56 Dr. Davy'5 observations on the changes which have 



formed of octohedrons of the red oxide of copper, intermixed 

 with crystals of the same form of metallic copper. These 

 crystals are most distinct at the surface ; they even adhere 

 to the calcareous crust, and may be detached with it, pre- 

 senting well- formed facets towards the part from which they 

 have been separated. Chemical examination shows that 

 they are actually composed of metallic copper, without the 

 least tarnish, and of the pure ruby protoxide of copper ; and 

 that the green rust consists principally of carbonate and sub- 

 muriate of copper, and the dirty white chiefly of oxide of 

 tin. The mineralizing process (if I may be allowed the 

 expression) which has produced these new combinations, in 

 general has penetrated very little into the substance of the 

 helmet. The incrustation and rust removed, the metal is 

 found bright beneath ; in some places considerably corroded, 

 in others very slightly. It proves on analysis to be copper 

 alloyed with 18.5 per cent, of tin. Its colour is that of our 

 common brass, and it possesses a considerable degree of 

 flexibility. 



An antient nail from a tomb in Ithaca, and an antient 

 mirror from a tomb at Samos, in Cephalonia, have afforded 

 me results very similar to the preceding, excepting that the 

 mineralized part, consisting of oxide of tin, submuriate, 

 carbonate, and protoxide of copper, each more or less col- 

 lected apart from the others into little masses, has exhibited 

 rather a crystalline structure than distinct well-formed 

 crystals, and has been without any appearance of crystals of 

 metallic copper. The copper in the mirror I have found 

 alloyed with about 6 per cent, of tin, and a very minute 

 quantity of arsenic and zinc. 



