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The term "X-patents" refers to the collection of US patents issued from 1790 to 1836.[1] The original copies of these documents were destroyed in a December 1836 fire, leaving the US government without any records of these patents.[2] The collection has subsequently been partially re-constructed via inventors' copies. These document numbers now currently begin with the letter "X" to designate them as part of this historic collection. There are about 10,000 documents in the collection.[1]

The USPTO now maintains an online collection of these documents, available at The USPTO Search Page.


  1. 1.0 1.1 MPEP manual, section 901.04 U.S. Patents [R-3]. USPTO Website, http://www.uspto.gov/web/offices/pac/mpep/documents/0900_901_04.htm. Accessed on November 10, 2008.
  2. "The Great Patent Fire of 1836." USPTO Website, http://www.uspto.gov/web/offices/ac/ahrpa/opa/kids/special/1836fire.htm. Accessed on November 10, 2008.

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