ALKALINE NITRATES. 331 



to contain a small quantity of nitrate of potash, soda, 

 or lime, which appears to produce nearly the same 

 effect as the salts of ammonia, rendering vegetation 

 vigorous and dark colored. The way in which these 

 salts are formed will be easily understood when we 

 remember that, whenever substances containing ni- 

 trogen decay in the neighborhood of lime or alkaline 

 salts, a portion of nitric acid is formed (166, 837). 

 Under these circumstances, the ammonia which would 

 otherwise be produced is oxidized, and nitric acid 

 and water are formed in place of ammonia; the acid 

 combines with the alkali, and nitrate of potash or 

 soda results. These salts are frequently found in 

 mixtures of decomposing organic manures ; they are 

 formed in the same way in the soil itself. 



900. The effects produced on different plants by 

 alkaline nitrates are very various ; to some they are 

 far more beneficial than others. Some plants, such 

 as the sun-flower, tobacco, lettuce, and many others, 

 always contain more or less of these salts. Others 

 do not contain them, but when supplied with nitrates, 

 are subsequently found to contain the base, without 

 the acid. The soda, potash, or lime is combined 

 with some organic acid, whilst the nitric acid has 

 disappeared. It is probable that in these cases the 

 nitrogen of the acid is assimilated by the plant, or 

 that it assists in the formation of gluten and albu- 

 men. 



901. Nitrates can have but very little value as 

 manures on the soils which naturally contain salts of 



