Lemon Shred Marmalade

Makes about 10 half-pints. Wash and peel the lemons thinly; remove the white pith and seeds and discard them. Cut the peel into fine shreds; reserve the pulp. Simmer the peel with 2 cups of the water in a covered preserving kettle for about 1 hour, or until tender. Drain the liquid from the lemon shreds and set both aside. Wash the grapefruit and cut it and the lemon pulp into small pieces; cover with the remaining 10 cups of water and simmer gently in a covered preserving kettle for 1 1/2 hours, or until the f