i6 



seems to assist the action of the nitric organisms ; while if 

 the supply is insufficient, their activity is hindered or ceases. 

 Schloesing obtained the following results in a long-continued 

 series of experiments bearing on this point : 



TABLE IV. 



These figures show clearly that the amount of nitric 

 acid formed is greater or less according as the soil is more 

 or less moist. It must be noticed, however, that the 

 amount of nitric acid formed is not in strict proportion to 

 the amount of water in the soil, but is, on the whole, pro- 

 portionately greater in the moister soils. Thus, com- 

 paring Column IV. with Column I., we see that in the 

 former, which is little more than twice as moist, about 

 three times as much nitric acid was formed during each 

 of the two periods of experiment. 



A certain degree of warmth is also necessary for the 

 action of the organisms. Below a temperature of about 

 40 Fahr., they are practically inactive ; but with greater 

 warmth, nitrification becomes more and more rapid up to 

 about 95 Fahr., which is the most favourable tempera- 

 ture. Above that, the rapidity of nitrification very soon 

 becomes less, and at about 120 Fahr. practically ceases. 

 Muntz found the following quantities of nitric acid formed 

 in similar nitrifying solutions kept at the temperatures named 

 for nearly two months : 



TABLE V. 



Nitric Acid 



Formed. 

 Milligrams. 



41 to 46 2-3 



57 ,,'61 19-5 



73 39-4 



80 59-7 



91 81-8 



There is here a steady increase in the amount of nitric 

 acid formed, corresponding to each increase of temperature 

 up to 98 Fahr., after which the quantity falls off rather 

 rapidly with each further increase. 



For the continued action 'of the micro-organisms, it is 

 also necessary that the soil should contain some "base" 

 that is, some substance which can combine with nitric acid 



Temperature. 

 .Deg. Fahr. 



