152 Introduction to the Study of Science 



compartments. As the compressed gas passes through the 

 coil and is cooled by running water, it condenses and finally 

 becomes liquid. The liquid ammonia collects in the lower 

 part of the condenser coil or in a reservoir located there. 



From the collecting reservoir the liquid is passed through 

 the regulating valve into the pipe leading to the coil in the 

 cooler or evaporating tank containing brine. The valve regu- 

 lates the pressure at which the liquid is liberated in the cooler 

 pipe. As it circulates in the coil at greatly reduced pressure, it 

 expands, takes up heat from the brine and other contents of the 

 tank and finally becomes ammonia gas. As -such it is drawn 

 into the cylinder of the compressor, where it is again compressed 

 and started on another round in the circulatory system. The 

 heart of the whole system is the compressor, for it provides 

 pressure and maintains circulation. Ammonia is the circulat- 

 ing fluid which gives up heat to the water in condensing to 

 liquid and again takes up heat and lowers the temperature of 

 the substances refrigerated, in expanding and becoming gas. 

 Note the " balance/' suggested in the diagram, between the 

 temperature of the waste or cooling water and the temperature 

 of the ice. 



Refrigeration. In refrigerating cold storage compartments, 

 the cold brine is forced through the refrigerating pipes by a 

 force pump. The brine circulating in the pipes takes heat from 

 the compartments and their contents. The temperature of 

 the brine may be regulated and thus adapted to the nature of 

 the substances to be preserved. For example, the tempera- 

 ture in which eggs, apples, milk, and the like are best kept is 

 between and 2 C. (32 F. to 36 F.) ; meat and fish may be 

 kept for long periods in a temperature of - 7 to - 15 C. 

 (about 20 F. to 10 F.). 



__ 58. The production of low temperatures. The usual sys- 

 tem of refrigeration depends for its operation upon the behavior 

 of ammonia gas. Some of the properties of ammonia are fa- 

 miliar from its use in the form of ammonia water in household 



