200 Dr. Matthiessen on Standards of Electrical Resistance, 



intend trying whether the conducting power of mercury when 

 solid is increased or decreased by the addition of traces of other 

 metals. 



To prove the assumption I have made as to the behaviour of 

 the third class of metals is probably correct, I have given in 

 Table V. some experiments. 



Table V. 

 Taking the conducting power of the hard-drawn gold-silver 

 alloys at 0°= 100, — Calculated 



conducting 

 power. 



Pure mercury conducts 24*47 at 18 C. 



alloyed with 0-1 per cent, pure 1 24 . 5g a( . lg . 6 24 . 46 



bismuth ) 



„ 001 per cent, pure tin 24-51 at 18-4 2450 

 „ 002 „ 24-54 at 18-0 24-52 



„ 0-05 „ 24-63 at 18 2 24-61 



„ 0-1 „ 24-76 at 18-8 2475 



„ 0-2 „ 25-04 at 190 25-02 



„ 0-5 „ 25-86 at 18-4 25"83 



„ 1-0 „ 26-62 at 18-6 27*19 



„ 20 „ 27-66 at 18-8 29-19 



„ 4-0 „ 29-69 at 19-0 35-09 



For the calculations, the conducting power of tin was taken at 

 172-09, that of bismuth 17'88; the specific gravity of mercury 

 13-573, that of bismuth 9*823, and that of tin 7"294. 



The resistances of the amalgams were determined in the same 

 tube as the mercury, so that any error in the measurement of the 

 length or diameter will not have any influence on the relative 

 values obtained. 



From the above Table we see that even bismuth, a worse con- 

 ductor than mercury, increases the conducting power of mercury, 

 as would be expected from the above assumption. The experi- 

 ments with the amalgams show how important it would be, if 

 mercury were to be taken as unit for determinations of resistances, 

 that it should be absolutely chemically pure. We cannot be 

 surprised to find discrepancies in the values obtained for mercury 

 by different observers, when such small traces of impurity so 

 materially affect its conducting power. 



7. Page 103 (2nd paper), M. Siemens gives a Table, from 

 which he deduces that the increase in the resistance of mercury 

 between 0° and 100° C. is in direct ratio with the increase of 

 temperature. In other words, M. Siemens assumes that the 

 formula 



w = l -\-at 

 expresses the resistance of mercury at any temperature between 

 0° and 100°. Let us now calculate from his results the values 



