The Elements of Qualitative Chemical Analysis, vol. 1, parts 1 and 2. / With Special Consideration of the Application of the Laws of Equilibrium and of the Modern Theories of Solution.

by Julius Stieglitz

The salt formed, HCO₂Na, is sodium formate, which is the first isolated product of the oxidation of formaldehyde.

It would appear, from this point of view, that the alkaline nature of the silver nitrate mixture is advantageous primarily because a base is required by the formaldehyde, the reducing agent, to convert it into some readily oxidizable form. And the proved efficiency of the alkaline mixture (see above) makes it appear probable that the advantage gained by this result more than offsets the loss in oxidizing power, suffered by the silver nitrate following the suppression of its real oxidizing component, the silver-ion, when, in the presence of ammonia, the latter is converted largely into the ion, Ag(NH₃)₂⁺. Ammonia, in turn, is employed in the oxidizing mixture, essentially with the object of preventing the precipitation of the silver-ion, as silver oxide, by the hydroxide-ion of an alkaline mixture. These conclusions, as well as, in particular, the main conception that in the oxidation of formaldehyde there is an actual transfer of electrical charges, may be fully confirmed with the aid of the chemometer.[585]

Exp. A small beaker, containing a platinum electrode, which is connected with the positive post of the voltmeter, is half filled with a solution of silver and sodium nitrates. A similar small beaker, containing a platinum electrode leading to the negative post of the voltmeter, is charged with a solution of sodium nitrate (to render the solution a good conductor) and with some formalin. The solutions in the two beakers are connected by means of a salt-bridge containing sodium nitrate. [p293]

Only a very slight current is produced under these conditions; the potential between silver nitrate and formaldehyde is found to be extremely small. If, now, sodium hydroxide is added to the formalin mixture, an enormous increase in potential is observed, proving, unmistakably, that the addition of the alkali to the formalin solution enormously increases the concentration of the reacting, oxidizable component.[586]

When some ammonia is added to the silver nitrate mixture, we find, as anticipated, that the oxidizing power of the silver solution is greatly reduced, the silver-ion being converted into the complex ion, Ag(NH₃)₂⁺; but the potential is still very much greater than the potential between silver nitrate and formalin without any alkali—which shows that the advantage of using alkali with the formaldehyde greatly outweighs the disadvantage of using ammonia with the silver nitrate.

An electric current may also be readily obtained by combining alkaline formaldehyde with other oxidizing agents—for instance with an oxygen electrode (p. [279]). We find (exp.) that the oxidation proceeds with remarkable ease under these conditions. Permanganate, dichromate, etc., may be substituted for oxygen, with the same general result.

Summary.

It also follows, from the conclusions reached, that, under proper experimental conditions, electricity, in the form of a current, must be capable of effecting the oxidation, or the reduction, of organic as well as inorganic compounds (p. [252]). Extended investigations have, indeed, shown that electric currents belong to the most important and efficient agents for this purpose, because the oxidation, or the reduction, of the organic compound becomes susceptible to the most exact control through the regulation of the potentials used.[587]

Tables and Summaries.

TABLE[A] OF EQUILIBRIUM (SOLUTION-TENSION) CONSTANTS (IN MOLAR TERMS) AND OF POTENTIAL DIFFERENCES BETWEEN ELEMENTS AND THEIR IONS IN UNIMOLAR AQUEOUS SOLUTIONS.