Friday, December 30, 2016

Smokeless Powders: Productionizing Gun Cotton: Early Experiments

In our last post, we saw how gun cotton was accidentally discovered. As was mentioned in our previous post, some early researches were done by French scientists, namely Henri Braconnot in 1832 and Theophile-Jules Pelouze in 1838, but the Swiss scientist Christian Schönbein in 1845, was the first to realize its potential to be used in firearms as a replacement for black powder. Schönbein sent out samples of his discovery to friends in England in 1846 and published details about his discovery, but kept his method of preparation a secret until he received a patent for his discovery. Schönbein also worked with a German scientist from the University of Frankfurt named Rudolf Böttger, who had discovered the same process independently during 1845, to improve the manufacturing process. By a strange coincidence, another German, a professor from the town of Braunschweig, Dr. F. J. Otto also made a similar discovery and published his process details in 1846 before Schönbein and Böttger,

The discoveries of Schönbein soon attracted the attentions of many other chemists (mostly French and German), who investigated the properties and chemical composition and came up with different variants. Some of these names include the above mentioned Pelouze (who revisited his earlier research and came up with a new process in 1846), Dr. Knopp, Dr. Bley, Von Kirchoff & Reuter, Porret, Teschemacher, Walter Crum and Dr. J.H. Gladstone.

In England, a company called John Hall & Sons Co. bought the patent rights to manufacture gun cotton from Schönbein in 1846 and built a new factory to do so at Faversham in early 1847. Unfortunately for them, the process and its associated dangers was not fully understood and a few months later, on 14th July 1847, there was a huge explosion that destroyed the factory and killed many workers, leading to the factory being closed soon afterwards. The manufacture of gun cotton was not attempted in Faversham again until 1873, when a different company opened a new plant at a new location outside town. But this was not the only tragedy -- only a year later, on 17th July 1848, 1600 kg. of gun cotton exploded in a factory at Bouchet near Paris. This explosion was so powerful that walls from 18 inches to a yard in thickness were reduced to powder, and heavy weights were hurled to great distances. These and other accidents, caused the French and German governments to appoint committees to study whether manufacturing of gun cotton was worthwhile or not. After 6 years of experiments, the French Commission reported that, "In the present condition of things, there is no use in continuing the experiments in relation to employment of gun-cotton in warlike arms."

However, all was not lost. Over in Austria, an officer named Wilhelm Freiherr Lenk von Wolfsberg (also known as Baron von Lenk and Von Lenk) was conducting his own experiments in 1849 on behalf of the Austrian military. Von Lenk was serving in a Field Artillery regiment when he began his experiments and he discovered the cause of the previous failures. He came up with a process of manufacture that was both safer and profitable. Due to his researches, a factory "K. K. Ärarische Schießwollanstalt" was set up in Hirtenberg to manufacture gun cotton in 1851. This factory was later absorbed into a larger artillery arms company that still exists today, Hirtenberger AG.

Major General Baron Von Lenk in 1865. Click on the image to enlarge. Public domain image.

The developments in Austria naturally attracted the attention of several European governments, and from England, a Major Young was sent over to Austria to learn everything that the Austrians were willing to disclose. In 1862, a committee was appointed by the British Association to inquire into the application of the new explosives for war purposes. The committee consisted of 3 chemists, the previously mentioned Dr. J.H. Gladstone, Professor W.A. Miller and Professor Frankland, and 6 engineers, William Fairbairn, J, Whitworth, James Nasmyth, J. Scott Russell, J. Anderson and Sir W.G. Armstrong. In case you think some names sound familiar, J. Whitworth is the gent that invented the Whitworth rifle and W.G. Armstrong invented the Armstrong gun and they later co-founded Armstrong, Whitworth & Co., a major armaments, shipbuilding, aircraft and engineering company. James Nasmyth is known for inventing the steam hammer, while John Scott Russell was an engineer who built the Great Eastern steamship, which was the largest ship in the world for 40 years. This superstar committee talked to General Von Lenk and presented a report in 1863 at Newcastle, with some details of the Von Lenk process which will be described below:

In the manufacture of gun-cotton, the end-goal is to produce a product that is as highly nitrated as possible. Von Lenk found that, in order to ensure the production of this, it was necessary to adopt several procedures, the most important of which were specified as:

  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. This was done by washing the product in a stream of water for several weeks; subsequently a weak solution of potash could be used as a final wash, but this wasn't essential.
We will study more details about the Von Lenk process in our next post.

