Sunday, July 24, 2016

Black Powder - VIII

In our last post, we saw how people started to manufacture corned black powder starting in the early 15th century. In today's post, we will look at how it was done from then on until the end of the 19th century.

As we saw in our last post, by the early 15th century people had started doing the pulverizing, mixing and caking of the three ingredients of gunpowder (i.e.) saltpeter, charcoal and sulfur, in one operation in a stamp mill, in order to keep the grain sizes consistent. We will look at the development of automated machines that did this.

A stamp mill from 1686. Click on the image to enlarge
Image taken from "Teatrum Machinarum Novum" by George Andreas Bockler of Nuremberg. Public domain image.

Parts of a stamp mill.

A stamp mill has a heavy block made of oak or beech wood (b in the diagram above), about 2 feet in thickness, in which a number of mortar holes (a) are carved into the block, to a depth of about 20 inches, with diameter of about 15 inches. At one time, those holes were cylindrical, but they were later carved into spherical shapes with a funnel-shaped opening at the top. At the bottom of each hole, a piece of hardwood (c) is inserted to act as an anvil. The block of wood is tied down by means of straps and bolts and rests on a foundation (usually a wooden grating), so that the bottom is supported to withstand the blows from the  stamp head.

The stamp rod stems (d) are rectangular in cross-section, about 7 to 10 feet long and 4 inches thick and made of maple or beech wood. At the end of each rod is attached a pear-shaped head (e) made of bronze. At the other end of each stamp rod, a lifting pin is wedged on.

Stamp mill in Austria. Public domain image.

By the 19th century, each mill usually had only one stamp rod per mortar hole, but before that it was common to use multiple stamp rods per hole. For instance, in Sweden, they would use four stamp rods per mortar and in Austria, they would use three rods, as the image above shows. Also, some machines used metal mortars instead of wooden ones, but this was abandoned because of sparking risks.

To drive the stamp rods, a cam-shaft (AB) with cams (c) attached to it is used. As the shaft rotates, the cams engage the lifting pins on the stamp rods and lift the rods vertically up to a certain point, whereupon the cam disengages from the pin and the stamp falls back due to gravity. The cam-shaft is driven by the wheel L, which is either powered from a water-wheel or animal-power.

Each rod is dropped about 16-17 inches and the weight is anywhere from 40-90 lbs. Each mortar is filled with the three ingredients of gunpowder in their proper proportions and the contents of each mortar weigh about 15-25 lbs., depending on the size of the machine. The mixture was originally moistened with water in the early part of the 16th century, to reduce chances of spontaneous combustion. Later on, vinegar was used as well and in the middle of the 16th century, it was considered good practice to moisten the mixture with "man's urine who drinks wine"!

The time of stamping also changed during the centuries. In the 16th century, they would generally let the procedure run for 6 hours; by the beginning of the 17th century, it had increased to 10 hours for cannon powder and 12 hours for musket powder; by the year 1700, the time of stamping was about 24 hours at the rate of about 1 blow per second.

In the UK, stamp-mills were prohibited by the 19th century, because of the dangers associated with them. Instead, incorporating mills were used in the UK, as well as Germany and Italy. The technology of incorporating mills was known as early as 1540 and mentioned by Biringuccio. They were imitations of olive oil mills, but were not used early on because they were considered dangerous. Later on, the technology improved and these were used in the UK, France, Germany, Sweden, Italy etc.

An incorporating mill. Click on the image to enlarge.
Image taken from "Teatrum Machinarum Novum" by George Andreas Bockler of Nuremberg. Public domain image.

Sweden got its first incorporating mill in Cnutberg in 1684. In France, they were first introduced in 1754 by Pater Ferry at Essonne. These mills have a rotating millstone running over a bed. Each millstone is powered by a system of gears driven by a water wheel. Millstones were made of marble in the early days and the beds made of copper or wood.

In our next post, we will study improvements to the pulverizing process.

