The weight of water

While writing a piece for Nature Chemistry about the hidden depths of the periodic table (the more than 3000 isotopes that could be stacked onto their elemental spots), I wandered across an interesting set of papers on heavy water and isotopic tracing, which led to another piece for Nature Chemistry (The weight of water). In one of the papers, future Nobelist George de Hevesy deuterates goldfish by crowding some twenty (albeit tiny) goldfish into 60 ml of water, in another he reports making thousands of distillations of urine to recapture the water, measure its density and track deuterium through the human body.

Heavy water (D₂O) is water where the hydrogens have been replaced with deuterium, an isotope of hydrogen that weighs about twice as much as standard hydrogen. Heavy water weighs just over 10% more than regular water, a tablespoon weighs only about a gram more, so it is probably not noticeable should you heft a glass of it.

And that's the question — should you heft a glass of it? In small amounts it is certainly safe to drink, and as I recently learned, used in human metabolic studies in doses of about 10 ml. An interesting question raised in the papers I read was about the taste of heavy water. One report suggests a burning sensation might be felt when drinking it, another (by Harold Urey, who discovered deuterium) suggests it tastes like undeuterated water. But other reports say it tastes sweet.

With a bit of help from my youngest son, I set up a repeat of Urey's blind taste test. And was surprised to find I could indeed taste the difference. It is sweet.

And for the next few weeks, until the last of the extra deuterium clears my systems, I'll be just a little bit heavier than usual.

Elements of revenge

I seriously can’t write fiction. I suspect it's not lack of imagination, but some odd form of writer’s block. Or perhaps it is too many years devoted to sifting defensible reality from experimental and computational data. Or is it that I’m unwilling to ask a reader to be confused about the real, the possibly real and the entirely imagined? Or maybe it is because the one and only piece of published fiction I wrote, came (almost) true within the year?  Would any other fiction I wrote become real? That’s clearly a flight of fancy, but even with one data point, do I want to take the risk?

I was invited to write a commentary on the elements that scientists thought they'd discovered (but hadn't) for Nature Chemistry's issue celebrating the International Year of the Periodic Table.  The IUPAC guideline for element names says that you can't re-use names already in circulation in the literature, even if they were ultimately discarded. Which got me thinking if that could be a way for an unscrupulous scientist to crush the dreams of a competitor of having an element named for them. Despite my demonstrated inability to write good fiction, I drafted an introduction to the essay that played out this idea.

In the end, I wrote a non-fictional introduction to the essay (which you can read here if you are of the mind to do so). But if I were to write a piece of fiction about the elements, it might begin like this:
_______________________________

Prof. Exuvgen leaned back in her desk chair and wondered for the thousandth time why she’d ever signed that retirement agreement. Time was slipping through her fingers.  In a month, she’d have to hand over the key codes and walk out the door.  No access to her data and worse yet, no access to the tools she would need to analyze it, that idiot of a director had made it clear her account would be wiped — wiped — at midnight on the 30th, and anything left in her office trucked out to the dumpster.  Tang Woh Kow, they maintained, was right. There were 243 elements in the universe and no more. When Tam Besper saw the traces of zuzenium in 2069, right in this building, that was the end of the era of the element hunters. The last chance to have your name remembered in every chemistry book in the solar system, if not the galaxy. Though if the Vulcans had their way, everyone would be using the systematic names.

Running her hands through her short grey hair, she turned again to the data on the screen.  She’d spent thirty years working toward puncturing Kow's ceiling on the elements, the last ten racing Sabaxoar’s extravagantly funded group on the moon. What was it Maxine had said at that last meeting? Oh, right. Time. That she wasn't in a hurry, she had years to work on this, given lunar life expectancies. And with that Maxine shook her blonde curls and floated off.  Would the director take her more seriously if she looked less weary, grey and face it, old?

Time. It's running out, was there enough to say, now, without a doubt, that they’d turned up an atom or two of 244 Sym in that last run? Maybe, though maybe that oxide of muscovium was rearing its ugly head, this wouldn't be the first umbral element sunk by 115. Certainly there was strong evidence of a new isotope of 243.  Time, there just wasn't enough time.

