«Degree of Ionization of an Electrolyte.»—The conductivity of a given weight of an electrolyte, for instance of its gram-equivalent weight, depends, then, at a given temperature on the extent to which it is ionized, the ions being the only carriers of the current in a solution of an electrolyte. The conductivity will also depend on the friction which the ions must overcome in moving through a solution, but, for sufficiently dilute solutions in a given solvent, the friction may be assumed to be approximately constant for given ions. For such solutions, then, the conductivity of a given weight of a given electrolyte at a given temperature may be said to depend wholly on the extent to which the electrolyte is ionized. Thus, the proportion of ionized electrolyte in a solution may be determined by measuring the conductivity. ‹The extreme limit of its conductivity, calculated for infinite dilution, represents complete ionization› of the electrolyte according to a fundamental postulate (§ 3, p. 41) of the theory of Arrhenius, and the ratio of the conductivity in a given solution to the conductivity of the same weight of electrolyte at infinite dilution represents then the ‹proportion of ionized electrolyte to the total electrolyte› used. This proportion is called its ‹degree of ionization› (commonly designated by α). If we call Λ_{‹v›} the conductivity of a gram-equivalent weight of an electrolyte in a given solution, and Λ_{∞} the limit of its conductivity for infinite dilution, then the degree of ionization is found from α = Λ_{‹v›} / Λ_{∞}. [p051] The method of calculation of α in a specific case may be illustrated as follows: the resistance of a cube of 1 cm. edge of a solution of hydrochloric acid, which contains 1.825 grams hydrogen chloride in a liter, is found to be 55.55 ohms at 18°. Its conductivity then is 1 / 55.55 reciprocal ohms. Now, 1.825 grams of hydrogen chloride is 1.825 / 36.5 or 1 / 20 gram-equivalent of the acid; a whole gram-equivalent of the acid would be contained in 20 liters or 20,000 c.c. Then Λ_{‹v›} = (1 / 55.55) × 20,000, or 360 reciprocal ohms. If we use the value at infinite dilution given above, α = 360 / 384, or 93.75%. That is, 93.75% of the hydrochloric acid is present in the ionized condition in such a solution, and 6.25% is not ionized. By making the assumption that ‹at infinite dilution electrolytes are completely ionized›, and by taking the ratio which the equivalent conductivity of a given solution of an electrolyte bears to the maximum limit-value (calculated for the conductivity at infinite dilution) ‹to be the degree of ionization of the electrolyte›, as just explained, the theory of Arrhenius has thus made it appear possible ‹to determine experimentally the proportion of ionized electrolyte present›.