GPT on Question 21, Sep 18

In the 18th century, black powder was usually made in specialized powder mills, because production was highly prone to accidental explosions. The process, in broad historical terms, was:

• 1.Preparing the ingredients
  Manufacturers separately purified saltpeter (potassium nitrate), sulfur, and charcoal. Saltpeter was commonly refined by dissolving and recrystallizing it. Charcoal quality mattered greatly and was often made from light woods such as willow, alder, or dogwood.

• 2.Grinding and incorporating
  The ingredients were ground separately, then combined in an incorporating mill, often using heavy stone or wooden edge-running wheels. The mixture was kept damp to reduce dust and ignition risk and to help distribute the ingredients evenly.

• 3.Pressing
  The damp powder mixture was compressed into dense slabs or “press cakes.” Pressing improved uniformity and made the finished powder burn more consistently.

• 4.Corning or granulating
  The cakes were broken into grains and passed through sieves. Different grain sizes were selected for cannon, muskets, pistols, priming powder, and mining.

• 5.Glazing and drying
  Grains were sometimes tumbled in barrels to round and strengthen them, occasionally with a small amount of graphite added to reduce dust and moisture absorption. They were then carefully dried and packed in wooden barrels.

Powder mills were deliberately divided into separate, lightly constructed buildings, spaced apart so that an explosion in one stage would not destroy the entire works. Workers used non-sparking tools, avoided exposed iron where possible, and observed strict rules about fire, footwear, and clothing. Even so, mill explosions were common.

Earlier “serpentine” powder was simply mixed and remained dusty and prone to separation; the pressed-and-granulated or corned powder typical of later manufacture was more powerful, durable, and predictable.