Since specific volume in the ocean is a nonlinear function of salinity and internal energy, mixing results in a change in the total volume. There is a contribution to the change in potential energy due to mixing, which depends on this change in volume and on the pressure at which mixing takes place. Fofonoff has made use of this fact in defining a "secondary stability" parameter. It might be speculated that, under conditions of (secondary) instability, turbulent mixing could be generated spontaneously or that the quality of mixing would be different from that under stable conditions. An experiment to detect this phenomenon was performed, with negative results.