Monday, July 18, 2016

Black Powder - VII: Corned Powder

In our last post, we looked at the manufacture of an early form of black powder called "serpentine powder". As we noted previously, there were a few problems with serpentine powder:

  1. The ingredients were mixed dry and there was a lot of dust raised and chances of spontaneous combustion.
  2. If the black powder was transported on rough roads, the vibration would cause the three ingredients to separate out.
  3. There wasn't much uniformity in the grain sizes or composition, so the power of black powder could vary from batch to batch, or even within the same barrel.
  4. It was difficult to manufacture large quantities at a time and took significant manual effort.
However, towards the early part of the 15th century, powder manufacturers found that it was safer to make powder in a wet state with water and then dehydrate it later, which produced much more consistent results. The addition of water while grinding the materials made it possible to lessen the problem of heat building up from friction while grinding the materials, thereby making it possible to use larger powered machinery to do the grinding and manufacture larger quantities of powder per batch. Wetting the ingredients during mixing also ensured that the ingredients would form a stable grain matrix with less problems of separation. The use of waterpower to drive the machinery also reduced the cost of production of powder.

The earliest forms of making serpentine powder involved repeatedly pounding the ingredients using a mortar made of wood or stone and a pestle made of wood, which was either lifted directly by hand, or by means of a pulley system. This method required a large number of people to work on it and by the 15th century, this process was improved by using stamp mills powered by animals or water to do the job.

A stamp mill from 1686. Click on the image to enlarge
Image taken from "Teatrum Machinarum Novum" by George Andreas Bockler of Nuremberg. Public domain image.

In the early days of corning powder, manufacturers found it safer to grind the three ingredients together in a wet state. In some cases, they would crush the charcoal and sulfur together in one mortar and crush the saltpeter in another mortar, then combine the three and grind them together in a separate operation. Grinding them together ensured that the particle sizes of the three ingredients were pretty close to each other, thereby ensuring better mixing.

After the grinding was done, the mixture was pressed into sheets or cakes and dried. After that, the sheets were sent into another stamp mill, where large wooden hammers would break off the sheets into grains. The grains were then tumbled together to remove sharp edges and then passed through mesh screens to sort by various grain sizes. The grain size of the largest grains were typically about the size of a grain of corn (which is why the powder got the name "corned powder") and were used for artillery pieces. Grains of powder that were too large or very tiny were simply recycled back into the wet slurry and used to make more powder.

In our next few posts, we will study some of the machinery used from the 15th to the 19th centuries in some detail.

Saturday, July 16, 2016

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.

Wednesday, July 13, 2016

Black Powder - V: Powder Grain Sizes in 19th Century England

In our last post, we looked into how black powder grains are classified by size and type in the US, from the 19th century onwards to the present day. In today's post, we will look at the classification of different powder types in England in the 19th century.

It must be remembered that before the invention of smokeless powder in the latter part of the 19th century, people used black powder for everything from the smallest pistol to large cannon. Therefore, they had to have different types of black powder to accomodate all these weapon types. In England, smoothbore weapons were used as well as rifled weapons. For instance, the Brown Bess musket (which is a muzzle loading smoothbore weapon) was produced by the British from 1722 to about 1860 or so.

We noted a couple of posts ago, that the average size of the grains is a huge factor in the combustion rate of gunpowder. With the introduction of rifled guns, it was considered a good idea to use a powder that would burn more gradually and strain the gun less, than the powder then in use for smoothbore guns. Rifled guns do more work than smoothbores because not only do they impart a forward velocity on the projectile, they also introduce a rotational velocity to it. The weight of projectiles in a rifled gun also tends to be greater than that of a smoothbore gun of the same caliber. For example, an 8-inch rifled cannon of that era threw a projectile of weight 180 lbs., whereas the standard load for a 8-inch smooth bore cannon was a 68 lbs. ball.