She tapped the bud in her ear, and started composing the manuscript of one last paper.  “We present here evidence for the creation of the 616 isotope of 243 Zz, half-life 82 msecs, along with traces of element 244, Uuq.” She glanced up at the list of proposed names for 244 her group had kept on the whiteboard, derived from the names of birthplaces and long dead mentors and far-flung galaxies and grinned wickedly. “…for which we propose the name sabaxorium, symbol Sx, in honor of our respected and long time competitor in this hunt, Maxine Sabaxoar.”

Four months later, Maxine wakes up to a tweetstorm of congratulations for having the first trans-zuzenium element named for her. She pulls up the paper and seeing the unmistakable traces of MvO in the accompanying supplementary data dump, shrieks, "I've been robbed.”
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Notes:  
In the 1970s, Tang Wah Kow of New Method College in Hong Kong suggested (based on an odd theory about triads and octaves) that the upper level for an element was Z=243. Further, he proposed that when that element was ultimately discovered, it should be called zuzenium (Zz). The suggested name he said was, "...deduced from a Chinese idiom 'The name stands behind Zun Zen, who (Zun Zen) came last on the list of successful candidates in a royal examination." [In "An Octagonal Prismatic Periodic Table" J. Chem. Ed. 49, 59 (1972)]

Eating periodically: is there thallium in your wasabi?

Wasabi, Iwasaki Kanen 1828
via Wikimedia Commons 

Could your wasabi peas be poisoning you?  Short answer. Maybe.

Delish recently posted an article on thallium — a highly toxic metal — in kale, the quintessential healthy green.  The Internet relished the irony of finding toxic metals in the highly touted greens. The piece points to an article in Craftsmanship magazine, which attempts to make a link between consumption of kale and thallium levels.  This is not new news.  There are dozens of reports, going back two decades, in the scientific literature of thallium in cruciferous vegetables, such as kale and brussell sprouts — and wasabi.

Thallium is definitely a nasty element, and has an infamous history of use as a poison in fact and fiction, starting with Ngaio Marsh's Final Curtain.  Read Deborah Blum's hair-raisingly fascinating Poisoner's Handbook (or her short article at Wired about a recent murder case in Princeton).  But as with everything, dose makes the poison, and the amounts of thallium in plants vary widely depending on the concentrations in the soil.  In highly contaminated soils, plants can contain enough thallium to be hazardous.  But if such highly contaminated soils were widespread, we'd have seen the effects already. (See this paper for some background.) (Also, you can leverage this ability and use it to clear out the thallium from a contaminated area.)

So how does thallium get into the plants? There is some evidence that thallium ions travel the same pathways as potassium ions (which play key roles in plant metabolism), and so might find their way into plants (and animals) though similar processes.

Thallium is also in the same column as boron, and elements in the same column of the periodic table often have similar behaviors, because their electrons are arranged in similar patterns.  For example, strontium, which is underneath calcium, sneaks into the body by way of the same processes calcium does. Boron is found in plants (coffee is a good source, and plants in the same family as kale are also heavy absorbers of boron); it is believed to be critical to cell wall formation.

And if there is boron and thallium, indium - in the same column is another likely companion. And yes, indium has been detected in plants in the cabbage family.  

As always, eating a wide variety of things is good advice, and it's key to remember that "natural" is not the same as "safe."

Eating periodically (not a quantum diet)

What elements are in chocolate?

Answer #1

Carbon (Chocolate)
Hydrogen (CHocolate)
Oxygen (ChOcolate)
Holmium (CHocolate)
Cobalt (ChoColate)
Lanthanum (ChocoLate)
Astatine (Chocol(ChocolAte)
Tellurium (ChocolaTe)

So you could have: CHoCoLaTe or CHOCOLate or....

Answer #2

(Presuming the letters are not required to be used in order - and yes, I wrote a piece of code to give me this for any word)
All of the above and
aluminum (Al), chlorine (Cl), calcium (Ca), cerium (Ce), helium (He), actinium (Ac), Technetium (Tc), thorium (Th), thallium (Tl) and tantalum (Ta)

Answer #3

Elements that have been detected in chocolate (in this case dark chocolate, rough percent of my recommended dietary allowance in parentheses assuming I eat only a 100 gram bar).

