The Science of Fireworks - with Chris Bishop

The lecture begins with an introduction to the science behind fireworks, highlighting their popularity and the scientific principles they illustrate. The speaker demonstrates the unique chemistry of fireworks by passing his hand through a flame, emphasizing the difference between this and regular fire. The historical discovery of this chemistry in a 19th-century fiction and the ancient Chinese recipe involving honey that led to gunpowder are mentioned. The speaker also touches on the origins of bangs in photography and encourages the audience, especially youngsters, to study science and mathematics to become professional scientists and enjoy the fun of scientific exploration.

This paragraph delves into the chemistry of gunpowder, starting with an ancient Chinese script that describes an early form of gunpowder made with sulfur, saltpeter, and honey. The demonstration of heating this mixture shows a primitive form of firework, but it lacks the explosive power of modern gunpowder. The key breakthrough in gunpowder development was the replacement of honey with charcoal, leading to the three main ingredients: potassium nitrate (saltpeter), charcoal, and sulfur. The speaker explains the role of each ingredient, particularly potassium nitrate as an oxidizer, and demonstrates the reaction of potassium nitrate with paper to show its oxygen-releasing properties. The paragraph concludes with a discussion on the different forms of carbon, including diamond, buckyball, and graphite, and the role of sulfur in aiding combustion.

The speaker explores the optimal proportions for making effective gunpowder, drawing an analogy with the reaction between hydrogen and oxygen to explain the importance of balance in chemical reactions. Through an experiment with balloons filled with varying ratios of hydrogen and oxygen, it is shown that the fastest reaction occurs when there is twice as much hydrogen as oxygen. This principle is then applied to gunpowder, with the historical proportions of 75% potassium nitrate, 15% charcoal, and 10% sulfur being identified as ideal. The chemical reaction of gunpowder is complex, producing solid substances like potassium carbonate and potassium sulfate, which contribute to the smoke produced during combustion. The paragraph concludes with the demonstration of making gunpowder by mixing the ingredients in the correct proportions.

In this segment, the speaker tests the combustion rate of homemade gunpowder by spreading it along a track and measuring how quickly it burns. The results show that the gunpowder takes about 13 seconds to burn, which is slower than expected for an explosive. The speaker hypothesizes that the particle size and lack of thorough mixing may be factors affecting the reaction rate. To test this theory, Lycopodium powder is burned both in its natural state and after being mixed with air, demonstrating that better mixing can increase the combustion rate. The paragraph concludes with a historical look at how commercial gunpowder is made, using large machinery to thoroughly mix and grind the ingredients.

The speaker discusses the factors that affect the speed of gunpowder combustion, including temperature and density. Through experiments with light sticks in water of different temperatures and a reaction between sodium hypochlorite and water, it is demonstrated that higher temperatures and greater concentrations increase the rate of chemical reactions. These principles are then applied to the combustion of gunpowder, with the speaker predicting that confining the gunpowder in a tight container would lead to a faster reaction due to increased pressure and temperature. The paragraph concludes with a dramatic demonstration of confined gunpowder producing a loud bang, illustrating the concept of thermal runaway.

This paragraph explores the chemistry behind flash powder, which was used in early photography to produce bright light for taking pictures. The speaker demonstrates the burning of magnesium and the use of flash powder, which contains magnesium and aluminum, to produce a bright flash. The importance of the oxidizer, potassium perchlorate, is highlighted in ensuring a rapid and bright reaction. The speaker also discusses the different chemistry used in flash powder compared to the hydrogen and oxygen reaction, emphasizing the excess of fuel in flash powder to produce light. The paragraph concludes with a demonstration of flash powder confined in a cardboard tube, showing the dramatic effect of confinement on the reaction rate.

The speaker explains how colored fireworks are created by adding compounds made from specific metals to the pyrotechnic mixture. Different metals produce different colors: strontium for red, calcium for orange, sodium for yellow, barium for green, copper for blue, and magnesium or aluminum for white. The paragraph includes a demonstration of a simple red flare using strontium carbonate, potassium perchlorate, and akroy resin. The speaker also discusses the structure of a firework shell, which is launched into the air by a gunpowder charge and explodes at its peak to display colored stars. The paragraph concludes with a look at the different categories of fireworks and the safety considerations associated with each.

This paragraph provides a detailed look inside a firework shell, explaining the components and their functions. The fuse is used to ignite the gunpowder charge at the base of the shell, which propels the shell into the air. A delay fuse is also点燃 (note: the original text seems to have a typo or missing word here, possibly 'lit' or 'activated'), which triggers a bursting charge at the shell's peak. This charge breaks the shell apart, releasing stars or other pyrotechnic effects. The speaker discusses the importance of gunpowder in fireworks, distinguishing between its use in shells and the use of flash powder for sharp bangs. The paragraph concludes with a discussion of different types of fuses used in fireworks, including black match, visco, and plastic igniter cord, each with their own advantages and disadvantages.

The speaker discusses the evolution of firework displays, moving from traditional fuses to modern electrical ignition systems. Electrical igniters provide precise control over the timing of fireworks, allowing for complex and synchronized displays. The paragraph includes a demonstration of an electrical igniter and a look at the setup of a professional firework display, with mortars, shells, and electrical cables connected to a central controller. The speaker also highlights the precision and flexibility offered by electrical systems, which can be timed to music or other cues. The paragraph concludes with a look at some of the unique effects that can be achieved with modern pyrotechnics, such as crackle, strobing, and whistling sounds.

This paragraph explores some of the special effects used in fireworks displays, such as crackle, strobing, and whistling. Crackle is created by stars that produce a series of small explosions, while strobing involves stars that flash on and off, creating a twinkling effect. Whistling is produced by a cardboard tube filled with pyrotechnic composition, which changes pitch as it burns. The speaker also discusses the challenges of smoke production in fireworks and introduces nitrocellulose, a smokeless alternative discovered by chemist Christian Friedrich Schönbein. The paragraph concludes with a demonstration of nitrocellulose and a combination of nitrocellulose with color chemistry, producing a colorful and smokeless firework effect.

The lecture concludes with a discussion of the effects of temperature on reaction rates, using the example of light sticks that were observed earlier in the lecture. The speaker also thanks Chris Brackstone for his contributions to the lecture. To end on a festive note, a model of Guy Fawkes made entirely of nitrocellulose is set on fire, symbolizing the traditional bonfire night celebration. The speaker bids farewell to the audience, wishing them an enjoyable bonfire night.