Ancient Alchemy in the Classroom: A Honey-Based, Deflagrating

Demonstration Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Ancient Alchemy in the Classroom: A Honey-Based, Deflagrating Pyrotechnic Adrian V. Wolfenden and Nathan L. Kilah* School of Natural SciencesChemistry, College of Science and Engineering, University of Tasmania, Dobson Road, Sandy Bay, Tasmania 7005, Australia S Supporting Information *

ABSTRACT: A simple, honey-based pyrotechnic demonstration is presented. The demonstration has been derived from alchemical writings and highlights the importance of alchemical preparations on the development of gunpowder, chemistry, and the scientific method. The demonstration involves the combustion of mixtures of honey, potassium nitrate, and sulfur which were observed to burn with brilliant flame, heat, smoke, and sound. The combustion was rapid, visually attractive, and surprising to chemist and nonspecialist viewer alike.

KEYWORDS: General Public, Demonstrations, History/Philosophy, Misconceptions/Discrepant Events, Consumer Chemistry, Descriptive Chemistry, Reactions

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the use of this “fire drug” for its medical application against ringworm, worms, and insects.4 The mixture that we know as gunpowder, or blackpowder, is a mixture of finely ground potassium nitrate, charcoal, and sulfur in a 75:15:10 mass ratio.5 This simple ratio belies the complexity of the combustion reaction, with numerous gaseous and particulate potassium salts formed as products and byproducts, and significant trial and error over many centuries was necessary to achieve the optimum reaction stoichiometry.4 A limiting factor in the development of gunpowder was the availability of potassium nitrate, the most difficult of the three ingredients to obtain in large quantities. The action of gunpowder varies greatly with the vessel used for its combustion: gunpowder deflagrates when burnt in an open vessel, while containment can be used to cause explosion or to launch projectiles.2 Early steps toward the development of gunpowder are evident in 10th century manuscripts, which detailed mixtures, including sulfur, potassium nitrate, and a carbon source, that could potentially deflagrate. However, this procedure is focused on the reagents being “subdued by fire”, thought to refer to the formation of potassium sulfate,4 rather than the creation of a proto-gunpowder. Later works identified an “elixir” containing honey, potassium nitrate, and sulfur, which were combined and combusted to great effect. Such mixtures were responsible for injury and property loss, and warnings were given in the Taoist text “Classified Essentials of the Mysterious Tao of the True

HISTORICAL BACKGROUND

Alchemy is often thought of as a fundamentally misguided and pseudoscientific detour on the path to modern science and chemistry.1 This impression misrepresents the importance of ancient investigations on the development of the protoscientific methods that were applied through repeated and considered trial and error. Many modern chemical techniques arose from breakthroughs during this period, including metallic extractions, an understanding of acids and their actions (including the gold-dissolving mixture aqua regia), purification by distillation, and crucially for this demonstration the most favorable composition of gunpowder for fireworks and weaponry.2 The scientific successes of alchemy were spread across the ancient world, including China, Europe, India, and the Islamic world. Advances in one geographical area eventually spread elsewhere through trade or conquest. The boundary between alchemy and chemistry is easily blurred, as many European alchemists continued their practice having abandoned their goal of the transmutation of base metals to gold.1 The transmutation of bismuth to gold was later achieved through the use of particle accelerator physics, albeit in small amounts of radioactive isotopes and at significant cost for the small number of atoms that were produced.3 The greatest achievement of the Chinese alchemists was the discovery of gunpowder and its application to pyrotechnics and warfare.4 The alchemy of China was primarily focused on elixirs of immortality, which can be seen in the Chinese word for gunpowder, huǒ yào, which has been translated literally as “fire drug”.2 Chinese texts from the 16th century make reference to © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: December 21, 2017 Revised: April 18, 2018