Carbon, hydrogen, nitrogen, oxygen, potassium (why cocoa is detectably radioactive), calcium (about 5% of my RDA), iron (125%), magnesium (70%), phosphorous, potassium (almost a gram, 20%), sodium, zinc (40%), nickel, sulfur, silicon, cadmium, lead (yep, lead, mostly from dust contamination during transport), mercury, arsenic, uranium (trace amounts, but yes, more radioactivity), aluminum, copper (from pesticides, but on the plus side gives you your RDA for this element), and manganese

Nearly one fifth of the known elements have been detected in chocolate, which clearly should be the backbone of any periodic diet.

What other elements are you eating?

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Just in case your chocolate doesn't have enough radioactivity for you:

Nitrogen in the snow

We are expecting another round of wintry weather tomorrow, and an article in the local paper noted that the snow and bitingly cold weather we have had recently are good for farmers.  The cold reduces the population of some pests, particularly the species making their way north.  The article also noted that snow contains nitrogen from the atmosphere, providing a little extra boost for lawns come spring.

The atmosphere is roughly 80% nitrogen, in the form of N₂.  The form matters.  Nitrogen gas is very unreactive, so much so that it many "air sensitive" materials are packed under pure nitrogen.  (The part of the air that is reactive is molecular oxygen, O₂.)  Snow certainly contains dissolved nitrogen gas.  Henry's law predicts the solubility of a gas in a solvent, water in this case, as a function of temperature.  It might seem at first glance counter intuitive, but gases are more soluble in cold solvents than in warm (the opposite is true of most solids, as anyone who has tried to dissolve sugar in cold ice tea knows).  An inch of snow contains about 7 milligrams of nitrogen gas per square foot, or about 1/3 of a kilogram in an acre of snow.  Given that fertilizers are spread onto fields at a field of roughly 300 kilograms per acre, it's not much.

The trouble is actually that this nitrogen isn't in a form that easily accessible to plants.  Nitrogen in the atmosphere must first be "fixed" or changed into a more reactive form, typically tetravalent nitrogen (ammonium) which is then converted to the nitrate ions that plants can use.  So where does the useful sort of nitrogen come from?

Industrially, nitrogen is fixed in the Haber process.  Since nitrogen is so unreactive, this requires pressures hundreds of times those of earth's atmosphere and temperatures more likely to be found on the surface of Venus (over 700^oF).  Nitrogen is fixed in the biosphere by microbes, which undertake an elaborate enzymatic dance to do this at low temperatures and pressures (and yes, scientists are on the job of trying to figure out how to get the enzymatic processes to work at industrial scales.)

Lightening strikes also convert minuscule amounts of N₂ in the atmosphere to nitrogen oxides, and industrial pollution has also injected nitrogen oxides into the atmosphere. Industrial pollutants are by far the biggest contributors. The nitrogen oxides become nitrate ions. These are the nitrogen sources that turn a blanket of snow into a gentle fertilizer.

To put it into perspective, snow and rain probably deposit about 5 kilograms total per acre over a year. It's not much, it's not quite all natural (the rates were much lower in pre-industrial days), but it's something.

An element by any other name would smell as sweet

Elemental naming was as fraught in the 19th century as it can be today (though now the IUPAC has rules and committees). Alternate names and symbols for elements persisted not merely for decades, but in some cases more than a century.

I've recently skimmed a number of articles about glucinium (Gl). Not familiar? It has 4 protons and these days is known as beryllium for the gemstone beryl, in which it can be found. Beryllium salts can taste sweet, hence glucinium. Beryllium was suggested early on an option, since the sweet taste of its salts was not a unique characteristic. Other metals, including lead and yttrium, form sweet tasting salts. Still, in 1890 many authors were insisting that glucinium was the preferred name, suggesting that the arguments were continuing nearly a century after the initial discovery. It took more than 150 years for the chemistry community to settle on beryllium.

Other elements have endured dueling names, including colombium (now niobium) and the sounds-too-awkward-to-be-real jargonium (hafnium!).

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In searching for an appropriate image, Google turns up lots of bathtubs, including this one. Not only does an antiquated elemental name appear in the description of this wild tub, but the term angstrom as well. Translation software, I'm sure, but what is being (mis)translated?

And I couldn't resist the post title, as one of my fellow Fellows at the Chemical Heritage Foundation is a Shakespeare scholar.

