xiii THE DECOMPOSITION OF THE ALKALIS 273 



substance which combined very strongly with one con- 

 stituent and thus set the other free. 



Berzelius and Hisinger (1803) decompose salts by the 

 electric current. Berzelius and Hisinger in 1803 made 

 the further discovery that dissolved salts were also 

 decomposed by the current, the acid of the salt collecting 

 with the oxygen round the positively-charged wire and the 

 base with the hydrogen round the negatively-charged 

 wire (Ann. de Chimie, 1804, 51, 172). 



Davy constructs an electric battery. On leaving the 

 Pneumatic Institute at Bristol in 1801 to take up the Pro- 

 fessorship of Chemistry at the Royal Institution, Davy at 

 once took up the work of investigating the decomposing 

 action of the electric current. He built up for this purpose 

 a large battery " containing 24 plates of copper and 

 zinc 12 inches square, 100 plates of 6 inches, and 

 150 of 4 inches square, charged with solutions of alum 

 and [nitric] acid." After describing, in his Bakerian lecture 

 of 1806, "a number of decompositions and chemical 

 changes produced by electricity," he concluded "that the 

 new methods of investigation promised to lead to a more 

 intimate knowledge than had hitherto been obtained, con- 

 cerning the true elements of bodies " which had not hither- 

 to been decomposed (A.C.R. VI. 5). 



Davy (1807) prepares a metal from potash. During the 

 autumn of the following year Davy used the experience 

 gained in these researches in his brilliant and successful 

 attempt to decompose the caustic alkalies. Although Black 

 had demonstrated fifty years earlier the relation of these 

 substances to the mild alkalies, nothing whatever was known 

 of their nature. They had usually been regarded as 

 elements. Davy himself, knowing that ammonia was a com- 

 pound of nitrogen and hydrogen, expected that the caustic 

 alkalies would prove to be compounds of nitrogen with other 

 combustible substances, perhaps sulphur or phosphorus. 



T 



