The same metals, and in the same proportion, constitute gun-metal. In the brass ordnance made at Woolwich, the proportion of tin varies from 8 to 12, to the 100 parts of copper. The purest copper requires the most. That the alloy is more sonorous than iron, is evident from the report of brass pieces, being louder than that occasioned by iron guns. When the alloy is 78 of copper and 22 of tin, it is chiefly used for clocks. There is, in the English metal, about five per cent. of zinc, and four per cent. of lead. The proportion of tin, in bell-metal, varies. In church bells, less tin is used than for small bells. In the latter, zinc is sometimes added. The _Tam-tam_, or _gong_ of the Chinese, used for cymbals, clocks, mirrors, &c. contains, according to analysis, 80 parts of copper, and 20 parts of tin. The proportions, however, are not always the same. The ancients made cutting instruments of an alloy of copper and tin. A dagger, analyzed by Mr. Hielm, consisted of 83-7/8 copper, and 16-1/8 tin. Vessels of bronze were frequently covered with silver. Some of this kind were found in the ruins of Herculaneum. Pliny observes, that ancient mirrors were made with a mixture of copper and tin; but that, in his time, those of silver were so common, that they were even used by the maid servants. The quantity of tin, to make the most perfect speculum, depends on the quality of the copper. If the proportion of tin be too small, the composition will be yellowish; if it be too great, the composition will be of a grayish-blue colour. Mr. Edwards casts the speculum in sand with its face downwards; takes it out while red-hot, and places it in hot wood-ashes to cool, otherwise it would break in cooling. The mixture is first granulated, by pouring it into water, and then fused a second time for casting. Mr. Little recommends the following proportions: 32 parts of the best bar copper, 4 parts of brass, or pin wire, 16-1/2 of tin, and 1-1/4 of arsenic. Whether for speculum metal, bronze, or gun-metal, the metals must be mixed exactly, and for this purpose be kept a long time in fusion, and constantly stirred; otherwise, the alloy will not be of a uniform quality, as the greater part of the copper will sink to the bottom, and the greater part of the tin rise to the surface. When we speak of _brass guns_, as that name is generally applied to them, we are to understand, that they are not made, like brass, of an alloy of copper and zinc.