Black Powder - VI: Serpentine Powder

In our last few posts, we looked at how grain sizes of black powder are/were classified in the US and in 19th century England. In today's post, we will look at an early form of black powder, that was called "serpentine powder".

In the earliest days of firearms, the three ingredients of gunpowder, namely saltpeter, charcoal and sulfur were combined together in a dry state. This powder was often referred to as "serpentine" powder. Why the name "serpentine"? Well, there were some early forms of cannon called the "Cannon serpentine" and "Serpentine". The table below shows some details:

Types of Cannon in England during the 16th-17th century. Public domain image. 

Note that serpentine cannon date back to a few hundred years before this list was made.

Some authorities say that "serpentine" artillery tended to be long and thin, resembling a snake, which is why they were named that way. Other authorities claim that "serpentine" is an allusion to the serpent in the Garden of Eden, who was Satan in disguise, and cannon were considered to be the work of the devil in the middle ages.

Also, in early matchlock weapons, the serpentine was an S-shaped lever that held the burning match. When the user pulled on one end of the serpentine lever, it would apply the other end with the burning match to the pan, thereby igniting the black powder. Perhaps the S shape resembled a serpent, thereby giving the name "serpentin" or "serpentine"

Early gun with serpentin trigger. Public domain image.

Whatever the origin of the name, the powder made for such weapons was called "serpentine powder".

To prepare serpentine powder, the saltpeter, charcoal and sulfur were first ground up separately using a mortar and pestle, then the three ingredients were mixed together in the desired ratio to form the serpentine powder.

Since the three ingredients were mixed together in a dry state, there was the potential of explosive dust floating around and many powder makers met with accidents during work. Even after it was mixed together, serpentine powder was somewhat unstable and had the tendency to absorb moisture from the air (due to impurities in the saltpeter), which could cause it to spoil. The reliability of serpentine powder was also not very good and its explosive force was hard to predict. If it is packed too tightly into a gun, the charge may fizzle out or it may develop cracks and detonate, destroying the gun.

One more problem with serpentine powder is since the ingredients are ground up separately and then combined, the ingredient particles would often be of different sizes. What this meant was when transporting a barrel of gunpowder in a cart across bumpy and muddy roads, the vibrations would cause the ingredient with the smallest particles to settle at the bottom of the barrel and the ingredient with the larger particles to move to the top. We discussed why this happens a few posts earlier. Since the three ingredients are particles of three different sizes, this would cause the ingredients to separate themselves, so pulling a sample of powder from the top of this barrel would consist of largely charcoal, but very little saltpeter or sulfur, which would not ignite very well. This meant that they would have to remix the ingredients again at their destination, to ensure the proper proportions of the gunpowder mixture. This was a hazardous procedure that produced clouds of explosive dust and wasn't convenient to do in the middle of a battle.

Due to the variable size of ingredients, serpentine powder has a variable burn rate as well and has about 50-60% the energy of modern black powder. The following video shows the burning rates of equal quantities of serpentine powder and modern black powder.

Video courtesy of fido969 at youtube.

As you can see from the video, there is a pretty big difference in the combustion rates of the two powders and serpentine powder produces less power.

In our next article, we will look into the corning process, which solves many of the problems of serpentine powders.

Black Powder - III

In our last post, we studied some of the physical and mechanical properties of gunpowder, information which will come in handy when we study manufacturing methods in some detail. In today's post, we will look at factors that influence the rate of combustion of black powder.

As we saw in the first post of our black powder series, the ratio of saltpeter, sulfur and charcoal in gunpowders varied at different times and in different countries, but by the 19th century, many people had generally settled to using the ratio of 75% saltpeter, 10% sulfur and 15% charcoal. However, powders made by different manufacturers had different pressures and combustion properties even when they were using the same ratio of the ingredients. We aren't even talking about manufacturers from different countries, they could be manufacturers in the same country or even different powders from a single manufacturer. Clearly there must be some other factors that explain why this happens. That is what we will study about in today's post.

