Peel watermelon rind, removing green and pink portions. Cut rind into 1 inch pieces. Dissolve salt in water; add rind and let stand for 6 hours or overnight. Drain; rinse.. Cover rind with cold water in a large sauce pot. Cook until tender, about 20 minutes; drain and set aside. Tie spices in a spice bag. Combine sugar, lemon slices, spice bag and vinegar in a large sauce pot. Bring mixture to a boil and cook for 10 minutes. Add rind, simmer until rind is transparent. Remove spice bag. Pack hot rind and liquid into hot jars leaving 1/4 in headspace. Remove air bubbles. Adjust 2 piece caps. Process 10 minutes in a boiling water canner.