of Mineral Species. 83 



case exactly similar to that of the blue crystals, as presented by 

 the specimens found in mines. 



Copper, in its pure metallic state, when exposed to the action 

 of the atmosphere, variously combines with the elements contain- 

 ed in that fluid. I have seen remains of Egyptian vessels, in the 

 possession of Major STEUART of the Hon. E. I. C. service, which 

 had formerly consisted of copper or bronze, and still presented the 

 exact outline of their original shape, with a pretty smooth sur- 

 face. Some of the fragments were nearly one-fourth of an inch 

 thick, but so complete was their disintegration, that they could 

 be easily broken across with the hands, presenting on their frac- 

 ture a compound mass full of small drusy cavities. In these the 

 octahedral crystals of the copper-ore, of which the whole mass 

 consisted, were distinctly visible. The curved surface of most of 

 the vessels was covered with atacamite, sometimes crystallised, 

 particularly on the concave sides. There were some white 

 patches also, which I did not then examine. During his resi- 

 dence in the Ionian Isles, Dr JOHN DAVY * paid much atten- 

 tion to similar changes, which have taken place in antique 

 Greek armour and coins. He found that the substances forming 

 green, red and white spots on the surface of these articles, which 

 consisted of alloys of copper and tin, were carbonate and submu- 

 riate of copper, octahedrons of protoxide of copper, and of pure 

 metallic copper, and oxide of tin. In several instances, there was 

 no metallic copper formed, and the protoxide was blackened by 

 an admixture of peroxide. Since it cannot be supposed that the 

 substances formed on the surface of these bronze articles, were 

 deposited from any solution, Dr DAVY infers, that an internal 

 movement of the particles must have taken place, caused by the 

 influence of electro-chemical powers. Dr DAVY'S opinion, that 

 such considerations will explain many phenomena, occurring in 



* Philosophical Transactions for 1826, p. 55. 



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