ATOMS. 13 



the gas chlorine ana the metal sodium unite, as will be 

 hereafter seen, to form common salt. When substances 

 become thus united by chemical affinity, the resulting 

 compound is not a mere mixture, with properties of 

 both constituents, as when salt and sugar are mixed ; 

 it is, on the contrary, a new substance with properties 

 of its own. 



8. DISTANCE OF ATTRACTION. The forces 



Do the forces , , , . ., t 



of Cohesion P* attraction above mentioned, with the ex- 

 and Chemical ce ption of gravitation, act only at immeasu- 



Affimty act at J 



great dlstan- rably small distances. Two plates of glass 

 an inch apart do not attract each other ; even 

 when brought close together they will not remain at- 

 tached. But if powerfully pressed, the atoms are brought 

 within the range of the force of cohesion, and cannot 

 again be separated. So iron and oxygen will not at- 

 tract each other from a distance, but when brought to- 

 gether, unite in consequence of their chemical attraction. 



9. ILLUSTRATION. The action of the three 



Illustrate the . 



three different is illustrated in a falling drop of water. Al- 



k tract S ion f "^ ^ n ^y nolds to g etner tne atoms of oxygen 

 and hydrogen which make up each particle 

 of water. Cohesion unites the particles of water thus 

 formed, to make the drop, and gravitation causes the 

 coherent drop to fall. 



10. THREE STATES OF MATTER. There 



What are the f 



three states of are three distinct states or conditions 01 

 matter? matter the solid, the liquid, and the gas- 



eous, and almost all substances may be made to assume 

 each of these states. Thus, a piece of solid sulphur, 

 if heated up to a eertain point, melts and becomes 



