332 Journal of Agricultural Research voi. xv, no. 6 



In conducting an investigation during the past year and a half to study 

 the rate and extent of solubility of soils by means of the freezing-point 

 method, it was noticed that when different classes of soil were washed 

 until their soluble salt content was greatly reduced, their lowering of the 

 freezing point was practically identical. For instance, the freezing- 

 point lowering of heavy sandy loams, loams, clay loam, and clays would 

 be about 0.007° C. and that of sands and light sandy loams about 0.005° C. 

 This identical depression of the different classes of soil suggested at 

 once the idea that at a comparatively high moisture content the influ- 

 ence of the unfree water on the concentration of the soil solution was 

 practically negligible, if not entirely absent. This idea led immediately 

 to the belief that at a high moisture content or in excess of water the 

 freezing-point method could be used to determine the absolute salt 

 content of all normal soils with a high degree of accuracy, and thus 

 afford a comparison of their relative absolute salt content. This belief 

 has been amply confirmed. 



There appeared one factor, however, which was thought might prevent 

 the realization of this method, and that is the effect of air-drying upon 

 the water soluble material of soils. It has generally been believed that 

 air-drying causes an increase in the quantity of the water soluble material 

 of soils. It was thought, therefore, that if air-drying did exert this 

 influence to any appreciable extent then the method could not be used, 

 at least very conveniently, as the procedure required the soils to be dry. 

 The recent work of Hoagland (7), however, made it very probable that 

 air-drying has practically no effect upon the concentration of the soil 

 solution. 



Since it was discovered that at a high moisture content the concen- 

 tration of the soil solution could be determined by means of the freezing- 

 point method with a very high degree of accuracy, it was decided to 

 investigate the influence of air-drying upon the water soluble material 

 of soils. The problem was investigated as follows : Samples of different 

 classes of soil were taken from the field and washed with distilled water 

 until practically all their free soluble salts were eliminated. As a rule, 

 a loo-gm. sample was washed, by the percolation process, with 500 cc. 

 of water. A portion of the washed sample was placed in the freezing 

 tube and its freezing-point depression determined. The remaining por- 

 tion was placed in the room or in the sun and allowed to dry. When 

 thoroughly dried, 15 gm. of it were weighed out and poured in the 

 freezing tube containing 10 cc. of distilled water and its freezing point 

 lowering determined as before. Care was always taken to have the 

 moisture content in both cases about the same. The study involved 

 a large number of soils representing many types and all classes. In 

 Table I are presented the results from a few representative soils employed. 



