180 SCIENCE OF COMMON THINGS. 



Expansion of water in freezing. 



der ordinary circumstances is reduced to 32 of heat, 

 water will no longer remain in a fluid state. 



118-4 Can water be cooled below 32, under any circumstances, without 

 freezing f 



If pure, recently-boiled water, be cooled very slowly 

 and kept very tranquil, its temperature may be low- 

 ered to 21 without the formation of ice ; but the least 

 motion causes it to congeal suddenly, and its tempera- 

 ture rises to 32. 



1185 Why is solid ice lighter than water ? 



Because water expands by freezing ; and as its bulk 

 is increased, its specific gravity must be less. 



Nine cubic inches of water become ten when frozen. 



118S Why are earthen or porcelain water vessels apt to break in a 

 frosty night ? 



Because the water in them freezes, and (expanding 

 by frost) bursts the vessels to make room for its increas- 

 ed volume. 



1187 Why does it not expand upwards (like boiling water) and run 

 over? 



Because the surface is frozen first ; and the frozen 

 surface acts as a plug , which is more difficult to burst 

 than the earthen vessel itself. 



1188 Why do tiles, stones, and rocks often split in winter f 



Because the moisture in them freezes, and (expand- 

 ing by frost) splits the solid mass. 



1180 In winter-time, footmarks and wheel-ruts are often covered with 

 an icy netivork, through the interstices of which the soil is clearly seen : why 

 does the water freeze in the form of network f 



Because it freezes first at the sides of the footprints ; 

 other crystals gradually shoot across, and would cover 

 the whole surface, if the earth did not absorb the water 

 before it had time to freeze. 



110 O In winter-time, these footmarks and wheel-ruts are sometimes 

 covered with a perfect sheet of ice, and not an icy network : why is this f 



Because the air is colder and the earth harder than 

 in the former case ; in consequence of which the entire 

 surface of the footprint is frozen over before the earth 

 has had time to absorb the water. 



