Capillary action occuring on paper

Apr 08, 2018 • 7:55 PM UTC

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Ronak Hati

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One thing we often do while preparing any wet mount is removing excess of mounting medium; mainly by making use of blotting paper. Wondered how blotting paper takes up the excess medium so quickly? A phenomenon called capillary action comes into play. Blotting paper consists of several hydrophilic substances and water (most common mounting media) gets attracted to it due to adhesion. Cohesion among the water molecules will drag along those water molecules not in direct contact with the material, and surface tension will hold the water together as it adheres to the surface.
This causes water to move against gravity too! Something responsible to transport water upwards in plants.
To observe capillarity, a blotting paper and red litmus paper were respectively sandwiched between coverslip and a glass slide. One end of the paper was dipped into a glassplate with water. Phone was attached to foldscope and the phenomenon recorded on video.
With red litmus paper :

It seems as if the paper got decolorized. This makes me think about something… why not use an alkaline substance next time instead of water so that we can actually see red litmus turns blue…
With blotting paper :