74 HOW CROPS FEED. 
It is also manifested by many metals, as zine, iron, and 
lead, and by any mixture evolving hydrogen, as, for ex- 
ample, putrefying organic matter. On the other hand, 
ozone instantly oxidizes nitrites to nitrates. 
Reduction of Nitrates and Nitrites to Ammonia, — 
Some of the substinces which convert nitrates into nitrites 
may also by their prolonged action transform the latter 
into ammonia. When smull fragments of zine and iron 
mixed together are drenched with warm solution of caustic 
potash, hydrogen is copiously disengaged. Ifa nitrate be 
added to the mixture, it is at once reduced, and ammonia 
escapes. If to a mixture of zinc or iron and dilute chlor- 
hydric acid, such as is employed in preparing hydrogen 
gas, nitric acid, or any nitrate or nitrite be added, the 
evolution of hydrogen ceases, or is checked, and ammonia 
is formed in the solution, whence it can be expelled by 
lime or potash. 
Nitric acid. Hydrogen. Ammonia. Water. 
NOH +. 8H..=. Nj eae 
The appearance of nitrous acid in this process is an in- 
termediate step of the reduction. 
Further Reduction of Nitric and Nitrous Acids—Un- 
der certain conditions nitric acid and nitrous acid are still 
further deoxidized. Nesbit, who first employed the reduc- 
tion of nitric acid to ammonia by means of zine and dilute 
chlorhydric acid as a means of determining the quantity 
of the former, mentions (Quart. Jour. Chem. Soc., 1847, 
p- 283,) that when the temperature of the liquid is allowed 
to rise somewhat, nitric owide gas, NO, escapes. 
From weak nitric acid, zinc causes the evolution of ni- 
trous oxide gas, N,O. 
As already mentioned, nitrate of ammonia, when heated 
to fusion, evolves nitrous oxide, N,O. Emmet showed 
that by immersing a strip of zine in the pa salt, nearly 
pure nitrogen gas is set free. 
