It is evident,[150] from Walden's equation showing the relation between the ionizing power and the dielectric constant of a solvent (p. 63), that the presumption is that hydrogen chloride in benzene solution is not absolutely non-ionized, but rather that it is ionized in traces.[151] No exact measurements of the [p085] ‹degrees of ionization of hydrogen chloride in benzene solution› have been made; that the solution shows an enormous resistance to the passage of the electric current and can be, at best, very little ionized, is all that has been established. In default of exact data, the semiquantitative determination by Kablukoff, showing that a 0.25 molar solution of hydrogen chloride in benzene has a resistance of 120 × 10^6 ohms, is of interest. From the meager data concerning the dimensions of the electrodes used, one may calculate (with the aid of a not unreasonable assumption as to the limiting value of the conductivity, at infinite solution) that the degree of ionization of the acid in the solution is perhaps of the order 5E−9, and the concentration of hydrogen-ion,[152] consequently, roughly 10^{−9}. Now, the evolution of hydrogen by means of zinc, in aqueous solutions, takes place according to the equation Zn ↓, + 2 H^{+} ⇄ Zn^{2+} + H_{2} ↑, and depends on a ‹ratio of the concentrations› of zinc-ion and hydrogen-ion[153] (Chapters XIV and XV, ‹q.v.›). Even if the concentration of hydrogen-ion is very small, zinc will liberate hydrogen, provided the conditions are such that the concentration of zinc-ion cannot reach a large enough value to satisfy the equilibrium ratio, and stop the action. Now, in an alkaline solution, zinc-ion is converted into zincate-ion (Zn^{2+} + 4 HO^{−} ⇄ ZnO_{2}^{2−} + 2 HOH) and a large concentration of zinc-ion cannot accumulate. The consequence is that zinc liberates hydrogen freely even from alkaline solutions, for instance from molar solutions of potassium hydroxide, in which the concentration of hydrogen-ion, roughly 10^{−14}, is ‹very much smaller› than that calculated for the benzene solution of hydrogen chloride (namely, 10^{−9}). Now, although the values of the solution-tension constants of elements change most decidedly with a change of solvent, it seems likely[154] that their ‹ratios›, on which their mutual displacement depends, will not be found materially altered. Zinc chloride being insoluble in benzene, the ratio for equilibrium may not be fulfilled for zinc in contact with a benzene solution of hydrogen chloride. Hence, with that solvent, ‹the evolution of hydrogen may, so far as it goes, very well be due to precisely the same machinery as that operating in aqueous solution›. The liberation goes on until the metal is protected against any further action by a film of the solid chloride. It seems, therefore, at least possible, that the evolution of hydrogen observed by Kahlenberg and his collaborators[155] is a purely ionic