Gunpowder

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Gunpowder

Overview. Europe did not learn of gunpowder until the late twelfth century. By that time, the Chinese had perfected the “barrel gun” and the cannon. However, it was not invented by people looking for better weapons or even explosives, but by alchemists in search of the elixir of immortality.

Saltpeter. Gunpowder has three main ingredients: salt-peter or potassium nitrate, sulfur, and charcoal. Long before saltpeter could be used as a component of explosives, it was used for its capability to turn ores into liquid and to dissolve other indissoluble minerals, such as cinnabar, into water solutions. Saltpeter was used for this purpose at least by the second century B.C.E., as well as for a flux to help metallurgical processes. The potassium flame test is crucial for detecting saltpeter, which burns with a violet or purple flame. This test for true saltpeter was used in China by at least the third century C.E., and the test was carried out by putting a sample of the saltpeter on a piece of charcoal and watching it burn. Sheng Xuanzi, in his book Illustrated Handbook on the Control of Mercury (1150), described the details of this kind of procedure.

Sulfur. The Chinese had the ability to purify sulfur by the second century C.E. By the eleventh century the Chinese had identified the method of obtaining pure sulfur by roasting iron pyrites piled up with coal briquettes in an earthen furnace. In 1067 the Song emperor issued an edict prohibiting the sale to foreigners of either sulfur or saltpeter and the private production of both commodities altogether. Large private enterprises in those commodities were thus forced to close their business, and the government established a monopoly.

Mixture. With saltpeter, sulfur, the readily available charcoal, and other substances, it was inevitable that alche-mists would eventually put these things together and invent gunpowder. By the mid seventh century Chinese alche-mists made some preparations, which included sulfur and saltpeter, but they were not flammable. By the beginning of the ninth century the Chinese had identified the method of subduing alum by fire through the mixture of two ounces of sulfur, two ounces of saltpeter, and one ounce of dried birthwort herb, which would contain sufficient carbon to make this mixture ignite suddenly and burst into flames, though it would not actually explode.

Protogunpowder. The first textual record of a proto-gunpowder formula is found in a book titled Secret Basics of the Strange Dao of the True Source of Things, published in 850 and preserved in the great collection of Daoist literature. The book included thirty-five dangerous elixir formulas, three of which involved saltpeter. Therefore, by 850 Chinese alchemists had created a formula that can be genuinely described as a gunpowder mixture.

Three Formulas. It was not until the year 1040 that an actual gunpowder formula was published for the first time. Certainly, true gunpowder and its uses had been known by this time for at least 100 years. Three gunpowder formulas were identified for three different weapons: a quasi-explosive bomb to be thrown by a kind of catapult; a burning bomb with hooks which could catch on to wooden structures and set them on fire; and a poison-smoke ball for chemical warfare. The gunpowder in these weapons was not explosive but burned with a sudden and sparkling combustion, creating a noise like a rocket. The bomb did not yet hold enough saltpeter to explode.

Small Explosion. In the gunpowder mixture, whatever the proportions, it is the sulfur that reduces the ignition heat to 250°C and, on combustion, raises the heat to the fusion point of saltpeter (335C). It also helps to increase the speed of combustion, but the explosive element in gunpowder is saltpeter, which burns at different rates even on its own. Gunpowder burns by taking oxygen from the saltpeter within it. The more saltpeter in the gunpowder, the more explosive it becomes. In the eleventh century Chinese gunpowder tended to hold about 50 percent saltpeter, and therefore was not really explosive. For a big explosion about 75 percent saltpeter is needed. The Chinese were slowly making progress toward this stronger proportion, which would eventually enable them to produce bombs, grenades, and mines in the following centuries.