The search for simple substances - National STEM Centre

The rch
for Simple
Substances
by Joan Solomon
Series editor Joan Solomon
!:mThe Association for
I:i:Ii Science Education
Ilr~~\lil~Un
N10886

Acknowledgements
The publishers would like to thank the following for
permission to reproduce illustrations on pages: 8 Indian
Tourist Office; 15 (top) J. M. Dent; 15 (bottom) Springer-Verlag,
Heidelberg; 27, 28, 30 Ann Ronan Picture Library; 34, 35, 46
The Director of the Royal Institution; 36 Penzance Town
Council; 42, 43 Nostovi Press Agency.
First published 1989by the Association for Science Education,
College Lane, Hatfield, Herts. ALI0 9AA. Telephone: 0707
267411.
© The Association for Science Education 1989
ISBN 0 86357 113 1
Illustrations by Deanna Hammond, ASE
Designed by Colin Barker MCSD
Printed by David Green Printers Limited, Kettering,
Northamptonshire

+The Search for Simple Substances
C€>nte
Chapter 1
Many different kinds of matter
Page 9 Chapter 2
The four elements
Page 17 Chapter 3
Islamic science - balance of the
elements
Page 25 Chapter 4
From tricks to unmixed
substances
Page 32 Chapter 5
Lots more elements

Valveless
bellows as used
for smelting iron
in the Sudan
I
Chop-_te_r_l _
Many different kinds
of matter
This is the story of how scientists have searched for
some simple substances from which everything else
might be made.
There are so many different materials in the world, and
most of them keep changing. The living stuff of animals
and plants grows, and then dies and seems to rot away. The
water in shallow ponds evaporates into the air. Ice and fat
melt into liquids when they are heated quite gently. Strong
fire can burn whole trees away to ashes.
Does anything stay the same? It must have seemed to
primitive people that only stone and rock were made of
substances which do not change.
Then at some time about 5,000 years ago someone discovered
the most amazing new change. There was a kind
of rock which could be changed by fire into a shining liquid
metal! Probably the earliest discovery was made somewhere
in modern Turkey, Iran or Iraq. The rocks people
5

Copper mine in
the Austrian
Tirol, c.looo BC
6
used were dull and black but the metal that they made
from them was gleaming copper. It was marvellous stuff
that could be used for weapons and for jewellery.
The usual way of working was to dig a mine down into the
right sort of rock. At the base of the mine-shaft a fire was
lit to produce the copper and to break up more of the rock
by its heat. The metal miners soon became a secret
underground group of people.
By the time the Bible was written copper, bronze and iron
mines were common in the desert of Sinai and in the south
of Israel. The author -ofthe Book of Job wrote:
"Iron is taken out of the earth,
And bronze is molten out of the stone.
Man sets an end to darkness ...
He breaks open a shaft far away from where people live ...
And underneath it is heated by {ire."
So much copper was produced in ancient Cyprus that the
name "cupric" came to be used for the metal itself. Much
of the copper was exported to Egypt.

Egyptian gold
workers, from a
tomb c.2400 Be.
Blow pipes
tipped with clay
are used at the
fire. Men on the
right beat out the
gold with stone
hammers
In Egypt another metal was known and used at the same
time as copper. That was gold. No fire change was required
to get the crude gold. All that was needed was to hammer
fragments of the right rock into pieces. After that they
ground it into a powder, and washed away the lighter part.
The bits of gold were left behind and could then be seen. In
some places the washing was done over a layer of sheepskin
fleeces. At the end of the process the gold particles
glinted in the wool of the fleece. (This may account for the
legend of "Jason and the Golden Fleece".)
Egyptian gold came in many different colours because it
was mixed with other metals. Some was almost as white as
silver, while gold from other mines could be a deeper
reddish colour. The Egyptians liked this variety and gave
different names to the different coloured alloys (mixtures)
of gold. They seemed to think these were different metals.
Soon the goldsmiths became skilled at changing one gold
alloy to another by heating it with special ingredientswith
silver, lead, copper, or even with salt and barley!
The use of iron began centuries later than copper, gold or
bronze. A much higher temperature and far more skill was
needed to get iron from rocks of the right kind. At first it
was so rare and valuable that iron was only used for
ornaments and jewellery. It was a splendidly strong metal
that could be hammered to give a sharp edge, but it was not
usually as unchanging as gold. Air and water turned iron
into useless rust.
The best iron workers in the ancient world were probably
those of north India. By 400 or 500 AD the craft of iron
casting had become so advanced that huge pillars could be
7

Iron pillar at
Delhi which
remains unrusted
since the 4th
century Be
8
made. A wrought iron column at Delhi weighs over 6
tonnes, is 8 metres high and 40 centimetres in diameter. It
would have been impossible to make anything like this in
Europe until the last century. The most mysterious thing
about this ancient column is that the iro.n has not rusted.
And no one knows why. Perhaps the Indian metal workers
had some secret way of treating the surface of the iron,
which we still do not understand.
By the third and second centuries BC the metal workers of
Egypt, China and India knew about many changes of
substance. Now, with the use of fires blown hot with
bellows, they could transform (change) many kinds of rock
and metal.
We have no idea whether these skilled craftsmen of the
ancient world had any explanations for how one substance
could change into another.

