NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



75 



(a variety of iron ore) and other substances packed tightly in an 

 iron tube. The positive electrode is a piece of copper sheathed in 

 iron to prevent oxidization of the copper. The arc flame gives a 

 brilliant white light, and, similar to the mercury arc, is inherently 

 limited to direct current. It burns in the open air at about 75 volts. 

 The lamp is made for 4-ampere direct current series circuits and 

 consumes about 310 watts and has an efficiency of about Ii-| lumens 

 per watt. 



The negative (iron tube) electrode now has a life of about 350 



LuAtiNOUS OR Magnetite Arc Lamp, 1902. 



This has a negative electrode containing magnetite which produces 

 a very luminous white flame in the arc stream. 



hours. Later, a higher efficiency, 4-ampere electrode was made which 

 has a shorter life but gives an efficiency of about 17 1-p-w, and a 6.6- 

 ampere lamp was also made giving an efficiency of about 18 1-p-w using 

 the regular electrode. This electrode in being consumed gives off 

 fumes, so the lamp has a chimney through its body to carry them off. 

 Some of the fumes condense, leaving a fine powder, iron oxide, in the 

 form of rust. The consumption of the positive (copper) electrode is 

 very slow, which is opposite to that of carbon arc lamps on direct 

 current. The arc flame is brightest near the negative (iron tube) 



