Almost perfect anti-reflection coating

If you are making a camera, telescope, solar cell or microscope, you don't want light being wasted by reflections or even more critically if you are in the military you don't want your position being given away by reflections.

So you want to coat your lenses with somthing to stop them reflecting. Traditionally this is done by adding a thin coating of another material of the right thickness so that the reflections from the surface and base of this cancel out giving no reflection. This is great, but it only works well for one colour, this is normally chosen to be green because it is in the centre of the spectrum, so the coating will not work as well for red and blue, so a coated lens will reflect some red and blue light giving it a purple sheen, hence why expensive optical equipment looks purple,

Fred Schubert from Rensselaer Polytechnic in New Your has taken a different approach, Reflections occur when the refractive index of a material changes rapidly, eg going from air to glass. If you can change the refractive index smoothly there will be no reflections. This has been known for a long time, the problem is that no natural solids have a refractive index close to that of air so there will allways be a reflection.

Fred has goat around this by depositing tiny silica nanorods onto a piece of glass. He can vary their density, so he can make a material which is mostly air, so it's refractive index can be as low as 1.05 compared to 1 for air. By changing their density and angle he can build up layers with gently changing refractive index to that of glass, making a near perfect anti-reflection coating.

31st Mar 2007

Canny birds in Chernobyl

Birds around Chernobyl seem to be avoiding radioactive nests. Anders Møller from the Marie Curie University in Paris and Tim Mosseau in South Carolina have been studying the birds around chernobyl.

The background radiation in the Red Forest, 2-3km away from the Cherobyl reactor, is very variable so they built nesting boxes for Great Tits and Pied Flycatchers in lots of different sites in the area.

Both birds but particularly the pied flycatcher avoided the most contaminated areas, with the Flycatchers only nesting in the least contaminated  areas. Although they have idea how they are doing it, this is a very sensible thing for the birds to be doing as the radiation will have a bad effect on the birds, although if wildlife is able to detect the really dangerous areas, this may be contributing to the huge growth in wildlife in the exclusion area around Chernobyl.

31st Mar 2007

Earth's oldest rainforest discovered in coal mine and why the plucky T. rex is a bit “chicken”

 

Earth's oldest rainforest discovered in coal mine and why the plucky T. rex is a bit “chicken”

 

A 300 million year old fossilized forest has been discovered in a coal mine in Illinois, USA. Covering an area of 10 square kilometres, its the largest fossil rainforest ever discovered and contains a diverse selection of extinct flora.

 

So how does a forest end up in a coal mine and what can the extinct flora tell us? Researchers from the UK and US team believe that a large earthquake shook the forest causing a large area of it to fall below sea-level it became peat and then coal. Dr Howard Falcon-Lang from the University of Bristol, UK, said “It was an amazing experience. We drove down the mine in an armoured vehicle, until we were at a hundred metres below the surface. The fossil forest was rooted on top of the coal seam, so where the coal had been mined away the fossilized forest was visible in the ceiling of the mine. We walked for miles and miles along pitch black passages with the fossil forest just above our heads.”

 

The find will have two major implications for current knowledge; the first concerns the coal in the mine and the other the plants. Not all coal is the same – coals are formed by different plants in different environments and this also effects the way they burn. By studying the coal from the mine, geologists will learn more about the period when they were buried, which happens to be at the height of peat formation. The plants in this rainforest are an unusual array of club mosses over 40 metres high which tower over a canopy of tree ferns, there are shrubs and tree-sized horsetails. It reveals information about the ecological preferences and community structure of such ancient plants; something which hitherto unknown.

 

It been a big fortnight for archaeological news as the discovery of some 68 million year old T. rex bones has been found to contain protein – changing current thinking on the fossilization process and proving birds are dinosaurs.

 

Scientists from the US have found collagen proteins in the bones, which when compared to those of living animals showed it to be structurally similar to chicken collagen. This finding has major implications for fossilization theories as up until now it was thought that organic matter would have decayed completely after a maximum if 100,000 years, the proteins gradually being replaced by mineral. Comparison of the fearsome T. rex's protein sequence have shown it to be structurally similar to the modern chicken, this provides evidence for the long-standing idea that birds are a group of dinosaurs (known as 'avian therapods') who survived the mass extinction which wiped out the other types of dinosaur. To date, this supposition had been based on the similarity of the architecture of their bones rather than, know researchers know this is true on the basis of related sequences.

28th Apr 2007

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January 1970

The Science of Catalysts And Catalytic Converters

Dr Emma Schofield, Johnson Matthey Technology Centre

Chris - First of all, everyone uses the word 'catalytic converter' but what is a catalyst and why is it important?

Emma - A catalyst is a substance that makes a chemical reaction happen more easily. You can get some really stroppy reactions in which you want to rearrange the atoms in them to make something useful, but it's just not playing. The starting material just isn't interested into becoming the product that you want. IF you put the right catalyst into the reaction, you can make this reaction happen either more quickly or using a lot less energy. Often you have to go into high temperatures and pressures to get the reaction to work.

Chris - How do they do that?

Emma - Imagine that you've got yourself a beach cottage and the beach is about a mile away from your cottage. Between you and the beach there is this massive great mountain. You have several options for reaching the beach. One of them is that you put lots of energy into it, so you put lots of energy to walk up the mountain and down the other side. Not great. The second option is to walk all the way around the mountain but it takes a heck of a long time. But if someone's gone and dug a tunnel from one side to the other then you can get to the beach pretty quickly and with a lot less energy. This is exactly what a catalyst does. So the catalyst does for a chemical reaction what the tunnel does for you: it takes an alternative pathway that allows the reaction to happen a lot more easily.

Chris - And just like a tunnel, it's not used up in the reaction. It's available forever if you like.

Emma - Yeah and that's why you only need a very small amount of catalyst when you have a chemical reaction. Because although the catalyst is changed during the reaction, it's regenerated at the end of it. So each little atom or each little molecule of catalyst that's in there can go on a react with hundreds and thousands of millions of reactant molecules.

Chris - Sounds fantastic, but how do we find these things? Why isn't there a catalyst for everything? Why isn't there a catalyst for my homework? How do we discover the chemicals that do these clever jobs?

