11 



and possibly to some extent upon the presence or absence of 

 organic matter. 



Nitrification. 



In order to study the influence upon the nitrifying bacteria, 

 the same method described under the determination of the ammon- 

 ifying power was used except that the incubation extended over a 

 period of 21 days. The per cent nitrates in the soil was then 

 determined by the usual method. The results are given in the 

 following table. 



EFFECT OF ARSENIC ON NITIFRICATION. 





Soil No. 1 



Soil No. 2 



Soil No. 3 



Arsenic 



Nitrogen 



Nitrogen 



Nitrogen 



in soil 



As NO 



3 



as N0 3 



as NO 



3 



percent. 



p.p.m. 



p.p.m. 



p.p.m. 



.001 



82 



310 



455 



.005 



114 



280 



350 



.010 



240 



275 



350 



.015 



66 



275 



320 



.050 



400 



210 



330 



.100 



88 



260 



375 



.250 



24 



260 



405 



Check 



80 



300 



370 



The influence of sodium arsenite on the nitrifying bacteria 

 was greatest in the red clay soil (No. 1). Here there was a decided 

 stimulation up to .05 per cent, followed by a rapid reduction in 

 nitrate content. In the other soils the influence was less marked. 

 In these the functions of the bacteria were apparently little 

 influenced even by excessive amounts of the arsenic. In soils 1 and 

 3 there was little correlation in the influence upon the ammonify- 

 ing and nitrifying bacteria while in soil No. 2 the action was 

 very similar. 



Chemical Activities. 



When any chemical salt is added to a soil it either combines 

 with or replaces substances already present or remains inactive and 

 is readily washed out by the rains. Still other salts are broken 

 up or decomposed after being added to the soil, one part being 

 washed out while the other remains fixed. This process is known 



