NO. 2 HISTORY OF ELECTRIC LIGHT SCHROEDER 57 



consisted of passing current through a carhonized filament in an 

 atmosphere of hydrocarbon vapor. The hot filament decomposed the 

 vapor, depositing graphite on the filament. The graphite coated fila- 

 ment improved it so it could operate at 3^ lumens per watt (initial efifi- 

 ciency) . Lamps of 20, 24, 32 and 50 candlepower were developed for 

 iio-volt circuits. Lamps in various sizes from 12 to 36 cp were made 

 for use on storage batteries having various numbers of cells and giving 

 a voltage of from 20 to 40 volts. Miniature lamps of from ^ to 2 cp 

 for use on dry batteries of from 2^ to 5^ volts, and 3 to 6 cp on 



« 



Standard Edison Lamp, 1894. 



This lamp had a " treated " cellulose filament, permitting an effi- 

 ciency of 3J^ lumens per watt which has never been exceeded in a 

 carbon lamp. This lamp is in the exhibit of Edison lamps in the 

 Smithsonian Institution. 



5^ to 12 volts, were also made. These could also be connected in 

 series on no volts for festoons. Very small lamps of -i- cp of 2 to 

 4 volts for use in dentistry and surgery were made available. These 

 miniature lamps had no bases, wires being used to connect them to 

 the circuit. 



Lamps for 220-volt circuits were developed as this voltage was 

 desirable for power purposes, electric motors being used, and a few 

 lamps were needed on such circuits. They are less efficient and more 

 expensive than iio-volt lamps, their use being justified however 

 only when it is uneconomical to have a separate iio-volt circuit for 

 lighting. The lamps were made in sizes from 16 to 50 candlepower. 



