ATMOSPHERIC AIR 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 hydrogen, i. e., hydrogen at the moment of 
liberation from some combination, may unite with free 
nitrogen to form ammonia, has been completely refuted by 
the experiments of Will, (Ann. Ch. u. Ph., XLV, 110.) 
The ammonia observed by older experimenters existed, 
ready formed, in the materials they operated with. 
2. It appears from recent researches (of Boettger, 
Schénbein, and Zabelin) that ammonia is formed in minute 
quantity from atmospheric nitrogen in many cases of com- 
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 tle 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 Ammon 
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 sulphate of ammo- 
nia) are exclusively obtained from these sources, 
When urine is allowed to become stale, it shortly smells 
