How long would it take it break down a body and what would be remaining after?
Don’t worry there’s an industry for that. https://www.webmd.com/balance/what-is-human-composting
I was just going to use kitchen scraps.
I’ve composted meat and bone. Meat breaks down very rapidly. It’s moist which is key, and everything likes to eat it from bug larva to bacteria. You can expect a nice cut of meat to be unrecognizable a week or two after you place it in the core of a healthy compost heap. I even had the opportunity to try this with human tissue: we saved and froze the placentas from my kids births and I composted them. They melted away very quickly.
Bone is another story entirely. My first year composting I decided to throw the bones from a rib family dinner into my pile. Thereafter I kept finding them when I’d turn my pile or sift out finished compost, and I would just throw them back in to take another turn.
It’s now about 12 years after that and I still occasionally find a rib. At first I tried breaking them up with a hammer but that was a bad idea because they shatter everywhere and turn into sharp shards that don’t break down any better :D Now I just throw them in the garbage when I find them.
So you would have a daily easy time getting down to a skeleton but then you’d be stuck with that AFAIK forever.
I guess I’d say first that I don’t have anything on hand to do that with, and I have a lot of shop and garden tools.
If you can turn a skeleton into powder, it’ll no longer be recognizable as a skeleton. It has nothing much to do with composting though. It’s debatable whether the powder would undergo any chemical change by microorganisms. Eggshells for example go into a compost pile and ride along into the soil eventually where they make minerals available to plants, but eggshells don’t get significantly broken down by the composting microorganisms.