Mingling of Molecules 269 



the cells of your body. You might breathe all you 

 liked, but breathing would not help you ; the air could 

 not get through the walls of your lungs into the blood. 

 Plants would begin to wither and droop, although they 

 would not die quite as quickly as animals and fishes 

 and people. But no sap could enter their roots and 

 none could pass from cell to cell. The plants would 

 be as little able to breathe through their leaves as we 

 through our lungs. 



If gas escaped in the room where you were, you could 

 not smell it even if you stayed alive long enough to try ; 

 the gas would rise to the top of the room and stay there. 

 All gases and all liquids would stay as they were, and 

 neither would ever form mixtures. 



It would not make so much difference in the dead 

 parts of the world if diffusion ceased ; the rocks, moun- 

 tains, earth, and sea would not be changed at all at first. 

 To be sure, the rivers where they flowed into the oceans 

 would make big spaces of saltless water; and when 

 water evaporated from the ocean the vapor would push 

 aside the air and stay in a layer over the ocean, instead 

 of mixing with the air and rising to great heights. But 

 the real disaster would be to living things. All of them 

 would be smothered and starved to death as soon as 

 diffusion ceased. 



Here is an experiment that shows how gases diffuse : 



Experiment 85. Take two test tubes with mouths of the 

 same size so that you can fit them snugly against each other 

 when you want to. Fill one to the brim with water and 

 ho!4 your thumb or a piece of cardboard over its mouth 

 while you place it upside down in a pan of water. Take 



