PROFESSOR TH0:S1AS GRAHAM'S SCIENTIFIC WORK. 



215 



Whether the absorption of hydrogen by palhxdium, alloyed or not with 

 another metal, was large or small, the density of the occluded hydro- 

 gen was found to be substantially the same. That the excessive re- 

 traction of the palladium wire on the discharge of its absorbed Isydro- 

 gen is not a mere effect of heat was shown by the charged wire under- 

 going a similar retraction when discharged electrolytically instead of by 

 ignition hi vacuo; and also by the original wire not undergoing any 

 sensible retraction as a result of annealing. That the retraction is 

 merely in length was shown by the absence of any difference in si)eciiic 

 gravity between the original and the discharged wire. Very curiously, 

 the shortening of the wire, b,y successive chargings and dischargings 

 of hydrogen, would seem to be interminable. Thus the following ex- 

 pansions of a particular wire, caused by variable charges of hydrogen, 

 were followed, on expelling the hydrogen, by the contractions recorded 

 in the other column : 



Fir.st fxi)eiiinciit.. 

 Si'fond fxpeiimeut 

 Third cxpcrinicnt . 

 Foiiith expei'iuieiit 



EL)n2,'atioa in 

 uullimcters. 



9.77 

 5.765 

 2. 30 

 3.482 



Retraction iu 

 luilliuH'rer.s. 



'J. 7(1 



(;.'jo 

 :!. 14 



4. 'Jo 



23. <J9 



The i)alladinm wire, which originally measured 009. 144 millimeters, 

 thus suffered, by four successive chargings and dischargings of hydro- 

 gen, an ultimate contraction of 23.99 millimeters, or a reduction of its 

 original length to the extent of nearly 4 per cent., each increnu'ut of 

 contraction below the original length usually exceeding the previous in- 

 crement of elongation above the original length of the wire. The alter- 

 nate expansion and contraction of palladinm by its occlusion and evo- 

 lution of hydrogen is ingeniously shown by a contrivance of 3Ir. 

 Roberts, in which a slip of palladium-foil, varnished on one side, is made 

 to curl and uncurl itself, as it becomes alternately the lu'gative and 

 positive electrode of a battery, or is alternately charged and discharged 

 of hydrogen on its free surfa(;e. 



That hydrogen is the vapor of a highly volatile metal has frcM^uently 

 been maintained on chemical grounds ; and from a consideration of the 

 physical properties of his hydrogenized i>alladium, Mr. Graham was led 



