This partly neutralised sulphonic acid represents a white, pasty mass, which is not particularly easily soluble in water, yielding a solution of milky appearance. Treated with the usual tannin reagents, it exhibits the following characteristics:-- Gelatine Light Flocculent precipitate. Bromine water Compete fixation. Ferric chloride Cherry-red coloration. Lead acetate Very slight Percipitate, insoluble HNO_3. Aniline hydrochlonde Slight percipitate. Solutions of this product in concentrations from 1°-8° Bé. exerted no tanning action whatever, whereas more concentrated solutions (15° Bé.) converted pelt in eight days into a leather very similar to a Neradol D leather in colour and feel, but considerably harder. In order to determine its phlobaphene-solubilising effects, samplesof the product were mixed with concentrated quebracho extract in the proportions 5,10, 20, and 30 per cent. on the weight of extract, and the following observations made:--5 and 10 per cent. were without effect, 20 and 30 per cent. showed some solubilising tendency, but on diluting the mixture with water the quebracho was completely thrown out of solution. Apparently this anhydride is, in this respect also, quite different from the partly neutralised diphenylmethanedisulphonic acid. 2. Condensation with Sulphur Chloride When sulphur chloride is allowed to act upon phenolsulphonic acid whilst heat is applied, a yellowish-grey mass results, which dissolves in water, forming a reddish-yellow solution. Neutralised to acidity 10, it exhibits the following reactions:-- Gelatine----------------Precipitate. Ferric chloride---------Deep blue coloration. Lead acetate------------White precipitate, insoluble HNO_3. Aniline hydrochloride---Precipitate. Bromine water-----------No reaction. The partly neutralised 2° Bé. solution of this product yielded a reddish-grey coloured leather, the qualities of which were very similar to that yielded by Neradol D. 3. Condensation with Phosphorus Compounds Schiff's well-known synthesis, [Footnote: Liebig's _Ann_., 178, 173.] in which phosphorus oxychloride interacts with phenolsulphonic acid, yields a product which exhibits some tannin reactions, but which, when acting on pelt, converts the latter into a leather which, when dried, is very cracky. If, on the other hand, cresolsulphonic acid is condensed with phosphorus oxychloride by heating the two together, products eminently suitable for tanning purposes result. These products are non-crystalline bodies easily soluble in water, and are coloured bluish-violet by ferric chloride and precipitate gelatine. Solutions of the free acids and acidified solutions of the salts convert pelt into firm and white leathers possessing great softness and pliability.[Footnote: Austr. Pat, 66,895.] 4. Condensation with Aldehydes