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Silver makes a really lovely bell-like ringing sound when it is tapped on, particularly when it is tapped on with another form of metal. If you want to try this out before tapping on your questionable silver, find a United States quarter made before 1965. These were made of 90% silver while US quarters made later than 1964 are made  of a copper-nickel alloy. The older quarter will give a high-pitched, clear ringing tone, while the newer quarters will give a dull thump of a sound. If it makes a sound like a bell ringing, you have a real silver coin in your hand. If it's dull, the silver is, most likely, mixed with other metals.
Try the ring test with any coin. Drop your own coin on a flat surface from about six inches above it.