SCIENTIFIC METHOD 65 



in the same vessel, and took note of the minute 

 differences in the weights recorded. Especially 

 were there differences in the weighings of nitrogen 

 made from certain of its compounds and nitrogen 

 obtained by removing oxygen, water, traces of 

 carbonic acid and other impurities from atmo- 

 spheric ah-. As the differences between the 

 weighings seemed greater than the possibilities of 

 error, the possibility suggested itself that the 

 nitrogen derived from the air might not be quite 

 pure. 



Now in 1785 Cavendish, in his analysis of air, 

 had also tried whether the removal of nearly 

 twenty -one volumes of oxygen and a small quan- 

 tity of carbonic acid from one hundred volumes of 

 atmospheric air left pure nitrogen. His testing left 

 a residual bubble of something. It might, Caven- 

 dish thought, have been introduced accidentally 

 during the manipulations, but he also suggested 

 that it might be a gas neither nitrogen nor oxygen, 

 and, if so, that there was about one volume of it 

 to every hundred of atmospheric nitrogen. For 

 more than a century the question rested. 



But in 1894 Lord Rayleigh and Sir William 

 Ramsay, in considering the discrepancies in the 

 weighings of atmospheric nitrogen, remembered 

 Cavendish's residual bubble, and Sir William 

 Ramsay speedily discovered that it consisted of 

 argon (about one and a hah" times as heavy as 



