440 Gooch and Gates — Decomposition of Hydrochloric Acid. 



From the results given it is obvious that, under the condi- 

 tions, oxygen was liberated only when the silver surface open 

 to attack was small and in no case attained the proportion 

 noted by Doumer. Though Doumer states, in regard to his 

 earlier experiments at least, that no chlorine or oxygen-acid of 

 chlorine was found in the anode liquid, according to our 

 experience when oxygen w T as set free it was always accom- 

 panied by at least a recognizable amount of chlorine, Silver 

 oxide in mixture with silver chloride was observed upon the 

 anode in every experiment, and the formation of the oxide 

 began as soon as the electrolysis was started. It seems plain 

 that so long as the anode exposes a large silver surface, open 

 to easy attack, both oxygen and chlorine attack it. Silver 

 chloride once attached may remain fixed upon the anode, but 

 silver oxide is subject to the action of the hydrochloric acid as 

 well as to that of liberated chlorine, ionized or molecular. 

 Only when the attackable surface becomes sufficiently limited 

 does the evolution of oxygen begin, and it was repeatedly 

 noted that an established evolution of oxygen could be easily 

 interrupted by disturbing the protecting film upon the anode. 



The formation of the easily diffusible colloidal silver chloride 

 which occurs when the free surface of the silver anode is 

 restricted and the potential across the electrodes rather high, 

 can hardly be due to the simple action of chlorine upon silver 

 since it does not take place when a silver anode surface is 

 freely exposed. Apparently the production of silver oxide 

 precedes the formation of the colloidal chloride. According 

 to our experience, when freshly precipitated silver chloride is 

 submitted to the action of dilute hydrochloric acid it gradually 

 becomes more crystalline, and not colloidal, while dilute 

 hydrochloric acid acts upon silver oxide to form finely divided 

 silver chloride, and the formation of cloudy colloidal 

 silver chloride takes place characteristically when silver oxide 

 held in platinum gauze is dipped into chlorine water, soluble 

 silver hypochlorite being, no doubt, formed simultaneously. 

 So it would seem that the condition under which colloidal 

 silver chloride is most likely to form in the electrolysis of 

 hydrochloric acid exists when silver oxide formed upon the 

 anode is liable to the attack of chlorine, some silver chloride 

 being formed in the direct action of chlorine upon silver 

 oxide, and some by the action of the hydrochloric acid of the 

 solution upon soluble silver hypochlorite. This, it seems to 

 us, is probably the action which in every case gave rise to a 

 cloud of colloidal silver chloride about the anode in the trans- 

 ference work of JN"oyes and Sammet* with solutions of 

 chlorides. 



*Loc. cit. 



