REFRIGERATION (Lat. refrigeratio, from refrigerare, to cool again). The art of produeing cold by artificial means. It has been practiced since very ancient times, but it is only in corn paratively recent times that improved systems and apparatus have enabled such operations to be conduct (4l profitably and on a commercial scale. Meehanical refrigeration is now employed in the manufacture of artificial lee; for the freez ing and chilling of freshly killed meat in slaugh ter houses; for the cooling of stores for meat, fish, fowl, fruits, vegetables, and other perish able provisions; for cooling the atmosphere of dwellings and hospitals; for certain engineering operations; and for a variety of manufacturing processes. The number and variety of refrig erating devices available for these purposes are very great, hut they all belong to one or the other of the following five classes: (1) Devices in which the more or less rapid liquefaction of a solid is utilized to abstract heat; (2) devices by which the abstraction of heat is effected by the evaporation of a portion of the liquid to be cooled; (3) devices in which the abstraction of heat is effected by the evaporation of a separate refrigerating agent of a more or less volatile nature, which agent 'is subsequently returned to its original condition by mechanical compression and cooling: (4) devices by which the abstrac tion of heat is effected by the evaporation of a separate refrigerating agent of more or less nature under the direct action of heat, which agent again enters into solution with a liquid; (5) devices in which air or other gas is first compressed, then cooled, and afterwards per mitted to expand while doing work. These live
processes of refrigeration are termed, respective ly, the liquefaction process, the vacuum process. the compression process, the absorption process, and the cold-air process.