CHEMISTRY. 251 



These results require little comment. "We have seen that pure copper alone 

 dissolves more rapidly in sea water than alloyed copper ; but if ;t be brought 

 into contact with a negative piece of copper, in which state copper alloys are 

 in relation to pure copper, then the pure copper will dissolve much more 

 rapidly with some of these alloys, to an extent of 33 per cent., which would 

 be very destructive upon a vessel if a mixture of pure and impure sheets were 

 used. However, looking upon these small laboratory experiments only in the 

 light of a finger-post. I shall pause to inquire what others have said and 

 found in similar inquiries and practice. 



A correspondent of the Mining Journal, commenting upon the subject of 

 sheathing two or three years ago, makes the following judicious remarks and 

 observations: 



"With your permission I will state some facts, which show that fine pure 

 copper is not the best adapted for the purpose under consideration. The cop- 

 per formerly produced in Anglesey is truly stated to have been pure and duc- 

 tile, but it proved to be very inferior when applied to sheathe ships so much 

 so, that a house in Liverpool who manufactured and sold this copper got into 

 great disrepute with shipowners on that account, so that they were obliged to 

 use Cornish copper, or at least a mixture of it, for sheathing. 



" Above twenty years ago, when the first copper of the Bolivar Mines was 

 smelted in this country, it was found to be very pure and malleable, and com- 

 manded a comparatively high price for export to the continent of Europe. 

 This copper was also applied by another Liverpool house for sheathing ships, 

 for which purpose it proved entirely unfit. The wear was so rapid that hi 

 about half the usual time the sheets were reduced to little more than a 

 tissue. 



" Here, then, are two well defined instances where copper of the purest de- 

 scription has signally failed when applied to sheathing ships. A curious cir- 

 cumstance connected with the Anglesey copper was related to me by a party 

 interested. A buoy, sheathed with this copper, was placed in the run of the 

 tide hi the Menai Straits, opposite the mansion of the noble proprietor of the 

 mines ; and this sheathing wore comparatively well, notwithstanding the fric- 

 tion of an almost constant strong current ; but sheathing made at the same 

 time, .from ffie same copper, and placed on the ship's bottom with the same nails, 

 wore unsatisfactorily. Knowing these facts, I am of opinion that copper so 

 pure and so ductile and malleable, as to be prized for other purposes, is not 

 the best for sheathing ships ; and that the assertions of shipowners, when they 

 meet with copper that has worn unsatisfactorily, that it was inferior and im- 

 pure, are the reverse of truth." 



In the Comptes Bendus we have the opinion of one of our continental 

 chemists upon this question of sheathing : 



"M. Bobierre has paid considerable attention to this subject, and has 

 arrived at the following conclusions as to the cause of the rapid destruction of 

 some copper and bronze sheathing: 1. "When unalloyed copper is employed, 

 the presence of arsenic appears to hasten its destruction. 2. All bronzes 

 which appear to have stood well contained from 4|- to 5^- per cent, of tin, that 

 quantity being necessary to form a homogeneous alloy. "When the per- 



