SOURCE OF NITROGEN TO MAX. 225 



existence of a man. Thus it is literally true, 

 that a large portion of our muscles and flesh 

 was once present in the air as a gas !* Such, 

 then, is the importance of an atmospheric in- 

 gredient, the whole amount of which, in up- 

 wards of eleven thousand cubic feet of air, has 

 been estimated to be about one grain ! 



The ordinary sources of ammonia in the atmo- 

 sphere are readily recognisable. It was a curious 

 fact, incidentally noticed in the experiments 

 which detected ammonia in rain-water, that the 

 ammonia thus procured always possessed the 

 " offensive smell of perspiration and animal ex- 

 crement;" and this plainly indicates one of the 

 most abundant sources of this valuable atmo- 

 spheric constituent. Whenever organic bodies 

 containing nitrogen undergo putrefaction, am- 

 monia is abundantly evolved. As the last pro- 

 duct of this process, it streams up from large 

 cities where heaps of decomposing animal mat- 

 ter pollute the pure air of heaven. It has also 

 been stated to escape from volcanos in the form 

 of a sulphate. A grotto exists near Naples in 

 which ammoniacal gas is discharged in large 

 quantities, apparently from some volcanic strata. 

 Combustion, and many economical and manu- 



* The remarkable results of M. Regnault show that in some 

 cases animals appropriate the nitrogen of the air and increase 

 in weight simply by the process of respiration. Vide p. 340. 



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