54 ELEMENTS OF GENERAL SCIENCE 



Likewise, liquids may be frozen into solid form. It follows, 

 then, that if gases are made of molecules, the same must be 

 true of solids and liquids. 



There are some differences, however. The molecules of a 

 liquid seem to move about readily almost as readily as they 

 do in a gas, but they do not have the same tendency to fly 

 apart. Thus the liquid changes form, but it remains the same 

 in volume. It does not readily expand and is not easily com- 

 pressed. The solid also is not easily compressible, since its 

 molecules do not readily shift their positions. It has a per- 

 manent shape. The spaces between molecules in a liquid or 

 a solid are much smaller than in a gas, but there must be 

 some space, else we could not dissolve substances in water. 

 Even so compact a substance as gold will absorb certain other 

 substances, and we believe that the molecules of the dissolved 

 substance find their way into the spaces between the molecules 

 of gold. 



If alcohol, which is lighter than water, is carefully poured 

 into a test tube which has been half filled with water, at first 

 most of the alcohol will float upon the water, but after some 

 time it will be found that the two liquids have become evenly 

 mixed. In a similar manner a lump of salt or sugar which 

 may be dropped into a vessel of water will dissolve and diffuse 

 throughout the water. Diffusion occurs in liquids as it does 

 in gases. 



