129 



II. That copper containing 0'25 per cent, tin conducts better 

 than that containing 0*13 per cent., may also be explained by 

 assuming that they absorbed different amounts of suboxide during 

 the process of fusion ; for although tin, in presence of suboxide of 

 copper, would be oxidized, yet copper retains the suboxide so 

 tenaciously, that portions will always remain with the copper. 



III. The fact that the conducting powers of the alloy of coppqr 

 containing 0'25 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 j otherwise a much lower conducting power ought to 

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

 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 4 7' 6, it would require T4 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 copper 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- 



