74 ilOW <^ROPS FEED. 



It is also nianifcst,ed by many miitals, as zinc, iron, and 

 lead, and by any mixture evolving hydrogen, as, for ex- 

 ample, putrefying org.inic matter. On the other hand, 

 ozone instantly oxidizes nitrites to nitrates. 



Reduction of Nitrates and Nitrites to Ammonia. — 



Some of the substances wliicli convert nitrates into nitrites 

 may also by their prolonged action transform the latter 

 into ammonia. When smiU fragments of zinc and iron 

 mixed together are drenclied with warm solution of caustic 

 potash, hydrogen is copiously disengaged. If a nitrate be 

 addecj. to tlie mixture, it is at once reduced, and ammonia 

 escapes. If to a mixture of zinc or iron and dilute chlor- 

 hydric acid, sucli as is em;>loyed in preparing hydrogen 

 gas, nitric acid, or any nitrate or nitrite be added, the 

 evolution of iiydrogen 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. 



NO3H + 8H = NPI3 + 3Hp 



The appearance of nitrous acid in this process is an in- 

 termediate step of the reduction. 



Further Reduction of Nitric and Nitrous Acids. — Tin- 

 der certain conditions nit ric acid nnd nitrous acid are still 

 further deoxidized. Nesbit, who first employed the reduc- 

 tion of nitric acid to ammonia by means of zinc and dilute 

 chlorhydric acid as a means of detL-rmining the cpiantity 

 of the former, mentions {Quart. Jour. Ghem. Soc, 1847, 

 p. 283,) that when the temperature of the liquid is allowed 

 to rise somewhat, nitric oxide gas, NO, escapes. 



From weak nitric acid, zinc causes the evolution of ni- 

 trous oxide gas, N'„0. 



As already mentioned, nitrate of ammonia, when heated 

 to fusion, evolves nitrous oxide, N^O. Emmet showed 

 that by immersing a strip of zinc in the melted salt, nearly 

 pure nitrogen. gas is set free. 



