vi THE COMPOSITION OF THE AIR 53 



is removed during the burning of the phosphorus or 

 not. 



Experiment 32 l 



Take a pear-shaped hard glass flask (such as is 

 sold for the preparation of oxygen) and clean and 

 dry it carefully, and fit it with a good tight-fitting 

 cork. Cut one of the quarter bits of phosphorus 

 in half. Examine it to see that it is perfectly clean, 

 dry it thoroughly, place it in the flask and cork it up. 



We have now got air and phosphorus corked up 

 together. 



Warm the flask gently over a spirit-lamp, keep- 

 ing it turning in the hand all the time. The 

 phosphorus will melt, catch fire, and run burn- 

 ing round the inside of the flask. As soon as the 

 phosphorus catches fire, remove the flask from the 

 flame and hold it out at arm's length, and turn your 

 head the other way, still turning the flask in your 

 hand. The flask is very apt to burst at this moment, 

 and should therefore be so held that if it does burst 

 it cannot injure the face. 



When the phosphorus has gone out, examine the 

 flask. A streak of unburnt phosphorus will be 

 noticed, showing that the phosphorus has gone 

 out before it was completely consumed. We may 

 therefore assume that it has exhausted the supply of 

 the body in the air necessary for its combustion, or it 

 would not have gone out. The flask also contains 



1 This experiment is the invention of Professor Armstrong, F. R. S. 



