Eric Flint wrote an alternate history story, Ring of Fire, published by Baen books, in which by some strange happenstance a small West Virginia town in 2000 was sent to central Germany and 1631. This has grown into an extensive literature with multiple co-authors. What has appealed to me from the growing number of short stories using the accepted cast of characters are those stories that get to grips with what we might described as accumulated knowledge.
For example, in the 17th century weapons ran to cannon and muskets, ships were wooden, medicine had yet to discover much in the way of effective cures, hygiene and sanitation were universally poor; mechanised printing was around the corner, but radio, mechanised travel and practically everything electrical was all unknown. So the stories showing how any of these might be achieved make fascinating reading — and writing.
Yet what has intrigued me the most is the failure we have in the modern world to grasp how we move almost anything from the raw to the concrete.
Take, for example, gunpowder.
Even I know that one must mix carbon, sulphur and saltpetre, KNO₃. I can see how to discover appropriate ratios of these: 75% KNO₃, 15% C, 10% S. I'm pretty sure carbon would be easy, such as charcoal; I remember that guano was in huge demand as a source of saltpeter but I don't know how to find sulphur. I know sulphur is yellow and found around volcanoes, but while that might be a reliable source I doubt that would meet the demand. Nor can I imagine any such acquisition being healthy. Yet a little reading, the very stuff made so difficult in 1632 if transplanted from 2000, tells me that sulphur ¹ is abundant—the tenth most abundant element, 3% of the planetary mass [1]. We generate a lot of sulphur from the refinement of gasoline, but with 1632 techniques one would go off to Etna or Vesuvius and try to collect it. Could we do better? How could we do that in Britain in 1632? Probably from taking the iron pyrites, FeS₂, out of coal by washing it. Extracting sulphur from that is harder; simply heating it requires temperatures around 600ºC (to FeS and S).
I read that a fair test for saltpeter is that it burns with a purple flame. [2] (And yes, I remember that from L6 chemistry). Again, how you purify that is a mystery. A little more reading [3] suggests that one might garner saltpeter from the sap of plants such as sunflower, common borage, celandine and tobacco. Imagine a conversation with a farmer growing military crops. Purification would probably be achieved by washing, filtering and drying. ² .[4] In practice, then, you'd soon need what we'd now call a laboratory—and a decent chemist, prepared to rediscover a load of long forgotten skills and practices.
I'm going to assume that we don't need to dispute the acquisition of charcoal; heat organic material such as wood in the absence of oxygen. Purification is again a problem — so is researching this, where the main use of charcoal is for purification of all sorts of other stuff. I looked eventually at quality control, so as to avoid words like 'purify', which all seems to lead to water (donkeys drinking, from my point of view). Quality assessment looks at a list of things [6, §8.2]. My reading suggests to me that the charcoal might well be improved chemically by further heating in the exclusion of air. For gunpowder purposes a little more sulphur would not be a problem if the proportion was consistent. I wonder if adding sulphur-rich vegetation to the charcoal fire might assist the process towards sulphur acquisition.
To make the gunpowder it self one adds the three ingredients in the proportions above, 75%, 15%, 10%. I cannot imagine the serious cost of acquiring the sulphur, which strikes me as the significant problem both in terms of logistics and cost. However, from here on, there are practical manufacturing issues. Many historical novels make mention of poor powder, so for the purposes of the 1632 genre, the issue has to be what one can do to raise the standard. My wider reading (of fiction) suggests that the solution lies in reliable quality: a reliable munition is the primary desire. I'll explain little more. Suppose the French have a 'poor' black powder; what that means is that their powder sometimes fails to ignite, that projectiles don't fire true because the powder is not consistent throughout. It doesn't matter as much about the chemical quality, which would affect the amounts needed, provided those amounts were, above all, consistent. Obviously better quality is better eventually, because less powder would be required for the same effect or more bang for similar volumes. But no doubt more bucks for each bang too, and there must be an interesting economist's graph to generate showing where the optimum benefit is achieved. I wonder if Nobel had such a thing.
I found someone experimenting, [7] who describes the grinding and sieving process with pictures. The mix (chemists get excited by calling this an intimate mixture) can be improved by wetting into a paste which is then stirred further. I can't imagine the subsequent drying being particularly safe. I could imagine keeping gunpowder soaked in an alcohol, though.
