THE ACTION OF FROST IX WATER-PIPES. 301 



As the temperature falls below this, the water rises gradu- 

 Ually in the stem until the freezing point is reached. 



This expansion amounts to ygV? part of the whole bulk 

 of the water, or 100,000 parts become 100,013. So far the 

 amount of expansion is very small, but this is only a fore- 

 taste of what is coming. Lower the temperature still 

 further, the water begins to freeze, and at the moment of 

 freezing it expands suddenly to an extent equalling ^ of 

 its bulk, i.e., of the bulk of so much water as becomes 

 solidified. The temperature remains at 32 until the 

 whole of the water is frozen. 



Fortunately for us, the freezing of water is always a slow 

 process, for if this conversion of every 15 gallons into 16 

 took place suddenly, all our pipes would rip open with 

 something like explosive violence. But such sudden freez- 

 ing of any considerable quantity of water is practically im- 

 possible, on account of the " latent heat" of liquid water, 

 which amounts to 142. All this is given out in the act of 

 freezing. It is this giving out of so much heat that keeps 

 the temperature- of freezing water always at 32, even 

 though the air around may be much colder. No part of 

 the water can fall below 32 without becoming solid, and 

 that portion which solidifies gives out enough heat to raise 

 142| times its own quantity from 31 to 32. 



The slowness of thawing is due to the same general fact. 

 An instructive experiment may be made by simply filling a 

 saucepan with snow or broken ice, and placing it over a 

 common fire. The slowness of the thawing will surprise 

 most people who have not previously tried the experiment. 

 It takes about as long to melt this snow as it would to 

 raise an equal weight of water from 32 to 174. Or, if a 

 pound of water at 174 be mixed with a pound of snow at 

 32, the result will be two pounds of water at 32; 142 

 will have disappeared without making the snow any 

 warmer, it will all have been used up in doing the work of 

 melting. 



The force with which the great expansion due to freez- 

 ing takes place is practically irresistible. Strong pieces of 

 ordnance have been filled with water, and plugged at muz- 

 zle and touch-hole. They have burst in spite of their great 



