I wondered that too. I guess it was a two part job: washing with gas first, then washing the gas out with soap. (?) But even so, wouldn't gasoline harm the clothes in it's own way?What I don't get is - after they scrub the clothes in a bowl of gasoline, HOW DO THEY GET THE SMELL OUT??
And I was surprised to see that dry cleaners used gasoline themselves. "Just the right amount" said the announcer. The wiki page for Dry Cleaning says...
"Early dry cleaners used petroleum-based solvents such as gasoline and kerosene. Flammability concerns led William Joseph Stoddard, a dry cleaner from Atlanta, to develop Stoddard solvent as a slightly less flammable alternative to gasoline-based solvents. The use of highly flammable petroleum solvents caused many fires and explosions, resulting in government regulation of dry cleaners."
Here's the whole film.