Unsafe slime? How bad is borax, really?

Slime is a fun bit of chemistry that anyone can do – but how safe is it?

It’s August, which means it’s the school summer holidays in the UK and, as is traditional, it’s been pouring with rain. This has left many a cabin-fevered child searching for ways to amuse themselves.

Start hunting around the internet for things to do and it’s not long before the concept of the “kitchen science” experiment turns up. There are actually loads of these, and it’s even possible to do some of them without permanently damaging anyone’s eardrums, dusting every surface with cornflour and leaving a parent rocking in the corner muttering “why did I encourage this?” over and over to themselves.

Which brings me to slime – surely the go-to fun science experiment. What’s not to love about taking some of that white, runny PVA glue found in gallon bottles in school classrooms everywhere and magically turning it into glorious, gloopy slime? Add some food colouring and you can even have coloured slime! Add glitter and… well you get the idea.

Many YouTubers love this stuff. A quick search for “make your own slime” turns up pages and pages of videos, giving instructions as to how to do just that.

In fact, it seems that slime-making is currently a bit of a craze, with children all over the world making all kids of different types. There’s unicorn slime, rainbow slime, fluffy slime – you name it. Brilliant, you might think, a whole generation of youngsters interested in chemistry. What’s not to like about that?

Well, as a few news reports have recently pointed out, there might be a problem if children are handling lots of borax, or certain other chemicals.

Polyvinyl alcohol

Slime, you see, is a really nice example of polymerisation – the same process that goes on when plastics are made. PVA glue, the usual starting material, is a polymer itself. The letters PVA stand for polyvinyl alcohol (its systematic name is poly(1-hydroxyethylene)), but literally no one calls it that, not even A-level chemistry teachers forced, kicking and screaming, to follow IUPAC naming conventions).

PVA is a long chain of carbon atoms with alternating CH2 groups and alcohol, OH, groups. As anyone who’s ever handled it will know, it’s quite runny. Thick, yes, but still runny. Basically, it’s a liquid.

But if you mix it with borax, aka sodium tetraborate, some magic happens. And when I say magic, I mean chemistry. The chains of atoms become linked together (essentially via hydrogen bonds), and as a result the new substance is a lot more solid. But it’s not quite solid. At least, not in the sense of something that keeps its own shape. No, this is weird, peculiar, stuff that sits somewhere in between solid and liquid.

Borax joins the chains of PVA together.

There’s something tactilely pleasing about slime. Put it in your hands and it feels cool and slightly moist – your fingers slide over and through it with a sort of squeaky sensation. Leave it alone for a few minutes and it flows to take the shape of its container, forming a perfect, mirror finish on its surface. Tip the pot over, and it will gradually creep toward the edge.

It is safe to handle. Here are my hands, handling it (we made this at the March for Science in Bristol back in April). You will notice that my skin is not falling off.

It’s white unless you dye it. We went for red, which is pleasingly disturbing.

I did, though, wash my hands after I took that photo. And that’s because, while the PVA is pretty harmless (as you know if, like me, you spent your primary school days painting your hands with glue just so you could peel it off later) the borax isn’t. At least, not entirely.

Before I go any further, let’s be clear: lots of things aren’t “entirely” safe. Most of the cleaning products in the average kitchen and bathroom have warning levels of varying degrees of severity on them, and we don’t think too much about it. Even things that are designed to be in contact with skin, like hand soap and shampoo, usually have warnings about eye irritation and statements like “if irritation occurs, discontinue use”. Even water is deadly in the wrong context (don’t try inhaling too much of it, for example). So when I say not entirely safe, I don’t mean to suggest that panic needs to ensue if your child has so much as looked at a borax solution.

Borax has traditionally been used in several household products, although admittedly more in the US than in the UK. Most people know it as a laundry additive, where it softens water, brightens whites and inhibits the growth of the bacteria and fungi which can make clothes stinky.

It’s not considered a lethal compound, in the sense that you’d have to eat a large quantity – far more than anyone might reasonably consume by accident – before it became deadly, and you’d almost certainly throw up long before then. Borax can irritate the skin (but see note at the end), and inhalation of the dust is well known to irritate the lungs. This is more of a concern for people working with borax on an industrial scale day in and day out – but it could become an issue if, say, someone were making slime every single day using large quantities of borax (not recommended).

Then there’s another concern. If borax is exposed to hydrochloric acid, it forms boric acid. Long-term exposure to boric acid can cause kidney damage and fertility problems, both in men and women. It’s also potentially teratogenic, which means it could cause harm to an unborn child. Borax and boric acid are not the same thing but, of course, our stomachs contain hydrochloric acid. Therefore, if you swallow borax, you’re effectively exposed to boric acid.

