892 



Popular Science Monthly 



In ammonia machines, high pressure is 



avoided by means of an automatic switch 



which stops the motor 



large amount of heat is absorbed from 

 the remainder of the water, which is 

 thereby cooled to the freezing point. 

 This heat apparently disappears in the 

 vapor, for the vapor is no warmer than 

 the water from which it comes. This 

 heat is said to be latent. Now should 

 the pan containing the cooled water be 

 connected with a pipe-coil located in a 

 refrigerator, the cold water would per- 

 form the same function as ice. In 

 practice, however, water is not used in 

 refrigerating machines, more volatile 

 liquids being used instead; the vapor 

 discharged by the pump is condensed and 

 returned to the evaporator to be again 

 evaporated. 



Of the several well-known types of re- 

 frigerating machines, the gas compression 

 and expansion machine is the one most 

 generally used for cooling household re- 

 frigerators. All compression machines 

 are made up of four distinct parts, viz.: 

 a compressor or pump, a condenser, a 

 refrigerating-coil, and an expansion valve 

 between the condenser and the refrigerat- 

 ing-coil. These are connected in a closed 

 cycle so that the compressor can suck 

 out the gas from the refrigerator-coil and 

 discharge it under high pressure into the 

 condenser, where the hot gas is cooled 

 by running water. The combined eflfect 

 of pressure and cooling causes the gas to 

 liquefy. This liquid passes through the 



expansion valve into the refrigerator- 

 coil where it evaporates because of the 

 low pressure maintained by the suction 

 of the compressor and the heat absorbed 

 from the articles being cooled. The func- 

 tion of the refrigerant is that of a heat- 

 carrier; it takes up heat in the refrigera- 

 tor and discharges it into the cooling 

 water. It is able to do this by reason of 

 the work of the compressor which main- 

 tains a high pressure in the condenser, 

 where the heat is discharged, and a low 

 pressure in the refrigerator-coil, where 

 the heat is absorbed. The refrigerants 

 most generally used are ammonia, sul- 

 phur-dioxide, and ethyl-chloride. 



The most essential requisite of a 

 household refrigerating machine is that 

 it shall be so nearly automatic that the 

 services of an expert attendant shall not 

 be required. 



A near approximation to this require- 

 ment seems to have been attained by 

 the machine shown on page 891. The 

 larger of the two hollow shells encloses 

 the compressor, and the shell itself is the 

 condenser and runs in cooling water, 

 while the smaller shell acts the same as 

 a refrigerator-coil. When completed this 

 device is charged with a suitable amount 

 of sulphur-dioxide and lubricating oil 

 and is then sealed up. As all the moving 

 parts are sealed up, the escape of gas is 

 effectually prevented. By reason of the 

 ingenious manner in which the com- 

 pressor is constructed all danger from 

 high pressure is overcome. 



The illustration on the preceding page 

 shows how this machine may be used 

 to cool a refrigerator on the dining-room 

 floor of a home, the machine itself 

 being in the basement. 



While ammonia is a most excellent 

 refrigerant in large machines, it is not 

 much used in household machines be- 

 cause of the danger of the high pressure 

 in the condenser and the possibility of 

 leakage. Ammonia machines for house- 

 hold use are usually so arranged that the 

 switch controlling the motor is closed 

 by the pressure of the water flowing to 

 the condenser, and whenever the water 

 fails or is turned off the machine is 

 automatically stopped. In this way 

 dangerously high pressures in the con- 

 denser are avoided. In all ammonia ma- 

 chines the pressure in the condenser 



