Sam Dann should have used a primer on U.S. coins before he wrote this episode. Larry Haines consults a coin dealer about the future-dated quarter dollar. The coin dealer professes to be "an expert only in numismatics," and then informs Haines that Washington quarters were made of silver up to 1963. After 1963, he says, quarters were made of a copper-silver alloy. Most Americans listening to this episode in 1977 would have laughed at Dann's and dealer's ignorance of coins. After 1964, dimes, quarters, and dollars were made not of silver, but of nickel & copper, the so-called "clad coins" still minted today. As explained below, by 1974 no US coins intended for circulation contained any silver. 

U.S. dimes, quarters, halves (50c), and dollar coins were minted from an alloy of 90% silver and 10% copper up to and including the year 1964. Then, LBJ pushed through the Coinage Act of 1965 which banned the use of silver for dimes, quarters, and dollar coins minted after 1964 and phased out silver in halves (40% silver, 1965-1970). Eisenhower dollars, minted 1971 through 1974, but only with the S (San Francisco) mintmark are 40% silver. In addition, after 1968, all silver certificates were no longer redeemable in silver, and the 25% gold backing of paper money was removed. JFK would resisted all this depreciation of the currency had he lived because JFK was a hard-money man, a firm believer in gold and silver backing of US money.