«Some Applications of the Chemical Activity of Ions to Qualitative Analysis.»—The knowledge that aqueous solutions of ionogens show the reactions of the ions contained in them, gives us a clear, sharply defined interpretation of many of the simpler facts of qualitative analysis. The elementary observation that a large number of hydrogen derivatives show acid properties and a considerable number of others do not (at least not to a sufficient extent to be appreciable), finds its simplest explanation in the fact that all solutions showing acid properties have these properties as the result of the presence of a common component, namely the hydrogen-ion. The acid properties are, in fact, the properties of this one substance and no other. Thus hydrochloric, nitric, sulphuric, carbonic acids are acids because they are dissociated more or less, liberating hydrogen ions; and compounds like marsh-gas CH_{4}, ammonia NH_{3}, benzene C_{6}H_{6}, in spite of the presence of a great deal of hydrogen in their molecules, are not acids, because they do not, to an appreciable extent,[160] ionize as do the first compounds mentioned. In the same way, glycerine C_{3}H_{5}(OH)_{3}, although it is a trihydroxide, does not show the characteristic actions of the hydroxides of potassium, barium, aluminium, of the metal hydroxides in general—the latter are more or less ionized, forming the characteristic ion of bases, the hydroxide-ion HO^{−}; but glycerine does not appear to ionize into C_{3}H_{5}^{3+} and HO^{−}. The well-known observation of qualitative analysis, that potassium chlorate solutions do not precipitate silver chloride from silver nitrate, while potassium chloride and other chlorides do so at once, is now understood as being the result of the fact that the chlorates produce the chlorate-ion ClO_{3}^{−} (see page 70 for the method of determining its composition), while the chloride-ion [p088] is required for the precipitation of silver chloride. Chlorplatinic acid H_{2}PtCl_{6}, in spite of the large proportion of chlorine in its composition, does not precipitate silver chloride, but rather silver chlorplatinate,[161] a yellow salt, insoluble in ammonia, and it does so because its ions[162] are H^{+} and (PtCl_{6}^{2−}).