Frequent exposure to borax might cause skin irritation (see note at end)

These risks are the reason borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010, which is the first step in restricting use of the chemical within the European Union. As far as I can establish, it’s still a “candidate”, but the European Chemicals Agency substance information card does state that borax may “damage fertility or the unborn child”.

Now, the chances of achieving the levels involved in “long-term exposure” from occasionally handling borax solutions are slim to none. It’s safe to handle dilute borax solutions (see notes at the end). Indeed, borax is even approved as a food preservative in the EU (E285). To put it into context, alcohol (ethanol) also causes organ damage and is a known teratogen and a carcinogen (which borax isn’t) and that turns up in all sorts of things we’re regularly in contact with, everything from antiseptic hand gels to mouthwashes to drinks (and it’s also approved as a food additive, E1510 – which is good news if you like liqueur chocolates).

I personally have no concerns about handling dry borax in small quantities to make up solutions myself. However, I wouldn’t let children do that part. Once made I’d consider the solution safe, so long as children were supervised and weren’t doing anything really silly like drinking it. I’d also tell children to wash their hands after handling the slime and, if I thought they had sensitive skin for any reason (eczema, say) I’d suggest plastic gloves.

Borax is easy to buy online.

Because of the European Regulations, it theoretically shouldn’t be that easy to get hold of borax in the UK. But I found it for sale on Amazon.co.uk. The listing says that it “can only be purchased by Professionals and by trade and business users,” (sic) but I ordered some and there were no checks. A plastic bag full of borax powder (the decahydrate, Na2B4O7.10H2O) arrived within a few days.

Most of the news reports doing the rounds have involved children suffering from severe skin irritation. For example, in February this year a woman from Manchester posted photos of chemical burns on her daughter’s hands online as a warning to other parents. However, looking into the details of that story it turns out that she wasn’t using borax. In fact, she used fabric detergent “as an alternative”.

Take a look at pretty much type of fabric detergent and you’ll find hazard warnings, usually indicating it’s corrosive and definitely saying “keep out of reach of children”. Those are there for a reason. Fabric detergent is designed to remove grease and  stains. In other words, to break down fats and proteins, and guess what your skin is made of? Yep. Don’t get neat fabric detergent on your hands. Even if your skin isn’t particularly sensitive, it’s almost certainly going to irritate it.

Fabric detergents are usually labelled corrosive.

Bottom line: don’t use fabric detergent as a borax alternative to make slime, because there’s a real risk that enough of it could get onto your (or your child’s) skin that it could irritate.

When it comes to borax itself, if I understand things correctly, it’s not actually restricted in the EU – including the UK – yet. (I might have this wrong – do correct me if you think I have.) It’s not something you can pop to the supermarket and buy, but as we’ve established you can buy it online fairly easily.

Borax solutions are extremely unlikely to cause harm, if used sensibly (boron chemist David Schubert agrees, see note at the end). But, once again: if you’re doing this experiment it’s best not to let children make up the solution – an adult should do that part.

A sensible quantity is about 1 gram of borax in 25 millilitres of warm water (for those without a metric scale: one level teaspoon of borax in half a cup measure of water). This will actually polymerise quite a bit of PVA – you don’t need that much. I recommend making the borax solution in a labelled plastic cup which you should throw away afterwards. Don’t leave it anywhere where someone might mistake it for their drink! Once the solution is made just add a little bit to some PVA in another plastic cup, give it a good stir with a spoon or a lolly stick, and the magic (chemistry) will happen. Add food colouring if you like (be aware that it can stain!) and enjoy the slimy goodness. (See additional note for teachers & technicians at the end.)

Do supervise any and all slime-making, don’t let children handle slime all day, every day, and if you know they have sensitive skin, make them wear plastic gloves. Make them wash their hands before they eat or drink anything.

If a child has made slime somewhere else, at a party or a science club, say, and they bring it home, again, there’s no need to worry. They can play with it perfectly safely. Don’t let them leave it on a radiator, though. That will end in disaster.

I am not a fan of the “it might be a bit dangerous, so no one should ever try it” mentality. I mean, that’s just no fun, is it? But I’m also not a fan of unnecessary risks – because trips to hospital are equally no fun. So if you want to try this experiment, I’ve summarised my guidance in this graphic.

Stay safe with slime by following this guidance

And if you want a even safer slimy experiment, and you can bear the mess, I suggest mixing cornflour with just enough water to make a thick paste in a shallow tray. Then let your kids stick their fingers in it, bounce things off it, and generally play with it. (Check out this link to find out more about why it behaves as it does.) I’m told it makes an even better mixture if you add basil seeds.

Have fun this summer, stay safe, and don’t eat the slime!

Note for teachers and technicians:
This post is aimed at people who might be making slime at home, and hence not have easy access to CLEAPSS guidelines. Anyone doing the experiment with students in school should, of course, refer to their department’s risk assessments and policies. For the record, at the time of writing, CLEAPSS classify 0.2M or 40g/dm³ (or more dilute) borax solutions as “low hazard”.

