Barium sufaa labelled with sulfur-35 was reduced, and hydrogen sulfide evolved from the reactions was entrained with carben dioxide. The gas was led into two absorbing cells in series, the first of which contrined a known amount of aqueous zinc acetaa, for radioactivity measurement, and the second contained cadmium carbonate for sufide deaction. When sufficient zinc sulfide was obtained in each absorbing cell, the flow was diverted to a new cell series so that many small equal fractions were obtained. The counting raa of each sample was measured by the infinite thickness method. (J.R.D.)