Forffiation of Minerals by Electro-Chemical Action. 331 



and other substances which occupy veins and beds, come in contact 

 with the mineral waters which rise from all parts of the earth's in- 

 terior. Time then becomes an element in the growth of the crystal- 

 line substances formed, an element which enters indefinitely into all 

 natural phenomena, but which we can employ only within certain 

 limits, sufficient, however, to obtain marked effects, as is shewn by 

 the results obtained during the period which has elapsed since 1845. 



Among the methods adopted in these experiments were the fol- 

 lowing: — 



First Process. — This consisted in making a solution of silica or 

 alumina in caustic potash or soda, react weakly upon a couple, formed 

 of a plate of oxidisable metal, and a copper or platinum wire, round 

 which the plate is bent, the whole being contained in a vessel closed 

 by a cork, and left to spontaneous action. 



In 1845 an apparatus was arranged, with a plate of amalgamated 

 zinc surrounding a copper wire, and a solution of silica in potash, 

 marking 22° on the areometer ; water was decomposed, with evolution 

 of hydrogen and formation of oxide of zinc, which dissolved. A 

 fortnight afterwards very small regular octahedral crystals began 

 to be perceptible on the zinc plate, the composition of which was 

 represented by the formula Zn 0, HO. The bulk of these crystals 

 increased gradually, without passing a certain limit, about one 

 millimetre, on each side. 



In operating with alkaline solutions, more or less concentrated, it 

 was observed that the crystals were larger and better defined when 

 the strength was not beyond 20° or 25°. Other arrangements 

 were made in 1845, by substituting for the zinc-copper couple a 

 lead-copper one, and employing an alkaline solution of 25°; the lead 

 was slowly attacked, the protoxide formed dissolving, and after sa- 

 turation was deposited upon the surface of the plate of lead in 

 anhydrous crystals. (Pb O.) 



These crystals, some of which measured several millimetres, were 

 transparent, of a darkish green colour, and gave on trituration a 

 yellowish powder. They were so grown together that only parts of 

 their extremities were visible. Other reasons make it probable that 

 the crystals are derivatives of a right rhombic prism. 



Second Process, — Sulphuret of lead or galena (Pb S) was made 

 to act upon a saturated solution of sulphate of copper and of chloride 

 of sodium, diluted with an equal volume of distilled water with a 

 view of obtaining compounds of lead, having analogues in nature. 



In May 1845 I made several arrangements of galena and th^ 

 mixture of chloride of sodium and sulphate of copper, which were 

 left to themselves until the present time. The following are the 

 products which have been formed, either upon the pieces of galena, 

 or the bottom or partitions of the vessels : — 



1. Chloride of sodium in cubes, cubic octahedrons, and eren beta- 



