By H. L. Haas, Ph.b. Electrometallurgy has, until very recently, been wholly in the hands of unscientific men, workmen who have never given it the proper attention as a science.
Formerly very little attention was paid to the composition of a plating solution, nor what chemical changes took place in it during electrolysis. When a solution did not deposit its metal properly, the plater thought it needed a handful of this or a spoonful of that, and threw it in, not knowing whether it was soluble in the solution or not or what change was produced. And when that did not work, he thought perhaps it needed another handful or spoonful of something else, irrespective of any exact quantity or what the chemical change would be by the addition of it. And when it still did not work he was at a loss what to do further, so did the only thing possible—threw it away and started to make a new one (because he was a plater and not a scientist). But the new solution was no better than the first. And why? Because he had made it with a handful of this and a spoonful of that and an unknown quantity of something else that he had forgotten the name of (because he was a workman and not a scientist).
If he bought certain chemicals, the nature of which he did not know, or what percentage of purity, he was again in trouble when his solution did not work properly, because he had made it in a careless manner with only a workman’s knowledge.
He had electric current, to use his expression, yet the solution did not deposit. He knew only that he had a current, because when he connected the positive and negative wires he obtained a spark.
The electroplater’s voltmeter was formerly an old, rusty file, which they used to put across the two wires, making the connection and obtaining a spark. Then they knew they had electric current, but they did not know or care how much they had, because they had never measured it.
Electroplaters should know the following in order to be thoroughly conversant with their work: First. Exactly what the depositing solution is made of. Second. What takes place in the solution during the action of the electric current.
Third. What chemicals they are using, their properties and purity.
Fourth. The solubility of the anodes.
Fifth. How much electric current is necessary to deposit the metal properly; how many volts and amperes are employed. Sixth. How much resistance the solution and anodes offer to this electric current.
Seventh. The distance between the cathodes and anodes, and whether it varies.
Eighth. The amount of metal that is dissolved in a given time by the action of the electric current on the anodes.
Ninth. The amount of metal that is being deposited on the cathodes.
In this manner the plater is in a position to determine at all times what is going on in his solution, and if anything is wrong can obviate the difficulty, because he knows instantly the remedy for it.
For example, as in the case of silver and gold, the best plating solution is composed of cyanide of silver or gold. Cyanogen is evolved at the anode and silver or gold, as the case may be, is deposited upon the cathode. Chemicals used for making these solutions are cyanide of potassium and chloride or nitrate of silver or gold, or cyanide of silver or gold.
It is a known fact that, when subjected to the electric current, these two metals are dissolved very rapidly at the anode. The consequence is, when plating with them, very small anodes are all that are requisite to keep the metallic strength of the solution up to the proper standard. In the case of copper and brass, which do not dissolve in cyanide of potassium as readily as the two former metals when subjected to the action of the electric current, a larger surface of these two metals should he employed as anodes than in the case of silver and gold.
With nickel, it is a known fact that this metal is only with great difficulty soluble in sulfate of ammonia (which is the regular solution used for nickel plating) by means of the action of the electric current, and as a consequence the largest possible surface of nickel anodes should be employed.
It has been practically demonstrated that the maximum plane surface of nickel anodes that can be placed in a lank of a given size, even wlien suspended cm both sides of the cathodes, were not sufficiently dissolved by the action of the electric current to give the same amount of metal to the solution that was deposited upon the cathode, consequently the solution would in time become too weak in metal; therefore a larger surface of nickel must be placed in the bath, and the only manner in which this can be accomplished is by adding metal in some form to the solution. Formerly this was done by means of the addition of fresh nickel salts dissolved in tne solution, which was both detrimental and expensive. Then the corrugated nickel anodes were, invented, and it was practically determined that if oue-tlurd more surface of nickel was subjected to the action of the electric current in a nickel solution, the same amount of.nickel would be dissolved into the solution as was deposited on the work, and as a consequence the solution remained almost constant in metallic nickel, thus obviating ? the addition of metal in any other form.
Some advocate that all plating solutions should be made as simple as possible. By this means the plater, knowing at all times what is taking place in his solution, can readily remedy any error. But if the solution is complicated, and there arc various chemicals that really have no special advantage, should the solution go wrong the plater is at a loss to know where the trouble lies, and therefore is apt to ruin his solution in trying to doctor it.
Some have been endeavoring for many years to bring this up to a scientific standard, and with many gratifying results.
At the present time platers are giving more attention to the composition of their solutions. They weigh their materials; they endeavor to acquaint themselves with the action that the electric current produces on a solution; they pay more attention to the electrical contact, their different connections, the advantages of keeping them clean and free from all corrosion. They are using voltmeters and ammeters for measuring their electricity, switchboards for reducing their current to the proper and best point for the proper deposition of the metal, and I am pleased to say that the results which are now obtained in plating of the various metals arc far better in every way than formerly. And I feel confident it will only be a few years when it will have reached the high standard of other sciences.
