French Silver Solders.-The following solder is used for soldering silver wares of the standard 950: In making this solder, it is recommended to previously alloy the zinc with twice its weight of copper, when the following proportions are used : He further states that these solders ought to be melted several times. The metal is then laminated into thin bands, which are granulated into spangles, ready to be mixed with borax. When arsenic is used, it is not added until after the fusion of the other metals. Gee denies that there is any advantage in remelting silver solder containing zinc several times, but that his experience is in direct opposition to this practice. Solders, into the com 1 Guide Pratique des Alliages Métalliques, pp. 324, 326. X SILVER SOLDERS 337 position of which volatile metals enter, become hard, brittle, and "drossy" by repeated remeltings, and are best only melted once. In 1635 Bate published the following directions for preparing silver solders. "Take a quarter of an ounce of silver and 3 pennyweights of copper, melt them together, and it is done." 1 The following solders are recommended for special Nos. I and II are recommended for work to be enamelled. No. III. Easy solder for filigree-work. No. IV. Easy solder for chains. No. V. Common easy solder. No. VIII. Easy silver solder. Nos. IX and X. Common easy solders. Silver solders are used for soldering other metals and alloys, such as cast-iron, steel, brass, German silver, gold alloys, etc. As already mentioned, the substance most commonly used as a flux in hard-soldering is borax. Powdered glass is occasionally used with very hard solders. In Vienna a substance is used termed "streu-borax," or "sprinkle-borax." It is composed of the following ingredients, which should be gently heated to expel the water of crystallisation, and the whole well pounded ready for use:— Calcined borax Parts by weight. 87 71 100 The object of the mixture is to prevent the rising of the solder, and to facilitate its flushing. It, however, encumbers the work with more flux than when borax alone is used, and, if kept for some time after mixing in the wet state, turns the solder yellow. IMITATION SILVER ALLOYS § 162. Clark's Patent Alloy.-Copper 75, nickel 14.5, zinc 7.5, tin 1.5, cobalt 1.5 per cent. Baudoin's Alloy.-Copper 72, nickel 16.6, cobalt 1.8, tin 2.5, zinc 7.1 per cent. About per cent of aluminium may also be added. Parisian Alloy.-Copper 69, nickel 19.5, zinc 6.5, cadmium 5 per cent. White Alloy.-Copper 64.5, tin 32, arsenic 3.5 per cent. Chinese Silver.-Copper 58, zinc 17.5, nickel 11.5, cobalt 11, silver 2 per cent. X SILVER ALLOYS 339 Warne's Alloy.-Tin 37, nickel 26, bismuth 26, cobalt 11 per cent. Minargent.-Copper 56, nickel 40, tungsten 3, aluminium 1 per cent. White Alloy.-Copper 59, tin 31, brass 8, arsenic 2 per cent. See also the chapter on German silvers, and also the alloys of silver, zinc, copper, and nickel. The above alloys are used for cheap jewellery and electroplated wares. Wires prepared from them may serve for stems of pins, brooch tongs, catches and joints, etc. They are harder and more difficult to work than ordinary silver alloys, but their hardness and tenacity adapt them for the purposes above mentioned. MIXING AND MELTING OF SILVER AND ITS ALLOYS § 163. The crucibles best adapted for melting silver are made of clay and plumbago and known as blacklead" and plumbago crucibles. They are capable of withstanding the action of heat and sudden changes of temperature much better than ordinary clay crucibles, and if previously annealed, can be used many times in succession without cracking or breaking. They also resist the corrosive action of slags and fluxes better than clay-pots. Alloys consisting of silver and copper only, may be prepared by melting the two metals together, as previously stated, under a layer of charcoal powder. When melted the mixture should be well stirred with an iron rod, and the metal, if at the proper temperature, poured. When zinc is a constituent of the alloy, that metal must be heated and cautiously added after the silver and copper are melted, and the whole then vigorously stirred. It should be borne in mind that zinc is a volatile metal, and that the volatility increases as the temperature rises, so that it is advisable to add the zinc as soon as the other metals are melted. The metal is generally poured into flat ingot-moulds, so as to produce a plate of silver suitable for rolling and for wiredrawing, and the same precautions apply as stated when treating of gold alloys. The charcoal powder employed should be of good quality, as defective alloys are sometimes produced by using bad charcoal. When tin is used, it should be added after melting the silver and copper, but this is not so necessary as in the case of zinc or arsenic. When scrap silver or silver alloys are added to the crucible alone, or along with new metal, certain impurities may also be admitted, and a flux will be necessary to remove them. In most cases carbonate of soda or borax is employed. The latter should be sparingly used. § 164. Lemel, as the filings and turnings, etc., are termed, is purified by burning off organic matter, and then melting in a skittle-shaped crucible with suitable fluxes. The following may be taken as a general guide : Saltpetre may be used instead of the sal-enixum, but either of these salts should be sparingly employed. The common salt should not be mixed with the silver and other fluxes, but kept as a covering for the mixture, as it prevents the mass rising too much, and overflowing the crucible. The crucible should not be more than half full to commence with. After the whole mass has become liquid, keep it in fusion for about half an hour. Then allow the contents gradually to cool, and break the pot to recover the lump of metal. Some manufacturers prefer to run down the “lemel” in an ordinary plumbago crucible, with carbonate of soda alone as the flux. When the metal is well fused, the mixture is well stirred with an iron rod from time to time, and the metal finally poured into an ingot-mould, ready for the refiner. |