. Technical paper. owing year some experiments were con-ducted in the chemical laboratory of the University of Missouri tocomplete and extend certain parts of the investigation. The author CONSTANTS OF THE THORIUM SERIES. 3 is pleased to express appreciation of the excellent cooperation givenhim in carrying on the experiments, and to acknowledge the help andgood will of the younger members of the staff in the experimentallaboratory and plant of the Welsbach Co. and of his colleagues inthe Bureau of Mines. CONSTANTS OF THE THORIUM SERIES OF ELEMENTS. The thorium series of radio-elements compris
. Technical paper. owing year some experiments were con-ducted in the chemical laboratory of the University of Missouri tocomplete and extend certain parts of the investigation. The author CONSTANTS OF THE THORIUM SERIES. 3 is pleased to express appreciation of the excellent cooperation givenhim in carrying on the experiments, and to acknowledge the help andgood will of the younger members of the staff in the experimentallaboratory and plant of the Welsbach Co. and of his colleagues inthe Bureau of Mines. CONSTANTS OF THE THORIUM SERIES OF ELEMENTS. The thorium series of radio-elements comprise the following suc-cessive members: Thorium, mesothorium 1, mesothorium 2, radiothd-rium, thorium X, thorium emanation, thorium A, thorium B, thoriumC, thorium C, thorium D. Thorium C, like its corresponding mem-ber in the radium and actinium series, appears to have two modes oftransformation. One branch, claiming 65 per cent of the atoms dis-integrating, represents a beta-ray change, producing ThC, which fi + Y a. Tfy A Th B P 2/2 Figure 1.—Branching of thorium series. changes almost at once with the expulsion of an alpha particle into theend member of this branch. The minor branch, claiming 35 per centof the atoms, represents an alpha-ray change producing thorium D,which expels both beta and gamma rays, and is responsible for theentire gamma radiation emitted from the products of thorium branching is shown in figure 1. In the table of constants. Table 1. page 7. the elements of thethorium series are placed in their genetic order. The atomic weightsand atomic numbers, following the experimental value for thorium,are theoretical values based upon the principle arrived at more or lessindependently by the several investigators, notably Soddy, Fleck,Russell, Fajans. and Von Hevesey (1)—connecting the position ofthe radio-elements in the periodic table and their atomic weightwith the nature of the radioactive change as the element is expulsion of the alpha
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