Growing snow
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| You'll need these materials. | |
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| Immerse the bottle in dry ice. | |
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| Cover the dry ice with aluminium foil. | |
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| See your snow flake grow. |
Over the next three weeks, activities will use frozen carbon dioxide – better known as ‘dry ice’. This material can be purchased through some party supply companies or direct from BOC Gases. Why not wait until you've collected all three activities and do them together!
Warning: Dry ice is not like water ice. Do not allow it to touch your skin; the extreme cold can cause harm. Wear thick gloves and safety goggles when doing this activity.
You will need
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Dry ice (approximately 3 cups)
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Clear drink bottle, 300ml or smaller
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Sponge
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Warm water
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Super-glue
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Thin copper wire OR fishing line and paper clip
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Hammer
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Nail
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Scissors
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Sticky tape
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Large Styrofoam cup (2-minute noodle Styrofoam bowls are perfect)
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Aluminium foil
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Gardening gloves
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Safety goggles
What to do
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Estimate 3cm from the bottom of the drink bottle and cut around the sides, removing it completely.
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Cut a circle from the sponge that will allow it to sit in the bottom of the drink bottle. Glue it in place with a hot glue gun or super glue.
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Use the hammer and nail to poke a hole through the sponge and the bottom of the drink bottle.
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Cut approximately 10cm of thin copper wire or fishing line. If using fishing line, tie a paperclip onto the end to weight it down.
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Thread this through the hole so it hangs down the centre of the bottle when the bottom is replaced.
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Knot it to keep it in place.
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Dampen the sponge with warm water.
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Replace the bottom of the drink bottle and secure it in place with sticky tape.
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Place the bottle upside down into the Styrofoam cup. Put on your gloves and safety goggles. Surround the bottle with dry ice.
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Cover the dry ice with aluminium foil, leaving the bottle poking up. The wire inside of it should be clearly visible.
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Wait about ten minutes for the first signs of a snowflake to appear. An hour later you should have a beautiful feather of snow inside your bottle.
What’s happening?
Your bottle is like an upside-down atmosphere. Instead of being colder the higher up you go, the cold part of your bottle is down below. The principles are quite similar, however. The warm water in the sponge evaporates to become gaseous water vapour in the surrounding air. As it sinks into the cold, the air can’t hold onto the vapour and it condenses onto the coldest surface it can find – in this case the copper wire.
Once a few water molecules have settled onto the wire, they act as a ‘nucleation’ site. In other words, for rain and snow to form there needs to be something for water to first cling to (like dust) before it collects more molecules.
In the cold air, the water molecules slow down and turn from a liquid into a solid phase. The water molecules themselves are somewhat like boomerang-shaped building blocks, which line up in a special way as they settle into a solid. This creates the crystal-like shapes you see growing on the wire.
Applications
Believe it or not, the shape of your snow flake can tell you a lot about the temperature at which it formed. If it looks like a fern leaf with broad, stretching needles of ice, your bottle made it to a chilly –15oC. If the flake looks more like a bird’s feather with the needles pointing more towards one end, the temperature only fell to about –5oC.
A number of factors can influence the shape and size of your snowflake, which is why it’s alleged that no two snowflakes are ever completely identical. The humidity, temperature and air pressure determines how the branches form and whether they will be fat or thin, long or short. Even tiny bumps on the surface of the nucleation site (in your case, the copper wire) will determine how the crystal will branch.