Microscopy Hot Plate

Microscopy Hot Plate

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

Making slidesGlycerine Jelly for pollen

To make a slide using glycerine jelly as the mountant, place the sample on a clean warm slide.  Then add a drop of molten jelly and place a warm cover slip on top. Glycerine jelly melts at a temperature around 60 – 65 C. It is available either as a clear jelly or with fuschin stain incorporated.

To mount pollen grains on a slide, glycerine jelly incorporating fuschin stain is used.  Pollen grains absorb the stain is which makes them easier to see under the microscope. Place the pollen and stained glycerine jelly on the slide and then add a cover slip on top.  Maintain the slide at a temperature of 60 – 65 C on the hot plate for a few minutes. This allows the pollen grains to absorb the molten jelly. The jelly swells the grains and stains them. Finally allow the slide to cool before viewing under the microscope.

If you want to mount parts of honeybee anatomy, especially transparent parts like wings or the cornea from the compound eye use clear glycerine jelly without the fuschin stain.

There are several other uses for a microscopy hotplate 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 is also useful to slowly dry ringing cement (nail varnish) used to seal a cover slip to the slide. Yet another application is evaporating the solvent from a permanent slide made using canada balsam substitute. In each of these additional applications setting the hot plate to a low temperature avoids any risk of damage to the mounted specimen.

DIY hotplate Home made hot plate

Many beekeepers improvise a hot plate for microscopy using a light bulb 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 incorporated into the design gives some control of power input and hence  the temperature achieved.

It is also useful to incorporate a means to see how brightly the bulb is illuminated as this helps to indicate the power input and likely temperature. I have used a 6mm diameter 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. If making your own hotplate, it is important that the wiring is carried out safely. You MUST earth the metal top to the box and make sure that the bulb does not overheat the box.  Provision also has to be made to allow the bulb to be replaced should it fail.