374 The Flocculation of Soils. ITJ 



with water and allowed to settle. The clay was then decanted. The re- 

 maining portion was treated with excess of lime water and left for one 

 day with frequent shaking. This portion was then filtered and washed 

 with hot water until the washings gave no colour with phenolphthalcin. 

 It was then shaken with water and allowed to settle after which the clay 

 was decanted. Two suspensions of the clay were thus obtained, one 

 depleted of its easily soluble bases and the other with as much lime as it 

 could retain against a hot water washing. These suspensions were then 

 adjusted so that 100 c.c. of each contained 0-2270 gm. clay (weighed after 

 ignition). The relative effect of Ca (OHjj and CaCL^ in various concentra- 

 tions was then observed on 10 c.c. portions of each of these suspensions. 

 It was found that the suspension.s of the acid extracted clay were 

 flocculated better by the Ca(0H)2 at all concentrations above about 

 A^/450, while the suspension of clay after treatment with Ca(0H)2 was 

 flocculated better by Ca{0H)2 at all concentrations above A^/1000. 



The amount of lime already held by the soil clearly affects the con- 

 centration of added Ca(0H)2 above which the abnormal effect of that 

 hydroxide is manifested. 



It must also be remarked that the clay which had been treated with 

 lime water and washed remained suspended in the control tubes very 

 much longer than the clay which had been extracted by acid and washed. 



2. A similar comparison of the flocculating powers of Ca(0H)2 and 

 CaCl2 was made with two different clays, one a fat Halifax clay and the 

 other a lean kaolin. The suspensions used contained 0-3044 gm. ignited 

 clay in 100 c.c. In the exjieriment with the fat clay the superior floc- 

 culating power of Ca(0H)2 was operative and very -pronounced at all 

 concentrations above N/500. In the experiment with the kaoUn the 

 superior flocculating power of Ca(0II)2 could be seen at all concentra- 

 tions above iV/1000: in the course of one or two minutes, however, the 

 neutral and alkaline suspensions were alike. The phenomenon could be 

 seen with the lean clay but was not very pronounced. 



Similar experiments with other clays showed that the superior floccu- 

 lating power of Ca{OH)o at higher concentrations was always more 

 pronounced in suspensions of fat clays than in suspensions of lean clays. 



D. The relative lime absorbing capacities of the core and of the 

 colloidal surface of soil particles. 



1. When a soil has been extracted with acid, its base absorbing 

 power and its power to decompose calcium carbonate are usuallv in- 



