Handbook of Nature-Study · Lesson CCXXI · Topic 36: Water and weather
221. Water forms: vapor, dew, frost and snow
Goal: Your child can explain evaporation and condensation with everyday examples, and can catch and look at snow crystals.
You'll need
- Two saucers of water and a box to cover one
- A glass of ice water
- A plastic bottle with a cap (for freezing)
- A piece of dark cloth (wool or flannel) kept cold outdoors
- 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 (demonstrations indoors; snow crystals outdoors; frost and dew in autumn or spring), and thirteen observations on evaporation, steam and mist, clouds, dew, frost, ice, frosted windows, snow crystals, hail and sleet. Photographs of snow crystals by W. A. Bentley are on these pages. Wilford M. Wilson's long chapter "The Weather" follows the lesson.
The lesson, step by step
When to do it
Parts of this lesson belong to different seasons. Do the saucers and the cold glass any day. Look for dew and frost on autumn or spring mornings. Save the snow crystals for a snowy winter day, best when the flakes are small and hard. Never go out while there is thunder or lightning.
The leading thought
Water occurs as an invisible vapor in the air and also as mist and rain; and when subjected to freezing, it crystallizes into ice and frost and snow.
Where does the water go?
Place a saucer filled with water near a stove or radiator; do not cover it nor disturb it. Place another saucer filled with water near this but cover it with a tight box. From which saucer does the water evaporate most rapidly? Why?
Will they dry more rapidly during a clear or during a damp day? Why? Will they dry more rapidly during a still or during a windy day? Why?
Water out of the air
Fill a glass with ice water and watch the outside.
Why does the ice pitcher, on a warm day, become covered on the outside with drops of water? Would this happen on a cold day? Why not?
At the kettle, the adult stays close and the child looks from a safe distance (steam burns):
Notice that near its spout there is no mist, but what we call steam is formed beyond this. Why is this so?
Dew and frost
On a still, clear morning, go out early.
What causes dew to form? When the grass is covered with dew, are the leaves of the higher trees likewise covered? Why not?
How many forms of frost crystals can you find on the grass on a frosty morning?
Ice
Fill a plastic bottle to the top, cap it, and leave it outdoors on a freezing night (or in the freezer) inside a bag. The book uses a glass bottle, which can shatter, so we use plastic.
How does the ice appear in it at first? What happens later? Why does the bottle break?
Snow crystals
When there is a fine, dry snow falling, take a piece of dark flannel and catch some flakes upon it. Examine them with a lens, being careful not to breathe upon them. How many forms of snow crystals can you find? How many rays are there in the star-shaped snow crystals?
Nature notebook
Draw three different snow crystals or frost patterns. Then write the words evaporate (water goes into the air) and condense (water comes out of the air), each with an example from today.
Afterwards
Over the coming weeks, look for dew, frost, fog and frosted windows, and add a drawing each time.
Tip
For older children, read from the weather chapter that follows: the Temple of the Winds at Athens, and how Benjamin Franklin found out that storms travel.
Answers to the book's problems
The uncovered saucer dries fastest because its vapor can escape into the air. Clothes dry fastest on clear, windy, warm days. Water vapor is invisible; the white "steam" is tiny droplets formed when the vapor cools, so there is a clear gap at the spout. Cold surfaces cool the air next to them and the vapor condenses into drops, which is how dew forms on clear, still nights when the ground cools. Water expands about one-ninth when it freezes, which bursts bottles and splits rocks. Snow crystals have six rays or six sides.
Worked out for this site from the scan. If a number in your copy differs, trust the book.