The action of black powder depends not only on the composition of its ingredients, but also the size of the grains, shape of the grains and the density of the grains among other things.There are other factors that influence the rate of burning, but these three are the most important. The reason is because black powder is surface-burning. Smaller grains of gunpowder will have more surface area exposed to ignition than a larger grain of the same weight, therefore smaller grain powder will burn faster than the larger grained type. However, if the powder is packed too densely, the flame cannot easily spread from grain to grain, than the same weight of powder packed in a less compact manner. Therefore, very small grain mealed powder and very large grain powder are both slower burning. The shape of the grain also will affect the burn rate, because of the surface area exposed to ignition. Shapes like cubes or spheres offer less surface area than irregular shaped grains of the same mass, therefore they burn slower. This is why laminated or flaky powders burn much faster than normal and diamond shaped grains burn more rapidly than rounded grains.

As a general rule, the larger the grain, the less violent will be the action of gunpowder (i.e.) its combustion will be more gradual. On the other hand, smaller grain powders also cause pellets to scatter much more rapidly than larger grain powders because a smaller grain powder expends all its force before the shot pellets reach the muzzle, whereas a larger grain powder causes the shot pellets to increase their velocity right up to the muzzle of the gun. Therefore, powder designed for weapons with shorter barrels, such as revolvers and pistols, must be of smaller grain, so that they can finish burning before the powder leaves the barrel. Similarly, powders meant for rifled guns are generally a larger grain than those intended for smooth bores, as a more gradual action is required to avoid putting too much strain on the gun barrel.

Since the same manufacturer often makes black powder of different grain shapes, densities and sizes for different types of guns, therefore the shooting qualities of black powder will vary accordingly. We will look at some powders from the 19th century:

Samples of different powders made by Britsh manufacturers.

Click on the image to enlarge. Public domain image.

The above image shows various black powders made in the 19th century by two large British manufacturers Curtis & Harvey and Pigou, Wilks & Laurence. As you can see, the "Revolver" powder is made of very small grains and designed to be fast burning, while Curtis & Harvey's "Col. Hawker's Duck Powder" and Pigou's "Special Punt Powder" are larger grained and designed to be used by very large bore punt guns. Similarly, Diamond #4 and Alliance #4 were generally used for hunting with shotguns, while #6, Rifle, and Martini-Henry powders were designed for rifles. Other large powder manufacturers in England included the E.C. Powder Company, Schultze Gunpowder Company, Kynoch Ltd., Hall, Coopal, Dittmar etc.

Powders made in other countries also varied in grain size, shape and density:

Black powders from different countries.

Click on the image to enlarge. Public domain image.

The above image shows some sample powders made in different countries. Of course, this is only a very small sample. For instance, in the United States in the late 19th century, there were various powder manufacturers, each making multiple types of powder for different applications: DuPont, Hazard Powder Company, Laflin & Rand, Hercules etc.

Various types of black powder made by DuPont

Various types of black powder made by Laflin & Rand.

Images courtesy of the Haglin Museum and Library

Incidentally, the reason why many of Laflin & Rand's black powder offerings were sold under the "Orange" brand name (e.g. Orange Ducking Powder, Orange Rifle Powder, Orange Lightning, Orange Extra Sporting etc.) is because their original production plant was named "Orange Mills" and happened to be located in Orange County, New York.

The quality of charcoal is also a significant factor in the burning rate of the black powder. If the charcoal is improperly charred, then the oxygen and hydrogen retained in it cause it to burn more rapidly than if it is reduced to a pure carbon. The source of wood for the charcoal is also a factor. Experiments conducted in the 19th century showed that there were significant differences in the amount of gas produced by charcoal made from different types of wood. For instance, dogwood charcoal was found to yield about 25% more gas than the same weight of charcoal made from fir, chestnut or hazel trees and 17% more gas than charcoal made from willow. This is why dogwood was preferred for black powder intended for pistols and rifles, while willow charcoal was preferred for making powder for cannons.

In our next post, we will study more into the classification of grain sizes and shapes.

Black Powder - II

In our last post, we studied the composition of different kinds of black powder as manufactured in various countries. In today's post, we will study some of the physical and mechanical properties of black powder. Gaining some knowledge of this will help understand the reasoning behind the processes of manufacturing the powder when we study that later on.

The first thing we should note about black powder is that it is a mixture and not a compound. Your humble editor will explain what that means:

A compound is formed when different substances combine with each other at a molecular level. The compound will often have properties different from its component substances. For instance, hydrogen and oxygen atoms can combine together to form water (a compound substance), which is a liquid at room temperature, whereas hydrogen and oxygen are gases at the same temperature. Oxygen can help substances burn rapidly, whereas water can be used to stop fires. So you can see that a compound (in this case, water) has quite different properties than its original ingredients (in this case, hydrogen and oxygen).

