Fo Fizzle

Apologies to Snoop Dogg, my nizzle. Not much sizzle. This is a tale of fizzling out, for now, brought to you to show the frequent failure of experiments that provide numerous learnings along the way. One of the things I love about watching Nile Red is that he fails often, and experiments until he figures it out. His mistakes are not usually rookie mistakes like mine, but it makes me feel better.

I have a number of experiments planned, but the weekend hit and I don't have the chemicals and parts I need yet. What to do? Since I have been teaching myself about Enthalpy of reactions (energy produced by a reaction), I thought of making something "easy" that is exothermic enough to cause a chain reaction. Exothermic means energy is released, generally in the form of heat and/or light. I have already done this with propane combustion, but I decided to consider black powder, or the old-fashioned gunpowder that the Chinese somehow invented 2000 years ago. It never ceases to amaze me what ancient people discovered.

So, if you mix 75% saltpeter (KNO3), 15% charcoal (~C with some hydrogen and oxygen), and 10% sulfur, you just need to ignite with a spark (such as caused by flint striking steel in old flintlock guns) and boom! In my case I just want to make a small line of it like a fuse and watch it burn.

What is saltpeter? I first heard the word when watching the musical 1776 in junior high.  It is a crystal of potassium nitrate that people have made and used for many purposes over the years. Food preservation was one use. Gunpowder was obviously an important application. In any case, it can form naturally from animal dung and urine combining over time, and is sometimes found growing near stockyards. Urea, formed in the kidneys, is the source of nitrogen. Anyway, I don't have the months of time nor desire to put my dog to work. Instead, I bought Spectricide brand stump remover, the main use of KNO3 that I know of at this point.  

Sulfur is easy. I have a chemical bottle of it, but check out this rock I collected from a live volcano in Taiwan once. I will not destroy my nice mineral sample, even for science.

Now, for charcoal, I felt like I needed to make something the hard way. So I quickly shaved 20g of pine off of some excess lumber with a pocket knife and set it ablaze. While it burned I wondered about the yield and combustion formula. Note that burning is really a combination of many reactions and things like wood are not chemicals in the sense that they easily fit into equations. They can be modeled, however. What I found on the internet disturbed me as it was all over the place and equations did not balance (even detailed ones). These were my main assumptions:

• Wood can be modeled, roughly, as C10H15O7 by measure of its constituents, and charcoal roughly as C7H4O. We lose some carbon (smoky soot and carbon gasses), as well as hydrogens and oxygens in numerous other gasses.
• While I found reactions that indicated 5/6th's of my carbon would remain in the char, that seemed kind of crazy. Wikipedia's entry on charcoal told me the most modern industrial methods have a 35-40% yield. 
• If carbon is 48.5% by weight of C10H15O7, and my optimistic yield is 30%, I figured I could perhaps extract 3g from my wood.

After it cooled, I measured the product. Including tar and ash, it weighed 3g on the same scale used earlier to measure 20g of wood. Success! So I put it in a mortar and ground it down. A few pieces were too big for my liking so I picked them out. I figured I had about 2g left after losing the tar and bigger chunks. Basically, I was lazy and should have measured precisely. Instead, I added the sulfur and saltpeter to my mortar, precisely measured to 1.3g and 10g respectively. Whether I was distracted by the Astros game or just too happy with the deep fine black powder, I dunno, but I am sure it was not exactly 2g of char. To further the potential mistakes, my burning of wood probably made a very lousy charcoal. It was obviously not a hot and long fire. Did I have some carbon? Yes, but who knows how much at this point.

  

I mashed everything together in the mortar a bit and it looked and smelled like gunpowder. I was feeling good about this. I probably underestimated the danger here; 13g of gunpowder is more than I realized and it is possible that I could have created a spark or heat from the mortar and pestle grinding. Still recovering from my bismuth burns, I don't need another.

When I layed out a little line on the ground and tried to light it with a simple flame, I could not get a chain reaction. I took a blow touch out to ignite it, and ultimately got it to sizzle down the line somewhat haphazardly. Did it work at all? I think so, a little bit, but not good enough to fire any musket balls or even make fuses. If I was Chinese 2000 years ago, I would have registered no apparent usefulness.

Is my sulfur good? Clearly. Is my saltpeter good? Um, I just assume it is actually KNO3 based on lack of ingredients listed, color, and crystallization. Not good enough!

So ensued a comedy of more errors. I burned some to see if I could see a characteristic lilac flame of testing potassium. That didn't work. It was too bright out and I could not see any flame. I had the stump remover in a stainless steel cup, and crystallization looked like potassium nitrite (KNO2). But I was distracted by some tiny lumps of metal that formed as a vapor on the side of the cup. Potassium? Really? I added water and nothing happened. It was not potassium. Then I realized the dish must have had some zinc plating and I just vaporized and condensed zinc droplets. Galvanized steel is starting to cause me a lot of problems. From now on, I assume all steel is galvanized.

Later, after some cooling and washing of the dish, I looked under a microscope, I saw these lovely crystals which formed while the dish was cooling. It turns out these are KNO3 crystals, which possibly reformed from the nitrite by reacting with oxygen. But at the time I was not sure.

Instead of attempting other chemistry to confirm KNO3, I decided to punt and search the internet. The makers of Spectricide go to great lengths to not disclose the ingredients or comment on its unintended uses. I am not the only one asking, mostly for a variety of reasons including gunpowder, rocketry, and tricking drug tests. Someone out there might be thinking of using it as phosphorus-free fertilizer, I don't know. But I prevailed. The government requires a safety sheet to be posted somewhere, and I found it finally on their web site. It revealed the contents as 100% KNO3 with a bunch of warnings that I did not heed. I like the irony of the safety sheet being so hard to find.

So the problem was either my lousy charcoal or my lousy measurement throwing off the mix. I'll redo this with good charcoal at a later time, then try to measure it precisely with homemade charcoal and compare.

In any case, an oversimplified reaction would be something like this:

2KNO3 + S + 3C -> K2S + N2 + 3CO2

More likely, potassium carbonates and sulfates and soot and carbon monoxide and water vapor all form. Again, burning is not one simple equation, and charcoal is not pure carbon.

Stay tuned for the redo! At least I learned a few lessons.    

Thanks for reading,

Paul