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The first bit of this went down quite well, so I’m going to play to the audience. Also I’m setting up my post about homeopathy. I know I’ve promised this for a long while, but I think it will be worth the wait.

It’s been snowing quite a lot over the past few days. Snow is ice, and ice is crystalline solid water. Snow flakes are ice crystals are hexagonal plates, or come in a variety of stellar forms all with six arms. Like a pentacle, but with six instead of five arms. They also form six-sided columnar or bullet shapes. Not all snowflakes have a six based configuration. Ice needles form at about -5C and are shaped as the name suggests.

All the forms are very pretty under the microscope. It’s claimed that no two snowflakes are exactly the same. It may well be true, but I’m not sure there’s a big enough sample size to truly represent the entire configurational population. What do you think? Whether it’s true or not I’d bet good money that some mildly obsessive propellor head has spent some time creating snowflakes under exacting laboratory conditions and trying to produce two identical ones.

Another interesting thing about snow. When the weather warms up, it melts, yes? Most of it does, but not all. Ice also undergoes a physical transformation known as sublimation, where it changes straight from a solid into a gas; strangely, if it didn’t, salt wouldn’t melt ice, but the theory there is pretty complex, so just believe me, OK? Some other substances also sublime. If you heat iodine crystals, they don’t melt at all, they simply turn straight into iodine vapour. Camphor is another. It will melt if you heat it, but at room temperature it sublimes, so you can use it as a moth repellant, like naphthalene. Even metals vaporise slowly. You all know the smell of copper coins, and the metal osmium has a name derived from the Greek word osmia  meaning smell. It has a slight smell of onions, and the oxide has a characteristic smoky aroma. Osmium’s also the densest and hardest metal known to man, but that’s neither here nor there. Anyway, trust me on this, snow does sublime to a small extent, so not all of it goes into flooding your cellar during the thaw. Just most of it.

Back to water. It’s a pretty good solvent for lots of small molecules. Salts, sugars, amino acids, lots of the building blocks for organisms to grow and function. It’s not very good with most big molecules: proteins, cellulose, complex carbohydrates, collagen… Just as well or nothing would be able to form any permanent functional components. We’d just be a puddle. No plants, no animals, no nuttin’.

Because water is such a good solvent, it’s ideal for transporting various metabolic bits and pieces around organisms. Plants, like humans, have two circulatory systems shoving stuff around. So water is damned useful and essential to life. That’s why scientists get excited about finding water on other planets. As far as we know, all life forms need water. No water no life. The corollary isn’t true. There’s water, it doesn’t mean there must be life. It doesn’t work like that. But if there is water it increases the chances of there being life.

Contrary to popular belief, pure water isn’t a very good electrical conductor. It’s very good when it’s contaminated with dissolved molecules, especially salts, but pure water really doesn’t conduct very well at all. This is not to say that you should stand in a bathful of water to change a light bulb, but it’s an odd property.

Another property of very pure water is that it doesn’t boil at 100 Celsius. You can superheat it to way beyond that. It won’t boil unless the steam bubbles have something to coalesce round, and that’s usually dust particles. Keep it dust free, it doesn’t boil. Well, not quite true. If you raise the temperature to above nominal boiling point and then knock the container, the shock waves will cause coalescence and things will boil pretty vigorously pretty fast. There are some urban horror stories about this happening when people are heating water in a microwave. It’s doesn’t boil, they open the oven to see what’s occurring, knock the glass or cup, and localised hotspots erupt violently. Nobody’s sure if this has ever actually happened in real life, but you can do it under laboratory conditions, so the stories are plausible at least.

What else? It has a small but measurable surface tension, partly because the molecules are polar. They have one end, the oxygen atom, that’s slightly negatively charged, while the hydrogen atoms are very slightly positively charged. Opposites attract, so the molecules tend to stick together. The molecules on the surface attract each other, and form  a sort of ‘skin,’ a bit like a very very delicate balloon. This skin is pretty elastic if you treat it nicely. Pond skaters, the insects not someone on skates, use this to great effect; they can actually stand on the skin. Whirligig beetles do the same. They don’t float they sort of whizz around on the elastic surface. Some insect larvae stick their rear ends out through the surface, and the surface tension holds the upside down in the water., so they can hunt prey and breathe at the same time. This does require that they breathe through their arses, but it’s better than drowning, isn’t it?