382 



Royal Society . 



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 



Silver 1000 



Golcl,|afo (J81 



Gold,^^!^ 840 



Cojjper, rolled 845 



Copper, cast 811 



Mercury 677 



Aluminium 665 



Zinc, forged 64 1 



Zinc, cast vertically .... 628 



Zinc, cast horizontally . . 608 



Cadmium 5 78 



The precision obtained b)'' 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 vertical^, 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 combinition 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 

 alloys of various metals, using equivalent proportions, and determined 

 their conducting powers. The general result obtained is, that alloys 

 may be classed under the three following heads : — 



1st. Alloys which conduct heat in ratio with the relative equiva- 

 lents of the metals composing them. 



2nd. Alloys in which there is an excess of equivalents of the worse 

 conducting metal over the number of equivalents of the better con- 

 ductor, such as alloys composed of ICu and 2Sn ; ICu and 3Sn; 

 ICu and 4Sn, &c., and which present the curious and unexpected 

 result that they conduct heat as if they did not contain a particle of 

 the better conductor ; the conducting power of such alloys being the 

 same as if the square bar which was used in the experiments were 

 entirely composed of the worse conducting metal. 



3rd. Alloys composed of the same metals as the last class, but in 



J 



