The Romance of Modern Chemistry

PRODUCTION OF LIGHT AND HEAT When gas (or a candle) bums in the air, the supply of oxygen is not sufficient for complete combustion of the carbon and the hydrogen, except in the outermost envelope of the flame, and the fact that we get any light at all from an ordinary gas or candle flame is due to a host of unbumt particles of carbon in the interior. These particles are raised to a white heat by the flame, and so make it luminous. That the ordinary gas or candle flame contains particles of carbon may be very easily shown by holding a cold surface just into the top of the flame, when a deposit of soot (that is, carbon in a finely divided form) is obtained. |( Q When the supply of air to a ------------gas flame is increased by mixing /-----------the gas with air just before it reaches the actual place where no. 3.—A Bunsen Eurn«. il is burned> then the COmbus- tion is more complete, the flame is hotter and no longer luminous. The particles of carbon which ordinarily make the flame luminous are now all converted into carbon dioxide, even in the interior of the flame, by the extra oxygen supplied. This is the principle of the well-known Bunsen burner, which finds application now, not only in the laboratory but in our houses, on incandescent burners and gas stoves. A simple Bunsen burner is shown in the accompanying diagram. The current of gas which rushes out at the central nozzle sucks in air through the surrounding holes at the bottom of the burner, while the mixture of air and gas ascends, and is burned at the top of the tube. 112