Mingling of Molecules 



271 



FIG. 150. The lower test tube is full of air; the upper, of gas. What will 

 happen when the cardboard is withdrawn? 



half is not too much time. Now have some one light a 

 match for you, or else go to a lighted Bunsen burner. 



Take the test tubes apart gently and hold the lower one, 

 which was full of air, with its mouth to the flame. What 

 has the gas in the upper tube done? Now hold the flame 

 to the upper test tube, which was full of gas. What happens ? 

 Has all the gas gone out of it ? 



As you well know, gas is much lighter than air ; you 

 can make a balloon rise by filling it with gas. Yet part 

 of the gas went down into the lower tube. The expla- 

 nation is that the molecules of gas and those of air were 

 flying around at such a rate that many of the gas mole- 

 cules went shooting down among the air molecules, and 

 many of the molecules of air went shooting up among 

 those of gas, so that the gas and the air became mixed. 



