26 CHEMISTRY. 



force is required to move the molecules and separate them ; in 

 liquid bodies the relative position of the particles is no long- 

 er permanent they glide past each other with perfect ease, 

 and less force is required than in the case of solids ; in gases 

 the mobility of the molecules is still greater than in liquids, 

 and the molecules tend constantly to recede from each other. 

 In Fig. 2 you have a rough representation of the way 

 molecules are separated from each other by heat. 



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Fig. 2. 



22. Atoms. As minute and intangible as these mole- 

 cules are, they are believed to be composed of still smaller 

 particles called atoms. We have already alluded to the 

 difference between Chemistry and Physics (or Natural Phi- 

 losophy), but this difference is now clearer when we state 

 that physical phenomena affect mainly the molecules, while 

 chemical science deals with atoms. Thus the physical 

 properties of an object refer to its condition, whether solid, 

 liquid, or gaseous ; crystalline form, color, hardness, specific 

 gravity, transparency or opacity, and the relations of the 

 body to heat, light, and electricity, are physical properties. 

 These you have studied in Part I. 



