If DIPHENYLMETHANE, (C_6H_5)_2CH_2, is heated with excess sulphuric acid, a dark blue mass, easily soluble in water, is obtained. The product gently heated with formaldehyde yields a brown, water-soluble condensation product; once condensation is complete, the product will stand stronger heat. If, on the other hand, more formaldehyde is added, brown, water-insoluble bakelites are formed. The water-soluble condensation product precipitates gelatine, but not aniline hydrochloride. Dissolved in water, it possesses tannoid properties: the pelt is, however, tanned on the surface only, the intermediary layers being merely pickled; after four days in the solution, the pelt after drying was found to be converted into a greyish-brown, badly coloured leather, which was empty, hard, and possessed but little tensile strength. CARBAZOLE (dibenzopyrrole), ^ _____ ^ | | | | | |__ __| | v v v N_3 on the other hand, was found a suitable base for the commercial production of synthetic tannins; its use is protected by Ger. Pat, 290,965. TRIPHENYLMETHANE, (C_6H_5)_3CH, heated with excess sulphuric acid, yields a nearly black mass which, when condensed with formaldehyde in the cold, and subsequently heated, yields a mass which is soluble in water. With gelatine and aniline hydrochloride it exhibits reactions similar to those given by the diphenylmethane condensation products; its tanning properties also are similar to those of the latter. The resultant leather is black, but is soft and full and possesses good tensile strength. Baeyer's observation, [Footnote: _Ber_., 1872, 5, 280, 1096.] that pyrogallol on condensation with formaldehyde yields an amorphous body soluble in water, which precipitates gelatine and is very similar to tannin, was confirmed by Caro [Footnote: _Ibid_., 1892, 25, 947.] and Kahl. [Footnote: _Ibid_., 1898, 31, 114.] These investigators found that by the condensation of phenols and hydroxybenzoic acids with formaldehyde, diphenylmethane derivatives were formed; pyrogallol yields hexahydroxydiphenylmethane-- C_6H_2(OH)_3 CH_2{ C_6H_2(OH)_3 Nierenstein [Footnote: _Collegium_, 1905, 221.] repeated these experiments, and found that in addition to the insoluble diphenylmethanes, water-soluble bodies were formed, which latter precipitate gelatine. The condensation product yielded by gallic acid was identified as hexahydroxyaurinecarboxylic acid-- _C_6H(OH)_3COOH C{-C_6H(OH)_3COOH | }C_6H(OH)_2COOH O which is formed in addition to hexahydroxydiphenylmethane-dicarboxylic acid-- C_6H(OH)_3COOH CH_2{ C_6H(OH)_3COOH Baeyer's experiment with pyrogallol probaly also yields, according to Nierenstein, another compound of the following constitution-- C_6H_2(OH)_3 C{-C_6H_2(OH)_3 |_}C_6H_2(OH)_2 O Nierenstein considers these bodies confirmation of his hypothesis of the existence of a "tannophor,"--CO--, in the tannins.