over a wide range and the torque of which is transmitted via an overload shearing clutch 26 and a cardan shaft to a driving shaft 27 which passes through a special stuffing box 28 provided in the removable top wall of the autoclave 16 in a pressure tight manner into the latter inside the autoclave 16 there is a device for measuring the torsional moment transmitted to the test element this device consists of a torsion rod 29 discs 30 attached to this rod and having radial grooves and two electromagnetic scanning heads 31 connected to leads passing through electrically insulated air tight passages in the autoclave wall out of the autoclave fig2 shows the special stuffing box 28 which seals the high speed driving shaft 27 against the autoclave 16 in the case of pressures of up to 2000 bars the sealing is effected in a fully automatic manner because the force of the internal pressure acting on the driving shaft 27 is transmitted via a longitudinal ball bearing 32 to a pressure ring 33 this force and the total force of the internal pressure acting on the ring shaped area of the pressure ring 33 are transmitted to a sealing ring 34 made of elastic material because of the aspect ratio between the total area and the ring shaped area of the pressure ring 33 the pressure in the sealing ring 34 will be always greater than the internal pressure the whole force is then transmitted via a pressure ring 35 a flange 36 and bolts 39 to the casing of the autoclave 16 in order to provide initial pressure for sealing in the lowest.