Number 14: Elephant's toothpaste

Here's a great example of biochemistry in action.

You'll need:

• A bottle of hydrogen peroxide. You can get this from most pharmacists. Try and get 9%, but 6% will do.
• Dried baker's yeast.
• Washing up liquid.
• An empty plastic bottle (500ml or so).
• A glass with a 20ml of water in it.
• A teaspoon.

Safety: 

Hydrogen peroxide is a mild bleach (which is why its used to make your hair go blond). Be careful with it and don't get it in yours eyes. Best get some adult supervision for this one. And it makes a bit of a mess so do it outside.

What to do.

1. Put about 2 teaspoons of yeast into the glass with the water. Mix it about until it looks like brown muddy water.

2. Squirt about 2 teaspoons of washing-up liquid into the plastic bottle.

3. Pour 50ml of hydrogen peroxide onto the washing-up liquid.

4. Pour the yeasty water into the plastic bottle. Stand back and ...

What's going on?

Remember the chemical formula for water? H₂O, meaning water is made from two hydrogens and one oxygen. Well hydrogen peroxide is almost the same except its got an extra oxygen, so its formula is H₂O₂. But whilst water is very stable (remember how we needed to put electricity through water to break it down in the hydrogen and oxygen), hydrogen peroxide is unstable, it slowly decomposes to water and oxygen. However when the yeast is added to the hydrogen peroxide that extra oxygen gets released really quickly and you end up with loads of oxygen gas (the washing up liquid is just there so that the gas gets trapped in all that foam). 

So why does adding yeast result in the oxygen being released so quickly? Well yeast contains an protein called catalase. It looks like this. 

Catalase is a type of protein called an enzyme. Enzymes¹ speed up specific chemical reactions. In this case the reaction is:

2 H₂O₂ → 2 H₂O + O₂

Which is just a way of saying that 2 hydrogen peroxide molecules turn into two water molecules plus 1 oxygen molecule. The really astonishing thing about catalase is how fast it works. One catalase molecule can break down 40 million molecules of hyrodgen peroxide every second!

¹ The word enzyme comes from the greek ενζυμον, meaning "in yeast". Plus things that speed up chemical reactions are called catalysts, hence the name catalase. So if you follow the etymology of these things you end up going around in circles.

The Geeks are Coming

Something a bit different for this post. No instructions on fun science experiments I'm afraid. Instead I want to recommend a book that everyone who loves science should read. It's called "The Geek Manifesto: Why Science Matters" (by Mark Henderson) and its a bit of a call to arms for scientist and science lovers everywhere. Amongst other things it describes how poorly scientists are represented in politics. In the UK just one (out of 650) of our Members of Parliament had a career in science before entering politics (and its not better in the USA). Consequently politicians fail to understand how science is conducted leading, amongst other things, to a systematic abuse of evidence to support their policies. 

But this evidence abuse and misunderstanding of the scientific method is not all their fault. Scientists too often fail to engage with politicians (and the media). So Mark calls for scientist to do just that, help support politicians, talk to them and make science (and evidence based policies) a vote winning issue.

One of the book's fans, Dave Watts, took Mark's message to heart. He thought that our politicians should read the book so he rallyed the troops and via an online pledge site got scientists to agree to send a copy of "The Geek Manifesto" to every MP in the UK parliament. With the help of the publishers (Transworld, who agreed to match the individual pledges)  the target has been reached and books are winging their way to MPs right now.

I joined in the fun and have sent a copy to my MP with the following accompanying letter.

Dear Graham, 

Within the next few days you should receive a copy of “The Geek Manifesto: Why Science Matters” by Mark Henderson (Head of Communications at the Wellcome Trust)  I hope you enjoy reading it. 

A few years ago we engaged on the Royal Society’s Scientist/MP pairing scheme. I found it a most useful insight into the workings of government and the role that science can play in the decision making process.

Unfortunately and despite excellent schemes, like those run by the RS, it seems to me, and many others, that science is greatly undervalued and misused in British politics. Many of our decision makers are unfamiliar with the scientific methods and how it can be applied to policies. 

This lamentable state is in no small part due to scientists’ failure to engage with politicians. But this is changing. In recent years scientists have started to form lobby and pressure groups to better make their cases heard. 

Mark Henderson’s book follows in this vein. It is acting as a call to arms, rallying scientists and persuading them to make science and evidenced based decision an electoral issue. Therefore many of us consider “The Geek Manifesto” to be an extremely timely and important book. It contains arguments that all rational thinkers should consider. With this in mind hundreds of scientist around the country have pledged to buy and send their MP a copy of the book.  Within the next few weeks every MP should receive a copy. 

