Dec. i, 1920 



Effect of Season and Crop Growth on Soil 



399 



soil suspensions were poured into burettes. After 24 hours the upper 

 10 cc. were carefully pipetted off into weighed dishes, and the total 

 residue was estimated after evaporation and drying at ioo° C. While 

 such a method unquestionably leaves much to be desired, it is neverthe- 

 less apparent that considerable changes in the colloidal state of the finer 



24-f=L/9A/TS 



*"» (\j O $ 'Q ^ 0) N 



Fig. 2. — Effect of crop on physical state and electrolyte concentration of the water extract of the soil. 



soil particles are reflected in the quantities of suspended material obtained 

 in this manner. 



The data have been expressed in the form of graphs with the time (in 

 weeks) plotted against values expressing the magnitudes of the suspended 

 material and also against the resistances of the extracts in ohms. Since 

 the concentration of the solution varies inversely as the resistance, the 

 scale has been inverted to bring out the relations more clearly. (Fig. 1-4.) 

 16916—20 5 



