554 Intelligence and Miscellaneous Articles. 



green; with magnesium very bright green; and with aluminium 

 whitish green. With coke-points the colour of the jet is bright blue, 

 which becomes bluish when the arc ceases ; this is due to the pro- 

 . duction of a little carburetted hydrogen gas, as I have ascertained 

 directly. 



It is in the upper part of the balloon, to which the metallic vapours 

 produced by the voltaic arc ascend, that these effects are most dis- 

 tinct. The streaks or stratifications of the electric light are still 

 more marked in these vapours than in rarefied gases. 



The augmentation of the intensity of the jet is most considerable 

 in the vapours of silver and copper. The galvanometer passes sud- 

 denly from 30° to 60° at the moment when the jet indicates, by its 

 change of colour, that it is transmitted through the vapours of those 

 metals. The increase, although less, is still very distinct in the 

 vapour of aluminium. It is much less, only from 10° to 20°, with 

 the vapours of zinc, cadmium; and magnesium. Lastly, the increase 

 is very great with the vapour arising from the arc formed by two 

 coke-points ; but here the effect is more complex in consequence of 

 the production of small quantities of carburetted hydrogen gas, which 

 it is difficult to avoid. 



I have also employed iron and platinum points. With the former 

 I have certainly observed a change in the colour of the electric jet 

 and a slight augmentation of its intensity ; with the latter no effect 

 was produced, except that the excessive elevation of the tempera- 

 ture caused an appreciable increase in the conductibility of the rare- 

 fied nitrogen, but too slight to be in any way compared with the 

 augmentations of which I have spoken above. This last experi- 

 ment proves that it is not to the heating of the rarefied nitrogen, 

 but to the presence of the metallic vapour produced by the voltaic 

 arc, that the very distinct augmentation of the conductibility above 

 indicated is due. This does not imply that the temperature has no 

 influence ; its influence is, on the contrary, very sensible, and is 

 manifested in all rarefied gases by a considerable increase in their 

 conducting-power. I have already determined this increase for 

 a great number of gaseous substances, and I shall make known the 

 results that I have obtained in this respect when my work is more 

 complete. 



I will not conclude this notice without indicating en passant a 

 phenomenon which I had the opportunity of observing in trying to 

 produce the voltaic arc with points of various alloys, namely, that 

 at these high temperatures all these alloys are decomposed. To 

 observe this decomposition more satisfactorily, I take as the negative 

 electrode a plate of coke ; the point of alloy serves as the positive 

 electrode, and consequently becomes heated and vaporized. Alloys 

 of copper and zinc, copper and tin, copper and aluminium, platinum 

 and silver, and of iron and antimony have all been decomposed at 

 these high temperatures, and I have collected upon the plates of coke 

 particles of the constituent metals of the alloys very distinctly sepa- 

 rated. This is a case of dissociation by heat, which indeed might 

 easily have been foreseen, and which comes as an addition to those 

 curious examples indicated by M. H. Sainte-Claire Deville in his 

 beautiful investigations. — Comptes Rendus, May 15, 1865, p. 1002. 



