It would be like this :a machine that vaporizes liquids or items (extracts,they aren't liquids, are they?) this vaporized extract would carry a syndrome or it would simply create blisters and/or make the targeted creature to faint. (well,the machine wouldn't have a target, it would be listed on the siege engine menu)as said before it wouldn't have a target it would simply vaporizes the liquid trought it nozzle like this :
X X X ^ X X X
X M MX
X X X X
X=Wall
M=Machine
^=nozzle or tube
It could have mutiple nozzles connected to it but it would need to larger (yes,adjustable size) and more Fuel to keep the steam steady,the nozzle would a separate part (or not) and it would only release the gas on the direction which it would be pointing.(it simble could be this simble ^) and it would need to be connected to an pipe wich is connected to the machine,but it could also be connect directly to the machine.
we're going to need some new plants or extracts to make this have some !!FUN!! effects,like an plant thats produces a powerful sedative wich when breathed by most creatures sedates then for like 15 days,giving time for them be arrested,or just make their bodys rot.
The machine would need one cauldron, one mechanism and one block per square build with a limit of 5 squares,the nozzle would be a separate object built from metal or stone and pipes could be be built with tubes or pipes.(there is going to be vertical and horizontal pipes.)
To make the machine work it would be needed to have water, the desired extract and one unit of coal (varies with size.)
The deactivation and activation of the machine would be exactly the same as the others siege engines.
I guess as we are DF players I don't need to say the infinite uses and aplications of this.
iscuss.