TlIK SIBSIAXCES OF TIIK KAKTll. 



15 



is suniciciii to ovei'coiuc the foi'ce of cohesion bv whieli 

 the molecules are attracted to one another, and they arc 

 sei)a rated or the rubber is broken. 



The Porosity of Matter. — All matter is more or less 

 porous. This is not only ti'ue of loose substances like 

 soil, but also of more solid substances, like wood and 

 ircm. The pores in the latter are, like atoms and mole- 

 cules, too small to be seen. 



/J C IF 



I 



Cross-section of Wood, magnified, showing Pores. 

 B, the bark : C, t/ie camhltun taijcr; 11', imod. 



It IS believed that neither atoms nor molecules ever 

 remain in absolute contact with each other, but that there 

 are always spaces between them. Through these spaces 

 atoms and molecules of other substances arc able to pass. 



A certain amount of salt and sugar may be dissolved 

 in water without increasing the volume of water. The 

 molecules of salt and sugar occupy the vacant spaces 

 between the molecules of water. 



Under heavy piTssui'c water has been forced through 

 the pores of iron. A piece of ii'on may be made smaller 

 by hammering. Its molecules are then driven nearer 

 together. 



A bottle fdled with gas will hold as much of another 

 kind of gas as if it were empty. 