In the spirit of trying to advance 16th century military techniques, I couldn't avoid thinking of ANFO, which is a mixture of ammonium nitrate and fuel oil. Of course, that presupposed access to both of these. I looked up the proportions, 94:6. The fuel oil can be replaced with any long chain alkane, even some sugars. Adding powdered aluminium (expensive, especially for 1632) makes it detonate more readily, which strikes me as a mixed result. ANFO is widely used in the US (80% of recognised explosive use, says [8]). It doesn't work if wet. Modern (which doesn't seem a good word in the context) malicious use relies on the high quality of easily-bought agricultural fertiliser. For 1632 purposes then, the issue would be primarily the acquisition of quality ammonium nitrate, where the acquisition of fuel is considered already pursued—if there is fuel for the transport, then ANFO is a story possibility. Substitutes for the fuel are another story line and another chemistry line. I'm more than a little bothered at where this is heading, looking like a terrorists guidebook— except that all I am discovering really is that the work involved is significant, not to mention the risks attached to handling things that go bang. I'm not proposing anything for destruction, I'm exploring story line. The 1600s in Europe were no-one's idea of a pacific society.
So ammonium nitrate is, like saltpetre, a nitrate. ³ But it is hard to find in nature since it is soluble and so washed out of soil by any water. Among its odd names are German and Swedish saltpetre. German saltpeter came indirectly from the Haber process (Germany, 1909), which I studied as part of school, in which nitrogen and hydrogen are caused to form ammonia—but it takes serious temperature and pressure to make work, so well beyond 1632 techniques. Swedish saltpetre brings us nicely to the 1632 content, since it was King Gustav, a fairly important character in the genre, who imposed the 'saltpetre tax'. This decree required farmers to excavate the urine soaked soil underneath their barns as being a rich source of saltpetre and these demands were repeated at five year intervals. I can imagine sensible farmers working on getting the urine to somewhere more useful and not under a structure. Processing involved boiling and leaching — basically washing the required saltpetre out of the raw material.
¹ sulphur or sulfur? Personally, that's the UK spelling followed by the US spelling. BUT it would appear that the international science business is tending to the American version. Disappointed. Bias in the ruling from theInternational Union of Pure and Applied Chemistry; no doubt the majority of funding is American. Thus, even British journals like Nature Chemistry use the "f" spelling. [1]
² from [4] The purification of the crystals of saltpetre is carried out by putting it into just enough water to dissolve it, and then it is heated to boiling, and when it is boiling, apparently coarse grains of salt will precipitate out, because the salt does not dissolve as easily as saltpetre. Black foam will be thrown up when it is boiling, and this should be removed. There follows a description of sampling the liquor to ensure it is of the right strength, involving taking a sample and putting it in a copper bowl which is then put into cold water so as to suddenly freeze the crystals by lowering the temperature, if the solution is sufficiently concentrated. Next, good wine vinegar is to be added, and the resulting black foam removed, this is to be done several times, and later finely crushed burnt alum is added, which “This will cause the saltpetre to form beautiful long shoots and can do it no harm”, although I didn’t see that actually happen. Then it is to be poured into a tall, well insulated vat and left for a couple of hours, during which a yellow sediment will fall to the bottom. Finally, when it is still hot, it should be poured into wooden pans or copper tubs which are sunk into the ground, for the final crystallisation.
I have problems with 'salt' precipitating from the initial solution—which salt, as CaCO₃ seems as likely to me as NaCl. I imagine that many salts in the KNO₃ would raise the water content and spoil the function of the gunpowder.
Another method is offered in [5], with fire, in which you take an iron or copper vessel, fill it with saltpetre, put a cover on it, melt the saltpetre, when well melted, sprinkle finely powdered sulphur on top, and he reckons the uncrousness will be burnt away, when it is left to cool the earthiness will be at the bottom and the saltpetre will be white and like marble. The chemists reviewing this had a low opinion of the worth of this second method [5]. uncrousness? No explanation offered, and a search returned the same paragraph.
³ Ammonium nitrate, nitram (a commercial product), ammonium nitricum (found in texts on homeopathy), ammonium saltpeter. They are all NH₄NO₃. Any saltpeter might well be called niter. Any nitrate would serve for gunpwder. With reference to Swedish saltpeter, they would have called it salpeter. For story purposes the life of a salpeter collection point salpetersjudare might make for some good scenes.
[1] https://www.livescience.com/28939-sulfur.html
[2] https://en.wikipedia.org/wiki/Gunpowder
[3] natural sources of saltpeter
[4] https://distillatio.wordpress.com/2015/01/25/purification-of-saltpetre-part-one/ describes trying to do this, very much in the spirit of 1632.
[6] http://www.fao.org/3/x5555e/x5555e09.htm
[7] https://www.askaprepper.com/how-to-make-gun-powder-the-old-fashioned-way-in-less-than-30-minutes/
[8] https://en.wikipedia.org/wiki/ANFO
[9] https://www.familysearch.org/wiki/en/Swedish_Occupation:_Saltpetersjudare