358 ANNUAL. REPORT OF THE Oflf. Doc. 



6. Denitrification and Loss of Free Nitrogen. 



Through the agency of bacteria present in all soils, nitrates under 

 certain conditions may be converted into lower oxides of nitrogen, 

 into ammonia or into free nitrogen. 



Goppelsroder/^ in 1862, made the obserration that in soils rich in 

 humus active denitrification took place. 



In 1882, Gayon and Dupetit" found that in river water containing 

 small quantities of nitrate of potash (0.02-0.2 grams per 1000) there 

 was a reduction of the latter salt to ammonia. 



The reduction of nitrates through the agency of bacteria was later 

 (1883) observed by Deh^rain and Maquenne,^^ and also by Springer,^^ 

 which reduction they held to be due to the agency of anaerobic forms, 

 similar to B. huti/ricus, which either reduced the nitrates to lower 

 oxides of nitrogen or to free nitrogen. 



Heraeus,^*^ in 188G, isolated from water two bacilli which posessed 

 to an eminent degree the power of reducing nitrates to nitrites. 

 Blasi and Fravoli,®^in 1888, found in Palermo soil 27 different species, 

 which they have studied as to their chemical action in gelatin con- 

 taining nitrates. They found that in 1-3 days the quantities of ni- 

 trates diminished with a simultaneous increase of nitrites. These 

 latter reached their maximum in 6-8 days, and after 25-30 days en- 

 tirely disappeared. 



Frankland,^^ in 1888, isolated from water some 32 different species 

 of bacteria, of which no less than 17 possessed the power more or 

 less completely of reducing nitrates to nitrites. Of these the most 

 strongly reducing were B. ramosus and B. pestifer. 



Br^al,^^ in 1892, isolated from straw and other refuse a ferment 

 which possessed strong reducing action. He found that if to straw 

 fermenting in water, nitrates w'ere added, the latter rapidly disap- 

 peared, while if sterilized straw were put into water and allowed to 

 ferment, no such reduction took place, thus showing the presence 

 upon the straw of some specific denitrifying organism. The nitrogen, 

 according to the author, appeared partly in organic combination and 

 partly as elementary nitrogen. 



Gilthay and Aberson,^* in 1892, isolated from both soil and atmos- 

 phere two organisms w-hich possessed active powers in reducing 

 Ditrates, and which they named Bacillus denitri-^cans var. a. and b. 

 Both of these liberated free nitrogen. 



Egunow,*^ in 1893, isolated from the surface of seed a bacillus 

 which possessed the power of reducing nitrates to nitrites, etc. 

 Egunow found that in flasks with broad flat bottoms, with mineral 

 media and nitrates, and with the fluid only a few millimetres thick, 

 the nitrates were finally converted into ammonia. Where the thick- 

 ness of the fluid was 10 mm., the nitrates were converted into am- 



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