1878.] Prof. Dewar. The physical constants of hydrogenium. 207 



November 4, 1878. 



Dr J. B. Pearson, Treasurer, in the Chair. 



Mr E. C. RowE, B.A., Trinity College, and Mr W. J. Sell, B.A., 

 Christ's College, were ballotted for and duly elected Fellows of the 

 Society. 



The following communications were made to the Society : — 



(1) Professor Dewar, F.R.S. .The physical constants of hy- 

 drogenium, Part II. 



This paper is a continuation of an investigation into the 

 Physical Constants of Hydrogenium. The first part appeared in 

 the Transactions of the Eoyal Society of Ediiihurgh, Vol. xxvii., 

 and had reference to the Specific Gravity, Specific Heat, and 

 Coefficient of Expansion of the occluded hydrogen. These obser- 

 vations led to the conclusion that the specific gravity was indepen- 

 dent of the amount of condensed gas, and had a mean value of 

 062. This result has been confirmed by the subsequent experi- 

 ments of Troost and Hautefeuille, and what is very remarkable, 

 they deduce an identical value for the density of hydrogen from 

 observations on the hydrides of potassium and sodium. The 

 specific heat, relatively to palladium, of the condensed hydrogen, 

 appeared to vary inversely as the charge, but taken relatively to 

 successive charges was nearly constant, and had the value 3'4, 

 which is identical with that of gaseous hydrogen at constant 

 pressure. The coefficient of the cubical expansion of the alloy is 

 about twice that of palladium, and that of the hydrogen in its 

 compressed state not more than three times that of mercury. 

 This communication deals with the Thermo-electric Relations and 

 Conductivity of Hydrogenium. It is shown that the electro- 

 motive force of a junction of hydrogenium palladium is at ordinary 

 temperature nearly equal to that of an iron copper junction, and 

 that it increases with the temperature according to the general 

 parabolic law ; the rate of the increase being however greater than 

 iron copper and subject to a regular variation on account of suc- 

 cessive heatings. The formation of thermo-electric piles, and of 

 neutral points in a uniform wire of this substance, along with the 

 continuous formation of thermo-electric currents through the 

 application of a hydrogen flame were explained and shown. 

 Experiments on the electric resistance shew that it increases 

 directly as the amount of condensed gas. 



