Weird Words of Chemistry: Frigorific

I ran across this word when my youngest, who I'm coaching for the thermodynamics event for Science Olympiad,asked me why the freezing point of water was 32^o on the Fahrenheit scale. The Celsius/centigrade scale was originally pinned to the freezing point and boiling point of pure water at 1 atmosphere of pressure. (Now it's pinned to absolute zero and the triple point of water.) What physical property was 0^o linked to? The freezing point of something other than water? I had to admit I didn't know and now that my curiosity was piqued, went off to hunt it down.

The zero of Fahrenheit's temperature scale was essentially pinned to the temperature of a "frigorific" mixture of ice, water and solid ammonium chloride in a 1:1:1 ratio, along with the freezing point of water and the temperature of the human body. Frigorific seems to have been coined by Robert Boyle to describe particles of cold that were transferred from body to body, and ultimately got attached to mixtures that achieved a particular temperature regardless of the starting temperatures of the materials. Wandering through the old chemistry literature, I found this table of frigorific mixtures "sufficient for all practical and philosophical purposes, in any part of the world in any season," useful in the days before refrigerators, still useful for those who need a constant temperature bath at low temperatures.

The size of a degree was set by bisecting the difference between the point at which ice and water were in equilibrium and body temperature six times, or 64 degrees (2⁶). Binary was easier to use when you had to make your own instrument than decimal.

Frigorific has essentially vanished from the chemist's vocabulary, though it's still apparently alive and well in the engineering literature. As words of science go, it sounds awkward to my ears — as roughly sharp as heaved Arctic ice.

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Nova has an excellent piece on the hunt for absolute zero. Thanks, Kathryn J for the reference!

For more on what I think about well-formed science words, you can read "Neolexia" at Nature Chemistry.

What makes a molecule beautiful?

I just finished a piece for the March issue of Nature Chemistry on what (in my mind) make a molecule beautiful. I will admit a preference for sparer, less baroque structures. (If you want to know more about my molecular aesthetic, you'll have to wait for the piece to appear!). In the meantime there is an article in this month's Nature Chemistry with the intriguing title "Quantifying the Chemical Beauty of Drugs" [Bickerton et al. Nature Chem. 4, 93-97 (2012), full text is free]. It's not so much beauty in the abstract these chemists are trying to quantitatively capture, but desirability. How attractive is this molecule as a target for drug development? Would a chemist be willing to surrender time and bench space to the synthesis of this molecule?

The model takes as its inspiration Lipinski's rule of 5. If most or all of Lipinski's five characteristics are present, a molecule has a good chance of being a viable candidate for an oral drug [Lipinkski et al. Adv. Drug Dev. Rev. 23 3-25 (1997)]. The goal is to develop an expert model system, one that mimics (or improves on) a chemist's intuition about what makes for a good drug.

Earlier work had suggested that chemical fashion sense is drifting toward more baroque structures for their drugs, despite various rule sets that suggest that bloated molecules are less likely to survive to clinical trials. Chemists apparently like their molecules "tractable" (which would seem to mitigate against molecular overelaboration?), synthetically and otherwise! Molecular docility is desirable.

For a somewhat darker take on chemical intuition and seat of the pants drug design read "Chemists in the Shadows" by Adam Piore in March's Discover Magazine. The article focuses on underground chemists who are developing new recreational pharmaceuticals that skirt current drug laws (steroids for athletes, and rave drugs). The conceptual framework used by some of these chemists would be familiar to any medicinal chemist (particularly in the early days, before QSAR).

Being a philosophess

"...as a Philosophess she will not be discouraged by one or two Failures" Benjamin Franklin, in a letter to William Brownrigg dated 7 November 1773, where he wonders if Mrs. Brownrigg has succeeded in making Parmesan cheese (which I have to admit, I did not think was a cheese that colonial Americans knew of).

I appreciate Franklin's confidence that a woman could conduct rational experiments, particularly as at this moment I am virtually sitting on top of the site of Franklin's house in Philadelphia — I can see it from my window — working at being a Philosophess myself. I began a two month stay at the Chemical Heritage Foundation in Philadelphia today, as the Herdegen Fellow in the History of Scientific Information. My project is looking at how chemists, now and in the 19th century, deal with critical commentaries on the primary literature. Where are the commentaries located and does location change their tenor and/or content. I'm off to learn a bit about ways to computationally evalauate emotional tone, and to find some compelling narratives of critique in the 19th century and the 21st century.

