A Question about Making a Crystal


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A Question about Making a Crystal

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Aug 10, 2010, 1:35am

A science experiment my kids and I have been doing hasn't worked out, and I'd like to know why not. We gradually stirred 1/4 cup of sugar into hot water until the water was too full to accept any more. Then we hanged a string in the solution and let it stand for several days.

A crystal was to have formed on the string, but that has not happened.

Does anyone have an idea of what we have done wrong?

It's from Physics Experiments for Children

Aug 10, 2010, 3:27am

One of the kids drank the lolly water while you weren't looking and substituted plain, unadulterated tap water. Any of them been running around the walls lately?

Aug 10, 2010, 6:21am

Did you put something on the string? (We always used a paper clip, but I've seen it done with a knot on the string too.)

Aug 10, 2010, 7:17am

>1 Toolroomtrustee:

I used to make crystals with my kids using salt, and tying a piece of salt at the end of the string. I always used boiling water (not just hot), to make sure that the solution was really supersaturated.

My mother used to make crystals with me using what she called "bluestone" (copper(ll) sulphate). Not a great idea for kids (the solution is toxic), but it made gorgeous crystals! Again, we started with a supersaturated solution, and tied a chunk of bluestone to the end of the string.

I'd try again, maybe using salt instead of sugar, and tying a piece of salt to the end of the string. Then be patient -- it does take a few days.

Aug 10, 2010, 2:58pm

With sugar, you really do need boiling water, as it will ensure supersaturation. Also, weighting the string helps. It's also going to depend on how humid the conditions are. Crystals form much faster in dry areas, since the water evaporates faster and precipitates the sugar more quickly.

Aug 29, 2010, 10:01pm

I did sugar crystals with a cub scout troop- You need to get lots of sugar into the water- I boiled it. They will grow faster if you provide a seed crystal- I rolled the damp string in a few grains of sugar- some must have stayed on as the crystals grew from several different spots. Did you leave the lid off so water can evaporate? I think it took at least a week for anything to show- then several more to grow fairly big.