The liquid phase photochemical exchange between chlorine and carbon tetrachloride was more reproducible than the thermal exchange, although still erratic. The improvement was most noticeable in the greater consistency among reaction cells prepared as a group on the same manifold. Rather large differences were still found between reaction cells from different manifold fillings. Some 80 reaction tubes from 13 manifold fillings were illuminated in the temperature range from 40 to 85 ` in a further endeavor to determine the cause of the irreproducibility and to obtain information on the activation energy and the effect of light intensity. In all cases there was readily measurable exchange after as little as one hour of illumination. By comparing reaction cells sealed from the same manifold temperature dependency corresponding to activation energies ranging from 11 to 18 ** f was observed while dependence on the first power of the light intensity seemed to be indicated in most cases.

It was possible to make estimates of the quantum yield by observing the extent of reduction of a uranyl oxalate actinometer solution illuminated for a known time in a typical reaction cell and making appropriate conversions based on the differences in the absorption spectra of uranyl oxalate and of chlorine, and considering the spectral distribution of the light source. These estimates indicated that the quantum yield for the exchange of chlorine with liquid carbon tetrachloride at 65 ` is of the order of magnitude of unity.