THE TANTALUM LAMP.« 



By Dr. W. von Bolton uiul Dr. O. Feuerlein. 



Part I. — P)y Dr. W. von Bolton. 



AAHiilst the carhon-filanient incandescent lamp remained for nearly 

 two decades the sole representativ^e of glow-lamp manufacture, prog- 

 ress was being quietly made in this art. The firm of Messrs. Siemens 

 & Halske has for many years been working at a solution of the prob- 

 lem of an economical incandescent lamp, and arriv^ed, some time ago,^ 

 at the fundamental principle that the visible part of the radiation of 

 an incandescent body increases progressiv^ely with its temperature. 

 This warrants the postulate that the most economical lamp will be 

 tiiat whose incandescent material will withstand the highest tem- 

 })erature. 



JVIessrs. Siemens & Plalske had arrived at this conclusion and 

 charged me several j^ears ago with the task of discovering a material 

 which should hav^e a melting point considerably above the tempera- 

 ture at which incandescent lighting becomes highly economical, so 

 that filaments made of such a material would not melt or disintegrate 

 at that temperature. Whilst our laboratory work, founded upon 

 this idea, was going on, the first two advances in incandescent light- 

 ing were made public, one being the " Nernst " and the other the 

 " Osmium " lamp. 



There are certain metals the melting points of wdiich are known to 

 be considerably above 2,000° C, and the task resolved itself into find- 

 ing one which, while fulfilling the above requirement, could be easily 

 worked to form a filament, and not be very rare or difficult to i)ro- 

 cure. It was early observed that brown vanadium pentoxide, which, 

 according to Berzelius, does not conduct electricity, is, as a matter of 



"Translation (through the courtesy of Mr. Alexander Siemens) of a paper 

 road before the Elelctrotechnischer Verein of Berlin on .Tannary 17, lOd."). 



Reprinted, by permission, from the Electrician, London, No. 1.30;i. Vol. LIV, 

 No. 15, .January 27, 1905. 



b Cf. W. Siemens in Elektrotechnische Zeitschrift, Vol. IV., p. 107. 1S83. 



129 



