pinball

A BIG hello to all, I'm not sure what to do with a coin collection I inherited a long time ago. I did venture to a shop in london with most of them, where after 3 of the sales assistance were quite excited about a lot of them said they would give me between £1500-2000 for the lot. one of the coins is a 'Cartwheel' believed to be silver ! This leads to my other question, how do you test a silver coin? I tried an ice-cube and it disappeared in seconds ( I read about this on the net ??). any help or a point in the right direction would be greatly appreciated. I'm in the Worcester park Surrey area. all the best Duncan