Van Name and Maryott — Chlorination of Benzene. 159 



elusive, and his results with toluene by no means conclusive, 

 as regards this point. 



Anode Potentials. 



As a more direct method of attacking this problem, we have 

 employed the well known principle that the presence, about an 

 electrode carrying the current, of a substance having a depolar- 

 izing effect, tends to lower the electrode potential. Thus a 

 substance which undergoes true anodic chlorination, i. e. an 

 active depolarizer for chlorine, should produce a measurable 

 lowering of the anode potential, unless its effect is so weak as 

 to be masked by the inevitable change in the nature of the 

 liquid caused by adding the depolarizer. 



The measurements were made by the Poggendorf compensa- 

 tion method, with a capillary electrometer. Acetic acid was 

 the solvent and lithium chloride the electrolyte in all cases. 

 To avoid contaminating the solution with water a special refer- 

 ence electrode was used, composed of a silver rod dipping into 

 an approximately normal solution of lithium chloride in acetic 

 acid to which a drop of a water solution of silver nitrate had 

 been added. Except for a short distance at its lower end, the 

 rod was coated with a layer of fused silver chloride to prevent 

 possible disturbing effects at the junction of air, metal, and 

 solution. The potential of this electrode was determined 

 before and after each set of measurements bv comparison with 

 a normal calomel electrode. JSTo appreciable changes in the 

 potential of the silver electrode occurred during the short 

 periods involved, but distinct changes took place upon long 

 standing. 



The electrolytic cell was a small glass jar of about 70 cc 

 capacity, fitted with a rubber stopper. Anode and cathode 

 were of bright sheet platinum, 21 x 50 mm and 11 x 25 mm respec- 

 tively, carried by short platinum wires sealed into glass tubes 

 passing through the stopper. The latter was also perforated 

 to admit the bent connecting tube of the vessel containing the 

 silver electrode, whose outlet was placed directly behind the 

 middle of the anode. 



After measuring the anode potential in the pure solution of 

 lithium chloride in acetic acid at a given current strength, the 

 benzene was added, the current adjusted to the previous value, 

 and the anode potential again determined. In every case the 

 benzene was found to cause a distinct rise in the potential. 



That the benzene, by depressing the ionization of the lithium 

 chloride and thus lowering the concentration of the CI 7 ions, 

 would have a tendency to raise the anode potential, would be 

 expected, and the obvious conclusion is, that in practice this 