Elemental tales: Strong waters

I ran across a reference to aqua fortis in one of the commentaries in Chemical News (1891). The conversation is about a suit in court where a chemist was injured when an inappropriately packaged bottle of aqua fortis spilled. (It had a cork, and according to the rather snarky commentator, the judge — and the chemist in question — should have known that aqua fortis should not be capped with a cork.)

Aqua fortis, literally strong water, was once the common name for nitric acid. Concentrated nitric acid is a strong oxidizing agent (I can still see the small scar on my mother's hand from a spill in her undergraduate days), and I imagine would rather quickly eat away any organic matter, such as a cork. Glass would obviously be the preferred medium for storage. The suit is a frivolous one!

The term aqua fortis has fallen out of fashion, but its companion term has not: aqua regia, the royal water that would dissolve even gold. Aqua regia, as any general chemistry text will tell you, is a mix of concentrated nitric acid and concentrated hydrochloric acid (a 1:3 ratio by volume). Neither acid alone with dissolve gold (or a variety of other hard to oxidize metals), but the trick lies in the shifting equilibria.

Nitric acid is able to oxidize small amounts of gold, turning elemental gold into ions, Au³⁺. These ions then react with the chloride ions from the hydrochloric acid to form the complex ion AuCl₄^—. As the gold ions are pulled into the chloroaurate complex, the nitric acid oxidizes a bit more elemental gold. This goes on until all the solid elemental gold has been turned in chloroaurate ions floating around in solution. Imagine putting out a bowl of pretzels, as the pretzels get eaten, you try to keep it full by adding more pretzels. Eventually you run out of pretzels. The trick of using complex ion formation to drive something that isn't very soluble into solution is a common one.

Arguably the most famous example of this happened when the Nazis invaded Copenhagen. Franck and von Laue had given their 23 karat Nobel prize medals to Bohr to prevent the Nazis from confiscating them. Bohr was reluctant to bury them, sure that wherever they were hidden, a search would eventually turn them up. A chemist on staff, de Hevesy, thought to use aqua regia to dissolve the medals. After the war the gold was precipitated out and recast into medals; Franck received his recast medal in the early 1950s. Those were strong waters indeed that Bohr and de Hevesy waded into.

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You can read a bit more about the saving of Franck and von Laue's medals at the Nobel site and see a video of aqua regia in action here.

Ephemeral Elements

The late 19th and early 20th centuries were hotbeds of elemental discoveries (literally and figuratively). New elements came — and on occasion went. Some were known elements in unknown guises, such as previously unrecognized allomorphs. Others, like didymium, weren't elements at all, but mixtures of as yet to be identified elements (in this case neodymium and praseodymium). Some were more ephermeral than others.

Yesterday I ran across a description of the discovery of a new element in an 1890 issue of Chemical News: damarium, oddly enough reported in the Notes & Queries section and not among the research papers. The report of the gaseous element, collected in Damara Land (present day Namibia) was a bit over the top, even for a time when flowery prose was in style in scientific papers: "One of the party had in his hat a branch of a shrub, which in a very short time lost its green colour and assumed a violet blue..."

One contemporary report assumes it is a hoax, but several sources were not so quick to dismiss the claim, particularly in a period when elemental identity was in flux. At least one commenter wondered if it might be "helium" — an element as yet undiscovered on earth.

I wonder if it's worth tracking down the original cite if I can (the Chemiker Zeitung is available on microfilm at the Othmer). Ah...Google books has it here.

German chemical humor or not? What do you think?

Bunsen and quantum mechanics

Today's Google doodle honors the 200th birthday of Robert Bunsen, the inventor (or not?)of the eponymous burner. The doodle is great, click on it and it bubbles and whirs.

"It is known that several substances have the property of producing certain bright lines when brought into the flame. A method of qualitative analysis can be based on these lines, whereby the field of chemical reactions is greatly widened and hitherto inaccessible problems are solved. We limit ourselves here to developing the method for alkali and earth-alkali metals and demonstrating its value by some examples.

The lines show up the more distinctly the higher the temperature and the lower the luminescence of the flame itself. The gas burner described by one of us (Bunsen, these Ann. 100, p. 85) has a flame of very high temperature and little luminescence and is, therefore, particularly suitable for experiments on the bright lines that are characteristic for these substances." Opening to Gustav Kirchhoff and Robert Bunsen, Annalen der Physik und der Chemie 110 (1860), 161-189.