Edit: 15th August 2017:
After I wrote and published this post I was contacted by someone who specialises in boron chemistry, David Schubert. Now, if anyone knows about boron safety, it’ll be the guy who spends all day writing risk assessments for boron-based chemicals! He told me that borax has been shown to be safe for skin contact. He also said that you absorb less boron through intact skin than you consume by eating a normal, healthy diet (boron is a naturally-occurring trace-mineral – nuts and pulses are good sources), and even provided me with a link to a research paper on the subject. I asked him about the high pH of boron solutions, since alkaline solutions can be irritating in general, and he told me that borax solutions are less alkaline than sodium carbonate and not at all irritating to skin. At this point I will stress that when we’ve seen reports of children suffering skin irritation after making slime, it hasn’t been clear exactly what they’ve been handling. It’s very likely they were adding other chemicals to their slime, and it was actually one of those causing the irritation. Perhaps they developed an allergy to something. It’s impossible to say. Either way, the bottom line is that borax solutions are pretty safe – there’s no need to worry. (Still don’t drink them though!)

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MMS and CD chemistry – the facts

The TL:DR version.

The TL:DR version.

About a year ago I wrote a post on the subject of MMS and CD. Many people have since praised that post, but others have complained that it’s rather long (it is) and contains too much opinion.

I believe that anyone that wants them should have easy access to the facts on this subject, and not just the information provided by proponents of MMS/CD use.

With this in mind I’ve written this post as a summary of the basics. I ask only that you credit me if you use this to write an article. A mention of my Twitter account, @chronicleflask, or a link to this page will suffice.

What is MMS?


MMS is usually sold as water purification drops

MMS stands for ‘master mineral solution’ or sometimes ‘miracle mineral solution’. It is a 22.4% solution of sodium chlorite in water. Sodium chlorite has the chemical formula NaClO2. So, MMS is 22.4 grams of NaClO2 dissolved in 100 mls of water. Sodium chlorite/MMS does not, on its own, act as a bleach.

Sodium chlorite’s LD50 (for rats) is 350 mg/kg. This means that, on average, if you feed rats 350 mg of it per kg of body weight, half the rats will die. If we assume its toxicity is similar in humans (and there’s no reason it should not be) that means that 5.25 grams would probably be enough to kill an average 4-year-old child weighing about 15 kg.

MMS is usually sold as ‘water purification drops’. Search for ‘sodium chlorite water purification’ in Google and you will quickly find it (usually alongside an ‘activator’ solution). Bottles for sale are usually 4 oz, or 114 mls. One quarter of one of these bottles would probably be lethal to a 15 kg 4-year-old.

What is CD (or CDS)?

CD is chlorine dioxide (and CDS stands for chlorine dioxide solution). Chlorine dioxide is ClO2. It is a bleach, used industrially to bleach wood pulp. It is also used to purify water and kill pathogens on certain foodstuffs. It is considered more effective than plain chlorine for water purification – it’s less corrosive and is particularly good at destroying legionella bacteria, as well as many viruses and protozoa.

Chlorine dioxide is more toxic than sodium chlorite. It’s LD50 is 292 mg/kg (the lower the number, the more toxic something is). For this reason, the concentrations used in food/water applications are very low. The US Environmental Protection Agency have set a maximum level of 0.8 mg/L chlorine dioxide in drinking water. That’s 0.00008 grams per 100 ml of water.

What’s the connection between MMS and CDS?

The chemistry of sodium chlorite (the substance in MMS) with acids.

The chemistry of sodium chlorite (the substance in MMS) with acids.

Chlorine dioxide evaporates quickly from solution, which means CD solutions cannot be stored – they have be made freshly as they’re needed. When sodium chlorite is mixed with an acid, usually citric acid (the acid in oranges and lemons), it forms chlorine dioxide. In short:
MMS + acid = CDS.

The chemistry behind this is complicated. It’s simpler if the acid used is hydrochloric acid (HCl), and this particular method of ‘activation’ is sometimes recommended by proponents of MMS/CD use.

If sodium chlorite is mixed with citric acid is used the reaction doesn’t happen in one step. Rather, chlorous acid (HClO2) forms, which ultimately breaks down to form ClO2. Several reactions are involved in this process. The concentration of chlorine dioxide in a solution made in this way is likely to be lower than if hydrochloric acid is used. However, it’s important to realise the the resulting solution is a mixture of harmful substances. Less chlorine dioxide does not necessarily mean safer.

How much chlorine dioxide forms when MMS is ‘activated’?

It’s not possible to answer this precisely, because it depends on several different factors. To begin with, it depends on whether hydrochloric acid or another acid (such as citric acid) is used. It further depends on temperature, and how much acid is added. We have no way of knowing exactly what someone mixing up these solutions at home is doing.

