584 STATE BOARD OF AGRICULTURE. 



The foregoing results together with those announced in the first report 

 prove absolutely that successive freezings effect the lowering of the 

 freezing point differently in the various soils. In such soils as .sand and 

 very light sandy loam and artificial substances such as kaolin, quartz 

 sand, etc., the depression is influenced very little, if any. With such 

 soils as heavy sandy loams, loams, silts, clays, etc., the depression de- 

 creases and the magnitude of diminution varies with the character of 

 the soil, it is smallest in the sandy types and reaches its maximum in 

 the heavy silt loams. In the former types of soil the diminution in the 

 depression amounts only to about 8% in some cases, while in the latter 

 types of soil it amounts to more than 25%. 



The- question now is, what causes this diminution of the freezing-point 

 depression with repeated freezings and why it occurs in the case of some 

 soils or substances and not in others. An attempt will now be made to 

 offer a possible explanation for this phenomenon. 



It was once thought that the soil solution at the low moisture con- 

 tent employed reached its saturation point in concentration and as it 

 cooled salts separated, for the solubility of salts diminishes of course 

 with falling temperature, and thus the solution became less concen- 

 trated. This hypothesis, however, would not explain the continued de- 

 crease in the 'depression with repeated freezings for if the soil solution 

 were (Concentrated to the saturation point at the low moisture content 

 all the excess of salts should separate the first time it is cooled below 

 0°C, and inasmuch as "probably not all of the separated salts would go 

 again into solution upon thawing — owing to the short length of time — - 

 the concentration of solution and hence the lowering of the freezing 

 point should remain more or less stationar3\ Hence this hypothesis 

 fails to explain the results. 



An hypothesis which appears to explain the results quite satisfac- 

 torily and which seems to be supported by a great amount of evidence is 

 as follows: The greatest portion of the water which the soils cause 

 to become inactive or unavailable and thus lose its solvent action is due 

 to the colloids Avhich the soils contain. This inactive or unavailable 

 water may exist in the colloids both as physically absorbed water and as 

 loosely chemically combined water. Upon freezing, their colloids coagu- 

 late and the bonds uniting them with the water break and the inac- 

 tive or unavailable water becomes liberated. This liberated w^ater be- 

 comes available or acts as a solvent and goes to dilute the original solu 

 tion and thereby decreases the lowering of the freezing point. Thus, 

 for instance, if there were only 5% of available moisture before the 

 first freezing was made, there were probably 7% at the end of the first 

 freezing, 7.5% at the end of the second freezing and so on until all or 

 most of the colloids are coagulated. Or if the freezing is greatly pro- 

 longed at a very low temperature as was done in the second investiga- 

 tion, then probablj^ all or most of the colloids are coagulated so that all 

 the inactive water that would become available is liberated at once. 



The foregoing hypothesis seems to find a large amount of confirma- 

 tion from both direct and indirect evidences. It is now generally be- 

 lieved that there are present in soils both hydrosols and hydrogels con- 

 sisting of organic substances, the humus compounds, and inorganic sub- 



