If, however, 1-methylamino-4-bromanthraquinone is condensed with sulphuric acid and formaldehyde, a condensation product is obtained which is but slightly soluble in water, but which precipitates gelatine. When phenanthrequinone is heated with excess of sulphuric acid for some time, a water-soluble, reddish-yellow coloured condensation product results. The latter, when treated with formaldehyde in the cold and then finally heated, gradually fixes the formaldehyde and forms a substance soluble in water. If the heating, however, is prolonged, insoluble bakelites are formed, which are neither soluble in alkali nor in alcohol. An aqueous solution of these condensation products gives no reactions with the usual tannin reagents, though it completely precipitates gelatine. When acting upon pelt, the partly neutralised dilute solution of the condensation product pickles the former, and after a few days the pelt is converted into a light brown, full, and rather soft leather possessing good tensile strength. When the condensation product is acted upon by bromine in hot aqueous solution, an additive compound is formed and the resulting product is soluble in water. The aqueous solution of the brominated product gives no special reactions with the usual tannin reagents, but precipitates gelatine completely. Its tanning action upon pelt is much slower than that of the original condensation product; the surface of the pelt only is tanned with brown colour, the inner pelt being only pickled (light brown colour). When dried, a hard and empty leather of good tensile strength is obtained, possessing mainly the properties of a pickled pelt. CO OH ^ ^ ^ QUINIZARENE, | | | | , treated with sulphuric acid | | | | v v v CO OH and formaldehyde, yields a condensation product which is but little soluble in water and which does not precipitate gelatine. QUINOLINE, when sulphonated and condensed with formaldehyde, yields a dark coloured condensation product, completely soluble in water; the solution does not precipitate gelatine. OXYQUINOLINE exhibits similar behaviour. On the other hand, the use of _retene_ (methylisopropylphenanthrene), CH_3 ^ ___________ ^ | | | | | |___CH:CH___| | C_3H_7 v v for the production of synthetic tannins, is protected by Ger. Pat., 290,965 [Footnote 1: _Cf_ Austr. Pat., 69,194] 5. Di- and Triphenylmethane Groups