ON NITRIFICATION 



487 



No. 5. Air with no change in composition (natural). 



After thirty days incubation at 25°C. the nitrates were 

 extracted, and determined by reduction and distillation. The 

 results are given in table 5. 



T.\BLE 5 



System no. 4 requires a little discussion. Sulphuric acid was 

 added in excess of the quantity needed for the neutralization of 

 the Na2C03, and apparently its action has been to absorb the 

 ammonia which was distilling from the culture itself; the final 

 nitrite content could be but low. It should also be stated that 

 no attempt was made to recover all the residual ammonia in the 

 soil. The quantity of nitrate formed in no. 3, if not accountable 

 by an experimental error in analysis, would require, according to 

 the ratio established by Winogradsky, a quantity of 0.01 mgm. 

 of carbon as CO2, a quantity which could easily have escaped 

 immediate absorption by the alkali used. 



The conclusions to be drawn from these experiments are, 

 then : (a) that nitrification is completely checked by the complete 

 absence of carbon dioxide in the system throughout the experi- 

 mental period (when a concentrated alkali is present therein); 

 (b) that when a small inoculum is used, in spite of the fact that 

 ignited soil holds carbon dioxide by absorption, and when the 

 supply of this gas is nil at the start, the phenomenon of nitroso- 

 fermentation is practically inhibited. 



In direct consequence of these facts stands the conclusion that, 

 since the inoculum was small and nitrification in no. 2 was negli- 

 gible, contrary to the results of experiments 229 and 229a, and 

 since in this case there was not an active production of carbon 



