What should you do when your King, gold crown and all, gets devoured by a wolf?

According to the 15th Century monk Basil Valentine, the right course of action is to light a bonfire and throw the wolf on the top. Once the wolf has been burned to a crisp, says Valentine, then the King will be brought back to life good as new.

This ludicrous story sounds as though it’s been plucked out of a fairy tale, but is in reality a nearly 600-year-old chemical equation.

The example, vividly brought to life in the engraving below, was used to illustrate the first of The Twelve Keys, a text now thought to have been written by several authors who used the name Basil Valentine as a pseudonym. Let’s face it, it’s a pretty unlikely name for anyone who isn’t an LA detective in a procedural cop show from the 80s.

According to chemist and historian Professor Lawrence Principe, Valentine’s text represents an allegorical set of instructions for the purification of gold. Gold, the so-called king of metals, is fed to the ravenous wolf representing stibnite, an ore of antimony which at the time was meant to be related to lead, the metal of Saturn. Molten stibnite easily dissolves metals, most of which react to form metal sulfides. Precious gold, however, is notably unreactive, and merely forms an alloy with antimony.

When the alloy, represented by the wolf with the king in its stomach, is heated, the antimony evaporates, leaving pure gold. Far from being mere superstition, this process works well and can easily be replicated today.

The next of Valentine’s twelve keys – each of which represents a different series of chemical reactions – describes making aqua regia, an acid mixture which can dissolve gold. This procedure was used by George de Hevesy in 1940 to hide two Nobel prizes from confiscation by the German forces invading Denmark – after the war the gold was recovered and successfully recast. The third of the keys describes making the dissolved gold ‘volatile’, allowing it to travel through the air as gold chloride and deposit red crystals elsewhere – a process of purification considered one of the greatest challenges of alchemy, not explained until independently rediscovered in 1895.

It is now believed that The Twelve Keys were published in this allegorical form in order to ensure the secrets of their discoveries never left the closed world of alchemists. However, alchemical texts were often obscured with allegory, or even written in code, for a host of other reasons. Medieval alchemists would naturally have been secretive about their search for the Philosopher’s Stone, for example, thought to turn common metals into gold, and would also have been keen to avoid persecution for what were perceived as occult practices.

Such secrecy lived on alongside alchemy well into the era of Enlightenment science. The 17th century Irish scientist Robert Boyle, best remembered today for Boyle’s Law of gasses, was a founder of the Invisible College, a precursor to the Royal Society to whom he left a list of unsolved scientific problems. Though considered the first modern chemist for his devotion to the scientific method, most of his work would certainly be characterised as alchemy.

Boyle’s notebooks were written in code to keep his secrets hidden from other alchemists of his day. Historians have deciphered some of his work from a partially-complete surviving key, but the decoded names would mean very little to modern scientists. You might guess that ‘spirit of wine’ represented distilled ethanol, and many elements’ names have remained unchanged, but could you prepare ‘butter of antimony’ (antimony trichloride), ‘liver of sulphur’ (potassium sulfide) or know where to collect ‘lunar caustic’ (silver nitrate) or ‘marine acid air’ (hydrogen chloride gas)?

As many chemicals of the day were named after the minerals or regions they were found in, their names could be wildly different between countries, or even neighbouring towns. While some processes had common names, (“spirit of” referring to a distilled substance, for example), these often bore little connection to the substance’s chemical properties or structure: “oil of vitriol”, for instance, could refer to the distinctly watery dilute sulphuric acid.

From Alchemy to Chemistry

It wasn’t until nearly a century after Boyle’s death that some element of standardisation began to be introduced. Antoine Lavoisier, alongside Boyle and others also often considered the first modern chemist, proposed a naming system in 1787 which treated all chemicals as combinations of fundamental elements. The notion of such elements dates back to at least the days of ancient Babylon, but had long been questioned for the fanciful belief that they were simply Earth, Air, Fire, and Water.

A theory proposed in 1667 by Johann Joachim Becher removed Air and Fire, and instead introduced three forms of earth: terra lapidea, the vitreous or glassy earth, terra fluida, the mercuric earth, and terra pinguis which gave substances their inflammable, sulphurous quality. Later renamed phlogiston, this third fundamental earth element was used to explain why things burn and lose mass: burning was simply the process of dephlogisticating. When 18th century experiments showed that metals actually gain mass upon burning, phlogiston theory rapidly began to break apart itself.

Lavoisier showed that burning was in fact the combination of oxygen with the substances being burned. He used this to identify oxygen as an element alongside 54 others, including elements such as chlorine, fluorine and boron which had not yet been isolated from their acids. His naming system allowed these elemental names to be combined and modified based on the oxygen content of a compound. For example, nitrous acid (HNO 2 ) has only two oxygen atoms while nitric acid (HNO 3 ) has three, and they form nitrite (NO 2 ) and nitrate (NO 3 ) salts respectively. Lavoisier believed that all acids were compounds of oxygen, hence why we still call ‘hydrogen chloride’ hydrochloric acid.

