Liquid: The Delightful and Dangerous Substances That Flow Through Our Lives Mark Miodownik Viking (2018)

We humans can’t help but have our views of reality skewed by our own experience. We take the physical conditions around us as the normal state of affairs and regard others as extreme. The chemist’s ‘standard temperature and pressure’ of 0° C under 105 pascals makes perfect sense as a reference in the human frame, but is quite unusual in the larger scheme of things. The rest of the Solar System, for example, often features temperatures and pressures much higher or much lower; the rest of (mostly empty) outer space is even worse. It’s the surface of Earth that is the outlier.

These uncommon conditions mean we experience something very rare in the higher and lower expanses of temperature and pressure: a wide variety of liquids. It is this odd realm that materials scientist Mark Miodownik explores in Liquid, his enjoyable successor to his 2013 paean to materials, Stuff Matters.

The book explores the histories, structures and properties of many different sorts of liquid, with excursions into the larger topics each brings up. Miodownik organizes his narrative around the conceit of an aeroplane journey, with various incidents and episodes setting off trains of thought. Alcohol makes an early appearance by way of the drinks trolley. Others are introduced through ocean waves observed below, the soap dispenser in the lavatory, the thought of refrigerants in the air-conditioning system, and so on. The framework is reasonably effective, although it gets a bit wearing, and a few digressions are surprisingly lengthy. (Then again, it is a transatlantic flight.)

The liquid state is a small part of most phase diagrams, a narrow range between a large solid zone and a large gaseous one. Conditions have to be just right for a substance to condense out of the gas phase but not to firm up into some kind of solidified mass. And for many simple compounds, those liquid conditions manage to overlap with how we’re used to seeing and handling them — which is why a plane journey can include so many useful examples. The one we all know best, of course, is water. The discovery of liquid water on another planet or moon, even far below the surface, somehow makes that world seem more real to us. But, as Miodownik explains, it’s one of the oddest liquids of all.

H2O is strangely sticky and viscous for a molecule with such a small molecular weight. It has abnormally high melting and boiling points compared with anything chemically similar, such as ammonia or hydrogen sulfide. When it freezes, its solid phase is actually less dense than its liquid one. That relatively rare characteristic leads to ice cubes and icebergs floating instead of sinking as any normal solid phase should do. (If there are sentient creatures somewhere in the Universe living next to lakes of superfluid liquid helium, they would probably be confused by water, which flows with weird side effects of friction and drag unknown in the superfluid world.)

Liquid distils a great deal of interesting information in accurate, readable form. As a chemist, I find it a relief to read such an overview without being distracted by mischaracterized or oversimplified details. Solid-state physicists and materials scientists will also celebrate Miodownik’s excellent efforts at tying the everyday properties of liquids to their molecular structure. He provides many vivid examples: among these are saliva (during the flight’s meal service, naturally) and jet fuel, which he notes is not an explosive, but still has more chemical energy per unit volume than nitroglycerine.

One of the things that chemistry and physics teach is that the information given by our senses is only a small part of the story: water is wet, our fingers can tell us that much. What we don’t feel are the water molecules themselves, interacting with the protein surfaces of our skin. Their very atoms and electron clouds come within range of each other, attracting and repelling and adding up to the sensations that our vivid (but often crude) senses interpret. That hidden world underlies every object we see and handle. Liquid gives readers a sense of this — no small feat.

And that brings up the question of who might read it. As with Stuff Matters, Miodownik is inspiring those in search of science in an accessible, entertaining format. Today, materials scientists are preparing exotic fluids packed with nanoparticles that can turn them into magnets or optical sensors, and nanotechnologists and molecular biologists are exploring the behaviour of water and other liquids on very small scales. Liquid will come in very useful for people eager to understand these advances.