A Candle’s Chemical History

In which we find we are all like candles.

Graphics in this chapter taken
from transcript of Faraday's
original candle lectures.
Early in my study, a book called Michael Faraday’s The Chemical History of a Candle with Guides to Lectures, Teaching Guides & Student Activities crossed my path. Among certain sets, Michael Faraday is famous, but this book was my introduction to him, and although you can find scads more information online and in other books, The New World Family Encyclopedia of 1954 describes Faraday as a “chemist and physicist … son of a blacksmith … apprenticed to a bookbinder … developed the first dynamo and formulated the laws of electromagnetic induction and electrolysis … ”

In 1860, near the end of his illustrious career, Faraday presented a series of lectures on the chemistry of a candle at the Royal Institution in London as part of its Christmas Lectures series. The Christmas Lectures began in 1825 and continue today, a British yuletide tradition aimed at the younger members of society but accessible to all. (In 2018, the topic is “Who Am I?”) Faraday’s lectures, titled “The Chemical History of a Candle,” included demonstrations of experiments which in 2016 Bill Hammack, a professor of chemical and biomolecular engineering at the University of Illinois at Urbana-Champaign, and Don DeCoste, of the department of chemistry, re-enacted, in a sense, modifying them for a modern audience and then making them available in modern ways. Their e-book is free; a printed version can be purchased online; videos on YouTube may be watched anytime.

I bought the book and watched the videos, learning a bit of chemistry and how a candle works—why it burns, the all-important movement of air, the coming together of elements, what the elements are, the combustion process, the inhale and exhale. It was, for the most part, news to me. I mean the particulars of it, the chemistry of it all, the interactions. It’s funny how we talk of chemistry between people, referring, I always thought, to something magical, unknowable, something that simply, somehow, exists between two people or a group of people that makes these people work not just as separate entities come together but as a singular entity with a common spark and O! the mystery of it: We just have this chemistry. As if chemistry were a desirable, mysterious romance rather than a dry high school subject. I mean, isn’t chemistry the antithesis of romance? Chemistry, a science, the facts. While romance—well, romance is a language, an art, a je ne sais quoi, a gay Paree. But in Faraday’s candle lectures we find both, together, topped off with a wish—
… a wish that you may, in your generation, be fit to compare to a candle; that you may, like it, shine as lights to those about you; that, in all your actions, you may justify the beauty of the taper by making your deeds honorable and effectual in the discharge of your duty to humankind.
Hammack and DeCoste’s version of the lectures is readable, watchable, and eminently enjoyable, but I wanted to see—to read—Faraday’s original lectures, which were first published in 1861, and I found online what claimed to be transcriptions of them. Mostly, of course, these were ocular whatchamacallits, digital reproductions, some of which were rather unreadable with all the goofy characters that result from the misreading of smudges and stray marks, but, anyway, still, versions of the original lectures by Faraday. One was readable enough, and in it one does find slightly different language from the twenty-first century remake. For instance, in the quote above, rather than “humankind” Faraday says “fellow-men.” I can almost hear Faraday and our modern-day chemists having a brief discussion about this change in language as they gather in a classroom lab of wood and metal, overhead lights, stools, beakers, tubes, candles (tapers, specifically) scattered about, a hissing gas flame, and whatnot.

Faraday: “Humankind?” Tell me about that.
Hammack: To include women.
Faraday: Women, you say.
DeCoste: Yes. “Fellow-men,” you see, appears to exclude all who are not men—women, children, all sorts of people that we don’t believe you would want to exclude and who we certainly don’t. We wish to include everyone, all humankind, as we hope and believe that was your original intent.
Faraday: Ah. So “fellow-men” no longer encompasses all.
Hammack: No. It’s actually a very narrow term, a limiting term, you see. In the past 150 years or so we have discovered so much, come to understand so much—well, some have, anyway—as surely you’d expect—and we must be sure to include all people because, as you see, we are all people. Just people. We see it in science, we see it in society, in culture, throughout the world. The importance of all people. So “fellow-men,” describing such a small fraction of what’s out there, proves not all-encompassing but rather portrays a mere sub-set of “humankind.”
Faraday: I see.
Hammack: Think of it as a twenty-first century thing.
Faraday: Yes. I wonder. In another century or two, will “humankind” prove too narrow?

