yj 



222 ANIMAL PROTEINS 



advantageous frequently to disturb or agitate the goods 

 in the lime pits. Up to ten weeks liming has sometimes 

 been given, but about three weeks is now generally con- 

 sidered sufficient, and the tendency is to shorten the time. 

 The lime and soda have also a detergent action on soiled 

 stock, and they probably assist in hydrolyzing the pigments 

 of the hair roots and sheaths. They also saponify and 

 emulsify the grease, and it is obvious, therefore, that liming can 



carried too far. Slaked lime, of course, must always be used. 



After liming the soaked, softened and plumped stock is 

 washed as thoroughly as possible. To do this it is necessary 

 to supply repeated batches of clean cold water. Some 

 manufacturers, however, use the warm water from the 

 evaporators. Wooden vats or brick pits with arrangements 

 for agitation, for draining off and for inspection, are used for 

 this purpose. The agitation may be carried out by means 

 of revolving shafts or drums with projecting curved spokes 

 or vanes. An American patent (Hoeveler's glue stock 

 washer) involves the use of a paddle wheel. It is combined 

 a settling tank to gather particles of 'stock. In the 

 washing the chalk, excess lime, dirt, etc., are quickly removed 

 and a slow deliming process is commenced. The sediment 

 from the washers and wash waters has some value in making 

 fertilizers. Deliming cannot be carried on further than 

 certain limits by water alone. Hence acid is often added to 

 finish off the process. Hydrochloric acid has the advantage 

 of forming soluble salts, but if they are not removed com- 

 pletely their lyotrope influence is to weaken the gelatine. 

 Sulphuric and sulphurous acids are even cheaper, and the 

 lyotrope influence of their salts is in the opposite sense. 

 The latter also has the advantage of destroying sulphides, 

 an important advantage for food gelatines. Whatever acid 

 is used, however, it is evident that an abundance of pure 

 cold water is the fundamental requirement of a pure product. 

 It is a sound maxim in gelatine manufacture to avoid, if at 

 all possible, the addition of any soluble substance, for it is 

 always present in a more concentrated state in the finished 

 article. Thus if its solubility be even moderate, one is 



