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.

Friday, September 2, 2016

Black Powder XXII - Compressed Powder

In today's post, we will look at a form of powder that was used during the Civil War, called compressed powder. The origin of this powder has to do with larger guns rather than firearms, but is still an interesting point of study, since it leads down to prismatic and pebble powders later down the line.

General Thomas J. Rodman. Public domain image.

The first breakthrough into compressed powders was due to a career US Army officer named Thomas Jackson Rodman. He was an inventive man with an interest in artillery, and early in his career, he was appointed as a brevet second lieutenant in the US Army Ordnance Department, where he started working at improving cannons.

At around 1856, he noted that ordinary service powder could not be used in larger guns, because the initial gas pressure developed was sometimes high enough to cause the gun to be destroyed. The range of the gun was also reduced. The reasons are as follows:

If a fine grained powder is used for a large gun, a large portion of it is burned at the moment of ignition, due to its larger surface area (remember that black powder is surface burning and the larger the outer surface area of the powder, the faster it burns). Therefore, this causes a very high maximum pressure to be generated at the beginning and then tapers off as the rest of the powder burns, which leads to a lower average force, compared to the initial force. In fact, the initial pressure may be high enough to cause the cannon to explode with disastrous results. Therefore, the rate of combustion of the gunpowder had to be reduced somehow.

Rodman found from his experiments that he could considerably reduce this initial pressure in the gun by using disks of compressed powder, perforated by holes. The disks were made of a diameter equal to that of the bore of the cannon and between 1 and 2 inches in thickness and perforated with a number of holes.

With this type of powder, the surface area of the powder is smaller initially and only develops enough pressure to overcome the inertia of the cannon ball. Consequently, the projectile properly engages the rifling and gets pushed out with a regular motion, which is very important because accuracy depends on uniform movement of the projectile in the barrel

Surface area comparison of ordinary powder (green) vs. Rodman's compressed powder (red cylinder). Click on the image to enlarge. Public domain image.

As the powder burns more, the surface area exposed increases due to the constant enlargement of the holes bored through the compressed powder. Due to the constant increase of the area of the burning surface, this causes a corresponding constant increase in the rate of production of the burning gases. This results in a longer and more consistent burn time inside the bore of the barrel. Therefore, the average pressure generated is higher and this increases the range of the gun significantly, without making the pressure rise to dangerous levels initially.

Rodman first published his discoveries in a scientific paper in 1861 ("Properties of Metals for Cannon and Qualities of Cannon Powder") and his ideas were put into practice in the Civil War. His special compressed powder was produced under the name "mammoth powder" and other inventors also benefited from his breakthrough, as we'll see in our next few posts.

As a result of his work, Rodman was promoted to brevet brigadier general at the end of the Civil War. He remained in the military for the rest of his life, being promoted to the permanent rank of lieutenant colonel in the US Army. Incidentally, in 1865, he was sent to Rock Island, Illinois and put in charge of supervising the construction of a new military facility, which became the Rock Island Arsenal, which still exists and is one of the largest government-owned weapons manufacturing factories in the United States.

Tuesday, August 30, 2016

Black Powder XXI - Damaged Powder

In our last post, we saw how black powder that had absorbed some moisture in the field, could be reworked to become useful again. However, this reworking process only worked if the black powder had absorbed a smaller amount of moisture from the air (< 7% by weight). Unfortunately there were situations where the powder could absorb a lot more than this. In today's post, we will discuss what they did with the powder in the 19th century when this happened.

Remember that black powder was not always stored indoors in a warehouse under dry conditions. It may have been transported in the cargo compartment of a ship, or perhaps it was shipped by cart to some distant battlefield. There were plenty of situations where the barrels could have been exposed to a lot of water (e.g.) water frequently seeped into cargo compartments inside the ships and had to be periodically pumped out, carts could be driven through thunderstorms, the barrels could have been frequently opened and closed in wet conditions in the field etc. In such situations, the barrels could absorb a lot more moisture than 7% by weight and the powder was considered damaged. Armies and Navies would typically send this damaged powder back to the factory, where they would deal with it.

At the factory, they would first figure out how much moisture the powder contained, using the method we studied in our previous post. If it was well below 7% by weight, it could be dried and recovered, as we pointed out in our previous post. Another technique was to take a small amount of the damaged powder and mix it with a barrel of newly manufactured powder, so that the overall moisture content of this mixed powder was within tolerable limits. For instance, the mix could consist of about 10% damaged powder and 90% new powder and would have pretty much the same propulsive force.

However if the powder was too badly damaged by moisture, then they would usually try to recover the potassium nitrate from the mixture, as it was the most valuable ingredient. Remember that saltpeter (the source of nitrates) was a hard-to-obtain substance for many centuries and England controlled the source of most of the world's supply for decades. Therefore, many countries found it worthwhile to try and extract as much nitrate as possible from the damaged powder. For instance, in the Confederate States, they had a Damaged Powder Works in Augusta, Georgia, to which all damaged powder from the field was sent to.

