Peel the skin from grapefruits and oranges, allowing a small portion of the white under skin to remain. Save seeds from fruit pulp and place in a small cheese - cloth bag. Add water to fruit peel, pulp, lemon slices and seeds; cover and let stand 12 - 18 hours in a cool place. Remove seeds and add sugar. Bring slowly to boiling point, stirring until sugar dissolves. Cook rapidly to jellying point, about 30 minutes, stirring frequently. Pour, boiling hot, into sterilized jars; seal. Yield: 4 (8 ounce) jars