210 NITRIFICATION 



essential in the purification of sewage by soil. They filled a glass 

 tube one meter long with ignited quartz sand and powdered lime- 

 stone. Sewage passed through his filter at first unchanged, but 

 later nitrates began to appear, and soon the filtrate contained 

 no ammonium salts. They suspected microorganisms as being 

 the active agent, and hence treated the contents with chloroform 

 vapor. Nitrification entirely ceased and was not renewed for 

 seven weeks, although the supply of chloroform w^as suspended. 

 A water extract of fresh garden soil added to the tube soon restarted 

 the process. 



These experiments were immediately repeated by Warington who 

 confirmed the results of Schlosing and Miintz and showed that: 

 (1) The power of nitrification could be communicated to media 

 which did not nitrify by simply seeding them with a nitrifying 

 substance; (2) the process of nitrification in garden soil is entirely 

 suspended by the presence of the vapor of chloroform or carbon 

 disulphid. Since these early experiments much additional proof 

 has been furnished by investigators showing that the process of 

 nitrification both in soils and waters is undoubtedly due to living 

 microorganisms. Some of these are the limits of temperature 

 within which nitrification is possible, the necessity of a suitable 

 food, and finally the isolation of specific organisms having the 

 power of producing nitrates. 



Schlosing and Miintz were unable to isolate any specific ferment 

 capable of causing nitrification, but the true nature of the process 

 not being known, many investigators turned to this phase of the 

 work and the race to see who would first reach the coveted goal be- 

 came intensely interesting. Celli-Zuco and Heraeus, in 1886, suc- 

 ceeded in isolating from water rich in nitrates a number of forms of 

 bacteria which they considered possessed very feeble nitrifying 

 properties. Inasmuch as the nitric acid in their cultures may have 

 been absorbed from the air, and as they did not succeed in isolat- 

 ing and proving any organism to be capable of nitrification their 

 experiments were considered to be inconclusive. Frank attempted 

 a similar isolation but without success, and he even concluded 

 that nitrification was not due to the direct action of microorganisms 

 but was a purely chemical process. But this view was opposed 

 by a number of writers, notably Landolt, Platt, and Baumann. 



Warington and Frankland studied a large number of soil organ- 

 isms, but neither was able to find any which produced active 

 nitrification. Frankland continued to maintain that the nitrify- 

 ing organism was present in soil, and in 1890 succeeded in isolating 

 a spherical organism about 0.8 M in diameter which possessed the 

 power of converting ammonium salts into nitrites, but not into 

 nitrates. The separation was made by means of the dilution 

 method, using only inorganic salts. 



