CHANGING SOIL STRUCTURE 121 



Hall (10) found that when nitrate of soda was applied in 

 large quantities to heavy soils at Rothamsted the tilth 

 of the land was destroyed. He concluded that this result 

 came about by the production of the deflocculating salt, 

 sodium carbonate. 



The presence of alkali salts was early observed by 

 Loughridge (15) and Hilgard (13) to have a bad effect 

 on the soil by puddling or deflocculating the particles 

 and a consequent compact condition which prevents the 

 rapid rise of water. Puddling was accompanied by large 

 contraction of volume. A similar action particularly in 

 clays was also observed by Bemmeln (i). 



Masoni (16) showed that not all soluble salts have a 

 deflocculating effect. Some of them have a decidedly 

 flocculating effect which is not dependent on the quantity 

 of salt but rather on ionic concentration and the degree 

 of dissociation. He considers the flocculating power to 

 be a function of the cation, the anion being without in- 

 fluence. If the value of the flocculating power for the 

 sodium ion be taken as i, then for the potassium or am- 

 monium it is 2.4, and for the calcium ion 5.7. 



Free (7) has pointed out that flocculation and defloccula- 

 tion are relative terms and that the action of salts, acids, 

 and alkalies in this connection are twofold and depend 

 on the mutual interpenetration of particle and medium 

 and on the electrical charge on the surface of the particle. 



Davis (6) has shown that even small quantities of soluble 

 salts are important in modifying the physical properties 

 of the soil including the apparent specific gravity which is 

 affected directly by the flocculation of the particles. The 

 effect of salts is shown to be very much greater in soils of 

 finer particles than in sands. It is usually in the finer, 

 heavier soils that alkali is found ; consequently, it is usually 

 only in these soils that the problem becomes troublesome. 



