Hidden figures: 2.303, slide rules and classrooms mired in the last century

A five -place table of logarithms from my dad's CRC Handbook of 

Mathematics (why is that set of values circled?) and a circa 

1958 Hemmi 257 slide rule designed for chemical calculations.  

 Wonder why random values of 2.303 are "hidden" in formulae? To make them easier to use with a slide rule.¹ 

A slide rule?  The last slide rule slid out the door of Keuffel & Esser in 1975 (they sent their engraving equipment to the Smithsonian).  You can still find them, used and even new - still packaged up to sell to engineers and scientists.  The Oughtred Society has a online museum, as well.

We still have my mother-in-law's K&E, in it's leather case with her name impressed into it.  Family history says she bought it with the money she earned tutoring Jackie Robinson in chemistry at UCLA.

I have an essay out in this month's Nature Chemistry, "It figures", about how the computational tools we use shapes what we teach and not necessarily in good ways. Given that slide rules were obsolete by the time many of my student's parents were born, why does their use still linger in general chemistry book?  (The 2.303's in texts are lowly going away. I checked texts running back about a decade.)

More critically to my mind why, several decades after  digital computing tools became ubiquitous on college campuses do many physical chemistry texts eschew any discussion of numerical techniques for solving the rate equations for a chemical reaction?  I suspect the chasm between the computational tools used in the field and those used in the classroom is a result of apathy. We teach what we learned as we learned it.  As I note in the article, I don't think it is defensible on intellectual grounds.

Don't know how to use a slide rule?  It's fun, it's geeky. No need to buy one to play, check out this simulator and the instructions at Nature Chemistry!

You can read the article here:  http://rdcu.be/sY5Q

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1.  2.303 is the natural log of 10. To change the base of logs recognize that
x = b^log_bx
so
ln(x) = ln(10^log₁₀x)
ln(x) = log₁₀x ln(10)
ln(x) =(log₁₀x)(2.303)
ln(x) = 2.303(log₁₀x)

Chemophobia: The Boy with a Thorn in His Joints

I'm at ScienceOnline2013 where Carmen Drahl and Dr. Rubidium just finished running a terrific session on chemophobia: how can we bridge the gap between "better living through chemistry" and ads for "chemical-free sleep aids." The thrust of the session was not how to convince people chemistry and chemicals are good, but more about how to inject nuance into the public conversation. Chemicals have risks and benefits — and of course, are unavoidable. But we current view chemical as synonymous with toxic, hazardous, unnatural or just plain bad.

What are the roots of this cultural shift? Can understanding these help scientists and writers communicate more clearly and in the end help people not only understand what is in their "stuff" — chemicals, it's all chemicals — but give them tools to work with and make decisions about the materials that make up the world — chemicals. As @docfreeride (ethicist Janet Stemmwedel) noted at another session yesterday, we can agree on facts, and still make different decisions based on them.

Today's New York Times has a perfect example of the various ways chemophobia presents in the Magazine: The Boy with a Thorn in His Joints. The piece chronicles Susannah Meadow's search for an effective treatment for her son's rheumatoid arthritis. She agonizes about the decision to give him methotrexate (which in high doses is used in anticancer treatment) and turns to alternative treatments, in particular four-marvels powder. There are intense arguments with the pediatricians and with her husband over the issue. I was struck by two things in this piece. First, the language Meadows uses to limn the controversy, and second her ignorance, not so much of the chemistry that is in your face (methotrexate), but of the ways in which chemistry is couched in alternative cultural schemes(four-marvels powder).

It makes me wonder how chemophobia is linked to the language we use to talk about it. It can be nearly impossible for an non-chemist to figure out what methotrexate is (beyond "a chemical"). The very name sounds harsh. Four-marvels powder is easy to parse: a powder with four effects. Its name rings with hope.

I also wonder if we worry more about stuff we are familiar with, we've heard more talk on the street about their risks. So we obsess about vaccines, because we hear and read about the side-effects of vaccines, but how many people know anyone who has died of measles? (One of my sister's friends died of measles when I was a child, before there was a vaccine.) So we get in the Times' piece "I was desperate to find a way...without the drugs." pushed up against "[My husband] has always been more comfortable with pharmaceuticals, more trusting in general."

Of course, four-marvel powder is a pharmaceutical, it's just from a different pharmacopoeia — the traditional Chinese — than the one Meadows or her husband is familiar with. Meadows can read the package insert with information on the side-effects of methotrexate, she may be unaware of the routine advice given in Chinese medicine programs (and yes, there are formal academic programs in Chinese medicine, e.g. at Nanyang Technical University) about four-marvels powder (it should never be given to pregnant women, for example, which might make you hesitate before giving it long term to infants or young children).

