Which country first used poison gas of any kind in any war?

How Stuff Works. "How Biological and Chemical Warfare Works." 2002. <http://www.howstuffworks.com/Biochem-war.htm>(10 January 2003). Roman Legions regularly used burning sulphur (SO2, SO3, H2S, H2SO4(in rain/fog) to at least irritate, incapacitate, or at best, kill enemies in immobile situations; fortified towns, settlements against geographic barriers; islands, cliffs, bodies of water, etc. Opinions differ as to whether the Legions developed poison gas themselves, or if their own survivors/allies reported how to use it after hard experience. Similarly, opinions differ about the logistics and practicality of raw sulphur transport, and the (un)liklihood of a somewhat bulky(and nasty)materiel being cheerfully carried by a notoriously lightly-packed Legionnaire. It is possible that free, native, naturally-occurring sulphur deposits were scouted, as would have been other staples, like water, wood, game, etc., and if present, utilized, from a point upwind any immovable objective.