336 
Sir Humphry Davy's further researches on 
wire was covered over with fine crystals of carbonate of 
lime ; and the same phsenomenon of the separation of 
carbonate of soda occurred, but in a less degree. In the 
third glass the wire was clean, but without depositions ; and 
the presence of alkaline matter could only be distinguished 
by chemical tests. In the fourth glass the copper was 
bright, evidently in consequence of a slight but general cor- 
rosion, but with a scarcely sensible deposit ; in the fifth, the 
deposit was very visible ; and in the seventh the wire was 
covered with green rust. 
These results, which showed that a very small quantity 
only of the imperfect or fluid conductor was sufficient to 
transmit the electrical power, or to compleat the chain, in- 
duced me to try if copper nailed upon wood, and protected 
merely by zinc or iron on the under surface, or that next the 
wood, would not be defended from corrosion. For this pur- 
pose I covered a piece of wood with small sheets of copper, 
a nail of zinc of about the part of the surface of the cop- 
per being previously driven into the wood : the apparatus 
was plunged in a large jar of sea water : it remained per- 
fectly bright for many weeks, and when examined, it was 
found that the zinc had only suffered partial corrosion ; that 
the wood was moist, and that on the interior of the copper 
there was a considerable portion of revived zinc, so that the 
negative electricity, by its operation, provided materials for its 
future and constant excitement. In several trials of the same 
kind, iron was used with the same results ; and in all these 
experiments there appeared to be this peculiarity in the 
appearance of the copper, that unless the protecting metal 
below was in very large mass, there were no depositions of 
