NO. 2 HISTORY OF ELECTRIC LIGHT SCHROEDER 8l 



air in the tube at this slight pressure as well as within the narrow 

 limits required. 



This was accomplished by a piece of carbon through which the air 

 could seep, but if covered with mercury would make a tight seal. As 

 the air pressure became low, an increased current would flow through 

 the tube, the normal being about a tenth of an ampere. This accord- 

 ingly increased the current flowing through the primary coil of the 

 transformer. In series with the primary coil was an electro-magnet 

 which lifted, as the current increased, a bundle of iron wires mounted 

 in a glass tube which floated in mercury. The glass tube, rising, 

 lowered the height of the mercury, uncovering a carbon rod cemented 

 in a tube connecting the main tube with the open air. Thus air could 

 seep through this carbon rod until the proper amount was fed into the 

 main tube. When the current came back to normal the electro-magnet 

 lowered the floating glass tube which raised the height of the mercury 

 and covered the carbon rod, thus shutting off the further supply of 

 air. 



As there was a constant loss of about 400 watts in the transformer, 

 and an additional loss of about 250 watts in the two electrodes, the 

 total consumption of the 180-foot tube was about 2250 watts. Nitro- 

 gen gas gave a yellow light, which was more efficient and so was later 

 used. On account of the fixed losses in the transformer and electrodes 

 the longer tubes were more efficient, though they were made in various 

 sizes of from 40 to 200 feet. The 200-foot tube, with nitrogen, had 

 an efficiency of about 10 lumens per watt. Nitrogen gas was supplied 

 the tube by removing the oxygen from the air used. This was accom- 

 plished by passing the air over phosphorous which absorbed the 

 oxygen. 



Carbon dioxide gas (CO2) gave a pure white light but at about half 

 the efficiency of nitrogen. The gas was obtained by allowing hydro- 

 chloric acid to come in contact with lumps of marble (calcium carbo- 

 nate) which set free carbon dioxide and water vapor. The latter was 

 absorbed by passing the gas through lumps of calcium chloride. The 

 carbon dioxide tube on account of its daylight color value, made an 

 excellent light under which accurate color matching could be done. 

 A short tube is made for this purpose and this is the only use which 

 the Moore tube now has, owing to the more efficient and simpler 

 tungsten filament incandescent lamp. 



