12 cups cold water
12 cups granulated sugar
With a very sharp paring knife, remove the outer green peel of the limes. Slice the peel into paper-thin strips and set aside.
Slice the lime pulp very thinly and remove any seeds. Discard end slices. Measure the peel and the lime slices (you should have 4 cups) and cover with the cold water. Allow this mixture to soak overnight.
The next day, place limes and liquid in an 8-quart or larger pot over moderate heat and cook, covered, for 20 minutes or until the lime rind is tender.
Remove from heat and measure the cooked mixture. You should have 12 cups. Add sugar and stir over moderate heat until the sugar dissolves. Boil rapidly, stirring frequently, until the marmalade reaches the jell point. Remove from heat and skim off foam with a metal spoon. Ladle into clean, hot jars, leaving 1/2-inch headspace; seal. Process in boiling water bath 10 minutes.
Yield 11 half pints.