-10differing magnetic field intensities gave the same fraction of the total beam in the +1 charge state. Table I presents the results of a series of runs on seven different masses. The fraction of the total beam present in each ionic charge state is given for each mass measured. from mass tomass. It is obvious that the charge pattern varies strongly In an attempt to understand the reason for the behavior of each mass chain, we have also tabulated the composition of each mass chain at the time of formation as calculated by Weaver et al. ! The lower part of Table I is arranged so that the elements making up the lower-mass chains (91, 97, and 99) are on the same row of the table as the homologous elements making up the higher-mass chains (131, 132, 141, and 143). While the prediction of chain composition cannot be regarded as reliable in the present state of knowledge of the fission process, it should serve as a general guide. some correlation of charge distribution with chemical properties is at once apparent. Masses 97 and 99, with similar precursors, have similar charge distribution patterns; so also do masses 131 and 132, Mass 91, for which the most abundant species is a noble gas, has a high abundance of single and double charges; mass 143 has a low abundance of the noble-gas member of the chain and a much lower abundance of single-charge beam than of doublecharge; mass 141 has a substantially higher abundanceof noble gas anda higher abundance of single charges. While the data are sparse and the predictions of chemical nature un- certain, there are enough indications of dependence of charge distribution on chemical nature to be quite interesting. At the same time, such a dependence makes the experimental measurement of independent isobaric yields by study of the low-charged fragments considerably more difficult than was anticipated. 5001839