Claude on Question 21, Sep 12

The Three Ingredients

Black powder was made from saltpeter (potassium nitrate), sulfur, and charcoal, in proportions that by the 18th century had converged on roughly 75:15:10 across most European arsenals. Getting good ingredients was actually the harder half of the problem — the mixing technology was comparatively simple.

Saltpeter was the bottleneck and the strategic commodity. Two sources dominated:

• •Niter beds: In France, Prussia, and the German states, saltpeter was extracted from nitrogenous earth — soil from stables, cellars, dovecotes, and deliberately constructed compost heaps of manure, straw, and lime that were periodically watered (often with urine) and turned over a period of years. Nitrifying bacteria converted the ammonia to nitrates. The earth was leached with water and the liquor boiled down. Crude "saltpeter of the first boiling" contained calcium and magnesium nitrates and had to be converted with potash (wood ash) and repeatedly recrystallized. In France this was organized as a royal monopoly with salpêtriers who had the legal right to enter private cellars and barns — a genuinely hated institution.
• •Bengal saltpeter: Britain largely sidestepped domestic production by importing crude saltpeter through the East India Company from the Ganges plain, where it occurred naturally in the soil. This gave Britain a decisive advantage in the mid-century wars and was refined at works near London.

Sulfur came chiefly from Sicilian volcanic deposits, purified by distillation or sublimation into "flowers of sulfur" or cast roll sulfur.

Charcoal quality mattered a great deal, and this was one of the century's real advances. Light, soft woods were preferred — willow, alder, black dogwood, hazel, hemp stalks. Traditional pit-burning was gradually replaced (notably in Britain and France in the 1780s–90s) by charring in closed iron cylinders or retorts, which gave more consistent, more reactive charcoal.

Processing

Grinding and mixing. Each ingredient was pulverized separately, then combined. The older method used stamp mills — vertical wooden pestles, driven by a water-powered camshaft, pounding the mixture in mortars. These were efficient but notoriously prone to detonation. Over the 18th century they were replaced in most of Europe by edge-runner mills: a pair of heavy stone or iron wheels, several tons each, rotating on a bed plate and rolling the damp mixture. This "incorporation" stage typically ran for hours and was always done with the charge moistened with water, which suppressed ignition and helped force the saltpeter into the pores of the charcoal.

Pressing. The incorporated "mill cake" was pressed into dense slabs between plates under a screw or hydraulic press. Density was closely tied to ballistic performance, and pressing was a key improvement of the late 1700s.

Corning (graining). The press cake was broken up and passed through sieves — originally parchment or leather with punched holes, later wire mesh — to sort grains by size. Different sizes served different purposes: fine powder for priming and small arms, coarse for cannon. The insight that grain size controlled burning rate was a major 18th-century refinement.

Glazing and drying. Grains were tumbled in rotating barrels to round off edges and reduce dust; toward the end of the century graphite was added to the tumbling barrels to give a polished, moisture-resistant coating. Powder was then dried — traditionally in the sun on canvas, increasingly in steam- or flue-heated drying houses, since open fire was obviously unacceptable.

Proving. Finished powder was tested with an éprouvette — a small mortar throwing a standard ball, or a spring- or wheel-type device measuring the force of a fixed charge. Government contracts specified minimum performance.

Industrial Organization and Danger

The century saw powder-making shift from scattered private mills to state-supervised or large private enterprises. France's Régie des poudres et salpêtres was reorganized in 1775 under Antoine Lavoisier, who applied chemical analysis to saltpeter refining and roughly doubled French output and quality — work that materially aided both French forces and the American Revolution. Britain purchased the Faversham mills in 1759 and established Waltham Abbey as a royal powder works in 1787. In the United States, Éleuthère Irénée du Pont, who had trained under Lavoisier, founded his mills on the Brandywine in 1802, importing French practice.

Mills were built along fast streams for waterpower, spaced far apart, with heavy earthen blast mounds and deliberately flimsy roofs and walls so explosions vented upward. Workers wore leather or felt shoes without nails, tools were bronze or wood, and floors were kept damp. Even so, explosions were routine and frequently fatal; Waltham Abbey and the Brandywine works each suffered dozens over their lifetimes.

If you're interested in a particular thread — the saltpeter trade and its geopolitics, Lavoisier's administrative reforms, or the archaeology of surviving powder mills — I'm happy to go deeper.