68 years of toning, gone. Poof!

Just to make sure we're on the same page here. If all you are doing is rinsing coins in acetone - then the only thing you need to do is rinse them distilled water afterwards. In other words, acetone does not need to be neutralized like a coin dip does. After using acetone you rinse the coin in distilled water for a completely different reason.

Proper procedures for using acetone are found here -
https://www.cointalk.com/threads/proper-acetone-procedure.193708/

Thought I made that clear, or at least I tried to. The answer your question is one, 1 coin.

If you dip a coin, you only use that bowl of dip on 1 coin. Then ya throw it away. When you neutralize a coin after dipping, you only do it with 1 coin, then ya throw it away. Same with final distilled water rinse, 1 coin then ya throw it away.

And if you want to do more coins, before doing anything else you thoroughly wash and rinse and dry the bowls - or get new clean bowls.