Chemistry. — “The Electromotive Behaviour of Aluminium”. II. *). 
By Prof. A. Smits and C. J. pe Groyrer. (Communicated by 
Prof. P. Zeeman). 
(Communicated at the meeting of May 28, 1921). 
1. In a previous communication on the same subject. we already 
pointed out that the Z-X-diagram of the four-component system 
Al —He"—Anion—H,O must be classified among the type in which 
the potential corresponding to the three-phase equilibrium, lies between 
the potentials of the two metals. Hence the potential of aluminium 
in an Al-salt solution might be expected to become less negative on 
addition of a mercury salt, whereas it was the reverse that was 
found. Already at the beginning of the study on the electromotive 
behaviour of aluminium we expressed the opinion that this remark- 
able phenomenon shows that as a rule the pure aluminium is passive, 
ie. is greatly disturbed in noble direction, and that small quantities 
of mercury, dissolved in aluminium, exert a positive catalytic influence 
on the establishment of the internal equilibrium, so that the disturb- 
ance disappears. 
In order to examine the influence of mercury on the aluminium 
potential more closely, measurements were carried out, in which the 
aluminium electrode was placed in an aqueous aluminium salt 
solution, to which a mercury salt solution was added at intervals. 
It should still be stated that to prevent the action of air-oxygen, 
the experiment was made in a nitrogen atmosphere, the solution 
being vigorously stirred. 
Then the interesting result was found that at first the potential 
of the aluminium became less negative, then reached a minimum, 
after which it rose to a strongly negative value, and at last a 
maximum appeared. Finally a great decrease was observed, during 
which the potential descended to near that of mercury. 
To past the just-mentioned maximum the aluminium electrode was 
covered with a greyish precipitate, but during the last stage the 
aluminium electrode. was mercurized to a shiny surface. 
Before proceeding to the further discussion of the study of this 
1) These Proc. Vol. XXII, N°. 9 and 10, p. 876. 
; se Vol. XXII, N®.-75 pe S66, 
