630 STATE BOARD OF AGRICULTURE. 



tration of solution, the following suggeslion is tentatively offered: It 

 is assumed that the soil solution contains sails oi- their ions, produced 

 by the reaction of the dissolved components of thv. soil minerals, hydro- 

 lysis of the minerals, a|)i)lication of fertilizers, decomi)osition of organic 

 matter, etc. These salts have, as a rule, a high solubility and would re- 

 quire a large amount of them to fonn a saturated solution. They are 

 formed relatively slowly and since the frequent and excessive rains, 

 especially in the humid regions, tend to leach them away, only a relative- 

 ly small amount of them is present at a time. At a high moisture con- 

 tent these salts are diluted jind the lowering of the freezing point is 

 small. As the moisture content, however, is reduced, they are con- 

 centrated and the lowering of the freezing point becomes greater. 



A critical consideration of the character of the soil system and a 

 thorough examination of the available data of the soil solution as ob- 

 tained through soil water extracts, drainage water, etc., lend consider- 

 able support to this hypothesis. 



The foregoing hypothesis, however, does not explain why the lowering 

 of the freezing point increases in a geometric progression while the 

 water content decreases in an arithmetic progression and not follow 

 an inverse proportionality law (approximately) as might be expected. 



In explanation of this fact the hypothesis is also offered that some of 

 the water contained by the soil might be either loosely chemically com- 

 bined or physically adsorbed, or both, in which event that portion of the 

 water is not free or available to dissolve the salts in the soil, but is 

 entirely removed from the liquid phase. If it is physically adsorbed 

 it is conceived that it is almost solid like water of crystallization. The 

 hypothesis would seem to explain the results. Thus, for example, if a 

 soil like clay causes 15% of water to become unavailable, or be removed 

 from the liquid phase, and at 36% moisture this soil gives a depression 

 of the freezing point of .034°C and at 18.8% moisture, .955°C, then at 

 the first case there is 20% moisture to dissolve the salts while in the 

 second case there is only 3% of moisture for the same purpose. The 

 depression of the freezing point at the low moisture content, therefore, 

 would be many times greater than that at the high moisture content, 

 than should be expected from the total percentages of moisture content. 



While no experimental proof is offered for the above hypothesis there 

 are data which seem to point towards its validity. Thus, it has been 

 observed that at a low moisture content the lowering of the freezing 

 point of all colloidal soils employed, becomes less or smaller with suc- 

 cessive freezings. This phenomenon might be explained under the sup- 

 position that at least part of the unavailable w^ater is adsorbed by the 

 colloids of the soil. Through the process of freezing this colloidal 

 material is coagulated and thereby releases the adsorbed water which 

 becomes free or available and goes to dilute the original solution. 



In the event, therefore, that the lowering of the freezing point at 

 the different moisture contents represents actual concentration of soln- 

 tion, then many extremely important and far-reaching consequences fol- 

 low: (1). The soil solution is not under all conditions dilute as is 

 generally believed. It is dilute only at the high moisture content, but 



