10 THE DISCOVERY OF ARGON AND HELIUM. 



depended upon the various properties of the substances from 

 which they were produced. 



The next portrait of a chemist who had to deal with air is also 

 that of an Englishman named John Mayow. He was a doctor 

 who lived about the same time as Robert Boyle, and he also 

 published some work on the subject of air. He proved that 

 there was no doubt one particular substance present which he 

 called fiery air, and that it was due to this fiery air, which was 

 present in ordinary air, that enabled substances to burn. This 

 was of very great importance, but was lost sight of for more than a 

 hundred years. Mayow also pointed out that this particular air, 

 which he called fiery air, was present also in nitre or saltpetre, 

 and in this way he discovered facts which were re-discovered very 

 much later by a French chemist named Lavoisier at the end of 

 last century. 



The next EngHsh chemist who had to do with air, and also 

 made a very large number of experiments, was a clergyman of the 

 name of Stephen Hales. He was more interested in the rise of 

 sap in plants and similar substances, and investigations of that 

 description, but he also made a very large number of experiments 

 on heating substances in closed vessels, collecting various airs or 

 gases, as we call them now, above water. He also proved that 

 probably air contained more than one particular kind of air, and 

 he examined the different airs which were produced by the decom- 

 position of all sorts of substances by heat and otherwise, collected 

 them above water, and made investigations on them, but, again, 

 his investigations seem rather to have been lost sight of, and not 

 to further science in any very great way. Air was still looked upon 

 by the chemist as an elementary substance, and not a substance 

 which was composed of different kinds of matter. 



About a century later than these three chemists came some 

 more English chemists, who still further advanced our knowledge 

 on the subject of air. This is a portrait of Dr. Black. Dr. Black 

 lived in Edinburgh, and he was the first to point out that there 

 was present in the air what he called fixed air, because he was able 

 to absorb this air from the atmosphere by means of such substances 

 as caustic potash, and also quickhme. He thought by this process 

 the air became fixed or absorbed by these solid substances — the 