Painting on an
A"ic vase
showing the
forge of
Hephaistos in the
6th century Be
I
Chap-_te_r_2 _
The four elements
The ancient Greeks had lots of theories about
substances. They sawall the changes going on
around them, but felt sure that things do not
disappear altogether. There might be some basic
element (simple substance), they thought, from which
everything is made. The element would always be there
behind all the changes.
Some Greeks thought that this basic element might be
water because their crops needed it to grow. Did that mean
that corn and fruit were made out of water? Water could be
frozen into ice. Ice could be melted back into water.
"Water", said some, "is the element out of which all other
substances come."
Air or steam seemed more important to others. Rain brings
water falling out of the air, but when the sun shines the
water turns back again into steam and rises up into the air.
We all need air to breathe. "Blow air out on to your hand
9

Four elements on
the large square,
four qualities on
the small square
10
and it is cold if your mouth is squeezed tight. Blow again
with your mouth wide open and it is warm. You see", they
said, "air is like life and heat. Air is the element of all
things."
There were other ideas too. Some thought that fire was the
basic element out of which all things are made. It could
certainly make powerful changes happen to rock or metal.
Others thought the elementary substance might be earth
or rock.
Finally there was a theory that all four elements-
EARTH, AIR, FIRE, and WATER-are needed to make all
the known substances. That included animals and· people.
Put the elements together in exactly the right amounts and
you get a living creature. At death all the elements
separate again. They might have shown how this worked
out in a compost heap. They could have pointed to the soil,
the steam, the heat and the moisture-all the four unmixed
elements were coming out of the dead material again.
Their theory must be right!
AIR
FIRE
WATER
EARTH
The Greeks were very good at this kind of guessing but not
so good at doing experiments. About 330 Be the theory
about elements met the people who could do the practical

Mithraic cameo
work. The Greek army under Alexander the Great
conquered Egypt. In the great city of Alexandria, named
after the conqueror, a new science of materials was going
to start.
This science was called "Alchemy" from Chern or Ham, an
old name for Egypt. Modern chemistry, which is still the
study of substances and what they are made from, grew out
of alchemy.
Alexandria was a bustling port with travellers from all
over the world. They brought precious substances and new
ideas. There was a great library there with hand-written
scrolls of all the books that were known. At one time there
were some 700,000books there. People came from far and
wide to read and discuss the ideas. There were Jews from
Israel with their religion of Judaism. In later times there
were also Roman soldiers with their religion of the god
Mithras. The Jews and the Romans learnt about the Four
Element Theory and found room for it in their own prayers
or writings.
"Oh first Element of the fire within me,
first Element of the water in me ... "
So prayed the Roman soldiers to their god Mithras,
perhaps even when they travelled far north into distant
Britain.
The theory about four elements which make up all
substances should have helped the metal workers. They
11

12
had been busy working with gold, silver and copper. They
could change the colour of a metal by alloying it with
another. They believed they had made quite new metals.
The Four Element Theory predicted that earth, air, fire
and water, in the right proportions, could make anythingthat
included gold.
Alchemists who were greedy for wealth, or just curious
about substances, became keen to do experiments. They
invented new pieces of apparatus and found many new
substances. It was an exciting time for science.
There had been an early method of purifying gold which
used an earthenware pot. (This was similar to the material
of a garden flower pot-not the plastic kind.) Impure gold
was put into it, lead was added, and it was heated strongly.
The impurities were driven off into the air, or into the
pores of the pot (like a lead glaze). At the end a pure
gleaming button of molten gold could be seen.
Now the alchemists wanted to mix substances together so
that the four elements in them could combine to make gold.
They used their traditional round earthenware pots with
lids. They sealed all round the lid with clay so that nothing
could escape. Then they heated the pot for days and days
hoping and praying that gold would be made. You can
imagine the excitement of breaking open the seal to look
inside!
We do not know what they found, but we still use the
phrase "hermetically sealed" after the name of an ancient
teacher of alchemy, Hermes Trismegistos.
They also wanted to separate out the elements from
substances. New kinds of apparatus were needed. Another
ancient alchemist called Mary the Jewess invented the
earliest kind of distilling apparatus. The substance was put
in the main flask at the bottom (see the diagram). This was
heated on a furnace and vapours from it went up into the
copper sphere at the top. Then it cooled, condensed, and
collected in flasks fitted to its three arms. The apparatus
was made of copper or bronze and each of its arms was a
tube nearly a metre long.

Distilling
apparatus said to
have been made
by Mary the
Jewess c.100 AD
Earthenware
tube
Copperhead
and tubes
At the top each tube had to be sealed carefully into the
sphere above the main flask. This was not so easy as it
would be today because neither cork stoppers nor rubber
bungs had been invented. Instead the alchemists made a
special sealing paste out of clay, camel dung and chopped
hair. This may have kept the vapours in but probably smelt
quite horrible when it got hot!
Another piece of apparatus that Mary was supposed to
have designed was a kind of water bath. The substance was
put in at A above the boiling water (see diagram on the
next page). The steam heated it quite gently and carried its
vapours to the top. Here it cooled a little and dripped down
into the dish at B. In French a water bath is still called
"bain Marie" in her honour to this day. Yet still no one
knows when or where she lived.
What experiments was this apparatus used for? We cannot
be quite sure. We know that early water baths were simply
used for keeping beeswax paints soft and ready to use.
They did not need a top on the apparatus for that. The
alchemists wanted to separate the elements of things. So
13

Early apparatus
for distillation
14
they heated all kinds of substances in these new sealed
distilling flasks.
When they heated sulphur alone in Mary's distilling
apparatus they got condensed crystals of sulphur
("flowers" of sulphur). When they heated mercury they got
condensed droplets of shining mercury. Some of the
alchemists may have begun to wonder if these two
substances-sulphur and mercury-could be the elements.
They certainly did not seem to change however hot they
had been heated.
Then some of these early chemists tried using boiling
sulphur instead of boiling water. The fumes of sulphur
inside the apparatus attacked any metals placed on the
sieve above (see the picture above). Copper turned black
and so did silver, but zinc turned white. They found these
colour changes magical and mysterious. Best of all were
the colours made by heating mercury with the sulphur.
Then they got a whole series of red and orange powders.
The alchemists among them, who hoped to make gold, may
have believed that they were getting nearer to the precious
metal itself.

