Experiments made by Professor Miers and Miss F. Isaac have shown how, by measurements of the refractive index, it is possible to determine for a supersaturated solution the temperature at which it passes from the metastable condition, in which it can only crystallize by inoculation with a crystal of the salt (or of a substance isomorphous with it), to the labile condition, in which it may (and often does) crystallize spontaneously. In a diagram in which concentrations are taken as ordinates and temperatures a abscissae the solubility curve represents the limit between the unsaturated and the metastable state; and the limit between the metastable and the labile state is represented by a similar curve, to which they have given the name ‘Supersolubility curve’.