1869.] 



of Hydrogen to Palladium. 



213 



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 1^ hour. A longer exposure was found not 

 to add sensibly to the charge of hydrogen acquired by the wire. The wire 

 was again measured and the increase in length noted. Finally the wire, 

 being dried with a cloth, was divided at the marks, and the charged por- 

 tion heated in a long narrow glass tube kept vacuous by a Sprengel aspi- 

 rator. The whole 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 609*144 millims. 

 (23*982 inches), and its weight 1*6832 grm. The wire received a charge of 

 hydrogen amounting to 936 times its volume, measuring 128 cubic centims., 

 and therefore weighing O'Ol 147 grm. When the gas was ultimately ex- 

 pelled, 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 com- 

 posed 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 density of the charged wire is re- 

 duced, by calculation, from 12*3 to 11*79. Again, as 100 is to 4*91, so the 

 volume of the palladium, 0*1358 cubic centim., is to the volume of the 

 hydrogenium, 0*006714 cubic centim. Finally, dividing the weight of the 

 hydrogenium, 0*01147 grm., by its volume in the alloy, 0*006714 cubic 

 centim., we find 



Density of hydrogenium 1*708 



The density of hydrogenium, then, appears to approach that of magnesium, 

 1*743, by this first experiment. 



Further, the expulsion of hydrogen from the wire, however caused, is 

 attended with an extraordinary contraction of the latter. On expelling 

 the hydrogen by a moderate heat, the wire not only receded to its original 

 length, but fell as much below that zero as it had previously risen above it. 

 The palladium wire first measuring 609*144 millims., and which increased 

 9*77 millims., was ultimately reduced to 599*444 millims., and contracted 

 9*7 millims. The wire is permanently shortened. The density of the pal- 



