ON THE ACTION OF AIR AND WATER UPON IRON. 15 
viz. the durability, be ensured, the vessels remaining clean under water is 
nearly, if not wholly attained, for both marine animals and plants adhere 
with obstinacy to the oxidized iron of a rusty ship’s bottom, on which they 
thrive and multiply, while to clean iron they will scarcely attach themselves. 
From the importance of this subject I have been induced to give it a very 
particular consideration, and propose here to enter somewhat fully into the 
principal agents of corrosion of iron ships, the directions in which these are 
found, or may be expected, to act most destructively; to describe the pecu- 
liar methods which I have been led to devise for preventing corrosion, and 
also those for preventing the “fouling,” which is admitted by the most san- 
~ guine advocates of iron ship-building to be at present the salient evil of the 
system. This matter has acquired increased importance from the recent 
discovery of Professor Daniell of the existence of sulphuretted hydrogen in 
the sea water of the tropics, which our previous experiments show acts most 
destructively on iron, as well as on the copper sheathing of timber vessels, 
331. The lower part of an iron ship’s floor is exposed to putrid bilge-water 
(if permitted to accumulate); this, on grounds already stated, is an agent of 
great corrosive power, and when heated, as beneath the boilers in steam- 
yessels, its effects are greatly increased, as far as action from the inside is 
concerned ; therefore the floor and futtocks may be expected soonest to re- 
quire restoration. This I am informed is actually the case in those thin sheet- 
iron “fly-boats” used for passengers in Scotland and Ireland on the canals, 
A remedy for this suggests itself which it would be highly desirable to make 
trial of, which could be of no inconvenience, and if snecessful, would have 
the additional advantage of destroying all smell of bilge-water in a vessel and 
of preserving her floor at all times sweet. 
It has been before remarked (1st Rep. 49, &c.) that a small quantity of an 
alkali in solution, even in salt water, is capable of arresting oxidation of iron ; 
it is highly probable that an alkaline earth-lime for instance in solution pos- 
sesses the same power, indeed Payen’s experiments make this certain; there 
would be no difficulty to keeping lime-water in the place of bilge-water over 
the floor of an iron ship, to any desirable degree of saturation. The ship’s 
well being periodically pumped out dry, fresh water let in, and a few lumps of 
dry lime dispersed, a fresh supply of lime-water would be kept up, which would 
not only preserve the bottom, but destroy the putridity of the bilge-water, of 
which some will be found eyen in the stanchest vessel. No injury would be 
likely to result to the few timbers which would be exposed to its contact. 
$32. Exteriorly the action of air and water will be greatest just between 
wind and water, and abreast of the paddle-wheels in steamers, where the 
constant splash from the paddles strikes, and wherever the shell of the vessel 
is heated by the contact or proximity of the boilers, &e., but the difference 
in other parts of the hull is not likely to be considerable unless in very fast- 
going vessels. 
_ 333. It has long been an opinion amongst those concerned in iron ship- 
building, that “an iron vessel when kept in constant use is not only free from 
oxidation, but presents no more appearance of corrosion than railway-bars, 
which (say the advocates of this doctrine) are well known to remain uncor- 
Toded so long as the carriages continue to roll over them.” “If the iron ship 
be kept in constant use, ¢.e. in constant motion through the water, there is 
no appearance of deterioration ; but lay her up for a few months, and the 
usual appearances of atmospheric action become visible, accompanied by a 
rapid corrosion of the points exposed.” With respect to this singular opinion 
as to railway bars, we shall have more to say presently; what analogy sub- 
sists however between a railway bar and an iron ship it is hard to see, I do 
