Michael Faraday's The Chemical History of a Candle

Guide to Lecture Five
105
The lecture then alludes to the differing rates of reaction.
In Lecture Two when we oxidized sugar with potassium
chlorate the reaction was very quick, but the result, the formation
of carbon dioxide and heat, is similar to respiration.
This reaction, though, is “different from respiration in its
form but not in its kind.” That is, “what occurs in [the]
lungs, taking in oxygen from another source, namely the
atmosphere, takes place between potassium chlorate and
sugar by a more rapid process.” We have also seen how
quickly potassium reacts with water: “the moment the
potassium was brought to the water, it acted.” When we
breathe or when we burn a candle, this chemical affinity, this
“attraction of the different parts one to the other is going
on.” A difference, though, is while the potassium starts
into action with water at once, the carbon in the candle
“will remain days, weeks, months, or years in the presence
of air.” Different substances will react at different rates. A
reaction that we may call spontaneous in that it will occur
does not mean that the reaction will occur immediately;
“some will wait till the temperature is raised a little, and
others till it is raised a good deal.” The lecture shows the
difference by comparing gunpowder and gun cotton when
we apply a heated glass rod to each. The gun cotton reacts
immediately, “but not even the hottest part of the rod is
now hot enough to fire the gunpowder.”
In contrast, the process of respiration waits no time.