170 



* JOO, they have obtained the relative conducting powers of the fol- 

 lowing metals : 



Silver ................ 1000 



981 

 840 



Copper, rolled ........ 845 



Copper, cast ....... ... 811 



Mercury .............. 677 



Aluminium ............ 665 



Zinc, forged .......... 641 



Zinc, cast vertically .... 628 



Forged iron 436 



Tin . 422 



Steel 397 



Platinum 379 



Sodium 365 



Cast iron 359 



Lead 287 



Antimony, cast horizontally 215 



Antimony, cast vertically 192 



Bismuth. . 61 



Zinc, cast horizontally . . 608 

 Cadmium 5 78 



The precision obtained by this process is such, that the authors 

 were able to determine the different conducting powers of the same 

 metal, when rolled or cast, as shown above. They were also able to 

 appreciate the influence of crystallization on conductibility, for they 

 found that the conducting power of a metal was different when it was 

 cast horizontally or vertically, from the different directions which the 

 axes of crystallization took under these circumstances. 



The importance of having the metals as pure as the resources of 

 chemistry allow, is shown by the action which one per cent, of im- 

 purity exerts on the conductibility of a metal, in some cases reducing 

 it one-fifth or one-fourth. Copper alloyed with one per cent, of various 

 metals gave different conducting powers, in the same manner as Mr. 

 Thomson has shown that the conduction of electricity by the same 

 metal is affected by a similar amount of impurities. 



Alloying a metal with a non-metallic substance also exerts an in- 

 fluence, as is shown in the case of the combination of iron with 

 carbon, thus 



Forged iron 436 



Steel 397 



Cast iron 359 



Similar results were obtained by combining small proportions of 

 arsenic with copper. 



The authors, with a view of ascertaining whether alloys are simple 

 mixtures of metals, or definite compounds, made a large number of 



