If any county or city board of education has issued and sold school warrants under the provisions of this article for school building purposes and if the proceeds of such warrants cannot now be used for school building construction due to priority regulations of the government of the United States, such board shall have the authority to invest the proceeds of such warrant sale in securities issued by the government of the United States of America having a fixed redemption value at the option of the holder of not less than the amount originally invested. County and city boards of education shall have the authority to use for debt service purposes any interest received on securities issued by the United States government in which the proceeds of school warrant sales are invested. When it becomes practicable for such boards of education to construct the school buildings for which said school warrants were originally issued, said boards of education shall have the authority to liquidate the securities in which the proceeds of warrant sales are invested and apply the same to the purposes for which the school warrants were originally sold.