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THE MOST FLAMMABLE SUBSTANCE EVER MADE
Chemistry really began when we mastered our first reaction: setting fire to stuff. The ability to create and control fire helped us to hunt, cook, ward off predators, stay warm in winter and manufacture primitive tools. Originally, we burned things like wood and fat, but it turns out that most substances are combustible.
Things catch alight because they come into contact with oxygen, one of the most reactive elements out there. The only reason things aren't bursting into flame all the time is that while oxygen is reactive it needs energy to get going. That's why starting a fire also requires something like warmth or friction. Oxygen has to be heated in order to combust.
The most flammable chemical ever made, though, far worse than oxygen, was created in 1930 by two scientists named Otto Ruff and Herbert Krug. Meet chlorine trifluoride.
Made from the elements chlorine and fluorine in a one-to-three ratio, chlorine trifluoride is unique in being able to ignite literally anything it touches, including flame retardants.
A green liquid at room temperature and a colourless gas when warmed, ClF3 will set fire to glass and sand. It will set fire to asbestos and Kevlar (the material from which firefighters' suits are made). It will even set fire to water itself, spitting out fumes of hydrofluoric acid in the process.
There are very few instances of ClF3 being used, though, because it has the inconvenient property of setting fire to almost anything with which it comes into contact. It takes a special kind of maniac to think, 'Hmm, I'll give that a go.'
The most spectacular ClF3 incident happened on an undisclosed date at a chemical plant in Shreveport, Louisiana. A ton of it was being moved across the factory floor in a sealed cylinder, refrigerated to prevent it reacting with the metal. Unfortunately, the cold temperature made the cylinder brittle and it cracked, spilling the contents everywhere. The ClF3 instantly set fire to the concrete floor and burned its way through over a metre in depth before extinguishing. The man moving the cylinder was reportedly found blasted through the air 150 metres away, dead from a heart attack. That was refrigerated chlorine trifluoride.
During the 1940s, a few cautious attempts were made to use it as a rocket fuel, but inevitably it kept setting fire to the rockets themselves so the projects were abandoned.
The only people who made a serious attempt to harness its power were the Nazi weapons researchers of Falkenhagen Bunker. The idea was to use it as a flame-thrower fuel, but it set fire to the flame-thrower and anyone carrying it so, again, it was deemed unusable.
Just think about that. Not only will it set fire to water, chlorine tri-fluoride is so evil even the Nazis didn't mess with it. What makes it so potent?
The answer is that fluorine behaves in a very similar way to oxygen but needs less energy to get started. It's the most reactive element on the periodic table and effectively out-oxygens oxygen at breaking other chemicals down. So, when you combine it with chlorine, the second most reactive element, you get an unholy alliance that starts fires without encouragement.
FIRE FROM WATER
The Greek philosopher Heraclitus was so enamoured with fire he declared it to be the purest substance – the basic matter from which reality was made. According to him, everything was somehow made from fire in one form or another. Fire was, in other words, elemental.
It's an understandable assumption to make since fire does appear to possess magical properties. Then again, Heraclitus lived on a diet of nothing but grass and tried to cure himself of dropsy by lying in a cow shed for three days covered in manure ... after which he was eaten by dogs. So perhaps we don't need to take Heraclitus's views too seriously.
The reason it was so difficult to identify elements in the ancient world was because, unknown to the early philosophers, very few elements occur in their pure state. Most of them are unstable and combine to form element fusions called compounds.
It works a bit like a singles' bar. Each person is unhappy on their own so they link up with others to form stable pairings. At the end of the evening, most individuals have formed compounds leading to greater stability all round. Only a handful of elements like gold, which doesn't mind being single, remain in their native state.
Almost everything we come across in nature is a compound, so while something like table salt may look pure, the game is being rigged. Table salt is actually a compound of sodium and chlorine – the true elements.
