TRANSFORMATIONS OF CARBON AND NITROGEN. 89 



the soil we always find large amounts of dead organic matter, 

 animal and vegetable. The purely carbonaceous bodies are 

 dissipated by processes already noted. The ureas, and the 

 more complex gelatins and proteids, are pulled to pieces and 

 reduced to simple forms. Even such hard substances as bone 

 undergo decomposition, for its nitrogenous ingredients furnish 

 food for bacteria and these, in time, accomplish the complete 

 disintegration of the mineral as well as the organic ingredients. 

 The nitrogen from all these bodies reaches a variety of end 

 products when the decomposition is finished. Part of it has 

 been wholly freed from combination and this passes off at once 

 into the air to join the great store of free nitrogen. Part of it 

 has been converted into ammonia, and since this is also a gas, 

 it is likewise exhaled from the decomposing soil into the air, 

 as is clearly indicated by the odor of ammonia characteristic 

 of decomposition. The ammonia is not all thus eliminated 

 from the soil, especially if acids be present, for it will readily 

 unite with various acids to form salts. If sulphuric acid be 

 present, as we have seen it is quite sure to be, it will form 

 ammonium sulpJiatc with the ammonia, and, with the carbon 

 eliminated from the decomposing products, ammonium carbo- 

 nate may be formed. These salts not being volatile will remain 

 in the soil where they may be later of direct use to plants, 

 either directly or after undergoing further modifications to be 

 noticed presently. But the denitrifying bacteria will not allow 

 all these ammonia salts to remain undisturbed, for, as we have 

 seen, denitrification is constantly setting free the nitrogen from 

 ammonia compounds. So long as this process of denitrifica- 

 tion continues there is a loss of nitrogen. It must be borne in 

 mind, however, that the actual loss of nitrogen by denitrifica- 

 tion from ordinary soil appears to be slight unless the amount 

 of organic matter undergoing decomposition is large. 



A considerable portion of the nitrogen, at the end of the 

 decomposition, reaches a different condition. In exactly what 



