ADSORPTION 407 



In this connection there is an interesting experiment due 

 to BayUss * which is designed to show that although in the 

 process of dyeing adsorption upon the surface to be dyed may 

 be the first step, yet chemical reaction between the dye and 

 the fibre may follow as a second stage. The experiment con- 

 sists in shaking up a blue solution of the acid of congo red 

 with well-washed aluminium hydroxide ; the latter at once 

 adsorbs the blue colour from solution, and settles down on 

 standing ; if it is now heated, the physically adsorbed congo 

 red acid combines with the aluminium hydroxide to form the 

 aluminium salt, a chemical reaction which is marked by the 

 change of colour from blue to red. 



In the same way Bayliss holds that in the case of enzyme 

 action adsorption of the substrate upon the surface of the 

 enzyme is the first stage, and that then, in consequence of the 

 intimate contact between the two, mass action accelerates the 

 reaction. 



It is, of course, easy to understand that if adsorption takes 

 place so readily between colloids, such as filter paper and congo 

 red, both of which bear negative charges in water, the pheno- 

 menon must take place still more easily between oppositely 

 charged colloids in which the mutual electrical discharge facili- 

 tates the deposition. 



Numerous practical applications of adsorption from solu- 

 tions are known, as for example in the removal of colouring 

 matter in the purification of cane sugar, or in the removal of 

 fusel oil from crude spirit by filtration through charcoal. 



Other substances besides charcoal, such as Fuller's earth 

 and china clay, have been similarly used on account of the large 

 surfaces which they present. 



From what has been said with regard to the structure of 

 gels and the assumption that they present a sort of network 

 with a considerable development of internal surface, it is easy 

 to find an explanation of the use of isinglass for clearing a 

 turbid solution or for the fact that colouring matter may be 

 extracted from a solution by precipitating gelatinous alu- 

 minium hydroxide in it. 



* Bayliss : " Z. chem. Ind. Koll.." 1908, 3, 224. 



