170 Conductivities and Viscosities in Pure and in Mixed Solvents. 



cally inert substances, such as charcoal and silica, would indicate that 

 the process is a physical one, the magnitude of the adsorption depending 

 upon the extent of the surface presented by the adsorbing medium. 

 On the other hand, some of the very earliest work with soils gave strong 

 evidence of the chemical replacement of the bases of the soil by the base 

 contained in the solution. With these facts in mind a series of experi- 

 ments were planned for the purpose of studying, (1) the effect of a short 

 time contact between the soil and the salt solution; and (2) the effect 

 of the extent of surface upon the amount and the rate of absorption. 



In the following experiments a sample of Durham sandy loam 1 soil from 

 Cabarrus County, North Carolina, was used as the absorbing medium 

 and potassium chloride as the material absorbed. For the first series of 

 experiments a sample of the soil was dried and passed through a 2 mm. 

 sieve. For the second series, a sample of the same soil type was 

 reduced to very fine condition by grinding for 4 days in a porcelain- 

 lined ball mill. The mechanical analyses of the two samples, as made 

 by the Bureau of Soils, United States Department of Agriculture, are 

 given in table 96. It will be seen from the table that practically all 

 of the sand has been reduced by the grinding to the silt and clay 

 groups, thereby making an enormous increase in the amount of surface 

 exposed by the two samples of what was otherwise identical material. 

 The solution used was potassium chloride of approximately five- 

 hundredth normal concentration. 



TABLE 96. Mechanical analyses of soil samples. 



DESCRIPTION OF THE APPARATUS. 



In order to secure a short time contact between the soil and the solu- 

 tion a special apparatus was used, whereby the solution could be per- 

 colated through the soil at any desired rate. The apparatus consists 

 of a porcelain-lined filter chamber A (fig. 17), into which is fitted a 

 short filter tube B, made by cutting off the upper end of a Pasteur- 

 Chamberland filter tube and forcing it down over the projection on the 

 rubber gasket C. Surrounding the filter tube is a brass jacket D, 

 which serves as a container for the soil. After the introduction of the 

 soil, the solution is poured into the outer jacket, the air-tight cap E is 



1 U. S. Bureau of Soils classification, Bui. 95, p. 32. 



