dissolve all of the organic material. what was left was primarily sulfuric acid. in a process called colorimetric testing, he added hydrochloric acid and zinc to the mix. >> as it bubbles through this device, the arsenic will react and form, if it's present, a purplish violet color. the more arsenic present, the stronger the more purple the color is. >> rod mccutcheon's chemical cocktail made forensic history. the solution turned a deep purple. conclusive proof of the presence of arsenic. the depth of color in the reaction showed that cordelia norton ingested a massive amount of arsenic. the test results on catherine's ashes were inconclusive. nevertheless, their deaths were ruled homicides.