4.1 Extraction thimbles, alundum or fritted glass, coarse porosity; or pre-extracted paper. NOTE 2: Fritted glass thimbles must be cleaned after each use by soaking overnight in a chromic acid cleaning solution. 42 Extraction apparatus, with ground glass joints, consisting of 4.2.1 Extraction flask, 250 mL 4.2.2 Soxhlet extraction tube inside diameter 30-40 mm, capacity to top of siphon about 100 mL 4.2.3 Graham or Allihn type condenser. 4.3 Glassware, weighing bottle, glass, preferably"shallow" type or weighing dish, aluminum, filtering flask, 1000 mL; Buchner funnel. 44 Heating device, to contain hot water; or steambath or electric heating mantle. 4.5 Chemical fume hood, having a face velocity of at least 24.4 m/min(80 ftlmin) or as required by local safety regulations.