EXPERIMENT STATION BULLETINS. 577 



results show. Hence, the experimental data agree almost perfectly with 

 the hypothesis. 



All evidences, therefore, are overwhelmingly in favor of the hypothesis 

 oflfered to explain the increase of concentration of the soil solution with 

 the decrease in the moisture content. 



Although the results obtained can be explained very satisfactorily 

 by the foregoing hypothesis, they can be explained just as satisfactorily 

 by still another hypothesis. This hypothesis involves the assumption 

 that the solubility product or constant of a soil substance is different 

 when the material is in contact with water in the film than 

 in the mass form. That is to say the solubility product of a substance 

 such as CaO for instance is different when the water present exists in the 

 film form than when it is in the mass form. As the film water varies, 

 the solubility product also varies. Although this hypothesis is entirely 

 contrary to the present views regarding the solubility constant of solid 

 substances, yet it is not at all unreasonable when we consider that we 

 have many powerful forces operative when the Avater exists in the film 

 form which are not operative when the water exists in mass. 



A. POSSIBLE EXPLANATION FOR THE INCREASE OF THE FREEZING-POINT DE- 

 PRESSION IN A GEOMETRIC PROGRESSION WHILE THE PERCENTAGE 

 OF WATER DECREASES IN AN ARITHMETIC PROGRESSION. 



The foregoing hypothesis offered to explain the increase in concentra- 

 tion of the soil solution with the decrease in moisture content does not 

 explain, however, why the lowering of the freezing point should increase 

 in a geometric progression while the percentage of water decreases in an 

 arithmetic progression and does not follow a direct inverse proportion- 

 ality ratio (approximately), as might be expected. 



In the first report no definite and proved explanation was presented 

 for this phenomenon, but only a tentative hypothesis was suggested. 

 This hypothesis has undergone a very thorough examination in the 

 present investigation and it appears that its validity is proven, and it is 

 here reoflered. 



The hypothesis assumes that a portion of the water found in the soils 

 is inactive and does not take part in dissolving the salts in the soil, and 

 is removed from the field of action as far as the lowering of the freez- 

 ing point is concerned. Under this assumption the increase of the 

 freezing-point depression in a geometric progression as the percentage of 

 water decreases in an arithmetic progression is explained as follows : 

 If a clay soil, for instance, causes 15% of water to become inactive, and 

 this clay at 39% of moisture produces a lowering of the freezing point 

 of .075 °C and at 22%, .987° C, then at the former moisture content there 

 is 24% of water free or available to dissolve the salts in the soil, while 

 at the latter water content there is only 7% available for the same pur- 

 pose. It would be natural, therefore, that the depression of the freezing 

 point would be many times greater at the low moisture content than at 

 the high than would be expected from the difference of the total moisture 

 content, just as the experimental data really indicate. 



This hypothesis also assumes (and the assumption seems to have been 

 proved) that the percentage of inactive water is greater at the low 

 than at the high moisture content and tends to decrease from the former 

 to the latter. 

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