Schlenk Lines
Purging a Schlenk tube
To obtain an inert atmosphere inside a Schlenk tube, the air must be removed (by application of vacuum) and the Schlenk tube refilled with an inert gas. This is achieved by turning the appropriate double oblique tap of the Schlenk line, where the Schlenk tube is connected. The Schlenk tube first needs to be opened to the vacuum manifold, whilst watching the pressure gauge and waiting for the air to be removed and a good vacuum to be re-established. The tap is then slowly turned to allow the Schlenk tube to be filled from the inert gas manifold. This needs to be carried out very carefully (particularly when the tap first begins to engage with the gas manifold), to slowly ‘bleed’ gas into the tube, keeping an eye on the oil bubbler that the pressure difference doesn’t cause the oil to be sucked out. The Schlenk tube needs to be fully refilled with inert gas, so that it is back at atmospheric pressure. When the tap is fully open and the original flow rate is maintained then this has been achieved. This process is usually repeated (typically at least three times) in order to ensure that any oxygen and water vapour have been removed from the Schlenk tube.
Evacuating a Schlenk tube
Check that the Schlenk tube is a closed system (an appropriate stopper is in place, not a rubber septum).
Close the Schlenk tap. This step ensures that you do not cause rapid evaporation (of liquids) or excitation of solids.
Turn the double oblique tap so that the vacuum pump evacuates the orange rubber tubing.
Open the Schlenk tap slowly and the vacuum pump will evacuate the tube. You should be able to hear the pump working (a different pitch) whilst the tube is evacuated.
Re-filling an evacuated vessel with inert gas
The flow rate of gas through the manifold should be set to a moderate rate. Make sure you can see the bubbler before opening or closing any taps, as this is your measure of control during the re-fill process.
With a Schlenk tube under vacuum, close both the Schlenk tap and the corresponding double oblique tap.
Open the double oblique tap to the gas manifold. You should notice the silicone oil being drawn back up the Dreschel head. You want to minimise the rise of the oil by opening the tap slowly.
Open the Schlenk tap slowly, whilst watching the silicone oil bubbler. Try not to draw oil out of the bubbler and into the trap. In order to do this you will have to control the flow of gas into the evacuated Schlenk tube, by closing and re-opening the Schlenk tap at timely intervals, or only opening it very slightly. Ask a demonstrator for help if you are unsure about this process, or if you accidentally fill the empty trap.
When the Schlenk tap is open to the gas manifold and the bubbler is showing a steady flow of gas, your flask has been re-filled successfully.
