A tale of chemistry, biochemistry, physics and astronomy – and shiny, silver balls

A new school term has started here, and for me this year that’s meant more chemistry experiments – hurrah!

Okay, actually round-bottomed flasks

The other day it was time for the famous Tollens’ reaction. For those that don’t know, this involves a mixture of silver nitrate, sodium hydroxide and ammonia (which has to be freshly made every time as it doesn’t keep). Combine this concoction with an aldehyde in a glass container and warm it up a bit and it forms a beautiful silver layer on the glass. Check out my lovely silver balls!

This reaction is handy for chemists because the silver mirror only appears with aldehydes and not with other, similar molecules (such as ketones). It works because aldehydes are readily oxidised or, looking at it the other way round, the silver ions (Ag+) are readily reduced by the aldehyde to form silver metal (Ag) – check out this Compound Interest graphic for a bit more detail.

But this is not just the story of an interesting little experiment for chemists. No, this is a story of chemistry, biochemistry, physics, astronomy, and artisan glass bauble producers. Ready? Let’s get started!

Bernhard Tollens (click for link to image source)

The reaction is named after Bernhard Tollens, a German chemist who was born in the mid-19th century. It’s one of those odd situations where everyone – well, everyone who’s studied A level Chemistry anyway – knows the name, but hardly anyone seems to have any idea who the person was.

Tollens went to school in Hamburg, Germany, and his science teacher was Karl Möbius. No, not the Möbius strip inventor (that was August Möbius): Karl Möbius was a zoologist and a pioneer in the field of ecology. He must have inspired the young Tollens to pursue a scientific career, because after he graduated Tollens first completed an apprenticeship at a pharmacy before going on to study chemistry at Friedrich Wöhler’s laboratory in Göttingen. If Wöhler’s name seems familiar it’s because he was the co-discoverer of  beryllium and silicon – without which the electronics I’m using to write this article probably wouldn’t exist.

After he obtained his PhD Tollens worked at a bronze factory, but it wasn’t long before he left to begin working with none other than Emil Erlenmeyer – yes, he of the Erlenmeyer flask, otherwise known as… the conical flask. (I’ve finally managed to get around to mentioning the piece of glassware from which this blog takes its name!)

It seems though that Tollens had itchy feet, as he didn’t stay with Erlenmeyer for long, either. He worked in Paris and Portugal before eventually returning to Göttingen in 1872 to work on carbohydrates, going on to discover the structures of several sugars.

Table sugar is sucrose, which doesn’t produce a silver mirror with Tollens’ reagent

As readers of this blog will know, the term “sugar” often gets horribly misused by, well, almost everyone. It’s a broad term which very generally refers to carbon-based molecules containing groups of O-H and C=O atoms. Most significant to this story are the sugars called monosaccharides and disaccharides. The two most famous monosaccharides are fructose, or “fruit sugar”, and glucose. On the other hand sucrose, or “table sugar”, is a disaccharide.

All of the monosaccharides will produce a positive result with Tollens’ reagent (even when their structures don’t appear to contain an aldehyde group – this gets a bit complicated but check out this link if you’re interested). However, sucrose does not. Which means that Tollens’ reagent is quick and easy test that can be used to distinguish between glucose and sucrose.

Laboratory Dewar flask with silver mirror surface

And it’s not just useful for identifying sugars. Tollens’ reagent, or a variant of it, can also be used to create a high-quality mirror surface. Until the 1900s, if you wanted to make a mirror you had to apply a thin foil of an alloy – called “tain” – to the back of a piece of glass. It’s difficult to get a really good finish with this method, especially if you’re trying to create a mirror on anything other than a perfectly flat surface. If you wanted a mirrored flask, say to reduce heat radiation, this was tricky. Plus it required quite a lot of silver, which was expensive and made the finished item quite heavy.

Which was why the German chemist Justus von Liebig (yep, the one behind the Liebig condenser) developed a process for depositing a thin layer of pure silver on glass in 1835. After some tweaking and refining this was perfected into a method which bears a lot of resemblance to the Tollens’ reaction: a diamminesilver(I) solution is mixed with glucose and sprayed onto the surface of the glass, where the silver ions are reduced to elemental silver. This process ticked a lot of boxes: not only did it produce a high-quality finish, but it also used such a tiny quantity of silver that it was really cheap.

