Something else to think about, if some potentiating invention would have taken place a few decades earlier, it would have been quite likely that by 1875 there would have been effective isotope analyses available.

Also the further back you go into the 19th century, the more likely it is that the potentiating invention would be completely unrelated to nuclear chemistry.

Regardless, that same potentiating invention (whatever it is) is surely responsible by now for a whole lot more things other than nuclear science.