Sxry.—Owidation of Gold. 841 
and I hope soon to be able to accomplish this to an extent which will 
enable me to throw a clear light upon the subject under consideration. 
Whatever may .be the precise nature, however, of the film thus induced 
upon gold, and of the reactions which result in the removal or alteration of 
this film as here described, it is certain that films of this kind must cover 
the surfaces of a portion of our native gold, and thus retard to a more or 
less extent, its complete amalgamation when milled. 
Thus what with the tendency of this metal to enfilm in presence of 
common water or alkaline solutions in the manner described, and its 
tendency to become sulphuretted when in contact with soluble sulphides, 
there can be but little doubt entertained that most of the natural surfaces 
of native gold are varnished as it were, with auriferous compounds, and 
these have to be decomposed by mercury ere amalgamation can proceed, 
except we use in conjunction with this metal a substance capable of 
decomposing such films, or else remove them mechanically, as is at present 
largely accomplished in the stamper boxes. 
With reference to mercury, the results I have as yet been able to get, do 
not point so distinctly to its oxidation by oxygen in presence of water, as 
those described above do to that of gold. Its mobility at the temperature I 
have to operate under, stands in the way of my observing indications of 
any superficial change I may have induced upon it in my experiments. 
Theoretically it would on first thought appear, that if gold or silver does 
oxidize, as I affirm, under the above circumstances, mercury should also 
oxidize under them, as it is certainly positive to both these metals in acid 
generally. It must be considered, however, in connection with this matter, 
that gold and silver at their fusing points are in a condition unfavourable 
to their oxidation, and so mercury (a metal which naturally classes with 
these), being used in my experiments at a temperature far above its fusing 
point, may for this reason be less readily oxidizable under the circumstances 
stated than either of the above metals in their solid state. It appears to me 
that we should take into consideration here, not only the temperature we 
are operating under, but the different physical conditions of mercury as 
compared with that of the above metals at this temperature. 
The only results I have yet obtained as to the oxidation of mercury, or 
otherwise under these circumstances seems to show that it is so oxidized. 
Thus I find that electric currents of some strength are generated by it in 
water containing a little sodic chloride ; also in aqueous solution of caustic 
or carbonated alkali; as the only conceivable effect of the salts named 
is to conduct the electricity thus generated and so render it detectable, 
I conclude that the action upon mercury which these currents indicate is 
not originated by such salts, but by the oxidation of this metal. 
