Need rock salt ?

[i-leonardo.livejournal.com]

I needed rock salt for metal working and the smallest container I could find was a 40# bag of the stuff, labeled "Morton's Whitecrystal Water Softener Salt".  It claims to be pure rock salt (large grain) suitable for use in a home water softening system.  I don't know anything about water softening, but I can assert that it's just fine for small-scale casting and soldering metal.  After taking what I need, there's still somewhere between 10 and 15 pounds in the bag.  Would much rather give it to someone else than surreptitiously add it to the city's snow removal pile under the deck of 93 near assembly square.