Let eggs stand at room temperature for 30 minutes. In a large bowl, whisk the cocoa, boiling water, 3 tablespoons sugar and 2 tablespoons oil; cool. and set aside.
In a large bowl, combine the flour, baking powder, salt and remaining sugar. In another bowl, whisk the egg yolks, water and remaining oil. Add to dry ingredients; beat until well blended. In another bowl, beat egg whites and cream of tartar until stiff peaks form; fold into batter.
Remove 2 cups of batter; stir into cocoa mixture. To the remaining batter, add orange zest. Alternately spoon the batters into an ungreased 10-in. tube pan. Swirl with a knife.
Gently spoon into an ungreased 10-in. tube pan. Cut through batter with a knife to remove air pockets. Bake on the lowest oven rack at 325° for 70-75 minutes or until cake springs back when lightly touched. Immediately invert pan; cool completely, about 1 hour.
Run a knife around side and center tube of pan. Remove cake to a serving plate.
For glaze, in a small bowl, combine the sugar, butter and enough orange juice to reach desired drizzling consistency. Add orange zest; Drizzle over cake.