146 MOVEMENT OF SOLUBLE SALTS 



from the alkali incrustations on top of alkali soil. Certain 

 of the soluble salts were absorbed by the soil, while others 

 moved somewhat more freely. Calcium sulphate was the 

 most abundant salt in the soil solution with magnesium 

 sulphate second, while sodium sulphate formed consider- 

 able of the efflorescent matter on the surface, and the 

 salts next the surface. Sodium chloride did not separate 

 as readily as some of the other salts. Very little calcium 

 sulphate left the soil to form part of the incrustation. 



Movement of Various Salts. - - It has been noticed by 

 numerous observers that the different salts move some- 

 what independent of each other so that in comparatively 

 short distances either vertically or horizontally rather 

 marked differences are found. Experimenters have come 

 to varying conclusions as to the ease of movement of the 

 different alkali salts. Practically all field investigations 

 have shown that the chlorides are the most sensitive to 

 water movement. Both under arid alkali soils and where 

 irrigation has shifted the salts to other positions, sodium 

 chloride is generally found in its highest concentration at 

 the point where the total salts are highest. Headden (12, 

 13) states that while retention of salts differs with the soil, 

 sodium sulphate was most markedly retained, sodium 

 chloride slightly, and sodium carbonate hardly at all, 

 and that "there is a tendency for the 'white alkali' to 

 pass into the deeper seated waters" and out of the region 

 where there is good drainage. King (18) reports sodium 

 sulphate as being readily absorbed by the soil, while 

 sodium chloride was not retained. The soil has a slight 

 retentive power for the acid radical of sulphates but none 

 for nitrates, chlorides, nor carbonates according to Waring- 

 ton (32). Dimo (4) noticed accumulations of sodium 

 chloride and sodium sulphate at a depth of 50 cm. in a 



