22 



wards the negative plate ; the effect being due to one con- 

 stant direction in which the hydrogen moves, uniting with the 

 oxygen at one pole, and becoming liberated from it at the other. 



We have already observed that the nature of the reduced 

 metal depends on the intensity of the current and the strength 

 of the solution. If the current be very intense, causing the evo- 

 lution of the hydrogen from the negative plate, it forms a fine 

 black powder ; if none evolves, the metal is generally thrown 

 down in its crystalline state. 



Mr. Smee observes, e( that the quantity of electricity passing 

 in a solution of copper curiously influences the state of the cry- 

 stals, for there are two varieties of this deposit ; one of which 

 arises from a deficiency of quantity, relation to the strength of 

 the solution, and in this state the new plate of metal is like an 

 aggregation of sand, in fact like common sandstone, the particles 

 having no more cohesion or consistence. In this state the plate 

 of metal is in the utmost state of brittleness, and this, we must 

 recollect, is produced by too small a quantity of electricity in a 

 strong metallic solution. The second variety of the crystalline 

 state of metals arises from a large quantity of electricity in re- 

 lation to the size of the plate ; thus, by using a very large posi- 

 tive pole, connected with a battery of feeble intensity, and by 

 employing at the same time a strong solution, large crystals, 

 possessing the utmost degree of hardness, will be thrown 

 down." 



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 pro- 

 blem of their formation is easily solved without having recourse 

 to the igneous theory*. 



* Mr. Fox has obtained an electro-type copper plate by the agency of these 

 subterranean currents. He found their natural direction to be from south to 

 north in Pennance mine. After a few days crystals were formed in the nega- 

 tive plate, but two months had nearly elapsed before the apparatus was removed 

 from the circuit. 



