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.

Wikipedia-logo © (link to wikipedia)





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.




WILLIAM HARVEY (1578-1657)

1628 – London, England

‘Circulation of the blood’

Portrait of WILLIAM HARVEY ©


As WILLIAM GILBERT had begun in physics, and FRANCIS BACON had subsequently implored, Harvey was the first to take a rational, modern, scientific approach to his observations in biology. Rather than taking the approach of the philosophers, which placed great emphasis upon thinking about what might be the case, Harvey cast aside prejudices and only ‘induced’ conclusions based on the results of experiments and dissections, which could be repeated identically again and again.

After what GALEN had begun and VESALIUS had challenged, Harvey credibly launched perhaps the most significant theory in his field of biology. He postulated and convincingly proved that blood circulated in the body via the heart – itself little more than a biological pump.

Galen had concluded that blood was made in the liver from food, which acted as a fuel, which the body used up, thereby requiring more food to keep a constant supply. Vesalius added little to this theory. Harvey, physician to Kings James I and later Charles I proved his theory of circulation through rigorous and repeated experimentation. He correctly concluded that blood was not used up, but is recycled around the body.

An illustration depicting William Harvey (April 1, 1578 - June 3, 1657), the medical doctor credited with first describing the properties of the human circulatory system, seeing a patient. ©


His dissections proved that the arteries took blood from the heart to the extremities of the body, able to do so because of the heart’s pump-like action. He could see that the pulses in arteries came immediately after the heart contracted, and became certain that the pulse was due to blood flowing into the vessels.
By careful observation he found that blood entered the right side of the heart and was forced into the lungs, before returning to the left side of the heart. From there it was pumped via the aorta into the arteries around the body.

Harvey realized that the amount of blood flowing around the system was too much for the liver to produce. The blood had to be circulating back to the veins; which, with their series of one-way valves, brought blood back to the heart.
Without a microscope it was impossible to see the minute capillaries that linked the arteries to the veins.

Exercitatio anatomica de motu cordis et sanguinis in animalibus William Harvey (1628)

Harvey published his findings in the 720 page ‘Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus‘ ( Anatomical Exercise on the Motion of The Heart and Blood in Animals ) at the Frankfurt Book Fair in 1628.

Initially supported by some academics, an equal number rejected his ideas. One area of weakness was that he was unable to offer a proven explanation for how the blood moved from the arteries to the veins. He speculated that the exchange took place through vessels too small for the human eye to see, which was confirmed shortly after his death with the discovery of capillaries by Marcello Malphigi with the recently invented microscope.

Even then, nobody knew what blood was doing. It would take another hundred years before ANTOINE LAVOISIER discovered oxygen and worked out what it did in the body.

In 1651, Harvey published ‘Exercitationes de Generatione Animalium‘ ( Essays on the Generation of Animals ), a work in the area of reproduction which included conjecture that rejected the ‘spontaneous generation’ theory of reproduction which had hitherto persisted. His belief that the egg was at the root of life gained acceptance long before the observational proof some two centuries later.

Wikipedia-logo © (link to wikipedia)


Related sites
  • The Old Operating Theatre (

ROBERT BOYLE (1627- 91)

1662 – England

‘The volume of a given mass of a gas at constant temperature is inversely proportional to its pressure’

If you double the pressure of a gas, you halve its volume. In equation form: pV = constant; or p1V1 = p2V2 where the subscripts 1 & 2 refer to the values of pressure and volume at any two readings during the experiment.

Born at Lismore Castle, Ireland, Boyle was a son of the first Earl of Cork. After four years at Eton College, Boyle took up studies in Geneva in 1638. In 1654 he moved to Oxford where in 1656, with the philosopher John Locke and the architect Christopher Wren, he formed the experimental Philosophy Club and met ROBERT HOOKE, who became his assistant and with whom he began making the discoveries for which he became famous.

Robert Boyle. New Experiments Physico-Mechanical. Oxford: Thomas Robinson, 1662

New Experiments Physico-Mechanical 1662

In 1659, with Hooke, Boyle made an efficient vacuum pump, which he used to experiment on respiration and combustion, and showed that air is necessary for life as well as for burning. They placed a burning candle in a jar and then pumped the air out. The candle died. Glowing coal ceased to give off light, but would start glowing again if air was let in while the coal was still hot. In addition they placed a bell in the jar and again removed the air. Now they could not hear it ringing and so they found that sound cannot travel through a vacuum.

