Clamps and support stands

When carrying out experiments it is vital that all apparatus is held in place securely during the procedure. It is essential that you know how to assemble supporting and securing equipment to the highest possible standards of safety. The most common types of supporting and securing equipment are shown in Fig. 5.1.

Support stands
These are also known as 'retort stands' and comprise an aluminium or steel rod screwed into a heavy metal base. Always check that the base sits level and that the rod is tightened fully in place.


Clamp holders
These are also described as 'clamp bosses' or 'bosses'. Make sure that the locking screws move freely and are not distorted. When you attach the clamp holder to the support stand, tighten the screw firmly and ensure that the open 'slot' to be used for the clamp is pointing upwards (Fig. 5.2).

Clamps
General-purpose clamps are used for securing glassware - therefore make sure that the inner surfaces of the clamp 'jaws' and the 'fingers' are covered with cork or rubber to provide a cushion for the glass: there must be no metal to glass contact in case you overtighten the clamp and crush the glass. Tighten the clamp firmly and ensure that the clamped glassware does not move.

Conical flasks should be clamped at the neck and ground-glass jointware should be clamped at the joint - this usually has the greatest thickness of glass.

*Note: Take particular care when using parallel-sided separatory funnels and chromatography columns (Fig. 5.3), where clamping in the middle of the funnel can be the same as squeezing the middle of a large-diameter glass tube. Clamp at the ground-glass joint using a 'wellcushioned' clamp.

In most clamps, only one of the jaws moves when turning the screw. When you use the clamp in a horizontal position, make sure that the movable jaw is at the top.

Burette clamps are specially designed to hold the burette vertically. Springs hold the burette at two points about 5cm apart - again check for the presence of a rubber or plastic 'cushion' at the points of contact - to prevent slipping and lateral movement. Since the burette clamp slides down the rod of the support stand, then provided the support stand is vertical, the burette will be vertical.

Support rings
These metal rings come in various diameters to support filter funnels and separatory funnels. Often these support rings are coated in plastic to provide the cushion between metal and glass.

If your support ring is metal, you can make a 'cushion' by finding a piece of thin-walled rubber tubing of the same bore as the metal of the ring, cutting it to a length equivalent to the circumference of the ring and then cutting down the length of the rubber tubing. You can then slide the tubing around the ring to provide the 'cushion'.

*Note: When using clamps, support rings and support stands make sure that the clamped/supported apparatus is always in position above the base of the support stand (Fig. 5.4) to prevent the stand toppling over.


Cork rings
These are used to hold round-bottom flasks on flat surfaces while manipulations are being carried out. Since they are light in weight they can be used to hold round-bottom flasks on a general-purpose balance.