of some chloride ions out of ‹N› into the space ‹C›, and, at the same time, a migration of the positive ions of space ‹C› into the division ‹N›. On examining the solution in ‹N›, we now find sodium chloride, with unchanged hydrochloric acid, exactly what we should expect from the migration of the ion Na^{+} toward the negative electrode.[124] If the positive ion were, say, [p072] NaO^{+}, we should expect to obtain either some of the hypochlorite NaOCl (NaO^{+} + Cl^{−}), or, at least, an evolution of oxygen in this place, since sodium chloride is formed. As a matter of experiment, no oxygen is evolved here, and no trace of hypochlorite is found in ‹N› round the negative pole, although the tests for hypochlorites are extremely sensitive. Comparatively simple methods, in principle of the nature outlined, enable us, then, to ‹determine experimentally› the composition of the ions into which ionizable compounds, salts, acids and bases, dissociate. Whenever any doubt may exist about the composition of the ions of a given electrolyte, this device may be employed to settle the matter, and there will presently be occasion to employ the U-tube for such a purpose. ‹Ionization and Chemical Activity.›—The fact that the theory of ionization gives us adequate explanations of the conductivity shown by dissolved electrolytes and of their abnormally high osmotic pressures, would have been in itself of interest to chemists; but, if its applications were limited to these phenomena, we should not be considering it in connection with qualitative chemical analysis, nor would the theory, presumably, have greatly affected the development of chemistry, as it has done. It is the fact that the electrolytic dissociation of an electrolyte into its ions involves ‹chemical› changes of the most profound nature, and most intimately affects ‹chemical› reactivity, that has made it play, in the last two decades, such a leading rôle in the development of chemistry, and that makes it necessary to include its consequences in the consideration of analytical problems, if one would understand, as far as present knowledge permits, the reactions involved in chemical analysis. Hydrogen chloride, as a perfectly dry gas, is a non-conductor of electricity and, at the same time, it is found to be chemically ‹inactive›—it does not combine, for instance, with dry ammonia[125] or act upon dry calcium carbonate[126] or on dry litmus. Hydrogen chloride, subjected to great pressure at a low temperature, is liquefied. The liquid is also a very poor conductor of [p073] electricity[127] and does not show the chemical activity of ordinary, aqueous hydrochloric acid; it does not combine with calcium oxide or attack marble, zinc, iron or even magnesium.[127] A solution of hydrogen chloride in a poorly ionizing medium, like benzene or toluene, is an extremely poor conductor. There is an extremely small conductivity indicating only a trace of ionization.[128]