Remove [and discard] the very green rind from a watermelon. Cut the [peeled] melon rind into small pieces and boil the pieces in water. Turn into a coarse sieve, and when the water has drained away completely, sprinkle these pieces with ground ginger. Use 1 tablespoon ginger for every glass of boiled rind and set it aside for 24 hours in a cold place. The next day, rinse off the ginger from the rind in lukewarm water, changing it several times so that no ginger remains on the rind. Then take several glasses of rind, the same number of glasses of fine sugar, and ¼ or ½ glass water for every glass of sugar. Cook up a syrup, drop in the rind, and cook thoroughly, as for any jam.