Pour grape juice, lemon juice and salt into refrigerator tray and freeze until firm.
Boil sugar and water together for 3 minutes and pour slowly into the stiffly beaten egg whites, beating constantly.
Cool to lukewarm.
Scrape up thin layers of the frozen grape juice with an invented spoon, and fold into egg white mixture.
Replace in the tray and freeze.
Serves 6 to 8.