HYDROGENIUM; THE RELATION OF HYDROGEN TO PALLADIUM. 77 
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 Hydro - 
genium. 
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 immersion in water, owing to a con¬ 
tinuous evolution of minute hydrogen bubbles which appears to be determined by con¬ 
tact 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 distension, over the surface of a flat graduated measure. 
The measure was graduated 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 deter¬ 
mined 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 1*5 
kilogramme, a weight sufficient to straighten the wire without occasioning any undue 
strain. The wire was charged' with hydrogen by making it the negative electrode of 
a small Bunsen’s battery consisting 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 extending the whole length of the latter within a tall jar filled with dilute sulphuric 
acid. The palladium wire had, in consequence, hydrogen carried to its surface, for a 
period of hour. A longer 'exposure was found not to add sensibly to the charge of 
hydrogen acquired by the with. The wire was again measured, and the increase in 
length noted. Finally, the wirb, bein’g dried with'a cloth, was divided at the marks, and 
the charged portion heated in a long narrow glass tube kept vacuous by a Sprengel as¬ 
pirator. The wh'ole occluded hydrogen was thus collected and measured; its volume 
is reduced by calculation to bar. 760 millims., and therm. 0° C. 
The original length of the palladium wire exposed was G09T44 millims. (22*982 
inches), and its weight 1*6832 grm. The wire received a charge of hydrogen amount¬ 
ing to 936 times its volume, measuring 128 cubic centims., and therefore weighing 
0-01147 grm. When the gas was ultimately expelled, the loss, as ascertained by direct 
weighing, was 0 - 01164 grm. The charged wire measured 618 923 millims., showing an 
increase in length of 9*779 millims. (0'385 inch). The increase in linear dimensions is 
from 100 to 101*605, and in cubic capacity, assuming the expansion to be equal in all 
directions, from 100 to 104*908. Supposing the two metals united without any change 
of volume, the alloy may therefore be said to be composed of 
By volume. 
Palladium..100 or 95*32 
Hydrogenium .... 4*908 or 4*68 
104*908 100 
The expansion which the palladium undergoes appears enormous if viewed as a change 
of bulk in the metal only, due to any conceivable physical force, amounting, as it does, 
to sixteen times the dilatation of palladium when heated from 0° to 100° C. The den¬ 
sity of the charged wire is reduced, by calculation, from 12*3 to 11*79. Again, as 100 
is to 4*91, so the volume of the palladium, 0*358 cubic centirn., is to the volume of the 
hydrogenium, 0*006714 cubic centirn. Finally, dividing the weight of. the hydroge¬ 
nium, 0*01147 grm., by its volume in the alloy, 0*006714 cubic centirn., we find— 
* Proceedings of the Royal Society, p. 422, 1868. 
