LECTURE V.] HISTORY OF CHEMISTRY. 79 



He does not appear, however, to have had many adherents in 

 this view, and, so far as hydrochloric acid is concerned, he also 

 assumed the existence of oxygen in it. Chlorine was looked 

 upon as oxygenated muriatic acid, and was supposed to be pro- 

 duced from muriatic (hydrochloric) acid by its taking up oxygen. 



These latter views were strengthened by the experiments of 

 Henry, and by the interpretation of them which he gave. 45 

 He passed electric sparks through gaseous hydrochloric acid, 

 which was confined over mercury, and obtained hydrogen, 

 while the metal was simultaneously attacked by what he 

 believed to be free oxygen. This led him to the assumption 

 of the presence of water in hydrochloric acid, a view which 

 found general approval since the investigations of others 

 appeared to be in agreement with it. 



In 1808, Davy had decomposed hydrochloric acid by 

 means of potassium, 46 and in this way had obtained hydrogen 

 and potassium chloride, the latter of which he had also pre- 

 pared by burning potassium in chlorine. He showed, in 1809, 

 that the chlorides (muriates) of the metals are not decomposed 

 by heating them with phosphoric glass, 47 or with silicic anhy- 

 dride, but that decomposition at once begins when aqueous 

 vapour is passed over the mixture. 48 Davy was of opinion that 

 Henry's hypothesis furnished the explanation of these experi- 

 ments, and that hydrochloric acid could only be separated as 

 soon as the quantity of water necessary for its existence was 

 supplied. Gay-Lussac and Thenard further showed, about the 

 same time, that water is produced as well as silver chloride by 

 the action of this acid upon silver oxide ; and, as formerly, they 

 assumed that this water was already present in the hydrochloric 

 acid. 49 They then effected the synthesis of the acid, by expos- 

 ing a mixture of chlorine and hydrogen to sunlight. 50 On this 

 occasion, they advance a complete theory regarding hydro- 



45 Phil. Trans. 1800, 191. 46 Ibid. 1809, 91; A.C.R. .9, 7. 



47 Phosphoric glass is calcium metaphosphate ; obtained by sufficiently 

 strongly heating monocalcium phosphate. 48 Phil. Trans. 1809, 93 ; 

 A.C.R. 9, 9. 49 Rech. phys. chim. 2, 118. 50 Ibid. 2, 159. 



