The primary three components of black powder are a fuel, an oxidizer and a stabilizer, mixed in various proportions. The fuel is usually charcoal or sugar, the oxidizer is usually potassium nitrate (KNO3) (or sometimes sodium nitrate, NaNO3) and the stabilizer is generally sulfur (S). The burning of the carbon (C) in the charcoal produces carbon dioxide and energy in the form of heat and light. Normally, the charcoal would burn at a normal rate when burnt in atmospheric air, but with an oxidizer that supplies extra oxygen, it burns much faster than usual. The final reaction produces nitrogen and carbon-dioxide gases and potassium sulfide. Gunpowder may be made using just potassium nitrate and charcoal, but the force is not as much as when sulfur is added. Sulfur also reduces the temperature at which the ignition takes place.
The proportions of the various ingredients of black powder have varied over time. Sir Francis Bacon's formula of 1268 called for 7 parts by weight of potassium nitrate, 5 parts of charcoal and 5 parts of sulfur, though some scholars maintain that he'd invented the modern ratio of 15:3:2 as well. By 1312, the records of the Battle of Crecy and the Battle of Agincourt show that the English had settled on a formula in the ratio 6:2:1 of KNO3, C and S, while the Germans were using 4:1:1 ratio. By the 1750s, the standard ratio for gunpowder used was 15:3:2 (i.e.) 75% potassium nitrate, 15% charcoal, 10% sulfur by weight and this ratio has stayed pretty much the same since. Other ratios were used for black powder not suitable for use for firearms (for instance, blasting powder used different ratios of the ame materials).
The charcoal used in the manufacture of black powder is generally manufactured from the wood of softwood trees. Softwood trees are preferred because the charcoal from hardwood trees leave too much ash behind after combustion. According to W.W. Greener's, The Gun and Its Development, Second Edition, trees such as willow, black dogwood, alder etc are/were traditionally used in England to manufacture charcoal. In India, the woods of the locally available Grambush plant (Cythus Cajan), Parkinsonia and Milk Edge (Euphorbia Tiraculli) are used. In America, cottonwood, soft pine, redwood and western cedar are the trees of choice. The trees are generally felled in springtime, because the bark is easier to remove from the tree trunks during this time, though winter wood may also be used. The removal of bark is a necessity because it prevents the scintillation of gunpowder. The wood is cut into chips or smaller pieces about 1-4 inches in diameter and put into a vessel with a tight fitting lid. There is a small hole on top of the vessel to allow the escape of other gases. The vessel is then placed on a hot fire and heated, until organic gases begin to escape from the wood through the small hole. The gas is called wood-gas and is primarily composed of methane. This gas may be ignited with a match as it is escaping through the hole. When the gas stops issuing out of the hole, the flame goes out and this indicates that the wood has been converted to charcoal. The time taken for charring depends on the thickness of the wood pieces, as well as the heat of the furnace. Charcoal made at 240 degrees centigrade will readily ignite at 330 degrees centigrade, whereas charcoal made at 950 degrees centigrade will take nearly 1900 degrees to ignite. Hence, the best charcoal for gunpowder is made at lower temperatures. The vessel is allowed to cool and then the charcoal is removed and ground up into a powder. For uniform results, the vessels used to make charcoal are all kept at the same temperature. After the powder is ground up, it is allowed to sit for a couple of weeks. The reason for this is that freshly ground-up charcoal is highly prone to spontaneous combustion, but if it is allowed to sit for 10-12 days, it loses this property and can now be used to make gunpowder more safely.
The second ingredient of black powder is Potassium Nitrate (KNO3), commonly known as saltpeter. This occurs naturally as an efflorescence on the ground in some parts of the world, such as India and Arabia and the Andalusia region of Spain, due to the weather conditions. In parts of Europe, it was manufactured by preparing beds of manure mixed with wood ashes and leaching with urine for a period of time. In France and Sweden, the mortar from old farm walls and stables were a source for saltpeter Another source was bat dung from caves. Sodium nitrate was also used as an alternative for a while, as it was available in the Chilean desert. In the 1600s, most of Europe was importing saltpeter from ports in the Gujarat region of India. By the late 1700s and early 1800s, England's source of potassium nitrate was entirely from the Gangetic plains of India, especially from the Bengal and Oudh regions where it was naturally occurring. The salt was collected here off the ground, mixed with water and boiled and the solution then placed in shallow troughs and allowed to evaporate in the sun, leaving behind impure saltpeter crystals (called "grough saltpeter"). These were then packed into gunny bags and shipped off to England for refining. On arrival at the Royal Waltham mills in England, about two tons of the grough saltpeter were put in a large vat and dissolved in 275 gallons of water. The mixture was heated for about two hours to allow the contents to boil, the specific gravity being 1.49 and the temperature of water getting close to 230 F. Scum rising to the surface was skimmed off until no more scum was generated. Then more cold water was added and the solution was heated and then allowed to cool to 220 F. The solution was then pumped into shallow trays and allowed to cool. The cooling would crystallize the excess potassium nitrate, while the solution would contain the impurities of sulphates, chlorides etc. The solution was gently agitated to prevent formation of large crystals and form a flour instead. The flour was then washed three times and a small sample was tested to make sure it was pure enough, before the batch was used.
These days, most potassium nitrate is generally mass-produced using the Haber process, which was invented by Fritz Haber shortly before WW-I. This consists of combining nitrogen with hydrogen in the presence of a catalyst, to produce ammonia (NH3). This ammonia is then oxidized to produce nitrates. The advantage of this process is that the raw ingredients are all abundantly available in nature (nitrogen and oxygen from the air and hydrogen and oxygen from water) and thus cannot be embargoed. During WW-I, the allies had access to large naturally occurring deposits of nitrates from Chile, but the Germans were cut off from this supply and had to produce their own. It was strongly suggested that without Haber's process, the Germans could not have gone to war or would have had to surrender much earlier. Haber received a Nobel prize for his discovery. Ironically, he was forced to leave Germany by the Nazis in the 1930s simply because he was Jewish.
Sulfur is also obtained naturally around the world, mostly around hot springs and volcanic regions. It is found naturally in Sicily, Japan, Chile, Indonesia etc. It was known in ancient China and India as well, where it was extracted from pyrite ores. In fact, the word "Sulfur" is actually of Sanskrit origin (sulvari). It is also found around petroleum deposits. Sulfur is generally refined by using distillation or sublimation. Historically, the two methods used for purifying sulfur were the Sicilian process (from ancient times) and the Frasch process (used from 1890s onward till about 2002). The Claus process extracts sulfur from hydrogen sulfide gas and is the process of choice in modern times.
In the next post, we will discuss how these ingredients are combined to make black powder.