14 



the filtrates obtained by passing the solution of sodium arsenite 

 through the soil as compared with a water extract. 



In order to magnify the action of sodium arsenite a series of 

 experiments was planned as follows : 200 grams each of the 3 

 types of soil was weighed into a large bottle and to this was added 

 1 litre of a solution containing 1 per cent sodium arsenite. Check 

 experiments were also made upon the soils using 1 litre of water. 

 These were well shaken at intervals for several days and allowed 

 to stand two weeks. They were then filtered and analyses made on 

 the filtrates, and humus determined in the soils. 



The following table shows the percent of humus removed from 

 the soil by treatment with sodium arsenite. 



HUMUS REMOVED FROM THE SOILS BY TREATMENT WITH 

 1 PER CENT. SODIUM ARSENITE SOLUTION. 



Humus 



Soil Humus in soil after Humus 



Number in soil. treatment dissolved. 



per cent. per cent. per cent. 



1 2.77 1.56 1.21 



2 1.68 1.80 0.00 



3 8.75 8.40 0.35 



In the next table is presented data relating to the changes in 

 composition of the sodium arsenite solution when in contact with 

 the soil. 



ANALYSES OF WATER AND ARSENIC EXTRACTS OF SOILS. 





Soil 



No. 1 



Soil 



No. 2 



Soil 



No. 3 





Water 



Arsenic 



Water 



Arsenic 



Water 



Arsenic 





extract 



extract 



extract 



extract 



extract 



extract 





mg. 



mg. 



mg. 



mg. 



mg. 



mg. 



Iron oxide 



trace 



716.0 



trace 



121.0 



trace 



90.0 



Calcium oxide . . . 



11.2 



84.0 



13.6 



124.0 



74.6 



126. 



Magnesium oxide 



3.6 



20.0 



10.8 



44.0 



7.4 



26.0 



Arsenic (As 2 0 3 ). 





396.0 





6000 





4480.0 



Arsenic fixed by 















200 gms. soil. . 





2640 





600 





2120.0 



The above figures represent miligrams per litre, excepting the 

 last column which gives miligrams of arsenic (As,0 3 ) fixed by 

 the soil. An analysis of the solution used shows an arsenic content 

 of 6600 miligrams per litre. 



From these data it is possible to advance several theories as 

 to the action of this chemical. The soluble action toward humus is 