A document on acidified sodium chlorite published by the Joint Expert Committee on Food Additives (JECFA) suggests that, at a pH of 2.3, a 50 ppm solution of sodium chlorite would produce 16 ppm chlorous acid (less at higher pHs). Starting with a 22.4% solution (as in MMS), and allowing for the stoichiometry suggested by the equations above, this could produce something in the region of 36 g of chlorine dioxide per litre of water.

The US EPA’s recommended safe limit for chlorine dioxide is 0.00008 grams per litre of water. Compare this to 36 grams per litre. Even if only a fraction is converted to chlorine dioxide, the resulting mixture is likely to be tens of thousands in excess of safe limits.

How are CD solutions used in food & drink production?

Very dilute solutions, with just a few ppm of chlorine dioxide, are used as sprays or dipping solutions for poultry, meats, vegetables fruit and seafood. However, in these applications the chlorine dioxide evaporates from the food long before anyone eats it – it’s not present in the final food product. Chlorine dioxide is also used in water treatment plants, but the concentration in the final water supply is strictly controlled so that it’s less than the recommended safe limits.

How are CD solutions used as ‘alternative treatments’?

There are groups of people who believe that drinking CD solutions, or using them to perform enemas can cure any and all diseases, illnesses and conditions. However, there is no evidence that CDS is at all efficacious, and no reasonable mechanism has ever been given for its supposed mode of action. Jim Humble, who coined the name MMS ten years ago and sparked the use of these ‘treatments’, claimed that he worked with the Red Cross to successfully treat a group of malaria patients in Uganda. The Red Cross strenuously deny these claims. Other commentators have explained very clearly why Humble’s claims are impossible.

There is a large group online, led by Kerri Rivera, who believe that CD solutions can cure autism. This is not true. Autism is a neurodevelopment disorder. There is no cure, although certain therapies may help those on the autistic spectrum to manage better in day-to-day life. The cause of autism is unclear, but it appears to have a strong genetic basis.

Humble and Rivera advocate drinking CD solutions and/or using them in enemas. Protocols for such treatments involve adding drops of CDS to water, milk or other liquids.

The number of drops used varies. Humble reportedly used 18 drops at a time in his malaria treatment. Usually this is added to further liquid, for example in a 250 ml bottle. Assuming a drop is 0.1 mls, this could be as much as 0.065 g of chlorine dioxide in 250 mls, or 0.26 grams per litre. Once again, US EPA’s recommended safe limit for chlorine dioxide is 0.00008 grams per litre.

The amounts recommended by MMS/CD protocols are likely to be at least 3000 times safe limits, and may be considerably more. Protocols exist which recommend drinking these mixtures every one or two hours, eight times a day or even more.

What would happen if someone drank a CD solution?

It would be ironic if it weren't so tragic.

Chlorine dioxide exposure may actually cause delays in the development of the brain.

It would depend on the concentration. The very low levels used in normal water purification are not be harmful (that’s why safe limits exist), however drinking large amounts (such as those usually recommended in MMS/CD protocols) would cause irritation to the mouth, oesophagus, and stomach. There is no evidence that chlorine dioxide causes cancer. The ATSDR‘s (Agency for Toxic Substances and Disease Registry) entry for chlorine dioxide says that “studies in rats have shown that exposure of pregnant animals to chlorine dioxide or exposure of pups shortly after birth can cause delays in the development of the brain” (see also PMID: 2213920).

Why are CDS enemas used, and what would be the effect?

Rivera in particular advocates CDS enemas to kill the ‘parasites’ which she and her followers believe cause autism. There is no evidence for the existence of these ‘parasites’. Photos published online which purport to show them have been condemned as actually showing intestinal lining and mucus, excreted as the direct result of harsh enema procedures.

Enemas, regardless of the liquid used, have risks. Repeated enemas can cause electrolyte imbalance, rupture of the bowel and damage to the rectal tissues. Enemas with CDS are likely to be particularly dangerous since it is corrosive. Proponents of CDS use claim it is ‘selective’ and only kills ‘harmful’ bacteria and parasites. This is not possible; chlorine dioxide is a strong oxidising agent and damages all cells it comes into contact with, regardless of the nature of those cells.

Children have thinner tissues than adults. The risks of regular enemas, particularly with a corrosive agent such as chlorine dioxide, and particularly when carried out at home by someone with no medical training, are likely to be considerably higher for children.

Is there any way to tell if someone has been using CDS in high concentrations?

