36 Prof. Wohler on the Action of the Flame 



of foil, which is then found to have been penetrated through 

 and through with carbon and rendered quite brittle. At the 

 time of that publication I believed that a peculiar affinity must 

 be supposed to exist between palladium and carbon; but the 

 remarkable discovery by Graham of the occlusion of hydrogen 

 by palladium makes it probable that the above phenomenon is 

 rather connected with this power of the metal to absorb many 

 hundred times its volume of hydrogen. 



The behaviour of palladium to oleflant gas appeared likely 

 to throw light upon this question. More than 6 grams of 

 chemically pure spongy palladium, which, as experiment had 

 shown, was capable of absorbing many hundred times its 

 volume of hydrogen, was placed in a tube, and a slow current 

 of ethylene led for some hours over the metal heated to 100°. 

 Neither at this temperature nor at other higher temperatures 

 below a red heat did any action take place; no gas was ab- 

 sorbed, no blackening of the metal could be observed. Only 

 when the glass tube in which the metal was placed was heated 

 to redness was carbon deposited with evolution of hydrogen. 

 But the point at which the decomposition of ethylene began 

 in presence of the metal was found to be lower than that neces- 

 sary to bring about decomposition of the gas in the absence of 

 palladium. Marsh-gas was also found to be without any action 

 on palladium. 



From the above experiment, it appears that palladium is un- 

 able to absorb ethylene or the gases of the alcohol-flame, but 

 that it is able to bring about the deposition of carbon from 

 such gases at a temperature lower than that at which ethylene 

 by itself undergoes decomposition. 



Possibly this action may be explained by the supposition 

 that a combination of hydrogen goes on contemporaneously 

 with the deposition of carbon, but that at the same time a 

 rapid dissociation of the hydrogen compound occurs — much in 

 the same way as we may explain the remarkable physical 

 changes which take place in copper when heated in ammonia- 

 gas by a temporary combination of the nitrogen. A circum- 

 stance which favours this explanation is, that the bright palla- 

 dium-foil, after it has been exposed to the action of the alcohol- 

 or ethylene-flame, has altogether lost its brilliancy as well as 

 its malleability. 



The fact that when palladium is fused with carbon it does 

 not take up any of this element, is a sufficient proof that the 

 phenomenon in question is not caused by the affinity of the 

 metal for carbon ; and this fact was proved in 1857 by Dr. Th. 

 Wood, who at my suggestion made an examination on the 

 relations of palladium to carbon compounds. His experi- 

 ments were afterwards carried out in Professor Bunsen's 



