United States. Department of the Treasury. "Bill Tender, September 1, 1967, Release Number f-1017," in United States. Department of the Treasury. "Volume 159," Press Releases of the United States Department of the Treasury (September 1, 1967 - November 29, 1967) : 4-5. https://fraser.stlouisfed.org/title/6111/item/587002/toc/540633 , accessed on May 5, 2024.