By PRAGYANSHARMA POLAVARAPU (Vrs.Somanchi)
INTRODUCTION
In the age of scientific
discoveries which began about 600 years ago the scientists and
philosophers like Copernicus, Kepler, Galelio and Sir Issac Newton made great
discoveries in astronomy and mechanics with the aid of advanced
mathematics. We may perhaps say that the later scientists turned
their attention to other challenging branches –like science of heat
energy and light energy and the vast new science of chemistry which tried
to understand how the millions of substances on earth are formed.We
are not discussing here the extraordinary discoveries in the life sciences of
Biology,Botany and Medicine.
In the modern universities
established in Europe 400,500 years back , serious and intensive studies
in mathematics, literature and philosophy and in sciences
were taken up. In addition lot of research in all sciences was
carried out under guidance of great professors. There was always great
respect for religion, spirituality and ancient philosophy among most of
the scientists.
DEVELOPMENT OF PHYSICS
AND CHEMISTRY DURING LAST 300 YEARS.
Let us concentrate on the
progress of science during the last 300 years.In that time Dr
Joseph Black(1728 – 1799) of Scotland was a famed
scientist. He was professor of medicine and chemistry for ten years at
University of Glasgow and after that for 30 years at University of Edinburg. He
was a most famous physicians and was one of the
founders of the Royal Society of Edinburgh and President of
the Royal College of Physicians of Edinburgh. He was editor of the medical
encyclopedia and was appointed as principal physician of the king .
It is said that students from other
parts of Europe came to study under him and that students preserved
his lecture notes for years to guide them and inspire them. He was
not only a great professor but also was among the foremost inventors .
His achievements are greatly respected in Scotland even today . The
chemistry laboratories at the above two universities are named after him.
Though there was great scientific
knowledge in those days the prevailing theories did not agree with modern views
about matter and energy. There was no encompassing atomic theory to
properly explain the the results of thousands of chemistry
experiments being performed in the various university laboratories. There
was no differentiation between chemical compounds and elements. Some very
important chemical compounds were treated as elements. However
many scientists generally believed in existence of atoms—the
smallest unbreakable particles constituting all matter. Even
ancient philosophers believed that only unbreakable minute
particles created all matter in the world.
Scientists in Europe in those
times believed in “five fundamental substances” which created all
matter in the world. They named these fundamental substances as
“Principles” . The five “Principles” were
(1)Water– considered as an
element,
(2)Salts– the many salts found dissolved
in sea water and some found also on land
(3) Earth–the mountains,hills and
rocks,the sand and the vast land ,
(4) Fire, and
(5) Metals—the pure metallic
substances of extreme purity and special metallic shine.
Scientists believed in “affinity” between
some of these “principles” under certain conditions and due to this
affinity different chemical compounds are formed
DR BLACK’S DISCOVERY OF LATENT HEAT
AND SPECIFIC HEAT
Though a chemist Dr Black is
more famous for his discovery of specific heat and latent
heat in the field of physics . The invention of thermometer (the instrument to
measure temperature) by the German scientist Fahrenheit in 1714 appears to have
accelerated research in the science of heat.
Dr Black noted surprising
facts in his two experiments (a) when ice changes to
water and (b) when hot water changes to steam. He noted during several control
experiments that
(1) When water/ice mixture in a
vessel is heated the temperature of the mixture does not rise until entire ice
is melted into water. We can observe that till all ice melts and changes into
water , then only the temperature starts to increase. We now in modern science
can guess the reason. Heat energy is used to lessen the attraction
between the H2O molecules existing in solid state — to change their bonding to
liquid state bonding. This utilization of heat energy cannot be noticed
by thermometer as the energy is used as a kind of work to lessen the
bonds between the billions of H2O molecules . The heat thus utilized
in a hidden way is called “Latent heat of Fusion” of ice i.e. hidden heat
energy used for melting ice.
(2) Similarly when already
boiling water in , say a narrow neck bottle, is still heated for some
more time— then also temperature of water does not increase above 100 degrees
centigrade. The temperature, shown by thermometer, stays only at 100
degrees centigrade till entire water changes to steam. The heat
energy being supplied is used for removing the mutual attraction between
the H2O molecules and to convert all water into the free
state of a gas. This hidden heat is called “Latent heat of Vaporization” of
water.
