222 THE CHEMISTRY OF CREATION. 



able quantity was collected and evaporated 

 down carefully. After this operation had been 

 long continued, at length brownish crystals 

 appeared in the fluid. The chemist's search 

 was about to Ixj crowned with success ; and 

 to his great gratification on analysing these 

 crystals, they proved to be the long-looked for 

 ammonia in the form of an ammoniacal salt. 



Quite recently, by a series of accurate expe- 

 riments, M. Fresenius has determined that 

 1,000,000 parts of atmospheric air contain, 

 during the day, 0'098 parts of ammonia; a 

 quantity equivalent to 0'283 parts of carbonate 

 of ammonia. During the night, singular to 

 state, the proportion is greater ; for the same 

 amount of air contains then 0'169 parts of am- 

 monia, or the equivalent of 0*474 parts of the 

 carbonate. It is not easy to trace the cause of 

 this excess during the night. This discovery 

 of the positive existence of ammonia in the 

 air proves of high importance, as we shall 

 immediately perceive. Ammonia is a com- 

 pound substance, formed of, by volume, three 

 of hydrogen, and one of nitrogen gases. Kow 

 it was long known that nitrogen was abso- 



o o 



lutely necessary to plants in order to supply 

 them with material for the formation of several 

 vegetable products containing nitrogen, such as 

 albumen, gluten, and fruits and seeds gene- 