Tuesday, December 27, 2016

Smokeless Powders: The Invention of Gun Cotton

In today's post, we will study one of the earliest developments in smokeless powder technology: the invention of gun cotton.

In 1832, a French chemist named Henri Braconnot found that mixing nitric acid and wood fibers would produce a very explosive material. A few years later in 1838, another Frenchman, Theophile-Jules Pelouze, produced explosive materials by treating paper and cardboard with nitric acid. However, both these discoveries very highly unstable and could not be used for practical explosives. It was left to a Swiss chemist named Christian Schönbein to discover a more practical solution. The discovery of gun cotton was actually the result of an accident:

Christian Schönbein. Public domain image.

Schönbein was a professor of chemistry at the University of Basel in Switzerland. His wife laid down an order to not conduct any chemical experiments at home, but he didn't always obey her and would do his experiments at home when she was not around. One day in 1845, his wife went out for some time and he went into the kitchen and mixed up a combination of nitric acid and sulfuric acid. Due to careless handling, he spilled the mixture onto the kitchen table. He quickly grabbed his wife's cotton apron and wiped the mess up and then hung her apron over the stove to dry, so she would not find out that he'd been doing experiments at home when she was away. To his surprise, the apron suddenly ignited and burned very rapidly, leaving almost no ash behind. What he had done was accidentally create nitrocellulose (gun cotton).

Let us understand the chemistry behind what he'd accidentally invented. The manufacture of guncotton (and other nitro compounds) consists of immersing the material (cotton, wood fibers, paper etc.) in a mixture of nitric and sulfuric acids and allowing the nitric acid to act upon it for a certain amount of time. The explosive material that is formed is then separated from the acids and washed until it loses all traces of acid. For example, in the case of gun cotton, the following reaction happens:

C12H20O10 + 6HNO3 = C12H14O4(O.NO2)6 + 6H2O

The cellulose combines with the nitric acid forming nitrocellulose and water (H2O). It would appear from this above equation that only nitric acid is needed for this reaction. However, note that one of the other byproducts of this reaction is water, which would end up diluting the remaining nitric acid and cause it to form other nitro-compounds instead. This is where the sulfuric acid comes in. The sulfuric acid takes care of the water formed by this reaction and also acts as a catalyst to form the NO2 ions.

In the original version of his process, Schönbein mixed three parts of sulfuric acid to one part of nitric acid by weight. Then, he would take twenty to thirty parts of this acid mixture into a porcelain vessel and dip one part of cotton at a temperature of around 10° to 15° C for an hour. After that, the liquid was poured out and the gun cotton was thoroughly washed in water and then in a dilute potash solution to eliminate acids. It was then again washed in water to dissolve any salts formed from the previous washing, then squeezed out to remove the water, then soaked in 0.6% solution of saltpeter, squeezed out again and finally dried at 65° C. Later on, Schönbein modified this process to use 14 parts of a mixture of equal volumes of nitric and sulfuric acids, to each part of cotton.

Gun cotton produces about six times the amount of gas than the same volume of black powder, while producing far less smoke and heat.

Now that we've studied the reaction at a high level, we will look at some of the machinery used for this process in the next few posts.

Friday, December 23, 2016

Smokeless Powders: Introduction

In the last several months, we have studied the production of various forms of black powder in depth. The next series of posts will deal with an in-depth study of smokeless powders. We had studied about this some years ago, but not really in detail.

So why smokeless powder?? First, let's go over some disadvantages of black powder:

  1. It is very flammable. Black powder can easily be ignited by a single stray spark, hard impact or a hot object and therefore, it requires careful handling.
  2. It leaves a lot of residue behind, which can cause fouling problems inside the firearm. The residue is also caustic, which can cause corrosion issues if it is not removed quickly. What this means is that firearms that use black powder need to be cleaned after firing just a few shots. 
  3. Black powder also produces a lot of smoke upon ignition. In fact, many infantry troops using black powder weapons faced a problem on the battlefield in that after firing a few shots, they would no longer be able to see the enemy due to the clouds of smoke produced by their own weapons.
  4. Black powder is hygroscopic (i.e.) it absorbs water from the atmosphere. This causes two problems: the first is that presence of water makes the powder less efficient and may even spoil it to the point where it doesn't ignite reliably. The second problem is that remnants of black powder in a firearm can cause the metal to rust rapidly. Due to this, it was necessary to clean firearms thoroughly immediately after use, especially in humid areas, in order to prevent the formation of rust.
  5. Black powder does not ignite when wet. This caused many soldiers to have their firearms rendered useless during rainstorms. This is the reason why many soldiers also carried a sword or a spear as a backup weapon.
By contrast, smokeless powders offer more propulsive power than the same weight of black powder and leave a lot less smoke and residue behind. This makes it possible to not only increase the range of firearms, but also shoot for longer periods of time without cleaning the weapon -- this is what made it possible to develop semi-automatic and automatic firearms. Early smokeless powders were somewhat unstable, but as technology improved, they became a lot more stable than black powder and don't require as much careful handling. They are also not affected by rainy weather and can even ignite underwater. 

