56 ANIMAL PROTEINS 



used varies enormously, and is invariably in great excess 

 of the actual requirements. " Probably 2-3 per cent, on 

 the green weight of the hides is all that can be really utilized, 

 the remainder being wasted." l This amounts to about 

 2j Ibs. lime per hide, but in practice it is more frequent to 

 find 7, 8, 9 or even 10 Ibs. per hide being used. The excess 

 is innocuous, owing to the limited solubility of lime. Some 

 excess is desirable, to replace in the liquor the lime adsorbed 

 by the goods in plumping, to assist bacterial activity (p. 21), 

 and also because in sharp lime liquors the undissolved 

 portions do not remain so long in suspension. The use of 

 sulphide and other alkalies does not " make it possible " to 

 reduce the amount of lime used, it merely renders the excess 

 more superfluous. The use of sulphide not only shortens 

 the process, but also sharpens it, on account of the caustic 

 soda produced by hydrolysis. Usually for sole leather, 

 however, it hardly sharpens it sufficiently, and it is very 

 common to add also caustic soda (or carbonate of soda) 

 to the limes. About 2 ozs. caustic soda (or its equivalent 

 in carbonate) is used per hide. The hides are limed generally 

 by the three-pit system, giving about three days in each pit. 

 They should be handled each day in the first pit (old lime) 

 and once in the other pits. 



Unhairing and fleshing by hand labour is still common, 

 in order to avoid great pressure on the plumped hide. 

 Scudding should be very light, and in some yards is entirely 

 omitted. Only the lime on the surface of the hide should 

 be removed by deliming, and this immediately prior to the 

 insertion of the butts into the tan liquor. This is to ensure 

 good colour and yet keep the butts plump. Boric acid is 

 the best for this purpose, using 10-15 Ibs. per 100 butts. 

 The goods are inserted (and preferably rocked) in a dilute 

 solution for a few hours only. About the same quantity of 

 commercial lactic acid may be substituted for the boracic. 

 This deliming can also be accomplished by adding the acid 

 to the worst suspender in the tanyard. 



To obtain firmness and plumping it is necessary that 

 1 Procter, "Principles of Leather Manufacture," p. 129. 



