Bronze

[Fr.] ( Metal.) An alloy of copper and tin, to which are sometimes added small portions of zinc and lead. Gun, bell, and speculum metal partake much of the nature of bronze. The manufacture of bronze is very ancient, having been brought to a considerable state of refinement 700 years before the Christian era. The ancients used it for weapons and tools, on account of its great hardne ; but it was at length superseded for these purposes by steel, and is now only employed for statuary and medals. For the former purpose, bronze is particularly well fitted, being tough, hard, and little affected by atmospheric influence, besides po e ing the valuable property of flowing freely when melted, and expanding when solidifying; by which means the most intricate detail in the mould is copied with sharpne . Bronze may be tempered in an exactly contrary manner to steel. If cooled suddenly, it becomes so soft that it may be hammered and turned in the lathe; but if allowed to cool slowly, it becomes brittle, hard, and elastic. In casting large statues or other works, the greatest skill and care are nece ary, from the circumstance that alloys of copper and tin have a tendency, when melted, to separate, the tin rising to the top of the melted ma , and forming a more fusible mixture. From the following analyses, it will be seen that bronze differs greatly in composition: - Ancient bronze from Celtic antiquities, - tin, 12; copper, 88. Egyptian bronze, tin 22; copper, 78. Chinese bronze, - tin, 20; copper, 80. Roman bronze, - tin, 15; copper, 85. Modern bronze from the statue of Louis XV.-copper, 82-45; zinc, 10-30; tin, 4-10; lead, 3:15. See SEC. II. Bronze, v. a. To color, harden, or give a superficial appearance to, as of bronze. -To make hard in a manner of feeling; to brazen. Bronze, AGE OF. ( Geol .) See STONE, (AGE OF.) Bronze-powder, n . See BRONZING. Bronzing, n. (Applied Chem.) The proce of covering plaster or clay figures, and articles in ivory, metal, and wood, so as to communicate to them the appearance of ordinary bronze. The materials usually employed for B. are termed Bronze powders . - The base of most of the secret compositions for giving the antique appearance is vinegar with sal-ammoniac. Skilful workmen use a solution of 2 ounces of that salt in a quart of French vinegar. Another compound which gives goo a results is made with an ounce of sal-ammoniac, and 14 ounce of salt of sorrel (bin oxalate of potash), di olved in vinegar. The piece of metal being well cleaned, is to be rubbed with one of these solutions, and then dried by friction with a fresh brush. If the hue be found too pale at the end of two or three days, the operation may be repeated. It is found to be more advantageous to operate in the sunshine than in the shade. In B. plaster figures a cement may be used or not; if used, the B will be more durable; the powders are mixed with strong gum-water or isingla , and laid on with a pencil. The subject may be covered with gold-size diluted with turpentine, and when nearly dry, rubbed with a piece of soft leather. - Copper coins and medals may be bronzed thus: di olve in vinegar two parts of verdigris and 1 part sal-ammoniac. Boil, skim, and dilute the solution with water until it ceases to let fall a white precipitate. The solution is then boiled and poured upon the objects to be bronzed, being previously made perfectly clean and free from grease; the articles are then washed and dried. - A deposit of bra or bronze may be thrown on objects by the electrotype proce , by employing a solution of 500 parts carbonate of potash, 20 parts chloride of copper, 40 parts sulphate of zinc, 250 parts nitrate of ammonia. - Dr. Wagner published in 1868 the formulas of metallic bronze powders that give the most favorable results. The metals employed are, for the most part, copper and zinc, an alloy of the two being reduced to an impalpable powder. The proportions are given as follows: for a bright yellow shade, 83 parts of copper, and 17 of zinc; for an orange shade, 90 to 95 of copper, and 5 to 10 of zinc; for copper red, 97 to 99 of copper, and 1 to 3 of zinc. Bronz'ing-liquid, n . ( Applied Chem.) A solution containing chloride of antimony and sulphate of copper, used for bronzing iron gun-barrels. Bra is sometimes bronzed by washing it over with a solution of chloride of platinum.