Combine the gelatin, 1/2 cup (125 ml) water, and the sugar in a small saucepan and heat, stirring constantly, over low heat until the gelatin is dissolved. Remove from the heat and add the remaining water, vinegar, lemon juice, and salt. Chill to the consistency of raw egg whites and fold in the cabbage, celery, and pimiento. Pour into a 5 cup mold or into individual molds and chill until firm. Serve on a bed of lettuce and top with a little mayonnaise. Serves 4 to 6.