142 ANIMAL PROTEINS 



plumped up. \Yith any method of liming, however, some 

 plumping is obtained, and this creates a problem of 

 practical importance. In the huge quantities of pelt 

 which go for chrome upper leathers, a primary considera- 

 tion is the soft, " kind," or mellow feel of the grain in the 

 finished leather. This is obtained only by tanning the 

 pelt when the grain at least is in a thoroughly deplumped 

 and inelastic condition. It is essential to delime not only 

 so that the alkaline plumping effect is completely removed, 

 but also so that no acid plumping effect succeeds it. The 

 practical problem is to decide whether, in any particular 

 instance, dung puers and bates are necessary to obtain 

 this result. Bating is clearly not very desirable, on 

 account of the length of the process, during which hide 

 substance would be lost unnecessarily, and also because 

 there will usually be a slight alkaline swelling. Puering 

 with dog-dung infusions is preferable ; it is not such a 

 long process, the liquor is just acid to phenolphthalein, 

 and the action is more intense, and by p tiering for a short 

 time only the loss of hide may be confined to the grain 

 and flesh only, whilst the desired inelasticity of grain-pelt 

 is soon obtained. Many large firms have admittedly 

 found themselves unable to dispense with puering, but 

 others have succeeded in substituting for it the use of 

 non-swelling deliming and lyotrope agents like ammonium 

 chloride and boric acid. In all cases it is futile to delime 

 or puer the grain and then allow the goods to stand until 

 the centre lime has diffused outwards. The goods must 

 pass into the chrome liquors when in the correct condition. 

 For heavy chrome leather a surface deliming with boric 

 acid is all that is necessary. Even that is superfluous 

 when the goods are to be pickled before tanning. 



Types of Two-bath Chrome-Tannage. Although the 

 original process of the Schultz patent is quite a practicable 

 one, many modifications have been introduced. These 

 modifications have been made to suit the class of goods 

 under treatment, to suit the particular mode of application 

 which is available or suitable, and to effect economies of 