You'll never find a lump of sodium in the ground or a cloud of chlorine drifting on the breeze because both are violently reactive. This makes them virtually undetectable, especially if you're working with the crude lab equipment of the first millennium.
There's also the fact that many elements are shockingly rare. Take the element protactinium used in nuclear physics research; the entire global supply comes from a single flake, weighing 125 g owned by the UK Atomic Energy Authority. With the odds stacked against them, Greek philosophers had no chance of getting things right.
It wasn't until the late seventeenth century that a German experimenter named Hennig Brandt proved everyday substances had elements locked inside them and most of the stuff we thought to be pure, wasn't at all.
On an unknown night in 1669, Brandt was boiling vast quantities of urine in his lab (you've got to have a hobby), probably because urine is gold-coloured and he was hoping to make a fortune by solidifying it into the precious metal.
After many hours of what must have been unpleasant work, Brandt was finally left with a thick red syrup and a black residue similar to the gunk you get after burning toast. He mixed these two things together and heated the mixture once more. What happened next made no sense.
His mixture of urine syrup and cookery schmutz suddenly formed a waxy solid, which smelled powerfully of garlic and glowed blue-green. Not only that, it was extremely flammable and gave off blinding white light as it burned. He had somehow extracted fire from water.
Brandt named his chemical phosphorus from the Greek for light-bringer, and spent the next six years experimenting with it in secret. And it wasn't a fun six years, either. Each 60-g batch of phosphorus required five and a half tons of urine to be boiled.
Eventually, running out of his wife's money, Brandt went public with the discovery and began selling phosphorus to Daniel Kraft, one of the first science popularisers, who took it around Europe giving demonstrations to amazed royals and scientific institutions.
Brandt, however, kept the method of extraction a closely guarded secret. Although how nobody figured it out has always been a puzzle. He must have had one hell of a cover story to explain why he wanted all that urine.
Nowadays we understand exactly what was going on in Brandt's methods. The human body's recommended intake of phosphorus is between 0.5 and 0.8 g a day, but since everything we eat contains it, we tend to consume over twice that amount. All this excess is passed into the urine and Brandt was just boiling everything else away.
His discovery marked a crucial moment for chemistry because the extracted phosphorus was so markedly different from its source. Urine doesn't glow in the dark (sadly) but it obviously contains a chemical that does. It was proof there were chemicals hiding in plain sight. The elements weren't out of reach.
THE MEN WHO PLAYED WITH FIRE
At the beginning of the eighteenth century, the German chemist Georg Stahl, armed with this new knowledge that everyday substances could be made from hidden elements, decided to put forward an explanation for fire.
When metals burn they form coloured powders, which were called calxes at the time. Calxes were notoriously difficult to set alight, so Stahl concluded that they were elements, difficult to ignite because their fire had been removed.
According to this hypothesis, anything flammable contained a substance that escaped into air when heated, leaving behind the charred remains. This substance was named phlogiston from the Greek phlogizein (to set alight) and Stahl argued that a fire was phlogiston being separated from a calx.
Stahl's fire hypothesis was important because, unlike previous ideas in chemistry, it was testable. If correct, it should be possible to trap phlogiston and combine it with a calx to regenerate the original metal. By putting forward an idea that could be proven wrong, Stahl gave us a genuine scientific hypothesis and, like most scientific hypotheses, it was quickly destroyed.
The first chink in the armour came from the French-British scientist Henry Cavendish. He was a notoriously shy man with a penchant for collecting furniture, beloved by physicists because he helped provide evidence for the force of gravitation. His greatest contribution to chemistry though was a series of experiments involving acid and iron.
The reaction between these two always released an invisible gas, which Cavendish collected. His first thought was that he had successfully got hold of phlogiston until he discovered something odd. The gas was explosive. If fire was the result of phlogiston escaping, how could phlogiston itself be burned? How could phlogiston escape from itself?
Stranger still, when Cavendish's gas (which he called flammable air) exploded, it generated pure water. If you could make water from other things, maybe water wasn't elemental either.
