In a large kettle, combine chopped onions and peppers, add 4 cups boiling water and let stand for 5 minutes, stirring once.
Drain the vegetables and return to the kettle with 2 cups vinegar and 2 cups water. Bring to a boil and simmer, stirring occasionally, for 5 minutes. Drain again and return vegetables to the kettle.
In a saucepan, combine 3 cups vinegar with 4 1/2 cups sugar and the salt. Heat gently, stirring until the sugar is dissolved. Pour this over the vegetables.
Bring to a boil and simmer, stirring occasionally, for 15 to 20 minutes until the syrup is slightly thickened and the vegetables are tender but have not lost their crispness.
Pour into sterilized canning jars, filling to within 1/4-inch of the tops. Wipe rims with a dampened towel and seal the jars.
Process in a boiling-water bath (water 2 inches above the jar tops) for 10 minutes.
Remove the jars to cool and store in a cool dry place.
Servings: 7 pints