1916] 



Sharp: Soluble Salts and Soil Colloids 



307 



TABLE IV 



Effect of Second Addition of NaCl on the Amounts of Suspended Matter 

 From NaCl + HoO Soil and H^O Soil 



Per cent 



of 



Suspended 



Matter 



on Dry 



Soil 



No. 

 1 

 2 

 3 

 4 

 5 



9 



11 



12 

 13 



Soil 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 

 25 grs. 



10 25 grs. 

 25 grs. 



25 grs. 



:o grs. 



Previous 

 Treatment 



NaCl washed out 



NaCl washed out 



NaCl washed out 



NaCl washed out 



NaCl washed out 



NaCl washed out 



HoO washed 



HoO washed 



HoO washed 



HoO washed 



HoO washed 



HoO washed 

 Boiled 



Concentration 



of NaCl Cc. of 



Suspending Suspending 



Solution Medium 



250 



N/1000 250 



N/500 250 



N/250 250 



N/100 250 



N/50 250 



250 



N/1000 250 



N/500 250 



N/250 250 



N/100 250 



N/50 



Weight of 



Suspended 



Matter 



.8345 grs. 

 .6375 

 .5615 

 .4570 

 .2305 

 .0170 

 .0695 

 .0740 

 .0660 

 .0615 

 Lost, but al- 

 most clear 



3.33 



2.55 



2.36 



1.82 



.92 



.07 



.27 



.29 



.26 



.24 



250 

 250 



.9060 



3.62 



The evidence presented in the last two tables supports the 

 view that the NaCl -j- H2O soil has suffered some physical altera- 

 tion which is not readily reversed by the second addition of 

 NaCl. The NaCl added to the soil already diffused by previous 

 treatment with that salt and water is here considered as a 

 physical agent, possessing the power to flocculate clay colloids. 

 To test the reversibility of the chemical reactions occurring when 

 salt solutions are allowed to act upon soils requires a soil treat- 

 ment involving the application of solutions containing, in appro- 

 priate form and quantity, the elements removed by the salt ap- 

 plications. Thus, to restore normal conditions in a soil which has 

 been diffused by a salt-and-water treatment would require the 

 replacement of the absorbed sodium by such metals as were 

 originally present in the soil. The larger amounts of NaCl re- 

 quired to flocculate the colloids of the diffused soil may be due 

 to the increased quantity of colloids present, or to the degree of 



