HEAVY CHROME LEATHERS 171 



liming should be about identical, but the hides for chrome 

 are generally given more sulphide and the depilation is 

 reduced to about a week. The methods used for deliming 

 differ widely in different factories. Some delime com- 

 pletely with mineral acids, some even pickle in acid and 

 salt, whilst others merely delime the grain with boric acid. 

 The last is really quite sufficient. Again, in tanning one 

 finds similar divergences of method. Drum tanning is 

 practised, but tannage in pits by suspension is more usual, 

 though, as this last involves more dilute liquors, it involves 

 also greater time to tan. In drum tannages a few days 

 only are sufficient. In pit tanning at least a week is given, 

 but sometimes up to a month, according to the strength 

 of the final liquor and the rate of progress of the goods 

 into stronger liquors. L/iquors containing over I per cent, 

 of chromium may easily be spent out so as to contain only 

 O'Oi per cent. L,abour and time are saved in pit tanning 

 by the use of rockers. The press system of avoiding 

 handling, however, so complicates the analytical control 

 that its advantage is doubtful, a better way being to shift the 

 liquors by an air ejector, which may also be used as an 

 agitator of the liquor and thus abolish the need for rockers 

 ("Forsare" patent). Chrome butts are tanned out in 

 suspension. No floats or layers are used. The neutralization 

 need not be so thorough as for light chrome uppers, as dyeing 

 is not practised and trouble^doesj[notjarise*with*emulsions 

 made from sulphonated oils. Thorough washing is advisable, 

 and the butts are usually then cut into bends and may 

 be oiled before drying if desired. The bends are dried 

 strained, to obtain flatness and smooth grain, for no 

 machines, such as strikers and rollers, are usually employed. 

 It is necessary to dry very thoroughly, for the bends are 

 waterproofed by dipping the dry leather into molten waxes. 

 The most commonly used wax and the cheapest is paraffin 

 wax with a m.p. of about 127 F. It is rather a brittle 

 wax, however, and as the finished leather consists of up 

 to one-third of the wax, it is better to use at least some 

 proportion of hard fat, Japan wax or ceresin wax, to 



