PACKING AND MARKETING FRUITS 39 



The cold temperature in the warehouses is usually 

 produced by either of two methods, commonly known 

 as the compression and the absorption systems. 



The compression system takes its name from the 

 fact that the refrigerating gas whether ammonia, 

 carbonic acid, or sulphuric acid is first compressed 

 in a machine called a compressor. Heat is generated 

 by the compression; the gas is then cooled and con- 

 densed in pipes or coils called the condenser, either 

 immersed in water or having water running over 

 them, and this converts the gas into a liquid. The 

 liquefied gas then passes an expansion valve to pipes 

 or coils called the refrigerator cooling coils or cooler, 

 where it is evaporated by the heat which is with- 

 drawn from the surroundings. The gas formed by 

 the evaporation of the liquid returns to the com- 

 pressor, is again condensed, then re-evaporated, and 

 the cycle of refrigeration is repeated over and over. 



In the absorption system the gas is obtained by 

 heating strong aqua ammonia in a still, thereby 

 driving off the ammonia gas. The gas is then re- 

 duced in a condenser to a liquid in a manner sim- 

 ilar to the compression system. The liquefied am- 

 monia produces refrigeration by evaporating in the 

 cooling coils, and the gas is then absorbed by weak 

 aqua ammonia in coils called an absorber. The 

 resulting strong liquor is then pumped back to the 

 still. The cycle of refrigeration is repeated contin- 

 uously, and consists, first, in the generation of a gas 

 by heating strong aqua ammonia in a still; second, 

 in condensing the gas which is deposited from the 

 water to a liquid in the condenser coils; third, in its 

 evaporation to a gas in the cooling or refrigerator 

 coils; fourth, in its absorption by the weak aqua 

 ammonia in the absorber; and fifth, the ammonia 

 liquor is piped to the still and redistilled. 



There are three general methods of producing the 



