20. 
jee 2 
re preservation of: the copper 
. sheathing of yessels having re- 
ceitly become. an object of peculiar 
interest to the public;.from the valuable 
experiments of Sir Humphrey Davy, 
with a view of preventing the corrosion 
of;copper by sea-water; and the doubt 
which yet exists in the minds of many 
nautical and mercantile. men, as to the 
efficacy of the mode recommended by 
‘Sir Humphrey, when submitted to the 
test of experiinent during long voyages ; 
I must beg a column or two of your 
valuable journal to offer a few remarks 
on the subject; accompanied by some 
recent facts, of the operation of iron in 
preventing the oxidation of copper by 
sea-water, 
It is not necessary, Mr.Editor, to ac- 
quaint your mercantile readers, that the 
destruction of the copper sheathing of 
shipping forms a very large item in the 
expenditure of ship-owners ; more espe- 
cially, in such ships as are employed in 
navigating the tropical seas—the corro- 
sion.of the copper being greatly accele- 
rated. by increase of temperature. In- 
deed,.a single. voyage to India or the 
South Seas is all that can be performed 
with any, degree’ of safety, without re- 
newing the copper.of a ship’s bottom. 
Neither is it necessary, here, to state 
any thing more than the result of the 
experiments of the President of the~ 
Royal Society ; undertaken with the view 
of discovering the law by which the 
destruction of copper by sea-water. is 
governed ; and, if possible, to’ prevent 
or neutralize its chemical agency. These 
experimeuts are given in detail by their 
author, in the two last volumes of the 
Transactions of the Royal Society, to 
which I beg to recommend such of your 
readers as may be desirous of following 
this illustrious‘chemist through his in- 
genious and profound researches. 
The results of these experiments are 
nearly..as follows :—If a polished. sur- 
face of sheet copper or copper sheathing 
be suffered to remain in sea-water, even 
for a few hours, it soon acquires a yel- 
low tarnish, and. the water becomes 
clouded, of a greenish-white, and after- 
wards green. Within twenty-four hours, 
the copper assumes a greenish hue near 
the surface, but reddish below, whilst a 
blue green, precipitate is deposited at 
the bottom of the liquid, which goes on 
increasing, if the sea-water be renewed, 
continually (as in the passage>of a vessel - 
through the water, or in a current); 
Preserpittion, of the Capper Sheathing of Vessels. 
To the Editor of the\Monthly Magazine.” ( 
Hi ere ~ decreases, if the! experiment bE madé'in 
(Auge, 
but this chemical agency,of ‘course, 
a limited quantity of seawater; "4in' pro- 
portion as the' water becoities Jess’ Sa- 
line ; by its muriatic acid uniting with 
the copper, forming ‘a ‘stib-inutiate ‘of 
copper ;/ or, as Sir H: Davy calls it, “a 
hydrated sub-muriate.”’ But the’ /pre- 
sence’ of atmospheric’ air seems to be 
essential in this case ;’ for, whef ‘copper 
was placed ‘in sea-water- which has been 
deprived of air by boiling, and placed in 
an exhausted receiver, ‘it underwent no 
change whatever. , ; 
Now, in’ order to neutralize’ this 
agency of sea-water on copper ‘(or, 
more accurately, the decomposing ac- 
tion of copper on sea-water), this €mi- 
nent philosopher suggested thé appliéa- 
tion of electro-chemical agency,‘or, in 
other words, of presenting other sub- 
stances in contact with the copper, 
which haye a greater attraction than 
copper for the saline matter of sea- 
water. Zinc and iron were the metals 
which offered the best probability’ of 
success for this object, from’ ‘théir 
powerful aftraction to oxygen. ' The 
price of zinc, however, forms an objec- 
tion to its being employed on a large 
scale; and, consequently, the: experi- 
ments of Sir Humphrey were ‘chiefly 
directed to the application of iron’ to 
the surface of. the sheathing of ships, so 
as to destroy, or rather to neutralize, 
_the action of sea-water. A 
The most extraordinary fact. result- 
ing from these experiments is, the small 
extent of surface of iron which)is’suffi- 
cient to protect a given surface’ of cops 
per. Inthe earlier experiments of Sir 
Humphrey, he allowed» too‘ great” an 
extent of the: protecting surfaces’ of 
iron.or zinc; amounting to from one 
twentieth to one-fiftieth ‘of that of ‘the 
surface of copper employed: “‘Therob- 
ject of these electro-chemical’ experi- 
ments was simply that of rendering the 
copper into a negative: state,' as’ cém- 
pared with the ssea-water (it® being 
slightly positive in» its’ ordinary) state): 
the smallest. quantity. of ‘iron’ or “zine 
that would accomplish» this pufpose 
was found ultimately to be thé best. 
For it was observed, that! inosome’ of 
the boats and smaller vesselsyibesides 
the Comet, steam-boat;:whiclht had been 
rotected by these:ribs| or’bars%ef “iron 
donee along the copper fromehead'to 
stern), though: the:copper was“not»per- 
ceptibly corroded after. some’: 
‘voyage, yet an evil occurred of scarcely 
less magnitude, so far as the sailing ned 
the 
