Weight, sound and color all should do it but the easiest way it to check for an 'S' mint mark. If it's not an 'S' it's not silver. If it is an 'S' it might be silver, but they're really easy to tell. If you find one you won't have any doubts. Good luck!
Is it true that there were no 90% silver Ikes or Susan B. Anthony's as well ? (only 40% with S mint mark)