94 Sir H. Davy on the Corrosion of [Aug. 



Article II. 



On the Corrosion of Copper Sheeting by Sea Water, and on 

 Methods of preventing this Effect ; and on their Application to 

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

 Pres. R. S.* 



1. The 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 con- 

 cerned in the naval interests of the country. Having had my 

 inquiries directed to this important object by the Commissioners 

 of the Navy Board, and a Committee of the Royal Society hav- 

 ing been appointed to consider of it, I entered into an experi- 

 mental investigation of the causes of the action of sea water 

 upon copper. In pursuing this investigation, 1 have ascertained 

 many facts which I think not unworthy 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 cop- 

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

 however, the action of sea water upon two specimens of copper, 

 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 contained 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 bluish-green 

 precipitate appears in the bottom of the vessel, which constantly 



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



