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XIV. Further Researches on the Preservation of Metals by Electro- 
chemical Means. By Sir HUMPHRY Davy, Bart. Pres. R.S.* 
[X 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 cop- 
per sheeting of ships might be preserved by this method ; but 
another and a no less important circumstance was to be at- 
tended to,—how far the cleanness of the bottom, or its freedom 
from the adhesion of weeds or shell fish, would be influenced 
by this preservation. 
The use of the copper sheathing on the bottom of ships is 
twofold: First, to protect the wood from destruction by worms: 
And secondly, to prevent the adhesion of weeds, barnacles, 
and other shel] 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 
and carbonate of copper, and carbonate of magnesia, forms 
upon it, to which weeds and shell fish adhere. 
As long as the whole surface of the copper changes or cor- 
rodes, no such adhesions can occur; but when this green rust 
has partially formed, the copper below is protected by it, and 
there is an unequal action produced, the electrical effect of 
the oxide, submuriate, and carbonate of copper formed, being 
to produce a more rapid corrosion of the parts still exposed 
to sea water; so that the sheets are often found perforated 
with holes in one part after being used five or six years, and 
comparatively sound in other parts. 
There is nothing in the poisonous nature of the metal which 
prevents these adhesions. It is the solution by which they are 
prevented—the wear of surface. Weeds and shell fish readily 
adhere to the poisonous salts of lead which form upon the 
lead protecting the fore part of the keel; and to the copper, 
in any chemical combination in which it is insoluble. 
In general, in ships in the navy the first effect of the adhe- 
sion of weeds is perceived upon the heads of the mixed metal 
nails, which consist of copper alloyed by a small quantity of 
* From the Philosophical Transactions for 1825, part ii. 
Vol. 67. No. 334. Feb. 1826. M tin. 
