SILVER is of a more pure white than any other metal; it has considerable brilliancy, and takes a high polish. Its specific gravity varies between 104, which is the density of cast silver, and 10.5 to 10.6, which is the density of rolled or stamped silver. It is so malleable and ductile, that it may be extended into leaves not exceeding a ten-thousandth of an inch in thickness, and drawn into wire much finer than a human hair. Silver melts at a bright-red heat, estimated by Mr. Daniell at 1873° of Fahrenheit's scale, and when in fusion appears extremely brilliant (Brande, 953.)
Silver is but little used in the pure unalloyed state on account of its extreme softness, but it is generally alloyed with copper in about the same proportion as in our coin, and none of inferior value can receive the "Hall mark."Diamonds are set in fine silver, and in silver containing 3 to 12 grs. of copper in the ounce, the work is soldered with pure tin.
The sheet metal for plated works is prepared by fitting together very truly, a short stout bar of copper, and a thinner plate of silver; when scraped perfectly clean they are tied strongly together with binding wire, and united by partial fusion without the aid of solder. The plated metal is then rolled out, and the silver always remains perfectly united and of the same proportional thickness as at first. Additional silver may be burnished on hot, when the surfaces are scraped clean as explained under gold: this is done either to repair a defect, or to make any part thicker for engraving upon, and the uniformity of surface is restored with the hammer. In addition to its use for articles of luxury, the important service of copper plated with silver for the parabolic reflectors of lighthouses must not be overlooked; these are worked to the curve with great perfection by the hammer alone.
Plated spoons, forks, harness, and many other articles, are made of iron, copper, brass, and German silver either cast or stamped into shape; the objects are then filed and scraped perfectly clean; and fine silver often little thicker than paper is attached with the aid of tin solder and heat: the silver is rubbed close upon every part with the burnisher.
The electrotype process is also used under Elkington and Co.'s patent for plating several of the metals with silver, which it does in the most uniform and perfect manner; the silver added is charged by weight at about three times the price of the metal; the German silver or albata is generally used for the interior substance, as when the silver is partially worn through, the white alloy is not so readily detected as iron or copper.
Mr. Brande says, "The alloy with copper constitutes plate and coin; by the addition of a small proportion of copper to silver, the metal is rendered harder and more sonorous, while its colour is scarcely impaired. Even with equal weights of the two metals, the compound is white: the maximum of hardness is obtained when the copper amounts to one-fifth of the silver. The standard silver of this country consists of 11 2/20 pure silver and 15/20 copper, or 11.10 silver and 0.90 copper. A pound troy, therefore, is composed of 11 oz. 2 dwt. pure silver, and 18 dwt. of copper. Its density is 10.3; its calculated density is 10.5; so that the metals dilate a little on combining. The French silver coin is constitated of 9 silver and 1 (Bramde, 968.) - The French billon coin, is 1 silver and 4 copper. (Kelly.) "For silver plate, the French proportions are, 9 1/2 parte silver, 1/2 copper; and for trinkets, 8 parts silver, 2 copper."
Silver solders are made in the following proportions: -
Hardest silver solder, 4 parte fine silver, and 1 part copper; this is difficult to fuse, but is occasionally employed for figures.
Soft silver solder for general use, 2 parte fine silver, and 1 part brass wire. By some few, 3/4 part of arsenic is added, to render the solder more fusible and white, but it becomes less malleable; the arsenic must be introduced at the last moment, with care to avoid its fumes.
Silver is also soldered with tin solder, (2 tin, 1 lead,) and with pure tin.