Microscopy Hot Plate

Microscopy Hot Plate

When making slides for use with a compound microscope, a hot plate can be a very useful piece of equipment. If making slides using glycerine jelly, then a hot plate is really essential.

If using glycerine jelly as the mountant, a sample is placed on the slide with a drop of molten jelly and then a warm cover slip is placed on top. Glycerine jelly melts at a temperature around 60 – 65C.

Slides of pollen grains are often made using glycerine jelly incorporating Fuschin stain. The stain is absorbed by the pollen grains making them easier to see under the microscope. Once the pollen and stained glycerine jelly are placed on the slide and the cover slip has been placed on top, the slide is maintained at a temperature of 60 – 65 C for a few minutes to allow the pollen grains to absorb the molten jelly. This swells the grains and stains them. The slide is then allowed to cool before being viewed under the microscope.

Clear glycerine jelly, without the fuschin stain, is also available and is used for mounting parts of honeybee anatomy, especially transparent parts like wings or the cornea from the compound eye.

Both types of glycerine jelly are available from our on-line shop here

There are several other uses for the hot plate when making slides. Gently warming slides to evaporate water from the sample before mounting, for example when drying a pollen slurry made from a pollen load before adding glycerine jelly. A hot plate can also be used to slowly dry ringing cement (nail varnish) used to seal a cover slip to the slide, or to evaporate the solvent from a permanent slide mounted using canada balsam substitute. In these latter cases a low temperature should be used to avoid any risk of damage to the mounted specimen.

Many beekeepers improvise a hot plate using a domestic light bulb mounted in a wooden box with a metal lid. The bulb must be an old style filament bulb, not a modern low energy version. A lamp dimmer switch can be incorporated into the design to give some control of power input and hence temperature achieved. In this case, it is also useful to incorporate a means of seeing how brightly the bulb is illuminated as this also helps gain an indication of the power input and likely temperature. I have used a 6mm dia piece of red plastic mounted in a suitable hole in the metal lid for this purpose. Making a hot plate in this way is not difficult but does require some basic woodworking skills and tools. It is also important that the wiring is carried out safely. The metal top to the box MUST be earthed. Provision also has to be made to allow the bulb to be replaced should it fail.