194 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



It is, however, a simpler matter to deduce the composition 

 of the gas by volume. Priestley and Lavoisier had shown 

 that charcoal burns in oxygen without producing any change 

 in the volume of the gas; 2-4 cubic inches of carbonic 

 anhydride would thus contain 2*4 cubic inches of oxygen 

 derived from nitrous oxide. The 5*2 cubic inches of nitrous 

 oxide, therefore, contained 5-1 cubic inches of nitrogen, and 

 2 -4 cubic inches of oxygen; or, speaking approximately, 

 nitrous oxide contains its own volume of nitrogen and half its 

 volume of oxygen. 



Composition of nitrous air or nitrous gas (nitric oxide). 

 Davy next turned his attention to the gas which Mayow 

 had prepared by the action of iron on nitric acid, and 

 Priestley had described under the name of " nitrous air." 

 This gas was described by Davy in 1800, and by Gay- 

 Lussac in 1809 and in 1816 as "nitrous gas." The modern 

 name of NITRIC OXIDE was introduced about the year 1818. 



It had been shown by Priestley in 1786 (Experiments 

 and Observations, 1786, VI. 304) that iron increased in 

 weight when heated by means of a lens in a jar of nitrous 

 air ; at the same time the volume of gas was diminished 

 about one half, the residue consisting of an inactive gas 

 resembling atmospheric nitrogen. Charcoal heated in the 

 same way produced carbonic anhydride and nitrogen (loc. 

 cit. p. 434), but the results were less trustworthy. Davy 

 repeated the experiment with charcoal and found that, 

 after applying the burning glass for four hours, 15-4 cubic 

 inches of nitrous gas gave 8*7 cubic inches of carbonic 

 anhydride and 7-4 cubic inches of nitrogen. From 

 these figures he calculated "that 100 grains of nitrous 

 gas contain 56-5 oxygen and 43-5 nitrogen" (Davy's 

 Works, III. 77-79). The composition by volume may 

 be deduced by assuming that the carbonic anhydride 

 contained its own volume of oxygen derived from the nitrous 

 gas. The 1 5 '4 volumes of nitrous gas would then contain 



