I appreciated watching an episode of Murdoch Mysteries (Concocting a Murderer) which showcased character traits of a good scientist. When a murder case is reopened, Detective Murdoch and the coroner, Ogden, are faced with the possibility that they sent an innocent man to prison. In the late 1800s , they had used a flame test to provide evidence that cocoa from the suspect’s home contained the poison thallium.
The case is reopened twelve years later when another investigator realized that the tin containers used at the time of conviction contained traces of copper, which like thallium could also have produced a green flame. Spectroscopes, which were now available, could distinguish between the hues produced by the two elements.
It was nice to see Ogden’s modesty and self-scepticism, two essential character traits in a person doing anything from coronary work to medical diagnosis and from detective cases to analytical chemistry.
With the help of her assistant, Ogden was testing herself to determine if, from the flame-test alone, she could discern the green hue of copper from that of thallium. For a while it seemed she was flawless until she inadvertently was given a sample of barium. She mistook it for copper.
Rebecca James( Assistant): I didn’t mean to trick you, Doctor.
Ogden: No it’s all right. I know you didn’t mean to.
Murdoch: But barium was never part of the investigation!
Ogden: Yes, but that’s not the point. Today I didn’t consider barium just like twelve years ago I didn’t consider copper. It’s possible that I “saw” thallium because I was looking for thallium.
Murdoch: So it’s possible we sent an innocent man to prison!
I was reminded of that effect just this morning when in dim light I was looking for a brown marker in my tool cabinet. For a split-second the shank of a drill bit was perceived as a marker’s butt-end.
Later in the episode when they used a spectroscope to look at the emission spectrum, it turned out that both thallium and copper were present in the cocoa. The strong and sole green line from thallium, which results from the electron-transition of an excited atomic state to a lower energy level, has a slightly longer wavelength than the trio of blue-green/ green lines of copper
I was slightly disappointed that, perhaps to simplify matters for viewers, they presented the following as the combined spectrum of thallium and copper, omitting three green lines of the latter. Murdoch also refers to the green line of copper as being to the right of thallium’s. Is that correct? Yes. The view is merely upside down from the spectra I used above. In both cases, thallium’s green line is in between that of copper’s green line of longer-wavelength and its pair of yellow lines.
But that minor error is far less important than the good practices and traits that they portrayed to a wide audience. It’s reminiscent of what the late Umberto Eco, a humanist, wrote about science:
Science does not advocate that what’s new is therefore right. On the contrary it’s based on the principle of fallibilism—science progresses by correcting itself, disproving its hypotheses by trial and error–science is the good philosophy that ought to be taught in schools.