Synthesis of Ammonia by Impacts of Slow Electrons.

E. Buch Andersen. Über die Synthese von Ammoniak durch Stoss langsamer Elektronen. Zeitschr. f. Physik. Vol. 10. No. 1. 1922.

In the Copenhagen chemical laboratory a series of investigations has begun connected with the study of the mechanism of reactions caused by impacts of slow electrons. The paper under review concerned the reaction of the recombination of nitrogen and hydrogen into ammonia in a field where there was a stream of electrons of definite velocity. The experiment was carried out as follows: into a glass sphere of about \(800\ \mathrm{cm}^3\) capacity two rectangular plates (\(12 \times 60\ \mathrm{mm}\)) were inserted, which served as the anode; between them was a tungsten filament \(25\ \mathrm{mm}\) long and \(0.048\ \mathrm{mm}\) in diameter. The gas mixture under investigation was taken from a gasometer and was first carefully purified by passage through \(KMnO_4\), heated palladium asbestos, concentrated sulfuric acid, and phosphorus anhydride. After the glass vessel had been filled with the desired mixture, the tungsten filament was heated and then, when the pressure in the vessel became established (it was measured with a MacLeod gauge),

an accelerating potential was applied and, from time to time, the pressure was read off; the change in pressure served as a measure of the rate of the chemical process. For control, Buch Andersen attached to the sphere two branches into which about 0.5 cm of 98-percent sulfuric acid was placed; this trapped the \(NH_3\) obtained from the mixture of hydrogen and nitrogen. The results of the experiments amounted to the following:

1. The pressure in the vessel fell rather rapidly, in the course of time reaching a certain constant limit.

2. The formation of \(NH_3\) begins at a certain critical voltage, approximately equal to 17.5 volts.

3. It may be thought that the critical voltage is most closely connected with the ionizing potential of one of the gases; but which one in particular is difficult to say on the basis of these experiments (probably nitrogen).

4. If the critical voltage has been reached, then the reaction rate is a continuous function of the voltage, having a series of successive relative maxima and minima. The presence of these extreme points indicates that the rate of the process probably has a selective character with respect to the velocities of the electrons.

Despite the absence of strictly quantitative relations, the work of Buch Andersen is very interesting from the point of view of the emerging quantum view of chemical processes and, together with the work begun in the Copenhagen laboratory, may prove valuable material in elucidating the nature of chemical and molecular forces.

A. Predvoditelev.