 |
 |
Grow Your Own Salticle
Fascinating Food
Teachers
Ask the class whether they have visited any underground caves. If so, ask what they observed. If stalactites or stalagmites are mentioned then start a discussion about how they may be formed. Lead on to this experiment.
Parents
Stalactites and stalagmites are formed when small amounts of calcium salts are dissolved as water seeps through rock. When the water evaporates, the calcium salt is left behind. Have a go at forming salticles!
Age range 7-14 with adult supervision
|
 
|
- Salt
- Two small jars
- Large paper clips
- Wool or string
- A small saucer
|
|
- Stir plenty of salt into a large glass of very hot water. Keep stirring. If all the salt dissolves, add more until it doesn’t. Allow the mixture to cool, and then pour half into each jar.
- Attach a paper clip to each end of a piece of wool about 40 cm long.
- Put one end of the wool in one of the bottles, and the other end of the wool in the other bottle. Make sure the ends of the wool are in the solution.
- Now make sure that the bottom of the loop of wool between the bottles is hanging below the level of the salt solution in the bottles.
- Place a saucer under the bottom of the loop of wool. Leave for a week. And behold a salticle will appear!
Tip: Make sure your wool is good and porous; it’s got to act as a passageway for the salty liquid. Also, make sure the wool doesn’t dry up during the week or you’ll be snookeroo’d.
|
|
The salt solution travels along the wool by capillary action. This is a physical effect by which water can travel upwards as if to defy gravity! It’s due to the interactions between the water molecules and the wool which contains tiny tubes and spaces for the solution to fill. Plants take advantage of capillary action to pull water from the soil into themselves.
As the salt solution travels along the wool it starts to drip from the lowest point in the loop of wool. The water evaporates and salt crystals are left behind. In time more and more salt solution drips down and the crystals of salt grow larger. Eventually it will form a ‘salticle’ or stalactite.
Stalactites and stalagmites, collectively known as speleothems, form due to water seeping through rock. As the water moves through the rock, it dissolves small amounts of limestone or calcium carbonate. When the water drips from a cave ceiling, small amounts of this limestone are left behind, eventually leaving an icicle-shaped stalactite. Limestone that reaches the cave floor "piles up" and forms ‘stalagmites’.
|
|
|
Use other salts e.g. baking soda (sodium bicarbonate).
Grow a woolly lamb:
Fold paper such as sugar paper (or other coarse grained paper) in half. Draw a sheep shape on it and cut it out. Make up a strong salt solution and put it into a Petri dish or a coffee jar lid. Place the feet of your sheep into the solution and over the next few days salt crystals will appear over the back and sides.
|
|
|
Science on the Shelves (University of York)
Woolly lamb by Mary-Jane Murray, from Saxton Primary School in North Yorkshire
|
 |
|
Treat hot water with care to avoid scalding injury.
|
|
