CHAPTER XXI 

 STUDY OF THE ACTIVE PART OF THE AIR. 



57. SEARCH FOR THE ACTIVE PART OF THE AIR. 



ALTHOUGH the properties of the active part of the air have been noted, 

 when mixed with four times its volume of the inactive part, the exact 

 properties of the former gas itself are not known. It is, however, ^afe 

 to predict that substances which burn in ordinary air will burn still 

 better in the unmixed active part. As the calces are formed as a result 

 of the active air becoming 

 united with the metal, it is 

 possible that they may be 

 made to yield it up again, 

 and so provide a supply of 

 the gas for examination. 



i. Gas produced by heating 

 ted lead. Place a little red 

 lead in a hard glass tube, and 

 strongly heat the tube as in 

 Fig. 94. Notice that the red 

 lead undergoes a change of 

 colour. Into the tube insert a 

 glowing splinter. Observe that 

 the splinter is re-kindled. Why 

 is this ? 



ii. Change produced by heat- 

 ing mercury calx. Repeat the 

 preceding experiment with some FlG 94._Method ot testing with a glowing 

 red oxide of mercury, and splinter. 



notice the formation of the 



silvery, mirror- like deposit of mercury, or quicksilver, round the cold 

 upper part of the tube. Insert a glowing splinter of wood and watch it 

 re-kindle. 



Where to look for the active part of air. Since, in suitable 

 circumstances, iron, copper and lead take the active part out of the 



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