Silver, Sul′phate of. Ag2SO4. Syn. Argenti-sulphas, L. Prep. By boiling silver in sulphuric acid; or, by precipitating a solution of the nitrate by another of sulphate of sodium. It dissolves in 80 parts of hot water, and falls in small colourless needles as the solution cools.
Silver, Sul′phide of. Ag2S. Syn. Sulphuret of silver; Argenti sulphuretum, L. Prepared by passing sulphuretted hydrogen through a solution of nitrate of silver; or, by melting its constituents together. It possesses a greyish-black colour, and is a strong sulphur-base.
Silver, Ox′idised. The high appreciation in which ornamental articles in oxidised silver are now held, renders a notice of the process followed interesting. There are two distinct shades in use, one produced by chlorine, which has a brownish tint, and the other by sulphur, which has a bluish-black tint. To produce the former, it is only necessary to wash the article with a solution of sal ammoniac. A much more beautiful tint may, however, be obtained by employing a solution composed of equal parts of sulphate of copper and sal ammoniac dissolved in vinegar. A fine black tint may be produced by a slightly warm solution of sulphide of potassium or of sodium. (‘Chem. Techn.’)
SILVER DUST. Syn. Silver powder; Argenti crocus, A. pulvis, L. Prep. 1. Pure pulverulent silver, obtained by any of the
methods explained on the previous page. Used to coat pills, by japanners, &c.
2. Heat oxide of silver to dull redness in a porcelain crucible, cool, triturate the powder in an agate mortar, and pass it through a fine sieve. Used at the hospital of Montpellier.
SILVER SHELLS. These are prepared and used like gold shells.
SIL′VERING. The art of covering the surfaces of bodies with a thin coating of silver. Leather, paper, wood, &c., are silvered by covering them with silver leaf, by a similar process to that employed for gilding them.
Silvering of Glass. Two distinct methods are adopted for this purpose—one of which consists in employing a layer of tin-foil and mercury, falsely called ‘silvering,’ the other in using a coating of real silver precipitated from a solution of that metal.
1. Plane surfaces, as those of mirrors, &c., are commonly silvered as follows:—A sheet of tin-foil corresponding to the size of the plate of glass is evenly spread on a perfectly smooth and solid marble table, and every wrinkle on its surface is carefully rubbed down with a brush; a portion of mercury is then poured on, and rubbed over the foil with a clean piece of very soft woollen stuff, or a hare’s foot, after which two rules are applied to the edges, and mercury poured on to the depth of a crown-piece, when any oxide on the surface is carefully removed, and the sheet of glass, made perfectly clean and dry, is slid along over the surface of the liquid metal, so that no air, dirt, or oxide can possibly either remain or get between them. When the glass has arrived at its proper position, gentle pressure is applied, and the table sloped a little to carry off the waste mercury, after which it is covered with flannel and loaded with heavy weights; in 24 hours it is removed to a wooden table and further slanted, and this position is progressively increased during a month, until it becomes perpendicular.