Sunday, January 22, 2017

Smokeless Powders: Developments in France

In our last post, we looked into the development of Schultze powder, one of the first smokeless powders. Today, we will look at developments in France at around the same time.

While the French were aware early on, of the discovery of gun cotton by Christian Schönbein, they stopped the use of gun cotton as an explosive material in 1852, as a result of a report by a military commission, which concluded that:
"in the present state during which, various attempts made by the Artillery and the various chemists and industrialists in the preparation of these products, there is no need to continue experiments with regard to their use in weapons of war."

The reason for discontinuing their research into gun cotton was due to two reasons:

  1. The instability of gun cotton, as seen by unexplained explosions of stored gun cotton. We now know that this instability was caused by presence of acid residues in the gun cotton, which act as catalysts for decomposition of the gun cotton.
  2. The combustion behavior of gun cotton, which caused higher pressures and was responsible for weapons exploding and causing accidents.
In France, they stopped research into gun cotton and studied other substances like picric acid instead. Meanwhile, as we saw in an earlier post, an Austrian officer, Baron Von Lenk, worked on solving the problems of gun cotton and discovered a process that enabled him to produce large quantities of gun cotton in 1862. Nevertheless, the Austrians also stopped production within a few years, due to explosions inside the two factories that produced their gun cotton. Some more improvements in the production process were made by the British chemist, Sir Frederick Abel, but there was an explosion in the factory at Stowmarket in 1871 and from then on, they only used gun cotton for underwater torpedoes and mines. In France, they also started production of gun cotton for use by the French Navy in 1873, for torpedoes and mines as well. The factory was in Moulin-Blanc near Brest, in the Brittany region of northwestern France, and it produced gun cotton using the methods pioneered by Abel. 

While the British discoveries had paved the way for safer manufacture of gun cotton, the problems of ballistics was still an obstacle to adoption for use in armaments: gun cotton burned too fast and weapons burst due to over-pressure. As one report of that time put it, "Rifles that support 30 grams (1.05 oz.) of black powder, burst with only 7 grams (0.25 oz.) of gun cotton. With a load of 2.86 grams (0.1 oz.) of gun cotton, rifles become worn out or unusable after 500 shots, whereas it takes 25,000 to 30,000 shots with ordinary black powder."

It was known at that time (thanks to the work of Captain Thomas Rodman of the United States Army) that greater performance could be obtained by powder that burned slower with gradually increasing pressure, than with powder that burned violently in a short period. This is why many experiments were done to reduce the rate of combustion, such as the 1865 development of a smokeless powder by Colonel Schultze in Germany. This was later improved by Frederick Volkmann of Austria, who improved the Schultze process and came up with a powder called Collodine. This was manufactured between 1872 and 1875, but the factory closed down in 1875, due to an Austrian state monopoly on powder manufacture. Some other similar powders were also made in the US (Reid in 1882). Most of these powders found some success as hunting powders.

One of the attempts to reduce combustion rates led to the production of prismatic powders, but this was only a partial success, because even when compacted properly, it didn't always burn progressively. Additionally, prismatic powder being a black powder, it produced a lot of smoke and residue. Meanwhile, the hunting powders in the paragraph above had the same issue of not burning evenly as well, due to lack of a consistent shape and uniform composition of the material.

It was in the 1870s that the French government decided to form a committee to study of the fundamentals of the combustion process of powders. The objectives of this group were to predict the ballistic behavior of a projectile from the characteristics of the explosive material and the weapon used. To do this, it was necessary to understand the process of combustion of the powder, the formation of gases at various temperatures and pressures, the movement of the projectile in the barrel and the its trajectory in the air etc. Such an analysis is very complex and it involves numerous subjects and disciplines that were not yet well understood in the 19th century: chemical thermodynamics, ballistics, mechanics of explosive reactions etc.

Way back in 1839, a French General named Guillaume Piobert had studied the combustion process of black powder and theorized that "burning takes place by parallel layers where the surface of the grain regresses, layer by layer, normal to the surface at every point." He concluded that combustion rates of the powder is affected by the layers and pressure has no effect on the combustion rate. We now know of this discovery as Piobert's law and it applies to solid propellants in general (not just black powder), but when he first proposed it, it was a very controversial theory.

In the light of new discoveries made since, the French decided to revisit his work in the 1870s. A famous French chemist named Pierre Eugene Marcellin Berthelot had already conducted several studies on chemical thermodynamics and explosions and he was appointed head of the French explosives committee.

Pierre Eugene Marcellin Berthelot.
Click on the image to enlarge. Public domain image.

