That irritating smell of chlorine familiar to anyone who’s been in a pool is, in fact, misattributed. Those mildly noxious fumes that waft from the water are in fact due to compounds known as chloramines, which form when chlorine and ammonia combine. For the average person, that distinction might as well be purely academic. Chlorine’s true odor is closer to that of bleach, which is hardly a more pleasant substitute. Although a substantial leak of the pure yellow-tinted gas would be quickly lethal to anyone exposed to it, thankfully, this is something that the public in general has little need to worry about as its use is relegated to only a few, specific locales such as heavy industry and laboratories. While there is actual, free chlorine gas in treated pools, and often even in tap water, the quantity is measured in only a few parts per million; too low a threshold to be noticed by human noses. It is, again, the metabolites those free Cl atoms form that alert one to the presence of befouled air.

And here’s a pure sample of the devil we speak of. Although quite pale, the yellow of this gas is easily appreciated against a white background that is well lit. Inside this acrylic cage there’s little chance of it being released into the air but even if it were intentionally broken into the amount is - luckily - too little to do much besides contort the faces of those present with a grimace of disgust.