Corning
In order for gunpowder to explode effectively, the combustible mixture needs to be reduced to the smallest possible particle sizes as intimately mixed with one another as possible. But once mixed, for better results in a gun it was discovered that the final product should be in the form of individual, dense, grains (originally the size of corn) which allow the fire to spread quickly from grain to grain, much as straw or twigs catch fire more quickly than a pile of sawdust.
Primarily for safety reasons, size reduction and mixing is done while the ingredients are damp, usually with water. After 1800, instead of forming grains by hand or with sieves, the damp millcake was pressed in molds to increase its density and extract the liquid, forming presscake. The pressing took varying amounts of time, depending on conditions such as atmospheric humidity. The hard, dense product was then broken again into tiny pieces which were separated with sieves to have a uniform product for each purpose; coarse powders were used for cannons, finer grained powders for muskets, and the finest for small hand guns and priming. Inappropriately fine-grained powder often caused cannons to burst before the projectile could move down the barrel, due to the high initial spike in pressure. Mammoth powder with large grains made for Rodman's 15-inch cannon reduced the pressure to only 20 percent as high as ordinary cannon powder would have produced.
In the mid-nineteenth century, measurements were made determining that the burning rate within a grain of black powder (or a tightly packed mass) is about 0.20 fps, while the rate of ignition propagation from grain to grain is around 30 fps, over two orders of magnitude faster.
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