And it turned out to be useful for more than just laboratory glassware. The German astronomer Carl August von Steinheil and French doctor Leon Foucault soon began to use it to make telescope mirrors: for the first time astronomers had cheap, lightweight mirrors that reflected far more light than their old mirrors had ever done.

People also noticed how pretty the effect was: German artisans began to make Christmas tree decorations by pouring silver nitrate into glass spheres, followed by ammonia and finally a glucose solution – producing beautiful silver baubles which were exported all over the world, including to Britain.

These days, silvering is done by vacuum deposition, which produces an even more perfect surface, but you just can’t beat the magic of watching the inside of a test tube or a flask turning into a beautiful, shiny mirror.

Speaking of which, according to @MaChemGuy on Twitter, this is the perfect, foolproof, silver mirror method:
° Place 5 cm³ 0.1 mol dm⁻³ AgNO₃(aq) in a test tube.
° Add concentrated NH₃ dropwise untill the precipitate dissolves. (About 3 drops.)
° Add a spatula of glucose and dissolve.
° Plunge test-tube into freshly boiled water.

Silver nitrate stains the skin – wear gloves!

One word of warning: be careful with the silver nitrate and wear gloves. Else, like me, you might end up with brown stains on your hands that are still there three days later…


Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2018. You may share or link to anything here, but you must reference this site if you do.

If you enjoy reading my blog, please consider buying me a coffee through Ko-fi using the button below.
Buy Me a Coffee at ko-fi.com

Advertisements

No need for slime panic: it’s not going to poison anyone

This is one of my favourite photos, so I’m using it again.

The school summer holidays are fast approaching and, for some reason, this always seems to get people talking about slime. Whether it’s because it’s a fun end-of-term activity, or it’s an easy bit of science for kids to do at home, or a bit of both, the summer months seem to love slimy stories. In fact, I wrote a piece about it myself in August 2017.

Which (hoho) brings me to the consumer group Which? because, on 17th July this year, they posted an article with the headline: “Children’s toy slime on sale with up to four times EU safety limit of potentially unsafe chemical” and the sub-heading: “Eight out of 11 popular children’s slimes we tested failed safety testing.”

The article is illustrated with lots of pots of colourful commercial slime pots with equally colourful names like Jupiter Juice. It says that, “exposure to excessive levels of boron could cause irritation, diarrhoea, vomiting and cramps in the short term,” and goes on to talk about possible risks of birth defects and developmental delays. Yikes. Apparently the retailer Amazon has removed several slime toys from sale since Which? got on the case.

The piece was, as you might expect, picked up by practically every news outlet there is, and within hours the internet was full of headlines warning of the dire consequences of handling multicoloured gloopy stuff.

Before I go any further, here’s a quick reminder: most slime is made by taking polyvinyl alcohol (PVA – the white glue stuff) and adding a borax solution, aka sodium tetraborate, which contains the element boron. The sodium tetraborate forms cross-links between the PVA polymer chains, and as a result you get viscous, slimy slime in place of runny, gluey stuff. Check out this lovely graphic created by @compoundchem for c&en’s Periodic Graphics:

The Chemistry of Slime from cen.acs.org (click image for link), created by Andy Brunning of @compoundchem

And so, back to the Which? article. Is the alarm justified? Should you ban your child from ever going near slime ever again?

Nah. Followers will remember that back in August last year, after I posted my own slime piece, I had a chat with boron-specialist David Schubert. He said at the time: “Borax has been repeated[ly] shown to be safe for skin contact. Absorption through intact skin is lower than the B consumed in a healthy diet” (B is the chemical symbol for the element boron). And then he directed me to a research paper backing up his comments.

Borax is a fine white powder, Mixed with water it can be used to make slime.

This, by the way, is all referring to the chemical borax – which you might use if you’re making slime. In pre-made slime the borax has chemically bonded with the PVA, and that very probably makes it even safer – because it’s then even more difficult for any boron to be absorbed through skin.

