284 Wells S Foote — One Hundred Years of Chemistry. 



The Inactive Gases. — As long ago as 1785, Cavendish, 

 that remarkable Englishman who first weighed the world 

 and first discovered the composition of water, actually 

 obtained a little argon in a pure condition by sparking 

 atmospheric nitrogen with oxygen converting it into 

 nitric acid (another discovery of his) and absorbing the 

 excess of oxygen. The volume of this residual gas as 

 estimated by him corresponds very closely to the volume 

 of argon in the atmosphere, as now known. 



It was more than a century later, in 1894, that Eayleigh 

 and Ramsay discovered argon in the air. Lord Rayleigh 

 had found that atmospheric nitrogen was about one-half 

 per cent heavier than chemical nitrogen, a fact which led 

 to the investigation. It was only necessary to repeat 

 Cavendish's experiment on a large scale, or to absorb 

 oxygen with hot copper and nitrogen with hot mag- 

 nesium, in order to obtain argon. The gas attracted 

 much attention, both on account of having but a single 

 atom in its molecule, and particularly because it failed to 

 enter into chemical combination of any kind. This gas 

 has been used of late for filling the bulbs of incandescent 

 electric lamps in cases where a gas-pressure without 

 chemical action is desired. 



In 1890 and 1891, Hillebrand published in this Journal 

 40, 384, 1890: 42, 390, 1891) a series of analyses of the 

 mineral uraninite and reported in some samples of the 

 mineral as much as 2-5 per cent of an inactive gas. 

 Hillebrand examined the gas spectroscopically but, just 

 missing an important discovery, he detected only the 

 spectrum lines of nitrogen. Ramsay, in searching for 

 argon in some sort of natural combination, and doubt- 

 less remembering Hillebrand's work, heated some 

 cleveite, a variety of uraninite, and obtained, not argon, 

 but a new gas. This gave a yellow spectrum-line cor- 

 responding to a line previously observed in the light of 

 the sun's corona and attributed to an element in the sun 

 called helium. Helium, therefore, in 1895 had been found 

 on the earth. This gas is a constant constituent of 

 uranium minerals, as it is produced by the breaking down 

 of radioactive elements. It has been found in very small 

 quantity in the atmosphere, and is the most difficult of all 

 known gases to liquefy, as its boiling point, as shown by 

 Onnes in 1908, is only 4° above the absolute zero. It has 

 not yet been solidified. 



