Crystals are the slowest experiment we do at club, and one of the most loved. Children check their jars every day and the change from one morning to the next is genuinely exciting. Here is how to grow your own over the summer holidays.
You will need
- A clean glass jar
- 300g of granulated sugar or 100g of table salt
- Hot water (a grown-up job)
- A pencil, a piece of cotton string and a paper clip
- Food colouring, if you like
Method
Ask a grown-up to pour about 200ml of hot water into the jar. Stir in the sugar or salt a spoon at a time until no more will dissolve and a little sits at the bottom. Add a drop of colouring.
Tie the string to the pencil, weigh the end with the paper clip, and rest the pencil across the top of the jar so the string hangs in the liquid without touching the sides. Leave the jar somewhere it won’t be moved, away from the air-conditioning vent.
What happens
As the water slowly evaporates, there isn’t enough water left to hold all the dissolved sugar or salt, so it comes out as solid crystals on the string. Salt crystals are small cubes; sugar crystals grow bigger and lumpier.
Take a photo every morning at the same time. The time-lapse at the end is the best bit.
Sugar crystals take about a week to start and two weeks to look impressive. If nothing happens after five days, the mixture probably needed more sugar, which is a useful result too.
