Feb. II, 1918 Freezing-Point Method and Soil Solution 



371 



moisture contents differed only slightly from the standard. It has 

 been shown by Bouyoucos and McCool that freezing-point depressions 

 vary with the water content of the soil, not usually in direct ratio, but in 

 such manner as to necessitate the assumption that a certain fraction 

 of the total water present is so combined that it does not form an effective 

 part of the soil solution and is not subject to freezing. The percentage 

 of combined water would vary greatly with the type of soil, clay soils 

 having a large proportion of their water in the unfree state. The above 

 considerations, advanced by Bouyoucos and McCool, have been made 

 the basis for the determinations of unfree water in the soils used in this 

 investigation. Portions of each soil were divided into two samples the 

 moisture contents of which were so adjusted as to give a difference of 

 about 5 per cent. Each sample was thoroughly mixed and kept over- 

 night in a tight jar. Careful determinations of total moisture and freez- 

 ing-point depression were then made. From these data it is possible 

 to calculate what proportion of the moisture must be subtracted from 

 the total in order that the percentages of free water may give the same 

 ratios as the freezing-point depressions. Such estimates may not have 

 a high degree of accuracy, but it is probably sufficient for the purposes 

 in hand. Table II presents the results for the unfree water in each 

 soil. 



Table II. — Estimation of unfree water in soils 



Soil No. 



iC 

 iC 

 2C 

 2C 

 3C 

 3C 

 4C 

 4C 



sc 

 sc 



6C 

 6C 



7C 

 7C 



Soil No. 



8C. 

 8C. 

 9C. 

 9C. 

 loC 

 loC 

 iiC 

 iiC 

 12C 

 12C 

 14C 

 14C 



Unfree 

 water. 



Per 



cent. 

 4.0 



6.0 



8.0 

 6.0 



4.0 



7-S 



SEASONAL VARIATIONS IN CROPPED AND IN UNCROPPED SOILS 



One of the primary objects of this investigation was to follow through 

 the season the concentrations of the soil solution in each soil and to com- 

 pare at each period of sampling the cropped soils with their uncropped 

 duplicates. The first determinations of freezing-point depressions were 

 made early in July, 1916, and at intervals from that date until the fol- 

 lowing May. The barley crop was planted in May, 1916, and harvested 



