The chemistry of Christmas crackers

Christmas has now just about finished for another year and I’m sure at some point over the festive period we all ate too much, drank too much and of course pulled a few Christmas crackers. Despite wondering if you’ll get a mini tape measure or tiny pack of cards, I doubt you’ve ever put much thought into what’s in a cracker. The distinctive bang comes from silver fulminate, AgCNO. Fulimates contain the fulimate ion, CNOand are referred to as friction explosives. This is what makes them perfect for crackers, as they produce the distinctive bang, a tiny explosion, when pulled. The silver fulminate is coated on a piece of card, this runs next to another piece of card which is abrasive- a bit like sandpaper. When the cracker is pulled the two bits of card are pulled apart, rubbing together, creating friction and igniting the silver fulminate. The tube around this amplifies the sound making it louder. Apart from its use here in Christmas crackers silver fulminate has very few other uses, it is extremely explosive and sensitive, so much so that a few grams would self detonate due to the force of its own weight.

I hope you had a cracking Christmas and a great new year!



Influenza – The Virus That Gets Away With Murder

The ‘flu season is quickly approaching, but I bet most people don’t have it marked in their diaries because no one dies of the ‘flu anymore, right? Wrong! Every year around 8,000 people die of the ‘flu in Britain, and that number is slowly rising. [1] This year, in a three week period after January the 23rd, 28,000 people died of the ‘flu – in the same three week period for the last five years the average has been 21,000 – this is a huge increase of a third. [2]

What does this murderous virus look like?Image result for influenza virus

Influenza, aka the ‘flu’, is caused by a virus which under an electron microscope looks like a ball of strands of nucleic acid enclosed in a protective coat that is spiked with antigens. This gives it the very iconic shape that all biologists associate with this underestimated virus.

What symptoms does the ‘flu virus cause?

In the next few months, people all over the country will be complaining to their doctors (or friends and family) that they have a fever, sore throat, headache, and are really tired. [3] Little do these people know, but they have probably been infected with the ‘flu. These symptoms are due to the body’s reaction to the virus infiltrating the cells in the throat, hijacking the DNA into producing more ‘flu viruses, and these viruses violently bursting from the infected cells. [4]

The sore throat experienced is due to the violent nature of this bursting from the cells. Many of the throat cells are damaged as this happens, and each generation of viruses infiltrates more and more cells and they reproduce rapidly.

Headaches can be due to the body producing mucus in the nose to try to stop any more infectious microorganisms entering the body. This mucus blocks the sinuses, which increases the pressure inside the head.

A fever is a very clever defence mechanism because the high temperature is not so high that it permanently damages (or ‘denatures’) human enzymes, but is high enough to denature the virus’ enzymes – slowing it down enough to allow the body’s white blood cells to swoop in and destroy it.

Symptoms of the ‘flu are very similar to the symptoms experienced during a rhinovirus infection (the common cold) but ‘flu symptoms are actually much worse. Many people, therefore, are tempted to dismiss ‘flu symptoms as a bad cold. This is actually their second mistake, but I’ll come back to the first mistake a bit later.

So why now?

Why is the ‘flu season so late in the year? Most diseases pop up in the summer months when the temperatures are warm and humid, and parasites, bacteria, and viruses can thrive…. but the ‘flu virus is weird – it prefers the winter months when temperatures are cold and all life seems to slow down.

A study carried out in October 2007 showed that guinea pigs were more likely to infect other guinea pigs in colder temperatures.[6] In addition, the ‘flu virus was also able to stay alive for different amounts of time in different conditions.

Why should this be? In cold temperatures, the protective coat on the virus hardens until it becomes rubbery. [5] This gives it the protection it needs to not only spread from person to person, but also to survive for 22 hours more than if temperatures were hotter. As temperatures rise, at around 90 degrees Fahrenheit the virus’ protective coat melts into a liquid and the virus then has very little protection from the elements. In this state, the virus is only able to stay alive for 1 hour. [6] It would seem a poor evolutionary step to develop this way, but the virus must give up its protective coat so that it can infect the host – the virus is only able to infect cells when its coat is in this liquid state.[5]

How does the virus travel from person to person?

The spread of this virus is by droplet. When an infected person coughs, sneezes or even talks, the virus can be projected from the mouth into the air, contained in droplets. In cold conditions, its outer coat protects the virus from some soaps and external conditions that could damage it. However, once a floating, infected droplet has been inhaled or swallowed by another person, the virus takes only 1 to 4 days to cause symptoms. [3]

You’ve got the ‘flu – what now?

If symptoms are not severe, keeping warm and hydrated at home can often be enough, with a few pain medications for aches. If the symptoms are severe, there are antiviral treatments available that stop the virus multiplying and help the body to battle the infection. [3]

So, what is the first mistake people make?

The first mistake many people make when it comes to the ‘flu is not taking it seriously enough. A ‘flu vaccination is available and should be taken by elderly people, young children, pregnant women and the immunosuppressed, as they may not be able to battle the virus by themselves. Unfortunately, the vaccination itself can give symptoms of the ‘flu because it contains live virus particles, but the strain of ‘flu causing infections may be different each year, and so it’s sensible to have the vaccination repeated each year with the current version of the virus so that your immune system is ready.

Can the ‘flu be prevented?

The good news is that preventing the spread of the ‘flu is simple. Washing hands regularly with soap is very important, as it removes any virus particles from your hands so they can’t be transferred to surfaces. [7] Staying away from infected people (or non-infected people if you have symptoms) and being very careful with hygiene are also crucial in the battle with the ‘flu.


The influenza virus kills thousands of people each year and yet most people consider it to be only mildly worse than the common cold. This ‘flu virus really is the virus that gets away with murder and if it is possible to minimise the amount of people who die from this virus yearly by preventing the spread of it, I think we should try.


[1] PUBLIC HEALTH ENGLAND. (2014) Public Health England and the NHS prepare for unpredictable flu season. [Online] Available from: [Accessed: 26th October 2015]


[2] CHRIS COOK. (2015) Death rate up by a third in January. [Online] Available from: [Accessed: 26th October 2015]


[3] NHS CHOICES. (2015) Flu. [Online] Available from: [Accessed: 26th October 2015]


[4] RUSSEL MCLENDON. (2013) How does the flu work? [Online] Available from: [Accessed: 26th October 2015]


[5] NIH NEWS. (2008) NIH Scientists Offer Explanation for Winter Flu Season. [Online] Available from: [Accessed: 26th October 2015]


[6] SITNFLASH. (2014) The Reason for the Season: why flu strikes in winter. [Online] Available from: [Accessed: 26th October 2015]

[7] CENTERS FOR DISEASE CONTROL AND PREVENTION. (2015) CDC Says “Take 3” Actions to Fight The Flu. [Online] Available from: [Accessed: 26th October 2015]