1843.] on the effects of Sea-water on Iron. 1081 



proved would be the result. In fact such a vessel's bottom might be 

 expected to present an appearance similar to that which an iron cable 

 would do after a ship has continued at anchor some months, shewing 

 evidences of corrosion only around the point immediately in contact 

 with the surface of the water. 



An opportunity of observing this difference in the condition of pro- 

 tected and unprotected iron placed in the same situation, and under the 

 same circumstances, was afforded me whilst Surgeon of the Pluto Iron 

 Steamer, which during a stay of nearly five months (repairing) in a 

 small port in the south of Portugal, never raised her mooring anchors. 

 It was found upon our departure, that an accumulation of testaceous 

 animals, at least one inch in thickness, had taken place upon her bot- 

 tom, covered or protected, as it was termed, with a coating of red lead 

 paint, and afterwards with several layers of coal-tar, whilst the naked 

 iron cables exposea* to exactly the same aqueous influences, came up as 

 clean as upon the day of our first anchoring. 



Many experiments have also been made to prove this fact, that iron 

 perfectly cleaned, will remain many months entirely submersed in 

 water, without the least change being observed upon its surface. 



I would also observe, that even the oxydization along the line of 

 immersion, where it is exposed to the united action of the atmosphere 

 and the water, is of such a character, as to afford no point for the 

 adhesion of marine animals, for forming in small scales, easily detached, 

 the attrition of the passing water is sufficient to remove them, and also 

 the embryo attachments of such animal life that may have been depo- 

 sited upon their surface. 



It is curious to observe, how theory has in the case of iron-built 

 ships, occasioned attention to be directed to an action in one situation 

 and determined it to be an evil, while in reality it is most beneficial, 

 and caused to be overlooked entirely the same action in another situa- 

 tion, where the corrosive influence exerts uncontrouled its fullest power, 

 namely, in the hold of the vessel, upon the internal surface of the iron. 

 Here, where there is always an accumulation of water to a certain 

 extent, oxydization finds every circumstance favorable for operation — 

 an increased temperature, water, both fluid and in a state of vapour, 

 and a continued wash from the rolling of the vessel, which removing 

 the newly-formed scales of oxydized metal, leaves again the naked 



