CHAPTER XXXVI. 
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: (1) 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. 
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