DETERMINING THE ABSOLUTE SALT CONTENT OF 

 SOILS BY MEANS OF THE FREEZING-POINT METHOD 



By George J. Bouyoucos, Research Associate in Soils, and M. M. McCool, 

 Professor of Soils, Michigan Agricultural Experiment Station 



When the idea was first conceived of using the freezing-point method 

 (sy for measuring the concentration of the soil solution directly in the 

 soil mass, the first problem which was desired to investigate was the 

 absolute salt content of soils. It was thought that if the method proved 

 successful it would afford a unique and excellent means of determining 

 the absolute salt content of soils and thus yield very important and 

 fundamental data on the comparative absolute salt content of soils. 

 When it was discovered, however, that the soils cause water to become 

 unfree and that this unfree water influenced greatly the concentration 

 of the soil solution (2), then a direct comparison of the absolute salt 

 content of soils had to be abandoned, and the investigation was con- 

 fined to determining the actual concentration of the soil solution of a 

 soil at any given moisture content. In this case it did not matter if 

 the unfree water influenced the concentration as long as it was the actual 

 concentration which existed in the soil solution. 



It was realized, however, at the very beginning that for comparative 

 studies the error caused by the unfree water was greatly minimized 

 when a high moisture content was employed. For making a comparison, 

 therefore, of the effect of application of salts upon the concentration of 

 the soil solution (j, 4) for determining the hme requirement of soils (z), 

 and for measuring the velocity of the reaction between soils and chemical 

 agents (5), high moisture content or an excess of water or solution vv'ere 

 employed. In studying the diffusion of salts in soils McCool and Wheet- 

 ing (8) also employed a high moisture content in making freezing-point 

 determinations. 



On account of the rather small concentration of the soil solution of 

 natural-normal soils at very high moisture content, however, no attempt 

 was made at the beginning to make a direct comparison of the absolute 

 salt content of soils. It was feared that on account of this rather small 

 concentration and on account of the influence of the unfree water, the 

 results would not be dependable, and possibly misleading. If the con- 

 centration of the soil solution were rather high at the high moisture con- 

 tent, any small errors that might enter in the determination would 

 probably not have been serious. 



' Reference is made by number (italic) to " Literature cited," p. 336. 



Journal of Agricultural Research, Vol. XV', No. 6 



Washington, D. C. Nov. 11, 1918 



qe (.33^) Key No. Mich.-9 



