What you Need
What to do
If you have some washing soda
Dissolve about 1/3 mug of washing soda in 1 2/3 mugs of water, you may have to heat it in the saucepan to get it all to dissolve.
if you are using bicarbonate of soda add about 1/3 of a mug full to 1 2/3 mugs of water and then heat it until it starts to boil. At 80-90°C it will start to fizz as carbon dioxide is driven off converting sodium bicarbonate (sodium hydrogen carbonate) into sodium carbonate - washing soda. Keep heating until it starts to boil properly - you will be able to tell because the bubbles will get a lot bigger.
While you are doing this set up two mugs on the plate or tray, with a piece of wool or string hanging loosely between them. You can secure the string by tieing a loop in each end and catching the loop on a fork.
Now fill the two mugs so they are nearly full of washing soda mixture, and make sure the string is hanging a bit below the level of the water.
Put the whole thing somewhere warm such as the airing cupboard and wait for 2-3 days.
Be very careful when pouring the boiling liquids as they are very hot!
Don't use an aluminium pan as it will dissolve in the washing soda.
You can try the same experiment with different concentrations of washing soda or using other things that will dissolve well in your kitchen.
What may happen
You should find that small crystals grow on the string. If you wait long enough you may find that you start to form a stalagtite on the dip of the string. If you
Why does it happen?
The sodium carbonate you buy is in fact millions of tiny crystals. A crystal is a repeating array of billions of atoms or molecules in a regular pattern. There can be more than one type of molecule in a single crystal. In sodium carbonate crystals there are Sodium ions, Carbonate ions and water molecules.
When you put the crystals in water the water molecules will bash into the sides of the crystal and tend to knock molecules off, these will wander off amongst the water and then eventually rejoin the crystal. The warmer the water the more violent the battering by the water molecules so it is harder for the crystals to reform and the water can hold more molecules in solution.
What happened in the experiment?
The wool attracts water well and because it has many closely spaced fibres surface tension draws the water up the wool, it can then run down the other side. In fact it acts as a syphon pulling water and the dissolved sodium carbonate up the short side and along the wool.
This means you have a string permanently soaked in sodium carbonate solution. The string has a large surface area so lots of water evaporates leaving behind the sodium carbonate, which will then form crystals.
Is this used in the real world?
Evaporating solutions is how most of the crystals you find in everyday life are made, such as salt or sugar. Sea salt is manufactured in huge shallow ponds in warm countries which sea water is allowed into and is then allowed to evaporate by the sun leaving the salt behind to form crystals that you put on your chips.