Put the gelatine in a saucepan, add the cold water and let it stand 10 minutes; then add the boiling water, set the saucepan in a vessel of boiling water and stir until gelatine is dissolved; beat the whites to a froth, add the juice and a little cold water; stir this into the gelatine, continue stirring until it boils, remove to side of stove and let it stand 5 minutes without boiling; then strain through a jelly bag and use as directed in following recipes.