Bonds issued pursuant to this chapter must be sold at a price of not less than par and accrued interest to the date of their respective deliveries. They must be sold after public advertisement of their sale in a newspaper of general circulation in South Carolina, or in a financial journal published in the city of New York. Such published notice shall appear not less than seven days prior to the occasion set for opening bids; provided, however, that any bonds issued pursuant to the provisions of this chapter may be sold at private sale to the United States of America or any agency or department thereof.