ALCHEMY

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.

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.

ALCHEMISTS AT WORK

THE EIGHTEENTH CENTURY

COMBUSTION and PHLOGISTON

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.

CALORIC

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.

CHRISTIAN THEOLOGY & WESTERN SCIENCE

HEAT

DANIEL FAHRENHEIT (1686-1736)

1715 – Netherlands

‘The kelvin scale is more suitable for scientific purposes and the celsius scale is neater, based on decimals. The advantage of using the fahrenheit scale is that it is designed with everyday use in mind, rarely needing negative degrees’

Even as late as the start of the eighteenth century, scientists had no reliable means of accurately measuring temperature and a uniform scale by which to describe the limited measurements they could make.

FAHRENHEIT THERMOMETER

GALILEO had used the knowledge that air expands when heated and contracts when cooled to build a primitive instrument. Using a cylindrical tube placed in water, he noted that when the air in the device was hotter, it pushed the level of the water downwards, just as it rose when the air-cooled. He realised that readings from the device were unreliable because the volume and therefore the behaviour of the air also fluctuated according to atmospheric pressure. Gradually scientists began using more stable substances to improve the accuracy of the reading, with alcohol being introduced as a possible substitute late in the seventeenth century.

Fahrenheit knew that the boiling points of different liquids varied according to fluctuations in atmospheric pressure; the lower the pressure, the lower the boiling point. A producer of meteorological instruments, he first achieved progress in 1709 with an improved alcohol thermometer. Building on the work of GUILLAUME AMONTONS (1663-1705) who investigated the properties of mercury, Fahrenheit took the measurement of temperature into another domain. He produced his first mercury thermometer, particularly useful in its application over a wide range of temperatures, in 1714.

In 1715 he complemented his breakthroughs in instrument making with the development of the fahrenheit temperature scale. Taking 0degrees to be the lowest temperature he could produce (from a blend of ice and salt), he used the freezing point of water and the temperature of the human body as his other key markers in its formulation.

In his initial calculations, he placed water’s freezing point at 30degrees F and the body’s temperature at 90degrees F. Later revisions changed this to 32degrees for the freezing point of water and 96degrees for the body temperature of humans. The boiling point of water worked out to be 212degrees F, giving a hundred and eighty incremental steps between freezing and boiling.

DANIEL FAHRENHEIT

TIMELINE

TEMPERATURE

PIETER VAN MUSSCHENBROEK (1692-1761) EWALD JURGEN VON KIELEL (1700- 48)

1745 – Holland/Germany

‘Electricity produced by electrostatic machines can be stored in a jar’

The Leyden Jar

In modern terms the Leyden jar is a capacitor or condenser.
In 1734 Stephen Gray (c.1666-1736), an English experimenter, discovered that electric charge could be conducted over distance. He also classified various substances into conductors and insulators of electricity. He suggested that metals were the best conductors and thus introduced the use of electric wire.

In 1734 Musschenbroek, a professor from Leyden in Holland discovered that electricity could be stored in a jar of water.
During the same year, von Kleist, a German scientist also discovered the same principle independently.
In later versions of what became known as the Leyden jar, water was replaced by copper foil inside and outside the jar.
The Leyden jar became a novelty and in village faires magicians used ‘electricity in a bottle’ to amaze and entertain villagers.

TIMELINE

ELECTRICITY

CAROLUS LINNAEUS (1707- 78)

1735 – Sweden

‘A system for naming organisms by assigning them scientific names consisting of two parts’

LINNAEUS

Each species is given a two-word Latin name – The genus name that comes first and begins with a capital letter, and the species name, which begins with a lower case letter. The genus name is often abbreviated, and the names are always written in italics or underlined. The Linnaean system has six classification categories – in descending order, kingdoms, phyla, classes, orders, genera and species. Only two are used for naming organisms.

German botanist Rudolph Camerarius (1665-1721) had shown that no seed would grow without first being pollinated. In 1729, Linnaeus wrote in a paper about ‘the betrothal of plants, in which … the perfect analogy with animals is concluded’. He insisted that it is the stamens where pollen is made (the ‘bridegrooms’) and the pistils where seeds are made (‘the brides’) that are the sexual organs, and not the petals as had been considered previously.

As botanists and zoologists looked at nature, or ‘Creation’, there was no way of classifying the animal kingdom depicted in bestiaries of the time but alphabetically; or of distinguishing the real from the mythical.

