CHROME LEATHER MANUFACTURE 149 



has been suggested as substitutes for hypo. Sulphides, 

 sulphuretted hydrogen, polysulphides, sulphites, bisulphites, 

 hydrogen peroxide, nitrous acid, lactic acid, etc., have 

 been used, but none are so easy to manipulate as thio- 

 sulphate. 



Types of One-bath Chrome Tannage. The one-bath 

 process is simpler than the two-bath process inasmuch as 

 only one kind of liquor is involved, viz. one in which the 

 chromium is in the chromic state. Hence the variants of 

 the one-bath process consist mainly of variations in the 

 composition of this liquor. The chief point of variation 

 is in the readiness with which chromium hydrate is adsorbed. 

 This is determined by the extent to which the chromic 

 salt is hydrolyzed to form the tanning sol and free acid, 

 and by the concentration and nature of this free acid as 

 well as of other substances. It is difficult unfortunately 

 to express these factors in terms which are comparable 

 under general conditions. Chromic salts are usually hydro- 

 lyzed to some extent, but this extent is very different even 

 in water, according to the nature of the acid radicle. The 

 degree of hydrolysis is also largely affected by the extent 

 to which the solution has been " made basic " by the 

 addition of alkalies. By the neutralization of the free 

 acid in this way there is further hydrolysis, the extent of 

 which is again influenced by the nature of the acid radicle 

 involved and other dissolved substances, especially of 

 organic matters. Again, the hydrolysis is largely affected 

 by the concentration of the solution even when the pro- 

 portions of the ingredients are constant, and this is practi- 

 cally important on account of the necessity for exhausting 

 the chrome liquors economically. Nor is the matter 

 entirely one of degree of hydrolysis, for (as we have noted 

 in the preceding section) the electrical condition of the 

 chroming sol is of great importance owing to the operation 

 of the valency rule and the possibility of zones of non- 

 precipitation. The alkaline, neutral or acid condition of 

 the goods when first introduced has also its influence on 

 all these points. 



