Thursday, October 20, 2016

Black Powder Substitutes - I

A few posts earlier, we saw a mention of something called "black powder substitute". We will study more about this topic in today's post.

As we saw in several posts on the topic of black powders, it is a mixture that was used as a propellant for hundreds of years. Some of the problems with using black powder include

  1. Ignites very easily and burns rapidly, which can cause accidents.
  2. Produces a sulfur smell and a lot of residue after burning.
  3. It is hygroscopic and can absorb water from the atmosphere, which causes the powder to degrade.
  4. Needs careful handling and storage to prevent accidents.
  5. Is generally corrosive in nature, which means that firearms need to be cleaned thoroughly after use.
In addition to all the above reasons, black powder also burns less efficiently than modern smokeless powders, which is why most modern firearms use smokeless powders. However, there are still quite a few black powder enthusiasts, who like to use firearms (or replica firearms) that their ancestors used in the past. Due to the unsafe nature of black powder, many areas have special regulations concerning the storage, sale and use of black powder, which makes it hard for people to buy it. This is where black powder substitutes come in.

The most common black powder substitute in use today is called "Pyrodex", which was invented by the Hodgdon Powder Company in 1975.

Pyrodex Powder. Click on the image to enlarge. Public domain image. 

Ordinary black powder can easily be ignited by impact forces, sparks or static electricity, which makes manufacturing and storing it more dangerous. In fact, the last factory manufacturing ordinary black powder in the US was closed in 1970 after an accidental explosion and new regulations came out that made many retailers reluctant to sell black powder any more. In 1975, the Hodgdon Powder Company invented the first black powder substitute: pyrodex.

Ordinary black powder consists of  just saltpeter (potassium nitrate), sulfur and charcoal (carbon). Pyrodex also has these three ingredients, but also contains graphite, potassium perchlorate and some other proprietary ingredients. These additional ingredients make the properties of pyrodex behave more like a smokeless powder and therefore, it is not subject to the same strict regulations of black powder. This means that pyrodex doesn't ignite as easily as black powder and can be stored and transported just like a smokeless powder, which is why many retailers sell it.

Pyrodex is actually about 27.5% less dense than ordinary black powder and is more efficient than it. So how does the substitution work then? Well, when measuring ordinary black powder for muzzleloading weapons, people have always specified powder loads by weight (e.g. grains in the US, grams in most other countries), but they have usually measured it out by volume. What this means is that if a muzzleloading rifle takes (say) 100 grains of black powder as a load, the user doesn't usually actually weigh out 100 grains of powder to load into the rifle. Instead the user has a powder measuring tube, which he (or she) fills with black powder and pours that into the rifle. If the user measures the weight of the black powder from the measuring tube, it will indeed weigh 100 grains (or something close to it). When using pyrodex, the user can use the same measuring tube to measure out a quantity of pyrodex. If the user weighs the contents of the measuring tube, it will weigh around 72.5 grains, since pyrodex is less dense than black powder. However, this 72.5 grains of pyrodex burns with about the same propulsive force as 100 grains of black powder, since pyrodex is a more efficient propellant. Therefore, if the user uses the same measuring tube to measure black powder or pyrodex, one can easily be substituted for the other, without affecting the pressures generated in the rifle. This makes pyrodex a "volume equivalent powder". 

It must be remembered that muzzleloading weapons are commonly loaded by volume using measuring tubes, this works out great when using a volume equivalent powder like pyrodex. However, black powder cartridges are loaded by weight. Therefore, if using pyrodex instead of black powder to load a cartridge, the user must actually load a lesser weight of pyrodex to retain the same amount of propulsive force. 

Pyrodex powder has a similar burning sulfur smell as black powder and is also very corrosive in nature and produces about the same amount of fouling as ordinary black powder. Therefore, users need to perform the same cleaning procedures as when using normal black powder. However, since pyrodex is less susceptible to ignition, it is subject to the same regulations as smokeless powder, instead of the the much stricter regulations of black powder. 

Pyrodex is normally sold in a few grain sizes: Pyrodex RS (Rifle/Shotgun), which is volume equivalent to FFg grain size black powder, and Pyrodex P (Pistol) powder, which is volume equivalent to FFFg grain size black powder. There is also Pyrodex "Select" powder, which is the largest grain size of all and is marketed as an "extremely consistent" grade of pyrodex, meant for muzzleloading rifles. 63.9 grains of Pyrodex "Select" powder have the same volume as 100 grains of black powder.

