LECTURE V.] HISTORY OF CHEMISTRY. 77 



of the ammonia employed was generated anew on the de- 

 composition of the green substance by the action of water 

 upon it. They explained these observations by the assumption 

 that potassium consisted of potash and hydrogen ; and that 

 the latter was liberated by treatment with ammonia, as well as 

 with water, the alkali combining simultaneously with the 

 ammonia or with water. Thus, in accordance with their view, 

 potassarnide was composed of ammonia and potash, and it was 

 decomposed into these constituents by the action of water 

 upon it. 



Davy, meanwhile, had reverted to his first explanation, and 

 he now attacks these latest results obtained by Gay-Lussac and 

 Thenard. 34 In so far as the accuracy of his experiments is 

 concerned, however, he falls short of his opponents, although 

 he is more fortunate and more masterly in the interpretation of 

 them. In his view, the evolution of hydrogen during the 

 action of potassium on ammonia, arises from the decomposition 

 of the latter. According to him the green substance is com- 

 posed of potassium and the residue from the ammonia gas. 

 On treating the green substance with water, the latter is 

 decomposed into its constituents, regenerating ammonia, and 

 giving its oxygen to the potassium which is thus converted into 

 potash. 35 In addition to this, since he considers fused caustic 

 potash to be free from water, he finds in the conditions 

 necessary for the preparation of potassium, a further argument 

 against its containing hydrogen. 



Gay-Lussac and Thenard persist, at first, in their previous 

 opinion that potassium and sodium are hydrogen compounds, 36 

 and in this they are supported by the contemporaneous state- 

 ments made by Berthollet 3T and by D'Arcet, 38 who regard fused 

 potash as containing water. In 1811, however, they adopt 

 Davy's view. 39 The reason for their change of opinion is to be 

 found in the following facts. They had observed that the 



34 Phil. Trans. 1808, 365 (Note). 33 Ann. Chim. 75, 168 et seq., 264. 

 36 Ibid. 75, 299. 37 Mem. d'Arcueil. 2, 53. M Ann. Chim. 68, 175. 

 Rech. phys. chim. 2, 250, etc. 