Linnaeus developed a system of classification. Starting with the plant kingdom, Linnaeus grouped plants according to their sexual organs – the parts of the plant involved in reproduction. Each plant species was given a two-part Latin name. The first part always refers to the name of the group it belongs to, and the second part is the species name.

Linnaeus divided all flowering plants into twenty-three classes according to the length and number of their stamens – the male organs – then subdivided these into orders according to the number of pistils – female organs – they possessed. A twenty-fourth class, the Cryptogamia, included the mosses and other non-flowering plants.

Many people were offended by the sexual overtones in Linnaeus’s scheme. One class he named Diandria, meaning ‘two husbands in one marriage’, while he said ‘the calyx might be regarded as the labia majora; one could regard the corolla as the labia minora’. For almost a century, botany was not seen as a decent thing for young ladies to be interested in.

Linnaeus’s scheme was simple and practical and in 1745 he published an encyclopedia of Swedish plants, when he began considering the names of species. Realizing he had to get the names in place before someone else gave plants other names, he gave a binomial label to every known plant species and in 1753 published all 5,900 in his Species Plantarium.

Believing his work on the plant kingdom complete, he turned his attention to the animal kingdom. In his earlier Systema Naturae of 1735, he had used the classification ‘Quadrupeds’ (four-legged creatures) but replaced this with Mammals, using the presence of mammary glands for suckling young as a more crucial distinguishing characteristic. The first or prime group in the Mammals was the primates, which included Homo sapiens (wise man). His catalogue of animals was included in the tenth edition of Systema Naturae, listed with binomial names.

By the time Linnaeus died it was the norm for expeditions around the world to take a botanist with them, hence CHARLES DARWIN’s famous voyage on the Beagle.

TIMELINE

DANIEL BERNOULLI (1700- 82) JAMES CLERK MAXWELL (1831- 79)

1738 – Switzerland
1859 – England

‘Gases are composed of molecules which are in constant random motion and their properties depend upon this motion’

The volume of a gas is simply the space through which molecules are free to move. Collisions of the molecules with each other and the walls of a container are perfectly elastic, resulting in no decrease in kinetic energy. The average kinetic energy of a gas increases with an increase in temperature and decreases with a decrease in temperature. The theory has been extended to provide a model for two states of matter – liquids and solids.

DANIEL BERNOULLI

Bernoulli had a great advantage over DEMOCRITUS. He knew that free atoms were more than simply tiny grains flying though space; they were tiny grains flying through space and obeying NEWTON’s Laws of Motion.
Bernoulli proposed a ‘bombardment theory’, which stated that a gas consisted of tiny particles in rapid, random motion like a swarm of angry bees. He realized that in the case of such a gas visualized as a host of tiny grains in perpetual frenzied motion, the atoms hammering relentlessly on the walls of any containing vessel would produce a force by bombarding the container. The effect of each individual impact would of course be vanishingly small. The effect of billions upon billions of atoms, hammering away incessantly, however, would be to push the walls back. A gas made of atoms would exert a jittery force that we would detect as a ‘pressure’.

Heating a gas would make its particles move faster.
The pressure of a gas such as steam was easy to measure using a piston in a hollow container. This was essentially a moveable wall. To deduce how the pressure of a gas would be affected by different conditions, Bernoulli first made some simplifying assumptions. He assumed the atoms were very small compared to the gulf between them. This allowed Bernoulli to ignore any force – whether of attraction or repulsion – that existed between them, as being unlikely to be ‘long range’. (This is an ‘ideal’ or ‘perfect’ gas. The behaviour of a real gas may differ from the ideal, for example at very high pressure). With the motion of each atom unaffected by its fellows, Newton’s laws dictated that it should fly at a constant speed in a straight line. The exception was when it slammed into a piston or the walls of the container. Bernoulli assumed that in such a collision a gas atom bounced off the walls of the surface without losing any speed, in the process imparting a miniscule force to the wall.

What would happen if the volume of the gas were reduced by applying an outside force to the piston? If the gas were reduced to half its original volume, the atoms would now have to fly only half as far between collisions, in any given time they would collide with the piston twice as many times and would exert twice the pressure. Similarly, if the gas were compressed to a third of its volume, its pressure would triple. This had been observed by ROBERT BOYLE in 1660 and named Boyle’s Law.

