THE FOOD OF PLANTS 



CHAP. 



the same white powder that was formed by the 

 burning phosphorus before (Experiment 31). 



Take a pudding basin, nearly fill it with water, and 

 as'soon as the flask is cool, plunge the neck under 

 the water, and then carefully ease out the cork, keep- 

 ing the neck under water all the time. As soon 

 as the cork is removed the water rushes into the 

 flask. 



Push the cork 

 back again into the 

 neck, lift the flask 

 out of the water, 

 shake it so as to 

 thoroughly cool it 



FIG. 14. > J 



by means of the 



water which has rushed in, plunge the neck under 

 water again, remove the cork as before, and lower the 

 flask into the water until the level of the water inside 

 and outside the flask is the same. Again insert the 

 cork and lift out the flask. 



The water has rushed in to occupy the space 

 formerly occupied by the part of the air which has 

 combined with the burning phosphorus. The greater 

 part of the air, however, has evidently remained 

 uncombined. Remove the cork and test with a 

 lighted taper the air which remains in the flask. 

 The lighted taper goes out, showing that this residual 

 air will not support combustion. 



We are thus led to believe that the air is 

 a mixture of two gases, one which combines 



