NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



89 



used to any extent in this country as an illuminant. They have an 

 efficiency of about 26 lumens per watt. Quartz is very difficult to 

 work, so the cost of a quartz tube is very great. The ordinary bun- 

 sen gas flame is used with glass, but quartz will only become soft in 

 an oxy-hydrogen or oxy-acetylene flame. 



Gas Filled Tungsten Lamp, 1913. 



By operating a coiled filament in an inert gas, Dr. Langmuir was 

 able to greatly increase its efficiency, the gain in light by the higher 

 temperature permissible, more than offsetting the loss of heat by con- 

 vection of the gas. This lamp is in the exhibit of Edison lamps in the 

 Smithsonian Institution. 



THE GAS-FILLED TUNGSTEN LAMP 



The higher the temperature at which an incandescent lamp fila- 

 ment can be operated, the more efficient it becomes. The limit in 

 temperature is reached when the material begins to evaporate rapidly, 

 which blackens the bulb. The filament becoming thinner more quickly, 

 thus rupturing sooner, shortens the life. If, therefore, the evaporat- 

 ing temperature can by some means be slightly raised, the efficiency 

 will be greatly improved. This was accomplished by Dr. Irving 

 Langmuir in the research laboratories at Schenectady, N. Y., by 

 operating a tungsten filament in an inert gas. Nitrogen was first 



