21. A free expansion is typically achieved by opening a stopcock that allows the gas to expand into a vacuum. 22. Domestic stopcock cover set into the pavement outside a house in north Birmingham, with the initials " CBWD" 23. These valves have also been used as a grease-free alternative to straight bored stopcocks common to Schlenk flasks. 24. Stopcocks are a smooth tampered plug or rotor with a handle, which fits into a corresponding ground glass female joint.25. The stopcock is a smooth tampered plug or rotor with a handle, which fits into a corresponding ground glass female joint. 26. Stopcocks are often parts of laboratory glassware such as burettes, separatory funnels, Schlenk flasks, and columns used for column chromatography.27. O = Open stopcock ; X = Closed stopcock; black-arrow = Gas flow direction, orange arrow = Liquid flow direction 28. O = Open stopcock; X = Closed stopcock ; black-arrow = Gas flow direction, orange arrow = Liquid flow direction 29. I had to dash to the stopcock to cut off the water from the tank, so then all my water was turned off. 30. Apiezon, silicone-based, and fluoroether-based greases are all used commonly in laboratories for lubricating stopcocks and ground glass joints.