Of course, and this really falls under the category of “things no one should have to say,” don’t eat slime. Don’t let your kids eat slime. Although even if they did, the risks are really small. As David said when we asked this time: “Borates have low acute toxicity. Consumption of the amount of borax present in a handful of slime would make one sick to their stomach and possibly cause vomiting, but no other harm would result. The only way [they] could harm themselves is by eating that amount daily.”

It is true that borax comes with a “reproductive hazard” warning label. Which? pointed out in their article that there is EU guidance on safe boron levels, and the permitted level in children’s’ toys has been set at 300 mg/kg for liquids and sticky substances (Edited 18th July, see * in Notes section below).

EU safety limits are always very cautious – an additional factor of at least 100 is usually incorporated. In other words, for example, if 1 g/kg exposure of a substance is considered safe, the EU limit is likely to be set at 0.01 g/kg – so as to make sure that even someone who’s really going to town with a thing would be unlikely to suffer negative consequences as a result.

The boron limit is particularly cautious and is based on animal studies (and it has been challenged). The chemists I spoke to told me it’s not representative of the actual hazards. Boron chemist Beth Bosley pointed out that while it is true that boric acid exposure has been shown to cause fetal abnormalities when it’s fed to pregnant rats, this finding hasn’t been reproduced in humans. Workers handling large quantities of borate in China and Turkey have been studied and no reproductive effects have been seen.

Rat studies, she said, aren’t wholly comparable because rats are unable to vomit, which is significant because it means a rat can be fed a large quantity of a boron-containing substance and it’ll stay in their system. Whereas a human who accidentally ingested a similar dose would almost certainly throw up. Plus, again, this is all based on consuming substances such as borax, not slime where the boron is tied up in polymer chains. There really is no way anyone could conceivably eat enough slime to absorb these sorts of amounts.

These arguments aside, we all let our children handle things that might be harmful if they ate them. Swallowing a whole tube of toothpaste would probably give your child an upset stomach, and it could even be dangerous if they did it on a regular basis, but we haven’t banned toothpaste “just in case”. We keep it out of reach when they’re not supposed to be brushing their teeth, and we teach them not to do silly things like eating an entire tube of Oral-B. Same basic principle applies to slime, even if it does turn out to contain more boron than the EU guidelines permit.

In conclusion: pots of pre-made slime are safe, certainly from a borax/boron point of view, so long as you don’t eat them. The tiny amounts of boron that might be absorbed through skin are smaller than the amounts you’d get from eating nuts and pulses, and not at all hazardous.

Making slime at home can also be safe, if you follow some sensible guidelines like, say, these ones:

Stay safe with slime by following this guidance

Slime on, my chemistry-loving friends!


Notes:
* When I looked for boron safety limits the first time, the only number I could find was the rather higher 1200 mg/kg. So I asked Twitter if anyone could direct me to the value Which? were using. I was sent a couple of links, one of which contained a lot of technical documentation, but I think the most useful is probably a “guide to international toy safety” pamphlet which includes a “Soluble Element Migration Requirements” table. In the row for boron, under “Category II: Liquid or sticky materials”, the value is indeed given as 300 mg/kg.

BUT, there is also ” Category I: Dry, brittle, powder like or pliable materials” and the value there is the much higher 1,200 mg/kg. Which begs the question: does slime count as “pliable” or “sticky”? It suggests to me that, say, a modelling clay product (pliable) would have the 4x higher limit. But surely the risk of exposure would be essentially the same? If 1,200 mg/kg is okay for modelling clay, I can’t see why it shouldn’t be for slime. In the Which? testing, only the Jupiter Juice product exceeded the Category I limit, and then not by that much (1,400 mg/kg).

Also (the notes are going to end up being longer than the post if I’m not careful), these values are migration limits, not limits on the amount allowed in the substance in total. Can anyone show that more than 300 mg/kg is able to migrate from the slime to the person handling it? Very unlikey. But again, don’t eat slime.

This is not an invitation to try and prove me wrong.

I suppose it’s possible that someone could sell slime that’s contaminated with some other toxic thing. But that could happen with anything. The general advice to “wash your/their hands and don’t eat it” will take you a long way.


Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2018. You may share or link to anything here, but you must reference this site if you do.

