Fraser, Thomas; Crentz, William L. & Barrett, Orrin T. Preparation Characteristics of Some Coals Available for the Synthetic Liquid Fuels Industry, report, 1950; (https://digital.library.unt.edu/ark:/67531/metadc12655/m1/1/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .