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ing in a soluble as well as a solid state ; therefore we should not 

 consider that the metals must necessarily be solid in their ori- 

 ginal state. Indeed there is some difficulty in preserving some 

 metals, especially iron and zinc, in their metallic state, in con- 

 sequence of their great affinity for oxygen ; and those metals 

 only which possess but little affinity for this element, such as 

 platinum, gold, silver and copper, are found formed and pre- 

 served in rocks in their metallic state. 



When w r e subject any metallic solution to the action of the 

 magnetic current, the metal will be reduced, in different states, 

 according to the strength of the solution and the intensity of 

 the current. 



In order to ascertain experimentally what are the circum- 

 stances which tend to produce these conditions, we have only to 

 procure a galvanic battery and connect it wdth 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 me- 

 tallic 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 ag- 

 gregated 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 so- 

 lution 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 crystal- 

 line, then a reguline, and subsequently a black deposit. 



The above variable state in which minerals are deposited by 



* See Smee's excellent work on this subject, Second Edition, p. 113. 



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