SECTION IV. CLARIFICATION AND 

 DECOLORIZATION 



AFTER the raw material has been appropriately prepared 

 and an aqueous extract or gelatine sol obtained therefrom, 

 there are certain refinements necessary before the weak sol 

 is evaporated. These purifying processes include (i) clarifi- 

 cation, (2) decolorization, and (3) bleaching. Whilst most 

 manufacturers have more or less successfully solved the 

 problems involved in these processes, the practical methods 

 that are in common use have been evolved and elaborated 

 in a purely empirical way, and the underlying principles have 

 been very imperfectly recognized, and indeed often confused 

 and misunderstood. Hence it is even yet not uncommon 

 to find these terms rather loosely used, and it is one aim of 

 this section to define and distinguish these various operations 

 in principle as well as in practice. 



Clarification consists essentially in the removal of 

 suspended matters, with the consequent production of a sol 

 or gel which is bright, clear, and apparently homogeneous. 

 Bleaching consists essentially in destroying the colouring 

 matters of the sol by chemical action, such as oxidation or 

 reduction. Decolorization involves the removal rather than 

 the destruction of colouring matters, and does not therefore 

 imply a chemical action in the ordinary sense. 



Clarification may be now considered more particularly. 

 It is necessary in this connection to consider what is meant 

 by " suspended matter." The modern view is that the 

 difference between a true solution and a muddy liquor or an 

 emulsion is one chiefly of degree. If the particles of matter 

 in suspension or emulsion (the disperse phase) be reduced 



