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14 THE DISCOVERY OF ARGON AND HELIUM. 



call it — ruin of the old theory (the phlogistic theory) he built up a 

 new edifice on which the modern system of chemistry stands. He 

 explained, first of all, the way we now accept the true theory of 

 combustion. He showed us how it was that substances were 

 burnt in air, and what happened when they did burn in the air — 

 that they absorbed the gas oxygen which was present there, and 

 in doing so gave out light and heat, and he built up the whole 

 theory of combustion such as we understand it at the present day. 

 He took up all the facts the other chemists had discovered, and 

 turned them to his own use and that of chemists in general. 



The last portrait I have to show you is that of another English- 

 man. This was Henry Cavendish, who was by far the most accu- 

 rate worker of them all. Cavendish without doubt obtained this 

 gas that 1 am going to tell you about, named argon, and later on 

 I will tell you how he did it. At present I will only mention that 

 he was the discoverer of the composition of water as well. His 

 analyses of air are almost as accurate as the most accurate analy- 

 ses ever made, and they were made by the most incomplete and 

 most inaccurate pieces of apparatus. 



All this brings us to the beginning of the century, and clears 

 the way for what I have now to tell you about the discovery of the 

 gas, argon. At the beginning of the century people thought that 

 they knew all about the air, and that there was no more to know ; 

 that all the gases had been discovered, and that there were no more 

 to discover ; but it was only two years ago that there suddenly 

 burst on the world this wonderful discovery of the gas, argon. Of 

 all the places to find it, in the air was the most unlikely, for, as I 

 have said, every chemist thought the very last had been said on 

 the subject of ordinary air. The reason that argon had not been 

 discovered before was that all analyses of air had been conducted 

 in the following way : — 



First of all, impurities such as water vapour and carbonic acid 

 had been got rid of by absorption ; there was then left merely 

 pure oxygen and nitrogen, then the oxygen was absorbed, and the 

 nitrogen was left, no easy method of absorbing nitrogen being then 

 known. The residue was supposed to be pure nitrogen, but, as it 

 so turned out, the residue was by no means pure nitrogen — it con- 

 tained over I per cent, of this gas, argon, which had never been 



