84 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



also made, but these were soon superseded by the tungsten-filament 

 lamp which appeared in 1907. 



THE TANTALUM LAMP 



Dr. Werner von Bolton, a German physicist, made an investigation 

 of various materials to see if any of them were more suitable than 

 carbon for an incandescent-lamp filament. After experimenting with 

 various metals, tantalum was tried. Tantalum had been known to 

 science for about a hundred years. Von Bolton finally obtained some 

 of the pure metal and found it to be ductile so that it could be drawn 



\ "1 



.'''^■< 



Tantalum Lamp, 1906. 



The tantalum filament could be operated at 50 per cent greater effi- 

 ciency than that of the regular carbon incandescent lamp. This lamp 

 is in the exhibit of Edison lamps in the Smithsonian Institution. 



out into a wire. As it had a low specific resistance, the wire filament 

 had to be much longer and thinner than the carbon filament. A great 

 number of experimental lamps were made so that it was not until 

 1906 that the lamp was put on the market in this country. It had an 

 initial efficiency of 5 lumens per watt and a good maintenance of 

 candle power throughout its life, having an average efficiency of about 

 4I 1-p-w. Th© usual sizes of lamps were 40 and 80 watts giving 

 about 20 and 40 candlepower respectively. It was not quite as 

 strong as the carbon lamp, and on alternating current the wire crystal- 

 lized more rapidly, so that it broke more easily, giving a shorter life 

 than on direct current. It disappeared from use in 1913. 



