The way I see it... From looking at the top pictures, the "thing" holds it's own small portion of the salt, or whatever. It would be stored in the bottom chamber. The big hole in the bottom plate is where it comes out. You'd turn the top plate to one of three positions: Pour (big hole), shake or sift (small holes), or closed (no holes at all). When you have depleted the supply of salt (or whatever), turn the plate to the big hole, fill it back up, close it and put in your pocket.
You know, back in the day, condiments were for more than flavor and taste, they were used to hide and disguise rot in meat and food. They didn't have 'fridges back then. Yes, they had ice boxes. But, cross country trips on horse back took weeks and months. Meat was salt cured or smoked, but still, they had to do something!