The Candle's Chemical History: Faraday's Candle Demonstrations at the Royal Institution

Overview

This Royal Institution presentation investigates the chemical history of the candle, revealing how wax vapor fuels the flame and what this teaches us about heat, light, and chemical processes. Through hands-on demonstrations and historical references to Faraday, the lecture turns a common household object into a window on natural philosophy.

Key insights

• The candle flame is powered by wax vapor rising from the wick, not the solid or liquid wax itself.
• Airflow and capillary action shape flame height and direction, illustrating fundamental fluid dynamics and transport phenomena.
• Light from candles is primarily due to incandescence of carbon particles, explained through black body radiation, Planck’s theory, and the concept of incandescence.
• A series of experiments demonstrates how candles produce water and carbon dioxide, and how these gases can be detected and analyzed to reveal the reaction pathways involved in combustion.

Introduction to candle chemistry as natural philosophy

The lecture frames the candle as a bridge between everyday observation and deep physical and chemical principles. The host, Professor Ricketts, notes that the candle provides a straightforward way to explore natural philosophy and the laws that govern the physical world through accessible demonstrations.

What really burns in a candle

Through a series of experiments, the candle is shown to burn via the vapor of melted wax rather than the solid wax or the liquid wax. A glass tube captures and reveals the wax vapor as it travels upward and lights at the flame, illustrating the essential role of vapor-phase fuel in combustion.

Smoke, flame and ignition: the vapor lighting the wick

The demonstrations show that the invisible wax vapor is what sustains the flame. A volunteer lights and reignites wax vapor streams from candles at different heights, highlighting the non-bright nature of some burning events and reaffirming that burning can occur without bright light.

Flame shape and air flow

Flame geometry is shaped by airflow. By exploring how heat rises and cool air is drawn in from the sides, the presenters explain how a flame forms its typical pear shape and how airflow changes can tilt or invert the flame, echoing the principles underlying lighting devices and safety lamps such as the Davy miner’s lamp.

From wick to flame: capillary action and wax transport

Tom’s capillary demonstration uses wet fibers to show how liquid wax travels up the wick. The wax is drawn into the flame as a liquid, heated and vaporized, and then combusted in the flame. This section connects familiar kitchen science such as capillary action with candle mechanics.

Light, heat and blackbody radiation

Light from the candle is discussed in the context of Planck’s blackbody radiation. The demonstration highlights that heating a carbon-rich material increases its emitance and shifts the emission spectrum toward visible light as the temperature rises, explaining why some flames glow yellow or white.

Gas products and the chemistry of combustion

Further experiments explore the products of candle burning. The apparatus collects and tests gases, showing how water (H2O) and carbon dioxide (CO2) emerge from burning wax, and how electrolysis and limewater tests reveal the presence of these products. The discussion connects candle combustion to broader topics in chemistry and energy.

Carbon dioxide, oxygen and hydrogen interactions

Using safe demonstrations, the presenters reveal how the air around a candle contains oxygen, and how the candle’s combustion consumes oxygen and produces carbon dioxide. A electrolysis setup demonstrates hydrogen and oxygen evolution, linking candle chemistry to electrochemical processes and energy storage technologies.

The candle as a window into molecular transformations

Throughout the lecture, the candle is used to illustrate the transformation of matter: solid wax to liquid wax, liquid wax to wax vapor, and vapor to combustion products such as water and carbon dioxide. The discussion touches on the historical context of electrochemistry and the discovery of elements at the Royal Institution, including Faraday’s contributions and the broader implications for chemistry and physics.

Conclusion and inspirational message

The talk closes with a reflection on how the candle’s chemistry illuminates not only light, but also our understanding of the natural world, echoing Faraday’s philosophy of inquiry and curiosity. The host ends with a call for young philosophers to shine in their own lives, mirroring the candle’s enduring metaphor for learning and service to others.