To wash figs, fill a bowl large enough to submerge the figs in water. Dissolve the salt and baking soda in the water. Using your hands, toss gently so as not to bruise the figs. Drain the water, rinse in clear water, and drain again.

Put the figs and sugar in a large pot over medium low heat. Stir gently as they begin to cook. Raise the heat to medium when syrup forms and let it come to a gentle boil. Simmer, uncovered, for about 3 hours, or until a foam appears around the edges of the pot. Stir occasionally.

Spoon the hot mixture into 5 hot sterilized pint-size preserving jars, filling to within 1/2 inch of the top. With a clean damp towel, wipe the rim and fit with a hot lid. Tightly screw on the metal ring. Process in a hot-water bath for 15 minutes.

Using tongs, remove the jars, place on a towel, and let cool. Test the seals. Tighten the rings. Store in a cool dark place. Let age for at least 2 weeks before using.