20 ANIMAL PROTEINS 



constituent fibrils, which fact assists very materially in obtain- 

 ing a quick and complete tannage, good weight, and a firm 

 leather. During the liming, the natural grease of the hide 

 is saponified or emulsified, which prepares for its removal 

 in scudding. L,iming is thus a complex process : the hair is 

 loosened, the hide is plumped, and the grease is " killed." 

 All these results may be hastened by the use of other 

 alkalies in addition, and most heavy leather yards assist 

 the liming by adding also sodium sulphide or caustic soda 

 or both. Sodium sulphide is a powerful depilatant, and will 

 alone unhair hides easily in strong solutions even in a few 

 hours. As in solution it forms caustic soda by hydrolysis, 

 it possesses also the powerful plumping and saponifying 

 powers characteristic of the latter. The addition of arsenic 

 sulphide (As 2 S 2 ) (realgar) to the lime when slaking causes 

 the presence of calcium sulphydrate in the lime liquors thus 

 made. This is also a powerful depilatant, but not much 

 used for heavy leather. 



The function of the lime in depilating is complex and 

 has occasioned much discussion. Its main purpose, how- 

 ever, is that of a partial antiseptic. When hides putrefy, 

 one of the first results is that the hair is loosened. In 

 America depilation by " sweating " is carried out com- 

 mercially by such a mild putrefaction, the lime liquor 

 permits a similar fermentation at a slower rate, and all 

 tannery lime liquors are swarming with putrefactive bacteria. 

 I/iming is thus a safer method than sweating, which may be 

 easily carried too far. Various workers have isolated 

 specific organisms Wood a bacillus, Schmitz-Dumont a 

 streptococcus but it seems highly probable that the 

 limeyard bacteria are just the common organisms of putre- 

 faction sorted out or selected by the exact nature of the 

 liquor and the method of working the limes. Many putre- 

 factive bacteria are very adaptable and could easily ac- 

 commodate themselves in this way. It is known that the 

 exact nature of the culture-medium has a great influence 

 on the rate of development of such organisms, and which 

 particular species thrive and obtain predominance in any 



