Trim green skin and pink flesh from watermelon rind; chop enough rind to yield 6 cups. In a large bowl, stir salt and 2 quarts warm water until salt is dissolved. Add 6 cups chopped rind. Cover and refrigerate 5-6 hours. Drain and rinse in cold water; drain. Cover rind with cold water and let stand 30 minutes. Drain. Transfer rind to a large saucepan; cover with water. Bring to a boil. Reduce heat; cover and simmer until just tender, 10-15 minutes; drain., To make preserves, in a stockpot, combine sugar, lemon juice and 7 cups water. Bring to a boil. Reduce heat; simmer, uncovered, 5 minutes. Stir in rind. Place cinnamon, cloves and cardamom on a double thickness of cheesecloth. Gather corners of cloth to enclose seasonings; tie securely with string. Add to stockpot. Return to a boil. Reduce heat; simmer, uncovered, until rind is clear, 30-45 minutes. Discard spice bag., Remove from heat. Ladle hot mixture into 6 hot sterilized half-pint jars, leaving 1/4-in. headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot mixture. Wipe rims. Center lids on jars; screw on bands until fingertip tight., Place jars into canner with water simmering, ensuring that they are completely covered with water. Bring to a boil; process 5 minutes. Remove jars and cool.