Studies have been made on the utilization of humus, a by-product of acid hydrolysis of soy bean cake in the glutamic acid industry, and also of lignin, a by-product of acid saccharization of wood. Experiments have been carried out on the preparation of tanning material, with the following results: when humus or lignin was oxidized with HNO
3 or Cl
2, both turned to reddish brown in color; after washing with water, dissolved in dil. alkali, flltered, and brownish yellow precipitates were formed when acidified.
These precipitates contained more than 74% of tanning constituents estimated by the hide powder method. Larger parts of these tanning materials were considered to be humic acid and hymatomelanic acid. The tanning power of these materials were improved by 11_??_6% when treated with chemicals such as phenol, cresol, Na-
p-phenolsulfonate, and β-naphthalensulfonate, in this order. Fairly good results had already been obtained in the tanning experiments with these tanning materials and Japanese patents (Nos. 148583, 148653, 156022, 159894) had already been given to this preparation process.
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