SECTION VII. COOLING AND DRYING 



THK conversion of a gelatine sol into cakes of gelatine has 

 been much simplified by the advent of the evaporator. 

 Before this machine was used much trouble was experienced 

 with putrefaction, and in hot and thundery weather, especially 

 on the Continent, it was often necessary to suspend opera- 

 tions. Evaporation has, however, materially contributed 

 to the possibility of rapid and satisfactory cooling and drying. 



From the time the weak sol is decolorized and bleached, 

 the finishing processes consist essentially in the removal of 

 water. This is now usually done partly by evaporation of 

 the sol, and partly by the desiccation of the gel. There is 

 an obvious elasticity in method, and factory practice does 

 actually vary considerably in the relative proportions of 

 these two alternatives. Some factories evaporate to a 

 20 per cent, sol, approximately, and rely upon drying 

 sheds and lofts to complete the desiccation : other factories 

 evaporate up to a 55 per cent, gelatine sol, and so can manage 

 with less shed room. Something depends upon local con- 

 ditions, but the main issue is between the cost of steam in 

 evaporation and the cost of land and buildings required for 

 sheds. On the whole the modern tendency is to evaporate 

 more, for this course has the additional advantage of speed, 

 involving both a quicker turnover and less liability of 

 putrefaction. lyower-grade products need relatively greater 

 evaporation to form a gel of equal rigidity. 



After evaporation and bleaching, the concentrated sol 

 is first cooled rapidly until it has set to a stiff gel, then cut 

 up into cakes according to the size required, these being dried 