If you enjoy reading my blog, please consider buying me a coffee (I’ll probably blow it on a really big bottle of PVA glue) through Ko-fi using the button below.
Buy Me a Coffee at ko-fi.com

 

Effective elements: some great periodic tables

My all-time favourite scarf (made by Rooby Lane on Etsy from a periodic table by Science Notes)

I’m a chemist (no, really? I hear you cry) and like all chemists, I love the periodic table. Why do we love this weird grid of boxes and letters and numbers? Because it’s awesome, that’s why.

No, really, it is. Can physics or biology summarise pretty much everything important about their subject with one, single page of information? (Hint: nope.) But chemists have been able to do just that for the best part of 150 years.

The person we have to thank (mostly) for this brilliant bit of insight is one Dmitri Mendeleev. He was born in Siberia in February 1834 (there’s a bit of an issue with the exact date due to the Russian switch to the Gregorian calendar in 1918 but most sources seem to have settled on the 8th). He was the youngest of more than 10 children, but the really incredible bit about his story is that when he was just 15 years old his mother took him to Moscow, a journey of best part of 1000 miles. There were, at this time, some freshly-built stretches of railway, but make no mistake, it would’ve been a long and difficult trip.

Mendeleev’s mother wanted her youngest son to attend the University of Moscow. But when they got there, the University refused to accept him. So they moved on to the Main Pedagogical Institute in Saint Petersburg, which fortunately had more sense.

Mendeleev’s life is actually pretty colourful and makes for a great story (why is there no film??), but I won’t go into any more detail here, except to say that he gave a formal presentation on his periodic table of the elements in 1869. (Oh, and he also helped to found the first oil refinery in Russia, and did a lot of work on the technique of industrial fractional distillation, which literally no one ever seems to mention.)

So the periodic table is amazing, and if anything its creator was even more so. But what I actually want to do in this post is list some of my most favourite periodic table sites. There are few out there, and they contain a host of useful information above and beyond the standard atomic weight, atomic mass type-stuff. So, without further ado…

  • Sir Martyn Poliakoff recording for Periodic Videos

    Periodic Videos – produced by Nottingham University, this has a video for each element in the periodic table, including the newest ones. The videos all feature the gloriously-haired Sir Martyn Poliakoff and are great fun to watch.

  • Science Notes periodic tables – if you ever need a high-resolution periodic table, fancy making your laptop background into a periodic table (surprisingly handy, actually), or just want to refer to their simple-but-effective interactive version, this is a great place to start (my scarf, pictured above, was made from a print of Science Notes’ 118 Element Periodic Table Poster with Hubble Stars and Nebula). 
  • The Royal Society of Chemistry’s Periodic Table – particularly useful for students, as you can mouseover each element and key information such as electronic configuration appears in a little box on the same page – no clicking required. It’s really fast and easy to use. And if you do click on an element, a host of extra information appears above and beyond the usual history and uses, such as links to podcasts, videos and information about supply risk.
  • MPSE: Merck’s Periodic Table of the Elements – if you want a periodic table app for your mobile device, this is a great one. It’s quick to load to beautiful to look at. Available for Apple and Android devices.
  • Nature Chemistry: In Your Element – a periodic table of interesting and insightful essays (and I’m not just saying this because I wrote one of them) about the different elements.The most recent piece is on vanadium.
  • The Periodic Table of Tech – this one is particularly focused on what the elements are used for. You might learn, for example, that californium isotopes are used to detect landmines, or that zirconium isn’t just good for making cubic zirconia gems; it’s also used in nuclear fuel rods. What I particularly like about this is that it has all the information on one page, so it’s particularly easy to browse.

There will be many others which I haven’t mentioned. If you have a different favourite, do comment below!


Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2017. You may share or link to anything here, including the images, but you must reference this site if you do.


All comments are moderated. Abusive comments will be deleted, as will any comments referring to posts on this site which have had comments disabled.

The Chronicles of the Chronicle Flask: 2016

2016 is limping to its painful conclusion, still tossing out last-minute nasty surprises like upturned thumb tacks in the last few metres of a marathon. But the year hasn’t been ALL bad. Some fun, and certainly interesting, things happened too. No, really, they did, honestly.

