Prior to the Patent Office fire in December 1836 patents were unnumbered. The Patent Office had a copy of each patent and the patent holder had the other copy. After the fire the Patent Office tried to reconstruct the sequence of patents that had been issued to that time, approximately 10,000 in all. They assigned X patent numbers sequentially in chronological order from the inventor's copies they were able to obtain and from one book that survived the fire. The problem was that more inventor's copies surfaced after the X patent numbers were assigned. In order to maintain chronological and sequential order, fractional X patent numbers were assigned. The first being X1678 1/2.
86 of the fractional patents are 1/2s, but there are 5 fractional patents between X8736 and X8737.
|Patent Number||Issue Date|
The Patent Office even put the fractional patents online. Links are provided in the patent listings.