how pure is the silver in a silver dollar
As a general rule-of-thumb, United States silver dollars dated 1964 or earlier are made from 90% silver, 10% copper - with a total silver content of around 0.77-0.78 troy ounces. However with silver dollars from 1965 onwards, things get more complex. For example, Eisenhower silver dollars (1971-1978) were issued in both proof and circulation versions; the circulation versions contained no silver, the proof versions contained 40% silver.