Dec. 13. 191S Effect of Arsenic Applied as a Spray for Weeds 463 



The rate and extent of fixation of arsenic vary in different soil types, 

 owing to the concentration and solubility of the basic constituents — i. e., 

 dissociation was found to be more rapid in some soils than others. To 

 illustrate, the soil absorbing the greatest amount of arsenic exhibited the 

 strongest alkalinity and showed the greatest chemical activity. Further- 

 more, this same soil contained the least amount of the soluble bases, cal- 

 cium, magnesium, and potassium, indicating that the chemical fixation 

 is influenced by the pressure of soluble bases. 



SUMMARY 



It has been shown herein that soils possess strong fbdng power for 

 arsenic and that when a sodium-arsenite spray is used for destroying 

 weeds the arsenic will ultimately be deposited in the surface soil, there to 

 remain in spite of the leaching effect of rains or irrigation. 



The chemical reactions involved in the fixation are a replacement 

 or solution of iron, calcium, magnesium, and humus, owing in part 

 to a hydrolysis of the sodium arsenite in solution, also a combination 

 with the dibasic and tribasic elements to form the difficultly soluble 

 arsenites or arsenates. 



