A dime is made from

91.67% Copper
8.33% Nickel

They stopped using silver in 1966. But if you had 90% silver in a dime and 10% copper, the silver would make up 93.8% of the weight. And if each dime weights 2.268 grams, each dime has 2.12 grams of silver, 1 ounce is 28.349 grams so you need 13.3 pre 1966 dimes for 1 ounce of pure silver (if you can remove the copper)