The podcast "American Carnage" is a great journey if you don't know anything about John Brown. They mention this sword in the podcast, it's got a hollow compartment in it that contains liquid mercury. The mercury flows forward when it's swung in a slash, changing the weight distribution of the blade to kill the enemies of abolition with greater prejudice. Based
Edit: My only source for this was the podcast I mentioned, so take it with a grain of salt. I hope it's true though. It's such an interesting idea for a sword.
No, I just did a little dive myself and you're right that there isn't much out there describing this. My only source was that it was mentioned in the podcast I mentioned. I'll edit my post to include error bars. Thanks for pointing this out.