98 Sir H. Davy on the Corrosion of Copper Sheeting. [Aug. 



copper underwent no change ; the undefended tarnished, and 

 deposited a green powder. 



Small pieces of zinc were soldered to different parts of a large 

 plate of copper, and the whole plunged in sea water : it was 

 found that the copper was preserved in the same manner as if a 

 single piece had been used. 



A small piece of zinc was fastened to the top of a plate of 

 polished copper, and a piece of iron of a much larger size was 

 soldered to the bottom, and the combination placed in sea 

 water. Not only was the copper preserved on both sides in the 

 same manner as in the other experiments, but even the iron ; 

 and after a fortnight, both the polish of copper and the iron 

 remained unimpaired. 



7. I am continuing these researches, and I shall communi- 

 cate such of them as are connected with new facts, to the Royal 

 Society. 



The Lords Commissioners of the Admiralty, with their usual 

 zeal for promoting the interests of the Navy by the application 

 of science, have given me permission to ascertain the practical 

 value of these results by experiments upon ships of war ; and 

 there seems every reason to expect (unless causes should inter- 

 fere of which our present knowledge gives no indications) that 

 small quantities of zinc, or which is much cheaper, of malleable 

 or cast iron, placed in contact with the copper sheeting of ships, 

 which is all in electrical connexion, will entirely prevent its cor- 

 rosion. And as negative electricity cannot be supposed favour- 

 able to animal or vegetable life ; and as it occasions the deposi- 

 tion of magnesia, a substance exceedingly noxious to land 

 vegetables, upon the copper surface ; and as it must assist in 

 preserving its polish, there is considerable ground for hoping 

 that the same application will keep the bottoms of ships clean, 

 a circumstance of great importance both in trade and naval 

 war. 



It will be unnecessary for me to dwell upon the economical 

 results of this discovery, should it be successful in actual prac- 

 tice, or to point out its uses in this great maritime and commer- 

 cial country. 



I might describe other applications of the principle to the 

 preservation of iron, steel, tin, brass, and various useful metals ;. 

 but I shall reserve this part of the subject for another communi- 

 cation to the Royal Society. 



