178 MR. CHARLES A. BURGHARDT ON THE 



cavities always present, which exhibit deposits of cuprous 

 oxide or hydrated ferric oxide in their interiors, and occa- 

 sionally amorphous silica and calcite. Gustav Rose (Mi- 

 neralogisch-geognostische Reise nach dem Ural, dem Altai 

 und dem kaspischen Meere, 1837) was of opinion, after 

 examining the copper formations in the Ural and Altai 

 districts, that the cuprite there was formed by direct oxi- 

 dation of the metal, and, secondly, that the large malachite 

 deposits were formed from the cuprite. This opinion pro- 

 bably well expresses the actual process which eventually 

 resulted in the formation of malachite, as the presence of 

 the clay surrounding the ore, the limestone formation, and 

 the hydrated ferric oxide and hornstone (amorphous siKca) 

 shows that the former neighbouring crystalline rocks must 

 have been submitted to the powerful action of water, which, 

 in all probability, contained carbonic acid gas. Rose does 

 not give (so far as I am aware) any experimental proofs of 

 his theory of the formation of the great copper deposits of 

 the districts above mentioned. I considered it therefore 

 necessary to endeavour to determine experimentally the 

 accuracy of his statement. For this purpose I placed per- 

 fectly clean polished strips of chemically pure copper sheet 

 in a glass tube, and covered them with distilled water sa- 

 turated with carbonic acid gas ; the tube was then sealed 

 up and heated in a water-bath at 100° for some time. In 

 three days I observed a decided formation of a film of 

 cuprous oxide (which was crystalline) upon the metal ; on 

 the seventh day there were small particles here and there 

 of a green substance, which was undoubtedly a basic copper 

 carbonate (very probably malachite) . On continuing the 

 heating of this tube for a few days longer at the same tem- 

 perature, a considerable amount of cupric oxide was formed 

 in scales, arising, doubtless, from the decomposition of the 

 malachite, as it is a well-known fact that malachite, on 



