ANIMAL PROTEINS 



pp. 55, 56). In this round the goods stay also for about 

 10 days. An alternative to the above process is to hasten 

 the earlier part of the liming by employing sodium sulphide 

 instead of realgar. More sulp hydrate may be obtained in 

 solution in this way, and the unhairing may be in about 

 half the time. The sulphide of soda also commences the 

 plumping action which follows in the next round, but this 

 alternative has the disadvantage that the skins are un- 

 haired whilst, the pelt is swollen with sulphide, which renders 

 the grain both harsh and tender and consequently more 

 liable to damage by the unhairer's knife. 



Deliming is by puering and drenching, and is often 

 associated with a further mechanical working of the goods. 

 The skins are inserted into a puer liquor at 85 F. and 

 thoroughly pulled down. The caustic alkalies should be 

 completely neutralized. A slight cut into a thick part at 

 the butt end should develop no pink colour with phenol 

 phthalein. The skins should be thoroughly relaxed, and 

 the swelling so much eliminated that they are quite soft, 

 weak and " fallen." The resilience and elasticity of the 

 plumped skins should have quite disappeared, and the 

 impressions of hand or thumb should be readily retained 

 by the pelt. The grain should appear white and possess 

 a soft and silky feel. In this condition they are again 

 worked over the beam to soften further if possible. They 

 are then rinsed and again worked over the beam. Drenching 

 follows with 10 per cent, of bran on the pelt weight, the 

 operation commencing at 85 to 95 F., and lasting till next 

 morning. The skins are next scudded thoroughly to remove 

 all dirt, but carefully so as not to damage the grain. 



In tanning, sumach and oak bark are the staple materials. 

 Sumach gives a much lighter colour, and hence it is used alone 

 for goods that are to be dyed the lighter shades, but oak 

 bark is a " faster " tannage and more preferable for dyeing 

 in those cases where blacks and very dark shades are 

 wanted. For ordinary purposes a blend is usually employed. 

 A feature of oak bark, also, is that it tends to make a firmer 

 leather, so that the proportion used must be adjusted with 



