Bromine puts the Purple in Tyrian Purple

Althouse commenter Palladian wrote an interesting comment a while back about Tyrian purple dye:

The ancient purple, Tyrian purple, is more akin to the color of a fresh Welch's grape juice stain on a white cotton shirt, only much more intense. Tyrian purple is made from the fresh mucous secretion of a big sea snail that is variously known as Murex brandaris and Haustellum brandaris. It requires harvesting and killing 10,000 of these gastropods to produce one gram of the dye, hence the astronomical price and rarity of the color. Link.

Palladian didn't mention bromine in his comment but I remembered his post after I started thinking about organobromine compounds.* He didn't give a pretty picture either, so here it is:

So what?  Well, it's bromine that gives it its striking color. Why do I say that?  Take away the two bromines and replace them with hydrogens and you get a dye called indigo:

I am interested in this stuff because I'm trying to understand and explain how organic dyes are used in DNA sequencing and also in OLED devices (futuristic electronic devices).  Subtle changes like changing substituents like bromine (or more commonly chlorine and fluorine) are important to those technologies.
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*Bromine is rare in natural compounds and, unlike chloride and iodide, bromide is not an essential element for humans. Due to its high water solubility, the world's bromide is mostly trapped in the oceans, where it cannot easily escape without help. Significant amounts of bromide are also trapped in fresh water brines and brackish waters, which is why Dow Chemical is in Michigan. Link

Hermetically Soiled

The Mercury Dime. The winged cap was supposed to be a Phrygian cap, symbolizing free thought: (footnote 1).  The design also featured a fascia on the reverse which was fitting, considering the time period.

I'm getting way ahead of myself in the Periodic Table, but elemental mercury is such cool stuff.  Here is a photo of a man floating on a vat of mercury, originally published in National Geographic Magazine:

Man floats on mercury

The acute toxicity of elemental mercury is overblown. Mercury is mainly a chronic poison, meaning it takes long term exposure to do serious damage. Mercury compounds--especially methyl mercury--are a different story. I have been slowly ridding myself of silver amalgam filings, but the brain damage may be too late. :)

Mercury has a long medicinal history. Alchemists believed that it had healing powers. When I was a kid, my dad would treat us with what we called "sting medicine." Marketed as mercurochrome, merbromin doesn't actually contain any chromium --rather the name "chrome" refers to the bright reddish orange dye attached to the mercuric ion. The last time I saw or used mercurochrome was in Italy in 1979. I "smuggled" some back, thinking it was a controlled substance. It is still freely--though not widely--available here. The Straight Dope wrote a piece on mercurochrome here: link.

Of course I played around with elemental mercury quite a bit as a chemist.  The most mercury I ever saw in one place was in a Toepler pump, a device which uses a mercury piston to collect and measure non condensable gases like methane and carbon monoxide.

Here's a modern quandary: incandescent bulbs use more watts of power than the newer mercury-containing CFL bulbs. Burning coal emits tons of mercury into the atmosphere. The EPA and others claim that smokestack emissions are not scrubbed link, even though the technology exists. Link

I think it's ironic that we need to disperse mercury in order to rid ourselves of mercury.

Blut und Eisen

The bond between blood and iron is ancient. The alchemist's symbol for iron is the same as the astrological one for the red planet and the god of war, Mars.* It's also the "male" symbol.

They say that blood smells and tastes like iron. I don't think this is literally true, but somewhere, back in time, someone no doubt burned blood and got rust. That's my theory for how the bond was first established.

Hematite (original)

The word hematite for high-grade iron ore has been around since the 16th century and it means "blood-ore". Lots of hematite was mined from Minnesota to feed the heart of the steel industry down stream. The high grade stuff is played out but there's still lots of taconite.

Ironically, the red color of blood doesn't come from iron: Fe(II) is light blue in color and Fe(III) is yellowish brown. The intense color comes instead from the molecular scaffold supporting iron atoms in hemoglobin. A ring of rings, with each little ring bearing a nitrogen base, stabilizes an iron, which otherwise would irreversibly find oxygen and turn to rust.  The so-called porphyrin ring supports the otherwise unstable iron and allows it to reversibly bind and transport oxygen throughout the bloodstream. The word porphyrin comes from the Greek word meaning purple. Even with central iron atom plucked out, porphyrin is a deep purple in color.

There's lots of blood history surrounding the word porphyrin. King George III famously suffered from porphyria. Could this be the source of our political term blue blood? There's more medical history on porphyria here.
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*The reddish color of Mars comes from a skin-deep layer of iron oxides.

Who first lichened politics to a type of moss?

The chemical definition for litmus disambiguates to the political expression "litmus test."

The OED says that the political usage first appeared in 1957. link

WTH happened in 1957?

[Update: Twitter friend Meadabawdy reports that Merriam-Webster dates the usage of "Litmus Test" back to 1952: link]

Pigments of My Imagination

I got sidetracked by vacation and few other things and lost my way regarding the chemical elements. The following inorganic pigments are mostly familiar.

Red is for red and white lead in striped lighthouses and also miniature manuscripts. The red color comes from lead tetroxide and the stark white comes from lead carbonate. Both pigments are impervious to the elements which is precisely why Michael Faraday chose them to coat Britain's lighthouses.
Red is also for Barn Red. Farmers in Europe started this tradition by adding ground up rust to the linseed oil they used to protect their barns and sheds (the iron inhibits mold).

Orange is for terracotta roof tiles: The color comes mainly from iron oxides.

Yellow is for yellow school buses.  Originally the pigment came from lead chromate (the color comes from the chromate, not the lead). It too was impervious to the elements. Lead chromate is no longer used to paint buses, but the traditional color stuck with us.

Green is for emeralds. Beryl and emerald are essentially the same material, viz., Be₃Al₂Si₆O₁₈. The only difference is that emerald also contains about 2% chromium, the source of its green color. Chromium also makes rubies red, and sapphires blue.  How does the same element do that?

Blue is for the Prussian Blue. I wrote about this back here. Gun bluing, a form of metal passivation, is another iron coating in disguise. Blue is also for cobalt blue.  As the saying goes: if it's blue, it's cobalt (II).

Indigo is for itself. Its color is challenged by some as a separate distinct color: link The most vivid indigo colors I ever saw were solvated electrons trapped as either sodium electride or as sodium benzophenone. What do electrons really look like? link

Violet is for purple permanganate, KMnO₄ which is actually pinkish purple but I couldn't think of a better example. Can you?

Chromatography is Just a Metaphor for Stains and Skid Marks

Chromatography once meant "color writing" but now it's just an analytical tool in chemistry.   Chromatography started out with scientists dipping paper in solutions of crushed plant juices.  Capillary action drew the solutions up the paper--just like the quicker-picker upper Bounty paper towel does.  Things in the solution-called analytes- lag behind the wetness line creeping up the paper.  You may have even seen this phenomenon if you've ever found an old paper coffee filter with annular stain rings.
Anyway, the phenomenon gets interesting if there are two or more colored substances in the solution which form two separate rings. In theory you can dry the filter and cut the paper up, isolating the two substances.  Voilà, chromatography!

In paper chromatography, the paper is what's called a stationary phase and the water is the mobile phase. Analytes flit between the two phases to different extents-whence the separation.  Nowadays there are a ton of different chromatographies--column chromatography, thin layer chromatography, high pressure chromatography, gas chromatography, chiral chromatography--but they all rely on similar principles.