If possible, maybe you or your students can bring in dehydrated edible food items, such as raisins, prunes, dried apples or dried apricots. They can observe some of their properties of dehydrated materials and then enjoy a tasty treat. From the book on mummies, read the section on Egyptian mummies. Students can compare and contrast certain fruits and their dehydrated counterparts, such as grapes and raisins, plums and prunes, apples and dried apples. Brainstorm ideas on how you dry out these objects.
Answers can include salting, baking, lying in the sun.
Let students choose simple objects that they wish to dehydrate. If the choose something that might be too watery or smelly, such as a watermelon slice, discuss why it might be a bad choice. In a small cup or bowl, students will pour about 1-2 inches of the salt. Then they will place the object in the cup and pour more salt over the object until the object is covered. With a permanent marker or masking tape, students should label the bowl with the name of the object and the date.