It CHEMICAL CHANGES 127 



an be naturally nitrified by properly - constructed filters, 

 II the expense of artificial nitrate should not be required. 

 Hugounenq and Doyon^ first noticed that B. coli comimmis 

 could decompose nitrates, setting free nitrogen and utilizing 

 the oxygen ; and Warington proved that the loss of nitrogen 

 from manure increased in proportion to the fermentable organic 

 matter.^ 



Burri and Stutzer's B. denitrificans II. liberated go per cent. 

 li of the nitric nitrogen from Giltay's solution as free N. Giltay 

 i himself obtained 80 per cent., Stutzer as much as gS'g to 99*6, 

 some of the nitric N being converted into organic N in the 

 protoplasm, etc. Much COo and some H was produced. The 

 organisms could thrive without air, but seemed to require air 

 when they first began to develop. In one of my own observa- 

 tions a tank effluent, free from nitrite and nitrate, was mixed 

 with a ninth of its volume of a coke-breeze filtrate containing 

 4*34 parts per 100,000 of N as nitrate and no nitrite, and the 

 mixture kept out of contact with air for five days at 15° C. By 

 this time the whole of the 0*434 part of nitric N in the mixture 

 had disappeared without the formation of either nitrite or free 

 nitrogen. The same liquid exposed to air and light afterwards 

 yielded nitrites in abundance. The loss of organic nitrogen 

 was not accounted for by the production of either nitric acid, 

 ammonia, or nitrogen gas. Other possible products are nitrous 

 and nitric oxides, NoO and N2O2 (p. 121) ; the occurrence of 

 the former was recorded by Gayon, of the latter by Adeney. 

 Both, being soluble and neutral, have no doubt often been over- 

 looked. In my experiment the rapid production of nitrite on 

 exposure to air appears to indicate the presence of nitric oxide. 

 P. Frankland notes that the common B. aquatilis does not form 

 nitrites, yet in its growth causes a considerable disappearance 

 of nitric nitrogen.^ A large number of organisms reduce nitrate 

 to N or N^O, acting generally by symbiosis, the intermediate 

 production of nitrous acid not being detectable, probably 

 because it is destroyed as soon as formed. Jensen* restricts 

 the term " denitrification " to this reaction, and mentions eleven 

 species of bacteria which effect it, including the pathogenic 

 B. pyocyaneus, and A. Stutzer^ confirms and extends these 

 results, early observed by Jordan and Richards. 



^ Ami. Chim. Phys., 1898, vii., 45. 



2 J 02irnal of the Royal Agricultural Society, 1897, III., viii., 577. 



^ Chemical Society's Transactions, 1888, 391. 



^ Bied. Central., 1900, xxiv., 273. 



•^ Centr. Bakt. Par., 1901, ii., 781. 