These days, pyrodex is also sold in pellet form, such as the image below:

Pyrodex pellets. Click on the image to enlarge. 

With this type of pyrodex, the user doesn't have to use a measuring tube to measure out the powder, since the pellets are all of a certain specific size. Instead the user simply takes a pellet or two and loads it directly into the firearm.   

We will study more about black powder substitutes in the next few posts.

Sunday, October 2, 2016

Black Powder Factories - II

In our last post, we studied how early gunpowder factories were often located in the middle of towns in the early days of firearms. Of course, placing a factory within your town walls made sense if you wanted to defend your town walls against attack, but there was the problem of accidents in the factory setting the town on fire. Towards the beginning of the nineteenth century, people began to think more about factory safety and several laws were passed specifying how far away a gunpowder factory could be away from people's houses and how much powder could be worked inside one building and so on. In today's post, we will study how one such factory was set up in the 1860s. Today's object of study will be the Confederate Powder Works.

A view of the remaining chimney of the Confederate Powder Works in Augusta, Georgia
Click on the image to enlarge.

Not much remains of the Confederate Powder Works these days, except for one 150-foot tall chimney, but in its day, it was a massive factory complex laid out over two miles in length and was the second largest gunpowder factory in the world then.

During the days leading up to the Civil War, the Confederate states did not have any significant gunpowder manufacturing facilties, except for a small mill in Tennessee. On July 10th, 1861, Confederate President Jefferson Davis authorized Major George Washington Rains to build whatever was necessary to keep the Confederate armies supplied with gunpowder.

Colonel George.W. Rains. Click on the image to enlarge.
This photograph was taken during the Civil War and is currently in the Augusta Museum of History.

Major Rains spent the next few days living in a railroad car, examining various places for a suitable location for a factory. On July 20th, he selected an area in Augusta, Georgia to be the site of the future factory. The reasons for picking this area for the new factory were several:

  1. It was centrally located and near the junction of some major railroads.
  2. The area was near enough to a big town (Augusta) to provide sufficient workers and materials.
  3. It was far enough from the front-lines that Union forces could not easily attack it.
  4. The Augusta canal and the Savannah river could also be used to transport over water.
  5. The Augusta canal was also a source of water power, which is useful to drive factory machinery.
  6. The area has temperate weather, which means the water supply does not generally freeze during the winter months, thereby ensuring unlimited water power during the whole year.
  7. Since he also intended to produce pure potassium nitrate (saltpeter) in the factory, he also needed abundance of water to wash and refine the minerals.
  8. The canal could also be used to transport supplies and materials from one factory building to the next. 
However, Rains had a few big problems: First, he had no idea about how to build a gunpowder factory, having never been inside one before! Luckily, he came across a book authored by a Major Fraser Baddeley of the Royal Artillery in England, called "Manufacture of Gunpowder as carried out at the Government Factory, Waltham Abbey", that described the entire process and machinery used by the Royal Gunpowder Factory at the Waltham Abbey works in Essex, England. While the book had the descriptions, there were no drawings or plans of the buildings or machines, therefore he had to research on his own to figure these out. Luckily for him, he happened to find an Englishman named Frederick Wright, who had moved to the Southern states and had worked at Waltham Abbey previously, so he asked him for assistance and produced some detailed word descriptions and preliminary sketches. 

The next problem was to find an experienced architect to build the plant while he was occupied with other duties for supplying the existing armies in the field. He hired a couple of young civil engineers/architects, Miller Grant and Charles Shaler Smith to do the job. Construction of the first building started in September 1861. By the time the factory was in full operation, 26 separate buildings were constructed over 140 acres of land that extended almost two miles along the banks of the canal.

