26 ANIMAL PROTEINS 



Drenching usually follows bating. Scudding sometimes 

 follows deliming. 



The theory of the volume and elasticity changes of pelt 

 during preparation will be better understood after consider- 

 ing the behaviour of gelatine gels (pp. 200-219). The 

 determining factors are the nett charge of hydroxyl ions on 

 the disperse phase, resulting from ionic adsorptions, and the 

 lyotrope influence of dissolved substances on the continuous 

 phase. 



In softening dried hides the swelling may be due to 

 either influence, but the latter tends to loss of hide substance 

 and the production of soft leather. 



In liming, the nett adsorption of hydroxyl ions is the 

 principal factor, but the lyotrope influence of the alkali 

 cations and of the impurities is important. Plump pelts 

 are those in which the contained water is in a relatively 

 greater average state of compression. Few substances can 

 assist plumping, but many can hinder it. In plumping all 

 lyotrope influence is objectionable, and "sharp" (pure) 

 alkali solutions are required. Mellow limes reduce elasticity 

 and plumpness by lyotrope influence. 



In bating and puering the essential change is that before 

 the process the swelling is due chiefly to adsorption of 

 hydroxyl ions, whereas afterwards it is due chiefly to a 

 composite lyotrope influence. 



REFERENCES. 



" Principles of Leather Manufacture," Procter, pp. 108-184. 



" The Manufacture of Leather," Bennett, pp. 49-113. 



"Lyotrope Influence and Adsorption in the Theory of Wetwork," 

 Bennett, J.S.L.T.C., 1920, pp. 75-86. 



"Analytical Examination of Bating," Bennett, Leather Trades 

 Review, 1911, p. 972, and 1912, p. 28. 



" The Bating, Puering and Drenching of Skins," by J. T. Wood. 



