Question: In the fireworks post you talked
a bit about black powder, but I am not sure what it would behave like.
You mentioned that it expands, but can also have a visual effect; do
you have any video of this?
Answer: Of course we do!
History Lesson | Science Lesson | Videos
Black
Powder (left) was first made in China during the Tang dynasty (~900
CE), and like everything else it was made by accident. There are some
early references to the concoction, but it wasn’t until the eleventh
century that it got its first real use. People used black powder for
weaponry (often launched by catapults or out of bamboo shoots), and
sometimes it was mixed with poisons like arsenic.
Gunpowder was later adapted for use in cannons and became widespread in Europe. As mentioned in the fireworks post, black powder has peace time uses such as the propellant for large fireworks displays. Furthermore, since the invention of more potent mixtures gunpowder has almost been completely phased out for warfare.
Black powder has three main ingredients: sulfur, charcoal, and saltpeter (potassium nitrate) and the general equation for its combustion is:
2(KNO3) + S + 3C → K2S + N2 + 3(CO2)
The results of this combustion are mostly solid (that would be the grainy burnt stuff you find). The products are 55.91% solid, 42.98 gaseous, and 1.11% water.
The mixture used today by most pyrotechnicians is 75% potassium nitrate, 15% softwood charcoal and 10% sulfur.
We placed the black powder on the ground for this experiment and used gasoline as the fuse. It worked out well. Note however, we don't recommend doing this at home, but if you do remember this:
When you light black powder there is a slight delay (it needs to reach the temperature at which it combusts); therefore, if it doesn't go off immediately, be patient!
The videos below are 7 megabytes and 5 megabytes respectively and are worth the wait:
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