46 



AIR AND FIRE 



placed under the mouth of the bottle of water. The air, being lighter 

 than water, will displace the water of the bottle. We can fill a bottle 

 exactly full of illuminating gas by attaching a " deli very tube" to the 

 gas outlet, and allowing the gas to displace water in the same way. 



46. Discovery of Oxygen. The phenomenon of fire, 

 or burning, has fascinated men for ages, but what the air 

 has to do with it no one understood until 1774. The 

 explanation was given by Lavoisier, a French scientist, and 

 was as important, in its way, as the explanation of gravity 

 by Newton (cf. 18) ; for it was the beginning of modern 

 Chemistry. Priestley, an English experimenter, had just 

 prepared oxygen (Aug. 1, 1774) by heating a red powder 

 which we now call mercuric oxide. 



Priestley's apparatus (Fig. 38) was a bottle filled completely with 

 mercury, and inverted in a "bath" of the same liquid. He put the 



mercuric oxide under the mouth of the 

 bottle; the oxide, being lighter, floated to 

 the top of the mercury. He then brought 

 sunlight to a focus (cf. 178) upon the 

 mercuric oxide by means of a burning 

 lens. The heat produced caused the red 

 powder to disappear; but a colorless gas 

 appeared in its place. When Priestley put 

 into the gas a splinter with a glowing tip, 

 the spark burst into flame. He also put 

 a live mouse into the gas, and, to his sur- 

 ppse, it continued to live. Priestley called 

 the gas -good air." 



47. The Air a Mixture. When Lavoisier heard of 

 Priestley's discovery, he reasoned that the gas obtained 

 by Priestley, which supported burning and life so much 



Sunlight 



