Sponge Cake

1 cup cake flour
1 cup sifted granulated sugar, divided
1 1/2 teaspoons grated lemon rind
2 tablespoons water
5 egg yolks
1 1/2 tablespoons lemon juice
5 egg whites
1/4 teaspoon salt
1/2 teaspoon cream of tartar

Sift flour once, measure, and sift four times. Add 1/2 cup sugar, lemon rind and water to egg yolks and beat with rotary egg beater until very thick and light. Add lemon juice gradually, beating constantly. Add flour all at once, then stir until just blended. Beat egg whites and salt with rotary egg beater or whisk. When foamy, add cream of tartar and beat until stiff enough to hold up in peaks, but not dry. Add remaining 1/2 cup sugar, about 2 tablespoons at a time, beating well with beater or whisk. Fold in egg yolk mixture. Turn into ungreased 9-inch tube pan. Cut gently through batter with knife to remove air bubbles. Bake at 325 degrees F for 1 hour, or until done. Remove from oven and invert pan for 1 hour or until cold.