I briefly wondered in my most recent Nature Chemistry Thesis column about what it meant for me to be working as both a historian of chemistry and a chemist, and how much of one field should we be exposing students of the other field to. Just how much history of chemistry does a chemist need to know to function well as a chemist? And if you do need to know something, what sorts of things? Dates? People? Materials? Methods? You can read my musings at Nature Chem, and those of Qian Wang and Chris Toumey on the same topic here. (Sorry...you or your institution need a subscription to see these, or if you would like a reprint of mine, drop me an email.)

Don't drink the water

"Don't drink the water from the sink!” read a sign taped to the mirror. As I was in rather desperate need of a glass of water before rehearsing the piece I would sing solo at Christmas, I was glad to find someone had left a gallon jug of distilled water and a stack of paper cups. Rehearsing the next day, as I went to grab a cup of water, a colleague pointed out that yesterday someone had mistakenly put out distilled water, which he had swapped for spring water. “Hopefully no one drank it!” he said.

“Why not?” I inquired.

“You’re not supposed to drink distilled water.”

Ah. Yes and no.

Distilled water is water that has been boiled, trapped as steam and condensed, leaving behind the non-volatile impurities (the stuff that doesn’t easily turn into a gas, like metal salts). Other components, like alcohols can still be carried along into the distillate.

Distilled water lacks most of the ions that tap water has, and thus, much of its flavor. Some of the ions (such as fluoride) in regular tap water may have health benefits, so a steady diet of distilled water may deprive you of certain useful trace elements. Conversely, drink water that is too hard (has a lot of ions in it) is correlated with kidney stones. It’s unlikely that the ionic content of your drinking water has a huge impact on your health (despite claims found here and there). All of the trace elements (including fluoride) can be found in other food sources. And distilled water’s osmotic pressure isn’t so different from that of plain water, therefore drinking it will not cause the cells in your body to suck up water until they burst and you begin to bleed internally (yes, this theory is out there, for both distilled water and deionized water). Bottom line, yes, you can drink distilled water.

That said, you probably shouldn’t drink the distilled water in most labs, as it is not tested to be free of bacterial contamination (which it can pick up in storage tanks) or volatile organic compounds. The same goes for bottled distilled water that hasn’t been tested to be certain it’s potable.

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And while we're on urban myths about water, it's impossible to completely remove all the ions from water. Water is always in equilibrium with hydronium ions (H₃O⁺) and hydroxide (OH^-).

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Image Copyright Filipe B. Varela, 2011. Used under license from Shutterstock.com

Changing exams

I just handed out a math assessment in my physical chemistry class, the same one I’ve used for the last several years. I generally don’t re-use exams (though I know colleagues who do), though I do re-use questions. By now I’ve been creating exams for more than a quarter of a century, and I wonder what the drift has been like over that time. How are the questions I ask now different (or not!) from what I asked 25 years ago? Or have the questions remained the same, and just the answers changed?

Fueling my introspection are the selections from the University of London’s 19th century bachelor’s degree exams. (H/T to a tweet from Nature Chemistry and the RSC). The chemistry question is one I could envision asking my students on an exam: “Explain the nature, from a chemical point of view, of the chief operations involved in the production of a photograph.”

The only catch, of course, is that the answer I’m expecting could be quite different than what the examiners in 1892 expected. In 1892, production of a photographic print necessarily involved silver, developers and fixing agents — and a darkroom. In 2011, production of a print could involve silicon and germanium, and a clean room. The theoretical underpinnings are less about pH and solution chemistry and more about semi-conductors and quantum mechanics.

What other reasonable exam questions might I ask, where the answers have changed so dramatically?

(And you have to love the example English question - just how important were werewolves in the 19th century?)

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Photo of 39/365 Kodak Vigilant Six-20 Antique Camera, by M.Christian on Flickr.

Can gender gaps impede scientific progress?

My commentary on Marie Curie and the paucity of women chemistry Nobel laureates ends wondering

"...if what underlies the inability to fully acknowledge the social biases that obscure and downplay women’s scientific achievements, and the ways in which our spaces silently speak to us about who belongs and who doesn’t, who appears capable and who does not, is the assumption that if a Marie doesn’t make a critical breakthrough, of course, a Pierre somewhere will. Will chemistry make all the critical leaps it could, without the contribution of half of its finest minds?"

