1084 



little salt is left on the wire which prevents the vaporization. We 

 found however that at equal temperatures a sprayed and a non- 

 sprayed tungsten wire .show an eqnal increase 

 of the electric resistance by the decrease of the 

 wire diameter, and eqnal loss in weight, while 

 in both cases, the tungsten condensate on the 

 wall of the bulb has the same weight. We thus 

 come to the conclnsion that the NaCl is active 

 in its solid phase and that in contrast with what 

 we liave seen in the case of K^TICI^, the decolo- 

 ration of the tungsten is not due to free chlorine. 

 The ditference between the behaviour of JSUiCl 

 and A', TlCl^ is especially evident by the following 

 experiment, in which a double-lamp was used. 

 When the wire in the inferior lamp is covered 

 with NaCl, but not that of the upper one, the 

 inferior lamp is found to blacken much less rapidly 

 than the upper one. When the experiment is 

 repeated with a similar combimUion, in which the 

 inferior lamp contains a small quantity of K^ Tli'l^ 

 instead of Na CI, such a difference is not observed. 

 The action of the NaCl is therefore local in contrast 

 with that of A\ 776V„. The chlorine developed by 

 'this latter substance is spread over the whole bulb 

 and attacks the tungsten precipitate both in the 

 inferior and in the upper pait. 



What may be the action of the thin salt layer 

 on the wall of the bulb upon the vaporized tungsten? 

 Is the observed decoloration due to the forma- 

 tion of some less coloured chemical compound oi- 

 do the NaCl and W remain on the wall chemically 

 unaltered, while they only give an arrangement 

 which absorbs less light? 

 The following experiments render it probable that we have not 

 to do with a chemical action. Firstly we stated, that also with other 

 metals a decoloration of the i)recipitate was found e.g. C, Mo, Ft, 

 Fe, Ni, An, Cu, A;/ gave all both at room temperature and at 

 liquid air temperature less dark precipitates when the wall of the 

 bulb was covered with a thin salt-layer than when this was not 

 the case. A chemical action at low temperature between Au and 

 NaCl e.g. may doubtlessly be considered as excluded. Moreover it 

 was found that not only NaCl, but nearly every other stable 



Fig. 1. 



