AMMONIA AND NITRIC ACID FORMED. 411 



be'capable of ministering to vegetable growth. Here caustic lime steps 

 in more quickly, and mild lime by slower degrees, to promote the fur- 

 ther decay. It induces the carbonaceous matter to take oxygen from 

 the air and from water and to form acids, and the nitrogen to unite with 

 the hydrogen of the water for the production of ammonia — thus help- 

 ing forward the organic matter in its natural course of decay, and 

 enabling it to fulfil its destined purposes in reference to vegetable life. 



3°. But the ammonia which is thus disengaged in the soil by decay- 

 ing organic matter, though not immediately worked up, so to speak, by 

 living plants, is not permitted to escape in any large quantity into the 

 air. The soil, as I have already stated, is usually absorbent enough to 

 retain it in its pores for an indefinite period of time. And as in nature 

 and upon the earth's surface the elements of matter are rarely permitted 

 to remain in a state of repose, the ammonia, though retained apparently 

 inactive in the soil, is yet slowly uniting with a portion of the surround- 

 ing oxygen and forming nitric acid (Lee. VIII., § 5, note.) When no 

 other base is present, this nitric acid, as it is produced, unites with some 

 of the ammonia itself which still remains, forming nitrate of ammonia 

 —but if potash or lime be present within its reach, it unites with them 

 in preference, and forms the nitrate of potash or of lime. 



But lime, if present, is not an inactive spectator, so to speak, of 

 this slov/ oxidation of ammonia. On the contrary, it promotes this- 

 final change, and by being ready to unite with the nitric acid as it 

 forms, increases and accelerates its production, at the expense of the 

 ammonia which it had previously been instrumental in evolving. 



4P. One other important action of lime, by which the same com- 

 pounds of nitrogen are produced in the soil, may in this place be most 

 properly noticed. It is a chemical law of apparently extensive applica- 

 tion, that when one elementary substance is undergoing a direct chemi- 

 cal union with a second in the presence of a third, a tendency is impart- 

 ed to tlie third to unite also with one of with both of the other two, al- 

 though in the same circumstances it w^ould not unite with either, if pre- 

 sent alone. Thus, when the carbonaceous matter of the soil is under- 

 going oxidation in the air — that is, combining with the oxygen of the 

 atmosphere — it imparts a tendency to the nitrogen also to unite with 

 oxygen, which when mixed with that gas alone, (the atmosphere con- 

 sisting, as you will recollect, of nitrogen and oxygen — Lee. II., § 4,) — 

 it has no known disposition to do. The result of this is the production of 

 a small, and always a variable, proportion of nitric acid during the de- 

 composition in the soil, of organic matter even, which itself contains no 

 nitrogen. 



Again, it is an equally remarkable chemical law, that elementary 

 bodies which refuse to combine, however long we may keep them to- 

 gether in a state of mixture, will yet unite readily when presented to 

 each other in what is called by chemists the nascent state — that is, at 

 the moment when one or other of them is produced or is separated 

 from a previous state of combination. 



Thus when the organic matter of the soil decomposes water in the 



presence of atmospheric air, its carbon unites with the greater part 



of the oxygen and hydrogen which are set at liberty, and at the same 



time with more or less of the oxygen of the atmosphere — but at the 



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