The buildings were constructed along the canal, coinciding with the process of making black powder (i.e.) the warehouses to store the raw materials were located first in line, the refinery to refine saltpeter was next and so on, until the final building at the end of the complex, which was used to store the finished gunpowder. The canal was used to transport materials from one building to the next, much like a modern assembly line. The most important buildings were built first: the Refinery, the Incorporating mills, the Mixing house, the Granulating house, the Pressing house and the Drying house and the Boiler house. Other buildings include a blacksmith's house, the stables, a carriage house, a laboratory etc. We will discuss the construction and use of these buildings in the next post or two. The refinery building in particular, was very beautiful to look at, being constructed in a Gothic revival style, influenced by the Smithsonian Institution in Washington DC and the British Houses of Parliament. The chimney in front of the refinery was shaped like an obelisk and is the only structure that survives today, located at 1717 Goodrich Street in Augusta. The buildings were separated from each other and designed to survive explosions, in accordance with the safety procedures used in other gunpowder factories in the 19th century.

The first gunpowder in the factory was made on April 13th, 1862; just nine months after Rains had been authorized to build the factory and construction of new buildings continued as the factory expanded. The factory remained in operation until the surrender of the South during the end of April 1865, which means it remained in operation for a little over three years. During this time, it managed to produce approximately 2,750,000 pounds of gunpowder at an average rate of around 7,000 pounds a day. In addition to this, the factory also produced other war material, such as time fuses, artillery pieces, wagons etc. Due to his efforts in building the factory, Major Rains was promoted to a full colonel by the end of the war.

After the Civil war ended, the factory fell into ruin. In 1872, a project to widen the Augusta canal resulted in most of the buildings to be destroyed, leaving only the tall chimney that can still be seen today. The chimney was spared, at the request of Colonel Rains, as a memorial to those who died in the Southern armies during the Civil war.

A view of the chimney as it exists today, courtesy the Augusta Historical Society.
Click on the image to enlarge. 

In 1880, a new mill was constructed in the old powder works area, called the Sibley cotton mill owned by the Sibley family. Bricks from the demolished buildings were used to construct the new mill and it was built with the appearance of a medieval castle or fortress, similar to the powder works buildings that it replaced.  The cotton mill was very successful and remained in operation until around 2006, making denim cloth for major clothing manufacturers. While the mill production has ended, the water-driven turbines still remain in operation and generate electricity that is sold to Georgia Power even today. 

Monday, September 26, 2016

Black Powder Factories - I

In the previous several posts, we have studied several aspects of black powder manufacturing. But what about the factories themselves? In the next few posts, we will study the layouts and processes used in the factories.

Curious though it may seem, even though people knew that black powder was potentially explosive from the earliest days, it was made for a considerable time within towns, probably because towns were often under siege and needed the factory to be inside to supply the gunpowder for the guns mounted on the town walls. Of course, there were accidents: For instance, in 1360, it is recorded that the town-hall of Lubeck, one of the largest and richest cities in the Hanseatic league (now in Northern Germany) was burned to the ground, thanks to the carelessness of the gunpowder makers of that town. In 1528, the town leaders of Breslau finally issued a law prohibiting manufacturing gunpowder within the town. In 1490, Venice passed a law to move gunpowder manufacture from the city center to the Venetian Arsenal (which was not in the city center, but pretty darn close to it), but many of its other factories (such as in Padua, Treviso, Verona, Brescia etc.) were located practically at the center of town. It took a major fire at the Venetian Arsenal in 1569, which forced the Council of Ten to pass a law to make both gunpowder manufacturing and storage outside the urban area of Venice. The new site was the small island of Sant'Angelo di Concordia (later renamed to Sant'Angelo della Polvere because of the gunpowder factory), which was located to the south-west of the main islands of Venice.

The Island of Sant'Angelo della Polvere in the Venetian lagoon.
Click on the image to enlarge. Image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license by Maurice Ohana

However, Venice was more of an anomaly because it had a strong navy and didn't need city walls because of protection by the sea. Most towns still continued to locate their gunpowder factories within their walls. And if the factories were located outside the heavily populated areas, the buildings were often located haphazardly.

It was only in the nineteenth century that regulations governing factory safety went into place in many countries. Laws were passed specifying the distance of the factory buildings from citizens' houses and from each other and also how much quantity of ingredients or powder may be worked on at a time in each building, materials to be used to construct the buildings and so on.

Since powder factories need a considerable amount of machinery to pulverize, mix and combine powder ingredients, they were generally erected in places where a large amount of water power is available, such as a fast flowing river or canal. In places where water power could not be reasonably applied, animal power (e.g. oxen, horses etc.) was used instead. For instance, we know that horses were used in Venice because various records of purchases of horses and hay for the Venetian powder factories from 1560-1570 have survived. Later on, when the steam engine was perfected in the 1760s by James Watt (although it was invented and worked on by other people many years before, James Watt made it much more practical for factory use), some gunpowder factories began to use steam power to drive their machinery, which made it possible to locate the factory away from flowing water.

