8 



Effect upon the Physical Condition of the Soil. 



One of the most noticeable effects of sodium arsenite in the 

 pot experiments was its action upon the physical condition of the 

 soil. It has a very strong deflocculating action which may be 

 attributed to either one or both of two reasons. First, arsenious 

 acid belongs to the class of weak acids such as phosphoric and 

 others, the alkali salts of which have a strong deflocculating effect 

 upon clay. Second, when sodium arsenite is added to the soil, a 

 process known as selective absorption takes place, setting free the 

 soda. This phase of the question is dealt with more thoroughly 

 under the chemical activities (p. 13). 



The mechanical condition of the soil as related to the move- 

 ment of soil moisture involves the maintenance of a loose crumby 

 structure. Hence, since sodium arsenite is such a strong defloccu- 

 lating agent it seemed imperative that its effect upon the rise and 

 flow of water be determined. 



Effect upon Eise of Moisture. 



Eor these experiments a column of soil several feet long and 

 1 inch in diameter was used, the bottom of the column standing in 

 a solution containing 200 parts per million of arsenic (As 2 Oj;) 

 from sodium arsenite. The following table gives the results 

 obtained : 





Soil 



No. 1 



Soil 



No. 2 



Soil 



No. 3 



Time 



Blank 



Arsenic 



Blank 



Arsenic 



Blank 



Arsenic 





cm. 



cm. 



cm. 



cm. 



cm. 



cm. 



1 hr 



16.0 



15.1 



15.9 



16.5 



22.4 



21.4 



3 " 



20.6 



19.8 



22.3 



22.5 



34.8 



33.5 



7 " 



24.0 



23.6 



28.8 



27.2 



46.0 



44.0 



22 " 



29.1 



28.9 



37.0 



34.7 



60.8 



58.4 



46 " 



33.4 



33.8 



44.1 



38.5 



69.7 



67.4 



68 " 



35.8 



36.4 



49.1 



41.7 



75.4 



72.7 



72 " 



37.6 



38.5 



52.4 



44.5 



79.3 



76.5 



116 " 



39.4 



40.2 



57.6 



49.7 



86.2 



83.2 



164 " 



41.8 



42.7 







90.7 



87.7 



These results show the rise of water to be diminished in two 

 soils and practically unaffected in the third. 



