So called from its power to dissolve gold, is a mixture of nitic acid (aquafortis) and muriatic acid, (spirits of salts,) deprived of its burning qualities by block-tin, which it dissolves. It is called by the chemist acid nitro-muriatic: the muriatic also contains a portion of alkali, which gives to red a vinous tint, and for which colour it is principally used.
The two substances should be of the purest quality, of a concentration of thirty-three degrees for the nitric acid and of twenty degrees for the muriatic. They must be mixed with the greatest precaution. Having provided a clear glass bottle, the neck rather long, capable of holding twice the quantity to be prepared, place it upon a bed of sand, the opening at top, and pour in one part of pure nitric acid and three of muriatic. Let the first vapours dispel, and then cover the orifice with a small phial, which must not confine the vapour too closely, as the bottle would be liable to burst, but which retains as much as possible without risk. Of block-tin, an eighth part of the weight of the acid must then be dropped into the bottle, in small pieces, a little at a time, covering the orifice with the phial. The acid will immediately attack the tin and dissolve it, when a second portion must be put in with the same precaution, and so on till the whole is dissolved. Malacca tin is the best for use, and if pure there will be no sediment; but, as it cannot always be obtained, a black sediment will be left. The vapour having ceased, the acid must be poured into bottles and secured with glass stoppers, to preserve it. When used, a part is taken and mixed with one quarter of its weight of distilled water.
It is usual with some workmen to perform this operation in a common drinking-glass; but, as the vapour is thereby all dispersed, the composition loses a considerable portion of its best quality, for it will be observed, if performed in a bottle as above directed, that the vapour assumes a red tint, which does not escape if the neck of the bottle be of sufficient length.
ANOTHER.
Some binders adopt the following method; but, as it is not capable of producing an equal beauty and clearness of colour with the one above given, it will not be advisable to use. The former, too, will be equally effective to an indefinite period, while this will not preserve more than two or three months.
Put in a brown freestone pot two ounces of powdered sal-ammoniac, six ounces of fine Malacca tin, in strips or drops, twelve ounces of distilled water, and, last, a pound of nitric acid, of thirty-three degrees. Leave the whole till the tin is dissolved, and then pour off and bottle as above directed.
VITRIOL-WATER.
Vitriol, as sold in the pure state, will not be proper to use in marbling or sprinkling, as it would corrode and destroy the leather. It must be weakened at least in proportion of one ounce of vitriol to three of water.
MARBLING-WATER.