This is a pretty basic but nonetheless awesome demo. Glycerine (Glycerol, 1,2,3-propantriol) is mixed with potassium permanganate (KMnO4), and within about 30 seconds, the pile starts to smoke, then burns with a very hot lavender colored flame.
-This is a hot-burning reduction/oxidation reaction. It doesn't spark as a thermite reaction would, but still, don't do something dumb like put it on a wood table.
-KMnO4 likes to stain stuff. If it comes into contact with moisture it will form a purple solution that will render anything purple permanently (your skin will turn brown but that comes off in a few days)
-Non-science types don't understand chemistry. People fear things they don't understand. In other words, many ignorant people think chemistry is evil/terrorism/just plain bad, so don't do this around people if you know they are going to flip.
-I am not liable in the event of fire, explosion, injury, disability, death, act of God/Goddess, rabid squirrel attacks, subpoena, lawsuits, or any other dumb situation you might manage to get yourself in. Use your brain and use basic common sense
Warning: Science content!
If you want to figure out how to get a stoichiometric reaction (basically molecule for molecule reaction, most efficient burn) you can start with this equation:
14 KMnO4 + 4 C3H5(OH)3 --> 7 K2CO3 + 7 Mn2O3 + 5 CO2 + 16 H2O + HEAT
That calculates out to be 6 g KMnO4 for 1 g glycerin. Honestly, there isn't any point to weighting it out, it works just as well mixing approximate amounts.
Step 1: Prepare Your Materials
You will definitely need:
-Potassium permanganate - this is sold at small hardware stores like Ace as filter cleaner - $5
-Glycerine - sold at RiteAid - $3
-Additionally, you can use antifreeze or windshield washer fluid if it contains the ingredient ethylene glycol. Ethylene glycol is C2H4(OH)2 whereas glycerin is C3H5(OH)3. It's the multiple alcohol group that makes it work. Also, make sure it is of the highest concentration possible. Water typically does not help with fire-making processes.
Stuff that's a good idea to have
-Burn plate - I used a granite tile I got as a sample from a countertop store
-Goggles - this isn't a super dangerous reaction, use your own discretion
-Sand - if for some reason you have to put it out - water will make a HUGE mess because it forms KMnO4 solution which stains anything and everything purple
Step 2: Prepare the KMnO4
Find a nice suitable place to be burning things. This should be away from flammable things, tall grass, small children etc.
Make a small pile of KMnO4. The size isn't critical, obviously the more permanganate you use the more glycerin you will need.
Furrow out a "bird's nest" in the middle of the pile. If you've ever made bread before (rustic method), it's the same concept.
Step 3: Add Glycerin
Pour the glycerin into the furrow. The ratio between KMnO4 and glycerin is very forgiving, but you should have about 1.5:1 KMnO4:glycerin, volumetrically.
Depending on the ambient temperature, the reaction might not self initiate at this point. Give it some time. If it doesn't start smoking after 45 seconds, either mix it with a stick, or drop some HCl onto it. The reaction is slow to start up, you will see smoke before the fire with enough time for you to react and get your hands away.
The chemistry here is called a hypergolic reaction. Compounds that are reactive enough to begin a reaction just by being in contact with each other are said to be hypergolic. Other examples include hydrazine and nitrous oxide, and sodium and water. The rate of reaction depends on the fuel used, the temperature, and water content. Water obviously retards the reaction.
Warning: Science Content!
Ethylene glycol: It has the smallest molecular weight, and thus the most active; concentrated or pure it will react very fast
Glycerin: Slightly less reactive than ethylene glycol, the reaction could be hypergolic on a hot day and not on a cold one.
Propylene glycol: The least reactive due to high molecular weight and lower reactivity (less function groups). Anything but pure might not react at all.
Alcohols: These won't work at all, they aren't reactive enough to start the reaction by itself.
Anecdote time! I had a Dixie cup full of the stuff in my hand (this was at the time when I had to set it off with HCl because it was colder) but that day was very hot. I saw it starting to smoke in my hand and I threw it, only to have it burst into flames mid-air.
Step 4: Fire!
Uses: Aside from a really neat chemistry demo, the reaction burns hot enough to initiate other reactions with exorbitant activation energies, namely, thermite. I don't have any thermite to play with, so I haven't tested it myself, but I've seen it work. The KMnO4/glycerin doesn't spark and cause excessive destruction around it, but if you use it to initiate a thermite reaction, the thermite WILL do what it's good at: melting and setting fire to everything around it, so take this into account when picking a location.