Abstract. A summary of the effect of metal, carbon, silicon, and oxygen impurities upon the various sulfide refractories is given and the proper procedures for elimination of the impurities are discussed. CeS which is properly prepared can be handled in air without danger of catching fire or appreciable oxidation. 650 satisfactory crucibles have been made to date using sulfides which were screened and pressed in air with less than 0.5% oxygen pickup. The other cerium and thorium sulfides are even more inert to oxidation than is CeS. Phase diagram possibilities are discussed for the cerium and thorium sulfide and oxy-sulfide systems. Further study of the ThS has shown that ThS crucibles are the highest melting and least volatile of the sulfide crucibles and ThS may be used for remelting of some metals up to 2000 degrees C. ThS crucibles appear to be the most suitable containers for metal reductions.