22 ANIMAL PROTEINS 



will unhair, and sulphides will also unhair without lime or 

 bacteria, but in the limeyard all three agencies are at work. 

 Putrefactive fermentation, however, obtains a good start. 

 JSrobic fermentation commences with the slaughter of the 

 animal, and the anaerobic organisms soon commence their 

 part, and are at work in the hide house and soaks. On 

 entering the limes, the purely chemical hydrolytic action 

 of lime is added to that of the bacterial enzymes as well 

 as the action of lime as bacterial assistant, and the three 

 continue to operate side by side. Each gives rise to the 

 formation of calcium sulphydrate, whose own special 

 solvent effect is superadded. If sulphydrates be deliberately 

 added to the liquors there is yet another factor assisting. 

 Speaking broadly, the bacterial enzymes have their maxi- 

 mum activity in the old limes, and the chemical action of 

 sulphydrate formed from the keratin cystine is also at a 

 maximum in these liquors. The chemical action of added 

 sulphide, and the simple hydrolytic action of calcium 

 hydrate have their maximum activity in the new limes. 

 Most observers would agree that in practice the bacteria 

 shoulder the greater part of the work. 



From the limeyard is^taken about the only waste bye- 

 products of the tannery, viz. the residues from the soak 

 and lime pits. These consist mainly of lime and chalk, with 

 some hair and dung, and possibly a little sulphide. The 

 sludge possesses some value as a manure, especially if from 

 the soak pits on account of the greater nitrogen content. 

 (Part VI., Section I.) 



The Beam House Work consists in the mechanical 

 removal of those parts of the hide not wanted for leather 

 manufacture. Unhairing removes the hair and the epider- 

 mis made loose in liming. The hides are placed over a 

 sloping " beam " with a convex surface, and the hair 

 scraped off with a blunt concave and double-handled knife. 

 The hides are then thrown into a pit of water. The hair 

 is carefully collected, washed well with water, preferably 

 centrifuged, and then dried out by a current of warm air. 

 It forms a valuable bye -product. White hair is usually 



