Obs. Several analyses have been made of ancient cutting instruments, from which it appears that the proportion of tin varies from 4% to 15%; a fact which tends to prove that more depends upon the exact mode of tempering
the alloy than on the relative proportions of the ingredients. Lead and zinc are inadmissible in bronze for this purpose. One or two per cent. of iron may, nevertheless, be added with advantage. The ancient bronze used for springs contained only 3% to 4% of tin. The edges and lips of bronze mortars must be carefully tempered by heating them to a cherry red, and then plunging them into cold water, as unless so treated they are very apt to be broken in use. See Bell-metal, Brass, Gun-metal, &c.
Bronze′-powder. Syn. Bronze. A name given to various powders having a rich metallic appearance, which they retain when applied on varnish, or when mixed with it, as in surface bronzing.
Prep. 1. Gold-coloured:—a. From Dutch-foil, reduced to an impalpable power by grinding. Cheap and looks well, and is very durable when varnished.
b. From gold-leaf, as the last.
c. Precipitated powder of gold.
d. From verdigris, 8 oz.; tutty powder, 4 oz.; borax and nitre, of each 2 oz.; bichloride of mercury, 1⁄4 oz.; grind them together, make the mixture into a paste with oil, and then fuse it; when cold, roll it into thin sheets or leaves, and grind it as in No. 1.
2. Iron-coloured:—Plumbago, in fine powder.
3. Red:—Sulphate of copper, 100 parts; carbonate of soda, 60 parts; mix, and apply heat until they unite into a mass; then cool, powder, and add of copper filings, 15 parts; again well mix, and keep the compound at a white heat for about twenty minutes; lastly, when cold, reduce the ‘residuum’ to an impalpable powder, wash it in pure water, and dry it.
4. Silver:—Bismuth and tin, of each 1 oz.; melt them together, and add of quicksilver, 1 to 11⁄2 oz.; when cold, powder it.