Simand (Dingl. Polyt. Jour., ccxlvi. 133) has recommended instead of precipitation with gelatin, the use of the gelatinous tissue of bones to remove the tannin. For this purpose porous bones, such as horn piths, are coarsely powdered, and after treatment with dilute soda solution to remove the fat, are steeped in weak hydrochloric acid till all the calcareous matter is dissolved. They are then thoroughly washed, ground wet through a steel mill, washed again and dried at a low temperature; the tannin is removed more quickly than by raw hide, and the amount of gelatinous matter dissolved by cold water is a very trifling one. This method, or that with purified hide-powder, is to be recommended for scientific research, since no element capable of precipitating substances other than those absorbed by the hide is introduced, while it is not certain in all cases that saturation with salt and acidification may not remove other constituents of the liquor besides tannins. It has, however, for technical purposes the great disadvantage of requiring a much longer time for absorption of the tannin than is the case with gelatin solution, and of the process being much more difficult of execution. If hide-powder be employed, it must be moistened with a small quantity of water before adding to the infusion, and this water must be taken into account in the quantity of the filtrate employed for the titration of the "non-tannin." The digestion with the hide- or bone-powder must be continued till the filtered liquid does not give the faintest clouding with a drop of clear gelatin solution, and it is always very difficult to be sure that the tannin is so completely removed as with gelatin and salt. Hide- or bone-powder may be employed to determine the actual weight of any unknown tannin absorbable by hide, by evaporating equal quantities of the original infusion and of that freed from tannin by digestion with the powder; the difference giving the tannin absorbed. The evaporation must be conducted as far as possible in absence of air, for instance in _vacuo_, or in a current of carbonic dioxide, and the residues both dried at 212° F. (100° C.) so long as they lose weight. The amount of matter dissolved from an equal quantity of the hide- or bone-powder by water must also be ascertained and taken into the calculation. Ammoniacal solution of cupric acetate or sulphate has been employed by several chemists to remove tannin from solutions. N. H. Darton of New York, who has a large practice in tannin analysis, employs cuprammonic sulphate in the following manner.