138 MARKET DAIRYING 



Manifestly for refrigerating purposes a liquid must be 

 used that can be evaporated at a very low temperature; 

 for the cold in mechanical refrigeration is produced by 

 the evaporation of the liquid in iron pipes, thfe heat for 

 the purpose being absorbed from the room in which the 

 pipes are laid. Anhydrous ammonia has thus far proven 

 to be the best refrigerant for ordinary refrigeration. 



Anhydrous Ammonia (Refrigerant). This substance 

 is a gas at ordinary temperatures but liquifies at 30° F. 

 under one atmospheric pressure. In practical refrigera- 

 tion the ammonia is liquified at rather high temperatures 

 by subjecting it to pressure. The ammonia is alternately 

 evaporated and liquified so that it may be used over and 

 over again almost indefinitely. 



Circulation of Ammonia. The cycle of operations in 

 mechanical refrigeration is as follows: The liquid am- 

 monia starts on its course from a liq.tdd receiver, and 

 enters the refrigerating coils in which it evaporates, ab- . 

 sorbing a large amount of heat in the process. By means 

 of a compression pump, operated by an engine, the am- 

 monia vapors are forced in the condenser coils where the 

 ammonia, under pressure, is again liquified by running 

 cold water over the coils. From the condenser coils it 

 enters the liquid receiver, thence again on its journey 

 through the refrigerating coils. 



The intensity of refrigeration is regulated by an ex- 

 pansion valve, which is placed between the liquid receiver 

 and the refrigerating coils. This valve may be adjusted 

 so as to admit the desired quantity of liquid ammonia to 

 the coils. 



Systems of Refrigeration. There are two ways in 

 which the cooling may be accomplished by mechanical 

 refrigeration: (i) by evaporating the liquid ammonia 



