The present volume, Thorium C5, deals with the compounds of thorium and sulfur, selenium, tellurium, and boron, as well as with oxoacid compounds of the three chalcogen elements. Thorium borates have already been treated in Thorium C2. In contrast to the corresponding compounds of uranium the thorium sulfides, etc., do not show any nuclear or other technological application; they are only of academic interest, despite some very interest ing electronic properties, especially of the 1: 1 compounds. The thorium-sulfur and the thorium boron systems in particular were studied in detail, so that we...