Sift together twice: flour, baking powder, and salt. Pour back into sifter.
In a large mixing bowl beat egg yolks and whole eggs with an electric mixer until thick and lemon colored (about 5 minutes). Gradually add sugar, beating after each addition. This should take about 10 minutes.
Fold in orange rind, orange juice, and lemon extract. Sift dry ingredients into egg and sugar mixture and fold in. Do not stir or beat. Add boiling water and fold in quickly, just until liquid is blended. Pour batter into one ungreased 10 inch tube pan.
Bake at 325 degrees F (165 degrees C) for 60 to 65 minutes. Turn cake over in pan on a wire rack and let cake hang for 1 hour or until cool. Loosen cake sides from pan with a spatula and shake from pan. Dust top lightly with confectioner's sugar or frost with Orange Butter Frosting.