308 VOLTO-CHEMICAL ACTION. SECT. XXIX. 



substances, metals, and alkalies go to the negative wire, while 

 acids and oxygen are evolved at the positive. The transfer of 

 these substances to the poles is not the least wonderful effect of 

 the Voltaic battery. Though the poles be at a considerable dis- 

 tance from one another, nay, even in separate vessels, if a com- 

 munication be only established by a quantity of wet thread, as 

 the decomposition proceeds the component parts pass through 

 the thread in an invisible state, and arrange themselves at their 

 respective poles. According to Dr, Faraday, electro-chemical 

 decomposition is simply a case of the preponderance of one set 

 of chemical affinities more powerful in their nature over another 

 set which are less powerful. And in electro-chemical action of 

 any kind produced by a continuous current, the amount of action 

 in a given time is nearly, if not rigorously, proportional to the 

 strength of the current. The great efficacy of Voltaic electricity 

 in chemical decomposition arises not from its tension, but from 

 the quantity set in motion and the continuance of its action. Its 

 agency appears to be most exerted on fluids and substances 

 which by conveying the electricity partially and imperfectly 

 impede its progress. But it is now proved to be as efficacious 

 in the composition as in the decomposition or analysis of bodies. 

 It had been observed that, when metallic solutions are sub- 

 jected to galvanic action, a deposition of metal, sometimes in the 

 form of minute crystals, takes place on the negative wire. By 

 extending this principle, and employing a very feeble Voltaic 

 action, M. Becquerel has succeeded in forming crystals of a great 

 proportion of the mineral substances, precisely similar to those 

 produced by nature. The electric state of metallic veins makes 

 it possible that many natural crystals may have taken their form 

 from the action of electricity bringing their ultimate particles, 

 when in solution, within the narrow sphere of molecular attrac- 

 tion. Both light and motion favour crystallization. Crystals 

 which form in different liquids are generally more abundant on 

 the side of the jar exposed to the light ; and it is well known 

 that still water, cooled below 32, starts into crystals of ice the 

 instant it is agitated. A feeble action is alone necessary, pro- 

 vided it be continued for a sufficient time. Crystals formed 

 rapidly are generally imperfect and soft, and M. Becquerel found 

 that even years of constant Voltaic action were necessary for the 



