Blue skies and copper demons: a story of mysterious purple crystals

Mystery purple crystals (posted with permission of Caroline Hedge, @CM_Hedge)

Today, a little story about some mysterious, purple crystals. On Tuesday, Twitter user Caroline Hedge posted this photo with the question: “What the %#&$ is lab putting down the drain to cause this?”

The post spawned lots of responses, some more serious than others. One of the sensible ones came from Roland Roesler, who thought that the pipe had corroded from the outside, suggesting that a leaky connection at the top right had allowed sewage to drip down the right-hand side of the copper pipe and drip from the bottom, which explained why the left-hand half of the pipe appeared unscathed.

I agreed. The pipe is clearly made of copper, and blue colours are characteristic of hydrated copper salts. Inside the pipe, the flow of water would wash any solution anyway before corrosion could occur, but on the outside, drips could sit on the surface for long periods of time. There’d be plenty of time for even a slow reaction to occur, and then for water to slowly evaporate, allowing the growth of spectacular crystals.

Hydrated copper(II) sulfate crystals are bright blue. (Image from Wikimedia Commons)

But what exactly where they? There were several theories, but for me the interesting thing was the colour. Hydrated copper(II) sulfate crystals are bright blue. The colour arises due to an effect called d orbital splitting, which is a tad complicated but, in short, means that complex absorbs light from the red end of the visible light spectrum, allowing all the other colours of light to pass through. As a result, our eyes “see” blue.

But these crystals, assuming it’s not a photographic effect, had a purplish hue. At least, some of them do. So… not copper sulfate, or not entirely copper sulfate (given the situation, a mixture seemed entirely likely). Which begs the question, which copper complex produces a purple colour?

A little bit of Googling and I was pretty sure I’d identified it: copper azurite, Cu₃(CO₃)₂(OH)₂. This fit for two reasons: firstly, it’s a mineral that could (does) readily form in the presence of water and air (which, of course, contains carbon dioxide), and secondly it’s exactly the right colour.

Many will recognise the word “azure” as being associated with the deep, rich blue of a summer sky, and in fact the English name of this mineral comes from the same word-root: the Persian lazhward, a place known for its deposits of another deep-blue stone, lapis lazuli (meaning “stone of azure”).

Blue-purple copper azurite and green malachite (image from Wikipedia)

Azurite is often found with malachite, the better-known green copper mineral that we recognise from copper roofs and statues. Malachite is sometimes simplistically described as copper carbonate, implying CuCO₃, but in truth it’s Cu₂CO₃(OH)₂ pure copper(II) carbonate doesn’t form in nature.

You can see malachite co-existing with azurite in the photo on the right. The azurite will, over time, tend to morph into malachite when the level of carbon dioxide in the air is relatively low, as in ‘normal’ air—which explains why we don’t usually see purple ‘copper’ roofs—but the carbon dioxide levels were probably higher in that cupboard. There was almost certainly acidic sewage reacting with carbonate, combined with a lack of ventilation, so it makes sense that we might see more azurite.

Azurite has an interesting history as a pigment. Historically blue colours were rare and expensive—associated with royalty and divinity—which is one reason why the Virgin Mary was often depicted wearing blue in paintings. Azurite was used to make blue pigments, but (as I mentioned above) it’s unstable, tending to turn greenish over time, or black if heated. Ultramarine blue (made from lapis lazuli) is more stable, particularly when heated, but it was even more expensive. A lot of blue pigments in medieval paintings have been misidentified as coming from lapis lazuli, when in fact they were azurite—a more common mineral in Europe at the time.

There’s a fun piece of etymology here, too. Copper, of course, has been valuable metal since, well, the Bronze Age. The presence of purple azurite and green malachite are surface indicators of copper sulfide ores, useful for smelting. This lead to the name of the element nickel, because an ore of nickel weathers to produce a green mineral that looks a little like malachite. And this, in turn, lead to attempts to smelt it in the belief that it was copper ore. But, since it wasn’t, the attempts to produce copper failed (a much higher smelting temperature is needed to produce nickel).

The mineral nickeline can resemble malachite, and was dubbed kupfernickel in Germany, literally “copper demon”

As a result, the mineral, nickeline, was dubbed kupfernickel in Germany, literally “copper demon”. When the Swedish alchemist Baron Axel Fredrik Cronstedt succeeded, in 1751, in smelting kupfernickel to produce a previously unknown silvery-white, iron-like metal he named it after the nickel part of kupfernickel.

And this is how we go from a corroded pipe to sky-blue colours to medieval paintings to copper demons to nickel. But what happened to the pipe in the original tweet? Well, in an update, Caroline Hedge told us that it had been removed and disposed of, and so we’ll never be completely sure what the pretty crystals were, but they certainly lead to an interestingly twisty-turny chemistry story.


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Marvellous Mushroom Science

Glistening ink caps produce a dark, inky substance.

Yesterday I had the fantastic experience of a “fungi forage” with Dave Winnard from Discover the Wild, organised by Incredible Edible Oxford. There are few nicer things than wandering around beautiful Oxfordshire park- and woodland on a sunny October day, but Dave is also an incredibly knowledgeable guide. I’ve always thought mushrooms and fungi were interesting – living organisms that are neither plants nor animals and which we rely on for everything from antibiotics to soy sauce – but I had lots to learn.

