Silver coins are a different matter so it is inadvisable to clean any silver coins, especially old ones which are dirty. Many collectors by the way prefer the older coins that way as it means a certain authenticity to the coins. Even then if you want to clean, use olive oil and rub it with a cloth/cotton gently.
Place aluminum foil in a pan shiny side up. Place silver dollars on top of foil. Add ½ cup baking SODA anf 2-4 cups boiling water. The hot water activates the baking soda, a chemical reaction occurs between the silver, foil and soda, and Voilã! Clean coins. Works on anything silver, even silver plate.