ARGON AND HELIUM. 125 



had been prepared by the magnesium process. It showed no trace 

 of nitrogen when examined in a vacuum tube. It boils at 



— i86-9''C, and melts at — i89-6°C. Its critical temperature is 



— i2i°C, and critical pressure 50-6 (?) atmospheres. 



Then we come to the question, What is argon ? Is it an 

 element, mixture, or compound ? The ratio of the sp. heats shows 

 that it is a monatomic element, or a mixture of monatomic ele- 

 ments. Again, the fact that it possesses both a definite boiling-point 

 and melting-point would seem to indicate that it is not a mixture. 

 On the other hand, argon has two spectra which can be separated 

 to some extent in a vacuum tube (Crookes), and this appears 

 to show that argon is a mixture. This fact is not quite so 

 definite as the other two. If argon is a monatomic element its 

 atomic weight will be about 40. 



HELIUM— A Constituent of certain Minerals. 



Soon after the discovery of argon. Prof. Ramsay, while trying 

 to find some substance which would combine with that gas, came 

 across a paper by Hillebrand. In this paper it was stated that on 

 boiling uraninite with dilute sulphuric acid a gas was given off which 

 proved to be nitrogen. On trying the experiment he found that only 

 ten per cent, of the gas was nitrogen, and the rest was a new gas. 

 His further ex|)eriments were carried on with the same gas obtained 

 from cleveite. On examining by means of the spectroscope he found 

 that the gas consisted of argon along with a totally new gas. In 

 the spectrum of this new gas was seen a bright yellow line, coinciding 

 with the line D3 in the solar chromosphere, and attributed to the 

 hypothetical element termed helium in 1868 by Profs. Lockyer and 

 Frankland. The investigation of this has been carried on by Prof 

 Ramsay, assisted by Dr. Collie and Mr. Travers. 



Terrestrial Sources of Helium. — The method of obtaining the 

 gas from these minerals was as follows : — The mineral (two to five 

 grms.) was coarsely powdered and heated in a hard glass bulb, 

 which had previously been exhausted. Any water and carbon 

 dioxide were absorbed by soda-lime and phosphorus pentoxide. 

 Then the gas was sparked with oxygen to remove hydrogen, and the 

 excess of oxygen was absorbed by alkaline pyrogallate. For spectro- 

 scopical analysis the gas was transferred to a vacuum tube by means 



