Combine flour and 1/3 c sugar. In a small mixer bowl, beat egg yolks at high speed 6 minutes or until thick. Combine orange peel and juice; add to yolks, beating at low speed until combined. Gradually add 2/3 c sugar and salt, beating at medium speed until sugar dissolves. Gradually add 1/4 of the flour mixture to yolk mixture, beating at low speed until combined. Repeat with remaining flour, 1/4 at a time, beating a total of 2 minutes. Thoroughly wash beaters. Combine egg whites and cream of tartar; beat at medium speed until soft peaks form. Gradually add remaining 1/2 c sugar, beating until stiff peaks form. Stir 1 c of the whites into yolk mixture. By hand, fold yolk mixture into remaining whites. Turn into an un greased 10-inch tube pan. Bake at 325 about 60 minutes. Invert cake in pan and cool completely. Loosen cake from pan before removing.