CHAPTER XXIII. 



MECHANICAL REFRIGERATION. 



In warm climates and in localities where ice is not 

 obtainable or only so at a high cost, cold may be produced 

 by artificial means known as mechanical refrigeration. 

 This system of refrigeration is also finding its way into 

 creameries that are able to procure ice at a moderate cost 

 but which are seeking more satisfactory means of control- 

 ling the temperature of their cream, refrigerator, make 

 room, etc. 



Refrigerating Machines. There are four kinds of 

 machines used for refrigerating purposes: (i) vacuum 

 machines in which water is used as the refrigerating 

 medium; (2) absorption machines in which a liquid of a 

 low boiling point is used as the refrigerating medium, the 

 vapors being absorbed by water and again separated from 

 it by distillation ; (3) compression machines which operate 

 practically the same as the absorption machines except 

 that the vapors in this case are compressed instead of 

 absorbed; and (4) mixed absorption and compression ma- 

 chines. 



Most of the machines in use at the present time 

 belong to the compression type ; the following discussion 

 will therefore confine itself strictly to this class of 

 machines. 



Principle. The principle employed in mechanical re- 

 frigeration is the production of cold by the evaporation 

 of liquids which have a low boiling point, like liquid 

 ammonia, liquid carbonic acid, ether, etc. 



205 



