you don't use it i'v tried and i went on here to find out and sorry this didn't help
section h
Use the pickax to break out.
you have to put your cursor in circles repeatedly
Look for it when you use the lighthouse to look for it then use the boat to go to the prison
You use it to discover who the robed ghost is by throwing the salt in the hooded ghost's face. Otherwise, you don't use it! You never even have to click the use button- it performs the action automatically.
go inside the woman in the window's castle.
you try and feed it to the bird at the top of the mountain at the main street
At the upper left, above the lighthouse. You can only search the reef after you talk to the ghost lighthouse keeper and use the searchlight.
you go to the bank and 'use' the money. Use the thermal camera under the dog when it starts matting and growling at the floor and after you talk to the guard. You shall see a ghost. I guarantee it.
"You dont" is NOT the answer. Whoever said that you don't is wrong. You use the salt to temporarily blind the Magistrate when you figure out that he is the ghost leaving roses by Fiona's grave. The reason why people don't notice is because it throws the salt automatically in stead of grabbing it from your inventory.
You use it to discover who the robed ghost is by throwing the salt in the hooded ghost's face. Otherwise, you don't use it! You never even have to click the use button- it performs the action automatically.
That's just a distraction from the rest of the island. You just need to deposit it. I know it's tempting, but there's nothing you can do with it.