What would happen to the pressure of gas in a closed cylinder if the gas were heated while its volume remained unchanged? Exploiting the insight that the temperature of a gas was a measure of how fast on average its atoms were flying about, that when a gas was heated, its atoms speeded up, he deduced that as the atoms would be moving faster they would collide with the piston more often and create a greater force. Consequently the pressure of the gas would rise. This was observed by the French scientist JACQUES ALEXANDRE CESARE CHARLES in 1787, and christened Charles’ law.

After 120 years MAXWELL polished Bernoulli’s ideas into a rigorous mathematical theory. In Germany, LUDWIG  BOLTZMANN championed the atomic hypothesis, but was refuted by the Austrian ERNST MACH, who was convinced that science should not concern itself with any feature of the world that could not be observed directly with the senses.

BERNOULLI’S PRINCIPLE

‘As the velocity of a liquid or gas increases, its pressure decreases; and when the velocity decreases, its pressure increases’

At a narrow constriction in a pipe or tube, the speed of a gas or liquid is increased, but its pressure is decreased, according to Bernoulli’s principle. This effect is named the Venturi effect (and a pipe or tube with a narrow constriction the Venturi tube) after the Italian G.B. Venturi (1746-1822) who first observed it in constrictions in water channels. An atomiser works on the same principle.

 

The principle is expressed as a complex equation, but it can be summed up simply as the faster the flow the lower the pressure.

An aircraft wing’s curved upper surface is longer than the lower one, which ensures that air has to travel further and so faster over the top than it does below the wing. Hence the air pressure underneath is greater than on top of the wing, causing an upward force, called lift.

TIMELINE

MECHANICS

ANDERS CELSIUS (1701- 44)

1742 – Sweden

‘The temperature difference between the freezing point and the boiling point of water is a hundred degrees’

ANDERS CELSIUS

The scale was called centigrade but was renamed Celsius in 1969

In the fahrenheit scale introduced by the German-Dutch physicist DANIEL GABRIEL FAHRENHEIT the freezing point of water is set at 32 degrees and the boiling point at 212 degrees. Fahrenheit’s scale has been superseded by the metric Celsius scale, with water freezing at 0degrees C and boiling at 100degrees C

A conversion can be made from Fahrenheit to degrees Celsius by subtracting thirty-two and multiplying this figure by five and dividing by nine.

The kelvin scale is preferred

TIMELINE

TEMPERATURE

BENJAMIN FRANKLIN (1706-1790)

1752 – The New World

BENJAMIN FRANKLIN

‘If you would not be forgotten when you are dead and rotten, either write things worth reading, or do things worth writing about’

Curious about how just about everything works, from governments to lightning rods, Franklin’s legacy, in addition to the many inventions such as lightning conductors, bifocal lenses and street lamps, was one of learning. He established one of the first public libraries as well as one of the first universities in America, Pennsylvania. He established the Democratic Party. Franklin was one of the five signatories of the Declaration of Independence from Great Britain in 1776 and was a later participant in the drafting of the American Constitution.

‘Benjamin Franklin’s choice for the signs of electric charges leads to electric current being positive, even though the charge carriers themselves are negative — thereby cursing electrical engineers with confusing minus signs ever since.
The sign of the charge carriers could not be determined with the technology of Franklin’s time, so this isn’t his fault. It’s just bad luck’

Franklin was a pioneer in understanding the properties and potential of electricity. He undertook studies involving electric charge and introduced the terms ‘positive’ and ‘negative’ in explaining the way substances could be attracted to or repelled by each other according to the nature of their charge. He believed these charges ultimately cancelled each other out so that if something lost electrical charge, another substance would instantly gain the same amount.

 

His work on electricity climaxed with his kite flying experiment of 1752. In order to prove lightning to be a form of electricity, Franklin launched a kite into a thunderstorm on a long piece of conducting string. Tying the string to a capacitor, which became charged when struck by lightning, vindicated his theories.

TIMELINE

ELECTRICITY

LEONHARD EULER (1707- 83)

1755 – Switzerland

LEONHARD EULER

‘Analytical calculus – the study of infinite processes and their limits’

Swiss mathematician. His notation is even more far-reaching than that of LEIBNIZ and much of the mathematical notation that is in use to-day may be credited to Euler.

The number of theorems, equations and formulae named after him is enormous.
Euler made important discoveries in the analytic geometry of surfaces and the theory of differential equations.

Euler popularised the use of the symbols  ‘Π‘ (Pi);  e , for the base of the natural logarithm; and  i , for the imaginary unit.
Euler is credited with contributing the useful notations   f (x) , for the general function of  x ; and   Σ , to indicate a general sum of terms.

