SECTION VI. EVAPORATION 



THE evaporation of the weak gelatine sols (3-9 per cent.) 

 obtained by the processes described in previous sections 

 into sols of such concentration (20-55 P er cent.) that they 

 readily set to a stiff gel on cooling, is now an essential feature 

 of gelatine manufacture, and is one of the most important 

 processes. 



In the early days of this industry, manufacturers aimed 

 at obtaining a concentrated sol, as this saved time in drying, 

 and so reduced the possibilities of putrefaction. The advent 

 of evaporation has reduced these possibilities to a minimum, 

 and has also enormously reduced the space required and 

 the capital outlay needed in the drying sheds. It has, in 

 addition, given the practical advantages involved in dealing 

 up to the last minute with a much less viscous liquor. As 

 the liquors extracted are weaker, the extraction is more 

 complete and the decolorization more easily effected. 



The earliest attempts at evaporation were not very 

 successful, partly on account of the prolonged " stewing " 

 which ruined the setting power, and partly because of the 

 poor economy of heat. Thus in the open evaporators the 

 sol was maintained at a high temperature for a long period, 

 and this process only proved suitable for low-grade products. 



A great stride forward was made by Howard's invention 

 of the Vacuum Pan. This made it possible to undertake 

 concentration at much lower temperatures, a most important 

 improvement in the case of gelatine and other organic 

 matters easily damaged by heat. The process, however, 

 was still slow, and the sol exposed to heat for a long time, 

 as must be the case when evaporation takes place in bulk. 



