654 June 18, 



decrements in the conducting-power of impure and pure metals be- 

 tween and 100 C., M IOQO and M' 10()0 their conducting-powers at 

 100 C. ; F is for most metals 29'307) from 



p-^v^v a) 



For when we consider the last two terms of the proportion, and bear 

 in mind that a trace of another metal has very little or no effect 

 upon X' 10()0 (when it represents the conducting-power of an alloy 

 consisting of one metal with only a trace of another metal), while it 

 alters X I(K)O to a very marked extent, it is evident that \' IW > may be 

 replaced by M IOQO . 



We verify this by comparing the conducting-power of a pure 

 metal directly determined, with the conducting-power of the same 

 metal deduced from a determination of the conducting-power of its 

 alloy with small quantities of other metals. It is a curious fact, 

 that the deduced values from experiments upon hard-drawn wires 

 are in reality the conducting-powers of the annealed wire of the pure 

 metal. After having thus verified the method, we have not hesitated 

 to employ it in the determination of the conducting-power of certain 

 metals which have not yet been experimented upon in a state of 

 purity. 



In the fourth part we point out, first, that the percentage de- 

 crement in the conducting-power of alloys between and 100 is 

 never greater than that of the pure metals composing them ; secondly, 

 that the conducting-power of alloys decreases with an increase of 

 temperature (some bismuth alloys form an exception to this law) ; 

 thirdly, that in some cases the percentage composition of an alloy 

 may be deduced from its conducting-power, with the aid of the per- 

 centage decrement in its conducting-power; fourthly, the method 

 which we have used for determining the class to which the metals 

 belong in respect to the conducting-power of their alloys; and 

 fifthly, that the results which we have obtained and described in this 

 memoir fully bear out the views put forward in a former one on the 

 chemical nature of alloys. 



