2i 4 BIO-CHEMICAL JOURNAL 



Gelatin, then, has a a specific adsorption affinity for acid fuchsin. 



The preference exhibited by silk for methylene-blue over congo- 

 red, previously described, may be explained in another way than by 

 specific adsorption, viz., by the probable greater negative charge of 



silk. 



That gelatin has a greater adsorption-affinity for calcium sulphate 



than it has for potassium chloride seems to be shown by the experi- 

 ments on washing out electrolytes, given in the earlier part of this 

 paper. It was found that KCI is more easily washed away than 

 calcium sulphate. 



VII. THE APPLICATION OF THE FACTS OF ADSORPTION-PROCESSES 

 TO VARIOUS PHENOMENA 



The theoretical interest of adsorption-processes has been pointed 

 out by Ostwald, 1 who suggests the possibility that a mechanical theory 

 of chemical affinity may be developed on the basis of a complete study 

 of these phenomena. 



From a more practical standpoint, it will be found that they play 

 a very important part in numerous processes. I may refer briefly to 

 a few of these. 



1. The Soil 



The power of the soil in holding back soluble salts and other 

 bodies is, no doubt, due to adsorption. By this means these bodies 

 are prevented from being readily washed away by the rain. 



2. Purification of sewage 



In the filter-process of nitrification, it appears that the complex 

 organic substances, which are inimical to the nitrifying organisms, are 

 kept back by adsorption in the upper layers of the filter.* 



3. The ash-constituents of organic compounds 



I have already given evidence that these are present in an 

 adsorbed form, and shown that the difficulty of removing the last 

 fractions of inorganic electrolytes is adequately explained on this basis. 



1. Op. cit., p. 1098. 



2. See Dr. Harriette Chick, Proc. Roy. Soc., 773, p. 247, 1906 



