So, there's a chance that Natasha recovered despite any "antidotes" administered!
But there was no "antidote" known until Bunsen discovered iron oxide hydrate would act as a kind of chelating agent in 1833.[4]
Arsenic was front of mind around the time Tolstoy came of age and was writing W&P. Marsh had invented his method of detecting arsenic in the body in 1841[5]. The English Parliament passed the Arsenic Act in 1851 and ... /5