Flat flange vessels are large volume reaction vessels which are regarded as an alternative to the round flasks and consist of a bottom part and a lid. These two parts are held together by means of a clamping ring. A seal or grinding grease prevent the grinding surfaces from tilting. The flat flange vessel can be combined with other components (e.g. dropping funnels, stirring shafts, ...) by means of various standard ground joints in the lid. Flat flange vessels are well suited for preparative work such as general reactions, distillations, evaporation and drying of solid and viscous substances. Due to their walls, flat flange vessels are suitable for safe working under pressure and vacuum.