Bunsen is not a name typically associated with the development of quantum mechanics, yet I might argue he is one of the key figures. The observation of line spectra and the realization that the lines are characteristic of particular elements is a significant step toward the development of quantum mechanics. It's one of the observations that Bohr was trying to explain in his model of the atom. General chemistry texts boast figures of line spectra to demonstrate the point - I showed several in my lecture last week. This apparatus developed by Kirchoff and Bunsen made possible the routine observation of such lines. I have a beautiful brass example in my office.

This paper goes on to note that sodium, even at very low concentrations produces quite bright lines. It reminds me of the many happy hours I spent playing with my mom's gas stove and making flame tests on anything I could scrounge up (most of which contained sodium). Is this the formative experience that impelled me toward quantum mechanics? Who knows! I do still think of sodium and line spectra every time the pasta boils over and the flame on my stove flares that characteristic sodium yellow-orange.

Happy birthday, Bunsen, I might not have a job without you!

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There is more on Bunsen beyond the burner at The Sceptical Chymist.

Elemental Audio Visual

A chemistry friend shared this cover of Lehrer's classic litany of the elements:



It's worth the 85 seconds it takes to watch! The subtext is fascinating....when the elements flash by you can see the alternate searches Google is proposing. The searches for oxygen bars, I get, but how many people really need to know the price of lutetium? ($5.89 per gram for 99.9% pure lutetium metal here, or $13.99 per gram for "used" on eBay — your choice, act fast if you want to bid, though).

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H/T to Dr. Lisa!

Fiat Lux 1: On Fire for Quantum Mechanics

My sailboat's name is the Fiat Lux — "let there be light" in Latin — drawing from both my theological and scientific personae. I sail a Laser, an Olympic class racing dingy, which is an apt boat for a quantum mechanic. The ability to amplify light by stimulating an existing emission process was first predicted by quantum mechanics, then the apparatus to actually do it was built. Laser is really an acronym: Light Amplification by Stimulated Emission of Radiation. The radiation is electromagnetic radiation, not the radioactive radiation.

There's been a smattering of conversation about light production around my house this weekend between sailing the Laser, setting off fireworks and observing fireflies. One of my teen guests wondered how the fire in fire flies was different from the fire in fireworks. All light is not created in quite the same way....though there are some fundamental similarities.

There are really two fires in fireworks, the thermal explosives that send them skyward, and the "rockets red glare" — the glittering burst of color in the sky. The heat from the thermal explosion (usually blackpowder or a similar substance) is what trigger the colors.

If you ever done a flame test, putting a solid substance or a concentrated solution on a wire loop and placing it in a flame to see what color is produced, you've done the same chemistry. The extreme heat excites electrons in an atom or molecule, and as they fall back down to their lowest energy, or ground state, emitting a photon (a bit of light) that just exactly matches the difference in energy between the excited state and the ground state. An orange flame meant you had sodium on the wire, while a violet flame suggested potassium. More properly this technique is called atomic emission spectroscopy.

For atoms the picture you usually see in a high school text of this process is of a ladder, where electrons are shown moving from rung to rung. The larger the distance between the two rungs (or states) the higher the energy of the photon emitted. If the distance corresponds to photons in the visible region, you see a color, otherwise you have to use something fancier to figure out the energy of the photons being released.

Different atoms have different spacings between states and so the colors they emit when heated to high temperatures are likewise different. There are in fact many states, and so many types of photons can be emitted, but few are in the visible region.

If you click here, you can see a simulation of the photons you'd expect to see when an excited sodium atom returns to the ground state. Are you surprised that sodium can be used for yellow-orange in fireworks? Some urban legends suggest that lead (or radioactive barium) are used in fireworks, but if you look at the line spectrum of lead you can see why it can't be true -- there is no rung to rung jump in lead that corresponds to a visible photon. So a lead firework would be invisible! (Lead used to be used to make the fireworks "crackle"...)

(And it's true that barium salts are used in fireworks, but they are not radioactive. There are no naturally occurring radioactive isotopes of barium.)

