TIIE SUBSTANCES OF THE EARTH. 17 



The expansive force of water in freezing, or crystal- 

 lising, is very great. A pitcher iilled with water, and 

 allowed to freeze, is sure to be broken. The moisture of 

 the soil in freezing beneath a building lifts it perceptibly 

 every winter. 



Siiowflakes illustrate the tendency of freezing water 

 to crystallize. When examined with a microscope, they 

 present a great variety of regular forms whose beauty 

 and accuracy it would be difficult to imitate. 



Snow Crystals. 



Other substances, like sugar, salt, and alum, show the 

 same tendency. When these are dissolved in water, as 

 their molecules slowly come together again by the evap- 

 oration of the water, they tend to arrange themselves in 

 regular forms. 



Organic and Inorganic Matter. Matter is sometimes 

 divided into two classes : organic and inorganic. 

 WINS. AGR. 2 