Of course, most of Lavoisier’s elements were already well-known substances that had already acquired their own standardised symbols. Metals in particular had strong mythological connections with the gods, and so the seven classical metals became associated with the planets of our Solar System, often using the appropriate astrological symbol: gold represented the Sun, silver the moon, copper Venus, iron Mars, and so on and so forth.

The Birth of the Atom

John Dalton, a contemporary of Lavoisier’s who worked in my home town of Manchester, proposed atomic theory at the turn of the 18th century. Like elements before them, atoms were also an old idea, originating with the Ancient Greeks and coming from the Greek ατομος, meaning indivisible. The atomist Greek philosophers such as Democritus imagined that by repeatedly cutting anything in half, they would find all matter consisted of objects so small they could could be cut in half no more. Thousands of years later, John Dalton was able to use the behaviour of gases to show that elements, and thus all substances, were indeed collections of such objects.

Improvements to the theory continued over the following decades. In the 1820s Jöns Jacob Berzelius set out to make more accurate measures of atomic weights than those Dalton provided, and strengthened the case for atomic theory by showing that compounds always consisted of whole-number combinations of such weights. Though atomic theory was widely accepted by chemists in the 19th century, physicists remained doubtful for over a hundred years after Dalton’s proposal. Ludwig Boltzmann’s suicide in 1905 may have been driven by the ridicule he received for his kinetic theory of gases, a theory which relied on the existence of atoms and which was in fact later used to prove their existence.

Berzelius’s primary contribution to chemical notation, however, was the introduction of simple one- or two-letter codes for elements, often based on their Latin names, which are now familiar to schoolchildren the world over.

Though some chemical symbols, such as those used in water (H 2 O) or carbon dixide (CO 2 ) are widely known, when most people think of a chemical they probably think of something like this:

That’s the structural formula for propranolol, a medicine used to treat high blood pressure and which is much less funny than it sounds. The complex-looking diagram above is really just a shorthand for the structure: though you can see oxygen and nitrogen atoms labelled by ‘O’ and ‘N’, every unlabelled junction represents a carbon atom, and it is assumed that enough hydrogen atoms exist to make sure each carbon has four bonds.

This notation is extremely useful to chemists, as it shows us exactly what a chemical is without resorting to an unwieldy name (“(RS)-1-(1-methylethylamino)-3-(1-naphthyloxy)propan-2-ol”, if you were wondering) and also shows us those areas where a molecule is most likely to react.

Modern Notation

With the rise of organic chemistry in the 1850s, Lavoisier’s naming system found itself increasingly unable to cope. The new chemicals being discovered weren’t simple salts or compounds of two elements anymore, but seemingly-infinite combinations of just a few elements, chiefly carbon and hydrogen.

It was up to German chemist August Kekulé to introduce the system used today, stipulating that compounds are made up of atoms in well-defined locations, joined to each other by bonds represented by lines, and where each element must form a certain number of bonds through single, double or triple bonding.

In the absence of modern analytical techniques to determine the structure of compounds, chemists at the time could know only a compound’s constituent elements by burning it and weighing the carbon, hydrogen, oxygen and nitrogen-containing combustion products. With careful consideration of the reactions they could perform, Kekulé’s structural theory allowed them to deduce the structure of many compounds known at the time.

Kekulé is most famous today for his work on benzene, a ring-shaped compound containing six carbon and hydrogen atoms, whose structure had been a mystery for a long time. While dozing by the fireside, Kekulé had a day-dream of a snake biting its own tail, and suddenly realised that the benzene molecule could itself form just such a ring. Like Coleridge’s Kubla Khan, this ‘day-dream’ may have been aided by opium, the inspirational properties of which have been immortalised in the English phrase “pipe dream”.

Kekulé’s greatest discovery, however, was suggesting that the benzene molecule rapidly alternated between two forms, shown above, with the double bonds constantly changing places. We now know that all of benzene’s bonds are equal, and can be considered somewhere between a single and double bond.

Even after all these years, chemical notation continues to change and evolve. The image at the top of this post is a new form of chemical notation known as chemical calligraphy, developed by the author of dscript, a writing system that turns words into beautiful glyphs which can be written in many directions. According to its inventor, chemical calligraphy isn’t intended as a replacement for Kekulé’s structural formulae, but as “a mnemonic device and art form” for creating scientific art.

Based on a small ‘alphabet’ that can be combined in near-infinite ways, organic chemistry lends itself well to calligraphy – these cryptic-looking forms are both fully functional, and reminiscent of the codes and symbols used at a time when chemistry was mostly mystery. The snake has once again started to eat its own tail.

Keir is a Mancunian chemist who knows absolutely nothing about opium or its effects no honest why are you looking at me like that? He has daydreams on Twitter @diglyme