A NUMBER of phomchemical investigations have been carried out in the past, and will doubtless be carried out in the future, in which the Schott mercury Uviol-glass lamp is used as the source of radiation, monochromatic illumination, if aimed at, being obtained by the use of filters. I n order to utilise fully the results of these investigations, a knowledge of the distribution of energy in the different p a r k of the spectrum of the lamp is necessary. I n default of direct determinations of

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... s distribution, it has been axsumed by some workers (Luther and Forbes, J. Amer. Chem. Soc., 1909, 31, 780; Plotnikov, Zeitsch. physikal. Chem., 1912, 79, 642) that the values obtained by Ladenburg (Physikal. Zeitsch., 1904, 5, 525 ; measurements of less value for this particular purpose were made by Pfliiger, Ann. Physik, 1908, [iv], 26, 789) for the quartz mercury lamp could be employed. Owing, however, to the greatkr transparency of quartz as compared with uviol-glass even for thO less refrangible regions of the ultra-violet, it is unlikely, as was pointed out by Winther (Zeitsch. Elektrochem., 1913, 19, 395) and by Bruner (ibid., 555) that calculations made on this basis ar0 of any value. The first attempt t o measure directly the ratios in question for