184 Proceedings of Royal Society of Edinburgh. [sess. 
the above formula. Taking into account the slightly different 
weights of the electrodes /3 and p , the electromotive force of the 
cell having the ratio of concentration of the hydrogen in the two 
electrodes, 14-40 should be 0*0333 Y. at 17° C. The actual 
electromotive force of the cell after standing eighteen hours was 
0*0071 Y. This is a maximum limit, however, and in all proba- 
bility this electromotive force would have decreased considerably 
if the cell had been allowed to stand for a still longer period. 
The conclusion to be drawn, then, is that the electromotive force 
of such a cell is either zero or else closely approximates to zero. 
In other words, the potential of a palladium electrode charged with 
hydrogen and immersed in dilute sulphuric acid is independent of 
the quantity of hydrogen occluded, at any rate, up to near the 
point of saturation of the palladium. 
This result is in good agreement with that obtained by Thoma 
( Centralblatt fur Elektrotechnik , xi. 131). The potential of a 
palladium wire against zinc in a saturated solution of zinc sulphate, 
was measured at intervals during charging, in some cases with the 
aid of a quadrant electrometer, in others with a galvanometer, and 
it was found that its potential remained constant at about 0’68 
Daniell (0*75 Y.) until minute bubbles of free hydrogen appeared 
on its surface. The potential then gradually diminished on 
further charging to 0*42 D, but on breaking the charging current 
the normal value was recovered. On removing the hydrogen by 
electrolytic oxygen the normal value was unaffected until all the 
hydrogen had been removed. 
Thoma concludes by saying that, as long as all the hydrogen is 
absorbed by the palladium, its position in the electromotive series 
is independent of the amount of absorbed hydrogen, and that until 
the point of supersaturation is reached we are not dealing with a 
phenomenon of polarisation at all. Supersaturated palladium, on 
the other hand, gradually approaches the position of zinc the richer 
it is in hydrogen, but nevertheless always remains negatively 
electrified. 
Knott, in a paper “ On the Electrical Resistance of Hydrogenised 
Palladium ” ( Proc . Roy. Soc. Edin ., xii. 181), incidentally measured 
the electromotive force of a charged palladium wire against plati- 
num in dilute sulphuric acid, and found that a slight charge of 
