= Solution
\b[The <wick> supplies <liquid> <wax> by <capillary action>; <wax> vapour reacts with atmospheric <oxygen>, releasing the <heat> that keeps the supply going.] The <wick> is a delivery system, rather than the principal <fuel>.
First, an external flame warms the <wick> and adjacent <wax>. <Melting> produces a small <liquid> reservoir, and <capillary action> draws it into the spaces between the <wick> fibres. Near the hot tip, <evaporation> and some <pyrolysis> supply gaseous <fuel>. <Melting> and <evaporation> are physical changes; <pyrolysis> and <combustion> change the <chemical substances> present. Once established, the <candle flame> transfers enough <heat> back to the <wax> to maintain this sequence.<The Chemical History of a Candle by Michael Faraday>[Lecture I, melting reservoir, <wick>, capillary attraction and combustible vapour]{ref}
The <candle flame> is a <diffusion flame>. Its relatively dark inner region contains newly supplied <fuel> with limited access to <oxygen>. In the yellow luminous region, incomplete conversion of the <hydrocarbons> produces small <soot> particles, which become incandescent. Farther out, mixing supplies enough <oxygen> to consume most of the remaining <fuel>, <carbon monoxide> and <soot>. Thus the yellow light is largely thermal emission from hot particles, rather than a yellow <gas>.<The Chemical History of a Candle by Michael Faraday>[Lecture II, deposition of <carbon> on a cold surface and the luminosity of heated <solid> particles]{ref}
For a representative <alkane> component of <paraffin wax>, complete <combustion> has the <chemical equation>
$$
\boxed{\mathrm{C}_n\mathrm{H}_{2n+2}+\frac{3n+1}{2}\mathrm{O}_2\longrightarrow n\mathrm{CO}_2+(n+1)\mathrm{H}_2\mathrm{O}.}
$$
Real candle materials are mixtures, and some, such as fatty materials, already contain <oxygen>; the displayed <chemical equation> is an illustrative <wax> model. The principal products of complete <combustion> are <carbon dioxide> and <water vapour>. <Convection> carries the hot <gases> upward and brings fresh <air> into the flame. A cold collector can reveal condensed <water>; collecting the <gases> and passing them into <limewater> gives a <calcium carbonate> cloudiness from <carbon dioxide>.
Removing the <oxygen> supply, cooling the reaction zone, or cutting off <wax> delivery extinguishes the flame. The smoking <wick> immediately afterwards can still emit combustible vapour; without sufficient <heat> at the mixing zone, that vapour need not sustain a flame.
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