302 



constituents also is comparatively small. I should, however, state 

 that the analytical results which I have given do not exclude the 

 presence of exceedingly minute quantities, even of other metals which 

 might have been detected if larger quantities of copper could have 

 been submitted to analysis. Some years ago, Max Duke of Leuch- 

 tenberg* examined the black precipitate formed at the anode in the 

 electrotype process, during the decomposition of sulphate of copper 

 by the galvanic current. In this precipitate, of which considerable 

 quantities accumulate by the gradual solution of large quantities of 

 copper passing through the process, he found the following consti- 

 tuents : 



Antimony 9 -22 



Arsenic 7'40 



Platinum O44 



Gold 0-98 



Silver 4-54 



Lead . 0-15 



Iron 0-30 



Nickel 2-26 



Cobalt 0-86 



Vanadium 0'64 



Tin 33-50 



Copper 9-24 



Oxygen 24*82 



Sulphur 2-46 



Selenium 1'27 



Sand .. 1-90 



" Of these constituents, the ten first metals were obviously derived 

 from the copper, in which they could have been scarcely detected 

 unless by this accumulative process. Of the remainder of the con- 

 stituents, the tin in a great measure is derived from the solderings. 



" The results obtained in the analysis of the copper wires which you 

 forwarded to me, appear to establish one fact in a satisfactory manner, 

 viz. that the diminution of conductivity observed in certain specimens 

 of copper is due to the presence in these specimens of a certain 

 amount of foreign matter, and not, as it has been supposed, to a 

 peculiar change in the physical condition of the metal ; for in the 

 specimens analysed the conductive power rises in the same order as 

 the total amount of impurities diminishes. 



" I have, &c., 



(Signed) "A. W. HOFMANN." 



"Professor William Thomson, F.R.S., fyc." 



It appears therefore that in the case of these four specimens, the 

 electric conductivity is in order of purity of the copper ; but yet 

 that only extremely small admixtures of other substances are to be 

 found even in those which have but half the conductivity of the 

 best. 



* Petersburg!! Acad. Bull. vii. p. 218. 



