I'm writing a short story set in the near future, wherein a Jack the Ripper style character serially murders several women. I was thinking of having him use chloroform to incapacitate his victims, but based on my research into chloroform (re: Google), quite a large amount of it is required to actually guarantee that a person passes out quickly. That is to say, simply clapping a rag soaked with chloroform over a woman's nose isn't enough to guarantee that she'll pass out or weaken considerably.
Er, I don't intend anything sinister, but... Could someone recommend an alternative to chloroform? What my character needs is something that would make the quick incapacitation of a conscious person possible within a few minutes, and that doesn't require specialized equipment (such as a mask).