On the other hand, a mixture is when multiple substances are physically mixed with each other, but do not react at a molecular level. This means that they may be separated from each other by some physical means and mixtures often retain the physical properties of their separate ingredients. For example, you can make a mixture of iron filings, sand and sugar crystals. However, the iron filings can easily be removed from the mixture by passing a magnet over it, while the sugar can be separated out by dumping the mixture in water and letting the sand settle at the bottom while the sugar dissolves in water. Another example could be sand and glass marbles, which can be mixed together easily, but trivially separated by passing the mixture through a sieve, which will allow the sand to pass through, but retain the glass marbles. Black powder is a mixture of potassium nitrate (saltpeter), sulfur and carbon (charcoal). The three substances do not chemically react with each other at room temperature and therefore it is a mixture. Only when the powder starts to burn do the three substances react with each other and form multiple compounds.

Since it is a mixture, the various ingredients of black powder must be ground into particles of roughly the same size as each other to stay mixed together (especially before corning of black powder was invented). Otherwise, the mixture could separate out where the ingredient with the smallest size particles ends up at the bottom of the box, given enough vibration to the box. This is because the smaller particles fit in easily between the gaps of the other particles and fall to the bottom, thereby pushing the bigger particles up. The same phenomenon can be observed with a bag of potato chips (it doesn't matter what flavor of chips!). Notice that when you buy a bag of potato chips, the smallest broken chips are always at the bottom of the bag, whereas the larger pieces end up on top. This is because the bag is shaken during transport from the factory to the grocery store and from the grocery store to your home and the smaller chips end up fitting into the gaps between the larger chips, making their way to the bottom of the bag eventually and thereby pushing the larger pieces upwards. The same principle used to apply to gunpowder before they learned to cake the grains and manufacture them to the same uniform particle sizes. In fact, one of the problems of early black powders (also called serpentine powders) was that when they transported the powder to the battlefield via carts drawn by horses or oxen, the bad roads would cause the barrels of gunpowder to shake heavily, thereby moving the smaller particles to the bottom of the barrel. Therefore, if the ingredients were ground up into particles of different sizes, the ingredients would separate out into three separate layers by the time the barrel got to the battlefield, with the sulfur ending up at the bottom of the barrel and charcoal rising to the top. This is why they would remix the ingredients right there in the field before the battle commenced, which was a somewhat hazardous procedure that produced clouds of potentially explosive dust.

Black powder can be ignited in three different ways: the first method is by contacting it with sparks or open flame, the second method is by a sharp blow and the third method is by increasing its temperature rapidly beyond a certain point.

The first method (exposing it to open flame or sparks) is the principle that different ignitions systems such as matchlocks, wheel locks, flintlocks, percussion locks etc. use. However, the source of the flame or sparks must be hot for the powder to ignite. It is possible for a shower of lower temperature sparks to fall upon black powder without igniting it, whereas a single spark of great intensity can start combustion.

The second method (striking it between two objects) is because black powder is somewhat impact sensitive. Experiments by Aubert, Lingke and Lampadius verified that black powder can be ignited by striking iron on iron, iron on brass, brass on brass, and less easily by a blow of iron on copper, or copper on copper. Of course, some of this might be explained away by the impact causing sparks which ignite the powder. Experiments in 19th century England showed that black powder is also ignited by striking brass on copper, iron on marble, quartz on quartz, lead on lead and lead on wood (a lead bullet was shot against a wooden pendulum covered with powder). Mining accidents over the years showed that striking copper on stone or even wood on stone could occasionally cause ignitions of black powder. One Dr. Dupre even showed that there is hardly any explosive, which, when laid in a thin layer on a wooden floor, will not explode, when it receives a glancing blow with a wooden broom-stick.