So how does a candle work? And how are candles like us? With all due apology to the true understanders and explainers of chemistry, I will do my best to tell you.

First, candles do not burn in a vacuum. Like us, they rely on a steady supply of oxygen and fuel to keep their flame alive, and it is not redundant to say that a steady, unwavering supply of oxygen and fuel results in a candle’s steady, unwavering flame. Any deprivation of fuel or oxygen will bring about a flickering flame and, eventually, death. But, like us, a candle’s flame can survive many erratic conditions, whether that of being swayed ever so slightly by wayward breezes or that of being emphatically knocked about by gusts of wind. The actions of the flame will portray these conditions, as will the candle’s body. In addition, candles will react to heat, to cold, to humidity, to air pressure—the same basic elements we all respond to. And just as our lives result in waste, so does a candle’s.


Touch a flame to the wick of a candle and the wick will burn. If it burns hot enough and long enough it melts that part of the candle nearest to it and this molten wax then crawls up the wick into the flame—capillary action in action—and continuous combustion begins. The grayish part of the flame, the part encircling the wick, indicates incomplete combustion resulting in carbon, carbon oxide, carbon dioxide, and water. The blue part of the flame indicates complete combustion of vaporized wax and oxygen resulting in carbon dioxide and water in the form of vapor. The yellow part of the flame is the glow of heated solid carbon particles which, by the time they have reached the tip of the flame, are consumed. Air currents drawn up alongside the candle and flame due to the heat of the flame not only feed the flame but carry away the remaining carbon dioxide and vapor. In basic chemical terms, it can be described like this, though for me this is akin to writing in a foreign language and I have just the slightest idea of what it all means:
C25 H52 (s) + 38O2 (g) → 25 CO2 (g) + 26 H2O(g)
But after all, this is just a general explanation. How any specific candle will burn and what it will exhale is dependent on several factors including:
  • the wick (its size, construction, what it is made of);
  • the wax (which may or may not even be wax, which may or may not be a combination of many or a few substances);
  • additives to the wax (scent now being the most common and obvious additive though once, as we shall see, arsenic was popular);
  • the candle’s shape (a tapering, or conical, shape being ideal);
  • and the environment in which the candle is lit and burned.
So perhaps it gets complicated. But a lot of what Faraday talked about and demonstrated was fun, and so I share the following excerpt from his original “Lecture I.—A Candle: The Flame—Its Sources—Structure—Mobility—Brightness.”
There is another condition which you must learn as regards the candle, without which you would not be able fully to understand the philosophy of it, and that is the vaporous condition of the fuel. In order that you may understand that, let me show you a very pretty but very commonplace experiment. If you blow a candle out cleverly, you will see the vapor rise from it. You have, I know, often smelt the vapor of a blown-out candle, and a very bad smell it is; but if you blow it out cleverly you will be able to see pretty well the vapor into which this solid matter is transformed. I will blow out one of these candles in such a way as not to disturb the air around it by the continuing action of my breath; and now, if I hold a lighted taper two or three inches from the wick, you will observe a train of fire going through the air till it reaches the candle (FIG. 56). I am obliged to be quick and ready, because if I allow the vapor time to cool, it becomes condensed into a liquid or solid, or the stream of combustible matter gets disturbed.
Perhaps you can see why Hammack and DeCoste endeavored to change some of the language, and I cannot resist doing the same. So in other words, if you are allowed to play with candles and matches, try this at home:
Blow out a candle without turning it into a big, dramatic, overblown event. Just blow it out gently, normally, then quickly put a lit match to the stream of vapor that results. If your timing is right, the vapor will ignite, the flame will follow the vapor back to the wick, and the candle will resume burning. If it doesn’t work at first, try, try again.

There is not a law under which any part of this universe is governed which does not come into play and is touched upon in these phenomena. There is no better, there is no more open door by which you can enter into the study of natural philosophy than by considering the physical phenomena of a candle.
Michael Faraday, The Chemical History of a Candle

Michael Faraday’s The Chemical History of a Candle with Guides to Lectures, Teaching Guides & Student Activities
The Royal Institution: History of the Christmas Lectures
Transcript, Faraday’s Original Lecture

This page added 10/25/18.

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