Select tart, red-skinned apples, cut them in small pieces with the skins on, retain the cores, and put them in a kettle with cold water to barely cover. When thoroughly cooked and mashed, put this pulp into the jelly bag, and allow the juice to drip as long as it will. Do not squeeze the bag, nor stir the pulp if you wish clear jelly. This dripping process is a matter of hours, and in the home kitchen may continue all night. Allow a pint of sugar to a pint of juice. Return the juice to the kettle, and allow it to simmer for twenty-five minutes or half an hour, skimming when necessary. In the meantime, heat the sugar, being careful not to melt or burn it. Stir the sugar gently into the juice, and boil five minutes. Test a little upon a saucer. It should show signs of jellying as it cools. Boil longer, if necessary. Finish as directed. Jelly often does not set until twenty-four hours have elapsed.