Where water power was used, the machinery required for a particular operation were arranged in pairs, so that there would be one machine on the left side and the other on the right side. The water wheel would be located at the center, or individual wheels would be placed on each side and the water routed via canals to either side. Power would be transmitted from the wheel to the machine using gears and gear shafts. In some cases, a large water wheel would transmit its power to various buildings using wire ropes and chain arrangements.

Animal power was used where water power was not readily available, but the machines in these factories were smaller. Running costs were higher because not only did the machines require repairs and greasing, but the factory also had to pay for the animals, their food, their stables and the people who were caring for those animals.

When steam power was used, there were two methods to transmit the power. The first method consisted of installing a large steam engine located centrally, which produced all the power required and this was transmitted to the various buildings using wire ropes. In this case, the steam engine was located in a central building and the other buildings were arranged in a circle around it, as was done in France in the factory at Sevran-Livry in Paris. The other option was that steam was produced in a large boiler plant and the steam was transported via an arrangement of pipes into the various buildings, where it was fed into smaller steam engines. With this method, the fire that produced the steam was kept away from the buildings containing the steam engines.

Water wheels are somewhat low in efficiency compared to other types of power, but they are very cheap to build and running costs are very low, with only application of grease and repairs to be done periodically, the water (which is the source of power) generally costing nothing. The technology of water wheels was well understood for many centuries, being used by the Egyptians, Greeks, Romans, Chinese, Indians, Arabs, Medieval Europe etc. The only thing to watch out for is floods and droughts, which could either wreck the factory or cause it to stop functioning. However, because of the low costs, water wheels were used anywhere that water power was readily available, and were competitive with steam engines well into the Industrial revolution.

Steam engines are higher in efficiency compared to water power and could be used as long as there was an adequate supply of fuel and water. Transmitting the power from a central engine to various buildings via wire ropes was fine over shorter distances, however the power losses can be considerable over larger distances. There is also much more lubrication needed for the ropes and pulleys and in case a rope breaks, a whole section of a factory could stop functioning. Therefore, many factories got around this by using a system of insulated pipes to transmit the steam to smaller steam engines located inside each building. Of course, the pipes had to be checked to ensure that they were not leaking steam and over-pressurization could cause pipes to break and stop work immediately, but using a system of smaller pipes and valves solved this issue somewhat because the valve of one pipe could be shut down for maintenance, while another parallel pipe or two could continue to carry steam to the machine while the first pipe was being examined and repaired and so on.

Thursday, September 22, 2016

Brown or Cocoa Powder

In the last several posts, we've studied about the development of black powder. In today's post, we will study another type of powder that was briefly used in the 19th century, which was called brown powder or cocoa powder on account of its color.

The purpose of cocoa powder was to make a powder that would burn at a slower rate than black powder, for use in large artillery guns and ship cannons. It was similar to black powder, but it could be used in larger guns than what black prismatic powder was used for.

Around 1880, a company called Rottweil Pulverfabrik (translation: "Rottweil Powder Factory") from the town of Rottweil, Germany invented a new form of powder that used a different type of charcoal that was reddish-brown in color. In case readers are wondering, yes, Rottweil is also the town where the Rottweiler breed of dog was developed.

View over a part of the Rottweil Powder Factory in 2014.
Click on the image to enlarge. Image licensed under the Creative Commons Share-Alike Attribution Version 3.0 license by Andreas Koenig.

This powder had a different composition than black powder, consisting of 79% niter, 3% sulfur and 18% charcoal (whereas most black powders of that era were around 75% niter, 10% sulfur and 15% charcoal) and also contained about 1-2% moisture. The charcoal for this powder was also made in a different manner. We've studied how charcoal was manufactured for black powder earlier. Brown or red charcoal is a charcoal that is made by under-burning organic material. The material used for producing this charcoal was rye straw. The straw was piled into large stacks and stored in open air for long periods of time, the stalks being large and thick, with the ears of rye removed from it. Then, the straw was placed in large wrought-iron chambers and superheated steam was pumped over the straw for several hours. The temperature of the superheated steam was carefully controlled. The superheated steam would dissolve most of the extractive matter from the straw, but would not char it fully and the result was a charcoal of a reddish or brown color (in French, this was called charbon roux). We studied about this charcoal production process using steam earlier.

