The chloride of this compound may again be condensed, for instance, with sodium aminotoluenesulphaminobenzene-sulphonate, and yields the compound-- ---NH---SO_2--- ^ ^ ^ ---NH---SO_2--- ^ | | | | | | | | | | | | | | | | v v ---NH---SO_2--- v v CH NaSO_3 CH_3 The three latter compounds, when dissolved in water and the solution acidified, exert tanning action. It is also possible to employ mixtures of arylsulphaminobenzylsulphonic acids in acidified aqueous solution for tanning purposes. According to Ger. Pat., 297,188, such mixtures are obtained by nitrating benzylchloride and heating with an equimolecular amount of sodium sulphite; the sodium nitrobenzylsulphonate thus obtained is reduced to aminobenzylsulphonic acid with iron and acetic acid, and finally condensed with the calculated amount of _p_-toluenesulphonic chloride. A mixture _o_- and _p_-toluenesulphaminobenzylsulphonic acid [Footnote 1: Cf. also Ger. Pat, 319,713 and 320,613.] thus results. Amongst _aromatic alcohols_ the dihydric alcohols show characteristic behaviour; the latter combine with sulphonic acids with the elimination of water, condensation taking place without formaldehyde, and the resulting products being soluble in water and possessing tannoid properties. [Footnote 2: Ger. Pat., 300,567, of 20th September 1917.] In addition to phenolic mono- and disulphonic acids (and higher sulphonation compounds), the homologues, cresols, xylenols, and naphthols enter into reaction. The two components condense with great ease, liberating heat; dilute solutions (of the components) are heated to about 100° C., the process being complete in a few minutes. The products obtained are exceedingly pure and are easily crystallisable. Employing 1, respectively 2, molecules of sulphonic acid, the reactions take place according to:-- OH CH_2.OH OH OH }C_6H_4 + HO.C_6H_3{ = H_2O + }C_6H_3-CH_2-C_6H_3{ HSO_3 CH_2.OH HSO_3 CH_2.OH OH OH CH_2.OH CH_2.C_6H_3{ }C_6H_4 + HO.C_6H_3{ = 2(H_2O) + HO.C_6H_3{ HSO_3 HSO_3 CH_2.OH | OH CH_2.C_6H_3{ HSO_3 OH CH_2.OH OH OH }C_6H_3.CH_3 + HO.C_6H_3{ = H_2O + }C_6H_2.CH_3.CH_2.C_6H_3{ HSO_3 CH_2.OH HSO_3 CH_2.OH