THE MANUFACTURE OF OTHER FERMENTED PRODUCTS 559 



The de-limed or bated hides go next to the "pickle," a dilute solu- 

 tion of NaCl and H2SO4. Here the remaining Ca(0H)2 separates as 

 crystals of CaS04 and is removed. The hides are "plumped" in the 

 pickle and increase in thickness. Formerly a fermenting mixture of^ 

 bran and water was used to plump the hides, but this has been almost 

 superseded by the mineral or lactic acid pickle. 



The plumped hides go progressively through a series of "tan-pits" 

 containing each a tannin solution of increasing strength,- that of the 

 last being saturated. Tan bark is used for ordinary leather and sumach 

 or other light colored tannin material for light colored leather. A 

 lactic acid fermentation occurs in the tan pits favoring osmotic action 

 which tends to keep the hides plumped and thick. The tannin prob- 

 ably acts as a mild antiseptic, keeping down putrefaction bacteria 

 (W. V. Cruess.). 



