50 HOW CROPS FEED. 
feather wet with vinegar or dilute chlorhydric acid becomes surrounded 
with a dense smoke when approached to the mouth of the bottle, the 
latter may bc removed, corked, and another put in its place. Three or 
four pint bottles of gas thus collected will serve to illustrate its proper- 
ties, as shortly to be noticed. 
Solubility in Water.—This character of ammonia is ex- 
hibited by removing, under cold water, the stopper of a 
bottle filled with the gas. The water rushes with great 
violence into the bottle as into a vacuum, and entirely fills 
it, provided all atmospheric air had been displaced. 
The agua ammonia, or spirits of hartshorn of the drug- 
gist, is a strong solution of ammonia, prepared by passing 
a stream of ammonia gas into cold water. At the freez- 
ing point, water absorbs 1,150 times its bulk of ammonia. 
When such a solution is warmed, the gas escapes abund- 
antly, sc that, at ordinary summer temperatures, only one- 
half the ammonia is retained. If the solution be heated 
to boiling, all the ammonia is expelled before the water has 
nearly boiled away. The gas escapes even from very di- 
lute solutions when they are exposed to the air, as is at 
once recognized by the sense of smell. : 
Composition.—When ammonia gas is heated to redness 
by being made to pass through an ignited tube, it is de- 
composed, loses its characteristic odor and other proper- 
ties, and is resolved into a mixture of nitrogen and hydro- 
gen gases. These elements exist in ammonia in the pro- 
portion of one part by bulk of nitrogen, to three parts of 
hydrogen, or by weight fourteen parts or one atom of 
nitrogen and three parts, or three atoms of hydrogen. 
The subjoined scheme exhibits the composition of ammo- 
hia, as expressed in symbols, atoms, and percentages. 
Symbol. At. w't. Per cent. 
N = 14 we 82.39 
Hs = 3 se 17.61 
NH; = dh os 100.00 
Formation of Ammonia.—1. When hydrogen and ni- 
trogen gases are mingled together in the proportions to 
