Goochand Gates — Decomposition of Hydrochloric Acid. 435 



Art. XLT. — The Phenomena of the Electrolytic Decomposi- 

 tion of Hydrochloric Acid; by F. A. Gooch and F. L. 

 Gates. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cciv.] 



According to the prevailing theory of electrolysis, all the 

 ions of a solution, of whatever nature, are acted upon by the 

 electric forces and all carry the current by moving through the 

 solution. If more than one kind of ion is present that kind 

 which has the lowest deposition voltage is first deposited at the 

 electrode. 



In the decomposition of hydrochloric acid the hydrogen ions 

 derived from the acid travel to the cathode and are there con- 

 verted into neutral hydrogen. The chlorine ions move to the 

 anode, and if the solution is fairly concentrated, are there dis- 

 charged and converted to neutral chlorine. Under such con- 

 ditions, the hydroxyl ions of the solvent, water, having a 

 higher decomposition value than the chlorine ions, take part in 

 the transfer only to an insignificant extent. As the concentra- 

 tion falls to the point where the diffusion of the acid in solution 

 is insufficient to replace the chlorine ions which are removed 

 from the layer of liquid in contact with the anode, the hy- 

 droxyl ions of water may take part in the transmission of the 

 current from the solution to the electrode, and the polarization 

 rises until in extremely dilute solution it approximates the 

 decomposition value of water. From strong solutions of 

 hydrochloric acid the gases evolved are hydrogen at the 

 cathode and chlorine at the anode, while as the concentration 

 decreases oxygen from hydroxyl is evolved in place of chlorine. 

 LeBlanc has shown experimentally the following decomposi- 

 tion values for varying concentrations of hydrochloric acid: 







Decomposit 



ion Value 



2 Normal HC1 



1-26 v 



olts 



i " 



a 



1-34 



a 



1 « 



6" 



a 



1-41 



a 



_1_ " 



16 



it 



1-62 



a 



"32 



it 



1-69 



it 



According to this theory the transmission of the current 

 from the solution to the electrode is effected at the highest 

 dilution primarily by the ions of water, while in the interior 

 of the solution the current is presumably carried almost 

 entirely by the ions of the acid. 



A recent series of articles by Doumer* contains the 

 account of experiments in the electrolysis of hydrochloric acid 

 *Compt. Rend., cxlvi, 687, 897. 



