EXPERIMENT STATION BULLETINS. 609 



types; at high moisture content, however, the lowering of the freezing 

 point is relatively very low and only slightly different for the diverse 

 classes of soil; in all the different soils with the exception of quartz 

 sand, the depression of the freezing point increases in a geometric 

 progression as the percentage of moisture decreases in an arithmetic 

 progression; in the case of quartz, however, the lowering of the freez- 

 ing point increases directly as the moisture content decreases; the 

 magnitude of concentration and osmotic pressure that the lowerings of 

 the freezing point represent at the low moisture content, are tremend- 

 ously high, especially in the complex types of soil, but at the high 

 moisture content, they are comparatively very small. 



It will at once be admitted, therefore, that these results are extremely 

 unusual and do not harmonize with the present views concerning the 

 soil solution. It is almost universally believed, for instance, that the 

 soil solution is very dilute, and according to a theory advanced by 

 Whitney and Cameron, (10), many years ago, the soil solution is not 

 only very dilute, but also, its magnitude of concentration tends to re- 

 main constant and to be the same for practically all soils, since it tends to 

 be saturated or in equilibrium with the mineral constituents of the soil. 

 They based their theory upon the assumption that the mineral sub 

 stances comprising the soil are complex salts with slight solubilities in 

 water, and consequently, only small amounts of them would be required 

 to go into solution to form a saturated solution. Since the solution is 

 saturated in respect to the mineral constituents of the soil, the addition 

 of a soluble salt, such as KCl, may not increase the concentration but 

 would force back the disociation of the corresponding ions and thus 

 maintain a constant concentration of solution. 



Since the discovery of the phenomena of absorption and adsorption 

 of salts by soils it has been suggested, especially by Schloesing,- and 

 at present very widely believed, that these properties control or regu- 

 late the concentration of salts in solution and that the concentration of 

 the solution of any given soil tends to remain practically constant. 

 This view is well expressed in' a recent paper by Bogue, (11). To quote: 

 "But, the concentration of the salts in the soil solution tends to remain 

 practically constant for any given soil. Thus, for example, if the con- 

 centration of potassium in the soil moisture should be lessened by the 

 leaching of heavy rains, or the taking up of potassium by the plants, or 

 by any other cause, this concentration would quickly be re-established 

 by the soil giving up of its absorbed potassium until the constant was 

 again reached. Or, if on the other hand, the concentration of potassium 

 in the soil solution should be increased as by the application of a 

 soluble fertilizer, or by evaporation of the soil moisture, the constant 

 would be restored by the absorption of the excess potassium by the 

 soil." 



The foregoing results on the lowering of the freezing point, as well 

 as other data subsequently to be presented, diametrically oppose the 

 above theories. Contrary to both these theories, the concentration of 

 the soil solution as indicated by the lowering of the freezing point, does 



(«o) Bui. 22, Bureau of Soils, U. S. Dept. of Agr., 1903. 

 (") Jour. Phys. Chem., 19, 66.5, 1915. 



77 



