Oh man. I'm only a chapter (plus introduction) in, and I'm having all sorts of "mysteries read" flashbacks already -- not only for Christie's writings but also for those of other writers.
E.g., those Styrian peasants get a really major nod towards the end of Dorothy L. Sayers's Strong Poison, and the initial setup of that book (the murder charge brought against Harriet Vane) is almost certainly largely inspired by the Madeleine Smith case.
Plus, poison books of course are also central to Christie's own Mysterious Affair at Styles, even though the poison used there isn't arsenic.
And dissolving arsenical flypaper in water as a beauty treatment (the hindsight-mind boggles!) plays a crucial role in P.D. James's short story The Boxdale Inheritance, which features a very young Sergeant Dalgliesh ...
Anyway -- I like Harkup's approach, tying each poison chiefly to one specific book by Christie; even if I'm already wishing now that she'd provided diagrams of the molecular structures of all the poisons discussed at the end of the book (instead of making me look up half of them online). But it's clear there's a chemist writing about her own subject here, so ... no fashion commentary, at least so far -- let's hope things stay that way! And that table charting every single Christie novel and short story and the murder methods listed there is great beyond belief.
I have a feeling this will be another one of those books I'll be referring to again and again in the future!