C04 STATE BOARD OP AGRICULTURE. 



they are conceutraled and the loAvering of the freezing point becomes 

 greater. 



A critical consideration of tlie cliaraclcr of the soil syslem and a 

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

 tained through soil water extracts, drainage water, etc., lend con 

 siderable support to this hypothesis. 



It appears very reasonable also to suppose that the solubility constant 

 or product of a solid substance is ditterent wlien the material is in con- 

 tact with water in the film than in the mass form. 



The foregoing hypotheses, however, do not explain why the lowering 

 of the freezing point of the agricultural soils increases in a geometric 

 progression while the water content decreases in au arithmetic pro- 

 gression, and does not follow an inverse proportionality law (approxi- 

 mately) as might be expected. 



In explanation of this phenomenon the hypothesis is also offered that 

 some of the water contained by the soil is either loosely chemically com- 

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

 water is not free or available to act as a solvent but is removed from the 

 liquid phase and takes no part in the lowering of the freezing point. 

 Under this assumption the results are easily explained. Thus, for ex- 

 ample, if a cLay causes 15% of the water to become inactive or unavail- 

 able and at 39% of moisture this clay gives a depression of .075°C and 

 at 22%, .987°C, then at the first case there is 24% of moisture to dis- 

 solve the salts while in the second case there is only 7% 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 would be expected from the total per- 

 centage of moisture. 



There is a tremendous amount of evidence which appears to prove 

 beyond any doubt that the soils cause water to become inactive or un- 

 available, and that the quantity varies with the character of the soil, 

 being smallest in the sandy typ^s and largest in the colloidal types. 

 Hence, the foregoing hypothesis seems to be valid. 



It was found that the magnitude of the lowering of the freezing point 

 of soils at the low moisture content decreases with successive freezings. 

 This was true, however, with the agricultural soils, but not with arti- 

 ficial substances such as quartz sand, kaolin, burned soils, etc. For ex- 

 plaining these phenomena the hypothesis is offered that the greatest 

 portion of the water which is made inactive or unavailable and thus re- 

 moved from the field of action as far as the freezing-point lowering is 

 concerned, is due to the colloids which the soils contain. This inactive 

 or unavailable water may exist in the colloids both as loosely chemically 

 combined, and as physically absorbed. Upon freezing these colloids 

 coagulate and the bonds uniting them with the water break and the 

 inactive or imavailable water becomes liberated. This liberated water 

 acts as a solvent and goes to dilute the original solution and thereby de- 

 creases the freezing point depression. Thus, for instance, if there were 

 only 5% of moisture at the beginning of the first freezing, there is 

 probably 7% at the end of the first freezing, 7.5% at the end of the second 

 freezing, and so on until all the colloids are coagulated. These soils in 

 Vv^hich the depression remains constant with successive freezings prob- 

 ablv do not contain colloids or if they do they are not coagulable. 