Emma - There are quite a lot of metals that are used as catalysts because there are two different types of catalysts: homogeneous catalysts and heterogeneous catalysts. In homogeneous catalysts, the reactants and the products are in the same phase. So if there are gases reacting, the catalyst will also be a gas. In heterogeneous reaction, the reagents are in a different phase from the catalyst. An example of homogeneous would be making plastic bags - high density polyethylene. The ethene and the catalyst are all going on in the same phase, in solution. That would be a homogeneous catalyst. In a heterogeneous catalyst, that would be carbon monoxide turning into carbon dioxide. That would happen on platinum metal.

Chris - They've got expensive tastes these things!

Emma - Platinum is very expensive but you often find that some of the most expensive metals turn out to be the best catalysts.

Chris - Why is platinum so good? What's special about the metal? How does it do what it does?

Emma - When people ask questions like this, a scientist's usual answer is: oh well, it's quantum. Actually it's to do with how well these gas molecules can stick to the surface. Platinum is very good at sticking molecules onto the surface of it. That's very important because that's where the reaction actually happens. The other thing that platinum is good for is, well, when you have a molecule, the atoms in the molecule are stuck together with chemical bonds, which are electrons. Platinum is very good at rearranging these electrons and allowing the molecules to turn into something else. Again, forming this alternative pathway by which a chemical reaction can happen.

Chris - So if you could zoom in to the surface of the platinum, what would it look like to make it so sticky and that things like it?

Emma - We always imagine it as lots of little balls stuck next to each other. One of the aims of being a catalyst chemist, which is what I am, is to try and make as much surface as possible. So we have our tiny little pieces of platinum which are stuck onto a ceramic support. We want as much platinum on the surface and as little platinum in the middle of these balls as possible. The platinum is part of the periodic table which has lots of d-orbitals, and it's these magic d-orbitals that makes it so good at catalysis and making things stick to it. So it very easily forms bonds with lots of different types of molecule.

Chris - And it brings them together in just the right way that they want to get married or do whatever you want them to do.

Emma - And provides them with a route which requires so little energy that it can happen essentially spontaneously or with very little energy on the metal's surface.

Chris - Ok so turning now to what comes out of your exhaust pipe, how does a catalytic converter on a car actually work? What are they doing?

Emma - The catalyst on a catalytic converter is essentially a can which is next to the engine. What it does is it purifies the exhaust gases. If it was ideal, we'd just get carbon dioxide and water out when fuel was burnt.

Chris - I'm sure people would argue that it would be ideal if we just had water and burning hydrogen, which is what Fraser is going to be talking to us about in a minute.

Emma - The problem being that you put fuel in at the beginning and you can destroy atoms as you go along. But what we also get out is carbon monoxide, which is a poison and binds so strongly to the blood that you can't bind oxygen anymore. There are also what's called NOx gases, which are oxides of nitrogen responsible for acid rain; and hydrocarbons which come together with NO-x to form smog. This is why in the 1970s Los Angeles got buried under this cloud of photochemical smog and what triggered all of the legislation about car pollutants. Also what comes out are particulates, which are essentially soot. This is linked with respiratory illnesses as well as cancer. So we obviously don't want these coming out of the backs of our cars. We need to put the catalytic converter between the engine and the exhaust pipe to catch these things as they go out. Inside the catalytic converter we have the monolith and the metal. The monolith is a ceramic and it's a honeycomb with a very large surface area and it's coated to give it an even greater surface area. If you spread it out it would cover about three football pitches. On the channels of this monolith you have little globules of the metal platinum, palladium, rhodium in various mixtures depending on whether you're a petrol or a diesel car, and these are so small that we call them nanoparticles. This is what we were talking about before. As these gases go past, which is a very quick reaction, it goes from the engine through the catalytic converter in less than a tenth of a second.

Chris - So it must be very fast.

Emma - Yes and it wouldn't happen normally unless there was a catalyst there.

Chris - So how much of the gases does the catalytic converter scavenge or convert? Does it do the lot?

Emma - It causes about a 90% decrease in the amount of pollution coming out, and what you mostly get out of the other end is nitrogen, water and carbon dioxide.

Chris - So it does a good job but there was a motivation for people to stop using leaded fuel because it makes your brain rot and causes dementia but also lead's quite toxic to catalysts.

Emma - Exactly. If you think about these little metal particles, the lead will stick onto the surface of them. The more you reduce the amount of surface there is, the less chance these pollutant gases have of sticking to the surface and making the catalyst catalyse.

Chris - So it's better to do without lead if we can for more reason than one.

Emma - It's better to do without lead and it's better to do without sulphur in petrol too, because sulphur is responsible, or used to be responsible when we had high sulphur petrol, for this eggy smell some people associate with catalytic converters. Now there's less sulphur in fuel, this is much less of a problem.

Chris - Now Emma, it's impossible to miss your t-shirt and on the subject of noisy engines, I was wondering if this was what we're talking about! It says NOISE. What is NOISE and why are you here today?

Emma - NOISE is the New Outlooks In Science and Engineering campaign. It's a group of young scientists who are there to give an alternative image for what scientists are like. Chris, when you think about the stereotype of a scientist, what is it that springs to mind?

Chris - Glasses more powerful than the Hubble space telescope, shocking teeth, 1960s get-up and muttering unintelligibly in a way that no-one can understand.

Emma - And the words fun and dynamic don't really feature in those descriptions.

Chris - But that's why people listen to the Naked Scientists!

Emma - And that's why NOISE is there. We need to change this. We're the new generation of young scientists and we have a website www.noisemakers.org.uk where there's this whole group of scientists that do lots of fun science that we want to tell people about. We have a snowboarding physicist and we have somebody who does robotics who is a scuba diver. The idea is to point out to people, especially kids who are thinking of going to university, that there's more to being a scientist than a white coat.

September 2006

The Wine Diet

Roger Corder from Queen Mary's College

 

Chris - One of the things you've risen to prominence for Roger is sussing out what's in red wine that makes it good for us.

Roger - Absolutely, that's been my work for the past six or seven years. I've focused on finding out what is in wine that improves blood vessel function and protects from heart disease.

Chris - So how did you go about that and what is the bottom line? Is it good for us?

Roger - All the evidence points to it being good for us. But it may be that certain types of wine are much better than other wines. What we did from a laboratory point of view is we studied exactly what substances in wine could change blood vessel function. In parallel with that we were looking at areas where people were living longer and drinking wine. And we saw that the wines in these areas were richer in a substance we identified, Procyanidin, which is a flavinoid polyphenol. People would know them as antioxidants but in terms of the effects that we were looking at, this causes a profound change in blood vessel function.