For larger cannon, a powder designated as "Large Grain" or L.G. was used, until the advent of rifled cannon, at which point a powder called R.L.G (Rifled Large Grain) was introduced. This powder worked well for cannon of smaller caliber, but when guns of 7 inches and larger calibers were introduced, it was found advisable to use a slower burning powder than R.L.G, at which point, Pebble powders (P and P2) were introduced. These were larger grain powders of cubical-shaped grains. P powder grains were about 5/8 inch per side and P2 powder grains were 1.5 inch cubes. We will study the manufacture of these powders in a later post.

For small arms, a more rapidly burning powder is required, and therefore these are much smaller grains on average than the ones above. In England, there were four grades of powder produced for small arms:
  1. Fine Grain (F.G.) powder to be used by smoothbore firearms (e.g.) the Brown Bess musket. This powder was also used for the charge of 7 pounder muzzle loading cannon and for the bursting charge of shrapnel shells.
  2. Rifle Fine Grain (R.F.G.) powder, to be used by most rifled small arms, except the Martini-Henry rifle and pistols.
  3. Rifle Fine Grain 2 (R.F.G.2) powder, to be used by the Martini-Henry cartridge.
  4. Pistol powder, to be used by pistols and revolvers such as the Colt Single Action revolver and the Deane-Adams revolvers. This is a quick burning powder and is suitable for shorter barrels, where a slower burning powder would not finish burning within the barrel completely. Since it is a very quick burning powder, it was also used for shrapnel shells.
These powders were classified based on grain size and density and were separated by passing the grains of powder through sieves. Sieves are designated according to the number of divisions per linear inch. Therefore, a 4-mesh sieve has 16 holes per square inch, an 8-mesh sieve has 64 holes per square inch and so on. R.F.G. powder should pass through a 12-mesh sieve, but not through a 20-mesh sieve, and have a density of about 1.6. R.F.G.2 powder should also pass through a 12-mesh sieve, but not through a 20-mesh sieve, however the density is higher than R.F.G. powder at 1.72. F.G. powder should pass through a 16-mesh, but not through a 36-mesh, while pistol powder should pass through a 44-mesh, but not a 72-mesh. 

In addition to these powders designated for service small arms, there were also powders classed as "Blank powders", used for training purposes. As with the above powders, these were also made in different grain sizes, (e.g. Blank R.L.G., Blank R.F.G., Blank F.G. and so on). These were made from recycled gunpowder from old shells and broken ammunition boxes and only used for firing salutes and training rounds, where the full power of ammunition was not considered critical. 

The following images show the markings of barrels containing different types of powder:
The above image shows a facsimile of a barrel containing P-grade powder (i.e. Pebble powder). The markings tell us the name of the manufacturer ("Waltham Abbey"), the weight (125 lbs.), the type of powder (P, printed in red paint), the manufacturing date and lot number. The 5th line in the image is also interesting, because it tells us the brand of powder (No. 33), the total number of barrels in this brand (56) and the number of this barrel in the brand (24). All this sort of information is put on a barrel containing newly manufactured powder.

In the above three barrels, the topmost one (No. 2) is a returned powder, which was examined on May 20th 1869 and determined to be still suitable for service. The grade of this powder is Large Grain (L.G.) and the letters L.G. are marked in red. The middle barrel (No. 3) is also a returned powder, which was examined, was re-dusted and repaired for service. It is a Rifle Large Grain (RLG) powder and like the one above it, the letters RLG are painted in red. The date of re-dusting is marked as well. The bottom barrel (No. 4) is different from the other two, as it contains Large Grain Blank powder, intended for military exercises and firing blanks. This is made from powder that was extracted from broken cartridges and old cannon shells and returned powders which were found to be too dusty or broken in the grain, to be used in active service.

These barrels were shipped to filling stations where cartridges, shells etc. were manufactured. To enable tracing where a cartridge or shell was filled, each station with a lab had its own unique monogram, as the illustration below shows:

Sunday, July 10, 2016

Black Powder - IV: Powder Grain Sizes

In our last post, we saw that the size of the black powder grains are a significant factor in the rate of combustion of the powder and therefore, the pressure curve as well. In today's post, we will look at how powder grain sizes are classified in the US.

Two different grades of black powder. Click on the image to enlarge.

