OH CH_2.OH OH OH }C_6H_4 + HO.C_6H_3{ = H_2O + }C_6H_3-CH_2-C_6H_3{ HSO_3 CH_2.OH HSO_3 CH_2.OH
OH OH CH_2.OH CH_2.C_6H_3{ }C_6H_4 + HO.C_6H_3{ = 2(H_2O) + HO.C_6H_3{ HSO_3 HSO_3 CH_2.OH | OH CH_2.C_6H_3{ HSO_3
OH CH_2.OH OH OH }C_6H_3.CH_3 + HO.C_6H_3{ = H_2O + }C_6H_2.CH_3.CH_2.C_6H_3{ HSO_3 CH_2.OH HSO_3 CH_2.OH
OH OH CH_2.OH CH_2.C_6H_2.CH_3{ }C_6H_3.CH_3 + HO.C_6H_3{ =2(H_2O) + HO.C_6H_3{ HSO_3 HSO_3 CH_2.OH | OH CH_2.C_6H_2.CH_3{ HSO_3
OH CH_2.OH OH OH }(C_10)H_6 + HO.C_6H_3{ = H_2O + }(C_10)H_5.CH_2.C_6H_3{ HSO_3 CH_2.OH HSO_3 CH_2.OH
OH OH CH_2.OH CH_2.(C_10)H_5{ }(C_10)H_6 + HO.C_6H_3{ =2(H_2O) + HO.C_6H_3{ HSO_3 HSO_3 CH_2.OH | OH CH_2.(C_10)H_5{ HSO_3
The condensation products above enumerated were tested with regard to their tanning power, both non-neutralised and partly neutralised (1:10, 1:20, and 1:30 c.c. N/10 NaOH) samples being examined. In all cases rapid tannage was observed yielding firm and soft leathers of light brown colour and varying degrees of swollenness.
Relatively to their reactions, all the products strongly precipitate gelatine, whereas only the condensation products of phenol, cresol, and xylenol derivatives give a characteristic coloration with iron salts.
The tannin contents of the non-neutralised condensation products lie between 72-80 per cent.—figures which clearly indicate the purity and efficiency of these substances.
Notable amongst aromatic acids is salicylic acid, C_6H_4.OH.COOH, which at higher temperatures is easily sulphonated with concentrated sulphuric acid; the sulphonation product represents a white solid, which easily dissolves in water forming a clear liquid. The sulphonic acid, when mixed with about one-third of its weight of water and heated to about 120° C., is easily condensed with formaldehyde. Towards the end of the reaction, considerable frothing sets in, but in spite of the high temperature required by this reaction no insoluble bakelites are formed. A reddish-brown fluid is obtained easily soluble in water, to which it imparts a brown colour. An aqueous solution of the product completely precipitates gelatine, gives a strong opalescence with aniline hydrochloride and a deep violet coloration with ferric chloride. Neutralised as usual, the product, in a 3° Bé solution, converts pelt within three days into a white, full leather of good tensile strength.