Breathing Deeply

The tunnels deep beneath New York that bring crystal clear water from the reservoirs upstate to the city are aging. Divers are busy assessing the infrastructure - and it's literally a high pressure job. In order to avoid time consuming daily decompressions, the divers are living in a high pressure environment for weeks at time, almost 20 times normal atmospheric pressure. As AP reports, the pressures require that the men breathe a helium-oxygen mixture. Unfortunately, the reason given in the article for breathing the squeaky voice inducing mix: "the nitrogen in regular air is too heavy at 600 feet and their lungs could not handle the pressure." is utter nonsense.

Nitrogen does not weigh more under pressure, and the total pressure of the gas in the divers lungs is high, regardless of the identity of the gas (oxygen gas weighs more than nitrogen does, in fact). The real reason has to do with Dalton's law of partial pressures, and the fact that at high pressures, neither oxygen nor nitrogen are benign substances.

Dalton's law says that the pressure of each gas in a mixture is a function of the percentage of that gas and the total pressure of all the gases. For example, at 30,000 ft, where the total pressure is 0.3 atm and the fraction of oxygen in the air is 21%, the partial pressure of oxygen is 0.063 (humans need a partial pressure of about 0.1 atm to oxygenate their blood).

At the depth of the NYC tunnels, the total pressure is just over 18 atm, so the partial pressure of oxygen would be 3.8 atm. Above a partial pressure of roughly 1.5 atm oxygen gas is seriously toxic. The partial pressure of nitrogen 600 feet below the surface is about 14 atm. Nitrogen narcosis, rapture of the deep, sets in at pressures above 4 atm. At these depths, nitrogen is essentially an anesthetic!

Introducing an inert gas into the breathing mix, such as helium, reduces the percentage of oxygen and nitrogen in the air, thus reducing their partial pressure and reducing the danger of oxygen toxicity and nitrogen narcosis. The need for the specialized breathing mix has nothing to do with the heaviness of the nitrogen and everything to do with the toxic effects of these gases at high partial pressures.

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Eliminating nitrogen completely from the mix can also reduce the potential for developing the bends (bubbles of gas that form in the tissues when pressure is reduced) - but that has to do with Henry's Law and ladies corsets, and is another blog post!

Hydrazine: Hype or Hypergol?

Last week the US government announced that it believes it has successfully breached the fuel tank on a dead satellite, effectively destroying the toxic fuel stored on board: 1000 pounds of hydrazine. Hydrazine is a simple nitrogen compound, two NH₂ groups joined by a NN single bond. How does such a simple compound power a rocket?

Hydrazine is a hypergolic propellant - one that ignites as soon as it comes into contact with an oxidant (something that will react with it to effectively strip away some electrons from the reactant and force the molecule to bond differently, the changes in the bonds between atoms are what release the energy). Hypergolic is apparently a term coined by the German rocket program from hyper (very) + ergon (Greek for work) + ol (from oleum, the Latin for oil). Hydrazine is that, a liquid (if not particularly oily one) that can be used to push satellites around in orbit - to do work.

Hydrazine is a solid in the satellite's tanks, and once thawed can be catalytically and rapidly decomposed. Almost any metal will do, though iridium is the usual choice. The reactions produce lots of very hot gases, which you can direct through a thruster:

3 N₂H₄ → 4 NH₃ + N₂
N₂H₄ → N₂ + 2 H₂
NH₃ + N₂H₄ → 3 N₂ + 8 H₂

A little thermochemistry can quickly tell you just how much energy you might produce from 1000 pounds of hydrazine. The overall reaction is:

5 N₂H₄ → 5 N₂ + 10 H₂

which releases 50,000 Joules of energy per mole of hydrazine. A mole of hydrazine weighs about 32 grams, so you get enough energy to make a cold cup of coffee hot from just over an ounce of hydrazine (do NOT try this at home!). If all the hydrazine in that satellite went up at once, it would release about 8 billion Joules (enough to keep the average US citizen in energy for more than a week).

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A photo of a standard satellite thruster.

Melting Points

Pain perdu - a delicious part of my New Orleans heritage and better known in most of the US as french toast - has a long history. The earliest extant recipe is in Latin and dates to the 4th or 5th century! Friday brought a snow day for my kids, and come evening, some experimental time for me in my favorite home lab.

After a day spent teaching and shoveling in the sleet, I made pain perdu aux pommes from Simon Hopkinson's Second Helpings of Roast Chicken. Think french toast, vanilla custard, apples and caramel sauce. The first step in making the caramel sauce is to melt sugar over high heat. As I stirred the dry sugar in my heaviest sauce pot, alert for the first sign of melting, I flashed back to my days in an organic chemistry research lab. Melting points were used both to identify products (though even then, spectroscopic methods such as NMR were the gold standard) and to verify purity. Taking an accurate melting point required patience - and being attentive to the appearance of that first glistening drop of liquid in the fine capillary tube. It looked almost as if the crystals were sweating.

