﻿126 Mr. T. Graham on the Relation of 



wire repeatedly, the curious retraction was found to continue, 

 and seemed to be interminable. The following expansions, 

 caused by variable charges of hydrogen, were followed on expel- 

 ling the hydrogen by the retractions mentioned : — 



Elongation. 



Retraction. 



1st Experiment 9*77 millims. 



. . 9-70 millims. 



2nd „ 5-765 „ 



. . 6-20 „ 



3rd „ 2-36 „ 



. . 3-14 „ 



4th „ 3-482 „ 



. . 4-95 „ 



23-99 



The palladium wire, which originally measured 609*144 mil- 

 lims., has suffered, by four successive discharges of hydrogen from 

 it, a permanent contraction of 23*99 millims. ; that is, a reduc- 

 tion of 3*9 per cent, on its original length. The contractions 

 will be observed to exceed in amount the preceding elongations 

 produced by the hydrogen, particularly when the charge of the 

 latter is less considerable. With another portion of wire the 

 contraction was carried to 15 per cent, of its length by the effect 

 of repeated discharges. The specific gravity of the contracted 

 wire was 12' 12, no general condensation of the metal having 

 taken place. The wire shrinks in length only. 



In the preceding experiments the hydrogen was expelled by 

 exposing the palladium placed within a glass tube to a moderate 

 heat short of redness, and exhausting by means of a Sprengel 

 tube ; but the gas was also withdrawn in another way, namely, 

 by making the wire the positive electrode, and thereby evolving 

 oxygen upon its surface. In such circumstances a slight film of 

 oxide of palladium is formed on the wire, but it appears not to 

 interfere with the extraction and oxidation of the hydrogen. The 

 wire measured 



Difference. 



Before charge . . 443*25 millims. 



With hydrogen . . 449*90 „ +6*65 millims. 



After discharge . . 437*31 „ -5-94 „ 



The retraction of the wire therefore does not require the con- 

 currence of a high temperature. This experiment further proved 

 that a large charge of hydrogen may be removed in a complete 

 manner by exposure to the positive pole (for four hours in this 

 case) ; for the wire in its ultimate state gave no hydrogen on 

 being heated in vacuo. 



That particular wire which had been repeatedly charged with 

 hydrogen, was once more exposed to a maximum charge, for the 

 purpose of ascertaining whether or not its elongation under hy- 

 drogen might now be facilitated and become greater in conse- 

 quence of the previous large retraction. No such extra elonga- 



