Gerald is correct - don't throw it away until you try it.
Mix up a small amount of 12-15%. Use equal amounts of ferric oxalate and coat a small piece of paper. With or without a negaitve, you will know in a couple of minutes in the sun whether or not the silver nitrate is still active. It wil begin to change color very rapidly and be basically brown in two minutes.
I have silver nitrate crystals well ove 30 years old which are still in good condition. Give it a try.
JIM