I hope you and your colleagues find the book to be an interesting read. 

An offer to help
I know from my experience on the scientist/MP pairing scheme that you are a extremely busy working to help you constituents.
In turn I believe that scientists must do more to help their MPs understand science and the scientific method. I would therefore like to offer my services in helping to form evidence based views and decisions.
My specialist expertise lies in chemistry and biochemistry. However my scientific skills are highly transferable, after all science is more about asking rational questions, solving problems and understanding date than it is learning facts and figures.

Meet the  Geeks  

Lastly, I would like to draw your attention to your local  “Café Scientifique” (details attached); a monthly meeting were local scientists talk, in an informal, setting to members of the public. You are welcome to come to our meetings, which would be an excellent opportunity for you to meet some of your ‘geek’ constituents.

I look forward to your reply, which I will post on my blog www.t2ah.com . 

Sincerely,  

Dr Mark Lorch

I'll keep you posted on any reply. In the mean time you can read more about the book and the pledge on blogs here and here and many others. And of course I heartily recommend reading the book.

Number 13: Solargraphy

Solargraphy is a way of tracking the suns movement across the sky usually using pinhole cameras. Its really easy to set up but the best images take months to collect, so you need some patients for this one. Its also best to start them when the sun is highest or lowest in the sky. And since we are only a couple of weeks away from the summer equinox (or winter equinox in the southern hemisphere)  now is an ideal time to get your solargraphic cameras ready so they can be deployed on 21st June.

You can collect some absolutely stunning images so its well worth having a go. For example here's six months from my bedroom window. And for more solargraphs take a look at Deigo's awesome collection at solarigrafia.com.

You'll need:

• A black film canister (or some other light tight container)
• Photographic paper
• Electrical Tape
• modelling knife
• A drink can
• Double sided tape
• A pin or needle
• Fine sandpaper

and in six months time you'll need

• a scanner ( or at a push a digital camera will do)

What to do
1. Cut a small square out of the side of the canister.

2. Cut  a square of tin out of your drink can. The square of tin needs to be significantly larger than the hole in the film canister.

3. Take the pin and gently push down on the tin square. DON'T push it all the way through, you just want to make a dimple on the opposite side of the tin.

4. Turn the tin square over and sand down the dimple.

5. Turn the tin over and gently push the pin in again, turn it back and sand down the fresh dimple. Repeat this 2 or 3 times until you have a very small hole in the tin.

6. Tape the square of tin over the hole in the canister (using the electricians tape). Make sure the pinhole is near the middle of the hole in the canister. 

EDIT: @solarigrafia pointed out that it hot countries you need more tape than I used here otherwise you end up with it melting and the pinhole falling off. So you might want to wrap the tape right around the canister. 

7. Do the next bit in subdued light (I didn't because then I couldn't show you the photos). Cut a section of photographic paper that's about  the circumference of the canister in length by a little under the canister's height. The paper needs to fit neatly inside the canister. Stick the paper to the canister (with the double sided tape), otherwise it rolls up over the course of the exposure. 

TOP TIP: Double and triple check that the paper is the right way round in the canister. The light sensitive side needs to be facing and opposite the pinhole. I've got that bit wrong before and there is nothing more annoying that coming back to the canister 6 months down the line and discovering you've made that school boy error.

8. Put the cap back on the canister and and if you want belts and braces tape it up.

9. Leave the canister facing out of a window, preferably south facing if you are in the northern hemisphere or north facing if you are in the southern hemisphere.

Top tip 2: Try putting your new pinhole camera somewhere overlooking a building site.

10. Wait for 6 months.

11. Take down the canister, open it up and scan the image. It will be a negative so you'll have to invert the image with some processing software. Anyway, I'll talk you through all that in six months time.

What's going on?

Remember the camera obscura? Well the same thing is going on here. Except this time we have some photographic paper to record the image. The pinhole lets in a tiny amount of light and the paper is actually quite insensitive to light (unless you use developing chemicals, which we aren't) so most of the paper needs a really long time to register  any image. But where the light hits the paper directly from the sun the paper is exposed much more quickly so the sun tracks are recorded really well.

We'll have a  chat about the details of the image in  6 months. But in the mean time you can take a look at my other solargraphs the solargraphy project and the solargraph group on flickr.

Now get on with it and we'll take a look at the result around Christmas time.