ingesting it certainly didn't do the emperor any good
wasn't all that fast acting tho.
if you want to poison someone, there are much quicker options. might be useful if you want to see them suffer for a long while before they die.
sprinking it on their charcoal heating burner might produce enough gas to irritate him, but it's take a much more substantial amount to kill*. or a small amt. in a small space... a charcoal burner itself can give off carbon monoxide, a more subtle killer. and one used to good effect by assassins in rome & other cultures on occasion. it would be easy enough to restrict the oxygen supply to the burner to produce the CO. just cut down on the room ventilation.
my favourite at the moment is the so. american golden poison frog
this little (5cm/2 in.) fellow has enough poison to kill 20 men. dogs have died from touching a paper towel a frog had walked across. darts dipped in it's poison stay lethal for over two years....
*- i've heard of men who climbed down into a pump room on an oil tanker where so2 had accumulated from high sulphur crude oil pump leaks, and died. their shipmate who went looking for them saw them collapsed on the deck & went down to rescue him, and died, the shipmate who went looking for the second also went down and died. after 5 they finally caught on, wore breathing apparatus to go down and collect the remains, and fans to ventilate the space. designs changed after that...