Unless someone admits to using CDS, there isn’t really any way to tell. For this reason there are very few reported cases of harm caused by CDS, as users tend to be extremely secretive. Unless an enema causes major trauma (which is a real risk) the symptoms are likely to be fairly vague gastrointestinal distress, which could be caused by any number of other things. There is no routine medical test to measure chlorine dioxide or chlorite in the body. There is a special test to measure chlorite in tissues, blood, urine, and feces, but the test cannot tell the extent of the exposure or whether harmful effects will occur. This test wouldn’t be performed unless exposure was expected. In other words, unless someone admits to using CDS on themselves or their child, it’s unlikely anyone will ever find out.

Has MMS/CDS been in the news?

Yes, on several occasions:

If there’s no cure for autism/cancer/some other condition, mightn’t it be worth trying…?

Medicine is all about risks vs. benefits. The benefit of using a particular treatment must always exceed the risk of using that treatment. In this case, there are no proven benefits of using MMS/CDS. There are considerable risks, as described above. The only thing MMS/CDS will do is make you feel sick and generally more unwell than you (or your child) might already. So no, it isn’t worth trying. Please don’t.


Comments will be left open on this page for as long as it takes for me to tire of dealing with “you’re a pharma shill!”, “this is all lies!”, “watch this YouTube video that proves it works!” and “I drink it every day and I’m fine!” type comments.

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Puzzling pool problems?

We’re half way thorough the Rio 2016 Olypics, and it will have escaped no one’s notice that there have been a few little problems with one of the pools.

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

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

First, the water turned a mysterious green colour. Then there were reports of a ‘sulfurous’ smell, with German diver Stephan Feck reported as saying it smelled like a “fart”.

The diving pool seemed to be the worst affected, but the water-polo pool next to it also suffered problems, and competitors complained of stinging eyes.

So what on earth was happening? An early suggestion was that copper salts were contaminating the water. It’s not unheard of for copper compounds to get into water supplies, and it would certainly explain the colour; copper chloride solutions in particular are famously greeny-blue. But what about that sulfurous smell? Copper chloride doesn’t smell of sulfur.

Was the strange pool colour due to algae bloom?

Was the strange pool colour due to an algae bloom, like this one in Lake Erie?

The most likely culprit was some sort of algae bloom – in other words rapid algae growth – with the smell probably coming from dimethyl sulfide, or DMS. There’s a singled-celled phytoplankton called Emiliania huxleyi which is particularly famous for producing this smelly compound. In fact, it actually has more than one very important role in nature: the smell is thought to alert marine life that there’s food nearby, but it also seeps into the atmosphere and helps with cloud formation, helping to control our planet’s temperature. Without these reactions, Earth might not be nearly so habitable.

But how did algae manage to grow in the pool? The pool chemicals should have prevented it, so what had happened? An Olympic official then went on to make the comment that “chemistry is not an exact science,” which of course led to much hilarity all around. Chemistry is, after all, incredibly exact. What chemistry student doesn’t remember all those calculations, with answers to three significant figures? The endless balancing of equations? The careful addition of one solution to another, drop by drop? How much more ‘exact’ would you like it to be?

But I had a bit of sympathy with the official, because I suspect that what they actually meant – if not said – was that swimming pool chemistry is not an exact science. And while that, too, is hardly accurate, it is true that swimming pool chemistry is very complicated and things can easily go wrong, particularly when you’re trying to work on an extremely tight schedule. They could hardly, after all, close down all the pools and spend several days carrying out extensive testing in the middle of the sixteen-day-long Olympic Games.

Rio 2016 Olympics Aquatics Stadium (Image: Myrtha Pools)

Rio 2016 Olympics Aquatics Stadium (Image: Myrtha Pools)

When a pool is first built and filled, things are, theoretically, simple. You know exactly how many cubic litres of water there are, and you know exactly how much of each chemical needs to be added to keep the water free of bacteria and other nasties. Those chemicals are added, possibly (particularly in a pool this size) via some kind of automated system, and the pH is carefully monitored to ensure the water is neither too alkaline (basic) nor too acidic.

There’s a certain amount of proprietary variation of swimming pool chemicals, but it essentially all comes down to chlorine, which has been used to make water safe now for over 120 years.

Originally, water was treated to make it alkaline and then chlorine gas itself was added. This produced compounds which killed bacteria, in particular sodium hypochlorite, but the practice was risky. Chlorine gas is extremely nasty stuff – it has, after all, been used as a chemical weapon – and storing it, not to mention actually using it, was a dangerous business.

However, hundreds of people swimming in untreated water is a recipe for catching all kinds of water-borne disease, so it wasn’t long before alternatives were developed.

The Chemistry of Swimming Pools (Image: Compound Interest - click for more info)

The Chemistry of Swimming Pools (Image: Compound Interest – click graphic for more info)

Those alternatives made use of the chemistry that was happening anyway in the water, but  allowed the dangerous bit, with the elemental chlorine, to happen somewhere else. And so hypochlorite salts began to be manufactured to be used in swimming pools.

