Early Bio-technology and Potassium Nitrate for Gunpowder

Early BioTechnology and the “Making” of Saltpetre

In the previous post, we discussed Gunpowder, a mixture of 75% Saltpetre (Potassium Nitrate), 15% Carbon (charcoal) and 10% sulfur.

Let’s now look at acquiring the Saltpetre.

The pre-technology (but not pre-biotechnology) source of Saltpetre is aged urea-soaked organic material (yes, this is probably considered a bit gross in these days of out-of-sigh, out-of-mind toilet habits). The aging of this material allows bacteria to convert the ammonium compounds into nitric acid. Note: this material must be protected from rain or flooding, as the desired compound is water-soluble.

To convert this nitrogen-rich organic material into Saltpetre, we can boil the source material with water. Then add a source of potassium (such as ashes from your fireplace). The resulting liquid can be evaporated to get crystals of Saltpeter (1).

We can mimic the process used by our pre-industrial ancestors by using the following steps from “The Do-It_Yourself Gunpowder Cookbook” (2):

1. Construct a filtering container by punching small holes in a 5 gallon bucket and forming a filter at the bottom by using a layer of cloth, a layer (1/2 cup) of wood ash, and another layer of cloth.
2. Fill the bucket with screened, nitrate-bearing soil/manure/guano. Leave room at the top.
3. Place the bucket over a collection container. Pour—very slowly—a gallon or so of boiling water over the soil in the bucket. You want the hot water to permeate and percolate uniformly through the soil.
4. Allow the drained solution to cool and settle. Then pour into a heat resistant container and boil the collected solution for 2 hours. Discard any salt that forms during this step.
5. After the solution has boiled down to half its original volume, let cool for ½ hour. Add an equal volume of alcohol (applejack, 12 year old scotch, or cheap vodka) and stir briefly. The small white crystals that form are Saltpetre. Collect and dry.
6. To refine further, re-dissolve and repeat the boiling step.

Unfortunately, this uses up your medicinal alcohol supply. We’ll save the production of alcohol for another post.

Another pre-industrial method is from the 5th Foxfire book (3):
1. Make a filtering container using wood slats in a “V” shape (wide at top, narrow at bottom). Line with straw-type material. At the bottom have a collection bowl.
2. Fill the V-container with nitrate-bearing soil/manure/guano. Pour boiling water over the material. Allow to permeate and percolate. Collect the leachant.
3. Repour the leachate through the nitrate material.
4. Combine the leachate with woodashes (which provides potassium hydroxide). A white precipitate (calcium hydroxide) forms and settles.
5. The woodash leachate is then boiled down until saltpetre (potassium nitrate) crystals form.

Conclusion: if you’re writing an alternative or speculative history novel, your characters will have access—through the above procedures—to the major ingredient of gunpowder. The next steps are:
1. Finding elemental sulfur or extracting it from minerals.
2. Charcoal (the way easy step)
3. The metallurgy required to smelt iron and forge gunbarrels (the ‘whew’ step).

As always, let me know if I missed something (or outright missed reality)!

(1)… http://www.rsc.org/chemistryworld/podcast/CIIEcompounds/transcripts/potassium_nitrate.asp

(2)… The Do-it-Yourself Gunpowder Cookbook

(3)… Foxfire 5

One thought on “Early Bio-technology and Potassium Nitrate for Gunpowder

  1. Jim Glenn

    Forgot I was looking at solubility curves for NO3 last week and based on purification by re-crystallization you would never get a 100% pure KNO3 compound. Looks like the first set of crystals would be higher in NaNO3 based on a super saturated solution. Also check the ammonia line you’re loosing it with higher temp.

    Check on formation energy / energy of formation of NaNO3 Vs KNO3 it may be that just by having the presence of the potash KNO3 formation is favored over NaNO3 … or just the simple fact that your supplying more available K over Na does the trick. Probably this second part does the trick. Regardless some impurities will be present but reduced as well as needed.



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