photo of an ancient document showing some of the symbols commonly used by alchemists

Alchemical symbols

Understanding of the alchemists is hampered by their predilection for making their writings incomprehensible ( instant knowledge was not to be available to the uninitiated ) and the popular view that their quest was simply to isolate the Philosophers’ Stone and to use it to transform base metals into gold. There was in fact a genuine search for mental and spiritual advance

Using a world-view totally unlike that recognised today, the alchemists’ ideas of ‘spirit’ and ‘matter’ were intermingled – the ability to use ‘spirit’ in their experiments was the difficult part.

alchemical symbol for gold

To transform copper to gold: – copper could be heated with sulphur to reduce it to its ‘basic form’ (a black mass which is in fact copper sulphide) – its ‘metallic form’ being ousted by the treatment. The idea of introducing the ‘form of gold’ to this mass by manipulating and mixing suitable quantities of spirit stymied alchemists for over fifteen centuries.

Whilst this transmutation of metals was the mainstream concern of alchemy, there emerged in the sixteenth century a school that brought the techniques and philosophies of alchemy to bear on the preparation of medicines, the main figures involved being PARACELSUS and JOHANN VAN HELMONT.

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Noticing that burning a candle in an upturned container, the open end of which is submerged in water, causes the water to rise into the container, Philon of Byzantium inferred correctly that some of the air in the container had been used up in the combustion. However, he proposed that this is because this portion of the air had been converted into ‘fire particles’, which were smaller than ‘air particles’.

In 1700 the German physician Georg Ernst Stahl (1660-1734) invoked ‘phlogiston’ to explain what happens when things burn. He suggested that a burning substance was losing an undetectable elementary principle analogous to the ‘sulfur’ of J’BIR IHBIN AYAM, which he re-named ‘phlogiston’. This could explain why a log (rich in phlogiston) could seem to be heavier than its ashes (deficient in phlogiston). The air that is required for burning served to transport the phlogiston away.

The English chemist JOSEPH PRIESTLY (1733-1804), although a supporter of the phlogiston theory, ironically contributed to its downfall. He heated mercury in air to form red mercuric oxide and then applied concentrated heat to the oxide and noticed that it decomposed again to form mercury whilst giving off a strange gas in which things burnt brightly and vigorously. He concluded that this gas must be ‘phlogiston poor’.

Priestly combined this result with the work of the Scottish physician Daniel Rutherford (1749-1819), who had found that keeping a mouse in an enclosed airtight space resulted in its death (by suffocation) and that nothing could be burnt in the enclosed atmosphere; he formed the idea that the trapped air was so rich in phlogiston that it could accept no more. Rutherford called this ‘phlogisticated air’ and so Priestly called his own gas ‘dephlogisticated air’.

In 1774 Priestley visited the French chemist ANTOINE LAVOISIER (1743-1794).
Lavoisier repeated Priestly’s experiments with careful measurements.
Reasoning that air is made up of a combination of two gases – one that will support combustion and life, another that will not; what was important about Lavoisier’s experiments was not the observation – others had reached a similar conclusion – but the interpretation.

Lavoisier called Priestley’s ‘dephlogisticated air’, ‘oxygene’, meaning ‘acidifying principle’, believing at the time that the active principle was present in all acids (it is not). He called the remaining, ‘phlogisticated’, portion of normal air, ‘azote’, meaning ‘without life’

Oxygen is the mirror image of phlogiston. In burning and rusting (the two processes being essentially the same) a substance picks up one of the gases from the air. Oxygen is consumed, there is no expulsion of ‘phlogiston’.

Lavoisier had been left with almost pure nitrogen, which makes up about four fifths of the air we breath. We now know azote as nitrogen. Rutherford’s ‘mephitic air’ was carbon dioxide.


Like phlogiston, caloric was a weightless fluid, rather like elemental fire, a quality that could be transmitted from one substance to another, so that the first warmed the second up.

It was believed that all substances contained caloric and that when a kettle was being heated over a fire, the fuel gave up its caloric to the flame, which passed it into the metal, which passed it on to the water. Similarly, two pieces of wood rubbed together would give heat because abrasion was releasing caloric trapped within.

What is being transmitted is heat energy. It was the crucial distinction between the physical and the chemical nature of substances that confused the Ancients and led to their minimal elemental schemes.





1772 – France



Scheele discovers oxygen two years before Joseph Priestly, but does not publish his findings until 1777.

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1789 – France

‘In a chemical reaction, the total mass of the reacting substances is equal to the total mass of the products formed’

Mass is neither created nor destroyed in a chemical change.

Lavoisier’s Table of Elements

Lavoisier’s Table of Elements

Antoine Lavoisier made the first list of the elements, established the idea of conservation of mass and discovered the true nature of burning and the role of oxygen. Lavoisier continued the work of ROBERT BOYLE. He radically reformed the concept of chemistry and killed off the ARISTOTLEIAN concepts of elemental matter. Lavoisier realised that every substance can exist in three phases – solid, liquid and gas – and proved that water and air are not elements, as had been believed for centuries, but chemical compounds. He thus helped to provide a foundation for DALTON’s atomic theory. He opened the way to the idea that air not only had mass but may be a mixture of gases.

Lavoisier was instrumental in disproving the phlogiston theory, a widely held view that when substances burn they give off ‘phlogiston’, a weightless substance. The phlogiston debate owed much to ALCHEMY and said that anything burnable contained a special ‘active’ substance called phlogiston that dissolved into the air when it burned. Therefore, anything that burned must become lighter because it loses phlogiston. This had become the scientific orthodoxy.

By carefully weighing substances before and after burning, Lavoisier showed that combustion was a chemical reaction in which a fuel combined with oxygen.

He burned a piece of tin inside a sealed container and showed that it became heavier after burning, while the air became lighter.
While the overall weight of the vessel remained the same during Lavoisier’s experiments – for example when burning tin, phosphorus or sulphur in a sealed container – the solids being heated could in fact gain mass. There was no change in total mass as substances were simply changing places.
It became apparent that rather than losing something (phlogiston) to the air, the tin was taking something from it. The explanation was that the weight gain was caused by combination of the solid with the air trapped in the container.

Full length picture of LAVOISIER


After meeting JOSEPH PRIESTLY in Paris, Lavoisier realised that Priestley’s ‘dephlogisticated air’ was not only the gas from the atmosphere that was combining with the matter but, moreover, it was actually essential for combustion. He renamed it ‘oxygen’ (‘acid producer’ in Greek) from the mistaken belief that the element was evident in the make up of all acids. He also noted the existence of the other main component of air, the inert gas nitrogen that he named ‘azote’.

Lavoisier’s wife Marie-Anne Pierrette assisted him in much of his experimental work and illustrated his book, Traite Elementaire de Chimie (Elementary Treatise on Chemistry). The text defined a chemical element, saying that it was any substance that could not be analysed further. With this definition he compiled a list of the then known elements, which founded the naming process for chemical compounds. Lavoisier’s list contained 23 ‘elements’. Many turned out not to be elements at all, but the list included sulphur, mercury, iron and zinc, silver and gold. Lavoisier’s name is still used in the title of the modern chemical naming system.
It took John Dalton to connect the concept of elements with the concept of atoms. Dalton noticed that when elements combined to make a compound, they always did so in fixed proportions.

During the French revolution, Lavoisier was guillotined.

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