate of alumina, free from iron, like that obtained from bauxite. Thealkaline aluminate is not very frequently used. There is much difference ofopinion as regards the preparation of the red liquor. According to puretheoretical views the quantity of acetate of lead should be so regulated thatall the sulphuric acid of the neutral sulphate of alumina contained in alum isprecipitated as sulphate of lead, leaving in the liquor acetate of alumina fullysaturated, and, if alum has been used, sulphate of ammonia or of potassa.There is no reason for using excess of acetate of lead so as to convert alsothe alkaline sulphates into acetates. Since this opinion was defended byM. Sebille, who advised the use of 125 parts of acetate to roo of alum, M. D.Koechlin-Schouch has put this matter to practical test, by using the samequantity by weight of alum and of water, with variable quantities of acetateof lead, when the proportions of this latter salt varied as much as from 75 to125 parts for 100 of alum, the quantity of water remaining the same. Thedyes obtained did not exhibit any difference at all. Below 75 the shadesbecame weaker, when the quantities of acetate of lead and water were leftthe same and the quantity of alum varied : it was found that the strongestmordant was formed when 3 parts of acetate to 4 of alum were used. Thetheory of M. Sebille would require 5 parts of acetate to 3 of alum. It isclear that these observations extend to sulphate of alumina as well, care beingtaken to alter the ratios; and we may therefore safely conclude that there isno need whatever to carry the double decomposition on to the point of com-plete exchange, and that a certain quantity of sulphuric acid may be left inthe liquid without fear of affedting injuriously the strength of the mordant.What is contained in the mordant prepared with 100 parts of alum and 75 ofacetate of lead cannot at present be determined with perfedt certainty. Inother words, we do not know anything certain about it. All that can be saidis, that the two acids present partake of the base in proportion to their bulk.Take the case of a mordant simply prepared with sulphate of alumina : this