CHAPTER III 

 REFRIGERATION 



FAMILIAR applications of low temperatures are made in re- 

 frigeration and in the manufacture of artificial ice. Refrigera- 

 tion used in cold storage, transportation, and distribution, makes 

 it possible for the whole world to contribute to every market its 

 produce, such as meat, fish, eggs, butter, fruits, and vegetables, 

 and secures a more equal distribution of foods throughout the 

 year. Ice manufacture renders man independent of the 

 caprices of winter and gives a product that is incomparably 

 purer and safer for all purposes than the natural ice. 



Cooling is exactly the reverse of heating. A stove, fireplace, 

 or radiator, having a temperature higher than that of surround- 

 ing objects, radiates heat. In cooling or refrigeration, some sub- 

 stance, such as ice or liquid ammonia, with a temperature far 

 lower than that of surrounding objects, absorbs and. takes from 

 them their heat. Ice is melted by the heat absorbed from other 

 things. Liquid ammonia in ice making takes heat from ad- 

 jacent substances and " boils," or passes into vapor. It be- 

 haves just as water does in taking up heat when it boils and 

 vaporizes. 



55. The household refrigerator. The common household 

 refrigerator (Fig. 40) depends for its efficiency upon several 

 conditions. It should be of more or less non-conducting ma- 

 terials. If made with double walls the space between them 

 should be filled with a blanket of " dead " air or some insulat- 

 ing substance, as hair felt, mineral wool, cork, or well-packed 

 excelsior. Second, a refrigerator must secure circulation of 



147 



