Introduce your child to this spooky science project for Halloween — or any time of the year! Dehydration is an ancient method for preserving everything from food to mummies. Using salt and baking soda, your child can carve and dehydrate (dry out) an apple to create mummified fruit.
Salt is a desiccant, which is another word for a chemical that’s good at pulling water out of other things. Not only does it speed drying, it kills any microbes that might cause the apple to spoil.
What You’ll Need
Safety Tips and Hints
Pumpkin carving tools are nice because they’re relatively safe for little hands, but if you don’t have one, an adult can carve a face in an apple using a sharp knife.
Don’t let kids eat Epsom salt.
What to Do
Step 1: Help your child carve a face in each apple.
Step 3: If you have a kitchen scale, ask your child to weigh the apples and record their weights to keep track of how much water they lose.
Step 4: Fill one container with enough salt to completely cover an apple. Label it with the date, the apple’s starting weight and write “salt” or “NaCl” on the container. Ask your child to put one of the apples in the container and cover it completely, packing salt into all of the holes. Close the container.
Step 7: After a few days, remove the apples, scrape out the salt and weigh them. Record their weight and return them to the salt. Check them every few days and continue to dry them in salt until they are shriveled up. Replace the salt with dry salt if needed.
Enrichment
How long did it take to mummify the apples? Which salts worked best?
Test apple slices in different salt mixtures to see which of them is the best desiccant. What keeps mold from growing? What preserves the apple’s color best? Which salt mixture keeps the apples from smelling bad?
MORE: Make Alien Monster Eggs for the Spooky Season
The Science Behind the Fun
In Ancient Egypt, natron was used to preserve mummies. Natron is a natural salt mixture containing the chemicals sodium carbonate, decahydrate (soda ash), sodium bicarbonate (baking soda), sodium chloride (table salt), and another salt called sodium sulfate.
These salts act as desiccants, which are chemicals that removes water from things. They also have anti-microbial properties, so they keep bacteria and fungi from growing.
The Egyptians dried mummies in natron inside windy tents in the dry desert air for 40 days before wrapping them for their final burial.
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You'll find projects like this one featured in Liz’s new book STEAM Lab for Kids: 52 Creative Hands-On Projects Using Science, Technology, Engineering, Art and Math (Quarry Books, 2018).
