ORIGIN OF SOME ORES OF COPPER. 257 



per cent. 



Cu 5625 



CI i4'29 



O io"9S 



HjO 18-51 



loo'oo 



It will readily be seen that the above analysis agrees 

 very closely with the one made by Field already referred 

 to ; whence it follows that the substance prepared by 

 myself is identical in composition with the atacamite of 

 Copiapo, Chili. The rationale of the formation is briefly 

 this : — The cuprous chloride beld in solution by the sodium 

 chloride takes up oxygen from the air very rapidly, giving 

 rise to the formation of cupric oxychloride and cupric 

 chloride (the latter soluble in water), both eventually be- 

 coming hydrated." The following equation expresses the 

 first stage of the reaction, viz. : — - 



3Cu,Cl, + 05=CuCl„3CuO + 2CuCl,. 



Nearly all specimens of atacamite are intimately associ- 

 ated with cuprite ; so that it appears highly probable that 

 the former mineral has been obtained from the latter in 

 the manner stated, more especially as atacamite is found 

 in veins of other copper-ores associated with quartz, chal- 

 cedony, &c. in diorite and syenite. Again, at Sierra de 

 Lembe, near Ambriz, on the west coast of Africa, there 

 is a large occurrence of atacamite in the malachite deposits, 

 the '' gangue mineral " being quartz. Debray (Zeitsch. f. 

 Chem. 1867, p. 276) prepared crystallized atacamite by 

 heating together basic cupric nitrate and a concentrated 

 sodium-chloride solution for several hours at 200° C, also 

 by heating copper-ammonium sulphate with a strong 

 sodium-chloride solution at 100° C. Up to the present 

 time I have not succeeded in preparing the mineral in a 



SER. III. VOL. VI. s 