So with that in mind, let’s have a look back at 2016 for the Chronicle Flask….

January kicked off with a particularly egregious news headline in a well-known broadsheet newspaper: Sugar found in ketchup and Coke linked to breast cancer. Turns out that the sugar in question was fructose. Yes, the sugar that’s in practically everything, and certainly everything that’s come from a plant. So why did the newspaper in question choose ketchup and Coke for their headline instead of, oh, say, fruit juice or honey? Surely not just in an effort to sell a few more newspapers after the overindulgent New Year celebrations. Surely.

octarineThere was something more lighthearted to follow when IUPAC  verified the discoveries of elements 113, 115, 117 and 118. This kicked off lots of speculation about the elements’ eventual names, and the Chronicle Flask suggested that one of them should be named Octarine in honour of the late Sir Terry Pratchett. Amazingly, this suggestion really caught everyone’s imagination. It was picked up in the national press, and the associated petition got over 51 thousand signatures!

In February I wrote a post about the science of statues, following the news that a statue to commemorate Sir Terry Pratchett and his work had been approved by Salisbury City Council. Did you know that there was science in statues? Well there is, lots. Fun fact: the God of metalworking was called Hephaestus, and the Greeks placed dwarf-like statues of him near their Hearths – could this be where the fantasy trope of dwarves as blacksmiths originates?

MCl and MI are common preservatives in cosmetic products

MCl and MI are common preservatives in cosmetic products

My skeptical side returned with a vengeance in March after I read some online reviews criticising a particular shampoo for containing a substance known as methylchloroisothiazolinone. So should you be scared of your shampoo? In short, no. Not unless you have a known allergy or particularly sensitive skin. Otherwise, feel free to the pick your shampoo based on the nicest bottle, the best smell, or the forlorn hope that it will actually thicken/straighten/brighten your hair as promised, even though they never, ever, ever do.

Nature Chemistry published Another Four Bricks in the Wall in April – a piece all about the potential names of new elements, partly written by yours truly. The month also brought a sinus infection. I made the most of this opportunity by writing about the cold cure that’s 5000 years old. See how I suffer for my lovely readers? You’re welcome.

In May I weighed in on all the nonsense out there about glyphosate (and, consequently, learned how to spell and pronounce glyphosate – turns out I’d been getting it wrong for ages). Is it dangerous? Nope, not really. The evidence suggests it’s pretty harmless and certainly a lot safer than most of its alternatives.

may-facebook-postSomething else happened in May: the Chronicle Flask’s Facebook page received this message in which one of my followers told me that my post on apricot kernels had deterred his mother from consuming them. This sort of thing makes it all worthwhile.

In June the names of the new elements were announced. Sadly, but not really very surprisingly, octarine was not among them. But element 118 was named oganesson and given the symbol Og. Now, officially, this was in recognition of the work of Professor Yuri Oganessian, but I for one couldn’t help but see a different reference. Mere coincidence? Surely not.

July brought another return to skepticism. This time, baby wipes, and in particular a brand that promise to be “chemical-free”. They’re not chemical-free. Nothing is chemical-free. This is a ridiculous label which shouldn’t be allowed (and yet, inexplicably, is still in use). It’s all made worse by the fact that Water Wipes contain a ‘natural preservative’ called grapefruit seed extract which, experiments have shown, only actually acts as a preservative when it’s contaminated with synthetic substances. Yep. Turns out some of Water Wipes claims are as stinky as the stuff they’re designed to clean up.

Maria Lenk Aquatic Enter, Tuesday, Aug. 9, 2016. (AP Photo/Matt Dunham)

Maria Lenk Aquatic Enter, Tuesday, Aug. 9, 2016. (AP Photo/Matt Dunham)

August brought the Olympics, and speculation was rife about what, exactly, was causing the swimming pools to turn such strange shades of green. Of course, the Chronicle Flask knew the correct solution…

August also saw MMS and CD reared their ugly heads on social media again. CD (chlorine dioxide) is, lest we forget, a type of bleach solution which certain individuals believe autistic children should be made to drink to ‘cure’ them. Worse, they believe such children should be forced to undergo daily enemas using CD solutions. I wrote a summary page on MMS (master mineral solution) and CD, as straight-up science companion to the commentary piece I wrote in 2015.

mugsSeptember took us back to pesticides, but this time with a more lighthearted feel. Did you know that 99.99% of all the pesticides you consume are naturally-occurring? Well, you do if you regularly read this blog. The Chronicle Flask, along with MugWow, also produced a lovely mug. It’s still for sale here, if you need a late Christmas present… (and if you use the code flask15 you’ll even get a discount!)