How is the purity of a compound related to its melting point? An impure sample will tend to melt over a few degree range, pure samples will melt at a sharp temperature. Impurities in a solid will also depress its melting point, in the same way that applying salt to ice (another application of chemistry appropriate for a snow day) lowers the freezing point. This phenomena also offers a low tech way to confirm the identity of a compound. Make a mixture of the sample to be identified and a known sample of (presumably) the same stuff. If the melting point is sharp and the same as the pure compound, the unknown is certain to be what you think it is. This will work even if the melting points of the two compounds are fortuitously the same.

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A nice film of a melting in a capillary tube can be found at Wellesley's organic chem lab site.

Repackaging Vitamins: Niacin

Vitamins are small molecules (where small is relative to proteins!) that a living organism cannot synthesize, but are nevertheless required. The word vitamin was coined by a Polish biochemist, Kazimierz Funk by sandwiching together "vital" and "amine". Not all vitamins turned out to be amines (molecules with an NH₂ group in them), however the name stuck.

One such non-amine "vital amine" has the structure shown below. It's a carboxylic acid (the COOH group). Originally designated as vitamin PP, it is now better known as the third of the B vitamin complex or B₃. PP stood for pellagra preventing factor. Pellagra is a nutritional deficiency, once common in Italy, that results in rough skin - pella is Italian for skin.

The original common chemical name for B₃ was nicotinic acid. (The synthetic form can be made by oxidizing nicotine with nitric acid.) In the late 1930s, niacin (NIcotinic ACid vitamIN) was adopted as the preferred name, to avoid confusion with nicotine. (I'm unclear why this was undesirable; smoking was pervasive.)

Repackaging scientific terms to make them less frightening for the general public is not just a historical phenomenon. Much more recently the application of NMR (nuclear magnet resonance) to medical imaging saw its "nuclear" dropped (thus forestalling any potential association with nuclear radiation) to become MRI (magnetic resonance imaging). It should be made clear, that like nicotinic acid, which contains no nicotine, NMR does not require nuclear radiation.

Ant-acids

I'm teaching general chemistry this semester. Acids and bases are currently on our agenda, in particular how to assess the strength of an acid based on its molecular structure. When dissolved in water, strong acids, such as hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) always transfer their protons (H) to water. For example: HCl + H₂O → Cl^– + H₃O⁺. Weak acids result when only some acid molecules transfer their protons to water. Organic acids, containing only carbon, oxygen, hydrogen and nitrogen, are generally weak acids. The archetypical weak organic acid is acetic acid, better known as vinegar: CH₃COOH. It's not the simplest organic acid, that would be formic acid: HCOOH.

Formic acid was first characterized in the late 17th century. Naturalists had observed that the vapors emitted by ant hills were acidic (using the equivalent of litmus paper), and in 1671 John Ray extracted the pure acid by distilling the crushed remains of red ants. Formica is Latin for ant, hence the name translates pretty literally as "ant acid". Formic acid is at least partially responsible for the sting in bee stings, ant bites and stinging nettles.

Even though chemists call formic acid weak, a 0.10 M solution has a pH of 2.4 (for comparison's sake, the same concentration of HCl has a pH of 1.0).

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I remember find ants all over my Formica counter in my post-doc days. Does the ubiquitous counter-top material have any connection to ants? Apparently not. It was originally created as a substitute for mica insulators. For mica....

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.

Carbon Dioxide Curiousities

• It won't burn.
• No matter how cold you make it, you can't turn it into a liquid at atmospheric pressures.
• It sublimes, going directly from a solid (dry ice) to a gas (one way to make very creepy fog).
• It's heavy. Burning 1 gallon of gasoline (weighing about 8 pounds) produced 25 pounds of CO2.
• You can make a supercritical fluid out of it - a state of matter that is neither solid, liquid, nor gas.
• It's a critical ingredient in chocolate chip cookies - produced in situ by the reaction of sodium bicarbonate and the potassium salt of tartaric acid.

Weird Words of Science: nonillion

“Do you know what a nonillion is?” queried my mathematician spouse as he plopped into the chair in front of our household computer, “Is it Latin or something?” “Something to do with nine I’m sure,” I offered from the sofa. “That’s OK, I can google it.” What’s the urgency I wonder? 1 vs. 100 is the issue. The mob won.

So what is a nonillion and does it have anything to do with nine? The short answers are: it depends and yes. Nonillion is a novelty number - a term I just coined for numbers that have names, but no uses. Like a googol. The early British usage of nonillion was for 10⁵⁴ - nine million millions. Americans used nonillion for 10³⁰ or 10^3+3x9. In other words, the result of multiplying a thousand (10³) by a thousand nine times.

The system of counting by thousands is sometimes called the “short scale” (from the French term echelle courte). The long scale (echelle longue) counts by millions. Most English speaking countries (both the US and UK included) use the short scale, while most of the rest of the world uses a version of the long scale.

It’s hard to get a sense of scale with these enormous numbers, but a nonillion (long scale) is (very) roughly the order of magnitude of the mass of the universe in kilograms. There are roughly 5 nonillion bacteria (short scale) on earth.

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Literary trivia: e.e. cummings used nonillion in the Enormous Room and in at least one poem.

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.