JOURNEYS MADE BY MOLECULES lOI 



There is no visible proof of the existence of molecules 

 and molecular spaces, because not only are our eyes unable 

 to see them directly, but even the most powerful microscope 

 cannot make them visible to us. They are so small that if 

 one thousand of them were laid side by side, they would 

 make a speck too small to be seen by the eye and but barely 

 visible under a powerful microscope. 



We cannot see molecules or molecular pores, but the phe- 

 nomena of compression and expansion, solubility and other 

 equally convincing facts, have led us to conclude that all 

 substances are composed of very minute particles or mole- 

 cules separated by spaces called pores. 



95. Journeys Made by Molecules. If a gas jet is turned 

 on and not lighted, an odor of gas soon becomes perceptible, 

 not only throughout the room, but in adjacent halls and even 

 in distant rooms. An uncorked bottle of cologne scents an 

 entire room, the odor of a rose or violet permeates the 

 atmosphere near and far. These simple everyday occur- 

 rences seem to show that the molecules of a gas must be in a 

 state of continual and rapid motion. In the case of the 

 cologne, some molecules must have escaped from the liquid 

 by the process of evaporation and traveled through the air to 

 the nose. We know that the molecules of a liquid are in 

 motion and are continually passing into the air because in 

 time the vessel becomes empty. The only way in which this 

 could happen would be for the molecules of the liquid to pass 

 from the liquid into the surrounding medium; but this is 

 really saying that the molecules are in motion. 



From these phenomena and others it is reasonably clear 

 that substances are composed of molecules, and that mole- 

 cules are not inert, quiet particles, but that they are in in- 

 cessant motion, moving rapidly hither and thither, sometimes 

 traveling far, sometimes near. Even the log of wood which 



