CR\PTER XXIII. 



MECHANia\L REFRIGERATION. 



Mechanical refrigeration has been considered expensive 

 and impracticable on a small scale until within a few 3'ears. 

 The science of producing cold artificially has been simplified 

 and reduced to such a practical basis that it is now used in 

 many large as well as small plants where formerly natural 

 ice was used altogether. The chief factors affecting the 

 cost of mechanical refrigeration may be said to be similar 

 to those affecting the economic running of the remaining 

 machinery, such as kind of fuel used, skill of fireman, style 

 and condition of boiler, proportion of boiler power to work 

 done, upon the correlative size of all machinery, upon 

 kind of insulation and care of cooling-rooms and upon 

 efficiency of compressor and whole refrigerating system. 



Chemicals Used. — The most common substances used 

 in mechanical refrigeration are ammonia and carbonic 

 acid. A number of others are in use, but from a creamery 

 standpoint these only are of importance. Ammonia is 

 used chiefly. It is efficient, cheap, and not so dangerous 

 to hfe and propert}- as are some of the others. Anh3'drous 

 ammonia has a boihng-point of 27° below zero at atmos- 

 pheric pressure. The latent heat of ammonia is also 

 great. Ammonia has great chemical stabiHty and is not 

 explosive in nature. Ammonia attacks copper and brass, 

 but has no effect upon iron and steel pipes. 



If ammonia should escape through a leak into a room, 

 the operator can protect himself from the effects of the 

 gas by breathing through a wet sponge held in the mouth. 



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