TIMELINE

MATHEMATICS

Related sites

• Leonhard Euler (usna.edu/)

JOSEPH BLACK (1728- 99)

1757 – Edinburgh

‘Different quantities of heat are required to bring equal weights of different materials to the same temperature’

JOSEPH BLACK

This definition relates to the concept of specific heat.

Through meticulous experimentation and measurement of results he discovered the concept of ‘latent heat’, the ability of matter to absorb heat without necessarily changing in temperature.
True in the transformation of ice into water at 0degrees C, the same principle applies in the process of transforming water to steam and indeed, all solids to liquids and all liquids to gases.
Through this work Black made the important distinction between heat and temperature.

JAMES WATT benefited from these discoveries during his development of the condensing steam engine.

‘Fixed Air’

Black’s insistence on the importance of quantitative experiments was a step towards setting the standard for modern chemistry.

Black found that heating or treating carbonate salts with acid resulted in the release of a gas that, he reasoned, must have been ‘fixed’ in the solids. He outlined the cycle of chemical changes from limestone (calcium carbonate) to quicklime (calcium oxide) and ‘fixed air’ (carbon dioxide) when heated; quicklime mixed with water to become slaked lime (calcium hydroxide); which when combined with ‘fixed air’ becomes limestone again (turning the solution cloudy).

Although JAN BAPTISTA VAN HELMONT had identified the existence of separate, distinct gases in air over a century before, Black is still often credited with the discovery of carbon dioxide (fixed air) – despite that van Helmont had clearly been aware of its existence.

Black was able to prove that carbon dioxide is made by respiration, through fermentation and in the burning of charcoal, but that the gas would not allow a candle to burn in it nor sustain animal life.

Black’s student Daniel Rutherford (1749 – 1819) called the gas ‘mephitic air’ after the mephitis of legend, a noxious emanation said to cause pestilence, for animals died in an atmosphere of the new gas. Rutherford’s ‘air’ is not, however, the same as Lavoisier’s mephitic air, which is nitrogen (azote).

Observing the effect that removing carbon dioxide from limestone made the latter more alkaline, Black deduced that carbon dioxide is an acidic gas.

TIMELINE

CHEMISTRY

JAMES WATT (1736-1819)

1765 – Glasgow, Lanarkshire, UK

‘Steam engine’

Watt’s steam engine was the driving force behind the industrial revolution and his development of the rotary engine in 1781 brought mechanisation to several industries such as weaving, spinning and transportation.

JAMES WATT

Although THOMAS NEWCOMEN had developed the steam engine before Watt was even born, Newcomen’s machines had been confined to the world of mining.

In 1764, when Watt was asked to repair a scale model of Newcomen’s engine he noted its huge inefficiency. The heating and cooling of the cylinder with every stroke wasted huge amounts of fuel; and wasted time in bringing the cylinder back up to steam producing temperature, which limited the frequency of strokes. He realised that the key to improved efficiency lay in condensing the steam in a separate container – thereby allowing the cylinder and piston to remain always hot. Watt continued to improve his steam engine and developed a way to make it work with a circular, rotary motion. Another of his improvements was the production of steam under pressure, thus increasing the temperature gap between source and sink and raising the efficiency in a manner later described by SADI CARNOT and elucidated by JAMES JOULE.

RICHARD ARKWRIGHT

RICHARD ARKWRIGHT was the first to realise the engine could be used to spin cotton, and later in weaving. Flour and paper mills were other early adopters, and in 1788 steam power was used to paddle marine transportation. In the same year, Watt developed the ‘centrifugal governor’ to regulate the speed of the engine and to keep it constant.

Watt 10hp engine

Watt was the first to coin the term ‘horsepower’, which he used when comparing how many horses it would require to provide the same pull as one of his machines. In 1882 the British Association named the ‘watt’ unit of power in his honour.

TIMELINE

HEAT

HENRY CAVENDISH (1731-1810)

1766 – England

‘Three Papers Containing Experiments On Factitious Airs’

(gases made from reactions between liquids and solids)

1798 – Density of the earth
Using a torsion balance and the application of NEWTON’s theory of gravity, Cavendish concluded that the earth’s density was 5.5 times that of water.

