Hahn, William Berton. Loading and Unloading Mechanism for Mixing-Drums or Other Receptacles, patent, May 27, 1913; (https://texashistory.unt.edu/ark:/67531/metapth853806/m1/4/: accessed April 18, 2019), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .