In the early part of the 19th century, a fine, white powder was all the rage among murderers (and some would-be beneficiaries). It was easy to acquire and easy to administer, too. Tasteless and colorless, it might be added to food or water and ingested. It was even called the "inheritor's powder" because it aided in the rapid passing of the rich and elderly.
What was arsenic doing on shelves to be purchased, you might ask? In the 19th century, arsenic was used in wallpaper, beer, wine, sweets, painted toys, insecticides, clothing, hat ornaments, coal, and candles (A further list...