As the lovely graphic from Compound Interest illustrates, sodium hypochlorite reacts with water to form hypochlorous acid, which in turn goes on to form hypochlorite ions. These two substances sit in an equilibrium, and both are oxidants, which is good because oxidants are good at blasting bacteria. The equilibria in question are affected by pH though, which is one reason why, quite apart from the potential effects on swimmers, it’s so important to manage the pH of pool water.

There are a couple of different chemicals which can be added to adjust pH. Sodium bicarbonate, for example, can be used to nudge the pH up if needed. On the other hand, sodium bisulfate can be used to lower pH if the water becomes too alkaline.

Open-air pools have particular problems

UV light breaks down the chemicals that are used to keep swimming pool water clean.

This can all be managed extremely precisely in an unused, enclosed pool. But once you open that pool up, things become less simple. Open-air pools have a particular problem with UV light. Chlorine compounds are often sensitive to UV – this is why CFCs are such a problem for the ozone layer – and hypochlorite is no exception. In the presence of UV it breaks down in a process called photolysis to form chloride ions and oxygen. This means that outdoor pools require more frequent treatments, or the addition of extra chemicals to stabilise the ‘free available chlorine’ (FAC) levels.

Sadly, I haven’t managed to make it over to Rio, but from what I’ve seen the Aquatic Centre has a roof which opens up, which means that the pool water is indeed being exposed to UV light.

So perhaps the chemical levels simply dropped too low, which allowed algae to proliferate? Possibly aggravated by environmental conditions? Indeed, initially this seemed to be the explanation. FINA, the international governing body of aquatics, issued a statement on Wednesday afternoon which said:

“FINA can confirm that the reason for the unusual water color observed during the Rio diving competitions is that the water tanks ran out of some of the chemicals used in the water treatment process. As a result, the pH level of the water was outside the usual range, causing the discoloration. The FINA Sport Medicine Committee conducted tests on the water quality and concluded that there was no risk to the health and safety of the athletes, and no reason for the competition to be affected.”

This prompted people to wonder how on earth chemical levels were allowed to run out in an event as significant as the Olympics – did someone forget to click send on the order? – but still, it seemed to explain what had happened.

FINA issued a new statement

FINA issued a new statement on Sunday

Until today (Sunday), when more information surfaced as Olympic officials announced that they were going to drain at least one of the swimming pools and refill it. This is no small feat and will involve considerable cost: after all, we’re talking about millions of gallons of water. But it seems to be necessary. As Rio 2016’s director of venue management Gustavo Nascimento said:

“On the day of the Opening Ceremonies of the Games, 80 litres of hydrogen peroxide was put in the water. This creates a reaction to the chlorine which neutralises the ability of the chlorine to kill organics. This is not a problem for the health of anyone.”

Whoops. Yes indeed. Hydrogen peroxide reacts with chlorine to produce oxygen and hydrochloric acid. In fact, hydrogen peroxide is actually used to dechlorinate water which contains levels of chlorine that are too high. It might not be the very worst thing you could add to the water (when you think of all the things that could end up swimming pools) but it’s definitely up there.

Why and how this happened doesn’t, at the moment, appear to be clear. Presumably someone is for the high jump, and not just on the athletics field.

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Gold! Bright and yellow, hard and cold

200px-Gold-49956Let’s talk about element number 79.  It’s one of the oldest known elements, used for quite literally thousands of years.  It’s constantly at the heart of conflicts and politics.  Poets have waxed lyrical about it, authors have written about it, economists and prospectors have hinged their livelihoods on it.  And, of course, chemists have studied it.

As an element it’s unusual.  It’s a metal, but instead of the boring silvery-grey of most metals it glows a warm yellow.  It’s also one of the most unreactive elements, and yet has found use a catalyst – speeding up chemical reactions that otherwise would be too slow to be useful.  It’s rare, making up only about 0.004 parts per million of the Earth’s crust, and yet its annual production is surprisingly high: 2700 tonnes in 2012.  Its density makes it heavy – weighing over nineteen times more than the same volume of water – but it’s also relatively soft, so soft that it’s possible to scratch a pure piece with your fingernail (in theory, and if you have fairly robust fingernails).

Yes, gold.  Chemical symbol Au, from its latin name aurum meaning ‘shining dawn’ or ‘glow of sunrise’ (how lovely is that?)

The history of gold is fascinating.  You could easily write a whole book about it.  In fact, someone has.  I won’t attempt anything so ambitious, but it does have some very interesting chemical stories associated with it.

Because of its unreactivity, gold is one of the relatively few elements that’s found uncombined in nature.  In other words, you can pick up a piece of pure gold from the ground or, more likely, out of a river bed.  Thanks to this property it’s very probably the first metal that humans as a species interacted with.  It’s too soft to be much use as a tool, so its earliest uses were almost certainly ornamental.  Decorations and jewellery had value and could be traded for other things, and ultimately (skipping over a chunk of history and early economics) this led to currency.

