One of the spectacular features of the hall is the sprung floor in the ballroom. Constructing the floor involved clever crossbracing of wood so that the floor has the ability to give under the dancers' feet. The guides on the tour trolleys that run up and down Chestnut street claim that the floor is held up by iron springs, but you should not believe them.
Here is a reminiscence of a different hall, in Boston:
Washington Hall, though a spacious one, was not highly decorated, but it possessed what was a special desideratum in those days, the best spring floor that ever rose and fell beneath the feet. (Sarah Anna Emery, My generation, Newburyport: Sargent, 1893. p. 91.)