Cryogenics

Vanderbilt Student Volunteers for Science

Fall, 2013

Safety Precautions

• Always wear safety googles. • Always pour from large nitrogen dewar to small

containers. Never fill a small container by dipping it in the large dewar.

• You risk frostbite if your skin is exposed to liquid nitrogen. The cotton gloves are provided only for use when pouring and will not provide protection should they become soaked with liquid nitrogen.

• Never place any objects in the large liquid nitrogen dewar since it is going to be used to make ice cream. There is a small dewar (one made from two clear plastic bottles with packing peanuts for insulation.)

II. Demo: Liquid Nitrogen• Give each student an

observation sheet.• Pour a small amount of liquid

nitrogen into the 10 oz. clear plastic cup.

• Ask the students to write down on their observation sheet what they see happening in and around the cup.

• Draw a picture of the cup on the board and ask the students to tell you what happened. Write these observations around the drawing. (See lesson for answers.)

III. Demo: Hammering with a Banana

• Show students the nail and piece of wood. Try to hammer the nail into the wood with the banana.

• Fill the small dewar about 2/3 full with liquid nitrogen.

• Put the banana in the small dewar. Wait 2-3 minutes for the liquid nitrogen to cool the banana.

• After 2-3 minutes, use a glove to pull the banana out of the liquid nitrogen and hammer the nail into the board.

IV. Demo: Freezing Rubber Tubing

• Make sure that the rubber has been slit open to prevent pressure buildup!

• Wear safety googles!• Use the small dewar/plastic

bottle of liquid nitrogen from Demonstration #2.

• Bend two pieces of rubber in half at the middle (not kinked but a little rounded) and while holding the rubber together at the open ends, immerse the bent middle portions into the small dewar containing the liquid nitrogen for about one minute.

IV. Demo: Rubber Tubing (cont.)

• Take out both pieces of the rubber tubing.

• For the first piece of rubber tubing quickly and forcefully hit the cold part against the top of the table. This should shatter the tubing.

• For the second rubber tubing, after a few minutes of warming to room temperature, it should be flexible again. You may want to forcefully hit it against the top of the table to show that it does not shatter.

V. Demo: Whistling Tea Kettle

• Ask students if they know what happens when water is boiled in a whistling tea kettle.

• Ask what causes the whistle.

• Use the ladle to put some liquid nitrogen into the kettle.

• Ask students to explain why the kettle is whistling.

VI. Demo: Shrinking a Balloon• Show an inflated balloon to the

class.• Put the bowl in a spot where

students can see it.

• Place the inflated balloon in the bowl.

• Pour a small amount of liquid nitrogen over the balloon.

• The balloon will shrink and crackle as it gets cold.

• Use a glove and remove the deflated balloon from the bowl.

• As you hold the balloon in the air, the students will be able to observe the balloon inflate and return to its original state.

VII. Demo: Reconstituting Dry Ice

• Using a glove, hold up a piece of dry ice.

• Place several small pieces of dry ice into an empty 20 oz. plastic coke bottle.

• Pour 6 oz of water into the bottle of dry ice. Tell students that the water is added to warm up the dry ice so the change from solid to gas happens faster.

• As the CO2 gas is being given off, place a balloon over the bottle.

• The balloon will fill up with CO2.

VII. Demo: Reconstituting Dry Ice (cont.)

• When the balloon is the size of a basketball (or a little smaller), remove the balloon from the bottle and tie a knot in the end.

• Place this balloon into the stainless steel bowl and pour liquid nitrogen over it.

• Once the balloon is deflated, lift it out of the bowl and cut it open with the scissors.

• Pour the dry ice into the clear plastic cup and show the students that the CO2 gas has returned to dry ice (solid CO2).

VII. Making Ice Cream• Open the ice cream mix and pour

it into the large stainless steel bowl.

• Pour ALL (1 quart) of the whole milk into the bowl and stir.

• Have one VSVS volunteer SLOWLY pour about half of the container of liquid nitrogen into the bowl while another volunteer stirs the mixture.

VIII. Making Ice Cream (cont.)• NOTE: The slower the liquid

nitrogen is added, the better the consistency of the ice cream. Pour the liquid nitrogen at about the rate of a drip coffee machine for about 20 to 30 seconds.

• Add the second half of the quart of milk and stir.

• SLOWLY add more liquid nitrogen.

• STOP if any of the liquid turns solid.

• Continue pouring the liquid nitrogen at a slow rate. Have the stirrer check every 20-30 seconds for the consistency of soft serve ice cream.

VIII. Making Ice Cream (cont.)

• Put a small amount in enough paper cups to serve all the students, teacher, and VSVS volunteers. Pass these out with the taster spoons.

Clean-Up

• Throw away milk carton and banana.• Empty water/dry ice bottle-make sure

there is no cap on the bottle!• Discard pieces of broken balloons and

small rubber tubing.• Put bowl and spoon back in the trash bag

and place them in the kit.• Make sure to RETURN both liquid nitrogen

dewar and the kit to VSVS lab.