And so it was that early alchemists, some two thousand years ago, became obsessed with the idea of a quick buck.  Could other metals be turned into gold?  They searched long and hard for the mythical philosopher’s stone (like in Harry Potter, only not exactly) which could turn base metals into gold or silver.  Of course they never found it, because it doesn’t exist.  It’s not possible to change one element into another during a chemical reaction.  This is because what defines an element is the number of protons in its nucleus, and chemistry is all about the electrons. Chemical processes don’t touch protons, which are hidden away in the nuclei of atoms.

But where there’s a will there’s almost always a way.  Two millennia after alchemists were hunting for a magical stone, the chemist Glenn Seaborg managed to transmute a minute quantity of lead, via bismuth, into gold by bombarding it with high-energy particles.  Apparently, these days particle accelerators ‘routinely’ transmute elements, albeit only a few atoms at a time.

The trouble is, this method costs a fortune – way, way more than the value of any gold produced.  Gold, after all, is ‘only’ worth about a thousand pounds for a troy ounce (31 grams).  Particle accelerators cost billions of pounds to build, and yet more in running costs.  If you really want gold so desperately, these days there may be more mileage in harvesting it from defunct bits of electronic equipment.

Or just ask people to send you their old jewellery through the post in exchange for cash.  Even Tesco have got into that game now.  Through the post!  Honestly, people fear putting a tenner in a birthday card but gold jewellery in a paper bag?  No problem.

But anyway, back to gold’s reactivity, or rather lack of it.  Gold isn’t the most unreactive element (depending on how you’re defining reactivity, that honour probably goes to iridium) but it’s up there.  Or perhaps I should say down there.  It keeps its shiny good looks even when it’s regularly in contact with warm, damp, salty, slightly acidic skin, which is quite handy from the jewellery and money point of view.

But there is one thing gold reacts with: aqua regia.  Aqua regia is a mixture of nitric and hydrochloric acid and ancient alchemists gave it its name – which literally means ‘royal water’ – because it dissolves the ‘royal’ metal, gold.  It’s pretty cool stuff, in a slightly scary way.  Freshly-prepared it’s colourless, but quickly turns into a fuming, reddish solution.  It doesn’t keep – the hydrochloric and nitric acids effectively attack each other in a series of chemical reactions which ultimately result in the production of nitrogen dioxide, accounting for the orange colour and nasty fumes. Screen Shot 2013-06-04 at 00.20.27The fire diamond (remember those?) for aqua regia has a 3 in the blue box, putting it on a nastiness par with pure chlorine, ammonia and, funnily enough, oxalic acid (the stuff in rhubarb).  It also has ‘ox’ in the white box, telling us it’s a powerful oxidising agent, which means it’s effectively an electron thief.

All atoms contain electrons but they can, and frequently do, lose or gain them during the course of chemical reactions.  Acids in general are often quite good at pinching electrons from metals, but aqua regia is particularly good at it, and especially with gold.  Much, much better than either nitric acid or hydrochloric acid on their own because, in fact, the two work together, as a sort of two-man gang of acid muggers.  When metal atoms lose electrons they become ions, and ions dissolve very nicely in water.  Hence, aqua regia’s fantastic property of being able to dissolve gold.

Which leads me to a really great story.  During World War II it was illegal to take gold out of Germany, but two Nobel laureates – Max von Laue, who strongly opposed the National Socialists, and James Franck, who was Jewish – discretely sent their 23-karat, solid gold Nobel prize medals to Niels Bohr’s Institute of Theoretical Physics in Copenhagen for protection.  All well and good, until the Nazis invaded Denmark in 1940.  Now, unfortunately, the evidence of von Laue and Franck’s crime was sitting on a shelf in a lab, just waiting to be found.  This was serious: if the Gestapo found the gold medals they would persecute von Laue and Franck, and probably take the opportunity to make things very unpleasant for Bohr as well, particularly since his institute had protected and supported Jewish scientists for years.

Nobel_PrizeWhat to do?  At the time a Hungarian chemist called George de Hevesy was working at the institute, and it was he that had the bright idea of dissolving the medals in aqua regia.

It would have taken ages, because although aqua regia dissolves gold, it doesn’t do it quickly, and these were chunky objects.  He must have been anxiously looking over his shoulder the whole time.  But he managed it, and eventually ended up with a flask of orange liquid that he stashed on a high shelf.  The Nazis searched the building but didn’t realise what the flask was, so they left it.  Iit stayed there undisturbed for years, in fact until after the war was over.  At which time, de Hevesy precipitated the gold back out and sent the metal back to the Swedish Academy, who recast the prizes  and re-presented them to Franck and von Laue.

So there we have it, you can’t turn lead into gold (at least, not without a particle accelerator) but, if you know what you’re doing, you might just be able to turn a flask of orange liquid into two solid gold Nobel prize medals!


