About :: On a transfer of property an interest therein may be created to accrue to any person with the condition superadded that in case a specified uncertain event shall happen such interest shall pass to another person, or that in case a specified uncertain event sha l not happen such interest shall pass to another person. In each case the dispositions are subject to the rules contained in sections 10, 12, 21, 22, 23, 24, 25 and 27.