Sleep-mist was a liquid that vaporized when exposed to air and formed a cloud of fumes that could knock out a species as large as a Luxan. It could be deployed in a soft handheld container that would burst on contact to release the mist.
The crew of Moya tried to use it on Ka D'Argo when he was under the influence of the Tavlek gauntlet, but the gauntlet supplied him with additional stimulants to counter its effects. ("Throne For a Loss")