ORIGIN OF SOME ORES OF COPPER. 255 



per cent. 



Cu 5638 



CI i4'95 



O 1078 



H^O 17-89 



the formula for this being CxL^O^Clj^ + gHJ^, or {Cn^O^Clj),, 

 + 9H,0. 



The third state of hydration is represented in the ata- 

 camite from Botallack^ Cornwall^ analyzed by Church 

 (Journ. Chem. Soc. [2] iii. 212)^ and that from TocopiJla, 

 near Cobija, Bolivia^ analyzed by Berthier (Ann. des Mines 

 [3] vii. 542) J the composition being as follows : — 



Botallack Atacamite. TocopiUa Afacamife. 



Cu 5^*90 Cu S3"^6 



01 1476 CI i4'92 



1019 O 9'37 



Hj,0 2215 Yi^O 22'4S 



and the formula C\x^0f^\^-\-6Hfi. 



Having given a general idea o£ the composition of the 

 various atacamites, I will now point out how some of them 

 can be prepared artificially. Field (Phil. Mag. [4] xxiv. 

 1862, p. 1 24) prepared the last-mentioned variety by adding 

 a solution of calcium hyj)ochlorite to an excess of cupric 

 sulphate and boiling the mixture for some time, when an 

 apple-green precipitate Avas observed which proved, on 

 analysis, to be identical with Berthier 's atacamite from 

 Cobija. If the ebullition were not sufficiently kept up, 

 the compound was found to contain only four atoms of 

 water. Proust prepared a green compound (which, no 

 doubt, was atacamite, although its exact composition is 

 not given) by exposing moist cuprous chloride to the air, 

 also by digesting a solution of cupric chloride with cupric 



