ATISrOSPHEItlC AIU AS THE FOOD OF PLANTS. 51 



form ammonia, they do not combine either spontaneously or 

 by aid of any means yet devised, but remain for an indef- 

 inite period as a mere mixture. The oft repeated assertion 

 that nascent hydro2;en, i. e., hydrogen at the moment of 

 libei'ation from some combination, may unite with free 

 nitrogen to form ammonia, has been completely refuted by 

 the experiments of Will, {Ann. Ch. u. PA., XLV, 110.) 

 The ammonia observed by older experimenters existed, 

 ready formed, in the materials they operated with. 



2. It appears from recent researches (of Boettgor, 

 Schonbein, and Zabeliu) that ammonia is formed in minute 

 quantity from atmospheric nitrogen in many cases of cona- 

 bustion, and is also generated when vapor of water and 

 the air act upon each other in contact with certain organic 

 matters, at a temperature of 120° to 160° F. To this sub- 

 ject we shall again recur, p. 77. 



3. Ammonia may result from the reduction of nitrous 

 and nitric acids, and from the action of alkalies and lime 

 upon the albuminoids, gelatine, and other similar organic 

 matters. To these modes of its formation we shall recur 

 on subsequent pages. 



4. Ammonia is most readily and abundantly formed from 

 organic nitrogenous bodies; e. g., the albuminoids and 

 similar substances, by decay or by dry distillation. It is 

 supposed *to have been called ammonia because one of its 

 most common compounds (sal ammoniac) was first prepared 

 by burning camels' dung near the temple of Jupiter Amiu' m 

 in Libya, Asia Minor. The name hartshorn, or spirits of 

 hartshorn, by which it is more commonly known, was 

 adopted from the circumstance of its preparation by dis- 

 tilling the horns of the stag or hart. 



The ammonia and ammoniacal salts of commerce (car- 

 bonate of ammonia, sal ammoniac, and sulpliate of ammo- 

 nia) are exclusively obtained from these sources. 



When urine is allowed to become stale, it shortly smelly 



