I have a slightly different idea for this concept. Instead of being discovered by some random chemist, gunpowder is instead discovered by a mystery cult dedicated to Vulcan. They view it as a sacred gift, and so the formula for gunpowder remains a tightly kept secret for at least a few decades. I think this would make for some really interesting changes to the development of gunpowder weapons. Instead of going for rockets or bombards first, you might see a greater focus on small scale weapons, mines and so on, since the cult doesn't have a ton of resources or space to work in secret, at least initially.
Down Styphon! (err... Vulcan)