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 nob for the initial cost of the refrigerating medium this 
elementary form of refrigerating system, in which the refrigerant 
is allowed to escape 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- :.&&.- 
•.-'y^Sf:, 
\/o/a+// L/ql//'g/ Or-um 
Br/ne Tank 
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 
