Nov. II, 1918 Determining the Absolute Salt Content of Soils 333 



Table I- — Effect of air-drying upon the freezing-point lowering of soils 



Soils. 



Natural 

 soils after 

 washing 

 and air- 

 drying. 



California Okley fine sandy loam . . 

 California Yolo fine sandy loam . . . 

 California Hanford fine sandy loam 



Michigan sandy loam 



Michigan silt loam 



Wisconsin Carrington silt loam .... 



Wisconsin Miami silt loam 



Michigan heavy siit loam 



Kentucky clay loam 



Michigan clay loam 



California Ramona clay loam 



Michigan heavy clay loam 



Wisconsin Superior clay 



Minnesota Superior clay 



Texas Crawford clay 



"C. 



o. 006 

 . 006 

 . 007 

 . 006 



. OIO 



. OIO 



. Oil 



. Oil 



. on 

 . 010 



. OIO 



. 012 



. OIO 

 . OIO 



. on 



An examination of the data in Table I shows at once that the freez- 

 ing-point depression of the soils did not increase by the process of air- 

 drying. It will be seen that the depression is practically the same after 

 drying as before drying, the difference is only about o.ooi, which is 

 within the experimental error. The conclusion is inevitable, therefore, 

 that air-drying, at least once, does not increase the quantity of the 

 soluble material of soils. 



From the above results it is also seen that the rate of solubility of 

 soils is very slow, or that saturation is not attained very rapidly as has 

 been claimed (6, p. 55-56). It took at least three hours and in some 

 cases 24 hours for the soils to dry, and yet hardly any material went 

 into solution during this time. These results are overwhelmingly sub- 

 stantiated by the very extensive investigations, to be reported later, on 

 the rate and extent of the solubility of soils, in which it is shown that 

 the depression of soils at optimum moisture content increases only 

 about 0.003° C. during the first 10 days, or from 0.010° to 0.013'', and 

 that this depression increases to about 0.025° at the end of 30 days, and 

 to about 0.040° at the end of 60 days. 



As a result of the foregoing facts it is firmly believed, therefore, that 

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

 content of soils at high moisture content with a very great degree of 

 accuracy. 



The procedure which has been adopted for making a comparative 

 study of the absolute salt content of all kinds of soils is as follows: The 

 soils are allowed to air-dry if freshly taken from the field. Then a 15- 

 gm. sample of soil is taken and poured into the freezing tube containing 

 10 cc. of distilled water. The soil is stirred, usually by shaking, allowed 

 to stand for a few minutes, and its freezing-point depression determined. 



