As will have been noted, certain of the processes tend to result in a limited amount of iron substantially on the surface of the alumina ball
. It is to be anticipated that such surface iron may tend to promote formation of carbon at the surfaceof the ball at the reducing conditions involved in retorting of the shale oil, which may tend to decrease somewhat the life of the balls. Of course, such carbon effectively will be substantially burned off at the time of air treatment of the ball. Processes of ball-making by which most of the iron is internal tend to minimize this effect. At the same time such surface iron is presently believed to be advantageous in promoting the shift of CO in the retort to CO2 and H2.