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As the above figures show, the percentage of zinc in the different kinds of brass lies between 27 and 34. Recently, alloys containing a somewhat larger quantity of zinc have been used, it having been found that the toughness and ductility of the brass are increased thereby, without injury to its tenacity. Alloys containing up to 37 per cent of zinc possess a high degree of ductility in the cold, and are well adapted for wire and sheet.
Gilders’ Sheet Brass.
—Copper, 1 part; zinc, 1 part; tin, 1/10 part; lead, 1/10 part. Very readily fusible and very dense.
White Brass.
—Birmingham platina is an alloy of a pure white, almost silver-white color, remaining unaffected by tolerably long exposure to the atmosphere. Unfortunately this alloy is so brittle that it can rarely be shaped except by casting. It is used only in the manufacture of buttons. The alloy is poured into molds giving rather sharp impressions and allowing the design on the button (letters or coat of arms) to stand out prominently with careful stamping. The composition of this alloy, also known by the name of platinum lead, is as follows:
| I | II | |
|---|---|---|
| Copper | 46.5 | 4 |
| Zinc | 53.5 | 16 |
III.—Zinc, 80 parts; copper, 10 parts; iron, 10 parts.
Britannia Metal.
Britannia metal is an alloy consisting principally of tin and antimony. Many varieties contain only these two metals, and may be considered simply as tin hardened with antimony, while others contain, in addition, certain quantities of copper, sometimes lead, and occasionally, though rarely on account of its cost, bismuth. Britannia metal is always of a silvery-white color, with a bluish tinge, and its hardness makes it capable of taking a high polish, which is not lost through exposure to the air. Ninety per cent of tin and 10 per cent of antimony gives a composition which is the best for many purposes, especially for casting, as it fills out the molds well, and is readily fusible. In some cases, where articles made from it are to be subjected to constant wear, a harder alloy is required. In the proportions given above, the metal is indeed much harder than tin, but would still soon give way under usage.
A table is appended, giving the composition of some of the varieties of Britannia metal and their special names.
| Tin | Antimony | Copper | Zinc | Lead | |
|---|---|---|---|---|---|
| English | 81.90 | 16.25 | 1.84 | — | — |
| English | 90.62 | 7.81 | 1.46 | — | — |
| English | 90.1 | 6.3 | 3.1 | 0.5 | — |
| English | 85.4 | 9.66 | 0.81 | 3.06 | — |
| Pewter | 81.2 | 5.7 |
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