Sift flour once, measure and sift flour four more times. Beat egg whites and salt on large platter with flat wire whip When foamy, add cream of tartar. Continue beating until eggs are stiff enough to hold up in peaks, but not dry. Fold in sugar, two tablespoons at a time. Fold in flour the same way, then flavoring. Pour batter into ungreased Angel food pan and bake at least one house in very slow oven. Begin at 275 degrees F. and after 30 minutes increase heat slightly (325 degrees F.) Remove from oven and invert pan for one hour, or until cold.