the preservation of metals hy electro-chemical means. 345 
I have mentioned these circumstances because they apply 
to ships already coppered, and because I have heard that a 
Liverpool ship, of which it was doubtful whether the copper 
was in a state such as would enable her to make another 
voyage to India with security, has, by the application of 
protectors of made this voyage,* without apparently any 
wear of her sheeting ; and that she is now preparing with 
the same protectors to make another voyage. 
In cases when ships are to be newly sheathed, the experi- 
ments which have been detailed in the preceding pages 
render it likely, that the most advantageous way of applying 
protection will be under, and not over the copper : the elec- 
trical circuit being made in the sea water passing through 
the places of junction in the sheets ; and in this way every 
sheet of copper may be provided with nails of iron or zinc, 
for protecting them to any extent required. By driving the 
nail into the wood through paper wetted with brine above the 
tarred paper, or felt, or any other substance that may be 
employed, the incipient action will be diminished ; and there 
is this great advantage, that a considerable part of the metal 
will, if the protectors are placed in the centre of the sheet, 
be deposited and re-dissolved : so there is reason to believe 
that small masses of metal will act for a great length of time. 
Zinc, in consequence of its forming little or no insoluble 
compound in brine or sea w^ater, will be preferable to iron 
for this purpose ; and whether this metal or iron be used, the 
waste will be much less than if the metal was exposed on 
the outside : and all difficulties witli respect to a proper 
situation in this last case are avoided. 
* The Dorpthy. 
