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DYEING AND CALICO PRINTING.

whatsoever ensuing, so that a simple washing in cold water eliminates all thealumina taken up. This happens, e.g ., with nitrate and sulphate of aluminaand with alum. Whenever it may be desirable to apply such salts for thepurpose of mordanting cloth it is necessary to pass the cloth, after it has beenimpregnated with the aluminous solution, through a bath containing sub-stances capable of precipitating within the fibres either hydrate of alumina orat least an insoluble basic salt of that base. Some of the salts of aluminaare decomposed by moist heat (steam), thereby giving up to the fibres of thecloth the whole or a portion of the alumina, or becoming converted into abasic salt. The acid set free is volatilised, or leaves the tissue. Thechloride, acetate, and hyposulphite of alumina are salts of this description.These salts become fixed by exposing the saturated tissues to a warm andmoist atmosphere. This result is not simply a dissociation of the constituentelements of the salt, but the intervention of the water is absolutely requiredfor the formation of the hydrate of alumina. The action is therefore to beconsidered as a saponification, in the more extended sense of this word asunderstood by chemists.

It is here the proper place to give a few particulars concerning theprocess just mentioned, and known as “ ageing.” The mordants generallyused for madder styles are the pyrolignites, or acetates of iron and alumina,which under the influence of ageing—which we are about to describe—are sodecomposed as to leave on the cloth either an insoluble oxide or a sub-salt,which becomes the intermediate agent for fixing on the fabric the colouringmatters of madder. The fixing of mordants by ageing was first pradticallycarried out by Mr. Walter Crum, an eminent and highly scientific calico-printer. On the proper ageing of printed goods, says Dr. Schunck, dependsin a great measure the success of many styles. Should a room be too hot ortoo dry, imperfect fixation of the colour ensues, and meagre and uneven tintsare obtained in the subsequent operations. To give some idea of the im-portance of this step in calico-printing, we may here state that “ ageingrooms,” as they are called, are in several print-works of enormous dimensions,and generally constitute a separate building. Those of Messrs. EdmundPotter and Co. and Messrs. T. Hoyle and Sons, all at or near Manchester,may be particularised as forming quite a feature in their works. The processof ageing in calico-printing is that by which a mordant, after being applied toa cotton fabric, is placed in circumstances favourable to its being completelyincorporated with and fixed in the fibre. It has generally been found desirablethat calico printed with a mordant should, before dyeing, be exposed to theatmosphere for some time in the ageing room, in single folds, which, generallyspeaking, requires several days, the objedt being to liberate the acetic acidfrom the acetates of iron or subacetates of alumina, and to oxidise theprotoxide of iron. It was for many years believed that oxygen was the onlynecessary agent; and although some printers had observed that moisturefacilitated the process, this fadt was not generally known until Mr. J*Thom, of Manchester, claimed the introdudfion of moisture as an importantagent in the process of ageing, in a patent which he took out in 1849.Mr. Walter Crum was, however, the first printer who applied this principlepradtically. He describes the process as adopted at Thornliebank (nearGlasgow) in the following words :— A building is employed 48 feet long