128 ANIMAL PROTEINS 



to chromic salts by the organic matter of the skin itself 

 and by the greases employed in dressing. The process, 

 however, was not a commercial success. In 1881 patents 

 were obtained by Eitner, an Austrian, whose process was 

 a combination chrome and fat tannage. The chrome was 

 employed as " basic chromium sulphate " made by adding 

 common soda to a solution of chrome alum until a salt 

 corresponding to the formula Cr(OH)SO 4 was obtained. 

 Such a solution is now known to be perfectly satisfactory, 

 but at first it proved difficult to devise satisfactory finishing 

 processes, and to supplement the chrome tannage with 

 the fat tannage. 



The first undoubted commercial success in chrome 

 tanning was obtained by the process of Augustas Schultz, 

 whose patent was the now widely known " two-bath 

 process," in which the skins are treated successively with 

 a chromic acid solution and with an acidified solution of 

 " hypo " (sodium thiosulphate) . The first bath was made 

 up commercially of potassium dichromate and hydro- 

 chloric acid, so that, strictly speaking, it contained potas- 

 sium chloride also. The second bath contained, in effect, 

 sulphurous acid, which reduced the chromic acid in the 

 skin fibres to the tanning chrome salts. Free sulphur is 

 also formed in this bath and in the skin, and contributes 

 to the characteristic product obtained by this process of 

 tanning. Many minor deviations from the original process 

 of Schultz have been introduced, but the main features 

 have been unchanged, and this method of tanning is widely 

 employed at the present time for both light and heavy 

 chrome leather. In 1893 tanning by basic chromic salts 

 was revived and the use of the basic chloride was patented 

 by Martin Dennis, who offered such a tanning solution 

 for sale. The validity of the patent has always been 

 doubtful on account of the previous work of Knapp and 

 others, but the process itself was commercially satisfactory, 

 and the many variants of this and of the basic sulphate 

 tannages are now generally known as the " one-bath 

 process " in contradistinction to the variants of the Schultz 



