28 



BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 



the evaporation of the liquid and the absorption of latent heat would 

 go on faster than ever. 



If it were not for the initial cost of the refrigerating medium this 

 elementary form of refrigerating system, in which the refrigerant 

 is allowed to esca]3e to the atmosphere after evaporation, might 

 find some commercial application, but as the refrigerants are expen- 

 sive, such a system would be very costly to operate. Therefore, 

 as the volatile liquids are valuable and can not be thrown away, 

 if the reverse action takes place, that is, if the volatile gas is again 

 converted into a liquid, it may be carried through the same cycle, 

 over and over again indefinitely, and if it were possible to have no 

 leakage one charge would be sufficient for all time. 



REFRIGERATING MACHINES. 



COMPRESSION SYSTEM. 



In order to make the system illustrated in figure 12 commercially 

 practical, it is necessary to provide some means for converting the 



Waste Gas- 



^L 



l/o/at/'/ £/Qu/d Orum 



Brine 7ank 



Fig. 12. 



gasified refrigerant back into the liquid state in order that it may 

 be again used for the purpose of absorbing heat. In other words, after 

 the refrigerant has evaporated in the expansion coils and absorbed its 

 fill of heat, much as a sponge sucks up its fill of water, the heat and 

 water with which the refrigerating gas and sponge are respectively filled 

 must be extracted before they can again perform the function of 

 absorption. The water is forced out of the sponge by the simple 

 application of pressure, but in the case of the refrigerating gas it 

 becomes necessary not only to supply pressure, thereby raising 

 the temperature of the gas by converting mechanical work into 

 heat, but since the heat can be made to "flow" only from a rela- 

 tively warmer to a relatively cooler substance, there must also be 

 provided some cooling medium which will absorb the heat from the 

 gas. Water being the cheapest and most convenient natural cooling 

 medium, it is used almost entirely for this purpose. 



Since the pressure and consequent temperature of the cold refrig- 

 erating gas returning from the expansion pipes must be raised before 



