[59] Or, on the basis of the accepted molecular weights, abnormally high osmotic pressures, abnormally great lowerings of the freezing-point, raisings of the boiling-point, etc., were obtained. Van 't Hoff, originally, on account of these discrepancies, considered this extension of the Avogadro Hypothesis to hold only for the "majority" of substances in solution, not for all (Arrhenius, ‹loc. cit.›). It was considered to have ‹universal› application (for dilute solutions) only after Arrhenius had explained the exceptions with the aid of his theory of electrolytic dissociation. [60] That is, hydrogen chloride, in aqueous solution, depresses the vapor tension and the freezing-point and elevates the boiling-point considerably more than an ‹equimolecular› quantity, for instance, of glucose does, and gives a considerably higher osmotic pressure. The differences are relatively greater, the more dilute the solutions used. [61] A fourth interpretation advanced at one time in opposition to the theory of ionization is that salts like sodium chloride and zinc chloride are ‹hydrolyzed› and thereby produce more solute molecules, ‹e.g.› NaCl + H_{2}O → NaOH + HCl. Aside from the fact that such hydrolysis of salts, when it does occur (Chapter X.), is easily detected, and that it can be proved not to occur appreciably in the case of sodium chloride (‹loc. cit.›), this interpretation fails utterly to account for the results obtained with ‹acids, e.g.› HCl, HNO_{3}, H_{2}SO_{4}, and with ‹bases›, ‹e.g.› NaOH, Ba(OH)_{2}, which in aqueous solutions show an increase in the number of molecules as great as shown by salts. This explanation is therefore untenable. [62] ‹Z. phys. Chem.›, «1», 631, (1887). Previous papers were published in the transactions of the Royal Academy of Sweden (Stockholm). For a history of the theory see Ostwald, ‹Z. phys. Chem.›, «69», p. 1 (1909), and Arrhenius, ‹The Willard Gibbs Address›, ‹J. Am. Chem. Soc.›, 1911 («Stud.»). [63] In the case of double salts, such as sodium-ammonium phosphate, and similar compounds, the dissociation leads to the formation of more than two products. The molecules of two or more different products may then be charged positively and, conversely, there may be two or more different products of dissociation carrying negative charges. We have, for instance, Na(NH_{4})HPO_{4} ⇄ Na^{+} + NH_{4}^{+} + H^{+} + PO_{4}^{3−} and Na(NH_{4})HPO_{4} ⇄ Na^{+} + NH_{4}^{+} + HPO_{4}^{2−}. In all cases the rule concerning the sum of all the charges, as expressed in (2), must be fulfilled, the charge on the phosphate ion, PO_{4}^{3−}, being three times as great as that on a sodium, ammonium, or hydrogen ion; that on the acid phosphate ion, HPO_{4}^{2−}, being twice as great. [64] Ion = the going or the migrating particle.