United States. Department of the Treasury. "Bill Tender, April 22, 1968, Release Number f-1222," in United States. Department of the Treasury. "Volume 161," Press Releases of the United States Department of the Treasury (March 4, 1968 - June 3, 1968) : 189-190. https://fraser.stlouisfed.org/title/6111/item/587004/toc/541026 , accessed on June 24, 2024.