RELATION OP SCIENCE TO ELECTRO-PLATE MANUFACTURES. 331 
and can direct them to our particular purposes. In the process 
of electro-plating, we understand the laws of the phenomena, 
and can direct them so as to obtain silver of a hard or soft 
quality, brittle or tough, crystalline silver, &c., according to 
our pleasure ; but if we had only an empirical knowledge of the 
subject, we could not thus vary the process. 
The great success of coating articles with silver by the 
electro process depends in a very large measure upon the 
demonstrable fact that alkaline cyanides have a strong 
affinity for noble metals, and but little affinity for base metals ; 
no other substance possesses this quality, or at least in 
so eminent a degree. In proof of this fact, I have twisted 
together two similar-sized and clean pieces of very thin wire, 
the one piece being gold and the other iron, and immersed the 
double wire in a solution of cyanide of potassium ; in about sis 
weeks the so-called “ indestructible ” metal, gold, was all 
corroded and dissolved, whilst the base and “ destructible” 
metal, iron, was as bright and perfect as ever. Further, if two 
pieces of wire, the one being of gold and the other of iron, are 
connected with the ends of a galvanometer, and their extre- 
mities immersed in a solution of cyanide of potassium, or other 
alkaline cyanide, the noble metal will be found to be electro- 
positive to the iron • and a galvanic battery of weak power 
might even be constructed of those three elements, which would 
present the singular anomaly of generating an electric current 
in an opposite direction to that in all other cases obtained. 
So great a resistance has iron, and so strong an affinity has 
silver to be dissolved by a solution of cyanide of potassium, 
that if a current of electricity is simultaneously sent through 
both into that liquid, the electricity will pass freely as long as 
there is a portion of the silver remaining, and the silver will 
dissolve rapidly ; but as soon as all the silver has dissolved 
the current will be nearly stopped, and the iron, instead of 
dissolving, will liberate bubbles of gas. 
This is precisely the condition that was required for the 
success of electro-plating, viz., a liquid which should not 
corrode (as acid liquids do) the articles of base metal immersed 
in it, and should easily dissolve and retain in solution the noble 
metals with which the articles were to be coated, and at the 
same time conduct electricity readily, and not lose those 
qualities by exposure to atmospheric air ; alkaline cyanides are 
the only known liquids that fulfil all these conditions. 
