44 REPORT — 1841. 



water being electro-neutral, and acting slowly on copper, a little sal-ammoniac was 

 added, to quicken the action without affecting the neutrality. The following table 

 shoWs the effects. 



Table II. — Loss in sea-water sharpened with sal-ammoniac. 



Plover. Linnet. New. Sanspareil. Minden. 



In three days 1-6 1-5 1-4 1-8 1-5 



In five days 2-5 27 2-5 3-0 26 



In twelve days ... 4"6 52 5-1 5-7 5 



Here the greatest waste was on the Sanspareil's copper, the most durable of all 

 in actual wear ; and the least that of the Plover, one of those which had suffered 

 most rapidly. Placed under like circumstances, the ratio of waste is quite different 

 from that in use ; which should therefore be more or less due to external conditions. 

 These may depend on the relations of the copper to the ship, or on the circumstances 

 of her employment. The upper edge and parts most subject to the wash of the sea, 

 and to air and froth, suffer most from friction, as well as chemical action. The 

 lower part wears much less when in deep water ; but when the vessel grounds at 

 low water in black mud, this part suffers most, from the action of sulphuretted hy- 

 drogen. The nails by which it is fastened to the ship can hardly be without their 

 influence. They are never made of pure copper ; are very numerous, all in metallic 

 contact with the sheets, their heads presenting also a large metallic surface to the 

 salt water, so as to give great effect to sUght electro-chemical differences. Such 

 effects had been very apparent on the Jane, whose copper had been worn out in four 

 years ; round some of the nails the copper being sound for an inch or two, although 

 worn ragged in other parts, whilst the converse effect was exhibited round other 

 nails, as though some had acted protectively, others destructively. Some instances 

 were exhibited upon the table. 



All the nails he had tried, though alloyed with tin and other electro-positive metals, 

 were electro-negative to copper whilst clean, though assuming the electro-positive 

 relation to it when crusted with verdigris, and the copper clean. 



To ascertain their operation in these respects, five slips of new copper from the 

 same sheet, and of the same size as above (4 X 0'5 in.), marked 0. i. ii. in. X, were 

 suspended equidistant, and at the same depth, in a vessel of sea- water from the West 

 Indies. 0. was unconnected ; i. n. in. X . were each in metallic contact with a nail, 

 driven tight into a hole punched in the copper, the nails being taken from four dif- 

 ferent samples. After twelve days they were taken out and reweighed, withdrawing 

 the nails ; the following are the results : 



Table III. — Electro-chemical effect of the nails. 



0. I. II. III. X. 



Loss in twelve days... 032 0-34 0-28 0-41 0-37 



All the nails, except one (which was from H-M. Dockyard), seem to have acted 

 destructively. No. 3. having been one of those which had exhibited the same in- 

 dications on Mr. Moore's ship Jane, quoted above. 



Here appears to be one instance of a protective nail ; not enough so to prevent all 

 waste of the copper, which experience has not shown to be desirable ; but doubtless 

 the preservative power may be increased to any requisite degree by attending to the 

 composition of the alloy, as will be presently explained. 



The waste due to the ships' employment may be owing, — 1. to excess of work; 

 2. to stress of weather, including electrical discharges; 3. to the effects of climate ; 

 4. to corrosive materials in the different waters. 



As the sheathing suffers from friction as well as from chemical action, the more 

 the ship is at sea the greater will be her waste by friction ; the more also will she 

 be subject to stress of weather, which will act in the same way, and to electrical 

 discharges, which will excite chemical action. 



The Plover and Linnet, being packets, were very likely to have suffered from these 

 causes (see Table I.) : and the Acorn, which had undergone much thunder and 

 lightning on the African coast, had lost of her copper 16 per cent, in 2^ j'ears. 



Climate. — That the sheathing suffers most in hot climates, is only what might 

 have been expected from the usual increase of chemical action with the temperature. 



Corrosive waters. — Did this property of heat, and also its tendency to promote 

 organic production and decomposition, render the tropical waters more corrosive ? 



