53.) Iodine

Atomic Weight 126.90447
Density 4.94 g/cm3
Melting Point 113.7 °C
Boiling Point 184.3 °C

Iodine sublimates into a beautiful violet vapor when heated: There's a torch under the plate in this photo. Iodine and iodine solutions were used as disinfectants before better antiseptic agents were found. Iodine was still used as a disinfectant as recently as my childhood, which I can assure you was fairly recent. I've personally seen it used to disinfect udders before milking, though it was a family dairy farm which probably wasn't on the cutting edge of disinfectant technology. It tends to both liquefy and sublime near the same temperature, which can make it difficult to handle without putting it into solution.

Iohexol is a contrast agent used in coronary angiographs, though why, I couldn't tell you. A contrast agent is simply something added that will allow greater detail of imagery with some sort of spectroscopy, like X-ray, gamma-ray, or MRI. MRI is peculiar because water acts as a partial contrast agent, making it easy to run without injecting other substances, but scientists still seek more resolution from compounds of heavier metals that hopefully won't interact with the body it's injected into. Technetium is even used as a contrast agent for gamma ray spectroscopy to image bones more clearly. This contrast agent just happens to interact clearly with x-rays, and helps image minute details of the heart and surrounding veins and arteries.

I found myself wondering when I first noticed that my salt was iodized why that would possibly be a good thing to do. Seemed silly to me, considering iodine might be a disinfectant but salt could already disinfect on its own without any help. But after looking further, I found out why, and also why it seems silly: it prevents goiter, which we've all but eliminated in this country partially thanks to iodized salt. Like scurvy and vitamin C, goiter is a condition that only occurs with alarmingly low levels of iodine present in the body. Essentially, the thyroid gland in your throat swells uncomfortably, with few harmful effects aside from looking like a bullfrog. But because of iodized salt, we don't have to even think about it anymore.