CHEMISTRY. 24:9 



ing. It is not anything- that may have remained in the copper during the 

 manufacture, or that it is sufficient if the copper be about 9S'5 or 99, rather 

 than 100. Without regard to what the 1 or 1-5 per cent, may be, the thing 

 required is pure copper, alloyed with a small portion of another pure metal ; 

 which other metal is best to use for this purpose, and the quantity, we are 

 not yet prepared to say, our investigations not being complete. 



There is another thing that is essential hi the way of sheathing, whatever 

 may be the quality used, that is, one equality of the quality over all the ship. 

 If this be not attended to, then certain sheets and parts will give way much 

 sooner than others a circumstance that has led to many disputes and erro- 

 neous impressions upon the question. One sheet wears well, nay, is hardly 

 affected, in the neighborhood of several that have decayed rapidly ; the sheet 

 is analysed and found very impure, and hence impure copper is recommended, 

 wliile it was the presence of that one sheet caused the rapid destruction of 

 the others, which, but for this, might have lasted well. 



This subject, we think worthy a more full investigation than yet has been 

 made : it is more a matter of time than expense ; and it our shipowners were 

 feeling more interested in the inquiry, and making arrangements so that data 

 would be obtained, such as retaining samples of the metal used for sheathing, 

 keeping a correct account of the work done by the vessel, and where ; and 

 then having such sheets found to wear well or ill tested and compared, as 

 well as the general loss by weight and time of renewal, &c., in a few years 

 we would not fail to have an amount of facts that would lead to the adoption 

 of what was really best. 



Yellow metal has been in use now these many years for sheathing, and is 

 very generally adopted in the merchant service. Its first cost is considerably 

 less than copper, which is an immediate inducement, and the uncertainty 

 attending the wear of copper sheathing brings other metals or alloys into 

 ready competition with it. 



The following experiments were recently made by Capt. James, K. N. : 

 Specimens of different coppers were kept in sea water for nine months ; the 

 loss of each per square inch is given thus : 



Electrotype copper lost 1-4 



Copper "with arsenic 12 



Copper with phosphorus none 



Copper (suppose cementing) 0-8 



Copper from Dock-yard 1-66 



Ditto 8- 



Ditto 2-48 



Ditto 2 33 



Yellow metal (Muntz's) 0'95 



Experiments from which we are to deduce an application to such purposes 

 as sheathing, may lead to false results, not being in accordance with the 

 conditions of application, such as where one sheet of copper overlaps another, 

 making a connection extending over the whole external surface of a ship, and 

 embracing thousands of plates. Where a slight variation in the composition 

 of a few will induce an electrical action throughout the whole, and thus give 

 results entirely different to suspending any single sheet, so that we must make 



