The physicist Kamerlingh Onnes, who was the first to liquify helium (1908), had written on the walls of his laboratory in Leiden: "From measur- ing to knowing." As true as this is at very low temperatures, it is just as applicable at the high temperatures of molten salts. Only on the basis of exact measurements by a plethora of experimental methods can any real understanding be reached of both classes of liquids. In both temperature ranges experimental...