1. Score the peels of the oranges, lemon, and lime into four lengthwise sections; remove peels. Scrape off white portions of peels; discard. Cut peels into thin strips. In a large saucepan bring peels, the water, and the baking soda to boiling; reduce heat. Simmer, covered, 20 minutes. Do not drain.

2. Meanwhile, working over a bowl to catch juice, section oranges, lemon, and lime. Add sections and juices to saucepan; return to boiling. Cover and simmer 10 minutes (you should have 3 cups fruit mixture).

3. In an 8- to 10-quart heavy pot combine fruit mixture and sugar. Bring to a full rolling boil, stirring constantly. Quickly stir in pectin. Return to a full rolling boil. Boil hard 1 minute, stirring constantly. Remove from heat. Quickly skim off foam with a metal spoon.

4. Ladle hot marmalade into hot, sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.

5. Process filled jars in a boiling-water canner 5 minutes (start timing when water returns to boiling). Remove jars; cool on wire racks. Allow to stand at room temperature 2 weeks to set.

Tip

To section citrus, working over a bowl to catch juice, remove fruit sections by cutting between a section and the membrane. Cut back between the section and the next membrane to release the section. Repeat until all fruits are sectioned.