Jabir's waterbath
(from -The
Works of Geber',
Englished by R.
Russell)
Jabir's apparatus
for distillation
with astrology
symbols in top
right-hand corner
(from -Die
Alchemie des
Geber' by E.
Darmstaedter)
These Egyptian and Greek chemists made great progress.
They found many new substances but their theory about
the four elements did not help them very much. Their
prediction from this was that gold could be made from
other substances which contained Earth, Air, Fire and
Water. When they tried this and failed to get gold they
could not guess what had gone wrong.
15

16
Far away in China the same unsuccessful hunt for gold
was also going on.
Probably the practical craftsmen, both in the West and in
the East, did not bother much with the theory. The metal
workers, dyers, glass makers, and chemists had plenty of
technological knowledge, and did not expect gold. The
philosophers, on the other hand, did no experiments at all.
They just hung on to their theory and even wrote
mysterious religious poetry about it. Without good
predictions which could be tested by new experiments, the
Four Element Theory remained little more than mere
imagination.

I
Chop-_te_r_3 _
Islamic science-
balance of the
elements
The year 622 AD was of great significance for Islam
and for the whole of the Middle East. It was also to be
very important for science. This was the year when
the prophet Mohammed began teaching the new
religion of Islam. His followers not only united all the Arab
tribes in Saudi Arabia, they also swept through country
after country spreading the teachings of Islam and the
Arabic language. In 640 AD the city of Alexandria fell to
them, and with it the centre of old Greek science. The great
library of the Museum had already been fought over more
than once, and many books had been damaged. This time it
was finally destroyed. It is said that the ancient handwritten
books in it-often the only copies in the whole
world-were burnt in a furnace and kept the public baths
heated for several months.
17

Jabir's theory of
how metals were
made from
mercury and
sulphur
18
The Arab armies marched west across North Africa and up
into Spain. They also went east across Iran and on to the
borders of China itself. It was an enormous empire; but one
of the things that made it different from the empires of
Greece and Rome·was that the Arabs left their language
and religion in country after country. This meant that all
the peoples who lived in the vast area from Spain to the
new city of Baghdad could speak together in Arabic. They
read the same books and shared the same religious view of
the world. Being able to understand the same language
was very important for the growth and spread of science.
The Arabs set up new centres of learning in Morocco and
Iran. They had the remaining Greek books on science
translated into Arabic, and they began their own experiments.
Within a century or so important new theories and
discoveries were already being made.
Ibn Hayyin, usually known as Jabir (or Geber), was the
first of the great Islamic chemists. (He was doctor to the
Caliph Haroun AI-Rashid famous from the stories of the
"Arabian Nights".)
In some ways Jabir continued the alchemy of Greek Egypt.
He accepted the Four Element Theory, but had a new idea
about sulphur and mercury.
Wet, cool
vapour
SULPHUR-fire + earth =dry and hot
MER CUR Y-air + water = wet and cool
FIRE
A'R0~RTH
~ WATER .
1__ -
Dry, hot
smoke
• SULPHUR
~
• MERCURY ~ Metals

Jabir's ·"Magic
Square" of
numbers
Gold could be made out of a combination of "Pure
Sulphur" and "Pure Mercury" in perfect proportions. If
either substance was impure-as they always were-the
result, he thought, would be some other metal.
Arab science was different in another way. They were
looking for perfect proportions and a pattern of numbers
which would describe how the different metals could be
made from sulphur and mercury. For this Jabir used the
"Magic Square" of numbers. Each number related to the
metal's proportions of the ideal elements.
See if you can find out what is special about this number
square by adding up the rows, columns and diagonals.
4 9 2
3 5 7
8 1 6
There is much more about Arabic alchemy which is hard
for us to understand now. They believed that the metals
were related to the sun, moon and planets. They were also
looking for an "elixir" which would help to make the
proportions of sulphur and mercury just right. This elixir
and the mysterious "philosopher's stone" would change
metals into gold, they thought. In the same way an "elixir"
was a medicine which would give back perfect health to
sick people. The Arabs thought that people, metals, the
planets and the universe itself all had their own
proportions and patterns. This gave them an explanation
for health, for the properties of metals, and for astronomy.
It was a model which could be used, they hoped, for
predicting the results of new experiments.
19

The Islamic
Theory of the
Four Elements in
the human body.
It shows the
characteristics of
people having
too much of
each, where they
are in the body,
and the seasons
of the year
which correspond
to the effects of
each element
Steam oven for
the distillation of
flowers to make
rose-water, from
a 14th century
Arab manuscript
20
autumn
J abir was a brilliant practical scientist. He left
instructions for making white lead (carbonate), sal
ammoniac, nitric acid, sulphuric acid, and many other
substances. He knew that the flame test for copper was
green, and how to use manganese dioxide to colour glass.
Jabir and other chemists improved the distilling apparatus
of the Greeks. They made alcohol-J abir called it "the fire
that burns at the mouth of bottles due to boiling wine and
salt". It was not, of course, used for drinking.

