Wash and cut up the apples, but do not peel or core. Put into a preserving pan with the sloes, just cover with water and simmer to a pulp. Put into a jelly bag and leave to strain overnight. Measure juice and allow 1 lb. sugar to each pint of juice. Cook over a low heat until sugar has dissolved, then boil rapidly until setting point is reached. Skim, pour into hot sterilized jars and cover tightly.