One of the modern conveniences which we take for granted is smokeless powder. It’s stable, predictable, and stores for a very long time. It’s also not hygroscopic, meaning that it doesn’t readily absorb water – a really good attribute for a propellant!
This wasn’t the case with early gunpowder, which we now refer to as black powder. (Even that’s not quite accurate, as the black powder of today is considerably more reliably formulated than that which was available in the 19th century, let alone before.) In the days of percussion arms, powder was not as consistent as today – and that’s before factoring in the non-dessicated storage conditions! As a result it was often necessary to test a keg of powder to determine how good it was. How do you do this without things like piezoelectric pressure transducers and electronic chronographs?
The answer was the eprouvette. While the form might vary from country to country (or from maker to maker), the idea was to fire a measured charge the suspect powder in a device that had a known amount of resistance. The amount of resistance that the powder charge could overcome was used to compare to other, known lots of powder.
The Firearm Blog recently showed some great pictures of a Belgian eprouvette, and the concept is very easily grasped. These are quite rare today; they were made in very small quantities compared to firearms. Have a look and marvel at what our ancestors went through just to keep from blowing themselves to pieces!
-=[ Grant ]=-