American journal of pharmacy . States Coast Survey, recommends that the engraved copperplates, &c., be coated in a battery with a thin film of silver, and afterwardswashed with a dilute solution of iodine in alcohol,—about one grain of theformer in a quart of the latter. Dusting with black lead, or spreading a little oil over the surface of thearticle, care being taken not to use an excess, will cause the metals toseparate easily. A little wax dissolved in spirits of turpentine also answerswell. 26 CHEMICAL AND PHARMACEUTICAL MANIPULATIONS. Solutions should be kept covered from the air and dus
American journal of pharmacy . States Coast Survey, recommends that the engraved copperplates, &c., be coated in a battery with a thin film of silver, and afterwardswashed with a dilute solution of iodine in alcohol,—about one grain of theformer in a quart of the latter. Dusting with black lead, or spreading a little oil over the surface of thearticle, care being taken not to use an excess, will cause the metals toseparate easily. A little wax dissolved in spirits of turpentine also answerswell. 26 CHEMICAL AND PHARMACEUTICAL MANIPULATIONS. Solutions should be kept covered from the air and dust; and the work-ing of the batteries is promoted by having the surrounding atmosphere of awarm temperature. A few drops of bi-sulphuret of carbon added to a silver solution will pro-duce a bright deposit. In inserting the articles in the solutions the air adhering to their surfiices,and which prevents a contact of the metals, may be dispelled by moving thearticles about in the liquid or by heating the solution. Fig. The plates attached to the positive poles Should be parallel to the articleson which the metal is to be deposited and present the same amount ofsurface. , A battery, if in proper working order, will, when the connections aremade, show a disengagement of gas at its negative metal; but no gas shouldbe seen to escape at either pole. Bronzing.—To give the copies of medals and other objects an antique orbronzed appearance like the original, several means are employed. A darkbronze is produced by dipping the object in very dilute nitric acid,—sayhalf an ounce of acid to a pint of water,—and, after drying, heating itgradually and uniformly. The color is deepened in proportion to the heatapplied. Sulphuretted hydrogen or hydrosulphuret of ammonia may alsobe used. Afterwards polish with a brush. Green bronzes are formed byimmersing the articles in a solution of chloride of ammonium or chloride ofsodium, or by exposing them to the fumes of chloride of lime. The
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