AGRICULTURAL CHEMISTRY. 143 



tals, and has a not unpleasant saline taste. In a state of purity its 

 solution in water may be kept indefinitely without change; but in 

 presence of a ferment, (an oxydizing albuminoid,) with which it is 

 always naturally associated, it speedily undergoes decomposition; and 

 by simply involving a certain amount of water in its change falls into 

 the same substances which we have so often referred to as among the 

 termini of vegetable and animal disorganization, viz: carbonic acid 

 and ammonia. The following scheme illustrates this change: 



One atom urea — C 2 N 2 H 4 2 



Two atoms water — H, 0„ 



Sum = C 2 N, H 6 0~ 



Equal to — 



Two atoms carbonic acid = C 2 4 



Two atoms ammonia — N„ EL 



Sum = C 2 N 2 H 6 4 



Besides urea there occurs in the urine of man, and in large quan- 

 tity in that of herbivorous animals, a body containing nitrogen which 

 bears the name Mppuric acid. In the urine of carnivorous animals, 

 and especially in the solid urine of birds and reptiles, is found uric 

 acid. Both these substances readily undergo conversion into carbo- 

 nate of ammonia. 



In the solid excrement of animals are found other bodies contain- 

 ing nitrogen, which by decay shortly restore the same to the atmos- 

 phere. 



The processes we have thus briefly noticed do not, as already inti- 

 mated, fully and immediately change the organized matter of vegeta- 

 bles and animals back again into the substances which, according to 

 our present knowledge, are to be regarded as the food of the plant. 

 In the immense coal beds of former epochs and in the vast deposits 

 of peat and sunken drift-wood that are now accumulating in marshes 

 and river deltas, an enormous quantity of carbon and of nitrogen too, 

 is, so far as the historical age is concerned, permanently set aside from 

 the great circulation of matter. 



What is of more agricultural importance, a large amount of nitro- 

 gen escapes in the free state into the atmosphere, and thus becomes 

 lost to the stapes of- nutriment for plants. But there are other re- 

 sources provided in nature's economy to maintain the requisite equi- 

 librium. 



The numerous volcanoes from which the smoke of central fires is 

 perpetually escaping, pour daily into the atmosphere vast volumes of 

 carbonic acid and not a little ammonia. In many regions, not in the 

 usual sense volcanic, the earth is full of fissures that give forth un- 

 ceasing streams of these gases. In the district of the Eifel, on the west- 

 ern shore of the Rhine, it has been estimated that 100,000 tons of 

 carbonic acid are annually thrown into the atmosphere. 



But the principal means of resupplying carbonic acid and ammonia 

 consists in the combustion of the coal and peat that represent the 



