83 
THE GEOLOGIST. 
influence of pressure and heat acting simultaneously upon different 
bodies whilst these bodies enter into chemical combination with 
one another. Nothing could be more simple than his mode of 
operating : Taking a thick glass tube, closed at one end, he places 
in it the substances intended to act upon each other, i. e., to pro- 
duce the combination he desires. To procure a great pres- 
sure, he makes use of highly volatile substances, such as 
ether or bisulphide of carbon which he adds to the contents 
of the tube. The latter is then hermetically sealed and 
placed in an oven, to which, at wiQ, a certain degree of heat 
(generally from 100 to 150 degrees centi-grade) can be given. 
In some cases Becquerel has added the action of a weak 
electric cuiTent to that exercised by heat and pressure in the 
experiments. 
By operating in this manner he has lately obtained Malachite or 
carbonate of copper, exactly imitating the natural species ; sulphide 
of silver, and Galena or sulphide of lead, have been obtained 
crystallised in thin laminae. Some beautiful samples of sulphide of 
copper were also produced in six-sided prisms, bearing the same 
angles and modifications, as those produced by nature herself. 
Protoxide of copper was obtained in fine octahedrons, and 
Aragonite or dimorphous carbonate of lime, in straight rectan- 
gular prisms so large as to permit an easy estimation of their 
angles. 
Before quitting the subject of Becquerel's experiments we would 
refer to an interesting fact, viz. : the formation of the last-named 
mineral species, in steam engines. The concretions formed in 
boilers of steam engines have been found, in cases where the 
incrustations were composed of carbonate of lime, to be almost 
always of that remarkable variety called Aragonite, distinguishable 
from the common carbonate or Iceland spar, not only by its pris- 
matic crystals, but also by their hardness which enables them to 
scratch those of the ordinary calcareous spar. It would seem from 
the foregoing observations, and from those formerly made by 
Gustav Rose, in Poggendorff's Annates, that wherever carbonate of 
lime is precipitated at a high temperature, and under a certain 
degree of pressure, we have production of Aragonite. 
