which imparts a light colour to the finished leather, and conveniently covers the dark colour imparted to the leather by other tanning materials; for this reason the former are often used in the lay-aways or in the finishing processes. Similar effects to those of Neradol D are exhibited by other salts of sulphonic acids, _e.g._, sodium benzylsulphanilate (Solvenol B.A.S.F., or solution salt ("Solutionsalz") Hoechst); the author prepared mixtures of such salts and untreated quebracho extract in order to determine their solubilising effects, and arrived at the following results:-- 30 parts Solvenol plus 70 parts quebracho extract: clear solution, no deposit. 25 parts Solvenol plus 25 parts quebracho extract: clear solution, very little deposit 20 parts Solvenol plus 80 parts quebracho extract: nearly clear solution, very little deposit. 15 parts Solvenol plus 85 parts quebracho extract: slightly opaque solution some deposit. Leathers tanned with these mixtures were more or less dark coloured according to the amounts used of solvenol and the consequent solubilisation of the phlobaphenes. A similar effect, though of opposite nature from a tanning standpoint, is exhibited by sulphonates on certain colloidal dark coloured substances. A phenolsulphonic acid, which had been overheated during sulphonation and subsequently condensed (crude Neradol), imparted a conspicuous greyish-brown colour to the leather; samples of this crude product were then partly neutralised with varying amounts of alkali, and these samples (containing increasing quantities of salts) tested for tannin and colour effects. It was found that the more highly neutralised samples imparted a darker colour to the solutions, but these dark products did not deposit the dark impurities on the pelt. One may therefore assume that tannoid substances are colloidally suspended, and when converted into true solutions are incapable of being fixed in insoluble form by the pelt.