20 REPORT—1843. 
being obtained, the whole is ground into a thin “ bodyless” paint with lin- 
seed oil; when the paint is long exposed to sea water in contact with zinc 
or copper, it is possible that a small quantity of the mercury may be reduced 
to the metallic state, and may amalgamate the surface of a zinc or copper 
plate in contact with it; but it cannot, under any conceivable circumstances, 
have the smallest protective power over iron, beyond that which the linseed 
oil alone gives, the greasy coating of which probably enabled the patentee’s 
prepared plates to resist the acids, &c. applied by those whose testimonials to 
that effect have been published. In some specimens of zine and iron which I 
received prepared according to this process, I found there was not the slightest 
protection from corrosion when once the greasy film of oil was removed. 
348. I now pass to the second class of methods of protection. Zine is 
the only known metal that can be practically used as an electro-chemical pro- 
tector to iron; it can be applied, in a massive form, locally or at particular 
centres of action, or it can be diffused in a thin coat or zinking over the 
whole surface. 
There is no considerable difficulty in the first mode of application in most 
cases, but it is, after the lapse of a greater or less time (generally only a few 
weeks), nearly useless, from one or both of two causes. Zinc is so slightly 
electro-positive to iron, that its protective power is nearly destroyed when- 
ever a few spots of red rust have formed anywhere upon the iron it is in 
contact with ; the peroxide acting as an acid towards its own base in both fresh 
and sea water, the surface of the zinc gets covered in the latter with a hard 
crystalline coat of hydrated oxide of zine and of cale-spar, which retards or 
prevents its further corrosion, and thus permits the iron to corrode. The de- 
tails of these reactions have been given at length in preceding Reports. 
349. These phenomena also occur when the surface of the iron is all 
zinked over; but the insurmountable objection to zinked iron is, that in 
about two years nearly the whole of the thin coat of zinc is oxidized and re- 
moved even in fresh water, and in less time in sea water; further, the ten- 
dency of zinc to oxidate when fluid and at a high temperature, say 700° 
Fahr., is so great, and the methods of cleaning the surfaces of iron to be zinked 
heretofore practised so imperfect, that the surface of iron is never perfectly 
covered; and wherever an uncovered spot occurs and is exposed to air and 
water, after a time red oxide is formed, with the results above stated. Zine, 
alone or unalloyed, at its fusing temperature in process of working gets its 
oxide mixed up with the metal, which adheres in minute patches to the iron, 
every one of which becomes a centre of subsequent oxidation. 
$50. I will not attempt here to enter upon the theoretical consideration of 
the process about to be described, but confine myself to a description of the 
methods to be pursued and the results obtained. These methods of prevent- 
ing the corrosion of iron, whether cast or wrought, or of steel, are applicable 
to articles formed of these metals of whatever sort; and the methods of pre- 
venting the “ fouling” of iron vessels, or vessels sheathed with iron, are ap- 
plicable to all articles of these metals immersed in sea or fresh water; I 
therefore propose their application to all manner of articles of cast iron, 
wrought iron, or steel ; but as by far their most important and valuable appli- 
cation is to the protection of ships built of iron, I will confine my description 
to the methods of applying my processes to such only, from which may be 
readily understood how it is to be applied to all other articles of iron, &e. 
351. By the word “ fouling,” as applied to ships, iron buoys, floating bea- 
cons, &c., is meant the attachment and adherence to their surfaces, when im- 
mersed in sea or certain fresh waters, of various marine or freshwater animals 
of the molluscous and testaceous classes, and of aquatic plants. 
a 
