Wash the barley and put it into a saucepan. Just cover with cold water and bring to the boil. Boil for four minutes and strain off the water. Put the barley into a large jug. Rub off the yellow part of the lemon rind on to the sugar and add this to the barley. Pour on a quart of boiling water. Stir to dissolve the sugar and leave until cold. Stir in the juice of the lemons. Strain into a jug, and chill.