24 ANIMAL PROTEINS 



pelt, or at any rate on the surface of the hide. This is a 

 preparation for the tan liquors. All the tannins and many 

 associated substances darken rapidly with oxidation when 

 in alkaline solution, so that to place the fully limed hide 

 in a tan liquor would give a dark-coloured leather. A 

 short insertion in a bath of weak acid would secure the 

 elimination of surface lime and the disappearance of this 

 difficulty, but there are other purposes in deliming. The 

 more completely lime is removed the more the plumped 

 pelt " falls " into a soft, pliable, unswollen and relaxed 

 condition, and this change assists very materially in the 

 production of a soft dressing leather, suitable for boot 

 uppers, bags, etc. For such leathers, therefore, the deliming 

 must be much more complete than for sole leather, in which 

 the object is to obtain a firm and plump leather. 



In the case of the softer dressing leathers, experience 

 indicates the advisability of allowing some further bacterial 

 action on the interfibrillar substance in order to produce 

 the requisite pliability and softness. This is secured by 

 " bating " the hides. This process consists in immersing 

 the goods into a cold fermenting infusion of hen or pigeon 

 dung. The infusion is made in a special tub or pit \\ith 

 warm water and allowed to stand for a day or two until 

 the fermentation has commenced, and then run into the 

 bating pit through a coarse filter such as sacking. The 

 hides are immersed for some days, but are handled fre- 

 quently to ensure an even effect. The bate is always 

 slightly alkaline. The caustic alkalinity increases rapidly at 

 first owing to the diffusion of caustic lime, then at a slower 

 rate, afterwards slowly declining. This is explained by the 

 production of organic acids, and their salts with weak bases 

 from the dung infusion by the action of bacteria. The total 

 alkalinity of the bate liquor increases rapidly at first owing to 

 the diffusion of lime and its liberation of organic bases, then 

 very slowly, but towards the end of the operation the total 

 alkalinity increases very rapidly indeed, owing probably to 

 the commencement of a violent anaerobic fermentation which 

 produces ammonia and other organic bases, and which 



