36 
BRITISH ASSOCIATION.— 1835 . 
with regard to iron. He found also that the corrosion of iron in 
sea-water is materially influenced by the depth of water in which 
the metal is immersed. He is of opinion that the w'ear of iron-work 
exposed to sea-water is more considerable the nearer the iron is to 
the surface or to the external air. The principal wear of the iron¬ 
work connected with the buoys seems to be at and within a few feet 
of the surface of the water; and this portion of the iron may be 
protected by attaching strong pieces of zinc to it. 
The corrosion of iron in sea-water, under ordinary circumstances, 
appears to arise from exposure of the water to the atmosphere, and 
the consequent gradual absorption of its oxygenous part. The 
protection of iron in sea-water by the contact of zinc seems due to 
a simple electrical action between the respective metals and the 
fluid ; water being decomposed, its hydrogen is evolved, its oxy¬ 
gen goes to the zinc, whilst the oxide of zinc as it forms seems to 
be deposited on the iron, at least in part. 
The author made a number of experiments to ascertain whether 
zinc would protect iron in sea-water if a very thin surface of glass, 
wood, paper, tow, &c. were severally interposed between those me¬ 
tals, but the results seemed clearly to prove that actual contact of 
the metals is indispensably necessary to that effect. 
Zinc will protect iron in fresh water. The author has made ex¬ 
periments on this subject, and has others still in progress ; the re¬ 
sults of which may admit of useful applications to valuable parts of 
machinery, &c. 
The author expressed his obligations to Mr. Hutcheson, the Har¬ 
bour-Master at Kingstown, for the kind and prompt assistance 
he afforded on every occasion, and for the interest he took in the 
progress of the experiments on the buoys, &c. 
On some recent Experiments made with a view to protect Tin Plate 
or tinned Iron from corrosion in Sea-water , with some probable ap¬ 
plications ; and on the power of Zinc to protect other Metals from 
corrosion in the Atmosphere. By Edmund Davy, F.R.S ., 
M.R.I.A ., fyc., Professor of Chemistry to the Royal Dublin So¬ 
ciety. 
If a piece of tin plate is exposed in sea-water for a few days, it 
will exhibit an incipient oxidation, which will gradually increase ; 
the tin will be preserved at the expense of the iron, which wall be 
corroded. But if a small surface of zinc is attached to a piece of 
tin plate and immersed in sea-water, both the tin and iron will be 
preserved, whilst the zinc will be oxidated, on the principle first 
made known by the late Sir H. Davy. 
The author has exposed for nearly eight months in sea-water a 
surface of tin plate nailed to a piece of wood by means of tinned iron 
tacks, inserting between the wood and the tin plate a small button 
of zinc. Under these circumstances the tin plate has remained 
