What Is A 1878 Liberty 1 Pound Silver Dollar Worth?

I think your going to find out it is only worth its weight in silver. If it is not marked for purity, I guessing it is the same as sterling, which is 925% pure. Fine metals are weighed using Troy weights.
Remember Troy weights are different.
31.3 grams = 1 troy ounce (not 28)
12 troy ounces = 1 troy pound, (not 16)
I hope this helps a little but you should get more then one opinion from a couple of reputable coin dealers where you live.
Hermit.