460 On the Conducting Power of Mercury, 



It is not improbable that the metals combine with mercury 

 in atomic proportions, and, in this event, that the resulting 

 compounds are dissolved in the overplus of mercury. 



Such a combination would undoubtedly modify the distances 

 of the compound atoms, and hence also the conductibility of the 

 mass. The conductibilities of tin, zinc, gold, and silver-amal- 

 gams from the tests in question show an expansion of the 

 molecules, those of lead and bismuth a contraction, supposing 

 that expansion of the molecules causes a decrement, and con- 

 traction an increment of conductibility. 



In adopting the opinion of a chemical combination and sub- 

 sequent solution, the very conditions prohibit the adoption of a 

 common formula which shall express with exactitude, for every 

 metal, its amalgam conductibility, unless that formula embody 

 a term embracing the effect of the combination and solution on 

 the atoms and density of the resulting compound, although the 

 formula which combines the conductibilities of the metals in a 

 fluid state, without being absolutely correct, is near enough 

 with some metals, when the per-centage of foreign metal in the 

 amalgam is not too great. And a more exact knowledge of the 

 nature of the atoms and of the origin of electrical resistance is 

 necessary before such a formula can be constructed. 



In these considerations I have supposed the methods em- 

 ployed by Drs. Matthiessen and Vogt, as well as their measure- 

 ments, to be correct. 



It is doubtful, however, if the thermometer-tubes employed 

 were not necessarily of so small a bore that filtration of poorer 

 amalgam into the tube while thicker remained in the cups was 

 not facilitated. Thus the known proportions of the mixture 

 poured into the cups would not have given a correct idea of the 

 contents of the amalgam in the tube, and the conducting powers 

 of the richer amalgams would have appeared lower than they 

 really were. 



It is also questionable if Drs. Matthiessen and Vogt have not 

 relied too much on the weights of the metals used in making up 

 the amalgams instead of analysing the latter after each test ; for 

 it is well known that amalgams of the easily oxidizable metals 

 change their proportions when in contact with the air by rapid 

 oxidation of the foreign metals. 



I diminished these sources of error by employing tubes of, at 

 least, 2 millims. diameter, and by analysing the contents of each 

 tube after each test, disregarding entirely the contents of the cups, 

 which were made removeable. 



94 Markgrafen Strasse, Berlin, 

 20th April, 1862. 



