IMAGE. A thermometer suspended away from the stirring bar.
Suspend the reservoir (the tip) of the thermometer below the surface of the solution, but do not allow the tip to touch the walls or bottom of the container. If the thermometer bulb touches the container, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.
Stirring the solution provides a better representation of the entire solution. Stirring ensures that the temperature gradients are minimized (that 'hot' or 'cold' spots in the solution are not measured). Stirring can be done manually or mechanically. Be careful with hot solutions. If mechanical stirring is used, make certain that the stirring bar will not touch the thermometer by suspending the thermometer well out of the way.
There are several techniques available to suspend a thermometer in a solution:
- use a commercial thermometer clamp
- attach string to the top of the thermometer and hang the thermometer from a stable piece of equipment
- insert the thermometer through a one-hole rubber stopper and clamp the stopper to a ring stand
- insert the thermometer through a short length of rubber tubing and clamp to a ring stand
NEVER clamp an unprotected thermometer. Thermometers are fragile and it is easy to break a thermometer by closing a clamp too tightly. Rubber tubing or stoppers will provide enough elasticity to reduce the risk of breaking a thermometer.