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ExposeExciteIgniteMay2012

Simply rotate the pliers

Simply rotate the pliers in the hole until it is the right size. 5. Remove all outside burrs from the hole with a fine file or sand paper. Careful! 6. Cut a length of strong fishing line - about 1 m or 3.3’ Poke or drill a small hole in the rim of the metal lid and tie the fishing line securely to the lid (Figure 2.8). 7. Position the cable tie close to the bottom end of the can but do not pull it tight yet (Figure 2.9). Figure 2.7 Figure 2.8 Figure 2.9 8. Now, tie the other end of the fishing line securely to the cable tie and then pull the cable tie tight. Operating the Bunny Can 1. Calculate the amount of butane gas required for combustion: Volume of can ÷ 32 = x mL butane. 2. Push the metal lid securely onto the can. 3. Hold the butane can upright and position the plastic syringe tip on the butane can nozzle and simply press the syringe down (Figure 2.10). The syringe plunger will shoot up. Fill to x ml. 4. Now inject the butane rapidly into the can to promote good mixing (Figure 2.11). Then cover the hole with your finger. The gas will slowly diffuse throughout the can - allow a few seconds. (To improve the 17

mixing, see ‘Adding a mixer’ on page 21). 5. Insert the gas lighter (figure 2.12), do the countdown and pull the trigger as sharply as possible (because the lighter may flood the tip with extra fuel) . . . Fire in the Hole! Safety: Aim away or well above your spectators. Figure 2.11 Figure 2.10 Figure 2.12 6. If it does not fire, withdraw the lighter, re-insert and try again. If still unsuccessful, open the lid, blow into the can to refresh the air supply and then repeat the procedure. Always refresh the air before firing again. Teaching Extensions Here are a few ideas to apply in your classroom or backyard research: 1. Why did the lid fly off and (luckily) not the lighter? Start with the definition of pressure (P): P = F/A where F is the force and A the surface area. Focus on the surface areas of the lid and lighter and remember that the pressure inside the can is equal in all directions. 2. Can your students calculate the ideal stoichiometric combustion ratio of methane (CH4) to air? How about other fuels? They first have to balance the equation CH4 + O2 ! CO2 + H2O + energy to get the molar ratio. The gas volume ratio is 1 : 9.4 18