In his group were a couple of people, Emile Sarrau, the manager of the French Depot Central des poudres et salpetres, and his new deputy, Paul Vieille, then only 27 years old and a recent university graduate.

Paul Vieille
Image released under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Sarrau and Vieille were tasked with the study of an apparatus called the crusher manometer (or crusher gauge), which was used to measure explosive forces. The device was invented by a British officer, one Captain Andrew Noble in the 1860s and he published a research on explosives along with the above mentioned Frederick Abel.

Crusher Manometer invented by Noble and Abel.
Click on the image to enlarge. Public domain image.

The Noble apparatus consists of crushing a small copper cylinder placed between a fixed anvil and a moveable piston and calculating the maximum pressure by measuring the deformation of the cylinder and comparing it against similar copper cylinders compressed under known loads. We already studied this process a few years ago, when we studied how chamber pressures were measured.

However, this process only gives approximate results, because there wasn't an accurate way to produce standard cylinders to measure against. It was possible to subject two identical cylinders to the same pressure and end up with different amounts of deformation. So Sarrau and Vieille began to improve the process of producing standard cylinders to measure against. They invented two methods to do so: in the first method, the cylinder was crushed slowly, until it bore a predetermined weight without further deformation. In the second method, a counterweight was moved slowly along the arm, with the aim of uniformly increasing the load supported by the copper cylinder, from zero load to a predetermined value. However, the crusher gauge only showed the maximum pressure of the explosion. In 1882, Vieille also invented a mechanical device to record the pressures generated over time for an explosion. His invention was a modification of the crusher gauge: he attached a pen to the piston, so it would produce a mark on a cylinder which was turning at a known speed. With this piece of equipment, he could measure the pressure curve of an explosion as well.

Vieille and Sarrau proved by the study of the crusher gauge, that explosives must be classified into two categories: that which have slower rates of combustion (low explosives) such as black powder, and those that have a fast rate of explosion (greater than speed of sound, i.e. high explosives) such as gun cotton and picrates. They found that previous studies on the maximum pressures of explosives were not quite correct because the height of the crushed cylinder depends on the piston mass and the speed of combustion. They developed rules and procedures to give exact measurements of maximum pressures generated by explosions and within the next few years, Vieille would use some of these studies to develop a new type of smokeless powder. We will study how that happened in the next post.

Tuesday, January 17, 2017

Smokeless Powders: Further Developments by Abel and Schultze

In our last post, we studied some discoveries by Baron Von Lenk, who succeeded in developing a process to manufacture gun cotton in larger quantities. The Austrian empire adopted his gun cotton as a propellant to replace black powder and supplied thirty howitzer batteries with gun cotton cartridges, as well as a new model of the Lorenz rifle (the M1862 model) to use gun cotton. Two factories in Austria started to manufacture gun cotton based on his process.

The gun cotton, as made by Von Lenk's process, retained the fibrous nature of the original cotton. The Austrians spun it into threads and braided them together, or wound them on wooden or paper bobbins, and arranged them in cartridges, so as to secure the desired air gaps in between and insure proper ignition. The Austrians found that this propellant was not affected by dampness, only required a charge of 1/4th to 1/3rd of the amount of black powder previously used, left less residue inside the barrel, produced less smoke and the gases evolved were also less harmful to the weapons and the men around them. France and England got interested in his discoveries and sent scientists to study the Austrian process as much as they were willing to reveal and Von Lenk also lent his expertise to scientists from both countries.

Unfortunately, there was an accident in 1862 in the factory at Hirtenberg, Austria, which blew up for some unknown reason. Soon after this, a British company called Thomas Prentice & Co. started to manufacture gun cotton in 1863, in a town called Stowmarket in England. Shortly thereafter, Sir Frederick Abel also began to research producing nitrocellulose safely at the Royal Gunpowder Mills at Waltham Abbey, England. His process was based on Von Lenk's process as described in our previous post, but he effected a more complete purification of the gun cotton by pulping it before the final washing process, thereby cutting the tubular fibers into short lengths and rendering it possible to remove the last traces of acid retained within the tubes by capillary action. Traces of acid remaining in the gun cotton was what caused it to decompose over time. He patented this method in 1865, just around the time that the second Austrian factory also blew up. The Austrians had also had some accidents with their guns and after the second factory blew up, they decided to stop using gun cotton in their military. Meanwhile, Abel continued to experiment in England with his pulped, purified gun cotton, which he could compress into various shapes and in 1867 and 1868, he got some very promising results when used with field artillery. However, the British military were still very wary of gun cotton and military authorities were concerned about safety issues more than the advantages of the smokeless powder technologies. Also, the Thomas Prentice & Co. factory in Stowmarket blew up in 1871 and this was another reason why the British military discontinued further research for artillery and small arms for about twenty years. Instead, the compressed gun cotton was used in naval mines and for filling torpedoes and this is where the entire gun cotton production at the Waltham Abbey factories went to for the next couple of decades.

