COMPOUNDS OF NITROGEN WITH OXYGEN. 37 



SO as to place the open end in a small cup of mercury ; the pressure 

 of the atmosphere upon the mercury in the cup sustains the mercury 

 in the column, as before mentioned. 



The use of the barometer as a weatherglass depends on the fact 

 that the pressure of the atmosphere varies at the same place ; and 

 the weather is generally found to be fair when the pressure is great- 

 est, or when the barometer stands high, and vice versa. 



The elasticity of the air, as well as of gases generally, depends 

 upon the degree of j/^resswre ; by the law of Mariotte, their volume is 

 always inversely as the pressure. 



COMPOUNDS OF NITROGEN WITH OXYGEN. 



These are Protoxide of Nitrogen, Deutoxide of Nitrogen, Hyponi- 

 trous Acid, Nitrous Acid, and Nitric Acid. 



Protoxide of nitrogen, NO, called also nitrous oxide, and laugh- 

 ing gas /—prepared by heating the nitrate of ammonia ; the rationale 

 is as follows : 



S Nitrogen ■~--,^^ 

 2 Oxygen _:^ 2 eq. Nitrous oxide. 

 3 Oxygen ^^ 



of ■< i >< 



Ammonia Mmmonia { Nitrogen /^ ^-^..^^ 



(^ f 3 Hydrogen ^-^ 3 eq. Water. 



p^op.— Colourless, transparent, almost inodorous ; sp. gr. 1-5 ; a 

 powerful supporter of combustion ; water dissolves nearly its own 

 volume ; may be condensed into a liquid at 45° by a pressure of 50 

 atmospheres ; when mixed with hydrogen in equal volumes, it ex- 

 plodes with violence by the electric spark, liberating its own measure 

 of nitrogen. Its most remarkable property is its exhilarating effect 

 on the animal system, when respired. 



Deutoxide or Binoxide of nitrogen, NO,; prepared by the action 

 of nitric acid on copper turnings ; part of the oxygen of the acid 

 combines with the copper, the oxide thus formed uniting with the 

 undecomposed nitric acid ; another portion of the oxygen unites with 

 the nitrogen to form the deutoxide. It is colourless, but has a strong 

 affinity for oxygen, acquires a dark red colour when it comes in 

 contact with the air, which will serve to distinguish it ; it is irre- 

 spirable ; a supporter of combustion in some cases, — as of charcoal 

 and phosphorus ; but it extinguishes a lighted candle. From its 

 affinity for oxygen, it may be used with advantage in eudiometry. 



Hyponitrous acid, NO3 ; prepared by adding four measures of 

 deutoxide of nitrogen to one of oxygen, and exposing the mixture to 

 a temperature of 0° F. ; they condense into a thin liquid of a greenish 

 colour ;— vapour, orange red; it is decomposed by water into nitric 

 acid and deutoxide of nitrogen ; it cannot be made to unite directly 

 with metallic oxides. 



4 



