230 Proceedings of Philosoph ical Societies. [March, 



series of experiments upon it, and has discovered a simple and 

 effectual mode of remedying the evil. Copper, when immersed 

 in sea-water, however pure and malleable it may be, becomes 

 covered with a coat of a green submuriate, a sort of rust, which, 

 when washed off, is succeeded by a similar one, and the process 

 continues until the metal is completely destroyed. 



It was evident that no alteration which could be effected in the 

 copper would prevent its corrosion ; the effect on different kinds 

 of copper might be somewhat different, but the principal diver- 

 sities must be owing to the variations in the saltness and tem- 

 perature of the sea-water. 



Sir Humphry was led to the discovery, by the same principle 

 which led him to that of the decomposition of the alkalies ; 

 namely, that chemical affinities might be balanced or destroyed, 

 by changing the electrical states of the substances : it thence 

 appeared that the corrosion of the copper might be prevented by 

 its being brought, by contact with another metal, into a nega- 

 tively electric state ; and he had accordingly found that by the 

 contact of tin, forming part of an electrical circuit, of T ^th part 

 the surface of the copper, the desired effect was completely 

 obtained. Other metals, positive in respect to copper, may be 

 employed, as lead and zinc, but tin is preferable, on account of 

 its capability of being brought into complete contact with the 

 copper, by means of solder, and also because its submuriate is 

 easily detached from the metal. 



The experiments were made with ribbands of tin, and it was 

 found that such a ribband, equal in substance to only -5-g-oth part 

 of the copper, effectually prevented the corrosion of the latter. 

 They were so entirely satisfactory, that not the smallest doubt 

 can be entertained of the perfect success of the method in prac- 

 tice ; and the Lords Commissioners of the Admiralty have made 

 arrangements for enabling the President to repeat them on the 

 largest scale, on ships of war. 



It is probable, Sir Humphry observes, that this method, besides 

 preventing oxidation, will also prevent the adherence of vegeta- 

 bles and marine animals to the sheathing. 



This interesting communication terminated with some allusions 

 to the great importance of the discovery it announced, in a 

 national point of view, with respect to our maritime and commer- 

 cial interests. 



The reading was likewise commenced of a paper, " On the 

 Development of Magnetical Properties in Iron and Steel by 

 Percussion, Part II." By W. Sc.oresby, Jun. FUSE. Commu- 

 nicated by Sir H. Davy. 



Jan. 29. — Thomas Amyot, Esq. VPSA. was admitted aFellow 

 of the Society, and the reading of Mr. Scoresby's paper was ter- 

 minated. 



This communication was a continuation of a former paper by 

 Mr. Scoresby, under the same title, which appeared in the Phil. 



