400 Intelligence and Miscellaneous Articles. 



distance of 1 millim. a repulsive force of 0"0255 railligr. With a 

 single Daniell's element, the density on the sphere of 1 millim., put 

 in communication with the pole, would be only the sixty-fifth part 

 of this, or 000039. 



This number 0'00039 measures in electrostatic units the difference 

 of potential at the two poles of a Daniell's element constituted as 

 indicated above. 



To assure myself that the balance worked properly, I ascertained, 

 by connecting the two balls with different series of Daniell's ele- 

 ments, that the results found were proportional to the number of the 

 elements — Comptes Rendus de VAcad. des Sciences, Aug. 12, 1872, 

 p. 431-435. 



NOTE ON THE SPECIFIC HEAT OF HYDROGENIUM. 

 BY JAMES DEWAR. 



The real specific heat of a substance, according to Clausius, 

 ought not to vary with the physical state ; and his calculation of the 

 theoretical true specific heats of compound gases assumes this con- 

 stant, in the case of the elementary bodies, to be identical in the free 

 and combined state. Kopp's value of the atomic heat of combined 

 oxygen is considerably in excess of that of the element, being 4 as 

 compared with 2*48, whereas hydrogen is taken as 2*3, nearly 

 agreeing with 2'4, that of the free element. As Kopp's numbers 

 rest on the assumption of the atomic heat of a compound being 

 equal to the sum of the individual atomic heats of the elements con- 

 tained in it, and as the data are few from which the value of 

 hydrogen has been determined, we cannot regard the mere coinci- 

 dence referred to as satisfactorily proving the constancy in the 

 combined condition. The results obtained by Kopp from calcula- 

 tion agree often remarkably M'ell with experiment ; and this is a 

 strong point in their favour. It would be useful to determine the 

 specific heat of either of the above elements in a condition ap- 

 proaching chemical union — that is, in the enormously condensed 

 state in which oxygen occurs in platinum black and hydrogen in 

 palladium. We know from Graham's beautiful researches, the 

 result of the absorption of hydrogen by palladium is to produce a 

 substance having all the characters of an alloy ; and the specific heat 

 of an alloy has been proved by Regnault to equal the sum of the 

 constituents. 



It is not my intention at present to describe with any detail the 

 experiments already made in this direction ; suflfice it to say that, by 

 means of a specially constructed calorimeter, the specific heat of 

 hydrogen in palladium is found to be 3'1 per atom weight, nearly 

 identical with that of gaseous hydrogen. The details of the experi- 

 ments, and some other physical constants of hydrogenium, will 

 shortly be given in a special paper. 



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