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IV. On the Corrosion of 'Copper Sheeting by Sea-Water, and on 

 Methods of preventing this Effect; arid on their Application 

 to Ships of War and other Ships. By Sir Humphry Davy, 

 Bart. Pres. R.S.* 



1. HPHE rapid decay of the copper sheeting of His Majesty's 

 -^ ships of war, and the uncertainty of the time of its 

 duration, have long attracted the attention of those persons 

 most concerned in the naval interests of the countiy. Having 

 had my inquiries directed to this important object by the 

 Commissioners of the Navy Board, and a Committee of the 

 Royal Society having been appointed to consider of it, I en- 

 tered into an experimental investigation of the causes of the 

 action of sea-water upon copper. In pursuing this investiga- 

 tion, I have ascertained many facts which I think not un- 

 worthy of the notice of the Royal Society, as they promise to 

 illustrate some obscure parts of electro-chemical science; and 

 likewise seem to offer important practical applications. 



2. It has been generally supposed that sea-water had little 

 or no action on pure copper, and that the rapid decay of the 

 copper on certain ships was owing to its impurity. On trying, 

 however, the action of sea-water upon two specimens of cop- 

 per, sent by John Vivian, Esq. to Mr. Faraday for analysis, 

 I found the specimen which appeared absolutely pure, was 

 acted upon even more rapidly than the specimen which con- 

 tained alloy : and, on pursuing the inquiry with specimens of 

 various kinds of copper which had been collected by the 

 Navy Board, and sent to the Royal Society, and some of which 

 had been considered as remarkable for their durability, and 

 others for their rapid decay, I found that they offered very 

 inconsiderable differences only in their action upon sea-water ; 

 and, consequently, that the changes they had undergone must 

 have depended upon other causes than the absolute quality of 

 the metal. 



3. To enable persons to understand fully the train of these 

 researches, it will be necessary for me to describe the nature 

 of the chemical changes taking place in the constituents of sea- 

 water by the agency of copper. 



When a piece of polished copper is suffered to remain in 

 sea- water, the first effects observed are, a yellow tarnish upon 

 the copper, and a cloudiness in the water, which take place 

 in two or three hours : the hue of the cloudiness is at first 

 white; it gradually becomes green. In less than a day a 

 blueish-green precipitate appears in the bottom of the vessel 



* From the Philosophical Transactions for 182-1, Part I. 



which 



