ORIGIN OF SOME ORES OF COPPER. 179 



being boiled in water, decomposes into cupric oxide, car- 

 bonic acid gas, and water. In order to see what eflfect 

 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 oxidizing 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 quan- 

 tities 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. cu- 

 prous oxide, cupric oxide, and malachite. 



3. By the action of water partially charged with sodium 

 chloride (derived from the surrounding rock-masses), 

 cuprous chloride and cupric chloride were formed and 

 carried down into the fissures below, where, by the action 

 of a heat which need not have exceeded 1 60°, the cuprous 

 chloride (for the cupric chloride would be completely re- 

 duced to cuprous chloride by the action of the iron-pyrites 

 which is universally present in all crystalline and meta- 

 morphic rocks) was decomposed into cuprite and cupric 



N 2 