The session at SciOnline2013 brainstormed about effective ways to help people develop a better sense of nuance around what is a chemical and what are the risks of this particular chemical? What strategies do you think would be most effective?

Hurricane Chemistry: Renovating Butter

Hurricane Sandy left us without power for several days and while a basement chest freezer remained solidly frozen, thermal equilbrium was unfortunately reached by our refrigerator and kitchen, at roughly 55^oF.  Saturday morning found us rooting through the refrigerator, deciding what had to be chucked (milk) and what didn't (ketchup).  Butter?  In this cool weather, it could stay, it would be unlikely to have turned rancid.

But coincidently, while breezing through a depression era Chemcraft chemistry set instruction book, I encountered directions for "renovating" rancid butter.  Around the same time that margarine made its debut, so did process butter, butter that had been treated to remove the objectionable materials.  As near as I can tell, it's an extraction process, presumably the rancid materials (such as butyric acid) dissolve in the cream and the remaining materials can be reworked into a solid mass.

Laws remain on the books in many places forbidding the sale of process butter without making clear to the consumer what is being purchased.  In the early part of the 20th century this was widespread enough for the US Department of Agriculture to print a booklet which "enable[s] any housekeeper, with only the usual facilities of the kitchen, to distinguish in the great majority of cases between genuine butter, renovated butter, and oleomargarine."

Next time the power goes out, I'll know how to "renovate" my butter, as long as I don't intend to sell it!

A curious invention: drawing chemical structures

I am currently wending my way through fragile but fascinating volumes of Chemical News - a journal published by Sir William Crookes in the late 19th and early 20th century. It was a major journal at the time, looking rather like the current Nature in it's breadth of coverage. The society journals of the time typically reserved their pages for papers read by members and abstracts of papers thought to be of interest to them, while Chemical News and it's ilk included book reviews, reports of papers from a wide swath of journals in several languages and two robust arenas for conversation between scientists, readers and editors: Correspondence and Notes & Queries. They were a bit more open, too, to offer space to offbeat bits of science.

The volume I just finished (1890) has a rather contentious conversational thread winding through the Correspondence on what it means to be a FCS (Fellow of the Chemical Society) and should membership be more tightly policed vis a vis their chemical credentials. (At one point the secretaries of the Chemical Society accuse a former board member of having used fake letterhead to secure support for his position!) Many participants in the conversation resort to pseudonyms, some of which carry a bit of snark with them, and it's interesting that this controversy is playing out primarily in a commercial journal and not in organs internal to the Society.

My project involves tracking the correspondence around primary reports of research findings, so these raucous conversations, while fun reads, are of peripheral interest. I'll admit to finding other interesting tidbits to tag in my electronic notebook. It doesn't pay to be overly focussed when doing archive work, as long as I can avoid being completely dragged down the rabbit hole.

The Notes & Queries section appears just above the one page of adverts included in each issue, and yesterday this ad caught my eye: "The Benzene Nucleus. — An India-rubber Stamp in nickel-plated locket with ink-pad enclosed" 3s. At the top of the page, the last bit of editorial content appears — a report of a curious invention: a stamp for making benzene rings. The first benzene ring in a journal appeared in Chemical News (in 1879, eight years after the first graphical structure was used), so perhaps it's apt that it report this "little contriviance" in its pages. (And the inventor is a Fellow of the Chemical Society!)


Nowadays chemical structure drawing programs are commonplace, but when I was a graduate student chemical structures had to be hand drawn, using India ink (permanent, not water soluble!) on vellum. The Rapidograph pens used were expensive and notorious for getting clogged (irreversibly so). Rings were made using stencils, text added using mechanical lettering guides. Jiggle your hand and you had trouble that white-out might not be able to rescue you from. Blots? Argh.

I don't miss the days of chancy ink drawings for slide and papers, though I do miss the delight of pulling out pens and ink and paper. I do wonder, though, if note taking organic students would appreciate a little ink stamp of a benzene ring on the end of their pencil or pen?

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Read about K&E lettering sets here.

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.

Are scientists palatable?

In the early part of the 19th century, the word scientist had yet to be coined. As the scope of materials and phenomena that natural philosophers and historians dealt with increased, there was a growing sense that these terms were inadequate to describing the task of this new breed of inquirers. In the 1830s, the British Association for the Advancement of Science explored potential candidates, but ultimately rejected various proposed terms, including scientist:

"Philosophers was felt to be too wide and too lofty a term,..; savans was rather assuming,..; some ingenious gentleman proposed that, by analogy with artist, they might form scientist, and added that there could be no scruple in making free with this termination when we have such words as sciolist, economist, and atheist — but this was not generally palatable."