Chris - There is a phenomenon called the Mediterranean Effect isn't there for people from the Mediterranean basin. And the French paradox as well. There are French people who manage to have an atrocious diet, smoke like chimneys, and live to be 500 years old. No one really understood how they did it, and what you're saying is that it's the red wine that they're drinking.

Roger - Exactly. The Mediterranean diet sprung out of research called the seven country study. That showed that people living on the island of Crete were living longer with less heart disease despite a fairly high fat diet. But an important part of their diet was to drink regular wine. Now I started to look at Sardinia because the highest concentration of centenarians were based on this island in terms of European population, and I found that their wines were richer in Procyanidins than wines from other areas. The Cretan wines were also particularly rich in this particular polyphenol. And so I then looked at the French population. And there's a regional variation in heart disease across France. And there's also a regional variation in terms of longevity. And what I found was that people living in South West France were drinking wines which were very rich in these polyphenols. But the interesting thing about this and the French paradox, is that this is one of the areas of France where they eat some of the fattiest foods. And so I became convinced that a) Wine should be part of a healthy diet, and b) some of the nutritional advice being pushed on the general public was actually not based on fact.

Chris - Is there a conflict of interest here Roger, because you're a wine connoisseur aren't you?

Roger - I wouldn't like to say I'm a wine connoisseur. Obviously we all like to have excuses for our habits. What I was, was somebody who was religiously following a low fat diet. And I suddenly started looking at the science of low fat diets, and realised that actually, if you wanted to have a healthy cholesterol level, it was the type of fats you ate, rather than having a low fat diet. Low fat diets are often boosting over-purified carbohydrates into people's food, and sugar into people's food. And that was actually changing their heart disease risk in an unfavorable way. And so this drove me to write a book to explain what it is about eating healthily that everybody should understand. It doesn't matter whether you're thin or fat. Wine can be part of it, but the food you eat is so crucial to your overall wellbeing.

Chris - Let's just focus in on the wine story for a second. You saw this effect, which was distributed across France, and the effect rose specifically in South West France. So what was going on there that meant that people, despite an atrocious diet, were protected? Presumably it wasn't just genetic.

Roger - I wouldn't say their diet was atrocious, it was just different. Essentially they were growing a grape down there called the Tannat grape that was very very rich in these protective polyphenols. But other wines are also good for you.

Chris - Is it just red wine though Roger? Because lots of people say you have to drink red wine, white wine's no good. Beer's no good.

Roger - Well, let me provide you with some evidence. Alsace has the lowest longevity in France. And it has some of the highest heart disease. That's a white wine drinking area.

Chris - So it is specific to the colour. Red wine grapes impart the protective chemicals.

Roger - Exactly.

Chris - What are those chemicals, how do they work and how does the grape make them?

Roger - Actually white grapes also have them. The difference between white wine and red wine is really the way in which the wines are made. The white wine is the fermented juice of the grape, where red wine is the fermented juice with the seeds and skin present. So the longer the time of the fermentation with the seeds, the more extraction of these polyphenols that you have. And so the higher the levels.

Chris - Ok so we know wine has this stuff in it. How do we actually get this stuff to where it needs to go, the blood vessels? Why does if affect your risk of vascular disease? How does it work?

Roger - Essentially, if you imagine that blood vessels are a tube, and they have a lining which is protective. It's important that they function in a healthy way. Now the chemicals in wine are able to boost the healthy characteristics of this lining. So that you reduce your risk of heart disease. Many people may be aware that chocolate has also been said to be helpful. Now the point about chocolate is that dark chocolate has the same polyphenols in, as a good red wine. As so for non wine drinkers, if they want to get these polyphenols into their diet from other sources then dark chocolate becomes a possibility.

Helen - So I bet people out there are dying to know. Can we say in a snapshot, what should people be eating? And how many glasses of red wine should I be drinking? Is there enough in one glass?

Roger - If you look at a glass of average supermarket wine there isn't probably enough to have much benefit. But with time we're going to change people's awareness of wine and also the way that it's labeled. If there was more details about the wine making process, one could read the label and think that if it's been fermented a long time it's much more likely to have a higher level of these compounds. But there's no information on wine. How much should you drink? All the scientific evidence about reduced heart disease actually reflects a consumption level that is similar to what government guidelines recommend. So for a woman that's no more than one to two small glasses per day, 125 mL. For a man, two to three glasses is ok. But an important factor about people benefiting from wine consumption is that it's part of a lifestyle pattern. It's not going to the pub and shoving down a few glasses of wine and then thinking, "I've got all the benefits". Because studies have shown that people who drink without food are more likely to have high blood pressure. High blood pressure increases your risk of heart disease and it increases the risk of a stroke. So it's important to understand fully, the lifestyle combinations.

 

January 2007

The Torso in the Thames

Dr Hazel Wilkinson, Jodrell Laboratory, Kew Gardens

Sabina - In 2001 the torso of a boy aged about 5 was found in the Thames near Tower Bridge, in London. Police believe this was a ritual killing and much forensic work took place to try and identify the boy and lead the Police to his killers. This forensic evidence included taking mineral samples from his bones which matched those in a rural area in south-western Nigeria. Police traveled there to try and obtain further clues as they think the boy, who they've named “Adam”, had only been in London for a short time before he was killed.

The contents of Adam's intestine included large amounts of plant matter and so they were sent to Dr Hazel Wilkinson of the Jodrell Laboratory at Kew Gardens for identification.

Hazel - In may 2003, material recovered from the lower intestine of the little boy known as Adam, was sent by the police forensic department.  Among the plant remains there were also quartz grains, small particles of gold small fragments of ground down bone. In addition, the police picked up the largest pieces, naturally, of plant material that they could find, and these are very characteristic of tropical bean seeds.

Sabina - The beans which Adam had been fed as part of the ritual had been ground up in a pestle and mortar so the fragments in his gut were extremely small. In order for Hazel to be able to identify the beans under a microscope, she needed some whole beans to compare the sample with.

Hazel - I got some calabar beans from our economic botany department, and I had to ask the herbarium for seeds of other beans; schwarzia, cassia. But when it came to the leaf material, unless I’ve got stomata, hair and glands on the speciment it’s extremely difficult to do anything at all.

Sabina - Those are the bits from the underside of the leaf?

