X Patents and Fractional X Patents

There was a fire at the patent office in 1836. At that time approximately 10,000 patents had been issued. They were unnumbered and there were two copies of each; the patent office held one copy and the other was sent to the patentee. Nearly all the patent office’s copies were destroyed by the fire but fortunately a list of the patentees and patent titles survived. The patent office asked that patentees send back their copy and about 2,700 have been recovered to date. The patent office tried to put them in chronological order and they assigned them numbers that began with an X. This distinguished them from patents issued after the fire that were assigned numbers starting with 1 (without an X). The patent office found itself in a bind as more patents were recovered that weren’t on the list that survived. They had already assigned the X numbers and to maintain chronological and numeric order they gave the newly recovered patents a fractional number! There is, for example,
a X-8736, X-8736 ¼, X-8736 ½, X-8736 ¾ and X-8736 ⅞ to squeeze in four patents between X-8736 and X-8737.

It is truly amazing that every few years another unrecovered patent surfaces. One I know about is X6037 which surfaced in 2012. The great great grandson of the patentee had an original copy. Images of it were sent to the patent office which put it online.