1916] Sharp: Soluble Salts and Soil Colloids 327 



into contact with the soil. Nevertheless, it is significant that 

 acids of the low concentration here employed are more efficient 

 flocculants than their salt solutions of similar concentrations. 

 Hence the unneutralized acid in very dilute concentrations un- 

 doubtedly exercises a pronounced flocculating power, so that this 

 factor is eliminated as the possible deflocculant in the case of 

 NaCl + H,0 soil. 



Solutions of the chlorides, sulphates, and bicarbonates of 

 calcium, sodium, ammonium, and potassium, were also studied 

 with regard to their effects on the colloidal matter of soils. These 

 salts in solutions ranging in concentration from N/1500 to N/500 

 possessed distinct flocculating powers. Solutions of higher con- 

 centrations were likewise flocculating in their effect, while more 

 dilute solutions behaved similarly to distilled water. Hence the 

 diffused condition of the NaCl -f H^O soil cannot be attributed 

 to the mere dilution of the neutral sodium salts or of the simple 

 salts formed by reactions between the added salts and the soil 

 silicates. As previously indicated, this statement must not be 

 construed to include the systems soil -j- NaOH, or soil -1- Na2C03, 

 but must be considerably modified to express the facts existing 

 in those cases. 



The Effects of Washing Various Salts from the 



Soil with Water 



The washing out of KCl and NH^Cl from the Davis soil with 

 water gave essentially the same results as accompanied the re- 

 moval of the sodium salts by the same means. On the other 

 hand, the leaching out of calcium salts seemed to leave the soil 

 colloids in a more flocculated condition than in the normal, un- 

 treated soil, though this eff'ect was by no means so pronounced 

 as when the calcium salts were allowed to remain in contact with 

 the soil particles. According to the ideas herein presented, the 

 effect of a salt solution, either while in contact with the solid 

 particles or after its removal from the soil by washing with dis- 

 tilled water, upon the physical condition of soils or complex 

 silicates of such a character as to admit of chemical exchange of 

 ions, is. in a measure, dependent upon the nature of the chemical 



