174 MADDER 



Printing, by William Crookes, F.R.S., contains some instructive matter connected 

 with the application of mordants in the use of madder: 



' Aluminate of soda is largely made and used in France, since the discovery of the 

 extensive deposits of bauxite in the southern parts of that country. It is obtained by 

 roasting, in a reverberatory furnace, a mixture of soda-ash and bauxite, until a small 

 sample taken from the fritted mass ceases to effervesce -with acids. When the opera- 

 tion is finished, the aluminate of soda is extracted by lixiviation with boiling water, 

 and the solution evaporated to drj-ness. It is a coarse powder, exhibiting a slightly 

 greenish colour, due to a trace of vanadium. It is infusible at the highest furnace- 

 heat, and readily soluble in hot and cold water. Dilute solutions (sp. gr. T072 to 

 l'089 = 14and 17 Tw.) remain limpid and clear for a long time, but stronger solutions 

 (sp. gr. 1-3 to 1-37 = 62 to 71^ Tw.) deposit granular alumina, while the supernatant 

 liquor contains a subaluminate and excess of caustic soda. This aluminate of soda 

 agrees in its properties with the corresponding potassa-salt. See AXUMINATE OF 

 SODA ; BAUXITE. 



' Since bauxite is a very pure native hydrate of alumina, the aluminate of soda pre- 

 pared with it is used for the production of acetate of alumina in the following 

 manner: The aluminate of soda is precipitated by the addition of a very slight excess 

 of hydrochloric acid; the gelatinous alumina thus obtained is thoroughly washed with 

 boiling water, and next dissolved in acetic acid. The percentage composition of the 

 pure aluminate of soda is 47'21 soda and 52 - 79 alumina; the commercial product, as 

 met with in the French market, is contaminated with about 9 per cent, of impurities, 

 due to the presence of sulphate of soda, and chloride of sodium in the soda -ash. 



' As regards the methods of fixing alumina upon woven fabrics, it must be in a 

 perfect state of solution, while it is also necessary that the hydrate of alumina should 

 be precipitated, in the best possible physical condition, within the fibre of the fabrics. 

 W. Crum found that the microscopic examination of fibres mordanted with acetate of 

 alumina and dyed, presented differences : inasmuch as, in the first instance, the coloured 

 lake, or combination of alumina and colouring-matter, was chiefly accumulated within 

 the central canal of the fibre ; in the second case, however, the periphery of the fibre 

 only was coloiired. 



'Alumina can be obtained in solution : (1) in the state of a saline solution of that 

 base; (2) as a basic salt; (3) as a soluble modification of the earth itself; (4) in 

 combination with alkali. Some of the salts of alumina can be brought into contact 

 with the cotton fibre without any decomposition whatsoever ensuing, so that a simple 

 washing in cold water eliminates all the alumina taken up. This happens, e.g., with 

 nitrate and sulphate of alumina and with alum. Whenever it may be desirable to 

 apply such salts for the purpose of mordanting cloth it is necessary to pass the cloth, 

 after it has been impregnated with the aluminous solution, through a bath containing 

 substances capable of precipitating within the fibres either hydrate of alumina, or at 

 least an insoluble basic salt of that base. Some of the salts of alumina are decom- 

 posed by moist heat (steam), thereby giving up to the fibres of the cloth the whole or 

 a portion of the alumina on becoming converted into a basic salt. The acid set free 

 is volatilised, or leaves the tissue. The chloride, acetate, and hyposulphite of alumina 

 .are salts of this description. These salts become fixed by exposing the saturated 

 tissues to a warm and moist atmosphere. This result is not simply a dissociation of 

 the constituent elements of the salt, but the intervention of the water is absolutely 

 required for the formation of the hydrate of alumina. The action is, therefore, to be 

 considered as a saponification, in the more extended sense of this word, as understood 

 by chemists. 



'It is here the proper place to give a few particulars concerning the process just 

 mentioned, and known as " ageing." The mordants generally used 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 so decomposed as to leave on the cloth 

 either an insoluble oxide or a subsalt, which becomes the intermediate agent for fixing 

 on the fabric the colouring-matters of madder. The fixing of mordants by ageing 

 was first practically carried out by Mr. W. Crum, an eminent and highly scientific 

 calico-printer. " On the proper ageing of printed goods," says Dr. Schunck, " depends 

 in a great measure the success of many styles. Should a room be too hot or too dry, 

 imperfect fixation of the colour ensues, and meagre and uneven tints are obtained in 

 the subsequent operations." To give some idea of the importance of this step in 

 calico-printing, we may here state that " ageing rooms," as they are called, are in 

 several print-works of enormous dimensions, and generally constitute a separate build- 

 ing. Those of Messrs. Edmund Potter and Co., and Messrs. T Hoglc and Sons, all 

 at or near Manchester, may be particularised as forming quite a feature in their 

 works. The process of ageing in calico -priuting is that by which a mordant, after 

 being applied to a cotton fabric, is placed in circumstances favourable to its being 



