35 
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 con- 
tinuing the heating of this tube for a few days longer at the 
same temperature, a considerable amount of cupric oxide 
was formed in scales, arising, doubtless, from the decomposi- 
tion of the malachite, as it is a well-known fact that mala- 
chite on being boiled in water, decomposes into cupric oxide> 
carbonic acid gas, and water. In order to see what effect 
pure distilled water would have upon metallic copper under 
similar circumstances, I placed a large strip of clean polished 
sheet-copper in a tube, covered it with distilled water and 
sealed the tube up, heating it in the water-bath as in the 
previous experiment. I was astonished to find on the third 
day that the copper was strongly coated with cupric oxide, 
so that it is evident that pure water has a greater chemical 
action as an oxidising agent than water containing carbonic 
acid gas. Having thus obtained the results described, I may 
be allowed to draw some conclusions from them, as regards 
the primary copper ore, and the eventual formation of the 
other ores from it, briefly as follows, viz. : — - 
1. In all probability the crystalline rocks contain dis- 
seminated throughout their mass extremely minute quanti- 
ties of metallic copper (when perfectly fresh ); Bischoff 
mentioning many rocks in which small quantities of cupric 
oxide have been detected, where its presence would never 
have been expected. 
2. By the action of water, or a solution of carbonic acid 
gas in water, the metallic copper particles were converted 
in situ into one of the three following substances, viz., 
cuprous oxide, cupric oxide, and malachite. 
3. By the action of water partially charged with sodium 
chloride (derived from the surrounding rock masses), 
