This section is from the book "Mrs. Rorer's Vegetable Cookery And Meat Substitutes", by Sarah Tyson Rorer. Also available from Amazon: Mrs. Rorer's Vegetable Cookery And Meat Substitutes.......
Wash the apples, cut them into quarters, remove the cores, but do not pare them. Weigh and put them into a porcelain-lined kettle, allowing to each pound one pint of cold water. Cover the kettle, boil twenty minutes; stir. Drain over night. Next morning measure the liquid and put it over the fire in a porcelain-lined kettle. Boil twenty minutes. Add a half pound of sugar to each pint of juice; boil ten minutes longer and begin to try the jelly. Put a teaspoonful in a saucer, and stand it in the cold. If it solidifies at once, remove the jelly from the fire, and pour it into the glass tumblers. Keep on trying it until it solidifies quickly. You may also try it by dropping it from a spoon. If, while hot, it drops in "chunks" and does not pour, it will be a solid jelly. When the jelly is cold, put a teaspoonful of formaldehyde into a pint of water. Take a perfectly clean piece of linen, dip it into the water mixture and wipe off the inside of the tumblers and the surface of the jelly. Fasten the tumblers with rounds of tissue paper. When all are fastened, dip a soft brush into the formaldehyde water and brush the tops of the papers. These will dry, shrink, and tighten. Be careful not to get too much formaldehyde on the jelly. It is not a dangerous poison, but all you want is to make sure that the top is clean and free from mould. Keep the jelly in a perfectly clean, dry closet, not necessarily dark. Damp, dark closets are conducive to mould.
Apple, quince, black currant, and Japanese quince jelly are all made after the same recipe.
Heat and mash the currants. Drain over night, allow a pint of sugar to each pint of juice. Boil the juice twenty minutes; add sugar, and finish the same as crab-apple jelly.