The Black Snake

I wanted to make the Pharaoh's Serpent, but then I read how toxic it is and I had no plan to manage that properly. In researching this, I saw the much less cool Black Snake experiment as another type of intumescent reaction. An intumescent is a substance that swells with heat exposure. These can come in handy as fire retardants. Both "snake" reactions are of this type where a substance appears to grow out of a hole as it expands. I have never been to Diwali in India, but apparently this is one of their favorite firecracker types. Personally, I have no recollection of these fireworks at all (but also am not that experienced). 

The way the reaction goes, sucrose (powdered sugar)and sodium bicarbonate (baking soda) are mixed in a  4:1 ratio, added on top of sand soaked in a fuel such as lighter fluid (butane), and then the fuel is ignited. In my case, I used isopropyl alcohol as the fuel. Fairly quickly, several reactions start at once:

1) The fuel combusts, making carbon dioxide and water vapor and - most importantly - heat.

2) As the baking soda heats up, it releases carbon dioxide gas and water vapor as it decomposes to sodium carbonate. This is known as thermal decomposition, and is a key reaction in baking.  

3) The sucrose combusts much like the alcohol, again creating carbon dioxide and water vapor; however, some of the sucrose forms carbon. Remember burning creates lots of different reactions. See below.  

C12H22O11 + 12O2 -> 12CO2 + 11H2O

C12H22O11 + 11O2 -> 12C + 11H2O

So what happens is pure carbon and sodium carbonate are formed as solids, but pushed up and out by the carbon dioxide gasses. It cools as a long continual "ash" that can look like a black snake slipping crawling out of a hole.

I tried this, but it wasn't hugely impressive. I think my dish was too small and after a while the flames were choked out by the sand losing its exposure to air. It could be that I just did not use enough reactants to get a long reaction and product. I went for a relatively small effect as I didn't necessarily want a huge long pile of ash and I had limited 91% alcohol to conserve. Perhaps I ran out of that and lost the chain of exothermic reactions.

Note that this is super kid-friendly except for one big caveat: the fire. The biggest mistake made is people add alcohol to the flame and it splashes and spreads flames which have been known to badly injure people. Never do that! Of course, in general it is easy top burn yourself or something else with fire. That much is obvious. I'm not sure it is much more dangerous that barbecuing, however. The only real difference is we are adding gasses from within to expand the ash.

This is what my snake looked like when it went out after about 10 minutes.

As you can imagine it would look better if longer and thinner. I think my dish was too small. The video is not quite impressive enough to share. Some videos online are sped up. Nevertheless, you can probably play with the process a bit and get much better results.

I thought about using my new ash for gunpowder, but it contains a fair amount of sodium carbonate, I think. I'm not sure what that would do to the reaction. All of these experiments involving an oxidizer and sugar or charcoal are very similar reactions. I might be better off just burning sugar directly to get carbon. The only twist we really added here, chemically, is the decomposition of baking soda. I think it might have also slowed the burn rate a bit by displacing some oxygen with carbon dioxide.

Thanks for reading,

Paul