By acidifying the concentrated solution the didepside is obtained as a white crystalline substance; a solution of which precipitates gelatine without, however, exhibiting any tanning effect upon animal hide. If, on the other hand, the above ester is converted into the chloride CH_3O.COO.C_4H_4SO_2.O.C_6H_4.SO_2Cl by treatment with PCl_5, and the chloride thus obtained further condensed with sodium phenolsulphonate, saponified, and the solution acidified, the pure tridepside HO.C_6H_4.SO_2.O.C_6H_4.SO_2.O.C_6H_4.SO_3Na is precipitated as white crystalline needles which not only precipitate gelatine, but are capable of converting animal hide into leather.[Footnote: _Chem. Ztg._, 1919, 43, 318.] Of the class of hydroxy-cymenes _thymol_, C_6H_3.CH_3.C_3H_7OH, was converted into the water-soluble sulphonic acid by warming with concentrated sulphuric acid at 50° C., the sulphonic acid being subsequently easily condensed with formaldehyde by slightly heating the mixture. The condensation product thus obtained is a viscous brown mass which is easily soluble in water, precipitates gelatine completely, gives a bluish-black coloration with iron salts, and gives a precipitate with aniline hydrochloride. To investigate its tannoid properties, the mixture was brought to the acidity 1 gm = 10 c.c. N/10 NaOH and a piece of bated calf skin was then introduced into a solution measuring about 2° Bé. After eighteen hours the pelt was nearly tanned through, and a further twenty-four hours completed the tanning process, after which a light fat-liquor was given. The dried leather was brownish-grey in colour, possessed soft and full feel and good tensile strength. On account of their importance, the three dihydroxybenzenes were examined with a view to test their suitability for conversion into tannoid substances.