WHAT IS AN ELEMENT ? 153 



Argon cannot be made to combine, and hence it is left 

 behind when the nitrogen and oxygen have been removed 

 from the atmosphere. 



Shortly after the discovery of argon, Ramsay found 

 that certain minerals when heated give off a gas similar 

 to argon, inasmuch as it forms no compounds, but with 

 a much lower atomic weight; for while argon possesses 

 the atomic weight forty, the atomic weight of helium (the 

 name given to this new gas) is only four. Now these 

 elements evidently belong to one series, for they are both 

 colourless gases, incapable of combining with other 

 elements. And it appeared almost certain that other 

 gases, similar in properties to these two, should be capable 

 of existence. And Ramsay, in conjunction with Travers, 

 spent several years in a hunt for the missing elements. 

 They heated upwards of a hundred minerals, to see 

 whether they evolved gas, and, if so, whether the gas 

 obtained was new; but although they discovered that 

 many minerals give off helium when heated, no new gas 

 was found. Mineral waters were boiled, so as to expel 

 dissolved gases ; again only argon and helium were 

 obtained. Even meteorites, or ' falling stars,' were 

 heated ; only one was found to give off gas incapable of 

 combination, and that gas consisted of a mixture of the 

 two which were already known. 



As a last attempt, Ramsay and Travers prepared a large 

 quantity of argon, by removing the oxygen and the 

 nitrogen from air, and then forced the gas into a bulb, 

 dipping in a vessel immersed in a tube full of liquid air, 

 which is so cold that the argon changed to liquid. It 

 forms a colourless, mobile liquid, just like water. When 

 the liquid air is removed, the argon begins to boil. 



It was hoped that the distillation of crude liquid argon 

 might separate from it other gases boiling at a lower or a 

 higher temperature ; that if it contained any other liquids 

 of lower boiling-point, these would distil over first, and 



