First of all, can you tell the date and mint mark? If it is a key date coin and worth a considerable sum - DON'T clean it. Seated coins aren't necessarily rare, but they definitely are not in the same class as Mercs or Rosies. If you clean a key date coin, it's ruined. The most you should ever do to silver coins that aren't rare, or for that matter any coin, is soak them in soapy water for about a week and then run clean water over it without rubbing them. Then use low pressure air to dry it.
There are many threads on this forum and coin collecting forums addressing cleaning of coins. The rule of thumb is first to know what you have before doing anything.
G.