I9I3] 



/. E. Greaves 



The mixtures were incubated at 28° C. to 30° C. for three weeks 

 and the nitrates determined by transferring the soil, by means of 

 250 c.c. of distilled water, to a mortar containing 2 gm. of quick 

 lime. The soil was triturated for 2 minutes and then transferred to 

 a closed bottle and allowed to stand for 12 hours. At the end of 

 this time an aHquot portion, 25 c.c, was measured into a 100 c.c. 

 beaker and evaporated to dryness. The residue was treated with 

 2 c.c. of phenol-disulphonic acid equally distributed over all the res- 

 idue and then allowed to stand for 10 minutes. The resulting Solu- 

 tion was diluted with water and the excess of acid neutralized with 

 dil. ammonium hydroxid sol. The ensuing color was compared 

 with that produced by a Standard Solution of potassium nitrate 

 treated in the same manner. The determinations were all made in 

 duplicate and compared with sterile blanks, so that each reported 

 result is the average of two or more closely agreeing determina- 

 tions. The results obtained for soluble arsenic (sodium arsenate) 

 are given in Table 3. 



TABLE 3 



Data pertaining to nitric nitrogen produced in 100 grams of soil containing dif- 

 ferent amounts of arsenic in the form of sodium arsenate 



A striking general similarity is seen to exist between the results 

 here presented and those found for the ammonification series. No 

 toxicity was noted until 100 parts per million were present. It is 

 likely that the main part of the soluble arsenic was transformed into 

 the comparatively insoluble iron and calcium arsenates, hence the 

 great similarity throughout the entire series. The Stimulation 

 caused when the concentration was from 75 to 85 parts per million 