Boyle proved Galileo’s proposal that all matter falls at equal speed in a vacuum.

He established a direct relationship between air pressure and volumes of gas. By using mercury to trap some air in the short end of a ‘J’ shaped test tube, Boyle was able to observe the effect of increased pressure on its volume by adding more mercury. He found that by doubling the mass of mercury (in effect doubling the pressure), the volume of the air in the end halved; if he tripled it, the volume of air reduced to a third. His law concluded that as long as the mass and temperature of the gas is constant, then the pressure and volume are inversely proportional.

Boyle appealed for chemistry to free itself from its subservience to either medicine or alchemy and is responsible for the establishment of chemistry as a distinct scientific subject. His work promoted an area of thought which influenced the later breakthroughs of ANTOINE LAVOISIER (1743-93) and JOSEPH PRIESTLY (1733-1804) in the development of theories related to chemical elements.

Boyle extended the existing natural philosophy to include chemistry – until this time chemistry had no recognised theories.

The idea that events are component parts of regular and predictable processes precludes the action of magic.
Boyle sought to refute ARISTOTLE and to confirm his atomistic or ‘corpuscular’ theories by experimentation.

In 1661 he published his most famous work, ‘The Skeptical Chymist’, in which he rejected Aristotle’s four elements – earth, water, fire and air – and proposed that an element is a material substance consisting at root of ‘primitive and simple, or perfectly unmingled bodies’, that it can be identified only by experiment and can combine with other elements to form an infinite number of compounds.

The book takes the form of a dialogue between four characters. Boyle represents himself in the form of Carneades, a person who does not fit into any of the existing camps, as he disagrees with alchemists and sees chemists as lazy hobbyists. Another character, Themistius, argues for Aristotle’s four elements; while Philoponus takes the place of the alchemist, Eleutherius stands in as an interested bystander.

In the conclusion he attacks chemists.

page from one of Boyle's publications“I think I may presume that what I have hitherto Discursed will induce you to think, that Chymists have been much more happy finding Experiments than the Causes of them; or in assigning the Principles by which they may be best explain’d”
He pushes the point further: “me thinks the Chymists, in the searches after truth, are not unlike the Navigators of Solomon’s Tarshish Fleet, who brought home Gold and Silver and Ivory, but Apeas and Peacocks too; For so the Writings of several (for I say not, all) of your Hermetick Philosophers present us, together with divers Substantial and noble Experiments, Theories, which either like Peacock’s feathers made a great show, but are neither solid nor useful, or else like Apes, if they have some appearance of being rational, are blemished with some absurdity or other, that when they are Attentively consider’d, makes them appear Ridiculous”

The critical message from the book was that matter consisted of atoms and clusters of atoms. These atoms moved about, and every phenomenon was the result of the collisions of the particles.

He was a founder member of The Royal Society in 1663. Unlike the Accademia del Cimento the Royal Society thrived.

Like FRANCIS BACON he experimented relentlessly, accepting nothing to be true unless he had firm empirical grounds from which to draw his conclusions. He created flame tests in the detection of metals and tests for identifying acidity and alkalinity.

It was his insistence on publishing chemical theories supported by accurate experimental evidence – including details of apparatus and methods used, as well as failed experiments – which had the most impact upon modern chemistry.

Wikipedia-logo © (link to wikipedia)





1774 – England

portrait of JOSEPH PRIESTLY (1733-1804) ©


‘Priestly stumbled upon oxygen in 1774 while heating mercury oxide and discovered that it greatly enhanced the burning of a candle’s flame’

Priestly did not realise the true impact of his findings and it was left to ANTOINE LAVOISIER whom he told of his findings in 1775 to establish the central place oxygen has in the fields of chemistry and biology.

Priestly named the gas ‘dephlogisticated air’, in keeping with the accepted theory that all flammable substances contained the elusive substance ‘phlogiston‘ which was central to the combustion process and was released (and lost) during it.

Wikipedia-logo © (link to wikipedia)




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.

Wikipedia-logo © (link to wikipedia)