On the Application of Mamires. 



255 



in wliat is called a nascent state that it will unite, nor do bodies 

 containing either hydrogen or oxygen in combination exert for it 

 the smallest affinity. 



Liebig therefore concludes that it is furnished to plants by the 

 decomposition of ammonia,* — a compound of nitrogen with hydro- 

 gen, — which, from its solubility in water and in acids, together with 

 the facility with which it is resolved into various and opposite 

 forms, seems exactly calculated to enter into the vegetable or- 

 ganization, and to supply the nitrogen which it requires. 



But is ammonia so uniformly present wherever plants are to be 

 found, as the foregoing explanation appears to assume ? 



Considering that this gas is the constant result of animal de- 

 composition, its presence in recently-manured soil, or even generally 

 near the great resorts of man, may perhaps be readily conceded ; 

 but are we authorized to regard it as the source of nitrogen in 

 plants that grow in places reixlote from human habitation, where 

 decaying animal matter cannot so constantly present itself? 



This question, which had embarrassed all those who formerly 

 indulged in speculations on the subject, seems at length to have 

 been set at rest by the researches of Liebig. 



Experiments made," he says, in his laboratory at Giessen, 

 with the greatest care and exactness, have placed the presence 

 of ammonia in rain-water beyond all doubt. It had hitherto 

 escaped observation, merely because no one thought of search- 

 ing for it," All the rain-water which he examined was col- 

 lected 600 paces west of Giessen, whilst the wind was blow- 

 ing towards the town in that direction. It could not therefore 

 have been derived from any animal exhalations proceeding from 

 that source. When several hundred pounds of this water were 

 distilled in a copper still, and the first two or three pounds that 

 came over had been evaporated with the addition of a little 

 muriatic acid, very distinct crystals of sal ammoniac were obtained. 



Hence there can be no doubt that ammonia must be constantly 

 present, combined probably with carbonic acid, in the atmosphere 

 we breathe, although in quantities too minute to be appreciable. 



Its amount, as inferred from the indications afforded by the rain 

 or snow-water that has been examined, appears to be very variable, 

 being greater in suiYimer than in winter, during long-protracted 

 drought than after a continuance of wet ; but this is no more than 



* May it not also be true that the converse likewise occurs in some case?, 

 and that hydrogen is assimilated whilst nitrogen is disengaged ? This I am 

 inclined to suspect, from having observed, in the court-e of my experiments 

 with respect to the action of light upon plants, that certain cruciferce, which, 

 from requiring animal manure, would seem to absorb a large amount of 

 ammonia, sometimes exhale pure nitrogen. 



See my Memoir in the Philos. Transactions for 1836. 



