Solutions for gold plating by means of the electric current may, like those for silver plating be made either by the aid of a battery, or by the chemical process; that made by the chemical process being more quickly made and we think capable of giving better satisfaction to the inexperienced.
The solution made by the battery process has the advantage of being perhaps a trifle more economical, and for this reason is often preferred by the experienced electroplater.
To make the solution by the chemical process, dissolve about one and a half ounces of chloride of gold in water or convert a little over an ounce of gold into chloride and dissolve in water, and add a solution of cyanide of potassium, slowly and at intervals with frequent stirring just as long as it produces a precipitate, but no longer. Great care must be taken to attain the exact neutral paint, that is, when it no longer produces a precipitate upon the addition of a very small quantity of either the cyanide or the chloride of gold solution.
A small quantity of the chloride of gold solution should be reserved and slightly diluted for this purpose, and if it is not all used it may be set away and protected fiom the Iight for future use.
Should the solution contain an excess of either the chloride or the cyanide some of the gold will be held in the clear solution and be poured off, hence the importance of exercising great care in this respect.
When the exact neutral paint has been attained, allow it to settle and pour off the clear liquid, which should be preserved in order to recover any traces of gold it may contain. Then wash the precipitate well by adding water, stirring briskly, and after it has settled, pouring off the clear liquid, repeating the operation a number of times so as.to thoroughly remove all traces of acid.
The wash waters should be preserved as they also are liable to contain traces of gold.
After the last wash water has been poured off pour the precipitate into a paper filter, add a small quantity of water and allow it to drain thoroughly, but not to become dry, as it may possibly contain a small amount of the fulminate of gold which is an extremely dangerous substance, and detonates with terrible violence upon the slightest friction or percussion. When the precipitate has thoroughly drained, collect it in a suitable vessel and add to it a strong solution of cyanide of potassium until barely the whole of it is dissolved, then, having observed the amount of cyanide solution necessary to merely dissolve the precipitate, add about one-fourth as much more to form what is termed by electroplaters "free cyanide" and finally dilute the whole with clean water to one gallon. The amount of gold in the solution may vary greatly from the amount we have given without injury to its working, but in order to obtain the best results it should not contain less than one half an ounce, nor more than ten ounces of gold per gallon. A rather dilute solution gives a somewhat better deposit but is less rapid in its operation than a.stronger one.
To prepare the gilding solution by means of a battery, dissolve two pounds of cyanide of potassium in one gallon of warm water, immerse two sheets of pure gold in this solution and connect them to a moderately strong battery, and allow them to remain in this position and occasionally stirring the liquid, until the proper amount of gold has been dissolved and held in solution. This may be determined by weighing both sheets of gold before placing them in the solution, and then by taking them out of the solution occasionally and weighing them, the amount of gold held in solution may be very easily determined.
Still another and a better means of ascertaining when the solution is ready for use, is to occasionally substitute for a short time a bright and clean sheet of copper, or light colored brass for the gold cathode, until it finally receives a satisfactory deposit. The solution is then ready for work and should be used at a temperature of about I500 Fahr.
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