X NITRE, NITRIC ACID, AND NITROGEN 205 



The oxidation of nitrogen in presence of potash may be 

 represented by the equations : 



2 N 2 + 5O 2 + 4KOH -> 4KNO 3 + 2H 2 O 



(Potassium 

 nitrate.) 



2N 2 + 3O 2 + 4KOH - 4KNO 2 + 2H 2 O 



(Potassium 

 nitrite.) 



The fact that a part of the nitre produced in this way was 

 "phlogisticated," i.e. in the "reduced" form as nitrite, was 

 noticed by Cavendish. 



B. OXIDES OF NITROGEN. 



Davy, in 1800, determined the composition by weight cf 

 the three gases which Priestley prepared from nitric acid, 

 as follows : 



Oxygen : Nitrogen. 



"Diminished nitrous air (Nitrous 



oxide, N 2 O) ......... 37 : 63 



"Nitrous air" (Nitric oxide, NO) 56*5 : 43-5 



Brown Fumes (Nitrogen peroxide, 



NO 2 or N 2 O 4 ) 70 : 30 



In the case of the two colourless oxides, he burned charcoal 

 in the gas and measured the quantities of nitrogen and 

 of carbonic anhydride which were produced. These are as 

 follows : 



Nitrous oxide 2N 2 O-f C >2N 2 + CO 2 (containing O 2 , \vol.} 

 i vol. i vol. \ vol. 



Nitric oxide 2NO -1- C-N 2 + CO 2 (containing O 2 , J voL\ 

 i vol. \ vol. \ vol. 



whence we have as the composition by volume : 



Nitrous oxide. Nitrogen : oxygen=-\ : J 

 Nitric oxide. Nitrogen : oxygen = \ : \. 



The composition of the brown gas was determined, but not 

 very accurately, by mixing known quantities of nitric oxide and 

 oxygen. 



