ON THE ACTION OF AIR AND WATER UPON IRON. o5 
protection; and also in the case of iron ships, to interpose between the cover- 
ing of alloy and the final coat of poisonous paint. 
370. It.was stated by Sir H. Davy, in his researches on the preservation 
~ of copper sheathing, that the sole cause why it did not become ‘‘ foul” when 
unprotected was, the continual loss of substance by solution and washing 
away of the salts produced (the suboxide and oxychloride of copper), and 
that the poisonous properties of the salts produced had nothing to do with the 
matter. The only proof, however, given of this was, that fouling rapidly took 
place upon a surface of Jead forming a portion of a coppered vessel's hull, 
upon which there existed an abundant production of carbonate of lead. Al- 
though fully aware of the powers of endurance possessed by the classes of 
animals which adhere to ships, such as those of the genera Balanus, Otion, 
Ascidia, Cineras, Anatifa, Ostrea, Mytilus, Dreissena, &c., still I doubted this 
conclusion, from remarking that they adhered to the surface of metals, such 
as zine in a rapid state of degradation or solution in sea water, but which did 
not produce poisonous salts. 
371. I also observed, that to perfectly clean metallic surfaces they showed 
little disposition to adhere; that either a thin coat of peroxide, or of calca- 
reous matter deposited from the sea-water, was necessary to their adherence ; 
that the testaceous animals seemed to disregard the nature of the metal to 
which they clung, provided they had a coating of calcareous matter to adhere 
to, and that the same applied, to a great extent, to the growth of sea-weeds. 
$72. I thence determined to make some direct experiments upon the effects 
of metallic poisons upon such common molluscous or testaceous animals as I 
could command, and for this purpose I chose the common oyster, the limpet 
(Patella), and some of the Actinie found along the shores of Dublin Bay: 
these were placed in glass vessels of sea water frequently renewed, and left 
for some time without disturbance, until it was certain that the condition of 
the animals was not in itself fatal or injurious to them. Then certain poison- 
ous metallic salts were gradually introduced into their respective receptacles, 
such as the soluble and insoluble salts of lead, copper, mercury, arsenic, &c. 
373. The results of these experiments, which were continued for a long 
time and made with care, showed that all these animals were more or less 
subject to annoyance from substances poisonous to the higher animals; that 
they were least affected by the salts of lead and mercury, and most so by 
those of copper; and that, unless present in such large quantity as to be at 
once fatal, the insoluble, or rather difficultly soluble salts of copper in sea 
water (such as the oxychlorides and the arsenite of copper) gave them much 
more uneasiness than the soluble ones. The poisonous matter, when difficultly 
soluble, was sometimes merely dropped into the sea water near the animal, at 
others was strewed upon a plate and the animal placed upon it. Jn every case, 
when the animal was killed, the poisonous matter (at least the copper, which 
was the only metal looked for) could be detected in its body after death. 
$74. From these experiments, I think I am justified in concluding that the 
other classes of “fouling” animals, whose habits are so analogous to those tried, 
are prevented from adhering to copper sheathing in virtue of the poisonous 
salts produced by the sea water acting upon it, and not merely by loss of con- 
tinuity ; and that in the case of the lead cited by Davy, the animals adherent 
must have been protected from the poisonous surface by a coat of calc-spar 
or carbonate of lime formed upon it, or by some other unexplained circum- 
stance; and that hence the production of an artificial poisonous surface upon 
the bottom of an iron ship, a buoy, &c., would prevent their “fouling” also. | 
375. I also made some experiments upon the effect of metallic poisons upon 
sea-weeds, choosing for this purpose portions of F’wct adherent to small loose 
