﻿Hydrogen through a Palladium Septum. 217 



The case is precisely analogous to the passage of water through 

 a semi-permeable diaphragm. But, in order that hydrogen 

 may pass through iron, it must be in the state in which it is 

 liberated by an electric current, or it must be hot. That 

 hydrogen will not pass through palladium at the ordinary 

 temperature appears to show that the compound of palladium 

 and hydrogen has practically no dissociation pressure at 

 ordinary temperature ; otherwise the hydrogen would pass by 

 solution, in the same manner as coal-gas passes through 

 india-rubber, or water through a semi-permeable diaphragm. 

 That it will not pass, even when liberated by an electric 

 current on one side of the palladium membrane, shows that it 

 at once enters into combination with the palladium, and is no 

 longer in statu nascendi, to use a generally understood ex- 

 pression which is independent of theory. But that it passes 

 through hot palladium appears to show that it is then in a 

 state analogous to that of electrically liberated hydrogen. 



It is known that electrified bodies are discharged if a flame 

 burns in their vicinity. This may be attributed to the 

 liberation of atomic oxygen in a kind of Grrotthus chain. For 

 it may be imagined that when a molecule of oxygen encounters 

 the oxidizable matter of a flame, it is dissociated : while one 

 atom serves to oxidize the carbon, the other exchanges with a 

 neighbouring molecule, and a succession of exchanges occur 

 till the atomic oxygen near the electrified body receives or 

 communicates a charge, and restores the potential of the 

 charged body to that of surrounding objects. 



To ascertain whether a flame of oxygen burning in hydrogen 

 would similarly cause the hydrogen to assume the atomic state, 

 a piece of apparatus was contrived in which such a flame 

 burned in close proximity to a very thin iron plate, on the 

 other side of which a Torricellian vacuum was maintained. 

 No hydrogen passed through the plate : hence either the 

 hydrogen was not atomically transferred, as oxygen is sup- 

 posed to be under similar circumstances, or such atoms were 

 unable to pass through the plate as they would have done if 

 liberated electrically. It must be noticed, however, that it is 

 conceivable that the double atom of hydrogen which we term 

 a molecule may have united directly with the oxygen, without 

 separating into its two components. The result of this ex- 

 periment is therefore inconclusive. 



It appears to me necessary to suppose that at a temperature 

 far above that at which hydride of palladium is capable of 

 existence, the palladium has still the power of so attracting 

 the hydrogen that the molecule is split. This necessarily 

 implies a gain of energy, so far as the splitting of the 