Last week, the president of Bryn Mawr College (where I teach) had an opinion piece in Inside Higher Ed about closing the gap for women in science and engineering. She, too, worries that progress in science and technology is impeded by lack of participation by women (and I would add the lack of recognition for women's work in these fields) President McAuliffe writes "As long as there is a gender gap in these fields, there will be an innovation gap."

Some readers of McAuliffe's essay had a hard time imagining that scientific progress could be impeded when women are underrepresented or sidelined in science and said so in the comments. Sam Kean's delightful Disappearing Spoon includes a clear counterexample: In 1934, Ida Noddak suggested the possibility of atomic fission. Her work was dismissed as "ill conceived and unfounded" by Emilio Segre (who won the Nobel prize in physics for the discovery of the anti-proton); Irene Joliet-Curie similarly thought it possible; Lise Meitner definitely discovered fission in 1939 (and Otto Hahn won the Nobel for the discovery).

Another example on the same theme: Lise Meitner also discovered the Auger effect, in 1922, a year before it was discovered by Pierre Auger (for whom it is named).

I realize these are historical examples, but they do prove the point. A blanket disregard (for whatever reason, be it gender, country of origin, venue for publication) for the contributions of a subset of scientists can impede the progress of science. As Matt

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Read about how the cover was made.

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Sex in the citadel of science

"The problem was to give birth to a boy
and not a girl," said the fathers of the atom bomb.
Marie Curie did not give birth to any joy.
Tenderly she leans toward jars of glowing radium,
as she had earlier at the bed
of her sleeping daughter Irene. (And then she bore Eve!)
Four years clothed in bitter smoke, in a shed,
stirring a mass in ebullition, nothing secretive,

an iron cauldron, iron rod nearly as big as herself,
a shed no one wanted, not fit for cadavers.
Science is the primordial interest of my life,
nor do I know whether I could live
without the laboratory. Her problem—to give breath,
to let there be light, out of slag, abandoned earth.

— from "Her Crucible: A Poem of Marie Curie" by Margaret Almon

In the latest issue of Nature Chemistry, I have a commentary speculating on why women, despite their increasing presence in the field, win the Nobel in chemistry less frequently than 100 years ago. The essay is framed around Marie Curie, the first woman to win the Nobel prize in chemistry. This year marks the 100th anniversary of Prof. Curie's Nobel (her second).

It's not about mathematical ability (sorry Larry Summers, there's hard data that punctures your theory) or lack of inherent interest. Instead, I wonder if it has to do with the built environment: the size, color, shape of the laboratory and its equipment:

Built space is not neutral, as Winston Churchill noted, “we shape our buildings, and afterwards our buildings shape us.” As much as scientists use labs to create science, labs themselves create scientists. (Read the rest here....)

Psychrometry - or how to tell when it's crazy hot out

The heat index is 107 ^oF (42^oC) at the moment. It's hot, and I'm procrastinating going outside by blogging.

My youngest son is doing summer theater, and their rehearsal space is not all air conditioned. So I bought him a cooling towel to help him stay comfortable. When he asked how it worked, I said it was like having a portable swamp cooler — a familiar item as my dad used one for years to cool his house.

The basic principle at work is that it takes energy to make water evaporate. Unless the relative humidity is 100% (in other words, the air has all the water it can hold), water will evaporate. If you keep running air past a wet surface (think a fan blowing past a damp towel, or the breeze blowing over your sweaty face), water will continue to evaporate as drier air is constantly being replenished. The energy to turn the water from a liquid into a gas has to come from somewhere, in this case, the surrounding air and the water itself. The air gets cooler. Whew!

The towel works similarly, there is a very large damp surface area (why the fancy $15 towel really does works better than a damp cotton lawn handkerchief, a much higher surface area than the smooth cotton weave) and as you move around, air moves past. The water evaporates, pulling energy from the water in the towel and makes it colder.

To get a sense of how much energy that is, it takes about 34,000 J to evaporate 15 grams of water (about a tablespoon). 34,000 J is roughly 8 nutritional calories. If you pulled all that energy out of a cup of water, the cup of water would cool off to about 41^o F. (In practice, you don't get things this cool!)

This whole endeavor depends on the air being able to soak up some water, so if the humidity is too high, you are going to be crazy hot towel or no. Swamp coolers work great in desert areas (where my dad lives, for example), and are pretty much useless in New Orleans.

