Put into a long wine-glass or thin narrow tumbler 2 fl. dr. of nitric acid to 1 oz. of hydrochloric acid - that is, the first acid is in the proportion of 1 to 4 parts of the latter. If the acids are of concentrated strength, a little water will be necessary to add to this mixture of acids; if they are of ordinary strength, water will be unnecessary. Place the glass vessel containing this mixture of acids in a saucer on the hob, so that, should the vessel crack, the liquid will not escape, or else place the vessel in a basin of hot water. The gentle heat afforded from either of these sources should be maintained until the gold is dissolved. Place the coin or scrap gold in the mixed acids, and stand on the hob, so that the fumes given off shall escape up the chimney. The above quantities of acid will generally be sufficient to dissolve a sovereign or its equivalent weight of scrap gold. If, however, the solvent action ceases before the gold is dissolved, add a little more acid. A great excess of acid should be avoided, because it renders their neutralisation or subsequent elimination more difficult. If pure leaf gold be employed, the solution will form a perfectly transparent yellow liquid.
In the case of the Australian gold coin, however, the small portion of silver alloyed with the coin will give a precipitate of silver chloride, which will give a cloudy appearance to the liquid. Pour this solution of gold into a basin, and add to it about 6 oz. of distilled water, and stir up the mixture with a glass rod. Next add some powdered chalk to the liquid to neutralise its acidity. The way to ascertain whether the acid is completely neutralised is to dip a piece of blue litmus paper or to drop a little tincture of litmus solution in the acid. If any acid be present, the paper will lose its blue colour, and be coloured pink or red. If the blue colour remains unchanged, then you know the acid is completely neutralised. Stir the chalk well up in the liquid, and then filter it into a bottle thus: Take a piece of clean white blotting paper, cut it into a circular form, fold this in half, and then fold again, so that it forms a quadrant - a quarter of a circle. Open this paper out, and place it in a glass funnel. Just moisten it with a little distilled water, to keep it in its place, and then stand the funnel in the neck of a clean bottle, capable of holding the solution of gold that filters through.
The chalk, having united with the acids, will have formed solid salts of lime, which are retained on the filter paper. The liquid solution that passes through is a solution of gold terchloride, fit for use in photography. As light partly reduces the gold into the metallic state, it is best to keep the bottle in the dark, or else closelven-veloped in black paper, pasted round it.
To obtain the terchloride in the crystallised state, the above solution must be evaporated until the salt crystallises out in reddish crystals. As these crystals imbibe water if placed in a moist atmosphere, and then form a yellow solution again, they should be stored up in hermetically sealed glass tubes. These tubes are easy of construction, thus: Take a piece of soft glass tubing, about 12 in. long and 1/4 in. bore; hold one-third of it in the flame of a spirit lamp or gas flame, twirling the tube round, so that it is uniformly heated. When the glass begins to bend, hold it away from the flame, and, holding the tube at both ends, pull them apart, like stretching a piece of elastic. The heated part of the glass will yield to the pull, and, stretching, become narrowed. Break the tube in two at this narrow part, and then hold each of these narrow ends in the flame for a few seconds, until the glass, recoiling on itself, closes the orifice. Put the crystals of terchloride in with a quill at the open end of the tube, and then close that by directing the flame of a blowpipe on the periphery of the orifice until the glass melts and closes the aperture.