CHAPTER VII 

 USES OF WATER 



WHEN pure water is cooled to Centigrade, or 32 

 Fahrenheit, it freezes, and ice is formed. With the 

 present stage of civilization, ice, which was once a luxury, 

 has become almost a necessity. Large quantities of ice 

 are cut from our lakes and ponds and stored for summer 

 use, but much larger quantities are manufactured in our 

 modern ice plants. 



The artificial ice has several advantages : it is usually 

 purer than the natural ice ; it is free from air spaces and 

 melts more slowly ; and since nearly every municipality 

 has its own ice plant, the distribution is a much simpler 

 problem than when the ice must be shipped in carload 

 lots to remote inland points. 



Manufacture of Ice. In nearly all of the modern ice 

 plants, the low temperature required for freezing the 

 water is produced by the evaporation of liquid ammonia. 

 We have already learned that evaporation is a cooling 

 process. It requires heat to evaporate liquids, and the 

 heat is taken from the surrounding objects, thus reducing 

 their temperature. The cooling resulting from evapora- 

 tion will be in proportion to the rate of evaporation. 

 The evaporation of liquid ammonia is very rapid, and in 

 the ice plant sufficient heat is used in the change to cool 

 the surrounding objects to a temperature below the 

 freezing point of water. At ordinary temperatures 

 ammonia is a gas. The temperature above which 



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