Peel the green skin from the rind, then cut in cubes.
Soak the watermelon rind in salted water and alum overnight, using 1 1/2 tablespoons salt to each 2 quarts water.
Cover with fresh water and bring to a boil, then drain.
Mix the sugar and 8 cups water and add lemons, gingerroot, cinnamon and allspice.
Cook until syrupy, then place the rind in boiling syrup.
Boil slowly until rind is tender.
Pack in hot sterilized jars and seal immediately.