BOOK XIV, 



CHEMISTRY. 



CHAPTER IX. 



. 



THE ELECTRO-CHEMICAL THEORY. 



AMONG the consequences of the Electro-chemical Theory, must be 

 ranged the various improvements which have been made in the 

 voltaic battery. Daniel introduced between the two metals a partition 

 permeable by chemical action, but such as to allow of two different 

 acid solutions be'ino; in contact with the two metals. Mr. Grove's bat- 



~ 



tery, in which the partition is of porous porcelain, and the metals are 

 platinum and amalgamated zinc, is one of the most powerful hitherto 

 known. Another has been constructed by Dr. Callan, in which the 

 negative or conducting plate is a cylinder of cast iron, and the posi- 

 tive element a cylinder of amalgamated zinc placed in a porous cell. 

 This also has great energy. 



The Number of Elementary Substances. 



There have not been, I believe, any well-established additions to 

 the list of the simple substances recognized by chemists. Indeed the 

 tendency at present appears to be rather to deny the separate elemen- 

 tary character of some already announced as such substances. Pelo- 

 piurn and Niobium were, as I have said, two of the new metals. But 

 Naumann, in his Elemente der Mineralogie (4th ed. 1855), says, in a 

 foot note (page 25) : " Pelopium is happily again got rid of; for 

 Pelopic Acid and Niobic Acid possess the same Radical. . Donarium 

 had a still shorter existence." 



In the same way, when Hermann imagined that he had discovered 

 a new simple metallic substance in the mineral Samarskite from Miask. 

 the discovery was disproved by H. Rose (Pogg. Ann. B. 73, s. 449). 

 VOL. II. 40. 



