Abstract: A nozzle for forming a liquid jet includes a flow passage having a circular inlet and a flat rectangular outlet and a cross section which gradually changes from a circular shape to a flat rectangular shape. The magnitude of the cross-sectional area of the flow passage gradually decreases in the flow direction of the liquid. The flow passage changes direction in a zone at the upstream beginning of the change of cross-sectional shape to assume a new direction which is at an acute angle of deflection to the original direction of the flow passage. The long sides of the rectangular cross section of the flow passage are perpendicular to a first imaginary plane containing both legs of the angle of deflection. The nozzle is formed of a first and a second nozzle part having, respectively, first and second edge faces. The nozzle parts are joined to one another by a face-to-face engagement between the edge faces.