Classed as a “low explosive” substance, gunpowder produces a large amount of pressure and gas after a rapid burn. This explosion of gas and pressure is ideal for propelling a projectile down the barrel of a firearm or cannon, as it is not intense enough to destroy the device. Gunpowder is composed of three ingredients, potassium nitrate, carbon and sulfur. Sulfur comprises the smallest component at about ten percent. The colonies imported it from Sicily, which has huge deposits. Carbon, the next biggest component at about fifteen percent, they could manufacture from charcoal, an abundant resource made by burning wood. Potassium nitrate is the most important at seventy-five percent and is the most difficult to obtain.
Potassium nitrate, or salt peter, accumulates in caves as the composted remains of bat manure, or guano. The substance acts as an oxidizer during the explosion, decomposing high temperatures. It provides oxygen for gunpowder’s chemical reaction when ignited. The early colonists knew of no natural sources of salt peter in the New World. Sources were found later on, but the need for this critical material during the Revolutionary War forced the colonists to find foreign sources. There is another way to produce salt peter, but it is a long process. Any organic matter that contains nitrogen is a potential source for potassium nitrate. Manure, blood from slaughterhouses, plant material of all kinds they gathered and put in a huge pile. They would water this pile from time to time with animal and human urine. This pile of organic matter would decompose, leaving compost behind. They would then leach the salt peter out of this compost with water. They could then recrystallize the salt peter by evaporating the resulting liquid in the sun. This process typically took a year to produce the salt peter needed for gunpowder. Caves in the Appalachian Mountains mountain provided another source, as the bats that lived in them produced an ample supply of guano from which they could procure saltpeter.
Ingredients and Recipe
Gunpowder manufacturers could use charcoal made from a variety of sources, however charcoal made from wood made the best, most powerful, gunpowder. Manufacturers also used charcoal made from other materials like grapevine, hazel, elder, laurel and even pine cones. Most manufacturers prefer light woods because they leave less ash after the charring process than heavier woods like oak, hickory and maple. Gunpowder mills in during the Colonial and Revolutionary period in the United States preferred to use cottonwood, soft pine and cedar. To make charcoal, they tended to cut trees between two and ten years old in the spring. At this time the trees contained the most sap, which lessens the dissolved salt content in the wood which creates less ash when charred. At this time of year it is also easier to debark the trees. Bark produces more ash when charred, so they preferred not to use it. After cutting and debarking they cut the wood into pieces about three feet long, split the pieces and placed them in an iron cylinder called a slip. After sealing the ends of the cylinder, they placed the slips in huge ovens to bake. The cylinders were placed in such a way as to expose its entire surface to the flames to produce an even temperature. They used different temperatures and baking times to produce different types of gunpowder, however generally it took from between three to six hours at approximately 300 degrees.
Sulfur and charcoal, or carbon, act as the fuel that provides the explosion when the gunpowder is ignited. Natural sources of sulfur were scarce in North America at this time, thus most sulfur was imported from the volcanic regions of Italy..
The Situation at the Beginning of the War
An army needed gunpowder to function. At the beginning of the Revolutionary War the supply of gunpowder available to Washington’s fledgling army proved wholly inadequate to its needs. One reason that the Siege of Boston lasted so long is that Washington did not have an adequate supply of gunpowder to evict the British from the city. Historians estimate that the amount of powder available in early 1775 was only sufficient to supply each soldier with about 20 cartridges. In a heated battle, this would last less than 15 minutes. The powder stored in magazines had been there since the end of the French and Indian War in 1763. The end of that war had ended the need to produce vast quantities of gunpowder and the colonial powder mills that produced it had fallen into disuse. The men that knew how to make the critical substance were also in short supply. It was cheaper to produce gunpowder in England and ship it to the colonies than it was to produce it locally, so domestic production had become almost extinct. If British General Howe, cooped up in Boston, had gained information on the sorry state of the rebel’s gunpowder supplies he could have ended the revolution before it had a chance to start.