484 SPECIAL METHODS OF DISCOVERY. 



one part of oxygen. He proved soon after that soda is a 

 compound of oxygen and another white metal, to which 

 he gave the name of sodium. Lime is a compound of 

 calcium, and oxygen, magnesia of magnesium and oxygen, 

 barytes of barium and oxygen, and strontia of strontium 

 and oxygen. In short, the fixed alkalies and alkaline 

 earths are metallic oxides. When lithia was afterwards 

 discovered by Arfvedson, Davy succeeded in decomposing 

 it into oxygen and a white metal, to which the name of 

 lithium was given.' 'Davy did not succeed so well in 

 decomposing alumina, glucina, yttria, and zirconia by the 

 galvanic battery they were not sufficiently good con- 

 ductors ; but nobody entertained any doubt that they also 

 were metallic oxides. They have been all at length de- 

 composed, and their bases obtained, by the joint action 

 of chlorine and potassium ; and it has been demonstrated 

 that they also are metallic oxides. Thus it has been ascer- 

 tained, in consequence of Davy's original discovery of the 

 powers of the galvanic battery, that all the bases formerly 

 distinguished into the four classes of alkalies, alkaline 

 earths, earths proper, and metallic oxides, belong in fact 

 only to one class, and are all metallic oxides.' J Davy 

 had a previous hypothesis that the alkalies were compound 

 substances. 



Numerous batteries, of improved kinds and greater 

 power, were subsequently invented at various intervals of 

 time, and applied to make discoveries. Amongst other 

 purposes, their currents have been applied to produce 

 electrolysis, until nearly every elementary substance has 

 been set free, and various new compounds formed by that 

 method. Kitter, in 1812, invented his < secondary pile,' 

 consisting of discs of copper and cardboard electrically 



1 Thomson, History of Chemistry , vol. ii. p. 264. 



