Sugar is a repository of chemical energy. Your body breaks it down enzymatically to release that energy, powering most everything you do. Such a potent fuel, one would half expect it to burn easily. But then, if you take a teaspoon of sugar and stick it in a candle, all you get is scorched sugar. Obviously something isn’t working right.
Fire requires three things: fuel (the sugar), an oxygen (or other oxidizer) source, and energy. Our sugar/candle combination is obviously lacking in either oxygen or energy. The oxygen is clearly present in low amounts, since the candle itself is consuming the local oxygen. A candle isn’t terribly hot either, so it doesn’t provide as intense a heat as we might require. Any good method for burning sugar, then, must address both heat and oxygen requirements. Here are two of my favorites, and then we’ll finish with a quick one.
The Chinese discovered gunpowder centuries ago, most likely by accident. They used a common chemical (potassium nitrate) to season food the way the Western world likes to use sodium chloride. Indeed, both are salts, and activate the same taste buds. In this case though, it gave them an advantage. An accidental mixing of their salt with the coals of a fire would produce a mixture that burned quickly and intensely. The addition of sulfur as a stabilizer finished off the recipe, at a later time. The potassium nitrate turns out to be the key, for it serves as a solid source of oxygen. (Nitrates have three oxygens in them.) The charcoal (carbon) acted as the fuel. Once the two components were thoroughly mixed, there was a continuous oxygen supply for the charcoal to burn, so it burned much more rapidly than in air, where combustion can only occur as fast as fresh oxygen can get to the flame.
Learning from the Chinese, we take sugar (powder form, or granulated, ground finely) as a fuel, and mix it with powdered potassium nitrate (KNO3). With this mixture, the oxygen is present, and sugar can burn quickly. Getting it started is still a little tricky – a wood match is just barely hot enough, if the flame is applied to the powder for a little while. Beware though, once the powder ignites, it burns Very Fast and Very Hot. Keep your distance, and even eye protection is a good idea. Also consider the surface that you’re working on. The heat is intense enough to destroy countertops, and can burn through aluminum foil with ease. This can be a fun experiment, so long as you take the proper precautions. You may also appreciate the lovely purple-white flame, a color characteristic of potassium in flames.
Water Makes Fire
I fell in love with chemistry the day my high school teacher pulled this stunt. But rather than jumping the gun, let’s go over the background chemistry. We still know we need oxygen and heat to make the sugar burn. What if they came from the same source? Namely, consider the chemical sodium peroxide (Na2O2). This is a much more dangerous chemical than potassium nitrate, so odds are that unless you are a chemist or teacher, you’ll have a tough time getting your hands on some. The properties that make it useful also make it dangerous. Most particularly, it is a strong oxidizer. Contact with moisture causes it to liberate oxygen and a lot of heat. (You see how it will be useful now, no doubt.)
To burn the sugar then, a mix of ground/powdered sugar and sodium peroxide are combined. Both are white solids, and you end up with an unimpressive little pile of white powder. My teacher of long ago placed the pile in a well ventilated can, to contain any spattering, and perhaps to contain the liberated oxygen as well. It does work out in the open however, if you don’t happen to have hole-punched metal coffee cans laying around. To ignite the mixture, you just need a few drops of water. They initiate the release of oxygen, and the heat generated soon ignites the sugar. The resulting yellow-orange flame comes from the sodium added to the carbon (sugar is a little under half carbon). As always, remember to be safe. A sugar fire is fun to see, but you don’t want it to be the last thing you see.
Dusts – fine particles – burn much more readily than larger pieces, no matter what the fuel. Because they are small, less heat is required to bring them to a high enough temperature to burn. Because they are small, they have a larger surface area (proportionately to their mass or volume), allowing greater exposure to atmospheric oxygen. Combining these two facts lets us burn iron dust, copper dust, flour, starch, lycopodium powder, and yes, sugar.
You could spend your time grinding some granulated sugar into a fine powder, but why not be nice to yourself and get some powdered sugar instead? If the powder is sprinkled over a flame (don’t drop clumps, you want it to be finely distributed in the air as it falls), it will ignite. The flame is very short-lived, since the sugar is consumed quickly. For a more dramatic fireball effect, you might try hurling a couple handfuls over a camp fire. I can’t guarantee whether you will be able to avoid the clumps, but I know it works well with flour, so bring a bag of flour as backup to avoid any disappointment. And be safe. You really don’t want to stick your face in a fireball, no matter how short-lived it may be. And if you get too close to the candle flame in the earlier example, the small powder flames also have the opportunity to burn your fingers. Keep your hands high.