14 THE APPLE IN COLD STORAGE. 



evaporation of the liquid returns to the compressor, is again condensed, 

 then reevaporated, 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 reduced in a condenser to a liquid in a manner similar to the com- 

 pression system. The liquefied ammonia 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 

 continuously, 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. 



THE UTILIZATION OF THE COLD TEMPERATURES. 



There are three general methods of producing the desired tempera- 

 tures in cold-storage rooms, and these are known as the direct-expan- 

 sion, the brine-circulating, and the indirect or air-circulating systems. 

 All three systems may be used in a cold-storage plant, and in a given 

 room or compartment the air-circulating system is sometimes used in 

 connection either with the brine or the direct-expansion systems. 



THE DIRECT-EXPANSION SYSTEM. 



In the direct-expansion system the liquefied gas evaporates directly 

 in the cooling refrigerator coils or pipes which are placed in the refrig- 

 erator rooms. The heat used in the evaporation of the gas is absorbed 

 from the room or from its contents, and the temperature is thereby 

 reduced. The gas then returns to the compressor in the compression 

 system, or to the absorber in the absorption system, and after being 

 distilled in the latter case begins the refrigerating cycle anew. 



THE BRINE-CIKCCLATING SYSTEM. 



In the brine-circulating system, the liquefied gas, instead of evapo- 

 rating directly in coils in the storage room, evaporates in pipes 

 surrounded by brine, or in a brine cooler. The heat used in the 

 evaporation of the gas is absorbed from the brine rather than from 

 the room and its contents, as in the direct-expansion system. The 

 cold brine is then pumped to coils in the storage room and the heat of 

 the room and its contents is absorbed by the cold brine. The warm 

 brine is then returned to the tank or cooler from which it started and 

 is recooled, while the gas returns to the condenser or to the absorber 

 to renew the cycle of refrigeration. 



