Mexican Chocolate Chiffon Cake
["3/4 cup hot coffee", "1/3 cup cocoa", "1 3/4 cups all purpose flour", "1 2/3 cups sugar", "1/2 tsp. salt", "1 1/2 tsp. baking soda", "1/2 cup pure vegetable oil", "7 egg yolks", "7 egg whites", "2 tsp. vanilla", "1/2 tsp. cream of tartar"]
["Preheat oven to 325 degrees."]
["hot coffee", "cocoa", "flour", "sugar", "salt", "baking soda", "vegetable oil", "egg yolks", "egg whites", "vanilla", "cream of tartar"]