1847.] The Organic Matter of Soil. 97 



sorbs it whenever it is freed from its combinations. Other modes 

 undoubtedly exist by which the nitrogenous compounds are sup- 

 plied with this essential element. Ammonia, too, has been 

 proved to be present at all times in the atmosphere, though only 

 in small proportions. 



One of the forms in which ammonia is found in the soil is 

 that of apocrenate of ammonia; a compound which is formed 

 from humic acid by its continued oxidation; the apocrenic acid 

 being merely a higher state of oxidation of the same substance. 

 In the chain of causes by which apocrenic acid is formed, nitric 

 acid is also generated, according to Mulder — this acid acts with 

 great vehemence upon humic acid. Admitting the fact of the 

 formation of nitric acid, and its subsequent action on humic acid 

 follows necessarily; and furthermore, we can understand how the 

 humic acid is oxidated and changed into apocrenic acid. Mul- 

 der says, p. 166, in his Chemistry of Vegetable and Animal Phy- 

 siology, W'hen apocrenic acid is found in the soil it is accompa- 

 nied with the production of caibonic acid; the ammonia of the 

 soil produced in it from the atmospheric air it has absorbed, may, 

 by the influence of decaying, organic substances and water, be 

 converted into nitric acid; and no doubt is so when the bases 

 required for nitrification are present. Saltpetre was long ex- 

 tracted from the soil exclusively, as in many places in Egypt, 

 India, &c. By the oxygen of the atmospheric air contained in 

 the soil, the hydrogen and nitrogen of ammonia produced from 

 the constituents of the air are oxidized; water and nitric acid as 

 soon as it is formed, meets with a substance in the soil, humic 

 acid and humin, which by its influence is converted into apo- 

 crenate of ammonia, and at the same time produces carbonic 

 acid. This change of humic acid into apocrenic acid takes 

 place in minute quantities; as is the case w^ith the formation of 

 ammonia which precedes it. Thus, to form one equivalent of 

 apocrenic acid, there are required two equivalents of humic acid 

 and one equivalent of ammonia and seventy-six equivalents of oxy- 

 gen. In this production of apocrenic acid, the ammonia from the 

 humate of ammonia is not only transferred to the apocrenic acid, 

 but it performs an intermediate part, namely, the fixing of oxy- 

 gen. Through the tendency of ammonia to form nitric acid, the 

 oxygen of the atmospheric air contained in the soil is combined 

 with the constituents of the humic acid; the ammonia itself re- 

 maining unchanged; neither leaving the soil, nor being oxidized 

 into nitric acid. If there be not an abundance of organic mat- 

 'ter, and if the air be moist, and lime, magnesia or potash be 

 present*, ammonia is first produced, and afterwards nitric acid. 

 If, on the contrary, instead of these leaves, organic substances are 

 in excess, humic acid is formed by their decay; at the same time, 

 7 



