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XV. Further researches on the preservation of metals by electro- 
chemical means. By Sir Humphry Davy, Bart, Pres, R. S, 
Read June 9, 1825. 
Xn two papers read before the Royal Society, I have de- 
scribed the effects of small quantities of electro-positive metals 
in preventing the corrosion or chemical changes of copper 
exposed to sea water, and I have stated that the results 
appear to be of the same kind, whether the experiments are 
made upon a minute scale, and in confined portions of 
water, or on large masses, and in the ocean. 
The first and preliminary experiments proved, that the 
copper sheeting of ships might be preserved by this method ; 
but another and a no less important circumstance was to be 
attended to, how far the cleanness of the bottom, or its free- 
dom from the adhesion of weeds or shell fish, would be 
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influenced by this preservation. 
The use of the copper sheathing on the bottom of ships is 
two fold : First, to protect the wood from destruction by 
worms : 
And secondly, to prevent the adhesion of weeds, barnacles, 
and other shell fish. No worms can penetrate the wood as 
long as the surface of the copper remains perfect ; but when 
copper has been applied to the bottom of a ship for a certain 
time, a green coating or rust, consisting of oxide, submuriate 
