The Royal Institution was founded in 1800 by leading British scientists under the guidance of Benjamin Thompson “for diffusing the knowledge and facilitating the general introduction of useful mechanical inventions and improvements, and for teaching by courses of philosophical lectures and experiments the application of sciences to the common purposes of life.” Thompson, perhaps better known as Count Rumford, was by all accounts a ruthless, arrogant, cunning, devious, unprincipled womanizer who was also a philanthropist and a clever scientist. His inventions included a kitchen stove and a percolating coffee pot, items proudly exhibited at the Institution. While the scientific displays were popular, it was the Institute’s public lectures on “natural philosophy” that drew the crowds. So much so that it resulted in the creation of the first one-way street in London. Albemarle Street had to be converted to one-way traffic to ease the congestion due to all the carriages bringing people to the lectures.
The most famous of these philosophical lectures were the Christmas lectures given to young people during the holidays, especially after Michael Faraday took over as lecturer in 1825. With his classic lecture on “The Chemical History of a Candle,” first given in 1848, Faraday amazed his audience by spending the whole evening talking about the science behind the burning of a candle. “There is not a law under which any part of this universe is governed which does not come into play, and is not touched upon, in these phenomena,” he began. Then he went on to discuss every known nuance of a candle flame.
Three things are needed to start a flame, Faraday explained. Fuel, which is the candle wax, oxygen, which comes from the air, and a source of ignition, which is a match. If combustion were perfect, the only products would be water and carbon dioxide. When the wick is first lit, Faraday explained, it melts a little of the wax which is drawn up the wick where it then vaporizes. It is actually the wax vapour that burns. Bonds between carbon and hydrogen atoms break, and bonds between hydrogen and oxygen, and between carbon and oxygen, form. Energy is needed to break chemical bonds and energy is released when bonds form. In the case of combustion, more energy is released by the formation of bonds than is required to break the bonds in the fuel, hence the extra energy is released as heat.
For complete combustion a high enough temperature has to be achieved, and an adequate oxygen supply has to be maintained. If these conditions are not met, soot forms, as it does in the cooler yellow regions of the flame. Indeed, the yellow colour, as Faraday enlightened the audience, is due to tiny glowing particles of soot. When combustion is complete, as when alcohol burns, the flame is blue. Faraday demonstrated incomplete combustion by placing a spoon in the yellow part of the candle flame where it immediately became covered with soot. Instead of reacting with oxygen, carbon atoms had linked together, much as they do in graphite, to form “lampblack” or “carbon black.” Not a totally useless material, Faraday explained, as it can be used to make pigments and ink. Were Faraday to give his lecture today, he would undoubtedly point out the use of lampblack to reinforce the strength of rubber in tires, and of course would discuss the role of combustion products in the “greenhouse effect".
The Royal Institution’s famous Christmas lectures continue to this day but you no longer have to struggle with the traffic on Albemarle Street. The lectures are televised and are also available online. This year’s lecturer (2019) is Dr. Hannah Fry, mathematician, author, radio and television presenter, podcaster and public speaker. She will discuss how mathematics applies to patterns of human behaviour and dating. You can count on a fascinating presentation.
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