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Continue washing in this manner till there is no acid or copperas taste; then add to the gold in the bottom of the dish from 1-1/2 to 2 oz. cyanuret potassa, dissolved in about 1/2 pint pure soft water. The solution is then ready for use. Gild by laying a piece of pure zinc in contact with the article to be gilded, in the solution.
Dissolve one ounce of nitrate of silver, in crystal, in 12 ounces of soft water; then dissolve in the water two ounces of cyanuret of potash; shake the whole together and let it stand until it becomes clear. Have ready some 1/2 ounce vials, and fill them half full of whiting, then fill up the bottles and it is ready for use.
The cyanuret of mercury, when heated in an open glass tube, is resolved into cyanogen gas and metallic mercury; if this substance is heated in a tube hermetically sealed, the decomposition occurs as before, but the gas, unable to escape, and shut up in a space several hundred times smaller than it would occupy as gas under the ordinary atmospheric pressure, becomes a fluid in that part of the tube which is kept cool.
At all events every particle of dirt and grease must be removed; then suspend the article in the cyanuret of gold solution, with a small strip of zinc cut about the width of a common knitting needle, hooking the top over a stick which will reach across the top of the vessel or bottle holding the solution. If the zinc is too large the deposit will be made so fast that it will scale off.
Now dissolve one ounce of cyanuret of potassium in one pint of pure rain water, to which add the gold, and it is ready to use. Clear the article to be plated from all dirt and grease with whiting and a good brush; if there are cracks it may be necessary to put the article in a solution of caustic potash.
And, again inversely, cyamelide can be converted into cyanuric acid and hydrated cyanic acid. We have three other bodies which pass through similar changes, in aldehyde, metaldehyde, and etaldehyde; and, again two, in urea and cyanuret of ammonia. Further, 100 parts of aldehyde hydrated butyric acid and acetic ether contain the same elements in the same proportion.
This will account for the long description of the cyanuret of potassium, while the preparation of the equally important and even more used acids, the sulphuric, muriatic, etc., commonly found in commerce, are altogether neglected.
The solution may be evaporated to dryness, and one part of the salt dissolved in six of water; one part of muriatic acid, sp. gr. 1.15, is then added, and the solution distilled, when the whole of the hydrocyanic acid passes over, and by being conducted into a solution of potassa, as in the former process, forms cyanuret of potassium.
Continue washing in this manner till no acid or salt taste remains; then add a quart or more of pure soft water, and cyanuret potassa enough to take it up, or nearly so. The solution is then nearly ready for use. Silver by laying a piece of zinc in contact with the article, the same as in gilding. If the article you are silvering or gilding corrodes or turns black, it wants a little more cyanuret.
By boiling, however, the ignited residue with spirits of wine this difficulty is said to be overcome, as the ferrocyanate is absolutely insoluble in that menstruum, while the cyanuret, at that heat, freely dissolves, and is as easily re-deposited on cooling. "There is, however, a much better process by which this salt may be formed, viz. by simply transmitting hydrocyanic acid through potassium.
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