The above image shows two cans of black powder of different grain sizes. Notice that on the top of the can on the left, we see the letters "FFg" and for the can on the right, we see the letters "FFFFg". Modern black powder purchased in the US since about the late 19th century, has been labeled with a combination of the letters F and g, for example Fg, FFg, FFFg etc. These indicate different grain sizes of powder and we'll see what this all means in a minute. The same grade is sometimes referred to by different names. For instance: "FFFg" grade is sometimes referred to as "3Fg", "3F", "FFF" etc.

The last letter of the black powder name indicates the grade of powder. Usually, for firearms applications, this last letter is always 'g'. But this is not the only grade of powder: there are two grades in use:

  1. "A" or "blasting grade" powder - the preferred powder of choice for fireworks manufacture.
  2. "g" or "sporting grade" powder - preferred for firearms use.
The primary difference between the 'A' and 'g' grades is in the manufacturing process. Both are manufactured in the same way initially, but at the end, the 'g' grade powders are polished in a tumbler with a tiny amount of graphite, to polish the grains and make them flow easily. The 'A' grade powders are not usually tumbled, and if they are tumbled, it is just for a short amount of time to remove any sharp edges. For purchasing the A-grade powder, the user will need to have a BATFE (Bureau of Alcohol, Tobacco, Firearms and Explosives) license and a BATFE-legal magazine to store the powder. Usually that is why it is not commonly seen in sporting goods stores and such. The g-grade is not subject to the same restrictions and is therefore available in gun stores and online shops (only need a BATFE license if purchasing more than 50 lbs. of g-grade powder). Notice that the two cans of black powder in the image above both end with the letter 'g' (One is labeled "FFg" and the other, "FFFFg"), which shows that these are intended mainly for firearms use.

Now on to the mystery behind the letter 'F'. The letter 'F' stands for "Fine" and dates back to the time when the grains were designated F or C (for "coarse" grains). The number of times the letter F occurs in the powder grade shows the average size of the powder grains. The more times the letter F occurs in the name, the smaller the grains. What this means is that the size of "FFFg" grains are smaller than "FFg" grains, and "FFFFg" is even smaller than these two. When black powder is manufactured, the grains are sorted through sieves of standard sizes and classified that way.

Powder Grade Mesh Size Average Size in mm.
Whaling4 mesh4.750 mm. (0.187 in.)
Cannon6 mesh3.35 mm. (0.132 in.)
Saluting (A-1)10 mesh2.0 mm. (0.079 in.)
Fg12 mesh1.7 mm. (0.0661 in.)
FFg16 mesh1.18 mm. (0.0469 in.)
FFFg20 mesh0.85 mm. (0.0331 in.)
FFFFg40 mesh0.47 mm.
FFFFFg75 mesh0.149 mm.

Note that the first 3 grades are intended for use with cannon. The A-1 grade is generally used for artillery blanks used for firing gun salutes. Fg is made for using in large bore rifles and shotguns (8-gauge and larger). FFg powder is used for historical small arms such as muskets, fusils, rifles and large pistols. FFFg powder is for smaller caliber rifles (below .45 caliber), pistols, cap-and-ball revolvers, derringers etc. FFFFg and FFFFFg are mostly used as priming powder for flintlocks. In the image above, the two grades of powder were intended to be used in a historical re-enactment and the FFg powder was meant for the main powder charge of a flintlock rifle, while the FFFFg powder was intended to be used in the pan of the flintlock as a priming powder.

Similarly, the A-grade powders are classified into various grain size ranges (FA, FFA, FFFA, FFFFA, FFFFFA, FFFFFFA, FFFFFFFA, Meal-D and Meal-F (Meal Fine) and Meal XF (Meal Extra-Fine)). However, since these A-grade powders are intended for fireworks and quarries, we will not study them here.

In our next post, we will study the grain size classifications that were used in the UK in the 19th century.

Wednesday, July 6, 2016

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.

Friday, July 1, 2016

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 matchlockswheel locksflintlockspercussion 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.