The third method (heating it beyond a certain temperature) has some interesting effects. Black powder may be ignited when heated rapidly above a certain temperature, even without the presence of an open flame. The temperature at which this happens depends on the nature of the powder and the proportions of its ingredients and grain size. An experiment by Horsley in the 1800s showed that black powder could be ignited by heating it to around 600 °F (about 315 °C) by heating a saucer in an oil-bath, with the temperature of the oil being taken by a thermometer dipped into it. Experiments by Leygue and Champion in 1871 used a more precise method to determine ignition temperatures and the found that a common sporting powder ignited around 550 °F (about 288 °C), while cannon powder ignited around 563 °F (about 295 °C). However, note that we said that the powder should be heated rapidly for it to ignite. What if it is heated slowly?? Leygue and Champion detail some interesting issues here: They discovered that the grains of corned black powder cake together on account of the sulfur they contain. However, note that black powder before ignition is a mixture, which means it retains many of the physical properties of its separate ingredients. When the temperature of black powder is slowly increased beyond 212 °F (about 100 °C, the temperature of boiling water), the sulfur begins to volatilize and turn into vapor. The volatilization of sulfur rapidly increases with temperature and if the temperature is slowly increased upwards, but kept below the boiling point of sulfur, then the sulfur can be completely driven out of the powder without any ignition taking place. When the sulfur is completely eliminated from the mixture, the temperature can be further increased, so that even the saltpeter melts, and the charcoal ends up floating on top of it, thereby separating out the two ingredients from each other. If, on the other hand, the temperature is rapidly increased before the sulfur is completely volatilized, then the sulfur vapor is ignited and causes the powder to explode. The shape and size of the grains of black powder have considerable influence on the temperature of ignition as well.

If a small quantity of black powder is ignited in open air, it merely burns, but if larger quantities are ignited, or if the powder is ignited under higher pressure or in a closed space, then it explodes. The larger the grain size, the slower the combustion rate. We will study more about this in the next post when we study more about grain sizes.

If good quality black powder is ignited over a sheet of white paper, it will burn rapidly and leave no residue on the paper. If black spots are found, then this indicates that either the mixture contains too much charcoal or the powder is badly mixed. The same can be said for sulfur if yellow spots are left behind. If unburned grains are found, this indicates that the saltpeter is impure. The powder should not burn holes into the paper, as only moist or otherwise bad black powder does so.

As early as 1765, Papacino d'Antoni found that lower air pressures make it more difficult for black powder to ignite. Later experiments by Munke, Hearder, Bianchi, Heeren and Sir Frederick Abel showed that gunpowder didn't explode in a vacuum tube, even in the presence of a platinum wire glowing white hot. Heeren tried to explain this phenomenon by suggesting that at normal pressures, the hot gas escaping from an exploding body would communicate the flame to neighboring particles, but under low pressure, the gas expands so rapidly on account of the lack of resistance of the surrounding air, that it cools down below the ignition temperature of neighboring particles.

On burning gunpowder under normal or high pressures, the various ingredients of the mixture combine with each other chemically and produce gases and solid residue. While this was known from the day that gunpowder was invented, the nature of the gases and solid residue was not. In fact, given the primitive state of chemistry for centuries, it was not known if the products of combustion was just one or several gases. For instance, in 1705, the great Issac Newton thought that sulfuric acid formed by the combustion of sulfur drove out the spirit of niter from the saltpeter and burned it. The same view with slight modifications, was held in 1771 by Majow, who thought a mysterious substance called "phlogiston" (thought to exist in all flammable substances) combined with the nitric acid. It was left to the famous French chemists, Joseph Louis Gay-Lussac and Michel Chevreul, to determine exactly what gases and solid residues were produced. Their experiments showed that among the gases produced were carbonic acid, nitrogen and carbonic oxide, while the solid residues were potassium sulfate, potassium carbonate, potassium sulfide, potassium thio-sulfate etc. Incidentally, Gay-Lussac was the first to prove that water is made of hydrogen and oxygen and also worked on alcohol-water mixtures, the results of which are still used to today to measure alcoholic beverages in many countries around the world (a fact that drinkers will surely appreciate!)

In our next post, we will look into the effects of grain sizes of black powder and how/why different grain sizes were used for different applications.

Black Powder - I

A while ago, we studied about black powder in two separate posts. Since we've studied the processes of obtaining the basic ingredients of black powder (saltpeter, charcoal and sulfur) in great detail in some of our previous posts in the last few months, we will study the processes of combining them into black powder in some detail in the next series of posts.

