The flow properties of dispersions of calcium soaps in hydrocarbon oils have been studied over a range of temperature from 35° to 90 °C., and rates of shear from 500 to 16,000 sec.−1 by extrusion through a capillary plastometer. The thixotropy of the system falls as the temperature is increased to 50 °C. and then rises to a maximum at 65 °C., after which it falls regularly. This behavior is due to the thermal weakening of the thixotropic bonds, followed by a strengthening of these bonds due to incipient swelling on the surface of the soap. As the surface of the soap particles continues to swell, cohesion of the particles increases to such an extent that breakdown does not take place and the coefficient of thixotropy falls to very small values. The coefficient of thixotropy found by this method bears a linear relation to the hardness of the dispersion as determined by a falling cone.