Tips for making images of chemicals under polarised light
By Carl Burrows
Ascorbic acid
Visualisation of chemical solutions under polarised light can bring untold fascination and beauty to liquids which are otherwise quite unremarkable. It’s not as difficult as you might imagine, and here are some straightforward tips to try.
If you are using tablets, you will need a small pestle and mortar to crush them into a fine powder. Put about 10mL 50% v/v isopropyl alcohol/distilled water into a suitable vessel – I use a one of those tiny jam jars used in hotels and boarding houses, because you need to be able to seal and shake it. Slowly add the powder a little at a time to achieve a saturated solution. This is largely a matter of trial and error, but it works this way. If you keep adding and shaking it you will get to the point where the solution appears lightly cloudy. As water has such a low viscosity it does not spread across the slide very well and a tip to overcome this is to moisten a cotton-bud with a isopropyl alcohol and rub that across the slide, this overcomes the problem.
Take a pipette and put a drop of the solution onto the slide about two thirds of the way along it. The size of the drop is also a matter of trial and error. Take another slide and present the narrow edge to the edge of the drop until the solution spreads along the width of the slide, then steadily draw the slide away from the drop which will leave the coating on the slide. If you have a heated slide dryer, place the slide on the dryer on a low setting. Alternatively find a suitable warm, (not hot) heat source and leave the slide to dry then until it has the appearance of a thin white coating. It is important that this is completely dry.
Prepare the microscope with an analyser and polariser. You may have these two items made for your instrument but if not, they can be cut from appropriate sheet polarising film.
Paracetamol
In my case, the head of the microscope is removed and the analyser drops into the light train, but you will have to adjust those accordingly, with the analyser somewhere near the top of the instrument and the polariser on top of the base light source. Put the slide on the adjustable stage and view it under the microscope, positioning the slide in several positions. You will find the end result is different in every position. For the first viewing, rotate the polariser until you have achieved ‘cross-polars’ which will give a black (or at least very dark) background. If set correctly, following further slight rotation the colours should begin to show. Focus and move the slide around on the microscope stage, focusing as you go. (If you do not have a rotating stage this will have to be done manually).
You will find in different positions there will be many differing results. The end result should be an aesthetically pleasing set of colourful images. To date I have used aspirin, paracetamol, ascorbic acid, magnesium sulphate, oxalic acid, pyrogallic acid, sodium bicarbonate, sodium carbonate, and sodium thiosulphate. I am sure there must be very many others suitable for this technique. Other substances also lend themselves to polarising microscopy:
Ocean Sand
Hair of a raccoon
Have fun!
Carl Burrows [email protected]