THE DISCOVERY OF ARGON AND HELIUM. 15 



separated out from the nitrogen before. This discovery, like a 

 great many discoveries, although it burst upon the world and 

 people heard nothing about it until they suddenly heard that the 

 gas had been discovered, was a discovery which had been built up 

 step by step. Few discoveries are made suddenly ; they usually 

 come by hard, persistent scientific work, and argon is no excep- 

 tion to that rule, whilst helium is no exception either. 



The work which led up to this was due to some excessively 

 accurate work that Lord Rayleigh had been carrying out on the 

 actual densities or weights of given volumes of various gases. 

 About ten years ago he started weighing oxygen and hydrogen, 

 trying to get them as pure as possible, and to find out exactly to 

 the third and fourth place of decimals what a given volume of 

 these gases weighed. After he had done this, in the year 1892 he 

 prepared nitrogen from a great number of different sources, and 

 he found that so long as he prepared nitrogen by chemical pro- 

 cess, by the decomposition of ordinary nitrogen compounds, the 

 nitrogen always weighed exactly the same. When, however, he 

 prepared his nitrogen from air by purifying the air and absorbing 

 everything in it except the nitrogen, this nitrogen present in the 

 air did not weigh quite the same, but very nearly the same, as the 

 nitrogen obtained from other sources. These results would, in 

 the hands of most people, have meant nothing ; but Lord Ray- 

 leigh had spent many years at the work, and he was quite certain 

 that this was due to something he could not explain. First of all, 

 he thought it was the chemical impurities that were present, and 

 he tried his best to get rid of every impurity, still he found that 

 this nitrogen which was obtained from the air was too heavy by a 

 very little, but still it was too heavy, and he was extremely puzzled 

 and could not find out what the reason of it was ; so he put the 

 matter in the hands of Professor Ramsay ; he and Professor 

 Ramsay joined forces, and then came the discovery of argon. It 

 was perfectly simple. It was the nitrogen which now had to be 

 absorbed. A residue was left, and that residue was argon. The 

 difficulty, however, was to absorb nitrogen, because no substance 

 easily absorbs nitrogen, and the way in which it was done was by 

 means of magnesium. Magnesium absorbs nitrogen very readily 

 at a red heat, and after it has been heated for a long time, and the 



