Molten ionic oxides possess important desirable properties: thermal stability, and useful chemical properties resulting from their acid or basic behaviour, i.e., from their capacity to accept or donate an oxygen ion, and, in several cases, relatively low melting points, well below 1000°c. Bismuth trioxide was found to effect a two‐temperature decomposition of ammonium chloride, yielding ammonia and hydrogen chloride. Molten antimony trioxide was found to attack rock phosphate and convert part of the phosphate to a water‐soluble form. Molten lead monoxide was found to dissolve calcium oxide readily, to dissolve chromic sesquioxide, to decompose chromite ore and to permit an extraction of iron‐free lead chromate into an upper layer of molten alkali chloride. Addition of lead sulphide to a lead monoxide melt caused formation of elemental lead and lead sulphate. Vanadium pentoxide was found to decompose ammonium chloride, yielding first, hydrogen chloride and then, ammonia. The reaction of a vanadium pentoxide melt with rock phosphate, studied in some detail, resulted in water‐solubilisation of the phosphate. The product formed in the melt is probably a calcium phosphate vanadate, from the aqueous solution of which calcium can be precipitated by ammonium carbonate; the ensuing ammonium phosphate and vanadate solution can be separated by known methods, permitting recovery of the vanadium pentoxide, and yielding ammonium phosphate.