At the Damaged Powder Works, they would empty 8 barrels (800 lbs.) of powder into a large copper vessel and then add about 200-240 gallons of water. The vessel was then heated until its contents began to boil. The boiling water would dissolve the potassium nitrates in the powder, while the sulfur and charcoal remained undissolved. After this, the hot water was pumped out of the vessel through a double filter arrangement and poured into shallow crystallizing pans, where the liquid would cool and form nitrate crystals. The crystallizing pans would be shaken while the liquid was cooling, so that the nitrate crystals formed would be of small size. Since charcoal and sulfur don't dissolve in water, they remain behind in the vessel and filters. This method could recover over 95% of the nitrate content in the damaged powder. The recovered nitrate crystals were then sent back to the gunpowder factory to be used to make black powder again.

In the case of lightly damaged powders, the Damaged Powder Works often reworked it to make blasting powder, which is a low-grade black powder with a lower percentage of niter and more dust. To do this, they would take the damaged powder and add more sulfur and charcoal, so that the percentage of niter was reduced. The mixture would then be incorporated for a short time and then granulated to form blasting powder.

The Damaged Powder Works not only recovered nitrates from damaged powder, they also tried to recover it from byproducts of the manufacturing process as well, since niter was such a precious substance. They would try to recover saltpeter from the sacks that it was shipped in, from sweepings from the factory floor of the powder mill and even from washing the workers' clothes. The remnants of the mother liquor from the niter refineries were also sent over, so that they could extract the last possible bit of nitrates from there.

Monday, August 29, 2016

Black Powder XX - Reworking and Re-Shaking

In our last post, we looked at different types of containers that black powder was shipped in, in the 19th century.

A stack of powder barrels. Click on the image to enlarge.

Now, it must be remembered that black powder is hygroscopic in nature, which means it tends to absorb water from the air. Despite the best efforts to provide a tight seal to the barrels, there is a chance that the powder inside may still absorb some moisture over a period of time, especially if there is a lot of relative humidity in the air. If the black powder absorbs sufficient moisture, then this reduces the burning rate and strength of the black powder. Moisture can also cause caking in the powder. Water also causes the potassium nitrate to separate out of the black powder and can cause corrosion of metal gun parts. Therefore, it was not a good idea to leave barrels stored in the warehouse untouched for many years. We will study some methods that were in use in the 19th century to handle the problem of the black powder absorbing water in today's post.

To handle the caking issue, barrels were generally filled to 90% of their capacity. For instance, in the above image, we see that the barrel holds 100 lb. of powder. The barrel is actually capable of holding about 110 lbs. of powder or so, but it is only filled with 100 lb. of powder, which leaves a little room available for the powder to move around. Therefore, the contents of the barrel are free to move during transport of the powder and this helps break up any large lumps. In England, they would roll the barrels every year over a copper plate on the floor of the magazine, with the idea that this redistributes the contents inside and prevent caking.

In many countries, it was standard procedure to examine the barrels after a certain amount of time had elapsed (which is why the date/year of manufacture was stamped on every barrel). For instance, in France, they examined the barrels once a year for moisture damage. First, they would put each barrel on its side and roll it on a floor covered with hair rugs. If the sound coming out of the barrel was uniform, that meant the powder was good. Any uneven sounds meant that there was likely some moisture absorbed and caked powder inside. In this case, they would open the barrel and determine the moisture content of the powder before deciding how to proceed.

To determine the moisture content in the powder, they would take three samples of powder, one from the top, one from the bottom and one from the middle of the barrel. The samples would be carefully mixed and then 5 grams of powder would be carefully extracted from this sample. This powder would then be subject to a drying process, like the ones we studied previously. After this, it would be weighed again and the difference in weight indicates the percentage of moisture content in the sample.

If the moisture content of the sample was found to be below 7%, then all the powder was simply taken out of the barrel and dried, either by using the sun, or by using an artificial drying process like the ones we studied a few posts before. The barrel was also dried separately. Then the powder was subjected to a dusting process and then re-packed into the barrel. If the powder inside the barrel was found to have clumps in it, then these were broken by hand and was put back into a dry barrel and re-shaken to break up any smaller lumps. 

If the moisture content of the sample was found to be greater than 7%, or if the saltpeter had begun to migrate out of the powder, then the powder was subjected to a chemical analysis to check if the proportions of the three ingredients were still within acceptable limits and if so, the powder was sent back to the mill to repeat the stamping process that we studied about a month ago.

Any barrel found to contain moisture was not put back to its original place in the warehouse after the reworking process. Instead, its position was swapped with another barrel from the stack of barrels, so that those that were in the bottom of the pile would now be on top and vice-versa. 

In Germany, they would expose the powder to sunlight at regular periods, whether the powder contained moisture or not. The Prussian procedure was to do this every two years, which later changed to every 8-10 years, if the barrels were located inside a dry powder magazine.

In our next post, we will study what was done if the powder was found to be in a damaged state.