These ingredients were then mixed together and compressed into hexagonal prisms with a central hole, using the production methods used for prismatic powder that we studied earlier. This brown powder burned at a slower rate than black powder, and for equal muzzle velocities of the projectile, it produced less pressures inside the bore of the gun than black powder, and also produced less smoke than black powder as well. The more gradual development of pressure and reduction of the maximum pressure produced increased the life of the barrel and made it possible to develop lighter cannon.

The Germans adopted cocoa powder for their military in 1880. In 1884, the British Royal Navy decided to use cocoa powder for their ship guns and they bought their supplies from Rottweil Pulverfabrik. Soon after this, the French Navy also started using cocoa powder, but they developed their own version called Slow Burning Cocoa (SBC) powder around 1887. It was so successful for use in larger guns that it was sought by other militaries around the world as well. In England, they began to substitute charcoal made from rye straw with red charcoal made from wood and carbohydrates (such as sugar), to keep up with demand.

However, this powder did not burn all that cleanly (one test showed that about 43% of the powder was burned, the remainder formed large clouds of smoke) and it also left deposits in the bore. Therefore, when smokeless powders, such as the French Poudre B and the British Cordite powder were developed, brown powders became obsolete shortly after.

Saturday, September 17, 2016

Black Powder XXV - Pellet Powder

In our last few posts, we saw some developments in compressed black powder technology, prismatic powders and pebble powders. In today's post, we will study another type of compressed powder called pellet powder, which was invented in the 19th century.

Pellet powder was a large grain powder designed to be used in larger guns. In our above example, each pellet is a formed cylinder of black powder about 1.25 inches in diameter with a hole in the center.

Sir John Anderson of Woolwich arsenal in England invented a machine in the 19th century for their manufacture, the details of which are below:

A machine for making pellet powder invented by Sir John Anderson. Click on the image to enlarge. Public domain image.

It consists of a disk of about 6 feet diameter (the pressing table) which revolves about one of the columns. The disk has teeth all around its circumference, which allows it to be rotated by means of a pinion and handle mechanism. The disk has four round metal plates placed symmetrically, about 2 inches thick and 1.5 feet in diameter. In each metal plate are drilled about 200 cylindrical holes of about 5/8 inch diameter. Above each plate is a movable covering-plate which can be pressed tightly against it, and into each of these 200 holes a small plunger enters, which goes through the bottom part of the disk and can be lifted from below by a hydraulic press.

Two opposite plates are always pressed at the same time. As soon as the movable plates are lifted, the molds are filled with meal powder, the plates are cleaned and excess powder wiped off, and the movable plates lowered and fixed so that they close the holes on the top. Then the plungers are pressed into the molds, causing the layer of powder to be compressed to 5/8 inches in height. After this, the movable plates are lifted and the plungers are pushed further into the holes, thereby pushing the formed pellets out of the mold holes.

Click on the image to enlarge. Public domain image.

After the pellets are pushed out, the disk is then rotated for a quarter turn and the pellets are taken off the two mold-plates. Meanwhile the same operation is then carried out with the other two plates.

The pressure applied to the powder by this machine is about 0.5 tons per square inch. The pellet formed is shaped like a cylinder with one or both bases having a hollow in the middle in the shape of a blunt cone. The size of the pellets made by this machine are 5/8 inch diameter, 5/8 inch height and depth of the hole is 1/4 inch and each pellet weighs about 100 grains.

In America, the Du Pont powder company made a hexagonal pressed pellet powder, which looks like two truncated hexagonal pyramids connected by a cylindrical layer of powder.

Du Pont Powder. Public domain image.

This powder was made by the following process: A lower plate in which a number of pyramidal holes were cut was covered with powder and a second similar plate was laid over it and then pressure was applied. Depending on the thickness of the layer of powder, the cylindrical part connecting the two pyramidal halves will be thicker or thinner. After pressing, the cake is broken, this causing the grains to break off on the edges of the cylindrical part.

