COMBINATION TANNAGES 193 



with alum, salt and flour and dried out for sorting, and are 

 then retanned in chrome by the one-bath process, and 

 finished as usual. Closely related to this is the method of 

 " pickling " in alum and salt and then chrome tanning. 



Another case is the combined one-bath, two-bath method 

 of chrome tanning. The goods are chromed by a one-bath 

 liquor containing dichromate (say 2 per cent.), and then pass 

 into a reducing bath. There is not much advantage in such 

 procedure, however. 



From a strictly commercial point of view the " dongola " 

 and " semichrome " leathers have proved the most successful 

 combination tannages, but there seem to be possibilities in 

 combinations of the vegetable tannins with synthetic tanning 

 materials. 



Many other substances are known to tan, e.g. iron salts, 

 cerium salts, sulphur, quinones, fatty acids, the halogens, 

 etc., etc. ; hence there is always the possibility that new 

 useful combination tannages may be discovered. 



REFERENCES. 



Bennett, " Manufacture of Leather," pp. 243, 374-5. 

 Procter, " Principles of Leather Manufacture," p. 236. 



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