Preheat oven to 325 degrees. Separate egg yolks from whites. In a large mixer bowl sift together cake or all purpose flour, sugar, baking powder and 1 teaspoon salt; make a well in the center. Add oil, egg yolks, peel, vanilla and 3/4 cup cold water. Beat at low speed of electric mixer until combined, then on high speed about 5 minutes or until satin smooth. Thoroughly wash beaters.
In a large mixing bowl combine egg whites and cream of tartar, beat until stiff peaks form. Pour batter in a thin stream over surface of egg whites; fold in gently by hand. Pour into an ungreased 10" tube pan. Bake in a 325 degree oven for 65 to 70 minutes. Invert; cool completely. Loosen cake from pan; remove. Serves 12.