While military interest in gun cotton had decreased, civilians were very interested in this new technology. In particular, sportsmen who liked to hunt, appreciated the lack of smoke combined with higher velocities and lack of fouling and the next few years of developments were largely done in response to their demands. Naturally, the goal was to reduce the force of the explosion, so that barrels would not rupture, as had happened in the previous years. Around 1863, a Prussian artillery officer, Captain Johann Edward Schultze, invented a powder made from well purified and partially nitrated wood. His process started by sawing the wood into thin sheets about 1/16th of an inch in thickness, which was then passed through a machine that punched out disks or grains of uniform size. The next step was to remove the resinous matter from the disks, which was done by boiling the disks in sodium carbonate solution, washing them, steaming them, bleaching them with chloride of lime and then drying them. After this, the cellulose was nitrated in an acid mixture similar to the Von Lenk process. After this, the nitrated wood was then steeped in a solution of potassium nitrate and barium nitrate and then dried, which completed the process of manufacturing process. Using this process, the nitrocellulose that was produced was diluted with unconverted cellulose and metallic nitrates, which allowed for an even rate of combustion.

The advantage of using nitrates and organic substances as diluents was soon copied by other people and many other powders were soon on the market, using potassium, sodium and barium nitrates, and potassium nitrate (saltpeter), while sugar, cellulose, charcoal, sulfur, starch, gums, resins and paraffin were all used as combustible diluents and cementing agents.

Schultze started manufacturing his smokeless powder in a factory in Potsdam, near Berlin, around 1864. His powder soon gained popularity among civilian hunters. However, in 1868, there was a major fire in his factory and it burned to the ground. Shortly after this event, over in England, near a town called Fritham in the New Forest area, at a site called Eyeworth Lodge, a new factory called the Schultze Gunpowder Factory was established by two businessmen, Clement Dale and William Bailey. There was already an earlier attempt about 7 years previously to establish a black powder factory at the same site, which was not successful. The new owners hoped to capitalize on smokeless powder technology as well as the name of Captain Schultze, from whom they obtained a license to manufacture the powder. It must be noted that while Captain Schultze was not really directly involved with the new Schultze Gunpowder Factory, they did use his original manufacturing process and subsequently improved it over the years as well.

Click on the image to enlarge.

Initially, the factory was not very successful and in 1871, they only had four employees. The November 1872 edition of Popular Science had this to say about the factory and its production process:

"Here and there at intervals wide apart are various buildings of light structure from one of which rises a tall chimney instrumental in raising steam to drive a 10HP sawing machine which rapidly creates the "wood powder". This is subjected to chemical washing leaving hardly anything behind save pure woody material, known as lignine or cellulose. The next operation involves the conversion of these cellulose grains into a sort of gun cotton material by digestion with a mixture of sulphuric and nitric acids. Next it is washed with carbonate of soda and dried. The resultant grains are stored away until the time of packaging and dispatch when they are charged with a definite percentage of a nitrate powder -- nitrate of baryta is preferred.  All the buildings requisite for manufacturing this explosive are cheap and flimsy so that if they did catch fire no loss would ensue. The plant and machinery is of small cost in comparison to that used for making black gunpowder and Schultze wood powder is sold at a price commensurate with its cheap production."

In 1874, a talented self-taught chemist named R.W.S. Griffiths was appointed as the general manager and he refined the production process. Soon after this, the company began to become famous for the quality of its powder, particularly after samples of powder were successfully tried out in a series of trials organized by The Field magazine. By 1878, it became a leader in the world's sporting powder market. Many of the famous cartridge manufacturers, such as Eley Brothers, Kynoch and Union Metallic Cartridge Co. (UMC), used Schultze powder in their cartridges. The company rapidly expanded and the population of the local village of Fritham expanded with it, causing a reservoir, a new church, a store and workers houses to be built. Nevertheless, powder manufacturing remained a dangerous process and therefore, the wages for workers at that factory were around double that of those working in agriculture at that time.

At its peak, the Schultze Gunpowder Factory also opened offices in Gresham Street, London and had agents in various cities around the world. They became the largest manufacturer of smokeless powder for sporting use and produced about 75% of the world's supply. In 1897, they formed an American branch in conjunction with E.C. Gunpowder Co. and called it American E.C. & Schultze Gunpowder.

One of the most famous users of Schultze powders was the legendary American exhibition shooter, Annie Oakley, who was the star of Buffalo Bill's Wild West Show.