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Read more:

An article at C&E News on the chemistry of fireworks

Related posts:

Jello lasers
Romancing the stone (lasers in the plot line of a romance novel)

Image from Wikimedia.

The pressure to preserve

Stephen Davey, associate editor for Nature Chemistry, blogged at the Sceptical Chymist about visiting the National Archives and seeing the Declaration of Independence, the Constitution and the Bill of Rights. He was surprised to find that the documents were stored under helium as opposed to argon - and wondered why. That started me wondering as well, particularly since the inert gases are not interchangeable in all circumstances (you can use helium to dilute the air mixture for diving, but not argon, for example.)

Helium is both more expensive (not an issue in this context, the cost of the gas inside the cases has got to be the least expensive piece!) and difficult to work with than argon. It can leak out through materials that seem air and water "tight". That's why those latex balloons that looked so cheery on the day of the party are withered and droopy by the morning. They're waterproof, but not helium proof.

In the 1950s the US National Bureau of Standards (now NIST) was charged with deciding on the best way to preserve the Charters of Freedom (the three founding documents of the United States of America). (You can read the full report here.) Helium was chosen, despite its propensity to leak through many materials, partly because a high purity, local source was readily available but most because of its thermal conductivity.

The designers of the encasements wanted a way to measure the pressure of the helium within the cases without having to open them, or remove a sample. Since the thermal conductivity of helium is very different than that of air, changes in the thermal conductivity (how heat moves between the panes) could be used to detect leaks. Argon's thermal conductivity is similar to air, so if argon leaked out and air in, the change would be hard to detect.

New casements were designed about ten years ago, with argon as the gas of choice this time. Sapphire ports are embedded to allow the atmosphere inside the cases to be monitored spectroscopically - by passing a beam of light through the port. Since the new methods of monitoring don't require the inert atmosphere to have a different thermal conductivity, it allows argon - which can't wiggle its way out the way helium can - to be used.

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The photo is from The Science News-Letter, vol. 62 (Dec. 6 1952), p. 359.

Sweet Stones

I was wandering the Cape Anne historical museum this winter and noticed in a 19th century ship's medical kit a vial labeled "sugar of lead." This is lead acetate, which tastes sweet -- and is reputed to have been used as a sweetener is days past. Other metal salts are sweet as well - yttrium salts and beryllium salts can both taste sweet.

Beryllium was first identified in 1798 by chemist Louis Vauquelin as an oxide in beryl and emeralds (emeralds are beryls with a bit of chromium added!). Since the chloride salt of the new element tasted sweet, the editors of the journal which published Vauquelin's findings suggested he call the oxide (or earth) glucina from the Greek, glyks (γλυκυς) for sweet. The elemental symbol used was Gl.

Beryllium was suggested as alternative once other sweet metal salts were found, for the gemstones in which the element was first identified. It took until 1949 for this to become the official IUPAC name of the element with four protons.

Beryls were used to make "reading stones," magnifying glasses, then eventually ground into lenses for eyeglasses.

Weird Words of Science: Lemniscate Elemental Landscapes

In reading an older paper about periodic tables, the author referred to the "lemniscate table of Gooch and Walker" - but didn't provide a figure, and I had to admit lemniscate was an unfamiliar descriptor. (It's not in the abridged Oxford English Dictionary on my iPod, either - so I don't feel all that ignorant!) Even a Google search was not particularly enlightening.

The full OED came to the rescue - "ribbon like", from the Latin for a ribbon. The term dates to the 17th century when Bernoulli used it to describe a set of curves. The term was new, the curves were not - Bernoulli's lemniscate was a special case of a set already described by Cassini.

Once I located a figure of Gooch and Walker's table, I would agree "ribbon-like" is a good description and it is certainly reminiscent of Cassini's figure eight curves (to give credit where credit is due).

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Figure of the periodic table from Outlines of inorganic chemistry‎ by Frank Austin Gooch, Claude Frederic Walker, Macmillan:New York, 1905. Figure of Bernoulli's lemniscate is from here.

It's Just a Phase

Video Recaps | Full Episodes | Webisodes

Allotropes are all the rage? Or at least sending Conan O'Brien over a very funny edge! The bit was inspired by this article in the NY Times science section. I'm not nearly this riveting when I lecture about allotropes, I've got to admit.

