Schlenk Lines
Schlenk glassware
Schlenk tubes
A Schlenk tube is a specially designed reaction vessel with a side-arm which allows the flask to be connected to a Schlenk line
To fit the apparatus together, vacuum grease is applied to both of the ground-glass joints and the tap is secured with plastic pieces and an O-ring (pictured above). Both the tap and the stopper (or Viking helmet) should be able to rotate freely, so you will have to apply a moderate quantity of vacuum grease.
Note: make sure to wipe the ground glass joints before applying grease, in order to remove any solids (rotating a stopper or tap with solids will score and possibly crack the glass).
Once assembled, a Schlenk tube can be attached to a Schlenk line via one of the rubber tubes so that it is connected to an oblique tap, as shown in below.
There are a number of alternative Schlenk tube designs. As would be expected, many different capacities exist, typically ranging from 10 mL up to about a litre. However, the arrangement of the ground glass fittings often varies, with two main designs.
Socket and stopper
This type of Schlenk tube has the reaction flask is fitted with a ground-glass socket which is sealed using a glass stopper. The ground glass socket enables the easy addition of other glassware fitted with ground glass joints, for example reflux condensers or dropping funnels. Septa can easily be inserted into the joint to provide a seal through which needles or cannulae can be inserted to enable the addition or removal of liquids. However, the downside of this type of Schlenk tube is that grease ends up on the inner surface of the socket, which makes the removal of solid material from inside difficult, and prone to grease contamination. Therefore, it is more common to use a cone and helmet Schlenk tube where removal of solid material is desired.
Cone and Viking helmet
This type of Schlenk tube features a cone rather than a socket, which makes it unusual for a reaction flask. Consequently few pieces of glassware can be attached to the Schlenk tube, or would need to be adapted before use. The cone does offer the advantage in that grease is on the outside of the flask, reducing the likelihood of contaminating products with grease, and makes the removal of solids from the flask much easier. Viking helmets are used to cap the flask when required. They can be secured with a keck clip in the same way as a socket/stopper, but the clip will have to be used the other way up. The joint is still capable of being sealed using a septum, so that liquids may be transferred using needles or cannulae, however these are more awkward to fit as they are not really designed for these joints.