Bell-Metal. The bronze of bells, or bell metal, is composed in 100 parts of 78 cop per and22 tin. This alloy has a fine com pact grain ; is very fusible and sonorous.
The other metals sometimes added are ra ther prejudicial; and merely increase the profit of the founders. Some of the Eng lish bells consist of 80 copper, 10.1 tin, 546 zinc, and 4.3 lead ; the latter metal, when in such large quantity, is apt to cause in sulated drops, hurtful to the uniformity of the alloy. A little phosphorus is some times added with advantage.
The Chinese gongs are composed of 78 parts copper, and 22 parts tin. This alloy ' when newly cast is as brittle as glass, but by being plunged at a cherry-red heat into cold water, and confined between two discs of iron to keep it in shape, it becomes tough and malleable. The Chi nese cymbals consist of 80 parts copper and 20 parts tin.
Common Metal consists of about 90 or 91 copper, and 9 or 10 of tin. Never less than 8 or more than 11 parts of tin in the 100 should be employed.
Speculum Metal. One part of tin and two parts (or more exactly 100 parts tin and 215 parts copper) form the ordinary speculum metal of reflecting telescopes, which is of all the alloys the whitest, the most brilliant, the hardest, and the most brittle. The alloy of 1 part tin and 10 of copper, is the strongest of the whole series. The bronze founder ought to melt his metals rapidly, in order to prevent the loss of tin, zinc, and lead, by their oxi dizement. Reverberatory furnaces have been long used for this operation, the best being of an elliptical form. The fur naces with dome tops are employed by bell founders, because their alloy being more fusible, they do not require so in tense a heat ; but they also world find an m advantage in using a more rapid mode of fusion. The surface of the melting met als should be covered with small charcoal or coke, and when the zinc is added it should be dexterously thrust to the bot tom of the melted copper. Immediately after stirring the melted mass so as to in corporate the ingredients, it should be poured out into the moulds. In general the metals most easily altered by the fire, as the tin, should be put in last. The coating should be as quick as possible in the moulds to prevent the metals separa thig from each other in the order of their destiny, as they are very apt to do so.
The addition of a little iron in the form of tin-plate, to bronze is reckoned to be ad vantageous.
Bronzing (of Objects in Imitation of Metallic Bronze). Plaster of Paris, paper, wood, and pasteboard, may be made to resemble pretty closely the appearance of articles of real bronze, modern or an tique. The simplest way of giving a brilliant aspect of this kind is with a var nish made of the waste gold leaf of the beater, ground up on a porphyry slab with honey or gum-water. A coat of drying linseed-oil should be first ap plied, and then the metallic powder put on with a linen dossil. Mosaic gold ground up with six parts of bone-ashes has been used in the same way. When it is to be put on paper, it should be ground up alone with white of eggs or spirit varnish, applied with a bnmsn, and burnished when dry. When a plate of iron is plunged into a hot solution of sul phate of copper, it throws down fine scales of copper, which being repeatedly washed with water, and ground along with six times its weight of bone-ashes, forms a tolerable bronze.
Powdered and sifted tin may be mixed with a clear solution of isinglass, applied with a brush, and burnished or not, ac cording as a bright or dead surface is de sired. Gypsum casts are commonly bron zed by rubbing brilliant blaek-lead, gra phite, upon them with a cloth or brush. Real bronze long exposed to the air gets covered with a thin film of carbonate of copper, called by virtuosi antique osrugo (patine antique, Fr).. This may be imita ted in a certain degree by several appli cations skilfully made. The new bronze being turned or filed into a bright surface, and rubbed over with dilute aequafortis by a linen rag or brush, will become at first grayish, and afterwards take a green ish blue tint; or we may pass repeatedly over the surface a liquor composed of 1 part sal ammoniac, three parts of carbo nate of potash, and 6 of sea salt, dis solved in 12 parts of boiling water, to which 8 parts of nitrate of copper are to be added; the tint thereby produced is at first unequal and crude, but it becomes more uniform and softer by time. A fine green-blue bronze may be obtained with very strong water of ammonia alone, rub bing it at intervals several times upon the metal.