The sum levied and collected under section 79-10,100 shall (1) constitute a special fund for the purposes for which it was voted, (2) not be used for any other purpose unless otherwise authorized by a fifty-five percent majority vote of the legal voters of the school district cast at the election under section 79-1098, (3) be paid over to the county treasurer of the county in which the administrative office of such school district is located, (4) be kept by the county treasurer and treasurer of the school district separate and apart from other district funds, and (5) be subject to withdrawal as provided in section 79-587. Any portion of such sum so levied and collected, the expenditure of which is not required to effectuate the purposes for which such sum was voted, may be transferred by the school board, at any regular or special meeting by the vote of a majority of the members attending, to the general fund of the district. All funds received by the district treasurer for such purpose shall be immediately invested by such treasurer in United States Government bonds or in such securities in which the state investment officer may invest the permanent school funds during the accumulation of such sinking fund.