Sxey.—Notes on Replacement of Metals in a Voltaic Cell. 343 
Arr. XLVIT.—WNotes on the alleged ‘‘ Replacement of Electro-positive by Electro- 
negative Metals in a Voltaic Cell.” By Wu.1M Sxezy, Analyst to the 
Geological Survey of New Zealand. - 
In a paper by Professor Gladstone, Ph.D., F.R.S., and Mr. Alfred Tribe, 
which was read before the Royal Society, November 25th, 1875, it is 
asserted that when zinc and platinum are: connected yoltaically in a solution 
of chloride of potassium, ‘‘ Potassium is set free in some form against the 
platinum, manifesting itself by the presence of free alkali and hydrogen - 
gas ;”’ and the authors of this paper, upon the supposition above stated 
and others based in a similar way, argue for the replacement of electro- 
positive by electro-negative metals, under conditions quite contrary to those 
we have hitherto held to be necessary for them, and they explain this 
‘**reversion’’ by assuming that some force superior to that of chemical 
affinity operates in the production of the phenomena they describe, and 
which is “ called into existence by contact.”’ 
I will not here discuss the propriety or otherwise of going back to the 
contact theory, which I had thought Professor Faraday long since proved 
to be untenable, but I would like to make a few observations upon two 
statements appearing in this paper. 
In the first place, as far as I can understand from the abstract of it 
given in “ Nature,” it is by no means clear that potassium is set free in 
the experiment described. The alkaline reaction upon which this theory 
of metallic reduction is based, may in reality be due to a cause quite 
different from that of such a reduction. 
For instance, an alkaline reaction can be readily obtained under cir- 
cumstances which are similar to those related there, except that contact of 
dissimilar metals in a voltaic arrangement is avoided, and under which it 
appears impossible that any metallic reduction takes place. Thus, an 
aqueous solution of potassic-chloride placed for a short time with amalga- 
mated zine, or for a longer time with zincyitself, becomes very alkaline. 
Even pure silver in a solution of this salt soon passes into this condition.* 
The containing vessels in my experiments for this were agate. 
This change in the character of these solutions is hardly wrought by 
metallic reduction, but rather in the first case by decomposition of water 
and the formation of ammonia (by the inter-action of nascent hydrogen 
thus liberated upon the nitrogen present) assisted perhaps by the formation 
of oxide of zinc by atmospheric oxidation, resulting finally in the formation 
of an oxy-chloride of this metal through substitution. 
* See ‘‘ Trans. N. Z. Inst.,” Vol. VIII, ‘On the Oxidation of Silver at Common Tem- 
perature by Oxygen in presence of Water.” 