Born of the English aristocracy and inheritor of a huge sum of money half way through his life, Cavendish is remembered for his work in chemistry.
He demonstrated that hydrogen (inflammable air) and carbon dioxide (fixed air) were gases distinct from ‘atmospheric air’. His claim to the discovery that water was not a distinct element – a view held since the time of ARISTOTLE – but a compound made from two parts hydrogen to one part oxygen, became confused with similar observations made by ANTOINE LAVOISIER.

CAVENDISH

1871 – England

Almost all his discoveries remained unpublished until the late nineteenth century when his notes were found and JAMES CLERK MAXWELL dedicated himself to publishing Cavendish’s work, a task he completed in 1879.
By then many potential breakthroughs, significant at the time, had been surpassed by history.

In 1871 the endowment of the Cavendish Laboratory was made to Cambridge University by Cavendish’s legatees.

TIMELINE

KARL WILHELM SCHEELE (1742- 86)

1772 – France

CARL WILHELM SCHEELE

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

TIMELINE

JOSEPH PRIESTLEY (1733-1804)

1774 – England

JOSEPH PRIESTLY

‘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.

TIMELINE

CHEMISTRY

JOSEPH MONTGOLFIER (1740-1810)

1783 – France

‘ Frenchmen Joseph-Michel Montgolfier and his brother Jacques-Etienne (1745-99) observed a simple natural phenomenon and realised the ‘unachievable’ ‘

Replica of the historic Montgolfier hot air balloon in flight

MONTGOLFIER BROTHERS

 
 

TIMELINE

GAS LAWS

CHARLES DE COULOMB (1736-1806)

1785 – France

‘The force of attraction or repulsion between two charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them’

COULOMB

The region around a charged object where it exerts a force is called its electric field. Another charged object placed in this field will have a force exerted on it. Coulomb’s rule is used to calculate this force.

Coulomb, a French physicist, made a detailed study of electrical attractions and repulsions between various charged bodies and concluded that electrical forces follow the same type of law as gravitation. Coulomb found a similar principle linking the relationship of magnetic forces. He believed electricity and magnetism, however, to be two separate ‘fluids’.
It was left to HANS CHRISTIAN OERSTED, ANDRE-MARIE AMPERE and MICHAEL FARADAY to enunciate the phenomenon of electromagnetism.

The SI unit of electric charge, coulomb (C), one unit of which is shifted when a current of one ampere flows for one second, is named in his honour.

He also articulated Coulomb’s rule of friction, which outlines a proportional relationship between friction and pressure.

TIMELINE

ELECTRICITY

JACQUES-ALEXANDRE-CESARE CHARLES (1746-1823)

1787 – France

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

JACQUES CHARLES

In other words, if you double the temperature of a gas, you double its volume. In equation form:  V/T = constant, or  V₁/T₁ = V₂/T₂,  where  V₁ is the volume of the gas at a temperature  T₁ (in kelvin) and  V₂ the new volume at a new temperature  T₂.

This principle is now known as Charles’ Law (although sometimes named after GAY-LUSSAC because of his popularisation of it fifteen years later – Gay Lussac’s experimental proof was more accurate than Charles’).
It completed the two ‘gas laws’.

A fixed amount of any gas expands equally at the same increments in temperature, as long as it is at constant pressure.

Likewise for a decline in temperature, all gases reduce in volume at a common rate, to the point at about minus 273degrees C, where they would theoretically converge to zero volume. It is for this reason that the kelvin temperature scale later fixed its zero degree value at this point.

CHARLES’ Law and BOYLE‘s Law may be expressed as a single equation, pV/T = constant. If we also include AVOGADRO‘s law, the relationship becomes pV/nT = constant, where n is the number of molecules or number of moles.

The constant in this equation is called the gas constant and is shown by R
The equation – known as the ideal gas equation – is usually written as pV = nRT

Strictly, it applies to ideal gases only. An ideal gas obeys all the assumptions of the kinetic theory of gases. There are no ideal gases in nature, but under certain conditions all real gases approach ideal behaviour.

TIMELINE
 
GAS LAWS

Related sites

• NASA (nasa.gov)

Combined Gas Laws

ANTOINE LAVOISIER (1743- 94)

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

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.

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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CHEMISTRY

BENJAMIN THOMPSON (1753-1814) known as Count Rumford

1798 – England

‘Mechanical work can be converted into heat. Heat is the energy of motion of particles’

Heat is a form of energy associated with the random motion of atoms or molecules. Temperature is a measure of the hotness of an object.

