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Mr. Graham on the Relation 



[Jan. 14, 



January 14, 1869. 

 Lieut. -General SABINE, President, in the Chair. 

 The following communications were read : — 

 I. " On the Relation of Hydrogen to Palladium." By Thomas 

 Graham, E.R.S., Master of the Mint. Received November 23, 

 1868. 



It has often been maintained on chemical grounds that hydrogen gas is 

 the vapour of a highly volatile metal. The idea forces itself upon the mind 

 that palladium with its occluded hydrogen is simply an alloy of this vola- 

 tile metal, in which the volatility of the one element is restrained by its 

 union with the other, and which owes its metallic aspect equally to both 

 constituents. How far such a view is borne out by the properties of the 

 compound substance in question will appear by the following examination 

 of the properties of what, assuming its metallic character, would have to be 

 named Hydrogenium. 



1. Density. — The density of palladium when charged with eight or nine 

 hundred times its volume of hydrogen gas is perceptibly lowered ; but the 

 change cannot be measured accurately by the ordinary method of immer- 

 sion in water, owing to a continuous evolution of minute hydrogen bub- 

 bles which appears to be determined by contact with the liquid. However, 

 the linear dimensions of the charged palladium are altered so considerably 

 that the difference admits of easy measurement, and furnishes the required 

 density by calculation. Palladium in the form of wire is readily charged 

 with hydrogen by evolving that gas upon the surface of the metal in a 

 galvanometer containing dilute sulphuric acid as usual*. The length of 

 the wire before and after a charge is found by stretching it on both occasions 

 by the same moderate weight, such as will not produce permanent disten- 

 tion, over the surface of a flat graduated measure. The measure was gra- 

 duated to hundredths of an inch, and by means of a vernier, the divisions 

 could be read to thousandths. The distance between two fine cross lines 

 marked upon the surface of the wire near each of its extremities was observed. 



Expt. 1. — The wire had been drawn from welded palladium, and was 

 hard and elastic. The diameter of the wire was 0"462 millimetre ; its 

 specific gravity was 12*38, as determined with care. The wire was twisted 

 into a loop at each end and the mark made near each loop. The loops 

 were varnished so as to limit absorption of gas by the wire to the measured 

 length between the two marks. To straighten the wire, one loop was 

 fixed, and the other connected with a string passing over a pulley and 

 loaded with T5 kilogramme, a weight sufficient to straighten the wire 

 without occasioning any undue strain. The wire was charged with hydro- 

 gen by making it the negative electrode of a small Bunsen's battery con- 

 sisting of two cells, each of half a litre in capacity. The positive electrode 

 was a thick platinum wire placed side by side with the palladium wire, and 

 * Proceedings of the Royal Society, p. 422, 1868. 



