ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 71 
unites with great avidity to all basic bodies, forming a 
long list of nitrates. ) f 
It is volatile, and evaporates on exposure to air, though 
not so rapidly as water. 
Nitric acid has a strong affinity for water; hence its 
vapors, when they escape into moist air, condense the 
moisture, making therewith a visible cloud or fume. For 
the same reason the commercial acid is always more or less 
dilute, it being difficult or costly to remove the water en- 
tirely. 
Nitric acid, as it occurs in commerce, is made by heat- 
ing together sulphuric acid and nitrate of soda, when 
nitric acid distils off, and sulphate of soda remains behind. 
Nitrateof Sulphuric Bisulphate of Nitric 
soda. acid. soda. acid. 
NO,Na + HSO, = HNaSO, + NO,H 
Nitrate of soda is formed in nature, and exists in im- 
mense accumulations in the southern part of Peru, (see 
p. 252.) 
Anhydrous Nitric Acid, N,O;, is what is commonly under- 
stood as existing in combination with bases in the nitrates. It isa 
crystallized body, but is not an acid until it unites with the elements of 
water. 
Nitrate of Ammonia, NH, NO,H, or NH, NO,, may 
be easily prepared by adding to nitric acid, ammonia in 
slight excess, and evaporating the solution. The salt read- 
ily crystallizes in long, flexible needles, or as a fibrous 
mass. It gathers moisture from the air, and dissolves in 
about halt its weight of water. 
If nitrate of ammonia be mixed with potash, soda, or 
lime, or with the carbonates of these bases, an exchange 
of acids and bases takes place, the result of which is ni- 
trate of potash, soda, or lime, on the one hand, and free 
ammonia or carbonate of ammonia on the other. 
Nitrous Oxide, N,.O.—When nitrate of ammonia is heated, it 
