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in 1878, Thomas Edison (or rather William Joseph Hammer) added an anode in a light bulb in order to catch the flux of electrons coming out from the carbon filament and reduce the phenomenon of blackening of the glass bulb.

However, am I right in saying that this was the wrong course of action? I understand the blackening is due to the accumulation of carbon oxides (such as CO and CO2) produced by the reaction between carbon (and, more recently, tungsten) vapour and the remainder of air present into the glass bulb. Thus, capturing electrons did not solve the problem of blackening (and that is why Edison did not find any use for the extra electrode).

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  • $\begingroup$ I am quite sure that the problem is the evaporation of tungsten (even tungsten, at those temperatures, has a non-negligible vapour pressure). The evaporation of tungsten is the (unwanted) process which lead to the development of halogen lamps. $\endgroup$ – The_Vinz Jun 16 '19 at 8:33
  • $\begingroup$ Esprit de l'escalier: sublimation $\endgroup$ – The_Vinz Jun 16 '19 at 8:39
  • $\begingroup$ And even before the blackening should have been carbon in some form rather than carbon (di)oxide, which are both colorless gases. $\endgroup$ – Alchimista Jun 16 '19 at 8:40

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