There was no actual snake oil in old timey snake oil (except when there was, of course). Rather, most of the lotions and potions sold by early 20th century miracle medicine salesmen actually contained mercury and lead. Now, don't you feel better? University of Detroit Mercy chemists recently analyzed the ingredients of several dozen patent medicine samples from the Henry Ford Museum's collection. From Smithsonian:
Their findings, which they presented yesterday at the annual meeting of the American Chemical Society in Atlanta, were that many of the pills, powders and ointments tested had beneficial ingredients like calcium and zinc—but that others had toxins such as lead, mercury and arsenic."What’s in Century-Old ‘Snake Oil’ Medicines? Mercury and Lead"
Back in the day, this was a very trial-and-error kind of field,” (chemist Mark) Benvenuto said in an interview. “The stuff that we think of as dangerous now, though it was dangerous, was as cutting-edge as they had at the time.”