252 ANNUAL OF SCIENTIFIC DISCOVERY. 



centage of tin is only 2'5 to 3*5, which, is very frequently the case, no definite 

 alloy is produced, and the mass is of unequal composition, and being 

 unequally acted upon, is soon destroyed. 3. "When impure copper is em- 

 ployed the alloy is never homogeneous, and is unequally acted upon in con- 

 sequence. We thus see that the so frequent destruction of the sheathing of 

 copper-bottomed vessels arises from the tendency to use inferior brittle cop- 

 per, and by diminishing the proportion of tin, to economize the difference 

 between the price of that metal and copper, at the same time that the cost 

 of rolling is also less, in consequence of the greater softness of the poor alloy. 

 Bobierre thinks that the addition of a very small portion of zinc very much 

 improves the bronze, by producing a more perfect and uniform distribution of 

 the positive metals, and consequently a much more definite alloy." 



It will be seen, however, that the above refers more to a certain quality of 

 bronze for sheathing than copper. 



For experiments of a different kind, we take the following from Sillirnan's 

 Journal : 



Copper Sheathing. Some interesting experiments on this useful branch of 

 the manufacture of copper have been made in the United States. Some which 

 had resisted the action of sea water for a considerable period were found to 

 contain no less than one ten-thousandth part of silver ; this was found sen- 

 sibly to modify the chemical relations of the metal, and observations had 

 indicated that the quality for sheathing was improved. The subject was 

 resumed again, when the argentiferous native copper of Lake Superior was 

 first rolled by the Eevere Copper Company ; the alloy contained four parts of 

 pure silver, or about 4 Ibs. of silver per ton. A proximate analysis of the 

 metal was taken, and it proved to be pure copper, throughout the mass of 

 which an alloy of copper and silver was evenly distributed, thus forming 

 either a mixture or compound alloy, in which one part of the copper is truly 

 combined with the silver, and the other larger part simply combines with the 

 alloy. It was assumed that the silver alloy would close the pores of the 

 copper and confer durability. If corrosion took place, it was in accordance 

 with observed cases that the silver alloy would act as a negative element, 

 and the copper alone would be removed. These inferences proved erroneous, 

 as the following results will show: The Chicora was coppered in January, 

 1847, taking 7,392 Ibs. of metal; she was employed in the China trade, but 

 wore her copper so rapidly that she was removed in March, 1849, 2,682 Ibs- 

 only remaining ; this was, after the usual operations, consolidated by "cold 

 rolling." The Hamilton was coppered in October, 1847, requiring 7,706 Ibs. of 

 metal ; this was in the annealed state ; she was engaged in the Indian trade, 

 but was obliged to be stripped in August, 1849; the copper remaining 

 was 3, 0&6 Ibs. The Carthage was coppered hi November, 1847, taking 

 8,727 Ibs. of ' : cold rolled," likewise in the Indian trade; her sheathing was 

 taken off in August, 1847; the copper remaining was 5, 8 10 Ibs. Allowing 

 the same rate of corrosion for each, it will be seen the vessels lost respect- 

 ively 64-45, 70-38, and 43*00 in 100. In the cases of the Hamilton and 

 Carthage, the influence of the different processes of manufacturing will be 

 seen on the durability of the copper, thereby exhibiting the superiority of 