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DOI: 10.1021/acs.jchemed.7b00978 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Origins of Things” against their preparation: “Some have heated together sulfur, realgar, and saltpeter with honey; smoke (and flames) result, so that their hands and faces have been burnt, and even the whole house (where they were working) burned down.”4 Similar warnings are repeated in later 13th century Latin sources “Beware lest the flames set the house and roof on fire.”4,6 We have recently re-examined the potential of mixtures of honey, potassium nitrate, and sulfur for the purposes of a lecture highlighting the development and chemistry of fireworks. No published procedures or compositions were found in the literature for this reaction, but a demonstration of a mixture of unknown composition was found online.7 We have therefore examined the blending and combustion of an alchemical “elixir of life” to highlight the unique and mostly forgotten role of alchemy in chemical history. The reaction is both thought provoking and visually appealing given the relatively simple starting materials. It has the advantage over the “Howling Gummy Bear” demonstration,8 as potassium nitrate is often more accessible than potassium chlorate. We envisage that others may find this demonstration suitable for the teaching and learning of mixtures, combustion, and reactions, while hoping to alter some misconceptions on the usefulness and significance of alchemy on modern chemical science. The composition of honey varies greatly with the nectar sources collected by the colony of bees, but is mostly composed of the simple sugars fructose, glucose, and sucrose, and water, with smaller amounts of larger carbohydrates,9 vitamins, minerals, and enzymes. A highly accessible summary of the composition of honey has been published in this Journal.10 Our attempts to optimize the deflagration combustion of honey were not focused on matching the stoichiometric combustion of the component sugars and sulfur with the potassium nitrate, but on providing a suitably vigorous, safe, and reproducible demonstration using these reagents. The mass ratio of potassium nitrate/honey/sulfur of 6:3:1 is convenient to prepare as an opaque, putty-like mixture on a 10 g scale, balancing safety and scale of the reaction (Figure 1). We do not

Table 1. Observations of Deflagration of Potassium Nitrate/ Honey/Sulfur Mixtures with a Total Mass of 10 g

a

Mass Ratio of KNO3/Honey/Sulfur

Deflagrates?

75/15/10 1/1/1 0/1/1 1/1/0

Yes Yes No Yes

6/3/1a

Yes

Comment Very vigorous. Excessively vigorous. No flames observed. Long delay and excessively vigorous. Short delay and vigorous reaction.

Recommended proportions for this demonstration.

gunpowder, with the sugars of the honey acting as a carbonbased fuel source, the sulfur as a fuel and flux, and the potassium nitrate as a source of oxygen at elevated temperatures. The close up video in the Supporting Information shows the formation of a red liquid, most likely molten sulfur, as the mixture is heated and immediately prior to deflagration. The importance of sulfur was apparent in the longer heating time required to initiate the deflagration of a 1:1:0 mass ratio mixture of potassium nitrate/honey/sulfur. The products of the reaction will include the gases carbon dioxide, nitrogen, and potentially oxides of sulfur, while solid products will include potassium sulfate and potassium carbonate. The water concentration of the honey in this demonstration functions as a fuse, with the slow evaporation providing a short amount of time between applying heat and the deflagration of the mixture. The combustion may begin, after significant buildup of audience expectation, without warning, and can be a source of great surprise to the viewers and demonstrators alike.

