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.
Strain, D. C., M. E. Stickney, W. C. Miller, Arnold O. Beckman, K. P. George, and George H. Hare. “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.