25. Income of settled property acquired on death of spouse. Where a husband or wife is entitled, either solely or jointly with the other, to the income of any property settled by the other under a disposition which took effect before the commencement of this Act and on his or her death the survivor becomes entitled to the income of the property (as distinguished from the property itself) settled by such survivor, estate duty shall not be payable in respect of that property until the death of that survivor.