This page from an 1871 edition of Harper’s Weekly contained an image of the grand Congressional Library, in all its fireproof glory. The accompanying article recounted the fires that devastated the library in previous decades. When Congress rebuilt the space in the 1850s, it was one of the Capitol's first uses of cast iron, which made up the columns, floors, shelves, and ceiling. Although general library use was limited to statesmen, visitors were also admitted during certain hours.
History, Art & Archives, U.S. House of Representatives, “The Congressional Library, Capitol, Washington,” https://history.house.gov/Collection/Listing/2011/2011-057-000/ (January 24, 2022)
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