1824.] Copper Sheeting by Sea Water, §c. 95 



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 solu- 

 tion 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 are now 

 generally adopted, it is evident that soda and magnesia cannot 

 appear in sea water by the action of a metal, unless in conse- 

 quence of an absorption or transfer of oxygene. It was therefore 

 necessary for these changes, either that water should be decom- 

 posed, or oxygene absorbed from the atmosphere. I found that 

 no hydrogen was disengaged, and consequently no water decom- 

 posed : necessarily, the oxygene of the air must have been the 

 agent concerned, which was made evident by many experi- 

 ments. 



Copper in sea water deprived of air by boiling or exhaustion, 

 and exposed in an exhausted receiver or an atmosphere of hydro- 

 gene gas, underwent no change; and an absorption in atmosphe- 

 rical air was shown when copper and sea water were exposed to 

 its agency in close vessels. 



4. In the Bakerian Lecture for 1806, I have advanced the 

 hypothesis, that chemical and electrical changes may be identi- 

 cal, or dependent upon the same property of matter: and I have 

 farther explained and illustrated this hypothesis in an elementary 

 work on chemistry, published in 1812. Upon this view, which 

 has been adopted by M. Berzelius and some other philosophers, 

 I have shown that chemical attractions may be exalted, modi- 

 fied, or destroyed, by changes in the electrical states of bodies; 

 that substances will only combine when they are in different 

 electrical states; and that, by bringing a body naturally positive 

 artificially into a negative state, its usual powers of combination 

 are altogether destroyed ; and it was by an application of this 

 principle that, in 1807, I separated the bases of the alkalies 

 from the oxygene with which they are combined, and preserved 

 them for examination ; and decomposed other bodies formerly 

 supposed to be simple. 



It was in reasoning upon this general hypothesis likewise, 

 that I was led to the discovery which is the subject of this 

 paper. 



Copper is a metal only weakly positive in the electro- chemical 

 scale ; and, according to my ideas, it could only act upon sea 

 water when in a positive state ; and, consequently, if it could 

 be rendered slightly negative, the corroding action of sea water 



