(_c_). _Alloy for the Chinese gong, cymbals, &c._ An alloy formed of 100 parts copper and 23 tin, appears from Dussaussoy’s experiments to form the compound of minimum density. It is used for making cymbals; and nearly accords with the composition of the Chinese gong. It is formed of 4 atoms of copper and 1 of tin. The Chinese gong analysed by Klaproth was composed of 100 copper and 28.2 tin; that by Dr. Thomson of 100 copper and 23.4 tin. (_d_). _Common bell-metal used for casting bells._ This alloy is commonly made of 3 parts copper and 1 of tin; but to be in due proportion for 3 atoms of copper and 1 of tin, it should be formed of 100 copper and 31 tin. It is hard, of a white colour, less malleable than the preceding alloys, and more sonorous. A specimen I analysed consisted of 100 copper and 36 tin. The exact proportion of 100 copper and 31 tin is not essential to produce a sonorous alloy. (_e_). _Speculum metal._ This compound has been investigated with great care by opticians. According to Mr. Mudge the best proportion is 32 parts copper to 14.5 tin, but Mr. Edwards finds 15 parts tin, 1 brass, 1 silver and 1 arsenic. The slightest variation in the proportions of copper and tin impairs the metal. The alloy is white, hard and close grained; it takes a beautiful polish. The use of the minute portions of zinc, silver and arsenic is perhaps to correct the colour of the alloy; though it seems in several alloys that very minute portions of metals apparently foreign to the alloy, improve the density and texture of the metal. It is remarkable with what precision this alloy accords with the atomic combinations of 2 copper with 1 tin. By calculation 32 copper would require 14.8 tin. Mr. Mudge finds 32 copper to 14½ tin, and observes that if ½ a part more of tin be added the metal is too hard. Mr. Edwards indeed says 32 copper and 15 tin; but then he adds 1 part brass, which containing ⅔ of a part of copper, it reduces his proportion to 32 copper and 14.7 tin, almost exactly that required by the theory. When 32 copper and 13½ tin are combined, Mr. Mudge asserts the metal is too soft.[21] [Footnote 21: This author obtained the Royal Society’s gold medal for his essay on the composition, &c. of specula for telescopes. Philos. Transact. 1787.] (_f_). _Copper and tin, equal parts._ This alloy is of blueish white colour, and of no particular use that I am acquainted with. It consists of the union of 1 atom of copper with 1 of tin. The other alloys of copper with a higher proportion of tin appear to be uninteresting, and have not been objects of much attention. * * * * * Not having an opportunity of forming these alloys synthetically, I contented myself with the analysis of several of them.