Grow a cupful of Epsom salt crystal needles in your refrigerator. It’s quick, easy, and safe
- Cup or small bowl
- Epsom salt (Amazon link: Epsom Salt)
- Hot tap water
- In a cup or small, deep bowl, mix 1/2 cup Epsom salt (magnesium sulfate) with 1/2 cup hot tap water (hot as it will get from the faucet).
- Stir about a minute to dissolve the Epsom salt. There will still be some undissolved crystals at the bottom.
- Place the cup in the refrigerator. The bowl will fill with needle-like crystals within three hours.
- Don’t use boiling water to prepare your solution. You will still get crystals, but they will be more threadlike and less interesting. The temperature of the water helps control the concentration of the solution.
- If you like, you can place a small object at the bottom of the cup to make it easier to remove your crystals, such as a quarter or plastic bottle cap. Otherwise, carefully scoop the crystal needles from the solution if you wish to examine them or save them.
Solubility (the amount of something that will dissolve) is tied to temperature. The hotter the water is, the better it is at dissolving the Epsom salt. If you had a way to see the atoms along the edge of the crystals, you would notice that some of magnesium sulfate (Epsom salt) was constantly leaving the crystal to dissolve in the water, while other bits of magnesium sulfate were constantly leaving the water to join the crystal. If everything balances, then the crystals stay the same size.
On the other hand, if the water is hot, the extra energy lets more of the salt leave, throwing off the balance. That means that the solid Epsom salt will dissolve, until it reaches a new balance. At that point, the salt stops dissolving.
When you put the cup in the refrigerator, heat energy from the cup moves to the surrounding area. With less heat energy in the water, the balance shifts again. Now you have more Epsom salt joining the crystals, so the crystals grow. This will continue until things reach a new balance. At that point, the crystals stop growing.
If you want to experiment further, you can continue to play with that balance point. Once your crystals have grown, pour off the water. In another cup, mix another batch of hot water and Epsom salt. This time, wait until the water cools almost to room temperature, and then carefully pour it into the cup with the crystals from your first experiment. This time, do not stir! Put it in the refrigerator.
If you get the balance right, then your original crystals will not redissolve completely. As the solution cools, more magnesium sulfate will be added to the original crystals, causing them to grow larger. You can try repeating this several times. If your balance is off, and the crystals dissolve, then just heat the water again, and start over. When you are done, you can let the crystals dry and put them on your shelf. If they get broken or dusty, just dissolve them, and grow them again.