1869.] 



of Hydrogen to Palladium. 



215 



contract nor expand, but remain of their proper volume on uniting. Dr. 

 Matthiessen has shown that in the formation of alloys generally the metals 

 retain approximately their original densities*. 



In the first experiment already described, probabty the maximum ab- 

 sorption of gas by wire, amounting to 935*67 volumes, is attained. The 

 palladium may be charged with any smaller proportion of hydrogen by 

 shortening the time of exposure to the gas (329 volumes of hydrogen were 

 taken up in twenty minutes), and an opportunity be gained of observing if 

 the density of the hydrogenium remains constant, or if it varies with the 

 proportion in which hydrogen enters the alloy. In the following state- 

 ment, which includes the three experiments already reported, the essential 

 points only are produced. 



Table. 



Volumes 

 of hydrogen 

 occluded. 



329 

 462 

 487 

 745 

 867 

 888 

 936 



Linear expansion in 

 millimetres. 



Density 

 of 



Hydrogenium. 



From 



To 



496-189 



498-552 



2-055 



493 040 



496 520 



1-930 



370-358 



373-126 



1-927 



305-538 



511-303 



1-917 



488-976 



495-656 



1-898 



556-185 



563-652 



1-977 



609-144 



618-923 



1-708 



If the first and last experiments only are compared, it would appear that 

 the hydrogenium becomes sensibly denser when the proportion of it is 

 small, ranging from 1*708 to 2*055. But the last experiment of the Table 

 it perhaps exceptional ; and all the others indicate considerable uniformity 

 of density. The mean density of hydrogenium, according to the whole 

 experiments, excluding that last referred to, is 1-951, or nearly 2. This 

 uniformity is in favour of the method followed for estimating the density 

 of hydrogenium. 



On charging and discharging portions of the same palladium wire repeat- 

 edly, the curious retraction was found to continue, and seemed to be inter- 

 minable. The following expansions, caused by variable charges of hydro- 

 gen, were followed on expelling the hydrogen by the retractions men- 

 tioned. 



Elongation. 



9 '77 millims 



5*765 „ 



2-36 „ 



3*482 „ 



1st Experiment 



2nd 



3rd 



4th 



Retraction. 

 9*70 millims. 

 6'20 „ 

 3*14 „ 

 4'95 „ 



23*99 



The palladium wire, which originally measured 609*144 millims., has 

 * Philosophical Transactions, 1860, p. 177. 



