Put the seeds into a small piece of cheese cloth and tie securely with thread to make a small bag.
Cut the pulp and rind into small pieces , or chop in a food processor. Put the juice, the bag of seeds, the rind and the pulp into a large bowl. Add the cold water.
Cover and let soak for 24 hours.
Put the contents of the bowl in a large heavy pot and boil for 2 hours, or until the liquid reduced by half. Warm the sugar in a 200~F oven.
Remove the bag containing the citrus seeds, squeezing it well to extract all the pectin.
Add the heated sugar to the reduced mixture. Bring slowly to a boil, stirring constantly, making sure that the sugar is thoroughly dissolved before the mixture boils.
Boil for approximately 30 minutes, or until the desired consistency is reached. Pour the marmalade into warm sterilized jars and seal.