On the in-between state of matter

kw: book reviews, nonfiction, materials science, liquids

Mercury is the only element of ordinary experience that is a liquid. These days, though, now that electronic thermometers have replaced medical thermometers containing mercury, and fluorescent tubes have been mostly replaced by CFL's and LED's, it's hard for someone to obtain a large enough bit of mercury to play with. But mercury is not the only element that is liquid at "room temperature", if you count the temperature of a southern house in July without air conditioning:

• Mercury, symbol Hg, melting point -40°C (-40°F). A silvery metal, all of whose compounds are toxic to varying degrees (methyl mercury is one of the worst).
• Bromine, symbol Br, melting point -7°C (19°F). A brown liquid, hard to extract from its compounds, very toxic as an element. In a bromide salt it is used medically.
• Gallium, symbol Ga, melting point 30°C (86°F). A silvery metal, solid at comfortable temperatures, but will melt when held in your hand. In compounds such as gallium arsenide it is the basis for LED's and certain very high speed semiconductors.
• Cesium, symbol Cs, melting point 28°C (83°F). A slightly yellowish, shiny metal, it will also melt in your hand, but it would be dangerous to do so unless it is in a sealed glass vessel. Cesium will draw water from your skin and explode, much more violently than potassium or sodium do when dropped into water.
• Francium, symbol Fr, melting point 27°C (81°F). A brown semi-metal, extremely radioactive (half life is 22 minutes), it can only be produced in quantities large enough to be seen and experimented with using a nuclear reactor.
• NaK, an alloy of sodium (Na) and potassium (K), is liquid at or below 25°C (77°F) when the proportion of sodium is between 10% and 60%.

All other liquids with which we are familiar are compounds or mixtures of compounds. A baker's dozen (including Hg) are discussed in an enjoyable book, Liquid Rules: The Delightful and Dangerous Substances that Flow Through Our Lives, by Mark Miodnownik. Dr. Miodnownik is a materials scientist, and while most materials science deals with solids such as metals and ceramics, liquids are definitely materials, and fascinating materials at that.

Other than mercury, the half-dozen liquids listed above are not discussed. They are outside ordinary experience. The author uses the framework of an airline flight from London to San Francisco to tell us of familiar liquids such as kerosene (jet fuel), water, alcohol, and a few near-solids such as tar (it flows about a million times more slowly than water) and the "rock" of Earth's mantle, which flows slowly (a few inches per year) in a convection pattern that pushes the continents around and creates earthquakes and volcanoes.

Discussing "alcohol", which for most of us is ethyl alcohol, or ethanol, he tells how we use its moderate toxicity to fuddle our thinking to various degrees. He just touches on other chemicals that are also alcohols, such as methanol. I didn't know before that fermentation of grains produces both ethanol and a little methanol, and that the various post-processing steps used to prepare beer remove the methanol, making it safer to drink; also that distilling raw beer into whiskey has to be done properly to discard the methanol so we don't get "blind drunk" from methanol-laced moonshine. We are also a little familiar with rubbing alcohol, a mixture in water of a different, slightly larger molecule called isopropanol. A chemistry professor once talked of the toxicity curve of the alcohols, that methanol (with one carbon) being very toxic, ethanol (with two carbons) being less so, low enough for us to imbibe, propanol and isopropanol (3 carbons) being much more toxic, and that the toxicity continues to increase as the carbon chain gets longer, but then decreases. He speculated that a long enough "alcohol", maybe with 15 carbons, would be no more toxic than ethanol, and might provide the basis for a different kind of befuddling beverage. Since long-chain alcohols are rare in nature, it is unlikely that our bodies would have the right enzymes to dispose of them.

I could babble on, but it's better to leave it at that and encourage you to read the book. From ballpoint pen ink to saliva, and freon to ketchup, it is likely you'll learn something new in every chapter.