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.

---

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.)