After payment of the reasonable cost of issuance, including printing or engraving costs, advertising expense and legal and other professional expenses, the proceeds of the sale of any bonds or notes shall be applied only to the purpose or purposes for which the obligations were authorized to be issued, and any excess amount thereof or any amount thereof which for any reason is not necessary for any such purpose, shall:

(1) Be applied to payment of such obligations at not more than their face value; and

(2) Be applied to payment of the first maturing installments of such issue.

9 Del. C. 1953, § ?4649; 56 Del. Laws, c. 103, § ?13;