In a large mixing bowl, beat the egg whites at low speed for about 1 minutes, until the whites are loose and have begun to foam. Increase the speed of the mixture to high. Gradually add the sugar and continue to beat for at least 5 minutes. Add the yolks and the lemon juice, continue beating. Sift the cake meal with the potato starch and add to the mixing bowl. Beat until thoroughly blended. Turn the batter into an ungreased 10 inch tube pan and bake in a preheated 350 degree F oven for 1 hour and ten minutes. Invert to cool for at least one hour.