398 



Journal of Agricultural Research 



Vol. XX, No. s 



method gives results of the same relative values as those obtained by 

 determining the total solids in water extracts or by estimates based on 

 depressions of the freezing point in the soil itself. It is justifiable to 

 assume that the conductivity measurements give at least a rough idea of 

 the changes taking place in the soil solution under the various conditions. 



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Fig. i. — Effect of crop on physical state and electrolyte concentration of the water extract of the soil. 



Unfortunately no methods exist which permit the determination of the 

 exact kinds or quantities of colloidal matter in the soil. We can measure 

 only approximately certain resultant effects by the use of empirical pro- 

 cedures. Of these, turbidity observations are doubtless as valuable as 

 any others. In the present experiments the samples of soil were mixed 

 with water, in the proportion of i part of soil to 2 parts of water, and the 



