﻿Hydrogen to Palladium. '. 127 



tion, however, was observed on charging the retracted wire more 

 than once; and the expansion continued to be in the usual pro- 

 portion to the hydrogen absorbed. The final density of the wire 

 was 12-] 8. 



The wire retracted by heat is found to be altered in another 

 way, which appears to indicate a molecular change. The metal 

 gradually 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 ex- 

 periment 330*5 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 by sending 

 through it an electrical current from a battery. The absorption 

 rose thereafter to 425 volumes of hydrogen, and in a second ex- 

 periment to 422*5 volumes. 



The wire becomes fissured longitudinally, acquires a thready 

 structure, and is much disintegrated on repeatedly losing hy- 

 drogen, 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, how- 

 ever, to recover its full power to absorb hydrogen, now conden- 

 sing 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 ob- 

 served. The wire measured 556*075 millims. before, and 555-875 

 millims. after heating; or a minute retraction of 0'2 millim. 

 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 annealing, 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 expe- 

 riments made on two different portions of it, by a load of 10 and 

 of 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 . . . 100 

 Tenacity of palladium and hydrogen 81*29 



The tenacity of the palladium is reduced by the addition of hy- 

 drogen, but not to any great extent. It is a question whether 



