Make Stalactites and Stalagmites

 Make Stalactites and Stalagmites

Ever had one of those science experiments that you thought was going to be a total failure? Well at first I thought this was going to be one of them when we wanted to make stalactites and stalagmites.

Stop! Before you close the screen and turn away … after all … who wants to read about a failed science experiment … it DID work eventually and we were fascinated by the results.

However, the process took longer than expected and was a great opportunity to learn along the way.

We were attempting to create stalactites and stalagmites … similar to those found in limestone caves.

What’s the difference between Stalactites and Stalagmites?

In case you’re like me and frantically trying to remember which formations are which, this play with words may help …

  • stalactites drop down from the cave ceiling (they have to hang on “tight”“tite”)
  • stalagmites grow up from the cave floor (they need “might” to push up against gravity – “mite”)

The Objective of This Experiment

We found this experiment on a website called, Home Training Tools.com. If you have a look at this link, you’ll find all the instructions.

Materials Required to Make Stalactites and Stalagmites

 Materials Needs to Make Stalactites and Stalagmites

We started with:

  • warm water (enough to fill each glass 2/3 full)
  • Epsom salts (for the first experiment in one set of glasses)
  • baking soda (for the second experiment in a separate set of glasses)
  • rope
  • 4 heavy washers
  • 4 glasses
  • 2 spoons
  • 2 jugs for mixing in.

Time for Maths

 Cut two lengths of rope

To start, we measured and cut off two 24 centimetre lengths of rope. One for each experiment. This may seem like an extra long piece of rope but it is all needed in order to tie on the washers.

Tie on the Washers

 Tie a washer to each end of the rope

The next step was to tie a washer to each end of the rope. The purpose of the washers was to weigh the rope down and keep the ends of the rope in the liquid once the experiment had been set up.

Time to Mix

 Stir Epsom Salts into the warm water

Using warm water, the boys began stirring in spoonfuls of Epson salts into the first glass jug …
 Stir baking soda into the warm water

… and baking soda into the second glass jug.

The idea was to stir in a spoonful at a time until it was dissolved. Then add another spoonful until finally, the salts/soda would no longer dissolve.

 We needed heaps of Epsom Salts!

It was amazing how much Epsom salts could be stirred in. I think we ended up using approximately half of the box!

The baking soda, however, was a different story. We couldn’t get much of the baking soda to dissolve at all.

Time to Set Up the Experiment

 Set the experiment up by using the two glasses

To set the experiment up, we placed 2 glasses on either side of a small plate. (We later changed the plate to a smaller bowl so we could move the glasses together further in order to create more of a drop in the rope).

Each pair of glasses was filled with liquid and the rope was strung between.

One pair of glasses contained the baking soda mixture …
 Set the experiment up by using the two glasses

… the other pair of glasses contained the Epsom Salts. (Ps: we added blue food colouring to the salts solution, hoping to get blue crystals. What can I say? We were experimenting!)

Time to Wait!

At first, the baking soda combination respond quickly. As the day progressed, the rope become wet and solution began dripping onto the plate between the glasses. Disappointingly, that’s all that happened. No crystals or stalactites formed.

 No stalactites but lots of capillary action

However, we could tell that someone had been doing their own experimentations as the days passed and the baking soda water dried on the glass table top! Hmmmm … should we have inspected for finger prints???

Okay … so the baking soda hadn’t created stalactites but we had definitely observed the process of capillary action.

We’d also observed how clear liquids can dry out leaving white powder all over the table. There’s probably a name for that process but at this moment, I have no idea what to call it. If you know, I’d love to hear.

More Time Passed!

As the days passed, we began to think that the Epsom Salts were just going to sit there without doing anything either.

 It worked! We have stalactites!

However, we were thrilled to find one morning that the process of a stalactite and stalagmite forming had begun! It was working!!!
 It worked! We have stalactites!

Several days later, the stalactite actually joined the (very small) stalagmite in the bowl.
 It worked! We have stalactites!

We left the experiment there for many days, watching to see if the formations would grow further. They eventually stopped but we were thrilled with the results.

The Final Surprise!

When it came time to finally clean the experiment away, we were in for a beautiful surprise.
 Stunning crystals had grown in the glass jars

Stunning crystals had formed around the washers in each glass.

Upon reflection, we could have probably put these crystals in the bath but this wasn’t something I thought of until after we’d watched the crystals dissolve under running water. It was fascinating watching them melt away!

Have you made stalactites or stalagmites with your children? We’d love to hear about your experiences. Please feel free to leave a comment here or on our facebook page.

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