192 Our Surroundings 



the reservoir to the middle of the burner, where its height is 

 regulated by a small thumb screw. A tall glass lamp chimney 

 encloses the burner and the top of the wick. 



Kerosene rises to the top of the wick by capillarity. When 

 the wick is lighted, the kerosene vaporizes and combines with 

 the oxygen in the air which flows through the holes in the burner. 

 This oxygen combines with the hydrogen in the kerosene vapor 

 to form water, and with the carbon to form carbon dioxide. There 

 is always a certain amount of carbon which does not combine, and 

 this, when heated in the flame, is the source of the light. If the 

 lamp smokes, it is getting too much carbon, and the wick should 

 be trimmed or turned down. 



The same condition may be shown with a Bunsen burner. 

 Light the gas and close the holes at the bottom of the burner. 

 Soot collects as in the case of the candle and the flame gives off 

 considerable light. If the holes at the bottom are opened the 

 flame becomes almost colorless. This is because the holes allow 

 the air to mix thoroughly with the gas before it begins to burn 

 and thus the carbon has an opportunity to become oxidized. 



When gas, kerosene, or gasoline is used for lighting, frequently 

 a mantle is placed over the flame. The mantle is a small bag 

 made of a fiber. It is soaked in a solution of a certain rare metal, 

 thorium, and coated with something to protect it We place this 

 mantle on the burner and burn off the protecting coat; then the 

 fiber burns out and leaves a network of the metal. Thorium is 

 used because it has been found to give off the best color for 

 lighting purposes. 



In such a burner, the light comes from heating the mantle 

 until it glows and not from the glowing of the carbon particles 

 in the gas. In fact, if the carbon is not burned, it collects on the 

 mantle and spoils the light. Such burners, then, must have holes 

 at the bottom to let in enough air to make sure that the carbon is 

 completely burned. The amounts of air and gas have to be 

 adjusted very carefully to give the best results. 



The most efficient light produced up to this time is the electric 

 light. This has two forms, the arc light and the incandescent 

 light. The arc light depends upon an electric current jumping a 



