The alloys of copper and tin are commonly called _bell-metal_; but they receive more particular names according to the purposes for which they are destined, as _bronze_, _speculum metal_, _gun-metal_, &c. those of them which are yellow are frequently confounded in common language with brass, as _brass guns_, &c. Indeed the ancient Greeks and Romans seem to have been in possession of these two alloys, under one and the same name. The =χαλκος= of the Greeks, being used for cutting-instruments, must have signified _bell-metal_, or the alloy of copper and tin as well as brass, as indeed is proved by the analysis of them. The _æs_ of the Romans seems also to have included the same compound. Ancient copper coins too are usually found to contain tin. Tin united to copper in certain proportions gives a surprising degree of hardness and tenacity to the alloy, much superior in these respects to either of the ingredients. In other proportions it makes the compound highly sonorous, as in _bell-metal_ properly so called. Tin also increases the fusibility of the compound in proportion as it abounds, being itself fusible at the low temperature of 440° Fahrenheit. The principal varieties in the alloys of copper and tin are enumerated below, beginning with those in which the copper is most abundant. The atom of copper is taken at 56 and that of tin at 52 weight, the hardness of these metals is denoted by 7.5 and 6 respectively, by Kirwan. (_a_). _Gun-metal._ The alloy for brass guns or cannon is made of 100 parts of copper and 11 or 12 of tin. A small portion of iron is found to improve the metal; this is best added in the state of tin-plate, as it more readily fuses and unites with the metal.[20] This compound is hard and extremely tenacious, exceeding in this respect any other alloy of the two metals. The addition or subtraction of 1 or 2 parts of tin materially impairs the tenacity of the alloy. It is constituted of 8 atoms of copper and 1 of tin. [Footnote 20: See a very excellent essay on the alloy of copper and tin by M. Dussaussoy, in the Annales de Chimie & Physique. 5--113.] (_b_). _Alloy for edge tools, printers’ cylinders, &c._ The best proportion for this compound seems to be 100 parts copper and 15 or 16 tin. When hammered and tempered duly it is fit for making edge tools not inferior to some kinds of steel. It is a compound of greater density than the preceding, though containing more tin; the grain is fine and the metal free from blisters and suited for turning in the lathe. It seems to be the best alloy of the kind for printers’ cylinders; but an analysis which I lately made of some turnings from one of these cylinders gave me much less tin than the above proportion. The alloy (_b_) is constituted of 6 atoms of copper and 1 of tin.