New Developments in Science 595 



is vaporized (turned into a vapor), mixed with air, and sprayed 

 into the fire box, where it is ignited. The various kinds of oil 

 burners accomplish these four steps by different methods. In the 

 "gun-type" burner the oil is forced through a nozzle that breaks 

 it up into fine mist. A stream of air is mixed with this oil mist. 

 The air helps to vaporize the oil and also adds the correct amount 

 of oxygen necessary for complete combustion of the oil vapor. 

 The mixture is ignited by either an electric spark or by a pilot gas 

 light. 



In the "rotary-atomizer type" of burner the oil is whirled out 

 by centrifugal force 1 in fine drops from slots in a rapidly turn- 

 ing plate in the center of the firebox. This plate is driven by an 

 electric motor. As the oil drops leave the plate they are mixed 

 with a stream of air, which helps vaporize them. In still another 

 type of burner, the oil is vaporized by heat. The gun type of 

 burner is gradually replacing all other types. Oil burners do away 

 with shoveling coal and ashes and are much cleaner than coal- 

 burning furnaces. 



Heating by Gas. Gas is sometimes used as a fuel in the 

 furnace, especially in regions where natural gas is available. In 

 steam and hot-water furnaces the gas flames heat the water in 

 the boiler. In hot-air furnaces a heavy plate made of material 

 that retains heat a long time is heated by the gas flames. Some 

 of the advantages of the gas furnace are that it does not require 

 expensive apparatus and it never needs refueling of storage tanks 

 or bins. 



Heating by Electricity. Since the application of the re- 

 sistance coil 2 to practical purposes, dozens of useful devices, such 

 as electric toasters, percolators, and heaters, have increased our 

 comfort and convenience. The electric furnace is one of the 

 more recent devices which make use of the resistance coil. Its 

 heating unit consists merely of numerous powerful resistance 

 coils. 



The essential feature of the electric furnace is a storage tank 

 made like a huge thermos bottle. Water is heated by the electric 



1 See definition on page 619. 



2 See description on page 231. 



