122 NOETH-CAEOLINA GEOLOGICAL SURVEY. 



power of decomposing the former and taking to itself its oxygen ; the hy- 

 drogen being liberated instantly combines with the nitrogen of the air in 

 the soil, and forms with it ammonia. Humic acid, too, by its strong affinity 

 for ammonia, rapidly absorbs it whenever it is freed from its combinations. 

 Other modes undoubtedly exist by which the nitrogenous compounds are 

 supplied 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 apo- 

 crenate 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 apo- 

 crenic 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. Mulder says, p. 166, in 

 his Chemistry of Vegetable and Animal Physiology, when apocrenic acid 

 is found in the soil it is accompanied with the production of carbonic acid; 

 the ammonia of the soil produced in it from the atmospheric air it has ab- 

 sorbed, 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 extracted 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 ammo- 

 nia 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 apocrenate 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 with 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 oxygen. 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 oxygen. 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 

 remaining unchanged; neither leaving the soil, nor being oxidized into 

 nitric acid. If there be not an abundance of organic matter, and if the air 

 be moist, and lime, magnesia or potash be present, ammonia is first pro- 

 duced, and afterwards nitric acid. If, on the contrary, instead of these 

 leaves, organic substances are in excess, humic acid is formed by their de- 

 cay; at the same time, ammonia is produced from the nitrogen of the at- 

 mosphere; and, finally, apocrenate of ammonia, carbonic acid and water." 



This long extract seemed to be required in order to put the reader in 