Hazel - Yes, the lower surface of the leaf. I was very fortunate that we had a visitor here from Ibadar in Nigeria, where Adam is believed to have come from and he brought with him some leaf material from one of the Ibadan markets. One of the leaves he gave me fitted exactly, which was so helpful, one of the leaves I found in Adam material. But it is really a very considerable battle to identify anything at all.

Despite the difficulty in identifying the stomach contents, Hazel was able to detect the presence of significant plants.

Hazel - I feel convinced that a small amount of calabar bean was probably in the meal that Adam had, but one of the most frequently found fragments are those of Datura – “Angels Trumpets”. It’s a member of the solanaceae, the potato and tomato family. Now I have bought, and also obtained from the herbarium, some seeds of datura, ground them up in a pestle and mortar and tried to compare them with the datura in Adams gut. I feel convinced that there is quite a lot of it. Datura is well known historically for being of a sedative, hallucinatory nature, and it’s still used for bad purposes today.

Sabina - Hazel needed some clues to help her narrow the search when it came to identifying the rest of the contents. She obtained a book of spells traditionally used in south-western Nigeria to give her an idea of what other plants might be present.

Hazel - “The Use of Plants in Yoruba Society” loads and loads of wonderful receipes supposed to do all sorts of things…

Sabina - “To appease one’s spirit counterpart”… “To send smallpox to someone”…

Hazel - Yes, most peculiar. “To kill somebody” – of course I’ve got a marker in that because I needed to look through these plants to see if there is anything in here.

Sabina - Hazel's findings helped the Police concentrate the investigation into specific channels which assisted in uncovering human trafficking ring between Nigeria and the UK. The Police have as yet, not been able to identify the perpetrators of this crime, but their investigations have further revealed underground sacrificial practices in London.

Hazel - It would seem that Adams sacrifice was to give somebody power and money. Now where is his head, we don’t know, but we do know that the head was considered to give the owner of it, especially in a child, youthfulness, extra brain power and above all access to more and more money.

June 2007

Investigating Forensic Science

Dr Trevor Emmett, Anglia Ruskin University

Chris - Thanks for coming in. Tell us what you actually do, how do you use science to solve crimes?

Trevor: Forensic science, strictly is the use of scientific techniques to solve crime, that’s the formal definition of forensic science. So basically, it’s any scientific information or technique that we can use for that purpose. The sort of thing we teach at Anglia Ruskin is primarily concerned with analytical science, we’re analysing small amounts of evidence collected from the crime scene; DNA of course, blood, fibres, glass, residue from gunshots… But any sort of scientific technique at all really!

Chris: Hasn’t Anglia set up a system where you actually stage crimes, then people come in and you take them through the various things you investigate and look for.

Trevor: Well the question is “what makes forensic science different from other sciences?” And clearly, it’s a matter of context. It’s not about what you’re doing; using microscopes or chemical analyses, it’s about collecting evidence and using that evidence in a court of law. The evidence has to be collected properly. We have to make sure that all the relevant evidence is collected. We have to make sure that evidence is stored properly, accounted for properly and then analysed properly at the end.

To do that most effectively in a teaching environment we can only really simulate a crime scene and send the students in to do what they have to do. It’s not just collecting evidence; it’s about securing the crime scene, controlling access, and all aspects of quality management of the evidence. If any of these steps are compromised then you can have the best scientific evidence in the world but it will be no good in a court of law, and that isn’t good forensic science.

Chris: You’ve been working on authenticating ancient documents as well, how do you do that?

Trevor: Again, it’s purely analytical science.

Chris: What are the give-aways? What are you looking for that says “this is a genuine old document” versus something I made to look old?

Trevor: It’s very hard to prove a negative, of course. So what we look for is positive evidence that the document isn’t what it purports to be. Some of the work I’ve been doing with the Fitzwilliam museum [Cambridge] on ancient Egyptian papyrus’ If we found on those paintings some pigments or dyes which were only invented in the 19^th century then straight away the provenance of that document is called into question.

Chris: How do you know they were only made in the 19^th century? What’s the chemical hallmark that says “I’m more recent than this ancient Egyptian one”?

Trevor: It’s relatively straightforward for ancient Egyptian works. Ancient Egyptian pigments are nearly all geological in character, they represent coloured ores and minerals from the surface of the earth. There are some organic ones, we’ve all heard of ‘imperial purple’ which is made from sea shells, and there are one or two others. But in the main what organic colours or dyes were available to ancient Egyptians were very limited. In the 19^th century with the development of the chemical industry all sorts of azo-dyes and amino-dyes were developed and a very wide range of colours were developed. SO if you find those materials, those compounds didn’t exist at all until they were first made in the 19^th century.

Chris: Have you flushed out any fakes?

Trevor: Not from the ancient Egyptian material, I have on one or two other things I’ve looked at.

Chris: What sorts of things have people tried to fake?

Trevor: They try and fake everything! I did some work on some castings, some statues, which were purportedly 2000 years old, and discovered that they contained an alloy which probably meant they were made in the 19^th century. Very straightforward.

Chris: How did you know that? What was the alloy, was it something that people 2000 years ago wouldn’t have been able to make?

Trevor: They wouldn’t have been able to make it, no, not at all.

Chris: So how do you do this? Do you drill in to it and take samples out? Because if it turned out to be genuine I wouldn’t be happy to have you drilling into my beautiful statue that I paid thousands of pounds for.

Trevor: I would never be allowed to drill into anything. I remember in one of my first discussions with a museum, we had a long discussion about what they wanted me to do. I thought asking for ten grams of material would be a very reasonable amount and I could almost hear the conservators on the other end of the phone fainting. Then they said they could send me some drillings and I was expecting to see one of those curly things that come out of your black and decker when you’re drilling some wood. I got about three specks of dust! When I was working in geology, I used to think that half a gram of material was a bit dodgy for analytical work. Now if I get a milligram I think I’m doing pretty well. You get very very small amounts.

Chris: So how do you actually analyse it? Was it a case with the metal of melting it down and doing some chemistry on it. What’s the way in which you actually flush out the chemical fingerprint?

Trevor: In that particular case, I took about a milligram of material. A milligram is about a quarter of a grain of sugar, a very small amount of material. I had to develop techniques for handling such a small amount of material, it’s very easy to lose it. Then basically we dissolved it in acid and analysed it in the way would analyse any other solution, and the results were conclusive.

