SECTION III. EXTRACTION 



THE term " extraction " is applied to that essential process by 

 which the gelatinous matter from whatever raw material is 

 used, is actually dissolved in water and removed from the 

 rest of the material. Extraction is often termed " boiling " 

 or " cooking." Whether one is treating hide fleshings and 

 pieces or whether one is dealing with raw or acidulated bones, 

 the general principles of extraction are much the same, and 

 most of this section is equally applicable to any class of 

 material. 



The chief principle of extraction is so to arrange the 

 process that both the material and the extracted liquor are 

 maintained at high temperatures for the shortest possible 

 time. As we have observed, gelatine is readily hydrolyzed 

 by hot water, and as hot water is needed for its extraction 

 or solution, care must be taken to remove the solution as 

 soon as possible from the source of heat. In practice this 

 can only be done somewhat imperfectly, as it is necessary 

 to obtain a gelatine sol of several per cent, strength before 

 removing it from the extraction vessel. The stronger this 

 sol is made before removal, the less the time, trouble and 

 expense is incurred in evaporation subsequently, but the 

 more is the exposure to heat with consequent weakening 

 of the gelatine. Hence in practice it is necessary to com- 

 promise. The matter is complicated further by the necessity 

 of obtaining a clear sol, for which it is desirable that the sol 

 obtained in extraction should not be too concentrated, as 

 impurities settle and filter much more readily from weaker 

 and less viscous sols. 



It will be understood, therefore, that whatever material 

 is being extracted, the most favoured procedure is to extract 



