Today in Salem History:
This was probably Haarlem Oil, a diuretic made in Holland since 1672 and still in demand in the early 20th century.
So popular was this remedy, practically every drugstore in America made their own blend. In 1906 it was estimated that "ten bottles of substitute are sold to one of the genuine."
Thackeray mentions it. Louis and Clark never went anywhere without it. So what was it?
In a time with few powerful medicines and no health insurance, Haarlem Oil was your basic safety blanket. It was said to ward off contagious diseases. It strengthened the eyes. It helped your kidneys, bladder, and stomach. It was good for your nerves. In fact, it was good for just about anything, according to its faithful consumers.
Speaking of faith, the "Dutch instructions" bore the Latin legend: Medicamentum Gratia Probatum which was translated as "remedy approved by Grace." This wasn't any potion derived from black magic or superstition. Haarlem Oil was Approved. Consumers were encouraged to have faith in its ability to heal them, whatever their hurt.
You might be wondering, what did the Oil contain?
The recipe for genuine Haarlem Oil was a close-kept secret. However, the American knock-offs tended to be mostly made up of balsam of sulfur and oil of turpentine.
I suppose if you were strong enough to survive the remedy, you were bound to get better.