An element so rarely gets singled out from the periodic table for its own star turn, and even less often when that element isn't even radioactive. But last night's episode of Eleventh Hour sent chlorine down the catwalk in two of its many guises. First up, Chlorine with a black hat, curly mustache and a tendency for evil laughter: Near the end of the episode, Special Agent Rachel Young and Special Scientist Jacob Hood were in a plumbing supply warehouse, hiding behind some shelves, watching drug dealers torture a guy for information. Young knew that, by FBI regs, they had to wait for backup before they could act. But the ever-impatient Hood grabbed a container of chlorine (presumably kept there to to sanitize pool water), threw it into a metal bucket, and contrived to light it on fire. The result was chlorine gas of the sort used in World War I to destroy the lungs of tens of thousands of Allied troops. When inhaled, chlorine reacts with the water in the upper part of human respiratory tract to form hyhypochlorous and hydrocloric acid, which then, in turn, burns away at the soft tissue of the nose, throat, and lungs. Even worse, chlorine gas is slightly heavier than air, so it stays low, where collapsed victims tend to be lying, and it disperses slowly (which is why it settled in WWI trenches). Symptoms include burning sensations in the nose and throat followed by weakness, dizziness and death. In Eleventh Hour, Young actually closes the door on the criminals and locks it. Whether they survived depended, I suppose, on how much chlorine Hood burned. Second, Chlorine with the tin star and easy-going drawl: Like so many things chemical related, it all began in New Jersey. In 1908, a water treatment employee in that fine state tossed some chloride of lime in the drinking water to kill off the bacteria and microbes that live there. The move kicked off a revolution in public health and clean water, as chlorine raised the ph of the water just enough to wiped out typhoid , dysentery , and a host of other water born diseases. Nowadays, nearly every water treatment plant in America, and a great many around the world, use chlorine as a cheap way to make drinking water safe. Last night, chlorine in the water played a crucial role in the plot. The aforementioned drug dealers had received their PCP supply in the form of PVC pipes. Unfortunately, those pipes had been shipped to an actual plumbing supplier, who sold them to a contractor who put them in the ground at new housing developments. In an unfortunate confluence of events, the water supplier flooded the reservoir with chlorine (called a free chlorine burn) to kill off the bacteria and other microbes from the runoff during the Texas rainy season. That chlorine flowed through the PCP piping, leaching the drug into the water. People who drank the water had some excitement in their lives as the PCP led to insane rages, hallucinations, and other bizarre behavior. Even Hood had himself a rage after he consumed PCP from his hotel shower water. Apparently, when Hood is high on drugs, he mutters to himself about philosophy and theories about the universe. I bet he was a hoot at Grateful Dead concerts.