282 LIGHT AND ITS ARTIFICIAL PRODUCTION. 



THE PROCESS OF COMBUSTION. 



Substances like rocks, which have no affinity for oxygen, do not 

 oxidize, do not burn, and furnish no light and heat. But what a strong- 

 affinity do carbon, hydrogen, and the hydrocarbons manifest for all- 

 consuming oxygen ! When these elements are brought together there 

 is a great development of heat attended most frequently by light 

 effects. 



If hydrogen is burned alone, water vapor is formed — that is, the com- 

 bination of hydrogen and oxygen. [Experiment showing the oxy- 

 hydrogen blowpipe.] If pure carbon is used, as when a diamond is 

 burned, carbon dioxide is ordinarily formed, although poisonous carbon 

 monoxide is formed with an insufficient supply of air. Both reactions 

 take place simultaneously in all free-burning flames in which chemical 

 compounds of carbon and hydrogen, so-called hydrocarbons, combine 

 with oxygen. The most commonly used illuminating materials, as 

 oils, tallow, fats, stearine, and wax consist principally of hydrocar- 

 bons and burn under favorable conditions. In order that oxygen may 

 combine with hydrogen and carbon with the development of light, the 

 combustible substance must both be in a gaseous state and be heated 

 to a high temperature. In the case of the gas flame the works furnish 

 the gaseous hydrocarbons, while the match supplies the necessary heat 

 for ignition. The hot gas is then immediately attacked by the oxygen 

 of the surrounding air with the formation of carbon dioxide and noncom- 

 bustible water vapor. The heat produced is sufficient to heat the gas 

 which follows so that this also can burn, and this action continues as 

 long as gas escapes from the burner and as long as the surrrouudihg 

 air contains sufficient oxygen. The processes involved in every com- 

 bustion are similar to those involved in the production of illuminating 

 gas on a large scale. Every fire is the luminous eifect of a gas under- 

 going the process of combustion. Every flame is a gas flame, and 

 mauy other sources of light, petroleum lamps, candles, etc., are there- 

 fore miniature gas works. 



Let us for a few moments consider the candle which, notwithstanding 

 its modest appearance, is a small miracle, and whose importance is indi- 

 cated by the fact that it forms the subject of six lectures by the cele- 

 brated English physicist, Faraday. The heat furnished by the match 

 takes the place of the fire under the retort in the gas works. The 

 stearine melts, rises in the wick, and is also vaporized by the heat of 

 the match, in the same manner as coal is made into gas in the retorts 

 by the heat of the fire beneath. The process of combustion from here 

 on is that described above, the hot hydrocarbon gas produced at the 

 end of the wick unites with the oxygen of the air, while the heat devel- 

 oped heats the gas which follows previous to its combustion. If all 

 these processes are to be continuous and harmonious, as is the case with 

 a candle which burns well and does not drip, we can not help admiring 



