CHEMICAL CHANGES 



119 



moderate amount of air. In many processes the purification 

 ;oes no farther, when nitrification is not subsequently active. 



The nitrosification change in the second stage gets rid of the 

 transition products — ammonia, amido-acids, and the amides — 

 )y double decomposition into water, or hydroxy-compounds 

 |[which are afterwards broken up by fermentation) and nitrogen 

 ras. As simple instances we have : 



NH3 + HNO2 



(NH2)CH,C00H + HNO2 

 Amido-acetic acid. 

 (NH2)C2H, + HN02 

 Ethylamine. 



2H2O + N2 



(OHjCHgCOOH + Hfi + N2 



GJycolic acid. 



C2HpH + H,0 + N2 



Alcohol. 



In the process, which takes place especially in the resting- 

 Full period of filters, nitrogen, and sometimes secondarily CO2, 

 ire evolved, but scarcely any hydrogen or methane. It is there- 

 Fore accompanied by a great loss of nitrogen, a smaller loss of 

 :arbon, and a removal of odour. 



Grimbert^ has shown that B. coli communis and B. typhosus 



lo not disengage gas in i per cent, solution of peptone plus 



per cent, potassium nitrate, but the gas is produced when the 



)eptone is replaced by meat extract, which contains simpler 



imido-compounds. The volume of nitrogen evolved is always 



ibout double the amount which the nitrate destroyed could - 



[possibly produce, proving that the gas is derived from the 



secondary reaction between amido-substances and the nitrous 



[acid produced by denitrification. The bacilli develop very well 



[in a medium containing i per cent, of nitrites, and disengage 



in equal or even larger quantity of nitrogen than in the same 



ledium containing i per cent, of nitrates. He believes that 



this is the explanation of the loss of nitrogen in the soil. 



Nitrous compounds also serve as carriers of oxygen from the 

 tir to the organic matter in a way similar to their well-known 

 [action in vitriol chambers. Muntz^ found that the calcium 

 [nitrite in sterilized soil, when CO2 was passed over it, gave off 

 initrous acid rapidly, but on exposure to air, or on passing COg 

 lairgely diluted with air, it was quickly oxidized to nitrate. The 

 ^following are examples from my own experience of the changes 

 in filter effluents (parts per 100,000) : 



1 Annales de VInstitut Pasteur, January, iSgg. 

 Comptes rendus^ 1891, cxii,, 1142. 



