1967 1968 Canadian Quarters

1967 5.83 grams , 1968 5.07 grams . Assuming you meant the 68 Silver 25cents .

for the 68, the silver is non magnetic, the nickel is.

for the 67, there is only 2 ways of telling between the 2 variations (there is a 3rd, but the Nickel version is extremely rare).

1) specific gravity test

2) XRF

if you are looking to buy/sell the 67 coins for their silver content, nobody who does this regularly would consider any of the dimes / quarters at the 80% point. normally they split the difference and use a 65% mark.