Grapefruit Chiffon Cake
["1 c. flour", "3/4 c. sugar", "1 1/2 tsp. baking powder", "1/4 tsp. salt", "3 eggs, separated", "1/4 c. oil", "1 1/2 tsp. shredded grapefruit peel", "1/3 c. grapefruit juice", "1/4 tsp. cream of tartar"]
["Sift together flour, sugar, baking powder and salt.", "Make a well in the middle.", "Add in order egg yolks, oil, peel and juice. Beat briefly until smooth."]
["flour", "sugar", "baking powder", "salt", "eggs", "oil", "shredded grapefruit peel", "grapefruit juice", "cream of tartar"]