This article has information on how to make a salt crystals as a science project. You will also find an second project on how to make sugar crystals. Doing both allows comparison of the salt crystal science project and the sugar crystal science project.

Introduction

This article presents a project for making salt crystals and an extension in which you make sugar crystals and compare the two.

Make Salt Crystals

In this project, students observe crystal formation as they make salt crystals.

Materials

• Clean, wide-mouthed glass jar
• Water
• Non-iodized table salt (up to ½ c)
• A pencil
• Sturdy string
• A spoon

Directions

1. Put tap water in the jar up to about the halfway point.
2. Add several Tbsp of salt and stir with a spoon until the salt dissolves. Continue adding salt, about a tsp at a time, until is starts collecting rather than dissolving.
3. Tie a length of the string around the center of the pencil. Adjust the string so that it ends just above the water.
4. Place the jar in a place where it will not be disturbed.
5. Check the jar after one day, and then every day or every other day (whichever you like) for up to 3 weeks. Record the progress of the crystal formation. Also note the change in the height of the water.

Note: do not eat the salt.

Make Salt Crystals Extension

In this project, students observe crystal formation as they make rock candy.

Materials

• 4 c granulated sugar
• 2 c water
• a saucepan
• a heat-proof spatula
• a clean glass jar
• pencil
• waxed paper or a coffee filter

Directions

1. Heat the water to a boil.
2. Pour in the sugar, stirring continuously, until it is clear.
3. Remove the saucepan from the heat, and cool the mixture.
4. Use the mixture to dampen the string, then either let it dry for a day or roll it in dry sugar, shaking off excess. Either of these techniques will prime the surface of the string for the growth of larger crystals.
5. Pour the contents into the jar (this may be best done in a sink).
6. Tie the string to the center of the pencil. Rest the pencil across the top of the jar, with the string extending into the center of the jar, not touching the sides.
7. Cover the top of the jar with a piece of waxed paper or a coffee filter, neither of which will prevent evaporation, but will keep dust, etc. out.
8. Carefully place the jar somewhere in which it can sit undisturbed for up to a week.
9. Check the growth daily, removing any sugar crust the form on the surface.
10. Compare the growth and the crystals to the salt: how are they similar? how do they differ?
11. Remove the rock candy when you are happy with its size. It can be eaten as is or dried first.
12. If crystals are tending to form on the jar, rather than on the string, you can gently remove the string and reheat the syrup, which will dissolve the crystals. Cool the syrup, pour it into a clean jar, and rehang the string (if you hang the string in warm syrup, the crystals that have already formed may begin to dissolve).

To extend the project, you can consider the following:

• Add food coloring to the water in which you make either salt or sugar crystals.
• Experiment with different lengths of string, i.e., hanging the string so that it is partially in the water as you create salt crystals.
• Hang a string into the salt or sugar water with a paper clip tied to the end.
• Hang multiple strings into the water close together. Hang multiple strings farther apart. What happens?
• Drop a length of string entirely into the salt water and see what happens.
• Try heating the water before putting it in the jar to make salt and compare the results.
• Try using different types of salt, such as iodized salt, sea salt, Kosher salt, and Epsom salts.
• Try adding flavoring to the sugar.