In October, fed up with endless arguments about the definition of the word ‘chemical’ I decided to settle the matter once and for all. Kind of. And following that theme I also wrote 8 Things Everyone Gets Wong About ‘Scary’ Chemicals for WhatCulture Science.

Just in case that wasn’t enough, I also wrote a chapter of a book on the missing science of superheroes in October. Hopefully we should see it in print in 2017.

Sparklers are most dangerous once they've gone out.

Sparklers are most dangerous once they’ve gone out.

I decided to mark Fireworks Night in November by writing about glow sticks and sparklers. Which is riskier? The question may not be as straightforward as you’d imagine. This was followed by another WhatCulture Science piece, featuring some genuinely frightening substances: 10 Chemicals You Really Should Be Scared Of.

And that brings us to December, and this little summary. I hope you’ve enjoyed the blog this year – do tell your friends about it! Remember to follow @ChronicleFlask on Twitter and like fb.com/chronicleflask on Facebook – both get updated more or less daily.

Here’s wishing all my lovely readers a very Happy New Year – enjoy a drop of bubbly ethanol solution and be careful with the Armstrong’s mixture…. 

See you on the other side!

new-year-1898553_960_720

What IS a chemical?

a_chemistry_teacher_explaining_an_experiment_8d41253v

You at the back there! Get your nose out of that dictionary and pay attention!

What do we mean when we use the word “chemical”? It seems like a simple enough question, but is it, really? I write about chemicals all the time – in fact my last WhatCulture article was about just that – and I’ve mentioned lots of different definitions before. But I’ll be honest, some of them have bothered me.

I don’t often like the definitions you find in dictionaries. Lexicography and chemistry don’t seem to be common bedfellows, and dictionary compilers haven’t, generally speaking, spent their formative years being incessantly nagged by weary chemistry teachers about their choice of vocabulary.

For example, in the Cambridge Dictionary we find:
any basic substance that is used in or produced by a reaction involving changes to atoms or molecules.”

Hm. Firstly, “basic” has a specific meaning in chemistry. Obviously the definition doesn’t mean to imply that acids aren’t chemicals, but it sort of accidentally does. Then there’s the implication that a chemical reaction has to be involved. So inert substances aren’t chemicals? Admittedly, “used in” doesn’t necessarily imply reacts – it could be some sort of inert solvent, say – but, again, it’s bothersome. Finally, “atoms or molecules”. Ionic substances not chemicals either, then?

Yes, it’s picky, but chemists are picky. Be glad that we are. A misplaced word, or even letter, on a label could have serious consequences. Trust me, you do not want to mix up the methanol with the ethanol if you’re planning cocktails. Similarly, fluorine is a whole other kettle of piranhas compared to fluoride ions. This stuff, excuse the pun, matters.

Dictionary definitions have their problems.

Dictionary definitions have their problems.

Let’s look at some more definitions (of the word as a noun):

The Free Dictionary tells us that a chemical is:
“A substance with a distinct molecular composition that is produced by or used in a chemical process.”

Merriam Webster says:
“of, relating to, used in, or produced by chemistry or the phenomena of chemistry <chemical reactions>”

And Dictionary.com goes with the simple:
“a substance produced by or used in a chemical process.”

That idea that a chemical reaction must be involved somehow seems to be pervasive. It’s understandable, since that’s the way the word is mostly used, but it’s not really right. Helium, after all, is still very much a chemical, despite being stubbornly unreactive.

Possibly the best of the bunch is found in the Oxford Living Dictionary:
“A distinct compound or substance, especially one which has been artificially prepared or purified.”

