438 Gooch and Gates — Decomposition of Hydrochloric Acid. 



cathode and an anode consisting of a silver disc about 3'5 cm in 

 diameter, the current density not exceeding 4*5 milliamperes 

 to the square centimeter, chlorine was not evolved ; but some 

 oxygen was liberated, and in every case silver chloride formed 

 a cloud about the anode. The transfer number calculated 

 from the total amount of silver deposited in the voltameter 

 and the change in the strength of the acid at the cathode 

 agreed very closely with the number based upon a comparison 

 of voltameter indication with the change in the chlorine con- 

 tent of the anode material, this chlorine content having been 

 found by determining the fixed silver chloride together with 

 that precipitable by silver nitrate from the anode liquid. The 

 titration of the anode liquid for acidity gave, however, utterly 

 discordant results, owing probably, it is said, to the liberation 

 of some oxygen at the electrode and the production of a cor- 

 responding quantity of acid. The transfer number calculated 

 for chlorine, upon the hypothesis that all the current was car- 

 ried by the ions of hydrochloric acid, varied somewhat with 

 the dilution and temperature, bat, at 29° for ]S T /20 and N/60 

 solutions, was on the average 166 # 6; but if it were assumed, 

 with Doumer, that one-third of the current passing is applied 

 to the electrolysis of hydrochloric acid, and one-third of the 

 entire indication of the voltameter were taken as the measure 

 of amount of current used solely in the electrolysis of hydro- 

 chloric acid, the transfer number for chlorine would become 

 499'8 and would indicate, as did Doumer's direct tests of 

 acidity at the anode and cathode, that the hydrogen and 

 chlorine ions have the same velocity. 



In the work of Noyes and Sammet conditions were adjusted 

 to restrict as far as possible the evolution of oxygen and 

 regeneration of acid. In that of Doumer conditions were 

 arranged to secure the maximum evolution of oxygen ; and 

 Doumer's inference that one-third of the current is always 

 utilized in electrolyzing hydrochloric acid rests fundamentally 

 upon the generalization that the proportion of anode oxygen 

 to cathode hydrogen is constant and independent of the 

 strength of current and of the concentration of the solution. 



In the work to be described we have further studied the 

 electrolysis of hydrochloric acid under various conditions. In 

 the experiments recorded in Table I, A, the apparatus used, 

 and shown in figure 1, was a Hoffman apparatus provided 

 with a Iiempel leveler, so that the gas measurements might be 

 made at the atmospheric pressure, and the electrodes were 

 introduced through rubber stoppers. In other experiments, 

 detailed in Table I, B, the apparatus was provided with an 

 anode which consisted either of a silver filtering crucible fitted 

 with an asbestos mat or of precipitated silver placed upon 



