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.