If we connect a 0.1-molar solution of ferric chloride with a 0.1-molar solution of ferrous chloride, by means of a "salt bridge" and a pair of platinum electrodes dipping into the solutions and connected with the voltmeter (see p. 253), a current is produced, the positive current entering the voltmeter from the electrode placed in the ferric chloride solution (‹exp.›). It is evident that, in the effort to establish equilibrium, ‹ferric ions› in the ferric chloride solution ‹are reduced› at the expense of the ‹oxidation of ferrous ions› in the ferrous chloride solution. If we consider only the ratio of the concentration of the ferro-ion to that of the ferric-ion in each of the salt solutions and leave out of consideration, for the moment, other, secondary, electrical forces,[544] it is clear that the ratio [p271] [Fe^{2+}]_{1} : [Fe^{3+}]_{1} in the ferrous salt solution, considered by itself, is far closer to the point of equilibrium[545] than the ratio [Fe^{2+}]_{2} : [Fe^{3+}]_{2} in the ferric chloride solution, in which the concentration of ferric-ion is enormously ‹greater› than that of ferro-ion, while the equilibrium constant demands that the ferro-ion should be in great ‹excess›. The strongest tendency to change must be toward a reduction of the concentration of the ferric-ion in the solution of ferric chloride, which is in agreement with the observed direction of the current. Equilibrium, it may be added, will be reached when the ‹ratio› of the concentration of ferro-ion to that of ferric-ion is the ‹same› in both solutions.[546] The addition of potassium fluoride to the ferric chloride solution converts the ferric-ion into the rather stable complex ferrifluoride-ion FeF_{6}^{3−}, whose potassium salt K_{3}FeF_{6} is formed. The [p272] concentration of ferric-ion being ‹decidedly› reduced, the system must be nearer to the condition of equilibrium, the potential must fall (‹exp.›). It is again evident (p. 255) that the ‹oxidizing agent› is clearly the ‹ferric-ion›, and not the total quantity of the ferric salt in the solution.