Chris: I heard a suggested technique was to fire x-ray beams at things like the statues you mentioned and the scatter pattern is indicative of what’s inside, so you don’t have to harm them. And because, as you’ve said, people are using different forms of metals these days compared with historically, this can sometimes be a give-away.

Trevor: Oh Yes. Many years ago I had a colleague who was very interested in looking at Elizabethan methods of lead smelting. We discovered that some of the artefacts that he had actually bought (and that’s always a dead give-away if you buy anything) actually contained stainless steel, which is another thing which didn’t exist before the 19^th century. If you have a statue that has been cast in bronze, the technique will vary with time and location in the world, and you can x-ray it just like you would x-ray a human body for a broken bone. Another thing that happens when you irradiate material with x-rays is that the atoms in the material will radiate their own, characteristic x-rays. That’s a technique called x-ray fluorescence, another very sensitive way of determining the composition of the material. The great advantage of x-ray fluorescence is that it’s entirely non-destructive, you don’t have to take samples of the material.

Chris: I heard that you can even get fingerprints from previously un-fingerprintable things using that technique. If people touch things, they can leave behind traces of sweat which has traces of metal ions in the sweat. If you zap that with highly focussed beams of x-rays, you can literally see the fingerprint flashing up again, even on things like skin, which previously wouldn’t have shown the print.

Trevor: I’ve not actually heard of that, it sounds a bit implausible, but then these things often do. I’ve certainly seen published techniques where people have looked at documents that have been handled. There are no apparent fingerprints but they use something called confocal fluorescence microscopy to be able to see under the surface of the document and actually see the ghostly imprint of a fingerprint on a document that’s not actually on a surface. The lipids from the fingerprint, the fatty material and the proteinaceous material have soaked into the document. This very powerful technique, used a lot in cellular biology, is able to reveal the fingerprint under the surface of the document.

Chris: Finally, talking about things leaching into other things, what about when people try to dispose of bodies in environments like peat bogs, where bodies are very rapidly dissipated. Can you tell from samples of peat if there was a body there?

Trevor: There are several ways this has been attempted, but it’s never been particularly successful. You can look for the decomposition products of the human body by organic analysis, but a new technique being developed by colleagues in Northern Ireland is to look for stable isotopes. Stable isotopes of carbon, nitrogen, oxygen in the ground water, and to try and look for bodies by using the natural water system in rivers and swamps and suchlike to try to look for the body itself.

June 2007

Hair Pollution

Dr Sarah Hall & Dr Karen Scott, Anglia Ruskin University

Sarah - We’re going to do the whole of the hair, rather than sections of the hair, so I’ll take it at the bottom of your head. I’ll try and cut it in the same region so you’re not left with too many spikes.

Azi - I’ve come to Anglia Ruskin University at the Department of Forensic Science and Chemistry, and I’m joined by Dr Sarah Hall, who’s a specialist in looking at heavy metal concentrations in hair.

Sarah - I think that’ll do. And there we go. OK?

Azi - Oh, right. So you’ve got a good lump of my hair. Fantastic!

Sarah - It’s a fair amount. Sorry!

Azi - No, no, it’s fine.

Sarah - OK. Now I’ll do mine. I think that’ll do. There we go.

Azi - Where would contamination of heavy metals come from?

Sarah - Well it would come from a number of exposures – atmospheric exposure, maybe from your food, your drinking water – but all hopefully low levels.

Azi - Now, it’s quite interesting with me, because I’ve only actually lived in Cambridge for the past three months, and before that I was living in London.

Sarah - I live in Ely [Cambridgeshire, UK], and I’ve lived in Ely for ten years, and hopefully we may see a difference between yourself and me living in Ely.

Azi - What sort of things would you expect to be exposed to in Ely?

Sarah - Traditionally, you’d think that there may be some exposure from farming practices, maybe herbicides. Traditionally, arsenic tended to be used in herbicides. But again legislation, and changes in farming practices, mean that we may not see that, but we may see a difference because you lived in a more built-up area.

Azi - Fantastic! Well that sounds really exciting. I was also wondering whether you’d be able to tell the difference between somebody’s diet, for example, because I don’t eat meat at all. I don’t even eat fish! But would my hair show up things that, perhaps, somebody who has a different diet practice would not show up, or the other way around?

Sarah - Actually, I’ve got a research student who I know is a meat-eater. Let’s see if we can talk her into taking a bit of hair.

Azi - Could we, please?

Sarah - Yes.

Azi - Excellent.

. . .

Azi - OK, so now that we’ve got three bits of hair – one from you, one from me and one from Lata – what are we going to do with them then?

Sarah - Well, first I think we should wash them in a soap solution, just basically to remove any sort of conditioner or any hair product. I’m just going to give these a little stir, and then we’re going to put them in the sonicator.

. . .

Sarah - All I’m going to do now is just decant the soap solution off, and then wash the hair with some de-ionised water, then a last wash with some methanol, dry it in a bit of filter paper, and then we should be able to easily cut it into smaller sections and get it into our containers.

. . .

Sarah - I’ve got your hair in the container now, so I’m just going to add nitric acid and hydrogen peroxide, and then pop it in the oven, as they say. And that's it - just leave them for about four hours to digest. Once they’ve digested, you’ve got your metals into solution, which then allows us to do the analysis.

Azi - Lovely. Alright, well, what I’ll do is, while we wait for everything to cook, I’ll pop across the corridor and have a chat with Dr Karen Scott.

Sarah - Yes, okay. And I’ll see you soon.

Azi - Yep, excellent. I’ll see you in a bit then.

. . .

Karen - Hi, I’m Dr Karen Scott. I work in the Department of Forensic Science and Chemistry at Anglia Ruskin University, and I’m a Forensic Toxicologist.

Azi - So, you look at all the components that get into people’s hair, but how do they actually get there to start with?

Karen - Well, basically, anything that is ingested into your body goes into your bloodstream, and our hair grows from components which are retrieved from the bloodstream. As the hair then grows out of the head, the drugs and other substances bind to melanin within your hair, so something that was there, say, a month ago, a month later will be one centimetre away from the point of start of growth of the hair.

Azi - What can hair tell you about a person?

Karen - It can tell you ethnicity. It can tell you which part of the body it’s been taken from. It can’t tell you whether the donor is male or female, unless you go down the DNA route. It can give you an indication, obviously, if they’ve dyed or treated their hair in any way. And also, it can tell us if they’ve ingested drugs in the past. So there are lots of different things that we can tell from the hair sample.

