LIQUID ELEMENTS OF THE VOLTAIC CIRCLE. 225 



tive metal acting as the zincoid, have thus been slowly produced, 

 in a single circle with a weak exciting fluid ; which products 

 have exhibited distinct crystalline forms, resembling natural 

 minerals, not otherwise producible by art. The hydrogen 

 evolved upon a platinum chloroid, immersed in the solution of 

 a copper or iron salt, may also reduce these metals upon the 

 surface of the platinum, in the form of brilliant octahedral crys- 

 tals. In the active cells themselves a secondary decomposition 

 is apt to occur, the hydrogen evolved decomposmg the salt of 

 zinc which accumulates in the liquid, and occasioning a depo- 

 sition of that metal upon the copper plate ; an occurrence which 

 may determine an opposite polarity, and cause the action of the 

 circle to decline. But on disconnecting the zinc and copper 

 plates, the foreign deposit upon the latter is quickly dissolved 

 off by the acid. The inconvenience of this secondary decom- 

 position in the exciting cells is avoided by dividing the cell into 

 two compartments, by a porous plate of earthenware, or by a 

 humid membrane, interposed between the zinc and copper 

 plates. The salt of zinc formed about that metal is prevented 

 from diffusing to the copper, by the diaphragm, although it 

 allows, from its porosity, a continuity of liquid polarizable par- 

 ticles between the metals. 



Before leaving the subject of the liquid and solid elements of 

 the voltaic circle, I may offer for consideration some opinions 

 respecting their internal constitution, of a more speculative 

 character, which the chemical theory of the voltaic circle sug- 

 gests. 



The phenomena of electricity of friction, and of high tension 

 appear to indicate that all compound bodies whatever are pola- 

 rizable, under an intense induction. On the chemical theory 

 this would imply that they are all binary compounds, or at least 

 capable of a binary disposition of their elements. And it is 

 remarkable that recent discovery has detected such a constitu- 

 tion in several bodies containing a large number of atoms, and 

 has rendered it probable in a great many others ; ether, for in- 

 stance, has been found to be the oxide of ethyl, benzoic acid 

 the oxide of benzoyl, and all the essential oils appear to be 

 bodies of a similar constitution. But the molecular constitution 

 of such complex compounds appears not to be fixed and inva- 

 riable. Alcohol for instance, when free may be the hydrate of 

 ether, that is a ternary compound ; but alcohol replaces water 



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