From this extensive paper it appears that the matters chiefly used in tanning are the bark of the oak, containing from 6.04 to 4.37 per cent. of tannin according to the season, that of willows, of the elm, and the birch. The leaves of the arbutus, employed in the governments of Kasan, Viatka, and Perm, contain about 16 per cent. of tannin, while the root of wild sorrel (_Rumex acetosella_) contains 12 per cent. For removing the hair from hides, a lye made from wood ashes is still employed. The softening of the leather is effected by means of the excrement of dogs, which acts on the leather by means of the biliary acid present, which forms with soda a kind of soap. After tanning, white Russia leather is coated with a mixture of tar and seal oil. Black Russia leather is dyed with alum, extract of sanders, and ferrous sulphate. Horse hides are tanned to a great extent for sole leather.--_M. Ryloff._ * * * * * IMPURITIES IN PHOTOGRAPHIC CHEMICALS, AND TESTS FOR SAME. [Table referred to in a paper read before the Birmingham Photographic Society by G.M. JONES, M.P.S.] ------------------+---------------------+---------------------------------- SUBSTANCE | IMPURITIES | TESTS. | POSSIBLY PRESENT. | ------------------+---------------------+---------------------------------- Ammonia, | Carbonic acid | Renders lime-water milky. NH_{3} | | Molec. Wt. 17 | Dissolved solid | Residue left on evaporation. | matter | | | | Chlorides | After acidulating with nitric acid, | | it gives a precipitate with silver | | nitrate, which after washing is | | readily soluble in ammonia and | | reprecipitated by nitric acid. | | | Sulphates | After acidulating with nitric acid, | | it gives a precipitate with | | barium nitrate. | | | Lime | A white precipitate with oxalate | | of ammonium. | | | Lead is often | Black precipitate with sulphureted | present, derived | hydrogen. | from the action | | upon flint glass | | bottles | | | Nitric acid. | Traces of | After dilution it gives a H, NO_{3} | sulphuric acid | precipitate with barium nitrate. Molec. Wt.