Before we start our study of black powder manufacture, let us discuss the proportions of the ingredients of black powder. While it is true that many countries had settled with the proportions of 75% saltpeter, 10% sulfur and 15% charcoal by the 18th and 19th centuries, this wasn't always true in all countries. Moreover, the proportions also varied a bit, depending on the use for the black powder. For instance, powder intended for military rifles differed in composition than powders intended for sporting applications, which differed from powders used for blasting purposes, powder used for fireworks etc. We have some information about the composition of powders made in various countries, courtesy of Oscar Guttman's book "Manufacture of Explosives" from 1895 (note that some of the countries have different names now)

	Saltpeter	Sulfur	Charcoal
(a) Rifle Powders:
Austria-Hungary	75	10	15
Belgium	75.5	12	12.5
China	75	10	15
France	75	10	15
Germany	74	10	16
Great Britain	75	10	15
Holland	70	14	16
Italy	75	10	15
Persia	75	12.5	12.5
Portugal	75.7	10.7	13.6
Russia	75	10	15
Spain	75	12.5	12.5
Sweden	75	10	15
Switzerland	75	11	14
Turkey	75	10	15
USA	75	10	15
(b) Cannon Powders:
Austria-Hungary	74	10	16
France	75	10	15
Germany	74	10	16
Great Britain	75	10	15
Switzerland	75	10	15
(c) Sporting Powders:
Austria-Hungary	76	9.4	14.6
France	78	10	12
Germany	74	10	16
Great Britain	75	10	15
Switzerland	78	9	13
(d) Blasting Powders:
Austria-Hungary	60.2	18.4	21.4
France	72	13	15
Germany	70	14	16
Great Britain	75	10	15
Italy	78	18	12
Russia	66.6	16.7	16.7

As can be seen above, many countries varied the proportions of the ingredients based on the intended use of the powder. Note that the blasting powders vary in proportion much more than the rest. This is because blasting powder's requirements were that it should be cheap and develop as much gas as possible at a high temperature. Actually, blasting powders were more varied than the table indicates because powders with different rates of burning were used for rocks of different hardness. So even though the table above suggests that the French were manufacturing blasting powder with the ingredients in 72%, 13% and 15% ratio, that was only one grade and the French Government factories actually made 3 grades of blasting powder:

	Saltpeter	Sulfur	Charcoal
Ordinary Powder	62	20	18
Slow Powder	40	30	30
Strong Powder	72	13	15

Similarly, some blasting powders in England were made of different proportions (e.g.) 65% saltpeter, 20% sulfur, 15% charcoal.

Powders manufactured in Belgium had the following compositions depending on the purpose:

	Saltpeter	Sulfur	Charcoal
Rifle Powder	75	12.5	12.5
Cannon Powder	75	12.5	12.5
Sporting Powder	78	10	12
Blasting Powder	75	12	13
Slow Powder or Pulverin	70	13	14 & 3% wood meal
Slow Powder in cartridges	70	13	14 & 3% dextrine
Export Powder	68	18	22

In France, "pulverin" was also manufactured for use in fireworks and contained 75% saltpeter, 12.5% sulfur and 12.5% charcoal mixed together.

In the next couple of posts, we will study the grain sizes of black powder in the 19th century.

Historical Manufacture of Charcoal - II

In our last post, we looked at the charcoal manufacturing process, as it was done from the 14th to the early 20th century. In today's post, we will look at some variations of the process.

As we saw in the last post, charcoal manufactured for the purposes of gunpowder had to be of a higher quality with uniform charring. Therefore it was manufactured in smaller batches using iron cylinders to heat the wood, instead of heating up large heaps. Our last post also described the process in England, where they used small iron cylinders, each holding about 80 lbs. of wood, being placed inside a furnace and heated. In today's post, we will study some variants of this basic method.

Instead of using fixed carbonizing cylinders, many black powder factories in England started switching towards using movable cylinders in the 19th century. Each furnace was provided with two cylinders, so that one could be refilled while the contents of the other were being carbonized. Each filled cylinder would be run into the furnace on rails, with the rails supporting them over the fire. An elaborate system of pipes and valves was used to distribute the gases and the wood distillation byproducts (wood gas, tar, volatile chemicals etc.), so that they could be redirected back to any one of the furnaces, or allowed to escape through the chimney.

The advantages of this process were:

1. Uniformity of the charcoal being produced.
2. The gases produced by distilling the wood could be reused to additionally heat the furnace, thereby saving on fuel costs
3. The charcoal was cooled down out of contact with the air, which took away the possibility of the charcoal catching fire.

In some British factories, vertical movable cylinders were used instead. The advantages of this were that more cylinders could be fired at the same time and the moving of the cylinders to the cooling room was easier.

