ON METALS. 289 



to be added*. It may in general be observed, that a less proper, 

 tion of tin is used for making church bells than clock bells, and 

 that they add i liitl, zinc for the bells of repeating watches and 

 other small hell*- This zinc becomes manifest on melting these 

 bells, by the blue flame which it <xhibits. 



There is a very remarkable experiment mentioned by Glaubert. 

 " Make." says he, u two balls of copper, and two of pure tin 

 not mix d with lead, of one and the same form and quantity, the 

 weight of which balls observe exactly ; which done, again melt 

 the aforesaid halls or bullets into one, and tirst the copper, to 

 which malted n.hi the tin, let much tin evnporate in the m- King, 

 and pre-<emi\ 1.0 >r out f he mixture melted into the mould of the 

 first balls, ami there will not come forth four, nor scarce three 

 balls, the weight of the four ball" lv ing resrvd." This subject 

 has been prosecuted since Glau'ter s tiinet, and it has been c'i-co- 

 vered, that when metallic substances are melted to.Hh r, it seldom 

 happens that a cul'ic inch of each of the two ingredients will form, 

 a mass exactly equal to two cubic inches ; the mixture will in some 

 instances be greater, and in other less than two cubic inches. In 

 the instance of t'n and copper, where the bulk of the mixture is 

 so much less than the sum of the bulks of the two component parts, 

 it might be expected that the compound metal would possess pro. 

 pcrties, not mere'y intermediate between those of copper and tin, 

 but essentially different from them both. And accordingly we find, 

 that this mixture is not only more brittle, more hard, and more 

 sonorous, than either copper or tin; but it is more dense also, 

 than either of them ; a cubic foot of it weighing, not only more 

 than a cubic foot of tin, but than a cubic foot of copper itself. 



Pot-metal is made ot copper and lead, the lead being one.fourth 

 or one-fifth the weight of the copper. In Pliny's time pot. metal 

 (ollaria temperatura) was made of a pound and a half or two 

 pounds of lead, and an equal portion of tin, mixed with 100 parts 

 of copper. Copper and lead seem not to be combined together 

 in the same way that copper and tin are ; for when pot. metal is 

 exposed to a melting Ktat, the lead is first fused, and shews itsetf 



* Waller. Min.r. vol. II. p. 842. New Chem. by Lewis, p. 66. Macq. 

 Cbcm. vol. I. p. 70. En<. Tran-.. 



+ Glaober's \Vork-, fol. ed. 1689, p. 81. 



f Gelh-rt'i Cliy. Metal. & Chem. Diet. art. Allay. 



VOL. TI. U 



