Intelligence and Miscellaneous Articles. 397 



rotation of the sun, or rather of its photosphere, is variable — which 

 accords with the results obtained by Sporer. — Comptes Eenclus de 

 VAcademie des Sciences, March 16, 1874. 



ON HYDROGENIZED PALLADIUM. 

 BY MM. L. TROOST AND P. HAUTEFEUILLE. 



The remarkable property possessed by palladium, of absorbing as 

 much as 982 times its volume of hydrogen gas, discovered by Gra- 

 ham, was at first presented by him as a phenomenon comparable 

 to solution or condensation ; and for it he invented the term oc- 

 clusion. 



Graham subsequently thought that palladium forms with hy- 

 drogen an alloy with " equal equivalents." This opinion is stated 

 in the memoir in which he proves that the density of palladium 

 charged with from 800 to 900 volumes of hydrogen is sensibly in- 

 ferior to that of the pure metal, that the tenacity and electric con- 

 ductivity are diminished as in the case of alloys in general, and the 

 magnetism augmented as when palladium is combined with a very 

 magnetic metal. 



His conclusions have been generally accepted, although (as the 

 author himself remarks) the maximum of 982 volumes of hydrogen 

 fixed corresponds to only 0*772 of an equivalent of hydrogen for 1 

 equivalent of palladium (H=l ; Pa =106*5). 



In a recent work M. Favre, like Graham, thinks that " the hy- 

 drogen fixes itself on its equivalent of palladium," on the ground 

 that, within the limits of his experiments*, the metal disengages 

 sensibly equal quantities of heat in absorbing equal weights of hy- 

 drogen. 



We shall prove that the phenomenon is more complex than has 

 hitherto been supposed. 



We will examine successively the two following points : — (1) Does 

 the hydrogen form a true combination with the palladium, or is it 

 merely dissolved in that metal? (2) If there is a combination, 

 what is the formula of the compound produced ? 



The study of the tensions taken by the hydrogen disengaged at 

 various temperatures by hydrogenized palladium will furnish us 

 with the elements necessary to solve both these questions apart 

 from any hypothesis. We know, in fact, that compounds formed 

 directly, by the combination of a solid with a gaseous body, are 

 partially decomposed by heat, the decomposition being measured by 

 a tension invariable for each temperature and independent of the 

 quantity of undecomposed product ; it is the tension of dissocia- 

 tion of the chemical combination. On the contrary, substances 



* M. Favre has not indicated the volumes of gas corresponding to his 

 different determinations, 



