248 CRYSTALLIZATION 



oxides are dissolved in the acids, they are che- 

 mically united with them, and thus maintained 

 in a state of transparent solution, like salts in 

 water, in opposition to their specific gravity ; 

 and may be crystallized by evaporation or by 

 cold.* 



Could we clearly explain why sugar, gums, 



* Philosophers have never yet determined fully, why innu- 

 merable bodies arrange themselves in the crystalline form, on 

 passing from the fluid to the solid state. But it is known, that 

 when salts, rocks, and many metals, are converted into the 

 liquid form, whether by the direct agency of caloric alone, or by 

 means of a chemical menstruum, their particles arrange them- 

 selves in regular series, at various angles, forming symmetrical 

 aggregates, that cohere in definite forms as they cool down. 

 When sulphur, iodine, camphor, benzoic acid, with many other 

 simple and compound bodies, are converted into the gaseous 

 state, they also crystallize in regular forms on cooling down, like 

 solutions of salts in water, or metals in acids. 



From some recent experiments performed by M. Bequerel and 

 Mr. Cross, it has been supposed that electricity is the agent by 

 which crystals are aggregated. But if electricity be regarded as 

 a distinct power sui generis, and the only cause of crystallization, 

 why does water and a thousand other liquids assume the solid 

 and symmetrical form on merely reducing their temperatures ? 

 There can be no doubt, that when a current of voltaic electricity 

 is directed for days, weeks, and months, upon salts and rocks, 

 as in the experiments of Mr. Cross, it decomposes and transports 

 their elements to the extremities of the battery, where they will 

 assume the crystalline form : but it is equally certain, that crys- 

 tallization is constantly going on in the laboratory of nature, 

 where no electric action can be detected by the most delicate 

 tests. 



The whole of this problem is resolvable into one of still higher 

 importance and generality; that is, whether electricity be only 



