lyzed behind this filter which was compensated, at each wave length, for the photochemical efficiency of this photolysis according to (unpublished) data by P. A. Leighton. Changes in total intensity and in spectral energy distribution are integrated by this device. The losses per hour in iodine value y were for seven carbon arcs, cored and uncored, plotted as ordinates against x, the reciprocals of times in which the same sources, without filters, produced a standard erythema. Roughly, yax. For the more efficient sources, y = ax + b is preferable. The indicated threshold value will be further studied. Similar chemical actinometers for such purposes as photography, antirachitic therapy or even chlorophyll assimilation are possible.

No abstract

of the rate equation is so great as to make such a determination impossible. On the other hand, if the concentration of the ferrous salt is made large, the retarding effect of the resulting ferric ion, which was observed by Winther, will be large in comparison to k6. When the concentration of oxygen is large, k6 and the first term of the equation may be neglected. Under these conditions the oxygen cancels out of the second term and the rate is independent of the oxygen concentrations.The discussion of the mechanism of the chains occurring in these reactions will be postponed until more work has been done on the reaction in acid solution and on the photochemical reaction.

No abstract

Several types of dispersion of sound which may be manifest in a dissociating gas are discussed. Of these only the heat-capacity dispersion and the dissociation dispersion need be considered under suitable experimental conditions. The expression derived by Einstein for the velocity of sound in a dissociating gas has been modified to include heat-capacity dispersion. The experimental procedure indicated by this for obtaining significant dissociation rate constants is outlined. Measurements on the velocity of sound in nitrogen tetroxide which have been made with apparatus of special design, are reported. The range of temperature studied is 0°C to 30°C, the range of pressure 132 mm to 670 mm, and the range of frequency 9 kc to 451 kc. The velocity of sound has been thus defined with an estimated error of ±0.1 m·sec.—1. The maximum dispersion which has been observed is about 5 m·sec.—1. From these measurements it appears that the rate constant of the dissociation reaction is 4.8×104±0.5×104 at 25°C and 260 mm. The activation energy obtained for the dissociation reaction is 13.9±0.9 kg·cal. The rate constant appears to diminish slightly as the pressure is reduced. Since an upper limit for the heat capacity of nitrogen tetroxide is fixed by experiment, it is necessary to suppose that the effective molecular diameters for the activation process are at least three times those for ordinary kinetic collisions.