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a PPl e_ g reen precipitate was 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 4 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 oxide. In a former 
communication to this Society (Proc. Lit. and Phil. Soc. 
XVII., 1877-78, 27 — 36) I mentioned that on heating 
some crystals of cuprous chloride in water in a sealed tube 
at a temperature ranging from 160° — 180° C, that minute 
green spots of a substance resembling atacamite were ob- 
served upon the sides of the tube. Further, on heating- 
cuprous oxide and a strong solution of chloride of sodium 
together in a sealed tube, at 150° — 180° chalcotrichite was 
formed, and also a green substance resembling atacamite. 
Wishing to ascertain whether atacamite could be prepared 
in larger quantity (in accordance with my supposition that 
all the copper ores are products of the decomposition of 
cuprous oxide, the latter substance being a secondary pro- 
duct of the oxidation of the metal itself) I made numerous 
experiments, mostly consisting in the heating of cuprous 
oxide with sodium chloride solution in sealed tubes, and ob- 
tained excellent results, by simply covering a quantity of 
cuprous oxide with a concentrated solution of sodium chlo- 
ride, exposing this mixture to the air at the ordinary tem- 
perature, and stirring it up occasionally. By proceeding in 
this way a very concentrated solution of cuprous chloride in 
sodium chloride can be obtained. After standing a few 
days this solution begins to decompose, a green insoluble 
substance separating out continually, which can easily be 
filtered off from the liquid portion and well washed in cold 
distilled water, in order to free it from all traces of cuprous 
chloride and sodium chloride. The substance thus obtained 
