Abstract: The invention comprises a method of and apparatus for forming in a liquid a solution of another material which may be in solid, liquid or gaseous phase.The method comprises establishing two zones of mixing with a partial rotating separator between them to cause rotation of the liquid around an axis and circulation within each zone due to the rotation of the separator and causing agitation within each zone by a plurality of axially extending rods which rotate in the liquid adjacent to the rotating separator.The apparatus is a dissolver comprising a tank, a separator capable of rotating in the tank at various levels above the bottom thereof which is provided with a plurality of axially extending rods above and below the separator.