Geology and Magnetism. 503 



■' In order to ascertain experimentally what are the circumstan- 

 ces which tend to produce these conditions, we have only to procure 

 a galvanic battery and connect it with two platinum poles, which 

 we place in a vessel to serve as the precipitating trough.* In this 

 trough we place a saturated solution of a metallic salt — for instance, 

 copper — when on examination, if the battery possess but feeble 

 power, we shall find that crystalline copper will be deposited ; if, 

 however, we dilute this solution with twice, thrice, or four times its 

 bulk of water, the metallic deposit will assume a very different aspect : 

 it will then be aggregated in a flexible state, or a reguline deposit. 

 If we now dilute this same solution to an infinitely greater extent, 

 the metal will still be reduced, but in the form of a very fine black 

 powder. 



" Almost all metallic solutions may be substituted for that of the 

 sulphate of copper, and the experiment will show nearly the same 

 result, namely, that the strength of the metallic solution influences 

 the nature of the deposit. 



" If we examine the converse of the experiment, and take a solution 

 of sulphate of copper, and use successively, first, one very small 

 battery, then two or three batteries arranged in a series, and lastly, 

 a very intense battery, we shall find that with this self-same solution 

 we can obtain by these means, first, a crystalline, then a reguline, 

 and subsequently a black deposit. 



" The above variable state in which minerals are deposited by the 

 battery is of very common occurrence in mineral veins • and even 

 the same vein presents large and small crystals, and often of variable 

 composition, within a very small compass." 



Mr. Hopkins concludes this portion of the subject by the 

 following remark, and allusion to the result obtained by Mr. 

 Fox, in his experiments in the mines of Cornwall : — 



" Comparing these facts with those observed in metalliferous de- 

 posits, we find a very striking coincidence ; and when we apply 

 similar laws and orders of deposition to mineral veins, the problem 



* See Smee's excellent work on this subject, second edition, p. 113. 



