SCT. XXIX. FORMATION OF CRYSTALS. 297 



considered to be simple bodies incapable of decomposi- 

 tion, were resolved by electric agency into their constit- 

 uent parts, and proved to be metallic oxides, by that 

 illustrious philosopher. / All chemical changes produced 

 by the electric fluid arfcs accomplished on the same prin- 

 ciple ; and it appears that in general, combustible sub- 

 stances, 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 distance from one another, 

 nay, even in separate vessels, if a communication be 

 only established by a quantity of wet thread, as the de- 

 composition 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. The great efficacy of Voltaic electricity in 

 chemical decomposition arises from the continuance of 

 its action ; and its agency appears to be most exerted 

 on fluids and substances which, by conveying the elec- 

 tricity partially and imperfectly, impede its progress. 

 But it is now proved to be as efficacious in the compo- 

 sition as in the decomposition or analysis of bodies. 



It had been observed that when metallic solutions are 

 subjected to galvanic action, a deposition of metal, some- 

 times in the form of minute crystals, takes place on the 

 negative wire. By extending this principle, and em- 

 ploying a very feeble Voltaic action, M. Becquerel has 

 succeeded in forming crystals of a great proportion of 

 the mineral substances, precisely similar to those pro- 

 duced 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 attraction already mentioned 

 as the great agent in the formation of solids. Both light 

 and motion favor crystalization. Crystals which form 

 in different liquids are generally more abundant on the 

 side of the iar exposed to the light : and it is well known 



