Put the sugar and 150 mls (¼ pint) of the juice in a saucepan, and heat gently until the sugar has dissolved. Add the rest of the juice and pour over the cherries in a bowl or enamel pan. Next day, bring everything to the boil, including the lemon juice, and boil rapidly until setting point is reached. Spoon into clean, hot jars, seal and label. Strawberry jam can be made in exactly the same way.