Handbook of Nature-Study · Lesson CCXII · Topic 33: Crystals, minerals and rocks
212. Salt
Goal: Your child dissolves salt, lets the water evaporate in different places, and finds that slow drying makes bigger cube-shaped crystals.
You'll need
- Table salt
- Three saucers and three small squares of dark paper
- A teaspoon and water
- A hand lens (magnifying glass)
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
The lesson has a leading thought, a method with saucers of salt water set in warm, cool and drafty places, and seven observations on dissolving, evaporation and salt crystals, and on where salt comes from.
The lesson, step by step
The leading thought
Salt dissolves in water, and as the water evaporates the salt appears in beautiful crystals.
Set it up
Let each pupil take five teaspoonfuls of water and add to this two spoonfuls of salt, stirring the mixture until dissolved.
Make three saucers. Write your name and the date on each square of paper and press it under the water. Put one saucer in a warm place, one in a cool place and one in a draft.
As you stir
When you pour the salt into the water, what becomes of it? How do you know when the water will hold no more salt?
Check every day
From which saucers did the water evaporate fastest—those in the warm places, or those in the cold? In which did the crystals form first?
Which saucers contained the largest crystals—those from which the water evaporated first, or those from which it evaporated more slowly?
Look through the lens
What is the shape of the perfect salt crystal? Do the smallest crystals have the same shape as the largest ones?
Look for "hopper" crystals: hollow, stepped cubes like tiny pyramids upside down.
Where salt comes from
How is dairy salt and table salt obtained? What is rock salt?
Why is the ocean called "the briny deep?"
Nature notebook
Draw the three saucers and the biggest crystal from each. Write one rule: fast drying makes ___ crystals; slow drying makes ___ crystals.
Afterwards
Check the saucers each day until they are dry, usually three days to a week.
Answers to the book's problems
Salt disappears into the water (dissolves); when grains stay on the bottom however long you stir, the water holds all it can. Warm and drafty saucers dry first. Slow drying makes the largest crystals. Salt crystals are cubes, the same shape large or small. Salt comes from evaporating sea water or brine and from mines of rock salt left by ancient seas. Lakes with no outlet, like the Great Salt Lake, grow salty because water leaves only by evaporating, leaving its salt behind.
Worked out for this site from the scan. If a number in your copy differs, trust the book.