50 or 80% silver . Try looking at the rim, if it looks all silver then its 80% http://www.coinsandcanada.com/coins-prices.php?coin=25-cents-1967&years=25-cents-1965-2015
Well if it's a P/L example it's 80%. As far as the rest, since they have the same reference weight and diameter, it's not possible that they will also have the same thickness since copper is less dense than silver. The one that has 80/20 silver/copper should be slightly thinner than the one that is 50/50. And of course the "ring" will sound different.
How's your scale? A 1967 80% should weigh 5.83 grams, a 1967 50% 5.05 grams. per the technical specs here: http://www.mint.ca/store/mint/learn/25-cents-5300010#25_1
I know several coin shops that just buy/sell them at 65% silver value to average them out... seems to work out and is much much easier than trying to figure out which is which!
