The wonderful thing about crystals is that they form amazing geometric patterns, sometimes perfect in shape. Thanks to The Helix’s reader, Billy Quist, you can grow your own crystals at home
A solution is a mixture of a solute and a solvent. In this example, the solute is sugar and the solvent is water. If you add a small amount of solute to the solvent, typically the solution is under-saturated. Adding more solute will cause the concentration of the solution to increase, until you cannot dissolve anymore solute. The solution is now called saturated.
By heating the solution it is possible to dissolve more solute, making the solution super-saturated. This is an unstable state for the solution and as soon as conditions change (for example the temperature lowers), some of the solute will reappear in solid form – precipitation.
To precipitate, the dissolved solute looks for a ‘seed’ to build upon. In the case of our experiment, it uses the sugar crystal. Over time, more of the solute precipitates on the outside of the seed, layer upon layer, forming a larger crystal. Once the solution returns to a saturated state, the crystal stops growing.
If you need a seed crystal large enough to tie on the end of your string, here’s an idea. Half fill a jar with water from the tap and stir in a few tablespoonfuls of sugar until the solution is saturated. Tie a piece of string to a pencil and balance it over the top of an open glass jar with the string hanging in the sugar solution. Place the jar in a sunny position and within a few days you should have a number of good-sized seed crystals
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