O'Brien gets the chemistry nearly right. My only quibble would be that he calls the different forms (the diagrams are the real thing, by the way) different phases, which they aren't really. They are technically allotropes, different structural forms within the same phase or state of matter. The quintessential example is the allotropes of solid carbon, graphite and diamond and a few others. All that said, when you draw a phase diagram for an element, you show the allotropes on it, and many chemists would characterize the change from one allotrope to another as a phase change.

Oxygen has some fascinating solid allotropes, including one that is a blue solid at room temperature!

Allotropes and architects: buckminsterfullerene

Responding to an earlier post on inert gases, a commenter wondered if buckminsterfullerene might act as an inhalation anesthetic - given that, like xenon, it's a large, polarizable ball of electron density. It might, if you could get enough to inhale. At room temperature, the vapor pressure is 5 x 10^-6 torr. Very roughly, that's about a billionth of atmospheric pressure. For comparison's sake, the pressure of xenon necessary to induce anesthesia is about 500 torr, or 65% of normal atmospheric pressure. If you want higher pressures, you need higher temperatures: buckminsterfullerene sublimes (goes directly from the solid to the gas phase, like dry ice) just above 1000F. Not great to breathe...

While likely impractical as an anesthetic, buckminsterfullerene has asthetic properties. It's a highly symmetric molecule - having iscosohedral symmetry. Kroto and Smalley discovered the new allotrope of carbon, C₆₀, in vaporized graphite and named it for the architect (Buckminster Fuller) who made famous the geodesic domes it resembled. Two more familiar allotropes of carbon are graphite and diamond.

Allotropes are differing forms of the same element. The roots of the word are Greek - allos for different and tropos for "turn of mind". A different turn of mind? It's what Smalley needed to propose the now iconic structure, over a beer at his kitchen table.

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Another allotrope of carbon is lonsdaleite - named for Kathleen Lonsdale, an Irish crystallographer who determined the structure of benzene and my brother-in-law's godmother.

Inert gases aren't always inert

Earlier this week I posted about the intoxicating effects of nitrogen gas at high pressures, which leads divers to substitute helium for nitrogen. An astute reader wondered in the comments why argon wasn't used, as it is substantially cheaper. It turns out that argon is even more potent intoxicant than nitrogen at high pressures! But aren't argon and helium inert gases?

The elements in the last column in the periodic table comprise what IUPAC (the International Union of Pure and Applied Chemists is to chemists what the IOC is to sports) calls Group 18, but what most of us learned in high school to call the noble or rare, gases. Helium, argon, neon, krypton, xenon and radon are indeed all gases under standard conditions, but the modifier misses the mark by a bit.

Rare? Take a deep breath, you've just inhaled about 100 mg of argon. Almost 1% of the atmosphere is argon; there is almost three times as much argon in the air as there is CO₂. "Noble" generally means "unreactive" to a chemist. The noble metals, such as gold and platinum are resistant to oxidation - they don't rust - unlike the "base" metals such as iron and copper. Much like gold and platinum, under the right conditions these inert gases can be made to react. The first noble gas compound - xenon hexafluoroplatinate - was synthesized in 1962, but there were earlier clues that these gases might not be completely unreactive. The anesthetic effect of xenon had been observed in the 1930s, and reports of its use in clinical settings appeared in the late 1940s.

The mechanism by which nitrogen, argon and xenon behave as anesthetics isn't completely understood. The best theories at the moment suggest that the gases interact with ion channels - but whether they binding chemically or physically is not clear.

Weird Words of Science: calcium

The isolation of metallic calcium was reported by Humphrey Davy 200 years ago this year. The name comes from the Latin for lime: calx. Compounds of calcium are like duct tape – they hold lots of stuff together. Calcium carbonate keeps clams covered, calcium oxide (lime) is the mortar that held the Roman Colliseum together, and calcium sulfate (plaster of Paris) has been holding broken bones in place for more than a millennium. Calcium keeps us from being a puddle on the floor as well. More than 90% of the body's calcium stores are in the bones.

Blue Color Workers

The title of this post was inspired by a student blooper in a sociology paper where the writer surely did not mean to say "blue color workers". Spell checkers have their limits. In the right context, however, blue color workers is not a candidate for Richard Lederer's next collection.

