﻿424 Mr. J. Dewar on the Motion of a Palladium Plate 



Even when the exhaustion had reached its utmost limit the ap- 

 pearance was quite unchanged. 



14. Nitrogen thus only furnishes the two known spectra ; and 

 without using a Ley den jar the first spectrum cannot be 

 changed into the second. Hence there is a considerable differ- 

 ence between the behaviour of hydrogen, oxygen, and nitrogen. 

 With the first two gases the same mode of discharge can yield 

 entirely different spectra in the enclosed gas, according to its 

 density. Hence this difference can have no other reason than 

 the higher or lower temperature to which the gas has been 

 heated, and which, as mentioned in § 7, depends on the different 

 density of the gas. It must be assumed that the emissive power 

 of both gases does indeed essentially vary with the temperature. 

 The case is different with nitrogen : the difference in tempe- 

 rature produced by the different density of the gas is not suffi- 

 cient to change the spectrum ; the mode of discharge must be 

 changed. Nitrogen can only be brought into the condition in 

 which it yields a spectrum of the second order, by the sudden 

 passage of large quantities of electricity, obtained by simul- 

 taneously interposing a Ley den jar in the circuit of the induc- 

 tion-coil, or by passing the discharge of a Leyden jar with the 

 Holtz's machine. Hence we may speak of an allotropic condi- 

 tion of nitrogen, which furnishes the second spectrum, and which 

 is formed by the sudden discharge of large quantities of electri- 

 city, which, however, returns to the ordinary form as soon as the 

 temperature diminishes. To be sure, no explanation is thus 

 given of the difference in deportment of nitrogen and other 

 gases; this can only be expected from further experiments, 

 which will be reported upon in due course. 

 Bonn, August 1868. 



LIX. On the Motion of a Palladium Plate during the Formation 

 of Graham's Hydrogenium. By James Dewar, F.R.S.E.* 



GRAHAM, in continuing his exhaustive researches on diffu- 

 sion, has recently examined the relation of gases to various 

 colloid septa. The remarkable discovery of Deville and Troost 

 of the permeability of platinum and iron by hydrogen at a red 

 heat, he has expanded into a general examination of the relative 

 rates of passage, at high temperatures, of the various gases 

 through different metallic septa. Further, he has proved that 

 different metals have a specific occluding power over certain 

 gaseous elements, retaining them in combination at low tempe- 

 ratures, although the absorption took place at a red heat. Of 



* Communicated by the Author, having been read before the Royal 

 Society of Edinburgh, March 1, 1869. 