About the same time the perfume industry began. The
Arabs used gallons of rose-water for sweets like turkish
delight, as well as for perfumes. They made it by putting
rose petals in a steam distillation apparatus so that the
flower oils were gently removed in the steam and then
condensed.
Al-Razi was a later Arabic chemist who lived near Teheran
in Iran. He was a famous doctor and teacher of science. He
is said to have distilled alcohol to use in medicine. He also
distilled paraffin from crude petroleum. Apparently he used
this paraffin in his laboratory heater-the very first kind of
bunsen burner!
Most of all Al-Razi should be remembered for the table of
substances that he drew up. He was the first person to
think of separating things into animal, vegetable and
mineral. He named at least 53 of the chemicals we know
today, and left instructions for making most of them. He
made hydrochloric acid which he called "spirits of salt" (as
some people still do). Perhaps he tried pouring his new acid
on to limestone because he wrote that it was "a very strong
liquid which can even break stone".
Mineral
Spirits
(distilled)
Mercury
Sulphur
etc
I
Vegetable
Solid
(metals)
Gold
Silver
Copper
Iron
lead
Tin
"Chine:e iron"
(Still no one knows
what that was)
ALL SUBSTANCES
I
Stones
(ores)
Pyrites
Haematite
Malachite
Glass
etc
Animal
Pearl
Blood
etc
Vitriols
(sulphates)
Blue
Red
Black
Yellow
etc
Borates
(rock)
Borax
etc
Man-made
Oxides
Acids
etc
Salts
Soda
AI-qali
Lime
Sugar
etc
21

University
mosque at Fez.
The university
was founded in
the 9th century
AD
22
So great were the discoveries of Arab chemistry that we
still use many of their words even now, more than a
thousand years later.
AI-qali
Natron
Elixir
Sugar
Alcohol
Cinnabar
Naphtha
(Potassium carbonate) hence "alkali"
(Sodium carbonate) and hence Na for sodium.
(the ore of mercury)
(distilled from petroleum),
... and several others.
Perhaps the greatest achievement of all was that the Arabs
stopped just writing about the four elements and began to
list all the real chemicals that they had made.

Illustration from
an ancient
Arabic book on
anatomy
One of the last of the great Arab scientists was Abu Ali ibn
Bina, known as Avicenna. He argued that metals could not
really be changed into gold at all. They could only look
like it.
"Such accurate imitations," said Avicenna, "could deceive even
the cleverest, but I do not think that real change happens. Indeed I
think it is quite impossible to split up one metal into another."
That doubt of Avicenna's was valuable. When new
experiments are done the results sometimes do not fit very
well with old ideas or theories. The theories of alchemy
were to take many centuries to give way to more modern
ones. This was partly because alchemy was so strongly
linked to the religious view of the world. Islam allowed
scientists complete freedom of thought, but old ideas are
often difficult to shift.
Avicenna had read about the old Greek theory of atoms
and began to write about them too. The remark he made
about metals not being split up suggests he had an idea
23

24
that metals might themselves be simple substances. He
wrote nearly 100books, not all of which still exist, and died
in 1036.(That is 30 years before William the Conqueror set
out to invade Britain!). After his death there were few to
carryon with his ideas.
As a doctor Avicenna used the Islamic idea of balance and
proportion between the four qualities in a healthy body.
They were hot, cold, dry and moist. Years later when the
work was translated into Latin his ideas were taught to
every European doctor. Unfortunately his views on
chemistry were not so widely known.

The laboratory of
Thomas Norton,
an alchemist of
lristol c.1477
Europe was in the "Dark Ages" while early Greek and
Arabic science was going on. None of the Greek
books on science were available. When, at last,
scholars heard about the knowledge of the Arabs they
had to go to Spain or Sicily to learn more and to read the
books. Both countries were occupied by the Arabs. The
Book of the Composition of Alchemy was published in 1144,
and translated in Spain from Arabic into Latin, by Robert
of Chester. This was the very first book on alchemy in
Europe. Others followed, and they raised a lot of interest.
There were plenty of good European craftsmen aroundmetal
workers, glass makers, dyers, painters who made
paints, and potters who made beautiful glazes. But the idea
of turning metals, such as lead, into gold was new and
exciting. The books were read to learn how to use the
"elixir" and "the philosopher's stone". Most of the readers
were far more interested in wealth than in science. They
thought they understood about the Four Element Theory,
25

Woman
laboratory
assistant, from a
book on brandy
published in
1512
26
and about Pure Sulphur and Pure Mercury. Some added
Salt to make a third basic element. They read every story
about alchemy they could find and believed every word,
but they did not understand at all the Islamic idea about
health and balance in the universe. No one knew that some
of the Arabs had already realised that the Four Element
Theory did not work out in practice.
For hundreds of years cheats pretended that they knew the
recipe for making gold, and far too many people listened to
them. Most were tricked out of their money by the sight of
a little "alchemical gold" which was supposed to be
especially bright and red. Even noblemen and kings fell for
the idea. Indeed our own King Charles II, who lived as late
as the seventeenth century, was keen on alchemy. So was
the great scientist Sir Isaac Newton.
It sometimes happened that a lock of hair from some great
person from the past was preserved in a casket after they
died. This can provide useful evidence about their health.
If people breathe in the fumes of mercury it can poison
them: traces of it are also absorbed into their bones and
hair. Recently scientists have analysed the hairs of Isaac
Newtonand Charles II. Both contained mercury. The
King's hair had enough in it to have sent him mad, and
killed him. Perhaps he had done too many alchemical
experiments heating mercury and sulphur together to
make gold!,

