548 Royal Society : — 



containing - 25 per cent, lead approaches the nearest of those which 

 I analysed to that of pure copper, is, in my opinion, a proof that the 

 alloy is probably a mechanical mixture of copper, traces of lead, and 

 enough suboxide to allow its being drawn into wire, and not a solution 

 of lead in copper ; otherwise a much lower conducting power ought to 

 have been found ; for, according to my own experiments, it recjuires 

 twice as many volumes per cent, of lead as of tin to reduce (within 

 certain limits) the conducting power of a metal (bismuth, silver, 

 &c, and copper, for it belongs to the same class) to the same value : 

 thus, to reduce the conducting power of silver to 67, it would require 

 0*9 volume per cent, of lead, or about 0*4 volume per cent, of tin; 

 to reduce it to 47'6, it would require 1*4 volume per cent, of lead, 

 or 0*7 volume per cent, of tin, &c. (Phil. Trans. 1860). Dr. Holz- 

 mann and myself repeatedly tried to draw pure copper alloyed with 

 0'25 of lead without success ; the alloy was perfectly rotten, which 

 also seems to indicate a mechanical mixture. 



IV. It is curious that the zinc alloys contained no suboxide. 



The reason, therefore, of the difference in our results is simply 

 that Messrs. Johnson and Matthey did not use those precautions in 

 fusing their copper and its alloys which are necessary to ensure good 

 results ; for had they taken those precautions to prevent the absorp- 

 tion of oxygen by their copper and its alloys which Dr. Holzmann 

 and myself did, and which are fully described in our paper on the 

 subject (Phil. Trans. 1860), the lead-copper alloys which they sup- 

 plied to Prof. Thomson would not have been superior in conductive 

 quality to the unalloyed electrotype copper ; and he would have 

 been led to the same conclusion as that which Dr. Holzmann and 

 myself arrived at, namely, that there are no alloys of cojrper which 

 conduct better than pure copper. Professor Thomson, in his paper, 

 states that it is his opinion that the differences he observed in the 

 conducting powers of his alloys must depend upon very small ad- 

 mixtures of probably non-metallic impurities. This conclusion is 

 completely borne out by the above, as well as by the investigation 

 carried out by myself in conjunction with Dr. Holzmann. 



The results obtained by Prof. Thomson show the marked influ- 

 ence of traces of foreign metals on the conducting power cf pure 

 copper, — which is fully confirmed in our research on the same 

 subject. Professor Thomson's best-conducting alloy has a much 

 higher conducting power than those found by some experimenters 

 for electrotype copper ; but it must be remembered that in all pro- 

 bability the copper had been previously fused, and therefore con- 

 tained suboxide of copper. The fact that electrotype copper may be 

 drawn without having been previously fused is, I believe, generally 

 not known ; Professor Buff of Giessen first drew my attention to it, 

 and stated that he always obtained high values for the conducting 

 powers of electrotype copper when drawn without previous fusion. 

 I can confirm this statement, having tested a great many specimens, 

 and found the values in all cases nearly the same. 