Did you know, for example, that fungi form some of the largest living organisms on our planet? And that without them most of our green plants wouldn’t have evolved and probably wouldn’t be here today?

And from a practical point of view, what about the fact that people once used certain fungi to light fires? I’ve always imagined fungi as being quite wet things with a high water content (unless they’re deliberately dried, of course), but some are naturally very dry. Ötzi, the mummified man thought to have lived between 3400and 3100 BCE, was found with two types of fungus on him: birch fungus, which has antiparasitic properties, and a type of tinder fungus which can be ignited with a single spark and will smolder for days.

Coprine causes unpleasant symptoms, including nausea and vomiting, when consumed with alcohol.

Then, of course, there’s all the interesting chemistry. Early on in the day, we came across some glistening ink caps.The gills of these disintegrate to produce a black, inky liquid which contains a form of melanin and can be used as ink. And there’s more to this story: as I’ve already mentioned, fungi are not plants and they can’t photosynthesise, but it seems that some fungi do use melanin to harness gamma rays as energy for growth. Extra mushrooms for the Hulk’s breakfast, then?

Moving away from pigments for a moment, a related species to the glistening ink cap, the common ink cap, contains a chemical called coprine. This causes lots of unpleasant symptoms if it’s consumed with alcohol, similar to Disulfiram, the drug used to treat alcoholism. For this reason one of this mushroom’s other names is tippler’s bane. The coprine in the mushrooms effectively causes an instant hangover by accelerating the formation of acetaldehyde (also known as ethanal) from alcohol. Definitely don’t pair that mushroom omelette with a nice bottle of red and, worse, you’ll need to stay off the booze for a while: apparently the effects can linger for a full three days.

Yellow stainer mushrooms look like field mushrooms, but are poisonous.

We also came across some yellow stainer mushrooms. These look a lot like field mushrooms, but be careful – they aren’t edible. They cause nasty gastric sympoms and are reportedly responsible for most cases of mushroom poisoning in this country, although some people seem to be able to eat them without ill effect. They had a slightly chemically scent that reminded me “new trainer” smell – sort of rubbery and plasticky. It’s often described as phenolic, but I have to say I didn’t detect that myself – although yellow stainers have been shown to contain phenol and this could account for their poisonous nature. Anyway, it was an aroma that wouldn’t be entirely unpleasant if I were opening a new shoebox, but it wasn’t something I’d really want to eat. Apparently the smell gets stronger as you cook them, so don’t ignore what your nose is telling you if you think you have a nice pan of field mushrooms.

4,4′-Dimethoxyazobenzene is an azo dye.

The real giveaway with yellow stainers, though, is their tendency to turn yellow when bruised or scratched, hence the name. This, it seems, is due to 4,4′-dimethoxyazobenzene. The name might not be familiar, but A-level Chemistry students will recognise the structure: it’s an azo-dye. Quite apart from being a very useful word in Scrabble, azo compounds are well-known for their characteristic orange/yellow colours. It’s not really clear whether it forms in the mushroom due to some sort of oxidation reaction, or whether it’s in the cells anyway but only becomes visible when the cells are damaged. Either way, it’s something to look out for if you spot a patch of what look like field mushrooms.

The blushing wood mushroom.

We also came across several species which are safe to eat. One I might look out for in future is the blushing wood mushroom. As is often the way with fungi, the name is literal rather than merely poetic. These mushrooms have a light brown cap, beige gills, and a pale stem, but they turn bright red when cut or scratched due to the formation of an ortho-quinone. It’s quite a dramatic colour-change, and makes them pretty easy to identify. Apparently they’re normally uncommon here, but we found quite a lot of them, which might be something to do with this year’s unusally hot and dry summer.

Red ortho-quinone causes blushing wood mushrooms to literally blush.

I tried to find out the reasons for these colour-changes. In the plant and animal kingdoms pigments are usually there for good reason: camouflage, signalling and communication or, as with chlorophyll, as a way of making other substances. Fruits, for example, often turn bright red as they ripen because it makes them stand out from the green foilage and encourages animals to eat them so that the seeds can be spread. Likewise, they’re green when they’re unripe because it makes them less obvious and less appealing. But what’s the advantage for the mushroom to change colour once it’s already damaged? Perhaps there isn’t one, and it’s just an accident of their biology, but if so it seems strange that it’s a feature of several species. I couldn’t find the answer; if any mycologists are reading this and know, get in touch!

Velvet shank mushrooms.

Other edible species we met were fairy ring champignons, field blewits and jelly ear fungus – which literally looks like a sort of transparent ear. I’ll definitely be looking out for all of these in the future, but it’s important to watch out for dangerous lookalikes. Funeral bell mushrooms, for example, look like the velvet shank mushrooms we found but, once again, the name is quite literal – funeral bells contain amatoxins and eating them can cause kidney and liver failure. As Dave was keen to remind us: never eat anything you can’t confidently name!


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Five science facts we learned at school?

This week a post called ‘Five Science ‘Facts’ We Learnt At School That Are Plain Wrong‘ popped into my Facebook feed from a few different sources.

It led to more than one argument, and the unearthing of some interesting titbits. Most of these facts aren’t directly about chemistry, but hey, still interesting. Let’s have a look:

We’re taught we only have five senses: smell, sight, hearing, touch and taste
True enough that there are more than five, but I clearly remember being told in school that balance and pain were also senses, so I’m fairly sure biology teachers have been quietly trying to dispel this one for decades.

plastic paperclips

Non-magnetic paper-clips. Ha!

Which of the following are magnetic: a tomato, you, paper-clips? (Answer: all of the above)
I think this is a misleading question. What do you mean when you say ‘magnetic’? I think most people understand that to mean something that’s capable of being magnetised or at least is attracted to your everyday fridge magnet. In other words, the ferromagnetic materials: iron, nickel, cobalt and most of their alloys. True enough tomatoes and people interact with magnetic fields (this is the basis behind MRI scanners – check out these beautiful images) but does that make them magnetic? We-ell….technically…. (there are lots of types of magnetism) but it seems a bit mean to criticise an assumption by asking a less-than-clear question about it. Besides, if you’re going to be pedantic about it, what’s that paper-clip made of hmm? Plastic and aluminium (both generally considered to be completely non-magnetic) paper-clips exist. Bad question. Next!

CMYKThe true primary colours for paints and pigments are cyan, magenta and yellow
Broadly fair enough, look at your printer cartridge. Although we really ought to include black as well (which the original article didn’t mention; it’s the K in the CMYK model). You can make something pretty close to black by mixing the others, but it’s not the nice, crisp, blackest black that people want for text and outlines. All that said, to actually get red from a mixture of magenta and yellow you have to have pretty pure pigments. Grab a paint box and try mixing something that looks like magenta with something that looks like yellow, and you’ll actually get something that looks like orangey-pink (serious artists agree that if you want really bright red, you’re better off just buying some red pigment). Whereas if you mix blue paint with yellow paint you will, fairly reliably, get green of one shade or another. I just worry that attempting to clear this one up is going to cause a lot of children to mess up their paintings. That’s all I’m saying.

A little addition here: this question then led to a debate about the colour spectrum of visible light. How many colours are there, exactly? It’s commonly held that Newton invented the colour indigo because he felt, possibly for superstitious reasons, that there ought to be seven colours. As a result, some people will tell you the spectrum actually consists of six colours rather than seven: red, orange, yellow, green, blue and violet. But hang on. Look at a spectrum (here’s one):

600px-Spectrum

What’s that colour in between blue and green there? You might say turquoise, but in a return to the original question it’s more accurately named cyan. That band is pretty obvious. I’d argue that if you’re going to include orange in the spectrum, then you ought to include cyan. And, in fact, some people think that’s exactly what Newton was doing. Except he didn’t call it cyan, he simply called it blue. The bit we think of as blue is what he named indigo. In other words, the spectrum is, in fact: red, orange, yellow, green, cyan, blue, violet. Still seven colours, they just don’t quite fit with the whole Richard Of York Gave Battle In Vain thing.

Of course, those of us in the know are aware that there are actually eight colours. But you need to have octagonal cells in your eyes to see the other one. Or be a cat.

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Debunked in 1974. Still hanging around like a bad smell or, er, taste.

Tongue taste maps are nonsense
Yep. This one is unambiguous: there aren’t regions for sweet, salt, bitter etc. on your tongue. This was debunked back in 1974, but it’s still hanging around for some reason.

There are more states of matter than just solid, liquid and gas
Ah-ha, a chemistry one! Again, this is true. The strict states of solid, liquid and gas are fine when you’re talking about elements and pure, fairly simple, compounds (water, for example), but matter can indeed take other forms. There are ‘liquid crystals‘ – you’re probably reading this right now using some – and yes, there’s plasma. Once you get into mixtures all bets are off (no, you can’t melt wood, sorry). And colloids are a whole other kettle of fish.

But I think this is one of those times where you have to ask yourself why are we bothering to talk about solids, liquids and gases in the first place? Is it purely so that students can memorise three words? No. It’s so that they can go on to understand the concepts of melting and boiling, and their partners freezing and condensing. These ideas are critical to understanding ideas of measuring temperature as solid liquid gaswell as what happens to particles when they warm up (or cool down). Adding other technical terms in at this early stage is just likely to cause confusion. I don’t think that learning about the transition from solid to liquid to gas precludes later learning about liquid crystals, colloids and the like (hey, it’s how I did it). You’re just adding more information to a simple model, and someone studying A-level sciences and beyond ought to be capable of dealing with that. No harm, no foul, I say.

So there we have it: less “Five Science ‘Facts’ We Learnt At School That Are Plain Wrong”, and more one thing your teacher probably tried to correct you on, one misleading question, one thing you might have learned incorrectly at school, and a couple that might be technically untrue but it doesn’t really matter that much in the long run. But I suppose that IS less of a snappy title for an article.

Truth, Justice, Freedom, Reasonably Priced Love, and a Hard-Boiled Egg.