The next mystery came in 1774 from the heretical English clergyman Joseph Priestley. Priestley was experimenting on calx of mercury (the red powdery substance you get when mercury is burned) and directing beams of sunlight at it with a magnifying glass.
He collected the gas given off and found that other things burned very well inside it, better than they did in normal air. Whatever it was, it was clearly good at removing phlogiston. Logically this gas had to be dephlogisticated because it was able to absorb phlogiston, so he called it 'dephlogisticated air'.
About two hundred years previously, the Polish magician Micha? S?dziwój had discovered air to be a mixture of two gases, one of which was 'the food of life' and one of which was useless. Could this be related?
Priestley decided to seal some mice in a box with his dephlogisticated gas and they survived without harm. He also discovered, after testing it on himself, that it was actually preferable to regular air and made him feel euphoric to breathe it. S?dziwój's food-of-life gas was apparently the same as his dephlogisticated gas.
Priestley also discovered that plants seemed to breathe the gas out, replenishing a room after a fire had burned. The whole thing was very confusing. Fires generating water, metals generating fire, plants generating air ... What was going on?
The answer to all the riddles came in 1775 when Priestley shared his phlogiston results with the French chemist Antoine Lavoisier.
Lavoisier worked for the French government collecting tax contributions but his real passion was science. He had already been experimenting on calxes by the time Priestley's experiments came to his attention and decided it was time to put the phlogiston hypothesis through its paces. If fire was the result of phlogiston leaving a substance, the leftover calx should weigh less.
Priestley had tried taking measurements with his magnifying glass and mercury calx, but precision equipment didn't exist in the eighteenth century. Imagine trying to distinguish a powder weighing 1 g from a powder weighing 1.1 g. Quite the challenge.
Lavoisier decided to scale up Priestley's experiment in order to get a clear result. The difference between 1000 kg and 1100 kg is a difference of 100 kg, which you could see with the naked eye. So, Lavoisier ordered the construction of a nine-foot magnifying glass and blasted a plateful of mercury calx with sunlight.
The results were unmistakable – calxes weighed more than the original metal. Everyone had it backwards. Fire wasn't the removal of phlogiston: it was something being added from the air itself. Substances like metals and phosphorus were the elements and fire was what happened when they combined with Priestley's gas.
As brilliant as this insight was, Lavoisier wasn't perfect and mistakenly thought Priestley's gas was also responsible for the sour taste of acids. He called it oxygène from the Greek oxys-genes (sour-maker), which translates into English as oxygen.
The exploding gas Henry Cavendish had isolated was a different element (contained within the acid, not the metal) and, when heated with oxygen, combined to form water. Lavoisier named this gas hydrogène from the Greek hydros-genes (water-maker), which translates into hydrogen. This new way of looking at things also explained why you couldn't breathe in a room after a fire had been burning. It wasn't because the fire was giving out a toxic substance: it was because air was partly made from oxygen and fires absorbed it, leaving the other gas behind.
This useless gas was eventually shown to react under extreme conditions and could make nitre, one of the key ingredients in gunpowder, so the statesman Jean Chaptal named it nitregène – nitrogen.
Science always progresses when a hypothesis is proven wrong and Lavoisier's experiments signed the death warrant on phlogiston. Air was an unreacted mixture of nitrogen and oxygen, water was a fused compound of hydrogen with oxygen, and fire was a reaction between oxygen and any available chemical. None of them was an element.
For his efforts, Lavoisier was taken to the guillotine in May 1794. Possibly because he worked as a taxman in pre-revolutionary France (never a good idea) but more likely because he criticised the inferior science of Jean-Paul Marat, who became a leading figure of the revolution. An unlucky end for a great mind, although that's nothing compared to the bad luck of a chemist named Carl Scheele.
