Sterilize canning jars and rings by simmering them in hot water for at least 10 minutes, until ready to use. Have lids nearby.
In anothe saucepan,dip fruit in boiling water and slip off skins. Cut in half, remove pits, and slice. Mix ascorbic or citric acid with water according to package directions and coat peaches to prevent darkening.
Pack peach slices in jars, almost to the top.
Bring the apple or white-grape juice to a boil and ladle it over the peaches, leaving 1/2-inch of headspace.
Adjust lids and process in a boiling water canner, with jars covered by 2-inches of boiling water, for 20 to 25 minutes. Remove jars from canner and allow to cool for 12 hours.
Unscrew metal rings to make sure lids are sealed.(Each lid should be indented in the center). Store in a cool, dark, dry place for not longer than one year.