Light 191 



with his friends around this fire where he could make use of the 

 light given off. He soon learned to carry blazing sticks a short 

 distance from this fire to help him in finding his way. Later he 

 came to use wood soaked in pitch, or in oil from the animals 

 he killed. Later still he learned to make candles from tallow 

 with strings through them for wicks, similar to the paraffin candles 

 of today. 



The candle was the principal source of artificial lighting 

 until long after the Revolutionary war. With the discovery of 

 petroleum, came the oil lamp. Then came natural gas, which is 

 found in many parts of the earth, usually in regions where 

 petroleum is procured. Man then learned to make gas from 

 coal. Later he learned to make acetylene, a gas which is formed 

 by the action of water on calcium carbide. Today we have electric 

 light. Houses, stores, and streets are ablaze with it. With its use 

 factories may operate all night when necessary. 



If a cold piece of glass is held over a candle flame, it will 

 soon be covered with black soot. Soot is finely divided carbon. 

 It comes from the paraffin of which the candle is made. Before 

 the paraffin burns, it melts and then turns to a gas. This gas has 

 hydrogen and carbon in it and, possibly, some other matter, depend- 

 ing on the materials of which the candle is made. The hydrogen 

 unites with the oxygen of the air and forms water. Watch the 

 glass carefully and a film of moisture may be seen, as well as the 

 soot. The carbon in the paraffin is in the form of solid particles 

 and as these particles rise through the flame they become so hot 

 that they glow. The glowing is the source of the light. When 

 these particles cool they collect on the glass as soot. 



Some of the carbon unites with the oxygen to form carbon 

 dioxide. This may be shown by allowing the candle to burn in 

 a deep dish. When the flame ceases on account of the lack of 

 oxygen, a little lime water poured into the dish will turn milky, 

 proving the presence of carbon dioxide. If all of the carbon 

 could be changed to carbon dioxide there would be very little 

 light as there would then be no separate carbon particles to glow. 



Kerosene lamps consist of a reservoir of kerosene at the top 

 of which is a burner pierced with air holes. A wick extends from 



