202 Intelligence and, Miscellaneous Articles. 



A METHOD OF DETECTING CHEMICAL UNION OF METALS. 

 BY DR. G. GORE, F.R.S. 



It is well known that evolution of beat during the mixing of two 

 substances is a sign of chemical union ; that considerable heat is 

 evolved during the melting together of certain metals, for instance 

 zinc and platinum ; and M. J. Regnauld has shown that whilst 

 zinc, during its amalgamation by mercury, absorbs heat and becomes 

 more electropositive, cadmium by amalgamation evolves heat and 

 becomes less electropositive (Comptes Renclus Acad. Sci. June 10, 

 1878 ; Chemical News, vol. xxxviii. p. 33). 



Having already found in a large number of instances that the 

 chemical union of two soluble substances, such as halogens, acids, 

 salts, &c, might be detected by the depression of voltaic energy which 

 occurs when the two dissolved substances are in the proportions of 

 their ordinary chemical equivalents (see Proc. Roy. Soc. vol. xlv. 

 p. 265; "Examples of Solution-compounds," Proc. Birm. Phil. 

 Soc. vol. vii. p. 33 ; Chemical News, 1890, vol. Ixi. p. 172), I 

 have adopted a similar method in this case, and have made a series 

 of experiments to ascertain the relative amounts of voltaic energy 

 in a one-per-cent. aqueous solution of common salt, of a series of 

 amalgams composed of different proportions of cadmium and mer- 

 cury, and observed whether there was a distinct depression of that 

 energy indicating chemical union, when the particular amalgam 

 composed of equivalent weights of the two metals was employed. 



As I had previously found that the amalgam changed in electro- 

 motive force spontaneously, in order to balance this influence, I 

 employed, instead of a voltaic couple composed of platinum and one 

 bar of a series of bars of different composition, a couple composed of 

 a bar of fixed composition formed of the two metals in the propor- 

 tions of their equivalent weights, and one bar of a series of bars of 

 different composition. The two bars in each experiment were con- 

 nected with an ordinary torsion-galvanometer of 50 ohms resist- 

 ance, and the amount of permanent deflexion of the needles after 

 about half a minute was recorded. This method was found suffi- 

 ciently sensitive for the purpose. The composition of the bars of 

 varied composition is shown below 7 by the chemical formulae. 



After some preliminary experiments, the results of w T hich agreed 

 with those given, the following series was made : — 



Voltaic couple. 



Deflexion. 



CdHg 



with Cd 



+ 5 



>? 



55 



Cd„Hg 10 



\ 3-3 



55 



55 



Cd 15 H gl0 



\ 3 



55 



55 



Cd 13 H gl „ 



\ 1 



,, 



55 



Cd 12 Hg 10 



\ 1 



55 



55 



Od 10 Hg 10 



S ° 



55 



55 



Cd I0 Hg 12 



\ + 4 



5? 



55 



Cd 10 Hg 13 



\ - 2 



55 



55 



Cd„Hg, 



\ ~ 9 



55 



55 



Cd 10 Hg 17 



\- 4 



55 



55 



Hg 



-5 to 6 



