Sift together the flour, sugar, baking powder, and salt into a mixing bowl. Make a well in these dry ingredients, and add (in this order) the oil, egg yolks, water, vanilla, and lemon rind. Beat until smooth. In a separate bowl beat the egg whites with the cream of tartar until the whites form quite stiff peaks---stiffer than is usual for cakes. Do not underbeat the egg whites or the texture and volume of the cake will suffer. Pour the flour mixture gradually over the egg whites, folding in gently with a rubber spatula. Do not stir. When blended, turn into an ungreased 10 inch tube pan. Bake in a preheated moderately slow oven, 325 degrees, for 55 minutes, then increase temperature to 350 degrees for 10 to 15 minutes, or until the top springs back when pressed lightly. Immediately invert the tube pan to stand on it's legs, or hang the pan by putting the tube over a bottle neck, or rest the pan on the edges of three or four teacups. When cool, loosen from the pan and remove. Chiffon cake are sometimes frosted, sometimes only dusted with powdered sugar.

Orange Chiffon Cake: Use orange juice instead of half the water, and instead of lemon rind and vanilla, use 1 to 1 1/2 tablespoons of grated orange rind. Chocolate Chiffon Cake: Add 1 ounce unsweetened chocolate, melted, after the oil and eggs yolks are added.

Mocha Chiffon Cake: In addition to the chocolate (see above), add 2 teaspoons powdered coffee.