BKONZE 537 



The alloys most proper for bronae to be afterwards struck for medals is composed 

 of from 8 to 12 parts of tin and from 88 to 92 of copper; to which if 2 or 3 parts in 

 the hundred of zinc be added, they will make it assume a finer bronze tint. The alloy 

 of the Kellers is famous for this effect. The metal should be subjected to three or 

 four successive stamps of the press, and be softened between each blow by being heated 

 and plunged into cold water. 



The addition of a small proportion of phosphorus has recently been recommended 

 to improve the quality of bronze. 



The bronze of bells, or bell-metal, is composed, in 100 parts, of copper 78, tin 22. 

 This alloy has a fine compact grain, is very fusible and sonorous. The other metals 

 sometimes added are rather prejudicial, and merely increase the profit of the founders. 

 Some of the English bells consist of 80 copper, lO'l tin, 5'6 zinc, 4'3 lead; the latter 

 metal, when in such large quantities, is apt to cause isolated drops, hurtful to the 

 uniformity of the alloy. 



The Tam-tams and Cymbals of Bronze. The Chinese make use of bronze instru- 

 ments forged by the hammer, which are very thin and raised up in the middle ; they 

 are called gongs, from the word tshoung, which signifies a bell. Klaproth has shown 

 that they contain nothing but copper and tin, in the proportion of 78 of the former 

 metal and 22 of the latter. Their specific gravity is 8-815. This alloy, when newly 

 cast, is as brittle as glass ; but 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 cymbals consist of 80 parts copper and 20 tin. 



Bronze vessels, naturally brittle, may be made tenacious by the same ingenious 

 process, for which the world is indebted to M. Darcet. Bronze mortars for pounding 

 have their lips tempered in the same way. 



Cannon Metal consists of about 90 or 91 copper, and 10 or 9 of tin. From the ex- 

 periments of Papacino d'Antony, made at Turin, in 1770, it appears that thf most 

 proper alloy for great guns is from 12 to 14 parts of tin to 100 of copper; 'but the 

 Comte Lamartilliere concluded, from his experiments made at Douay, in 1786, that 

 never less than 8 nor more than 11 of tin should be employed in 100 parts of 

 bronze. 



Gilt Ornaments of Bronze. This kind of bronze should be easy of fusion, and take 

 perfectly the impression of the mould. The alloy of copper and zinc (brass) is, when 

 fused, of a pasty consistence, does not make a sharp cast, is apt to absorb too much 

 amalgam, is liable to crack in cooling, and is too tough or too soft for the chaser or 

 turner ; and if the quantity of zinc was increased, to make the metal harder, it would 

 lose the yellow colour suitable to the gilder. A fourfold combination of copper, zinc, 

 tin, and lead is preferable for making such ornamental bronze articles ; and the 

 following proportions are probably the best, as they unite closeness of grain with 

 the other good qualities. Copper 82, zinc 18, tin 3 or 1, lead 1 or 3. In the 

 alloy which contains most lead, the tenacity is diminished and the density is in- 

 creased, which is preferable for pieces of small dimensions. Another alloy, which is 

 said to require for its gilding only two-thirds of the ordinary quantity of gold, has the 

 following composition : copper 82'247, zinc 17'481, tin 0'238, lead 0'024. 



The antique bronze colour is given to figures and other objects made from these 

 alloys by the following process : Two drachms of sal-ammoniac, and half a drachm 

 of salt of sorrel, (binoxalate of potash,) are to be dissolved in fourteen ounce measures 

 (English) of colourless vinegar. A hair pencil being dipped into this solution, and 

 pressed gently between the fingers, is to be rubbed equally over the clean surface of 

 the object slightly warmed in the sun or at a stove ; and the operation is to be repeated 

 till the wished-for shade is obtained. 



The bronze founder ought to melt his metals rapidly, in order to prevent the loss 

 of tin, zinc, and lead by their oxidisement. Eeverberatory furnaces have been long 

 used for this operation, the best being of an elliptical form. The furnaces with dome 

 tops are employed by the bell founders, because, their alloy being more fusible, they 

 do not require so intense a heat; but they also would find their advantage in using 

 the most rapid mode of fusion. The surface of the melting metals should be covered 

 with small charcoal or coke ; and when the tin is added, it should be dexterously thrust 

 to the bottom of the melted copper. Immediately after stirring the melted mass so 

 as to incorporate its 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 

 cooling should be as quickly as possible in the moulds, to prevent the risk of the 

 metals separating from each other in the order of their density, as they are very apt 

 to do. The addition of a little iron in the form of tin plate to bronze, is reckoned 

 to be advantageous. 



One part of tin, and two parts of copper (nearly one atom of tin and four of 





