Fig 1: Basic Grant waterbath
Summary
A desktop bath used for gently heating substances.
Operation
Most schools have water baths that are used to gently heat mixtures to a desired temperature, melt waxes or warm yeast. Baths vary from the very basic on-off type with no temperature control to more sophisticated devices with temperature control and thermal trip switches etc.
Older water baths that do not have a temperature control usually have a fixed temperature range to which they work. These units are most commonly used in commercial laboratories where they are used to heat a particular substance to a specific temperature, as such they are not very helpful in schools especially if you use the bath for different applications.
There are many types of the more sophisticated temperature controlled water baths on the market today with Clifton and Grant being the most popular manufacturers.
Most use the same principle for heating. An element is usually housed inside at the bottom of the bath with a wire mesh or grille over the top. The bath is filled with water to the desired level (usually 5-10cm above the grille depending on what type of vessel is being heated) and then turned on. Temperature regulation is usually controlled via a dial on the side of the unit. Thermal controls ensure that the water is heated to near enough that temperature and remains at that level. On newer units, an LED or LCD array may show you the desired temperature and another may show the actual temperature. Obviously the price increases with the more features available.
It is important to keep the insides of the baths clean regularly as scale and scum may build up after time. Some baths may advise you to only use distilled water. This is advisable as it will leave less scale over time although it still needs to be cleaned regularly.
Full water baths are heavy so try to use trolleys where possible when moving the units, if this is not possible, empty the bath first before moving. Not only will this make the unit safer to carry but it will stop you from getting wet!
Lids for most units are available which condense the water vapour back into the bath. Most have a pointed top which allow the condensed water to run down the sides rather than drip into the vessels you are heating.
Most new units come with a thermal trip which is actuated if the unit overheats. This could occur if all of the water evaporates or if there is not enough water to dissipate the heat from the element. Depending upon the type of unit you have, you may have to open the side to reset this trip switch, others may have a button on the outside. Refer to your unit's instruction manual for details. If in doubt, post your query on our forum – no doubt another school has the same model and someone who can help.
Safety
The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.