ORIGIN OF SOME ORES OF COPPER. i77 



the reaction between the sodium chloride and cuprous oxide, 

 and this cuprous chloride was decomposed into cuprous 

 oxide again and deposited on the sides of the tube as above 

 described. I shall refer to the importance of the occurrence 

 of chalcotrichite in conjunction with cuprite when I come 

 to consider the origin of all the copper-ores in a future 

 paper, and will therefore describe another series of expe- 

 riments, having for their object the direct formation of 

 malachite. 



Malachite. — Great difficulty was experienced in carrying 

 out these experiments for any length of time, owing to the 

 frequent bursting of the tubes, due, no doubt, to their being 

 somewhat weakened by the formation of silicates upon the 

 surface of the glass. Pure artificially prepared cuprous 

 oxide was placed in a glass tube, and covered with distilled 

 water saturated with perfectly pure carbonic acid gas, and 

 then sealed up and heated in the air-bath at a temperature 

 varying from 150° to 175°. After heating about fifteen 

 days, the tube was opened and allowed to stand exposed to 

 the air, when a thin film of malachite was observed coating 

 the small clumps of suboxide here and there. The action 

 of oxygen was found to be absolutely essential in the pro- 

 duction of malachite by this method, there being no sign 

 of any such formation in the tube before it was opened. 

 Thus there can be no doubt that the greater part of the 

 malachite formations have been produced by the action of 

 water contaiug carbonic acid gas in solution upon cuprous 

 oxide, as the malachite of the Gumeschewskoi Mine, near 

 Ekaterinenburg, in Russia, is found deposited in a dark- 

 coloured clay which penetrates a small limestone ridge, the 

 whole formation finally resting upon chloritic slate. I 

 have examined numerous specimens of malachite from all 

 parts of the world, and have always observed strong evidence 

 of the action of water upon them, there being numerous 



SEE. III. VOL. VI. N 



