Constructing a grenade (for a novel I'm writing.)

Question

Ok, before any eyebrows get raised, this is for a novel that I'm writing and inspired by this answer from worldbuilding and this reference answer. I just want to make sure the device I'm trying to use is as close to accurate as can be.

So, in the novel, I've devised a compartmentalized glass urn. The urn contains three compartments, one will house a mixture of a finely powdered combination of charcoal, sulfur, and saltpeter. The second compartment would contain slightly acidic water and the third one would contain limestone. What I'm expecting is that when the urn is dropped, the shattering of the glass would cause the water to react with lime resulting in an exothermic reaction which would help to ignite the gunpowder mixture. Is this idea liable to work or is too quixotic and fanciful to consider ? If so, what adjustments can I make to it so that it works? Do keep in mind that the sources have to be natural as it is an apocalyptic world.

Also, can I just call it a mixture of a finely powdered combination of charcoal, sulfur, and saltpeter or does it need to be prepared in a special way or maybe there is a special term for it?

Apologies if this is not the right place to ask the question but I could not think of any other apt place.

Answer 1

In short-no your technique will not work. Reacting limestone with acid does not release enough energy to reach an appropriate temperature to ignite gunpowder and the acid would hinder combustion.

Fear not though, spontaneous ignition may be achieved by mixing glycerol and potassium permanganate which works well and is a classic example. If you would like to be more out of the ordinary, zinc powder and ammonium nitrate with a minor amount of copper or ferric chloride and water will also create a spontaneous ignition for your gunpowder.

Answer 2

I agree, your technology will not work. A good place to start is the US army field manual "Improvised Munitions Handbook". They describe methods that known to work.

Can you say more about the time of your world? In most cases you can use fire cord to delay explosion. You can control timing by the length of the cord. Fire cord is made by soaking any paper in KNO3. You must have KNO3 to make gunpowder anyway.

If you plan to drop these bombs from airplane then your world is very modern. Making a flying airplane is actually quite a challenge. You still can use the technology of early bombs. Roughly speaking you have multiple matches inserted in the bottom of the barrel. On contact with ground matches are pushed in against sand paper. Some of them will ignite and ignite the gunpowder. You can use H2SO4/KMnO4 in one compartment and alcohol in the second compartment. H2SO4 is known since classical antiquity. Ethanol distillation is known since 13 century. KMnO4 is prepared by baking KOH with MnO2 and is also known for a while. If you can't get MnO2 you cannot fly an airplane either. I say this because an airplane needs high quality jet fuel and will not fly on olive oil. A glider isn't going to lift heavy enough bomb. Another way is to place a small incandescent lamp in powder, connect it to a battery and attach the switch to the bottom of a barrel. 19 century mining technology used electricity to initiate explosion because it is much more reliable.

By the way, how much gunpowder are you planning to use? The only way to produce KNO3 is by collecting it from (I beg your pardon) manure. Medieval peasants had KNO3 tax. They had to collect it and send to the king. Modern methods are different, but you cannot use them without a trained group of chemical engineers. If you don't have an access to reasonable amounts of KNO3 you will not be able to make enough powder. If you have, then you should prepare some modern explosives.

Answer 3

As others have noted, the idea as stated will not work. The temperature rise produced by the reaction of mildly acidic water with limestone is very small -- nowhere near enough to ignite black powder (over 400°C.)

We could possibly suggest improvements -- whilst avoiding giving bomb-making advice! Blackpowder is pretty easy to ignite, and without giving any realistically helpful advice to maniacs, there are a lot of ways it could be done (some have already been suggested.)

However it isn't clear what your conditions are. The device you describe is quite primitive -- is your novel set in the distant past, or in some sort of post-apocalyptic scenario? In that case, the most plausible igniter is something like the flintlock percussion mechanism that was actually developed in the Early Modern Era.

I just want to make sure the device I'm trying to use is as close to accurate as can be.

This discussed in multiple questions on writing.se. But in general, for a novel, it is neither necessary nor desirable that you describe a technical device (e.g. a bomb) in such detail that an expert thinks "Hmm, that could really work." You are, after all, writing a story -- not a terrorists' manual. In fact the majority of casual readers will be bored by too much technical detail. You want to add colour, atmosphere, plot development, characterisation. Not instructions.

I'm no novelist, but consider something like this:

As he lifted the vase to examine the strange powder inside it, he heard a sharp click. He froze -- for a moment, nothing seemed to happen. Then a slight "clunk" came from within the vase, a faint whirring noise, and a glint of brass gears turning. In a moment, he realised what it was and flung the vase behind the pillar as he dove to the ground....