Copper Sheathing - Humphry Davy's Experiments With Copper Sheathing

Humphry Davy's Experiments With Copper Sheathing

In the late 18th to early 19th century, Sir Humphry Davy performed many experiments where he had various thicknesses of copper submerged on the shore and then measured how much the sea water had degraded each one. Sheets of different metals remained in the seawater for four months and then were examined. Two harbour ships were also used in this test, one with a zinc and the other with an iron band. Both the zinc and iron became covered in a carbonate which allowed weeds, plant life and insects to attach themselves to the metal. The sheets that had cast iron or zinc were free of any attached life forms or discoloration. The main purpose of these experiments was to determine how to lessen the corrosion that the seawater caused on unprotected copper sheathing. Unprotected copper, such as that which was not covered in another metal such as iron, would quickly go from a reddish color to a greenish color of corrosion. When the other metal was mixed in copper in ratios from 1/40 to 1/150, there was no visible sign of corrosion and minimal weight loss. When the ratio was changed to 1/200 and 1/400, there was significant corrosion and weight loss. Davy concluded that cast iron, which was the cheapest to manufacture, was the best for protection of the copper since malleable iron and zinc wore down faster.