Feb. II, 1918 Freezing-Point Method and Soil Solution 387 



It seems quite clear from an inspection of these data that the concen- 

 tration of the soil solution may be reduced to an extremely low point 

 through leaching and that this condition is maintained over a considerable 

 period of time. Leaching has been shown by Lipman (5) to inhibit 

 bacterial action markedly, and in the absence of such activity, it seems 

 that the ability of the soil to recover its high level of concentration is 

 very limited. 



RELATION OF WATER EXTRACTS TO SOIL SOLUTION 



Before entering upon the final discussion it is desirable to consider at 

 this point certain more detailed relations of water extracts to the soil 

 solutions, as indicated by the freezing-point method. The work of 

 Bouyoucos and McCool enables us to obtain very useful and interesting 

 estimates of the concentration of the soil sola i ion, but obviously it is 

 only the total concentration which is measured. We are quite unable to 

 predict the nature of the substances whose resultant effect is expressed 

 by the lowering of the freezing point. Only by some method of water 

 extraction is it possible to gain any insight into the proportions of indi- 

 vidual elements. Various comparisons between osmotic pressures in 

 the soil solution and concentrations in water extracts may, however, be 

 made, which, in certain directions, make possible very interesting 

 deductions. 



When different soils are to be compared, the first inquiry must be 

 concerned with the amount of lowering of the freezing point which 

 occurs for each 100 p. p. m. of total solids. This phase of the question 

 has already been investigated by Bouyoucos and McCool, who found 

 that extracts of varied types of soil gave very nearly constant results, 

 approximately 0.0032° C. depression for each 100 p. p. m. of total solids 

 in the solution. The writers have obtained closely similar figures for the 

 soils used in this investigation as is made evident by the following data : 



Freezing-point depression per 100 p. p. m. of total solids 



Soil No. "C. 



2 o. 0032 



4 0031 



9 0032 



10 0030 



8 0034 



5 0030 



Average. 0032 



By the use of this constant the approximate strength of the soil solution 

 in terms of parts per million of total solids may be calculated, and this 

 has been done in Table VII. 



