33 
chalcotrichite. Continuing to heat the tube, on the 
eighteenth day it was opened, when it was found that no 
further formation of the prismatic substance had taken 
place, but there was a beautiful deposit of highly crystalline 
violet-red coloured cuprite on the sides of the tube. The 
fibrous substance was dissolved in nitric acid (after having 
been boiled in distilled water for several hours and carefully 
washed) and tested for chlorine, which was found to be 
entirely absent, whilst copper was present in large amount : 
hence there can be no doubt that this prismatic substance 
was the rare mineral chalcotrichite. From this experiment 
it is evident that cuprous chloride was formed at first by 
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 
experiments 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 vary- 
ing from 150° — 175°. After heating 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 production of 
malachite by this method, there being no sign of any such 
