According to this article, you’d have to breath it for about 5 minutes to become unconscious. The way it’s used in movies is about as accurate as when they show someone get conked on the head by a bottle, then fall unconscious for a few minutes, then wake up with no ill effects and continue on their way.
One problem with ‘knock out gas’ in general is that knocking someone unconscious is pretty much ‘shut their body down until they’re almost dead, but stop before they’re actually dead’. Getting someone solidly unconscious without killing them generally takes some pretty careful dosing, and the amount of gas that will knock out a large, healthy man is probably going to kill a smaller person (like a child) or someone in worse physical condition. There’s a reason an ‘anesthesiologist’ is a well paid medical professional - if you could just spray some knockout gas and knock someone out, you wouldn’t need someone to go to school to learn how to do it safely.
Speaking from experience*, the effects of chloroform are indeed pretty rapid. If you can force someone to take deep, full breaths of it, then you can indeed make them lose consciousness within a few seconds. But if someone is actively resisting, and holding their breath, then you’re going to have a much harder time of it. And in any case, you’ll need to keep administering it to them, because once it’s removed they will regain consciousness very quickly.
*Of self-administration, and of watching others self-administer—not administering it to others against their will!
Yeah, but they also use this trope in other, more respectable movies, too. It’s used twice in Silence of the Lambs, for instance, and I know I’ve seen it used countless times elsewhere.
This actually seems to support the movie concept somewhat: the fight-or-flight response includes taking deep breaths, even as you struggle and your heartbeat is raised. Someone would have to have a very controlled response to not try to take deep breaths as their airway is cut off.
Hardware store? Chemical retailer? I’m not even sure the shopkeeper would hesitate to sell it to kids unless it were patently obvious they were going to sniff it.