In Italy, they made compressed pellets in cubical form, sold under the brand name "Fossano Powder", because it was first manufactured in a gunpowder factory at the town of Fossano in northern Italy. Fossano powder is a type of "Progressive Powder" and was invented by Colonel Quaglia (the factory director) and his assistant, Captain de Maria.

Fossano Powder. Public domain image.

The manufacture of Fossano powder was done in multiple stages. In the beginning stage, meal powder was pressed into cakes of density about 1.79. Each cake was then broken up into irregular grains of about 1/8 to 1/4 inch in thickness. Then grains were then mixed again with a certain quantity of meal powder and then pressed into cakes again, with a density of 1.776. This second cake was then broken up into cubes. Therefore, each cube would be composed of powder pieces of higher density enclosed in a powder material of lower density, sort of like raisins inside a plum-pudding. The idea behind this was that due to the differing densities of powder, more gas would be produced after the powder has been partially burnt, than at the start of ignition of the powder, leading to the 'progressiveness' of the explosion (which is why it is called a "progressive powder"). This allows the pressure on the projectile to be maintained during its course in the bore and possibly increased while it is moving away.

Pellet powders burn slower than other ordinary large grained powders due to their larger grain sizes and is therefore less violent in action. Experiments in England showed that these could produce muzzle velocity greater than ordinary large-grained powder with peak pressure hitting about half that of large-grained powder.

Pellets are still available today for black powder enthusiasts:

Pyrodex 50/50 grain pellets/

Click on the image to enlarge.

Click on the image to enlarge

The above images show modern pellets available today in many sporting goods stores. However, these are made of black powder substitute, not original black powder. Black powder substitute is less sensitive to ignition than real black powder and is more energetic.

Saturday, September 10, 2016

Black Powder XXIV - Pebble Powders

A couple of posts ago, we saw why larger grain black powders were more suitable for larger guns and artillery, and studied two powders that were developed to handle this: compressed powder and prismatic powder. In today's post, we will study another type of black powder designed for larger calibers, which was in use in the 19th century. Today's object of study will be pebble powders.

Pebble powders were generally made in two grades: the P type (which were cubes of approximately 1/2 to 5/8 inches in size) and the P2 type (which were 1.5 inch cubes).

The process of manufacturing pebble powders started off similar to manufacturing other finer grain powders, until the process of pressing the powder into cakes. The pressed cakes were formed into slabs of about 15 inches x 30 inches and thickness depending on whether P type or P2 type was being made (i.e. 1/2, 5/8 or 1.5 inches).

For P type powders, the pressed cake slabs were then fed into a cutting machine:

A cutting machine for manufacturing P type pebble powders. Click on the image to enlarge. Public domain image.

The exploded view of the machine above was invented by a Major Morgan and was in use at the Royal Gunpowder Mill in Waltham Abbey, England. It consists of two pairs of phosphor-bronze rollers which are at right angles to each other and at different heights. Each roller has knives attached to its circumference, with spaces between the knives corresponding to the required size of the powder cubes. The pressed cake enters the first pair of rollers and is cut into long thin strips and these strips then fall on to a conveyor belt which carries them to the second pair of rollers, which are at right angles to the first pair. The second pair of rollers cut the long strips into cubes.

It may be seen that if a first pair of rollers were fixed, then the second long strip cut would fall onto the first and the third one on to the second and so on and the result would be long strips piling up in one location on the lower conveyor belt. To avoid this, the upper pair of rollers are mounted on a board which is arranged to move back and forth, the basic mechanism of which is shown below.

The bottom of the board has a fixed slotted bar. The chain has a pin on one of its links that engages the slotted bar. As the chain moves along its two rollers, it pulls the board above it in a back and forth motion. This results in the long strips cut from the first set of rollers falling side by side instead of one above the other.

For P2 type powders, the cubes were generally cut by hand, by using lever-knives (i.e.) knives hinged at one end, with an handle at the other, much like a modern day paper trimmer. The press cakes were cut into long strips and then cut across into cubes.

After this, both P and P2 type powders were sent through a glazing and dusting process, to ensure that edges and corners of the cubes were rounded off and sharp edges removed. This ensured that the cubes would have a harder surface and would not produce dust or waste when being stored or transported around.