Azi - Dr. Sarah Hall is actually showing me how she can get heavy-metal exposures from hair samples.

Karen - Yes, so that will give you an idea of things like diet. Most people, when they think of forensics, are thinking of crimes being committed – maybe somebody’s been poisoned, or someone’s been taking drugs – but we can also look at environmental effects in terms of exposure to chemicals which we shouldn’t be exposed to.

Azi - Thank you very much. It’s been a pleasure.

. . .

Azi - Well, Dr. Hall, you’ve been looking at these samples and you’ve got the analysis, so can we have a look and see what you’ve got?

Sarah - I have to say, we have no cadmium or lead, but Lata had quite an unusual high concentration of nickel. However, she does tell me that her diet is based on a lot of pulses and lentils, and nickel is found in that sort of food.

Azi - But was there anything to differentiate her meat-eating diet with our vegetarian diet?

Sarah - Well, I tried to look at that, so I was looking at iron – because I thought it would be rich in meat and liver – and zinc is quite a lot found in meat, shellfish, dairy foods and cereals. But it doesn’t really show in the results much difference between the meat-eaters and vegetarians, I’m afraid.

Azi - So what about the phosphates? Did we find anything that was different between the three of us that perhaps indicated the levels that you might be exposed to in Ely?

Sarah - No. Actually, I had a lower phosphate level than Lata and yourself. In fact, Lata had a higher phosphorus level than both of us, but it might be because of the diet, because there’s a fair amount of phosphorus in red meat and fish. So, that might be the difference between the vegetarian and meat-eaters.

Azi - What else has been interesting?

Sarah - The only thing there was an increase on was copper, and, again, Lata had a higher copper level than we had. Copper is found in shellfish and offal. Lata tells me she doesn’t eat too much shellfish, but I think she eats a fair amount of red meat, and maybe offal.

Azi - I think you mentioned that Lata has an Asian background. Is that right?

Sarah - That’s correct, yes.

Azi - And I know that some Asian families use copper to serve food on or even to cook food in. Would that have something to do with it?

Sarah - Ah, yes. Well, it could do, because a lot of lead pollution years ago came from cooking implements and drinking vessels that were actually made of lead compounds. So yes, that could be true.

Azi - Excellent. Well, thank you very much. It’s been absolutely fascinating, and I’m really thrilled that I’m quite healthy and I can carry on with my healthy vegetarian diet. Thank you.

June 2007

	Is it true that a scald from water boiled in a microwave is worse than water boiled in a kettle? John
	Yes it can be true.  If you heat water very gently in a very clean container, you can actually get it to be above 100°C, maybe 105°C or 106°C.  So if the temperature of the water is 105°C it will do you more damage more quickly. Also if you put in some sugar then it will boil quickly and explode all over you, and some people have been badly hurt by putting spoons into things and heating it in the microwave.
	June 2007

	Is it true that a scald from water boiled in a microwave is worse than water boiled in a kettle? John
	Yes it can be true.  If you heat water very gently in a very clean container, you can actually get it to be above 100°C, maybe 105°C or 106°C.  So if the temperature of the water is 105°C it will do you more damage more quickly. Also if you put in some sugar then it will boil quickly and explode all over you, and some people have been badly hurt by putting spoons into things and heating it in the microwave.
	June 2007

	If female mammals have mammary glands, then why do male mammals also have similar mammary glands? Do all males have them and why bother having them at all if they don’t do anything? Una in Croydon
	It’s an evolutionary thing. If you look at how we develop in utero, for the first few weeks male and female babies look absolutely identical. It’s only subsequently that you start, under the power of the hormones pumped out, to change and alter your anatomy. But because you develop a lot of these surface structures and appearances when you’re very early on in development, you’ve got them whether you need them or not. There is one example that I’ve managed to find that’s a male and uses it’s breasts to potentially breast feed as they certainly lactate. That’s a Dayak fruit bat and they live in Indonesia. The male produces about a tenth of the amount of milk that the female does.
	March 2007

White bread and the wonder of enzymes

What you need

A slice of cheap white bread

A mouth to put it in

What to Do

1 - Take half a slice of bread and chew it and chew it and chew it! Even if the bread becomes disgusting, you should still keep chewing amd remember - don't swallow or you'll spoil the experiment!

2 - Pay attention to how the flavour of the bread changes.

3 - Once you think you have the answer, you can swallow the bready mush or (this is probably best!) spit it out.

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What may Happen

As you chew the bread, you may have noticed that it slowly tastes sweeter. Particularly the juice that is coming out.

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What is going on?

Bread is made up of starch and starch is made by plants. But how do plants make starch in the first place?

When plants take in light, they convert it into sugars through a process called photosynthesis. Once the sugar is made, they need to store it in their cells. The problem is that when there is a lot of sugar in a cell, the proportion of water in that cell is less relative to a cell with hardly any sugar in it. If there are some cells with a lower water concentration (or more sugar) than others, then a concentration gradient is established. This can be thought of as a slope: at the top of the slope are cells with lots of water (and little sugar) and at the bottom of the slope are cells with relatively little water (and lots of sugar).

If you put lots of water at the top of a slope, then it will trickle down to the bottom. This is exactly what happens in cells: the cells with a high concentration of water have some of their water sucked out and it is taken up by the cells with a low concentration of water. This continues until all the cells have an equal concentration of water and the gradient (or slope) disappears. This process of water moving between cells depending on the concentration of other small molecules (such as sugar) is called osmosis.

So what's the problem? Well plant cells are surrounded by a tough cell wall made of cellulose, and this gives the cell strength. However, if the cell is full of sugar from photosynthesis and water from other cells rushes in by osmosis, then the cell wall starts to strain. If too much water enters the cell, the cell wall will eventually give way and explode - just like a balloon that's been blown one puff too far.

Exploded (and thus dead) cells are bad news for plants, so they've had to come up with a cunning storage solution. What they do is take all the sugar molecules and glue them together into a long chain. It is this chain of sugar molecules that we call starch. Because starch is a long molecule, it doesn't alter the overall water concentration (or osmotic pressure) of the cell like small sugar molecules do. This means that having starch in the cell doesn't establish a large concentration gradient, doesn't cause water to rush in, and the cells don't explode.

