1079 



§ 1. Action o J gases or substances ivhich develop gases by 



dissociation. 



The simplest action is that of small quantities of gas that are 

 introdnced into the bulb. In this i-espeot es|)eciallj chlorine and 

 oxygen are remarkable. 



Langmuir') has shown, that at room temperature and even at 

 200° chlorine acts hardly or not at all upon the lungsten precipi- 

 tate on the bidb. When a small quantity of dry chlorine is introduced 

 into a lamp, in which a tungsten precipitate has been formed alieady 

 on the bulb, the chlorine will not act upon it. When however the 

 lamp glows, the tungsten precipitate vanishes rapidly. Langmuir 

 explains this by the assumption that the chlorine is dissociated by 

 the glowing wire; the very active chlorine atoms which at the low 

 pressure of the chlorine fly directly to the walls of the bulb, act 

 upon the tungsten and form with it the colourless JI^CV,. 



One might thijik, therefore, that by the introduction of a small 

 quantity of chlorine the lamp could be improved. The result, however, 

 does not answer this expectation, as the pressure of the chlorine 

 necessary to double the life") of a normal lamp must be not less 

 than \ mm. '). 



At this pressure the chlorine cannot act in the above 

 mentioned way, the free path of the atoms being much loo short. 

 A reaction between the tungsten vapour however and the chlorine 

 will be possible, which can prevent the formation of a tungsten 

 precipitate. vSuch a gas filling however offers several difficulties. 



At a pressure of | mm. the conduction of heat by the gas is 

 already rather high, which lowers the efficiency, while at least 

 at the higher voltages electric discharges through the lamp, which 

 might destroy it, are not excluded. But moreover the tungsten 

 vaporizes gradually only, so that already before a considerable 

 tungsten precipitate can be formed, the chlorine will have destroyed 

 the lamp by other reactions. 



Langmuir found namely that also without dissociation of the halogen 

 reactions may take place between W and 67. The velocity of 

 reaction is greatest at ± 1500° K., greater than at higher and 



') I. Langmuir, Joiirn. Amer. Ghem. Soc. (37), 1142, 1915. 



") By the lil'e is generally understood the time in whicli the intensity of the 

 light is decreased by 200/,,. 



^) The quantity of tungsten e.g. which is vaporized in a 110 Volt and 50 can die 

 lamp and which absorbs 20% of the light is about 0,26 mgr. To form with this 

 PFC'/g 0,3 mg. chlorine is necessary, corresponding to a pressure of ± Ys mm- 



70 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



