This paper describes the use of an older style of glass prism in a new spectrophotometer made by Beckman Instruments. This new spectrophotometer would become the Model B, the glass prism making it a cheaper alternative to the DU, which used a crystal prism.
George, K. P., W. C. Miller, D. C. Strain, George H. Hare, M. E. Stickney, and Arnold O. Beckman. “A New Spectrophotometer Employing a Glass Fery Prism,” May 1949. Beckman Historical Collection, Box 17, Folder 16. Science History Institute. Philadelphia. https://digital.sciencehistory.org/works/kk91fm322.