COUNT RUMFORD

In the eighteenth century, scientists imagined heat as a flow of a fluid substance called CALORIC. Each object contained a certain amount of caloric. If caloric flowed out, the object’s temperature decreased; if more caloric flowed into the object, its temperature increased.

Like PHLOGISTON, caloric was a weightless fluid, a quality that could be transmitted from one substance to another, so that the first warmed the second up. What is being transmitted is heat energy.

Working for the Elector of Bavaria, Rumford investigated the heat generated during the reaming out of the metal core when the bore of a cannon is formed. According to the caloric theory, the heat was released from the shards of metal during boring; Rumford noticed that if the tools were blunt and removed little or no metal, more heat was generated, rather than less.

Rumford postulated that the heat source had to be the work done in drilling the hole. Heat was not an indestructible caloric fluid, as LAVOISIER had argued, but something that could come and go. Mechanical energy could produce heat and heat could lead to mechanical energy.

One analogy he drew was to a bell; heat was like sound, with cold being similar to low notes and hot, to high ones. Temperature was therefore just the frequency of the bell. A hot object would emit ‘calorific rays’, whilst a cold one would emit ‘frigorific rays’ – an idea raised in Plutarch’s De Primo Frigido. Cold was an entity in itself, not simply the absence of heat.

Rumford thought there was no separate caloric fluid and that the heat content of an object was associated with motion or internal vibrations – motion which in the case of the cannon was bolstered by the friction of the tools. He had recognized the relationship between heat energy and the physicists’ concept of ‘work’ – the transfer of energy from a system into the surroundings, caused by the work done, results in a difference in temperature.
This transfer of energy measured as a temperature difference is called ‘heat’.

Half a century was to pass before in 1849, JAMES JOULE established the ‘mechanical equivalent of heat’ and JAMES CLERK MAXWELL launched the kinetic theory. According to Maxwell, the heat content of a body is equivalent to the sum of the individual energies of motion (kinetic energies) of its constituent atoms and molecules.

US born Rumford founded the Royal Institution in London and invented the calorimeter, a device measuring heat.

TIMELINE

HEAT

EDWARD JENNER (1749-1823)

EDWARD JENNER

1798 – England

Vaccination

TIMELINE

MICROBES

THOMAS MALTHUS (1766-1834)

1798 – England

‘If unchecked, the human population would grow geometrically while the food supply could only grow arithmetically. In two centuries the population would be to the food supply 256:9’

(In an arithmetic series of numbers there is a common difference between any number and its successor, while in a geometric series each number is a constant multiple of the preceding number)

When Malthus, an obscure country curate, published his Essay on the Principle of Population it excited much attention and placed its author in the centre of a controversial political debate on population. The essay was denounced as unholy, atheistic and subversive of the social order. FRIEDRICH ENGELS, the cofounder of communism, criticised Malthus’ essay for underestimating science;

‘But science increases as fast as population – in the most normal conditions it also grows in geometrical progression – and what is impossible for science? ‘

THOMAS MALTHUS

Malthusian ideas form the foundations of some theories on the relationship between economics, population and the environment.
DARWIN wrote in his book ‘The Origin of Species’ that his theory ‘is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms’.

TIMELINE

JOSEPH LOUIS PROUST (1754-1826)

1799 – France

‘Chemical compounds contain elements in definite proportions by mass’

LOUIS JOSEPH PROUST

Proust’s law is now referred to as the law of constant composition or the law of definite proportions.

Claude Berthollet (1748-1822), then the recognised leader of science in France, rejected Proust’s law. Berthollet believed that the force of chemical affinity, like gravity, must be proportional to the masses of acting substances. He suggested that the composition of chemical compounds could vary widely. Proust showed that Berthollet’s experiments were not done on pure compounds, but rather on mixtures. Thus for the first time a clear distinction was made between mixtures and compounds.

When Dalton proposed his atomic theory, Proust’s law helped to confirm the hypothesis. According to Dalton, atoms would always combine in simple whole number ratios. For example, all water molecules are alike, consisting of two atoms of hydrogen and one atom of oxygen. Therefore, all water has the same composition.

Proust’s law has been confirmed by experiments. For example, water always contains 11.2 percent hydrogen and 88.8 percent oxygen.

In recent years chemists have discovered certain rare compounds in which elements do not combine in simple whole number ratios. These compounds are known as ‘berthollides’.
In contrast, compounds in which elements do combine in simple whole number ratios are sometimes referred to as ‘daltonides’.

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CHEMISTRY