Nit Etc ACID AND THE NITRATES 89 



for oxygen, for it is incapable of combustion in air or 

 oxygen excepting at enormously high temperatures. It 

 is to be expected, therefore, that nitric acid and the nitrates 

 would lose oxygen easily and act as powerful oxidising agents. 

 Pour a little of the strong nitric acid on to some red-hot 

 charcoal contained in a crucible. Is there evidence of 

 oxidation of the carbon? Mix together some powdered 

 charcoal, sulphur, and nitre. Ignite the mixture. Do 

 the charcoal and sulphur now burn so readily as to 

 lead to the belief that the nitre provides the oxygen for 

 combustion ? 



To act as an explosive, the combustible mixture must contain enough 

 oxygen for combustion in absence of air. Its power as an explosive 

 will chiefly depend upon the rapidity with which complete ignition 

 occurs, and the amount of the gaseous products. The average composition 

 of the gunpowders made at Waltham Abbey is : — Nitre, 74.5 per cent.; 

 sulphur, 10. 1 per cent.; charcoal, 14. i per cent. The gaseous products of 

 explosion, chiefly consisting of nitrogen and carbonic acid gas, occupy 

 about 280 times the volume of these powders. 



The oxidising effect of nitric acid renders its action on metals 

 entirely different from that of dilute sulphuric acid. To a piece 

 of granulated zinc in a test-tube add a little of the nitric acid. 

 Note that the gas evolved is not hydrogen, it being incom- 

 bustible. Repeat the experiment with granulated tin, and note 

 that the tin is oxidised to the white oxide of tin. This can 

 only be at the expense of the nitric acid, and the gases evolved 

 must therefore be products of its reduction, either nitrogen 

 i'self, or gaseous oxides containing less oxygen than nitric 

 % nhydride. 



These gaseous reduction products are : — 



Nitrogen peroxide, NOg ; a red gas. 



Nitric oxide, NO ; a colourless gas, but combining with oxygen to form 

 the red peroxide. 



Nitrous oxide, NgO ; a colourless gas, and powerful supporter of com- 

 bustion like oxygen ; does not combine with free oxygen. It is 

 twenty times as soluble as oxygen. 



Nitrogen, N ; a colourless gas and non-supporter of combustion. 



