THE FLOCCULATION OF SOILS. Til. 



By NORMAN M. COMBER. 

 (Department of Agriculture, The University, Leeds.) 



In the previous papers' it has been deduced that the fiocculation of soil 

 particles by calcium hydroxide is the net result of its deflocculating action 

 on the cores of the particles and its precipitating action on the colloidal 

 matter. Calcium hydro.xide will deflocculate or flocculate according to 

 which of these actions is dominant. 



In the present communication further support of the earlier deductions 

 is offered from experimental observations on 



(i) The fiocculation of particles other than soil particles. 



(ii) The effect of colloidal silica on the suspensibility of particles. 



(iii) The effect of concentration on the relative flocculating powers 

 of calcium hydroxide and calcium chloride. 



(iv) The relative hme absorbing capacities of the core and of the 

 colloidal surfaces of soil particles. 



(v) The effect of heat on soils. 



Experimental. 



A. The fiocculation of particles other than soil particles. 



1. Experiments such as those described in the first of these papers 

 were made with a variety of relatively insoluble powders, in order to 

 ascertain whether any substances other than clay were precipitated from 

 their suspensions better by calcium hydroxide than by a neutral calcium 

 salt. It was difficult to get very durable suspensions of many of these 

 powders. However, such e-xamination as could be made indicated that 

 the abnormal fiocculation by calcium hydroxide was not shoum in sus- 

 pensions of zinc oxide, zinc carbonate, ferric oxide, barium sulphate, 

 ferric phosphate (ignited), lead carbonate and Canadian apatite. It was 

 shown in suspensions of aluminium phosphate (unignited or ignited), 



» Journ. Agric. Sci. 1920, 10 (4); 1921, 11 (4). 



