2i 4 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



three others almost filled with water were used to dissolve 

 the gas. By surrounding the bottles with ice, Berthollet 

 obtained yellow crystals which he considered to be the 

 solidified gas (A.C.R. XIII. 13-14) ; these have since been 

 shown to be a compound of the gas with water. 



Berthollet found that solutions of chlorine in water were 

 decomposed by exposure to light, oxygen being liberated 

 and muriatic acid reproduced. Scheele had regarded 

 chlorine as muriatic acid which had " lost one of its 

 constituents," namely, phlogiston ; he would therefore have 

 interpreted this experiment as a decomposition in which 

 water was robbed of its phlogiston by the chlorine, whilst 

 the oxygen which it contained was set free. This view may 

 be expressed by the equation : 



Chlorine + water -> muriatic acid + oxygen. 



(Hydrogen +oxygen.) (Chlorine-)- hydrogen.) 



Berthollet preferred, however, to regard the change as a 

 simple decomposition of chlorine into muriatic acid and 

 oxygen : 



Chlorine -> muriatic acid + oxygen 



(Muriatic acid+oxygen.) 



The fundamental weakness of Berthollet's theory lay in 

 the fact that chlorine by itself could not be decomposed into 

 muriatic acid and oxygen even by the most drastic treat- 

 ment. This was in direct contradiction to his own view 

 that in chlorine 



" the vital air .... adheres so feebly to the marine acid 

 that the action of light suffices to disengage it promptly" 

 (A.C.R. XIII. 20). ^ 



Berthollet shows that chlorine is not an acid. Another 

 difficulty in regarding chlorine as a compound of muriatic 

 acid with oxygen arose when Berthollet himself discovered 

 that chlorine was not an acid. He points out that " Scheele 