Charles II
Almost everyone believed in alchemy right up until the
seventeenth century. It needed a very confident person to
cast doubt on it.
Then, in 1677,the Irish scientist Robert Boyle did just that.
He challenged the theory of the elements, both the
Mercury Sulphur Theory and the Greek Four Element
Theory . Boyle wrote a book called The Sceptical Chemist
(sceptical means difficult to convince). He wrote it as a
discussion between friends most of whom believe in the old
theory of the elements. Just one of them does not and he
gives Boyle's own point of view. Put into modern English
the arguments ran like this .
• How could you tell which are the simple and unmixed
substances? Can you separate things into their
elements?
• Take a piece of wood. If you burn it on the open fire
you get soot and ashes. Are these its elements?
27

Robert Boyle
28
• Take another piece of wood and heat it inside your
distilling apparatus. This time you get oil, spirit, vinegar,
water and charcoal. Are these its elements?
• Two elements or five?
"Oh dear" s'aid Boyle. "Neither three elements (mercury,
sulphur, and salt) nor four elements. What has gone wrong
with your theory?"
• Now think about how soap is made. You mix water and
salt, with oil or grease. You heat it in the fire and it all
combines into one lump. Then you heat it hotter still
and it separates again. This time it makes a soapy part
and a watery part.
• I knew a lawyer once who heated gold and silver in
closed flasks for 100days non-stop. In the end both
metals looked the same and weighed just exactly what
they did at the beginning.

Boyle and other
chemists called
their distilling
flasks "pelicans"
because they
looked like birds.
Did they?
"So you see, I don't think that fire does separate
substances into their elements," said Boyle. "Or do you
think that both gold and silver are elements?"
• So you believe that this vitriolic acid is made of
mercury because it is cold and wet, do you? And
turpentine too?
• Well I heated the two together, very carefully so that
they did not explode, and then distilled off the vapour.
It made solid sulphur! It looked like sulphur, smelled
like sulphur, and burned with a blue flame like sulphur.
"That must be worrying for you" said Boyle. "I thought
you said that sulphur was the opposite element to
mercury?"
After the book was published nothing in chemistry was
quite the same again. Robert Boyle said elements must be
simple and unmixed substances, but he did not think anyone
yet knew which ones they were. So the race was on to
find out which substances really were elements-and it
was just as hard as Boyle had expected.
One experiment difficult to understand was how plant
substances grow. One scientist grew a willow tree in a tub
for over five years giving it only water. He weighed it at
29

Antoine Lavoisier
30
the beginning and at the end. Of course it had gained
enormously in weight, but the soil in the pot had only lost
a little weight. Perhaps, he thought, wood is made from
water. (Do you know how the woody substance was made?)
Robert Boyle and others did experiments on air. In a closed
jar neither breathing nor burning can go on indefinitely.
But is the air used up? It still seems to be there. No one was
sure.
There had been explosions inside bubbling flasks. Are
there different kinds of air?
When things burn do they get heavier or lighter?
During the century after BoyIe's book was published lots
of careful experiments were done. The great French
chemist Antoine Lavoisier showed how burning could be
understood, and collected pure oxygen. Others contributed
experiments which included careful weighing. By 1789
Lavoisier was ready to write a book. In it he gave a list of
what he thought were "simple and unmixed substances",
as Boyle had said elements ought to be.

Light
TABLE OF SIMPLE SUBSTANCES (according to Lavoisier)
Caloric (heat)
Oxygen
Nitrogen
Hydrogen
Sulphur
Phosphorus
Charcoal
Muriatic (?)
(from the sea)
Fluoric (?)
Boracic (?)
Antimony
Arsenic
Bismuth
Cobalt
Copper
Gold
Iron
lead
Manganese
Mercury
Molybdena
Nickel
Silver
Tin, Tungsten,
Zinc
Lime
Magnesia
Barytes
Clay
Siliceous or
glassy rock
Lavoisier guessed that he had not got it all right. He was
particularly worried about the last column of "simple
earthy substances"-but it was the best he could do.
Lavoisier wrote:
"Thus chemistry advances towards perfection by dividing and
sub-dividing. It is impossible to say where it is going to end. And
these things, that we at present suppose to be simple, may soon turn
out to be otherwise."
Lavoisier wanted to go on with his experiments but the
French Revolution broke out. In 1793he was arrested and
thrown into prison. The next year he was charged with
"plotting with the enemies of France" (which he had not).
He was executed by guillotine, without a trial, on the
following day.
31

Davy's ba"ery
32
I
ChaR_te_r_5 _
Lots more elements
The search for elements went on. One of the next to be
discovered was the choking green gas we call
"chlorine". Lavoisier had it called "muriatic",
thinking it was in salt and in hydrochloric acid.
There was a lot of argument about whether it really was an
element, or if it contained oxygen. How could you be sure?
How were chemists ever to know if they had got a new
element or a combination of other elements?
The Arabic scientists of a thousand years earlier had
already thought of one way to answer this important
question-"Find a pattern of numbers that all the elements
will fit into". Jabir, you will remember, thought this
pattern might be the Magic Number square. He wanted to
fit the "proportions" of the elements into it-but it never
quite worked out. Now the later European scientists had to
find a pattern to make sense of all their elements. Then
they could be more sure about new ones. Each element
would have a"special place or number to fit into.
The first signs of a pattern began to appear, very dimly,
from the work of an enthusiastic young chemist called
Zinc and silver plates in acid
+

