154 
was carefully dried over calcium chloride until its weight 
was constant, and portions weighed out and analysed quan- 
titativly with the following result, viz. : — 
Cu 
Cl 
.... 14-29 
0 
10-95 
h 2 o .. 
.... 18-51 
100-00 
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 my- 
self is identical in composition with the atacamite of 
Copiapo, Chili. The rationale of the formation is briefly 
this — “the cuprous chloride held in solution by the sodium 
chloride takes up oxygen from the air very rapidly, giving 
rise to the formation of cupric oxychloride and cupric chlo- 
ride (the latter soluble in water), both eventually becoming 
hydrated.” The following equation expresses the first stage 
of the reaction, viz. : — - 
3Cu 2 C1 2 + 0 3 = CuC1 2 3CuO + 2CuC1 2 . 
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, chalcedony, &c., 
in diorite and syenite. Again, at Sierra do Lembe, near 
Ambriz, on the West Coast of Africa, there is a large occur- 
rence of atacamite in the malachite deposits, the “ gangue 
mineral” being quartz. Debray (Zeitsch. f. Chem. 1867, 
276) prepared crystallised 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 crystalline state. A curious fact 
I may mention, viz., that natural cupric oxychloride should 
increase in hydration by three atoms of water. 
