Solid/liquid extraction unit is fitted with an external steam or electrically heated thermosyphon reboiler. Pure solvent vapor generated in the boiler rises through the jacketed column and is condensed in a vertical water-cooled condenser. Liquid solvent passes through a solvent cooler, which controls the solvent temperature - a flow rate indicator and into the extraction chamber. The solvent is directed either upward through the solid bed or downward through a sparge ring. The extract solution passes into the reboiler where pure solvent is regenerated. Samples of extract solution and reboiler contents can be taken and their compositions determined by density measurement. The plant operation is controlled from a free-standing control panel fitted with a mimic diagram, flow controllers, temperature and pressure indicators and services controllers.