Humphry Davy. He used a new way to split up substances
using electricity. The electric battery had only just been
invented. One of the first experiments Davy did was to
show that when electricity was passed through water it
split it up into hydrogen and oxygen. He noticed that you
got nearly twice as much hydrogen as oxygen. But
"nearly" was not good enough for Davy. He felt sure that
the two to one proportion should be exact. To get a really
accurate answer he changed his apparatus. First he used
different kinds of glass, then he made it of different metals.
He guessed that some of the gases were being absorbed into
the glass. At last, in the purest conditions possible, he
managed to get the elements hydrogen and oxygen in
proportions of exactly two to one, as far as he could tell.
Davy was triumphant. He really enjoyed the fun of doing
experiments and proving that his predictions were right.
He loved showing them off to audiences too!
The electric battery was a wonderful gift to chemistry. We
might say it was a new technology. With its help Davy was
to separate at least four new elements.
tfNothing," said Davy, tftends so much to the advancement of new
knowledge as a new instrument."
The first of his new elements was potassium. Most people
thought that potash (from the old Al-qali that the Arabs
had first separated from wood ash) was itself an element.
But Lavoisier had not been sure about this, and neither
was Davy. When potash was dissolved in water,
electrolysis with a battery only gave hydrogen and
oxygen-probably from the water. So Davy used the potash
dry and heated it until it melted into a liquid. Now he
found that it would not conduct electricity at all. So he
tried again, moistening the potash very slightly-and
suddenly it worked. There was smoke and flame. At the
negative side of the battery small globules of a shining
metal could be seen appearing and then bursting into
bright purple flames.
33

Davy's
experiment to get
potassium from
potash
Gilray cartoon of
a ledure by
Humphry Davy
at the Royal
Institution~ during
which laughing
gas was given to
a fat gentleman
34
Platinum (negative)
It was all so exciting that Davy simply danced around the
laboratory shouting. His brother said it was a full half
hour before he could get a word of sense out of him. Davy
was even more delighted when he found out what a curious
metal potassium was-so light that it floated in water, so
soft that you could cut it with a knife, and so explosive
that it burst into flame in air or in water! Davy gave it the
name "potassium", and wrote that it was like the kind of
metal that ancient alchemists had imagined.
A few days later Davy tried to split up soda (sodium oxide)
with electricity. Again he was successful and got another
light, soft metal. This time it burnt with a yellow flame
(like yellow street lights). Davy called it "sodium".

Miners' safety
lamps
Then Davy wanted to use electricity to split up Lavoisier's
"earthy substances" into their elements, but he fell ill.
Davy was always interested in doing practical explorations
to invent ways of helping people. Much earlier in his life
he had bravely shown that a gas-"laughing gas"-could
be breathed safely. It made him happy and light-headed. He
promptly suggested that doctors could use it as an
anaesthetic for painless operations. No one took any
notice. Anaesthetics were not used for another 50 years.
Later in his life Davy invented a way to prevent corrosion
of copper. He also made a safety lamp to be used by miners.
It provided light without setting fire to the explosive gas
which was such a danger in coal mines.
Just as Davy was going to start investigating lime and
magnesia-the "earthy substances"-someone asked for
his help again. There were bad fevers among prisoners in
Newgate jail. Could Davy invent a ventilation system to
keep the air pure? He went off to have a look at the prison
and caught the fever himself. He very nearly died. When at
last he recovered Davy heard that a French chemist had
just succeeded in separating two new elements. They were
calcium and magnesium, from lime and magnesia.
Davy became very famous while he was still quite young.
He was awarded a medal for his work by the French, even
though Britain was then at war with France. He actually
travelled to Paris to receive the medal from the Emperor
35

Sir Humphry
Davy
36
Napoleon himself. (It is hard to imagine an English
scientist being given a medal by Germans during the
Second World War. Even harder to think of travelling
through enemy territory to receive it from Hitler!)
While Davy was in France he heard about a new substance
made from iodic acid. This was the element iodine. He
rushed to examine it and was soon convinced that it
behaved like chlorine did.
Humphry Davy was knighted for his work and became
President of the Royal Society, the top position for a
scientist in Britain. He continued working hard to show
that sodium and potassium were really elements and did
not contain other substances. Altogether 40 different
elements were known in Davy's time-the first 30 years of
the nineteenth century. He thought that this was likely to
be too many.

Maybe the
positive and
negative parts of
substances attract
each other
Davy suspected that what were called metal elements
might have hydrogen combined in them. After all they
reacted with acids to give off hydrogen. Perhaps the
hydrogen came from them? Or did it come from the acid? It
was hard to say. Davy was shown to be right about
ammonia which others thought might be a metal. It did
contain hydrogen; but we do not now think he was right
about the others.
He also had a theory that all the elements had electric
charges in them which they used for combining together.
He guessed that was why electricity split the compounds
apart, but he could not quite prove it by experiments.
Humphry Davy was usually brilliant at doing experiments
but not so interested in thinking about theories.
"Hypotheses (new ideas)", he said, "are only useful if they lead to
new experiments."
That was how he had discovered so many new elements.
Sometimes it is necessary to imagine a whole new theory if
you want to make sense of many different experiments. A
theory gives you a new way of looking at things and may
suggest a new pattern to look for. There was a theory at
that time about all substances being made up of tiny
unseen atoms. Davy himself had done an experiment to
show that water was made up of exactly twice as much
hydrogen as oxygen. Most other scientists at that time
thought this proved that there were two atoms of hydrogen
and one of oxygen joined together to make water. Davy did
not even believe that substances were made up of atoms.
~.
37

38
. What Davy's work did show was that there were groups of
similar elements. Potassium was very like sodium. Iodine
was very like chlorine. Davy was well aware of these
similarities, but he could not use them to make a new
theory for all the elements. It was only a beginning to
finding an important pattern for the elements.

