80 HYDROGENIUM ; THE RELATION OF HYDROGEN TO PALLADIUM. 
moved 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 hydrogen might now be facilitated and become greater in consequence 
of the previous large retraction. No such extra elongation, however, was observed on 
charging the retracted wire more than once ; and the expansion continued to be in the 
usual proportion to the hydrogen absorbed. The final density of the wire was 12-18. 
The wire retracted by heat is found to be altered in another way, which appears to 
indicate a molecular change. When the gas has been expelled by heat, the metal gra¬ 
dually loses much of its power to take up hydrogen. The last wire, after it had already 
been operated upon six times, was again charged with hydrogen for two hours, and was 
found to occlude only 320 volumes of gas, and in a repetition of the experiment 330 ‘d 
volumes. The absorbent power of the palladium had therefore been reduced to about 
one-third of its maximum. , , . ...... 
The condition of the retracted wire appeared, however, to be improved by raising its 
temperature to full redness bv sending through it an electrical current from a battery 
The absorption rose thereafter to 425 volumes of hydrogen, and in a second experiment 
to 422-5 volumes. . , , . , . . 
The wire becomes fissured longitudinally, acquires a thready structure, and is much 
disintegrated on repeatedly losing hydrogen, particularly when the hydrogen has been 
extracted by electrolysis in an acid fluid. The palladium in the last case is dissolved by 
the acid to some extent. The metal appeared, however, to recover its full power to 
absorb hydrogen, now condensing upwards of 900 volumes of gas. _ 
The effect upon its length of simply annealing the palladium wire by exposure in a 
porcelain tube to a full red heat was observed. The wire measured 566'07o millims. 
before and 555-875 millims. after heating ; or a minute retraction of 02 millirn. was 
indicated. In a second annealing experiment, with an equal length of new wire, no 
sensible change whatever of length could be discovered. There is no reason, then, to 
ascribe the retraction after hydrogen, in any degree, to the heat applied when the gas is 
expelled. Palladium wire is very slightly affected in. physical properties by such an¬ 
nealing, retaining much of its first hardness and elasticity. . , . 
2. Tenacity. _A new palladium wire, similar to the last, of which 100 millims weighed 
0-1987 grm., was broken, in experiments made on two different portions of it, by a load 
of 10 and 10’17 kilogrammes. Two other portions of the same wire, fully charged with 
hydrogen, were broken by 8*18, and by 8:27 kilogrammes. Hence we have— 
Tenacity of palladium wire. 1 ??.oq 
Tenacity of palladium and hydrogen. 81-9 
The tenacity of the palladium wire is reduced by the addition of hydrogen, but not to 
anv sreat extent. It is a question whether the degree of tenacity that still remains is 
reconcilable with any other view than that the second element present possesses of itself 
a degree of tenacity such as is only found in metals. ..... t 
3. Electrical Conductivity.— Mr. Becker, who is familiar with the practice of testing 
the capacity of wires for conducting electricity, submitted a palladium wire, before and 
after being charged with hydrogen, to trial, in comparison with a wire of German silver 
of equal diameter and length, at 10-5°. The conducting-power of the several wires was 
found as follows, being referred to pure copper as 100 
Pure copper.^0 
Palladium.. • .. 
Alloy of 80 copper-f 20 nickel. 6 33 
Palladium+hydrogen. 5 99 
A reduced conducting power is generally observed in alloys, and the charged palladium 
wire falls 25 percent. But the conducting-power‘remains still considerable, and the 
result may be construed to favour the metallic character of the second constituent of the 
wire. Dr. Matthiessen confirms these results. 
C To be continued.) 
