154 
Sir Humphry Davy on the 
examination ; and decomposed other bodies formerly sup- 
posed to be simple. 
It was in reasoning upon this general hypothesis likewise, 
that I was led to the discovery which is the subject of this 
Paper. 
Copper is a metal only weakly positive in the electro- 
chemical scale ; and, according to my ideas, it could only 
act upon sea water when in a positive state ; and, conse- 
quently, if it could be rendered slightly negative, the cor- 
roding action of sea water upon it would be null ; and 
whatever might be the differences of the kinds of copper 
sheeting and their electrical action upon each other, still 
every effect of chemical action must be prevented, if the 
whole surface were rendered negative. But how was this 
to be effected ? I at first thought of using a Voltaic battery ; 
but this could be hardly applicable in practice. I next thought 
of the contact of zinc, tin, or iron : but I was for some time 
prevented from trying this, by the recollection that the copper 
in the Voltaic battery, as well as the zinc, is dissolved by the 
action of diluted nitric acid ; and by the fear that too large a 
mass of oxidable metal would be required to produce decisive 
results. After reflecting, however, for some time on the 
slow and weak action of sea water on copper, and the small 
difference which must exist between their electrical powers 
and knowing that a very feeble chemical action would be 
destroyed by a very feeble electrical force, I resolved to try 
some experiments on the subject. I began with an extreme 
case. I rendered sea water slightly acidulous by sulphuric 
acid, and plunged into it a polished piece of copper, to which 
