RATE OF ALKALI MOVEMENT 149 



percolation was increased, but that where soils treated 

 with these salts were leached the rate of percolation was 

 diminished. In one experiment it was noticed that the 

 quantity of suspended matter leached from soil containing 

 sodium chloride was ten times that from the check and that 

 the rate of percolation had been diminished to about one- 

 tenth that of the check. It was further learned that once 

 the sodium chloride was leached from the soil a larger 

 quantity was required again to flocculate the soil and that 

 it was more difficult thereafter to repair the deflocculated 

 condition. A large number of investigators have noted 

 an increase of calcium and magnesium and a decrease in 

 sodium in alkali water after it had percolated through a 

 soil. This exchange of bases is said by Sharp to result 

 from displacement of calcium and magnesium by the 

 sodium in the colloidal substances of the soil and the re- 

 sulting increased diffusibility to be the cause of the retarded 

 movement of the water. The removal of the calcium and 

 magnesium from the soil is thought by him to be of less 

 importance than the increased diffusibility of the colloids, 

 although these bases are recognized as being important 

 in the deflocculation of the colloids and in maintaining 

 the proper physical properties of the soil. Contrary to 

 Sharp's results, Pagnoul (26) did not find the sodium of 

 sodium sulphate, nor to an appreciable extent sodium 

 carbonate, to replace lime of the soil, and other experi- 

 menters do not report sodium sulphate as replacing lime 

 except where sodium chloride was also present. Pagnoul 

 agrees with Sharp that lime replaces the bases of chlorides 

 of potash, soda, and ammonia. If the degree of per- 

 meability to water can be taken as a measure of the de- 

 flocculation of soils, experiments by Beeson (i) show 

 sodium chloride to be more than twice as powerful as 