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DEMONSTRATION The demonstration space must first be examined for other flammable materials, adequate ventilation, and the presence of functioning fire extinguishing equipment. The reaction is performed in a ceramic evaporating dish free of cracks or chips. Finely ground potassium nitrate (6.0 g), honey (∼3.0 g), and finely ground sulfur (1.0 g) are placed into the ceramic evaporating dish and are mixed together with a wooden stick or metal spatula to form a thick, opaque paste (Figure 1). The ceramic evaporating dish is mounted to a clamp stand using a metal ring as support in a suitably ventilated fume hood. It is recommended that heatproof/flameproof mats are placed underneath the reaction apparatus in case of breakage (Figure 2). A Bunsen burner is ignited, and a blue working flame is applied closely to the bottom of the ceramic evaporating dish to commence heating. Water is slowly evaporated from the mixture, until such time as combustion begins, producing flames, sparks, smoke, and noise (Figure 3). The initial deflagration, marked by rapid ignition, is followed by a less vigorous combustion. The Bunsen burner heat source can be removed or turned off after the deflagration reaction has been deemed to have finished. Viewing the videos in the Supporting Information is recommended to visualize the distinction between the deflagration and combustion. After the combustion reaction has been given suitable time to complete burning and cool down, the residue from the reaction may be dissolved and cleaned from the ceramic evaporating dish with water and may be disposed of into municipal wastewater systems. The mixture can be made in advance as any water absorbed into the mixture will be lost in the heating process. Mixtures stored on

Figure 1. Thick, opaque, and putty-like mixture of 6:3:1 potassium nitrate, honey, and sulfur used for this demonstration.

recommend increasing this scale as there is potential risk of thermal runaway or explosion if the reaction is subject to containment. Small quantities will deflagrate, but are less impressive for the viewing audience. Many different mixtures were observed to deflagrate to varying amounts as summarized in Table 1. Examples of deflagrations for these mixtures are included in a video in the Supporting Information. The reaction between the components is similar to the combustion of B

DOI: 10.1021/acs.jchemed.7b00978 J. Chem. Educ. XXXX, XXX, XXX−XXX

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in a well-ventilated fume hood with the sash closed. The audience members should be at a minimum distance of 4 m from the demonstration and do not require personal protective equipment if precautions have been made with the fume hood sash. The reaction has not been attempted on a larger scale, and we do not recommend scaling up the reaction due to potential risk of thermal runaway, or explosion. The reaction should only be performed in an open vessel, as any containment will increase the risk of explosion and injury. The Bunsen burner and the combusting honey mixture are sources of ignition, and the surroundings must be cleared of any additional combustible material. Once the heating of the ceramic evaporating dish has commenced, the mixture should be given sufficient time for the reaction to commence. The honey is approximately 20% water, and a significant quantity of this water must be evaporated before the reaction will initiate. Failure to wait a sufficient amount of time, followed by interference with the hot mixture, may expose the chemist to unexpected combustion causing burns to clothing or the body. The hot honey mixture remains as a viscous fluid which could stick to skin causing significant burns. The combustion generates gases, including oxides of sulfur, smoke, and fumes which will include solids such as potassium carbonate and potassium sulfate. Therefore, the reaction should be undertaken only in a well-ventilated fume cabinet. The ceramic evaporating dish will remain hot for some time after combustion has ceased, as will the Bunsen burner and the metal ring stand. On occasion during our optimization of the demonstration, the heat of the Bunsen burner and the reaction cracked the ceramic evaporating dish. Potential demonstrators of this reaction are encouraged to closely check the condition of their ceramic evaporating dish prior to commencing heating of the mixture, and to ensure that in the event of a ceramic evaporating dish breaking it will not inflict injury or damage. While every effort has been made to list as many hazards and precautions as reasonably practicable, we can not account for all circumstances or oversights.

Figure 2. Simple apparatus setup for the combustion reaction of potassium nitrate, honey, and sulfur.

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CONCLUSIONS A simple honey-based pyrotechnic demonstration, derived from Chinese alchemical proto-gunpowder, has been described. The mixture is easily prepared, and is a surprising and visually impactful demonstration of the principles of oxidant-assisted combustion. Many misconceptions persist around the contribution of alchemy to the development of chemistry and the scientific method. It is our intention that this demonstration be used as a dramatic starting point for discussions to challenge student understanding and preconceptions of the role of alchemy in the history of chemistry, and specifically in the development and refinement of gunpowder. We hope that suitably cautious and prepared chemists can make use of this demonstration to educate, excite, and inspire future generations of chemists.

