85-7-2131. Funds for payment of each series of bonds to be kept distinct. When more than one series of bonds shall have been issued by a district, the funds for the payment of each series shall be kept separate and distinct. When contract is made between the district and the United States, accompanying which bonds of the district have not been deposited with the United States, as provided in 85-7-1906, the funds for the payment to be made under any such contract shall be kept separate and distinct.