50 ANIMAL PROTEINS 



The actual drying out before, after and between the 

 various mechanical operations, each have an appropriate 

 degree of wetness. In this country the drying is usually 

 under the prevailing atmospheric conditions and is known 

 as " weather drying." The goods are suspended by 

 hooks or strings or by laying over poles in special sheds 

 fitted with louvre boards by which the rate of drying can 

 be roughly controlled. Weather drying is cheap, but 

 exceedingly slow, and in unfavourable weather is very un- 

 reliable. The goods, moreover, need constant attention to 

 obtain an even result. Steam pipes are usually laid along 

 the shed floors, and are used in winter and damp weather to 

 accelerate the drying, and also in the final shed stove to 

 remove the last traces of moisture. Wet weather, however, 

 will not stand a high temperature, and steam drying is 

 better avoided when possible. Air-dried leather still con- 

 tains about 14 per cent, of moisture. Many systems of shed 

 ventilation have been suggested to hasten the drying and 

 to secure a better control of the process. In one system a 

 screw fan is fitted at one end of a shed (without louvre 

 boards) and sucks air through the goods from an inlet at 

 the other end. The air can be heated by a steam coil near 

 the inlet. In another system a centrifugal fan blows air 

 through an arrangement of pipes which distributes it to 

 the drying sheds, and discharges it close to the floor by 

 various branch pipes. The outlets are near the roof. A 

 system of dampers permits hot air, warm air and the used 

 wet air to be blended in the desired proportions. In America 

 turret drying has been used. The sheds are vertically 

 above one another and have latticed floors. Heated air is 

 admitted at the bottom and rises through the goods up the 

 building just as in a chimney. For many of the finishing 

 operations it is important to obtain the leather in a uniformly 

 half dry or " sammed " condition. This may be done by 

 careful drying, and wetting back the parts that have 

 become too dry with tepid water or weak sumac liquor, 

 and then leaving the goods " in pile" until of uniform 

 humidity. It may also be done by " wetting back " leather 



