I9I3] 



/. E. Greaves 



man's^ method, with slight modifications. Beakers covered with Petri 

 dishes were sterilized and into these were weighed loo-gm. portions 

 of the air dried soil and i gm. o£ dry blood. Sodium arsenate was 

 added from a Standard Solution with the proper proportion of sterile 

 water. The dry insoluble Compounds were thoroughly mixed with 

 the soil and then the water content of the soil made up to i8 percent 

 with distilled sterile water. The samples were incubated at 28° C. 

 to 30° C. for four days and the ammonia determined by transferring 

 to Kjeldahl flasks with 250 cc. of distilled water, adding 2 grams of 

 magnesium oxide and distilling into n/io sulfuric acid sol. The 

 determinations were made in duplicate and compared with sterile 

 blanks, so that each reported result is the average of two er more 

 closely agreeing determinations. The results for soluble arsenic 

 (sodium arsenate) are given in Table i. 



TABLE I 



Data pertaining to the ammonia produced in 100 grams of soil containing dif- 

 ferent amounts of arsenic in the form of sodium arsenate 



From the above results it may be seen that, in dilute Solution, 

 sodium arsenate stimulated the activity of the ammonifying organ- 

 isms of the soil, the greatest influence having been exerted at a con- 

 centration of 3 parts per million. The eff ect was quite marked up to 

 a concentration of 7 parts per million. Part of this stimulating 

 action, however, may have been due to the anion and not to the 

 cation, as Lipman in his work has noted a stimulating effect with 

 some sodium Compounds. No retarding influence was noted untilthe 

 concentration of the sodium arsenate reached 20 parts per million, 



2 Lipman : Centralbl. f. BakterioL, 1912, xxxii, p. 8. 



