In the Royal Tibian Adventurers Academy where Seymour is in Rookgaard, you just go 2 floors down in The Academy and Training Centre. You'll find the Poisons and Acids Research Lab where the book about Report X-1345 and X-1346 is located. There's a flask of urine and also slime, and also what appears to be the vapour, however, when I try to use where the vapour is it just puts "corrupted soil" which is the walls nearby so it won't let me actually look at the vapour :P Also, there's a Strange Hovering Plant which I believe only appears here in Rookgaard according to Tibia Wiki Br
When I used TibiaSecret's "Librarian" tool I wasn't able to find exactly related articles on this matter. The whole idea of Sulphur and vapors reminds me of Zao Brimstone bugs where you spawn The Keeper for Mission 3 of Wrath of the Emperor by putting poison on a plant, but I just think it's unrelated.