of mixing chamber 3 in the axially middle region thereof are provided a plurality of axially extending alongated discharge slots 7 connected to the upper planar rim of mixing chamber 3 by weldings such as at 9 is a first set of impeller blades preferably made of stainless steel and generally indicated as 11 and connected to the first set of impeller blades 11 by welding such as at 13 is a shaft 15 also preferably of stainless steel and situated above the first set of impeller blades 11 and coaxial with the mixing chamber 3 the first set of impeller blades 11 comprises three identical impeller blades 17 see fig2 disposed angularly offset by 120 u00b0 for each other around the central axis 5 each of the impeller blades 17 comprises a leading portion 19 leading in the direction of rotation 34 r 34 of the mixer and disperser head 1 and a trailing portion 21 as best seen in fig4 and 5 the leading portion 19 of each of the impeller blades 17 has a first part 23 extending in a plane perpendicular to the axis 5 and a second part 24 bent inward about 90 u00b0 from the first part 23 and connected by welding such as at 9 to the upper rim of the mixing chamber 3 the radially inner end of the first part 23 is connected to the shaft 15 by means of welding such as at 13 the trailing portion 21 forms as best seen in fig4 an obtuse inward angle with the first part 23 of the leading portion 19 and has the shape of a sector of an annulus its trailing edge has indentations in the.