GERMAN

See also:

• SILVER

SILVER  or NICKEL SILVER, an alloy of copper, nickel and zinc, prepared either by melting the copper and nickel together in a crucible, and adding piece by piece the previously, heated zinc, or by heating the finely divided metals under a layer ' of charcoal . To destroy its crystalline structure and so render it fit for working, it is heated to dull redness, and then allowed to cool . German silver is harder than silver; it resembles that metal in colour, but is of a greyer tinge . Exposed to the air it tarnishes slightly yellow, and with vinegar affords a crust of verdigris . At a bright red heat it melts, losing its zinc by oxida- tion unless protected from the atmosphere . At a heat above dull redness it becomes exceedingly brittle . German silver in various modifications of composition is much used in the arts . Alloys, of which about 5o% is copper and the residue zinc and nickel in about equal proportions take a fine polish, and are used as imitation silver for knives and forks . With a somewhat higher proportion of copper an alloy is formed suitable for rolling and for wire . In Chinese white silver or packfong (paktong) the amount of copper is smaller, about 40%, with about 32 % of nickel, 25 of zinc, and 2 or 3 of iron . German silver for casting contains 2 or 3 % of lead, which like iron increases the whiteness of the alloy . German silver, having a high specific resistance and a low temperature coefficient, has been used for electrical resistance coils, and these qualities are possessed in a still greater degree in manganin, which contains manganese in place of zinc, its composition being 84% of copper, 12 of manganese and 4 of nickel .

The addition of a trace of

tungsten to German silver, as in platinoid, also largely increases the resistance .