LECTURE V.] HISTORY OF CHEMISTRY. 75 



i8o8, 19 first proved that potassium is solid at ordinary tempera- 

 tures. They used purer materials, and, by their method, they 

 had much larger quantities of the new substances at their 

 disposal. 



I cannot enter here into the complete history of potassium 

 and sodium, although the subject becomes highly interesting 

 from the facts that all Davy's experiments are at once checked 

 by the French chemists ; that the latter then bring forward 

 independent results, which Davy doubts ; and so forth. But 

 one point in this somewhat vigorously sustained discussion 

 seems to me to be of sufficient importance to deserve attention, 

 namely, the views concerning the constitution of potassium 

 and of sodium, and those concerning their relation to the 

 alkalies. 



In the decomposition of the alkalies, Davy had observed 

 that the potassium and sodium appear at the negative pole, 

 whilst oxygen is simultaneously evolved at the positive pole. 20 

 He had further found that the new substances possessed the 

 property of reducing metallic oxides ; 21 and he believed that 

 the alkalies were reproduced when the metals were burned in 

 oxygen. 22 From these results he draws the conclusions that 

 the alkalies are the oxides of metals, and that the substances 

 he has discovered are the metals themselves. 23 The physical 

 properties of the substances, especially their metallic lustre, 

 supported this view, although their low specific gravity seemed 

 to be an argument, but not a sufficient one, against his con- 

 clusions. Davy accordingly proposes, for the substances, the 

 names Potassium and Sodium, in which the termination is 

 intended to indicate their metallic nature. 



Davy now holds so firmly to this hypothesis regarding the 

 constitution of the alkalies, that he also regards as oxides many 

 other substances about whose composition the evidence is not 

 yet by any means so clear. Thus, like his contemporaries, he 



19 Ann. Chim. 65, 325. 20 Phil. Trans. 1808, 6 ; A.C.R. 6, 10. 

 21 Phil. Trans. 1808, 19; A.C.R. 6, 22. ** Phil. Trans. 1808, 8; 



A.C.R. 6, ii. 23 Phil. Trans. 1808, 32; A.C.R. 6, 34. 



