pared by dissolving a certain quantity of the metal in aqua regia, evaporating the resulting chloride to dryness, and, when cold, dissolving the mass in a small quantity of sulphuric ether or alcohol. This solution is applied with a brush to the parts of the surface to be oxidized. The spirit or ether almost instantly evaporates, leaving a film of platinum behind which, according to its thickness, imparts either a steel-gray or nearly black lustre to the surface. Instead of the ethereal or alcoholic solution, a hot aqueous solution of the platinic chloride may be used with equally satisfactory results. (Consult Platinizing by Simple Immersion, Chap. XLIV., p. 357.) Dr. Elsner (Chem. tech. Mittheilungen) produces a brownish tint on plated goods, by applying to the surface a solution of sal-ammoniac, and a finer tint by means of a solution of equal parts of sulphate of copper and sal-ammoniac in vinegar. For a fine black effect, the same author uses a warm solution of sulphide of potassium or sodium. Watt (Electro-Metallurgy, 134) gives the following formula, which is a modification of that of Elsner above given, viz: Sulphate of copper 2 parts. Nitrate of potassium (saltpetre) 1 part. Dissolve in a little acetic acid, and apply with a camel'shair brush to the surfaces to be "oxidized." The articles should be slightly warmed before applying the mixture. Fearn's procedure for imparting a pink coloration on silver surfaces, consists in immersing the article for a few seconds in a hot, concentrated solution of chloride of copper (cupric chloride). The article must then be well washed in water and dried, or may be dipped in alcohol, and the spirit allowed to burn off. "Oxidized" silvering is intended, in many cases, as a substitute for the nielled silver, of which a description follows. “Dead” Silver.—A very pleasing “dead” appearance, which resembles frosted silver, may be obtained on plated articles, by depositing a blush of copper on the surface in a sulphate of copper solution, and laying a very thin coat of silver over the copper. Satin-Finish.-The sand-blast is in use in certain establishments to produce the peculiar dead, lustrous finish, known technically as satin-finish, on plated goods; a template of some tough resistant material, like vulcanized-rubber, is made of the proper design, and when placed over the article protects the parts which it is desired to leave bright, from the depolishing action of the sand; while only the open portions of the template are exposed to the blast. The apparatus employed for this purpose consists of a wooden hopper with a longitudinal slit below, through which a stream of fine sand is allowed to fall by opening a sliding cover. Closely surrounding the base of the hopper is a rectangular trunk of wood, extending some distance below the base of the hopper and tapering towards the bottom, to concentrate the sand jet. This trunk is closed about the sides of the hopper and open below, and is designed to direct the stream of sand upon the surface of the article presented beneath its orifice. To increase the rapidity of the depolishing action of the sand, a current of air under regulated pressure is admitted into the upper part of the trunk, which, when the sand valve is opened, propels it with more or less accelerated velocity upon the metallic surface below. For this purpose, either a "blower," or an air-compressor with accumulator may be used; and the pressure may be regulated. at will. The sand is thus driven with more or less velocity down the trunk by the air-blast admitted above, and, falling upon the surface of the article presented at the bottom, rapidly depolishes the exposed parts, while those protected by the template are not affected. The articles are presented at the orifice of the trunk by the hands of the operator, which are suitably protected by gloves, and as rapidly as the depolishing proceeds he turns the article about until the work is done. The progress of the work is viewed through a glass window set in a hori zontal table which surrounds the apparatus and which forms the top of a large box, into which the sand falls, and which is made tight to prevent the sand from flying about. A portion of this box in front, where the workman stands, is cut away, and over the opening is hung a canvas apron which the operator pushes aside to introduce the work. The sand that accumulates in the box below is transferred again to the hopper as required, and is used over and over again. The satin-finish produced by the sand-blast is exceedingly fine and perfectly uniform, and the work is done more rapidly than with the use of brushes in the usual way. Niel, or Nielled Silvering.-This product, which still bears the name of the inventor, is obtained by the sulphuration of certain parts of a silver object. But this sulphu ration instead of being made directly upon the surface, as in the method just described, is made by inlaying the silver surface with a sulphide of the same metal prepared beforehand. Nielling may therefore be called a species of enamelling. After having prepared the nielling composition, an operation which consists in forming a triple sulphide of silver, lead, and copper,* and reducing it to a fine pow *For preparing the nielling composition a certain proportion of sulphur is introduced into a stoneware retort, or a deep crucible. A mixture of silver, copper, and lead is heated in another crucible, and der, which is mixed with a small proportion of a solution of sal ammoniac, the artist executes the engraving upon a silver surface, and covers the whole, hollows and reliefs, with the nielling composition. The article is then heated in the muffle until the composition melts, when it will be found to adhere firmly to the metal. The design is brought out in very effective contrast by denuding the portions in relief, without touching the hollows, which retain a fine black. This method is costly, since each article must be engraved. The arts have called to their aid another and a cheaper process, which consists in engraving in relief a steel plate, which, applied to a sheet of silver, subjected to powerful pressure in a die, reproduces a faithful copy of the engraving. The silver sheet thus stamped is ready to receive the nielling. A large number of copies may be obtained from the same matrix. Such is the method by which a quantity of nielled when melted is poured into the fused sulphur, which transforms these metals into sulphides. A small portion of sal ammoniac is then added, and, after being removed from the crucible, or retort, the product is pulverized and is then ready for use. We give herewith the proportions indicated by Mr. Mackenzie, who has paid much attention to the subject. Charge of the first crucible : Flowers of sulphur Sal ammoniac 750 parts. 75 66 Charge of the second crucible, which, after fusion, is poured into the first : Roseleur is of the opinion that it is preferable to diminish the proportion of lead, the sulphide of which impairs the blue shade of the nielling, and corrodes too deeply. articles are manufactured, such as so-called Russian snuffboxes, cases for spectacles, bon-bon boxes, etc. Roseleur suggests the following plan for obtaining effects similar to nielled silvering, which he recommends to the attention of artists and manufacturers: a pattern of the design cut out of thin paper, like lace paper is dipped into a thin paste of nielling composition, or into a concentrated solution of some sulphides, and then applied upon the plate of silver which is afterwards heated in the muffle. The heat will destroy the organic substance, and a pattern will remain formed by the composition absorbed by the paper. CHAPTER XLII. DISSOLVING SILVER FROM SILVERED ARTICLES (“STRIPPING”). WHEN a silvering operation has failed from want of adherence of the deposit, or by reason of a granular surface, or when we desire to replate old and worn articles, it is absolutely necessary to remove the silver in order to restore the surface of the metal to its primitive state, and to permit of the proper repetition of the series of cleansing operations. The operation is conducted either in the cold, or with the aid of heat. The following is the procedure recommended by Roseleur and other experienced electro-platers for dissolving silver in the cold, viz: The objects are suspended in a large vessel (Fig. 130) filled with the following mixture: Sulphuric acid of 66° Baumé (concentrated oil of vitriol), 100 parts; nitric acid of 40° Baumé (concen |