COOLING FACILITIES FOR CREAMERIES. 325 



latent heat is absorbed. When water in a kettle on the stove 

 begins to boil and passes off into steam, no higher temperature 

 can be reached. No matter how much heat is applied under 

 those same conditions, the temperature remains the same. 

 This extra heat is used in transforming the water into steam. 

 If this steam were confined, and that heat removed, by cooling, 

 the steam would again pass into a liquid state. We are familiar 

 with the coolness produced by rapid evaporation of perspira- 

 tion from the body. Mechanical refrigeration is virtually a 

 process of evaporation of the cooling media, during which 

 heat is absorbed and liquefaction of the cooling medium by 

 compression and cooling to remove that absorbed heat. To 

 increase the ability of the cooling medium to absorb heat it 

 is compressed and liquefied. So we might say that any com- 

 pression refrigerating system has three separate operations 

 necessary to form the complete cycle of mechanical refrigeration, 

 viz.: 



1. Compression of the ammonia gas. 



2. Condensation of the ammonia gas. 



3. Expansion of the ammonia gas. 



1. The machine which causes the compression of the am- 

 monia gas is called the compressor. In construction it is much 

 like a steam-engine. Small machines are single, but large 

 machines are double acting. Gas is drawn in, on the suction 

 stroke, compressed and discharged on the return stroke. The 

 pressure generated varies between 120 and 175 pounds per 

 square inch. During the compression heat is developed in 

 proportion to pressure exerted. The greater the pressure the 

 higher the temperature of the gas. Part of the heat of com- 

 pression is carried off by means of a continuous stream of 

 water running through a jacket around the cylinder. 



2. From the compressor the gas is forced through the pipes 

 into the condensing coils, in which the warm compressed gas 

 is cooled still more. When sufficient heat has been removed 

 from this gas, it assumes a liquid condition and is ready to 

 expand into a gaseous form for the purpose of absorbing heat 



