I remember I played a homebrew D&D game with that sort of item (although, it was a frigging sarcophagus one of us had to lug around on our back) which had a sort of sign saying "something interesting will happen when you put something in" and the item we put in to test was a bottle of troll blood, since we'd just killed half a dozen trolls and gotten 20-something bottles of blood.
We had an alchemist/potion maker/whatever with a recipe to turn troll blood into something like HP potions (instant 1d8 HP) that also gave something along the lines of HP regen (roll 2d6 every round, recover the higher of the two, if you roll the same thing on both dice, the effect ends but you recover the sum of both dice). However, the other ingredients, while more common than troll blood, were rare. However, another effect of troll blood is that, unprocessed, it's rather toxic, and has a nasty smell that drives away most monsters. So we made ourselves some sachets infused with troll blood that would keep shit away, refreshing the smell every now and then, and if we encountered anything, the first thing we did was to all chuck a bottle of blood at it.
These stones, meanwhile, are probably best used to, like, shove down something's throat and suffocate it? Or, like, maybe a semi-auto arm-mounted catapult? (Two cups on either end of one rod, which rotates around a central axle) Have it on the outside edge of one arm, hold the jar in that arm, and just rapidly take stones out and load them into the thing, which rotates half a turn whenever a weight is placed into the cup. It wouldn't be that hard to get a fire rate of ~100 shots/min with a bit of practice. The main problem is litter...