1 56 
Sir Humphry Davy on the 
water ; and so far from its surface being corroded, in many 
parts there was a regeneration of zinc or of iron found 
upon it. 
6. In pursuing these researches, and applying them to 
every possible form and connection of sheet copper, the re- 
sults were of the most satisfactory kind. A piece of zinc 
as large as a pea, or the point of a small iron nail, were found 
fully adequate to preserve forty or fifty square inches of 
copper ; and this, wherever it was placed, whether at the 
top, bottom, or in the middle of the sheet of copper, and 
whether the copper was straight or bent, or made into coils. 
And where the connection between different pieces of copper 
was completed by wires, or thin filaments of the fortieth or 
fiftieth of an inch in diameter, the effect was the same ; every 
side, every surface, every particle of the copper remained 
bright, whilst the iron or the zinc was slowly corroded. 
A piece of thick sheet copper, containing on both sides 
about sixty square inches, was cut in such a manner as to 
form seven divisions, connected only by the smallest filaments 
that could be left, and a mass of zinc, of the fifth of an inch 
in diameter, was soldered to the upper division. The whole 
was plunged under sea water ; the copper remained perfectly 
polished. The same experiment was made with iron : and 
now, after a lapse of a month, in both instances, the copper is 
as bright as when it was first introduced, whilst similar pieces 
of copper, undefended, in the same sea water, have undergone 
considerable corrosion, and produced a large quantity of 
green deposit in the bottom of the vessel. 
A piece of iron nail about an inch long was fastened by a 
piece of copper wire, nearly a foot long, to a mass of sheet 