The need remained, however, and a decade later, William Whewell, a philosopher and biologist pushed the issue again: “We need very much a name to describe a cultivator of science in general. I should incline to call him a Scientist.” This time it stuck.

Once the name stuck, an image quickly became attached -- wild hair, lab coats and odd apparatus all became part and parcel of what it means to be a scientist. My most recent Thesis columnin Nature Chemistry -- Men of Mystery -- takes up popular images of scientists, and considers the impact the images might have on public discourse about science.

UPDATED: See Snail's Tails post about philosophy and philosophical instruments. The ad for the "philosophical instrument makers" is fascinating!

Chemistry on Holiday: Science Cookies

'tis the season for baking on the home front. It's been mostly biologically based leavening (yeast) at my house, but some strictly chemical rising has been going on as well. For an interesting mix of chemistry and biology in the kitchen check out Not So Humble Pie's science cookies: zebrafish, drosophila, gel electrophoresis and atoms are on the menu. Something to keep in mind for the next snow day around here...

Nobel quote

After I won a Nobel Prize I suddenly turned into an omniscient sage, whereas formerly I was simply a workaholic.

Richard Ernst, Chemistry 1991

(H/T to Nature Chemistry's October editorial)









Photo of Dirac's Nobel Medal is from: rubberpaw at Flickr

Anti-Archimedes

The recipe for pulled pork called for 1/2 cup of brown sugar to be dissolved into 1 1/2 cups of apple cider vinegar. What I had in the cabinet was solid as a rock - there was no way I was packing this into a measuring cup. (Yes, I know I could have done this in the microwave...) My scale came to the rescue. I hacked off chunks until I had the correct mass of brown sugar (110 grams more or less). I dumped the three large hunks into the vinegar in a 2 cup glass measure, and noted that the total volume was just about 2 cups. Nice job.

Then I stirred it to dissolve the sugar. And watched the volume decrease to just over 1 1/2 cups of solution! Have I just proved Archimedes wrong? The volume of sugar at first seemed to have displaced the equivalent volume of liquid, but then seemed to vanish...well not exactly into thin air, but vanish nonetheless. As my 15-year old might say, "What's up with that?"

Yes, Archimedes was correct, but his theory did not address substances that dissolve in the liquid. This is a good demonstration of how much "empty "space is in a liquid. The sugar molecules (and other things in brown sugar, which is not terribly pure as chemicals go) insert themselves between water molecules, without needing to push the water molecules further apart. To a good first approximation the volume of a solution made from a solvent and soluble solid is the volume of the solvent used, not the sum of the two volumes.

Try it...it's fun to watch, and it still intrigues me to think about the amount of unused space there is in a liquid that seems so substantial at the macroscopic level!

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The pulled pork was a keeper...though the kids found the BBQ sauce too spicy for their taste. Try it on challah rolls!

Cold as Ice

This article in the Atlantic monthly caught my eye, if only because it included an experiment and less because of my refined palate. Wayne Curtis is writing about the unsung hero or villian of mixed drinks: ice.

"I went into the kitchen with another bartender, Stephen Cole, who hunted up a scale and thermometer. He placed the two kinds of ice into separate cups filled with water. We let them sit for 10 minutes. The cheater-ice water proved to be colder (34 degrees compared with 40 degrees), but the ice had lost a full quarter of its weight, compared with just a 14 percent loss in the chunk ice. A cheater-ice cocktail is thus chillier (numbing the taste buds) and more watery (making it flat)."

He describes a bar which stocks eight different types of ice - though the classification system is not quite what a physical chemist might use - or even Kurt Vonnegut. I suspect, however, a serious flaw in the experiment, and therefore in the conclusions drawn about the effect of ice type on a drink.

Take a mixture of ice and water that has been thermally isolated (put in a thermos!) and allow it to come to thermal equilibrium (let it sit until the temperature doesn't change any longer). When the contents of the thermos reach equilibrium, if there are both ice and water present, the temperature is 32 degrees (Fahrenheit). It does not matter how cold the ice was to start, how much water is present, how warm or cold the water was - it will be 32 degrees. Not 40. Not 34.

Also known to those who know how to read a phase diagram, ice at normal pressures will not start to melt until it reaches 32 degrees, and its temperature will not rise above 32 degrees until it has all melted. Curtis' experiment isn't quite as sophisticated as the thermos one I've sketched out, but assuming that the rate of heat loss to the room was small (air - or any gas - isn't a very good thermal conductor, so over the short term this is not a bad assumption), and that the ice and water used were pure, and that a very large amount of water was used relative to the ice - I find it untenable that the "cheater-ice" cocktail is different in temperature than the one made with less porous ice. More watery, yes, colder, no.