Not bad. Well done Oxford. No mention of chemical reactions here – it’s just a substance. We do most often think of chemicals as things which have been “prepared” somehow. Which is fair enough, although it can lead to trouble. In particular, ridiculous references to “chemical-free” which actually mean “this alternative stuff is naturally-occurring.” (Except of course it often isn’t: see this article about baby wipes.) The implication, of course, is that thing in question is safe(r), but there are lots and lots of very nasty chemicals in nature: natural does not mean safe.

You keep using that word. I do not think it means what you think it means.

Sometimes people will go the other way and say “everything is chemicals.” We know what this means, but it has its problems, too. Light isn’t a chemical. Sound isn’t a chemical. All right, those are forms of energy. What about neutrinos, then? Or a single proton? Or a single atom? Or, going the other way, some complicated bit of living (or once living) material? In one debate about this someone suggested to me that a “chemical was anything you could put in a jar,” at which point I pedantically said, “I keep coffee in a jar. Is that a chemical?” Obviously there are chemicals in coffee, it works from the “everything is chemicals” perspective, but it’s a single substance that’s not a chemical.

Language is annoying. This is why chemists like symbols and numbers so much.

Anyway, what have we learned? Firstly, something doesn’t necessarily have to be part of a chemical reaction to be a chemical. Secondly, we need to include the idea that it’s something with a defined composition (rather than a complex, variable mixture, like coffee), thirdly that chemical implies matter – light, sound etc don’t count, and fourthly that it also implies a certain quantity of stuff (we probably wouldn’t think of a single atom as a chemical, but collect a bunch together into a sample of gas and we probably would).

So with all that in mind, I think I shall go with:

So what IS a chemical?

A chemical is…

(Drum roll please….)

Any substance made of atoms, molecules and/or ions which has a fixed composition.

I’m not entirely convinced this is perfect, but I think it more or less works.

If you have a better idea, please do comment and let me know!


Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. In need of a groovy new mug? Check out this page.


All comments are moderated. Abusive comments will be deleted, as will any comments referring to posts on this site which have had comments disabled.

 

No element octarine, but Nanny will be pleased…

After lots of speculation over the last few months, the names of the new elements were finally announced by IUPAC yesterday. There will now be a five-month public review, ending on 8 November 2016, but it looks likely that these names will be accepted. They are:

  • 113: Nihonium, Nh, from ‘Nihon’, meaning Japan or ‘The Land of the Rising Sun’, home of RIKEN;
  • 115: Moscovium, Mc, in recognition of the Moscow region, where JINR is based;
  • 117: Tennessine, Ts, for the Tennessee region, home of ORNL;
  • and 118: Oganesson, Og, named after a very important individual*.
New-Element-Names-768x378

New Element Names, by Compound Interest (click image for more info)

As you can see, octarine sadly didn’t make the cut. Perhaps the million to one chance rule just doesn’t work so well on roundworld. Oh well.

But look, they didn’t completely forget about us! They just misspelled ‘Ogg and Son’. It’s easily done. I’m sure Nanny will still be pleased.

nanny_ogg_by_hyaroo-d6mnot6

Nanny Ogg. Image byHyaroo, http://hyaroo.deviantart.com/

*Oganesson actually recognises Professor Yuri Oganessian (born 1933) for his pioneering contributions to transactinoid elements research. But perhaps he’s a distant relative?


Follow The Chronicle Flask on Facebook and Twitter for regular updates and other interesting bits and pieces from around the internet.

Feet of clay? The science of statues

Concept art for the Terry Pratchett statue (c) Paul Kidby

Concept art for the Terry Pratchett statue (c) Paul Kidby

Yesterday we received the exciting news that a statue to commemorate Sir Terry Pratchett and his work has been approved by Salisbury City Council. Hurrah! So, even if we don’t quite manage to get octarine into the periodic table (and thus into every science textbook for ever more), it’s looking very likely that there will still be something permanent to help keep his memory alive.

But this got me thinking about everyday chemistry (who am I kidding, I’m always thinking about everyday chemistry!) and, in particular, bronze – the material from which the statue will be made.

Bronze, I hear you say, what’s that good for apart from, well, statues? And maybe bells? Is it really that interesting?

