During the second act, when West enters the funhouse at the Hannibal Amusement Park he first encounters a bug-eyed monster in the darkness. The monster was originally a rejected design concept for the alien visitors in the film, It Came from Outer Space (1953); a design which two years later became the basis for the monstrous Metaluna mutants in the film This Island Earth (1955).
The name "franconium" suggests an element, but it is described as a chemical, suggesting a compound of some kind. There is an element; Francium; its existence was predicted in 1870 on the basis of its position in the periodic table, but was not positively identified and named until 1939. It was the last naturally-occurring element to be discovered, and is the second-rarest element, with only 30 grams in existence at any given time in the entire Earth's crust.
Part of the context of this episode is the currently ongoing Franco-Prussian War which means that this episode was set between July of 1870 and May of 1871. While Captain West works in support of the French (led by Napoleon III) they were the eventual losers of this conflict which led to the unification of Germany.
Jim West mentions he hasn't had cotton candy in years. That would be impossible because cotton candy wasn't invented until 1897 (by a dentist , ironically; William Morrison). The series is set during Grant's presidency (1869-77).
The detector used to show the presence of franconium is actually a Crookes radiometer (invented 1873), a device in which the vanes revolve when exposed to visible light. It continues to exist to this day as a novelty item. Other types of radiometers are activated by other types of electromagnetic radiation.