Exposure to silver can cause argyria, in which the skin turns a grey-blue color as a result of deposits in the dermis of metallic silver and silver compounds. Unlike the orange coloration that eating too many carrots can cause, the dark grey cast of argyria is permanent. The condition can be striking if the entire body is affected. Barnum & Bailey's Blue Man was found at autopsy to have argyria, perhaps from exposure while working as a silver miner: a real blue color worker.

Argyria in this century is more likely a result of exposure to quantities of silver in non-industrial settings. Silver preparations were used pharmaceutically in the early 20th century, and much of the literature about silver and skin discoloration dates to that time. There are reports of cases of argyria arising from use of colloidal silver compounds. Externally applied, salts of silver are effective antiseptics, hence the marketing of these silver solutions as nutritional supplements "to support the immune systems" and as "all-natural antibiotics". There is no evidence that these compounds are effective in these ways when taken internally - and the risk of being permanently blue is not one to be taken lightly! The FDA has ruled that products containing silver or colloidal silver are "not safe and effective" and may not be sold as having any medicinal benefits. Despite this, colloidal silver is readily available.

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The photo is of Rosemary Jacobs, who suffers from argyria, and is used with her permission. In 2006, Stan Jones, ran as the Libertarian candidate for U.S. Senate in Montana. He took a colloidal silver compound in 1999 and now has argyria as a result.

Elemental Tales: Reduced Iron

In the 1970's I was a TV news junky. Dinner was typically late - my dad commuted an hour plus from LA in those days - and my mother would kick me and my homework off the table a bit before 6. I'd duck into the den to get the update on the war (Vietnam, not Iraq!) that my friends' older brothers were fighting. Even then, I was clearly not the advertisers' target demographic. The ads ran the gamut from DentuGrip to Phillip's Milk of Magnesia. And of course, Geritol - exhausted wives re-energized by curing their "iron poor blood" with Geritol, much to their husbands' delight ("My wife. I think I'll keep her!")

More than one in ten adult women (12-49) in the US do suffer from "iron poor blood" or more technically iron deficiency anemia, and world-wide it is the most common nutritional deficiency. (By some estimates two-thirds of pregnant women in developing countries are anemic, primarily due to lack of iron in their diets.)

The body does an impressive job of holding onto the iron it needs not only for synthesizing the oxygen carrying protein hemoglobin, but for enzymes used in other key processes. Total body stores of iron run from about 2 to 4 grams, about two-thirds circulating around in hemoglobin, and twenty percent held in reserve in the bone marrow. The daily loss ranges from 1 milligram to about 1.5 mg in women of child-bearing age. Which begs the question, why is the FDA's recommended dietary allowance of iron 20 mg?

The answer has much to do with the ability of the body to extract iron from various sources. The best form of iron, in terms of its bioavailability, is heme-iron, or iron bound to the plate-like heme structure found in hemoglobin. Non-heme iron, found in plants like the iconic iron source spinach, is tougher for the body to extract and use - estimates are only 10 to 15% of the iron can be absorbed. So to get that 1 mg a day, you need to consume about 10 mg a day. If spinach is not your cup of tea, try dark chocolate; there's 2.3 mg of iron in a 100 gram bar, about the same as in the identically sized serving of spinach.

Lots of Americans get their iron from fortified cereals. Read your box of Total. You'll find that a cup gives you 18 mg of iron. Check the ingredients and you'll notice that it's added in the form of reduced iron. Reduced iron is not iron on a diet, but iron is the pure metallic form. That's right, there's tiny iron filings in your cereal. If you're feeling experimental, toss a couple of cups with milk into the blender, then run a magnet through it. You'll pick up the filings on the magnet. The acid in your stomach turns the metal into an ionic form (Fe²⁺).

Better yet, cook in cast iron. Scramble your eggs in a cast iron frying pan and you can triple the iron content (from 1.5 mg to almost 5 mg). Cook something acidic, like spaghetti sauce and you can up the iron content by a factor of ten.

Husbands of tired wives might thus consider a nice box of dark chocolate covered apricots rather than replacing the window shades with ads for Geritol...it might cure more ills than just iron deficiency. I would not advise a cast iron frying pan with a bow!

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Dried apricots have twice the iron content of spinach and are much tastier when drenched in chocolate.

The heme figure is taken from here.