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salts to this solution causes precipitation of the alumina. The carbonic acidof the air also slowly causes the decomposition of this liquor, especially if itis exposed in thin layers : most of the neutral salts, when mixed with thisfluid, precipitate the alumina, as, for instance, sal-ammoniac, the sulphates ofmagnesia and zinc, and all other soluble metallic salts. This readtion is madeuse of in the process of mordanting with aluminate of potassa, since the clothpreviously impregnated with this liquid is dunged, with the addition of someof these salts to fix the alumina, sal-ammoniac or a salt of zinc being pre-ferred. The oxide of zinc simultaneously precipitated has very little affinityfor the cloth, and is detached in washing, but any iron salt present is decom-posed and deposited in the fibres along with the alumina, and, according tothe quantity present, it dyes up with madder a dull chocolate instead of red.

Aluminate of soda is largely made and used in France, since the discoveryof 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-ashand bauxite, until a small sample taken from the fritted mass ceases toeffervesce with acids. When the operation is finished, the aluminate of sodais extracted by lixiviation with boiling water, and the solution evaporated todryness. It is a coarse powder, exhibiting a slightly greenish colour, due to atrace of vanadium. It is infusible at the highest furnace-heat, and readilysoluble in hot and cold water. Dilute solutions (sp. gr. 1-072 to 1-089= 14 and 17° Tw.) remain limpid and clear for a long time, but stronger solu-tions (sp. gr. 1-3 to 1-37 = 62° to 7i£° Tw.) deposit granular alumina, whilethe supernatant liquor contains a subaluminate and excess of caustic soda.This aluminate of soda agrees in its properties with the corresponding potassasalt.

Since bauxite is a very pure native hydrate of alumina, the aluminate ofsoda prepared with it is used for the production of acetate of alumina in thefollowing manner:—The aluminate of soda is precipitated by the addition ofa very slight excess of hydrochloric acid ; the gelatinous alumina thus obtainedis thoroughly washed with boiling water, and next dissolved in acetic acid.The percentage composition of the pure aluminate of soda is 47-21 soda and52-79 alumina; the commercial product, as met with in the French market, iscontaminated with about g per cent of impurities, due to the presence of sul-phate of soda and chloride of sodium in the soda-ash.

As regards the methods of fixing alumina upon woven fabrics, it must he ina perfect state of solution, while it is also necessary that the hydrate ofalumina should be precipitated, in the best possible physical condition, withinthe fibre of the fabrics. W. Crum found that the microscopic examination offibres mordanted with acetate of alumina and dyed, and similar fibres mor-danted with chloride of aluminium and dyed, presented differences, inasmuchas in the first instance the coloured lake, or combination of alumina andcolouring matter, was chiefly accumulated within the central canal of thefibre; in the second case, however, the periphery of the fibre only wascoloured.

Alumina can he obtained in solution—(1), in the state of a saline solu-tion of that base; (2), as a basic salt; (3), as a soluble modification of theearth itself; (4), in combination with alkali. Some of the salts of aluminacan be brought into contact with the cotton fibre without any decomposition