74 HISTORY OF CHEMISTRY. [LECTURE V. 



galvanic currents are only produced simultaneously with the 

 occurrence of chemical decompositions. He assumed that 

 electrical phenomena are the consequences of chemical pro- 

 cesses, but that mere contact is not sufficient to produce 

 different electrical conditions. 



Davy's theory could not be brought into harmony with 

 these views, and accordingly it was given up. This was not, 

 however, on chemical but on physical grounds. A new system 

 had in fact already arisen, which was able effectively to take the 

 place of the old one. This was the electro-chemical theory of 

 Berzelius. I postpone its discussion until the next lecture, 

 because otherwise I should require to enter fully into the re- 

 searches of Berzelius ; whereas I desire at this place to explain 

 more clearly the influence of Davy upon chemistry, by giving 

 some account of the discovery of potassium and sodium, and 

 of the discussion regarding the nature of these substances. 



In the course of his investigations respecting the conversion 

 of water into acid and basic substances, Davy had had oppor- 

 tunity of gaining a knowledge of the decomposing power of the 

 electrical current, since neither glass, agate, nor felspar had 

 proved able to resist its effects. He thus hit upon the idea of 

 exposing the alkalies also to this action, in order to separate 

 them into their constituents if any such were present in them. 18 

 For these experiments he first employs concentrated aqueous 

 solutions of potassium and of sodium hydroxides ; and as he 

 does not succeed in obtaining products of their decomposition 

 in this way, he next passes the current through the fused 

 alkalies. He now observes the formation of small metallic 

 globules, which burn, however, with great brilliancy, as soon as 

 they come into contact with the air. Yet, by suitable arrange- 

 ments, he succeeds in isolating small quantities of potassium 

 and of sodium, and in studying their most important properties. 

 I remark, in passing, that he only obtained potassium in the 

 fused state. Gay-Lussac and Thenard, who showed how to 

 effect the reduction of the alkali metals by means of iron, in 



18 Phil. Trans, 1808, i ; A.C.R. 6, 5. 



