Why was it difficult to identify poisons before the 19th century? What scientific discoveries allowed chemists to discover the presence of poisons in a human corpse?

As Blum describes the numerous murder cases in The Poisoner’s Handbook, she borrows the writing style and tone of the crime fiction genre. Why does Blum choose to do this? How does it change the reader’s understanding of the text?

Blum describes how “industrial innovation” fundamentally altered American society, with the presence of chemicals and toxins becoming a fact of daily life for most Americans. Was this innovation harmful or beneficial for Americans in the 1920s? Use three specific chemicals discussed in the text as examples for your argument.