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 will, 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 current 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 

 crj'stallised in thin lammee. Some beautiful samples of sulphide of 

 copper were also produced in six-sided prisms, beaiing the same 

 angles and modifications, as those produced by nature herself. 

 Protoxide of copper was obtained in fine octahedrons, and 

 Ai'agonite 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, \iz. : the formation of the last-named 

 mineral species, in steam engines. The concretions formed in 

 boilers of steam engines have been fomid, m 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 Annalcs, that wherever carbonate of 

 lime is precipitated at a high temperature, and under a certaiu 

 degree of pressui'e, we have production of Ai'agonite. 