Figure 3. Typical deflagration of a mixture of potassium nitrate, honey, and sulfur, showing flames, sparks, and smoke.

the bench in the open air for two months were observed to deflagrate as expected when heated.

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HAZARDS Experienced chemical practitioners interested in reproducing this demonstration should first be familiar with the recently updated Safety Guidelines for Chemical Demonstrations prepared by the Safety Committee of the Division of Chemical Education of the American Chemical Society.11 Periodic updates to the Guidelines are published on the Division of Chemical Education’s webpage.12 All chemists interested in attempting this demonstration must perform their own detailed risk assessment. Any chemical demonstration involving fire and deflagration comes with many potential hazards. These hazards can be minimized through appropriate preplanning and equipment checks, but many cannot be eliminated or removed completely for this demonstration. Personal protective equipment is essential for the demonstrator, specifically a laboratory coat and impact rated safety glasses, goggles, or face shield. We do not use disposable gloves for the deflagration as they may provide another potentially combustible material and may be difficult to remove if on fire. The reaction should be performed

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00978. Video showing reaction with 6/3/1 potassium nitrate/ honey/sulfur, including close up (AVI) Video showing reaction with different reaction compositions (AVI) C

DOI: 10.1021/acs.jchemed.7b00978 J. Chem. Educ. XXXX, XXX, XXX−XXX

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Adrian V. Wolfenden: 0000-0002-0495-8297 Nathan L. Kilah: 0000-0002-0615-3791 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported under the Australian Research Council’s Discovery Early Career Research Award Funding Scheme (Project Number DE150100263). The authors would also like to thank Inspiring Australia, The University of Tasmania, and the Royal Australian Chemical Institute for their support of a chemistry outreach event which led to our interest in this topic.

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REFERENCES

(1) Principe, L. M. The Secrets of Alchemy; The University of Chicago Press: Chicago, 2013. (2) Kelly, J. Gunpowder; Atlantic Books: London, 2004. (3) Aleklett, K.; Morrissey, D. J.; Loveland, W.; McGaughey, P. L.; Seaborg, G. T. Energy Dependence of 209Bi Fragmentation in Relativistic Nuclear Collisions. Phys. Rev. C: Nucl. Phys. 1981, 23 (3), 1044−1046. (4) Needham, J.; Ping-Yü, H.; Gwei-Djen, L.; Ling, W. Science and Civilisation in China, Vol. 5: Chemistry and Chemical Technology. Part 7: Military Technology; The Gunpowder Epic; Cambridge University Press: Cambridge, 1986. (5) Gray, E.; Marsh, H.; McLaren, M. A Short History of Gunpowder and the Role of Charcoal in its Manufacture. J. Mater. Sci. 1982, 17, 3385−3400. (6) Partington, J. R. A History of Greek Fire and Gunpowder; Johns Hopkins University Press: Baltimore, 1999. (7) Bishop, C. The Science of Fireworks!. The Royal Institute, https://www.youtube.com/watch?v=rmtK2BgmGCw (accessed Apr 2018). (8) Sullivan, D. M. The Howling Gummy Bear. J. Chem. Educ. 1992, 69 (4), 326. (9) Doner, L. W. The Sugars of Honey − A Review. J. Sci. Food Agric. 1977, 28, 443−456. (10) Ball, D. W. The Chemical Composition of Honey. J. Chem. Educ. 2007, 84 (10), 1643−1646. (11) Cesa, I. G.; Finster, D. C.; Sigmann, S. B.; Wilhelm, M. R. Revising the Division of Chemical Education Safety Guidelines for Chemical Demonstrations. J. Chem. Educ. 2018, 95, 502−503. (12) American Chemical Society Division of Chemical Education. Safety Guidelines for Chemical Demonstrations. http://www.divched. org/content/safety-guidelines-chemical-demonstrations (accessed Apr 2018).

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DOI: 10.1021/acs.jchemed.7b00978 J. Chem. Educ. XXXX, XXX, XXX−XXX