464' Royal Society. 



elongation of 1*629 on 100, or cubic expansion of 4*97 on 100. 

 The weight of the wire was 3*483 grms., its volume 0*3041 cub. 

 centim. The absolute volume of occluded hydrogen was 125*1 cub. 

 centims., of which the weight is 0*01120896. The volume of the 

 hydrogenium was 0*015105 cub. centim. The resulting density of 

 hydrogenium is 0*742. 



In a repetition of the experiment upon another portion of the 

 same wire, 407*7 volumes of hydrogen were occluded, and the wire 

 increased in length from 609*601 millims. to 619*44 millims. This 

 is a linear expansion of 1*614 part on 100, and a cubic expansion of 

 4*92 on 100. The absolute volume of hydrogen gas occluded was 

 124*0 cub. centims., and its calculated weight 0*01111 grm. The 

 volume of the hydrogenium being 0*1496 cub. centim., the density 

 of hydrogenium indicated is 0*741 . The two experiments are indeed 

 almost identical. The wire returned in both experiments to its ori- 

 ginal length exactly, after the extraction of the gas. 



4. Palladium, Nickel, and Hydrogenium. — The alloy, consisting 

 of equal parts of palladium and nickel, was white, hard, and readily 

 extensible. Its specific gravity was 11*22. This alloy occluded 

 69*76 volumes of hydrogen, with a linear expansion of 0*2 per cent. 

 It suffered no retraction below its normal length on the expulsion of 

 the gas by heat. 



An alloy of equal parts of bismuth and palladium was a brittle mass 

 that did not admit of being rolled. It occluded no hydrogen, after 

 exposure to that gas as the negative electrode in an acid fluid for a 

 period of 18 hours. It seems probable that malleability and the 

 colloid character, which are wanting in this bismuth alloy, are essen- 

 tial to the occlusion of hydrogen by a palladium alloy. 



An alloy of 1 part of copper and 6 parts of palladium proved mo- 

 derately extensible, but absorbed no sensible amount of hydrogen. 

 The metallic laminae which remain on digesting this alloy in hy- 

 drochloric acid, and which were found by M. Debray to be a defi- 

 nite alloy of palladium and copper (Pd Cu), exhibited no sensible 

 occluding power. 



The conclusions suggested as to the density of hydrogenium, by 

 the compound with palladium alone and by the compounds with 

 palladium alloys, are as follows : — 



Density of 

 Hydrogenium observed. 



When united with palladium 0*854 to 0*872 



When united with palladium and platinum .... 0*7401 to 0*7545 



When united with palladium and gold 0*711 to 0*715 



When united with palladium and silver 0*727 to 0'742 



The results, it will be observed, are most uniform with the com- 

 pound alloys, in which retraction is avoided ; and they lie between 

 0*711 and 0*7545. It may be argued that hydrogenium is likely 

 to be condensed somewhat in combination, and that consequently 

 the smallest number (0*711) is likely to be the nearest to the truth. 

 But the mean of the two extreme numbers wall probably be admitted 

 as a more legitimate deduction from the experiments on the com- 



