Capillary action occuring on paper

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 : 


Ronak Hati,

Ramnarain Ruia Autonomous College, Mumbai.

4 Comments Add yours

  1. Manu Prakash says:

    Dear Ronak
    I wrote a long response; and unfortunately lost it on the website. I will try to recreate it here.

    I am so thrilled reading your posts. You are an incredibly creative individual – please keep up your passion for science and your curiosity. I am just blown away with your explorations.

    1) Love the first video. One idea of why the color seems to go away could be – because of refractive index matching between water and cellulose. Since air and cellulose has a big refractive index mismatch; and color is essentially the amount of light scattered (which scatters more with a mismatch in refractive index) – the colors should “dim” by this addition of a new refractive media (water). Try to put oil and see what happens.

    2) Washburn in 1920’s proposed the law of dynamics of capillary rise. It is still an important paper – and predicts the speed of capillary rise based on pore size.
    It occurred to me – using your method and a little bit of math, we can predict average pore size of any given paper by measuring the speed of the capillary wetting wave from one side to another. That’s interesting – because this can be a easy way to test different kind of papers.

    3) The world is filled with puzzles and problems, which remain unsolved. While thinking about what you did, another paper that just came out in 2018 (why regular sponge – used to wash dishes – swells as you put it in water). See paper below. you might enjoy looking at the figures.

    Best wishes. Keep exploring; you have an incredibly curious eye to observe – and I am so thrilled we somehow met via this platform.

    Best wishes – and hopefully we will meet in person some day.


    Poro-elasto-capillary wicking of cellulose sponges
    Jonghyun Ha1, Jungchul Kim2, Yeonsu Jung1, Giseok Yun1, Do-Nyun Kim1 and Ho-Young Kim1,*
    See all authors and affiliations
    Science Advances 30 Mar 2018:
    Vol. 4, no. 3, eaao7051
    DOI: 10.1126/sciadv.aao7051

    1. Ronak Hati says:

      It did not occur to me what you wrote in second point… A brilliant idea indeed that is!

  2. dorithockman says:

    Such a great idea! So creative and interesting! Keep it up!

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