When we use plants to make food such as bread, it is still in its starchy (or long chain carbohydrate) form. This is great, but we can't absorb it into our bodies in this long chain form. The only way round it is to chop it up. Thanks to evolution, there's an enzyme in our spit called amylase which specifically cuts up starch and turns it back into small sugar molecules. This is why the bread starts to taste sweet after lots of chewing - the amylase enzyme is breaking down the starch and turning it into glucose.

Amylase isn't the only enzyme to break down food into molecules we can absorb. Another example is the enzyme lactase. This breaks down lactose (which we can't absorb) into galactose and glucose (which we can). People who stop producing lactase will stop breaking down lactose, meaning that lactose is left behind in the gut. Bacteria that live in the gut see this otherwise ignored lactose and begin to break it down themselves. This produces large quantities of gas, and explains why people with lactose intolerance find that they become rather windy after a glass of milk. The lactose is acting as the fuel for a large bacterial fermentation plant!

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Strange Glows from Sugar

How to make strange unearthly glows by torturing sugar cubes...

What you need

	Some Lumpy Sugar, or sugar lumps.
	A Pair of Pliers
	A very very dark room

What to Do

Get the Pliers and a lump of sugar somewhere you can find them in the dark.

Turn off the lights and wait for at least 2 minutes - this will make your eyes much more sensitive.

Carefully crush a lump of sugar in your pliers. - watch the sugar and see what happens.

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What may Happen

With any luck you should see little flashes of blue-green light as you crush the sugar.

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What is going on?

When you crush the lump of sugar, you are fracturing sugar crystals, sugar crystals are slightly asymetric and on a molecular scale some areas are slightly positive and some slightly negative.

if the crystal breaks it will sometimes have more positive charge on one side of the fracture and more negative on the other.

 

 If the two halves of the crystal are pulled apart you are seperating the positive and negative charges which takes quite a lot of energy (a bit like pulling two magnets apart). Voltage is a measure of how much energy each charge has got so the voltage builds up.

At some point this voltage gets large enough for the charge to flow through the air as a spark. In order to do this it has to rip air molecules apart, giving them lots of energy. They release some of this as light which creates the strange glows.

This effect is called triboluminesence, and similar effects can be seen in lots of different materials, from sellotape to flint pebbles on the beach

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How to make a forcefield

This week Derek and Dave are venturing bravely into the future to make their very own forcefield. Providing the man power to do it are Matthew and Robbie from Campers Playscheme, which is held at Hunsbury Park Primary School.

What you need

Empty coke can
Piece of polystyrene
A full head of hair

What to Do

1 - Take the polystyrene and rub it on your hair for about one minute.

2 - Wave the polystyrene near the fizzy drink can and see what happens.

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What may Happen

When the polystyrene is placed near to the can, the can moves towards you, you will have to be careful

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What is going on?

All materials contain electrons; tiny particles that are part of an atom. Electrons from one material can be passed to another material when they come into contact. It's a little bit like headlice: if one person has headlice (with the lice representing electrons) and their lice-free friend brushes past, then headlice can be passed from one to the other. If they keep their heads together long enough, then there's a chance that the rogue headlice will crawl back again. However if they quickly pull their heads apart, then the headlice have no way of returning to their original owner. This results in an overall headlice gain for the previously lice-free friend.

The same principle can be applied when thinking about the transfer of electrons: when two materials are brought together, electrons can move from one side to the other (and potentially back again). Whether electrons have enough time to get back again will determine whether a material ends up with more or less electrons than it started with.

Now it's all very well and good that materials swap a few electrons, but some materials will on average take a lot more electrons from other materials than they give back. These electron-loving materials can take an especially large amount of electrons if they only come into contact with the other material for a short amount of time - they take lots of electrons but the connection is broken before they can return to their rightful owner. An example of a material that behaves in this way is polystyrene (although polystyrene likes gaining electrons, whereas using the first example, no - one likes to get headlice!)

The perfect partner for an electron-loving material is one that wants to get rid of electrons. An example of this is hair. Each strand of hair donates some electrons as it comes into direct contact with the polystyrene. As soon as the polystyrene is rubbed on another part of your head, the contact with the original strand of hair is lost and the electrons can't jump back again.

The overall effect is a slow accumulation of electrons on the polystyrene, and this gives the polystyrene a negative charge. The charge is negative because electrons are negatively charged particles.

Once you've stopped rubbing your head, what you're left with is a negatively charged piece of polystyrene full of electrons that have been 'stolen' from your hair. But why does this attract coke cans?

Playing with magnets demonstrates that like-charges repel - ie: negative repels negative and positive repels positive. When the negatively charged polystyrene is placed near the coke can, it forces all the electrons in the metal as far away as possible (to the far side of the can). As the electrons in the metals move away, it makes the side of the can nearest to the polystyrene relatively positive. Positive and negative charges attract, which is why the coke can is pulled towards the polystyrene.

It is important to note that polystyrene is an insulator and coke cans are made of metal. Electrons in insulating materials can't move around very well, which is why they are bad conductors of heat an electricity. In contrast, electrons can move around very easily in metal, making it perfect for electrical wiring and saucepans.

When the coke can and the polystyrene are brought together, the electrons in the polystyrene pretty much stay where they are (because they find it difficult to move) while the electrons in the metal can whizz round to the other side. If the electrons didn't move to the other side, the can wouldn't polarise (have a positive and a negative side). If there is no polarisation, then the can won't be attracted to the polystyrene.

If you put the polystyrene near to another insulator, such as a plastic bottle, the bottle would not be attracted nearly as strongly. This is because the electrons in the plastic cannot move easily, the material cannot polarise and thus the bottle stays where it is.

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The Science of Energy in the Gym

If you've ever wondered how much energy you are capable of putting using your own body and whether that's enough to power the appliances around you - this kitchen science is for you. This week Derek, Dave and Ali are in a gym trying to investigate how many houses Ali can power using her own and whether it would be worthwhile to hook the nations gyms up to the electricity grid. Imagine having to cycle to watch your TV!

What you need

• An exercise bike with a fancy energy readout in Calories or Watts.
• A person like Dave, who knows how much energy appliances use
• A person like Ali, who will do anything in the name of science

What may Happen

Ali had a go at powering a couple of small lights using a small hand cranked generator. When both lights were off turning the handle was easy, when the 5W bulb was turned on it got a bit harder and when the 10W bulb was turned on it got significantly more difficult.

