jimei2, 1916 Influence of Arsenic upon Soil Organisms 405 



There is still the possibility that the arsenic liberates the phosphorus 

 from its insoluble compounds in the soil and thus makes it more available 

 to the micro-organisms. If this be the case, one would think that the 

 addition of soluble phosphates to the soil investigated would increase its 

 nitrogen-fixing powers. Experiments, however, did not bear out this 

 assumption, for just as large a quantity of nitrogen was fixed in the 

 absence of the soluble phosphate as in its presence. This was probably 

 due to the fact that the soil under investigation was well supplied in the 

 natural condition with soluble phosphorus. But that the arsenic did 

 have an influence upon the solubility of the phosphorus of the soil was 

 shown by the following experiment: loo-gm. portions of the soil were 

 placed in covered tumblers. Of these, 24 received 0.0728 gm. of lead 

 arsenate each, while the other 24 received none. The moisture was made 

 up to 18 per cent and incubated for 20 days. At the end of this time the 

 water-soluble phosphorus was determined in 12 of the treated and 12 of 

 the untreated soils by extracting with 500 c. c. of distilled water and deter- 

 mining the phosphorus in the extract (Greaves, 1910). As an average of 

 the 12 closely agreeing determinations of the soil treated with arsenic 

 there was obtained 0.59 mgm. of water-soluble phosphorus, while the 

 untreated soils yielded 0.52 mgm. This is a slightly greater quantity 

 in the arsenic-treated soil than in the untreated, which is probably 

 due to the fact that more of the phosphorus had been changed in the bodv 

 of the soil organisms to nucleoproteins or phosphoproteins. That this is 

 the correct interpretation is shown by the results obtained from the 

 remaining samples. Twelve of these samples, six with and six without 

 arsenic, were digested for six hours with 100 c. c. of 12 per cent hydro- 

 chloric acid and the phosphorus determined in the filtrate. The other 

 samples were ignited and the phosphorus extracted by the 12 per cent 

 hydrochloric acid determined. The average of the results thus obtained 

 is given in the tabular form below : 



Samples not ignited: 



Soil with arsenic 105. 6 mgm. of phosphorus. 



Soil without arsenic 100. o mgm. of phosphorus. 



Excess of acid-soluble phosphorus in 

 soil with arsenic 5. 6 mgm. of phosphorus. 



Samples ignited: 



Soil with arsenic 107. 7 mgm. of phosphorus. 



Soil without arsenic 100. 8 mgm. of phosphorus. 



Excess of acid-soluble phosphorus in 

 soil with arsenic 6. 9 nigm. of phosphorus. 



This would give by the Schmoeger method 2.10 mgm. of organic phos- 

 phorus in the arsenic- treated soil, while in the untreated soil there was 



