118 APPLIED SCIENCE 



pipe. Oxygen and hydrogen gases are. directed upon the 

 ball or disk of lime from separate vessels or gasometers through 

 a flame arising from alcohol. This light, invented by Cap- 

 tain Drummond, is probably the most powerful known, and 

 can be seen a distance of 30 miles. It is now much used for 

 light-houses. 



121. Gas Lighting. Luminosity depends upon the re- 

 flection of glowing particles, and since a yellow flame heats 

 many of these small particles of carbon, it gives off more 

 light than does a blue flame. Consequently, the yellow flame 

 is extensively used for gas lighting. The most effective 

 gas light is produced by using a mantle. (A mantle is a 

 screen which glows when the gas is lighted.) 



122. Natural Gas. A form of gas called natural gas is 

 obtained from the earth by drilling a deep well. Such gas 

 is formed as the result of decomposition of organic matter 

 under pressure and heat. It comes to the surface often 

 under great pressure and requires but little preparation for 

 use. In different districts natural gas is of different composi- 

 tion, but its principal constituent is always "marsh gas," 

 a compound of carbon and hydrogen that has a very low 

 lighting but a very high heating value. It is used for both 

 heating and lighting. 



123. Manufactured Gas. Manufactured or artificial gas 

 is used in most places in this country and is made by 

 heating coal gas, that is, gas obtained by distilling coal. 

 Artificial gas is used for both heating and lighting, but its 

 cost tends to be prohibitive for the former purpose. 



