136 ANIMAL PROTEINS 



Special Qualities of Chrome Leather. A few words 

 on the special peculiarities of the leather formed by 

 chroming will not be out of place at this stage. One of 

 the greatest disadvantages of the chrome tannage has 

 been the absence of what is known as the " crust " or 

 " rough leather " stage. In chrome tanning, the finishing 

 operations have had to follow on immediately after the 

 tannage. Chrome leather, after tanning, may be dried 

 out like other leathers, but if thoroughly dried, or if kept 

 in a dried condition for any time, it will not " wet back " 

 again with water. Various suggestions have been made 

 to overcome this difficulty but none yet have found much 

 favour in practice. The discovery of the reversibility of 

 the tannage, however, ought to solve this difficulty, and 

 the author would suggest that any of the substances used 

 for " dechroming " might also be suitable for " wetting 

 in " chrome leather which has been well dried out. A 

 piece of chrome leather, dried out well after neutralizing, 

 and kept in a warm place for four years, wetted back 

 easily in ammonium acetate, in the author's laboratory. 



Another peculiarity of the chrome tannage is that any 

 defects in the raw material always seem more obvious 

 in chrome than in vegetable leather. This often necessi- 

 tates the use of a better quality hide or skin. Weak grain 

 or loose grain becomes very obvious. The presence of 

 short hair which both unhairing and scudding have failed 

 to remove also is usually more evident. 



A more serious disadvantage of chrome leather is its 

 tendency to stretch. In the case of belting leather this 

 feature is an obvious nuisance, and has inevitably led 

 manufacturers to use powerful stretching machines upon 

 the goods before they are marketed. In chrome sole 

 leather also there is a tendency to spread and throw the 

 boot out of shape. 



Further disadvantages arise from the fact that the 

 chrome tannage is an " empty " tannage. Compared with 

 the vegetable tannage, very little of the tanning agent is 

 adsorbed. Hence there is little matter of any kind between 