In Sweden, some factories used rotating cylinders, with each cylinder being rotated 90 degrees on its horizontal axis every 30 minutes. This allowed the heat to act upon each side evenly and this process gave a more uniform carbonization and saved fuel as well.

Another method of carbonizing wood used superheated steam to do the job. Pressurized steam was produced by passing water through a coil of wrought iron heated by a fire. For the production (from dogwood) of charbon roux (brown charcoal) containing 70% carbon, the temperature of the steam had to be around 280° Fahrenheit; by using steam heated to about 350°, charcoal containing about 77% carbon could be produced, and by heating both the cylinders and the steam to about 450° fahrenheit, charcoal of about 89% carbon content could be produced. The charcoal produced by this method was very uniform in composition, but the method was later abandoned because it gave a larger yield of charbon roux, but not so much black charcoal, as the ordinary method of carbonization using iron cylinders; and the lightly-burnt charcoal was only required for sporting powders. Also, the cost of production of charcoal using superheated steam apparatus was greater.

In 1887, one Mr. H. Guttler of Reichenstein, Germany, invented a process of carbonizing wood (he received British patent # 8929 on June 22nd, 1887 for his idea "Improvement in the Manufacture of Charcoal for Explosives and other Purposes, and Apparatus for that Purpose"). His idea consisted of putting the material to be carbonized into a suitable air-tight cylinder fitted with a pressure gauge and pyrometer and using an arrangement of two furnaces to heat it. One is a normal charring furnace and the other is a producer-furnace, which produces carbon dioxide gas by blowing air through burning coke using a fan. The heated carbon dioxide gas is then piped into the cylinder (similar to the superheated steam process we saw above) and the carbonization takes place. The pressure of the carbon dioxide in the cylinder can be varied as needed. The temperature is regulated by admitting cold air to the muffle and by varying the supply of heated gas into the cylinder. After the charring is completed, cooled carbon dioxide is passed through the charcoal, which rapidly cools and absorbs the carbon dioxide in its pores. The advantage of this process over using superheated steam was that it didn't leave the charcoal produced in a moist state, which the steam process did. It could also be used to produce charcoal from cheaper materials such as wood cuttings, pulp, straw, peat etc. Another advantage was that since it used carbon dioxide instead of air, the charcoal produced could not spontaneously ignite.

In the next post, we will look at the historical production methods of the third ingredient of gunpowder: sulfur.

Historical Manufacture of Charcoal

After spending the last few weeks studying the history of saltpeter manufacturing around the world, we will spend some time today studying another component of gunpowder: charcoal. We actually studied this topic briefly when studying about black powder many months ago. We will revisit this topic in more detail today.

Strictly speaking, the chemical element that is used for gunpowder is carbon, which is supplied by the charcoal. The carbon acts as a fuel in the gunpowder.

Since the very early days of firearms, it was found that the quality of charcoal is a pretty important factor in the quality of the gunpowder produced. Therefore the process of manufacturing high quality charcoal was regarded as a closely-guarded state secret. Charcoal made by burning wood in heaps or kilns is not very suitable for gunpowder. Instead, to make high quality charcoal, the wood must be selected very carefully and burned uniformly in ovens or iron vessels. The procedure to do so hadn't changed very much from the fourteenth to the twentieth century. We will look at the process used at Waltham Abbey in England, during the early 20th century.

First, the choice of wood for making charcoal for gunpowder: Soft and light woods are preferred, as they leave less ash. At one time, the charcoal for black powder in England was exclusively made from alder wood, but later other soft woods were also used. In England, dogwood was extensively used, especially for small grain powders, and for larger grain powders, alder and willow wood were used, with straw charcoal being used for brown powders used in heavy ordnance; In America, cottonwood, redwood, soft pine and western cedar trees were used; In Germany, alder and willow were mostly used; in Austria, hazel and alder; in Switzerland, hazel trees; in France, dogwood was exclusively used in military and sporting powders, but as it became more difficult to procure, alder, poplar and lime were tried out; in Russia, alder was commonly used; in Spain, yew, oleander, willow, hemp stems and vine; in Italy, hemp stems were used mostly.