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Photography by Sue Stafford. Used under Creative Commons license.

All that glitters...may be tin

While medieval alchemists were searching for the secrets of turning base metals, such as lead and tin, into gold, medieval artists had already figured out how to do this. Gold was often applied to manuscripts in medieval Europe and the Middle East to “illuminate” them, an illuminated page would have the functional equivalent of little mirrors scattered across it, making the most of dim interior lighting. In addition to being reflective, gold does not corrode or oxidize, so gold will not discolor with time. There is a fine collection of medieval illuminated manuscripts at a library near me, and as you turn the pages of Book of Hours that is half a millenia old (wearing gloves, of course), the golden decorations wink at you as brightly as the day they were applied.

Gold is expensive, and hard to handle, particularly in the thin sheets necessitated by the cost. One alternative is to use a tin base, then brush on a saffron oil glaze. Polish it up and you might not notice. The glaze blocks out the oxygen and moisture in the air, preventing many of the chemical reactions which can cause the metal to discolor. The resulting preparation is called auripetrum - Peter’s gold. Peter had a good idea - whoever he was.

Does anyone know more about the source of this name? I'd love to know.

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

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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!

Shell Games

I'm an unrepentant Trekkie, I'll admit it. Remember when Spock, Scotty, Uhura, Sulu, Chekov, Kirk and McCoy went back in time to San Francisco to rescue the humpback whales? Scotty got a local company to whip up some transparent aluminum to use to build a whale tank in the ship to bring the whales back to save the Earth.

In the latest issue of Nature, Robert Richie's group at Lawrence Berkeley Labs reports that they have created a composite material that mimics aluminum alloys in strength. Following nature's lead, they use ice as a template to build layers aluminum oxide and polymethacrylate into a strong ceramic similar in structure to nacre - the stuff of which shells are made.

The materials extraordinary strength relative to the component materials is due to the stacking of the layers, which make it difficult for macroscopic cracks to form. Could this type of process lead to transparent aluminum alloy?

Grapes of Wrath

My youngest came home from a father-son event with a new interest in healthy foods. I put grapes on the table with dinner. "There are grapes for dinner," he exclaimed. Who are you and what have you done with son? ran through my mind.

At the end of dinner he puts two grapes on his plate and carefully cuts them nearly in half. Then he ducks into the kitchen. "Come on, Mom!" Warm grapes? He'd eaten all the chicken, there was nothing left on his plate to veronique.

He hits the start button and suddenly the grapes start arcing, and one actually bursts momentarily into flame. I'm stunned. No metal, but the arcing is clear. We try various experiments - do you have to leave the grapes connected (no), does it work with other things (carrots), can you char a grape (yes).

What's going on? Hang on, we were producing plasmas in the kitchen. Not the kind that circulates in your veins, but the kind that stars are made out of. Plasma is often called the 4th phase of matter - the iconic triad being solid, liquid and gas. (There are many other phases in which substances can exist, in fact - such as liquid crystals and supercritical fluids.)

Plasmas are gases in which a large number of electron are "free", rather than associated with a molecule or atom.

I'm still trying to come to grips with the idea that I can create a (very tiny) ball of plasma in my kitchen.

(Read more in the paper : "Microwave Mischief and Madness" by H. Hosack, N. Marler, D. MacIsaac of Northern Arizona University, The Physics Teacher 40, 14 (2002).

Protecting Groups

The whole family was at camp last week, living in tents, sleeping on cots, eating in the mess hall. Every camp has them, squirrels and chipmunks that survive on the crumbs of campers' treats (or sometimes the whole banana). We were warned - no food in the tents except in metal boxes.

The boys had the tent next door to ours. I came back from dinner one night to find a very happy squirrel just making off with a chip container from the kids tent. At which point I remembered the dried fruit I'd left in my pack after the morning hike. Whew...it was still there. The rodents had been attracted to the far more tasty snack leavings next door. The boys tent is serving as (a chemist would say) a protecting group.

Chemical protecting groups work similarly. Say you have two sites on a molecule that can react with a reagent, but you only want one to undergo the reaction. If you can put a protecting group on the site you want left unmolested, like a cover, you can run the reaction, change the other site and then take off the protecting group. (See the scheme for an example.)

It works wonderfully for many reactions, and is keeping my pack safe from marauders.

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.

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.