46 REPORT — 1841. 



in such a case, where enough attention was paid to the subject to have the copper 

 analysed, it might be supposed that so extensive an action from the nails could hardly 

 have passed unnoticed. The author hoped yet to obtain some of the copper from the 

 Quarantine and Eddystone tenders, and other samples from consistent instances,which 

 should fix the fault upon the copper itself. Comparative analysis may then discover 

 methods both to manufacture and to distinguish the sheet-copper best suited for this 

 important purpose. Meanwhile, as nails must be used, advantage may be taken of 

 their electro-chemical protection, by making them slightly positive to'copper. The 

 addition of zinc for this purpose need not injure their flexibility nor enhance their 

 ' price. They are now alloyed chieflfy with tin ; but the care of the manufacturer is 

 to make them sufficiently hard and flexible, without much regard to the presence of 

 other metals. If they were made just so much electro-positive as to protect the 

 sheathing so far as is compatible with their own durability, they would seem to offer 

 the simplest, most perfect, and most convenient mode of electro-chemical protection. 

 The test by the galvanometer would be easily applied (after a little practice) in 

 making up the metal, if it be important to continue the present system of their ma- 

 nufacture. 



A different method of preservation came out in the course of these investigations, 

 which has since been made the subject of some probably conflicting patents. 



It was above noticed, that the upper part of the copper on the Eddystone tender, 

 which bears the wash and friction of the waves, continues sound ; whilst the bottom 

 is fast wearing out. This exception, or rather subversion of the usual conditions, is 

 owing to a coating of fish-oil, laid on when the copper was new, to keep it bright, 

 and not extended over the parts out of sight. Such a permanent effect could never 

 have been anticipated from an oil which is not drying ; and strongly indicates the 

 facility, as well as efficacy, of this mode of protection. A still more striking case 

 presented itself in the vessel which supplied the observations on the apparent influ- 

 ence of the nails. During the examination of her copper, Mr. Moore called his at- 

 tention to the complete preservative effect of some coal-tar, which had trickled over 

 the copper from the wood-work above. This had crossed the sheets where most 

 subject to the wash and friction ; and whilst the naked metal had been quite worn 

 away, the coal-tarred streaks remained entire ; the surface of the copper, on melting 

 off the tar, being as perfect as when fresh from the rolls. The specimen was shown 

 on the table. 



Hence coal-tar seems to be an efficient preservative; but then recurs the question 

 which encumbers this subject— will it keep a clean surface, free from organic ad- 

 hesions and earthy incrustations ?— the solution of which can be obtained only from 

 time and experiment. 



To embrace the opportunity for both, the vessel was then sheathed with copper 

 on one side and yellow metal on the other ; and her fore- quarters to her midlength 

 varnished with coal-tar, laid on hot upon the metal, also heated by fires of chips 

 round the sides. She has now been twelve months at sea, and by the last account of 

 her, the varnished as well as the metallic surfaces kept quite clean. In the present 

 stage of this investigation, Mr. Prideaux had not found the difference between durable 

 and perishable samples of sheathing explained by comparative analyses, nor by com- 

 parison of their physical qualities. In parallel conditions in the laboratory, they did 

 not observe the same order of waste as at sea; hence external causes must have 

 had a principal share in the difference, namely, friction, as well as chemical action, 

 in sea-going ships; — sulphureous exhalations upon those which lie on the black 

 mud ; — increased temperature, and heavy electrical discharges, in tropical climates, 

 both exciting chemical action ;— corrosive contents of some sea-waters. The nails 

 used for fastening it have also considerable electro-chemical influence. 



But allowing for all these causes, there are cases where the fault appears to be in 

 the copper itself. The electro-chemical influence of the nails may be easily rendered 

 protective ; and coal-tar seems to afford an effective mechanical protection. Labo- 

 ratory experiments must however, in such cases, be taken chiefly as indications for 

 others on the working scale, which require opportunity as well as time. By sending 

 ships to sea, each having her two sides sheathed with different coppers, but fastened 

 with the same nails, the shipwright would soon learn whose copper he can best 

 confide in, and the chemist would be supplied with materials for satisfactory com- 

 parative analyses. 



