Have students identify the object that made the imprint. Pour sand into the glass until full. Pour water into the glass until full. Pour salt, slowly, into the glass. With every person on earth counting one of these atoms a second, it would take about 5 million years to count them all.
Half fill the beaker with vinegar.
Put a spoon of salt in the beaker and stir the contents of the beaker. Observe the pennies. Discuss why the pennies become bright. Carefully pour the liquid into another beaker. Observe the liquid.