94 



Naturally the degree of fineness of the adsorbent is important. 

 The following case wUl illustrate this point : — 



Bauxite Mesh. Activity. 



40/60 1-0 



60/80 - 1-7 



In point of fact the activity — all experimental conditions being the 

 same — is approximately directly proportional to the mesh. A con- 

 venient method of demonstrating this point consists in treating a 

 100 c.c. of coloured solution (as e.g., that aheady mentioned) with 

 varying weights of decolourant, matching the filtered resultant solution 



with the standard solution in a Nessler iar (C. c.cs.) and plotting " 



against C. Ordinates at C = 50 give directly the reciprocals of the 

 masses required to remove 50 per cent, of the colour. Thus with 

 floridin : — 



Mesh. Mass. 



Passing 180 50/320 



Passing 80 and retained on 180 - - - - 50/170 



Passing 20 and retained on 30 - - - - 50/44 

 and with Bauxite 



Passing 80 50/175 



Passing 60 and retamed on 80- - - - - 60/80 



Passing 20 and retained on 30 - - - - 50/30 



Little can be said as to the relationship between the chemical 

 composition of the material and its adsorbent properties. Apparently 

 hydrated siUca or alumina is effective after combined water is expelled, 

 but no general statement can be made. Substances giving the same 

 analytical figures may behave quite differently, and again, bodies of 

 dissimilar chemical composition may be equally effective as decoloiu'- 

 ising agents. 



The essential feature of all effective adsorption agents is develop- 

 ment of surface, hence mineral gels containing water of combination 

 which, on ignition, possess a characteristic structure are decidedly 

 likely to possess decolourising and desulphurising properties. 



Very characteristic is the behaviour of bauxite (say, 40/60 mesh) 

 on being gently agitated with kerosene or benzene. Apparently a 

 process of peptisation goes on, for a considerable amount of very finely 

 divided material separates in sus]3ension in the petroleum, and is 

 sufficiently fine to pass readily through filter paper (see W. Bancroft, 

 Vol. II. Report on Colloid Chemistry, 1918, page 2 et seq). 



A highly important contribution to the appHcation of colloid 

 chemistry to industry was made by Clifford Richardson (" The Modern 

 Asjohalt Pavement " and reprint of a paper read before the St. Paul 

 Engineering Societj^ 1917). This investigator showed that the 

 durability of anasphalt pavement is directly connected with the fine- 

 ness of the mineral aggregate, i.e., with the extent of the surface 

 developed. The capacity factor of the surface energy is measured by 

 the absolute surface displayed and the intensity factor by the particular 

 surface tension of the materials employed. As a case in point, a 



