26 REPORT—1843. 
pebbles, and thus capable of transfer to a glass vessel. The results here were 
not so distinct as with the animals, but proved that copper salts in solution 
were decidedly deleterious to their existence. I ascertained also that marine 
plants would with the greatest difficulty attach or grow upon greasy or . 
varnished substances free from any film of calcareous matter or oxide of 
iron. 
876. From these experiments, I have been led to propose the peculiar 
poisonous paint already described as a preventive to “ fouling” of iron ships; 
it is in fact a method of bringing their immersed surfaces as nearly as possible 
to the condition of a copper-sheathed vessel without injury to the iron. The 
paint, therefore, is only a vehicle for poisonous matter, for which purpose it 
is requisite that it should have sufficient adhesion to resist the ship's motion, 
but still should have a slight degree of solubility in water, so that the poison- 
ous matter may be taken up by the absorbent or capillary vessels of an ad- 
hering animal or plant. This latter property is given it by the addition of 
the resinous soap, the proportion of which must be varied to suit frigid or 
tropical climates. I prefer using the oxychloride of copper as the poisonous 
matter of this paint; indeed it is simply the formation of this salt that pre- 
vents “fouling” of ordinary copper sheathing, but other salts will answer the 
purpose. 
377. The cost of protecting, by the methods described, the hull of an iron 
ship, of say 130 feet keel, materials and Jabour included, and preparing her 
against fouling, would add about ten shillings per ton to the cost of her 
hull, an amount quite inconsiderable when balanced against durability, safety, 
and speed. 
378. When no attempt is made to procure complete protection from cor- 
rosion, a considerable palliative consists in heating all the plates before being 
put together to nearly a “ black-red” heat in a boiler-maker’s oven, immedi- 
ately plunging them into boiled coal tar, and taking them out while still warm, 
so that a firm varnish may form upon them; but spots of rust soon appear 
even upon plates so treated. 
379. It is very desirable in every iron ship, that a layer of felt saturated 
in coal tar, boiled to the consistence nearly of pitch, should be interposed be- 
tween not only every metallic body electro-negative to iron, as before observed, 
but also between every piece of timber, of whatever sort, placed in contact 
with the hull below the water-line, and most especially in the bilge. Besides 
obvious mechanical reasons, this is important from the fact, that as soon as 
timber begins to decay in contact with iron and sea water, the rotten wood 
possesses the power of decomposing the sulphate of lime of the sea water, re- 
ducing it to sulphuret, while carbonic acid evolved from the decayed timber 
again decomposes the latter, producing sulphuretted hydrogen, which cor- 
rodes the iron locally with great rapidity. 
380. Soft wood not only rots soonest, but decays in a way that produces 
these effects more rapidly than the harder timber: this fact I wouid press 
upon the attention of iron ship-builders. 
These remarks might be extended, with many others of importance to the 
practical constructor, but for which this is not the place. 
381. In conclusion, when the durability of iron vessels, as regards corro- 
sion, and this is admitted alone to limit their existence, is compared with that 
of timber ships in reference to their decay, the balance undoubtedly seems at 
first in favour of the latter. We have examples of ships, such as the Royal Wil- 
liam, built in 1719, lasting more than 100 years; the Sovereign of the Seas, 
built in 1639, forty-seven years; the Barfleur, built in 1768, more than forty- 
four years, &c.; but these are the rare exceptions, not the rule. 
