We will turn now to the consideration of evidence bearing on the theory of ionization, found in the data on osmotic pressure. The apparent molecular weight of hydrogen chloride is found to be smaller than 36.5, when determined in aqueous solution (p. 37), and it is found to approach the limit 18.25 as a more and more dilute acid is used.[114] The value found represents the average molecular weight of all the molecules in any solution, the osmotic pressure, freezing-point or boiling-point of which has been taken. It is evident that, if there is dissociation of hydrogen chloride into hydrogen and chloride ions, the average values found for the molecular weight must be lower than 36.5, ‹must be variable›, and must ‹approach› the ‹limit› 18.25, as the dissociation into the smaller molecules becomes more and more complete. Such a result is, therefore, what we would anticipate on the basis of the theory of ionization. For a salt like potassium chloride KCl, a similar tendency toward a minimum, average molecular weight of (K^{+} + Cl^{−}) / 2 or (39.1 + 35.5) / 2 = 37.3 would be anticipated, and, as a matter of fact, molecular weight determinations with potassium chloride in aqueous solution give results agreeing with such a tendency.[115] For a salt like calcium chloride, on the other hand, we would expect that its ionization into ‹three› ions, according to the equation CaCl_{2} ⇄ Ca^{2+} + 2 Cl^{−}, would give a minimum, not of one-half the formula weight, but of one-third, viz., (Ca^{2+} + 2 Cl^{−}) / 3 or (40 + 71) / 3 = 37, when the molecular weight determination is carried out in aqueous solution. As a matter of fact, with salts of this type, the determinations, by osmotic pressure methods, indicate a dissociation into ‹three› smaller components, as required by the theory. It may be added that, for [p068] a salt, sodium mellitate, Na_{6}(C_{12}O_{12}), the salt of a hexabasic acid, Taylor found average molecular weights tending to a minimum of ‹one-seventh› of the formula weight, as we should expect from the ionization of the salt into seven smaller molecules, (C_{12}O_{12})Na_{6} ⇄ 6 Na^{+} + (C_{12}O_{12})^{6−}.