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1 week ago

ExposeExciteIgniteMay2012

actually hear the fire

actually hear the fire racing forward (it sizzles) and see the tiny sparks around the combustion area due to the higher oxygen supply. The simplest fuse I have ever prepared is made in a similar way. Wash thin packing string in hot water with soap. Rinse it well and dunk in the potassium nitrate solution for a few minutes, remove and let dry. Voila! This slow burning pyrotechnic fuse is only suitable for indoor use. To increase the combustion output simply take the rocket fuel mix (saltpetre/ sugar), prepare a paste with water and dip the washed string in the paste for a minute. Remove and leave to dry. What is happening? We have performed a very simple ‘nitration’ process of paper and string that is similar to the sugar-nitrate rocket system but different to the nitration process in guncotton and flash-paper preparation. In guncotton nitration processes new nitrate compounds form that are thermodynamically unstable: 3HNO3 + C6H10O5 ! C6H7(NO2)3O5 + 3H2O Guncotton is a cellulose trinitrate which contains 12.5 to 13.5% nitrogen and is classified an explosive. Our paper and string did not form cellulose nitrate. After the water has evaporated, the potassium nitrate was still present on the paper in a very finely divided state. The glowing match supplied the activation energy to get the combustion started and the decomposing potassium nitrate produced oxygen that sustained the combustion. 2KNO3 ! 2KNO2 + O2 C6H10O5 + O2 ! CO2 + H2O + energy Key Terms Reaction surface area, reaction rate, activation energy, exothermic reactions, deflagration, decomposition, nitration processes References 1. KN Sucrose propellant, Nakka, R., http://www.nakka-rocketry.net/ sucrose.html Great website on experimental rocketry. 2. Stine G. H., Handbook of Model Rocketry, 7th edition, John Wiley & Sons, 2004 3. Have a look at the inspiring and challenging project named the “Sugar Shot to Space Program (SS2S)”. The underlying goal of this program is to loft a rocket powered by "sugar propellant" into space, that is, 100 km (62 miles) above the earth's surface. Visit: www.sugarshot.org 107

108 Figure 9.15 Meat preservation - another application for saltpetre that is very exo-tasty