206 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



Gay-Lussac, in 1807, determined more accurately the compo- 

 sition of nitric oxide (which does not readily part with its oxygen) 

 by burning metallic potassium in it : 



i vol. \ vol. 



In 1816, he determined the composition of nitrogen peroxide 

 by measuring the contraction produced on adding oxygen to a 

 known volume of nitric oxide, and conversely. He found that 

 the same contraction (192 volumes) was produced by adding 

 nitric oxide to 100 volumes of oxygen, or oxygen to 204 volumes 

 of nitric oxide. Oxygen and nitric oxide therefore combined in 

 the ratio of 100 volumes of oxygen to 204 volumes of nitric oxide, 

 or very nearly one volume of oxygen to two of nitric oxide. As 

 two volumes of nitric oxide contained one volume of nitrogen 

 and one volume of oxygen, the composition of the product was 

 as follows : 



Nitrogen peroxide. Nitric oxide : oxygen = 2 : i 

 Nitrogen : oxygen=\ : 2. 



The combination of the two gases may be represented by the 

 equation : 



2NO + O 2 -> N 2 O 4 or 2NO 2 . 



2 VOls. I VOl. I VOL 2 VOls. 



At low temperatures the product consists mainly of the 

 colourless oxide N 2 O 4 , and the volume is reduced, as Gay- 

 Lussac found, almost to one-third. Above 150 it consists 

 entirely of the brown oxide NO 2 , and occupies two-thirds of the 

 original volume. 



R. W. Gray, in 1905 (Trans. Chem. Soc., 1905, 87, 1601-1620), 

 heated nickel in nitric oxide, and by using modern methods 

 was able to weigh both the nitrogen and the oxygen present in 

 a known weight of nitric oxide. The flask A (Fig. 40) 

 was provided with a glass stopper, B, leading through 

 a stopcock to a capillary ground-glass joint, D. A small 

 platinum boat, H, containing finely-divided nickel was sur- 

 rounded by a coil of platinum wire, which could be heated to 

 any desired temperature by an electric current, supplied through 

 the stout platinum electrodes, EE. The bulb M, containing 



