The county commission shall declare the result of the election; and, where the electors have voted so as to require the levy of a tax, the county commission shall levy said special tax and cause the tax assessor to assess the same on the taxable property in said county or in said rural or city school tax district, as the case may be, which shall not exceed $.30 on each $100.00 worth of taxable property in said county or in said rural or city school tax district, as the case may be. Any special tax levied hereunder shall not be for a shorter term than two years. In all elections hereafter held, if the specific purposes for which said tax, when levied, shall be used is printed on the ballots to be used in said election, it shall be unlawful for the county board of education to apply it to any other purpose.