2 3 o EIGHTEENTH CENTURY. PT. ill. 



burn, nor could animals live in it ; but when a light was 

 brought near it, it took fire and burnt with a pale blue flame 

 inside the bottle. Then, instead of being heavy like ' fixed 

 air,' it was lighter than the atmosphere, and for this reason 

 it was soon used for filling balloons. It had also another 

 remarkable peculiarity, that, when mixed with air in a bottle, 

 it exploded with a loud noise directly a light was brought 

 near it, leaving drops of moisture inside the bottle. Caven- 

 dish did not understand the cause of this explosion at first, 

 but in 1784 (after Priestley had discovered oxygen) he mixed 

 pure oxygen and hydrogen in a closed vessel, and lighted 

 them by an electric spark, and then he made the great dis- 

 covery that these two gases, when lighted, combine together 

 and form wafer, which is therefore a compound substance 

 made of oxygen and hydrogen. 



Oxygen discovered by Priestley in 1774, and by 

 Scheele in 1775. The next gas discovered was oxygen, 

 the most common and the most useful of all the substances 

 in our globe. It was discovered independently by two men 

 Priestley, a dissenting minister at Leeds, and Scheele 

 (bom 1742), a small apothecary at Kjoping, a little village 

 in Sweden. 



There is no doubt that Scheele deserves as much credit 

 for this discovery as if Priestley had never made it, for he had 

 not heard of his experiments, and he added many useful 

 facts which Priestley did not know. Still, as they both went 

 over much the same ground, we cannot afford space here to 

 give Scheele's experiments. You must not, however, forget 

 his claim, for though the world often forgot him because he 

 remained a poor apothecary all his life, yet Scheele was 

 really one of the first chemists of Europe. We owe to him 

 the discovery of chlorine ; and of manganese, baryta, fluoric 

 acid, and many other substances whose names I cannot 



