From Popular Science.

It’s a little complicated to weigh a dying person on a hospital bed, but that didn’t deter Duncan MacDougall. In the early 20th century, MacDougall’s unique bed-scale detected that 21 grams left the human body at the moment of death.

He had finally discovered it: the weigh of the human soul … or so he thought.

Read more about the cultural legacy of MacDougall’s flawed but influential experiment: https://www.popsci.com/science/21-grams-experiment/