The legendary Annie Oakley. Click on the image to enlarge. Public domain image.

Annie Oakley had mentioned in several interviews, that she only used Schultze powder for her performances. Interestingly, when the Wild West Show toured France in 1889, she brought along fifty pounds of Schultze powder with her and then discovered at the dock that there was a French law that forbade the import of foreign gunpowders! At that time, the quality of French powders was not as good, because of a government monopoly on powder manufacturing and she didn't have the time to experiment with a new brand anyway. Fearing that her accuracy would be affected, there was only one thing she could do: smuggle the powder in! She obtained five hot-water bottles and enlisted four other lady riders with the show as co-conspirators. They filled the hot-water bottles with Schultze powder and each woman wore a dress with a bustle, hiding the bottles within. In fact, Annie had never worn a bustle in her life before that day, but she admitted that on this occasion she was glad to do so. She led the women safely through the customs line and into France. As she later admitted, "We sure did attract some attention when we went down the gang plank, for although the bustle originated in France, it was going out of fashion at that time". Even then, as the tour went on in France, her supply of powder eventually ran out and her shooting accuracy was affected because she had to use French powder. In fact, the French powder exploded one of her best guns and gave her a big bruise and her husband noted that no matter how carefully one loaded French powder into cartridges, no two ever fired alike. Luckily for her, in Marseilles, she received a notice to go to the Customs House to pick up a box mailed to her by some friends in England. The box was rather large and inside it were two dozen fresh eggs and an unsigned note telling her that she should try the packing material out in her gun before throwing it away. The eggs were packed in Schultze powder! She gladly paid the 40 cent import duty on the eggs and as she reported, "I never shot better in my life than I did the next three days, either winning or dividing every event. It may be that I was in better form, but I'm sure my Schultze load had a great deal to do with my good scores."

By the early 1900s, Schultze Gunpowder Company expanded so much that they had to move to Redbridge in Southampton, which was more suitable for transportation of its products. However, the company really suffered during the World War I period due to anti-German sentiment. In fact, the company had to take out newspaper advertisements declaring that despite their German-sounding name, all the owners, management and workers were British! Soon afterwards, a bunch of British powder manufacturers all combined together to form Nobel Industries, which later combined with three other companies in 1920 to form ICI (Imperial Chemical Industries),which was Britain's largest manufacturer for most of its history. This was around the time that the Schultze factory at Eyeworth Lodge was closed. All that remains there today are a few buildings and a farm.

In our next post, we will how gun cotton started to attract the interest of militaries once again.

Monday, January 16, 2017

Smokeless Powders: The Von Lenk Process

In our last post, we learned that an Austrian officer, Wilhelm Freiherr Lenk von Wolfsberg, had come up with a method to produce gun cotton efficiently. We will study more about his exact process in today's post:

Baron von Lenk in 1866. Click on the image to enlarge. Public domain image.

The Von Lenk process involves the following general guidelines:
  1. The cotton should be cleansed and perfectly dessicated (i.e. dried out) previous to its immersion in acids.
  2. The acids used should be the strongest available.
  3. The steeping of the cotton in a fresh strong mixture of acids after the first immersion and partial conversion into gun cotton.
  4. The steeping should be continued for 48 hours.
  5. The gun cotton should be thoroughly purified afterwards and every trace of free acid should be removed.
The process started by spinning the cotton into hanks of about 85 grams (about 3 oz.) each, suspended on hooks in a hot solution of potash. An under-heated iron boiler was used for this purpose, the water in the boiler containing sufficient potash to give it a specific gravity of about 1.022. The cotton was immersed in the boiling potash solution for about 2 to 3 minutes, according to the amount of grease contained in the cotton strands. The potash solution acts as a soap and removes the grease. Then the cotton hanks were put in a centrifugal machine and spun around at high speeds to drive out some of the potash solution (the same idea is used in modern washing machines as well). Then the cotton hanks were put in perforated zinc baskets and swung to-and-fro in pure water to remove any remaining traces of soap, after which they were wrung out again and allowed to completely dry out. This completed the stage 1 of the process, cleaning out the cotton and drying it.

The acid mixture was prepared by taking strong nitric acid of specific gravity 1.48 to 1.49 (at 17.5° C or 63.5° F) and strong sulfuric acid of 1.835 specific gravity and streaming them from two taps into an earthenware vessel. The proportion was usually 1 part of nitric acid to three parts of sulfuric acid. The process of mixing the two acids produces heat, so the mixture was allowed to cool in the earthenware jars and stored until ready for use.

