  We have studied the ultrasonic velocity and ac susceptibility of $URu_2Si_2$
in d. c. magnetic fields up to 45T. A significant difference between the
constructed H-T phase diagram and that extracted from earlier pulsed fields
measurements can be explained in terms of a large magnetocaloric effect. A
hysteresis of metamagnetic transition at low temperatures and a new phase
separation line have been observed for the first time.
