Ben Carter
Candles have been the subject of scientific inquiry for centuries, with scientists like Michael Faraday giving lectures on the Chemical History of a Candle as early as 1860. Candle flames have even been studied in microgravity conditions by NASA. The combustion process of a candle involves both physical and chemical properties. The physical properties of a candle include its colour, size, shape, odour, and physical state. The physical properties of the wax in a burning candle also play a crucial role in its behaviour during combustion. These include the wax's melting point, viscosity, combustibility, and volatility.
| Characteristics | Values |
|---|---|
| Physical State | Solid |
| Size | Variable, e.g. 20 cm high with a 3 cm diameter |
| Shape | Cylindrical |
| Odor | Variable, often fragrant |
| Color | Variable, typically white |
| Construction | Wick embedded in wax or another flammable substance |
| Melting Point | 40-70°C |
| Viscosity | High |
| Combustibility | Flammable |
| Volatility | Vaporizes at high temperatures |
| Soot Formation | Incomplete combustion produces soot |
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What You'll Learn
Physical state, size, shape, odour, and colour
Physical State
A candle's physical state is solid, but it can change to a liquid state when the wax melts. This is a physical change because the chemical composition of the wax remains the same—it is still wax, just in a different state. The wax can also soften or harden depending on the temperature, but its chemical composition remains unchanged.
Size
The size of a candle is a physical property because it is a measurable characteristic that does not alter the substance itself. For example, a candle may be described as having a height of 20 cm and a diameter of 3 cm.
Shape
The shape of a candle flame is teardrop-shaped when burning in normal conditions. However, in microgravity, such as during NASA's space shuttle experiments, a candle flame takes on a spherical shape due to the absence of convection currents.
Odour
The odour of a candle is a physical property. While the scent of a candle can vary, the odour itself does not alter the chemical makeup of the candle.
Colour
The colour of a candle is also a physical property. Typically, candles are white, but they can also be found in other colours such as blue. Colour is an observable characteristic that does not involve a change in the substance's chemical makeup.
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Melting point
The melting point of a candle refers to the temperature at which the solid wax melts and turns into a liquid. This is a crucial physical property of a candle, as it determines the candle's performance and safety.
Different types of wax have different melting points. Soy wax, for example, has a melting point of 45-54°C (113-127°F), while beeswax has a higher melting point of 62-65°C (144-149°F). The melting point of gel wax is even higher, at around 82°C (180°F).
Knowing the correct melting point for each wax type is essential for candle-making. Melting wax at the right temperature ensures a smooth finish, optimal fragrance, and even burning. Overheating the wax can degrade its quality, leading to discolouration and a poor texture. It can also cause issues like frosting, cracks, and uneven surfaces.
Additionally, the melting point affects the binding of fragrance oils. If the wax is too hot, the fragrance may evaporate, and if it's too cool, the fragrance may not bind properly. Therefore, candle makers need to refer to melting temperature guides to achieve the desired results.
The melting point of a candle is an important factor in determining its quality and performance. By understanding and controlling this physical property, candle makers can produce candles that burn evenly, look aesthetically pleasing, and have a strong fragrance.
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Viscosity
Due to its high viscosity, the liquid wax adheres to the wick and rises through capillary action, supplying fuel to the flame. The viscosity of candle wax can vary depending on the type of wax used. For example, paraffin wax, a common type of candle wax, has a relatively low melting point, typically between 37°C and 99°F. However, by adding branching to the carbon backbone chain, the viscosity of paraffin wax can be increased, creating a modified paraffin with a higher viscosity and smaller crystalline structure.
The needle penetration measurement test is used to measure the hardness of wax, and each type of wax has a different congealing point, or temperature at which it begins to harden. Synthetic waxes, such as fatty acid amide and polyolefin, are man-made and typically have higher viscosities than natural waxes. The viscosity of candle wax also affects the formation of soot. When wax does not burn completely, it can release carbon particles in the form of soot, which can accumulate on the wick and produce a black residue.
Additionally, the viscosity of candle wax can be altered by adding certain substances. For example, stearic acid was added to paraffin wax to increase its melting point, which was initially too low. The production of paraffin wax, a major advancement in the candle-making industry, boomed in the early 20th century due to the availability of byproducts from the oil and meatpacking industries, such as paraffin and stearic acid.
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Combustibility
The wax in a candle is a flammable substance, which means it can burn and release energy when exposed to a flame. This is due to the chemical composition of wax, which is made up of hydrocarbons, or hydrogen (H) and carbon (C) atoms. When a candle is lit, the heat melts a small amount of the solid wax, which then vaporises and combines with oxygen in the air to form a flame. This is the combustion process.
The combustion process is self-sustaining. The flame melts the top of the wax, which moves up through the wick and is continually burned, maintaining a constant flame. The heat of the flame also breaks down the hydrocarbons into molecules of hydrogen and carbon. These molecules react with oxygen from the air, creating heat, light, water vapour, and carbon dioxide. This combustion releases approximately one-fourth of the energy created by the candle, with the heat radiating in all directions.
The combustion process can be affected by the presence of additives or fragrances in the candle. Incomplete combustion can lead to the formation of soot, which is made up of carbon particles that have not been burned and have escaped from the flame. This soot can accumulate on the wick and produce a black residue, sometimes seen as black smoke or a blackened wick.
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Volatility
The wax in candles is typically made of hydrocarbons, which are largely composed of hydrogen and carbon atoms. When the wax is heated and vaporized, it breaks down into these individual molecules. The vaporized wax molecules contribute to the formation of the visible flame and provide fuel for the combustion process. The combustion process of a candle is self-sustaining, as the heat from the flame melts and ignites more wax, which is drawn up through the wick to be burned.
The volatility of candle wax is an important factor in the candle's behavior during combustion. The vaporization of wax molecules allows them to react with oxygen and form a flame, releasing heat energy. This heat radiates in all directions and also melts more wax, sustaining the combustion process. The heat also causes the breakdown of hydrocarbons into hydrogen and carbon atoms, which react with oxygen to produce water vapor and carbon dioxide.
The volatility of wax is influenced by its melting point, which is relatively low for candle wax, typically between 40 to 70 degrees Celsius. This property allows the solid wax to melt and turn into a liquid when heated by the flame. The melted wax has a high viscosity, which means it is thick and resistant to flow. This viscosity helps the liquid wax adhere to the wick and rise through capillary action, supplying fuel to the flame.
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