I
Chop-_te_r_6 _
The pattern appears,
at last
By the nineteenth century science was going on in
most of the European countries, and many of the
scientists were doing the same kind of studies. They
had begun to travel, as Davy had done, to meet each
other and discuss their experiments. By 1860, when our
Queen Victoria had already been on the throne for nearly
30 years, the problem of scientists keeping in touch with
each other was becoming quite serious. It would have been
stupid to do an experiment that another scientist had
already done, so they wanted to know what was going on.
They needed to talk together and swap ideas. Finally all
the scientists who were interested in atoms and elements,
arranged to have an international conference. Nowadays
there are many conferences, and scientists get to travel
quite widely; but this was the first international conference
on chemistry.
They met in Karlsruhe, a town in West Germany.
Scientists came from countries as far away as Italy and
Russia. They had a lot of problems about elements and
atoms to argue about.
By this time most chemists believed in the tiny invisible
atoms. These were far too small to measure or to weigh
directly, but scientists were busy trying to find out how
heavy they were compared with each other. It was easy to
guess that the lead atoms were heavier than the hydrogen
atoms-but how much heavier were they? Scientists
already knew that water was made from the elements
hydrogen and oxygen. It was not too hard to find out how
39

40
much heavier steam was than hydrogen-but how many
atoms were joined together in hydrogen? And how many
were there in steam?
Was hydrogen like this ® or like this?

So 200 milligrams of mercury combined with 8 milligrams
of oxygen. Were the weights of the mercury and oxygen
atoms in the ratio of 200 to 8?
Or were there two mercury atoms to each one oxygen atom
like this (fJ)j§fffy?
That would mean a ratio of 100 to 8. How could you tell?
By the time of the Karlsruhe conference some chemists
thought one answer was right. Some thought the other was
right.
One of the scientists at the conference was a Sicilian-
Stanislao Cannizzaro. He had been a revolutionary as a
young man. He fought for the freedom of Sicily against the
King of Naples, but the rebellion failed. Cannizzaro was
one of the last to give in: he had escaped at the last
moment, in a small boat, to go to France. By the time of the
famous conference, Cannizzaro had been allowed back into
Italy to be a professor of chemistry in Genoa. He travelled
eagerly to Karlsruhe.
At the meeting Cannizzaro spoke about his new ideas for
finding out the weights of atoms of the different elements.
He also suggested that scientists should all agree to take
the hydrogen atom, the lightest of them all, as atomic
weight 1. Then if something was ten times as heavy, atom
for atom, it would have "atomic weight" of 10. And so on.
He thought this would be a great step forward from
comparing everything with the weight of air. (Why was air
not a good idea?) The others soon agreed with him.
You may have guessed that one of the useful results of this
agreement was that there was now a number for every
element. Each had atoms of a different weight. If there
were numbers, perhaps a pattern could be found?
During the next ten years at least three separate scientists
started seeing patterns for the elements. One was an
Englishman, one a German, and one a Russian. All three
saw that the similar elements-sodium and potassium,
chlorine and iodine-had similar places with special
numbers ... but ...
41

Dimitri Ivanovich
Mendeleev
42
It would be best to go back to the beginning and explain
how just one of these discoveries came about. This, then, is
the story of "Mendeleev's Table".
Dimitri Ivanovich Mendeleev was born 26 years before the
famous conference at Karlsruhe, thousands of miles away
in distant Siberia. He was the fourteenth and youngest
child. His mother was a remarkable woman. When her
husband died she brought up her large family, and ran the
family's glass factory. She taught her son science, too.
When she saw how gifted young Dimitri was, she spent all
her savings taking him to Moscow to be educated. Dimitri
said that her dying words to him were "Search patiently
for the truth about religion and about science."
Dimitri worked hard as a research scientist, first in Russia
and later in Germany. He was there when the international
conference about atoms was held. So he went to Karlsruhe
to listen. He heard Cannizzaro's talk about atomic weights,
and was very interested.

Russian peasants
before the
Revolution
Mendeleev returned home the next year, just as the Czar of
Russia was freeing the serfs (farm slaves owned by the
landlords). Many in the country were very poor and
Mendeleev spent quite a lot of his time using his
knowledge of science to help them. He travelled round the
country giving advice on cheese-making to groups of
farmers and freed serfs. He studied what was known about
exploring for petroleum to help make Russia richer. He
carried out experiments in agriculture on his own farm.
Finally his ideas became too democratic to please the Czar
and he was forced to retire from being a professor.
While Mendeleev was a professor of chemistry he had
classes of university students to teach. When he found that
there was no good chemistry textbook for them, he began
writing his own. There were so many elements discovered
by then-more than 6o-and now, thanks to Cannizzaro
they all had fairly reliable atomic weights. Mendeleev
wondered how he should arrange them in his book so that
the ones that were like each other could go together. In his
first chapter he described Davy's metals-sodium and
potassium and added three other new ones which were like
them. Then he described the "earth metals" calcium,
magnesium and a new metal called beryllium which
seemed to be like them.
43

