MAXIMUM SPECIFIC ELECTRICAL CONDUCTIVITY IN CHEMISTRY. 121 
of the air into water and free chlorine, the solution here also gaining in specific 
conductivity.* 
The equation for this reaction may be put in the following form— 
(x+4)HCl+yH,0 + 0, — «HCl + (y + 2)H,0 + 2C1,. 
In this form the equation clearly indicates that the progress of the reaction in the 
direction indicated by reading from left to right involves a dilution, whereas its 
progress in the opposite direction involves a concentration of the hydrochloric acid. 
When the concentration of the free chlorine or of the dissolved oxygen is so small 
as to have only a negligible influence on the conductivity, the concentration of the 
maximal solution of hydrogen chloride coincides with the concentration at which 
equilibrium is established. 
OXIDATION OF HyproGEN CHLORIDE IN AQUEOUS SOLUTION BY CHROMIC ACID. 
Experiments were made in order to determine the relationship between the 
specific conductivities of known solutions of hydrochloric acid of different con- 
centrations and the time required to oxidise a small constant proportion of the 
hydrogen chloride contained in these solutions. 
Chromic acid was chosen as the oxidising agent for this purpose, because it gives 
rise to a marked change of colour on reduction. A difliculty arises, however, owing to 
the fact that the addition of this oxidising agent, itself a strong electrolyte, affects the 
conductivity of the whole system. Practically nothing is known of the conductivity 
of such mixtures. 
To obviate this difficulty, the quantity of chromic anhydride added was small. 
Further, the ratio of CrO, to HCl was kept the same for all the solutions. Under these 
conditions no serious error is incurred by regarding the conductivity in each case as 
being simply that of the aqueous solution of hydrogen chloride. It was found 
that the oxidation of the hydrogen chloride, as indicated by the change of colour 
due to the reduction of the chromic acid, proceeded more and more slowly the 
more closely the concentration of the solutions of hydrogen chloride taken approached 
that corresponding to maximum specific conductivity. 
It was not found possible to determine the end points with accuracy in the 
diluter solutions, as in them the reaction is very slow. The results of one series of 
| experiments are given in Table I. 
* Comp. BackeLanpt, Bull. de V Académie royale de Belgique, 3™ série, t. xl., N™ 3, 1886. 
