Good morning...welcome back to war! (again..and again...) yesterday, I talked about hydrochloric acid (muriatic acid) (which can be combined with nitric acid= aqua regia) ...on the IIWW the US army used Cyanogen Chloride chemical gas weapon against the japonese, because its simple crosses the gas masks. Cyanogen Choloride is the mix of hydrochloric acid (don't pay attention to homemade recipes with bleach...) and urea (that I already explain how to get it...3 times boiled and 3 times freezed urine, to get powder) . Now this will naturally create a massive killing weapon, not only on the subway! ..because if dropped at the soil, it remains weeks producing effects.