Periodic Table
according to D. I.
Mendeleev, 1869
44
About this time, while Mendeleev was arranging the
elements for writing his book, he had a break-through. He
had just written down the names of some of the elements
with their atomic weights beside them. Suddenly he could
see the beginnings of a pattern. He got excited about this.
Mendeleev was used to playing the card game "patience"
by himself while he was travelling. He had the idea of
making a pack of cards for the elements. He wrote the
name and the atomic weight of each element on a separate
card and began sorting them out-and an amazing thing
happened. If he dealt out his element-cards in piles in the
order of their atomic weights, Mendeleev found that he
could get piles of the similar elements. First he dealt out 2,
then 7, then another 7 on top of them, then 12in a separate
pile, then another run of 7 on to the earlier piles. It was
amazing. Not only did the sodium and potassium group
come together but also the chlorine and iodine group. So
did most of the other elements.
Was it just a lucky chance? Mendeleev became more and
more convinced that his discovery was important when he
found that the shapes of crystals, and how the atoms of the
elements linked together, also fitted the same run of
numbers. The idea for the patterns ("periods" he called
them) came to him in a single day, but he spent three years
getting it right before he published his famous book on
chemistry for his students.
H=1
Be= 9,4
B=l1
C=12
N=14
0=16
F=19
Li=7 Na=23
Mg=24
AI=27,4
8i=28
P=31
8=32
CI=35,5
K=39
Ca=40
?=45
?Er=56
?Yt=60
?In=75,6
Ti=50
V=51
Cr=52
Mn=55
Fe=56
Ni=Co=59
Cu=63,4
Zn=65,2
?=68
?=70
As=75
8e=79,4
Br=80
Rb=85,4
8r=87,6
Ce=92
La=94
Di=95
Th=118?
Zr= 90
Nb= 94
Mo= 96
Rh=104,4
Ru=104,4
Pd=106,6
Ag=108
Cd=112
Ur=116
8n=118
8b=122
Te=I28?
J=127
Cs=133
Ba=137
?=180
Ta=182
W=186
Pt=197,4
Ir=198
Os=199
Hg=200
Au=197?
Bi=210?
TI=204
Pb=207

Convincing other scientists was more difficult. After all he
had given no reason for his "Periodic Table". It seemed
pretty far-fetched to most people. Why those numbers?
"Why not use the first letter of the names of the elements
to make your table?", wrote one sarcastic scientist.
Then Mendeleev scored his first triumph. He saw that the
new element beryllium looked more like magnesium than
aluminium where its weight fitted in. Obviously, thought
Mendeleev, we have got its atomic weight wrong. It should
be 9.4 and not 14. Within three years it had been measured
again by several other chemists who all found that
Mendeleev's prediction was absolutely correct.
That was only a small triumph compared with what
happened next. Mendeleev found three gaps in his table.
He guessed that there were new elements yet to be
discovered. Now he could make quite detailed predictions
about these missing elements. In a published paper, that
everyone could read, he described what these new elements
would be like. No one had yet seen them but Mendeleev
could predict how much they would weigh, what
combinations they would make with other elements, and
what shapes their crystals would have.
Six years later a French chemist announced his discovery
of a new metal which he named gallium (after the ancient
name for France). Mendeleev read about it and decided
that it should fill the missing place in aluminium's
group-but the atomic weight did not fit. Instead of being
disappointed about this, Mendeleev was confident enough
to write to the scientist and suggest that if he measured it
again it would come to 68. The French scientist was
unconvinced but he did what Mendeleev suggested. He
found, to his astonishment, that he had indeed got it
wrong. It was exactly what Mendeleev had predicted, even
though he had never seen the new metal. After that no
scientist ever laughed at Mendeleev's Table!
The second missing element was found four years later by a
Swedish chemist who called it scandium (can you guess
why?). The third and last of Mendeleev's missing elements
was discovered seven years later still. It was named
45

The paHern of
electrons in an
atom, 1913
46
germanium. (You can guess the nationality of the chemist
who discovered it). Not only was this element just what
Mendeleev expected, but it was to have a great future.
Sixty years later on, just after the Second World War,
germanium was the metal which launched a great
technological revolution. The earliest transistors were
made of germanium, and from them came the world's first
computers and all the marvels of modern microelectronics.
After all these successful predictions no one could
seriously doubt the value of Mendeleev's Table. It gave a
number pattern into which all the elements fitted. It
seemed like the fulfilment of the Islamic dream of finding a
universal number pattern. Gone were the doubts of
Lavoisier and Davy. Substances which fitted the Table
were elements-others were not.
The search for simple substances still goes on. There are
now over 110 elements, and they all fit into Mendeleev's
Table. But that is not the end of the story, nor the end of
the questions. Why do the elements show this number
pattern? Mendeleev could give no reason for that. When he
was an old man a British scientist discovered a tiny
particle called an electron. He claimed that it was a part of
all atoms. Humphry Davy would have been pleased
perhaps, but Mendeleev never believed it.

Yet it was this electron which began to show scientists a
reason why the atoms arrange themselves in the way they
do. It gave them a model for imagining the tiny world of
the atom itself. It began to explain the numbers 2, 7, 7, etc
but the explanation is still not complete. Who will add the
next piece to the puzzle of why all the simple substances of
the world fit into the Periodic Table of Dimitri Ivanovich
Mendeleev?
47