204 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



Composition of the oxides and acids of nitrogen. Gay- 



Lussac had now determined the composition of the two 

 acids derived from saltpetre as well as of the three gaseous 

 oxides which could be prepared from it. He summarised 

 his results in a table which, on substituting modern names 

 for the different compounds, reads as follows : 



Nitrogen. Oxygen. 

 Nitrous oxide ... ... ... 100 50 



Nitric oxide ... ... ... 100 100 



Nitrous acid ... ... ... 100 150 



Nitrogen peroxide... ... ... 100 200 



Nitric acid ... ... ... 100 250 



This table, the sequence of which was anticipated in a 

 remarkable way by Scheele in 1777, affords an exception- 

 ally good illustration of the laws of chemical combination, 

 the proportions of oxygen in the five compounds being in 

 the ratios 1:2:3:4:5. 



SUMMARY AND SUPPLEMENT 

 A. NITROGEN. 



Cavendish, in 1781, found nitric acid in the water obtained 

 by exploding hydrogen with an excess of oxygen and concluded 

 that it had been produced by oxidation of atmospheric azote. 

 In 1784, by sparking over potash a mixture of three parts 

 of air with five parts of oxygen, he succeeded in absorbing 

 almost the whole of the gas and obtained 1*4 grains of nitre. 

 By sparking with an excess of oxygen, which was afterwards 

 absorbed by liver of sulphur, he oxidised the whole of the 

 azote except about 1 ^ ; the azote therefore consists almost 

 entirely of a gas from which nitre can be prepared and to 

 which Chaptal in 1790 gave the name nitrogen ; the residue was 

 shown by Rayleigh and Ramsay in 1895 to contain an inactive 

 gas which they called argon. 