THE UNLUCKIEST MAN IN THE HISTORY OF CHEMISTRY
Cavendish, Lavoisier and Priestley were geniuses of a new science and other people quickly joined the hunt. Everyone wanted the glory of discovering a new element, although agreeing on who makes a discovery isn't always obvious.
Some elements have been around since antiquity so it's impossible to know who originally discovered them. The Old Testament contains passages dating back three thousand years that refer to gold, silver, iron, copper, lead, tin, sulfur (correctly spelled with an f – see Appendix I) and possibly antimony.
Then there are instances of someone predicting an element without actually obtaining a sample. Johan Arfwedson deduced there was an element hidden within petalite rock and named it lithium from the Greek lithos (rock), but it wasn't until 1821 that William Brande extracted it.
In order to avoid confusion and settle debates we tend to talk about the first person to isolate an element rather than discover it. Credit goes to the first person who manages to hold a pure sample of an element and recognise it as such. Which brings us to the Swedish chemist Carl Scheele.
In 1772, Scheele successfully made a brown powder, which he named baryte from the Greek barys, meaning heavy. He knew there was an element hidden inside (barium) but it was Humphry Davy who isolated it and got the glory.
In 1774, Scheele discovered the gas chlorine (from the Greek chloros, meaning green) but didn't realise it was an element. It was again Humphry Davy who made this link in 1808, thus getting the credit.
That same year, Scheele discovered calx of pyrolusite but failed to isolate the elemental manganese inside, achieved a few months later by Johan Gahn.
Then it happened again in 1778 when Scheele identified molybdenum, before it was isolated by Peter Hjelm. And then again in 1781 when he deduced the existence of tungsten but failed to isolate it before Fausto Elhuyar, who got the credit.
Scheele even discovered oxygen in 1771 – three years before Priestley – but his manuscript was delayed at the printers and, by the time it was published, Priestley had got his results out.
To commemorate his many contributions to chemistry, the mineral Scheelite was named after him ... until it was officially renamed calcium tungstate and Scheele was once again nudged out of the history books. If there is a god of chemistry, he apparently hates Carl Scheele.CHAPTER 2
DIAMONDS, PEANUTS AND CORPSES
In 1812 the German chemist Friedrich Mohs invented a 1 to 10 scale to classify the hardness of minerals. Tooth enamel has a score of 5, for example, while iron ranks as a 4. This means your teeth will technically dent a lump of iron but not the other way around. Although I don't recommend you try it because if you accidentally bite steel (iron with carbon impurity), which has a hardness of around 7.5, you'll regret it.
Diamonds were given a value of 10 because they were the hardest things known at the time. Their claim to the crown was only overthrown in 2003 when a group of researchers from Japan managed to make something even harder – a hyperdiamond.(Continues…)
Excerpted from "Elemental"
Copyright © 2019 Tim James.
Excerpted by permission of Abrams Books.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
INTRODUCTION A Recipe for Reality, 1,
CHAPTER ONE Flame Chasers, 5,
CHAPTER TWO Uncuttable, 15,
CHAPTER THREE The Machine Gun and the Pudding, 25,
CHAPTER FOUR Where Do Atoms Come From?, 37,
CHAPTER FIVE Block by Block, 49,
CHAPTER SIX Quantum Mechanics Saves the Day, 61,
CHAPTER SEVEN Things that Go Boom, 73,
CHAPTER EIGHT The Alchemist's Dream, 87,
CHAPTER NINE Leftists, 101,
CHAPTER TEN Acids, Crystals and Light, 115,
CHAPTER ELEVEN It's Alive, It's Alive!, 127,
CHAPTER TWELVE Nine Elements that Changed the World (and One that Didn't), 141,
APPENDIX I Sulfur with an 'f ', 163,
APPENDIX II Half a Proton?, 167,
APPENDIX III Schrödinger's Equation, 171,
APPENDIX IV Neutrons into Protons, 177,
APPENDIX V The pH and pKa Scales, 181,
APPENDIX VI Groups of the Periodic Table, 187,