on the Preservation of Metals by Electro-chemical Means. 99 
protected, and have returned after voyages to the West Indies, 
and even to the East Indies. The proportion of protecting 
metal in all of them has been beyond what I have recom- 
mended, 1-90th to 1-70th; yet two of them have been found 
perfectly clean, and with the copper untouched after voyages 
to Demarara; and another nearly in the same state, after two 
voyages to the same place. ‘Two others have had their bot- 
toms more or less covered with barnacles; but the preserva- 
tion of the copper has been in all cases judged complete. The 
iron has been placed along the keel on both sides ; ‘and the 
barnacles, in cases where they have existed, have been generally 
upon the flat of the bottom; from which it may be concluded, 
that they adhered either to the oxide of iron, or the calcareous 
deposits occasioned by the excess of negative electricity. 
In the navy the proportion adopted has been only 1-250th 
of cast iron, at least for vessels in actual service, and when the 
object is more cleanness than the preservation of the copper. 
In is very difficult to point out the circumstances which 
have rendered results, such as these mentioned with respect 
to Liverpool traders, so different under apparently the same 
circumstances, 7. e. why ships should exhibit no adhesions or 
barnacles after two voyages, whilst on another ship, with the 
same quantity of protection, they should be found after a 
single yvoyage*. This may probably depend upon one ship 
having remained at rest in harbour longer than another, or 
having been becalmed for a short time in shallow seas, where 
ova of shell fish, or young shell fish existed ; or upon oxide of 
iron being formed, and not washed off, in consequence of calm 
weather, and which consolidating, was not afterwards sepa- 
rated in the voyage. From what I can learn, however, the 
chance of a certain degree of foulness, in consequence of the 
application of the full proportion of protecting metal, will not 
prevent ship-owners from employing this proportion, as the 
saving of copper is a very great object ; and as long as the cop- 
per is sound, no danger is to be apprehended from worms. 
It ought to be kept in mind that the larger a ship, the more 
the experiment is influenced by the imperfect conducting 
power of the sea water, and consequently the proportion of 
protecting metal may be larger without being in excess. 
I have mentioned these circumstances because they apply to 
ships already coppered, and because I have heard that a Liver- 
pool ship, of which it was doubtful whether the copper was in a 
state such as would enable her to make another voyage to India 
* The quality of the copper may be another cause, 
N2 with 
‘ 
