OXIDATION 



101 



ties, are formed in this way. There are two distinct kinds 

 of bacteria involved. One, the nitrous bacteria, oxidizes 

 the ammonia to nitrous acid which forms nitrites with bases, 

 and the other, the nitric bacteria, oxidizes the nitrous to 

 nitric acid, giving nitrates with bases. A striking pecuh- 

 arity of these two classes of organisms is that they may live 

 entirely on inorganic food materials, are proto-autotrophic, 

 prototrophic for oxygen (aerobic) and autotrophic for the 





Fig. 67. — Sprinkling filters of the Colum]:)us sewage-disposal plant — 

 devices which provide a good supply of oxygen for the bacteria that oxidize 

 the organic matter in the sewage. 



other elements. Their carbon is derived from CO2 or car- 

 bonates. The importance of such organisms in keeping up 

 the supply of nitrates in the soil can scarcely be overesti- 

 mated. 



The oxidation of the H2S, which is formed in the putre- 

 faction of proteins, to free S by the sulphur bacteria and the 

 further oxidation of this free S to sulphuric acid, and of the 

 phosphorus, so characteristic of the nucleins, to phosphoric 



