220 NITRIFICATION 



amount will check it entirely. Thus Warington found that the 

 presence of 0.032 per cent, of bicarbonate of soda distinctly retarded 

 nitrification, and in the presence of 0.096 per cent, nitrification was 

 only barely possible. The same author also showed that the 

 presence of 0.0477 per cent, of ammonia in urine rendered it unnitri- 

 fiable. Dumont and Crochetelle found that potassium carbonate 

 added to soil at the rate of from 1 to 2.5 grams per 1000 grams of 

 soil markedly increased nitrification, but larger applications of the 

 salt progressively diminished the rate of nitrification, and that the 

 addition of 8 grams per 1000 grams of soil completely checked it. 

 A heavy dose of lime by unduly increasing the alkalinity of the 

 soil may at first check or suspend nitrification until the said lime 

 has been converted into carbonate. This, however, takes place, 

 rapidly, diminishing in turn its strong alkaline properties and per- 

 mitting nitrification to commence more actively than before. 



Food Requirements of Nitrifiers. The nitrifying organisms require 

 the same elements as do other bacteria, and hence will be considered 

 in this chapter only in a very general way, except in regard to 

 the source of the required elements. 



Winogradsky found that the nitrosomonas were able to grow in 

 a medium consisting of 2.25 grams of ammonium sulphate, 2 grams 

 of common salt, and 1 grams of magnesium carbonate in 1 liter of 

 well water. For the nitrobacter the ammonia is replaced by 

 sodium nitrite. In media such as the above, devoid of organic 

 carbon, the nitrifying organisms are able to function in the dark 

 and form from the inorganic carbon, organic carbon compounds. 

 He proved by numerous quantitative determinations that during 

 nitrification an increase in the amount of carbon compounds takes 

 place. "Since this bound carbon in the cultures can have no 

 other source than the carbon dioxid and since the process itself 

 can have no other cause than the activity of the nitrifying organ- 

 ism, no other alternative was left but to ascribe to it the power of 

 assimilating carbon dioxid. 



"Since the oxidation of ammonia is the only source of chemical 

 energy which the nitrifying organisms can use, it is a priori that 

 the yield in assimilation must correspond to the quantity of oxi- 

 dized nitrogen. It turned out that an approximately constant 

 ratio exists between the values of assimilated carbon and those of 

 oxidized nitrogen." This is illustrated by the following results: 



No. 5. No. 6. No. 7. No. 8. 



Oxidized nitrogen . 722.0 506.1 928.3 815.4 



Assimilated carbon . 19.7 15.2 26.4 22.4 



Ratio nitrogen: carbon 36.6 33.3 35.2 36.4 



It is evident that 1 part of assimilated carbon corresponds to 

 about 35.4 parts of oxidized nitrogen or 96 parts of nitrous acid. 



