Dec. 13,1915 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 fixing 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. 
