Section 19. For the purpose of maintaining, distributing and providing at reasonable rates during time of war, public exigency, emergency or distress a sufficient supply of food, other common necessaries of life and temporary shelter for their inhabitants, towns may raise and appropriate money outside of any limit imposed by law upon their tax rate or debt; but any bond, note or certificate of indebtedness issued therefor shall be payable in not more than two years from the date of its issue. The receipts from any undertaking or service authorized by this section shall not by applied to municipal purposes, other than those herein described, so long as there are any obligations outstanding issued on account of any such undertaking or service. The expenditure of all money so appropriated shall be under the direction of the mayor, or of an officer appointed by the mayor, with the approval of the city council in cities other than Boston, and in towns shall be under the direction of the selectmen or of an officer appointed by them.