330 Sir Humphry Davy's further researches on 
depressions in the copper, and in the parts where the diffe- 
rent sheets join, and afford a soil or bed in which sea weeds 
can fix their roots, and to which zoophytes and shell fish 
can adhere. 
As far as my experiments have gone, small quantities of 
other metals, such as iron, tin, zinc, or arsenic, in alloy in 
copper, have appeared to promote the formation of an inso- 
luble compound on the surface ; and consequently there is 
much reason to believe must be favourable to the adhesion 
of weeds and insects. 
I have referred in my last paper to the circumstance of the 
carbonate of lime and magnesia forming upon sheets of cop- 
per, protected by a quantity of iron above parts, when 
these sheets were in harbour and at rest. 
The various experiments that I have caused to be made at 
Portsmouth, sho w all the circumstances of this kind of action, 
and I have likewise elucidated them by experiments made 
on a smaller scale, and in limited quantities of water. It 
appears from these experiments, that sheets of copper at 
rest in sea water, always increase in weight from the depo- 
sition of the alkaline and earthy substances, when defended 
by a quantity of cast iron under of their surface, and if 
in a limited or confined quantity of water, when the propor- 
tion of the defending metal is under 4^^. With quantities 
below these respectively proportional for the sea, and limited 
quantities of water, the copper corrodes ; at first it slightly 
increases in weight, and then slowly loses weight. Thus a 
sheet of copper 4 feet long, 14 inches wide, and weighing 
9 lb. 6 oz., protected by of its surface of cast iron, gained 
in ten weeks and five days, 12 drachms, and was coated 
