Historical Aspects and Black Powder Manufacturing

By

Michael A. Rosen, Ph.D., M.D.
Dade Behring Diagnostics™
Medical Products Division-DuPont Chemical®

Black powder was the original gunpowder and practically the only known propellant and explosive until the middle of the 19th century. Although it can explode (only when tightly compressed), its principal use is as a propellant. Gunpowder was invented by Chinese chemists in the 9th century. Originally, it was made by mixing elemental sulfur (S), charcoal (C), and “saltpeter” properly named potassium nitrate (KNO3). For the most powerful black powder "meal" a wood charcoal is used. The best wood for the purpose is pacific willow, however, grapevine, hazel, elder, laurel and even pine cones have been used. Charcoal is not the only carbon fuel that can be used. Sugar is used instead in many pyrotechnic applications.The ingredients are mixed as thoroughly as possible. This is achieved using a ball mill with non-sparking grinding apparatus (using lead balls), or similar device. The ingredients are mixed as thoroughly as possible.

When the ingredients were carefully ground together, the end result was a powder that was called 'serpentine.' The ingredients tended to require remixing prior to use, so making powder did involve significant of risk. Powder works realized that a large portion of the risk could be mitigated by making certain that the serpentine remained wet through out all but the last step of its manufacture.

Black powder was  also “corned” as a simple but effective means by which its burn rate could be adjusted. The initial step of the corning process was to compress the fine black powder "meal" into wet cakes or blocks of a “standardized” density (1.7 g/cm³ or grams per cubic centimeter). The blocks, once allowed to dry would harden and become brittle, then broken up into granules. The granules would then sorted by size to yield the various “grain sizes” or grades of black powder. Standard grades of black powder run from the coarse and slower burning Fg grade used in large bore rifles and small cannon though FFg (medium and small-bore rifles), FFFg (pistols), and FFFFg the very fine and faster burning (small-bore, short pistols and priming flintlocks). Very coarse black powder was used in mining before the development of nitroglycerine and dynamite.

 

Chemistry, Composition and Combustion of Black Powder

The optimum proportions for gunpowder are: 74.64% saltpeter, 13.51% charcoal, and 11.85% sulfur (by mass). The current standard for black powder manufactured by pyrotechnicians today is 75% potassium nitrate, 15% softwood charcoal and 10% sulfur. A simple, commonly cited, chemical equation for the combustion of black powder is:

2 KNO3 + S + 3C K2S + N2 + 3CO2

 

A more accurate, but still simplified, equation is:

10 KNO3 + 3S + 8C →2K2CO3 + 3K2SO4 + 6 CO2 + 5N2

The products of burning do not follow any simple equation. One study's results showed it produced (in order of descending quantities): 55.91% solid products: Potassium carbonate, Potassium sulfate, Potassium sulfide, Sulfur, Potassium nitrate, Potassium thiocyanate, Carbon, Ammonium carbonate. 42.98% gaseous products: Carbon dioxide, Nitrogen, Carbon monoxide, Hydrogen sulfide, Hydrogen, Methane. 1.11% water

Black powder is classified as a low explosive, that is, it deflagrates (burns) rapidly. High explosives detonate at a rate approximately 10 times faster than the burning of black powder. Although black powder is not a high explosive, the United States Department of Transportation classifies it as a "Class A High Explosive" for shipment because it is so easily ignited. Highly destructive explosions at fireworks manufacturing plants are rather common events, especially in Asia. Complete manufactured devices containing black powder are usually classified as "Class C Fireworks", "Class C Model Rocket Engines", etc. for shipment because they are harder to ignite than the loose powder.

To summarize, black powder consists of a fuel (charcoal or sugar) and an oxidizer that supplies oxygen to the reaction during combustion (saltpeter or niter), and sulfur, a “matrix constituent” that allows a more stable, hotter, even burning combustion reaction. The carbon from the charcoal plus oxygen forms carbon dioxide and energy. The reaction would be slow, like a wood fire, except for the oxidizing agent. In order to burn efficiently carbon (charcoal) must be able draw oxygen rapidly from the air. The saltpeter (potassium nitrate) provides that extra oxygen. Potassium nitrate, sulfur, and carbon react together to form large volumes of nitrogen and carbon dioxide gases and potassium sulfide. The large volume of expanding gases, nitrogen and carbon dioxide, provide the propelling force imparted to projectiles by black powder combustion.

 

Here are some questions regarding Civil War black powder:

1. What is the ignition temperature of Civil War black powder?  Potassium nitrate black powder can be ignited with a low temperature flame, but ignites more readily with a hotter flame closer to the decomposition temperature of potassium nitrate which is about 400°C. It is ignited in firearms using concussion and friction/spark. Merely heating it up won't ignite the propellant.

2. What is the detonating temperature of Civil War black powder?  It doesn't explode.

3. Is it highly sensitive to impact?  No. Friction - if it leads to sparking, static electricity, spark, and flame. Static Electricity is a spark finer powder FFFG & FFFFG could be more susceptable; spark - yes by design; flame - yes by design

4. If you drop a Civil War shell could it explode?  It could if it has a percussion, fulminate of mercury (mercury diisothiocyanate), detonator on its nose and if the slider is able to move freely.  The percussion cap also has to be resting on the nipple in order for the slider to strike against the anvil cap.  This is highly unlikely that a excavated percussion fuzed shell would explode when dropped.

5. Does the powder get stronger with age?  No

6. Does the powder turn to Nitro Glycerin?  No

 

rev1 publish date July 30, 2006