 

Considering a conventional light bulb uses 60-100W of power Ali wasn't doing very well so we decided to try using the biggest muscles in Ali's body - her legs.

We found a gym with an exercise bike with a power rating built in. When Ali worked quite hard on the exercise bike she generated around 150 Watts, enough to power a decent sized television. When Ali works really hard, she generates 280 Watts, enough to power a computer without a monitor. Unfortunately she's not fit enough to keep that pace up for long.

 

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What is going on?

If you move a magnet near a coil of wire, you will push the electrons back and forth. If there is somewhere for them to you they will flow producing an electric current.

Here you can see Ali moving a strong magnet in and out of a coil of wire. This makes a current in the wire which you can see on the meter.

Moving magents and coils is is how virtually all the power in the world is generated (except a little using photovolatic solar cells) the only thing that changes is what you use to move the magnets. Unfortunately this power does not come for free, a circulating electric current produces a magnetic field that fights the movements you are making. This means that the more current you draw from the could the harder it is to move the magnet and so you have to do more work to generate more power.

How much power would all the gyms in the country generate?

If you had 50 million people on the planet generating on average 100 Watts each, that's about 5 gigawatts or as much as a large coal powered station. However few people spend even 1% of their time in the gym and even less of that actually doing exercise, so the figure is probably closer to a few megawatts - about the same as 3-4 windmills and it would probably be cheaper and more environmentally friendly to install the windmills.

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Why Put Salt on the Roads?

If you've ever wondered why we salt the roads in Winter time - this kitchen science is for you. This week Dave is live in the studio, trying to investigate what happens when you add some salt to an icecube!

What you need

• Some Ice
• Some salt
• A piece of thread
• A bowl or mug

What to Do

1. Put a piece of ice into the bowl. This experiment works best if the ice is a bit wet, just starting to melt.
2. Take some cotton and lay it over the top of your ice cube. If you have a particularly big ice cube you may need to fold it over a few times to make it stronger.
3. Sprinkle a little bit of salt over the top of the ice cube, on top of the cotton.
4. Leave it for about 10 seconds.
5. Try to pick the cotton up!

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What may Happen

The ice cube should stick to the thread and you should be able to pick the ice cube up using the thread lying on top of it.

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What is going on?

If you measure the temperature of an icecube, it's about zero degrees centigrade. If you then put salt on it and measure the temperature, it plummets down to about -8 or -10 degrees. It's even possible to get down to around -18. In fact, the lowest temperature in the Farenheit scale is actually the lowest temperature you can get by adding salt to ice. If you imagine ice as a big grid or matrix structure, of all these little water molecules are all stuck together a bit like magnets. All the molecules are vibrating a little bit, some more than others. Some of them are vibrating so much they can just leap off the ice and melt into the liquid around it. This takes energy out of the ice cube. Normally another molecule from the water then jumps back in it's spot, giving the energy back to the ice and keeping everything at about the same temperature, about 0 degrees centigrade. With the salt in the way however, the water molecule that has melted gets lost in all the salt molecules, and before another water molecule can rejoin the ice, another one has escaped, and then another. So lots more water escapes, and the ice melts. Melting ice requires loads of energy. Normally when ice is melting, that energy comes from the air, the water that has already melted, whatever is around it. But if you forcibly melt it by adding salt, that energy has to come from the ice itself. This is why it gets so much colder!

What's happening with the thread then?

In the places where the salt is, the icecube is forcibly melted and also those places get very very cold. In the other places where salt didn't land, you now have melted water sitting on a much colder icecube. This causes those parts to quickly refreeze. This sticks the tread to the icecube, and you can pick it up!

So why salt the roads?

The reason they do that is salt on the roads will melt the ice, making the roads less slippery. The icy water now freezes at perhaps -5 rather than 0. So it has to be a colder day to make the roads ice up. If you get down to -20 or -30, the ice will no longer work. At these temperature you now need to add a different chemical. Sodium Acetate is the vinegar flavour in salt and vinegar crisps, and it works beautifully and isn't too bad for the environment, either!

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Electric Slime

Make some seemingly normal slime that behaves very strangely with electricity

What you need

Some Cornflour

Some vegetable Oil

A mug and a spoon

A balloon, or some polystyrene

Some hair

What to Do

Put 2-3 tablespoons of cornflour in the mug

Mix in the vegetable oil until you get a consistancy like that of thick cream.

Charge up the balloon or the polystyrene, by rubbing it on your hair.

Poar some of the mixture out of the spoon, and then move the charged part of the balloon near it.

What happens?

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What may Happen

When you move the charged balloon near the slime, it will start to behave strangely, moving towards the balloon, and becoming much thicker.

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What is going on?

The cornflour is made up of tiny particles of starch, each less than 10 thousandth of a mm across. When the particles get near to the positively charged balloon, electrons will move towards the balloon inside the particle, making the side nearest the balloon negative and the side furthest positive. Because the positive is nearest the balloon it will be attracted more strongly than the other end is repelled, this is why dust is attracted to charged objects.

In the slime there are billions of these tiny particles surrounded by an insulating liquid so the charges can't escape. So you get lots of particles with positive at the balloon end and negative at the other, these are all attracted together sticking the particles together making the slime much more solid.

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Electric Slime

Make some seemingly normal slime that behaves very strangely with electricity

What you need

	Some cornflour (cornstarch)		Some vegetable oil
	Some polystyrene (styrofoam) or a balloon		A cup
	A spoon

 

 

What to Do

Put 2-3 tablespoons of cornflour in the mug

Mix in the vegetable oil until you get a consistancy like that of thick cream.

Charge up the balloon or the polystyrene, by rubbing it on your hair.

Pour some of the mixture out of the spoon, and then move the charged part of the balloon near it.

What happens?

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What may Happen

When you move the charged balloon near the slime, it will start to behave strangely, moving towards the balloon, and becoming much thicker.

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What is going on?

The cornflour is made up of tiny particles of starch, each less than 10 thousandth of a mm across. When the particles get near to the positively charged balloon, electrons will move towards the balloon inside the particle, making the side nearest the balloon negative and the side furthest positive. Because the positive is nearest the balloon it will be attracted more strongly than the other end is repelled, this is why dust is attracted to charged objects.

In the slime there are billions of these tiny particles surrounded by an insulating liquid so the charges can't escape. So you get lots of particles with positive at the balloon end and negative at the other, these are all attracted together sticking the particles together making the slime much more solid.

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test

What you need