Burning a candle involves a sophisticated process where the solid wax, composed primarily of hydrocarbon molecules, is consumed by the flame. The wax serves as the fuel source for the light and heat. The wick acts as the delivery system, ensuring a continuous supply of this fuel. The question of where the wax goes is answered by a sequence of physical state changes and a final chemical reaction.
Melting and the Role of the Wax Pool
The process begins when the heat from the flame radiates outward, melting the solid wax immediately surrounding the wick. This phase transition from solid to liquid creates a small reservoir, commonly known as the melt pool or wax pool. The formation of this pool is the first step in the wax’s journey to becoming fuel.
The wax pool is a temporary holding area for the liquid fuel, sustained by the flame’s heat. This pool must be wide enough to ensure an even burn across the candle’s diameter. If the melt pool is too small, a phenomenon called tunneling can occur, wasting the un-melted wax on the sides. The melted wax ensures the wick remains saturated, ready for the next stage of the burning cycle.
Capillary Action: Fueling the Flame
Once the wax has liquefied in the melt pool, it is drawn upward against gravity by the wick through capillary action. The wick, often made of braided cotton fibers, contains tiny spaces that function like miniature tubes. Surface tension and adhesive forces pull the liquid wax up these channels.
This upward movement sustains the flame, as the wick itself is not the primary fuel source. The wick’s main purpose is to transport the liquid wax to the hottest part of the candle system. A properly sized wick is essential, as it must deliver the fuel at the same rate the flame consumes it to maintain a stable, clean burn.
Combustion: The Chemistry of Disappearance
The liquid wax that reaches the top of the wick encounters the flame’s intense heat, which is typically over 1,000 degrees Celsius. At this extreme temperature, the liquid wax instantly vaporizes, turning into a hot gas. This wax vapor, still composed of hydrocarbon molecules, is the true fuel that burns.
The gaseous hydrocarbon molecules then mix with oxygen from the surrounding air and undergo a combustion reaction. In a complete burn, the hydrogen and carbon atoms from the wax chemically combine with oxygen to produce two main, invisible products: carbon dioxide (CO2) and water vapor (H2O). These gaseous byproducts are released into the air, which is the final destination for the majority of the wax.
The energy released during this chemical transformation is what generates the light and heat of the flame, perpetuating the melting and transport cycle. Trace amounts of uncombusted carbon particles, sometimes seen as soot or smoke, can also be produced if the combustion is incomplete, but these are a minor residue.