is obtained, when the whole may be made up to one hundred parts, and will be approximately of the same strength as a 10 per cent. solution of chrome-alum. A little heat may be needed to start the reaction, but too much should be avoided, as considerable heat is evolved by the oxidation; and as much carbonic anhydride is produced, which causes the solution to effervesce briskly, the vessel used should be of ample size. In place of cane-sugar, a good quality of glucose may be used, but some samples contain some impurity which produces a violet solution which will not tan satisfactorily. This liquor is in regular use in many tanneries, producing a good quality of chrome calf, but is somewhat variable in its effects according to the temperature employed in its preparation, and it appears to have no real advantage over a simple solution of chrome-alum, rendered basic by soda and with some addition of salt. A somewhat similar preparation is Eberle’s “chromalin,”[122] in which some organic substance, probably crude glycerine, is used to reduce the bichromate. The organic matters, and especially the organic acids which result from the oxidation of the sugar or glycerine, are not without influence on the tanning properties of the liquor. Of course these solutions may be rendered still more basic by the addition of sodium carbonate. A good stock-liquor, of approximately the same strength as that above described, is made by dissolving 10 parts of chrome-alum in 80 parts of tepid, but not hot water,[123] and adding with constant stirring a solution of 2¹⁄₂ to 3¹⁄₂ parts of washing soda in 10 parts of water. The chrome alum dissolves somewhat slowly without the aid of heat, and the solution is best made either in a small drum driven by power, or by suspending the crystals in a basket near the surface of the liquor, so that the saturated solution can descend. [120] Martin Dennis, U.S.A. Pat. 495028, 1893; and 511411, 1893, 7732, 1893. E. Pat. Gallagher. [121] Leather Trades Review, Jan. 12, 1897. [122] Compare Eberle’s German patents, 119042, 1898, and 130678, 1899. The last of these appears to be anticipated, at least as regards the use of glucose, sugar and starch, by the writer’s publication in 1897 above cited. [123] Leather Trades Review. Later investigations have shown that the temperature of the water is unimportant if alkali be added, but chrome-alum dissociates to some extent in hot water, and comparative experiments have shown that solutions of the normal salt made with the aid of heat act on skin as if more acid than those made in the cold.