100 



HOW WE LIGHT OUR HOMES 



FIG. 144. REPLICA OF 

 EDISON'S FIRST ELEC- 

 TRIC LIGHT 



in paraffin, followed. It became the principal source 

 of artificial illumination for several centuries until 

 after 1850. With the discovery about 1860 of how to 

 produce fuels from crude petroleum came the kero- 

 sene lamp. 



The greatest developments in artificial illumination 

 have taken place during the 

 past hundred years. The inven- 

 tion of the incandescent bulb by 

 Thomas Edison and the refine- 

 ments made on it since by other 

 workers are probably the out- 

 standing contributions of this 

 period and are greatly responsi- 

 ble for the brilliant illumination 

 found today in our homes and 

 communities. 



What happens in a candle, a 

 kerosene lamp, and a gasoline 

 lamp when they produce light? 

 A candle flame is composed of 

 three distinct regions. The cen- 

 tral, cone-shaped region, which appears darker than 

 the rest of the flame, is transparent and gives off very 

 little light. The bright yellow section of the flame 

 furnishes most of the light. Along the outer edge 

 of the flame is a pale blue region which can be seen 

 if the candle is brought close to the eye. 



If you hold a wooden splint across the lower part 

 of the flame until it just starts to burn, then with- 

 draw the splint quickly and 

 extinguish the flame, you 

 will notice that the part of 

 the splint that was in the 

 central part of the flame is 

 not charred. Since this re- 

 gion is transparent and not 

 burning, of what does it 

 consist? If you blow out the 

 burning candle and bring a 

 lighted match within a 

 quarter of an inch of the 

 wick it will burst into flame again. This shows that 

 a combustible gas or vapor is near the wick. Where 

 does this gas come from? 



The heat from the flame of the burning candle 

 melts the solid paraffin (see Fig. 140). No doubt you 

 have observed the melted wax in the cup formed at 

 the base of the wick. The melted wax is absorbed by 

 the wick and rises to the top of it by capillary attrac- 

 tion. Here it is changed by the intense heat to a gas 

 and burns. It should be clear now that it is not the 

 solid portion of the candle which is burning, but a gas 

 produced from it. 



Candle wax contains carbon and hydrogen. As it 



FIG. 145. THOMAS A. EDISON 



burns, oxygen in the air unites with the carbon to 

 form carbon dioxide. In the pale blue region of the 

 flame practically all of the carbon is burned. In the 

 yellow region much of the carbon is unburned be- 

 cause of a lack of sufficient oxygen in that area. The 

 unburned carbon goes off into the air as smoke. While 

 the unburned particles are in the flame, the heat causes 

 them to glow, and this is the source of the light. If 

 sufficient air is mixed with a gas flame, the entire 



WATER-VAPOR (HaO) 

 CARBON DIOXIDE 



SOOT-UNBURNED 

 CftRbON 



CHIMNEY 



BURNING CASE 

 LIQUID KEHOSEN 



FLAME 



IURNER 



HOLES IN 

 BASE OF BURNER 



KEROSE NE~J^^ -. 



RESERVOIR 



FIG. 146. KEROSENE LAMP 



flame will be pale blue and will give off very little 

 light. Have you ever noticed this in a gas stove where 

 we are interested in obtaining heat and not light? 

 The hydrogen combines with oxygen from the air 

 also and forms water. The products of a burning 

 candle then are water and carbon dioxide. 



Much that we have learned about the candle also 

 applies to a kerosene lamp. In the candle we started 

 with a solid which was changed to a liquid and then 

 to a gas, while with a kerosene lamp we begin with 

 matter already in the liquid state. The common kero- 

 sene lamp has a wick that extends into a bowl of 

 kerosene. The kerosene is absorbed by the wick and 

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

 of the lamp is lighted, the heat formed changes the 

 liquid kerosene into a gas which burns when mixed 

 with air. As the kerosene is vaporized by the heat, 

 more of it rises from the bowl through the wick. As 

 the wick is slowly used up, it is turned up by means 

 of a screw that is a part of the burner. 



