In the first place, if the formation of ions occurs primarily during the exchange of atoms in ‹collisions of molecules›, then, as Whetham[85] has shown, the specific conductivity (of 1 cm.^3) of an electrolyte, like hydrochloric acid, must increase with the concentration and must increase, approximately, as a function of the ‹third› power of the concentration. The more concentrated the solution, the more frequent the collisions between the dissolved molecules must be. As a matter of fact, as shown in the following table, the conductivity [p053] increases a ‹little less› than proportionally to the ‹first› power of the concentration—‹which is in conflict with the assumption made in the hypothesis of Clausius›, but in perfect agreement with the hypothesis of Arrhenius. The small ‹decrease› with increasing concentration, in the simple ratio between conductivity and concentration, is due to the decreasing degree of ionization in the more concentrated solutions, as demanded by the hypothesis of Arrhenius. The table gives, in the first column, the specific conductivities of hydrochloric acid at 18°, and, in the second column, the concentrations; these concentrations are expressed in moles or gram-equivalents per cubic centimeter; the last column gives the ratio of conductivity to concentration. Conductivity Conductivity of 1 c.c. Concentration ───────────── Concentration. 0.00370 0.00001 370 0.00734 0.00002 367 0.01092 0.00005 364 0.01800 0.00005 360 0.03510 0.00010 351 Furthermore, facts admitted by Clausius to be inexplicable by his own assumptions receive, in the theory of Arrhenius, at least a quantitative formulation borne out by a mass of corroborative evidence. The difference in conductivity between pure water and sulphuric acid is such a fact, mentioned by Clausius. Determinations of the ionization of sulphuric acid and of water, by the conductivity methods which are based on the theory of Arrhenius, show that, while sulphuric acid is very considerably ionized (see p. 104), water is scarcely ionized at all. The ionization of water (see p. 104) has been determined quantitatively by at least four independent methods of examination,[86] and, minimal as the ionization is, the results agree so well with each other that van 't Hoff[87] was led to write: "If one is not previously convinced of the correctness of the theory of electrolytic dissociation, hardly any result won by means of it is so convincing, as the agreement between the conclusions reached in completely different ways as to the degree of dissociation of water itself. After such an agreement, it is hardly conceivable that the basis on which all these results rest should further be altered."