40 ATMOSPHERIC AIR. 



it is distilled on black oxide of manganese, which 

 gives more oxygen to it. 



Nitric acid is extremely caustic; that is, acts 

 powerfully upon animal substances. It unites with 

 the alkalis and earths ; it oxidates all the metals 

 except gold and platina ; it thickens and blackens 

 oils, converting them into a coal, or inflaming 

 them, according to the nature of the oil, and the 

 degree of the concentration of the acid. 



The combinations of nitric acid with different 

 bases are called nitrates. 



When the nitrogen and oxygen gases are mingled 

 together, they form a compound exactly resembling 

 common or atmospheric air. 



Atmospheric Air 



Is, indeed, essentially composed of these two gases: 

 and its analysis or decomposition has been one of 

 the most interesting discoveries of modern che- 

 mistry. It is curious that one of the ingredi- 

 ents of this substance, so necessary to animal life, 

 should, by itself, be highly deleterious. 



It has been completely proved, that the air of 

 the atmosphere is a compound body, formed by the 

 mixture of oxygen gas and nitrogen gas. The first 

 is the only one of them that supports combustion ; 

 and when combustion takes place in common air, 

 it is this part that unites to the burning body, form- 

 ing either an oxide or an acid. If mercury be 

 heated in a given quantity of atmospheric air for 

 some time, it will become changed into a red pow- 

 der, which will weigh more than the mercury ; the 

 air will be found to be diminished in quantity, and 



13 