With that said, there are a few misnomers about smokeless powder that we should clear up before we go in-depth with our study. First, the name is misleading: smokeless powder is not actually 100% smokeless. There is some smoke produced, but it is much less than that produced by black powder. The second misnomer is that there is no single formula for smokeless powder. In fact, there are multiple types of smokeless powders, each made with different chemicals. This is unlike black powder, where the three ingredients are always carbon, sulfur and potassium nitrate (albeit with different proportions of the ingredients and different grain sizes).

In our next post, we will study the first development in the family of smokeless powders: guncotton.

Sunday, December 4, 2016

Black Powder - Chemical Examination

In our last few posts, we saw how people would determine the quality of black powder by measuring the physical properties of the powder, such as color, size, shape, density, hygroscopic properties etc. In today's post, we will study some of the chemical properties that people would examine to determine the quality of powder.

The first type of test was the Qualitative Examination test, which was done if the ingredients of the powder were not known (e.g. some powders did not have sulfur, others may have sodium nitrate instead of potassium nitrate, still others may have charcoal made of wood, wood pulp, bark, straw etc.).

Recall a few months ago, we had stated that black powder is a mixture and not a compound at room temperature. It only forms various chemical compounds when it starts to burn. Therefore, since it is a mixture, it retains properties of its component parts.

Therefore, to determine the kind of nitrate contained in the powder, a small quantity of powder would be put in a filter and then hot water poured over it, which dissolves the nitrate salt. The filtered liquid was then chemically analyzed to determine the type of nitrate. Next, to determine if the powder contains sulfur or not, a small quantity was placed in a beaker and carbon disulfide was poured on top and allowed to stand for a little while. The solution was then poured out and evaporated. If any sulfur was present in the powder sample, it would crystallize out. To determine the type of charcoal used, they would first remove the sulfur from the sample using the carbon disulfide solution, then they would filter it and then wash with hot water to extract the saltpeter out, then they would dry out the remaining residue and examine it under a microscope, which would show whether the carbon was made from charcoal, wood pulp, wood bark, straw etc.

Of course, the above qualitative tests would show the presence of the ingredients in the powder, but not the proportions of the ingredients. To do that, they would do quantitative analysis tests, which determine the percentages of the ingredients. To do this, they would first dry a sample of powder as much as possible. Then, they would take a known quantity of powder, run hot water through it several times to dissolve all the saltpeter and then evaporate the solution to recover the saltpeter crystals, which could then be weighed.

After the saltpeter had been removed from the sample of powder, the next was to determine the amount of sulfur in the remaining sample. This could be done either directly, or by converting the sulfur into sulfuric acid. The direct method was due to Berzilius: The sample of powder after the saltpeter was extracted, was dried and weighed and then transferred into one of the bulbs of a double bulbed tube. A current of dry hydrogen was passed over the mixture while it was gradually heated. This heat would cause the sulfur to vaporize and the sulfur fumes would be carried along with the current of hydrogen into the second bulb, where it would cool down and crystallize in the second bulb. The decrease in weight in the first bulb and the increase in weight in the second bulb could be measured and this would show the amount of sulfur in the sample. Another technique was to dissolve the sulfur in a carbon disulfide solution and then evaporate it to recover the sulfur crystals, which could then be weighed to determine the percentage of sulfur in the sample.

After the saltpeter and sulfur have been removed, the remainder was dried and weighed to determine the amount of carbon in the sample.

It is also possible to determine all the components of black powder simultaneously, using special apparatus, such as that invented by Linck in the 19th century.

Click on the images to enlarge. Public domain images.

This involves using various pieces of equipment to precisely extract the components of the powder, using carbon disulfide, hot water, barium chloride, lead acetate etc. to determine the exact quantities of the various ingredients in the sample.