The Chemical History of a Candle

Summary

The Chemical History of a Candle prints six lectures that Michael Faraday gave to a 'juvenile audience' at the Royal Institution in London over the Christmas season of 1860–61. Faraday opens by declaring that no door into natural philosophy is more open than the burning candle, and he keeps the whole course tied to that single object while it leads him through heat, chemistry, the air and the living body. Lecture I looks at the candle itself: tallow dips, stearin and spermaceti, wax, the cup of melted fuel kept cool by the rising current of air, the capillary climb of fuel up the wick, and the shape and brightness of the flame. Lecture II shows that the flame needs air, that it has dark and bright regions, and that solid particles of carbon, glowing in the heat, give it its light; a glass held over the flame collects a dew. Lecture III identifies that dew as water, bursts stoppered iron bottles by freezing the water inside them, and decomposes water with potassium and iron to obtain hydrogen. Lecture IV burns hydrogen back into water, then uses a voltaic battery to split water into its two gases and introduces oxygen, in which iron and phosphorus blaze. Lecture V proves that air is mostly nitrogen with a fifth part oxygen, weighs air, shows its pressure with a pair of hollow brass hemispheres and a boys' sucker made of india-rubber, and turns to the other product of the candle, carbonic acid (carbon dioxide), made also from chalk and marble. Lecture VI follows carbon through charcoal and coal-gas and ends with respiration: the lungs burn carbon from food much as the candle burns its wax, the breathed-out carbonic acid feeds plants, and Faraday closes by wishing that his hearers might be like candles, shining as lights to those about them. Throughout he performs experiments with his assistant Mr. Anderson, and he speaks plainly, teasing his listeners with questions and urging them to ask 'Why?' whenever something new happens. The lectures were taken down and edited by the chemist William Crookes and published in 1861; the library text is a 1908 Chatto and Windus reprint that adds Crookes's preface, explanatory footnotes and Faraday's evening lecture on platinum of 22 February 1861. Faraday had given a candle course before, in 1848, and his choice to repeat it shows how highly he rated the subject for teaching. The book has remained in print and is still used to introduce combustion and experimental method to young students.

Top Lessons

• Ask the cause of what you see

  Faraday tells his listeners that whenever something happens, especially something new, they should ask what the cause is, and that patient asking will find the reason. Each lecture models the habit, turning an ordinary flame into a sequence of small questions answered by experiment.

• Mistakes can teach

  A guttering candle is a failure, yet Faraday says that faults of this kind bring instruction that would never come if they had not occurred. The badly made fluted candle teaches more about air currents than the good one.

• Use before ornament

  Faraday judges the pretty fluted and coloured candles bad burners and says that the perfection of a process lies in its usefulness. The best-acting thing, not the best-looking thing, is the most advantageous.

• One order joins flame and breath

  The last lecture links the candle to the human body and to plants: burning and breathing are the same kind of process, and what is waste to animals is food for vegetation. Faraday sees nature as tied together so that one part serves another.

Verified Quotes

Medical Lens

The lectures are chemistry, not medicine, but Lecture VI gives a clear mid-Victorian account of respiration as slow combustion: food carried in the blood meets air across a thin membrane in the lungs, carbon combines with oxygen, carbonic acid is breathed out and animal heat is produced. The view descends from Lavoisier's work on respiration and was standard physiology in 1860. Faraday quotes daily figures for the carbon converted by a man, a cow and a horse, and for the carbonic acid produced by breathing in London. He also demonstrates that a single breath spoils a volume of air for a candle and uses this to argue for proper ventilation in crowded dwellings, a theme of the sanitary movement of the period.

• Lecture VI

  Breathing into a closed jar extinguishes a taper; Faraday applies the result to poorly ventilated houses where air is breathed over and over.

• Lecture VI

  Account of the lungs, where blood and air are separated by a thin surface and carbon from food is converted to carbonic acid with the production of heat.

• Lecture VI

  Daily carbon output by respiration in a man, a cow and a horse, and the exchange by which plants take up the carbonic acid animals exhale.