Separate the eggs while cold. Use a large mixing bowl for the yolks, medium for the whites. Let whites and yolks warm to room temperature.

In a 1-1/2-quart pan, boil the water and 1 cup of the sugar until it spins a thread, 230 to 232°F on a candy thermometer.

Meantime beat the egg yolks until very thick and lemon-colored. Slowly beat in the hot syrup (this can be done with an electric mixer using medium speed or with a rotary beater). When all the syrup is added, continue beating until the mixture is light, fluffy, and thick. Set aside to cool.

Sift the flour 5 or 6 times with the salt to incorporate as much air as possible. Beat the egg whites until frothy, beat in the cream of tartar, sprinkle with 1/4 cup sugar, and continue beating until stiff.

Fold the flour into the cooled egg yolk mixture, along with the orange rind. Fold in the whites and turn immediately into an ungreased 10-inch tube pan.

Bake in a preheated 350°F oven about 1 hour or until the cake springs back when pressed lightly in the center and has pulled away from the sides of the pan. Invert the pan to cool the cake. When cool, remove by loosening with a fork.