THE DISCOVERY OF ARGON AND HELIUM. 13 



potash and the lime — and proved that after it had been fixed or 

 absorbed in that manner it could be produced again either by the 

 addition of acids or by heating. He was the first to prove con- 

 clusively that a substance named carbonic acid, or, as he called it, 

 fixed air, was present in the atmosphere, and this was really one of 

 the first noticeable facts in our knowledge of the air. 



This is a portrait of another Scotch chemist, of the name of 

 Rutherford. He did not, however, study chemistry very com- 

 pletely, and he did not study it all his life, but he is the discoverer 

 of one of the constituents of air, which he called mephitic air, 

 and we now know it by the name of nitrogen. It is that gas 

 which is present in the largest proportion in air ; about 80 per cent. 

 of air, or four-fifths, being composed of this gas nitrogen, and 

 Rutherford was the first to point out that this mephitic air was 

 different from the fixed air that Black obtained ; also, that it would 

 not support combustion, that substances would not burn in it, and 

 also the more important fact that it would not support life — that 

 animals died in it. Rutherford, therefore, was the discoverer of 

 nitrogen. After having absorbed the other gases in the air by 

 means of various heated substances which absorbed them — such 

 as oxygen and so on — he obtained this gas nitrogen. 



The next portrait is of another English chemist of the name of 

 Dr. Priestley. He was the discoverer of the other chief consti- 

 tuent of air. About 120 years ago he obtained oxygen in the 

 pure state for the first time, and proved that this gas, which he 

 called dephlogisticated air, was present in ordinary air, and that it 

 was due to this gas that animals could live in ordinary air, and also 

 that substances burnt very much more brilliantly in pure oxygen 

 or pure dephlogistic air than in ordinary air. That brings us to 

 the end of the last century, and these are the people who had, in 

 fact, most to do with the discovery of the various gases in the air. 

 Black discovered the carbonic acid, Rutherford the nitrogen, and 

 Dr. Priestley the oxygen, the oxygen and nitrogen being the two 

 most important constituents in the atmosphere. 



This portrait is a portrait of the French chemist Lavoisier, and 

 perhaps in a way he was greater than all of them. It was Lavoi- 

 sier who gathered up all these scattered details ; it was Lavoisier 

 who put them together ; and from the absolute — one might almost 