The nitration process was done in cast-iron dipping pans divided into three compartments, with a grating fitted over the middle one. Two hanks of cotton at a time were put into 300 times their weight of acid mixture in the first two compartments of a dipping pan. The hanks were turned over and squeezed with spatulas until the acid had completely penetrated through the cotton hanks. Next, they were transferred to the grating and squeezed again to free out most of the excess acid, the cotton being allowed to retain about 9.5 parts of acid. When about 2 kg. (4.4 lbs.) of cotton had been treated this way, the acid mixture was emptied out and fresh acid was put into the dipping pan. When six hanks of cotton had been nitrated, they were put into another earthenware pot standing in the third compartment of the dipping pan. A weighted disk was put into the pot to make sure that the cotton was completely submerged in the acid and then the pot was closed with a lid and allowed to stand for between 24 to 48 hours in a special temperature-controlled room, where the temperature was not allowed to fall below 5° C (41° F) or go above 25° C (77° F). In order to maintain the temperature within these limits (remember that air-conditioning technology wasn't really well developed yet), the room had to be heated during winter and the exterior of the pots was cooled by running water in the summer. During the first two to six hours, the pots had to be watched carefully and the heating was prevented either by adding some fresh acid or passing cold water around the pots.

After the nitration was finished, the crude gun-cotton was then put into centrifugal machines and spun around again to remove some of the excess acid. Then they were washed with a large quantity of water in copper drums and then finally treated in running water in special washing boxes for six weeks. The gun-cotton was then wrung out  again in a centrifugal machine, treated with a boiling potash solution, then again through the centrifugal machine, washed with pure water, through the centrifugal machine once more and then dried. After this, it was dipped into a solution of sodium silicate of 1.072 specific gravity, then a spin cycle through a centrifugal machine again and then finally exposed to the air for three days. During this time, the sodium silicate was decomposed by the action of carbonic acid in the air and silica (or an insoluble silicate) would precipitate on the fibers of the gun-cotton. After three days, the product was again washed in pure water, passed through another spin cycle in the centrifugal machine and then dried in open air, or in a drying house, at a temperature not exceeding 35° C (95° F) and making sure to avoid direct exposure to the sun's rays. While all of this washing and wringing the cotton in the centrifugal machines may seem excessive, it was necessary to do this to ensure that even minute traces of acid were removed from the treated gun-cotton, in order to ensure its stability.

This process would yield about 165-167 parts of gun-cotton for every 100 parts of dry untreated cotton. The structure of the gun cotton threads were carefully examined and hanks containing torn threads were discarded. Then, a small portion of the gun cotton was tested for strength and if found satisfactory, the batch was packed.

Unlike the processes of previous inventors such as Schonbein, Otto etc., which could only be used to manufacture small quantities at a time, Von Lenk's process could be scaled up to produce large quantities.

Baron Von Lenk patented his process and was invited to give lectures in France and England detailing his methods. While in France, he was personally awarded the Commander's Cross of the Legion of Honor from Emperor Napolean III and was also given a box studded with diamonds for his discoveries.

In Austria, another army officer, Ritter von Lorenz (Joseph Lorenz) was working on the design of a rifle which was first approved in 1854 and subsequently updated in the following years. The version that was manufactured in 1862 used a steel barrel instead of a cast-iron one, in order to use gun-cotton cartridges. The gun-cotton cartridges and the M1862 Lorenz rifle model came to the attention of Dr. Theodore Canisius, the US consul to Austria at that time. Dr. Canisius saw the advantages of gun-cotton over black powder and began to send back regular reports to the State Department about various Austrian experiments with gun-cotton propellants. In August 1863, Dr. Canisius returned to the US with an M1862 Lorenz rifle and some Austrian ammunition samples, and arranged meetings with several key officials (including then Secretary of State, William Seward, Secretary of War, Edwin Stanton and some military officers) to try and convince them to adopt this new technology. While the military were not entirely convinced, the Austrian military had decided to switch to gun-cotton entirely and therefore, a lot of their Lorenz rifles designed for black powder were now available for sale. As a result of this, a large number of Lorenz rifles were purchased by both the Union and Confederate sides during the US Civil war, with the Union purchasing over 225000 rifles and the Confederates buying 100,000 rifles. In fact, the Lorenz rifle was the third most used rifle during the Civil war.

However, Von Lenk's process was abandoned by Austria around the end of 1865, due to explosions in two factories and a fear about the stability of gun-cotton. Nevertheless, scientists in other countries were hard at work trying to improve on his processes. The next breakthroughs were by a Prussian artillery officer, Johann Edward Schultze, a French scientist, Paul Vielle and a British scientist, Sir Frederick Abel, and we will study about their discoveries in the next few posts.