1 52 
Sir Humphry Davy on the 
Navy Board, and sent to the Royal Society, and some of 
which had been considered as remarkable for their durability, 
and others for their rapid decay, I found that they offered 
very inconsiderable differences only in their action upon sea 
water ; and, consequently, that the changes they had under- 
gone must have depended upon other causes than the absolute 
quality of the metal. 
3 . To enable persons to understand fully the train of these 
researches, it will be necessary for me to describe the nature 
of the chemical changes taking place in the constituents of 
sea water by the agency of copper. 
When a piece of polished copper is suffered to remain in 
sea water, the first effects observed are, a yellow tarnish 
upon the copper, and a cloudiness in the water, which take 
place in two or three hours : the hue of the cloudiness is 
at first white ; it gradually becomes green. In less than a 
day a bluish-green precipitate appears in the bottom of the 
vessel, which constantly accumulates ; at the same time that 
the surface of the copper corrodes, appearing red in the water, 
and grass-green where it is in contact with air. Gradually 
carbonate of soda forms upon this grass-green matter ; and 
these changes continue till the water becomes much less 
saline. 
The green precipitate, when examined by the action of 
solution of ammonia and other tests, appears principally to 
consist of an insoluble compound of copper, ( which may 
be considered as a hydrated sub-muriate) and hydrate of 
magnesia. 
According to the views which I developed fourteen years 
ago, of . the nature of the compounds of chlorine, and which 
