All solutions for gold plating should be used at a temperature of about 1500 Fahr., and when not in use should be carefully covered over to protect it from the dust and other impurities. The amount of gold held in the solution may vary greatly without materially affecting it working, provided always, that it also contains a proportionate amount of cyanide of potassium. The proportions of gold and cyanide of potassium in the solution may vary within certain limits, generally from twenty-five to fifty per cent, more than is required to simply dissolve the cyanide of gold (see page 49) without impairing its usefulness.
Too much cyanide of potassium causes the deposit to have a dirty discolored appearance. After the solution has been in use for some time it often works badly in consequence of the proportions of gold and cyanide becoming dis¬arranged. This is caused sometimes by using anodes with greater or less surface than the articles to be plated.
When the anode presents a larger surface in the solution than the articles to be plated, the solution rapidly becomes richer in gold, which uniting with the free cyanide, soon uses it all up in forming the double cyanide of gold and potassium, leaving but very little or none at all to form the "free cyanide" so essential to its perfect working.
This condition is indicated by the anode becoming covered with crust or sediment, and is remedied by using an anode with smaller surface than the articles to be plated, or a sufficient amount of a solution of cyanide of potassium may be added.
When the anode becomes black, and has a slimy appearance, the solution needs more gold, which may be supplied by using an anode of greater surface until the solution is again properly proportioned, which will be indicated by the anode remaining bright and clean and giving a good deposit. By carefully observing these indications, and applying the proper remedy, the solution may be kept in order
almost indefinitely, but after very long continued use it becomes contaminated with various impurities, some of them accidentally introduced, and others set free by the dissolving of the anode.
Gold anodes invariably contain traces of silver, which is dissolved in the solution, and by being deposited with the gold increases its paleness of color. When from any of these reasons the solution ceases to work satisfactorily, all the metal held in solution may be recovered separately, and used to start out anew,
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