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Understanding Stalactites and Stalagmites

Things Needed:

  • Baking Soda

  • 2 paper clips

  • Water

  • Wool yarn (about a meter long)

  • 2 glasses

  • Spoon

  • Saucer


  1. Fold the yarn in half. Fold it in half again and twist it tightly.

  2. Attach a paper clip to either end of the yarn.

  3. Place the glasses on the table, with the saucer placed between them.

  4. Fill both the glasses with hot water until they are half full.

  5. Add baking soda in both the glasses. Mix using a spoon. Turn this into a saturated solution by adding as much baking soda as possible, till it stops dissolving in the water.

  6. Insert the ends of the yarn in the glasses. The paper clips act as weights and keep the yarn submerged in the solution.

  7. Adjust the glasses in such a way that there is a slight dip in the centre of the yarn (the yarn passing above the saucer).

  8. Leave the setup undisturbed for 2-3 days. Crystals will start appearing on the string.

How does it work?

The yarn transfers the water and the dissolved soda onto the saucer. This process is called capillary action and is a process that enables plants and trees to transfer water and nutrients from the ground to the branches and the leaves. The yarn uses capillary action to soak itself in the baking soda solution. Once the yarn is over-saturated, the excess water drips off onto the saucer. As water cools, it leaves behind baking soda deposits on the saucer. Stalactites are crystals growing down from the yarn and stalagmites are crystals growing up from the saucer.


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