Mk. Napier on Copper Sheaihing. 171 



Cornish ores, and in most of the Spanish and South American ores. Out 

 of twenty-one samples of sheet copper obtained in the market, the analyses 

 of which I have either made or seen, not one was entirely free from antimony, 

 and while some had only a trace, one sample had as much as one-half per 

 cent. Only three of these contained tin, two had sulphur, and none zinc. 

 From upwards of fifty commercial samples of ore from as many mines in 

 Cornwall and Devonshire, not one was free from antimony, and only fourteen 

 contained tin. However, the character of mines varies in a series of 

 years, ' and the ores obtained fifty years ago from these Iccalities may 

 have been purer. 



The absence of lead in any of the analyses given is another thing worthy 

 of remark. Mr. Prideaus mentions that a little lead is put into the 

 refining, but says it is only to scorify the tin, and reduce any suboxide, 

 but it does not remain in the copper. This is not the only reason for lead 

 being put into copper. Lead, where there is antimony, is essential to 

 enable the copper to roll. Copper with from three to five hundred of a 

 per cent, of antimony, would be hard and brittle without lead, but I have 

 seen copper with 0-65 per cent, of antimony having been made tough 

 to roll by lead, and in use as sheathing. Two analyses out of many will 

 suffice : — 



Hard copper would not roll. 



Copper, 99-40 



Iron, 0-10 



Antimony, 0'06 



Sulphur, trace 



99-56 



Copper in sheets saiil to roll well. 



Copper, 99-35 



Iron, -08 



Antimony, '15 



Lead, "H 



99-69 



Hero then the presence of antimony is not only bad in itself, but it neces- 

 sitates the addition of another impurity to it, and one I consider also 

 deleterious to sheathing. The external appearance also of the sheets favours 

 this view of the question. "Recent sheathing," says Mr. Prideaux, "is 

 complained of as being less smooth and compact than old sheathing;" 

 exactly what the presence of these alloys will give as they become scori- 

 fied on the surface during the annealing and rolling. " Good sheathing 

 becomes quickly covered with a thin scale or crust of green, which 

 adheres all over, and seems to remain. Bad sheathing keeps brighter, 

 or takes on a soft blue crust, with patches or edges of purple." These 

 are exactly wliat the experiments of Sir H. Davy, and the view here 

 taken of the subject, would lead us to expect from pure and alloyed 

 copper. 



I have also had my laboratory experiments, extending over many 

 months, and not yet complete, hoping to find some data to follow, but 

 so far as results have been obtained, I am still bound by the inferences 

 drawn by Sir H. Davy. I have taken all the published analyses of sea 

 water from different localities, and made up little quantities accordingly, 

 and submitted pieces of copper of the same quality to tiicir action. Tiic 



