Preheat oven to 325. Grease and flour a 10 inch tube pan. In a large bowl, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in vanilla. In another bowl whisk flour, salt and baking powder, add to the creamed mixture alternately with milk, beating after each addition just until combined. Remove 2 1/3 cups of batter to a small bowl; stir in preserves and raspberry extract until blended. Pour half of plain batter, next raspberry batter and last more of the plain batter. Cut through batter with knife to swirl. Bake 1 1/4 hours, test after 1 hour. Cool in pan 20 minutes before removing. Top with confectioners sugar if desired or glaze if you wish.