In connection with the recent treatment of radium and the actinides, the Gmelin Institute is carrying out the description of thorium and its compounds. The Supplement Volumes A 2, A 3, A 4, and A 5 with the history, isotopes, uses, the recovery of thorium and general properties of thorium atom and ions, the thermodynamics of its compounds and solutions, spectroscopic data and analytical chemistry, biological behavior, health protection and safety control have already been published. The Supplement Volumes C 1, C 2 and C 3 describing the compounds with the noble gases, hydrogen, oxygen...