Quite different properties are exhibited by sodium phenolsulphonate, which completely converts quebracho tannin into a water-soluble substance, the aqueous solution of which deposits no insolubles. The partly neutralised condensation product of phenolsulphonic acid and formaldehyde exhibits similar properties [Footnote: Grasser, _Collegium_, 1913, 521, 478.] (see later). F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat., 291, 457; Austr. Pat., 61, 057.] Neradol D is a viscous liquid, measuring about 33° Bé., which is similar to extracts of natural tannins. One of its characteristics is its phenolic odour; it is completely soluble in water, forming a clear, semi-colloidal solution, but is insoluble in all organic solvents with the exception of alcohol, glacial acetic acid and ethyl acetate, which dissolve all but its inorganic constituents. The latter owe their presence to the neutralisation of the crude Neradol with caustic soda, and are composed of sodium salts of the sulphonic acid in addition to Glauber salts. The aqueous solution of Neradol D shows properties similar to those exhibited by solutions of natural tannins and reacts as follows:--[Footnote: Grasser, _Collegium_, 1913, 520, 413.] Methyl orange Acid reaction. Barium chloride White precipitate, insoluble in HNO_3. Ferric chloride Deep blue coloration. Silver nitrate Slight opalescence. Bromine water No precipitate. Formaldehyde hydrochloric acid No precipitate. Gelatine Complete precipitation. Aniline hydrochloride Strong precipitate. The reactions with ferric chloride and gelatine should be especially noted, since they are analogous to those given by natural tannins. On the other hand, the reactions with BaCl_2, bromine water and formaldehyde hydrochloric [Footnote: Stiasny carries out the reaction with formaldehyde-hydrochloric acid as follows:--50 c.c. of the tannin solution, plus 5 c.c. concentrated hydrochloric acid and 10 c.c. formaldehyde (40 per cent.) are heated under reflux condenser for ten minutes; most natural tannins are completely precipitated (_Collegium_, 1906, 435; 1907, 52 _et_ 188).] acid prove the different chemical composition of Neradol D as compared to that of the natural tannins.