So how cool can you get? To figure it out you need the dry bulb temperature and the wet bulb temperature of the air. The dry bulb temp is just the temperature of the air measured in the usual way (being careful to keep the thermometer out of the sun). The web bulb temperature is obtained by blowing air over a thermometer whose bulb is fitted with a tiny damp sock. For that you can use a sling psychrometer (see the video).

Too hot to be slinging thermometers around? Look up the dew point (your favorite weather app will likely have it) and you can estimate the wet bulb temp this way:

1. Subtract the dew point from the ambient temperature (what your regular thermometer reads)
2. Divide what you get in step 1 by 3.
3. Subtract the result in step 2 from the ambient temperature.

Right now the thermometer outside my window reads 100^o F, the National Weather Service says the dew point is 70^o F, so I take 100-70=30; 30/3 = 10; so the approximate wet bulb temperature is 100-10 or 90^o F.

Once you've got the wet bulb temp you can figure out just how much cooling you can get with a fan and a damp towel!

1. Subtract the wet bulb temp from the ambient temp (the dry bulb temperature)
2. Multiply the difference by 0.8 (assuming the process is about 80% efficient, which is a pretty reasonable estimate)

My calculations suggest that the best I could do to produce cool air in my study this afternoon would be 80% of *100-90) or 8 degrees of cooling. 100^o F or 92^o F? Both are way too hot...I think it's time to stop writing for the day and head for the pool!!

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There are more sophisticated ways to do this, talk to the meteorologists if you want to know more.

Psychrometry comes from the Greek for cold ("psuchron") and should not be confused with anything psychiatric (unless you are talking about mad dogs and Englishmen...)

Writing (in) blocks

I'm writing this summer on a wide range of projects, which means writing for a substantial period every day. That said, I recently took a bit more than a full week away from the keyboard, doing no writing at all (not even email) except for few (handwritten) sentences each day. In their delightful piece in Nature on turbocharging your writing (free), Maria Gardiner and Hugh Kearns point out that "binge writing" — writing on the rare occasions when you have huge blocks of time — is generally not as effective as "snack writing" writing often (nearly every day) for shorter periods. (In my life it can be a challenge in some weeks to find an uninterupted 45 minutes or hour each day.)

Gardiner and Kearns note the barrier to writing again when it's been a long time since you last sat down to write can be huge. I won't argue with that. As I sat down this weekend to work on a 500-600 word column due this morning (at the latest!) after my week off, I could feel the creaks and groans. Really, 500 publishable words? How about I warm up with a blog post or write a couple of emails? Fortunately, deadlines are great motivators, especially those that are hard and fast as this one is (the paper goes to bed on Tuesdays, with or without my column). The piece went off this morning, and I'm ready to really dig into a couple of project tomorrow morning.

I would add to Gardiner and Kearns good advice that interruptions — those that knock at your door and your own desktop temptations — are a real hazard. Silence the phone, close the email browser, barricade the door (necessary in my house, the cat opens it otherwise), tell students/colleagues/kids that you cannot be disturbed for anything short of (fill in your favorite catastrophe here). Some research suggests that each interruption costs 5 to 10 minutes of time to refocus on the task at hand (plus whatever time it took to deal with the situation that led to the interruption). If you only have 45 minutes to write, and are interrupted twice, you may have lost nearly half your writing time.

If you want more advice about writing for the professional science journal, join me on Thursday, July 14 for a one hour conversation I'm moderating for the American Chemical Soceity with Dr. Cynthia Burrows (senior editor at Journal of Organic Chemistry) and Dr. George Schatz (editor in chief of Journal of Physical Chemistry.) More details are here. They are taking questions live, so sign up (it's free, but you need to register) and ask away.

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Photo is by Brandi Korte. Used under Creative Commons license.

Two thousand mockingbirds

I'm writing final exams for two intro chem courses. I try for a light touch brush of humor on at least a couple of the questions, it's stressful enough without every question probing deeply important things.

Some useful (in this context) unit conversions:

2000 mockingbirds = 2 kilomockingbirds
10^-6 fish = 1 microfiche
454 graham crackers = 1 pound cake
10 millipedes = 1 centipede
10 monologs = 5 dialogues
2 monograms = 1 diagram
8 nickels = 2 paradigms
10^-2 mental = 1 centimental

Have more to suggest?