The trees chosen were usually between two and  ten years old. The trees were generally cut down in spring for a few reasons. First, this is the time when trees are the most full with sap, which means the sap is very watery and contains less dissolved salts in it, thereby producing less ash. The second reason is that trees cut down in spring are easiest to separate the wood from the bark, which is good because the tree bark contains a large portion of the ash produced. The wood was seasoned for at least 1.5 to 3 years, to allow most of the sap in it to dry out. The method of doing this varied by location and type of wood. For instance, in Germany, it was customary to keep the wood inside sheds in Dresden, but at Spandau, they kept the wood out in the open. In England, dogwood was covered with thatch, but the willow and alder woods were dried out in the open.

After drying, the wood was split into pieces about 3 feet long by 1 inch thick. These pieces were placed in iron cylindrical cases called slips. Each cylinder was about 2 feet in diameter and 3.5 feet long. The lid was fastened to each slip, with two openings (about 4 inches diameter) being left in the bottom of each slip. The slips were then placed in horizontal cylinders, the end of the slip with the openings going to the further end of the cylinder, in which end there were openings corresponding to those in the slips. The cylinders were then lifted with pulleys into a furnace, where they could be heated as uniformly as possible. The cylinders were placed such that the furnace flames surrounded the cylinder entirely, so the heat acted upon the whole surface as much as possible. The higher the temperature and the longer the heating time, the lower was the percentage of hydrogen and oxygen in the charcoal, which made it harder and more difficult to ignite. Therefore the type of wood and the type of gunpowder that the charcoal was meant to be used for, determined how long the cylinders were heated. For instance, to make R.F.G (Rifle Fine Grain) powder or M.G. (Machine Gun powder for Nordenfelt guns) powder in Waltham Abbey, dogwood was heated for abuot 4 hours. Alder and willow for R.L.G (Rifle Large Grain) powder was heated for 3.5 to 4 hours and for P grade gunpowder, it was heated for 6 hours. Smaller cylinders were used, to make the composition of the charcoal more uniform, since high temperature is not needed to carry the heat to the center of the wood pile in each cylinder. However, the use of small cylinders reduces the efficiency and raises the cost of production. In England, most cylinders were only large enough to hold about 80 lbs. of wood. Incidentally, for a given temperature, slow carbonization produces much more charcoal than quick carbonization at the same temperature.  Also, the lower the temperature used for carbonization, the lower the temperature at which the charcoal burns. Therefore charcoal made at 260-280 degrees centigrade burns at around 340-360 degrees centigrade, whereas charcoal made at 950 degrees burns at around 1900 degrees.

As the cylinders were heated, the volatile chemicals and tar in the wood would be released by the decomposition of the wood. Normally, these gases could be condensed by using a condenser and used to make useful chemicals like lime acetate and wood spirit. However, charcoal produced by gunpowder mills were generally on a much smaller scale that the charcoal used for metallurgy, therefore it was not considered to be worth the effort to do so. Instead, the gases were removed via a pipe and fed back into the furnace, where they could be burnt. Doing this saved a considerable amount of fuel, thereby reducing costs. When the wood was sufficiently charred, the color of the flame would change to a bluish violet, indicating the formation of carbonic oxides. At this point, the furnace is opened and the cylinder is taken out using pulleys and replaced by a fresh cylinder. The cylinder taken out was placed in a larger cylinder with a tight fitting lid and allowed to cool for about 4 hours, until all the fire in the wood could be extinguished. It is necessary to do this cooling out of contact with the air, otherwise the charcoal could catch fire. The charcoal was then emptied into smaller cylinders and carefully picked by hand to ensure that it is properly and evenly burnt. It was cooled in the smaller cylinders for about one to two weeks, to reduce the danger of spontaneous combustion (caused by the charcoal absorbing oxygen from the air), before being sent to be ground.

Charcoal intended for firearms use was generally jet black in color and so soft that it could not even scratch a copper plate. The following table shows an analysis of the charcoal produced for different powder grades:

Note that the Spanish Hemp Charcoal has a higher percentage of ash than the others. This is because it was manufactured by burning the charcoal in pits holding about 0.5 to 1 ton of wood each (unlike in England, where each cylinder only held about 80 lbs of wood). Also in the Spanish method, when the wood had carbonized enough, the pit was covered with a woolen cloth upon which earth was placed, which accounts for the higher percentage of ash produced.

Inferior quality charcoal was generally used for powders shipped to Africa and Brazil, since the locals there seemed to value the shiny quality of the black powder rather than its shooting properties.

In our next post, we will look at some variations of this process used by factories in England, Sweden and elsewhere.