Observations on Temperature Variations in Liquid Mounts During Light Microscopical Investigations
THE MICROSCOPE
2018, Volume 66:2, pp. 65–70
DOI
https://doi.org/10.59082/CXYU2484
AUTHOR
Jan Burmeister
ABSTRACT
The precise measurement of refractive indices (RIs) of transparent small particles in a liquid mount slide preparation (using classical light microscopy and polarized light microscopy techniques) requires exact knowledge of the slide preparation temperature, and that the necessary temperature coefficient calculation be performed for the liquid before reporting final measurement results. Commercially available RI standards for microscopy are supplied as liquids in bottles with the temperature coefficient printed on the label or available from the manufacturer. Previous proposals for temperature measurements in a microscope’s light path (as published in handbooks and online articles) may be misleading due to the large and thermally inert mass of the mercury-containing thermometer bulbs that are routinely used today. An experimental setup was devised and duly calibrated using a miniature negative temperature coefficient (NTC) thermistor as the temperature sensor and a high-resolution ohmmeter to observe temperature effects in a way that is much closer to reality than the older, obsolete procedures. The results for this particular setup show that only negligible thermal effects are observed in slide preparations containing three drops of immersion liquid. Extrapolation calculations for situations with less liquid show that, in such cases, the expected temperature effects are also small to negligible.