Alloys by the aid of the Induction-balance. 59 



If the curves for Lead- Tin and Gold-Silver are compared 

 with those given by Matthiessen* for the same alloys, their 

 similarity will at once be evident. On the other hand, the 

 induction-balance curve of the Tin-Copper series, while bear- 

 ing some general resemblance to Matthiessen's curve of con- 

 ductivity, differs essentially from it in certain parts. Mat- 

 thiessen's curve falls rapidly from 93 (the conductivity of 

 pure copper) to 9 (that of the alloy containing 85 volumes 

 per cent, of copper). It then passes horizontally in a line which 

 is approximately straight to 13, the conductivity of Tin. 



Some light would appear to be thrown on the difference 

 between the two curves by the work of M. Alfred Richf on 

 the density of alloys of copper and tin. He showed that 

 copper and tin contract in alloying, the contraction being 

 regular from pure tin up to the alloy containing 38 per cent, of 

 tin, the density of which is higher than that of pure copper. 

 M. Rich's experiments were conducted on alloys both in the 

 form of powder and ingots ; the latter have alone been given 

 in the curve marked with his name on the Plate; and the rela- 

 tion between the two curves, especially at the points a, a f , b, 

 V, is too evident to need comment. 



It may ultimately prove that if the alloys were rolled or com- 

 pressed the curve would be modified; and, on the other hand, 

 further experiments on the conductivity of the alloys may 

 reveal points of identity between the conductivity and induc- 

 tion-balance curves; the part where the former from being 

 vertical becomes horizontal would be especially worth exami- 

 nation. It may be w r ell to point out that the alloys SnCu 3 

 and SnCu 4 , wmich occupy critical positions on the induction 

 curve, have been shown by M. Rich to be singularly free from 

 the disturbing influence of liquation. 



The work would appear to be interesting as showing that 

 the induction-balance may afford a simple means for detecting 

 variations in the molecular structure of alloys and for indica- 

 ting allotropy in metals with greater accuracy than has hitherto 

 been possible. 



Practical application. — The possibility of ascertaining the 

 standard fineness of alloys by the aid of electricity long ago 

 occupied the attention of physicists. In 1823 M. BecquerelJ 

 suggested that trustworthy indications might be afforded by 

 the electromotive force developed when the alloy is placed in 

 an exciting fluid, together with an alloy of known composition. 



* Op. cit. p. 46, and Watts's Dictionary of Chemistry, vol. iii. p. 943. 

 t Ann. de Cliimie et de Phys. tome xxx. 1873. 

 \ Ibid, txxiv. p. 343(1823). 



