Mercury 



THE AIR A MIXTURE 47 



better than air, must be present in the air. So he planned 

 an experiment to prove that he was right. 



Lavoisier set up the apparatus shown in Fig. 39, putting some 

 mercury in the glass retort. The drawn-out tube of the retort was 

 bent so that it dipped into the pan of mercury. Over the end of this 

 tube, and dipping below the mer- 

 cury, was the bell jar. The air of 

 the bell jar and of the retort was 

 thus cut off from the outer air, 

 and nothing but mercury could 

 get into the apparatus. Lavoisier 

 then heated the retort for 12 days. 

 Gradually a red powder collected 

 on the mercury in the retort. At 

 the same time the atmospheric 

 pressure pushed some mercury into 

 the bell jar. This showed that the 



volume of air in the apparatus became smaller. When no further 

 change took place, Lavoisier let the apparatus become cool, and found 

 that only 4 / 5 of the air remained. The air that was left "put out" a 

 burning candle, and mice could not live in it. So Lavoisier reasoned 

 that the active part of the air was removed by the heated mercury, and 

 that it makes up about 1 / 6 of the air. 



Fio. 39. 



Lavoisier's Experiment. Heating Mercury 

 in a Confined Portion of Air. 



When Lavoisier heated the red powder that had collected 

 in the retort, he obtained all the gas that had been lost 

 by the air. When he applied to this gas the tests which 

 Priestley had used for his "good air," he obtained the 

 same results as Priestley. Lavoisier had thus proved that 

 the air consists of two substances, one of them active, 

 and able to support burning and life; the other, inactive. 

 The active gas is oxygen; the inactive one, nitrogen (cf. 

 also 54). 