The title of this post comes from a poem by the British poet, Thomas Hood, 1799-1845. Here it is in full:

Gold! Gold! Gold! Gold!
Bright and yellow, hard and cold
Molten, graven, hammered and rolled,
Heavy to get and light to hold,
Hoarded, bartered, bought and sold,
Stolen, borrowed, squandered, doled,
Spurned by young, but hung by old
To the verge of a church yard mold;
Price of many a crime untold.
Gold! Gold! Gold! Gold!
Good or bad a thousand fold!
How widely it agencies vary,
To save – to ruin – to curse – to bless –
As even its minted coins express :
Now stamped with the image of Queen Bess,
And now of a bloody Mary.

The acid that really does eat through everything

acid burnThanks to the big screen, many of us think of acids as dangerous, burn-through-anything substances.  Think of those scenes in the Alien movies, where the alien’s blood drips through solid metal, destroying everything in its path.

Of course the vast majority of acids are much more boring.  Vinegar (which contains ethanoic acid) and citric acid (found in, guess what, citrus fruits) are common acids that we eat all the time, and they don’t burn holes in your mouth.  There’s an even stronger acid, hydrocholoric acid (HCl), in your stomach and not only does it not burn you from the inside out (usually), it actually helps you to digest your food and keeps you safe from nasty bacteria.

But there is an acid that’s really, properly scary.  And its name is hydrofluoric acid.

Hydrofluoric acid has the chemical formula HF, but unlike HCl you won’t find this one in a school laboratory, and if it turns up in your stomach you’re in very big trouble.  In true movie-acid style it’s capable of dissolving many materials, and is particularly well-known for its ability to dissolve glass (which is mainly silicon dioxide).  It will also dissolve most ceramics (which contain aluminosilicates: compounds made of chemically-bonded aluminium, silicon and oxygen).  And, like many other acids, it also reacts with metals, so storing it is a bit tricky.  Where do you put something that eats through its container? Well, these days it’s stored in special plastic bottles, but in the 17th century when it was first discovered chemists had to use glass bottles coated inside with wax, and hope the coating was a good one.

HF has been an important industrial chemical for centuries.  It’s used to etch patterns into, and clean, glass and ceramics, and also to dissolve rock samples, for example to extract chemicals or fossils from rocks.  It’s also used to clean stainless steel and, in more recent times, to prepare silicon wafers (used to make silicon chips) in the electronics industries.

The chemist Carl Wilhelm Scheele (him again – he just keeps turning up doesn’t he?) was the first person to produce HF in large quantities in 1771.  Scheele is particularly famous for his bad habit of sniffing and tasting any new substances he discovered.  Cumulative exposure to mercury, arsenic, lead, their compounds, hydrofluoric acid, and other substances took their toll on him and he died on 21 May 1786 at the age of just 43.  And that’s why your science teacher was endlessly telling you not to eat or drink in the laboratory.

So why is hydrogen fluoride so nasty?  For starters the gas is a severe poison that immediately and permanently damages the lungs and the corneas of the eyes – lovely. Hydrofluoric acid solution is a contact-poison that causes deep, initially painless burns which result in permanent tissue death. It also interferes with calcium metabolism, which means that exposure to it can and does cause cardiac arrest (heart attack) and death.  Contact with as little as 160 square centimeters (25 square inches) of skin can kill – that’s about the area of the palm of your hand.

And now for a gruesome and tragic tale: in 1995 a chemist working in Australia was sitting working at a fume cupboard and knocked over a small quantity (100-230 millilitres, about the equivalent of a drinking glass full of water) of hydrofluoric acid onto his lap, splashing both thighs.  He immediately washed his legs with water, jumped into a chlorinated swimming pool at the rear of the workplace, and stayed there for about 40 minutes before an ambulance arrived.  (Should you ever need to know, the proper treatment for HF exposure is calcium gluconate gel: calcium gluconate reacts very quickly with hydrofluoric acid to form non-toxic calcium fluoride, rendering it harmless.)  Sadly, his condition deteriorated in hospital and, despite having his right leg amputated 7 days after the accident, he died from multi-organ failure 15 days after hydrofluoric acid spill.  Remember, that was a spill the size of a glass of water.

Because hydrofluoric acid interferes with nerve function, burns from it often aren’t painful to begin with. Small accidental exposures can go unnoticed, which means that people don’t seek treatment straight away, making the whole thing worse.  Do a Google image search on ‘hydrogen fluoride burns’ and you’ll see some images that will really turn your stomach.

So which would you rather meet?  An alien with acid blood and a habit of laying eggs in your stomach or an invisible gas that destroys your tissues and leaves you, if not dead from multiple organ failure, then suffering with horribly disfiguring burns?  You might stand a better chance against the alien…