256 ANIMAL PROTEINS 



out on network frames arranged in tiers, through which a 

 draught of air is usually forced or induced. This general 

 description is of course applicable to many factories with 

 innumerable variations in detail, most of which variations 

 originate in local convenience and are unessential parts of 

 the manufacture. 



An essential principle is that the cooling or gelation 

 should be done rapidly, not only to avoid putrefaction but 

 also to avoid the action of heat on the elasticity of the gel. 

 A hot sol or gel is liable to hydrolysis and loss of setting 

 power, and should have its temperature quickly reduced, 

 but a warm sol or gel (say 100 F.) is most liable to putre- 

 faction, so that the cooling should be continued quickly. 

 On the other hand, the gel should not be frozen. For cooling 

 purposes a copious supply of cold water is most usually 

 employed, but some factories have installed refrigerators. 

 These plants operate by the rapid evaporation of liquefied 

 gases such as carbon dioxide, sulphur dioxide, or ammonia, 

 so arranged as to cool a solution of common salt, which 

 forms the circulating liquor and is returned after use to the 

 refrigerator. Where such plants are used, it is natural that 

 their use should be extended to the drying sheds to cool the 

 air entering in the height of summer. In some factories 

 the cooling is attained neither by cold water nor cooled brine, 

 but merely by cold air. 



The kind of vessel in which gelation is induced varies 

 widely in different factories. For lower-grade products 

 metal boxes are used, heavily galvanized iron being the 

 most common material. If the liquor be muddy, deep 

 boxes are preferred, but if clear, rapid cooling is best attained 

 by having them long and shallow, and so exposing a relatively 

 greater area to the cooling action. In either case the boxes 

 may contain up to J cwt. of jelly. I^ambert mentions 

 boxes 24" X 6", which are 5" deep ; Cavalier suggests rect- 

 angular moulds holding 30 litres. In place of galvanized 

 sheet iron, boxes of sheet zinc or of wood lined with zinc 

 are sometimes used. In any case the most scrupulous 

 cleanliness should be observed in all cooling-house work, 



