ON NITRIFICATION 489 



practical failed to give satisfaction. In presence of MgCOs. 

 Mg (OH) 2 as a neutralizing base, ammonium hydroxide added 

 in small amounts at a time was easily volatilized and removed 

 from the nitrifying system : only 7 mgm. of nitrogen were trans- 

 formed to nitrite in eleven days although 30 mgm. of nitrogen as 

 ammonium hydroxide were added during this period, in small 

 amounts ranging from 2 to 9.4 mgm. at one time. This source 

 of ammonia even though undergoing slow nitrification did not 

 seem to hinder the action of the organisms, since the same culture 

 which had received the hydroxide additions was capable, after 

 this treatment, of nitrifying in three days 2 cc. of a 10 per cent 

 solution of ammonium sulphate for every 100 cc. of culture 

 solution'. 



Although the results obtained pointed to the possibility of 

 nitrification of ammonium hydroxide, it was thought that a study 

 of a non-carbonated base to be used in the cultures would prove 

 more satisfactory. Magnesium oxide was chosen since it has 

 a lower solubility of the carbonate and would give results directly 

 comparable to the conditions existing in the ordinary culture 

 solution as used in the present paper. Calcium oxide and 

 hydroxides as well as the oxides and hydroxides of the other metals 

 were discarded a priori on account of their greater solubility and 

 greater alkalinity. The aim was to use a base that would serve 

 to neutralize the acids arising from the reactions taking place 

 during nitrification rather than to exert its physiologically 

 alkaline properties. That the oxide chosen is not toxic is to be 

 assumed from the fact that the carbonate, used in all the pre- 

 vious experiments, contained one molecule of the oxide for 

 every molecule of the carbonate. 



Experiment 234 



Six flasks with very large flat bottoms received 50 cc. of the 

 ordinary Omeliansky solution made up with tap water. After 

 sterilizing and cooling, flasks 1, 2 and 3 received the addition 

 of a sterile suspension of Mg CO3. Mg (OH) 2, while flasks 4, 

 5 and 6 received a sterile suspension of MgO. All except nos. 



