ON NITRIFICATION 



481 



per acre was used. Three 100 gram lots in the air-dry condition 

 were each moistened with 20 cc. of a 0.5 per cent solution of 

 ammonium sulphate and incubated at room temperature under 

 the following conditions: no. 1, together with a beaker of water, 

 under a bell-jar sealed with vaseline to a glass plate; no. 2, under 

 a bell-jar together with a beaker of soda-lime; no. 3, in the open 

 laboratory air. After thirty days the soils were extracted with 

 water, and the nitrates determined in the extract by means of 

 the phenoldisulphonic acid method. The results obtained are 

 summarized in table 1. 



TABLE 1 



It thus appears that the process of nitrification in American 

 soils is appreciably hindered by the removal of the free carbon 

 dioxide. At first it would seem as if these results were contrary 

 to those given by Godlewsky, since even in presence of soda lime 

 a certain amount of nitrification did take place. Nevertheless, 

 the arrangement of the experiment may account for this. The 

 soil was in Erlenmeyer flasks and the bell-jars used were of 5000 

 cc. capacity. Had the soda-lime been in the immediate vicinity 

 of the soil, the carbon dioxide removal would have been more 

 complete. Furthermore, in a soil containing organic matter, 

 decompositions are always taking place, and by virtue of the 

 great surface and high retentive power of soils for gases, enough 

 carbon dioxide may easily have been retained to furnish a source 

 of this gas in the immediate vicinity of the bacterial cells. IJsing 

 the ratio N/C = 36 established by Winogradsky, the quantity 

 of carbon fixed in the nitrification of 4.3 mgm. of nitrogen, would 

 be 0.1 mgm. a quantity easily retained by the soil. 



