Understand in about 5 minutes
Six lectures in which Faraday uses the chemistry of a burning candle to teach the whole of natural philosophy, from capillary action and combustion to the composition of air and the analogy between fire and human respiration.
Mind Map
Core Message
Faraday opens by declaring that there is not a law under which any part of the universe is governed that is not touched upon in the phenomena of a candle. The candle is not a simple object but an inexhaustible lesson in physics and chemistry.
Every part of a burning candle performs a distinct and necessary function: the cup of wax, the wick, the capillary rise of fuel, the dark inner cone of vapour, and the glowing outer ring where air and fuel meet. Understanding each part reveals how combustion sustains itself.
Faraday traces the candle's invisible products: water condensed from the flame proves it contains hydrogen; carbonic acid precipitates lime-water white and proves the presence of carbon. Together these products account for nearly all the wax that disappears into air.
In his final lecture, Faraday shows that exhaled breath extinguishes a candle for exactly the reason burnt air does: the lungs remove oxygen and produce carbonic acid just as the flame does. The living body and the taper run on the same chemistry.
Summary
The Chemical History of a Candle began as a series of six Christmas Lectures delivered at the Royal Institution to a juvenile audience in 1860 and 1861. Faraday chose the candle deliberately: a cheap, familiar object that, examined closely, opens every door of natural philosophy. He told his audience that there is no better way to enter the study of science than by considering the physical phenomena of a candle, because every law that governs any part of the universe is touched upon there.
The first two lectures move from the material to the mechanism. Faraday surveys the variety of candles (tallow dips, stearin, spermaceti, beeswax, paraffin) and then asks how a solid can possibly supply a flame. He demonstrates capillary attraction in salt columns and strips of cane; shows how rising current of air forms the characteristic cup of melted wax; and identifies the distinct zones of the flame: the dark vaporous core, the luminous shell of burning carbon particles, and the hot outer ring where air and fuel meet. Air, he proves with a covered jar, is not merely required. Fresh air is required, because the candle consumes only the oxygen in it.
Lectures three and four follow the products of combustion. A cold spoon held over the flame collects drops of water, which potassium decomposes violently, confirming their identity. Faraday then shows that water is a compound: an electric current through acidified water releases hydrogen at one electrode and oxygen, twice as much by volume, at the other. Burning the hydrogen reproduces water, closing the cycle. The remaining substance the candle takes from the air must therefore be oxygen, the same element that supports all combustion.
Lecture five characterises the atmosphere. Faraday separates nitrogen from oxygen by burning phosphorus in a closed jar and leaving a gas that refuses to support any flame. He gives the composition of air (one part oxygen, four parts nitrogen by volume) and explains why the dilution matters: pure oxygen would burn iron grates and make combustion uncontrollable. Nitrogen moderates the flame and carries carbonic acid away from city air to feed vegetation far off.
The sixth and final lecture closes the argument by completing the analogy. Carbon, when burned, dissolves cleanly into carbonic acid with no ash, unlike lead or iron, which is what makes it fit to be the fuel of both fires and living bodies. Faraday demonstrates that exhaled breath extinguishes a candle for the same reason used air does: the lungs take oxygen from the air and return carbonic acid, consuming food as fuel just as the candle consumes wax. He closes by expressing a wish that his young audience may, like a candle, shine as lights to those about them.
Key Concepts
The force by which melted wax climbs the cotton wick against gravity, carrying fuel continuously to the flame. Faraday illustrates it with a column of salt drawing up coloured liquid and with a cane soaked in camphine.
It explains why a candle is self-sustaining: without capillary action the wax would pool uselessly below the wick, and the flame would go out.
A burning candle produces two principal invisible products: water (from the hydrogen in the wax combining with oxygen) and carbonic acid (from the carbon in the wax combining with oxygen). Both can be captured and identified by simple tests.
Identifying the products turns a visible event, a flame, into a legible chemical equation, and it establishes the method of tracing any reaction by what it leaves behind.
The lungs perform the same chemistry as a flame: they combine oxygen from inhaled air with carbon from food, producing carbonic acid and warmth. Exhaled breath whitens lime-water exactly as candle vapour does.
It unifies biology and chemistry under one framework, showing that the metabolic fire keeping warm-blooded animals alive obeys exactly the same laws as a candle burning on a table.
Mental Models
Faraday treats the candle not as a trivial thing but as a transparent window onto all of science. Any common phenomenon, examined with precision, leads outward to every principle of natural philosophy.
It teaches that curiosity need not wait for exotic apparatus: the right question asked of any ordinary object can begin a scientific education.
Throughout the lectures, Faraday's method is to catch what vanishes from the flame, condensing it, weighing it, decomposing it, so that the invisible becomes measurable. What the eye loses, the experiment recovers.
It models the experimental habit of turning negative results (something disappeared) into positive data (here is where it went), disciplining intuition with evidence.
Nitrogen does nothing dramatic: it does not burn, support burning, dissolve in water, or react with acids. Yet Faraday shows it is indispensable precisely because its inertness dilutes oxygen to a safe and manageable level.
It challenges the assumption that useful things must be active: sometimes the most important role in a system is played by the component that does least.
Selected Quotes
What diamond can shine like flame?
It is wonderful how, by means of oxygen, we get combustion accelerated.
thus look upon the food as fuel.
Source
Source text: Project Gutenberg edition of The Chemical History of a Candle by Michael Faraday, edited by William Crookes.
HTML text: https://www.gutenberg.org/cache/epub/14474/pg14474.txt
Project Gutenberg states that this eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever.
Delivered as a Christmas Lecture series at the Royal Institution in 1860 and 1861; first published in book form in 1861, edited by William Crookes.