A lot of people have heard of “noble gases” - this is that rightmost column of the periodic table: Helium, Neon, Argon, Krypton, and Xenon. They exist pretty much on their own; it is very hard to make a compound out of them, and when you manage to, they’re fleeting sorts of things, waiting to react with whatever’s around.

Another series of noble compounds exists; the noble metals. These are named “noble” for the same reason - their relative lack of reactivity (the idea being that there are “noble” metals that hold onto their electrons in a dignified fashion, and “base” metals that deign to react with the other peasant molecules). Because of their lack of reactivity, they occur as the “native” metal much more often than the base metals (which occur as ores).

All that aside, when you want a metal that won’t react, you’re pretty good with platinum. Platinum is also very high-melting, so the development of a crucible made of platinum was a help, since various things could be heated in it without reacting with their vessel. These are curious objects. If you have any platinum jewelry, you know it really doesn’t wear. Unless it’s polished, though (and Pt crucibles usually are just brushed), it just looks like stainless steel. It doesn’t look like as expensive or special as it is until you pick it up - then you realize it’s denser than gold, and nearly twice as dense as lead - and maybe you are holding something a little bizzare.

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Here is another distinctly unfriendly-looking molecule, arsphenamine. For 30-40 brutish years, this was our single best treatment for syphilis. We owe this distinct pleasure to Paul Ehrlich, father of chemotherapy (coined the term, along with “Magic Bullet.”) In the early 20th century, he was working on histology, or staining cells. He reasoned that if we had compounds that stained only certain types of cells, maybe we could find one that would kill certain cells. Like syphilis spirochetes.

While this was a primitive theory of selectivity, Elrich used it to good effect, and six hundred five dead ends later, he released arsphenamine upon the world:

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Mercury is a weird one. It’s quite toxic, and you’ll do well not to handle it casually, but as the metal it’s actually not that bad. If a thermometer breaks, you can probably clean up the area as best you can, then sprinkle zinc dust or sulfur (disputed, see here) on it to keep it from evaporating. If you spill it in, say, an oven, like in the lab, or spill a great deal, it can be a bigger problem - some labs have mercury bubblers with literally pounds of the stuff in them - for most applications, you can use mineral oil, but especially in academic labs, you see a lot of mercury still floating around.

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