- 836 Transactions.—Chemistry. 
silver in Cyanide of Potassium, as supposed, but very decidedly negative; 
thus metallic gold in contact with a solution of mercuric cyanides would 
rapidly dissolve and mercury be reduced. 
A knowledge of this fact prompted me to determine the electro-motive 
order in Cyanide of Potassum, of the various metals which occur in our 
_ gold fields, or are employed in any way for milling gold. In the following 
list most of these will be found, it runs from negative downwards to 
positive :— 
Electro-motive order of metals in Potassic Cyanide. 
Carbon. Lea 
Platinum. Gold 
on. Silver 
Arsenic. ‘Pin, 
Antimony. Copper. 
Mercury. Zine. 
~ Most, if not all the sulphides or other ores occurring in nature, are 
negative to the whole series. Any of these metals will generally precipitate 
the ores named below it from its cyanide solution. As already stated, gold 
and silver thus precipitate mercury, taking its place in the liquid,* which 
as is already known, silver precipitates gold. In relation to this, however, 
I find these two metals (gold and silver) are so nearly alike in their affinities 
for cyanogen, that this precipitation is a very slow process; cyanide of 
potassium even in contact with an alloy of silver and gold dissolves both, 
the silver however to the greater extent. 
Thus it appears, a loss of gold by solution of it, must frequently happen 
whenever cyanide of potassium is employed to assist in the amalgamation 
of blankettings, or other auriferous stuff. In fact all that loss of metal 
occasioned by its solution, and most of which is, as we have seen a neces- 
sity involved in the working of the process itself, falls upon the gold and 
silver present, the mercury being positively protected from the action of 
this salt by these more valuable metals. 
Further, as the rapidity of action of any exciting solution upon the 
positive element of a voltaic pair is (other things being equal) the greater 
the more electro negative to this solution the negative element is, it will 
happen that the solution and consequent loss of gold and silver in such 
operations will be the greater when they are carried on in berdans, as the 
* The precipitation of mercury upon gold from a solution of mercuric cyanide is a 
very delicate and easy test for gold in stone, even when in the form of specks so minute 
aé to be only visible by aid of a microscope; the yellow colour persistent at a red heat of 
the speck to be tested, and the instantaneous whitening of it occasioned by this cyanide 
may be taken conjointly as proving that it is gold, 