The concepts of “Latent heat of
Fusion”(ice to water) and “Latent heat of Vaporization”(hot water to steam)
helped organize heat science into a highly organized mathematics-based
discipline called Thermodynamics.
SPECIFIC HEAT
Dr Black proved
that different substances( like metals, wood, rubber,
stone ) require different amounts of heat energy to heat them in the same
range of temperature . Suppose we take same weight of all these substances and
heat them carefully and accurately in same temperature range ( say from
20 degrees centigrade to 40 degrees centigrade ).
It can be seen from such
experiments that each substance requires a different amount
of heat energy for the same increase in temperature. This individual heat
energy requirement of different substances is a constant quantity and
is called “specific heat” of that substance.
Dr Black like all great
scientists of his time must have believed that all matter is made
up of indivisible minute particles called atoms . The billions of
atoms/molecules in a substance are held together by mutual attraction.
The specific heat of a substance helps in exactly calculating the heat
energy required by it to raise its temperature from one initial
temperature to a required high temperature very accurately.
DR BLACK’S OTHER FAMOUS
EXPERIMENTS .
(a) CARBON DIOXIDE.
Dr black realized that the common air
all around us is also to be treated as a “principle” substance just like
the other five principles–water, salt,earth, fire,metal.
He found that air contains very
pure gases. He is the inventor of carbon dioxide which he called “fixed
air”. The modern system of nomenclature for chemical compounds did not exist
then. He obtained CO2 gas by strong heating of sea shells or by heating
chalk(calcium carbonate) with dilute acid .CO2 gas had
special properties— turning lime water milky and putting out a burning candle.
He found that the air we exhale during breathing process also shows exactly the
same property(of turning lime water milky and extinguishing flame). Thus he
discovered existence of pure CO2 which he called “Fixed Air”.
(b) INVENTION OF MODERN LABORATORY
BALANCE
In 1750, while still a student,
Dr Joseph Black developed the highly sensitive “modern laboratory balance”
(the analytical balance). It is a small sized laboratory weighing
scale made of most delicate and clean metal parts. It had a metal
beam balanced on a wedge-shaped fulcrum with metal pans hanging at
the two ends of the beam. The balance was enclosed in a glass box .It
had standardized metal weights. Everything was made of shining metal and
manufactured with great accuracy. The balance could weigh even a grain of sand
and because of its high accuracy this model of the balance immediately began to
be used in almost all chemical laboratories of the world!
( c )HE WAS ALSO INVENTOR OF
THE ELEMENT MAGNESIUM .
THE CONDITION OF CHEMISTRY IN
THE TIME OF DR JOSEPH BLACK
At that time scientists were still
unable to differentiate between elements and chemical compounds. They treated
even some “pure chemical compounds” as elements. We can call those
times age of “old science” as compared to our new science
existing after discovery of electron!
But the incessant search for
“pure chemical compounds” led to the discovery of more and more
“elements”. Electricity was not yet discovered . All the following
discoveries/inventions came only later—the atomic theory of Dalton,
Avogadro’s theory of molecules, Mandeliev’s table of chemical
elements,the modern system of Nomenclature of chemical
compounds as per acidic/basic or metal/nonmetal radicals.
The gas laws and absolute
temperature scale were not invented. The electrical cell, Ohm’s law
, Faraday’s magnetic lines of force, Dynamo and Motor, Electrical nature
of chemical reactions, Faraday’s laws of electrolysis, Discovery of
spectroscopy and electromagnetic spectrum, Electrolysis of water—all these were
not known and only came later.
Medieval scientists treated water and
air as elements. We now know that water is a chemical compound called H2O and
that air is a mixture of O2 and N2 –oxygen and nitrogen molecules. We
know that in nature many pure gaseous chemical compounds like CO2,
NO2, CO, SO2, SO3 exist.
Medieval scientists could not
understand what combustion scientifically meant —from viewpoint of science of
chemistry.They did not know the chemistry of candle flame,
big fire, burning of dry wood or paper , burning of oil soaked cloth etc . They
could not understand that flame was only a very hot region of visible
chemical reaction of very hot gases reacting chemically.
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