Well, let’s see. Bronze is an alloy. Alloys are mixtures that contain at least one metal, but they’re stranger than the word ‘mixture’ might perhaps suggest. Imagine combining, say, sand and stones. You still be able to see the sand. You could see the stones. You could, if you could be bothered to do it, separate them out again. And you’d expect the mixture to behave like, well, stony sand.

Alloys aren’t like this. Alloys (other well-known examples include steel, brass and that silver-coloured stuff dentists use for filling teeth) look, on all but the atomic level, like pure metals. They’re bendy and shiny, they make pleasing ringing sounds when you hit them and they’re good electrical conductors. And unlike more simple mixtures, they’re difficult (though not impossible) to separate back into their constituents.

Perhaps the most interesting this about alloys is that their properties are often very different to any of the elements that went into making them. Bronze, in particular, is harder than either tin or copper, and hence The Bronze Age is so historically significant. Copper is one of the few metals that can (just about) be found in its pure form, and so is one of the oldest elements we know, going back at least as far as 9000 BC. But while quite pretty to look at, copper isn’t ideal for making tools, being fairly soft and not great at keeping an edge. Bronze, on the other hand, is much more durable, and was therefore a much better choice for for building materials, armour and, of course, weapons. (War, what is it good for? Er, the development of new materials?)

Hephaestus was the God of fire and metalworking; according to legend he was lame.

Hephaestus was the God of metalworking. According to legend he was lame, could it have been because of exposure to arsenic fumes?

Today we (well, chemists anyway) think of bronze as being an alloy of tin and copper, but the earliest bronzes were made with arsenic, copper ores often being naturally contaminated with this element. Arsenical bronzes can be work-hardened, and the arsenic could, if the quantities were right, also produce a pleasing a silvery sheen on the finished object. Unfortunately, arsenic vaporises at below the melting point of bronze, producing poisonous fumes which attacked eyes, lungs and skin. We know now that it also causes peripheral neuropathy, which might be behind the historical legends of lame smiths, for example Hephaestus, the Greek God of smiths. Interestingly, the Greeks frequently placed small dwarf-like statues of Hephaestus near their hearths, and this is might be where the idea of dwarves as blacksmiths and metalworkers originates.

Tin bronze required a little more know-how (not to mention trade negotiations) than arsenical bronze, since tin very rarely turns up mixed with copper in nature. But it had several advantages. The tin fumes weren’t toxic and, if you knew what you were doing, the alloying process could be more easily controlled. The resulting alloy was also stronger and easier to cast.

teaspoon in mugOf course, as we all know, bronze ultimately gave way to iron. Bronze is actually harder than wrought iron, but iron was considerably easier to find and simpler to process into useful metal. Steel, which came later, ultimately combined superior strength with a relatively lower cost and, in the early 20th century, corrosion resistance. And that’s why the teaspoon sitting in my mug is made of stainless steel and not some other metal.

Bronze has a relatively limited number of uses today, being a heavy and expensive metal, but it is still used to make statues, where heaviness and costliness aren’t necessarily bad things (unless, of course, someone pinches the statue and melts it down – an unfortunately common occurrence with ancient works). It has the advantages of being ductile and extremely corrosion resistant; ideal for something that’s going to sit outside in all weathers. A little black copper oxide will form on its surface over time, and eventually green copper carbonate, but this is superficial and it’s a really long time before any fine details are lost. In addition, bronze’s hardness and ductility means that any pointy bits probably won’t snap off under the weight of the two-millionth pigeon.

So how are bronze statues made? For this I asked Paul Kidby, who designed the concept art for the statue. He told me that he sculpts in Chavant, which is an oil-based clay. It’s lighter than normal clay and, crucially, resists shrinking and cracking. He then sends his finished work away to be cast in bronze at a UK foundry, where they make a mould of his statue and from that, ultimately (skipping over multiple steps), a bronze copy. Bronze has another nifty property, in that it expands slightly just before it sets. This means it fills the finest details of moulds which produces a very precise finish. Conveniently, the metal shrinks again as it cools, making the mould easy to remove.

And just for completeness, Paul also told me that the base of the statue will most likely be polished granite, water jet cut with the design of the Discworld sitting on the back of Great A’Tuin. I can just imagine it – it’s going to be beautiful.

Follow The Chronicle Flask on Facebook and Twitter for regular updates.