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ExposeExciteIgniteMay2012

1. Make a Tube Whistle &

1. Make a Tube Whistle & Jump [] This demonstration can be performed in a classroom but is better performed in an area with more head space. The tube can easily fly to 6 metres (20’) if all goes well. Warning: In a room the tube may dent the ceiling and be deflected back. What you will need • Balloons filled with hydrogen gas. You could fill them with lab grade H2 or prepare your own as indicated in the previous chapter. It is convenient to have these balloons sealed off with balloon clips • Tall Pringles ® Tube • Small nail (1 to 2 mm diameter, (1/16”)) and hammer • Sticky stuff (BluTack ® ) • Fire lighter (long stemmed) • Ear protection, goggles, lab coat Here’s how 1. Empty the tube (yummy!) and wipe the inside with a cloth. Hammer a nail through the center of the metal base of the tube. It should be between 1 and 2 mm (1/16”) in diameter. 2. Poke a number of holes around the circumference of the tube through the cardboard, 5 mm (0.2”) from the edge of the open end. These are the air inlet holes - the size is not important. (Figure 4.7) Hole in metal base covered with sticky stuff 3. Hold the tube vertical, with the metal base at the top. Remove the lid and cover the small hole at the top with a small blob of sticky stuff (BluTack ® ). 4. Take the hydrogen balloon, remove the balloon clip and slowly, over one minute, discharge all of the the H2 gas from it into the tube (Figure 4.7). The tube should be held vertical. The dense air will be displaced with less dense hydrogen gas. Or connect the balloon to an air blowgun, insert the nozzle into the tube and squeeze the trigger (see previous chapter). Air inlet holes through cardboard Hydrogen balloon Figure 4.7 39

5. Keep the tube upright (metal base with BluTack ® at top). Replace the tube’s lid and stand it upright on a solid wooden table. Check that there is nothing above the tube, eg. lights, ceiling fans or (even worse) a video projector. Safety: Caution the audience to cover their ears as there is a small chance of immediate combustion when igniting the H2. Make the audience stand off at least 5 metres. Check that you have protected your ears and eyes. 6. Steady the tube with one hand on the side of the tube and remove the BluTack ® (roll it off). Now light the H2 with a long stem lighter so your hand isn’t close by if the tube does explode. You have a few seconds to light the flame when opened, so take your time . . . You should hear a light ‘pop’ sound when the gas ignites and if you dim the lights, should see a yellow flame burning at the hole (Figure 4.8). Warning: If you have not displaced all of the air inside the tube, there is a chance that the tube may explode when you light it. It is a frighteningly loud experience but won’t cause any harm to anyone. More of a nuisance to refill a balloon and re-do the demo. 7. Once the flame is lit, step back and indicate to the students the yellow colour of the flame that is a characteristic flame colour of sodium. (You used sodium hydroxide in the preparation of the gas). It may take up to 3 minutes before the tube explodes. And now for the surprise! After a while the flame and tube will start to resonate! First as a faint whining sound and then picking up in intensity and volume, delivering a great explosive crescendo! We have a singing, exploding tube. Enjoy! Yellow flame will shrink in size What is happening here? Why the delay before the explosion? The escaping hydrogen gas spews through the hole due to the column of very buoyant hydrogen gas below it. It mixes with air on the outside, ignites and combusts. The flame does not drop back into the tube because of the gas pressure from within. The flame is actually suspended above the metal surface. During the combustion process water forms and this can sometimes be detected as tiny water Figure 4.8 40