The powder was then dried similar to the process of drying the smaller grain powders, except that the temperature of drying was lower and the drying period was correspondingly longer. The drying process was slower to avoid forming cracks on the cubes. After this, a finishing process followed, with the powder being run in wooden barrels, which combined sifting the powder along with a finish glaze. A small quantity of graphite powder was introduced into the finishing barrels to give the grains a glossy finish and render them less hygroscopic.

In our next post, we will look at pellet powders.

Monday, September 5, 2016

Black Powder XXIII - Prismatic Powder

In our last post, we studied the invention of compressed black powder by General Thomas Rodman of the US Army. While this idea had sound theoretical fundamentals and also could be demonstrated successfully in trials, there were some practical difficulties encountered when manufacturing this powder in bulk and deploying the compressed powder cakes in the field. The main issues were that it was hard to press such large, heavy cakes of powder in the presses of the time and the large perforated cakes of powder also had structural integrity problems and tended to break up into smaller grains during transport, or while being handled in a battlefield.

A solution to this problem was proposed by another American, Professor Robert Ogden Doremus, a professor of chemistry, and a co-founder of New York Medical College.

Robert Ogden Doremus. Click on the image to enlarge. Public domain image.

Doremus' idea was that instead of pressing together a large cake of powder equal to the bore of the cannon, he suggested manufacturing them into hexagonal prisms of a smaller size, with comparatively smaller holes running through them. This powder was called prismatic powder.

The number of holes in each prism could be less in number (usually between 1 and 7) and these could be stacked together to form a rigid cartridge, much less liable to break up during manufacturing and transport. Due to their smaller sizes, it was easier to manufacture a number of smaller hexagonal cakes, rather than one large cake weighing several pounds in weight.

Another idea also due to Professor Doremus was to make different sections of a cartridge with different densities of powder, whereby the density would affect the rate of combustion and maintain a higher average pressure. The idea was to pack the first part of the cartridge under high pressure, then make two more layers on the same cartridge under lower pressures.

During the Civil War, a Russian military commission visited the United States and were greatly impressed by the results shown by Doremus' prismatic powder and undertook to develop and use prismatic powder in their large guns as well. Doremus also visited Paris and impressed the French with his new powder and was authorized by the French ministry of war to modify the machinery at a French powder factory to produce his prismatic powder. In fact, a large portion of the Frejus Rail Tunnel between France and Italy was blasted away with "la poudre comprimée". Pretty soon, many European countries (Italy, Germany, France, UK etc.) started to manufacture prismatic powder as well.

The cakes were generally made from granulated powder, which was then compressed under pressure, either using a press driven by gears, cams and pistons, or by a press driven by hydraulic pressure.

A cam-press for making prismatic powder.
This press was built by the Grunsonwerk of Buckau, Germany. 
Click on the image to enlarge. Public domain image.

A hydraulic press for making prismatic powder.
This press was manufactured by Taylor and Challen of Birmingham for the Royal Gunpowder Factory, Waltham Abbey, England
Click on the image to enlarge. Public domain image,

To make this powder, granulated powder containing about 4% moisture was put into the hopper of the press. The more moist the powder, the easier it is to press it into shape, but the powder can't be too moist, otherwise the saltpeter will migrate to the powder's surface while drying. The powder was filled into several molds, the height of which was adjusted depending on the moisture content of the powder and the moisture content in the air that day. Then, the press was activated and pressure was applied to the powder in the molds, to form prisms of the required shape and size. The sizes and densities of the prisms varied by country. For instance, in England, the prisms were about 1.5 inches high and had a desnity of 1.78, whereas in Germany, the prisms were about 1 inch high and 1.575 inches over the angles, with the weight being about 1.41 ounces and density of 1.66. Hydraulic presses were generally used in England, Germany and France towards the latter part of the nineteenth century, but cam-presses were still in use in some parts.

After pressing, the prisms were dried in special drying-houses using trays. The trays were made of narrow wooden strips, with enough gaps between them to let air pass through, but not big enough to let the powder fall through. At Waltham Abbey, the drying process was done slowly for 140 hours and the dried powder contained less than 1% moisture. At Spandau, Germany, they would dry the powder at a faster rate by using air at a temperature of 122 °F for about 48 hours, after which the powder would contain less than 0.75% moisture.

In our next post, we will look into another type of powder called "pebble powder", which was manufactured in the 19th century.