Physics. — ''On the. influence of different .nihstances on the absorption 

 of light hi/ thin tungsten lagers". By L. Hamburger, G. Holst, 

 D. Lely and E. Oosterhuis. (Comiiiunieated by Prof. H. 

 Kamerlingh Onnes). 



(Communicated in the meeting of November 30, 19 18^ 



[ntroduction. The investigation that will be communicated iiere 

 shortly, refers to a subject of great im})Ortance for the glowlamp 

 industry viz. the prevention of the l)lackening during the burning 

 of vacuum tungsten lamps. 



It is well-known, that the efliciency of such a lamp increases, 

 as the temperature of the wire is raised. Now iji this way 

 a very high efficiency may be obtained in the beginning, but 

 by the vaporization of the lilament, which increases exceedingly 

 rapidly with the temperature, the glass bulb is covered with a thin 

 layer of tungsten, which can absorb so much light, that aftei- a short 

 time the economy of the lamp sinks below thai of a similar lamp 

 that burns at a less high temperature. 



Of course, many methods have been tried to prevent this l)l{;icken- 

 ing of the bulb. The means that have been applied may be divided 

 into two groups. 



l*'^ It is tried to decolorate the tungsten precipitate by the intro- 

 duction of certain substances, so that it becomes less inconvenient. 



2"'^ The velocity of vaporization of the tungsten is decreased b}' 

 the introduction of a gas under high pressure. This last method is 

 applied in the so-called half-watt lamps. 



Here however we shall exclusively treat the tirnt method and 

 investigate by what substances the blackening of the vacuum lamps 

 can be prevented and in what way these substances act. 



Two principal groups of substances may be discerned. 



1^'. Gases which are chemically active with the \aporized tungsten 

 and form with it a less coloured compound, and substances which 

 during the burning of the lamp develop active gases. 



2"^. Substances of which we cannot simply say that they aie 

 chemically active with the vaporized tungsten. 



This last group especially will be discussed here. First we must 

 however make son)e remarks on the tii-st. 



