Chemistry. — “Metals and Non- Metals’. By Prof. A. Smits. (Com- 
municated by Prof. P. Zeeman). 
(Communicated in the meeting of May 3, 1919). 
Introduction. 
In a few previous communications I already discussed the un- 
attackable electrodes and their efficiency as gas-electrodes. Only the 
hydrogen electrode was, however, discussed in detail. It was pointed 
out that the nnattackable electrodes are among the most inert metals, 
being so inert that even in contact with an electrolyte they do not 
assume internal equilibrium, so that they are almost always in 
disturbed condition, and we do not even know the potential of the 
really unary metal. 
When such a metal is immersed in the aqueous solution of an 
acid, while hydrogen is passed through, the electron concentration 
of the metal equilibrium in the electrolyte, which we represent by 
the equation : 
— i" . 
M, 2M, +16, 
becomes equal to the electron concentration of the hydrogen equilibrium: 
H, 2H, + 26, 
in agreement with the pressure of the hydrogen that is passed through, 
which means that the hydrogen phase and the hydrogen-containing 
metal-phase possess the same potential, the electromotive force of 
the circuit metal-electrolyte-hydrogen being given by the equation: 
Rr On 
ln 
A Owe 
Hence the hydrogen-electrode indicates the potential belonging to 
the three-phase equilibrium metal phase + hydrogen phase + electrolyte 
in accordance with the prevailing pressure, temperature, and total ion 
concentration (/7°)-+ (/”). As, however, as was already stated in 
the discussion of the #,X-fig., the said electrolyte contains an entirely 
negligible concentration of ions of the so-called unattackable electrode, 
we may substitute the words: hydrogen-ion-concentration for “total- 
ion-concentration”’ 
k= — 
(1) 
